Texture evolution in metal nitride (aluminum nitride, titanium nitride, hafnium nitride) thin films prepared by off-normal incidence reactive magnetron sputtering
We studied the development of crystallographic texture in aluminum nitride (AlN), titanium nitride (TiN) and hafnium nitride (HfN) films deposited by off-normal incidence reactive magnetron sputtering at room temperature in N2/Ar mixtures. Texture measurements were performed by x-ray pole figure analysis of the (0002) (AlN), (111) and (200) (TiN and HfN) diffraction peaks. We report a strong dependence of fiber texture tilt angle on the angle of deposition and gas composition in AlN. We present a Monte Carlo simulation model to describe the phenomenon of sudden c-axis (0002) AIN tilt. The model is based on the competition among grains with tilted and non-tilted orientations due to mobility difference on the islands and shadowing effects. For a deposition angle of 40° from substrate normal, we found that TiN orientation is close to the substrate normal and TiN orientation is close to the direction of the deposition source, showing substantial in-plane alignment. We also introduced a 150 eV ion beam at 55° with respect to substrate normal during RF sputtering of TiN. Ion beam enhancement caused TiN to align its out-of-plane texture along orientation. For comparison, we found that HfN deposited at 40° without ion bombardment has a strong orientation parallel to the substrate normal. We also prepared HfN films with and without added oxygen during RF sputtering. As the oxygen partial pressure is increased in the range of 10-7 to 10-6 Torr, HfN out-of-plane orientation changed to with a substantial in-plane alignment in direction as well. We attribute the existence of biaxial texture formation in thin films to kinetic constraints such as geometrical confinements and limited adatom surface diffusions due to oxygen or water vapor presence during deposition. When thermodynamics rather than kinetics controls the texture formation, as in the case of HfN and ion beam assisted deposition (IBAD) of TiN, films have strong fiber textures with thermodynamically favored orientations normal to the substrate.
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