In Situ Phosphorus-doped Polysilicon For Integrated Mems

Abstract

In this paper we present a detailed study of in situ phosphorus-doped polysilicon deposition for microstructure fabrication. The dependence of deposition rate, resistivity and residual stress of the polysilicon films on the phosphine to silane mole ratio (PH/sub 3/ / SiH/sub 4/) and the deposition temperature are examined. Deposition at 590/spl deg/C and a PH/sub 3/ / SiH/sub 4/ mole ratio of 3.2x10/sup -3/ followed by rapid thermal annealing (RTA) at 900/spl deg/C for 60 s results in films with a deposition rate of 42 /spl Aring//min, a resistivity of 0.8 m/spl Omega/cm and a tensile residual stress of 36 MPa. In addition, films deposited at 585/spl deg/C and a PH/sub 3// SiH/sub 4/ mole ratio of 3.2x10/sup -3/ followed by RTA at 900/spl deg/C have a very small strain gradient and therefore exhibit little microstructure warpage. A 2 /spl mu/m thick, 1000 /spl mu/m long polysilicon cantilever beam shows an end deflection of less than 0.2 /spl mu/m.