Improving thermal expansion coefficients and mechanical properties of interconnect copper by doping Al2O3 nanoparticles: insights from atomistic simulations

Abstract

With the development of through-silicon via (TSV) technology, the thermal reliability of integrated circuits suffers from the thermal expansion mismatch between interconnect copper and the silicon substrate. Embedding the Al₂O₃ particles into Cu has been an effective and promising way to reduce the thermal expansion coefficient (CTE) difference. In this work, the CTE and mechanical properties of nanocrystalline copper embedded with Al₂O₃ particles have been systematically investigated by employing the atomistic level simulations. The results indicate that interfacial energy significantly affects the CTE of composites. With the increase of the defect density, the grain boundary energy will become higher, resulting in more pronounced non-harmonic thermal vibrations and higher CTE. The in-depth physical analysis shows that the Cu–Al₂O₃ interfaces play a crucial role in restricting the thermal expansion. The intricate interfaces formed at grain boundaries exhibit a positive effect on thermal expansion. It is also found that the distribution of doped Al₂O₃ nanoparticles has a significant effect on CTE. For particles doped inside the grains, the composite system shows lower interfacial energy and CTE. While for particles doped at the grain boundaries, the stability of the grain boundaries is enhanced and the elastic modulus increases, leading to higher phonon softening rates and larger CTE. As the temperature increases, the atomic spacing expands, leading to increased vibrational amplitudes, lowered phonon frequencies, and elevated CTE. These findings enhance the profound understanding of the thermal expansion mechanisms in Cu–Al₂O₃ nanocomposites, and provide theoretical guidance for improving the thermal–mechanical performance in Cu-filled TSV applications.