Impact of long, high temperature anneals on residual stress in polysilicon

This work is intended to facilitate the development of surface micromachined polysilicon MEMS with post-processed on-chip circuitry. It evaluates the impact of a 1200°C, 16 hour anneal upon the residual stress in CVD polysilicon under 6 different sets of processing conditions. It shows that (i) undoped polysilicon has a final stress of 10-20 MPa even though the films are vastly different as deposited; (ii) an RTA step at 1000°C before the long anneal increases the final tension to ≈300 MPa; and (iii) phosphorous doping introduces a compressive trend that is evident only after the long anneal. TEM and X-ray diffraction studies of the polysilicon are also presented, as is the effect of the long anneal on wet thermal and CVD oxides