Plasma-Enhanced Atomic Layer Deposition and Substrate Engineering of Low-Resistivity Ultrathin MoCx Films for Advanced Interconnect Applications

As Copper (Cu) interconnect dimensions continue to shrink, conventional tantalum/tantalum nitride (Ta/TaN) liner/barrier layers occupy an increasing fraction of the available interconnect volume and introduce additional electrical resistance because of their relatively high resistivity. Therefore, a key challenge is to develop ultrathin liner/barrier materials that can maintain low resistivity while providing effective Cu diffusion-barrier performance. In this work, we demonstrate MoC x as a liner-free barrier material using plasma-enhanced atomic layer deposition (PEALD). For this PEALD-grown film, cycloheptatriene molybdenum tricarbonyl, (η 6 -C 7 H 8 )Mo(CO) 3 , was first introduced as a precursor to synthesize ultrathin molybdenum carbide (MoC x ) films. The effects of plasma reactants, plasma power, deposition temperature, film thickness, and substrate types were systematically evaluated to clarify how PEALD process conditions and substrate chemistry influence the electrical performance of ultrathin MoC x films. We observed nucleation differences during the growth based on the substrate; MoC x films deposited on Al 2 O 3 consistently exhibited lower resistivity than those grown on SiO 2 . Using the optimized deposition process, amorphous MoC x films thinner than 5 nm showed resistivities as low as ~230 μΩ·cm without any post-deposition annealing. For reference, current Ta/TaN liner/barrier layers typically exceed 500 μΩ·cm resistivity in the sub-5 nm thickness regime. Sub-5 nm MoC x film also showed good Cu adhesion and effective Cu diffusion-barrier behavior after thermal annealing of up to 500 °C. These results demonstrate the potential of ultrathin amorphous MoC x as a low-resistivity liner-free barrier material for advanced Cu interconnects.