Study Of Low Temperature Cu-Cu Bonding Technology Based On Self-Propagating Reaciton Joinning

With the rapid development of the microelectronics manufacturing industry,three-dimensional package manufacturing technology came into being,and achieved higher integration,higher performance,and lower power consumption by stacking integrated circuits in the vertical direction.However,because of the large reduction in feature size,the original micro-connection and backend packaging process can no longer meet the new requirements of packaging.In this paper,the self-propagation reaction bonding process of Cu foils with single Sn layer,Sn-Cu and Sn-Ni alternating multilayer film were systematically studied,with the support of the National Key Basic Research and Development Program,“The formation and Performance Control of three-dimensional high-density micro-interconnect structure array”.And we also further explored and studied the low-temperature bonding process of large-scale Cu bumps array.?1?Cu substrates electroplated Al/Ni nanofoil with Sn layers of different thicknesses from 1?m to 7?m,were bonded under a pressure of 5 MPa through igniting the Al/Ni nanofoil with an electric spark generated by a 15 V DC power source.When the thickness of the Sn plating layer is less than 4?m,the defects like holes and cracks reduced significantly with the increasing of the Sn layer thickness,and became stable at 4?m.The thickness of the Cu6Sn5 layer at the Sn/Cu interface increased as the thickness of the Sn layer increased,then slowed down when Sn layer was beyond 4?m and stablized at 6?m.The shear strength showed the same changing trend with the thickness of Cu6Sn5 layer and was considered to be highly correlated with the thickness of Cu6Sn5 layer.After aging treatment at 150°C,the thickness of the IMC layer increased significantly with the time of aging treatment,while the shear strength decreased.The low growth rate of Sn-Cu IMC in Cu-Cu self-propagating reaction bonding is presumably because of the hindrance of Ni element diffusion to Cu and Sn atoms at the interface.?2?The Sn-Sn-Cu-Sn-Cu multilayer film was prepared on the surface of the Cu substrates by alternatly plating process.Electrical spark was also utilized to ignite the nanofoil and realized the Cu-Cu self-propagating reaction bonding under 5 MPa.Compared with that of the bonds with Sn single layer of same thickness,the shear strength of bonds with Sn-Cu showed some increase,which was far less than the increase of the Cu6Sn5 layer thickness.It was mainly ascribed to the small pores and stress concentration caused by the volume shrinkage during the formation of Cu6Sn5.When the Sn/Cu thickness ratio was increased to 2?m/1?m,the thickness of the Cu₆Sn₅ layer was substantially stable,while the shear strength was reduced because of the cracks caused by the stress concentration.While compared with the bonds with the Sn-Cu multilayer film of same thickness setting,,the bonds with Sn-Ni-Sn-Ni-Sn multilayer film showed higher density,less micro-voids defects and higher shear strength.And the shear strength was also greatly improved.The EDX analysis of the frature surface suggested that the fracture mainly occured at the interface between Ni3Sn4 and Sn within the Sn-Ni multilayer.In general,the Cu-Cu self-propagating reaction bonding with Sn-Ni multilayer was better than that with Sn-Cu multilayer,especially in the bonding defects and shear strength.?3?The high density Cu bumps array was electroplated with Sn-Ni alternating multilayer film on the surface through alternatly plating.After alignment,the Cu bumps were bonded at one time by rapid heating high to 4K/s.When the Sn/Ni thickness ratio was 250 nm:250 nm,the stratification between Sn and Ni layers disappeared,with a large area of network structure of Ni3Sn4.When the Sn/Ni thickness ratio was increased beyond500 nm:250 nm,the reaction and conversion of Sn and Ni was slowed,while the stratification phenomenon was clearly visible.The Sn layer next to the Cu bump was exhausted and left a very thin layer because of the high activity of Cu.The shear strength of the bonds measured were all higher than 100MPa,which could be mainly attributed to the denser bonding interface with few defects,stronger bonding force between the Sn/Ni multilayer with the electroplated Cu bumps,and the staggered effect of the two sides interfaces between Ni3Sn4 IMC and residual Sn?or Ni?.As the Sn/Ni thickness ratio increased,Ni3Sn4 increased and the shear strength increased from 107.8MPa to 162.5MPa.When the Sn/Ni thickness ratio of Sn/Ni increases to 1000nm:250nm,there are more Sn remaining,and the fragile interface between Sn and IMC reduced the shear strength.