Influence of composition and growth conditions on TiN nanocrystallite formation in TiN-metal films

Abstract

The nanostructure of Ti in TiN-Cu films grown by Pulsed Layer Deposition (PLD) is investigated using Extended X-Ray Absorption Fine Structure (EXAFS) spectroscopy at the Ti-K edge. The TiN-Cu films were grown on Si (100) crystal wafers using either Ti (99.95%) and Cu (99.99%) elemental targets or a TiCu intermetallic target (99.95%), under flowing N2 (99.999 %). The influence of varying either the Ti concentration or the N2 partial pressure (PN2) was explored in a series of TiN-Cu films, in an effort to distinguish how these parameters affect the degree of TiN nanocrystalline formation. The Ti-K-EXAFS analysis results proposes that the growth of stoichiometric TiN nanocrystallites is favoured in all studied films, however the extent of TiN formation is strongly modulated as a consequence of changing growth conditions and film composition. In particular, when growth proceeds from a TiCu intermetallic target under constant PN2, decreasing the Ti concentration promotes the formation of a (Ti, Cu) solid solution at the expense of the formation of TiN nanocrystallites. Thus, PLD growth using intermetallic targets yields TiN-Cu films with extended TiN nanocrystalline regions embedded in a rich-amorphous Cu phase, where the excess of Ti atoms are also incorporated. When Cu and Ti elemental targets are used (Ti:Cu = 50:50), Ti preferentially bonds to N2 upon increasing PN2. The extent of TiN nanocrystalline formation is enhanced, while bond formation between the unreacted Ti atoms and the amorphous Cu regions is also revealed. Consequently, it can be proposed that a proper control of growth conditions and film composition can permit growth of TiN-metal films with improved mechanical response.