Development of preferred orientation in polycrystalline NaCl-structure δ-TaN layers grown by reactive magnetron sputtering: Role of low-energy ion surface interactions

We have investigated the effects of low-energy ion irradiation on texture evolution during growth of B1–NaCl-structure polycrystalline δ-TaN layers on SiO2 by ultra-high-vacuum reactive magnetron sputter deposition at 350 °C in mixed Ar+15%N2 discharges. In parallel sets of experiments, the ion-to-metal flux ratio Ji/JTa was varied from 1.3 to 10.7 while maintaining the incident ion energy Ei constant at 20 eV, and Ei was varied from 8.5 to 30 eV with Ji/JTa=10.7. All TaN layers, irrespective of Ji/JTa or Ei, were overstoichiometric with N/Ta=1.13±0.03. Layers grown with Ei=30 eV are multiphase consisting of hexagonal ε-TaN and δ-TaN, while those grown with Ei⩽20 eV are single-phase δ-TaN. With Ei=8.5 eV, the δ-TaN layers have a mixed 111/002/022/113 texture, even for film thicknesses t up to 500 nm. In contrast, δ-TaN layers deposited with Ei=20 eV initially exhibit competitive texture evolution until a single texture dominates at t≳200 nm. The preferred orientation of 500-nm-thick Ei=20 eV layers can be selectively and continuously varied from predominantly 111 to nearly complete 002 by increasing Ji/JTa from 1.3 to ⩾ 7.4. The change in texture is primarily due to an increased steady-state atomic N coverage, resulting from collisionally induced dissociative chemisorption of incident energetic N2+ ions, with increasing Ji/JTa. 111-oriented δ-TaN layers are underdense with both inter- and intracolumnar porosity and a tensile stress of ≃ 1.4 GPa, while 002-oriented layers are fully dense and have small compressive stresses, ≲ 0.7 GPa.