Atomic structures during homoepitaxial growth on a Si(111)7 x 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 degrees C, rocking curves during growth are very similar to that of the Si(111)7 x 7 DAS structure. It is concluded that the surface structures during growth at the high temperatures are the DAS structures including 3 x 3, 5 x 5 and 9 x 9. At 280 degrees 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 degrees C a mixed phase of 5 x 5 and 7 x 7 structures is observed with RHEED intensity oscillation during growth. In STM images of isolated silicon hillocks formed on the Si(111)7 x 7 surface, we observed stable (long lifetime) shapes of 5 x 5 hillocks, and found magic numbers of the 5 x 5 units in the hillocks. For 7 x 7 hillocks, however, it is hard to find stable ones in STM images. We discuss the relation between the formation of the 5 x 5 DAS structure at the growth surface and the stability of the isolated 5 x 5 hillocks.
