Structural and morphological instabilities of the Si(111)-7 x 7 surface during silicon growth and etching by oxygen and selenium

Using in situ reflection electron microscopy and ex situ atomic force microscopy, we have studied the morphological stability of large-scale (similar to 10-100 mu m) Si(1 1 1)-7 x 7 terraces during silicon growth and etching by oxygen and selenium. On the large-scale terraces, silicon growth at substrate temperatures T = 600-770 degrees C and Si deposition rates R = 0.002-0.2 BL/s proceeds in multilayer mode. Based on RMS surface roughness scaling W proportional to Theta(beta), we have discerned three modes of morphological instability caused by (I) effective adatom diffusion along step edges at low T and R (beta approximate to 0.33), (II) effective diffusion and fast step motion along disordered 1 x 1 regions in 7 x 7 domain boundaries at intermediate T and R (beta approximate to 0.2), and (III) accumulation of Si adatoms in high-atom density 1 x 1 regions on the uppermost terraces at high T and R (beta approximate to 0.5). The etching of the singular Si(1 1 1)-7 x 7 surface by oxygen leads to the slow development of multilayer morphology, while selenium-induced etching preserves flat surface morphology with periodic 2D vacancy island nucleation, growth, and coalesce, which is attributed to Se adatom diffusion. On the step-bunched surface, the Si or Se adatom diffusion to the step bunches leads to the self-organization of pyramidlike or valley-like morphology during Si growth or Se-induced etching, respectively.

Automated summary

Through in situ reflection electron microscopy and ex situ atomic force microscopy, the research investigated the morphological stability of large-scale Si(111)-7x7 terraces during silicon growth and etching by oxygen and selenium. The study identified three modes of morphological instability, with oxygen etching leading to slow multilayer development and selenium-induced etching preserving flat surface morphology with periodic 2D vacancy island formation. Additionally, on step-bunched surfaces, Si or Se adatom diffusion to step bunches results in self-organized pyramidlike or valley-like morphology during Si growth or Se-induced etching.