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

Cryogenic Atomic Layer Etching (cryo-ALE) of SiO(2) based on alternating a C(4)F(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(4)F(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.