Clean SiO atomic layer etching based on physisorption of high boiling point perfluorocarbon.

This study aimed to evaluate the SiO atomic layer etching (ALE) process that is selective to SiN based on the physisorption of high boiling point perfluorocarbons (HBP PFCs; CF, CF, CF, and CF have boiling points above room temperature). The lowering of the substrate temperature from 20 °C to -20 °C not only increased SiO etch depth per cycle (EPC) but also increased etch selectivity of SiO/SiN to near infinity. Due to the differences in fluorocarbon adsorption at a temperature during the physisorption depending on boiling points of PFCs, the desorption time and ion bombardment energy during the desorption step needed to be optimized, and higher ion bombardment energy and longer desorption time were required for higher HBP PFCs. Even though near infinity etch selectivity of SiO/SiN was obtained, for the SiO etching masked with SiN patterns, due to the adsorption of PFC on the sidewall of the SiN layer, the difficulty in anisotropic etching could be observed. By adding an O descumming step in ALE processes, an anisotropic SiO etch profile could be obtained with no adsorption of fluorocarbon on the chamber wall. Therefore, it is believed that the HBP ALE processes can be applicable for achieving high selective SiO/SiN with more stability and reliability.