Stability of W as electrical contact on 6HSiC: phase relations and interface reactions in the ternary system WSiC

In this study the system WSiC was investigated under two aspects, metallurgical and electrical, in order to understand the formation and the properties of W electrical contacts on 6HSiC. We combined two different approaches. For the examination of the phase relations in the ternary system we prepared bulk diffusion couples of W and monocrystalline SiC which were annealed and investigated using an SEM (secondary electron images, backscattered electron images, energy dispersive X-ray analysis), Secondly arc furnace molten powder samples, annealed at different temperatures, were analysed by X-ray diffraction. To investigate the electrical properties of a W/SiC junction transmission line contact patterns were sputter deposited onto wafer strips. These samples were subjected to similar heat treatments and the current/voltage characteristics were measured with a source measure unit, Individual contact resistivities could be evaluated using a special contact geometry. esult we discovered a four-phase equilibrium in the WSiC system at 1400 ± 100°C: 3W5Si3 + 7Si8WSi2+7WC. This is in qualitative agreement with thermodynamic calculations. At 1300°C the equilibrium WSi2 + WC exists, At 1000°C the reaction kinetics are too slow to be detected in a bulk sample, The phase sequence developing in a bulk W/SiC diffusion couple at 1300°C is W/W5Si3/WC/SiC. s ohmic contacts on n-type 6HSiC which are stable up to 1000°C for at least several hours. From 1200°C upwards a reaction between W and SiC leads to the formation of tungsten silicides and carbides and hence a deterioration of the electrical properties. The films disintegrate into small crystals of WC and W3Si5 leading to a large spread of the resistances of the individual contacts.