Site Specific Microstructural Evolution of Thermo-mechanically Fatigued Copper Films

Copper metallizations used in modern power semiconductors have to withstand cyclic thermo-mechanical loading over the full operational life-time. Hence, detailed knowledge about the microstructural changes is required to better understand ongoing fatigue mechanisms and specifically to enable improvement of the fabrication process. Therefore, a microstructural characterization method was applied which combines a site-specific analysis using atomic force microscopy (AFM) and electron backscatter diffraction (EBSD) throughout thermal cycling. Studying the same surface area with AFM and EBSD enables a determination of global microstructural parameters, such as surface roughness, grain size, and grain boundary characteristics with cycling, and hence exhibits a great potential for universal microstructural analysis regardless of the loading process. We report about combining topographical and crystallographic information by tracking the identical surface area. Our observations indicate diffusional mass transport at grain boundaries, quantified by height profile evolution, grain growth, and twin boundary migration.