J. Phys. IV France 04 (1994) C9-155-C9-158
Nitruration initiale par NH3 à basse température de Si(111) 1x1-HJ.P. Lacharme1, N. Safta1, J.E. Bonnet2, C. Casado2, M. Iqbal1 and C.A. Sebenne1
1 Laboratoire de Physique des Solides, URA 154 du CNRS, Université P. et M. Curie, BP. 79, 75252 Paris cedex 05, France
2 LURE, associé CNRS-CEA, Bât. 209D, Université de Paris-Sud, 91405 Orsay cedex, France
Silicon samples have been chemically treated in order to get a Si(111) 1x1 : H surface under ultrahigh vacuum. This surface was exposed to doses of NH3 in the 102 to 103 Langmuir range, either kept at room temperature or Joule-heated at 400° C. The Si2p core level spectra were recorded upon synchrotron light beam excitation at a surface - sensitive photon energy wavelength of 128 eV. The N2s nitrogen peak binding energy at 20 eV was also recorded. While at room temperature the hydrogenated surface remained unperturbed whatever the dose of unexcited NH3, a reaction occurred as soon as the temperature reached about 400° C . The large chemical shift of the Si2p peak shows that nitrogen atoms are imbedded in the silicon surface. The temperature of 400° C at which the reaction occurs is below the lowest one at which H starts leaving the purely hydrogenated surface (over 450° C) . It is also lower than the temperature needed to start loosing hydrogen from a clean Si(111) surface which has been saturated by NH3 : these results suggest that the H-induced 1x1 relaxed reconstruction of the Si(111) surface facilitates the surface reaction of nitridation in a similar way as alkali metal atoms enhance the oxidation process along Si surfaces.
© EDP Sciences 1994