Investigations into plasmonic lithography concepts for high resolution nanoscale feature patterning
Sreekanth Kandammathe Valiyaveedu
Date of Issue2012
School of Mechanical and Aerospace Engineering
Plasmonic lithography, which is not restricted by free space diffraction limit, is one of the potential research thrust areas as it offers the possibility for high resolution nanopatterning. This thesis investigates novel concepts and relative configurations of plasmonic lithography to fabricate nanoscale periodic structures, which can find variety of potential applications. Initially, the theoretical and experimental investigation of multiple beam conventional laser interference lithography (LIL) was carried out. It is shown that this technique is diffraction limited and hence cannot be useful for sub-wavelength feature fabrication. A near-field multiple beam interference lithography such as evanescent wave interference lithography (EWIL) beyond the conventional free space diffraction limit has been investigated for sub-wavelength feature patterning. Both theoretical and experimental investigation of the technique was carried out. However, this technique was unable to provide high aspect ratio features, due to the exponentially decaying evanescent fields. In this context, it was envisaged that surface plasmon interference lithography (SPIL) could be one of the straightforward solution to subdue this problem and to obtain high resolution good aspect ratio features. Various configurations of plasmonic lithography are proposed and investigated. Multiple beam (two and four) surface plasmon (SP) interference generation based on prism coupling technique is theoretically analyzed and presented. The proposed concepts and methodologies were then numerically and experimentally illustrated by employing aluminum and silver metal at 364 nm illumination wavelength to realize high resolution and good aspect ratio 1D and 2D periodic nanoscale features on the recording medium. Further, a planar layer concept for surface plasmon interference lithography to fabricate periodic nanoscale structures was also proposed and illustrated. It is found that high electric field distribution compared to conventional prism based configuration is possible for this and hence facilitates improved exposure depth and good intensity contrast. The effect of metal films such as Al and Ag on UV excited surface plasmon interference lithography is investigated using the proposed configuration. The obtained periodic features show good exposure depth and high contrast when Al is used as the metal film. A comparative analysis between interferometric lithography techniques such as conventional laser interference, evanescent wave interference, and surface plasmon interference is experimentally carried out and illustrated. It is found that SPIL can provide high resolution periodic features with good aspect ratio as compared to the other two (LIL and EWIL) interference lithography techniques. An investigation into nanoparticle (array) based system configuration to improve the feature resolution also carried out as a part of the research. One of the two concepts proposed and numerically demonstrated is one employing periodic metal (Ag and Al) nanoparticle array to fabricate sub-40 nm periodic nanostructures. Secondly, a novel plasmonic lithography technique beyond the diffraction limit based on the excitation of gap modes in a metal particle-surface system is also investigated and demonstrated by numerical simulation means. The theoretical simulation result shows that by employing Al nanosphere-Ag surface system, this configuration can provide strong enhanced field to give shorter wavelength of surface plasmons to fabricate sub-30 nm periodic structures. Also, 2D and 3D resist profile cross sections obtained using cellular automata model are presented. Detailed investigation is carried out for extending the proposed concepts for potential applications as well as to subdue some of the limitations of plasmonic lithography. Thus focus the future work directions, which includes (i) investigation into compensation of LSP loss by optical gain medium for nanoparticle assisted plasmonic lithography, (ii) experimental investigation of nanoparticle assisted plasmonic lithography, (iii) experimental demonstration of metal nanograting based SPR sensors, and (iv) fabrication of 2D plasmonic crystals using patterned dot array features. The details of the initial studies of these future work directions are presented in the appendix section.