Paper EM-WeM5
Epitaxial CVD of Metallic HfB2 on SiC Substrates

Wednesday, October 17, 2007, 9:20 am, Room 612

HfB2 is an attractive candidate for many technological applications owing to its refractory melting temperature (3250°C), high mechanical hardness (29 GPa), low electrical resistivity (15 μΩ-cm), high optical reflectivity, and chemical inertness at high temperatures. The epitaxial growth of HfB2 is particularly interesting because the (0001) plane has a small lattice mismatch with the compound semiconductors GaN (1.5%) and SiC (-2%) and the coefficients of thermal expansion are reasonably close for these three materials. In principle, epitaxial HfB2 could be used as a growth template and/or as an electrical contact in a multilayer compound semiconductor device while maintaining crystallographic continuity. We report that high quality HfB2 thin films can be deposited on SiC(0001) substrates by chemical vapor deposition using the single source precursor Hf(BH4)4. This precursor is a solid which sublimes at room temperature with a vapor pressure of 15 Torr, such that no carrier gas or heated delivery lines are needed; and it contains no organic or halogen groups. The HfB2 microstructure is strongly dependent on temperature. Films deposited at low substrate temperature are (0001) textured and polycrystalline, as indicated by SEM and XRD analysis. An increase of deposition temperature increases the grain size and reduces the mosaic spread. Films deposited under optimal deposition conditions are extremely flat. The (0001) rocking curve has a FWHM of only 0.26°, indicating a very high epitaxial quality. The room temperature resistivity is < 20 μΩ-cm, close to the bulk value. The surface morphology of the epitaxial film is sensitive to the surface finish of the SiC substrate: film coalescence can be delayed by substrate surface imperfections.