Electroplating copper onto resistive barrier films

An analytical solution for the metal resistance-controlled plating current distribution on circular wafers is obtained for determining the conditions under which a uniform metal film can be electrodeposited on a resistive film. Results indicate that, when using conventional copper plating solutions, uniform films cannot be deposited on 500 Angstrom thick barrier layers consisting of Ta (or more resistive metals) on 200 mm wafers, regardless of plating current density or the use of pulse reverse plating. 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, i(o). By lowering the copper concentration and thus i(o) in the plating bath by one or two orders of magnitude below levels that are commonly employed, the terminal effect can be reduced to the point where a uniform conformal conduction layer can be electrode posited. Subsequently, the bulk copper film can be plated at high rates. (C) 2000 The Electrochemical Society. S0013-4651(99)02-070-4. All rights reserved.