The effects of post-deposition processes on polysilicon Young's modulus

Polysilicon films deposited by low pressure chemical deposition (LPCVD) are the most widely used structural material for microelectromechanical systems (MEMS). However, the properties of LPCVD polysilicon are known to vary significantly, depending on deposition conditions as well as post-deposition processes. This paper presents extensive experimental results, investigating the effects of phosphorus doping and texture on Young's modulus of polysilicon films. Polysilicon films are deposited at 585, 605 and 625 degrees C to a thickness of 2 mu m. Specimens with varying phosphorus doping levels are prepared by diffusion doping at various temperatures and times using both POCl(3) and phosphosilicate glass (PSG) as the source. 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 decreases with increasing doping concentration, and increases with increasing [111] texture. The polysilicon grain size and grain boundaries could also have an influence on Young's modulus, which remains to be further investigated.