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 Si(2)H(6) has been characterized by using four-wavelength spectroscopic ellipsometry. When a Si(100) surface is exposed to Si(2)H(6) under VUV irradiation, the (Psi, Delta) points designating the ellipsometric angles shift immediately 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 surface is passivated immediately by a Si hydride layer as a result of the sticking of photolysis products. The sticking step is self-limiting to produce a monoatomic hydride layer at pressures between 1 x 10(-4) and 4 x 10(-3) Torr, but ramified chains consisting of SiH(2) and SiH(3) species are created at pressures above 4 x 10(-3) Torr. When the Si(2)H(6) is evacuated, the hydride layer decomposes quickly. (C) 1999 Elsevier Science B.V. All rights reserved.