A thick-Cu process for add-on interconnections using photosensitive varnish for thick interlayer dielectric

A thick-Cu process suitable for the fabrication of add-on interconnections for microwave passive elements on ULSIs has been developed. The following three novel techniques were employed: electroless plating for a Ru/Ni cap layer on a Cu film to prevent oxidation, a simple thick-Cu interconnection fabrication process using a positive-type photosensitive varnish, and a thick interlayer dielectric film (ε=2.9) under the Cu interconnections to reduce RF power loss in a regular silicon substrate. By using these techniques, spiral inductors with high quality factors (Q_max of 38) and a co-planar waveguide with low losses (<0.2 dB/mm) were obtained