Failure analysis methodology on donut pattern failure due to photovoltaic electrochemical effect

This paper described a low yield case which resulted in a donut shape failing pattern. It also described a scenario where static fault localization is ineffective and a systematic problem solving approach based on symptoms, induction, hypothesis and verification was engaged to resolve the issue with understanding on the root cause and the failure mechanism. The low yield is due to residual light in the dilute HF clean tool which results in photovoltaic electrochemical effect on the exposed metal, through via holes, connecting to large PN junction. This results in subsequent resistive via formation and analogue failure.