Plasma-surface kinetics and feature profile evolution in chlorine etching of polysilicon

Abstract

Chlorine-based plasma etching of polysilicon was characterized as a function of the impinging Cl+, Cl–to–Cl+ flux ratio, ion bombardment energy, ion bombardment angle, and the flux of etching by-products (SiCl2) using a multiple beam scattering apparatus. The ion-enhanced etching yield was a strong function of the neutral-to-ion flux ratio, and scaled linearly with the square root of the ion energy. The ion-enhanced etching yield was independent of the ion bombardment angle at near normal ion incidence angles, but decreased almost linearly above 40° off-normal angles. The presence of SiCl2 greatly suppressed the etching of polysilicon by either Cl+ or Cl+ with Cl. A Monte Carlo based profile simulator was constructed which incorporated the dominant reaction mechanisms of surface chlorination under ion bombardment, surface re-emission, and ion reflection. The profile evolution of patterned samples etched by Cl and Cl+ beams were simulated. Quantitatively good agreement was found between the simulated profiles and the measured profiles. A sensitivity analysis of the recombination probability of Cl on photoresist suggested that the recombination of atomic chlorine on the photoresist had a significant impact on the profile evolution.