JPS6165107A - Inspecting method for surface defect - Google Patents

Abstract

PURPOSE:To inspect a fine uneven defect by converting the fine unevenness of an optically transparent substance to be inspected into a density picture by a phase difference microscope optical system to detect the fine unevenness as a defect. CONSTITUTION:Transmitting illumination light 25 radiated from a transmitting illumination light source 10 is irradiated to a substance 14 (magnetic bubble memory) to be inspected through a collector lens 11, a ring slit 12 and a condensor lens 13. Direct light 29 modulated at its amplitude in accordance with the transmissibility of the substance 14 and diffracted light 26 modulated at its phase on the basis of its refractive index are made interfere with each other through a phase plate 16 and an adsorption film 18 and a density signal corresponding to the phase difference is detected by a television camera. Then, the light source 10 is switched to a vertical illumination light source 24, the vertical illumination light 28 is irradiated through a half mirror 22 and an objective lens 15 and the reflected light is detected by a camera 23. A picture having a bright or dark background is obtained in accordance with the selection of a phase plate 16, and in case of the bright background, specific points existing in both the picture and the background are decided as foreign substances. On the other hand, a specific point existing in one side is decided as an uneven part. In case of the dark background, specific points existing in both the sides are decided as an uneven part.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a defect inspection method suitable for detecting defects such as minute irregularities on a parallel flat plate object that is optically transparent.

[Background of the invention]

There is a method that uses light emitted as a means of measuring minute irregularities on the surface of an optically transparent object.

As an example of this, the Mikelson dry ea as shown in Figure 5
There is something called t. The Michelson interferometer is described, for example, in ``Applied Optics'' by Hiroshi Kubota, published by Iwanami IIF Store (1958), pages 8 to 100, and its principle will be explained using FIG.

A beam of light emitted from a coherent light source 1 such as a Rede beam is divided into two beams by a beam splitter 2, one of which is projected onto the surface of an object to be inspected 40 through an objective lens 3, and the other beam is generally projected through an objective lens. The reference IJ[K is projected through an objective lens 5 with a magnification equal to 3.

The reference mirror 6 has a mirror surface with high planar accuracy within the field of view of the objective lens 5. The reflecting mirrors from the object to be inspected 4 and the reference theory 6 serve as objectives, respectively.

The light is focused by lenses 3 and 5, and beam splitter and beam 2
The two images are synthesized at the image plane 7, and a dry image is formed on the image plane 7.

The principle of interference in this case is the difference between the distance OQ+ between the point O on the reflective surface of the mirror 2 and the point Q1 on the object to be inspected 4, and the distance number 2 between the point O and the point Q2 on the reference mirror 6. If Δ2 is an odd multiple of ÷λ, where λ is the wavelength of the light beam used, the reflected light from the object to be inspected 4 and the reflected light from the reference mirror 6 will weaken each other due to interference, while Δχ is above λ If it is an even number multiple of , both reflected lights will mutually strengthen each other. That is, when the position of the reference A6 is moved in the optical axis direction, the image plane 7
repeats brightness and darkness, and each time the above-mentioned 1 becomes darker by an integer of λ, the image plane 7 reaches its maximum brightness.

According to this principle, the irregularities on the sample to be inspected 4 are observed on the image plane 7 as bright and dark with a period of ÷λ depending on the irregularities.

Such a method of detecting minute irregularities on the surface of an optically transparent object using light interference is described, for example, in Japanese Patent Application Laid-Open No. 57-1999.
It is described in No. 120805. In this official seal example, the reference mirror 6 of the mickeyson interferometer is slightly moved relative to the optical axis to ensure that at least one pair of bright and dark interference fringes is generated within the detection range, thereby changing the background interference conditions. , it is possible to obtain conditions for detecting minute irregularities defects on the object to be inspected with good contrast.

However, the methods described in these publicly known articles only consider the reflection from the inspection target (objective lens 4 or reference mirror 6), and the reflection from the objective lens 3, objective lens 5, etc. is inserted into the optical path. No consideration is given to light reflected from objects.

In particular, it is usually necessary to use a combination lens such as the plan objective lens shown in Figure 6, which is a combination of multiple lenses in order to correct aberrations, especially for the objective lens 3.5, etc., and the bottom surface of each lens. Reflected light from? 1° Since various lights such as #2+I-yL and the reflected light from the reference mirror 6 interfere with each other and are detected as background noise on the image plane 7, noise caused by minute irregularities on the object to be inspected 4. There was a drawback that it was difficult to recognize the interference image on the image plane 7.

In addition, when the reflectance of a foreign object such as dust on the object to be inspected 4 is high, it is impossible to distinguish the reflected light from this foreign object from the reflected light from the object to be inspected that is in the same phase. If the ratio is low, no interference image will be obtained on the image plane 7, but if the background near the foreign object is bright on the image plane 7, it will be observed in the same way as the irregularity defect on the object to be inspected 4, so the interference image will not be obtained on the image plane 7. This method has the disadvantage that it is not possible to accurately detect only uneven defects on an object.

[Purpose of the invention]

It is an object of the present invention to eliminate the drawbacks of the conventional methods described above, to provide a method for inspecting minute irregularities on the surface of an optically transparent object to be inspected, and to further eliminate the minute irregularities and foreign matter such as dust. The purpose is to provide a method for separating and recognizing them.

[Summary of the invention]

The main point of the present invention is that since the light passing through the object to be inspected undergoes an additional change depending on the thickness of the object to be inspected, it is possible to detect minute irregularities defects on the object to be inspected by measuring the amount of phase change. .

As a means of measuring phase difference, there is a phase contrast microscope, which is used to observe objects that are transparent and have little difference in brightness or color tone, such as raw cells or bacteria.

An example of the optical system of a phase contrast microscope is shown in FIG. 2, where the direct light 8 modulated by the transmission of the object to be tested 14 is used as a backlight, and the phase is changed by changes in the refractive index or thickness of the object to be tested. A phase plate 16 is used to change the phase of the modulated diffracted light 9 so that it interferes with the direct light, and the object to be inspected 14 is
The image plane 17 was busy observing the phase change due to the brightness and darkness contrast. Here, 1o is the light source, 11
is a collector lens, and 12 is a Ringes! 1, ), 13 is a condenser lens, and 15 is an objective lens.

Although the direct light 8 having a large width is reduced by the absorption film 18 so that the direct light 8 and the diffracted light 9 interfere, the fidelity of the object to be inspected 14 is not significantly impaired considering the main use of the phase contrast microscope. So, the absorption rate of the absorption membrane per day is 90%.
To a certain extent.

For the purposes of the present invention, it is sufficient to detect the presence or absence of a phase difference. Therefore, if the direct light 8 is further reduced or not transmitted at all, and the diffracted light 9 is mainly detected, the phase difference caused by the object to be inspected 14 can be reduced. That is, minute irregularities on the object to be inspected 14 can be detected with high sensitivity.

Depending on how the direct light 8 and the diffracted light 9 are caused to interfere with each other by the phase plate 16, that is, when the phase relationship between the two lights is the same,
The background contrast 19 caused by the direct light 8 is bright, but becomes dark when the object is inverted. By the way, when foreign matter such as dust is on the object to be inspected 14, J4w is
However, when the background contrast 19 is dark, it cannot be detected, and conversely, when the background contrast 19 is bright, it can be detected. However, it is difficult to distinguish the detected foreign matter from the minute unevenness defect 1c on the object to be inspected 14. On the other hand, for example, when normal transmitted illumination or epi-illumination is used, minute unevenness defects cannot be detected, but foreign objects etc. can be easily +C detected.

Therefore, we developed a phase-contrast microscope optical system and, for example, Ringes! I,
)12 is removed in conjunction with passing illumination (usually a microscope),
As shown in FIG. 5, when the background contrast of the image plane 19 by the optical system of the phase contrast microscope is bright, the defect 20 and 21 shown in #(a), which is detected in the same way by a normal microscope, is a foreign object. Otherwise, the undetected defect 20 can be identified as a minute unevenness defect on the object 14 to be inspected. Fourth
As shown in Figure 5iC, the background contrast of the image plane 19 by the phase contrast microscope optical system is dark.The detected defect 20 shown in (α) is a minute irregularity defect on the limb inspection object.
Defects detected by K are identified as foreign substances. In FIGS. 5 and 4, the portions marked with hyf'' represent dark portions in the field of view.

The present invention will be explained in detail below using examples with reference to the drawings, but these are merely illustrative! However, various modifications and improvements may be made without exceeding the scope of the present invention.
Of course you can get it.

[Embodiments of the invention]

Referring to FIG. 1, the transmitted R bright light 25 emitted from the transmitted illumination light source 10 is transmitted through the collector lens 11.9. Congenchi lens 15'lA is the object to be inspected 1
4 (@Qi bubble memory is made by growing a magnetic garnet transparent BArl! film such as CPt1GpsOt2 etc. in this liquid bath as a substrate. Therefore, it is necessary to measure the unevenness of this transparent base.)
to illuminate. The object to be inspected 14 is illuminated by the transparent illumination light 25.
From this, IS light 29 is amplitude-modulated as a raw material depending on the transmission rate of the object to be inspected, and diffracted light 26 is mainly phase-modulated depending on the thickness or refractive index of the object to be inspected.

The direct light 29 undergoes a phase change of 4 or 1 by the phase plate 16, is attenuated by the absorption film 18, and is converted into interference with the diffracted light 26.

With this, it is possible to detect an III light signal on the image plane of the television camera 23 according to the amount of phase difference of the object to be inspected.

On the other hand, the epi-illumination light 28 from the epi-illumination light source 24 has its optical axis bent by the half mirror 221C, and the objective lens 15
The object to be inspected 14 is illuminated by epi-illumination. The reflected light 27 given an amplitude according to the reflectance of the test food 140 is detected by the television camera 23.

The object to be inspected 14 is illuminated by either the transmitted illumination light source 10 or the epi-illumination light source 24. When the transparent illumination light source 25 is used, the phase contrast microscope illumination optical system is replaced by the epi-illumination light source. When using 22,
Depends on obtaining normal microscope illumination.

Depending on how the phase plate 16 is selected, an image as shown in FIG. 3 with a bright background or as shown in FIG. 4 with a dark background can be detected by the television camera 23. In the case of Fig. 3, the singular point 21 that exists in both Fig. 5 (4) obtained with the phase contrast microscope optical system and Fig. 3 (4) obtained with the illumination of a normal microscope may be a foreign object such as dust. ), (It can be determined that the singular point 20 present in Rinoki is a minute unevenness defect. In the case of Fig. 4, the singular point (eL) obtained by the phase contrast microscope optical system is a minute unevenness defect. , the singularity (J) obtained under normal microscope illumination
can be determined to be foreign matter such as dust.

In the above embodiment, the phase-contrast microscope field illumination and the epi-illumination of the normal microscope were combined, but the illumination method of the normal microscope arm in combination with the phase-contrast microscope illumination may be the pond illumination method, for example, the transparent layer FJA or the dark microscope arm illumination method. Combination with Shuzhaomeng or differential interference microscope F) May be the enemy.

[Effect of invention]

As explained above, let's get started! According to AVc, it is capable of highly sensitively detecting minute irregularities defects on optically transparent objects to be inspected that cannot be identified with normal microscopes, and can also distinguish between these defects and foreign objects such as dust. Effects can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an apparatus for carrying out the surface defect inspection method according to the present invention, FIG. 2 is a schematic diagram showing the configuration of a phase difference microscope optical system, and FIG. 3(a). (-I!-) and Figures 4 (CG) and C4) are respectively... Diagrams showing the images observed with a differential microscope jump optical system and a normal microscope, and Figure 5 shows the images used in the conventional surface defect inspection method. FIG. 6 is a schematic diagram showing the (S configuration) of the interference optical system shown in FIG. 5. 10... transmitted illumination light source, 11...・Contact lens, 12...9 lengths, 15...Contact lens, 14...Object to be inspected, 15...Objective lens,
16... Phase plate, 17... Image plane, 18... Technique recording film, 19... Background contrast, 20... Consideration of minute unevenness defects, 21... Image of foreign matter such as dust, 22... Half mirror 123... Television camera, 24... Epi-illumination light source, 25... Transmitted illumination light, 26... Diffracted light, 2
7... Reflected light, 28... Epi-illumination light, 29... Direct light.

Claims (1)

[Claims] 1. Microscopic irregularities on an optically transparent object to be inspected, characterized in that a phase-contrast microscope optical system is used to convert minute irregularities on the object to be inspected into a grayscale image and to detect them as defects. Unevenness defect inspection method. 2. Only unevenness defects are detected by combining minute unevenness detected using the phase contrast microscope optical system and foreign matter detected using a normal microscope. Surface defect inspection method.