18 January 1977 Detection Of Microscopic Imperfections On High Quality Surfaces
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While developing a fiber diameter measuring instrument that is based on lateral interferometry (LI), we became aware of another application which opens up exciting opportunities - the automatic-noncontact detection and monitoring of imperfections in high quality surfaces. Quality assurance for such surfaces has become a major problem in the semiconductor industry where such surfaces are regularly produced on silicon disks. Comparable, or higher surface quality requirements also exist in other branches of the laser optics industry. The proposed surface quality monitor utilizes a high precision optical interference pattern which is projected onto a target surface to determine the presence and size of imperfections. The measurement technique involves the use of a low power laser beam which is split into two beams of slightly different frequency us,ng an acoustic-optical (A-0) device. When the split beam is again merged, a small (in the order of lmm2), accurate optical interference pattern is produced on the test surface. This interference pattern consists of a large number of fringes that move rapidly in a direction perpendicular to the fringe planes. The AC component of the optical radiation, back scattered from the exposed (illuminated) portion of the test surface contains the information on the surface quality of that segment of the surface. By using conventional raster scan techniques, the whole test surface is scanned systematically. The paper describes analytical and experimental results together with a brief review of potential applications.
© (1977) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Martin Tarabocchia, Martin Tarabocchia, Sandor Holly, Sandor Holly, "Detection Of Microscopic Imperfections On High Quality Surfaces", Proc. SPIE 0092, Practical Applications of Low Power Lasers, (18 January 1977); doi: 10.1117/12.955091; https://doi.org/10.1117/12.955091


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