Texture and Stress Evolution in HfN Films Sputter-Deposited at Oblique Angles

In this study, polycrystalline hafnium nitride (HfN) thin films were grown by oblique angle deposition (OAD) technique to investigate the relationship between column tilt angle, texture development and residual stress evolution with varying inclination angle alpha of the substrate. The films (-1 mu m thickness) were grown at various angles (alpha = 5 degrees, 25 degrees, 35 degrees, 65 degrees, 75 degrees, and 85 degrees) with respect to the substrate normal by reactive magnetron sputtering at 0.3 Pa and 300 degrees C. The film morphology, crystal structure and residual stress state were characterized by scanning electron microscopy and X-ray diffraction (XRD), including pole figure and sin(2)psi measurements. All HfN films had a cubic, NaCl-type crystal structure with an [111] out-of-plane orientation and exhibited a biaxial texture for alpha >= 35 degrees. XRD pole figures reveal that the crystal habit of the grains consists of {100} facets constituting triangular-base pyramids, with a side and a corner facing the projection of the incoming particle flux (indicative of a double in-plane alignment). A columnar microstructure was formed for alpha >= 35 degrees, with typical column widths of 100 nm. It is observed that the column tilt angle beta increases monotonously for alpha >= 35 degrees, reaching beta = 34 degrees at alpha = 85 degrees. This variation at microscopic scale is correlated with the tilt angle of the (111) crystallographic planes, changing from -24.8 to 11.3 degrees with respect to the substrate surface. The residual stress changes from strongly compressive (-5 GPa at alpha = 5 degrees) to negligible or slightly tensile for alpha >= 35 degrees. The observed trends are compared to previous works of the literature and discussed based on existing crystal growth and stress models, as well as in light of energy and angular distribution of the incident particle flux calculated by Monte Carlo. Importantly, a decrease of the average kinetic energy of Hf particles from 22.4 to 17.7 eV is found with increasing alpha due to an increase number of collisions.