JPS62190724A - Alignment system - Google Patents

Abstract

PURPOSE:To align masks and wafers accurately at a high speed by obtaining a plurality of different detected images by introducing incident light from a plurality of different angles, combining the detected images and aligning them. CONSTITUTION:Laser emitting units 1, 17 are controlled by a laser controller 3 via control lines 5a, 5b to switch the incident angle of emitting light source. The light emitted from the unit 1 passes a beam splitter 2, then passes a window 27 on a mask 12 through a lens 11 to become a light trace 8'' to be emitted on the alignment pattern 24 on a wafer 13. The traces 8' and 3'' of the light are emitted in the same pattern but are emitted at different incident angles. Thus, the images detected by a photodetector 12 are different. A photodetected image combining unit 4 combined the images of two types, and aligned by the optimized imaged. The quantities of light of the units 1, 17 are controlled by the laser controller to be detected by photodetectors 5A, 5B. The levels of the reflected lights are controlled to become near values.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for aligning a pattern on a wafer and a pattern on a mask in a semiconductor printing apparatus.

(Prior Art) Conventionally, a method for aligning a pattern on a wafer and a pattern on a mask has been known as a method for aligning a wafer and a mask in an apparatus for printing semiconductors and the like.

As such a conventionally known positioning method, a method described in Japanese Patent Laid-Open No. 122128/1983 is known.

The alignment method described in JP-A-56-122128 has alignment patterns formed on a wafer and a mask, one of which has a predetermined pitch, and the other pattern with the same pitch. It consists of a first pattern group of approximately half the number of patterns repeated at a pitch of , and a second pattern group whose phase is shifted by 172 pitches from the pitch of this first pattern and whose pitch interval is the same as that of the first pattern. By doing so, alignment using the "'O'' potential is made possible.

This method will be explained with reference to FIGS. 3 to 7.

In FIG. 3, 11 is a pattern projection lens, 12
13 is a mask, 13 is a wafer, and 14, 15, and 16 are directions of light for pattern printing. Further, 17 is a laser light source, 18 is a trajectory of the emitted laser beam, 19 is a trajectory of this laser beam on the opposite side, 20 is a trajectory of light diffusely reflected by a pattern on a wafer, and 21 is a trajectory of a pattern on a wafer. This is the trajectory of light projected onto the mask 12 through the lens 11.

In this configuration, the alignment pattern on the wafer 13 is irradiated with laser light from the laser light source 17, and the intensity of the light is detected by the detectors 22A and 22B. Although only one detector is shown in FIG. 3, two detectors are actually arranged along the pattern.

FIG. 4 shows an example of alignment patterns formed on a mask and a wafer, where 23 is a pattern on the mask, 24 is a pattern on a wafer, and the pitch intervals of these patterns are the same. has been done. Note that the pattern 23 on the mask and the pattern 24 on the wafer may be formed on opposite objects. In the figure, 25 is a reflective portion, and 26b is a non-reflective portion. Pattern 2 on the mask
In the part 3, there are a large number of rectangular windows 27 and non-transparent parts 26a shown at 27 and 28 at the same intervals, and which pass the light.
They are formed with a phase shift of 172 pitches in the lB portion. Then, the reflective portion 2 of the pattern 24 on the wafer 13
The light emitted from the window 2 passes through the rectangular window 27 or 28 on the mask 12, and the light that passes through the window 27 is sent to the detector 22A.
The light passing through 8 is detected by a detector 22B.

In the state shown in FIG. 4, the pattern on the mask 12 and the wafer 1
3. The pattern above matches perfectly within the range of A,
In part B, there is a complete shift, so the output of the detector 22A is the maximum, and the output of the detector 22B is the minimum.

Next, as the wafer is moved in the direction of arrow
In the range , the overlap between the window 28 and the reflective portion 25 gradually increases, so the output of the detector 22B gradually increases. When the wafer moves 172 pitches in the direction of arrow X, the outputs of the detectors 22A and 22B are completely reversed, and when the wafer moves one pitch, the above relationship returns to its original state.

FIG. 5(a) shows the relationship between the output voltages of the detectors 22Δ and 22B and the amount of movement of the wafer in the direction of the arrow X, where the horizontal axis represents the amount of relative movement between the mask 12 and the wafer 13. , and the vertical axis shows the output voltage of the detector. In the figure, W1 indicates the output voltage of the detector 22A, and W2 indicates the output voltage of the detector 22B. In the same figure, the points indicated by a and b are when the mask 12 and the wafer 13 are in the positional relationship shown in FIG. 4, and as the wafer moves in the direction of the arrow X in FIG. changes in the direction shown by arrow X in FIG. 5(a). Point C is the output voltage of each detector when the wafer moves by 172 pitches, and the point C is the output voltage of each detector when the wafer moves 172 pitches.
The output voltage of 2A and the output voltage of detector 22B are equal.

Next, the curve indicated by W3 in FIG. 5(b) is
This is a curve obtained by subtracting the output voltage of the detector 22B and the output voltage of the detector 22B using a reducer. As is clear from the figure, this curve swings positive and negative around the 'O' potential. Here, the point indicated by n corresponds to the 0 point in FIG. 5(a), and when the output voltages of the detectors 22A and 22B are equal,
That is, this is when the wafer moves by 172 pitches in the X direction.

Therefore, if this state is set as a state in which alignment has been completed, the mask 1 is
2 and the wafer 130 can be aligned.

By the way, in general, there is a slight difference in the reflectance of the reflective portion 25 on the wafer depending on the position, and it is also possible that there is a deviation in the direction perpendicular to the direction in which the patterns are arranged, and the light intensity of the laser light source 17 also changes over time. However, this method has the advantage that the S/N ratio is good because the changes in the portion B and the portion B cancel each other out, and that it is not affected by changes in the object and the incident light. Additionally, since this method uses only reflected light, it has the advantage of not being affected by the gap between the mask and the wafer.

(Problems to be Solved by the Invention) However, in the alignment method described in JP-A-56-122128, due to the relationship between the three-dimensional shape of the pattern and the incident angle of the laser beam, .2
8 and the reflected portion 2 of the pattern 271 on the wafer 13
5 and the non-reflective portion 26b becomes unclear, making alignment difficult.

This problem will be explained below with reference to FIGS. 6 to 9.

FIG. 6 shows the case where the incident light beam 81 is made incident on the wafer 13 at a shallow angle when the alignment pattern 24 on the wafer 13 is aligned with the window 27 of the pattern 23 on the mask 12. This is an example. Note that in the figure, β is the width of the window 27.

In this example, the light reflected from the flat surface of the pattern 24 is detected as a dark portion that does not pass through the window 27 of the pattern 23 of the mask 12. Since light enters the window 27 of the mask 12 only from below, the upper edge of the window 27 cuts off unnecessary scattered light and the outline of the window 27 appears clearly.

FIG. 7 is a diagram showing the same positional relationship as FIG. 6, but when the incident light beam 82 is made to enter the pattern 24 of the wafer 13 almost perpendicularly through the window 27 of the pattern 23 of the mask 12. This is an example.

In the example shown in FIG. 7, the light rays are incident on the wafer 13 almost perpendicularly, so they are incident on the edge portions of the pattern 24 on the wafer 13 at a very shallow angle, and therefore the reflected light rays 203 and 204 are incident on the mask pattern 24. I will not return to the 23rd side. On the other hand, the ratio of the light rays reflected toward the mask pattern 23 by the reflective portion 25 excluding the non-reflective portion 26b of the pattern 24 becomes extremely large, and this reflected light follows the same path as 82 and passes through the window 27 of the mask pattern 23. via detector 2
Detected at 2A. Therefore, in the case of the example shown in FIG. 7, the portion of the pattern 26 on the wafer 13 appears dark up to its edge portion E, and the reflective portion 25 appears particularly bright.
The contours of the pattern 26 and the reflective portion 25 appear clearly.

(Problems to be Solved by the Invention) However, in the example shown in FIG. 6, the incident light ray 81 is confined at a shallow angle, and the rising angle of the edge portion E of the pattern 24 is slightly inclined from 90'. The light rays 201 and 202 reflected by this edge portion F are also detected by the detector 22A, and the boundary of the non-reflection portion 26b is located at a position slightly shifted from the center position of the window 27. There is a problem that variations occur in the positions. The range of this variation depends on the process used to form the pattern 24, but with current process technology 0.
This appears as a variation of 1 to 0.2 μm, and as shown in FIG.
However, an unclear portion U occurs.

In the example shown in FIG. 7, the light beam incident through the window 27 of the mask pattern 23 is 20f1
．． In addition to being reflected as shown by 20f2, 20f3, and 20f4 and being diffusely reflected on the inner surface of the window 27, the wafer 13
Non-reflective portion 26b and reflective portion 2 of upper pattern 24
5 is not a strictly flat surface, there is a problem in that blur U' occurs around the window portion 27, as shown in FIG.

Therefore, an object of the present invention is to provide an alignment method that makes clear the contours of the window portion of the mask pattern and the contours of the reflective and non-reflective portions of the wafer pattern that are visible when alignment is performed through the window portion. The purpose is to

(Means for Solving the Problems) In order to achieve the above object, the present invention overlaps a pattern formed on a mask and a pattern formed on a wafer with the same pitch with a certain gap between them. In an alignment method in which a light beam is incident on a pattern and alignment is performed by detecting a relative displacement between a mask and a wafer based on a change in the intensity of reflected light caused by each of the patterns, at least one pattern on the mask or the wafer is The correspondence relationship between the first pattern group and the other pattern group and the correspondence relationship between the second pattern group and the other pattern group are set to be approximately 1/1/2 of each other.
It is characterized in that the positional relationship is shifted by two pitches, the incident light beam is made incident from a plurality of different angles to obtain a plurality of different detected images, and the plurality of detected images are combined to perform alignment.

(Function) In the present invention, the respective detection images for the light rays incident at two different angles are combined and synthesized by combining the parts that have the advantages of both, so that the parts with unclear outlines due to diffuse reflection of the light rays are It is calibrated and clear, allowing for rapid and highly accurate alignment.

(Example) An embodiment of the present invention will be described below.

It should be noted that since the present invention is the same as the conventional system shown in FIG. 3 except for the number of light sources and detectors, the same parts are given the same reference numerals and redundant explanations will be omitted.

FIG. 1 shows an example of the configuration of the alignment method of the present invention. In the figure, 11 is a lens, 12 is an original mask, 1
3 indicates the wafer, and 14, 15, and 16 indicate the direction of light for pattern printing. 17 is a laser emitting device, 18 is a locus of emitted light, and 19 is a specularly reflected locus of the light. Further, a large number of arrows indicated by 20 indicate the locus of light that is diffusely reflected on the alignment pattern. 21, the alignment pattern on the wafer passes through the lens 1;
Conversely, it shows the locus of light projected toward the mask 2.

However, in this embodiment, in addition to the above conventional configuration,
Furthermore, another laser emitting device 1, a beam splitter 2, a laser control device 3, a light receiving image combining device 4, and light receiving elements 5A and 5B such as a television camera are provided. Note that, like the detectors 22A and 22B, two light receiving elements 5A and 5b are also arranged along a pattern for positioning.

The laser emitting devices 1 and 17 are controlled by the laser control device 3 using control lines 5a and 5b, and the incident angle of the irradiating light source is switched. 8' and 8'' indicate the trajectory of the light emitted from the laser emitting device 1. This light passes through the beam splitter 2, passes through the window 27 on the mask 12, and then passes through the lens 11. 8'' and illuminates the alignment pattern 24 on the wafer 13. The light trajectories 8 and 8'' illuminate the same pattern but have different incident angles, so that the images detected by the light receiving element 12 are different.

A light receiving image synthesizing device 4 synthesizes these two types of images so that alignment can be performed using the optimized image.

Note that the light quantities of the laser emitting devices 1 and 17 are controlled by the laser control device 81 so that the levels of the reflected light detected by the light receiving elements 5A and 5B are approximately close to each other.

As explained in the examples of FIGS. 8 and 9, the image detected by the laser emitting device 17 shows that the upper edge of the window 27 cuts unnecessary scattered light and clearly flattens the outline of the window 27. Since the image detected by the laser emitting device 1 clearly shows the boundary between the reflective portion 25 and the non-reflective portion 26b of the pattern 24, the composite image of these is a composite image in which the advantageous portions of both are superimposed. This calibrates ambiguous contours due to diffused reflection of light beams, making it possible to perform quick and highly accurate positioning.

The results are shown below.

In addition, in this method, changes in parts A and B cancel each other out, so the S/N ratio is good, and it is not affected by changes in the object or incident light, and only reflected light is used. Another advantage is that it is not affected by the gap between the mask and the wafer.

(Effects of the Invention) As described above, the present invention achieves positioning with higher precision than before by combining the respective detection images of light rays incident at two different angles and combining the advantages of both. It becomes possible.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a method according to an embodiment of the present invention, and FIG. 2 is a plan view showing the alignment pattern of a mask after alignment is performed according to this embodiment, as seen through the window. Figure 3 is a block diagram of the conventional alignment method, Figure 4 is a plan view showing the alignment pattern, and Figure 5 (a>, (
b) is a waveform diagram showing the waveform detected in the alignment method shown in FIG. 3; FIGS. 6 and 7 are diagrams showing the path of the detection light in the conventional alignment method, respectively;
FIGS. 8 and 9 are plan views showing detected images obtained by these methods.

Claims (4)

[Claims] (1) A pattern formed on a mask and a pattern formed on a wafer with the same pitch are overlapped with a certain gap, and a light beam is incident on each of these patterns, and the reflected light generated by each of the patterns is In an alignment method that performs alignment by detecting relative displacement between a mask and a wafer by a change in intensity, a pattern on at least one of the mask or the wafer is divided into a first pattern group and a second pattern group. The correspondence relationship between the first pattern group and the other pattern group and the correspondence relationship between the second pattern group and the other pattern group are shifted by approximately 1/2 pitch from each other, and the incident light beam is A positioning method characterized in that a plurality of different detection images are obtained by making the light incident from a plurality of different angles, and alignment is performed by composing these plurality of detection images. (2) At least one of the light rays incident from a plurality of different angles is incident at a perpendicular or nearly perpendicular angle to the wafer surface, and at least one of the other light rays is incident at a shallow angle to the wafer surface. 2. The alignment method according to claim 1, wherein the alignment method comprises: (3) At least one of the light rays incident from a plurality of different angles is incident through a mask, and at least one of the other light rays is incident without passing through the mask. The alignment method described in Section 1. (4) The alignment method according to any one of claims 1 to 3, characterized in that the light incident from the plurality of different angles is switched to be incident.