Solid-State Reaction in Cu/a-Si Nanolayers: A Comparative Study of STA and Electron Diffraction Data.

Area of Science:

• Materials Science
• Solid-State Chemistry
• Thin-Film Technology

Background:

• Understanding the reaction kinetics of thin-film systems is crucial for developing new materials and devices.
• The copper-silicon system is of interest due to its applications in microelectronics and interconnects.
• Previous studies have explored copper-silicon reactions, but detailed kinetic analysis of sequential phase formation in thin films is less explored.

Purpose of the Study:

• To investigate the solid-state reaction kinetics between nanolayers of polycrystalline copper and amorphous silicon in a Cu/a-Si thin-film system.
• To determine the sequential phase formation and their kinetic parameters.
• To compare kinetic parameters obtained from different experimental techniques.

Main Methods:

• Electron diffraction for structural analysis and kinetic parameter estimation.
• Simultaneous Thermal Analysis (STA), including Differential Scanning Calorimetry (DSC) and Thermogravimetry (TG), for thermal behavior and kinetic analysis.
• Model description of thermo-analytical data using a four-stage kinetic model.

Main Results:

• The solid-state reaction proceeds sequentially, forming η″-Cu3Si followed by γ-Cu5Si (Cu + Si → η″-Cu3Si → γ-Cu5Si).
• Kinetic parameters for η″-Cu3Si and γ-Cu5Si formation obtained via electron diffraction showed good agreement with DSC results.
• The formation enthalpies were estimated as ΔHη″-Cu3Si = -12.4 ± 0.2 kJ/mol and ΔHγ-Cu5Si = -8.4 ± 0.4 kJ/mol.
• The solid-state transformations are best described by a four-stage kinetic model: R3 → R3 → (Cn-X) → (Cn-X).
• Kinetic parameters for η″-Cu3Si formation: E = 199.9 kJ/mol, log(A, s⁻¹) = 20.5, n = 1.7.
• Kinetic parameters for γ-Cu5Si formation (determined for the first time): E = 149.7 kJ/mol, log(A, s⁻¹) = 10.4, n = 1.3.

Conclusions:

• The study successfully elucidated the sequential phase formation and reaction kinetics in the Cu/a-Si thin-film system.
• The agreement between electron diffraction and DSC data validates the kinetic parameter estimations.
• The newly determined kinetic parameters for γ-Cu5Si provide valuable insights for controlling thin-film reactions and material design.