Characteristics of clean SiO₂ atomic layer etching based on C₆F₆ physisorption

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.