Three-dimensional Simulation Of The Interaction Between The Micro-bump Joints And Cu Protrusion In Cu-filled TSVs And Its Effect On Reliability Of The Joints In 3D Integration

In recent years,electronic products have become increasingly miniaturized and multifunctional,and the integrated circuit packaging and integration technologies have been developing rapidly.Notably,three-dimensional(3D)integration has been seen as a more feasible solution to increase the number of transistors per unit volume so as to extend the so-called Moore's law.As one of the most important approaches for realizing 3D integration,through silicon via(TSV)technology enables massive silicon chips to stack and to be interconnected vertically,which has been applied in the field like high performance computing(HPC)and artificial intelligence(AI).However,owing to severe mismatch in coefficient of thermal expansion(CTE)between Cu and Si,protrusion of Cu filler often occurs obviously at the mouth of the Cu-filler via and high thermal stresses are generated in TSV structures,resulting in plastic deformation of Cu fillers.Generally,micro-sized bumps are used to connect the TSV chips by stacking perpendicularly,and there exists direct interaction between the micro-bump joint and the end of Cu-filled TSV,that is,Cu protrusion in the TSV under the alternating and/or cyclic stress can push the micro-bump joint,vice versa,the micro-bump joints can restrict Cu protrusion to some extent.In this thesis study,based on the finite element theory and using COMSOL Multiphysics,single-layered TSV chip structure model without micro-bump joints and two-layered TSV chip structure model with micro-bump joints,as well as four-layered chip stack(4-hi)and eight-layered chip stack(8-hi)High Bandwidth Memory(HBM)structure models are constructed.The mechanical behavior of Cu-filler TSVs and micro-bump joints under different loading conditions of temperature cycling and temperature-electric cycling are characterized,and the fatigue bahavior of the joints is also studied.The influences of the joint geometry on Cu protrusion and fatigue performance of the joints,i.e.,the joint size effect,have also been investigated.The simulation results show that the height of Cu protrusion increases with peak temperature rises in thermal cycling,and the height in two-layered chip TSV structure model is slightly lower than that in the one-layered model.During temperature cycling,at 125 ? the Cu protrusion height is affected more prominently by h,and with increasing h/d ratio,Cu protrusion height exhibits a largely increasing trend at 125 ? while showing declining trend at 25 ?.When h/d ratio increases,the fatigue life of micro-bump joints prolong,and shrinking geometries of micro-bump joints result in dramatic decline in fatigue life of the joints.Thus,more attention should be paid to the reliability of micro-bump joints with the decreasing size.From the fatigue property point of view,8-hi stack HBM model is superior to 4-hi stack HBM model,and the fatigue life prediction obtained based on twenty temperature cycles is more reliable than that predicted from four temperature cycles.Therefore,in purpose-oriented research or engineering applications a sufficient number of temperature cycles should be applied so as to obtain reliable data.Under electro-thermo-mechanical multi-physical fields,not only is Joule heat generated,but also electric current crowding occurs at the corner between Cu pad and the micro-bump joint.Cu protrusion height varies significantly depending on coupled physical fields,which appears to be the largest under the electro-thermo-mechanical fields,the second largest under the thermo-mechanical fields and the smallest under the electro-mechanical fields.