Thermal stability of electroplated Cu films with different microstructure by annealing treatment

Copper has replaced Aluminum in the high-end electronic products for its excellent electrical conductivity, thermal conductivity and electromigration resistance, which is widely used as interconnection structure as Redistribution Layer (RDL), Cu Pillar Bump, Through Sillcon Via (TSV), and so on. Electroplating Cu with damascene process is the main manufacturing technology in industry production. However, in order to accelerate Cu layer growth from bottom to up, different organic and inorganic additives are used in electroplating process, which causes Cu structure instability. As a result, it is easy to occur recrystallization and grain growth in the process of self-annealing or aging, which affects the mechanical properties and service reliability. For example, in Cu-Cu direct bonding process, the extremely anisotropic grain growth will cross the bonding interface and enhance the bonding strength. In this work, three different structure Cu films, commercial polycrystalline copper (CP-Cu), highly (111)-orientated nanotwinned Cu ((111)-ntCu) and micro-cone arrays with vertical nanotwins Cu (micro-cone ntCu) were electroplated by changing the additives and electrodeposition modes to study their microstructure stability during annealing process. Secondary ion microscopy of three kinds of copper films after aging 1 hour and 4 hours at 400℃ were obtained by Focused Ion Beam and texture orientations were tested by X-ray Diffraction (XRD). The thermal stability of different microstructure during annealing was studied by the above experiments. CP-Cu grain growth was controlled by Ostwald ripening mechanism to reduce surface energy. Nanotwin boundaries and high angle grain boundaries formed stable structure and storage large stress, which facilitated extremely anisotropic grain growth.