Ar and excess N incorporation in epitaxial TiN films grown by reactive bias sputtering in mixed Ar/N2 and pure N2 discharges

Abstract

Epitaxial TiN films were grown on (100), (110), and (111) oriented MgO by reactive magnetron sputtering from a Ti target in both mixed Ar/N2 and pure N2 discharges. An applied negative substrate bias Vs (0≤Vs≤600 V) was used to vary the flux and energy of impinging Ar+ and/or N+2 ions. The film microstructure was analyzed by transmission electron microscopy and electron channeling and the relative concentration CAr of trapped Ar was measured by energy-dispersive x-ray analysis. For a given value of Vs, CAr initially increased with increasing substrate temperature Ts above the epitaxial temperature Te∼550 °C due to more efficient Ar channeling as the crystals became better ordered. However, CAr reached a maximum for all film orientations at Ts∼750 °C and decreased at higher Ts due to Ar loss by segregation to the surface and desorption. At a given Ts and Vs, CAr increased with the channel width in the order: (110)>(100)>(111). Gas bubbles formed in films deposited at 550≤Ts<800 °C and 400≤Vs≤600 V due to precipitation from a supersaturation of implanted Ar and/or N. The most stable shape for pure N2 bubbles was observed to be a {100} cube with {110} and, to a lesser extent, {111} facets indicative of anisotropy in TiN surface energies γ with γ100<γ110<γ111. The spacing of moiré fringes observed in transmission electron micrographs indicated that in at least some N2 bubbles, nitrogen was present in the face-centered-cubic solid phase.