SELECTIVE SURFACE MODIFICATIONS WITH A SCANNING TUNNELING MICROSCOPE

A combination scanning tunneling microscope (STM) and scanning electro n microscope has been used to selectively pattern and image Si(111) an d Si(001) surfaces in a SEM chamber. Both positive and negative STM ti p polarities produce marks on the surface with linewidths as small as 20 nm. We have transferred these patterns to the silicon substrate via selective wet chemical etching. We demonstrate a well-defined voltage threshold for patterning at negative tip bias. The modifications are consistent with a model based on hydrogen depassivation and electric f ield mediated deposition. The physical mechanism for positive tip bias patterning is shown to be different than that for negative bias. At p ositive bias, the patterning is consistent with selective surface cont amination. (C) 1997 American Institute of Physics.