Mechanism understanding in cryo atomic layer etching of SiO₂ based upon C₄F₈ physisorption

Area of Science:

• Materials Science
• Chemical Engineering
• Plasma Physics

Background:

• Atomic Layer Etching (ALE) is crucial for precise thin-film deposition.
• Cryogenic conditions can enhance ALE selectivity and reduce plasma damage.
• Understanding molecule-surface interactions is key to optimizing ALE processes.

Purpose of the Study:

• To investigate the mechanism of C4F8 physisorption on SiO2 for cryogenic ALE.
• To optimize cryo-ALE parameters for high-precision SiO2 etching.
• To achieve a self-limiting and linear etching process.

Main Methods:

• Utilized Quadrupole Mass Spectrometry (QMS) to analyze C4F8 residence time and SiF4 byproduct.
• Employed spectroscopic ellipsometry to evaluate C4F8 physisorption on SiO2.
• Developed and tested a cryo-ALE process at -90°C.

Main Results:

• Determined C4F8 residence time dependence on temperature and pressure.
• Demonstrated self-limiting etching behavior via QMS monitoring of SiF4.
• Achieved a highly linear SiO2 etch over 150 cycles with an etch amount per cycle of 0.13 nm/cycle.

Conclusions:

• A deeper understanding of cryo-ALE mechanisms enables process enhancement.
• Optimized cryo-ALE using C4F8 and Ar plasma provides precise SiO2 etching.
• The developed process is suitable for high-aspect-ratio and nanoscale fabrication.