Overcoming sheet resistance effects to enable electroplating of copper onto seedless barrier films

An analytical solution for the metal resistance-controlled plating current distribution on circular wafers is obtained to determine the conditions under which a uniform metal film can be electro-deposited on a resistive film. Results indicate that, when using conventional copper plating solutions, uniform films cannot be deposited on 500 Å thick barrier layers consisting of Ta (or more resistive metals) on 200 mm wafers, regardless of plating current density. Uniformity can be characterized by a dimensionless polarization parameter that reflects the influences of current density and physical and chemical properties. Of these properties, the only one that can be varied enough to allow Cu plating on a barrier film is the plating exchange current density, io. By lowering the copper concentration and thus io in the plating bath by one or two orders of magnitude below levels that are commonly employed, a uniform conformal conduction layer can be electro-deposited, subsequently allowing the bulk copper film to be plated at high rates