JP2004309138A - Method and apparatus for inspecting defect inside quartz glass - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a defect inspection method and a defect inspecting apparatus for easily, accurately, and quickly detecting defects contained in a quartz glass material, especially minute defects, such as bubbles, and foreign objects. <P>SOLUTION: In the method for inspecting defects inside the quartz glass material using a schlieren method, the quartz glass material to be inspected is irradiated with a plurality of parallel light having different irradiation directions, and only abnormal light caused by reflection and/or bending by defects inside the quartz glass material is detected from light applied to the quartz glass material. The defect inspecting apparatus by the method for detecting defects inside the quartz glass material is included. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method and an inspection apparatus for inspecting a defect contained in a quartz glass material.
[0002]
[Prior art]
In a photolithography process in semiconductor manufacturing, a glass material used for a photomask, a lens, or the like used when transferring a circuit pattern by ultraviolet light or the like needs to have high light transmittance and uniform light transmittance. 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 matter, and striae including minute ones.
[0003]
Conventionally, minute defects such as bubbles and foreign substances contained in quartz glass material are illuminated with strong light from a projector or fluorescent lamp, and abnormal light such as reflected light or refracted light due to the defect is visually observed. (For example, see Non-Patent Document 1).
[0004]
[Non-patent document 1]
Shin Kuzuu, K Books 111 “The World of Quartz Glass”, pp. 77-101, published by the Industrial Research Institute, April 5, 1999 [0005]
[Problems to be solved by the invention]
However, when a defect inside the glass is visually inspected, an abnormal light such as a reflected light or a refracted light due to a minute defect is very small, and therefore, the defect is likely to be missed. In addition, there is a problem that the inspection requires skill and furthermore, the inspection requires time.
[0006]
An object of the present invention is to provide an inspection method and an inspection apparatus that can easily, accurately, and in a short time detect a defect included in a quartz glass material, in particular, a minute defect such as a bubble or a foreign substance.
[0007]
[Means for Solving the Problems]
In view of the above-mentioned current situation, the present inventors have conducted intensive studies and as a result, when inspecting for defects inside the quartz glass material using the schlieren method, the quartz glass material to be inspected has a plurality of irradiation directions different from each other. Of the quartz glass material by detecting only the extraordinary light caused by the reflection and / or refraction due to the defect inside the quartz glass material from the light irradiated on the quartz glass material. The present inventors have found that minute defects such as bubbles and foreign matters, and, in some cases, striae can be detected easily, accurately, and in a short time, and have completed the present invention.
[0008]
That is, the present invention is a defect inspection method inside a quartz glass material using the Schlieren method, and irradiates a quartz glass material to be inspected with a plurality of parallel lights having different irradiation directions, and irradiates the quartz glass material. Is a defect inspection method for detecting only abnormal light caused by reflection and / or refraction due to a defect inside the quartz glass material, and further includes a plurality of quartz glass materials to be inspected having different irradiation directions. Illumination system for irradiating parallel light, sample stage for loading quartz glass material, and abnormality caused by reflection and / or refraction due to defects inside quartz glass material from light irradiated to quartz glass material The present invention relates to a defect inspection apparatus inside a quartz glass material, which includes a light focusing system and a light shielding system for extracting only light, and a detection system for detecting extracted extraordinary light.
[0009]
Hereinafter, the present invention will be described in detail.
[0010]
The Schlieren method is a method for visualizing non-uniformity of the refractive index such as striae inside a quartz glass material. The Schlieren method transmits parallel light through a glass material, focuses the transmitted light with a lens or concave mirror, places a knife edge near the focal point, projects the spread light on the screen after focusing, etc. To observe the image. 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 striae existing inside the glass material does not pass through the focal point because the traveling direction is different from that of the parallel light. The knife edge cuts either the light refracted by the striae or the parallel light transmitted through the glass material as it is, thereby enhancing the contrast of non-uniform refractive index areas such as striae compared to normal visual observation. It is possible to observe.
[0011]
In the defect inspection method inside the quartz glass material of the present invention (hereinafter referred to as “the present invention method”), the quartz glass material to be inspected is irradiated with a plurality of parallel lights having different irradiation directions, and the quartz glass material is irradiated. It detects only extraordinary light (hereinafter, sometimes simply referred to as “extraordinary light”) due to reflection and / or refraction due to defects inside the quartz glass material from the light, and as described above, Schlieren By utilizing the features of the method, it is possible to inspect defects contained in the quartz glass material, particularly minute defects such as bubbles and foreign substances, and, in some cases, striae inside the quartz glass material.
[0012]
In the method of the present invention, even when the extraordinary light due to the defect inside the quartz glass material has directionality, by irradiating a plurality of parallel lights having different irradiation directions, only one parallel light is irradiated. In comparison, extraordinary light can be generated in a wider angle range, and only extraordinary light due to a defect inside the quartz glass material can be accurately detected.
[0013]
The quartz glass material to be inspected in the method of the present invention means a glass mainly composed of only quartz (silicon dioxide: SiO ₂ ), and has a transparency capable of transmitting parallel light from the viewpoint of utilizing the feature of the Schlieren method. The quartz glass material described above may contain components other than silicon dioxide.
[0014]
Defects contained in the quartz glass material, especially minute defects such as bubbles and foreign matter, are reflected and refracted at the interface when parallel light is transmitted, and abnormal light with different light direction and polarization state is generated. I do. Since the direction of the light beam is different from that of the parallel light, it can be observed in principle by the Schlieren method. However, since the extraordinary light due to the minute defect is weak, it is not easy to determine the abnormal light. For this reason, in the method of the present invention, after a plurality of parallel lights having different irradiation directions transmitted through the quartz glass material are condensed to a focal point by a condensing lens or a concave mirror, the condensed light is shielded by a knife edge or the like and all cut off. However, by extracting and observing substantially only the extraordinary light due to the defect inside the quartz glass material, the defect can be easily identified.
[0015]
In the present invention, a plurality of parallel lights having different irradiation directions are irradiated. However, after passing through the quartz glass material, it is necessary to collect and shield all the parallel lights. A single condenser lens, a concave mirror, and a knife edge may be used for condensing and shielding, or separate condenser lenses, a concave mirror, and a knife edge may be used for each parallel light.
[0016]
In the method of the present invention, the light transmitted through the quartz glass material is condensed by a lens or a concave mirror, but extraordinary light due to a defect inside the quartz glass material is dispersed without passing through the focus of the lens or the concave mirror. Here, as the focal length of the condenser lens or the concave mirror becomes shorter, the dispersion of the extraordinary light due to the defect becomes smaller. Therefore, as the size of the defect inside the quartz glass material, the extraordinary light due to a minute defect having a maximum diameter of 1000 μm or less. Is detected, the focal length of the condenser lens or the concave mirror is preferably 500 mm or less, more preferably 300 mm or less.
[0017]
In addition, using a polarizer and an analyzer, the quartz glass material is irradiated with parallel light of linearly polarized light, and the light transmitted through the quartz glass material is collected directly or as described above, and the glass extracted by shading. A change in the polarization state of the extraordinary light due to a defect inside the material may be detected.
[0018]
The defect inspection apparatus inside the quartz glass material of the present invention (hereinafter, referred to as “the present invention apparatus”) includes an illumination system for irradiating a plurality of parallel lights having different irradiation directions to the quartz glass material to be inspected, and a quartz glass material. A sample stage for loading the sample, a condensing system and a shading system for extracting only the extraordinary light due to the defect inside the quartz glass material from the light irradiated on the quartz glass material, and detecting the extracted extraordinary light And a detection system.
[0019]
Here, the illumination system has a function of converting light emitted from a light source such as a halogen lamp into parallel light by a collimator lens or the like, and converts a parallel light of linearly polarized light using a polarizer according to the purpose. It may be caused. In order to obtain a plurality of parallel lights having different irradiation directions, a plurality of light sources may be used, or an optical system may be used. In addition, in order to easily adjust the irradiation direction of the parallel light irradiating the quartz glass material, it is preferable that the irradiation angle of each parallel light can be changed.
[0020]
There is no particular limitation on the shape of the quartz glass material to be inspected, but when the quartz glass has an external shape that is slightly uneven and has an external shape such that parallel light is refracted, the quartz glass has a similar refractive index. It is good to be immersed in a liquid or the like.
[0021]
As a sample stage for loading a quartz glass material, it is preferable that the sample stage can be moved, and as long as it can be moved in each direction perpendicular to the direction of the parallel light and in the direction parallel thereto, In particular, by being movable in two perpendicular directions, the irradiation area of the parallel light on the glass material can be moved, and the entire inside of the glass material larger than the irradiation area of the parallel light can be inspected. In addition, by enabling movement in a direction parallel to the direction of the parallel light, an image can be made clearer at the time of detecting abnormal light, and the work becomes easier and more accurate.
[0022]
A lens or a concave mirror may be used as a light focusing system for extracting extraordinary light due to a defect inside the quartz glass material from light transmitted through the quartz glass material, and the focal length thereof is 500 mm or less as described above, and furthermore, It is preferably 300 mm or less.
[0023]
As a light-shielding system for extracting only the extraordinary light due to the defect inside the quartz glass material from the light transmitted through the quartz glass material, if the light-shielding system has the function of shielding the condensed light as described above, There is no limitation, for example, a knife edge is used.
[0024]
There is no particular limitation on the detection system for detecting the extracted extraordinary light, but when using the parallel light of the above-described linearly polarized light, it is preferable to use a detection system for detecting a change in the polarization state. Extraordinary light can be detected more accurately.
[0025]
In the present invention, the abnormal light due to the defect can be visually observed. For example, the abnormal light due to the defect is captured using a CCD camera, and the image processing is performed according to the purpose to more accurately capture the defect inside the quartz glass material. You can also. When a single condenser lens, concave mirror, and knife edge are used for condensing and shielding, a single detection system may be used.However, when a separate condenser lens, concave mirror, and knife edge are used for each parallel light, Requires a plurality of detection systems corresponding to the number.
[0026]
FIG. 1 shows a schematic configuration of an inspection apparatus according to one embodiment of the present invention. The diffused lights from the halogen lamps 11, 12, and 13 pass through the pinholes 14, 15, and 16 respectively, are collimated by collimator lenses 17, 18, and 19, and irradiate a glass material 21 to be inspected. The incident surface and the outgoing surface of the parallel light beam are polished to mirror surfaces, and a glass material 21 is provided. The glass material 21 is installed on the sample stage 2 that can move in the XYZ directions, and by moving the glass material 21, parallel light can be applied to the entire glass material. On the opposite side of the glass member 21 from the collimator lenses 17, 18, and 19, a condenser lens 31 that collects three parallel lights transmitted through the glass member is provided, and the lens collects three parallel lights. The knife edge 32 is set at the position. From the viewpoint of chromatic aberration and spherical aberration, it is desirable to use an achromatic lens for the collimator lens and the condensing lens, and a lens having a focal length of 500 mm or less is used as the condensing lens. The knife edge 32 has a shape capable of blocking each of the three condensed parallel lights, and is provided with a camera lens 41 and a CCD camera 42 so that only the extraordinary light due to the defect 22 inside the glass is incident. By monitoring the image from the CCD camera 42 while moving the glass material 21 in the XYZ directions, it is possible to easily inspect the internal defect and its existing position.
[0027]
In the above description, the knife edge is used to shield the parallel light, but instead, a glass plate or the like partially opaque-treated may be used.
[0028]
In addition, a polarizer is inserted between the collimator lenses 17, 18, and 19 and the glass material 21, and an analyzer is inserted between the glass material 21 and the condenser lens 31, so that the polarization state change of the extraordinary light due to the defect 22 inside the glass is prevented. It may be detected.
[0029]
Although the method and apparatus for inspecting a defect inside a quartz glass material of the present invention have been described based on the embodiments, the present invention is not limited to these embodiments, and various modifications are possible.
[0030]
【Example】
Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to these embodiments.
[0031]
Example 1
A defect inspection apparatus having a configuration as shown in FIG. 1 was prepared. That is, pinholes 14, 15, and 16 having a diameter of 1.0 mm are installed in front of the halogen lamps 11, 12, and 13 respectively. Achromatic lenses 17, 18, and 19 having a distance of 200 mm were installed. An achromatic lens 31 having a lens diameter of 50 mm and a focal length of 200 mm is installed at a position 500 mm away from the front of the achromatic lens 18, and a knife edge 32 having two slits 200 mm away from the achromatic lens 31 is formed. installed. Immediately after the knife edge 32, a monochrome CCD camera 42 having 410,000 pixels with a zoom lens 41 having a focal length of 28 to 70 mm was installed and connected to a monitor. The lights of the halogen lamps 11, 12, and 13 having passed through the achromatic lens 31 were shielded by being condensed at three points on the knife edge 32, respectively, and adjusted so as not to enter the CCD camera 42 through the zoom lens 41. Thereafter, the sample stage 2 movable in two directions perpendicular to the optical axes of the achromatic lens 18 and the achromatic lens 31 was installed, and the defect inspection device was completed.
[0032]
Using the apparatus prepared as described above, an inspection was performed for bubbles and foreign substances present inside the quartz glass block whose surface having a width and depth of 154 mm and a height of 300 mm was polished to a mirror surface. The voltage of the power supply of the halogen lamp was adjusted to 12 V (volt), and the block was set on the sample table so that the side surface was perpendicular to the optical axes of the achromatic lens 18 and the achromatic lens 31. By monitoring the image from the CCD camera while irradiating the parallel light, the presence or absence of abnormal light due to an internal defect was confirmed. By operating the sample stage and moving the glass block, the entire inside of the glass block was inspected.
[0033]
As a result of this inspection, nine foreign substances were detected from inside the glass block. In each case where the inspection was performed by rotating the glass block and changing the side surface of the block facing the achromatic lens 18, the inspection results were the same. 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 90 μm.
[0034]
Comparative Example 1
The halogen lamps 11 and 13, the pinholes 14 and 16, and the achromatic lenses 17 and 19 were removed from the apparatus used in the first embodiment, and the bubbles and foreign substances present inside the quartz glass block inspected in the first embodiment were inspected. Was. In this inspection, nine foreign substances were detected from inside the glass block. However, when the glass block is rotated and the side of the block facing the achromatic lens 18 is changed and the inspection is performed, only eight foreign substances are detected. There were two sides. The foreign matter whose detectability changed had a flat shape of 130 μm in size and was opaque.
[0035]
【The invention's effect】
In the present invention, a quartz glass material to be inspected is irradiated with a plurality of parallel lights having different irradiation directions using a Schlieren method, and the parallel lights transmitted through the quartz glass material are collected by a lens or a concave mirror having a focal length of 500 mm or less. After light, by shading,
(1) Even if the shape of the defect is distorted and the refracted light has directionality, it can be easily detected regardless of the detection direction;
(2) easy to detect refraction and reflected light even if the defect is opaque;
(3) Since the amount of refraction increases, it is easier to detect clearly.
It is possible to achieve a unique effect. For this reason, by detecting only the abnormal light due to the defect inside the glass material, it is possible to easily, accurately, and in a short time to detect a defect contained in the quartz glass material, particularly a fine defect of 1000 μm or less, such as a bubble or a foreign substance. It can be detected and is extremely useful for quality control of quartz glass materials.
[Brief description of the drawings]
FIG. 1 is a schematic configuration (side view) of an embodiment of a defect inspection apparatus of the present invention using a lens.
[Explanation of symbols]
1: Illumination systems 11, 12, 13: Halogen lamps 14, 15, 16: Pinholes 17, 18, 19: Collimator lens 2: Sample table 21: Inspection object (glass material)
22: Defect inside glass material 3: Optical system 31: Condensing lens 32: Knife edge 4: Detection system 41: Camera lens 42: CCD camera

Claims (8)

A defect inspection method inside a quartz glass material using the Schlieren method, wherein a quartz glass material to be inspected is irradiated with a plurality of parallel lights having different irradiation directions, and quartz light is irradiated from the light irradiated on the quartz glass material. A method for inspecting a defect inside a quartz glass material, wherein the method detects only abnormal light caused by reflection and / or refraction due to a defect inside the glass material. 2. The quartz glass according to claim 1, wherein the plurality of parallel lights having different irradiation directions applied to the quartz glass material are respectively condensed by a lens or a concave mirror having a focal length of 500 mm or less, and then the condensed light is shielded. Inspection method for defects inside materials. The quartz glass material according to claim 1 or 2, wherein the quartz glass material is irradiated with a plurality of parallel lights having different irradiation directions of linearly polarized light, and a change in the polarization state of the linearly polarized light is detected. Defect inspection method. 4. The defect inspection method according to claim 1, wherein the maximum diameter of the defect inside the quartz glass material is 1000 μm or less. An illumination system for irradiating a plurality of parallel lights with different irradiation directions to the quartz glass material to be inspected, a sample table for loading the quartz glass material, and the inside of the quartz glass material from the light irradiated on the quartz glass material Defect inspection inside a quartz glass material, comprising: a light collecting system and a light shielding system for extracting only extraordinary light caused by reflection and / or refraction due to a defect of the object; and a detection system for detecting the extracted extraordinary light. apparatus. 6. The defect inspection apparatus according to claim 5, wherein a condenser lens having a focal length of 500 mm or less or a concave mirror is used as the condenser system. 6. An illumination system for irradiating the quartz glass material with a plurality of linearly-polarized parallel lights having different irradiation directions, and a detection system for detecting a change in the polarization state of the linearly-polarized light. A defect inspection apparatus inside a quartz glass material according to claim 6. The defect inspection apparatus according to any one of claims 5 to 7, wherein the sample stage is movable and a CCD camera is used as a detection system.

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