JP4684215B2 - Surface defect inspection equipment - Google Patents

Description

  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 a surface defect inspection apparatus having an interference phase measurement system and a scattered light detection system. .

In general, a surface defect inspection apparatus that optically inspects a surface defect such as a magnetic disk or its substrate is provided with a plurality of detection systems in consideration of differences in the shape, size, optical properties, etc. of the defect. . One example is an interference phase measurement system that uses interference between reflected light from a reference surface and regular reflected light from a surface to be measured, as described in Patent Document 1, for example. The interference phase measurement system is suitable for detecting the height of a projection 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 the interference phase measurement system.
JP 2000-121318 A

  Conventionally, a surface defect inspection apparatus including an interference phase measurement system and a scattered light detection system requires a separate light projection system for each detection system, and the configuration of the apparatus has been 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.

  An object of the present invention is to simplify the configuration of a surface defect inspection apparatus that performs inspection using an interference phase measurement system and a scattered light detection system.

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

The surface defect inspection apparatus according to the present invention includes a light source that generates a light beam, a branching unit that splits the light beam generated by the light source into two lights having different polarization planes, and a light beam that is split by the branching unit at different frequencies. The first and second modulation means for modulating the light beam, the light beam modulated by the first modulation means reflected by the surface to be measured, and the light beam modulated by the second modulation means reflected by the reference surface with the plane of polarization of the reflected light is divided into two different light dividing means having a polarizer tilting the polarization plane of the two reflected light 45 degrees, from one divided by the split means, by the measurement surface Interference detection means for detecting an interference component between the reflected light reflected by the reflected light and the reflected light reflected by the reference surface, and a scattered light detection means for detecting scattered light from the other divided by the dividing means, and the polarization of the dividing means vessel is, the two reflected light, the It is to divide the light having a polarization plane which does not transmit light and the polarizer having the polarization plane of transmitting light unit.

  When there is a defect on the surface to be measured, the reflected light reflected by the surface to be measured includes regular reflected light and scattered light scattered by the defect on the surface to be measured. By dividing the reflected light reflected by the surface to be measured by the dividing means, using one as the interference detecting means and using the other as the scattered light detecting means, an interference phase measuring system and a light beam generated by the same light source can be used simultaneously. The scattered light detection system can be inspected. The splitting means is provided with a polarization function 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. Since it can be used in the detection system, the amount of light that can be used in the interference phase measurement system is larger than when the polarization unit is provided separately from the dividing unit.

  Further, in the surface defect inspection apparatus of the present invention, the scattered light detection means converges the specularly reflected light included in the other divided by the dividing means, and the vicinity of the focal point of the specularly reflected light focused by the converging means. And a second blocking unit for blocking the diffracted light of the specularly reflected light that has passed through the periphery of the first blocking unit.

  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 means is blocked by the second blocking means. Therefore, the scattered light detection means can efficiently block the regular reflection light by the first and second blocking means. On the other hand, the scattered light is scattered in its direction, 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 the present invention, since the inspection by the interference phase measurement system and the inspection by the scattered light detection system can be performed using the same light projecting system, the configuration of the surface defect inspection apparatus can be simplified. The splitting means is provided with a polarization function 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. Since it can be used in the detection system, the amount of light that can be used in the interference phase measurement system is larger than when the polarization unit is provided separately from the dividing unit.

  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 at the same time, so that the inspection time can be shortened.

  FIG. 1 is a diagram showing a schematic configuration of a surface defect inspection apparatus. 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, 23B, polarization beam splitters 21, 24, 25, acousto-optic modulators (AOM) 22A, 22B, quarter-wave plates 26A, 26B, and objective lenses. 27A and 27B, the polarizing plate 28, the line sensor 30, and the detection circuit 31 are comprised. The scattered light detection system 40 includes a beam splitter 41, a condensing lens 42, masks 43 and 45, a lens 44, an imaging lens 46, and a light receiving element 47.

  The laser light source 10 generates laser light 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 to the acoustooptic element 22A and the other to the acoustooptic element 22B. Eject.

  The acoustooptic device 22A modulates the laser beam branched by the polarization beam splitter 21 at a predetermined frequency fa. The laser light modulated by the acoustooptic device 22A is reflected by the reflecting mirror 23A, passes through the polarizing beam splitters 24 and 25, and is irradiated to the reflecting mirror 20 through the quarter-wave plate 26A and the objective lens 27A. The The reflecting surface of the reflecting mirror 20 serving as the reference surface is placed at a position where the optical distance is equal to the surface of the magnetic disk 1 serving as the surface to be measured. The reflected laser beam 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 converted from linearly polarized light to circularly polarized light by the quarter-wave plate 26A, and thus reflected by the polarization beam splitter 25 and emitted to the beam splitter 41.

  On the other hand, the acoustooptic device 22B modulates the laser beam branched by the polarization beam splitter 21 at a predetermined frequency fb different from the frequency fa. The laser beam modulated by the acousto-optic element 22B is reflected by the reflecting mirror 23B, reflected by the polarization beam splitters 24 and 25, and then passed to the surface of the magnetic disk 1 via the quarter-wave plate 26B and the objective lens 27B. Irradiated. If there is a defect 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 regular reflected light and scattered light. 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. The reflected light that has reached the polarizing beam splitter 25 is converted from linearly polarized light to circularly polarized light by the quarter-wave plate 26B, and thus passes through the polarizing beam splitter 25 and is emitted to the beam splitter 41.

  The beam splitter 41 divides the reflected light from the reflecting mirror 20 and the reflected light from the surface of the magnetic disk 1 into two parts, and emits one to the polarizing plate 28 and the other 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 light transmitted through the polarizing plate 28 interferes with the reflected light from the reflecting mirror 20 and 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. . The detection circuit 31 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 based on the electrical signal from the line sensor 30.

  The condensing lens 42 condenses the other light divided | segmented by the beam splitter 41, and condenses the regular reflection light of them. The scattered light scattered by the defects on the surface of the magnetic disk 1 has different directions and is not focused by the condenser lens 42. The mask 43 is provided in the vicinity of the focal point of the specularly reflected light focused by the condensing lens 42 and blocks the specularly reflected light focused by the condensing lens 42.

  2A is a top view of the mask 43, and FIG. 2B is a cross-sectional view taken along the line AA of FIG. 2A. FIG. 3 is a diagram for explaining the operation of the scattered light detection system. The mask 43 has a disk shape, and its diameter is small so as not to block scattered light. Therefore, a part of the specularly reflected light C shown by the solid line in FIG. 3 is focused by the condenser lens 42 and then diffracted and passes around the mask 43, and the diffracted light shown by the two-dot chain line in FIG. D. The diffracted light D passes through the lens 44 to become a parallel light beam and is irradiated onto the mask 45.

  2C is a top view of the mask 45, and FIG. 2D is a cross-sectional view of the BB portion of FIG. 2C. The mask 45 is disk-shaped and has a hole in the 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 help understanding the above operation. By providing the masks 43 and 45, the path indicated 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 a hole provided in the mask 45. The scattered light that has passed through the hole of the mask 45 is irradiated to the light receiving element 47 through 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 electrical signal.

  FIG. 4 is a diagram showing a schematic configuration of a surface defect inspection apparatus according to an embodiment of the present invention. The difference from the surface defect inspection apparatus 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 the same as those of the surface defect inspection apparatus shown in FIG. The polarizer 29 tilts the polarization plane of the light incident from the polarization beam splitter 25 by 45 degrees, and transmits light having a polarization plane that passes through the polarizer 29 to the line sensor 30 and light having a polarization plane that does not pass through the polarizer 29. Is emitted to the condenser lens 42.

  In the surface defect inspection apparatus shown in FIG. 1, half of the laser light incident on the polarizing plate 28 has a polarization plane that does not pass through the polarizing plate 28 and is emitted in a direction perpendicular to the transmitted light. On the other hand, according to the embodiment shown in FIG. 4, since the light emitted in the direction perpendicular to the transmitted light can be used in the scattered light detection system 40, the amount of light that can be used in the interference phase measurement system is small. Become more.

  According to the embodiment described above, the scattered light detection system 40 can efficiently block the regular reflection 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 a magnetic disk or its substrate, and can be used for inspection of various object surface defects .

It is a figure which shows schematic structure of a surface defect inspection apparatus. 2A is a top view of the mask 43, FIG. 2B is a cross-sectional view of the AA portion of FIG. 2A, FIG. 2C is a top view of the mask 45, and FIG. It is sectional drawing of the BB part of). It is a figure explaining operation | movement of a scattered light detection system. It is a figure which shows schematic structure of the surface defect inspection apparatus by one embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Magnetic disk 10 Laser light source 20, 23A, 23B Reflector 21, 24, 25 Polarization beam splitter 22A, 22B Acousto-optic device 26A, 26B Quarter wave plate 27A, 27B Objective lens 28 Polarizer 29 Polarizer 30 Line sensor 31 Detection Circuit 40 Scattered Light Detection System 41 Beam Splitter 42 Condensing Lenses 43 and 45 Mask 44 Lens 46 Imaging Lens 47 Light-Receiving Element

Claims (2)

A light source that generates a light beam;
Branching means for branching the light beam generated by the light source into two lights having different polarization planes;
First and second modulation means for modulating the light beams branched by the branching means at different frequencies, respectively;
Two light beams having different polarization planes are reflected light that is reflected by the surface to be measured by the light beam modulated by the first modulation unit and reflected light that is reflected by the reference surface by the light beam that is modulated by the second modulation unit. And a splitting means having a polarizer that tilts the polarization plane of the two reflected lights by 45 degrees ,
From one divided by the pre-Symbol dividing means, and interference detection means for detecting the interference component and the reflected light reflected by the reflection light and the reference surface reflected by the measurement surface,
A scattered light detecting means for detecting scattered light from the other divided by the dividing means,
A surface defect inspection apparatus, wherein the polarizer of the dividing unit divides the two reflected lights into light having a polarization plane that passes through the polarizer and light having a polarization plane that does not pass through the polarizer. . The scattered light detection means includes
Focusing means for focusing the specularly reflected light contained in the other divided by the dividing means;
First blocking means provided in the vicinity of the focusing point of the specularly reflected light focused by the focusing means;
The surface defect inspection apparatus according to claim 1, further comprising: a second blocking unit that blocks diffracted light of the specularly reflected light that has passed around the first blocking unit.

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