Lpcvd Polycrystalline Silicon Thin Films: The Evolution of Structure, Texture and Stress

Abstract

ABSTRACTAn investigation of undoped LPCVD polycrystalline silicon films deposited at temperatures ranging from 605 to 700 C and silane pressures from 300 to 550 mTorr revealed large variations in stress with processing conditions and a correlation between stress and texture. TEM and HRTEM analysis show that morphology differences also exist. At lower temperatures (≈605 C) and higher pressures (≈400 mTorr), the films appear to deposit in an amorphous state and crystallize during the deposition to form microstructures characterized by equi-axed grains, tensile residual stress, and a texture with {110} and {11/} (/=2 or 3) components. Higher temperatures (between 620 and 650 C) produce films that nucleate at the Si02 interface, creating a {110} oriented columnar microstructure. At 700 C, the grains are still columnar, but the dominant texture is {100}. Films deposited at temperatures greater than 620 C exhibit compressive stress, and some contain regions of hexagonal silicon. This paper proposes possible causes of the varying stresses, textures, and microstructures in the films.