High aspect ratio single crystalline silicon microstructures fabricated with multi layer substrates

This paper reports a method for making high aspect ratio single crystalline silicon (SCS) microstructures on multi layer substrates using chemical mechanical polishing (CMP), silicon fusion bonding (SFB) and reactive ion etching (RIE) techniques. First Si-SiO₂-PolySi-SiO₂-Si sandwich wafers were fabricated using CMP and SFB. Then microstructures were fabricated on these sandwich wafers using an one run self-aligned RIE process, where polysilicon was used as the sacrificial layer. Polishing and bonding of low pressure chemical vapour deposition (LPCVD) polysilicon were studied. A LPCVD Si_3+xN₄ polishing stop layer technique was developed to accurately control the final thickness of the device layer. The uniformity of the device layer was improved as well