Numerical simulation and validation of subsurface modification and crack formation induced by nanosecond-pulsed laser processing in monocrystalline silicon
Hiroki Kiyota, K. Hara, Marc Jankowski, M. M. Fejer
Abstract
We describe a numerical simulation of subsurface modification and crack formation in monocrystalline silicon induced by nanosecond-pulsed laser irradiation. In this model, we assume the residual stress generation due to material transfer caused by volume reduction during melting and resolidification to be the dominant factor in creating subsurface mechanical stress and cracks. In order to quantitatively determine the geometry of the modified region, we numerically model the nonlinear propagation and absorption of the laser beam and the thermal transport. We find that during a single pulse, the lattice temperature distribution results in melting, material transfer, and structural changes on resolidification. The residual stress generated within the monocrystal adjacent to the modified region is subsequently assessed for crack formation in the substrate. The validity of the proposed model is confirmed through agreement with a number of experimental results, including the transmitted power, the timing of the onset of the phase transition during laser irradiation, the processing threshold, the geometry of the modified region, and the formed crack length.