Effect of exposure parameters and annealing on the structure and morphological properties of nanopatterned sapphire substrates prepared by solid state reaction

Nanopatterned sapphire substrates were prepared by solid state reaction of patterned Al films obtained by E-Beam lithography of a PMMA/copolymer bilayer resist and lift-off. The effect of exposure parameters and annealing on the structure and morphological properties of nanopatterned sapphire substrates prepared by solid state reaction were investigated by a scanning electron microscope (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), and Raman, respectively. The circular Al patterns with diameter/spacing being 500 nm/1000 nm were obtained by optimal exposure diameter/exposure dosage of 400 nm/200 μC/cm2. Patterned Al films were subsequently subjected to solid state reaction by dual stage annealing due to the melting temperature of Al thin films (660 °C). The hillocks formation on Al films was minimized with an oxidation anneal at 450 °C. Moreover, the little change in the morphology of Al patterns was observed after annealing at 450 °C. The SEM and AFM results show the patterns were retained on sapphire substrates after high temperature annealing at less than 1200 °C. The XRD and Raman results reveal that the composition and orientation of island patterns prepared by solid state reaction for 24 h at 450 °C, and 1 h 1000 °C were the same as that of the sapphire (0001) substrates.