Paper PS-ThM3
A Numerical Simulation Method for Plasma-induced Damage Profile in SiO₂ Etching

Thursday, November 3, 2011, 8:40 am, Room 201

To create high performance metal-oxide semiconductor devices, it is necessary to reduce variations in the critical dimension, the etching profile, and the amount of damage caused. Recent advancements in plasma processing for the gate electrode, sidewall, and high aspect contact hole have highlighted the importance of fully understanding how plasma induces damage and how to control this damage. We also need to find a way to quantitatively predict the damage depth profile using a numerical simulation that takes a realistic surface reaction into consideration, because it is quite difficult to observe the distribution of damage in the patterns with high aspect ratios. One commonly used simulation method, molecular dynamics (MD) calculation, unfortunately has a very limited range and cannot simultaneously consider a time-dependent etching profile in the 100 nm scale.

We developed a numerical simulation method for the distribution of plasma-induced physical damage to the SiO₂ and Si layers during fluorocarbon plasma (C₄F₈/O₂/Ar) etching. In our method, the surface layer is assumed to consist of two layers: a C-F polymer layer and a reactive layer. Physical and chemical reactions in the reactive layer divided into several thin slabs and in the deposited C-F polymer layer, which depends on etching processes are considered in detail considering reactivity of radicals, dangling bonds ratio, and generation of by-products (CF₂, SiF₂, and SiF₄) with ion energy dependence. As for ion and radical fluxes, we used the results from our previous experiments.

We used our simulation method to calculate the SiO₂ etch rate, the thickness of the C-F polymer layer (T_C-F), the selectivity of SiO₂ to Si layer, and the O₂ dependence of both the SiO₂ etch rate and the selectivity during C₄F₈/O₂/Ar plasma etching in the steady state. Results demonstrated that calculation of the absolute values as well as their behaviors were consistent with those of our experimental data. We also successfully predicted depth profiles of physical damage to the Si and SiO₂ layers in the steady state introducing our re-gridding method, which were affected by the T_C-F value. When we calculated the time-dependence of the amount of Si damage, we found that much of the damage was generated in the pre- and early stages of the over etching step during the SiO₂/Si layer etching, in spite of the high selectivity. After that, the amount of damage was gradually decreased by etching and finally became constant.

These results demonstrate that the T_C-F value and the over etching time must be carefully controlled by process parameters to reduce the amount of damage during fluorocarbon plasma etching.