MOCVD growth of (100)-oriented CeO2 thin films on hydrogen-terminated Si(100) substrates

Ceria (CeO2) with a fluorite structure is supposed to be an ideal buffer layer for fabricating epitaxially grown perovskite materials on silicon substrates because of its thermal stability and excellent lattice match with Si. On the other hand, there are still technical difficulties in forming CeO2(100), which is more attractive for applications compared to that of (111) orientation. We report the preparation of CeO2 thin films on hydrogen-terminated Si(100) substrates by metal-organic chemical vapor deposition (MOCVD) using Ce(DPM)4 as an MO-source. The surface microroughness of the substrates was investigated using Fourier-transform infrared-attenuated total reflection (FT-IR-ATR) and atomic force microscopy (AFM). Si-wafers cleaned by RCA method were immersed in H2O2-added 0.5% HF solutions for hydrogen-termination, and preferential Si–H2 vibrational peaks accompanied with weak Si–H3 peaks were observed. The root mean square roughness of the substrates estimated by AFM was around 0.2 nm. The crystallinity and orientation were characterized by X-ray diffraction (XRD). The films were polycrystalline, and preferentially orientated to the 〈100〉 direction. The preferential orientation factor defined by Lotgering was 0.83. The microstructures were characterized by a field-emission scanning electron microscopy (FE-SEM), an AFM and a transmission electron microscopy (TEM). The grains were ‘non-equiaxed’ columnar, growing perpendicular to the surface at the expense of other columns. The surface texture of a 50 nm-thick film characterized by AFM was rectangular in shape, with a typical size of 100×200 nm. They were aligned in the same direction, and the edges of the rectangular are parallel to the Si(011) facets, suggesting a possible in-plane orientation. Cross-sectional HR-TEM analyses of a 150 nm thick film verified the thickness of the amorphous layer formed at the CeO2/Si(100) interface to be around 2 nm.