Dewetted silver thin films as mask for dry etching of silicon nano molds

Abstract

Scope of this work is the development of a simple and cost-effective way to produce silicon molds for embossing technologies.<br />To create a mold with sub micron structures a silver hard mask was applied to a silicon substrate, afterwards plasma etching is used to create three-dimensional structures. The molds created in this work shall be used to form an optical metamaterial. For this purpose sub-wavelength structures are required.<br />Pillars or needles having small diameters and high aspect ratios shall be used to create the mold for the metamaterial. The scope of this work was to control the size and density of the needle-like structures.<br />In chapter two, theoretical background to the proposed process sequence is given. First, the basics of dewetting of thin films, particularly metallic films are explained. After that, methods for anisotropic etching of silicon are presented, with emphasis put on reactive ion etching. Next, alternatives for micro-molding of thermoplastic polymers are described, with hot embossing in the focus. Additionally some considerations about fabrication of surface gradients are featured.<br />Finally, suitable characterisation methods for the aimed micro/nanostructures are presented.<br />In chapter three, dewetting experiments of sputtered silver thin films on glass and Si (100) substrates are depicted; dependence on process parameters and initial layer thickness is investigated. Annealed layers are characterized by scanning electron microscopy and in situ resistivity measurements.<br />In chapter four, reactive ion etching experiments using different plasma chemistries are described, where etching of silicon nanopillars is aimed. Basic connections between the process parameters and qualitative results are revealed.<br />