Side etch control of n⁺-polysilicon with nitrogen added chlorine plasma

n⁺-polysilicon etching with both high anisotropy and high selectivity has been realized in our previous work by irradiating the nitrogen added chlorine plasma under a low ion energy condition using an ultraclean ECR etcher. In the present paper, mechanisms of the side etch of n⁺-polysilicon with pure and nitrogen added chlorine plasmas are discussed. 1100 and 4500 A thick n⁺-polysilicon films with mask SiO₂ films were etched with nitrogen added (<20%) chlorine plasmas under a highly selective condition at 4 mTorr using and ultraclean ECR plasma etcher described previously. The lateral etch length was determined by cross sectional SEM observation.