Study of Cu Bimetallic Corrosion in CMP Chemical Environments Using Optical Scanning and Micropattern Corrosion Screening

On-chip corrosion within Cu interconnect microstructures can result in increased defectivity that causes serious reliability issues and decreases production yield. This active bimetallic corrosion is especially of concern when Cu/barrier contacts are directly exposed to corrosive chemicals during CMP and post CMP clean processes. In this paper, a new, rapid, corrosion screening metrology was developed using both micropattern corrosion testing and high resolution 3-D optical profilometry. Micropattern screening revealed that gallic acid, often perceived as anti-oxidant, is actually rather corrosive to Cu at pH >= 9. Increased Cu corrosion rates were found in oxygen rich ambients and with direct contact to nobler barriers like Ru. Efficient micropattern screening also enabled the discovery of new Cu corrosion inhibitors. The initial inhibition activation on the Cu surface was studied by 3-D optical profilometry.