Characterization and control of laser induced modification inside silicon

Internal modification of silicon is important for wafer stealth dicing. In this paper, the authors report experimental and simulation results of three-dimensional modification inside silicon wafers using laser pulses with 1.55 μm wavelength and 3.5 ns pulse duration. Permanent modification is generated inside silicon by tightly focusing and continuously scanning the laser beam inside samples, without damaging the front and back surface. Cross sections of these modifications are observed after cleaving the samples and are further analyzed after mechanical polishing followed by chemical etching. The shape of the modification is found to depend on the input beam shape, laser power, and scanning speed. With proper conditions, a nearly circular modification is obtained, which has potential application for waveguide writing inside silicon.