Reactive-ion-beam-sputtered WNx films on silicon: Growth mode and electrical properties

Abstract

WN films were deposited on clean Si(100) substrates via reactive-ion-beam sputtering a W target by a nitrogen ion beam in an UHV system. The energy of the incident ions varied in the range of 0.250 to 3 keV. The growth mode dependence of the films on the nitrogen ion energy was studied by in situ Auger electron spectroscopy measured as a function of coverage. Nitridation of the Si at the first stage of deposition has been found. This nitridation was more pronounced for the lower N beam energies, and minimal for the 2 keV beam. A similar trend was observed for the bulk film composition. In a complementary way, the dependence of electrical properties of the WN/Si junctions on the nitrogen energy has been studied. A higher barrier height on p-type Si than on n-type Si was found, unlike the expectation for regular metallization of W and its compounds on Si. The electrical characteristics can be attributed to the deposition technique. For the low-energy beams, the formation of the interfacial layer was probably dominating, while at higher energies radiation damage and possibly also N implantation played a more important role.