MOCVD GROWTH OF (100)-ORIENTED CEO2 THIN-FILMS ON HYDROGEN-TERMINATEDSSI(100) SUBSTRATES

Ceria (CeO2) with a fluorite structure is supposed to be an ideal buff er layer for fabricating epitaxially grown perovskite materials on sil icon substrates because of its thermal stability and excellent lattice match with Si. On the other hand, there are still technical difficult ies in forming CeO2(100), which is more attractive for applications co mpared 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. T he surface microroughness of the substrates was investigated using Fou rier-transform infrared-attenuated total reflection (FT-IR-ATR) and at omic force microscopy (AFM). Si-wafers cleaned by RCA method were imme rsed in H2O2-added 0.5% HF solutions for hydrogen-termination, and pre ferential Si-H-2 vibrational peaks accompanied with weak Si-H, peaks w ere observed. The root mean square roughness of the substrates estimat ed by AFM was around 0.2 nm. The crystallinity and orientation were ch aracterized by X-ray diffraction (XRD). The films were polycrystalline , and preferentially orientated to the [100] direction. The preferenti al orientation factor defined by Lotgering was 0.83. The microstructur es were characterized by a held-emission scanning electron microscopy (FE-SEM), an AFM and a transmission electron microscopy (TEM). The gra ins 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 si ze of 100 x 200 nm. They were aligned in the same direction, and the e dges 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 forme d at the CeO2/Si(100) interface to be around 2 nm. (C) 1998 Elsevier S cience S.A. All rights reserved.