An integrated plasma equipment - feature scale model for the Bosch deep Si etch process

Abstract

Summary form only given. The Bosch Si etch process combines the desirable etching characteristics of SF/sub 6/ with the polymerization properties of fluorocarbon gases to anisotropically etch deep and narrow features at a high etch rate. This process is currently being explored for SCALPEL (Scattering with Angular Limitation in Projection Electron Beam Lithography) mask fabrication. Due to the large number of process variables available, optimization of the Bosch process is a nontrivial task. There are also stringent requirements for etch rate, uniformity and feature sidewall angle. To aid in Bosch etch process development, an integrated plasma equipment feature scale model has been developed. This model couples a 2-dimensional simulation of the plasma reactor (based on Hybrid Plasma Equipment Model from the University of Illinois) with a string based feature profile model. The chemical mechanisms for the etching (SF/sub 6//O/sub 2/) and passivation (c-C/sub 4/F/sub 8/) plasmas incorporate known information about electron impact processes in these gases, as well as many heavy particle collisions. The surface etching and passivation mechanisms for the feature scale simulation are based on qualitative information available in the published literature. Quantitative data such as sticking coefficients has, however, been inferred indirectly from process experiments. The resulting model closely replicates experimentally observed plasma and etch characteristics. In this presentation, we describe the integrated model, discuss our experimental validation strategy and apply the model to understanding the Bosch etch process. Results show that Si etching is mainly due to F atoms, polymerization in c-C/sub 4/F/sub 8/ is due to sticking of C and CF/sub x/ radicals under ion bombardment, and polymer is etched through ion-assisted physical sputtering. An optimum etch process is obtained by carefully controlling polymerization and etching times, wafer temperature, ion energy and process variables that control species fluxes to the wafer.