JPH061183B2 - Defect inspection method and apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention is suitable for detecting defects such as minute unevenness of the object to be inspected and nonuniformity of refractive index by discriminating from foreign matter such as dust. An inspection method and an apparatus thereof.

[Background of the Invention]

The human eye's ability to discern light and dark differences and color differences is quite good, but if it becomes a transparent object like glass, it cannot be distinguished unless it is a very large scratch or stain. As a means of observing the very small difference in refractive index and thickness in a transparent object, it is used to observe objects such as raw cells and fungi that are transparent and have little difference in brightness and color tone. There is a phase contrast microscope. The phase-contrast microscope is described, for example, in the literature entitled "Phase-contrast microscope and interference microscope" by Toshikazu Horizontal in "Science of Living Body" Vol. The principle of the phase contrast microscope will be described with reference to FIG.

In FIG. 3, 10 is a light source, 11 is a collector lens, and 15 is an objective lens. An annular slit 12 is placed at the front focal position of the condenser lens 13, and an annular absorption film 18 and a phase plate 16 are placed at the rear focal position of the objective lens 15 where an image of the slit 12 can be formed. The absorption film 18 attenuates the direct light 8 having a significantly higher intensity than the diffracted light 9 and balances the intensity of the diffracted light and the direct light. The direct light 8 is modulated by the transmittance of the inspected object 14. On the other hand, the diffracted light 9 is modulated by the change in the refractive index or the change in the thickness of the inspected object 14. Since the direct light 8 and the diffracted light 9 are out of phase with each other by π / 2, they do not interfere with each other as they are.
However, since the phase plate 16 is provided on the optical path of the diffracted light 9 and the phase of the diffracted light is changed so as to interfere with the direct light, the direct light 8 is used as the background intensity and the diffracted light by the inspected object 14 is contrasted with light and dark. Can be observed on the image plane 17. That is,
It is possible to observe the change in the phase amount such as the change in the refractive index and the change in the thickness of the object to be inspected with the light-dark contrast.

However, this light-dark contrast occurs even if foreign matter such as dust is present on the surface of the inspection object. Therefore, the phase contrast microscope can detect defects such as unevenness of the inspection object itself and the foreign matter, but cannot distinguish the defect and the foreign matter. Therefore, conventionally, after an image of the object to be inspected is obtained by a phase contrast microscope, the object to be inspected is re-inspected using a passage illumination microscope obtained by removing the slit 12 in FIG. I'm confirming.

However, it is difficult to confirm the image of the foreign matter with the above-mentioned transmission illumination microscope, and moreover, the inspection is performed at least twice, so that the inspection takes time.

[Object of the Invention]

The object of the present invention is to solve the above-mentioned problems of the prior art with high sensitivity and clearness of fine irregularities and refractive index non-uniformity defects existing in the inspected object itself and foreign matter defects adhering to the inspected object surface. (EN) Provided are a defect inspection method and an apparatus therefor capable of discriminating and inspecting.

[Outline of Invention]

As a means for detecting foreign matter on the surface of the object to be inspected with good contrast, there is an oblique illumination microscope as illustrated in FIG. In this oblique illumination microscope, the light source 20 is arranged so as to have a shallow illumination angle with respect to the inspection object 22 and
The reflected light 27 of the illumination light 23 when there is no unevenness is prevented from directly entering the objective lens 21. Then, when a foreign matter 26 or the like exists on the inspected object 22, diffracted light 24 is generated,
The image of the foreign matter 26 can be detected with good contrast on the image plane 25.

That is, in order to achieve the above object, the present invention provides a high sensitivity to a fine unevenness or a defect of refractive index nonuniformity existing in the inspected object itself and a foreign matter defect adhering to the inspected object surface only by the phase contrast microscope. In addition, focusing on the fact that it cannot be clearly discriminated and inspected, the first illumination luminous flux is illuminated substantially perpendicularly to the inspected object, and the second luminous flux having a wavelength different from the first luminous flux is further inspected. Illuminate the surface of the
Diffracted light amplitude-modulated according to the amount of phase difference obtained from the object to be inspected illuminated by the illumination luminous flux, and diffracted reflected light from the surface of the object to be inspected illuminated obliquely by the second illumination luminous flux. Each of them is imaged through a phase-contrast microscope detection optical system composed of an objective lens, a phase plate, an absorption film, and a central transmission part, and separated by wavelength, and the diffracted light image formed by the separation is The photoelectric conversion means 1 receives the grayscale image signal according to the thickness or the refractive index of the object to be inspected, and the detected grayscale image signal is converted into the first binarized image signal by the binarization means. The separated and imaged diffracted reflected light image is received by the second photoelectric conversion means to detect the image signal of the foreign matter on the surface of the object to be inspected, and the detected image signal of the foreign matter is detected. The second binarization means converts the second binarized image signal, The converted first binarized image signal and the second binarized image signal are compared with each other to find fine irregularities or defects of refractive index nonuniformity of the inspection object and foreign matter defects on the surface of the inspection object. It is a defect inspection method characterized by discriminating and detecting.

Further, according to the present invention, the first illumination light beam illuminates the object to be inspected substantially perpendicularly, and further the second light beam having a wavelength different from the first light beam illuminates the surface of the object to be inspected from an oblique direction. Means, an objective lens, a phase plate, an absorption film, and a central transmission part, and the amplitude is modulated according to the phase difference amount obtained from the object to be inspected illuminated by the first illumination light beam by the illumination means. Second by light and said lighting means
Of the diffracted and reflected light from the surface of the object to be inspected, which is illuminated in an oblique direction by the illuminating light flux, is imaged through the objective lens, the phase plate, the absorbing film, and the central transmitting portion. And a separation optical system for separating the diffracted light and the diffracted reflected light imaged by the phase contrast microscope detection optical system by wavelength, and separated by the separation optical system and imaged by the phase difference microscope detection optical system. First photoelectric conversion means for receiving a diffracted light image to detect a grayscale image signal corresponding to the thickness or refractive index of the object to be inspected, and the separation optical system for separation, and the phase difference microscope detection optical system for separation. Second photoelectric conversion means for detecting the image signal of the foreign matter on the surface of the object to be inspected by receiving the image of the diffracted reflected light that has been formed, and the grayscale image signal detected by the first photoelectric conversion means are desired. Binarize with the threshold of First be converted into one binary image signal
And a second binarizing unit that binarizes the image signal of the foreign matter detected by the second photoelectric conversion unit with a desired threshold value and converts the image signal into a second binarized image signal. , The first two
The first binarized image signal obtained by the binarizing means and the second binarized image signal obtained by the second binarizing means are compared with each other to form minute unevenness or uneven refractive index of the object to be inspected. A defect inspection apparatus comprising: a defect detection unit that discriminates and detects a defect of a property and a defect of a foreign substance on the surface of an object to be inspected.

Example of Invention

An embodiment of the present invention will be described below with reference to FIGS. 1 and 2. The same components as those shown in FIG. 3 are designated by the same reference numerals in the following description.

In FIG. 1, collector lens 11 and annular slit 12
An optical filter 30 that transmits only a certain wavelength of light between
And an optical filter 31 having the same characteristics as the optical filter 30 is disposed in front of the image plane 17. The other structure of the phase contrast microscope is the same as that of FIG.

The illumination light source 32 of the oblique illumination microscope integrally incorporated in a part of the phase contrast microscope optical system is arranged so as to have a shallow illumination angle with respect to the inspection object 14, and the illumination light source 32 and the inspection object 14 are provided. An optical filter 33 that transmits light having a wavelength different from that of the filter 30 is interposed between the two. Then, a half mirror 34 is arranged in front of the optical filter 31, and reflected light from the half mirror 34 is focused on an image plane 36 through an optical filter 35 having the same characteristics as the optical filter 33.

Illumination light from the illumination light source 10 of the phase microscope passes through the collector lens 11, the filter 30, and the slit 12 and illuminates the inspected object 14 by the condenser lens 13. The image of the slit 12 arranged at the front focus position of the condenser lens 13 forms an image on the absorption film 18 placed at the rear focus position of the objective lens 15, so that the direct light 37 passing through the inspected object 14 is Attenuated, and becomes coherent with the diffracted light 38 by the phase plate 16,
It becomes the background light of the image detected by the phase contrast microscope.

On the other hand, the diffracted light 40 due to foreign matter on the object 14 to be inspected by the illumination light 39 of the illumination light source 32 in the oblique illumination microscope forms an oblique illumination microscopic image on the image plane 36 through the objective lens 15 and the half mirror 34. To do. The diffracted light 40 does not form an image at the position of the absorption film 18 and is hardly affected by the absorption film 18.

As described above, since the filters 30 and 31, and 33 and 35 are used, the object 1 to be inspected by the phase contrast microscope and the oblique illumination microscope 1
4 images can be obtained at the same time. As the filter, a multilayer thin film filter, a colored glass filter or the like can be used.

According to the phase contrast microscope, minute irregularities of the object 14 to be inspected, the state of nonuniform refractive index, and the foreign matter on the object to be inspected are detected with good contrast. On the other hand, according to the oblique illumination microscope, the foreign matter on the inspected object 14 is mainly detected with good contrast. The oblique illumination microscope can detect a large step or the like on the object 14 to be inspected, but it is difficult to detect minute unevenness, especially a gradually changing inclination. However, this can also be detected with a phase contrast microscope. Therefore, by comparing the image detected by the phase contrast microscope and the image detected by the oblique illumination microscope,
Foreign substances can be discriminated and only defects of the inspection object itself can be identified. In other words, if both detected images are detected together, it can be judged as a foreign substance, and if detected only in the image obtained by the phase contrast microscope, it can be judged as a defect.

FIG. 2 is a block diagram of the defect discriminating apparatus. Image plane of Fig. 1
The respective images of the object to be inspected formed on 17 and 36 are converted into electric signals by the television cameras 51 and 52 such as photoelectric conversion elements. And
Next, the binarization circuits 55 and 56 binarize, and the obtained binarized outputs V1 and V2 are determined by the determination circuit 57 as follows.

V _D = V _{1 .2} V _A = V ₁ .V ₂ where V _D is a signal indicating that there is a defect, V _A is a signal indicating that there is a foreign substance, and V ₁ and V ₂ are when there is a detection signal. 1, 0 if none

In FIG. 1, the objective lens 15, the absorption film 18, the phase plate
Although 16 is generally commercially available as an objective lens for a phase contrast microscope, according to the present embodiment, an objective lens that is difficult to adjust can be used without any remodeling. If a color television camera or the like is used as the photoelectric conversion element, the half mirror 34, the filter 31,
Of course, 35 is unnecessary.

Although the above embodiments have been described by using the transmission type phase contrast microscope, the reflection type is not limited to the transmission type and may be the reflection type. The use of the epi-illumination type has the effect that the object to be inspected can be inspected even if it is not transparent.

Thus, the image of the defect and the foreign matter of the inspection object itself can be obtained at the same time, and the two can be easily distinguished, so that the automation of the defect inspection apparatus can be easily achieved.

〔The invention's effect〕

According to the present invention, the first illumination light beam is illuminated substantially perpendicularly to the object to be inspected, and the second light beam having a wavelength different from that of the first light beam is illuminated to the surface of the object to be inspected from an oblique direction. Diffraction light whose amplitude is modulated according to the amount of phase difference obtained from the object to be inspected illuminated by the first illumination light beam and diffraction from the surface of the object to be inspected illuminated obliquely by the second illumination light beam. Each of the reflected light is imaged through a phase-contrast microscope detection optical system and separated by wavelength, and the separated and imaged diffracted light image and diffracted reflected light image are respectively separated into first and second photoelectric The converting means receives the light and shade image signal according to the thickness or refractive index of the object to be inspected and the image signal of the foreign matter on the surface of the object to be inspected, and detects the gray image signal and the image signal of the foreign matter. The first and second binarized images by the binarizing means. Into a signal, which is the converted first
And the second binary image signal are compared with each other to detect the minute irregularities of the object to be inspected or the defect of non-uniformity of refractive index and the foreign matter defect on the surface of the object to be inspected. With this configuration, foreign matter defects can be discriminated and inspected without being affected by the refractive index or reflectance of the inspected object at all, and minute irregularities and refractive index on the inspected object that cannot be identified only by a phase contrast microscope. This has the effect of inspecting defects of non-uniformity and foreign matter defects such as dust adhering to the surface of the object to be inspected with high sensitivity and clearly discriminating.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of a defect inspection apparatus according to an embodiment of the present invention, FIG. 2 is a block diagram of a defect discrimination apparatus, FIG. 3 is a block diagram of a phase contrast microscope, and FIG. The figure is a block diagram of an oblique illumination microscope. 10, 32 ... Light source, 11, 13, 15 ... Lens, 12 ... Slit, 14
… Inspected object, 17,36… Image plane, 30, 31, 33, 35… Filter.

Claims (2)

[Claims] 1. An object to be inspected is illuminated with a first illumination light beam substantially perpendicularly, and a second light beam having a wavelength different from that of the first light beam is illuminated onto the surface of the object to be inspected from an oblique direction. Diffraction light amplitude-modulated according to the amount of phase difference obtained from the object to be inspected illuminated by the first illumination light beam and diffraction reflection from the surface of the object to be inspected illuminated obliquely by the second illumination light beam. Each of the light is imaged through a phase contrast microscope detection optical system composed of an objective lens, a phase plate, an absorption film, and a central transmission part, and separated by wavelength.
The separated photoelectrically formed diffracted light image is received by the first photoelectric conversion means to detect a grayscale image signal according to the thickness or the refractive index of the object to be inspected, and the detected grayscale image signal is An image signal of a foreign substance on the surface of the object to be inspected is converted by the binarizing means into a first binarized image signal, and the separated and imaged diffracted reflected light image is received by the second photoelectric conversion means. Is detected, the detected image signal of the foreign matter is converted into a second binarized image signal by the binarizing means, and the converted first binarized image signal and second binarized image are converted. A defect inspecting method, which compares a signal with a signal to detect a fine unevenness or a non-uniformity in refractive index of an inspected object and a foreign matter defect on a surface of the inspected object. 2. An illuminating means for illuminating an object to be inspected substantially vertically with a first illuminating light beam and illuminating a surface of the object to be inspected with a second light beam having a wavelength different from that of the first light beam from an oblique direction. And an objective lens, a phase plate, an absorption film, and a central transmission part, and the diffracted light amplitude-modulated according to the amount of phase difference obtained from the object to be inspected illuminated by the first illumination light flux by the illumination means. And the diffracted and reflected light from the surface of the object to be inspected, which is illuminated by the second illumination light flux by the illumination means in an oblique direction, through the objective lens, the phase plate, the absorption film, and the central transmission portion. A phase difference microscope detection optical system, a separation optical system for separating the diffracted light and the diffracted reflected light imaged by the phase difference microscope detection optical system according to wavelength, and the phase difference microscope separated by the separation optical system. First photoelectric conversion means for receiving a diffracted light image formed by the detection optical system and detecting a grayscale image signal according to the thickness or refractive index of the object to be inspected, and separated by the separation optical system, Second photoelectric conversion means for detecting the image signal of the foreign matter on the surface of the object to be inspected by receiving the diffracted and reflected light image formed by the phase difference microscope detection optical system, and detected by the first photoelectric conversion means. A first binarizing unit that binarizes the generated grayscale image signal with a desired threshold value and converts the binarized image signal into a first binarized image signal, and an image signal of the foreign matter detected by the second photoelectric conversion unit. Second binarizing means for binarizing with a desired threshold value and converting into a second binarizing image signal; a first binarizing image signal obtained by the first binarizing means; 2 of 2
Defects that are detected by comparing the second binarized image signal obtained by the binarizing means to discriminate between fine irregularities of the object to be inspected and defects of uneven refractive index and foreign matter defects on the surface of the object to be inspected. A defect inspection apparatus comprising: a detection unit.