Mechanical properties of phosphorus-doped polysilicon films

Polysilicon films deposited by low pressure chemical vaper deposition (LPCV D) are the most widely used structural material in microelectromechanical s ystems (MEMS). However, the structural properties of LPCVD polysilicon film s are known to vary significantly, depending on deposition conditions as we ll as past-deposition processes. This paper investigates the effects of pho sphorus doping and texture on Young's modulus of polysilicon films. Polysil icon films are deposited at 585 degrees C, 605 degrees C, and 625 degrees C to a thickness of 2 mu m. Specimens with varying phosphorus doping levels are prepared by the diffusion process at various temperatures and times usi ng both POCl3 and phosphosilicate glass (PSG) source. Texture is measured u sing an X-ray diffractometer. Young's modulus is estimated from the average values of the resonant frequencies measured from four-different size later al resonators. Our results show that Young's modulus of diffusion doped pol ysilicon films decreases with increasing doping concentration, and increase s with increasing < 111 > texture.