The optimization of the double mask system to minimize the contact resistance of a Ti/Pt/Au contact

The fabrication of Ti/Pt/Au ohmic contacts on diamond using two transmission line model masks during the photolithography step was modified as a result of the adverse effects on the resistance from the rectifying lip created by the overlap of the two masks, and the possible inhibition of carbide formation due to the presence of oxygen on the diamond surface before metallization. The first modification consisted of decreasing the rectifying lip by diffusing a small amount of Ti from beneath the contact defined by the first mask, and decreasing the overlap of the two masks from 5 to 2 μm, which is close to the minimum allowable by our photolithography techniques. The second modification consisted of the desorption of oxygen from the diamond surface using a heat treatment in vacuum and cool down in purified hydrogen. As a result of these changes, the contact resistance was decreased by more than two orders of magnitude from 8.1 × 10-2 Ω-cm2 to 1.2 × 10-4 Ω-cm2.