CORROSION AND PROTECTION OF THIN-LINE CONDUCTORS IN VLSI STRUCTURES

Thin metallic lines in VLSI circuit structures are usually encapsulated in a dielectric in order to protect them from the atmosphere and prevent corrosion. However, during processing the lines are unprotected. Some of the steps to which they are subjected during processing are quite aggressive and can result in a significant yield loss. This paper pertains to the loss which is due to corrosion during processing. It focuses on the corrosion behavior of the two of the most commonly used conductors, aluminum and copper. Aluminum alloyed with small amounts of copper is also considered. The corrosion-related behaviors of aluminum and copper are vastly different, as is shown by their reaction with water and several processing solutions. The challenge of minimizing corrosion during processing as well as during subsequent storage and use is discussed, using suitable examples drawn from studies of thin films of the metals exposed to chemical etching, reactive ion etching, and cleaning.