Liquid Metal Alloy Ion Sources Research Articles

GaBi alloy liquid metal ion source for microelectronics research

A GaBi alloy liquid metal ion source has been studied. From an analysis of the source mass spectra as a function of emission current, a mechanism is suggested for the production of single- and double-charged ions. There is good agreement with the results of Swanson's investigations of a pure Bi source.

Investigation of FIB assisted CoSi 2 nanowire growth

The ion beam synthesis process of CoSi 2 by writing stoichiometric ion implantation and subsequent annealing has been studied. For this a Focused Ion Beam (FIB), equipped with a Co 36Nd 64 alloy liquid metal ion source, was applied. Si(1 0 0) and (1 1 1) wafers were implanted with 60 keV Co 2+ ions in the dose range of 2 × 10 16–2 × 10 17 cm −2. The implantation parameters, like pixel dwell time, relaxation time, dose rate as well as the pixel overlapping factor were investigated. During subsequent annealing CoSi 2 nanostructures with dimensions down to 10 nm have been achieved. To investigate the silicide formation more in detail the annealing process was done in situ in a transmission electron microscope (TEM) on a pre-dimpled and FIB implanted samples of a Si(1 1 1). The formation of the cobalt silicide nano-crystals was monitored by plane-view TEM imaging during a 30 min heat treatment at 600 °C in vacuum.

CoSi 2 nanostructures by writing FIB ion beam synthesis

A mass separated focused ion beam (FIB) is a very useful tool to fabricate nanostructures by writing implantation within an ion beam synthesis process. In these investigations the IMSA-OrsayPhysics FIB, equipped with a Co 36Nd 64 alloy liquid metal ion source, was applied. Si(100) and (111) wafers were implanted with 60 keV Co ++ ions in the dose range of 2 · 10 16 to 2 · 10 17 cm − 2 . Implantation parameters were investigated, like pixel dwell time, relaxation time (time between two cycles), dose rate as well as the pixel overlapping factor. The subsequent annealing was done in a two step process, namely 600 °C for 60 min and 1000 °C for 30 min in a N 2 ambient. The results obtained by SEM investigations in terms of continuous nanowire structures following the <110> direction and interrupted CoSi 2 pattern in the <100> direction show a clear dependence on the time scale as well as the scanning mode of the irradiation. Structure sizes as small as 10 nm are demonstrated. The formation of CoSi 2 nanostructures is explained by precipitation, Ostwald ripening and coarsening leading to a shrinking of the initial implanted profile.

On the temperature dependence of the mass spectra of AuGe and AuGeSi liquid metal alloy ion sources

This reports on an extensive study of the characteristics of AuGe and AuGeSi liquid metal alloy ion sources as a model system for new semiconductor compatible FIB sources. Such characteristics include ion beam mass spectra. A careful investigation has been undertaken where the emitter temperature is the main variable parameter. This work concerns the temperature dependence of the mass spectra of two needle-type liquid metal alloy ion sources (LMAISs), namely Au77Ge14Si9 (Tm = 364°C) and Au73Ge27 (Tm = 365°C). The sources are important for producing SiGe implanted layers. The experimental results, in conjunction with existing theories, strongly points towards the co-existence of two mechanisms for the emission of doubly-charged monomer ions: direct filed-evaporation and post-ionisation.

Alloy liquid metal ion sources and their application in mass separated focused ion beams

For special purposes like writing ion implantation or ion mixing in the micrometer- or sub-micrometer range different ion species are needed. Therefore alloy liquid metal ion sources (LMISs) are used. The energy distribution of the ions from an alloy LMIS is one of the determining factors for the performance of a FIB column. Different source materials like Au 73Ge 27, Au 82Si 18, Au 77Ge 14Si 9, Co 36Nd 64, Er 69Ni 31, and Er 70Fe 22Ni 5Cr 3 were investigated with respect to the energy spread of the different ion species as a function of emission current, ion mass and emitter temperature. The alloy LMISs discussed above have been used in the Rossendorf FIB system IMSA especially for writing implantation to fabricate sub-micrometer pattern without any lithographic steps. A Co-FIB was applied for the ion beam synthesis of CoSi 2 micro-structures. Additionally, the possibility of varying the current density with the FIB by changing the pixel dwell time was used for radiation damage investigations in Si and SiC at elevated implantation temperatures. Furthermore, a broad spectrum of ions was employed to study the sputtering process depending on temperature, angle of incidence and ion mass on a couple of target materials using the volume-loss method. Especially this technique was used for the fabrication of various kinds of micro-tools.

Study of a liquid metal field ion emitter for the production of Si ions

The study of AuSi liquid metal alloy ion sources (LMAIs) for the production of Si ions is not new. However, the present work encompasses in a concise form almost all fundamental aspects of source behaviour, in particular of a Au82Si18 source. A key finding, manifested in the behaviour of the ion extraction voltage with temperature, is the abnormal behaviour of the surface tension coefficient of the alloy with temperature. An important deduction, however, concerns the mechanisms responsible for the creation of doubly charged ions: reasons of self-consistency suggest that while Si++ is directly field-evaporated, Au++ must form by the post-ionization of Au+.

The temperature dependence of the energy distribution of the beam emitted by an Au82Si18 liquid metal field-ion emitter

The energy distribution of the monomer ion species is studied as a function of emitter temperature for an Au82Si18 eutectic liquid metal alloy ion source (LMAIS). Secondary peaks, or shoulders, in the distribution of some of the species are explained in terms of Hornsey's model, which involves the fast movement of the jet in conjunction with a space–charge energy broadening mechanism within the beam. Moreover, the results confirm an earlier conclusion that whereas Au+, Si+ and Si++ are emitted by direct field-evaporation from the liquid surface, Au++ forms by the post ionization of Au+.

The temperature dependence of the energy distribution of the beam emitted by an Au 82Si 18 liquid metal field-ion emitter

The energy distribution of the monomer ion species is studied as a function of emitter temperature for an Au 82Si 18 eutectic liquid metal alloy ion source (LMAIS). Secondary peaks, or shoulders, in the distribution of some of the species are explained in terms of Hornsey's model, which involves the fast movement of the jet in conjunction with a space–charge energy broadening mechanism within the beam. Moreover, the results confirm an earlier conclusion that whereas Au +, Si + and Si ++ are emitted by direct field-evaporation from the liquid surface, Au ++ forms by the post ionization of Au +.

Study of a liquid metal field ion emitter for the production of Si ions

The study of AuSi liquid metal alloy ion sources (LMAIs) for the production of Si ions is not new. However, the present work encompasses in a concise form almost all fundamental aspects of source behaviour, in particular of a Au 82Si 18 source. A key finding, manifested in the behaviour of the ion extraction voltage with temperature, is the abnormal behaviour of the surface tension coefficient of the alloy with temperature. An important deduction, however, concerns the mechanisms responsible for the creation of doubly charged ions: reasons of self-consistency suggest that while Si ++ is directly field-evaporated, Au ++ must form by the post-ionization of Au +.

A GaMn liquid metal ion source for spintronic device fabrication

A new alloy liquid metal ion source (LMIS) has been developed which may be used for the focused ion beam patterning of magnetic elements into GaAs wafers. The GaMn alloy source had a composition of 90% Ga and 10% Mn by atomic weight. The source displayed good operating characteristics with stable and low emission currents. Typical turn-on currents were about 10 μA at an extraction voltage of −6 kV. The maximum current attained for the Mn 2+ beam was 0.8 nA (current density ∼0.1 A/cm 2), which would allow the real-time patterning of approximately (100 μm) 2 of Ga 0.95Mn 0.05As during the wafer growth. Beam resolution was 5 μm, and with the excellent mass separation between the different ion species, and reasonably large beam currents, it demonstrates the suitability of the source for high-resolution device patterning.

Characteristics of erbium-ions-producing liquid metal ions sources

Focused ion beams (FIBs) are of importance as direct write tools in the microelectronics industry, and beams containing Er ions are of importance for optoelectronics applications. Microstructures doped with Er are attractive because of their intra-4f transition of Er3+ at a wavelength of 1.54μm, which corresponds to the minimum of attenuation of optical wave-guides. We describe the electric characteristics and mass spectra of two liquid metal alloy ion sources; namely Er70Fe22Cr3Ni5 and Er69Ni31. For the first time in the literature the energy spread of triply charged ions (Er 3+) is reported.

Maskless Mn implantation in GaAs using focused Mn ion beam

Fifteen kiloelectronvolts focused Mn ion beam was implanted on molecular beam epitaxy-grown Si-δ-doped GaAs which was mesa-etched to form Hall-bar geometry and annealed at 840 °C for 10 s in hydrogen and argon mixed gas ambient. Au–Si–Mn liquid metal alloy ion source was fabricated to perform both Mn and Si ion implantation. From the Hall resistance measurement at 77 K, non-linear behavior and hysteresis were observed in the Hall resistance in the Mn implanted region. The present result indicates that a ferromagnetic layer is formed in GaAs by the Mn ion implantation.

Fundamental properties of erbium-ions-producing liquid metal alloy ion sources

We describe the electric characteristics and mass spectra of two liquid metal alloy ion sources; namely Er 70Fe 22Cr 3Ni 5 and Er 69Ni 31. Erbium ions are of great interest for optoelectronic applications. For the first time in the literature the energy spread of triply charged ions (Er 3+) is reported.

On the temperature dependence of the electric characteristics and mass spectra of liquid metal alloy ion sources

This paper reports on an extensive study of the characteristics of AuGeSi and CoNd liquid metal alloy ion sources (Focused Ion Beams From Liquid Metal Ion Sources, Research Studies Press, Taunton, Somerset, UK, 1991). Such characteristics include current–voltage curves and ion beam mass spectra. A careful investigation has been undertaken where the emitter temperature is the main variable experimental parameter. Theoretical models, or theoretical attempts in certain cases, tend to support the experimental results. The experimental results, in conjunction with existing theories, suggest that simply for reasons of self-consistency two mechanisms must be operative for the production of doubly-charged ions from the AuGeSi source: direct field-evaporation and post-ionisation.

A study of liquid metal alloy ion sources for the production of ions of interest in the microelectronics industry

This is a comprehensive study of the characteristics of an AuGeSi and CoNd liquid metal alloy ion sources [Focused ion beams from liquid metal ion sources, 1991]. Such characteristics include current–voltage curves and ion beam mass-spectra. A careful investigation has been undertaken where the temperature is one of the main variable experimental parameters. Theoretical models support the experimental results.

Effect of temperature on the emission characteristics of liquid metal alloy ion sources

In spite of the fact that a great deal of research has been carried out on liquid metal ion sources, surprisingly few results exist on the temperature dependence of their emission characteristics. In this article we study two liquid metal alloy ion sources (LMAISs), namely Co36Nd64 and Au77Ge14Si9. While the results of the former source were as expected, the latter displayed an entirely different dependence of its emission characteristics on temperature. The unusual results of the Au77Ge14Si9 LMAIS are explained in terms of the abnormal behavior of the surface tension of the alloy with temperature.

Temperature dependence of emission spectra of liquid metal alloy ion sources

The variation with temperature of the ion mass spectra of a liquid metal alloy ion source (LMAIS) (Au77Ge14Si9) is reported. Analysis of our results suggests the co-existence of two different ion creation mechanisms for the doubly charged atomic ions. Whereas some doubly charged ions are post-ionised from the singly charged state, others are directly field-evaporated. The temperature dependence of the abundance of the ionic clusters emitted by the source has also been investigated.

Temperature dependence of the electric characteristics of liquid metal alloy ion sources

In spite of the fact that a great deal of research has been carried out on liquid metal ion sources, surprisingly few results exist on the temperature dependence of their electric characteristics. In this article we study two liquid metal alloy ion sources (LMAISs), namely Co36Nd64 and Au77Ge14Si9. While the results of the former alloy were as expected, the latter displayed an entirely different dependence of its electric characteristics on temperature. The unusual results of the Au77Ge14Si9 LMAIS are explained in terms of the abnormal behaviour of its surface tension coefficient with temperature.

Investigation and optimization of the emission parameters of alloy liquid metal ion sources

Liquid metal ion sources (LMIS) are one of the key elements in focused ion beam (FIB) technology. For special tasks, alloy LMIS are needed which have to be operated in the most cases at elevated temperatures. For the adjustment of an optimal beam performance in a FIB system, the source parameters, temperature of the ion emitter and the energy spread of the different ion species used are of fundamental importance. Emitters wetted with Au 73Ge 27, Au 77Ge 14Si 9 and Co 36Nd 64 alloys were investigated with respect to the influence of the source temperature on the emission current–extraction voltage characteristics, the mass distribution, as well as the energy spread of the different emitted ions using an equipment containing an ExB mass filter and a retarding field energy analyser. The energy spread significantly determines the available FIB spot size and depends also on the emission current, the charge state, and the mass of ions or clusters. The axial angular intensity and the resulting target current of the FIB were measured as a function of the source parameters. Two operating regimes were found. Either one works in a high stable target current mode with lower resolution (emission current ∼10 μA), or in the high resolution, high chromatic angular intensity mode (emission current a few μA), with a reduced target current and less current stability, both at source temperatures some 10 K above the melting point.

Electron emission characteristics of solidified gold alloy liquid metal ion sources

Solidified liquid metal ion sources (LMISs) operating with Au alloy wetted hair-pin emitters can be used as high-intensity electron point sources for application in the field of ultrahigh vacuum techniques. A nanotip emitter on a solidified LMIS emitter can be formed by quenching during ion emission mode. I–V characteristics and the performance of the electron emitting LMIS are presented.