LATERALLY ISOLATED POLYSILICON BEAM PROCESS

Abstract

This paper describes a process technology to make MEMS devices with laterally integrated polysilicon beam as the structural material instead of single crystal silicon for sensors/ actuators. The process consists of fabricating deep silicon trenches, which are then seamlessly filled with the layers of thermal oxide and polysilicon. The polysilicon on the surface is etched back, leaving behind the polysilicon only inside the trenches. The beams are then released by isotropically etching away the silicon surrounding the polysilicon/ silicon oxide structure. This results in free standing polysilicon beams, which form the MEMS structures. The thermal oxide surrounding the polysilicon can be removed by wet HF etch or by isotropic plasma etch. This process can serve as a general platform for realising various types of high aspect ratio MEMS devices. The various stages of the process development, in realising a low stress polysilicon beams and electrical isolation structures are described in the paper.