Effects of high-flux low-energy (20–100 eV) ion irradiation during deposition on the microstructure and preferred orientation of Ti0.5Al0.5N alloys grown by ultra-high-vacuum reactive magnetron sputtering

The effects of incident ion/metal flux ratio Ji/JMe and ion energy Ei on the microstructure, texture, and phase composition of polycrystalline metastable Ti0.5Al0.5N films produced by reactive magnetron sputtering have been investigated using x-ray diffraction (XRD), plan-view and cross-sectional transmission electron microscopy, and Rutherford backscattering spectroscopy. The films, typically ≂1 μm thick, were deposited at a pressure of 20 mTorr (2.67 Pa) in pure N2 on thermally oxidized Si(001) substrates at 250±25 °C. The N2+ ion flux to the substrate was controlled by means of a variable axial magnetic field superimposed on the permanent magnetic field of the magnetron. Films deposited at Ei=20 eV (≂10 eV per incident accelerated N) with Ji/JMe=1 exhibited a complete (111) texture with a porous columnar microstructure and an average column size of ≂30 nm. Increasing Ei from 20 to 85 eV, while maintaining Ji/JMe constant at 1, resulted in a small change in texture as the XRD intensity ratio I002/(I111+I002) increased from ≂0 to 0.14, a decrease in average column size to 25 nm, and a reduction in intracolumn porosity. The stoichiometric ratio N/(Ti+Al) increased from 1 at Ei=20 eV with Ji/JMe=1 to 1.23 at Ei=85 eV indicating trapping of excess N while the lattice constant a0 increased from 0.4157 to 0.4188 nm due to compressive stress. Ei values ≥100 eV led to alloy phase separation. In contrast, maintaining Ei at ≂20 eV and increasing Ji/JMe from 1 to ≥5.2 resulted in a change from a porous (111) texture to a dense completely (002)-oriented microstructure with an increase in the average column size to 35 nm. N/(Ti+Al) and a0 remained essentially constant and the alloy remained single phase. Mechanistic pathways leading to microstructure and texture changes through variations in Ei at constant Ji/JMe and in Ji/JMe at constant Ei were found to be quite different. The average energy deposited per metal atom, 〈Ed〉=Ei(Ji/JMe), is therefore not a universal parameter, as has been previously proposed, for describing film growth.