Analysis of stress effect on (110)-oriented single-gate SOI nMOSFETs using a silicon-thickness-dependent deformation potential

The stress effect in uniaxially strained (100)- and (110)-oriented single-gate (SG) silicon-on-insulator (SOI) n-type metal-oxide-semiconductor field-effect transistors (MOSFETs) was analyzed. A model of a silicon-thickness-dependent deformation potential (D_ac-Tsi) was used for accurate calculation of mobility using a Schrödinger-Poisson solver. The simulation results obtained using the D_ac-Tsi model exhibited excellent agreement with the measured mobility for both strained and unstrained conditions. The enhancements in electron mobility under conditions of longitudinal tensile strain were analyzed as a function of the silicon thickness and strain. As the silicon thickness decreased, the mobility enhancement in (100) SG MOSFETs reached a peak, whereas it diminished in (110) SG MOSFETs. As the strain increased, mobility enhancement increased in the (110) case, whereas it saturated in the (100) case. Therefore, larger mobility enhancement in the (110) orientation is expected. These differences in enhancement between the (100) and (110) cases resulted from differences in the quantization mass, which affect the energy difference between the 1st subbands of two-fold and four-fold degenerate valleys, as well as occupancy change.