JPS63208747A - Optical inspecting device - Google Patents

Abstract

PURPOSE:To converge scattered light efficiently and to evade the detection of unnecessary light by allowing to inspection light to impinge on the 1st focus of a body to be inspected and condensing the scattered light from a 1st focus part by a reflecting mirror. CONSTITUTION:The 1st focus P1 is formed on the inspection surface of a wafer 2 at its top surface side, and an elliptic reflector 28 as the reflecting mirror which forms a 2nd focus P2 at the side of a photodetector 6 as a photodetecting means is installed. This beam-shaped laser light 36 emitted by a laser light source 6 is projected on the 1st focus P1 from one window 32. The scattered light 38 from foreign matter such as dust and a flaw present at the 1st focus P1 is reflected by the reflecting mirror 30 and condensed on the 2nd focus P2, and the light is guided into a dark box 14 through the window 15 of the dark box 14 and detected by the photodetector 16. Consequently, the scattered light 38 is condensed efficiently and the detection of the unnecessary light is evaded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical inspection device used for inspecting the surface condition of an object to be inspected.

[Conventional technology]

FIG. 6 shows a conventional optical inspection apparatus used for inspecting the surface of, for example, a semiconductor wafer as an object to be inspected.

This optical inspection device places a wafer 2 as an object to be inspected on a rotatable inspection table 4, and irradiates the surface with laser light 8 from a laser light source 6 through an integrating sphere 10.
Scattered light 12 due to scratches or foreign matter on the surface is collected by an integrating sphere 10 and guided to a photodetector 16 installed in a dark box 14 for reception.

The integrating sphere 10 is installed as a condensing means for the scattered light 12,
The inner surface is a total reflection surface, and the laser beam 8 is irradiated from the window 18.20 to the wafer 2.
Direct reflection from the window 22 is allowed to escape from the window 22. Scattered light 12 passing through a path other than the optical path of laser light 8
is reflected inside the integrating sphere 10 and sent to the photodetector 1 through the window 24.
6 and convert it into, for example, an electrical signal.

[Problem that the invention seeks to solve]

When such an integrating sphere 10 is used, the light 26 that strays through the window 18 is also totally reflected within the integrating sphere 10 and guided to the photodetector 16 together with the scattered light 12 to be detected. Stray light generated from refraction due to such factors is also guided, resulting in a decrease in the optical S/N ratio. It is difficult for such an integrating sphere 1o to perform ideal total reflection, and light attenuation occurs during repeated reflections, resulting in a decrease in the detection signal level.

Therefore, the present invention avoids the influence of unnecessary light and prevents the attenuation of scattered light.

[Means for solving problems]

As shown in FIG. 1, the optical inspection apparatus of the present invention has a first focus P1 on the surface of an object to be inspected (wafer 2), and a second focus P2 on a portion other than the surface of the object to be inspected. A mirror (elliptic reflector 28, elliptical reflector 29 in FIG. 5) and a light detection means (photodetector 1) on the second focal point P2 side.
6), the inspection light (laser light 36) is applied to the first focus of the object to be inspected, and the scattered light 38 from the first focus portion is
The light is collected by a reflecting mirror and detected by a light detection means.

[For production]

With this configuration, the scattered light 38 generated from the first focal point P1 can reach the light detection means (photodetector 16) by - times of reflection, and unnecessary light can be transmitted to the second focal point P2.
Since the probability of light convergence on the target is lowered, detection accuracy can be improved.

〔Example〕

FIG. 1 shows an embodiment of the optical inspection apparatus of the present invention.

For example, a wafer 2 as an object to be inspected is placed on a rotatable inspection table 4.

On the upper surface side of this wafer 2, a first focal point P1 is placed on the inspection surface.
At the same time, an elliptical reflector 28 is installed as a reflecting mirror that connects the second focal point P2 to the photodetector 16 side as a photodetector. As shown in FIG. 2 and FIG.
The lower surface and side surfaces are open, and windows 32 and 34 are formed on the back surface.

Therefore, a narrow beam of laser light 36 emitted by a laser light source 6 serving as an inspection light source that emits inspection light is irradiated from one window 32 to the first focal point PI. In this case, the incident angle of the laser beam 36 as the inspection light is 4, as is clear from the comparison with the reference line forming a right angle on the surface of the wafer 2.
Set to 5° or less. In this way, the laser beam 36 irradiated onto the wafer 2 and reflected on its surface escapes to the outside through the window 34 of the elliptical reflector 28, and the scattered light 38 from foreign objects such as dust and scratches present at the first focal point P1 is The light can be received by the reflective surface 30, reflected, and focused on the second focal point P2. That is, the scattered light 38 is reflected only once on the reflective surface 30 of the elliptical reflector 28 and is condensed at the second focal point P2 without attenuation, and is transmitted from the window 15 of the dark box 14 to the dark box 1.
4 and detected by a photodetector 16. Scattered light 38
Since there is less attenuation, the S/N ratio becomes higher.

If the photodetector 16 is configured with a light receiving element that converts light into an electrical signal, it can detect the scattered light 38 as an electrical signal.

In addition, stray light 40 as unnecessary light that enters the inspection surface through the windows 32 and 34 due to reflection from dirt in the optical system has a low probability of hitting the first focal point P, and after being reflected from the surface of the wafer 2, Although it is reflected by the surface 30, the probability of convergence on the second focal point P2 is extremely low, so the photodetector 16 does not detect it as a signal.

In particular, since the elliptical reflector 28 is made up of 174 parts of a perfect ellipsoid, it can easily condense the scattered light 38 from the foreign object into a light of 90'' or more in any direction of the entire solid angle.
This allows the light to be efficiently guided to the photodetector 16.

Incidentally, the dark box 1-4 is opened with a window 15 to take in the scattered light 38, but a diaphragm plate 42 may be attached, for example, as shown in FIG. The diaphragm plate 42 forms a slit 44 in the center of which the front surface is narrow and becomes larger with an inclined surface toward the inside of the dark box 14 in order to pass the necessary scattered light 38.
Cylindrical hood 4 to block unnecessary light around the
6 will be provided. By using such a diaphragm plate 42, it is possible to suppress the incidence of unnecessary light such as natural light and stray light, and improve the S/N ratio.

In addition, in the embodiment shown in FIG.
The elliptical reflector 28 was formed from four parts, and as shown in FIG. A similar effect can be expected even if the light is guided through the rectangular window 15.

Although the embodiment has been described using the wafer 2 as an example of the object to be inspected, the present invention can be used for optical inspection of the surface condition of various polished metal surfaces.

〔Effect of the invention〕

According to the present invention, scattered light can be efficiently collected without attenuation, detection of unnecessary light can be avoided, and highly reliable optical inspection can be realized.

[Brief explanation of the drawing]

1 and 2 are diagrams showing an embodiment of the optical inspection device of the present invention, FIG. 3 is a sectional view taken along line mm in FIG. 2, and FIGS. 4 and 5 are diagrams showing an embodiment of the optical inspection device of the present invention. FIG. 6 is a diagram showing a conventional optical inspection device. 2... Wafer (object to be inspected), 16... Photodetector (light detection means), 28.29... Elliptical reflector (reflector), 36... Laser light (inspection light). Figure 6 Figure 2 Figure 3 V Rumors Figure 5

Claims (1)

[Claims] A reflecting mirror having a first focus on the surface of the object to be inspected and a second focus on a part other than the surface of the object to be inspected, and a light detection means on the second focal point side, are equipped to direct the inspection light to the object to be inspected. 1st
An optical inspection device that focuses light on a focal point, collects scattered light from the first focal point using a reflecting mirror, and detects the collected light using a light detection means.