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

Polysilicon films deposited by low-pressure chemical vapor deposition (LPCV D) exhibit tensile or compressive residual stresses, depending on the depos ition temperature. Polysilicon films composed of alternating tensile and co mpressive layers can display any overall stress value between those of the individual layers, including a state of zero overall residual stress, depen ding 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-ze ro stress gradient (<less than or equal to>0.2 MPa/mum) polysilicon film, c ontaining flat cantilever beams whose length-thickness ratios exceed 150. U sing multilayer deposition to control the stresses and stress gradients of polysilicon films is termed the MultiPoly process.