Chemistry studies of SF_6/CF_4, SF_6/O_2 and CF_4/O_2 gas phase during hollow cathode reactive ion etching plasma

摘要

In this work, mass spectrometry and optical emission spectroscopy techniques were used to monitor the molecular and atomic neutral species during SF_6/CF_4, SF_6/O_2 and CF_4/O_2 plasmas generated in a radiofrequency Hollow Cathode Reactive Ion Etching (HCRIE) reactor keeping constant the following operational conditions: total gas flow rate, gas pressure, and discharge power. The investigations were aimed to understand the chemistry behavior of plasmas generated with SF6 and CF_4 mixtures or mixed separately with O_2. The neutral mass spectrometry analysis showed a high concentration of gas species namely SF_5~+(parent specie = SF+6), SF_3~+ (SF_4), CF_3~+ (CF_4) and HF~+ (HF) in SF_6/CF_4 plasmas, SF_5~+, SF_3~+, O_2~+ (O_2), F~+ (F) and HF+ in SF_6/O_2 plasmas and CF_3~+, O_2~+, CO_2~+ (CO_2) and HF~+ in CF_4/O_2 plasmas. The presence of other species was observed in quantities lower than 1% of total gas pressure. It was used the actinometry method to monitor the atomic fluorine (F) concentration during discharge operation. Higher density of F was observed in all experiments, varying from (2.8-9.5)×10~(19)m~(-3) in SF_6/CF_4 plasmas, (0.2e1.7)×10~(20)m~(-3) in SF_6/O_2 plasmas and (0.06-1.17)× 10~(20)m~(-3) in CF_4/O_2 plasmas. The addition of CF_4 in SF_6 plasma reduces monotonically the F concentration when compared with the SF_6/O_2 and CF_4/O_2 plasmas that promotes an increase of F for low O_2 concentrations. This effect shows the importance of oxygen species in the dissociative processes of the fluorine-based plasma also for this type of plasma reactor. Moreover, it is highlighted the higher concentrations of HF in gas phase that promotes reactions paths that decrease the F species in gas/plasma phase.