Comparison of forming gas, nitrogen, and vacuum anneal effects on X-ray irradiated MOSFETs

The effects of radiation intensive lithography and three different anneal treatments on nMOS hot-carrier vulnerability have been studied. The gate oxides of devices irradiated with X-rays after complete processing and subjected to forming gas, nitrogen, and vacuum anneals were characterized using photoinjection and channel hot-carrier stressing experiments. Photoinjection characterizations indicate that neutral as well as positively charged electron traps are present in the bulk oxide after the anneal treatments, with no discernible ambient dependence. Channel hot carrier stressing over the full range of CMOS operating points, however, indicates that the device treatments improve the stability of the interface to varying degrees depending on the anneal ambient. The X-ray irradiated and nitrogen annealed devices were found to be least vulnerable to channel hot-carrier degradation.