Circuit technique to electrically characterize block mask shifts

Abstract

A physical test integrated circuit has a plurality of repeating circuit portions corresponding to an integrated circuit design. A first of the portions is fabricated with a nominal block mask location, and additional ones of the portions are deliberately fabricated with predetermined progressive increased offset of the block mask location from the nominal block mask location. For each of the portions, the difference in threshold voltage between a first field effect transistor and a second field effect transistor is determined. The predetermined progressive increased offset of the block mask location is in a direction from the first field effect transistor to the second field effect transistor. The block mask overlay tolerance is determined at a value of the progressive increased offset corresponding to an inflection of the difference in threshold voltage from a zero difference. A method for on-chip monitoring, and corresponding circuits, are also disclosed.