Formation and decomposition of a Si hydride layer during vacuum ultraviolet-excited Si homoepitaxy from disilane

The precursor state involved in vacuum ultraviolet (VUV)-excited Si growth from Si2H6 has been characterized by using four-wavelength spectroscopic el lipsometry. When a Si(100) surface is exposed to Si2H6 under VUV irradiatio n, the (Psi, Delta) points designating the ellipsometric angles shift immed iately toward the Psi direction at 4.3 and 3.4 eV, whereas the shifts at 2. 3 and 1.5 eV are more toward the Delta direction. This indicates that the s urface is passivated immediately by a Si hydride layer as a result of the s ticking of photolysis products. The sticking step is self-limiting to produ ce a monoatomic hydride layer at pressures between 1 x 10(-4) and 4 x 10(-3 ) Torr, but ramified chains consisting of SiH2 and SiH3 species are created at pressures above 4 x 10(-3) Torr. When the Si2H6 is evacuated, the hydri de layer decomposes quickly. (C) 1999 Elsevier Science B.V. All rights rese rved.