FABRICATION OF MULTILAYER SUBSTRATES FOR HIGH-ASPECT-RATIO SINGLE-CRYSTALLINE MICROSTRUCTURES

This paper reports a new method for making multi-layer substrates (MLS ) for high aspect ratio single crystalline movable microstructures usi ng a group of technologies, such as direct wafer bonding (DWB), chemic al mechanical polishing (CMP), and reactive ion etching (RIE). As a fi rst example, Si-SiO2-polySi-SiO2-Si sandwich wafers were fabricated us ing CMP and DWB. Subsequently, free-standing micro cantilever beams an d double side clamped bridges were fabricated on these sandwich wafers using a one-run self-aligned RIE process, where polysilicon was used as the sacrificial layer. Polishing and bonding of low pressure chemic al vapour deposition (LPCVD) polysilicon were studied. An LPCVD Si3+xN 4 polishing stop layer technique was presented to accurately control t he final thickness of the device layer. The uniformity of the device l ayer was improved as well. (C) 1998 Elsevier Science S.A. All rights r eserved.