JPH0547901A - Alignment method of wafer - Google Patents

Abstract

PURPOSE:To provide a method wherein, in a foreign matter inspection equipment using a comparison method of adjacent chips, corresponding same patterns are correctly selected from the similar shape patterns of two symmetrical IC chips, X, Y coordinate values of high precision are obtained from image data whose pattern is indistinct, and high precision alignment of a wafer is enabled. CONSTITUTION:Image data of the same parts selected from patterns PTa, PTb of two IC chips are compared by a pattern matching unit 6f, and the identity is confirmed. Image data of perpendicularly intersecting parts of both of the confirmed same parts are processed by a filing unit 6g, and the respective contour curves S1, S2 are extracted. From these curves, the angle deviation of wafers are calculated, by obtaining X, Y coordinate (xa, ya), (xb, yb) of perpendicularly intersecting points Pa, Pb of both of the perpendiclarly intersecting parts. The wafer is rotated by the angle deviation amount, and IC chip rows in the X-direction are aligned in the X-axis direction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wafer alignment method, and more particularly, to two adjacent I on a wafer surface.
The present invention relates to a method for aligning a wafer angle in a correct direction in a foreign matter inspection device of a method of comparing C chips.

[0002]

2. Description of the Related Art In the manufacture of semiconductor ICs, a large number of IC chips (hereinafter simply referred to as chips) having the same pattern are formed on a wafer made of a material such as silicon.
A foreign matter inspection is performed at this stage. The foreign matter inspection is performed by projecting a laser beam onto the wafer surface and receiving the reflection or light thereof, but since scattered light is scattered from the pattern together with the foreign matter, it is necessary to distinguish them and detect only the foreign matter. And important. As an adaptation to this, there is an inspection method in which two chips adjacent to each other are compared with each other.

2 (a) and 2 (b) show a schematic structure of a foreign matter inspection apparatus based on the above-described adjacent chip comparison method. In (a), a large number of chips 11 are formed in a matrix on the surface of the wafer 1 to be inspected with an orientation flat (OF) as a reference line (X direction). The wafer is placed on a moving / rotating stage 5, an inspection optical system 2 is provided for the wafer, and a laser beam L from a light source 2a is provided.
Is irradiated onto the surface of the wafer through the light projecting lens 2b. The wafer is moved in the X direction by the moving / rotating stage, and the laser beam scans the chip row 11X in the X direction shown in (b). The scattered light on the wafer surface is received by the objective lens 2c, and is input to the CCD sensor 2f via the half mirrors 2d and 2e. Here, two adjacent chips shown in (b) are 11r and 11s. First, the scattered light from the chip 11r is received,
The detection signal of each pixel of the CCD sensor is sequentially detected by the detection processing unit 3
To enter. Each detection signal is digitized by the A / D converter 3a and stored in the memory (MEM) 3b. Then, digital detection data similarly obtained from the scattered light of the chip 11s is input to the difference circuit 3c and stored in the MEM. The difference data from the detected data of the chip 11r being output is output. In this case, the same pattern P _T (abbreviated with a dotted line) is formed on each chip as shown in FIG. 2B, and the scattered light of each pattern has almost the same intensity, so this is shown in the difference data. Only the foreign substance data is erased and outputted, and this is taken into the computer (CPU) 3d and displayed on the display unit 3.
Mapped to e.

In the above method of comparing adjacent chips,
In order to erase the pattern detection data, it is a necessary condition that the patterns of both chips have the same shape, and that the laser beam scans the same position of both chips. For this reason, the wafer 1 mounted on the stage 5 is tentatively aligned so that the OF of the reference line is in the X-axis direction, but it is still not sufficiently accurate. Therefore, two chips that are symmetrical with respect to the center of the wafer are taken, and the XY coordinate values of the patterns corresponding to both chips are obtained,
The wafer is rotated by the moving / rotating stage in accordance with the angle deviation obtained from the coordinate values, and the scanning direction of the laser beam is accurately aligned in the direction of the chip row 11X (X axis). When the patterns of the adjacent chips are misaligned in the X direction, each chip is detected by a separate detection mechanism and the wafer is moved in the X direction to be corrected and inspected. FIGS. 3 (a) to 3 (c) illustrate a method for obtaining the X, Y coordinates of each pattern described above and the angular deviation of the wafer. The method will be described with reference to FIG. Figure 3 (a)
At, the two chips 11a and 11b located symmetrically with respect to the center of the wafer 1 are taken. For these,
The alignment control system 4 shown in FIG.
The white light is converted into a pattern P _Ta , P corresponding to each chip by a.
The same portion of _Tb is illuminated, and each reflected light is branched by the half mirror 2e and received by the TV camera 4b. Receiving data is processed in the alignment signal processing section 4c, quadrature point p _a of the two identical parts shown in FIG. 3 (b), X a p _b, Y-coordinate value _{p a (x a, y a} ), p b (x _b , y _b ) is required. These X and Y coordinate values are fetched by the CPU 3e and shown in (c).
Angular deviation amount δθ of the line segment p _a -p _b is calculated with respect to the axis, the wafer a wafer is rotated δθ is aligned by moving / rotating stage.

[0005]

Recently, in order to increase the degree of integration of ICs, the pattern width is becoming more and more thin, and the pattern configuration is complicated, and there are many portions having similar shapes. ing. Due to such thinning, the image data of the pattern becomes unclear due to a decrease in contrast, and because of the similar shape, it is very difficult to select the same part of the corresponding patterns P _Ta and P _Tb of each chip. Has become. On the other hand, there is an urgent need for a method for surely selecting the corresponding corresponding pattern from patterns having many similar shapes and for obtaining more accurate XY coordinate values from unclear image data. The present invention has been made in view of the above, and confirms the identities of both selected patterns, and further obtains highly accurate X and Y coordinate values from unclear image data. It is intended to provide a method for alignment.

[0006]

SUMMARY OF THE INVENTION The present invention is a wafer alignment method which achieves the above-mentioned object, wherein
In the foreign matter inspection device for the C chip, the image data of the same portion selected from the patterns of the above two chips is compared by a pattern matching unit to confirm the sameness. The image data of the orthogonal portions in the both identified portions are processed by the filtering unit to extract the respective contours, and the X and Y coordinate values of the orthogonal points of the both orthogonal portions are respectively obtained from the extracted contours to obtain the wafer. Calculate the angle deviation. The wafer is rotated by the calculated angle deviation, and the IC chip row in the X direction is aligned in the X axis direction.

[0007]

In the above-mentioned alignment method, both identical portions selected from the patterns of two chips are compared by the pattern matching unit to confirm their identity. Then, the video data of the orthogonal parts in these same parts are processed by the filtering unit to extract respective contours. The X and Y coordinate values of the orthogonal points of the two orthogonal portions are obtained from this contour, the angle deviation of the wafer is calculated from these, the wafer is rotated by the angle deviation, and the IC chip row in the X direction is aligned in the X axis direction. It In the above, the pattern matching unit compares the two sets of image data to determine the identity of the shapes of the two sets. By this, the identity of the same portion of both patterns is confirmed. There is no mistake with the part. Further, the filtering unit extracts the contour of the pattern, whereby the image data of both orthogonal portions are processed to extract a clear contour, and X,
The Y coordinate value is obtained with high accuracy.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment of the present invention. FIG. 1 (a) is the same as FIG.
Alignment signal processing unit 4 in the foreign matter inspection device of (a)
c is the alignment control unit 6 according to the present invention, and the same components as those in FIG. The wafer 1 to be inspected is placed on the moving / rotating stage 5, and the two chips 11 at the symmetrical positions shown in FIGS. 3 (a) and 3 (b) are provided.
The same portions (probably) of the patterns a, 11b corresponding to each other are imaged by the TV camera 4b. The image data of both the same captured images are input to the alignment control unit 6, digitized by the A / D converter 6a for each pixel, and temporarily stored in the frame memory 6d via the changeover switches 6b and 6c under the control of the CPU 3e. Remembered. The stored pixel data are converted into analog data by the D / A converter 6e and compared by the pattern matching unit 6f. When it is determined that the two have the same shape, the matching signal is given to the CPU to determine the identity. It is confirmed. If they do not match, another part is selected again and the same process is performed to confirm the identity. After the above confirmation, the video data of both the same parts output by the TV camera is input to the filtering unit 6g again by switching the changeover switches 6a and 6b, the orthogonal points of both the same parts are processed, and the contours thereof are processed. Is extracted and the contour data is stored in the frame memory 6d. Figure 1 (b)
The processing method of the filtering unit 6g will be described below. In (a), the unit 6g extracts the minimum value or the maximum value of each pixel data of the pattern P _T sequentially input by the soft window W, and the extracted value is followed by the two minimum values. Between the two, or between the maximum values, that is, the contour of the pattern P _{T in} the cross section perpendicular to the X or Y direction is extracted. Pixel data of the same portion of the patterns P _Ta and P _Tb whose identity is confirmed by the above,
Input to the filtering unit 6g sequentially. When the scattered light at the edges on both sides of each pattern is reduced as shown in (b), the two lowest values are extracted and the curve S ₁ showing the contour of the pattern is obtained. The pattern width l _X or l _Y is calculated from the contour curve S _{1 and the} coordinates (x) of the respective center points, that is, the orthogonal points p _a and p _b shown in FIG.
_a, y _a) and (x _b, obtaining a y _b). (C) is a case where the scattered light on both edges protrudes upward, and the contour curve S ₂ opposite to the above is obtained, and the coordinate values of the orthogonal points p _a and p _b are obtained in the same manner as above. As described above, even in a fine and unclear pattern, the scattered light of the edge changes, so that the contour is extracted and the coordinate value of the pattern can be accurately obtained. Figure 1 again
(a), the respective quadrature points are Introduction by the p _a, the p _b coordinate _{(x a, y a),} (x b, y b) is taken into CPU3e, the method of FIG. 3 (c) above The angle deviation δθ of the line segment p _a −p _{b with} respect to the X-axis is calculated by the stage control circuit 6h to control the moving / rotating stage 5 to rotate the wafer by δθ. Two
(See (b)) is aligned in the X direction. The pattern matching unit 6f and the filtering unit 6g are widely used in the image processing technology and are commercially available, so it is preferable to use them. Further, a method of calculating the angle deviation δθ from each coordinate value is well known, and therefore its explanation is omitted.

[0009]

As described above, in the alignment method according to the present invention, the pattern matching unit confirms the identity of the same portion of both selected patterns, so that it may be mistaken for other portions having similar shapes. In addition, a clear contour is extracted from the image data of the orthogonal portion by the processing of the filtering unit, whereby the X and Y coordinate values of the orthogonal points are obtained with high accuracy and the wafer is accurately aligned. There is a large part that contributes to the foreign material inspection of the IC chip by the comparison method.

[Brief description of drawings]

FIG. 1 shows an embodiment of the present invention, (a) is a schematic configuration diagram of a main part, and (b) is an explanatory diagram of a filtering processing method.

FIG. 2A is a schematic configuration diagram of a foreign substance inspection apparatus by a method of comparing adjacent IC chips, and FIG. 2B is a diagram showing scanning of a laser beam L on a chip row.

3A and 3B are diagrams for explaining the wafer alignment method in FIG. 2, where FIG. 3A is a diagram showing two symmetrical IC chips, and FIG. 3B is a diagram showing orthogonal points of the same pattern of both IC chips; (c) is a diagram showing the coordinate values of both orthogonal points and the angle deviation of the wafer.

[Explanation of symbols]

1 ... Wafer, 11, 11a, 11b ... IC chip, chip, 11r,
11s ... Adjacent chip, 11X ... Chip array in X direction, 2 ... Inspection optical system, 2a ... Light source, 2b ... Projection lens, 2c ... Objective lens, 2d, 2e ... Half mirror, 2f ... CCD sensor,
3 ... Detection processing unit, 3a ... A / D converter, 3b ... Memory (MEM), 3c ... Difference circuit, 3d ... Foreign matter detection unit, 3e
... Computer (CPU), 3f ... Display section, 4 ... Alignment control system, 4a ... Light source section, 4b ... TV camera, 4c
... Alignment signal processor, 5 ... Moving / rotating stage,
6 ... Alignment control unit, 6a ... A / D converter, 6b, 6
c ... Changeover switch 6d ... Frame memory, 6e ... D / A converter, 6f ... Pattern matching unit, 6g ... Filtering unit, 6h ... Stage control circuit, L ... Laser beam, P
_T ... pattern, p _a, orthogonal point p _b ... pattern, W ... window, S _1, S ₂ ... pattern sectional contour curve.

Claims (1)

[Claims] 1. A plurality of IC chips having the same pattern formed on the surface of a wafer are to be inspected, and the two IC chips located at symmetrical positions with respect to the center of the wafer are taken and correspondence of each pattern is obtained. The same portion is selected, the respective XY coordinate values are obtained from the image data of the both same portions, the wafer is aligned according to the XY coordinate value, and then the IC chip row in the X direction is scanned with a laser beam to be mutually In a foreign matter inspection device that detects foreign matter adhered to each IC chip on the basis of difference data for the reflected light of two adjacent IC chips, the image data of the same two selected parts are compared by a pattern matching unit. The identity is confirmed, and the image data of the orthogonal portion in the both identified portions is confirmed,
The contours are extracted by processing by the filtering unit, the X and Y coordinate values of the orthogonal points of the two orthogonal portions are obtained from the contours to calculate the angular deviation of the wafer, and the wafer is rotated by the angular deviation. A method of aligning a wafer, wherein the IC chip row is aligned in the X-axis direction.