Using a 10-keV X-Ray Source for Hardness Assurance

The feasibility of using a 10-keV x-ray source as a cornerstone of a hardness assurance program is demonstrated for several of Sandia's integrated-circuit technologies. We present test structure and functional part data that illustrates how an x-ray source may be used for wafer lot acceptance for silicon-gate CMOS devices that either employ guard-bands or hardened field oxides for device isolation. We also show that the radiation response of silicon-nitride based nonvolatile memory transistors can be evaluated equally as well with a 10-keV x-ray source as with a Co-60 source. Finally, a description is presented of test structure and full-functional part radiation data from a device lot that was known to exhibit memory failures because of the detailed interplay among transistor threshold voltage shifts and mobility degradation. Even for such a complicated failure mechanism, 10-keV x-irradiations induced memory failures at the same doses as Co-60 irradiations. Moreover, insight into the cause of the memory failures was gained from a comparison of the Co-60 and the 10-keV x-ray data. This illustrates that a variable dose rate 10-keV x-ray source can be very useful in failure analysis.