Mechanism understanding in cryo atomic layer etching of SiO₂ based upon C₄F₈ physisorption

Cryogenic Atomic Layer Etching (cryo-ALE) of SiO₂ based on alternating a C₄F₈ 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 C₄F₈ molecules versus temperature and pressure on SiO₂ surface. QMS monitoring of the SiF₄ etching by-product also enabled to follow the self-limiting etching behavior. Finally, a SiO₂ 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.