X-ray nanodiffraction was used to measure the thermal stress of 10 µm nanotwinned Cu bumps in Cu/SiO2 hybrid structures at -55 °C, 27 °C, 100 °C, 150 °C, and 200 °C. Bonding can be achieved without externally applied compression. The X-ray beam size is about 100 nm in diameter. The Cu bump is dominated by (111) oriented nano-twins. Before the hybrid bonding, the thermal stress in Cu bumps is compressive and remains compressive after bonding. The average stress in the bonded Cu joint at 200 °C is as large as -169.1 MPa. In addition, using the strain data measured at various temperatures, one can calculate the effective thermal expansion coefficient (CTE) for the 10 µm Cu bumps confined by the SiO2 dielectrics. This study reports a useful approach on measuring the strain and stress in oriented metal bumps confined by SiO2 dielectrics. The results also provide a deeper understanding on the mechanism of hybrid bonding without externally applied compression.
Keywords: Cu/SiO2 hybrid bonding; X-ray nanodiffraction; nanotwinned Cu; synchrotron radiation; thermal strain distribution.