Thin copper seed layers in interconnect metallization using the electroless plating process

In this paper, we present a process for growing a Cu seed layer on a Ta/SiO2/Si substrate using an electroless plating (ELP) process at an extremely low temperature (similar to30degreesC). In this process, the activation treatment of the Ta/SiO2/Si substrate was carried out by immersion in a PdCl2/HCl solution prior to electroless Cu deposition. The optimum activation time for the substrate was clearly observed to be 7 min. The Cu seed layer was uniformly and smoothly deposited using a CuSO4 concentration of 30 mM for 80 s with an average roughness of 14 nm under a thin film of 50 nm thickness. The grain size of the Cu seed layer was 34 nm. After annealing in hydrogen ambience at 250-350degreesC, the average roughness of the Cu seed layer was reduced to 4 nm. A proposed mechanism for the ELP of Cu seed layers on Ta/SiO2/Si substrates is also presented.