Advanced Filtration for Copper Electrochemical

Copper has become established as the material of choice for reducing interconnect time delay in the 90nm manufacturing node and below. Copper process parameters are sufficiently understood to make copper plating an accepted and enabling technology. The key issues in copper plating include controlling trench/via profiles and aspect ratios, achieving desired seed layer properties, stable levels of organic additives and bath chemistry management. The reduction of defects in the copper film will lead to productivity gains. As process engineers work to wring out incremental productivity gains, optimization of the filtration scheme employed is receiving attention as an area for productivity improvement.

When considering compatibility issues, one must be certain that the filter is not altered by extended contact with copper plating solution components, and that the filter materials are benign in regard to their impact on the fluid and its components.

Current filtration requirements vary based on overall system design and cleanliness. Pointof- use filters used in recirculation mode are typically 0.1 um and, increasingly trending towards 0.05 um as cleanliness requirements are becoming more stringent. The addition of appropriate filtration to the copper plating process will immediately reduce sub-micron particle counts in the plating tank to very low levels and contribute to defect reduction.

Proper filtration will result in cleaner plating baths and fewer potential defects. Selecting a finer filter can lower particle counts further. The trade off to using a finer filter is the increased flow resistance and membrane thickness (if conventional membranes are used). This slows bath turnover rates and can exceed system pumping capacity. Conventional membrane designs achieve acceptable flows by over packing filter surface area.

Unfortunately, this may increase compatibility, additive stripping, extractible and disposal concerns. By using the Varaclean CET filter’s highly asymmetric membrane structure, it's possible to achieve primarily mechanical retention down to 50 nanometers with minimal impact on flow.