A micromachining post-process module for RF silicon technology

Abstract

A bulk-micromachining post-process module, based on twolevel structuring of RF silicon substrates and a 4 -p thick one-level sub-surface metal pattern, is presented. This allows for fabricating three-dimensional structures for novel RF components and has potential in more compact integration. Next to a concise description of the relevant aspects of the fabrication process, mechanical stability of the postprocessed wafers is analyzed. Sub-surface spiral inductors with good quality and low coupling to inductors built at the wafer surface are presented, thus demonstrating the feasibility of three-dimensional integration of RF components.

A Through-Wafer Interconnect in Silicon for RFICs

“…However, unconventional techniques have achieved better crosstalk suppression, such as porous silicon [7], [8], metal-filled trenches [6], and SOI on metal with Faraday cage [25]. A comparison between different crosstalk isolation schemes is difficult due to different references structures and test structure design.…”

“…A key consideration when evaluating crosstalk isolation schemes is the footprint of the isolation structure and nonstandard fabrication processes. For example, in [6] the metal trench is 60-m wide and in [8] 100-m wide, and [25] uses a buried metal ground.…”

“…Future systems will require densely packed circuits operating at high frequency. This has motivated substantial work in the development of substrate crosstalk isolation schemes [6], [8], [21]- [25].…”

“…Through-wafer vias in silicon have initially been demonstrated using KOH etching [5], [6]. However, this approach results in a poor aspect ratio with a large footprint at the wafer surface.…”

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

“…The results presented here are based on conference publications at ESSDERC'2000 and IEDM'2000 [8], [9]. In Section II, we explain the basic concept of the post-process module.…”