Passive multiplexer test structure for fast and accurate contact and via fail rate evaluation

Abstract

Complexity of integrated circuits has led to many millions of contacts and vias on every chip. To allow accurate yield evaluation, it is required to determine fail rates of < 10 faults per billion which requires test structures with huge chains of 1 million or more contact and vias. At the same time contacts and vias are getting smaller and thus their resistance is increasing for every new technology node. Consequently, the resistance of such chains becomes impossible to measure. To overcome this limit without increasing the number of measurement pads, we are proposing a Passive Multiplexer Array of via chains, which breaks up a huge contact/via chain in many individually measurable sub-chains. Accuracy of fail rates will be increased, since the fail rate can be determined based on many sub-chains, instead of being determined based on one huge chain only. Furthermore, this test structure better supports failure analysis, since it is faster to locate a faulty contact or via. No additional devices or process steps are required which allows implementation as short flows for fast process problem debugging.