Fourier-transform infrared measurements of $CHF3/O2$ discharges in an electron cyclotron resonance reactor

Knowledge of the neutral gas composition in a discharge is important for understanding the chemical processes involved in both etching and deposition environments. We have performed Fourier-transform infrared absorption spectrometry measurements of $CHF3/O2$ plasmas in an electron cyclotron etching tool. Spectral bands were observed from both gas-phase and surface-phase species (deposited on the vacuum windows). The primary gas-phase species were $CF4,$ $H2O2,$ and HF. Strong absorption bands due to $CFx,$ where $x=1,$ 2, or 3, deposition on the vacuum windows were also observed. The densities of the gas-phase species were calculated from the strength of the measured absorption. It was found for typical discharge powers that the HF density was approximately 80% of the total gas density and depended on the plasma density and neutral pressure. In addition, because HF, $H2O2,$ and $CF4$ are not the feed gas, these data clearly show that recycling of the daughter species $(C, CFx, Fx,$ etc.) on the chamber walls play an important role in determining the plasma chemistry in this high-electron density, $>1011 cm−3,$ low neutral pressure, <10 mTorr, discharge.