ON THE ORIGIN OF THE NOTCHING EFFECT DURING ETCHING IN UNIFORM HIGH-DENSITY PLASMAS

We present a two-dimensional Monte Carlo simulation of profile evoluti on during the overetching step of polysilicon-on-insulator structures, which considers explicitly (a) electric field effects during the char ging transient, (b) etching reactions of energetic ions impinging on t he poly-Si, and (c) forward inelastic scattering effects. Realistic en ergy and angular distributions for ions and electrons are used in traj ectory calculations through focal electric fields near and in the micr ostructure. Transient charging of exposed insulator surfaces is found to profoundly affect local sidewall etching (notching). Ion scattering contributions are small but important in matching experimental notch profiles. The model is validated by capturing quantitatively the notch characteristics and also the effects of the line connectivity and ope n area width on the notch depth, which have been observed experimental ly by Nozawa et al. [Jpn. J. Appl. Phys. 34, 2107 (1995)]. Elucidation of the mechanisms responsible for the effect facilitates the predicti on of ways to minimize or eliminate notching. (C) 1997 American Vacuum Society.