Versatile Photosensitive Polymer Applied in Low-Temperature Hybrid Bonding with Nanocrystalline Cu

This study utilizes a polymer material that can act as the organic passivation component and bonding material in hybrid bonding for 3D packaging purposes. Combined with nanocrystalline copper (nc-Cu), an alternative to current inorganic passivation/metal contact hybrid bonding is proposed. The polymer material is photosensitive and is used to define the vias for nc-Cu deposition in a damascene-like process flow for chip-to-wafer (C2W) hybrid bonding. The photolithographic characteristics were determined, and optimal exposure conditions of 100 mJ/cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> exposure energy and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$0\ \mu \mathrm{m}$</tex> focus were used for patterning uniform, circular vias. Nc-Cu was then deposited and planarized by CMP. The polymer's ability to be bonded at low temperatures, along with nc-Cu's demonstrated fusion temperature of l50°C, allowed for subsequent hybrid bonding at 150°C and 40 MPa. Cross-sectional SEM-FIB and TEM images were taken to observe the polymer-polymer and nc-Cu/nc-Cu bonding interfaces, which showed good metal fusion with no observable voids. This study showcases a versatile photosensitive polymer material with bonding capabilities that were demonstrated in a Class 100 facility setting, thereby providing backend fabs with a potential solution for hybrid bonding without stringent particle cleanliness requirements.