Biennial Report 2016/2017

Reports
Reactive Ion Beam Etching for Ultraprecise Fabrication of Optical
Elements: A Progress Report
R. Fechner, A. Finzel, G. Dornberg, M. Mitzschke, S. Görsch, A. Nickel, F. Frost
in collaboration with
F. Koch, D. Lehr, O. Schönbrodt, T. Glaser, Carl Zeiss Jena GmbH, Microstructured Optics, Germany
Introduction
(Reactive) ion beam etching ((R)IBE) becomes
more and more a versatile and indispensable
technology step in the fabrication chain of high
precision optical elements. An example for the
crucial importance of RIBE is the pattern transfer
of 3D resist or metal masks into hard optical
materials, especially for the fabrication of highend
optical diffraction gratings [1,2].
Today gratings can be manufactured using
various sophisticated techniques, e. g.,
interference lithography, mechanical ruling,
volume holography, laser direct writing
lithography, electron-beam writing, and Talbot
lithography. While for some applications the resist
grating is sufficient, the vast majority of
applications demands grating patterns to be
transferred into glass, silicon, metals, or other
substrate materials. Due to the very high flexibility
and degree of freedom RIBE is predestined for
this. Thus, due to process optimized gas mixture
used for etching, the selectivity (ratio of the etch
rates of the substrate material related to the etch
rate of the mask material) can be varied over
several orders of magnitude making it possible to
compress or stretch surface profiles during the
pattern transfer, according to the respective
optical application. Owing to the spatial separation
of ion generation and substrate, RIBE steps at
non-normal ion incidence additionally offers a
targeted alteration of the surface profile, e. g., the
implementation of undercut patterns or lanted
gratings or the realization of blazed gratings
starting with symmetrical mask profiles. Moreover,
RIBE is a key step in the ion beam planarization
technique, for example, for smoothing of diamond
turned metal surfaces with sub-nm roughness
values [3].
In this report research activities in the core area
Ion Beam assisted Technologies will be
summarized. The work focused mainly on
improvement of technical infrastructure, the
integration and further optimization of in-situ
measurement techniques, the implementation of
sophisticated processing algorithms, which allow
a RIBE processing of workpieces larger than the
extension of the ion beam and the development of
RIBE processing steps for high-end diffraction
gratings.
Technical Infrastructure
The improvement in the technical infrastructure
was one of the key issue in recent years. Thanks
to the funding provided by BMBF within the
SHAPION project [4] and with the additional help
of European Regional Development funding and
funding from the Free State of Saxony a total of
three new RIBE facilities (ISA 200, SHAPION,
RIBE 450) could be taken into operation recently.
All RIBE systems are equipped with Kaufmantype
ion sources (grid apertures of 180 mm),
configured for Fluorine-based etching gases, and
were partially upgraded with different optical and
mass spectroscopic in-situ measurement
technologies which guarantee for a high process
stability and reliability. All machines allow a base
pressure of 1 × 10 -7 mbar and are able to execute
process variable user defined recipes. Both ISA
200 as well as the SHAPION RIBE plant enable
the processing of workpieces up to 245 mm in
diameter. With the former also a defined ion beam
sputter deposition of, e.g. metals, during etching
is possible in order to investigate ion beam driven
self-organized pattern formation processes with
and without co-deposition. Within the extended
research infrastructure a new state-of-the-art
Figure 1: View in the RIBE 450 plant with 5-axis-motion
system for workpieces up to 450 mm diameter.
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