MEMS Process Flow Insensitive to Timed ETCH Induced Anchor Perimeter Variation on SOI and Bulk Silicon Wafer Substrates

This paper describes a novel silicon on insulator (SOI) process flow with an electrically isolated mechanical substrate anchor perimeter insensitive to SiO₂ sacrificial layer timed hydrofluoric acid etch variation. A novel low electrical resistance substrate connection is facilitated between the top SOI layer and silicon substrate using a polysilicon trench refill via process step. A process combining both the silicon nitride substrate anchor perimeter etch stop and polysilicon substrate electrical contact is provided with device characterization results. Additionally, this trench refill process is applied to bulk micromachined devices by utilizing SiO₂ and heavily boron doped polysilicon as the trench refilled EDP/TMAH etch stop films. A capacitive accelerometer suspended over 80 mum above the silicon wafer substrate is also demonstrated using this process technique.