JPS6148751A - Method for detecting surface defect - Google Patents

Abstract

PURPOSE:To catch a titled surface defect precisely by irradiating the surface of moving material to be inspected from a prescribed angle by an emitter and picking up the neighbourhood of a regular reflected image including the regular reflected image of the emitter reflected to the surface of the material to be inspected from the prescribed angle by a two-dimensional optical sensor. CONSTITUTION:The surface of the material 101 to be inspected moving on a conveyor 102 at a specified speed is widely irradiated by the emitter 103 which is arranged above the conveyor 102 and emits homogeneous light around and alike, the regular reflected image 103' of the emitter 103 reflected to the surface of the material 101 to be inspected and the neighbourhood of the regular reflected image are picked up from the prescribed angle by the two-dimensional optical sensor 104 such as a TV camera or the like. Then, the surface defect 100 of the material 101 to be inspected is detected from the reflected image except the regular reflected image 103'' of the emitter 103 appearing on an image face plate 108 of the two-dimensional optical sensor 104.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention provides a method for optically detecting surface defects in flat materials whose surfaces are finished to a glossy surface close to glass or mirror surfaces, such as glazed substrates and silicone unicorns. Regarding.

[Conventional technology]

Glazed substrates (ceramic substrates with glass coating on the surface) used in facsimile thermal print heads and silicon wafers used as substrates for semiconductor devices are subject to strict regulations regarding surface flaws, cleanliness, flatness, etc. Currently, such surface inspections are performed visually by inspectors.

However, there is a risk that defects may be overlooked with visual inspection, and it is difficult to increase the line speed due to limitations in visual inspection ability, so recently various devices that optically detect this type of surface defect have been developed. being developed. For example, the "defect detection device" disclosed in Japanese Patent Application Laid-open No. 52-10793, as shown in FIG. The specular reflection light e01) from each irradiation part is sequentially irradiated onto the sheet material (1) through the specular reflection light receiver (91).
Then, the diffusely reflected light 02) is received separately by the diffusely reflected light receiver (92), and the optical q? The defect is detected by converting the ja difference (change in the received photoelectricity) into an electrical signal. This device uses a specular reflection receiver (9
If there is a change in the amount of light received only in 1), the detection defect is a light absorption type defect such as discoloration, and the specular reflection light receiver (91
) and the diffuse reflection receiver (92) at the same time, the type of defect can be identified at the same time as the surface defect is detected, such as that the detected defect is a scattering defect such as a scratch. It is possible.

In addition, the "surface flaw detection apparatus" disclosed in Japanese Patent Application Laid-Open No. 53-65777 is as shown in FIG. Irradiation light (4)
is irradiated at a constant irradiation angle (ψ), and only the scattered light from the entire irradiation part (6) is detected at a detector (5) equipped with a photoelectric element from the irradiation angle (ψ) and an angle different from the reflection angle (6). ) to detect defects.In this device, the flaw detection surface (3
) When there is a flaw in the irradiation part (6), the flaw detection signal is output only when the electrical signal of the strong scattered light is input, so the signal-to-noise ratio is high. signal strength ratio) is obtained.

[Problem that the invention seeks to solve]

However, with any of the conventional detection devices described above, it is difficult to detect a pole (gentle unevenness defect (100)) with a width (width of 110 mm or less, height) of about several μm as shown in FIG.

In other words, when the inspection surface is irradiated from a certain angle, the scattered light from the extremely gentle unevenness defect 00ω is reflected at an angle that is almost the same as the specularly reflected light from the defect-free area.
In the apparatus shown in FIG. 2, most of the scattered light is received by the specular reflection light receiver (91), and the specular reflection light receiver (91), which always receives strong and strong specular reflection light, is received by the specular reflection light receiver (91). ), it is not possible to easily determine the change in the amount of received light due to the incident of the scattered light.

In addition, a photodetector (5) as in the device shown in FIG.
is placed at an angle different from the specular reflection angle of the irradiated light (4),
With a method that detects only the scattered light from the irradiation part (6), it is almost impossible for the detector (5) to capture the scattered light from the extremely gentle unevenness defect 000), considering its arrangement. That's why.

The present invention was developed in view of the above circumstances, and is capable of detecting extremely smooth surfaces that were conventionally difficult to detect in optical surface inspection of materials that require perfect flatness, such as glazed substrates and silicon wafers. The present invention aims to provide a method for detecting surface defects that can detect uneven defects with a high signal-to-noise ratio and also allow identification of the degree and type of detected defects.

Hereinafter, the present invention will be described in detail based on the accompanying drawings.

[Means for solving problems]

FIGS. 1(a) and (b) are schematic diagrams explaining the method of the present invention, in which (101) is a test material being transported at a constant speed in the direction of the arrow on a transport table 002), and 003) is a transport stage 0o2. 004) is a light-emitting body that emits uniform light around a mercury lamp or the like fixedly placed above ), and 004) is a specular reflection image of the light-emitting body (103) reflected on the surface of the inspection material 001), and its vicinity is a lens 005). a two-dimensional optical sensor such as a television camera placed in the field of view; (106) an image processing device that converts the image of light captured by the lens of the sensor into a video signal;
007) is a television monitor.

As shown in the figure, the method of the present invention transfers the surface of the inspection material 001) moving at a constant speed on the transport stage 002) to the transport stage 002).
) Luminous body 003 that emits uniform light around the surroundings placed above
) and the specular reflection image (103) of the light emitting body (103) reflected on the surface of the inspection material (101) 7) and the vicinity of the specular reflection image with a two-dimensional optical sensor such as a television camera from a predetermined angle. 004), and the image was taken in Figure 1 (b).
), the imaging screen (1) of the two-dimensional optical sensor 004)
From the reflection image α00) other than the specular reflection image 003) of the light emitter (103) appearing in 08), the surface defect of the inspection material 001) is 0.
00).

That is, while illuminating the surface of the inspection material 001) with a light emitter 003) with a wide and uniform brightness, the specular reflection image 003) of the light emitter 003) reflected on the inspection material α01) from a predetermined angle and its vicinity are captured using two-dimensional optics. If the image is captured by the sensor (104), uneven defects such as scratches (100
), the image capturing screen 008) captured by the lens 005) of the sensor 004) includes a reflected image 00 of light from the defective (100) surface, in addition to the regular reflected image (103) of the light emitter 003). appear.

This reflected image 000) is as shown in FIG.
1) The light emitter (103
) is reflected at an angle equal to the angle of incidence and is captured by the lens 005) of the sensor 00υ, so the light of the light emitter 003) that is always captured by the lens (105) is It can be clearly detected on a television monitor 007) due to the strong luminance signal equivalent to that of the reflected image 003).

can. In this case, the luminescent material 00 from the test material 001)
3) The specularly reflected light (indicated by the solid line) is cut, and the imaging screen is set to 0.
If masking processing is applied to 08) so that the regular reflection image qO center of the light emitter is not reflected, the reflection image 00d) from the defect qOω can be obtained.
can be detected more clearly.

Furthermore, as shown in FIG. 5, the reflected image (100') detected on the imaging screen 008) of the lens α05) is detected at a farther position than the specularly reflected image 003). The inclination angle (δ0) of 100 is large, and the inclination angle (δa) of the specular reflection image (detected at a position near 10) is small. Luminous body q03) captured by 008)
Since the position of the regular reflection image (10:3') of It is also possible to judge the degree.

Note that (δ1) is the minimum detectable angle, and a defect 00ω on a slope that is gentler than this angle (δ1) is
The width (Z',
), indicating that it cannot be detected. As shown in FIG. 6, this limit detection angle (δ1) is as follows: )
The center of If it is the width, it is determined by the following formula 0.

In other words, the limit detection angle (δ1) is determined by the geometrical positional relationship between the above (Zl), the light emitter 003), and the two-dimensional optical sensor α04), so the angle can be adjusted as appropriate according to the inspection standards, etc. It can be done.

For example, as shown in Figure 7, (el) is 2828 mm
, (rnt) is set to 283 mm, (el) is set to 45° (straight line X), and (11) is 3450 caps (ml)
When 345- (δ1) is set to 30° (straight line Y
), even if (Zl) is the same, for example, 4 mm, the limit detection angle (δ1) is 0.3° on the straight line X, while it is as small as 0.2° on the straight line Y.

Furthermore, in both cases of the straight line X and the straight line Y, it is possible to further reduce the limit detection angle (δ1) by decreasing the value of (Zl). As a method of reducing the value of (Zl), for example, as shown in FIG.
The light emitter (103) and the test material 001) are reflected several times by
Recommended methods include increasing the distance from the light source and minimizing the width (Zl) of the image (103') of the light emitter reflected on the inspection material (101).

FIG. 8 shows another embodiment of the method of the present invention, in which the number of light emitters is increased to two.

In this case, the imaging screen 008 of the two-dimensional optical sensor 00◇)
is a regular reflection image of two light emitters (103aX103b) (
IO3a) and (103b) are projected with a certain gap, and two reflected images (10da) (10
0'b) will be captured. In other words, the reflected image (
10da) is the light emitting body (103a) incident on the rear side slope (ll)I)) of the defect α00) as seen from the lens 005).
The reflected light (indicated by the dashed-dotted line) from the light emitter (103b) that entered the front slope (Pa) of the defect 000) is captured. This is a statue that captures Therefore, as shown in FIG. 9, for example, even if the defect 000 has a shape in which the angles of the rear side slope (Po) and the front side slope (Pa) are extremely different,
Two reflected images 000'a) appearing on the imaging screen (108)
(100b) Each specular reflection image (103', )
By checking the position from (103'b), it is possible to recognize approximately the actual degree of the defect.

In addition, in this example, the limit detection angle of defect 000) is determined by the light beam from the light emitter (103a) and by the light beam from the light emitter (103a).
The limit detection angle (δ1) for the light beam from the light emitting body (103a) can be determined by the above formula 0, and the limit detection angle (δ1) for the light beam from the light emitting body (103b) needs to be determined in advance for both the case of the light beam from the light emitting body (103b). The limit detection angle (δ2) due to the light beam from the light emitter (103
b) One point on the top is (C), the incident angle at the time of specular reflection of the light beam from the 0 point is (θ2), and the light emitting body (103) reflected on the surface of the test material is
If the width of the image in b) is (z2), it is determined by the following equation 0.

In addition, the method of the present invention can detect not only angular irregularities but also stains attached to the surface of the inspection material.

That is, as shown in FIG. 11, the dirt 01ω attached to the surface of the test material (101) absorbs light, and the test material 001
) The reflectance is lower than that of the good surface area.

Therefore, the lens (105) of the two-dimensional optical sensor captures the irregularity defect as a dark area (UC; ) with low brightness, which can be easily detected through a TV monitor (007), etc. .

In addition, the extraction screen (10
8), it is best to set an image window 011) as shown in Fig. 12 to limit the defect detection range on the surface of the inspection material 001). Vertical direction within the screen +7 when setting
) Light (7) Brightness wo At Al+A2 A'! , A3
Specular reflection image of As (measured as D, light emitter 003) (
103'') position, even if the regular reflection image (103') reflected on the surface of the inspection material 001) moves due to vibrations of the transport table 002), the image window (111)
Accurate defect detection can be performed by shifting the position up and down.

Next, examples will be described.

Example] A surface inspection of a glazed substrate used as a thermal print head for facsimile/millimeter printing was carried out according to the method of the present invention.

As shown in FIG. 13, the glazed substrates 001 mounted on the cassettes (1121) are sent one by one to the transfer table (10), and as they are moved in the direction of the arrow, the surface of the glazed substrates 001 being moved is Irradiated with a rod-shaped mercury lamp 003), the glazed substrate 00 was moved with a TV camera (10◇).
The surface of 1) was imaged with the specular reflection image of the mercury lamp 003) reflected on the surface as the center. Normally, in the case of this type of glass coating material, it is sufficient to detect irregularities of '/1000, so the limit detection angle is 0.5° (azeta>10
"0.057°) is required. From this, mercury lamp 00
3) is 2500 to 350 for glaze substrate 001)
Arranged to irradiate light from a position 0 mm away, Chimpi Camera 00 ◇ is 30 ~
The arrangement was such that a regular reflection image of the mercury lamp 0o3) reflected on the substrate 0o1) could be captured from an angle of 45°.

Furthermore, in order to increase the distance of the mercury lamp 003) and increase the detection limit, the light of the mercury lamp 003) was reflected several times by two parallel mirrors (109) (109). The image captured by the television camera 004) is converted into a video signal by the image processing device 006), and then sent to the television monitor (10).
7) so that it can be observed.

As a result, the glaze substrate 00 moving on the transport table 00
1) If there is an irregularity defect of 0.5° or more on the surface, the glaze group projected on the TV monitor α07), temporary (Lo
On the surface of glaze substrate 00L), a reflected image of strong brightness from the defect appeared due to the light from the mercury lamp 003), making it possible to completely detect even the mildest defects on the surface of glaze substrate 00L) without missing them. At the same time, by finding dark areas with low brightness appearing on the surface of the glaze substrate 001) of the television monitor 007), it was also possible to completely detect dirt attached to the surface of the glaze substrate 001).

〔Effect of the invention〕

As explained above, according to the method of the present invention, uneven defects on the surface of the inspection material are detected as reflected images with strong brightness even if they are at a very gentle angle, so the signal-to-noise ratio is high (and no defects are overlooked).

In addition, it is possible to not only judge the degree of unevenness of surface defects by the distance of the detection position of the reflected image based on the regular reflection image of the light emitter, but also to detect dirt on the surface of the inspection material. Excellent effects such as being able to detect as

[Brief explanation of drawings]

FIG. 1 is a diagram schematically explaining the outline of the method of the present invention, in which (a) is a perspective view and ■ is a side view of the main part. FIGS. 2 and 3 are diagrams explaining an example of conventional optical surface inspection, FIG. 4 is a cross-sectional diagram showing the shape of a gently uneven defect, and FIG. 5 is a diagram explaining the detection angle of the defect. Figure 6 is a diagram explaining the limit detection angle (δ1), and Figure 7 is the limit detection angle (δ1).
Fig. 8 is a diagram illustrating another embodiment of the method of the present invention, Fig. 9 is a linear diagram showing the relationship between the width of the image of the light emitter reflected on the inspection material (Zl), and Fig. 9 shows the angle of the slope being different between the front and back. 10 is a diagram illustrating the limit detection angle (δ2); FIG. 11 is a diagram illustrating stain detection by the method of the present invention; FIG. 12 is a diagram illustrating the image window; FIG. 13 is a diagram illustrating an embodiment of the method of the present invention. 100: Defect, 100 second reflection image, 101: Inspection material, 1
02: Transport table, 103: Light-emitting body, 103': Image of the light-emitting body reflected on the inspection material, 103: Specular reflection image of the light-emitting body projected on the imaging screen of the two-dimensional optical sensor, 104: Two-dimensional optical sensor, 105 : Lens, 107: TV monitor, 1
08: Imaging screen, 110: Dirt 110: Dirt image,
δ1. δ2: Limit detection angle Fig. 7 Zl (mm) Fig. 5 100a Fig. 6

Claims (1)

[Claims] (1) The surface of the moving inspection material is irradiated from a predetermined angle with one or more illuminants that emit uniform light, and specular reflection images, including the regular reflection image of the above-mentioned illuminants, are reflected on the surface of the inspection material. A method for detecting surface defects, comprising: imaging the vicinity of the inspection material from a predetermined angle with a two-dimensional optical sensor, and detecting surface defects on the inspection material from reflected images other than the regular reflection image appearing on the imaging screen.