Epitaxial Growth of SiC on AlN/Sapphire Using Hexamethyldisilane by MOVPE
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Epitaxial Growth of SiC on AlN/ Sapphire Using Hexamethyldisilane by MOVPE Kasif Teker, Ki Hoon Lee, Chacko Jacob*, Shigehiro Nishino*, and Pirouz Pirouz Department of Materials Science and Engineering, Case Western Reserve University, Cleveland, OH 44106, U.S.A *Department of Electronics and Information Science, Kyoto Institute of Technology, Kyoto, 606, Japan ABSTRACT High quality SiC and AlN films allow the fabrication of metal/AlN/SiC MIS structures and SiC/AlN heterostructures that require a low lattice mismatch and excellent thermal stability. Epitaxial SiC on AlN/sapphire was grown using hexamethyldisilane (HMDS) by MOVPE. 2HAlN is epitaxially grown on sapphire by MOCVD, and subsequently SiC is deposited on it. The growth of high quality SiC was achieved in a one step process without any nucleation step using dilute hydrogen in argon (12% H2 + Ar) as the carrier gas, which is less explosive than pure H2. The effect of growth temperature and thickness of AlN on the SiC crystal quality and the surface smoothness were studied. All films were analyzed using reflection high energy electron diffraction (RHEED), Nomarski differential interference contrast microscopy (NDIC), X-ray diffraction (XRD), and atomic force microscopy (AFM). Optimum temperature for SiC growth was between 1300oC and 1350oC. At these temperatures, the grown films show strong epitaxial relationship with AlN and very smooth surfaces (RMS ~ 0.1- 0.75 nm). At temperatures below 1300oC, the film becomes polycrystalline. At 1400oC, the films show highly textured features, observed by XRD. In the RHEED, however, weak rings appear superimposed on the spot pattern, which implies the grown films are polycrystalline but highly textured. In order to evaluate the effect of underlying AlN thickness on the SiC film, layers with various thicknesses (50, 200, 400 nm) have been used at 1350oC. The SiC film on a 50 nm thick AlN layer shows a very smooth surface (RMS ~ 0.1 nm) compared to the SiC film on a 400 nm (RMS ~ 0.7 nm) AlN layer. This seems to be caused by the increasing roughness of the underlying AlN, as it becomes thicker. However, all the films show highly epitaxial growth features, which implies that 50 nm is sufficient to relieve the mismatch strain of the underlying AlN/sapphire. INTRODUCTION Crystal growth of high quality SiC on AlN substrate attracts interest due to the creation of semiconductor-on-insulator structures. For power applications, insulating substrates are superior to semiconductor substrates leading to a better electrical isolation of the individual devices. The low lattice mismatch (~1%) and excellent thermal stability of AlN makes this a very attractive substrate for SiC growth. Nishino et al. [1] and Dmitriev et al. [2] reported SiC growth on AlN/Al2O3 and AlN/6H-SiC substrates, respectively. Later, Chaudhuri et al. [3] reported CVD growth of SiC on AlN/Al2O3 substrates using silane and ethane. We employed epitaxial growth of high quality SiC on AlN using HMDS in a one-step process. The conditions for epitaxial growth of SiC on
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