Modern fabrication techniques for nanostructures and photonic components

Aalto University, P.O. Box 11000, FI-00076 Aalto www.aalto. fi Author Mikhail Erdmanis Name of the doctoral dissertation Modern fabrication techniques for nanostructures and photonic components Publisher School of Electrical Engineering Unit Department of Microand Nanosciences Series Aalto University publication series DOCTORAL DISSERTATIONS 167/2014 Field of research Nanotechnology Manuscript submitted 8 August 2014 Date of the defence 5 December 2014 Permission to publish granted (date) 23 October 2014 Language English Monograph Article dissertation (summary + original articles) Abstract This thesis introduces novel microand nanofabrication methods and their applications developed in Micronova, the clean room facilities of Aalto University. The work is performed with silicon, which is robust, stable, and easy to process material with good electrical and optical properties. The developed fabrication methods facilitate technologically challenging types of nanostructures and their fabrication on non-planar surfaces.This thesis introduces novel microand nanofabrication methods and their applications developed in Micronova, the clean room facilities of Aalto University. The work is performed with silicon, which is robust, stable, and easy to process material with good electrical and optical properties. The developed fabrication methods facilitate technologically challenging types of nanostructures and their fabrication on non-planar surfaces. The presented research consists of two parts. The first part is focused on nanofabrication, mostly via top-down fabrication approach. The second one describes the modification of photonic devices and waveguides by \mbox{atomic-layer-deposited} thin films. The three main types of processing involved in the thesis are: atomic layer deposition, exposure by focused ion beam, and dry etching. As a result of this study, several fabrication methods were developed. One of them utilizes focused ion beam lithography for nanofabrication on multilevel and strongly corrugated surfaces. This process has a great potential for general 3D integration and for microand nanofluidics. The same approach enables the fabrication of suspended nanostructures and gives a platform for accurate measurement of material properties and realization of lab-on-achip concepts. Another separately developed process is a grayscale lithography that provides a control over the height of patterned features at nanometer scale. It gives an effective way to fabricate miniature diffractive optics components for extreme ultraviolet and soft X-ray radiation. It also allows for new designs and improved performance of photonic grating couplers. Finally, the work shows how atomic layer deposition can be used to tune the operational parameters of photonic components. In particular, the dispersion properties of photonic nanostrip waveguides were optimized, and microring resonators were tuned towards polarization-independent regime in a broad wavelength range. In summary, the work extends the applications of nanotechnology for sensing and integrated optics. The shown nanofabrication methods provide fast prototyping due to the minimized number of process steps. Atomic layer deposition of thin films was demonstrated to be very effective for tuning of photonic waveguides and devices. The presented techniques and methods have a showcase character and provide a room for further research focused on other materials and applications.