Electroplating of conductive polymers for the metallization of insulators

Electrodeposition of copper was investigated on thin films of poly(3,4-ethylenedioxythiophene) (PEDOT). This conducting polymer can be processed from solution and exhibits a high specific conductivity of about 300 S/cm. N-(3-Trimethoxysilyl-propyl)pyrrole was applied as a primer in order to adhere PEDOT to the substrates. The lateral propagation or front velocity of the copper front and the uniformity of the copper deposit were determined as a function of sheet resistance of the PEDOT films, type of PEDOT counterions, and of the temperature, applied potential and composition of the electrochemical baths. The experimental data obtained are interpreted using a simple mathematical model to describe transient thickening during electrodeposition on electrodes of high ohmic resistance. A good agreement with experimental data is obtained, especially for the front velocity being inversely proportional to the square root of the sheet resistance. Quantitative analysis of uniformity data shows that the affinity for nucleation is much higher on the conducting polymer than on the deposited metal. This conclusion is supported by activation energies as determined from temperature-dependent metallization experiments. Finally, adhesion of copper deposits as a function of copper thickness and morphology of the substrate are discussed.