Thermal decomposition of NH3 on the Si(100) surface

The adsorption and thermal reaction of NH3 on the Si(1 0 0) surface are investigated by high-resolution core-level photoemission spectroscopy using synchrotron radiation. The existence of different reaction products and their chemical bonding configurations at different substrate temperatures are revealed from N 1s and Si 2p core-level spectra. We clearly, identified a series of Si-NH2, Si(2)dropNH and Si(3)dropN species in N 1s spectra indicating a successive N-H bond dissociation during thermal decomposition. The depth distribution and the population changes of each N species with annealing suggest that (i) the intermediate Si-2=NH species include insertion into the back-bond site between the first and the second Si layers as well as bridging Si dimer site and (ii) the fully dissociated N atoms are incorporated into the Si subsurface layers first. At a high temperature above 900 K, the incorporated N atoms partly segregate back to the surface to form stoichiometric silicon nitride patches. The Si 2p core levels consistently show progressive changes in subnitride formation and the liberation of H atom upon increase of annealing temperature. The implication of the present result on the proposed reaction mechanism is discussed. (C) 2003 Elsevier B.V. All rights reserved.