PROPERTIES AND PREPARATION OF AlN THIN FILMS BY REACTIVE LASER ABLATION WITH NITROGEN DISCHARGE

Abstract

Highly oriented AlN thin films have been deposited on (100) and (111) Si wafers by reactive laser ablation with nitrogen discharge at low substrate temperature. The composition and microstructure of films strongly depend on deposition parameters. X-ray photoelectron spectra showed that nitrogen discharge is of great importance to the composition of the films. The effect of substrate temperature on the preferred orientation of films has been investigated carefully by means of X-ray diffraction. Under optimizing deposition parameters — 1.0 J/cm 2 laser fluence, 5 Hz pulse frequency, 100 mTorr nitrogen pressure, 650 V discharge voltage and 200°C substrate temperature — the AlN films deposited on silicon substrates were smooth, dense and stoichiometric with very good preferred orientation. The orientation relationships between films and substrates were AlN(100)//Si(100) and AlN(110)//Si(111). The average refractive index was found to be 2.05 with the usage of an ellipsometer. The films had a band gap of 6.2 eV as measured by UV–visible absorption. The IR spectrum had an absorption characteristic of AlN. Examination of electric properties of films that was carried out on the metal–insulator–semiconductor structure of Au/AlN/Si showed that the dielectric constant, resistivity and breakdown field were 8.3, 2 × 1013 Ω· cm and 3 × 106 V/cm , respectively.