Detecting asymmetrical transistor leakage defects

Abstract

A method of detecting low-probability defects in large transistor arrays (such as large arrays of SRAM cells), where the defects manifest themselves as asymmetrical leakage in a transistor (such as a pulldown nFET in an SRAM cell). These defects are detected by creating one or more test arrays, identical in all regards to the large transistor arrays up until the contact and metallization layers. Leakage is measured by applying an appropriate off-state voltage (e.g., 0V) by a common connection to all of the gates of the transistors in the test array, then measuring the aggregate drain/source leakage current, both forward and reverse (e.g., first grounded source and positively biased drain, then grounded drain and positively biased source) comparing the difference between the two leakage current measurements.