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.

Damage-free plasma etching of porous organo-silicate low-k using micro-capillary condensation above -50 °C.

The micro-capillary condensation of a new high boiling point organic reagent (HBPO), is studied in a periodic mesoporous oxide (PMO) with ∼34 % porosity and k-value ∼2.3. At a partial pressure of 3 mT, the onset of micro-capillary condensation occurs around +20 °C and the low-k matrix is filled at -20 °C. The condensed phase shows high stability from -50 < T ≤-35 °C, and persists in the pores when the low-k is exposed to a SF6-based plasma discharge. The etching properties of a SF6-based 150W-biased plasma discharge, using as additive this new HBPO gas, shows that negligible damage can be achieved at -50 °C, with acceptable etch rates. The evolution of the damage depth as a function of time was studied without bias and indicates that Si-CH3 loss occurs principally through Si-C dissociation by VUV photons.