JPS6239816B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a pattern inspection method, and more particularly to an improvement in a pattern comparison inspection method that compares video signals of two actual patterns to determine the quality of the pattern.

2. Description of the Related Art As an apparatus for inspecting photomasks used in the manufacture of semiconductor devices, there is a pattern surface inspection apparatus that sequentially compares and inspects a plurality of real patterns of the same type formed in alignment on a photomask two by two. In this method, the video signals of two real patterns are superimposed, the difference signal between these video signals is detected, and the quality of the pattern is determined based on the presence or absence of the difference signal (if the difference signal is detected, patterns are judged to be defective).

However, in the above-mentioned conventional method, for example, when projecting and arranging multiple real patterns of the same type on a mask substrate by the step-and-repeat method, mechanical errors and vibrations in stage feeding cause problems between the real patterns. If the relative position of the actual pattern is shifted, when the video signals of the two actual patterns are superimposed, a difference signal corresponding to the positional shift will be detected, and the actual pattern to be inspected will be detected within the pattern. There was a problem in that even if there were no defects, it was determined to be defective.

In view of the above-mentioned problems, the present invention distinguishes a difference signal caused by a relative positional shift between a standard actual pattern and an actual pattern to be inspected, that is, a condensed defect signal, from an original defect signal caused by a defect in the pattern. The purpose of the present invention is to provide a comparative inspection method for distinguishing and determining pass/fail, and to improve inspection accuracy.

That is, the present invention superimposes the video signal patterns of the reference real pattern and the real pattern to be inspected,
Detects the difference signal pattern between both video signal patterns,
In a pattern inspection method for determining a defective pattern based on the presence or absence of the difference signal pattern, among the difference signals, the difference signal is in contact with the same side of two opposing sides of the reference video signal pattern, and is equal to the tangent side. The present invention is characterized in that it includes a step of distinguishing a difference signal pattern having a length and a uniform width from other difference signal patterns and excluding it from defect display targets.

Examples of the present invention will be described below. Fig. 1 is a block diagram of the main configuration of a pattern inspection apparatus used in an embodiment of the method of the present invention, and Figs. A detailed explanation will be given using the drawings and a top view of the process in another embodiment shown in FIG.

For example, as shown in FIG. 1, the pattern inspection apparatus used in the method of the present invention includes a stage 2 for fixing a mask 1 to be inspected, a pair of optical systems (microscopes) 3a
b A pair of video signal pattern forming units 4a, 4b equipped with a photoelectric conversion device, a pair of signal binarizing units 5a,
5b, a pair of screen memory forming parts 6a and 6b, a pair of screen memory outline recognition parts 7a and 7b, a memory pattern outline comparison part 8, a defective memory outline recognition part 9, a defective memory shape inspection part 10, a defective signal output part 11,
It has an output gate 12.

In this apparatus, a plurality of mask actual patterns of the same type, which are formed in alignment on the mask 1 to be inspected, are sequentially moved down to a pair of optical systems 3a and 3b for comparative inspection. FIG. 1 shows a state in which a comparison inspection is performed on a mask actual pattern B using the mask actual pattern A as a reference pattern, and in this state, the mask actual pattern A and the mask actual pattern B projected by the optical systems 3a and 3b are shown. The optical images of B are first converted into analog video signal patterns in video signal pattern forming sections 4a and 4b, respectively. Next, the analog video signal patterns are passed through signal binarization units 5a and 5, respectively.
The screen memory forming portions 6a, 6
In step b, a screen memory of each pattern is formed. This state is shown in Figure 2a.
Ma indicates the screen memory pattern of mask pattern A as a reference, and Mb indicates the screen memory pattern of mask pattern B to be inspected. Next, the outlines of these screen memory patterns are determined by 1 [memory bit] in the screen memory outline recognition units 7a and 7b, respectively.
It is recognized by the width of . This state is shown in Figure 2b, where Ca is the reference mask actual pattern A.
Cb indicates the outer shape (contour) memory pattern of the mask actual pattern B to be inspected. Next, these external memory patterns are superimposed and compared in a memory pattern external shape comparison section 8, and a difference between both external memory patterns Ca and Cb is detected.The difference is regarded as a defect, and the defect external shape recognition section 9
In this process, the external memory pattern of the defect is recognized.
This state is shown in Fig. 2c. In this case, if there is no defect inside the mask actual pattern and the relative positions of the A and B actual patterns are slightly shifted only in the X direction, there is a defect. External memory pattern D ₁ , D ₂
appears with a constant width on one side of the reference mask pattern A, which is in contact with the entire two sides of the external memory pattern C _A in the Y direction. Therefore, the lengths of the sides facing the X and Y directions of the reference contour memory C _A are x _c1 , x _c2 and y _c1 , y _c2 , and the lengths of the defect contour patterns D ₁ and D ₂ are y _{d1 ,} respectively. , y _d2 , their widths are x _d1 , x _d2 , and their interval is x _s , then x _s =
x _c1 (however, x _c1 = x _c2 ), y _d1 = y _c1 , y _d2 = y _c2 ,
x _d1 = x _d2 . These points are determined by the defect shape inspection unit 10 as a memory pattern of the defect outline.
Confirm by comparing D ₁ and D ₂ with the external memory pattern Ca of the mask pattern A serving as a reference. In addition, for ease of understanding, the screen memory Ma of the mask actual pattern A and the mask actual pattern B are shown in FIG.
The state in which the screen memories Mb of are superimposed is also shown, and D' ₁ and D' ₂ indicate the areas surrounded by D ₁ and D ₂ , respectively. If the external shape memory pattern of the defect satisfies the above conditions, the external shape inspection section 1
0 to the gate section 12, and the defect signal that has already been output from the defect signal output section 11 in response to the abnormality command from the memory pattern outline comparison section 8 is turned off at the gate section 12.

In addition, FIG. 3 shows a case where there is a relative positional deviation only in the Y direction between mask actual patterns A and B in the defect pattern outline inspection process, and in this case, the reference shape outline memory C _A Let the length of the sides be x _C1 , x _C
2 and y _c1 , y _c2 , and the external pattern of the defect D ₃ ,
The length of _D4 is x _d3 , x _d4 , and its width is y _d3 ,
If y _d4 and the interval is y _s , then y _s = y _c1 , x _d3 =
x _c1 , x _d4 = x _c2 , y _d3 = y _d4 .

In the case of actual pattern defects such as pinholes and light-shielding film residues, the shape of the defective portion cannot satisfy all of the above conditions. Therefore, an actual pattern having an original defect is recognized in this process separately from the above-mentioned condensed defect, and an ON signal is sent from the outer shape inspection section 10 to the gate section 12 to turn on the gate and output a defect signal to the defect signal output section. The signal from 12 is output to the outside.

In the above embodiments, the method of the present invention was carried out by converting the optical image of the actual pattern into a digital electrical signal, but the method of the present invention can also be carried out using analog electrical signals as they are. Furthermore, the method of the present invention can also be applied to comparative inspection of a plurality of real patterns of the same type formed in alignment on a semiconductor substrate. Furthermore, the method of the present invention can also be applied when comparing the drawing data memory of the actual pattern with the actual pattern to be inspected.

As explained above, according to the present invention, the video signals of a reference real pattern and a real pattern to be inspected are superimposed, a difference signal pattern between the two video signal patterns is detected, and a defective pattern is detected based on the presence or absence of the difference signal pattern. In the pattern inspection method for determining the quality of the pattern to be inspected, it is possible to distinguish the coagulated defects caused by the relative positional deviation between the reference pattern and the pattern to be inspected from the original defects inside the pattern. Therefore, inspection accuracy is greatly improved.
Further, there is no need for a circuit or mechanism for correcting positional deviations, the configuration is simple, and furthermore, it can be easily applied even when positional deviations are large.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the main configuration of a pattern inspection device used in one embodiment of the present invention, FIGS. 2 a to c are process sectional views in one embodiment of the present invention, and FIG. 3 is another embodiment. It is a process sectional view in . In the figure, 1 is the mask to be inspected, 2 is the stage,
3a and 3b are optical systems (microscopes); 4a and 4b are video signal pattern forming units; 5a and 5b are signal binarization units; 6a and 6b are screen memory forming units; 7a and 7b
1 is a screen memory outer shape recognition section, 8 is a memory pattern outer shape comparison section, 9 is a defective memory outer shape recognition section, 10 is a defective memory shape inspection section, 11 is a defective signal output section, 1
2 is the output gate section, A is the reference mask actual pattern, B is the mask actual pattern to be inspected, Ma and Mb are screen memory patterns, Ca is the external memory pattern of the reference pattern A, and Cb is the external memory of the pattern B to be inspected. The patterns D ₁ , D ₂ , D ₃ , and D ₄ are defect outline memory patterns, and x _s and y _s are intervals between the outline memory patterns.

Claims (1)

[Claims] 1. In a pattern inspection method in which the video signal patterns of a reference actual pattern and the actual pattern to be inspected are superimposed, a difference signal pattern between the two video signal patterns is detected, and a defective pattern is determined based on the presence or absence of the difference signal pattern. , among the difference signal patterns, a pair of difference signal patterns of uniform width that are in contact with the same two opposing sides of the reference video signal pattern and have the same length as the tangent sides,
A pattern inspection method comprising the step of distinguishing from other difference signal patterns and excluding them from defect display targets.