Stress Buffer for TSV Package Interconnects

A stress buffer layer is introduced as an intermediary component between the TSV contacts and the substrate. This buffer layer has a coefficient of thermal expansion (CTE) that is intermediate between the high-CTE TSV material (typically copper) and the lower-CTE silicon substrate. The stress buffer absorbs and redistributes the thermal expansion mismatch stress, preventing direct stress transmission to the substrate and TSV interfaces, thereby maintaining package reliability while reducing substrate stress.

The stress buffer layer is formed using composite material structures, such as alternating layers of dielectric materials with different CTE properties (e.g., silicon oxide and silicon nitride). This composite structure allows the buffer to exhibit tailored effective CTE that matches the intermediate value needed, while also providing mechanical compliance to absorb thermal stress. The composite nature enables simultaneous achievement of stress relief and structural integrity.

The stress buffer layer is formed prior to TSV contact formation and extends partially through the substrate depth. This preliminary placement of the stress buffer ensures that when subsequent processing steps (etching, filling, planarization) are performed, the buffer is already in position to manage stress during thermal cycling. The buffer's preliminary presence prevents stress-induced defects from forming during manufacturing, thereby maintaining higher yield and reducing rework costs.

The stress buffer layer changes the effective thermal and mechanical parameters of the TSV structure. By introducing a layer with intermediate CTE and appropriate elastic modulus, the overall thermal stress distribution in the stack is modified. The buffer's depth (less than full TSV depth) and material composition are optimized to achieve the desired stress reduction while maintaining electrical performance, thereby improving yield without requiring complete substrate replacement or redesign.