Towards 200mm 3D RF interposer technology

Abstract

With the advent of modern and autonomous electronics, applications using RF (radio frequencies) up to millimeter waves and beyond are proliferating. The systems integration becomes increasingly challenging due to variety of devices and passives that typically compose such RF modules, and careful choices of materials are needed for low loss interconnects. One way to minimize RF losses is to integrate the module with high performance interconnect using Si technology, where the different device are mounted on the interposer and the passive are integrated into the silicon. Thanks to the TSV (Through Silicon Via) technology and use of High Resistivity Si substrate, it is possible to have small form factor modules. Such integration approach allows to benefit from the well-established base of 200mm foundries together with the recent progress made in High Resistivity substrate manufacturing. In this work, the process development of a 3D RF interposer technology based on a 200mm process line is reported. The build-up contains 2 levels of metals processed by Cu damascene technology, including a thick 2μm top metal for the lower frequencies applications, an integrated MIM (Metal Insulator Metal) capacitor and use trough silicon via in 5kOhm high resistivity 85μm thick substrate. The TSV are 20μm diameter and 85μm deep made in via first manner with via reveal using temporary carrier handling. Various RF passivation techniques for the silicon have been investigated and a comparison to quartz based on similar test structure is discussed.. Variety of passive devices, transmission line and filter have been processed and characterized. The technology yields 1μm pitch interconnect routing layer, a line loss of 0.34 dB/mm at 40 GHz, and high quality factors inductors larger than 30.