Model Analysis of the Feature Profile Evolution During Si Etching in HBr-containing Plasmas

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 Cl-2-based plasmas. Experiments were made with Cl-2/O-2/HBr chemistry by varying the HBr mixing ratio, using a commercial ultrahigh-frequency electron cyclotron resonance plasma etching reactor, where HCl/O-2 chemistry was also employed to compare with that of Cl-2/O-2 and HBr/O-2. 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 Br-2, HBr, and Cl-2 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 Cl-2/O-2/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.