Broad Beam Plasma Enhanced Low-Temperature Growth of Oriented Aluminum Nitride Thin Films

Aluminum nitride (AlN) thin films with (0002) orientation have exceptional piezoelectric and optoelectronic properties for various applications. It remains challenging to grow highly oriented AlN films at low temperature (e.g., below 200 °C) using conventional magnetron sputtering. This study introduces a broad beam ion source-enhanced pulsed DC magnetron sputtering, which enables the growth of (0002) preferentially oriented polycrystalline AlN films at room temperature. The effects of the ion energy and ion flux on surface roughness, crystal orientation, and piezoelectric properties are systematically studied. The film crystallinity is significantly improved under an optimum ion energy; X-ray diffraction shows that the full width at half-maximum (FWHM) of the (0002) peak decreases from 0.7298 to 0.3751°. The average surface roughness is reduced from 2.65 to 0.95 nm. The effective piezoelectric d₃₃^eff value increases from 1.69 to 6.06 pm/V. These findings demonstrate that the ion beam facilitates crystal growth under nonthermal equilibrium conditions, offering significant advantages over conventional thin film growth.