Failure Mechanism of Avalanche Photodiodes in the Presence of Water Vapor

Avalanche photodiodes (APD) failed in the field due to corrosion resulting from water vapor inside a hermetic package. The APD was part of a hybrid IC receiver manufactured by an outside vendor. Certain packaging lots contained excess water. To understand the root cause mechanism of the failure, a large scale experiment (approximately 200 devices) was performed. The APD dark current of devices without lids was measured as a function of time, temperature (T), relative humidity (RH), and voltage (V). The failures were caused by short circuits resulting from growth of semiconductor corrosion product, as found in the field failures. The median life was obtained as a function of T, RH, and V. Optical and SEM examination of the devices, coupled with the dependence of median life on V and RH, led to a model for failure. In the model, corrosion current flows through the passivating SiN from the semiconductor to the surface and then along the surface to the metal pad. Based on this understanding of the mechanism, several recommendations to increase robustness in the presence of water vapor have been made.