Abstract

The rapidly growing IoT industry sets new demands for MEMS devices, the central building blocks of smart systems. Advanced MEMS devices are commonly built on thick-film bonded Silicon-On-Insulator wafers (BSOI) but the tightening requirements on SOI wafer specification and device layer thickness uniformity in particular are driving traditional planarization technologies like CMP to their limits.

Okmetic’s new process with superior thickness variation control fully independent of SOI film thickness and suitable for high volume production complements today’s manufacturing technologies perfectly. This new trimming technique for thick-film SOI processes reduces film thickness variation by a factor of five achieving a typical thickness variation of 20-30 nm (1σ) across a 200 mm SOI wafer. This is clearly beyond those achievable through traditional BSOI volume production. The process performance has no equal for film thicknesses above 5 µm but it can also be used in applications previously dominated by alternative SOI technologies in the range < 2 µm such as specific high-performance MEMS sensors, SOI-based smart power devices and silicon photonic devices. The process also brings significant advantages for MEMS applications in which SOI film thickness variation is critical, such as silicon oscillators and pressure sensors.