Impact of Si Impurities in HfO2: Threshold Voltage Problems in Poly-Si/HfO2 Gate Stacks

다국어 초록 (Multilingual Abstract)

We perform first-principles theoretical calculations to study the atomic and the electronic
structures of Si impurities in HfO2. We also examine the impact of Si impurities on the threshold
voltage problems in ploy-Si/HfO2 gates and the growth morphology of HfO2 films on Si substrates.
In the ploy-Si/HfO2 interface region, Si atoms easily migrate from the poly Si and remain as ionized
interstitials. A charge transfer from the oxide to poly Si induces interface dipoles, which may cause
high flat-band voltage shifts, especially for p+ poly Si electrodes. In addition, since interstitial Si
atoms behave as negative-U traps, these defects are suggested to be the origin of the threshold
voltage instability. Under O-rich growth conditions, the Si impurities favorably substitute at the
Hf sites, resulting in the formation of Hf-silicate layers at the oxide/Si substrate interface. On the
other hand, under O-poor growth conditions, the Si impurities tend to be interstitials, binding
with the Hf atoms and forming a Hf-silicide structure.

참고문헌 (Reference)

1 C. Leroux, "Tech. Dig. - Int.Electron Devices Meet." 737-, 2004

2 E. Cartier, "Proceedings of 2004 Symposium on VLSI Technology Digest of Technical Papers" 4444-, 2004