Epitaxial growth of TiZrNbTaN films without external heating by high-power impulse magnetron sputtering

In this work, we demonstrate epitaxial growth of multiprincipal-element alloy TiZrNbTa nitride thin films at substrate temperature below 50 degrees C. They were deposited on c-plane sapphire substrates by reactive high-power impulse magnetron sputtering (HiPIMS) without external heating. Reference layers were also grown by direct current magnetron sputtering (DCMS) at 400 degrees C as well as without external heating on the same type of substrates. X-ray diffraction and transmission electron microscopy analysis showed single phase films, with the HiPIMS films having a reduced mosaicity along both in-plane and out-of-plane orientations as compared to the DCMS layers grown at 400 degrees C. The optical and electrical properties determined by spectroscopic ellipsometry and room-temperature four-point probe measurements showed that the HiPIMS films exhibit higher absorbance in the near-infrared wavelength and higher electrical resistivity than the DCMS films deposited at 400 degrees C. Furthermore, ion-beam analysis of the HiPIMS grown films revealed nitrogen-to-metal ratio close to unity. This study shows that epitaxial film growth of multiprincipal-element nitrides can be realized without the need of intentional substrate heating provided that the growing film surface is irradiated by metal ions. This reduces the total process energy consumption by similar to 50 % (as compared to DCMS film at 400 degrees C) with the added benefit of possibility to grow film on temperature-sensitive substrates.