JPH01143334A - Method and apparatus for inspecting defect of mask - Google Patents

Abstract

PURPOSE:To enable defects to be inspected at high speed and easily by allowing one image pickup pattern which was divided in a direction symmetrical in reference to a line to be subject to mirror inversion and to allow it to be compared with the other pattern. CONSTITUTION:A mask to be inspected is scanned by laser beam, laser beam which penetrates through the mask is detected by a photosensor 18 and is AD converted 41, and is stored in an image memory 42. The main direction of scanning should be in a direction which is at right angle in reference to the center line (symmetrical in reference to a line) of the mask. One of patterns which are symmetrical in reference to a line (from one edge of mask to the center line) is stored in the image memory for each main scanning line. When the other pattern (from the center line to the other edge) is output from the photosensor 18, the image memory 42 is read in reverse and is compared by a comparison circuit 48. Then, the defect of mask can be inspected in real time with less memory capacity for a large mask such as shadow mask of CRT.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a technique for inspecting defects in masks, and particularly relates to a technique for inspecting defects in masks, particularly in large-sized masks formed with line-symmetrical patterns, such as the shadow masks of television CRTs. The present invention relates to a mask defect inspection method and a defect inspection apparatus that can easily inspect masks.

(Prior Art) Conventionally, it has been difficult to automatically inspect large masks (generally 300 mmφ or more) such as the shadow mask of a television CRT, and the current situation is to rely on visual inspection. This visual inspection poses problems in terms of labor management, such as putting a great deal of mental stress on the inspection engineer, quality control problems in that defects are easily overlooked, and production efficiency problems in that the inspection takes a long time. I have the above problem. These problems are
If mask defects are automatically inspected instead of visually, the problem can be solved at once, and therefore there is a strong demand for an automatic inspection device.

On the other hand, to inspect masks for LSI manufacturing, inspection apparatuses using a die comparison inspection method or a database comparison inspection method are widely used. It is conceivable to utilize such a method to automate the defect inspection of large masks, but in this case there are the following problems. That is, in the case of the database comparison method, a minicomputer-class computer is required because data is input, stored, and requires some kind of real-time data processing for comparison with imaging data. Furthermore, real-time data processing is usually the bottleneck for inspection speed.
Speeding up is difficult. Further, in the case of the die comparison method, it cannot be applied unless it is a method in which a plurality of patterns are arranged on one mask. Otherwise, it would be necessary to compare two masks with the same pattern, which would increase the size of the apparatus.

(Problems to be solved by the invention) Conventionally, in order to automatically inspect defects on large masks, there have been problems such as requiring a minicomputer-class computer, difficulty in increasing the speed, and the need for larger equipment. Therefore, it was difficult to conduct defect inspection easily.

The present invention has been made in consideration of the above circumstances, and its purpose is to provide a mask defect inspection method and a defect inspection apparatus that can automatically and easily inspect large masks for defects. There is a particular thing.

(Means for Solving the Problems) The gist of the present invention is to compare and match masks made of line-symmetric patterns with each other.

That is, the present invention provides a mask defect inspection method for inspecting a mask to be inspected having a line-symmetrical pattern for defects, in which one imaged pattern divided in a line-symmetrical direction is mirror-inverted and compared with the other imaged pattern. This is how I did it.

The present invention also provides a mask defect inspection apparatus for carrying out the above method, including: an imaging means for imaging a pattern of a mask to be inspected having a line-symmetrical pattern; temporary storage means for storing an image signal obtained by imaging a part or the entire pattern; an image signal obtained by imaging the other pattern and an image signal read from the temporary storage means corresponding to the signal; and determining means for determining that there is a defect on either side that is symmetrical with respect to the portion where the comparison results obtained by the comparing means do not match.

(Function) According to the present invention, one of the symmetrical patterns is stored in the temporary storage means, and the other pattern is compared with the pattern obtained by reading backwards from the temporary storage means, thereby inspecting the mask for defects. It can be carried out. Therefore, unlike the database method, it is not necessary to store all the data of the mask pattern in advance, and furthermore, it is not necessary to store all the image signals of the mask pattern as imaging data.

Therefore, storage capacity can be significantly reduced. Moreover,
By reading the data stored in the temporary storage means backwards, comparison and verification can be performed in real time, and defect inspection can be performed quickly and easily. Also,
Unlike the die comparison method, there is no need for two masks with the same pattern, and it is possible to suppress the increase in size of the device.

(Example) Hereinafter, details of the present invention will be explained with reference to illustrated embodiments.

This embodiment uses a method in which a mask to be inspected is scanned with a laser beam and the transmitted light is received by a photosensor, and FIG. 1 is a schematic configuration diagram schematically showing the main scanning optical system. A laser beam emitted from a laser oscillator 1 is reflected by a focusing mirror 2, and then reflected by a polygon mirror 14 driven and rotated by a motor 13 to become a scanning beam. This passes through the fθ lens 15a, changes direction at the reflection mirror 6a, and scans the mask 17 in the X direction. The transmitted beam changes its direction by a reflection mirror 16b, and is changed by approximately 1
The light is focused on a point and imaged by the photosensor 18. An encoder 19 that rotates coaxially with the motor 13 has the role of detecting the beam position in the X direction (main scanning direction).

FIG. 2(a) is a top view of the stage section responsible for sub-deflection, and FIG. 2(b) is a side view including the stage drive section. The stage 20 can be moved in the X direction on the two guideways 21 by rotation of a feed screw 22, and the feed screw 22 is driven by a motor 23. There is a mask holder 24 on the stage 20, on which the mask 17 is set. The mask holder 24 is rotated by a motor 26 around a fulcrum 25.
It can be rotated slightly in the direction. An encoder 27 is installed coaxially with the Y drive motor 23, and with this the stage 20
The Y position of is detected. Note that 28 indicates an origin sensor for determining the origin position of the stage 20.

Figure 3 shows the control system of this inspection device. Main control unit 3
] has a built-in microcomputer and controls the input/output of the console 32 and the entire inspection sequence. The drive unit 33 is the polygon mirror drive motor]3.
It has built-in drivers for a stage drive motor 23 and a θ drive motor 26, and drives each motor 13°23.26 according to commands such as speed, direction, and 5TART/5TOP from a main control unit 31. The comparison unit 34 includes the photosensor 18. Signals from the encoder 1'9.27 and the origin sensor 28 are input to compare and match patterns as described later, and the main control unit 31 controls the inspection sequence.

FIG. 4 shows the comparison unit 34 in a block diagram, and FIG. 5 shows its main operations in a time chart.

The image signal detected by the photosensor 18 is sent to the ADC 4
1, and is stored in the image memory 42 as follows. A face origin pulse generated at the starting point of each mirror surface is inputted from the encoder 19 which rotates together with the polygon mirror 14, which presets the X position counter 43 and flips the flip-flop (FF) 4.
4 and clear the FIFO register 45. The frequency of the other pulse train is divided by a frequency divider 46, and its output (in the embodiment, 1 hμ77Z) is input to the X position counter 43 and counted down. The output of the X position counter 43 addresses the image memory 42, and digital image data is stored in the write mode. The 0 detector 47 detects the point in time when the X position counter 43 becomes 0, and sets the FF 44 to put the X position counter 43 in count-up mode and the image memory 42 in read mode. This X position corresponds to a position passing through the center line of a mask having a line-symmetric pattern.

After this, the output of the ADC 41 and the output of the image memory (reverse reading) are compared (subtracted) in the comparison circuit 48, and if the threshold value set by the main control unit 31 is exceeded, a defect signal is output. , the current X position is stored in the FIFO register 45. If even one defect signal is output, the FF 49 is set, so the main control unit 31 receives an interrupt that tells the origin of the next FACE (next scan), checks the FF 49, and if it is set, the FIFO register 45 is set. (X coordinate where the defect was detected) and the contents of the Y position counter 5 (X coordinate where the defect was detected) are read and stored in the defect information file. In addition, in FIG. 4, 52 is the main control unit 3.
This is a latch circuit that latches the X offset from 1 and provides it to the X position counter 43.

Incidentally, in this type of defect inspection, alignment is required before the inspection, and this alignment is performed as follows. FIG. 6 shows four alignment marks previously drawn on the mask to enable automatic alignment. By inputting these alignment mark coordinates from the console 32 by the operator, the positions are first determined at the Y coordinates of the Ml and M2 marks, and the beam is scanned to compare M] and M2. The main control unit 3
1 changes the X offset data little by little to determine the X offset value at which no defects are detected.

Next, the stage 20 is set to M3. After positioning at the Y coordinate of M4, the θ-axis is moved slightly, and if no defects are detected, the alignment is completed.

Thus, according to this embodiment, even a large mask such as a shadow mask of a television CRT can be automatically inspected for defects. In this case, one side of the line-symmetric pattern is compared and verified for each line, so the memory capacity is extremely small and real-time processing is possible. Furthermore, there is no need to store all the data of mask patterns in advance, and there is no need to use multiple masks, making it possible to inspect masks for defects easily and at high speed. In other words, instead of simply increasing the size of the device using the conventional database method or die comparison method, this embodiment can realize a simple and inexpensive defect inspection device.

Note that the present invention is not limited to the embodiments described above. FIG. 7 is a modification of FIG. 1, in which the light reflected by the reflection mirror 16 is irradiated onto the mask 17 through the half mirror 71,
The light reflected from the mask 17 is separated by a half mirror 71, and returned to the original direction by a mirror 72 in the opposite direction to the projected beam.
This method uses a second focusing mirror 73 to project the image onto the photosensor 18 and capture the image. Even with such a system, the same effects as in the previous embodiment can be obtained. It is also possible to perform defect inspection using an electron beam instead of light. In this case, as shown in FIG. 8, the electron beam emitted from the electron gun 12-81 is focused on the mask surface by the electromagnetic lens 82 and scanned in the X direction by the deflection coil 83. The reflected electrons from the mask 17 are converted into electrical signals by a photomultiplier tube 84 and used as image signals. FIG. 9(a) shows the scanning current applied to the deflection coil 83, which is stored in or read out from the image memory using the time-divided clock shown in FIG. 9(b) and counted.
Let it be a position counter in the direction.

In addition, in the example, defects were inspected for each line, but
It is also possible to perform defect inspection for each of multiple lines. Furthermore, instead of transmitted light, reflected light, and instead of reflected electron beam, 2
It is also possible to use secondary electron beams. In addition, various modifications can be made without departing from the gist of the present invention.

(Effects of the Invention) As detailed above, according to the present invention, one of the line-symmetrical patterns is stored in the temporary storage means, and the other pattern is compared with a pattern obtained by reading backwards from the temporary storage means. By comparison, it is possible to inspect the mask for defects. Therefore, even large masks such as shadow masks for television CRTs can be automatically and easily inspected for defects, and are extremely useful.

[Brief explanation of the drawing]

FIGS. 1 to 6 are for explaining a mask defect inspection apparatus according to an embodiment of the present invention, and FIG. 1 is a schematic configuration diagram schematically showing a main scanning optical system, and FIG. 3 is a block diagram showing the configuration of the control system, FIG. 4 is a block diagram showing the configuration of the comparison unit, and FIG. 5 is a timing diagram showing the operation of the comparison unit. The chart, FIG. 6 is a plan view showing an example of arrangement of alignment marks, and FIGS. 7 to 9 are diagrams for explaining modified examples, respectively. 11... Laser oscillator, 14... Polygon mirror,
17... Mask to be inspected, 18... Photo sensor, 1
9°27...Encoder, 20...Stage, 28
...Origin sensor, 3'''1...Main control unit, 3
3... Drive unit, 34... Comparison unit, 42
...Image memory, 43...X position counter, 48.
...Comparison circuit, 51...Y position counter. Applicant's agent Patent attorney Yumi Suzue Takehiko, 0

Claims (4)

[Claims] (1) When performing defect inspection of a mask to be inspected having a line-symmetrical pattern, one of the imaged patterns divided in the line-symmetrical direction is mirror-inverted and compared with the other imaged pattern. Defect inspection method. (2) An imaging means for imaging a pattern of a mask to be inspected having a line-symmetrical pattern, and storing an image signal obtained by imaging a part or the whole of one pattern divided in the line-symmetrical direction of the mask. and a comparison means that compares an image signal obtained by imaging the other pattern with an image signal read from the temporary storage means corresponding to the signal, and a comparison result by the comparison means does not match. What is claimed is: 1. A mask defect inspection apparatus, comprising: determining means for determining that there is a defect on either side that is line symmetrical with respect to the portion. (3) Mount the mask to be inspected on a portable table, scan the mask with a single light beam in a direction perpendicular to the direction of movement of the table, and condense the transmitted or reflected light to one point. An image is captured by a sensor, an image signal obtained by scanning first is stored in a temporary storage means, and an image signal obtained by scanning later is compared with a mirror image signal obtained by reading backwards from the temporary storage means. A mask defect inspection device according to claim 2, characterized in that: (4) Mount the mask to be inspected on a portable table, scan the mask with a single electron beam in a direction perpendicular to the direction of movement of the table, and image the reflected electrons or secondary electrons with an electronic sensor; The image signal obtained by scanning first is stored in a temporary storage means, and the image signal obtained by scanning later is compared with the mirror image signal obtained by reverse reading from the temporary storage means. A mask defect inspection device according to claim 2.