Amorphization and Ablation of Crystalline Silicon Using Ultrafast Lasers: Dependencies on the Pulse Duration and Irradiation Wavelength

Using lasers to achieve controlled crystallographic phase changes in silicon with high spatial precision promises new manufacturing solutions in semiconductor technologies, including silicon photonics. Recent demonstrations of improved amorphization thicknesses position ultrafast lasers as an optimum tool to meet current challenges. Here, the literature on silicon transformations is reviewed and complemented with new experimental data. This includes amorphization and ablation response as a function of pulse duration (τ = 13.9 to 134 fs at λ = 800 nm) and laser wavelength (λ = 258 to 4000 nm with τ = 200 fs pulses). For pulse duration-dependent studies on Si(111), the amorphization fluence threshold decreases with shorter durations, emphasizing the significance of non-linear absorption in the range of considered conditions. For wavelength-dependent studies, the amorphization threshold increases sharply from λ = 258 to 1030 nm, followed by near-constant behavior up to λ = 3000 nm. Conversely, the ablation threshold fluence increases in these specified ranges. Differences in the obtained amorphization thicknesses on Si(111) and Si(100) are also discussed, identifying an anomalously large fluence range for amorphization at λ = 258 nm. Finally, the question of the lateral resolution, shown as independent of the interaction nonlinearity is addressed.