Optimisation of copper electrodeposition processes for Si technology based inductive microsystems

Electrodeposition has been demonstrated as a useful technique for the fabrication of inductive devices formed by thick Cu coils with low stress and good adherence to silicon-based substrates, as required for advanced microsystems compatible with Si technology. Different baths with variable amounts of electrolytes and additives were tested. Stress and microstructural properties of copper deposits were analysed. Best deposits were obtained from acidic solutions containing high Cu(II) concentrations and moderated amounts of three additives. In these conditions, low stress measurements and no preferential orientation of copper were observed, especially on Si/SiO2/Ti/Cu substrates. At optimised conditions, several microns thick copper coils of different aspect ratio were prepared, which showed good adherence on the substrate after removing the resin mask and the seed layer. The characterisation of these devices corroborates the interest and suitability of the optimised electrochemical processes for advanced Si technology microsystem applications.