METHOD AND DEVICE FOR OPERATING A LIQUID METAL-ION SOURCE OR LIQUID METAL ELECTRON SOURCE AS WELL AS A LIQUID METAL-ION SOURCE OR LIQUID METAL ELECTRON SOURCE

Abstract

The invention relates to a liquid metal-ion beam system (1) or liquid metal electron beam system, comprising: a conductive emitter electrode (2), a conductive extractor electrode (3) opposite to the emitter electrode (2), a liquid metal reservoir (4) which is fluidically connected to the emitter electrode (2) for transporting liquid metal to the emitter electrode (2), a control unit (5) which is configured to apply a periodically varying operating voltage between emitter electrode (2) and extractor electrode (3).

Claims

1-11. (canceled)

12. A liquid metal-ion beam system or liquid metal electron beam system comprising: a conductive emitter electrode, a conductive extractor electrode opposite to the emitter electrode, a liquid metal reservoir which is fluidically connected to the emitter electrode for transporting liquid metal to the emitter electrode, and a control unit which is configured to apply a periodically varying operating voltage between the emitter electrode and the extractor electrode.

13. The liquid metal-ion beam system or liquid metal electron beam system according to claim 12, wherein an operating voltage threshold is predetermined which defines a voltage amount above which liquid metal, which is not ionized or is only slightly ionized at the emitter electrode, is extracted by emitted ions or electrons accelerated in the direction of the extractor electrode, wherein the control unit is configured to vary the periodically varying operating voltage between a below-threshold voltage, which is below the operating voltage threshold in terms of amount, and an above-threshold voltage, which is above the operating voltage threshold in terms of amount.

14. The liquid metal-ion beam system or liquid metal electron beam system according to claim 12, wherein the operating voltage is generated by a constant high voltage source for providing a constant high voltage and a pulse voltage source for providing a periodically varying pulse voltage, connected in series with the arrangement of the emitter electrode and the extractor electrode, wherein the sum of the voltages of the constant high voltage source and the pulse voltage source yields the periodically varying operating voltage.

15. The liquid metal-ion beam system or liquid metal electron beam system according to claim 14, wherein the pulse voltage source is connected to a reference potential, in particular a ground potential.

16. The liquid metal-ion beam system or liquid metal electron beam system according to claim 12, wherein the emitter electrode is configured to be a tip electrode or a capillary electrode.

17. The liquid metal-ion beam system or liquid metal electron beam system according to claim 12, wherein the control unit is configured to adjust the periodically varying operating voltage by a regulated operation, wherein the operating voltage is reduced in terms of amount below the operating voltage threshold, when the current flow through the arrangement of emitter electrode and extractor electrode exceeds in terms of amount a current intensity above a predetermined current threshold and/or when a current gradient rises in terms of amount above a predetermined gradient threshold, and wherein the operating voltage is raised above the operating voltage threshold, when the current flow through the arrangement of emitter electrode and extractor electrode falls below a current intensity above a predetermined current threshold in terms of amount and/or a current gradient falls below a predetermined gradient threshold in terms of amount.

18. The liquid metal-ion beam system according to claim 12, wherein the pulse frequency of the operating voltage is more than 100 kHz and less than 100 MHz.

19. The liquid metal electron beam system according to claim 12, wherein the pulse frequency of the operating voltage is more than 1 MHz and less than 1 GHz.

20. A method for operating a liquid metal-ion beam system or liquid metal electron beam system, comprising: a conductive emitter electrode, a conductive extractor electrode opposite to the emitter electrode, a liquid metal reservoir which is fluidically connected to the emitter electrode for transporting liquid metal to the emitter electrode, wherein a periodically varying operating voltage is applied between the emitter electrode and the extractor electrode.

21. A system comprising a liquid metal-ion beam system and a liquid metal electron beam system, the system comprising: a conductive emitter electrode, a conductive extractor electrode opposite to the emitter electrode, a liquid metal reservoir which is fluidically connected to the emitter electrode for transporting liquid metal to the emitter electrode, and a control unit which is configured to apply a periodically varying operating voltage between the emitter electrode and the extractor electrode, wherein the control unit applies a positive operating voltage between the emitter electrode and the extractor electrode to emit ions from the emitter electrode, wherein the control unit applies a negative operating voltage between the emitter electrode and the extractor electrode to emit electrons from the emitter electrode, and wherein the operating voltages relate to a same reference potential.

22. The system according to claim 21, wherein the liquid metal-ion beam system and the liquid metal electron beam system are operated with identical pulse frequencies, in particular phase-shifted, in order to reduce an alternating load of an electrical energy storage device.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Embodiments are explained in more detail below with reference to the accompanying drawings, wherein:

[0041] FIG. 1 shows a schematic representation of a liquid metal-ion beam system;

[0042] FIGS. 2a to 2c show different variants of the generation of the pulsed operating voltage for the liquid metal-ion source or liquid metal electron source.

DESCRIPTION OF EMBODIMENTS

[0043] FIG. 1 shows a schematic representation of a liquid metal-ion beam system 1 having a conductive emitter electrode 2, which may be in the form of a conductive tip electrode (as shown) or which alternatively may be in the form of a capillary electrode, and a conductive extractor electrode 3 opposite the emitter electrode 2 for accelerating charge carriers. The extractor 3 may be configured to be a pinhole.

[0044] A liquid metal reservoir 4 is arranged near the emitter electrode 2, which reservoir is fluidically connected to the area of the emitter electrode 2 for transporting liquid metal to the emitter electrode 2. A very pointed liquid metal cone is formed at the tip of the emitter electrode 2 from which, upon operation, the metal-ions are extracted and accelerated toward the extractor electrode 3. The material of metal-ions thus extracted is replaced from the liquid metal reservoir 4.

[0045] A control unit 5 is provided which applies a positive operating voltage V.sub.E between emitter electrode 2 and extractor electrode 3. The operating voltage V.sub.E is of an amount which causes ions Ito be extracted at the emitter electrode 2 and accelerated in the direction of the extractor electrode 3. This causes a current to flow in the μA range.

[0046] If the current rises above a threshold current, in addition to the ion current, lightly charged microdroplets T may be extracted and discharged from the tip of the emitter electrode 2, thus significantly increasing the consumption of liquid metal without these droplets T contributing significantly to the ion beam.

[0047] The configuration of FIG. 1 may also be operated as a liquid metal electron beam system if the control unit 5 applies a negative operating voltage V.sub.E between emitter electrode 2 and extractor electrode 3. The amount of the operating voltage V.sub.E is such that electrons are emitted at the emitter electrode 2.

[0048] When operating as an electron source, a liquid metal cone is formed at the tip of the electrode, which leads directly to the generation of the electron current. The electrons are always emitted in a pulsed manner, since the electrons ionize neutral atoms in the vicinity, which are attracted with their positive charge by the negatively charged tip of the emitter electrode. This bombardment leads to a intense local heating of the tip and to an intensifying emission of electrons as a result. This avalanche effect leads to a very high electron current, which causes the liquid metal cone at the tip of the emitter electrode 2 to evaporate. This process leads to a consumption of liquid metal and to an intense abrasion of the emitter electrode 2.

[0049] In order to avoid these effects, it is hence envisaged to operate the liquid metal-ion beam system or the liquid metal electron beam system with a pulsed operating voltage V.sub.E. In this case, the operating voltage V.sub.E applied between the emitter electrode 2 and the extractor electrode 3 is varied periodically between a below-threshold voltage, which is below an operating voltage threshold V.sub.thr in terms of amount, and an above-threshold voltage, which is above an operating voltage threshold V.sub.thr in terms of amount. The operating voltage threshold corresponds to a voltage threshold above which droplet generation or liquid metal extraction occurs.

[0050] The pulse frequency of the operating voltage V.sub.E is selected such that the above-mentioned effects are avoided, i.e. droplet generation when operating as an ion source and evaporation when operating as an electron source. The pulse frequency may be fixed, and may in particular be more than 100 kHz and less than 100 MHz for liquid metal-ion sources, and may be more than 1 MHz and less than 1 GHz for liquid metal electron sources.

[0051] The pulse shape may be rectangular, sinusoidal, sawtooth or may have another shape.

[0052] In principle, several variants are conceivable for generating the periodically varying operating voltage V.sub.E.

[0053] As shown in FIG. 2a, the extractor electrode 3 may be connected to a reference or ground potential B. The emitter electrode 2 is connected to an operating voltage source 6, which is periodically varied and which directly generates the operating voltage V.sub.E. Voltage pulses are illustrated in the voltage-time diagram shown. The complexity of such an arrangement is relatively low, since only the operating voltage source 6 is necessary. However, this operating voltage source has to provide high voltage pulses with very high voltages, which voltages may only be generated in a very complex fashion. The below-threshold voltage may have a potential corresponding to the reference potential B or corresponding to a potential between the reference potential B and the operating voltage threshold V.sub.thr. Also, the emitter electrode 2 should be configured to be a tip electrode, since the time to build up a liquid metal cone depends on the geometry of the electrode and, in the case of emitter electrodes configured to be capillaries, usually requires more time than is provided by the pulse width of the operating voltage V.sub.E (duration of the application of the above-threshold voltage).

[0054] The embodiment of FIG. 2b shows a connection of the extractor electrode 3 with the reference potential (ground potential) B, wherein a constant high voltage HV is applied to the emitter electrode 2 by use of a constant high voltage source 7, the level of which is below the operating voltage threshold, below which no ion or electron current is emitted. In addition, a pulsed voltage source 8 is connected in series, which uses a pulsed voltage to raise or lower the operating voltage V.sub.E applied to the emitter electrode 2 above the operating voltage threshold V.sub.thr. Thus, the high voltage source 7 and the pulsed voltage source 8 form the operating voltage source of FIG. 2a. By applying the below-threshold voltage in the range of the operating voltage threshold V.sub.thr, in particular in a range between 70% and 90% of the operating voltage threshold, the build-up of a liquid metal cone is enabled, but no emission of ions or electrons is caused. By adding the pulse voltage source 8 in a pulsed manner, which pulse voltage source only has to provide a lower voltage, the liquid metal-ion source or liquid metal electron source may now be operated with reduced liquid metal consumption.

[0055] In the embodiment shown in FIG. 2c, the extractor electrode 3 may be operated at a high constant potential HP below the operating voltage threshold V.sub.thr in the reverse polarity with respect to the emitter electrode 2. By use of a pulse voltage source 8, a periodic pulse voltage is generated and applied to the emitter electrode 2. In contrast to the previous embodiment, this requires no high-voltage isolation, and it also requires only a relatively small voltage swing to raise the total potential between emitter electrode 2 and extractor electrode 3 above the operating voltage threshold V.sub.thr.

[0056] The operating voltage source 6 or the pulse voltage source 8 are configured to raise the total voltage between the emitter electrode 2 and the extractor electrode 3 from the below-threshold voltage above the operating voltage threshold V.sub.thr in a pulsed operation to an above-threshold voltage and to lower it below. The adjusting frequency may be fixed or adjusted by a regulated operation. At the fixed frequency, a frequency between 100 kHz and 100 MHz should be selected for a liquid metal-ion source, and a frequency in the range between 1 MHz and 1 GHz should be selected for a liquid metal electron source.

[0057] Upon regulated operation, the lowering below the operating voltage threshold V.sub.thr may be performed when the ion or electron current exceeds in terms of amount a current above a predetermined current threshold or when the current gradient rises above a predetermined gradient threshold. After lowering the operating voltage V.sub.E to the below-threshold voltage, the above-threshold voltage may be reapplied or the operating voltage V.sub.E may be increased again after a dead time to restart the cycle.

LIST OF REFERENCE SIGNS

[0058] 1 Liquid metal-ion beam system

[0059] 2 Emitter electrode

[0060] 3 Extractor electrode

[0061] 4 Liquid metal reservoir

[0062] 5 Control unit

[0063] 6 Operating voltage source

[0064] 7 Constant high voltage source

[0065] 8 Pulse voltage source

[0066] B Reference potential

[0067] HP High voltage potential

[0068] V.sub.thr Operating voltage threshold

[0069] V.sub.E Operating voltage