INITIAL-STAGES OF THE THERMAL NITRIDATION OF THE SI(100) SURFACE WITHNH3 AND NO - A SURFACE SENSITIVE STUDY OF SI 2P CORE-LEVEL SHIFTS

During thermal nitridation of the Si(100) surface, nitride regions gro w laterally on the surface. Already at small coverages they have nearl y the thickness which is found for the closed him. This thickness depe nds on the annealing temperature and is 10 Angstrom for 800 K and 15 A ngstrom for 1200 K. The coordination of the silicon atoms with nitroge n atoms is determined by the heating temperature. At 800 K only a smal l fraction of the silicon atoms in the nitride is bound to four nitrog en atoms, whereas for 1200 K the majority of the silicon atoms is foun d in this environment, which is characteristic for stoichiometric sili con nitride. For 1200 K, growth mode, thickness, and chemical composit ion are independent of the nitrogen containing gases. For the stoichio metric closed nitride film we measured the edges of the band gap and t he position of the Fermi level therein. Defect-induced unoccupied stat es could be detected within the band gap.