Mitigating challenges in aberration-corrected electron-beam lithography on electron-opaque substrates.

Area of Science:

• Materials Science
• Nanotechnology
• Physics

Background:

• Aberration-corrected electron-beam lithography (AC-EBL) demonstrates high resolution on thin membranes.
• AC-EBL on thick substrates is crucial for top-down fabrication of quantum devices.

Purpose of the Study:

• Investigate AC-EBL performance on thick, electron-opaque substrates.
• Address challenges in pre-exposure beam focusing for thick substrates.
• Evaluate the impact of substrate thickness on nanometer-scale patterning.

Main Methods:

• Measured lithographic point spread function using a 200 keV aberration-corrected scanning transmission electron microscope.
• Fabricated positive and negative patterns in poly (methyl methacrylate) (PMMA) on SiO₂/Si substrates.
• Printed hole arrays on SiN_X/Si substrates with varying Si thickness using developed focusing methods.

Main Results:

• Successfully implemented AC-EBL on thick substrates, overcoming pre-exposure focusing issues.
• Achieved 26 nm pitch hole arrays in PMMA on SiN_X/Si.
• Proximity effects from 50 nm SiN_X membranes limited resolution to 20 nm pitch.
• Substrate thickness showed minimal effect on pattern quality down to the 20 nm pitch limit.

Conclusions:

• AC-EBL is viable for nanometer-scale patterning on thick substrates for quantum devices.
• Novel resists are needed to mitigate proximity effects for finer features.
• Developed methods improve AC-EBL focusing on challenging substrates.