Selective Copper Metallization for Advanced Packaging

Abstract

Interconnects are one of the most difficult steps in the manufacturing process, particularly at advanced process nodes with more metal layers to connect, both internally and externally. The Cu damascene process is widely applied in BEOL of IC industry for interconnect formation while conventional Cu electrochemical deposition (ECD) approach is standard process flow in the packaging area. Conventional Cu ECP has low cost but has limitation on the width of line/space, the process cost will dramatically increase for smaller pitches. At same time, the shrinkage of line/space cannot be prevented with device density increasing. The Cu damascene process can easily achieve sub-micron line/space, it is the dominant interconnect technology for advanced semiconductor chip manufacturing. In a traditional process, trenches and via in dielectric layers are filled by ECD of copper followed by chemical mechanical planarization (CMP) for removal of the metal from field areas of the wafer, CMP has been an enabling technology for the use of copper in damascene technology. It has rapidly become one of the most important and widespread processes, also very costly one. For this application and for any similar process sequence, substantial savings are possible if the metal could be deposited in a selective manner and focused primarily into the features of interest rather than following the traditional inefficient approach of depositing a blanket layer. A novel method for selective deposition (Selectroplating®) has been developed and evaluated for several types of metallization applications. This technology is based on a selective chemical modification (SCM) of field areas of a wafer or substrate and can be implemented for either a fill-based integration, such as Cu dual damascene, or an additive process such as plating of wide conductive lines. In either integration, the primary benefit of selective deposition is to prevent metal from being deposited in areas between desired features thus eliminating the need to remove excess bulk in the next step. Cost savings are realized in two ways: 1) less metal is consumed from the plating bath thus extending bath life and lowering the average deposition cost, and 2) substantially less bulk metal must be removed in the subtractive step which lowers the polish or etch time. This improves throughput and further decreases cost.