Reticle capture arrangement for a lithographic apparatus

Abstract

A stage arrangement including an electrostatic clamp for clamping an object such a reticle. The electrostatic clamp includes at least one primary power supply for providing power at least to the electrostatic clamp; and at least one backup power supply operable to provide power to the electrostatic clamp to retain the object for at least a time period in the event of the at least one primary power supply not providing power to the electrostatic clamp, wherein the at least the one backup power supply is configured to supply a current no larger than mA and / or the backup power supply and the electrostatic clamp store no more than 10 J. In addition an arrangement is described to move the reticle stage to a pre-defined location and capture the reticle.

Description

RETICLE CAPTURE ARRANGEMENT FOR A LITHOGRAPHIC APPARATUSCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority of US application 63 / 668,578 which was filed on 08 July 2024 and which is incorporated herein in its entirety by reference.FIELD

[0002] The present disclosure relates to exposure apparatuses or lithographic apparatuses used in the manufacture of, for example, integrated circuits. In particular, the present disclosure relates to, for example, reticle capture arrangements for such apparatuses for capturing a reticle, for example in the event of power failure.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.SUMMARY

[0005] EUV lithographic devices use reflective optics to prevent the absorption of the EUV radiation by transmissive elements. These reflective optics include the patterning device, typically referred to as the “mask” or “reticle” (all three terms are synonymous). Due to this, EUV reticles are clamped from the backside face-down within the lithographic apparatus. The clamping is performed using a high- voltage electrostatic clamp (the reticle environment is a vacuum, again to prevent EUV absorption, and therefore the use of vacuum clamps is not particularly feasible). This means that the reticle should be clamped at all times to prevent it from falling down into the lithographic apparatus.

[0006] Safety catches are typically provided to catch the reticle should there be a power failure or other lithographic apparatus (e.g., clamp) malfunction, so to prevent the reticle falling down into the lithographic apparatus. These safety catches add a non-negligible weight to the moving mass of the reticle stage, which is an additional mass which needs to be accelerated by one or more stage actuators.

[0007] It would be desirable to improve present reticle capture arrangements, such as the safety catchesdescribed.

[0008] In a first aspect, there is provided a stage arrangement comprising an electrostatic clamp for clamping an object, the electrostatic clamp comprising: at least one primary power supply for providing power at least to the electrostatic clamp; and at least one backup power supply operable to provide power to the electrostatic clamp to retain the object for at least a time period in the event of the at least one primary power supply not providing power to the electrostatic clamp, wherein the at least the one backup power supply is configured to supply a current no larger than 5 mA and / or the backup power supply and the electrostatic clamp stores no more than 10 J.

[0009] In a second aspect, there is provided a stage arrangement comprising an electrostatic clamp for clamping an object, the electrostatic clamp comprising: at least one primary power supply for providing power at least to the electrostatic clamp; at least one backup power supply operable to provide power to the electrostatic clamp to retain the object for at least a time period in the event of the at least one primary power supply not providing power to the electrostatic clamp; and a static capture arrangement operable to catch the object and / or maintain the object in place in the event of no clamping force or insufficient clamping force to hold the object being provided by the electrostatic clamp, wherein the static capture arrangement is not comprised within a moving mass of the stage arrangement and object.

[0010] In a third aspect, there is provided a stage arrangement comprising: an electrostatic clamp for clamping an object; and a static capture arrangement operable to catch the object and / or maintain the object in place in the event of no clamping force or insufficient clamping force to hold the object being provided by the electrostatic clamp, wherein the static capture arrangement is not comprised within a moving mass of the stage arrangement and object.BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which:Figure 1 depicts a lithographic system comprising a lithographic apparatus and a radiation source;Figure 2a is schematic drawing of a human safe power supply arrangement for a reticle clamp according to a first example;Figure 2b is schematic drawing of a human safe power supply arrangement for a reticle clamp according to a second example;Figure 3 a is schematic drawing of a human safe power supply arrangement for a reticle clamp according to a third example;Figure 3b is schematic drawing of a human safe power supply arrangement for a reticle clamp according to a fourth example;Figure 4 depicts a first example static capture arrangement according to concepts disclosed herein;Figure 5 depicts a second example static capture arrangement according to concepts disclosed herein;Figure 6 depicts a third example static capture arrangement according to concepts disclosed herein; andFigure 7 depicts a reticle with a pellicle frame, illustrating a region on the reticle with which the static capture arrangements according to concepts disclosed may contact during capture.DETAILED DESCRIPTION

[0012] 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 (or reticle stage) 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.

[0013] The illumination system IL is configured to condition the EUV radiation beam B before the EUV radiation beam B is incident upon the patterning device MA. Thereto, the illumination system IL may include a facetted field mirror device 10 and a facetted pupil mirror device 11. The faceted field mirror device 10 and faceted pupil mirror device 11 together provide the EUV radiation beam B with a desired cross-sectional shape and a desired intensity distribution. The illumination system IL may include other mirrors or devices in addition to, or instead of, the faceted field mirror device 10 and faceted pupil mirror device 11.

[0014] After being thus conditioned, the EUV radiation beam B interacts with the patterning device (or reticle) MA. The support structure MT, hereafter a reticle stage, may support the patterning device MA by clamping it electrostatically, and may be configured to scan the patterning device MA during exposures. As a result of the interaction of EUV radiation beam B and patterning device MA, a patterned EUV radiation beam B’ is generated. The projection system PS is configured to project the patterned EUV radiation beam B’ onto the substrate W. For that purpose, the projection system PS may comprise a plurality of mirrors 13,14 which are configured to project the patterned EUV radiation beam B’ onto the substrate W held by the substrate table WT. The projection system PS may apply a reduction factor to the patterned EUV radiation beam B’, thus forming an image with features that are smaller than corresponding features on the patterning device MA. For example, a reduction factor of 4 or 8 may be applied. Although the projection system PS is illustrated as having only two mirrors 13,14 in Figure 1, the projection system PS may include a different number of mirrors (e.g. six or eight mirrors).

[0015] 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.

[0016] 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.

[0017] 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.

[0018] In EUV lithographic apparatuses, mechanical safety catches are provided which capture and retain the reticle / patterning device in the event of clamping failure or malfunction (e.g., due to a power failure or other event). It can be appreciated that, even if a malfunction does not in itself result in a loss of power to the clamping electrodes, the power may have to be shut down to repair or remedy the malfunction. This is because a power supply used to supply the clamp electrodes may not be human safe, and therefore cannot remain on if human access is required to the reticle stage / vacuum compartment.

[0019] Such mechanical safety catches are actively opened while loading / unloading a reticle, and closed in order to contain the reticle in the event of electrostatic clamp failure. These safety catches are small and fairly complex mechanisms comprising many parts. Due to this complexity, they can be prone to sensor, mechanical, and / or actuator failure. They also typically add 1-2 kg of mass to the fast-moving reticle stage which increases the requirements for the one or more reticle stage actuators to achieve the necessary reticle stage acceleration.

[0020] Additionally, the safety catches typically involve design compromises in the chuck design to accommodate these catches and their actuators. For example, they can require holes in the chuck, causing defectivity issues. The long legs of the safety catches may limit servo performance due to their vibrations. Because reticles can be loaded at a variety of offsets, the positions of the safety catches are configured to accommodate a wide range of reticle positions.

[0021] Furthermore, dropping a reticle onto the safety catches will likely create contaminants, e.g., glass and steel particles, which may result in major defectivity risks both for the dropped reticle and for other reticles (by cross-contamination via the safety catches, and possibly via the reticle masking module (ReMa)). In addition, the reticles themselves may become scratched and damaged in the fall.

[0022] A number of improved reticle retainment and / or capture arrangements will now be described, which improve on reticle capture arrangements embodied by the aforementioned safety catches.

[0023] In each case, the method may comprise providing a human safe power supply with redundancy (e.g., one or more backup supplies or uninterruptable power supplies) operable to maintain a charge on the electrostatic clamp should there be a machine malfunction (loss of power to the clamp). Such a human safe uninterruptable power supply (UPS) may have a (e.g., dedicated) controller or control circuit. By providing a human safe backup supply, it is possible to allow human access to the vacuum chamber (chamber comprising the reticle stage).

[0024] A current primary power supply (high voltage power amplifier) may be made human safe by placing the (or each) primary power supply within a (e.g., tamper-resistant) grounded case (to prevent human contact with high voltage components inside) and to provide at least one resistor at the output of the (or each) primary power supply in order to limit the maximum current that the power supply candeliver.

[0025] In this context, human safe may be defined as comprising a stored energy less than 10 J and / or a current less than 5mA. The stored energy condition may be met intrinsically by the clamping electrodes themselves (electrode capacitance is on the order of microfarads or less), but not necessarily by a backup circuit (UPS circuit) comprising a battery or a high-capacity capacitor. However, in embodiments or examples which use such a battery or a high-capacity capacitor, the backup circuit can be made intrinsically safe by adding a resistor to the backup circuit between the energy storage and any output of the device that could be accessed by an operator, (e.g., of the order of 100 kohm (e.g., 500 kohm) for a 500 V backup or on the order of 1 Mohm (e.g., 5 Mohm) for a 5000 V primary supply). However, the actual resistance will be dependent on the supply voltage being made human safe.

[0026] Figures 2(a) and 2(b) illustrate two variations on a first example, where a primary power supply arrangement (comprising a high voltage power amplifier) may be modified to provide redundancy and make it human safe. For example, there may be provided first and second uninterruptible power supplies UPS1, UPS2 (e.g., two high voltage power amplifiers) to ensure complete redundancy. Each of the two power supplies UPS1, UPS2 may comprise a built-in power back-up sources BPS (e.g., battery or capacitor based) so as to be uninterruptible, and output protective resistors PR to make them human safe. Each of the two primary power supplies UPS1, UPS2 may be completely isolated from each other, and may have independent cabling to connect to the clamp (such that if one cable fails, the other maintains the clamp charged to hold the reticle). More specifically, in this example each uninterruptible power supply UPS1, UPS2 comprises at least one amplifier AMP (e.g., two amplifiers providing respectively a -1-kV order magnitude and -kV order magnitude output). Each amplifier provides power to a respective electrode El, E2, E3, E4 of a reticle clamp CMP, so as to retain reticle MA. The amplifiers are controlled via a logic controller LGC receiving a control signal CTL.

[0027] The only difference between the examples of Figure 2(a) and Figure 2(b) is the position of the protective resistors PR: respectively at the amplifier AMP outputs or between the back-up supply BPS and amplifiers AMP.

[0028] Figures 3(a) and 3(b) illustrate variations on an alternative arrangement, where a primary power supply design is unmodified and a separate backup supply BPS arrangement provided, e.g., between the clamp CMP and primary high voltage power supply HVPS. In an arrangement, a controller LGC is arranged to disconnect the primary power supply HVPS from the clamp CMP either in the event of primary power failure or other malfunction / switch off event, or disconnect the primary power supply each time a reticle MA is clamped. This may be achieved by controlling switches SW. In the latter case, the controller LGC may disconnect the primary power supply HVPC after charging the clamp every time that the clamp is charged. The backup power supply BPS can be connected and maintain the charge on the clamp until a time that the clamp is to be turned off (the reticle is to be released), at which point the primary power supply HVPS is reconnected in place of the backup supply. Alternatively, in the event of a malfunction or emergency, the backup power supply BPS may be configured to supply powerto the clamp CMP in place of the primary power supply HVPS, which is disconnected (isolated). This may comprise monitoring one or more selected from: the clamp voltage, primary power supply voltage and / or power on status of the lithographic apparatus.

[0029] In one such example, two separate uninterruptible power supplies UPS1, UPS2, each comprising a respective backup power supply BPS, is connected in series with the clamp CMP. The reticle clamp CMP typically comprises two pairs of clamping electrodes El, E3; E2, E4, and it is proposed that a back-up supply BPS is connected respectively to each pair of clamping electrodes. This provides redundancy in case one of the back-up supplies fails. To maximize redundancy, the cabling for each backup power supply BPS can also be separated and made independent. . It will be appreciated that the electrodes could be constituted by any pair such as E2, E3; El, E4. Furthermore, the electrodes could be single-ended and not paired. Appropriate circuit arrangements would be implemented to enable the various configurations to function effectively.• The backup power supplies may each comprise: a capacitor or battery; e.g., a low voltage battery of 24 V or less. This may be charged via a low voltage charging supply Vch;• a high voltage step-up DC-DC transformer SUT; e.g., to raise the battery output to a voltage to a magnitude (positive and negative) of the order of thousands of volts (e.g., more than 1,000 V magnitude and less than 20,000 V magnitude);• an output protective resistor PR on each output terminal (in the Figure 3(a) example) which limits the current that the power supply can output below the 5 mA (or less, e.g., below 4 mA, below 3 mA or below 2 mA) threshold for human safety; and• a control circuit LGC or switching circuit.

[0030] In the Figure 3(b) example, the protective resistor is placed between the back-up power supply BPS and the step-up transformer SUT. In this example, the resistor (on the order of 100 ohms) may be used to limit the input current to the step-up transformer such that the output current of the step-up transformer is limited to below 5 mA. The benefit of this configuration is that no part of the circuit (even within the sealed box) can reach levels of voltage and current which pose a risk to human safety.

[0031] Each control circuit LGC or switching circuit may be configured, in the event of power failure or shut down, to maintain the voltage on the respective clamp electrodes to which it is connected, until power is restored or until the reticle stage has moved above a static capture arrangement for capturing the reticle (examples of static capture arrangements will be described). In case of normal operation, it may be configured not to interfere. Each control circuit LGC may monitor a heartbeat signal from the primary power supply HVPS and monitor the voltage of the two clamp electrodes El, E3; E2, E4 to which it is connected. Based on the status of this monitoring (e.g., indicating loss of power or other malfunction), the control circuit LGC (and / or another external controller which receives the status) may intervene and implement one or both backup supplies BPS.

[0032] In another example, the backup supply BPS may be embodied as an additional capacitorcomprised within the clamp circuit, which is charged by the primary power supply, thereby increasing the discharge time of the clamp CMP in case of failure / power down. In such an embodiment, the primary power supply HVPS may be configured to disconnect from the capacitor in event of failure. Depending on the size of the capacitor, a resistor PR may also be added (as has been described) to ensure human safety.

[0033] In another example, the backup supply may be embodied within the clamp and / or the reticle, i.e., by the inherent capacitance of the clamp and / or reticle, or modifying one of the clamp and / or reticle. For example, the primary power supply may be configured to intentionally charge the reticle backside (e.g., prior to load) such that the reticle stays clamped in event of power failure / power down. This can be achieved by, for example, using ionizers or using materials like electrets (which can retain charge). Alternatively or in addition, the inherent capacitance of the clamp (i.e., the clamped reticle assembly) may be used to a similar effect. The primary power supply may be configured to separate from the clamp in the event of power failure / power down.

[0034] In all the examples described above, the backup power supply may be completely isolated from and / or autonomous with the primary power supply.

[0035] The human safe backup power supply (UPS 1 , UPS2) of any of the examples described herein may be configured, in the event of power failure or shut down, to maintain the voltage on the respective clamp electrodes to which it is connected until power is restored. However, in an alternative embodiment, such a backup power supply may be provided in combination with a static capture arrangement for capturing the reticle. In such examples, the backup power supply may be configured to provide a clamping force for only a short time period until the reticle stage is moved to a position where the reticle will be caught by the reticle capture arrangement. For example, where the backup power supply is battery or capacitance based, the charge provided need only be sufficient to provide a clamping force for a short time period. Such a short time period may be less than a minute, less than 30 s, less than 10 s, less than 1 s, less than 0.5 s, less than 0.3 s, less than 0.2 s or less than 0.1 s for example. In this way, a backup supply source (e.g., battery or capacitor) need only have a small capacity.

[0036] The static capture arrangement may be “static” in the context that it is not attached to and / or does not move with the reticle stage as is the case with the presently used safety catches; nevertheless, at least part of the static capture arrangement may be movable. In this way, the static capture arrangement does not add to the moving mass of the reticle stage and does not need to be accelerated by the one or more reticle stage actuators. Instead, the static capture arrangement may be located at one or more positions below the reticle scan path, where the scan path describes the path covering the full stroke of the reticle stage long-stroke module, i.e., the full extent over which the reticle moves during exposures.

[0037] It is typically not possible to provide a static capture arrangement over the full scan path due to conflict with other modules (such as the reticle exchange module), and therefore a backup supply may be provided to retain the reticle until at least the reticle stage can be moved to a location above the staticcapture arrangement.

[0038] The static capture arrangement may comprise any static means for capturing and holding the reticle as it falls from the clamp. As such, the static capture arrangement may be mounted to any module at any suitable position directly below the reticle scan path.

[0039] One such suitable module may comprise a fluid supply module (e.g., gas supply module) for providing a purging fluid to and / or in the vicinity of the reticle. By way of a specific example, the static capture arrangement may be mounted to a respective top surface of one or more Y-nozzles (some present EUV lithographic apparatuses comprise two Y-nozzles). A Y-nozzle is a nozzle for purge gas supply directed along the reticle in the scanning direction (conventionally the Y-direction).

[0040] The static capture arrangement may be configured to capture the reticle at a very small distance below the clamp, e.g., such that the reticle falls only a very small distance when dropped. As such, the static capture arrangement may be located at only a short distance below the reticle (when it is positioned above). This distance may be less than 5 mm, less than 3 mm, less than 2 mm or less than 1 mm for example. Alternatively, or in addition, this may be achieved by making the static capture arrangement actuatable toward the reticle in the event of power loss to the clamp, i.e., once the reticle stage has moved to a position above the static capture arrangement. In this case, the static capture arrangement may be configured to prevent the reticle from falling at all, or such that it falls a negligible or very small distance. In such an example, during recovery, and after reticle clamping voltage is restored to a sufficient level, the safety features can then be lowered before the reticle stage starts to move. Of course, the movement of the static capture arrangement towards the reticle may be sufficiently slow to make a soft contact with the reticle.

[0041] Minimizing the drop height has an advantage of, for example, minimizing damage to the reticle, minimizing the production of debris and contaminants caused by the reticle falling onto the capture arrangement and / or (if sufficiently small) enabling the reticle to be recovered by the clamp electrostatically when power is restored.

[0042] The static capture arrangement may have a soft material on its one or more capture (contact) surfaces with the reticle to (further) minimize reticle damage. This should be possible as a static capture arrangement may be placed away from the EUV beam. Such as soft material may be a thermoplastic polymer such as polyether ether ketone (PEEK). Alternatively or in addition, the static capture arrangement may have sufficient flexibility, again to minimize risk of reticle damage, and / or may be (dissipatively) conducting to avoid risk of flashovers and discharges.

[0043] A proposed static capture arrangement and / or its associated backup power supply may further comprise a dedicated control module (e.g., control electronics) to bring the reticle to a position above this static safety feature. This dedicated control module may be powered by the human safe uninterruptable backup. The backup supply may be located within the vacuum vessel, for example.

[0044] The proposed static capture arrangement may comprise a number (e.g., at least 3, desirably at least 4) of support features (e.g., pads, legs or other point-like features), or a pair of rail features, forexample.

[0045] Figure 4 illustrates a first arrangement for the static capture arrangement. Shown is a top-down view showing a Y-nozzle module (top surface) 200, reticle mask blades 205, a reticle stage 210 in a first position (e.g., centrally in the reticle scan path). Shown dotted are the reticle positions 215, 220 at the furthest extent at each end of the reticle scan path (i.e., the reticle is scanned back and forth between positions 215, 220 during exposures. The region labeled 225 (e.g., in the region of the uniformity correction module) is not able to be used for supporting the static capture arrangement due to conflict with the reticle exchange module (not shown). In this example, four supports 230 are provided on the Y-nozzle module 200 top surface, e.g., at a position where the reticle can be captured along the reticle scan path. Here the supports 230 are provided above the reticle at the furthest extent of the scan path away from region 225; however the supports may be placed anywhere below the reticle scan path (between positions 215, 220) where there is no conflict with other modules or parts (e.g., also away from region 225).

[0046] Figure 5 shows a similar arrangement to Figure 4, except the support features 230’ (only one labeled) are located more centrally along the scan path. Such support features may be provided at any point along the scan path which will not result in a conflict with any other modules or components.

[0047] Figure 6 shows a similar arrangement to Figures 4 and 5, but where safety rails 235a, 235b or support rails are provided rather than the support features described. In this specific example, the safety rails are provided in two sections: a first pair of rails 235a and second pair of rails 235b, with a gap between to prevent conflict with the reticle mask blades 205. The second set of rails do not extend into the area labeled 225 due to the aforementioned conflict with the reticle exchange module. It can be appreciated, however, that only one of these pairs of rails is necessary in such an example. Furthermore, whether one or both of these pairs of rails are provided, they may differ in length from shown (provided they are sufficiently long to capture and support the reticle). The safety rail may be attached to and / or supported by the top surface of one or more of the Y-nozzles 200 (or any other module directly below the scan path depending on the apparatus configuration). The advantage of rails is that they provide a greater capturing length along the scan path, and therefore control precision of the reticle stage is less important prior to the reticle becoming unclamped.

[0048] Such an arrangement may also allow for a passive construction that pulls the reticle stage sufficiently towards the module below (e.g., Y-nozzle) to allow for a shorter drop. This may comprise a passive device, for example a (e.g., low-stiffness) spring which acts to constantly pull the reticle stage towards the reticle capture location. During normal operation, the motors of the reticle stage counteract the stiffness of this spring. In the event of a power failure, the spring will pull the reticle stage to the reticle capture location. This spring could be incorporated into the cables and hoses which deliver power and water to the reticle stage, and already have stiffness. The passive device may comprise a ramp and a system of wheels, rollers, or sliders, such that in the event of power loss to the stage, the stage will roll down the ramp to the location of the reticle capture device.

[0049] The static capture arrangement may be configured to capture the reticle via contact at only peripheral areas on either side of the reticle in the non-scanning or X-direction. These peripheral areas may be areas between the reticle edge and pellicle frame. This region may be the peripheral regions on either side which extend up to 6 mm from each edge toward the reticle center in the X-direction.

[0050] Figure 7 illustrates a reticle 500, and pellicle frame 510, illustrating the peripheral regions 520 which may be contacted by the static capture arrangement when captured.

[0051] The capture mechanism could be configured to allow retrieval of the reticle after the system has recovered from the emergency or power loss event. The reticle capture mechanism could have a pneumatic bellows, stepper motor, or other mechatronic system to allow it to lift the reticle towards the reticle clamp, such that the clamp could activate and clamp the reticle. After clamping the reticle the capture mechanism could again be retracted, and the reticle stage could then move to unload the reticle from the system.

[0052] As an aside, static capture arrangement may also be used to hold a dummy reticle, with the reticle clamp above this dummy reticle, during venting (and e.g., during service actions to the bottom module) to protect the reticle clamp from contamination.

[0053] Removing safety catches from the moving mass can reduce the moving mass of the reticle stage by about 7%, resulting in a corresponding acceleration increase.

[0054] 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. Possible other applications include 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.

[0055] Although specific reference may be made in this text to embodiments of the invention in the context of a lithographic apparatus, embodiments of the invention may be used in other apparatus. Embodiments of the invention may form part of a mask inspection apparatus, a metrology apparatus, or any apparatus that measures or processes an object such as a wafer (or other substrate) or mask (or other patterning device). These apparatus may be generally referred to as lithographic tools. Such a lithographic tool may use vacuum conditions or ambient (non- vacuum) conditions.

[0056] 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, where the context allows, is not limited to optical lithography and may be used in other applications, for example imprint lithography.

[0057] Where the context allows, embodiments of the invention may be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the invention may also be implemented as instructions stored on a machine -readable medium, which may be read and executed by one or more processors. A machine -readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, amachine -readable medium may include read only memory (ROM); random access memory (RAM); magnetic storage media; optical storage media; flash memory devices; electrical, optical, acoustical or other forms of propagated signals (e.g. carrier waves, infrared signals, digital signals, etc.), and others. Further, firmware, software, routines, instructions may be described herein as performing certain actions. However, it should be appreciated that such descriptions are merely for convenience and that such actions in fact result from computing devices, processors, controllers, or other devices executing the firmware, software, routines, instructions, etc. and in doing that may cause actuators or other devices to interact with the physical world.

[0058] Aspects of the invention are described in the following numbered clauses.1. A stage arrangement comprising an electrostatic clamp for clamping an object, the electrostatic clamp comprising: at least one primary power supply for providing power at least to the electrostatic clamp; and at least one backup power supply operable to provide power to the electrostatic clamp to retain the object for at least a time period in the event of the at least one primary power supply not providing power to the electrostatic clamp, wherein the at least one backup power supply is configured to supply a current no larger than 5mA and / or the at least one backup power supply and the electrostatic clamp store no more than 10 J.2. The stage arrangement as in clause 1 , wherein the at least one backup power supply is configured to supply a current no larger than 2 mA.3. The stage arrangement as in clause 1, wherein the at least one backup power supply is configured to supply a current no larger than 1 mA.4. The stage arrangement as in any preceding clause, wherein the at least one primary power supply is configured to supply a current no larger than 5 mA.5. The stage arrangement as in clause 4, wherein each at least one primary power supply comprises a resistor at its output to maintain its supplied current to be no larger than 5 mA.6. The stage arrangement as in clause 4, wherein each at least one primary power supply comprises a resistor between its power source and a step-up transformer comprised therein to maintain the supplied current at the output of the transformer to be no larger than 5 mA.7. The stage arrangement as in any preceding clause, wherein the at least one primary power supply is configured to be disconnected from the electrostatic clamp each time that the electrostatic clamp is charged, until a time that the electrostatic clamp is to be discharged, the at least the one backup power supply being connected to the electrostatic clamp during the time period that the at least one primary power supply is disconnected.8. The stage arrangement as in any preceding clause, wherein the at least one primary power supply is configured to be disconnected from the electrostatic clamp in the event of the at least one primary power supply not providing power to the electrostatic clamp.9. The stage arrangement as in any preceding clause, wherein the object comprises a patterning device.10. The stage arrangement as in clause 9, wherein the patterning device comprises a reflective patterning device.11. The stage arrangement as in any preceding clause, wherein the at least one primary power supply comprises a first uninterruptible primary power supply and the at least one backup power supply comprises a second uninterruptible primary power supply.12. The stage arrangement as in clause 11, wherein each of the first uninterruptible primary power supply and second uninterruptible primary power supply comprise respective separate cabling to connect to the electrostatic clamp.13. The stage arrangement as in clause 11 or clause 12, wherein each of the first uninterruptible primary power supply and second uninterruptible primary power supply comprise a respective backup power source.14. The stage arrangement as in any preceding clause, wherein the at least one backup power supply comprises a respective separate backup power supply for each of a first pair of clamping electrodes of the electrostatic clamp and a second pair of clamping electrodes of the electrostatic clamp.15. The stage arrangement as in any preceding clause, wherein each at least one backup power supply comprises a battery power source.16. The stage arrangement as in any preceding clause, wherein each at least one backup power supply comprises a capacitor power source.17. The stage arrangement as in clause 16, wherein the capacitor power source is provided by a capacitance of the electrostatic clamp and / or the object.18. The stage arrangement as in any preceding clause, wherein each at least one backup power supply comprises a resistor at its output to maintain its supplied current to be no larger than 5 mA.19. The stage arrangement as in any preceding clause, wherein each at least one backup power supply comprises one or more resistors or one or more other current limiting devices at the input to an amplifier or step-up transformer comprised within each at least one backup power supply, to prevent the amplifier or step-up transformer from delivering current of more than 5 mA.20. The stage arrangement as in any preceding clause, further comprising a static capture arrangement being operable to catch the object and / or maintain the object in place in the event of no clamping force or insufficient clamping force to hold the object being provided by the electrostatic clamp, wherein the static capture arrangement is not comprised within a moving mass of the stage arrangement and object.21. The stage arrangement as in clause 20, wherein the static capture arrangement is located below a scan path of the electrostatic clamp.22. The stage arrangement as in clause 21, wherein the static capture arrangement is mounted to at least one module located below the scan path of the electrostatic clamp.23. The stage arrangement as in clause 22, wherein the at least one module comprises at least one purge fluid nozzle module.24. The stage arrangement as in any of clauses 20 to 23, wherein the static capture arrangementcomprises at least one set of capture features.25. The stage arrangement as in clause 24, wherein each at least one set of capture features comprises at least three features.26. The stage arrangement as in clause 24 or clause 25, wherein the at least one set of capture features comprises at least one pair of capture rails.27. The stage arrangement as in any of clauses 20 to 26, operable to move to the object to a position above the static capture arrangement in the event of the at least one primary power supply not providing power to the electrostatic clamp.28. The stage arrangement as in clause 27, comprising a passive device to bring the object to the position above the static capture arrangement in the event of the at least one primary power supply not providing power to the electrostatic clamp.29. The stage arrangement as in clause 28, wherein the passive device comprises a spring or ramp.30. The stage arrangement as in clause 27, clause 28 or clause 29, wherein the at least one backup power supply comprises a power source sufficient to retain the object clamped at least until the object has moved to the position above the static capture arrangement.31. The stage arrangement as in any of clauses 20 to 30, wherein the static capture arrangement is operable to move towards the object once the object has moved to the position above the static capture arrangement.32. The stage arrangement as in any of clauses 20 to 31, wherein the static capture arrangement comprises a soft contact surface.33. The stage arrangement as in any of clauses 20 to 32, wherein, once the object has moved to the position above the static capture arrangement, the static capture arrangement is located less than 2 mm below the object.34. The stage arrangement as in any of clauses 20 to 32, wherein, once the object has moved to the position above the static capture arrangement, the static capture arrangement is located less than 1 mm below the object.35. The stage arrangement as in any of clauses 20 to 34, wherein the static capture arrangement is operable to contact the object at only two peripheral regions at each edge of the object in a non-scanning direction.36. The stage arrangement as in clause 35, wherein the two peripheral regions comprise the outermost 6 mm at each edge of the object in the non-scanning direction.37. The stage arrangement as in any of clauses 20 to 34, wherein the static capture arrangement is dissipatively conducting.38. The stage arrangement as in any of clauses 20 to 37, wherein the static capture arrangement is actuatable to move the object towards the electrostatic clamp to aid retrieval of the object when power is restored.39. The stage arrangement as in any preceding clause, wherein the at least one backup power supplycomprises a power source sufficient to retain the object clamped for up to one second.40. The stage arrangement as in any preceding clause, wherein the at least one backup power supply comprises a power source sufficient to retain the object clamped for up to half a second.41. A stage arrangement comprising an electrostatic clamp for clamping an object, the electrostatic clamp comprising: at least one primary power supply for providing power at least to the electrostatic clamp; at least one backup power supply operable to provide power to the electrostatic clamp to retain the object for at least a time period in the event of the at least one primary power supply not providing power to the electrostatic clamp; and a static capture arrangement operable to catch the object and / or maintain the object in place in the event of no clamping force or insufficient clamping force to hold the object being provided by the electrostatic clamp, wherein the static capture arrangement is not comprised within a moving mass of the stage arrangement and object.42. A stage arrangement comprising: an electrostatic clamp for clamping an object; and a static capture arrangement operable to catch the object and / or maintain the object in place in the event of no clamping force or insufficient clamping force to hold the object being provided by the electrostatic clamp, wherein the static capture arrangement is not comprised within a moving mass of the stage arrangement and object.43. A lithographic apparatus comprising the stage arrangement of any preceding clause, being configured to support a patterning device.44. The lithographic apparatus as in clause 43, further comprising: projection optics for projecting patterned radiation onto a substrate, the patterned radiation having been patterned by the patterning device; and a substrate support for supporting the substrate.

[0059] While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. The descriptions above are intended to be illustrative, not limiting. Thus it will be apparent to one skilled in the art that modifications may be made to the invention as described without departing from the scope of the claims set out below.

Claims

CLAIMS1. A stage arrangement comprising an electrostatic clamp for clamping an object, the electrostatic clamp comprising: at least one primary power supply for providing power at least to the electrostatic clamp; and at least one backup power supply operable to provide power to the electrostatic clamp to retain the object for at least a time period in the event of the at least one primary power supply not providing power to the electrostatic clamp, wherein the at least one backup power supply is configured to supply a current no larger than 5mA and / or the at least one backup power supply and the electrostatic clamp store no more than 10 J.

2. The stage arrangement as claimed in claim 1, wherein the at least one primary power supply is configured to supply a current no larger than 5 mA.

3. The stage arrangement as claimed in claim 2, wherein each at least one primary power supply comprises a resistor at its output to maintain its supplied current to be no larger than 5 mA.

4. The stage arrangement as claimed in any preceding claim, wherein the at least one primary power supply is configured to be disconnected from the electrostatic clamp each time that the electrostatic clamp is charged, until a time that the electrostatic clamp is to be discharged, the at least the one backup power supply being connected to the electrostatic clamp during the time period that the at least one primary power supply is disconnected.

5. The stage arrangement as claimed in any preceding claim, wherein the at least one primary power supply is configured to be disconnected from the electrostatic clamp in the event of the at least one primary power supply not providing power to the electrostatic clamp.

6. The stage arrangement as claimed in any preceding claim, wherein the object comprises a patterning device.

7. The stage arrangement as claimed in any preceding claim, wherein the at least one primary power supply comprises a first uninterruptible primary power supply and the at least one backup power supply comprises a second uninterruptible primary power supply.

8. The stage arrangement as claimed in claim 7, wherein each of the first uninterruptible primary power supply and second uninterruptible primary power supply comprise respective separate cabling to connect to the electrostatic clamp.

9. The stage arrangement as claimed in any preceding claim, wherein each at least one backup power supply comprises a battery power source or a capacitor power source.

10. The stage arrangement as claimed in any preceding claim, further comprising a static capture arrangement being operable to catch the object and / or maintain the object in place in the event of no clamping force or insufficient clamping force to hold the object being provided by the electrostatic clamp, wherein the static capture arrangement is not comprised within a moving mass of the stage arrangement and object.

11. The stage arrangement as claimed in claim 10, wherein the static capture arrangement is located below a scan path of the electrostatic clamp.

12. The stage arrangement as claimed in any of claims 10 or 11, operable to move the object to a position above the static capture arrangement in the event of the at least one primary power supply not providing power to the electrostatic clamp.

13. The stage arrangement as claimed in claim 12, comprising a passive device to bring the object to the position above the static capture arrangement in the event of the at least one primary power supply not providing power to the electrostatic clamp.

14. The stage arrangement as claimed in claim 12 or claim 13, wherein the at least one backup power supply comprises a power source sufficient to retain the object clamped at least until the object has moved to the position above the static capture arrangement.

15. A stage arrangement comprising an electrostatic clamp for clamping an object, the electrostatic clamp comprising: at least one primary power supply for providing power at least to the electrostatic clamp; at least one backup power supply operable to provide power to the electrostatic clamp to retain the object for at least a time period in the event of the at least one primary power supply not providing power to the electrostatic clamp; and a static capture arrangement operable to catch the object and / or maintain the object in place in the event of no clamping force or insufficient clamping force to hold the object being provided by the electrostatic clamp, wherein the static capture arrangement is not comprised within a moving mass of the stage arrangement and object.

16. A stage arrangement comprising:an electrostatic clamp for clamping an object; and a static capture arrangement operable to catch the object and / or maintain the object in place in the event of no clamping force or insufficient clamping force to hold the object being provided by the electrostatic clamp, wherein the static capture arrangement is not comprised within a moving mass of the stage arrangement and object.

17. A lithographic apparatus comprising the stage arrangement of any preceding claim, being configured to support a patterning device.

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