| Thin films of AlN are of current interest for a wide variety of engineering applications: piezoelectric devices, optical waveguides, coatings on lenses and mirrors, a transparent insulator for high power laser applications, and as a refractory. In this study, AlN films were grown by reactive rf sputter deposition using an Al target in a nitrogen-bearing discharge. The effect of various nitrogen/argon atmospheres, cathode voltage, and base pressure were investigated. Depositions were made on water-cooled (111)-cut silicon, Suprasil 2, and glass substrates.; Optical emission spectroscopy was used to study the aluminum and nitrogen species in the plasma. The results show that AlN was formed at the target surface. Al atoms and AlN molecules were sputtered from the target and arrived at the substrate. N(,2)('+) molecules striking the substrate surface dissociated and combined with the adsorbed aluminum to form AlN. Therefore, the amount of N(,2)('+) in the plasma controlled the amount of excess Al in the films.; After deposition the films were analyzed by XPS, SEM, x-ray diffraction, and optical spectroscopy in the IR-VIS-UV. All films were found to be AlN with excess Al present. Crystallographic orientation was dependent on the amount of nitrogen in the plasma. Films deposited in pure nitrogen were orientated with 0002 planes parallel to the substrate. As the nitrogen concentration in the plasma was decreased, films became randomly orientated.; In addition to excess Al oxygen was present as an impurity. The impurity concentration was independent of base pressure. The amount of incorporated oxygen was dependent on film micro-structure. Upon exposure to the atmosphere oxygen diffused along the grain boundaries and combined with Al at the surface to form aluminum oxide.; In this study, the fundamental processes necessary to reproducibly grow AlN films with properties identical to the bulk are defined. This was achieved by: (1) Investigating the effect of three processing parameters on film chemistry, crystallography, and microstructure. (2) Associating each processing parameter with a discharge chemistry range. These results can be applied to the reactive sputter deposition of other metal nitrides in which the metal can not chemisorb N(,2). |
