Monitoring of the Initial Stages of Diamond Growth on Aluminum Nitride Using In Situ Spectroscopic Ellipsometry

The high thermal conductivity of polycrystalline diamondmakesit ideally suited for thermal management solutions for gallium nitride(GaN) devices, with a diamond layer grown on an aluminum nitride (AlN)interlayer atop the GaN stack. However, this application is limitedby the thermal barrier at the interface between diamond and substrate,which has been associated with the transition region formed in theinitial phases of growth. In this work, in situ spectroscopic ellipsometry(SE) is employed to monitor early-stage microwave plasma-enhancedchemical vapor deposition diamond growth on AlN. An optical modelwas developed from ex situ spectra and applied to spectra taken insitu during growth. Coalescence of separate islands into a singlefilm was marked by a reduction in bulk void fraction prior to a spikein sp(2) fraction due to grain boundary formation. Parametersdetermined by the SE model were corroborated using Raman spectroscopyand atomic force microscopy.