Composition changes in N 2+ bombarded Ti/Si bilayers and multilayers: interplay between random and chemically guided effects

We have studied with Auger Electron Spectroscopy and Rutherford Backscattering Spectrometry the composition changes in Ti/Si bilayers and multilayers (Ti at the surface) induced by bombardment with 30 keV N ₂⁺ ions. In addition, the chemical bonding was investigated by Auger line-shape analysis. In N ₂⁺-bombarded systems the changes in the Si profiles and line shapes point to a sequence of chemical environments with SiN bonds near the Ti/Si interface, quasi-elemental Si plus overstoichiometric TiN at intermediate depths, and SiTi bonds near the surface. There is thus extensive transport of Si towards the surface. We conclude that chemistry plays at least four different roles in the system Ti/Si: chemically enhanced transport (Si in TiN), chemically inhibited transport (Si in Ti), bond formation in a binary situation (SiTi), and bond formation in a ternary situation (TiN). The latter case could also be described as preferentiality in bond formation (TiN but not Si ₃N ₄).