Comparisons of NF3 plasma-cleaned Y2O3, YOF, and YF3 chamber coatings during silicon etching in Cl2 plasmas

Optical emission spectroscopy was used to investigate the effect of Y2O3, YOF, and YF3 chamber wall coatings on the relative number densities of gaseous species during etching of Si in Cl2/Ar inductively coupled plasmas. Etching plasmas were alternated with NF3/Ar plasma chamber-cleaning steps. Small differences were found for the three materials. Si-to-Cl emission ratios were similar for Y2O3 and YOF, and somewhat larger for YF3. SiClx=1–3 emissions were similar for the Y2O3 and YOF-coated liners, but significantly less stable with time for YF3. Compared with Cl2/Ar plasmas, Cl2/O2/Ar plasmas produced nearly time-independent and much more consistent Cl number densities during etching. This takes place despite a consistent upward drift in SiClx=0–3 emissions for all three materials. A conditioning procedure for the YOF coating was shown to reduce drift during Si etching in Cl2 plasmas. Specifically, a Cl2/O2/Ar plasma pretreatment was briefly operated with substrate bias, generating SiClx etching products that rapidly remove F from the liner surface. When the O2 flow was extinguished, etching continued with much less changes in Cl and SiClx relative number densities.