Fourier-transform infrared and optical emission spectroscopy of CF4/O2/Ar mixtures in an inductively coupled plasma

Characterization of CF4/O2/Ar inductively coupled plasmas by Fourier-transform infrared (FTIR) spectroscopy and optical emission spectroscopy (OES) in a Gaseous Electronics Conference reference cell has been carried out. Characterization was performed at three mixture compositions (80/10/10, 60/20/20, and 40/30/30), powers of 200 and 300 W and pressures between 10 and 50 mTorr. Quantitative estimates of CF4, CO, COF2, and SiF4 etch products are made via FTIR, while the OES combined with actinometry allows for qualitative characterization of conversion of CF4 to atomic C, CF, and C2, and molecular oxygen to atomic oxygen. Qualitative measurements of F density and etch products Si and SiF are also made by OES. Results are explained by a combination of electron-impact dissociation and recombination processes. In the absence of significant capacitive coupling, etch species are believed to be formed primarily by window interactions with atomic F. Rotational temperatures are estimated by both FTIR and analysis of emission spectra. The FTIR technique tends to estimate temperatures several hundred K lower than OES data due to the absorption of colder gas species outside of the plasma.