Thermal process of a silicon wafer under a CW laser and 100-10000 Hz pulsed laser irradiation.

The thermal process of a (001) silicon wafer subjected to a continuous-wave (CW) laser and 100-10000 Hz pulsed laser irradiation is investigated experimentally and numerically. The temperature evolution of the spot center is measured using an infrared radiation pyrometer. The waveforms of the temperature evolution curves provide valuable information about melting, solidification, vaporization, and fracture. To gain a better understanding of the thermal process, a three-dimensional finite element model is established, and numerical simulations are conducted to analyze the temperature, stress, and dislocation field. The results show that the 10 kHz laser exhibits the highest heating efficiency before vaporization, but the lowest ablation efficiency after vaporization due to the shielding effect of vapor. The diffusion time of vapor is found to be more than 50 µs. Fracture occurs during 1 kHz laser irradiation. The motion of liquid may play a significant role, but it cannot be evidenced by a simulation due to complex dependence of material parameters on dislocation. This issue should be addressed as a priority in future studies.