A phenomenological model has been developed to simulate the feature profile evolution for nanometer-scale control of the profile and critical dimension during plasma etching. Attention was focused on the feature profile evolution of infinitely long trenches etched in Si with chlorine chemistries. The model takes into account the transport of ions and neutrals in microstructures, multilayer surface reactions through ion-enhanced etching, and the resulting feature profile evolution, where the transport is analyzed by a two-dimensional particle simulation based on successively injected single-particle trajectories with three velocity components. To incorporate an atomistic picture into the model, the substrates are taken to consist of a large number of small cells or lattices in the entire computational domain of interest, and the evolving interfaces are modeled by using the cell removal method; the Si atoms are allocated in the respective two-dimensional square lattices of atomic scale. Moreover, the Monte Carlo calculation is employed for the trajectory of incident Cl+ ions that penetrate into substrates. The present model has a prominent feature to phenomenologically simulate the multilayer surface reaction, the surface roughness, and also the feature profile evolution during etching. The etching of planar Si substrates was simulated for a test of validity of the present model, showing the structure of surface reaction layers, the distribution of Cl atoms therein, and the surface roughness that depend on incident neutral-to-ion flux ratio and ion energy. The etch yield as a function of neutral-to-ion flux ratio for different ion energies gave a similar tendency to the known experimental data, indicating that the present model properly reflects synergistic effects between neutral reactants and energetic ions in the ion-enhanced etching. The feature profile evolution during etching was then simulated for sub-100 nm line-and-space patterns of Si, exhibiting the reactive ion etching (RIE) lag that occurs depending on neutral-to-ion flux ratio and ion energy. The degree of RIE lag was found to be more significant at higher flux ratios and higher energies, being associated with the difference in surface chlorination at the feature bottom; in effect, for narrow pattern features of the order of sub-100 nm, the bottom surfaces tend to starve for neutral reactants owing to severe effects of the geometrical shadowing.

Atomic-scale cellular model has been developed to simulate the feature profile evolution during poly-Si gate etching in high-density Cl2 and Cl2∕O2 plasmas, with emphasis being placed on the formation of passivation layers on feature surfaces. The model took into account the behavior of Cl+ ions, Cl and O neutrals, and etch products and byproducts of SiClx and SiClxOy in microstructural features. The transport of ions and neutrals in microstructures and in substrates was analyzed by the two-dimensional Monte Carlo calculation with three velocity components. The surface chemistry included ion-enhanced etching, chemical etching, and passivation layer formation through surface oxidation and deposition of etch products and byproducts. The computational domain was taken to consist of two-dimensional square cells or lattices of atomic size, and the evolving interfaces were represented by removing Si atoms from and/or allocating them at the cells concerned. Calculations were performed for different line-and-space pattern features of down to 30nm space width, with an incoming ion energy, ion flux, and neutral reactant-to-ion flux ratio of Ei=50eV, Γi0=1.0×1016cm−2s−1, and Γn0∕Γi0=10. Numerical results reproduced the evolution of feature profiles, critical dimensions, and their microscopic uniformity (or aspect-ratio dependence) on nanometer scale, depending on substrate temperature, incoming flux of oxygen and etch byproducts, and sticking probability of etch products and byproducts on feature surfaces: the lateral etching on sidewalls is suppressed by surface oxidation thereon. The oxidation also reduces the etch rate on bottom surfaces, leading to a transition from regular to inverse reactive ion etching (RIE) lag with increasing flux of oxygen; in practice, the RIE lag remains almost unchanged for narrow space features owing to reduced oxygen fluxes thereinto, thus leading to regular and inverse RIE lags coexistent in a series of different pattern features. The deposition or redeposition of etch products (desorbed from feature surfaces) onto sidewalls results in the sidewall tapering, which is more significant for narrower space features; in contrast, the deposition of byproducts (coming from the plasma) onto sidewalls results in the tapering, which is more significant for wider features. Synergistic effects between the deposition of etch products/byproducts and surface oxidation enhance the passivation layer formation on feature surfaces, which in turn increases the sidewall tapering and the degree of regular and inverse RIE lags depending on feature width. The present model also enabled the authors to simulate the surface reaction multilayers and passivation layers on atomic scale, along with their chemical constituents and surface roughness.

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.

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.