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

摘要

We have investigated the effects of low-energy ion irradiation on texture evolution during growth of B1-NaCl-structure polycrystalline δ-TaN layers on SiO_(2) by ultra-high-vacuum reactive magnetron sputter deposition at 350℃ in mixed Ar+15 N_(2) discharges. In parallel sets of experiments, the ion-to-metal flux ratio J_(i)/J_(Ta) was varied from 1.3 to 10.7 while maintaining the incident ion energy E_(i) constant at 20 eV, and E_(i) was varied from 8.5 to 30 eV with J_(i)/J_(Ta)=10.7. All TaN layers, irrespective of J_(i)/J_(Ta) or E_(i), were overstoichiometric with N/Ta=1.13±0.03. Layers grown with E_(i)=30 eV are multiphase consisting of hexagonal ε-TaN and δ-TaN, while those grown with E_(i)≤20 eV are single-phase δ-TaN. With E_(i)=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 E_(i)=20 eV initially exhibit competitive texture evolution until a single texture dominates at tapprox.>200 nm. The preferred orientation of 500-nm-thick E_(i)=20 eV layers can be selectively and continuously varied from predominantly 111 to nearly complete 002 by increasing J_(i)/J_(Ta) 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 N_(2)~(+) ions, with increasing J_(i)/J_(Ta). 111-oriented δ-TaN layers are underdense with both inter- and intracolumnar porosity and a tensile stress of approx-1.4 GPa, while 002-oriented layers are fully dense and have small compressive stresses, approx.<0.7 GPa.