Evaluation of hybrid bonding technology of single-micron pitch with planar structure for 3D interconnection

In this paper, we describe hybrid bonding technology of single-micron pitch with planar structure for three-dimensional (3D) interconnection. Conventionally, underfill method utilizing capillary force was used after the bonding of microbump. However, the filling becomes insufficient in a gap less than 10 μm between chips or bumps. One promising technology is the hybrid bonding technology that microbumps and an adhesive can be simultaneously bonded. To realize a single-micron pitch hybrid bonding, we fabricated a planar structure that consists of 8 μm-pitch Cu/Sn microbumps and a non-conductive film (NCF) by a chemical mechanical polishing (CMP) of resin. After planarization, the Cu/Sn bumps and the NCF were simultaneously bonded at 250 °C for 60 s. Cross-sectional scanning electron microscope (SEM) images and energy dispersive X-ray spectroscopy (EDX) images show that the adhesive resin on the bump surface was successfully removed by the CMP. In addition, SEM images of the bonded sample show that the adhesive filled the 2.5-μm gap between the chip and substrate. The Cu/Sn bumps were properly bonded in a corner on the chip. The proposed bonding method is expected to enable single-micron pitch interconnection for ultra-high density 3D LSI of next generation.