KR20040089814A - Focus monitoring system in wafer stepper - Google Patents

Abstract

PURPOSE: A focus monitoring system of wafer exposure equipment is provided to monitor a best focus by using a wafer stage mark and a reticle reference mark. CONSTITUTION: A light source is used for irradiating light of predetermined wavelength. A reticle(22) is installed at a lower part of the light source and includes a reticle reference mark having a shielding pattern and a transmitting pattern. A lens part(23) is used for focusing and reducing the light transmitting the reticle reference mark. A wafer stage(24) is installed at a lower part of the lens part and includes a wafer stage mark having four transparent patterns. A CCD camera(21) is installed at an upper part of the reticle in order to detect an overlapping state between pattern images of the wafer stage mark and a pattern image of the reticle reference mark.

Description

Focus monitoring system in wafer exposure equipment {Focus monitoring system in wafer stepper}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wafer exposure apparatus used in a manufacturing process of a semiconductor device, and more particularly, to a focus of a wafer exposure apparatus capable of maintaining a constant focus between a reticle and a wafer stage. A focus monitoring system.

In order to form a manufacturing pattern of a desired semiconductor product on a semiconductor wafer, an exposure process is performed several times during the manufacturing process of a semiconductor device. Prior to performing the exposure process, a focus must be focused between the reticle and the wafer stage on which the wafer is seated. .

1 to 4 are diagrams for explaining a focus monitoring system of a wafer exposure apparatus according to the prior art, Figure 1 is a block diagram of a focus monitoring system of a conventional wafer exposure equipment, Figure 2 is a view of the reticle shown in FIG. 3 is a plan view of the wafer stage shown in FIG. 1, and FIG. 4 is an enlarged view of the wafer stage mark shown in FIG. Referring to these drawings, a focus monitoring system of a conventional wafer exposure apparatus will be described.

The focus monitoring system of a conventional wafer exposure apparatus includes a light source unit (not shown) for injecting light of a predetermined wavelength, a reticle 12 having a chip region defined at the center, and a lens unit for accumulating and reducing light incident from the light source unit ( 13), the wafer stage mark 140 is formed on the upper surface while being driven up, down, left, and right, and during exposure, the wafer stage mark 140 is positioned on the upper surface of the reticle 12 and the wafer stage 14 on which the wafer is seated. And a CCD camera 11 for detecting the reflected image.

As shown in FIG. 4, the wafer stage mark 140 is formed by alternately arranging a plurality of opaque patterns 141 and a plurality of transparent patterns 142. The wafer stage mark 140 may be manufactured in various shapes and sizes by using a combination of the opaque pattern 141 and the transparent pattern 142. However, the general shape of the wafer stage mark 140 may include the vertical shape of the opaque pattern 141 and the transparent pattern 142. A horizontal grid group consisting of a grid group and a horizontal grid is joined to each other. The width of the opaque pattern 141 is formed to be 1 μm or more, and the transparent pattern 142, which is a gap portion between the opaque patterns 141, also has the same width as that of the opaque pattern 141.

The focus monitoring of the conventional wafer exposure equipment detects an image of the wafer stage mark 140 on which the incident light is reflected by the wafer stage mark 140 and is projected by the CD camera 11, and provides the best focus. Focus detection method is to drive the wafer stage 14 up, down, left, and right while setting the best contrast to the point where the contrast of the image of the wafer stage mark 140 formed on the CD camera 11 is maximized. do. However, in this best focus detection method, since the size of the pattern 141 and / or 142 of the wafer stage mark 140 is larger than 1 μm, the change in image contrast due to the focus change is not so severe. There is a problem in reproducibility and accuracy because the method is to measure the image contrast by specifying a wide driving range in the up, down, left and right directions and then find the point where the image contrast is maximized. For this reason, the focus monitoring system of the conventional wafer exposure equipment is not suitable in the present situation where the best focus stability of the exposure equipment is required.

Accordingly, an object of the present invention is to provide a focus monitoring system for wafer exposure equipment that can accurately monitor the best focus between the reticle and the wafer stage, as well as improve reproducibility.

1 to 4 are diagrams for explaining a focus monitoring system of a wafer exposure apparatus according to the prior art.

5 to 11 are views for explaining a focus monitoring system of the wafer exposure equipment according to the first embodiment of the present invention.

12 to 18 are diagrams for describing a focus monitoring system of a wafer exposure apparatus according to a second embodiment of the present invention.

<Explanation of symbols for the main parts of the drawings>

11, 21, 31: CD camera 12, 22, 32: Reticle

13, 23, 33: lens 14, 24, 34: wafer stage

220, 320: Reticle reference marks 221, 321: Light shielding pattern

222, 322: Transmissive patterns 140, 240, 340: wafer stage marks

141, 241, 341: opaque pattern 142, 242, 342: transparent pattern

221I, 321I: shading pattern image 241I, 341I: opacity pattern image

242a and 342a: first phase shift transparent pattern

242b and 342b: second phase shift transparent pattern

242c and 342c: third phase shift transparent pattern

242d and 342d: fourth phase shift transparent pattern

The focus monitoring system of the wafer exposure apparatus according to the embodiment of the present invention for achieving the above object is located in the light source unit for injecting light of a predetermined wavelength, the light source unit is located, the light shielding pattern and the light transmission pattern are alternately arranged A reticle having a formed reticle reference mark, a lens unit for accumulating and reducing light incident from the light source unit and passing through the reticle reference mark, and positioned at a lower side of the lens unit to be driven up, down, left and right, and having an opaque pattern therebetween with a phase of 80 A wafer stage mark having a wafer stage mark formed of a structure in which 4 transparent patterns having a difference of 100 to 100 degrees are formed, and a pattern image of a wafer stage mark and a pattern image of a reticle reference mark overlapping the upper surface of the reticle It consists of a CD camera.

In the above, the light shielding pattern of the reticle reference mark is formed such that its size and shape correspond to the opaque pattern of the wafer stage mark, and the light transmission pattern of the reticle reference mark is formed so that its size and shape correspond to the transparent pattern of the wafer stage mark. It is characterized by.

In the above, the opaque pattern of the wafer stage mark is formed in a width of 0.2 to 1㎛, the transparent pattern of the wafer stage mark is characterized in that it is formed with a width of three times or the same width with respect to a predetermined width of the opaque pattern. .

In the above, the wafer stage mark includes a first phase shift transparent pattern having a phase of about 0 degrees, a second phase shift transparent pattern having a phase of about 90 degrees, a third phase shift transparent pattern having a phase of about 180 degrees, and a phase with an opaque pattern interposed therebetween. The fourth phase shift transparent pattern of about 270 degrees, and the first phase shift transparent pattern having a phase of about 0 degrees, are characterized in that the phase is repeated in order of being arranged.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but will be implemented in various different forms, only this embodiment to make the disclosure of the present invention complete, and to those skilled in the art the scope of the invention It is provided for complete information.

5 to 11 are views for explaining a focus monitoring system of the wafer exposure equipment according to the first embodiment of the present invention, Figure 5 is a configuration of the focus monitoring system of the wafer exposure equipment according to the first embodiment of the present invention FIG. 6 is a plan view of the reticle shown in FIG. 5, FIG. 7 is a plan view of the wafer stage shown in FIG. 5, FIG. 8 is an enlarged view of a portion of the reticle reference mark shown in FIG. 6, and FIG. 9 is 7 is an enlarged view of a portion of the wafer stage mark illustrated in FIG. 7, and FIG. 10 is a view in which the pattern image of the reticle reference mark of FIG. 8 and the pattern image of the wafer stage mark of FIG. 9 overlap each other. Referring to these drawings, a focus monitoring system of a wafer exposure apparatus according to a first embodiment of the present invention will be described.

In the focus monitoring system of the wafer exposure apparatus according to the first embodiment of the present invention, a light source unit (not shown) for injecting light of a predetermined wavelength, a chip region is defined at a central portion thereof, and a plurality of reticle reference marks 220 are defined at an edge thereof. Is formed on the reticle 22 and the lens unit 23 that accumulates and reduces the light incident from the light source unit and passes through the reticle reference mark 220 of the reticle 22, and is positioned above and below the lens unit 23. A plurality of wafer stage marks 240 are formed on the upper surface while being driven left and right, and upon exposure, the wafer stage 24 and the reticle 22 are positioned on the wafer stage 24 and the pattern image of the wafer stage marks 240. And a CD camera 21 for detecting that the pattern image of the reticle reference mark 220 is overlapped.

Two wafer stage marks 240 may be formed in two directions, left and right, and symmetrically, or four as shown in FIG. 7, and a plurality of opaque patterns 241 and a plurality of transparent patterns 242, as shown in FIG. 9. The alternating arrangement of the four transparent patterns 242a, 242b, 242c, and 242d having a phase difference of 80 to 100 degrees with an opaque pattern 241 therebetween is repeated. . That is, the wafer stage mark 240 has a first phase shift transparent pattern 242a having a phase of about 0 degrees with an opaque pattern 241 therebetween, and a second phase shift transparent pattern having a phase of about 90 degrees. 242b, the third phase shift transparent pattern 242c having a phase of about 180 degrees, the fourth phase shift transparent pattern 242d having a phase of about 270 degrees, and the first phase shift transparent pattern 242a having a phase of about 0 degrees again. It consists of a structure in which the phases are repeated in the order of arrangement. The wafer stage mark 240 may be manufactured in various shapes and sizes as well as vertical and horizontal lattice shapes by a combination of the opaque pattern 241 and the transparent pattern 242. The width of the opaque pattern 241 is 0.2 to 1 μm, and the width of the transparent pattern 242, which is a gap between the opaque patterns 241, is three times the width of the opaque pattern 241. do. The reason why the phase difference between the transparent patterns 242a, 242b, 242c, and 242d is about 90 degrees is because the movement of the pattern due to defocus is greatest when the phase difference is 90 degrees. On the other hand, the smaller the width of the opaque pattern 241, the greater the degree of movement of the pattern due to defocus, and the larger the number of the opaque patterns 241 is averaged, the higher the reproducibility of the measurement is. Therefore, it is desirable to make the width of the opaque pattern 241 as narrow as possible and the number as large as possible.

In the above, the first to fourth phase shift transparent patterns 242a, 242b, 242c, and 242d sequentially formed with the opaque pattern 241 interposed therebetween are transparent portions 242a and 242b of the wafer stage mark 240. , 242c and 242d may have different thicknesses of materials through which light can pass, so that the phase difference may occur, or light may pass through each of the transparent portions 242a, 242b, 242c and 242d of the wafer stage mark 240. The different phases may be formed by forming different kinds of materials, or the different heights of the opaque portions 241 of the wafer stage mark 240 may be formed.

Two reticle reference marks 220 are formed in two, or left and right, up and down symmetrically or four as shown in FIG. 6, as shown in FIG. 8, a plurality of light blocking patterns 221 and a plurality of light transmitting patterns 222. This is done alternately. The reticle reference mark 220 may be manufactured in various shapes and sizes as well as vertical and horizontal lattice shapes by combining the light blocking pattern 221 and the light transmitting pattern 222.

The reticle reference mark 220 is formed to correspond to the wafer stage mark 240. Specifically, the light shielding pattern 221 of the reticle reference mark 220 is formed such that its size and shape correspond to the opaque pattern 241 of the wafer stage mark 240, and the light transmission pattern 222 of the reticle reference mark 220 is formed. ) Is formed such that its size and shape correspond to the transparent pattern 242 of the wafer stage mark 240. Meanwhile, the size of the reticle reference mark 220 is determined not only according to the size of the wafer stage mark 240, but also in consideration of the magnification of the exposure equipment. For example, when using an exposure apparatus 4 times smaller like a scanner and the width of the opaque pattern 241 is 0.2 μm, the light shielding pattern 221 is formed to have a width of 0.8 μm. That is, the reticle reference mark 220 and the wafer stage mark 240 may be similar.

In the focus monitoring of the wafer exposure apparatus according to the first embodiment of the present invention, the light incident from the light source unit is reflected on the wafer stage mark 240 to be projected onto the reticle reference mark 220 to shield the light as shown in FIG. 10. The pattern image 221I and the opaque pattern image 241I overlap each other, and the overlapped pattern images 221I and 241I are detected by the CD camera 21. Since the position of the wafer stage mark 240 changes according to defocus, the focus of the exposure apparatus is monitored by measuring the degree of movement of the wafer stage mark 240 relative to the reticle reference mark 220. The pattern images 221I and 241I detected by the CD camera 21 obtain a waveform shown in FIG. 11 through a signal processing process. FIG. 11 is an example of measuring a degree of movement when a wafer stage mark is moved relative to a reticle reference mark according to defocus. FIG. 11 (a) is a signal waveform when it is in best focus, and FIG. 11 (b). Is a signal waveform in the case of plus defocus, and FIG. 11C is a signal waveform in the case of minus defocus. By monitoring the best focus of the exposure equipment in this way, the accuracy and reproducibility of the focus monitoring can be increased and the best focus can be monitored regardless of the exposure conditions.

12 to 18 are views for explaining a focus monitoring system of the wafer exposure equipment according to a second embodiment of the present invention, Figure 12 is a configuration of the focus monitoring system of the wafer exposure equipment according to a second embodiment of the present invention FIG. 13 is a plan view of the reticle shown in FIG. 12, FIG. 14 is a plan view of the wafer stage shown in FIG. 12, FIG. 15 is an enlarged view of a portion of the reticle reference mark shown in FIG. 13, and FIG. A partial enlarged view of the wafer stage mark shown in FIG. 14, and FIG. 17 is a view in which the pattern image of the reticle reference mark of FIG. 15 and the pattern image of the wafer stage mark of FIG. 16 overlap each other. Referring to these drawings, a focus monitoring system of a wafer exposure apparatus according to a second embodiment of the present invention will be described.

In the focus monitoring system of the wafer exposure apparatus according to the second embodiment of the present invention, a light source unit (not shown) for injecting light of a predetermined wavelength, a chip region is defined at a central portion thereof, and a plurality of reticle reference marks 320 are formed at an edge thereof. Is formed on the reticle 32, the lens unit 33 for accumulating and reducing light incident from the light source unit and passing through the reticle reference mark 320, and is positioned on the lower side of the lens unit 33 and is driven up, down, left, and right. A plurality of wafer stage marks 340 are formed on the wafer stage 34, and upon exposure, the wafer stage 34 and the reticle 32 are positioned on the upper side of the reticle 32. CDD camera (CCD camera) 31 for detecting that the pattern image of the superimposed ().

Two wafer stage marks 340 are formed in two directions, left and right symmetrically, or four as shown in FIG. 14, and a plurality of opaque patterns 341 and a plurality of transparent patterns 342 are illustrated in FIG. 16. The alternating arrangement of the four transparent patterns 342a, 342b, 342c, and 342d having a phase difference of 80 to 100 degrees with an opaque pattern 341 therebetween is repeated. . That is, the wafer stage mark 340 has a first phase shift transparent pattern 342a having a phase of about 0 degrees with an opaque pattern 341 therebetween, and a second phase shift transparent pattern having a phase of about 90 degrees. 342b, a third phase shift transparent pattern 342c having a phase of about 180 degrees, a fourth phase shift transparent pattern 342d having a phase of about 270 degrees, and a first phase shift transparent pattern 342a having a phase of about 0 degrees again. It consists of a structure in which the phases are repeated in the order of arrangement. The wafer stage mark 340 may be manufactured in various shapes and sizes as well as vertical and horizontal lattice shapes by a combination of the opaque pattern 341 and the transparent pattern 342. The width of the opaque pattern 341 is 0.2 to 1 μm, and the width of the transparent pattern 342, which is a gap portion between the opaque patterns 341, is formed to be the same width as that of the opaque pattern 241. The reason why the phase difference between the transparent patterns 242a, 242b, 242c, and 242d is about 90 degrees is because the movement of the pattern due to defocus is greatest when the phase difference is 90 degrees. On the other hand, the smaller the width of the opaque pattern 241, the greater the degree of movement of the pattern due to defocus, and the larger the number of the opaque patterns 241 is averaged, the higher the reproducibility of the measurement is. Therefore, it is desirable to make the width of the opaque pattern 241 as narrow as possible and the number as large as possible.

In the above, the first to fourth phase shift transparent patterns 342a, 342b, 342c, and 342d sequentially formed with the opaque pattern 341 interposed therebetween are transparent portions 342a and 342b of the wafer stage mark 340. , 342c and 342d may have different thicknesses of materials through which light can pass, so that the phase difference may occur, or light may pass through each of the transparent portions 342a, 342b, 342c, and 342d of the wafer stage mark 340. Different phases may be formed by forming different kinds of materials, or different phases may be formed by forming different heights of the opaque portions 341 of the wafer stage mark 340.

Two reticle reference marks 320 are formed in two, or left and right, up and down symmetrically, or four as shown in FIG. 13, and a plurality of light blocking patterns 321 and a plurality of light transmitting patterns 322 as shown in FIG. 15. This is done alternately. The reticle reference mark 320 may be manufactured in various shapes and sizes as well as vertical and horizontal lattice shapes by combining the light blocking pattern 321 and the light transmitting pattern 322.

The reticle reference mark 320 is formed to correspond to the wafer stage mark 340. Specifically, the light shielding pattern 321 of the reticle reference mark 320 is formed such that its size and shape correspond to the opaque pattern 341 of the wafer stage mark 340, and the light transmission pattern 322 of the reticle reference mark 320 is included. ) Is formed such that its size and shape correspond to the transparent pattern 342 of the wafer stage mark 340. Meanwhile, the size of the reticle reference mark 320 is determined not only according to the size of the wafer stage mark 340, but also in consideration of the magnification of the exposure equipment. For example, when using an exposure apparatus 4 times smaller like a scanner and the width of the opaque pattern 341 is 0.2 μm, the light shielding pattern 321 is formed to have a width of 0.8 μm. That is, the reticle reference mark 320 and the wafer stage mark 340 may be similar.

In the focus monitoring of the wafer exposure apparatus according to the second embodiment of the present invention, the light incident from the light source unit is reflected on the wafer stage mark 340 and is projected onto the reticle reference mark 320 to block light as shown in FIG. 17. The pattern image 321I and the opaque pattern image 341I overlap, and the overlapped pattern images 321I and 241I are detected by the CD camera 21. Since the position of the wafer stage mark 340 changes according to defocus, the degree of movement of the wafer stage mark 340 relative to the reticle reference mark 320 is measured to monitor the focus of the exposure apparatus. The pattern images 321I and 341I detected by the CD camera 31 obtain a waveform shown in FIG. 18 through a signal processing process. FIG. 18 is an example of measuring the degree of movement when the wafer stage mark is moved relative to the reticle reference mark according to the defocus. As can be seen from the signal waveform shown in FIG. 11, the intensity of light detected when the best focus is detected is shown in FIG. It will be the least and the greater the defocus, the more the intensity of the detected light will increase. In this way, monitoring the best focus of the exposure equipment can increase the accuracy and reproducibility of the best focus monitoring because the signal change due to the defocus is large, and the best focus can be monitored regardless of the exposure conditions.

As described above, the present invention corresponds to a wafer stage mark composed of a structure in which four transparent patterns having a phase difference of 80 to 100 degrees with an opaque pattern interposed therebetween, and a light shielding pattern and a transparent pattern corresponding to the opaque pattern. By monitoring the best focus of the exposure equipment by using a reticle reference mark made up of a light-transmitting pattern, the accuracy and reproducibility of the best focus monitoring can be increased, and the equipment maintenance time can be reduced by monitoring the focus without directly exposing the wafer. Can be.

Claims (10)

A light source unit for injecting light of a predetermined wavelength; A reticle positioned under the light source unit and having a reticle reference mark formed by alternately arranging a light blocking pattern and a light transmitting pattern; A lens unit configured to accumulate and reduce light incident from the light source unit and passing through the reticle reference mark; A wafer stage formed at a lower side of the lens unit and driven up, down, left and right, and having a wafer stage mark having a structure in which four transparent patterns having a phase difference of 80 to 100 degrees with an opaque pattern therebetween are repeated; And And a CD camera positioned at an upper side of the reticle and detecting a pattern image of the wafer stage mark and a pattern image of the reticle reference mark overlapping the reticle. The method of claim 1, The light shielding pattern of the reticle reference mark is formed such that its size and shape correspond to the opacity pattern of the wafer stage mark, and the light transmission pattern of the reticle reference mark has the size and shape of the transparent pattern of the wafer stage mark. Focus monitoring system of the wafer exposure equipment, characterized in that formed to correspond to. The method according to claim 1 or 2, The size of the reticle reference mark is formed by multiplying the size of the wafer stage mark by the reduction factor of the exposure equipment. The method according to claim 1 or 2, The opaque pattern of the wafer stage mark is formed with a width of 0.2 to 1㎛, the transparent pattern of the wafer stage mark is formed with a width three times the width of the predetermined width of the opaque pattern Focus monitoring system. The method according to claim 1 or 2, The opaque pattern of the wafer stage mark is formed to a width of 0.2 to 1㎛, the focus pattern of the wafer exposure equipment, characterized in that the transparent pattern of the wafer stage mark is formed to the same width as the predetermined width of the opaque pattern system. The method according to claim 1 or 2, Each of the reticle reference mark and the wafer stage mark is two or four symmetrically, up and down symmetrically formed, the focus monitoring system of the wafer exposure equipment. The method of claim 1, The wafer stage mark includes a first phase shift transparent pattern having a phase of about 0 degrees, a second phase shift transparent pattern having a phase of about 90 degrees, a third phase shift transparent pattern having a phase of about 180 degrees, and a phase between the opaque patterns. And a fourth phase shift transparent pattern having a phase of about 270 degrees, and a phase repeated in order of disposing the first phase shift transparent pattern having a phase of about 0 degrees. The method of claim 7, wherein The first to fourth phase shift transparent patterns may vary in thickness of a material through which light may pass through respective portions to cause phase differences. The method of claim 7, wherein The first to fourth phase shift transparent patterns may form different types of materials through which light may pass through respective portions to make a phase difference. The method of claim 7, wherein And the first to fourth phase shift transparent patterns form different heights of the opaque patterns of the wafer stage marks to cause a phase difference.