Electromigration reliability indicators

There are many requirements for different types of test for different stages in the development and use of an interconnect technology. For a new technology, metal alloy or layer structure, deposition process etc., there is a need for a full evaluation in order to reassure the user. The classical batch accelerated testing is used because the degree of acceleration is not excessive and the test conditions are not too removed from field use. There is a need for a faster secondary test, preferably at wafer level on unpackaged test structures, which can be used with some confidence on samples produced during the early evaluation stages ofa process or for use to decide preferences between process options. Finally there is a need for very fast, wafer-level tests for routine statistical process control of the fabrication process which can give some indication ofthe sample quality in minutes so that there is rapid feedback. In this case it need not test for electromigration failure itself but should also be sensitive to more basic problems such as unevenness in the photolithography ofthe line width, cracks etc. The aim is to produce a high quality and homogeneous product since it is the device with the shortest lifetime, rather than the statistical average which matters.<
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