Nanocrystalline copper and nickel as ultra high-density chip-to-package interconnections

Nanocrystalline (nc) copper and nickel are being explored as candidate interconnect materials for nanoscale interconnections to meet the requirements of fine pitch, superior electrical and mechanical performance while also catering to the environmental and cost concerns. Bulk nanocrystalline copper and nickel (99.999% purity) specimens of average grain size of about 50 nm were prepared by equichannel angular extrusion (ECAE). Both micro- and nanohardness measurements showed a significant increase in the hardness of the bulk specimens. The grain size analysis shows that copper is stable up to 100°C and the activation energy for grain growth was calculated to be around 35 KJ/mol. The nickel specimens were found to be stable up to 250°C. The tensile strength of these materials has been found to be 5-6 times of the conventional microcrystalline forms and the fracture toughness, J_IC, values for nc- copper and nickel have been found to be 21.66 KJ/m² and 12.13 KJ/m², respectively, which are high for these strength levels indicating considerable capacity for plastic deformation in these materials prior to fracture.