Modeling insights into amorphous carbon etching by SO2/O2 low-pressure plasma

Amorphous carbon exhibits distinctive properties that make it a superior choice over traditional silicon-based materials for hard masks in high-aspect-ratio etching processes. However, due to the challenging recipes used for plasma etching, it is not clear how to protect the ACL mask in harsh plasma conditions. In the present paper, we propose both gas-phase and surface reaction mechanisms which can be used to model the etching of the ACL mask by SO2/O2 low-pressure plasma. These mechanisms are used in a one-dimensional fluid plasma model to understand the influence of SO2 partial pressure on the amorphous carbon etching by low-pressure inductively coupled plasma. The results of these studies are compared with the experimental data from Ishikawa et al., Appl. Surf. Sci. 645, 158876 (2024). Our results reveal that increased SO2 partial pressure results in a decreased carbon etch rate. This reduction is attributed to two factors: sulfur atom-induced passivation of the carbon surface and a diminished atomic oxygen flux to the wafer, which suppresses carbon oxidation.