Impact of gate capping and SOI thickness with compressive stresses on partially depleted MOSFETs

Silicon nitride gate capping by contact etch-stop layer (CESL) was used in this study to induce high and low tensile and compressive stresses on 50-, 70-, and 90-nm thick silicon-oninsulator (SOI) n-/p-MOSFETs. The devices with thicker SOI show a higher interface state, particularly the highly strained devices, although they exhibit higher mobility. The carrier mobilities of different CESL configurations are sensitive to the tSOI effect, but the carrier mobilities of different tSOI are less sensitive to external compressive stress compared with those of CESL configurations. The CESL-induced compressive devices show higher piezoresistive coefficients than the tensile CESL devices, yielding an external stress of up to about 45.7 MPa for both longitudinal and transverse configurations. This probably results from nonlinear stress-strain relations on the CESLinduced strained channel.