Purgeless atomic layer etching of SiO2

Atomic layer etching (ALE) typically proceeds through four sequential steps of surface modification, purging, removal of the modified surface, and a second purging. This serial process is repeated to achieve atomic-scale precision etching by removing material layer by layer. However, it is is challenging for ALE to play a bigger role in semiconductor fabrication due to its low productivity. Among various obstacles, the time-consuming purging steps between the surface modification and removal steps of the ALE cycle have been a major hurdle hindering the ALE process. In this work, we experimentally demonstrate a purgeless SiO2 ALE methodology in which the surface modification and removal steps are controlled solely by pulsed C4F8 injection into continuous Ar plasma. The working principle of this simple approach is based on the conventional fluorocarbon (FC) plasma SiO2 etching mechanism, where the SiO2 etch rate decreases to zero when the thickness of an FC film on the SiO2 is above a certain level. Here, a thick FC film is considered to act as a protective layer against residual FC radicals in the surface removal step, allowing the purging step between the surface modification and removal steps to be omitted. The proposed approach is expected to facilitate the improvement of ALE equipment costs and potentially lead to wider employment of ALE technology in semiconductor manufacturing.