Studies of Passivation (Si3N4/SiO2) Qualification Method in Wafer Fabrication

In wafer fabrication, silicon nitride (Si3N4) and silicon oxide (SiO2) layers are widely used as passivation layer to protect the Al metal underneath from corrosion. To qualify the passivation layers, the traditional chemical recipe PAE (H3PO4 + HNO3) is used to conduct passivation pinhole test. If pinholes or cracks are present in the passivation layer of Si3N4/SiO2, the sample immersion in the test solution duration will allow HNO3 acid to chemically react with the Al layer underneath. Therefore, a black colored pinhole-like defect will be observed during optical inspection after the pinhole test. In this situation, the wafer sample fails the pinhole test and is not qualified.If there is no pinhole or crack in the passivation layers of Si3N4/SiO2, after the sample immersion in the testing solution time, HNO3 acid cannot chemically react with the underneath aluminum layer. The black pinhole-like defect during optical inspection is unable to be detected, and the wafer sample passes the pinhole test. However, this traditional method has its limitation. If the pinholes or cracks do not completely penetrate the entire passivation layer, in this case HNO3 acid cannot flow into the pinholes or cracks and could not chemically react with the underlying aluminum. As a result, those pinholes or cracks could not be detected.In this study, we proposed a new test method to replace the traditional pinhole test method by using fluorescent dye method. We have developed a fluorescence microscopy method which can be applied to qualify the passivation layer. Using this new method, we could detect pinholes/cracks in passivation layer in wafer fabrication which had totally or partially penetrate the entire passivation (Si3N4/SiO2) layer. The smallest microcrack size currently detected can reach 72nm. All micro-pinhole defects can be detected by fluorescence microscopy method, which can detect not only full perforation defects, but also those partially perforated defects.