Electroless Copper Deposition for Ultralarge-Scale Integration

Abstract

The characteristics of electroless copper plating on different substrates of TiN/SiO2/Si, Cuseed/Ta/SiO2/Si, and Cuseed/TaN/SiO2/Si have been investigated. Continuous copper films with good surface morphology are obtained, and hydrogen-induced blister formation is inhibited by optimizing plating solution and conditions. Surface roughness of the electrolessly plated copper films increases with increasing film thickness, and the average roughness is 11 nm at a film thickness of 1 μm on CuseedTaN/SiO2/Si substrate. Conformal copper deposition with excellent step coverage completely fills deep subquarter-micrometer features of high aspect ratios up to five. Copper growth orientation depends on the underlayer structure. A copper film with strong (111) texture is plated on the (111) textured copper seed layer of CuseedTaN/SiO2/Si substrate, while no preferred orientation is found on the other substrates. After thermal annealing at 400 °C in N2/H2 for 1 h, Cu(111) texture is enhanced in all systems. By thermal annealing, defects in the plated copper are reduced, and the electrical resistivity of the plated copper is lowered to 1.75 μΩ cm at room temperature.