Modeling and Analysis of Plasma-Assisted Etching Reactor Phenomena

Abstract

Mathematical models were developed in order to analyze the effect of plasma reactor operating conditions on phenomena controlling etch rate, degree of anisotropy and uniformity of etching thin films. The shape evolution of a microscopic cavity was simulated using Boundary Element methods and a moving boundary scheme. Gas-phase ion scattering and ion defocusing owing to local, lateral electric field forces in the near-cavity region, resulted in loss of etch anisotropy even in the absence of chemical (spontaneous) etching. The formation of curved trench sidewalls was accompanied by a decrease in etch rate as a function of trench depth. Both phenomena can cause problems in deep trench etching applications. A macroscopic plasma reactor engineering model was then formulated. The unique feature of the model was that explicit account was taken for the ion-assisted component of etching, by considering the ion transport in the sheath as an integral part of the model. Convective-diffusion and chemical reactions of the etchant species were also included as well as the state of the plasma, for the case of the oxygen discharge. Important dimensionless system parameters were identified and their effect on etch rate, degree of etch anisotropy and uniformity was examined. The model predictions agreed with experimental data on etch rate of photoresist in an oxygen plasma as a function of pressure, power, and flow rate. Experimentally observed changes in uniformity patterns with flow rate were also predicted by the model.