THERMALLY GROWN SI3N4 THIN-FILMS ON SI(100) - SURFACE AND INTERFACIALCOMPOSITION

Synchrotron photoemission measurements of the Si(2p, and N(1s) levels have been made on Si3N4 thin films grown in situ by high-temperature r eaction of Si(100) with NH3. Surface sensitivity is enhanced in compar ison to laboratory photoemission experiments by selecting photon energ ies that minimize the photoelectron mean free path in the nitride film . From the results, we are able to determine not only the types of che mical species present, but their approximate location within the film as well. Careful analysis of the Si(2p) photoemission spectra reveals the presence of a unique silicon species with a Si(2p) binding energy intermediate between elemental silicon and silicon in Si3N4. Furthermo re, the persistence of this species with increasing nitride-film thick ness supports its assignment to a monolayer of silicon at the outermos t surface layer, on top of the growing stoichiometric Si3N4 film. Thes e surface silicon atoms can be distinguished from silicon atoms in int ermediate oxidation states at the Si3N4/Si interface. The spectroscopi c evidence for chemically distinct surface, nitride, and interfacial s ilicon is discussed in terms of the silicon nitridation mechanism.