Preparation of scandium aluminum nitride thin films by using scandium aluminum alloy sputtering target and design of experiments

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Scandium aluminum nitride alloy (ScxAl1−xN) thin films were prepared using rf magnetron sputtering with a scandium aluminum alloy (Sc0.42Al0.58) target on n-type (100) silicon substrates. We have investigated the effects of 4 sputtering control factors, which are substrate temperature, sputtering pressure, nitrogen (N2) concentration and cathode power, on the piezoelectric constant d33 of ScxAl1−xN films using design of experiments. Consequently, it is statistically proved that N2 concentration in sputtering gas is the most important control factor. The piezoelectric constant d33 indicates the maximum value of 19.0 pC/N at N2 concentration of 25%. The composition of ScxAl1−xN films prepared under optimized sputtering conditions is Sc0.38Al0.62N, and there is the composition difference between the ScAl alloy target and the thin film. However, the piezoelectric constant of the Sc0.38Al0.62N film is coincident with that of Sc0.38Al0.62N films prepared by dual co-sputtering. Thus, it is possible to prepare high piezoelectric ScxAl1−xN films by using the ScAl alloy sputtering target. ScAl alloy targets are effective for keeping scandium concentration constant in ScxAl1−xN thin films.