Improvement of 155 Wright etch and its application in failure analysis of in-line QBD failure in wafer fabrication

The work presented here shows that a significant improvement on the 155 Wright etch has been made. To completely remove the polysilicon layer on the large capacitor structure and obtain better Wright etch results, a new polysilicon etchant, HB91, has been introduced into the new procedures of 155 Wright etch. HB91 is actually a mixture solution of two chemical namely nitric acid (HNO₃) and buffer oxide etchant (BOE) in a 9:1 ration. Using it, the polysilicon layer on the large capacitor structure can be easily removed in 8-10 secs. It has been applied in failure analysis of the QBD failure in the 0.8 μm EEPROM process in wafer fabrication. The application results showed that this new Wright etch method is more effective on checking stacking faults or silicon crystalline defects especially for those devices with large capacitor structure.