JP2939582B2 - Pattern alignment method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pattern inspection method for inspecting a pattern formed on a green sheet or a film carrier, and more particularly, to an alignment method for aligning a master pattern with a pattern to be measured. .

[0002]

2. Description of the Related Art Conventionally, PGA (Pin Grid Array) has been known as a mounting technique suitable for a demand for increasing the number of pins of ICs and LSIs. In PGA, a ceramic substrate is used as a base of a package for attaching a chip, and wiring is performed to a lead wire extraction position. To make this ceramic substrate, a so-called green sheet made by kneading alumina powder with a liquid binder is used, and a paste containing a high melting point metal is screen-printed on the green sheet. By firing such a sheet, so-called simultaneous firing, in which the green sheet is sintered and the paste is metallized, is performed.

[0003] As another mounting technique, TAB is used.
(Tape Automated Bonding) is known. TAB method is a polyimide film carrier (TAB tape)
The copper foil pattern formed thereon is joined to the electrode of the IC chip to form an external lead. The copper foil pattern is formed by attaching a copper foil to a film with an adhesive and etching this.

In such a green sheet or film carrier, a pattern is visually inspected by a human using a microscope after the pattern is formed. However, visually inspecting a fine pattern requires skill and has a problem of overworking the eyes. Therefore, as an alternative to the visual inspection, a technique has been proposed in which a pattern formed on a film carrier or the like is imaged by a TV camera and automatically inspected (for example, Japanese Patent Application Laid-Open No. 6-27313).
No. 2, Japanese Unexamined Patent Publication No. Hei 7-110863, Japanese Patent Application No. Hei 8-108
No. 302807). In these inspection methods, it is necessary to align the master pattern and the pattern to be measured in order to compare the pattern to be measured captured by the camera with the reference master pattern. And this alignment
This has been done by matching the position of the positioning mark provided in the master pattern in advance with the position of the corresponding positioning mark of the pattern to be measured.

[0005]

However, in the above-described positioning method, there is a problem that the position of the master pattern having no positioning mark for positioning and the pattern to be measured cannot be aligned. Was. The present invention has been made in order to solve the above problems, even if the pattern is not provided with a positioning mark,
An object of the present invention is to provide a positioning method capable of performing positioning.

[0006]

According to the present invention, there is provided an alignment method for aligning a master pattern and a pattern to be measured using a center of a land as a reference point for alignment. A divided area of a predetermined size at a position corresponding to the reference point of the master pattern is extracted from the image of the pattern to be measured, and a first histogram indicating the number of pixels for each X coordinate in the divided area is created. A second histogram indicating the number of pixels for each coordinate is created, and a point at which both the first and second histograms show the maximum value is set as a candidate for a reference point of the pattern to be measured corresponding to the reference point of the master pattern. The direction of the pattern connected to the land including is in the direction specified in advance, and the candidate point closest to the reference point of the master pattern is set as the reference point of the pattern to be measured,
The position of the reference point of the master pattern and the position of the reference point of the pattern to be measured are aligned to perform the alignment of the master pattern and the pattern to be measured.

According to a second aspect of the present invention, there is provided an alignment method for aligning a master pattern and a pattern to be measured by using a corner of the pattern as a reference point for alignment. A divided area of a predetermined size at a position corresponding to the reference point of the pattern is taken out, a pattern having the largest area in the divided area is selected, and two straight pattern edges forming corners of this pattern and the divided area are selected. A straight line connecting the intersections with the sides of the line is obtained, and the longest perpendicular line perpendicular to the straight line and reaching the pattern edge from the straight line to the direction specified in advance is obtained. A straight line is obtained from each of a plurality of points on the pattern edge that are at least a predetermined distance from the intersection, and the intersection of the two straight lines is used as the reference point of the pattern to be measured, and It is obtained so as to align the master pattern and the pattern to be measured by matching the position of the reference point of the reference point and the measured pattern of the over down.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION

1. Embodiment 1. FIG. 1 is a flowchart illustrating a pattern inspection method according to a first embodiment of the present invention, and FIG. 2 is a block diagram of a pattern inspection apparatus used in the inspection method. In FIG. 2, 1 is a green sheet, 2 is an XY table on which the green sheet 1 is placed, 3 is a line sensor camera for imaging the green sheet 1, 4 is a reference master pattern and a pattern to be measured imaged by the camera 3. An image processing apparatus 5 for inspecting the pattern to be measured by comparison, a host computer 5 for controlling the entire apparatus, and a display device 6 for displaying the inspection result.

First, a master pattern created before inspection will be described. Host computer 5
Is read out by a magnetic disk device (not shown), for example, green sheet design value data (hereinafter referred to as CAD data) created by a CAD (Computer Aided Design) system and written on a magnetic disk, for example.

Subsequently, pattern edge data is extracted from the read CAD data. The edge data is a set of pixels “1” indicating a pattern edge. Then, the area surrounded by the pixel “1” indicating the pattern edge is defined as “1”.
A pattern (the background other than the pattern is “0”) painted with the pixel “1” is set as a reference master pattern for inspection (step 101 in FIG. 1). In addition,
It goes without saying that the green sheet 1 is produced based on the CAD data and a pattern is screen-printed on the sheet 1.

Next, the inspection of the pattern to be measured will be described. First, the green sheet 1 is placed on the XY table 2, and the green sheet 1 is imaged by the line sensor camera 3.
At this time, the size of the image captured by the line sensor camera 3 is, for example, 4096 pixels in the X direction.
When the camera 3 captures an image while moving the XY table 2 in the Y direction under the control of the host computer 5, the size of the image in the Y direction becomes, for example, 8192 pixels. The image processing device 4 is composed of 2 of 4096 horizontal pixels × 8192 vertical pixels imaged by the camera 3.
The two-dimensional gray image is digitized and stored in an internal image memory (not shown) (step 102).

Subsequently, the image processing device 4 binarizes the grayscale image of the measured pattern stored in the image memory (step 103). The grayscale image data of the pattern to be measured includes the pattern and the other background (a base material such as a green sheet). However, since there is a density difference between the pattern and the background, the density value of the pattern and the background If a value between the density values is set as a threshold value, the pattern is converted to “1” and the background is converted to “0”. In this way, it is possible to obtain a pattern to be measured in which the pattern edge and the inside thereof are filled with the pixel “1”.

Next, the image processing device 4 aligns the measured pattern subjected to the binarization processing with the master pattern (step 104). FIG. 3 is a flowchart showing the positioning process, and FIGS. 4 and 5 are diagrams for explaining the positioning process. FIG. 4A shows a part of the master pattern, and the center of the circular land R0 is predetermined as a reference point P0 for positioning.

First, the image processing apparatus 4 performs positioning of the master pattern and the entire pattern to be measured (step 201 in FIG. 3). Since the position on the pattern to be measured placed on the XY table 2 and the position on the master pattern roughly correspond to each other, the whole position can be aligned. Subsequent processing is processing for performing positioning with higher precision.

Subsequently, the image processing apparatus 4 separates a predetermined area (hereinafter referred to as a window) having a predetermined size as shown in FIG. 4B at a position corresponding to the reference point P0 of the master pattern.
W is cut out from the binary image of the pattern to be measured (step 202). The size of the window W is, for example, 512 horizontal.
Pixels × 480 vertical pixels. The position of the window W in the binary image is set in advance according to the reference point P0 of the master pattern.

Then, the image processing device 4 controls the window W
Histogram HX showing the number of pixels for each X coordinate in
Similarly, a second histogram HY indicating the number of pixels for each Y coordinate is created (step 203). Histogram HX
, HY have two maximum values corresponding to the circular lands R1 and R2, respectively. Next, the image processing device 4 discards the data of the area (the hatched portion in FIG. 5A) specified by the X coordinate or the Y coordinate of the intersection of the edge of the pattern to be measured and each side of the window W ( Step 204).

In FIG. 5A, the intersection between the edge of the pattern connected to the land R1 and the left side of the window W is a
1, a2. As a result, the data in the area specified by each Y coordinate of the points a1 and a2 is discarded (the pixel having the value “1” is set to “0”). Similarly, the intersection between the edge of the pattern connected to the land R2 and the upper side of the window W is a
3, a4. As a result, the data of the area specified by each X coordinate of the points a3 and a4 is discarded. The reason for performing such data discarding will be described later.

Next, as shown in FIG. 5 (b), the image processing device 4 performs a first histogram HX indicating the number of pixels for each X coordinate in the window W, and a second histogram HX indicating the number of pixels for each Y coordinate. Of the histogram HY (step 2)
05). As in the case of FIG. 4B, the histogram HX
, HY have two maximum values corresponding to the lands R1 and R2.

A point at which both the histograms HX and HY show the maximum value is a candidate for a reference point of the pattern to be measured corresponding to the reference point P0 of the master pattern. In the present embodiment, points at coordinates X1 and Y1 and points at coordinates X2 and Y2 are candidates for reference points. Next, the image processing apparatus 4 covers the candidate point closest to the reference point P0 of the master pattern in a direction in which the direction of the pattern connected to the land including the candidate point is the direction designated in advance and among these candidate points. It is selected as a reference point of the measurement pattern (step 206).

The designated direction indicates the direction in which the pattern connected to the land including the reference point of the measured pattern corresponding to the reference point P0 of the master pattern extends.
As shown in (c), there are four types: a diagonally upper right direction Dru, a diagonally lower right direction Drd, a diagonally lower left direction Dld, and a diagonally upper left direction Dlu. In the present embodiment, the land including the reference point of the measured pattern corresponding to the reference point P0 is R1. Since the pattern B1 connected to the land R1 extends obliquely downward to the left from the land R1, the specified direction is set to Dld.

Therefore, the image processing apparatus 4 selects the points of the coordinates X1 and Y1 as the reference points of the pattern to be measured corresponding to the reference point P0 of the master pattern. Then, the image processing apparatus 4 matches the position of the reference point P0 of the master pattern with the reference point of the measured pattern determined as described above (step 207). Thus, the positions of the pattern to be measured and the master pattern can be matched.

In the above description, the alignment using one reference point has been described. However, in actuality, it is necessary to perform the alignment using at least two reference points. Next, the reason why image data is discarded in step 204 will be described with reference to FIG. In the examples of FIGS. 4 and 5, an example has been described in which the pattern connected to the land is inclined with respect to the X direction or the Y direction. However, as shown in FIG. 6A, when the pattern B connected to the land R is parallel to the X direction, a distinct maximum value that can be identified does not appear in the histogram HX for each X coordinate. The accuracy of finding the center is reduced.

Therefore, as shown in FIG. 6 (b), after discarding the data of the area specified by the Y coordinate of the intersection of the pattern edge and the left side of the window W (the hatched portion in FIG. 6 (b)), X If a histogram HX is prepared for each coordinate, a clear maximum value corresponding to the land R can be obtained. Thus, the accuracy of finding the center of the land R can be improved.

If the pattern is parallel to the Y direction, a similar effect can be obtained by discarding data in the area specified by the X coordinate of the intersection of the pattern edge and the top or bottom of the window W. Since a clear maximum value cannot be obtained in the histogram HY after the image data is discarded, the maximum value of the histogram HY created before discarding the data is used.

That is, if the pattern edge crosses the left or right side of the window W and the image data of the area specified by the Y coordinate of the intersection is discarded, the value of the histogram HY corresponding to this area is Use the one created before discarding. Similarly, when the pattern edge intersects the top or bottom of the window W and discards the data in the area specified by the X coordinate of the intersection, the data of the histogram HX corresponding to this area is discarded. Use the one created earlier. Finally, the image processing apparatus 4 compares the measured pattern with the master pattern, inspects the measured pattern, and passes the inspection result to the host computer 5. The host computer 5 displays the inspection result on the display device 6 (Step 105 in FIG. 1).

Embodiment 2 FIG. 7 is a flowchart showing a positioning process according to another embodiment of the present invention;
FIG. 8 and FIG. 9 are diagrams for explaining this positioning process. Also in the present embodiment, processes other than the alignment are the same as those in the first embodiment, and thus only the alignment process will be described.

FIG. 8A shows a part of the master pattern, and the corner of the pattern is predetermined as a reference point P0 for positioning. At this time, a pattern having the largest area is used as a pattern for arranging the reference point P0. First, the image processing apparatus 4 aligns the master pattern with the entire pattern to be measured (step 30 in FIG. 7).
1) A window W as shown in FIG. 8B at a position corresponding to the reference point P0 of the master pattern is cut out from the binary image of the pattern to be measured (step 302).

Subsequently, the image processing device 4 sets the window W
The pattern C having the largest area is selected from the patterns in (step 303). Then, the image processing device 4
As shown in FIG. 9A, a straight line L connecting the intersection of each of two straight pattern edges E1 and E2 forming an angle in the pattern C and the side of the window W is obtained (step 304). .

At this time, the one that crosses the pattern C is not selected. That is, between intersections a5 and a6, between a7 and a8, a
A straight line L between 5, a7, a5, a8, and a6, a7
It does not become. Next, the image processing apparatus 4 obtains the longest perpendicular line that is perpendicular to the straight line L and reaches the pattern edge from the straight line L in a predetermined direction (step 305).

The designated direction here indicates the direction in which a pattern including the reference point P0 of the master pattern and the reference point of the pattern to be measured exists, and four directions are the same as in FIG. 5C. is there. In the present embodiment, since the pattern C including the reference point of the pattern to be measured corresponding to the reference point P0 exists diagonally downward and leftward from the straight line L, the specified direction is set to Dld.

As a result, a perpendicular line that reaches the pattern edge from the straight line L in the designated direction Dld is obtained. In FIG. 9A, the length of the perpendicular D (the length from the straight line L to the pattern edge) is the longest. The direction in which the perpendicular line is drawn is specified by the pattern C as shown in the example of FIG.
May be present in plural.

Next, as shown in FIG. 9 (c), the image processing device 4 uses a plurality of points on the pattern edges E1 and E2 that are respectively separated from the intersection P between the perpendicular D and the pattern edge by a predetermined distance or more. L1 and L2 are obtained, and the intersection of these two straight lines is set as the reference point of the pattern to be measured (step 30).
6). The distance from the intersection P is, for example, 20 pixels. From the plurality of pixels on the pattern edge E1 separated by 20 pixels or more, a straight line L1 passing through the plurality of pixels is obtained by, for example, the least square method. Similarly, a straight line L2 passing through a plurality of pixels on the pattern edge E2 separated by 20 pixels or more is obtained.

The intersection of the straight lines L1 and L2 is set as a reference point of the pattern to be measured. In FIG. 9, the reference point and the intersection P of the pattern to be measured are the same. However, since the actual pattern edge is not a straight line like E1 and E2 but has undulation, even when the intersection P of the perpendicular D and the pattern edge is obtained, the point P does not always coincide with the reference point. Therefore, straight lines L1 and L2 are obtained as shown in FIG. 9C, and the intersection of these straight lines is set as a reference point of the pattern to be measured.

Then, the image processing device 4 matches the position of the reference point P0 of the master pattern with the reference point of the measured pattern determined as described above (step 307). Note that it is the same as in the first embodiment that it is necessary to perform the alignment using at least two reference points. Also,
In the above embodiment, the master pattern is created from the CAD data. However, the master pattern may be created by capturing an image of the pattern to be measured that is determined to be non-defective.

[0035]

According to the present invention, as described in claim 1, a divided region at a position corresponding to the reference point of the master pattern is extracted from the image of the pattern to be measured, and the number of pixels for each X, Y coordinate is determined. First and second histograms are created, and a point at which both the first and second histograms show the maximum value is set as a candidate for the reference point of the pattern to be measured, and the direction of the pattern connected to the land including the candidate point is determined. The candidate point in the direction specified in advance and closest to the reference point of the master pattern is set as the reference point of the pattern to be measured, and the positions of the reference point of the master pattern and the reference point of the pattern to be measured are aligned, so that the master pattern and the pattern to be measured are aligned. The alignment of the measurement pattern can be performed. Therefore, since the center of the land can be used as a reference point for positioning, positioning can be performed even for a pattern in which no positioning mark is provided.

Further, as described in claim 2, a divided area at a position corresponding to a reference point of a master pattern is extracted from an image of a pattern to be measured, and a pattern having the largest area is selected, and a corner is formed in this pattern. A straight line connecting the intersection of the pattern edge and the side of the divided area is obtained, and the longest perpendicular to the pattern edge is determined from this straight line in a direction designated in advance, and a predetermined line is obtained from the intersection of the perpendicular and the pattern edge. A straight line is obtained from a plurality of points on the pattern edge separated by a distance or more, the intersection of the two straight lines is used as a reference point of the pattern to be measured, and the reference point of the master pattern is aligned with the reference point of the pattern to be measured. And the pattern to be measured can be aligned. Therefore, since the corner of the pattern can be used as a reference point for alignment, alignment can be performed even for a pattern in which no positioning mark is provided.

[Brief description of the drawings]

FIG. 1 is a flowchart illustrating a pattern inspection method according to a first embodiment of the present invention.

FIG. 2 is a block diagram of a pattern inspection apparatus.

FIG. 3 is a flowchart illustrating a process of aligning a pattern to be measured with a master pattern.

FIG. 4 is a diagram for explaining a process of aligning a pattern to be measured and a master pattern.

FIG. 5 is a diagram for explaining a process of aligning a measured pattern and a master pattern.

FIG. 6 is a diagram for explaining a process of aligning a measured pattern and a master pattern.

FIG. 7 is a flowchart illustrating a positioning process according to another embodiment of the present invention.

FIG. 8 is a diagram for explaining a process of aligning a measured pattern and a master pattern.

FIG. 9 is a diagram for explaining a process of aligning a pattern to be measured with a master pattern.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Green sheet, 2 ... XY table, 3 ... Line sensor camera, 4 ... Image processing apparatus, 5 ... Host computer, 6 ... Display device.

Continuation of front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G01B 11/00 G06T 7/00

Claims (2)

(57) [Claims] 1. A pattern inspection method for inspecting a pattern to be measured by comparing a master pattern as a reference with a pattern to be measured imaged by a camera, wherein the center of the land is a reference point for positioning and the master pattern and the measured pattern are measured. A positioning method for performing pattern positioning, comprising extracting a predetermined-sized divided region at a position corresponding to a reference point of a master pattern from an image of a pattern to be measured, and determining the number of pixels for each X coordinate in the divided region And a second histogram indicating the number of pixels for each Y coordinate is generated. A point at which both the first and second histograms have a local maximum corresponds to a reference point of the master pattern. As a reference point candidate for the pattern to be measured, the direction of the pattern connected to the land containing the candidate point is the direction specified in advance, and The candidate point closest to the reference point of the pattern is set as the reference point of the pattern to be measured, and the master pattern and the pattern to be measured are aligned by aligning the reference point of the master pattern with the reference point of the pattern to be measured. The alignment method of the pattern. 2. A pattern inspection method for inspecting a pattern to be measured by comparing a master pattern as a reference with a pattern to be measured imaged by a camera, wherein a corner of the pattern is used as a reference point for positioning and the master pattern and the pattern to be measured. This is a positioning method for performing pattern alignment, in which a predetermined size of a divided region at a position corresponding to a reference point of a master pattern is extracted from an image of a pattern to be measured, and a pattern having the largest area in the divided region is determined. A straight line connecting the intersections of two straight pattern edges forming an angle in this pattern and the sides of the divided area is obtained,
From the straight line, the longest perpendicular line that reaches the pattern edge in a direction designated in advance and that is perpendicular to the straight line is obtained. On the pattern edge that is at least a predetermined distance from the intersection of the perpendicular line and the pattern edge, A straight line is obtained from each of a plurality of points, and the intersection of the two straight lines is used as a reference point of the pattern to be measured. By aligning the reference point of the master pattern with the reference point of the pattern to be measured, the master pattern and the pattern to be measured are aligned. Performing a pattern alignment.