In magnetron sputtering with a suitable magnetic field configuration it is also possible to control the microstructure, chemical and phase composition of the growing film. Besides balanced discharges, two types of unbalancements are possible: type I and type II.
In type I, the plasma that is not strongly confined on the target, does not interact with the substrate. This magnetic assessment is specially used for sputtering multi-compositional films containing low melting point elements. In type II the plasma is confined both on the target and in a secondary confinement that bombards the growing film with a flux of ions extracted from the plasma. In such latter case, the ion bombardment has an effect of “plasma washing” of the film in the mean time it grows. Impurities weakly bounded to the film are knocked out from the impinging ions. That results into a strong increase of purity of the films in the substrate regions touched by plasma, while all the rest has higher impurity content. In the magnetron source we built, it is possible to pass from the balanced to unbalanced regime, just changing the magnetic core, without breaking vacuum.
The drawback of magnetically unbalanced configurations is that the plasma cone flushin the substrate has very narrow dimensions.
We have developed an electrostatic imbuto that opens the cone of plasma extending the unbalancement effect to larger dimension substrates.