Bake induced charge gain in NOR flash cells

Charge gain, caused by localized defects in the tunnel oxide of floating gate devices, is one of the central reliability concerns of flash memory. In this work, we show that charge motion in the poly sidewall spacers of flash cells can also result in substantial charge gain, for nonoptimized processes. Data showing the time, temperature, and field dependencies of this charge gain mechanism are presented. It is shown that the threshold voltage shift caused by charge motion in the poly sidewall spacers follows the simple factorial expression: /spl Delta/V/sub th/=C/spl middot/V/sub fg//spl middot/t/sup /spl alpha///spl middot/e/sup -/spl epsiv/(a)/kT/.