Thermal and electrical stability of TaN x diffusion barriers for Cu metallization
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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.
KeywordsLeakage Current Density Reactive Sputtering Flat Band Voltage Electrical Failure Metal Oxide Semiconductor Capacitor
The authors are grateful to the Natural Sciences and Engineering Research Council (NSERC) of Canada for providing research funding through a Strategic Project Grant and to Micralyne Inc. and Glen Fitzpatrick for supplying the metallized wafers and for valuable discussions. In addition, the Alberta Centre for Surface Engineering and Science (ACSES) is acknowledged for providing the SIMS analysis. The authors would also like to thank Dr Douglas Barlage from University of Alberta for providing access to the semiconductor analyzer.
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