SILICON ROUGHNESS INDUCED BY PLASMA-ETCHING

A parametric study of single-crystal silicon roughness induced by an S F6 plasma has been carried out by means of atomic force microscopy. An helicon source (also called resonant inductive plasma etcher) has bee n used to study the relation between plasma parameters and subsequent surface damage. The surface damage has been examined in terms of heigh t roughness analysis and in terms of spatial (lateral) extent of the s urface roughness. The central result is that roughness scales with the ratio of the ion flux over the reactive neutral flux (J+/J(F)), Showi ng the combined role of both ionic and neutral species. At low ion flu x, the neutrals smooth the surface, while at higher ion flux, they pro pagate the ion-induced defects, allowing the roughness to be enhanced. Influences of other parameters such as exposure duration, ion energy, or substrate temperature have also been quantified. It is shown that the roughness growth is well described by an empirical law: rms(is-pro portional-to)(1/square-root E)(J+/J(F))(eta)t(beta), with eta almost-e qual-to 0.45 and beta almost-equal-to 1 (rms is the root mean square o f the roughness). In other respects, we analyze the data with a Fourie r transform analysis. The main advantage is to minimize noise and to s eparate the magnitude of the roughness, the lateral correlation length on which the roughness is growing, and the behavior of short and long range roughness. The results are identical to the rms analysis, espec ially, the above scaling law. The time evolution of the lateral correl ation length follows a scaling law (which is not accessible by means o f the rms) leading to a fractal dimension of 2.67. Also is observed a variation of the short range roughness as a function of the substrate bias voltage. Consequence for further scaling down of integrated circu its is called to mind.