Laminated wafer with conductive diamond layer formed by surface-activated bonding at room temperature for micro-electro mechanical system sensors

Abstract

We propose the use of a laminated wafer with a conductive diamond layer for forming cavities as an alternative silicon-on-insulator wafer for micro-electro mechanical system (MEMS) sensors. Since this wafer has no insulator such as a buried oxide (BOX) layer but a conductive layer, it is not charged during plasma treatment in MEMS sensor fabrication processes. The conductive diamond layer was formed on a base wafer doped with boron of more than 2 × 1021 atoms cm−3 by microwave-plasma-enhanced chemical vapor deposition. The resistivity of this layer was 0.025 Ω cm, and this layer can be selectively etched to a base wafer made of silicon crystal, such as a BOX layer. In addition, a silicon wafer can be bonded to its layer without voids with gaps of more than 2 nm by surface-activated bonding. Therefore, we believe that the laminated wafer studied here is useful for the fabrication processes for MEMS sensors that may otherwise be damaged by plasma treatment.