Nanoscale ion-beam mixing of Ti/Si interfaces: An X-ray photoelectron spectroscopy and factor analysis study

Titanium/silicon interfaces produced by Ti thin film deposition on Si substrates were ion-beam mixed using Ar+ ions in the energy range of 2-5 keV at room temperature (RT). The ion-beam mixing (IBM) has been studied by means of X-ray photoelectron spectroscopy (XPS) and factor analysis (FA). FA of the Si 2p and Ti 2p core levels show that the kinetics of interface formation by IBM is characterized by two stages. During the first stage, a strong decrease of metallic Ti species is observed up to ion doses of ∼2 × 1016 ions/cm2, due not only to sputtering but also to the solution of Si in Ti and to the formation of titanium silicide. The concentration of the species associated with the initial solution of Si in Ti reaches a maximum during this stage, decreasing subsequently due to its transformation into titanium silicide related species. The second stage, is characterized by the parallel evolution of the titanium silicide species related to Ti and Si, respectively, therefore suggesting that the stoichiometry of the titanium silicide formed is nearly constant. Finally, with increasing sputtering time, the signals associated with the silicide slowly decrease, and pure Si0 species begin to appear, since no free metallic titanium atoms are available to react with the unlimited silicon supply from the substrate. Angle resolved XPS (ARXPS) shows that the in-depth distribution of the different Si and Ti species formed during IBM is rather homogeneous in the near surface region. Comparison of the experimental ARXPS results with those obtained from TRIDYN simulations suggests that, in addition to pure ballistic ion mixing mechanisms, other radiation-enhanced diffusion processes could contribute considerably to the IBM of Ti/Si interfaces by low-energy Ar+ bombardment at RT.