Analytical modeling of silicon etch process in high density plasma

Plasma etching of silicon is one of the important etching processes used in modern integrated circuit manufacturing and micro-electro-mechanical systems fabrication. A good understanding of this process leads to better models which are the key to easier and less costly plasma etching process design. The main focus of this paper is on the simulation of the ion reflection from feature sidewalls and the resulting microtrenches. Pure Cl 2 plasma was used for experiments because of the simple chemistry. SPEEDIE (Stanford etching and deposition profile simulator) was used in this work. Langmuir adsorption model was used for etching kinetics. Self-consistent calculations were done for fluxes using surface coverage dependent sticking probabilities. For ion reflection, it was assumed that the reflected ions come off with a distribution about the specular reflection angle. This distribution is modeled as cos nθ (θ is the deviation from the specular angle) and is important in getting the correct shape for microtrenches in simulations. A three-dimensional (3D) calculation of the reflection flux was done taking into account the 3D angular distribution of the incoming ions. The ion reflection efficiency was deducted from the silicon ion enhanced etching yield versus ion angle of incidence data. The simulation results match the experimental profiles fairly well.