Model analysis of the feature profile evolution during Si etching in HBr-containing plasmas

Abstract

Feature profiles of Si etched in HBr-containing plasmas have been analyzed through a comparison between experiments and simulations. The emphasis was placed on a mechanistic understanding of the difference in the evolution of profile anomalies (such as tapering, footing, and microtrenching) during Si etching between HBr- and Cl2-based plasmas. Experiments were made with Cl2/O2/HBr chemistry by varying the HBr mixing ratio, using a commercial ultrahigh-frequency electron cyclotron resonance plasma etching reactor, where HCl/O2 chemistry was also employed to compare with that of Cl2/O2 and HBr/O2. Numerical simulations of feature profile evolution were made using a semiempirical atomic-scale cellular model based on the Monte Carlo method that we developed for Si etching in Br2, HBr, and Cl2 plasmas, where surface chemistry and kinetics include the effects of ion reflection from and/or penetration into feature surfaces on incidence. The experiments showed more vertical sidewalls with less footing and microtrenching with HBr; concretely, with increasing HBr mixing ratio in Cl2/O2/HBr plasmas, the tapering is reduced and minimized at 80% HBr where slight lateral or side etching tends to occur, the footing is reduced gradually, and the microtrenching fades away at more than 20% HBr. A comparison with simulations, with the help of separate analyses of ion reflection from surfaces on incidence, indicated that the smaller reflection probability and reflected energy fraction of Br+ on tapered sidewalls (compared to Cl+) are responsible for reduced tapering, footing, and microtrenching in HBr-containing plasmas; moreover, chemical etching effects of neutral H atoms at the feature bottom and sidewalls, arising from the larger reaction probability of H (compared to Cl), are also responsible for reduced microtrenching and for reduced tapering (and the lateral or side etching induced) therein.