Sn-Cu thin film transient liquid phase bonding test with different underlayers using fully-in-vacuum wafer aligner/bonder

This paper compares different diffusion barriers for thin film transient liquid phase (TLP) bonding. Thin film TLP bonding has some advantages such as low process temperature and a large tolerance of bonding surface roughness. However, metal diffusion phenomena in TLP bonding is so complicated that bonding strength is dependent on metal systems. In this study, Sn-Cu TLP system was selected and its bonding strengths with several diffusion barriers were evaluated by die shear test. The microstructure of the bonded metal part was examined by scanning electron microscopy and energy dispersive X-ray spectrometry. The diffusion barriers of multilayered Cu/Cr, Cr-Cu and Ni worked, and the best bonding strength was obtained using Au/Sn/Cu/Cr-Cu/Cr metal system (10/200/1000/100/100 nm), where Cu thickness is doubled compared with the other samples. This paper also describes a new wafer bonder in which alignment, surface treatment and bonding can be performed without breaking vacuum.