Investigation of reactively sputtered silicon nitride films by complementary use of backscattering and nuclear-reaction microanalysis results

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Abstract
The composition and properties of silicon nitride layers deposited by dc reactive sputtering in a mixture of argon and nitrogen slightly contaminated by oxygen traces were studied. Both MeV 4He backscattering and direct observation of nuclear reactions on nitrogen and oxygen were used to analyze the deposits. The films appear uniform with depth. Their stoichiometry and the incorporations of oxygen and argon vary with the partial pressure PN2 of nitrogen. For small values of PN2 there is a large amount of argon (Ar/Si=11%), while the oxygen amounts are low (O/SiPN2 increases, an abrupt decrease of argon incorporation (down to Ar/Si 5 2%) is associated with an abrupt increase of oxygen incorporation (up to O/Si=15%). The N/Si ratio increases practically linearly with PN2 up to a saturation value of 1.5 corresponding to an excess of nitrogen with respect to stoichiometric Si3N4. Argon incorporation does not seem to have a large effect on properties of the films such as etching rate, resistivity, and thermal stability which appear, on the other hand, strongly dependent on the N/Si and O/Si values. The mechanisms of dc reactive sputtering are discussed in light of the results.

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