Effect of H Plasma Treatment of the Nucleation Layer on AlN Epitaxy in Microwave Plasma Chemical Vapor Deposition

The crystallinity of nucleation layers has significant influence on the crystallinity of aluminum nitride (AlN) epilayers. In this work, the etching effect of hydrogen (H) plasma was used to improve the nucleation-layer crystallinity. AlN nucleation layers were first cooled in a H-plasma atmosphere; then, AlN films were deposited on the processed nucleation layers, and the whole epitaxial process was carried out in high-temperature microwave plasma chemical vapor deposition (MPCVD) without the participation of ammonia. X-ray rocking curves (XRCs) showed that the cooling process obviously improved the crystal quality of AlN films, which was attributed to the preferential etching effect of H plasma on low-crystallinity nucleation islands. When a H2 flow rate of 135 sccm was used to process the nucleation layer, the AlN film with the narrowest (002) XRC full width at half-maximum (FWHM) of 86 arcsec was obtained. Possible growth mechanisms were suggested for the observations.