NL2013692A - Method for mounting optical elements, suspension arrangements for optical elements, optical apparatus and lithography apparatus. - Google Patents

Description

METHOD FOR MOUNTING OPTICAL ELEMENTS, SUSPENSION ARRANGEMENTS FOR OPTICAL ELEMENTS, OPTICAL APPARATUS AND LITHOGRAPHY APPARATUS

FIELD

The present invention relates to a method of mounting optical elements and suspension apparatuses for optical elements. In particular, the invention relates to such methods and apparatuses for optical elements forming part of an optical apparatus used in lithographic apparatus.

BACKGROUND

[0001] A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. comprising part of, one, or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned.

[0002] Lithography is widely recognized as one of the key steps in the manufacture of ICs and other devices and/or structures. However, as the dimensions of features made using lithography become smaller, lithography is becoming a more critical factor for enabling miniature IC or other devices and/or structures to be manufactured. A theoretical estimate of the limits of pattern printing can be given by the Rayleigh criterion for resolution as shown in equation (1):

(1) where λ is the wavelength of the radiation used, NA is the numerical aperture of the projection system used to print the pattern, kl is a process dependent adjustment factor, also called the Rayleigh constant, and CD is the feature size (or critical dimension) of the printed feature. It follows from equation (1) that reduction of the minimum printable size of features can be obtained in three ways: by shortening the exposure wavelength λ, by increasing the numerical aperture NA or by decreasing the value of kl.

[0003] In order to shorten the exposure wavelength and, thus, reduce the minimum printable size, it has been proposed to use an extreme ultraviolet (EUV) radiation source. EUV radiation is electromagnetic radiation having a wavelength within the range of 5-20 nm, for example within the range of 13-14 nm. It has further been proposed that EUV radiation with a wavelength of less than 10 nm could be used, for example within the range of 5-10 nm such as 6.7 nm or 6.8 nm. Such radiation is termed extreme ultraviolet radiation or soft x-ray radiation. Possible sources include, for example, laser-produced plasma sources, discharge plasma sources, or sources based on synchrotron radiation provided by an electron storage ring.

[0004] EUV radiation may be produced using a plasma. A radiation system for producing EUV radiation may include a laser for exciting a fuel to provide the plasma, and a source collector module for containing the plasma. The plasma may be created, for example, by directing a laser beam at a fuel, such as particles of a suitable material (e.g. tin), or a stream of a suitable gas or vapor, such as Xe gas or Li vapor. The resulting plasma emits output radiation, e.g., EUV radiation, which is collected using a radiation collector. The radiation collector may be a mirrored normal incidence radiation collector, which receives the radiation and focuses the radiation into a beam. The source collector module may include an enclosing structure or chamber arranged to provide a vacuum environment to support the plasma. Such a radiation system is typically termed a laser produced plasma (LPP) source.

[0005] In lithographic apparatuses typically many moving parts are provided with various degrees of freedom, and the positions (including linear and angular position (orientation), velocities and accelerations) are controlled automatically via numerous actuation and suspension arrangements. Actuation and suspension arrangements may be electromagnetically operated, pneumatically of hydraulically operated. They are often constrained to effect movement in only one degree of freedom (linear or rotational). Where the moving parts are to be controlled in plural degrees of freedom, more complex mechanisms may be provided, or multiple single-degree mechanisms may be combined.

[0006] Because of the need for extreme accuracy, and because additionally of the need to work in a vacuum environment with high reliability, designing actuator and suspension arrangements for EUV lithography apparatus is particularly demanding.

[0007] An example where arrays of actuators and suspensions are required is in the facetted mirrors of an illumination system of an EUV optical system. Numerous individual mirror facets may be provided in an array, each of which may need to be oriented in different directions to effect different illumination profiles at a target location. Actuation and suspension arrangements for field facet mirrors are described for example in the published international patent application WO 2011/000671 A1 which is hereby incorporated by reference.

[0008] Field facet mirrors absorb some of the radiation incident upon them, which causes them to heat up. This heat needs to be transported away from the mirror to prevent overheating and/or distortions of the mirror. As EUV systems increase in output power, the heat load on each mirror increases and more heat needs to be transported away from the mirror.

SUMMARY

[0009] It is desirable to facilitate heat transport away from optical components such as field facet mirrors.

[0010] In a first aspect of the invention there is provided a method of mounting an optical component comprising a first mating surface to a suspension component comprising a second mating surface, said method comprising: introducing a liquid thermally conductive material between said first mating surface and second mating surface; and fastening together said first mating surface and second mating surface thereby forming a thermally conductive joint.

[0011] In a second aspect of the invention there is provided an optical device comprising : an optical component comprising a first mating surface; and a mounting plate comprising a second mating surface; a fastener for fastening said optical component to said mounting plate; and a further thermally conductive material between the two mating surfaces.

[0012] In a third aspect of the invention there is provided a suspension arrangement for providing one or more degrees of freedom of movement to a component mounted thereto, wherein said suspension arrangement comprises a flexible corrugated element having a corrugated wall, wherein said corrugated wall comprises a plurality of flexible corrugated layers.

[0013] In a fourth aspect of the invention there is provided a suspension arrangement for providing one or more degrees of freedom of movement to a component mounted thereto wherein said suspension arrangement comprises a liquid thermally conductive material for improving heat conductance from a first end of said suspension arrangement to a second end of said suspension arrangement.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] 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, and in which:

Figure 1 depicts a lithographic apparatus according to an embodiment of the invention;

Figure 2 is a more detailed view of the apparatus 100:

Figure 3 is a more detailed view of the source collector module SO of the apparatus of Figures 1 and 2;

Figure 4 depicts an alternative example of an EUV lithographic apparatus;

Figure 5a is a first cross sectional view of part of an illumination system of a lithographic apparatus in which methods and apparatuses embodying an embodiment of the invention may be used;

Figure 5b is a second cross sectional view of the apparatus of Figure 5 a showing adjustment of a field facet mirror to address two associated pupil facet mirrors;

Figure 6a depicts a novel mirror element mounting process;

Figure 6b depicts a novel mirror element mounting after completion of the mounting process;

Figure 7 illustrates a an actuator and suspension arrangement according to an embodiment of the invention;

Figure 8 illustrates a detail of a flexible multi-walled bellows section according to an embodiment of the invention;

Figure 9(a) illustrates a an alternative actuator and suspension arrangement according to an embodiment of the invention;

Figure 9(b) is an external and partially cut away view of a field facet mirror module according to an embodiment of the invention;

Figure 10 is a section through the central axis of a flexible bellows section according to an embodiment of the invention; and

Figure 11 illustrates a further alternative actuator and suspension arrangement according to an embodiment of the invention;.

DETAILED DESCRIPTION

[0015] Figure 1 schematically depicts a lithographic apparatus 100 including a source collector module SO according to one embodiment of the invention. The apparatus comprises: an illumination system (illuminator) IL configured to condition a radiation beam B (e.g. EUV radiation). a support structure (e.g. a mask table) MT constructed to support a patterning device (e.g. a mask or a reticle) MA and connected to a first positioner PM configured to accurately position the patterning device; a substrate table (e.g. a wafer table) WT constructed to hold a substrate (e.g. a resist-coated wafer) W and connected to a second positioner PW configured to accurately position the substrate; and a projection system (e.g. a reflective projection system) PS configured to project a pattern imparted to the radiation beam B by patterning device MA onto a target portion C (e.g. comprising one or more dies) of the substrate W.

[0016] The illumination system may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic or other types of optical components, or any combination thereof, for directing, shaping, or controlling radiation.

[0017] The support structure MT holds the patterning device MA in a manner that depends on the orientation of the patterning device, the design of the lithographic apparatus, and other conditions, such as for example whether or not the patterning device is held in a vacuum environment. The support structure can use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device. The support structure may be a frame or a table, for example, which may be fixed or movable as required. The support structure may ensure that the patterning device is at a desired position, for example with respect to the projection system.

[0018] The term “patterning device” should be broadly interpreted as referring to any device that can be used to impart a radiation beam with a pattern in its cross-section such as to create a pattern in a target portion of the substrate. The pattern imparted to the radiation beam may correspond to a particular functional layer in a device being created in the target portion, such as an integrated circuit.

[0019] The patterning device may be transmissive or reflective. Examples of patterning devices include masks, programmable mirror arrays, and programmable LCD panels. Masks are well known in lithography, and include mask types such as binary, alternating phase-shift, and attenuated phase-shift, as well as various hybrid mask types. An example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be individually tilted so as to reflect an incoming radiation beam in different directions. The tilted mirrors impart a pattern in a radiation beam which is reflected by the mirror matrix.

[0020] The projection system, like the illumination system, may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic or other types of optical components, or any combination thereof, as appropriate for the exposure radiation being used, or for other factors such as the use of a vacuum. It may be desired to use a vacuum for EUV radiation since other gases may absorb too much radiation. A vacuum environment may therefore be provided to the whole beam path with the aid of a vacuum wall and vacuum pumps.

[0021] As here depicted, the apparatus is of a reflective type (e.g. employing a reflective mask).

[0022] The lithographic apparatus may be of a type having two (dual stage) or more substrate tables (and/or two or more mask tables). In such “multiple stage” machines the additional tables may be used in parallel, or preparatory steps may be carried out on one or more tables while one or more other tables are being used for exposure.

[0023] Referring to Figure 1, the illuminator IL receives an extreme ultra violet radiation beam from the source collector module SO. Methods to produce EUV light include, but are not necessarily limited to, converting a material into a plasma state that has at least one element, e.g., xenon, lithium or tin, with one or more emission lines in the EUV range. In one such method, often termed laser produced plasma ("LPP") the required plasma can be produced by irradiating a fuel, such as a droplet, stream or cluster of material having the required line-emitting element, with a laser beam. The source collector module SO may be part of an EUV radiation system including a laser, not shown in Figure 1, for providing the laser beam exciting the fuel. The resulting plasma emits output radiation, e.g., EUV radiation, which is collected using a radiation collector, disposed in the source collector module. The laser and the source collector module may be separate entities, for example when a C02 laser is used to provide the laser beam for fuel excitation.

[0024] In such cases, the laser is not considered to form part of the lithographic apparatus and the radiation beam is passed from the laser to the source collector module with the aid of a beam delivery system comprising, for example, suitable directing mirrors and/or a beam expander. In other cases the source may be an integral part of the source collector module, for example when the source is a discharge produced plasma EUV generator, often termed as a DPP source.

[0025] The illuminator IL may comprise an adjuster for adjusting the angular intensity distribution of the radiation beam. Generally, at least the outer and/or inner radial extent (commonly referred to as σ-outer and σ-inner, respectively) of the intensity distribution in a pupil plane of the illuminator can be adjusted. In addition, the illuminator IL may comprise various other components, such as facetted field and pupil mirror devices. The illuminator may be used to condition the radiation beam, to have a desired uniformity and intensity distribution in its cross-section.

[0026] The radiation beam B is incident on the patterning device (e.g., mask) MA, which is held on the support structure (e.g., mask table) MT, and is patterned by the patterning device. After being reflected from the patterning device (e.g. mask) MA, the radiation beam B passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W. With the aid of the second positioner PW and position sensor PS2 (e.g. an interferometric device, linear encoder or capacitive sensor), the substrate table WT can be moved accurately, e.g. so as to position different target portions C in the path of the radiation beam B. Similarly, the first positioner PM and another position sensor PS 1 can be used to accurately position the patterning device (e.g. mask) MA with respect to the path of the radiation beam B. Patterning device (e.g. mask) MA and substrate W may be aligned using mask alignment marks Ml, M2 and substrate alignment marks PI, P2.

[0027] The depicted apparatus could be used in at least one of the following modes: 1. In step mode, the support structure (e.g. mask table) MT and the substrate table WT are kept essentially stationary, while an entire pattern imparted to the radiation beam is projected onto a target portion C at one time (i.e. a single static exposure). The substrate table WT is then shifted in the X and/or Y direction so that a different target portion C can be exposed. 2. In scan mode, the support structure (e.g. mask table) MT and the substrate table WT are scanned synchronously while a pattern imparted to the radiation beam is projected onto a target portion C (i.e. a single dynamic exposure). The velocity and direction of the substrate table WT relative to the support structure (e.g. mask table) MT may be determined by the (de-)magnification and image reversal characteristics of the projection system PS. 3. In another mode, the support structure (e.g. mask table) MT is kept essentially stationary holding a programmable patterning device, and the substrate table WT is moved or scanned while a pattern imparted to the radiation beam is projected onto a target portion C. In this mode, generally a pulsed radiation source is employed and the programmable patterning device is updated as required after each movement of the substrate table WT or in between successive radiation pulses during a scan. This mode of operation can be readily applied to maskless lithography that utilizes programmable patterning device, such as a programmable mirror array of a type as referred to above.

[0028] Combinations and/or variations on the above described modes of use or entirely different modes of use may also be employed.

[0029] Figure 2 shows the apparatus 100 in more detail, including the source collector module SO, the illumination system IL, and the projection system PS. The source collector module SO is constructed and arranged such that a vacuum environment can be maintained in an enclosing structure 220 of the source collector module SO. An EUV radiation emitting plasma 210 may be formed by a discharge produced plasma source. EUV radiation may be produced by a gas or vapor, for example Xe gas, Li vapor or Sn vapor in which the very hot plasma 210 is created to emit radiation in the EUV range of the electromagnetic spectrum. The very hot plasma 210 is created by, for example, an electrical discharge causing an at least partially ionized plasma. Partial pressures of, for example, 10 Pa of Xe, Li, Sn vapor or any other suitable gas or vapor may be required for efficient generation of the radiation. In an embodiment, a plasma of excited tin (Sn) is provided to produce EUV radiation.

[0030] The radiation emitted by the hot plasma 210 is passed from a source chamber 211 into a collector chamber 212 via an optional gas barrier or contaminant trap 230 (in some cases also referred to as contaminant barrier or foil trap) which is positioned in or behind an opening in source chamber 211. The contaminant trap 230 may include a channel structure. Contamination trap 230 may also include a gas barrier or a combination of a gas barrier and a channel structure. The contaminant trap or contaminant barrier 230 further indicated herein at least includes a channel structure, as known in the art.

[0031] The collector chamber 211 may include a radiation collector CO which may be a so-called grazing incidence collector. Radiation collector CO has an upstream radiation collector side 251 and a downstream radiation collector side 252. Radiation that traverses collector CO can be reflected off a grating spectral filter 240 to be focused in a virtual source point IF. The virtual source point IF is commonly referred to as the intermediate focus, and the source collector module is arranged such that the intermediate focus IF is located at or near an opening 221 in the enclosing structure 220. The virtual source point IF is an image of the radiation emitting plasma 210.

[0032] Subsequently the radiation traverses the illumination system IL, which may include a facetted field mirror device 22 and a facetted pupil mirror device 24 arranged to provide a desired angular distribution of the radiation beam 21, at the patterning device MA, as well as a desired uniformity of radiation intensity at the patterning de vice MA. Upon reflection of the beam of radiation 21 at the patterning device MA, held by the support structure MT, a patterned beam 26 is formed and the patterned beam 26 is imaged by the projection system PS via reflective elements 28, 30 onto a substrate W held by the wafer stage or substrate table WT.

[0033] More elements than shown may generally be present in illumination optics unit IL and projection system PS. The grating spectral filter 240 may optionally be present, depending upon the type of lithographic apparatus. Further, there may be more mirrors present than those shown in the Figures, for example there may be 1- 6 additional reflective elements present in the projection system PS than shown in Figure 2.

[0034] Collector optic CO, as illustrated in Figure 2, is depicted as a nested collector with grazing incidence reflectors 253, 254 and 255, just as an example of a collector (or collector mirror). The grazing incidence reflectors 253, 254 and 255 are disposed axially symmetric around an optical axis O and a collector optic CO of this type is preferably used in combination with a discharge produced plasma source, often called a DPP source.

[0035] Alternatively, the source collector module SO may be part of an LPP radiation system as shown in Figure 3. A laser LA is arranged to deposit laser energy into a fuel, such as xenon (Xe), tin (Sn) or lithium (Li), creating the highly ionized plasma 210 with electron temperatures of several 10's of eV. The energetic radiation generated during de-excitation and recombination of these ions is emitted from the plasma, collected by a near normal incidence collector optic CO and focused onto the opening 221 in the enclosing structure 220.

[0036] Figure 4 shows an alternative arrangement for an EUV lithographic apparatus in which the spectral purity filter SPF is of a transmissive type, rather than a reflective grating. The radiation from source collector module SO in this case follows a straight path from the collector to the intermediate focus IF (virtual source point). In alternative embodiments, not shown, the spectral purity filter 11 may be positioned at the virtual source point 12 or at any point between the collector 10 and the virtual source point 12. The filter can be placed at other locations in the radiation path, for example downstream of the virtual source point 12. Multiple filters can be deployed. As in the previous examples, the collector CO may be of the grazing incidence type (Figure 2) or of the direct reflector type (Figure 3).

[0037] The following description presents optical apparatus and methods that can condition a radiation beam being directed at a target location on an object. The object can be, for example, a lithographic patterning device MA for generating a circuit pattern to be formed on an individual layer in an integrated circuit, or a substrate W on a substrate table WT of a lithographic apparatus. The target location may be an area of the patterning device MA illuminated by the illumination system IL. Example patterning devices include a mask, a reticle, or a dynamic patterning device. The reticles can also be for use within any lithography process, while the emphasis in this application will be on EUV lithography. Within the illumination system, actuators with suspension arrangements embodying the novel principles described above are used to move reflective elements so as to select different illumination modes.

[0038] Figure 5 a schematically shows a cross sectional view of an exemplary optical apparatus 20 for conditioning a radiation beam in the illumination system IL of a lithographic apparatus of the type shown in Figures 1 to 4. Apparatus 20 includes a first optical component in the form of facetted field mirror device 22 and a second optical component in the form of facetted pupil mirror device 24. Facetted field mirror device 22 comprises a plurality of primary optical elements, some particular ones schematically indicated in Figure 5a and referred to as field facet mirror elements 22a, 22b, 22c and 22d. The second optical component 24 comprises a plurality of secondary optical elements including, for example, the particular secondary optical elements referred to as pupil facet mirror elements 24a, 24b, 24c, 24d, and 24a’, 24b’, 24c', 24d’.

[0039] Generally, the field facet mirror elements 22a-d direct respective parts of incoming radiation beam B towards the pupil facet mirror elements 24a-d, 24a’-d’. Although only four field facet mirror elements 22a-d are shown, any number of field facet mirror elements may be provided. The field facet mirror elements may be arranged in a generally two-dimensional array , which does not mean that they should lie strictly in a flat plane. Although only eight pupil facet mirror elements 24a-d, 24a’-d’ are shown, any number of pupil facet mirror elements may be provided, the number being typically a multiple of the number of field facet mirror elements. The pupil facet mirror elements may be arranged in a two-dimensional array. The shapes and configurations of the field facet mirror elements and pupil facet mirror elements may be square, rectangular, circular, or more complicated in shape, according to design.

[0040] Each field facet mirror element 22a-d reflects a portion of the radiation beam B received by the first reflective component (22) in the form of a sub-beam of radiation towards a different pupil facet mirror element 24a-d of the pupil mirror device 24. For example, a first sub-beam Ba is directed by a first field facet mirror element 22a to a first pupil facet mirror element 24a. Second, third and fourth sub-beams Bb, Be and Bd are directed by second, third and fourth field facet mirror elements 22b, 22c, and 22d respectively to second, third and fourth pupil facet mirror elements 24b, 24c, and 24d. The spatial intensity distribution of the radiation beam B at the pupil mirror device 24 cA define an illumination mode of the lithographic apparatus. In one embodiment, the field facet mirror elements 22a-d have adjustable orientations, and they may be used with different ones of the pupil facet mirror elements 24a-d, 24a’-d’, to form different spatial intensity distributions at the pupil plane P, thereby providing different illumination modes. This option, which is known per se, will be described later with reference to Figure 5b. The pupil facet mirror elements 24a-d may also be adjustable in orientation.

[0041] Each of the field facet mirror elements 22a-d is shaped so as to form an image of the intermediate focus IF at a different pupil facet mirror element 24a-d, of the pupil mirror device 24. In practice, the intermediate focus IF will be a virtual image of the plasma source, the image having a finite diameter (e.g. 4-6 mm). Consequently, each field facet mirror element 22a-d will form an image of the virtual source point IF which has a finite diameter (e.g. 3-5 mm) at the pupil facet mirror elements 24a-d. The pupil facet mirror elements 24a-d, may each have a diameter which is larger than the aforementioned image diameter (to avoid radiation falling between pupil facet mirror elements and thereby being lost). The intermediate focus IF and images of the intermediate focus IF are shown as points in the figures for ease of illustration only.

[0042] The facetted mirror devices 22 and 24 together form a so-called “fly’s eye” illuminator, by which non-uniformities present in the radiation source are eliminated to illuminate area E with more even distribution, and with more control. Each one of the pupil facet mirror elements 24a-d may form an image of its associated field facet mirror element 22a-d at or near the field plane wherein the patterning device MA is located during exposure of a substrate. These images are substantially overlapping and together form an illumination area E. As a result, a spatially non-uniform intensity distribution in a cross section of the radiation B as emanating from the source SO and received by the apparatus 20 is conditioned to have a substantially spatially uniform intensity distribution in the illumination area E. The shape of the illumination area E is determined by the shape of the field facet mirror elements 22a-d. In a scanning lithographic apparatus the illumination area E may for example be a rectangle or a curved band, when viewed in two dimensions which in the scanning direction has a width narrower than the width in a direction perpendicular to the scanning direction.

[0043] A wavelength of the desired part of radiation may be an EUV wavelength in the range 5-20nm, for example 13.5nm. The beam B may also include large amounts of unwanted radiation, for example at DUY wavelengths. Other patent publications disclose techniques for reducing the transmission of unwanted radiation through the illuminator.

[0044] As mentioned already, each field facet mirror element 22a-d of field mirror device 22 may have more than one associated pupil facet mirror elements of pupil mirror device 24. A field facet mirror element 22a of field mirror device 22 can be controlled to cooperate with different ones of its associated pupil facet mirror elements 24a at different times. For example, as shown in Figure 5b, field facet mirror element 22a has two associated pupil facet mirror elements 24a and 24a’. These are used in different illumination modes of illuminator 20. Field facet mirror element 22a may thus be controlled in a second mode to direction EUV radiation towards pupil facet mirror element 24a’ instead of 24a, while radiation with an undesired wavelength, such as DUV radiation may be scattered to fall onto neighboring pupil facet mirror elements like 24c, 24d, 24b’ or 24c’. In some embodiments, pupil facet mirror elements may also have controllable orientation. Again, the design can be made such that the pupil facet mi rror elements most closely surrounding the associated mirror will direct the scattered DUV radiation away from the target (illumination area E).

[0045] Mounting of the field facet mirrors to the suspension arrangement presents challenges due to the need to transport heat away from the field facet mirror elements through the mounting. Laser welding of the field facet mirror elements to a mounting plate (forming part of the suspension and actuator arrangement) is an option, although this presents limitations. In particular, using laser welds limits the materials from which the mirrors can be manufactured when the suspension is made of copper. Copper is desirable for the suspension and mirror mounting due to its excellent heat conducting properties. Use of laser welding with copper suspension means that the mirrors need also be copper, and that materials such as ultra low expansion glass, quartz and silicon cannot be used. However it is difficult to produce EUV of sufficiently high quality at the output following transport via copper mirrors. Also there is a limit to the maximum allowed temperature of copper mirrors. This limited temperature (compared with silicon mirrors, which may be heated up to temperatures greater than 150°C) severely limits the heat load capacity of the apparatus. Also, welded joints make it difficult to repair, replace or realign a mirror element, as it is difficult to undo a welded join.

[0046] Another option would be to attach the mirror by screwing, bolting or clamping. However, it is known that screwing or clamping processes present a main disadvantage of having low heat conductivity. The mirror and mounting plate would only be in contact at a few points of the joint, which become the only points which are in thermal communication. Between these few points is a non-conducting vacuum.

[0047] Figure 6a illustrates a novel mounting process for mounting optical components, such as the field facet mirror elements or pupil facet mirror elements described above. Figure 6b illustrates the same apparatus subsequent to completion of the mounting process.

[0048] Shown is a field facet mirror element 22a being attached to a mounting plate 520. During mounting of the field facet mirror element 22a, a few microliters (for example less than 10 μΐ) of a thermally conductive material may be introduced within the gap 530 between the mating surfaces of the field facet mirror element 22a and mounting plate 520. The thermally conductive material acts as a thermal interface between mating surfaces of the field facet mirror element 22a and mounting plate 520. The field facet mirror element 22a can then be attached to the mounting plate 520 by a fastener 510 such as a screw, bolt or similar, to form joint 550. The mounting plate 520 may be, for example, a component of the bellows section 540 of a flexible suspension arrangement (such as any disclosed below).

[0049] The conductive material should be vacuum compatible (i.e. very low or no outgassing) and simple to disassemble when required. Consequently, thermal grease (such as that used to mount power transistors to cooling plates) is not ideal as its outgassing rate does not match EUV vacuum environment requirements. It is therefore proposed to use a low vapour pressure, high thermal conductivity (k) liquid metal. Suitable liquid metals may have a maximum vapour pressure of 10'8 mbar, and preferably less than 10"10 mbar and may have a minimum thermal conductivity coefficient of 2.5 W/m/K, and preferably greater than 25 W/m/K. The higher the thermal conductivity coefficient value for the liquid metal, the lower the thermal resistance. This allows the filled gap to be larger, or the mating surface area to be smaller. The thermal resistance of the assembled joint should be at most 1 K/W, and preferably less than 0.1 K/W.

[0050] By way of example, the liquid metal may comprise gallium (Ga) (k = 40 Wm^K"1) or alternatively a gallium alloy, such as those comprising indium (In) and/or tin (Sn). In specific examples, it is proposed that Eutectic Gallium-Indium (k = 50 Wm4K_1), or GalnSn may be used. Of course, other non-Gallium based metals may be used instead.

[0051] The thermal conductivity of the joint 550 is given by summing the conductance within the conductive material and the conductivity of the mating interfaces. The conductance (σ) of the conductive material within gap 530 when said mirror element 22a is mounted as shown in Figure 6, is given by Equation (2): (7 = 1 /Rth=kA/L (2), where R* is the thermal resistance of the conductive material, A is the cross sectional area at the mating interface, k the thermal conductivity (in SI units Wm 'K'1) of the conductive material used and L the gap width. Note that it is preferable that gap L be set to the minimum value imposed by the manufacturing process.

[0052] It can be shown that Gallium or a Gallium based alloy material fulfils the thermal conductivity requirements for EUV applications. It can also be shown that Gallium and Gallium based alloys meet EUV vacuum environment requirements (pressures less than 10"8 -10"10 mbar for most materials).

[0053] As the conductive material is in a liquid state during the mounting process, the process should be carried out at a temperature reaching, at least, the melting point of the selected metal material. Skilled persons will know that Gallium or Gallium based alloy have melting temperatures which are within an easily achievable temperature range. In addition to this, the good wettability on metallic and non-metallic surfaces (for example, glass or quartz) of Gallium or Gallium based alloys helps it to adhere on solid surfaces, and thus, to fill gap 530.

[0054] The conductive material may be in a liquid or solid state during normal operation, after mounting. Being solid means that the conductive material may act like an adhesive between mating surfaces of the mirror element 22a and mounting plate 520. However, an increase in volume has to be taken into account during the change of state between liquid into a solid. For example, the volume of Gallium material increases by 3.1% when the material solidifies.

[0055] Note that several metals may react with or dissolve in Gain alloys. Where such alloys (or similar) are used as the conductive material, a protective coating material may be provided on the mating surfaces to avoid such unwanted corrosion of material. For example, a layer of nickel material (for, example of the order of lpm in thickness) may be deposited onto the mating surfaces prior to the introduction of the conductive material (i.e. nickel plating). Other materials may be also employed, for instance gold, magnesium, lead, tungsten or tantalum for high resistance to corrosion and, to a lesser extent, titanium or molybdenum.

[0056] Also note that by cooling the joint 550 below the freezing point of the metal material, the metal material becomes even stronger, reducing the apparatus sensitivity to shock forces, for instance during transportation.

[0057] Advantages of the arrangement described above, as compared to the prior art, include easier dismantling and repair and that the mirror elements (or mounting plates) can be made of a wider range of materials including non-metallic materials, for example ultra low expansion glass, quartz or silicon.

[0058] It should be noted that this mounting process is not only applicable to mounting of optical components but also for forming other thermal interfaces within lithographic systems such as EUY lithographic systems.

[0059] Figure 7 illustrates an embodiment of a field facet mirror 22 including a novel flexible actuation and suspension apparatus 700. The apparatus 700 comprises a number of actuator assemblies 705, one for each mirror element 22a. For actuation, each actuator assembly 705 comprises coil pairs located below a moving magnet that is mounted on rod 732. Each actuator assembly 705 is generally cylindrical in form, allowing it to cluster side by side with similar actuator assemblies 705 for the other mirror elements 22a in the apparatus. The actuator assembly mounting plate 720 and rod 732 are supported on upper casing 728 by a suspension comprising a combination of a flexible element (such as a flexible corrugated element hereafter referred to as bellows) 740 and three or four (or any other number) tendons 710. Each tendon 710 is fixed at its bottom end (as illustrated) into the wall of casing section and at its top end into actuator assembly rod 732, passing through apertures 750. Mounting plate 720 may be attached to mirror element 22a using the mounting method described in relation to Figures 6a and 6b.

[0060] It will be appreciated that the bellows 740 permits two dimensional tilting motions dRx and dRy that are desired to adjust the angle of mirror element 22a. With regard to other degrees of freedom, tendons 710 effectively form a tripod/tetrapod which constrains against translation of the pivot point of mirror element 22a in X, Y, and Z directions, while bellows 740 constrains rotation Rz around the Z axis. “Constraining” in this context means providing a very high degree of stiffness against the relevant degree of freedom, sufficient to act effectively as a rigid mounting.

[0061] For compatibility with the vacuum environment within EUV lithography apparatus, bellows 740 may for example be made of corrugated metal.

[0062] Figure 8 shows a detail of the bellows 740 in cross-section. As can be seen, bellows 740 comprises multiple thin and flexible bellows components 740a, 740b, 740c arranged concentrically, rather than a single thicker bellows component. Skilled persons will know that, in an example arrangement comprising rectangular leaf springs with thickness d, the bending force is proportional to d3 and the maximum stress and thermal conductivity scale with d. By replacing a single spring, having thickness D, with n springs of thickness d=D/n, the maximum stress (at the surface of a single leaf spring) is reduced by a factor n and the bending force is reduced by a factor n3/n=n2. This lower stress level can be used for a larger angular range, while still ensuring sufficient component lifetime. These advantages are realised with the bellows 740 comprising bellows components 740a, 740b, 740c, compared to a single thicker bellows component. Three bellows components are shown here, but other numbers are possible.

[0063] In addition, the total cross section of the bellows 740 will be the same as that of a single bellows component, provided that there are n bellows components each having a thickness 1/n times that of the single bellows component. Therefore, the thermal conduction is the same for both arrangements. Consequently with this arrangement, the compromise between stiffness force and thermal conduction of the bellows 740 turns to be considerably more advantageous than for a single thick walled bellows (for example, n times thicker). Single walled bellows may comprise walls of 70 μιη - 100 μπι thickness, and therefore bellows components 740a, 740b, 740c may have a thickness of approximately 1 ΟΟμπι/n, where n is the number of bellows components. In an embodiment with three bellows components 740a, 740b, 740c, each bellows component 740a, 740b, 740c may be between 20pm and 40 μιη thick.

[0064] . To increase the thermal conduction of the bellows 740, they may be made of an alloy with good conductance and high mechanical properties (high fatigue strength). For example, materials such as beryllium copper (BeCu) or so-called Wieland-K88 copper alloy may be used.

[0065] Bellows 740 may be formed by hydraulically forming concentric metal sheet cylinders in a mold. The bellows components 740a, 740b, 740c may be made of different alloys, e.g. copper bellows, for a better heat conduction, in combination with a stainless steel material for the innermost and outermost bellows to maintain high fatigue properties.

[0066] The extremities of bellows 740 may be connected, for example, to a mounting plate 720 (at the mirror end) and/or a cooling plate (at the end opposite the mirror end) via laser welding. This ensures that the very small gaps between each of the bellows components 740a, 740b, 740c are enclosed. Therefore, any debris particles that may be formed by the surfaces of bellows components 740a, 740b, 740c contacting and sliding against each other as they move (i.e. during switching of illumination mode) will remain confined within the enclosed space as long as the inner and outer bellows are not punctured. Figure 8 shows bellows 740 attached to mounting plate 720 via a laser weld 800.

[0067] Figure 9 shows (a) an alternative flexible actuation and suspension apparatus 900 and (b) a detail of one of the actuator assemblies 905. As before the actuator assemblies 905 are applied to effect movement of reflecting elements serving as field facet mirror components 22a in the illumination system of an EUV lithography apparatus such as the ones described above.

[0068] Concerning the suspension, it will be seen that the single bellows 740 that enclosed the upper part of the mechanism in Figures 6a and 6b is replaced by two narrower bellows 940a and 940b extending between the actuator assembly head 922 and two opposite sides of a chassis part 928. Four tendons 910, two of which are in the center of the bellows 940a and 940b, extend from anchoring points on the chassis part 928 to the mounting plate 920 (tendons 910 may number more or less than four). As in the case of the three tendons 710 of the previous example, these tendons 910 point towards a virtual pivot point, and define the x, y, z position of this point. The bellows 940a and 940b constrain the Rz degree of freedom.

[0069] Therefore, where the previous example had a suspension arrangement comprising a tripod/tetrapod of tendons 710 and a single bellows 740, the suspension arrangement in this example comprises a tetrapod of tendons 910, and two bellows 940a, 940b in V-shape which prevent rotation around the Z axis. The tendons 910 are uniformly spaced around the actuator assembly’s 905 central (Z) axis. The suspension arrangement again provides two degrees of freedom for tilting the mounting plate 920 in direction Rx and Ry. Movement in the Z direction as well as translation in X and Y are substantially or completely prevented. Mounting plate 920 may be attached to mirror element 22a using the mounting method described in relation to Figures 6a and 6b.

[0070] It will be appreciated that the two bellows 940a, 940b of the suspension forming part of apparatus 900 may also comprise multiple thin and flexible bellows components, as illustrated in Figure 8 and described above.

[0071] In conclusion, the multi-wall flexible bellows 740, 940a, 940b shows various improvements when compared to prior art arrangements, such as the ability to handle higher heat loads, a larger angular range, reduced bearing length and reduced motor forces.

[0072] As already explained, thermal conductivity of flexible suspension components such as bellows 740, 940a, 940b, is important to transport heat away from the mirror elements 22a. It is known to include within the bellows, a large number of thin copper wires, also known as Litze wire. The fill grade of such Litze wires is maximum 50%, which limits the thermal conductivity within the bellows. To address this, in an embodiment, it is proposed to increase thermal conductance of the bellows 740, 940a, 940b by filling the bellows 740, 940a, 940b with a highly thermally conductive liquid. It should be appreciated that this concept is applicable to both the multi-wall flexible bellows 740, 940a, 940b described above, or to any other bellows arrangements (e.g. single wall bellows). By using liquid filled bellows, the stiffness introduced by the links is minimized and the hysteresis is cancelled.

[0073] It is proposed that the conductive liquid may comprise a metal which has sufficient thermal conductivity and which is liquid at room or operating temperature. Mercury may be used, but is not preferred due to its toxicity. Less toxic and therefore preferred alternatives include gallium-based alloys such as eutectic Gain or GalnSn.

[0074] The overall thermal conductivity of the apparatus may be calculated by summing the thermal resistance of the conductive liquid (given by Equation (2) where in this case L is the length of the bellows and A the cross sectional area of the bellows) and the resistance of the contact interfaces (Rc).

[0075] Figure 10 illustrates a bellows arrangement according to a further embodiment. The type of bellows illustrated is bellows 940a or 940b as shown in Figure 9, although the basic concept is applicable to other types of bellows arrangements. It shows a cross section of bellows 940a, the inside of which comprises alternate convex 960a and concave 960b conductive (e.g. copper) disks arranged in a similar pattern to that of a vertebral column, such that they are able to move or rotate with respect to each other. In this configuration, the disks 960a, 960b are immersed in the conductive liquid. In this arrangement, most conduction occurs through the highly conductive disks 960a, 960b (assuming copper - k = 400 Wnf'K"1). Conduction thorough the liquid (which has a lower conductivity than the disks) only occurs at the gaps between adjacent conductive disks 960a, 960b and the gaps between the end disks 960a and the plugs 970a, 970b.

[0076] Providing figures purely as an example , the flexible bellows 940a, 940b of this embodiment may be 30 mm long with an inner diameter of 4 mm. Bellows 940a, 940b may comprise, for example, 4 mm long nickel connectors. The thermal resistance of a bellows 940a, 940b filled with convex and concave copper disks 960a, 960b, as described above, and immersed in Ga(InSn) liquid, may be calculated using Equation (3): R,h - LNi /(AkNi) + LCu KAkCui) + LGaln/(AkGaln) + NxRr (3), where N is the number of interfaces, R the thermal resistance of the material, A the cross sectional area of the bellows, L the length of the bellows, the subscript Ni denotes nickel material, the subscript Cu denotes copper material and Gain denotes Gain alloys. The liquid layer thickness between the disks of the copper assembly, having 16 interface layers, is of the order of 0.1 mm. This gives Rth= 12 KW'1.

[0077] In a suspension arrangement comprising, for example, two bellows per bearing the total resistance of the apparatus be 6 KW'1 or better. The apparatus resistance is able to accept heat loads of the order of 250 W from Laser-produced plasma (LPP) and discharge-produced plasma (DPP) sources.

[0078] As mentioned previously, several metals react with or dissolve in Gain alloys and therefore surfaces which may come into contact with these metals may be coated or plated with nickel or another material which does not react with the alloy.

[0079] Figure 11 illustrates, in cross-section, a further embodiment of a suspension and actuator arrangement. It comprises a field facet mirror component 1022a which is actuatable around a pivot point 1010 via spherical-type joint 1020. Joint 1020 comprises a (part) ball section 1030 and base section 1040. Ball section 1030 connects the field facet mirror component 1022a to an actuator rod 1032 and magnet 1050 (which is actuated by electromagnetic coils (not shown). Consequently, actuation of the magnet 1050 actuates field facet mirror component 1022a such that joint 1020 allows rotation around the X-axis and Y-axis, centered on pivot point 1010, while constraining translation of the pivot point 1010 in X, Y, and Z directions. As with previous embodiments, rotation around the Z-axis may be constrained by a bellows (not shown). Such a bellows may be located at the field facet mirror element 1022a (around the circumference of ball section 1030) and a body of the suspension and actuator arrangement, such as part of base section 1040. The bellows may also be filled with liquid thermally conducting material in accordance with some of the embodiments described above.

[0080] To improve heat conduction through the joint 1020, the gap 1060 between the bearing surfaces of joint 1020 is filled with a highly thermally conductive liquid. The thermally conductive liquid may of the thermally conductive liquids described in relation to the previous embodiments, for example a gallium alloy.

[0081] 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 multiple processed layers.

[0082] 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, for example imprint lithography, and where the context allows, is not limited to optical lithography. In imprint lithography a topography in a patterning device defines the pattern created on a substrate. The topography of the patterning device may be pressed into a layer of resist supplied to the substrate whereupon the resist is cured by applying electromagnetic radiation, heat, pressure or a combination thereof. The patterning device is moved out of the resist leaving a pattern in it after the resist is cured.

[0083] The term “lens”, where the context allows, may refer to any one or combination of various types of optical components, including refractive, reflective, magnetic, electromagnetic and electrostatic optical components.

[0084] While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. For example, the invention may take the form of a computer program containing one or more sequences of machine-readable instructions describing a method as disclosed above, or a data storage medium (e.g. semiconductor memory, magnetic or optical disk) having such a computer program stored therein. 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 clauses set out below. Other aspects of the invention are set-out as in the following numbered clauses.

CLAUSES 1. A device comprising : a first component comprising a first mating surface; and a suspension component comprising a second mating surface; a fastener for fastening said component to said suspension component mounting plate; and a thermally liquid conductive material between the two mating surfaces being part of a thermally conductive joint. 2. A device as claused in clause 1 wherein said liquid thermally conductive material comprises a liquid metal. 3. A device as claused in clause 2 wherein said liquid metal has a maximum vapour pressure of 10"8 mbar and a minimum thermal conductivity coefficient of 2.5 W/m/K,. 4. A device as claused in clause 2 or 3 wherein said thermally conductive material comprises gallium or a gallium based metal. 5. A device as claused in clause 4 wherein one or more surfaces in contact with said gallium or gallium based metal comprise a protective coating. 6. A device as claused in any preceding clause wherein said suspension component forms part of the suspension arrangement of any of clauses 21 to 53 7. A device as claused in any preceding clause wherein said liquid thermally conductive material comprises a liquid metal. 8. A device as claused in any of clauses 1 to 6 wherein said liquid thermally conductive material comprises a solid metal, said solid metal having been liquid during fastening of said optical component to said suspension component. 9. A device as claused in clause 7 or 8 wherein said thermally conductive material comprises gallium or a gallium based metal. 10. A device as claused in clause 9 wherein one or more surfaces in contact with said gallium or a gallium based metal comprise a protective coating. 11. A device as claused in any preceding clause wherein said suspension component comprises a metallic material and said first component comprises a non-metallic material. 12. A device as claused in clause 11 wherein said non-metallic material comprises one of a glass, quartz or silicon material. 13. A device as claused in any preceding clause wherein said thermally conductive material is vacuum compatible. 14. A device as claused in any preceding clause wherein said fastener comprises a screw or a clamp. 15. A device according to any preceding clauses wherein said first component is an optical component. 16. An optical apparatus comprising a series of said devices as claused in clause 15 arranged such that said first components receive a radiation beam from a radiation source to process and deliver the beam to a target location. 17. An optical apparatus as claused in clause 16 wherein said devices form part of an illumination system for conditioning said beam and delivering it to a target location on a patterning device, and wherein said optical components are movable to vary an incidence angle of the conditioned beam at the target location. 18. An optical apparatus as claused in clause 16 or 17 wherein a plurality of such devices with associated suspension apparatuses and actuators are provided as part of a fly’s eye illuminator. 19. An optical apparatus as claused in any of clauses 16 to 18 wherein said optical components are reflective components and said illumination system is an EUV illumination system operable with radiation with a wavelength in the range 5 to 20 nm. 20. A lithographic apparatus, comprising: an illumination system configured to condition a radiation beam; a support constructed to support a patterning device, the patterning device being capable of imparting the radiation beam with a pattern in its cross-section to form a patterned radiation beam; a substrate table constructed to hold a substrate; a projection system configured to project the patterned radiation beam onto a target portion of the substrate; and an optical apparatus according to any of clauses 16 to 19 configured to condition at least one of the radiation beam in the illumination system and the patterned radiation beam in the projection system. 21. A suspension arrangement for providing one or more degrees of freedom of movement to a component mounted thereto, wherein said suspension arrangement comprises a flexible element having a wall, wherein said wall comprises a plurality of flexible layers. 22. A suspension arrangement as claused in clause 21 wherein said plurality of flexible layers are arranged concentrically. 23. A suspension arrangement as claused in clause 21 or 22 wherein said plurality of flexible layers comprise a plurality of flexible corrugated layers. 24. A suspension arrangement as claused in clause 22 wherein said flexible corrugated element has been formed by hydraulically forming concentric metal sheet cylinders in a mold. 25. A suspension arrangement as claused in any of clauses 21 to 26 wherein said plurality of flexible layers are each comprised of a metal. 26. A suspension arrangement as claused in any of clauses 21 to 25 wherein one or more layers comprise a material optimized for good fatigue properties. 27. A suspension arrangement as claused in any of clauses 21 to 26 wherein one or more layers comprise a material optimized for good thermal conduction. 28. A suspension arrangement as claused in any of clauses 21 to 27 wherein different layers of said plurality of flexible layers comprise different materials. 29. A suspension arrangement as claused in clause 28 wherein the innermost and outermost layers comprise a material optimized for good fatigue properties and the remaining layers comprise a material optimized for good thermal conduction. 30. A suspension arrangement as claused in any of clauses 21 to 29 wherein said flexible element is attached to one or more other components of said suspension arrangement such that the gaps between each of said plurality of flexible layers is sealed. 31. A suspension arrangement as claused in any of clauses 21 to 30 wherein said flexible element is attached to one or more other components of said suspension arrangement by laser welding. 32. A suspension arrangement as claused in any of clauses 21 to 31 wherein said suspension arrangement is operable to provide two degrees of freedom of movement and said flexible element is operable to allow said two degrees of freedom of movement while constraining a third degree of freedom of movement. 33. A suspension arrangement as claused in any of clauses 21 to 32 wherein said flexible element contains a liquid thermally conductive material for conducting heat from a first end of said flexible element to a second end of said flexible element. 34. A suspension arrangement as claused in clause 33 wherein said liquid thermally conductive material comprises a liquid metal. 35. A suspension arrangement as claused in clause 34 wherein said thermally conductive material comprises gallium or a gallium based metal. 36. A suspension arrangement as claused in clause 35wherein one or more surfaces in contact with said gallium or a gallium based metal comprise a protective coating. 37. A suspension arrangement as claused in any of clauses 34 to 36 wherein said flexible element contains a plurality of disk elements between said first end and second end, such that said disk elements and said liquid thermally conductive material forms a conductive path between said first end and second end. 38. A suspension arrangement as claused in clause 37 wherein said disk elements comprise alternate first and second disks, said first disks having convex top and bottom surfaces and second disks having concave top and bottom surfaces. 39. A suspension arrangement as claused in any of clauses 21 to 36 wherein said flexible element contains a ball joint and a liquid thermally conductive material is comprised between the bearing surfaces of said ball joint. 40. A suspension arrangement as claused in any of clauses 21 to 39 wherein said suspension arrangement comprises an optical component mounted thereto. 41. A suspension arrangement for providing one or more degrees of freedom of movement to a component mounted thereto wherein said suspension arrangement comprises a liquid thermally conductive material for improving heat conductance from a first end of said suspension arrangement to a second end of said suspension arrangement. 42. A suspension arrangement as claused in clause 41 wherein said liquid thermally conductive material comprises a liquid metal. 43. A suspension arrangement as claused in clause 42 wherein said thermally conductive material comprises gallium or a gallium based metal. 44. A suspension arrangement as claused in clause 43 wherein one or more surfaces in contact with said gallium or a gallium based metal comprise a protective coating. 45. A suspension arrangement as claused in any of clauses 41 to 44 comprising a ball joint, wherein said liquid thermally conductive material is comprised between the bearing surfaces of said ball joint. 46. A suspension arrangement as claused in any of clauses 41 to 45 comprising a flexible element, wherein said liquid thermally conductive material is contained within said flexible element. 47. A suspension arrangement as claused in clause 46 wherein said flexible element is a flexible corrugated element. 48. A suspension arrangement as claused in clause 47 or 48 wherein said liquid thermally conductive material is operable to conduct heat from a first end of said flexible element to a second end of said flexible element. 49. A suspension arrangement as claused in clause 47. 48 or 49 wherein said flexible element contains a plurality of disk elements between said first end and second end, such that said disk elements and said liquid thermally conductive material forms a conductive path between said first end and second end. 50. A suspension arrangement as claused in clause 49 wherein said disk elements comprise alternate first and second disks, said first disks having convex top and bottom surfaces and second disks having concave top and bottom surfaces. 51 A suspension arrangement as claused any of clauses 34 to 50 wherein said suspension arrangement is operable to provide two degrees of freedom of movement and said flexible element is operable to allow said two degrees of freedom of movement while constraining a third degree of freedom of movement. 52. A suspension arrangement as claused any of clauses 34 to 51 wherein said liquid thermally conductive material is vacuum compatible 53. A suspension arrangement as claused any of clauses 34 to 52 wherein said suspension arrangement comprises an optical component mounted thereto. 54. An optical apparatus comprising a series of optical components arranged to receive a radiation beam from a radiation source to process and deliver the beam to a target location, wherein said optical components include one or more movable optical components mounted on suspension arrangement as claused in any of clauses 15 to 53. 55. An optical apparatus as claused in clause 54 wherein said movable optical component forms part of an illumination system for conditioning said beam and delivering it to a target location on a patterning device, and wherein said movable component is movable to vary an incidence angle of the conditioned beam at the target location. 56 An optical apparatus as claused in clause 54 or 55 wherein a plurality of such movable components are provided as part of a fly’s eye illuminator. 57. An optical apparatus as claused in any of clauses 54 to 56 wherein said optical components are reflective components and said illumination system is an EUV illumination system operable with radiation with a wavelength in the range 5 to 20 nm. 58. A lithographic apparatus, comprising: an illumination system configured to condition a radiation beam; a support constructed to support a patterning device, the patterning device being capable of imparting the radiation beam with a pattern in its cross-section to form a patterned radiation beam; a substrate table constructed to hold a substrate; a projection system configured to project the patterned radiation beam onto a target portion of the substrate; and an optical apparatus according to any of clauses 54 to 57 configured to condition at least one of the radiation beam in the illumination system and the patterned radiation beam in the projection system. 59. A method of mounting a component comprising a first mating surface to a suspension component comprising a second mating surface, said method comprising: introducing a liquid thermally conductive material between said first mating surface and second mating surface; and fastening together said first mating surface and second mating surface thereby forming a thermally conductive joint. 60. A method as claused in clause 59 wherein said liquid thermally conductive material comprises a liquid metal. 61. A method as claused in clause 60 wherein said liquid metal has a maximum vapour pressure of 10"8 mbar and a minimum thermal conductivity coefficient of 2.5 W/m/K,. 62. A method as claused in clause 60 or 61 wherein said thermally conductive material comprises gallium or a gallium based metal. 63. A method as claused in clause 62 wherein one or more surfaces in contact with said gallium or gallium based metal comprise a protective coating. 64. A method as claused in any of clauses 59 to 63 wherein said thermally conductive material remains in a liquid state subsequent to forming of said joint. 65. A method as claused in any of clauses 59 to 63 wherein said thermally conductive material solidifies subsequent to forming of said joint. 66. A method as claused in any of clauses 59 to 65 wherein the suspension component is an optical component. 67. A method as claused in any of clauses 59 to 66 wherein said suspension component comprises a metallic material and said optical component comprises a non-metallic material. 68. A method as claused in any of clauses 59 to 67 further comprising the step of subsequently disassembling said joint for maintenance and/or repair. 69. A method as claused in any of clauses 59 to 68 wherein said fastening together of said two mating surfaces comprises mechanically fastening the devices together with a fastener. 70. A method as claused in clause 69 wherein said fastener comprises a screw, bolt or a clamp. 71. A method as claused in any of clauses 59 to 70 wherein said suspension component comprises a mounting plate. 72. A method as claused in any preceding clause wherein said suspension component comprises the suspension arrangement of any of clauses 21 to 53. 73. A method according to any preceding clauses wherein the component is an optical component.

Claims (1)

A lithography device comprising: an exposure device adapted to provide a radiation beam; a carrier constructed to support a patterning device, the patterning device being capable of applying a pattern in a section of the radiation beam to form a patterned radiation beam; a substrate table constructed to support a substrate; and a projection device adapted to project the patterned radiation beam onto a target area of the substrate, characterized in that the substrate table is adapted to position the target area of the substrate in a focal plane of the projection device.