High-Density 3-D Interconnect of Cu–Cu Contacts With Enhanced Contact Resistance by Self-Assembled Monolayer (SAM) Passivation

摘要

Self-assembled monolayer (SAM) of alkane-thiol is applied on Cu damascene structures with the aim to protect the surface against contamination and oxidation prior to bonding. Three-dimensional interconnects are realized with bumpless Cu-to-Cu thermocompression bonding by wafer-on-wafer stacking. Based on cross-bar Kelvin structure measurements, up to a 17.3% reduction in the contact resistance of Cu–Cu bonds is measured with the application of SAM when the time lapse between recess and bonding is 3 h. Daisy chain with 15- $muhbox{m}$ pitch of Cu–Cu contacts is achieved with 100% bonding yield at 350 $^{circ}hbox{C}$. Ohmic contact and continuity are achieved for a maximum of 10 000 bonding contacts. The contacts are robust, and continuity of the daisy chain is preserved even after 1000 cycles of thermal stressing ($-$ 40 $^{circ}hbox{C}$ to 125 $^{circ}hbox{C}$). This provides a feasible platform of high integrated circuit (IC)-to-IC connection density $(sim!!hbox{4.4} times hbox{10}^{5} hbox{cm}^{-2})$ suitable for future wafer level 3-D integration of ICs to augment Moore''s law.