JPS6024510B2 - pattern inspection equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a pattern inspection apparatus that is capable of inspecting only a portion of a two-dimensional pattern.

Conventionally, optical, electrical, magnetic, and other physical information (this is collectively referred to as pattern information, and hereinafter abbreviated as pattern) is composed of a two-dimensional array.

) is commonly used for pattern inspection and the like. Common types of processing equipment of this type are:
A video input device such as a television camera that sequentially scans a two-dimensional pattern and converts it into an analog time series signal, a binarization circuit that digitizes this analog signal, and a division system that samples and spatially divides this digital signal. It is equipped with a circuit and a storage circuit that stores the main part of the divided digital signal, that is, the pixel signal, and is mainly used for identifying patterns, inspecting defects in patterns, etc. There are a wide variety of patterns that are subject to the pattern inspection, but conventionally it has been sufficient to inspect the entire pattern, such as a label attached to an article.

In recent years, as the performance of this type of equipment has improved, its uses have gradually expanded, and it has come to be used to inspect precision products such as semiconductor products, but this type of equipment is inherently susceptible to slight defects. Even if it does exist, it often consists of parts that have a large effect on all functions and parts that do not. In addition, for products that have a parallel redundant configuration in advance for anticipated defects, even if a defect is found in a certain part, it may be considered that the corresponding specific part is deemed to have passed the test if there is no defect. It may be necessary to know the detailed distribution of defects. Conventionally, a pattern enlargement/reduction process has been used as a method of limiting the inspection portion.

For example, when inspecting only the outer periphery of a pattern, the stored original pattern is reduced to an appropriate size, the pixel signals of this reduced pattern and the pixel signals of the original pattern are ANDed, and the result is "0". The configuration may be such that the defect inspection is performed only on the portion where the logic output of "1" is obtained, that is, the outer periphery of the original pattern.Conversely, in the above case, it is possible to have a configuration where the defect inspection is performed only on the portion where the logic output of "1" is obtained. , only the inside of the original pattern can be inspected. Since such area-limiting techniques are mainly achieved by hardware means, they have the disadvantage of complicating the circuitry. Therefore, if you try to extend the follow-up technology as it is when defining a region with a crowded shape or when defining a large number of regions that are separated from each other, a huge amount of hardware will be required and it will not be economically viable. It becomes difficult. The present invention has been made in view of the above-mentioned conventional problems, and its purpose is to provide a pattern inspection device that can inspect a two-dimensional pattern by limiting it to a portion thereof with a simple configuration. Our goal is to provide the following. Hereinafter, details of the present invention will be explained with reference to the drawings. The pattern inspection apparatus of the present invention can be used to inspect various patterns, but as an example, a pattern in which aluminum electrodes are formed concentrically on a circular silicon substrate will be described as shown in FIG.

In FIG. 1, a is a plan view of the inspection pattern 100, and b is a plan view of the inspection pattern 100.
is its QQ′ cross-sectional view, 101 is a silicon substrate, 1
Reference numerals 02, 103, 104, and 105 are Al electrodes formed on the substrate in concentric circles. In a normal product, electrode 10
All of Nos. 2 to 105 are matted so as not to cause specular reflection. The pattern to be inspected includes a black defect 106 and a white defect 107, as illustrated. Using a video input device such as a television camera, the surface of the pattern to be inspected is scanned from above, and defects are inspected based on the time-series video signals obtained as a result. FIG. 3C shows a scanning output signal on the QQ' line in a, which includes a concave waveform 106' of the video output corresponding to the black defect 106 and a protrusion waveform 107' of the video output corresponding to the white defect 107, respectively. The present invention can detect the presence or absence of this type of defect with high accuracy. The present invention will be explained below with reference to an embodiment shown in FIG. A video input device 204 such as a television camera two-dimensionally scans the surface of the pattern to be inspected 201 and outputs a time-series analog video signal corresponding to the brightness and darkness of the surface. 202 is an illuminator that illuminates the pattern to be inspected.

When the position detector 203 composed of a photoelectric switch, a proximity switch, etc. detects that the pattern to be inspected 201 has arrived within the visual field of the video input device 204 and has stopped, it sends a detection signal to the control circuit 229 and the progress counter 228. send and start both of them. The activated control circuit 229 generates a sequence of pattern tests. The progress counter 228 counts the number of imaging functions required to synchronously execute the processing except for the processor. The burn to be inspected 201 is connected to a video input device 204 (hereinafter abbreviated as "camera 204", represented by a television camera).

), the camera 204
The video signal is output to the amplifier 205. Here, the predetermined rise time means that when there is no pattern within the camera field of view, the amount of light incident on the camera is small, but when a pattern arrives within the field of view, it increases rapidly and settles down to a certain camera sensitivity as shown in Figure 4. However, in this case, it refers to a predetermined number of fields (several screen scanning periods). With this device,
In order to detect defects with high precision, each process is executed after a certain level of camera sensitivity is obtained. The analog video signal amplified by the amplifier 205 is quantized in amplitude by the binarization circuit 206, which has a value intermediate between the output levels corresponding to each of the pattern and background included in the object, and the pattern is " It is converted into a digital signal in which the signal is "1" and the background is "0". To ensure that this kind of digitization can be performed reliably, a background with a large contrast to the pattern should be selected. For example, if the pattern is dark, choose a whitish background, and if the pattern is whitish, choose a black background. Select each. This digital signal is sampled in a quantization circuit 207,
A quantized signal that is also spatially quantized is supplied to the pattern edge detection circuit 208 . Pattern edge detection circuit 20
8 is the tip of the pattern where the quantized signal changes from the background to the pattern. ) and the transition point from the pattern to the background (referred to as the "pattern trailing edge"). is detected and a detection signal is sent to the pattern machine memory 209. A specific example of the pattern end detection circuit 208 is a combination of a shift register having an appropriate number of stages and capable of parallel output from each stage, and a logic circuit that performs logical operations on the combination of these parallel outputs. . An example of the total pattern detection circuit 208 configured in this way is such that a predetermined number of "0"s continuously exist in the first half of the shift register in the shift direction, and a predetermined number of "1s" continuously exist in the second half. When the pattern reaches the tip, it is detected and a tip detection signal is output. Similarly, the pattern end detection circuit 208 detects a predetermined number of "1"s in the first half of the shift register in the shift direction.
exists continuously and a predetermined number of "0"s exist in the latter half, it is detected that the trailing edge of the pattern has arrived, and a trailing edge detection signal is output. The scan position counter 231 receives a scan synchronization signal from the scan synchronization signal generation circuit 227 and supplies a scan position signal indicating the horizontal and vertical positions of the scan point of the camera 204 to the pattern end memory 209 . The pattern edge memory 209 takes in the above-mentioned scanning position signals when receiving the pattern leading edge signal and pattern trailing edge signal from the pattern edge detection circuit 208, and stores these signals as pattern leading edge coordinates and pattern trailing edge coordinates on the scanning surface, respectively. Record. The processor 230 stores the pattern edge memory 2
The pattern end coordinates are read from 09 and the pattern position is calculated by filling them.

If the pattern shape is circular as shown in Figure 1, calculate the center coordinates of the pattern from the edge of the pattern,
It is detected how much the pattern to be inspected 201 has deviated from the reference position and stopped. If the pattern shape is an arbitrary shape with poor rotational symmetry, the center of gravity of the pattern or an appropriate point similar to it is determined in advance, and the coordinates of the point are compared to locate the pattern to be inspected 201 at the reference position. Detect how much deviation from the stop occurs. Subsequently, the processor 230 uses the stop position deviation information to correct the pattern end coordinates of one or more reference level sampling area patterns stored in the reference level sampling area memory 214. The above pattern represents a region of stable, non-uniform bells that serves as a reference level on the object to be inspected. The above pattern is stored in a normalized position on the reference level sampling area memory 214. In the modification of the pattern machine described above, as illustrated in FIG.
' is shifted by the stop position deviation (0→0'). When modifying the pattern end seat collar, use memory 21.
If each pattern information of the normal position stored on the pattern information is directly corrected at the time of inspection, it will be difficult to use it at the time of the next judgment.

As an example of correcting and reading out information in memory without destroying it, the vertical position of the screen is taken as an address, the pattern edge width at that vertical position is stored as the content of that address, and when reading, an adder/subtractor is used to read out the vertical position. The configuration is such that an offset corresponding to the address is added. In this case, the same configuration is applied to the pattern end coordinates in the horizontal direction. The reference level sampling area memory 214 similarly stores the rear end coordinates from the time when the scanning position signal received from the scanning position counter 231 in synchronization with the subsequent screen scan matches the leading edge coordinates of the reference level sampling area pattern stored by itself. A sampling signal of a predetermined period is output over a period up to the point of coincidence.

This sampling signal is applied to a video signal integration circuit 210 and a sampling time integration circuit 211. The video signal integration circuit 210 integrates the video signal of the camera 204 over the sampling time, and divides the video signal into the division circuit 212.
Output to. The sampling time integration circuit 211 divides an output proportional to the sampling time into a division circuit 212.
Output to. The division circuit 212 divides the integral value of the input video signal by the sampling time and outputs the quotient to the level holding circuit 213. The above integration circuit 210, 21 1
is reset at the start of every screen scan. After the reference level sampling area pattern memory 214 is corrected, the above processing is executed during the subsequent one screen scanning period, and the level holding circuit 213 holds the output of the division circuit 212 at the end of the one screen scanning period.

The entire circuit constituted by the integrating circuits 210, 211, the dividing circuit 212, and the level holding circuit 213 functions to obtain the reference level of the object to be inspected, that is, the average video signal level of the area to be inspected. This also includes DC changes in floor current due to temperature of the camera signal. Above mentioned bell holding circuit 2
13 is input to one input terminal of the differential amplifier circuit 216.

The amplifier 205 is connected to the other input terminal of the differential amplifier circuit 216.
The video signal from is input. When the average level calculation for the reference level sampling area is completed, in the subsequent screen scan, the differential amplifier circuit 216 detects that the signal in the reference level area on the object to be inspected becomes low, and the level lower than this becomes negative. Conversely, the video signal is level-shifted and output so that the higher level becomes positive. The output of the differential amplifier circuit 216 is supplied to comparison circuits 217 and 221. The comparison circuit 217 detects the presence of a white defect as exemplified by the waveform 107 in FIG. On the other hand, the comparator circuit 222 detects the presence of a black defect as exemplified by the waveform 106' in FIG.
is supplied to one input terminal of the Inspection area limited memory 21
5 stores one or more pattern edge coordinates specifying an inspection area on the object to be inspected.

The pattern end position is shifted and corrected by the amount of the stop position deviation until the average level of the reference level sampling area is obtained on the same plane as the reference level sampling area pattern. The contents of the reference level sampling area memory 214 and the inspection area limited memory 215 may match. In the subsequent screen scan after the average level of the reference level sampling area is obtained, the inspection area limitation memory 215 stores the scanning position signal received from the scanning position counter 231 as an inspection limitation corrected for the accumulated stop position deviation. Continuous "
1'' signal is generated and supplied to AND circuits 219 and 223.

Therefore, only those generated within the limited inspection area among the quantized defect detection signals are transmitted to the AND circuits 219 and 22.
3 and input to defect integration circuits 220 and 224. The defect integration circuits 220 and 224 integrate the input defect detection signals. These integration results are read by the processor 2301 at the end of a valid screen scan, and if necessary, generate another reference level sampling area pattern to calculate a new average reference level, or create a new inspection area limiting pattern. When the necessary inspection of the object to be inspected is completed, the processor 23
0 is an example of a process that processes defect information and outputs it to the outside.The allowable number of defects for each inspection limited area is stored in advance, and the detected number and allowable number are compared for each inspection area. It is also possible to adopt a configuration in which the pass/fail determination result is output to the outside via the interface circuit 226.

Next, the pattern inspection process according to the present invention will be explained in detail with reference to FIG.

First, assuming that the field of view of the camera 204 is as shown by 300, and assuming that the pattern to be inspected 301 (center coordinates 0) is located within the field of view 300, the area surrounded by broken lines 302 and 303 is defined as a reference level sampling area. is stored in the reference level sampling area memory 214.

Furthermore, if the inspection areas are 304 and 305, these areas are stored in the inspection area limited memory 215. Assume that after performing such processing, actual pattern inspection begins, and the actual pattern to be inspected 301' (center coordinates 0') stops at a shifted position within the field of view 300. The video signal of the pattern to be inspected 301' is transmitted through the amplifier 205 and the binarization circuit 206.
, pattern edge detection circuit 208 via the quantization circuit 207
A change point in the pattern is detected, and the coordinates of this change point are written into the pattern machine memory 209. The processor 23 reads the pattern edge coordinates from the pattern edge memory 209, and based on this, determines the pattern position, for example, in the example of FIG. 3, the center coordinate 0' of the pattern to be inspected 301'.
Calculate. Furthermore, the processor 230 calculates the positional deviation between the patterns to be inspected 301' and 301. Further, the video signal from the camera 204 is applied to the video signal integration circuit 210 via the amplifier 205, and integration is performed only during the period when the signal is applied from the reference level sampling area 214, but in this case, the broken line 302, When the video signal in the area surrounded by 303 is integrated by the video signal integrating circuit 210, the video signal in the area outside the pattern to be inspected 301' is also integrated, making it impossible to measure the correct reference level. Therefore, as described above, the processor 230 calculates the deviation (0 → 0') between the patterns to be inspected 301 and 301', corrects the area output from the reference level sampling area memory 214 by this deviation, and actually 302, 303
By performing integration in the video signal integration circuit 210 as a region surrounded by , a correct reference level is determined using the sampling time integration circuit 211, the division circuit 212, and the level holding circuit 213. The reference level held by the level holding circuit 213 is applied to the differential amplifier 216 together with the video signal amplified by the amplifier 205, and after the difference is amplified, it is applied to the comparators 217 and 221 to detect black and white defects. is detected. However, this comparator 217,2
Since the output signal 21 is a video signal from the entire field of view of the camera 204, it also includes signals outside the pattern to be inspected 301' and signals from unrelated portions within the pattern to be inspected 301'. However, black and white defects are detected only in a limited area.
Inspection areas 304 and 305 of inspection area limited memo IJ215
If this continues, an unrelated part of the pattern to be inspected 301' will be inspected, so the inspection area limited memory 215
The area output from is corrected by this deviation to create area 30.
', 105'. As a result, the pattern to be inspected 30
The defect integration circuit 220 detects only the defects in the correct inspection area of 1'.
, 224. In this way, according to the apparatus of the present invention, it is possible to easily define an arbitrary shape and an arbitrary number of inspection areas, so that detailed inspection can be performed.

For example, in the semiconductor device illustrated in FIG. 1, if each electrode is formed in a separate process, the quality of each process can be determined separately by inspecting each electrode for defects. Furthermore, the number of defects in each electrode is determined first-in.
It is also possible to store the information in a first-out memory, perform statistical processing after the pass/fail judgment is completed, detect abnormalities in the manufacturing process of the object to be inspected, and abnormalities in the inspection equipment, and issue an alarm to the outside. . Furthermore, in one embodiment of the present invention, since the video signal and its reference level are compared by continuous screen scanning, it is possible to completely eliminate direct current fluctuations due to temperature characteristics of the camera, etc.

[Brief explanation of the drawing]

Fig. 1 is a conceptual diagram for explaining the operation of a general pattern inspection device, Fig. 2 is a functional block diagram of an embodiment of the present invention, and Fig. 3 is a conceptual diagram for explaining the operation of Fig. 2. Conceptual diagram,
FIG. 4 is a diagram showing the rise characteristics of the television camera. loo, 201... Pattern to be inspected, 204... Television camera, 208... Pattern edge detection circuit, 209
...Pattern end memory, 214...Reference level sampling area memory, 215...Inspection area limited memory, 220...Defect integration circuit, 230...Processor. Figure 1 Figure 3 Figure 4 Figure 2

Claims (1)

[Claims] 1. A video input device that sequentially scans a two-dimensional pattern that has stopped after arriving at the inspection space and converts it into a time-series signal, a means for detecting pattern end coordinates from the time-series signal, and a reference stop position of the pattern stop position. means for detecting a deviation from the pattern end coordinates based on the pattern end coordinates; means for storing a reference level sampling area; correcting the reference level sampling area according to the stop position deviation; means for sampling a reference level from a two-dimensional pattern; means for quantizing the time-series signal with reference to the reference level; means for storing an inspection limited area; A pattern inspection apparatus comprising: means for correcting and outputting the quantized signal within the corrected limited area.