Deposition and Characterization of 3-Aminopropyltrimethoxysilane Monolayer Diffusion Barrier for Copper Metallization

Diffusion barrier capability of 3-aminopropyltrimethoxysilane (APTMS) against the diffusion of copper into the dielectric is studied. A self-assembled monolayer (SAM) of APTMS was deposited on SiO₂/Si substrate. Cu/SiO₂/Si and Cu/SAM/SiO₂/Si test structures were compared for their thermal stability using X-ray diffraction (XRD) characterization, sheet resistance variation, and Capacitance-Volatage (C-V) characterization. The samples were annealed at different temperatures starting from 473 K (200 °C) up to 973 K (700 °C) in vacuum for 30 minutes each. XRD results indicated that combination of SiO₂/SAM worked as diffusion barrier up to 873 K (600 °C), whereas SiO₂ alone could work as a barrier only up to 673 K (400 °C). Sheet resistance of these samples was measured as a function of annealing temperature, which also supports XRD results. C-V curves of these structures under the influence of biased thermal stress (BTS) were analyzed. BTS was applied with different parameters, i.e., 1.25 MV cm⁻¹ at 323 K (50 °C), 1.25 MV cm⁻¹ at 373 K (100 °C), and 2.5 MV cm⁻¹ at 423 K (150 °C). A change in threshold voltage (∆V _t) was observed for each BTS. Results showed that in the case of higher electric field, i.e., 2.5 MV cm⁻¹ at 423 K (150 °C), V _t of the Cu/SiO₂/Si/Al structure was changed significantly even after 15 minutes of stress, while V _t of the Cu/APTMS/SiO₂/Si/Al structure was almost unchanged for up to 60 minutes.