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Increased Visibility of Defects in Optical Birefringent Images

IP.com Disclosure Number: IPCOM000087823D
Original Publication Date: 1977-Mar-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Matthews, JW: AUTHOR [+2]

Abstract

Optical birefringence can be used to observe dislocations and other defects in crystals. The technique can be used to observe dislocations with arbitrary line directions and Burgers vectors, and is ideal for the detection of low concentrations of dislocations in very large crystals. It is proposed to use this technique for determining the perfection of large nonmetallic crystals, such as gadolinium gallium garnet, silicon, and III-V compounds, before beginning the costly steps of sectioning these materials into wafers and then polishing the wafers.

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Increased Visibility of Defects in Optical Birefringent Images

Optical birefringence can be used to observe dislocations and other defects in crystals. The technique can be used to observe dislocations with arbitrary line directions and Burgers vectors, and is ideal for the detection of low concentrations of dislocations in very large crystals. It is proposed to use this technique for determining the perfection of large nonmetallic crystals, such as gadolinium gallium garnet, silicon, and III-V compounds, before beginning the costly steps of sectioning these materials into wafers and then polishing the wafers.

In order to make optical birefringence techniques suitable for the purpose described above, dislocation visibility is increased by an order of magnitude in order to reduce the amount of time taken to scan a sample by a factor of ten. Much shorter exposures are required if there is an appropriate long range stress superimposed on the stress-field of the dislocation being observed. The image of a dislocation in a stress-free crystal consists of a pale pattern against a dark background. However, if a long range stress is superimposed, the background contrast will be changed from dark to grey. The image of a dislocation appears darker than the grey background in some parts and lighter than the grey background in others. Suitable exposures for recording these dislocation images are those which record the background as grey. Thus, the long range stress not only r...