JPS62259045A - Stray light removing method for transparent substrate inspection instrument - Google Patents

Abstract

PURPOSE:To remove stray light from a defect inspecting which inspects a transparent substrate by using a laser beam by providing a black-painted glass plate which absorbs the laser beam on the opposite side from the laser beam. CONSTITUTION:A mask substrate 1 is irradiated with the laser beam 3 and reflected light from the substrate 1 is received by a photodetector to inspect the defect of the substrate 1. In this case, the 1st glass 11-1 and the 2nd glass 11-2 which have their reverse surfaces painted in black are provided on the opposite side of the substrate from the laser beam 3. Then, transmitted light 3-1 from the substrate 1 is absorbed by the 1st glass 11-1 and part of it is reflected by 90 deg., made incident on the 2nd glass 11-2, and reflected in the opposite direction from the laser beam 3. At this time, the 1st glass 11-1 and the 2nd glass 11-2 absorb the majority of the incident light. Thus, stray light which is transmitted through the mask substrate 1 and reflected by the surface of a moving mechanism under the substrate 1, so the mask substrate 1 is inspected with high accuracy.

Description

[Detailed Description of the Invention] [Industrial Field of Application] This invention removes stray light caused by a laser beam projected onto the substrate surface in a scent detection device for a transparent substrate such as a mask substrate substrate for manufacturing IC devices. It is about the method.

[Prior Art] ゛: In order to manufacture a four-conductor IC element, a mask with an enlarged pattern is first manufactured. Since the mask is an original plate, if there is a defect, there is a possibility that all the TCs made from it will be defective, and defect inspection is the most important task.

The mask substrate is usually a square transparent substrate made of quartz. Conventionally, optical methods using laser beams have been used to inspect such substrates. This will be explained with reference to FIG. 3(a). In the figure, a mask substrate 1 is placed on a frame-shaped mounting table 8 shown in FIG. 4, and narrowed down to a small diameter spot by a lens system (not shown) to irradiate the mask substrate 1 and scan between points 91 in the X-axis direction. 5 indicates the scanning line of the spot.

In order to irradiate the entire area of the mask substrate 1, the mask substrate 1 is moved along with the substrate Jdii and the yr table 8 by the Y-axis moving mechanism 9.
Move in the axial direction. When a defect exists in the mask substrate 1, the scattered light 6 from the spot enters the light receiver 7 and the defect is detected.

In 1-, since the mask base kl is transparent, a part of the irradiated laser beam passes through the mask substrate 1, and the moving part 9-1 of the Y-axis moving mechanism 9 moves 1! (If the laser beam is reflected by the laser beam, the reflected light passes through the mask substrate l and the - part becomes so-called stray light and enters the light receiver 7. This stray light The intensity of the light changes as it scans, and it behaves just like scattered light, making it impossible to distinguish between them. In other words, the S/N ratio deteriorates and the detection performance deteriorates.

This countermeasure is to prevent the reflection of the laser beam 3 on the surface of the moving part 9-1.
Although the surface of the laser beam 3 is coated with a black coating with low reflectance, the luminous intensity of the laser beam 3 is extremely strong, and even a small amount of reflected light becomes quite strong stray light, making it ineffective. Conventionally, a trap hoe 710 shown in FIG. 4 is sometimes used for round transparent substrates. The trap horn 10 collects the laser beam 3 at the tip 10-1 of the horn no matter what direction the laser beam 3 is incident on, and does not reflect back to the input end. This allows stray light to be removed. However, in the case of a rectangular mask substrate 1, the size of the mask substrate has become large recently, and the trap horn that encloses the substrate needs to have a large diameter.
This is difficult to use. This is why a simple and effective stray light removal method is needed.

[Object 1 of the Invention] In view of the circumstances described below, this invention is used in an inspection device for transparent substrates such as rectangular mask substrates to effectively eliminate stray light based on transmitted light of a laser beam. The second object of the present invention is to provide a method for removing stray light in a mask substrate inspection apparatus, which removes stray light.

[Means for solving the problem] Fig. 1 is a principle diagram of a method for removing stray light in a mask substrate JfA scanning device according to the present invention. A first glass plate 11 whose back surface is painted black and absorbs the light and reflects it in the right angle direction.
-1 is provided, further absorbs this reflected light, and a part of it is
l) A second glass plate 11-2 whose back surface is painted black and reflects the light in the right angle direction is provided, and most of the transmitted light 3-1 is transmitted to the first glass plate 11-2.
The second glass plate absorbs the reflected light 12 and allows a small portion of the reflected light 12 to escape in the direction opposite to the mask substrate 1.

[Function] In 1-, the first and second glass plates whose back surfaces are painted black each absorb approximately 95% of the incident light, and the reflected light is only about 5%. Therefore, the second
The reflected light reflected by the glass plate and traveling in the opposite direction to the mask substrate has a microtS of about 1/400 of the transmitted light 3-1.
1, and even if some of the various components provided at the bottom of the mask substrate 1 have a high reflectance, very little stray light will enter the light receiver as stray light.

[Embodiment] Fig. 2 shows an embodiment of the method for removing stray light in a transparent substrate inspection apparatus according to the present invention. A first glass plate 11-1 whose back surface is painted black and which covers the range of the scanning line 5 and receives and absorbs the transmitted light 3-1 is provided, and its reflection direction is set at right angles. Further, a second glass plate 11-2 is provided to receive and absorb this reflected light, and the direction of reflection is set at right angles, so that the reflected light 12 is directed in the opposite direction to the mask substrate 1.

1-, since the mask substrate 1 itself moves when scanning the mask substrate 1 in the Y-axis direction, stray light is effectively removed even during this scanning.

[Effects of the Invention] As is clear from the explanation of [Yu], according to the method for removing stray light in a transparent substrate inspection apparatus according to the present invention, some of the laser beam irradiated on the mask substrate passes through the mask substrate,
Since stray light reflected on the surface of the Y-axis moving mechanism and the like is removed, the S/N ratio in mask substrate inspection increases by -1, which has a significant effect on the efficiency of defect inspection.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of the principle of stray light removal in the stray light removal method of a transparent substrate inspection apparatus according to the present invention, and FIG.
Examples for illustrations! P & key figures, Figure 3 (a) and (
b) is an explanatory diagram of the structure of an inspection apparatus for a transparent mounting plate such as a mask substrate and the generation of stray light, and FIG. 4 is an explanatory diagram showing a trap horn conventionally used for removing stray light. DESCRIPTION OF SYMBOLS 1... Mask substrate, 2... Laser light source, 3...
... Laser beam, 3-1... Transmitted light, 4... Oscillating mirror, 5... Scanning line, 6... Scattered light,
7... Light receiver, 8... Auxiliary plate, 9
...Y-axis movement mechanism, Tod.. Moving part, To2.
・Fixed part, 10... Trap horn, 10-1-・
・Tip! I-1...first glass plate, +1-2.
...Second glass plate, 12...Reflected light.

Claims (1)

[Claims] In a transparent substrate inspection device that irradiates a laser beam onto a transparent substrate and detects the defect by receiving scattered light due to a surface defect existing on the transparent substrate, a laser beam is placed opposite to the light source side of the laser beam with respect to the transparent substrate. A first glass plate whose back surface is painted black absorbs the laser beam and reflects a part of the laser beam in a right-angled direction; A method for removing stray light from a transparent substrate inspection device, comprising: a second glass plate whose back surface is painted black and reflects light in a direction opposite to the light source.