Thermodynamic and experimental investigations on the growth of thick aluminum nitride layers by high temperature CVD

To achieve AlN bulk growth, high temperature CVD process using chlorine chemistry was investigated. High growth rate and high crystalline quality are targeted for both polycrystalline and epitaxial AlN films grown on (0 0 0 1) αα-Al2O3Al2O3 Sapphire and (0 0 0 1) off axis 4H SiC or on axis 6H SiC single crystal substrates. Thermodynamic calculations were carried out to select the more appropriate inert materials for the reactor and to understand the chemistries of Al chlorination and AlN deposition steps. The reactants were ammonia (NH3NH3) and aluminum chlorides (AlClxAlClx) species formed in situ   using chlorine gas (Cl2Cl2) reaction with high purity Al wires. Deposition temperature was varying from 1100 to 1800∘C. Influences of temperature, total pressure, Cl2Cl2 flow rate and carrier gas (Ar or H2H2) on growth rate, surface morphology and crystalline state are presented. As results, films morphology is related to a variation of the thermodynamic supersaturation. As-grown AlN layers surface morphologies were studied by SEM, FEG-SEM and AFM. Crystalline state, crystallographic orientations and epitaxial relationships with substrates were obtained from θ/2θθ/2θ X-ray diffraction and X-ray pole figure, respectively. Growth rates up to 200μmh−1 have been reached for polycrystalline AlN layers.