JP2003121385A - Method and device for inspecting inside of vitreous silica material for defect - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and device for inspecting inside of vitreous silica material for defect by which minute defects, particularly, bubbles, foreign matter, etc., contained in a vitreous silica material can be detected easily and accurately in a short time. SOLUTION: The method for inspecting inside of vitreous silica for defect uses the schlieren method. In the method, only abnormal light rays caused by defects contained in the vitreous silica material to be inspected are detected out of the light rays transmitted through the material by projecting parallel rays of light upon the material. The device for inspecting inside vitreous silica material for defect uses this method.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an inspection apparatus for inspecting defects contained in a quartz glass material.

[0002]

2. Description of the Related Art In a photolithography process in semiconductor manufacturing, glass materials used for applications such as photomasks and lenses used for transferring circuit patterns by ultraviolet light have high light transmittance and uniform light transmittance. Needed. For this reason, a quartz glass material having excellent light transmittance in the ultraviolet region is used, and it is desirable that the inside of the glass material is free from defects such as bubbles, foreign matters, and striae, including minute ones.

Conventionally, for minute defects such as bubbles and foreign substances contained in the quartz glass material, the glass material is irradiated with strong light from a projector or a fluorescent lamp, and abnormal light such as reflected light or refracted light due to the defect is visually observed. It was inspected by the method of confirming with.

[0004]

However, when visually inspecting defects inside the glass, abnormal light such as reflected light or refracted light due to minute defects is very small, and therefore defects are likely to be missed. Also, inspection requires skill,
Further, there is also a problem that the inspection takes time.

An object of the present invention is to provide an inspection method and an inspection apparatus which can easily and accurately detect defects contained in the inside of a quartz glass material, in particular, minute defects such as bubbles and foreign matters. It is in.

[0006]

Means for Solving the Problems The inventors of the present invention have made earnest studies in view of the above-mentioned situation, and as a result, by using the Schlieren method, a quartz glass material to be inspected is irradiated with parallel light to obtain a quartz glass material. By detecting only the extraordinary light due to the defects inside the quartz glass material from the light transmitted through, the defects contained in the quartz glass material, especially minute defects such as bubbles and foreign substances, and in some cases striae can be detected. Then, they have found that they can be detected easily, accurately and in a short time, and have completed the present invention.

That is, the present invention is a method for inspecting defects in a quartz glass material using the schlieren method, in which the quartz glass material to be inspected is irradiated with parallel light, and the light transmitted through the quartz glass material is This is a method for inspecting defects inside a quartz glass material that detects only abnormal light due to defects inside the quartz glass material. Furthermore, an illumination system for irradiating the quartz glass material to be inspected with parallel light and a quartz glass material are loaded. Sample stand, a condensing system and a light-shielding system for extracting only the extraordinary light due to defects inside the quartz glass material from the light transmitted through the quartz glass material, and the detection for detecting the extraordinary light extracted The present invention relates to a defect inspection device inside a quartz glass material including a system.

The present invention will be described in detail below.

The Schlieren method is a method for visualizing the nonuniformity of the refractive index such as striae inside the quartz glass material. This Schlieren method allows parallel rays to pass through the glass material,
The transmitted light is condensed by a lens or a concave mirror, a knife edge is placed in the vicinity of the focal point, and after the condensed light is projected on the screen, the image is observed. The parallel light transmitted through the glass material passes through the focal point of the lens or the concave mirror, but the light refracted by the striae present inside the glass material does not pass through the focal point because the traveling direction is different from the parallel light. By cutting either the light refracted by the striae or the parallel light transmitted through the glass material as it is with the knife edge, the contrast of the refractive index non-uniform part such as striae is emphasized compared to normal visual observation. It is possible to observe.

The method of inspecting defects inside the quartz glass material of the present invention (hereinafter referred to as "the method of the present invention") is one in which the quartz glass material to be inspected is irradiated with parallel light and the light transmitted through the quartz glass material is It detects only extraordinary light due to defects inside the quartz glass material, and as described above, by utilizing the characteristics of the Schlieren method, defects contained inside the quartz glass material, in particular, minute defects such as bubbles and foreign matter, In some cases, the striae inside the quartz glass material are inspected.

The quartz glass material to be inspected in the method of the present invention is a glass mainly made of quartz (silicon dioxide: SiO ₂ ) and is capable of transmitting parallel light from the viewpoint of utilizing the characteristics of the Schlieren method. The transparent quartz glass material may contain components other than silicon dioxide.

With respect to defects contained in the quartz glass material, particularly minute defects such as bubbles and foreign substances, when parallel rays are transmitted, reflection and refraction occur at the interface between them, resulting in abnormalities in which the ray directions and polarization states differ. Light is generated. Since the ray direction is different from parallel light, it can be observed in principle by the Schlieren method. However, since abnormal light due to a minute defect is weak, it is not easy to distinguish it. Therefore, in the method of the present invention, after collimating the parallel light transmitted through the quartz glass material to the focal point by a condenser lens or a concave mirror, the condensed light is shielded by a knife edge or the like to be cut off, and substantially The defect can be easily identified by extracting and observing only the abnormal light due to the defect inside the glass material.

Further, in the method of the present invention, the light transmitted through the quartz glass material is condensed by the lens or the concave mirror, but the abnormal light due to the defect inside the quartz glass material is dispersed without passing through the focus of the lens or the concave mirror. Here, the shorter the focal length of the condenser lens or the concave mirror, the smaller the dispersion of the abnormal light due to the defect. Therefore, the size of the defect inside the silica glass material is 1000 μm or less. In order to detect, the focal length of the condenser lens or concave mirror is 5
It is preferably 100 mm or less, more preferably 300 mm or less.

Further, by using a polarizer and an analyzer, the quartz glass material is irradiated with parallel polarized light, and the light transmitted through the quartz glass material is directly or as described above condensed and shielded for extraction. It is also possible to detect a change in polarization state of abnormal light due to a defect inside the glass material.

An apparatus for inspecting defects inside a quartz glass material of the present invention (hereinafter referred to as "invention apparatus") has an illumination system for irradiating a quartz glass material to be inspected with parallel light and a quartz glass material. Sample stage, a condensing system and a light-shielding system for extracting extraordinary light due to defects inside the quartz glass material from the light transmitted through the quartz glass material, and a detection system for detecting the extraordinary light extracted And consists of.

Here, the illumination system has a function of collimating light emitted from a light source such as a halogen lamp by a collimator lens or the like, and a linearly polarized light is used by using a polarizer depending on the purpose. Parallel light may be generated.

The shape of the quartz glass material to be inspected is not particularly limited, but when the external shape of the quartz glass is somewhat uneven and the parallel light is refracted, the same degree of refraction is possible. It is better to immerse it in a liquid having a certain rate.

It is preferable that the sample table for loading the quartz glass material is movable. If the sample table can be moved in each of the directions perpendicular to the direction of the parallel light and the parallel directions. However, it is possible to move the parallel light irradiation site in the glass material particularly by allowing the movement in two vertical directions, and it is possible to inspect the entire inside of the glass material that is larger than the parallel light irradiation range. Further, by making it movable in the direction parallel to the direction of the parallel light, the image can be made clearer when the abnormal light is detected, and the work becomes easier and more accurate.

A lens or a concave mirror may be used as a condensing system for extracting extraordinary light due to defects inside the silica glass material from the light transmitted through the silica glass material, and its focal length is 500 mm as described above. Below 300m
m or less is preferable.

The light-shielding system for extracting only the abnormal light due to the defects inside the quartz glass material from the light transmitted through the quartz glass material has a function of shielding the condensed light as described above. If it exists, there is no particular limitation, and for example, a knife edge is used.

The detection system for detecting the extracted extraordinary light is not particularly limited, but when the above-mentioned linearly polarized parallel light is used, a detection system for detecting a change in polarization state is used. Well, abnormal light due to defects can be detected more accurately. Further, according to the present invention, the abnormal light due to the defect can be visually recognized, but the abnormal light inside the quartz glass material can be more accurately detected by capturing the abnormal light by using a CCD camera and performing image processing according to the purpose. You can also

FIG. 1 shows a schematic configuration of an inspection apparatus according to an embodiment of the present invention. The diffused light from the halogen lamp 11 passes through the pinhole 12, is collimated by the collimator lens 13, and is irradiated onto the glass material 21 to be inspected.
The plane of incidence and the plane of emergence of the parallel rays are mirror-polished, and the glass material 21 is installed so as to be perpendicular to the optical axis direction. The glass material 21 is installed on the sample table 2 which is movable in the XYZ directions, and by moving the glass material 21, it is possible to irradiate the entire area of the glass material with parallel light. On the opposite side of the glass material 21 from the collimator lens 13, a condenser lens 31 for condensing the parallel light transmitted through the glass material is installed, and a knife edge 32 is disposed at a position where the parallel light is condensed by this lens. . As the collimator lens and the condenser lens, it is desirable to use an achromatic lens from the viewpoint of chromatic aberration and spherical aberration, and as the condenser lens, a lens having a focal length of 500 mm or less is used. Knife edge 32
The camera lens 41 and the CCD camera 42 are installed so that only the extraordinary light due to the defect 22 inside the glass is incident on the position where the condensed parallel light is blocked. Glass material 21
By monitoring the image from the CCD camera 42 while moving in the XYZ directions, it is possible to easily inspect the internal defect and its existing position.

Although a knife edge is used for shielding parallel light in the above description, a glass plate partially opaque-treated may be used instead.

Further, the collimator lens 13 and the glass material 2
It is also possible to insert a polarizer between 1 and an analyzer between the glass material 21 and the condenser lens 31 to detect a change in the polarization state of the extraordinary light due to the defect 22 inside the glass.

FIG. 2 shows a schematic structure of an inspection apparatus according to one embodiment of the present invention. After passing through the pinhole 12, the diffused light from the halogen lamp 11 is collimated by the concave mirror 13a, and irradiates the glass material 21 to be inspected. The plane of incidence and the plane of emergence of the parallel rays are mirror-polished, and the glass material 21 is installed so as to be perpendicular to the optical axis direction. The glass material 21 is installed on the sample table 2 which is movable in the XYZ directions, and by moving the glass material 21, it is possible to irradiate the entire area of the glass material with parallel light. On the opposite side of the glass material 21 from the concave mirror 13, a concave mirror 31a for reflecting and condensing the parallel light transmitted through the glass material is installed, and a knife edge 32 is installed at a position where the parallel light is condensed by the concave mirror.
A concave mirror having a focal length of 500 mm or less is used.
The knife edge 32 is aligned with the position where the condensed parallel light is blocked, and the camera lens 41 and the CCD camera 42 are installed so that only the abnormal light due to the defect 22 inside the glass enters. While moving the glass material 21 in the XYZ directions, CCD
By monitoring the image from the camera 42, it is possible to easily inspect the internal defect and its existing position.

Although a knife edge is used to shield parallel light in the above description, a glass plate partially opaque-treated may be used instead.

Further, even if a polarizer is inserted between the concave mirror 13 and the glass material 21 and an analyzer is inserted between the glass material 21 and the concave mirror 31, a change in the polarization state of the extraordinary light due to the defect 22 inside the glass is detected. I do not care.

Although the method and apparatus for inspecting defects in the quartz glass material of the present invention have been described above based on the embodiments, the present invention is not limited to these embodiments and various modifications can be made.

[0029]

Embodiments of the present invention will be described below with reference to the drawings, but the present invention is not limited to these embodiments.

Example 1 A defect inspection apparatus having a structure as shown in FIG. 1 was prepared. That is, a pinhole 12 with a diameter of 1.0 mm is installed in front of the halogen lamp 11, and 200 mm from the pinhole 12
50mm lens diameter and 200mm focal length at remote positions
The achromatic lens 13 is installed. An achromatic lens 31 having a lens diameter of 50 mm and a focal length of 200 mm was installed at a position 300 mm away from the achromatic lens 13, and a knife edge 32 was installed at a position 200 mm apart from the achromatic lens 31. Immediately after the knife edge 32, the focal length is 28 to 70.
A black and white CCD camera 42 having 410,000 pixels with a mm lens 41 was installed and connected to a monitor. The components are installed with their optical axes aligned, and the light of the halogen lamp 11 that has passed through the achromatic lens 31 is blocked by being condensed on the knife edge 32 and adjusted so as not to enter the CCD camera 42 through the zoom lens 41. did. After that, the sample stage 2 movable in two directions perpendicular to the optical axis was installed between the achromatic lens 13 and the achromatic lens 31, and the defect inspection apparatus was completed.

Using the device prepared as described above,
The surface of the quartz glass block having a width and depth of 154 mm and a height of 300 mm, which had been mirror-polished, was inspected for bubbles and foreign matters. The voltage of the halogen lamp power supply was adjusted to 12v (volts), the block was installed on the sample stand so that the side surface was perpendicular to the optical axis, and the image from the CCD camera was irradiated while the glass block was irradiated with parallel light. The presence or absence of abnormal light due to internal defects was confirmed by monitoring. The entire inside of the glass block was inspected by operating the sample table and moving the glass block.

As a result of this inspection, eight foreign matters were detected from the inside of the glass block. The inspection time was 15 minutes. When the size of the detected foreign matter was measured using a long working distance microscope, the size of the largest foreign matter was 880 μm and the size of the smallest foreign matter was 9 μm.
It was 0 μm.

Comparative Example 1 While allowing the light of a fluorescent lamp to pass through the inside of the quartz glass block inspected in Example 1, a visual inspection of bubbles and foreign matters existing inside the quartz glass block was performed. In this inspection, only 6 foreign matters were detected from the inside of the quartz glass block. The inspection time was 45 minutes. When this inspection result was collated with the inspection result in Example 1, it was found that a foreign matter having a size of 170 μm and a foreign matter having a size of 90 μm were not detected.

[0034]

In the present invention, the schlieren method is used to irradiate the quartz glass material to be inspected with parallel light, and the parallel light transmitted through the quartz glass material is condensed by a lens or concave mirror having a focal length of 500 mm or less, By shielding only the abnormal light due to defects inside the glass material by blocking light, defects contained in the quartz glass material, particularly minute defects of 1000 μm or less such as bubbles and foreign substances, can be easily and accurately
It can be detected in a short time and is extremely useful for quality control of quartz glass materials.

[Brief description of drawings]

FIG. 1 is a schematic configuration (side view) of an embodiment of a defect inspection apparatus of the present invention using a lens.

FIG. 2 is a schematic configuration (side view) of an embodiment of the defect inspection apparatus of the present invention using a concave mirror.

[Explanation of symbols]

1: Lighting system 11: Halogen lamp 12: Pinhole 13: Collimator lens 13a: concave mirror for collimator 2: Sample stand 21: Inspection object (glass material) 22: Defect inside glass material 3: Optical system 31: Condensing lens 31a: Concave concave mirror 32: knife edge 4: Detection system 41: Camera lens 42: CCD camera

Claims (8)

[Claims] 1. A method of inspecting an inside of a quartz glass material by using the schlieren method, wherein a quartz glass material to be inspected is irradiated with parallel light, and the quartz glass material is selected from the light transmitted through the quartz glass material. A method for inspecting defects inside a quartz glass material, which is characterized by detecting only abnormal light due to internal defects. 2. The inside of the quartz glass material according to claim 1, wherein parallel light transmitted through the quartz glass material is condensed by a lens or a concave mirror having a focal length of 500 mm or less, and then the condensed light is shielded. Defect inspection method. 3. A defect in the quartz glass material according to claim 1 or 2, wherein the quartz glass material is irradiated with linearly polarized parallel light to detect a change in polarization state of the linearly polarized light. Inspection method. 4. The maximum diameter of defects inside the quartz glass material is 100.
It is 0 micrometer or less, The defect inspection method inside the quartz glass material in any one of Claims 1-3 characterized by the above-mentioned. 5. An illumination system for irradiating a quartz glass material to be inspected with parallel light, a sample stand for loading the quartz glass material, and a light from the light transmitted through the quartz glass material inside the quartz glass material. A defect inspection apparatus inside a quartz glass material, comprising: a light-collecting system and a light-shielding system for extracting only abnormal light due to a defect, and a detection system for detecting the extracted abnormal light. 6. A defect inspection apparatus inside a quartz glass material according to claim 5, wherein a condensing lens or a concave mirror having a focal length of 500 mm or less is used as a condensing system. 7. A quartz glass material is provided with an illumination system for irradiating parallel light of linearly polarized light and a detection system for detecting a change in polarization state of the light of linearly polarized light.
Alternatively, the defect inspection device inside the quartz glass material according to claim 6. 8. The sample stage is movable, and C is used as a detection system.
A defect inspection apparatus for the inside of a quartz glass material according to any one of claims 5 to 7, wherein a CD camera is used.