Pulsed bias temperature stress-An accurate and fast technique to determine mobile ion concentrations in gate and field oxides

Abstract

Mobile ion contamination is a recurring reliability problem in MOS integrated circuit technology. In this paper, we suggest a fast and simple technique to determine the ion concentrations and kinetics by measuring the threshold voltage shift of an active or field MOS transistor after high temperature bias stress at the stress temperature. The I/sub D/ vs. V/sub GS/ characteristics are measured with a pulsed sweep voltage applied to the gate. Between the pulses, the gate voltage is switched back to the stress bias value in order to restore the prepulse ion concentrations at the interfaces. By avoiding the time consuming and cumbersome heating/cooling cycles of the traditional BTS technique and making use of the exponential time dependency of the threshold voltage shift, the test can be executed in less than 60 seconds.