Infrared Analysis Technique for Determining Aluminum-Phosphosilicate Reaction

One of the major causes of semiconductor failure is inversion. This condition is frequently caused by the build-up of trapped charges in the vicinity of the silicon/silicon dioxide interface after the devices are reverse-biased at elevated temperatures. Inversion poses a severe reliability exposure, resulting in both junction and transistor leakage. A phosphosilicate layer (P2O5) introduced into the silicon dioxide structure has been found to substantially reduce the silicon dioxide structure has been found to substantially reduce the failure incidence due to inversion. However, aluminum interconnections deposited upon the oxide passivation and, therefore, on the phosphosilicate layer have been found to react chemically with the oxide effectively reducing the phosphosilicate layer. This, in turn, increases the probability of failures by inversion. Reflection infrared spectroscopy has been found to be a practical non-destructive technique in determining phosphosilicate layer thickness on oxidized silicon wafers. Using this technique, experiments have shown that depletion of the phosphosilicate layer occurs because of interaction with aluminum under various times and temperatures. The experiments prove the practical aplicability of this infrared method in the quantitative determination of the depletion of the phosphosilicate layer. The experimental findings discussed in this paper show that the reflection technique can be effectively used in process development and in production control of transistors and diodes utilizing aluminum as interconnection.