IBM (NYSE:IBM) is currently testing wafer pruning on its 45 nm process. Wafer pruning is actually quite simple – once you get the idea.
A wafer consists of a number of individual dies and between these dies IBM puts various test patterns. During the manufacturing process IBM will frequently measure these test patterns and check them for errors. If errors are found in the test patterns, they probably also exist on the dies next to the test pattern – and if there are too many, then the wafer is automatically discarded – or pruned.
Building test patterns into wafers is not exactly new – they have been used for a long time to measure drifts in the process during manufacturing, but only after the wafer was finished. What is new is discarding them earlier in the process, saving time and money.
The end result is a higher yield when the remaining wafers are completed – and in theory it should result in better utilisation of the equipment and thereby also higher profits. Savings could amount to as much as 15% according to Semiconductor Research Corp., which funded development of the technique at the University of California at Los Angeles (UCLA).S|A
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