JPS6412383B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method and apparatus for inspecting patterns on photomasks for printed circuit boards. Conventionally, printed circuit boards are created by creating a photomask from an original plate and then subjecting it to development and fixing processing. In this case, defects such as small conductor widths, small conductor spacings, black spots, pinholes, protrusions, and chips occur on the pattern due to dust in the developer or contact with the substrate during pattern formation. Conventionally, such defects have been detected and corrected by visual inspection using a stereomicroscope or the like. However, as photomask patterns have become increasingly finer and denser in recent years, conventional visual inspections are no longer sufficient to detect defects, and inspections using scanning light beams, electron beams, etc., have become necessary. . An example of inspection using light beams, electron beams, etc. is "Print board mask inspection device using laser light" by Yuji Inagaki et al.
(OPTRONICS magazine, No. 6, 1982). This content uses two types of SMART methods: the length measurement method for detecting line width defects and the SMART method for random defect detection, and the latter SMART method is similar to the present invention in terms of local area processing. However, if there is even one bit different from the others within 100 microns of the pattern, it is considered a defect. For this reason
There is a problem that defects with a maximum value of 100 microns cannot be detected. Another example is Nobuyuki Goto, “A Method of Mask Pattern Inspection” (Television Society Technical Report, 1977, Vol. 1, No. 3).
has been disclosed. In this case, a 3x3 matrix method is used to measure the pattern width and gap for line width detection, and to detect minute defects.
The latter 3x3 matrix method is similar to the present invention in that it processes local areas, but it has the problem that it only checks 3x3 pixels and can only detect defects smaller than this. Therefore, methods are being sought to more accurately perform inspections by scanning with light beams, electron beams, or the like. In view of the above-mentioned background, it is an object of the present invention to be able to inspect the minimum conductor width and minimum conductor spacing, which are inspection standards, by processing only a local area, and furthermore, to not detect defects even though they are not normal. It is an object of the present invention to provide a method and apparatus for inspecting a photomask that can exclude defects from defects. According to the present invention, the image data obtained by reading a photomask with a scanner is used to detect two sets of pixels for inspecting the minimum conductor width and the minimum conductor spacing, which are inspection standards for the photomask. The 17 pixels consisting of the apex coordinates and center coordinates of the octagon are used as the measurement unit, and each pixel of the eight apex coordinates of the outer octagon is used to test the minimum conductor width. A state where the value corresponds to a non-conductor part, and the pixel opposite in the vertical direction of the opposing pixel and the pixel at the center coordinate of the octagon all have a value corresponding to the conductor part, and the 8 inner octagons. Each pixel at the apex coordinates of is used to test the minimum conductor spacing, and the values of the opposing pixels among these pixels correspond to the conductor part, and the values of the pixels that are opposite in the vertical direction of the opposing pixels and the center coordinates of the octagon are This is achieved by providing a photomask inspection method characterized by detecting a state in which all pixels have a value corresponding to a non-conductor portion, and further, according to the present invention, the photomask is moved in the X-Y direction. a scanner for scanning the pattern of the photomask projected by the optical means and outputting image data corresponding to the brightness and darkness of the pattern; and 2 for binarizing the image data output by the scanner. a digitization means, a storage means for storing the image data binarized by the binarization means as bit/pixel data, and a predetermined number of pixels from among the bit/pixel data stored in the storage means. Using each pixel at the apex coordinates and center coordinates of the two sets of octagons formed by There is a state in which the opposing pixels all have values corresponding to non-conductor parts, and the pixels opposite in the vertical direction of the opposing pixels and the pixel at the center coordinates of the octagon all have values equivalent to the conductor parts. Each pixel at the coordinates of eight vertices of a certain octagon is used to inspect the minimum conductor spacing, and the pixels that are opposite to each other among the pixels have values corresponding to the conductor part, and the pixels that are opposite in the vertical direction of the opposite pixels and A detection means for detecting a state in which all pixels at the center coordinates of an octagon have a value corresponding to a non-conductor portion, a display means for displaying a result detected by the detection means, and an operation of the scanner and each means. This is achieved by providing a photomask inspection apparatus characterized by comprising a control section that performs control. Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing an apparatus for implementing the photomask inspection method according to the present invention. In FIG. 1, 1 indicates a photomask which is a sample to be inspected, 2 indicates an automatic feeding means for moving the photomask 1 on an X-Y stage, and 3 indicates an optical means for projecting the pattern of the photomask 1. Reference numeral 4 denotes a scanner which outputs the photomask pattern projected by the optical means as image data corresponding to the brightness and darkness of the pattern, and uses, for example, a line scan type solid-state imaging device. Further, 5 is a binarization means that binarizes the image data outputted by the scanner after correcting the variation between the solid-state image sensors since the image data is included in the image data.
6 is 1 bit/bit binarized by the binarization means.
It is a storage means for storing image data of pixels as bit/pixel data, and 7 reads out the bit/pixel data sequentially to detect defects in the pattern, and when it is determined to be a defective part, records its position coordinates and stores it in the photo mask. 1 is a detection means that outputs an output after the completion of the entire test, and each consists of a plurality of AND circuits, OR circuits, and NOR circuits. Reference numeral 8 denotes a display means for displaying the coordinates of the position determined to be a defective portion by the detection means, and for example, an X-Y plotter is used. Reference numeral 9 denotes a control unit that controls the operation of each of the means 2 to 8 described above. In such a configuration
- The defective portion of the photomask is corrected by comparing the output diagram showing the defective portion finally shown on the Y plotter 8 with the aforementioned photomask. FIG. 2 is a layout diagram showing the arrangement of pixels for carrying out the photomask inspection method according to the present invention. In Figure 2, a1 to d4 and m are located at the vertex coordinates and center coordinates of two sets of octagons.
It is a measurement unit consisting of 17 pixels. The minimum conductor width is tested by each pixel at the eight vertex coordinates of the outer octagon and the pixel at the center coordinate, and the minimum conductor spacing is checked by each pixel at the eight vertex coordinates of the inner octagon and the pixel at the center coordinate. will be inspected. The positions of pixels corresponding to each measurement unit are as follows. a1 is (i-10, j), a2 is (i-7, j) a3 is (i+6, j), a4 is (i+10, j) b1 is (i, j-10), b2 is (i, j -7) b3 is (i, j+6), b4 is (i, j+10) c1 is (i-7, j+7), c2 is (i-4, j
+4) c3 is (i+5, j-5), c4 is (i+7, j
-7) d1 is (i-7, j-7), d2 is (i-5, j
-5) d3 is (i+4, j+4), d4 is (i+7, j
+7) m is (i, j), and as mentioned above, a1, a4,
b1, b4, c1, c4, d1, d4 are conductor widths,
a2, a3, b2, b3, c2, c3, d2, d
3 is for inspecting conductor spacing. In this example, the minimum conductor width is used as the inspection standard.
200 μm and the minimum conductor spacing is 130 μm, so if the image data is input at 10 μm/pixel, the conductor width is 19 pixels or less and the conductor spacing is 12 pixels or less as a defect. In the diagonal direction, the conductor width is 19/√2≒
A defect is defined as 13 pixels or less and conductor spacing of 12/√2≒8 pixels or less. However, the number of pixels needs to be changed depending on the reading unit (μm/pixel) of image data and the inspection standard. In this example, the second
As shown in the figure, two pixels are added. Further, it is assumed that 1 in the image data corresponds to a conductor portion and 0 corresponds to a non-conductor portion. Regarding the conductor width in the vertical and horizontal directions in the drawing, a1, a
4, b1, b4 measurement units are inspected, a1, a4
are all 0, and b1, b4, and m are all 1
When , the conductor width can be determined to be 19 pixels or less. Regarding the conductor spacing in the vertical axis direction, a2, a3, b2, b3
Inspect. a2 and a3 are both 1, and b
When 2, b3, and m are all 0, it can be determined that the conductor spacing is 12 pixels or less. Other directions can be similarly inspected using other measurement units. 3a and 3b are detailed circuit diagrams of the detection means 7 in the photomask inspection apparatus according to the present invention. FIG. 3a shows a circuit for testing the conductor width in two directions, and FIG. 3b shows a circuit for testing the conductor spacing in two directions, and the present invention requires circuits for four directions. In FIG. 3a, NOR circuit 11(1) outputs 1 when measurement units 10(1) and 10(2) are both 0. In FIG. NOR circuit 11 (2) is measurement unit 1
When both 0(3) and 10(4) are 0, 1 is output. AND circuit 12(1) has a unit of measurement of 10
When (1), 10(2), and 10(5) are all 1, 1 is output. AND circuit 12(2) outputs 1 when measurement units 10(3), 10(4), and 10(5) are all 1. AND circuit 13(1) outputs 1 when both NOR circuit 11(1) and AND circuit 12(2) are 1. AND circuit 13 (2)
outputs 1 when both the NOR circuit 11(2) and the AND circuit 12(1) are 1. The OR circuit 14 outputs 1 when either of the AND circuits 13(1) and 13(2) is 1, and determines that the conductor width is small. The NOR circuit 16(1) in FIG. 3b has a unit of measurement of 15
When (1), 15(2), and 15(5) are all 0, 1 is output. NOR circuit 16 (2) has a measurement unit of 1
When 5(3), 15(4), and 15(5) are all 0, 1 is output. AND circuit 17(1) is 1 when measurement units 15(1) and 15(2) are both 1.
Output. AND circuit 17(2) is measurement unit 1
When both 5(3) and 15(4) are 1, 1 is output. AND circuit 18 (1) is NOR circuit 16
(1) and AND circuit 17 (2) both output 1 when they are 1. AND circuit 18 (2), NOR circuit 16 (2) and AND circuit 17 (1) are both 1
Outputs 1 when . The OR circuit 19 outputs 1 when either of the AND circuits 18(1) and 18(2) is 1, and determines that the conductor spacing is small. The relationship between the units of measurement in FIGS. 2 and 3 is shown in the table below.

[Table] Examples inspected by the photomask inspection method according to the present invention will be explained with reference to FIGS. 4a to 4i. The shaded portion in FIG. 4 is a conductor portion, and the other portions are non-conductor portions. In FIG. 4a, the conductor width is small (19 pixels) in the horizontal direction. Both measurement units b1 and b4 are 0, and a
Since 1, a4, and m are all 1, it can be determined that the defect has a small conductor width. In FIG. 4b, the conductor spacing is small (12 pixels) in the horizontal direction. Both measurement units b2 and b3 are 1,
Since a2, a3, and m are all 0, it can be determined that the defect has a small conductor spacing. In FIG. 4c, the conductor width is small (13 pixels) in the diagonal direction. Both measurement units d1 and d4 are 0, and c
Since 1, c4, and m are all 1, it can be determined that the defect has a small conductor width. In FIG. 4d, the conductor spacing is small (8 pixels) in the diagonal direction. The units of measurement d2 and d3 are both 1 and c
Since 2, c3, and m are all 0, it can be determined that the defect has a small conductor spacing. In Fig. 4e, the conductor width is small for three pixels (19 pixels) due to chipping. In this case, the determination can be made in the same manner as in FIG. 4a. In FIG. 4f, the conductor spacing is small (12 pixels) for three pixels due to the protrusion. In this case, the determination can be made in the same manner as in FIG. 4b. In FIG. 4g, the conductor spacing is small (12 pixels) for three pixels due to black dots. In this case, the determination can be made in the same manner as in FIG. 4b. In Fig. 4h, the conductor width is reduced by three pixels (18 pixels) due to the pinhole. In this case, the determination can be made in the same manner as in FIG. 4a. The pattern i in FIG. 4 is a normal pattern but has irregularities caused by binarization, or it is not a normal pattern but cannot be detected as a defect. Such a pattern is detected as a defect only when the conductor spacing is small due to the recesses or the conductor width is small due to the protrusions. In this case, in this embodiment, it is not determined as a defect. As described above in detail, by using the photomask inspection method and apparatus according to the present invention, pattern defects can be accurately detected.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the photomask inspection apparatus according to the present invention, FIG. 2 is a layout diagram showing the arrangement of measurement units for carrying out the photomask inspection method according to the present invention, and FIG. Figures a, b
1 is a circuit diagram showing in detail the detection means in the apparatus shown in FIG. 1, and FIGS. 4 a to 4 i are diagrams illustrating an example of inspecting a photomask in the measurement unit of the arrangement shown in FIG. 2. (Explanation of symbols), 1...Photomask, 2...
Automatic feeding means, 3... Optical means, 4... Scanner, 5... Binarization means, 6... Storage means, 7...
Detection means, 8...Display means, 9...Control unit, a1
~d4,m,10(1)~10(5),15(1)
~15(5)...Unit of measurement, 11(1), 11
(2), 16(1), 16(2)...Nor circuit, 1
2(1), 12(2), 13(1), 13(2), 1
7(1), 17(2), 18(1), 18(2)...
...AND circuit, 14,19...OR circuit.

Claims (1)

[Scope of Claims] 1. Image data obtained by reading a photomask with a scanner is analyzed using two sets of octagonal pixels each consisting of pixels for inspecting the minimum conductor width and minimum conductor spacing, which are inspection standards for the photomask. The 17 pixels consisting of the vertex coordinates and center coordinates are used as the measurement unit, and each pixel of the eight vertex coordinates of the outer octagon is used to inspect the minimum conductor width. A state in which the pixels opposite in the vertical direction of the opposing pixels and the pixel at the center coordinates of the octagon both have values corresponding to the conductor part, and the coordinates of the eight vertices of the inner octagon. Each pixel is used to test the minimum conductor spacing, and the values of the opposing pixels among the pixels correspond to the conductor part, and the pixels that are opposite in the vertical direction of the opposing pixels and the pixel at the center coordinates of the octagon are 1. A method for inspecting a photomask, comprising: detecting a state in which a value corresponding to a non-conductor portion is detected. 2 automatic feeding means for moving the photomask in the X-Y direction; a scanner for scanning the pattern of the photomask projected by optical means and outputting image data corresponding to the brightness and darkness of the pattern; Binarization means for binarizing the image data, storage means for storing the image data binarized by the binarization means as bit/pixel data, and bit/pixel data stored in the storage means. Using each pixel at the vertex coordinates and center coordinates of two sets of octagons made up of a predetermined number of pixels from the data as a measurement unit, each pixel at the eight vertex coordinates of the outer octagon is the minimum conductor. The pixels used for width inspection have values that correspond to non-conductor parts, and the pixels opposite in the vertical direction of the opposite pixels and the pixel at the center coordinates of the octagon both correspond to conductor parts. , and each pixel at the coordinates of the eight vertices of the inner octagon is used to test the minimum conductor spacing. a detection means for detecting a state in which pixels facing each other in the vertical direction of the pixels and a pixel at the center coordinates of the octagon both have a value corresponding to a non-conductor portion;
A photomask inspection apparatus comprising: a display means for displaying a result detected by the detection means; and a control section for controlling the operation of the scanner and each means.