SU955126A1 - Mask flaw recognition device - Google Patents

Description

(54) DEVICE FOR RECOGNITION OF PHOTOSHABLON DEFECTS

one

The invention relates to automation and computing, in particular to devices for recognizing images of planes in systems with line-by-line scanning. Devices for recognizing defects in photomasks are known.

The first of the known devices comprises a scanning beam-type scanning sensor, an optical dividing system, two photoelectric converters, and a subtraction circuit 1.

The disadvantage of this device lies in the low reliability of the recognition of defects.

Closest to the present invention is a device comprising a television sensor, the output of which is connected via a ADC to a first delay element connected to group selectors, a memory block connected to a counter and to a control unit, first and second selectors connected to a second delay element 2 .

However, the device is not characterized by high reliability of recognition.

The purpose of the invention is to increase the reliability of recognition of defects in photomasks.

The goal is achieved in that the device containing an analog-to-digital converter connected to the scanning sensor and the first delay element, whose outputs are connected to the group selectors, has a first counter connected to the first selector and one input of the first memory block, another input whom

10 is connected to the input of the device, the second selector connected to the output of the corresponding group selector, and the second delay element whose output is connected to the output of the device are inserted into the second unit of the pair, connected to the second selector, the descriptor whose inputs are connected to the second selector and to the second memory block, adders, whose inputs are connected to the second memory block and to the decoder, 20 comparison block, connected to the adders, to the decoder and to one input of the And element, the other input of which is connected to the second selector, Connecting to the corresponding adder and the output of AND element is connected to the second memory blocks, and

delay element, and a second counter connected to another input of element I. In FIG. 1 is a block diagram of the device; in fig. 2 is a schematic block diagram of a normal topology; in fig. 3 is a structural diagram of the contour identification block.

The device includes a scanning sensor 1, an analog-to-digital converter 2, a first delay element 3, a group of 4 selectors 5 and 6, first and second 8 selectors, a second delay element 9, the first memory block 10, the first counter 11, the normal topology node 12, containing a contour identification block 13, a second memory block 14 and a second counter 15. At that, block 13 contains a decoder 16, first 17 and second 18 adders, comparison block 19 and AND 20.

The drawing (Fig. 1) also shows the computational bls (to 21.

The device works as follows. The image of the photomask consists of objects whose contours are formed by straight line segments located at certain angles to each other. The straight edge segments are connected by corners (curved contour sections) with a known rounding radius, determined by the resolution of the photographic equipment used in the manufacture of photomasks. Photomask defects are random objects that are almost always randomly shaped, i.e., their contour is curved. The materiality of a defect (i.e. its effect on the quality of an integrated circuit fabricated thereon) depends on the parameters of the defect (dimensions, area, perimeter, etc.) and location (coordinates).

Thus, in order to recognize defects in photomasks, the following operations must be performed: selection of object contours; analysis of contour sections for the purpose of their classification into linear and curvilinear; classification of curved sections into permissible angles and defects; measurement of parameters and coordinates of defects.

Scanning sensor 1 sequentially scans the image of the photomask and generates a video signal. The video signal is fed to the input of the analog-to-digital converter 2, at the output of which digital video pulses are formed, taking the value "1 when scanning objects and" O - when scanning the background. Digital video pulses are input to the element 3 delay. This element has two outputs, and the video pulses at the second output are delayed relative to the video pulses at the first output for a certain time interval (for example, 16 lines). The value of the delay time depends on the type of photomask.

Video pulses from the first output of the element 3 delays arrive at the input of the first selector 5 of group 4. At the output of the selector 5 of the contour elements, codes are formed corresponding to the contour element in the adjacent

scan lines. The code of the contour element characterizes the length of the contour element, its angle of inclination relative to the direction of the horizontal scanning, as well as the topological features — initial, final, or near interstitial. From the output of the first selector 5 of group 4, codes corresponding to the contours are fed to the input of the second selector 8 of connectivity. The second selector 8 of connectivity selects the connected areas of the contours of the images of the objects. As a result

5, each contour branch (i.e., a contour section between the start and end contour element) is assigned its own index. (Number).

From the second output of the element 3 delay

Q delayed digital video pulses arrive through the second selector 6 of group 4 to the input of the first selector 7 of connectivity. The selector 6 of the circuit elements and the selector 7 of the connectivity are made similar to the first selector 5 of group 4 and the second selector 8

connectivity respectively, but working with a lag. The lag time is determined by the delay element 3. Thus, the output of the device, i.e., the input to the computing unit 21, receives codes corresponding to the elements of the contours and their indices.

From the output of the second selector 8, the codes corresponding to the contour element and its index go to node 12 of the normal topology. In node 12 of the normal topology, each contour branch is analyzed separately, i.e., each sequence of contour element codes with the same index is analyzed separately. In the course of this analysis, node 12 divides each contour branch into straight and curved sections and classifies the curved sections into allowable angles and defects. In the event of a defect, the index of the branch of the contour of this defect, as well as the line number on which this defect started, are recorded in the second delay element 9.

Similarly, at the point in time when node 12 recognizes the end of the defect, information about this (the index of the contour branch and the number of the line on which the defect has ended) will be recorded on the second delay element 9.

Reading the recorded information from the element 9 in the computing unit 21 will occur at the time when the second input of the computing unit 21 will go

Claims (2)

the code of the contour element and its index corresponding to the beginning (or end) of the defect. In this case, the incoming information from the delay element 9 is controlling, since, depending on the incoming code, the calculation of the defect parameters starts (in the case of the beginning of the defect) or stops (in the case of the end of the defect). The processing of the incoming sequence of circuit element codes is performed for each sequence from the moment the information about the beginning of the defect arrives to the moment the information about the end of the defect arrives. After the completion of the calculation of defect parameters, its parameters are recorded in the memory unit 10. Counter 11 of the objects counts the elements of the photomask topology. Since the number of topology elements is known for each defective photo gage, comparing it with the counting results allows one to detect defects such as missing a piece or the appearance of flat elements. For better understanding of the operation of the device, consider the operation of the node 12 (Fig. 2). Codes of the contour elements from the output of the selector 8 of the connectivity are fed to the first input of the block 13 and the address input of the block 14. At the same time, the input code of the block 13 receives the code corresponding to the circuit element (its length, angle) and the address code of the block 14 receives the index code contour branches. Thus, each contour branch corresponds to a cell in block 14. The second input of block 13 receives a code from the output of counter 15, which counts the number of scan lines. At the moment when the code arrives at the inputs of the blocks 13 and 14, information from the corresponding cell is read into block 13, which processes the code of the contour element received from the second selector 8 of connectivity. In this case, two main situations are possible: there was no previous defect on this branch; on this branch earlier. started and the defect has not yet ended. In the first case, block 13 determines whether the received contour element code can correspond to the beginning of the defect (i.e., the straight line section of the contour is finished). In the event that the line runs out, then block 13 reads the code from the output of counter 15 and writes it to block 14. If the subsequent lines show that the defect really started (i.e., it is not a corner), then the index code of this The branches and the recorded line number from the output of block 13 are fed to the variable delay element 9. In the case of a fire, block 13 determines if the received loop element code can be the beginning of a straight line. If it can, then the code from the output of the counter 15 is written through block 13 to block 14. If on the subsequent lines it turns out that the defect has ended (i.e., it really started right). then the index code of this branch and the recorded line number from the output of block 13 arrive at the second delay element 9. One of the possible options for building block 13 is shown in FIG. 3. Block 13 contains a decoder 16, the first input of which is connected to block 14, and the second to the output of the second selector 8 of connectivity. The first and second outputs of the decanter 16 are connected to the control inputs of the first and second adders 17 and 18, respectively. The first adder 18 is connected, in addition, with the output of the second selector 8 of connectivity. The outputs of the first and second adders are connected, the control input of which is connected to the output of the decipher 16, and the output to the control input of the I 20 element. The inputs of this element are connected to the output of the second connectivity selector 8 and the counter 15, and the output to the input of the second element 9 delays. The introduction of new nodes and blocks, as well as new constructive links, made it possible to increase the reliability of recognition of defects, especially small ones, by 1.2-1.5 times. A device for recognizing defects in photomasks, comprising an analog-to-digital converter connected to a scanning sensor and to a first delay element whose outputs are connected to group selectors, a first counter connected to a first selector and to one input of a first memory block, another input connected to the input of the device, the second selector connected to the output of the corresponding group selector, the second delay element, the output of which is connected to the output of the device and the element AND, is different If, in order to increase the recognition reliability, it contains a second memory block connected to the second selector, a decoder whose inputs are connected to the second selector and the second memory block, adders whose inputs are connected to the second "memory block and a comparator unit of comparison, connected to adders, descrambler and to one input of the element And, the other input of which is connected to the second selector connected to the corresponding adder, and the output of the element And is connected to the second memory block and the element of delay, and th counter connected to another input of the element I. Sources of information taken into account during the examination 1. US patent number 4123170, cl. G 01 B 11/00, published 1978 2. US patent number 4074231, cl. 340-146.3, pub. 1978 (prototype). f Fg / g j. / fj