JPH0521319A - Projection exposure device - Google Patents

Abstract

(57) [Summary] [Purpose] The imaging characteristics of the projection optical system are measured and corrected in real time without using a test reticle, and astigmatism, eccentricity, or spherical aberration that has not been corrected in the past is used. Provided is a projection exposure apparatus capable of suppressing the influence on the image formation characteristic due to. A focusing state detecting means 32A detects a focusing state at at least two places (reference numerals 21a to 21e in FIG. 3) of an exposure region by the projection optical system PL, and at least 2
The image formation characteristic measuring means 32B measures the image formation characteristic of the projection optical system PL from the detection result of the in-focus state at each position. By providing a first pattern extending in the saddle direction and a second pattern extending in the medial direction and measuring the in-focus state by the light passing through these patterns, astigmatism difference, eccentricity, or spherical surface is obtained. Calculate the difference and correct it.

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 for forming an image of a transmitted light flux of a mask pattern on a photosensitive substrate on a stage through a projection optical system, and more particularly, to efficiently form an image forming characteristic of the projection optical system. This is an improved model that enables accurate measurement. This type of projection exposure apparatus is used for manufacturing semiconductor integrated circuits and large-sized liquid crystal substrates.

[0002]

2. Description of the Related Art Techniques for measuring the image forming characteristics of a projection optical system and correcting the projection optical system so that the image forming state of a mask pattern is the best are disclosed in JP-A-60-26343 and JP-A-60-26343. 63-306626 or JP-A-1-27.
It is disclosed in Japanese Patent No. 3318.

The one disclosed in Japanese Patent Application Laid-Open No. 60-26343 is a test reticle having a minute line element,
A light receiving element that is installed on the stage and receives the transmitted light of the test reticle through a minute slit, and based on a change in the output signal from the light receiving element that is obtained when the stage is moved up and down on the Z axis, The characteristics of the projection optical system, for example, the inclination of the image plane and the curvature of the image plane are obtained. Then, the projection optical system is corrected based on this measurement result.

The one disclosed in JP-A-63-306626 or JP-A-1-273318 is a reference reticle having a reference mark provided on a stage and a test reticle having a special reference mark. And irradiating the reference member from its lower surface, and receiving the light flux transmitted through each reference mark of the reference member and the test reticle to measure the image forming characteristics of the projection optical system. Then, a change in the image forming characteristic of the projection optical system due to a temperature rise due to the absorption of the exposure light is predicted in advance, and based on the result, the change in the image forming characteristic at the time of exposure is predicted and corrected. According to these devices, it is possible to correct, in real time, the image forming characteristics of the projection optical system due to thermal energy during exposure, such as variations in image plane inclination and field curvature.

[0005]

However, in such a conventional apparatus, the test reticle is indispensable, and the image forming characteristics of the projection optical system cannot be measured with the actual reticle set. Therefore, there is no guarantee that variations in the imaging characteristics of the projection optical system due to variations in atmospheric pressure and temperature during actual exposure can be corrected accurately. Therefore, especially when the required line width is 0.3 to 0.4 μm as in the next-generation 64M DRAM, sufficient focusing accuracy cannot be expected by the conventional correction of the imaging characteristics by the predictive control. Further, when the test reticle is set and the imaging characteristics are measured and the projection optical system is corrected every time the wafer is exchanged, the throughput is inevitably lowered.

Further, in this type of projection exposure apparatus,
In addition to the above-mentioned field curvature and image plane tilt, astigmatism (hereinafter referred to as "as" in the present specification), eccentricity, or spherical aberration are factors that affect the imaging characteristics of the projection optical system. Although known to exist, these conventional devices
Since the eccentricity or the spherical aberration is not measured, the desired focusing characteristics may not be obtained if the line width becomes extremely thin as described above. The as is the difference between the focal positions in the Medior and Sadital directions, and is due to the astigmatic difference.

When the image formation characteristic of the projection optical system is detected by using a real reticle without using a test reticle, the focus state is measured by using marks formed around the exposure area. The focus cannot be detected in the central part of the area, and therefore, the field curvature, the field inclination, or the astigmatism cannot be measured.

Although it has been conventionally practiced to perform a test print using a test reticle before the start of exposure and to correct the image forming characteristic based on the test print, it is not possible to follow variations in the image forming characteristic during exposure. Also, trial baking for each wafer reduces throughput, which is not realistic.

It is an object of the present invention to enable real-time correction by measuring the image forming characteristic of a projection optical system without using a test reticle, and to obtain astigmatism, eccentricity or spherical surface which has not been conventionally corrected. It is an object of the present invention to provide a projection exposure apparatus capable of suppressing the influence of the convergence on the image forming characteristics.

[0010]

To explain the present invention, referring to FIG. 1 showing an embodiment, the present invention forms an image of a transmitted light flux of a mask pattern R on a photosensitive substrate W on a stage via a projection optical system PL. It is applied to a projection exposure apparatus. And the above-mentioned object is achieved by the following composition. A reference pattern 21 installed on the substantially same surface as the photosensitive surface of the photosensitive substrate W, and illumination light is guided to the lower surface of the reference pattern 21, and transmitted light of the reference pattern 21 is masked through a projection optical system PL. Illuminating means LL that makes the light incident on the stage 14, the light receiving means 28 that receives the reflected light flux from the back surface of the mask pattern by the transmitted light flux of the reference pattern 21 via the projection optical system PL and the reference pattern 21, and the stage 14 to the light of the projection optical system PL. Focus state detecting means 32 for detecting the focus state based on the output signal obtained from the light receiving means 28 when the focus state is moved in the axial direction.
A and at least two locations (reference numerals 21a to 21e in FIG. 3) of the exposure area by the projection optical system PL, the focusing state detection means 32A detects the focusing state, and based on the detection result of the at least two focusing states. An image forming characteristic measuring unit 32B for measuring the image forming characteristic of the projection optical system PL is provided. The image forming characteristic measuring means 32B in the projection exposure apparatus according to claim 2 is
The in-focus state detecting means 32A detects the in-focus state in at least three places in the exposure area by the projection optical system PL, and the image plane tilt is measured from the detection result of the in-focus state in at least three places. The image forming characteristic measuring means 32B in the projection exposure apparatus according to claim 3 detects the in-focus state by the in-focus state detecting means 32A at at least one center of the exposure area formed by the projection optical system PL and at least three peripheral areas. The field curvature is measured based on the detection results of the in-focus state at four places. In the projection exposure apparatus according to claim 4, the reference pattern 21 is the first patterns 21bs to 21e extending in the saddle direction.
s and the second pattern 21 extending in the direction of the medal
bm to 21 em, the imaging characteristic measuring unit 32B includes
The first and second patterns 21bs to 21 are formed at least at four locations around the exposure area of the projection optical system PL.
The in-focus state detecting means 32A detects the in-focus state for each of the transmitted light fluxes es, 21bm to 21em, and the astigmatic difference is measured from the detection results of the eight in-focus states obtained at at least four places. The invention of claim 5 is applied to the same projection exposure apparatus as in claims 1 to 4, is installed in the same plane as the photosensitive surface of the photosensitive substrate W, is arranged on the optical axis of the projection optical system PL, and is a sagittal. The first pattern 21 extending in the direction
As, and a projection pattern including a reference pattern 21 including a second pattern 21am extending in the medium direction, an illumination unit LL similar to the above, a light receiving unit 28, and a focus state detecting unit 32A. The first pattern 21a extending in the saddle direction of the exposure region by PL
Focusing state detection means 32A based on illumination light passing through s
In addition to detecting the in-focus state, the in-focus state detecting means 32A detects the in-focus state based on the illumination light passing through the second pattern 21am extending in the medal direction, and detecting these two in-focus states. An image forming characteristic measuring means 32B for measuring the image forming characteristic of the projection optical system PL from the result is provided. The image formation characteristic measuring means 32B according to claim 6 is the first measured in advance.
From the correlation between the amount of deviation of the focused state and the eccentricity of the second patterns 21as and 21am, the projection optical system P
Measure the eccentricity of L. The image forming characteristic measuring means 32 according to claim 7.
B is the first and second patterns 21a measured in advance.
The spherical difference of the projection optical system PL is measured from the correlation between the shift amount of the focused state and the spherical difference for s and 21am.

[0011]

The reference pattern 21 is illuminated from the lower surface, and the light reflected by the back surface of the mask pattern R through the projection optical system PL is received from the projection optical system PL through the aperture pattern 21.
The focus state is detected based on the output signal obtained from the light receiving unit 28 when the stage 14 is moved up and down in the optical axis direction of the projection optical system PL, and the focus state is detected in at least two positions of the exposure area. The imaging characteristic of the projection optical system PL is measured from the detection results of the in-focus state at at least two places. Therefore, the imaging characteristics of the projection optical system PL can be measured without using a test reticle, and the imaging characteristics of the projection optical system PL can be measured even when the actual mask pattern is set. By correcting the image characteristics, a highly accurate focused state can be obtained. Furthermore, since the imaging characteristics can be measured based on the measurement results of two or more positions in the exposure area, it is possible to easily measure the curvature of field, the inclination of the field, the astigmatism, etc. without trial burning. Further, in the projection exposure apparatus according to any one of claims 5 to 7, the first extension of the exposure region by the projection optical system PL extends in the saddle direction.
Focusing state detecting means 32A detects the focusing state based on the illumination light passing through the pattern 21as, and the focusing state detecting means based on the illumination light passing through the second pattern 21am extending in the medial direction. The in-focus state is detected by 32A, and the eccentricity and the spherical aberration, which are the imaging characteristics of the projection optical system PL, are measured from the detection results of these two in-focus states. The eccentricity and the spherical error are the correlation between the deviation amount of the focused state and the eccentricity of the first and second patterns 21as and 21am measured in advance, or the first and second patterns 21as measured in advance. , 21 am for the in-focus state and the spherical difference.

Incidentally, in the section of means and action for solving the above problems for explaining the constitution of the present invention, the drawings of the embodiments are used for the purpose of making the present invention easy to understand. It is not limited to.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (Exposure Optical System) FIG. 1 is a schematic view of an embodiment in which the present invention is applied to a projection exposure apparatus for manufacturing a semiconductor integrated circuit. In FIG. 1, an illumination light source 1 for exposure such as an ultra-high pressure mercury lamp and an excimer laser light source is a wavelength (exposure wavelength) at which a resist layer such as g-line, i-line or ultraviolet pulsed light (for example, KrF excimer laser) is exposed. Illumination light IL
To occur. The illumination light IL passes through a shutter 2 that closes and opens and closes an optical path of the illumination light, and a semi-transmissive mirror 4 that allows most (90% or more) of the illumination light to pass therethrough, and then passes through an optical integrator (fly-eye lens) or the like. It reaches the illumination optical system 6 including. The mirror 22 is retracted from the optical path in the normal state (during exposure), and is inserted on the optical axis only when measuring the imaging characteristics of the projection optical system PL, as described later.

The shutter 2 is driven by a drive unit 3 so as to control transmission and blocking of illumination light. A part of the illumination light reflected by the semi-transmissive mirror 4 enters a photodetector (power monitor) 5 such as a PIN photodiode. The power monitor 5 photoelectrically detects the illumination light IL and inputs light information (intensity value) PS to the main control system 32. This optical information PS
Is basic data for obtaining a variation amount of the image forming characteristic of the projection optical system PL in the main control system 32 (details will be described later).

The illumination light IL, which has been made uniform in luminous flux and reduced in speckles in the illumination optical system 6, is reflected by the mirror 7, passes through the relay lenses 9a and 9b and the variable blind 10, and then is mirrored. The light is reflected vertically downward at 12 to reach the main condenser lens 13, and illuminates the pattern area PA of the reticle R with a uniform illuminance. Since the surface of the variable blind 10 is in a conjugate relationship with the reticle R, the illumination field of the reticle R can be arbitrarily selected by opening and closing the movable blades forming the variable blind 10 by the drive motor 11 to change the opening shape. it can.

Further, in the present embodiment, the reflected light generated from the wafer W or the like by the irradiation of the illumination light IL passes through the mirror 7 and enters the photodetector (reflection amount monitor) 8. . The reflection amount monitor 8 photoelectrically detects the reflected light and inputs the light information (intensity value) RS to the main control system 32. Here, the optical information RS serves as basic data for obtaining a variation amount of the image forming characteristic of the projection optical system PL (details will be described later).

The reticle R is placed on a reticle stage RS which can move two-dimensionally in a horizontal plane, and the pattern area PA
Is positioned so that the center point of the optical axis coincides with the optical axis AX of the projection optical system PL. Initialization of the reticle R is performed by finely moving the reticle stage RS based on a mark detection signal from a reticle alignment system RA that photoelectrically detects an alignment mark (not shown) around the reticle. The reticle R is used after being appropriately replaced by a reticle exchanger (not shown). Especially when performing high-mix low-volume production,
Exchanges are frequent.

Illumination light IL passing through the pattern area PA
Enters the projection optical system PL that is telecentric on both sides. The projection optical system PL superimposes the projected image of the circuit pattern of the reticle R on one shot area on the wafer W which is held so that the resist layer is formed on the surface and the surface is substantially aligned with the image plane. Project (image).

(XY Stage, Z Stage, and Leveling Stage) The wafer W is placed on a leveling stage (not shown), and the leveling stage is a Z stage 14 which can be finely moved in the optical axis direction (Z direction) by a drive motor 17. It is installed on top. The Z stage 14 is mounted on the XY stage 15 which can be two-dimensionally moved by the step-and-repeat method by the drive motor 18, and the XY stage 15 completes the transfer exposure of the reticle R to one shot area of the wafer W. Then, the next shot area on the wafer is moved until it coincides with the exposure area of the projection optical system PL. The two-dimensional position of the XY stage 15 is the interferometer 1
9 always detects with a resolution of, for example, about 0.01 μm. Therefore, a movable mirror 14m that reflects the laser beam from the interferometer 19 is fixed to the end of the Z stage 14. The interferometer 19 and the movable mirror 14m are provided in pairs for position detection in the X and Y directions.

A dose monitor 16 is provided on the Z stage 14 so as to substantially coincide with the surface position of the wafer W. The irradiation amount monitor 16 is composed of, for example, a photodetector having a light receiving surface having substantially the same area as the projection area of the image field or reticle pattern of the projection optical system PL, and mainly controls the light information LS concerning the irradiation amount of the shot area. Input to system 32. This optical information LS is the projection optical system PL
It becomes basic data for obtaining the variation amount of the image forming characteristic of (described later in detail).

(Aperture pattern) On the Z stage 14, a reference member 20 used for measuring the image forming characteristics of the projection optical system PL, such as the focus position, the image surface curvature, the image surface inclination and the astigmatism, is also provided. Has been. As shown in FIG. 3, the reference member 20 has a grid shown in FIG. 2 (a) at positions corresponding to one central portion and four peripheral portions of the exposure area (image field IF) of the projection optical system PL. Five sets of opening patterns 21am, 21as to 21em, and 21es, each of which is a pair of the pattern and the lattice pattern shown in FIG. 2B, are provided. In FIG. 3, a circular area IF having a radius r indicates the maximum exposure area of the projection optical system PL, and a square inscribed in this circle indicates the maximum chip area where the wafer can be actually exposed.

In FIGS. 2A and 2B, the black background is the light shielding portion and the white background is the light transmitting portion. In FIG. 3, the opening patterns 21am to 21em with the subscript m are for measuring the imaging characteristics of the projection optical system PL in the medal direction, and the opening patterns 21as to 21es with the subscript s are the saddles of the projection optical system PL. This is for measuring the imaging characteristics in the direction, and each grating pattern has inclinations of 45 degrees and 135 degrees with respect to the X axis. Hereinafter, the medial direction is called the M direction and the saddle direction is called the S direction.

If five or more openings 21 are provided, more image forming characteristic information (for example, curvature of the image plane) can be obtained. However, in this embodiment, the image forming state is taken into consideration in consideration of throughput and simplification of the measuring optical system. One aperture 21 on the optical axis where
a is in the exposure area to be actually used, and the four apertures 2 are provided in the peripheral portion of the image height of 100% where the image forming characteristic is most disadvantageous.
1b-21e are arranged, respectively. In addition, in this specification, a pair of opening patterns 21am, 21as to 21e.
m and 21es are collectively referred to as the opening 21.

(Measurement Illumination System LL) The opening 21 is illuminated by the measurement illumination system LL from below. The measurement illumination system LL includes a mirror 22, a half mirror 23, a lens 24, an optical fiber 25, a lens 26, and a mirror 27, which are inserted into the optical path of the illumination light IL by a driving device (not shown). Lead into 15. The illumination light emitted from the opening 21 reaches the reticle R via the projection optical system PL, is reflected by the back surface thereof, and returns to the opening 21 via the projection optical system PL again. After passing through the opening 21, the reflected light is incident on a photodetector 28 including a photomultiplier, SPD, etc. via a mirror 27, a lens 24, an optical fiber 25, a lens 26 and a half mirror 23, and the photodetector is detected. It is photoelectrically converted at 28 and output as an electric signal. Here, although not shown, five sets of openings 2 are provided.
1a to 21b are individually illuminated and reflected light is individually received. It should be noted that the entire back surface of the opening 21 is illuminated and the five pairs of openings 21a in the photodetector 28 are
21b may be configured to individually receive the reflected light from each of .about.21b. Alternatively, only one set of the illumination system and the light receiving system may be prepared, and the measurement may be performed by temporally moving the opening.

(Oblique Incidence Type Detection Optical System) In FIG. 1, reference numeral 34 is an oblique incidence type detection optical system.
It is disclosed in Japanese Patent No. 10361. The oblique incidence type detection optical system 34 detects the position of the wafer surface in the vertical direction (Z direction) with respect to the best image plane of the projection optical system PL, and detects the focus state of the wafer W and the projection optical system PL. The focus detection system 29 is combined with a horizontal position detection system 30 that detects the inclination of a predetermined region on the wafer W with respect to the image plane.

Focus detection system 29 and horizontal position detection system 30
Are light sources 29a and 30a that emit illumination light that is incident on the wafer surface from an oblique direction with respect to the optical axis AX, a half mirror 31a, light receiving optical systems 29b and 30b that receive reflected light on the wafer surface, and half And a mirror 31b.
The illumination light emitted from the illumination optical system 29a is an imaging light flux that forms an image of a pinhole or a slit, and the illumination light emitted from the illumination optical system 30a is a parallel light flux.

In this embodiment, the angle of the parallel flat glass (plane parallel) (not shown) provided in advance inside the light receiving optical system 29b is adjusted so that the best designed image plane becomes the zero point reference. Then, the focus detection system 29 is calibrated, and when the wafer surface and the image plane are aligned with each other, the parallel light flux from the irradiation optical system 30a is divided into four light receiving elements (not shown) inside the light receiving optical system 30b. The horizontal position detection system 30 is calibrated so that the light is focused at the center position of the.

(Image Forming Characteristic Correcting Section of Projection Optical System PL) The image forming characteristic correcting section IC is provided above the projection optical system PL, and the lens elements (40, 41) constituting the projection optical system PL. , 43, 45 are independently driven to correct the imaging characteristics such as projection magnification, distortion, field curvature, and astigmatism. The lens elements 40 and 41 of the first group closest to the reticle R are fixed by a support member 42, the lens elements 43 of the second group are fixed by a support member 44, and the lens element 45 of the third group.
Are fixed to the support member 46. Lens element 4
The lens elements below 5 are the projection optical system P, respectively.
It is fixed to the L lens barrel portion 47.

In the present embodiment, the optical axis AX of the projection optical system PL refers to the optical axis of the lens element fixed to the lens barrel portion 47.

The support member 46 is a stretchable drive element 50.
It is connected to the lens barrel portion 47 of the projection optical system PL by a, 50b and 50c (FIG. 4). The support member 44 is connected to the support member 46 by extendable drive elements 49a, 49b, 49c (FIG. 4), and the support member 42 is connected to the support member 44 by extendable drive elements 48a, 48b, 48c (FIG. 4). Has been done.

FIG. 4 is a view of the projection optical system PL as seen from above (from the reticle side), and is a plan view of the above-mentioned image formation characteristic correction section IC. 12 drive elements 48a-48c
The drive element control unit 33 is arranged at a position rotated by 0 °.
Allows independent control. Drive elements 49a-4
Similarly, 9c and 50a to 50c are also arranged by rotating by 120 °, respectively, and can be independently controlled by the drive element control unit 33. Drive elements 48a, 49a and 5
0a is offset from each other by 40 °, and drive elements 48b, 49b and 50b and 48c, 49c and 50c are also offset from each other by 40 °.

For example, an electrostrictive element or a magnetostrictive element is used as the driving elements 48 to 50, and the displacement amount of the driving element according to the voltage or magnetic field applied to the driving element is obtained in advance. Although not shown here, in consideration of the hysteresis of the drive element, a position detector such as a capacitive displacement sensor or a differential transformer is attached to the drive element, and the drive element corresponding to the voltage or the magnetic field applied to the drive element is provided. The position is monitored to enable highly accurate driving.

Here, in the present embodiment, the drive element controller 3
The lens element (4
0, 41), 43, and 45 are movable, but these elements have a greater effect on projection magnification, distortion, field curvature, and astigmatism characteristics than other lens elements (not shown). It's getting easier.

In the present embodiment, since the movable lens element is composed of three groups, the range of movement of the lens element can be increased while suppressing fluctuations of other various aberrations, and various shape distortions (trapezoid, rhombus, barrel). Mold, pincushion, etc.), field curvature and astigmatism. Therefore, even if the temperature of the projection optical system PL rises due to the absorption of the exposure light and the imaging characteristics thereof change, it is possible to sufficiently cope with it. It should be noted that the movement of the lens element is performed within a range in which the influence on other aberrations (for example, spherical aberration) of the projection optical system PL that cannot be corrected in this embodiment can be ignored. Alternatively, by adjusting the distance between the lens elements, other aberrations (magnification, magnification,
A method of correcting distortion (field curvature) may also be adopted.

With the above-described structure, the three peripheral edge points of the lens elements (40, 41), 43, and 45 of the three groups are independently formed by the amount corresponding to the drive command given from the main control system 32, and the projection optical system PL. It can be moved in the optical axis AX direction. As a result, each of the lens elements (40, 41), 43, and 45 of the three groups can be translated substantially along the optical axis AX, and can be arbitrarily tilted with respect to a plane substantially perpendicular to the optical axis AX. It becomes possible. The lens elements are assumed to be tilted with the optical axis AX as a virtual tilt reference.

The main control system 32 obtains optical information from the power monitor 5, the reflection amount monitor 8 and the irradiation amount monitor 16, respectively, calculates the variation amount of the image forming characteristic of the projection optical system PL as described later, and drives it. The element control unit 33 and the entire device are centrally controlled.

(Measuring Procedure of Imaging Characteristics) Next, the measuring procedure of the field curvature, the image plane inclination and the astigmatism in this embodiment will be described. While the reticle R is mounted on the reticle stage RS, the center of the opening 21 on the reference member 20 is placed on the optical axis AX of the projection optical system PL while monitoring the position of the XY stage 15 with the interferometer 19. Then, the XY stage 15 is moved by the motor 18. At this time, the motor 17 is driven at the same time to move the Z stage 14 from a position (design value) considered to be the optimum focus position (best focus position) of the projection optical system PL to several times its depth of focus (± DOF) (for example, Two
・ Lower (or up) about DOF).

At the same time, the mirror 22 is moved to the optical path to guide the illumination light LL to the opening 21, and the back surface (pattern surface) of the reticle R is illuminated via the specific pattern of the opening 21 and the projection optical system PL. The illumination light reflected from the reticle R passes through the projection optical system PL and the aperture 21 again, and then the mirror 2
The light enters the photodetector 28 through the lens 7, the lens 26, the optical fiber 25, the lens 24, and the half mirror 23. After that, in this state, the Z stage 14 is moved upward (or downward) by the motor 17 by the moving amount (2.D
Scan about twice (OF). At this time, the output of the photodetector 28 (that is, the photoelectric signal corresponding to the intensity of the reflected light that has passed through one of the five sets of aperture patterns 21a to 21e) and the output of the focus detection system 29 (the position of the Z stage 14). Corresponding to the A / D) at the same time, for example, for each unit movement amount of the Z stage 14 (about 0.02 μm).
When converted, the relationship shown in FIG. 5 is obtained.

(Detection of Focused State by Output of Photo Detector 28 and Output of Focus Detection System 29) This can be explained as follows. The opening 21 has a projection optical system P on the back surface of the reticle R.
When it is in the defocus region of L, that is, when the two are not in a conjugate relationship optically, the illumination light emitted from the aperture 21 forms a blurred image of the lattice pattern on the back surface of the reticle R via the projection optical system PL. create. The illumination light reflected on the back surface of the reticle enters the opening 21 again via the projection optical system PL.
It is an image of a more blurred grid pattern. Therefore, when this reflected light passes through the lattice pattern, the blurred portion does not pass through the light-transmitting portion of the lattice pattern, and the amount of transmitted light is reduced accordingly.

On the other hand, when the opening 21 is on the focal plane (imaging plane) of the projection optical system PL with respect to the back surface of the reticle, that is, when the two optically have a conjugate positional relationship, the opening 2
Since the illumination light emitted from 1 forms a sharp image on the back surface of the reticle, when the reflected light enters the opening 21, the reflected light forms a sharp image of the lattice pattern. Therefore, when the reflected light passes through the grating pattern, there is almost no reflected light that reaches the light-shielding portion (is eclipsed by the light-shielding portion), and the amount of light received by the photodetector 28 is larger than that when defocused. Therefore, in FIG. 5, the output value f obtained by the focus detection system 29 at the peak output of the photodetector 28 becomes the optimum focus position (best focus position) of the projection optical system PL. Focusing state detection unit 32 of main control system 32
A obtains its peak value from the output of the photodetector 28, and obtains the focus position from the output value of the focus detection system 29 at that time. This processing is performed for each opening 21am to 21es in total of 10 times.
When repeated, each pattern 21am to 21 as shown in FIG.
The focus position of es is obtained as the output value of the focus detection system 29. In this embodiment, the reference member 20 is provided with five sets of opening patterns 21a to 21e, and reflected light from each of the opening patterns 21am, 21as to 21em, and 21es can be individually received. In the above measurement operation, the Z stage 14 needs to be scanned once in the Z direction.

Based on the result of FIG. 6, the relationship between the image height (the distance from the optical axis AX to the periphery of the exposure area) of the output of the focus detection system 29 is obtained, and the graph of FIG. 7 is obtained. Reference numeral M in FIG. 7 indicates an imaging characteristic in the medial direction, and reference numeral S indicates an imaging characteristic in the saddal direction. Further, the image forming characteristic of FIG. 7 is a superposition of the image plane inclination and the image plane curvature. In FIG.
The output values of the focus detection system 29 of 100% image height in the M direction are f5 and f4, and the output values of the focus detection system 29 of 100% image height in the S direction are f3 and f2, respectively.
Further, Z1 is the lowest focus position of the M image with the field curvature removed, Z3 is the lowest focus position of the S image with the field curvature removed,
Z2 is the lowest focus position of the image surface with the field curvature removed, Z4
Is the maximum focus position of the S image with the field curvature removed, Z6 is the maximum focus position of the M image with the field curvature removed, Z5 is the maximum focus position of the image surface without the field curvature, and Z7 is the image plane tilt. The highest focus position of the removed S image, Z9 is the highest focus position of the M image with the image plane tilt removed, and Z8 is the highest focus position of the image plane with the image plane tilt removed.

In FIG. 7, central openings 21am and 21a
openings 21bm, 21bs to 21em, 21es excluding s
Z1 to Z6 are obtained by the following equation from the graph of Z1 = f1-(f5-f4) / 2 Z3 = f1-(f3-f2) / 2 Z4 = f1 + (f3-f2) / 2 Z6 = f1 + (f5-f4) / 2 Z2 = (Z1 + Z3) / 2 Z5 = (Z4 + Z6) / 2

Data Z1 and Z6 having an image height of 100% are connected as the image plane inclination characteristic in the M direction, data Z4 and Z3 having an image height of 100% are connected as the image plane inclination characteristic in the S direction, and Z5 is an average value characteristic. And Z2 are connected, the image plane inclination characteristic shown in FIG. 8 is obtained. In the figure, symbol A represents the inclination of the entire image plane and is obtained as an average value in the M direction and the S direction.
The image plane inclination ΔZ is ΔZ = Z5−Z2. Further, the image plane tilt in the M direction is ΔZm = Z6−Z1 and the image plane tilt in the S direction is ΔZs = Z4−Z3.

The graph shown in FIG. 7 is corrected by the image plane inclination obtained in FIG. 8, and the four corner openings 21bm and 21bs are corrected.
Focus detection system 2 corresponding to the center openings 21am and 21as at the output of the focus detection system 29 corresponding to 21em and 21es
When the field curvature is obtained by adding the output of 9, the graph shown in FIG. 9 is obtained. In FIG. 9, there is a relationship of Z7 = (f2 + f3) / 2 Z9 = (f4 + f5) / 2 Z8 = (Z7 + Z9) / 2.

Here, the field curvature Δrm in the M direction is Δrm = Z9-f1, and the field curvature Δrs in the S direction is Δrs = Z7-f1. Therefore, the entire field curvature Δr _A is shown in FIG. As indicated by symbol A, it is obtained as the average of Δrs and Δrm, and Δr _A = (Δrm + Δrs) / 2 = Z8-f1. As is the difference between the field curvature in the M direction and the field curvature in the S direction, and thus is represented by a graph as shown in FIG.

The calculation of the image plane tilt, the field curvature, and the astigmatism described above is performed by the image formation characteristic measuring section 32B of the main control system 32.

As can be seen from FIG. 9, the average focus position f _{A (} not shown) is represented by f _A = f1 + Δr _A / 2 = f1 + (Z8-f1) / 2. Therefore, the output of the focus detection system 29 is f
_{When the} Z stage 14 is controlled so as to coincide with _A , the front surface of the wafer becomes optically conjugate with the back surface of the reticle R, and good image formation can be obtained. As a result, even when the field curvature and the astigmatism to be described later are not sufficiently corrected, a better image can be obtained than in the conventional case. The zero point reference of the focus detection system 29 is f
It is desirable to calibrate so that it becomes _A. Further, the focus detection system 29 may be calibrated on a surface that minimizes the maximum deviation between the imaging surface and the wafer surface.

Further, for example, in the case where the field curvature as shown in FIG. 11 is obtained, half the exposure area (see FIG. 1).
1 only the left half of the center line 80),
When the leveling stage is driven and exposed so as to be optimized only in the left half as in 82, good image forming characteristics can be obtained.

Further, when the linearity guarantee range (in other words, the detectable range) of the focus detection system 29 is small, the following can be done. First, a position sensor such as an encoder is attached to the motor 17, and the Z stage is scanned by this value to obtain the relationship as shown in FIG. 5, that is, the horizontal axis represents the encoder value and the vertical axis represents the output of the photoelectric detector 28. Get the graph. After that, while driving the herbing glass in the focus optical system 29, the value of the encoder and the output of the focus detection system 29 are made to correspond to each other, and finally the output of the photoelectric detector 28 to the focus detection system 29 is obtained.

Further, the approximate focus position may be found in advance by driving the herbing glass of the focus detection system 29 by the predictive control described later. In this case, the scanning range of the Z stage 14 can be reduced, the Z stage can be scanned only by the output of the focus detection system 29, the time required for scanning can be shortened, and the throughput can be increased.

(Field curvature and astigmatism correction procedure) Next, the procedure for correcting the image curvature and astigmatism will be described. Basically, as described above, by tilting the lens elements (40, 41), 43, and 45 of the three groups of the projection optical system about the optical axis direction or an axis perpendicular to the optical axis as the center of rotation, a desired image is formed. Get the status. Here, for simplicity of explanation, only the image curvature and the astigmatism are explained, but the projection magnification and the distortion can be corrected.

Changes in field curvature and astigmatism due to the driving of the lens elements (40, 41) will be described with reference to FIG. It should be noted that FIG. 12 is an example and is not necessarily general, and the manner of change differs depending on the configuration of the lens element.
By moving the lens elements (40, 41) of this embodiment in the optical axis direction, the field curvature changes as shown in FIG. 12 (a) and the astigmatism changes as shown in FIG. 12 (b). Here, since the optical system is set so that the astigmatism increases when the field curvature is reduced, the total focus difference of the projection optical system PL (in the shot including all of the field curvature, the image surface inclination, the ass, etc. It is desirable to drive the lens elements (40, 41) so that the curvature of field and the astigmatism have optimum values, with a focus on the focus (image formation) position difference (in the exposure area).
It should be noted that, for example, the driving lens may be changed, the number of lenses to be driven may be increased, or the curvature and the refractive index of the lens may be changed to reduce the astigmatism when the field curvature is reduced.

When the lens element is driven to correct the field curvature and the astigmatism, the magnification, the distortion, and other aberrations (for example, coma aberration) may be deteriorated.
Since it is possible to drive multiple lens elements,
It is possible to correct desired field curvature and astigmatism while correcting these aberrations.

The above is the image forming characteristic correction unit I of the projection optical system PL.
The procedure for correction by C is the lens element (4
0, 41), 43, or 45 may cause the image plane to move up and down, but if the focus detection system 29 is electrically or optically offset according to the amount of change, , The wafer W is always set on the best image plane, so that this influence can be prevented. If the projection optical system PL is completely telecentric on both sides, it can be corrected by moving the reticle up and down.

(Correction of inclination of image plane) The inclination of the image plane is electrically or optically detected by the horizontal position detecting system 30 by using the focus differences (image plane inclinations) at the four corners of the exposure area obtained from the above-mentioned measurement as offsets. Give and correct. That is, the image plane tilt is corrected by driving the leveling stage and tilting the wafer W while detecting the horizontal position of the wafer surface by the horizontal position detection system 30 to which the offset is applied.

(Actual Usage) Next, a specific usage of this embodiment will be described. (1) The field curvature, the field tilt, and the astigmatism that the projection optical system PL has in the initial state may be optimized at the time of system setup according to the procedure described above.

(2) When the focus position, the field curvature, the image plane inclination and the astigmatism of the projection optical system PL change due to environmental changes such as atmospheric pressure or ambient temperature or absorption of illumination light,
When those changes are relatively slow, or when the amount of change in the measurement interval is negligible, the Z stage 14 is periodically scanned, for example, at the time of wafer replacement, and the signal obtained from the photodetector 28 at this time is scanned. The imaging characteristics are measured based on the lens element (40, 41), 43, 4
5 and the leveling stage are driven to optimize the above-mentioned image forming characteristics.

(3) When the focus position, the field curvature, the image plane inclination, and the change in the astigmatism of the projection optical system PL due to the change of the environment or the absorption of the illumination light are relatively fast, the light flux passing through the aperture 21 is changed. The desired accuracy can be obtained by using the correction of the imaging characteristics used and the correction by the conventionally known predictive control together.

(Predictive control) Predictive control is disclosed in, for example, Japanese Patent Application Laid-Open No. 1-273318.
The image forming characteristic that varies depending on the amount of heat received by the projection optical system PL from the exposure light is measured and stored in advance, and the image forming characteristic at the time of actual exposure is corrected based on this memory value.

The change characteristic of the image formation state of the projection optical system PL is
The amount of heat is measured using the open / close information of the shutter 2 and the outputs RS and LS of the reflection amount monitor 8 and the irradiation amount monitor 16, and the Z stage 14 is scanned at time intervals at which changes in the imaging characteristics can be sufficiently measured. Then, the imaging characteristic is obtained based on the light receiving signal of the light flux passing through the opening 21, that is, the output signal of the photodetector 28. Then, the state variable of the imaging characteristic with respect to the amount of heat is stored in the memory of the main control system 32. The amount of heat is calculated based on the output value of the irradiation amount monitor 16 that detects irradiation energy per unit time and the open time of the shutter 2.

At the time of exposure, projection is performed according to the optical information RS and LS respectively input from the reflection amount monitor 8 and the irradiation amount monitor 16, the open / close information of the shutter 2 and the change characteristics stored in the above-mentioned memory. The amount of change in the imaging characteristics due to the heat absorption of the optical system PL is calculated. When the image formation state of the projection optical system PL changes due to other factors such as atmospheric pressure change, data measured in advance and stored (for example, data of image formation characteristic change with respect to atmospheric pressure change). These changes are also totaled based on The barometer can be installed in the projection optical system PL. Optimum correction amounts for the field curvature, the field tilt and the astigmatism are calculated for this total value, and the lens elements (40, 41),
43 and 45 are driven by drive elements 48 to 50 to perform correction.

Here, the focus position adjustment is performed by driving the Z stage 14 and moving the wafer W up and down while detecting the focus position by the focus detection system 29 provided with the offset. The correction of the image plane tilt is performed by driving the leveling stage and tilting the wafer W while detecting the horizontal position of the wafer surface by the horizontal position detection system 30 to which the offset is applied.

In this manner, for example, when the variation amount of the image forming characteristic of the projection optical system PL due to the environmental change or the like exceeds a predetermined allowable value during the exposure of one wafer, the lens element The (40, 41), 43, 45 and the Z stage 14 are driven by predictive control, and further, periodically, for example, every wafer exchange or every unit processing number, while scanning the Z stage 14 in the same manner as described above. When the signal from the detector 28 is detected and the focus position, the field curvature, the image surface inclination, and the astigmatism are corrected, the predictive control is calibrated periodically, and the imaging characteristics of the projection optical system PL are changed. improves. The exposure operation may be stopped immediately when the variation amount of the image forming characteristic of the projection optical system PL exceeds the allowable value, and the image forming characteristic may be measured and corrected as in the above embodiment.

Further, even when the reference member 20 is tilted, the tilt can be measured in advance, and the tilt can be corrected based on the measured value when measuring the imaging characteristics by the opening 21. The inclination of the reference member 20 can be measured while changing the position of the XY stage with the oblique incidence detection optical system and its harving glass, or can be measured with an electronic micro while moving the XY stage in the manufacturing process.

(Modification I of Aperture 21) In the above embodiments, the pattern of the aperture 21 is described as the combination pattern of the light transmitting portion and the light shielding portion as shown in FIGS. 2 (a) and 2 (b).
A pattern equivalent to that of FIG. 2 can be formed by using a phase shift pattern that shifts the wavelength of the measurement light by ¼ wavelength.

This principle will be described with reference to FIG. FIG.
As shown in (a), when the phase pattern 51 is illuminated from below, diffraction light is generated. At this time, compared with 0th order light ±
The phase of the primary light is shifted by a quarter wavelength. These light rays are reflected by the lower surface of the reticle R and return to the pattern 51 again. When the pattern 51 is in the focal plane, FIG.
As shown in, the ± first-order light is diffracted again, and (+1), (−
The ray indicated by 1) returns along the same optical path as the 0th order ray. At this time, the phases of the light rays indicated by (+1) and (−1) are further shifted by ¼ wavelength, and the phase of the ½ wavelength is shifted from that of the 0th-order light. Therefore, they are indicated by (+1) and (−1). The light beam acts to cancel the 0th order light.

When the pattern 51 is not on the focal plane of the projection optical system PL, the phase difference between the 0th-order light and the ± 1st-order light does not become 1/2 wavelength, so that the light is not canceled. From the above,
The best focus is when the output of the aperture 51 is minimized as shown in FIG. According to this method, all the reflected light from the back surface of the reticle passes through the pattern 51, as compared with the method described above, so that the S / N ratio becomes high and the best focus point can be detected more easily.

(Modification II of Opening Pattern 21) In the above, the ten openings 21am and 21as of the reference member 20.
Although the case where 21em and 21es are provided has been described,
In this case, strictly speaking, different regions are observed in the M direction and the S direction. If this is a problem,
The following openings can be used.

As shown in FIG. 15, ECD of a small area
By arranging (electrochromic devices) or the like in a matrix and controlling the voltage applied to each microelement, a lattice pattern as shown in FIG. 2A or 2B can be formed. In this case, as shown in FIG. 16, five openings 21a to 21e may be provided, which is advantageous in terms of space saving and downsizing of the signal processing circuit. The procedure for measuring the curvature of field, the inclination of the field, and the astigmatism by this configuration is almost the same as the above-mentioned case, but in the above-described embodiment in which the opening patterns in the M direction and the S direction are provided, the Z stage 14 is scanned once. Although the M direction and the S direction can be simultaneously measured with, the Z stage 14 must be scanned for each of the lattice patterns in the M direction and the S direction in this configuration.

(Modification III of Opening Pattern) When an electric element such as an ECD is used to form a grid pattern, it is possible to measure all points with only one opening 21a. That is,
The XY stage 15 is moved to position the opening 21a at a position corresponding to each of the openings 21b to 21e in the exposure area IF of the projection optical system PL, and a pattern in the M direction and the S direction is formed at each point to form Z. Stage 14, each time,
When scanning in the optical axis direction, the field curvature, field tilt and astigmatism at each point can be measured with only one aperture 21a. At this time, instead of forming the grid pattern with an electric element such as an ECD, for example, the grid pattern may be formed with a light-shielding portion such as chrome as in the above embodiment. However, in this case, it is necessary to make the lattice pattern rotatable in a horizontal plane. However, as described above, the two opening patterns 2
It is not necessary to form 1am and 21as, and there is an advantage that only one opening pattern (either one of 21am and 21as) is sufficient.

(Modification IV of Aperture Pattern) FIG. 2A,
When the aperture pattern shown in (b) or the phase shift type pattern shown in FIG. 13 is used, if the reference member 20 itself or the Z stage on which the reference member 20 is provided can be rotated, an ECD or the like can be obtained. Similar to the pattern with electric elements, only one opening pattern can
The field curvature, field tilt and astigmatism can be measured at the points (21a to 21e). That is, for example, the aperture pattern of FIG. 2A is rotated 45 degrees with respect to the X axis on the optical axis of the exposure region to measure in the medal direction, and further rotated 135 degrees with respect to the X axis to perform the saddle direction. Is measured. This may be done at each point.

(Modification V of the opening pattern) Two openings 2
It is also possible to use 1am and 21es. In this case, the paragraph number above

Although the operation is the same as that described above, there is an advantage that the ECD is unnecessary and the optical system is easy.

(Modification in which a plurality of focus detection systems are provided) The case where only one focus detection system 29 for measuring the optical axis center of the projection optical system PL is provided has been described above, but measurement is performed at various points in the exposure area. It is also possible to provide a plurality of focus detection systems as possible. At this time, a plurality of focus detection systems 2
If the reference member 20 is tilted, if 9 can measure the points 21am, 21as to 21em, and 21es in FIG.
Alternatively, even if the inclination changes, it can be measured without error. On the contrary, if the reference member 20 can be held strictly horizontally, the plurality of openings 21 of the reference member 20 can be used for calibration of the plurality of focus detection systems 29.

Further, in this case, more precise focusing is possible in consideration of the unevenness of the image plane and the unevenness of the wafer. For example, it is also possible to intentionally bend the image plane according to the warp of the wafer W and perform exposure. The focus detection system 29 and the horizontal position detection system 30 are not limited to the configuration of this embodiment. For example, by illuminating the four corners of the rectangular shot area on the wafer and each of the centers thereof with an image of a slit or a pinhole, a height detection position (position in the Z direction) at each point is detected. With this configuration, the inclination amount of the wafer surface can be obtained from the heights at the five points without providing a horizontal position detection system.

(Measurement Method of Decentering of Projection Optical System PL and Spherical Sphere Difference) The eccentricity or spherical surface difference of the projection optical system PL can be measured and corrected by using the above-mentioned projection exposure apparatus.

-Measurement and removal of eccentricity-When all the optical axes of the lens elements constituting the projection optical system PL are aligned, an image of the formed optical axis center (that is, the projection optical system P
Astigmatism does not occur in the image formed at the center of the exposure area IF of L). That is, the opening 21am in FIG.
There is no deviation between the focus points measured at 21as. Therefore, the eccentricity of the projection optical system PL can be measured by obtaining the deviation between the measured value at the opening 21am and the measured value at the opening 21as. Then, for example, the lens element (40,
The eccentricity can be removed by moving any of 41), 43, and 45 so as to correct the measured eccentricity amount in the vertical plane orthogonal to the optical axis.

-Measurement / removal of spherical surface difference-When there is a spherical surface difference, the waveform of FIG. 5 or FIG. 14 is distorted, for example, left and right become asymmetrical, or the contrast deteriorates. Therefore, if the signal distortion when the spherical difference is generated is obtained in advance by simulation, the difference amount can be measured from the distortion of the detection signal. Then, by inserting a parallel plate glass between the projection optical system PL and the wafer W, the spherical difference can be removed.

(Modification of Illumination of Illumination Light from the Reticle Side) In the above, the reference member 20 having the opening pattern 21 is arranged on the Z stage 14, and the imaging characteristics of the projection optical system PL are arranged from below the stage. The measurement illumination light is emitted, and the reflected light from the back surface of the reticle is again received by the photodetector 28 via the projection optical system PL and the opening 21, but the measurement illumination light is emitted as follows. You may.

A test reticle having an aperture pattern is used, and the aperture pattern and projection optical system P are arranged from above the reticle.
The reference reflecting surface on the wafer stage is irradiated with the measurement illumination light via L, and the reflected light from the reference reflecting surface is received by the photodetector through the projection optical system PL and the opening pattern of the reticle. In this case, the photodetector is arranged at a position substantially conjugate with the reticle. Here, even if the test reticle is not used, the imaging characteristics can be similarly obtained by providing the aperture pattern shown in FIG. 3 at a plurality of positions of the device reticle.

Although the reduction projection exposure apparatus for manufacturing a semiconductor integrated circuit has been described above, the present invention is not limited to the projection exposure apparatus, for example, an exposure apparatus used for manufacturing a large liquid crystal device. Can also be applied to.

Here, in the above embodiment, a mechanism (imaging characteristic correction section IC) for driving a part of the lens elements constituting the projection optical system PL is used as means for correcting the imaging characteristic of the projection optical system PL. However, the correction means applicable to the present invention is not limited to the above-mentioned mechanism. For example, a method of driving the reticle R, or a two-dimensional movement of a field lens arranged between the reticle R and the projection optical system PL,
Or a method of inclining, or sealing a space sandwiched between two lens elements forming the projection optical system PL,
Any method of adjusting the pressure of the sealed space or a combination thereof may be adopted.
The measurement of the image forming characteristics of the projection optical system as in the above embodiment may be performed every unit time or every predetermined number of processed wafers.

In the above embodiment, each of the opening patterns 21am, 21as to 21em and 21es of the reference member 20 is independently illuminated, and the reflected light from each opening pattern is individually received. However, for example, the entire back surface of the reference member 20 is configured to be illuminated, and a variable stop is arranged between the reference member 20 and the end surface of the fiber 25 to change the focus position at each aperture pattern position. The diaphragm may be driven so that the illumination light is emitted only to a desired aperture pattern.
In this case, the fiber 25 and the photodetector 28 are
Only a set is required, and the advantage that the configuration of the measurement illumination system LL can be simplified is obtained.

Further, in the above-described embodiment, the image forming characteristic of the projection optical system is corrected by the image forming characteristic correcting unit IC based on the measurement result, and each difference is suppressed to almost zero in advance. However, without performing the above correction, the projection optical system PL is based on the measurement results (field curvature, image inclination, astigmatism, etc.).
The average image forming plane is obtained, and the focus detection system 29 and the horizontal position detecting system 30 are calibrated (or electrically or optically offsetted) so that the average image forming plane serves as a zero point reference. But it doesn't matter. At this time, the average image forming surface calculated as described above is evaluated, and the change amount of this average image forming surface with respect to the ideal image forming surface (design value) has a predetermined allowable value (focus detection system 29 or It is also possible to perform only the calibration if it is within a detectable range of the horizontal position detection system 30, a value uniquely determined by the movable range of the leveling stage, or the like, and to perform the above correction if it exceeds the allowable value. good. For the difference that cannot be corrected by the imaging characteristic correction unit IC in the above embodiment or the remaining difference that cannot be completely corrected, the focus detection system 29 and the horizontal position detection system 30 are calibrated.
It goes without saying that it may be removed by giving an offset electrically or optically.

When the predictive control is also used in the above embodiment, the number of wafers setting means (counter) for setting, for example, how many wafers the imaging characteristics of the projection optical system as described above are measured. Etc.) are provided. Generally, from the start of the exposure operation to the predetermined number of wafers, the difference (calculation error) between the image formation characteristic calculated by the calculation in the predictive control and the actual image formation characteristic obtained by the above measurement is small, In particular, even if the above measurement is not performed, the image formation characteristic can be suppressed within a predetermined allowable value only by the predictive control. Therefore, the number of sheets to be set in the sheet number setting means may be large before starting the exposure operation, and here it is set to 10 sheets, for example. As a result, the above measurement is performed every time the exposure of 10 wafers is completed.

When the number setting means is used as described above,
After measuring and correcting the imaging characteristics before starting the exposure operation,
The wafers up to the tenth wafer are exposed while the imaging characteristics are corrected only by the predictive control, and the above measurement is performed at the time when this exposure is completed. Then, this measurement result is compared with the imaging characteristic calculated by calculation, and the difference (calculation error) is a predetermined permissible value (a value determined by the depth of focus of the projection optical system or the control accuracy of the imaging characteristic). In the case of the above, the image forming characteristic is immediately corrected based on the above measurement result, and the number of processed sheets (for example, about 8 sheets) is set in the sheet number setting means. On the other hand, if the difference does not reach the allowable value, the number of sheets set in the sheet number setting means is experimentally or empirically changed according to the difference. That is, it is determined how many more wafers will be exposed and the difference will be equal to or more than the allowable value, and the set number is changed, for example, set to two. Next, when the exposure of the two wafers is completed, the above-mentioned measurement is executed to correct the image formation characteristic, and the number of sheets set in the sheet number setting means is set to about eight. This is because, as the number of processed sheets increases, the above difference gradually increases from the start of the exposure operation to the elapse of a predetermined time. After that, the above operation is repeatedly executed, and when the actual image forming characteristics are almost stabilized, the number of sheets set in the sheet number setting means is fixed, and the remaining number is determined by the measurement and prediction control for each sheet number. Are exposed to all the wafers. By adopting such a sequence, it is possible to reduce the number of times of the above measurement and improve the throughput.

In the present invention, since the image of the opening pattern on the reference member 20 is projected on the back surface (pattern surface) of the device reticle, the intensity of the reflected light from the reticle is reduced depending on the shape of the reticle pattern. You can In such a case, it is desirable to shift the measurement point in the exposure area IF of the projection optical system PL and measure again.

At the measurement points (the positions corresponding to the opening patterns 21b to 21e in FIG. 3) set in the vicinity of the outer periphery of the exposure area IF, the projection image of each opening pattern is previously formed in the pattern forming area of the reticle R. The positions of the opening patterns 21b to 21e on the reference member 20 may be set so as to be deviated from the above. In this embodiment, one of the advantages is that the opening patterns are provided at the four corners (each difference is maximum and the actual use area) in the exposure area, which makes the measurement at the maximum difference position reliable. It is highly likely. There may be a difference if the opening pattern is outside the exposure area.

In the structure of the above embodiment, the reticle R is the mask pattern, the wafer W is the photosensitive substrate, the opening pattern 21 is the reference pattern, the photodetector 28 is the light receiving means, and the focus state detecting section 32A is used. Is the focus state detection means,
The image forming characteristic measuring unit 32B constitutes an image forming characteristic measuring means.

[0089]

As described in detail above, according to the present invention, in the projection exposure apparatus for forming an image of the transmitted light flux of the mask pattern on the photosensitive substrate on the stage through the projection optical system, the reference pattern is provided on the stage side. When the reference pattern is illuminated from the bottom surface and the light reflected on the back surface of the mask pattern through the projection optical system is received through the aperture pattern from the projection optical system and the stage is moved in the optical axis direction of the projection optical system. The focus state is detected based on the output signal obtained from the light receiving means, and at least 2 of the exposure area is detected.
The focus state is detected at one location, and the imaging characteristics of the projection optical system are measured from the results of detection of the focus state at at least two locations. Therefore, the imaging of the projection optical system can be performed without using a test reticle. The characteristics can be measured, and the imaging characteristics of the projection optical system can be measured even when the actual mask pattern is set. Furthermore, since the imaging characteristics can be measured based on the measurement results of two or more locations in the exposure area, it is possible to easily measure the curvature of field, the inclination of the image surface, the astigmatism, etc. without trial burning. Thus, the image forming characteristic is corrected to obtain an extremely highly accurate focused state. In detail,
The fact that you can measure with a real reticle without using a test reticle means that errors between reticles due to reticle sag, etc.
There is no error due to dust mixed during reticle setting, and the temperature of the reticle can be measured under the same conditions as during exposure, that is, the reticle can be measured under the same conditions as during exposure, and therefore highly accurate measurement can be performed. Furthermore, the focus state is detected by the focus state detection means based on the illumination light passing through the first pattern extending in the saddle direction on the optical axis of the exposure area by the projection optical system, and the light is extended in the medial direction. The focus state detecting means detects the focus state based on the illumination light passing through the existing second pattern, and from the detection results of these two focus states, the eccentricity and the spherical focus which are the image forming characteristics of the projection optical system. Since the difference is measured, it is possible to correct the image forming characteristic due to the eccentricity of the projection optical system or the spherical aberration, which has not been performed in the past, and a highly accurate focused state can be obtained.

[Brief description of drawings]

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

FIG. 2 is a diagram illustrating an opening pattern.

FIG. 3 is a diagram showing opening installation locations in an exposure area.

FIG. 4 is a top view of a projection optical system PL.

FIG. 5 is a graph showing the relationship between the output of the focus detection system 29 and the output of a photodetector that receives the measurement reflected light that has passed through the aperture 21.

FIG. 6 is a graph showing the relationship of FIG. 5 for five sets of openings.

FIG. 7 is a graph showing the output of the focus detection system 29 with respect to the image height, including the curvature of field and the tilt of the field.

8 is a graph showing the output of the focus detection system 29 with respect to the image height, in which the image plane tilt component is extracted from the graph of FIG.

9 is a graph showing the output of the focus detection system 29 with respect to the image height, in which the field curvature component is extracted from the graph of FIG.

FIG. 10 is a graph showing the output of the focus detection system 29 with respect to the image height, showing only the asbestos component extracted from the graph of FIG.

FIG. 11 is an explanatory diagram when only half of the exposure area is used.

FIG. 12A is a graph for explaining removing field curvature, and FIG. 12B is a graph for explaining removing astigmatism.

FIG. 13 is a diagram illustrating a phase shift pattern.

FIG. 14 is a graph showing the relationship between the output of the focus detection system 29 and the output of a photodetector that receives the measurement reflected light that has passed through the aperture 21 when a phase shift pattern is used.

FIG. 15 is a diagram illustrating a case where an opening is formed of ECD.

FIG. 16 is a diagram illustrating an arrangement of openings when the openings are formed of ECD.

[Explanation of symbols]

1 light source 2 shutter 14 Z stage 15 XY stage 19 Interferometer 20 Reference member 21 opening 21 am-21em Pattern direction for medium 21as-21es Sadital direction pattern 28 Photodetector 29 Focus detection system 30 Horizontal position detection system 32 Main control system 32A Focusing state detector 32B Imaging characteristic measurement unit 33 Drive element control system 40, 41, 43, 45 Lens element 48, 49, 50 drive elements R reticle W wafer PL projection optical system

Claims (7)

[Claims] 1. A projection exposure apparatus for forming an image of a transmitted light flux of a mask pattern on a photosensitive substrate on a stage via a projection optical system, wherein a reference pattern is provided in substantially the same plane as the photosensitive surface of the photosensitive substrate. Illuminating means for guiding the illuminating light to the lower surface of the reference pattern and allowing the transmitted light of the reference pattern to enter the mask pattern through the projection optical system, and a reflected light flux from the back surface of the mask pattern by the transmitted light flux of the reference pattern A light receiving means for receiving light through the projection optical system and a reference pattern, and a focus state is detected based on an output signal obtained from the light receiving means when the stage is moved in the optical axis direction of the projection optical system. Focusing state detecting means, and the focusing state detecting means detects the focusing state in at least two places of the exposure area by the projection optical system. Kutomo projection exposure apparatus according to claim 2 of the focus state of the locations detection result that includes the image formation characteristic measuring means for measuring the imaging characteristic of the projection optical system. 2. The projection exposure apparatus according to claim 1, wherein the image formation characteristic measuring unit detects the in-focus state by the in-focus state detecting unit in at least three positions of an exposure area by the projection optical system, A projection exposure apparatus characterized by measuring an image plane inclination from detection results of in-focus states at three locations. 3. The projection exposure apparatus according to claim 1, wherein the image formation characteristic measuring means is in focus state by the focus state detecting means at one center of an exposure area by the projection optical system and at least three peripheral areas. Is detected, and the field curvature is measured from the detection result of the in-focus state at at least four places. 4. The projection exposure apparatus according to claim 1, wherein the reference pattern includes a first pattern extending in a saddle direction and a second pattern extending in a medial direction, and the image formation characteristic measuring unit. At each of at least four locations around the exposure area of the projection optical system, the focusing state detecting means detects the focusing state for each of the transmitted light fluxes of the first and second patterns. A projection exposure apparatus, which measures an astigmatic difference from the obtained detection results of eight focused states. 5. A projection exposure apparatus for forming an image of a transmitted light flux of a mask pattern on a photosensitive substrate on a stage via a projection optical system, wherein the projection exposure apparatus is installed in a plane substantially the same as a photosensitive surface of the photosensitive substrate. A reference pattern including a first pattern extending in the saddle direction and a second pattern extending in the medial direction in the exposure area of the system, and an illumination light is guided to the lower surface of the reference pattern to transmit the transmitted light of the reference pattern. Illumination means for making the mask pattern incident through the projection optical system, and a light receiving means for receiving the reflected light flux from the mask pattern rear surface by the transmitted light flux of the reference pattern through the projection optical system and the reference pattern, The focus state is detected based on the output signal obtained from the light receiving means when the stage is moved in the optical axis direction of the projection optical system. A focus state detection unit detects a focus state by the focus state detection unit based on illumination light passing through a first pattern extending in a saddle direction of an exposure area by the projection optical system, and in the medial direction The focusing state is detected by the focusing state detection means based on the illumination light passing through the extending second pattern,
A projection exposure apparatus comprising: an image forming characteristic measuring unit that measures an image forming characteristic of the projection optical system based on the detection results of these two in-focus states. 6. The projection exposure apparatus according to claim 5, wherein the image formation characteristic measuring unit is configured to determine, based on a correlation between a deviation amount of a focused state and eccentricity of the first and second patterns measured in advance, A projection exposure apparatus characterized by measuring the eccentricity of a projection optical system. 7. The projection exposure apparatus according to claim 5, wherein the image formation characteristic measuring unit determines, from a correlation between a deviation amount of a focused state and a spherical difference of the first and second patterns measured in advance, A projection exposure apparatus, which measures a spherical difference of the projection optical system.