WET CHEMICAL ETCHING OF SI(100) SURFACES IN CONCENTRATED NH4F SOLUTION - FORMATION OF (2X1)H RECONSTRUCTED SI(100) TERRACES VERSUS (111) FACETING

Etching of hydrogen terminated Si(100) wafer surfaces in 40% aqueous N H4F solution was investigated by scanning tunneling microscopy. In NH4 F solution monohydride terminated Si atoms represent the most stable c onfiguration: Etching proceeds via formation of small, (2 x 1)H dimer row reconstructed (100) terraces and evenly distributed square pyramid s with (111) facets of up to 70 angstrom height, which coexist in equi librium. Both pyramid formation and the uncorrelated etching of differ ent (100) terraces lead to a continuous roughening of the surface duri ng etching.