Built-in Self-Test of High-Density and Realistic ILV Layouts in Monolithic 3D ICs

Abstract

Nano-scale inter-layer vias (ILVs) in monolithic 3D (M3D) ICs have enabled high-density vertical integration of logic and memory tiers with significant improvement in power, performance, and area (PPA) over 2D and 3D-stacked ICs. However, the sequential assembly of M3D tiers via wafer bonding is prone to variability in the immature fabrication process and manufacturing defects. The yield degradation due to ILV faults can be mitigated via dedicated test and diagnosis of ILVs using built-in self-test (BIST). Prior work has carried out fault localization for a regular one-dimensional placement of ILVs in the M3D layout where shorts are assumed to arise only between unidirectional ILVs. However, to minimize wirelength in M3D routing, ILVs may be irregularly placed by a place-and-route tool and shorts can also occur between an up-going ILV and a down-going ILV. To test and localize faults in realistic ILV layouts, we present a BIST framework that is optimized for test time and PPA overhead. We present a graph-theoretic approach for representing potential fault sites in the ILVs and carry out inductive fault analysis to drop non-critical sites. We describe a procedure for optimally assigning ILVs to the BIST pins and determining the BIST configuration for test-cost minimization. Evaluation results for M3D benchmark circuits demonstrate the effectiveness of the proposed framework.