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Method and Apparatus for Detecting Defects and Delaminations on a Thin Film Disk

IP.com Disclosure Number: IPCOM000111740D
Original Publication Date: 1994-Mar-01
Included in the Prior Art Database: 2005-Mar-26
Document File: 2 page(s) / 55K

Publishing Venue

IBM

Related People

Horne, DE: AUTHOR [+3]

Abstract

Disclosed is a device for detecting defects and delaminations on a thin film disk. This device uses a low power (less than 0.5 mW) laser diode at 780 nm which is directed at an angle onto a thin film disk surface. The laser is S polarized since the disk is more reflective for S polarization and more sensitive to disk defects and delaminations.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 71% of the total text.

Method and Apparatus for Detecting Defects and Delaminations on a
Thin Film Disk

      Disclosed is a device for detecting defects and delaminations
on a thin film disk.  This device uses a low power (less than 0.5 mW)
laser diode at 780 nm which is directed at an angle onto a thin film
disk surface.  The laser is S polarized since the disk is more
reflective for S polarization and more sensitive to disk defects and
delaminations.

      The apparatus, shown in the Figure, consists of a polarized
laser diode which is directed into a non-polarizing beam splitter.
The split part of the beam is directed into a photodiode whose output
is fed back to the current regulation of the laser in order to
stabilize the laser's power output.  The straight-through part of the
beam is directed onto a focusing lens where it is focused to a spot
of 5 to 10 microns in diameter.

      After the beam reflects from the carbon-coated disk surface, it
enters a port in an integrating sphere, where the light intensity is
measured with a photodiode located at a second port in the sphere.  A
defect in the disk surface will cause the light intensity to decrease
and a simple peak detection technique will mark disk defects.  The
defect causes light to be scattered out of the beam, and hence the
intensity measured within the integrating sphere will be decreased.
The equation is of the form

Incident intensity = Diffusely scattered intensity + Specularly
reflected intensity + Absorbed inte...