JPH0145735B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for inspecting defects in patterns, and more particularly to a method for inspecting defects in reticle patterns used in the manufacture of semiconductor integrated circuits.

One of the current processes for manufacturing integrated circuits is the process of photoetching silicon wafers. That is, a mask is placed on a silicon wafer in close contact with the silicon wafer, and visible light or ultraviolet rays are irradiated from above to perform photoetching. If there is a defect in the mask on which this pattern is printed, the yield of integrated circuit manufacturing will be significantly adversely affected. This mask is formed by depositing a metal film such as chromium on a glass plate that has been polished to a sufficiently flat surface, and then baking a predetermined pattern on it, but if there are pinholes in the metal deposition film, the pattern may be baked in. defects may occur.
Furthermore, even if there are no pinholes in the metal vapor deposited film, there may be defects in the mask after the pattern is baked.

FIG. 1 is a diagram showing a mask for manufacturing an integrated circuit as described above. In FIG. 1, a mask 1 has a large number of chip patterns 3 defined by a large number of scribe lines 2 extending in the vertical and horizontal directions. The patterns of these patterns 3 are made identically.

FIG. 2 is a diagram showing an image of a part of the pattern of the mask 1 on which the pattern has been printed, observed under a microscope. This mask part has no defects and is perfect. The pattern of the mask 1 is composed of transparent parts 4 and opaque parts 5. FIG. 3 is a diagram showing a microscopic observation image of the same pattern portion having a defect. Parts A and B in the figure show the state in which the deposited film remains. In part A, the lands, which should originally be separated, are connected. On the other hand, since the remaining deposited film in portion B is in space, it may not cause a defect in the integrated circuit in some cases. In part C, part of the land is missing. However, since the land has not reached the point where it breaks, it may not cause a failure of the integrated circuit. In portion D, the land is completely cut off, causing a defect.

Conventionally, in order to inspect the above-mentioned mask pattern defects, the applicant has proposed Japanese Patent Publication No. 54-31347,
No. 54-37475 provides an apparatus that can accurately and quickly inspect patterns for defects. However, with the above-mentioned equipment, recent
It has not been possible to obtain sufficient accuracy to remove defects in high-density patterns of ICs, LSIs, etc., especially pseudo-defects that should not originally be determined as defects. Therefore, in Japanese Patent Application No. 56-144740, the applicant has proposed a PG (Pattern) used when creating a mask master plate.
We are developing a device that can perform highly reliable defect inspection by comparing the information stored on a (Generation) tape and the actual pattern produced based on this tape. However, because this device displays a very accurate image of the PG tape pattern, false defects, especially at the corner portions of the pattern, were sometimes determined to be defects when compared with the actual pattern. That is, when forming a pattern, the corners of the pattern are not etched with sufficient accuracy and the corners are usually rounded, which has the disadvantage that false defects are more likely to occur at the corners.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and provide a method for reducing false defects by rounding the corners of a pattern signal from a PG tape used as a reference pattern for comparison.

The present invention detects defects in a pattern of an object to be inspected, particularly defects in a pattern of a mask used for manufacturing semiconductor integrated circuits, using a pattern obtained from reference information read from a recording medium that stores reference information corresponding to the pattern of the object to be inspected. In a defect inspection method that automatically detects defects by comparison, before the comparison, preprocessing is performed to round off corners of patterns that are likely to generate false defects among the patterns represented by the reference information based on the principle of majority voting. By doing so, false defects can be removed and highly accurate defect inspection can be performed.

The present invention will be described in detail below with reference to the drawings.

FIG. 4 is a block diagram showing the overall structure of a pattern defect inspection apparatus for carrying out the pattern defect inspection method of the present invention. The overall configuration is broadly classified into three units: a stage unit 10, a video signal conversion unit 30, and a control unit 40. The operation of each part will be briefly explained below in the order described above.

First, in the stage unit 10, a pattern (for example, a reticle mask, etc.) that is the object 18 is
is irradiated with light from a light source 11, and the transmitted light enters the bit array to obtain scanning data and output it to the control section 40. Light from the archery lamp 11 is incident on an XY stage on which an object to be examined, for example, a reticle mask 18 is fixed. If the transmitted light is directly incident on the bit array of the image sensor 23, there is a problem in the accuracy of obtaining scanning data due to the physical size of the bit array. Therefore, in the present invention, the transmitted light is magnified by, for example, 25 times by an objective lens 17 equipped with an automatic focusing mechanism 14 and projected onto the bit array of the image sensor 23. The automatic focusing mechanism used in this example is the same as the mechanism proposed in Japanese Patent Publication No. 54-31348 by the applicant. The structure of the light receiving bit array consists of a bit array consisting of 1000 elements to convert the received light into scanning data at 1000 points, and a bit array consisting of 12 spare elements at the left end and right end. It has a bit array consisting of a total of 1024 light receiving elements. The bit array was installed to receive light in the X direction, and its width was set to approximately 25 mm, which corresponds to 1 mm above the subject, and the pitch of the bit array was set to 25 μm.
As shown in the figure, scanning is performed by driving the X-Y stage stepwise in the Y direction. Therefore, since the entire screen cannot be scanned in the X direction in one scan, the above-described operation is repeatedly performed. Further, in this case, the actual pattern measurement unit of the reticle or the like is set to 1 μm, but it may of course be set to other values.

The biggest problem when performing this scan is
This is correction in the Y direction. First, when attaching the reticle mask 18 to the X-Y stage in FIG. Attach it so that As mentioned above, the scan is
5. Move the Y table 16 to the step motor 13,1
2, the control in each direction is performed by linear encoders 19 and 20, respectively. That is,
The movements of the X and Y tables 15 and 16 are monitored by linear encoders 19 and 20 and supplied to a stage position collector 21. Here, the deviations in the X and Y directions are compared and a correction signal is sent to each step motor 1.
3 and 12 for correction. Also,
Since this correction alone has a problem in terms of accuracy, especially in the X direction, a correction signal for the amount of deviation in the X direction from the stage position collector 21 is supplied to the image sensor driver 22, and Of the light incident on the bit array, the remaining 12 bits at the left and right ends are used to obtain scanning data at 1000 points, shifted to account for the error.

Next, the video conversion unit 30 shown in FIG. 4 will be explained. Created using CAD system etc.
The PG tape is converted into an inspection reticle tape 31 having the format of this system and supplied to a video conversion unit. This reticle tape 3
1 is attached to the tape unit 32, and then
Under the control of the CPU in the control unit 40, the file corresponding to the reticle mask 18 being inspected on the stage section 10 is read out from the reticle tape 31 via the magnetic tape control section 36, and is read out from the reticle tape 31 through the magnetic tape control section 36. The data is stored in one of the two (magnetic tape memory 33 in the figure). From the coordinate group of points from the reticle tape 31 stored in this magnetic tape memory, the magnetic tape control unit 3
After being converted into an image by a video signal converter 35 under the control of a synchronization signal from 6, the image is stored in one of the two video memories (video memory 38 in the figure). The data stored in the video memory as an image is read out by the video signal output control section 39 in accordance with the portion scanned by the image sensor 23 of the stage section 10 under the control of the magnetic tape control section 36, and then sent to the control unit 4.
0 is input to the comparator 45. The reason why the magnetic tape memory and the video tape memory are provided in two units each as described above is to prevent idle time from occurring due to the output synchronization not matching due to the slow comparison operation in the control unit 40. To explain using the example shown in FIG. 4, data from the reticle tape 31 is stored in the magnetic tape memory 33, and at the same time, data already stored in the magnetic tape memory 34 is converted into an image by a video signal converter and stored in the video memory. 38 and, at the same time, the images already stored in the video tape memory 37 are outputted to the control unit 40 via the video signal output control section 39.

Both outputs from the stage unit 10 and video conversion unit 30 created as described above are as follows.
It is supplied to the control unit 40. Control unit 4
0, both output signals are compared by a comparator 45 in order to detect the defective portion.

A signal after the comparison operation has been completed via the comparator 45 is supplied to a data processing section 47, where various processing is performed. The data processing section 47 is composed of various I/O interfaces, RAM, ROM, CPU, and display section, and the processed data is outputted from the printer 48.

FIGS. 5A to 5C are diagrams showing the principle of the pretreatment method in the pattern defect inspection method of the present invention. A circuit implementing this pattern preprocessing method is provided in the comparator 45 in the control unit 40, and rounds off the corners of the digital data from the PG tape used as a reference during the comparison according to the majority voting principle described below. ing. As shown in FIG. 5, as a pattern preprocessing method of the present invention, the central pixel p(i,
We are considering a 3×3 window in which pixel j) is the pixel to be processed. Here, assuming that black is 1 and white is 0, if the value of the following formula P _{(i, j)} is 5 or more, then black is 4
If it is below, white and pixel (i, j) are determined.

P _(i,j) = ₃ 〓 ^k=1 ₃ 〓 ¹⁼¹ p(i+k-2,j+1-2) For example, in Figure 5 A, B, and C, the value of P _(i,j) are 2, 4, and 2, respectively, and it can be seen that the corner portion shown in FIG. 5B changes from black to white and the corner is rounded. Further, if the target pixel p(i,j) is not a corner, that is, in the case of FIGS. 5A and 5C, the data does not change due to the processing. Furthermore, by changing i and j in order, the entire screen can be preprocessed.

The above-mentioned processing can be easily achieved with a computer software program, but when used in combination with a pattern defect inspection device as shown in Figure 4, the processing speed, especially the data readout speed, will depend on the circuitry of other parts. Since it is significantly slower than , it actually uses a hardware circuit. Figure 6,
FIG. 7 is a circuit diagram for implementing the pattern preprocessing method of the present invention.

In the embodiment shown in FIG.
The video signal read out from the PG tape is supplied to the
This signal is supplied in series to the 1-line delay circuits 61 and 62, and a non-delayed signal, a 1-line delayed signal and a 2-line delayed signal are supplied in series.
Get the line delay signal. The non-delayed signal is supplied in series to 1-bit delay circuits 63 and 64, the 1-line delayed signal is supplied in series to 1-bit delay circuits 65 and 66, and the 2-line delayed signal is supplied in series to 1-bit delay circuits 67 and 68. supply In this way, a non-delayed signal, a 1-bit delayed signal and a 2-bit delayed signal are created for each of the non-delayed signal, 1-line delayed signal and 2-line delayed signal. The 2-line delayed signal, 1-line delayed signal and non-delayed signal are connected to resistors 69, 70 and 71, respectively.
(2 lines + 1 bit) delayed signal,
The (1 line + 1 bit) delayed signal and the 1 bit delayed signal are combined through resistors 72, 73 and 74, respectively, and the (2 line + 2 bit) delayed signal,
(1 line + 2 bits) delay signal and 2 bit delay signal are combined via resistors 75, 76, 77,
These combined signals are further combined and an adder 78
supply to. As a result, the sum P _(i,j) of all the signals within the 3×3 bit window shown in FIG. 5 is obtained. This sum is supplied to a comparator 79 and compared with a reference voltage provided by a potentiometer 80, resulting in a preprocessed video signal at an output terminal 81.
Although in the example described above the values of resistors 69-77 were all equal, they could also have different values in conjunction with appropriate weighting.

The configuration for obtaining the delayed signal in the embodiment shown in FIG. 7 is the same as that in the embodiment shown in FIG. 6, and is indicated by the same reference numeral. In this example, the nine signals thus obtained are supplied to the P-ROM 82.

This P-ROM 82 is programmed in advance with an operation for rounding corners based on the principle of majority voting, so that a preprocessed video signal can be obtained at the output terminal 81. In this example, P-ROM82
The resistors 69 to 77 are omitted because the center pixel P _(i,j) can be weighted by the program inside.

By comparing the standard pattern signal whose angle has been preprocessed and rounded in this way with the video signal obtained by scanning the actual mask, it is possible to suppress the occurrence of false defects at the corners, allowing for highly accurate defect detection. becomes possible.

[Brief explanation of drawings]

FIG. 1 is a plan view showing the configuration of a reticle mask for integrated circuit manufacturing suitable for inspection with a pattern defect inspection device; FIG. 2 is a view showing a microscopic image of a portion of a pattern without defects; 3 is a diagram showing a microscopic observation image of the same part of a defective pattern, FIG. 4 is a block diagram showing the overall configuration of a pattern defect inspection apparatus for carrying out the pattern defect inspection method of the present invention, and FIG. A to C are diagrams showing the principle of the pattern-based defect inspection method of the present invention, FIG.
FIG. 7 shows an embodiment of a circuit for carrying out the pattern defect inspection method according to the present invention. 10...Stage unit, 30...Video signal conversion unit, 40...Control unit, 78...
... Adder, 79 ... Comparator, 82 ... P-
ROM.

Claims (1)

[Scope of Claims] 1 Defects in the pattern of an object to be inspected, particularly defects in the pattern of a mask used in the manufacture of semiconductor integrated circuits, can be detected from reference information read from a recording medium that stores reference information corresponding to the pattern of the object to be inspected. In a defect inspection method that automatically detects a defect by comparing it with a pattern obtained, before the comparison, corners of the pattern where false defects are likely to appear among the patterns represented by the reference information are detected based on the principle of majority voting. 1. A pattern defect inspection method, characterized in that it is configured to perform a highly accurate defect inspection by removing false defects by performing rounding pre-processing. 2. The pattern defect inspection method according to claim 1, wherein the principle of majority voting is carried out using a 3×3 window.