The team also implement the dry release of nanostructures and demonstrate the fabrication of suspended nanobridges across the inclined walls of micron-scale grooves. Such released nanostructures provide a platform for various types of sensing and thermal conductivity measurements. Realization of suspended nano-networks on multilevel and corrugated surfaces brings, among others, new functionalities for micro- and nanofluidics, and lab-on-a-chip applications.

The challenges of corrugated surfaces

Nanofabrication on corrugated surfaces is generally very challenging since it requires preserving conformal resist distribution, good focusing, and equal etching rates for different height levels. The application of ALD and FIB effectively solves the problems with resist deposition and exposure. The difficulties associated with non-uniform etching speed are addressed by solely utilizing dry etching for both the resist development and release etching steps. The group from Aalto University demonstrates the fabrication of only 50 nm-wide suspended TiO2 nanobridges that follow the inclined Si wall of a micron-scale groove and retain their width from the top to the bottom.

A fast, reproducible and tolerant method

The shown fabrication of released nanostructures provides a platform for the consequent deposition of other materials. The authors also realize suspended nanowires through the bilayer TiO2/Al2O3 resist, where the Al2O3 underlayer is mechanically robust and has good etch-stop properties. The practical value of the proposed method is in its universal character, since it can tolerate arbitrary surface corrugation (trenches, grooves etc.). The method is also fast and reproducible due to the minimized number of process steps and absence of wet etching.

Future research includes experiments on new combinations of ion-sensitive resist materials (e.g. ALD nanolaminates) and new types of structures. In addition, the chemistry utilized in dry etching allows for application of the process to a number of polymers.

More information can be found in the journal Nanotechnology 25 335302 (IOPselect article).

Further reading

Patterning technique prepares graphene nanoribbons for photodetector applications (Jan 2014)
Patterning horizontal silicon nanowire growth at vertical sidewalls (feb 2013)
Resist layer correlation joins up nanopatterns (Sept 2012)