Study On The Field Regulation Of Anisotropic Hot Melt Diffusion Of Ag Interconnect

With the continuous development of microelectronics technology,the degree of integration of integrated circuits is constantly improving.The pattern transfer technology based on traditional optical lithography has gradually failed to meet the demand due to its own characteristics.In the next generation of pattern transfer technologies,nanoimprint technology stands out due to its high fidelity,high yield and low cost.The interconnects for IC devices or MEMS devices can be directly obtained by nanoimprinting using pseudoplastic nano metal particles as transfer media.However,there is organic solvent between the particles of the resulting interconnect,which with loose structure,low density and poor conductivity.In order to improve the mechanical and electrical properties of the interconnects,the subsequent auxiliary process is needed to optimize the imprinted interconnects,mainly by increasing the hot-melt diffusion between particles and reducing the void ratio.In this thesis,heat treatment is used to optimize the characteristic properties of the wire.The densification and conductivity of the wire can be effectively improved by using non mechanical contact ultrasonic assisted sintering at the same time of heat treatment.Ultrasonic waves act on the interconnections to achieve anisotropic shrinkage of the interconnections,so that the shrinkage of the wire in the vertical direction is greater than the shrinkage in the horizontal direction,ensuring that the wire will not break while being densely hot-melted.The optimization effect of ultrasonicassisted sintering is closely related to the frequency and propagation distance of the ultrasonic.When the ultrasonic amplitude is fixed and the frequency is 110 k Hz,the shrinkage of the interconnection reaches the maximum.Compared with the wire without ultrasonic sintering,the shrinkage increased by 30.8%,and the resistivity decreased by 30.7%.The shorter the propagation distance of ultrasonic waves in the air,the smaller the energy loss,and the better the optimization effect.When the ultrasonic frequency is too low,the sound pressure is small,and the wire shrinks less.When the frequency is too high,the ultrasonic attenuation rate is too fast,so that the energy reaching the wire is small and the wire shrinkage is not obvious.By using scanning electron microscope(SEM)and atomic force microscope(AFM)to scan the internal and surface structure of the wires,it was observed that the change trend of the particles is the same as the change trend of the shrinkage rate.Finally,through the hot press sintering model,the experimental results are reasonably analyzed.Silver is not magnetic and will not be affected in the magnetic field,so a small amount of nickel particles are doped into the silver nanoparticles,and the nickel particles are attracted by the magnetic field magnetization to squeeze the silver particles to produce stress.The experimental results show that the nickel doping concentration and the strength of the applied magnetic field will affect the shrinkage of the wire.Among them,the silver interconnection with a doping nickel mass fraction of 5 wt.% reaches the maximum shrinkage rate under the 15 m T magnetic field assisted sintering,and the conductivity also the best.If it is only doped with nickel particles,the density and conductivity of the interconnects without magnetic field during hot melt diffusion are poor.When the magnetic field strength is small,the shrinkage rate does not increase significantly.When the magnetic field is too large,the inside of the wire will be destroyed by the excessive stress of nickel particles and affect the performance of the wire.Observation of the microstructure by SEM and AFM revealed that the particles had become bigger.