Modeling and direct extraction of band offset induced by stress engineering in silicon-on-insulator metal-oxide-semiconductor field effect transistors: Implications for device reliability

We study the performance and reliability of metal-oxide-semiconductor field effect transistors fabricated on strained and unstrained silicon on insulator substrates, sSOI and SOI, respectively. The biaxial strain strongly enhances electron mobility and changes the threshold voltage, V(t), of the devices. We show that the V(t) shift in the "ideal SOI structures," i.e., with no oxide defects, is due to the conduction band offset induced by strain Delta E(c) and therefore can be used for the stress monitoring. The biaxial strain also affects the gate oxide leakage current. A new method to extract Delta E(c) from the leakage current measurements is proposed. This method is less sensitive to the gate oxide defects than the one based on V(t) shift. A complete modeling of leakage current in SOI and sSOI transistors is presented. Due to the strong confinement at the Si/SiO(2) interface the leakage current in the Fowler-Nordheim (FN) regime mainly results from electron tunneling in the subband associated to the ground level E(0)(Delta 2). A simple FN model is therefore used to extract the Delta E(c) from the variation in the effective barrier height phi(FN)(b) between the Si film and the SiO(2) oxide. Based on this experimental and accurate extraction of Delta E(c), realistic values of the deformation potentials in Si are finally proposed. The final part of the paper discusses the different implications of this band offset Delta E(c) on device performance and reliability. It is demonstrated that strained devices exhibit reduced leakage currents and a superior reliability, in terms of interface state density and oxide breakdown, than unstrained devices. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3126506]