Low damage sputter deposition of tungsten for decanano compound semiconductor transistors

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This article investigates sputter-induced damage caused by direct current magnetron sputter coating of tungsten on GaAs based high electron mobility transistor layer structures with channels buried less than 20nm from the surface. Van der Pauw structures were used to study the effect of tungsten sputtering on the transport properties of these shallow channels. Using this approach we established that substrate damage can be minimized by using low sputtering currents, a large source to substrate distance, and a high sputtering pressure. Unfortunately such sputtering conditions do not produce the best quality dense films necessary for device fabrication and it was necessary to establish conditions which were a compromise of film quality and substrate damage. Postsputter annealing was found to significantly reduce the damage and a loss of 10% in semiconductor conductivity was obtained for good quality tungsten films.