EPITAXIAL-GROWTH OF OXIDES ON SEMICONDUCTORS USING FLUORIDES AS A BUFFER LAYER

The success in epitaxial growth of oxides on Si using an intermediate fluoride layer largely depends on the reactivity of the fluoride with the oxide and the stability of the fluoride against oxidation. The fluoride-oxide reaction was studied by Rutherford backscattering spectrometry and x-ray diffractometry. It is found that a large number of oxides are stable on CaF2, while some containing K, Li, and Ba react with CaF2. The results are consistent with thermodynamic predictions, and correlate well with the equalized electronegativity of the oxides. The stability of bare CaF2 on Si is found to be strongly related to the ambient. The CaF2 surface remains intact after annealing at 650-degrees-C in 25% O2/N2, although Ca-silicate formation takes place at the Si-CaF2 interface. When annealing is conducted in air, Ca-carbonate is readily formed at the surface. The results provide guidelines for epitaxial growth of oxides on semiconductor/fluoride structures. The potential application of using fluorides as buffer layers is demonstrated in epitaxial growth of SrTiO3 on (100)Si/CaF2.