Abstract
We perform first-principles density functional calculations to investigate the effects of Al incorporation on the p-type Schottky barrier height and the effective work function for various high-k/metal gate stacks, such as TiN/HfO2 with interface Al impurities, Ti1−xAlxN/HfO2, and TiAl/TiN/HfO2. When Al atoms substitute for the interface Ti atoms at TiN/HfO2 interface, interface dipole fields become stronger, leading to the increase of and thereby the n-type shift of effective work function. In Ti1−xAlxN/HfO2 interface, linearly increases with the Al content, attributed to the presence of interface Al atoms. On the other hand, in TiAl/TiN/HfO2 interface, where Al is assumed not to segregate from TiAl to TiN, is nearly independent of the thickness of TiAl. Our results indicate that Al impurities at the metal/dielectric interface play an important role in controlling the effective work function, and provide a clue to understanding the n-type shift of the effective work function observed in TiAl/TiN/HfO2 gate stacks fabricated by using thegate-last process.
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