Thermal and electrical stability of TaN x diffusion barriers for Cu metallization |
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Authors: | Neda Dalili Qi Liu Douglas G. Ivey |
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Affiliation: | 1. Department of Chemical and Materials Engineering, University of Alberta, Edmonton, AB, T6G 2V4, Canada
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Abstract: | Amorphous TaN x thin films (14 and 62 nm) were deposited by reactive sputtering on Si substrates. Crystallization and the metallurgical failure mechanism for Si/TaN x /Cu metallization stacks were investigated by resistivity measurements, X-ray diffraction analysis, detailed electron microscopy and elemental depth profiling on samples annealed in 5 %H2/95 %N2 gas for 30 min at various temperatures ranging from 300 to 900 °C. Amorphous TaN x thin films crystallized at 600 °C to hexagonal Ta2N by a polymorphous transformation. Depending on film thickness, polycrystalline Ta2N diffusion barriers were effective up to 700–800 °C. Failure occurred by diffusion of Cu to the Si/TaN x interface to form Cu3Si particles followed by outdiffusion of Si and formation of Cu3Si and TaSi2 precipitates on the outer surface. The TaN x barriers were integrated in metal–oxide–semiconductor devices (Cu/10 nm TaN x /26 nm SiO2/Si) to evaluate their electrical failure after bias-temperature-stress (BTS) testing using capacitance–voltage and current–voltage measurements. The shift in flat-band voltage and the leakage current were monitored before and after BTS. The electrical test results were compared with compositional and morphological information obtained from elemental depth profiling and electron microscopy. No evidence of Cu diffusion to SiO2 was found for capacitors with large leakage currents. |
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