Atomic structures of Si(111) surface during silicon epitaxial growth

Abstract

Atomic structures during homoepitaxial growth on a Si(111)7 × 7 surface are investigated by reflection high-energy electron diffraction (RHEED) and scanning tunneling microscopy (STM). Analyzing RHEED intensity rocking curves by dynamical calculations, we conclude that backbonds of adatoms on the dimer-adatom-stacking-fault (DAS) structure are broken by two adsorbed silicon atoms at an initial stage of the deposition. Subsequently the structure is reconstructed into a pyramidal cluster-type one. At temperatures higher than 400°C, rocking curves during growth are very similar to that of the Si(111)7 × 7 DAS structure. It is concluded that the surface structures during growth at the high temperatures are the DAS structures including 3 × 3, 5 × 5 and 9 × 9. At 280°C, however, the rocking curve is very different from the curves by the DAS structures. Analyzing the curve by RHEED dynamical calculations, we have found that the pyramidal cluster-type structure is formed on the surface during growth. From these results and instability of the pyramidal cluster-type structure, we conclude that the formation of the metastable structure promotes successive epitaxial growth accompanied with stacking-fault dissolution at the dimer-stacking-fault framework. At substrate temperatures from 400 to 600°C a mixed phase of 5 × 5 and 7 × 7 structures is observed with RHEED intensity oscillation during growth. In STM images of isolated silicon hillocks formed on the Si(111)7 × 7 surface, we observed stable (long lifetime) shapes of 5 × 5 hillocks, and found magic numbers of the 5 × 5 units in the hillocks. For 7 × 7 hillocks, however, it is hard to find stable ones in STM images. We discuss the relation between the formation of the 5 × 5 DAS structure at the growth surface and the stability of the isolated 5 × 5 hillocks.