JPH06129844A - Inspection device - Google Patents

Abstract

PURPOSE:To provide a highly contrasted clear contrast pattern by providing a shielding body at a rear side focus or its nearby position so as to cut off a part of the reflecting light heading to the measuring face and also irradiating the light at larger angle of incidence than that of the parallel light to a sample. CONSTITUTION:A surface 2a of a plate-shaped sample 2 is irradiated with the light in the normal direction and the diagonal direction from each of light sources 5a-5c of light irradiating means A-C, and the reflected light from the sample face 2a is led to a screen 4 via a collimator lens 8, a half mirror 11, and an aperture diaphragm 3 so as to form a contrast pattern. In this way, measurement can be carried out with focusing on the sample face 2a, and also a definition of the contrast pattern is improved as diffused light can be eliminated by the aperture diaphragm 3. As the contrast difference of the contrast pattern can be emphasized by converting the irradiation direction or an angle of incidence by the light irradiation means B, C, the highly contrasted and clear contrast pattern can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inspection device, and more particularly to an inspection device having an improved Schlieren optical system.

[0002]

2. Description of the Related Art Conventionally, Schlieren has been used as an inspection device for detecting the surface condition (waviness, dimples, protrusions, cleaning failure or buff damage) of an as-grown wafer or a mirror-finished wafer or a glass substrate used for manufacturing semiconductor integrated circuits. An inspection device using an optical system is known.

The Schlieren optical system used in this inspection apparatus is one of the typical optical systems that represents the change in the refractive index and the change in the reflectance due to the unevenness of the sample surface as the difference in brightness. This optical system collimates the light from a point light source by an optical element (lens), irradiates the sample surface from its normal direction, converges the reflected light or transmitted light by an optical element (lens), and the rear side. Knife edge (shield) installed at the focal point
Is configured to block a part of the diffused light, and an image of the sample surface is observed behind it by the naked eye or a camera.

According to this optical system, light is diffused when the sample surface has irregularities, but of the diffused light, the light striking the knife edge is blocked. As a result, when the image is observed behind the knife edge, the image of the portion corresponding to the diffused light blocked by the knife edge becomes darker than the images of other portions.
As a result, a bright / dark pattern corresponding to the state of the sample surface can be obtained. As a result, the state of the sample surface can be detected from this bright and dark pattern.

On the other hand, by removing the knife edge from the Schlieren optical system and slightly shifting the focus of the observation surface in the direction of the optical axis, it is possible to observe the state of the sample surface by selecting a location with a relatively high contrast. Inspection devices are also known.

[0006]

However, these conventional inspection apparatuses have the following problems.

That is, in the former inspection apparatus using the Schlieren optical system, a bright / dark pattern corresponding to the state of the sample surface can be obtained behind the knife edge, but this bright / dark pattern also includes diffused light not blocked by the knife edge. Since a large amount is included, the difference between light and dark is soft (the contrast is low), and there is a disadvantage that the state of the sample surface cannot be detected accurately.

On the other hand, in the case of the latter inspection device in which the observation surface is moved along the optical axis direction, the diffused light is hardly blocked, so that the contrast becomes lower than that of the inspection device using the Schlieren optical system. However, there is a disadvantage that the precision of the inspection becomes lower.

Further, since both of the inspection devices are provided with only one light irradiation means, when the sample has a rough surface, the amount of light entering the imaging lens due to diffuse reflection is remarkably reduced, resulting in a bright and dark pattern. Akibe (highlight)
As a result of the extreme decrease in brightness, the contrast becomes extremely low and the reflected image (transmission image) becomes unclear. To prevent a decrease in the brightness of the bright part in the light-dark pattern,
Although it is sufficient to increase the power of the light source, in that case, the lightness of the dark part (shadow) becomes high due to insufficient blocking of the diffused light, and as a result, the contrast cannot be improved.

The present invention has been made in view of the above problems, and an object thereof is to provide an inspection apparatus capable of obtaining a clear bright and dark pattern with high contrast.

[0011]

The invention according to claim 1 is
It is configured to illuminate the sample with parallel light, converge the reflected light or transmitted light, and observe the sample surface behind the rear focus, and provide a shield at or near the rear focus. And an optical system for blocking a part of the reflected light toward the observation surface, and a light irradiating means for irradiating the sample with light at an incident angle larger than that of the parallel light.

According to a second aspect of the present invention, a plurality of light irradiating means are provided in the inspection apparatus according to the first aspect, and at this time, the plurality of light irradiating means are arranged so that their incident surfaces do not coincide with each other.

According to a third aspect of the present invention, an aperture stop is provided as a shield in the inspection apparatus according to the first or second aspect.

[0014]

According to this inspection apparatus, it is possible to enhance the light-dark difference in the light-dark pattern by changing the light irradiation direction or the incident angle of the light irradiation means, or inserting the polarizer or moving the sample, and at the same time, shield the light. Since a part of unnecessary reflected light can be blocked by the body, a bright and dark pattern with high contrast can be obtained.

If an aperture stop is used as the shield,
Since unnecessary reflected light can be further removed as compared with the case of using a knife edge, it is possible to further emphasize the difference between light and dark in the light and dark pattern.

[0016]

Embodiments of the inspection apparatus according to the present invention will be described below.

(1) First Example FIG. 1 shows an optical system 1 of the inspection apparatus of the first example. The optical system 1 will be described.
Illuminates the surface (hereinafter referred to as the sample surface) 2a of the flat plate-shaped sample 2 from the normal direction and the oblique direction, converges the reflected light from the sample surface 2a, and reflects it at the rear of the rear focal point. The image is projected on the screen 4 for observation, and in the observation, the light (diffused light) scattered by the sample surface 2a is scattered by the aperture stop (shield) 3 placed at the rear focal point. It is designed to shut off.

The optical system 1 will be described in detail below.

The optical system 1 comprises three light irradiation means A, B,
Equipped with C. Each light source 5 of this light irradiation means A, B, C
The a, 5b, and 5c are not particularly limited, but a xenon lamp, a halogen lamp, or the like is used. What is used as the light sources 5a, 5b, 5c is preferably determined by the property of the inspection object (sample 2). For example, when inspecting a relatively high reflectance such as a mirror-polished wafer, either a halogen lamp or a xenon lamp may be used, but a relatively low reflectance such as a glass substrate may be used. For inspection, it is desirable to use a xenon lamp with high brightness.

Each light source 5a, 5b, 5c is provided with an elliptical reflector 6a, 6b, 6c. In this case, the respective light sources 5a, 5b, 5c are elliptical reflectors 6a, 6b, 6c.
It is installed at one focus. Each elliptical reflector 6a, 6
Pinholes 7a, 7b, 7c are provided at the other focal points of b, 6c.
Is placed. As a result, the light reflected by the elliptical reflectors 6a, 6b, 6c due to the nature of the ellipse will be reflected by the pinhole 7
It is converged at a, 7b and 7c. As a result, the state is the same as when a point light source is placed at this convergence point. A parabolic reflector may be used instead of the elliptical reflectors 6a, 6b and 6c. In this case, since the light emitted from the parabolic reflector travels in parallel to the optical axis thereof, a collimating lens is separately provided and the collimating lens is used to converge the light at the pinhole.

Further, wavelength selection filters 10a, 10b, 10c for transmitting only light in a desired wavelength range are installed near the pinholes 7a, 7b, 7c. As the wavelength selection filters 10a, 10b, 10c, for example, interference filters are used. This wavelength selection filter 1
The installation of 0a, 10b, 10c is optional, and the installation location is not limited to the vicinity of the pinholes 7a, 7b, 7c,
For example, it may be behind the half mirror 11. The wavelength selection filters 10a, 10b, 10c have a sensitivity adjusting function of the optical system 1, and when the peak-to-valley of the unevenness of the sample surface 2a is small, it is desirable to select a short wavelength region.

Further, in the light irradiating means A, a collimator lens 8 for converting the light transmitted through the wavelength selection filter 10a into parallel light is provided between the pinhole 7a and the sample 2. The collimator lens 8 is installed at a position where the pinhole 7a comes to the front focus. As the collimator lens 8, it is desirable to use one having a small aberration in order to reduce light loss as much as possible.

Further, in the light irradiation means A, a half mirror 11 is installed between the wavelength selection filter 10a and the collimator lens 8. The half mirror 11 is used for dividing the optical path, and is used for bending the optical path of the reflected light from the sample surface 2a. The half mirror 11 bends the optical path of the reflected light toward the screen 4.

An aperture stop 3 is provided between the half mirror 11 and the screen 4. The aperture stop 3 is not particularly limited, but an iris stop is used,
The diameter of the concentric opening can be continuously changed by moving the movable adjusting portion. By changing the diameter of the opening, a reflection image suitable for the type of inspection (waviness inspection, dimple inspection, scratch inspection, etc.) can be obtained.

In FIG. 1, the light irradiation means B, C
Are drawn as if their incident surfaces are coincident with each other, but the light irradiating means B and C are installed so that the incident surfaces do not coincide with each other, and more preferably, the incident surfaces are orthogonal to each other. In addition, the incident angle of light from the light irradiating means B and C is not particularly limited, but is set to be 60 ° or more. The incident surfaces are coincident with each other, and the light irradiation means B, C
When the incident angle of the light from the same is the same, the specular reflection component of the light from the light irradiating means B and C enters into the other light irradiating means, and this is reflected by the reflector and irradiated again on the sample surface 2a, This is because there is a risk of causing noise and damaging the optical elements forming the light irradiation means B and C by heat. Further, if the incident angle is increased, the specular reflection component of the light from the light irradiating means B and C is reflected again by the collimator lens 8 and irradiated on the sample surface 2a, which may cause noise. .

According to the inspection device configured as described above,
The light emitted from the light sources 5a, 5b and 5c is elliptical reflector 6.
a, 6b, 6c are converged at the pinholes 7a, 7b, 7c to form a point light source, and the light from this point light source is applied to the sample surface 2a through the wavelength selection filters 10a, 10b, 10c and the like. .

The reflected light from the sample surface 2a is collimated lens 8, half mirror 11 and aperture stop 3.
And is guided to the screen 4 through which the light-dark pattern is formed.

When observing another portion of the sample surface 2a, the sample 2 may be relatively moved by moving the table 13 (including rotational movement) or moving the optical system 1 in whole or in part. . The relative movement of the sample 2 not only has the meaning of changing the observation portion, but also has the meaning of changing the light irradiation direction and the incident angle of the light irradiation means B and C.

The inspection apparatus of the embodiment thus configured has the following effects.

That is, according to the above-mentioned inspection device, the sample surface 2a can be focused and observed, and most of the diffused light can be removed by the aperture stop 3, so that the sharpness of the bright-dark pattern is significantly improved.

Further, according to this inspection apparatus, since the light-dark difference in the light-dark pattern can be emphasized by changing the light irradiation direction and the incident angle by the light irradiation means B and C, a clear light-dark pattern with high contrast can be obtained. Even if the sample surface 2a is rough, a precise inspection can be performed.

(2) Second Embodiment FIG. 2 shows an optical system 30 of the inspection apparatus of the second embodiment. The optical system 30 is an optical system that is particularly useful for detecting scratches. The optical system 30 is different from the optical system 1 of the first embodiment in that the sample 2 is irradiated with light by four light irradiation means A,
Possessing B, C and D (however, in FIG. 2, only light irradiation means A, B and D are shown for convenience), and possessing two half mirrors 11 and 21 for optical path division. That is, the reflected light whose optical path is bent by the half mirror 21 is received by the one-dimensional image sensor 26 through the imaging lens system 24.

Of the light irradiating means A, B, C and D, three light irradiating means A, B and C have the same structure as that of the first embodiment except that the light irradiating means B and C are installed. Has become.
On the other hand, the light irradiation means D includes a light source 5e and an elliptical reflector 6
e, the pinhole 7e and the wavelength selection filter 10e are the same as those of the light irradiation means B and C, but the collimator lens 27 and the cylindrical lens 28 are provided between the pinhole 7e and the wavelength selection filter 10e.
Is different in that it is provided. The incident surfaces of the light irradiating means B, C, D are not particularly limited, but are set to have an angle of 120 ° with each other.

Of the half mirrors 11 and 21, the image forming optical system behind the half mirror 11 has the same structure as that of the first embodiment. Further, as the image forming lens system 24 behind the half mirror 21, an image forming lens system similar to that in the camera is used, and the image forming lens system 24 guides the reflected light to the one-dimensional image sensor 26.

According to the inspection apparatus of the second embodiment, the linear convergent light is intensively applied to the sample surface 2a by the action of the cylindrical lens 28 of the light irradiation means D. on the other hand,
The reflected light from that portion (the reflected light in this case includes not only the light emitted by the light emitting means D but also the light emitted by the light emitting means A, B, C) is received by the one-dimensional image sensor 26. Then, the state of the scratch is detected by the change in the amount of light received by the one-dimensional image sensor 26.

According to the inspection apparatus of the second embodiment, although depending on the irradiation direction and the incident angle of the convergent light, the light irradiation means A,
The difference between light and dark can be emphasized more than in the case of only B and C.

Although the embodiments of the present invention have been described above, it is needless to say that the present invention is not limited to the embodiments and various modifications can be made without changing the gist thereof. .

For example, in the inspection devices of the first and second embodiments, the light from the half mirror 11 is directly guided to the aperture stop 3, but a lattice filter may be installed immediately before that. Since the lattice filter functions to diffract light, it becomes easier to find scratches with a large scattering angle.

Further, in the inspection devices of the first and second embodiments, the light from the half mirror 11 is observed on the screen 4, but an optical system for observing with a CCD, a camera or the naked eye may be used. .

Further, in the inspection apparatus of the first and second embodiments, the case of inspecting the flat plate-shaped sample 2 has been described. However, in the case of inspecting a sample surface such as a cylinder, a cylindrical lens is attached to the light irradiation means A. Incorporating a plano-convex lens for surface inspection of a sphere, etc.
The light may be emitted from the normal direction. Also,
Depending on the case, it is also possible to use a cylindrical lens even in the case of the flat plate-shaped sample 2 so that the unevenness in a certain direction is emphasized and observed.

Further, although the iris diaphragm is used as the aperture diaphragm 3 in the inspection devices of the first and second embodiments, an aperture diaphragm having a fixed circular aperture is provided, and this aperture diaphragm is used as the optical axis. It may be used by moving it in the direction, or a knife edge may be provided instead of the aperture stop 3.

Further, in the inspection apparatus of the first and second embodiments, the aperture stop 3 is provided at the rear focus, but the installation position may be near the rear focus.

Furthermore, although the inspection devices of the first and second embodiments are configured to observe the reflected light from the sample surface 2a, when the sample is transmissive, its surface condition and Of course, in order to observe the internal state, the configuration may be such that the transmitted light of the sample is observed.

Further, a polarizer and an analyzer may be appropriately incorporated in the optical systems 1 and 30 to adjust the sensitivity and the light amount.

Further, a reflection image or a transmission image may be observed without using a half mirror by slightly setting the incident angle of light on the light irradiating means A and slightly tilting the observation surface. In this case, the pinhole 7a
It is possible to eliminate the effect of the bright spots caused by.

In the above embodiment, the light source is the halogen lamp or the xenon lamp, but other light sources may be used. For example, a laser may be used as the light source of the light irradiation means D.

[0047]

According to the present invention, the sample is irradiated with parallel light, the reflected light or the transmitted light is converged, and the sample surface is observed behind the rear focal point.
An optical system is provided that blocks a part of the reflected light toward the observation surface by providing a shield at or near the rear focal point, and irradiates the sample with light at an incident angle larger than that of the parallel light. Since the light irradiating means is provided, a bright and dark pattern with high contrast can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an optical system of an inspection apparatus according to a first embodiment.

FIG. 2 is a schematic configuration diagram of an optical system of an inspection device according to a second embodiment.

[Explanation of symbols]

 1 Optical System 2 Sample 2a Sample Surface 3 Aperture Stop 30 Optical System

Claims (3)

[Claims] 1. The sample is irradiated with parallel light, the reflected light or transmitted light thereof is converged, and the sample surface is observed behind the rear focal point, and the rear focal point or the vicinity thereof. An optical system was provided to block a part of the reflected light traveling toward the observation surface, and a light irradiation means for irradiating the sample with light at an incident angle larger than that of the parallel light was provided. An inspection device characterized by the above. 2. The inspection apparatus according to claim 1, wherein a plurality of the light irradiating means are provided, and the plurality of light irradiating means are arranged so that their incident surfaces do not coincide with each other. 3. The inspection apparatus according to claim 1, wherein the shield is an aperture stop.