Electrostatic clamp device

Abstract

The present disclosure relates to an electrostatic clamp device comprising: a clamp member comprising at least one electrode and a first conductive layer; a mounting member including a second conductive layer on which the clip member is mounted; and a dielectric layer sandwiched between the first conductive layer and the second conductive layer.

Description

Cross Reference to Related Applications

[0001] This application claims priority to EP application 23183982.0, filed on July 6, 2023, which is incorporated herein in its entirety by reference. TECHNICAL FIELD

[0002] The present invention relates to an electrostatic clamping arrangement. In particular, the electrostatic clamping arrangement can be configured to clamp an object such as a lithography substrate. The electrostatic clamping arrangement can form part of a lithography apparatus or a lithography tool. BACKGROUND

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

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

[0005] A substrate patterned by the lithography apparatus is held on a moveable substrate table. The substrate table includes a clamping arrangement configured to hold the substrate firmly on the substrate table while the substrate is being patterned, and then to allow the substrate to be removed from the substrate table once the patterning has been completed. In EUV systems, the clamping arrangement is an electrical (or electrostatic) clamp (conventional vacuum clamps cannot be used because EUV lithography apparatuses use a vacuum environment). A possible problem associated with existing clamping arrangements is that if it is desired to accelerate the substrate table more quickly, the clamping arrangement will need to exert a greater clamping force on the substrate to prevent the substrate from moving relative to the substrate table as the substrate table is moved. The need for the clamping arrangement to exert a greater clamping force on the substrate can conventionally require an increase in the size of the clamping arrangement and / or an increase in the power supplied to the clamping arrangement. Such an increased size and / or increased supply power can not be feasible in all applications.

[0006] It can be desirable to address the above problems in a manner which is not disclosed or suggested by the prior art. SUMMARY

[0007] According to a first aspect of the present application, there is provided an electrostatic chuck apparatus, the electrostatic chuck apparatus comprising: a chuck member, the chuck member comprising at least one electrode and a first electrically conductive layer; a mounting member, the mounting member comprising a second electrically conductive layer, the chuck member being mounted on the second electrically conductive layer; and a dielectric layer, the dielectric layer being sandwiched between the first electrically conductive layer and the second electrically conductive layer.

[0008] The dielectric layer can be fixed to the second electrically conductive layer.

[0009] The dielectric layer can be discontinuous.

[0010] The dielectric layer can be fixed to the first electrically conductive layer.

[0011] The chuck member can comprise a body and a plurality of burls, the body comprising the at least one electrode, the plurality of burls depending from the body.

[0012] The first electrically conductive layer can be positioned on the plurality of burls.

[0013] The second electrically conductive layer can be formed from at least one of chromium, tungsten, vanadium or titanium.

[0014] The first electrically conductive layer can be formed from at least one of chromium nitride, silicon carbide, siliconized silicon carbide, electrically conductive diamond, titanium nitride or doped chromium nitrate (e.g. CrNAl).

[0015] The dielectric layer can be formed from at least one of silicon oxide, diamond, boron nitride, zirconium oxide, aluminium nitride, silicon nitride or aluminium oxide.

[0016] The electrostatic chuck apparatus can further comprise a power supply.

[0017] The power supply can be electrically connected to the at least one electrode.

[0018] The first electrically conductive layer can be electrically connected to ground.

[0019] The second electrically conductive layer can be at a set voltage, a floating voltage or a bias voltage.

[0020] The electrostatic chuck apparatus can further comprise a switch, the switch being electrically connected to the second electrically conductive layer and ground (or other set voltage, e.g. a voltage set by the power supply).

[0021] The switch can have a first configuration in which the switch does not electrically connect the second electrically conductive layer to ground (or other set voltage), and a second configuration in which the switch electrically connects the second electrically conductive layer to ground (or other set voltage). Where the second configuration of the switch electrically connects the second electrically conductive layer to ground, the switch can have a third configuration in which the switch electrically connects the second electrically conductive layer to the other set voltage.

[0022] The at least one electrode can comprise a first electrode and a second electrode.

[0023] The power supply can be connected to the first electrode and the second electrode.

[0024] The power supply can be configured to place the first electrode at a first positive voltage and the second electrode at a second negative voltage, wherein the first voltage is not the same as the second voltage, such that there is an offset between the first voltage and the second voltage.

[0025] The second conductive layer can be electrically connected to the power supply, the power supply being configured to place the second conductive layer at a desired non-ground voltage.

[0026] The second conductive layer can be discontinuous, such that the second conductive layer comprises a first conductive portion and a second conductive portion that are electrically isolated from each other.

[0027] The second conductive portion can be connected to an electrical ground.

[0028] The first conductive portion can be at a bias voltage or a set voltage.

[0029] The first conductive portion can be electrically connected to the power supply to drive the first conductive portion, such that the first conductive portion is at the set voltage.

[0030] According to a second aspect of the application, there is provided a lithographic apparatus comprising an electrostatic clamp apparatus according to the preceding aspect.

[0031] The lithographic apparatus can further comprise an illumination system and a projection system.

[0032] According to a third aspect of the application, there is provided a method of operating an electrostatic clamp apparatus, the electrostatic clamp apparatus comprising: a clamp member comprising at least one electrode and a first conductive layer; a mounting member comprising a second conductive layer; a dielectric layer; and a power supply; the method comprising: mounting the clamp member to the mounting member such that the dielectric layer is clamped between the first conductive layer and the second conductive layer; electrically connecting the first conductive layer to ground; and electrically connecting the power supply to the at least one electrode, such that the power supply places the at least one electrode at a voltage and thereby generates an electrostatic force that pushes the clamp member towards the mounting member.

[0033] Features of different aspects of the application can be combined together where appropriate. BRIEF DESCRIPTION OF DRAWINGS

[0034] Embodiments of the application will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 A lithographic system comprising a lithographic apparatus and a substrate table according to embodiments of the application is schematically depicted; Figure 2 a schematic side view of a prior art clamp apparatus is shown; Figure 3 a schematic side view of a clamp apparatus according to an embodiment of the application is shown; Figure 4 a schematic side view of a clamp apparatus according to another embodiment of the application is shown; and Figure 5 a schematic top view of a conductive layer of a mounting member according to an embodiment of the application is shown. DETAILED DESCRIPTION

[0035] Figure 1 A lithographic system is shown, the lithographic system comprising a radiation source SO and a lithographic apparatus LA. The radiation source SO is configured to generate and supply a beam B of EUV radiation 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, a measurement system MS, and a substrate loading system SL. The lithographic system further comprises two substrate tables WT1, WT2 configured to support a substrate W. Each substrate table WT1, WT2 can be according to an embodiment of the application. The support structure MT can be according to an embodiment of the application. As explained further below, the substrate clamp can comprise an electrostatic clamp and a Johnsen-Rahbek clamp.

[0036] The illumination system IL is configured to condition the beam B of EUV radiation before it is incident upon the patterning device MA. To this end, the illumination system IL can include a facetted field mirror device 10 and a facetted pupil mirror device 11. The facetted field mirror device 10 and the facetted pupil mirror device 11 together provide the beam B of EUV radiation outgoing from the lithographic apparatus LA with a desired cross-sectional shape and a desired intensity distribution. In addition to the facetted field mirror device 10 and the facetted pupil mirror device 11, or instead of these, the illumination system IL can include other mirrors or devices to further condition the beam B of EUV radiation.

[0037] After being thus adjusted, the EUV radiation beam B interacts with the patterning device MA. As a result of this interaction, a patterned EUV radiation beam B' is generated. The projection system PS is configured to project the patterned EUV radiation beam B' onto a substrate W. To this end, the projection system PS can include a plurality of mirrors 13, 14, which are configured to project the patterned EUV radiation beam B' onto a substrate W held by a substrate table WT2. The projection system PS can apply a reduction factor to the patterned EUV radiation beam B', thus forming an image with features that are smaller than corresponding features on the patterning device MA. For example, a reduction factor of 4 or 8 can be applied. Although the projection system PS is illustrated in Figure 1 Fig. 1 as having only two mirrors 13, 14, the projection system PS can include a different number of mirrors (for example, six or eight mirrors).

[0038] The substrate W can include a pre-formed pattern. In that case, the lithography apparatus LA aligns the image formed by the patterned EUV radiation beam B' with the pre-formed pattern on the substrate W.

[0039] A relative vacuum, i.e. a small amount of gas (for example, hydrogen) at a pressure much lower than atmospheric pressure, can be provided in the radiation source SO, in the illumination system IL and / or in the environment of the projection system PS (which can also contain the measurement system MS).

[0040] Figure 1 The radiation source SO shown in Fig. 1 is, for example, of a type that can be referred to as a laser-produced plasma (LPP) source. A laser system 1 (which may, for example, comprise a CO2laser) is arranged to deposit energy into a fuel, such as tin (Sn) provided from, for example, a fuel emitter 3, via a laser beam 2. Although reference is made to tin in the following description, any suitable fuel can be used. The fuel may, for example, be in liquid form and may, for example, be a metal or an alloy. The fuel emitter 3 can comprise a nozzle configured to direct the tin, for example in the form of micro-droplets, along a trajectory towards a plasma formation region 4. The laser beam 2 is incident on the tin at the plasma formation region 4. Deposition of laser energy into the tin creates a tin plasma 7 at the plasma formation region 4. Radiation, including EUV radiation, is emitted from the plasma 7 during de-excitation and recombination of electrons with ions of the plasma.

[0041] EUV radiation from the plasma is collected and focused by a collector 5. The collector 5 comprises, for example, a near-normal incidence radiation collector 5 (sometimes more generally referred to as a normal-incidence radiation collector). The collector 5 can have a multilayer mirror structure arranged to reflect EUV radiation (e.g. EUV radiation having a desired wavelength such as 13.5 nm). The collector 5 can have an ellipsoidal configuration, having two focal points. A first of the focal points can be at the plasma formation region 4, and a second of the focal points can be at an intermediate focus 6, as described below.

[0042] The laser system 1 can be spatially separated from the radiation source SO. In that case, the laser beam 2 can be delivered from the laser system 1 to the radiation source SO by means of a beam delivery system (not shown), which includes, for example, suitable directing mirrors and / or a beam expander, and / or other optics. The laser system 1, the radiation source SO and the beam delivery system can together be considered a radiation system.

[0043] The radiation reflected by the collector 5 forms an EUV radiation beam B. The EUV radiation beam B is focused at the intermediate focus 6 to form an image of the plasma present at the plasma formation region 4 at the intermediate focus 6. The image at the intermediate focus 6 acts as a virtual radiation source for the illumination system IL. The radiation source SO is arranged such that the intermediate focus 6 is positioned at or near an opening 8 in an enclosing structure 9 of the radiation source SO.

[0044] The measurement system MS of the lithographic apparatus is configured to perform measurements of properties of a substrate W held on the substrate table WT1. The measurement system MS comprises an alignment system configured to measure the position of alignment marks on the substrate with reference to alignment marks on the substrate table WT1. The measurement system also comprises a level sensor configured to measure the topography of the substrate W. These measured properties are used to ensure accuracy when a pattern is subsequently projected onto the substrate W.

[0045] The lithographic apparatus LA is a dual stage lithographic apparatus. That is, the lithographic apparatus comprises two substrate tables WT1, WT2 and is configured such that a substrate W held on one of the substrate tables WT1 is measured by the measurement system MS at the same time as a pattern is being applied to a substrate W held on the other substrate table WT2. For ease of terminology, one of the substrate tables WT1 can be referred to as the first substrate table and the other substrate table WT2 can be referred to as the second substrate table. A dual stage lithographic apparatus advantageously provides a higher throughput (i.e. substrate exposures per hour) than a single stage lithographic apparatus, which typically performs a measurement at the same time as a substrate is being exposed. Once the substrate W held on the first substrate table WT1 has been measured and the substrate W held on the second substrate table WT2 has been exposed, the substrate table WT1 supporting the measured substrate W is moved under the projection system PS. At the same time, the exposed substrate W supported by the second substrate table WT2 is moved to the substrate load system SL.

[0046] The substrate load system SL comprises a substrate handler (not depicted) which is configured to remove the patterned substrate W from the second substrate table WT2 and then load a new substrate to be patterned onto the second substrate table. Once the substrate has been loaded onto the second substrate table WT2, the measurement system MS is used to measure the position of the alignment marks and the topography of the substrate. At the same time, the substrate W held on the first substrate table WT1 is exposed by the lithographic apparatus.

[0047] The above method is repeated a number of times to expose a number of substrates using the lithographic apparatus.

[0048] Each substrate table WT1, WT2 comprises a substrate clamp arrangement according to an embodiment of the application. The substrate clamp arrangement is switched off before the exposed substrate is to be removed from the substrate table, thereby allowing the substrate handler of the substrate load system to easily remove the substrate from the substrate table. The unexposed substrate is then placed on the substrate table WT1 (or WT2) and subsequently the substrate clamp arrangement is switched on.

[0049] Figure 2A schematic diagram showing parts of a known substrate clamp apparatus. The parts of the clamp apparatus shown are parts of an electrostatic clamp apparatus. The clamp apparatus comprises a clamp member 20 which comprises a first electrode 22a and a second electrode 22b. In particular, the clamp member 20 comprises a body 20a (which comprises the electrodes 22a, 22b) and a plurality of tabs 20b, 20c, 20d and 20e which project from the body 20a. The electrodes 22a, 22b can form part of an electrostatic sheet positioned within the clamp member 20. The electrostatic sheet takes the form of an electrode encapsulated in a dielectric material. The clamp member 20 further comprises a first conductive layer. The first conductive layer takes the form of a plurality of layer portions 24a, 24b, 24c and 24d which are each positioned on a respective tab such that the first conductive layer can be said to be positioned on the plurality of tabs 20b to 20e.

[0050] The clamp apparatus further comprises a mounting member 26 (which can also be referred to as a mirror block, in some applications it can be mounted with a mirror to facilitate accurate measurement of its position). The mounting member 26 further comprises a second conductive layer 28.

[0051] In use, the clamp member 20 is mounted on the mounting member 26. Both the first and second conductive layers are electrically connected to ground.

[0052] A power supply 30 is connected to each of the electrodes 22a, 22b. In the apparatus shown, the clamping device can be said to be bipolar. This is because the power supply 30 is configured to place one of the electrodes 22a at a positive voltage and the other electrode 22b at a negative voltage.

[0053] The voltage applied to the electrodes creates an electrostatic force which attracts the clamp member 20 to the mounting member 26, thereby clamping the clamp member to the mounting member 26.

[0054] The clamping pressure between the clamp member 20 and the mounting member 26 is defined by the following equation: (1) where P is the clamping pressure, F is the electrostatic force, A is the area over which the electrostatic clamp force is distributed, η is the electrode / barrier ratio, ε0 is the dielectric constant of the vacuum between the clamp member 20 and the mounting member 26, ε r is the relative dielectric constant of the dielectric material of the electrostatic sheet, g is the vacuum gap (i.e. the separation between the underside of the body 20a of the clamp member 20 and the conductive layer 28), d is the thickness of the dielectric material of the electrostatic plate (i.e. the distance between each electrode 22a, 22b and the vacuum gap between the clamp member 20 and the mounting member 26), and V is the voltage applied to each of the electrodes 22a, 22b (relative to ground). In the present embodiment, since the electrodes are bipolar devices, each electrode will have the same magnitude of voltage, but opposite polarity.

[0055] In one example, d is 100 pm, V is 3200 V, g is 10 pm, h is 0.9, and e r is approximately 4. This will result in a chucking pressure of approximately 44 kPa.

[0056] As can be seen from the above equation, in order to increase the chucking pressure P, it is desirable to increase the applied voltage or to decrease the vacuum gap and / or the dielectric thickness. However, increasing the voltage is limited by the operating characteristics of the power supply powering the electrodes, decreasing the dielectric thickness is limited by the dielectric breakdown strength of the relevant dielectric, and decreasing the vacuum gap is limited by particle sensitivity and electrostatic charging effects. Furthermore, higher voltages increase the electric field strength in the (vacuum) gap between the clamp member and the mounting member. This can increase the risk of electrostatic discharge.

[0057] The chucking pressure applied by the chucking device is a key factor in determining whether the clamped substrate and / or the clamp member will move relative to the substrate table as a result of acceleration of the substrate table when the substrate table is formed part of the lithographic apparatus. It will be appreciated that any movement of the clamped substrate and / or the clamp member relative to the substrate table is unacceptable, since the position of the substrate and / or the clamp member relative to the rest of the lithographic apparatus is critical to ensure that the substrate is processed correctly. The acceleration of the substrate table is a key factor in determining the processing speed of the lithographic apparatus. In view of this, if it is desired to increase the processing speed of the lithographic apparatus, it can be desirable to increase the acceleration of the substrate table, and this can be done by increasing the chucking pressure of the chucking device.

[0058] The present invention seeks to provide an alternative chucking device which provides an increase in chucking pressure without the need to increase the applied voltage or decrease the dielectric thickness and / or the vacuum gap.

[0059] Figure 3 A schematic illustration of part of a chucking device according to an embodiment of the present invention is shown.

[0060] Figure 3 Features within the illustrated embodiments which are equivalent to features illustrated in Figure 2 Features illustrated in the figures have been given the same reference numerals. The following discussion focuses only onFigure 3 The embodiment shown differs from Figure 2 the prior art shown in two main ways. Structurally, there are two main differences. First, the dielectric layer 32 is sandwiched between the first conductive layers (24a, 24b, 24c and 24d) and the second conductive layer 28. Second, the second conductive layer 28 is no longer electrically connected to ground.

[0061] In the embodiment shown, a switch 34 is provided which can be used to temporarily electrically connect the second conductive layer 28 to ground, the importance of being able to do so will be discussed in more detail below. However, in other embodiments, the clamp device according to the present application need not be provided with any means of temporarily grounding the second conductive layer, such that in these embodiments the second conductive layer is permanently electrically decoupled from ground.

[0062] The dielectric layer 32 is fixed to the second conductive layer 28 such that it forms part of the mounting member 26. In other embodiments, as discussed in more detail below, this need not be the case.

[0063] Furthermore, in the present embodiment, the dielectric layer is continuous. That is, the dielectric layer covers the entire upper surface of the second conductive layer 28. The dielectric layer 32 can be said to be continuous in that it is configured such that, in use, when the burls (20b, 20c, 20d and 20e) contact the mounting member, the dielectric layer 32 is not only positioned beneath each of the burls, but also extends beneath the spaces between adjacent burls.

[0064] The second conductive layer 28 can be formed from any appropriate material. Given that the layer is electrically conductive, it will be apparent that the material forming the layer must be electrically conductive. Furthermore, in order to improve the durability of the clamp device, the material forming the second conductive layer is preferably relatively hard. For example, the material can have a Mohs hardness of 6.0 or higher, or 7.0 or higher. Suitable materials include metals such as chromium, tungsten, vanadium and titanium.

[0065] The first conductive layers (24a, 24b, 24c and 24d) must also essentially be formed from an electrically conductive material, similar to the second conductive layer 28. Again, in order to improve the durability of the clamp device, the material is preferably relatively hard. For example, the material can have a Mohs hardness of 6.0 or higher, or 7.0 or higher. Example materials include the metals mentioned previously, chromium nitride, silicon carbide, siliconized silicon carbide or electrically conductive diamond, titanium nitride and doped chromium nitrate, for example CrNAl.

[0066] It is desirable for the first conductive layers to have a surface roughness in the range of about 1 nm to about 10 nm. This measure of roughness is defined as the average deviation from the average height, which can also be referred to as Ra.

[0067] The dielectric layer 32 can be formed of any suitable dielectric material. As is well known, a dielectric material is an electrical insulator but a material that can be polarized by the application of an electric field. The dielectric layer can be formed of any suitable dielectric material. Examples of suitable dielectric materials include silicon oxide, diamond, boron nitride, zirconium oxide, aluminium nitride, silicon nitride and aluminium oxide.

[0068] The at least one electrode (in this case electrodes 22a and 22b) forms part of an electrostatic plate arrangement. The electrostatic plate arrangement takes the form of one or more electrodes (in this case electrodes 22a and 22b) formed of any suitable electrically conductive material, such as copper, encapsulated in a dielectric material. The dielectric material can be any suitable dielectric material, for example quartz.

[0069] As previously mentioned, the second conductive layer 28 is no longer permanently connected to electrical ground. When the second conductive layer 28 is not connected to electrical ground, the second conductive layer 28 can be said to be at floating voltage. In view of the second conductive layer 28 being at floating voltage, the electrostatic potential across the dielectric layer 32 above the second conductive layer 28 of the mounting member results in an additional electrostatic force being exerted across the dielectric layer 32 between the mounting member 26 and the clamp member 20.

[0070] In the present embodiment, the dielectric layer 32 has a thickness of approximately 100 nm, and the first conductive layer (24a, 24b, 24c and 24d) has a surface roughness of approximately 10 nm. These geometrical dimensions are significantly smaller than the geometrical dimensions of other parts of the clamping arrangement (the thickness of the dielectric in the electrostatic plate is 100 pm, and the vacuum gap is 10 pm). This means that a much lower voltage is required to generate a significant additional clamping pressure at the interface between the clamping member (and in particular the burls of the clamping member) and the mounting member. This is because, as has been discussed in relation to equation 1, the clamping pressure is inversely proportional to the square of the distance.

[0071] In summary, with the dielectric layer according to the present application, a greater clamping pressure can be generated with the same voltage, or the same clamping pressure can be obtained with a lower voltage and / or a clamp member / mounting member having a reduced thickness. Furthermore, the present application ensures that the clamping force between the clamp member and the mounting member is applied exactly where it is needed, at the interface between the clamp member (and for example, in particular the burls of the clamp member) and the mounting member.

[0072] It can be beneficial to be able to generate the same clamping pressure using a reduced voltage or to generate a greater clamping pressure using the same voltage, since one disadvantage of using an increased voltage to provide clamping pressure is that the increased voltage also increases the deflection of the body of the clamping member between the nubs. This can cause the upper surface of the body of the clamping member to become uneven. It will be appreciated that if the clamp member is used to support a wafer being processed by a lithographic apparatus, unevenness of the upper surface of the body of the clamping member can cause the wafer to be supported in an uneven manner. This can cause errors in processing the wafer by the lithographic apparatus.

[0073] Further additional clamping pressure can be obtained by operating the electrodes of the clamp apparatus at a bias voltage rather than at an equilibrium voltage. For example, where a bipolar electrostatic clamp has previously been operated at an equilibrium voltage of + / - 3.2kV, in accordance with the present application the power supply can be configured so that the electrodes 22a, 22b are operated in a biased manner, for example, a bias of 20V so that one electrode is operated at +3220V and the other electrode is operated at -3180V. The bias in the voltage applied to the electrodes causes electrostatic potentials to be generated in the floating conductive layer 28 of the mounting block 26. The electrostatic potentials induced in the conductive layer 28 cause additional electrostatic attraction between the mounting member and the clamping member.

[0074] As previously mentioned, in some embodiments a switch 34 is provided which can temporarily electrically connect the second conductive layer 28 to ground. The ability to ground the conductive layer 28 of the mounting member 26 provides additional control. This is because, when required, the second conductive layer 28 can be placed at an electrostatic potential of 0V. When this occurs, this reduces any electrostatic attraction caused by the electrostatic potentials induced in the second conductive layer 28 to zero. This can assist with relative repositioning of the clamp member 20 relative to the mounting member 26 when desired, for example, when the clamp member 20 is mounted at a desired position relative to the mounting member 26.

[0075] In view of the switch being configured to electrically connect the second conductive layer to electrical ground as discussed above, in other embodiments the switch can additionally or alternatively electrically connect the second conductive layer to a set voltage. For example, the switch can connect the second conductive layer to a power supply which drives the second conductive layer to a desired potential relative to ground or an electrode within the clamp member.

[0076] The present invention relies on electrostatic positioning generated at the interface between the clamping member 20 and the mounting member 26, wherein the conductive layers (24a, 24b, 24c, 24d, and 28) of the mounting member 26 are spaced apart by dielectric layers 32. The above embodiment achieves this by allowing the second conductive layer 28 of the mounting member 26 to be at a floating voltage and thus allowing electrostatic positioning to be induced therein. As those skilled in the art will understand, various other ways exist to induce potentials between the clamping member and the mounting member. Such methods can be applied as alternatives or additional solutions to floating the aforementioned second conductive layer 28. In one example, instead of the mounting member 26, the second conductive layer 28 is allowed to be at a floating voltage; the second conductive layer 28 can be driven by a power source such that the second conductive layer 28 is at an offset voltage relative to the voltage of one or more electrodes 22a, 22b of the clamping member 20. Another option is to drive the first conductive layer (24a to 24d) using a suitable power source, placing the first conductive layer (which is grounded in the discussed embodiment) at an offset voltage relative to the second conductive layer 28.

[0077] Figure 4 A schematic diagram of a portion of an electrostatic clamping device according to another embodiment of the present invention is shown. Similarly, features in this embodiment that are equivalent to those discussed in the foregoing figures have been given the same reference numerals.

[0078] Figure 4 The illustrated embodiments and Figure 3 The main difference between the embodiments shown is that, instead of Figure 4 In the illustrated embodiment, the dielectric layer is continuous above the upper surface of the second conductive layer 28 (e.g., Figure 3 In the illustrated embodiment, the dielectric layer is discontinuous. Specifically, in Figure 4 In the illustrated embodiment, the dielectric layer comprises four discrete portions (32a, 32b, 32c, and 32d). Given that the portions of the dielectric layer are discrete, the dielectric layer is referred to as discontinuous.

[0079] As previously mentioned, as long as the dielectric layers 32a to 32d are sandwiched between the first conductive layers 24a to 24d and the second conductive layer 28, the electrostatic clamp device will operate in accordance with the present application as previously discussed when the electrostatic clamp device is in use. It will be appreciated that in some embodiments, portions of the dielectric layers 32a to 32d can be secured to the first conductive layers 24a to 24d (of the respective portions). Whereas in other embodiments, portions of the dielectric layers can be secured to the second conductive layer 28. In both options, it will be appreciated that there is an advantage to securing portions of the dielectric layers to the first conductive layers as opposed to the second conductive layer 28. The reason for this is that when portions of the dielectric layers are secured to the first conductive layers, the dielectric layers will be sandwiched between the first conductive layers and the second conductive layer regardless of where the clamp member 20 is positioned on the mounting member 26. In contrast, if portions of the dielectric layers are secured to the second conductive layer 28, it is necessary in use to position the clamp member 20 at the correct position on the mounting member 26 so that the dielectric layers are sandwiched between the first conductive layers and the second conductive layer as required.

[0080] Figure 5 A top view schematic of an alternative second conductive layer 28a is shown. Whereas the second conductive layer 28 shown in relation to the previously described embodiments of the present application can be said to be generally continuous (such that the second conductive layer is generally uniform / planar and covers the entire upper surface of the mounting member 26), Figure 5 the second conductive layer 28a shown in Figure 4 can be said to be discontinuous. In particular, the second conductive layer 28a comprises a first conductive portion 28b which is electrically isolated from a second conductive portion 28c. The first conductive portion 28b is electrically isolated from the second conductive portion 28c by an intermediate electrically isolating portion 28d which is formed from an electrically isolating (i.e. non-conductive) material.

[0081] It can be seen that the first conductive portion 28b is shaped such that it forms a row of pads 28e which are coupled by connecting tracks 28f. The pads 28e have a width WP in the plane of the conductive layer which is greater than the width WT of the tracks 28f. The pads 28e are positioned such that they correspond to the position of the burls of the clamp member when the clamp member 20 is positioned on top of the mounting member 26 in use.

[0082] The first conductive portion 28b can be referred to as a tab-facing portion and the second conductive portion 28c can be referred to as a space-facing portion. As previously mentioned, it will be appreciated that the tab-facing portion 28b faces, in use, the corresponding tab (20b to 20e) of the clamp member 20 that is positioned over the respective pad 28e of the first conductive portion 28b. The space-facing portion 28c of the conductive layer 28a faces, in use, the space between the adjacent tabs (20b to 20e) of the clamp member 20 that is positioned over the space-facing portion 28c of the conductive layer 28a.

[0083] In embodiments such as the presently illustrated embodiment, it is envisaged that the space-facing portion 28c will be electrically connected, in use, to ground. It is also envisaged that the tab-facing portion 28b will be electrically connected, in use, to a power supply 30a that is capable of placing the conductive portion 28b at a bias potential. Any suitable bias potential can be used to generate the desired clamping force between the mounting member 26 and the clamp member 20. In one embodiment, the conductive portion 28b is placed at a bias potential of 100 V.

[0084] An advantage of the apparatus is that by making the conductive layer 28a of the mounting block discontinuous, it enables the relevant portion of the conductive layer that is positioned directly below the tabs (in this case, the pads 28e) to be placed at a bias potential, while leaving the portion of the conductive layer that is positioned directly below the spaces between the tabs (in this case, the second conductive portion 28c) electrically grounded. This ensures that the electrostatic attractive force generated between the mounting member 26 and the clamp member 10 is primarily an electrostatic force exerted between each tab (20b to 20e) and the corresponding portion of the tab-facing conductive portion of the conductive layer 28a. This reduces the electrostatic pressure exerted on the body of the mounting member that is positioned below the conductive layer 28a, and thereby reduces the potential for wear of the body of the mounting member. Wear of the body of the mounting member can eventually result in misalignment of the clamp member 20 relative to the mounting member 26 and, therefore, misalignment of any wafer clamped by the clamp member 20. As such, wear is undesirable because it can require repair, refurbishment or replacement of the mounting member.

[0085] In the above described embodiments of the application, it is envisaged that the dielectric layer is sandwiched between the mounting member and the clamping member, the dielectric layer being attached to only one of i) a portion of the mounting member (e.g. on the upper surface of the second conductive layer) or ii) a portion of the clamping member (e.g. on the lower surface of the first conductive layer). However, it is also possible that the dielectric layer is formed from two portions, a first portion of the two portions being secured to a portion of the clamping member and a second portion of the two portions being secured to a portion of the mounting member. In use, the first portion secured to the clamping member contacts the second portion secured to the mounting member, such that the first portion secured to the clamping member and the second portion secured to the mounting member are sandwiched between the clamping member and the mounting member.

[0086] In view of the presently described embodiments taking a relatively one-dimensional form in that it comprises a row of burls of the clamping member positioned along a corresponding portion of the mounting member, in other embodiments the clamp apparatus can be relatively two-dimensional, such that the burls of the clamping member form a two-dimensional array having rows and columns of burls, the rows and columns of burls positioning themselves across a corresponding relatively two-dimensional surface of the mounting member. In this case, it will be appreciated that not only do the rows and columns of burls form a relatively two-dimensional array, but also the spaces between adjacent burls also have a relatively two-dimensional footprint, having a width and a depth, such that the footprint is generally rectangular, such that the space defined by the footprint is generally cuboid.

[0087] Although specific reference can be made in this text to the use of lithographic apparatus in the manufacture of ICs, it should be understood that the lithographic apparatus described herein can have other applications. Possible other applications include the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat-panel displays, liquid-crystal displays (LCDs), thin-film magnetic heads, etc.

[0088] Although specific reference can have been made in this text to embodiments of the application in the context of optical lithography, it should be understood that the application has many applications and embodiments, including but not limited to those in which the processes described are carried out in the context of other processes such as optical, magnetic or other propagation techniques. Where the disclosure is appropriate, embodiments can be used in combination with optical, magnetic or other propagation techniques. The application is not limited to optical lithography applications.

[0089] While specific embodiments of the application have been described above, it will be appreciated that the application can be practiced otherwise than as described. The description is not intended to limit the application. Accordingly, those skilled in the art will recognize that modifications and variations of the described implementation can be made without departing from the scope of the application.

Claims

1. An electrostatic clamping device, comprising: A clamping component, the clamping component comprising at least one electrode and a first conductive layer; The mounting component includes a second conductive layer, and the clamping component is mounted on the second conductive layer; as well as A dielectric layer is sandwiched between the first conductive layer and the second conductive layer.

2. The electrostatic clamping device according to claim 1, wherein the dielectric layer is fixed to the second conductive layer; and optionally, wherein the dielectric layer is discontinuous.

3. The electrostatic clamping device according to claim 1, wherein the dielectric layer is fixed to the first conductive layer.

4. The electrostatic clamping device according to any of the preceding claims, wherein the clamping member includes a body and a plurality of protrusions, the body including the at least one electrode, the plurality of protrusions protruding from the body, wherein the first conductive layer is positioned on the plurality of protrusions.

5. The electrostatic clamping device according to any of the preceding claims, wherein the second conductive layer is formed of chromium.

6. The electrostatic clamping device according to any of the preceding claims, wherein the first conductive layer is formed of chromium nitride.

7. The electrostatic clamping device according to any of the preceding claims, wherein the dielectric layer is formed of silicon oxide.

8. The electrostatic clamping device according to any of the preceding claims further includes a power source, wherein the power source is electrically connected to the at least one electrode.

9. The electrostatic clamping device according to any of the preceding claims, wherein the first conductive layer is electrically connected to ground.

10. The electrostatic clamping device according to any of the preceding claims, wherein the second conductive layer is electrically connected to electrical ground or electrically connected to a power source, the power source being configured to place the second conductive layer at a desired non-ground voltage.

11. The electrostatic clamping device according to any of the preceding claims, wherein the second conductive layer is discontinuous, such that the second conductive layer includes a first conductive portion and a second conductive portion, the first conductive portion and the second conductive portion being electrically isolated from each other.

12. The electrostatic clamping device according to any of the preceding claims further includes a switch electrically connected to the second conductive layer and ground, the switch having a first configuration and a second configuration, wherein in the first configuration the switch does not electrically connect the second conductive layer to ground, and in the second configuration the switch electrically connects the second conductive layer to ground.

13. The electrostatic clamping device according to claim 8 or any claim dependent to claim 8, wherein the at least one electrode comprises a first electrode and a second electrode, wherein a power supply is connected to the first electrode and the second electrode, and wherein the power supply is configured to apply a first positive voltage to the first electrode and a second negative voltage to the second electrode, wherein the first voltage and the second voltage are not the same, such that there is an offset between the first voltage and the second voltage.

14. An electrostatic clamping device according to any of the preceding claims other than claim 12 or any claim dependent on claim 12, wherein the second conductive layer is electrically connected to a power source configured to place the second conductive layer at a desired non-ground voltage.

15. A photolithography apparatus comprising an electrostatic clamping device according to any of the preceding claims.

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