Deposition and Characterization of In-Situ Boron Doped Polycrystalline Silicon Films for Microelectromechanical Systems Applications

Abstract

In an effort to develop thick, p-type polycrystalline silicon (polysilicon) films for microelectromechanical systems (MEMS) applications, in-situ boron-doped polysilicon films were deposited by a single-step APCVD process at susceptor temperatures ranging from 700°C to 955°C. The process produces boron-doped films at a deposition rate of 73 nm/min at 955°C. Spreading resistance measurements show that the boron doping level is constant at 2 × 1019 /cm3 throughout the thickness of the films. Doped films deposited at the low temperatures exhibit compressive stress as high as 666 Mpa; however films deposited at 955°C exhibited stress as low as 130 MPa. TEM and XRD show that the microstructure strongly depends on the deposition conditions. Surface micromachined, singly clamped cantilevers and strain gauges were successfully fabricated and used to characterize the residual stress of 5.0 µm-thick doped films deposited at a susceptor temperature of 955°C.

MEMS Technology: A Review

“…At 600°C, the grains are small and equiaxed, whereas at 625°C, the grains are large and columnar [77]. The inclusion of boron generally increases the deposition rate of polysilicon relative to undoped films, whereas phosphorus reduces the rate [24,78]. In SiO2 doping is commonly used to produce conductive films for electrostatic devices, but has also been used to create polysilicon-based piezoresistive strain gauges, with gauge factors as high as 15 having been reported [79].…”