Corrosion features rate with time

The metallization for some integrated circuits with submicron features is made up of the Ti/TiN/Al/TiN stack. Lateral undercutting of up to 20 pm of aluminum from the middle of the stack has been observed (Fig. 9-16). Residual chloride from the reactive-ion etch initiates the aluminum corrosion process that is stimulated galvanically by titanium nitride (Jones, 1992). Titanium nitride, being more noble, serves as the cathode in this electrochemically driven process. The corrosion rate of the more active metal increases as the cathode-area/anode-area ratio increases. At the time of the rinse... 

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