Gas supply device and apparatus and method for particle beam-induced processing of a sample

Abstract

A gas supply device (100) for an apparatus (200) for particle beam-induced processing of a sample (202), comprising a liquid container (102) with a saturated salt solution (104) received therein for producing a process gas (106) at a surface (108) of the salt solution (104) and a gas feed line (120) connected to the liquid container (102) for gas transfer and serving to feed the produced process gas (106) to a work location (206) of the apparatus (200).

Description

[0001] Carl Zeiss SMT GmbH 1 GAS SUPPLY DEVICE AND APPARATUS AND METHOD FOR PARTICLE BEAM-INDUCED PROCESSING OF A SAMPLE The present invention relates to a gas supply device, to an apparatus for particle beam-induced processing of a sample, having such a gas supply device and to a method for particle beam-induced processing of a sample. The content of the priority application DE 102024129909.6 is incorporated by reference in its entirety. Microlithography is used to fabricate microstructured components, for example integrated circuits. The microlithography process is carried out using a lithography apparatus comprising an illumination system and a projection system. The image of a mask (reticle) illuminated by means of the illumination system is projected by means of the projection system onto a substrate, for example a silicon wafer, which is coated with a light-sensitive layer (photoresist) and is arranged in the image plane of the projection system, in order to transfer the mask structure to the light-sensitive coating of the substrate. Driven by the need for ever smaller structures in the fabrication of integrated circuits, EUV lithography apparatuses that use light at a wavelength in therange from 0.1 nm to 30 nm, in particular 13.5 nm, are currently underdevelopment. The photomask used in microlithography (i.e. the lithography mask) has microstructures that are projected onto the substrate in reduced scale. The structures of the photomask themselves are already very small and have dimensions of a few micrometres to a few nanometres, for example. In order to fabricate microstructured components with high accuracy by microlithography, the structures on the photomasks used also have to be manufactured very Carl Zeiss SMT GmbH 2 precisely, and the photomasks have to be free of defects (e.g. defective structures and contaminations). Another reason why a defect-free microlithographic photomask is very important is because a photomask is typically used for a multitude of exposures. Therefore, a high degree of time and effort goes into examining photomasks for defects and repairing defects found. Typical defects of photomasks include lack of planned structures, for example because an etching process was unsuccessful, or else the presence of unplanned structures, for example because an etching process proceeded too quickly or had its effect at a wrong site. These defects can be eliminated by selective etching of excess material or by selective depositing of additional material at the appropriate positions. This is possible in a very targeted manner, for example, by particle beam-induced processing (e.g. focused electron beam-induced processing, FEBIP). This involves providing a particle beam and a process gas (e.g. etching gas or deposition gas and / or additive gases) at a site on the photomask to be processed. The particle beam activates a local chemical reaction between a material of the photomask and the process gas, as a result of which material is locally removed from or deposited on the photomask. In the particle beam- induced processing of a sample such as a photomask, the gas flow rate and the gas pressure of the process gas at the site on the photomask to be processed are of crucial importance to the processing operation.Furthermore, also other samples (e.g., wafers such as wafers with semiconductorcomponents produced in the microlithography process) need to be free ofcontaminations and defects (e.g., particles, lack of desired structures and / orpresence of undesired structures). Against this background, a problem addressed by the present invention is that of providing an improved gas supply for an apparatus for particle beam-induced processing of a sample. Carl Zeiss SMT GmbH 3 According to a first aspect, a gas supply device for an apparatus for particle beam-induced processing of a sample is proposed. The gas supply device comprises a liquid container with a saturated salt solution received therein for producing a process gas at a surface of the salt solution. Moreover, the gas supply device comprises a gas feed line connected to the liquid container for gas transfer and serving to feed the produced process gas to a work location of the apparatus. For thermodynamic reasons, a saturated salt solution at a given temperatureprovides only exactly one relative humidity (RH) – and thus exactly one vapourpressure. Hence, the vapour pressure of the produced process gas in the proposed gas supply device depends only on the type of saturated salt solution (and its temperature). That is to say, the vapour pressure of the produced process gas, andhence the gas flow rate at the work location of the apparatus, is defined byfundamental physical-chemical properties in the present case. This represents an advantage over conventional gas supply devices that are based on a liquid reservoir. This is because in conventional gas supply devices that are based on a liquid reservoir, the gas flow rate at the work location of the apparatusis set – apart from the temperature of the liquid being set – on the basis of e.g.orifice plates that limit the gas flow of the produced process gas or with the aid of valves that repeatedly interrupt the gas flow of the produced process gas (e.g. pulsed gas supply) in order thus to achieve a reduction in the gas flow rate on average. Conventionally, already produced process gas is also e.g. at least partially withdrawn from a feed line in order thus to set the gas flow rate. All these mechanical methods are afflicted by inaccuracies. For example, a problem that arises when the gas flow rate is regulated with the aid of orifice plates is that orifice plate diameters of the orifice plates supplied are subject to manufacturing-related variations, and this results in different flow values for the gas flow to the work location in the case of otherwise unchanged parameters. Producing a pulsed gas Carl Zeiss SMT GmbH 4 feed is accompanied by the disadvantage that the process gas is fed to the work location with a flow that varies greatly over time, and hence the availability of process gas at the work location changes over time. Consequently, it is difficult to accurately set a gas flow rate using the aforementioned mechanical methods. This relates in particular to setting a low gas flow rate. Problems also arise when the gas flow rate at the work location is set merely by way of setting the temperature of the liquid in the liquid reservoir. Especially in the case of water as process gas, setting the desired gas flow rate often requires frozen water in the liquid reservoir to be cooled to very low temperatures (≤ -40°C) and the temperature to be kept constant, for example with an accuracy of at least + / -0.2°C. This is technically difficult and complex and / or not possible without much outlay.By contrast, in the proposed gas supply device, the gas flow rate may be set – atleast primarily – by way of the choice of saturated salt solution. Hence the setequilibrium vapour pressure of the produced process gas, and hence the gas flow rate at the work location of the apparatus, depends at least primarily only on the thermodynamic properties of the saturated salt solution. Hence the gas flow rate at the work location of the apparatus can be set more easily and more accurately. The invention is based on the principle that the vapour pressure of e.g. water vapour above a saturated salt solution is reduced by a characteristic absolute value in comparison with water without salt at the same temperature (vapour pressure reduction of the saturated salt solution). The relative humidity of a saturated salt solution could also be said to be reduced by a characteristic absolute value in comparison with the solvent (e.g. water) without salt at the same temperature. The lower the relative humidity of the saturated salt solution, the lower the equilibrium vapour pressure of the saturated salt solution and hence the lower the vapour pressure of the produced process gas. Carl Zeiss SMT GmbH 5 The article L. Greenspan 1977, "Humidity Fixed Points of Binary SaturatedAqueous Solutions" (Journal of Research of the National Bureau of Standards – A.Physics and Chemistry, Vol. 81A, No. 1, January-February 1977) provides an overview of the relative humidity that may be set using different salts dissolved in water. Accordingly, for example, a saturated caesium fluoride solution at 15°C has a relative humidity of only approximately 4% in comparison with water without salt. Further accordingly, for example, a saturated potassium sulphate solution at 15°C has a relative humidity of approximately 98% in comparison with water without salt. The relative humidity of a selection of saturated salt solutions from L. Greenspan 1977 is shown in Table 1 below with rounded numerical values. Consequently, the choice of saturated salt solution type allows the vapour pressure in the liquid container to be varied over a broad pressure range (e.g. over almost two orders of magnitude). Moreover, the suitable saturated salt solution allows a lower vapour pressure of the produced process gas, for example H2O, D2O or HDO, and hence a lower gas flow rate at the work location of the apparatus, to be set easily in comparison with the salt-free solution. Hence the proposed gas supply device is particularly well-suited, inter alia, to set low gas Relative humidity [%] Salt Solubility in water at 20°C 0°C 10°C 20°C 30°C 40°C 50°C 60°CSodium hydroxide NaOH1090 g / l 8.9 7.6 6.3 4.9 3.6Lithium chloride LiCl832 g / l 11.2 11.3 11.3 11.3 11.2 11.1 11.0 Carl Zeiss SMT GmbH 6 Magnesium chloride MgCl2542 g / l 33.7 33.5 33.1 32.4 31.6 30.5 29.3Sodium chloride NaCl358 g / l 75.5 75.7 75.5 75.1 74.7 74.4 74.5Table 1: Equilibrium humidity over saturated salt solutions The apparatus for particle beam-induced processing of a sample serves, forexample, to repair a defect of the sample. The defect is, for example, an unwantedstructure (e.g., an unwanted absorber structure of a photomask and / or anunwanted electronic structure of a wafer) and / or a foreign particle of the samplewhich is etched with the apparatus. This means that material is removed locally from the sample in the region of the defect. The defect may also be a missingstructure of the sample (e.g., a missing absorber structure of the photomaskand / or a missing electronic structure of the wafer) which is repaired bydepositing material with the apparatus. This means that material (a deposit) isdeposited locally on the sample in the region of the defect. The apparatus is used to provide a particle beam, e.g. an electron beam or an ion beam, and an etching gas or a deposition gas at a site on the sample to be processed. The particle beam activates a local chemical reaction between a material of the sample and the etching gas or deposition gas, as a result of which material is locally removed from the sample or deposited on thesample. The etching gas comprises, for example, xenon difluoride (XeF2), sulphur hexafluoride (SF6), sulphur tetrafluoride (SF4), nitrogen trifluoride (NF3), phosphorus trifluoride (PF3), chlorine (Cl2), hydrogen chloride (HCl), hydrogen fluoride (HF), nitrosyl chloride (NOCl), nitrosyl fluoride (NOF) and / or triphosphorus trinitrogen hexafluoride (P3N3F6). Carl Zeiss SMT GmbH 7 In particular, alkyl compounds of main group elements, metals or transition elements are considered as deposition gas suitable for the deposition or for growing of elevated structures (e.g. deposits). Examples thereof include cyclopentadienyl(trimethyl)platinum (CpPtMe3Me = CH4), methylcyclopentadienyl(trimethyl)platinum (MeCpPtMe3), tetramethyltin (SnMe4), trimethylgallium (GaMe3), ferrocene (Cp2Fe), bisarylchromium (Ar2Cr), and / or carbonyl compounds of main group elements, metals or transition elements, such as for example chromium hexacarbonyl (Cr(CO)6), molybdenum hexacarbonyl (Mo(CO)6), tungsten hexacarbonyl (W(CO)6), dicobalt octacarbonyl (Co2(CO)8), triruthenium dodecacarbonyl (Ru3(CO)12), iron pentacarbonyl (Fe(CO)5), and / or alkoxide compounds of main group elements, metals or transition elements, for example tetraethoxysilane (Si(OC2H5)4), tetraisopropoxytitanium (Ti(OC3H7)4), and / or halide compounds of main group elements, metals or transition elements, such as for example tungsten hexafluoride (WF6), tungsten hexachloride (WCl6), titanium tetrachloride (TiCl4), boron trifluoride (BCl3), silicon tetrachloride (SiCl4), and / or complexes with main group elements, metals or transition elements, for example copper bis(hexafluoroacetylacetonate) (Cu(C5F6HO2)2), dimethylgold trifluoroacetylacetonate (Me2Au(C5F3H4O2)), and / or organic compounds such as carbon monoxide (CO), carbon dioxide (CO2), aliphatic and / or aromatic hydrocarbons, and the like. In addition to an etching gas or deposition gas, use can also be made for example of one or more added gasses (additive gases). Added gases include, for example, oxygenous and / or oxidizing gases such as oxygen (O2), ozone (O3), water (H2O), hydrogen peroxide (H2O2), nitrous oxide (N2O), nitric oxide (NO), nitrogen dioxide(NO2), nitric acid (HNO3) and other oxygenous gases, and / or halides such aschlorine (Cl2), hydrogen chloride (HCl), hydrogen fluoride (HF), iodine (I2), hydrogen iodide (HI), bromine (Br2), hydrogen bromide (HBr), phosphorus trichloride (PCl3), phosphorus pentachloride (PCl5), phosphorus trifluoride (PF3) Carl Zeiss SMT GmbH 8 and other halogen-containing gases (e.g. CF4, NOCl), and / or reducing gases, such as hydrogen (H2), ammonia (NH3), methane (CH4) and other hydrogenous gases. These added gases can be used, for example, for etching processes, as buffer gases, as passivating media and the like. For example, the process gas produced with the aid of the liquid container with the saturated salt solution is an added gas (additive gas) that is used in addition to an etching gas or a deposition gas. For example, the added gas serves to improve an etching process or deposition process. The added gas may also be used to passivate a surface of thesample. In addition to the liquid container with the saturated salt solution, the gas supply device may also comprise containers for one or more etching gases, one or more deposition gases and / or one or more (further) added gases. The sample is, for example, a flat extended object. The sample may have, for example, a rectangular shape, squared shape and / or circular shape in its main plane of extension. The sample includes, for example, a substrate, a photomask and / or a wafer, Inparticular, the sample includes, for example, a microlithographic photomask, asubstrate for a microlithographic photomask and / or a mask blank for amicrolithographic photomask. The sample may also include, for example, asubstrate (e.g., of a wafer), a wafer, a silicon wafer, a semiconductor wafer, a dicedwafer, a singulated wafer, a piece of such a wafer, a die and / or a semiconductor die.The microlithographic photomask as an example of a sample is, for example, aphotomask for use in an EUV lithography apparatus. EUV here stands for "extreme ultraviolet" and denotes a wavelength of the operating light of between Carl Zeiss SMT GmbH 90.1 nm and 30 nm, in particular 13.5 nm. At these wavelengths, it is necessary touse reflective optical elements, and this applies to the photomask as well. In an EUV lithography apparatus, a beam shaping and illumination system is used to guide EUV radiation to the photomask ("reticle"), which takes the form of a reflective photomask. Therefore, the photomask comprises a layer that reflects EUV radiation and e.g. takes the form of a Bragg mirror, and a structured absorbing layer ("absorber structures") on the reflective surface. Such masks are also referred to as binary lithography masks. The pattern of the structured absorbing layer (i.e. the pattern of the absorber structures) of the photomask is imaged with reduced size on a wafer by means of a projection system of the EUV lithography apparatus. For example, the microlithographic photomask comprises a mask substrate, a reflective multilayer coating arranged on the mask substrate and a structured coating arranged thereon. In addition, for example, there may also be a capping layer including ruthenium, for example, arranged between the multilayer coating and the structured coating. For example, the mask substrate comprises silicon dioxide (SiO2), e.g. fused quartz. For example, the multilayer coating comprises an alternating sequence of molybdenum and silicon layers. For example, the structured coating comprises tantalum (Ta), one or more tantalum compounds, tantalum nitride (TaN) and / or tantalum oxide (TaxOy). The mask substrate, the multilayer coating and / or the structured coating (absorber structures) may also comprise other materials. However, the microlithographic photomask may also be a photomask for use in a DUV lithography apparatus, for example. DUV here stands for "deep ultraviolet"and denotes a wavelength of the operating light of between 30 nm and 250 nm, inparticular 193 nm or 248 nm. In particular, a photomask for a DUV lithography Carl Zeiss SMT GmbH 10 apparatus takes the form of a transmissive optical element (transmissive photomask).Further, the photomask may also be a mask for nanoimprint lithography (NIL).Instead of a photomask, the sample may, for example, also be a (semiconductor)wafer, diced wafer and / or (semiconductor) die. The wafer, diced wafer and / or dieincludes, for example, semiconductor structures and / or semiconductorcomponents. The semiconductor structures and / or semiconductor componentsinclude, for example, electronic components, photonic components, integratedcircuits (e.g., electronic integrated circuits and / or photonic integrated circuits),and / or electronic and / or photonic (inter-)connections and / or interposer. The wafer,diced wafer and / or die includes, for example, multiple layers of semiconductorstructures and / or semiconductor components printed onto a substrate of the wafer.A material of the wafer, diced wafer and / or die includes, for example, silicon (Si), silicon oxide (SiO), sapphire (Al2O3), silicon carbide (SiC), gallium nitride (GaN), indium phosphide (InP), germanium (Ge), gallium arsenide (GaAs), aluminumgallium arsenide (AlxGa1-xAs), zinc oxide (ZnO) and / or cadmium sulfide (CdS).Furthermore, the sample includes, for example, a wafer, diced wafer and / or dieduring and / or after a manufacturing process. The sample includes, for example, a partially manufactured wafer and / or a pre-manufactured wafer. The sample includes, for example, a wafer onto which one or more of a planned number oflayers of semiconductor structures have been arranged (e.g., printed). The sampleincludes, for example, a wafer before or after dicing it into multiple dies. The sample includes, for example, a die before housing it into a housing.When the sample is processed with the apparatus for particle beam-inducedprocessing, the sample is provided in a process atmosphere of the apparatus. Forexample, the process atmosphere is an atmosphere with a controlled composition Carl Zeiss SMT GmbH 11 and a controlled pressure (for example in the range from 10-1to 10-8mbar). For example, the process atmosphere is a high vacuum with a pressure of 10-7mbar or less. For example, the process atmosphere is provided within an evacuated housing (for example in a vacuum chamber) of the apparatus. Furthermore, at least one etching gas or deposition gas, the process gas produced by means of the liquid container with the saturated salt solution and the particle beam are provided inthe process atmosphere when processing the sample with the apparatus.The process gas produced by means of the liquid container with the saturated salt solution is fed to the work location of the apparatus. The work location of theapparatus for particle beam-induced processing of a sample comprises, inparticular, a focal point of the particle beam. The work location of the apparatus comprises, in particular, a focal point of the particle beam in a plane of theapparatus which is configured to position the sample. In a state in which a sampleis positioned in the apparatus for processing the sample, the work location of theapparatus comprises, in particular, a processing location on the sample at whichthe focused particle beam is incident on the sample. For example, the processinglocation of the sample is a portion of a repair region (e.g. defect region) of thesample. For example, the focused particle beam is raster-scanned over the samplein the repair region. Apart from the connected gas feed line, the liquid container for example is a closed- off liquid container (e.g. gas-tight, liquid-tight and / or fluid-tight container). For example, the liquid container is manufactured from a corrosion-resistant material. For example, the liquid container is manufactured from stainless steel (e.g. V4A and / or 316L quality stainless steel). Moreover, the liquid container is for example embedded in a thermally insulating environment. For example, the gas feed line is fed into a vacuum housing of the apparatus for particle beam-induced processing and, at an end arranged within the housing, Carl Zeiss SMT GmbH 12 comprises a nozzle serving to release the process gas at the work location of the apparatus. For example, the gas feed line may connect the liquid container to a further gas feed line, with the further gas feed line comprising the nozzle. In particular, the salt solution comprises at least one salt that is dissolved in a liquid solvent (e.g. water). In particular, the salt solution is a homogeneous mixture of the at least one salt and the solvent (e.g. water). The salt solution is a saturated salt solution, i.e. there is a solution equilibrium between the solvent (e.g. water) and the dissolved substance (i.e. the at least one salt). In other words, a concentration of the at least one salt dissolved in the solvent is equal to its saturation concentration. The saturation concentration of a saturated salt solution for a given temperature is thermodynamically defined. As a rule, the at least one salt is present in the liquid container not only in the form of the saturated salt solution, in which the at least one salt is dissolved, but also as a solid (precipitate, e.g. settlings). The liquid container with the saturated salt solution produces the process gas at the surface of the salt solution (i.e. in the liquid container) with a predetermined vapour pressure (equilibrium vapour pressure). The at least one dissolved salt (in contrast to the solvent, e.g. water, in which it is dissolved) is preferably non-volatile, i.e. it preferably does not contribute to the vapour pressure of the saturated salt solution. The at least one dissolved salt is preferably chemically stable, especially in a temperature range in which the liquid reservoir is operated. Moreover, the at least one dissolved salt is nontoxic, for example. Additionally, the at least one dissolved salt preferably does not release any volatile species. Furthermore, the at least one dissolved salt is for example non-corrosive vis-à-vis a material of the liquid container. Carl Zeiss SMT GmbH 13 In particular, the saturated salt solution is a liquid saturated salt solution. A further advantage of the saturated salt solution is that it has a lower freezing point vis-à-vis the pure solvent (e.g. pure water). Hence, the liquid reservoir provided by the liquid container with the liquid saturated salt solution may be operated over a broader range of temperatures than would be the case with a pure solvent (e.g. pure water). In particular, the liquid state is advantageous over the solid state (e.g. frozen state) since gas may evaporate from a well-defined surface of the liquid in this case. It may also be advantageous that the temperature dependence of the relative humidity of the saturated salt solution (and hence of the vapour pressure in the liquid container) is relatively low. Hence, the vapour pressure in the liquid container and hence also the gas flow rate at the work location of the apparatus are less susceptible to unwanted temperature fluctuations. In this context, the term "liquid reservoir" is understood to be a combination of a liquid container with a liquid received therein (e.g. the liquid container with the saturated salt solution received therein). According to an embodiment, the gas supply device comprises at least one further liquid container with at least one further saturated salt solution received therein for producing at least one further process gas at a surface of the at least one further salt solution. The saturated salt solution and the at least one further saturated salt solution comprise mutually different relative humidities at a given temperature. Moreover, the at least one further liquid container is connected for gas transfer to the gas feed line and / or at least one further gas feed line, in order to feed the produced further process gas to the work location of the apparatus. Carl Zeiss SMT GmbH 14 Hence, a suitable process gas, in particular a process gas with a suitable vapourpressure, when processing the sample may be selected by making a selection fromamong the liquid container with that saturated salt solution and each of the at least one further liquid container with the at least one further saturated salt solution. In particular, the liquid container and the at least one further liquid container are integrated in the gas supply device such that a selection can be made from among various saturated salt solutions and hence various vapour pressures without needing to exchange the salt solution in a single liquid container. The saturated salt solution and the at least one further saturated salt solution comprise mutually different relative humidities at a given temperature. The reason being that the saturated salt solution and the at least one further saturated salt solution are mutually different salt solutions in terms of a salt dissolved therein. A solvent (e.g. water) of the saturated salt solution and the at least one further saturated salt solution may be the same in particular. This also means that the saturated salt solution and the at least one further saturated salt solution comprise different equilibrium vapour pressures at a given temperature. Consequently, the vapour pressure of the produced process gas may be set by the choice of saturated salt solution. The at least one further liquid container may comprise all features and properties of the liquid container described above and below. Likewise, the at least one further saturated salt solution may comprise all features and properties of the saturated salt solution described above and below, for as long as these solutions differ from each other in terms of the relative humidity and the equilibrium vapour pressure. The further process gas may also comprise all features and properties of the process gas described above and below, for as long as these gases differ from each other in terms of the vapour pressure and the gas flow rate at the work location. Carl Zeiss SMT GmbH 15 According to a further embodiment, the saturated salt solution and / or the at least one further saturated salt solution comprises at least one salt that is dissolved in water. Hence, gaseous water, i.e. water vapour, may be produced as process gas with the aid of the liquid container with the saturated salt solution and may be fed to thework location of the apparatus. For example, a surface of the sample can bepassivated with the aid of water vapour. For example, water vapour is used as additive gas during an etching process. The use of water vapour as an additive gas allows the etching process to be slowed down, whereby a homogeneous etching procedure is promoted, and a subsequent passivation of the surface is achieved. For example, absorber structures in the case of EUV photomasks predominantly comprise tantalum-based materials, in particular tantalum nitride (TaN). Xenon difluoride (XeF2) is usually used as an etching gas in the case of TaN absorber structures when opaque defects of EUV photomasks are repaired, i.e. excess absorber structures are removed, by way of electron beam-induced etching. At the same time, gaseous water is used as additive gas in order to achieve a homogeneous etching procedure and a subsequent passivation of the surface by way of the formation of a Ta2O5layer. In so doing, precise metering of gaseous water at the repair site is required. According to a further embodiment: the saturated salt solution and / or the at least one further saturated salt solution comprise one or more salts, each of which comprises a chemical compound made of an anion and a cation, and / or the saturated salt solution and / or the at least one further saturated salt solution comprise one or more salts from a group comprising: caesium fluoride, Carl Zeiss SMT GmbH 16 calcium chloride, lithium bromide, zinc bromide, potassium hydroxide, sodium hydroxide, lithium chloride, calcium bromide, lithium iodide, potassium fluoride, magnesium chloride, sodium iodide, potassium carbonate, magnesium nitrate,sodium bromide, cobalt chloride, potassium iodide, strontium chloride, sodiumnitrate, sodium chloride, potassium bromide, potassium chloride, strontium nitrate, potassium nitrate, potassium sulphate and potassium chromate. The aforementioned group of saturated salt solutions is sorted, in particular, in the sequence of increasing relative humidity at a given temperature. For example, caesium fluoride at 25°C has a relative humidity of approximately 3% whereas potassium chromate at 25°C has a relative humidity of approximately 98%. This also means that the aforementioned group of saturated salt solutions is sorted in the sequence of increasing equilibrium vapour pressure. In other words, theaforementioned group of saturated salt solutions is sorted in the sequence ofdecreasing vapour pressure reduction. Furthermore, the aforementioned anion and / or the aforementioned cation of the chemical compound is for example an inorganic anion and / or an inorganic cation. For example, the inorganic anion comprises fluoride, chloride, bromide, iodide, sulphate, nitrate, carbonate, chromate and / or hydroxide. The inorganic cation comprises e.g. a sodium ion (Na+), a potassium ion (K+), a lithium ion (Li+), a zinc ion (Zn2+), a cobalt ion (Co3+), a calcium ion (Ca2+), a caesium ion (Cs+), a magnesium ion (Mg2+) and / or a strontium ion (Sr+). However, suitable organic anions may for example also be used in place of inorganic anions, e.g. organic anions that are non-volatile on account of a high molar mass (e.g. polymer) or high charge (polyanion). Furthermore, suitable organic cations may for example also be used in place of inorganic cations, e.g. organic cations that are non-volatile on account of a high molar mass (e.g. polymer) Carl Zeiss SMT GmbH 17 or high charge (polycation). For example, while ammonium salts in general might emit unwanted gaseous NH3, quaternary ammonium salts generally do not release any NH3. According to a further embodiment, a freezing point of the saturated salt solution and / or the at least one further saturated salt solution is at -10°C or lower and / or - 20°C or lower. Lowering the freezing point of the saturated salt solution and / or the at least one further saturated salt solution to a freezing point of -10°C or lower and / or -20°C or lower allows a liquid reservoir to be operated over a much greater temperature range than would be possible using the pure solvent (e.g. pure water). For example, a freezing point of a saturated sodium chloride solution (NaCl solution) is -21°C, and it is -50°C for a saturated calcium chloride solution (CaCl2solution). Hence, by exploiting the lowering of the freezing point, the corresponding liquid reservoir may for example be operated in a temperature range of e.g. -21°C to +20°C in the case of a saturated sodium chloride solution. In the case of a saturated CaCl2solution, the corresponding liquid reservoir may even be operated in a temperature range of e.g. -50°C to +20°C. According to a further embodiment, a change in the relative humidity of the saturated salt solution and / or the at least one further saturated salt solution in a temperature range from 0°C to 20°C is 1.5% or less, 1.0% or less, 0.5% or less, 0.2% or less and / or 0.1% or less. As a result of the low temperature dependence of the saturated salt solution and / or of the at least one further saturated salt solution over the aforementioned Carl Zeiss SMT GmbH 18 temperature range, there are hardly any changes in relative humidity and hence in vapour pressure (and hence also in gas flow rate at the work location of the apparatus) even in the case of unwanted temperature variations. For example, the relative humidity of a saturated potassium carbonate solution varies by less than 0.05% over the temperature range of 0°C to 20°C. For example, the relative humidity of a saturated lithium chloride solution varies by less than 0.1% over the temperature range of 0°C to 20°C. For example, the relative humidity of a saturated magnesium chloride solution varies by less than 1.0% over the temperature range of 0°C to 20°C. For further values of the relative humidity of saturated salt solutions, reference is also made to the aforementioned article L. Greenspan 1977, "Humidity Fixed Points of Binary Saturated Aqueous Solutions". According to a further embodiment, a relative humidity of the saturated salt solution and / or the at least one further saturated salt solution at a temperature of 20°C or less is 50% or less, 30% or less and / or 10% or less. Hence, a saturated salt solution for which the effect of vapour pressure suppression is particularly large is chosen. Hence, the selected saturated salt solution is particularly suited to the provision of a low equilibrium vapour pressure and hence a low gas flow rate at the work location of the apparatus. Examples of saturated salt solutions whose relative humidity at 20°C is 50% or less comprise caesium fluoride, lithium bromide, zinc bromide, potassium hydroxide, sodium hydroxide, lithium chloride, calcium bromide, lithium iodide, potassium fluoride, magnesium chloride, sodium iodide and potassium carbonate. Carl Zeiss SMT GmbH 19 According to a further embodiment, a relative humidity of the saturated salt solution and / or further saturated salt solution at a temperature of 20°C or less is 85% or more, 90% or more and / or 95% or more. Hence, a saturated salt solution for which the effect of vapour pressure suppression is rather low is chosen. Instead, the effect of lowering the freezing point is prioritized here. Examples of saturated salt solutions whose relative humidity at 20°C is 85% or more comprise potassium chloride, strontium nitrate, potassium nitrate, potassium sulphate and potassium chromate. According to a further embodiment, the saturated salt solution and / or the at least one further saturated salt solution comprises at least one salt that is dissolved in water, and the at least one salt is additionally received as a solid in the liquid container and / or the at least one further liquid container. That is to say, the at least one salt is present in the liquid container not only in the form of the saturated salt solution, in which the at least one salt is dissolved, but also as a solid (deposit, precipitate, e.g. settlings / sediment). In particular, the solvent (e.g. water) in the liquid container is provided with such a large amount of the at least one salt that the at least one salt is partially dissolved in the solvent, specifically up to saturation, and moreover remains in the liquid container as a solid salt. In that case, an equilibrium state is present between a dissolution reaction and a precipitation reaction. Should the saturated salt solution emit solvent (e.g. water) in gaseous form as a process gas, and henceshould the salt concentration of the solution increase, then excess saltprecipitates out of the solution again as a solid. Hence the solution always Carl Zeiss SMT GmbH 20 remains saturated (and in particular is not supersaturated either), and the vapour pressure does not change. For example, the initial amount of salt remains in the liquid container over the use duration of the corresponding liquid container. During operation, only gaseous solvent (e.g. gaseous water) is transported from the liquid container to the worklocation of the apparatus (e.g. a repair site on the sample). The liquid containercan be refilled by virtue of adding an amount of liquid solvent (e.g. water) that together with the salt remaining in the liquid container yields a saturated solution. According to a further embodiment, the gas supply device comprises an ultrasonic and / or megasonic unit arranged on the liquid container and / or a further ultrasonic and / or megasonic unit arranged on the at least one further liquid container, for exciting ultrasonic vibrations or megasonic vibrations of the liquid container or a further liquid container. The saturated salt solution can be intermixed in the liquid container with the aid of the ultrasonic and / or megasonic unit. This allows promotion of a dissolution reaction of the at least one salt in the solvent (e.g. water). Exciting the liquidcontainer to perform an ultrasonic vibration (e.g. at a frequency between 20 kHzand 400 kHz) or a megasonic vibration (e.g. at a frequency between 400 kHz and2 MHz) with the aid of the ultrasonic and / or megasonic unit may be implementedat various times after the filling of the liquid reservoir and during its periods of operation. The described features apply correspondingly to the further liquid container. Intermixing of the saturated salt solution in the liquid container with the aid of the ultrasonic and / or megasonic unit is in particular implemented before and / orduring a particle beam-induced processing of a sample. For example, in relation toa method for particle beam-induced processing of a sample described below, Carl Zeiss SMT GmbH 21 intermixing the saturated salt solution with the aid of the ultrasonic and / or megasonic unit is carried out in method step a) ("producing a process gas at a surface of a saturated salt solution"). According to a further embodiment, the gas supply device comprises a temperature control unit for setting a temperature of the saturated salt solution and / or at least one further temperature control unit for setting a temperature of the at least one further saturated salt solution. Setting a temperature of the saturated salt solution allows the equilibrium vapour pressure of the saturated salt solution to be set finely. However, some saturated salt solutions have a relative humidity, and hence an equilibrium vapour pressure, with a very small temperature dependence, and so only a small change in the equilibrium vapour pressure is achieved in these cases by way of a change in temperature. Additional use can be made of the fact that in the case of most salts the effect of vapour pressure reduction is amplified for thermodynamic reasons in the event of a temperature increase and reduced in the event of the temperature being lowered. For example, the temperature control unit and / or the further temperature control unit comprises one or more Peltier elements that are in physical contact with the liquid container or the at least one further liquid container. According to a further embodiment, the gas supply device comprises: at least one orifice plate arranged in the gas feed line and / or in the at least one further gas feed line and serving to set a gas flow rate at the work location and / or one or more valves arranged in the gas feed line and / or in the at least one further gas feed line and serving to set a gas flow rate at the work location. Carl Zeiss SMT GmbH 22 Hence the gas flow rate of the process gas at the work location may be influencedby mechanical methods – in addition to the choice of the saturated salt solution ofthe liquid container. For example, the at least one orifice plate may limit the gas flow of the produced process gas. Furthermore, the gas flow of the produced process gas may be interrupted repeatedly with the aid of the one or more valves (e.g. such that a pulsed gas supply arises), in order thus to obtain a low gas flow rate on average. Moreover, a discharge line, for example, may also be provided on the gas feed line in order to discharge some of the produced process gas from the gas feed line in order to thus set the gas flow rate. According to a second aspect, an apparatus is proposed for particle beam-inducedprocessing of a sample. The apparatus comprises a gas supply device as describedabove.The apparatus for particle beam-induced processing of a sample comprises aparticle beam provision device for provision of an activating particle beam on asurface of the sample.For example, the apparatus is a repair apparatus for repairing samples (e.g.,microlithographic photomasks and / or wafers). For example, the apparatus is amodified scanning electron microscope.The apparatus for particle beam-induced processing of a sample comprises, forexample, a sample stage for arranging, holding and positioning the sample to be processed. The sample stage is actuatable e.g. in two or preferably in three Carl Zeiss SMT GmbH 23 spatial directions. Moreover, the sample stage may be mounted in tiltable androtatable fashion in order to position the sample.The particle beam provision device comprises, for example, a particle source (e.g. electron source or ion source) for producing the particle beam (e.g. electron beam or ion beam); a particle beam guiding device (e.g. scanning unit) which is configured to direct the particle beam to a particular pixel of a repair region of the sample; a particle beam shaping device (e.g. particle, electron and / or beam optics unit) which is configured to shape, in particular to focus, the particle beam; and at least one detector for detecting secondary electrons and / or backscattered electrons. The activating particle beam is provided, for example, by means of the particle beam guiding device, successively at each pixel of a region of a defect (e.g. a repairshape of the defect) of the sample. The activating particle beam remains at eachpixel for a predetermined dwell time in order to initiate the chemical reactionbetween the etching gas or deposition gas and optional additive gases and a samplematerial at the site of the respective pixel. For example, the dwell time is 100 ns.However, the dwell time may also adopt other values. According to a third aspect, a method is proposed for particle beam-inducedprocessing of a sample. The method comprises the following steps:a) producing a process gas at a surface of a saturated salt solution, b) feeding the produced process gas to a work location of the apparatus and c) providing an activating particle beam at the work location. According to an embodiment, the method includes the following steps: providing multiple liquid containers with in each case a saturated salt solution received therein, wherein the multiple salt solutions in the multiple liquid containers have mutually different relative humidities at a given temperature, ascertaining a desired gas flow rate at the work location of the apparatus, Carl Zeiss SMT GmbH 24 selecting a liquid container with the saturated salt solution received therein from the multiple liquid containers on the basis of the ascertained desired gas flow rate, and carrying out steps a) and b) with the aid of the selected liquid container. "A(n)" in the present case should not necessarily be understood as restrictive to exactly one element. Instead, there may also be provision for multiple elements, for example two, three or more. Any other numeral used here should also not be understood as a restriction to exactly the stated number of elements. Rather, unless indicated otherwise, numerical variances upward and downward are possible. The embodiments and features described for the gas supply device apply correspondingly to the proposed apparatus and to the proposed method, and vice versa. Further possible implementations of the invention also comprise combinations not explicitly mentioned of features or embodiments described hereinabove or hereinafter with regard to the exemplary embodiments. A person skilled in the art will also add individual aspects as improvements or supplementations to the respective basic form of the invention. Further advantageous configurations and aspects of the invention are the subject of the dependent claims and of the exemplary embodiments of the invention that are described hereinafter. The invention is elucidated in greater detail hereinafter on the basis of preferred embodiments with reference to the appended figures.Fig. 1 shows a gas supply device according to an embodiment; Carl Zeiss SMT GmbH 25Fig. 2 shows an apparatus for particle beam-induced processing of a sample,having a gas supply device according to an embodiment; andFig. 3 shows a flowchart of a method of particle beam-induced processing of asample according to an embodiment. In the figures, identical or functionally identical elements have been provided with the same reference signs, unless indicated otherwise. Further, it should be noted that the representations in the figures are not necessarily true to scale.Fig. 1 shows a gas supply device 100 according to an embodiment. The gas supplydevice 100 can be used in an apparatus 200 (Fig. 2) for particle beam-inducedprocessing of a sample 202. In particular, the gas supply device 100 is configuredto provide a process gas 106 at a work location 206 (Fig. 2) of the apparatus 200(i.e. also at a processing location of the sample 202). In the following, the sample 202 is described as a microlithographicphotomask 202 and the apparatus 200 is described as an apparatus 200 forparticle beam-induced processing of a microlithographic photomask 202.However, although not described in detail in the following, in other examples, thesample 202 may also be another object different from a microlithographicphotomask 202. The sample 202 may, for example, be a (semiconductor) wafer,diced wafer and / or (semiconductor) die. Further, in other examples the apparatus 200 may be configured for particle beam-induced processing of another objectdifferent from a microlithographic photomask 202. The apparatus 200 may, forexample, be configured for particle beam-induced processing of a wafer, diced wafer and / or die.As evident in Fig. 1, the gas supply device 100 comprises a liquid container 102.The gas supply device 100 moreover comprises a saturated salt solution 104 Carl Zeiss SMT GmbH 26 received in the liquid container 102. With the aid of the liquid container 102 with the saturated salt solution 104, it is possible to produce a process gas 106 at a surface 108 of the salt solution 104. In particular, the process gas 106 evaporates from the salt solution 104 at the surface 108. Together, the liquid container 102 and the saturated salt solution 104 form a liquid reservoir 110 in particular. For example, the saturated salt solution 104 is at a temperature T1. Moreover, at the given temperature T1, the saturated salt solution 104 has a relative humidity RH1 that is thermodynamically defined for the selected saturated salt solution 104. As a result of the relative humidity RH1 of the saturated salt solution 104, an equilibrium vapour pressure EP1of the saturated salt solution 104 is also thermodynamically defined at the given temperature T1. That is to say, the equilibrium vapour pressure EP1 of the saturated salt solution 104 and hence the vapour pressure of the process gas 106 may be set by way of the choice of the type of saturated salt solution 104. In particular, the saturated salt solution 104 comprises at least one salt 114 that is dissolved in a solvent 112. The solvent 112 is preferably water.As illustrated in Fig. 1, the salt 114 may also be present as a solid 118 in theliquid container 102. That is to say, in addition to the saturated salt solution 104, in which the at least one salt 114 is present in dissolved form, the at least one salt 114 is also present in the liquid container 102 as a deposit 118 (e.g.precipitate, sediment).Moreover, the gas supply device 100 comprises a gas feed line 120 connected to the liquid container 102 for gas transfer (i.e. connected so as to conduct gas). The gas feed line 120 is configured to feed the produced process gas 106 to the worklocation 206 of the apparatus 200 (Fig. 2). Carl Zeiss SMT GmbH 27 Optionally, the gas supply device 100 may moreover comprise an ultrasonic unit 122 arranged on the liquid container 102. The ultrasonic unit 122 might also be an ultrasonic and / or megasonic unit. The ultrasonic unit 122 is configured to excite ultrasonic vibrations of the liquid container 102. The ultrasonic vibrations allow the saturated salt solution 104 to be better intermixed in the liquid container 102. This allows promotion of a dissolution reaction of the at least one salt 114 in the solvent 112 (e.g. water 116). Optionally, the gas supply device 100 may comprise a temperature control unit 124for setting a temperature T1 of the saturated salt solution 104, as shown in Fig. 1.For example, the temperature control unit 124 comprises a Peltier element 126 that is in physical contact with the liquid container 102. For example, the temperature control unit 124 additionally comprises a water-cooling system (notshown) for dissipating heat from a warm side of the Peltier element 126.Setting the temperature T1 of the saturated salt solution 104 allows the equilibrium vapour pressure EP1 to be set finely. In particular, the equilibrium vapour pressure EP1of the saturated salt solution 104 is primarily set thermodynamically by way of the choice of the type of saturated salt solution 104. Moreover, the equilibrium vapour pressure EP1 can be set finely within a small range by setting the temperature.As depicted schematically in Fig. 1, the gas supply device 100 may optionally alsocomprise conventional mechanical elements for setting a gas flow rate F of theprocess gas 106 at the work location 206 of the apparatus 200 (Fig. 2). For example,the gas supply device 100 may comprise at least one orifice plate 128 (Fig. 1)arranged on the gas feed line 120 and serving to set the gas flow rate F at the work location 206 of the apparatus 200. In addition to that or in an alternative, the gas supply device 100 may comprise one or more valves 130 arranged on the gas feed line 120 and serving to set the gas flow rate F. Carl Zeiss SMT GmbH 28 Fig. 2 shows a schematic drawing of an apparatus 200 for particle beam-induced processing of a sample 202 such as a photomask 202 according to an embodiment. The apparatus 200 comprises a housing 210 which is evacuated by a vacuumpump 212 to a pressure in the range of 10-1 – 10-8 mbar in order to create aprocess atmosphere 214 in the housing 210. The apparatus 200 additionally comprises a particle beam provision device 216, arranged in the vacuum housing 210, for provision of a focussed particle beam 218. The particle beam provision device 216 comprises a particle source 220 and one or more beam guiding and / or beam shaping units 222, 224 that steer the particle beam 218 in the desired manner onto a surface 226 of the photomask 202. For example, the particle beam provision device 216 is an electron column configured to provide a focused electron beam 218. Moreover, the apparatus 200 comprises one or more detectors 228, for example for detection of secondary electrons. The apparatus 200 also comprises a sample stage 230 for holding and positioning the photomask 202 to be processed. The sample stage 230 is actuatable in two or preferably in three spatial directions. Moreover, the sample stage 230 may be mounted so as to be tiltable and rotatable in order to position the photomask 202. In particular, the sample stage 230 is mounted with vibration damping and is mechanically decoupled from the rest of the structure (not shown). The apparatus 200 further comprises a gas supply device 100' for providing the at least one process gas 106. For example, the gas supply device 100' might be thegas supply device 100 shown in Fig. 1. Fig. 2 shows a further embodiment of thegas supply device 100'. The gas supply device 100' in Fig. 2 has all the features ofthe gas supply device 100 in Fig. 1. Additionally, the gas supply device 100' inFig. 2 comprises at least one further liquid container 102' with at least onefurther saturated salt solution 104'. Even though Fig. 2 shows only one further Carl Zeiss SMT GmbH 29 liquid container 102' with one further saturated salt solution 104', the gas supply device 100' may comprise multiple further liquid containers 102', each with a further saturated salt solution 104'. Given a temperature T1 T2 (i.e. T1 = T2), the saturated salt solution 104 in the liquid container 102 differs from the further saturated salt solution 104' in the further liquid container 102' in particular in terms of a relative humidity RH1, RH2 and hence in terms of an equilibrium vapour pressure EP1, EP2. For example, the gas supply device 100' is arranged partly outside the vacuum housing 210. Moreover, the gas supply device 100' comprises at least one gas feed line 120, which leads into the housing 210 and opens into a nozzle 132 at its end. The nozzle 132 is, for example, an annular nozzle from which the process gas 106exits in a ring shape and is supplied to the work location 206. Fig. 2 shows, as anexample, such a ring nozzle 132 in schematic cross section. The liquid containers 102, 102' are configured in particular to produce additive gases 106, 106', in particular water vapour, with different vapour pressures EP1, EP2.A further gas feed line 134 is shown in Fig. 2. Although not apparent in Fig. 2,the gas feed line 134 is also connected for gas transfer to a storage container and / or a gas production unit. For example, the further gas feed line 134 is configured to feed etching gas and / or deposition gas. In addition to the gas feed lines 120, 134 shown, the liquid containers 102, 102' shown and the described storage containers and / or gas production units, any additional number of further such components may be provided in order to make available the required process gases, etching gases and deposition gases for the particle beam-induced processing of the photomask 202. Carl Zeiss SMT GmbH 30 In the apparatus 200, an extraction unit (not shown) may additionally be provided in order to extract surplus process gas 106 from the process atmosphere 214, in particular from the surface 226 of the photomask 202. For this purpose, the suction unit comprises, for example, a further pump.There follows a description, with reference to Fig. 3, of a method of particle beam-induced processing of a sample 202 according to an embodiment.In an optional first step S1 of the method, multiple liquid containers 102, 102'(Fig. 2) with in each case a saturated salt solution 104, 104' received therein areprovided. At a given temperature T1, T2(i.e. T1= T2), the multiple salt solutions 104, 104' in the multiple liquid containers 102, 102' have mutually different relative humidities RH1, RH2. In an optional second step S2 of the method, a desired gas flow rate F at the work location 206 of the apparatus 200 is ascertained. In an optional third step S3 of the method, one of the multiple liquid containers 102, 102' with the saturated salt solution 104, 104' received therein is selected on the basis of the ascertained desired gas flow rate F. If optional steps S1 to S3 are carried out, then the subsequent steps S4 and S5 can be carried out with the aid of the liquid container 102, 102' selected in step S3. In a fourth step S4 of the method, a process gas 106, 106' is produced at a surface 108, 108' of a saturated salt solution 104, 104'. In a fifth step S5 of the method, the produced process gas 106, 106' is fed to a work location 206 of the apparatus 200. Carl Zeiss SMT GmbH 31 In a sixth step S6 of the method, an activating particle beam 218 is provided at the work location 206. Moreover, an etching gas or deposition gas may also be provided at the work location 206 in step S6. By way of the proposed gas supply device 100, 100' and the proposed method, the gas flow rate F can be set at least primarily by way of the choice of the saturated salt solution 104, 104'. Hence the set vapour pressure EP1, EP2of the produced process gas 106, 106' and thus the gas flow rate F at the work location 206 of theapparatus 200 for the particle beam-induced processing of the sample202 dependat least primarily only on thermodynamic properties of the saturated salt solution 104, 104'. Hence the gas flow rate F can be set more easily and more accurately. Although the present invention has been described with reference to exemplary embodiments, it is modifiable in a variety of ways.

[0002] Carl Zeiss SMT GmbH 32 LIST OF REFERENCE SIGNS1 Projection exposure apparatus2 Illumination system3 Light source4 Illumination optics unit5 Object field6 Object plane7 Reticle8 Reticle holder9 Reticle displacement drive10 Projection optics unit11 Image field12 Image plane13 Wafer14 Wafer holder15 Wafer displacement drive16 Illumination radiation17 Collector18 Intermediate focal plane19 Deflection mirror20 First facet mirror21 First facet22 Second facet mirror23 Second facet100, 100' Gas supply device102, 102' Container104, 104' Salt solution106, 106' Process gas108, 108' Surface Carl Zeiss SMT GmbH 33110 Reservoir112 Solvent114 Salt116 Water118 Solid120 Feed line122 Ultrasonic unit124 Temperature control unit126 Peltier element128 Orifice plate130 Valve132 Nozzle134 Gas feed line200 Apparatus202 Sample206 Work location210 Vacuum housing214 Process atmosphere216 Particle beam provision device218 Particle beam220 Particle source222 Beam guiding unit224 Beam shaping unit226 Surface228 Detector230 Sample stageEP1, EP2PressureF FlowM1-M6 Mirror Carl Zeiss SMT GmbH 34 RH1, RH2 Relative humidityS1-S6 Method stepT1, T2 Temperature

Claims

Carl Zeiss SMT GmbH 35 CLAIMS1. Gas supply device (100) for an apparatus (200) for particle beam-inducedprocessing of a sample (202), comprising a liquid container (102) with a saturated salt solution (104) received therein for producing a process gas (106) at a surface (108) of the salt solution (104) and a gas feed line (120) connected to the liquid container (102) for gas transfer and serving to feed the produced process gas (106) to a work location (206) of the apparatus (200).

2. Gas supply device according to Claim 1, comprisingat least one further liquid container (102') with at least one further saturated salt solution (104') received therein for producing at least one further process gas (106') at a surface (108') of the at least one further salt solution (104'), wherein the saturated salt solution (104) and the at least one further saturated salt solution (104') comprise mutually different relative humidities (RH1, RH2) at a given temperature (T1, T2), and the at least one further liquid container (102') is connected for gas transfer to the gas feed line (120) and / or at least one further gas feed line, in order to feed the produced further process gas (106') to the work location (206) of the apparatus (200).

3. Gas supply device according to Claim 1 or 2, wherein the saturated saltsolution (104) and / or the at least one further saturated salt solution (104') comprises at least one salt (114) that is dissolved in water (116).

4. Gas supply device according to any of Claims 1 to 3, whereinthe saturated salt solution (104) and / or the at least one further saturated salt solution (104') comprise one or more salts (114), each of which comprises a chemical compound made of an anion and a cation, and / orCarl Zeiss SMT GmbH 36 the saturated salt solution (104) and / or the at least one further saturated salt solution (104') comprise one or more salts (114) from a group comprising: caesium fluoride, calcium chloride, lithium bromide, zinc bromide, potassium hydroxide, sodium hydroxide, lithium chloride, calcium bromide, lithium iodide, potassium fluoride, magnesium chloride, sodium iodide, potassium carbonate, magnesium nitrate, sodium bromide, cobalt chloride, potassium iodide, strontium chloride, sodium nitrate, sodium chloride, potassium bromide, potassium chloride, strontium nitrate, potassium nitrate, potassium sulphate and potassium chromate.

5. Gas supply device according to any of Claims 1 to 4, wherein a freezing pointof the saturated salt solution (104) and / or the at least one further saturated salt solution (104') is at -10°C or lower and / or at -20°C or lower.

6. Gas supply device according to any of Claims 1 to 5, wherein a change in therelative humidity (RH1, RH2) of the saturated salt solution (104) and / or the at least one further saturated salt solution (104') in a temperature range from 0°C to 20°C is 1.5% or less, 1.0% or less, 0.5% or less, 0.2% or less and / or 0.1% or less.

7. Gas supply device according to any of Claims 1 to 6, wherein a relativehumidity (RH1, RH2) of the saturated salt solution (104) and / or the at least one further saturated salt solution (104') at a temperature of 20°C or less is 50% or less, 30% or less and / or 10% or less.

8. Gas supply device according to any of Claims 1 to 6, wherein a relativehumidity (RH1, RH2) of the saturated salt solution (104) and / or further saturated salt solution (104') at a temperature of 20°C or less is 85% or more, 90% or more and / or 95% or more.Carl Zeiss SMT GmbH 379. Gas supply device according to any of Claims 1 to 8, wherein the saturatedsalt solution (104) and / or the at least one further saturated salt solution (104') comprises at least one salt (114) that is dissolved in water (116), and the at least one salt (114) is additionally received as a solid (118) in the liquid container (102) and / or the at least one further liquid container (102').

10. Gas supply device according to any of Claims 1 to 9, comprising an ultrasonicand / or megasonic unit (122) arranged on the liquid container (102) and / or a further ultrasonic and / or megasonic unit arranged on the at least one further liquid container (102'), for exciting ultrasonic vibrations or megasonic vibrations of the liquid container (102) or the further liquid container (102').

11. Gas supply device according to any of Claims 1 to 10, comprising atemperature control unit (124) for setting a temperature (T1) of the saturated salt solution (104) and / or at least one further temperature control unit for setting a temperature (T2) of the at least one further saturated salt solution (104').

12. Gas supply device according to any of Claims 1 to 11, comprisingat least one orifice plate (128) arranged in the gas feed line (120) and / or in the at least one further gas feed line and serving to set a gas flow rate (F) at the work location (206) and / or one or more valves (130) arranged in the gas feed line (120) and / or in the at least one further gas feed line and serving to set a gas flow rate (F) at the work location (206).

13. Apparatus (200) for particle beam-induced processing of a sample (202),having a gas supply device (100, 100') according to any of Claims 1 to 12.

14. Method of particle beam-induced processing of a sample (202), including thefollowing steps:Carl Zeiss SMT GmbH 38 a) producing (S4) a process gas (106) at a surface (108) of a saturated salt solution (104), b) feeding (S5) the produced process gas (106) to a work location (206) of the apparatus (200) and c) providing (S6) an activating particle beam (218) at the work location (206).

15. Method according to Claim 14, includingproviding (S1) multiple liquid containers (102, 102') with in each case a saturated salt solution (104, 104') received therein, wherein the multiple salt solutions (104, 104') in the multiple liquid containers (102, 102') have mutually different relative humidities (RH1, RH2) at a given temperature (T1, T2), ascertaining (S2) a desired gas flow rate (F) at the work location (206) of the apparatus (200), selecting (S3) a liquid container (102) with the saturated salt solution (104) received therein from the multiple liquid containers (102, 102') on the basis of the ascertained desired gas flow rate (F), and carrying out steps a) and b) with the aid of the selected liquid container (102).

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