Test strategy sensitivity to defect parameters

This paper demonstrates that the detection of defect depends on two classes of parameters: the predictable and unpredictable parameters. The demonstration is made with two very different types of defects (the interconnect short and the interconnect open) considering the static voltage, dynamic voltage and static current strategies. The value of the short resistance is the unpredictable parameter of the interconnect short and the polysilicon-to-bulk capacitance of the interconnect open. It is shown that any test strategy is able to detect shorts and opens each one for a given range of the unpredictable parameter called the 'analog detectability interval'. It is then demonstrated that the fundamental criterion for test strategy efficiency evaluation is the consideration of the analog detectability Intervals together with the unpredictable parameter distributions. It is finally shown that for realistic situations the voltage strategies exhibit a very good efficiency for a very reasonable cost making the use of expensive current strategy difficult to justify.