Electrical measurement of local stress and lateral diffusion near Source/Drain extension corner of uniaxially stressed n-MOSFETs

Abstract

-On a 1.27-nm gate oxide n-MOSFET that undergoes longitudinal stress via a layout technique, subthreshold current is measured as a function of the gate edge to shallow-trench isolation (STI) spacing and is transformed via bandgap shift into the source/drain extension corner stress. The extracted local stress is quantitatively comparable with those of the channel as created by the gate direct tunneling measurement in inversion, the mobility measurement, and the threshold voltage measurement. In addition, its dependencies on the gate edge to STI spacing confirm the validity of the layout technique in controlling the corner or channel stress. The gate edge direct tunneling (EDT) measurement in accumulation straightforwardly leads to the quantified gate-to-source/drain-extension overlap length. Particularly, a retarded diffusion length of 1.1 nm for a stress change of -320 MPa and the resulting strain-induced activation energy both are in satisfactory agreement with those of the process simulation. A physically oriented analytic model is, therefore, reached, expressing the lateral diffusion as a function of the corner stress.