Reaction of N2+ beams with aluminum surfaces

Abstract

Reactions of N2+ ion beams with the surface of clean polycrystalline aluminum over the energy range of 300–4000 eV are studied by the techniques of x-ray and UV photoelectron spectroscopy (XPS and UPS) and Auger electron spectroscopy (AES). The reaction produces a nitride layer which the depth–concentration profiles reveal to be a superposition of two distributions: the first is a continuous AlN phase at the near surface to a depth of ∼20 Å and the second is a region of lower nitrogen concentration tailing deeper into the Al substrate where a complete AlN phase has not been established. The AlN film is characterized by the agreement of the binding energies of the N 1s (397.3 eV) and Al 2p (74.1 eV) lines, of the kinetic energy of the Al KLL line (1338.9 eV), and of the Auger parameter (1463.0 eV) with a known standard of AlN. The N/Al ratio initially increases linearly with the nitrogen ion dose at low concentrations and finally reaches a steady state condition, determined by the opposing rates of nitridation and sputtering by impinging ions, at a dose of ∼1×1016 ions cm−2. The reaction cross section is found to vary from 2.0×10−16 to 4.7×10−17 cm2 over the ion energy range of 0.3–1.0 keV. A reaction mechanism which is supported by these results is discussed.