Thermal nitridation and oxygen-induced etching reactions: A comparative study on Si(100) and (111) surfaces by scanning tunneling microscopy

Comparative studies of the thermal nitridation and subsequent oxygen-induced etching reactions on Si(100) and Si(111) surfaces were done using a scanning tunneling microscope. Both surfaces were thermally nitrided by exposure to nitrogen gas at 700°C and subsequently reacted with oxygen under an oxygen partial pressure of 1 × 10-7 Torr. Silicon nano-structures were formed via selective local oxygen etching of silicon using the silicon nitrides as masks against the oxygen exposure. Resultant silicon nano-structures showed distinct differences between the two surfaces. Very narrow size distribution of silicon dots with an average size of ∼ 5nm was obtained on the Si(100) surface, whereas a broad size distribution of silicon protrusions ranging from 5 to 20nm was obtained on the Si(111) surface. We discuss the observed differences between Si(111) and (100) surfaces considering the thermal mobility of nitrogen species and the lattice and symmetry mismatches between the silicon nitride layer and Si.