A comprehenssive study on the discharge physics and atomic layer etching with radio frequency biased inductively coupled plasma in Ar/C₄F₆ mixture

In recent years, with the scaling-down of device and growing demand for damage-free etching techniques in the semiconductor industry, interest in the atomic layer etching (ALE) process has significantly increased. Even in the case of the high aspect ratio (HAR) trench etch process, the ALE is being used as the final etch step technique after the HAR etch for achieving the flattening of the bottom layer and the vertical side-wall. Among plasma sources, inductively coupled plasma (ICP) can be a candidate for ALE, but studies linking discharge physics and ALE processes have not been actively conducted. As an etching gas for ALE, C₄F₆ (hexafluoro-1,3-butadiene) with a low global warming potential is one of the challenging topic in ALE because it generates excessive polymer film. In this study, we investigated the discharge physics of ICPs with radio-frequency (RF) bias and Ar/C₄F₆ mixture to be considered in the ALE process¹. For the modification step of ALE, the ICP characteristics were investigated in pure Ar and Ar/C₄F₆ mixture, and the RF biased ICP characteristics were investigated for the removal step of ALE. Based on the discharge characteristics, the ALE windows for silicon-based thin films such as a-Si, poly c-Si, SiO₂, and Si₃N₄ were founded, and flat and vertical etch profile was obtained through the ALE even on patterned wafer.