Materials Science and Engineering A 387–389 (2004) 302–306 Investigating the elastic properties of -SiC films G.F. Dirras a,∗ , P. Djemia a , Y. Roussigné a , K.M. Jackson b a LPMTM-CNRS, Institut Galilée, Université Paris 13, 99 Avenue Jean-Baptiste Clément, 93430 Villetaneuse, France b Department of Mechanical Engineering, The Johns Hopkins University, 3400 N. Charles Street, Baltimore, MD 21218, USA Received 26 August 2003; received in revised form 5 January 2004 Abstract Direct elastic properties measurements of -SiC films have been made using the interferometric strain gage displacement (ISDG) technique and compared with data acquired by the Brillouin light scattering (BLS) technique. BLS permits to selectively determine the three independent elastic constants (c 11 = 395 GPa; (c 11 - c 12 )/2 = 136 GPa and c 44 = 236 GPa) of a -SiC single crystal epitaxial film from the analysis of a number of different surface acoustic modes. The calculated Voigt average values of the elastic constants for the 〈111〉 textured polycrystalline films (C 11 = 500 GPa, C 33 = 534 GPa, C 44 = 166 GPa, C 66 = 201 GPa, C 13 = 62 GPa) using the single crystal constants provides good agreement with experimental results on Young’s modulus measured by the ISDG technique. Nevertheless, BLS gave more accurate values of Poisson’s ratios. © 2004 Elsevier B.V. All rights reserved. Keywords: -SiC; Thin films; Brillouin light scattering; Elastic properties; Interferometric strain gage displacement; Microelectromechanical systems 1. Introduction The flourishing technology of microelectromechanical systems (MEMS) is showing great promises in various areas such as the automotive industry, aerospace, cellular communications, biochemistry and other critical application such as weapons. Silicon carbide (SiC) is being considered as a useful ma- terial for MEMS as it surpasses polysilicon in applications in harsh environments including high temperature, intense vibrations, etc. [1]. SiC exhibits a form of one-dimensional polymorphism called polytypism. The 3C-SiC polytype, also known as -SiC, is the only polytype with a cubic structure and can be epitaxially grown on single crystal silicon sub- strates. Such epitaxial 3C-SiC films are well suited for bulk micromachined structures like diaphragms and cantilever beams. In the present study, elastic properties of single and poly- crystalline -SiC films have been measured by means of the interferometric strain gage displacement (ISDG) and Bril- louin light scattering (BLS) techniques. ∗ Corresponding author. Tel.: +33-1-4940-3488; fax: +33-1-4940-3938. E-mail address: dirras@lpmtm.univ-paris13.fr (G.F. Dirras). 2. Experimental procedures The materials studied were single (1 m thick) and poly- crystalline (30 m thick) -SiC films (on silicon wafers) elaborated at Case Reserve Western University and Mas- sachusetts Institute of Technology, respectively [2–4]. The films were deposited by chemical vapor deposition with a combination of silane and propane as precursors [5,6]. The ISDG technique [7] enables direct and accurate recording of the strain on a thin film and has been used to measure the elastic properties of the films. This technique has proved to be well suited for measuring the mechanical properties of small-sized samples [8–10]. In a BLS experiment, a beam of monochromatic light (514.5 nm) is used as a probe to reveal acoustic phonons that are naturally present in the medium under investiga- tion. The power spectrum of these excitations is mapped out from frequency analysis of the light scattered within a solid angle, by means of a multi-pass Fabry-Perot interferome- ter. A number of acoustic modes confined within the film material can thus be revealed, and the elastic constants of the film determined [11,12]. The wavelength of the acoustic waves probed in this experiment is typically 300 nm. The BLS technique has been used here to measure all the inde- pendent elastic constants of the SiC thin films and allows 0921-5093/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.msea.2004.03.082