STM STUDIES ON THE STRUCTURAL EVOLUTION OF N-2(-INDUCED NITRIDE FORMATION ON SI(111)-7X7 SURFACE() ION)

The initial stage of N-2(+) ion induced nitridation of Si(lll)-7x7 sur face was investigated by using At room temperature, deposition of NS i ons on Si(lll)-7x7 surface formed an amorphous surface morphology. Wit h submonolayer dose of N-2(+) ions and post-annealing at temperatures above 950 degrees C, silicon nitride islands appeared preferentially a t the step edges implying that those had acted as step pinning sites t o result in the rough step edges. Inside the silicon nitride island, t hree-directional periodicity whose symmetry axes deviated from those o f Si(lll)-7x7 was observed and the low energy electron diffraction pat tern showed the coexistence of 7x7 and quadruplet domains. On the surf ace area preserving the 7x7 periodicity, Si adatoms which reacted with nitrogen ions appeared dark preferentially on the center adatom sites to corner ones of the dimer-adatom-stacking-fault model. Frequent obs ervation of Si(lll)-7x7 phase boundary and the formation of lattice-mi smatched silicon nitride islands could be closely related with each ot her. With higher dose of N-2(+) ions and post-annealing at temperature s above 950 degrees C, the surface 2 was covered with small patches of silicon nitride islands and Si-7x7 domains. Post-annealing of this su rface at temperatures above 1050 degrees C resulted in a very rough mo rphology and prolonged annealing above 1105 degrees C recovered very f lat and clean Si(lll)-7x7 surface.