Ion-assisted low-temperature (≤ 150 °C) epitaxial growth of TiN on Cu by reactive magnetron sputter deposition

Abstract

TiN films were grown at ≤ 150°C on polycrystalline Cu substrates, with grain sizes of 10–30 μm, by magnetically-unbalanced reactive magnetron sputtering in mixed Ar/N 2 discharges. The applied negative substrate bias V s and the ion/metal ratio J i/ J Ti incident at the growing film (> 96% of the ions were Ar +) were varied independently: V s = 0–300 V with J i/ J Ti = 0.4, and J i/ J Ti = 0.4–9 with V s = 100 V. Films grown with J i/ J Ti = 0.4 were polycrystalline, with average grain sizes < d〉 much smaller than underlying Cu grains, and underdense. Increasing V s, at J i/ J Ti = 0.4, increased 〈 d〉 from 10 to 20 nm and resulted in densification, although intercolumnar boundaries remained partially voided. Unbiased J i/ J Ti = 0.4 films were randomly oriented while biased samples grew epitaxially with the underlying grains for thicknesses up to ∼30 nm before the growth front gradually broke down locally to initiate competitive columnar growth. In sharp contrast, TiN films grown with J i/ J Ti≥4 and V s = 100 V were found to be dense and to grow completely epitaxially over entire Cu grains. In addition to (001) “cube-on-cube” epitaxy, more complex relationships were observed on differently oriented Cu grains in which the TiN overlayers exhibited self-organized crystallographic tilts and/or rotations in order to reduce interfacial misfit and, hence, long-range epitaxial strain. Examples are (001) TIN||(011) Cu with [100] TIN||[21̄1] Cu and (001) TIN||(011) Cu with [01̄1] TIN||[100] Cu.