Self-assembled near-zero-thickness molecular layers as diffusion barriers for Cu metallization

Devising ultrathin barrier layers to prevent Cu diffusion into SiO2-based d ielectrics is a major challenge that must be met to increase the speed, num ber density, and performance of microelectronics devices. Here, we demonstr ate the use of near-zero-thickness (<2-nm-thick) self-assembled molecular m onolayers (SAMs) as candidates for this application. Cu/SiO2/Si(001) metal- oxide-semiconductor capacitors, with and without SAMs at the Cu/SiO2 interf ace, were annealed at 200 degreesC in a 2 MV cm(-1) electrical field. Capac itance-voltage and current-voltage measurements of SAM-coated capacitors in dicate that SAMs with aromatic terminal groups inhibit Cu diffusion into Si O2. They consistently show more than four-orders-of-magnitude lower leakage currents and a factor-of-4 higher time to failure when compared with the c orresponding values from samples without SAMs at the interface. SAMs with s hort tail lengths or aliphatic terminal groups are ineffective in hindering Cu diffusion, indicating that the molecular length and chemical configurat ion are key factors determining the efficacy of SAMs as barriers. We propos e that the steric hindrance offered by the terminal groups in the SAMs are responsible for the barrier properties. (C) 2001 American Institute of Phys ics.