Non-invasive pre-bond TSV test using ring oscillators and multiple voltage levels

Defects in TSVs due to fabrication steps decrease the yield and reliability of 3D stacked ICs, hence these defects need to be screened early in the manufacturing flow. Before wafer thinning, TSVs are buried in silicon and cannot be mechanically contacted, which severely limits test access. Although TSVs become exposed after wafer thinning, probing on them is difficult because of TSV dimensions and the risk of probe-induced damage. To circumvent these problems, we propose a non-invasive method for pre-bond TSV test that does not require TSV probing. We use open TSVs as capacitive loads of their driving gates and measure the propagation delay by means of ring oscillators. Defects in TSVs cause variations in their RC parameters and therefore lead to variations in the propagation delay. By measuring these variations, we can detect resistive open and leakage faults. We exploit different voltage levels to increase the sensitivity of the test and its robustness against random process variations. Results on fault detection effectiveness are presented through HSPICE simulations using realistic models for 45nm CMOS technology. The estimated DfT area cost of our method is negligible for realistic dies.