Study Of TVS's Passivation Technology And Reliability

Silicon nitride thin film is important electric dielectrics with excellent mechanical and passivation properties. It will be widely used in microelectronics.Passivation characteristic and manufacturing process of TVS (Transient voltage suppressor)'s Si3N4 passivation layers are studied. Analysis of surface characteristic and passivation protection shows that surface effect is the main reason for leakage current. Leakage current can be obviously reduced by appropriate passivation. The results showed large interface stress existed in the surface between Si and Si3N4 when passivation layer just made up of single Si3N4 film. The interface stress would influence reliability of device. In that case, Poly-Si and Si3N4 dual passivation layer was proposed. And it was applied in TVS passivation. The electrical parameters showed very good after test. Then reliabilities were compared among SiO2, single Si3N4 and Poly-Si/Si3N4 passivation layers by HTRB (High Temperature Reverse Bias) test. The results showed Poly-Si/Si3N4 passivation layer has the best performance (0.8% failed) than SiO2 (9.2% failed) and single Si3N4 (4.4% failed).Based on the above study, failure analysis is performed using PEM (Photon Emission Microscopy) and SEM (Scanning Electron Microscope). Results showed most of failure chips damaged by thermal runaway in the dicing zone. It was also found that present dicing method would cause passivation layer damage in the front side of chips. So back side cutting was proposed. The experimental results prove that it could reduce HTIR (High temperature reverse leakage) largely, it also increase the reliability after dicing.