WO2024251485A1

WO2024251485A1 - Lithographic apparatus, and method of expelling a contaminant in a lithographic apparatus

Info

Publication number: WO2024251485A1
Application number: PCT/EP2024/063444
Authority: WO
Inventors: Sandra Van Der Graaf; Sebastiaan Karel SIEMONS; Samuel Carl BIESMANS
Original assignee: ASML Netherlands BV
Current assignee: ASML Netherlands BV
Priority date: 2023-06-09
Filing date: 2024-05-15
Publication date: 2024-12-12
Anticipated expiration: 2025-12-09
Also published as: TW202501172A; CN121311822A

Abstract

A lithographic apparatus (LA) comprising: a first environment (11) in which a source of a contaminant (9) is located; a second environment (12); a passage (10) through which a light path between the first and second environments is provided, wherein the passage is at least in part defined by first and second wall sections (21, 22), and a gap (312) is present between the first and second wall sections; and a contaminant expelling system comprising an in-gap gas outlet (412) provided in the gap, wherein the contaminant expelling system is configured to supply gas to the in-gap gas outlet, thereby preventing at least a portion of the contaminant present outside the passage from entering into the passage through the gap.

Description

LITHOGRAPHIC APPARATUS, AND METHOD OF EXPELLING A CONTAMINANT IN A

LITHOGRAPHIC APPARATUS

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority of EP application 23178379.6 which was filed on 9 June 2023 and which is incorporated herein in its entirety by reference.

FIELD

[0002] The present invention relates to expelling a contaminant in a lithographic apparatus.

BACKGROUND

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

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

[0005] Once the EUV radiation has been generated, it is directed through the lithographic apparatus by a plurality of mirrors to a patterning surface of the patterning device, which imparts the desired pattern to the EUV radiation.

[0006] Contaminants, including gaseous molecules and solid particles, are generated when the radiation beam impinges on an optical surface, e.g. on a patterning device, or on mirrors and lenses. Once generated, if not appropriately controlled, contaminants may travel to various environments within the lithographic apparatus, and may deposit on various surfaces. Contaminants deposited on an optical surface may cause a degradation in optical performance.

SUMMARY OF THE INVENTION

[0007] Therefore, an object of the present invention is to reduce optics lifetime deterioration and/or reduce defectivity (contamination due to solid particles) by controlling the flow of contaminants. In particular, an object of the present invention is to reduce or eliminate the amount of contaminant flowing from one environment to another environment within the lithographic apparatus.

[0008] According to an aspect of the present invention, there is provided a lithographic apparatus comprising: a first environment in which a source of a contaminant is located; a second environment; a passage through which a light path between the first and second environments is provided, wherein the passage is at least in part defined by first and second wall sections, and a gap is present between the first and second wall sections; and a contaminant expelling system comprising an in-gap gas outlet provided in the gap, wherein the contaminant expelling system is configured to supply gas to the in-gap gas outlet, thereby preventing at least a portion of the contaminant present outside the passage from entering into the passage through the gap.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which corresponding reference symbols indicate corresponding parts.

[0010] Figure 1 depicts a lithographic apparatus.

[0011] Figure 2 depicts a comparative arrangement of a passage between first and second environments within a lithographic apparatus.

[0012] Figure 3 depicts a passage between two environments within a lithographic apparatus in accordance with an embodiment of the present invention.

[0013] Figure 4 depicts a passage between two environments within a lithographic apparatus in accordance with an embodiment of the present invention.

[0014] Figure 5 shows a simplified flow model.

[0015] Figure 6 shows contaminant suppression performance results.

[0016] Figure 7 depicts a passage between three environments within a lithographic apparatus in accordance with an embodiment of the present invention.

[0017] The features shown in the Figures are not necessarily to scale, and the size and/or arrangement depicted is not limiting. It will be understood that the Figures include optional features which may not be essential to the invention. Furthermore, not all of the features of the apparatus are depicted in each of the figures, and the Figures may only show some of the components relevant for describing a particular feature.

DETAILED DESCRIPTION

[0018] Figure 1 shows a lithographic system comprising a radiation source SO and a lithographic apparatus LA. The radiation source SO is configured to generate an EUV radiation beam B and to supply the EUV radiation beam B to the lithographic apparatus LA. The lithographic apparatus LA comprises an illumination system IL, a support structure MT configured to support a patterning device MA (e.g., a mask), a projection system PS and a substrate table WT configured to support a substrate W.

[0019] The illumination system IL is configured to condition the EUV radiation beam B before the EUV radiation beam B is incident upon the patterning device MA. Thereto, the illumination system IL may include a facetted field mirror device MO and a facetted pupil mirror device ML The faceted field mirror device MO and faceted pupil mirror device Ml together provide the EUV radiation beam B with a desired cross-sectional shape and a desired intensity distribution. The illumination system IL may include other mirrors or devices in addition to, or instead of, the faceted field mirror device MO and faceted pupil mirror device ML

[0020] After being thus conditioned, the EUV radiation beam B interacts with the patterning device MA. As a result of this interaction, a patterned EUV radiation beam B’ is generated. The projection system PS is configured to project the patterned EUV radiation beam B’ onto the substrate W. For that purpose, the projection system PS may comprise a plurality of mirrors M3, M4 which are configured to project the patterned EUV radiation beam B’ onto the substrate W held by the substrate table WT. The projection system PS may apply a reduction factor to the patterned EUV radiation beam B’, thus forming an image with features that are smaller than corresponding features on the patterning device MA. For example, a reduction factor of 4 or 8 may be applied. Although the projection system PS is illustrated as having only two mirrors M3, M4 in Figure 1, the projection system PS may include a different number of mirrors (e.g. six or eight mirrors).

[0021] The substrate W may include previously formed patterns. Where this is the case, the lithographic apparatus LA aligns the image, formed by the patterned EUV radiation beam B ’ , with a pattern previously formed on the substrate W.

[0022] A relative vacuum, i.e. a small amount of gas (e.g. hydrogen) at a pressure well below atmospheric pressure, may be provided in the radiation source SO, in the illumination system IL, and/or in the projection system PS.

[0023] The radiation source SO may be a laser produced plasma (LPP) source, a discharge produced plasma (DPP) source, a free electron laser (FEL) or any other radiation source that is capable of generating EUV radiation.

[0024] When the radiation beam B impinges on an optical component, gaseous molecules and/or solid particles are often generated. These gaseous molecules and/or solid particles may be generated at various optical components within the lithographic apparatus LA, such as the patterning device MA, as well as various mirrors, lenses and sensors. The solid particles may be generated due to disintegration of the optical component when exposed to the radiation beam B, or may be introduced during assembly of the lithographic apparatus LA. Gaseous molecules may be generated due to chemical reactions caused by the radiation beam B. For example, a pellicle with a MoSiN membrane, a patterning device MA made of silicon, or a fiducial may each generate silane (S i H4) molecules and/or silicon particles. Other gaseous molecules may be generated or released, such as water vapor, nitrogen, or hydrocarbons. These solid particles and gaseous molecules are examples of contaminants. These contaminants, if not adequately evacuated, may travel within the lithographic apparatus LA and deposit on various surfaces. These contaminants, especially gaseous molecules, may build up on various optical surfaces within the lithographic apparatus LA, causing a degradation of optical performance, and thus increased defectivity in devices manufactured using the lithographic apparatus LA.

[0025] Referring to Figure 2, the lithographic apparatus LA comprises a first environment 11 and a second environment 12. As shown, a source of a contaminant 9 is located in the first environment 11. The lithographic apparatus LA comprises a passage 10 between the first and second environments 11, 12. A light path (not shown) is provided through the passage 10. It should be understood that the light path may be one along which light travels from the first environment 11 towards the second environment 12, or from the second environment 12 towards the first environment 11. Light may also travel through the passage 10 twice, namely from the second environment 12 toward the first environment 11 and back to the second environment 12, or vice versa. The light path may be any of the paths of the radiation beam B mentioned above.

[0026] The lithographic apparatus LA may have a modular design. That is, different components of the lithographic apparatus LA may be assembled together as modules. For various reasons, a gap will often exist between modules of the lithographic apparatus LA. One reason for allowing a gap is manufacturability, namely to allow a certain amount of manufacturing tolerance in components of the lithographic apparatus. Certain components of a lithographic apparatus LA may have large dimensions, resulting in correspondingly large gaps. Another reason for allowing a gap between components is to reduce vibration transmission between the components. A further reason to allow a gap between components is to improve serviceability, namely to facilitate removal and installation of the components (certain components of the lithographic apparatus LA could weigh several tonnes, sometimes over 10 tonnes, which must be manoeuvred using heavy equipment). Flexible seals are generally not used to close the gaps or absorb vibrations because, under the conditions within a lithographic apparatus LA, flexible seals are prone to deteriorate and/or evaporate over time, which creates large amounts of contaminants. Therefore, gaps between components of the lithographic apparatus LA cannot be easily eliminated. To give a sense of magnitude, a gap of about 10 to 20 mm, such as 15 mm, may exist between the projection system PS and an adjacent component. A gap of about 1 to 10 mm, such as 2 to 5 mm, may exist between the illuminator IL and an adjacent component.

[0027] As shown, in the comparative arrangement of Figure 2, the passage 10 connects the first and second environments 11, 12, and is at least in part defined by first and second wall sections 21’, 22’. A gap 312’ is present between the first and second wall sections 21’, 22’. The first wall section 21’ may be part of a first component of the lithographic apparatus LA; the second wall section 22’ may be part of a second component of the lithographic apparatus LA. [0028] Still referring to Figure 2, the contaminant 9 may travel in different directions in the lithographic apparatus LA. For example, some of the contaminant 92, 93 may travel directly into passage 10. However, it is possible that some of the contaminant 9 may enter the passage 10 indirectly. For example, the contaminant 9 may initially flow in a space outside the passage 10, and enter into the passage 10 through the gap 312’. Thereafter, the contaminant 94’ that has entered through the gap 312’ may continue to flow towards the second environment 12 and may build up on surfaces within the second environment 12. As noted above, for example, contaminant 94’ may build up on optical surfaces within the second environment 12 and cause a degradation of optical performance. Therefore, it may be desirable to reduce or eliminate the amount of contaminant 94’ entering into the passage 10 through gap 312’.

[0029] According to the present invention, as shown in Figure 3, in order to reduce or eliminate the amount of contaminant 9 entering into the passage 10 through gap 312, a contaminant expelling system (not labelled) is included. As shown in Figure 3, the contaminant expelling system comprises an in-gap gas outlet 412. As shown, the in-gap gas outlet 412 is provided in the gap 312. The contaminant expelling system is configured to supply gas to the in-gap gas outlet 412, thereby preventing at least a portion of the contaminant 9 present outside the passage 10 for entering into the passage 10 through the gap 312. Gas supplied to the in-gap gas outlet 412 may be supplied at a higher pressure than the pressure within the passage 10 and/or outside the passage 10. As shown in Figure 3, as the gas is ejected from the in-gap gas outlet 412, the gas may fill the gap 312 and may split into two streams, one flowing into the passage 10, and the other flowing towards the space outside the passage 10.

[0030] By comparing Figures 2 and 3, it can be seen that the provision of gas through the in-gap gas outlet 412 may effectively expel at least a portion of contaminant 94 present outside the passage 10. The amount of contaminant 94 entering into the passage 10 through gap 312 may therefore be reduced or entirely eliminated.

[0031] As found by the present inventors, a relatively small gas flow through the in-gap gas outlet may be enough to effective reduce the amount of contaminant 94 entering through the gap 312. For example, as a fraction of the total “flow budget”, at most 50%, at most 30%, at most 15%, at most 10%, or at most 5% of the flow budget may be provided through the in-gap gas outlet 412. The remainder of the flow budget may be directed in or around the area of the passage 10 through other outlets. More specifically, the flow budget may be the total flow rate of gas supplied via one or more gas outlets at least partially into the passage 10. Examples of these other gas outlets include gas outlets 401 and 411, which will be described in more detail below.

[0032] Because a relatively small flow rate of gas through the in-gap gas outlet 412 may be adequate, the supply of gas through the in-gap gas outlet 412 may result in little or no increase to the overall flow budget. Generally, it may be desirable to keep the passage 10 under vacuum as far as possible because any presence of gas (e.g. hydrogen) is likely to attenuate the light travelling through the passage 10, thereby incurring a “transmission penalty”. At the same time, a flow of gas may be needed to prevent excessive amounts of contaminant 9 in the first environment 11 from travelling to the second environment 12. Therefore, it may be generally desirable to keep the flow budget as small as possible while ensuring adequate expulsion of contaminants 9.

[0033] Hypothetically, without the in-gap gas outlet 412, some reduction of the amount of contaminant 94’ entering the passage 10 through the gap 312’ may be achieved by increasing the gas flow through other gas outlets, but this may necessitate an overall increase of the flow budget, and therefore increase the transmission penalty. In particular, as the natural behaviour of the injected gas is generally to follow the path of least resistance, an increase of gas flow through the gap 312’ may come at the expense of an even larger increase of gas flow through the passage 10. Therefore, the required suppression of contaminants through the gap 312’ may be achievable only at the expense of a large transmission penalty. Therefore, it may not be desirable to expel contaminant 94’ by increasing flow through other gas outlets. By contrast, by providing the in-gap gas outlet 412, it may be possible to reduce or eliminate the amount of contaminant 94 entering the passage 10 through the gap 312 with little or no increase to the flow budget. Therefore, contaminants 94 outside the passage 10 may be prevented from reaching the second environment 12 without incurring additional transmission penalty.

[0034] It should be understood that, although the first and second wall sections 21, 22 are depicted in Figure 3 as defining a complete perimeter around a section of the passage 10, this need not be the case. Each of the first and second wall sections 21, 22 may define a part of the perimeter around a section of the passage 10. Furthermore, although Figure 3 shows that the gap 312 as a planar region substantially perpendicular to a longitudinal axis of the passage 10, this need not be the case. The gap 312 may be in any direction as a result of a particular arrangement of the wall sections 21, 22 that at least partially define the passage 10. Furthermore, the gap 312 need not lie in a flat plane. For the purpose of the present invention, the gap 312 may be of any shape as long as it exists between first and second wall sections 21, 22 which at least partially define the passage 10 and creates a fluid communication path between the passage 10 and outside the passage 10.

[0035] It follows that the gap 312 may have a length that depends on the specific implementation. Irrespective of the geometry or length of the gap 312, it may be desirable to prevent contaminant 94 from entering into the passage 10 at substantially all points along the length of the gap 312. Therefore, the in-gap gas outlet 412 may be substantially co-extensive with the full length of the gap 312. That is, the in-gap gas outlet 412 may be shaped to supply gas substantially evenly along the full length of the gap 312. The in-gap gas outlet 412 may comprise a single or a plurality of orifices (not shown). For example, the in-gap gas outlet 412 may be formed as a single, continuous slit. Alternatively, the in-gap gas outlet 412 may comprise a plurality of orifices, such as round holes. In arrangements where the in-gap gas outlet 412 comprises a plurality of orifices, the orifices may be substantially evenly spaced along the length of the gap 312. This may ensure an even supply of gas along the length of the gap 312. Of course, where the gap 312 has a non-constant width along its length, the in-gap gas outlet 412 may be configured accordingly to provide a non-uniform gas flow along the length of the gap 312 to compensate for the non-constant width of the gap 312. This may help prevent the formation of weak points where contaminants 9 could otherwise enter into the passage 10.

[0036] In the arrangement shown in Figure 3, the in-gap gas outlet 412 is provided on the side of the first wall section 21. However, as shown in Figure 4, it is equally possible to provide the in-gap gas outlet 412 on the side on the second wall section 22. It should also be understood that the arrangements shown in Figures 3 and 4 may be combined, so that an in-gap gas outlet 412 may be provided on the side of each of the first and second wall sections 21, 22.

[0037] As noted above, the contaminants expelling system may comprise one or more gas outlets in addition to the in-gap gas outlet 412. Referring to Figures 3 and 4, the passage 10 may have a first end 211 opening into the first environment 11. As shown, the contaminant expelling system may further comprise a passage-end gas outlet 401 and may be configured to supply gas to the passage-end gas outlet 401. As shown, the passage-end gas outlet 401 may be configured to direct the gas supplied thereto to prevent at least a portion of the contaminant 9 (labelled 91), present in the first environment 11 from entering into the passage 10 through the first end 211 of the passage 10. In addition to preventing a portion of the contaminant 91 from entering into the passage 10 through the first end 211 of the passage 10, the gas from the passage-end gas outlet 401 may also direct the contaminant 91 away from the light path in the first environment 11.

[0038] As shown, although the gas from the passage-end gas outlet 401 may prevent at least a portion of the contaminant 91 present in the first environment 11 from entering into the passage 10 through the first end 211 of the passage 10, a portion of the contaminant 92 may nevertheless enter into the passage 10 through the first end 211 of the passage 10. As shown in Figures 3 and 4, the contaminant expelling system may further comprise an exhaust 419. As shown, the passage 10 may have a second end 221 opening into the second environment 12. The exhaust 419 may be fluidly connected to the passage 10. The exhaust 419 may be positioned intermediate the first and second ends 211, 221 of the passage 10. Suction (or vacuum) may be applied to the exhaust 419. In other words, the exhaust 419 may be held at a pressure lower than that in the passage 10. Because of the position of the exhaust 419, at least a portion of the contaminant 92 that has entered into the passage 10 through the first end 211 of the passage 10 may be carried by the gas flow within the passage 10 towards the exhaust 419. Typically, the exhaust 419 may be positioned such that the position at which the gap 312 meets the passage 10 is intermediate the exhaust 419 and the second end 221 of the passage 10. More specifically, the exhaust 419 may be provided through the first wall section 21.

[0039] Although a majority of the contaminant 92 present in the passage 10 would generally be carried by gas supplied through the passage-end gas outlet 401 towards the exhaust 419, a portion of the contaminant 93 may escape and travel further into the passage 10. As such, the contaminant expelling system may further comprise an in-passage gas outlet 411 and may be configured to supply gas to the in-passage gas outlet 411, as shown in Figures 3 and 4. The in-passage gas outlet 411 may be configured to direct the gas supplied thereto to prevent at least a portion of the contaminant 93 present within the passage 10 from exiting the passage 10 through the second end 221 of the passage 10. This may further reduce the amount of contaminant 9 reaching the second environment 12. Specifically, the in-passage gas outlet 411 may be positioned intermediate the exhaust 419 the second end 221 of the passage 10. More specifically, the in-passage outlet 411 may be positioned such that the position at which the gap 312 meets the passage 10 is intermediate the in-passage gas-outlet 411 and the second end 221 of the passage. The in-passage gas outlet 411 may be provided through the first wall section 21. Due to the position of the in-passage gas outlet 411, a portion of the remaining contaminant 93 that is present in the passage 10 may be prevented from travelling as far as the gap 312. Specifically, the remaining contaminant 93 (or a portion thereof) may be carried by gas from the in-passage gas outlet 411 towards the exhaust 419.

[0040] To sum up, it is contemplated in the present disclosure that, in one arrangement, the contaminant expelling system may comprise gas outlets at three locations to reduce or substantially eliminate the amount of contaminant 9 from the first environment 11 form reaching the second environment 12 through the passage 10. That is, gas from the in-gap gas outlet 412 may prevent contaminant 94 present outside the passage 10 form entering into the passage 10 through gap 312 between the first and second wall section 21, 22. Gas from the passage-end gas outlet 401 may prevent a portion of the contaminant 91 from entering the passage 10 through the first end 211 of the passage 10, and carry another portion of the contaminant 92 that has entered through the first opening 211 of the passage 10 towards the exhaust 419 means of a “downflow”. An in-passage gas outlet 411 may be provided to create an “upflow” which carries at least a portion of any remaining contaminant 93 in the passage 10 towards the exhaust 419. Additionally or alternatively, gas from the passage-end gas outlet 401 and/or the in-passage gas outlet 411 may prevent contaminants (not shown) from flowing from the second environment 12 to the first environment 11.

[0041] As noted above, a relatively small gas flow through the in-gap gas outlet may be enough to effective reduce the amount of contaminant 94 entering through the gap 312. A first flow rate of gas may be supplied to the in-gap gas outlet 412, a second flow rate of gas may be supplied to the inpassage gas outlet 411, and a third flow rate of gas may be supplied to the passage-end gas outlet 401. The first flow rate may be at most 50%, at most 30%, at most 15%, at most 10%, or at most 5% of the sum of the first, second and third flow rates. The sum of the first, second and third flow rates may correspond to the total “flow budget”.

[0042] The flow kinematics are explained in more detail with reference to a simplified model shown in Figure 5. As shown, a flow injection is provided through in-passage gas outlet 411 into passage 10. The gas flow through the in-gap gas outlet 412 (not shown in Figure 5) creates a flow of thgap through the gap 312 towards the outside of the passage 10. Part of the gas flow through the in- gap gas outlet 412 enters the passage 10. A resultant upflow m_up is generated in the passage 10 towards the first environment 11.

[0043] Two suppression zones as shown in Figure 5 may be considered, one in the gap 312 and the other in the passage 10 between the gap 312 and the first opening 211 of the passage 10. In each suppression zone, at least a portion of the contaminant 9 is prevented from travelling through the passage 10 towards the second opening 221 of the passage 10.

[0044] The portion of contaminant 9 that is suppressed may be modelled by a ID molecular suppression factor S = exp(Pe), where Pe = is the Peclet number, and where DP is the

diffusion constant of the contaminant 9 in the injected gas (diffusion coefficient D is inversely proportional to pressure).

[0045] For laminar ideal isothermal gas: P — P = G X F X m_up, where G and F are geometrical (encapsulating e.g. aspect ratio, size, shape, etc.) and fluid properties. In the simplified model shown in Figure 5, it may be assumed that G = F = pR_sT. With m = UAp and applying the ideal gas

law, we find LUP =

. Therefore, the suppression factor of the upflow may be modelled as:

where Rs is the specific gas constant.

[0046] Similarly, the suppression factor of the flow through gap 312 may be modelled as:

[0047] Combining S_up and S_gap, the total suppression S may be modelled by:

[0048] The required amount of total suppression may thus achieved by equating the up and side suppressions for a given flow budget. The required gas flows may also be determined based on the geometries of the passage 10, the gap 312, and the various outlets and exhaust 419.

[0049] Figure 6 shows some performance results obtained using computational fluid dynamics (CFD) simulation of contaminant expulsion in a passage adjacent the mini-environment surrounding a patterning device MA. The data series labelled “CFD Machine” refers to CFD analysis of the relevant part of the lithographic apparatus LA with the gap 312 left open. The data series labelled “CFD FUMO No Gap” refers to a functional mockup of the relevant part of the lithographic apparatus LA but with the gap 312 closed. The CFD was verified with argon. The term “functional mockup” refers to a model based on the actual design of the relevant part of the lithographic apparatus LA, with simplified geometries in order to fit within the test bench. Finally, the data series “CFD Machine No Gap” refers to a CFD simulation using the actual (non-simplified) design of the relevant part of the lithographic apparatus LA, and with gap 312 closed. The contaminant selected for simulation is silane (Si PL). and the gas supplied by the contaminant expelling system is hydrogen.

[0050] As shown by the data series “CFD Machine” (with gap) the suppression performance remains relatively low even as the amount of upflow is increased. By contrast, as shown by the data series “CFD FUMO No Gap”, an improved suppression can be observed as the amount of upflow increases. The three data points of the data series “CFD Machine No Gap” agree with the data series “CFD FUMO No Gap”, which demonstrates that the functional mock up is a valid approximation of the actual design and can be used to predict the suppression performance of a lithographic apparatus LA with the gap 312 closed. The difference in the level of suppression shown in Figure 6 shows that the gap 312 is responsible for a significant transmission of the contaminant 9 from the first environment 11 to the second environment 12. Accordingly, by providing the in-gap gas outlet 412 to prevent at least a portion of the contaminant 94 from entering the passage 10 through the gap 312, the overall contaminant suppression performance may be expected to approach a level where the gap 312 is closed.

[0051] Figure 7 depicts a more elaborate embodiment of the present invention. As noted above, the gap 312 may not necessarily lie in a plane perpendicular to a longitudinal axis of the passage 10. As shown in Figure 7, a portion of the gap 312 is formed by a portion of the second wall 22 surrounding the first wall section 21. Therefore, the gap 312 may have a certain extent in the longitudinal direction of the passage 10.

[0052] Furthermore, instead of supplying gas to the in-passage gas outlet 411 and the in-gap gas outlet 412 separately, gas may be supplied to both outlets via a manifold 42 to which both the inpassage gas outlet 411 and the in-gap gas outlet 412 are connected. The contaminant expelling system may be configured to supply gas to these two outlets via the manifold 42. This arrangement may be advantageous because it may reduce the number of supply lines required to feed gas from a gas supply to the respective outlets. Furthermore, an existing lithographic apparatus LA already equipped with an in-passage gas outlet 411 and manifold 42 may be modified to implement the in-gap gas outlet 412 by machining the outlet through the material of the first wall section 21 into the manifold 42. In other words, the present invention may be retrofitted into some existing lithographic apparatuses LA.

[0053] As noted above, the first environment 11 may be any environment within the lithographic apparatus LA where a contamination source 9 is present. One example of the first environment 11 is the environment containing the patterning device MA. Correspondingly, the second environment 12 may be one which is adjacent the environment containing the patterning device MA. For example, the second environment 12 may be part of the illumination system IL or part of the projection system PS. During operation of the lithographic apparatus LA, as radiation beam B impinges on patterning device MA, contaminants 9 including solid particles and/or gaseous molecules (e.g. silane) may be generated. With the present invention, these contaminants 9 may be prevented from travelling into the illumination system IL and/or the projection system PS, each of which contains optics whose performance may be degraded by a build-up of contaminant 9.

[0054] As shown in Figure 7, the lithographic apparatus LA may comprise a third environment 13. One end 221 of the passage 10 may open into both the second and third environments 12, 13. In this arrangement, in addition to the first and second wall sections 21, 22, the passage 10 may additionally be at least in part defined by a third wall section 23. Furthermore, the presence of a third wall section 23 may create additional gaps through which the contaminant 9 may enter into the passage 10. Specifically, a gap 313 may be present between the third wall section 23 and the first wall section 21. Similarly, a gap 323 may be present between the second wall section 22 and third wall section 23. Without any mitigation, contaminant 9 may enter into the passage 10 through gap 313 and/or gap 323. [0055] Therefore, the contaminant expelling system may further comprise an in-gap gas outlet 413 provided in the gap 313 between the first and third wall sections 21, 23, and the contaminant expelling system may be configured to supply gap to this in-gap gas outlet 413. This may prevent at least a portion of the contaminant 9 present outside the passage 10 from entering into the passage 10 through the gap 313. Similarly, the contaminant expelling system may additionally or alternatively comprise an in-gap gas outlet 423 provided in the gap 323 between the second and third wall sections 22, 23, and the contaminant expelling system may be configured to supply gas to this in-gap gas outlet 423. This may prevent at least a portion of the contaminant 9 present outside the passage 10 from entering into the passage 10 through this gap 323.

[0056] One example where the passage 10 is at least in part defined by three wall sections 21, 22, 23 is the passage 10 between the patterning device MA, the illumination system IL and the projection system PS. For example, the first environment 11 may contain the patterning device MA, the second environment 12 may be part of the illumination system IL, and the third environment 13 may be part of the projection system PS. In arrangements such as this, light may travel from the second environment 12 through the passage 10 into the first environment 11, and again from the first environment through the passage 10 into the third environment 13.

[0057] The passage 10 may be of a generally conical shape (or, more precisely, frustoconical shape). In particular, the passage 10 between the environment containing the patterning device MA, the illumination system IL and the projection system PS may have a conical shape. It should be understood that passage 10 may comprise one or more other parts which are not conical, and the passage 10 may not necessarily follow the precise shape of a cone. The narrower end of the conical part of the passage 10 may open into the first environment 11. The wider end of the conical part of the passage 10 may open into one or both of the second and third environments 12, 13.

[0058] In addition to a lithographic apparatus LA, the present disclosure also contemplates a method of expelling contaminants in a lithographic apparatus LA, as well as a method of manufacturing devices using the lithographic apparatus LA.

[0059] Although specific reference may be made in this text to the use of lithographic apparatus in the manufacture of ICs, it should be understood that the lithographic apparatus described herein may have other applications, such as the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat-panel displays, liquid-crystal displays (LCDs), thin film magnetic heads, etc. The skilled artisan will appreciate that, in the context of such alternative applications, any use of the terms “wafer” or “die” herein may be considered as synonymous with the more general terms “substrate” or “target portion", respectively. The substrate referred to herein may be processed, before or after exposure, in for example a track (a tool that typically applies a layer of resist to a substrate and develops the exposed resist), a metrology tool and/or an inspection tool. Where applicable, the disclosure herein may be applied to such and other substrate processing tools. Further, the substrate may be processed more than once, for example in order to create a multi-layer IC, so that the term substrate used herein may also refer to a substrate that already contains one or multiple processed layers.

[0060] Although specific reference may have been made above to the use of embodiments of the invention in the context of optical lithography, it will be appreciated that the invention may be used in other applications.

[0061] Aspects of the invention are described in the following numbered clauses.

1. A lithographic apparatus (LA) comprising: a first environment (11) in which a source of a contaminant (9) is located; a second environment (12); a passage (10) through which a light path between the first and second environments is provided, wherein the passage is at least in part defined by first and second wall sections (21, 22), and a gap (312) is present between the first and second wall sections; and a contaminant expelling system comprising an in-gap gas outlet (412) provided in the gap, wherein the contaminant expelling system is configured to supply gas to the in-gap gas outlet, thereby preventing at least a portion of the contaminant present outside the passage from entering into the passage through the gap.

2. The lithographic apparatus of clause 1, wherein at most 50%, at most 30%, at most 15%, at most 10%, or at most 5% of a total flow rate of gas is supplied to the in-gap gas outlet, the remainder of the total flow rate of gas being supplied via one or more other gas outlets (401, 411) at least partially into the passage. 3. The lithographic apparatus of any one of the preceding clauses, wherein the in-gap gas outlet is substantially co-extensive with the full length of the gap.

4. The lithographic apparatus of any one of the preceding clauses, wherein the in-gap gas outlet comprises a plurality of orifices.

5. The lithographic apparatus of any one of the preceding clauses, wherein a first end (211) of the passage opens into the first environment.

6. The lithographic apparatus of clause 5, wherein the contaminant expelling system further comprises a passage-end gas outlet (401) and is configured to supply gas to the passage-end gas outlet; wherein the passage-end gas outlet is optionally configured to direct the gas supplied thereto to prevent at least a portion of the contaminant (91) present in the first environment from entering into the passage through the first end of the passage.

7. The lithographic apparatus of clause 5 or clause 6, wherein a second end (221) of the passage opens into the second environment.

8. The lithographic apparatus of clause 7, wherein the contaminant expelling system further comprises an exhaust (219) connected to the passage, and the exhaust is preferably positioned intermediate the first and second ends of the passage.

9. The lithographic apparatus of clause 8, wherein the position at which the gap meets the passage is intermediate the exhaust and the second end of the passage.

10. The lithographic apparatus of any one of clauses 7 to 9, wherein the contaminant expelling system further comprises an in-passage gas outlet (411) and is configured to supply gas to the inpassage gas outlet; wherein the in-passage gas outlet is configured to direct the gas supplied thereto to prevent at least a portion of the contaminant present within the passage from exiting the passage through the second end of the passage.

11. The lithographic apparatus of clause 10, wherein: a first flow rate of gas is supplied to the in-gap gas outlet (412), a second flow rate of gas is supplied to the in-passage gas outlet (411), and a third flow rate of gas is supplied to the passage-end gas outlet (401); and the first flow rate is at most 50%, at most 30%, at most 15%, at most 10%, or at most 5% of the sum of the first, second and third flow rates.

12. The lithographic apparatus of clause 10 or clause 11, wherein the in-passage gas outlet is positioned intermediate the exhaust and the second end of the passage.

13. The lithographic apparatus of any one of clauses 10 to 12, wherein the position at which the gap meets the passage is intermediate the in-passage gas outlet and the second end of the passage.

14. The lithographic apparatus of any one of clauses 10 to 13, wherein the contaminant expelling system further comprises a manifold (42) to which both the in-passage gas outlet and the in-gap gas outlet are connected, and the contaminant expelling system is configured to supply gas to the inpassage gas outlet and the in-gap gas outlet via the manifold. 15. The lithographic apparatus of any one of the preceding clauses, wherein the first environment comprises a patterning device (MA).

16. The lithographic apparatus of any one of the preceding clauses, wherein the second environment is part of an illumination system (IL) or of a projection system (PS).

17. The lithographic apparatus of any one of the preceding clauses, further comprising a third environment (13), wherein one end of the passage opens into both the second and third environments.

18. The lithographic apparatus of clause 17, wherein the passage is at least in part defined by a third wall section (23) in addition to the first and second wall sections.

19. The lithographic apparatus of clause 18, wherein a gap (313) is present between the first and third wall sections, the contaminant expelling system further comprises an in-gap gas outlet (413) provided in the gap between the first and third wall sections, and the contaminant expelling system is configured to supply gas to the in-gap gas outlet in the gap between the first and third wall sections, thereby preventing at least a portion of the contaminant present outside the passage from entering into the passage through the gap between the first and third wall sections.

20. The lithographic apparatus of clause 18 or clause 19, wherein a gap (323) is present between the second and third wall sections, the contaminant expelling system further comprises an in-gap gas outlet (423) provided in the gap between the second and third wall sections, and the contaminant expelling system is configured to supply gas to the in-gap gas outlet in the gap between the second and third wall sections, thereby preventing at least a portion of the contaminant present outside the passage from entering into the passage through the gap between the second and third wall sections.

21. The lithographic apparatus of any one of clauses 17 to 20, wherein the second environment is part of an illumination system (IL), and the third environment is part of a projection system (PS).

22. The lithographic apparatus of any one of clauses 17 to 21, configured such that light from the second environment travels through the passage into the first environment, and that light from the first environment travels through the passage into the third environment.

23. The lithographic apparatus of any one of the preceding clauses, wherein at least a part of the passage is of a conical shape.

24. The lithographic apparatus of clause 23, wherein the narrower end of the conical part of the passage opens into the first environment.

25. The lithographic apparatus of any one of the preceding clauses, wherein the contaminant comprises gaseous molecules and/or particulate matter.

26. The lithographic apparatus of any one of the preceding clauses, wherein the contaminant comprises silane.

27. A method of manufacturing devices using the lithographic apparatus of any one of the preceding clauses.

28. A method of expelling a contaminant in a lithographic apparatus (LA), wherein the lithographic apparatus comprises: a first environment (11) in which a source of the contaminant (9) is located, a second environment (12), and a passage (10) through which a light path between the first and second environments is provided, wherein the passage is at least in part defined by first and second wall sections (21, 22), and a gap (312) is present between the first and second wall sections; wherein the method comprises: supplying gas to an in-gap gas outlet (412) located in the gap, thereby preventing at least a portion of the contaminant present outside the passage from entering into the passage through the gap. 29. The method of clause 28, wherein at most 50%, at most 30%, at most 15%, at most 10%, or at most 5% of a total flow rate of gas is supplied to the in-gap gas outlet, the remainder of the total flow rate of gas being supplied via one or more other gas outlets (401, 411) at least partially into the passage.

[0062] While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described.

[0063] The descriptions above are intended to be illustrative, not limiting. Thus, it will be apparent to one skilled in the art that modifications may be made to the invention as described without departing from the scope of the claims set out below.

Claims

2. The lithographic apparatus of claim 1, wherein at most 50%, at most 30%, at most 15%, at most 10%, or at most 5% of a total flow rate of gas is supplied to the in-gap gas outlet, the remainder of the total flow rate of gas being supplied via one or more other gas outlets (401, 411) at least partially into the passage.

3. The lithographic apparatus of any one of the preceding claims, wherein the in-gap gas outlet is substantially co-extensive with the full length of the gap.

4. The lithographic apparatus of any one of the preceding claims, wherein the in-gap gas outlet comprises a plurality of orifices.

5. The lithographic apparatus of any one of the preceding claims, wherein a first end (211) of the passage opens into the first environment.

6. The lithographic apparatus of claim 5, wherein the contaminant expelling system further comprises a passage-end gas outlet (401) and is configured to supply gas to the passage-end gas outlet; wherein the passage-end gas outlet is optionally configured to direct the gas supplied thereto to prevent at least a portion of the contaminant (91) present in the first environment from entering into the passage through the first end of the passage.

7. The lithographic apparatus of claim 5 or claim 6, wherein a second end (221) of the passage opens into the second environment.

8. The lithographic apparatus of claim 7, wherein the contaminant expelling system further comprises an exhaust (219) connected to the passage, and the exhaust is preferably positioned intermediate the first and second ends of the passage.

9. The lithographic apparatus of claim 8, wherein the position at which the gap meets the passage is intermediate the exhaust and the second end of the passage.

10. The lithographic apparatus of any one of claims 7 to 9, wherein the contaminant expelling system further comprises an in-passage gas outlet (411) and is configured to supply gas to the inpassage gas outlet; wherein the in-passage gas outlet is configured to direct the gas supplied thereto to prevent at least a portion of the contaminant present within the passage from exiting the passage through the second end of the passage.

11. The lithographic apparatus of claim 10, wherein: a first flow rate of gas is supplied to the in-gap gas outlet (412), a second flow rate of gas is supplied to the in-passage gas outlet (411), and a third flow rate of gas is supplied to the passage-end gas outlet (401); and the first flow rate is at most 50%, at most 30%, at most 15%, at most 10%, or at most 5% of the sum of the first, second and third flow rates.

12. The lithographic apparatus of claim 10 or claim 11, wherein the in-passage gas outlet is positioned intermediate the exhaust and the second end of the passage.

13. The lithographic apparatus of any one of claims 10 to 12, wherein the position at which the gap meets the passage is intermediate the in-passage gas outlet and the second end of the passage.

14. The lithographic apparatus of any one of claims 10 to 13, wherein the contaminant expelling system further comprises a manifold (42) to which both the in-passage gas outlet and the in-gap gas outlet are connected, and the contaminant expelling system is configured to supply gas to the inpassage gas outlet and the in-gap gas outlet via the manifold.

15. The lithographic apparatus of any one of the preceding claims, wherein the first environment comprises a patterning device (MA).

16. The lithographic apparatus of any one of the preceding claims, wherein the second environment is part of an illumination system (IL) or of a projection system (PS).

17. The lithographic apparatus of any one of the preceding claims, further comprising a third environment (13), wherein one end of the passage opens into both the second and third environments.

18. The lithographic apparatus of claim 17, wherein the passage is at least in part defined by a third wall section (23) in addition to the first and second wall sections.

19. The lithographic apparatus of claim 18, wherein a gap (313) is present between the first and third wall sections, the contaminant expelling system further comprises an in-gap gas outlet (413) provided in the gap between the first and third wall sections, and the contaminant expelling system is configured to supply gas to the in-gap gas outlet in the gap between the first and third wall sections, thereby preventing at least a portion of the contaminant present outside the passage from entering into the passage through the gap between the first and third wall sections.

20. The lithographic apparatus of claim 18 or claim 19, wherein a gap (323) is present between the second and third wall sections, the contaminant expelling system further comprises an in-gap gas outlet (423) provided in the gap between the second and third wall sections, and the contaminant expelling system is configured to supply gas to the in-gap gas outlet in the gap between the second and third wall sections, thereby preventing at least a portion of the contaminant present outside the passage from entering into the passage through the gap between the second and third wall sections.

21. The lithographic apparatus of any one of claims 17 to 20, wherein the second environment is part of an illumination system (IL), and the third environment is part of a projection system (PS).

22. The lithographic apparatus of any one of claims 17 to 21, configured such that light from the second environment travels through the passage into the first environment, and that light from the first environment travels through the passage into the third environment.

23. The lithographic apparatus of any one of the preceding claims, wherein at least a part of the passage is of a conical shape.

24. The lithographic apparatus of claim 23, wherein the narrower end of the conical part of the passage opens into the first environment.

25. The lithographic apparatus of any one of the preceding claims, wherein the contaminant comprises gaseous molecules and/or particulate matter.

26. The lithographic apparatus of any one of the preceding claims, wherein the contaminant comprises silane.

27. A method of manufacturing devices using the lithographic apparatus of any one of the preceding claims.

28. A method of expelling a contaminant in a lithographic apparatus (LA), wherein the lithographic apparatus comprises: a first environment (11) in which a source of the contaminant (9) is located, a second environment (12), and a passage (10) through which a light path between the first and second environments is provided, wherein the passage is at least in part defined by first and second wall sections (21, 22), and a gap (312) is present between the first and second wall sections; wherein the method comprises: supplying gas to an in-gap gas outlet (412) located in the gap, thereby preventing at least a portion of the contaminant present outside the passage from entering into the passage through the gap.

29. The method of claim 28, wherein at most 50%, at most 30%, at most 15%, at most 10%, or at most 5% of a total flow rate of gas is supplied to the in-gap gas outlet, the remainder of the total flow rate of gas being supplied via one or more other gas outlets (401, 411) at least partially into the passage.