| AVS 61st International Symposium & Exhibition | |
| Plasma Science and Technology | Tuesday Sessions |
| Session PS-TuP |
| Session: | Plasma Science and Technology Poster Session |
| Presenter: | Qiaowei Lou, University of Houston |
| Authors: | Q. Lou, University of Houston S. Kaler, University of Houston D.J. Economou, University of Houston V.M. Donnelly, University of Houston |
| Correspondent: | Click to Email |
CH3F plasmas are widely used in selective SiNx etching over Si or SiO2 with additives like O2 or CO2. In this work, inductively coupled CH3F/CO2 discharges were studied by optical emission spectroscopy (OES), with rare gas actinometry, as a function of feed gas composition and power (5–400 W), at a constant pressure of 10 mTorr. SiNx(300 nm on Si) and Si (10 nm on Ge) etching was also studied in “plasma beams” created from both CH3F/CO2 and CH3F/O2 feed gases. Surfaces and film thicknesses were characterized in situ by vacuum-transfer XPS, and ex situ by spectroscopic ellipsometry. An abrupt transition in H, F, and O number densities was observed when the CO2 feed gas was increased above 74-80 vol. %, similar to the enhancement in the number densities of these species above 48% O2 in CH3F/O2 plasmas. These step changes were ascribed to the transition from polymer-covered to polymer-free reactor walls as increasing O2 or CO2 additions cause the film etching rate to exceed the deposition rate. Absolute H, F, and O number densities increased with power in CH3F/CO2 (20%/80%) plasmas, reaching 0.24, 0.81 and 1.92 x1013/cm3, respectively, at 300W. This gas composition results in polymer-free wall conditions. Compared with CH3F/O2 (50%/50%) plasmas, the F and H number densities were lower and the O number density was higher in CH3F/CO2 plasmas. A maximum SiNx etching rate (no bias) of 75 Å/min was observed using a plasma beam effusing from a 50%/50% CH3F/O2 compact ICP. A lower maximum SiNx etching rate of 34 Å/min was found for CH3F/CO2 at 25%/75% composition.