Atomic force microscope (AFM) nanofabrication properties based on mechano-chemical processing due to diamond tip sliding on silicon in ambient atmosphere are studied. The processed height and depth dependencies on load and diamond tip radius were evaluated. Diamond tip of about 200nm radius sliding produces protuberances on the silicon surface. In contrast, about 50nm radius tip sliding produces grooves on the silicon surface. Using about 100nm radius tip, both protuberance and groove are produced. To clarity the mechanism of silicon protuberance and groove processing by diamond tip sliding in an atmosphere, the contact stress analysis were perfomed by boundary element method. Oxidation of silicon is speculated to be caused at the rear edge of sliding contact area that the elongation stress is the highest. This reaction forms silicon oxide in both protuberance and groove processing. To clarify the possibility of these processed parts on silicon surface for the application to wet etching mask, etching properties with KOH solution were evaluated at room temperature. The sliding of diamond tips produces the silicon oxide layer that works as KOH etching protective mask. AFM mechanochemical processing layers are expected to act as etching mask for selective wet etching.