Insights into ALD Growth of Al-Based Dielectric Stack on 4H-SiC.

Area of Science:

• Materials Science
• Semiconductor Device Physics
• Nanotechnology

Background:

• Silicon carbide (4H-SiC) is a promising semiconductor for high-power and high-frequency applications.
• Effective gate insulators are crucial for optimizing 4H-SiC device performance.
• Atomic Layer Deposition (ALD) offers precise control over thin film growth for gate dielectrics.

Purpose of the Study:

• To investigate the effects of different aluminum oxide (Al2O3) deposition methods on an aluminum nitride (AlN) interface layer for 4H-SiC gate insulators.
• To compare the insulating properties of Al2O3/AlN stacks fabricated using thermal ALD (T-ALD) and plasma-enhanced ALD (PEALD).

Main Methods:

• Synthesis of 10 nm (001)-oriented AlN on 4H-SiC followed by 20 nm amorphous Al2O3 using sequential T-ALD and PEALD.
• In situ ellipsometry to monitor interface evolution during deposition.
• Ex situ structural and electrical characterization to analyze material properties.

Main Results:

• The Al2O3/AlN interface was significantly affected by oxygen plasma in PEALD, leading to O-Al-N bond formation.
• The Al2O3/AlN bilayer grown by T-ALD exhibited excellent insulating behavior with a dielectric constant of 8.7.
• The Al2O3/AlN bilayer grown by PEALD showed poor insulating properties.

Conclusions:

• The deposition method for Al2O3 critically impacts the performance of Al2O3/AlN gate insulators on 4H-SiC.
• T-ALD is a preferred method for fabricating high-quality Al2O3/AlN gate dielectrics, ensuring good insulating properties for 4H-SiC devices.
• PEALD processes, particularly those involving oxygen plasma, can degrade the insulating characteristics due to undesirable interfacial reactions.