Low thermal budget low stress thick polysilicon films for MEMS using ultra-high vacuum e-beam evaporation

This paper describes the use of Ultra-High Vacuum (UHV) E-beam evaporation of silicon to produce remarkably low stress thick polysilicon films at a significantly low thermal budget. The surface morphology, crystallinity, micro-structure, resistivity, and Young´s Modulus of boron doped and undoped e-beam evaporated silicon films have been studied at various substrate deposition temperatures and deposition rates. Furthermore, annealing of as-deposited films at 600°C can reduce stress to the desired level. Smooth boron doped polysilicon films as thick as 30μm with residual stress as small as 19MPa, stress gradient of 1.7MPa/μm and Young´s modulus of 161GPa have been achieved at a deposition temperature of 500°C followed by an hour of annealing at 600°C.