Browsing by Author "Amusan, Akinwumi A."

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    Ag films grown by remote plasma enhanced atomic layer deposition on different substrates
    (American Vacuum Society, 2015-11) Amusan, Akinwumi A.; Kalkofen, Bodo; Gargouri, Hassan; Wandel, Klauss; Pinnow, Cay; Lisker, Marco; Burte, Edmund P.
    Plasma-assisted atomic layer deposition (PALD) was carried for growing thin boron oxide films onto silicon aiming at the formation of dopant sources for shallow boron doping of silicon by rapid thermal annealing (RTA). A remote capacitively coupled plasma source powered by GaN microwave oscillators was used for generating oxygen plasma in the PALD process with tris(dimethylamido)borane as boron containing precursor. ALD type growth was obtained; growth per cycle was highest with 0.13 nm at room temperature and decreased with higher temperature. The as-deposited films were highly unstable in ambient air and could be protected by capping with in-situ PALD grown antimony oxide films. After 16 weeks of storage in air, degradation of the film stack was observed in an electron microscope. The instability of the boron oxide, caused by moisture uptake, suggests the application of this film for testing moisture barrier properties of capping materials particularly for those grown by ALD. Boron doping of silicon was demonstrated using the uncapped PALD B2O3 films for RTA processes without exposing them to air. The boron concentration in the silicon could be varied depending on the source layer thickness for very thin films, which favors the application of ALD for semiconductor doping processes
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    Application of atomic layer deposited dopant sources for ultra‐shallow doping of silicon
    (WILEY‐VCH Verlag GmbH, 2014-01) Kalkofen, Bodo; Amusan, Akinwumi A.; Lisker, Marco; Burte, Edmund P.
    The advanced silicon semiconductor technology requires doping methods for production of ultra‐shallow junctions with sufficiently low sheet resistance. Furthermore, advanced 3‐dimensional topologies may require controlled local doping that cannot be achieved by ionimplantation. Here, the application of the atomic layer deposition (ALD) method for pre‐deposition of dopant sources is presented. Antimony oxide and boron oxide were investigated for such application. Ozone‐based ALD was carried out on silicon wafers by using triethylantimony or tris‐(dimethylamido)borane. Very homogeneous Sb2O5 deposition could be achieved on flat silicon wafers and in trench structures. The thermal stability of antimony oxide layers was investigated by rapid thermal annealing experiments. The layers were not stable above 750 °C. Therefore, this material failed to act as dopant source so far. In contrast, ultra‐shallow boron doping of silicon from ALD grown boron oxide films was successful. However, pure B2O3 films were highly unstable after exposure to ambient air. The boron oxide films could be protected by thin Sb2O5 or Al2O3 films that were in‐situ grown by ALD. Low temperature ALD of Al2O3 at 50 °C from trimethylaluminium (TMA) and ozone was investigated in detail with respect of its protective effect on boron oxide. Interestingly, it was observed that already one ALD cycle of TMA and O3 resulted in significant increase in stability of the boron oxide in air.
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    Design and Simulation of 1.28 Tbps Dense Wavelength Division Multiplex System Suitable for Long Haul Backbone
    (DE GRUYTER, 2018-10) Amusan, Akinwumi A.; Amusan, Elizabeth A.
    Wavelength division multiplex (WDM) system with on/off keying (OOK) modulation and direct detection (DD) is generally simple to implement, less expensive and energy efficient. The determination of the possible design capacity limit, in terms of the bit rate – distance product in WDM – OOK –DD systems is therefore crucial, considering transmitter/receiver simplicity, as well as energy and cost efficiency. A 32-channel WDM system is designed and simulated over 1000 km fiber length using Optsim commercial simulation software. The standard channel spacing of 0.4 nm was used in the C–band range from 1.5436 to 1.556 nm. Each channel used the simple non return to zero – on/off keying (NRZ – OOK) modulation format to modulate a continuous wave (CW) laser source at 40 Gbps using an external modulator, while the receiver uses a DD scheme. It is proposed that the design will be suitable for long haul mobile backbone in a national network, since up to 1.28 Tbps data rates can be transmitted over 1000 km. A bit rate length product of 1.28 Pbps.km was obtained as the optimum capacity limit in 32 channel dispersion managed WDM – OOK – DD system.
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    Investigation of oxide thin films deposited by atomic layer deposition as dopant source for ultra-shallow doping of silicon
    (Elsevier B.V., 2013-09) Kalkofen, Bodo; Amusan, Akinwumi A.; Lisker, Marco; Burte, Edmund P.
    Atomic layer deposition of solid dopant sources for silicon was carried out by using triethylantimony and ozone, and tris-(dimethylamido)borane and ozone as precursors for antimony or boron containing oxides, respectively. It was proved that homogenous antimony oxide deposition could be achieved on flat silicon wafers and in trench structures. Little growth was found below 100 °C deposition temperature and linear temperature dependence on the growth rate between 100 and 250 °C. The oxide films were not stable above 750 °C and therefore failed to act as dopant source for silicon so far. Boron containing films were only obtained at a deposition temperature of 50 °C. These films were highly instable after exposure to air but degradation could be delayed by thin films of antimony oxide or aluminium oxide that were in situ grown by ALD as well. Only little boron was found by ex-situ chemical analysis. However, rapid thermal annealing of such boron containing dopant source layers resulted in high concentrations of active boron close to the silicon surface. The dependence of the doping results on the thickness of the initial boron containing films could be shown.
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    Spin-hall-active platinum thin films grown via atomic layer deposition
    (AIP Publishing, 2018-05) Schlitz, Richard; Amusan, Akinwumi A.; Lammel, Michaela; Schlicht, Stefanie; Tynell, Tommi; Bachmann, Julien; Woltersdorf, Georg; Nielsch, Kornelius; Goennenwein, Sebastian T. B.; Thomas, Andy
    We study the magnetoresistance of yttrium iron garnet/Pt heterostructures in which the Pt layer was grown via atomic layer deposition (ALD). Magnetotransport experiments in three orthogonal rotation planes reveal the hallmark features of spin Hall magnetoresistance. To estimate the spin transport parameters, we compare the magnitude of the magnetoresistance in samples with different Pt thicknesses. We check the spin Hall angle and the spin diffusion length of the ALD Pt layers against the values reported for high-quality sputter-deposited Pt films. The spin diffusion length of 1.5 nm agrees well with that of platinum thin films reported in the literature, whereas the spin Hall magnetoresistance Δρ/ρ=2.2×10−5 is approximately a factor of 20 smaller compared to that of our sputter-deposited films. Our results demonstrate that ALD allows fabricating spin-Hall-active Pt films of suitable quality for use in spin transport structures. This work provides the basis to establish conformal ALD coatings for arbitrary surface geometries with spin-Hall-active metals and could lead to 3D spintronic devices in the future.
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    Use of B2O3 films grown by plasma-assisted atomic layer deposition for shallow boron doping in silicon
    (American Vacuum Society, 2015-04) Kalkofen, Bodo; Amusan, Akinwumi A.; Bukhari, Muhammad S. K.; Garke, Bernd; Lisker, Marco; Gargouri, Hassan; Burte, Edmund P.
    Plasma-assisted atomic layer deposition (PALD) was carried for growing thin boron oxide films onto silicon aiming at the formation of dopant sources for shallow boron doping of silicon by rapid thermal annealing (RTA). A remote capacitively coupled plasma source powered by GaN microwave oscillators was used for generating oxygen plasma in the PALD process with tris(dimethylamido)borane as boron containing precursor. ALD type growth was obtained; growth per cycle was highest with 0.13 nm at room temperature and decreased with higher temperature. The as-deposited films were highly unstable in ambient air and could be protected by capping with in-situ PALD grown antimony oxide films. After 16 weeks of storage in air, degradation of the film stack was observed in an electron microscope. The instability of the boron oxide, caused by moisture uptake, suggests the application of this film for testing moisture barrier properties of capping materials particularly for those grown by ALD. Boron doping of silicon was demonstrated using the uncapped PALD B2O3 films for RTA processes without exposing them to air. The boron concentration in the silicon could be varied depending on the source layer thickness for very thin films, which favors the application of ALD for semiconductor doping processes.