1. Purpose of the gate
Test vehicles show the array yielding on a trend that supports a product die, with the main fail mechanisms understood and repair able to cover what remains.
A product die is only worth taping out on a process whose arrays yield well enough, or are clearly on their way. This review looks at the learning trend rather than a single number: is defect density falling lot by lot, are the top fail signatures understood and being fixed, and does the yield model show that the planned redundancy and error correction will make the product die viable.
It is also reliability's first formal look at the cell on real silicon. Retention, disturb and endurance behaviour on test vehicle structures either confirms the cell margins from simulation or shows where they fall short, early enough to adjust the design's correction and repair.
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