JPH08335548A - Exposing apparatus, exposing condition determining method and aberration measuring method - Google Patents

Abstract

PURPOSE: To measure the optimum exposing condition and aberration of projecting optical system, in higher accuracy and higher speed, corresponding to a kind of photoresist in the exposing apparatus without using expensive apparatus. CONSTITUTION: A first process to form a plurality of photosensitive images of pattern by continuing a plurality of times of exposure and transfer of the predetermined pattern under the different exposing conditions onto a photosensitive substrate W, a second process 105 to picks up a plurality of photosensitive images and then converting it into electrical signal, a third process 108 to obtain the information about the shape of photosensitive images based on such signal and a fourth process 109 to determine the optimum exposing condition based on the information obtained in above process.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exposure apparatus used in a lithography process or the like for manufacturing an LSI or the like, and a method for measuring the exposure condition or the aberration of a projection optical system thereof.

[0002]

2. Description of the Related Art In recent years, in this type of exposure apparatus, the degree of integration of circuit patterns has increased, and the line width of the pattern to be transferred has become on the order of submicron, so that the resolution of the projection lens can be stably maintained. Therefore, it is becoming important to accurately set the exposure amount and the focus.

Conventionally, an image of a pattern (hereinafter referred to as an L / S pattern) composed of a plurality of linear patterns arranged at regular intervals is used for each shot as exposure conditions, that is, a focus position and an exposure amount (shutter time). After printing on the photosensitive substrate while changing at least one of the above, the optimal exposure condition is determined by developing the photosensitive substrate and measuring the line width of each line of the L / S pattern image with an optical microscope or line width measuring device. are doing.

For example, in a step-and-repeat exposure apparatus, exposure is performed by changing the exposure amount (shutter time) by a constant amount while keeping the focus value constant in the lateral direction of the shot area arrangement on the wafer. In the vertical direction of the shot array, the exposure amount is kept constant and the focus value is changed by a constant amount. After development, the line width of each line of the L / S pattern image in each formed shot is detected by an SEM (scanning electron microscope), and the optimum focus position and the optimum exposure amount of the projection lens are calculated.

[0005]

However, in the prior art, the line width of each line of the L / S pattern image is S
The processing speed is extremely slow because it is measured by EM, etc.
There is a problem that the device price is also extremely expensive.

In view of the problems of the prior art as described above, an object of the present invention is to provide an exposure apparatus with optimum exposure conditions and projection optical system that correspond to the type of photoresist with high accuracy and high speed without using an expensive apparatus. Is to be able to measure the aberration.

[0007]

To achieve this object, the present invention forms a plurality of photosensitive images of a predetermined pattern by exposing and transferring a predetermined pattern on a photosensitive substrate a plurality of times under different exposure conditions. Of the photosensitive image is converted into an electric signal, information on the shape of the photosensitive image is obtained based on this signal, and the optimum exposure condition is determined based on the obtained information. Alternatively, a predetermined pattern is exposed and transferred onto a photosensitive substrate via a projection optical system to form a photosensitive image, the photosensitive image is picked up and converted into an electric signal, and the shape of the photosensitive image is related based on this signal. Information is obtained, and the aberration of the projection optical system is obtained based on the obtained information.

Here, the predetermined pattern is preferably a pattern portion in which pattern portions are periodically arranged, for example, an L / S pattern having a duty factor of 1: 1. The information on the shape of the photosensitive image is, for example, based on the electric signal, the signal level of the image of each pattern portion is integrated in the direction perpendicular to the certain direction, and a predetermined threshold value is applied to this. The edge or width and position of each detected pattern portion. The exposure conditions include, for example, the position of the photosensitive substrate in the optical axis direction of the projection optical system and the exposure amount. Further, when astigmatism is obtained as the aberration of the projection optical system, one having two kinds of patterns periodically arranged in mutually different directions is used as the pattern, and the exposure condition is set to the light of the projection optical system. The photosensitive substrate position in the axial direction is set, and each pattern is arranged at the same position with respect to the projection optical system to obtain the optimum exposure condition for each pattern, that is, the image plane position (focus position). Further, when obtaining the image plane curvature and image plane inclination of the projection optical system, the patterns are arranged at different positions with respect to the projection optical system, and the image plane position is obtained for each position.

[0009]

In this structure, for example, the duty is 1: 1.
When the L / S pattern of 1 is transferred, the duty of the photosensitive image at the focus position and the optimum exposure amount that optimize the position of the photosensitive substrate and the exposure amount as the exposure conditions is also 1: 1.

Therefore, by using a mask on which a pattern for measuring exposure conditions having periodicity in one direction, such as an L / S pattern, is formed, the condition of at least one of the exposure amount and the position of the photosensitive substrate is changed and Then, the duty of the pattern image exposed and transferred is detected, and the duty is compared with the optimum duty of 1: 1 to obtain the focus position of the projection optical system and the optimum exposure amount with high accuracy and high speed.

[0011]

EXAMPLE This example will be described below with reference to the drawings. FIG.
FIG. 3 is a diagram showing a configuration of an exposure condition measuring apparatus according to an embodiment of the present invention.

In the figure, 101 is a reduction projection lens for projecting a circuit pattern on the reticle R surface onto a wafer W. The optical axis is indicated by AX in the figure, and the optical axis AX
Are parallel to the Z direction. Reference numeral 100 denotes a wafer stage that attracts a wafer and moves in the X, Y and Z directions.
Reference numeral 03 is an illumination system, 102 is a semi-transparent mirror that reflects a part of the exposure light from the illumination system 103, 104 is a detection optical system that detects the light reflected by the semi-transparent mirror 103, and 105 is an ITV or a photoelectric converter such as a two-dimensional image sensor. A conversion device is an imaging device that converts a captured image into a two-dimensional electric signal, and a two-dimensional device 106 is a sampling pitch λs determined by the optical magnification of the projection optical system 101 and the detection optical system 104 and the pixel pitch of the imaging surface. An A / D converter for converting into a two-dimensional discrete electric signal sequence corresponding to the XY address of the upper pixel, 1
Reference numeral 07 is a projection integration device, 108 is a pattern detection device, 10
Reference numeral 9 is a control device.

The exposure apparatus also includes a focus position control device and an exposure amount control device. FIG. 2 is a diagram showing a partial configuration of the focus position control device and the exposure amount control device. First, focus position control will be described. 203 is a high-intensity light source such as a semiconductor laser, 2
Reference numeral 04 denotes an illumination optical system that illuminates the wafer W with light from the light source 203, and 205 denotes light from the illumination optical system 204.
A bending mirror that reflects upward, 206 is a bending mirror that changes the direction of light reflected on the wafer W, 207 is a position detection optical system that detects the position of the wafer W, and 208 is C.
A two-dimensional position detecting element including a CD camera or the like for detecting the incident position, and 210 is a focus control device for controlling the focus position of the wafer W. The light emitted from the light source 203 passes through the pinhole from the illumination optical system 204, the direction of the light flux is changed by the mirror 205, and the light is incident on the surface of the wafer. The light flux reflected at the measurement point of the wafer is mirror 206
The direction is changed by and the light enters the two-dimensional position detecting element 208 via the position detecting optical system 207. A change in the position of the projection lens 101 on the wafer in the optical axis AX direction can be detected as a deviation of the incident position on the two-dimensional position detecting element 208. Therefore, the position in the optical axis AX direction is an output signal from the two-dimensional position detecting element 208. And controls the position of the wafer stage.

Next, the exposure amount control will be described. 21
Reference numeral 5 is a light source such as a mercury lamp which emits exposure light, 212 is a semi-transparent mirror 213 which reflects a part of the exposure light from the light source 215.
Is a sensor for detecting the illuminance of the exposure light reflected thereby, 214 is a shutter arranged on the optical path of the exposure light from the light source 215, and 209 is integrated exposure control for controlling the opening and closing of the shutter 214 based on the output of the sensor 213. It is a device. The integrated exposure control device 209 adjusts the exposure amount to be constant based on the illuminance of the exposure light detected by the sensor 213.
The opening / closing time of the shutter 214 is controlled.

Mx and My in FIG. 4 represent L / S patterns, which are rectangular patterns having the same line width and formed of chromium extending in the X and Y directions, respectively, and arranged in parallel. The reticle on which the L / S patterns Mx and My are formed is set in an exposure device, a wafer coated with a positive type resist is set, and the pattern is stepped.
Exposure is performed sequentially by the and repeat method. At this time, by using the focus position control device and the exposure amount control device described above, the exposure amount is changed and set according to the shot position in the X direction, and the focus offset is changed by a constant amount for the shot in the Y direction. Expose.

FIG. 3 is a sectional view of a resist pattern after development on the wafer thus exposed. In the figure, (A)-
(C) is when the exposure amount is changed at the best focus position,
(D) to (F) show the case where the exposure amount is changed at the defocused position.

Next, the developed wafer is placed on the wafer stage 1
No. 00, the illumination system 103 illuminates the pattern on the wafer, and captures the image of the pattern at a predetermined magnification.
An image is formed on the image pickup surface of 05.

The pattern image converted into a two-dimensional electric signal by the image pickup device 105 (CCD camera) is converted by the A / D converter 106 into the optical magnification of the projection optical system 101 and the detection optical system 104 and the pixel pitch of the image pickup surface. Is converted into a two-dimensional discrete electric signal sequence corresponding to the addresses in the XY directions of the pixels on the two-dimensional device by the sampling pitch λs determined by After setting a predetermined two-dimensional window including the pattern Mx shown in FIG. 5, the projection integration device 107 performs pixel integration in the window Wx in the Y direction shown in FIG. 5, and in the X direction shown in FIG. It outputs a discrete electric signal sequence (projection integrated signal). Pattern detection device 108
Is a ratio of the width and interval of each line of the resist pattern by setting an appropriate slice level L for the inputted electric signal sequence s (x) and detecting the edge of the resist pattern as shown in FIG. Wl / Ws is calculated and the result is output to the control device 109.

6 (a) to 6 (c) exemplify projection integrated signals obtained by imaging a pattern when exposed by changing the focus with a CCD camera. In the case of the optimum focus position shown in FIG. 7A, if the duty of the L / S pattern formed on the reticle is 1: 1, Wl / Ws is also closest to 1 in the resist pattern. As shown in FIG. 7, in the defocus state, Ws is larger than Wl, so Wl / Ws is small, and is maximum at the optimum focus position. Therefore, the control device 109 calculates the maximum focus position from the Wl / Ws corresponding to each focus position by, for example, the least square method, and outputs the optimum focus position.

FIG. 8 shows a projection integration signal obtained by capturing an image of a pattern with a CCD camera when exposure is performed while changing the exposure amount. Generally, regarding the optimum exposure amount, the exposure amount at which a resist image is formed with the same duty as the duty of the L / S pattern formed on the reticle is appropriate. Therefore, the duty of the L / S pattern formed on the reticle is 1:
In the case of 1, the resist pattern ratio Wl / Ws is 1: 1.
The closest exposure state, in other words, the exposure amount at which Wl / Ws becomes 1 can be defined as the optimum exposure amount. then,
As shown in FIG. 9, the control device 109 calculates the exposure amount corresponding to each exposure amount when the value of Wl / Ws is 1, for example, by the least square method, and outputs it as the optimum exposure amount.

The calculated focus value is fed back to the focus control device 210 in FIG. 2 so that the wafer can always be set at the best focus position. The exposure amount can also be set to the optimum exposure amount by feeding back to the integrated exposure control device 209 in FIG.

The optimum focus position and the optimum exposure amount are calculated as described above, and the optimum exposure condition is always calculated by repeating the above processing according to the change of the resist type and the film thickness.

Although the resist pattern after development is detected in the above processing, the optimum focus position and the optimum exposure amount can be determined by detecting the latent image before development. If the latent image is detected, the developing process can be omitted, so that the exposure conditions can be automatically measured on the projection exposure apparatus, and the setup time can be greatly shortened.

The L / S pattern shown in FIG.
Since they are arranged in the X-direction and the Y-direction, the astigmatism of the projection optical system can be measured by detecting the optimum focus positions in the X-direction and the Y-direction at the same position. At that time, the projection integrating device 107 sets a predetermined two-dimensional window Wy including the pattern My shown in FIG. 5, and then X shown in FIG.
Pixels are integrated in the window Wy in the Y direction, and a discrete electric signal sequence s (y) is output in the Y direction. Then, as in the X direction, Wl / W of each resist image is calculated from the signal of s (y).
The optimum focus position and the optimum exposure amount in the Y direction can be measured by calculating the ratio of s and calculating the relationships shown in FIGS. 7 and 9. In this way, by detecting the optimum focus positions of the patterns whose directions are different from each other, it is possible to measure the actual astigmatism when passing through the resist process of the projection lens.

Further, the actual curvature of field and the inclination of the field can be detected by performing the measurement by the L / S pattern at a plurality of positions of the center and the outer peripheral position in the exposure area. However, it is desirable that the number of lines in the L / S pattern is large in terms of accuracy improvement, and it goes without saying that the detection accuracy of the ratio Wl / Ws can be improved by averaging the measured values. When detecting the aberration of the projection lens in this way, it is not necessary to use a resist that actually exposes the circuit pattern, and any material can be used as long as it is a photosensitive material. For example, a magneto-optical material or a photochromic material may be used.

In the present embodiment, the reduction projection lens or the exposure device was used both when the L / S pattern image was exposed on the wafer and when the resist pattern was detected. The observation optical system may be used. Thereby, the influence of the aberration of the projection lens itself on the measurement result can be reduced.

Further, in this embodiment, the exposure condition when the projection optical system is used is obtained, but the present invention can be applied to a promity type exposure apparatus which does not use the projection optical system. . At that time, the distance between the mask and the wafer is changed instead of the focus position.

[0028]

As described above, according to the present invention,
An optimum exposure condition is determined by exposing and transferring a pattern to be exposed, for example, a pattern formed by a light-shielding portion or a light-transmitting portion and having a periodicity in a constant direction, and detecting information on the shape of this pattern image, for example, a duty factor. Therefore, the optimum exposure condition corresponding to the photosensitive substrate can be obtained with high accuracy and in a short time. In addition, by setting the exposure condition as the position of the photosensitive substrate and the optimum exposure condition as the focus position, the patterns are arranged at various positions with respect to the projection optical system to obtain the focus positions, or the focus is adjusted by using patterns having different periodicity. By obtaining the position, it is possible to easily obtain the aberration of the projection optical system, for example, the field curvature, the field tilt, or the astigmatism.

[Brief description of drawings]

FIG. 1 is a diagram showing an exposure condition measuring apparatus in an exposure apparatus according to an embodiment of the present invention.

2 is a diagram showing a partial configuration of focus detection and exposure amount control of the exposure apparatus of FIG.

3 is a cross-sectional view of a pattern formed on a resist in the exposure apparatus of FIG.

4 is a diagram showing a pattern formed on a mask which is a measurement target of the exposure condition measuring method in the exposure apparatus of FIG.

5 is a diagram showing a relationship between a pattern formed on a wafer and a two-dimensional window in the exposure apparatus of FIG.

FIG. 6 is a diagram showing an example of a projection integrated signal obtained by capturing an image of a pattern when exposed by changing the focus in the exposure apparatus of FIG.

7 is a diagram plotting the L / S ratio of a resist image corresponding to each focus position in the exposure apparatus of FIG.

FIG. 8 is a diagram illustrating an example of a projection integrated signal obtained by capturing an image of a resist pattern with a CCD camera when exposure is performed by changing the exposure amount in the exposure apparatus of FIG.

9 is a diagram in which the L / S ratio of the resist image corresponding to each exposure amount in the exposure apparatus of FIG. 1 is plotted.

[Explanation of symbols]

100: Wafer stage, 101: Reduction projection lens, 1
02: Half mirror, 103: Illumination system, 104: Detection optical system, 105: Imaging device, 106: A / D conversion device, 1
07: Projection integrating device, 108: Pattern detecting device, 10
9: control device, 203: high-brightness light source, 204: illumination optical system, 205, 206: bending mirror, 207: detection optical system, 208: two-dimensional position detection element, 209: integrated exposure control device, 210: focus control device 213: sensor, 214: shutter, 215: light source.

Claims (17)

[Claims] 1. A first step of exposing and transferring a predetermined pattern onto a photosensitive substrate a plurality of times under different exposure conditions to form a plurality of photosensitive images of the pattern, and capturing the plurality of photosensitive images into an electric signal. A second step of converting, a third step of obtaining information on the shape of the photosensitive image based on the signal, and a fourth step of determining an optimum exposure condition based on the obtained information. A method for determining a characteristic exposure condition. 2. A first step of forming a photosensitive image by exposing and transferring a predetermined pattern on a photosensitive substrate through a projection optical system,
A second step of capturing the photosensitive image and converting it into an electrical signal;
An aberration measuring method comprising: a third step of obtaining information on the shape of the photosensitive image based on this signal; and a fourth step of obtaining an aberration of the projection optical system based on the obtained information. . 3. The method according to claim 1, wherein the photosensitive substrate is a photoresist-coated wafer. 4. The method according to claim 3, wherein the imaged photosensitive image is formed by a photoresist obtained by developing the photosensitive image formed by the exposure transfer. 5. The method of claim 3, wherein the photosensitive image is a latent image. 6. The method according to claim 1, wherein the pattern has a periodicity in a certain direction. 7. The method according to claim 1, wherein the exposure condition is an exposure amount. 8. The method according to claim 2, wherein the pattern is formed at a plurality of positions on the original plate. 9. In the first step, a plurality of photosensitive images of the pattern are formed while sequentially positioning the photosensitive substrate at a plurality of different positions in the optical axis direction of the projection optical system. 2. The method described in 2. 10. The method according to claim 9, wherein the pattern has a periodicity. 11. The method according to claim 10, wherein the exposure condition is an image plane position of the projection optical system. 12. The pattern is one in which predetermined pattern portions are periodically arranged in a fixed direction, and in the third step, the signal level of the image of each pattern portion is fixed based on the electric signal. The method according to claim 1 or 2, wherein the integration is performed in a direction perpendicular to the direction, and a predetermined threshold value is applied to the integrated value to detect the edge or width and the position of each pattern portion. 13. An exposure apparatus for exposing and transferring a pattern on an original onto a photosensitive substrate, an original having a test pattern for setting exposure conditions in which predetermined pattern portions are periodically arranged in a certain direction, and an image of this test pattern , A test pattern transfer means for sequentially exposing and transferring to different positions on the substrate while sequentially changing a predetermined exposure condition, and capturing an image of the test pattern exposed and transferred on the photosensitive substrate and converting it into an electric signal Image pickup means, pattern detection means for detecting the position and width of the edge or the pattern portion in the constant direction of the test pattern image based on this signal, and means for obtaining the optimum exposure condition based on the detection result. An exposure apparatus characterized by: 14. An exposure apparatus according to claim 13, further comprising a projection optical system, wherein the transfer of the test pattern and the image capturing thereof are performed via the projection optical system. 15. The pattern detecting means integrates the signal level of the image of each pattern portion in a direction perpendicular to the certain direction based on the electric signal, and applies a predetermined threshold value to this to add each pattern portion. 15. An edge or a width and a position of the edge are detected.
The exposure apparatus described. 16. The test pattern has two kinds of test patterns periodically arranged in mutually different directions, and the exposure condition is a position of the substrate in an optical axis direction of the projection optical system, The exposure apparatus according to claim 14 or 15, wherein the optimum exposure conditions are obtained at the same position with respect to the projection optical system for each test pattern. 17. The exposure condition is a position of the substrate in the optical axis direction of the projection optical system, and the optimum exposure condition is obtained at different positions for the test pattern with respect to the projection optical system. Item 16. The exposure apparatus according to item 14 or 15.