MECHANICAL-PROPERTIES OF THIN-FILMS FROM THE LOAD DEFLECTION OF LONG CLAMPED PLATES

A plane-strain load-deflection model for long plates clamped to a rigi d support is developed, The analytical model describes the nonlinear d eflection of plates with compressive or tensile residual stress and fi nite flexural rigidity under uniform load. it allows for the extractio n of the residual stress and plane-strain modulus of single-layered th in films, properties of compressively and weakly prestressed materials are extracted with an accuracy achieved previously only with tensile samples. Two approximations of the exact model are derived. The first reduces the plates to membranes by neglecting their flexural rigidity. Considerable errors result from this simplification, The second appro ximation provides an exact expression for the linear plate response. U sing the model, mechanical properties were extracted from two plasma-e nhanced chemical-vapor deposition (PECVD) silicon nitride films with w eakly tensile and compressive prestress, respectively. Measured residu al stresses are 1.3 +/- 3.8 and -63 +/- 12.4 MPa, respectively. Corres ponding plane-strain moduli are 134.4 +/- 3.9 and 142 +/- 2.6 GPa, res pectively.