Thin Copper Seed Layers in Interconnect Metallization Using the Electroless Plating Process

摘要

In this paper, we present a process for growing a Cu seed layer on a Ta/SiO_2/Si substrate using an electroless plating (ELP) process at an extremely low temperature (～30℃). In this process, the activation treatment of the Ta/SiO_2/Si substrate was carried out by immersion in a PdCl_2/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 CuSO_4 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 250-350℃, 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/SiO_2/Si substrates is also presented.