Microfabrication of massive parallel micromirror-lenses by X-ray LIGA technique: recent advances and prospects
ABSTRACT Modern microfabrication techniques enable to obtain novel 2D lens systems which are the marriage of warped microchannel plates and Fresnel lenses. They rely on a multitude of precisely inclined micromirrors, acting together as very efficient macroscopic lenses for all electromagnetic wavelengths from the infrared, up to X-rays and even for particles like neutrons. Especially interesting is the fabrication of some-cm apertured lenses in the VUV and EUV region. X-ray LIGA is a favorite candidate for the fabrication of such lenses due to its inherent technological precision and capability to produce high aspect ratio structures. Theoretical consideration and limits for the design of such lens systems are presented, together with first investigations concerning surface-smoothing by spin-on glass in order to make such lens systems to work in the X-ray region.
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ABSTRACT: Densely packed high aspect ratio structures are difficult to fabricate due to surface adhesion effects which lead to pattern collapse during processing. However, it is possible to fabricate such structures in SU-8 by means of a top-plate support member which stiffens the overall structure and prevents pattern collapse. We have fabricated a variety of structures in SU-8 up to 1.5 mm high and with feature sizes in the 10–50 µm range. We investigate theoretical, computational and experimental approaches for predicting the thickness of the top-plate supports as a function of the aspect ratio and spacing of the structures. We demonstrate the fabrication of a number of densely packed high aspect ratio structures with top-plate supports that approach the minimal thickness sufficient to prevent pattern collapse.Journal of Micromechanics and Microengineering 03/2005; 15(5):978. DOI:10.1088/0960-1317/15/5/012 · 1.73 Impact Factor
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ABSTRACT: Deep x-ray lithography is a well-known technique used to pattern ultra high aspect ratio microstructures. It relies on the fact that higher energy synchrotron x-rays have the ability to penetrate millimeters of resist layers. However, the spectral shape of the beam will vary as a function of penetration depth, sometimes by design, so as to distribute the dose differently for different thickness structures and always as a result of filtering of lower energies. Some studies have shown that in PMMA sidewall roughness can be affected by spectral issues. SU-8 is now the resist of choice for certain high aspect ratio structures due to its high sensitivity and contrast. As sidewall roughness is a key parameter in several potential applications of high aspect ratio structures, we therefore investigated the surface roughness of 500 µm thick SU-8 structures exposed using beam spectra with peak energies between 3 keV and 12 keV. Results indicate that as the x-ray energy increases so too does the surface roughness. The surface roughness also increases as a function of feature depth. We attribute this to the random secondary physical processes of photo and Auger electron scattering both of which are strongly energy dependent.Journal of Micromechanics and Microengineering 08/2006; 16(10):1975. DOI:10.1088/0960-1317/16/10/009 · 1.73 Impact Factor
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ABSTRACT: We have previously demonstrated that it is possible to fabricate densely-packed high aspect ratio structures in SU-8 by means of a top-plate support member which stiffens the overall structure and prevents pattern collapse. In this work we have computed the tensile stresses induced in the top-plate structures due to the capillary forces that arise between the columns due to the surface tension of the drying liquid. We have further studied the dynamic behavior of the structure after an instantaneous force. Based on these results, we have shown that the predicted optimal thickness of the top-plate structure is sufficient to maintain structural integrity.Microsystem Technologies 03/2007; 13(5):487-493. DOI:10.1007/s00542-006-0201-4 · 0.95 Impact Factor