Since the beginnings, the reliability problems draw attention in the field of electrical devices. The needs to understand the failure mechanism of unreliable components is permanent. One of the most challenging problems is the thermomechanical stress, which is considered mainly due to the mismatch of the thermal expansion coefficient of the different components. Temperature and mechanical stress are important variables, that must be monitored during the entire production process, firstly, and working phase, secondly. Indeed, local deviations can lead to uncontrolled changes. To evaluate the stress effects, Raman spectroscopy measurements were performed.

In this work, the local stress was analyzed in three case studies: the active layer of commercially available GaN-based LEDs and in Silicon and Silicon Nitride chips. Specifically, great attention was used examining how stress varies depending on bonding processes, such as temperature and pressure of soldering, as well as the impact of bonding and substrate materials on stress evolution. Raman spectroscopy was selected as the primary technique: it is non-destructive and allows for the analysis of materials both before and after bonding. The Raman investigation was performed on both metal and semiconductor properties of the materials of the integrated circuits. Stress phenomena were determined by 2D Raman mapping of the surface, in a wide temperature range, from -50 to 180° C. From the determination of the Raman peak position of Silicon, centered around 520 cm^-1, Si3N4, centered around 865 cm^-1, and GaN, centered around 568 cm^-1, the presence of tensile and compressive stresses on the samples were evaluated. Finally, the results were correlated to the process parameters to suggest possible optimization procedure to reduce the reliability problems in the structure of optoelectronic devices.