LETTER TO THE EDITOR Roughness scaling of plasma-etched silicon surfaces

Abstract. Atomic force microscopy reveals scaling behaviour of silicon surfaces etched by plasma. The experimental results are compared with some theoretical models. It is shown that plasma-induced roughness is driven by a phenomenon that can be described by shadowing instabilities resulting in columnar microstructure growth. The same scaling properties as are predicted by a growth model are obtained. The problem of interface roughness has received particular attention, especially on a theoretical basis [1]. This is due to its practical connection to thin-film growth. However, rather little effort has been made to interpret experimental data in terms of kinetic roughening as can be done for the interaction of plasma with materials [2]. Our aim in the present work is to analyse plasma-etched silicon surfaces in terms of various roughness growth models. The possibilities offered by scanning probe methods as regards this problem have been stressed in various articles [3, 4]. In a previous paper [5], we have described experiments dealing with a quantitative study of the roughness induced by SF6 plasma etching of silicon surfaces. The advantage of independently varying the plasma parameters was found to carry over. As a major result, an empirical analytical form describing the surface roughness as a function of these parameters has been established. What we want to discuss here is the time dependence of this roughness. Using an atomic force microscope, topographical maps of the surface have been recorded. The root mean square value of the roughness height h.x; y / was found to obey the following phenomenological power law [5]