Theoretical investigations on multiple-reflection and Rayleigh absorption-emission-scattering effects in laser drilling

A fundamental study of laser drilling was performed with computational analysis. High power Q-switched diode-pumped laser drilling simulations were conducted on N-type silicon wafers. In the numerical model, the volume of fluid method was adopted to trace the free surface of the drilled-hole with the governing equations including continuity, momentum, and energy equation. The laser beam was considered as a surface heat flux with near-Gaussian distribution. The simulation model took into account the physical phenomena, taking place during drilling of the silicon wafer, such as the effects of recoil pressure producing a narrow and deep profile, Fresnel absorption transferring the energy from laser beam to workpiece, multiple-reflection raising the absorption of laser energy, and Rayleigh absorption-emission-scattering absorbing and distributing the entrance laser energy. In particular, a novel model for laser drilling was proposed from the view point of the transmitted, absorbed, emitted, and scattered light.