Feature profile evolution during the high density plasma etching of patterned polysilicon

The two-dimensional Monte Carlo profile evolution simulator developed was used to explain the origin of artifacts such as double faceting of photoresist masks and feature bottom trenching observed during the high-density plasma etching of polysilicon. A designed set of experiments was performed earlier on photoresist patterned polysilicon samples on a Lam TCP 9400SE etcher varying the top power, bottom power and Cl-2 gas flow rate. The catalog of SEM micrographs generated suggested strong dependencies of the artifacts mentioned above on feature aspect ratio, product formation rate and product residence time in the etching chamber. In particular, the surface composition at the top of the photoresist lines was found to govern the top facet angle; greater the deposition of silicon-based etching by-products, the less steep the facet. The lower facet angle was found to be controlled by the feature aspect ratio and the sticking probabilities and fluxes of the depositing materials. Feature bottom trenching was strongly linked to sidewall bowing. Trenching was found to begin when the passivating species were unable to prevent the sidewalls from bowing; the focussing effect of the curved sidewalls on the directional ions was determined to cause trenching.