Electroless copper deposition for ultralarge-scale integration

The characteristics of electroless copper plating on different substrates of TiN/SiO2/Si, Cu-seed/Ta/SiO2/Si, and Cu-seed/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 mum on Cu-seed/TaN/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 Cu-seed/TaN/SiO2/Si substrate, while no preferred orientation is found on the other substrates. After thermal annealing at 400 degreesC in N-2/H-2 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 mu Ohm cm at room temperature. (C) 2000 The Electrochemical Society. All rights reserved.