Two-step method for the deposition of AlN by radio frequency sputtering

article i nfo This paper presents a detailed study of the influence of deposition conditions on structural and morphological properties of AlN thin films synthesized on c-sapphire substrates by radio frequency (RF) reactive sputtering. After the optimization of deposition parameters such as RF power and substrate temperature, the substrate bias has been identified as a critical variable to improve the structural properties of the AlN layers. The use of neg- ative bias leads to a decrease of the full-width at half-maximum (FWHM) of the rocking curve of the AlN­(0002) x-ray reflection and an increase of the grain size. However, 2θ/ω x-ray scans of layers grown under negative bias reveal lattice disorder at the AlN/sapphire interface, which is attributed to the highly accelerated positive ions (Al + ,N + ,N 2 + ) arriving to the substrate at the initial stages of the deposition process. In order to prevent this in- terface degradation, we propose a two­step deposition method which consists of starting the growth with an un- biased AlN buffer layer, at least 30 nm thick, followed by AlN deposition under negative bias. This procedure results in high-quality AlN layers with FWHM of the rocking curve of the (0002) reflection of 1.63°, grain size of ~40 nm and root-mean-square surface roughness of 0.4 nm.