Transmission electron microscopy investigation of the microstructure and chemistry of Si/Cu/In/Cu/Si interconnections

Si/Si interconnections, obtained using a Cu metallization and an In interlayer and joined by diffusion soldering are presented. The Si/Cu/In/Cu/Si bonds were accomplished due to isothermal solidification and subsequent interdiffusion of In and Cu in the samples held at 180 °C. Application of a transmission electron microscope (TEM) with an attachment for high-resolution chemical analysis allowed characterizing the microstructural and microchemical feature of the intermetallics formed in the joint. Appearance of two phases, namely η(Cu2In) and δ(Cu7In3), was confirmed by electron diffraction patterns and energy-dispersive X-ray (EDX) analysis. The bond quality and the high melting point of the phases (≈630 °C) indicate a great potential of this technique for joining of integrated circuits in electronics.