Unbalanced magnetron sputtering with auxiliary cathode

Abstract

An improved unbalanced magnetron sputtering (UMS) apparatus in accordance with the invention having a conventional target and arrangement of magnets wherein a central portion of the target is backed by a first magnetic pole and the peripheral portion of the target is backed by a second magnetic pole, the poles carrying unequal numbers of lines of magnetic flux. One of the poles has a greater number of flux lines entering or leaving than does the other pole. The field lines extending from the higher flux pole which do not close in the lower flux pole extend into space in a range of directions and generally toward a substrate to be sputter coated. Adjacent the target and electrically isolated therefrom and overlying the higher flux pole is an independently-controllable auxiliary electrode, preferably a cathode, formed of a non-ferromagnetic material and having a surface facing in the same general direction as the sputterable surface of the target. Electrons emitted from the auxiliary electrode are controlled at an energy level optimal for ionization of the working gas. These electrons are not constrained near the surface of the cathode but instead may migrate freely along the field lines toward the substrate, resulting in increased plasma density throughout the coating range, especially in the vicinity of the substrate, and biasing an insulated substrate at a potential related to the potential of the secondary cathode. A plurality of UMS devices having auxiliary cathodes may be grouped in concert to produce a coating range plasma trap.