Tantalum Films Triode-Sputtered in Mixtures of Argon and Water Vapor

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Abstract
Tantalum films have been deposited in a triode sputtering system operating at a total pressure of 5×10−4 Torr that was maintained by continuously adding an argon-water vapor mixture. Because of the low operating pressure, a mass spectrometer mounted directly in the chamber was used, without any differential pumping, to monitor mass spectra before, during, and after sputtering. The mass spectra show that the water vapor is dissociated in the discharge, and the resultant oxygen is gettered into the film. The oxygen content of the films was determined from the anodization efficiency, and it increased linearly with the inlet rate of water vapor. Measurements of the electrical properties show that the oxygen is incorporated in the films in the same way for water vapor and oxygen doping. The resistivity is increased from 50 to 1014μΩ cm with increasing oxygen content. The rapid increase in resistivity from 50 to 200 μΩ cm between 4 and 11 at.% is due to the change from bcc to the β-Ta structure. These results show that very low outgassing rates of water vapor may be sufficient to produce β-Ta in many sputtering systems.

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