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Broad ion beams have shown their wide applications for materials modification. Focused ion beams can be used in a similar way while simultaneously providing process monitoring. Here, we demonstrate this on a new kind of ion-induced structural evolution. Sub-micrometer Sn spheres were irradiated in a helium ion microscope with a sub-nm beam of 30 keV He ions. Above a fluence of ~10^17/cm², Sn extrusions appeared on the surface of the spheres, which were imaged using the secondary electron signal. Initially, small, pyramid-like faceted extrusions form at the equator of the spheres (north pole pointing to the ion source). Later, each sphere becomes completely covered by the extrusions. A model was developed that assumes that each He ion generate ~70 Frenkel pairs. The implanted helium atoms, interstitials, and vacancies will be confined by the oxide skin of the spheres. Some He atoms will occupy vacancies, which partially prevent their recombination with interstitials. Furthermore, the ion irradiation leads to erosion and opening of the SnO skin. The interstitials can now escape from the interior of the Sn sphere and form an epitaxial regular Sn lattice on the exterior. Transmission electron microscopy, Auger electron spectroscopy as well as TRI3DYN [1] and 3D kinetic lattice Monte Carlo [2] simulations support these findings. In addition, we provide a perspective on focused ion beams from our in-house development and production of liquid metal alloy ion sources, which can be used for applications from self-organized patterning, over altering magnetic or electrical properties, to quantum photonics and computation [3]. [1] Möller, Nucl. Instr. Meth. B 322 (2014) 23 [2] Strobel et al., Phys. Rev. B 64 (2001) 245422 [3] www.hzdr.de/fib

This study addresses the complementary metal-oxide-semiconductor-compatible fabrication of vertically stacked Si/SiO2/Si nanopillars (NPs) with embedded Si nanodots (NDs) as key functional elements of a quantum-dot-based, gate-all-around single-electron transistor (SET) operating at room temperature. The main geometrical parameters of the NPs and NDs were deduced from SET device simulations using the nextnano++ program package. The basic concept for single silicon ND formation within a confined oxide volume was deduced from Monte-Carlo simulations of ion-beam mixing and SiOx phase separation. A process flow was developed and experimentally implemented by combining bottom-up (Si ND self-assembly) and top-down (ion-beam mixing, electron-beam lithography, reactive ion etching) technologies, fully satisfying process requirements of future 3D device architectures. The theoretically predicted self-assembly of a single Si ND via phase separation within a confined SiOx disc of < 500 nm³ volume was experimentally validated. This work describes in detail the optimization of conditions required for NP/ND formation, such as the oxide thickness, energy and fluence of ion-beam mixing, thermal budget for phase separation and parameters of reactive ion beam etching. Low-temperature plasma oxidation was used to further reduce NP diameter and for gate oxide fabrication whilst preserving the pre-existing NDs. The influence of critical dimension variability on the SET functionality and options to reduce such deviations are discussed. We finally demonstrate the reliable formation of Si quantum dots with diameters of less than 3 nm in the oxide layer of a stacked Si/SiO2/Si NP of 10 nm diameter, with tunnelling distances of about 1 nm between the Si ND and the neighboured Si regions forming drain and source of the SET.

Robis requires an Abstract, but this poster doesn't have one, so here's the one from a conference talk about the same contents: We report on 3D lattice kinetic Monte Carlo (3DlkMC) simulation of nanostructure formation during rapid quenching in gas-atomization (up to 108K/s) of droplets of AlSi alloy melt. The nanostructured Si particles (with the Al selectively etched away) promise to enable about 10x the capacity of the current state-of-the-art graphite in lithium-ion batteries by mitigating Si pulverization. This work reproduces the experimentally found nanosponge and core-shell particles and reveals heteronucleation at Al2O3 sites resulting from trace oxygen at the surface as the formation mechanism for core-shell particles. The computer simulation uses a memory-efficient bit-encoded lattice, enabling large scale atomistic calculations, while kinetics is implemented via CPU-efficient bit-manipulation for atom jumps between lattice sites. The jump probabilities are described by the metropolis algorithm with a look-up-table of energies calculated with an angular dependent potential for the Si-Al-Au system in LAMMPS. This work is supported by the federal ministry for economic affairs and climate protection under grant number 01221755/1.

Enhanced interstitial diffusion in tin is a phenomenon often observed during ion-beam irradiation and in lead-free solders. For the latter, this not very well understood, strain-driven mechanism results in the growth of whiskers, which can lead to unwanted shorts in electronic designs. In ion-beam physics, this phenomenon is often observed as a result of the enhanced formation of Frenkel pairs in the energetic collision cascade. Here, we show how epitaxial growth of tin extrusions on tin-oxide-covered tin spheres can be induced and simultaneously observed by implanting helium using a helium ion microscope. Calculations of collision cascades based on the binary collision approximation and 3D-lattice-kinetic Monte Carlo simulations show that the implanted helium will occupy vacancy sites, leading to a tin interstitial excess. Sputtering and phase separation of the tin oxide skin, which is impermeable for tin atoms, create holes and will allow the epitaxial overgrowth to start. Simultaneously, helium accumulates inside the irradiated spheres. Fitting the simulations to the experimentally observed morphology allows us to estimate the tin to tin-oxide interface energy to be 1.98 J m−2 . Our approach allows the targeted initiation and in situ observation of interstitial diffusion-driven effects to improve the understanding of the tin-whisker growth mechanism observed in lead-free solders.

Enhanced interstitial diffusion in tin is a phenomenon often observed during ion-beam irradiation and in lead-free solders. For the latter, this not very well understood, strain-driven mechanism results in the growth of whiskers, which can lead to unwanted shorts in electronic designs. In ion-beam physics, this phenomenon is often observed as a result of the enhanced formation of Frenkel pairs in the energetic collision cascade. Here, we show how epitaxial growth of tin extrusions on tin-oxide-covered tin spheres can be induced and simultaneously observed by implanting helium using a helium ion microscope. Calculations of collision cascades based on the binary collision approximation and 3D-lattice-kinetic Monte Carlo simulations show that the implanted helium will occupy vacancy sites, leading to a tin interstitial excess. Sputtering and phase separation of the tin oxide skin, which is impermeable for tin atoms, create holes and will allow the epitaxial overgrowth to start. Simultaneously, helium accumulates inside the irradiated spheres. Fitting the simulations to the experimentally observed morphology allows us to estimate the tin to tin-oxide interface energy to be 1.98 J m−2 . Our approach allows the targeted initiation and in situ observation of interstitial diffusion-driven effects to improve the understanding of the tin-whisker growth mechanism observed in lead-free solders.

Herausforderungen bei der TEM-Probenpräparation von neuartigen Elektroden-Materialen für Li-Ionen-Batterien

Broad ion beams have shown their wide applications for materials modification. Focused ion beams can be used in a similar way while simultaneously providing process monitoring. Here, we demonstrate this on a new kind of ion-induced structural evolution. Sub-micrometer Sn spheres were irradiated in a helium ion microscope with a sub-nm beam of 30 keV He ions. Above a fluence of ~10^17/cm², Sn extrusions appeared on the surface of the spheres, which were imaged using the secondary electron signal. Initially, small, pyramid-like faceted extrusions form at the equator of the spheres (north pole pointing to the ion source). Later, each sphere becomes completely covered by the extrusions. A model was developed that assumes that each He ion generate ~70 Frenkel pairs. The implanted helium atoms, interstitials, and vacancies will be confined by the oxide skin of the spheres. Some He atoms will occupy vacancies, which partially prevent their recombination with interstitials. Furthermore, the ion irradiation leads to erosion and opening of the SnO skin. The interstitials can now escape from the interior of the Sn sphere and form an epitaxial regular Sn lattice on the exterior. Transmission electron microscopy, Auger electron spectroscopy as well as TRI3DYN [1] and 3D kinetic lattice Monte Carlo [2] simulations support these findings. In addition, we provide a perspective on focused ion beams from our in-house development and production of liquid metal alloy ion sources, which can be used for applications from self-organized patterning, over altering magnetic or electrical properties, to quantum photonics and computation [3]. [1] Möller, Nucl. Instr. Meth. B 322 (2014) 23 [2] Strobel et al., Phys. Rev. B 64 (2001) 245422 [3] www.hzdr.de/fib

Six carbon atoms of graphite of lithium ion battery (LIB) anodes can store one lithium atom, whereas one Si atom can store nearly four lithium atoms. Theoretically, the replacement of graphite by silicon could reduce the weight of the anode by a factor of nearly 10. However, due to the strong swelling of silicon upon lithiation, Si anodes suffer from pulverization which reduces drastically the life cycle of LIBs. It has been shown that nanostructured silicon with structure sizes <200nm can withstand pulverization. There are many activities to develop an economic large-scale fabrication of such nanosilicon. We form Si nanostructures by phase separation during quenching of AlSi alloy droplets. At atomization of the AlSi melt the microdroplet solidify extremely fast which results in nanoscale Si pattern. Subsequently the Al is removed by selective etching leading to nanoporous Si microspheres. We show that the structure depends strongly on the AlSi composition, the particle sizes and impurities. Promising nanosilicon for LIB anodes with a good cycling have been found. This work is supported by the German federal ministry for economic affairs and climate protection under grant number 01221755/1.

Low-power logic and memory circuits remain a main task for the next generations of energy-efficient electronic devices. Single Electron Transistors (SETs) are extremely low energy dissipation devices. However, SETs operate usually at cryogenic temperatures and have some serious drawbacks. Fortunately, Field Effect Transistors (FETs) and SETs are complementary: The SET is the champion of low-power consumption while FETs advantages, like high-speed, driving, voltage gain and input impedance can compensate exactly for SET's intrinsic drawbacks. To overcome the drawback of cryogenic temperature operation, each SET has to be manufactured with a quantum dot of a size of just a few nanometers, and this dot has to be located not more than about one nanometer apart from the electrodes. The large-scale implementation of SETs in room-temperature electronics is hampered by its unresolved manufacturability because such requirements are beyond the limits of present lithography. We employed self-organization to overcome the present-day limits of lithography. On 5…8nm thick SiO2 layers of (001)Si wafers about 30nm thick a-Si layers have been deposited and subsequently irradiated with 50 keV Si+ ions. The irradiation leads to ion beam mixing at the upper and lower Si/SiO2 interfaces and transforms the buried SiO2 layer to SiOx with x~1. Then, pillar arrays have been fabricated from such layer stacks using electron beam lithography and plasma etching. Arrays of pillars with different diameters from 100nm down to less than 20nm have been produced, where the smallest pillar diameters have been further reduced to ~10nm by plasma oxidation and selective oxide etching (sacrificial oxidation). In this manner we manufactured SiOx disks of ~10nm diameter and 5nm thickness sandwiched between the Si of the pillars. During Rapid Thermal Processing (RTP) of such pillars at 1050°C for 60s, phase separation SiOx  (1-x/2)Si + x/2SiO2 occurs via formation of Si nuclei and Ostwald ripening. Close to

We report on 3D lattice kinetic Monte Carlo (3DlkMC) simulation of nanostructure formation during rapid quenching in gas-atomization (up to 108K/s) of droplets of AlSi alloy melt. The nanostructured Si particles (with the Al selectively etched away) promise to enable about 10x the capacity of the current state-of-the-art graphite in lithium-ion batteries by mitigating Si pulverization. This work reproduces the experimentally found nanosponge and core-shell particles and reveals heteronucleation at Al2O3 sites resulting from trace oxygen at the surface as the formation mechanism for core-shell particles. The computer simulation uses a memory-efficient bit-encoded lattice, enabling large scale atomistic calculations, while kinetics is implemented via CPU-efficient bit-manipulation for atom jumps between lattice sites. The jump probabilities are described by the metropolis algorithm with a look-up-table of energies calculated with an angular dependent potential for the Si-Al-Au system in LAMMPS. This work is supported by the federal ministry for economic affairs and climate protection under grant number 01221755/1.

The data included in the publication are results of SET device simulations, Monte-Carlo simulations of physical processes (ion-beam mixing, phase seepration, Si nanodot formation) and micrographs taken by electron and ion microscopes.

Raw data for the publication: "Epitaxial lateral overgrowth of tin spheres driven and directly observed by helium ion microscopy". It contains helium ion microscopy, transmission electron microscopy, scanning electron microscopy as well as gallium focused ion microscopy images and XPS data. It shows how the irradiation of tin spheres with keV He ions causes epitaxial lateral overgrowth.

Broad ion irradiation of nanoobjects can considerably change their shape. Examples are ion-beam hammering [1], ion-induced shaping of buried particles [2], and ion-induced viscous flow of nanopillars [3]. Such shape changes are mainly driven by the kinetics of defects generated by binary collisions of ions and recoils. Here we report a new kind of ion-induced structure evolution. Sub-micrometer Sn spheres were irradiated with 30 keV He+ ions in a Helium Ion Microscope (HIM). Above a He+ fluence of ~ 10E17 /cm², Sn extrusions appear on the surface of the spheres and were imaged with the HIM. Initially, small, pyramid-like facetted extrusions form at the equator of the tin spheres (north pole pointing to the ion source). Later, each sphere becomes completely covered with tin and appears like a facetted single crystal cube. No Sn extrusions were observed for tin spheres with diameters smaller than ~100 nm. Transmission Electron Microscopy and Auger electron spectroscopy studies show that the tin spheres are covered with a few nm thick SnOx skin and that the extrusions are single crystals. A model was developed which assumes that the He+ ions generate Frenkel pairs in the body-centered tetragonal lattice of tin. The point defects are confined to the tin sphere by the SnO skin, and there is no preferred nucleation or annihilation of the point defects at the Sn-SnO interface. The recombination of interstitials with vacancies is partly inhibited by occupation with He atoms. This results in an increasing pressure of the “interstitial gas”. Simultaneously, He+ ion erosion creates openings in the SnO skin. The sputter coefficient increases with the angle of incidence, so that openings in the SnO skin form in the equator regions first. Once the tin interstitials find an opening in the SnO skin, they can escape from the interior of the Sn sphere and form an epitaxial regular Sn lattice on the outside. Due to the high Sn-SnO bond strength, the extruded tin wets the outer SnO sur

The inherent three-dimensional topology of vNWs imposes several constraints to their fabrication and their integration in other circuits. We present here the use of Hydrogen silsesquioxane (HSQ) for the fabrication of single electron transistors (SETs) based on vNWs.

Single Electron Transistors (SETs) open the way to semiconductor devices with extremely low power consumption. Quantum mechanical effects are used in such transistors: field-controlled tunneling of single electrons from a source to a drain via a quantum dot. SETs can be manufactured as thin Si pillars (source and drain) with a Si oxide layer in-between containing one Si quantum dot (Fig. 1). After SiOx formation by ion beam mixing, a thermally activated phase separation including Ostwald ripening results in a self-organization of Si nanocrystals in the SiO2 layer acting as Si quantum dots (Si NDs). For SET operation at room temperature, the diameter of the Si pillars needs to be < 12 nm, the Si ND diameter must be in the range of 2…3 nm and the distances between Si NDs and source/drain cannot be larger than 1.5 nm allowing quantum mechanical tunneling of the electrons. Thus, Transmission Electron Microscopy (TEM) must be used for the structural characterization of these SETs. Si NDs inside the SiO2 matrix can only be detected by using the Si plasmon loss in the energy-filtered TEM mode. TEM sample preparation is challenging because of the very small 3D structure of the pillars (Fig.2) and the need for very thin TEM lamellae (30…40 nm in thickness). The Focused Ion Beam (FIB) lift-out technique can be used to prepare such samples. Setting markers and gradual thinning of the lamella from both sides (with TEM inspection in between) is necessary. Surprisingly, comprehensive TEM studies uncovered that the oxide layer of a Si/ SiO2/Si layer stack can become dramatically thinner in pillars fabricated from this stack by Reactive Ion Etching (RIE). The oxide layer thinning depends on the pillar diameter. For instance, an originally 8 nm thick SiO2 layer is reduced to 2.6 nm in 15 nm diameter pillars. In order to prove that this oxide shrinkage is caused by RIE and not by sample preparation the most critical process in the FIB preparation - which is the electron-beam-assisted

Broad ion irradiation of nanoobjects can considerably change their shape. Examples are ion-beam hammering [1], ion-induced shaping of buried particles [2], and ion-induced viscous flow of nanopillars [3]. Such shape changes are mainly driven by the kinetics of defects generated by binary collisions of ions and recoils. Here we report a new kind of ion-induced structure evolution. Sub-micrometer Sn spheres were irradiated with 30 keV He+ ions in a Helium Ion Microscope (HIM). Above a He+ fluence of ~ 10E17 /cm², Sn extrusions appear on the surface of the spheres and were imaged with the HIM. Initially, small, pyramid-like facetted extrusions form at the equator of the tin spheres (north pole pointing to the ion source). Later, each sphere becomes completely covered with tin and appears like a facetted single crystal cube. No Sn extrusions were observed for tin spheres with diameters smaller than ~100 nm. Transmission Electron Microscopy and Auger electron spectroscopy studies show that the tin spheres are covered with a few nm thick SnOx skin and that the extrusions are single crystals. A model was developed which assumes that the He+ ions generate Frenkel pairs in the body-centered tetragonal lattice of tin. The point defects are confined to the tin sphere by the SnO skin, and there is no preferred nucleation or annihilation of the point defects at the Sn-SnO interface. The recombination of interstitials with vacancies is partly inhibited by occupation with He atoms. This results in an increasing pressure of the “interstitial gas”. Simultaneously, He+ ion erosion creates openings in the SnO skin. The sputter coefficient increases with the angle of incidence, so that openings in the SnO skin form in the equator regions first. Once the tin interstitials find an opening in the SnO skin, they can escape from the interior of the Sn sphere and form an epitaxial regular Sn lattice on the outside. Due to the high Sn-SnO bond strength, the extruded tin wets the outer SnO sur

This work reports the CMOS compatible and monolithic fabrication of a conventional planar field effect transistor (FET) co-integrated with a quantum dot (QD) based single electron transistor (SET). The FET process fabrication is adapted to fulfill the restrictions imposed by the pre-fabricated SET, such as reduced thermal budget, extra protection layers and modified doping in order to obtain low threshold voltage. The resulting FET presents good subthreshold characteristics and the SET preserves its integrity at the end of the fabrication.

SETs (Single-Electron-Transistors) arouse growing interest for their very low energy consumption. For future industrialization, it is crucial to show a CMOS-compatible fabrication of SETs, and a key prerequisite is the patterning of sub-20 nm Si Nano-Pillars (NP) with an embedded thin SiO2 layer. In this work, we report the patterning of such multi-layer isolated NP with e-beam lithography combined with a Reactive Ion Etching (RIE) process. The Critical Dimension (CD) uniformity and the robustness of the Process of Reference are evaluated. Characterization methods, either by CD-SEM for the CD, or by TEM cross-section for the NP profile, are compared and discussed.

Si nanopillars of less than 50 nm diameter have been irradiated in a helium ion microscope with a focused Ne+ beam. The morphological changes due to ion beam irradiation at room temperature and elevated temperatures have been studied with the transmission electron microscope. We found that the shape changes of the nanopillars depend on irradiation-induced amorphization and thermally driven dynamic annealing. While at room temperature, the nanopillars evolve to a conical shape due to ion-induced plastic deformation and viscous flow of amorphized Si, simultaneous dynamic annealing during the irradiation at elevated temperatures prevents amorphization which is necessary for the viscous flow. Above the critical temperature of ion-induced amorphization, a steady decrease of the diameter was observed as a result of the dominating forward sputtering process through the nanopillar sidewalls. Under these conditions the nanopillars can be thinned down to a diameter of ∼10 nm in a well-controlled manner. A deeper understanding of the pillar thinning process has been achieved by a comparison of experimental results with 3D computer simulations based on the binary collision approximation.

Si nanopillars for the fabrication of vertical nanowire gate-all-around Single Electron Transistors [1], have been irradiated with Si++, Pb+, Pb++, Au +, Au++, Au2 +, and Au3 + ions accelerated by 30 kV. A FIB of mass separated ions, extracted from a Liquid Metal Alloy Ion Source [2], has been scanned over regular arrays of Si nanopillars of different diameters and pillar distances. The irradiations have been performed at RT and 400∘C. Different morphological changes of the pillars like thinning, height reduction, tilting etc. have been observed which can be attributed to ion erosion (sputtering), impact-induced viscous flow or even transient nanosecond-scale melting [3]. The pillars were imaged by AFM, SEM, TEM and HIM. 3D Monte Carlo simulations [4] of ion and recoil trajectories based on the Binary Collision Approximation and Molecular Dynamics calculations have been carried out in order to discriminate the dominating processes. [1] EU project Ions4SET, Horizon 2020 grant No. 688072 [2] L.Bischoff, et al., Appl. Phys. Rev. 3 (2016) 021101 [3] C. Anders, K.-H. Heinig, H. Urbassek, Phys. Rev. B87 (2013) 245434 [4] W. Möller,NIM B322 (2014) 23

Ion beam induced amorphization of semiconductor nanostructures limits the applicability of ion beam processing to semiconductor nanostructures. Here, we present an approach that not only avoids this amorphization but in addition allows to tailor the lateral device dimensions of pillars and fins used in modern GAA and Fin-FET designs. Si nanopillars (diameter: 25–50 nm) have been irradiated by either 50 keV broad beam Si + or 25 keV focused Ne + beam from a helium ion microscope (HIM) at various temperatures using fluences of 2×10 16 cm −2 and higher. While at room temperature strong deformation of the nanopillars has been observed, the pillar shape is preserved above 325 ∘ C. This is attributed to ion beam induced amorphization of Si at low temperatures allowing plastic flow due to the ion hammering effect and surface capillary forces. Plastic deformation is suppressed for irradiation at elevated temperatures. Above 325 ∘ C, as confirmed by diffraction contrast in BF-TEM, the nanopillars remain crystalline, and are continuously thinned radially with increasing fluence down to 10 nm. This is due enhanced forward sputtering through the sidewalls of the pillar, and agrees well with 3D ballistic computer simulations. Supported by the H-2020 under Grant Agreement No. 688072.

Helium Ion Microscopy (HIM) [1, 2] is best known for its high resolution imaging capabilities of both conductive as well as insulating samples. However, since the introduction of Ne as an imaging gas for the gas field ion source (GFIS) an increasing number of nano-fabrication applications are realized. While the use of Neon as an imaging gas results in a somewhat lower lateral resolution (1.8 nm for 25 keV Ne compared to 0.5 nm for 30 keV He) the user usually benefits from the much higher cross section for nuclear stopping. The latter results in a larger number of sputtered atoms and bonds broken directly by small impact parameter collisions. After a brief introduction of the technique I will present results obtained using direct write milling low fluence ion beam irradiation and ion beam based mixing. In all three cases the electronic or magnetic properties of the target material will be altered at the nano-scale in a controlled way to achieve new functionality. The examples comprise ∙ The fabrication of semiconducting graphene nano-ribbons by direct milling [3] ∙ The fabrication of a lateral spin valve structure using low fluence ion irradiation [4] ∙ The formation of individual 3 nm Si clusters for a room temperature single electron transistor [5] For all presented examples the critical length scale of the nanostructure is smaller or in the range of collision cascade. This size regime can not be accessed with traditional broad beam based ion irradiation and holds many promises but also challenges that need to be overcome to enable new device concepts and new functional materials on the nano-scale. This work is supported by the European Union’s H-2020 research project ‘IONS4SET’ under Grant Agreement No. 688072

Ion beam irradiation of vertical nanopillar structures can be utilized to fabricate a vertical gate-all-around (GAA) single electron transistor (SET) device in a CMOS-compatible way. After irradiation of Si nanopillars (with a diameter of 35 nm and a height of 70 nm) by either 50 keV broad beam Si+ or 25 keV focused Ne+ beam from a helium ion microscope (HIM) at room temperature and a fluence of 2e16 ions/cm2, strong deformation of the nanopillars has been observed which hinders further device integration. This is attributed to ion beam induced amorphization of Si allowing plastic flow due to the ion hammering effect, which, in connection with surface capillary forces, dictates the final shape. However, plastic deformation can be suppressed under irradiation at elevated temperatures (investigated up to 672 K). Then, as confirmed by bright-field transmission electron microscopy, the substrate and the nanopillars remain crystalline and are continuously thinned radially with increasing fluence down to a diameter of 10 nm. This is attributed to enhanced forward sputtering through the sidewalls of the pillar, and found in reasonable quantitative agreement with the predictions from 3D ballistic computer simulation using the TRI3DYN program. This work is supported by the European Union’s H-2020 research project ‘IONS4SET’ under Grant Agreement No. 688072.

The usage of ion beam irradiation on vertical nanopillar structures is a prerequisite for fabricating a CMOS-compatible, vertical gate-all-around(GAA) SET device. After either 50 keV broad beam Si+ or 25 keV focused Ne+ beam from a helium ion microscope (HIM) irradiation of the nanopillars (with diameter of 35 nm and height of 70 nm) at room temperature with a medium fluence (2e16 ions/cm2), strong plastic deformation has been observed which hinders further device integration. This differs from predictions made by the Monte-Carlo based simulations using the program TRI3DYN. We assume that it is the result from the ion beam induced amorphization of Si accompanied by the ion hammering effect. The amorphous nano-structure behaves viscously and the surface capillary force dictates the final shape. To confirm such a theory, ion irradiation at elevated temperatures (up to 672 K) has been performed and no plastic deformation was observed under these conditions. Bright-field transmission electron microscopy micrographs as well as Electron Beam Diffraction confirmed the crystallinity of the substrate and nanopillars after HT-irradiation. In addition, a steady thinning process of the nanopillars to a diameter of 10 nm has been observed at higher fluencies. As the original pillar diameter is comparable to the size of the collision cascade, instead of direct knock-on sputtering, enhanced forward sputtering through the sidewalls of the pillar is responsible for this effect. The relation between ion beam energy, flux and temperature with the observed thinning of the nanopillars has been studied experimentally and compared to TRI3DYN simulations. Such a reliable and CMOS-compatible process could serve as a potential downscaling technique for large-scale fabrication of nanopillar-based electronics.

Ion beam irradiation of vertical nanopillar structures may be utilized to fabricate a vertical gate-all-around (GAA) single electron transistor (SET) device in a CMOS-compatible way. After irradiation of Si nanopillars (with a diameter of 35 nm and a height of 70 nm) by either 50 keV broad beam Si+ or 25 keV focused Ne+ beam from a helium ion microscope (HIM) at room temperature and a fluence of 2e16 ions/cm2, strong deformation of the nanopillars has been observed which hinders further device integration. This is attributed to ion beam induced amorphization of Si allowing plastic flow due to the ion hammering effect, which, in connection with surface capillary forces, dictates the final shape. However, plastic deformation can be suppressed under irradiation at elevated temperatures (investigated up to 672 K). Then, as confirmed by bright-field transmission electron microscopy, the substrate and the nanopillars remain crystalline and are continuously thinned radially with increasing fluence down to a diameter of 10 nm. This is attributed to enhanced forward sputtering through the sidewalls of the pillar and found in reasonable quantitative agreement with the predictions from 3D ballistic computer simulation using the TRI3DYN program. This work is supported by the European Union’s H-2020 research project ‘IONS4SET’ under Grant Agreement No. 688072.

Ion beam induced collateral damage is becoming an issue in FIB processing, as it limits the application of ion beams for nanostructure fabrication. This is of special importance for the application of focused ion beams for nanostructure fabrication. Here, we present an approach to mitigate the ion beam induced damage inflicted on semi - conductor nanostructures during ion beam irradiation. Nanopillars (with a diameter of 35 nm and a height of 70 nm) have been irradiated with both, a 50 keV Si + broad beam and a 25 keV focused Ne + beam from a helium ion microscope (HIM). Upon irradiation of the nanopillars at room temperature with a medium fluence (2x10 16 ions/cm2), strong plastic deformation has been observed which hinders further device integration. The shape and crystallinity has been studied by HIM and TEM. This differs from predictions made by Monte-Carlo based simulations using the TRI3DYN. However, irradiation at elevated tem- peratures with the same fluence not only preserves the shape of the nanopillars but allows for controlled diameter reduction by as much as 50 % without significant change in pillar height. It is well known that above a critical temperature amorphization of silicon is prevented in- dependent of the applied fluence. At high enough temperatures and for not too high flux this prevents the ion beam hammering and viscous flow of the nanostructures. These two effects are responsible for the shape change observed at low temperature. We find that ir- radiation above 650 K preserves the crystalline nature of the pillars and prevents viscous flow. In addition, a steady thinning process of the nanopillars to a diameter of 10 nm with- out a significant change in height is observed for higher fluencies at elevated temperatures. As the original pillar diameter is smaller than the size of the collision cascade, enhanced forward sputtering through the sidewalls of the pillar is responsible for this pillar-thinning effect. Results for various ion beam e

The European H2020 project “ion4SET” is directed to the development of advanced computation and communication devices with significantly lower power consumption. The general objective is to demonstrate the manufacturability of single electron transistors (SETs) using CMOS compatible technology. The basic idea of this SET is a nano-pillar (NP) transistor having a single Si nanodot (ND) in the oxide layer separating source and drain. The ND is formed by ion beam mixing and post annealing from a Si top layer. The ion irradiation under normal incidence is a crucial process for the small nano-pillars which are only 10 to 30 nm in width and about 80 nm in height. In this work the evolution nano-pillars shape is investigated under heavy ion irradiation from a mass separated focused ion beam (FIB) for different ion energies at RT and 400°C target temperature. In particular Si (60 keV), Pb (30 and 60 keV), Au (30 and 60 keV) ions as well as polyatomic projectiles Au2 and Au3 (Uacc = 30 kV) with a fluence of 5 x 1015 cm-2 were applied. Whereas the Si ion irradiation of Si pillars at elevated temperatures only deforms the pillar tip, the heavy ion irradiation leads depending on the fluence up to a total removing of the pillar. The fluence variation was obtained on the slope of the beam profile. The irradiation at RT with Pb ions at 30 keV showed a more pronounced bending of the pillar due to the high energy deposition caused stress and viscous flow than that at 60 keV. The influence of the irradiation is also depending on the thickness and the distance of the pillars in different lithographic prepared fields. For a better comprehension of the irradiation results the experiments were simulated using the TRI3DYN code.