Scanning spreading resistance microscopy for failure analysis of nLDMOS devices with decreased breakdown voltage

Scanning Spreading Resistance Microscopy (SSRM) is successfully applied to investigate failing nLDMOS test devices that exhibit a lowered break down voltage (BVDSS) in electrical test. Cross-sectional, two-dimensional maps of the local sample resistivity from fail and reference (pass) devices reveal significant differences of the dopant concentration in individual, specific regions. This important information enables unambiguous identification of the root cause of the device failure to be dopant related. Furthermore, from a set of hypothesis, which explains the failed electrical test, SSRM results confirm exactly one and rule out the other. These are two important steps towards root cause identification. Since a relative comparison of fail and pass SSRM scans is sufficient for this failure analysis, an extensive data calibration for the absolute dopant concentration by means of additional SSRM measurements on test samples with known dopant concentration is not required. The ability of SSRM to prove or disprove miscellaneous fail hypothesis even without data calibration makes this method a very powerful tool for analysis of dopant related failure types.