Effects of metal redeposition in plasma sputtering

Ion sputtering, whereby atoms on target surfaces are bombarded by energetic ions, is a key process in the film-coating industry. However, its detailed mechanism has not yet been clarified and remains an empirical operation. This article demonstrates that the redeposition of metal on the target surface significantly enhances the sputtering rate. Although the effect differs depending on the metal species, significant enhancement in the sputtering rate occurs in glow-discharge plasma sputtering––a maximum increase of approximately 2.4 times was observed under experimental conditions. The experimental data agree well with the model equation, which superimposes two processes: sputtering by the desorbed redeposited metal and reduction of the enthalpy of sublimation by the adsorbed redeposited metal. The results of this study demonstrate that the metal redeposition effect is a key mechanism missing in the plasma sputtering process and that taking redeposition into account frees us from its empirical use. These findings are expected to address several of the existing questions related to sputtering, enabling the development of a wide variety of applications.