Influences of buried-oxide interface on inversion-layer mobility in ultra-thin SOI MOSFETs

This paper reports on a study of the inversion-layer mobility in n-channel Si MOSFETs fabricated on a silicon-on-insulator (SOI) substrate. In order to make clear the infuences of buried-oxide interface on the inversion-layer mobility in ultra-thin film SOI transistors, SOI wafers of different quality at the buried-oxide interface were prepared, and the mobility behaviors were compared quantitatively. The transistors with a relatively thick SOI film exhibited the universal relationship between the effective mobility and the effective normal field, regardless of the buried-oxide interface quality. It was found, however, that Coulomb scattering due to charged centers at the backside interface between SOI films and buried oxides has great influence on the effective mobility in thin SOI thickness region, depending on the buried-oxide interface quality. This means that Coulomb scattering due to charged centers at the buried-oxide interface can degrade the mobility with decreasing the SOI thickness, unless the SOI wafer quality at the buried-oxide interface is controlled carefully.