Control of Stress with Growth Conditions and Mechanical Parameters Determination of 3C-SiC Heteroepitaxial Thin Films
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CONTROL OF STRESS WITH GROWTH CONDITIONS AND MECHANICAL PARAMETERS DETERMINATION OF 3C-SiC HETEROEPITAXIAL THIN FILMS C. Gourbeyre1, T. Chassagne2, M. Le Berre1, G. Ferro2, C. Malhaire1, Y. Monteil2, D. Barbier1 1
: Lab. Physique de la Matière, UMR CNRS 5511, INSA de Lyon, 20 Av. A. Einstein, 69621 Villeurbanne Cedex, France. 2 : Lab. Multimatériaux et Interfaces, UMR CNRS 5615, U.C.B. Lyon 1, Bat. 731, 43 Bd du 11 Novembre 1918, 69622 Villeurbanne Cedex , France. ABSTRACT We report here on the influence of the epitaxial growth conditions on the residual stress of heteroepitaxial 3C-SiC grown on silicon using atmospheric-pressure chemical vapour deposition (APCVD) and on the determination of its mechanical properties. 3C-SiC films were grown on (100) Si substrates in a vertical reactor by APCVD. SiH4 and C3H8 are used as precursor gases and H2 as carrier gas. The growth procedure involves the formation of a carburization buffer layer at 1150°C under a mixture of H2 and C3H8. The epitaxial growth occurs then at 1350°C by adding SiH4. For as-deposited films the measurement techniques implemented are substrate curvature measurements, AFM, and nano-indentation. For micromachined self-suspended SiC membranes, load deflection measurements were used. The substrate curvature measurement leads to the determination of the residual stress in the deposited SiC film. We show that we can achieve 3C-SiC layers with a compressive or a tensile state having equivalent crystallinity. Whereas thermal mismatch just accounts for tensile stresses, we demonstrate that 3C-SiC thin films may have compressive stresses by using specific conditions for the formation of the buffer layer. The early stage of growth is indeed of major importance. Regarding the mechanical properties, the 3C-SiC Young’s modulus was determined using nano-indentation. Its mean value reaches 378 GPa comparable to the calculated value of 307 GPa. As test structures, we have processed self-suspended SiC membranes. Load deflection measurements enable the determination of the Young’s modulus and the residual stress of the self-suspended films. For self-suspended SiC membranes, the absolute value of the residual stress in the SiC thin films decreases compared to the as-deposited films and takes a mean value of 170 MPa in a tensile state. INTRODUCTION Silicon carbide is an outstanding material for its mechanical hardness, chemical inertness, high thermal conductivity and electrical stability at temperatures well above 300°C and therefore stands as an excellent candidate for high temperature MEMS [1]. In particular, deposition of heteroepitaxial β-SiC on Si (100) substrates presents a low cost advantage over 6H- and 4H-SiC polytypes. In this scope, the control of stresses in as-deposited samples and in micromachined microstructures is desirable and thus is the focus of this paper.
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EXPERIMENTS The depositions were carried out by atmospheric pressure chemical vapor deposition (APCVD) in a cold wall vertical reactor. Silane (1% in H2) and propane (5% in H2) were used
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