JPH01147349A - Detecting method for solid particle in transparent thin film - Google Patents

Abstract

PURPOSE:To detect all solid particles without generating artificial defect by composing an image for comparative inspection of images of an element which are picked up while dark visual field lighting is performed in plural directions, and comparing formed images of two elements with each other. CONSTITUTION:Light from a light source 10 illuminates a wafer 23 to be inspected through a lens 11, a light shield plate 12, a reflecting mirror 13, and the periphery of an objective 14. Its reflected light forms its image on a TV camera 16 through the lens part of the objective 14, the reflecting mirror 13, and an image forming lens 15. While the light shield plate 31 of the light shield plate 12 is put in the optical path and while the light shield plate 32 is put in the optical path, the same element is picked up by the TV camera 16 and a smaller signal between two video signals is stored in a memory 20 through an A/D converter 17 and a minimum value composing circuit 19. The minimum value composing circuit 19 calculates minimum values for other elements similarly. The output of the minimum value composing circuit 19 and the image output stored in the memory 20 are inputted to an absolute value arithmetic circuit 21 to calculate the absolute value of the difference, thereby detecting a defect through a binarizing circuit 22.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for inspecting the appearance of transparent elements such as thin-film magnetic heads used in magnetic disks for computers. The present invention relates to a visual inspection method suitable for detecting lump particles mixed into a transparent protective narrow width.

[Conventional technology]

As the prior art closest to the present invention, ordinary dark field illumination -
This method of detecting bulk particles in a transparent thin film will be explained.

Figure 6 is a partial cross-sectional view of the thin film head, showing the coil conductor 1.
．． Insulating layer 2. It is composed of a magnetic material 4 and a transparent &a film 3. The presence of lumpy particles 5a, 5b in the retaining film results in effective & k k r.

The thickness becomes thinner and the reliability of the child decreases.

In addition, the lumpy particles 5b are present on the surface of the protective film, and if the lumpy particles fall onto the surface during use of the disk, it will cause serious accidents such as damage to the device or loss of tape. I feel safe. As shown in FIG. 6, lump particles 5a.

Since 5b has an irregular shape, by illuminating it with dark field, even if it is a transparent material that cannot be detected with bright field illumination, light is scattered at the interface and it can be detected brightly. The image obtained by dark-field illumination includes the scattered light by the above-mentioned lumpy particles and the inclination fi of the pattern forming the element e4.
The specularly reflected light from the + part (for example, the #!fP+ parts 41 and 42 of the magnetic material 4) and the scattered light from the pattern edge are included. Therefore, two elements having the same shape are imaged with dark field illumination and compared. By doing so, you can maintain! ! A lumpy particle in the abdomen can be detected as a discrepancy between images.

A method for detecting lumpy particles (foreign matter) attached to a semiconductor wafer is to illuminate the wafer obliquely with a laser and detect the scattered light.
It is stated in No. 35.

[Problem that the invention seeks to solve]

In the conventional method of detecting lump particles in a transparent thin film by imaging two elements of the same shape with dark field illumination and comparing them, the lump particles existing on the sloped part 41 of the pattern are detected as shown in FIG. Particle 5C has some defects that make it 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 slope portion 41 located below the lump particles, and the scattered light from the lump particles 5C and the pattern slope portion 41 (/ Detects specularly reflected light at the same time,
It is difficult to detect lumpy particles (/J) by comparing two elements.

In addition, the pattern slope portion 41 has variations in slope angle and height for each element due to subtle fluctuations in conditions during the 70 process of manufacturing, and when dark field illumination is performed, the specularly reflected light intensity varies for each element. It will be very different. For this reason, when two elements are imaged using dark field illumination and compared, mismatches occur in the sloped portions of the patterns, resulting in a large number of false defects.

SUMMARY OF THE INVENTION An object of the present invention is to solve the problems of the prior art described above and to provide a method for detecting massive particles in a transparent thin film with high reliability without generating false defects.

[Means for solving problems]

In order to achieve the above object, the present invention provides means for performing dark field illumination from a plurality of different directions, instead of illuminating the device from all directions simultaneously when performing dark field illumination of the element. The feature is that the device is imaged for each illumination, the multiple images obtained are combined to create a new image for 1/9 ratio inspection, and the created images are compared between the two devices. There is. The image for comparison inspection is created by selecting the minimum value for each corresponding pixel of a plurality of images obtained by capturing each illumination from each direction.

[Effect]

Agglomerated particles in a transparent thin film can detect their scattered light regardless of the direction of dark-field illumination, but the sloped part of the turn can only detect specularly reflected light from dark-field illumination from a certain direction. Unable to detect.

Therefore, multiple Q] images taken with dark-field illumination from different directions commonly include scattered light from the same lumpy particles, but specularly reflected light from the pattern slope is common (this is Rarely, only specularly reflected light from different pattern slopes is detected.Therefore, six images were taken using dark-field illumination from different directions of the decimals (in contrast, for each corresponding pixel, A new image ζ for comparison inspection created by calculating the minimum value of The images for comparison inspection obtained in this way are compared to two images with the same shape.
] By comparing between the elements, all lump particles, including the lump particles present on the turn inclination 8+ portion, can be detected without generating pseudo defects.

〔Example〕

Hereinafter, one embodiment of the present invention will be explained with reference to the first factor and FIG. FIG. 1 is a schematic diagram of an embodiment of the present invention. The light emitted from the light source 10 passes through the condenser lens light shielding plate 12
15 per reflection. @The wafer 23 to be inspected is illuminated through the periphery of the viewing objective lens 14. The reflected light from the wafer to be inspected 23 is transmitted to the lens portion of the dark field objective lens 14,
After passing through a reflecting mirror 15 (only the periphery is a mirror and light passes through the center), an image is formed on the TV left camera 6 through an imaging lens 15i. The light shielding plate 12 has two types of light shielding plates 31 and 52 as shown in FIG.
By moving the light-shielding plate 12 up and down with reference to FIG. 1, the dark field illumination direction can be switched to the left and right in the -j diagram.

Is this book implemented below? 1J(1) The operation will be explained. 1 on the wafer 23 to be inspected with the light shielding plate 31 inserted into the optical path.
The two elements are imaged by the TV camera 16 and the output is A/D.
After being converted into a digital quantity by a converter 17, it is stored in a memory 18. Next, with the optical plate 12 moved and the optical plate 62 inserted into the optical path, the same element was imaged with the 1゛V camera 16, and the output was digitalized with the A/D converter 17.
Jk:, I'll throw it. At this time, in synchronization with the output of the A/D converter 17Q, the image previously stored in the memory 18 is displayed, and together with the output of the A/D converter 17, the minimum value synthesis circuit 1
Enter 91. The minimum value synthesis circuit 19 is designed to always output the smaller of the two input video signals, and its output is stored in the memory 20E. X-
The Y/θ stage 24 is moved, and another element having the same shape is imaged on the wafer 23 to be inspected (/J) using the same procedure as in J. The minimum value is also calculated from the image by the minimum value synthesis circuit 19. At this time, in synchronization with the output of the minimum value synthesis circuit 19, the image previously stored in the memory 201 is read out and the output of the minimum value synthesis circuit 19 is calculated. The difference absolute value calculation circuit 21 calculates the absolute value of the difference between the two input signals, and the output is converted to an appropriate threshold T by the binarization circuit 22.
By binarizing with h, it is possible to detect a defect, that is, a lump particle mixed in the transparent suppurative spread on the wafer 23 to be inspected.

Is Fig. 3 one step of the minimum value synthesis circuit 19? 11 is shown.

2 Q' input signals to comparator 41 and multiplexer 4
2 (Input to both /J. The magnitude relationship of the two input keys (this causes the output of the comparator to switch to 10" or 1",
The multiplexer always outputs the smaller signal of these two input signals.

FIG. 4 is a block diagram of another embodiment of the present invention.

By simultaneously performing dark-field illumination from different directions in different wavelength bands and detecting the TV right camera for each wavelength band, it is possible to simultaneously detect a plurality of images illuminated from different directions. In order to realize this, the dark field optical path insertion T6 light shielding plate 33 is constructed as shown in FIG. In the figure, -C35c is a light shielding part that does not transmit the original light, and 65a is a color filter that transmits light in a long wavelength band (red light) and reflects light of other wavelengths.

It is a color filter that only transmits light in a short wavelength band (blue light) and reflects light of other wavelengths. Furthermore, in order to separate and detect two wavelength bands, a dichroic mirror 34 is inserted in the detection optical path in the configuration diagram shown in FIG. The evening clock mirror 34 is one that transmits red light and reflects blue light. The images detected by the two U and J TV cameras 16a and 16b are combined into a minimum value synthesis circuit 19f.
Enter this. The configuration after the minimum value synthesis circuit is the same as the actual M example shown in FIG. In the case of a false flow, two images (/J plane images) in the illumination direction can be detected simultaneously, so the inspection time can be shortened. [Effects of the Invention] As explained above, according to the present invention, This method has a remarkable effect on improving the reliability of products because it is possible to detect lumpy particles with high reliability without generating false defects, regardless of where they are present.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of 8 examples of the present invention, Fig. 2 is a diagram showing the light shielding plate shown in Fig. 1, and Fig. 3 is an example 1 of the method for detecting lump particles according to the present invention. Figure 4 is a configuration diagram of an actual CIJ example in addition to the present invention; Figure 5 shows the light shielding plate shown in Figure 4; Figure 6 shows the part of the thin film magnetic head; FIG. 12... Light shielding plate 13... Reflection ridge 14...
・Dark field objective lens 16... TV right camera 19... Minimum value synthesis circuit 35... Light shielding plate 41 River comparator 42... Multiplexer\, Agent Patent attorney Masaru Ogawa 2 Figure 46 Figure 4 Figure Sheath 5 Figure Blank 6 Figure 47 Figure 2 Disconnected layer 5 U J j Round particle

Claims (1)

[Claims] 1. Apply dark-field illumination from a plurality of different directions using a dark-field illumination means, take an image using an imaging means for each illumination from each direction, and use a calculation means to calculate the minimum value for each corresponding pixel of the plurality of images taken. A lumpy particle in a transparent thin film is characterized in that a value is calculated and the calculated result is compared between two elements by a comparison means to detect lumpy particles mixed into the protective film of an element protected by a transparent thin film. Particle detection method.