Mechanical stress in thin film microstructures on silicon substrate

Analysis of residual stress in thin films and its influence on silicon microstructures was performed. Deflection behaviour of silicon membranes due to built-in stress in deposited thin films was investigated in the scope of different bilayer structures which are commonly met in microstructures such as piezoresistive pressure sensors. Silicon membranes are usually covered by thin films such as thermal oxide, LPCVD or PECVD nitride, as required by the actual fabrication process. In our case, high compressive stress was determined for stoichiometric LPCVD nitride (1.2 GPa) and PECVD nitride (706 MPa) while for thermal oxide tensile stress of 298 MPa was determined. Furthermore, thin film cantilever and bridge microstructures were designed, fabricated and investigated, showing that by a proper combination of thin films in the stacked layer, residual stress can be reduced to a reasonable amount without compromising the dielectric properties of thin films.