SIMS Analysis for the Threshold Voltage Shift of Power MOS Caused by Abnormal Dopant Diffusion

Threshold Voltage (Vt) of MOSFET controls transistor’s on and off state. Vt is usually depends on gate oxide thickness and operating temperature. Systematic failure analysis for a Vt shift issue, should also consider the channel doping which affects the inversion layer formation. In this article, the failure case of a shift in the Vt of a Power MOSFET V is studied. Secondary Ion Mass Spectrometry (SIMS) is found to be the most direct way for detecting any abnormality in the channel doping profiles. A comprehensive simulation is performed showing that the Phosphorus level diffusion from substrate was so high that it affects the doping concentration of channel.