Second Generation High-k Gate Insulators
Very high (k>25) permittivity materials have been investigated as a second step high-k gate insulator. These are all formed by adding other materials to the basic HfO2. Hafnium titanate thin films were deposited by chemical vapor deposition (CVD). It was observed that both the interfacial layer (IL) EOT and the permittivity increase with Ti content and that films with higher Ti content are also more immune to crystallization. Permittivities as high as 50 were achieved. In the MOSFET devices with the hafnium titanate films, normal transistor characteristics were observed, including electron mobility degradation. In SrHfO3 films, deposited by physical vapor deposition (PVD), a permittivity as high as 35 was achieved. These films appear to be highly stable upon high temperature annealing, but show a thick, anomalous interfacial layer.
M. Li et al., "Second Generation High-k Gate Insulators", Advances in Science and Technology, Vol. 45, pp. 1342-1350, 2006