The Micro-mechanical Investigation And Life Prediction Method Of Electromigration Phenomenon

With the minimization and higher integration of electronic products,the current density in the metal micro interconnects increases rapidly.The higher current density will easily lead to the electromigration phenomenon occurred in the micro interconnections.This paper focused on the electromigration failure problem of metal micro interconnect structure,and operated the electromigration acceleration test by taking different influence factors into consideration,and analyzed the failure mechanism of two types of electromigration modes.At the same time,from the perspective of atomic diffusion and mechanical properties,this paper analyzed reliability of different crystals and their interface structure via molecular dynamics simulation,and revealed the influence of various factors on the electromigration lifetime at the microscopic level.On the macro level,based on the theoretical system of atomic density integration,by considering the degradation behavior of materials and developing adaptive time step algorithm,this paper optimized the efficiency and accuracy of the algorithm.Firstly,based on the electromigration speed test platform,the failure modes of solder joints under different current density and temperature are analyzed via electromigration experiments.By comparing the distribution of IMC?Intermetallic Compound?inside the solder joints,the consumption of pads and the location of voids and cracks in different working conditions,and the isothermal aging results,the failure mechanism of two types of electromigration failure modes?atomic diffusion dominated and crack penetration dominated?are studied.At the same time,considering the inhibition of atom diffusion between pad and solder with Ni/Au barrier layer,this paper analyzed the effect of pad on the formation of IMC and the work of Ni/Au barrier layer on electromigration failure mode.In addition,the EBSD?Electron Backscattered Diffraction?technology is used to analyze the crystal structure of solder joints.It can be found that each solder joint contains only severial grains.Therefore,more attention should be paid to material properties corresponding to grain level.Secondly,addressing to the abnormal consumption of pad during the electromigration and aging experiments,this paper studied the different grain interface structures on the micro scale via molecular dynamics simulation.From the perspective of atomic diffusion behavior,crystal mechanical properties and the interface structure strength,this paper analyzed the Ag₃Sn,Cu₃Sn and the interface structure that constructed by different grains,and investigated the influence of stress and crystal orientation on the reliability of grain interface.Results show that compressive stress can promote the diffusion of atoms,while the tensile stress has the opposite effect.The orientation of the pad also directly affects the atomic diffusion and the interfacial strength,which depends on the interface matching between the pad and the Cu₃Sn interface.For the macroscopic aspect,based on the theory of atomic density integration method,this paper taken the degeneration of electrical resistivity during the electromigration into consideration,and developed the adaptive time step algorithm to improve the computational efficiency and accuracy,and the SWEAT structure was used here for the verification.Meanwhile,this paper investigated the effect of common and non common twin structure on the reliability of electromigration,and gave the guideline for electronic packaging industry.