JPH0690143B2 - Method for detecting agglomerated particles in transparent thin film - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for inspecting the appearance of an element covered with a transparent protective film, such as a thin film magnetic head used for a magnetic disk for a computer, and more particularly to a transparent protective method. The present invention relates to a method for detecting agglomerated particles in a transparent thin film, which is suitable for detecting agglomerated particles existing in a film.

[Conventional technology]

The partial cross section is shown in FIG. 7, and the thin film axial head is composed of a coil conductor 1, an insulating layer 2, a magnetic body 4 and a transparent protective film 3. By the way, a problem in the process of forming the protective film 3 is that the transparent protective film 3 may not be uniformly formed, and lump particles 5a and 5b may be generated as shown in FIG. Agglomerated particles 5a, 5 in the transparent protective film 3
This is because if b exists, the effective film thickness will be reduced and the reliability of the device will be reduced. In addition, if the lump particles 5b are present on the surface of the transparent protective film 3, if the lump particles 5b fall onto the disc surface during use of the disc, a serious accident such as damage to the device or loss of data may occur. Inspection is needed.

By the way, a conventional method for detecting agglomerated particles in a transparent thin film by dark field illumination will be described.
As shown in the figure, since the agglomerated particles 5a, 5b have an irregular shape, by illuminating them in the dark field, even transparent agglomerated particles that cannot be detected by bright-field illumination have their surfaces. Since light is scattered, it is detected as bright. However, as shown in FIG. 8, in the image obtained by dark-field illumination, scattered light by the agglomerated particles 5c and the positive light from the inclined portions of the pattern forming the element (for example, the inclined portions 41 and 42 of the magnetic body 4) are included. The reflected light and the scattered light from the pattern edge (for example, the edge of the coil conductor 1) are included. Therefore, by capturing and comparing two elements having the same shape with dark-field illumination, the agglomerated particles in the transparent thin film can be detected as a mismatched portion between the images.

As a method for detecting the lump particles (foreign matter) attached on the semiconductor wafer, there is a method of illuminating the wafer from a diagonally upper direction with a laser and detecting the scattered light thereof.
No. 35 publication. This method utilizes the fact that the polarization characteristics are disturbed when the laser light is scattered by the foreign matter, and only the foreign matter is detected without being affected by the reflected light from the pattern. However, the pattern of the thin-film magnetic head has a rougher surface than the pattern of the semiconductor wafer, and the polarization characteristics of the laser light are disturbed even on the pattern surface, so the scattered light from the pattern and the scattered particles from the lump particles in the protective film are Since the discrimination cannot be made, the conventional method cannot be applied to the inspection of the magnetic head.

[Problems to be solved by the invention]

However, in the conventional method of detecting agglomerated particles in a transparent film by imaging and comparing two shapes having the same shape with dark field illumination, the pattern exists in the upper direction of the pattern inclined portion as shown in FIG. It is difficult to detect agglomerated particles (5c). That is, the intensity of the scattered light from the agglomerated particles (5c) is weaker than the intensity of the specular reflection light from the pattern slanted portion existing therebelow, and the scattered light from the agglomerated particles (5c) and the pattern slanted portion It is difficult to detect specular reflection light at the same time and detect only the aggregated particles (5c) by comparing two elements.

In addition, even in the pattern tilted part, there are variations in tilt angle and height for each element due to subtle fluctuations in the manufacturing process, and when dark field illumination is performed, the intensity of specularly reflected light differs greatly for each element. It becomes a thing. For this reason, when two devices are imaged and compared by dark field illumination, a large mismatch occurs in the pattern inclined portion, and many pseudo defects occur.

An object of the present invention is to provide a method for detecting agglomerated particles in a transparent thin film, which enables highly reliable detection of agglomerated particles present in a transparent thin film without generating pseudo defects.

[Means for solving problems]

The above-mentioned purpose is to process four types of images of the two elements imaged corresponding to these directions in a predetermined manner after the two elements are imaged in the dark field illumination from the opposite directions separately To be achieved.

[Action]

The scattered particles of the agglomerated particles in the transparent thin film can be detected regardless of the direction of the dark field illumination, but the pattern inclined portion can detect only the specular reflection light for the dark field illumination from a certain direction. Therefore, the two images captured under the dark-field illumination from the two opposite directions include the scattered light from the same lumpy particles in common, but the specular reflection light from the same pattern inclined portion is included. Are not included in common, and only specular reflection light from different pattern inclined portions is detected. By the way, when agglomerated particles are present in the upper part of the pattern inclined portion, one of the two images imaged under the dark field illumination from the two opposite directions separately has scattered light from the agglomerated particles in the lower part. Although it is detected by being buried in the regular reflection light component from the pattern inclined portion, on the other hand, only the scattered light component from the agglomerated particles is detected without being affected by the underlying pattern. Therefore, two elements are imaged by dark-field illumination from one direction, and a pattern inclined portion that is brightly detected by illumination from that direction is set as an inspection prohibited area, and the two images thus picked up are compared and inspected. By switching the illumination direction, all the aggregated particles can be detected without generating a pseudo defect in the pattern inclined portion. Since the inspection prohibited area is set by binarizing the difference between the two images obtained by illumination from two opposite directions, the inspection prohibited areas set for each illumination direction do not overlap each other, and By combining the inspection results for each illumination direction, the inspection can be performed over the entire area.

〔Example〕

 Hereinafter, the present invention will be described with reference to FIGS. 1 to 6.

First, the outline of the lumpy particle detecting apparatus according to the present invention will be described with reference to FIG. 2 as follows.

That is, the light from the light source 10 is condensed by the condenser lens 11 and the light blocking plate 1.
2. A wafer 17 to be inspected on which a plurality of elements that should be the same are formed via the periphery of the reflecting mirror 13 and the dark field objective lens 14.
It is designed to illuminate. Reflected light from the wafer 17 to be inspected is a central lens portion of the dark-field objective lens 14, a reflecting mirror (a mirror is only around the periphery and light can be transmitted through the center) 13, and an imaging lens 15.
An image is formed on the TV camera 16 via the.
By the way, the shading plate 12 has two kinds of shading parts as shown in FIG.
31 and 32, the portions 31a and 32a transmit light, and the portion 31
Since b and 32b are designed to block light, the dark-field illumination direction can be switched between left and right by moving the light-shielding plate 12 up and down in FIG.

Now, the operation of the device will be described. First, one element on the wafer 17 to be inspected is set on the TV with the light shielding part 31 inserted in the optical path.
An image is picked up by the camera 16, and its output is converted into a digital amount by the A / D converter 19 and then stored in the memory 20a. Next, while moving the light shielding plate 12 and inserting the light shielding portion 32 in the optical path, the device is imaged by the TV camera 16 and then the memory 2 is transmitted via the A / D converter 19.
It is supposed to be stored in 0b. After this, the shading plate 12 again
XY stage 18 with the light shield 31 moved in the optical path
The other elements having the same shape on the wafer 17 to be inspected are imaged by the TV camera 16 and stored in the memory 20c through the A / D converter 19, and the light shielding plate 12 is further moved to shield the light. 32
Is inserted in the optical path, the other elements are imaged by the T camera 16 and stored in the memory 20d via the A / D converter 19.

The four images stored in the memories 20a to 20d as described above are input to the defect determination circuit 40, which will be described in detail below, and the lump particles existing in the transparent protective film are detected. The images of the two elements must be pre-registered with each other. Although the alignment method is not directly related to the present invention and its detailed description is omitted, a method of precisely positioning the XY stage 18 to align the two elements and then imaging with the TV camera 16, and the memory 20a. There is a method of aligning the two elements by electrically shifting the image stored in 20d.

FIG. 1 shows a configuration of an example of the defect judgment circuit in FIG. Below, in order to simplify the explanation, the second
In the figure, the dark-field illumination direction with the light shield 31 inserted in the optical path is L, and the dark-field illumination direction with the light shield 32 inserted in the optical path is R. Also, 2 to compare
The image of the element A taken in the illumination direction L is A _L , the image of the element B is B _L , and the image of the element A taken in the illumination direction R is A _{R Is} described as B _R , it is as follows.

In other words, the defect determination circuit 40 memory 20a, 20b, 20c, the previously stored image A _L to 20d, A _R, B _L, enter the B _R is processing these in a predetermined, its configuration is A _L and B Absolute value circuit 44a, 44b for comparing _L , A _R , B _R , absolute value circuit 44a, 44b for these difference
Of the outputs from the selectors 45a and 45b and the selectors 45a and 45 for masking those corresponding to a predetermined area (inspection prohibited area)
Binarization circuits 46a, 46b for binarizing the output from 5b,
A logical sum circuit 47 for synthesizing the results of comparison and inspection from the binarization circuits 46a and 46b for each illumination direction L and R to obtain a final inspection result, and further imaged for each illumination direction L and R. Comprised of arithmetic circuits 41a to 41d, binarization circuits 42a to 42d, and AND circuits 43a and 43b for calculating an inspection prohibited area (hereinafter referred to as M _L and M _R ) when performing a comparative inspection of the images. It has become a thing.

Now, the circuit operation will be described with reference to FIG. 4 showing the relationship between processes. The subtraction circuit 41a for subtracting the image A _R from the image A _L.
, And the result is binarized by the threshold value (positive value) Th _{1 in the} binarization circuit 42a. This binarization result is obtained when the element A is dark-field illuminated in the illumination direction L. It is obtained as a result of extracting only the area corresponding to the pattern inclination portion from the brightly detected area portion. That is, a portion that is brightly detected along with the illumination directions L and R (a lump particle portion or a flat (horizontal) portion with a rough surface (by the way,
A _L , A _R , B _L , and B _R shown in Fig. 4 are not displayed as a bright state in the part corresponding to the flat (horizontal) part where the surface is rough due to the simplification of the drawing)) and lighting The inclination corresponding to the pattern inclination portion which is detected bright in the direction R is excluded. Similarly, the subtraction circuit 41c subtracts the image B _R from the image B _L, and the binarization circuit 42c subtracts the result from the threshold value Th ₁
When the element B is illuminated in the dark field from the illumination direction L by performing binarization with
Only the area corresponding to the pattern inclination portion is extracted. After that, the outputs of the binarization circuits 42a and 42c are AND circuits 4
By logical product of 3a
A, although common brightly the detected pattern inclined portion at B is detected, this is not an inspection inhibited area M _L in the case of performing the comparison of the two elements in the illumination direction L.

On the other hand, the absolute value of the difference between A _L and B _L is calculated by the difference absolute value circuit 44a, that is, the amount of mismatch is calculated, and the result can be output from the selector 45a. Alternatively, whether "0" is output depends on the state of M _L from the AND circuit 43a. When M _L is “1”, the selector 45a outputs “0”,
When M _L is “0”, the output of the absolute difference circuit 44a is output as it is. Therefore, in the output of the selector 45a, the dark field illuminated from the illumination direction L is detected to be dark and bright. The scattered light from the agglomerated particles existing in the area other than the pattern inclined portion is included, and the agglomerated particles can be detected by binarizing the scattered light with the threshold value Th ₂ by the binarizing circuit 46a. Is. By the same operation as described below, the lump particles existing in the area other than the pattern inclined portion which is brightly detected when the dark field illumination is performed from the illumination direction R are detected as the output of the binarization circuit 46b. Finally, the outputs of the binarization circuits 46a and 46b are logically summed by the logical sum circuit 47 so that all the lump particles existing on the device can be detected. In FIG. 4, the result is ORed and then binarized, but the same result is obtained in any case. By the way, the logical sum processing is required because the scattering state from the agglomerates is generally different depending on the dark-field illumination direction, and its size needs to be detected more reliably. Although not shown in FIG. 1, the noise component is removed by determining the size of the “1” area included in the result of the logical sum processing thereafter.

Now, FIG. 5 shows the configuration of another embodiment of the present invention. Dark field illumination is performed simultaneously from two opposite directions with light of different wavelength bands, and the image is detected by the TV camera for each wavelength band, so that two images of the element illuminated from the opposite two directions are detected simultaneously. It is to try. In order to achieve this, the light shield plate 21 inserted in the dark field optical path is, as shown in FIG. 6, a light shield portion 23 that does not transmit light, and transmits only light in the long wavelength band (red light) and transmits light of other wavelengths. A color filter 24a that reflects light and a color filter 24 that transmits only light in the short wavelength band (blue light) and reflects light of other wavelengths
It is composed of b. Further, as shown in FIG. 5, in order to separate and detect light in two wavelength bands,
A dichroic mirror 22 is inserted in the detection optical path (the dichroic mirror 22 is one that transmits red light and reflects blue light). In this state, the images detected by the two TV cameras 16a and 16b are A / D converters 19 and 19b.
The images of other elements after the movement of the XY stage 18 are stored in the memories 20a and 20b via the memory 20c and 20d, respectively.

In this way, in this example, two images of the element illuminated from two opposite directions can be detected at the same time, so that the inspection can be performed quickly.

〔The invention's effect〕

As described above, according to the present invention, like a thin film magnetic head used in a magnetic disk for a computer, agglomerated particles existing in a protective film of an element covered with a transparent protective film are affected by the pattern of the element. In addition, since the high reliability is detected without generating pseudo defects, the reliability of the product is improved.

[Brief description of drawings]

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 schematic configurations 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 details, FIG. 4 is a diagram showing an inter-process relation in the defect determination circuit shown in FIG. 1, and FIGS. 5 and 6 are other examples of the lump particle detecting device according to the present invention. FIGS. 7 and 8 are diagrams showing a schematic structure and details of a light-shielding plate in the structure, and FIGS. 7 and 8 are partial cross-sectional views of a thin-film magnetic head for explaining the problems of the conventional technique. 12,21 Shield plate, 13 ...... Reflector, 14 ...... Dark field objective lens, 16,16a, 16b ...... TV camera, 19,19a, 19b ...... A / D
Transducer, 20a to 20d ... Memory, 40 ... Defect determination circuit, 41
a to 41d ... subtraction circuit, 42a to 42d, 46a, 46b ... binarization circuit, 43a, 43b ... AND circuit, 44a, 44b ... difference absolute value circuit, 45a, 45b ... selector, 47 ...... OR circuit.

Claims (2)

[Claims] 1. A transparent thin film protects the upper surface of each of the two inspected elements A and B, which have the same shape, and are separately dark-field illuminated from opposite two directions L and R. Imaged, dark field illumination direction L, R for each device A, B to be inspected
Corresponding multi-level digital image data A _L , A _R , B _L , B _R
By a predetermined process to detect the presence or absence of agglomerated particles existing in the transparent thin film, and a multi-value for each of the inspected elements A and B related to the visual field illumination direction L is obtained. Absolute value difference image data | A _L −B _L | is calculated from the digital image data A _L , B _L , and multivalued digital image data A _R , a _R -B _R | | absolute value difference image data from the B _R while obtaining the difference image data a _L -A _R, extracts the examination forbidden region M _L in field illumination the illumination direction L from the B _L -B _R, the difference image data _{a R -A L, B R -B} L extracts the examination forbidden region M _R in field illumination the illumination direction R from the absolute value difference image data in a state masked by the inspection inhibited area M _L | a _L −B _L |
Binarization result and the absolute value difference image data in a state masked by the inspection prohibited area M _R for | A _R -B _R | from the OR result of the binarization results for bulk present in the transparent thin film A method for detecting agglomerated particles in a transparent thin film, wherein the presence or absence of particles is detected. 2. The inspection-prohibited area M _L is an inspection-prohibited area as a logical product result of a binarization result for the difference image data A _L -B _{L and} a binarization result for the difference image data B _L -B _R. M _R is the binarization result for the difference image data A _R , A _L and the difference image data B _L
Each of which is extracted as a logical result of the binarization result for the -B _R, massive particle detection method in the transparent thin film of the appended claimed range first term of.