Thickness dependence of Al <inf>0.88</inf> Sc <inf>0.12</inf> N thin films grown on silicon

The thickening behavior of aluminum scandium nitride (Al 0.88 Sc 0.12 N) films grown on Si(111) substrates has been investigated experimentally using X-ray diffraction (XRD), transmission electron microscopy (TEM), atomic force microscopy, and residual stress measurement. Al 0.88 Sc 0.12 N films were grown with thicknesses spanning 14 nm to 1.1 μm. TEM analysis shows that the argon sputter etch used to remove the native oxide prior to deposition produced an amorphous, oxygen-rich surface, preventing epitaxial growth. XRD analysis of the films show that the AlScN(002) orientation improves as the films thicken and the XRD AlScN(002) rocking curve full width half maximum decreases to 1.34° for the 1.1 μm thick film. XRD analysis shows that the unit cell is expanded in both the a- and c-axes by Sc doping; the a-axis lattice parameter was measured to be 3.172 ± 0.007 Å and the c-axis lattice parameter was measured to be 5.000 ± 0.001 Å, representing 1.96% and 0.44% expansions over aluminum nitride lattice parameters, respectively. The grain size and roughness increase as the film thickness increases. A stress gradient forms through the film; the residual stress grows more tensile as the film thickens, from −1.24 GPa to +8.5 MPa.