An Advanced Remote-Plasma Assisted Ozone-Ethylene Radical (OER) Process for Cu-SiO₂ Hybrid Bonding Yield Enhancement

The Ozone-Ethylene Radical generation technology (OER) process generates large amounts of electrically neutral OH radicals by mixing an unsaturated hydrocarbon gas with a highly concentrated ozone gas under dust- and water-free conditions. Here, we examined the potential of using the OER process as a pretreatment to activate chip surfaces before hybrid bonding. Through real-time semi-quantitative radical concentration measurement, we confirmed that a large amount of OH radicals can be supplied to the surface of a bonding substrate placed in a custom-made vacuum chamber by mixing highly concentrated (>80%) ozone gas and ethylene gas under optimized process conditions. We also confirmed that the OER process is suitable as a pretreatment before hybrid bonding in the sense that both dielectric layer hydrophilization for strong adhesive bonding and a negligibly small Cu-Cu interface resistance are satisfied simultaneously. A connection test using a daisy chain of 5000 Cu electrodes assembled after OER pretreatment and hybrid bonding showed that overall interface resistance was as small as that afforded by a conventional citric acid hydration process. In addition, for surfaces for which OER is less effective at activation compared with plasma treatment (i.e., that of silicon thermal oxide films), sequential treatment with a mild remote plasma followed by OER works well for producing reliable, strong hybrid bonding. In summary, because the OER process is plasma- and water-free, the use of OER pretreatment not only simplifies the overall hybrid bonding process but also provides an interface with improved reliability.