A two-dimensional computer simulation for dry etching using Monte Carlo techniques

Abstract

This work introduces a novel two-dimensional dry-etching simulation technique and presents experimental verifications of etching profiles based on an algorithm that calculates the transport of charged particles across a plasma sheath, the etch rate at each node, and the overall time evolution of the simulated structure. Monte Carlo techniques are applied to solve for the transport of ions across the plasma sheath to obtain the angular ion-distribution functions at the wafer surface. The etch rates are calculated from the particle fluxes and energies on the wafer during each time step. These fluxes depend on the relative position of the node with respect to the general geometry of the structure. Different etching mechanisms are decoupled into a chemical component proportional to the reactive neutral concentration in the gas and an ion-enhancement component proportional to the energy flux deposited on the wafer. The chemical component is assumed to be uniform and perpendicular to the surface being etched; the ion-enhancement component is calculated from the angular ion-distribution function. These mechanisms are incorporated into a two-dimensional computer-simulation program that computes their interaction as a function of time. The simulation program allows the addition of secondary effects as input options, such as energy and flux thresholds, glancing ions, and inhibitor layers. The predictions based on the simulations agree well with experimental results obtained on extreme cases of chemical and ion-enhanced etching.