ANALYSIS OF ELECTRICAL BREAKDOWN FAILURES BY MEANS OF SFM-BASED METHODS

Electrical breakdown failures in Si devices may occur within ESD (elec trostatic discharge) protection structures as well as in other parts o f the circuit due to electrical overstress. Those kinds of failure ver y often show topographical irregularities due to material flow within the breakdown channel. Depending on the current and correlated materia l, flow channels may be observable by means of SEM. For devices tested with CDM (charge device model), which implies very low breakdown curr ents, this task gets more difficult to fulfil even with a high-resolut ion SEM. SFM offers an extremely high resolution in the lateral as wel l as vertical direction, and is therefore chosen as an appropriate too l for imaging small features. Besides the purely topographical informa tion, additional data obtained in parallel, such as conductivity or ca pacitance, can give the necessary hints for an unequivocal interpretat ion. Here a comparison of SEM and SFM results demonstrates the capabil ities of SFM topography analysis in the identification of breakdown ch annels. Furthermore, conducting SFM and capacitance investigations ill ustrates the usefulness of parallel detection of topography and curren t (or capacitance respectively) for the explanation of breakdown pheno mena and material transport.