Study of low load and temperature, high heat-resistant solid-phase Sn-Ag bonding with formation of Ag<inf>3</inf>Sn intermetallic compound via nanoscale thin film control for wafer-level 3D-stacking for 3D LSI

Abstract

Through-silicon via (TSV) technology for 3D-LSI is attracting much attention as a means of alleviating the miniaturization limits on advanced semiconductor devices. Despite a great deal of research, low load (<;1MPa), low temperature (<;200°C) and short time (<;5min) solid phase bonding with high heat resistance (>350°C) to prevent the damage of weak low-k dielectric material etc. has not been realized. In this work, we examine a new Sn-Ag thin film bonding system to replace Cu-Cu bonding. It is found that Ag/Sn/nano Ag-nano Ag/Sn/Ag thin film bonding systems (especially when the film thickness of the surface Ag is controlled to around 10nm) is a promising approach because 1) it enables low load (<;0.4MPa), low temperature (<;180°C) and short time (<;5min) bonding, and 2) the bonded interface has a high heat resistance (>400°C) and joint strength (>29MPa). We simulate the effects of the surface Ag from the viewpoint of energy stability at the nanoscale bonding level. It is found that it may be possible to realize an optimal solid phase bonding system for wafer-level 3D-stacking for 3D LSI which can satisfy a hierarchical temperature based bonding method that include TSV formation.