| AVS 54th International Symposium | |
| Plasma Science and Technology | Monday Sessions |
| Session PS1-MoM |
| Session: | Plasma Modeling |
| Presenter: | J. Hoang, University of California at Los Angeles |
| Authors: | J. Hoang, University of California at Los Angeles C.C. Hsu, University of California at Los Angeles J.P. Chang, University of California at Los Angeles |
| Correspondent: | Click to Email |
Predictive modeling of feature profile evolution is critical to understand the complex plasma-surface interactions and aid the design of etch chemistry and development of etch systems. In this work, a direct simulation Monte Carlo (DSMC) method is used to develop a simulator that predicts profile evolution during shallow trench isolation etch (STIE) in Cl-based plasmas. Due to the discretized cells inherent in the model, a segmented surface advancement algorithm was developed to capture surface normals and particle fluxes. Plasma parameters such as particle densities and mean ion energy are determined from a reactor scale model, while ion energy distribution (IED) and ion angular distribution (IAD) are verified by a particle-in-cell (PIC) model.1 A fractional factorial design of experiments determined major processing parameters affecting profile evolution in a Cl2, O2, and N2 plasma in a dual coil inductively coupled plasma reactor. Out of seven parameters investigated, chamber pressure and DC ratio (current ratio of inner and outer coils) had the most effect on the feature side wall angle (SWA), one of the most critical parameters defining the success of STIE. Additional experiments were performed to assess the effect of O2 addition as well as to ascertain the effects of source power and DC ratio. Scanning electron microscopy (SEM) was used to assess the profile evolution in various plasma chemistries under different etch conditions. Slight microtrenching was observed in features etched by pure chlorine (no O2) and was accurately predicted by the profile simulator, sampling only ions (Cl+), neutral etchants (Cl), and a minute ratio of neutral passivants (e.g. SiCl2). Changes in plasma density and substrate bias (translating to ion energy) were found to significantly alter the sidewall tapering and etch depth. The profile simulator captured these changes by determining the full-width half maximum of the IAD as a function of substrate bias and adjusting the neutral to ion ratio which is affected by pressure and source power. The erosion of the hard mask during STIE was found to occur in a high density plasma under high substrate bias, affirming an etching threshold energy of the hard mask, and the simulator successfully predicted the double facets on the hard mask and the resulting profile.
1A. C. F. Wu, M. A. Lieberman, and J. P. Verboncoeur, Journal of Applied Physics 101, 056105 (2007).