Theoretical and Experimental Analysis of Residual Stress Mitigation in Piezoresistive Silicon Nitride Cantilever

In this work, we reports the design and technology optimization with residual stress balancing of piezo resistive silicon nitride micro cantilever stress sensors, which can be used for surface stress measurements in the liquid medium. In this context, the residual stresses of the thin films in a 600 nm thick cantilever stack (Si3N4/Poly Si/Si3N4/Au) were evaluated by curvature measurement on a test wafer to refine the balancing of the structure. In particular, the thickness of bottom silicon nitride was optimized to 300 nm to achieve the best trade-off between stress compensation and sensitivity. The cantilever bending curvature angle was calculated to be 45° and 19° with and without Au, as a top immobilization layer for the micro cantilever device. Further, finite element analysis results shows that for the low length/width ratio of cantilever, the stress sensitivity was better as compared to high aspect ratio.