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 NH4F solution was investigated by scanning tunneling microscopy. In NH4F solution monohydride terminated Si atoms represent the most stable configuration: Etching proceeds via formation of small, (2 x 1)H dimer row reconstructed (100) terraces and evenly distributed square pyramids with (111) facets of up to 70 angstrom height, which coexist in equilibrium. Both pyramid formation and the uncorrelated etching of different (100) terraces lead to a continuous roughening of the surface during etching.