In situ TEM study of stability of TaRhx diffusion barriers using a novel sample preparation method

Area of Science:

• Materials Science
• Solid-State Physics
• Nanotechnology

Background:

• Diffusion barriers are crucial for preventing interdiffusion between materials in microelectronic devices.
• Tantalum-rhodium (TaRhx) alloys are investigated as potential diffusion barriers for copper (Cu) metallizations due to their thermal stability.
• Understanding the atomic mechanisms of diffusion barrier failure is essential for improving device reliability.

Purpose of the Study:

• To investigate the atomic diffusion mechanisms leading to the metallurgical failure of TaRhx diffusion barriers in Cu metallizations.
• To analyze the role of barrier thickness and surface diffusion in the failure process.
• To develop and validate a sample preparation technique for in situ transmission electron microscopy (TEM) studies of diffusion barriers.

Main Methods:

• In situ transmission electron microscopy (TEM) with heating was employed to observe atomic diffusion and failure mechanisms.
• Focused ion beam (FIB) preparation was used for cross-sectional TEM samples.
• A carbon (C) capping layer was applied to suppress surface diffusion of copper (Cu).

Main Results:

• Copper (Cu) layer in Si/(13 nm)TaRhx/Cu stacks exhibited grain growth and void formation above 550°C.
• Thicker Si/(43 nm)TaRhx/Cu stacks delayed Cu grain growth to 700°C and prevented void formation.
• Failure initiated with RhSi particle nucleation at the Si/TaRhx interface, leading to Rh depletion and subsequent Cu diffusion to form Cu3Si.

Conclusions:

• Barrier thickness significantly influences the thermal stability and failure temperature of TaRhx diffusion barriers.
• Surface diffusion of Cu must be controlled to accurately observe bulk diffusion and reaction mechanisms.
• The developed in situ TEM sample preparation method is effective for studying diffusion barrier failure and can be applied to other barrier systems.