Si etching in high-density SF 6 plasmas for microfabrication: surface roughness formation E. Gogolides * , C. Boukouras, G. Kokkoris, O. Brani, A. Tserepi, V. Constantoudis Institute of Microelectronics, National Center for Scientific Research NCSR – ‘‘Demokritos’’, Aghia Paraskevi, Attiki 15310, Greece Available online 14 March 2004 Abstract Silicon etching and Si surface-roughness formation in high density SF 6 plasmas was studied. Etching rates and surface roughness were measured and correlated with ion flux and neutral F atom flux measured in situ. Etching rates are an increasing function of F atom flux, while surface roughness is not a monotonic function of F atom flux, or the etching rate. In fact, it is shown that one can achieve high etching rates and small surface roughness, a result of great practical importance to MEMS fabrication. Surface roughness increases with time, while scaling analysis of the AFM data shows that in most cases the Si surfaces develop periodic mound structures with a high roughness exponent (0.8) and a small correlation length (80 nm). Ó 2004 Elsevier B.V. All rights reserved. Keywords: Si etching; Surface roughness; Scaling analysis; Plasma etching induced roughness; Roughness simulation 1. Introduction For application of Si etching in fields such as microoptics, microelectronics, and microsensors, the quality of processed surfaces is often of crucial importance to the optimal operation of the fabri- cated device. For example in Si-based MEMS, it has been found that the fracture strength of the plasma-etched microfabricated structures is related to the etching process and the quality of the surface produced [1]. Therefore, studies of the dependence of the surface roughness on processing conditions and of the mechanisms responsible for its forma- tion are of great interest recently [2,3]. SF 6 plasmas are often used for Si etching and their mixtures or alternating fluxes with fluorocarbon gases add an- isotropy as in the case of the Bosch process. How- ever, to understand roughness formation one should first start with the simplest possible system. For this reason, in this work, the surface roughness of Si surfaces etched in pure SF 6 in a high-density plasma (ICP) reactor is studied as a function of the processing conditions. Simultaneously, etching rates under various plasma conditions are deter- mined, the plasma gas phase is characterized and correlations to surface roughness are sought. * Corresponding author. E-mail address: evgog@imel.demokritos.gr (E. Gogolides). 0167-9317/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.mee.2004.02.059 www.elsevier.com/locate/mee Microelectronic Engineering 73–74 (2004) 312–318