Material properties of electroless 100-200 nm thick CoWP films

Thin CoWP films have been electrolessly deposited for VLSI interconnect and packaging application. The films stick well to copper, however do not react with copper until about 500C. Therefore, it can be used under the copper as barrier layers or above as capping layers to protect the copper from corrosion. The CoWP film can be deposited on Si or SiO2 coated with specific seed layer that initiates the self-catalytic electroless deposition reaction. We deposited CoWP on sputtered Cu, Co and on wet activated by diluted PdCl2: HCI solution in DI water. In this work, we present the basic electrical and material structure and composition of electroless deposition of CoWP on those three activated surfaces. We established a calibration curve that defines the W content in the solid versus the tungstate ion concentration in the solution for Pd activated surface, We also compared the results for various analytical methods and found some discrepancies. We focus on film with about similar to 90 similar to 80002) that was strong on copper, weaker on cobalt and much weaker on Pd activated. High resolution SEM show that CoWP has different morphology on different seeds, probably due to different nucleation conditions that leads to different growth patterns. Thin as deposited film resistance was in the range of 40 mu Omega-cm. on Cu, 80 mu Omega-cm. on Co and more than 100 mu Omega-cm. on Pd activated surface.