Preparation of epitaxial oxide thin films on Si(100) substrates with CoSi 2 surface layers

Abstract

Yttria-stabilized ZrO 2 (YSZ) and CeO 2 films have been epitaxially grown by electron beam evaporation on Si(100) substrates with CoSi 2 buffer layers prepared by ion implantation and annealing. Microstructure and morphology of these films have been characterized by X-ray diffraction (XRD), Rutherford backscattering spectroscopy with channeling (RBS-C), and scanning electron microscopy (SEM). θ-2θ scan XRD spectra show that CeO 2 films have (111) orientation on CoSi 2 Si(100) substrates. However, the orientation of YSZ films is related with the deposition parameters. In the high oxygen pressure range (∼ 10 −6mbar), YSZ films have the pure (100) orientation, whereas in the low oxygen pressure regime (∼ 10 −7mbar), YSZ films have (111) and (100) mixed orientations. For a CeO 2/YSZ/CoSi 2/Si(100) multilayer system deposited under the optimum conditions, each layer grown epitaxially has the same orientation as the Si substrate. RBS-C measurements prove that both YSZ and CeO 2 films have considerably good crystalline quality, the minimum yield, X min, for Ce signal is only 18%. In RBS-C spectra, there is no interdiffusion between films and the Si substrate. ø XRD scans indicate that in-plane epitaxial alignment is the same in respect to the Si(100) substrate. The thermal and chemical stability of CoSi 2 layer makes the growth of YSZ and CeO 2 films easier on the CoSi 2 Si(100) structure than on pure the Si(100) substrate. Surface morphology of YSZ and CeO 2 films can be optimized by the control of oxygen pressure and deposition rate. It was found that roughness of films was minimized by reducing the deposition rate ( ∼ 0.5 A ̊ / s ). Pinholes in the film can be avoided at a relatively high oxygen pressure (∼ 10 −6mbar).