Study On The Controllable Generation And Performance Evolution Of Micro-interconnect Interfaces

Three-dimensional integration of microelectronics is a disruptive technology that drives the development of multi-functional,small-sized,high-density and low-cost products and has become the high ground of the world’s high-technology competition.The copper pillar microbump in 3D integrated package is the core structure of chip interconnection,and the continuous size reduction brings system integrity and reliability challenges.There is a lack of research on the growth pattern of intermetallic compound(IMC)and its impact on the mechanical properties of microbump during service;secondly,the anisotropy of microbump with several grains is prominent,and the IMC selective growth behavior and thermomigration failure problems need to be investigated;in addition,the full-IMC microbump has high strength and melting point,which is beneficial for the microbump to resist collapse and remelt during the chip stacking process,and its impact on reliability is unclear.Therefore,an in-depth study of micro-interconnect interfaces controllable generation techniques and reliability-related mechanisms is of great theoretical and practical application value.In this thesis,we propose a temperature gradient method to control IMC generation,and systematically study the strength degradation behavior of microbump in service and the size effect law of atomic selective diffusion behavior in finite Sn grain microbump under temperature gradient.The method of introducing high temperature gradient during thermocompression bonding to rapidly prepare full-IMC microbump is proposed to optimize the mechanical properties of microbump.The main research results are as follows:(1)The Cu/Sn-3.5Ag microbump with/without Ni barrier layer of 25μm diameter was subjected to 400 h isothermal aging and shear tests,and it was found that the Ni barrier layer effectively inhibited IMC growth(53 %)and better enhanced the shear strength of the microbump(19.1 %).During 150 °C isothermal aging,Cu/Sn atomic interdiffusion caused rapid growth of interfacial IMC,and volume shrinkage was limited in the solid Sn-3.5Ag solder,forming a weak IMC/Sn-3.5Ag interface,causing the fracture site of Cu/Sn-3.5Ag microbump to shift from the Sn-3.5Ag solder region to the IMC/Sn-3.5Ag interface,and the microbump strength was weakened.(2)The effect of Cu/Ni/Sn-3.5Ag microbump size on microbump reliability was investigated,and from mutual verification by mathematical modeling and shear tests,it was found that microbump size shrinkage led to accelerated IMC growth and degradation of microbump strength.After 400 h of isothermal aging,the microbump diameter shrinks from 100 μm to 25 μm,the IMC growth rate increases by 12.7 %,and the microbump strength decreases by 15 %.A multi-parameter coupled shear strength prediction model based on neural network(ANN)for IMC thickness,microbump height and diameter was proposed and the accuracy of the model was verified by experiments.(3)The IMC growth at the microbump interface of finite Sn grains shows a significant anisotropy and exhibits meritocratic growth under the temperature gradient.IMC grew rapidly along the high orientation difference grain boundaries(>15°)and in Sn grains where the grain c-axis was at a low to medium angle to the temperature gradient(<55°),and grew slowly along other locations.The mechanism of thermomigration leading to interconnection failure was explored,and the high orientation difference grain boundaries where tensile stresses accumulate and the hot end IMC/Sn-3.5Ag interface are prone to crack generation,resulting in thermomigration failure.In addition,the hourglass-shaped microbump is ineffective in suppressing the thermomigration failure.(4)The high temperature gradient introduced in the thermocompression bonding process has successfully produced full-IMC microbumps with significantly higher melting points and shear strength than conventional microbumps,meeting the requirements for collapse resistance and remelting resistance of microbumps in 3D integrated package chip stacks.The liquid-solid interface reaction is accelerated under the temperature gradient,and the IMC grows diffusely,so that the volume can shrink freely without creating tensile stresses and void interfaces that weaken the microbump strength.The strength of 40 μm diameter full-IMC microbump is 2 times higher than that of 100 μm conventional microbump(49.8 MPa),which effectively solves the problem of degradation of microbump strength due to size reduction during service.