Ion Projection Lithography for Nano Patterning
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A. HEUBERGER and W. BRUENGER Fraunhofer-Institute for Silicon-Technology (ISiT) Fraunhofer Str. 1, D- 25524 Itzehoe, Germany, Phone: +49-4821-17-4211 Fax: +49-4821-17-4250, e-mail: bruenger @ isit.fhg.de ABSTRACT As a result of continuous improvement of the resist process, the experimental ion projector in the Fraunhofer Institute in Berlin (manufactured by Ion Microfabrication Systems, IMS, Vienna) has been able to print 75 nm lines and spaces into 180 nm thick standard DUV resist UV II HS without pattern collapse. A new wafer flow process for more reliable open stencil mask making was developed by IMS -Chips, Stuttgart (Germany), based on SOT wafers. Resistless direct surface modification by He and Xe ions has been tested on metallic and magnetic films in the Berlin projector. This method opens up a new possibility for the production of patterned media for future magnetic storage disks. INTRODUCTION In the European MEDEA Project for the development of ion projection lithography (IPL) for next generation lithography (NGL) the Fraunhofer Institute ISiT has taken the part of resist process development. Standard deep UV chemically amplified resists have been found very useful also for ion irradiation and the latest results are reported in the following. However, in special cases the contact of a resist with the surface to be structured is not wanted. This situation may arise, because of chemical reactions with the resist (high temperature super-conductors) or the fear of topography change and residues after resist removal (thin magnetic films for storage media). Ions have the unique feature that they can directly modify a surface without the need for a resist. Compared to electrons of the same energy, ions deposit their energy in a shorter range near the surface because they do not penetrate as much. Since direct ion processing takes place in vacuum, it can be useful for all substrates which cannot be exposed to air for example in the case of an intermediate step in in-situ processing. In order to demonstrate this technology of direct ion processing, tests have been performed in the Berlin ion projector to structure metallic and magnetic films. For the production of magnetic nano dots other techniques are competing like optical interference lithography [1,2], e-beam lithography [3], and nano imprint lithography [4,5]. All of these methods use some kind
of resist process which is not desirable to keep the topography of a surface unchanged. This is extremely important for magnetic disks with a surface roughness of a few nanometers. EXPERIMENTAL Exposures have been performed with the ion projector IPLM-02 at the Fraunhofer Institute in Berlin [6]. H" or He' ions pass an open stencil mask at a beam energy of 3.5 keV and are accelerated behind the mask to 75 keV( see Fig. 1 ). Mask features are projected with 8.7 times demagnification via the ion optical lens system onto the wafer. The original duoplasmatron ion source has been exchanged with a multicusp ion source developed at the Lawrence Berkeley Laboratory with reduc
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