A new technique for producing large-area as-deposited zero-stress LPCVD polysilicon films: the MultiPoly process

Abstract

Polysilicon films deposited by low-pressure chemical vapor deposition (LPCVD) exhibit tensile or compressive residual stresses, depending on the deposition temperature. Polysilicon films composed of alternating tensile and compressive layers can display any overall stress value between those of the individual layers, including a state of zero overall residual stress, depending on the relative thickness of each layer. The residual stress gradient can be similarly controlled by the layer thicknesses and distribution. This has been demonstrated with a ten-layer near-zero stress (<10 MPa), near-zero stress gradient (/spl les/0.2 MPa//spl mu/m) polysilicon film, containing flat cantilever beams whose length-thickness ratios exceed 150. Using multilayer deposition to control the stresses and stress gradients of polysilicon films is termed the MultiPoly process.