Monte Carlo Simulation of Defects of a Trench Profile in the Process of Deep Reactive Ion Etching of Silicon

A numerical model of the evolution of a 2D profile during cryogenic etching of Si in SF6/O2 plasma is proposed and implemented. To calculate the fluxes of species a Monte Carlo method is used. The etch profile is presented with the help of square cells. The model is meant to investigate diverse defects in a profile of stochastic nature. For this, the state of a model cell is presented as a combination of states of several subcells randomly chosen upon each interaction of the species with the surface, which makes it possible to study small-scale profile defects without loss of calculation performance. They are compared with the experimental data, and good qualitative agreement is observed. Surface defects typical of high aspect ratio cryogenic etching are investigated numerically. They include the depth-dependent sidewall roughness, formation of cavities, trench splitting, and formation of “nanograss.”