Thin films stress extraction using micromachined structures and wafer curvature measurements

Internal stresses present in thin dielectric films are studied for mono and multi-layers composed of thermal oxide, LPCVD nitride and densified PECVD oxide. The stress measurements were obtained using two different techniques. The first was based on wafer curvature measurements to extract the stress in individual layers in order to foresee the mechanical behavior of multilayers composed of those materials. The second technique relies on micromachined microstructures using silicon as the sacrificial layer. The stress values obtained using these two techniques are in good agreement. The techniques were extended to multilayers composed of the three layers which were found tensile around 80 MPa with a strain gradient of 0.78%/@mm. These results are promising for the achievement of low stressed membranes to be used for instance in suspended sensors.