On optimizing test cost for Wafer-to-Wafer 3D-stacked ICs

The increasing demand for more sophisticated ICs with more functionality mostly was realized by downscaling and increasing the number of transistors. A technology that promises further increase of transistor density (in addition with heterogeneous integration, better performance and less power dissipation at a smaller footprint) is the three-dimensional stacked ICs (3D-SICs). Several stacking approaches are under development to manufacture such 3D-SICs. Wafer-to-Wafer (W2W) stacking seems the most favorable approach when high manufacturing throughput, thinned wafers and small die handling is required. However, efficient and optimal test approaches to satisfy the required quality are still subject to research. Each manufactured 3D-SIC undergoes a test and therefore optimizing test cost will have a large overall impact. This paper discusses test cost optimization for W2W 3D-SICs. It first introduces a framework covering different test flows for 3D W2W ICs. Test flows that include pre-bond tests can benefit from wafer matching; in wafer matching a software algorithm is used to increase the compound yield by stacking wafers with similar fault distributions. Subsequently, the paper proposes a cost model to evaluate and estimate the impact of test flows on the overall 3D-SIC cost. Our simulation results show that test flows with pre-bond testing in general significantly reduce the overall cost. These test flows benefit mostly from the yield increase due to wafer matching.