Surface inspection method and surface inspection device

Abstract

A surface inspection method for projecting a laser beam to an inspection surface and for scanning and detecting foreign objects or the like on the inspection surface, comprising a step of being had a required number of detecting regions by a photodetector against a projecting site of the laser beam, a step of receiving a detection light at the photodetector so that a detection light intensity is varied between the detecting regions, a step of acquiring a required number of output signals with different detection light intensities on an inspection site, and a step of selecting an output signal which is an unsaturated output signal and has the highest value among the required number of output signals as a surface detection signal.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram to show a relation between projection range of a laser beam and detecting regions and a relation between projected light intensity distribution and detecting regions in a first embodiment of the present invention;

FIG. 2 is a diagram to show a relation between detection light intensity and output signal level in each of the detection regions in the first embodiment of the invention;

FIG. 3 is a diagram to show a relation between detection light intensity and output signal level in each of the detection regions in a second embodiment of the invention;

FIG. 4 is a diagram to show a relation between projection range of a laser beam and detecting regions and a relation between projection light intensity distribution and the detecting regions in a different projection light intensity distribution;

FIG. 5 is a diagram to show a relation between projection range of a laser beam and the detecting regions and a relation between projection light intensity distribution and the detecting regions in a still other different projection light intensity distribution;

FIG. 6 is a schematical block diagram of a signal processing unit in a surface inspection device according to an embodiment of the present invention;

FIG. 7 is a drawing to show an example of a photodetector to be used in the present invention;

FIG. 8 is a perspective view to show approximate arrangement of the surface inspection device;

FIG. 9 is a diagram to show an example of an output signal from a conventional type scattering light detector; and

FIG. 10 is a diagram to show a relation between detection light intensity and output signal level in a conventional example.

Claims

1. A surface inspection method for projecting a laser beam to an inspection surface and for scanning and detecting foreign objects or the like on the inspection surface, comprising a step of being had a required number of detecting regions by a photodetector against a projecting site of said laser beam, a step of receiving a detection light at said photodetector so that a detection light intensity is varied between said detecting regions, a step of acquiring a required number of output signals with different detection light intensities on an inspection site, and a step of selecting an output signal which is an unsaturated output signal and has the highest value among the required number of output signals as a surface detection signal.

2. A surface inspection method according to claim 1, wherein said laser beam is projected to have such light intensity distribution that the light intensity varies at said projected site, and a required number of detecting regions are set so that detection light intensities are varied.

3. A surface inspection method according to claim 1, wherein the light amount is adjusted by an optical filter so that the detection light intensity is varied between said detecting regions.

4. A surface inspection method according to claim 1, wherein said detecting regions are divided with a predetermined pitch in a direction crossing the scanning direction, and a feeding pitch to perpendicularly cross the scanning direction is equal to the dividing pitch.

5. A surface inspection device, comprising an inspection light projecting system for projecting a laser beam to an inspection surface, a scattering light receiving system for detecting scattering lights, and an arithmetic operation unit for performing calculation to detect foreign objects or the like based on scattering light detection output of said scattering light receiving system, wherein said scattering light receiving system has a required number of detecting regions and detects detection lights so that the scattering light intensities to receive the detection light are varied between the detecting regions, and said arithmetic operation unit selects an unsaturated scattering light detecting output with the highest value among a plurality of scattering light detecting output obtained at the same site as a surface inspection signal, and foreign objects or the like are inspected based on the surface inspection signal.

6. A surface inspection device according to claim 5, wherein said inspection light projecting system projects said laser beam to have such light intensity distribution that the light intensity varies at the projected site, and said detecting regions are set so that the detection light intensity is varied.

7. A surface inspection device according to claim 5, wherein an optical filter is provided in said scattering light receiving system so that detection light intensity is varied between said detecting regions.

8. A surface inspection device according to claim 5, further comprising a rotating position detector, a feeding position detector, a photodetector for issuing photodetection signals individually for each region, and a memory unit arranged to match each region, wherein the photodetection signals are stored in each memory unit by associating with the rotating position and the feeding position, said arithmetic operation unit extracts a photodetection signal with the same rotating position and the same feeding position in the each memory unit and selects an unsaturated photodetection signal with said highest value as a surface inspection signal.