Temperature-Dependent HfO₂/Si Interface Structural Evolution and its Mechanism.

Area of Science:

• Materials Science
• Solid State Physics
• Thin Film Technology

Background:

• Hafnium oxide (HfO2) is a crucial gate dielectric material in modern microelectronics.
• Understanding the thermal stability and crystallization of HfO2 thin films on silicon is vital for device performance.
• The role of annealing temperature in HfO2 film and interface evolution requires detailed investigation.

Purpose of the Study:

• To investigate the effect of post-deposition annealing temperature on the crystallization of HfO2 thin films.
• To analyze the structural changes occurring at the HfO2/Si interface under varying thermal budgets.
• To correlate annealing temperature with the phase transformation and composition of the interfacial layer.

Main Methods:

• Remote plasma atomic layer deposition of HfO2 on p-type Si substrates.
• Rapid thermal annealing in a nitrogen atmosphere at temperatures ranging from below 400°C to above 550°C.
• Characterization using field emission transmission electron microscopy (FETEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and atomic force microscopy (AFM).

Main Results:

• Oxygen diffusion from HfO2 to the Si interface was observed during annealing.
• Below 400°C, HfO2 films and the interfacial layer (HfO2/SiO2 mixture) remained amorphous.
• Between 450°C and 550°C, HfO2 films became multiphase polycrystalline with crystalline SiO2 at the interface.
• Above 550°C, HfO2 films transformed to single-phase polycrystalline, and the interfacial layer fully converted to crystalline SiO2.

Conclusions:

• Post-annealing temperature significantly influences the crystallization of HfO2 thin films and the HfO2/Si interface.
• The interfacial layer evolves from an amorphous HfO2/SiO2 mixture to crystalline SiO2 with increasing annealing temperature.
• Controlled annealing is essential for tailoring the microstructure of HfO2/Si stacks for semiconductor applications.