Y2O3 wall interactions in Cl2 etching and NF3 cleaning plasmas

Time-dependent behavior of chlorine inductively coupled plasmas is presented for Si etching, following NF3-Ar plasma cleaning of a chamber coated with Y2O3. Optical emission intensities were recorded throughout the processes for Cl, O, F, Si, SiClx=1-3, SiF, and N2, as well as from added trace rare gases Xe and Ar for determination of number densities for selected species by actinometry. Time-dependent Langmuir probe measurements of ion and electron number densities and electron energy distributions were also carried out. Ex situ x-ray photoelectron spectroscopy measurements of the surface composition of Y2O3 coupon pieces after different etching and clean processes were also performed. Initially fluorinated yttria surfaces are shown to have a relatively high probability for loss (“recombination”) of Cl through formation of both Cl2 and SiClx. As etching proceeds, SiClx abstracts F from the surface and deposits Si and Cl, lowering of the heterogeneous recombination of Cl. The initially high recombination coefficient for Cl is explained by the weakening of the surface binding energy for Cl and SiClx at YFx sites, due to the highly electronegative nature of F, allowing recombination reactions forming Cl2 and SiClx to become energetically favorable.