Abstract

In the authors' previous paper, we studied the defects from Fluorine-Induced Corrosion on microchip Al bondpads using SEM, EDX, TEM, AES, IC, XPS and TOF-SIMS techniques. An unknown F-Al compound was found and identified as [AlF6]3-. In this paper, we will further study the chemical mechanisms of Fluorine-Induced Corrosion on microchip Al bondpads and propose a theoretical electrochemical model to reveal the secrets of Fluorine-Induced Corrosion on Al bondpads. To support this new theoretical model, we will provide substantiating data from TOFSIMS analysis and other failure analysis techniques. According to the theoretical model of Fluorine-induced Corrosion proposed, fluorine contamination on Al bondpads will cause two types of corrosions. First, fluorine reacts with Al and forms a complex compound [AlF6]3- on the affected area, which we will refer to as Fluorine Corrosion. Once the compound of [AlF6]3- forms on Al bondpads, it will form an Anode and cause further electrochemical reactions from O2, N2 and H2O (moisture) at the Cathode. The new products of further electrochemical reactions will be [OH]- and [NH4]+ ions. The new product of [OH]- ions will react with Al and cause further Al corrosion on bondpads and form corrosive product consisting of Al(OH)3, which we will refer to as [OH]- Corrosion. The new product of [NH4]+ ions will combine with [AlF6]3- and form a corrosive complex compound (NH4)3(AlF6). This proposed corrosion mechanism results in non-stick bondpad problem.

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