JPH10261567A - Projection aligner and optical characteristic measurement method of projection optical system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure the optical characteristics of a projection optical system by correcting an error due to the running characteristics of a substrate stage and an error due to the flatness characteristics of a wafer holder. SOLUTION: The data on the amount of floating and sinking caused by the running characteristics of a substrate stage 22 and the flatness of a substrate holder 24 are measured in advance and are stored in a storage 23 in a projection aligner. When the optical characteristics of a projection optical system PL are measured, the position of the substrate stage in Z direction is corrected so that the substrate stage does not float or sink due to the running characteristics of the substrate stage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a projection exposure apparatus and a method for measuring optical characteristics of a projection optical system provided in the projection exposure apparatus.

[0002]

2. Description of the Related Art Conventionally, when a semiconductor device or the like is manufactured using photolithography technology, a pattern formed on a photomask or reticle (hereinafter, referred to as a mask) is exposed to light such as a photoresist through a projection optical system. 2. Description of the Related Art A projection exposure apparatus that projects and exposes each shot area on a photosensitive substrate such as a semiconductor wafer or a glass plate coated with an agent is used. As a projection exposure apparatus, a photosensitive substrate is placed on a substrate stage that is two-dimensionally movable in XY directions,
This substrate stage repeats the operation of stepping the photosensitive substrate in the XY directions and sequentially exposing the mask pattern image to each shot area on the photosensitive substrate. Projection exposure apparatuses are frequently used. Also, a step-and-scan projection exposure apparatus that performs pattern exposure on each shot area on a photosensitive substrate by reduced projection and scanning exposure, and moves between shots by stepping is also used. I have.

One method for measuring the optical characteristics of the projection optical system of these projection exposure apparatuses, for example, the imaging characteristics in the Z direction (the optical axis direction of the projection optical system) such as curvature of field, tilt of the image plane, and depth of focus. As a method, there is a method of using a measurement mask having evaluation marks formed at a plurality of predetermined positions. In this case, the evaluation marks of the measurement mask are exposed on a plurality of shot areas of the photosensitive substrate by gradually changing the Z-direction position (focusing position) of the photosensitive substrate, and the marks are placed in the just-focused state for each evaluation mark. The Z-direction imaging characteristic of the projection optical system is evaluated by obtaining the Z-direction position of the photosensitive substrate when the exposure is performed.

Incidentally, the surface of the photosensitive substrate placed on the substrate stage is not completely flat due to a change in the thickness of the substrate itself or the flatness of the substrate holder holding the photosensitive substrate by suction. It usually has some undulations. If the surface of the photosensitive substrate has such an undulation, the imaging characteristic of the projection optical system in the Z direction measured by the above method includes an error corresponding to the undulation.

The positional fluctuation in the optical axis direction between two points on the photosensitive substrate due to the undulation of the surface of the photosensitive substrate is smaller as the distance between the two points on the photosensitive substrate is smaller. It becomes statistically indeterminate as the distance increases. Therefore, in order to reduce the measurement error caused by the surface shape of the photosensitive substrate, when measuring the optical characteristics of the projection optical system by the above-described method, the illumination area of the measurement mask is limited by the mask bride and formed on the measurement mask. The evaluation marks are illuminated one by one, the substrate stage on which the photosensitive substrate is mounted is moved for each exposure of the evaluation marks, and all the evaluation marks are sequentially exposed to a narrow area on the photosensitive substrate. ing.

FIG. 6 is a view for explaining a method of exposing an evaluation mark by moving a substrate stage. When the measurement mask is exposed in one shot, the evaluation marks M1 to M5 are dispersed and exposed in one shot area S on the photosensitive substrate.
If the evaluation marks M1 to M5 are far apart from each other, as described above, the evaluation value of the projection optical system in the Z direction is affected by the undulation of the photosensitive substrate surface.

Therefore, the evaluation marks M1 to M5 formed on the measurement mask are not exposed by one shot at a time, and the evaluation marks M1 to M5 are cut out one by one by a blind of a mask illumination system and illuminated. that time,
By moving the substrate stage, the evaluation mark M1 is exposed to a mark position M1 ′ close to the position of the evaluation mark M5. Similarly, by moving the substrate stage,
The evaluation mark M2 is placed at the mark position M2 ', and the evaluation mark M3
At the mark position M3 ', and the evaluation mark M4 at the mark position M
Expose each to 4 '. After the exposure, the photosensitive substrate is developed, and each of the evaluation marks M1 ', M2', M3 ', M4', M5
Is observed with a scanning electron microscope or the like to evaluate a focused state or the like. Then, the evaluation value of each evaluation mark is stored in the shot position (marks M1, M
2, M3, M4, etc.), the influence of the surface shape of the photosensitive substrate is eliminated.

[0008]

When the evaluation mark of the measurement mask is exposed on the photosensitive substrate to evaluate the optical characteristics of the projection optical system, the substrate stage is moved to cover a narrow portion in the shot area of the photosensitive substrate. According to the method of exposing all the evaluation marks, measurement errors due to the surface shape of the photosensitive substrate can be reduced. However, when the movement of the substrate stage itself has a displacement amount in the direction of the optical axis of the projection optical system or the substrate mounting surface of the substrate holder is not completely flat, the substrate stage is moved by moving the substrate stage. The ups and downs of the photosensitive substrate due to the running characteristics and the flatness characteristics of the substrate holder enter the measurement results of the optical characteristics of the projection optical system as errors.

The two-dimensional position, yawing, pitching, and rolling of the substrate stage can be detected by detecting the distance between the movable stage fixed to the substrate stage and the laser interferometer. Axial position fluctuations cannot be constantly monitored. Therefore, conventionally, the measurement was performed while allowing the movement of the photosensitive substrate in the Z-axis direction due to the running characteristics of the substrate stage. However, errors occur in the measurement results of various aberrations of the projection optical system, and accurate measurement results are obtained. I couldn't do that.

The present invention has been made in view of the above-mentioned problems of the prior art, and corrects an error due to the running characteristic of the substrate stage, which is the amount of ups and downs due to the position of the substrate stage, and an error due to the flatness characteristic of the wafer holder. And
An object of the present invention is to provide a projection exposure apparatus capable of accurately measuring the optical characteristics of a projection optical system.

Another object of the present invention is to provide a method for measuring an optical characteristic of a projection optical system by correcting an error caused by the running characteristic of the substrate stage and an error caused by the flatness characteristic of the wafer holder.

[0012]

In order to solve the above problems, according to the present invention, data on the running characteristics of the substrate stage and the amount of ups and downs caused by the flatness of the substrate holder are stored in a storage device in the projection exposure apparatus. Configuration. The data is obtained using the auto-focus mechanism of the projection exposure
The measurement is performed in advance in a matrix or continuously finely in accordance with the XY direction position of the substrate stage. Then, at the time of measuring the optical characteristics of the projection optical system, the position of the substrate stage in the Z direction is corrected so that ups and downs of the photosensitive substrate do not occur due to the running characteristics of the substrate stage and the flatness of the substrate holder.

That is, the present invention provides a mask (M, M0)
Optical system (PL) that projects the pattern formed on the photosensitive substrate (W), a substrate stage (21, 22) that holds the substrate (W) and moves two-dimensionally, and a substrate stage (21). , 22) for detecting the position of (22)
In the projection exposure apparatus provided with
Substrate stage (21, 22) resulting from the movement of (1, 2)
Displacement amount detecting means (1, 2, 3, 4, 5, 6, 6) for detecting the displacement amount of the projection optical system (PL) in the optical axis direction relating to 2).
7, 8, 9, 10, 11, 12, 13, 14), the detection result of the displacement detecting means, and the position of the substrate stage (21, 22) detected by the position detecting means (27). Storage means (23) for storing.

The displacement amount detecting means includes a substrate stage (2)
An irradiation system (1,2,3,4,5) for irradiating the substrate (W) held on the substrate (1,22) with a light receiving system (6,7,4) for receiving the light reflected on the substrate (W). 8, 9, 10, 11, 1
2).

Further, according to the present invention, a substrate (W) is held,
By controlling the substrate stages (21, 22) movable in a two-dimensional plane, the image of the pattern (K1 to K5) of the mask (M0) is exposed on the substrate (W) by the projection optical system (PL).
In a measuring method for measuring optical characteristics of a projection optical system (PL), a projection optical system (PL) related to a substrate stage (21, 22) caused by movement of the substrate stage (21, 22).
Detecting the amount of displacement of the substrate stage (21, 22) in the optical axis direction based on the detection result, and performing exposure. .

Further, according to the present invention, the pattern (K1 to K5) of the mask (M0) is moved by the projection optical system (PL) while moving the substrate stage (21, 22) holding the substrate (W) in a two-dimensional plane. In the measurement method for exposing the image of (1) to the substrate (W) and measuring the optical characteristics of the projection optical system (PL), the projection on the substrate stage (21, 22) caused by the movement of the substrate stage (21, 22). Patterns (K1 to K5) by correcting position fluctuations of the optical system (PL) in the optical axis direction
Is performed.

According to the present invention, when measuring various aberrations of the projection optical system based on the running of the substrate stage, the running characteristics of the substrate stage and the substrate holder measured in advance and stored in the storage device of the projection exposure apparatus. By using the data on the flatness of the XY coordinate position of the substrate stage,
Since the Z-direction position of the substrate stage is corrected, highly accurate measurement can be performed without being affected by the running characteristics of the substrate stage and the flatness of the substrate holder.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic view of a projection exposure apparatus according to the present invention provided with an oblique incident light type focus position detecting means (hereinafter, referred to as an AF system). Exposure light (i-line, KrF, ArF excimer laser) from an illumination system (not shown) has an illumination area limited by a blind 20 driven by a blind drive unit 19 to uniformly illuminate a pattern formed on a mask M. . The pattern of the mask M illuminated with the exposure light is projected and exposed on a photosensitive substrate W mounted on a substrate stage by a projection optical system PL.

The substrate stage has an XY stage 22 movable in the XY directions orthogonal to the optical axis of the projection optical system PL, and a Z stage 21 movable in the optical axis direction (Z direction) of the projection optical system PL. . A substrate holder 24 is provided on the Z stage 21, and the photosensitive substrate W is held by vacuum suction on the substrate mounting surface of the substrate holder 24. The XY stage 22 includes an XY stage driving unit (including a motor control circuit and a position output circuit).
The Z stage 21 is driven by driving a Z stage drive motor 18 by a Z stage drive unit (Z-DRV) 16. Further, a movable mirror 26 is fixed to the substrate stage, and the XY coordinate position of the substrate stage is detected by measuring the distance between the movable mirror 26 and the laser interferometer 27. The output PS of the laser interferometer 27 is supplied to the main controller 15.

The AF system 25 uses a non-photosensitive illumination light IL for the photoresist applied on the photosensitive substrate W to shift the best focus position of the projection optical system PL and the surface of the photosensitive substrate W. Is detected. Illumination light IL that is not photosensitive to the photoresist illuminates the slit plate 1.
The illumination light passing through the slit of the slit plate 1
The photosensitive substrate W is irradiated obliquely through the mirror 3, the objective lens 4, and the mirror 5, and an image of the slit is formed on the surface of the photosensitive substrate W. The slit image light beam reflected by the photosensitive substrate W is re-imaged on the light receiving slit plate 11 via the mirror 6, the objective lens 7, the vibration mirror 8, and the plane parallel plate 10, and the light beam transmitted through the slit plate 11 is a sensor. The light is received at 12.

The vibrating mirror 8 is for slightly vibrating a slit image formed on the slit plate 11 for receiving light in a direction orthogonal to the longitudinal direction. This is for shifting the relative relationship between the reflection slit image from the photosensitive substrate W and the vibration center in the direction orthogonal to the slit longitudinal direction. The oscillating mirror 8 is oscillated by a mirror driving unit (M-DRV) 9 driven by a driving signal from an oscillator (OSC) 13.

When the slit image reflected by the vibrating mirror 8 vibrates on the light receiving slit plate 11, the intensity-modulated light flux transmitted through the slit of the light receiving slit plate 11 is received by the sensor 12. A signal from the sensor 12 is input to a synchronous detection circuit (PSD) 14. This PSD14
, An AC signal having the same phase as the drive signal from the OSC 13 is input, and synchronous detection is performed based on the phase of the AC signal. The detection signal FS is transmitted to the main controller 15
Is output to The detection output signal FS is called an S-curve signal, and the slit center of the light receiving slit plate 11 and the photosensitive substrate W
Becomes zero when the center of vibration of the reflected slit image coincides with the positive level, and becomes a positive level when the photosensitive substrate W is displaced upward from that state, and a negative level when the photosensitive substrate W is displaced downward. Become. Light receiving slit plate 11
The positional relationship between the center of the slit and the center of vibration of the reflected slit image from the photosensitive substrate W is calibrated in advance by adjusting the inclination of the plane parallel plate 10. Therefore, the height position of the photosensitive substrate W at which the output signal FS becomes zero level is detected as the focal point. For details of this AF system 25,
For example, it is described in JP-A-5-190423.

The main controller 15 is connected to a storage device 23. The main controller 15 has a function of setting the inclination of the plane parallel plate 10, and an AF output signal F output from the PSD 14.
A command signal D to a Z-stage drive unit (Z-DRV) 16 that drives a Z-stage drive motor 18 based on S
The function of outputting S, the function of outputting a command to the driving unit (XY-DRV) 17 for driving the XY stage 22, and the XY of the substrate stage by the output PS from the laser interferometer 27.
It has a function to detect the coordinate position.

Next, the function of the projection exposure apparatus according to the present invention will be described. FIG. 2 is an explanatory diagram schematically showing running characteristics of the substrate stage. FIG. 2 shows that the substrate stage is Y
Although the state is shown in which the substrate stage is moved linearly in the direction, a Z-direction displacement occurs in the substrate stage due to a manufacturing error of the substrate stage moving mechanism or the like. On the surface of the substrate moving into the actual exposure field of the projection optical system PL, the Z-direction displacement based on the running characteristics of the substrate stage and the Z-direction displacement based on the flatness of the substrate holder 24 are combined. Occurs.

In the present invention, the amount of ups and downs reflecting the running characteristics of the substrate stage and the flatness of the substrate holder is measured using the AF system 25 provided in the projection exposure apparatus. For this purpose, a substrate having a very good flatness is placed on the substrate holder 24, and while the substrate stage is continuously moved in the XY directions by the XY stage driving unit 17, the ups and downs of the substrate surface are measured using the AF system 25. . The amount of displacement of the substrate surface in the Z direction measured by the AF system 25 is stored in the storage device 23 as a function of the XY position of the substrate stage measured by the laser interferometer 27.

At this time, if the surface of the substrate is not completely flat, a measurement error occurs due to the flatness of the substrate surface. The error due to the flatness of the substrate surface is considered to be statistically random, so remove it by performing multiple measurements using multiple substrates and averaging the multiple measurements. Can be. Or,
The height distribution (flatness) of the substrate surface is precisely measured in advance using an interferometer or the like, and the measured value of the AF system 25 is corrected by using the data of the height distribution measured in advance. May be eliminated due to the flatness of.

FIG. 3 is an exaggerated three-dimensional view of the Z-direction displacement measured by the AF system 25. The broken line indicates an ideal case where there is no displacement in the optical axis direction due to the movement of the substrate stage, and the solid line indicates the measurement data. FIG. 3 shows an example in which ups and downs are continuously measured while moving the substrate stage in the Y direction. Therefore,
Although there is an XY coordinate position where there is no measurement data, data relating to a position where data is not measured can be obtained from the measured data by an interpolation method such as approximation function interpolation, linear interpolation, or spline interpolation. The data measured in this way and the data calculated by the interpolation are XY of the substrate stage.
It is stored in the storage device 23 of the projection exposure apparatus as a function of the coordinate values.

Next, a method for measuring the optical characteristics of the projection optical system according to the present invention will be described. A measurement mask M0 in which a plurality of evaluation marks K1 to K5 are dispersed and arranged as schematically shown in FIG. 4 is mounted on the projection exposure apparatus shown in FIG.
The photosensitive substrate W is mounted on the substrate holder 24 of the substrate stage. The main controller 15 instructs the XY stage driving unit 17 to move the XY stage 22 step by step,
., S (n−1), S (n), S (n + 1),... Are exposed to the evaluation marks K1 to K5 of the measurement mask M0, respectively. . In the exposure of each shot area, as described with reference to FIG. 6, each evaluation mark K1 to K5 on the measurement mask M0 is cut out one by one by the blind 20 of the mask illumination system and exposed.

The evaluation marks K1 to K1 are added to the shot area S (n).
Explaining the case of exposing K5 as an example, first, the evaluation mark K5 of the measurement mask M0 is cut out by the blind 20 and exposed as it is at the center of the shot area S (n) as the mark M5 (n). Next, when exposing the evaluation mark K1, the main controller 15 controls the shape of the blind 20 by the blind driving unit 19 to illuminate only the evaluation mark K1 with the mask illumination system.
By instructing the Y stage driving unit 17 to drive the XY stage 22, if the entire measurement mask M0 is exposed by one shot, the evaluation mark K1 exposed at the mark position M1 (n) is marked M5 (n). Is exposed as a mark M1 '(n) at a position close to. Similarly, with respect to the other evaluation marks K2 to K4, the portions exposed to the mark positions M2 (n) to M4 (n) after one shot exposure are represented by X
By moving the Y stage 22, the mark M5 (n)
Are exposed as marks M2 '(n) to M4' (n) at positions close to. This is to eliminate the influence of the flatness of the photosensitive substrate W from the measurement result, as described above.

Here, the main controller 15 sets the evaluation mark K
At the time of exposures 2 to K4, a command is issued to the Z stage drive unit 16 based on the data stored in the storage device 23, and XY
The Z stage 21 is moved so that ups and downs of the photosensitive substrate W caused by moving the substrate stage in the coordinate system are cancelled.
Is driven in the Z direction. By the position correction of the Z stage 21, a measurement error due to the running characteristics of the substrate stage and a measurement error due to the flatness of the substrate holder 24 can be eliminated.

When the exposure of the shot area S (n) is completed, the process proceeds to the exposure of the shot area S (n + 1). At this time, the main controller 15 instructs the Z stage control unit 16 to drive the Z stage 21 while detecting the position of the photosensitive substrate W in the Z direction based on the detection signal FS of the AF system 25, thereby driving the Z stage 21. The position in the Z direction is changed by a minute amount ΔZ. After that, in the same procedure as the exposure of the shot area S (n), the evaluation marks K1-
K5 is sequentially exposed as marks M1 ′ (n + 1) to M5 ′ (n + 1) in the central area of the shot area S (n + 1).

In the subsequent exposure of the shot area (n + 2), the main controller 15 instructs the Z stage controller 16 while detecting the position of the photosensitive substrate W in the Z direction by the detection signal FS of the AF system 25 again. By driving the stage 21, the position of the photosensitive substrate W in the Z direction is further reduced by a small amount Δ
Change by Z. Thereafter, similarly, the measurement mask M
The evaluation marks K1 to K5 formed at 0 in the central area of the shot area S (n + 2) are marked M1 ′ (n + 2) to M
Exposure is performed sequentially as 5 '(n + 2).

When the operation of exposing the evaluation marks to a plurality of shot areas is completed while changing the position of the photosensitive substrate W in the optical axis direction by ΔZ for each shot, the photosensitive substrate W is removed from the substrate holder 24 and developed. Evaluation marks M1 ′ (n) formed on photosensitive substrate W by development
M4 '(n), M5 (n) [n = 1, 2, 3,...] Are observed by an observation means such as a scanning electron microscope, and the evaluation marks K1 to K5 of the measurement mask M0 are evaluated. Finds the shot area in which the sharpest is formed, and finds the position of the shot area in the Z direction at that time. As a result, for example, the evaluation mark K1
1 is the sharpest in the shot area, and the evaluation mark K2 is most sharply exposed in the shot area in the Z direction position of Z2. It is possible to precisely evaluate the imaging characteristics in the directions. In this evaluation, the positions of the marks M1 ′ (n) to M4 ′ (n) are the mark positions M
1 (n) to M4 (n) for evaluation.

The data stored in the storage device 23 is
The present invention can be used other than when measuring the optical characteristics of the projection optical system PL. For example, when exposing a certain shot area on the photosensitive substrate, the auto-focus operation of the projection exposure apparatus using the AF system 25, that is, the driving of the Z stage 21 to the in-focus position is performed by pattern formation near the shot area. It may be performed in other places that are not done. In this case, after performing the autofocus operation, it is necessary to drive the XY stage 21 to move the shot area to the exposure field of the projection optical system PL. If there is a displacement in the Z direction due to running characteristics, the exposure pattern will be defocused. However, this defocus amount (Z
Direction displacement) can be known from the data stored in the storage device 23, and the Z direction displacement caused by the running characteristics of the substrate stage during autofocus is taken as an offset.
By moving the stage 21, defocus can be eliminated.

[0035]

According to the present invention, the running characteristics of the substrate stage are measured in advance, and the ups and downs due to the movement of the substrate stage are corrected based on the data, so that the projection optical system can be controlled based on the running of the substrate stage. It is possible to eliminate a measurement error when performing the optical characteristic measurement, and to perform a highly accurate measurement.

[Brief description of the drawings]

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

FIG. 2 is a diagram schematically showing running characteristics of a substrate stage.

FIG. 3 is a schematic diagram of ups and downs caused by running characteristics of a substrate stage.

FIG. 4 is a schematic view of a measurement mask.

FIG. 5 is a view for explaining evaluation mark exposure for measuring optical characteristics of a projection optical system.

FIG. 6 is a diagram illustrating a method of exposing an evaluation mark by moving a substrate stage.

[Explanation of symbols]

Reference numerals 1, 11: slit plate, 2: lens system, 3, 5, 6: mirror, 4, 7: objective lens, 8: vibration mirror, 9: mirror drive unit, 10: parallel plane plate, 12: sensor, 13:
Oscillator (OCS), 14: Synchronous detection circuit (PSD), 1
5: Main controller, 16: Z stage drive unit (Z-DR
V), 17 ... XY stage drive unit (XY-DRV), 1
Reference numeral 8: Z stage drive motor, 19: blind drive unit, 21: Z stage, 22: XY stage, 23: storage device, 24: substrate holder, 25: AF system, 26: moving mirror, 27: laser interferometer, M: mask, PL: projection optical system, W: photosensitive substrate, M0: measurement mask

Claims (4)

[Claims] A projection optical system that projects a pattern formed on a mask onto a photosensitive substrate; a substrate stage that holds the substrate and moves two-dimensionally; and a position detection unit that detects a position of the substrate stage. A projection exposure apparatus comprising: a displacement amount detection unit configured to detect a displacement amount of the projection optical system in the optical axis direction with respect to the substrate stage due to the movement of the substrate stage; and a detection result of the displacement amount detection unit. And a storage unit for storing the position of the substrate stage detected by the position detection unit in a corresponding manner. 2. The projection exposure apparatus according to claim 1, wherein the displacement amount detecting unit irradiates the substrate held by the substrate stage with light, and receives light reflected by the substrate. And a projection exposure apparatus. 3. A substrate stage, which holds a substrate and is movable in a two-dimensional plane, is exposed to an image of a pattern of a mask on the substrate by a projection optical system, and the optical characteristics of the projection optical system are adjusted. In the measuring method for measuring, a step of detecting a displacement amount of the projection optical system in the optical axis direction with respect to the substrate stage due to the movement of the substrate stage, based on the detection result, the optical axis direction of the substrate stage. Performing the exposure after correcting the position of the measurement. 4. A measuring method for exposing an image of a pattern of a mask to a substrate by a projection optical system while moving a substrate stage holding the substrate in a two-dimensional plane, and measuring optical characteristics of the projection optical system. 5. The measurement method according to claim 1, wherein the exposure of the pattern is performed by correcting a positional change in the optical axis direction of the projection optical system with respect to the substrate stage caused by the movement of the substrate stage.