Diaphragm cleaning device

Abstract

A diaphragm cleaning apparatus for removing particles from a diaphragm, comprising: a diaphragm support; and an electric field generation mechanism. And the diaphragm supporting piece is used for supporting the diaphragm. The electric field generating mechanism is configured to generate an electric field near the diaphragm when the diaphragm is supported by the diaphragm support. The electric field generating mechanism may include: one or more collectors; and a mechanism for applying a voltage across the diaphragm supported by the diaphragm support and one or each of the one or more collectors.

Description

[0001] This application is a divisional application of the patent application with application number 201980079386.0 and invention name “Diaphragm Cleaning Equipment”, which entered the Chinese national phase on May 27, 2021 (international application date is 2019-11-22, international application number is PCT / EP2019 / 082184). Technical Field

[0002] The present invention relates to a diaphragm cleaning apparatus and related method. The apparatus and method have particular application for cleaning pellicles used in lithographic apparatus. Background Art

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

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

[0005] Unwanted particles present on the patterning device may contribute to the pattern imparted to the radiation beam. In a lithographic apparatus, this may result in errors in the pattern applied to the substrate. Therefore, it is important to prevent particles from reaching and thereby contaminating the patterning device. It is known to provide a diaphragm between a particle source and the patterning device in a lithographic apparatus to prevent particles from reaching the patterning device. Diaphragms used for this purpose are referred to in the art as pellicles.

[0006] The pellicle is spaced from the patterning device so that it is not in the field plane and therefore any particles on the pellicle should not be imaged (and therefore should not contribute to errors in the pattern applied to the substrate). However, particles on the pellicle may lead to increased absorption of the radiation during exposure of the substrate and therefore to local hot spots on the pellicle, which may lead to failure of the pellicle. Additionally, particles on the surface of the pellicle facing the patterning device may be transferred to the patterning device, whereby they may cause errors in the pattern applied to the substrate.

[0007] It may be desirable to provide an apparatus and associated methods for cleaning a membrane (eg, a diaphragm). Summary of the invention

[0008] According to a first aspect of the present invention, there is provided a membrane cleaning apparatus for removing particles from a membrane, the apparatus comprising: a membrane support for supporting the membrane; and an electric field generating mechanism for generating an electric field near the membrane when the membrane is supported by the membrane support.

[0009] The device according to the first aspect of the invention provides an arrangement in which an electric field can be used to remove particles from a diaphragm. In use, the diaphragm can be supported by a diaphragm support. The electric field generating mechanism can be used to generate an electric field near the diaphragm when the diaphragm is supported by the diaphragm support so as to expel particles from the surface of the diaphragm. Additionally or alternatively, the electric field generating mechanism can be used to generate an electric field near the diaphragm when the diaphragm is supported by the diaphragm support so as to transport particles away from the surface of the diaphragm.

[0010] It will be appreciated that, as used herein, an electric field generating mechanism is intended to denote any arrangement of devices that can generate an electric field. In particular, the term electric field generating mechanism is not intended to imply any mechanically moving parts.

[0011] The electric field generating means may comprise: one or more collecting electrodes; and means for applying a voltage across the diaphragm supported by the diaphragm and the or each of the one or more collecting electrodes.

[0012] This provides a convenient mechanism for generating an electric field near the diaphragm.

[0013] The apparatus may include means for inducing mechanical oscillations in the diaphragm when the diaphragm is supported by the diaphragm support.

[0014] Advantageously, this arrangement is particularly well suited for cleaning membranes, which may be relatively thin and flexible, as now discussed.

[0015] The mechanism for inducing mechanical oscillations in the diaphragm will in turn induce mechanical oscillations in particles located on the diaphragm. Such oscillations of such particles located on the diaphragm may be large enough to remove particles from the diaphragm. Furthermore, any such particles removed by the mechanism for inducing mechanical oscillations may be transported away from the diaphragm by the electric field generated by the electric field generating mechanism.

[0016] The mechanism for inducing mechanical oscillations may induce mechanical oscillations via pulsed electrostatic pressure.

[0017] The means for inducing mechanical oscillations in the diaphragm when the diaphragm is supported by the diaphragm support may include: an actuation electrode; and a means for applying a time-varying voltage across the actuation electrode and the diaphragm supported by the diaphragm support.

[0018] When a time-varying voltage is applied across the actuation electrode and the diaphragm supported by the diaphragm support, a time-varying electrostatic force will be applied between the actuation electrode and the diaphragm. Since the diaphragm is flexible, this will cause the diaphragm to deform in a time-varying manner and undergo mechanical oscillations.

[0019] In some embodiments, the excitation electrodes of the mechanism for inducing mechanical oscillations in the diaphragm may also serve as the collecting electrodes of the electric field generating mechanism.

[0020] The means for inducing mechanical oscillations in the diaphragm when the diaphragm is supported by the diaphragm support may include two electrodes positionable proximate a surface of the diaphragm when the diaphragm is supported by the diaphragm support and means for applying a time varying voltage across the two electrodes.

[0021] When a time-varying voltage is applied across the two electrodes, a time-varying surface charge will be induced in the diaphragm. This, in turn, will cause a time-varying electrostatic force to act on the diaphragm (due to the induced surface charge). Thus, this arrangement allows mechanical oscillations to be induced in the diaphragm via the induced surface charge.

[0022] The two electrodes may be adjacent to each other.The two electrodes may be movable relative to the diaphragm support so that they may scan across the surface of the diaphragm when the diaphragm is supported by the diaphragm support.

[0023] When the mechanism applies a time-varying voltage across two electrodes, the potential of the diaphragm may be floating (ie, not fixed), or alternatively, may be fixed (either to ground or with a DC bias voltage).

[0024] A mechanism for inducing mechanical oscillations in a diaphragm when the diaphragm is supported by a diaphragm support may include two electrodes, each of which may be positioned proximate a different one of two opposing surfaces of the diaphragm when the diaphragm is supported by the diaphragm support, and a mechanism for applying a time-varying voltage to each of the two electrodes.

[0025] For such an embodiment, the electric field generating mechanism is operable (via two electrodes on opposite sides of the diaphragm) to generate an electric field near two opposing surfaces of the diaphragm when the diaphragm is supported by the diaphragm support. The directions of the electric fields near the two opposing surfaces of the diaphragm may be opposite. It will be appreciated that in order to induce mechanical oscillations in the diaphragm, the electric field generated near one of the two opposing surfaces of the diaphragm may be different from the electric field generated near the other of the two opposing surfaces of the diaphragm.

[0026] The two electrodes and a mechanism for applying a time-varying voltage to each of the two electrodes can be arranged so that the magnitude of the time-averaged pressure applied by the two electrodes on one of the two opposing surfaces is substantially equal and the direction is opposite to the time-averaged pressure applied by the two electrodes on the other of the two opposing surfaces.

[0027] For example, the magnitude of the time-averaged pressure applied by the two electrodes on the two opposing surfaces may be equal to within 50%, such as within 10%. For example, the time-averaged electrostatic pressure applied to the diaphragm may be substantially zero. The time-averaged electrostatic pressure may be averaged over a period of 10 μs to 10 ms.

[0028] The mechanism for applying a time-varying voltage to each of the two electrodes can be arranged so that: the waveform of the voltage applied to one of the two electrodes is substantially equal to the waveform of the time-varying voltage applied to the other of the two electrodes; the magnitude of the voltage applied to one of the two electrodes is substantially equal to the magnitude of the time-varying voltage applied to the other of the two electrodes.

[0029] With this arrangement, the capacitive coupling of the diaphragm to each of the two electrodes can be substantially the same. For example, the two electrodes can have substantially the same area and can be disposed at substantially the same distance from the diaphragm. The polarity of the voltage applied to one of the two electrodes can be the same or opposite to the polarity of the time-varying voltage applied to the other of the two electrodes.

[0030] Even for embodiments in which the time-averaged electrostatic pressure across the diaphragm is zero and / or the waveform and magnitude of the voltage applied to the two electrodes are substantially the same, it will be appreciated that in order to induce mechanical oscillations in the diaphragm, the electric fields generated near the two opposing surfaces of the diaphragm may be different. Therefore, the two electrodes and / or a mechanism for applying a time-varying voltage to each of the two electrodes may be arranged to ensure that the electric fields generated near the two opposing surfaces of the diaphragm are different.

[0031] In some embodiments, it is possible that the position of one of the electrodes is not aligned with the position of the other electrode in a plane parallel to the plane of the membrane.

[0032] That is, although on opposite sides of the diaphragm, the two collecting electrodes can be described as being laterally offset from each other. With this arrangement, the electric fields generated on opposite sides of the diaphragm will also be offset. In this way, each electrode will exert an attractive force on a different part of the diaphragm and will induce mechanical oscillations in the diaphragm (even when the same voltage is applied to both electrodes).

[0033] For such an embodiment, the time-varying voltage applied to one of the two electrodes may be substantially in phase with the time-varying voltage applied to the other of the two electrodes.

[0034] The two electrodes may be positioned so that the maximum distance between the two collectors in a plane parallel to the plane of the diaphragm is 1 cm. This distance may be referred to as the lateral offset. The two electrodes may be positioned so that the maximum distance between the two collectors in a plane parallel to the plane of the diaphragm is 1 mm.

[0035] The mechanism for applying a time-varying voltage to the two electrodes may be configured such that the two electrodes are maintained at voltages that are substantially equal in magnitude and opposite in polarity.

[0036] In some embodiments, there may be a non-zero phase difference between the time-varying voltage applied to one of the two electrodes and the time-varying voltage applied to the other of the two electrodes.

[0037] For such an embodiment, the position of one of the electrodes may be generally aligned with the position of the other electrode in a plane parallel to the plane of the diaphragm.

[0038] The electric field generating mechanism that generates an electric field proximate the diaphragm when the diaphragm is supported by the diaphragm support may be operable to generate an electric field proximate two opposing surfaces of the diaphragm, the electric field having a magnitude of at least 100 kV / m.

[0039] For example, in some embodiments, the electric field near two opposing surfaces of the diaphragm can have a magnitude of at least 1 MV / m.

[0040] The apparatus may also include a mechanism for applying a voltage to the diaphragm while the diaphragm is supported by the diaphragm support.

[0041] The mechanism for applying a voltage to the diaphragm when the diaphragm is supported by the diaphragm support may be configured such that the polarity of the voltage applied to the diaphragm is opposite to the polarity of the voltage applied to the two electrodes.

[0042] The apparatus may also include a mechanism operable to maintain the diaphragm at a voltage close to or equal to ground.

[0043] For example, the apparatus may be configured to maintain the voltage across the membrane between -100 V and +100 V. For example, the apparatus may be configured to maintain the voltage across the membrane between -10 V and +10 V.

[0044] The mechanism operable to maintain the diaphragm at a voltage close to or equal to ground may include: one or more auxiliary electrodes positionable proximate two opposing surfaces of the diaphragm when the diaphragm is supported by the diaphragm support, and maintaining the one or more auxiliary electrodes at a voltage close to or equal to ground.

[0045] The apparatus may be configured such that the magnitude of the electric field between the diaphragm and the electrode is at least ten times greater than the magnitude of the electric field between the diaphragm and the auxiliary electrode.

[0046] For example, the apparatus may be configured such that the magnitude of the electric field between the diaphragm and the electrode is at least one hundred times greater than the magnitude of the electric field between the diaphragm and the auxiliary electrode.

[0047] The area of ​​the surface of each electrode closest to the diaphragm may be smaller than the area of ​​the diaphragm.

[0048] The area of ​​the surface of each electrode closest to the diaphragm may be less than or equal to 1 cm 2 For example, the area of ​​the surface of each of the two electrodes closest to the diaphragm may be less than or equal to 10 mm 2 .

[0049] The largest dimension of each electrode may be aligned perpendicular to the plane of the diaphragm.

[0050] The or each electrode may be positioned such that, in use, the maximum distance between the electrode and the diaphragm supported by the diaphragm support is 5 mm. For example, the or each electrode may be positioned such that, in use, the maximum distance between the electrode and the diaphragm supported by the diaphragm support is 0.5 mm.

[0051] The time-varying voltage may include a plurality of pulses spaced apart in time.

[0052] Advantageously, the arrangement will excite oscillations having different frequency ranges. By controlling the repetition rate of the pulses and / or the shape of the pulses, the different frequency ranges of oscillations that are excited can be controlled.

[0053] Applying a pulse voltage across the excitation electrode and the diaphragm can generate a pulse electric field between the excitation electrode and the diaphragm. The pulse electric field can apply a force that brings the electrode and the diaphragm closer to each other. The electrode and the diaphragm support can generally be arranged so that they are fixed in the device as a whole. In use, the diaphragm can generally be arranged so that it is supported by the diaphragm support only at the periphery of the diaphragm. Therefore, the applied force can cause the diaphragm portion that is not supported by the diaphragm support to accelerate in the direction of the electrode. During the portion of the voltage pulse where the electric field is not generated, the diaphragm accelerates in the direction opposite to the acceleration caused by the electric field (for example, due to tension in the diaphragm). As the on-off characteristic of the electric field is repeated, this causes mechanical oscillations of the diaphragm.

[0054] The duration of each pulse of the plurality of temporally spaced pulses may be less than 10 μs. The duration of each pulse of the plurality of temporally spaced pulses may be less than 1 μs.

[0055] The or each time-varying voltage may comprise a plurality of successive pulse trains spaced apart in time. The duration of each pulse train may be less than 10 ms. For example, the duration of each pulse train may be less than 1 ms. By providing the pulses in such a pulse train (also referred to as a pulse train), unwanted heating of the diaphragm may be limited or prevented. Advantageously, this may prevent rupture of the diaphragm.

[0056] The duty cycle of each of the plurality of consecutive temporally spaced pulse trains may be lower than 50%. For example, the duty cycle of each of the plurality of consecutive temporally spaced pulse trains may be lower than 10%.

[0057] The duty cycle of each of the plurality of successive temporally spaced pulse trains may be low enough so that the power dissipation in the diaphragm is less than 30 W / cm2 on a time scale of about 0.1 ms to 10 ms. 2 For example, the duty cycle of each of a plurality of successive temporally spaced pulse trains may be low enough so that the power dissipation in the diaphragm is less than 0.3 to 30 W / cm2 on a time scale of about 0.1 to 10 ms. 2 .

[0058] The or each time-varying voltage may comprise a voltage waveform having a general shape and having one or more parameters that may be selected (and varied) to obtain a desired excitation spectrum.

[0059] The or each time-varying voltage may comprise two pulse trains, spaced apart in time, in succession, the polarity of the two pulse trains being reversed.

[0060] This may be useful for removing both negatively and positively charged particles from the membrane.

[0061] The mechanism for applying a time-varying voltage (either across an actuation electrode and a diaphragm supported by a diaphragm support or across both electrodes) may be operable to generate a time-varying electric field near the diaphragm having a magnitude of at least 10 kV / m.

[0062] For example, the time-varying electric field near the diaphragm may have a magnitude of at least 100 kV / m. For example, the pulse voltage applied across the actuation electrode and the diaphragm may have a maximum value between 100 V and 10,000 V, and the actuation electrode and diaphragm assembly may be arranged such that the spacing between the actuation electrode and the diaphragm is between 1 mm and 10 mm.

[0063] The or each time varying voltage may have a duty cycle of less than 50%.

[0064] The time-varying voltage (applied across the actuation electrode and the diaphragm supported by the diaphragm support or across both electrodes) may have a duty cycle of less than 10%.

[0065] Advantageously, this limits the amount of heating of the membrane by current charging and discharging the capacitor formed by the diaphragm and the collector.

[0066] The mechanism for inducing mechanical oscillations in the diaphragm when the diaphragm is supported by the diaphragm support may include a radiation source operable to generate a pulsed radiation beam incident on at least a portion of the diaphragm supported by the diaphragm support.

[0067] The mechanism for inducing mechanical oscillations may be operable to induce oscillations in only a localised portion of the diaphragm.

[0068] Advantageously, by limiting the mechanical oscillations to a localized portion of the diaphragm, a more precise, faster and more energy efficient cleaning process may be achieved.

[0069] For embodiments where the mechanism for inducing mechanical oscillation comprises an excitation electrode, this may be achieved by using an electrode having dimensions smaller than the dimensions of the diaphragm.

[0070] For embodiments where the means for inducing mechanical oscillation comprises a radiation source operable to produce a pulsed radiation beam, this may be achieved by focusing the pulsed radiation beam onto only a portion of the diaphragm.

[0071] The means for inducing mechanical oscillation may be operable to induce oscillations within a range of frequencies.

[0072] The means for inducing mechanical oscillations may be operable to induce oscillations between 30 kHz and 30 MHz.

[0073] For example, the mechanism for inducing mechanical oscillations may be operable to induce oscillations between 100 kHz and 10 MHz.

[0074] Advantageously, this can induce resonance of particles having different size ranges, typically in the range of 0.5 μm to 5 μm. The lower limit of the frequency range (e.g. 100 kHz) can be selected to ensure that the frequency range is not close to the resonance frequency of the diaphragm, at which the fundamental mode of a typical EUV full-scale pellicle is in the range of 1 kHz to 10 kHz.

[0075] The mechanism for inducing mechanical oscillation may be operable to remove particles having a size between 0.5 μm and 5 μm from the diaphragm.

[0076] The apparatus may also include a mechanism for controlling the temperature of at least a portion of the membrane.

[0077] By controlling the temperature of a portion of the diaphragm, the tension in that portion can be controlled. In particular, if the temperature of at least a portion of the diaphragm can be controlled independently of the frame that tensions the diaphragm, the tension within the diaphragm can be controlled.

[0078] This is particularly advantageous for embodiments that include a mechanism for inducing mechanical oscillations in the diaphragm when the diaphragm is supported by the diaphragm support. As described above, the mechanism for inducing mechanical oscillations in the diaphragm will in turn induce mechanical oscillations in particles located on the diaphragm. This oscillation of such particles located on the diaphragm can be large enough to remove particles from the diaphragm. Furthermore, any such particles removed by the mechanism for inducing mechanical oscillations can be transported away from the diaphragm by the electric field generated by the electric field generating mechanism. In particular, if the mechanism for inducing mechanical oscillations can cause resonance of particles on the diaphragm, they can be removed from the diaphragm. The resonant frequency of the oscillation of particles on a substantially massless diaphragm depends on the tension of the diaphragm and the mass of the particles. In particular, the resonant frequency of the oscillation of particles on a substantially massless diaphragm is proportional to the square root of the tension of the diaphragm and is proportional to the inverse of the square root of the mass of the particles. As the tension increases, it may also be necessary to provide a resonant frequency to remove particles of a given size.

[0079] By controlling the temperature of a portion of the membrane, the tension in the membrane can be controlled, and therefore the range of particle sizes that can be removed from the membrane for a particular range of oscillation frequencies can also be controlled.

[0080] The means for controlling the temperature of at least a portion of the diaphragm may comprise a radiation source operable to provide radiation to the diaphragm.The radiation source may comprise a focused light source.

[0081] Alternatively, the means for controlling the temperature of at least a portion of the diaphragm may comprise an induction heater operable to heat the diaphragm.

[0082] The diaphragm may comprise an electrically and thermally conductive material.

[0083] The electric field generating mechanism may be operable to generate electric fields adjacent two opposing surfaces of the diaphragm when the diaphragm is supported by the diaphragm support, the electric fields adjacent the two opposing surfaces of the diaphragm being in opposite directions.

[0084] Advantageously, this arrangement is particularly suitable for cleaning diaphragms that may be thin enough that they may be susceptible to rupture under sufficient lateral (out of the plane of the diaphragm) loads. By applying an electric field near two opposing surfaces of the diaphragm, where the electric fields are in opposite directions, the pressure on both sides of the diaphragm can be at least partially equalized. In turn, this allows the use of larger electric fields, which can provide higher levels of cleaning.

[0085] The electric field may be generated by two collecting electrodes disposed on opposite sides of the plane of the diaphragm.

[0086] The area of ​​the surface of each current collector closest to the diaphragm may be smaller than the area of ​​the diaphragm.

[0087] The area of ​​the surface of each collector closest to the diaphragm may be less than or equal to 1 cm 2 For example, the area of ​​the surface of each collector closest to the diaphragm may be less than or equal to 10 mm 2 .

[0088] In some embodiments, it is possible that the position of one of the current collectors is not aligned with the position of the other current collector in a plane parallel to the plane of the diaphragm.

[0089] That is, despite being on opposite sides of the diaphragm, the two collectors may be described as being laterally offset from each other. The two collectors may be positioned so that the maximum distance between the two collectors in a plane parallel to the plane of the diaphragm is 1 cm. This distance may be referred to as a lateral offset. The two collectors may be positioned so that the maximum distance between the two collectors in a plane parallel to the plane of the diaphragm is 1 mm.

[0090] Each collector may be held at a substantially equal voltage, and the apparatus may be configured to hold the diaphragm at a voltage of opposite polarity to the voltage at which the collectors are held.

[0091] The two collectors may be connected together (ie, they may be at the same potential).

[0092] The magnitude of the electric field may be substantially equal on both sides of the diaphragm.

[0093] The electric field near two opposing surfaces of the diaphragm may have a magnitude of at least 100 kV / m.

[0094] For example, the electric field near two opposing surfaces of the membrane may have a magnitude of at least 1 MV / m.

[0095] The electric field near the two opposing surfaces of the diaphragm may be a DC (ie, time-invariant) electric field.

[0096] At least a portion of one or more current collectors may be provided with an insulating coating.

[0097] The insulating coating prevents charge transfer between the collector and any particles that have been attracted from the diaphragm to the collector. This can prevent particles from being transferred from the collector to the diaphragm. The breakdown strength of the insulating coating can exceed the electric field generated by the voltage source during use of the diaphragm cleaning device. Once particles are electrostatically transferred to the collector, the insulating coating prevents charge leakage and reduces the risk of reverse transfer of particles from the collector to the diaphragm.

[0098] The apparatus may also include a plasma generating mechanism.

[0099] The plasma generating mechanism may be operable to generate plasma between a diaphragm supported by the diaphragm support and the or each of the one or more collecting electrodes.

[0100] The plasma between the diaphragm supported by the diaphragm support and the collector or each of the one or more collectors provides a mechanism by which the particles on the diaphragm can be charged. In addition, in the presence of a bias voltage applied by a mechanism for applying a voltage, carriers of opposite charge in the plasma will be subjected to opposite electrostatic forces. When such a bias voltage is applied, the plasma can be considered to form a virtual electrode adjacent to one or both surfaces of the diaphragm. The virtual electrode is provided by the plasma sheath adjacent to the diaphragm surface and has the same polarity as the collector facing the surface of the diaphragm. Under such conditions (conditions of the plasma and the applied voltage), since the virtual electrode is closer to the diaphragm than the collector (e.g., about 100 μm, rather than about 30 mm to 300 mm), the plasma will produce a significantly greater electric field strength near the diaphragm surface at a given bias voltage. In turn, this can result in significantly better cleaning of the diaphragm.

[0101] In the presence of plasma and applied voltage, there will be a current flowing through the diaphragm. The magnitude of the current will depend on the applied voltage and the density of the plasma. In turn, this current will cause Joule heating of the diaphragm. The diaphragm can have dimensions of about 10cm x 10cm and can have a thickness of about 100nm. The diaphragm can have a resistance of about 100Ω. The time frame of these conditions (with plasma and applied voltage) can be limited so that the heat generated by the current flowing through the diaphragm can be dissipated without heating the diaphragm to a temperature at which the diaphragm will fail. This can be controlled by controlling the time frame of the applied voltage and / or controlling when the plasma is turned on. It may be necessary to ensure that the temperature of the diaphragm does not exceed 500°C.

[0102] The means for applying a voltage across the diaphragm supported by the diaphragm support and the or each of the one or more current collectors may be arranged to apply a pulsed voltage across the diaphragm supported by the diaphragm support and the or each of the one or more current collectors.

[0103] Applying a pulsed voltage across a diaphragm supported by a diaphragm support and a collector or each of the one or more collectors limits the time that current flows through the diaphragm. It will be appreciated that the duty cycle may be limited to ensure that heat generated by the current flowing through the diaphragm can be dissipated without heating the diaphragm to a temperature at which the diaphragm will fail. For example, the duty cycle may be 10% or less, such as 1% or less.

[0104] The pulse voltage may have a duty ratio of 1% or less.

[0105] The pulse voltage may have a frequency between 1 Hz and 10 kHz.

[0106] The pulse duration of the pulse voltage may be less than 1 ms.

[0107] For example, the pulse duration of the pulse voltage may be less than 10 μs.

[0108] In some embodiments, to provide adequate cleaning, the electric field strength near the diaphragm is at least 10 kV / m, more preferably at least 100 kV / m. It will be appreciated that the electric field strength depends on the applied bias voltage and the distance between the diaphragm and the collector. However, the electric field strength also depends on the plasma (e.g., the type of plasma, the density of the plasma, etc.), and the plasma will generally reduce the voltage that should be applied to achieve the desired target electric field strength.

[0109] The magnitude of the pulse voltage may be at least 100V.

[0110] For example, the magnitude of the pulse voltage may be at least 1000V.

[0111] Each pulse of the pulse voltage may include a first portion having a first polarity and a second portion having an opposite second polarity.

[0112] Advantageously, with this arrangement, during the first portion, the plasma will charge the particles with a charge corresponding to the polarity of the potential of the electrode facing the particle. In the second portion, the polarity of the bias voltage is reversed. If this operation is done quickly enough, any particle disposed on the diaphragm that has acquired a charge via the plasma will be acted upon by electrostatic forces directed away from the diaphragm towards the electrode facing the particle. For sufficiently large bias voltages, these forces will exceed the binding forces between the particle and the diaphragm (e.g., van der Waals forces), and the particle will be accelerated away from the diaphragm towards the collector electrode facing the surface of the diaphragm on which the particle is disposed. It will be appreciated that the bias voltage polarity should be switched quickly (between the first and second portions), for example on a time scale of <0.1 ms.

[0113] The plasma generating mechanism may be arranged such that the plasma is switched on between subsequent pulses of the pulsed voltage and is switched off during a pulse of the pulsed voltage.

[0114] By synchronizing the plasma generation mechanism with the pulsed voltage in this way, and in particular shutting off the plasma during the pulses of the pulsed voltage, the amount of current flowing through the diaphragm can be limited. With this arrangement, any restrictions on the size and time range of the voltage pulses can be relaxed. It is possible that with this arrangement, there are no restrictions on the size and time range of the voltage pulses (for example, if the voltage is applied in a manner that ensures that the electrostatic pressures on opposite sides of the diaphragm are substantially balanced).

[0115] The apparatus may further comprise a chamber and a pump device operable to control the pressure within the chamber.The diaphragm support may be disposed within the chamber.

[0116] The chamber may be a vacuum chamber. For embodiments in which the electric field generating mechanism comprises one or more collectors, the one or more collectors may also be disposed within the chamber. The pump device may be operable to reduce the pressure of the chamber to near vacuum conditions. During operation of the diaphragm cleaning device, the pressure inside the chamber may be maintained at less than 10 mBar, for example less than 0.01 mBar.

[0117] The pump device may be operable to maintain the pressure inside the chamber at 10 -3 For example, the pressure inside the chamber can be less than 10 -5 mBar.

[0118] According to a second aspect of the invention, there is provided a method for removing particles from a diaphragm, the method comprising: inducing mechanical oscillations in the diaphragm; and generating an electric field near the diaphragm using a collector electrode to exert an electrostatic force between particles on the diaphragm and the collector electrode.

[0119] Advantageously, this method is particularly suitable for cleaning membranes, which may be relatively thin and flexible, as now discussed.

[0120] Inducing mechanical oscillations in the diaphragm will in turn induce mechanical oscillations in particles located on the diaphragm. Such oscillations of such particles located on the diaphragm may be large enough to dislodge particles from the diaphragm. In turn, any such particles removed by the mechanism for inducing mechanical oscillations may be transported away from the diaphragm by the electric field.

[0121] Inducing mechanical oscillations in the diaphragm may include applying a time-varying voltage across the supported diaphragm and an actuation electrode.

[0122] Inducing mechanical oscillations in the diaphragm may include applying a time-varying voltage between two electrodes located proximate a surface of the diaphragm.

[0123] Inducing mechanical oscillations in the diaphragm may include applying a time-varying voltage to each of two electrodes located proximate opposing surfaces of the diaphragm.

[0124] The time-averaged pressure exerted by the two electrodes on one of the two opposing surfaces is substantially equal in magnitude to the time-averaged pressure exerted by the two electrodes on the other of the two opposing surfaces, but is opposite in direction.

[0125] In some embodiments, it is possible that the position of one of the electrodes is not aligned with the position of the other electrode in a plane parallel to the plane of the membrane.

[0126] In some embodiments, there may be a non-zero phase difference between the time-varying voltage applied to one of the two electrodes and the time-varying voltage applied to the other of the two electrodes.

[0127] The time-varying voltage or each time-varying voltage (applied across an excitation electrode and a diaphragm supported by a diaphragm support; applied across two electrodes positioned close to a surface of the diaphragm; or applied to each of two electrodes positioned close to opposing surfaces of the diaphragm) can have a duty cycle of less than 10%.

[0128] Inducing mechanical oscillations in the diaphragm may include irradiating at least a portion of the diaphragm with a pulsed radiation beam.

[0129] The induced mechanical oscillations may include oscillations within a range of frequencies.

[0130] The induced mechanical oscillations may include oscillations between 30 kHz and 30 MHz.

[0131] For example, the induced mechanical oscillations may include oscillations between 100 kHz and 10 MHz.

[0132] The induced mechanical oscillations may be suitable for removing particles having a size between 0.5 μm and 5 μm from the membrane.

[0133] The method may also include controlling a temperature of at least a portion of the membrane.

[0134] By controlling the temperature of a portion of the diaphragm, the tension in that portion can be controlled. This, in turn, provides control over the resonant frequency of the oscillation of the particles on the diaphragm. In particular, it provides control over the range of particle sizes that can be removed from the diaphragm for a particular range of oscillation frequencies (e.g., defined by a time-varying voltage).

[0135] The method may also include varying the temperature of at least a portion of the membrane over time.

[0136] By varying the temperature of at least a portion of the membrane over time (ie, sweeping or scanning the temperature), the range of particle sizes removed from the membrane may be varied (eg, while the range of oscillation frequencies remains fixed).

[0137] Controlling the temperature of at least a portion of the membrane may be achieved by irradiating at least a portion with radiation.

[0138] The method according to the second aspect of the present invention may use the apparatus according to the first aspect of the present invention.

[0139] According to a third aspect of the present invention, there is provided a method for removing particles from a membrane, the method comprising: generating an electric field near two opposing surfaces of the membrane, the electric fields near the two opposing surfaces of the membrane being in opposite directions.

[0140] Advantageously, this method is particularly suitable for cleaning diaphragms, which may be thin enough that they may be susceptible to rupture under sufficient lateral (out of the plane of the diaphragm) loads. By applying an electric field near two opposing surfaces of the diaphragm, where the electric fields are in opposite directions, the pressure on both sides of the diaphragm can be at least partially equalized. In turn, this allows the use of larger electric fields, which can provide higher levels of cleaning.

[0141] The method according to the third aspect of the present invention may use the apparatus according to the first aspect of the present invention.

[0142] According to a fourth aspect of the invention, there is provided a method for removing particles from a membrane, the method comprising: providing a plasma adjacent to at least one surface of the membrane to charge the particles; and generating an electric field near at least one surface of the membrane to cause the charged particles to leave the membrane.

[0143] The plasma provides a mechanism by which the particles on the diaphragm can be charged.

[0144] The electric field may be generated using one or more electrodes and applying a bias voltage to the one or more electrodes.

[0145] In the presence of plasma and applied voltage, there will be a current flowing through the diaphragm. The magnitude of the current will depend on the applied voltage and the density of the plasma. In turn, this current will cause Joule heating of the diaphragm. The diaphragm may have dimensions of about 10 cm x 10 cm and may have a thickness of about 100 nm. The diaphragm may have a resistance of about 100 Ω. The time frame of these conditions (with plasma and applied voltage) may be limited so that the heat generated by the current flowing through the diaphragm can be dissipated without heating the diaphragm to a temperature at which the diaphragm will fail. This can be controlled by controlling the time frame of the applied voltage and / or controlling when the plasma is turned on.

[0146] The bias voltage may be a pulse bias voltage.

[0147] Each pulse of the pulse voltage may include a first portion having a first polarity and a second portion having an opposite second polarity.

[0148] Advantageously, with this arrangement, during the first portion, the plasma will charge the particles with a charge corresponding to the polarity of the potential of the electrode facing the particle. In the second portion, the polarity of the bias voltage is reversed. If this operation is done quickly enough, any particle disposed on the diaphragm that has acquired a charge via the plasma will be acted upon by electrostatic forces directed away from the diaphragm towards the electrode facing the particle. For sufficiently large bias voltages, these forces will exceed the binding forces between the particle and the diaphragm (e.g., van der Waals forces), and the particle will be accelerated away from the diaphragm towards the collector electrode facing the surface of the diaphragm on which the particle is disposed. It will be appreciated that the bias voltage polarity should be switched quickly (between the first and second portions), for example on a time scale of <0.1 ms.

[0149] Providing the plasma adjacent to at least one surface of the membrane may cause the plasma to be switched on between subsequent pulses of the pulsed voltage and switched off during pulses of the pulsed voltage.

[0150] By synchronizing the plasma generation mechanism with the pulsed voltage in this way, and in particular shutting off the plasma during the pulses of the pulsed voltage, the amount of current flowing through the diaphragm can be limited. With this arrangement, any restrictions on the size and time range of the voltage pulses can be relaxed. It is possible that with this arrangement, there are no restrictions on the size and time range of the voltage pulses (for example, if the voltage is applied in a manner that ensures that the electrostatic pressures on opposite sides of the diaphragm are substantially balanced).

[0151] The method according to the fourth aspect of the present invention may use the apparatus according to the first aspect of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0152] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which:

[0153] - Figure 1 The photolithography system is shown, showing the pellicle in use;

[0154] - Figure 2 An embodiment of a diaphragm cleaning device and a diaphragm according to the present invention is shown;

[0155] - Figure 3 yes Figure 2 A schematic diagram of a portion of the diaphragm is shown, illustrating the use of Figure 2The mechanism by which the diaphragm cleaning device can remove particles from the diaphragm is shown;

[0156] - Figure 4 a shows the use of Figure 2 A graph of example voltage applied across a diaphragm and electrodes as a function of time is shown for a diaphragm cleaning apparatus;

[0157] - Figure 4 b is Figure 4 A first schematic diagram of an excitation spectrum corresponding to an applied voltage of the form shown in a, showing the excitation force applied to the membrane as a function of the frequency of the excitation force, and schematically indicating the frequency content of the pulse voltage and how this frequency content is varied by modulation of the pulse repetition frequency;

[0158] - Figure 4 c is the second schematic diagram of the excitation spectrum, schematically indicating Figure 4 a shows the frequency content of the pulse voltage and how to change the frequency content by modulating the pulse repetition frequency and the pulse shape;

[0159] - Figure 5 Another embodiment of the diaphragm cleaning device and the diaphragm according to the present invention is shown;

[0160] - Figure 6 Another embodiment of the diaphragm cleaning device and the diaphragm according to the present invention is shown;

[0161] - Figure 7a and 7b Schematic diagram of the use Figure 6 A mechanism by which the diaphragm cleaning apparatus shown can remove particles from the diaphragm;

[0162] - Figure 8a shows a part of another embodiment of a diaphragm cleaning device and a diaphragm according to the present invention;

[0163] - Figure 8b shows a part of another embodiment of a diaphragm cleaning device and a diaphragm according to the present invention;

[0164] - Figure 8c shows a part of another embodiment of a diaphragm cleaning device and a diaphragm according to the present invention;

[0165] - Fig. 9 shows a part of another embodiment of a diaphragm cleaning device and a diaphragm according to the present invention;

[0166] - Fig.10a shows a part of another embodiment of a diaphragm cleaning device and a diaphragm according to the present invention;

[0167] - Fig.10bshows a portion of another embodiment of a diaphragm cleaning device and a diaphragm according to the present invention;

[0168] - Fig.10c shows a portion of another embodiment of a diaphragm cleaning device and a diaphragm according to the present invention; and

[0169] - Fig.10d A part of another embodiment of a diaphragm cleaning device and a diaphragm according to the invention is shown. DETAILED DESCRIPTION

[0170] Figure 1 A lithographic system is shown comprising a radiation source SO and a lithographic apparatus LA. The radiation source SO is configured to generate an EUV radiation beam B and to supply the EUV radiation beam B to the lithographic apparatus LA. The lithographic apparatus LA comprises an illumination system IL, a support structure MT configured to support a patterning device MA (e.g. a mask), a projection system PS, and a substrate table WT configured to support a substrate W.

[0171] The illumination system IL is configured to condition the EUV radiation beam B before it is incident on the patterning device MA. Furthermore, the illumination system IL may comprise a faceted field mirror arrangement 10 and a faceted pupil mirror arrangement 11. The faceted field mirror arrangement 10 and the faceted pupil mirror arrangement 11 together provide a desired cross-sectional shape and a desired intensity distribution for the EUV radiation beam B. In addition to or instead of the faceted field mirror arrangement 10 and the faceted pupil mirror arrangement 11, the illumination system IL may comprise other mirrors or devices.

[0172] After the EUV radiation beam B is thus conditioned, it interacts with the pattern forming device MA. As a result of this interaction, a patterned EUV radiation beam B' is generated. The projection system PS is configured to project the patterned EUV radiation beam B' onto the substrate W. To this end, the projection system PS may include 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' so as to form an image having features that are smaller than corresponding features on the pattern forming device MA. For example, a reduction factor of 4 or 8 may be applied. Although in Figure 1 The projection system PS is shown with only two mirrors 13, 14, but the projection system PS may comprise a different number of mirrors (eg six or eight mirrors).

[0173] The substrate W may include a previously formed pattern. In this case, the lithographic apparatus LA aligns an image formed by the patterned EUV radiation beam B′ with a pattern previously formed on the substrate W.

[0174] A relative vacuum, ie a small amount of gas (eg 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.

[0175] 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 capable of generating EUV radiation.

[0176] Some lithographic apparatus (e.g., EUV and DUV lithographic apparatus) include a pellicle 15. The pellicle 15 may be attached to the support structure MT, or alternatively, the pellicle 15 may be attached directly to the pattern forming device MA. The pellicle 15 includes a thin diaphragm 16 of a transmissive film (typically less than about 70 nm) mounted on a frame 17. The pellicle diaphragm 16 is spaced a few millimeters (typically less than 10 mm, for example 2 mm) from the pattern forming device MA. Particles received on the pellicle diaphragm 16 are in the far field relative to the pattern of the pattern forming device MA, and therefore have no significant effect on the quality of the image projected onto the substrate by the lithographic apparatus LA. If the pellicle 15 is not present, these particles may be located on the pattern forming device MA and may obscure a portion of the pattern on the pattern forming device MA, thereby preventing the pattern from being correctly projected onto the substrate W. Therefore, the pellicle 15 plays an important role in preventing particles from adversely affecting the image formed on the substrate W by the lithographic apparatus LA.

[0177] Before the pellicle 15 is attached to the support structure MT or patterning device MA used in the lithographic apparatus LA, the pellicle membrane 16 may become dirty. That is, as described above, before the pellicle 15 is used in the lithographic apparatus LA, there is a possibility that particles are incident on the pellicle membrane 16. Activities such as transporting the pellicle 15, packaging the pellicle 15, and mounting the pellicle membrane 16 on the frame 17 may cause particles to be incident on the pellicle membrane 16.

[0178] It has been found that during lithographic exposure, some particles present on the pellicle membrane 16 break away from the pellicle membrane 16 and travel from the pellicle membrane 16 to the patterning device MA, thereby negatively affecting the pattern projected onto the substrate W. Particles with sizes between 0.5 μm and 5 μm have been reported to migrate. It will be appreciated that in other arrangements, particles with one or more sizes outside of this range may migrate.

[0179] The pellicle 15 may be formed of one or more layers, which may be formed on a supporting substrate. The supporting substrate allows the thin membrane 16 of the pellicle 15 to be formed without the risk of the membrane 16 rupturing. Once the layers of the membrane 16 are formed, the supporting substrate may be removed (e.g., by etching) to form the final thickness of the membrane 16. The pellicle 15 whose membrane 16 is found to be too dirty to be used may be discarded. Although there are some methods for cleaning the membrane, these methods are generally used before the final thickness of the membrane 16 has been achieved, that is, when the membrane 16 is still disposed on the supporting substrate. These known methods for pellicle cleaning include wet cleaning or applying heat. However, once the final thickness of the membrane 16 has been achieved, the known methods are not suitable for use because they risk rupturing the thin pellicle membrane 16. In addition, cleaning methods involving the application of heat may also lead to weakening of the pellicle membrane 16, thereby shortening the service life of the pellicle 15, mainly due to stresses at the interface of materials with different thermal expansion coefficients and / or due to the conversion of temperature inhomogeneities into mechanical stresses.

[0180] Embodiments of the present invention relate to apparatus and related methods for removing particles from membranes using electric fields. In particular, some embodiments of the present invention are particularly suitable and adapted for cleaning fragile, relatively thin membranes such as, for example, pellicle membranes.

[0181] Some embodiments of the present invention take advantage of the fact that a relatively thin diaphragm (such as, for example, a pellicle diaphragm) is relatively flexible by inducing mechanical oscillations in the diaphragm. In turn, this will also induce mechanical oscillations of particles located on the diaphragm. This oscillation of such particles located on the diaphragm can be large enough to dislodge particles from the diaphragm. In turn, any such particles removed by the mechanism for inducing mechanical oscillations can be transported away from the diaphragm using an electric field. Referring now to Figures 2 to 5 Examples of these embodiments are described.

[0182] Now refer to Figure 2 , Figure 3 and Figure 4 A diaphragm cleaning apparatus 200 according to a first embodiment of the present invention is described.

[0183] Figure 2A cross section through the diaphragm cleaning device 200 is shown, and the diaphragm cleaning device 200 includes: a combined excitation electrode / collector 202; a voltage source 205; and a conductive support 204. The conductive support 204 is an electrical conductor. The combined excitation electrode / collector 202 is in the form of a generally rectangular plate, having a generally cubic shape, with the length of one dimension being substantially shorter than the lengths of the other two dimensions. The conductive support 204 is in the form of a generally rectangular plate, with a central rectangular hole, so that the shape of the conductive support 204 can be described as a rectangular frame. The generally rectangular shape formed by the combined excitation electrode / collector 202 and the generally rectangular shape formed by the conductive support 204 are substantially equal in size. The combined excitation electrode / collector 202 and the conductive support 204 are arranged so that the plane in which the combined excitation electrode / collector is located and the plane in which the conductive support is located are substantially parallel.

[0184] exist Figure 2 In the illustrated embodiment, the membrane cleaning device 200 further includes a spacer segment 203. The spacer segment 203 is an electrical insulator. The spacer segment 203 has substantially the same shape as the conductive support 204 (i.e., a substantially rectangular frame). The spacer segment 203 is disposed between the combined excitation electrode / collector 202 and the conductive support 204.

[0185] exist Figure 2 In the illustrated embodiment, the membrane cleaning apparatus 200 further comprises a vacuum chamber 201 . The combined excitation electrode / collector electrode 202 , the spacer segment 203 and the conductive support 204 are disposed in the vacuum chamber 201 .

[0186] exist Figure 2 Also shown is a diaphragm assembly 208. The diaphragm assembly 208 includes a diaphragm 211, which in turn is supported by a generally rectangular frame 212. In use, the diaphragm assembly 208 is disposed on a conductive support 204. The conductive support 204 is arranged to support the frame 212 of the diaphragm assembly 208. The frame 212, as well as one or more surfaces of the diaphragm 211, are coated with a conductive (e.g., metal) coating 209, such that this conductive coating 209 is in electrical contact with the conductive support 204.

[0187] The voltage source 205 is operable to apply a voltage across the combined excitation electrode / collector 202 and the conductive support 204. Figure 2In the embodiment shown, this is achieved through the use of wires 206a, 206b and vacuum feedthroughs 207a, 207b. The vacuum feedthroughs 207a, 207b are disposed within the wall of the vacuum chamber 201. The voltage source 205 is disposed outside the vacuum chamber 201. One electrical terminal of the voltage source 205 is electrically connected to the conductive support 204 via a wire 206a and a vacuum feedthrough 207a. The opposing electrical terminal of the voltage source 205 is electrically connected to the combined excitation electrode / collector 202 via a wire 206b and a vacuum feedthrough 207b.

[0188] In use, a voltage applied across the combined excitation electrode / collector 202 and the conductive support 204 results in a voltage across the combined excitation electrode / collector 202 and the diaphragm 211, because the diaphragm 211 is typically formed of a material having a non-zero conductivity (such as doped polysilicon) and / or is provided with a conductive coating 209 located on at least one side of the diaphragm 211. The combined excitation electrode / collector 202 and the diaphragm 211 are not part of a closed loop. Therefore, charge can accumulate on the combined excitation electrode / collector 202 and the diaphragm 211. This effect is similar to the charging of opposing plates in a capacitor.

[0189] The charge accumulated on the combined excitation electrode / collector 202 and the diaphragm 211 generates an electrostatic attraction force between the combined excitation electrode / collector 202 and the diaphragm 211. Since the diaphragm 211 is relatively thin and therefore flexible, the diaphragm 211 will deform due to this attraction force.

[0190] In some embodiments of the present invention, the accumulation of charge is utilized, which generates an electrostatic force near the diaphragm assembly 208. Specifically, by configuring the temporal characteristics of the electrostatic force, mechanical oscillations are induced in the diaphragm 211. According to the current embodiment of the present invention, this is achieved by applying a time-varying voltage across the combined excitation electrode / collector 202 and the diaphragm 211. The time-varying voltage utilized for this purpose includes a plurality of pulses spaced apart in time. This mechanism will be described in detail below.

[0191] Vacuum pump equipment (for simplicity, in Figure 2The vacuum pump 200 may be operable to control the pressure inside the vacuum chamber 201. For example, the vacuum pump may be operable to reduce the pressure of the vacuum chamber 201 to near vacuum conditions. During operation of the diaphragm cleaning apparatus 200, the pressure inside the vacuum chamber 201 may be maintained at less than 10 mBar. Alternatively, the pressure of the vacuum chamber 201 may be maintained at less than 0.01 mBar. Advantageously, when the diaphragm cleaning apparatus 200 is used to clean the diaphragm 211, maintaining the interior of the vacuum chamber 201 at a low pressure reduces the air resistance experienced by the oscillating diaphragm 211.

[0192] Figure 3 2 shows a cross section through a diaphragm 211 cleaned by a diaphragm cleaning apparatus 200 when a voltage provided by a voltage source 205 is applied across the combined excitation electrode / collector 202 and the conductive support 204. Also shown are particles 210 disposed on the diaphragm 211. Since the diaphragm 211 is typically flexible and the combined excitation electrode / collector 202 is typically rigid, the electrostatic attraction between the combined excitation electrode / collector 202 and the diaphragm 211 produces a mechanical deformation 301 in the diaphragm 211.

[0193] In an embodiment of the present invention, the voltage applied across the combined excitation electrode / collector 202 and the conductive support 204 may follow Figure 4 The waveform 400 shown in a shows a graph of the voltage V changing with time t. The voltage is time-varying. Specifically, the waveform 400 of the voltage is periodic, so that the voltage can be described as a pulse voltage 401. The pulse voltage 401 includes alternating on portions 402 and off portions 403. It will be appreciated that Figure 4 The voltage waveform 400 shown in FIG. 4 is merely an example of a pulse voltage 401 that may be generated by the voltage source 205. In other embodiments, it is possible to use alternative pulse shapes and pulse repetition frequencies, and / or pulse patterns, such as pulse trains, pulse sequences / pulse trains.

[0194] Figure 4 The pulse voltage 401 shown in FIG. 4 includes a DC component (where the off portion 403 corresponds to a non-zero potential difference between the combined excitation electrode / collector 202 and the conductive support 204). In an alternative embodiment, a similar waveform 400 may be used, but without a DC component (where the off portion 403 corresponds to a zero potential difference between the combined excitation electrode / collector 202 and the conductive support 204). Using the pulse voltage 401 with a DC component produces a stronger time-averaged electric field between the combined excitation electrode / collector 202 and the diaphragm assembly 208, which can improve the transport of particles 210 toward the combined excitation electrode / collector 202, as described below.

[0195] The pulse voltage 401 generates a pulsed electrostatic attraction force between the combined excitation electrode / collector 202 and the diaphragm 211. During the on portion 402 of the pulse voltage 401, an electrostatic attraction force exists between the combined excitation electrode / collector 202 and the diaphragm 211, resulting in a mechanical deformation 301 of the diaphragm 211 as described above. The pulsed pressure that generates this electrical force or electromotive force (charge) can typically be between 0.01 Pa and 100 Pa. Following the applied pressure, all or at least some portions of the diaphragm are accelerated toward the electrode 202.

[0196] During the off portion 403 of the pulse voltage 401 having a DC component, the electrostatic attraction force between the combined excitation electrode / collector 202 and the diaphragm 211 is reduced compared to during the on portion 402. For embodiments in which the pulse voltage 401 has no DC component, there is no electrostatic attraction force between the combined excitation electrode / collector 202 and the diaphragm 211 during the off portion 403 of the pulse voltage 401. Therefore, during the off portion 403 of the pulse voltage 401 (regardless of whether a DC component is included), the tension of the diaphragm 211 causes the diaphragm 211 to accelerate in the opposite direction to the mechanical deformation 301 caused during the on portion 402 of the pulse voltage 401. As the on portion 402 and the off portion 403 of the pulse voltage 401 are repeated, mechanical oscillations are induced in the diaphragm 211.

[0197] In an embodiment of the present invention, the voltage applied across the combined excitation electrode / collector 202 and the conductive support 204 has a duty cycle of less than 10%. Advantageously, this limits the amount of heating of the diaphragm 211 by current charging and discharging the capacitor formed by the diaphragm 211 and the combined excitation electrode / collector 202.

[0198] The particles 210 may be present on a surface of the membrane 211 that faces the combined excitation electrode / collector electrode 202 .

[0199] Averaged over time, there is a net electric field between the combined energizing electrode / collector 202 and the diaphragm assembly 208 due to the pulse voltage 400 .

[0200] The particles 210 with non-zero surface conductivity disposed on the surface of the diaphragm 211 facing the combined excitation electrode / collector 202 may have acquired charge from the diaphragm 211 due to the pulse voltage 401. The charge of the particles 210 causes an electrostatic force to exist, which attracts the particles 210 toward the combined excitation electrode / collector 202.

[0201] Additionally or alternatively, the particles 210 may have acquired a charge through triboelectric interaction with the surface of the diaphragm 211 facing the combined excitation electrode / collector 202. The charge of the particles 210 may be positive or negative. In use, the polarity of the voltage pulse 400 may be selected to provide an attractive force between the triboelectrically charged particles and the electrode 202; the polarity of the voltage pulse (DC component and / or pulse component) may be varied to cover the case of different materials (different signs of triboelectric charge).

[0202] Due to the Van der Waals attractive forces between the particles 210 and the surface of the membrane 211 where the particles 210 exist, each particle 210 present on the surface of the membrane 211 will generally move with the surface of the membrane 211 when the membrane oscillates.

[0203] Each particle 210 on the membrane 211 under pre-tension can be considered as an independent oscillator. The resonant frequency of such an oscillator can vary depending on the properties of the particle 210 and the membrane 211.

[0204] For example, the resonant frequency of the particles 210 can vary with the mass M of the particles 210. The resonant frequency can vary with d: d is the ratio of the radius of the vibration 303 induced in the diaphragm 211 (defined by the amplitude and excitation frequency of the oscillation) to the size of the contact point 304 of the particle 210 on the diaphragm 211 (defined by typical short-range van der Waals interactions). Typically, for a diaphragm 211 being cleaned using the diaphragm cleaning device 200, d can be between 100 and 1000,000. The resonant frequency of the particles can also vary with the thickness 305 of the diaphragm 211, i.e., h. Typically, for a diaphragm 211 being cleaned using the diaphragm cleaning device 200, h can be between 10 nm and 100 nm. The resonant frequency can also vary with the pretension σ of the diaphragm 211. Typically, for a diaphragm 211 being cleaned using the diaphragm cleaning device 200, σ can be between 50 MPa and 500 MPa.

[0205] The fundamental frequency of the oscillator, or base frequency v0, can be described by the following equation: For typical particle densities and for particle radii between 0.5 μm and 5 μm, v0 may be between about 10 MHz and 0.3 MHz. If the excitation frequency applied to the diaphragm 211 is close to the resonant frequency of the particle 210, the amplitude 301 of the oscillation of the particle 210 may increase. As the amplitude of the oscillation of the particle 210 increases, the diaphragm-particle spacing 302 may likewise increase because the inertia due to particle acceleration may exceed the van der Waals forces.

[0206] The magnitude of the van der Waals force is inversely proportional to the square of the spacing 302 between the atoms or molecules on which the force acts. At a certain threshold membrane-particle spacing 302, the van der Waals attraction between the particle 210 and the surface of the membrane 211 is attenuated to the point where the electrostatic force that attracts the particle 210 toward the combined actuation electrode / collector 202 (i.e., away from the membrane) overcomes the van der Waals force between the particle 210 and the membrane 211. Above the threshold membrane-particle spacing 302, the particle 210 can therefore be removed from the membrane 211. The particle 210 will be disposed in the space between the membrane 211 and the combined actuation electrode / collector 202 and will be accelerated toward the combined actuation electrode / collector 202.

[0207] Due to mass dependence, the resonant frequency of the particle 210 varies with the size of the particle 210. In order to remove particles 210 having a certain size range, the pulse voltage 401 can be configured to cause oscillations of a certain frequency range of the diaphragm 211. The frequency range of the induced oscillations of the diaphragm 211 can be referred to as an "excitation spectrum". The excitation spectrum is given by the Fourier transform of the waveform 400 of the pulse voltage 401 applied by the voltage source 205. The components of the excitation spectrum come from the time characteristics of the pulse voltage 401. Features that repeat over a relatively long time produce components of the excitation with relatively low frequencies, and vice versa.

[0208] Figure 4 b and 4c show the Figure 4 Schematic graph of an excitation spectrum 404 corresponding to a pulse voltage 401 of the form shown in FIG. The excitation spectrum 404 schematically shows the relative electrostatic attraction force F exerted on the diaphragm, which varies according to the oscillation frequency f at which this force is exerted. The excitation spectrum 404 includes a first portion 405 and a second portion 406.

[0209] The first portion 405 of the excitation spectrum 404 originates from the time feature of the pulse voltage 401 having the longest duration: the time period or time cycle 407 of the pulse of the pulse voltage 401. The center frequency 408 of the first portion 405 is defined by the inverse of the time period 407 (this center frequency 408 can be referred to as the pulse frequency or repetition rate). In some embodiments, the repetition rate of the pulse voltage 401 can be in the range of 30 kHz to 30 MHz. Figure 4 The shaded area 409 of c corresponds to shifting the center frequency 408 of the first portion 405 via modulating the time period 407. An increase in the time period 407 results in a decrease in the center frequency 408 of the first portion 405 (and vice versa).

[0210] The second portion 406 of the excitation spectrum 404 originates from a temporal feature of the pulse voltage 401 having a shorter duration than the time period 407. The second portion 406 is defined by: a full width at half maximum (FWHM) 410 of the on portion 402 of the pulse of the pulse voltage 401; and a rise time 411 and a fall time 412 of the pulse of the pulse voltage 401. A lower frequency limit 413 of the second portion 406 is defined by the inverse of the FWHM 410. An upper frequency limit 414 of the second portion 406 is defined by the inverse of the one of the rise time 411 and the fall time 412 having the shortest duration. Figure 4 The shaded area 415 of c corresponds to shifting the lower frequency 413 and the upper frequency 414 of the second portion 406 by modulating the FWHM 410 and the rise time 411 and the fall time 412. An increase in the FWHM 410 results in a decrease in the lower frequency 413 of the second portion 406 (and vice versa). An increase in the one of the rise time 411 and the fall time 412 having the shortest duration results in a decrease in the upper frequency 414 of the second portion 406 (and vice versa).

[0211] Figure 4 The pulse voltage 401 of the form shown in a is relatively simple. Therefore, it can be easily implemented by those skilled in the art. Advantageously, although the waveform 400 of the pulse voltage 401 is simple, it provides several configurable parameters (including time period 407, FWHM 410, rise time 411, and fall time 412) that can be selected (and changed) to achieve the desired excitation spectrum.

[0212] Use as a pair Figure 4 As an alternative to a pulse voltage 401 of the form shown in FIG. 1 a, an arbitrary function generator connected to a voltage amplifier can also be used to generate any desired pulse shape, which can be configured to induce a desired excitation spectrum.

[0213] In this embodiment, Figure 4 The voltage waveform 400 shown in FIG. 4 can be considered to have a general shape and have one or more parameters (e.g., any one of the time period 407, FWHM 410, rise time 411, and fall time 412) that can be selected (and changed) to achieve a desired excitation spectrum. It will be appreciated that in other embodiments, different voltage waveforms can be used, but different voltage waveforms can also be considered to have a general shape and have one or more parameters that can be selected (and changed) to achieve a desired excitation spectrum.

[0214] In the arrangement of the current embodiment, the combined excitation electrode / collector 202 and diaphragm assembly 208 are arranged such that the spacing between the combined excitation electrode / collector 202 and the diaphragm 211 is between 1 mm and 10 mm.

[0215] In the arrangement of the present embodiment, the pulse voltage 401 applied across the combined excitation electrode / collector 202 and the conductive support 204 has a maximum potential difference between 100V and 10,000V.

[0216] In the arrangement of the present embodiment, the net (time-averaged) electric field between the combined energizing electrode / collector 202 and the diaphragm assembly 208 (due to the pulse voltage 401) has a value greater than 10 V m -1 or below -10V m -1 The field strength.

[0217] In the arrangement of the current embodiment, the pulse voltage 401 is configured to excite the oscillation of the diaphragm 211 in a frequency range between 30 kHz and 30 MHz (and thereby excite the particles 210 disposed on the diaphragm 211). For example, the pulse voltage 401 may be configured to excite the oscillation of the diaphragm 211 in a frequency range between 100 kHz and 10 MHz.

[0218] In the arrangement of the current embodiment, the pulse voltage 401 does not induce an oscillation frequency of the diaphragm that is close to the fundamental frequency (defined only by the frame width and length and the membrane pretension, thickness and density) of the cleaning diaphragm 211. For example, in the arrangement of the current embodiment, the pulse voltage 401 does not induce an oscillation of the diaphragm 211 below 30 kHz. This is useful because it can help avoid rupturing the diaphragm 211.

[0219] In the arrangement of the current embodiment, the pulse voltage 401 is not a voltage that varies in a sinusoidal manner. By ensuring that appropriate off portions 403 are incorporated into the shape of the pulse, the dissipated power into the conductive coating 209 on the diaphragm assembly 208 can be kept low. This is useful to allow radiative cooling to maintain the temperature of the diaphragm 211 within safe limits.

[0220] Using the arrangement described above, particles 210 having a size between 0.5 μm and 5 μm may be removed from the diaphragm 211 using the diaphragm cleaning apparatus 200 .

[0221] The pulse voltage 401 can be applied as a separate pulse train / pulse sequence. One pulse train can be followed by another pulse train. A separate pulse train can be applied, wherein the polarity of the pulse voltage is reversed in a continuous pulse train. This may be useful for releasing both negatively charged and tribo-positively charged particles and attracting them to the collector. The duration of each pulse train can be configured so that: before the next pulse train (with reversed voltage polarity) is applied, the particles 210 have enough time to be transferred to the combined excitation electrode / collector 202. It will be appreciated that charged particles can typically discharge when in contact with the excitation electrode / collector 202. Therefore, when the polarity of the voltage is reversed, these particles are not transferred back to the diaphragm 211.

[0222] Now refer to Figure 5 A diaphragm cleaning device 500 according to a second embodiment of the present invention is described, which shows a cross section through the diaphragm cleaning device 500.

[0223] Figure 5 The diaphragm cleaning device 500 shown shares the Figure 2 The illustrated diaphragm cleaning devices 200 have several features in common, ie, the same. Figure 5 The diaphragm cleaning device 500 shown is generally similar to Figure 2 The features of the diaphragm cleaning device 200 shown correspond to and may be generally Figure 2 Any features of the illustrated diaphragm cleaning apparatus 200 that are identical share common reference numerals.

[0224] The following will only discuss in detail Figure 5 The diaphragm cleaning device 500 and Figure 2 The differences between the diaphragm cleaning devices 200 shown.

[0225] In particular, the diaphragm cleaning apparatus 500 comprises: a conductive support 204 , a spacer section 203 , wires 206a , 206b and vacuum feedthroughs 207a , 207b . In addition, in use, a diaphragm assembly 208 (comprising a diaphragm 211 and a generally rectangular frame 212 ) is disposed on the conductive support 204 .

[0226] The membrane cleaning device 500 also includes an electrode 502 and a voltage supply device 505. The electrode 502 can generally be Figure 2 The combined excitation electrode / collector 202 shown is of the same form, although, as will be discussed further below, the electrode 502 of this embodiment acts only as a collector. Similarly, the voltage supply 505 can generally be the same as Figure 2The voltage supply 505 is of the same form as shown, although, as will be discussed further below, the voltage supply 505 may be arranged to apply a constant or DC voltage (as opposed to a time varying voltage comprising a plurality of pulses).

[0227] Figure 5 The diaphragm cleaning device 500 shown is Figure 2 One major difference between the diaphragm cleaning apparatus 200 shown is that Figure 5 The illustrated diaphragm cleaning apparatus 500 includes various mechanisms for inducing mechanical oscillations in the diaphragm 211 , as will now be discussed.

[0228] The diaphragm cleaning device 500 includes a mechanism for inducing mechanical oscillations in the diaphragm 211, wherein the mechanism for inducing mechanical oscillations includes a radiation source (e.g., a laser) operable to generate a pulsed radiation beam that is incident on at least a portion of the diaphragm 211 when the diaphragm 211 is supported by a conductive support member 204.

[0229] In particular, the membrane cleaning device 500 comprises a laser 514 for this purpose. The laser 514 is operable to generate a pulsed laser beam 516.

[0230] Figure 5 The diaphragm cleaning apparatus 500 shown includes a modified vacuum chamber 501 similar to Figure 2 The vacuum chamber 201 is shown as above, but further includes a window 512. A laser source 515 is disposed outside the vacuum chamber 501. The window 512 is formed of a light-transmitting material through which a pulsed laser beam 516 can propagate so as to be incident on the diaphragm 211.

[0231] The diaphragm cleaning apparatus 500 also includes a beam delivery system 518 including optics 520 , 522 for directing and / or shaping the pulsed laser beam 516 output by the laser 514 .

[0232] In this embodiment, the beam delivery system 518 is operable to focus a pulsed laser beam 516 through the window 512 onto a localized beam spot portion on the diaphragm 211. This portion of the diaphragm 211 receives radiation pressure from the incident laser beam 516. Since the diaphragm 211 is generally flexible, the radiation pressure can produce a mechanical deformation 301 in the diaphragm 208. The local pressure applied by the laser beam 516 is given by the force applied by the laser beam pulse on the diaphragm 211 to the area of ​​the beam spot region. In turn, the force applied by the laser beam pulse on the diaphragm 211 is given by the rate of change of momentum of the photons absorbed by the diaphragm 211. The momentum of each photon is given by the ratio of the energy of that photon to the speed of light, and, therefore, the pressure applied by the laser beam pulse on the diaphragm 211 is given by the power density [W / m2 ] is given by the ratio of the speed of light. It will be appreciated that here, for simplicity, the effect of reflected light on the diaphragm is omitted.

[0233] The laser beam 516 generated by the laser radiation source 515 is a pulsed laser beam 516. Between laser pulses (when no laser radiation is incident on the diaphragm 211), the internal structural forces of the diaphragm 211 may cause an acceleration of the diaphragm 211 in a direction opposite to the mechanical deformation caused by the radiation pressure. Therefore, applying the pulsed laser beam 516 to the diaphragm 211 may induce mechanical oscillations in the diaphragm 211.

[0234] In this embodiment, laser beam 516 is operable to induce oscillations only in a localized portion of diaphragm 211 (ie, near the beam spot portion). Advantageously, by confining the mechanical oscillations to a localized portion of diaphragm 211, a more precise, faster, and more energy-efficient cleaning process can be achieved.

[0235] To allow cleaning of all portions of the diaphragm 211, at least a portion of the laser 514 and / or beam delivery system 518 is movable relative to the window 512. The diaphragm cleaning apparatus 500 can be used to deliver a focused pulsed laser beam 516 to each critical particle 210 (which needs to be removed) on the diaphragm 211 through the window 512. Alternatively, the diaphragm cleaning apparatus 500 can be used to scan or step the pulsed laser beam 516 over the surface of the diaphragm 211 to clean the entire diaphragm 211.

[0236] The voltage source 505 can apply a voltage across the electrical terminals of the voltage source 505, resulting in a voltage across the electrode 502 and the diaphragm 208. Figure 2 As discussed in the diaphragm cleaning device 200 shown, this will apply an attractive electrostatic force to at least some of the particles 210 on the diaphragm 211. Since the mechanical oscillation is caused by the pulsed laser beam 516, the particle 210 (which can be regarded as an independent oscillator) can move away from the diaphragm 211, reducing the binding force between the particle 210 and the diaphragm 211. If the frequency of the diaphragm 211 oscillation is close to the resonant frequency of the particle 210, the amplitude of the oscillation of the particle 210 can increase. As the amplitude of the oscillation of the particle 210 increases, the diaphragm-particle spacing 302 can also increase. In the case of a certain threshold diaphragm-particle spacing 302, the van der Waals attraction between the particle 210 and the surface of the diaphragm 211 is no longer able to keep the particle 210 attached to the surface of the diaphragm 211 (for example, when the diaphragm 211 is accelerated away from the collector 502 between pulses). Therefore, the particle 210 is removed from the diaphragm 211 and will be accelerated toward the electrode 502.

[0237] The use of the conductive support 204 in the first and second embodiments of the diaphragm cleaning apparatus 200, 500 can improve the electrical coupling, i.e., the electrical connection, between the voltage source 205, 505 and the diaphragm 211. However, it will be appreciated that in alternative embodiments, the diaphragm cleaning apparatus 200, 500 can be configured without the conductive support 204, and the voltage source 205, 505 can be directly coupled, i.e., connected to the diaphragm 211.

[0238] Similarly, the use of spacer segments 203 (formed of an electrical insulator) in the first and second embodiments of the diaphragm cleaning apparatus 200, 500 can provide a convenient arrangement for providing a specific spacing between the diaphragm 211 and the electrode 202, 502. In addition, it can provide a convenient arrangement for supporting the diaphragm assembly 208 by the electrode 202, 502 via the electrically insulating spacer segments 203. However, it will be appreciated that in alternative embodiments, the diaphragm cleaning apparatus 200, 500 can be configured without the spacer segments 203. For example, in alternative embodiments, the wires 206a, 206b that provide connections between the voltage source 205, the diaphragm 211, and the electrode 202, 502, respectively, can be strong enough to support the diaphragm 211 and the electrode 202, 505.

[0239] Some embodiments of the present invention utilize an electric field generating mechanism operable to generate an electric field near two opposing surfaces of a diaphragm to be cleaned, the electric fields near the two opposing surfaces of the diaphragm being in opposite directions. In some embodiments, the electric field strengths may be substantially equal in magnitude on opposite sides of the diaphragm (despite being arranged in opposite directions). Advantageously, this arrangement is particularly suitable for cleaning diaphragms that may be thin enough to be susceptible to rupture under sufficient lateral (out of the plane of the diaphragm) loading. By applying an electric field near the two opposing surfaces of the diaphragm, the electric fields near the two opposing surfaces of the diaphragm being in opposite directions, the electrostatic pressures on both sides of the diaphragm can be at least partially equalized. This, in turn, allows the use of larger electric fields, which can provide higher levels of cleaning. Now referring to Figure 6 An example of such an embodiment is described through FIG. 7 .

[0240] Now refer to Figure 6 , Figure 7a and Figure 7b A third embodiment of a diaphragm cleaning device 600 according to the present invention is described.

[0241] Figure 6 A cross section through a cleaning device 600 is shown, the cleaning device 600 comprising: a conductive support 602 , two collecting electrodes 604 , 606 and a voltage source 608 .

[0242] The conductive support 602 is formed of a conductive material and is used to support a membrane (eg, a diaphragm) to be cleaned using the apparatus 600. Figure 6 Also shown in FIG. 2 is a diaphragm assembly 208. The diaphragm assembly 208 includes a diaphragm 211 supported by a generally rectangular frame 212. The conductive support 602 is arranged to support the frame 212 of the diaphragm assembly 208.

[0243] The two collectors 604, 606 are disposed on opposite sides of the plane of the diaphragm 211 supported by the conductive support 602. The two collectors 604, 606 are connected together (ie, they are at the same potential). Figure 6 In the illustrated embodiment, each of the two collectors 604, 606 forms a portion of a two-part assembly that defines an interior chamber 614 in which the diaphragm 211 can be disposed for cleaning. The first collector 604 can generally form a cover portion of the two-part assembly, and the second collector 606 can generally form a body portion of the two-part assembly. Each of the two collectors 604, 606 includes a base 604a, 606a and a protrusion 604b, 606b. The bases 604a, 606a of the two collectors 604, 606 work together to define an interior chamber 614 in which the diaphragm 211 can be disposed for cleaning. It will be appreciated that the two collectors 604, 606 can be separated to provide access to the interior chamber 614. In particular, this allows for loading of the diaphragm assembly 208 into the interior chamber 614 , for cleaning of the diaphragm assembly 208 , and for unloading of the diaphragm assembly 208 from the interior chamber 614 once the diaphragm assembly 208 has been cleaned.

[0244] A seal 616 is disposed between the two collectors 604, 606 so as to seal the internal chamber 614 from the outside of the internal chamber 614 at the mating surfaces where the two collectors 604, 606 are in contact. The seal 616 can be arranged so as to hermetically seal the internal chamber 614 so as to create an airtight seal between the two collectors 604, 606. In this configuration, the internal chamber 614 can act as a vacuum chamber. One or more vacuum pumps (not shown) can be provided to control the pressure within the internal chamber 614.

[0245] The protrusions 604b, 606b of the two collectors 604, 606 are each in the form of a generally cubic protrusion protruding from the base 604a, 606a, respectively. The protrusions 604b, 606b of the two collectors 604, 606 protrude into the internal cavity 614 so that when the two collectors 604, 606 are engaged with each other, the protrusions 604b, 606b are generally parallel to each other.

[0246] The conductive support 602 is connected to the base 606a of the second collector 606 via an insulating support 618. The insulating support 618 is formed of a non-conductive material and includes one or more spacer holes 620. Both the conductive support 602 and the insulating support 618 are in the form of a rectangular frame, i.e. a generally rectangular plate with a central rectangular hole.

[0247] A voltage source 608 is arranged to apply a voltage across each of the two collectors 604, 606 and the diaphragm 211 supported by the conductive support 602. The voltage source 608 is disposed outside the internal chamber 614 formed by the two collectors 604, 606. A first electrical terminal of the voltage source 608 is electrically connected to the second collector 606 (which in turn is in electrical contact with the first collector 604) via a first wire 622. A second electrical terminal of the voltage source 608 is electrically connected to the conductive support 602 via a second wire 624. The second collector 606 is provided with a vacuum feedthrough 626. The second wire 624 passes through the vacuum feedthrough 626.

[0248] The conductive support 602 may be considered as a diaphragm support for supporting the diaphragm 211 or the diaphragm assembly 208. The voltage source 608 and the two collectors 604, 606 may be considered as an electric field generating mechanism for generating an electric field near the diaphragm 211 when the diaphragm 211 is supported by the conductive support 602.

[0249] As now discussed, the diaphragm cleaning device can be used to clean the diaphragm 211. The diaphragm 211 can be a pellicle diaphragm 16 and can be formed of a material having a non-zero electrical conductivity, such as doped polysilicon. The diaphragm assembly 208 can also include a conductive (e.g., metal or conductive ceramic) coating 209 located on one or both sides of the plane of the diaphragm 211.

[0250] In use, the diaphragm assembly 208 is arranged such that the frame 212 is supported by the conductive support 602 such that the conductive surface 209 of the diaphragm assembly 208 is in electrical contact with the conductive support 602 .

[0251] As previously described, one or more vacuum pumps (not shown) may be provided to control the pressure within the interior chamber 614. In particular, a vacuum pump device (not shown) may be used to reduce the pressure of the interior chamber 614 to near vacuum conditions. For example, one or more vacuum pumps may be operable to reduce the pressure within the interior chamber 614 to less than 10 -3 mBar, preferably reduced to less than 10 -6 mBar. The spacer holes 620 in the insulating support 618 enable the pressure of the internal chamber 614 to be equal on opposite sides of the plane of the diaphragm 211.

[0252] The voltage source 608 is operable to apply a voltage across the electrical terminals of the voltage source 608, resulting in a voltage across the conductive surface 209 of the diaphragm assembly 208 and the collectors 604, 606 (the two collectors 604, 606 are electrically connected to each other). The conductive surface 209 of the diaphragm assembly 208 and the collectors 604, 606 are not part of a closed loop. Therefore, charge accumulation can occur on the collectors 604, 606 and the diaphragm 211. This charge accumulation generates an electric field near the diaphragm 211, and the electric field has opposite directions on opposite sides of the plane of the diaphragm 211.

[0253] exist Figure 6 Also shown are two particles 630 , 632 disposed on opposing surfaces of the diaphragm 211 . Figure 7a and 7b Shown are enlarged portions of the diaphragm 211 and the protrusions 604 b , 606 b of the two current collectors 604 , 606 at two different times during a cleaning process using the diaphragm cleaning apparatus 600 .

[0254] Due to the voltage applied by the voltage source 608, particles 630, 632 with non-zero surface conductivity disposed on either surface of the diaphragm 211 may have acquired a charge from the diaphragm 211. The charge of the particles 630, 632 is such that there is an electrostatic force that attracts the particles 630, 632 toward the collectors 604, 606 (facing the surface of the diaphragm 211 on which the particles 630, 632 are disposed). Note that both the conductive and dielectric particles 630, 632 on either side of the diaphragm 211 experience this induced charge (even the dielectric particles have a finite, non-zero surface conductivity).

[0255] Additionally or alternatively, the particles 630, 632 may have acquired an electric charge through triboelectric interactions with the surface of the diaphragm 211. The charge of the particles 630, 632 may be positive or negative. The charge of the particles 630, 632 is such that there is an electrostatic force that attracts the particles 630, 632 toward the diaphragm 211 or the collectors 604, 606 (facing the surface of the diaphragm 211 on which the particles 630, 632 are disposed) (depending on the sign of the charge of the particles 210). It will be appreciated that when a sufficiently large voltage is applied (by a voltage source 608) across the diaphragm 211 and each of the two collectors 604, 606, the charge induced is greater than any triboelectric charge induced. Furthermore, as further described below, by using two collectors 604, 606 disposed on opposite sides of the plane of the diaphragm 211, Figure 6The illustrated embodiment of the diaphragm cleaning apparatus 600 is capable of generating a relatively large electric field (and thus charge) without rupturing the diaphragm 211. Figure 6 With the illustrated embodiment of diaphragm cleaning apparatus 600, triboelectrically induced charges may be insignificant or irrelevant.

[0256] Thus, applying a voltage across the electrical terminals of the voltage source 608 will result in forces F1, F2 being applied to at least some of the particles 630, 632 on the diaphragm 211, which attract the particles 630, 632 toward the collectors 604, 606 (facing the surface of the diaphragm 211 on which the particles 630, 632 are disposed). The magnitude of the electrostatic attraction forces F1, F2 is proportional to the square of the strength of the electric field experienced by the particles 630, 632. For sufficiently large voltages, these forces F1, F2 will exceed the binding forces (e.g., van der Waals forces) between the particles 630, 632 and the diaphragm 211, and the particles 630, 632 will be accelerated away from the diaphragm 211 toward the collectors 604, 606 (facing the surface of the diaphragm 211 on which the particles 630, 632 are disposed).

[0257] The protrusion 604b, 606b of each of the two collectors 604, 606 is provided with an insulating coating 634, 636. The insulating coating 634, 636 prevents charge transfer between the collectors 604, 606 and any particles 630, 630 that have been attached to the collectors 604, 606 via the above-mentioned electric field. This can prevent the particles 630, 632 from being transmitted from the collectors 604, 606 to the diaphragm 211. The insulating coating 634, 636 can have a breakdown strength that exceeds the electric field that will be generated by the voltage supply 608 during use of the diaphragm cleaning device 600.

[0258] The strength of the electric field experienced by the particles 630, 632 can be controlled by controlling the voltage applied across the diaphragm 211 and the collectors 604, 606. In addition, the strength of the electric field experienced by the particles 630, 632 can be controlled by controlling the separation distance 638, 640 between the diaphragm 211 and each collector 604, 606; and / or controlling the electromagnetic properties and / or thickness 642, 644 of the insulating coating 634, 636.

[0259] The diaphragm cleaning apparatus 600 is configured such that, in use, the distance 638, 640 between the diaphragm 211 and each collector 604, 606, and the thickness 642, 644 of each insulating coating 634, 636 are selected so as to substantially balance the electric field strength on the two opposing surfaces of the diaphragm 211. By balancing the electric field strength on the two opposing surfaces of the diaphragm 211, the electrostatic pressure applied to both sides of the diaphragm 211 is also balanced (schematically represented by arrows 646, 648).

[0260] like Figure 7b As shown, once the particles 630, 632 have been electrostatically transferred to the collectors 604, 606, the insulating coatings 634, 636 prevent charge leakage and reduce the risk of particles being transferred back from the collectors 604, 606 to the diaphragm 211. Therefore, the electrostatic attractive forces F1, F2 now push the particles 630, 632 onto the insulating coatings 634, 636, thereby holding the particles 630, 632 in place unless the bias voltage applied by the voltage source 608 is removed. Once the bias voltage is removed, the particles 630, 632 will be constrained or bound to the insulating coatings 634, 636 via van der Waals interactions.

[0261] Figure 6 The illustrated diaphragm cleaning apparatus 600 provides an arrangement in which an electric field may be used to remove particles 630, 632 from the diaphragm 211. In use, the diaphragm assembly 208 may be supported by a conductive support 602. A voltage source 608 and two collectors 604, 606 may be used to generate an electric field near the diaphragm 211 when the diaphragm 211 is supported by the conductive support 602 so as to remove or dislodge particles 630, 632 from the surface of the diaphragm 211 and transport such particles 630, 632 away from the surface of the diaphragm 211.

[0262] Figure 6 This embodiment of the diaphragm cleaning device 600 shown is particularly suitable for cleaning the diaphragm 211, which may be thin enough to be easily broken under sufficient lateral (outside the plane of the diaphragm) loading. For example, for the surface membrane 15, applying a lateral pressure of about 100Pa or more may cause the diaphragm to break. Since the two collectors 604, 606 are arranged on opposite sides of the plane of the diaphragm 211, it is possible to simultaneously (when the diaphragm 211 is supported by the conductive support 602) generate an electric field near the two opposing surfaces of the diaphragm 211, so that the electric fields near the two opposing surfaces of the diaphragm 211 are in opposite directions. Advantageously, this allows the pressure on both sides of the diaphragm 211 to be at least partially equalized. In turn, this allows the use of a larger electric field, which can provide a higher level of cleaning.

[0263] In some embodiments, diaphragm cleaning apparatus 600 may be arranged such that the magnitude of the electric field is substantially equal on both sides of diaphragm 211 (the direction of the electric field is different on opposite sides of diaphragm 211 ).

[0264] In some embodiments, the membrane cleaning apparatus 600 may be arranged to generate an electric field in the vicinity of the membrane 211 that exceeds the typical electric field that the pellicle 15 in the EUV lithography apparatus LA may experience. Figure 1 ), the pattern forming device MA can be attached to the support structure MT via an electrostatic clamp. The pellicle 15 can also be attached to the support structure MT so that it covers the pattern forming device MA. With this arrangement, the electrostatic clamp can generate a clamping voltage of about 1 to 10 kV (for example 4 kV), and the pellicle 15 can be set at a distance of about 1 to 5 mm (for example 2 mm) from the pattern forming device MA. With this arrangement, an electric field of about 2 to 20 MV / m can be generated near the pellicle 15. In turn, this may exert a force on any particles on the pellicle 15 that exceeds the binding force (for example Van der Waals force) that binds the particles to the pellicle 15, thereby accelerating the particles away from the pellicle 15 toward the pattern forming device MA. In addition, within the EUV lithography equipment, there may be a low-pressure supply of gas (for example hydrogen) that can form an EUV plasma when exposed to EUV radiation. Such EUV-induced plasma may have a finite (non-zero) conductivity and may provide electrical contact between the pellicle 15 and one or more portions of the electrostatic chuck which may be biased up to several kV (relative to the pellicle 15) and may be provided with a thin insulating coating. Figure 6 The diaphragm cleaning apparatus 600 shown is used to clean the pellicle 15, particularly by generating an electric field near the diaphragm assembly that exceeds the typical electric field that the pellicle within the EUV lithography apparatus LA may be subjected to, so that substantially all particles that may be transferred to the pattern forming device MA within the EUV lithography apparatus may be removed before using the pellicle 15.

[0265] Thus, in some embodiments, the diaphragm cleaning apparatus 600 may be operable to generate an electric field strength of approximately 1 to 20 MV / m near the diaphragm 211. This may be accomplished, for example, by providing a distance of approximately 0.1 to 2 mm between the diaphragm 211 and each collector 604, 606, and providing a voltage source 608 operable to generate a voltage of approximately 0.1 to 40 kV across the electrical terminals of the voltage source 608 (resulting in a voltage across the conductive surface 209 of the diaphragm assembly 208 and the collectors 604, 606).

[0266] The inventors have recognised that it may be necessary to generate an electric field in the vicinity of the diaphragm 211, which may cause the diaphragm to rupture if the electric field is generated on only one side of the diaphragm. Figure 6 The illustrated diaphragm cleaning apparatus 600 avoids this situation by generating substantially equal and opposite electric fields on both sides of the diaphragm to at least partially balance the applied pressure.

[0267] Generally, in some embodiments, any conductive component of the diaphragm cleaning device 600 may be provided with rounded edges to reduce the risk of sparking or bulging that may occur at electric field concentration (sharp) points or edges (particularly when a large voltage is applied by the voltage source 608). Figure 6 As can be seen in the figure, for this reason, the collectors 604, 606 (particularly the protrusions 604b, 606b of the collectors 604, 606) and the conductive support 602 are provided with rounded edges. In addition, the diaphragm assembly 208 can be additionally provided with a cover or wrap to hide or cover any sharp edges (e.g. on the frame 212) and / or metallized edges (omitted for simplicity).

[0268] It will be appreciated that although in this embodiment the two collectors 604, 606 are in electrical contact (i.e., at substantially the same voltage), in alternative embodiments the collectors may not be connected, but still maintained at substantially equal voltages. In further alternative embodiments, the collectors may not be connected and may be maintained at different voltages, which may be desirable (e.g., if the two collectors 604, 606 are positioned so that they are not equidistant from the diaphragm 211) in order to still ensure that the electrostatic forces on both sides of the diaphragm 211 are substantially balanced.

[0269] It will be appreciated that although this embodiment includes a conductive support member 602, in alternative embodiments, the first wire 622 and the second wire 624 may be directly connected to the diaphragm 211, or alternatively, a conductive member that does not support the diaphragm assembly 208 may be provided (for example, it may be connected to the upper surface of the diaphragm frame 212).

[0270] Some embodiments of the present invention utilize an electric field generating mechanism operable to generate an electric field near at least one surface of a membrane to be cleaned in combination with a plasma generating mechanism operable to generate a plasma adjacent to the at least one surface of the membrane. The electric field generating mechanism is operable to reverse the direction of the electric field. Referring now to Figure 8a , 8b and 8c describe two examples of such embodiments.

[0271] Figure 8aA cross section of a portion of a cleaning device 800 is shown, comprising two electrodes 802,804 and a voltage source 806. The voltage source 806 is connected to the two electrodes 802,804 via wires 808,810 and is arranged to apply a voltage across the two electrodes 802,804.

[0272] The diaphragm 211 to be cleaned is disposed between the two electrodes 211. Although not shown, it will be appreciated that the diaphragm 211 may form part of a diaphragm assembly and may be supported by a diaphragm support. Such diaphragm assemblies and diaphragm supports may generally be in the form of corresponding diaphragm assemblies and diaphragm supports described above for other embodiments of the present invention.

[0273] Diaphragm cleaning apparatus 800 also includes a plasma generating mechanism operable to generate plasma 812 adjacent to both surfaces of diaphragm 211 .

[0274] Figure 8b A cross section of a portion of a cleaning device 820 is shown, which also includes two electrodes 802, 804 and a voltage source 806. Figure 8a In contrast, the cleaning device 800 shown Figure 8b The voltage source 806 of the cleaning device 820 shown is connected so that one terminal of the voltage source 806 is connected to the two electrodes 802, 804 via wires 808a, 808b, and the other terminal of the voltage source 806 is connected to the conductive portion 209 of the diaphragm 211 via wire 810. Thus, the voltage source 806 is arranged to apply a voltage across the diaphragm 211 and each electrode 802, 804.

[0275] Again, although not shown, it will be appreciated that the diaphragm 211 may form part of a diaphragm assembly and may be supported by a diaphragm support (and electrical connection between the lead 808b and the diaphragm 211 may be achieved via a conductive portion of such a diaphragm support). Such a diaphragm assembly and diaphragm support may generally be in the form of corresponding diaphragm assemblies and diaphragm supports described above with respect to other embodiments of the invention.

[0276] Diaphragm cleaning apparatus 820 also includes a plasma generating mechanism operable to generate plasma 812 adjacent to both surfaces of diaphragm 211 .

[0277] Figure 8c A cross section of a portion of a cleaning device 850 is shown, comprising one electrode 802 and a voltage source 806. The voltage source 802 is connected to the electrode 802 and the conductive portion 209 of the diaphragm 211 via wires 808, 810 and is arranged to apply a voltage across the electrode 802 and the diaphragm 211.

[0278] Again, although not shown, it will be appreciated that the diaphragm 211 may form part of a diaphragm assembly and may be supported by a diaphragm support (and electrical connection between the lead 810 and the diaphragm 211 may be achieved via a conductive portion of such a diaphragm support). Such a diaphragm assembly and diaphragm support may generally be in the form of corresponding diaphragm assemblies and diaphragm supports described above for other embodiments of the invention.

[0279] Cleaning apparatus 850 also includes a plasma generating mechanism operable to generate plasma 812 between electrode 802 and diaphragm 211 (ie, adjacent to a surface of diaphragm 211 that faces electrode 802 ).

[0280] exist Figures 8a to 8c In each of the cleaning devices 800, 820, 850 shown, the plasma 812 can have a relatively low pressure. As used herein, a relatively low pressure plasma 812 can mean a plasma density such that any bias voltage applied between the diaphragm 211 and the (multiple) electrodes 802, 804 does not result in sparking or other high current discharges (e.g., does not discharge at a current exceeding 100 mA).

[0281] Figure 8a An advantage of the arrangement of the cleaning apparatus 800 shown is that this arrangement does not require any electrical connections to the membrane 211 being cleaned.

[0282] Figure 8b An advantage of the arrangement of the cleaning device 820 shown is that it allows the generation of opposite electric fields on opposite sides of the diaphragm 211 (in a manner similar to Figure 6 If the electric field strengths on opposite sides of the diaphragm 211 are substantially equal (but opposite), the electrostatic pressure applied to the two opposite sides of the diaphragm can be substantially equal, which reduces the risk of rupturing the diaphragm and increases the amount of bias voltage that can be applied by the voltage source 806.

[0283] exist Figures 8a to 8c In each of the cleaning apparatuses 800, 820, 850 shown, due to the difference in mobility of electrons and ions in the plasma 812, in the absence of a bias voltage applied by the voltage source 806, all surfaces in contact with the plasma will become negatively charged. In particular, the surface of the diaphragm 211 will become negatively charged. This is one mechanism by which particles 814, 816 that are poor conductors of electricity (and thus may be poorly cleaned by the previous embodiments of the diaphragm cleaning apparatuses 200, 500, 600) may become charged.

[0284] exist Figures 8a to 8cIn some embodiments of the cleaning apparatus 800, 820, 850 shown, the voltage source 806 may be operable to apply a bias voltage that will generate an electric field near at least one surface of the diaphragm 211. Thus, there will be a bias voltage between the diaphragm 211 and the electrodes 802, 804. This will cause current to flow through the finite conductivity plasma 812, which in turn will cause charge to be deposited on the surfaces of the poorly conductive particles 814, 816. Thus, due to the finite (non-zero) conductivity of the plasma 812, the diaphragm 211 and any particles 814, 816 on the diaphragm 211 acquire the potential (and corresponding charge) of the nearest bias electrode (802, 804). This is a method of providing an enhanced charge on particles 814, 816 that are poorly conductive and do not follow a sufficiently good electric field on the diaphragm 211, and are therefore poorly cleaned by the previously described embodiments of the diaphragm cleaning apparatus 200, 500, 600. This bias voltage may be referred to as a charging voltage.

[0285] exist Figures 8a to 8c In each cleaning apparatus 800, 820, 850 shown, when a bias voltage is applied by a voltage source 806, the plasma can be considered to form a virtual electrode adjacent to one or both surfaces of the diaphragm 211. This virtual electrode is provided by the plasma sheath adjacent to the surface of the diaphragm and has the same polarity as the collector 802, 804 facing the surface of the diaphragm 211.

[0286] The voltage source 806 is operable to provide a bias voltage that forces particles 814, 816 that have received charge from the plasma to move away from the diaphragm. This bias voltage may be referred to as a release voltage. For embodiments where charge is acquired from the plasma alone (in the absence of a bias voltage from the voltage source 806), this is achieved by applying a bias voltage that forces (negatively charged) particles 814, 816 to move away from the diaphragm 211. For embodiments where charge is acquired from the plasma (in the presence of a bias voltage from the voltage source 806), this is achieved by reversing the polarity of the bias voltage. If the release bias voltage is turned on quickly enough, any particle 814, 816 that has acquired charge via the plasma 812 disposed on the diaphragm 211 will be subject to an electrostatic force that points away from the diaphragm 211 and toward the electrode 802, 804 that the particle 802, 804 is facing. For a sufficiently large bias voltage, these forces will exceed the binding forces (e.g., van der Waals forces) between the particles 814, 816 and the diaphragm 211, and the particles 814, 816 will be accelerated away from the diaphragm 211 and toward the collectors 802, 804 facing the surface of the diaphragm 211 on which the particles 814, 816 are disposed. Optionally, the plasma generation mechanism may be arranged such that the plasma 812 is turned off before the release voltage is turned on. This may reduce the effects of charge decay on the particles after the bias voltage polarity is reversed.

[0287] Note that for these embodiments, the distance between the diaphragm 211 and the electrodes 802, 804 will generally be greater than the distance between the diaphragm 211 and the collectors of the other embodiments described above, in order to support the plasma 812 between the diaphragm 211 and the collectors 802, 804. The diaphragm 211 may have a diameter of approximately 100 cm. 2 The area of ​​the diaphragm 211 is 200 mm, and in order to generate and support the plasma 812 between the diaphragm 211 and the electrodes 802, 804, the distance between the diaphragm 211 and the electrodes 802, 804 can be about 30 mm to 300 mm. The bias voltage required for releasing particles is a function of the distance between the diaphragm 211 and the electrodes 802, 804, but for a distance between the diaphragm 211 and the electrodes 802, 804 of about 30 mm to 300 mm, the bias voltage can be about 100 V to 1000 V.

[0288] Since the surface film usually has a conductive layer, in this embodiment, the bias voltage can be directly applied to the surface film (such as Figure 8b and Figure 8c Alternatively, the diaphragm 211 may be mounted between two electrodes 802, 804, and a bias voltage may be applied to one or both of these electrodes 802, 804 (e.g., as in Figure 8a As previously mentioned, this latter solution can reduce the risk of mechanical damage to the diaphragm 211 because no direct connection to the diaphragm 211 is required.

[0289] In order to minimize ion current flowing from the plasma 812 to the membrane 211 (which would result in charge neutralization of the particles 814, 816), the release bias voltage should be turned on quickly, for example on a time scale of less than 0.1 ms.

[0290] For embodiments where the plasma 812 remains on while the bias voltage is applied, particles released by the bias voltage are trapped in the plasma 812 and may be transported elsewhere.

[0291] In the presence of plasma 812 and the voltage applied from voltage source 806, there will be a current flowing through the diaphragm 211. The magnitude of the current will depend on both the applied voltage and the density of plasma 812. In turn, this current will cause Joule heating of the diaphragm 211, which may be undesirable. The diaphragm 211 may have dimensions of approximately 10 cm×10 cm and may have a thickness of approximately 100 nm. The diaphragm 211 may have a resistance of approximately 100 Ω. The time range of these conditions (with plasma 812 and applied voltage) may be limited so that the heat generated by the current flowing through the diaphragm 211 can be dissipated without heating the diaphragm 211 to a temperature at which the diaphragm 211 will fail. This can be controlled by controlling the time range of the applied voltage and / or controlling when the plasma 812 is turned on. It may be necessary to ensure that the temperature of the diaphragm does not exceed 500°C.

[0292] In some embodiments, the bias voltage may be applied as a pulse voltage in order to limit Joule heating of the membrane 211. Applying the pulse voltage limits the period of time that current flows through the membrane 211. In this mode of operation, the particles 814, 816 can be released with minimal heating and minimal neutralization of ion pair charges.

[0293] It will be appreciated that the duty cycle of the pulse voltage may be limited to ensure that heat generated by the current flowing through the diaphragm 211 can be dissipated without heating the diaphragm 211 to a temperature at which the diaphragm 211 will fail. For example, the duty cycle may be 10% or less, such as 1% or less. The frequency of the pulse voltage may be between 1 Hz and 10 kHz. Also to limit Joule heating, the pulse duration of the pulse voltage may be less than 1 ms. For example, the pulse duration of the pulse voltage may be less than 10 μs.

[0294] In some embodiments, to provide adequate cleaning, the electric field strength near the diaphragm is at least 10 kV / m, more preferably at least 100 kV / m. It will be appreciated that the electric field strength depends on the bias voltage applied by the voltage source 806, and the distance between the diaphragm 211 and the collectors 802, 804. However, the electric field strength also depends on the plasma 812 (e.g., the type of plasma, the density of the plasma, etc.), and the plasma 812 will generally reduce the voltage that should be applied to achieve the desired target electric field strength. In some embodiments, the magnitude of the pulse voltage can be at least 100 V. For example, the magnitude of the pulse voltage can be at least 1000 V.

[0295] In some embodiments, each pulse of the pulse voltage may include a first portion having a first polarity (and may be referred to as a charging voltage) and a second portion having an opposite second polarity (and may be referred to as a releasing voltage). Advantageously, with this arrangement, during the first portion, the plasma 812 will charge the particles 814, 816 with a charge corresponding to the polarity of the potential of the electrode 802, 804 facing the particle 814, 816. During the second portion, the polarity of the bias voltage is reversed. If this is done quickly enough, any particle 814, 816 disposed on the diaphragm 211 that has acquired a charge via the plasma 812 will be subject to an electrostatic force directed away from the diaphragm and toward the electrode 802, 804 that the particle 814, 816 is facing.

[0296] Additionally or alternatively, the plasma 812 may be switched off with a delay of at most 1 ms, preferably at most 1 μs, before polarity reversal.

[0297] For example, the plasma generation mechanism may be arranged such that the plasma 812 is switched on between subsequent pulses of the pulsed voltage and is switched off during a pulse of the pulsed voltage.

[0298] By synchronizing the plasma generation mechanism with the pulsed voltage in this manner, and in particular shutting off the plasma 812 during the pulses of the pulsed voltage, the amount of current flowing through the diaphragm 211 can be limited. With this arrangement, any restrictions on the magnitude and time range of the voltage pulses can be relaxed. It is possible that with this arrangement, there are no restrictions on the magnitude and time range of the voltage pulses (for example, if the voltage is applied in a manner that ensures that the electrostatic pressures on opposite sides of the diaphragm are substantially balanced).

[0299] With this arrangement, as the plasma 812 decays, it may still charge the poorly conductive particles 814 , 816 on the membrane 211 , but will not cause high currents to flow through the membrane 211 .

[0300] This process of introducing a bias voltage to remove particles 814, 816 can be repeated at any convenient frequency. For example, the process of reversing the bias voltage to remove particles 814, 816 can be repeated at a frequency between about 1 Hz and 10 kHz. It has been found that this arrangement can effectively and quickly remove substantially all particles having a size of about 30 nm or greater. For example, it has been found that this arrangement can effectively and quickly remove more than 99% of particles having a size of about 30 nm or greater in a cleaning time of less than 1 second.

[0301] Now refer to Fig. 9 A diaphragm cleaning device 900 according to a fifth embodiment of the present invention is described, which shows a cross section of the diaphragm cleaning device 900 .

[0302] Fig. 9 The diaphragm cleaning device 900 shown shares the Figure 5 The illustrated diaphragm cleaning apparatuses 500 share several features in common. Fig. 9 The diaphragm cleaning device 900 shown is generally Figure 5 Any features of the illustrated diaphragm cleaning apparatus 500 that correspond and may be substantially identical share common reference numerals.

[0303] The following will only discuss in detail Fig. 9 The diaphragm cleaning device 900 and Figure 5 The differences between the diaphragm cleaning device 500 shown.

[0304] The diaphragm cleaning apparatus 900 includes a vacuum chamber 901, a window 912, wires 206a, 206b, and vacuum feedthroughs 207a, 207b, similar to Figure 5 Diaphragm cleaning device 500 is shown.

[0305] The diaphragm cleaning apparatus 900 also includes: a support 904; two electrodes 902a, 902b; a voltage source 905; a laser 914; and a beam delivery system 918. In use, the diaphragm assembly 208 (including the diaphragm 211 and the generally rectangular frame 212) is disposed on the support 904.

[0306] Voltage source 905 can be generally Figure 2 The voltage source 905 is of the same form as shown. The voltage source 905 may be arranged to apply a time-varying voltage (eg, a time-varying voltage comprising a plurality of pulses).

[0307] Fig. 9 The diaphragm cleaning device 900 shown is Figure 5 The difference between the diaphragm cleaning devices 500 shown is that Fig. 9The illustrated diaphragm cleaning device 900 includes different mechanisms for inducing mechanical oscillations in the diaphragm 211 .

[0308] Fig. 9 The diaphragm cleaning device 900 and Figure 5 Another difference between the illustrated diaphragm cleaning apparatus 500 is that the laser 914 and beam delivery system 918 of diaphragm cleaning apparatus 900 are configured to control the temperature of at least a portion of diaphragm 211 .

[0309] Fig. 9 The diaphragm cleaning device 900 and Figure 5 Another difference between the illustrated diaphragm cleaning device 500 is that the arrangement of electrodes 902 a , 902 b differs from the arrangement of electrodes 502 .

[0310] One terminal of the voltage source 905 is connected to the electrode 902a using a wire 206a that runs through a vacuum feedthrough 207a. The opposite terminal of the voltage source 905 is connected to the electrode 902b using a wire 206b that runs through a vacuum feedthrough 207b. The two electrodes 902a, 902b are adjacent to each other. The electrodes 902a, 902b are disposed on the same side of the diaphragm 211 of the diaphragm assembly 208. The two electrodes 902a, 902b may include a tapered portion having a smaller cross-sectional area at its end adjacent to and facing the diaphragm 211.

[0311] In use, the potential of the diaphragm 211 of the diaphragm assembly 208 may be floating (ie, not fixed). Alternatively, the diaphragm 211 of the diaphragm assembly 208 may be held at a fixed potential (such as a fixed DC bias voltage or ground). Having the diaphragm 211 at a floating potential may be preferred.

[0312] The potential of the diaphragm 211 can be controlled by connecting the diaphragm 211 to a voltage source (not shown). Alternatively, the potential of the diaphragm 211 can be controlled by connecting the support 904 to a voltage source (not shown). The conductive coating 209 of the diaphragm assembly 208 is in contact with the support 904, thereby ensuring electrical contact between the support 904 and the diaphragm 211. Charge can accumulate on the diaphragm 211.

[0313] When the diaphragm 211 is supported by the support 904, the two electrodes 902a, 902b can be positioned close to the surface of the diaphragm 211. In use, the electrodes 902a, 902b are arranged close to the diaphragm 211. The voltage source 905 applies a voltage across the electrodes 902a, 902b. Therefore, charge can be accumulated on the electrodes 902a, 902b. The potential of the diaphragm 211 is fixed or floating, and there may be a general potential difference (bias voltage) between the diaphragm 211 and the electrodes 902a, 902b.

[0314] When charge accumulates on the electrodes 902a, 902b, an electric field exists in the vicinity of the electrodes 902a, 902b and the diaphragm 211. Charge carriers within the diaphragm 211 may be displaced, thereby inducing charge in the diaphragm 211. Particles 210 present on the diaphragm 211 may also acquire the induced charge.

[0315] As charge accumulates on the electrodes 902a, 902b (and the diaphragm 211), an electrostatic attraction will exist between each electrode 902a, 902b and the diaphragm 211.

[0316] Since the diaphragm 211 is relatively thin and therefore flexible, the diaphragm 211 will deform due to any attractive forces between the diaphragm 211 and each electrode 902a, 902b.

[0317] In the current embodiment, the accumulation of charge is utilized, which generates an electrostatic force near the diaphragm assembly 208. Specifically, by configuring the temporal characteristics of the electrostatic force, mechanical oscillations are induced in the diaphragm 211. According to the current embodiment of the invention, this is achieved by applying a time-varying voltage across the electrodes 902a, 902b and by floating the potential of the diaphragm 211 or by maintaining the diaphragm 211 at a fixed potential (i.e., a fixed voltage).

[0318] As mentioned above Figure 2 , Figure 3 and Figure 4 As described in detail, the pulsed electrostatic force can induce oscillations in the diaphragm 211. The particle 210 and the diaphragm 211 on which the particle is disposed can act as a composite oscillation system, and, for a specific (resonant) frequency of oscillation of the diaphragm 211, the spacing between the particle 210 and the diaphragm 211 can be increased to such an extent that the particle 210 is no longer bound to the diaphragm 211. This principle of removing the particle 210 from the diaphragm 211 by inducing oscillations at the resonant frequency of the particle 210 in the diaphragm is utilized in the diaphragm cleaning device 900.

[0319] During the application of the time-varying voltage across the electrodes 902a, 902b, there may be a time-averaged net electric field between the diaphragm 211 and the electrodes 902a, 902b. As discussed above, any particle 210 removed from the diaphragm 211 may have acquired an electric charge. This charge of the particle 210 and the net electric field between the diaphragm 211 and the electrodes 902a, 902b may cause any particle 210 removed from the diaphragm 211 using the diaphragm cleaning apparatus 900 to be attracted toward the electrodes 902a, 902b.

[0320] The electrodes 902a, 902b are used to induce oscillations in the diaphragm 211. Therefore, the electrodes 902a, 902b can be referred to as excitation electrodes. After removal from the diaphragm 211, the particles 210 can be attracted to one or both of the electrodes 902a, 902b, depending on the charge of the particles 210 and the polarity of each electrode 902a, 902b. Therefore, the electrodes 902a, 902b can be referred to as collectors.

[0321] When used in a lithographic apparatus (such as a lithographic apparatus LA), the side of the membrane 211 facing the patterning device (such as the patterning device MA) can be referred to as the "critical side" of the membrane 211, because it is from this critical side that particles 210 disposed on the membrane 211 may be transported to the patterning device MA and affect the lithographic performance. When used in a lithographic apparatus, the opposite side of the membrane 211 facing away from the patterning device can be referred to as the "non-critical side".

[0322] exist Fig. 9 In the illustrated membrane cleaning apparatus 900, the electrodes 902a, 902b are arranged relative to the membrane 211 so that the electrodes 902a, 902b face the critical side of the membrane 211. With this arrangement, it may be advantageous to arrange the application of a time-varying voltage across the electrodes 902a, 902b so that there is a time-averaged net electric field between the membrane 211 and the electrodes 902a, 902b. This net electric field can ensure that any particles 210 removed from (the critical side of) the membrane 211 using the membrane cleaning apparatus 900 can be attracted toward the electrodes 902a, 902b.

[0323] The arrangement of electrodes 902a, 902b relative to the diaphragm 211 may be different from Fig. 9 In contrast, the electrodes 902a, 902b may be arranged such that the electrodes 902a, 902b face the non-critical side of the diaphragm 211. For example, the diaphragm assembly 208 may be arranged in a manner similar to Fig. 9 The electrodes 902a, 902b may be placed on the support 904 in a different orientation than shown, and / or the electrodes 902a, 902b may be placed in a different orientation than shown in the vacuum chamber 901. Fig. 9 In different zones of the zones shown.

[0324] In an arrangement where the electrodes 902a, 902b face the non-critical side of the diaphragm 211, an electric field will exist between the electrodes 902a, 902b and the diaphragm 211, but this electric field will generally not extend beyond the diaphragm 211. There will generally be no electric field near the critical side of the diaphragm 211. In this arrangement, oscillations can be induced in the diaphragm 211, and particles 210 deposited on the diaphragm 211 can be removed from the diaphragm 211, as described above with reference to Fig. 9 However, in this arrangement, due to the momentum of the particle 210 after being effectively "launched" from the diaphragm 211, the particle 210 removed from the critical side of the diaphragm 211 can be transported away from the diaphragm 211. That is, after the particle is removed from the critical side of the diaphragm 211, the electric field may not affect the transport of the particle 210 away from the critical side of the diaphragm 211. In addition, the electrodes 902a, 902b and the diaphragm 211 can be arranged relative to each other so that after the particle is removed from the critical side of the diaphragm 211 (by the induced oscillation), gravity also helps to remove the particle from the diaphragm 211.

[0325] It will be appreciated that this modification of the diaphragm cleaning apparatus 900, in which the electrodes 902a, 902b face the non-critical side of the diaphragm 211, can be described as comprising: a diaphragm support for supporting the diaphragm 211; and an electric field generating mechanism for generating an electric field near the diaphragm 211 when the diaphragm 211 is supported by the diaphragm support.

[0326] It will also be appreciated that this modification of diaphragm cleaning apparatus 900 may be described as including a mechanism for inducing mechanical oscillations in diaphragm 211 when diaphragm 211 is supported by a diaphragm support.

[0327] The diaphragm cleaning apparatus 900 is used to induce oscillations in the diaphragm 211 in a manner similar to the manner in which the diaphragm cleaning apparatus 200 is used to induce oscillations in the diaphragm 211. In particular, both the diaphragm cleaning apparatus 900 and the diaphragm cleaning apparatus 200 use a time-varying (e.g., pulsed) electrostatic force between one or more electrodes and the diaphragm 211 to induce oscillations in the diaphragm. In the diaphragm cleaning apparatus 900, the time-varying or pulsed electrostatic force between the diaphragm 211 and the electrodes 902a, 902b occurs due to the application of a time-varying or pulsed voltage from the voltage source 905.

[0328] The time-varying voltage used to induce oscillations in the diaphragm 211 may include a plurality of pulses spaced apart in time. Figure 2 The pulse voltage provided by the voltage source 205 of the membrane cleaning device 200 shown in FIG. 20A and the time characteristics of the voltage provided by the voltage source 905 can be configured to cause oscillation of the desired frequency range (ie, the desired excitation spectrum) of the membrane 211. Figure 4As described in detail, due to the mass dependence of the fundamental (or eigen) frequency v0, the resonant frequency of the particle 210 can vary with the size of the particle 210. In order to remove particles 210 having a certain size range, the pulse voltage provided by the voltage source 905 can be configured to produce an excitation spectrum that is customized or adapted to remove particles 210 having a size within a predetermined range.

[0329] It will be appreciated that, as described thus far, the diaphragm cleaning apparatus 900 ( Fig. 9 ) Use with diaphragm cleaning device 200( Figure 2 ) The particles 210 are removed from the diaphragm 211 using essentially the same method. Fig. 9 The arrangement of electrodes 902a, 902b in Figure 2 The arrangement of the electrodes 202 in is different. Figure 2 Compared with the arrangement of the electrode 202 in Fig. 9 The arrangement of electrodes 902a, 902b in can allow for more spatially localized excitation of the diaphragm 211. Advantageously, Fig. 9 Such an arrangement of electrodes 902a, 902b in the membrane may need to be coupled to an electrode that is large enough to induce oscillations over a larger area of ​​the membrane 211 (such as Figure 2 This can be described as improving the efficiency of the diaphragm cleaning device 900. In addition, Fig. 9 The arrangement of electrodes 902a, 902b in Figure 2 The amplitude of the oscillations caused by the electrode 202 in the membrane 211 is greater (for a given amplitude of the applied voltage) than the amplitude of the oscillations of a portion of the membrane 211. This can be described as improving the membrane cleaning efficacy.

[0330] The diaphragm cleaning device 900 is configured to control the temperature of at least a portion of the diaphragm 211. The diaphragm cleaning device 900 is configured to control the temperature of at least a portion of the diaphragm 211 during the mechanical oscillation of the diaphragm 211. The diaphragm cleaning device 900 is configured to increase the temperature (i.e., heat) of at least a portion of the diaphragm 211. In particular, the diaphragm cleaning device 900 can heat a portion of the diaphragm 211 while the portion of the diaphragm 211 is undergoing mechanical oscillation. Heating the portion of the diaphragm 211 that is undergoing mechanical oscillation can cause expansion of the portion of the diaphragm 211. This can cause a reduction in the local tension in the portion of the diaphragm 211. Alternatively, the tension of the diaphragm 211 can be referred to as the pre-tension of the diaphragm 211. The mechanism used to heat the diaphragm 211 is now described.

[0331] Laser 914 includes a laser source 915. Beam delivery system 918 includes optics 920. In use, laser source 915 generates laser beam 916. Optics 920 of beam delivery system 918 are arranged such that beam delivery system 918 shapes laser beam 916 so that it propagates through window 912 and impinges on the surface of diaphragm 211.

[0332] The portion of the diaphragm 211 that is incident with the laser beam 916 can be described as a "laser spot region". The beam delivery system 918 can shape the laser beam 916 so that the laser spot region covers a desired small portion of the surface of the diaphragm 211 (such as Fig. 9 211). Alternatively, the beam delivery system 918 can shape the laser beam 916 so that the laser spot area covers the entirety of the diaphragm 211 within the frame 212. The beam delivery system 918 can be configured to control the spatial intensity distribution of the laser beam 916. For example, the beam delivery system 918 can shape the spatial intensity distribution of the laser beam 916 so that it is flat (i.e., "top hat").

[0333] When the laser beam 916 is incident on the surface of the diaphragm 211, part of the (radiated) energy will be received by the surface of the diaphragm 211. This may increase the temperature of the diaphragm 211 in the laser spot region of the diaphragm 211. Any portion of the diaphragm 211 whose temperature is increased may therefore experience thermal expansion. The thermal expansion of a portion of the diaphragm 211 may change the tension σ of the diaphragm 211. In particular, the thermal expansion may reduce the tension σ of the diaphragm 211.

[0334] The frame 212 of the diaphragm assembly 208 is not typically heated. In particular, the frame 212 is not typically heated by the laser beam 916. As a result, the diaphragm 211 may experience thermal expansion while the frame 212 may not. This can be described as the diaphragm 211 experiencing thermal expansion within the fixed frame 212. This can result in what can be described as the diaphragm 211 "drooping or sagging" within the frame 212.

[0335] As discussed above, the fundamental frequency v0 of the oscillator can be described by the following equation: The fundamental frequency v0 is Thus, for a particle 210 of fixed mass M (which can be assumed to correspond to a particle 210 of fixed size), a reduction in the tension of the diaphragm 211 reduces the fundamental frequency of the oscillating system defined by the diaphragm 211 and the particle 210 .

[0336] Due to the time-varying voltage applied across electrodes 902a, 902b by voltage source 905, an excitation spectrum occurs in diaphragm 211. Voltage source 905 may typically correspond to a pulsed voltage source available on the market. Such a voltage source may have an upper limit on the frequency at which voltage pulses may be provided. As can be seen from the equation given in the previous paragraph, this corresponds to a lower limit on the mass (and therefore, size) of particles that can be removed by causing mechanical oscillations of diaphragm 211.

[0337] Increasing the frequency of the oscillations induced in the diaphragm 211 would enable the removal of smaller particles 210 from the diaphragm 211, but this may not be possible due to the above-mentioned upper frequency limit of the voltage source 905. However, by reducing the tension of the diaphragm 211 (e.g., by using a laser beam 916 as described above to locally heat the diaphragm 211 near the particle 210), the fundamental frequency of the oscillation of the particle 210 on the portion of the diaphragm with reduced tension is also reduced. Therefore, the upper frequency limit of the voltage source 905 will correspond to the fundamental frequency of particles 210 with lower mass than would be the case if the tension of the diaphragm 211 was not reduced. Therefore, advantageously, reducing the pre-tension of the diaphragm 211 (e.g., by using a laser beam 916 as described above) can remove smaller particles 210 from the diaphragm 211 than would be the case if the tension of the diaphragm 211 was not reduced.

[0338] Diaphragm cleaning apparatus 900 illustrates an embodiment of the present invention in which time-varying or pulsed electrostatic attraction is used to remove particles 210 from diaphragm 211 and laser beam 916 is used to heat at least a portion of diaphragm 211, thereby advantageously increasing the size range of particles 210 that can be removed from diaphragm 211.

[0339] Heating only a portion of the diaphragm 211 may result in a redistribution of tension within the diaphragm 211. This may limit the effectiveness of reducing tension in the irradiated portion of the diaphragm 211 using the laser 914. It may be beneficial to configure the beam delivery system 918 so that the laser spot area covers the entirety of the diaphragm 211 within the frame 212, as this may limit any redistribution of tension within the diaphragm 211. The laser spot area may cover substantially all of the surface of the diaphragm 211 within the frame 212. The laser spot area may cover approximately 50% of the surface of the diaphragm 211 within the frame 212. The laser spot area may cover less than 50% of the surface of the diaphragm 211 within the frame 212. The laser spot area may cover approximately 10% of the surface of the diaphragm 211 within the frame 212. The laser spot area may cover less than 10% of the surface of the diaphragm 211 within the frame 212.

[0340] In some embodiments, the laser source 915 can be configured to provide a laser beam 916 having a power between 1 W and 100 W. As discussed above, the laser spot area can cover a portion of the surface of the diaphragm 211 (such as Fig. 9 In some embodiments, the optical device 920 of the beam delivery system 918 can shape the laser spot area so that the power density of the laser beam 916 on the diaphragm 211 is within 1 W cm -2 and 10W cm -2 In some embodiments, the temperature of a portion of the diaphragm 211 may be increased by between 10° C. and 1000° C. In some embodiments, the temperature of a portion of the diaphragm 211 may be increased by between 200° C. and 500° C. In some embodiments, the tension of the irradiated portion of the diaphragm 211 may be reduced by between 10 and 100 times.

[0341] In some embodiments, the lateral spacing 922 between the particle 210 and the nearest electrode 902b can be less than 10 mm. In some embodiments, the lateral spacing 922 between the particle 210 and the electrode 902b can be less than 1 mm. In some embodiments, the spacing 924 between the diaphragm 211 and the electrode 902b can be less than 1 mm. In some embodiments, the spacing 924 between the diaphragm 211 and the electrode 902b can be less than 0.1 mm.

[0342] It has been described above how the use of laser beam 916 to heat at least a portion of membrane 211 advantageously increases the size range of particles 210 that can be removed from membrane 211. In use, it may be desirable to remove particles 210 having a range of sizes from membrane 211.

[0343] In the membrane cleaning apparatus 900, removal of particles 210 having a range of sizes from the membrane 211 can be achieved by varying (sweeping) the tension of the irradiated portion of the membrane 211 (e.g., by varying the power of the laser beam 916), while the voltage source 905 and the electrodes 902a, 902b induce oscillations in the membrane. During the sweep of the tension, the frequency of the oscillations induced in the membrane 211 can be fixed.

[0344] In the diaphragm cleaning apparatus 900, removal of particles 210 having a range of sizes from the diaphragm 211 can be achieved by varying (sweeping) the frequency of oscillations induced in the diaphragm 211 (e.g., by varying the frequency of individual pulses providing the pulse voltage generated by the voltage source 905), while the laser beam 916 is used to provide a relatively low tension to the irradiated portion of the diaphragm 211. During the sweep of the frequency, the power of the laser beam 916 can be fixed.

[0345] In use, the diaphragm assembly 208 can be moved relative to the electrodes 902a, 902b so that different portions of the diaphragm 211 can be cleaned using the diaphragm cleaning apparatus 900. The two electrodes 902a, 902b can be moved relative to the support 904 so that the electrodes can be scanned across the surface of the diaphragm 211 when the diaphragm 211 is supported by the support 904. In use, the diaphragm assembly 208 can be moved relative to the laser spot region so that different portions of the diaphragm 211 can be irradiated using the laser beam 916 of the diaphragm cleaning apparatus 900. In use, the beam delivery system 918 can be configured to control the position of the laser spot region on the surface of the diaphragm 211.

[0346] Advantageously, in any embodiment of the diaphragm cleaning apparatus configured to heat at least a portion of the diaphragm 211, the resonant frequency of a fixed mass of particles 210 disposed on the diaphragm 211 is reduced, thereby enabling smaller particles 210 to be removed from the diaphragm 211 than would be the case if the diaphragm 211 were not heated.

[0347] It will be appreciated that several features have been introduced in the membrane cleaning apparatus 900, but these features need not be used together in a single embodiment. It will also be appreciated that the features of the membrane cleaning apparatus 900 can be used in combination with features of other embodiments (eg, features of the membrane cleaning apparatus 200).

[0348] A method for heating the diaphragm 211 while inducing mechanical oscillations in the diaphragm 211 (as described above with reference to Fig. 9 described) can be used with Fig. 9 In the different equipment configurations shown. For example, the membrane cleaning equipment may include Fig. 9 The laser 914 and beam delivery system 918 (for heating the diaphragm 211) may also include Figure 2 A combined excitation electrode / collector 202 (for removing particles 210 from the diaphragm 211 ) is provided.

[0349] Alternative components for heating the diaphragm 211 may be used. For example, the diaphragm cleaning device may include an induction heating device (for heating the diaphragm 211), and a combined excitation electrode / collector 202, electrodes 902a, 902b, or a completely different electrode arrangement that is configured to induce mechanical oscillations in the diaphragm 211. In some embodiments, the antenna of the induction heating device may be sized so that the antenna is less than or approximately equal to the size of the frame 212. In some embodiments, the antenna and diaphragm 211 may be separated by less than 10 cm. In some embodiments, the antenna and diaphragm 211 may be separated by less than 1 cm.

[0350] Now refer to Fig.10aA diaphragm cleaning device 1000 according to a sixth embodiment of the present invention is described, which shows a cross section through the diaphragm cleaning device 1000 .

[0351] Fig.10a The illustrated diaphragm cleaning device 1000 shares several features in common with other diaphragm cleaning devices described herein. Any features of the diaphragm cleaning device 1000 illustrated in FIG. 10 that generally correspond to and may be identical to features of other diaphragm cleaning devices described herein share common reference numerals therewith.

[0352] The following will only discuss in detail Fig.10a The differences between the diaphragm cleaning apparatus 1000 shown and the other diaphragm cleaning apparatuses described herein.

[0353] The diaphragm cleaning apparatus 1000 comprises: a vacuum chamber 1001; wires 1006a, 1006b, 1006c; vacuum feedthroughs 1007a, 1007b, 1007c; a conductive support 1004; two electrodes 1002a, 1002b; and a voltage source 1005. In use, the diaphragm assembly 208 (comprising the diaphragm 211 and the generally rectangular frame 212) is disposed on the conductive support 1004.

[0354] The two electrodes 1002a, 1002b are arranged on opposite sides of the plane of the diaphragm 211. The electrodes 1002a, 1002b are arranged close to the opposite surface of the diaphragm 211. The two electrodes 1002a, 1002b do not extend adjacent to the entire diaphragm 211. The two electrodes 1002a, 1002b may include a tapered portion having a smaller cross-sectional area at its end adjacent to the diaphragm 211 and facing the diaphragm 211. Each of the two electrodes 1002a, 1002b is arranged close to a portion of the diaphragm 211 (the portion may, for example, correspond to a portion overlapping with the cross section of the tapered portion of the electrodes 1002a, 1002b). The portion of the diaphragm 211 adjacent to each electrode 1002a, 1002b depends on the position of each electrode 1002a, 1002b in a plane parallel to the plane of the diaphragm 211. In this embodiment, the position of electrode 1002a in a plane parallel to the plane of diaphragm 211 is not aligned with the position of electrode 1002b. That is, although on the opposite side of diaphragm 211, electrodes 1002a, 1002b can be described as offset from each other in the lateral direction. Electrodes 1002a, 1002b can be positioned so that the maximum distance between electrodes 1002a, 1002b in a plane parallel to the plane of diaphragm 211 is 1cm. This distance can be referred to as lateral offset. Electrodes 1002a, 1002b can be positioned so that the maximum distance between electrodes 1002a, 1002b in a plane parallel to the plane of diaphragm 211 is 1mm. As described above, in a cross section parallel to the plane of diaphragm 211, the area (e.g., the area of ​​the tapered portion) of each electrode 1002a, 1002b closest to diaphragm 211 is less than the area of ​​diaphragm 211. In a cross section parallel to the plane of the diaphragm 211, the area of ​​each electrode 1002a, 1002b closest to the diaphragm 211 may be less than or equal to 1 cm 2 , for example less than or equal to 10mm 2 The largest dimension of each electrode 1002a, 1002b is generally aligned perpendicular to the plane of the diaphragm 211.

[0355] The electrodes 1002a, 1002b are connected to a common terminal of a voltage source 1005 via wires 1006a, 1006b and vacuum feedthroughs 1007a, 1007b. The conductive support 1004 is connected to an opposite terminal of the voltage source 1005 via wires 1006c and vacuum feedthroughs 1007c. In a variation of the current embodiment, the opposite terminal of the voltage source 1005 may alternatively be directly connected to the diaphragm assembly 208. In such a variation, it is possible that the conductive support 1004 is replaced by a non-conductive diaphragm support 100.

[0356] Voltage source 1005 can be generally Figure 6 1002a, 1002b can be maintained at substantially equal voltages, and diaphragm 211 can be maintained at a voltage whose polarity is opposite to the polarity of the voltage at which electrodes 1002a, 1002b are maintained. The magnitude of the electric field can be substantially equal on both sides of diaphragm 211. The voltage applied across the terminals of voltage source 1005 can be configured to achieve this result. In particular, the voltage applied across the terminals of voltage source 1005 can be configured to make the electric field near the two opposing surfaces of diaphragm 211 have a magnitude of at least 100kV / m. The voltage applied across the terminals of voltage source 1005 can be configured to make the electric field near the two opposing surfaces of diaphragm have a magnitude of at least 1MV / m. At least a portion of one or more of electrodes 1002a, 1002b can be provided with an insulating coating.

[0357] Diaphragm cleaning equipment 1000( Fig.10a ) can be used with the diaphragm cleaning device 600 ( Figure 6 ) The particles 210 can be removed from the membrane 211 in substantially the same manner as described above in detail. That is, the electrodes 1002a, 1002b can generate an electric field that attracts the particles 210 away from the membrane 211. Fig.10a The arrangement of electrodes 1002a, 1002b in Figure 6 The arrangement of electrodes 604, 606 in is different. Fig.10a 1002a, 1002b in the embodiment can allow local deformation of the diaphragm 211 in space. Advantageously, Fig.10a Such an arrangement of electrodes 1002a, 1002b in may be required to operate Figure 6 The relatively large electrodes 604, 100b of the diaphragm 211 require less energy to operate (in order to achieve the same magnitude of electric field near two opposing surfaces of the diaphragm 211). This can be described as improving the efficiency of the diaphragm cleaning device 1000.

[0358] The diaphragm cleaning apparatus 1000 may include a mechanism for controlling the position of the diaphragm assembly 208 relative to the electrodes 1002a, 1002b. In use, the diaphragm assembly 208 may be moved relative to the electrodes 1002a, 1002b so that different portions of the diaphragm 211 may be cleaned using the diaphragm cleaning apparatus 1000. Additionally or alternatively, the two electrodes 1002a, 1002b may be moved relative to the conductive support 1004 so that when the diaphragm 211 is supported by the conductive support 1004, the electrodes may scan across the surface of the diaphragm 211.

[0359] It will be appreciated that when electrodes 1002a, 1002b are as described above with reference to Fig.10a When used as described, the electrodes 1002a, 1002b may be described as collecting electrodes.

[0360] Alternatively, the voltage source 1005 may be substantially the same as Figure 2 The voltage source 1005 may be arranged to apply a time-varying voltage (e.g., a time-varying voltage comprising a plurality of pulses). In use, the time-varying voltage may be applied across the electrodes 1002a, 1002b and the conductive support 1004. The time-varying voltage may be applied such that the electrodes 1002a, 1002b are maintained at voltages of substantially equal magnitude and the same polarity, and the diaphragm 211 may be maintained at a voltage of opposite polarity to the voltage at which the electrodes 1002a, 1002b are maintained.

[0361] Diaphragm cleaning equipment 1000( Fig.10a ) can be used with the diaphragm cleaning device 200 ( Figure 2 ) removes particles 210 from the diaphragm 211 in substantially the same manner as described above in detail. That is, oscillations are induced in the diaphragm 211 using the diaphragm cleaning device 1000 in a manner similar to the manner in which oscillations are induced in the diaphragm 211 using the diaphragm cleaning device 200. In particular, both the diaphragm cleaning device 1000 and the diaphragm cleaning device 200 use a time-varying (e.g., pulsed) electrostatic force between one or more electrodes and the diaphragm 211 to induce oscillations in the diaphragm. In the diaphragm cleaning device 1000, the time-varying or pulsed electrostatic force between the diaphragm 211 and each electrode 1002a, 1002b occurs due to the application of a time-varying or pulsed voltage from the voltage source 1005. In contrast to the diaphragm cleaning device 200, due to the arrangement of the electrodes 1002a, 1002b and the voltage applied thereto, adjacent portions of the diaphragm 211 are attracted to the electrodes 1002a, 1002b in opposite directions. That is, a portion of the diaphragm 211 close to the electrode 1002a will be attracted to the electrode 1002a, and a portion of the diaphragm 211 close to the electrode 1002b will be attracted to the electrode 1002b.

[0362] The time-varying voltage used to induce oscillations in the membrane 211 may include a plurality of pulses spaced apart in time. The pulses of the time-varying voltage across the electrode 1002a occur in phase with the pulses of the time-varying voltage across the electrode 1002b. Thus, the attraction of a portion of the membrane 211 to the electrode 1002a occurs in phase with the attraction of an adjacent portion of the membrane 211 to the electrode 1002b. Similar to Figure 2The pulse voltage provided by the voltage source 205 of the membrane cleaning device 200 is shown, and the time characteristics of the voltage supplied by the voltage source 1005 can be configured to induce a desired frequency range (ie, a desired excitation spectrum) of oscillation of the membrane 211. Figure 2 , Figure 3 and Figure 4 As described in detail, the pulse voltage provided by the voltage source 1005 can be configured to produce an excitation spectrum that is tailored or adapted to remove particles 210 having a size within a predetermined range.

[0363] Now refer to Fig.10b A diaphragm cleaning device 1020 according to a seventh embodiment of the present invention is described, which shows a cross section through the diaphragm cleaning device 1020 .

[0364] Fig.10b The diaphragm cleaning device 1020 shown shares the Fig.10a The membrane cleaning apparatus 1000 described herein has several common features. Fig.10b The diaphragm cleaning device 1020 and Fig.10a The differences between the diaphragm cleaning device 1000 shown.

[0365] The diaphragm cleaning apparatus 1020 includes: a vacuum chamber 1021; wires 1026a, 1026b; vacuum feedthroughs 1027a, 1027b; a support 1023; two electrodes 1022a, 1022b; and a voltage source 1025. In use, the diaphragm assembly 208 (including the diaphragm 211 and the generally rectangular frame 212) is disposed on the conductive support 1023. Similar to the arrangement of the electrodes 1002a, 1002b in the vacuum chamber 1001 of the diaphragm cleaning apparatus 1000 ( Fig.10a ), electrodes 1022a and 1022b are arranged in a vacuum chamber 1021.

[0366] Diaphragm cleaning equipment 1000( Fig.10a ) and diaphragm cleaning equipment 1020( Fig.10b ) is how the voltage source is connected to the electrodes 1022a, 1022b and the diaphragm assembly 208. Fig.10a In the diaphragm cleaning device 1000, both electrodes 1002a, 1002b are connected to the same terminal of the voltage source 1005 (and are therefore maintained at the same voltage), and the diaphragm 211 is connected (directly or indirectly) to the opposite terminal of the voltage source 1005. Fig.10bIn the diaphragm cleaning apparatus 1020, the electrode 1022a is connected to a first terminal of a voltage source 1025 via a wire 1026a and a vacuum feedthrough 1027a, and the electrode 1022b is connected to an opposite terminal of the voltage source 1025 via a wire 1026b and a vacuum feedthrough 1027b. The diaphragm assembly 208 may not be electrically connected to an assembly having a defined voltage, and the diaphragm assembly 208 (and the diaphragm 211) may therefore be described as being "floating".

[0367] In addition to how to connect the voltage source to the diaphragm cleaning device 1000 ( Fig.10a ) and diaphragm cleaning equipment 1020( Fig.10b ), the two membrane cleaning apparatuses 1000, 1020 may be similar in other respects and may operate in a similar manner, except for the electrodes and the membrane assembly 208 in FIG.

[0368] Diaphragm cleaning equipment 1020( Fig.10b ) can be used with the reference above Fig.10a The method of removing particles 210 from the diaphragm 211 is substantially the same as the pulse electrostatic cleaning method described in detail. In contrast to the diaphragm cleaning device 1000, the diaphragm 211 is not maintained at a voltage opposite to the voltage at which the electrodes 1022a, 1022b are maintained. Instead, the electrodes 1022a, 1022b are maintained at voltages that are substantially equal in magnitude and opposite in polarity, and the diaphragm assembly 208 (and the diaphragm 211) is floating. However, due to the arrangement of the electrodes 1022a, 1022b (particularly due to the lateral offset between the two electrodes 1022a, 1022b) and the voltage applied thereto, adjacent portions of the diaphragm 211 are still attracted to the electrodes 1022a, 1022b in opposite directions. That is, a portion of the diaphragm 211 close to the electrode 1022a will be attracted to the electrode 1022a, and a portion of the diaphragm 211 close to the electrode 1002b will be attracted to the electrode 1002b.

[0369] The time-varying voltage used to induce oscillations in the diaphragm 211 may include a plurality of pulses spaced apart in time. The pulses of the time-varying voltage across the electrode 1022a occur in phase with the pulses of the time-varying voltage across the electrode 1022b. Thus, the attraction of a portion of the diaphragm 211 to the electrode 1022a occurs in phase with the attraction of an adjacent portion of the diaphragm 211 to the electrode 1022b. Figure 2 The pulse voltage provided by the voltage source 205 of the membrane cleaning device 200 shown, the time characteristics of the voltage provided by the voltage source 1005 can be configured to cause the desired frequency range (ie, the desired excitation spectrum) of the oscillation of the membrane 211. Figure 2 , Figure 3 and Figure 4As described in detail, the pulse voltage provided by the voltage source 1025 can be configured to produce an excitation spectrum that is tailored or adapted to remove particles 210 having a size within a predetermined range.

[0370] The diaphragm cleaning device 1020 may include a mechanism for controlling the position of the diaphragm assembly 208 relative to the electrodes 1022a, 1022b. In use, the diaphragm assembly 208 may be moved relative to the electrodes 1022a, 1022b so that different portions of the diaphragm 211 may be cleaned using the diaphragm cleaning device 1020. Additionally or alternatively, the two electrodes 1022a, 1022b may be moved relative to the support 1023 so that when the diaphragm 211 is supported by the support 1023, the electrodes may scan across the surface of the diaphragm 211.

[0371] Now refer to Fig.10c A diaphragm cleaning device 1040 according to an eighth embodiment of the present invention is described, which shows a cross section through the diaphragm cleaning device 1040.

[0372] Fig.10c The diaphragm cleaning device 1040 shown shares the Fig.10a The membrane cleaning apparatus 1000 described herein has several common features. Fig.10c The diaphragm cleaning device 1040 and Fig.10a The differences between the diaphragm cleaning device 1000 shown.

[0373] The diaphragm cleaning apparatus 1040 includes: a vacuum chamber 1041; wires 1046a, 1046b, 1046c; vacuum feedthroughs 1047a, 1047b, 1047c; a conductive support 1044; two electrodes 1042a, 1042b; and a voltage source 1045. In use, the diaphragm assembly 208 (including the diaphragm 211 and the generally rectangular frame 212) is disposed on the conductive support 1044. The electrodes 1042a, 1042b are arranged within the vacuum chamber 1041 so that they are disposed close to the opposite surface of the diaphragm 211. In a plane parallel to the plane of the diaphragm 211, the position of the electrode 1042a is generally aligned with the position of the electrode 1042b. That is, in this embodiment, there is substantially no lateral offset between the two electrodes 1042a, 1042b on opposite sides of the diaphragm 211.

[0374] Diaphragm cleaning equipment 1000( Fig.10a ) and diaphragm cleaning equipment 1040( Fig.10c ) is that, as will be discussed further below, Fig.10cThe diaphragm cleaning device 1040 applies a time-shifted voltage to two laterally aligned electrodes 1042a, 1042b. This is similar to applying substantially the same voltage (which may be a time-varying voltage) to two laterally offset electrodes 1002a, 1002b (such as Fig.10a In the embodiment of ) on the contrary.

[0375] Diaphragm cleaning equipment 1000( Fig.10a ) and diaphragm cleaning equipment 1040( Fig.10c ) is how the voltage source is connected to the electrodes and diaphragm assembly 208. In diaphragm cleaning apparatus 1000, both electrodes 1002a, 1002b are connected to the same terminal of voltage source 1005 and are therefore held at the same voltage, and diaphragm 211 is connected (directly or indirectly) to opposite terminals of voltage source 1005. However, in diaphragm cleaning apparatus 1040, electrode 1042b is connected to one terminal of voltage source 1045 via wire 1046b and vacuum feedthrough 1047b, and electrode 1042a is connected to the same terminal or opposite terminals of voltage source 1045 via wire 1046a and vacuum feedthrough 1047a. Fig.10c The fact that electrodes 1042a, 1042b can be connected to the same terminal of voltage source 1045 (and thus can be maintained at a voltage of the same polarity) or to opposite terminals of voltage source 1045 (and thus can be maintained at voltages of opposite polarities) is schematically illustrated by switch 1045s in FIG. It will be appreciated that switch 1045s is included merely to illustrate the concept, and in physical embodiments of the present invention, switch 1045s may or may not be included.

[0376] Conductive support 1044 is connected to ground via wire 1046c and vacuum feedthrough 1047c. In a variation of the current embodiment, alternatively, ground can be directly connected to diaphragm assembly 208. In this variation, conductive support 1044 can be used instead of non-conductive diaphragm support. In another variation of the current embodiment, diaphragm assembly 208 can be directly (e.g., via wire 1046c) or indirectly (e.g., via conductive support 1044) connected to a voltage close to ground. In any case, diaphragm cleaning device 1040 can be referred to as including a mechanism for maintaining diaphragm 211 at a voltage close to or equal to ground.

[0377] In addition to how to connect the voltage source to the diaphragm cleaning device 1000 ( Fig.10a ) and diaphragm cleaning equipment 1040( Fig.10c ), the two membrane cleaning apparatuses 1000, 1040 may be similar in other respects and may operate in a similar manner, except for the electrodes and the membrane assembly 208 in FIG.

[0378] Diaphragm cleaning equipment 1040( Fig.10c ) can be used with the reference above Fig.10a The method similar to the pulse electrostatic cleaning method described in detail removes particles 210 from the diaphragm 211. That is, a time-varying voltage can be applied to each electrode 1042a, 1042b to cause oscillation in the diaphragm 211. The time-varying voltage can include multiple pulses spaced apart in time. However, in contrast to the diaphragm cleaning device 1000, the diaphragm 211 is not maintained at a voltage opposite to the voltage at which the electrodes 1042a, 1042b are maintained. On the contrary, the electrodes 1042a, 1042b are maintained at a voltage substantially equal in magnitude (and of the same or opposite polarity), and the diaphragm assembly 208 (and the diaphragm 211) is maintained in an (electrical) grounding state. In addition, in a plane parallel to the plane of the diaphragm 211, the electrodes 1042a, 1042b are usually aligned. That is, there is no lateral offset between the two electrodes 1042a, 1042b.

[0379] When a voltage is applied to the electrode 1042a or the electrode 1042b, the portion of the diaphragm 211 close to the electrode 1042a, 1042b is attracted to the electrode. Since the electrodes 1042a, 1042b are generally co-aligned, if a voltage is applied to both electrodes 1042a, 1042b at the same time, the electrostatic attraction force applied to the diaphragm 211 by each electrode 1042a, 1042b can generally be balanced and the diaphragm 211 may not be deformed. Therefore, oscillations may not be induced in the diaphragm 211.

[0380] Advantageously, the pulse of the time-varying voltage applied to electrode 1042a is subject to a time delay 1049 (relative to the pulse of the time-varying voltage applied to electrode 1042b). That is, regardless of whether the polarity of the time-varying voltages applied to the two electrodes 1042a, 1042b is equal or opposite, the pulse of the time-varying voltage applied to electrode 1042a occurs substantially out of phase with the pulse of the time-varying voltage applied to electrode 1042b. Thus, attracting a portion of the diaphragm 211 proximate to electrode 1042a occurs substantially out of phase with attracting the same portion of the diaphragm 211 to electrode 1042b. Thus, in a single voltage "pulse" generated by voltage source 1045, the portion of the diaphragm 211 proximate to electrode 1042b is attracted to electrode 1042b, and then, subsequently (after time delay 1049) the same portion of the diaphragm 211 is attracted to electrode 1042a. It will be appreciated that including component 1049 in Fig.10cIn the example, the time delay between the voltage applied to the electrode 1042a and the voltage applied to the electrode 1042b is only for schematic illustration. In particular, the mechanism for controlling this time delay can form part of the voltage source 1045.

[0381] Similar to Figure 2 The pulse voltage provided by the voltage source 205 of the membrane cleaning device 200 shown, the time characteristics of the voltage supplied by the voltage source 1045 can be configured to induce a desired frequency range (ie, a desired excitation spectrum) of oscillation of the membrane 211. Figure 2 , Figure 3 and Figure 4 As described in detail, the pulse voltage provided by the voltage source 1045 can be configured to produce an excitation spectrum that is tailored or adapted to remove particles 210 having a size within a predetermined range.

[0382] The diaphragm cleaning device 1040 may include a mechanism for controlling the position of the diaphragm assembly 208 relative to the electrodes 1042a, 1042b. In use, the diaphragm assembly 208 may be moved relative to the electrodes 1042a, 1042b so that different portions of the diaphragm 211 may be cleaned using the diaphragm cleaning device 1040. Additionally or alternatively, the two electrodes 1042a, 1042b may be moved relative to the conductive support 1044 so that the electrodes may scan across the surface of the diaphragm 211 when the diaphragm 211 is supported by the conductive support 1044.

[0383] Now refer to Fig.10d A diaphragm cleaning device 1060 according to a ninth embodiment of the present invention is described, which shows a cross section through the diaphragm cleaning device 1060 .

[0384] Fig.10d The diaphragm cleaning device 1060 shown shares the Fig.10c The membrane cleaning apparatus 1040 described herein has several common features. Fig.10d The diaphragm cleaning device 1060 and Fig.10c The differences between the diaphragm cleaning device 1040 are shown.

[0385] The diaphragm cleaning apparatus 1060 comprises: a vacuum chamber 1061; wires 1066a, 1066b, 1066c, 1066d; vacuum feedthroughs 1067a, 1067b, 1067c, 1067d; a support 1063; two electrodes 1062a, 1062b; a voltage source 1065; and two auxiliary electrodes 1070a, 1070b. In use, the diaphragm assembly 208 (comprising the diaphragm 211 and the generally rectangular frame 212) is disposed on the support 1063. The electrodes 1062a, 1062b are arranged in the vacuum chamber 1061 in the same co-aligned configuration as the electrodes 1042a, 1042b are arranged in the vacuum chamber 1041.

[0386] Diaphragm cleaning equipment 1040( Fig.10c ) and diaphragm cleaning equipment 1060( Fig.10d ) is that, although both diaphragm cleaning devices 1040, 1060 include mechanisms for maintaining diaphragm 211 at a voltage close to or equal to ground, these mechanisms are different. In contrast to diaphragm cleaning device 1040, when diaphragm 211 is disposed on support 1063, diaphragm 211 is not physically connected (directly or indirectly) to ground or a low voltage. Also in contrast to diaphragm cleaning device 1040, diaphragm cleaning device 1060 includes two auxiliary electrodes 1070a, 1070b.

[0387] The auxiliary electrodes 1070a, 1070b are disposed proximate to opposing surfaces of the diaphragm 211. The auxiliary electrodes 1070a, 1070b may be substantially flat or planar and may extend adjacent to a majority of the area of ​​the diaphragm 211. The auxiliary electrodes 1070a, 1070b may be disposed substantially parallel to the plane of the diaphragm 211. The auxiliary electrodes 1070a, 1070b may each include a hole. The auxiliary electrode 1070a may be disposed such that the electrode 1062a protrudes through the hole of the auxiliary electrode 1070a. The auxiliary electrode 1070b may be disposed such that the electrode 1062b protrudes through the hole of the auxiliary electrode 1070b. Fig.10dIn the example embodiment of the diaphragm cleaning device 1060 shown in , each auxiliary electrode 1070a, 1070b is connected to ground via wires 1066c, 1066d and vacuum feedthroughs 1067c, 067d, respectively. In a variation of the current embodiment, the auxiliary electrodes 1070a, 1070b can be connected to a voltage close to ground. In another variation of the current embodiment, more than one auxiliary electrode can be provided near each of the two surfaces of the diaphragm 211. Therefore, the mechanism for maintaining the diaphragm 211 at a voltage close to or equal to ground can be described as including one or more auxiliary electrodes close to each side of the plane of the diaphragm 211, wherein the one or more auxiliary electrodes are maintained at a voltage close to or equal to ground.

[0388] The diaphragm 211 (when the diaphragm assembly 208 is provided in the diaphragm cleaning device 1060) can be described as floating (i.e., it is not physically electrically connected to any component having a predefined voltage). Capacitive coupling may exist between the auxiliary electrodes 1070a, 1070b and the diaphragm 211. The auxiliary electrodes 1070a, 1070b can maintain the diaphragm 211 at a voltage close to or equal to ground via this capacitive coupling. In particular, the auxiliary electrodes 1070a, 1070b, the electrodes 1062a, 1062b, and the voltage source 1065 can be configured so that the magnitude of the electric field between the diaphragm 211 and the electrodes 1062a, 1062b is at least ten times greater than the magnitude of the electric field between the diaphragm 211 and the auxiliary electrodes 1070a, 1070b. Auxiliary electrodes 1070a, 1070b, electrodes 1062a, 1062b, and voltage source 1065 may be configured such that the magnitude of the electric field between diaphragm 211 and electrodes 1062a, 1062b is at least one hundred times greater than the magnitude of the electric field between diaphragm 211 and auxiliary electrodes 1070a, 1070b.

[0389] It will be appreciated that the magnitude of the electric field between the diaphragm 211 and the electrodes 1062a, 1062b and the magnitude of the electric field between the diaphragm 211 and the auxiliary electrodes 1070a, 1070b depend on the capacitive coupling between the diaphragm 211 and the electrodes 1062a, 1062b and the capacitive coupling between the diaphragm 211 and the auxiliary electrodes 1070a, 1070b, respectively. It will also be appreciated that the capacitive coupling between the diaphragm 211 and the electrodes 1062a, 1062b, the electrodes 1070a, 1070b will generally depend on the overlap area and spacing between the diaphragm 211 and the electrodes 1062a, 1062b, the electrodes 1070a, 1070b.

[0390] When cleaning diaphragm 211 in a diaphragm cleaning apparatus, it may be desirable to maintain the voltage of diaphragm 211 close to or equal to ground. However, due to, for example, the fragility of diaphragm 211 and / or relatively non-conductive layers accumulated on diaphragm assembly 208, it may be difficult to achieve good electrical contact between diaphragm 211 and another component. Furthermore, the process of electrically connecting diaphragm assembly 208 to another component may itself generate contaminant particles 210, which is disadvantageous. Advantageously, Fig.10d The mechanism described in for maintaining the diaphragm 211 at a voltage close to or equal to ground (auxiliary electrodes 1070a, 1070b) does not require any physical contact between the diaphragm assembly and any other components, thereby overcoming the above-mentioned problems.

[0391] The auxiliary electrodes 1070a, 1070b and the diaphragm 211 may be considered to form a capacitive voltage divider.

[0392] Auxiliary electrodes 1070a, 1070b provide additional advantages. In particular, the capacitive coupling between auxiliary electrodes 1070a, 1070b and diaphragm 211 can focus the electric field generated by electrodes 1062a, 1062b to a specific local area of ​​diaphragm 211. Advantageously, this can lead to more precise and more effective spatial positioning when using diaphragm cleaning device 1060 for diaphragm cleaning.

[0393] The voltage source 1065, the switch 1065s, the time delay 1069, the wires 1066a, 1066b, the vacuum feedthroughs 1067a, 1067b, and the electrodes 1062a, 1062b can be respectively connected to the membrane cleaning device 1040 ( Fig.10c )'s voltage source 1045, switch 1045s, time delay 1049, wires 1046a, 1046b, vacuum feedthroughs 1047a, 1047b, and electrodes 1042a, 1042b are of the same type and can perform the same functions as them.

[0394] Diaphragm cleaning equipment 1060( Fig.10d ) can be used with the reference above Fig.10c The membrane cleaning apparatus 1040 of the present invention can be used to remove particles 210 from the membrane 211 using a method similar to the pulse electrostatic cleaning method described in detail in the embodiment of the present invention. That is, a time-varying voltage can be applied across the electrodes 1062a, 1046b to induce oscillations in the membrane 211.

[0395] When a voltage is applied to the electrode 1042a or the electrode 1042b, the portion of the diaphragm 211 close to the electrode 1042a, 1042b is attracted to the electrode. Since the electrodes 1042a, 1042b are generally co-aligned, if a voltage is applied to both electrodes 1042a, 1042b at the same time, the electrostatic attraction force applied to the diaphragm 211 by each electrode 1042a, 1042b can generally be balanced and the diaphragm 211 may not be deformed. Therefore, oscillation may not be induced in the diaphragm 211.

[0396] Regardless of whether the polarity of the time-varying voltages applied to the two electrodes 1062a, 1062b is equal or opposite, the pulses of the time-varying voltage applied to electrode 1062a occur substantially out of phase with the pulses of the time-varying voltage applied to electrode 1062b. Thus, attracting a portion of diaphragm 211 proximate electrode 1062a occurs substantially out of phase with attracting the same portion of diaphragm 211 to electrode 1062b.

[0397] Similar to Figure 2 The pulse voltage provided by the voltage source 205 of the membrane cleaning device 200 shown, the time characteristics of the voltage supplied by the voltage source 1065 can be configured to induce a desired frequency range (ie, a desired excitation spectrum) of oscillation of the membrane 211. Figure 2 , Figure 3 and Figure 4 As described in detail, the pulse voltage provided by the voltage source 1065 can be configured to produce an excitation spectrum that is tailored or adapted to remove particles 210 having a size within a predetermined range.

[0398] The diaphragm cleaning device 1060 may include a mechanism for controlling the position of the diaphragm assembly 208 relative to the electrodes 1062a, 1062b. In use, the diaphragm assembly 208 may be moved relative to the electrodes 1062a, 1062b so that different portions of the diaphragm 211 may be cleaned using the diaphragm cleaning device 1060. Additionally or alternatively, the two electrodes 1062a, 1062b may be moved relative to the support 1063 so that when the diaphragm 211 is supported by the support 1063, the electrodes may scan across the surface of the diaphragm 211.

[0399] According to the above reference Figures 10a to 10d In the described embodiments, the arrangement of electrodes connected to a voltage source can be described as an electric field generating mechanism operable to generate an electric field near two opposing surfaces of the diaphragm 211 when the diaphragm 211 is supported by the diaphragm support. The electric fields near the two opposing surfaces of the diaphragm 211 are generally in opposite directions.

[0400] According to the above reference Figures 10a to 10dIn the described embodiment, the magnitude of the electric field may be substantially equal on both sides of the diaphragm 211 .

[0401] According to the above reference Figures 10a to 10d In the described embodiments, the electric field may have a magnitude of at least 100 kV / m. The magnitude may be at least 1 MV / m.

[0402] According to the above reference Figures 10a to 10d In the described embodiments, the magnitude of the electrostatic pressure applied to the two opposing surfaces of the diaphragm 211 (averaged across multiple pulses spaced apart in time) can be similar but opposite in direction. In particular, there may be a percentage difference of up to 50% between the time-averaged magnitudes of the electrostatic pressure applied to the two opposing surfaces of the diaphragm 211. There may be a percentage difference of up to 10% between the time-averaged magnitudes of the electrostatic pressure applied to the two opposing surfaces of the diaphragm 211. The electrostatic pressure applied to a portion of the diaphragm 211 (averaged over time) can be substantially zero. The electrostatic pressure applied to a portion of the diaphragm 211 (averaged during a time period between 10 μs and 10 ms) can be substantially zero.

[0403] According to the above described embodiment of pulsed electrostatic cleaning using the membrane, each voltage pulse may be shorter than 10 μs. Each voltage pulse may be shorter than 1 μs. This may result in efficient induction of oscillations in the membrane 211. Advantageously, this may result in efficient removal of particles 210.

[0404] According to the above-mentioned embodiment of pulsed electrostatic cleaning using a diaphragm, the voltage pulse train can be shorter than 10ms. The voltage pulse train can be shorter than 1ms. The voltage pulse train can also be described as a pulse "train". The duty cycle of the voltage pulse train can be less than 50%. The duty cycle of the voltage pulse train can be less than 10%. By providing pulses in such a train, unwanted heating of the diaphragm 211 can be prevented. Advantageously, this can prevent the diaphragm 211 from rupturing. In some embodiments, the duty cycle of the voltage pulse train can be limited so as to avoid power dissipation at the diaphragm 211, for example, greater than 0.3W / cm on a time scale of approximately 0.1ms to 10ms. 2 Up to 30W / cm 2 Continuously applying pulses at a relatively high frequency will heat the diaphragm 211 and possibly cause damage (either directly or via loss of tension due to thermal expansion). Advantageously, using a pulse train (or burst) can allow mechanical oscillations in the diaphragm 211 to be excited without causing excessive heating of the diaphragm 211.

[0405] In some embodiments, the time-varying voltage may include a plurality of successive temporally spaced pulse trains, and the repetition frequency of pulses within such a train may vary within a range, such as being swept across the range.

[0406] As mentioned above Fig. 9 , Figures 10b to 10d As described, embodiments of the diaphragm cleaning apparatus may be configured to maintain the voltage of the diaphragm 211 at a voltage close to or equal to ground. Fig. 9 , Figures 10b to 10d As described, embodiments of the membrane cleaning apparatus may be configured to maintain a voltage across the membrane 211 between -100 V and +100 V. As described embodiments of the membrane cleaning apparatus may be configured to maintain a voltage across the membrane 211 between -10 V and +10 V.

[0407] According to the embodiments of the present invention described herein (e.g., Figures 10a to 10d Embodiments described), electrodes ( Fig.10d The electrodes may be positioned such that the maximum distance between the electrodes and the diaphragm 211 is 5 mm. The electrodes may be positioned such that the maximum distance between the electrodes and the diaphragm 211 is 0.5 mm.

[0408] According to the embodiments of the diaphragm cleaning apparatus described herein, the environment within the vacuum chamber can be maintained at a relatively low pressure. The pressure close to the diaphragm 211 can be maintained at a relatively low pressure. The pressure close to the diaphragm 211 can be maintained at less than 10 －3 mBar. The pressure close to the diaphragm 211 can be maintained below 10 －5 mBar.

[0409] Electrostatic pressure can define the effectiveness of diaphragm cleaning. That is, a higher electrostatic pressure applied to diaphragm 211 can correspond to a higher diaphragm cleaning effectiveness. Therefore, for a diaphragm cleaning device, it may be necessary to apply a relatively high electrostatic pressure to the diaphragm. However, the greater the force applied to diaphragm 211, the higher the risk of rupture of diaphragm 211. Therefore, it may be necessary to construct a diaphragm cleaning device that applies a relatively high pressure on diaphragm 211 while only applying a relatively low force on diaphragm 211. The inventors have recognized that this can be achieved by using an electrode having a relatively small size close to the diaphragm (such as the electrode described above with reference to FIG. 1 ). Figures 10a to 10d Another advantage of using such an electrode is that inducing oscillations in the diaphragm 211 using such an electrode can result in a relatively low amount of heating of the diaphragm 211 (compared to inducing oscillations in the diaphragm 211 using a large electrode). Advantageously, this can maximize the redistribution of tension in the diaphragm 211 during cleaning, which can maximize the cleaning efficacy of the diaphragm cleaning apparatus. In some embodiments (such as those described above with reference to Figures 10a to 10dIn the embodiment described above, the area of ​​the surface of each electrode (e.g., electrodes 1002a, 1002b; 1022a, 1022b; 1042a, 1042b; 1062a, 1062b) closest to the diaphragm 211 may be smaller than the area of ​​the diaphragm 211. The area of ​​the surface of each electrode (e.g., electrodes 1002a, 1002b; 1022a, 1022b; 1042a, 1042b; 1062a, 1062b) closest to the diaphragm 211 may be less than or equal to 1 cm 2 , for example less than or equal to 10mm 2 .

[0410] Refer to above Figures 10a to 10d In the depicted embodiments, the repetition rate of the pulsed voltage applied to the electrodes (eg, electrodes 1002a, 1002b; 1022a, 1022b; 1042a, 1042b; 1062a, 1062b) may be in the range of 30 kHz to 30 MHz.

[0411] Refer to above Figures 10a to 10d In the depicted embodiment, the electrodes 1002a, 1002b; 1022a, 1022b; 1042a, 1042b; 1062a, 1062b act as excitation electrodes. In some embodiments, these electrodes 1002a, 1002b; 1022a, 1022b; 1042a, 1042b; 1062a, 1062b may also act as collector electrodes.

[0412] It will be understood that any wiring shown in the figures is only for the purpose of illustrating the principles of the present invention and is by no means limiting. When constructing a diaphragm cleaning device according to the present invention, modifications may be made to the wiring shown while adhering to the principles of the present invention, and these modifications fall within the scope of the present invention defined by the claims.

[0413] It will be appreciated that the terms "particle size" and "particle mass" may be used interchangeably above. A particle of greater mass generally corresponds to a larger particle, and a distinction between these terms is generally not intended.

[0414] It will be appreciated that in any of the above-described diaphragm cleaning apparatuses 200, 500, 600, 800, 820, 850, 900, 1000, 1020, 1040, 1060, the diaphragm assembly 208 may be a diaphragm for use in an EUV lithography apparatus. In particular, the diaphragm assembly 208 may include Figure 1 A diaphragm 15 is shown (which comprises a thin membrane 16 mounted on a frame 17).

[0415] It will be appreciated that in any of the above-described diaphragm cleaning devices 200, 500, 600, 800, 820, 850, 900, 1000, 1020, 1040, 1060, the diaphragm 211 of the diaphragm assembly 208 may optionally be provided with a high conductivity coating 209. The high conductivity coating 209 may, for example, include a metal or conductive ceramic coating. The high conductivity coating 209 may be applied on at least one side of the diaphragm 211. It will be appreciated that the high conductivity coating 209 may be applied to either side of the diaphragm 211. It will also be appreciated that in some embodiments, the diaphragm 211 may not have such a high conductivity coating 209. For example, the diaphragm 211 itself may be a sufficiently good conductor (e.g., the diaphragm 211 may be formed of a material having a non-zero conductivity, such as doped polysilicon).

[0416] Although in this context specific reference may be made to the use of lithographic equipment in the manufacture of ICs, it should be understood that the lithographic equipment 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 (FCDs), thin film magnetic heads, etc.

[0417] Although embodiments of the present invention may be specifically mentioned herein in the context of lithographic equipment, embodiments of the present invention may be used in other devices. Embodiments of the present invention may form part of a mask inspection device, a metrology device, or any device for measuring or processing an object such as a wafer (or other substrate) or a mask (or other pattern forming device). These devices may generally be referred to as lithographic tools. Such lithographic tools may use vacuum conditions or ambient (non-vacuum) conditions.

[0418] Although specific embodiments of the present invention have been described above, it will be appreciated that the present invention may be practiced in a manner other than that described. The above description is intended to be illustrative rather than restrictive. Therefore, it will be apparent to those skilled in the art that modifications may be made to the described invention without departing from the scope of the aspects set forth below.

[0419] 1. A membrane cleaning device for removing particles from a membrane, the device comprising:

[0420] a diaphragm support member for supporting the diaphragm; and

[0421] An electric field generating mechanism is used to generate an electric field near the diaphragm when the diaphragm is supported by the diaphragm support.

[0422] 2. The apparatus according to aspect 1, wherein the electric field generating mechanism comprises:

[0423] one or more collectors; and

[0424] Means for applying a voltage across a diaphragm supported by the diaphragm support and one or each of the one or more current collectors.

[0425] 3. Apparatus according to aspect 1 or 2, comprising means for inducing mechanical oscillations in the diaphragm when the diaphragm is supported by the diaphragm support.

[0426] 4. Apparatus according to aspect 3, wherein the means for inducing mechanical oscillations in the diaphragm when the diaphragm is supported by the diaphragm support comprises:

[0427] an excitation electrode; and

[0428] Means for applying a time varying voltage across the actuation electrode and the diaphragm supported by the diaphragm support.

[0429] 5. Apparatus according to aspect 3, wherein the means for inducing mechanical oscillations in the diaphragm when the diaphragm is supported by the diaphragm support comprises:

[0430] two electrodes positionable proximate to a surface of the diaphragm when the diaphragm is supported by the diaphragm support; and

[0431] A mechanism for applying a time varying voltage across the two electrodes.

[0432] 6. The apparatus according to aspect 4 or aspect 5, wherein the time-varying voltage comprises a plurality of pulses spaced apart in time.

[0433] 7. An apparatus according to any one of clauses 4 to 6, wherein the time-varying voltage comprises a voltage waveform having a general shape and having one or more parameters that can be selected (and varied) to obtain a desired excitation spectrum.

[0434] 8. The apparatus according to any one of aspects 4 to 7, wherein the time-varying voltage comprises two pulse trains that are consecutively spaced apart in time, the two pulse trains being of opposite polarity.

[0435] 9. Apparatus according to any one of aspects 4 to 8, wherein the means for applying a time-varying voltage is operable to generate a time-varying electric field having a magnitude of at least 10 kV / m in the vicinity of the diaphragm.

[0436] 10. The apparatus of any one of clauses 4 to 9, wherein the time-varying voltage has a duty cycle of less than 10%.

[0437] 11. Apparatus according to aspect 3, wherein the means for inducing mechanical oscillations in the diaphragm when the diaphragm is supported by the diaphragm support comprises:

[0438] A radiation source is operable to generate a pulsed radiation beam incident on at least a portion of the diaphragm supported by the diaphragm support.

[0439] 12. Apparatus according to any one of aspects 3 to 11, wherein the means for inducing mechanical oscillations is operable to induce oscillations in only a localised portion of the diaphragm.

[0440] 13. Apparatus according to any one of aspects 3 to 12, wherein the means for inducing mechanical oscillations is operable to induce oscillations over a range of frequencies.

[0441] 14. Apparatus according to any one of aspects 3 to 13, wherein the means for inducing mechanical oscillations is operable to induce oscillations between 30 kHz and 30 MHz.

[0442] 15. Apparatus according to any one of aspects 3 to 14, wherein the means for inducing mechanical oscillations is operable to remove particles having a size of between 0.5 μm and 5 μm from the diaphragm.

[0443] 16. Apparatus according to any preceding aspect, further comprising means for controlling the temperature of at least a portion of the membrane.

[0444] 17. The apparatus of aspect 16, wherein the mechanism for controlling the temperature of at least a portion of the diaphragm comprises a radiation source operable to provide radiation to the diaphragm.

[0445] 18. The apparatus of aspect 16, wherein the mechanism for controlling the temperature of at least a portion of the diaphragm comprises an induction heater operable to heat the diaphragm.

[0446] 19. An apparatus according to aspect 1 or 2, wherein the electric field generating mechanism is operable to generate an electric field near two opposing surfaces of the diaphragm when the diaphragm is supported by the diaphragm support, the electric fields near the two opposing surfaces of the diaphragm being in opposite directions.

[0447] 20. The apparatus of clause 19, wherein the electric field is formed by two collecting electrodes disposed on opposite sides of the plane of the diaphragm.

[0448] 21. The apparatus of aspect 19 or aspect 20, wherein the magnitude of the electric field is substantially equal on both sides of the diaphragm.

[0449] 22. The apparatus of any one of aspects 19 to 21, wherein the electric field has a magnitude of at least 100 kV / m near two opposing surfaces of the diaphragm.

[0450] 23. Apparatus according to any of aspects 19 to 22 as appended to aspect 2, wherein at least a portion of one or more current collectors is provided with an insulating coating.

[0451] 24. The apparatus of aspects 1, 2 or 19 to 23, further comprising a plasma generating mechanism.

[0452] 25. Apparatus according to aspect 24 when directly or indirectly dependent on aspect 2, wherein the plasma generating mechanism is operable to generate plasma between a diaphragm supported by the diaphragm support and the one or each of the one or more collecting electrodes.

[0453] 26. An apparatus according to aspect 25, wherein the mechanism for applying a voltage across the diaphragm supported by the diaphragm support and the one or each of the one or more collectors is arranged to apply a pulse voltage across the diaphragm supported by the diaphragm support and the one or each of the one or more collectors.

[0454] 27. The apparatus of clause 26, wherein the pulse voltage has a duty cycle of 1% or less.

[0455] 28. Apparatus according to aspect 26 or aspect 27, wherein the pulse voltage has a frequency between 1 Hz and 10 kHz.

[0456] 29. The apparatus according to any one of aspects 26 to 28, wherein the pulse duration of the pulse voltage is less than 1 ms.

[0457] 30. The apparatus of any one of aspects 26 to 29, wherein the magnitude of the pulse voltage is at least 100V.

[0458] 31. An apparatus according to any one of aspects 26 to 30, wherein each pulse of the pulsed voltage comprises a first portion having a first polarity and a second portion having an opposite second polarity.

[0459] 32. Apparatus according to any one of aspects 26 to 31, wherein the plasma generating mechanism is arranged such that the plasma is switched on between subsequent pulses of the pulsed voltage and is switched off during a pulse of the pulsed voltage.

[0460] 33. Apparatus according to any preceding aspect, further comprising a chamber and a pump device operable to control the pressure inside the chamber, and wherein the diaphragm support is disposed within the chamber.

[0461] 34. A method for removing particles from a membrane, the method comprising:

[0462] inducing mechanical oscillations in the diaphragm; and

[0463] An electric field is generated near the diaphragm using a collector electrode so as to exert an electrostatic force between particles on the diaphragm and the collector electrode.

[0464] 35. The method of clause 34, wherein inducing mechanical oscillations in the diaphragm comprises applying a time-varying voltage across the supported diaphragm and an actuation electrode.

[0465] 36. The method of clause 34, wherein inducing mechanical oscillations in the diaphragm comprises applying a time-varying voltage across two electrodes positioned proximate to a surface of the diaphragm.

[0466] 37. A method according to aspect 35 or aspect 36, wherein the time-varying voltage has a duty cycle of less than 10%.

[0467] 38. The method of clause 34, wherein inducing mechanical oscillations in the diaphragm comprises irradiating at least a portion of the diaphragm with a pulsed radiation beam.

[0468] 39. A method according to any one of aspects 34 to 38, wherein the induced mechanical oscillations comprise oscillations within a range of frequencies.

[0469] 40. A method according to any one of aspects 34 to 39, wherein the induced mechanical oscillations comprise oscillations between 30 kHz and 30 MHz.

[0470] 41. The method of any one of aspects 34 to 39, wherein the induced mechanical oscillations are suitable for removing particles having a size between 0.5 μm and 5 μm from the membrane.

[0471] 42. The method of any one of aspects 34 to 41, further comprising controlling the temperature of at least a portion of the membrane.

[0472] 43. The method of aspect 42, further comprising varying the temperature of at least a portion of the diaphragm over time.

[0473] 44. The method of aspect 34 or aspect 43, wherein controlling the temperature of at least a portion of the membrane is achieved by irradiating the at least a portion with radiation.

[0474] 45. A method according to any one of aspects 34 to 44, wherein the method uses an apparatus according to any one of aspects 1 to 18.

[0475] 46. ​​A method for removing particles from a membrane, the method comprising:

[0476] An electric field is generated near two opposing surfaces of the diaphragm, and the electric fields near the two opposing surfaces of the diaphragm are in opposite directions.

[0477] 47. A method according to aspect 46, wherein the method uses an apparatus according to any one of aspects 19 to 33.

[0478] 48. A method for removing particles from a membrane, the method comprising:

[0479] providing a plasma adjacent to at least one surface of the membrane to charge the particles; and

[0480] An electric field is generated near at least one surface of the membrane to force the charged particles away from the membrane.

[0481] 49. A method according to aspect 48, wherein the electric field is generated using one or more electrodes and applying a bias voltage to the one or more electrodes.

[0482] 50. The method of clause 49, wherein the bias voltage is a pulsed bias voltage.

[0483] 51. The method of clause 50, wherein each pulse of the pulsed voltage comprises a first portion having a first polarity and a second portion having an opposite second polarity.

[0484] 52. The apparatus of aspect 50 or aspect 51, wherein the plasma is provided adjacent to at least one surface of the diaphragm such that the plasma is switched on between subsequent pulses of the pulsed voltage and is switched off during a pulse of the pulsed voltage.

[0485] 53. A method according to any one of aspects 48 to 52, wherein the method uses an apparatus according to any one of aspects 24 to 33.

Claims

1. A membrane cleaning device for removing particles from a membrane, the device comprising: A diaphragm support member, used for supporting the diaphragm; an electric field generating mechanism for generating an electric field in the vicinity of the diaphragm when the diaphragm is supported by the diaphragm support, and A plasma generating mechanism is operable to generate plasma adjacent at least one surface of the diaphragm.

2. The device according to claim 1, wherein: The electric field generating mechanism comprises: one or more electrodes; and Means for applying a voltage across a diaphragm supported by the diaphragm support and one or each of the one or more electrodes.

3. The device according to claim 1, wherein: The electric field generating mechanism comprises: an excitation electrode; and Means for applying a time varying voltage across the actuation electrode and the diaphragm supported by the diaphragm support.

4. The device according to claim 3, wherein: The time-varying voltage includes a plurality of pulses spaced apart in time.

5. The device according to claim 3 or 4, wherein: The time-varying voltage includes a voltage waveform having a general shape and having one or more parameters that can be selected and / or varied to obtain a desired excitation spectrum.

6. The device according to claim 3 or 4, wherein: The time-varying voltage includes two pulse trains that are sequentially spaced apart in time, and the polarities of the two pulse trains are opposite.

7. The apparatus according to claim 1, further comprising: A radiation source is operable to generate a pulsed radiation beam incident on at least a portion of the diaphragm supported by the diaphragm support.

8. The device according to any one of claims 1 to 4, wherein: The electric field generating mechanism is operable to induce oscillations in only a localized portion of the diaphragm.

9. The device according to claim 1 or 2, wherein: The electric field generating mechanism is operable to generate an electric field proximate two opposing surfaces of the diaphragm when the diaphragm is supported by the diaphragm support, the electric fields proximate the two opposing surfaces of the diaphragm being in opposite directions.

10. The apparatus of claim 4, further comprising a chamber and a pump device operable to control a pressure within the interior of the chamber, and wherein the diaphragm support is disposed within the chamber.

11. The device according to claim 2, wherein: The plasma generating mechanism is operable to generate plasma between the diaphragm supported by the diaphragm support and the one or each of the one or more electrodes.

12. The device according to claim 2, wherein: The means for applying the voltage across the diaphragm supported by the diaphragm support and the one or each of the one or more electrodes is arranged to apply a pulsed voltage across the diaphragm supported by the diaphragm support and the one or each of the one or more electrodes.

13. The device according to claim 12, wherein: The pulse voltage has a frequency between 1 Hz and 10 kHz.

14. The apparatus according to claim 12 or 13, wherein: The pulse duration of the pulse voltage is less than 1 ms.

15. The apparatus according to claim 12 or 13, wherein: The magnitude of the pulse voltage is at least 100V.

16. The apparatus according to claim 12 or 13, wherein: Each pulse of the pulse voltage includes a first portion having a first polarity and a second portion having an opposite second polarity.

17. The apparatus according to claim 12 or 13, wherein: The plasma generating mechanism is arranged such that the plasma is switched on between subsequent pulses of the pulsed voltage and is switched off during a pulse of the pulsed voltage.

18. A membrane cleaning apparatus for removing particles from a membrane, the apparatus comprising: A diaphragm support member, used for supporting the diaphragm; An electric field generating mechanism for generating an electric field near the diaphragm when the diaphragm is supported by the diaphragm support member, and. Means for applying a time varying voltage across the actuation electrode and the diaphragm supported by the diaphragm support.

19. The apparatus according to claim 18, wherein: The time-varying voltage includes a plurality of pulses spaced apart in time.

20. The apparatus according to claim 18 or 19, wherein: The or each time-varying voltage comprises two pulse trains, spaced apart in time, in succession, the two pulse trains being of opposite polarity.

21. The apparatus according to claim 18 or 19, further comprising: A radiation source is operable to generate a pulsed radiation beam incident on at least a portion of the diaphragm supported by the diaphragm support.

22. The apparatus of claim 18 or 19, further comprising a mechanism for controlling the temperature of at least a portion of the membrane.

23. The apparatus of claim 22, wherein: The means for controlling the temperature of at least a portion of the diaphragm includes a radiation source operable to provide radiation to the diaphragm.

24. The apparatus of claim 22, wherein: The means for controlling the temperature of at least a portion of the diaphragm comprises an induction heater operable to heat the diaphragm.

25. The apparatus of claim 18 or 19, wherein: The electric field generating mechanism is operable to generate an electric field proximate two opposing surfaces of the diaphragm when the diaphragm is supported by the diaphragm support, the electric fields proximate the two opposing surfaces of the diaphragm being in opposite directions.

26. The apparatus of claim 25, wherein: The electric field is formed by two collecting electrodes arranged on opposite sides of the plane of the diaphragm.

27. The apparatus of claim 26, wherein: The position of one of the collectors is not aligned with the position of the other collector in a plane parallel to the plane of the diaphragm.

28. The apparatus of claim 26, wherein: Each of the collectors is held at a substantially equal voltage, and wherein the apparatus is configured to hold the diaphragm at a voltage having a polarity opposite to the polarity of the voltages at which the collectors are held.

29. The apparatus of claim 26, wherein: The magnitude of the electric field is substantially equal on both sides of the diaphragm.

30. The apparatus of claim 26, wherein: At least a portion of one or more current collectors is provided with an insulating coating.

31. The apparatus of claim 18 or 19, further comprising a plasma generating mechanism.

32. The apparatus of claim 31, wherein: The plasma generating mechanism is operable to generate plasma between a diaphragm supported by the diaphragm support and the one or each of the one or more collecting electrodes.

33. The apparatus of claim 32, wherein: The means for applying a voltage across the diaphragm supported by the diaphragm support and the one or each of the one or more current collectors is arranged to apply a pulsed voltage across the diaphragm supported by the diaphragm support and the one or each of the one or more current collectors.

34. The apparatus according to claim 33, wherein: Each pulse of the pulse voltage includes a first portion having a first polarity and a second portion having an opposite second polarity.

35. The apparatus of claim 33, wherein: The plasma generating mechanism is arranged such that the plasma is switched on between subsequent pulses of the pulsed voltage and is switched off during a pulse of the pulsed voltage.

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