Laser assisted surface conditioning of a residual pattern on single crystal silicon induced by ultra-precision cutting

Abstract

Fabrication of a silicon lens using an ultra-precision machining tool generates a periodic cutting texture, which can cause light diffraction and scattering, resulting in a significant degradation of the optical performance. This phenomenon usually appears in the form of rainbow patterns. In this study, a single-crystal silicon wafer, after diamond turning, is polished by a nanosecond laser mounted on a four-axis ultra-precision machine lathe. It’s found that the rainbow pattern has been effectively eliminated after laser irradiation through the observation of surface topography. Effects of defocus, scanning velocity, and pitch on polishing were investigated. This polishing method is able to obtain surface roughness Sa better than 1 nm for silicon surface without removing or adding material to the workpiece, and high throughout can be achieved through easy integration with the existing cutting process.