This study focuses on studying the effective electron mobility in direct contact La-silicate/Si structure based nMOSFETs and searching for the difference of the mobility characteristics compared with the SiO 2 MOSFETs. In this study, three types of gate electrode structure were prepared to investigate the mobility characteristics over a wide EOT range; W for EOT of 1.63 nm, TiN/W for EOT of 1.02 nm and metal-inserted poly-Si (MIPS) for EOT of 0.71 nm. Since the silicate formation is basically caused by the presence of oxygen, Si layer in MIPS can suppress the oxygen in-diffusion from atmosphere, resulting in scaled EOT. It is found that the E eff dependence of mobility with La-silicate is observed to differ from the mobility of SiO 2 MOSFETs. The electron mobility with La-silicate shows the weaker E eff dependence than the mobility of SiO 2 nMOSFETs in middle and high E eff region. This suggests an existence of additional mobility component related to the direct contact La-silicate/Si structure. The effective electron mobility is degraded with decreasing EOT in entire E eff region. This means that the scattering sources including Coulomb scattering, phonon scattering and surface roughness scattering are located not at La-silicate/Si interface but the inside of gate stacks and approach the Si inversion channel. Coulomb scattering and phonon scattering are thought to be strengthened by increasing k-value because of the enhancement of Coulomb scattering potential and higher ionicity in La-silicate gate dielectrics. The influence of metal/high-k interface is also considered to affect on the mobility with decreasing the EOT.
- Direct-contact high-k/Si structure
- Effective mobility
- Rare earth oxides