Lattice Parameter Measurements of 3C-SiC Thin Films Grown on 6H-SiC(0001) Substrate Crystals

Abstract

The lattice parameters of 3C-SiC thin films epitaxially grown on 6H-SiC(0001) substrate crystals have been precisely determined by using high resolution x-ray diffraction methods. Reciprocal space maps recorded around symmetrical and asymmetrical x-ray reflections revealed a pseudomorphic growth of the thin film in relation to the substrate lattice, whereas perpendicular to the surface the interplanar spacing of the lattice planes differ slightly ∆d/d = 8.7⋅10. This implicates inherent thin film strain (e) and stress (σ ) components. The in-plane components are found to be ei = 4.8⋅10 and σi = 2.26⋅10 N/m, whereas perpendicular to the surface the thin film strain component is found to be e^ = 2.8⋅10. Introduction Silicon Carbide (SiC) occurs in many polytypes which differ in their periodic stacking sequences of hexagonal and cubic Si-C bilayers. The SiC lattice parameters differ slightly from polytype to polytype [1]. Using x-ray diffraction methods the lattice parameters of 4Hand 6H-SiC single crystal wafers [2] have been determined precisely (Table 1). Unfortunately, large 3C-SiC single crystals are not available. However, 3C-SiC thin films can be easily grown and used to derive the lattice parameters of compact 3C-SiC crystals if one takes the inherent stress, induced by the thin film growth, into account. The 3C-SiC thin films (thickness ≈ 1.2 μm) were grown by solid-source molecular beam epitaxy on (0001)-oriented on-axis 6H-SiC crystal wafers at deposition temperatures between 780°C to 950°C and with growth rates between 30 nm/h to 120 nm/h [3]. High resolution x-ray diffraction of 3C-SiC thin films Although the lattice parameters of the different SiC polytypes differ only slightly, the x-ray diffraction pattern showed, close to each other but well separated, so-called family reflections of the 3C-SiC thin film and 6H-SiC substrate. Using the well known 6H-SiC bulk crystal values (Table 1) as a reference, we could determine the lattice parameters of the 3C-SiC thin films with a corresponding accuracy of 10 for Da/a and 10 for Dc/c. Reciprocal space maps recorded around symmetrical and asymmetrical x-ray reflections (Fig. 1) revealed a pseudomorphous growth of the 3C-SiC thin films in relation to the substrate lattice (Fig. 2). There is no difference between the lateral interplanar spacing of the lattice planes, but perpendicular to the surface their interplanar spacing differ by ∆d/d = 8.7⋅10. The growth direction of the 3C-SiC thin film was found to be [111] with respect to the surface normal. Silicon Carbide and Related Materials (2001). 319-322 319