The effects of fluorine on parametrics and reliability in a 0.18-μm 3.5/6.8 nm dual gate oxide CMOS technology

Fluorine was introduced into the gate oxide by implantation at various doses into the gate polysilicon, After complete processing, the fluorine remaining in the system was characterized by secondary ion mass spectroscopy (SIMS) and then correlated to a number of important technological device parameters. The threshold voltages of thin (3.5 mn) and thick (6.8 nm) field-effect transistors (FETs) were measured, and an increase in interface trap density with increasing fluorine content was identified. An increase in oxide thickness and improvement in hot-carrier immunity were observed, Little change to oxide dielectric integrity was noted, but the negative bias threshold instability (NBTI) shift was improved with the introduction of fluorine, These data indicate that benefits may be obtained by introducing fluorine into the p-type FET (PFET), but that the increase in interface traps makes fluorine in the NFET less attractive from a technological perspective. These data are in agreement with a previously proposed mechanism [1] whereby fluorine removes hydrogen-related sites from the oxide.