Characteristics of clean SiO2 atomic layer etching based on C6F6 physisorption

Abstract

SiO2 atomic layer etching (ALE) techniques are widely used to improve the etch issues related to nanoscale semiconductor device etching such as self-aligned contact (SAC) etching requiring high etch selectivity of SiO2/Si3N4. For more precise and cleaner SiO2 ALE, cryo-ALE methods using physisorption of fluorocarbon gas at a cryotemperature are also being investigated. In this study, to avoid the use of cryotemperature for clean SiO2 ALE, a high boiling point (HBP) gas such as C6F6, having 80 °C of boiling point (global warming potential: 7), has been used as the physisorption gas without using cryotemperatures. At a substrate temperature lower than −15 °C, due to the adequate physisorption of C6F6 on the SiO2 and Si3N4 surfaces, high SiO2 etch depth per cycle (EPC) and high etch selectivity of SiO2/Si3N4 could be achieved through the higher chemical reaction of the fluorocarbon layer with SiO2 than that of Si3N4. For the etching of Si3N4 line patterned SiO2, an O2 descumming step was added after every 50 cycles of ALE process to prevent fluorocarbon layer deposition on the sidewall of the Si3N4 mask. Finally, anisotropic SiO2 etch profiles with high etch selectivity of SiO2/Si3N4 could be obtained without contamination of chamber sidewalls.