The Effects of Texture and Doping on The Young's Modulus of Polysilicon

Polysilicon films deposited by low pressure chemical deposition (LPCVD) are the most widely used structural material for microelectromechanical systems (MEMS). However, the structural properties of LPCVD polysilicon films are known to vary significantly, depending on deposition conditions as well as post-deposition processes. This paper investigates the effects of phosphorus doping and texture on Young's modulus of polysilicon films. Polysilicon films are depostied at 585°C, 605"C, and 625°C to a thickness of 2µm. Specimens with varying phosphorus doping levels are prepared by diffusion doping at various temperatures and times using both POCl3 and phosphorsilicate glass (PSG) as the source. Texture is measured using an X-ray diffractometer. Young's modulus is calculated by taking the average of the values calculated from the resonant frequencies of four-different size lateral resonators. Our results show that Young's modulus of diffusion doped polysilicon films decreases with increasing doping concentration, and increases with increasing texture.