JP2705764B2 - Defect detection device for transparent glass substrate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for detecting a defect such as a scratch on a transparent glass substrate used as a photomask for manufacturing an integrated circuit.

[0002]

2. Description of the Related Art For example, a transparent glass substrate is used as a photomask used for exposing a circuit pattern for manufacturing an integrated circuit. Defects such as scratches and dirt on the glass substrate may cause defects, so it is necessary to inspect the glass substrate to reliably detect the defect.

Conventionally, defect detection has been performed by irradiating a glass substrate placed in a dark room with light. Since the scattered light is generated when the irradiated light is incident on a scratch or the like on the glass substrate, the presence or absence of a defect can be determined by visually detecting the scattered light. When the scratch is fine, the amount of scattered light is small, and it is necessary to increase the illuminance of the irradiation light. In particular, it is difficult to visually detect a scratch of 1 μm or less unless the illuminance is extremely high. However, as the illuminance of the light increases, the danger of the reflected light from the substrate surface entering the eyes increases. Therefore, the illuminance of the irradiation light cannot be simply increased. The illuminance of the irradiation light can be increased only to about 200,000 lux at most, and there is a limit in improving the detection accuracy with the naked eye.

For this reason, various devices have been developed for inspecting surface defects without using human eyes. Japanese Patent Application Laid-Open No. 62-105038 discloses a light receiving system of a glass substrate surface inspection apparatus that irradiates and scans a glass substrate with a light beam and detects scattered reflected light generated at a defective portion. Japanese Patent Application Laid-Open No. 63-200043 discloses an apparatus for detecting a surface defect of a sheet-like object for detecting a defect such as a scratch or dirt on the surface of a glass plate or a plastic plate. Japanese Patent Application Laid-Open No. 63-208746 discloses a defect inspection apparatus having uniform detection sensitivity over the entire inspection area.

Although these devices irradiate a glass substrate with laser light or the like and detect the transmitted light or the backscattered light, they are not always effective as compared with a visual inspection. In the case of a glass substrate for a photomask,
With the improvement in the degree of integration of integrated circuits, the allowable defect size has shifted to 1 μm or less, and a defect detection device capable of reliably detecting a defect of less than 1 μm in a non-contact state without any glass is desired.

In addition to the above-described defect inspection method, there is also a method of detecting a defect using an electron microscope or the like. However, in addition to the necessity of forming a gold film or the like on the subject, the observation field of view is extremely narrow, and the inspection per substrate takes an enormous amount of time, which is not practical. Very shallow defects may not be detectable.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide an inspection apparatus for detecting a defect existing on the surface of a transparent glass substrate with high sensitivity and reliability. And

[0008]

In order to achieve the above object, the present inventors use an inspection apparatus shown in FIG. 3 and irradiate a defect 3 of a transparent glass substrate 2 with inspection light from various directions and angles. The relationship between the incident direction of the inspection light and the scattered light was examined.

The apparatus shown in FIG. 3 uses an XY table (not shown).
The transparent glass substrate 2 is placed on a rotary stage 10 placed on the surface of a scattered light detector (CCD camera) 18 on one side. The light source 14 is movable and can irradiate the transparent glass substrate 2 with inspection light from various directions . The scattered light generated by the defect 3 on the surface of the substrate 2 is detected by a scattered light detector 18.

First, the present inventors can obtain strong scattered light either when the inspection light is applied to the transparent glass substrate 2 from the scattered light detector 18 side or when the inspection light is applied to the transparent glass substrate 2 from the opposite side. A test was conducted. 1 × 5μ on the surface
A transparent glass substrate 2 having a defect of 5 × 100 μm, 1 × 2 μm is prepared, and scattered light generated by irradiating inspection light at 45 ° to the normal 6 is captured by a scattered light detector 18. Was.

FIGS. 4, 5 and 6 show damage caused by backscattered light 7 generated by irradiating inspection light from the scattered light detector 18 side.
Other defects of the stain image, according to FIG. 7, 8 and 9 forward scattered light 7 generated by irradiating an inspection light from the opposite side missing
It is an image of a fall . The size of the defect in FIGS. 4 and 7 is 1 ×
5 μm, the size of the defect in FIGS. 5 and 8 is 5 × 100 μm
m, the size of the defect in FIGS. 6 and 9 is 1 × 2 μm. In the case of a minute defect such as 1 × 2 μm, backscattered light was not detected (see FIG. 6). From the comparison of the amount of scattered light shown in FIGS. 4 to 9, it is understood that stronger scattered light 7 can be obtained by irradiating the inspection light from the side opposite to the scattered light detector 18.

[0012] Next, the inspection light and the angle formed with the normal line 6 of the glass substrate 2 theta (see FIG. 3), and, by changing the incident direction of the inspection light to the glass substrate 2, the incident orientation dependency of the scattered light 7
Properties and incident angle dependence were studied. The incident azimuth of the inspection light is an angle φ between a reference azimuth 17 arbitrarily set on the surface of the glass substrate 2 and a projection line 15 that vertically projects the optical path of the inspection light onto the glass substrate 2 as shown in FIG. Is shown.
FIG. 11 shows a scattered light detectable range 11 when irradiating inspection light to a 1 × 3 μm defect, and FIG. 12 shows a scattered light detectable range 12 when irradiating inspection light to a 0.5 × 20 μm defect. Show. According to these results, the scattered light intensity is greatly affected by the angle θ between the inspection light and the normal of the transparent glass substrate 2 and the incident azimuth φ of the inspection light. It can be seen that this occurs only when light is incident upon satisfying a specific condition corresponding to the condition. For example, when the inspection light is incident perpendicular to the longitudinal direction of the defect, strong scattered light is obtained, and when the inspection light is incident parallel to the longitudinal direction of the defect, only weak scattered light is obtained. If the defect is shallow, scattered light may not be detected at all.

The present inventors have examined the above test results and found that the glass substrate was irradiated with inspection light from at least three directions on the scattered light detector side, and the angle θ between the inspection light and the normal to the glass substrate was determined. When the angle is set to 10 ° to 40 °, it has been found that minute defects existing on the surface of the glass substrate can be reliably detected, and the present invention has been completed.

That is, in the apparatus for detecting defects of a transparent glass substrate according to the present invention, as shown in FIG. 1 corresponding to one embodiment, a transparent glass substrate 2 is provided on one side of a transparent glass substrate 2 to be inspected.
From at least three incident directions toward a point
A plurality of light sources for irradiating an inspection light 5 _1, 5 _2, 5 ₃ which has at the same time 4
₁ , ₂ , 4, and ₃ are arranged. The angle θ ₁ · θ ₂ · θ ₃ between the inspection light 5 ₁ 5 ₂ 5 ₃ and the normal 6 of the transparent glass substrate 2 is 10 to 4
0 °. On the other side of the transparent glass substrate 2, one scattered light detector 8 for detecting forward scattered light 7 generated by the defect 3 of the transparent glass substrate 2 is arranged.

As the transparent glass substrate 2 to be inspected, there is, for example, a glass substrate for a photomask.

As the light sources 4 ₁ , 4 ₂ , 4 ₃ , those having a light condensing function capable of irradiating a spot on the surface of a glass substrate are used. For example, a laser light generator such as a helium neon halogen lamp or a mercury lamp can be used. If a light source having no light-condensing action is used, it becomes difficult to detect the scattered light 7 due to the defect 3, and the detection sensitivity is reduced.

The inspection light 5 ₁ , 5 ₂ , 5 ₃ irradiates the transparent glass substrate 2 from at least three directions . It is better to have many irradiation directions . If the irradiation direction is less than three directions , the scattered light 7 may not be generated depending on the shape of the defect 3 and the defect 3 may not be detected. Further, the illuminance of the inspection light 5 _1, 5 _2, 5 ₃ the higher is preferred. It is also possible to use a ring illumination system capable of converging ring-shaped light.

The angles θ ₁ , θ _2, and θ ₃ between the inspection light 5 ₁ , 5 ₂ , 5 ₃ and the normal of the transparent glass substrate 2 are set to 10 to 40 °.
If the angle θ ₁ · θ ₂ · θ ₃ of less than 10 ° or, 40 °
When the value exceeds the above, the scattered light 7 may not be generated depending on the shape of the defect 3 and the defect 3 may not be detected. For example, 3
When irradiating the inspection light 5 ₁ , 5 ₂ , 5 ₃ from the direction , the inspection light 5 ₁
- 5 ₂ - 5 ₃ and the normal and the angle theta _1, theta _{2-theta 3} of the glass substrate 2 is more preferably set to 10 to 25 °.

When the inspection light beams 5 ₁ , 5 ₂ , 5 ₃ are irradiated from three directions , the optical paths of the inspection light beams 5 ₁ , 5 ₂ , 5 ₃ are formed by projecting lines perpendicularly projected onto the glass substrate 2. It is preferable to arrange the light sources 4 ₁ , 4 ₂ , 4 ₃ so that the angle δ does not exceed 60 °. If the angle exceeds 60 °, the defect 3 may not be detected. In addition, the optical path of each inspection light 5 ₁ , 5 ₂ , 5 ₃ is
The light sources 4 ₁ , 4 ₂ , 4 ₃ are arranged so that the angle δ between the projection lines projected perpendicularly to each other and the angle obtained by dividing 180 ° by the number of inspection light 5 ₁ , 5 ₂ , 5 ₃ coincide. It is desirable to do. For example, in the case of four directions, the angle δ is set to 45 °, and in the case of five directions , the angle δ is set to 36 °.

[0020]

[Action] light source 4 _1, 4 _2, 4 ₃ inspection light 5 _1, 5 irradiated from
_{When 2-5 3} passes through the transparent glass substrate 2, the inspection light 5 _1, 5 _2, 5 ₃ and a defect 3 are scattered in the transmissive portion. The defect 3 is detected by detecting the scattered light 7 with the scattered light detector 8. The inspection light 5 ₁ , 5 ₂ , 5 ₃ forms an angle of 10 to 40 ° with the normal 6 of the transparent glass substrate 2 and enters the transparent glass substrate 2 from the opposite side of the scattered light detector 8 so that the scattered light 7
And scattered light 7 is generated even when the defect 3 is minute. Even when the shape of the defect 3 is elongated, the light source 4 ₁ 4 ₂ 4 ₃
Any of the inspection light 5 ₁ , 5 ₂ , 5 ₃ radiated from above enters the defect 3 intersecting with its longitudinal direction, so that scattered light 7 is generated. Therefore any shape defect 3 can also be reliably detected in the.

[0021]

Embodiments of the present invention will be described below. FIG. 1 is a side view of an embodiment of a transparent glass substrate defect detecting apparatus to which the present invention is applied, and FIG. 2 is a plan view thereof. This device uses X
A microscope in which a transparent glass substrate 2 as an object is placed on the upper surface of a microscope rotary stage 10 (manufactured by Nikon Corporation) placed on a Y table (not shown), and a scattered light detector 8 is arranged above the transparent glass substrate 2 It is. The scattered light detector 8 has a stereoscopic microscope (manufactured by Nikon Corporation) and a CCD camera (manufactured by Protec Japan) attached thereto, and has a × 5 lens inserted into its optical system. 3 below the transparent glass substrate 2
Halogen lamps 4 ₁ , 4 ₂ , 4 ₃ (Yamada Kogaku) are provided. In each of the halogen lamps 4 ₁ , 4 ₂ , 4 ₃ , the inspection light 5 ₁ , 5 ₂ , 5 ₃ to be irradiated makes an angle of 25 ° with the normal 6 of the transparent glass substrate 2, and a point on the surface of the transparent glass substrate 2 Are arranged to intersect. An angle δ between projection lines perpendicularly projecting the optical path of each inspection light 5 ₁ , 5 ₂ , 5 ₃ onto the glass substrate 2.
Is set to 60 °.

The inspection lights 5 ₁ 5 ₂ 5 ₃ emitted from the halogen lamps 4 ₁ 4 ₂ 4 ₃ cross the surface of the transparent glass substrate 2 and enter the transparent glass substrate 2. When there is no defect 3 in the transparent glass substrate 2, each inspection light 5 ₁ , 5 ₂ , 5
₃ passes through the transparent glass substrate 2 as it is, and does not generate scattered light. When the inspection light 5 ₁ , 5 ₂ , 5 ₃ enters the defect 3, scattered light 7 is generated and detected by the CCD camera 8.

Hereinafter, an embodiment in which a defect of the synthetic quartz glass substrate 2 for a photomask is detected will be described.

Example 1 Ten synthetic quartz glass substrates 2 for photomass of 127 × 127 × 2.3 mm which have been subjected to precision polishing after precision polishing are prepared as transparent glass substrates 2. Each glass substrate 2
2 × 20 μm, 2 × 2 μm, 1 × 10 μm, 1 × 3
μm, 1 × 1 μm, 0.5 × 20 μm, 0.5 × 5μ
m, 0.5 × 1 μm, 0.3 × 0.7 μm, 0.3 ×
It has a scratch 3 of 0.3 μm.

[0025] The inspection light 5 _1, 5 _2, 5 ₃ from the halogen lamps 4 _1, 4 _2, 4 _3, after adjusted to 200,000 lux on the surface of the substrate 2, for the synthesis of these photomasks The quartz glass substrate 2 was placed on the rotating stage 10 in order, and it was determined whether the defect could be detected.

Example 2 A defect detection was attempted in the same manner as in Example 1 except that the illuminance on the surface of the substrate 2 was set to 600,000 lux.

Next, for comparison, an attempt was made to detect defects by a method other than applying the present invention. Comparative Example 1 The glass substrate 2 used for the inspection in Example 1 was placed in a clean room, and the surface of the substrate 2 was illuminated at 200,000 lux and visually inspected for defects.

Comparative Example 2 A defect was detected in the same manner as in Example 1 except that the number of halogen lamps was changed to two.

Comparative Example 3 Example ₁ except that the halogen lamps 4 ₁ , 4 ₂ , 4 ₃ were moved to the scattered light detector 8 and irradiated with inspection light to detect back scattered light.
A defect was detected in the same manner as described above.

Comparative Example 4 A defect was detected in the same manner as in Example 1 except that the angle between the inspection light 5 ₁ , 5 ₂ , 5 ₃ and the normal line of the glass substrate 2 was 5 °.

Table 1 shows the detection results of the examples and comparative examples.

[0032]

[Table 1]

According to the results shown in Table 1, it can be seen that the apparatus for detecting defects on a transparent glass substrate of the present invention can detect defects on the glass surface of 1 μm or less.

Although a CCD camera is used as the scattered light detector 8 in the above embodiment, an image pickup tube may be used. By attaching a magnifying lens to the optical system of the scattered light detector 8, it is possible to further enhance the defect detection power.

Further, by combining the apparatus of the present invention with the automatic scanning of the glass substrate 2, it is possible to assemble a highly reliable and highly sensitive automatic defect detection apparatus. Further, it is possible to determine whether the defect 3 is dirty or flawed, depending on the difference in the scattered light intensity depending on the light irradiation angle of the defect 3.

[0036]

As described above in detail, the apparatus for detecting a defect on a transparent glass substrate of the present invention can detect minute defects of 1 μm or less because the intensity of scattered light generated by the defect is large. Further, since the glass substrate is irradiated with the inspection light simultaneously from three or more directions, scattered light is generated regardless of the shape of the defect, and the defect can be reliably detected with high sensitivity.

[Brief description of the drawings]

FIG. 1 is a side view showing one embodiment of a transparent glass substrate defect detection apparatus to which the present invention is applied.

FIG. 2 is a plan view of the transparent glass substrate defect detection apparatus shown in FIG.

FIG. 3 is a schematic side view of an apparatus for obtaining a defect detection condition of a transparent glass substrate.

FIG. 4 is a diagram showing backscattered light generated by a defect.

FIG. 5 is a diagram showing backscattered light generated by a defect.

FIG. 6 is a diagram showing backscattered light generated by a defect.

FIG. 7 is a diagram showing forward scattered light generated by a defect.

FIG. 8 is a diagram showing forward scattered light generated by a defect.

FIG. 9 is a diagram showing forward scattered light generated by a defect.

FIG. 10 is an explanatory diagram of an incident direction of inspection light.

FIG. 11 is a diagram showing a range in which scattered light can be detected.

FIG. 12 is a diagram showing a range in which scattered light can be detected.

[Explanation of symbols]

2 is a transparent glass substrate, 3 is a defect, 4 ₁ , 4 ₂ , 4 ₃ , 14 is a light source, 5 ₁ , 5 ₂ , 5 ₃ is inspection light, 6 is a normal of the transparent glass substrate, 7 is scattered light, 8 18 is a scattered light detector, 10 is a rotating stage, 11 and 12 are scattered light detectable ranges, 15 is a projection line, and 17 is a reference direction.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Atsushi Watanabe 28-1, Nishifukushima, Oku-ku, Kushiro-mura, Nakakushiro-gun, Niigata Pref. Shin-Etsu Chemical Co., Ltd. Synthetic Technology Laboratory (56) JP, A) JP-A-61-25042 (JP, A) JP-A-61-186806 (JP, A)

Claims (2)

(57) [Claims] 1. A on one side of a transparent glass substrate which is an object to be inspected, at least three toward a point of the transparent glass substrate
From the incident direction, double for irradiating an inspection light is converged at the same time
Number of light sources are arranged, and the inspection light and the normal of the transparent glass substrate form an angle of 10 to 40 °, and forward scattered light generated by a defect of the transparent glass substrate on the other side of the transparent glass substrate. 1. A defect detecting apparatus for a transparent glass substrate, wherein a single scattered light detector for detecting a defect is disposed. 2. The transparent glass substrate defect detecting apparatus according to claim 1, wherein the transparent glass substrate is a photomask glass substrate.