Real-time time-dependent DFT study of laser-enhanced atomic layer etching of silicon for damage-free nanostructure fabrication

Abstract

Atomic layer etching (ALE) has emerged as a promising technique that enables the manufacturing of atomically controlled nanostructures toward next-generation nanoelectronics. However, the high-energy ion bombardment (typically 40–60 eV for Si) in current plasma ALE would cause damage to structures and even underlying substrates, which is detrimental to processing controllability as well as device performances. This problem could be addressed by introducing an additional laser source into the plasma ALE process to reduce the required ion energy, namely, laser-enhanced ALE. To elucidate the fundamental role of photons in laser-enhanced ALE, we explored the laser–matter interaction in laser-enhanced ALE of Si using real-time time-dependent density functional theory. The results show that with time evolution the incident laser would produce repulsive forces between the modified and bulk Si atoms. The magnitude of these forces can be up to 1.94 eV/Å when a large laser intensity and a short wavelength are employed. Under such large forces, the corresponding bonds are weakened with electron distribution decreasing significantly and can be even broken directly as time propagates. Low-energy ions can, therefore, be used to selectively remove the modified Si atoms whose bonds are already weakened by the additional laser, thereby minimizing and even eliminating the unwanted surface damage.