In reactive ion etching, redeposited materials from the plasma and the trench can significantly alter the trench profile. A simple model, which takes into account simultaneous ion-assisted etching and redeposition mechanisms, is presented. Using this model, a computer simulation, based on the string-point model, is performed on the evolution of a deep trench profile. The redeposited materials from the plasma and the trench region, coupled with a moving boundary scheme, allow the shape evolution of the etching profile to be computed. The computer simulation shows that defected ions, polymer deposition, and polymer sputtering are important factors in determining the etching profile of silicon trench. Under significant bombardment of deflected ion on the sidewalls of the trench, the redeposited material from the trench is found to be more effective in blocking the etching of the sidewalls during trench etching. copyright. © 1990, The Electrochemical Society, Inc. All rights reserved.