Study On Wafer Thinning Containing TSV Heterostructure Based On Molecular Dynamics

In the technology of 3D high-density integration based on Through Silicon Via(TSV),wafer thinning is one of the key processes.During the thinning,many unknown problems concerning interface and surface are encountered,such as surface micro-cracks,interface diffusion,and stacking faults,dislocations,etc.,which seriously affect the consistency of the process and the reliability of the device.This dissertation studied TSV contained wafer thinning by the classic molecular dynamics(MD)method.The specific research contents are as follows:Initially,the MD models of single/polycrystalline copper nano-thinning were established,and the influence of abrasive particles on the surface morphology of workpiece and the propagation of internal defect were studied.Studies showed that the surface damages of single/polycrystalline copper after grinding were amorphous structures,and the damage in the subsurface area mainly showed as stacking faults on the {111} planes caused by dislocation motions,forming phase transitions from Face-centered-cubic(FCC)to Hexagonal-centeredpackaging(HCP).The grain boundary of polycrystalline copper prevented the extension of dislocations and the expansion of HCP,but the unit dislocations were much denser at the grain boundary.The crystal orientation affected the grinding force,and the grinding force fluctuated when the abrasives passed through the grain boundary.Secondly,the MD models of nano-thinning on dielectric layer-insulation layer/substrate were established,and the surface/subsurface damages of the material and the effects of the thickness of the dielectric layer on the damages were studied.The study showed that phase transition from FCC to Body-centered-cubic(BCC)was produced under the action of hydrostatic pressure,and the dense BCC structure caused a sharp rise in normal grinding force when the abrasive pressed into the workpiece surface.The thickness of the dielectric layer Cu affected the grinding process of the dielectric layer-substrate.The influence of the interface was weakened by increasing the Cu thickness,and the internal phase changes and defects caused by grinding were reduced.The thicker copper layer had fewer Shockley dislocations,and the dislocation defects were concentrated at the squeeze area on either side of the abrasive,as was irrelated to the Cu-Si interface.Finally,the MD models of the dielectric layer-barrier nano-thinning were established,the surface morphology of the workpiece and the material removal of heterogeneity were studied.The results showed that the thickness of the amorphous layer of the dielectric layer was about one atomic layer,which evenly covered the surface of the workpiece.The chips accumulated in the front of the abrasive.However,the chips of the barrier layer flowed to both sides of the abrasive,and the thickness of the amorphous layer on the surface of the barrier layer(monocrystalline titanium)was 7(?).The interface damage was manifested as a gap in the exposed interface after thinning,and the thickness of the interface in the thinning direction increased by amorphous atoms filling,forming a cut along the thinning direction.