Quasi-Monolithic Integration (QMI) Enables New Possibilities for Sensor and MEMS Applications

Abstract:
Monolithic integration is the traditional approach in semiconductor technology, where all the components of a circuit (such as transistors, resistors, capacitors, etc.) are fabricated on a single silicon chip. In quasi-monolithic integration, the approach is similar, but there are certain distinctions and more modular elements. Features of quasi-monolithic integration are combined chiplets: In some cases, the integration may involve chips/chiplets or components that, while physically separate, are connected in such a way that they function together as if they were a single monolithic system. Fraunhofer IPMS uses this approach to integrate sensor-, MEMS-, AI- and ASIC-chiplets together on one wafer. This allows e.g. for sensor- and/or actuator arrays with a high count of interconnects. In this paper we report on the detailed integration concept featuring QMI on silicon wafers. Additionally, first results are shown regarding the preparation of the wafer/interposer for the assembly of the chiplets. This involves the fabrication of pocket wafers, where we compare deep dry etching in bulk material with the fabrication of pocket wafers with two bonded wafers (BSOI approach). It is demonstrated that the BSOI approach features exact geometries and low bottom surface roughness suitable for the following QMI steps.