JPH01140047A - Detection of massive particle in transparent thin film - Google Patents

Abstract

PURPOSE:To attain high reliability by a method wherein two elements are picked up with dark-field illumination from one direction, an inclined part of a pattern detected with the illumination in that direction is set to be an inspection prohibition area, and then two images are subjected to comparative inspection by switching the direction of the illumination. CONSTITUTION:A construction is made so that dark-field illumination from a light source 10 can be switched over to the right and left by two kinds of light-intercepting parts provided in a light-intercepting plate 12. Next, one light- intercepting part is inserted into an optical path, one element on a wafer 17 is picked up by a TV camera 16 and an output thus obtained is stored in a memory 20a, while a pickup output obtained through the other light-intercepting part is stored in a memory 20b. Subsequently another element on the wafer 17 is picked up in the same way and outputs are stored in memories 20c and 20d respectively. Then, four images stored in the memories 20a-20d are inputted to a defect judging circuit 40, the images of the two elements are compared with each other while the inclined part of a pattern detected brightly is set to be an inspection prohibition area, and a massive particulate is detected thereby. Accordingly, detection can be executed with high reliability.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for inspecting the appearance of elements covered with a transparent protective film, such as thin-film magnetic heads used in magnetic disks for computers. In particular, the present invention relates to a method for detecting lump particles in a transparent thin film, which is suitable for detecting lump particles present in a transparent protective film.

[Prior Art] As shown in FIG. 7, a partial cross section of which is shown, the thin film head has a coil conductor 1. Insulating layer 2. It is composed of a magnetic material 4 and a transparent protective film 3. By the way, a problem in the process of creating the protective film 3 is that the transparent protective film 3 is not created uniformly, and lump-like particles 5a and 5b may be generated as shown in the figure. This is because if the bulk particles 5a, 5b are present in the transparent protective film 3, the effective film thickness will become thinner and the reliability of the device will decrease. In addition, if the lumpy particles 5b are present on the surface of the transparent protective film 3, if the lumpy particles 5b fall onto the disk surface during use of the disk, it will cause serious accidents such as damage to the device or loss of data. A thorough inspection is required.

By the way, if we explain the method of detecting lump particles in a transparent thin film using normal dark field illumination according to the prior art, the seventh
As shown in the figure, the bulk particles 5a and 5b have irregular shapes, so by illuminating them in the dark field, even if they are transparent bulk particles that cannot be detected with bright field illumination, the surface of the particles can be detected. Because the light is scattered, it is detected as a bright object. However, as shown in FIG. 8, the image obtained by dark-field illumination includes light scattered by the lumpy particles 5C and positive light from the sloped parts of the pattern that constitutes the element (for example, the sloped parts 41 and 42 of the magnetic material 4). The light includes reflected light and scattered light from pattern edges (for example, the edges of the coil conductor 1). Therefore, by imaging two elements having the same shape using dark field illumination and comparing them, it is possible to detect lumpy particles in a transparent thin film as a mismatched portion between images.

As a method for detecting lumpy particles (foreign matter) attached to a semiconductor wafer, a method is disclosed in Japanese Patent Application Laid-Open No. 1983-1983 in which the wafer is illuminated diagonally from above with a laser and the scattered light is detected.
No. 99735.

This method utilizes the fact that the polarization characteristics are disturbed when laser light is scattered by a foreign object, and only the foreign object is detected without being affected by the reflected light from the pattern. However, compared to the pattern on a semiconductor wafer, the pattern on a thin-film magnetic head has a rougher surface, and the polarization characteristics of the laser beam are disturbed even on the pattern surface. Since the magnetic head cannot be distinguished, conventional methods cannot be applied to the inspection of magnetic heads.

[Problem that the invention seeks to solve]

However, in the conventional method of detecting lump particles in a transparent thin film by imaging and comparing two identical shapes using dark-field illumination, lump particles exist in the upper direction of the inclined part of the pattern, as shown in Figure 8. The lump particles (5c) are difficult to detect. That is, the intensity of the scattered light from the lumpy particles (5c) is weaker than the intensity of specularly reflected light from the pattern sloped part existing below, and the scattered light from the lumpy particles (5c) and the pattern sloped part are weaker than the intensity of the specularly reflected light from the pattern sloped part existing below. This means that it is difficult to detect only the lump particles (5c) by simultaneously detecting the specularly reflected light and comparing the two elements.

In addition, even in the sloped part of the pattern, the slope angle and height vary from element to element due to subtle variations in the manufacturing process, and when dark-field illumination is performed, the intensity of specularly reflected light varies greatly from element to element. It becomes something. For this reason, when two elements are imaged and compared using dark-field illumination, a large mismatch occurs in the sloped portion of the pattern, resulting in a large number of pseudo defects.

An object of the present invention is to provide a method for detecting lump particles in a transparent thin film that can detect lump particles in a transparent thin film with high reliability without generating pseudo defects.

[Means for solving problems]

The above purpose is to obtain an image after each of the two elements is imaged with dark field illumination separately from opposite directions.

This is achieved by predetermined processing of four types of images of the two elements taken in correspondence with these directions.

[Effect]

The scattered light of bulk particles in a transparent thin film can be detected regardless of the direction of dark-field illumination, but the sloped portion of the pattern can only detect specularly reflected light from dark-field illumination from a certain direction. Therefore, two images captured under separate dark-field illumination from two opposing directions commonly include scattered light from the same lumpy particles, but specularly reflected light from the same pattern slanted part. are not included in common, and only specularly reflected light from different pattern slope portions is detected. Now, when there is a lumpy particle at the top of the pattern slope part, in one of the two images taken with separate dark field illumination from two opposing directions, the scattered light from the lumpy particle is present at the bottom. On the other hand, only the scattered light component from the massive particles is detected without being affected by the underlying pattern, although the light component is buried in the specularly reflected light component from the inclined part of the pattern. Therefore, we imaged the two elements using dark-field illumination from one direction.

By setting the sloped part of the pattern that is brightly detected by illumination from that direction as an inspection prohibited area, and then comparing and inspecting the two captured images by switching the illumination direction, false defects can be detected in the sloped part of the pattern. All lump particles can be detected without being generated. Since the inspection prohibited area is set by binarizing the difference between two images obtained by illumination from two opposing directions, the inspection prohibited areas set for each illumination direction do not overlap. By combining the inspection results for each illumination direction, it is possible to inspect the entire area.

〔Example〕

The present invention will be explained below with reference to FIGS. 1 to 6.

First, the outline of the bulk particle detection device according to the present invention will be explained below with reference to FIG.

That is, the light from the light source 10 passes through the condenser lens 11, the light shielding plate 12, the reflector 13, and the dark field objective lens 14, and illuminates the wafer 17 to be inspected on which a plurality of elements that should be originally the same are formed. It has become.

The reflected light from the wafer to be inspected 17 is reflected by the dark field objective lens 1.
The central lens portion of 4 is a reflection fi (mirrored only at the periphery, light can pass through the center) 13, and an image is formed on the TV camera 16 via the imaging lens 15. By the way, the light shielding plate 12 has two types of light shielding parts 31 and 32 as shown in FIG.
In FIG. 2, by moving the light shielding plate 12 up and down, the dark field illumination direction can be switched left and right.

Now, to explain the operation of the device, first, one element on the wafer to be inspected 17 is imaged by the TV camera 16 with the light shielding part 31 inserted into the optical path, and the output is sent to the A/D converter 1.
After being converted into a digital quantity in step 9, it is stored in the memory 20a. Next, the light shielding plate 12 is moved and the light shielding part 32 is inserted into the optical path, and the device is imaged with the TV camera 16.
The data is stored in the memory 20b via the /D converter 19. After this, the light shielding plate 12 is moved again and the light shielding part 31 is moved.
The XY stage 18 is moved with the T
After taking an image with the V-camera 16 and storing it in the memory 20c via the A/D converter 19, furthermore, with the light-shielding plate 12 moved and the light-shielding part 32 inserted into the optical path, images of other elements are taken with the TV camera 16. Memory 20 via A/D converter 19
It is designed to be stored in d.

4 stored in the memories 20a to 20d as described above.
The two images are input to a defect determination circuit 40, which will be described in detail below, to detect lumpy particles present in the transparent protective film. I need to be there.

The alignment method is not directly related to the present invention and a detailed explanation thereof will be omitted, but there is a method of precisely positioning the XY stage 18 to align the two elements, and then capturing an image with the TV camera 16, and There is a method of aligning two elements by electrically shifting the image stored in 20d.

FIG. 1 shows the configuration of an example of the defect determination circuit shown in FIG. 2. In FIG. Below, in order to simplify the explanation, the second
In the figure, the dark-field illumination direction with the light shielding part 31 inserted into the optical path is indicated, and R is the dark-field illumination direction with the light shielding part 32 inserted into the optical path. Also, 2 things to compare
The image of element A taken in the illumination direction is A L r The image of element B is B L +
An image of element A taken in the illumination direction R is taken as an image of element B.
The following is an explanation of the image as BR.

That is, in the defect determination circuit 40, the memories 20a, 20b, 2
0c.

Images ALs AR+ BL+ stored in advance in 20d
BR is input and processed as specified, but its configuration is A.
Difference absolute value circuits 44a, 44b for comparing L and BL+AR+BR, these difference absolute value circuits 44a,
A predetermined area (inspection prohibited area) of the output from 44b
selectors 45a, 45 for masking the corresponding ones;
b, Binarization circuits 46a, 46b, Binarization circuit 46 for binarizing the output from the selectors 45a, 45b.
an OR circuit 47.a and 46b for synthesizing the comparison inspection results for each illumination direction and for each R to obtain a final inspection result; Furthermore, subtraction circuits 41a to 41d and binarization circuits 42a to 42d are used to calculate inspection prohibited areas (hereinafter referred to as ML and MR) when comparing and inspecting images captured for each R in each illumination direction. and AND circuits 43a, 43b
It is more structured.

Now, the 41st item that shows the throughput relationship regarding the circuit operation!
! To explain with reference to I, the image AR is subtracted from the image AL by the subtraction circuit 41a, and the result is sent to the binarization circuit 42.
It is binarized by the threshold value (positive value) Th at a, and this binarization result shows a pattern slope portion that is brightly detected when the element A is illuminated in the dark field in the illumination direction. Similarly, the image BR is subtracted from the image BL by the subtraction circuit 41c, and the result is binarized by the binarization circuit 42c using the threshold Th. , a brightly detected pattern slope portion is extracted. After that, the binarization circuit 42a,
The output of 42c is ANDed by the AND circuit 43a to detect a pattern slope portion that is bright in common in elements A and B depending on the illumination direction. This is the inspection prohibited area ML when the inspection is carried out.

On the other hand, the absolute value of the difference between AL and BL, that is, the amount of mismatch, is calculated by the absolute difference circuit 44a, and the result can be output from the selector 45a. Whether O11 is output is determined by the AND circuit 43
It depends on the state of ML from a.

When ML is 1'', selector 45a selects II OII.

When ML is 410 II, the output of the absolute difference circuit 44a is output as is. Therefore, the output of the selector 45a includes scattered light from the lumpy particles existing in the area other than the sloped part of the pattern, which is detected brighter when dark field illumination is performed than in the illumination direction, and this is transmitted to the binarization circuit 46a. Therefore, the threshold value Th2 is 2
By converting it into a value, the agglomerated particles can be detected. By the same operation as described above, the lump particles existing in the region other than the pattern slope portion that is detected brightly when dark field illumination is performed from the illumination direction R are removed by the binarization circuit 46.
This is detected as the output of b. Finally, the outputs of the binarization circuits 46a and 46b are logically summed by an OR circuit 47, so that all the lump particles present on the element can be detected. In FIG. 4, the values are logically summed and then binarized, but the same result can be obtained either way. Incidentally, the logical sum processing is required because the state of scattering from lumpy particles generally differs depending on the direction of dark field illumination, and it is necessary to detect the size more reliably. Although not shown in Figure 1, “
1" by determining the size of the area.

Noise components are removed.

Now, FIG. 5 shows the configuration of another embodiment of the present invention. By simultaneously performing dark-field illumination from two opposing directions with light in different wavelength bands and detecting images with a TV camera for each wavelength band, two images of the element illuminated from the two opposing directions can be obtained simultaneously. It is intended to be detected. In order to achieve this, the light shielding plate 21 inserted into the dark field optical path has a light shielding part 23 that does not transmit light, and a light shielding part 23 that does not transmit light, and a light shielding part 23 that transmits only light in the long wavelength band (red light) and blocks light of other wavelengths, as shown in FIG. It is composed of a reflective color filter 24a and a color filter 24b that transmits only short wavelength band light (blue light) and reflects light of other wavelengths. Also,
In order to separate and detect light in two wavelength bands, a dichroic mirror 22 is inserted into the detection optical path as shown in FIG.
2 uses a material that transmits red light and reflects blue light).

In this state, the images detected by the two TV cameras 16a and 16b are stored in the memory 20a via A/D converters 19a and 19b, respectively.

At 20b, images of other bare hands after the XY stage 18 has been moved are stored in memories 20c and 20d.

In this manner, in this example, two images of the element illuminated from two opposing directions can be detected simultaneously, so that inspection can be performed quickly.

〔Effect of the invention〕

As explained above, according to the present invention, the lumpy particles present in the protective film of an element covered with a transparent protective film, such as a thin film magnetic head used in a magnetic disk for computers, are affected by the pattern of the element. This has the effect of improving the reliability of the product because it can be detected with high reliability without causing false defects.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a configuration of an example of a defect determination circuit according to the present invention, and FIGS. 2 and 3 are a diagram showing a schematic configuration of an example of a lump particle detection device according to the present invention and a light shielding plate in the configuration. FIG. 4 is a diagram showing the details, and FIG. 4 is a diagram showing the throughput relationship in the defect determination circuit shown in FIG. 1. FIGS. FIGS. 7 and 8 are diagrams showing a general configuration and details of a light shielding plate in the configuration, and are partial cross-sectional views of a thin film magnetic head for explaining the problems of the prior art. 12, 21... Light shielding plate, 13... Reflector, 14...
・Dark field objective lens, 16.16a, 16b-T
V camera, 19.19a. 19b...A/D converter, 2(la to 20d...memory, 4o...defect determination circuit, 41a to 41d-
Subtraction circuits, 42a-42d, 46a. 46b=-Binarization circuit, 43a, 43b-AND circuit, 44a. 44b...Absolute value circuit of difference, 45a, 45b...
Selector, 47...OR circuit. 2nd Prisoner 3 Figure 11 Large Rape Figure 5 Figure 6 21 "24b

Claims (1)

[Claims] 1. Two devices to be inspected, each having a transparent thin film and originally having the same shape, are imaged under separate dark field illumination from two opposing directions; The first method of detecting lumpy particles detects lumpy particles existing in a transparent thin film as a mismatched part by processing the multivalued digital image data obtained corresponding to the dark field illumination direction in a predetermined manner.
The absolute value image data of the first difference is obtained by comparing the multivalued digital image data of the first and second devices under test related to the dark field illumination direction, and the first and second devices related to the second dark field illumination direction are compared. While comparing the multi-value digital image data of the second device to be tested and obtaining the absolute value image data of the second difference, the multi-value digital image data of the first and second devices to be tested related to the first dark-field illumination direction are compared. The areas that are both brightly detected in the image data are
At the same time, a region that is brightly detected in both the multivalued digital image data of the first and second devices to be tested in the second dark field illumination direction is extracted as the second inspection prohibited region. , a binarized version of the absolute value image data of the first difference while masking the multi-value digital image data included in the first inspection-prohibited area, and the multi-value digital image included in the second inspection-prohibited area. A method for detecting lump particles in a transparent thin film, characterized by detecting a mismatched portion as a defect by logically ORing the data with the binarized absolute value image data of the second difference while masking the data. . 2. The first inspection prohibited area is determined from the multi-value digital image data of the first device to be inspected in the first dark-field illumination direction to the multi-value digital image data of the first device to be inspected in the second dark-field illumination direction. The result of subtracting digital image data is binarized,
The result of subtracting the multi-value digital image data of the second device to be tested in the second dark-field illumination direction from the multi-value digital image data of the second device under test in the first dark-field illumination direction is calculated as 2. As a logical product with the values, the second inspection prohibited area is determined from the multivalued digital image data of the first device under test related to the second dark field illumination direction to the multilevel digital image data of the first device under test related to the second dark field illumination direction. A first dark field image is obtained from the binarized result of subtracting the multi-value digital image data of the first device under test and the multi-value digital image data of the second device under test related to the second dark field illumination direction. A lump in the transparent thin film according to claim 1, which is extracted as a logical product of the result of subtracting the multivalued digital image data of the second device to be inspected in the field of view illumination direction and the binarized result. Particle detection method.