IC-compatible two-level bulk micromachining process module for RF silicon technology

This paper presents a novel two-level silicon bulk micromachining for integration of RF devices. The RF devices are fabricated at the frontside of Si(100) wafers using conventional IC technology. A post-processing module is applied from the wafer backside with precise alignment to the frontside. This module can provide a blanket ground plane at an optimum position beneath the wafer surface, a frontside contact from the wafer surface to that ground plane, and trenches to suppress crosstalk through the conductive silicon by adding two mask levels. An extension to four masks allows for an integration of large passive components beneath circuitry for a much reduced chip area, lowering chip size and cost. The feasibility of the novel post-process module is demonstrated through the fabrication of microstrip transmission lines, conductor-backed spiral inductors, trench-barriers against crosstalk through the conductive silicon substrate, and high-quality subsurface spiral inductors.