Pitch Polishing of Semiconductor Optical Materials Using Continuous Iterative Interferrogram Analysis

Semiconductor optical materials including Germanium, Silicon, ZnS and ZnSe are widely used to fabricate high precision optical components for focusing infrared radiation to the detector of thermal imaging system. For better performance of thermal imager, the quality of optical components in terms of surface accuracy, surface quality and other fabrication parameters must meet tighter tolerances. In the present work, we report a conventional pitch polishing technique using continuous slurry polishing to maintain surface accuracy of the order of sub micron accuracy and surface quality as per MIL-O-13830A. A phase shift laser interferometer with wavelength 632.8 nm is used as in-process measurement of surface accuracy. The hardness and viscosity of pitch, slurry concentration, polishing pressure and pitch lap compliance has been monitored and optimized for optimum polishing time and best results. During polishing, surface wedge was also monitored and controlled within 30 s of an arc.