EP1709844A2

EP1709844A2 - Methods and devices for the production of solid filaments in a vacuum chamber

Info

Publication number: EP1709844A2
Application number: EP05700929A
Authority: EP
Inventors: Manfred Faubel; Ales Charvat; Jürgen TROE; Bernd Abel; Eugene Lugovoi
Original assignee: Max Planck Gesellschaft zur Foerderung der Wissenschaften eV; Georg August Universitaet Goettingen
Current assignee: Max Planck Gesellschaft zur Foerderung der Wissenschaften eV; Georg August Universitaet Goettingen
Priority date: 2004-01-26
Filing date: 2005-01-14
Publication date: 2006-10-11
Also published as: US20080296799A1; WO2005072027A2; WO2005072027A3; DE102004003854A1; JP2007519193A

Abstract

Disclosed are methods for producing a solid filament (1) from a liquid (2) in a vacuum chamber (70), comprising the following steps: a gas is liquefied in a heat exchanger apparatus (20) to produce the liquid (2); and the liquid (2) is delivered into the vacuum chamber (70) via a supply duct (27) and through a nozzle (30). Liquefying of the gas in the heat exchanger apparatus (20) encompasses adjusting a p-T operating point of the liquid (2) at which the liquid (2) is transformed into the solid aggregate state and forms a collimated and stable jet after being discharged from the nozzle (30) into the vacuum chamber (70). Also disclosed are nozzle arrangements for producing solid filaments (1) in a vacuum.

Description

Methods and devices for producing solid filaments in a vacuum chamber

The invention relates to methods for producing solid filaments by supplying a liquid, in particular a liquefied gas, into a vacuum chamber with the features of the preamble of claim 1. The invention also relates to nozzle arrangements which are set up to carry out such methods, and to a radiation source with such a method Nozzle arrangement and a vacuum chamber.

X-ray radiation sources are known in which a liquid target material is injected with a nozzle arrangement into a vacuum chamber and there is brought into a plasma state by laser radiation in which material-specific X-ray fluorescence radiation is emitted. It is desirable that the target material fed into the vacuum chamber forms a liquid jet (jet) or a solid filament (frozen liquid jet) with the highest possible spatial stability and the lowest possible divergence. These interrelated requirements serve to increase the stability and reproducibility of the X-rays generated with each laser irradiation. Furthermore, there is an interest in carrying out the laser irradiation with the greatest possible distance from the nozzle arrangement, because the plasma state of the target material also emits ions and other fast particles which can lead to erosion and damage to the nozzle.

The requirements mentioned are only unsatisfactorily met with conventional X-ray sources. Liquid jet len have a certain decay length within which fluctuations in the liquid build up until the jet breaks up into drops. The decay length depends on the surface tension of the liquid and its viscosity. Until now, laser radiation had to be at a distance from the nozzle that is less than the decay length.

US 2002/0044629 AI describes a nozzle arrangement for supplying liquefied xenon into a vacuum chamber. The nozzle arrangement has a nozzle heater with which undesired deposits of the target material on the nozzle which adversely affect the flow shape are to be avoided. This technique improves the reproducibility of the flow formation. However, it is disadvantageous that the target material itself is not influenced by the nozzle heating, so that instabilities or fluctuations in the flowing target material cannot be reduced. The inflowing material does not form a stable jet, but rather a flow section that disintegrates into drops or a spray after a short distance. For example, when the liquid material flowing into the vacuum chamber freezes, a flow section of solid material is formed, which disintegrates after a short time and forms a spray. The technique described in US 2002/0044629 AI therefore has a limited effectiveness, the focus of the laser radiation must be localized close to the nozzle.

The instabilities mentioned in the flowing target material occur in particular in the case of X-ray radiation sources, the liquid target material of which is formed by the condensation of a gas. The condensation takes place in a heat exchanger, such as. B. is described in EP 1 182 912 AI or WO 02/085080 AI. Conventionally used heat exchangers have zen typically a condensation vessel, the walls of which are filled with a cooling medium, such as e.g. B. cooled liquid nitrogen. Both in a connected nitrogen reservoir and during liquefaction in the condensation vessel, bubbles form and delay in boiling occurs. This will

Vibrations that are transmitted to the jet emanating or even interruptions of the jet. Such interruptions are, however, for the application z. B. from X-ray sources in practice unacceptable, where an uninterrupted runtime of hours or days is required.

If the heat exchanger works with an evaporative cooler, the compressor of which is mechanically connected directly to the nozzle (see, for example, WO 02/085080 AI), instabilities in the flowing target material can also be caused by vibrations emanating from the compressor.

The problems mentioned occur not only in conventional X-ray sources, but also in other applications of thin liquid jets as a target for physico-chemical investigations in high vacuum, such as. B. in the generation of EUV radiation or in the coupling of technical or medical sample liquids to mass spectrometers. In these cases, too, there is an interest in compact, reliable and maintenance-friendly jet injection systems.

The object of the invention is to provide improved methods for producing solid filaments in a vacuum chamber, with which the disadvantages of the conventional techniques are overcome. The task consists in particular in the provision of processes with which solid filaments from liquefied gases with increased temporal and spatial Stability can be generated. The filaments should also be distinguished by an uninterrupted nature and increased directional stability (or: reduced divergence). Another aspect of the object of the invention is that the method should be compatible with conventional vacuum devices, in particular with radiation sources or mass spectrometers available per se, and should have an expanded area of application with regard to the gases that can be fed into the vacuum. The object of the invention is also to provide improved nozzle arrangements with which the disadvantages of the conventional arrangements are overcome and which are particularly suitable for the temporally and spatially stable injection of target material and for the long-term production of long filaments, in particular of liquefied gases under high vacuum. The nozzle arrangements according to the invention should be particularly suitable for the injection of different target materials or should be easily adaptable for the supply of different target materials.

These objects are achieved with methods and nozzle arrangements with the features according to claims 1 or 17. Advantageous embodiments of the invention result from the dependent claims.

In terms of the process, the invention is based on the general technical teaching of first liquefying a gas to produce solid filaments in a vacuum and then injecting the liquefied gas into the vacuum via a nozzle, the liquefaction of the gas being associated with an adjustment of state variables of the liquid , which are selected so that the liquid is transferred to the solid state after exiting the nozzle by relaxation in a vacuum and the associated cooling. The state variables include the pressure and the temperature of the liquid. she determine a pT operating point in the liquid area of the phase diagram, which is selected in the immediate vicinity of the liquid-solid phase boundary. In contrast to conventional condensation liquefaction, according to the invention, a predetermined operating point of the liquid is set in a heat exchanger device, at which the liquid forms a collimated and stable jet in the solid state of aggregation after emerging from the nozzle. The jet is a straight, thread-like structure in the solid state (filament), which continues in a vacuum without decay. The free beam is stable in time and space.

Advantageously, the length of the initially liquid jet in vacuum (or the duration of the liquid state) can be set and minimized or even reduced to almost zero by setting the operating point. As a result, the cross-sectional shape of the liquid jet, which is predetermined by the shape of the nozzle, is directly impressed on the freezing liquid which forms the solid filament. Non-reproducible jet broadening, which occurs with conventional liquid injections in a vacuum, is avoided.

The transition to the fixed physical state is advantageously carried out at high speed by setting the operating point. It can be observed as a sharp boundary at a distance from the nozzle, which is also known as the freezing length. Irregularities in the solid state due to fluctuations that may still be in the liquid state are suppressed. The transition to the solid state of matter preferably takes place immediately after the liquid exits the nozzle. The freeze length is shorter than the decay length of the liquids. In general, the setting of the predetermined pT operating point of the liquid comprises the setting of pressure and / or temperature values. Basically, it is possible to set the desired working point at a certain temperature in the heat exchanger device via the pressure of the gas flowing in via the supply line or correspondingly via the flow rate of the liquid through the heat exchanger device. According to a preferred embodiment of the invention, however, the setting of the predetermined pT operating point comprises a temperature setting. The setting of an operating point temperature T ₀ in the heat exchanger device such that the liquid immediately changes to the solid state after exiting the nozzle can take place in particular as a function of the flow velocity in the heat exchange device. Advantageously, if the liquid-solid phase boundary in the phase diagram is essentially independent of pressure under conditions of practical interest, as is the case, for example, with xenon, the temperature can be set independently of the flow rate or the pressure of the liquid.

If a pressure setting is additionally provided after the temperature setting, the stability and collimation of the beam can advantageously be improved further. The pressure setting enables a fine adjustment of the desired working point.

If the temperature and pressure conditions of the liquid are specified in the case of a specific application, the p-T operating point can be set according to a further variant of the invention by setting a desired line diameter of the supply line. It is particularly preferred to set a critical temperature of the liquid which is less than 1 degree Kelvin, in particular 0.5 degrees, for example one or a few tenths above the triple point of the liquid. Advantageously, premature freezing of the liquid in the heat exchanger device is avoided, the conditions for ice formation in the free jet being advantageously realized as soon as the liquid is released after exiting the nozzle.

According to a further preferred embodiment of the invention, the temperature of the liquid is carried out while it is flowing through a supply line. In contrast to the use of condensation vessels in conventional heat exchangers, the liquefaction and temperature setting of the liquid takes place in the supply line. A slow, gentle condensation of the inflowing gas is advantageously achieved, so that undesired vibrations caused by a delay in boiling can be avoided. The temperature setting for the selection of the desired pT operating point can be made taking into account a temperature gradient that may occur up to the nozzle. For example, slight heating can occur between the heat exchanger device and the nozzle, which is compensated for as far as possible when the temperature is set in the heat exchanger device. Since this is only possible to a limited extent, particularly when cooling close to the triple point of the liquid, the distance between the heat exchanger device extending along the supply line and the nozzle is kept as small as possible. According to a preferred embodiment of the invention, the heat exchanger device extends along the supply line to the nozzle, which can be integrated in the heat exchanger device or can be arranged directly adjacent to it. Accordingly, the in the temperature of the liquid set in the heat exchanger device is substantially equal to the temperature of the liquid in the nozzle, so that the pT operating point of the liquid can advantageously be set with increased accuracy.

The liquefaction along the supply line can be realized with various types of heat exchanger devices, such as. B. with heat exchanger devices, in which cooling takes place by the supply of a cooling medium or on the basis of the thermoelectric effect. The temperature setting according to the invention is particularly preferably carried out using a liquid cooling medium. When using a gaseous cooling medium, locally undesirable temperature gradients can occur, which cause local freezing or local bubble formation. The use of a liquid cooling medium, on the other hand, enables a more homogeneous temperature setting in the heat exchanger device. Unwanted local temperature gradients are excluded. This enables the liquid to be cooled as close as possible to the desired working point, in particular to the triple point.

If the temperature of the cooling medium in the heat exchanger device is set with a thermostat, there may be further advantages for the accuracy of the setting of the pT operating point. The use of a thermostat means that the temperature of the cooling medium can be fixed. In contrast to conventional liquefaction devices, in which cooling is carried out on the condensation vessel and counter heating is carried out to avoid freezing of the liquid, so that temporal and spatial temperature fluctuations occur, thermostating is provided according to the invention, under the effect of which desired working point can be set with high accuracy and temporal stability.

If through the thermostat operation, e.g. B. mechanical vibrations can be caused by compressors, there is preferably a vibration decoupling between the thermostat and the nozzle arrangement. The thermostat is preferably operated spatially separated from a vacuum chamber with the nozzle arrangement and connected to the heat exchanger device via coolant lines, in the course of which undesired mechanical vibrations can be damped.

Special advantages for the precise and stable setting of the p-T operating point of the liquid can result if the temperature of the cooling medium is set with at least one of the following control loops. According to a first variant, a temperature measurement can be carried out in the heat exchanger device with at least one temperature sensor. The measured temperature can be compared with specified reference values. In the event of a deviation, the supply and / or temperature of the cooling medium can be controlled. According to a second variant, optical detection of the free jet of the tempered liquid emerging into the vacuum and in particular the freezing length of the jet can be provided. In this case, the supply and / or temperature of the cooling medium can be regulated depending on the result of the optical measurement of the spatial phase boundary between the liquid jet and the solid filament which is formed in a vacuum.

The pT operating point of the liquid is preferably set such that the freezing length of the liquid is less than 10 mm, particularly preferably less than 5 mm. Generally, the nozzle through which the liquid exits into the vacuum can be formed by the end of the supply line. According to a particularly preferred embodiment of the invention, however, a separate nozzle (nozzle head) is provided, in which the liquid is subjected to a jet formation. The jet formation comprises the formation (or stabilization) of a certain flow profile in the jet and / or the setting of a certain cross-sectional profile of the liquid jet. In particular, a tapering of the cross-sectional profile is provided. For a vortex-free liquid outlet, the flow cross section is narrowed in the flow direction in the nozzle head, in which the liquid runs through an inwardly curved inner contour of the nozzle head, which is convex towards the center.

A particular advantage of the method according to the invention is that it does not target a specific target material, e.g. B. is limited for radiation sources, but can be easily adapted to a wide variety of gases and liquids. For example, according to the invention, filaments can be produced from nitrogen, hydrogen, water or organic liquids. However, special advantages with stable nozzle operation can be seen in the injection of liquefied noble gases, such as. B. helium, argon, krypton or xenon. The invention is particularly preferably implemented with liquefied xenon, since this has a high effectiveness in plasma-based radiation generation.

Device-related, the above-mentioned object is achieved by the provision of a nozzle arrangement, in particular for the production of solid filaments in vacuum, with a heat exchanger device for gas liquefaction and a feed line with a nozzle, the heat exchanger device providing the above-mentioned pT operating point of the liquefied gas is adjustable. The use of the heat exchanger device for setting a predetermined pT operating point of the liquid has the advantage that the nozzle arrangement can be constructed compactly and with the vacuum chambers which are provided for typical applications of the invention, such as, for. B. vacuum chambers of radiation sources or mass spectrometers, is compatible. The heat exchanger device forms an adjusting device with which at least one state variable of the flowing liquid can be controlled in a predetermined manner.

If the heat exchanger device according to a preferred embodiment of the nozzle arrangement according to the invention extends along the supply line of the gas, the above results. Advantages for a particularly gentle and vibration-free liquefaction. It is particularly preferred to provide a heat exchanger device in which the nozzle head is integrated or which extends as far as the nozzle head, since in this case the operating point of the liquid emerging from the nozzle head can be set with particular accuracy. There are further advantages for homogeneous, uninterrupted liquefaction in the supply line.

If the supply line is wound, for example spirally through the heat exchanger device with a cooling medium, this can be advantageous for a particularly compact structure of the nozzle arrangement. Alternatively, the feed line can have a straight shape.

The heat exchanger device of the nozzle arrangement according to the invention is preferably a countercurrent cooler, at the downstream end of which a cooling medium is supplied and at the upstream end of which the cooling medium is discharged again. The countercurrent principle means that shaped temperature setting in the heat exchanger device reached.

The heat exchanger device of the nozzle arrangement according to the invention preferably comprises a cylindrical vessel through which the supply line runs and in which the cooling medium is arranged. For example, a tubular cooling jacket is provided, which is closed at one end pointing towards the vacuum with the nozzle and at the opposite end with a connecting plate for the passage of gas and cooling medium lines.

Advantages for increased flexibility when using the nozzle arrangement can arise if the nozzle head can be disassembled or with a variable discharge direction on the cooling jacket and / or the entire heat exchanger device can be arranged with a variable discharge direction, for example tiltable or pivotable on a vacuum chamber. In these cases, the nozzle arrangement can be easily adapted to different tasks and liquids.

Compatibility with the available vacuum technology can be improved if the cooling jacket of the heat exchanger device is equipped with a fastening device which is suitable for pressure-tight fixing to the nozzle arrangement on a vacuum flange of a vacuum chamber.

According to a particularly preferred embodiment of the invention, the heat exchanger device is connected to a thermostat. In this case, there may be advantages to setting a certain coolant temperature. Temporal and spatial temperature gradients, as they occur with conventional condensers with counter heating, are avoided. The thermostat is preferably of the heat Exchanger device arranged vibration-decoupled so that the effect of mechanical vibrations that occur during thermostat operation on the gas liquefaction is suppressed as possible. For this purpose, the thermostat is connected to the heat exchanger device via coolant lines and positioned separately from the vacuum chamber. If the cooling medium lines are thermally insulated and z. B. run vacuum-insulated through a vacuum hose, heat loss along the lines is advantageously avoided and the accuracy of the temperature setting is increased.

Further advantages of the invention can result if the nozzle arrangement is equipped with a temperature or vapor pressure sensor in the heat exchanger device and / or an optical measuring device for detecting in particular the outlet opening of the nozzle. These measuring devices simplify the provision of the above-mentioned. Control circuits to stabilize the coolant temperature.

If, according to a further modification of the nozzle arrangement, the nozzle has a convex inner contour, there can be advantages for the jet formation of the emerging liquid. The liquid flows out of the nozzle head essentially without swirls and in this stabilized state changes to the solid state immediately after entering the vacuum.

The nozzle is preferably connected to the end of the supply line via a seal with a high thermal conductivity. This reduces temperature gradients between the supply line in the heat exchanger device and the nozzle head. The seal is preferably made of an alloy of copper and beryllium or brass. In order to avoid a backflow of the liquefied gas solely under the action of capillary forces, a pore filter can be provided in the feed line.

The invention has the following further advantages. The

Nozzle arrangement forms a compact, temperature-stable high-pressure nozzle system that can work in the temperature range from 2 K to 600 K. The filaments frozen in a vacuum can be produced with a length of at least 10 cm, in particular at least 20 cm and a diameter in the range from 10 μm to 100 μm. In this way, in particular for the generation of X-ray or UV radiation, a considerably increased distance of the focus of the laser radiation on the frozen filament from the nozzle head is achieved. The erosion of the nozzle head is avoided or delayed, so that the service life of the radiation sources is extended. Furthermore, filaments with an extremely high directional stability can be produced.

Another advantage of the invention is that the nozzle arrangement can be operated with different, in particular horizontal or vertical, dispensing directions. With the nozzle arrangement according to the invention, solid filaments in particular can be injected horizontally or vertically upwards into a vacuum chamber.

By setting the pT operating point of the liquid, the solidification can be achieved along a path length in the vacuum that is less than 5 mm. For example, xenon is solidified after a path length of 1 to 2 mm. This targeted solidification immediately after the nozzle head cannot be achieved with conventional nozzles. Another advantage of the nozzle arrangement according to the invention is the small diameter of the cooling jacket of the heat exchanger device. Sufficient space can be made available around the nozzle in order to achieve the highest possible mean free path of the vaporized particles. With a high pumping rate, rapid evaporation and thus rapid cooling of the liquid can be supported. The smaller the diameter, the greater the working roughness range accessible to the respective experiment. The nozzle arrangement can easily be changed in relation to the installation length in a vacuum.

Further advantages and details of the invention will become apparent from the description of the accompanying drawings. Show it:

FIG. 1: a schematic illustration of the setting of the working point of a liquid according to the invention injected into a vacuum,

FIG. 2: a phase diagram of xenon,

FIG. 3: a schematic perspective view of a preferred embodiment of the nozzle arrangement according to the invention,

FIG. 4: a schematic representation of the attachment of a nozzle arrangement according to the invention to a vacuum chamber,

FIGS. 5 and 6: further details of the nozzle arrangement according to FIG. 3 and its connection to a thermostat, FIG. 7: an enlarged sectional view of a nozzle used according to the invention,

FIG. 8: a schematic perspective view of a further embodiment of the nozzle arrangement according to the invention,

Figure 9: Photographs illustrating essential advantages of the invention, and

Figure 10 is a schematic illustration of an X-ray source which is equipped with a nozzle arrangement according to the invention.

Embodiments of the invention are described below by way of example with reference to the production of xenon filaments in the vacuum chamber of an X-ray radiation source. However, the implementation of the invention is not limited to this application, but rather is also possible with other target materials, beam and filament dimensions, sources for other types of radiation and other technical tasks.

With reference to FIGS. 1 and 2, thermodynamic considerations for putting the invention into practice are first explained. FIG. 1 shows a schematic sectional view of the free, projecting end of a nozzle arrangement 10 according to the invention with a heat exchanger device 20 which extends along a feed line 27 and a nozzle which is formed by a nozzle head adjoining the feed line 27. To produce a solid filament 1, e.g. B. as a target material for X-ray generation, a gas is liquefied in the heat exchanger device 20 and the liquid through the nozzle head 30 in introduced the vacuum. A free liquid jet 2 (jet 2) is first formed. As it emerges from the nozzle head 30, the liquid undergoes a pressure reduction (relaxation). When exiting into the vacuum, evaporation begins from the surface of the liquid jet 2, the temperature of which drops due to the evaporative cooling. As soon as the temperature drops below the freezing point of the liquid, the transition to the solid state follows (see arrow). An essential feature of the invention is that the state variables of the liquid in the supply line 27 are set to a pT operating point such that the distance a (freezing length a, see FIG. 1) of the solidification point from the outlet end 31 of the nozzle head 30 is less than the decay length the liquid is adjusted, preferably minimized and reduced to almost zero.

To explain the setting of the pT operating point, reference is made to the xenon phase diagram shown by way of example in FIG. The phase diagram illustrates the solid (s), liquid (1) and gaseous (g) states as a function of the state variables pressure (p) and temperature (T). The curve branches in the phase diagram represent the phase boundaries, they touch at the triple point T _τ . According to the invention, the pT operating point of the liquid is set in the hatched area of the liquid state in which the transition to the solid state is achieved by a slight temperature reduction. Advantageously, the liquid-solid transition for xenon and other target materials of interest in the pressure area of interest is essentially pressure-independent (vertical profile of the s-1-

Branches above the triple point T _τ ) or with a slight pressure dependence. This makes it easier to initially provide the desired pT operating point exclusively via the temperature setting with the heat exchanger device 20. and then, if necessary, make a fine adjustment for collimation of the jet by adjusting the working pressure (pressure with which the gas is supplied in the supply line).

The operating point temperature T ₀ , which is set with the heat exchange device 20 in the liquid which flows through the supply line 27, is selected as follows with a small temperature difference over the triple point T _τ . On the one hand, the temperature difference must be large enough in the nozzle head to avoid unwanted freezing out due to thermodynamic fluctuations and, for setting the freezing length a (see FIG. 1), below z. B. 5 mm should be chosen to be sufficiently small, a temperature gradient also having to be taken into account, which can form between the heat exchanger device 20 and the outlet end 31 of the nozzle head 30. In the case of xenon, the set operating point temperature is in the range from 161.5 K to 165 K. In general, the liquid is cooled down to fractions of a degree K at the triple point (e.g. less than 1 degree).

The flow rate of the liquid in the supply line is at a working pressure of approx. 1 bar approx. 10 m / s and at a working pressure of approx. 100 bar approx. 100 m / s. A flow velocity of around 50 m / s is typically set.

For the precise and stable setting of the freezing length a, it is also important that the operating point temperature T _{0 is set} with great accuracy and stability over time. For this purpose, on the basis of the thermodynamic properties of the liquid to be injected and the materials of the nozzle arrangement, which are known per se from tables, and from the operating parameters of the nozzle arrangement, tion, in particular the volume flow of the liquid through the nozzle arrangement 10 and the length of the supply line 27 along the heat exchanger device 20, the required cooling capacity in the heat exchanger device 20 and thus the desired temperature and flow rate of the cooling medium are determined. These variables are particularly preferably selected such that the temperature difference between the liquid and the cooling medium essentially disappears after passing through the heat exchanger device. In this case, the set temperature is independent of the flow velocity in the line and the stability of the temperature setting is improved.

For example, the volume or mass flow of the liquid in the supply line 27 can be calculated using the Bernoulli laws from the working pressure of the nozzle arrangement (pressure of the supplied gas) and the diameter of the supply line 27. At a working pressure p = 40 bar, a flow cross-section of 200 μm results in a volume flow of 1.53 cm ³ / s and mass flow of 4.6 g / s. For a beam cross section of 20 μm, a volume flow of 0.0153 cm ³ / s and a mass flow of 0.046 g / s result. The amount of heat to be removed from the heat exchanger device 20 for cooling the initially supplied gas stream, for condensing it and finally for setting the operating point temperature can be determined from the volume or mass flow and the thermodynamic properties of the working material. For xenon, the required cooling capacity of approx. 110 W. To generate a xenon beam with a diameter of 30 μm, approx. 15 W required.

For an exact cooling of the liquid to the working point temperature, the geometric parameters of the heat Exchanger device 20 and the feed line 27 running in this, preferably optimized on the basis of the following considerations. The temperature difference between the flowing liquid and the wall temperature of the feed line depends in particular on the length of the feed line through which flow and the volume flow of the liquid. According to a characteristic length Lχ _{/ 2} = Vol 'σ' c _p ^* λ ^_1 . 0.053 halves the temperature difference (vol: volume flow, σ: mass density, c _p : specific heat, λ: heat conduction). For xenon, with a beam diameter of 32 μm and a working pressure of 40 bar, a half-value cooling length of approx. 16 cm. In order to set the relative temperature deviation less than 1%, the length of the supply line in the heat exchanger device is set in accordance with a multiple of the half-value cooling length. This size, also referred to as the heat exchanger length, is preferably at least 5 times, particularly preferably at least 10 times longer than the half-value cooling length L _2/2 . For xenon, the desired cooling results in approx. 100 K with the given example values and a heat exchanger length of approx. 80 cm a relative temperature deviation that is less than 0.2 K. This can be a critical advantage for precision applications of the invention compared to conventional nozzle systems.

Analogous estimates for argon as the target material result in a heat exchanger length that is approximately a quarter of the heat exchanger length for xenon. The heat exchanger length increases linearly with the desired mass flow of the gaseous target material. For a 200 μm xenon beam, a heat exchanger length of approx. 8 m required.

The setting of the temperature in the cooling medium in the heat exchanger device 20 can finally be taken into account tion of the heat conduction properties of the wall material of the supply line. The thickness of the wall material is chosen with a view to sufficient compressive strength and good heat transfer, for example 0.5 mm.

The thermodynamic considerations illustrated here show that the setting of the p-T operating point for minimizing the freezing length a can be derived with sufficient accuracy solely from material sizes and operating parameters of the nozzle arrangement. According to preferred embodiments of the invention, it is alternatively or additionally possible to regulate the operating point temperature as a function of a temperature or vapor pressure measurement in the heat exchanger device 20 or an optical observation of the freezing length. The optical observation takes place, for example, with a

Microscope, the beam path of which is directed through a transparent window of a vacuum chamber onto the nozzle 30. Since the target material does not undergo any further changes in a vacuum after freezing, the free filament length b can be increased considerably. The laser beam 4 is focused on the filament 1, for example with a filament length b of 20 cm.

A preferred embodiment of the nozzle arrangement 10 according to the invention is illustrated with further details in FIG. 3. The nozzle arrangement 10 comprises the heat exchanger device 20 and the nozzle head 30. The heat exchanger device 20 comprises a cooling medium vessel which is formed by a cooling jacket 21 which has an end wall at its free, vacuum-side end 22 and the nozzle head 30 and at its opposite end End is closed with an end plate 23. The vessel serves to hold a cooling medium, which can be supplied through a first cooling medium line 24 and a second cooling medium line 25 can be removed. The cooling medium lines 24, 25 are connected to a thermostat 50 (see FIG. 4). To implement a countercurrent cooler, the first cooling medium line 24 extends to the free end 22 of the cooling jacket, while the second cooling medium line 25 ends at the connection plate 23.

A temperature sensor 24 is arranged in the heat exchange device 20, the sensor signals of which can be derived to the outside via a connecting line through the connecting plate 23.

The supply line 27 for the target material extends in a spiral from the connecting plate 23 to the nozzle head 30. The supply line 27 is a capillary with an inside diameter of 1/16 (corresponding to approximately 0.16 mm).

The cooling jacket 21 consists, for. B. made of stainless steel. It has an inner diameter of approx. 12 mm. The length of the cooling jacket can be selected depending on the desired heat exchanger length of the feed line 27 and is, for example, 17 cm or 40 cm. The supply line consists of an inert material, for example stainless steel or titanium, and has a wall thickness of approx. 0.5 mm.

The nozzle head 30 shown below for more details

7, is connected to the end of the feed line 27 via a seal with high thermal conductivity, which preferably consists of a Cu-Be alloy.

FIG. 4 shows the attachment of the nozzle arrangement 10 according to the invention to the wall of a vacuum chamber 70. The cooling medium supply and discharge lines 24, 25 lead to a thermostatic th 40. The feed line 27 is connected to a reservoir 61 of a target source 60.

According to the invention, the nozzle arrangement can be equipped with a shielding device which is arranged in front of the nozzle 30 for thermal insulation in the exit direction. For example, a heat shield or shield 35, for example made of steel or graphite, is provided as a diaphragm with a passage opening for the filament 1. The shielding shield 35 is arranged between the radiation site (focus 4 of the laser, see FIG. 1) and the nozzle 30 and is fastened, for example, to the wall of the vacuum chamber 70. It suppresses undesired heating of the nozzle and improves the rigid coupling of the nozzle temperature to the temperature in the heat exchanger. The distance of the shield 35 from the nozzle 30 is 5 cm, for example.

The orientation of the nozzle arrangement 10 can be chosen to deviate from the vertical direction with the exit from top to bottom. In particular, a horizontal alignment or a vertical alignment with the exit from bottom to top (“overhead arrangement”) can be provided. In this case, a wire bundle or a pore filter, which have a wicking effect, can be provided in the feed line in order to avoid undesired backflow through the feed line. The wire bundle consists for example of pieces of wire with a length of 10 mm and a diameter of 10 μm.

According to a preferred embodiment of the invention, the nozzle arrangement 10 is equipped with a fastening device 40 which is used for fixing to a vacuum flange of the vacuum chamber 70 and is shown in more detail in FIG. 5. The fastening device 40 comprises a collar 41 running around the side. On one side of the collar 41, a circumferential groove 42 is provided for receiving a seal when attaching the fastening device 40 to the connecting flange. On the opposite side, the collar 41 has a holding tube 43, with which the cooling jacket 21 of the heat exchange device 20 can be releasably connected in a pressure-tight manner, and a projection 44 with an external thread for attaching a shielding sleeve 44 of the cooling medium lines (see FIG. 6). The cooling jacket 21 is connected to the holding tube 43 by means of a crimped screw connection with easily exchangeable, known high and low temperature resistant plastic seals or metal cutting rings.

A particular advantage of the fastening device 40 is that the nozzle arrangement 10 can be quickly assembled or disassembled with little effort. This is particularly important for applications in production processes in practice when replacing nozzle heads. An exchange of a nozzle arrangement according to the invention, including the required thawing and cooling times, advantageously takes only approx. 30 minutes.

The thermostat 50 is a commercially available circulation cryostat known per se. The cooling medium is moved with a circulation pump via the cooling medium supply line 24 into the heat exchanger device 20 and via the cooling medium discharge line 25 back to the cryostat. Isopentane, for example, is used as the cooling medium, which is particularly advantageous for nozzle operation in the range from −130 ° C. to 0 ° C. Alternatively, methane or a cold gas such as nitrogen or helium vapor can be used, for example. The cooling medium lines 24, 25 are thermally insulated by the sleeve 51 and a flexible vacuum jacket 52 (see FIG. 6). This will result in energy losses along the lines avoided, and the setting of the operating point temperature in the heat exchanger device improved. Furthermore, precipitation from the ambient air on the lines 24, 25 is advantageously avoided. The sleeve 51 can be connected to the projection 44 of the fastening device 40 via the screw thread (at 53) (see FIG. 5).

The spatial separation of the nozzle arrangement 10 and the thermostat 50 has the additional advantage that vibrations which are caused by the thermostat operation are damped. For this reason, the cooling medium supply and discharge lines 24, 25 preferably have a length of at least 1 m.

FIG. 7 illustrates the outlet end 31 of the nozzle 30 in an enlarged sectional view. The nozzle 30 has a tapered, continuous inner contour 32 which is convexly curved inwards. For a vortex-free exit of the liquid jet from the nozzle 30, an angle of inclination of the inner contour 32 relative to the nozzle axis 33 is preferably chosen that is less than 45 °. The nozzle 30 is made, for example, of quartz glass or another inert, low-corrosion material. The diameter at the outlet end is approx. 20 to 60 μm.

For the production of solid filaments 1 in the vacuum chamber 70 according to the invention, there is first a start-up phase in which the gaseous target material flows from the reservoir 61 under pressure through the nozzle arrangement 10 while it is being cooled. As soon as the cooling in the heat exchanger device 20 is sufficient to liquefy the target material, the liquid jet 2 is injected into the vacuum chamber 70. The further temperature setting up to the desired operating point temperature can be carried out by measuring the temperature in the heat exchanger device and correspondingly controlling the coolant temperature at the cryostat and / or the optical observation of the freezing length a (see Figure 1).

A modified embodiment of the nozzle arrangement 10 according to the invention is illustrated with further details in FIG. The nozzle arrangement 10 comprises the heat exchanger device 20 and the nozzle head 30, which is connected, for example screwed, to the heat exchanger device 20 and the supply line 27 via an additional intermediate piece 34. The intermediate piece 34 facilitates the interchangeability and possibly adjustability of the nozzle 30. The other details correspond to the structure in FIG. 3.

The intermediate piece 34 can be angled and the exit direction of the nozzle can be angled, for example, by 90 ° relative to the axis of the cooling jacket. In this case there may be advantages for a simplified installation of the nozzle arrangement in a vacuum chamber.

A bellows connection can be provided between the nozzle 30 or the intermediate piece 34 and the cooling jacket. The bellows connection, which is part of the cooling jacket, for example, enables flexible adjustment of the outlet direction of the nozzle. The capillary-shaped feed line 27 can advantageously follow such an adjustment due to its flexibility.

FIG. 9 illustrates the advantages of the invention using the example of images of the exit end of a nozzle taken with a microscope. With conventional technology (without setting the desired working point), the jet breaks down into irregular partial flows that extend into the room like a spray (left picture). According to the invention, the stable beam is generated, which decays into the Vacuum extends (right picture). The phase boundary can be seen immediately after the nozzle ends.

An example of an X-ray source according to the invention is illustrated schematically in FIG. The x-ray source comprises a target source 60, which is connected to a temperature-controllable vacuum chamber 70, an irradiation device 71 and a collecting device 72.

The target source 60 comprises the reservoir 61 for a target material, the feed line 27 and the nozzle arrangement 10 according to the invention, which is connected to the thermostat (not shown). With an actuating device (not shown), which comprises, for example, a pump or a piezoelectric conveying device, the target material is guided to the nozzle arrangement 10 and injected into the vacuum chamber 70 as described above.

The irradiation device 71 comprises a radiation source 73 and a radiation optics 74, with which radiation from the radiation source 73 can be focused on the target material 1. The radiation source 73 is, for example, a laser, the light of which is possibly directed towards the target material 1 with the aid of deflecting mirrors (not shown). Alternatively, an ion source or an electron source can be provided as the radiation device 71, which is also arranged in the vacuum chamber 70.

The collecting device 72 comprises a pickup 75 z. B. in the form of a funnel or a capillary, which removes the target material, which has not evaporated under the action of the radiation, from the vacuum chamber 70 and passes it into a collecting container 76. The vacuum chamber 70 comprises a housing with at least a first window 77, through which the target material 1 can be irradiated, and at least a second window 78, through which the generated X-ray radiation emerges. The second window 78 is optionally provided in order to couple the generated X-ray radiation out of the vacuum chamber 70 for a specific application. If this is not necessary, the second window 78 can be omitted. The vacuum chamber 70 is also connected to a vacuum device 79 with which a vacuum is generated in the vacuum chamber 70. This vacuum is preferably below 10 ^{~ 5} mbar. The radiation optics 74 is also arranged in the vacuum chamber 70. If the vacuum device 79 is a cryopump, undesirable mechanical vibrations in the vacuum chamber are advantageously avoided.

The second window 78 consists of a window material transparent to soft X-rays, e.g. B. from beryllium. If the second window 78 is provided, an evacuable processing chamber 90 can be connected, which is connected to a further vacuum device 91. In the processing chamber 90, the x-ray radiation for material processing can be imaged on an object. An X-ray lithography device 92 is provided, for example, with which the surface of a semiconductor substrate is irradiated. The spatial separation of the X-ray source in the vacuum chamber 70 and the X-ray lithography device 92 in the processing chamber 90 has the advantage that the material to be processed is not exposed to deposits of evaporated target material.

The X-ray lithography device 92 comprises, for example, a filter 93 for selecting the desired X-ray wavelength, a mask 94 and the substrate 95 to be irradiated. In addition imaging optics (for example mirrors) can be provided in order to direct the x-ray radiation onto the x-ray lithography device 91.

The invention is not restricted to the preferred exemplary embodiments described above. Rather, a large number of variants and modifications are possible which also make use of the inventive idea and therefore fall within the scope of protection.

Claims

claims

1. A method for producing a solid filament (1) from a liquid (2) in a vacuum chamber (70), comprising the steps:

- liquefaction of a gas in a heat exchanger device (20) to produce the liquid (2), and - supply of the liquid (2) via a supply line (27) and through a nozzle (30) into the vacuum chamber (70), characterized in that

- The liquefaction of the gas in the heat exchanger device (20) comprises the setting of a pT operating point of the liquid (2), at which the liquid (2) after exiting the nozzle (30) into the vacuum chamber (70) in the solid state is transferred and forms a collimated and stable beam.

2. The method of claim 1, wherein the setting of the p-T operating point of the liquid (2) comprises tempering the liquid in the heat exchanger device (20) to an operating point temperature T ₀ , below which the liquid becomes solid.

3. The method of claim 1 or 2, wherein the setting of the pT operating point of the liquid (2) comprises a temperature control of the liquid (2) in the heat exchanger device (20) to an operating point temperature T ₀ , which is less than 1 degree above the triple point T _{τ of} the liquid (2).

4. The method according to at least one of the preceding claims, wherein the temperature of the liquid (2) takes place while it is flowing through the supply line (27).

5. The method of claim 4, wherein the temperature of the liquid (2) along the supply line (27) to the nozzle (30).

6. The method according to at least one of the preceding claims, in which a temperature gradient is formed along the supply line (27) in the heat exchanger device (20), which is less than 2 degrees / cm.

7. The method according to at least one of the preceding claims, wherein the temperature control in the heat exchanger device (20) is carried out with a liquid cooling medium.

8. The method according to claim 7, wherein the temperature of the cooling medium is adjusted with a thermostat (40).

9. The method according to claim 7 or 8, in which a temperature or a vapor pressure of the cooling medium is measured in the heat exchanger device (20).

10. The method according to at least one of the preceding claims, in which an optical measurement of the liquid (2) emerging in the vacuum chamber (70) is carried out.

11. The method according to claim 9 or 10, wherein at least one of the parameters pressure of the gas, supply volume of the cooling medium and temperature of the cooling medium in the heat exchanger device (20) is set depending on the result of the temperature measurement, the vapor pressure measurement or the optical measurement.

12. The method according to claim 11, in which a control loop is formed for setting the at least one parameter.

13. The method according to at least one of the preceding claims, wherein the liquid (2) in the nozzle (30) is subjected to a beam shaping.

14. The method according to at least one of the preceding claims, wherein the gas supplied is a noble gas.

15. The method of claim 14, wherein the gas supplied is xenon.

16. The method according to at least one of the preceding claims, in which the pT operating point of the liquid (2) is selected such that the liquid (2) becomes solid within a freezing length (a) after it emerges from the nozzle (30) is less than 10 mm.

17. A nozzle arrangement (10), in particular for producing solid filaments (1) in a vacuum, which comprises: - a heat exchanger device (20) for producing a liquid (2) from a gas, and

- A feed line (27) with a nozzle (30) through which the liquid (2) can exit into the vacuum, characterized in that - the heat exchanger device (20) is set up in this way for setting a pT operating point of the liquid (2) that the liquid (2) can emerge from the nozzle (30) in the vacuum in the solid state and a collimated and stable jet shape.

18. A nozzle assembly according to claim 17, wherein the heat exchanger device (20) extends along the supply line (27).

19. A nozzle arrangement according to claim 18, wherein the heat exchanger device (20) extends along the supply line (27) to the nozzle (30).

20. Nozzle arrangement according to at least one of claims 17 to

19, in which the heat exchanger device (20) extends over a length of at least 40 cm along the supply line.

21. Nozzle arrangement according to at least one of claims 17 to

20, in which the supply line (27) winds through the heat exchanger device (20).

22. Nozzle arrangement according to at least one of claims 17 to 21, in which the feed line (27) has a wall thickness in the range from 0.1 mm to 0.5 mm.

23. Nozzle arrangement according to at least one of claims 17 to

22, in which the heat exchanger device (20) is a counterflow cooler.

24. Nozzle arrangement according to at least one of claims 17 to

23, in which the heat exchanger device (20) contains a liquid cooling medium.

25. Nozzle arrangement according to at least one of claims 17 to 24, in which the heat exchanger device (20) has a tubular cooling jacket (21), at the end (22) of which the nozzle (30) is arranged.

26. Nozzle arrangement according to claim 25, wherein the nozzle (30) is removably arranged on the cooling jacket (21).

27. Nozzle arrangement according to claim 25 or 26, in which the nozzle (30) is adjustably arranged on the cooling jacket (21), so that the orientation of a discharge direction of the nozzle (30) is variable relative to the longitudinal extent of the cooling jacket (21).

28. Nozzle arrangement according to at least one of claims 27 to

27, in which a shielding device (35) is provided, which serves for thermal insulation of the nozzle (30).

29. Nozzle arrangement according to at least one of claims 25 to

28, in which a fastening device (50) is provided for fastening the cooling jacket (21) to a vacuum flange.

30. Nozzle arrangement according to at least one of claims 25 to 29, in which the heat exchanger device (20) with a

Thermostat (40) is connected, with which the cooling medium in the heat exchanger device (20) can be tempered.

31. Nozzle arrangement according to claim 30, in which the thermostat (40) is arranged in a vibration-decoupled manner relative to the heat exchanger device (20).

32. Nozzle arrangement according to claim 30 or 31, in which the heat exchanger device (20) is connected to the thermostat via thermally insulated lines (24, 25).

33. Nozzle arrangement according to at least one of claims 17 to 32, in which a temperature or vapor pressure sensor is arranged in the heat exchanger device (20).

34. Nozzle arrangement according to at least one of claims 17 to 33, in which at the nozzle (30) the supply line (27) with a predetermined convex inner contour (32) opens into an outlet opening.

35. Nozzle arrangement according to at least one of claims 17 to 34, wherein the nozzle (30) is detachably connected to the supply line (27), a seal being arranged between the nozzle (30) and the supply line (27) consists of an alloy of copper and beryllium.

36. Device with a vacuum chamber (70) and a nozzle arrangement (10) according to at least one of the preceding claims for producing a solid filament from a liquid in the vacuum chamber (70).

37. Use of a method or a nozzle arrangement according to at least one of the preceding claims for producing a frozen filament with a length of at least 10 cm and a diameter in the range from 10 μm to 100 μm.