Au/Ti and Au/Ni-Cr Metallization of CVD Diamond Substrates for Multichip Module Applications

Abstract

AbstractMultichip Modules (MCMs) have recently received widespread attention in the electronics industry. Owing to its high thermal conductivity, CVD diamond holds great promise for solving thermal management problems in MCMs. Also, large diameter free standing diamond substrates have recently become available. It is thus necessary to develop a reliable metallization for diamond substrates. As Au does not adhere to diamond, refractory metals, viz., Ti, W and Mo have been used as glue layers, as they form carbides above 800 °C. Since CVD diamond looses its properties at these temperatures, there is a need to obtain adherent metallizations at much lower temperatures. In the work reported here, tenaciously adherent Au/Ti and Au/Ni80-Cr20 metallization systems were sputter deposited on CVD diamond substrates for potential use as interconnects in MCMs. The adhesion values obtained by Sebastian V stud pull tester were in the range of 12 Kpsi, with post-deposition anneal temperature as low as 150 °C. The key to good adhesion was preconditioning of the diamond surface using in-situ sputter-etch technique. The effect of post-deposition annealing (up to 450 °C) on the interdiffusion of Au with the underlying metals was studied using AES, EDX, Optical Microscopy and sheet resistance measurements. Results indicate mixing of C from diamond with refractory metals at low temperatures which may be contributing to strong adhesion.