Etching of polysilicon in inductively coupled Cl2 and HBr discharges. I. Experimental characterization of polysilicon profiles

Photoresist and oxide masked polysilicon samples were etched in a Lam TCP 9400SE, using both Cl2 and HBr discharges. A three variable (inductive power/rf bias power/flow rate) fractional factorial set of experiments was performed for the photoresist and oxide masked polysilicon samples. Complete experimental sets of profiles for polysilicon etching with both photoresist and oxide masks using Cl2 and HBr are presented. Additional experimental profiles showing the profile evolution with time are documented. The most striking features exhibited in the profiles are: (1) the greater polysilicon-to-photoresist selectivity exhibited by HBr over Cl2; (2) the increased sidewall deposition associated with photoresist over oxide masks; (3) the greater curvature or bowing of the sidewalls associated with the combination of photoresist masking, spacing, and Cl2 plasmas; (4) the more vertical sidewalls achieved with HBr; (5) the double faceting of the feature sidewalls under etching conditions accompanied by significant deposition; (6) the variation of photoresist facet angle associated with product deposition; (7) the delay in the onset of microtrenching while etching photoresist-masked samples with Cl2; (8) the greater microtrenching exhibited with oxide masking and Cl2 plasmas; and (9) the lack of microtrenching for the HBr etching.