Dissociative adsorption of SiH2Cl2 on Si(111)7x7

Adsorption and reaction of SiH2Cl2 (DCS) with Si(111)7 x 7 at 300 K were investigated by spectroscopic (XPS, AES) and atomically resolved topographic (STM) measurements. It is shown that DCS adsorption proceeds under scission of a Si-Cl bond to produce SiH2Cl and Cl, where the former adsorb at a rest atom or corner hole dangling bond, while the Cl atom reacts with an adjacent adatom dangling bond. This is explained in a four center reaction mechanism, involving two neighboring dangling bonds of the substrate and two centers of the polar DCS molecule. Evaluation of the Cl site occupation, including pair correlation and site blocking effects, shows a preferential Cl termination of center adatoms. This mechanism also explains the observed second order kinetics for DCS adsorption.