TRG-OES measurements of electron temperatures during fluorocarbon plasma etching of SiO2 damage test wafers

We report measurements of electron temperatures (T_e) during the etching of silicon dioxide damage tester wafers. The high-density plasma feed gases consisted of a mixture of C₂F ₆, C₄F₈, Ar, and Ne. T_e was measured by trace rare gases optical emission spectroscopy. Full emission spectra were recorded with a CCD array detector spectrometer every 0.5 s during the full etching process (including stabilization and cleaning steps) for a batch of 44 wafers (22 damage testers and 23 blank Si wafers). Measurements were made as a function of selected variables such as the Ar-to-Ne carrier gas ratio, pressure, and total gas flowrate. As expected, T_e increased with the fraction of added Ne, but exhibited an unusual pressure dependence, decreasing with decreasing pressure below ~ 30 mtorr