Thermal stress characteristics of monocrystalline silicon induced by ns pulse laser under auxiliary heating

Abstract

Aiming at the problems of unsmooth notch and even crack caused by thermal stress in the laser processing of monocrystalline silicon, the temperature and thermal stress under auxiliary heating (AH) induced by the ns pulse laser (NPL) and their distribution characteristics are studied. Based on the theory of heat conduction and elastic–plastic mechanics, a two-dimensional axisymmetric geometric model for the temperature and thermal stress distribution of monocrystalline silicon irradiated by the NPL under AH is established, and the effect of AH on laser-induced temperature and thermal stress field is calculated and analyzed. The results show that the temperature of monocrystalline silicon irradiated by the NPL increases over auxiliary heating temperature (AHT), but it is not a simple superposition between the AHT and the temperature induced by the NPL, but the temperature change rate gradually decreases. When the temperature is lower than the target melting point, the thermal stress at the target surface is always negative as compressive stress, and the change law is the same as that of the temperature. When the temperature is more than the target melting point, the thermal stress in the melting zone is released immediately. The thermal stress decreases with the AHT increasing, and the change rate gradually decreases too. The negative effect of thermal stress can be overcome by using the correlation between temperature and thermal stress. Finally, an experiment was introduced to validate the theoretical model and calculation result preliminary. This study can provide a theoretical basis for the new technology of laser processing-monocrystalline silicon.