Selective and Blanket Electroless Copper Deposition for Ultralarge Scale Integration

Abstract

Electroless Cu thermodynamics, electrochemistry, mechanism, kinetics, and mass transport are reviewed. Electroless Cu deposition is a thermodynamically favorable and kinetically inhibited process, with two electrochemical reactions including anodic oxidation of a reducing agent and cathodic reduction of metal ions occurring simultaneously, with a multistep catalytic redox mechanism, an Arrhenius type of rate equation, and mass‐transport limited reaction in narrow and deep features such as subhalf micron trenches and vias of high aspect ratios (>3). Selective and blanket electroless Cu deposition from formaldehyde‐based solutions with ethylenediaminetetraacetic acid as a complexing agent was investigated for trench/via filling applications. A single‐wafer electroless Cu deposition system with up to 8 in. wafer capability has been designed and manufactured. An electroless Cu deposition solution and operation conditions have been optimized to obtain electroless Cu films at high deposition rate (∼75 to 120 nm/min), with low resistivity (ρ 2 μΩ cm), low surface roughness (R _a ∼ 10 to 15 nm for ∼1.5 μm thick deposits) and good electrical uniformity (std dev in situ Al dissolution in the plating bath. Electroless Cu films blanket deposited on sputtered Cu/Al seed layer were conformal with 100% step coverage. A novel wet seeding method has been developed with Cu contact displacement deposition on a TiN diffusion barrier to provide selective and blanket electroless copper plating. Subhalf micron (down to 0.3 μm) trenches and vias of high aspect ratios (up to 5:1) were completely filled for both blanket and selective electroless deposition modes.