JPH0936018A - Projection exposure device - Google Patents

Abstract

(57) [Abstract] [Problem] To constantly detect the amount of light passing through the projection optical system,
Finely correct the imaging characteristics of the projection optical system. SOLUTION: A light amount of illumination light IL reflected by a beam splitter 10 provided between a light source 1 and a reticle R by a predetermined ratio is measured by an integrator sensor 40 to detect a basic output value I ₀ . At the same time, the basic energy dose P ₀ transmitted through the projection optical system 14 at that time is detected by the dose monitor 20 provided on the Z stage 15. And
Thereafter, if necessary, the energy dose P (t) transmitted through the projection optical system 14 is calculated from the photoelectric output value I (t) of the integrator sensor 40 as P (t) = P ₀ · I (t) / I ₀ . Then, the change in the imaging characteristic due to the energy dose P (t) is corrected by the pressure adjuster 30 connected to the projection optical system 14.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection exposure apparatus used in a photolithography process for manufacturing a semiconductor device, a liquid crystal display device, an image pickup device (CCD, etc.), a thin film magnetic head, etc. It is suitable to be applied to a projection exposure apparatus having a function of correcting the image forming characteristic of the projection optical system according to the exposure amount.

[0002]

2. Description of the Related Art For example, one of the important performances of a projection exposure apparatus such as a stepper for reducing and projecting a pattern of a reticle (or a photomask) onto a wafer (or a glass plate) through a projection optical system is used. Accuracy is mentioned. That is, since a semiconductor element or the like is formed by stacking different circuit patterns on a wafer in multiple layers, it is necessary to precisely superimpose the reticle on which the circuit pattern is drawn and the pattern of each shot area on the wafer. is there. An important factor that affects the overlay accuracy is a magnification error (distortion) of the projection optical system. The size of patterns used in VLSIs and the like has become more and more miniaturized year by year, and along with this, the demand for improvement in overlay accuracy on a wafer is also increasing. Therefore,
There is a growing need to keep the projection magnification at a predetermined value.

The projection magnification of the projection optical system depends on a slight temperature change of the apparatus, a slight atmospheric pressure change of the atmosphere in a clean room where the projection exposure apparatus is placed, a temperature change, and exposure light to the projection optical system. Depending on the irradiation history of the irradiation energy (energy rays), etc., it varies in the vicinity of a predetermined magnification. Therefore, as a recent projection exposure apparatus, one having a magnification correction mechanism for finely adjusting the magnification of the projection optical system to realize a predetermined magnification is also used. As the magnification correction mechanism, specifically, a mechanism for changing the distance between the reticle and the projection optical system, a mechanism for changing a predetermined lens distance in the projection optical system, and a predetermined air provided in the projection optical system. Mechanisms such as adjusting the pressure in the chamber have already been proposed. Further, the focus position (image plane position) also moves due to the same variation factor as the magnification. Therefore, as a recent projection exposure apparatus, one having a focus correction mechanism is also used.

Now, among the factors of variation of the above-mentioned image forming characteristics,
As for the influence of the energy rays on the image forming characteristics of the projection optical system, as disclosed in, for example, Japanese Patent Laid-Open No. Sho 60-78454, they are provided in the projection optical system according to the irradiation history of the energy rays. A predetermined projection state can be controlled by a method of adjusting the pressure of the air chamber. Regarding the energy dose returning to the projection optical system by reflection on the projection surface on the wafer, see Japanese Patent Laid-Open No. 183522/1987.
As disclosed in the publication, a method using a reflected energy detector such as a reflectance monitor for measuring the returned energy dose is proposed.

However, the energy dose that passes through the projection optical system and contributes to image formation is determined by the exposure conditions determined by the open / closed state of the shutter, the exposure light intensity (light intensity of the light source), the reticle transmittance, and the like. The amount of energy that has actually passed through the projection optical system before exposure of the wafer (basic energy dose) is measured using a photoelectric sensor provided on the wafer stage, and the basic energy dose is stored. Was there. The basic energy dose does not change during subsequent exposure, and the energy dose during exposure is determined according to the open / closed state of the shutter.

FIG. 4 shows an explanatory view of a conventional method for determining the energy dose during exposure. FIG. 4A shows the relationship between time and the open / closed state of the shutter, and FIG. 4B shows the relationship between time and the energy dose. This figure 4
In (a), the horizontal axis represents time t, and the vertical axis represents the shutter open / closed state function S (t). The value of the shutter open / closed state function S (t) is 1 in the open state and 0 in the closed state. There is.
Further, in FIG. 4B, the horizontal axis represents time t, and the vertical axis represents the energy dose E (t) passing through the projection optical system.

In FIG. 4A, the open / close state function S (t) of the shutter is, as represented by a solid line 101 having a rectangular wave shape, between time t _11A and time t ₁₂ and between time t ₁₃ and time t 12. _It is in the open state 1 between ₁₄ and _14, and is in the closed state 0 at other times. Then, as shown by the solid line 102 in FIG. 4B, the energy dose E (t) is between the time t _11A and the time t ₁₂ and between the time t ₁₃ and the time t ₁₄ , that is, the shutter is opened. The basic energy dose E ₀ is obtained in the state 1, and is ₀ at other times, that is, when the shutter is in the closed state 0. That is, the energy dose E (t) transmitted through the projection optical system at time t is E (t) = E ₀ × S
The image forming characteristic of the projection optical system is corrected via the correction control system based on the energy dose E (t) calculated at (t).

[0008]

According to the above prior art, since there is no effective method for measuring the energy dose transmitted through the projection optical system especially during exposure, the value of the basic energy dose E ₀ is once After the measurement, it is assumed that a certain period (usually the exposure time for one lot of wafers, or the period until the mask or blind (variable field diaphragm) is changed) does not change, and the amount of delicate change in energy dose during that period. Was ignored. However, recently regarding this,
A photoelectric sensor (integrator sensor) for continuously measuring the amount of illumination light even during actual exposure of the wafer is provided. Moreover, the energy dose was calculated using only the completely opened / closed state of the shutter, and the intermediate state of opening / closing was not taken into consideration. Nowadays, there is an increasing demand for miniaturization for highly integrated circuits such as VLSI, and there is a problem that the conventional method cannot sufficiently correct the imaging characteristics such as the projection magnification of the projection optical system.

In view of the above point, the present invention can always measure the amount of light transmitted through the projection optical system regardless of during exposure, and when the shutter is used, for example, the shutter goes through an intermediate state of completely opened and closed states. It is an object of the present invention to provide a projection exposure apparatus capable of highly accurately correcting an image forming characteristic in response to a subtle change.

[0010]

A projection exposure apparatus according to the present invention illuminates a pattern on a mask (R) with illumination light (IL) from a light source (1) for exposure and projects the pattern on a projection optical system ( A first photoelectric sensor (20) for measuring the amount of illumination light (IL) that has passed through the projection optical system (14) in a projection exposure apparatus that transfers the light onto a photosensitive substrate (W) via 14). , The illumination light from the light source (1) (I
L) a second photoelectric sensor (40) for measuring the light amount of at least a part, and the amount of change in the imaging characteristics of the projection optical system (14) is calculated based on the measurement values of the first and second photoelectric sensors. And an image formation characteristic correction means (30) for correcting the image formation characteristic of the projection optical system (14) based on the calculation result of this operation means.

According to the projection exposure apparatus of the present invention having the above structure, when the amount of light transmitted through the projection optical system (14) cannot be measured by the first photoelectric sensor (20), for example, during actual exposure, exposure is performed in advance. Before entering, the amount of light transmitted through the projection optical system (14) is measured by the first photoelectric sensor (20). In this case, the measured light quantity is, for example, the initial light quantity P ₀ . At the same time, a part of the light quantity is measured by the second photoelectric sensor (40). In this case, the photoelectric output value of the second photoelectric sensor (40) is I ₀ . The amount of light detected by the second photoelectric sensor (40) is assumed to be a constant ratio with respect to the amount of light transmitted by the projection optical system (14) and detected by the first photoelectric sensor (20). For example, the amount P of light transmitted through the projection optical system (14) at the time of actual exposure is P = P ₀ · I / I ₀ from the photoelectric output value I of the second photoelectric sensor (40) at that time.
Is calculated by

At the time of actual exposure, the projection optical system (14)
The amount of light that passes through changes due to various factors, and the imaging characteristics of the projection optical system (14) change. In the past, there was no effective method for detecting the amount of transmitted light of the projection optical system (14) during exposure, and therefore the amount of light on the substrate (W) during exposure is not taken into consideration without considering the fluctuation of these amounts of light. Since it is assumed to be constant, an error occurs in the image forming characteristic of the projection optical system (14). However, according to the present invention, the amount of light transmitted through the projection optical system (14) is finely detected during the exposure, and the projection means (31) calculates the projection optical system (1) based on it.
4) The amount of change in the image forming characteristic of the projection optical system (14) is calculated because the image forming characteristic correcting means (30) finely corrects the image forming characteristic of the projection optical system (14). The error is reduced.

In this case, a light amount adjusting means (3) for adjusting the light amount of the illumination light (IL) incident on the projection optical system (14) is provided, and the second photoelectric sensor (40) is used as the light source (1). And the projection optical system (14) thereof. As a result, when the light amount adjusting means (3) adjusts the light amount incident on the projection optical system (14) to an appropriate light amount as necessary, the second photoelectric sensor (40) causes the projection optical system (14). The change in the amount of light incident on can be accurately measured.

Further, the second photoelectric sensor (40) is provided between the second photoelectric sensor (40) and the calculating means (31).
Transfer line (24,
41) is preferably provided. At this time, the detection signal from the second photoelectric sensor (40) is supplied to the calculation means (31) in almost real time through the transfer line,
The amount of light passing through the projection optical system can be accurately calculated in almost real time.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION An example of an embodiment of a projection exposure apparatus according to the present invention will be described with reference to FIGS. In this example, the present invention is applied to a stepper type projection exposure apparatus that collectively exposes a reticle pattern onto each shot area on a wafer. The projection exposure apparatus of this example is disclosed in JP-A-60-78454 and JP-A-62-1.
This is a development of the projection exposure apparatus disclosed in Japanese Patent Publication No. 83522.

FIG. 1 shows a schematic configuration of the projection exposure apparatus of this example. In FIG. 1, the illumination light IL from a light source 1 composed of a mercury lamp is condensed by an elliptical mirror 2 and a shutter 3 is opened. In the state, the light passes through the vicinity of the shutter 3 and is reflected by the dichroic mirror 4. Shutter 3
The shutter 3 is opened / closed by a shutter control unit 32 that controls the opening / closing operation of the shutter 3 and the exposure time. Further, the shutter control unit 32 is controlled by the main control system 31, and the main control system 31 controls the opening signal S for controlling the opening / closing operation of the shutter 3.
T is supplied to the shutter control unit 32. As a light source for exposure, a mercury lamp, a harmonic generator of a YAG laser, or an excimer laser light source such as a KrF excimer laser or an ArF excimer laser is used. However, when a pulse light source such as an excimer laser light source is used, the illumination light is opened and closed by the laser light source, and the shutter is not used.

After being reflected by the dichroic mirror 4,
Illumination light IL converted into a substantially parallel light flux by the input lens 5
Is a light flux of a specific exposure wavelength (for example, i at a wavelength of 365 nm).
It is incident on an optical integrator 8 composed of a fly-eye lens through an optical filter 6 which selects only the line. A large number of secondary light source images are formed on the exit surface of the optical integrator 8, and the illuminance distribution of the illumination light on the reticle R is made uniform. Optical integrator 8
An aperture stop 9 is disposed near the exit surface of the beam splitter 10 and the illumination light IL from the secondary light source image passes through the aperture stop 9 and then reflects the rest with a transmittance of about 98%, for example. To the dichroic mirror 11. The illumination light that has entered the dichroic mirror 11 is transmitted through the beam splitter 10.

On the other hand, the illumination light reflected by the beam splitter 10 is condensed on a light receiving surface of an integrator sensor 40 which is a photoelectric sensor through a condenser lens 39. As an example, the light receiving surface of the integrator sensor 40 is substantially conjugate with the pattern forming surface of the reticle R and the exposure surface of the wafer W, and the light amount corresponding to the irradiation amount on the wafer W is incident on the integrator sensor 40. The detection signal (photoelectric conversion signal) of the integrator sensor 40 is supplied to the signal line 24,
And to the main control system 31 via the A / D converter 41. The detection signal from the integrator sensor 40 is A / D
After being converted into digital data by the converter 41, it is sent to the main control system 31. The main control system 31 stores conversion coefficients and the like for obtaining the irradiation amount (exposure amount per unit time) on the wafer from the detection signal of the integrator sensor 40, and the main control system 31 performs A / D conversion. The irradiation amount on the wafer is calculated from the digital data from the device 41, and each irradiation amount is integrated to obtain the integrated exposure amount on the wafer.

The illumination light transmitted through the beam splitter 10 is bent at a substantially right angle on the surface of the dichroic mirror 11, passes through an illumination field stop (reticle blind) 13 via a condenser lens 12, and then is placed on a reticle R. Illuminate the pattern area with a uniform illuminance distribution. The illumination field diaphragm 13 shields a portion of the reticle R that does not need to be exposed in an arbitrary shape.
The illumination light that has passed through the pattern portion requiring the upper exposure forms a reduced image of the pattern portion on the shot area of the wafer W via the projection optical system 14. The pupil plane 14 of the projection optical system 14
An aperture stop is arranged at a. Here, the Z axis is taken parallel to the optical axis AX of the projection optical system 14, and the X axis and the Y axis are taken on a plane perpendicular to the Z axis.

The wafer W is mounted on the Z stage 15, and the Z stage 15 is mounted on the XY stage 16 so as to be movable in the optical axis AX direction (Z direction). The XY stage 16 is moved on the XY plane by a drive unit 17 such as a motor.
The wafer W is dimensionally movable, and the XY stage 16 positions the wafer W at an arbitrary position. Also, Z
A movable mirror 18 for vertically reflecting a laser beam LB from a laser interferometer (not shown) for detecting a two-dimensional position of the Z stage 15 (or wafer W) is fixed to an end of the stage 15. ing. Immediately above the movable mirror 18, a light blocking plate 19 is fixed to the end of the Z stage 15 without directly contacting the movable mirror 18. This shading plate 1
Reference numeral 9 prevents the movable mirror 18 from being heated by the irradiation of the illumination light that has passed through the projection optical system 14.

Further, although not shown, an image of a pinhole, a slit pattern or the like is projected obliquely with respect to the optical axis AX toward the exposure surface of the wafer W near the image forming surface of the projection optical system 14. An oblique incidence type focus position detection system including an irradiation optical system and a light receiving optical system that re-images the image from the reflected light beam from the projected image is provided. Wafer W
The position in the Z direction on the surface of is detected by this focus position detection system and sent to the main control system 31. The main control system 31 controls the drive system in the Z stage 15 based on this information.

The projection optical system 1 is mounted on the Z stage 15.
An irradiation amount monitor 20 including a photoelectric sensor that detects the amount of illumination light that has passed through 4 is provided. The size of the light receiving surface of the irradiation amount monitor 20 is set to be equal to or larger than the size of the projected image of the pattern area of the reticle R, and the irradiation amount monitor 20 moves the projection optical system 14 after passing through the reticle R. It receives all the illumination light that passes through.

Further, in this example, an air pressure type image forming characteristic correcting mechanism for correcting the image forming characteristic of the projection optical system 14 is provided. This image formation characteristic correction mechanism changes the air pressure in the air chamber between the predetermined lenses in the projection optical system 14 by the main control system 31 via the pressure adjuster 30 and the pipe 23, thereby projecting the optical system 14. The image forming characteristics (projection magnification and focus position) are controlled by a minute amount. in this case,
The pressure adjuster 30 inputs from the main control system 31 a pressure control value capable of momentarily correcting fluctuations in the imaging characteristics due to the transmission of illumination light of the projection optical system 14, and in response thereto, the projection optical system 14 receives. Adjust the pressure of the air supplied to the internal air chamber.

Further, the main control system 31 is also supplied with a signal AS relating to environmental information such as atmospheric pressure and atmospheric temperature around the projection optical system 14 from an environment sensor (not shown), and the main control system 31 is connected to the integrator sensor. Based on the detection signal of 40, the magnification variation amount and the focus variation amount due to the incidence of the exposure illumination light in the projection optical system 14 are estimated, and the control pressure value of the air chamber for correcting this variation amount is set as the environmental information. Calculated with consideration.

Next, the method of calculating the amount of transmitted light and the correcting operation of the projection optical system 14 in this example will be described with reference to FIGS. As described above, the illumination light emitted from the light source 1 of FIG. 1 enters the beam splitter 10 through some optical members. The beam splitter 10 reflects a part of the illumination light IL and transmits the remaining light. The transmitted light is incident on the dichroic mirror 11, but the reflected light is incident on the integrator sensor 40, and the detection signal I corresponding to the amount of light incident from the integrator sensor 40.
Is output.

The ratio of the reflected light and the transmitted light of the illumination light IL at the beam splitter 10 is constant, and the ratio does not change even with the intensity of the incident light. Therefore, if this ratio is known, the amount of light incident on the projection optical system 14 from the reticle R side can be calculated by constantly monitoring the amount of light incident on the integrator sensor 40. In this example, the energy dose transmitted through the projection optical system 14 is constantly detected with high accuracy by utilizing the characteristics of the beam splitter as described above and by using the irradiation amount monitor 20 and the integrator sensor 40 in combination. It is a thing. Hereinafter, a specific calculation method will be described.

First, the reticle R is set, the reticle blind 13 is set to a predetermined shape and size, and then,
The XY stage 16 is positioned so that the entire exposure field of the projection optical system 14 enters the light receiving surface of the dose monitor 20. Then, based on a command from the main control system 31, the shutter 3 is opened and the pattern of the reticle R is projected on the light receiving surface of the dose monitor 20, and the energy dose P transmitted through the projection optical system 14 is measured. The measured value of is stored in the main control system 31 as the basic energy dose P ₀ , and the detection signal I of the integrator sensor 40 is taken in. The detection signal I fetched at that time is converted into the basic output value I _0.
Is stored in the main control system 31.

After that, the main control system 31 is based on the detection signal I of the integrator sensor 40, according to the equation (1),
The energy dose P transmitted through the projection optical system 14 is calculated. P = P ₀ · I / I ₀ (1) FIG. 2 is a graph showing the above formula (1). In FIG. 2, the horizontal axis represents the detection signal I of the integrator sensor 40.
And the vertical axis represents the energy dose P transmitted through the projection optical system 14. As shown in FIG. 2, when the detection signal I is 0, the energy dose P is 0, and when the detection signal I has the basic output value I ₀ , the energy dose P is the basic energy dose P _{0 as shown in FIG.} Is indicated by a straight line 50.

Therefore, if the relational expression represented by this straight line 50 is stored, the exposure dose monitor 20 during exposure of the wafer W is determined.
Even when the energy dose transmitted through the projection optical system 14 is not incident on the detection signal I of the integrator sensor 40.
From this, the energy dose P transmitted through the projection optical system 14 can be calculated. The amount of illumination light absorbed and reflected by the reticle R, and the amount of light absorbed and reflected inside the projection optical system 14 may not be proportional to the amount of illumination light IL. Therefore, when further accuracy is required, the illumination light I
It is only necessary to change the light amount of L and perform the same measurement for a plurality of exposure amounts to obtain the relationship between the detection signal I of the integrator sensor 40 and the energy dose P of the irradiation amount monitor 20.

The actual measurement results measured by the above method are shown in FIG. FIG. 3A shows the open / closed state of the shutter, the horizontal axis represents time t, and the vertical axis represents the open / closed state function S of the shutter.
(T) is represented. In FIG. 3A, the value of the open / close state function S (t) is 1 in the open state and 0 in the closed state. Further, FIG. 3B is a plot of the detection signal I (t) of the integrator sensor 40 against time t, the horizontal axis represents the time t, and the vertical axis represents the detection signal I (t) of the integrator sensor 40. It represents. Then, FIG.
Is a plot of energy dose P (t) against time t, the horizontal axis represents time t, and the vertical axis represents energy dose P (t).

In FIG. 3A, the shutter is in the completely closed state 0 from the start time t ₀ to the time t ₁ as shown by the trapezoidal solid polygonal line 51, and the time t ₂ and the time t. _{Between 3} and _3, it is in the completely open state 1. Then, between the time t ₁ and the time t ₂ , the closed state 0
From the open state 1 to the open state 1, and between the time t ₃ and the time t ₄ there is a transition state from the open state 1 to the closed state 0. Then, the operation from the start time t ₀ to the time t ₄ is repeated after the time t ₄ . That is, time t ₄
Between the time t ₅ and the time t _5, and in the period after the time t ₈ are in the completely closed state 0, and in the time between the time t ₆ and the time t ₇ are in the completely open state 1 and the time t ₅ and Between time t ₆ and time t ₇ and time t ₈ , there are a transition state from the closed state 0 to the open state 1 and a transition state from the open state 1 to the closed state 0, respectively.

In this example, the conventional concept shown in FIG.
, The shutter is closed at a certain time, for example
It is not assumed that the state 0 suddenly changes to the open state 1 and the state shown in FIG.
As shown in (a), from the closed state 0 to the open state 1
Transition state and transition state from open state 1 to closed state 0
To consider. The shutter is this figure against time
Integral when opened / closed as shown in 3 (a)
The detection signal I (t) of the data sensor 40 is shown in FIG.
As the shutter is closed 0, 0
Sometimes the basic output value I₀Is shown in solid line 52
The shutter 3 to open and close.
Become For example, time t₁In, the line 52 is
It does not stand up, it rises at a certain inclination angle, time t_TwoTo
Basic output value I₀Reach Also, time t_Threesmell
Suddenly the detection signal I (t) does not become 0,
The time t _FourAt the detection signal I (t)
It becomes 0. Time t_Five~ Time t₈The same applies to.
In this way, the amount of light when the shutter 3 is in the transition state
To monitor changes with the integrator sensor 40
Is the sampling period in the A / D converter 41 of FIG.
Should be set sufficiently fine with respect to the transition time. With one example
Then, for example, at time t in FIG.₁From time t_TwoFor up to
When the transition time is about 50 msec, the A / D converter 41
Sampling cycle at 2 msec (frequency is 50
It may be set to about 0 Hz).

Detection signal I of the integrator sensor 40
(T) also changes due to factors other than the open / closed state of the shutter. As shown by the polygonal line 52, when the shutter 3 is in the open state 1, the detection signal I (t) changes at time t ₂
From time t ₉ to time t _9, it rises again from time t ₉ and reaches the basic output value I ₀ at time t ₃ . Similarly, when the shutter 3 is in the open state 1, the detection signal I (t)
Becomes larger than the basic output value I ₀ from time t ₆ to time t ₁₀ , gradually decreases toward time t ₁₁ and becomes smaller than the basic output value I ₀ , and again at time t ₇ , the basic output value I 0 _{It is 0} . That is, the shutter is in a constant open state 1
Even in the case of, the illumination light amount changes due to the change of the light source output, the opening of the aperture stop, and other factors, and the detection signal I (t) of the integrator sensor 40 changes.

By substituting the detection signal I (t) of FIG. 3 (b) into the equation (1), the energy dose P (t) transmitted through the projection optical system 14 is calculated and plotted with respect to time t. As shown in FIG. 3C, the broken line 52 in FIG.
A solid polygonal line 53 having a similar shape is obtained. As shown by the polygonal line 53, the energy dose P (t) is equal to the shutter 3
Is 0 when the shutter is in the closed state 0, and is approximately the basic energy dose P ₀ when the shutter 3 is in the open state 1. In addition, a transitional state in which the shutter 3 changes from the closed state 0 to the open state 1,
In the transition state in which the open state 1 changes to the closed state 0, the change of the energy dose P (t) also changes at a certain inclination angle so as to be proportional to the detection signal I (t) of FIG. 3B. Further, the energy dose P (t) is the time t
₉ and at times t ₁₀ and t ₁₁ , the detection signal I of FIG.
The change is similar to (t).

Then, the main control system 31 determines the energy dose P (t) previously obtained from the calculated energy dose P (t) passing through the projection optical system 14 and the air chamber in the projection optical system 14. The control correction value of the pressure supplied to the air chamber is calculated based on the relationship with the control pressure, and the pressure of the air chamber is finely controlled via the pressure regulator 30.

Conventionally, as shown in FIG. 4, the shutter opening is considered only in two states of 0 (fully closed state) and 1 (fully opened state). It has been considered that the energy dose transmitted through the optical system is constant corresponding to the opened / closed state of the shutter. However, in reality, the energy dose transmitted through the projection optical system fluctuates even when the shutter is constant and changes stepwise when the shutter is opened and closed, so that an error has occurred in the imaging characteristics of the projection optical system.

However, in this example, the integrator sensor 4
By skillfully utilizing the detection signal of 0, the variation of the amount of light transmitted through the projection optical system 14 is grasped finely and the imaging characteristic of the projection optical system 14 is corrected based on it, so that the imaging characteristic of the projection optical system is corrected. Error is significantly reduced. In addition,
Basic output value I of the integrator sensor 40 that serves as a reference value
₀ and the basic energy dose P ₀ transmitted through the projection optical system
Is detected every time the reticle is replaced and every time the size (or shape) of the reticle blind 13 is changed.

Further, in this example, as the projection state adjusting means, the example in which the image forming characteristic of the projection optical system 14 itself is corrected by the pressure control of the predetermined air chamber has been shown, but as the other projection state adjusting means, , A mechanism for changing the distance between the reticle R and the projection optical system 14, and a specific lens element in the projection optical system 14 (for example, a lens closest to the reticle R).
A mechanism for moving the optical axis in the optical axis direction can be applied as it is.

Further, in FIG. 1, the integrator sensor 40 is used.
The light receiving surface of the integrator sensor 40 is set to be a surface conjugate with the surface of the wafer W.
It may be set in the vicinity of a surface (pupil surface) that optically has a Fourier transform relationship with respect to the surface of. Further, the present invention is not limited to the batch exposure type projection exposure apparatus, but is similarly applied to a scanning exposure type projection exposure apparatus such as a step-and-scan method for performing exposure by relatively scanning a reticle and a wafer. it can.

As described above, the present invention is not limited to the above-described embodiment, and various configurations can be adopted without departing from the gist of the present invention.

[0041]

According to the projection exposure apparatus of the present invention, the amount of light transmitted through the projection optical system can always be indirectly detected by the second photoelectric sensor. Therefore, for example, fluctuation of the light source during exposure or opening / closing of the shutter. It is also possible to detect a transitional fluctuation of the light amount and the like, and there is an advantage that the fluctuation amount of the imaging characteristic due to the incidence of the illumination light on the projection optical system can be corrected with higher accuracy. This makes it possible to cope with miniaturization of VLSI and the like. In particular, by increasing the sampling frequency of the detection signal of the second photoelectric sensor, for example, it is possible to cope with a high-speed transient change when the shutter is opened and closed.

Further, a light amount adjusting means (including a shutter) for adjusting the light amount of the illumination light incident on the projection optical system is provided,
When the second photoelectric sensor is arranged between the light source and the projection optical system, the second photoelectric sensor causes the light to enter the projection optical system even when the light amount is adjusted by the light amount adjusting means during exposure. It is possible to accurately measure the change in the amount of light, and based on that, it is possible to accurately correct the imaging characteristics.

When a transfer line for sequentially outputting the measured value of the second photoelectric sensor is provided between the second photoelectric sensor and the calculation means, the detection signal is calculated in almost real time through the transfer line. Since it is supplied to the means, there is an advantage that it can cope with more rapid changes.

[Brief description of drawings]

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

FIG. 2 is a diagram showing the relationship between the detection signal of the integrator sensor 40 of FIG. 1 and the energy dose transmitted through the projection optical system.

3A is a diagram showing an open / closed state of a shutter in the embodiment of the present invention, FIG. 3B is a waveform diagram showing a change in a detection signal of the integrator sensor 40 corresponding to FIG. 3A, and FIG. ) Is a diagram corresponding to FIG. 3A and showing an energy dose transmitted through the projection optical system.

FIG. 4 is an explanatory diagram of a conventional method of calculating an energy dose that passes through a projection optical system.

[Explanation of symbols]

 R Reticle W Wafer IL Illumination light 1 Light source 3 Shutter 10 Beam splitter 14 Projection optical system 20 Irradiation amount monitor 23 Piping 30 Pressure regulator 31 Main control system 40 Integrator sensor 24 Signal line 41 A / D converter

Claims (3)

[Claims] 1. A projection exposure apparatus that illuminates a pattern on a mask with illumination light from an exposure light source and transfers the pattern onto a photosensitive substrate via a projection optical system, wherein the projection optical system is transmitted. Based on the first photoelectric sensor that measures the light amount of the illumination light, the second photoelectric sensor that measures the light amount of at least a part of the illumination light from the light source, and the measurement values of the first and second photoelectric sensors And an image forming characteristic correcting unit for correcting the image forming characteristic of the projection optical system based on the calculation result of the calculating unit. Projection exposure apparatus. 2. The projection exposure apparatus according to claim 1, further comprising a light amount adjusting means for adjusting a light amount of the illumination light incident on the projection optical system, the second photoelectric sensor being the light source and the projection optical system. A projection exposure apparatus, which is arranged between the system and the system. 3. The projection exposure apparatus according to claim 1, further comprising: a transfer line between the second photoelectric sensor and the arithmetic means for sequentially outputting a measured value of the second photoelectric sensor. A projection exposure apparatus, which is provided.