Source vessel, light source, EUV-utilization system and method for controlling a source material

Abstract

There is provided a source vessel of a laser produced plasma source, the vessel including a collector region, and an intermediate focus (IF) region, wherein the vessel is configured to provide at least two different temperature zones wherein a temperature zone including the IF region is hotter than a temperature zone including the collector region. Also provided is a light source and an EUV-utilization system including such a source vessel. Also described is a method for controlling source material within a source vessel, and the use of such source vessel, light source, or EUV-utilization apparatus, or method in a lithographic method or system.

Description

SOURCE VESSEL. LIGHT SOURCE. EUV-UTILIZATION SYSTEM AND METHOD FOR CONTROLLING A SOURCE MATERIALCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority of US application 63 / 514,469 which was filed on 19-Jul-2023 and which is incorporated herein in its entirety by reference.FIELD

[0002] The present disclosure relates to source vessel of a laser produced plasma source, in particular, but not exclusively, for the generation of EUV light. The source vessel can be used in connection with a EUV utilization apparatus. An EUV utilization apparatus could, for example, be a lithographic apparatus, particularly, but not exclusively, an EUV lithography apparatus to form a lithographic system. The EUV utilization apparatus could also be an inspection apparatus, e.g. a mask inspection apparatus. The present disclosure also relates to a light source for a lithographic system including such a source vessel. In addition, the present disclosure relates to a lithographic system including such a source vessel or light source. Further, the present disclosure relates to a method for controlling a source material within a source vessel. It will be appreciated that such a method also includes controlling source material within a light source and within a lithographic system. The present disclosure also relates to the use of such a source vessel, light source, lithographic system, or method in a lithographic method or system, particularly, but not exclusively in an EUV lithographic method or system.BACKGROUND

[0003] A lithographic apparatus is a machine constructed to apply a desired pattern onto a substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). A lithographic apparatus may, for example, project a pattern at a patterning device (e.g., a mask) onto a layer of radiation-sensitive material (resist) provided on a substrate.

[0004] To project a pattern on a substrate a lithographic apparatus may use electromagnetic radiation. The wavelength of this radiation determines the minimum size of features which can be formed on the substrate. A lithographic apparatus, which uses extreme ultraviolet (EUV) radiation, having a wavelength within the range 4-20 nm, for example 6.7 nm or 13.5 nm, may be used to form smaller features on a substrate than a lithographic apparatus which uses, for example, radiation with a wavelength of 193 nm.

[0005] Methods for generating EUV light include, but are not limited to, altering the physical state of a source material, also known as a target material, to a plasma state. The source materials include a compound or an element, for example, xenon, lithium, or tin, with an emission line in the EUV range.In one such method, often termed laser produced plasma (“LPP”), the required plasma is produced by irradiating a source material, for example, in the form of a droplet, stream, or cluster of source material, with an amplified light beam that can be referred to as a drive laser. For this process, the plasma is typically produced in a sealed vessel, for example, a vacuum chamber, which is typically referred to as a source vessel. Where droplets are used, they are provided via a droplet generator apparatus, which is supplied with high pressure liquid source material.The source material needs to be managed as it can be transferred to other parts of the source vessel, and indeed, other parts of the light source or lithographic system of which it is a component. In some cases portions of the vessel are heated to temperatures higher than the melting point of the source material such that any accumulated source material melts and can be removed. However, the resulting liquid source material can then drip or spit onto sensitive parts of the apparatus, such as the collector, thereby reducing its reflectivity and reducing the efficiency of the lithographic apparatus and lithographic system.SUMMARY

[0006] According to a first aspect there is provided a source vessel of a laser produced plasma source, the vessel including a collector region and an intermediate focus (IF) region, wherein the vessel is configured to provide at least two different temperature zones wherein a temperature zone including the IF region is hotter than a temperature including the collector region.

[0007] Management of source material has been conducted via heating walls of a source vessel to greater than the melting point of the source material in order to melt the source material. Whilst this is effective in removing accumulated source material, there is a risk of the liquid source material dripping or spitting onto optical elements, such as a collector, or other sensitive elements. Another option has been to increase the density of gas within the source vessel in order to limit the distance which the source material can travel through the vessel. Even so, by providing a denser gas, there is greater absorption of any light generated within the source vessel, which is undesirable. According to the present disclosure, there is a spatially dependent gas temperature which optimizes both transmission of light generated, such as EUV light, and also management of source material, such as tin. By keeping the temperature of gas within the vessel at a lower temperature in the area containing the collector, namely the collector region, the degree of ion stopping and hindrance of the source material travelling through the gas is increased. The collector region is sensitive to source material contamination because contamination of the collector will reduce the amount of light being collected and focused by the collector. In addition, there is a greater amount of source material within the collector region since the light is produced from the plasma source, which is the source material, in an area in front of the collector. In the IF region, there is a lower amount of source material and so there is less need to control the distance which source material can travel meaning that the temperature of this region can be higher to increase transmission of light. As such, the pressure of gas, such as hydrogen, within the vessel can besubstantially uniform, but the density of the gas within the at least two different temperature zones is different. Due to the difference in density of gas as a result of the different temperatures in the different regions / zones within the vessel, it is possible to optimize for transmission and control of source material contamination. The collector region and the IF region are the portions on the vessel which surround the collector and IF respectively. Due to the structure of a source vessel, such regions are at opposite ends of the vessel.

[0008] An intermediate region between the collector region and the IF region may be provided. As such, the vessel may be configured to provide a third temperature zone between the temperature zone including the IF region and the temperature zone including the collector region. In this way, the source vessel may include three temperature zones.

[0009] At least one of the at least two temperature zones is provided by one or more of i) supplying a heated gas to the at least one different temperature zone, ii) heating a wall defining the at least one different temperature zone, and iii) heating a component located within the at least one different temperature zone.

[0010] A low pressure gas, preferably hydrogen, is provided within the source vessel and so it is possible to provide zones having different temperatures by providing gas which is at different temperatures. For example, the gas provided to the collector region may be at a low temperature and the gas provided to the intermediate focus may be heated to a higher temperature. Since the different regions are all part of the same vessel, the overall pressure is substantially uniform, but the density of gas is lower at the higher-temperature region(s) and the density of the gas is higher in the cooler region(s). In this way, the balance between transmissivity of the gas and the stopping ability of the gas can be controlled. Another way to provide regions of different temperature is to selectively heat the walls which define a region. In an example, the walls surrounding the collector region may be at ambient temperature, the walls defining an intermediate region may be selectively heated to a temperature higher than that of the collector region, and the wall defining the IF region may be heated to a higher temperature than the intermediate region. Again, this will result in the presence of three zones of different temperature and therefore gas density (since pressure will be substantially uniform across the source vessel, subject to minor fluctuations). Alternatively or additionally, a component which can be heated may be provided within a region in order to control the temperature, and therefore density of the gas within such a region. Since there is a constant flow of gas in the source vessel when in use and since the gas pressure is low, there is insufficient time for the temperature of the gas to become uniform meaning that it is possible to have zones of different temperatures. Given the source material deposition profile observed in use, having a different temperature at the collector as compared to at the intermediate focus can main source material management performance at the same time as increasing light transmission, particularly EUV light transmission.

[0011] The temperature zone including the IF region may be at a temperature of around 180°C or higher, around 190°C or higher, around 200°C or higher, around 210°C or higher, around 220°C or higher, or around 230°C or higher.

[0012] The temperature zone including the collector region may be at a temperature of around 100°C or lower, around 90°C or lower, around 80°C or lower, around 70°C or lower, around 60°C or lower, or around 50°C or lower.

[0013] The Beer-Lambert law can be used to equate the transmission of light through a gas depending on the density of the gas, the absorption cross section of the gas and the path length. As such, by lowering the density of the gas, the transmission can be increased.

[0014] The source vessel may be configured to vary the temperature of the at least two different temperature zones to actively control the density of gas within the at least two different temperature zones. In operation, the source vessel may be operated under different use conditions and so the ability to selectively change the temperature within at least one of the zones of different temperature can accommodate such different use conditions.

[0015] According to a second aspect of the present disclosure, there is provided a light source for an EUV utilization apparatus including the source vessel according to the first aspect of the present disclosure. An example of an EUV utilization apparatus could be an inspection apparatus, or more specifically a mask inspection apparatus. The EUV utilization apparatus could further be a lithographic system including the source vessel according to the first aspect of the present disclosure.

[0016] The light source may additionally include droplet generating apparatus configured to provide droplets of source material to the source vessel. The light source may include one of more lasers to convert source material within the source vessel into a plasma from which light is emitted.

[0017] According to a third aspect of the present disclosure, there is provided an EUV-utilization system including the source vessel according to the first aspect of the present disclosure or the light source according to the second aspect of the present disclosure. The EUV utilization system may be an EUV lithographic system or an inspection apparatus, particularly a mask inspection apparatus.

[0018] According to a fourth aspect of the present disclosure, there is provided a method controlling a source material within a source vessel, the method including providing at least two different temperature zones within the source vessel with a temperature zone including an IF region being hotter than a temperature including a collector region.

[0019] By providing temperature zones of different temperatures, the pressure of gas within the vessel is substantially uniform but the density of gas within the at least two different temperature zones is different. Due to the difference in density, the transmissivity of the gas and the ability of the gas to control movement of source material through the gas can be controlled.

[0020] The method may include providing a third temperature zone between the temperature zone including the IF region and the temperature zone including the collector region. Such a thirdtemperature zone may be provided in an intermediate region between the collector region and the IF region.

[0021] The method may include one or more of i) supplying a heated gas to the at least one different temperature zone, ii) heating a wall defining the at least one different temperature zone, and iii) heating a component located within the at least one different temperature zone in order to provide at least one of the at least two different temperature zones.

[0022] The method may include controlling the temperature of the temperature zone including the IF region to a temperature of around 180°C or higher, around 190°C or higher, around 200°C or higher, around 210°C or higher, around 220°C or higher, or around 230°C or higher.

[0023] The method may include controlling the temperature of the temperature zone including the collector region to a temperature of around 100°C or lower, around 90°C or lower, around 80°C or lower, around 70°C or lower, around 60°C or lower, or around 50°C or lower.

[0024] The method may include varying the temperature of at least one of the at least two different temperature zones to actively control the density of gas within the at least two different temperature zones.

[0025] According to a fifth aspect of the present disclosure, there is provided the use of a source vessel according to the first aspect, a light source according to the second aspect, an EUV utilization system according to the third aspect, or the method according to the fourth aspect of the present disclosure in a lithographic method or system.

[0026] The features described in respect of any of the aspects may be combined with the features described in respect of any of the other aspects of the present invention.

[0027] The present invention will now be described with reference to an EUV lithography apparatus. However, it will be appreciated that the present invention is not limited to EUV lithography and may be suitable for other types of lithography.BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which:Figure 1 depicts a lithographic system comprising a lithographic apparatus and a radiation source;Figure 2 is a schematic depiction of a radiation source showing the different temperature zones; Figures 3a and 3b are schematic images of simulations comparing the EUV absorption within a source vessel having ambient temperature walls (3a) and having heated walls (3b).DETAILED DESCRIPTION

[0029] Figure 1 shows a lithographic system comprising a radiation source SO, which may also be referred to as a light source, and a lithographic apparatus LA. The radiation source SO is configured togenerate an EUV radiation beam B and to supply the EUV radiation beam B to the lithographic apparatus LA. The lithographic apparatus LA comprises an illumination system IL, a support structure MT configured to support a patterning device MA (e.g., a mask), a projection system PS and a substrate table WT configured to support a substrate W. A pellicle 15 may be provided to protect the patterning device MA from contamination.

[0030] The illumination system IL is configured to condition the EUV radiation beam B before the EUV radiation beam B is incident upon the patterning device MA. Thereto, the illumination system IL may include a facetted field mirror device 10 and a facetted pupil mirror device 11. The faceted field mirror device 10 and faceted pupil mirror device 11 together provide the EUV radiation beam B with a desired cross-sectional shape and a desired intensity distribution. The illumination system IL may include other mirrors or devices in addition to, or instead of, the faceted field mirror device 10 and faceted pupil mirror device 11.

[0031] After being thus conditioned, the EUV radiation beam B interacts with the patterning device MA. As a result of this interaction, a patterned EUV radiation beam B’ is generated. The projection system PS is configured to project the patterned EUV radiation beam B’ onto the substrate W. For that purpose, the projection system PS may comprise a plurality of mirrors 13,14 which are configured to project the patterned EUV radiation beam B’ onto the substrate W held by the substrate table WT. The projection system PS may apply a reduction factor to the patterned EUV radiation beam B’, thus forming an image with features that are smaller than corresponding features on the patterning device MA. For example, a reduction factor of 4 or 8 may be applied. Although the projection system PS is illustrated as having only two mirrors 13,14 in Figure 1, the projection system PS may include a different number of mirrors (e.g., six or eight mirrors).

[0032] The substrate W may include previously formed patterns. Where this is the case, the lithographic apparatus LA aligns the image, formed by the patterned EUV radiation beam B’, with a pattern previously formed on the substrate W.

[0033] A relative vacuum, i.e. a small amount of gas (e.g. hydrogen) at a pressure well below atmospheric pressure, may be provided in the radiation source SO, in the illumination system IL, and / or in the projection system PS.

[0034] The radiation source SO shown in Figure 1 is, for example, of a type which may be referred to as a laser produced plasma (LPP) source. A laser system 1, which may, for example, include a CO2 laser, is arranged to deposit energy via a laser beam 2 into a fuel, such as tin (Sn) which is provided from, e.g., a fuel emitter 3. Fuel emitter 3 may be connected to a droplet generator apparatus according to the present disclosure. Although tin is referred to in the following description, any suitable fuel may be used. The fuel is in liquid form, and may, for example, be a metal or alloy. The fuel emitter 3 may comprise a nozzle configured to direct tin, e.g. in the form of droplets, along a trajectory towards a plasma formation region 4. The laser beam 2 is incident upon the tin at the plasma formation region 4. The deposition of laser energy into the tin creates a tin plasma 7 at the plasma formation region 4.Radiation, including EUV radiation, is emitted from the plasma 7 during de-excitation and recombination of electrons with ions of the plasma.

[0035] The EUV radiation from the plasma is collected and focused by a collector 5. Collector 5 comprises, for example, a near-normal incidence radiation collector 5 (sometimes referred to more generally as a normal-incidence radiation collector). The collector 5 may have a multilayer mirror structure which is arranged to reflect EUV radiation (e.g., EUV radiation having a desired wavelength such as 13.5 nm). The collector 5 may have an ellipsoidal configuration, having two focal points. A first one of the focal points may be at the plasma formation region 4, and a second one of the focal points may be at an intermediate focus 6, as discussed below.

[0036] The laser system 1 may be spatially separated from the radiation source SO. Where this is the case, the laser beam 2 may be passed from the laser system 1 to the radiation source SO with the aid of a beam delivery system (not shown) comprising, for example, suitable directing mirrors and / or a beam expander, and / or other optics. The laser system 1, the radiation source SO and the beam delivery system may together be considered to be a radiation system.

[0037] Radiation that is reflected by the collector 5 forms the EUV radiation beam B. The EUV radiation beam B is focused at intermediate focus 6 to form an image at the intermediate focus 6 of the plasma present at the plasma formation region 4. The image at the intermediate focus 6 acts as a virtual radiation source for the illumination system IL. The radiation source SO is arranged such that the intermediate focus 6 is located at or near to an opening 8 in an enclosing structure 9, also referred to as a source vessel, of the radiation source SO.

[0038] Figure 2 is a schematic depiction of a radiation source according to the present disclosure showing the different temperature zones. The region including the collector 5 includes the plasma formation region 4. This region has the highest concentration of source material and so by having this region at the lowest temperature means that the density of the gas within this region is the highest. The higher density of the gas limits the distance which source material can travel and therefore controls the source material within the source vessel 9. As such, a first temperature zone 16 is provided which includes the collector region. As depicted an intermediate region 17 and an intermediate focus (IF) region 18 are provided, although it will be appreciated that the intermediate region 17 is optional. A temperature zone including the IF region 18 is at a higher temperature than the temperature zone including the collector region 16. It will be appreciated that the source vessel will have a substantially uniform pressure of gas, typically hydrogen, therein and the different temperatures will cause the gas in the different regions to have a different density.

[0039] Figure 3a depicts a simulation of the EUV absorption of the gas within a source vessel having ambient temperature walls. Figure 3b depicts a simulation of the EUV absorption of the gas within a source vessel having heated walls. As can be seen, there is greater absorption (shown by a darker colour) adjacent the cool walls of Figure 3a as compared to the simulation in which the walls are heated, as depicted in Figure 3b. Based on such simulations in which the wall is heated by 100°C,there will be a lower absorption of EUV radiation near to the walls when the walls are heated as compared to when the walls are not heated. This results in an increased amount of EUV light being transmitted through the intermediate focus, which could be around 2%, which is a significant increase.

[0040] The use of the source vessel in the present disclosure is not limited to the use with a lithographic system. It can be used with any other EUV utilization apparatus, such as, for example, an inspection apparatus, or, more specifically, a mask inspection apparatus. Such inspection apparatus may be configured to inspect a mask for potential defects. This could be achieved by illuminating the mask by EUV light generated by means of the EUV source vessel. The inspection apparatus may include an illumination system and an optical detection system. The EUV light may be reflected by means of the optical detection system to the mask to be inspected. In this way an image may be formed on a detector. This detector could, for example, be a time-delay integration camera. For the avoidance of doubt an EUV-utilization apparatus is an apparatus which relies on EUV light to achieve a desired effect, whether that be patterning a resist or detecting potential flaws.

[0041] In summary, the present invention provides for a source vessel, light source, lithographic system, and method in which two different temperature zones are provided, with a lower temperature zone being provided in a region containing the collector and a higher temperature zone being provided in a region containing the intermediate focus, such that the pressure of gas therein is substantially uniform, but, due to the differences in temperature between the different regions, the density of the gas is different. A higher density in the region in which the plasma is formed is preferred due to its increased resistance to source material travelling therethrough, and a lower density is preferred elsewhere in order to improve transmission of light. Whilst the pressure could be increased overall, this would decrease the transmission of light and, alternatively, if the pressure were decreased overall, this would increase the likelihood of contamination of sensitive components, such as the collector. This being the case, it has been found that by providing different temperature zones, different characteristics can be optimized in different regions of a source vessel.

[0042] While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. The descriptions above are intended to be illustrative, not limiting. Thus it will be apparent to one skilled in the art that modifications may be made to the invention as described without departing from the scope of the claims set out below.

[0043] The implementations can be further described in the following numbered clauses:1. A source vessel of a laser produced plasma source, the vessel including a collector region, and an intermediate focus (IF) region, wherein the vessel is configured to provide at least two different temperature zones wherein a temperature zone including the IF region is hotter than a temperature zone including the collector region.2. The source vessel according to clause 1, wherein the vessel is configured to provide a third temperature zone between the temperature zone including the IF region and the temperature zone including the collector region.3. The source vessel according to clause 1 or clause 2, wherein at least one of the at least two different temperature zones is provided by one or more of i) supplying a heated gas to the at least one different temperature zone, ii) heating a wall defining the at least one different temperature zone, and iii) heating a component located within the at least one different temperature zone.4. The source vessel according to any preceding clause, wherein the temperature zone including the IF region is at a temperature of around 180°C or higher, around 190°C or higher, around 200°C or higher, around 210°C or higher, around 220°C or higher, or around 230°C or higher.5. The source vessel according to any preceding clause, wherein the temperature zone including the collector region is at a temperature of around 100°C or lower, around 90°C or lower, around 80°C or lower, around 70°C or lower, around 60°C or lower, or around 50°C or lower.6. The source vessel according to any preceding clause, wherein the vessel is configured to vary the temperature of the at least two different temperature zones to actively control the density of gas within the at least two different temperature zones.7. A light source for an EUV-utilization apparatus lithographic system including the source vessel according to any of clauses 1 to 6, optionally wherein the EUV-utilization apparatus is an EUV lithographic system or an inspection apparatus, particularly a mask inspection apparatus.8. A lithographic-utilization system including the source vessel according to any of clauses 1 to 7 or light source according to clause 7, optionally wherein the EUV-utilization apparatus is an EUV lithographic system or an inspection apparatus, particularly a mask inspection apparatus.9. A method for controlling a source material within a source vessel, the method including providing at least two different temperature zones within the source vessel with a temperature zone including an IF region being hotter than a temperature zone including a collector region.10. The method according to clause 9, wherein the method includes providing a third temperature zone between the temperature zone including the IF region and the temperature zone including the collector region.11. The method according to clause 9 or clause 10, wherein the method includes one or more of i) supplying a heated gas to the at least one different temperature zone, ii) heating a wall defining the at least one different temperature zone, and iii) heating a component located within the at least one different temperature zone in order to provide at least one of the at least two different temperature zones.12. The method according to any of clauses 9 to 11, wherein the method includes controlling the temperature of the temperature zone including the IF region to a temperature of around 180°C or higher, around 190°C or higher, around 200°C or higher, around 210°C or higher, around 220°C or higher, or around 230°C or higher.13. The method according to any of clauses 9 to 12, wherein the method includes controlling the temperature of the temperature zone including the collector region to a temperature of around 100°C or lower, around 90°C or lower, around 80°C or lower, around 70°C or lower, around 60°C or lower, or around 50°C or lower. 14. The method according to any of clauses 9 to 13, wherein the method includes varying the temperature of at least one of the at least two different temperature zones to actively control the density of gas within the at least two different temperature zones.15. The use of a source vessel, light source, EUV-utilization system according to any of clause 1 to 8 or a method according to any of clauses 9 to 14 in a lithographic method or system.

[0044] The above-described implementations and other implementations are within the scope of the following claims.

Claims

CLAIMS1. A source vessel of a laser produced plasma source, the vessel including a collector region, and an intermediate focus (IF) region, wherein the vessel is configured to provide at least two different temperature zones wherein a temperature zone including the IF region is hotter than a temperature zone including the collector region.

2. The source vessel according to claim 1, wherein the vessel is configured to provide a third temperature zone between the temperature zone including the IF region and the temperature zone including the collector region.

3. The source vessel according to claim 1 or claim 2, wherein at least one of the at least two different temperature zones is provided by one or more of i) supplying a heated gas to the at least one different temperature zone, ii) heating a wall defining the at least one different temperature zone, and iii) heating a component located within the at least one different temperature zone.

4. The source vessel according to any preceding claim, wherein the temperature zone including the IF region is at a temperature of around 180°C or higher, around 190°C or higher, around 200°C or higher, around 210°C or higher, around 220°C or higher, or around 230°C or higher.

5. The source vessel according to any preceding claim, wherein the temperature zone including the collector region is at a temperature of around 100°C or lower, around 90°C or lower, around 80°C or lower, around 70°C or lower, around 60°C or lower, or around 50°C or lower.

6. The source vessel according to any preceding claim, wherein the vessel is configured to vary the temperature of the at least two different temperature zones to actively control the density of gas within the at least two different temperature zones.

7. A light source for an EUV-utilization apparatus lithographic system including the source vessel according to any of claims 1 to 6, optionally wherein the EUV-utilization apparatus is an EUV lithographic system or an inspection apparatus, particularly a mask inspection apparatus.

8. A lithographic-utilization system including the source vessel according to any of claims 1 to 7 or light source according to claim 7, optionally wherein the EUV-utilization apparatus is an EUV lithographic system or an inspection apparatus, particularly a mask inspection apparatus.

9. A method for controlling a source material within a source vessel, the method including providing at least two different temperature zones within the source vessel with a temperature zone including an IF region being hotter than a temperature zone including a collector region.

10. The method according to claim 9, wherein the method includes providing a third temperature zone between the temperature zone including the IF region and the temperature zone including the collector region.

11. The method according to claim 9 or claim 10, wherein the method includes one or more of i) supplying a heated gas to the at least one different temperature zone, ii) heating a wall defining the at least one different temperature zone, and iii) heating a component located within the at least one different temperature zone in order to provide at least one of the at least two different temperature zones.

12. The method according to any of claims 9 to 11, wherein the method includes controlling the temperature of the temperature zone including the IF region to a temperature of around 180°C or higher, around 190°C or higher, around 200°C or higher, around 210°C or higher, around 220°C or higher, or around 230°C or higher.

13. The method according to any of claims 9 to 12, wherein the method includes controlling the temperature of the temperature zone including the collector region to a temperature of around 100°C or lower, around 90°C or lower, around 80°C or lower, around 70°C or lower, around 60°C or lower, or around 50°C or lower.

14. The method according to any of claims 9 to 13, wherein the method includes varying the temperature of at least one of the at least two different temperature zones to actively control the density of gas within the at least two different temperature zones.

15. The use of a source vessel, light source, EUV-utilization system according to any of claim 1 to 8 or a method according to any of claims 9 to 14 in a lithographic method or system.

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