Design of process monitoring structures for residual stresses in MEMS membranes

Understanding and managing the inherent stress within deposited films is crucial in various microfabrication processes. This aspect is becoming even more vital, particularly in MEMS (Micro-Electro-Mechanical Systems) applications, especially when thick layers are involved. In this work, we use a structure that is stress sensitive to measure residual stresses in a copper film in a MEMS process. These strain sensors are fabricated using surface sacrifice technology. It can amplify the residual strain in film. Once the residual strain is released, the sensors will generate significant distortion, which can be clearly observed under a microscope, according to the value of residual strain in film. In this way, the expansion (or shrink) of structures on the film can be measured precisely.We performed a simulation study of the structure using COMSOL Multiphysics. A finite element model of the stress sensitivity of the micro-rotating beam was established to study the relationship between the stress sensitivity characteristics of the rotating beam's end displacement and the parameters of the test structure. The results indicate that the sensor’s performance meets the desired design criteria.