A New Finding of Cu-Al IMC Corrosion and Investigation of Fluorine Contamination Influence on Cu-Al IMC Corrosion

Abstract

Cu wire is widely used in the electronics industry for wire bond material for IC packages due to lower cost compared to Au wire. IC package miniaturization and increasing connection density are resulting in new challenges in terms of reliability and long-term stability. Harsher environments in automotive electronics also lead to several reliability issues. Corrosion effects, especially at Al/Cu wire bond interfaces are the interaction result of factors such as temperature, moisture, and biased electrical driving force with halides as the corrosion initiator. The influence of Cl (chlorine) on the interfacial corrosion of wire bond contacts is well known. Very small amounts of chlorine can result in Cu/Al corrosion and cause electrical open failures in humidity related stresses (e.g., HAST, Autoclave, THB, etc.). However, the influence of fluorine (F) on Cl induced corrosion is not as well understood. This paper introduces a new failure mechanism: Cl- induced IMC corrosion. In this mechanism, not only the IMC and Al pad but also the Cu corrodes. To understand the corrosion mechanism, the paper presents the first step in an initial investigation with the goal to get knowledge about whether F is a contributing factor in the Cu/Al corrosion process. An experimental study was done using three different wafers (a special wafer fabrication process to artificially generate different level of F contamination on the Al pads). Fluorine contamination was characterized on the bonding pads by AES (Auger Electron Spectroscopy) then the wafers were assembled into packages and then tested using THB (Temperature Humidity Biased) stress. Final test after THB stress was the major response for the experiment. The result shows that the level of F contamination studied not sufficient to show the impact. Further study is needed for higher levels of fluorine contamination. However, fluorine contamination should still be well controlled and monitored in Cu wire bonded package because it may worsen the wire bond performance potentially impacting wire bond robustness against corrosion.