JPH09260252A - Imagery characteristics evaluation method of projection optical system, and projection aligner using the method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To rapidly and accurately detect imagery characteristics of a projection optical system used for a projection aligner, without being affected by the flatness of a running guide surface of a wafer stage. SOLUTION: Calibration of a reference surface of a plurality of measurement points with multipoint focus position detecting systems 4a, 4b of an oblique incidence system is performed by using a reference plane board 8 arranged on a Z tilt stage 7. A specified surface region of a wafer 3 is transferred in the exposure field of a projection optical system. Positions in the Z direction of a plurality of measurement points on the wafer 3 are simultaneously measured with the focus position detecting systems 4a, 4b, and images of a pattern IP for measurement of a reticle 2 are exposed on a plurality of the measurement points. After similar operations are repeated while the position in the Z direction of the wafer 3 is shifted little by little, the wafer 3 is developed, and imagery forming characteristics of a projection optical system 1 are calculated from the exposed image formed on the wafer 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention projects a pattern on a mask onto a photosensitive substrate in a photolithography process for manufacturing, for example, a semiconductor device, a liquid crystal display device, an image pickup device (CCD etc.), a thin film magnetic head or the like. The present invention relates to an image forming characteristic evaluation method for a projection optical system and a projection exposure apparatus using this image forming characteristic evaluation method.

[0002]

2. Description of the Related Art For example, in a photolithography process for manufacturing a semiconductor device or the like, a pattern formed on a reticle as a mask is transferred onto a wafer (or a glass plate or the like) as a photosensitive substrate through a projection optical system. A projection exposure apparatus such as a stepper that transfers with high accuracy is used. In these projection exposure apparatuses, a projection optical system for transferring a reticle pattern image on a wafer with high resolution is required to have excellent imaging characteristics. Therefore, for example, image forming characteristics such as image plane inclination and image surface curvature of the projection optical system are regularly measured, and the image forming characteristics are corrected based on the measurement result.

By the way, in the projection exposure apparatus, the position of the wafer in the height direction (Z direction) and the tilt angle are usually adjusted to Z.
Two-dimensional plane (XY plane) for tilt stage and wafer
The wafer stage is equipped with an XY stage that is positioned at a desired position above. Then, based on the premise that the guide surface (running guide surface) of a wafer stage on which a wafer is placed, particularly an XY stage, is a substantially perfect plane, the following method is used to determine the imaging characteristics of the projection optical system. The measurement was taking place.

FIG. 11 is a diagram for explaining a conventional method of measuring an image forming characteristic, and FIG. 12 is a plan view of a part of FIG. 11 and 12 show a state in which the image plane at the position A at the end of the exposure field IAR of the projection optical system 1 is being measured. In FIG. 11,
An oblique incidence type focus position detection system (hereinafter, referred to as "focus position detection systems 50a and 50b") including a light sending optical system 50a and a light receiving optical system 50b for detecting the focus position of the wafer 3B on the left and right side surfaces of the projection optical system 1. ) Is installed, and the detection light FL is obliquely directed to the optical axis AX from the light transmission optical system 50a toward the detection point C on the wafer 3B that substantially intersects the optical axis AX of the projection optical system 1. Is irradiated. For example, a slit image is projected on the detection point C. Hereinafter, the optical axis A of the projection optical system 1
The Z axis is taken parallel to X, and the X axis and Y axis are taken on a plane perpendicular to the Z axis for explanation.

The detection light FL irradiated on the wafer 3B is reflected on the wafer 3B, and the reflected light is received by the light receiving optical system 50b.
Incident on. The light receiving optical system 50b outputs a detection signal corresponding to the height position of the measurement point P ₁ on the wafer 3B corresponding to the detection point C. As shown in FIG. 11, the surface S of the wafer 3B has undulations. In order to prevent the undulation from affecting the image plane measurement, the exposure is performed in the following sequence.

First, the XY stage 5 is driven to move a measurement point P ₁ on the surface S of the wafer 3B coated with a two-dot chain line coated with photoresist to a detection point C of the focus position detection systems 50a and 50b, and to move Z The tilt stage 7 is driven to set the position of the measurement point P _{1 in} the Z direction to a desired position. Next, with the Z tilt stage 7 locked, the XY stage 5 is driven so that the measurement point P ₁ is positioned at the position A of the image plane measurement target at the end of the exposure field IAR. In FIG. 11, the curve indicated by the solid line shows the state after the movement of the wafer 3B. As shown in FIG. 12, by this operation, the area AR1 indicated by the two-dot chain line on the wafer 3B corresponding to the exposure field IAR is moved to the exposure field IAR. Then, with the wafer 3B kept in that state, an illumination optical system (not shown) irradiates the pattern for image formation evaluation on the reticle with the illumination light for exposure, and the pattern is projected onto the measurement point P ₁ on the wafer 3B. The image IPA is exposed. The pattern image IPA in this example is a pattern image composed of a plurality of slit-shaped marks extending in the X direction and a plurality of slit-shaped marks extending in the Y direction.

Next, the Z tilt stage 7 is driven,
The height of the wafer 3B is changed and the above operation is repeated at a plurality of heights. In this case, the exposure position on the wafer 3B is slightly shifted in the XY plane so that the already-exposed pattern and the newly-exposed pattern do not overlap on the wafer 3B. Next, the above operations 1 to 3 are performed at a plurality of positions other than the position A in the exposure field IAR.

Next, the wafer 3B exposed by the above operation is developed, and the exposed pattern Z is most resolved at each position in the exposure field IAR.
Detect the position in the direction. By the above operation,
How much the image forming plane at each position in the exposure field IAR is curved or inclined with reference to the running guide surface of the XY stage 5 is required.

[0009]

In the prior art as described above, the XY stage 5 moves until the exposure is performed by the operation after the height of the measurement point P ₁ is set (measured) by the above operation. Therefore, unless the flatness of the running guide surface of the XY stage 5 is sufficiently high, there is an inconvenience that a measurement error of the imaging characteristic occurs. There is a limit to the flatness of the running guide surface of the XY stage 5, and it is impossible to obtain perfect flatness. Further, in some projection exposure apparatuses used, the flatness of the running guide surface of the XY stage decreases with the lapse of the usage period. In particular, recently, the numerical aperture of the projection optical system has increased in response to the miniaturization of circuits such as semiconductor elements,
Along with that, the depth of focus required is becoming shallower. Therefore, the demands on the image forming characteristics of the projection optical system, such as the field curvature and the image surface inclination, are becoming stricter, so that the image formation due to the lack of flatness of the running guide surface of the XY stage, which is difficult to avoid by the conventional method. The error in the characteristics cannot be ignored.

Further, it is necessary to repeat the above operation for each of a plurality of measurement positions in the exposure field IAR, and the measurement time becomes long in proportion to the number of measurement positions, and the throughput (productivity) is lowered. There are also inconveniences. In view of the above problems, the present invention provides quick and highly accurate imaging characteristics such as field curvature and field tilt of a projection optical system without being affected by the flatness of the travel guide surface of a stage for positioning a wafer. It is an object of the present invention to provide a method for evaluating the imaging characteristics of a projection optical system that can be evaluated. A further object of the present invention is to provide a projection exposure apparatus that uses such an image forming characteristic evaluation method for a projection optical system.

[0011]

According to the method for evaluating the image forming characteristics of a projection optical system according to the present invention, an image of a projection optical system (1) for projecting and exposing an image of a predetermined pattern onto a photosensitive substrate (3) is formed. In the characteristic evaluation method, the positions of the projection optical system (1) in the optical axis (AX) direction are detected at a plurality of measurement points (13A to 13E) on the photosensitive substrate (3), and the photosensitive substrate (3) is detected. Exposing each of the plurality of measurement points (13A to 13E) above with an image of an evaluation pattern (IP);
An image (I) of an evaluation pattern formed on the photosensitive substrate (3) corresponding to the plurality of measurement points (13A to 13E).
The imaging characteristics of the projection optical system (1) are evaluated based on the information obtained from P1 to IP3) and the positions of the plurality of measurement points (13A to 13E) in the optical axis (AX) direction. And stages.

According to the image forming characteristic evaluation method of the projection optical system of the present invention, a plurality of measurement points (13) on the photosensitive substrate (3) are provided.
The measurement of the position of the optical axis (AX) direction of (A to 13E) and the exposure of the image of the evaluation pattern (IP) onto the plurality of measurement points (13A to 13E) are simultaneously performed. Therefore, since it is not necessary to move the photosensitive substrate (3) between the measurement of the positions of the measurement points (13A to 13E) in the optical axis direction and the exposure thereof, the photosensitive substrate (3) is generated along with the movement of the photosensitive substrate (3). The projection optical system (1) is not affected by the flatness of the running guide surface of the stage device, which causes a measurement error in the optical axis direction.
The imaging characteristics of can be evaluated with high accuracy. Moreover, since a plurality of measurement points on the photosensitive substrate (3) are detected at once, the measurement time can be shortened.

In the projection exposure apparatus according to the present invention, the image of the transfer pattern on the mask (2) is exposed to the photosensitive substrate (1) through the projection optical system (1) under the illumination light (IL) for exposure. 3) In a projection exposure apparatus for projecting onto a projection exposure apparatus, a height adjusting stage (7) for moving the photosensitive substrate (3) in the optical axis (AX) direction of the projection optical system (1) and the photosensitive substrate (3). Focus position detection means (4a, 4b) for detecting the position of the projection optical system (1) in the optical axis (AX) direction at the plurality of measurement points (13A to 13E) above, and the focus position detection means. And a storage unit (9) for storing the unevenness information of the surface of the photosensitive substrate (3), and a predetermined photosensitive substrate (3) is connected to the projection optical system of the projection optical system via the height adjusting stage (7). When set at multiple positions in the optical axis (AX) direction,
The unevenness information of the surface of the predetermined photosensitive substrate (3) detected by the focus position detection means (4a, 4b) is stored in the storage means (9).

According to the projection exposure apparatus of the present invention, the photosensitive substrate (3) is set at a plurality of positions in the optical axis (AX) direction of the projection optical system (1), and the photosensitive substrate (3) is exposed at the plurality of positions. In order to simultaneously measure the positions of the plurality of measurement points (13A to 13E) on the substrate (3) in the optical axis (AX) direction and obtain the unevenness information of the surface of the photosensitive substrate (3) based on the measurement result,
The image forming characteristics of the projection optical system (1) can be adjusted with high accuracy based on accurate information on the unevenness of the photosensitive substrate (3) at the position in the optical axis direction.

In this case, it is preferable to provide a reference member (8) whose surface flatness is known on the height adjusting stage (7). As a result, the focus position detecting means (4a, 4b) can be accurately calibrated using the reference member (8), and the accurately calibrated focus position detection system (4a, 4b). Can be used to accurately measure the positions of a plurality of measurement points on the photosensitive substrate (3) in the optical axis (AX) direction.

Further, it is preferable that the height adjusting stage (7) further adjusts the inclination angle of the photosensitive substrate (3). This allows the surface of the photosensitive substrate (3) to be aligned with the measured image plane.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION An example of an embodiment of the present invention will be described below with reference to FIGS. In this example,
The present invention is applied to the case where the image forming characteristics of the projection optical system are evaluated in a stepper type projection exposure apparatus that collectively exposes the shot area on the wafer with the pattern of the reticle via the projection optical system.

FIG. 2 is a perspective view of the overall schematic configuration of the projection exposure apparatus used in this example. In FIG. 2, the light source, the fly-eye lens for uniformizing the illuminance distribution on the reticle, and the reticle are shown. The illumination light IL for exposure emitted from the illumination optical system LA including a variable field diaphragm that limits the illumination range in (1), a condenser lens, and the like is applied to the reticle 2 with a uniform illuminance distribution. As the illumination light IL, for example, i-line or g-line which is a bright line of an ultra-high pressure mercury lamp, excimer laser light such as KrF excimer laser light or ArF excimer laser light, or a harmonic wave of a copper vapor laser or a YAG laser is used. To be The illumination light IL that has passed through the reticle 2 transfers and exposes an image of the circuit pattern onto each shot area on the wafer 3 coated with the photoresist, via the projection optical system 1. In the following description, the Z axis is taken in the direction parallel to the optical axis AX of the projection optical system 1, and the orthogonal coordinate system on the plane perpendicular to the Z axis is the X axis and the Y axis.

At this time, the reticle 2 is placed on a reticle stage (not shown) that can be finely moved on a two-dimensional plane perpendicular to the optical axis AX. Cross-shaped reticle alignment marks RMA and RMB for aligning the reticle 2 are formed on both sides of the pattern area on the reticle 2 of this example. Further, five evaluation patterns 12A to 12E for measuring the image forming characteristics of the projection optical system 1 are formed in the four corners of the pattern area on the reticle 2 and in the vicinity of the optical axis AX. Hereinafter, these evaluation patterns 12A to 12E will be collectively described as a measurement pattern IP. Note that FIG.
In these, these evaluation patterns 12A to 12E
Is shown in a state in which a plurality of slit-shaped patterns each long in the X direction or the Y direction are arranged, but actually, as shown in FIG. 8, it is composed of a plurality of basic diamond-shaped marks. Details will be described later.

On the other hand, the wafer 3 is vacuum-sucked to a wafer holder (not shown) on the Z tilt stage 7, and the Z tilt stage 7 is fixed to the back side of the three corners of the Z tilt stage 7 and is capable of expanding and contracting focus leveling. Mechanisms 6a-6c
It is mounted on the X stage 5X that is movable in the X direction on the Y stage 5Y via the. The focus / leveling mechanisms 6a to 6c are controlled by a main control system 9 that controls the entire apparatus, and during normal exposure, the main control system 9 is used.
The height and tilt angle of the Z tilt stage 7 are adjusted so that the image surface of the pattern coincides with the surface of the wafer 3 based on the command of. In addition, the Y stage 5Y includes the wafer base 10
The upper part is configured to be movable in the Y direction. The Y stage 5Y and the X stage 5X constitute an XY stage 5, and the XY stage 5 and the Z tilt stage 7 constitute a wafer stage. The XY stage 5 is controlled by a main control system 9, and the main control system 9 controls the XY stage 5 based on position information of the XY stage 5 from an interferometer (not shown) to position the wafer 3 two-dimensionally. Then
Exposure is performed by a so-called step-and-repeat method. During the evaluation of the image forming characteristics of the projection optical system 1, the image of the measurement pattern IP on the reticle 2 is exposed and transferred onto the unexposed wafer 3.

Further, the projection optical system 1 of the projection exposure apparatus of this example
The side surface of the wafer receives the reflected light from the wafer 3 of the light-transmitting optical system 4a for projecting slit images at a plurality of positions in the exposure field IAR, and the detection light FL emitted from the light-transmitting optical system 4a. An oblique incidence type multi-point focus position detection system (hereinafter, referred to as “focus position detection systems 4a and 4b”) including a light receiving optical system 4b for re-forming the slit images is installed. The light sending optical system 4a is arranged above the wafer stage on the lower side surface side which is rotated by 45 ° counterclockwise with respect to the Y axis of the projection optical system 1, and is symmetrical with respect to the light sending optical system 4a with respect to the optical axis AX. 4b is installed. The focus position detection systems 4a and 4b accurately measure the Z-direction positions (focus positions) at a plurality of points on the surface of the wafer 3.
In this case, the light-transmitting optical system 4a irradiates the wafer 3 with detection light FL having a wavelength that does not expose the photoresist on the wafer 3, and the reflected light of the detection light FL from the wafer 3 is received by the light-receiving optical system 4b. Is received by. The displacement of the wafer 3 in the Z direction with respect to a predetermined reference plane is detected as the positional deviation of the slit image re-formed by the reflected light, and a plurality of focus signals corresponding to the positional deviations are supplied to the main control system 9. It Based on these focus signals, the main control system 9 adjusts the focus / leveling mechanisms 6a to 6c so that the surface of the wafer 3 matches the image plane of the projection optical system 1.
Drive.

The detection light FL of the focus position detection systems 4a and 4b forms a plurality of slit images corresponding to the plurality of measurement points so that the focus positions of the plurality of measurement points in the exposure field IAR can be measured. To project. In the drawing, the detection light F
As L, the chief ray of the light flux forming each slit image is shown. Then, the tilt component of the wafer 3 is detected from the focus positions at a plurality of measurement points in the exposure field IAR. Usually, as described later, offset adjustment of a plurality of focus signals is performed so that the image forming surface of the projection optical system 1 becomes a zero point reference, and autofocus is performed so that each focus signal from the light receiving optical system 4b becomes zero. And auto leveling is performed.

A reference plane plate 8 for calibrating the multipoint focal position detection systems 4a and 4b is installed at the corners of the Z tilt stage 7 in the + X and -Y directions. . The reference plane plate 8 has high flatness and reflectance, and is installed so that its surface is at the same height as the surface of the wafer 3. The plane state of the reference plane plate 8 in a state where the center of the reference plane plate 8 is matched with the center of the exposure field IAR and the expansion / contraction amount of the focus / leveling mechanisms 6a to 6c is set to a predetermined reference value is as follows. It is measured by a predetermined measuring device, and the measured value is stored in the main control system 9. During calibration of the focus position detection systems 4a and 4b, the reference plane plate 8 is arranged in the exposure field IAR of the projection optical system 1 (see FIG. 3). In the following, for convenience of description, the plane of the reference plane plate 8 is assumed to be regarded as a substantially perfect plane. The reference flat plate 8 may be made of any material (metal, glass substrate, etc.) that has a small surface deformation, excellent heat resistance, and a reflectance of a certain level or more.

Next, a method of evaluating the field curvature and the field tilt of the projection optical system 1 in this example will be described with reference to the flowchart of FIG. As an evaluation procedure, first, the multi-point focus position detection systems 4a and 4b are calibrated (calibrated), and then the calibrated focus position detection systems 4a and 4b are used to bend the image plane and the image plane of the projection optical system 1. Measure the tilt.

FIG. 1 is a flow chart for explaining the method of evaluating the field curvature and the field tilt of the projection optical system 1 in this example. As shown in FIG.
At 01, the XY stage 5 of FIG. 2 is driven to move the center of the reference plane plate 8 to the exposure field IAR of the projection optical system 1.
The focus position detection systems 4a and 4b are calibrated by positioning the focus / leveling mechanisms 6a to 6c at a predetermined reference value.

FIG. 3 is a view for explaining a method of calibrating the focus position detection systems 4a and 4b, and is a view of the projection optical system 1 of FIG. 1 viewed from a position rotated 135 ° clockwise from the X axis. is there. As shown in FIG. 3, in step 102, a plurality of measurement points in the exposure field IAR of the reference flat plate 8 are irradiated with slit images by the detection light FL.
In FIG. 3, measurement points f _A , f _C , and f _{E on} the surface of the reference plane plate 8 are shown.
Slit images are radiated in the vicinity.

In the state where the focus position detection systems 4a and 4b are not calibrated, the reference planes (planes where the focus signal becomes 0) of the slit images at the respective measurement points are different. For example, in FIG. 3, the reference plane of the measurement point f _A is the plane H _A
The focus signal above and corresponding to the measurement point f _A corresponds to the difference in the height (position in the Z direction) between the surface of the reference plane plate 8 and the plane H _A (hereinafter referred to as “Z direction displacement”) Z _A. Output. Similarly, the measurement points f _C, for even f _E, each of the reference plane H _C, Z-direction displacement Z _C and H _E and the surface of the reference plane plate 8, a focus signal corresponding to Z _E is output. Here, it is assumed that the output values of the focus signal are displayed as they are in the Z-direction displacements Z _A , Z _C , and Z _E. In this way, in the state before the focus position detection systems 4a and 4b are calibrated, the output values Z _A , Z _C , and Z _E of the focus signal at each measurement point are arbitrary values.
The output values Z _A , Z _C and Z _E are supplied to the main control system 9. Similarly, Z-direction displacements (focus signals) at other measurement points are also supplied to the main control system 9.

Next, at step 103, hardware or software adjustment is performed so that the output values of the focus signals corresponding to the respective measurement points from the focus position detection systems 4a and 4b are aligned. That is, the focus position detection systems 4a and 4b
Between the output values (for example, Z _A , Z _C , and Z _E ) of the focus signal corresponding to each measurement point of Z _A = Z _C = Z _E = 0
The focal position detection systems 4a and 4b are calibrated (origin calibration) by adjusting so that the relationship of

FIG. 4 shows the focus position detection systems 4a and 4 after calibration.
The state of the output value of each focus signal in FIG.
At the measurement points f _A and f of the focus position detection systems 4a and 4b.
_The heights of the reference planes at _C , f _E and other measurement points and the surface of the reference plane plate 8 are the same, and in this case the light receiving optical system 4
The output value of the focus signal corresponding to each measurement point in b becomes the same. In this case, the displacement of the focus signal at each measurement point in the Z direction is based on the change in the output of the focus signal corresponding to each measurement point when the reference plane plate 8 is vertically displaced at appropriate intervals in the Z direction as shown by the broken line. It is also possible to measure and adjust the sensitivity to. With the above, the focus position detection system 4
Calibration of a and 4b is completed. Next, the position of the image plane of the projection optical system 1 is measured using the calibrated focus position detection systems 4a and 4b.

FIG. 5 is a view for explaining a method of measuring the image plane of the projection optical system 1 by the focus position detection systems 4a and 4b, and FIG. 6 is a plan view of a part of FIG. As shown in FIG. 6, the focus position detection systems 4a and 4b detect the focus positions at the five measurement points A to E at the four corners and the center of the exposure field IAR. In FIG. 5, three measurement points A, C and E out of the five measurement points are shown. In this measuring method, the position (height) in the Z direction at each measurement point of the wafer 3 is measured by the focus position detection systems 4a and 4b, and the wafer 3 is moved through the focus / leveling mechanisms 6a to 6c of FIG. The surface is slightly shifted and laterally displaced in the vicinity of the reference plane where the focus signals of the focus position detection systems 4a and 4b are 0, and set to a plurality of positions in the Z direction.
Of the measurement pattern IP on the reticle 2 at each height position of the exposure field IA of the projection optical system 1.
The pattern I for measurement is exposed and transferred near each measurement point in R.
The state of the image of P is measured. FIG. 5 shows a state in which the wafer 3 is arranged at three positions (average positions) R1 to R3 in the Z direction. Further, in FIGS. 5 and 6, a region within the exposure field IAR of the surface S of the wafer 3 at each of the positions R1 to R3 is defined as a surface region (shot region) S.
1, S2, S3. The surface areas S1 to S3 are areas on the wafer 3 which are slightly laterally displaced from each other in the same size as the exposure field IAR. 5 and 6 show a state in which the surface area S2 overlaps the exposure field IAR.

First, at step 104, the XY stage 5 is driven so that the center of the surface area S1 of the wafer 3 is located at the center of the exposure field IAR of the projection optical system 1. Next, as shown in FIG. 5, the surface of the wafer 3 is set at a position R1 in the vicinity of the image plane of the projection optical system 1, and measurement points 13A to 13A on the wafer 3 corresponding to the measurement points AE in FIG. 13E
The amount of displacement in the Z direction from the reference plane (the plane where the focus signals of the focus position detection systems 4a and 4b are zero) KS (see FIG. 7) is measured. For example, as shown in FIG. 5, at the measurement point 13A, the displacement amount in the Z direction is Z _A1 . Similarly, for the other measurement points 13B to 13E, the amount of displacement in the Z direction from the reference plane KS is measured. The data of these displacement amounts are supplied to the main control system 9 and stored in the main control system 9.
In this state, the measurement pattern IP on the reticle 2 in FIG.
Illumination light IL is irradiated onto the wafer 3 to expose and transfer the image of the measurement pattern IP to the measurement points 13A to 13E on the surface area S1 of the wafer 3. The measurement pattern IP is composed of a plurality of evaluation patterns as described above, and the position of the reticle 2 is set so that the image of each evaluation pattern is projected onto the measurement points A to E in the exposure field IAR. Has been done.

Next, the wafer 3 is slightly shifted in the Z direction, and preset positions R2 and R3 of the wafer 3 in the Z direction are set.
In the same manner as above, the amount of displacement of the wafer 3 in the Z direction at each of the measurement points A to E is measured and the measurement pattern IP is exposed. In this case, as shown in FIG. 6, the XY stage 5 is driven to shift the position of the wafer 3 in the X and Y directions by an appropriate amount so that the surface areas S1, S2 and S3 of the wafer 3 do not overlap each other. The images of the measurement pattern IP exposed at are not overlapped.

By the above operation, as shown in FIG. 5, for example, the displacement amount Z in the Z direction at the measurement points 14A and 15A on the wafer 3 corresponding to the measurement points A at the positions R2 and R3.
_A2 and Z _A3 are measured, and the amount of displacement in the Z direction is similarly measured at other measurement points. All of these measured values are supplied to the main control system 9 and stored in the main control system 9. Further, an image of the measurement pattern IP on the reticle 2 is exposed on the wafer 3 at each position R1 to R3 in the Z direction of the wafer 3. FIG. 6 shows the images 12AR to 12ER of the measurement pattern IP projected at the four corners and the center of the surface area S2 that coincides with the exposure field IAR having a substantially square shape.
Actually, the position of the wafer 3 in the Z direction is set to a large number of four or more positions with the necessary measurement resolution as a unit, and the exposure is performed. Next, in step 105, the exposed wafer 3 is developed, and the measurement pattern I
The state of the image of P is measured.

FIG. 7 shows a state of an image of the measurement pattern IP exposed on the wafer 3. In FIG. 7, in the surface area S2 on the wafer 3 and in the vicinity thereof, the position R in the Z direction is
An image of the measurement pattern IP exposed in 1 to R3 (hereinafter, referred to as “exposure image”) is formed laterally displaced. For example, exposure images IP1 to IP3 are formed at measurement points 13A to 15A at three positions R1 to R3 in the Z direction corresponding to one measurement point A in the exposure field IAR. Measurement points 13B to 15B, 13C to 15C, 13D to 15 on the wafer 3 corresponding to the other measurement points B to E
D, 13E to 15E also have exposure images IP1 to IP3, respectively.
Are formed. 6 and 7, the exposure image is shown in the state where a plurality of slit-shaped pattern images that are long in the X direction or the Y direction are arranged, but in reality, as shown in FIG. It is composed of a diamond-shaped basic mark.

FIG. 8 shows the actual structure of the exposure image IP1 shown in FIG. 7. In this FIG. 8, the exposure image IP1 is formed by four basic diamond-shaped diamonds formed in the X direction at a predetermined pitch and extending in the Y direction. An X-axis evaluation pattern 16X including marks 17a to 17d, and a Y-axis evaluation pattern 16Y including four diamond-shaped basic marks 17e to 17h formed in the Y direction at a predetermined pitch and extending in the X direction. It consists of The same applies to exposure images at other measurement points. In addition,
The shape and the number of the basic marks are not limited to the rhombus and four, and an appropriate shape and number may be set according to the purpose.

Next, the diamond-shaped basic marks 17a-17
From the state of h, the image forming characteristics of the projection optical system 1 such as the field curvature and the image surface inclination are measured. Below, basic marks 17a to 17h
An example of calculating the image formation characteristic of the projection optical system 1 from the state will be described. For example, the closer the focus position of the measurement point on the wafer 3 (position in the Z direction) is to the position of the image plane of the projection optical system 1 (hereinafter, simply referred to as “image plane position”), the higher resolution is obtained, and the diamond-shaped The widths of the basic marks 17a to 17h in the long axis direction become long. Therefore, the state of the diamond-shaped basic mark is measured using an appropriate length measuring device. As the length measuring device, for example, an alignment sensor attached to a projection exposure device that scans a slit-shaped laser beam to detect diffracted light from a measurement target mark can be used. First, the average length (mark length) in the Y direction of each of the four basic marks 17a to 17d of the X-axis evaluation pattern 16X is measured.
Similarly, the average length (mark length) in the X direction of the four basic marks 17e to 17h of the Y-axis evaluation pattern 16Y is measured. If these measured values are measured by an external length measuring device, the operator supplies them to the main control system 9 via an input device (not shown). Then, step 106
In, the main control system 9 calculates the imaging characteristics of the projection optical system 1 based on the supplied data as follows. In addition,
The calculation of the imaging characteristics may be performed by another host computer.

First, the mark length of the X-axis basic marks 17a to 17d of the exposure image measured at the measurement point 13A in FIG.
X _A1 . Similarly, four basic marks 17e of the Y-axis evaluation pattern 16Y of the exposure image measured at the measurement point 13A.
The mark length of -17h is LY _A1 . Measurement point 13A
The average mark length L _A1 (= (LX _A1 + LY _A1 ) / 2), which is the average value of the X-axis and Y-axis mark lengths in, is calculated.
Similarly, for the measurement points 14A and 15A in FIG. 7, the mark length and the average mark length of each of the four basic marks on the X-axis and the Y-axis are calculated. Here, the X-axis mark lengths at the measurement points 14A and 15A are LX _A2 and LX _A3 , and the Y-axis mark lengths are LY _A2 and LY _A3 .
The average mark lengths at the measurement points 14A and 15A are L _A2 and L _A3 , respectively. These measurement points 13A to 15A
The mark length in can be regarded as the mark length of the evaluation mark image when the measurement point A in the exposure field IAR is set at the positions Z _{A1 to} Z _A3 (deviation from the reference plane KS) in the Z direction. In addition, the mark length is actually required at more positions in the Z direction.

FIG. 9 shows the relationship between the position of the wafer 3 in the Z direction at the measurement point A and the average mark length at that position. In FIG. 9, the horizontal axis represents the wafer 3 at the measurement point A in FIG. The displacement amount ΔZ in the Z direction from the reference surface KS on the surface is represented, and the vertical axis represents the average mark length L. In FIG. 9,
The curve 18 plots the average mark length when the position in the Z direction of the wafer 3 at the measurement point A is set to a large number of positions including the positions of the displacement amounts Z _A1 , Z _A2 , Z _A3 , and is approximated by a curve. Interpolation is performed, and the displacement amount ΔZ _A that gives the maximum average mark length L _M on this curve 18 is obtained. That is, the reference plane KS
The position in the Z direction displaced by ΔZ _A from is detected as the image plane position (best focus position) of the projection optical system 1 at the measurement point A. Similarly, the measurement points 13B and 14 in FIG.
By measuring and plotting the average mark lengths at B, 15B to 13E, 14E, and 15E, the image plane positions at the other measurement points B to E are detected. The displacement amounts ΔZ of the image plane positions at the respective measurement points _{B to E} detected here are respectively designated as ΔZ _B to ΔZ _E.

FIG. 10 shows the amount of displacement of the image plane position at the measurement points A to E in the exposure field IAR obtained by the above calculation. In FIG. 10, the displacement of the image plane position at the measurement points A to E is shown. The amount of displacement ΔZ _{A to} ΔZ _E is Z on the reference plane KS.
The image plane 19 of the projection optical system 1 can be obtained by subjecting the points 20A to 20E taken in the direction to curved surface approximation using an appropriate interpolation method. As a result, the state of curvature of field and tilt of the field of the projection optical system 1 is found. Based on this result, for example,
The surface of the wafer 3 is imaged by adjusting the offset of each focus signal so that the focus signals of the focus position detection systems 4a and 4b become 0 on the image plane 19 and performing autofocus and autoleveling in that state. Aligned with face 19. Alternatively, the image plane 19 may be adjusted to be as flat as possible by, for example, controlling the inclination angle of a predetermined lens forming the projection optical system 1.

In this example, five measurement points A to E are set in the exposure field IAR of the projection optical system 1 and exposure and measurement are performed at many positions on the wafer 3 in the Z direction.
The arrangement of the measurement points is not limited to that, and the number and the arrangement of the measurement points may be determined according to the measurement accuracy of the image plane position of the projection optical system 1. Further, in this example, the projection optical system 1
As an example of the image forming characteristics of the above, an example in which the field curvature and the image surface inclination are measured has been described. For example, the following is obtained from the exposure image formed at the measurement point on the wafer 3 corresponding to each measurement point A to E. It is also possible to find the astigmatism of the projection optical system 1.

That is, from the mark lengths LX _{A1 to} LX _A3 of the X-axis evaluation pattern 16X on the measurement point A, the image plane position (best focus position) of the projection optical system 1 is calculated according to the method described in FIG. ) Is calculated. The image plane positions for the basic patterns of the X axis are similarly obtained for the other measurement points B to E. The displacement amounts of the image plane positions on the respective measurement points A to E obtained here from the reference plane KS are defined as ΔLX _{A to} ΔLX _E. Similarly, the image plane position of the projection optical system 1 is calculated from the mark lengths LY _{A1 to} LY _A3 of the Y-axis evaluation pattern 16Y on the measurement point A, and the other measurement points B to E are similarly measured on the Y-axis. Obtain the image plane position of the basic pattern. If the calculated displacements of the image plane positions are ΔLY _{A to} ΔLY _E , the astigmatism of the projection optical system 1 is determined by the difference between the displacements ΔLX _{A to} ΔLX _E and the displacements ΔLY _{A to} ΔLY _E. You can ask.

As described above, according to the present embodiment, the multi-point focus position detection systems 4a and 4b are calibrated by the reference plane plate 8 installed on the Z tilt stage 7, and the focus position detection systems 4a and 4b are calibrated.
The reference planes of the respective focus signals of are the same. Then, using the calibrated focus position detection systems 4a and 4b, the measurement points A to E are measured.
The operation of simultaneously measuring the position of the wafer 3 in the Z direction at, and exposing the images of the measurement pattern IP on the reticle 2 at these plural measurement points is repeated at the plural positions in the Z direction.
The image forming characteristic of the projection optical system 1 is calculated based on the exposure image. Therefore, it is not necessary to move the XY stage 5 between the operation of measuring the positions of the plurality of measurement points on the wafer 3 in the Z direction and the operation of exposing the pattern of the reticle 2 on those measurement points. The imaging characteristics of the projection optical system 1 can be detected with high accuracy regardless of the accuracy of the running guide surface of the XY stage 5. Further, the focal positions at a plurality of measurement points on the wafer are simultaneously measured by the multipoint focal position detection systems 4a and 4b, and the measurement pattern images are simultaneously exposed to these measurement points. The time is greatly shortened, and the throughput (productivity) is greatly improved accordingly.

The present invention is not limited to the stepper type projection exposure apparatus, and the reticle and the wafer are synchronously scanned while a part of the reticle pattern is projected on the wafer through the projection optical system. The present invention can be similarly applied to a scanning exposure type projection exposure apparatus such as a step-and-scan method for exposing and transferring a pattern to each shot area on a wafer. As described above, the present invention is not limited to the above-described embodiment, and can take various configurations without departing from the gist of the present invention.

[0044]

According to the image formation characteristic evaluation method of the projection optical system of the present invention, the positions of a plurality of measurement points on the photosensitive substrate in the optical axis direction are simultaneously measured, and the image of the evaluation pattern is exposed at the same time. To do. Therefore, it is not necessary to move the photosensitive substrate between the measurement of the position of the measurement point in the optical axis direction and the exposure thereof.
For example, there is no measurement error in the optical axis direction caused by the movement of the photosensitive substrate due to the influence of the flatness of the running guide surface of the stage for positioning the photosensitive substrate (wafer or the like). Therefore, there is an advantage that the imaging characteristics of the projection optical system can be evaluated with high accuracy. Further, since the measurement of a plurality of measurement points is performed simultaneously and the image of the evaluation pattern is exposed to the plurality of measurement points at the same time, there is an advantage that the measurement time is shortened and the throughput is improved.

Further, according to the projection exposure apparatus of the present invention, the method of evaluating the image forming characteristic can be implemented. That is, there is an advantage that the image forming characteristic of the projection optical system can be measured based on the accurate concave and convex information of the photosensitive substrate at the position in the optical axis direction. Further, when a reference member whose surface flatness is known is provided on the height adjustment stage, the focus position detecting means can be accurately calibrated by using this reference member. Is used, there is an advantage that the positions of a plurality of measurement points on the photosensitive substrate in the optical axis direction can be accurately detected.

When the height adjusting stage further adjusts the tilt angle of the photosensitive substrate, the surface of the photosensitive substrate can be accurately aligned with the measured image plane.

[Brief description of drawings]

FIG. 1 is a flowchart showing an example of an embodiment according to the present invention.

FIG. 2 is a perspective view showing a schematic configuration of a projection exposure apparatus used in the embodiment of the present invention.

FIG. 3 is a diagram for explaining a calibration method of the focus position detection system of FIG.

FIG. 4 is a diagram showing a state of a focus position detection system calibrated by the calibration method of FIG.

FIG. 5 is an explanatory diagram showing an operation of measuring the focus positions at a plurality of measurement points by changing the height of the wafer 3 in the embodiment of the present invention.

6 is a plan view showing the arrangement of measurement points in the exposure field IAR of FIG.

FIG. 7 is an enlarged plan view showing the arrangement of the images of the measurement patterns exposed on the wafer 3 in the embodiment of the present invention.

8 is an enlarged plan view of an image of a measurement pattern at one measurement point in FIG.

9 is a diagram showing the relationship between the amount of displacement in the Z direction at one measurement point A in FIG. 6 and the average mark length of the projected measurement pattern image.

10 is a perspective view showing a state of an image plane of a projection optical system, which is obtained based on the method shown in FIG.

FIG. 11 is an explanatory diagram of a conventional method of measuring the position of the image plane of the projection optical system.

FIG. 12 is a plan view showing the measurement points of FIG. 11.

[Explanation of symbols]

1 Projection Optical System AX Optical Axis 2 Reticle IP Measurement Pattern 3 Wafer 4a Light Transmitting Optical System (Focus Position Detection System) 4b Light Reception Optical System (Focus Position Detection System) 5 XY Stage 5X X Stage 5Y Y Stage 6a to 6c Focus / Leveling mechanism 7 Z tilt stage 8 Reference plane plate 9 Main control system IAR Exposure field A to E Measurement points 13A to 13E, 14A to 14E, 15A to 15E Measurement points IP1 to IP3 Exposure image 16X Evaluation pattern (X axis) 16Y evaluation Pattern (Y axis) 17a to 17h Basic mark

Claims (4)

[Claims] 1. A method of evaluating an image forming characteristic of a projection optical system for projecting and exposing an image of a predetermined pattern on a photosensitive substrate, comprising: measuring a plurality of measurement points on the photosensitive substrate in an optical axis direction of the projection optical system. A step of detecting a position and exposing each of a plurality of measurement points on the photosensitive substrate with an image of an evaluation pattern, and an evaluation pattern formed on the photosensitive substrate corresponding to the plurality of measurement points. Based on the information obtained from the image of the pattern and the position of each of the plurality of measurement points in the optical axis direction,
And a step of evaluating an image forming characteristic of the projection optical system. 2. A projection exposure apparatus which projects an image of a transfer pattern on a mask onto a photosensitive substrate through a projection optical system under illumination light for exposure, wherein the photosensitive substrate is connected to the projection optical system. A height adjustment stage that moves in the optical axis direction, a focus position detection unit that detects the position of the projection optical system in the optical axis direction at a plurality of measurement points on the photosensitive substrate, and a focus position detection unit that detects the position. A storage unit that stores the unevenness information of the surface of the photosensitive substrate, and when a predetermined photosensitive substrate is set at a plurality of positions in the optical axis direction of the projection optical system via the height adjustment stage, A projection exposure apparatus, characterized in that the storage means stores the unevenness information of the surface of the predetermined photosensitive substrate detected by the focus position detection means. 3. The projection exposure apparatus according to claim 2, wherein a reference member whose surface flatness is known is provided on the height adjustment stage. 4. The projection exposure apparatus according to claim 2, wherein the height adjustment stage further adjusts an inclination angle of the photosensitive substrate.