Site preferences of oxygen and boron atoms during dissociative reaction ofHBO2 molecules onto the Si(111)-7x7 surface

Using scanning tunneling microscopy (STM), we succeeded in observing the in itial process of the HBO molecule on the Si(111)-7X7 surface for the first lime. Since HBO2 molecules are commonly used as the B source in the molecul ar beam epitaxy system, and the dominant flux from the HBO, source in the o rdinary condition is the form of HBO, analysis of the HBO reaction process is highly important. When the substrate temperature was kept at room temper ature during the molecular irradiation, the adsorbed HBO molecules remained on the surface without dissociation. With the substrate temperature being increased, the dissociation process was activated, and the oxygen- and boro n-related adatoms were produced at the corner and center adatom sites in th e 7x7 units, respectively. The site dependence was well determined by the b ias voltage dependent STM. The selective reaction site of oxygen atoms was comprehensively explained by their electronegativity and charge distributio n in the Si(111)-7x7 surface adatoms. On the other hand, regarding the sele ctivity for the boron atoms, introduction of the surface strain effect was found to be essential. (C) 2000 American Vacuum Society. [S0734-2101(00)116 04-5].