Molecular Dynamics Study On Mechanical And Interfacial Properties Of TSV Thinned Wafer

As electronic devices move toward thinner and lighter,integrated circuit?IC?chips continue to increase integration and reduce feature size in accordance with Moore's Law,and silicon wafer is the primary substrate for IC chip fabrication.In order to meet the current thin,light,and miniaturized packaging requirements,silicon wafer needs to be thinned.In the silicon wafer thinning process,the surface and subsurface damage are inevitable,which imposes a direct impact on the strength of the wafer.How to detect and reduce the depth of the subsurface damage layer is an important research content of nano-scale grinding processes.It is of great significance to study the related mechanical problems in the back-grinding thinned process of Through Silicon Via?TSV?wafer by molecular dynamics?MD?simulation,which can provide theoretical guidance for the development of wafer thinning process.The MD model of nano-scale grinding of monocrystalline silicon was established,and the grinding mechanism and damage mechanism were studied.The results show that the nano-grinding process of monocyrstalline silicon mainly focuses on extrusion and shear deformation,and the phase transition is the main deformation mechanism and damage layer is mainly amorphous silicon.The study found that when the grinding speed is 160 m/s,the depth of the subsurface damage layer is the smallest;and with the increase of the grinding depth,the subsurface damage layer depth is also gradually increasing.At the same time,the mechanical properties of the damaged layer were studied.The results show that the Young's modulus of the damaged layer is2.49%lower than that of the ideal monocrystalline silicon,and the ultimate tensile strength is decreased by 43.58%.That is to say,the thinning process causes the strength of the wafer to decrease.The residual stress generation and distribution of monocrystalline silicon during nano-grinding were studied by Raman spectroscopy,MD simulation and theoretical model.The results show that the grinding surface is mainly composed of residual compressive stress,with the increase of depth,the residual stress gradually changes from compressive stress to tensile stress.The greater depth of the grinding,the greater residual stress on the surface.The cause of the residual stress in the nano-grinding process is mainly the phase transition.The phase change causes the shrinkage of the model volume.The uneven volume change causes residual stress in the thinned wafer.In order to study the mechanical properties of polycrystalline copper filled in TSV wafer,the MD model of nanocrystalline copper was established,and the effects of strain rate,grain size and temperature on the mechanical properties and deformation mechanism of nanocrystalline copper were studied.The results show that the mechanical properties are sensitive to high strain rate and insensitive to low strain rate.The dominant mechanism of plastic deformation of nanocrystalline copper with a grain size from 4.65 to 12.41 nm is grain boundary sliding and grain rotation.Dislocation nucleation and expansion are no longer the dominant factors of plastic deformation.The elastic modulus and flow stress increase with the increase of grain size and decrease with the increase of temperature.The interfacial properties of the TSV wafer contained the Cu-Ta,Ta-SiO₂,SiO₂-Si intefaces were systematically studied by molecular dynamics simulation.The interface tensile strength,shear strength and failure strain of the three interfaces were obtained.At the same time,the cohesive model parameters of the TSV wafer interface at the micro/nano scale were obtained,and the Finite Element-Cohesive Zone model?FE-CZM?of the TSV wafer back-grinding thinning was established.Interfacial failure mechanism during the back-grinding process showed that the interface failure occurs firstly in the Cu-Ta interface,and the other interfaces subsequently fail.