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Amorphous W-Zr Films As Diffusion Barriers Between Al And Si

  • F. C. T. So (a1), X.-A. Zhao (a2), E. Kolawa (a1), J. L. Tandon (a3), M. F. Zhu (a4) and M-A. Nicolet (a1)...

Abstract

Cosputtered W70Zr30 and W40Zr60 films are investigated as diffusion barriers between Al and Si. W-Zr alloys of both compositions were determined by x-ray diffraction to crystallize at 900°C on Al2O3 substrates. On <111>Si the W-Zr alloy reacts with the substrate above 700°C, forming a uniform, polycrystal line layer of W and Zr suicides. Despite the high crystallization temperatures, an Al overlayer interacts with W-Zr and the Si substrate at ∼500°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 Al. Electrical measurements on shallow junction diodes with <Si>/W-Zr/Al contacts show that the device junctions were thermally stable after a 30 min annealing at 450°C but were all shorted after heat treatments at 500°C or above.

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