Fine-pitch hybrid bonding with Cu/Sn microbumps and adhesive for high density 3D integration

In this study, we developed single-pitch hybrid bonding technology for high density 3D integration. To realize the single-pitch, smaller than 10-μm pitch, hybrid bonding, 8 μm-pitch Cu/Sn microbumps and nonconductive film (NCF) were used. The planar structure to simultaneously bond was formed by chemical mechanical polishing (CMP). After the planarization, the Cu/Sn bumps and NCF were simultaneously bonded at 250 °C for 60 s. Cross sectional observation of the bonded sample by scanning electron microscope (SEM) indicated that 8 μm-pitch bump bonding was carried out successfully and the NCF filled the 2.5-μm gap between the chip and substrate without significant voids. In addition, a tensile test was performed as a mechanical reliability test. The tensile strength was 3.86 MPa. From SEM observation of the fractured surface after the tensile test, the fractured surface of the bumps was intermetallic compound (IMC) layer between Cu and Sn. These results indicated that hybrid bonding was effective method for single-pitch bonding and underfilling.