Formation mechanisms of etched feature profiles during Si etching in Cl2/O2 plasmas

Abstract

Feature profiles of poly-Si etched in Cl2/O2 plasmas have been analyzed through a mechanistic comparison between experiments and simulations. The emphasis was placed on a comprehensive understanding of the formation mechanisms for profile anomalies of tapering, microtrenching, and footing (or corner rounding near the feature bottom). Experiments were conducted in a commercial etching reactor with ultra-high-frequency plasmas by varying O2 percentage, wafer stage temperature, rf bias power, and feed gas pressure. Simulations of the feature profile evolution were done by using a semiempirical, atomic-scale cellular model based on the Monte Carlo method that we have developed. The experiments indicated that sidewall profiles become more tapered with increasing O2 addition to Cl2 plasmas, while microtrenching and footing are pronounced in pure Cl2 plasma, being suppressed with increasing O2. A comparison with the simulations indicated that the tapered profiles are caused by the deposition of etch products/by-products on feature sidewalls from the plasma, being enhanced with increasing oxygen flux (due to synergistic effects between deposition of products/by-products and surface oxidation) and being reduced with increasing ion energy and neutral reactant flux. On the other hand, the footing is attributed to the redeposition of etch products on sidewalls from the feature bottom being etched, being reduced with increasing oxygen flux, ion energy, and neutral reactant flux. Microtrenching is caused by the ion reflection from feature sidewalls on incidence, being reduced with increasing oxygen flux (partly due to surface oxidation of the feature bottom) and being enhanced and then reduced with increasing ion energy and neutral reactant flux. The tapering, footing, and microtrenching were found to be closely related to each other: the footing near the feature bottom fades away under conditions of increased tapering of sidewalls, and the microtrenching is affected significantly by the degree of footing as well as the taper angle of the sidewalls.

Analysis of optical emission spectroscopy data during silicon etching in SF6/O2/Ar plasma

“…For HAR etching, it is imperative to form narrow and deep trenches while maintaining a steep anisotropic profile. As the aspect ratio increases with device miniaturization, more precise control of the etch profile is necessary, and an aspect ratio dependent etching lag control is required [11].…”

Science-based, data-driven developments in plasma processing for material synthesis and device-integration technologies

“…In plasma etching, multiscale models have been developed to simulate both the gas-phase reactions and transportation phenomena in Cl 2 /Ar plasma chambers, as reported by Osano and Ono, [154][155][156][157][158] Kushner et al, [159][160][161][162] Chang and Sawin, [163][164][165] Graves, et al, 166,167) Hamaguchi et al, [168][169][170] and Tinck and Bogaerts. [171][172][173] Kuboi et al modeled the surface reactions and plasmainduced damage on SiO 2 and Si 3 N 4 with fluorocarbon plasma using the voxel-slab model developed by Kuboi.…”

Assessing neutral transport mechanisms in aspect ratio dependent etching by means of experiments and multiscale plasma modeling

“…Inverse RIE lag, on the other hand, indicates the opposite effect. The former is often associated with low incident neutral-to-ion flux ratios, whereas the latter more commonly occurs at high ratios [7][8][9][10]. In these cases, the neutrals correspond to depositing polymerizing or passivating species that slow down the etch rate (see e.g.…”

“…A lower flux of such neutrals reaching the bottom of narrow trenches relative to wider ones is therefore often used to explain inverse RIE lag (see e.g. [7,8,10,16,17]). The transition between regular and inverse RIE lag is namely attributed to a competition between etching and deposition reactions, as well as the much stronger shadowing effect for neutrals in comparison to ions.…”