Silicon nitride and silicon etching by CH₃F/O₂ and CH₃F/CO₂ plasma beams

Silicon nitride (SiN, where Si:N ≠ 1:1) films low pressure-chemical vapor deposited on Si substrates, Si films on Ge on Si substrates, and p-Si samples were exposed to plasma beams emanating from CH₃F/O₂ or CH₃F/CO₂ inductively coupled plasmas. Conditions within the plasma beam source were maintained at power of 300 W (1.9 W/cm³), pressure of 10 mTorr, and total gas flow rate of 10 sccm. X-ray photoelectron spectroscopy was used to determine the thicknesses of Si/Ge in addition to hydrofluorocarbon polymer films formed at low %O₂ or %CO₂ addition on p-Si and SiN. Polymer film thickness decreased sharply as a function of increasing %O₂ or %CO₂ addition and dropped to monolayer thickness above the transition point (∼48% O₂ or ∼75% CO₂) at which the polymer etchants (O and F) number densities in the plasma increased abruptly. The C(1s) spectra for the polymer films deposited on p-Si substrates appeared similar to those on SiN. Spectroscopic ellipsometry was used to measure the thickness of SiN films etched using the CH₃F/O₂ and CH₃F/CO₂ plasma beams. SiN etching rates peaked near 50% O₂ addition and 73% CO₂ addition. Faster etching rates were measured in CH₃F/CO₂ than CH₃F/O₂ plasmas above 70% O₂ or CO₂ addition. The etching of Si stopped after a loss of ∼3 nm, regardless of beam exposure time and %O₂ or %CO₂ addition, apparently due to plasma assisted oxidation of Si. An additional GeO_xF_y peak was observed at 32.5 eV in the Ge(3d) region, suggesting deep penetration of F into Si, under the conditions investigated.