The statistical analysis of substrate current to soft breakdown in ultra-thin gate oxide n-MOSFETs

Abstract

In this work, the characteristics of the substrate current (I/sub sub/) to soft breakdowns (SBDs) in n-MOSFETs were studied under constant voltage stress (CVS). The jump of the substrate current can be regarded a soft breakdown (SBD) event. Both the time-to-breakdown (t/sub BD/) obtained from I/sub sub/ jumps and the SBD substrate current increment (/spl Delta/Isub/sub (SBD)/) followed Weibull distribution. The Weibull slopes of t/sub BD/ and /spl Delta/Isub/sub (SBD)/ increased with increasing test temperature, but the temperature dependence of the characteristic /spl Delta/Isub/sub (SBD)/ (63% /spl Delta/Isub/sub (SBD)/) is different. On the other hand, the relation between the I/sub sub/ and I/sub g/ (gate current) alter SBDs was studied. Both the forming process and jumps of I/sub sub/ under CVS were described and explained by the variable frequency light pumping effect (VFLP).