Stress effects on MOSFETs.

Strained silicon has the ability to improve the metal-oxide-semiconductor field-effect transistor (MOSFET) performance. Therefore, the silicon industry has developed a significant interest in strained silicon in recent years. There are two types of stress: structural stress and mechanical stress. Structural stress (SiGe, Si3N4, etc.) introduces high stress to increase performance deliberately. Mechanical stress, such as packages, introduces modest unintentional stress, but sufficient to alter MOSFET performance. This dissertation focuses on mechanical stress effects on MOSFET performance. The MOSFET parameters were determined from current-voltage measurements with and without stress. The MOSFET parameters depend on applied mechanical stress. The threshold voltage increased with increased compressive stress. The pn junction leakage current decreased under tensile stress. The substrate current of the short channel n-MOSFETs increased with increased tensile stress. The drain current, transconductance, and effective mobility increased under tensile stress and decreased under tensile for n-MOSFETs. For p-MOSFETs, the three parameters increased under compressive stress and decreased under tensile stress when the stress was longitudinal to the current flow and vice versa when the stress was transverse to the current flow. The mechanical stress effect has a dependence on the channel length of MOSFETs; the longer devices exhibit a higher mechanical stress effect. Wider p-MOSFETs have a higher mechanical stress effect than narrower devices. The gate area dependence is more suitable for presenting mechanical stress effect on such devices.