JPH061179B2 - Defect inspection method and apparatus - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a defect inspection method and apparatus for detecting a defect on a transparent object to be inspected, and more particularly to a minute unevenness defect of the object to be inspected and the object to be inspected. The present invention relates to a defect inspection method and apparatus for inspecting foreign matter defects such as dust adhering to the surface by clearly distinguishing them.

[Background of the Invention]

The human eye has a great ability to discriminate light and dark differences and color differences, but when it becomes a transparent object like glass,
You can't tell this unless you have very large scratches or dirt. As a means to measure the difference in the refractive index and the thickness that exist in the transparent object very slightly, it is used for observing transparent objects such as raw cells and fungi that have little difference in brightness and color tone. There is a phase contrast microscope. The phase-contrast microscope is, for example, "Science of Living Body" Vol.
6th year) by Toshikazu Horizontal in the article entitled "Phase-contrast microscope and interference microscope".

FIG. 5 is a principle configuration diagram of the phase contrast microscope. 10 is a light source, 11 is a collector lens, 12 is a ring-shaped slit, 13 is a condenser lens, and the slit 12 is arranged at the front focus position of the condenser 13. Reference numeral 15 denotes an objective lens, and a phase plate 16 having an absorption film 18 is arranged at the back focal position of the objective lens 15 capable of forming an image of the slit 12. This absorption film 18
Is to attenuate the direct light (0th-order diffracted light) 8 having a remarkably large intensity as compared with the diffracted light 9 to balance the intensity of the diffracted light (higher-order diffracted light) 9 and the direct light 8.

With such a configuration, the condenser lens 13 and the objective lens 15
Diffracted light whose amplitude is modulated according to the phase difference of the refractive index change or the thickness change of the inspected object 14 with the direct light 8 modulated by the transmissivity of the inspected object 14 placed between When a phase change is applied to 9 by using the phase plate 16 so as to directly interfere with the light, the phase change due to the object 14 to be inspected can be observed in the image 17 with a contrast of light and dark.

As described above, if a phase contrast microscope is used, it is possible to observe the difference in the refractive index and the thickness, which are present in a transparent object, as a light and dark contrast, but the diffracted light 9 is caused by foreign matter such as dust on the sample. Since foreign matter also occurs, the foreign matter is also observed as light and dark contrast. On the other hand, a phase contrast microscope has a halo with a very high contrast called a halo,
The observed image is often very different from the real image. Therefore, it is very difficult to discriminate between the unevenness defects existing in the sample, which are observed as a difference in the refractive index and the thickness, and the foreign matter such as dust adhering to the surface.

Therefore, conventionally, after obtaining an image based on uneven defects and foreign matter with a phase contrast microscope, for example, using a phase contrast microscope as a transmission illumination microscope by removing the slit from the phase contrast microscope, whether the image is due to foreign matter. It was reconfirmed with the naked eye whether or not. Therefore, it takes a long time to inspect the object to be inspected, which is an obstacle to the automation of the inspection.

[Object of the Invention]

An object of the present invention is to eliminate the above-mentioned drawbacks of the conventional method, and to detect the minute unevenness defect of the object to be inspected and the foreign matter defect such as dust adhering on the surface of the object to be inspected with high sensitivity and clearly discriminating. To provide a defect inspection method and an apparatus therefor.

[Outline of Invention]

The present invention, in order to achieve the above object, focusing on the fact that it is not possible to inspect by clearly discriminating the minute unevenness defect of the inspection object and the foreign matter defect on the inspection object surface only by the phase contrast microscope,
The thickness of the object to be inspected obtained by illuminating the object to be inspected with the first and second illumination light beams having concentric and different wavelengths substantially perpendicularly, and obtaining the object from the object to be inspected illuminated by the first illumination light beam or Each of the high-order diffracted light amplitude-modulated according to the phase difference amount based on the refractive index and the light amplitude-modulated by the reflectance or the transmittance from the surface of the object to be inspected illuminated by the second illumination light flux, An image is formed through a phase-contrast microscope detection optical system composed of an objective lens, a phase plate and an absorption film that are concentric with respect to the optical axis of the objective lens, and a central transmission portion, and the images are separated by wavelength, and the separated and combined. The imaged higher-order diffracted light image is received by the first photoelectric means to detect a grayscale image signal corresponding to the thickness or refractive index of the object to be inspected, and the detected grayscale image signal is converted to a second value by the binarizing means. For binary image signal of 1 Conversion, and said isolated by optical image that has been amplitude-modulated by the imaging reflectance or transmittance second
The photoelectric conversion means detects light to detect an image signal of a foreign matter, the binarizing means converts the detected image signal of the foreign matter into a second binarized image signal, and the converted first two A defect inspection method characterized by comparing a binarized image signal with a second binarized image signal to discriminately detect a fine unevenness defect of an inspected object and a foreign matter defect on the surface of the inspected object. .

Further, according to the present invention, an illuminating means for illuminating an object to be inspected with first and second illuminating light fluxes which are concentric and have mutually different wavelengths, and an objective lens and a concentric optical axis of the objective lens. According to the phase difference amount based on the thickness or the refractive index of the inspected object obtained from the inspected object illuminated by the first illumination light flux by the illuminating means. Of the high-order diffracted light amplitude-modulated by the illumination means and the light amplitude-modulated by the reflectance or the transmittance from the surface of the object to be inspected illuminated by the second illumination light flux by the illumination means. And a phase microscope detection optical system for forming an image through the absorption film and the central transmission portion, and an amplitude due to the higher order diffracted light and the reflectance or the transmittance formed by the phase difference microscope detection optical system. Separation optical system for separating modulated light by wavelength, and the thickness of the object to be inspected by receiving the high-order diffracted light image separated by the separation optical system and formed by the phase contrast microscope detection optical system. First photoelectric conversion means for detecting a grayscale image signal corresponding to a refractive index, and light separated by the separation optical system and amplitude-modulated by the reflectance or the transmittance imaged by the phase difference microscope detection optical system. Second, which receives an image and detects an image signal of a foreign matter on the surface of an object to be inspected
And a first binarizing unit that binarizes the grayscale image signal detected by the first photoelectric converting unit with a desired threshold value and converts the binarized image signal into a first binarized image signal. Second binarization means for binarizing the image signal of the foreign matter detected by the second photoelectric conversion means with a desired threshold value and converting it into a second binarized image signal; and the first binarization. A first binarized image signal obtained by means and a second binarized image signal obtained by the second binarization means.
A defect inspection apparatus comprising: a defect detection unit that compares a binarized image signal with each other to discriminate and detect a minute unevenness defect of an inspection object and a foreign matter defect on the surface of the inspection object.

Example of Invention

An embodiment of the present invention will be described below with reference to FIGS. 1 to 4.

FIG. 1 is a principle configuration diagram of a defect inspection apparatus according to the first embodiment of the present invention, and the same members as those shown in FIG. 5 are designated by the same reference numerals.

In the defect inspection apparatus according to the present embodiment, as the slit inserted between the collector lens 11 and the condenser lens 13,
The filter 12 'shown in FIG. 2 is a circular green filter.
20 and a ring-shaped red filter arranged on the outer periphery of the filter 20. Then, the phase plate 16 and the image plane 17
A dichroic mirror 22 that transmits red light and reflects green light is arranged in the optical path between the two, and an image of green light is formed on the image plane 23. That is, the defect inspection apparatus of this embodiment is adapted to obtain an image by a phase contrast microscope with red light and an image with a transmission illumination microscope with green light.

With such a configuration, the red light 25 emitted from the transmissive illumination light source 10 and passing through the red filter 21 of the filter 12 'passes through the collector lens 13 and illuminates the inspected object 14. The red illumination light 25 causes the object 14 to be inspected
Direct light 8 whose amplitude is mainly modulated by the transmittance of
Diffracted light 9 which is amplitude-modulated according to the thickness or refractive index of the object 14 to be inspected and has a phase change of λ / 4 is emitted. The direct light 8 is converted into λ / 4 or −λ / 4 by the phase plate 16.
Is absorbed by the absorption film 18,
It is converted so that it can interfere with the diffracted light 9. Since both the direct light 8 and the diffracted light 9 are red, the dichroic mirror 22
And a grayscale image corresponding to the phase difference amount of the inspection object 14 is formed on the image surface 17.

On the other hand, the green light 24 emitted from the illumination light source 10 and passing through the green filter 20 of the filter 12 passes through the condenser lens 13 and illuminates the sample 14 to be inspected. The green light 24 causes the inspected object 14 to emit a light beam 26 whose amplitude is mainly modulated by the transmittance of the inspected object 14. The light ray 26 passes through the objective lens 15, the phase plate 16 and the absorbing film 18. The phase change by the phase plate 16 does not change the amplitude modulation characteristic of the light ray 26 at all, and the absorption film 18 is minute, so that it does not significantly affect the photoelectric 26. Therefore, the light ray 26 is almost the same as the light ray obtained by a normal passing illumination optical system. This ray
26 is reflected by the dichroic mirror 22, and the image
A transmitted illumination detection image, that is, a dust image is formed on 23.

Then, as shown in FIG. 3, photoelectric conversion elements such as television cameras 27 and 28 are arranged on the image plane 17 and the image plane 23, respectively, and the electric signals 29 and 30 are binarized by the binarization circuits 31 and 32, respectively. Then, if the outputs of the binarization circuits 31 and 32 are set to V ₁ and V ₂ , respectively, and the following determination is performed using the determination circuit 33, the defect detection outputs V _D and V _A are automatically obtained.

V _1, V ₂ each signal, when it becomes that there is binarized after detection signal 1 is obtained as _{V D = V 1 · ▲ 2} ▼ V A = V 1 · V 2 0 when a no. The signal V ₁ is 1 when there are uneven defects or dust, and the signal V ₂ is 1 when dust is present.
Becomes Therefore, when the signal V _D is 1, it can be determined that it is an irregular defect, and when the signal V _A is 1, it can be determined that it is dust.

In addition, the dichroic mirror 22 shown in FIG. 1 is replaced with a prism or a half mirror, and the slit 12 of FIG. 5 is used without using the filter 12 ′. Needless to say, a green filter may be arranged on the front surface. Also, dichroic mirror 2
2. When both images of red light and green light are formed on the image surface 17 without using the image surface 23, these may be received and separated by a color television camera.

According to the present embodiment, it is possible to obtain an observation image by a phase contrast microscope and an observation image by a transmission illumination microscope at the same time using a single light source. There is an effect that the foreign matter can be easily identified. Also, the central portion 20 of the slit 12 'in FIG.
Since the light that passes through is used, there is an effect that the light source can be effectively used. Further, in a commercially available phase difference objective lens, the objective lens 15, the phase plate 16 and the absorption film 18 are usually integrated in FIG. 1, but according to this embodiment, it is difficult to adjust the objective lens. There is an effect that a commercially available product can be used without modifying the lens at all.

FIG. 4 is a principle block diagram of the defect inspection apparatus according to the second embodiment of the present invention, in which the same members as those shown in FIG. 5 are designated by the same reference numerals. In the present embodiment, the epi-illumination microscope optical system is integrally incorporated in the phase-contrast microscope optical system so that an image obtained by the phase-contrast microscope is obtained by red light and an image obtained by the epi-illumination microscope is obtained by green light.

In FIG. 4, 34 is a light source for epi-illumination, 38 and 40 are red filters, 35 and 41 are half mirrors, 36 is a relay lens, 37
Is a green filter, and 39 is an image plane.

The principle of obtaining an image by a phase contrast microscope with red light is the same as that of the first embodiment described above, and will be omitted. In the epi-illumination microscope optical system, the illumination light from the light source 34 passes through the half mirror 41 and the relay lens 36, and then only the green light is transmitted by the green filter 37. This green light illuminates the inspected object 14 through the half mirror 35, the phase plate 16 and the objective lens 15. Reflected light containing information such as dust on the surface of the object 14 to be inspected travels in the same optical path as described above in the reverse direction, reaches the half mirror 41, is reflected by the half mirror 41, and is imaged on the image plane 39.

By processing the signals of the respective images on the image planes 17 and 39 in the same manner as described with reference to FIG. 3, it is possible to obtain the detection signal of only the uneven defects.

Also in this second embodiment, the red filter 40, the relay lens 36, the half mirror 41, and the image plane 39 are eliminated, and an image obtained by the epi-illumination microscope is formed on the image plane 17, and this image and the phase contrast microscope are used. Needless to say, the color image may be separated from the image by the color television camera.

In each of the above embodiments, the red filter, the green filter and the like were used, but this may be another combination, that is, an image obtained by a phase contrast optical microscope and an image obtained by another microscope such as a transmission illumination microscope can be separated. If

〔The invention's effect〕

As described above, according to the present invention, the first and second illumination light fluxes having concentric and different wavelengths are illuminated substantially perpendicularly to the object to be inspected, and the high-order amplitude modulation is performed according to the phase difference amount. Each of the folded light and the light amplitude-modulated by the reflectance or the transmittance is imaged through a phase-contrast microscope detection optical system, separated by wavelength, and amplitude-modulated according to the amount of the phase difference separated and imaged. A high-order diffracted light image and a light image amplitude-modulated by reflectance or transmittance are received by the first and second photoelectric conversion means, and a grayscale image signal corresponding to the thickness or refractive index of the object to be inspected. And the image signal of the foreign matter is detected, and the detected grayscale image signal and the image signal of the foreign matter are respectively detected by the binarizing means.
The image data is converted into a binarized image signal, and the converted first binarized image signal and second binarized image signal are compared with each other to detect minute unevenness defects of the inspection object and foreign matter defects on the surface of the inspection object. Since it is configured to detect by discriminating between and, the minute unevenness defect of the inspected object that cannot be identified only by the phase contrast microscope, without being affected by the shape of the defect, such as dust attached to the inspected object It has the effect of being highly sensitive to foreign matter defects and capable of being clearly discriminated and inspected.

[Brief description of drawings]

FIG. 1 is a principle block diagram of the defect inspection apparatus according to the first embodiment of the present invention, FIG. 2 is a block diagram of the filter shown in FIG. 1, and FIG.
FIG. 4 is a video signal processing circuit diagram, FIG. 4 is a raw material configuration diagram of a defect inspection apparatus according to a second embodiment of the present invention, and FIG. 5 is a principle configuration diagram of a general phase contrast microscope. 10 ... Transmitted illumination light source, 11 ... Collector lens, 12 ... Slit, 12 '... Filter, 13 ... Condenser lens, 14 ... Inspected sample, 15 ... Lens, 16 ... Phase plate, 18 ... Absorption film, 22 ... Dichroic mirror, 17, 23, 39 ... Image plane, 34 ... Epi-illumination light source, 35, 41 ... Half mirror, 37 ... Green filter, 38,
40 ... Red filter.

Claims (2)

[Claims] 1. An object to be inspected is illuminated substantially vertically with first and second illumination light beams having concentric and different wavelengths from each other,
The high-order diffracted light amplitude-modulated according to the phase difference amount based on the thickness or the refractive index of the object to be inspected obtained from the object to be inspected illuminated by the first illumination light beam and the second illumination light beam. An objective lens, a phase plate and an absorption film concentric with respect to the optical axis of the objective lens, and a central transmitting portion are provided for each of the light whose amplitude is modulated by the reflectance or the transmittance from the illuminated surface of the object to be inspected. Imaged through the phase-contrast microscope detection optical system composed of and separated by wavelength,
The separated high-order diffracted light image is received by the first photoelectric conversion means to detect a grayscale image signal corresponding to the thickness or the refractive index of the object to be inspected, and the detected grayscale image signal is detected. Two
An image of the foreign matter is obtained by converting the first binarized image signal into a first binarized image signal by the binarizing means, and receiving the separated optical image amplitude-modulated by the reflectance or the transmissivity by the second photoelectric conversion means. A signal is detected, the detected image signal of the foreign matter is converted into a second binarized image signal by a binarizing means, and the converted first binarized image signal and second binarized image signal. A defect inspection method, which compares the image signals with each other to discriminate and detect a fine unevenness defect of an inspection object and a foreign matter defect on the surface of the inspection object. 2. An illuminating means for illuminating an object to be inspected with first and second illuminating light beams which are concentric and have mutually different wavelengths, and an objective lens and a concentric optical axis of the objective lens. Depending on the phase difference amount based on the thickness or the refractive index of the object to be inspected obtained from the object to be inspected, which is composed of the phase plate, the absorbing film, and the central transmitting portion, and is illuminated by the first illumination light flux by the illuminating means. The high-order diffracted light that has been amplitude-modulated and the light that has been amplitude-modulated by the reflectance or the transmittance from the surface of the object to be inspected illuminated by the second illumination light flux by the illumination means are provided with the objective lens, the phase plate, and A phase-contrast microscope detection optical system that forms an image through the absorption film and the central transmission part, and an amplitude change due to the higher-order diffracted light imaged by the phase-contrast microscope detection optical system and the reflectance or the transmittance. The separation optical system for separating the separated light according to the wavelength, and the thickness or refraction of the object to be inspected by receiving the high-order diffracted light image separated by the separation optical system and formed by the phase difference microscope detection optical system. A first photoelectric conversion means for detecting a grayscale image signal according to the ratio, and an optical image separated by the separation optical system and amplitude-modulated by the reflectance or the transmittance formed by the phase difference microscope detection optical system. Second photoelectric conversion means for receiving the light to detect the image signal of the foreign matter on the surface of the object to be inspected, and the grayscale image signal detected by the first photoelectric conversion means are binarized with a desired threshold value to obtain a first First binarizing means for converting into a binary image signal, and the image signal of the foreign matter detected by the second photoelectric converting means is set to 2 with a desired threshold value.
Second binarizing means for binarizing and converting to a second binarized image signal; first binarized image signal and second binarization obtained by the first binarizing means; A defect detection means for comparing the second binary image signal obtained by the means to discriminate between the minute unevenness defect of the inspection object and the foreign matter defect on the surface of the inspection object. Defect inspection device.