Study on Electromigration of Nano-Silver Paste with Different Hot Pressing Sintering Conditions

Abstract

Silver is suitable for use as a interconnect material due to its good thermal conductivity and electrical conductivity. Additionally, nano-sized silver particles (or pastes) can be rapidly sintered at related low temperatures (<250°C ) due to their high surface to volume ratio. The nano-sized silver particle paste developed in this study can be hot-pressed at 250°C and 10 Mpa to form a low porosity (6.2%) and low-resistivity (2.9*10-8 Ω-m) interconnect, which is comparable to that of commercial available products. With the demand for higher packing density of integrated circuit, the interconnect line width decreases and the current density increases. In general, if the current density is increased to higher than 105 A/cm2, electro-migration phenomenon would become more serious and could cause unpredictable failure of interconnect. In order to understand the electro-migration mechanism of silver interconnect made by nano-paste followed by hot pressing sintering, the porosity of samples with different hot-pressing parameters was measured. Subsequently, current-stressing tests (at 250°C and 105 A/cm2 ) of interconnects were carried out. Through observations of changes in the surface morphology and cross-sectional microstructures during current-stressing tests, the failure mechanism and electro-migration phenomenon are investigated in detail. It is observed as shown in the figure that the electro-migration occurred in early stage (within about 1 day) that resulted in the decrease of porosity near cathode and increase of porosity near anode respectively. Figure 1 Figure 1