Initial stage of silicon nitride nucleation on Si(111) by rf plasma-assisted growth

The nucleation of silicon nitride films on Si(111) using a radio frequency nitrogen plasma source has been investigated by scanning tunneling microscopy. The initial nucleation of Si3N4 is always observed at the steps, i.e., either at the step-edges of the initial Si(111) surface or at the step edges of vacancy islands (etch pits) formed on the terrace areas. With increasing nitridation temperature the nitrified patches become larger with lower density and show a triangular shape. After post annealing the triangular nucleation patches at the step-edges disappear and free-standing Si3N4 islands are observed with a hexagonal shape. Nitridation at high temperatures or post-annealing improves the crystalline quality of the nitride films and an atomically resolved honeycomb-like "8x8" surface reconstruction is observed in STM for thin Si3N4 films grown at 850 degrees C.