Nihon Kikai Gakkai ronbunshu (Oct 2015)
Cu/Cu bonding and SiO2/SiO2 bonding by surface activated bonding at room temperature for hybrid bonding technique
Abstract
It has been said that the end of Moore’s law will be reached in 10 to 20 years. Three dimensional integration technology is expected to be a possible solution in the post-Moore era. The bonding of the metal electrode and insulator hybrid interfaces is one of key technique in three dimensional technology. The hybrid bonding technique is highly challenging issue. Surface activated bonding (SAB), which is a bonding method carried out at room or low temperatures, is expected to solve various problems which caused by heating process. Metal materials such as Cu or Al are easy to directly bond by SAB method at room temperature, but insulator materials such as SiO2 or SiN is very difficult. First, we investigated the bonding interface of Cu/Cu by transmission electron microscopy (TEM) observations. No intermediate layers or voids were visible at the bonding interface. The bonded specimen fractured not at the interface of the bonded Cu/Cu, but at the interface between the thermal oxide layer and Ti film by tensile test. The current-voltage characteristic of the bonding interface was linear. Secondly, we proposed a new bonding technique for bonding of SiO2/SiO2 using Si ultra-thin films by applying the SAB method. The amorphous Si layer with the thickness of about 7 nm was observed at the bonding interface by TEM observation. The bonded specimen fractured at the glue interface and not the bonded interface by tensile test. The bonding strength is estimated to be higher than the adhesive glue for tensile test. We have shown that the SAB method at room temperature is a bonding technique that can fulfill requirements for hybrid bonding, which serves as both mechanical bonding and electrical connection, in 3D integration technology.
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