Influence of Surface Absorption Characteristics on Reactively Sputtered Films Grown in the Biased and Unbiased Modes

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Abstract
A series of metals have been reactively sputtered in N2–Ar mixtures. The results indicate that surface adsorption characteristics greatly influence compound growth and/or gas incorporation. It will be shown that the functional relationship between the measured nitrogen concentrations and P N2 places these metals into one of three groups: (1) metals which chemisorb molecular nitrogen and form a nitride, e.g., W; (2) metals which do not chemisorb nitrogen but form a nitride, e.g., Ni; and, (3) metals which neither chemisorb nitrogen nor form a nitride, e.g., Au. It will also be shown that bias sputtering causes the nitrogen content of tungsten and nickel to decrease while it causes the nitrogen content of gold to increase. The increase for gold is caused by bombardment of the film with energetic N2 +, which results in increased sorption of nitrogen. The same effect is present in tungsten and nickel but is overshadowed by resputtering of the previously sorbed nitrogen. It is suggested that the high sputtering yield found for chemisorbed gases is related to a poor mass fit between the sorbed atoms and the metal lattice.