High-resolution stamp fabrication by edge lithography

Abstract

The aim of the project was to create high resolution stamps for thermal nanoimprint applications. The creation of nanoridges with sub-100 nm resolutions was explored by means of edge lithography via top-down routes, i.e. in combination with micromachining technology. Edge lithography is an add-on technology which allows to use any lithographic techniques for primary pattern definition. The project started from the fabrication of SiO2 nanoridges by oxidizing vertical Si edges using SiNx as the mask. Vertical Si sidewalls were created taking advantage of Si wafers and anisotropic Si etching by OPD4262. SiO2 nanoridges with sub-20 nm width were fabricated. In Chapter 2, we have presented the idea of reinforcing the SiO2 nanoridges by an additional SiNx deposition to make the stamps reusable in T-NIL; however, the over-deposition led to the loss of sub-20 nm resolution. The fabrication of monocrystalline Si nanoridges by advanced edge lithography is demonstrated in Chapter 3. The width of Si nanoridges was co-determined by Si anisotropic etching, lateral retraction of SiNx and LOCOS. We have demonstrated the capability of fabricating Si nanoridges with a width down to 10 nm by the advanced edge lithography. In Chapter 4, the fabrication of multi-Si nanoridges has been explored and triple Si nanoridges of 120 nm high and 40 nm wide with ca. 40 nm spacing have been created by a repeated advanced edge lithography scheme. In this case, OPD 4262 was replaced by 20% KOH used at room temperature and selective etching of SiNx and SiO2 was alternately performed using 50% HF and hot H3PO4. In Chapter 5, the fabrication of nanoridges was extended to arbitrary contours using dry plasma etching methods to avoid the dependence of Si crystal orientation. A cryogenic Si etching recipe was developed according to black silicon method. Two fabrication schemes have been demonstrated capable of producing nanoridges with circular contours with a width down to 60 nm. In the scheme where photoresist and Cr function as the masking layers, Si nanoridges with perfect vertical sidewall profile but rough sidewall surface finish have been produced. Although Si nanoridges with slightly positive tapered sidewalls are fabricated in the SU-8 scheme, the sidewall surface finish is smooth which is beneficial for nanoimprint applications. We demonstrated the successful implementation of the monolithic Si nanoridges to alternative nanofabrication approaches in Chapter 6. Assemblies of light harvesting antenna complexes with a resolution of 80 nm have been created by thermal nanoimprint lithography and self-assembly techniques. Composite PDMS-glass stamps with high resolution line structures have been fabricated by both thermal nanoimprint lithography and capillary force lithography. By using the high resolution composite PDMS-glass stamp, we have demonstrated the fabrication of Au nanolines with a width of ca. 80 nm by microcontact printing.