JP2003207457A - Surface defect-inspecting apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To simplify the configuration of a surface defect-inspecting apparatus for inspecting by an interference phase measuring system and a scattered light detection system. <P>SOLUTION: Laser beams that are generated by a laser source 10 are branched by a polarization beam splitter 21, are modulated at each different frequency by acoustic optical elements 22A and 22B, and are applied to a reflector 20 or the surface of a magnetic disk 1. A beam splitter 41 divides reflection light from the reflector 20 and that from the surface of the magnetic disk 1 into each two portions. A condensing lens 42 condenses the split beams of light and condenses regular reflection light in it. A mask 43 shields the condensed regular reflection light, and a mask 45 shields the diffraction light of the regular reflection light passing through the periphery of the mask 43. Almost all of the scattered light is not shielded by the mask 43, passes through a hole that is provided on the mask 45, and is detected by a light receiving element 47. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface defect inspection apparatus for inspecting a surface of a magnetic disk or its substrate (substrate) for defects, and more particularly to an interferometric phase measurement system and a scattered light detection system. The present invention relates to a surface defect inspection device.

[0002]

2. Description of the Related Art Generally, a surface defect inspection apparatus for optically inspecting defects on the surface of a magnetic disk or a substrate thereof has a plurality of detections in consideration of differences in defect shape, size, optical properties and the like. It has a system. One of them is, for example, an interference phase measurement system as described in Japanese Patent Laid-Open No. 2000-121318, which utilizes interference between reflected light from a reference surface and specularly reflected light from a surface to be measured. The interference phase measurement system is suitable for detecting the height of a protrusion or the like on the surface to be measured. Apart from this, there is a scattered light detection system that uses scattered light scattered by defects on the surface to be measured. The scattered light detection system is suitable for detecting minute defects that are difficult to detect with an interference phase measurement system.

[0003]

Conventionally, a surface defect inspection apparatus equipped with an interference phase measuring system and a scattered light detecting system requires a separate light projecting system for each detecting system, and therefore the apparatus configuration is It was complicated. Further, since the inspection by the interference phase measurement system and the inspection by the scattered light detection system are separately performed, there is a problem that the inspection time becomes long.

It is an object of the present invention to simplify the structure of a surface defect inspection device for inspecting by an interference phase measuring system and a scattered light detecting system.

Another object of the present invention is to shorten the inspection time by the interference phase measuring system and the scattered light detecting system.

[0006]

According to another aspect of the present invention, there is provided a surface defect inspection apparatus including a light source for generating a light beam, a branching unit for branching the light beam generated by the light source, and a light beam branched by the branching unit. First and second modulating means for modulating the beams at different frequencies, reflected light obtained by reflecting the light beam modulated by the first modulating means on the surface to be measured, and light beam modulated by the second modulating means. A dividing means for dividing the reflected light reflected by the reference surface, and an interference detecting means for detecting an interference component of the reflected light reflected by the measured surface and the reflected light reflected by the reference surface from one of the divided means. And a scattered light detecting means for detecting scattered light from the other divided by the dividing means.

When the surface to be measured has a defect, the reflected light reflected by the surface to be measured includes specularly reflected light and scattered light scattered by the defect on the surface to be measured. The reflected light reflected by the surface to be measured is split by the splitting means, one of which is used as the interference detecting means, and the other of which is used as the scattered light detecting means. The scattered light detection system can be inspected.

According to a second aspect of the present invention, in the surface defect inspection apparatus according to the first aspect, the scattered light detecting means focuses the specular reflection light included in the other divided by the dividing means, and the focusing means. A first blocking means provided near a focal point of the specularly reflected light focused by the means, and a second blocking means for blocking the diffracted light of the specularly reflected light that has passed around the first blocking means. It is a thing.

Most of the specularly reflected light focused by the focusing means is blocked by the first blocking means provided near the focusing point. The diffracted light of the specularly reflected light that has passed around the first blocking unit is blocked by the second blocking unit. Therefore, the scattered light detecting means can efficiently block the specularly reflected light by the first and second blocking means. On the other hand, the scattered light has different directions, is not focused by the focusing means, and is detected without being blocked by the first blocking means and the second blocking means.

According to a third aspect of the present invention, in the surface defect inspection apparatus according to the first aspect, the interference detecting means includes a polarizing means, and the dividing means also serves as the polarizing means of the interference detecting means.

Generally, the interference detecting means is provided with a polarizing means for causing the reflected light reflected by the surface to be measured and the reflected light reflected by the reference surface to interfere with each other. Half of the light that has entered the polarization means has a plane of polarization that does not pass through the polarization means, and is emitted in the direction perpendicular to the transmitted light that passes through the polarization means. Since the splitting means also serves as the polarizing means of the interference detecting means, the light emitted from the polarizing means in the direction perpendicular to the transmitted light can be used in the scattered light detection system. Therefore, when the splitting means is provided separately from the polarizing means. In comparison, the amount of light available in the interference phase measurement system increases.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a diagram showing a schematic configuration of a surface defect inspection apparatus according to an embodiment of the present invention. The surface defect inspection apparatus includes a laser light source 10, an interference phase measurement system, and a scattered light detection system 40. The interference phase measurement system includes reflecting mirrors 20, 23A and 23B, polarization beam splitters 21, 24 and 25, an acousto-optic device (AO).
M: Accousto-Optic Modulato
r) 22A, 22B, quarter wave plates 26A, 26B,
The objective lens 27A, 27B, a polarizing plate 28, a line sensor 30, and a detection circuit 31 are included. The scattered light detection system 40 includes a beam splitter 41 and a condenser lens 4.
2, masks 43 and 45, lens 44, imaging lens 46,
And a light receiving element 47.

The laser light source 10 generates a laser beam having a predetermined wavelength as a light beam. The polarization beam splitter 21 splits the laser light generated by the laser light source 10 into two lights (P-polarized light and S-polarized light) whose polarization planes are different by 90 degrees, one of which is directed to the acousto-optic element 22A and the other of which is directed to the acousto-optic element 22B. To eject.

The acousto-optic element 22A modulates the laser beam split by the polarization beam splitter 21 at a predetermined frequency fa. The laser light modulated by the acousto-optic element 22A is reflected by the reflecting mirror 23A, and the polarization beam splitter 2
The light passes through 4 and 25 and is irradiated onto the reflecting mirror 20 through the quarter-wave plate 26A and the objective lens 27A. The reflecting surface of the reflecting mirror 20 serving as the reference surface is placed at a position having the same optical distance as the surface of the magnetic disk 1 serving as the measured surface.
The reflected light, which is the reflected laser light reflected by the reflecting mirror 20, reaches the polarization beam splitter 25 via the objective lens 27A and the quarter-wave plate 26A. The reflected light that has reached the polarization beam splitter 25 is a quarter-wave plate 26A.
Since the linearly polarized light is converted to the circularly polarized light by the
It is ejected to 1.

On the other hand, the acousto-optic element 22B modulates the laser beam split by the polarization beam splitter 21 at a predetermined frequency fb different from the frequency fa. Acousto-optic element 2
The laser beam modulated by 2B is reflected by the reflecting mirror 23B, reflected by the polarization beam splitters 24, 25, and is applied to the surface of the magnetic disk 1 via the quarter-wave plate 26B and the objective lens 27B. . When a defect exists on the surface of the magnetic disk 1, a part of the irradiated laser light is specularly reflected and a part is scattered by the defect. Therefore, the reflected light from the surface of the magnetic disk 1 includes specularly reflected light and scattered light. The reflected light from the surface of the magnetic disk 1 reaches the polarization beam splitter 25 via the objective lens 27B and the quarter-wave plate 26B. Polarizing beam splitter 25
Since the reflected light that has reached (1) has been converted from linearly polarized light to circularly polarized light by the quarter-wave plate 26B, it passes through the polarization beam splitter 25 and is emitted to the beam splitter 41.

The beam splitter 41 splits the reflected light from the reflecting mirror 20 and the reflected light from the surface of the magnetic disk 1 into two, one of which is emitted to the polarizing plate 28 and the other of which is emitted to the condenser lens 42. The polarizing plate 28 tilts the polarization plane of the light incident from the beam splitter 41 by 45 degrees and emits the transmitted light to the line sensor 30. The transmitted light of the polarizing plate 28 is
The reflected light from the reflecting mirror 20 interferes with the reflected light from the surface of the magnetic disk 1, and the line sensor 30 converts the intensity into an electric signal and outputs it to the detection circuit 31. Detection circuit 3
1 detects the phase difference between the reflected light from the reflecting mirror 20 and the reflected light from the surface of the magnetic disk 1 by the electric signal from the line sensor 30.

The condenser lens 42 is a beam splitter 41.
The other light split by is condensed, and the specularly reflected light is focused. The directions of scattered light scattered by defects on the surface of the magnetic disk 1 are scattered, and the condensing lens 4
Not focused by 2. The mask 43 is a condenser lens 42.
It is provided in the vicinity of the focal point of the specularly reflected light that has been focused by, and blocks the specularly reflected light that has been focused by the condenser lens 42.

FIG. 2A is a top view of the mask 43, and FIG.
2B is a cross-sectional view taken along the line AA of FIG. Further, FIG. 3 is a diagram for explaining the operation of the scattered light detection system. The mask 43 is disk-shaped, and its diameter is made small so as not to block scattered light. Therefore, a part of the regular reflection light C shown by the solid line in FIG.
Diffract the light around the mask 43 and pass through it to become the diffracted light D shown by the two-dot chain line in FIG. The diffracted light D passes through the lens 44 and becomes a parallel light beam, which is applied to the mask 45.

FIG. 2C is a top view of the mask 45, FIG.
2D is a cross-sectional view taken along the line BB in FIG. 2C. The mask 45 is disk-shaped and has a hole in its center. The mask 45 blocks the diffracted light D that has been converted into parallel rays by the lens 44. Note that the dotted line in FIG. 3 shows the path of the specularly reflected light C when the masks 43 and 45 are not provided, in order to facilitate understanding of the above operation. By providing the masks 43 and 45, the path shown by the dotted line is blocked.

On the other hand, most of the scattered light is not blocked by the mask 43 and passes through the holes provided in the mask 45. The scattered light that has passed through the holes of the mask 45 is applied to the light receiving element 47 via the imaging lens 46. The light receiving element 47 is composed of an avalanche photodiode (APD), a pin photodiode, or the like, and detects scattered light and converts its intensity into an electric signal.

FIG. 4 is a diagram showing a schematic structure of a surface defect inspection apparatus according to another embodiment of the present invention. The difference from the embodiment shown in FIG. 1 is that the beam splitter 41 is not provided and a polarizer 29 is provided instead of the polarizing plate 28. Other configurations are similar to those of the embodiment shown in FIG. The polarizer 29 tilts the polarization plane of the light incident from the polarization beam splitter 25 by 45 degrees, and directs the light having the polarization plane passing through the polarizer 29 to the line sensor 30 and the polarizer 29.
Light having a polarization plane that does not pass through is emitted to the condenser lens 42.

In the embodiment shown in FIG. 1, the polarizing plate 28
Half of the laser light that entered the laser had a polarization plane that did not pass through the polarizing plate 28 and was emitted in the direction perpendicular to the transmitted light. On the other hand, according to the embodiment shown in FIG. 3, the scattered light detection system 40 detects the light emitted in the direction perpendicular to the transmitted light.
Therefore, the amount of light that can be used in the interference phase measurement system increases.

According to the embodiment described above, the scattered light detecting system 40 can efficiently block the specularly reflected light by the masks 43 and 45 and detect only the scattered light.

The surface defect inspection apparatus of the present invention is not limited to the magnetic disk or its substrate, and can be used for inspection of various surface defects of an object. Further, in the present invention, the example of the laser beam is shown as the light beam, but it may be white light, ultraviolet light or the like.

[0025]

According to the present invention, since the inspection by the interference phase measuring system and the inspection by the scattered light detecting system can be performed using the same light projecting system, the structure of the surface defect inspection apparatus can be simplified. it can.

Further, according to the surface defect inspection apparatus of the present invention, the inspection by the interference phase measurement system and the inspection by the scattered light detection system can be performed simultaneously, so that the inspection time can be shortened.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of a surface defect inspection apparatus according to an embodiment of the present invention.

2A is a top view of a mask 43, FIG. 2B is a cross-sectional view taken along the line AA of FIG. 2A, FIG. 2C is a top view of the mask 45, and FIG. It is sectional drawing of B part.

FIG. 3 is a diagram illustrating an operation of a scattered light detection system.

FIG. 4 is a diagram showing a schematic configuration of a surface defect inspection apparatus according to another embodiment of the present invention.

[Explanation of symbols]

1 ... Magnetic disk 10 ... Laser light source 20, 23A, 23B ... Reflector 21, 24, 25 ... Polarizing beam splitter 22A, 22B ... Acousto-optic element 26A, 26B ... Quarter wave plate 27A, 27B ... Objective lens 28 ... Polarizing plate 29 ... Polarizer 30 ... Line sensor 31 ... Detection circuit 40 ... Scattered light detection system 41 ... Beam splitter 42 ... Condenser lens 43, 45 ... Mask 44 ... Lens 46 ... Imaging lens 47 ... Light receiving element

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Takayuki Ishiguro             Hitachi Electronics, 3-16-3 Higashi, Shibuya-ku, Tokyo             Engineering Co., Ltd. (72) Inventor Hiroshi Okumura             Hitachi Electronics, 3-16-3 Higashi, Shibuya-ku, Tokyo             Engineering Co., Ltd. F term (reference) 2F065 AA49 BB03 BB25 CC03 DD02                       DD06 FF04 FF52 GG04 JJ01                       JJ02 JJ05 JJ18 JJ25 LL12                       LL30 LL33 LL34 LL36 LL37                       LL57 QQ25 QQ28 QQ31                 2G051 AA71 AB02 AB07 BA10 BB20                       BC10 CB01 CB05

Claims (3)

[Claims] 1. A light source that generates a light beam, a branching unit that branches the light beam generated by the light source, and first and second modulations that modulate the light beams that are branched by the branching unit at different frequencies. Means, and a splitting means for splitting the reflected light in which the light beam modulated by the first modulation means is reflected on the surface to be measured and the reflected light in which the light beam modulated by the second modulation means is reflected on the reference surface From one divided by the dividing means, interference detection means for detecting an interference component of the reflected light reflected on the surface to be measured and the reflected light reflected on the reference surface, from the other divided by the dividing means, A surface defect inspection apparatus comprising: scattered light detecting means for detecting scattered light. 2. The scattered light detecting means is provided in the vicinity of a converging means for converging the regular reflection light included in the other divided by the dividing means, and a converging point of the regular reflection light converged by the converging means. The surface defect according to claim 1, further comprising: a first blocking unit; and a second blocking unit that blocks the diffracted light of the specular reflection light that has passed through the periphery of the first blocking unit. Inspection device. 3. The surface defect inspection apparatus according to claim 1, wherein the interference detection unit includes a polarization unit, and the division unit also serves as the polarization unit.