Characterization of Nanoscopic Cu/Diamond Interfaces Prepared by Surface-Activated Bonding: Implications for Thermal Management

The microstructures of Cu/diamond interfaces prepared by surface-activated bonding at room temperature are examined by cross-sectional scanning transmission electron microscopy (STEM). A crystalline defect layer composed of Cu and diamond with a thickness of approximately 4.5 nm is formed at the as-bonded interface, which is introduced by irradiation with an Ar beam during the bonding process. No crystalline defect layer is observed at the 700 °C annealed interface, which is attributed to the recrystallization of the defect layer due to the high-temperature annealing process. Instead of the defect layer, a mating interface layer and a copper oxide layer are formed at the interface. The mating interface layer and the copper oxide layer play a role in relieving the residual stress caused by the difference between the thermal expansion coefficients of diamond and Cu. The thermal boundary resistance (TBR) of the as-bonded interface is measured to be 1.7 ± 0.2 × 10–8 m2·K/W by the time domain pulsed-light-heating thermoreflectance technique. These results indicate that the direct bonding of diamond and Cu is a very effective technique for improving the heat-dissipation performance of power devices.