HIGH-TEMPERATURE CONTACTS TO CHEMICALLY VAPOR-DEPOSITED DIAMOND FILMS- RELIABILITY ISSUES

Refractory metals (Ti, Mo, W and Ta) with precious metal overlayers (A u and Pt) were used to form ohmic contacts to polycrystalline boron do ped chemically vapour deposited diamond films. Refractory metals affor d high resistance to thermal and environmental stresses. In addition, many refractory metals show a chemical affinity for carbon, resulting in the formation of a metal-carbide reaction layer with reduced Schott ky barrier height at the contact interface. Low resistance ohmic conta cts can be formed by heavy boron doping of the diamond film in the con tact region. The viability and reliability of various refractory metal contact schemes were assessed to determine their upper operating temp eratures and life expectancies in hostile environments. Reverse engine ering of the contacts and detailed material analysis revealed likely f ailure mechanisms. It was found that Mo/Au gave the highest degree of thermal stability, while Ti gave the lowest contact resistance. The co ntact resistance was strongly dependent on the doping level of the dia mond film.