Development of Cu Interconnects for 20nm Technology Node LSI

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Copper (Cu) has long been used as the wire material for high performance ultra large-scale integrated circuits (ULSIs). However, the significant increase in the resistivity of Cu wire with line widths less than 100 nm is a critical issue^< (1-3)>. In order to lower resistivity, both the coarsening of the grain sizes and the reduction in the thickness of high-resistivity barrier metals in Cu wires are crucial. However, a powerful grain size coarsening process to reduce electron scattering has not yet been developed up to now. It was recently reported that contamination in Cu films depress their grain growth during annealing^< (6)>.This implies that low resistivity Cu wires could be created if high-purity very narrow wires can be formed. Hence, we have focused our attention on the purification of Cu wires and the investigation of a forming process using ultra-high purity 9N-Cu anode and high purity 6N-CuSO_4・5H_2O electrolyte.Using the above high purity process, we have realized 50 nm wide Cu wires with about 21% lower resistivity than those made with the conventional process. It was also found that the low resistivity Cu wires formed with the new process have large grain sizes with a lower spread, and a much smaller amount of oxygen than those made with the conventional process.