Effect of Substrate Bias on Tantalum Films Sputtered in an Oxygen-Argon Mixture

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Abstract
Tantalum films have been deposited on biased glass and ceramic substrates by dc sputtering in an oxygen-argon mixture The resistivity of the films was approximately 800 μΩ cm when the substrate bias was zero, but decreased when either positive or negative potential was applied to the substrate. Resistivities of approximately 200 μΩ cm were obtained by applying +100 and −100 V, and resistivities as low as 50 μΩ cm were obtained at a substrate bias of −200 V. The oxygen content of the films, measured by an anodization technique, was approximately 35 at.% on unbiased substrates but decreased with substrate bias. While films deposited at −100 V bias contained approximately 10 at.% oxygen, only half of this amount was present in those deposited at +100 V. The reduction in oxygen content, and thus in resistivity, can be explained by a combination of two effects. For positive and low negative bias, increased gettering due to enhanced sputtering rate is most important, but for higher negative bias, removal of oxygen by argon-ion sputtering is also important.

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