Focused Ion Beams

Introduction

Focused ion beams (FIB) are promising tools in micro- and nanotechnology as well as in material analytics. Characteristic properties are the Nanometer spot size, the energy range from some eV up to 200 keV, the high current density and a broad spectrum of ion species. In commercial FIB systems Ga liquid metal ion sources (LMIS) are usually employed, but in some rare cases also liquid metal alloy ion sources (LMAIS) are used. FIB systems allow to create structures of arbitrary shape with dimensions on the nm scale.

Production

The ion fine beam laboratory in the institute has equipment and extensive experience for the development and production of liquid metal hairpin-type ion sources for different source materials, a few are listed as examples below:

Material	Melting point (°C)	Application
Au73Ge27	365	Au: sputtering, nanoclusters; Ge: doping, SixGe1-x
Au77Ge14Si9	365	Si: contamination free processing, Imaging
Au82Si18	365	same as above
Co36Nd64	566	Co: CoSi2 synthesys, Nd: optics and magnetismn
Co27Ge73	817	Co: magnetic applications
Er69Ni31	765	Er: optical applications
Er70Fe22Ni5Cr3	862	Fe,Ni,Cr: magnetic applications
Sn74Pb26	183	Sn: doping
In14Ga86	14.2	In: 3-5 semiconductors
Mn45Ge55	720	Mn: doping
Ga38Bi62	222	Ga: doping, milling; Bi: doping
Ga35Bi60Li5	250	Li: high resolution applications
Ga	29.7	All conventional FIB applications
Bi	271.5	surface modification

Test und characterization

The following parameters are determined for the test and characterisation of the sources:

• current-voltage characteristics, emission stability, lifetime and emitter-temperature behaviour, long-term stability.
• Mass spectra (Fig. 3 for GaBi LMAIS)
• Angular distribution and angular intensity by means of a rotating Faraday cylinder
• Ion energy distribution as well as energy shift of each emitted component of the source through a mass filter and a retarding field energy analyzer

Fig. 1: Glowing LMAIS during the wetting process	Fig. 2: Ion emitting AuSi LMAIS	Fig. 3: Mass spectra of emitted ions from a Gallium-Bismuth ion source

Instrumentation

• Carl Zeiss NVision 40 CrossBeam Ga-FIB for standard applications like ion beam lithography or TEM lamella preparation
• 2x Orsay Physics CANION Z31Mplus mass-separated FIBs (semi-commercial), which can provide various ion species using in-house developed ion sources, for dedicated research Topics
• Carl Zeiss ORION NanoFab Helium Ion Microscope He/Ne-FIB
• Hitachi Ion Milling System ArBlade 5000 for sample crosssectioning, 500µA of 10 keV Ar, sputtering of > 1 mm / h

Fig. 4: FIB cut into a processor	Fig. 5: Eye of a fruit fly

Current projects

Demonstration of Raith-Focused-Ion-Beam-Systems for the Fabrication of magnetic Nano-structures (03/2020 – 02/2022)

Grant no.: ZF4494801 DF7 

The VELION (Raith), a modern two-beam system, consists of a column for mass-separated focused ion beams (FIB), a scanning electron microscope (SEM) and a laser interferometer-controlled stage. A major advance is the use of liquid metal alloy ion sources, which offer the possibility to use ion beams of different ion species, which is interesting for both basic research as well as industrial technology. One goal of this project, for example, is the fabrication and modification of magnetic nanostructures. This is of great importance for information technology (IT) in terms of a gradual reduction of the structure size and the operation speed while improving the energy efficiency by using spintronic technology. This project focuses on the modification of individual magnetic nanostructures and the formation of large-area magnonic arrays, so called magnonic crystals.

Former Projects

Development of LMAIS for nano- and quantumtechnology (11/2017 – 12/2019)

Grant no.: ZF4330902 DF7 

Raith develops lithography systems for the structuring and manufacturing of next-generation quantum and nanotechnology devices. The Helmholtz-Zentrum Dresden-Rossendorf develops novel ion sources for use in research and development. In the proposed project, both systems will be integrated into a novel, industrially usable ion beam lithography system for structuring the components of the next quantum and nano technology generation. The aim of the project is the development of an ion beam lithography system unique in its architecture, software and performance, which can address new applications in nano and quantum technology thanks to specific alloy ion sources. In terms of plant engineering, the development is based on Raith's existing know-how of the ionLINE PLUS system. On the material side, the alloys AuGeSi, AuSiCr, AuBGeNi and GaBiLi will be investigated by the HZDR with regard to their specifics with regard to their use in the new ion beam lithography system to be developed. The spectrum of the investigated materials results from the application scenarios to be covered by the new FIB system.

Self-organized surface patterns on Germanium by heavy cluster ions (01/2011 - 02/2014)

Grant no.: DFG project FOR 845  BI 508 / 14-1 

Ion beam induced surface patterning of a new quality has been observed for the surface erosion of Ge by heavy Bi₂⁺ und Bi₃²⁺ cluster ions in the HZDR in the end of 2009. The new quality concerns the excellent short range order and the large amplitude of the dot patterns, which exceeds previous results for elementary semiconductors. The implanted Bi is concentrated in the dots. Also, a qualitative step during cluster ion erosion is observed: While during perpendicular FIB irradiation with Bi⁺ ions the Ge surface layer obtains the well known spongy structure, for Bi₃²⁺ cluster with the same energy per atom (>10 keV) self-organized, crystalline dots, with a spacing below 50 nm und a height of 30 - 40 nm are obtained. Thus, this kind of self-structuring is dominated by a Bi cluster effect and not by single atom impacts. Contrary to the regular self-structuring of Ge with 3 -4 nm shallow holes by bombardment with 5 keV Ga single ions, models like Bradley-Harper or Kuramoto-Sivashinsky are not directly applicable in this case. ...

Ga+ FIB implantation and selective wet etching for 3D nanostructures (2010)

More Information

Masking effects in silicon during wet chemical and dry etching can be utilized by means of silicon doping with high concentration as well as by silicon surface modification with ion beams. The masking effect occurs on p⁺-layers when silicon is doped by a sufficiently high concentration of boron. The same effect has been found for gallium which is also a p-type dopant in silicon.

For maskless nano-patterning of silicon gallium is of special interest because it is used in most focused ion beam (FIB) tools. Ga⁺ FIB irradiation of semiconductors for different purposes is a well established technique and the beam diameter can be optimized nowadays down to 10 nm. Combining Ga⁺ FIB implantation into (100)-oriented silicon with subsequent selective and anisotropic wet chemical etching (e.g. in KOH), 3D silicon structures on the nanometer scale can be fabricated due to etch rate retardation at Ga⁺ FIB-treated silicon areas when the Ga concentration in Si exceeds 5 x 10¹⁹ cm^-3.

Investigation of conducting nanostructures on ta-C films made by FIB lithography ( 04/2010 – 08/2013)

Grant no.: BI 508 / 13-1 

Tetrahedral amorphous carbon (ta-C) films with high sp³ content produced by mass filtered vacuum arc deposition were modified by Ga⁺ FIB irradiation. Surface swelling occurs as a function of fluence, caused by ion induced conversion of sp³ to sp² hybridized carbon atoms. A model for diamond swelling was applied to ta-C films to estimate the swelling for fluences up to 1 x 10¹⁶ cm^-2. For higher fluences data from TRIDYN simulations were included due to sputtering in a good agreement with the experiments. Van der Pauw structures were produced by means of Ga+ FIB lithography. A decrease of the sheet resistance with increasing fluences due to the evolution of graphitic regions was observed. The lowest value of 290 Ω/ was achieved at 1.6 x 10¹⁷ cm^-2. Additionally, conducting graphitic wires were produced (length: 10 µm, width: 300 nm to 5 µm). The wire resistivity was measured within 130 kΩ (5 µm width) and 3 GΩ (300 nm width). Ion induced graphitization of ta-C films by FIB offers prospective applications in nano technology to fabricate conductive nanostructures in an insulating thin film.

Micro- und nanostructures by local FIB ion milling (2006)

FIB irradiation with Ga⁺ or other heavy ions, i.e. Ge⁺, Au⁺, rare earth-elements, allows the fabrication of surface patterned structures with defined geometrical dimensions by direct writing ion beam milling (sputtering). For example, nano-holes were milled into an AFM tip, which should act as an aperture for single ion implantation experiments. Furthermore, a lot of different thin magnetic films were patterned (locally modified or sputtered away to study magnetic properties on sub-micrometer or nanometer scale.

Focussed ion beam synthesis of nanostructures (07/2004 – 06/2006)

Grant no.: DFG – project Schm 1490 / 6-1

Locally Focused Ion Beam (FIB) implantation and subsequent annealing were investigated to synthesize nanowires (NWs) with feature dimensions smaller than 100 nm. For example, silicide NWs are of great interest for low-resistivity interconnect lines in future highly integrated circuits and Si NWs for CMOS-compatible nanowire devices.

For example, cobalt FIB ion implantation is applied to study ion beam synthesis of cobalt disilicide nanowires in silicon. Two mechanisms of CoSi₂ nanowire formation are investigated: (a) conventional synthesis by 60 keV Co⁺⁺ FIB implantation at elevated temperatures into silicon along the in-plane <110>Si crystal direction and subsequent annealing, and (b) self-aligned CoSi₂ nanowire growth in cobalt supersaturated silicon on FIB-induced defects at room temperature during subsequent annealing. The obtained CoSi₂ nanowires are 20-100 nm in diameter and several micrometers long. The growth stability of long NWs embedded in Si sensitively depends on the accuracy of FIB trace alignment relative to the preferred growth directions, namely, the in-plane <110> Si crystal directions. A small misalignment of the FIB trace of a few degrees leads to the decay of the CoSi₂ NWs into shorter parts and a larger deviation causes a periodic chain of CoSi₂ nanoparticles. These observations of NW growth, their stability and decay are in good agreement with predictions of KLMC simulations, carried out in the theory group of our Institiute.

Defect formation and dynamic annealing during FIB implantation (06/1996 – 02/2000)

Grant no.: DFG – project Te 250 / 1-1

Applying FIB implantation the ion current density (or the ion flux) on the target may be varied by six orders of magnitude by varying the beam movement velocity. So a quasi-stationary beam can have a density in the focus of about 10 A/cm² whereas a fast scanning beam (pixel dwell time < 1µs) only reach a density in the order of µA/cm². In collaboration with the theory group of our Institute the defect formation and dynamic annealing as a function of the implantation temperature were studied on Si, Ge as well as on SiC.

All publications

Recent publications

2021

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2019

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