Metal organic chemical vapor deposition of ultrathin ZrO2 films on Si(100) and Si(111) studied by electron spectroscopy

The growth of ultrathin ZrO2 films on Si(100)-(2 x 1) and Si(111)-(7 x 7) has been studied with core level photoelectron spectroscopy and X-ray absorption spectroscopy. The films were deposited sequentially by chemical vapor deposition in ultra-high vacuum using zirconium tetra-tert-butoxide as precursor. Deposition of a > 50 angstrom thick film leads in both cases to tetragonal ZrO2 (t-ZrO2), whereas significant differences are found for thinner films. On Si(111)-(7 x 7) the local structure of t-ZrO2 is not observed until a film thickness of 51 angstrom is reached. On Si(100)-(2 x 1) the local geometric structure of t-ZrO2 is formed already at a film thickness of 11 angstrom. The higher tendency for the formation of t-ZrO2 on Si(100) is discussed in terms of Zr-O valence electron matching to the number of dangling bonds per surface Si atom, The Zr-O hybridization within the ZrO2 unit depends furthermore on the chemical composition of the surrounding. The precursor t-butoxy ligands undergo efficient C-O scission on Si(100), leaving carbonaceous fragments embedded in the interfacial layer. In contrast, after small deposits on Si(111) stable t-butoxy groups are found. These are consumed upon further deposition. Stable methyl and, possibly, also hydroxyl groups are found on both surfaces within a wide film thickness range. (c) 2006 Elsevier B.V. All rights reserved