Cryogenic atomic layer etching of SiO<sub>2</sub> based on cyclic CF<sub>4</sub>/Ar plasma
Madjid Amine ADJABI, Thomas Tillocher, Philippe Lefaucheux, Eva Kovačević, Rémi Dussart
Abstract
Abstract This study demonstrates the feasibility of a cryogenic atomic layer etching (cryo-ALE) process for Silicon Dioxide (SiO 2 ) using a CF 4 plasma adsorption step and a surface removal step based on Argon plasma. In situ ellipsometry was used to monitor the amount of SiO 2 etched during each cycle. To improve the process, several parameters were optimized. First, the sample temperature was varied from 20 °C, temperature of which CF 4 is in etching regime, to −130 °C, switching the plasma process to a deposition regime. Then, CF 4 plasma parameters, including the pressure, inductively coupled plasma (ICP) power and its duration were studied. For a lower pressure, a higher ICP power and a longer plasma time, the process switches from etching to over-deposition. Finally, after optimization of the CF 4 plasma parameters, an average etch rate per cycle (EPC) of 0.4 nm/cycle was found with a process synergy determined to be 99%.