Co-W Barrier Layers for Metallization of Copper Interconnects: Thermal Performance Analysis.

Area of Science:

• Materials Science
• Semiconductor Manufacturing
• Nanotechnology

Background:

• Downscaling of back-end-of-line (BEOL) copper interconnects to single-digit nanometer nodes presents challenges for traditional diffusion barrier materials like Ta/TaN.
• The electrical performance of smaller copper (Cu) lines is constrained by existing barrier systems, necessitating investigation into alternative materials.

Purpose of the Study:

• To evaluate the performance of physical vapor deposition (PVD) deposited equimolar cobalt-tungsten (Co-W) films as a diffusion barrier for copper interconnects.
• To compare the dewetting resistance and electrical properties of Co-W films against traditional tantalum (Ta) adhesion layers under various vacuum annealing conditions.

Main Methods:

• Characterization of Cu/Co-W and Cu/Ta stacks using scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), and scanning transmission electron microscopy (STEM) with energy-dispersive X-ray spectroscopy (EDX) mapping.
• Assessment of film performance under different vacuum annealing temperatures.

Main Results:

• Copper (Cu) film on Co-W exhibited grain growth starting at 300 °C, with abnormal grain growth observed at 450 °C.
• Minimum sheet resistance of 7.07 × 10^-6 Ω/sq for Cu/Co-W and 6.03 × 10^-6 Ω/sq for Cu/Ta were achieved after annealing at 450 °C.

Conclusions:

• Equimolar Co-W films demonstrate potential as an alternative diffusion barrier material for advanced copper interconnects.
• Co-W films exhibit competitive electrical performance and dewetting resistance compared to Ta layers, particularly after annealing at elevated temperatures.