In situ detection of laser-induced slip initiation on the silicon wafer surface

We propose a real-time in situ method to detect slip initiation on the surface of silicon wafers during high-power laser beam irradiation. In this method, light is collected from the surface of a silicon wafer subjected to laser irradiation. When the slip is initiated, it strongly scatters the laser beam, allowing detection of the time of the slip initiation based on the resulting sudden increase in the scattering signal. To demonstrate the performance of this method, a silicon wafer specimen was illuminated by a near-infrared continuous-wave fiber laser beam (of wavelength 1070 nm) at four different laser powers, and the scattered light was detected. The scattering signal increased suddenly at the time of slip initiation. To confirm the occurrence of slip, the surface morphologies of the silicon specimens after laser irradiation were analyzed using an optical microscope; surface slips were observed only in the specimens for which the sudden increase in scattering had been detected. Thus, the proposed method is shown to be very effective for the real-time in situ detection of surface slip initiation induced by high-power laser beam irradiation on silicon wafers.