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Cu/dielectric hybrid bonding at low temperatures of no more than 200°C remains challenging because of the different features of Cu-Cu and dielectric-dielectric (such as SiO2-SiO2) bonding. This paper reports a combined surface activated bonding (SAB) technique for low-temperature Cu-Cu, SiO2-SiO2, and SiO2-SiNx bonding. This technique involves a combination of surface irradiation using a Si-containing Ar beam and prebonding attach-detach process prior to bonding in vacuum. Wafer bonding experiments were conducted at either room temperature or 200°C. Results of bonding strength measurements, transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS) observations, and X-ray photoelectron spectroscopy (XPS) analysis were reported and discussed to understand the present combined SAB technique.

Flip chip nanobonding and interconnect system (NBIS) equipment with high precision alignment has been developed based on the surface activated bonding method for high-density interconnection and MEMS packaging. The 3σ alignment accuracy in the IR transmission system was approximately ±0.2 μm. The performance of the NBIS has been preliminarily investigated through bonding between relatively rough surfaces of copper through silicon vias (Cu-TSVs) and gold-stud bumps (Au-SBs), and smooth surfaces of silicon wafers. The Cu-TSVs of 55 μm diameter and the Au-SBs of 35 μm diameter with ∼6-10 nm surface roughness (RMS) were bonded at room temperature after surface activation using an argon fast atom beam (Ar-FAB) under 0.16 N per bump. Silicon wafers of 50 mm diameter with ∼0.2 nm RMS surface roughness were bonded without heating after surface activation. Void-free interfaces both in Cu-TSV/Au-SB and silicon/silicon with bonding strength equivalent to bulk fracture of Au and silicon, respectively, were achieved. A few nm thick amorphous layers were observed across the silicon/silicon interface that was fabricated by the Ar-FAB. This study in the interconnection and bonding facilitates the required three-dimensional integration on the same surface for high-density electronic and biomedical systems.

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As the trend of microelectronic integration such as ultrafine density flip chip or bumpless interconnect system, it is neccessary to develolp a low cost, ultra-high density, lowdamage and low-temperature interconnect technology. To satisfy this requirement, a new bonding method, the Surface Activated Bonding (SAB), was introduced. In the process, the bonding pads on chip and bumps on substrate are cleaned at first by Ar plasma or atom beam irradiation, precisely aligned with accuracy of less than *O.Spm. Then they are bonded directly to each other only by contact at the room temperature or low temperature in a newly developed flip chip bonder. The procedure that enables the bonding in inert ambient of N2 under the atmospheric pressure cut down the bonding condition requirements and decreased the process cost. Some preliminary experiments led to Au-Au and Au-Cu direct bonding demonstrated a performance of the new bonding system.