Metalorganic chemical vapor deposition of aluminum from methylpyrrolidine alane complex

The low pressure chemical vapor deposition (CVD) of Al metal using a recently developed metalorganic precursor, methylpyrrolidine alane (MPA) complex, has been studied. Al films were deposited by thermal and laser assisted processes and characterized by various surface analytical techniques. The growth of Al films is strongly dependent on the nature of the substrate surface, showing deposition selectivity. In general, Al films deposit easily on metallic substrates such as TiN and Cu, but not on semiconducting and dielectric substrates such as Si and SiO2. The film growth typically follows a 3-D nucleation mode. The discrete Al islands form on the substrate initially and then coalesce to produce continuously Al films. It is believed that the deposition selectivity is closely related to the wettability and reactivity of the substrate. The metal substrates can lower the nucleation barrier and catalyze the deposition reaction. The growth of Al films on transition metal oxides suggests that the oxidation-reduction reaction between the precursor and the substrate occurs on the surface. Al deposition on metallic surfaces starts at ∼100°C and the growth rate increases with the substrate temperature. Above ∼180°C, the growth rate saturates at about 90-100 nm/min and even decreases with temperature due to the dissociation of precursor in the gas phase. Al films deposited on TiN are carbon-free and do not have preferred orientations. The surface roughness of films increases as the deposition proceeds. The laser deposition of Al is likely a hybrid of the pyrolytic and photolytic processes. The film growth and microstructure are strongly dependent on the laser power and irradiation time. The deposition rate increases linearly with the laser power and ranges 0.2-1.3 mum/min within experimental conditions. The laser deposition rate is much higher than that of a thermal CVD process. The Al dot grows in thickness as well as in diameter during the laser irradiation. The surface roughness increases rapidly during deposition and the grain size reaches 1-2 mum.