INDUCTORS USING 2.5D SILICON INTERPOSER WITH THICK RDL AND TSV-LAST TECHNOLOGIES

Abstract

Abstract Silicon interposers represents an interesting alternatives to organic packages for the fabrication of complex System In Package (SIP) modules especially for RF application. Among the advantages of this technology are the capability to fabricate fine-pitch redistribution layers and also to embed high quality passive components inside the interposer. This allows the passive components to be very close to the active chips resulting in highly integrated and high performance systems. To keep the technology at a reasonable cost these last add-on features need to be fabricated with no or minor additional process steps that the ones needed for the fabrication of the interposer itself. In this work we present the design and the fabrication of various design of planar and 3D inductor devices fully compatible with the realization of a silicon interposer that is used to host an RF transmitter system operating in the 0.4 to 1 GHz frequency range. The inductors are built using two thick levels of copper RDL, on both sides of a high resistive silicon substrate and connected by through silicon via-last (TSV-last). This later doesn't require additional metallization to be realized. A dedicated test vehicle was designed to study various inductor types including planar spirals, 3D solenoids and 3D torus. To facilitate the design work, parameterized cells were built for each type of inductors. The structures geometry are designed and optimized, using electromagnetic simulator, to target inductance values in the range of 0.5 to 10 nH while addressing a quality factor greater than 20. The second part of the paper focuses on the process used to build the test vehicle, especially the realization of thick copper RDL layers on both sides of the interposer silicon wafer and the TSV-last module. Physical and DC electrical characterizations are presented to assess the integrity of the individual technology modules like thick copper RDL and TSV. The last part of the work is dedicated to the electrical characterization of the inductor devices in the targeted RF frequency range. Experimental results are presented and discussed in order to give some insight on the impact of the different design parameters on the performances of the inductors.