Amorphous W-Zr Films as Diffusion Barriers between Al and Si

摘要

Cosputtered W70Zr30 and W40Zr60 films are investigated as diffusion barriers between Aq and Si. W-Zr alloys of both compositions were determined by x-ray diffraction to crystallize at 900 deg C on A1203 substrates. On <111>Si the W-Zr alloy reacts with the substrate above 700 deg C, forming a uniform, polycrystalline layer of W and Zr silicides. Despite the high crystallization temperatures, an A1 overlayer interacts with W-Zr and the Si substrate at approx. 500 deg C. MeV He backscattering spectrometry, SEM and EDAX indicate that this reaction is laterally nonuniform with the formation of deep pits penetrating into the Si substrate. We believe this to be a consequence of fractures in the W-Zr layer induced by reaction with A1. Electrical measurements on shallow junction diodes with /W-Zr/Al contacts show that the device junctions were thermally stable after a 30 min annealing at 450 deg C but were all shorted after heat treatments at 500 deg C or above.