NL2022156B1 - Plasma source control circuit - Google Patents

Abstract

Methods and systems for controlling plasma sources positioned in vacuum are disclosed. A charged particle exposure system for exposing a target comprises: - a vacuum chamber; - a projection optical column arranged within said vacuum chamber, said projection optical column arranged for projecting eXposure radiation onto said target, - a plasma source arranged within said vacuum chamber, the plasma source comprising a plasma chamber and a power coupling component for coupling power into gas present within said plasma chamber, and an outlet for plasma and/or radicals formed within said plasma chamber, - a power source arranged for supplying power to the power coupling component, said power source arranged outside said vacuum chamber, and - a first match unit arranged within said vacuum chamber and connected to said ower coupling component and to said power source, said first match unit providing impedance match between the power source and the plasma source.

Description

PLASMA SOURCE CONTROL CIRCUIT

TECHNICAL FIELD The invention relates to methods and systems for generation of plasma. In particular, the invention relates to plasma sources positioned in vacuum and to methods and arrangements for controlling these. Further, the invention relates to cooling arrangements for plasma sources.

BACKGROUND In charged particle beam systems a target surface is exposed to one or more charged particle beams directed to and focused on the surface with high accuracy. In charged particle multi-beam lithography systems, structures are formed on the surface with high accuracy and reliability by the interaction of the charged particle beams with a resist on the surface. The pattern formed on the surface is determined by the position of the individual beams on the surface. In charged particle beam inspection systems or electron microscopes samples are analyzed based on the interaction of the charged particle beams with the sample. Therefore, the properties of charged particle beams impinging on the target surface, such as beam position and current, are of high importance. The accuracy and reliability of these properties can be negatively influenced by contamination on surfaces within the system, in particular on surfaces of charged particle optical components.

An arrangement and a method for removing contamination within charged particle beam systems, and a charged particle lithography system comprising such arrangement, is described in US 2015/028223 Al. The arrangement includes a plasma source and a guiding body, the guiding body guiding radicals formed in the plasma source towards an area or volume at which deposited contamination is to be removed.

US 2017/304878 Al describes a method and a system for preventing and/or removing contamination in charged particle beam systems, in particular at charged particle beam transmitting apertures.

Plasma sources are generally controlled by a control circuit including a match circuit for maximizing power delivery from a power source to the plasma load,

minimizing power reflectance and other losses in the transmission line. Such match circuits are configured for matching the load impedance formed by the plasma source to the impedance of the power source powering the plasma source.

US 2013/0249399 Al describes a plasma processing apparatus including a plasma reactor arranged in a vacuum chamber for plasma processing, an RF power source and an RF power transmission unit for providing and transmitting RF signals to the plasma reactor inside the vacuum chamber. The RF power transmission unit includes a transmission line for transmitting RF signals and an outer conductor for shielding the electromagnetic field around the transmission line, in order to avoid the problem of electric discharge when RF signals are transmitted through a vacuum chamber.

Although the methods and arrangements described in US 2015/028223 Al and US 2017/304878 Al enable removal and/or prevention of contamination within charged particle systems, it is desirable to further improve the efficiency and/or the stability of the process. It is an object of the present invention to provide a method and an arrangement enabling improved control and/or efficiency of the plasma generation. Further it is an object of the invention to reduce or minimize thermal influence of a plasma source on other components within a vacuum system.

SUMMARY OF INVENTION According to a first aspect, a charged particle exposure system for exposing a target is provided, the charged particle exposure system comprising: - a vacuum chamber; - a projection optical column arranged within said vacuum chamber, said projection optical column arranged for projecting exposure radiation onto said target; - a plasma source arranged within said vacuum chamber, the plasma source comprising a plasma chamber and a power coupling component for coupling power into a gas present within said plasma chamber, and an outlet for plasma and/or radicals formed within said plasma chamber; - a power source arranged for supplying power to the power coupling component, said power source arranged outside said vacuum chamber; and

- a first match unit arranged within said vacuum chamber and connected to said power coupling component and to said power source, said first match unit providing an impedance match between the power source and the plasma source.

The arrangement according to the present invention has been seen to enable efficient power transmission to the plasma source, even when this is located within the vacuum chamber, at a distance from the walls of the vacuum chamber, as is typically the case when used for removal and/or prevention of contamination as described above. At the same time, drawbacks related to high currents through and/or voltage along the transmission line, as present in the prior art described above, are reduced.

The present invention is particularly suitable for application within systems where the plasma source is located at a distance from the boundary of the vacuum chamber, whereby the transmission line connecting the power source to the plasma source, via the first match unit and an eventual second match unit, extends through vacuum environment. By placing the first match unit within the vacuum chamber, close to the plasma source, the current through the transmission line and/or the voltage over the transmission line may be reduced in comparison to the situation where the matching unit is located completely outside the vacuum chamber. Drawbacks related to the high electrical current through the transmission line, including thermal loads and/or electro-magnetic fields, and/or related to the high voltage, including high electric fields and a risk of discharge, which are particularly disadvantageous within vacuum systems, in particular within charged particle beam systems, have been observed to be overcome or at least reduced.

The first match unit generally comprises components forming part of a resonance circuit comprising resistive, capacitive and inductive components, commonly also referred to as RLC resonance circuit. The plasma source, including the power coupling component, forms part of the RLC resonance circuit.

When the power coupling component 1s realized as an inductive coil (inductively coupled plasma, ICP), the RLC resonance circuit is configured to, while being fed by a relatively low current, enable a relatively high current circulating there through during operation of the plasma source, providing a high power plasma source. The first match unit may be configured to increase the current by somemultiples, for example the current in the RLC resonance circuit may be four to five times higher than the current in the transmission line. Advantages of the arrangement described herein, hence include that the circuit part which is located within vacuum can be operated at high power while supplying a relatively low current.

When the power coupling component is realized as an electrode forming a part of a capacitor (capacitively coupled plasma, CCP), the RLC resonance circuit is configured to provide a high voltage over the plasma source. Hence, in this case, locating the first match unit within the vacuum chamber, at a distance from the vacuum walls, a high voltage over the transmission line can be avoided, while having a high voltage over the capacitor of the plasma source. Thereby, high electrical fields and the chance of discharge along the transmission line can be avoided.

The first match unit is preferably arranged close to the plasma source, minimizing or at least reducing the length of an electrical conductor through which a high current passes, and/or over which a high voltage is present. Heat radiation and/or electromagnetic fields along the transmission line between the power source and the plasma source, in particular along the portion of the transmission line extending through vacuum, is thereby reduced, also for a plasma source operating at high power. Hence the need for cooling the transmission line and/or for providing electromagnetic shielding is eliminated or at least reduced.

The power source is an RF power source, providing an alternating voltage or current having a frequency within the radio frequency spectrum.

The specific gas introduced into the plasma chamber is selected dependent on the intended application of the plasma source. The gas may be oxygen, a gas comprising oxygen, or a gaseous mixture comprising oxygen gas, in particular when the plasma source is applied for removing and/or preventing carbonaceous contamination. Alternatively another gas may be used, for example hydrogen or nitrogen, or a gas comprising hydrogen or nitrogen.

The first match unit is preferably configured for providing said impedance match during standard operating conditions of said plasma source. The standard operating conditions related to the conditions availing while operating the plasma source under standard or pre-set parameters, at least within certain ranges. Typically the RF source has an impedance of 50 Q, whereby the first match unit is arranged toprovide a load impedance, as seen by the RF source, of 50 Q at standard operating conditions. The standard or pre-set parameters may include the inlet gas flow, the specific gas introduced into the plasma source, i.e. the plasma chamber thereof, the pressure at the outlet of the plasma chamber, the frequency of the power source, etc., 5 which in principle are variable. Other parameters are fixed, such as the geometry and materials of the plasma chamber, the geometry and arrangement of the power coupling component with respect to the plasma chamber, etc. The plasma chamber may be formed of quartz. The first match unit generally comprises elements having fixed and/or pre-set reactance. Moving parts, such as an actuator for changing the reactance of a variable capacitor, are thereby avoided within the vacuum chamber. Space requirements are reduced as variable type capacitors, inductors, or resistors generally require more space than non-variable capacitors, inductors or resistors, respectively. An advantage of the present design hence further includes that the circuit part which is located within vacuum requires relatively small volume.

Alternatively or additionally, as long as intended vacuum levels can be maintained, the first match unit may comprise one or more elements having a variable reactance, allowing tuning or adjusting the impedance as seen by the power source.

The first match unit typically comprises capacitors, at least when the power coupling component comprises an inductive coil, as described below. The capacitors are selected such that the impedance of the first match unit and the plasma source, which in operation forms a plasma load, substantially matches the impedance of the power source, in particular under the standard operating conditions.

The capacitors of the first match unit are vacuum compatible, and preferably provide minimal heating. The capacitors are typically of a type having high Q factor and low ESR (equivalent series resistance), such as to be suitable for RF applications and to avoid power losses within the capacitors. Preferably, the capacitors are mounted to oxygen free copper holder electrodes, to which they preferably are soldered via reflow soldering, minimizing contact resistance between the capacitors and the holder electrodes.

The plasma source arrangement further preferably comprises one or more tuning units for tuning or adjusting one or more operating parameters of said plasma source arrangement.

This can be advantageous during start-up of the plasma source arrangement, since prior to plasma ignition the operating conditions of the plasma source differ from the conditions during standard operation.

During start-up, gas flow into the plasma chamber is started and/or the power coupling component is turned on.

Igniting plasma from the gas or species therein, present within the plasma chamber, i.e. exciting the gas into plasma, may be facilitated by tuning or adjusting one or more operating parameters of the plasma source arrangement.

In this manner, the part of the arrangement, in particular the part of the control circuit, which is located within a vacuum environment is not unduly occupied or burdened with components which are to be operated only temporarily.

Alternatively or additionally, the tuning unit may be active during operation of the plasma source, even after plasma ignition, tuning one or more operating parameters in response to fluctuations in plasma conditions, e.g. caused by fluctuations in gas flow into and/or out of the plasma chamber.

The tuning unit can be realized in various ways, as will be described herein below.

One or more of these ways may be combined.

In an embodiment, the tuning unit comprises a second match unit arranged for tuning said impedance match, said second match unit arranged outside said vacuum chamber.

The first match unit and the second match unit are hence located at physically separated locations, and are typically connected by a coaxial cable forming the transmission line.

The first and second match units form a match circuit enabling tuning or adjusting the impedance of the match circuit and the plasma load, the plasma load being formed by the plasma source and the plasma generated therein, to substantially match the impedance of the power source.

The second match unit typically comprises elements having variable reactance.

Preferably at least two elements having variable reactance are provided, such as variable capacitors.

Further, elements having fixed reactance are generally included, such as resistors, capacitors, and inductors.

The second match unit may also comprise an RLC circuit.

Alternatively or additionally, the tuning unit may comprise a frequency controller for controlling a frequency of the power source. Such frequency controller may be part of the power source, e.g. incorporated as a part of the power source. The frequency of the current and voltage through the circuit, comprising the first match unit and the power coupling component, can thereby be tuned. Since the impedances of the elements of the first match unit and of the power coupling component depend on the frequency of the current and/or voltage passing there through, the impedance match between the power source and the plasma load can be tuned by tuning the frequency of the power source.

Alternatively or additionally, the tuning unit may comprise a flow regulator adjusting a gas flow into said plasma source.

According to embodiments, a feedback network is provided for controlling the tuning unit. By the feedback network the variable reactance components of the second match unit and/or the frequency of the power source can be controlled.

In embodiments, the plasma source comprises a plasma chamber and the power coupling component comprises: - a coil arranged adjacent and/or at least partly surrounding said plasma chamber, or - an electrode arranged within said plasma chamber.

When the power coupling component is provided as a coil, the resulting plasma is referred to as inductively coupled plasma (ICP). The coil may also be referred to as inductor or coil antenna. The coil may be arranged at least partly surrounding at least a part of said plasma chamber, and arranged substantially coaxial with the chamber. The plasma source may be a plasma source as described in US 2015/028223 Al.

When the power coupling component is provided as an electrode, this electrode forms one of the electrodes of a capacitor, and the plasma is referred to as capacitive coupled plasma. A ground electrode and/or component connected to electrical ground may form the other electrode of the capacitor.

In embodiments, the vacuum chamber comprises a main frame having a substantially fixed position within said vacuum chamber and a sub-frame coupled to said main frame via a vibration damping arrangement, wherein said plasma source and said first match unit are supported by said sub-frame. This enables positioningthe plasma chamber in a vibrationally decoupled part of the vacuum system. The sub-frame may be suspended from the main frame or supported on the main frame via vibrational mounts, preventing transmission of vibrations from the main frame to the sub-frame. In this embodiment, the charged particle beam system may comprise a charged particle optical column which is supported by the sub-frame. By supporting the plasma chamber by the sub-frame, for example mounting it within the sub-frame, it can be arranged close to one or more charged particle optical elements or other components of the charged particle optical column. Thereby a cleaning agent, such as oxygen radicals, formed in the plasma chamber can be guided toward these elements or components for removing and/or prevent accumulation of contaminants on these.

In embodiments, said plasma source arrangement is arranged for removal of contamination from and/or prevention of contamination on one or more components comprised in said charged particle exposure system.

The various alternatives and embodiments described above may be combined.

According to a second aspect a vacuum system is provided, comprising: - a vacuum chamber; and - a plasma source arrangement, said plasma source arrangement comprising: - a plasma source arranged within said vacuum chamber, the plasma source comprising a power coupling component for coupling power into a gas present within said plasma source; - a power source arranged for supplying power to the power coupling component, said power source arranged outside said vacuum chamber; and - a first match unit arranged for providing an impedance match between said power source and a plasma load formed by said plasma source when in operation, wherein said first match unit is arranged within said vacuum chamber.

The vacuum system according to the second aspect may be combined with any one or more of the embodiments and alternatives described above with relation to the first aspect, achieving corresponding technical effects and advantages. The vacuum system may comprise a charged particle beam exposure system, for example a charged particle exposure system as described above, or parts of such exposuresystem. In particular, the plasma source is arranged at a distance from the walls of the vacuum chamber.

According to a third aspect a plasma source arrangement is provided, in particular for use in the charged particle exposure system of the first aspect or the vacuum system of the second aspect, the plasma source arrangement comprising: - a plasma chamber having an inlet for introducing a gas into said plasma chamber and an outlet for plasma and/or radicals formed within said plasma chamber; - a power coupling component for coupling power into said gas when present within said plasma chamber; - a power source arranged for supplying power to the power coupling component; - a first match unit arranged for providing an impedance match between said power source and said plasma source; - a tuning unit for adjusting one or more parameters of said plasma source arrangement, wherein said tuning unit comprises a second match unit arranged for tuning said impedance match; wherein said first match unit and said tuning unit are configured to be arranged at physically separated locations, and wherein said plasma chamber, said power coupling component, and said first match unit are configured as vacuum compatible components.

The first match unit and the second match unit are advantageously arranged to be displaceable with respect to one another. Thereby, the first match unit and the plasma source may be arranged vibrationally decoupled from the second match unit and the power source, as described above. The first match unit and the second match unit may be first and second match units as described above. The arrangement of the third aspect may be combined with one or more of the embodiments of the exposure system and/or vacuum system described above.

The first match unit and the plasma chamber may be mounted to a common support.

The plasma source preferably comprises an outlet tube connected to said outlet for directing said plasma and/or radicals to an element.

According to a fourth aspect, the plasma source arrangement according to the third aspect is used for removal and/or prevention of contamination on an optical or charged particle optical element.

According to a fifth aspect a method for operating a plasma source arrangement is provided, the plasma source arrangement comprising: - a plasma chamber having an inlet for introducing gas into said plasma chamber; -a power coupling component for coupling power into said gas present within said plasma chamber; - a power source arranged for supplying power to the power coupling component; - a first match unit arranged for providing an impedance match between said power source and a plasma load formed by said plasma chamber and said power coupling component during operation; - a tuning unit for tuning one or more parameters of said plasma source arrangement, wherein said tuning unit comprises a second match unit arranged for tuning said impedance match, wherein said first match unit and said second match unit are arranged at physically separated locations; the method comprising the steps of: - configuring said first match unit to provide substantially impedance match between said plasma source and said power source during standard operating conditions of said plasma source; - introducing one or more gases into said plasma chamber; - powering the power coupling component using said power source; - igniting a plasma in said plasma chamber by operating said tuning unit to tune one or more parameters of said plasma source arrangement, wherein said tuning one or more parameters comprises tuning one or more reactance values of said second match unit; - after igniting said plasma, maintaining a substantially constant gas flow into said plasma chamber according to said standard operating conditions.

The method may be performed using the vacuum system, the charged particle exposure system, and/or the plasma source described above. The method may be applied for removal and/or prevention of accumulation of contamination of one or more elements located along or within a charged particle beam path, such as an element having one or more current limiting apertures.

As described above, the operating conditions of the plasma source arrangement, such as the impedance of the plasma load, during start-up of the plasma source arrangement generally differ from the standard operating conditions. The geometry and the materials of the plasma chamber and the power coupling component being fixed and determined, and the flow rate of the one or more inlet gases being set to a standard value under standard operating conditions, together with the one or more gases being used, may represent standard operating conditions of the plasma source.

By operating the tuning unit to tune one or more operating parameters, impedance matching can be substantially achieved also during start-up, or activation, of the plasma source arrangement, and/or during fluctuations of operating conditions of the plasma source.

According to a sixth aspect, an exposure system for exposing a target is provided, said exposure system comprising: - a vacuum chamber; - a projection optical column arranged within said vacuum chamber, said projection optical column arranged for projecting exposure radiation onto said target; - a plasma source arrangement comprising: - a plasma chamber and a power coupling component for coupling power into a gas or gaseous mixture present within said plasma chamber; - a first match unit connected to said power coupling component; - a shield element arranged between the plasma chamber and the first match unit; - an outlet for one or more species from said plasma chamber; and - a heat conductive base arranged for receiving thermal energy from the plasma chamber, wherein said shield element is in thermal contact with saidheat conductive base and wherein the plasma chamber, the power coupling component, and/or the first match unit is supported by the heat conductive base; wherein said plasma source arrangement is arranged within said vacuum chamber, and wherein said plasma source arrangement is arranged such that species formed or generated in said plasma chamber can be directed into said projection optical column via said outlet.

Plasma generation is associated with the generation of heat in the plasma chamber and its associated power coupling component, such as an inductive coil.

When the components of the match circuit are arranged remote from the plasma source, as is conventionally the case, heat radiation from the plasma source does not influence the components of the match circuit. However, in the various aspects described above, the first match unit is arranged close to the power coupling component and the plasma chamber. Since the first match unit comprises electrical components, such as capacitors, which may degrade and/or loose performance if being subject to heat load, it is desirable to limit or minimize such heat load.

The shield element, sometimes also referred to as thermal shield element, is arranged between the plasma chamber and the first match unit to shield the first match unit from thermal radiation from the plasma chamber and/or the power coupling component. Thereby, the risk of damage or degradation of the first match unit due to thermal energy from the plasma source is reduced. Alternatively and/or additionally, the shield element may be arranged for shielding electromagnetic fields.

The thermal contact between the shield element and the heat conductive base enables thermal energy to be transferred, e.g. by thermal conductance, from the shield element to the heat conductive base. The shield element may be connected to the heat conductive base or may be formed monolithic with said heat conductive base.

Since the heat conductive base supports the plasma chamber, the power coupling component and/or the first match unit, the heat conductive base may receive thermal energy from the plasma chamber and/or the power coupling component, via thermal radiation and/or thermal conduction. The plasma chamber, the powercoupling component, and/or the first match unit may be fixedly or removably mounted or fastened to the heat conductive bas, directly or indirectly. The exposure system may form part of a charged particle exposure system according to the first aspect.

The projection optical column generally comprises charged particle optical elements for generating and projecting multiple charged particle beams onto the target, for example for exposing a pattern in accordance with pattern data. The plasma source arrangement, in particular the outlet thereof, may be arranged to direct species toward one or more of these elements.

The exposure system may further comprise a main frame having a substantially fixed position within said vacuum chamber and a sub-frame supporting said projection optical column and said plasma source, wherein said sub-frame is coupled to said main frame via a vibration damping arrangement.

As described with respect to the charged particle exposure system of the first aspect, this enables the plasma source arrangement to be vibrationally decoupled from the main frame, thereby preventing or at least reducing transmission of vibrations from the main frame to the plasma source.

In an embodiment, the exposure system further comprises a target holder for holding said target, wherein said plasma source arrangement is arranged in a portion of said projection optical column or said sub-frame facing said target. Such location can be used, e.g., when the plasma source arrangement is used for directing radicals and/or other species formed in the plasma chamber onto elements within the projection optical column.

The heat conductive base is advantageously provided with one or more base channels for passage of a fluid, such as a cooling fluid. Such cooling fluid absorbs thermal energy from the heat conductive base and transports this away from the heat conductive base. An example of cooling fluid is water, in particular ultra-pure water which is commonly used in cooling circuits in semiconductor fabs.

Preferably, any bends of said one or more base channels have a substantially continuous shape. This can be achieved by forming the one or more base channels from tubes which are mold or casted inside a solid material forming said base.

Avoiding sharp or abrupt bends reduce vibrations caused by the fluid flowing through the channels.

Also, the flow rate of cooling fluid can be reduced.

In some applications, the plasma source arrangement is positioned in a charged particle exposure apparatus, for example according to the first aspect, and/or the exposure system if the sixth aspect may be a charged particle beam exposure system, where the exposure radiation comprises charged particle beams, such as electron beams.

In such apparatus electromagnetic fields, such as external magnetic fields and/or magnetic fields generated by the plasma source, may cause disturbance to charged particle beam trajectories and/or to the electro-magnetic field provided by charged particle optical elements.

Magnetic fields generated by the plasma source may be shielded by providing the plasma source arrangement with a housing comprising (further described below) a material providing high frequency magnetic shielding.

The heat conductive base may also comprise such material.

The housing at least partly encloses the plasma source and the first match unit.

The heat conductive base and the housing may be formed of for example aluminum, which provides a magnetic shielding effect.

In order to avoid disturbances from external magnetic fields, the heat conductive base may comprise or be provided with a magnetic shielding material, for example u-metal.

The shield element comprises a metal or a ceramic material.

The specific material is selected taking into account the electrical and thermal properties of the material, as well as its machining properties and the geometry of the shield element.

The first match unit may be mounted to the heat conductive base.

Alternatively, the first match unit may be mounted to the shield element.

The heat conductive base is generally electrically conducting, whereby the first match unit is mounted thereto via an insulating member.

Preferably, when mounted on the heat conductive base, the components of the first match unit are mounted at a distance from the shield element.

In embodiments, the first surface of the shield element is reflective to thermal radiation, whereby heat radiated from the plasma source is at least partly reflected, in a direction away from the first match unit.

In this embodiment the heat conductive base, and, if present, a housing surrounding the plasma source, are not thermally reflective, but arranged to receive the thermal radiation reflected from the firstsurface of the shield element. Thereby, thermal radiation can be prevented from reaching the first match unit.

Alternatively, the first surface of the shield element is arranged to absorb thermal radiation. In this embodiment, the first match unit at a distance from the second surface of the shield element. Thereby, and due to the thermal connection with the heat conductive base, heating of the first match unit is prevented.

In an embodiment, the heat conductive base is arranged for absorbing thermal radiation from the plasma chamber and/or the power coupling component.

In an embodiment, the power coupling component comprises a coil arranged adjacent and/or at least partly surrounding said plasma chamber. The coil may be provided with a coil channel for passage of a fluid, such as a cooling fluid as described above. The coil channel may be connected to the one or more base channels, forming a cooling circuit therewith.

In embodiments, cooling tubes may be arranged at least partly enclosing said plasma chamber and said power coupling component. The cooling tubes may be arranged to define one or more planes.

In further embodiments, the arrangement comprises a housing at least partly enclosing said cooling tubes and said plasma chamber. The cooling tubes may be arranged within the walls of the housing. The plasma source arrangement is thereby provided in the form of an at least partly closed housing, whose outer surfaces do not reach excessive temperatures. The housing may be formed of an electrically insulating material, such as alumina. Alternatively, the housing may be formed of aluminum, which, as described above, provides high frequency magnetic shielding.

In an embodiment, the housing is arranged for absorbing thermal radiation from the plasma chamber and/or the power coupling component. As described above, this prevents thermal radiation from being transmitted, e.g. by reflectance, to the first match unit.

In addition to the channels for cooling fluid described above, the shield element may comprise a shield channel arranged for passage of a fluid. The shield channel may be provided at least partially within said shield element.

One or more of the base channels, the coil channel, the cooling tubes, and the shield channel may be connected with one another, forming one or more coolingfluid circuits. The channels are preferably formed by a material which is not sensitive to corrosion. For example, they may comprise and/or be coated with titanium, or a material comprising titanium.

The exposure system according to the sixth aspect and the various features thereof is advantageously used in the systems, arrangements and methods of the aspects described above.

According to a seventh aspect, a plasma source arrangement for generating plasma is provided, the plasma source arrangement comprising: - a plasma chamber having an inlet for introducing gas into said plasma chamber; -a power coupling component for coupling power from a power source into said gas when present in said plasma chamber; - a first match unit connected to said power coupling component; - a shield element arranged between the plasma chamber and the first match unit for shielding the first match unit from thermal radiation from the plasma chamber and/or the power coupling component, said shield element comprising a first surface and a second surface, said first surface facing said plasma chamber and said power coupling component, and said second surface facing said first match unit; and - a heat conductive base; wherein said shield element is in thermal contact with said heat conductive base and wherein the plasma chamber, the power coupling component, and/or the first match unit is supported by the heat conductive base.

The plasma source arrangement according to the seventh aspect preferably forms a module or unit. It may form the plasma source arrangement in the exposure system of the sixth aspect.

According to an eighth aspect, a vacuum system is provided, comprising: - a vacuum chamber; and - a plasma source arrangement according to the seventh aspect arranged within said vacuum chamber.

The various aspects described above, as well as the different features, embodiments and alternatives thereof, may be combined. The embodiments of anyone of the aspects described above may be combined or applied in any other one of the other aspects described above. Hereinafter, embodiments of the invention will be described in further detail. It should be appreciated, however, that these embodiments should not be construed as limiting the scope of protection for the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS Various aspects of the disclosure will be further explained with reference to embodiments shown in the drawings wherein: FIG. 1 schematically shows a vacuum system comprising a plasma source arrangement according to an embodiment; FIG. 2 shows a schematic representation of an electrical circuit for a plasma source arrangement according to an embodiment; FIG. 3a and 3b schematically illustrate a part of a plasma source arrangement including a cooling arrangement; and FIG. 4 shows a further detail of the plasma source arrangement of FIG. 3a and 3b.

DESCRIPTION OF EMBODIMENTS Various embodiments of charged particle beam systems including a plasma source arrangement provided with an impedance matching arrangement, as well as methods of operating such plasma source arrangement are described below, given by way of example only and with reference to the figures.

FIG. 1 shows a vacuum system 1 comprising a vacuum chamber 2 in which a plasma source 4 is arranged. The plasma source 4 comprises a plasma chamber 6 and an inductive coil 8, forming a power coupling component, surrounding at least a part of the plasma chamber and arranged substantially coaxial there with. The plasma chamber 6 is provided with an inlet 7 for introducing one or more gases into the plasma chamber. The inlet is connected to a gas supply (not illustrated) located outside the vacuum chamber. The outlet 5 of the plasma chamber is directed towardone or more elements located within the vacuum chamber. One or more vacuum pumps (not illustrated) are provided for creating and maintaining a vacuum in the vacuum chamber. The coil 8 is powered by an RF power source 10 providing a radio frequency (RF) voltage or current for powering the plasma source. Plasma can be generated within the plasma source 4 by introducing one or more gases into the plasma chamber 6 and supplying power to the coil 8 by the power source 10. When the coil 8 is properly energized, one or more gases present in the plasma chamber 6 are energized to form plasma. Species emitted from the plasma chamber 6 via the outlet 5 can be used for various types of processing within the vacuum chamber 2.

A match circuit 12 is connected between the RF power source 10 and the coil

8. The match circuit 12 is configured for minimizing power reflection within the circuit, maximizing power transmission from the power source 10 to the plasma source 4.

Since the plasma source 4 is arranged at some distance from the walls of the vacuum chamber 2 the transmission line 14 connecting the power source 10 to the inductive coil 8 extends partly within the vacuum chamber 2. As described above, heat load and/or electromagnetic fields associated with the RF voltage and current transmitted through the transmission line are undesirable in certain applications. In order to address these problems the match circuit 12 is divided into a first match unit 16 positioned within the vacuum chamber 2 and a second match unit 18 located outside the vacuum chamber 2. The first match unit 16 is advantageously mounted to a common support with the plasma chamber 6, minimizing the distance, and hence the length of electrical connections, between the first match unit and the coil. As described above and further herein below, the first match unit 16 and the coil 8 form a resonance circuit, through which a high current circulates and/or which enables applying a high voltage across the power coupling component. It has been observed that the drawbacks and disadvantages described above are overcome or at least reduced to an acceptable level by providing at least a part of the match circuit within the vacuum chamber, close to the plasma source.

The first match unit 16 generally comprises elements having fixed reactance values, providing coarse tuning of the match circuit 12. The first match unit 16provides an approximate impedance match between the RF power source 10 and the plasma load under standard operating conditions, as described above.

The second match unit 18 comprises adjustable components, as well as components having fixed reactance, and can be seen as enabling a fine tuning, or adjustment, of the match circuit 12. By tuning the second match unit 18, impedance matching between the RF power source 10 and a circuit 12° (see FIG. 2), formed by the match circuit 12 and the coil 8, can be achieved also during operating conditions deviating from the standard operating conditions, in particular during ignition of plasma.

Hereby, the input impedance of the load, as seen from the RF power source 10, can be tuned to match the impedance of the RF power source 10. The variable components of the second match unit 18 are preferably controlled by an electrical feedback network (not illustrated). Alternative to the second match unit 18, or in addition thereto, a frequency controller may be provided, for tuning the frequency of the power signal generated by the RF power source, thereby adjusting the impedance match between the power source and the load.

Further alternatively or additionally, the tuning unit may comprise a flow regulator adjusting a gas flow into the plasma chamber 6 via the one or more inlets 7, for example by controlling a gas supply control valve.

Alternative to the coil 8, the power coupling component may be provided by an electrode, as described above.

The system of FIG. 1 further comprises a sub-frame 22 suspended from a main frame 24 via pendulums 26, providing vibration isolation of the sub-frame 22. The main frame 24 has a substantially fixed position within the vacuum chamber, and is arranged to carry the weight of the sub-frame 22 as well as any components arranged within or supported by the sub-frame 22. Examples of such vibration isolated systems are described in US 2014/0197330. Alternatively, the sub-frame 22 may be mounted to the main frame 24 via vibration damping mounts.

The plasma source 4, including the first match unit 16, is supported by, in particular mounted in, the sub-frame 22 and thereby vibration isolated from the environment.

The plasma source is thereby statically arranged with respect to components arranged within or supported by the sub-frame 22, such as charged particle optical elements.

The plasma source arrangement described herein is particularly useful for charged particle multi-beam systems such as lithography systems or inspection systems. In these systems the plasma source arrangement finds use in prevention of accumulation of contamination on charged particle optical elements, in particular at current limiting apertures of such elements. In such applications the inlet gas advantageously comprises oxygen (O;}, resulting in the creation of oxygen radicals (O") in the plasma source. Alternatively, a hydrogen or nitrogen comprising gas may be used. In the illustrated embodiment, the vacuum system 1 comprises a charged particle beam optical column 30, also referred to as projection optical column, which is supported by the sub-frame 22. The charged particle beam system may for example be a multi-beam lithography system, an inspection system, and/or an electron microscope. The charged particle optical column 30 generally comprises, among other components, a beam generator 34 for generating a charged particle beam 36, a lens 38 for collimating the charged particle beam, an aperture array 40 for splitting the charged particle beam 36 into a plurality of charged particle beamlets 36a, a blanker array 42 for controlling individual charged particle beamlets 36a, 36b, a beam stop array 44 for blocking beamlets 36b which are deflected by the blanker array, and a projection lens array 46 for focusing beamlets 36a passing through the beam stop array on the surface of the target 32. A control unit (not illustrated) is provided for controlling the components of the charged particle optical column. The charged particle optical column 30 may be a charged particle optical column as described in more detail in U.S. patents 6,897,458; 6, 958,804; 7,019,908;

7.084,414; 7,129,502; 7,709,815; 7,842,936; 8,089,056 and 8,254,484; and in U.S. patent application publications 2007/0064213; 2009/0261267, 2011/0073782 and 2012/0091358, assigned to the applicant of the present application and hereby incorporated by reference in their entirety. At least some of the arrays, for example the beam stop array 44, form current limiting apertures blocking at least a part of the charged particle beam 36 or beamlets 36a, 36b. Current limiting apertures have been seen to be prone to contamination. In the illustrated embodiment, the outlet 5 of the plasma source is arranged to directspecies formed in the plasma source 4 towards the beam stop array 44 for preventing accumulation of contamination thereon. FIG. 2 presents a schematic representation of an electrical circuit 12° for controlling the plasma source 4 of the system illustrated in FIG. 1, where the power coupling component is provided in the form of an inductive coil 8. If the power coupling component 1s provided by a capacitor electrode, the electrical circuit will be realized differently, while applying the principle of dividing the match unit into two parts.

The dashed line 2° schematically indicates the location of the vacuum boundary provided by the vacuum chamber 2. The part of the circuit located to the right of the line 2” 1s located within vacuum, while the part to the left of 2’ is located outside vacuum.

The circuit 12° comprises both the match circuit 12 and the coil 8 of FIG. 1.

The coil 8 and the first match unit 16 form the circuit part indicated by reference number 17. The circuit part 17 comprises the first match unit 16, here represented by a first capacitor C1 and a second capacitor C2, and the inductance 8’, representing both the ideal representation of the inductance coil 8 and a deviation, or disturbance, from the ideal coil. The inductance 8’ encompasses a plasma load formed by the inductance of the inductive coil 8, the plasma chamber 6 as well as any gas and/or plasma present in the plasma chamber 6. The impedance of the plasma load is influenced by the properties of the power coupling component, the geometry of the plasma chamber 6 and its inlets 7 and outlets 5, as well as the operating parameters of the plasma source 4. The operating parameters comprise the frequency of the signal generated by the power source, the pressure and temperature within the plasma chamber 6, the inlet gas flow and the outlet gas flow, the properties of the inlet 7 and outlet 5, the pressure at the outlet 5, etc.

The power source 10 has internal impedance RI, generally 50 ©. As described above, the circuit 12’, including the first and second match units 16, 18, is arranged for providing impedance matching between the power source 10 and the plasma load, by bringing the impedance of the circuit 12° to substantially match the impedance of the power source 10.

In the embodiment illustrated in FIG. 2 the reactance elements of the first match unit, included in the circuit portion 17, are provided by two capacitors C1, C2. The capacitor C1 is connected in series with the coil 8’, and the capacitor C2 is connected in parallel with the capacitor C1 and the coil 8’. Furthermore, one or more resistors (not illustrated) may be provided. As discussed above, these reactance elements are selected such that under standard operating conditions of the plasma source the input impedance of the circuit portion 17 and the transmission line 14 is substantially matched or at least close to the impedance of the power source 10. The circuit portion 17, in particular the capacitors C1, C2, is designed such that at the specific frequency of the signal supplied by the power source 10, a high current circulates there through, whereby the plasma source 4 operates at high power.

The second match unit 18 is arranged at a distance from the plasma source 4, and connected thereto by the transmission line 14. The second match unit 18 enables tuning the impedance of the match circuit 12, for example for reaching plasma ignition. To this end, the second match unit 18 comprises variable reactance elements, in the embodiment provided by two variable capacitors C3, C4, generally controlled via an automatic feedback network (not illustrated) included in or connected to the second match unit 18. In addition to the variable capacitors C3, C4, the second match unit 18 comprises fixed reactance elements, represented by fixed capacitances C5 and C6 and fixed inductance L1. Furthermore, one or more resistors (not illustrated) may be provided.

The plasma source arrangement described with reference to FIG. 1 and 2 is advantageously operated as follows. The first match unit is configured, i.e. designed, to substantially provide impedance matching between the plasma source 4 and the power source 10 during standard operating conditions of the plasma source. Since the standard operating conditions are generally known, and the geometries of the plasma chamber 6 and the coil 8 are fixed, impedance matching is achieved by the selection of the capacitors C1, C2.

One or more gases are introduced into the plasma chamber and power is supplied to the power coupling component, e.g. the coil 8, using the power source 10. By opening one or more supply valves or similar, provided between the gas supplyand the inlet 7, gas starts flowing in to the plasma chamber 6. During this phase, when the gas in the plasma chamber has not yet been excited into plasma and/or has not reached the standard operating pressure, the operating conditions and hence the impedance of the power coupling component differ from the operating conditions which prevail once plasma has been ignited. The impedance of the circuit formed by the power coupling component, the first match unit 16, and the transmission line 14 may not sufficiently match the impedance of the power source 10 to provide sufficient power transmission from the power source 10 to the power coupling component to excite the gas into plasma. Therefore, a tuning unit, provided by one or more of the second match unit 18, an RF power source frequency controller, and a flow rate controller described above, is operated to tune one or more operating parameters of the plasma source arrangement to excite gas present in the plasma chamber into plasma state. Such tuning may be performed manually or preferably with an electrical feedback circuit. As described above, when the tuning unit comprises a second match unit 18, its variable capacitors C3, C4 are adjusted or tuned such as to reach impedance match and ignite plasma.

Once plasma has been achieved, the plasma generation in the chamber is maintained by operating the plasma source arrangement under standard operating conditions. Eventual fluctuations in the plasma conditions during operation of the plasma source arrangement may be compensated for by operating the tuning unit, preferably under control of the electrical feedback circuit or network.

FIG. 3a shows a perspective view of a portion of a plasma source arrangement 46, which forms a module or unit. FIG. 3b shows a cut-through view thereof. FIG. 4 shows the plasma source arrangement of FIG. 3a, 3b provided with a housing 60. The plasma source arrangement 46 may correspond to the plasma source arrangement described with reference to FIG. 1 and 2. FIG. 3a, 3b and 4 show the components thereof which are arranged in vacuum. In particular cooling arrangements of the plasma source arrangement are shown.

The plasma source arrangement 46 comprises the plasma chamber 6 having an inlet 7 and outlets 5, and an inductive coil 8. The plasma source arrangement 46 further comprises a first match unit 16 configured, as described above, to provide anat least approximate impedance match between the power source and the plasma load formed by the plasma chamber 6, the gas present therein and the coil 8. The first match unit 16, the plasma chamber 6 and the coil 8 are supported by a heat conductive base 50. The first match unit 16 is arranged close to the plasma chamber 6 and the coil 8. In order to avoid heat generated by the plasma source to cause damage or degradation of the capacitors of the first match unit 16 a shield element 48 is arranged between the plasma chamber 6 and the first match unit 16, shielding the first match unit 16 from the heat generated in the plasma chamber 6 and/or by the coil 8. The shield element 48 comprises a plate having a first surface 48a facing the plasma chamber 6 and the coil 8, and a second surface facing the first match unit 16. The first surface 48a may be heat reflective, such that heat radiation from the plasma source is at least partly reflected by the shield element 48. The reflected heat radiation is absorbed by the heat conductive base 50 and/or the housing 60 (see Fig. 4), which are actively cooled via the conduits 56, 58.

Alternatively, as discussed above, the first surface 48a of the shield element 48 may not be heat reflective, but rather arranged to absorb the radiated heat. In this case it is advantageous if the first match unit is mounted to the base 50, such that there is a gap between the first match unit 16 and the second surface 48b.

Heat load on the first match unit 16 is further prevented or at least reduced by the heat conductive base 50, which is in thermal contact with the shield element 48 to allow thermal energy to be conducted from the shield element to the heat conductive base. The heat conductive base 50 further may absorb thermal energy from the plasma chamber and/or the coil.

In the illustrated embodiment, the first match unit 16 is mounted to the base 50 via an electrically insulating member 52, to avoid electrical contact between the base and the first match unit.

The plasma source arrangement 46 further comprises a cooling arrangement for circulation of a cooling fluid removing heat from the plasma source arrangement, and a heat exchanger (not illustrated) for removing heat from the cooling fluid. The cooling arrangement is provided by channels for passage of the cooling fluid, as shown in FIG. 3a, 3b and 4. The coil 8 is provided with a coil channel 54 and thebase 50 is provided with one or more base channels 56, the channels 54, 56 forming part of the cooling arrangement.

As illustrated in FIG. 4, the heat conductive base 50 is provided with one or more base channels 56, enabling active cooling of the heat conductive base. The one or more base channels 56 may be connected with the coil channel 54, forming a common cooling circuit therewith. Further, cooling tubes 58 are arranged at least partly enclosing the plasma chamber 6 and the coil 8, providing a cooling circuit at least partly surrounding the plasma source. The cooling tubes 58 are provided within walls of a housing 60 at least partly enclosing the plasma source. The heat conductive base 50 may form part of the housing. By the cooling fluid the housing has a limited temperature on its outer surface, which enables mounting the plasma source arrangement adjacent various components or elements without exposing these to heat generated within the plasma source arrangement.

In the embodiment illustrated in FIG. 3a and 3b, the outlet region of the plasma chamber 6 comprises an inclined tube part connecting the outlets 5 to the plasma chamber 6. The invention is however not limited to this geometry, but also encompasses other shapes, such as a straight tube section, a shorter tube section, a straight or inclined funnel shaped conduit, etc. The specific geometry of the outlet region is selected based on the location in which the plasma source is to be arranged and the specifics thereof, such as the space available and the location of one or more elements towards which species from the plasma source are to be directed.

In the system illustrated in FIG. 1, the plasma source is arranged in the vicinity of charged particle optical elements and charged particle beam trajectories, and relatively close to the target 32 to be exposed by the charged particles. In such applications it is important not to introduce disturbances to the electromagnetic fields provided by the charged particle optical elements and the charged particle beam trajectories. In order to avoid disturbances to the charged particle beam system, in particular to the charged particle beam trajectories, by magnetic fields, the heat conductive base 50 may comprise or be coated with a material providing magnetic shielding, and/or the heat conductive base and the housing may comprise or be formed of a material providing (high-frequency) magnetic shielding.

The system and method of the present invention have been described by reference to certain embodiments discussed above.

These embodiments are susceptible to various modifications and alternative forms without departing from the scope of protection defined in the appended claims.

CLAUSES SET 1

1. Charged particle exposure system for exposing a target, the charged particle exposure system comprising: - a vacuum chamber (1); - a projection optical column (30) arranged within said vacuum chamber, said projection optical column arranged for projecting exposure radiation (36a) onto said target; - a plasma source (4) arranged within said vacuum chamber, the plasma source comprising a plasma chamber (6) and a power coupling component (8) for coupling power into a gas present within said plasma chamber, and an outlet (5) for plasma and/or radicals formed within said plasma chamber; - a power source (10) arranged for supplying power to the power coupling component (8), said power source arranged outside said vacuum chamber; and - a first match unit (16) arranged within said vacuum chamber and connected to said power coupling component (8) and to said power source (10), said first match unit providing an impedance match between the power source and the plasma source.

2. Charged particle exposure system according to clause 1, wherein said vacuum chamber comprises a main frame (24) having a substantially fixed position within said vacuum chamber and a sub-frame (22) coupled to said main frame via a vibration damping arrangement, wherein said projection optical column, said plasma source and said first match unit are supported by said sub-frame.

3. Charged particle exposure system according to any one of the preceding clauses, wherein said first match unit (16) comprises elements (C1, C2) having a fixed and/or pre-set reactance.

4 Charged particle exposure system according to any one of the preceding clauses, further comprising a tuning unit for adjusting one or more parameters of said plasma source (4) and/or said power source (10).

5. Charged particle exposure system according to clause 4, wherein said tuning unit comprises a second match unit (18) arranged outside said vacuum chamber (2), said second match unit arranged for tuning said impedance match.

6. Charged particle exposure system according to clause 4 or 5, wherein said tuning unit comprises a frequency controller for controlling a frequency of said power source (10).

7. Charged particle exposure system according to any one of the preceding clauses, wherein said first match unit (16) is configured for providing said impedance match during standard operating conditions of said plasma source (4).

8. Charged particle exposure system according to clause 5 or any one of clauses 6 and 7 when dependent on clause 5, wherein said second match unit (18) comprises elements (C3, C4) having a variable reactance arranged for providing substantially impedance matching between said power source (10) and an impedance of a circuit (12°) comprising said second match unit, said first match unit, and said power coupling component.

9. Charged particle exposure system according to any one of the preceding clauses, wherein said plasma source arrangement is arranged for removal of contamination from and/or prevention of contamination on one or more components comprised in said charged particle exposure system.

10. Vacuum system (1) comprising: - a vacuum chamber (2); and - a plasma source arrangement, said plasma source arrangement comprising: - a plasma source (4) arranged within said vacuum chamber, the plasma source comprising a power coupling component (8) for coupling power into a gas present within said plasma source; - a power source (10) arranged for supplying power to the power coupling component, said power source arranged outside said vacuum chamber; - a first match unit (16) arranged for providing an impedance match between sald power source (10) and a plasma load formed by said plasma source (4) when in operation, wherein said first match unit is arranged within said vacuum chamber (2); and - a tuning unit for adjusting one or more parameters of said plasma source arrangement, said tuning unit comprising a second match unit (18) arranged outside said vacuum chamber (2), said second match unit arranged for tuning said impedance match.

11. Vacuum system according to clause 10, wherein said first match unit (16) is configured for providing said impedance match during standard operating conditions of said plasma source (4).

12. Vacuum system according to clause 10 or 11, wherein said first match unit (16) comprises elements (C1, C2) having fixed and/or pre-set reactance.

13. Vacuum system according to any one of clauses 10-12, wherein said second match unit (18) comprises elements (C3, C4) having a variable reactance arranged tor providing substantially impedance matching between said power source (10) and an impedance of a circuit (12°) comprising said second match unit, said first match unit, and said power coupling component.

14. Vacuum system according to any one of clauses 10-13, wherein said tuning unit further comprises a frequency controller for controlling a frequency of said power source.

15. Vacuum system according to any one of clauses 10-14, wherein said plasma source comprises a plasma chamber (6) and wherein said power coupling component comprises: - a coil (8) arranged adjacent and/or at least partly surrounding said plasma chamber, or - an electrode arranged within said plasma chamber.

16, Vacuum system according to any one of clauses 10-15, wherein said vacuum chamber comprises a main frame (24) having a substantially fixed position within said vacuum chamber and a sub-frame (22) coupled to said main frame via a vibration damping arrangement, wherein said plasma source (4) and said first match unit (16) are supported by said sub-frame.

17. Vacuum system according to any one of clauses 10-16, further comprising a charged particle beam system, wherein said plasma source arrangement is arranged for removal of contamination from and/or prevention of contamination on one or more components comprised in said charged particle beam system.

18. Vacuum system (1) comprising: -avacuum chamber (2); and - a plasma source arrangement, said plasma source arrangement comprising;

- a plasma source (4) arranged within said vacuum chamber, the plasma source comprising a power coupling component (8) for coupling power into a gas present within said plasma source; - a power source (10) arranged for supplying power to the power coupling component, said power source arranged outside said vacuum chamber; - a first match unit (16) arranged for providing an impedance match between said power source (10) and a plasma load formed by said plasma source (4) when in operation, wherein said first match unit is arranged within said vacuum chamber (2); wherein said vacuum chamber comprises a main frame (24) having a substantially fixed position within said vacuum chamber and a sub-frame (22) coupled to said main frame via a vibration damping arrangement, wherein said plasma source (4) and said first match unit (16) are supported by said sub-frame.

19. Vacuum system according to clause 18, wherein said first match unit (16) is configured for providing said impedance match during standard operating conditions of said plasma source (4).

20. Vacuum system according to any one of clauses 18 or 19, wherein said plasma source arrangement further comprises a tuning unit for adjusting one or more parameters of said plasma source arrangement, wherein said tuning unit comprises a second match unit (18) arranged outside said vacuum chamber (2), said second match unit arranged for tuning said impedance match.

21. Vacuum system according to any one of clauses 18-20, further comprising a charged particle beam system, wherein said plasma source arrangement is arranged for removal of contamination from and/or prevention of contamination on one or more components comprised in said charged particle beam system.

22. A plasma source arrangement comprising: - a plasma chamber (6) having an inlet (7) for introducing a gas into said plasma chamber (6) and an outlet (5) for plasma and/or radicals formed within said plasma chamber; -a power coupling component (8) for coupling power into said gas present within said plasma chamber (6); - a power source (10) arranged for supplying power to the power coupling component;

- a first match unit (16) arranged for providing an impedance match between said power source and said plasma source; - a tuning unit for adjusting one or more parameters of said plasma source arrangement, wherein said tuning unit comprises a second match unit (18) arranged for tuning said impedance match; wherein said first match unit (16) and said tuning unit are configured to be arranged at physically separated locations, and wherein said plasma chamber (4), said power coupling component (8), and said first match unit (16) are configured as vacuum compatible components.

23. Plasma source arrangement according to clause 22, wherein said first match unit (16) and said second match unit are arranged to be displaceable with respect to one another.

24. Plasma source arrangement according to clause 22 or 23, wherein said first match unit (16) and said plasma chamber (6) are mounted to a common support (50).

25. Plasma source arrangement according to any one of clauses 22 to 24, wherein said first match unit (16) comprises elements (C1, C2) having a fixed and/or pre-set reactance.

26. Use of the plasma source arrangement according to any one of clauses 22 to 25 for removal and/or prevention of accumulation of contamination on an optical or charged particle optical element.

27. Method for operating a plasma source arrangement, said plasma source arrangement comprising: - a plasma chamber (6) having an inlet (7) for introducing a gas into said plasma chamber; -4 power coupling component (8) for coupling power into said gas present within said plasma chamber; - a power source (10) arranged for supplying power to the power coupling component (8); - a first match unit (16) arranged for providing substantially an impedance match between said power source (10) and a plasma load formed by said power coupling component (8, 8”) and said plasma chamber (6) when in operation;

- a tuning unit for tuning one or more parameters of said plasma source arrangement, wherein said tuning unit comprises a second match unit (18) arranged for tuning said impedance match, wherein said first match unit and said second match unit are arranged at physically separated locations; the method comprising the steps of: - configuring said first match unit (16) to provide substantially impedance match between said power source (10) and said plasma load during standard operating conditions of the plasma source arrangement; - introducing one or more gases into said plasma chamber; - powering the power coupling component using said power source; - igniting a plasma in said plasma chamber (6) by operating said tuning unit to tune one or more parameters of said plasma source arrangement, wherein said tuning one or more parameters comprises tuning one or more reactance values of said second match unit; - after igniting said plasma, maintaining a substantially constant gas flow into said plasma chamber according to said standard operating conditions.

28. Method according to clause 27, wherein said tuning one or more parameters comprises tuning an impedance of a circuit portion comprising said first match unit (16) and said power coupling component (8).

29. Method according to any one of clauses 27 or 28, wherein said tuning of one or more parameters further comprises adjusting a frequency of said power source (10).

30. Method according to any one of clauses 27 to 29, wherein said power coupling component (8), said plasma chamber (6), and said first match unit (16) are arranged within a vacuum chamber (2) and wherein said power source (10) and said tuning unit are arranged outside said vacuum chamber.

CLAUSES SET 2

1. Exposure system for exposing a target, said exposure system comprising: - a vacuum chamber (2);

- a projection optical column (30) arranged within said vacuum chamber, said projection optical column arranged for projecting exposure radiation (36) onto said target (32); - a plasma source (4) arrangement arranged within the vacuum chamber (2), the plasma source arrangement comprising: - a plasma chamber (6) and a power coupling component (8) for coupling power into a gas or gaseous mixture present within said plasma chamber; - a first match unit (16) connected to said power coupling component (8); - a shield element (48) arranged between the plasma chamber (6) and the first match unit (16); - an outlet (5) for one or more species from said plasma chamber (6); and - a heat conductive base (50); wherein said shield element (48) is in thermal contact with said heat conductive base (50) and wherein the plasma chamber (6), the power coupling component (8), and/or the first match unit (16) is supported by the heat conductive base (50); wherein said plasma source arrangement is arranged such that species formed or generated in said plasma chamber can be directed into said projection optical column via said outlet.

2. Exposure system according to clause 1, further comprising: - a main frame (24) having a substantially fixed position within said vacuum chamber (2); - a sub-frame (22) supporting said projection optical column and said plasma source arrangement; wherein said sub-frame is coupled to said main frame via a vibration damping (26) arrangement.

3. Exposure system according to clause 1 or 2, further comprising a target holder for holding said target, wherein said plasma source arrangement (4) is arranged in a portion of said projection optical column (30) or said sub-frame (22) facing said target. 4 Exposure system according to any one of the preceding clauses, wherein the plasma chamber (6) is supported by the heat conductive base (50).

5. Exposure system according to any one of the preceding clauses, wherein the shield element (48) is mounted on said heat conductive base (50), or is monolithic with said heat conductive base (50).

6. Exposure system according to any one of the preceding clauses, wherein said power coupling component (8) comprises a coil (8) arranged adjacent and/or at least partly surrounding said plasma chamber (6), and wherein said heat conductive base (50) comprises or is provided with a magnetic shielding material.

7. A plasma source arrangement for generating plasma, the plasma source arrangement comprising: - a plasma chamber (6) having an inlet (7) for introducing gas into said plasma chamber; -a power coupling component (10) for coupling power from a power source into said gas when present in said plasma chamber; - a first match unit (16) connected to said power coupling component; - a thermal shield element (48) arranged between the plasma chamber (6) and the first match unit (16) for shielding the first match unit from thermal radiation from the plasma chamber and/or the power coupling component, said shield element comprising a first surface (48a) and a second surface (48h), said first surface facing said plasma chamber and said power coupling component, and said second surface facing said first match unit; and - a heat conductive base (50); wherein said thermal shield element (48) is in thermal contact with said heat conductive base (50), and wherein the plasma chamber (6), the power coupling component (8), and the first match unit (16) are supported by said heat conductive base.

8. Plasma source arrangement according to clause 1, wherein the heat conductive base (50) is provided with one or more base channels (56) for passage of a fluid.

9. Plasma source arrangement according to clause 2, wherein any bends of said one or more base channels (56) have a substantially continuous shape.

10. Plasma source arrangement according to clause 2 or 3, wherein the one or more base channels (56) are formed by tubes which are mold or casted inside a solid material forming said base (50). Il. Plasma source arrangement according to any one of the preceding clauses, wherein said heat conductive base (50) comprises or is provided with a material providing magnetic shielding.

12. Plasma source arrangement according to any one of the preceding clauses, wherein said first match unit (16) is mounted to said second surface (48b) of said shield element.

13. Plasma source arrangement according to any one of clauses 1-5, wherein said first match unit (16) is mounted to said heat conductive base (50).

14. Plasma source arrangement according to any one of the preceding clauses, wherein the shield element (48) comprises a metal or a ceramic material.

15. Plasma source arrangement according to any one of the preceding clauses, wherein said first surface (48a) of the shield element is reflective to thermal radiation.

16. Plasma source arrangement according to any one of clauses 1-8, wherein said first surface (48a) of the shield element (48) is arranged for absorbing thermal radiation, and wherein said first match unit (16) is mounted at a distance from said second surface (48b) of the shield element.

17. Plasma source arrangement according to any one of the preceding clauses, wherein said heat conductive base (50) is arranged to absorb thermal radiation from said plasma chamber (6) and/or said power coupling component (8).

18. Plasma source arrangement according to any one of the preceding clauses, wherein said power coupling component (8) comprises a coil arranged adjacent and/or at least partly surrounding said plasma chamber (6).

19. Plasma source arrangement according to clause 12, wherein said coil (8) is provided with a coil channel (54) for passage of a fluid.

20. Plasma source arrangement according to any one of the preceding clauses, wherein cooling tubes (58) are arranged at least partly enclosing said plasma chamber (6).

21. Plasma source arrangement according to clause 14, further comprising a housing (60) at least partly enclosing said cooling tubes (58).

22. Plasma source arrangement according to clause 15, wherein said housing is arranged to absorb thermal radiation from said plasma chamber and/or said power coupling component.

23. Plasma source arrangement according to any one of the preceding clauses, wherein said first match unit (16) is arranged for providing an impedance match between said power source (10) and a circuit portion (17) formed by said first match unit (16) and a plasma load, wherein said plasma load is formed by said plasma chamber (6), said power coupling component (8), and said gas and/or plasma present in said chamber (6) during operation of said power coupling component.

24. Vacuum system (1) comprising: - a vacuum chamber (2); and - a plasma source arrangement according to any one of the preceding clauses arranged within said vacuum chamber.

Claims (30)

CONCLUSIONS Charged particle exposure system for illuminating a target, the charged particle exposure system comprising: -a vacuum chamber (1); - a projection optical column (30) arranged inside the vacuum chamber, the projection optical column arranged for projecting exposure radiation (36a) onto the target; - a plasma source (4) arranged inside the vacuum chamber, the plasma source comprising a plasma chamber (6) and a power supply component (8) for feeding power to a gas contained within the plasma source, and an outlet (5) for plasma and / or radicals formed within the plasma chamber; - a power source (10) arranged to supply power to the power supply component (8), the power source being arranged outside the vacuum chamber; and - a first matching unit (16) arranged inside the vacuum chamber and connected to the power supply component (8) and to the power source (10), the first matching unit providing impedance matching between the power source and the plasma source. The charged particle exposure system of claim 1, wherein the vacuum chamber comprises a main frame (24) which has a substantially determined position within the vacuum chamber and a sub frame (22) connected to the main frame via a vibration damper, the projection optical column, the plasma source and the first adapter are supported by the subframe. Charged particle exposure system according to one or more of the preceding claims, wherein the first matching unit (16) comprises elements (C1, C2) which have an established and / or predetermined reactance. Charged particle exposure system according to one or more of the preceding claims, further comprising a tuning unit for setting one or more parameters of the plasma source (4) and / or the power source (10). Charged particle exposure system according to claim 4, wherein the tuning unit comprises a second matching unit (18) arranged outside the vacuum chamber (2), the second matching unit arranged for adjusting the impedance matching mmg. Charged particle exposure system according to claim 4 or 5, wherein the tuning unit comprises a frequency controller for controlling a frequency of the power source (10). Charged particle exposure system according to any of the preceding claims, wherein the first matching unit (16) is directed to provide impedance matching during standard operating conditions of the plasma source (4). Charged particle exposure system according to claim 5 or one or more of claims 6 and 7 when dependent on claim 5, wherein the second matching unit (18) comprises elements (C3, C4) having variable reactance adapted to provide substantial impedance matching between the power source (10) and an impedance of a circuit (12 °) comprising the second matching unit, the first matching unit, and the power supply component. Charged particle exposure system according to one or more of the preceding claims, wherein the plasma source device 1s is arranged to remove contamination from and / or to prevent contamination of one or more components in the charged particle exposure system. A vacuum system (1) comprising: -a vacuum chamber (2); and - a plasma source device, the plasma source device comprising: - a plasma source (4) arranged inside the vacuum chamber, the plasma source comprising a power supply component (8) for feeding power to a gas contained within the plasma source; - a power source (10) arranged to supply power to the power supply component (8), the power source being arranged outside the vacuum chamber; - a first matching unit (16) arranged to provide impedance matching between the power source (10) and a plasma charge generated by the plasma source (4) when in use, the first matching unit being arranged inside the vacuum chamber (2); and - a tuning unit for setting one or more parameters of the plasma source device; the tuning unit comprising a second matching unit (18) arranged outside the vacuum chamber (2), the second matching unit arranged for adjusting the impedance matching, Vacuum system according to claim 10, wherein the first matching unit (16) is arranged to provide impedance matching during standard operating conditions of the plasma source (4). Vacuum system according to claim 10 or 11, wherein the first matching unit (16) comprises elements (C1, C2) which have established and / or predetermined reactance. Vacuum system according to one or more of claims 10-12, wherein the second matching unit (18) comprises elements (C3, C4) having variable reactance adapted to provide substantial impedance matching between the power source (10) and an impedance of a circuit (12 °) including the second matching unit, the first matching unit, and the power supply component. Vacuum system according to any of the claims according to 10-13, wherein the tuning unit further comprises a frequency controller for controlling a frequency of the power source. Vacuum system according to one or more of claims 10-14, wherein the plasma source comprises a plasma chamber (6) and wherein the power supply component comprises: - a coil (8) arranged next to and / or at least partly around the plasma source, or - an electrode arranged inside the plasma chamber. Vacuum system according to one or more of claims 10-15, wherein the vacuum chamber comprises a main frame (24) which has a substantially fixed position within the vacuum chamber and a sub-frame (22) connected to the main frame via a vibration damping device, the plasma source (4) and the first adapter (16) are supported by the subframe. A vacuum system according to any of claims 10-16, further comprising a charged particle beam system, wherein the plasma source device is adapted to remove contamination from and / or to prevent contamination of one or more components in the charged particle beam system. A vacuum system (1) comprising: - a vacuum chamber (2); and - a plasma source device, the plasma source device comprising: - a plasma source (4) arranged inside the vacuum chamber, the plasma source comprising a power supply component (8) for feeding power to a gas contained within the plasma source; - a power source (10) arranged to supply power to the power supply component (8), the power source being arranged outside the vacuum chamber; - a first matching unit (16) arranged to provide impedance matching between the power source (10) and a plasma load generated by the plasma source (4) when in use, the first matching unit being arranged inside the vacuum chamber (2); the vacuum chamber comprising a main frame (24) having a substantially fixed position within the vacuum chamber and a sub-frame (22) connected to the main frame via a vibration damper, the plasma source (4) and the first adapter (16) being supported by the subframe. Vacuum system according to claim 18, wherein the first matching unit (16) is directed to provide impedance matching during standard operating conditions of the plasma source (4). A vacuum system according to any of claims 18 or 19, wherein the plasma source device further comprises a tuning unit for setting one or more parameters of the plasma source device, the tuning unit comprising a second adjustment unit (18) arranged outside the vacuum chamber (2) wherein the second matching unit is adapted to set the impedance matching. A vacuum system according to any of claims 18-20, further comprising a charged particle beam system, wherein the plasma source device is adapted to remove contamination from and / or to prevent contamination of one or more components in the charged particle beam system. A plasma source device comprising: - a plasma chamber (6) having an inlet (7) for introducing a gas into the plasma chamber (6) and an outlet (5) for plasma and / or radicals formed inside the plasma chamber; - a power supply component (8) for supplying power to the gas contained within the plasma chamber (6); - a power source (10) arranged to supply power to the power supply component; - a first matching unit (16) arranged to provide impedance matching between the power source and the plasma source; - a tuning unit for setting one or more parameters of the plasma source device, the tuning unit comprising a second matching unit (18) directed to measure impedance matching; wherein the first matching unit (16) and the tuning unit are arranged to be oriented at physically separated locations, and wherein the plasma chamber (4), the power supply component (8), and the first matching unit (16) are arranged as vacuum compatible components. The plasma source device of claim 22, wherein the first adapter (16) and the second adapter are arranged to be movable relative to each other. The plasma source device according to claim 22 or 23, wherein the first adapter (16) and the plasma chamber (6) are mounted on a common chassis (50). Plasma source device according to one or more of claims 22 to 24, wherein the first matching unit (16) comprises elements (C1, C2) which have an established and / or predetermined reactance. Use of the plasma source device according to any of claims 22 to 25 for removing and / or preventing accumulation of contamination on an optical or charged particle optical element. A method of using a plasma source device, the plasma source device comprising: - a plasma chamber (6) having an inlet (7) for introducing a gas into the plasma chamber; - a power supply component (8) for supplying power to the gas contained within the plasma chamber; - a power source (10) arranged to supply power to the power supply component (8); - a first matching unit (16) oriented to substantially provide an impedance matching between the power source (10) and a plasma charge formed by the power supply component (8, 8 ") and the plasma chamber (6) when in use; - a tuning unit for setting one or more parameters of the plasma source device, the tuning unit comprising a second matching unit (18) arranged for setting impedance matching, the first matching unit and the second matching unit being arranged at physically separate locations, the method comprising the steps of: - arranging the first matching unit (16) to substantially provide impedance matching between the power source (10) and the plasma load during standard operating conditions of the plasma source device; - introducing one or more gases into the plasma chamber; - feeding power into the power supply component through the power source; - establishing a plasma in the plasma chamber (6) by using the tuning unit to set one or more parameters of the plasma source device, the setting of one or more parameters setting one or more reactance values of the second matching unit includes; - after plasma generation, maintaining an essentially constant gas supply in the plasma chamber according to standard operating conditions. The method of claim 27, wherein setting one or more parameters comprises setting an impedance of a circuit part, the circuit part comprising the first matching unit (16) and the power supply component (8). The method of any one of claims 27 or 28, wherein adjusting one or more parameters further comprises adjusting a frequency of the power source (10). The method of any one of claims 27 to 29, wherein the power supply component (8), the plasma chamber (6), and the first adapter (16) are arranged in a vacuum chamber (2) and wherein the power source (10) and the tuner are arranged outside the vacuum chamber.