Ab initio simulations of ultrashort laser pulse interaction with Cl-Si(100): implications for atomic layer etching

Due to the remarkable resistance of SiCl against photo-induced desorption, achieving atomic layer etching (ALE) of Cl-Si(100) through a laser-based method has remained a formidable challenge. In this study, we investigate the interaction between ultrashort laser pulses and the Cl-Si(100) surface via ab initio simulations that combine real-time time-dependent density functional theory and molecular dynamics. Our results demonstrate the direct desorption of the stubborn SiCl layer through the application of appropriate femtosecond laser pulses. Notably, the desorption process is enhanced by pulses with higher laser intensity, shorter wavelength, and longer pulse duration. There is a threshold intensity beyond which the SiCl can be directly desorbed under laser pulses with a wavelength of 488 nm and a pulse duration of 40 ℏ eV^-1 (26.3 fs). Analysis of electron localization function reveals a critical bond breaking length of 2.98 Å between Si-Si, connecting SiCl to the bulk material. The time evolution of bond lengths and forces reveals that the desorption of SiCl is primarily driven by repulsive forces generated within the Si-Si bond. Furthermore, electron density difference analysis and Keldysh factor calculations indicate that these repulsive forces arise from multiphoton ionization. This study provides crucial atomic-level insights into the interaction of ultrashort laser pulses with Cl-Si(100), thereby propelling the advancement of laser-induced atomic layer etching techniques.