Optics: measuring and testing – Crystal or gem examination
Patent
1988-08-05
1990-05-15
Evans, F. L.
Optics: measuring and testing
Crystal or gem examination
356445, 356448, G01N 2155
Patent
active
049252984
ABSTRACT:
A method for measuring and plotting the etch pit density on the surface of an etched monocrystalline test wafer is described. In accordance with the described method a beam of light is generated and focussed on the surface of a polished reference wafer. The wafer surface is oriented in a plane perpendicular to the beam of light. The intensity of light reflected normally from the reference wafer surface is measured to obtain a reference intensity R.sub.o. Thereafter, the beam of light is focussed on the etched test wafer surface which is also oriented in a plane perpendicular to the beam of light. The intensity R.sub.e of light reflected normally from the etched test wafer surface is measured. The etch pit density on the test wafer surface is computer from the ratio of light intensity reflected from the test wafer to light intensity reflected from the reference wafer. The formula EPD=-(1/Ap)log (R.sub.e /R.sub.o), where EPD is etch pit density and AP is the average area of the etch pits is used. The computation of etch pit density is repeated for a plurality of locations on the test wafer surface. The locations are automatically determined by stepwise movement of the etched test wafer.
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