Plasma and process characteristics of high aspect ratio contact SiO2 etching in ultralow-pressure inductively coupled plasma using C3F6/C4F8 chemistry

This study used an inductively coupled plasma (ICP) system to etch high aspect ratio contact (HARC) SiO2 using C3F6/C4F8 plasma under ultralow pressure. The C3F6-based etching behavior was compared with that of the conventional CF4/C4F8 process under identical process conditions. As the C3F6 fraction increased, the SiO2 etch rate increased monotonically, while higher SiO2-to-amorphous-carbon-layer selectivity and near-vertical profiles were maintained over a wide composition range. When combined with plasma diagnostics, including optical emission spectroscopy and Langmuir probe measurements, the results indicated that these phenomena were mainly influenced by the fluorocarbon surface chemistry rather than changes in the bulk plasma properties. Postetching exhaust gas analysis also showed that using C3F6 instead of CF4 could reduce emissions of substances with a high global warming potential. These results elucidated the plasma-surface interaction mechanism of C3F6/C4F8-based HARC SiO2 etching and demonstrated its potential as a process-stable alternative to CF4-based chemistry in advanced ICP etching applications.