Reliability And Die Attaching Structure Of Low Temperature In-situ Sintering Mechanism Of Micron Copper Paste

Compared with traditional silicon-based devices,silicon carbide(SiC)high-power semiconductor devices have the advantages of lower power loss,higher efficiency,and higher thermal conductivity.And with the increase of semiconductor power,the requirements for high-temperature resistance of bonding materials are becoming more strict.With its superior electrical and thermal properties,good resistance to electromigration,and high cost performance,metallic Cu particles have obtained greater development potential in the field of low-temperature sintering of connecting materials.However,the easily formed oxides(Cu O or Cu₂O)on the Cu surface increase the difficulty of the low-temperature sintering.To solve the problems of low-temperature sintering of micron Cu and particle oxidation,a low-temperature in-situ reduction sintering technology of micron Cu paste was designed,which provides a solution for the reliable packaging of third-generation semiconductor devices.In this paper,a reducing organic solvent was used to prepare micron Cu paste,which were paste Gl(containing glycerol),pase As A+Gl(containing glycerol+ascorbic acid)and paste diluent(without reducing agent).Through the thermal analysis and sintering experiment of the paste,it was found that the addition of a reducing agent can effectively reduce the sintering temperature of micron Cu and improve the mechanical properties and the density of sintered structure.Based on the shear strength and the thermal conductivity test of the interconnection structure,the pastes containing different types of reducing agents and their sintering time were optimized and compared.With the addition of the strong reducing agent ascorbic acid,the porosity,shear strength,and thermal conductivity of the interconnected structure obtained by the paste As A+Gl under different sintering pressures were all higher than those of the paste Gl.With the sintered pressure of 20 MPa,the shear strength and the thermal conductivity of the interconnection structure were significantly improved,reaching 50.1 MPa and 103.4 W/(m·K),respectively.The in-situ reduction sintering of micron Cu paste can effectively solve the problem which oxides on the surface of Cu particles hinder the diffusion of surface atoms and deteriorates performance.The effect of pre-oxidation of Cu particles on its sintering performance was studied,and the micromorphology of the particles after oxidation was compared.The initial Cu particles with a small amount of Cu₂O on the surface were slightly oxidated to form a thin film with a thickness of less than 2 nm.Stored in the air at 90?for 2 h,the content of the oxidation reaction product(Cu₂O)increased and was distributed on the surface of the particles in the form of particles with a diameter of about 15 nm.With the sintering test,the paste prepared by pre-oxidized Cu particles showed excellent performance.Using such paste,the obtained sintered structure,interface densification connection,interconnected structure shear strength,and sintered structure thermal conductivity were all higher than those of the initial Cu particles under different sintering conditions.During the sintering process,the nano Cu particles generated from the Cu₂O nanoparticles on the surface of the Cu particles in the paste Gl+oxidized after the in-situ reduction reaction,increase the overall energy and accelerate the sintering reaction rate.Under the conditions of a sintering temperature of 250?,a sintering pressure of 20 MPa,and a sintering time of 15 min,the shear strength of the interconnect structure and the thermal conductivity of the sintered structure are 55.7 MPa and 94.2 W/(m·K),respectively.The reliability of the micron Cu paste prepared by the oxidized particles was investigated by the temperature cycle test.With the increase of the cycle period,the shear strength of the interconnection structure gradually decreases.When the cycle period of 300(600 h),the strength of the interconnection structure was still greater than 20 MPa,which was in line with application requirements.And with the increase of the cycle period,many Cu oxide particles appear at the cross-section,which should be the main reason for the failure of the interconnection structure.