A Model Analysis of Feature Profile Evolution and Microscopic Uniformity during Polysilicon Gate Etching in Cl₂/O₂ Plasmas

Abstract

A phenomenological model has been developed to simulate the feature profile evolution of polycrystalline silicon (poly-Si) gate etching in Cl 2 /O 2 plasmas. The model takes into account the deposition of etch products, surface oxidation, and the forward reflection of energetic ions on feature sidewalls. To describe the formation of multilayer SiCl x or SiCl x O y on feature surfaces during etching, the substrates consist of a number of small cells or lattices of atomic size in the computational domain; this model provides a nanometer-scale representation of the feature geometry and the chemical constituents therein. The inelastic or nonspecular reflection of incoming ions from feature surfaces and the penetration of ions into substrates are incorporated into the model by calculating the trajectory of ions through successive binary collisions with substrate atoms. Etching experiments were performed to evaluate and improve the accuracy of the model. To analyze the effects of the control variables of a plasma reactor on profile evolution, the simulated profiles for different gas flow ratios and incident ion energies were compared with the etched profiles obtained in the experiments. The numerical results reproduced the behaviors of profile anomalies such as sidewall tapering and microtrenches at the corner of the feature bottom, upon varying the incident fluxes of O neutrals and etch by-products, and the incident energy of ions. Moreover, the simulated profiles exhibited passivation layers deposited on feature sidewalls, which is a similar geometry to those obtained in the experiments.

Surface roughening and rippling during plasma etching of silicon: Numerical investigations and a comparison with experiments

“…The ASCeM-3D methodology has been described in part in our previous papers, 46,47 together with the surface chemistry and kinetics concerned, which is basically an extension of the ASCeM-2D. [40][41][42][43][44][45] In more detail, the simulation domain is a square W ¼ 50 nm on a side with a depth of 630 nm, consisting of a number of small cubic cells of atomic size L ¼ q Si À1/3 ¼ 2.7 Å (185 Â 185 Â 2333 % 8 Â 10 7 cells in total), where q Si ¼ 5.0 Â 10 22 cm À3 is the atomic density of Si substrates. The substrates initially occupy a lower 620-nm-deep layer therein (or the substrate surfaces are initially flat, being located 10 nm downward from the top of the domain).…”

“…Moreover, the ASCeM-3D takes into account two-body elastic collisions between energetic ions and substrate Si atoms, 41,47 to analyze the ion reflection or scattering from feature surfaces on incidence into vacuum and the ion penetration into substrates. 59,60 The analysis is also based on the 3D Monte Carlo calculation of ion trajectories according to the momentum and energy conservation through successive collisions with substrate Si atoms; then, the ions reflected from the surface into vacuum move further toward another surfaces of the feature or go out of the simulation domain.…”

“…75 or grazing incidence) are considered to be due to both effects of the ion reflection or scattering and the ion channeling on roughened feature surfaces, as previously suggested, 24,28 where the reflection probability from surfaces on incidence increases with increasing incidence angle h i . 41,47 However, a more relevant understanding of the mechanisms for surface rippling during plasma etching will require a further study including experimental demonstrations of it.…”

“…21 We have developed a semi-empirical, atomic-scale cellular model (ASCeM) for simulating plasma-surface interactions and the resulting feature profile evolution during plasma etching of Si, based on the Monte Carlo algorithm with the cell removal method for interface evolution; [40][41][42][43][44][45][46][47] in effect, a two-dimensional ASCeM model (ASCeM-2D) reproduced the evolution of nanometer-scale profile anomalies on sidewalls and bottom surfaces of the feature, together with pattern-size or aspect-ratio dependences of them, during Si trench etching in Cl 2 and Cl 2 /O 2 plasmas. [40][41][42][43][44][45] However, the ASCeM-2D was found to be insufficient to reproduce the nanoscale surface roughness formed during plasma etching, probably because the formation and evolution of roughness is 3D as well as stochastic. 24,28 Therefore, we have recently developed a 3D ASCeM model (ASCeM-3D) to simulate the evolution of 3D feature profiles, including nanoscale surface features such as roughness, during Si etching in Cl-based plasmas.…”

Atomic-scale cellular model and profile simulation of poly-Si gate etching in high-density chlorine-based plasmas: Effects of passivation layer formation on evolution of feature profiles

“…The taper angle is larger or the deposition is more significant for wider space features, owing to the geometrical shadowing for incoming etch byproducts ͑or surface inhibitors͒, which has been observed experimentally in Si etching with Cl 2 , 40,45,46 Cl 2 / O 2 , 40,45 HBr, 46 and Cl 2 / HBr/ O 2 47,48 plasmas. This is in contrast to the sidewall tapering caused by redeposition of etch products desorbed from feature surfaces, which is more significant for narrower features ͑see Fig.…”