Transient behaviors of radicals and ions of CxFy and SFx during alternative injections C4F8 and SF6 in Ar plasma

Cyclic processes using alternate injections of C 4 F 8 and SF 6 gases in Ar plasma are widely employed in high-aspect-ratio (HAR) silicon trench etching. This study investigated the transient behavior of radicals and ions during a cyclic process using quadrupole mass spectrometry (QMS), which detected species including fluorocarbons and sulfur-fluorides. Using these QMS measurements, gas-phase reaction dynamics during the cycle were clarified. Introduction of halogen-containing gases reduced Ar partial pressure as observed from phase-resolved pressure behavior. During C 4 F 8 injection, C x F y + ions exhibited characteristic temporal variations, including a decrease during gas injection and an increase after its cessation, indicating a strong dependence on electron density. During SF 6 introduction, a brief rise in fluorine-rich SF 5 + occurred before declining with electron density, followed by limited recovery and secondary SF 2 + formation. Post-injection, sulfur-fluoride ions became fluorine-lean, indicating transient compositional changes linked to partial pressure. These results provide insight into the dynamic evolution of ion composition during cyclic gas injection processes, which is important for understanding and optimizing plasma etching mechanisms.