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 transm ission line model masks during the photolithography step was modified as a result of the adverse effects on the resistance from the rectifyi ng lip created by the overlap of the two masks, and the possible inhib ition of carbide formation due to the presence of oxygen on the diamon d surface before metallization. The first modification consisted of de creasing the rectifying lip by diffusing a small amount of Ti from ben eath the contact defined by the first mask, and decreasing the overlap of the two masks from 5 to 2 mu m, which is close to the minimum allo wable by our photolithography techniques. The second modification cons isted of the desorption of oxygen from the diamond surface using a hea t treatment in vacuum and cool down in purified hydrogen. As a result of these changes, the contact resistance was decreased by more than tw o orders of magnitude from 8.1 x 10(-2) Ohm-cm(2) to 1.2 x 10(-4) Ohm- cm(2).