Apparatus and method for dry milling of non-planar features on a

Abstract

An ion milling technique for forming non-planar features on a semiconductor wafer into relatively planar features for further layer deposition replaces the conventional polishing technique currently in use. The technique employs a first ion gun directing a beam normal to the wafer surface and operative to impact the features uniformly to exaggerate the hills of the feature into steep peaks and to form the valleys therebetween into shallow valleys. The technique also employs a second ion gun directed normal to the steep slopes of the peaks and aimed at a portion of the radius of the wafer while the wafer is rotated. The second beam takes advantage of the fact that the peaks mill at a rate twice as fast as the shallow valleys and the first ion beam operates to magnify the aspect ratio between the peaks and the valleys to ensure that the different rates of milling actually occurs when the second ion beam is brought into play.