Control of Photocorrosion in the Copper Damascene Process

Since chemical mechanical polishing for damascene processes producing copper interconnections is a wet-chemical treatment, corrosion control is indispensable. In addition to ordinary corrosion due to chemical and galvanic reactions with slurries, a new type of corrosion, pattern-specific corrosion, was found. It was clarified to be a kind of anodic corrosion observed only when the damascene process was used to make copper interconnections for active devices, occurring after the metal polishing is completed and the electrodes are electrically separated from each other. A positive potential is generated on the copper electrodes connected to the p + -diffused region against that connected to the n + -diffused region of a p-n junction when the fabrication is carried out in a light environment. The positively biased electrodes corrode quickly, especially in diluted rather than undiluted slurries, resulting in pattern-specific photocorrosion. Less corrosive slurries, especially in diluted state, or corrosion-preventing cleaning methods are therefore needed.