Buckling of polysilicon microbeams during sacrificial layer removal

In situ observations of buckling evolution of polysilicon microbeams during etch of the underneath sacrificial layer were carried out under an optical microscope. The surface geometry was obtained by AFM measurements. As the etching progressed, three buckling patterns were identified. Closed formulas were derived from theoretical analysis based on both boundary conditions: simply supported and clamped. The theory predicts either the buckling pattern for a given residual stress or the compressive stress level for a given buckling pattern. The residual stress evaluated from the buckling pattern agrees with that measured by the curvature method.