Matthias Nestler, Marcel Demmler, Manuela Lötsch, Karl Gündel
The production of surface relief gratings plays a crucial role in nano-structuring today. Applications range from laser mirrors to manufacturing of waveguides for mixed and augmented reality. Augmented (AR) and mixed reality (MR) applications have recently gained large interest. For in- and out-coupling optics, mainly Slanted Relief Gratings (SRG) are used. Nano-imprint lithography (NIL) is one way to produce such optical gratings., ,  For this procedure, NIL master stamp is pressed into a polymer for replication of the pattern. These NIL master stamps have to be structured previous to the NIL process. The manufacturing of those masters is realized by a pattern transfer of a masked substrate by ion beam etching technology. This technology enables the tilting of the substrate in the respect to the ion beam, the so-called incident angle of the ions, and, hence, the slant angles can be defined. Additionally, applying different process parameters, such as ion energy, beam current density and the mixture of process gas, the ratio between the physical, anisotropic etching and chemical isotropic etching can be adjusted. This ratio defines the shape of the slanted gratings. Two types of ion beam process are available, the Reactive ion beam etching (RIBE) for structuring the complete substrate surface simultaneously and the reactive ion beam trimming (RIBT) a locally resolved etching method enabling manufacturing of slanted gratings with both varying slant angle and varying trench depth. This work shows process results for these two manufacturing approaches.
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Mathias Franz, Mahnaz Safian Jouzdani, Lysann Kaßner, Marcus Daniel, Frank Stahr and Stefan E. Schulz
In this work, we present the development of an atomic layer deposition (ALD) process for metallic cobalt. The process operates at low temperatures using dicobalt hexacarbonyl-1-heptyne [Co2(CO)6HC≡CC5H11] and hydrogen plasma. For this precursor an ALD window in the temperature range between 50 and 110 °C was determined with a constant deposition rate of approximately 0.1 Å/cycle. The upper limit of the ALD window is defined by the onset of the decomposition of the precursor. In our case, decomposition occurs at temperatures of 125 °C and above, resulting in a film growth in chemical vapour deposition mode. The lower limit of the ALD window is around 35 °C, where the reduction of the precursor is incomplete. The saturation behaviour of the process was investigated. X-ray photoelectron spectroscopy measurements could show that the deposited cobalt is in the metallic state. The finally established process in ALD mode shows a homogeneous coating at the wafer level.
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We will introduce the latest results for etching of slanted relief grating (SRG) used as in- and out-coupling gratings in waveguides for augmented or mixed reality devices. The smaller input grating diffracts light coming from a display into the waveguide. At the out-coupler grating, light is diffracted in direction of the viewer. The geometrical dimension is below the wavelength of the light. Different approaches for the design of coupling gratings exist. One type is the so called SRG, which has a higher coupling efficiency compared to other types. For SRG, tilted trenches are etched in the waveguide, which is typically a plate made of a high refractive index material. The manufacturing challenges are the control of etching depth, slant angle and bottom angle. We will introduce a reactive ion beam milling tool for manufacturing of those gratings in mass production. We will give examples how to vary process parameters in order to control the grating geometry.
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David Stark, Carsten Schulze, Marcel Demmler, Matthias Nestler, Michael Zeuner – scia Systems GmbH
Augmented and mixed reality applications have recently gained large interest. In order to fabricate lightweight near eye displays surface relief gratings are used for coupling the light from the source into the light guide and out of the light guide towards the eye. To suppress higher diffraction orders and thus maximize the light yield those gratings are slanted. In order to achieve high field of view variation of the slant angle is desirable yet rather difficult to achieve. Ion beam trimming (IBT) is a method well established in MEMS and sensor manufacturing to locally modify the thickness of a layer or substrate in order to achieve a desired target topography. This method has been adapted towards fabrication of surface relief gratings with both varying slant angle and varying trench depth.
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H. Bartzsch; J. Hildisch ; K. Täschner ; S. Barth – Fraunhofer FEP; R. Rückriem ; M. Nestler – scia Systems GmbH
Reactive magnetron sputter deposition is shown to be a suitable method for depositing Fluorine doped silica films for temperature compensated SAW devices.
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C.Schulze, M. Nestler, M.Zeuner - scia Systems GmbH
A significant portion toward understanding evolution of the universe comes from x-ray astronomy since many astronomical objects of interest, such as black holes, supernovae and distant galaxies, emit radiation in the x-ray band. As basically all materials have almost unity refractive index for x-rays focusing x-ray beams is only possible by reflection at grazing incidence. Due to the low photon fux of the objects under study (few photons per hour) each individual photon is of particular interest. Thus, the collective area of x-ray telescopes needs to be as large as possible which is achieved by a large amount of concentrically nested x-ray mirrors whose shape needs to be ideal fitting to the designed geometry for high image quality. Due to the mirrors' curvature even state of the art mechanical machining and chemical mechanical polishing processes leave a residual surface error of several hundred nanometers. Those residual errors can be significantly reduced by ion beam figuring.
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M. Nestler, S. Rumbke, E. Loos - scia Systems GmbH, A. Böhnke, N. Dohmeier - Bielefeld University
We demonstrate that high quality CoFeB/MgO/CoFeB magnetic tunnel junctions (MTJs) can be produced by combining magnetron sputtering, UV lithography, and ion beam milling (IBM). Particularly, we study the effect of different milling angles on the tunneling magnetoresistance (TMR). Furthermore, we investigate the quality of devices manufactured by depositing the insulator in situ subsequent to milling. Using a secondary ion mass spectrometer (SIMS), all layers can be detected while milling, enabling us to precisely define the mill stops. We found TMR values of up to 140 % for a milling angle of 30° and 90 % for a two angles milling process at 20° and 65°, proving that no critical sidewall redeposition of conductive material takes place.
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R. Rückriem, M. Zeuner - scia Systems GmbH, R. Köhler - DIAS INFRARED GMBH
Ion beam etching of pyroelectric sensors made of lithium tantalate (LT) is presented in order to get a higher specific detectivity D* compared to standard sensors. We present the etching tool which applies argon ion beam etching in production environment. The etching homogeneity was investigated by a standard silicon oxide etch and a twelve hour silicon etch with photoresist mask. Both show a homogeneity of +/- 0.7 % and a good compliance. Further investigations were done in a twelve hour process regarding the stability of the ion current regulation and ion current density. In the first two hours after process start, the main variation of power and ion current density takes place. Afterwards, the system reached a steady-state. After etching of the LT samples, an analysis of the removed material and emerged etching walls was done. Finally, the important D* was compared between an ion-etched and a non-ion etched pyroelectric sensor.
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M. V. Daniel, M. Demmler – scia Systems GmbH
Ion beam sputtering is well established in research and industry, despite its relatively low deposition rates compared to electron beam evaporation. Typical applications are coatings of precision optics, like filters, mirrors and beam splitter. Anti-reflective or high-reflective multilayer stacks benefit from the high mobility of the sputtered particles on the substrate surface and the good mechanical characteristics of the layers. This work gives the basic route from single layer optimization of reactive ion beam sputtered Ta2O5 and SiO2 thin films towards complex multilayer stacks for high-reflective mirrors and anti-reflective coatings. Therefore films were deposited using different oxygen flow into the deposition chamber Afterwards, mechanical (density, stress, surface morphology, crystalline phases) and optical properties (reflectivity, absorption and refractive index) were characterized. These knowledge was used to deposit a multilayer coating for a high reflective mirror.
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D. Klaas, J. Becker, M. C. Wurz - Institute of Micro Production Technology, Leibniz Universität Hannover,
J. Schlosser, M. Kunze – scia Systems GmbH
A new coating system for the deposition of sensors and thin-layers directly onto components of arbitrary size has been invented at the Institute of Micro Production Technology. This system allows for thinner sensors without any carrier substrate and with a higher measuring accuracy. Within this paper, the basic setup and the functional principle of the new coating system is presented. The deposition process sequence is described and the system is characterized concerning layer homogeneity and evacuation time.
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M.Zeuner, K.Gündel, T.Dunger, M.Demmler, M.Nestler – scia Systems GmbH
The manufacturing of devices for mobile communication technology demands an extremely high precision regarding geometrical dimensions. In case of acoustic wave ﬁlters, surface acoustic wave (SAW) and bulk acoustic wave (BAW) resonators, the quality depends a lot on the dimensions of several layers consisting of different material, hence an adjustment regarding homogeneity in sub-nm range has to be guaranteed. Thin ﬁlm deposition processes, used commonly in the industrial mass production in semiconductor industry, are not able to reach these demanding requirements in order to achieve the necessary device quality. On account of this a space-resolved correction of layer dimensions as a subsequent manufacturing step is mandatory [1, 2]. Within the article a technology of space-resolved correction of device wafer is described. The correction takes place due to a focused broad ion beam and a movement of wafer in front of it. Hence the ion beam etches the surface of the wafer and the modulated dwell time of the beam on a certain position of the wafer deﬁnes the amount of ablated material in order to achieve the target geometry or thickness all over the wafer.
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