Mechanism understanding in cryo atomic layer etching of SiO ₂ based upon C ₄F ₈ physisorption

Abstract

Cryogenic Atomic Layer Etching (cryo-ALE) of SiO ₂ based on alternating a C ₄F ₈ molecule physisorption step and an argon plasma step, has been enhanced thanks to a better understanding of the mechanism. First, we used Quadrupole Mass spectrometry (QMS) and spectroscopic ellipsometry analyses to evaluate the residence time of physisorbed C ₄F ₈ molecules versus temperature and pressure on SiO ₂ surface. QMS monitoring of the SiF ₄ etching by-product also enabled to follow the self-limiting etching behavior. Finally, a SiO ₂ cryo-ALE process was proposed at a temperature of − 90 °C resulting in a very linear etch over 150 cycles and an Etch amount Per Cycle as low as 0.13 nm/cycle.