Effects of Electromigration on Microstructural Evolution and Mechanical Properties of Preferential Growth Intermetallic Compound Interconnects for 3D Packaging

Abstract

The full preferential growth intermetallic compound (IMC) interconnects are fabricated on a (111) Cu single crystal substrate by the method named current driven bonding (CDB), and the morphology, orientation, electromigration resistance and mechanical properties of the full preferential growth Cu6Sn5 grains in the (111) Cu/IMC (30 µm Cu6Sn5)/Cu interconnects are investigated. The CDB method successfully controls the crystal orientation and maintains the preferential growth of Cu6Sn5 grains on (111) Cu single crystal substrate. The prism-type Cu6Sn5 grains show a texture feature and the continuous preferential epitaxial growth of Cu6Sn5 form the full IMC interconnect with Cu6Sn5 directions paralleling to the current flowing direction. The fabrication of full preferential growth IMC interconnects provides an approach to unify the orientations of the IMC interconnects, which effectively eliminates the random distribution of grain orientations and thus the anisotropy of interconnects. The full (111) Cu/Cu6Sn5/Cu IMC interconnects exhibite an excellent electromigration resistance and high mechanical reliability even after having experienced high temperature aging and high current stressing. There is no obvious damage after aging and current stressing (2.0×104 A/cm2) at 150 oC and 180 oC even for 500 h. The average tensile strength of full preferential growth IMC interconnects remaines unchanged, i.e., 111.1 MPa and 108.1 MPa, even after aging at 150 oC for 500 h and current stressing (2.0×104 A/cm2) at 150 oC for 500 h, respectively, which are similar to that of the as-soldered state (118.8 MPa). This work is expected to provide theory support and guidance for the application of full preferential growth and high strength IMC interconnects in 3D IC packaging.