Thermal stability and bonding interface in Cu/SiO2 hybrid bonding on nano-twinned copper

Abstract

Cu/SiO2 hybrid bonding has been developed for the application of heterogeneous bond interfaces in 3D integrated circuits in which thermal stability and bonding behavior are important. Thus, nano-twinned Cu (NT-Cu) is selected as the bonding material, and the thermal stability of NT-Cu and the bonding behavior of the interface between NT-Cu are investigated using a scanning electron microscope, electron backscatter diffraction, and focused ion beam. In addition to the microstructure analysis, nano-indentation and nano-scratch are employed to characterize the mechanical properties of the matrix and the interface between NT-Cu. As the bonding temperature increases from 200 to 300 °C for NT-Cu, the average grain sizes increase from 0.64 to 0.87 µm, and the rate of grain coarsening increases from 0.14 to 0.25 µm/h1/2. In addition, the fraction of voids at the bonding interface for NT-Cu interconnects decreases from 0.814% to 0.005%, and the penetration depth increases from 228 to 745 nm with an increase in the temperature from 200 to 300 °C. The hardness of the bonding interface obtained by nano-scratch and nano-indentation array testing is ∼1.8 GPa.