JP3040845B2 - Alignment mark - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alignment mark suitable for use in positioning a wafer, particularly in global alignment of a semiconductor manufacturing apparatus.

[0002]

2. Description of the Related Art As a manufacturing process of a semiconductor integrated circuit, there is a step of sequentially transferring a pattern on a mask or a reticle to each of divided areas on a wafer. In this transfer step, in order to transfer another pattern onto the pattern that has already been transferred and formed in the previous step, the pattern formed in the previous step and the pattern to be transferred are accurately aligned prior to the transfer step. For this purpose, global alignment for positioning the wafer itself with high accuracy is required. In this global alignment, the positioning accuracy is on the order of submicron (0.2 μm).
m), so that generally high-magnification alignment optics are used to increase the resolution,
For example, one having a narrow narrow field of view of 100 μm or less on one side is used. However, the accuracy of the mechanical pre-alignment of the wafer may reach an error of about several hundred μm, and the center of the alignment mark on the wafer is not always included in the field of view of the alignment optical system. For this reason, it is necessary to search for the center of the alignment mark, and various measures have been taken to quickly and accurately put the center of the alignment mark in the field of view from the viewpoint of improving throughput and yield. .

[0003] The present applicant has also disclosed Japanese Patent Laid-Open No.
No. 112223 proposes an alignment mark 31 as shown in FIGS. 6A and 6B. FIG.
6A is an overall view of the alignment mark 31, and FIG. 6B is a partial detailed view showing the width of the line pattern and the interval between the line patterns of the alignment mark 32 from the center to the end with respect to one axis. Assuming that the horizontal direction of the paper is the X-axis direction and the vertical direction is the Y-axis direction with the center of alignment as the origin, the alignment marks 32 are line-symmetric with respect to each axis, that is, the line pattern width is the origin. , The line pattern interval is narrower, and the line pattern interval is wider as it is closer to the origin. Have each. Specifically, assuming that alignment is performed using an alignment optical system in which one side of a square visual field is 70 μm, the sum of a pair of line pattern widths and line pattern intervals is 30 μm. That is, the leftmost line interval in FIG.
0 μm, the next line and the line interval are 4 μm and 26 μm, respectively, and the sum is 30 μm. Further, since different information must be obtained at arbitrary different coordinates, focusing on one side from the central axis with respect to a certain axis of position information,
All line pattern widths and line pattern intervals are different.

[0004] If this alignment mark 31 is used,
Since a black and white pattern having two or more line patterns or line pattern intervals is included in a square visual field having a side of 70 μm, the distance and direction from the origin to the center of the visual field can be obtained based on the black and white pattern. .

[0005]

However, since various kinds of materials are stacked on the mark on the wafer in the process of forming the semiconductor integrated circuit, only the edge of the mark is sometimes emphasized, and the mark is differentiated from the mark image. Therefore, the black and white pattern cannot be distinguished. Therefore, if alignment is performed based on the black and white pattern as described above, there is a problem that quick and accurate alignment cannot be performed. As a method for solving this problem, it is conceivable to take out the edge signal of the alignment mark and specify the position coordinates of the alignment mark from the arrangement of the data of the edge interval. For example, as for the mark processing in the uniaxial (X-axis) direction, as shown in Table 1, the edge interval data of the mark pattern in the order of element numbers j in the -X direction to the + X direction based on the design data in advance, as shown in Table 1. S
[J] and distance data X [j] from the mark edge position on the −X direction side of the two edges of the array and the corresponding edge interval to the center axis are created in advance.

[0006]

Next, an edge detection process is performed on the data taken in from the image, an interval for each adjacent edge is obtained from the data of the edge position, and this is sequentially converted into the measurement array data P [j] in the -X direction. substitute. For example, in FIG. 6, since there are four edges in the field of view F, the measured value of the interval between adjacent edges is substituted into the array P [j] from the −X direction. Here, assuming that three P array data such as P [1] = 9.5 P [2] = 24.5 P [3] = 5.8 are input, then the arrangement of the P array data is as follows. Is the most correlated in the sequence of S-array data. When the S array data is examined in this manner, the X array data of the element number becomes the distance to the central axis. That is, in the above case, since the correlation is highest with the arrangement of three data of S [26] = 10 S [27] = 24 S [28] = 6 in the S array, the first array S [26] ] From the X [26] array data, which is the same as the element number, the distance from the edge of the P [1] data to the center of the field of view is -153 μm. In this manner, the distance and direction from the center of the visual field to each axis can be obtained by comparing the edge intervals of each line pattern in the visual field and the arrangement thereof with the predetermined shape of the entire alignment mark.

However, in the above case, there is a problem that the pattern shape corresponding to the alignment mark, the direction and the distance to the center at that time must be stored in advance, and the measurement data due to the image deterioration is required. In order to take into account the variation in, it is necessary to perform complicated calculations such as pattern matching using cross-correlation, so that there is a problem that high-speed alignment cannot be performed.

The present invention has been made in view of such a problem, and enables quick and accurate alignment without storing mark shape data and performing complicated calculations. An object of the present invention is to provide an alignment mark that can be used.

[0010]

In order to achieve the above object, the present invention provides an alignment mark having a plurality of alignment marks arranged along a predetermined direction in order to perform alignment at a central portion of the alignment. Wherein said plurality of alignment marks are configured so that the distance between any adjacent edges thereof is a function of the distance to said alignment center, and said alignment is performed by comparing the distances between successive edges. It is configured so that the direction of the center can be identified.

[0011]

As described above, the alignment mark is formed by determining the distance between adjacent edges as a function of the distance to the alignment center.
In addition, if the configuration is such that the direction of the center of alignment can be identified by comparing the distances between successive edges, the edge pattern of at least three alignment marks is included in the field of view of the alignment optical system, and the interval between two edges is observed. if you can,
The distance from the one edge interval to the center of the alignment can be obtained, and the direction of the center of the alignment can be identified by comparing the two edge intervals. Alignment can be performed quickly and accurately without performing complicated calculations.

[0012]

FIG. 1 shows a first embodiment of the present invention. This alignment mark 1 is a positioning mark 2
In the quadrangular pattern constituting the above, the position information in the X-axis direction is given to the interval between the sides parallel to the Y-axis, and the position information in the Y-axis direction is given to the interval between the sides parallel to the X-axis. That is, as the origin of the center of the alignment mark 1 and the center of the alignment becomes farther away from the orthogonal center axis, the sides of the rectangle and the distance between the sides and the adjacent rectangles, that is, the sides of the respective sides ignoring the square pattern, The edge interval is configured to be reduced in accordance with an arithmetic progression having a certain distance difference. Specifically, one side is about 75μ
Assuming that alignment is performed using an alignment optical system having a square field of view of m, the intervals (μm) between symbols A to U in FIG. 1 are configured as shown in Table 2.

[0013]

With such a configuration, by measuring the edge interval p at an arbitrary position, it is easy to determine the number of the edge from the origin and the number of places from the end from the equation of the arithmetic progression. Can be sought. In this embodiment, the distance X from the edge position to the target center position (origin) can be obtained by calculating X = p · (1−p) / 2 + 250 [μm]. Moreover, even if an error occurs in the edge interval p of the actually measured data, the influence on the distance X to the obtained center is extremely small.
It does not matter as a ratio of the error to the center mark visual field. In addition, the alignment mark 1 is about 7
When observed with an alignment optical system having a square visual field of 5 μm, at least three edge patterns are included in the visual field, and thus at least two interval data are obtained. Therefore, the central axis direction is known by comparing the adjacent interval data. be able to.

As described above, according to this embodiment, the distance to the X-axis and the Y-axis can be obtained by substituting arbitrary interval data of the pattern in the visual field into a predetermined formula, The center direction can be obtained by comparing at least two distance data of
The center position of the alignment mark 1 can be relatively easily and accurately aligned with the center of the visual field of the alignment optical system.

FIG. 2 shows a second embodiment of the present invention. Similar to the first embodiment, this alignment mark 11 is provided with the position information in the X-axis direction at the interval between the sides parallel to the Y-axis of the square pattern forming the alignment mark 12 and the side parallel to the X-axis. In this embodiment, the distance between the sides of the rectangle and the side and the adjacent rectangle, that is, the edge interval is set at the center of the alignment mark 11 and the position of the alignment mark 11 is adjusted. Is set to be a constant multiple of the distance from the center axis perpendicular to the origin. Specifically, assuming that alignment is performed using an alignment optical system having a square visual field with a side of about 75 μm, the intervals (μ
m) is configured as shown in Table 3.

[0017]

With this configuration, by measuring the edge interval p at an arbitrary position and multiplying it by a constant, it is easy to determine the number of the edge from the origin and the number of points from the end. Can be sought. In this embodiment, by calculating X = p · 10 [μm], the distance X from the edge position to the target center position (origin) can be obtained. Also,
When the above alignment mark 11 is observed with an alignment optical system having a square visual field with a side of about 75 μm, even at the outermost peripheral portion having the widest mark interval, at least three edge patterns are included in the visual field. Is obtained, the center axis direction can be known by comparing the adjacent interval data. Thus, according to this embodiment, simply multiplying any interval data of the pattern in the field of view by 10 increases the X-axis and Y-axis.
Since the distance to the axis can be obtained and the center direction can be obtained by comparing at least two distance data in the visual field, the center position of the alignment mark 11 can be determined by the alignment optical system as in the first embodiment. Can be relatively easily and accurately aligned with the center of the visual field.

Hereinafter, specific alignment using the above-described alignment mark according to the present invention will be described. FIG. 3 shows an example of the configuration of an alignment optical system used when performing global alignment. The alignment optical system converts light from a light source (not shown) into an optical fiber 21, a beam splitter 22, and an objective lens 2.
3 is projected onto the wafer 24, and the image is
3. The light is received by the image sensor 27 via the beam splitter 22, the imaging lens 25, and the imaging lens. The size of the field of view of the alignment optical system is about 70 μm. The image pickup device 27 is constituted by a solid-state image pickup device and an image pickup tube, and its video signal is supplied to an image processing device (not shown), where about 480 pixels are arranged so that one pixel corresponds to about 0.15 μm on the wafer 24.
× 512 horizontal pixels are sampled and a required operation is performed.

In performing global alignment using the alignment optical system shown in FIG. 3, first, the wafer 24 is transferred to a predetermined position on a wafer stage by a wafer transfer means, and then the alignment mark on the wafer is aligned with the alignment optical system. Mechanical alignment to be within the field of view. In this case, the positioning accuracy depends on the mechanical pre-alignment accuracy. However, the alignment range of the alignment mark on the wafer 24, that is, one side of the alignment mark is usually about 500 μm. And the mechanical pre-alignment causes the field of view of the alignment optics to be located within the alignment mark. Next, the image signal of the alignment mark from the image sensor 27 is taken into the image processing device to read the position information, and the alignment is performed such that the center of the alignment mark is near the center of the visual field of the alignment optical system based on the position information. I do. Here, when there is no alignment mark center near the center of the visual field, or when the positioning accuracy is insufficient, the video signal from the image sensor 27 is similarly read to read the position information, and based on the position information, The operation of positioning is repeated so that the center of the alignment mark is near the center of the visual field of the alignment optical system. When a fine alignment mark is specially provided at the center of the alignment mark, high-accuracy alignment is performed using the mark.

FIG. 4 shows a flowchart of the alignment when no special fine alignment mark is provided. First, the wafer is set so that the alignment mark on the wafer is within the field of view. Next, it is checked whether or not the alignment has been performed with the required accuracy. If the alignment has been performed, the alignment has been completed. If not, the position information has been read from the interval data of the marks in the field of view and moved. The amount and direction are calculated, and the operation of moving the wafer is repeated based on the calculated amount and direction to perform positioning. FIG. 5 shows a flow chart of the alignment when a special fine alignment mark is provided. In this case, the alignment mark has two parts: a coarse alignment mark part for center search and a fine alignment mark part having position information for performing high-precision alignment at the center part. After setting the wafer so that the alignment mark of the wafer is within the field of view, check whether the center of the mark is within the field of view, and if not, read the position information from the interval data of the coarse alignment mark and move The amount and direction are calculated, and the operation of moving the wafer is repeated based on the calculated amount and direction, and positioning is performed so that the center of the mark falls within the field of view. After that, it is checked whether or not the alignment has been performed with the necessary accuracy. If not, then the position information is read from the interval data of the fine alignment mark to calculate the movement amount and direction, and The operation of moving the wafer based on the position is repeated to perform high-accuracy positioning.

[0022]

As described above, according to the present invention, a plurality of alignment marks constituting an alignment mark are provided.
Since the distance between any adjacent edges is configured to be a function of the distance to the alignment center, and the direction of the alignment center can be identified by comparing the distance between the successive edges. It is not necessary to store mark shape data or perform complicated calculations when performing alignment. Therefore, the production of the program can be simplified, and the positioning can be performed quickly and accurately with a simple calculation processing program.

[Brief description of the drawings]

FIG. 1 is a diagram showing a first embodiment of the present invention.

FIG. 2 is a diagram showing a second embodiment of the present invention.

FIG. 3 is a diagram illustrating a configuration of an example of an alignment optical system.

FIG. 4 is a view showing an example of an alignment flowchart when an alignment mark according to the present invention is used.

FIG. 5 is a diagram showing another example of the alignment flowchart when the alignment mark according to the present invention is used.

FIG. 6 is a diagram for explaining a conventional technique.

[Explanation of symbols]

 1,11 Alignment mark 2,12 Alignment mark

Claims (1)

(57) [Claims] 1. An alignment mark having a plurality of alignment marks arranged along a predetermined direction in order to perform alignment at a center portion of an alignment, wherein the plurality of alignment marks are arranged at any adjacent positions. The distance between edges is configured to be a function of the distance to the alignment center, and the configuration is such that the direction of the alignment center can be identified from a comparison of the distance between the successive edges. Alignment mark