Surface inspection by amplitude modulated specular light detection

Abstract

An apparatus for detecting defects on a disk surface includes a light source that generates a light beam and a beamsplitter that splits the light beam into a first light beam portion and a second light beam portion. The first light beam portion illuminates the surface of the disk and produces a reflected light beam. An acoustic-optic deflector deflects the reflected light beam and the second light beam portion producing a deflected output beam having a deflection angle. A detector detects an incident beam translation signal corresponding to reflected light beam angular deflection and acoustic-optic deflector beam angular deflection from the deflected output beam.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates generally an amplitude modulated specular light advanced optical inspection system for inspecting disk surfaces according to one embodiment of the present invention.

FIG. 2 illustrates a delivery module of a sensor optical illumination module for the amplitude modulated light advanced optical inspection system according to one embodiment of the present invention.

FIG. 3 illustrates the sensor optical illumination module and a sensor brightfield collection optical module for the amplitude modulated specular light advanced optical inspection system according to one embodiment of the present invention.

FIG. 4 illustrates the signal processing electronics for the amplitude modulated specular light advanced optical inspection system according to one embodiment of the present invention.

FIG. 5 illustrates a chirp signal timing diagram for an acousto-optic deflector according to one embodiment of the present invention.

FIG. 6 is a flowchart depicting steps performed within an apparatus for detecting defects on a disk surface in accordance with one embodiment of the present invention.

Claims

1. An apparatus for detecting defects on a disk surface, comprising: a light source that generates a light beam;a beamsplitter that splits the light beam into a first light beam portion and a second light beam portion, the first light beam portion illuminating the surface of the disk and produces a reflected light beam;an acoustic-optic deflector that deflects the reflected light beam and the second light beam portion producing a deflected output beam having a deflection angle; anda detector that detects an incident beam translation signal corresponding to reflected light beam angular deflection and acoustic-optic deflector beam angular deflection from the deflected output beam.

2. The apparatus for detecting defects on a disk surface according to claim 1, wherein the deflected output beam is based on an illumination spot size and a disk rotation speed.

3. The apparatus for detecting defects on a disk surface according to claim 1, wherein the detector includes a prism mirror and photomultiplier tubes.

4. The apparatus for detecting defects on a disk surface according to claim 3, further comprising a differential amplifier, a summation amplifier and a divider network.

5. The apparatus for detecting defects on a disk surface according to claim 4, wherein output signals from the photomultiplier tubes are differentially summed and normalized by the differential amplifier, the summation amplifier and the divider network.

6. The apparatus for detecting defects on a disk surface according to claim 5, wherein the summed and normalized signal is amplitude modulated by a disk surface circumferential slope.

7. The apparatus for detecting defects on a disk surface according to claim 1, wherein the light source is fiber optic coupled with polarization maintaining fibers.

8. The apparatus for detecting defects on a disk surface according to claim 1, further comprising a plano-convex lens providing an illumination spot on the surface of the disk.

9. The apparatus for detecting defects on a disk surface according to claim 1, wherein the acoustic-optic deflector is driven with a frequency chirped wave.

10. The apparatus for detecting defects on a disk surface according to claim 1, further comprising a lens that collimates the deflected output beam from the acoustic-optic deflector.

11. A method for detecting defects on a disk surface, comprising: generating a light beam;splitting the light beam into a first light beam portion and a second light beam portion, the first light beam portion illuminating the surface of the disk which produces a reflected light beam;deflecting the reflected light beam and the second light beam portion to produce a deflected output beam having a deflection angle; anddetecting an incident beam translation signal corresponding to reflected light beam angular deflection and acoustic-optic deflector beam angular deflection from the deflected output beam.

12. The method for detecting defects on a disk surface according to claim 11, wherein the deflected output beam is based on an illumination spot size and a disk rotation speed.

13. The method for detecting defects on a disk surface according to claim 11, further comprising summing and normalizing the detected incident beam translation signal.

14. The method for detecting defects on a disk surface according to claim 13, wherein the summed and normalized signal is amplitude modulated by a disk surface circumferential slope.

15. The method for detecting defects on a disk surface according to claim 11, further comprising providing an illumination spot on the surface of the disk.

16. The method for detecting defects on a disk surface according to claim 11, further comprising generating the deflection angle with a frequency chirped wave.

17. The method for detecting defects on a disk surface according to claim 11, further comprising collimating the deflected output beam.

18. A system for detecting defects on a disk surface, comprising: a light source that generates a light beam;a beamsplitter that splits the light beam into a first light beam portion and a second light beam portion, the first light beam portion illuminating the surface of the disk and produces a reflected light beam;an acoustic-optic deflector that deflects the reflected light beam and the second light beam portion producing a deflected output beam having a deflection angle;a detector that detects an incident beam translation signal corresponding to reflected light beam angular deflection and acoustic-optic deflector beam angular deflection from the deflected output beam; anda processor coupled to the detector that determines the presence of a defect based on the incident beam translation signal.

19. A system for detecting defects on a disk surface according to claim 18, wherein the deflected output beam is based on an illumination spot size and a disk rotation speed.

20. A system for detecting defects on a disk surface according to claim 18, wherein the detector includes a prism mirror and photomultiplier tubes.