Copper / Benzocyclobutene Multi Layer Wiring - A flexible base Technology for Wafer Level Integration of passive Components

This paper describes the wafer level integration of coils, capacitors and resistors using copper/benzocyclobutene (Cu / BCB) thin film multi layer wiring. Examples for the application of this technology like integration of passives as above chip structures, realization of integrated passive devices as well as fabrication of thin film substrates with integrated passives prove Cu/BCB multi layer wiring to be a versatile base technology for the application-specific integration of passive components. The basic approach of using BCB as dielectric material is discussed to allow integrating high quality, but only small value capacitors in the range of some Pico Farads, which is due to the low dielectric constant of the material. In order to increase the capacitance density a new process allowing to replace the BCB locally by a thin glass layer in the areas of capacitors was evaluated. Since the BCB is only replaced in the areas of capacitors and still present in the other areas of the multi layer construction, the advantages of using BCB as dielectric material for multi layer wiring still apply. The evaluation of the new capacitor dielectric shows, that a 0.5 mum thick glass dielectric features a 26 times higher capacitance density compared to BCB with a thickness of 8 mum, as it has been used in the standard build-up for RF LC-filter integration so far. In order to show the capability of the new glass dielectric regarding size reduction, an existing layout of an integrated passive device with LC-filters is compared with a redesign based on the new technology. By using a 1 mum thick glass layer as dielectric instead of 8 mu thick BCB the total size of the device could be reduced by 28 %.