Fabrication of various metal nanostructures with hole mask colloidal lithography

Öztürk, İbrahim Murat
In this work, a novel surface nanostructuring technique called hole mask colloidal lithography (HMCL) is investigated and utilized to fabricate large area metal nanostructures with several geometries with photoresist over exposure and over develop as the undercutting method. Some extends of this method has been examined with constant angled deposition of dimer structures. HMCL takes advantage of directional nature of thermal evaporation method for metal deposition through the nanoscale holes that are placed at a controlled distance away from the substrate surface. When an angle is applied between the normal vector of the surface and deposition direction, position of deposited material can be precisely controlled with respect to the hole. Colloidal nanospheres are employed to decorate the the surface with nanoscale holes, which offers fast and convenient large area decoration. What makes HMCL a superior lithography technique is its ability to parallelly fabricate both simple and complex nano geometries on large areas with variable minimum feature sizes and controllable surface coverages. Hole generation is the most crucial part to achieve successful results with HMCL. It has been proposed and successfully employed in this thesis that undercutted holes at a controllable distance away from the surface can be fabricated by using a positive tone photoresist film on the surface as a sacrificial layer. Undercutting of photoresist is achieved by over exposure and over development. Spherical nanoparticles with two sizes (750 and 262 nm) are used to decorate over this resist film to later leave their places to holes. Process steps are investigated and optimized for successful hole generation. Same procedure is found to be applicable to both sizes of holes. The success of the holes are investigated by deposition of dimers, trimers and quadromers on the substrates and examined with optical and electron microscopy. After defining a successful procedure, positional precision examined by fabrication of close and distant dimer disks. Asymmetrical deposition possibilities with dimers are examined next. Three main asymmetrical structure fabrication possibilities are found. Asymmetrical thickness deposition, asymmetrical angled deposition and asymmetries arising from clogging of the holes. Several dimer structures are fabricated with asymmetrical thickness deposition and asymmetrical angle deposition under different conditions to comprehend the extend of asymmetrical possibilities.
Citation Formats
İ. M. Öztürk, “Fabrication of various metal nanostructures with hole mask colloidal lithography,” M.S. - Master of Science, Middle East Technical University, 2014.