Electrochemical study of atomically flattening process of silicon surface in 40% NH₄F solution

From AFM observations, we found that atomic flattening of Si(111) surfaces in 40% NH₄F solutions was accelerated by removing oxygen using a chemical deoxygenator. Furthermore, the surfaces became flatter by treatment in solutions without oxygen. The dissolution of Si in 40% NH₄F solutions can be electrochemically monitored as anodic currents. From the measurements of the anodic currents, we found that the dissolution rate of Si was enhanced by removing oxygen from the solution. These results suggest that oxygen blocks the reactive sites on Si from the attacks of etching species in solution. At low temperature and in the absence of oxygen, although the morphological change was slow, the surface became very flat.