THE INFLUENCE OF HYDROGEN ON CVD-GROWTH ON SI(111) SURFACES

Time-resolved scanning tunneling microscopy has been used to study the influence of atomic hydrogen on the growth behavior in silicon homoep itaxy and the etch attack of atomic hydrogen onto the silicon surface above 500 degrees C. In CVD of silicon on Si(lll) using disilane (Si2H 6) as gas phase precursor the presence of hydrogen on the surface play s an essential role in all stages of growth. At temperatures above 400 degrees C, for each Si atom deposited on the surface one H atom is ad sorbed additionally. Under the influence of hydrogen the density of is lands increases during nucleation on the bare substrate. The nucleatio n behavior in CVD, when quantitatively analyzed, differs distinctly fr om the one during MBE-growth. As opposed to MBE, the density of nuclei as a function of temperature and growth rate cannot be understood in terms of classical rate equation based nucleation theories. Under the influence of a closed hydrogen layer the topmost silicon layer is larg ely immobilized and lateral island coarsening can only take place afte r hydrogen desorption. At a high flux of disilane the growth rate is l imited by this hydrogen desorption. The surface, which then has a hydr ogen-coverage close to saturation, roughens linearly with coverage and completely decays into facets of the [110]-zone. When the flux of the precursor gas is interrupted the surface flattens with a time constan t determined by the hydrogen desorption. Atomic hydrogen is able to re move silicon from the surface visible in STM as step retrac tion. Abov e 500 degrees C we found a linear increase of the removal rate with te mperature.