Feb 22, 2012
Scanning probe lithography: ultrasonic vibration assisted nanomachining with an AFM
Researchers from North Carolina State University, US, are using ultrasonic vibration assisted nanomachining lithography to fabricate nano-patterns on PMMA films with increased writing speed and tunable feature dimensions. Scanning probe lithography offers a low-cost route to fabricating master patterns or masks, but in traditional AFM setups the line-width of the nanomachined features is determined mainly by the size of the AFM tip, which can place a restriction on the dimensions that are available.
In the team's apparatus, a lab-designed nano-vibrator is attached to the AFM to provide ultrasonic sample vibration in x-y and z directions. The ultrasonic z-vibration of the sample and the resulting ultrasonic force provide a reliable method to regulate fabrication depth, as the ultrasonic force mostly depends on the vibration amplitude and is insensitive to the oscillation frequency.
A high-frequency in-plane circular vibration is introduced to control the width of the fabricated features, and to improve the speed of nanolithography. Only a thin slice of material is removed during each cycle as the tip is rotated in the x-y plane, which significantly reduces the interaction force between the tip and the sample, and increases the machining speed. In the meantime, the lateral dimensions of the feature can be regulated by changing the amplitude of the circular motion.
One pass machining
Compared with mechanical scratching and dynamic ploughing, ultrasonic vibration regulated nanomachining lithography provides much faster fabrication speed and greater control of the fabricated features. Slots with dimensions spanning from tens of nm to hundreds of nm are fabricated in one scan with a lithography speed of tens of microns per second, which is significantly higher than other known mechanical modification-based nanolithography methods.
In the study, features written on a PMMA film were transferred to a silicon substrate with high fidelity by reactive ion etching, which provides a cost-effective approach for fabricating nanostructures.
More details can be found in the journal Nanotechnology.
About the author
This work was carried out by researchers at North Carolina State University. The group is led by Dr Jingyan Dong who is an assistant professor in the Department of Industrial and Systems Engineering. His current research focuses on micro/nano-scale manufacturing systems and processes. The nanomachining and testing using AFM was carried out by Li Zhang, a PhD student in Dr Dong's group, who is currently working on the modelling and application of tip-based nanofabrication.