Comparative study of electrical characteristics in (100) and (110) surface-oriented nMOSFETs with direct contact La-silicate/Si interface structure

摘要

This study reports on the electrical characteristics of (110)-oriented nMOSFETs with a direct contact La-silicate/Si interface structure and the detailed comparison with (100)-oriented nMOSFETs. Precise control of oxygen partial pressure can provide the scaled EOT down to 0.73 nm on (110) orientation in common with (100) orientation. No frequency dispersion in C_(gc)-V characteristic for (110)-oriented nMOSFETs is successfully demonstrated at scaled EOT region, while higher amount of available bonds on (110) surface results in a larger interface state density, leading to the degradation of sub-threshold slope. High breakdown voltages of 2.85 V and 2.9 V for (100)- and (110)-oriented nMOSFETs are considered to be due to superior interfacial property. The electron mobility on (110) orientation is lower than that on (100) orientation because of the smaller energy split between fourfold valleys and twofold valleys as well as the larger density of states for lower-energy valleys in the (110) surface. Moreover, electron mobility is reduced with decreasing EOT in both (100)- and (110)-oriented nMOSFETs. It is found that threshold voltage instability by positive bias stress is mainly responsible for bulk trapping of electron even with a larger interface state density in (110) orientation and influence of surface orientation on threshold voltage instability is negligibly small.