JP2002025880A - Projection exposure apparatus, projection exposure method, light cleaning method, and semiconductor device manufacturing method - Google Patents

Abstract

An object of the present invention is to set an illuminance of exposure light on a photosensitive substrate to a target value regardless of a change in transmittance of an optical system which changes with time. Prior to the start of exposure of a first wafer, 20,000 pulses are blanked. 1st time and 20
At the time of the 000 th pulse laser oscillation, the output signals of the integrator sensor 10 and the illuminance sensor 28 are taken in, the transmittance at two points in the optical system is calculated, and a transmittance time change prediction line is calculated from the two transmittances. . When the exposure is started, the intensity of the exposure light is controlled by calculating the transmittance of the optical system based on the elapsed time of the exposure based on the transmittance change prediction line. Therefore, the illuminance on the wafer can be compensated according to the actual transmittance variation. Further, the integrated light amount of the exposure light incident on the wafer 25 is adjusted so that the exposure dose on the wafer 25 becomes a target value. Thus, even if the transmittance of the illumination optical system or the projection optical system fluctuates during exposure, the wafer 25
The above exposure dose becomes the target value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mask or a reticle (photomask) in an optical lithography process for manufacturing a semiconductor device such as an LSI, an imaging device such as a CCD, a liquid crystal display device, or a thin film magnetic head. A projection exposure apparatus for exposing a pattern of an original such as a mask) to a photosensitive substrate such as a wafer, a projection exposure method using the exposure apparatus, an optical system light cleaning method for the projection exposure apparatus, and a semiconductor device And a method for producing the same.

[0002]

2. Description of the Related Art Along with the high integration of semiconductor devices, projection exposure apparatuses used in optical lithography processes, which are important for manufacturing the semiconductor devices, have made great progress. The resolution of the projection optical system mounted on the projection exposure apparatus is, as is well known by Rayleigh's equation,
R = k × λ / NA. Here, R is the resolution of the projection optical system, λ is the wavelength of the light for exposure, NA is the numerical aperture of the projection optical system, and k is a constant determined by the process in addition to the resolution of the resist.

In order to realize the required resolution in the projection optical system in response to the high integration of semiconductor elements, as can be seen from the above equation, the wavelength of the light source for exposure must be shortened and the numerical aperture of the projection optical system must be reduced. Efforts to increase the so-called high NA have been continued. In recent years, using a krypton fluoride excimer laser (KrF excimer laser) having an output wavelength of 248 nm as an exposure light source, an exposure apparatus having a projection optical system having a numerical aperture of 0.6 or more has been put into practical use. Exposure of various patterns is becoming possible.

In particular, recently, as a light source following the krypton fluoride excimer laser, an argon fluoride excimer laser (ArF excimer laser) having an output wavelength of 193 nm is used.
Is attracting attention. If an exposure apparatus using this argon fluoride excimer laser as an exposure light source can be realized, 0.1
It is expected that microfabrication ranging from 8 μm to 0.13 μm will be possible, and vigorous R & D has been actively conducted.

In the wavelength range of the output wavelength (193 nm) of the argon fluoride excimer laser, two materials that can be used as lenses from the viewpoint of transmittance at this stage are synthetic quartz glass and calcium fluoride (fluorite). Therefore, as an optical material for this type of exposure apparatus, a material having sufficient transmittance and internal uniformity has been energetically developed. Synthetic quartz glass has an internal transmittance of 0.
At 995 / cm or more, calcium fluoride reaches a level where the internal absorption can be ignored.

[0006] The material for the anti-reflection film coated on the surface of the optical material has a very narrow selection range as compared with that of the output wavelength (248 nm) of the krypton fluoride excimer laser, and the degree of freedom in design is increased. Subject to major restrictions. However, the problem has been overcome by vigorous development efforts, and the loss on each lens surface has been realized to a level of 0.005 or less.

[0007]

In a wavelength range shorter than the wavelength of such a KrF excimer laser beam, the surface of an optical element constituting an optical system (illumination optical system, projection optical system) in a projection exposure apparatus is exposed. There is a problem that the transmittance of the optical system is reduced due to adhesion of moisture and organic substances. This is because moisture or organic matter generated from the gas in the space between the plurality of optical elements or the inner wall of the lens barrel supporting the optical system adheres to the surface of the optical system.

FIG. 12 shows a time change characteristic of the transmittance of the optical system. During laser irradiation, while continuously emitting pulsed laser light from the laser light source, the illuminance of the exposure light between the laser light source and the mask and the illuminance of the exposure light on the wafer are measured at predetermined time intervals. The optical system transmittance, which is the ratio of, is calculated and represented at each measurement time. While the laser is stopped, the laser is irradiated at appropriate time intervals, and the same optical system transmittance is calculated and expressed for each time.
As can be seen from FIG. 12, the transmittance gradually increases after the irradiation of the laser beam, and becomes substantially saturated after a certain period of time. The phenomenon in which the transmittance of the optical system gradually recovers is because moisture and organic substances attached to the surface of the optical system are removed from the surface of the optical system by laser irradiation. For this reason,
It is conceivable that the transmittance is almost saturated by irradiating the laser beam for exposure for a predetermined time before the start of exposure, and then the exposure operation is started after that. Oscillation for a long time leads to a decrease in the durability of the laser light source, which is not preferable. In addition, it is difficult to continuously irradiate the laser beam for exposure even when exchanging a wafer or a mask.

A first object of the present invention is to provide a projection exposure method and a projection exposure method capable of always setting the illuminance of exposure light on a photosensitive substrate to a target value irrespective of a temporal change in transmittance of an optical system. It is to provide a device. A second object of the present invention is to provide a light-emitting device, which has a structure in which the transmittance of an illumination optical system or a projection optical system changes.
The integrated light amount (exposure dose) of the exposure light on the photosensitive substrate
It is an object of the present invention to provide a projection exposure method and a projection exposure apparatus which can always control an appropriate value according to the sensitivity of a photosensitive substrate. A third object of the present invention is to provide a method for optically cleaning an optical system while predicting a temporal change in transmittance of an illumination optical system or a projection optical system. A fourth object of the present invention is to provide a method of manufacturing a semiconductor device in which the yield is improved by exposing a circuit pattern or the like to a semiconductor substrate while estimating a temporal change in transmittance of an illumination optical system or a projection optical system. It is to be.

[0010]

According to the present invention, there is provided an optical system for projecting an image of a pattern illuminated by exposure light from an exposure light source onto a photosensitive substrate. The present invention is applied to a projection exposure apparatus that changes with time and its projection exposure method. And the above object is to measure the transmittance of the optical system for light having substantially the same wavelength as the exposure light at a plurality of different times, based on the plurality of measured transmittance,
This is achieved by estimating the temporal change characteristic of the transmittance of the optical system and projecting a pattern on the photosensitive substrate based on the estimation result. It is preferable to measure the transmittance using exposure light from an exposure light source. The multiple measurements of the transmittance are made at the time before the pattern is projected onto the photosensitive substrate, i.e., before irradiating the optical system with light having substantially the same wavelength as the exposure light, and at the light having substantially the same wavelength as the exposure light. Can be performed at a point in time after irradiating the optical system with light for a predetermined time. Also, a plurality of measurements of the transmittance, the time before projecting the image of the pattern illuminated with exposure light on the photosensitive substrate, and after projecting the image of the pattern illuminated with the exposure light on the photosensitive substrate It may be a point in time. For example, the plurality of measurement time points are the time points before the image of the pattern illuminated with the exposure light is projected on one photosensitive substrate,
This is a time point after the image of the pattern illuminated with the exposure light is projected onto one photosensitive substrate. Alternatively, the plurality of measurement time points may be a time point before the image of the pattern illuminated with the exposure light is projected on a predetermined area on the photosensitive substrate, and a time point after the image of the pattern illuminated with the exposure light is projected on the predetermined area. It is. In this case, for each exposure area of one chip or for each exposure area of one shot. When the optical system has an illumination optical system that illuminates a pattern with exposure light, and a projection optical system that projects an image of the pattern illuminated by the illumination optical system onto a photosensitive substrate, the optical system whose transmittance varies It is preferable to predict only the transmittance time change.

According to the present invention, the intensity of the exposure light applied to the photosensitive substrate can be adjusted based on the predicted time change characteristic of the transmittance. Alternatively, it is possible to control the integrated light amount of the exposure light irradiated onto the photosensitive substrate to an appropriate value according to the sensitivity of the photosensitive substrate based on the calculated transmittance time change characteristic. In the control method of the integrated light amount,
When projecting the pattern formed on the mask onto the photosensitive substrate by emitting the exposure light of the pulse beam from the exposure light source, the mask is generated from the mask in synchronization with the relative movement of the mask with respect to the exposure light. When the photosensitive substrate is relatively moved with respect to the exposure light passing through the projection optical system, the intensity of the exposure light incident on the photosensitive substrate based on the time change characteristic of the transmittance,
Adjusting at least one of the width of the exposure light on the photosensitive substrate in the moving direction of the photosensitive substrate, the moving speed of the photosensitive substrate in the moving direction, and the oscillation frequency of the exposure light source, the integrated amount of the exposure light Can be controlled to an appropriate value according to the sensitivity of the photosensitive substrate.

Further, the present invention comprises an optical system for projecting an image of a pattern illuminated by exposure light from an exposure light source onto a photosensitive substrate, wherein the transmittance of the exposure light in the optical system changes with time. The present invention is applied to a method of manufacturing a semiconductor device in an apparatus. The above-described object is to measure the transmittance of the optical system with respect to light having substantially the same wavelength as the exposure light at a plurality of different points in time, and to predict the time change characteristic of the transmittance of the optical system based on the plurality of measured transmittances. Then, it is achieved by projecting a pattern on a photosensitive substrate based on the prediction result and manufacturing.

Further, the present invention comprises an optical system for projecting an image of a pattern illuminated with exposure light from an exposure light source onto a photosensitive substrate, wherein a projection exposure system in which the transmittance of the exposure light in the optical system changes with time. It is applied to the optical cleaning method of the apparatus. The above-described object is to measure the transmittance of the optical system for light having substantially the same wavelength as the exposure light at a plurality of different points in time, and based on the measured plurality of transmittances, to determine the time change characteristic of the transmittance of the optical system. This is achieved by optically cleaning the optical system while predicting

A projection exposure apparatus according to the present invention comprises an original illuminance detector for detecting the illuminance of exposure light emitted from an exposure light source to an original, and a substrate illuminance detector for detecting the illuminance of exposure light on a photosensitive substrate. Calculating the ratio of the illuminance of the exposure light irradiated on the substrate detected by the original illuminance detector and the illuminance of the exposure light irradiated on the substrate detected by the substrate illuminance detector a plurality of times, and the projection optical system Prediction means for predicting the time-varying characteristic of the exposure light transmittance, and a control device for adjusting the integrated light amount of the exposure light incident on the photosensitive substrate based on the predicted time-varying characteristic and the ratio of the two illuminances. Can be configured. When the exposure light source is a pulse light source, the control device:
Pulse exposure applied to the photosensitive substrate based on the predicted time change characteristic and the ratio of both illuminances, so that the integrated amount of exposure light applied to the photosensitive substrate becomes an appropriate value corresponding to the photosensitive substrate. A control device for adjusting at least one of the light intensity and the number of pulses may be used.

According to the projection exposure method of the present invention, the ratio between the illuminance of exposure light emitted from an exposure light source and the illuminance of exposure light on a photosensitive substrate is calculated a plurality of times, and an illumination optical system and a projection optical system are calculated. A step of estimating the time change characteristic of the transmittance of the exposure light in at least one of the illuminance of the exposure light emitted from the exposure light source, the ratio of the illuminance of the exposure light on the photosensitive substrate, and the predicted And adjusting at least one of the intensity of the pulse exposure light incident on the photosensitive substrate and the number of pulses on the basis of the time change characteristic of the transmittance.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a schematic configuration of a projection exposure apparatus according to the present invention. As shown in FIG. 1, an ArF excimer laser light source 1 oscillating pulse light having an output wavelength of, for example, 193 nm emits a laser beam as a substantially parallel light beam, and transmits light through a shutter 2 on the main body side of the projection exposure apparatus. Guided to window 3. Shutter 2
For example, during the replacement of the wafer or the reticle, the illumination light path is closed, whereby the light source 1 self-oscillates to stabilize (adjust) the beam characteristics including at least one of the center wavelength, the wavelength width, and the intensity of the pulse light.

Here, the main body of the projection exposure apparatus is housed in a chamber 100, and is controlled so that the temperature is kept constant. The laser light passing through the light transmission window 3 is
One of a plurality of ND filters (ND in FIG. 1) formed into a laser beam having a predetermined cross-sectional shape by the beam shaping optical system 4 and having different transmittances (darkening rates) provided on the turret plate TP.
The light passes through 1), is reflected by the reflection mirror 5, and is guided to a fly-eye lens 6 as an optical integrator. The fly-eye lens 6 is configured by bundling a large number of lens elements, and on the exit surface side of this lens element,
A large number of light source images (secondary light sources) corresponding to the number of lens elements constituting the light source are formed.

In this embodiment, the turret plate TP is 6
It holds two ND filters ND1 to ND6 (only ND1 and ND2 are shown), and rotates the turret plate TP by the motor MT1 so that the six ND filters are interchangeably arranged in the illumination optical system. Has become. Here, the six ND filters are determined by the sensitivity of the resist on the wafer 25, the variation in the oscillation intensity of the light source 1, the control accuracy of the exposure dose on the wafer 25, and the like. It is appropriately selected according to the number of pulsed lights to be irradiated to the point (the number of exposure pulses). In other words, the number of exposure pulses refers to a region conjugate to the illumination region on the reticle 16 defined by the variable field stop 12 and the projection optical system 23 (that is, an image of a part of the pattern of the reticle 16 existing in the illumination region). Is the number of pulsed lights applied to a point on the wafer 25 while the point crosses the point along the scanning direction.

In place of the turret plate TP shown in FIG. 1, for example, two plates each having a plurality of slits are arranged to face each other, and the two plates are relatively moved in the slit arrangement direction so that the pulse The light intensity may be adjusted.

The light source 1 oscillates pulsed light in response to a trigger pulse sent from the light source control circuit 45, and the light source control circuit 45 adjusts a voltage (charge voltage) applied to the light source 1 so that the light source 1 The intensity of the pulse light emitted from the device is adjusted. The light source control circuit 45 includes a main controller (control circuit) 4 that controls the entire projection exposure apparatus.
The light source 1 is controlled according to a command from 0.

In this embodiment, the reticle 16, ie, the wafer, is controlled by at least one of the adjustment of the oscillation intensity of the light source 1 by the light source control circuit 45 and the adjustment of the transmittance (dimming rate) of the pulse light by the turret plate TP. 25, the intensity of the pulse light can be adjusted.

Further, as disclosed in, for example, JP-A-7-142354, in this embodiment, the reticle 16 and the wafer 25 are moved synchronously to expose the wafer 25 with an image of the pattern of the reticle 16. While the motor MT2
This causes the mirror 5 to rotate (vibrate). Therefore, during scanning exposure, interference fringes such as speckles move within the illumination area on the reticle 16 defined by the variable field stop 12, thereby making the integrated light quantity distribution of the pulse light on the wafer 25 substantially uniform. . At this time, the interference fringes are moved at least once while one point on the reticle 16 crosses the illumination area along the scanning direction. In addition, it is preferable that the reflection mirror 5 be vibrated so that the interference fringes move in the scanning direction and the direction orthogonal to the scanning direction in the illumination area. When the interference fringes are moved along the scanning direction of the reticle 16 in the illumination area, the reticle 1 is moved in consideration of the distance that the reticle 16 moves during the pulse emission.
The swing angle of the reflection mirror 5 between the pulse emission, that is, the movement amount of the interference fringe is determined so that the positional relationship between the one point and the interference fringe changes while the one point on 6 crosses the illumination area. .

Although one fly-eye lens 6 is provided in this embodiment, for example, as disclosed in Japanese Patent Application Laid-Open No. 1-259533, a reflection mirror 5 and a turret plate T are provided.
A fly-eye lens as a second optical integrator may be provided between P and P. Further, instead of the fly-eye lens, an internal reflection type rod-shaped optical member may be used as the optical integrator.

As will be described later, a plurality of aperture stops 7a to 7h having at least one of a shape and a size different from each other are formed at positions where a large number of secondary light sources formed by the fly-eye lens 6 are formed. A turret plate 7 is provided. The turret plate 7 is driven to rotate by a motor 8, and one aperture stop is selected according to the pattern of the reticle 16 to be transferred onto the wafer 25 and inserted into the optical path of the illumination optical system. The turret plate 7 and the motor 8
This constitutes a variable aperture stop device for the illumination system.

Light beams from a number of secondary light sources formed by the fly-eye lens 6 pass through the variable aperture stop of the turret plate 7 and are split into two light paths by the beam splitter 9. Detector) 10
And the illuminance (intensity) of the illumination light is detected. A signal corresponding to the detected illuminance is input to the control circuit 40. On the other hand, the transmitted light is reflected by a reflection mirror 14 through a relay lens 11, a variable field stop 12 defining a rectangular aperture, and a relay lens 13, and then is condensed by a plurality of lenses and other refractive optical elements. The light is collected by the system 15. Thereby, the illumination area on the reticle 16 defined by the opening of the variable field stop 12 is illuminated almost uniformly in a superimposed manner. Then, an image of the circuit pattern on the reticle 16 is formed on the wafer 25 by the projection optical system 23, and the resist applied on the wafer 25 is exposed to light.
The circuit pattern image is transferred onto the top.

The illumination area on the reticle 16 defined by the variable field stop 12 has a smaller width in the scanning direction of the reticle 16 than the pattern area and has a smaller width in a direction perpendicular to the scanning direction than the pattern area. It is getting wider. Furthermore, the illumination area extends around the optical axis AX of the projection optical system 23 and along its diameter within the circular image field of the projection optical system 23.

The shape and size of the rectangular aperture of the variable field stop 12 can be changed by moving at least one blade constituting the variable field stop 12 by the motor MT3. In particular, when the width of the rectangular opening in the short direction is changed, the width of the illumination area on the reticle 16 in the scanning direction changes, and as a result, a plurality of pulsed light beams irradiated to one point on the wafer 25 by the scanning exposure are changed. Can be adjusted. This is because the number of pulsed lights applied to one point on the wafer 25 while the point crosses the rectangular area conjugate with the illumination area on the reticle 16 along the scanning direction with respect to the projection optical system 23 is changed. That's because.

Here, as described above, in the present embodiment, the oscillation frequency of the light source 1 can be changed by the trigger pulse sent from the light source control circuit 45, thereby irradiating one point on the wafer 25 during the scanning exposure. It is possible to adjust the integrated light amount of the plurality of pulsed lights to be performed. Further, by changing the scanning speed of the wafer 25 (and the reticle 16), the scanning speed of the wafer 25 (and the reticle 16) can be changed.
It is possible to adjust the integrated light amount of a plurality of pulsed lights applied to a point. Similarly, as described above, by changing the oscillation frequency and the scanning speed, a point on the wafer 25 irradiates a projection area conjugate with the illumination area on the reticle 16 while the point crosses the projection area along the scanning direction. This is because the number of pulsed lights is changed.

In the scanning projection exposure apparatus, the wafer 2
At least one of the intensity of the pulse light on the wafer 5 and the number of the pulse light applied to each point on the wafer 25 during the scanning exposure is adjusted, whereby the wafer 25 exposed with the pattern image of the reticle 16 is adjusted. The integrated light amount (exposure dose) of a plurality of pulsed lights respectively irradiated to each point in the upper region is
The value is controlled to an appropriate value according to the sensitivity of the photoresist on the wafer 25.

As described above, in the present embodiment, the light source 1
Of the pulse light on the wafer 25 by changing at least one of the oscillation intensity and the transmittance of the pulse light. The intensity can be adjusted, thereby optimizing the exposure dose. In the present invention, instead of such optimization of the exposure dose by adjusting the pulse light intensity,
The exposure dose may be optimized by adjusting the number of pulsed lights applied to each point on the wafer 25.
That is, in this embodiment, the opening width of the variable field stop 12 described above, that is, the width of the pulse light (corresponding to the above-described projection area) in the scanning direction on the wafer 25, the oscillation frequency of the light source 1, The scanning speed of each of the laser beams 25 can be changed. By changing at least one of the width of the pulse light, the oscillation frequency, and the scanning speed, the pulse light applied to each point on the wafer 25 can be changed. The number of can be adjusted. Of course, the exposure dose can be optimized by adjusting the intensity of the pulse light on the wafer 25 and the number of the pulse light applied to each point on the wafer 25, respectively.

That is, in the present embodiment, the oscillation intensity of the light source 1, the transmittance (dimming rate) of the pulse light, the width of the pulse light on the wafer 25, the oscillation frequency of the light source 1, and the
By adjusting at least one of the scanning speeds, the exposure dose at each point on the wafer 25 can be set to an appropriate value, or the control accuracy of the exposure dose can be set within a required accuracy (for example, ± 1 to 2%). .

Incidentally, the projection optical system 23 of this embodiment is composed entirely of optical elements such as a refracting lens.
An aperture stop Ep is arranged at the position of the third pupil (entrance pupil). The aperture stop Ep may have a mechanism that can change its size so that the numerical aperture of the projection optical system can be changed. In this case, the aperture stop Ep in the projection optical system and the variable aperture in the illumination optical system are used. The stops 7a to 7h are arranged at optically conjugate positions.

The reticle 16 is held and fixed to a reticle stage 18 by a reticle holder 17. The reticle stage 18 is provided on the base 22 so as to move two-dimensionally along a plane orthogonal to the plane of FIG. A mirror 21 is provided on the reticle holder 17, and laser light from the laser interferometer 20 is reflected by the mirror 21 and enters the laser interferometer 20, and the position of the reticle stage 18 is measured by the laser interferometer 20. The position information is input to the control circuit 40. Based on the position information, the control circuit 40 drives the reticle stage driving motor 19 to control the position of the reticle 16, the speed of the reticle 16 during scanning exposure, and the like. I have.

The wafer 25 is held and fixed on a wafer stage 27 by a wafer holder 26. Wafer stage 27
Is provided so as to move two-dimensionally along a plane orthogonal to the paper surface of FIG. A mirror 31 is provided on the wafer stage 27, and laser light from the laser interferometer 30 is reflected by the mirror 31 and enters the laser interferometer 30,
The position of wafer stage 27 is measured by laser interferometer 30. The position information is input to the control circuit 40. Based on the position information, the control circuit 40 drives the wafer stage driving motor 29 to control the position of the wafer 25, the speed of the wafer 25 during scanning, and the like. An illuminance sensor (photoelectric detector) 28 is provided on the wafer stage 27, and detects the illuminance of exposure light applied to the wafer 25. The detection signal of the illuminance sensor 28 is input to the control circuit 40.

In the projection exposure apparatus of this embodiment, the illumination optical system is provided in an atmosphere of an inert gas such as nitrogen gas. Therefore, as disclosed in, for example, JP-A-6-260385, an inert gas supply device for supplying an inert gas to a housing of an illumination optical system (not shown) and an inert gas contaminated from the housing are provided. And an inert gas discharging device for discharging. In addition, an inert gas such as nitrogen gas is also supplied to a plurality of spaces formed between a plurality of optical members constituting the projection optical system 23, and contaminated inert gas is discharged from the plurality of spaces. Therefore, the inert gas supply device 41
And an inert gas discharge device 42 are provided.
Numeral 1 supplies a dry inert gas such as nitrogen to the inside of the projection optical system 23 via a pipe 43, and a discharge device 42 discharges the gas inside the projection optical system 23 to the outside via a pipe 44. The inert gas is not limited to nitrogen, but may be a gas such as helium or argon.

Next, a description will be given of a variable aperture stop device for changing the numerical aperture of the illumination optical system (that is, the shape and size of the secondary light source) in the projection exposure apparatus. As shown in FIG. 1, the illumination optics determined by the principal ray Ri parallel to the optical axis AX from the outermost edge (outermost diameter) of the aperture stop inserted into the optical path of the illumination optical system on the turret plate 7. The numerical aperture of the system is NA
i (= sin θi), and the aperture stop E of the projection optical system 23
a principal ray R parallel to the optical axis AX from the outermost edge (outermost diameter) of p
When the numerical aperture on the illumination optical system side of the projection optical system 23 determined by 0 is NAo (= sin θ0), the σ value as a coherence factor is defined by the following equation.

Σ = NAi / NAo

The aperture stop Ep arranged at the position of the pupil (entrance pupil) of the projection optical system 23 and the variable aperture stop on the turret plate 7 of the illumination optical system are optically conjugate. Since the image of the variable aperture stop (the image of the secondary light source) is formed on the pupil of, the diameter of the image of the variable aperture stop is D7,
When the diameter of the aperture stop Ep of the projection optical system 23 is D23, the σ value as the maximum coherence factor can be defined by the following equation.

## EQU2 ## σ = D7 / D23

In general, the σ value of the projection exposure apparatus in the photolithography process is set to be in the range of 0.3 to 0.8. In this example, the turret plate 7 shown in FIG. 1 is provided with a plurality of aperture stops 7a to 7h shown in FIG. 2, and one of the aperture stops is selected according to the use as described later.

As shown in FIG. 2, a turret plate 7 made of a transparent substrate such as quartz is provided with eight aperture stops 7a to 7h. Five aperture stops 7a, 7 having a circular aperture
e to 7h are for positively changing the σ value, of which three aperture stops 7e, 7f and 7g are aperture stops used during an actual exposure operation, and the remaining two aperture stops are provided. 7a and 7h are aperture stops used at the time of the optical cleaning operation. The light cleaning is to remove a contaminant such as moisture or an organic substance adhering to the lens surface from the lens surface by irradiating a laser to improve the transmittance.

The aperture stop 7b having three deformed apertures
Reference numeral 7d is for improving the resolving power (depth of focus) of the projection optical system 23 by using it during the exposure operation. The aperture stops 7c and 7d are orifices having annular apertures having different annular ratios (ratio between the inner diameter and the outer diameter of the annular aperture). The remaining one aperture stop 7b has four eccentric secondary light sources. Is a diaphragm with four eccentric apertures to form.

The turret plate 7 having eight aperture stops 7a to 7h is rotated by a motor 8 shown in FIG. 1, and one of the eight aperture stops, that is, an aperture having a desired aperture shape is formed. It is arranged close to the exit surface of the fly-eye lens 6. In other words, the secondary light source is formed by the fly-eye lens 6 and is set to the emission-side focal plane. The driving of the motor 8 is controlled by the control circuit 40.

FIG. 3 shows a state in which images of the aperture stops 7a and 7e to 7h having circular apertures of different sizes are formed on the aperture stop Ep in the projection optical system 23. Details of each aperture stop (1) to (5)
This will be described below.

(1) When the aperture stop 7e having the smallest circular aperture is set in the illumination optical path, the numerical aperture NAi of the illumination optical system becomes the smallest, and at this time, the aperture stop Ep having the aperture diameter D23a. , An image of the aperture stop 7e having the aperture diameter D7e is formed, and the σ value is set to 0.4. That is, σ = D7e / D23a = NAi / NAo = 0.4
Is established. Therefore, when the aperture stop 7e is set in the illumination light path, the reticle 1 is set under the σ value of 0.4.
6 can be transferred onto the wafer 25.

(2) When the aperture stop 7f having a circular aperture larger than the aperture stop 7e is set in the illumination optical path, the numerical aperture NAi of the illumination optical system is determined when the aperture stop 7e is set in the illumination optical path. Larger than. At this time, the opening diameter D2
An image of the aperture stop 7f having the aperture diameter D7f is formed inside the aperture stop Ep having 3a, and the σ value is set to 0.6.
That is, σ = D7f / D23a = NAi / NAo =
A relationship of 0.6 is established. Therefore, when the aperture stop 7f is set in the illumination light path, the pattern of the reticle 16 can be transferred onto the wafer 25 under the σ value of 0.6.

(3) When an aperture stop 7g having a circular aperture larger than the aperture stop 7f is set in the illumination optical path, the numerical aperture NAi of the illumination optical system is determined by the value obtained when the aperture stop 7f is set in the illumination optical path. Larger than. At this time, the opening diameter D2
An image of the aperture stop 7g having the aperture diameter D7g is formed inside the aperture stop Ep having 3a, and the σ value is set to 0.8.
That is, σ = D7g / D23a = NAi / NAo =
A relationship of 0.8 is established. Therefore, when the aperture stop 7g is set in the illumination light path, the pattern of the reticle 16 can be transferred onto the wafer 25 under the σ value of 0.8.

(4) When the aperture stop 7h having a larger circular aperture than the aperture stop 7g is set in the illumination optical path, the numerical aperture NAi of the illumination optical system is determined by the case where the aperture stop 7g is set in the illumination optical path. Larger than. At this time, the aperture stop E
An image of the aperture stop 7h having the same aperture diameter D7h as the aperture diameter D23a of p is formed, and the σ value is set to 1.0. That is, σ = D7h / D23a = NAi / NAo
= 1.0 holds. Therefore, the aperture stop 7h
Is set in the illumination optical path, the effective diameter of the optical element constituting the condenser optical system 15 of the illumination optical system, the effective diameter of the optical element such as the lens constituting the projection optical system 23, and furthermore, these optical elements The illumination light flux can be guided sufficiently to a portion exceeding the effective diameter of For this reason, moisture, organic substances, and the like attached to the surfaces of these optical elements can be eliminated by the light cleaning effect of the illumination light beam for exposure.

(5) When the aperture stop 7a having a circular aperture larger than the aperture stop 7h is set in the illumination optical path, the numerical aperture NAi of the illumination optical system is determined when the aperture stop 7h is set in the illumination optical path. Larger than. At this time, the opening diameter D2
An image of the aperture stop 7a having the aperture diameter D7a is formed so as to include the aperture stop Ep having 3a, and the σ value is set to 1.2. That is, σ = D7a / D23a = NAi / NAo
= 1.2 is established. Therefore, the aperture stop 7a
Is set in the illumination optical path, the effective diameter of the optical element constituting the condenser optical system 15 of the illumination optical system and the effective diameter of the optical element such as the lens constituting the projection optical system 23 are of course The illumination light flux can be sufficiently guided to the peripheral portion of the lens exceeding the effective diameter of the optical element. Therefore, it is possible to sufficiently obtain the effect of optically cleaning water, organic substances, and the like attached to the surfaces of these optical elements.

Next, the operation of this embodiment will be described.
First, as shown in FIG. 1, a dry inert gas such as nitrogen is supplied from a gas supply device 41 to the inside of the projection optical system 23 via a pipe 43, and is completely filled.
2 discharges the gas inside the projection optical system 23 to the outside through the pipe 44. The entire optical path of the exposure light of the illumination optical system has a hermetically sealed structure like the projection optical system 23. Similarly, an inert gas such as dry nitrogen is supplied and charged, and the internal gas is exhausted by an exhaust device.

It is preferable that the gas supply device 41 and the discharge device 42 are always operated during the exposure to keep the atmosphere between the optical elements such as the lens chamber dry and clean at all times, but prior to the exposure operation. After the gas in the space formed between the optical elements such as the lens chamber is purified, the supply device 41 and the discharge device 42 may be stopped. The same applies to the illumination optical system.

Next, the reticle 16 on which the pattern to be transferred is drawn is transported and placed on the reticle stage 18 by a reticle loading mechanism (not shown). At this time, the position of the reticle 16 is measured by a reticle alignment system (not shown) so that the reticle 16 is set at a predetermined position, and the reticle 1 is controlled by a reticle position control circuit (not shown) according to the result.
The position 6 is set to a predetermined position.

Next, before the exposure step is started, a transmittance time change prediction straight line (transmittance time change characteristic) of the projection optical system 23 is calculated as indicated by reference numeral C1 in FIG. FIG. 4 is a graph in which the horizontal axis represents the exposure time and the vertical axis represents the transmittance. This transmittance is the transmittance of an optical system (hereinafter, this optical system is referred to as a transmittance measuring optical system) from the half mirror 9 that branches the exposure light to the integrator sensor 10 to the wafer surface.

First, the illuminance sensor 28 is arranged on the optical axis of the projection optical system 23, and the laser light source 1 is driven to
000 pulses are performed. For example, in synchronization with the first pulse, the integrator sensor 10 and the illuminance sensor 2
At step 8, the illuminance of the exposure light is acquired. At this time, the ratio LW / LI of the output LI of the integrator sensor 10 and the output LW of the illuminance sensor 28 is calculated. This is the transmittance P0 at the start of exposure in FIG. Then, for example, 20
The illuminance of the exposure light is captured by the integrator sensor 10 and the illuminance sensor 28 in synchronization with the 001th pulse. At this time, the ratio LW / LI of the output LI of the integrator sensor 10 and the output LW of the illuminance sensor 28 is calculated. This is the transmittance P at the exposure time t1 in FIG.
It is one.

Water and organic substances adhering to the surface of the transmittance measuring optical system including the projection optical system 23 are peeled off from the lens surface by the self-cleaning effect by the blanking of the laser pulse.
The transmittance of the transmittance measuring optical system is improved, and the transmittance P1> P0
Becomes The two transmittances P0 and P1 are connected by a straight line to calculate a transmittance time change prediction straight line C1.

FIG. 5 is a flowchart showing a procedure for performing exposure while calculating a transmittance time change characteristic line. In step S1, the variable aperture stop of the illumination optical system, the type of the reticle, and the numerical aperture NA of the projection optical system are determined and input. Based on this, the turret plate 7 is driven to rotate by the motor 8, an aperture stop forming a secondary light source having a shape and a size corresponding to the type is inserted into the illumination optical path, and the numerical aperture of the projection optical system 23. NA is adjusted by the aperture stop Ep. Further, the determined reticle 16 is transported from the reticle library and set on the reticle stage 18.

In step S2, the wafer stage 2 is moved so that the illuminance sensor 28 is positioned on the optical axis of the projection optical system 23.
Move 7 In step S3, the laser light source 1 is driven to emit laser light (blank shot), and the illuminance LI of the exposure light reflected from the mirror 9 by the integrator sensor 10 is measured.
And the illuminance LW of the exposure light on the wafer stage 27 is detected by the illuminance sensor 28. In step S4, those detection results are stored and stored as the first detected illuminance. If it is determined in step S5 that the 20,000 pulse idling is completed, the process proceeds to step S6. In step S6, the pulse laser of the 200001th pulse is emitted, the illuminance LI of the exposure light reflected from the mirror 9 is detected by the integrator sensor 10, and the illuminance LW of the exposure light on the wafer stage 27 is detected by the illuminance sensor 28. . Step S7
Then, those detection results are stored and saved as the last detected illuminance of the blank shot.

In step S8, a transmittance time change prediction line is calculated based on the first and last detected illuminances. As shown in FIG. 4, the predicted straight line is a transmittance P based on the first detected illuminance ratio LW / LI.
0 and transmittance P1 based on the ratio LW / LI of the last detected illuminance
Is calculated, and is approximated by a straight line connecting these points P0 and P1. This transmittance time change prediction line can be stored as a linear function, or can be stored in a storage device 57 described later as a table of transmittance with respect to exposure time.

In this manner, the transmittance time change prediction line C1
Is determined, exposure is started with the first wafer 25 facing the optical axis of the projection optical system 23 in step S9 in FIG. A resist, which is a photosensitive material, is previously applied to the surface of the wafer 25 to which the pattern of the reticle 16 is transferred. In this state, the wafer 25 is transported by a wafer loading mechanism (not shown) and
7. The wafer 25 is aligned and held and fixed on the wafer stage 27. In the first transfer of the pattern, the wafer 25 placed on the wafer stage 27 has no pattern on the wafer 25, and the wafer 25 is placed at a predetermined position on the wafer stage 27, for example.
It is installed at the position determined by the outside diameter standard. After that, the pattern is transferred onto the wafer 25. In this transfer, a part of the pattern on the reticle 16 is selectively illuminated by the variable field stop (reticle blind) 12, and the reticle 16 is moved by the reticle stage 18 to the variable field stop 1.
2. The so-called scanning type transfer in which the wafer 25 is moved relative to the projection area conjugate to the illumination area with respect to the projection optical system 23 by the wafer stage 27 in synchronization with the movement relative to the illumination area defined by 2. (Step and scan method). Alternatively, a step-and-repeat method in which the entire surface of the pattern region on the reticle 16 to be transferred is illuminated and transferred at a time may be used.

FIG. 6 is a block diagram of the present invention in which the intensity of the laser beam is feedback-controlled to the target illuminance on the wafer. For example, it can be provided in the control circuit 40 in the form of software or hardware. The target value setting circuit 51 sets a target illuminance on the wafer which is determined according to the sensitivity characteristics of the resist. As described above, the integrator sensor 10 outputs the detection signal LI according to the illuminance of the exposure light uniformized by the fly-eye lens 6, and the illuminance sensor 28 detects the detection signal LW according to the illuminance of the exposure light on the wafer stage 27. Is output. Therefore, before starting the exposure operation, the illuminance sensor 28 is moved on the optical axis AX of the projection optical system 23, and the measured value LI of the integrator sensor 10 and the measured value LW of the illuminance sensor 28 are held by the sample hold circuit 52. I do. The ratio between the detection signal LI of the integrator sensor 10 and the detection signal LW of the illuminance sensor 28 (output LW of the sensor 28 / output LI of the sensor 10) is calculated by the divider 53, and the gain α calculator 54 calculates the LW / LI
Is multiplied by a predetermined coefficient K1 to calculate a gain α. During the exposure operation, the multiplier 55 uses the integrator sensor 10.
Is multiplied by the gain α, and the estimated actual illuminance LPR is output. In other words, the estimated actual illuminance LPR is equal to the measured value of the integrator sensor 10 at the start of the exposure.
If the illuminance on the wafer is 50 in the above, 50/10
The illuminance on the wafer is estimated by multiplying a gain α obtained by multiplying a ratio of 0 by a predetermined coefficient K1 by an output signal of the integrator sensor 10 during exposure. That is, the gain α is set as an optimal value when there is no change in transmittance.

The estimated actual illuminance LPR obtained by multiplying the detection signal of the integrator sensor 10 by the gain α by the multiplier 55 is further multiplied by the gain β by the multiplier 56 to obtain the estimated actual illuminance LPRC after correction on the wafer. Is calculated. Gain β
Is calculated as follows. The storage device 57 stores the transmittance time change prediction straight line that is predetermined as described above. The timer 58 measures the elapsed time from the start of the exposure, and accesses the storage device 57 based on the measured time to read the transmittance. The read result is the gain β
The gain β arithmetic unit 59 is input to the arithmetic unit 59, and calculates the gain β by multiplying the read transmittance by a predetermined coefficient K2. For example, if the transmittance is 80%, the gain β
Is set to 0.8 × K2.

In this manner, the integrator sensor 10
The signal LPRC obtained by multiplying the detection signals of the above by the gains α and β represents a value obtained by estimating the actual illuminance on the wafer stage 27,
This signal is input to the deviation unit 60. The deviation unit 60 calculates a deviation between the target illuminance on the wafer output from the target value setting circuit 51 and the estimated actual illuminance after correction, and calculates this deviation as PI
Input to the D operation circuit 61 to perform a PID operation, and send the operation result to the light source control circuit 45 to control the light source 1;
That is, the oscillation intensity is adjusted.

Now, between the time points t1 and t2 in FIG.
Assuming that the pattern image is projected on 5, the transmittance used during the exposure between t1 and t2 is calculated from the predicted straight line C1 based on the elapsed time (exposure time) during the exposure.

When the exposure of the first wafer 25 is completed in step S9 in FIG. 5 (time t2 in FIG. 4), in steps S10 to S12, the above-described steps S2 to S4
Similarly, the integrator sensor 10 at time t2
Then, the transmittance P2 is calculated from the ratio LW / LI of the illuminance sensor 28, the transmittance P2 is stored, and the process proceeds to step S13.
In step S13, as in step S8,
The transmittance P1 at time t1 and the transmittance P2 at time t2 are linked,
As shown in FIG. 4, a transmittance time change prediction straight line C2 is calculated.

Next, in step S14, exposure of the next (second) wafer 25 is started. In the second exposure, similarly to the first exposure, the transmittance is calculated from the elapsed time from time t2 to t3 based on the prediction line C2, and the exposure amount is calculated using the gain β calculated from the transmittance. Is controlled.

In the case of the second and subsequent transfer of the pattern to the wafer 25, since the pattern exists at least on the wafer 25, the mark attached to the previously transferred pattern is set to a wafer alignment (not shown). The position of the pattern on the wafer 25 is measured by measuring with a system, and according to the result, the pattern to be transferred from the pattern previously transferred onto the wafer 25 has a predetermined positional relationship. , The positions of the reticle stage 18 and the wafer stage 27 are controlled.

In the above embodiment, the idle pulse of the 20011 pulse is performed between the time points t0 and t1, but the pulse number of the empty pulse is not limited to the 20001 pulse. In addition, the transmittance is predicted by calculating the transmittance time change prediction line by connecting the two transmittances at the time points t0 and t1 and the time points t1 and t2. However, even if three or more transmittances are used. Good. The approximation method is not linear approximation, but may be a regression line or regression curve that does not directly connect the calculated transmittance. Any method such as polynomial approximation, power approximation, exponential approximation, and modified exponential approximation may be used.

Here, the method of calculating the transmittance time change prediction line based on the transmittance at three or more points as described above will be described in detail with reference to FIG. FIG. 7 is a view similar to FIG. 4 and shows a transmittance time change prediction straight line C1 calculated based on the transmittance at three points prior to exposure of the second wafer.
FIG. Before starting the exposure of the second wafer, the transmittance P0 at time t0 shown in FIG.
1 and the transmittance P2 at time t2
(T0, P0), (t1, P1), (t
2, P2), an approximate straight line C11 is calculated by the least square method of the following equation.

(Equation 3)

Then, the exposure end point t of the second wafer
3 is calculated in the same manner as described above, and before starting exposure of the third wafer, the transmittance P1 at time t1, the transmittance P2 at time t2, and the transmittance P2 at time t3 shown in FIG. Three data of the transmittance P3 (t1, P
1) Based on (t2, P2) and (t3, P3), an approximate straight line C21 is calculated by the least square method of the following equation.

(Equation 4)

Similarly, when exposing the fourth and subsequent wafers, a transmittance time change prediction line is similarly formed based on the latest three data sets, and exposure control is performed in accordance with the transmittance time change prediction line. Perform

Furthermore, in the above description, after the exposure of the first wafer is completed, the transmittance is measured before the start of the exposure of the next wafer, and the transmittance time change prediction line is calculated.
The prediction straight line may be calculated every two wafers, every three wafers, or the like within an allowable range of the error. That is, the exposure amount control may be performed on a plurality of wafers based on the transmittance calculated from the common predicted straight line. FIG. 8 is a flowchart showing the exposure procedure in such a case.

FIG. 8 is a flow chart showing an example of the procedure for performing exposure by calculating a transmittance time change prediction line not for each wafer but for a plurality of wafers. The same parts as those in FIG. 5 are denoted by the same reference numerals and differences will be mainly described. The transmittance time change prediction straight line calculated in step S8 is commonly used until exposure processing is performed on m wafers in step S21. If it is determined in step S21 that the exposure processing on the m wafers has been completed, it is determined in step S22 whether all the exposure processing has been completed. When it is determined that all the processes are completed, the processes in FIG. 8 are all completed. If step S22 is denied and the wafer exposure process is to be continued, a transmittance time change prediction line is newly calculated from the previous transmittance and the current transmittance in steps S10 to S13. Then, the process proceeds to step S9, and the exposure process is performed while controlling the exposure amount using the new transmittance time change prediction line.

As described above, according to the procedure of FIG. 8, if the fluctuation of the transmittance is not so large, the transmittance time change prediction line is calculated for each of a plurality of wafers.
Exposure can be performed with an appropriate exposure amount accurately without significantly reducing the throughput.

In the case where the fluctuation of the transmittance fluctuates to an unacceptable level during the exposure of one wafer, it is preferable to calculate the prediction straight line for each chip or every two chips. FIG. 9 is a flowchart showing an exposure procedure in such a case.

FIG. 9 is a flowchart showing an example of a procedure in which exposure is performed by calculating a transmittance time change prediction line for each of N chips on one wafer, not for each wafer. The same parts as those in FIG. 5 are denoted by the same reference numerals and differences will be mainly described. The transmittance time change prediction straight line calculated in step S8 is used in common until exposure processing is performed on N chips in step S31. Step S
At 32, it is determined whether or not the exposure processing for one wafer has been completed. If not, step S10 to step S
In step 13, a transmittance time change prediction line is newly calculated from the previous transmittance and the current transmittance. Then step S31
The exposure processing for the next N chips is performed while controlling the exposure amount using the new transmittance time change prediction line. If it is determined in step S32 that the exposure processing for one wafer has been completed, it is determined in step S33 whether all the exposure processing has been completed. When it is determined that all the processes are completed, all the processes in FIG. 9 are completed. If step S33 is denied and the exposure processing of a new wafer is subsequently performed, the process proceeds to steps S10 to S13, where a new transmittance time change prediction line is calculated, and the processing after step S31 is performed.

As described above, according to the procedure shown in FIG. 9, when the fluctuation of the transmittance is large, the transmittance time change prediction straight line is calculated every time N chips are exposed in one wafer. Therefore, it is possible to accurately perform exposure with an appropriate exposure amount. The number of chips using the common transmittance time change prediction line is one or more and an appropriate number.

Further, when the change in the transmittance is reduced to an allowable level, the exposure control based on the transmittance time change prediction line may be stopped. FIG. 10 is a flowchart showing an exposure procedure in such a case. The same parts as those in FIG. 5 are denoted by the same reference numerals and differences will be mainly described.

In FIG. 10, the process proceeds to step S44 until it is determined in step S41 that the transmittance is equal to or greater than the predetermined reference value, and the process proceeds to step S14 using the transmittance time change prediction line calculated immediately before. Exposes the next wafer. If it is determined in step S41 that the transmittance is equal to or greater than the predetermined reference value, the process proceeds to step S41.
The process proceeds to step S42, where a flag is set. In step S43, the value of the gain β is determined on the assumption that there is no change in the transmittance over time. For example, as described with reference to FIG. 6, when the gain β is obtained by multiplying the coefficient K2 by the transmittance, the gain β is determined by multiplying the coefficient K2 by the predetermined transmittance determined in step S41. Then, in step S14, the next wafer is subjected to exposure processing. If it is determined in step S15 that all the exposure processing has not been completed, the state of the flag is determined in step S45.
If it is not set to 14, the process proceeds to step S10.

As described above, according to the procedure shown in FIG. 10, if the transmittance exceeds a predetermined value, there is no need to calculate a transmittance time change prediction line, and the processing time can be shortened and the throughput can be improved.

When measuring the illuminance on the wafer 25 by the illuminance sensor 28, the following points must be noted. The transmittance of the reticle is affected by the pattern density of the reticle 16, and if the position of the reticle is different each time the illuminance sensor 28 measures the illuminance on the wafer 25, accurate transmittance cannot be measured. Therefore, the wafer 25 is detected by the illuminance sensor 28.
When the illuminance is measured above, the reticle 16 needs to be set at the same position on the reticle stage 18.

Further, the ratio of the pattern area (the area of the light-shielding portion (chrome)) to the reticle surface area (the area of the rectangular area where the pattern is formed) is small, and the ratio of the pattern area to the reticle surface area is a so-called white reticle. The transmittance of a reticle having a large value, that is, a so-called black reticle, differs greatly. The black reticle has a low transmittance of the exposure light to be illuminated.
May be lower than the sensitivity of the sensor 28 in some cases. In this case, the measurement of the illuminance on the wafer 25 is practically impossible, so that it is not possible to calculate the transmittance time change prediction line.

In order to measure the illuminance on the wafer 25 by using the reticle 16 having the measurement transparent area RA formed outside the reticle pattern area RP as shown in FIG. The illuminance sensor 28 may be moved to a position conjugate to the system 23 to measure the illuminance on the wafer stage. PE indicates the position of the pellicle frame. The shape and quantity of the transparent area are not limited to those shown in FIG. Even if the transparent area RA is not used, the illuminance sensor 28 may be arranged at a position conjugate with the area where the pattern density of the reticle 16 is low and the projection optical system 23. Alternatively, the reticle stage 18 itself may be provided with an opening through which illumination light passes. The reticle stage 18 may be completely retracted from the illumination optical path and measured by the illuminance sensor 28.

In the above embodiment, the time change of the transmittance of the optical system from the integrator sensor 10 to the wafer stage 26 is predicted or measured, and the intensity of the exposure light emitted from the light source 1 is adjusted. Thus, the integrated light quantity (exposure dose) of the plurality of pulsed lights respectively irradiated to each point on the wafer is controlled to an appropriate value. However, for example, in a scanning projection exposure apparatus (scanning stepper) using a pulse beam as exposure light, according to the transmittance predicted as described above or the intensity of the exposure light on the wafer obtained from the transmittance. Adjusting the number of pulsed light beams irradiated to one point on the wafer by the scanning exposure, that is, the width of the exposure light on the wafer in the scanning direction,
At least one of the oscillation frequency of the light source 1 and the scanning speed of the wafer may be adjusted to control the exposure dose to an appropriate value. In short, the exposure dose (exposure amount) given to the wafer by the scanning exposure is adjusted to an appropriate value by adjusting at least one of the intensity of the exposure light, the width of the exposure light, the oscillation frequency, and the scanning speed on the wafer. do it. At this time, the intensity of the exposure light on the wafer is adjusted by changing the voltage applied to the light source 1 to adjust the emission intensity, or by rotating the turret plate TP in FIG. The adjustment can be performed by using the adjustment of the ND filter together with the replacement of the ND filter.

In a scanning projection exposure apparatus (scanning stepper) that uses continuous light as exposure light, the light emission intensity of the light source is calculated according to the above-described predicted transmittance or the intensity of exposure light on the wafer. The above-mentioned exposure dose is adjusted to an appropriate value by adjusting at least one of the transmittance (dimming rate) of the light amount adjuster such as the middle turret plate TP, the width of the exposure light on the wafer, and the scanning speed of the wafer. What is necessary is to control. Further, in a projection exposure apparatus (stepper) that uses a pulse beam as exposure light and exposes a wafer with a reticle pattern image while the reticle and the wafer are stationary,
At least one of the intensity of the exposure light (emission intensity of the pulse light source, etc.) on the wafer and the number thereof may be adjusted. In a stepper that uses continuous light as exposure light, at least one of the intensity of the exposure light (emission intensity of a light source, etc.) on the wafer and the irradiation time may be adjusted.

If the fluctuation of the transmittance of the illumination optical system and the projection optical system cannot be ignored during the exposure, the above-mentioned adjustment (for example, the adjustment of the intensity of the exposure light on the wafer and the number of pulses) is performed during the exposure. Alternatively, in particular, in a scanning stepper using a pulse beam, the number of exposure pulses may be determined by further considering the amount of change (or change rate) in transmittance during scanning exposure.

By the way, in the above-described embodiment (FIG. 1), the projection optical system 23 is composed of only a refractive optical element such as a lens. May be combined, and a so-called catadioptic optical system may be used, or an optical system consisting of only a reflective optical element may be used.

Although the ArF laser has been described as the exposure light, the present invention can be applied to a projection exposure apparatus using EUVL such as a soft X-ray having a shorter wavelength. Also,
The transmittance of the optical system was measured at a plurality of times using the exposure light to calculate the transmittance time change prediction line, but using another light source that emits light having a wavelength substantially equal to the wavelength of the exposure light Is also good. Further, when the transmittance of the projection optical system does not fluctuate or is small, the transmittance time-change characteristic may be obtained only for the illumination optical system. In this case, an illuminance sensor is arranged on the reticle stage and the integrator sensor 1
The transmittance is measured based on 0 and the output value of the illuminance sensor. Conversely, when there is no or little change in the transmittance of the illumination optical system, the transmittance time change characteristic may be obtained only for the projection optical system. In this case, the illuminance may be measured by extracting exposure light from between the illumination optical system and the projection optical system. When determining the transmittance time change characteristic of one of the projection optical system and the illumination optical system, exposure light may be used, or another light source that emits light having a wavelength substantially equal to the wavelength of the exposure light may be used.

An exposure apparatus for calculating a transmittance time prediction characteristic and performing exposure control based on this prediction characteristic electrically or mechanically or chemically converts a large number of components described in the present embodiment. Assembled by connecting.

[0087]

As described above, according to the present invention, the transmittance time change prediction characteristic is calculated, and the exposure is controlled based on the prediction characteristic. Therefore, the transmittance of the illumination optical system or the projection optical system is controlled. Even if the value fluctuates during exposure or when the apparatus is stopped, the photosensitive substrate can be properly exposed. For example, the illuminance on the photosensitive substrate can be controlled to an appropriate value, or the integrated amount of exposure light (exposure dose) on the photosensitive substrate can always be controlled to an appropriate value according to the sensitivity of the photosensitive substrate. Further, according to the present invention, even if the conditions for exposing the photosensitive substrate or the conditions for illuminating the mask are changed, or the intensity distribution of the exposure light on the pupil plane of the projection optical system, that is, in the illumination optical system, Even if at least one of the intensity distribution (ie, shape and size) of the secondary light source, the pattern on the mask to be transferred to the photosensitive substrate, and the numerical aperture of the projection optical system is changed, the transmittance time during the exposure processing is changed. Since the change prediction characteristic is calculated, it is possible to prevent a change in exposure dose on the photosensitive substrate due to a change in transmittance of the illumination optical system or the projection optical system. Furthermore, if the transmittance time change characteristic is calculated by irradiating light having substantially the same wavelength as the exposure light before exposure, the transmittance time change characteristic can be calculated simultaneously with the light cleaning before the exposure processing. Also, a decrease in throughput is prevented. Further, according to the present invention, since the transmittance time change prediction characteristic is calculated and the semiconductor device is manufactured by controlling the exposure based on the prediction characteristic, the manufacturing yield of the semiconductor device can be improved. .

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration of a projection exposure apparatus according to the present invention.

FIG. 2 is a view showing a variable aperture stop formed on the turret plate shown in FIG. 1;

3 is a diagram showing a state of a variable aperture stop in an illumination optical system formed at a pupil position of a projection optical system in the projection exposure apparatus in FIG.

FIG. 4 is a graph showing the relationship between exposure time and transmittance.

FIG. 5 is a flowchart showing a procedure for exposing a pattern on a wafer while calculating a transmittance time change prediction line.

FIG. 6 is a block diagram of a feedback system for controlling the illuminance target value of the exposure light on the wafer.

FIG. 7 is a graph showing the relationship between exposure time and transmittance.

FIG. 8 is a flowchart showing another example of a procedure of exposing a pattern on a wafer while calculating a transmittance time change prediction line.

FIG. 9 is a flowchart showing still another example of a procedure for exposing a pattern on a wafer while calculating a transmittance time change prediction line.

FIG. 10 is a flowchart showing still another example of a procedure for exposing a pattern on a wafer while calculating a transmittance time change prediction line.

FIG. 11 is a plan view of a reticle provided with a transparent area for measurement provided on a reticle with a pellicle.

FIG. 12 is a diagram illustrating a transmittance that varies according to an exposure time.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 ArF excimer laser light source 7 turret plate 7 a to 7 h variable aperture stop in illumination optical system 10 integrator sensor 16 reticle 23 projection optical system 25 wafer 28 illuminance sensor 40 control circuit 51 illuminance target value setting circuit 54 gain α calculator 57 storage device 58 Timer 59 Gain β calculator Ep Aperture stop in projection optical system

Claims (43)

[Claims] 1. A projection exposure apparatus comprising: an optical system for projecting an image of a pattern illuminated by exposure light from an exposure light source onto a photosensitive substrate, wherein the transmittance of the exposure light in the optical system changes with time. In the projection exposure method, the transmittance of the optical system with respect to light having substantially the same wavelength as the exposure light is measured at a plurality of different times, and the transmittance time of the optical system is determined based on the measured plurality of transmittances. A projection exposure method, wherein a change characteristic is predicted, and the pattern is projected on the photosensitive substrate based on the prediction result. 2. The projection exposure method according to claim 1, wherein light having substantially the same wavelength as the exposure light is emitted from a light source that emits the exposure light. 3. The projection exposure method according to claim 1, wherein the plurality of different time points is a time point before irradiating the optical system with light having substantially the same wavelength as the exposure light, and substantially the same as the exposure light. A projection exposure method, wherein the method is a time point after irradiating the optical system with light having a wavelength for a predetermined time, and the both time points are before projecting the pattern onto the photosensitive substrate. 4. The projection exposure method according to claim 1, wherein the plurality of different times include a time before the image of the pattern illuminated with the exposure light is projected onto the photosensitive substrate, and the exposure light. A time point after the image of the pattern illuminated in step (c) is projected onto the photosensitive substrate. 5. The projection exposure method according to claim 2, wherein the plurality of different time points are: a time point before an image of the pattern illuminated with the exposure light is projected onto one photosensitive substrate; A projection exposure method, which is a time point after an image of the pattern illuminated with exposure light is projected on one photosensitive substrate. 6. The projection exposure method according to claim 2, wherein the plurality of different points in time are points before projecting an image of the pattern illuminated with the exposure light onto a predetermined area on the photosensitive substrate; A projection exposure method, which is a time point after an image of the pattern illuminated by the exposure light is projected onto the predetermined area. 7. The projection exposure method according to claim 6, wherein said predetermined area is an exposure area of one chip. 8. The projection exposure method according to claim 6, wherein the predetermined area is an exposure area of one shot. 9. The projection exposure method according to claim 2, wherein the optical system illuminates the pattern with the exposure light and an image of the pattern illuminated by the illumination optical system. A projection optical system for projecting on a transparent substrate, wherein the transmittance is measured a plurality of times by at least one of the illumination optical system and the projection optical system, and the transmittance of the at least one optical system changes with time. A projection exposure method comprising predicting characteristics. 10. The projection exposure method according to claim 1, wherein the optical system has an illumination optical system that illuminates the pattern with the exposure light, and a variation in transmittance of the illumination optical system is the optical system. In the case of contributing to the variation of the transmittance, the transmittance of the illumination optical system with respect to light having substantially the same wavelength as the exposure light is measured at a plurality of different points in time to predict the time change characteristic of the transmittance of the optical system. A projection exposure method. 11. The projection exposure method according to claim 10, wherein said optical system further comprises a projection optical system for projecting an image of said pattern illuminated by said illumination optical system onto said photosensitive substrate, When a change in the transmittance of the illumination optical system and the projection optical system contributes to a change in the transmittance of the optical system, a plurality of transmittances of the illumination optical system and the projection optical system with respect to light having substantially the same wavelength as the exposure light are used. A time-varying characteristic of transmittance of the optical system by measuring at different points in time. 12. The projection exposure method according to claim 1, wherein the optical system has a projection optical system that projects the image of the pattern onto the photosensitive substrate with the exposure light. When the change in the transmittance contributes to the change in the transmittance of the optical system, the transmittance of the projection optical system with respect to light having substantially the same wavelength as the exposure light is measured at a plurality of different times, and the transmittance of the optical system is measured. A projection exposure method, wherein a time change characteristic of the projection exposure is predicted. 13. The projection exposure method according to claim 12, wherein said optical system further comprises an illumination optical system for illuminating said pattern with said exposure light, and said illumination for light having substantially the same wavelength as said exposure light. When the variation in the transmittance of the optical system and the projection optical system contributes to the variation in the transmittance of the optical system, the transmittance of the illumination optical system and the projection optical system is measured at a plurality of different points in time, and the transmittance of the optical system is measured. A projection exposure method characterized by estimating a time change characteristic of a rate. 14. The projection exposure method according to claim 1, wherein the integrated light amount of the exposure light irradiated onto the photosensitive substrate is calculated based on the predicted time change characteristic of the transmittance. A projection exposure method, wherein the exposure value is controlled to an appropriate value according to sensitivity. 15. The projection exposure method according to claim 1, wherein the intensity of the exposure light applied to the photosensitive substrate is adjusted based on the predicted time change characteristic of the transmittance. Projection exposure method. 16. The projection exposure method according to claim 1, wherein said exposure light source emits a pulse beam of exposure light from said exposure light source to project said pattern formed on a mask onto said photosensitive substrate. When the photosensitive substrate is relatively moved with respect to exposure light generated from the mask and passing through the projection optical system in synchronization with the relative movement of the mask with respect to light, Based on the time change characteristic, the intensity of the exposure light incident on the photosensitive substrate, the width of the exposure light on the photosensitive substrate with respect to the moving direction of the photosensitive substrate, and the photosensitive substrate with respect to the moving direction And adjusting at least one of a moving speed of the exposure light source and an oscillation frequency of the exposure light source to control an integrated light amount of the exposure light to an appropriate value corresponding to the sensitivity of the photosensitive substrate. . 17. The projection exposure method according to claim 1, wherein the calculation is performed based on a ratio between the illuminance of the exposure light emitted from the exposure light source and the illuminance of the exposure light on the photosensitive substrate. A time-varying characteristic from a plurality of transmittances. 18. A projection exposure apparatus comprising an optical system for projecting an image of a pattern illuminated with exposure light from an exposure light source onto a photosensitive substrate, wherein the transmittance of the exposure light in the optical system changes with time. Measuring means for measuring the transmittance of the optical system with respect to light having substantially the same wavelength as the exposure light at a plurality of different points in time; and based on the measured plurality of transmittances, the time change of the transmittance of the optical system. A projection exposure apparatus comprising: a prediction unit that predicts characteristics. 19. The projection exposure apparatus according to claim 18, wherein the light having substantially the same wavelength as the exposure light is exposure light emitted from the exposure light source. 20. The projection exposure apparatus according to claim 18, wherein the plurality of different time points are a time point before irradiating the optical system with light having substantially the same wavelength as the exposure light, and substantially the same as the exposure light. A projection exposure apparatus, wherein the point of time is a point in time after light of a wavelength is irradiated onto the optical system for a predetermined time, and the two points in time are before the pattern is projected on the photosensitive substrate. 21. The projection exposure apparatus according to claim 19, wherein the plurality of different times include a time before the image of the pattern illuminated with the exposure light is projected onto the photosensitive substrate, and the exposure light. A projection exposure apparatus, which is a point in time after projecting the image of the pattern illuminated in step (c) onto the photosensitive substrate. 22. The projection exposure apparatus according to claim 19, wherein the plurality of different time points are: a time point before an image of the pattern illuminated with the exposure light is projected onto one photosensitive substrate; A projection exposure apparatus, which is a point in time after projecting an image of the pattern illuminated with exposure light onto one photosensitive substrate. 23. The projection exposure apparatus according to claim 19, wherein the plurality of different points in time are points before projecting an image of the pattern illuminated with the exposure light onto a predetermined area on the photosensitive substrate; A projection exposure apparatus, which is a point in time after projecting an image of the pattern illuminated with the exposure light onto the predetermined area. 24. The projection exposure apparatus according to claim 23, wherein the predetermined area is an exposure area of one chip. 25. The projection exposure apparatus according to claim 23, wherein the predetermined area is an exposure area of one shot. 26. The projection exposure apparatus according to claim 19, wherein the optical system includes an illumination optical system that illuminates the pattern with the exposure light, and an image of the pattern illuminated by the illumination optical system. A projection optical system for projecting on a transparent substrate, wherein the measurement unit performs the measurement of the transmittance a plurality of times at least one of the illumination optical system and the projection optical system, and the prediction unit is the at least one of the at least one A projection exposure apparatus for estimating a temporal change characteristic of the transmittance of an optical system. 27. The projection exposure apparatus according to claim 19, wherein said optical system has an illumination optical system for illuminating said pattern with said exposure light, and said optical system has a variation in transmittance. The measurement means measures the transmittance of the illumination optical system with respect to light having substantially the same wavelength as the exposure light at a plurality of different times, and the prediction means performs the measurement multiple times. A projection exposure apparatus, wherein a time change characteristic of the transmittance of the optical system is predicted based on a result. 28. The projection exposure apparatus according to claim 27, wherein said optical system further comprises a projection optical system for projecting an image of said pattern illuminated by said illumination optical system onto said photosensitive substrate, When a change in the transmittance of the illumination optical system and the projection optical system contributes to a change in the transmittance of the optical system, a plurality of transmittances of the illumination optical system and the projection optical system with respect to light having substantially the same wavelength as the exposure light are used. The projection exposure apparatus is characterized in that the measurement is performed at different points in time, and the predicting unit predicts a time-dependent characteristic of the transmittance of the optical system based on a result of the plurality of measurements. 29. The projection exposure apparatus according to claim 18, wherein the optical system has a projection optical system that projects the image of the pattern onto the photosensitive substrate with the exposure light. When the change in the transmittance contributes to the change in the transmittance of the optical system, the measuring unit measures the transmittance of the projection optical system with respect to light having substantially the same wavelength as the exposure light at a plurality of different times,
The projection exposure apparatus, wherein the prediction unit predicts a temporal change characteristic of the transmittance of the optical system based on a plurality of measurement results. 30. The projection exposure apparatus according to claim 29, wherein the optical system further includes an illumination optical system for illuminating the pattern with the exposure light, and a transmittance of the illumination optical system and the projection optical system. When the change contributes to the change in the transmittance of the optical system, the transmittance of the illumination optical system and the projection optical system is measured at a plurality of different points in time, and the predicting unit performs the optical measurement based on the results of the multiple measurements. A projection exposure apparatus for predicting a time change characteristic of the transmittance of a system. 31. The projection exposure apparatus according to claim 18, wherein the integrated light amount of the exposure light irradiated onto the photosensitive substrate is calculated based on the predicted time change characteristic of the transmittance. A projection exposure apparatus comprising integrated exposure amount control means for controlling an appropriate exposure value according to sensitivity. 32. The exposure exposure apparatus according to claim 18, wherein the intensity of the exposure light applied to the photosensitive substrate is adjusted based on the estimated time-dependent transmittance characteristic. A projection exposure apparatus comprising: 33. A projection exposure apparatus according to claim 18, wherein said exposure light source emits a pulse beam exposure light from an exposure light source and projects said pattern formed on a mask on said photosensitive substrate. When the photosensitive substrate is relatively moved with respect to exposure light generated from the mask and passing through the projection optical system in synchronization with the relative movement of the mask with respect to Based on the change characteristics, the intensity of the exposure light incident on the photosensitive substrate, the width of the exposure light on the photosensitive substrate with respect to the moving direction of the photosensitive substrate, and the photosensitive substrate with respect to the moving direction. A control unit that adjusts at least one of a moving speed and an oscillation frequency of the exposure light source to control an integrated light amount of the exposure light to an appropriate value according to the sensitivity of the photosensitive substrate. To throw Exposure apparatus. 34. The projection exposure apparatus according to claim 18, wherein said predicting means is a ratio of illuminance of exposure light emitted from said exposure light source to illuminance of said exposure light on said photosensitive substrate. A projection exposure apparatus that calculates the time-varying characteristics of the transmittance based on a plurality of transmittances calculated based on the above. 35. A projection exposure apparatus comprising an optical system for projecting an image of a pattern illuminated with exposure light from an exposure light source onto a photosensitive substrate, wherein the transmittance of the exposure light in the optical system changes with time. In a method of manufacturing a semiconductor device, the transmittance of the optical system to light having substantially the same wavelength as the exposure light is measured at a plurality of different times, and the transmittance of the optical system is determined based on the measured plurality of transmittances. A time-varying characteristic of the semiconductor device, and projecting the pattern on the photosensitive substrate based on the result of the prediction to manufacture the semiconductor device. 36. A projection exposure apparatus comprising an optical system for projecting an image of a pattern illuminated with exposure light from an exposure light source onto a photosensitive substrate, wherein the transmittance of the exposure light in the optical system changes with time. In the optical system light cleaning method, the transmittance of the optical system to light having substantially the same wavelength as the exposure light is measured at a plurality of different times, and the transmittance of the optical system is determined based on the measured plurality of transmittances. Optical cleaning of an optical system of a projection exposure apparatus, wherein the optical system is optically cleaned while predicting the time change characteristic of the optical system. 37. The optical cleaning method according to claim 36, wherein the plurality of different time points are a time point before irradiating the optical system with light having substantially the same wavelength as the exposure light, and a time point having substantially the same wavelength as the exposure light. An optical system light cleaning method for a projection exposure apparatus, wherein the optical system is irradiated with light for a predetermined time, and the two time points are before the pattern is projected onto the photosensitive substrate. 38. An illumination optical system for illuminating an original on which a predetermined pattern is formed with exposure light emitted from an exposure light source;
A projection optical system for projecting the pattern of the original illuminated by the illumination optical system onto a photosensitive substrate, wherein the transmittance of the exposure light in the projection optical system changes with time. An original illuminance detector that detects the illuminance of the exposure light applied to the original, a substrate illuminance detector that detects the illuminance of the exposure light on the photosensitive substrate, and an original detected by the original illuminance detector. Calculating the ratio between the illuminance of the exposure light to be irradiated and the illuminance of the exposure light to be applied to the substrate detected by the substrate illuminance detector a plurality of times, and changing the exposure light transmittance in the projection optical system with time; And a control device that adjusts the integrated light amount of the exposure light incident on the photosensitive substrate based on the predicted time change characteristic and the ratio of the two illuminances. Projection exposure apparatus. 39. In the projection exposure apparatus according to claim 37, when the transmittance of the exposure light in the illumination optical system changes with time, the predicting means includes an optical system of the illumination optical system and the projection optical system. A projection exposure apparatus for estimating a time change characteristic of an exposure light transmittance in a system. 40. An illumination optical system for illuminating an original on which a predetermined pattern is formed with exposure light emitted from an exposure pulse light source, and projecting the pattern of the original illuminated by the illumination optical system onto a photosensitive substrate. A projection optical system, wherein the transmittance of the exposure light in at least one of the illumination optical system and the projection optical system changes with time, wherein the exposure light source irradiates the original from the exposure light source. An original plate illuminance detector that detects illuminance, a substrate illuminance detector that detects the illuminance of exposure light on the photosensitive substrate, and an illuminance of the exposure light irradiated on the original plate detected by the original plate illuminance detector and the substrate Predicting means for calculating the ratio of the illuminance of the exposure light applied to the substrate to the illuminance detected by the illuminance detector a plurality of times and estimating the time change characteristic of the exposure light transmittance in the projection optical system The photosensitive substrate, based on the predicted time change characteristic and the ratio of the two illuminances, such that the integrated amount of exposure light applied to the photosensitive substrate becomes an appropriate value according to the photosensitive substrate. A control device for adjusting at least one of the intensity and the number of pulses of the pulse exposure light applied to the projection exposure device. 41. An illumination optical system for illuminating an original on which a predetermined pattern is formed with exposure light emitted from an exposure pulse light source, and projecting the pattern of the original illuminated by the illumination optical system onto a photosensitive substrate. A projection optical system, wherein the transmittance of the exposure light in at least one of the illumination optical system and the projection optical system changes with time, the projection exposure method of the projection exposure apparatus, the exposure light emitted from the exposure light source Calculating the ratio between the illuminance and the illuminance of the exposure light on the photosensitive substrate a plurality of times, and predicting a time-change characteristic of the transmittance of the exposure light in at least one of the illumination optical system and the projection optical system; Step, the illuminance of the exposure light emitted from the exposure light source, the ratio of the illuminance of the exposure light on the photosensitive substrate, based on the time change characteristics of the predicted transmittance Projection exposure method characterized by comprising the step of adjusting at least one of the intensity of the pulsed exposure light incident on the photosensitive substrate and the number of pulses. 42. An illumination optical system for illuminating an original plate on which a predetermined pattern is formed with exposure light emitted from an exposure light source;
A projection optical system for projecting an image of the pattern of the original plate illuminated by the illumination optical system onto a photosensitive substrate, wherein the transmittance of exposure light in at least one of the illumination optical system and the projection optical system is time-dependent. In the exposure method of the projection exposure apparatus that changes with, the ratio of the illuminance of the exposure light emitted from the exposure light source and the illuminance of the exposure light on the photosensitive substrate is calculated a plurality of times, the illumination optical system And a step of estimating the time change characteristic of the transmittance of the exposure light in at least one of the projection optical system; and the illuminance of the exposure light emitted from the exposure light source, and the exposure light on the photosensitive substrate. Adjusting the intensity of the exposure light applied to the photosensitive substrate based on the ratio with respect to the illuminance and the estimated temporal change characteristic of the transmittance. 43. An illumination optical system for illuminating an original on which a predetermined pattern is formed with exposure light emitted from an exposure light source;
A projection optical system for projecting the pattern of the original illuminated by the illumination optical system onto a photosensitive substrate, wherein the transmittance of the exposure light in the projection optical system changes with time. The ratio of the illuminance of the exposure light emitted from the exposure light source to the illuminance of the exposure light on the photosensitive substrate is calculated a plurality of times, and the time change characteristic of the transmittance of the exposure light in the projection optical system is calculated. The step of predicting, the illuminance of the exposure light emitted from the exposure light source, the ratio of the illuminance of the exposure light on the photosensitive substrate, and based on the time change characteristics of the predicted transmittance, Adjusting the intensity of the exposure light applied to the photosensitive substrate.