Structural, optical and electronic properties of oxidized AlN thin films at different temperatures

We report on the properties of a novel insulator, AlO:N for application in semiconductors produced by thermally oxidizing AlN thin films. The process steps were similar to those used for SiO2, creating the possibility of a new technology for metal-insulator-semiconductor field effect devices and integrated circuits. Thin films of AlN were deposited by radio-frequency magnetron reactive sputtering on p-type silicon or fused quartz substrates. As-deposited AlN film thickness ranged from 0.05 to 0.7 mu m, with polycrystalline structure revealed by x-ray diffraction. Oxidation was performed under O-2 flow at 800 to 1100 degrees C for 1-4 h. AlN films were oxidized partially or fully into Al2O3, depending on initial thickness, oxidation temperature and time. X-ray diffraction indicates the presence of several phases of Al2O3 at 1000 degrees C, whereas at 1100 degrees C, only the alpha-Al2O3 phase was found. Considering the importance of surface field effect device applications, the surfaces of oxidized films were examined with atomic force microscopy in air, and a clear change was observed in the surface structure of the oxidized film from that of as-deposited ALN films. Capacitance-voltage measurements of metal-oxide-semiconductor structures yielded a dielectric constant of AlO:N between 8-12 and a net oxide-trapped-charge density of similar to 10(11) cm(-2). Using Fourier transform infrared spectrometry transmittance and reflectance, some alpha-Al2O3 modes were observed. In this paper, we describe the general properties of the oxide thin films, bulk and interface, at different temperatures.