Design dependent process monitoring for back-end manufacturing cost reduction

Abstract

Short-loop process monitoring structures (usually simple device I - V, C - V measurements made after M1 fabrication) are commonly put in wafer scribe-lines. These test structures are almost always design independent and measured/monitored by the foundry to keep track of process deviations. We propose a design-dependent process monitoring strategy which can accurately predict design performance based on simple I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">eff</sub> -based delay and I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</sub> -based leakage power estimates. We show that our strategy works much better (0.99 correlation vs. 0.87) compared to conventional design-independent monitors. Further, we use the predicted delay and leakage power for early yield estimation for pruning bad wafers to save test and back-end manufacturing costs We show that wafer pruning based on our approach can achieve upto 98% of the maximum achievable benefit/profit. We design the measurement and prediction schemes so as to minimize data as well as computation that needs to be kept track of during wafer fabrication. Such design-dependent process monitoring can help target process control/optimization effort, enable quicker yield ramp besides saving test and manufacturing costs.