Characterization of Nanoscopic Cu/Diamond Interfaces Prepared by Surface-Activated Bonding: Implications for Thermal Management
Jianbo Liang, Yutaka Ohno, Yuichiro Yamashita, Yasuo Shimizu, Shinji Kanda, Naoto Kamiuchi, Seongwoo Kim, Koyama Koji, Yasuyoshi Nagai, Makoto Kasu, Naoteru Shigekawa
Abstract
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.