Passive permutation multiplexer to detect hard and soft open fails on short flow characterization vehicle test chips

Abstract

Short flow characterization vehicle test chips are a major contributor to fast learning cycles especially for BEOL process steps. While hard open fails can be easily detected even in large via chains, it is very difficult to detect soft open fails like a 100 times larger via resistance of just one via within a large chain of vias. A Passive Permutation Multiplexer (PPM) is presented to optimize the signal to noise ratio for detecting soft open fails. The PPM implements a balanced routing access to a local population of resistive Devices Under Test (DUT) such as via or contact chains. Thus, soft open fail are easily recognizable as outliers of all measured resistance values within such a local population of DUTs. Compared to traditional passive multiplexers, the PPM contains up to twice as many DUTs. Furthermore, significantly larger Design of Experiments (DOE) can be implemented, since the PPM can hold more than just one DOE level within the same array.