Photochemical vapor deposition of Al thin films on Ti, TiO2, and Pd surfaces

Al thin films were deposited via photochemical vapor deposition on catalytic layers of Ti, TiO2, and Pd, using dimethylaluminum hydride. Deposition was carried out at low gas pressures to induce a surface reaction based on adsorption and subsequent decomposition of adsorbates. Of these three layers Ti was so effective as a catalyst that the Al films were thermally deposited even at a low substrate temperature of 60°C with a growth rate of 0.5 nm/min. The UV light generated by a deuterium lamp helped increase the growth rates. On the other hand, Al could be deposited on TiO2 layers only under irradiation at a substrate temperature of 120°C. It took several minutes to cover the TiO2 surface with Al and initiate the Al filmʹs growth. An entirely opposite result was observed for Al deposition on Pd layers. Here, the UV light inhibited the Al growth on the surface, whereas the films were deposited thermally. X-ray photoelectron spectroscopy showed the formation of a photolytic production of the adsorbate, which acts presumably as a center that inhibits further Al growth.