Detailed study of surface and interface properties of lc-Si films A. Abramov a,b , D. Daineka a , Y. Djeridane a, * , P. Roca i Cabarrocas a a Laboratoire de Physique des Interfaces et des Couches Minces, UMR 7647, CNRS, Ecole Polytechnique, F-91128 Palaiseau cedex, France b A.F. Ioffe Physico-Technical Institute, St.-Petersburg, 194021, Russia Available online 4 March 2008 Abstract The properties of surfaces and interfaces of microcrystalline films deposited by radio-frequency plasma enhanced chemical vapor deposition (RF-PECVD) were studied by spectroscopic ellipsometry. The effect of the low-power reactive ion etching (RIE) on the prop- erties of the films was investigated. The surface properties could be effectively improved using RIE to eliminate of the top porous part of the films, without deterioration of bulk layer properties. Ellipsometric measurements from both film and substrate sides were used for the study of the interface properties of the various samples deposited on fused silica substrates. We show that the crystalline fraction that determined from modeling of ellipsometric spectra measured from the film side could be overestimated. Ó 2007 Elsevier B.V. All rights reserved. PACS: 68.35.Ct; 68.55.Nq Keywords: Nanocrystals; Ellipsometry; Microcrystallinity; Porosity 1. Introduction Microcrystalline silicon (lc-Si) is a material with better electronic properties and excellent stability as compared to amorphous silicon. It is well known that lc-Si is a het- erogeneous material composed of crystalline, amorphous and voids phases and that the ratio between these phases may vary with depth. The interface and surface layers usu- ally have a higher amorphous and/or voids fraction in comparison with the bulk [1,2]. These layers could affect the performance of devices based on lc-Si via enhanced surface recombination in the case of diodes or lower chan- nel mobility or higher contact resistance in the case of thin film transistors (TFTs). Spectroscopic ellipsometry (SE) in the wavelength range from IR to UV allows obtaining the information on the whole volume of lc-Si films [3]. To get insight on the evo- lution of the film properties with depth a four-layer optical model consisting the interface, bulk, subsurface and rough- ness layers can be used [1,2,4]. In our previous work, we have shown that fully crystallized films with similar bulk can have strong differences in the surface properties [5]. It seems reasonable to suppose that etching of the top porous part, for example by RIE, could improve the surface prop- erties of lc-Si films. The objective of this work is to obtain detailed information on the film structure and on the effect of RIE on the film properties, which we achieve by combin- ing SE measurements and etching of various types of films. 2. Experimental We have used conventional radio-frequency plasma enhanced chemical vapor deposition for the growth of sil- icon films [6]. Films were deposited from SiH 4 or SiF 4 con- taining gas mixtures onto Corning 1737 glass and fused silica substrates at temperatures in the range of 150– 175 °C. Optical properties of the films were studied by spectroscopic ellipsometry (SE) in the photon energy range from 1.5 to 4.7 eV. For the fitting of ellipsometric spectra we have used a four-layer model that consists of interface, 0022-3093/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2007.10.099 * Corresponding author. Tel.: +33 1 69 33 43 11. E-mail address: yassine.djeridane@polytechnique.edu (Y. Djeridane). www.elsevier.com/locate/jnoncrysol Available online at www.sciencedirect.com Journal of Non-Crystalline Solids 354 (2008) 2218–2222