Raman microprobe analysis of strained polysilicon deposited layers

Microscopic strain distributions in varying thicknesses of polysilicon layers deposited as bridges over silicon substrates were determined by high resolution micro-Raman spectroscopy. In particular, we mapped the dependence of the first order Raman spectrum as a function of the position across polysilicon bridges (approximately 550 × 230 μm2), over tunnels etched in the silicon substrate. Shifts in Raman band frequencies as a function of position on the bridge structures were observed to be dependent upon the thickness of the membrane layer (between 1 and 3 μm) as well as the annealing conditions. Assuming a simplified uni-axial stress parallel to the surface, the effective tensile stress at the center of the bridge of thickness 2.5 μm is reduced by annealing from 2.5 GPa to 0.18 GPa.