Process And Mechanism Of Cu/SiO₂ Low-temperature Hybrid Bonding Uing Ammonia Assisted Activation

With the continuous evolution of semiconductor technology,beyond Moore's Law has attracted more and more attention.Three-dimensional packaging technology is an important technology beyond Moore's Law.3D packaging technology forms a highly integrated system by vertically stacking and connecting various materials,technologies,and functional components.In order to pursue a three-dimensional package with a smaller interconnection pitch and a higher density,hybrid bonding has emerged,and the Cu/SiO₂hybrid bonding technology is the focus of competition in the semiconductor industry.In order to achieve the Cu-SiO₂ hybrid bonding,we Need to be compatible with Cu-Cu and SiO₂-SiO₂ bonding process,and Xperi company strictly keeps the relevant process confidential.The purpose of this article is to develop a low-temperature Cu/SiO₂ hybrid bonding process.In this paper,an ammonia-water-assisted bonding low-temperature hybrid bonding process is used to achieve Cu/SiO₂ hybrid bonding.For Cu wafers,the introduction of ammonia water will chemically react with the Cu wafers,which can dissolve CuO and Cu(OH)2 and change the surface chemical structure.The plasma has a bombardment effect on the Cu wafers and at the same time allows the Cu surface a higher energy.The Cu-Cu bonding quality was characterized by SAT,SEM,and tensile experiments.The SAT results showed that the bonding area of the bonded sample was close to 100%.Except for a small number of bonding voids and incomplete bonding regions,other regions were well bonded;the figures of SEM shows that the Cu-Cu interface is tightly connected without any cracks or delamination.The tensile strength test shows that when the Ar+2min ammonia water assisted activation method is used,the interface strength reaches 8.8MPa.For SiO₂-SiO₂,the effect of ammonia water is non-chemical,but a physical surface cleaning.As an inorganic solution,ammonia water can safely remove the oxide film on the surface of SiO₂ wafers without any residue.At the same time,the ammonia water is free of-OH can combine with Si atoms to form Si-OH,which is conducive to the realization of the hydrophilic bonding of SiO2;the effect of plasma on SiO₂ wafers is similar to that of ammonia,but its mechanism of action is different.The plasma is physically bombarded.The oxide on the surface of the SiO₂ wafer is removed,and the collision of high-energy particles makes the surface atoms of the SiO₂ wafer have higher activation energy and are more likely to be in an unstable state,so it is easier to adsorb-OH,thereby forming hydrophilic Si-OH.Ammonia-assisted activation of the low-temperature hybrid bonding process,this paper obtains a good Cu/SiO2 hybrid bonding sample,SAT shows that the Cu/SiO₂hybrid bonding sample has a good bonding area,and SEM shows that the Cu/SiO₂ hybrid bonding interface is either Cu-Cu,SiO₂-SiO₂ homogeneous interface or Cu-SiO₂heterogeneous interface,there is no defect and delamination phenomenon at the interface.The model construction and mechanism analysis of the Cu/SiO₂hybrid bonding process are carried out.The ammonia activation treatment and the addition of Ar plasma synergistically enhance the-OH density on the surface of SiO₂,making its hydrophilic bonding tendency stronger,while for Cu-For Cu bonding.The activation of ammonia water and the addition of Ar plasma remove the oxide film and contaminants on the Cu surface,and at the same time increase the activation energy of Cu atoms,enhance their diffusion tendency,and finally complete reliable bonding in the process of hot-press bonding and annealing strengthening.