Etching of SiO2 features in fluorocarbon plasmas: Explanation and prediction of gas-phase-composition effects on aspect ratio dependent phenomena in trenches

Abstract

A model to calculate etching rates in SiO2 features in fluorocarbon plasmas is presented. The model can predict several aspect ratio dependent phenomena such as reactive ion etching (RIE) lag, etch stop, inverse RIE lag, and aspect ratio independent etching (ARIE) at least for a limited range of aspect ratio values. The model includes three components: (a) a surface model for open area etching of SiO2 (and Si) [Gogolides et al., J. Appl. Phys. 88, 5570 (2000)]; (b) a flux calculator, which calculates local fluxes on each elementary surface of the feature being etched; and (c) a coupling of the two models (a) and (b), the focal point of coupling being the simultaneous calculation of the neutral species fluxes and the corresponding effective sticking coefficients. The model is applied for trench etching and the gas phase conditions considered correspond to a generic fluorocarbon gas. A different approach is presented by which the gas phase composition is divided (i.e., mapped) into regions leading to (a) deposition, (b) RIE lag with no etch stop, (c) intense RIE lag and etch stop, (d) inverse RIE lag, and (e) ARIE. Based on the proposed model an explanation of the aspect ratio dependent phenomena and ARIE is attempted, and a comparison with experimental data is done. Two parameters were found to be important in this explanation: the polymer surface coverage at the bottom of the etched feature and the effective sticking coefficients of the neutral species on the sidewalls of the etched feature.