Measurements of the mechanical properties of composite membranes by load-deflection method with a profilometer

Composite membranes are basic mechanical components frequently used in MEMS for different tasks like signal trasduction (pressure sensors), isolation (microheaters) or merely as a support (passive microwave devices). The design of membranes for these and other applications requires the exact knowledge of mechanical properties of the single materials composing the membrane, like internal stress and Young modulus. Both are influenced by process conditions and therefore have to be determined for each material. To this purpose, the membrane itself can be used as test structure. In this work the use of a commercial profilometer to conduct load-deflection measurements on composite membranes is presented. The use of the profilometer results in a simpler measurement set-up with respect to the more traditional techique of appliying a controlled pressure difference. The approach is tested on composite membranes of poly-Si and silicon nitride that were designed to this purpose and are apart of test structures that can be inclusded in a MEMS fabrication process. Internal stress measurements of poly-Si are presented and compared with measurements obtained with the cantilever beam technique