First-principles study of copper contamination in silicon semiconductor

Abstract

Copper (Cu) has been widely used as interconnect materials in semiconductor industry, due to its advantages of high electrical, thermal conductivities, good electro-migration resistance and low cost. Since Cu is very reactive, contamination like physical diffusion from Cu to silicon (Si) and the chemical combination between Cu and Si is commonly observed and detrimental for Si semiconductor devices. Besides experimental study of the interaction between Cu and Si at macro scale, the physical diffusion and chemical combination also need to be understood at atomic level. Based on density functional theory (DFT), a crystal structure of Cu/Si heterojunction has been established to study the Cu/Si interfacial diffusion mechanism, including the diffusibility of vacancy and interstitial diffusion. No energy barrier exists when vacancy located at the top site, and diffusion from outside to bridge site is also possible by overcoming a relative low energy barrier. The occurrence of interstitial diffusion is also proved, but the energy barrier is higher than that of vacancy diffusion. The deeper of interstitial diffusion, more energy is required to overcome the increased energy barrier. In terms of first-principles study of chemical combination, complexes of Cu and Si have been structuralized in trigonal, hexagonal and tetragonal crystals. Stability of the crystal structures has been investigated from the aspect of mechanical and lattice stability. Tetragonal Cu3Si is proved to be the only crystal structure with both mechanical and lattice stabilities. The elastic constants, electronic structure and thermodynamical properties of the stable Cu3Si are also revealed. The results indicate the tetragonal Cu3Si exhibits metallic behaviors with good thermodynamical properties. The current study could provide meaningful insights on the inhabitation of Cu contamination and performance improvement.