JP2004309137A - Defect inspection method and defect inspection device inside quartz glass material - Google Patents

Abstract

A defect inspection method and a defect inspection apparatus capable of easily, accurately, and in a short time detecting a defect contained in a quartz glass material, particularly, a minute defect such as a bubble or a foreign matter.
A quartz glass material to be inspected is irradiated with parallel light and diffused light having different irradiation directions, and reflection and / or refraction due to a defect inside the quartz glass material is selected from the light irradiated on the quartz glass material. A defect inspection method and a defect inspection device inside a quartz glass material characterized by simultaneously detecting extraordinary light caused by the defect.
[Selection diagram] None

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 a defect inspection method and a defect inspection apparatus that can easily, accurately, and in a short time detect a defect contained in a quartz glass material, particularly, a minute defect such as a bubble or a foreign matter. is there.
[0007]
[Means for Solving the Problems]
The present inventors, in view of the current situation as described above, as a result of intensive studies, irradiate the quartz glass material to be inspected with parallel light and diffused light having different irradiation directions, and apply the light illuminated to the quartz glass material. By simultaneously detecting abnormal light caused by reflection and / or refraction due to defects inside the quartz glass material from inside, defects contained in the quartz glass material, particularly minute defects such as bubbles and foreign substances, and in some cases, The inventors have found that striae can be detected easily, accurately, and in a short time, and have completed the present invention.
[0008]
That is, the present invention irradiates the quartz glass material to be inspected with parallel light and diffused light having different irradiation directions, and reflects and / or refracts the light irradiated on the quartz glass material due to a defect inside the quartz glass material. A defect inspection method inside a quartz glass material characterized by simultaneously detecting anomalous light caused by light, and an illumination system for irradiating the quartz glass material to be inspected with parallel light and diffused light having different irradiation directions. And a sample stage for loading the quartz glass material, and a condensing system for extracting only extraordinary light caused by reflection and / or refraction due to a defect inside the quartz glass material from light irradiated on the quartz glass material Also, the present invention relates to a defect inspection apparatus inside a quartz glass material, comprising: a light shielding system; and a detection system for detecting the extracted abnormal light.
[0009]
Hereinafter, the present invention will be described in detail.
[0010]
When the defect inside the quartz glass material is opaque, when irradiated with parallel light and diffused light, abnormal light due to reflection and / or refraction due to the defect is likely to occur in a direction different from the light irradiation direction, The defect can be recognized by observing from a direction different from the light irradiation direction.
[0011]
Further, as a method for visualizing non-uniformity of the refractive index such as striae inside the quartz glass material, there is a Schlieren method. In the Schlieren method, a parallel light beam is irradiated toward a glass material to be inspected and a condensing system disposed behind the glass material for condensing the irradiated light, and transmits the light transmitted through the glass material to a lens or The light is condensed by a concave mirror, a knife edge is placed near the focal point, and after condensing, an image is observed by projecting the spread light on a screen. 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 that has passed through the glass material as it is, thereby enhancing the contrast of the non-uniform refractive index, such as the striae, compared to normal visual observation. This is a method that enables observation.
[0012]
On the other hand, the defect inspection method inside the quartz glass material of the present invention (hereinafter referred to as “the method of the present invention”) irradiates the quartz glass material to be inspected with parallel light and diffused light having different irradiation directions. Abnormal light resulting from reflection and / or refraction due to a defect inside the quartz glass material is simultaneously detected from light irradiated on the quartz glass material. As described above, light reflection and / or light due to an opaque defect is detected. By detecting the extraordinary light caused by refraction not only by using the features of the Schlieren method but also by using diffused light that is not used by the Schlieren method, defects, particularly bubbles, contained inside the quartz glass material can be detected. Inspection of minute defects such as foreign matter and, in some cases, striae inside the quartz glass material.
[0013]
The method of the present invention is to irradiate a quartz glass material to be inspected with parallel light and diffused light having different irradiation directions, and to irradiate the parallel light from a certain direction irradiated toward a condensing system such as the Schlieren method. It is preferable to use not only the parallel light but also the parallel light and the diffused light which are irradiated in a direction not directed to the light collecting system. By doing so, the opaque defect inside the quartz glass material to be inspected can be more accurately detected.
[0014]
Further, it is more preferable that the parallel light and the diffused light used in the present invention use a plurality of parallel lights having different irradiation directions, a plurality of diffused lights, or a plurality of both of them in order to achieve the effect of the present invention.
[0015]
When a plurality of parallel lights having different irradiation directions are used, the quartz glass material may be irradiated with light such that part or all of the parallel lights are directed to a direction not incident on the detection system. As a mode of directing the parallel light in a direction not incident on the detection system, for example, using a half mirror, without irradiating the parallel light directly to the quartz glass material to be inspected, after irradiating the quartz glass material through the mirror In addition, a mode can be adopted in which the quartz glass material is irradiated with light again by the reflecting mirror disposed on the opposite side of the quartz glass material with respect to the half mirror.
[0016]
The quartz glass material to be inspected in the method of the present invention is a glass mainly composed of only quartz (silicon dioxide: SiO ₂ ), and obtains light reflection and / or light refraction from defects contained in the glass material. From the viewpoint, any quartz glass material having transparency capable of transmitting parallel light and diffused light may contain components other than silicon dioxide.
[0017]
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, the quartz glass material is irradiated with linearly polarized light while detecting the abnormal light described above, and the change in the polarization state of the linearly polarized light transmitted through the quartz glass material is detected. In addition, the defect can be easily determined.
[0018]
In the method of the present invention, the quartz glass material to be inspected is irradiated with parallel light and diffused light having different irradiation directions. As described above, among the irradiated parallel light and diffused light, a collection of parallel light in one or more directions is performed. Light and shading are performed to extract only the extraordinary light due to the defect inside the quartz glass material. The parallel light and diffused light irradiated in other directions are used to obtain reflected light due to defects inside the quartz glass material. At this time, extraordinary light due to reflection and / or refraction due to defects inside the quartz glass material is used. It is necessary to irradiate the quartz glass material with light so that light does not directly enter the detection system so as not to hinder detection.
[0019]
In the method of the present invention, of the parallel light and the diffused light transmitted through the quartz glass material, part or all of the parallel light is condensed by a lens or a concave mirror. Are dispersed without passing through the focal point of the lens or 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.
[0020]
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.
[0021]
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 quartz glass material to be inspected with parallel light and diffused light having different irradiation directions, and a quartz glass. A sample stage for loading the material, a condensing system and a light-shielding system for extracting only extraordinary light caused by reflection and / or refraction due to a defect inside the quartz glass material from light irradiated on the quartz glass material; And a detection system for detecting the extracted extraordinary light.
[0022]
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 parallel light and diffused light having different irradiation directions, a plurality of light sources may be used, or an optical system may be used. Further, it is preferable that the irradiation direction of the light irradiating the quartz glass material can be changed so that the parallel light or the diffused light transmitted through the quartz glass material does not directly enter the detection system.
[0023]
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.
[0024]
As a sample stage for loading the quartz glass material, the direction from the parallel light to the quartz glass material is the X axis direction, the direction perpendicular to the X axis and the horizontal direction is the Y axis direction, and the direction perpendicular to the X axis is the vertical and lengthwise. When the direction is the Z-axis direction, it is preferable to be able to move in any direction, and by making it movable in two perpendicular directions, it is possible to move the irradiated part of the quartz glass material with the parallel light. This makes it possible to inspect the entire inside of the glass material that is larger than the irradiation range of the parallel light. 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.
[0025]
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.
[0026]
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.
[0027]
There is no particular limitation on a detection system for detecting extraordinary light caused by reflection and / or refraction due to a defect inside the quartz glass material. It is preferable to use a detection system for detection, and abnormal light due to a defect can be detected more accurately. In the present invention, abnormal light caused by reflection and / or refraction due to a defect can be visually observed. For example, an abnormal light due to a defect inside a quartz glass material is captured using a CCD camera, and image processing is performed according to the purpose. By applying the method, the defect inside the quartz glass material can be more accurately caught.
[0028]
FIG. 1 shows a schematic configuration 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 collimator lens 13, and is irradiated on the glass material 21 to be inspected. The incident surface and the outgoing surface of the parallel light beam are polished to a mirror surface state, and the glass material 21 is set so as to be perpendicular to the optical axis direction. 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 material 21 from the collimator lens 13, a condenser lens 31 for collecting parallel light transmitted through the glass material is provided, and a knife edge 32 is provided at a position where the parallel light is collected by this lens. . 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. Halogen lamps 14 and 15 are installed above and below the condenser lens to irradiate the glass material 21 with diffused light. The knife edge 32 is set at a position where the converged parallel light is blocked, and the camera lens 41 is set so that only the reflected light of the diffused light due to the defect 22 inside the glass and the extraordinary light extracted by the condensing system and the shading system enter. And a CCD camera 42. 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.
[0029]
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.
[0030]
Further, a polarizer may be inserted between the collimator lens 13 and the glass material 21 and an analyzer may be inserted 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. I do not care.
[0031]
FIG. 2 shows a schematic configuration 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 a collimator lens 13, reflected by a half mirror 14, and irradiates a glass material 21 to be inspected. The incident surface and the outgoing surface of the parallel light beam are polished to a mirror surface state, and the glass material 21 is set so as to be perpendicular to the optical axis direction. 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 material 21 from the half mirror 14, there is provided a mirror 15 for reflecting the parallel light transmitted through the glass material, and the mirror irradiates the parallel light from both surfaces of the glass material 21. Behind the half mirror, a condenser lens 31 for condensing parallel light transmitted through the glass material is provided, and a knife edge 32 is provided at a position where the parallel light is condensed by this lens. The condenser lens 31 has a focal length of 500 mm or less. The knife edge 32 is positioned so as to block the converged parallel light, and the camera lens 41 and the CCD camera so that only the reflected light due to the defect 22 inside the glass and the extraordinary light extracted by the condensing system and the shading system enter. 42 is installed. 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.
[0032]
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.
[0033]
Further, a polarizer may be inserted between the mirror 15 and the glass member 21 and an analyzer may be inserted between the glass member 21 and the concave mirror 31 to detect a change in the polarization state of the extraordinary light due to the defect 22 inside the glass.
[0034]
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.
[0035]
【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.
[0036]
Example 1
A defect inspection apparatus having a configuration as shown in FIG. 1 was prepared. That is, a pinhole 12 having a diameter of 1.0 mm was set in front of the halogen lamp 11, and an achromatic lens 13 having a lens diameter of 50 mm and a focal length of 200 mm was set at a position 200 mm away from the pinhole 12. An achromatic lens 31 having a lens diameter of 50 mm and a focal length of 200 mm is installed at a position 300 mm away from the achromatic lens 13, and halogen lamps 14 and 15 are directed above and below the achromatic lens 31 toward the achromatic lens 13. The knife edge 32 was set at a position 200 mm away from the achromatic lens 31. 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. Each component is installed with its optical axis 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 so that it does not enter the CCD camera 42 through the zoom lens 41. did. Thereafter, the sample stage 2 movable in two directions perpendicular to the optical axis was set between the achromatic lens 13 and the achromatic lens 31, and the defect inspection apparatus was completed.
[0037]
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 11 is adjusted to 12 V (volt), the voltage of the power supply of each of the halogen lamps 14 and 15 is adjusted to 6 V (volt), and the block is set on the sample table so that the side surface is perpendicular to the optical axis. Then, while irradiating the glass block with parallel light and diffused light, the image from the CCD camera was monitored to confirm the presence or absence of reflected light due to internal defects and abnormal light. By operating the sample stage and moving the glass block, the entire inside of the glass block was inspected.
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.
[0038]
Example 2
A defect inspection apparatus having a configuration as shown in FIG. 2 was prepared. That is, a pinhole 12 having a diameter of 1.0 mm was set in front of the halogen lamp 11, and an achromatic lens 13 having a lens diameter of 50 mm and a focal length of 200 mm was set at a position 200 mm away from the pinhole 12. A half mirror 14a was installed at a position 100 mm away from the achromatic lens 13 so that the light beam direction changed by 90 degrees. A mirror 15a having a diameter of 50 mm was installed at a position 300 mm away from the half mirror 14a. An achromatic lens 31 having a lens diameter of 50 mm and a focal length of 200 mm was installed immediately after the half mirror 14a, and a knife edge 32 was installed at a position 200 mm away from the achromatic lens 31. 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. Each component is installed with its optical axis 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 so that it does not enter the CCD camera 42 through the zoom lens 41. did. Thereafter, the sample stage 2 movable in two directions perpendicular to the optical axis was set between the mirror 15a and the achromatic lens 31, and the defect inspection apparatus was completed.
[0039]
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 11 was adjusted to 15 V (volt), and the block was set on the sample table so that the side surface was perpendicular to the optical axis. By monitoring the image, the presence or absence of reflected light due to internal defects and abnormal light was confirmed. By operating the sample stage and moving the glass block, the entire inside of the glass block was inspected.
[0040]
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.
[0041]
Comparative Example 1
The halogen lamps 14 and 15 were removed from the apparatus used in Example 1, and the bubbles and foreign substances present inside the quartz glass block inspected in Example 1 were inspected. 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.
[0042]
【The invention's effect】
In the present invention, the quartz glass material to be inspected is irradiated with a plurality of parallel lights and diffused lights having different irradiation directions, and the reflected light due to a defect inside the quartz glass material, and transmitted through the quartz glass material using the Schlieren method. After condensing the collimated light with a lens or concave mirror with a focal length of 500 mm or less, by blocking light,
(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.
By detecting only the extraordinary light due to the defect inside the glass material, and simultaneously detecting the extraordinary light due to the reflection and / or refraction due to the defect inside the quartz glass material, the defect contained in the quartz glass material, particularly bubbles, It is possible to easily and accurately detect minute defects of 1000 μm or less, such as foreign substances, in a short time, which 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 plurality of light sources.
FIG. 2 is a schematic configuration (side view) of one embodiment of the defect inspection apparatus of the present invention using a single light source.
[Explanation of symbols]
1: Illumination system 11: Halogen lamp 12: Pinhole 13: Collimator lens 14, 15: Halogen lamp 14a: Half mirror 15a: Mirror 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 (11)

The quartz glass material to be inspected is irradiated with parallel light and diffused light having different irradiation directions, and out of the light irradiated on the quartz glass material, extraordinary light caused by reflection and / or refraction due to a defect inside the quartz glass material. A defect inspection method inside a quartz glass material, wherein the defect is simultaneously detected. The defect inspection method according to claim 1, wherein a plurality of parallel lights and / or a plurality of diffuse lights having different irradiation directions are irradiated. 2. The method according to claim 1, further comprising: irradiating a part or all of the parallel light to the quartz glass material, condensing the transmitted light by a lens or a concave mirror having a focal length of 500 mm or less, and blocking the condensed light. Or the defect inspection method inside the quartz glass material according to claim 2. 4. The method for inspecting a defect in a quartz glass material according to claim 3, wherein the diffused light and a part or all of the parallel light are directed to a direction that does not enter the detection system, and the quartz glass material is irradiated with light. The method for inspecting a defect inside a quartz glass material according to any one of claims 1 to 4, wherein the quartz glass material is irradiated with linearly polarized light, and a change in the polarization state of the linearly polarized light is detected. The defect inspection method according to any one of claims 1 to 5, wherein the maximum diameter of the defect inside the quartz glass material is 1000 µm or less. An illumination system for irradiating the quartz glass material to be inspected with parallel light and diffused light having different irradiation directions, a sample stage for loading the quartz glass material, and a quartz glass material from among the lights irradiated on the quartz glass material Defects inside the 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 internal defects; and a detection system for detecting the extracted extraordinary light. Inspection equipment. 8. The defect inspection apparatus according to claim 7, wherein a condenser lens having a focal length of 500 mm or less or a concave mirror is used as the condenser system. 9. The illumination system according to claim 7, wherein an irradiation direction of light to the quartz glass material is variable so that parallel light or diffused light transmitted through the quartz glass material does not directly enter the detection system. 8. A defect inspection apparatus inside a quartz glass material according to item 8. 10. An illumination system for irradiating a linearly-polarized parallel light to a quartz glass material, and a detection system for detecting a change in a polarization state of the linearly-polarized light. Inspection device for quartz glass inside. The defect inspection apparatus according to any one of claims 7 to 10, wherein the sample stage is movable and a CCD camera is used as a detection system.

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