Suppression of resist contamination during photolithography on carbon nanomaterials by a sacrificial layer

To suppress photoresist residues on carbon nanotubes (CNTs) resulting from photolithography, CNTs are covered by a sacrificial layer during photolithography. Using aluminum oxide (Al2O3) deposited by low temperature atomic layer deposition as the sacrificial layer, the fabricated suspended CNT field-effect transistors exhibit low on-state resistances as low as 91 kΩ and low gate hysteresis of 0.5 V in ambient air. The effectiveness of this technique in suppressing residues on CNTs was affirmed by atomic force microscopy, scanning electron microcopy, and micro Raman spectroscopy. The etchants of Al2O3, hydrofluoric acid and phosphoric acid, were found not to cause defects in CNTs while removing the sacrificial Al2O3 layer. With the protection of the Al2O3 layer, oxygen plasma ashing can be performed without causing further defects in CNTs, and the minimum thickness was determined to be between 9 nm and 17 nm. This simple and effective approach can be easily implemented in different resist-based lithography processes to fabricate carbon nano-devices that are free of resist residues.