2018 年 84 巻 868 号 p. 18-00273
For designing sensors, it is very important to know the mechanical strength of constituent thin film materials. Although material strength is generally measured by tensile experiment, it is difficult to apply it to thin films. In this work, we developed a new method which can easily evaluate the fracture strength of thin film. In the method, first, silicon nitride and silicon oxide are alternatively deposited on a silicon substrate. Then, a target thin film is deposited on the top surface of the specimen and the silicon substrate of the back side is removed to form a diaphragm at the central region. Since the substrate around the diaphragm is thick, the specimen can be easily handled without fracture. The multilayered diaphragm realizes to break the target film by tensile deformation. After an air pressure is applied to the top surface of specimen until the diaphragm is broken, the fracture strength of the target film is obtained by stress analysis based on the experiment results. Adapting this method to a titanium thin film of 230 nm thickness, the fracture strength was evaluated to be 2.3 ± 0.2 GPa.