A sealing assembly

Abstract

A sealing assembly for capturing stray particles in a gas flow along a gas flow path is proposed, the sealing assembly comprising a collection region being part of the flow path of the gas, comprising an electric field generating unit structured to generate a static electric field across the gas flow for removing charged stray particles from the gas flow. The electric field generating unit comprises a first and second electrode positioned spaced apart from each other and facing each other in a direction more or less perpendicular to the gas flow through the collection region, and the collection region comprises a third electrode, shielding one of the first or second electrode from the gas flow, wherein the third electrode is formed as a perforated or grid formed electrode.

Description

[0001] TITLE

[0002] A sealing assembly.

[0003] TECHNICAL FIELD

[0004] The present disclosure relates to a sealing assembly for capturing stray particles from a gas flow.

[0005] BACKGROUND OF THE DISCLOSURE

[0006] The semiconductor industry is constantly racing to keep up with the exponential miniaturization trend predicted by Moore’s law. A key factor to tackle in order to meet the increasing standard of accuracy, productivity and yield in manufacturing is the cleanliness of equipment and substrates, at both atmospheric pressure and in vacuum environments.

[0007] The origin of contaminants in the processing chamber in the semiconductor industry is known to have various sources. For example, airborne molecular contaminants, small airborne particulates, or chemical residues are detrimental to the semiconductor manufacturing, since these contaminants could end up on the substrate creating local differences in the to-be processed layer.

[0008] Commonly known producers of such contaminants are mechanical bearings, moving parts and pressure gaps, which are all present in so-called InVacuum Robot (IVR) arms. Regardless, these IVR arms are highly desired in lithographic systems since they outperform the traditional chamber-transferring systems in both time and cleanliness.

[0009] An attempt at reducing the spreading of contaminating particles by the IVR arms has been made through differential seals. Here small holes of less than 20 pm are formed between the inside being at a higher pressure and the outside being at a lower pressure of the IVR arm, wherein these holes are purged with a high-purity nitrogen gas catching any contaminating particles that were to diffuse to the outside of the IVR arm.

[0010] Unfortunately, this approach requires very tight manufacturing tolerances to achieve correct hole size, surface treatments to harder the surface and non-contaminant containing high-purity nitrogen, which make this approach very costly. Additionally, a non-negligible amount of nitrogen leaks into the lithography chamber hampering the lithographic process.

[0011] Therefore, a need exists for an in-situ non-contact cleaning technology, which prevents possible damage to the substrate due to stray particles. This would lead to a twofold benefit from the industrial point of view, namely, a reduction of downtime and an increase of yield, which is the goal of the current invention.

[0012] SUMMARY OF THE DISCLOSURE

[0013] According to a first example of the disclosure, a sealing assembly for capturing stray particles in a gas flow along a gas flow path is proposed. The sealing assembly comprises a collection region being part of the flow path of the gas. The collection region comprises an electric field generating unit structured to generate a static electric field across the gas flow for removing charged stray particles from the gas flow.

[0014] The sealing assembly according to this example is beneficial over existing differential (gas) seals by being able to filter out the unwanted contaminating particles without hampering the vacuum. Here, the sealing assembly can be effectively mounted or accommodated in e.g. an IVR arm in particular at the hinging link of two movable arms. As stipulated in the introduction, the hinging link of two movable arms of an IVR arm are prone to generating stray molecules due to sliding contacts, which stray molecules are becoming electrically charged due to the sliding friction, and such charged stray particles cause a certain risk upon diffusion to the outside of the IVR arm.

[0015] T o avoid diffusion of the charged stray particles to the outside of the IVR arm, the contaminating charged stray particles are displaced by means of the gas flow being induced, such that the charged particles are move into a collecting portion along the flow path of the gas flow, where a static electric field exists.

[0016] The static electric field removes the electrically charged stray particles from the gas flow, resulting in a clean gas flowing out of the IVR arms. Accordingly, because of the improved cleanliness level of the gas flow thus obtained and a reduced diffusion of damaging and contaminating stray particles towards the outside of e.g. an IVR arm, the current disclosure can be implemented in systems, which do not require tight tolerances and high level surface treatments for their mechanical bearings, moving parts and pressure gaps, such that also a reduction in cost is achieved. According to another example of the disclosure the electric field generating unit of the sealing assembly comprises a first electrode and a second electrode positioned spaced apart from each other and facing each other in a direction more or less perpendicular to the gas flow through the collection region.

[0017] Having two electrodes opposite of each other perpendicular to the gas flow allows the electric field generating unit to generate an electric field also perpendicular to the flow of the gas. With this design the contaminating yet electrically charged particles need to change their trajectory independent of the charge they have . Namely, their direction of motion is changed by for example 90 degrees, being first in the direction of flow to being advantageously perpendicular to the flow. This way filtering, isolation and capturing of the unwanted contaminating already charged particles can be done effectively.

[0018] In yet another example the collection region of the sealing assembly comprises a third electrode, which shields one of the first or the second electrode from the gas flow, wherein the third electrode is formed as a perforated or grid formed electrode.

[0019] Having a third electrode being formed as a perforated or grid formed electrode is beneficial, since this third electrode can take active part in the generation of the static electric field, but its perforations creates passage holes for the attracted charged contaminating particles to divert or move past the third electrode ending up in a dead region not being part or not being influenced by the gas flow.

[0020] In an alternative example of the disclosure, the third electrode is grounded to earth potential. This results in a more straight forward design, with less complex connectivity requirements,

[0021] In another preferred example the electrode being shielded from the gas flow is configured to function as a stray charged particle detection electrode.

[0022] Having a particle detector integrated in the sealing assembly is beneficial, since it allows each sealing assembly to actively measure the number of charged contaminating stray particles being collected at a certain point in time at the position where the sealing assembly is located or mounted. This measurement can give insight into whether certain devices, processing steps or actions in the lithographic chamber are causing an excessive generation of contaminating particles, such that these steps or actions can be skipped, altered, or circumvented.

[0023] In a further advantageous example of the sealing assembly according to the disclosure, it furthermore comprises a plasma source, which is structured to form a plasma from the gas in a plasma region being part of the flow path of the gas. The plasma region adjoins the collection region along the gas flow path upstream the collection region seen in the direction of the gas flow. In this example, contaminating yet un-charged stray particles are first electrically charged due to the induction of a plasma. Thereafter, the charged particles are displaced by means of the gas flow, such that the charged particles are moved into the collecting portion along the flow path of the gas flow, where the static electric field exists.

[0024] In preferred examples, the plasma source is a pulsed voltage plasma source or an Alternating Current plasma source and in another preferred example the plasma source is a capacitive plasma source, an inductive plasma source or a microwave plasma source.

[0025] Various sources for plasma generation can be used in the present disclosure with the advantages that they can be positioned inside the chamber or space contacting the gas flow, or inside the chamber not contacting the gas flow, or even outside the chamber depending on the constructional configuration or situation in which the plasma sealing assembly is being implemented.

[0026] Additionally, a gas injector for inducing the gas flow along the gas flow path can be provided in the sealing assembly according to the disclosure in order to achieve the proper induced gas flow through the assembly.

[0027] In an example according to the disclosure the collection region and the plasma region of the plasma sealing assembly are combined in one joined region.

[0028] Having the plasma sealing assembly and the collection region combined in one joined region allows the plasma sealing assembly to be constructed more compact, and this miniaturization allows that the device can be applied in smaller spaces.

[0029] In a preferred example the plasma sealing assembly comprises a control unit structured to energize the plasma source and the electric field generating unit in a successive alternating manner.

[0030] The compact plasma sealing assembly can more effectively remove contaminating particles from the flow of gas when the formation of a plasma and the formation of a static electric field are a repeating sequential order in time. The presence of a static electric field would otherwise affect the plasma formation and affect the general gas flow. Therefore an alternating generation and occurrence of a plasma and a static electric field can separate contaminating particles from the gas flow in a more effective manner. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The disclosure will now be discussed with reference to the drawings, which show in:

[0032] Figure 1A a schematic view of a first example of the sealing assembly implementing two electrodes;

[0033] Figure 1 B-1C a schematic view of a second example of the sealing assembly implementing three electrodes;

[0034] Figure 2A a schematic view of a third example of the sealing assembly implementing two electrodes as well as a plasma source;

[0035] Figure 2B-2C a schematic view of a fourth example of the sealing assembly implementing three electrodes as well as a plasma source;

[0036] Figures 3A-3B schematic views of two operational modes of a compact sealing assembly according to the disclosure;

[0037] Figure 4 a further sixth example of a sealing assembly according to the disclosure;

[0038] Figures 5A-5B schematic views of yet a further seventh example of a sealing assembly according to the disclosure.

[0039] DETAILED DESCRIPTION OF THE DISCLOSURE

[0040] For a proper understanding of the disclosure, in the detailed description below corresponding elements or parts of the disclosure will be denoted with identical reference numerals in the drawings.

[0041] Figure 1 depicts a first example of a sealing assembly 1000 for capturing stray particles in a gas flow. The sealing assembly 1000 comprises a gas injector 400 structured to induce the gas flow along a gas flow path, the gas flow path being depicted with the arrow in Figure 1 (in all Figures). However, it is noted, and this pertains to all examples according to the disclosure, that the gas injector 400 is an optional component of the examples depicted in this patent application. The gas injector 400 can be omitted in those examples, as a gas flow can occur in various ways (induced or non-induced) along the gas flow path through the various examples of the sealing assemblies in this application.

[0042] The gas flow as shown by the arrow follows a flow path dictated by the inner, open space structure 100 of an equipment implemented in (low)vacuum environments such as in the semiconductor industry. An example of such equipment which is prone generate contaminating stray particles are mechanical bearings, moving parts and pressure gaps e.g. present in so-called In-Vacuum Robot (IVR) arms. Accordingly, although the Figures depict the gas flow as following a flow path along or through a straight flow channel 100, it should be understood that the flow path does not necessarily follow a straight flow direction, but is bound by the inner space structure 100 of an equipment in which undesired, contaminating stray particles are created and where the sealing assembly 1000 according to the disclosure is mounted I located in order to capture those stray particles. And it will be understood that the inner space structure 100 of that equipment not necessarily forms a straight flow path.

[0043] In Figures 1A-1 B-1C, a polluted gas, comprising gas molecules 4 and contaminating stray particles 5 flows through the sealing assembly 1000, optionally injected by means of a gas injector 400. The polluted gas flows sequentially through an initial gas region 10, , a collection region 40 and finally through a clean gas region 50. These regions are well defined from each other, and their sequential order as depicted in the various examples is dictated by the direction of the gas flow (marked by the arrow) through the flow channel 100 formed or bound by the inner space structure 100 of an equipment in which undesired, contaminating stray particles are created and where the sealing assembly 1000 according to the disclosure is mounted I located. In Figure 1A-1C, as an example, the gas is depicted to flow from the left to the right, moving through the above-mentioned different regions of the inner space structure 100 of the sealing assembly 1000. For clarity sake, the initial gas region 10 is considered upstream, and the clean gas region 50 is considered downstream, seen in the direction of the arrow of the gas flow.

[0044] The gas flow may contain stray molecules 5 due to sliding contacts, which stray molecules are becoming electrically charged due to the sliding friction resulting in a significant presence of electrically charged contaminating stray particles 5q. Accordingly, the gas flow comprises mostly bound state gas molecules 4 and a large number of charged contaminating stray particles 5q. Ultimately, the gas flow will reach the collection region 40, since here the charged contaminating stray particles 5q can and need to be separated from the bound state gas molecules 4 in order to avoid further transportation towards the region 50 and into the inner space structure 100 of the equipment and prevent diffusion into e.g. a vacuum chamber where these charged stray particles 5q may cause damage due to impingement on sensitive surfaces of e.g. a wafer substrate or a lens or mirror.

[0045] Upon generation of an electric field between a first electrode 1 and a second electrode 2 by the electric field generating unit 300, see Figure 1 A, the charged contaminating stray particles 5q are moved towards either electrode based on their charge, such that they collide with the surface of either electrode and adsorb onto it. Accordingly, the charged contaminating stray particles 5q are removed from the gas flow in the collection region 40. The continuous gas flow ensures that the gas molecules 4 are unaffected by the electric field and continue to flow into the clean gas region 50. As a result the gas flow in the clean gas region 50 has been cleaned from contaminating stray particles 5q as compared to the gas in the initial gas region 10. Herewith it is prevented that the contaminating stray particles 5q are not transported towards the region 50 and not into the inner space structure 100 of the equipment.

[0046] The strength of the static field between the electrodes 1 and 2 and the length of the collection region 40 seen along the gas flow direction are tailored towards the mass and charge of the charged stray particles 5q and to the flow rate of the gas. In general, the exact mass and change of the charged stray particles 5q is difficult to determine, but in practice the inventors have constructed the length of the collection region 40 to be slightly longer than required and the electric field to be stronger than required, such that with those settings most of the charged contaminating stray particles 5q can be captured. Alternatively, when the user of the sealing assembly 1000 finds out that the layer of the substrate to be processed, still contains too many contaminants the flow rate of the gas could be reduced. This would allow for more time for the charged stray particles 5q to change their momentum from going in the direction of the gas flow path to being perpendicular to the gas flow path.

[0047] In Figures 1 B-1C another (second) example of a sealing assembly according to the current disclosure is shown, denoted with reference numeral IOOO2. The sealing assembly IOOO2 has the same components as the sealing assembly 1000 of Figure 1A, but additionally comprises a third electrode 3, which shields one of the first electrode 1 or the second electrode 2 from the gas flow. In this example, the third electrode 3 is formed as a perforated or grid formed electrode.

[0048] For example in Figure 1 B (and Figure 1C) the first electrode 1 is shielded by the third electrode 3 from both the collecting region 40 and the second electrode 2. The electrode 3 is also being connected to the electric field generating unit 300. In this case an electric field might be generated by the electric field generating unit 300 between the second electrode 2 and the third electrode 3, such that the charged contaminating stray particles 5q are attracted towards the third electrode 3. Upon arrival at the surface of the third electrode 3, the stray contaminating particles have enough momentum that they continue through the perforations of the third electrode 3 and end up in a dead region 60 outside the collecting region 40.

[0049] In this dead region 60 being bound by both the first electrode 1 and the third electrode 3, the contaminating stray particles 5 / 5q are not affected by the gas flow, such that they are unable to re-enter into the gas stream and are thereby effectively removed from the gas. The contaminating stray particles 5 / 5q might also end up on the surface of the first electrode 1 , such that they adsorb onto it and are thereby removed from the gas.

[0050] Alternatively, the electric field might be generated between the first electrode 1 and the second electrode 2, and the third electrode is inactive or even grounded to earth potential 3q, see the example of Figure 1C. In this configuration of Figure 1C the grid-like third electrode 3 has no active part in the generation of the electric field, but mainly serves to separate the diverted / captured charged contaminating stray particles 5 / 5q from the main gas flow in a dead region 60, such that the charged stray particles 5q cannot pick up momentum from colliding with gas molecules 4 of the gas flow, such that they do not accidently re-enter into the just- cleaned gas flow.

[0051] The perforated third electrode 3 may be made out of a sheet material in which perforations or holes are punched, wherein the perforations can be oriented in various way, such as array-like structures like cubical, hexagonal, rectangular, triangular etc. or in randomly arranged perforations. Alternatively, the third electrode is made from wires arranged in a mesh-like configuration, which could be welded, or woven etc. This mesh may be arranged hexagonal, rectangular, cubical, or as parallel wires etc.

[0052] The material of the electrodes should be electrically conductive and may therefore be chosen to be iron, steel, copper, gold, or the like. Additionally, the material of the electrodes is chosen to be chemically inert against the gas molecules 4 and the contaminating stray molecules 5. Moreover, the surface roughness, cleanability, and replicability are of importance for choosing the electrodes, such that charged stray particles 5q stick well enough to the surface of the electrode, such that the surfaces of the electrodes can be easily cleaned by washing, or burning / heating, and such that the electrodes can be easily replaced during down-time of the processing chamber where the sealing assembly IOOO2 is positioned in, respectively.

[0053] Even greater functionality of the sealing assembly IOOO2 can be obtained when the electrode being shielded from the gas flow is configured to function as a stray particle counting electrode. In Figure 1 B and 1 C, the first electrode 1 could be configured to be a counting electrode, which allows each sealing assembly 1000 to actively measure the number of contaminating stray particles 5 / 5q that are removed from the gas flow at a certain point in time. The number of capture / removed stray contaminating particles 5 / 5q can give insight into which devices, processing steps or actions are causing an excessive generation of contaminating particles 5 / 5q. This information can be used to skip, alter, or circumvent these steps or actions and thereby improve the cleanliness of the process.

[0054] A particle counting electrode could be achieved through optical means, capacitive means, mass / weight measurements, time-of-flight measurements or the like. These methods could be implemented in the dead region 60 of the plasma sealing assembly IOOO2 for example with a camera tracking the movement of the stray particles 5 / 5q in the dead region 60. Alternatively, the (in Figure 3) first electrode 1 could be equipped with capacitive lead or resistor, which changes the capacitance or resistance upon charge and weight addition or removal.

[0055] As shown in Figure 2A-2C, the alternative examples IOOO3-IOO4 of a sealing assembly comprise a plasma source 200, which is structured to form a plasma from the injected gas in a plasma region 20 + 30 being part of the flow path (flow channel 100) of the gas. The collection region 40 of the examples of Figures 1A-1C is also part of the flow path (flow channel 100) of the gas, adjoining the plasma region 20 + 30 downstream the plasma region 20 + 30 as seen in the direction of the gas flow. Similarly, the collection region 40 comprises the electric field generating unit 300 that is structured to generate a static electric field across the gas flow for removing charged stray particles from the gas flow.

[0056] The plasma region 20 + 30 may comprise two separate regions; the main plasma region 20 and the plasma afterglow region 30, the latter being downstream from the main plasma region 20. The plasma source 200 excites the gas molecules 4 to form a plasma in the main plasma region 20 resulting in a significant presence of electrically charged gas molecules 4q. Furthermore, the contaminating stray particles 5 present in the gas also get electrically charged 5q in the plasma region 20. The continuous gas flow will cause the plasma to not stay contained within the main plasma region 20 and therefore a plasma afterglow region 30 is formed, wherein the plasma continues to exist, but no active energy source is adding energy to the gas to stay in an excited state in the plasma afterglow region 30 and the plasma slowly fades. The size of the plasma afterglow region 30 is dependent on the flow rate of the gas.

[0057] Because no energy is added to the plasma, the electrically charged gas molecules 4q fall back into bound state gas molecules 4, whereas the charged contaminating stray particles 5q maintain their charge over a longer period of time. Therefore, the region after the plasma afterglow region 30 comprises mostly bound state gas molecules 4 and a large number of charged contaminating stray particles 5q. This region is mentioned by the inventors as the collection region 40, since here the charged contaminating stray particles 5q can and need to be separated from the bound state gas molecules 4 in order to avoid further transportation towards the region 50 and into the inner space structure 100 of the equipment and prevent diffusion into e.g. a vacuum chamber where these stray particles 5q may cause damage due to impingement on sensitive surfaces of e.g. a wafer substrate or a lens or mirror.

[0058] Upon generation of an electric field between a first electrode 1 and a second electrode 2 by the electric field generating unit 300, the charged contaminating stray particles 5q are moved towards either electrode based on their charge, such that they collide with the surface of either electrode and adsorb onto it. Accordingly, the charged contaminating stray particles 5q are removed from the gas flow in the collection region 40. The continuous gas flow ensures that the gas molecules 4 are unaffected by the electric field and continue to flow into the clean gas region 50. As a result the gas flow in the clean gas region 50 has been cleaned from contaminating stray particles 5q as compared to the gas in the initial gas region 10. Herewith it is prevented that the contaminating stray particles 5q are not transported towards the region 50 and not into the inner space structure 100 of the equipment.

[0059] The strength of the static field between the electrodes 1 and 2 and the length of the collection region 40 seen along the gas flow direction are tailored towards the mass and charge of the charged stray particles 5q and to the flow rate of the gas. In general, the exact mass and change of the charged stray particles 5q is difficult to determine, but in practice the inventors have constructed the length of the collection region 40 to be slightly longer than required and the electric field to be stronger than required, such that with those settings most of the charged contaminating stray particles 5q can be captured. Alternatively, when the user of the plasma sealing assembly 1000 finds out that the layer of the substrate to be processed, still contains too many contaminants the flow rate of the gas could be reduced. This would allow for more time for the charged stray particles 5q to change their momentum from going in the direction of the gas flow path to being perpendicular to the gas flow path.

[0060] The plasma sealing assembly I OOO3-I OOO4 according to this example is beneficial over existing differential (gas) seals by being able to filter out the unwanted contaminating particles 5q without hampering the vacuum. Namely, the formation of plasmas can occur at very low pressures, whereas traditional differential (gas) seals need a high enough pressure or fast enough gas flow in order to “capture” stray particles. Whereas the current disclosure exploits the difference in charge decay time between the gas molecules 4 and the contaminating stray particles 5 to separate the two.

[0061] Another beneficial effect of the sealing assembly 1000-1 OOO2-I OOO3- I OOO4 of the current disclosure (depicted in Figures 1A-1 C and 2A-2C) is that it can be effectively mounted or accommodated in e.g. an IVR arm in particular at the hinging link of two movable arms, since this design can be made very small and since it is not compulsory that the gas flow should be linear. As long as the gas is guided through the different regions of the plasma sealing assembly I OOO-I OOO2-I OOO3-I OOO4, the gas flow path can take on any shape or channel as mentioned above. Therefore, Figures 1A-1 C and 2A-2C should be considered to only illustrate the characteristic regions of the flow channel 100 in the sealing assembly IOOO-IOOO2-IOOO3-IOOO4 and their sequence of stray particle removal.

[0062] To avoid diffusion of the stray particles 5 to the outside of the IVR arm, the contaminating stray particles 5 are first electrically charged 5q due to the induction of a plasma. Thereafter, the charged particles 5q are displaced by means of the gas flow being induced, such that the charged particles 5q are moved into a collection region 40 along the flow path of the gas flow, where a static electric field removes the electrically charged stray particles 5q from the gas flow, resulting in a clean gas flowing out of the IVR arms.

[0063] As shown also in Figures 2A-2C (similarly as in Figures 1A-1 C) the static field generating unit 300 of the plasma sealing assembly IOOO3 and I OOO4 comprises a first electrode 1 and a second electrode 2 positioned spaced apart from each other and facing each other in a direction more or less perpendicular to the gas flow through the collection region 40. The two electrodes 1 + 2 being opposite of each other and being perpendicular to the gas flow allows the electric field generating unit 300 to generate an electric field also perpendicular to the flow of the gas. In this case, charged stray particles 5q need to change their trajectory independent of the charge they obtained by 90 degrees, thereby moving almost perpendicular to the flow of the gas. They then will adsorb onto the surface of either one of the first electrode 1 or the second electrode 2, such that they are removed from the gas flow. This design allows for maximum difference between the direction of motion of the gas molecules 4 and the charged stray particles 5q, thereby improving the efficiency of removal of the unwanted particles 5 / 5q.

[0064] The plasma source 200 generating the plasma in the plasma region 20 may be a pulsed voltage plasma source or an Alternating Current plasma source. Alternatively it may be a capacitive plasma source, an inductive plasma source or a microwave plasma source. For the purpose of this patent application, it will be understood that any of the above mentioned plasma generating techniques can be implemented, e.g. depending on the type of equipment and form and structure of the inner space structure 100 of that equipment.

[0065] The type of plasma source 200 heavily depends on the use-case of the plasma sealing assembly 1000. For instance, a plasma sealing assembly 1000 utilized in semiconductor IVR arm handling robots might be exposed to low-vacuum and the electrodes of the plasma source 200 are not allowed to be inside the chamber. Alternatively, the plasma sealing assembly 1000 might be used at atmospheric pressures, where the electrodes of the plasma source 200 are supposed to be in contact with the gas. The utilization of the plasma sealing assembly 1000 in these different scenarios may therefore require different properties of the plasma source 200.

[0066] Figures 2B and 2C show the same configuration of the dead region 60 being bound by both the first electrode 1 and the third electrode 3 as in Figure 1 B and 1C. The detailed explanation of Figures 1 B and 1C is equally applicable for the explanation of the two examples of the plasma sealing assembly IOOO3-IOOO4, the contaminating stray particles 5 / 5q are not affected by the gas flow, such that they are unable to re-enter into the gas stream and are thereby effectively removed from the gas.

[0067] In Figures 3A-3B another (fifth) example of a plasma sealing assembly 1000raccording to the disclosure is shown being of a more compact form factor, wherein the collection region 40 and the plasma region 20 (+ 30) of the plasma sealing assembly 1000 are combined in one joined region. A smaller form factor plasma sealing assembly IOOO5 can be more effectively employed in a IVR robotic handling arm, since that would not limit is range of motion or make it bulkier. Note that in Figure 3A-3B the plasma region does not necessarily need to comprise the plasma after glow region 30. Moreover, this design comprises a control unit 500 connected to the plasma source 200 and the electric field generating unit 300. The two different operational states of the compact plasma sealing assembly IOOO3 are depicted in Figure 3A and Figure 3B, respectively.

[0068] In Figure 3A a first operational state of the plasma sealing assembly IOOO5 is shown, wherein the plasma source 200 is energized by the control unit 100. In an analogue manner as in the examples of Figure 1 and 2, a plasma is formed charging the gas molecules 4q and the contaminating stray particles 5q. Subsequently in time, in a second operational state, the control unit 500 turns off the plasma source 200 and energizes the electric field generating unit 300, as shown in Figure 3B. In this second operational state, the charged gas molecules 4q will fall back into bound state gas molecules 4, whereas the charged contaminating stray particles 5q will retain their charge. And due to the generation of an electric field, the contaminating stray particles 5q will move towards the dead region 60, where they are contained to adsorbed onto the first electrode’s 1 surface.

[0069] Because of a continuous in flux of gas, the control unit 500 is structured to energize the plasma source 200 (in particular in the example where the plasma source is configured as an Alternating Current plasma source) and the electric field generating unit 300 in a successive alternating manner, thereby switching from the first operational state (Figure 3A) to the second operational state (Figure 3B) and vice- versa. This way, the uncharged incoming stray particles 5 are getting charged in the overlapping region, when the plasma is active and are removed by the static electric field before they can escape out of the overlapping region towards the clean gas region 50. The time that either the plasma source 200 or the electric field generating unit 300 are active do not necessarily have to the equal. In other words the duty cycle of the switching between the two operational states is not limited to be 50%.

[0070] For this compact plasma sealing assembly IOOO5, the duration of the combined operational states, the duty cycle ,and the gas flow are factors that can be tuned based on the use-case of the plasma sealing assembly 1000 and the type of contaminating particles 5 that are to be removed from the gas flow. The compact plasma sealing assembly 1000s of Figures 3A-3B can remove contaminating particles 5 / 5q from the flow of gas more effectively when the formation of a plasma and the formation of a static electric field are a repeating sequential order in time. The switching between the two functional states is of importance, because the presence of a static electric field would otherwise affect the plasma formation and affect the general gas flow. Therefore an alternating generation of a plasma and a static electric field is needed.

[0071] In an alternative non-alternating control example, the control unit 500 may be configured to control the electric field generating unit 300 to apply a DC voltage signal between the electrodes 2 and 3, which DC voltage is applied continuously, thus creating a continuous electric field across the combined collection region 40 and plasma region 20. Further, the control unit 500 may simultaneously control the plasma source 200 to apply an alternating or pulsed voltage signal between the electrodes 2 and 3, which alternating or pulsed voltage is imposed on the DC voltage signal. This control configuration achieves, that during the continuous electric field being applied, plasma is created in a varying manner conformal to the varying alternating or pulsed voltage signal applied by the plasma source 200.

[0072] In other words, with this alternative configuration, simultaneous plasma generation and charged particle capturing can be achieved within the combined collection region 20 and plasma region 40. Alternative control configurations can be that a combined DC voltage and alternating / pulsed voltage are applied on the one and the same electrode of electrode 2 or 3, wherein the other one of the electrodes 3 or 2 is either connected to earth potential, or alternative provided with a further DC signal and / or alternating / pulsed signal e.g. to achieve a stable, efficient plasma.

[0073] Although not depicted in Figures 3A and 3B, it is noted that the electric field might be generated between the first electrode 1 and the second electrode 2, and that the third electrode is inactive or even grounded to earth potential 3q, similar as in the example of Figure 2B. Also in this configuration of Figures 3A and 3B, the earthed grid-like third electrode 3 has no active part in the generation of the electric field.

[0074] Figure 4 depicts a further (sixth) example of a plasma sealing assembly 1000e for capturing stray particles in a gas flow, which is implemented in a pressure gap present in a so-called In-Vacuum Robot (IVR) arm (schematically denoted with reference numeral 5000). The plasma sealing assembly IOOO4 comprises a gas injector 400 structured to induce the gas flow along the gas flow path 100 in the direction of the outlet choke 5003. The plasma source (electrode) 200 and the first electrode 1 are shielded by an insulator material (e.g. a plastic) 5004 and are mounted on a dielectric plate 5002 and have the same functionality as in the examples of Figures 1 , 2A-2B and 3A-3B. A plasma is created in the the plasma region 20 and the charged contaminating stray particles are removed from the gas flow in the collection region 40 due to the electric field generated by the electric field generating unit 300. Reference numeral 5001 denotes a metal end plate, e.g. aluminium.

[0075] Figures 5A and 5B depicts a further (seventh) example of a plasma sealing assembly 1000? for capturing stray particles in a gas flow, wherein the gas flow path 100 has a cylindrical configuration, with a center plasma electrode 201 electrically connected with the plasma source 200 and a center second electrode 2 electrically connected with the electric field generating unit 300. The first electrode 1 and the third electrode 3 are likewise electrically connected with the electric field generating unit 300 and are mounted at the outer circumference of the cylindrical gas flow path 100 forming a dead region 60 outside the collecting region 40.

[0076] Both the center plasma electrode 201 and the second electrode 2 are mounted within the cylindrical gas flow path 100 along its center axis and are electrically isolated from each other by means of insulator element 9b. The center plasma electrode 201 and the outer plasma electrode 202 create a plasma in the plasma region 20, whereas any charged contaminating stray particles are removed from the gas flow in the collection region 40 due to the electric field generated by the electric field generating unit 300 between the center second electrode 2 and the outer third electrode 3 and the outermost first electrode 1.

[0077] Likewise, insulator elements 9a-9b-9c maintain an electric isolation between the cylindrical gas flow path 100 and both the center plasma electrode 201 and the second electrode 2. The center plasma electrode 201 and the second electrode 2 are kept in place at the center axis of the cylindrical gas flow path 100 by means of spacer elements 8 interconnecting the insulator elements 9a-9b-9c with the cylindrical gas flow path 100 in an electrically isolated manner. See Figure 5B. LIST OF REFERENCE NUMERALS USED

[0078] 1 first electrode

[0079] 2 second electrode

[0080] 3 third electrode

[0081] 3z earth potential (Figure 2B)

[0082] 4 gas molecule

[0083] 4q charged gas molecule

[0084] 5 contaminating particle

[0085] 8 spacer element

[0086] 9a-9b-9c insulator element

[0087] 5q charged contaminating particle

[0088] 10 initial gas region

[0089] 20 main plasma region

[0090] 30 plasma afterglow region

[0091] 40 collection region

[0092] 50 clean gas region

[0093] 60 dead region

[0094] 100 inner space forming the gas flow path

[0095] 200 plasma source

[0096] 201 center plasma electrode

[0097] 202 outer plasma electrode

[0098] 300 electric field generating unit

[0099] 400 gas injector

[0100] 500 control unit

[0101] 1000 sealing assembly (first example)

[0102] IOOO2-IOOO5 sealing assembly (second, third, fourth and fifth example)

[0103] 5000 In-Vacuum Robot (IVR) arm

[0104] 5001 metal end plate

[0105] 5002 dielectric plate

[0106] 5003 outlet choke

[0107] 5004 insulation

Claims

CLAIMS1. A sealing assembly for capturing stray particles in a gas flow along a gas flow path, the sealing assembly comprising: a collection region being part of the flow path of the gas, adjoining the plasma region along the gas flow path downstream the plasma region seen in the direction of the gas flow, comprising an electric field generating unit structured to generate a static electric field across the gas flow for removing charged stray particles from the gas flow, wherein the electric field generating unit comprises a first and second electrode positioned spaced apart from each other and facing each other in a direction more or less perpendicular to the gas flow through the collection region and wherein the collection region comprises a third electrode, shielding one of the first or second electrode from the gas flow, wherein the third electrode is formed as a perforated or grid formed electrode.

2. The sealing assembly according to claim 1 , wherein the third electrode is grounded to earth potential.

3. The sealing assembly according to claim 1 or 2, wherein the electrode being shielded from the gas flow is configured to function as a stray particle detecting electrode.

4. The sealing assembly according to any one or more of the preceding claims, further comprising a plasma source structured to form a plasma from the gas in a plasma region being part of the flow path of the gas, the plasma region adjoining the collection region along the gas flow path upstream the collection region seen in the direction of the gas flow.

5. The sealing assembly according to claim 4, wherein the plasma source is a pulsed voltage plasma source or an Alternating Current plasma source.

6. The sealing assembly according to claim 4, wherein the plasma source is a capacitive plasma source, an inductive plasma source or a microwave plasma source.

7. The sealing assembly according to any one or more of the preceding claims, further comprising a gas injector for inducing the gas flow along the gas flow path.

8. The sealing assembly according to any one or more of the claims 4-7, wherein the collection region and the plasma region are combined in one joined region.

9. The sealing assembly according to any one or more of the claims 4-8, further comprising a control unit structured to energize the plasma source and the electric field generating unit in a successive alternating manner.

Images