JPS6142419B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a projection type mask aligner used when manufacturing semiconductor components such as ICs and LSIs.

A conventional projection type mask aligner is constructed as shown in FIG. In other words, 1 is a mercury lamp, 2 is a condenser lens, 3 is a photomask, 4 is a projection lens, 5 is a wafer, and 30 is formed so as to be able to go in and out of the optical path.
31, a filter that only passes the line, g line and h line)
is a filter that is formed to be able to enter and exit the optical path and that passes only e-rays that are not sensitive to the photoresist; 32 is a total reflection mirror; 19 is a semi-transparent mirror that reflects the image of the alignment pattern; 34 is an objective lens; 35 is an eyepiece lens. By the way, generally, photoresist is coated on the wafer 5, and when it is irradiated with exposure light for exposure, there is a problem in that it is printed. Therefore, as shown in FIG. 1, in the conventional projection mask aligner, when aligning the photomask 3 and the wafer 5, a filter 31 that passes light that is not sensitive to the photoresist is inserted into the optical path, and a line 38 that does not expose the photoresist is inserted into the optical path. It takes the form of irradiating. However, the projection lens 4, which projects and exposes the pattern formed on the mask 3 onto the wafer 5, is only allowed to use light of a single wavelength due to its specifications, and using light of a different wavelength reduces image resolution and makes the photoresist insensitive. The imaging position of the e-line 38 for exposure and the g-line 37 for exposure, to which the photoresist is effectively exposed, differs due to chromatic aberration. Therefore, conventionally, when alignment is performed using a semi-transparent mirror 33, an objective lens 34, and an eyepiece 35, an e-line 38 is used, which is not sensitive to the photoresist formed by the filter 31, and the filter 3 is used during exposure.
G-line 3 of photoresist exposure formed by 0
7 (or h-line, g-line and h-line),
It was necessary to install a fine movement mechanism to correct vertical displacement of the wafer due to this chromatic aberration. However, when adjusting the vertical fine movement using this correction fine movement mechanism,
Occurrence of lateral misalignment during alignment and exposure has been an unavoidable problem. In addition, in order to avoid this problem of chromatic aberration, a pair of diagonal reflecting mirrors are inserted between the projection lens 4 and the wafer 5, as disclosed in Japanese Patent Application Laid-Open No. 47-24334.
The upper alignment pattern is irradiated with non-sensitizing light, the photomask 3 is irradiated with exposure light, and the light image of the alignment pattern of the photomask reflected from each of the pair of opposing mirrors is aligned with the wafer. A projection type mask aligner is known that performs alignment by focusing a light image of a pattern on the same point as the optical image of the mask pattern. However, since this projection type mask aligner also has the pair of reflecting mirrors that can be moved in and out, a positional shift occurs between alignment and exposure, making it impractical. That is, the position of the pair of reflecting mirrors inserted between the projection lens 4 and the wafer 5 is 0.03
There is no guarantee that the positioning can be performed within micrometers, and as a result, positional deviations will occur between alignment and exposure.

As a projection type mask aligner that solves these problems, the one shown in FIG. 2 can be considered. That is, 1
2 is a mercury lamp used for detecting and exposing the alignment pattern; 2 is a condenser lens for effectively focusing light on the entrance pupil 8 of the projection lens 4; the size is approximately the same as that of the photomask 3; It is. 3 is a photomask, and the circuit pattern on this is projected onto the wafer 5 through a projection lens 4 with a magnification of 1/1.
This is to transfer it to the correct position on the top. Therefore, during exposure, the exposure light emitted from the mercury lamp 1 is condensed by the condenser lens 2, and the photomask 3
The circuit pattern is projected onto the wafer 5 through the projection lens 4.
transferred on top. On the other hand, during alignment, light of the same wavelength as the exposure light emitted from the mercury lamp 1 illuminates the alignment pattern 6 of the photomask 3 through the semi-transparent mirror 19, and as a result, the alignment pattern 9 on the wafer 5 is illuminated through the projection lens 4. The reflected light is focused on the position 6 of the photomask 3 through the projection lens 4, and the image and the image of the alignment pattern 6 on the photomask 3 are reflected by the semi-transparent mirror 19 and focused by the imaging lens 20. The image is converted into a video signal by the detector 21, positional deviation between the two is detected, and alignment is performed. In this way, since the same wavelength of light was used during exposure and alignment, the imaging relationship by the projection lens 4 is the same,
Eliminates positional deviation between alignment and exposure,
Achieves high-precision transcription.

After accurately aligning the photomask and wafer, it is necessary to print the circuit pattern on the photomask onto the wafer. For this purpose, a target pattern formed especially for alignment is used. Third
FIG. 3A shows a target pattern (alignment pattern) on a photomask, and FIG. 3B shows a target pattern (alignment pattern) on a wafer. A large number of chips 13 with integrated fine circuit patterns are arranged on the photomask 3, and a pair of target patterns 14 symmetrically formed at a predetermined distance are used to transfer the patterns onto the wafer 5.
is formed by a chrome window as shown in the enlarged view. In the figure, the areas filled with dots are made of chrome and are opaque. Target pattern 1 for alignment already formed on the wafer in the previous process
5 is back-projected from bottom to top by a projection lens 4 to form an image on the mask 3. Figure c is a diagram in which images of the target pattern 14 on the photomask and the target pattern 15 on the wafer are observed simultaneously.The left and right patterns are detected visually or with an automatic detector, and the positions of the mask and wafer are determined by , Y, and θ directions.

By the way, when trying to detect a target pattern for mask alignment, for example in FIG. 2, there is no filter 31 unlike in FIG. 1, so when the mercury lamp 1 is turned on, other circuit patterns are exposed at the same time. As shown in FIG. 2, a shutter 10 that is larger than the photomask 3 and has a small window 11 is inserted between the semi-transparent mirror 19 and the photomask 3 in close proximity to the top surface of the photomask 3 so as to cover the entire surface of the photomask 3. If an attempt is made to do so, only a small area in the vicinity of the target pattern will be illuminated, and other circuit patterns will be prevented from being exposed on the wafer 5 at the same time.

However, in this case, when exposing and printing the circuit pattern of the photomask 3 onto the wafer 5 using the projection lens 4, the shutter 10, which is large enough to cover the entire surface of the photomask, is moved with a stroke larger than the size of the photomask to remove it. There must be. As described above, it is necessary to mechanically move the large shutter 10, which is large enough to cover the entire surface of the photomask, into and out during alignment and exposure. Therefore, the weight of the shutter 10 increases and the mechanism for moving it in and out becomes complicated. As a result, vibrations are likely to occur in the location where the photomask is installed, which may affect the alignment accuracy between the photomask and the wafer, and it is also difficult to install the above mechanism near the photomask due to space considerations. There are problems.

In addition, in the case of the alignment device shown in Fig. 2,
A semi-transparent mirror 19 is arranged at an angle of 45 degrees directly above the alignment pattern 6 of the photomask 3, and the imaging lens 4
Since the optical axis of the projection lens 4 is not on the extension of the straight line connecting the entrance pupil 8 of the projection lens 4 and the center of the alignment pattern 6 of the photomask 3, the reflected light of the alignment pattern 9 on the wafer 5 passes through the projection lens 4 to the photomask. The image formed at position 6 of 3 is reflected by the upper end of the semi-transparent mirror 19, and a part of the light is imaged on the detector 21 using the outer periphery of the imaging lens 20. Originally, the image formed by the reflected light from the alignment pattern 9 on the wafer 5 through the projection lens 4 at the position 6 of the photomask 3 is weak, so if a part of the light misses the imaging lens 20, it will not be detected. The optical image formed on the device 21 becomes even weaker, making alignment difficult. In order to prevent this, the size of the imaging lens 20 must be significantly increased, which poses the problem of making it difficult to install it in the peripheral area between the photomask 3 and the condenser lens 2. Ta.

In view of the above-mentioned drawbacks of the prior art, an object of the present invention is to
In order to eliminate chromatic aberration, the same exposure light as during projection exposure is used during alignment, and the alignment can be performed under the same conditions as during projection exposure.In addition, it is larger than the size of the photomask and has a small window so as to cover the entire surface of the photomask. To provide a projection type mask aligner which eliminates the need to insert a shutter close to the top surface of a photomask, positions a photomask and a wafer with high precision, and enables highly accurate projection exposure.

That is, in order to achieve the above object, the present invention provides an alignment light source that irradiates light of the same wavelength (g-line) as the exposure light source on the side separately from the exposure light source, and Light of the same wavelength as the exposure light is reflected by a small reflecting mirror installed above the alignment pattern on the photomask, and is spot-irradiated only onto the alignment pattern area on the photomask through a projection lens. A condensing optical system is provided to irradiate the alignment pattern area on the wafer, and a detector is provided to detect the relative deviation between the alignment pattern on the photomask and the alignment pattern on the wafer. an imaging lens that forms on the detector an image of the alignment pattern on the photomask reflected by the reflecting mirror and an image back-projected from the alignment pattern on the wafer through the projection lens; This is a projection type mask aligner that is characterized by being able to perform alignment with a high precision of 0.1 μm. A further object of the present invention is to fix the reflecting mirror to prevent it from becoming a source of vibration, and to simplify the mechanism.
If the reflecting mirror is fixed in this manner, it is no longer possible to form a circuit pattern in the area where the reflecting mirror is located, so it is necessary to make the reflecting mirror as small as possible. Also, in the imaging lens, it is necessary to eliminate chromatic aberration and image distortion of the image of the alignment pattern so that the detector can detect the alignment pattern with high precision. Therefore, the present invention aims at downsizing the reflecting mirror by positioning the center of the reflecting mirror on an extension of the straight line connecting the entrance pupil of the projection lens and the center of the alignment pattern on the photomask, and also aims to reduce the size of the reflecting mirror. The above-mentioned extension line is made to coincide with the line whose direction is changed by the reflecting mirror, thereby eliminating chromatic aberration and image distortion of the imaging lens, and enabling the alignment pattern to be detected with high precision by the detector. It is something to do.

The present invention will be specifically described below based on embodiments shown in the drawings.

FIG. 4 is a diagram showing an embodiment in which only the alignment target pattern is spot-illuminated in the projection type mask aligner of the present invention. That is, an optical system for spot illuminating only the area of the alignment target pattern 14 is provided separately from the exposure optical system consisting of the mercury lamp 1 and the condenser lens 2. This optical system includes a light source 24 obtained by guiding another light source or a part of the light source 1 through an optical fiber;
It is composed of a condenser lens 25, a semi-transparent mirror 26, and a fixed reflecting mirror 19. That is, the light from the light source 24 obtained by guiding another light source or a part of the light source 1 through an optical fiber is condensed by a condenser lens 25 and directed to a semi-transparent mirror 26 provided on the optical axis 23 for pattern detection. guess. This light is imaged onto the entrance pupil 11 by a reflecting mirror 19. In this way, a separate illumination system identical to the illumination system created by the mercury lamp 1 and condenser lens 2 is created, and only the area of the alignment target pattern is locally illuminated with the same wavelength (g-line) as the exposure light. You can. When detecting the alignment target pattern using this illumination system, it is possible to realize a projection type alignment device that illuminates only the area of the alignment target pattern and does not illuminate or expose other circuit patterns. can. That is, since the above optical system is configured to spot-illuminate only the area of the alignment target pattern with light having the same wavelength as the exposure light, the photomask 3 can be illuminated as usual.
It is not necessary to insert the shutter 10, which is larger than the photomask 3 and has a small window 11, between the semi-transparent mirror 19 and the photomask 3 in close proximity to the upper surface of the photomask 3 so as to cover the entire surface of the projection lens 4. This also prevents the image formation position shift due to chromatic aberration, and it has become possible to align the photomask and wafer with high precision and to project, expose, and print the circuit pattern on the photomask onto the wafer with high precision.

In particular, the chromatic aberration of a projection lens becomes larger as the reduction ratio becomes larger in a reduction projection lens than in the case of a 1/1 projection lens. Therefore, the effect of using light of the same wavelength as during exposure becomes significant when reducing the projection to 1/10 or the like.

On the other hand, as described above, if only the target pattern area for positioning is spot-illuminated during alignment, a shutter larger than the size of the photomask and having a small window is placed close to the top surface of the photomask so as to cover the entire surface of the photomask, as in the conventional method. No insertion is required, excellent alignment accuracy can be maintained, and highly accurate projection exposure can be achieved.

Next, the detection optical system will be explained using FIG. That is, if the line connecting the center of the alignment target pattern 14 on the photomask 3 and the entrance pupil 11 (the direction in which the light returns) is the detection optical axis 23, then the light in the diagonally shaded area 22' (the region in which the light returns) is An image can be formed on the detector 21 at the center of the detection imaging lens 20, and the detector 21 can effectively detect with high resolution since the chromatic aberration of the imaging lens 20 and image distortion are eliminated. I can do it. In this way, the center of the alignment target pattern 14 on the photomask 3 and the entrance pupil 11
The extension line of the line connecting the lines is set as the detection optical axis 23. For example, when the detection optical axis 23 is set in the horizontal direction, the reflecting mirror 1
9' with the horizontal direction is α = π/4 - θ/2 (where θ is the angle between the optical axis of the projection lens 4 and the
This is the angle formed by the line connecting the entrance pupil of the image and the center of the alignment target pattern 14 on the photomask. ). If the center of the reflecting mirror 19' is placed on an extension of the above line, the image of the alignment target pattern can be effectively reflected at the center of the reflecting mirror 19', and the reflecting mirror 19' can be made smaller. Therefore, even if the reflecting mirror 19' is fixed, the area shaded by the reflecting mirror 19' during projection exposure can be kept as small as possible, and the area of the alignment pattern area on the wafer can be kept as small as possible. Therefore, a large number of semiconductor integrated circuits can be obtained from a wafer. Furthermore, by fixing the reflecting mirror 19', vibrations and the like are prevented from occurring, and the alignment state is maintained until the time of projection exposure, making it possible to perform projection exposure with high precision.

Furthermore, by aligning the optical axis of the imaging lens 20 with the detection optical axis 23, the imaging lens 20 can be made smaller, and since the center of the lens 20 is used, distortion of the lens is also reduced. The detector 21 can detect the image of the alignment target pattern even with high resolution.

As explained above, according to the projection type mask aligner of the present invention, only the region of the target pattern for alignment is spot-illuminated with light having the same wavelength as the exposure light, so that it is possible to cover the entire surface of the photomask as in the conventional method. It is not necessary to insert a shutter that is larger than the photomask size and has a microscopic window close to the top surface of the photomask, and the problem of chromatic aberration caused by the projection lens can be solved.
The effect is that alignment between the photomask and the wafer can be realized with high precision of 0.1 μm or less.

Furthermore, according to the present invention, the reflecting mirror can be made small, and the area shaded by the reflecting mirror during projection exposure can be minimized, making it possible to obtain a large number of semiconductor integrated circuits from a wafer. It is also effective. Further, according to the present invention, since the image of the alignment target pattern is formed at the center of the imaging lens, the detector can detect the alignment target pattern even with high resolution, and alignment can be performed with high precision. Is possible.

Further, according to the present invention, it is possible to keep the alignment target pattern illumination optical system and the detection optical system fixed, and it is also possible to downsize the imaging lens and the detector, so the projection type It also has practical effects that can simplify the mask aligner and significantly reduce the cost.

[Brief explanation of the drawing]

Figure 1 is a diagram showing an example of a conventionally used projection type mask aligner, Figure 2 is a diagram showing another example of a conventional projection type mask aligner, and Figure 3 is a diagram for alignment on a mask and a wafer. FIG. 4 is an explanatory diagram showing a spot illumination system of the projection type mask aligner of the present invention, and FIG. 5 is an explanatory diagram showing the detection optical system of the projection type mask aligner of the present invention. . Explanation of symbols, 2... Condenser lens, 3... Photomask, 4... Projection lens, 5... Wafer, 11... Entrance pupil, 14... Target pattern for alignment, 1
9'...Reflector, 20...Imaging lens, 21...Detector, 23...Optical axis for detection, 24...Light source, 25...Condenser lens, 26...Semi-transparent mirror.

Claims (1)

[Scope of Claims] 1. A projection type mask aligner that aligns a photomask and a wafer based on the amount of relative deviation detected through a projection lens that transfers and prints a circuit pattern formed on a photomask onto a wafer. A small reflecting mirror whose center coincides with the extension of the straight line connecting the entrance pupil of the projection lens and the center of the alignment pattern provided on the periphery of the photomask, and whose center is inclined with respect to the photomask, is provided to reflect the exposure light. A light source that emits light of the same wavelength as the exposure light is provided, and the light of the same wavelength as the exposure light emitted from the light source is spot-irradiated only onto the alignment pattern area on the photomask, and the position on the wafer is projected through the projection lens. A condensing optical system for irradiating the alignment pattern area is provided, a detector is provided to detect the relative deviation amount between the alignment pattern on the photomask and the alignment pattern on the wafer, and an imaging lens for forming an image of the alignment pattern on the photomask reflected by the reflecting mirror of the wafer and an image back-projected from the alignment pattern on the wafer through the projection lens onto the detector; A projection type mask aligner characterized in that the optical axis of the imaging lens is aligned with a line obtained by changing the direction of the extension line by the small reflecting mirror. 2. The circumferential projection type mask aligner according to claim 1, wherein the projection lens is constituted by a reduction projection lens.