SiH4 chemical vapor deposition on Si(111)-(7x7) studied by scanning tunneling microscopy

The initial growth of silicon on Si(111)-(7 x 7) from SiH4 as the precursor gas was studied in the temperature range from 690 to 925 K under ultra-high vacuum (UHV) conditions (UHV-CVD) by scanning tunneling microscopy. At the onset of hydrogen desorption at around 690 K the evolution of a bulk-like monohydride-terminated (1 x 1) structure is observed. It is shown that growth proceeds by both the formation of homogeneously distributed adlayer islands and heterogeneous nucleation at translational domain boundaries of the initial surface. During the (7 x 7)-->(1 x 1):H conversion a site-selective etch reaction is observed, where center adatoms are etched preferentially. Annealing of the (1 x 1):H surface structure results in the reappearance of dimer-adatom stacking-fault (DAS) structures in addition to metastable non-DAS structures. It is shown that the diffusion barrier for mobile fragments to cross over terrace/island edges strongly depends on the step orientation. With increasing substrate temperature, defective (5 x 5) and (7 x 7) DAS structures are formed and growth is dominated by heterogeneous nucleation at domain boundaries and step flow. Finally, at the highest temperatures a well-ordered (7 x 7) structure grows exclusively via step flow. Step propagation in the [(1) over bar (1) over bar 2)] directions is preferred in the entire temperature range investigated. The sticking probability of SiH4 on presputtered Si(111) is enhanced, but at the expense of crystalline quality. (C) 1997 Elsevier Science B.V.