Nanostructuring with Bonding and Structural Studies of Plasma Assisted Wafer Bonding

Mette Poulsen

    Research output: Book/ReportPh.D. thesisResearch

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    Abstract

    The work presented within this thesis consists of two parts both related to wafer bonding and x-ray scattering.

    The first purpose of this project has been to investigate low temperature plasma assisted wafer bonding. This was done by performing x-ray reflectivity measurements at the bonded interfaces in combination with other characterization methods e.g. bond strength measurements. The mechanism behind the low temperature plasma assisted bonding is unknown and the aim of the x-ray reflectivity measurements was therefore to obtain structural information about the bonding interface and thereby contribute to a better microscopic understanding of the system. The need for a more detailed microscopic understanding of the low temperature bonding process is important, both to optimize the process, but also to ensure stability of devices fabricated using the bonding step.

    Oxygen plasma activated bonding of silicon wafers at room temperature has been investigated systematically using a reactive ion etch (RIE) and an inductively coupled RIE (ICP-RIE) system. The influence of various process parameters on the oxide thickness, bond strength and the density profile across the interface were studied, and the bond strength measurements were used to optimize on the activation process in order to obtain highest possible bond strengths. Highest bond strengths were found to be around to 1.6Jm−2, which is comparable to standard fusion bonded wafers annealed at 500-700 degrees.
     The second purpose of the project was to use our knowledge within water bonding to fabricate x-ray wave guides. X-ray wave guides can be used to produce x-ray micro or nano beams with high flux and significant small cross section and open op a whole range of new area of applications within scattering, microscopy and spectroscopy with a real space resolution in the nanometer range.
    The wave guides made and investigated in this project were made by etching nano structures in silicon wafers and using wafer bonding techniques for closing these etched structures. In this way nano dimensional air channels buried in silicon were obtained and since air is used as the guiding medium in principle no problems of intensity decrease caused by absorption were expected. The x-ray beam was coupled into the the guide from the front and for a certain combination of dimensions and incidence angles a standing wave inside the cavity is obtained. Far field intensities of the propagating modes were measured and compared to theoretical calculations. The success of waveguiding depends on the quality of the etch cavity structures. The roughness of the channel surfaces has to be minimizied and if guiding in two dimensions, it also has to be considered whether the sidewalls are perpendicular. The waveguide fabricated in this project was made by RIE etching and both one dimensional and two dimensional wave guiding were observed.
    Original languageEnglish
    Place of PublicationKgs. Lyngby
    PublisherTechnical University of Denmark
    Number of pages175
    Publication statusPublished - Jun 2006

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