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Cryogenic Etching of the Electroplating Mold for Improved Zone Plate Lenses
KTH, School of Engineering Sciences (SCI), Applied Physics. (Biomedical and X-Ray Physics (Biox))
2010 (English)Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

The fabrication of zone plate lenses that are used for focusing X-rays relies on nanofabrication techniques such as e-beam lithography, reactive ion etching, and electroplating. The circular grating-like zone plate pattern can have a smallest half-period, a so-called zone width, of down to 20 nm while it also needs to have a height that is 5 to 10 times the zone width to have good diffraction efficiency. This high aspect ratio structuring is a very challenging field of nanofabrication.

This diploma project has focused on improving the process step of fabricating the electroplating mold by cryo-cooling the polymer during the reactive ion etching with O2. The low temperature causes passivation of the sidewalls of the mold during etching which results in a more ideal rectangular profile of the high aspect ratio plating mold.

By etching at -100 °C, structures with highly vertical sidewalls and no undercut were realized. The experiments showed that there is a tradeoff between the anisotropy of the zone profile and the formation rate of polymer residue, so-called RIE grass. Through a proper choice of process parameters the grass could be completely removed without introducing any undercut.

Place, publisher, year, edition, pages
2010. , 40 p.
Trita-FYS, ISSN 0280-316X ; 2010:09
Keyword [en]
etching, plasma etching, zone plate, x-ray, nanofabrication, sidewall passivation, cryo, cryogenic, undercut
National Category
Other Engineering and Technologies Condensed Matter Physics
URN: urn:nbn:se:kth:diva-12109ISRN: KTH/FYS/--10:09--SEOAI: diva2:302193
Physics, Chemistry, Mathematics
QC 20100414Available from: 2010-04-14 Created: 2010-03-04 Last updated: 2010-04-28

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