Weak temperature dependence of non-coulomb scattering component of HfAlOx-limited inversion layer mobility in n+-polysilicon/HfAlOx/SiO2 N-channel metal-oxide-semiconductor field-effect transistors

We propose a new extraction method for mobility limited by high-k dielectrics, and discuss the scattering mechanism for halfnium aluminate (HfAlOx) in the strong inversion region. In our method, mobility degradation properties are evaluated as a function of interfacial SiO2 thickness. The temperature dependence of the mobility in the strong inversion region is analyzed with the expression 1/µ=1/µRexp (-2kFTint)+1/µSiO2/Si, where µ is the measured mobility, µR is the prefactor mobility limited by a high-k dielectric, kF is the Fermi wavenumber of the channel carriers, Tint is the thickness of the interfacial SiO2 layer, and µSiO2/Si is the mobility for n+poly-Si/SiO2 n-channel metal–oxide–semiconductor field-effect transistors (MOSFETs). This analysis method is applied to n+poly-Si/HfAlOx [Hf/(Hf+Al)=60 at. %]/SiO2/p-Si n-channel MOSFETs. It is found that the mobility limited by the HfAlOx film, µR, decreases with a temperature increase in the range of 77–297 K. This temperature dependence indicates the predominance of non-Coulomb scattering for the mobility limited by HfAlOx in the strong inversion region. The mobility due to the non-Coulomb scattering shows a weak temperature dependence that is explainable by surface optical phonons (i.e., those appearing at the Si-surface channel region due to the longitudinal-optical (LO) modes of HfAlOx) with the corresponding transverse-optical (TO) phonon energy in the range of 10–20 meV.