PhD for Toine van den Boogaard on new multilayer growth techniques

13 December 2011
Dr. Toine van den Bogaard successfully defended his PhD thesis on 13 December at Twente University. As a PhD-student at the Rijnhuizen Nanolayer Surface and Interface Physics department he investigated advanced techniques to improve multilayer mirrors for eXtreme UltraViolet light (XUV). Van den Boogaard also showed how to move to three-dimensionally structured multilayer optics. Such advanced concepts allow for new optics applications in XUV and other areas of the spectrum.

Polishing and diffraction

In his research, Van den Boogaard showed that polishing a newly deposited multilayer mirror with ions of noble gasses such as Xenon will smoothen the mirror layers and improve the optic's performance. He discovered that treating the mirror with Hydrogen before polishing increases the material's porosity, further increasing the effect of the polishing step.

Van den Boogaard has also discovered techniques to deposit multilayer mirrors on substrates that are not smooth, but have for instance been pre-shaped to form a diffraction grating. The resulting multilayer still reflects XUV radiation, while at the same time removing unwanted light with other wavelenghts from the beam via diffraction.

Multilayer mirrors have applications in the development of new generations of computer chips, but also in material analysis techniques and even space telescopes. The structures consist of a sandwich of up to hundred layers of alternating reflective and partly transparant materials. These layers each have a thickness of only a few nanometers (a billionth of a meter). Multilayers are ideal tools to reflect XUV radiation, a type of light that cannot be manipulated with ordinary optics such as mirrors or lenses.

Industrial cooperation

The nSI department holds the world record for XUV-reflection with multilayer mirrors: over 70%, close to the theoretical maximum. The optics developed are being used in the new generation of computer chip lithography machines developed by ASML. In the two Industrial Partnership Programmes XMO and CP3E, nSI, ASML and Carl Zeiss work together to cover the entire knowledge chain in XUV multilayer optics, from fundamental research to practical application. As part of this cooperation, FOM has created research positions for young scientists in the laboratories of both ASML and Rijnhuizen.

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Research in the nSI department and in its research group AXO
nSI, Carl Zeiss and ASML cooperate in Industrial Partnership Programme CP3E