We present results on the investigation of the substrate bias effect on the growth behavior of iridium films deposited on A-plane sapphire by radio frequency (rf) sputtering at low substrate temperatures. Films deposited without substrate bias were compared to films deposited with simultaneous application of a second rf-plasma on the substrate. Resulting films were characterized by scanning electron microscopy, X-ray diffraction, and electron backscattering diffraction. We find that the application of an additional substrate bias has a strong effect on the growth behavior of Ir in such a way that preferential growth of iridium (001) on sapphire (11-20) at high deposition rates and at substrate temperatures as low as 350 degrees C becomes feasible.