| Laser ablation of silicon with its fast processing speed and high precision provides an important silicon micromachining alternative for the electronic and semiconductor industry. It is therefore important to understand the basic physics underlying laser silicon ablation phenomena and being able to describe the behavior of ablation results under different laser parameters before applying laser micromachining technique to certain applications for creating devices.; We will present theoretical calculations and experimental measurements of laser silicon ablation results including removal rate, mechanical properties and morphology changes under nanosecond pulses and femtosecond pulses. For nanosecond pulses, the laser intensities vary from 0.5 GW/cm2 to 150 GW/cm2 with wavelength of 355nm. Three distinct irradiance regimes are identified based on laser intensity. At low intensity, laser silicon interaction is characterized by surface evaporation with proper gas dynamics taking into account the ablation vapor plume kinetics. At medium high intensity, laser silicon ablation is dominated by the strong nonlinear shielding effects of a laser generated plasma. At high intensity, the laser ablation speed increases drastically beyond a certain threshold, and silicon is removed mostly by explosive ejection. A probe beam transmission method is utilized for analyzing the time evolution of the explosion.; Experimental results are compared with theoretical calculations based on the delayed phase explosion model. For femtosecond pulses, the laser intensities vary from 10 TW/cm2 to 300 TW/cm2, with a laser wavelength of 800nm. The ablation process is identified to be characterized by the energy exchanges between the ultrashort laser field and the laser-excited plasma, as well as between the plasma and the unexcited ions and atoms. We will also present the laser silicon ablation results under water confinement in both nanosecond and femtosecond regimes. A larger than two fold improvement in the ablation rate and distinct ablation outcomes are demonstrated and explained based on our understanding of the mechanisms of the different physical processes involved in the laser matter interaction. |
