This work presents a new and low cost multi-level 3D copper interconnect process for RF and microwave applications. This process extends 3D interconnect integration technologies from silicon to above-IC polymer. Therefore, 3D passive devices and multi-level interconnects can be integrated using a single electroplating step making the process suitable for 3D-MMIC integration. 3D interconnects are realized by patterning the SU-8 to specific locations to create the desired 3D shape. A 3D seed layer is deposited above the SU-8 and the substrate to insure 3D electroplating current flow. The BPN is used as a thick mold for copper electroplating with an aspect ratio as high as 16:1. An optimized electroplating process is later used to grow copper in a 3D technique, insuring transition between all metallic layers. Finally, high-Q (60 @ 6 GHz) power inductors have been designed and integrated above a 50 W RF power LDMOS device, using this process.
IntroductionToday, RF and microwave applications demands for increased functionality, higher density integration, better passive device performance, reduced footprint and cost are stressing for new and enhanced integration technologies. To meet these requirements, technologies like 3D-MMIC were introduced [1]- [4]. These technologies look promising because they offer a solution for both miniaturization and passive device performance issues. However, their complexity, cost and processing time increase quickly with each addition of a dielectric or a metallic layer, which hindered their large scale usage. Moreover, the performance of the passive devices is severely limited by the relatively thin dielectric layers. Thus, stacking several dielectric layers is required to improve the performance of these devices which often induces more complications like increased residual stress on the chip and the frequent need for mechanical dielectric leveling steps.In another hand, to overcome 3D-MMIC limitations, a specific 3D interconnect technology is needed to replace current planar technologies used for implementation of passive circuits such as filters, matching networks, transformers ... or for the integration of inductors often realized from bond wires. This implies that the technology must allow the integration of both the interconnect and the vias for underneath connection.Finally, current 3D interconnect technologies are focused on the 3D stacking of integrated circuits, at the IC-fab, or, at package level, to achieve a higher integration density and a smaller footprint of electronic components [5]. Such a technology would be more attractive if it could be applied as well for above-IC passive devices integration. However, this