Deposition of aluminum thin films by photochemical surface reaction

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Abstract
Aluminum thin films have been deposited from dimethylaluminum hydride (DMAlH) on silicon substrates illuminated with a deuterium lamp or an ArF laser. DMAlH was found to be useful as a new source gas for photodeposition of aluminum films at a low carbon level if it was used with photons with wavelengths below 200 nm. Illumination is effective not only to produce films at a substrate temperature lower than required by thermal decomposition, but also to reduce the electrical resistivity of the deposited films. To emphasize surface, rather than gas-phase, reactions, the vapor pressure in a reaction cell was lowered (typically at 6.7×10−3 Pa). Evidence for the photochemical surface reaction has been provided by area selectivity and the time needed to renew the adlayer on the surface. In spite of low vapor pressure, the deposition rate was typically 19 nm/min for the lamp and 0.06 nm/pulse for the laser at a substrate temperature of 200 °C. A rate equation, which included both photodissociation and photoinduced desorption, accounted for the observed dependence of deposition rate on substrate temperature, light intensity, vapor pressure, and laser pulse repetition rate. The role of secondary reactions that follow initial photodissociation was discussed briefly. The electrical resistivity for the film produced at 270 °C under illumination was 6.2 μΩ cm, while a much higher resistivity of 140 μΩ cm was observed for a thermally grown film. The carbon level was low (2–3%) in agreement with the low film resistivity. The surface was rough, leaving room for improvement.