High-aspect-ratio contact (HARC) SiO2 etching at ultralow pressure offers fundamental advantages in ion transport but has been difficult to implement in practice due to plasma instability and limited etch rates in conventional capacitively coupled plasma systems. In this work, a stable HARC SiO2 etching process is demonstrated at an ultralow pressure of 3 mTorr using an inductively coupled plasma (ICP) system. The complementary roles of low-frequency bias power and ICP source power are systematically investigated. Increasing the bias power enhances ion-energy-driven surface reactions, resulting in a monotonic increase in the SiO2 etch rate while maintaining stable SiO2/amorphous carbon layer selectivity. In contrast, increasing the source power increases plasma density and reactive flux, leading to a substantial etch-rate enhancement without degrading profile anisotropy. As a result, SiO2 etch rates of approximately 190 nm/min are achieved with vertical sidewalls and acceptable mask selectivity. These results demonstrate that ultralow-pressure ICP operation provides a practical and robust route for advanced HARC SiO2 etching.
WEI et al. (Tue,) studied this question.