Apparatus and method including electrostatic clamp

Abstract

An apparatus comprising: an electrostatic clamp for clamping a component; and a mechanism for generating free charges adjacent to the electrostatic clamp. The electrostatic clamp comprises an electrode or a plurality of electrodes. The apparatus is configured to: operate in a first mode in which the or each electrode is set to a potential such that a clamping electric field is generated between the electrostatic clamp and the component to clamp the component; operate in a second mode in which the or each potential of the electrodes is set such that clamping of the component is released; and operate in a third mode in which the or each potential of the electrodes is set such that the flux of free charges generated by the mechanism to a surface of the component adjacent to the electrostatic clamp is increased compared to operating in the first or second mode.

Description

[0001] Cross-references to related applications

[0002] This application claims priority to EP 19173683.4, filed on 10 May 2019; EP 19178628.4, filed on 6 June 2029; and EP 19186258.0, filed on 15 July 2019, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This invention relates to an apparatus including an electrostatic clamp and a method of operating said apparatus. More particularly, but not exclusively, the apparatus may include a photolithography apparatus, wherein the electrostatic clamp is configured to hold components such as pattern forming apparatus during photolithographic patterning. Background Technology

[0004] A photolithography apparatus is a machine configured to apply a desired pattern onto a substrate. Photolithography apparatus can be used, for example, in the manufacture of integrated circuits (ICs). It can project a pattern from a patterning apparatus (e.g., a mask) onto a radiation-sensitive material (resist) layer disposed on a substrate.

[0005] To project a pattern onto a substrate, a photolithography apparatus can use electromagnetic radiation. The wavelength of this radiation determines the minimum size of the feature that can be formed on the substrate. Compared to a photolithography apparatus using radiation with a wavelength of, for example, 193 nm, a photolithography apparatus using extreme ultraviolet (EUV) radiation with wavelengths 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 the substrate.

[0006] Photolithography equipment typically uses high-voltage electrostatic clamps to hold patterning apparatus, for example, during patterning operations. The electrostatic clamps and patterning apparatus are often maintained in a low-pressure, hydrogen-rich environment. This environment is non-conductive. Therefore, it will be understood that charge can accumulate on dielectric or ungrounded surfaces. For example, during operation, charge can accumulate on dielectric or ungrounded surfaces by touching components (e.g., mask clamps) or by particle collisions during gas flow.

[0007] It should also be understood that, due to the generation of EUV-induced hydrogen plasma, EUV radiation may cause the hydrogen-rich environment to become conductive. Free charges generated within the EUV-induced hydrogen plasma can be attracted to (or repelled by) the electric field generated by the electrostatic clamp. On the other hand, in the absence of EUV-induced plasma, or in areas separated from or well-shielded from any EUV-induced plasma, charges can accumulate on dielectric or ungrounded surfaces and may persist even after any electric field has been removed.

[0008] In addition to charge accumulation, very strong electrostatic fields (e.g., approximately ~1 kV / cm to 100 kV / cm) can also be generated between the components of the electrostatic clamp and other system components. Specifically, the high voltage applied to the electrodes of the electrostatic clamp causes nearby conductors (e.g., conductive coatings that may be present on the surface of the mask) to become polarized. Thus, a strong electrostatic field is generated, especially at sharp features (e.g., the edges of the conductive mask coating). Summary of the Invention

[0009] According to a first aspect of the invention, an apparatus is provided, comprising: an electrostatic clamp for clamping a component; and a mechanism for generating free charge adjacent to the electrostatic clamp: wherein the electrostatic clamp includes one or more electrodes, wherein the apparatus is configured to: operate in a first mode in which the electrode or each electrode is set at a potential such that a clamping electric field is generated between the electrostatic clamp and the component to clamp the component; operate in a second mode in which the potential of the electrode or each potential of each electrode is set such that the clamping of the component is released; and operate in a third mode in which the potential of the electrode or each potential of each electrode is set such that, compared to operation in the first or second mode, the flux of free charge generated by the mechanism toward the surface of the component adjacent to the electrostatic clamp is increased.

[0010] This allows for accelerated neutralization of residual charge during mask unloading. Consequently, it enhances the compensation of residual charge on the mask by EUV-induced plasma during mask unloading / loading operations. This prevents electrical breakdown that could damage the mask surface. Additionally, it enables throughput-neutral mask grounding.

[0011] The electrostatic clamp may include the plurality of electrodes, and in the third mode, the device may be configured such that the potential of the edge electrode closest to the edge of the electrostatic clamp is set positive. This can provide an additional negative bias to the second surface of the mask (i.e., the surface adjacent to the clamp), which increases the positive ion flux toward the mask MA.

[0012] In the third mode, the device can be configured such that the potential of the electrodes, or each potential of each electrode, is set such that the potential of the electrodes, or the average potential of the plurality of electrodes, is negative. This can capacitively induce a negative potential on the mask, which attracts positive ions toward the second surface of the mask.

[0013] In the third mode, the device can be configured such that the potentials of the plurality of electrodes are set such that the average potential of the plurality of electrodes is approximately 0V. This means that the capacitively induced potentials on the mask (particularly on the second surface of the mask) remain unchanged.

[0014] The electrostatic clamp may include the plurality of electrodes, and in the third mode, the device may be configured such that the potential of the edge electrode closest to the edge of the electrostatic clamp is set to negative, and the potentials of the remaining portions of the plurality of electrodes are set such that the average potential of the plurality of electrodes has a smaller negative value compared to the potential of the edge electrode.

[0015] In the third mode, the device can be configured such that the potential of the electrodes, or each potential of each electrode, is set such that the surface of the component adjacent to the electrostatic clamp has a positive potential before the component moves from being held by the electrostatic clamp to being spaced apart from the electrostatic clamp. This means that the residual charge on the mask at the unloading point can be neutralized by electrons (rather than by positive ions), thus achieving neutralization much faster.

[0016] In the third mode, the potential of the electrode or the average potential of the electrode can be set to a predetermined negative value, such that during the movement of the component from being held by the electrostatic clamp to being spaced apart from the electrostatic clamp, the surface of the component has a potential approximately the same as the potential of the electrode or the average potential of the electrode. This prevents the mask from becoming charged during exposure.

[0017] In the third mode, the potential of the electrode or the average potential of the electrode can be set to the predetermined negative value such that the component has approximately zero charge after exposure. This could mean that during unloading, the potential difference between the second surface of the mask and the clamping surface of the fixture does not increase relatively significantly.

[0018] In the third mode, the potential of the electrode or each potential of each electrode can be set to last for at least one of the following times: the time period before the component moves from being held by the electrostatic clamp to being spaced apart from the electrostatic clamp; part or all of the time spent moving the component from being held by the electrostatic clamp to being spaced apart from the electrostatic clamp; and part or all of the time spent moving the component from being spaced apart from the electrostatic clamp to being held by the electrostatic clamp.

[0019] In the third mode, the potential of the electrode or the average potential of the electrode can be set to sustain the generation of free charge by the mechanism for at least a portion or all of the time.

[0020] The mechanism for generating free charges adjacent to the electrostatic clamp may include: a gas source; and an ionizing radiation source configured to ionize the gas supplied by the gas source.

[0021] The ionizing radiation source may include at least one of EUV source, VUV source, soft X-ray source and radioactive source.

[0022] The electrostatic clamp may include additional electrodes or a plurality of additional electrodes, wherein the additional electrodes or the plurality of additional electrodes may be positioned at least partially around a volume extending in a direction away from the surface of the electrostatic clamp adjacent to the component, wherein the device may be configured such that the potential of the additional electrodes or each potential of each additional electrode is set such that the flux of free charge generated by the mechanism toward the surface of the component adjacent to the electrostatic clamp is reduced.

[0023] The device may be configured to: measure the charge or current from the voltage supply device to the electrode or each electrode using at least one charge or current measuring device; calculate the capacitance of the electrode or each electrode using the measured charge or current to the electrode or each electrode; and determine the potential of the surface of the component adjacent to the electrostatic clamp using the calculated capacitance of the electrode or each electrode.

[0024] At least one measuring device can be used to calculate the capacitance of the electrode or each electrode. The device may include at least one measuring device. The device may include at least one charge measuring device. The device may include at least one current measuring device.

[0025] According to a second aspect of the invention, there is provided a photolithography apparatus arranged to project a pattern from a pattern forming apparatus onto a substrate, wherein the photolithography apparatus includes an irradiation system configured to adjust a radiation beam and a device as described above, wherein the irradiation system is configured to project the radiation beam onto the pattern forming apparatus, and wherein the pattern forming apparatus includes a component to be clamped, wherein the photolithography apparatus includes the device as described above.

[0026] According to a third aspect of the invention, a method of operating a device is provided, the device comprising: an electrostatic clamp; and a mechanism for generating free charge at a location adjacent to the electrostatic clamp, the electrostatic clamp including one or more electrodes, the method comprising: disposing a component at a location adjacent to the electrostatic clamp; controlling the mechanism for generating free charge to generate free charge at a location adjacent to the electrostatic clamp; operating the device in a first mode, in which the electrode or each electrode is positioned at a potential such that a clamping electric field is generated between the electrostatic clamp and the component to clamp the component; operating the device in a second mode, in which the potential of the electrode or each potential of each electrode is set such that the clamping of the component is released; and operating the device in a third mode, in which the potential of the electrode or each potential of each electrode is set such that, compared to operation in the first or second mode, the flux of free charge to the surface of the component adjacent to the electrostatic clamp is increased.

[0027] The electrostatic clamp may include multiple electrodes, and the method may further include: in the third mode, setting the potential of the edge electrode closest to the edge of the electrostatic clamp to be positive.

[0028] The method may further include: in the third mode, setting the potential of the electrode or each potential of each electrode such that the potential of the electrode or the average potential of the plurality of electrodes is negative.

[0029] The method may further include: in the third mode, setting the potential of the plurality of electrodes such that the average potential of the plurality of electrodes is approximately 0V.

[0030] The electrostatic clamp further includes additional electrodes or a plurality of additional electrodes, which are at least partially positioned around a volume extending in a direction away from the surface of the electrostatic clamp adjacent to the component. The method may further include setting the potential of the additional electrodes or each potential of each additional electrode such that the flux of free charge to the surface of the component adjacent to the electrostatic clamp is reduced.

[0031] The method may further include: measuring the charge or current from the voltage supply device to the electrode or each electrode using at least one charge or current measuring device; calculating the capacitance of the electrode or each electrode using the measured charge or current to the electrode or each electrode; and determining the potential of the surface of the component adjacent to the electrostatic clamp using the calculated capacitance of the electrode or each electrode.

[0032] According to a fourth aspect of the invention, an apparatus is provided, comprising: an electrostatic clamp for holding a component; and a mechanism for generating free charge adjacent to the electrostatic clamp: wherein the electrostatic clamp includes one or more electrodes, wherein the electrode or the plurality of electrodes is positioned at least partially around a volume extending in a direction away from a surface of the electrostatic clamp adjacent to the component, wherein the apparatus is configured such that the potential of the electrode or each electrode or each potential is set such that the flux of free charge generated by the mechanism toward the surface of the component adjacent to the electrostatic clamp is reduced.

[0033] This can have the advantage of preventing or at least reducing the charge on the mask. This can prevent electrical breakdowns that could damage the surface of the attached mask (e.g., during mask unloading).

[0034] The electrode or the plurality of electrodes may be located on one side of the component.

[0035] The electrode or the plurality of electrodes may always extend around the volume.

[0036] The potential of the electrode, or each potential of each electrode, can be set to negative.

[0037] The potential of the electrode, or each potential of each electrode, can be set to positive.

[0038] The electrode, or each electrode, may be in electrical contact with the surface of the component adjacent to the electrostatic clamp.

[0039] At least one or more edges of the electrode or the surface of each electrode adjacent to the component may be rounded.

[0040] The electrodes, or each electrode, may have rounded corners in the area corresponding to the corner of the component.

[0041] The potential of the electrode, or each potential of each electrode, can be set to last for at least one of the following times: at least a portion or all of the time during which the mechanism generates free charge, and the time period before the component moves from being held by the electrostatic clamp to being spaced apart from the electrostatic clamp.

[0042] The mechanism for generating free charges adjacent to the electrostatic clamp may include: a gas source; and an ionizing radiation source configured to ionize the gas supplied by the gas source.

[0043] The ionizing radiation source may include at least one of EUV source, VUV source, soft X-ray source and radioactive source.

[0044] According to a fifth aspect of the invention, there is provided a photolithography apparatus arranged to project a pattern from a pattern forming apparatus onto a substrate, wherein the photolithography apparatus includes an irradiation system configured to adjust a radiation beam and a device as described above, wherein the irradiation system is configured to project the radiation beam onto the pattern forming apparatus, and wherein the pattern forming apparatus includes a component to be clamped, wherein the photolithography apparatus includes the device as described above.

[0045] According to a sixth aspect of the invention, a method for operating a device is provided, the device comprising: an electrostatic clamp; and a mechanism for generating free charge at a location adjacent to the electrostatic clamp, the electrostatic clamp including one or more electrodes positioned at least partially around a volume extending in a direction away from a surface of the electrostatic clamp adjacent to the component, the method comprising: disposing a component at a location adjacent to the electrostatic clamp; controlling the mechanism for generating free charge to generate free charge at a location adjacent to the electrostatic clamp; and setting the potential of the electrodes or each potential of each electrode such that the flux of free charge to the surface of the component adjacent to the electrostatic clamp is reduced.

[0046] The method may also include setting the potential of the electrode or each potential of each electrode to negative.

[0047] The method may further include setting the potential of the electrode or each potential of each electrode to positive.

[0048] The method may further include controlling the potential of the surface of the component adjacent to the electrostatic clamp via an electrical connection between the electrode or each electrode and the surface of the component adjacent to the electrostatic clamp.

[0049] According to a seventh aspect of the present invention, an apparatus is provided, comprising: an electrostatic clamp for holding a component; and a mechanism for generating free charge adjacent to the electrostatic clamp: wherein the electrostatic clamp includes one or more electrodes, wherein the apparatus is configured to: measure charge or current from a voltage supply device to the electrode or each electrode using at least one charge or current measuring device; calculate the capacitance of the electrode or each electrode using the measured charge or current to the electrode or each electrode; and determine the potential of a surface of the component adjacent to the electrostatic clamp using the calculated capacitance of the electrode or each electrode.

[0050] This can have the advantage of providing reliable control over the potential of the surface of the component adjacent to the electrostatic clamp. It can also have the advantage of preventing or at least reducing mask charging. This can prevent electrical breakdowns that could damage the surface of the attached mask (e.g., during mask unloading).

[0051] At least one measuring device can be used to calculate the capacitance of the electrode or each electrode. The device may include at least one measuring device. The device may include at least one charge measuring device. The device may include at least one current measuring device.

[0052] The device can be configured such that the potential of one or more of the plurality of electrodes is set such that the potential of the surface of the component adjacent to the electrostatic clamp is approximately a predetermined value.

[0053] The predetermined value of the potential of the surface of the component adjacent to the electrostatic clamp can be at least one of positive, negative, and approximately zero.

[0054] The device can be configured to measure the ratio of the capacitances of the plurality of electrodes.

[0055] The device can be configured to set the potential of at least one of the plurality of electrodes based on the ratio of the capacitances of the plurality of electrodes.

[0056] The device can be configured to set the potential of at least one of the plurality of electrodes based on the potential of the electrodes or the variance of the capacitance of each electrode.

[0057] The device can be configured to change the potential of the plurality of electrodes by a predetermined amount in a stepwise manner, and after each potential change, use the at least one charge or current measuring device to measure the charge or current from the voltage supply device to the electrode or each electrode to determine the individual capacitance of the plurality of electrodes.

[0058] The potential of the electrode or each electrode may be set to last for at least one of the following times: before at least a portion or all of the time during which the mechanism generates free charge; and before the component moves from being held by the electrostatic clamp to being spaced apart from the electrostatic clamp.

[0059] The mechanism for generating free charges adjacent to the electrostatic clamp may include: a gas source; and an ionizing radiation source configured to ionize the gas supplied by the gas source.

[0060] The ionizing radiation source may include at least one of EUV source, VUV source, soft X-ray source and radioactive source.

[0061] According to an eighth aspect of the invention, there is provided a photolithography apparatus arranged to project a pattern from a pattern forming apparatus onto a substrate, wherein the photolithography apparatus includes an irradiation system configured to adjust a radiation beam and a device as described above, wherein the irradiation system is configured to project the radiation beam onto the pattern forming apparatus, and wherein the pattern forming apparatus includes a component to be clamped, wherein the photolithography apparatus includes the device as described above.

[0062] According to a ninth aspect of the present invention, a method for operating a device is provided, the device comprising: an electrostatic clamp; and a mechanism for generating free charge at a location adjacent to the electrostatic clamp, the electrostatic clamp including one or more electrodes, the method comprising: disposing a component at a location adjacent to the electrostatic clamp; controlling the mechanism for generating free charge to generate free charge at a location adjacent to the electrostatic clamp; measuring a charge or current from a voltage supply device to the electrode or each electrode using at least one charge or current measuring device; calculating the capacitance of the electrode or each electrode using the measured charge or current to the electrode or each electrode; and determining the potential of a surface of the component adjacent to the electrostatic clamp using the calculated capacitance of the electrode or each electrode.

[0063] The method may further include setting the potential of one of the plurality of electrodes or each electrode such that the potential of the surface of the component adjacent to the electrostatic clamp is approximately a predetermined value.

[0064] The method may further include setting the potential of one of the plurality of electrodes or each electrode such that the predetermined value of the potential of the surface of the component adjacent to the electrostatic clamp is at least one of positive, negative, and approximately zero.

[0065] The method may further include setting the potential of at least one of the plurality of electrodes based on the ratio of the capacitances of the plurality of electrodes.

[0066] The method may further include setting the potential of at least one of the plurality of electrodes based on the variance of the capacitance of the electrodes or each electrode.

[0067] According to a tenth aspect of the invention, a computer program is provided, comprising computer-readable instructions configured to cause a processor to perform the methods described above. This has the advantage of not requiring additional hardware.

[0068] According to an eleventh aspect of the present invention, a computer-readable medium is provided, the computer-readable medium carrying a computer program as described above.

[0069] According to a twelfth aspect of the present invention, a computer device for operating a device is provided, comprising: a memory storing processor-readable instructions; and a processor arranged to read and execute the instructions stored in the memory; wherein the processor-readable instructions include instructions arranged to control the computer to perform the methods described above. Attached Figure Description

[0070] Embodiments of the invention will now be described by way of example only with reference to the accompanying schematic drawings, in which:

[0071] - Figure 1 Describes a lithography system including lithography equipment and a radiation source;

[0072] - Figures 2a to 2c An electrostatic fixture and pattern forming apparatus used in a photolithography apparatus according to an embodiment of the present invention are described;

[0073] - Figures 3a to 3c An electrostatic fixture and pattern forming apparatus used in a photolithography apparatus according to an embodiment of the present invention are described;

[0074] - Figures 4a to 4c An electrostatic fixture and pattern forming apparatus used in a photolithography apparatus according to an embodiment of the present invention are described;

[0075] - Figure 5 An electrostatic fixture and pattern forming apparatus used in a photolithography apparatus according to an embodiment of the present invention are described;

[0076] - Figure 6 Depicting based on Figure 5 A plan view of the electrostatic fixture and pattern forming apparatus used in a lithography apparatus;

[0077] - Figure 6a An electrostatic fixture and pattern forming apparatus used in a photolithography apparatus according to an embodiment of the present invention are described;

[0078] - Figure 7A plan view depicting an electrostatic fixture and pattern forming apparatus used in a photolithography apparatus according to an embodiment of the present invention;

[0079] - Figure 8 A plan view depicting an electrostatic fixture and pattern forming apparatus used in a photolithography apparatus according to an embodiment of the present invention;

[0080] - Figure 9 A plan view depicting an electrostatic fixture and pattern forming apparatus used in a photolithography apparatus according to an embodiment of the present invention;

[0081] - Figure 10 A schematic circuit diagram depicting an electrostatic fixture and pattern forming apparatus used in a photolithography apparatus according to an embodiment of the present invention is provided. Detailed Implementation

[0082] Figure 1 A lithography system including a radiation source SO and a lithography apparatus LA is shown. The radiation source SO is configured to generate an EUV radiation beam B and supply the EUV radiation beam B to the lithography apparatus LA. The lithography apparatus LA includes an irradiation system IL, a support structure MT configured to support a pattern forming apparatus MA (e.g., a mask or photomask), a projection system PS, and a substrate stage WT configured to support a substrate W.

[0083] The irradiation system IL is configured to adjust the EUV radiation beam B before it is incident on the pattern forming apparatus MA. Additionally, the irradiation system IL may include a faceted field mirror assembly 10 and a faceted pupil mirror assembly 11. The faceted field mirror assembly 10 and the faceted pupil mirror assembly 11 together provide the EUV radiation beam B with a desired cross-sectional shape and a desired intensity distribution. Besides, or in place of, the faceted field mirror assembly 10 and the faceted pupil mirror assembly 11, the irradiation system IL may include other mirrors or devices.

[0084] After such adjustment, the EUV radiation beam B interacts with the patterning apparatus MA. As a result of this interaction, a patterned EUV radiation beam B' is generated. The projection system PS is configured to project the patterned EUV radiation beam B' onto the substrate W. For this purpose, the projection system PS may include a plurality of mirrors 13, 14 configured to project the patterned EUV radiation beam B' onto the substrate W held by the substrate stage WT. The projection system PS can apply a reduction factor to the patterned EUV radiation beam B', thus forming an image with features smaller than the corresponding features on the patterning apparatus MA. For example, a reduction factor of 4 or 8 can be applied. Although the projection system PS in Figure 1 The image is shown with only two mirrors 13 and 14, but the projection system PS may include a different number of mirrors (e.g., six or eight mirrors).

[0085] The substrate W may include a previously formed pattern. In such a case, the photolithography apparatus LA aligns the image formed by the patterned EUV radiation beam B' with the pattern previously formed on the substrate W.

[0086] A relative vacuum can be provided in the radiation source SO, the irradiation system IL, and / or the projection system PS, i.e., a small amount of gas (e.g., hydrogen) at a pressure sufficiently below atmospheric pressure.

[0087] The radiation source SO can be a laser-generated plasma (LPP) source, a discharge-generated plasma (DPP) source, a free-electron laser (FEL) or any other radiation source capable of generating EUV radiation.

[0088] Figure 2a A cross-section of the support structure MT is shown in more detail. This cross-section is in the x-plane, extending vertically in the z-direction and horizontally in the y-direction in the shown orientation. The y-direction can be considered as the scanning direction of the lithography apparatus, and the x-direction can be considered as perpendicular to the scanning direction. The support structure MT includes an electrostatic clamp 100 configured to hold the pattern forming apparatus MA during lithography operations. The clamp 100 includes a generally planar clamping surface 102 and clamping electrodes A to D disposed within the clamp body. Electrodes 104A to 104D are separated from the clamping surface 102 of the clamp 100 by a dielectric coating. Protrusions (not shown) can protrude from the clamping surface 102 and are used to separate the clamped pattern forming apparatus MA from the clamping surface 102. The protrusions may, for example, have a height of about 10 μm and may collectively cover about 1% of the surface of the clamp 100. It should be understood that many features of the fixture 100 (such as wiring, additional electrodes) have been omitted for simplicity.

[0089] The fixture 100 can be considered as part of the lithography apparatus LA, or as a part of the apparatus forming the lithography apparatus LA or separate from the lithography apparatus LA. The lithography apparatus LA or the apparatus itself may include mechanisms for generating free charges.

[0090] The pattern forming apparatus MA is generally planar and has a first planar surface 122 and a second planar surface 124 opposite to each other. In use (e.g., as...) Figure 1As shown in the diagram, the first surface 122 is configured to reflect the radiation beam B, resulting in a pattern being applied to the beam B. Specifically, areas of the first surface 122 can be patterned to cause the radiation beam B to become patterned. The patterned areas of the first surface 122 have a conductive coating. The first surface 122 may be referred to as the front side, or front face, of the pattern forming apparatus MA. That is, the front side of the mask is the surface of the pattern forming apparatus MA that faces away from the electrostatic fixture 100.

[0091] In order for the electrostatic clamp 100 to hold the pattern forming apparatus MA, the second surface 124 has a conductive coating that typically covers most of the second surface 124. The second surface 124 may be referred to as the back surface of the pattern forming apparatus MA. That is, the back surface of the pattern forming apparatus MA is the surface of the pattern forming apparatus MA facing the electrostatic clamp 100. In other words, the back surface of the pattern forming apparatus MA is the surface of the pattern forming apparatus MA adjacent to the electrostatic clamp 100.

[0092] A base plate 126 facing the first surface 122 of the pattern forming apparatus MA is located on the opposite side of the electrostatic fixture 100. The base plate 126 is part of an exchange device for transferring the mask MA to and from the photolithography apparatus LA. The base plate 126 is grounded and can be at approximately 0V.

[0093] It should be understood that the electrostatic clamp 100 can use a voltage of approximately several kV to clamp the pattern forming apparatus MA. For example, the clamp 100 can be a bipolar electrostatic clamp, wherein a first subset 104A, 104C of electrodes 104A to 104D is connected to one or more voltage supply devices (not shown) of approximately +1 to 10 kV (e.g., +2 kV), and a second subset 104B, 104D of electrodes 104A to 104D is connected to one or more voltage supply devices of approximately -1 to 10 kV (e.g., -2 kV). In this way, a high electric field can be established between the clamp 100 and the pattern forming apparatus MA, thereby causing the pattern forming apparatus MA to be attracted to the clamp 100. Specifically, charges are induced in the conductive coating region of the second surface 124 adjacent to the electrodes 104A to 104D. These charges have the opposite sign to the applied voltage and create an attractive force between opposite charges across various locations of the clamp 100 and the pattern forming apparatus MA. The region of the clamp 100 configured to support the pattern forming apparatus MA can be referred to as a support region. Furthermore, the region of the clamp 100 configured to generate a clamping force when the clamp 100 is operated to hold the pattern forming apparatus MA can be referred to as a clamping region.

[0094] The electrostatic clamp 100 can operate in a first mode, in which electrodes 104A to 104D are set to multiple potentials such that a clamping electric field is generated between the electrostatic clamp 100 and the mask MA to clamp the mask MA. In this first mode, electrodes 104A to 104D can be balanced, i.e., the average potential of electrodes 104A to 104D can be approximately 0V. The electrostatic clamp 100 can operate in a second mode, in which electrodes 104A to 104D are set to multiple potentials such that no clamping electric field or a relatively small clamping electric field is generated between the electrostatic clamp 100 and the mask MA. For example, a minimum of 300V is typically required to overcome the gravity of the mask MA. Therefore, clamping will not exist below 300V. This value can vary depending on the quality of the clamping surface, and thus can be 100V or 200V, etc. Therefore, in the second mode, the potentials of electrodes 104A to 104D are set such that the clamping of the mask MA is released. In the second mode, electrodes 104A to 104D can also be balanced, meaning the average potential of electrodes 104A to 104D can be approximately 0V. Operating the clamp 100 in both the first and second modes can be considered normal operation.

[0095] Each of the electrodes 104A to 104D has a rectangular shape and is arranged such that they are substantially parallel to each other. In such an arrangement, the four electrodes illustrated each span the width of the clamped pattern forming apparatus MA in the x-direction and each covers approximately one-quarter of the length of the pattern forming apparatus MA in the y-direction. It should be understood that in other embodiments, different numbers of electrodes may be used, such as 1, 2, 3, 5, 6, 7, 8 or more.

[0096] During normal operation of the fixture 100, an electric field will be established between the surface of the fixture 100 and the surface of the patterning apparatus MA. Furthermore, electrostatic discharge (ESD) may occur due to the close separation / separation between the various charged surfaces (including other components within the lithography apparatus, such as, for example, shielding blades). That is, ESD can occur between any charged surfaces, with the possibility that the discharge increases with increasing electric field strength. ESD can damage components. ESD can generate particles from the surface and can also release particles previously attached to surfaces within the lithography apparatus. It should be understood that such particle release is undesirable in the lithography apparatus because particles may fall onto critical areas of the apparatus, potentially causing patterning defects in the processed substrate.

[0097] The high electric field generated by the electrostatic fixture strongly attracts any free charges. Free charges are those that are not bound to the solid substrate but move freely according to the electric field lines (positive charges, such as ions, or negative charges, such as electrons). Furthermore, sufficient free charges are generated during EUV exposure. For example, electrons can be generated by light emission and also from EUV-induced plasma, which is typically generated in the presence of hydrogen gas (often present in lithography tools). Positive ions can also be generated within the EUV plasma.

[0098] The plasma generation process will now be discussed in more detail. It should be understood that the EUV photons within beam B ionize hydrogen molecules, thereby generating H2+ ions and free electrons. In the example using 13.5 nm EUV radiation, each photon can have an energy of approximately 92 eV, where the ionization energy of molecular hydrogen is approximately 15 eV. Therefore, the resulting free electrons can have sufficient energy (e.g., >75 eV) and range to generate secondary plasma relatively far from the initial ionization event. Furthermore, electrons released in this way (i.e., with an energy of approximately 75 eV) can ionize one, two, or even three additional hydrogen molecules. Thus, even if primary plasma is generated only at the EUV photon incident point, secondary plasma can be generated near the fixture.

[0099] In the embodiments, it should be understood that EUV-induced plasma needs to be generated, which provides a source of free charge to the vicinity of the pattern forming apparatus MA.

[0100] In some embodiments, a secondary ionization source may be provided, thereby allowing plasma to be generated near the electrostatic clamp by means other than the EUV source SO. This arrangement can reduce the overall output load of the EUV source SO. It should be understood that the embodiments described above can impose additional requirements on the EUV source SO by requiring additional EUV output compared to the EUV output needed for imaging. Additionally, in some embodiments, the EUV source may not be able to generate power continuously. Similarly, it is not possible and / or desirable for the EUV source to provide arbitrary EUV pulse energy within the range of 0% to 100% of the nominal output power while simultaneously ensuring clean collector operation and pulse energy stability.

[0101] Thus, in some embodiments, alternative mechanisms may be preferably provided for generating regions with increased gas conductivity compared to the primary EUV source.

[0102] For example, the source can be positioned close to the electrostatic clamp 100 and the pattern forming apparatus MA held therein. Multiple sources can be used. For example, the source can be a soft X-ray source or a VUV source capable of operating in a clean environment at pressures below 1 bar. The source can include a low-power ionizer with a power of about 0.1 W to 1 W. In some embodiments, the source can include a radiation source or an electron beam source.

[0103] Typically, both the EUV source SO and the source (which may include, for example, a soft X-ray source or a VUV ionizer) can be considered examples of ionizing radiation sources. Additionally, such a source combined with a hydrogen (or other) gas source can be considered a mechanism for generating free charges. That is, a hydrogen plasma containing both positive ions and free electrons can be considered a cloud of free charges. Furthermore, such free charges include both positive and negative free charges.

[0104] A considerable voltage can be established between the clamp 100 and the pattern forming device MA after the pattern forming device MA is removed from the clamp 100.

[0105] It should be understood that capacitance exists between several components in the lithography apparatus LA. Specifically, the capacitance between the clamping surface 102 and the second surface 124 of the patterning apparatus MA can be considered a variable capacitance, varying depending on the gap between the clamping surface 102 and the second surface 124. Similarly, the capacitance between the substrate 126 and the first surface 122 of the patterning apparatus MA can be considered a variable capacitance, varying depending on the gap between the substrate 126 and the first surface 122.

[0106] It should be understood that in a closed system, under conditions where no charge can enter or leave the system and for a given initial charge state, any change in the separation between the fixture 100 and the pattern forming apparatus MA, and any change in the separation between the pattern forming apparatus MA and the base plate 126, will result in a corresponding change in the variable capacitance. Furthermore, this change in capacitance will also cause the voltage across the capacitor to potentially change significantly depending on the change in separation.

[0107] Specifically, the relationship Q = CV must always be maintained for each capacitor (assuming no charge is injected). Therefore, if the capacitance C changes while the amount of charge Q contained in the capacitor remains the same, the voltage V must change inversely proportional to the changed capacitance C. This can result in significant voltage amplification. The most significant voltage change occurs on the back side of the patterning apparatus MA, specifically between the clamping surface 102 and the second surface 124 of the patterning apparatus MA.

[0108] The resulting high voltage should be understood as significantly increasing the risk of discharge due to the dissociation / breakdown of hydrogen near the patterning apparatus MA and the electrostatic clamp 100 (e.g., due to the voltage at the surface of the patterning apparatus MA exceeding the minimum Paschen limit of hydrogen, which is approximately 250V).

[0109] Therefore, an opportunity for electrostatic discharge exists within the lithography apparatus LA during the unloading of the patterning apparatus MA after clamping. Charge can become trapped at the dielectric surface of the clamp 100. Furthermore, residual charge can remain on the clamped patterning apparatus MA once it has been released. As the released patterning apparatus MA is moved away from the clamp surface, the increased separation between the clamp surface and the patterning apparatus surface can lead to a decrease in capacitance and an amplification of voltage. That is, given the proportional relationship between charge and voltage in a closed system (i.e., Q = CV), any decrease in capacitance (inversely proportional to the separation between the parallel plates) will result in a proportional increase in voltage. Therefore, as the patterning apparatus MA separates from the clamp 100, the voltage of the patterning apparatus may rise sufficiently to cause hydrogen breakdown. This discharge can lead to damage to the patterning apparatus MA, the electrostatic clamp 100, and / or particle generation, which may result in subsequent defects.

[0110] The effects of changing capacitance can be mitigated to some extent by introducing free charges during the unloading process. For example, a standalone ionization source, or in fact, the EUV source SO described above, can be used to generate hydrogen plasma, which provides free charges (as described in detail above) and allows relaxation, i.e., loosening of the field established across various dielectric components (and gaps), during the removal process.

[0111] Providing free charges can lead to a significant reduction in the voltage established between various system components. That is, the electric field established by a high voltage can be compensated for by introducing additional free charges. These charge sources are effectively provided by hydrogen plasma. The free charges within the plasma are driven by any electric field that begins to be established and cause those fields to collapse / collapse.

[0112] In this way, the potential problems associated with establishing a significant voltage across the patterning apparatus MA after removal from the electrostatic clamp 100 can be mitigated or completely avoided. As mentioned above, it should be understood that this effect is not binary, and some (reduced intensity) field can still be established if insufficient charge is provided. However, it should be understood that even a reduction (rather than complete avoidance) of the voltage amplification can be beneficial, especially if the voltage is thus always kept below the minimum Paschen limit of hydrogen (approximately 250V).

[0113] Furthermore, free charges can be provided at various times during the separation of the pattern forming apparatus MA from the clamp 100. In practice, it should be understood that when the pattern forming apparatus MA is clamped, free charges may have difficulty penetrating between adjacent surfaces. Therefore, there can exist an effective minimum separation degree for optimally providing free charges.

[0114] The mask (patterning apparatus) may suffer irreversible damage due to residual charges accumulating on the front and rear surfaces of the mask during EUV radiation exposure and mask transport (e.g., mask loading and unloading). As mentioned, such residual charges can cause electrical breakdown during mask unloading, resulting in the overall loss of the mask. The mask can be removed from the lithography apparatus LA, where the mask potential is approximately 600V, corresponding to a very large negative residual charge of approximately 50nC.

[0115] Due to EUV radiation, the mask acquires charge, generating rapid electrons that charge the floating mask surface to a small potential of approximately -10V. Alternatively, residual charge on the back side of the mask may be caused by triboelectric charging (i.e., friction between the mask surface and jig protrusions made of different materials).

[0116] As mentioned, during mask unloading, the capacitance of the mask-fixture system decreases, causing the potential on the back side of the mask to increase to approximately -600V. In some cases, this can lead to electrical breakdown, resulting in damage to the attached mask surface.

[0117] The residual charge on the mask BS also causes a high field between the front side of the mask and the base plate, resulting in particle hopping from the base plate to the mask FS during mask transport in the scanner.

[0118] Mask grounding can be achieved without additional hardware by utilizing EUV-induced plasma as a charge source capable of reducing mask potential. However, the amount of charge carriers, such as 50 nC, provided to the back surface of the mask is limited by the amount of plasma generated by EUV radiation. Furthermore, the plasma density is reduced due to the complex geometry of the environment surrounding the mask and the constraints of the hardware associated with mask unloading. Therefore, achieving mask grounding (i.e., soft grounding) using EUV-induced plasma without additional assistance may result in a throughput loss, i.e., an increased time spent transferring the substrate W through the lithography apparatus LA, which is undesirable.

[0119] Figure 2aThe diagram shows the general relative values ​​of the polarity and potential of the four electrodes 104A to 104D of the electrostatic clamp 100 operating in the third mode. Specifically, in one embodiment, electrodes 104A and 104D have positive potentials (+), and electrodes 104B and 104C have negative potentials (--, -), wherein the value of electrode 104B is greater than the values ​​of the other electrodes. This means that the average potential of all electrodes 104A to 104D is negative.

[0120] The pattern forming apparatus MA has an edge 128 (or end point), which in this embodiment is closest to the EUV radiation beam B and therefore closest to the EUV-induced plasma. Electrode 104A may be referred to as the edge electrode. In this embodiment, the edge electrode 104A has a positive potential, as mentioned above.

[0121] Electrodes 104 to 104D are set to these potentials before EUV radiation is turned on to generate plasma. In the absence of plasma, the mask MA will float, and since the average potential of all electrodes 104A to 104D is negative and the base plate 126 is located on the other side of the mask MA, a capacitively induced negative potential will exist on the mask MA. For example, the base plate 126 may be at approximately 0V, the clamp 100 may be at approximately -1000V, and therefore the mask MA may be at approximately -900V due to capacitively induced current. Since the second surface 124 of the mask MA is closer to the clamp 100, which has a negative potential, the second surface 124 will have a more negative value than the first surface 122 of the mask MA. In other embodiments, the base plate does not need to be in place, and in other embodiments, the base plate can be interchanged with different components. In other embodiments, the electrodes can be set to these potentials when EUV radiation has already been turned on, i.e., during plasma generation.

[0122] This electrode arrangement provides an increased positive ion flux to the second surface 124 of the patterning apparatus MA, while suppressing the positive ion flux toward the clamping surface 102 (and other clamping surfaces) of the jig 100. The arrangement of electrodes 104A to 104D provides a positive near field at the mask edge 128 and provides additional negative bias to the second surface 124 of the mask MA (i.e., the surface adjacent to the jig 100), which increases the positive ion flux toward the mask MA. This is because electrode 104A at the edge 128 is positive and thus pushes positive ions away from the jig 100 toward the mask MA, and also because the capacitance-induced potential of the overall average negative potential from electrodes 104A to 140D on the mask MA attracts positive ions toward the second surface 124 of the mask MA. Since the second surface 124 has a more negative value compared to the first surface 122, more positive ion flux will be attracted to the second surface 124.

[0123] It should be understood that operation of the electrostatic clamp 100 in the third mode means that, compared to normal operation of the electrostatic clamp 100 (i.e., operation in the first or second mode), electrodes 104A to 104D have a potential that increases the positive ion flux to the mask MA. Previously, the clamp was not intended to be set to an overall average negative or positive potential with the electrodes, and therefore the flux of free charge (electrons or ions) to the mask would not increase significantly when EUV radiation is turned on. Furthermore, it should be understood that the third operating mode of the electrostatic clamp 100 may include operating such that the electrostatic clamp 100 clamps the mask MA and / or operating such that the electrostatic clamp does not clamp the mask MA.

[0124] Figure 2b and Figure 2c The electrostatic clamp 100 is shown operating in a third mode, having a similar electrode arrangement with a positive edge electrode 104A and the average potential of electrodes 104A to 104D being negative. However, in Figure 2b In this configuration, electrode 104C has a positive potential, while electrodes 104B and 104D have negative potentials. The potential of electrode 104B is still greater than the potentials of the other electrodes. Figure 2c In the figure, electrode 104B has a positive potential and electrodes 104C and 104D have negative potentials, wherein the potential of electrode 104C is greater than the potential of the other electrodes.

[0125] These arrangements of electrodes 104A to 104D, and more specifically, the particular arrangement of the voltages applied to electrodes 104A to 104D, enable accelerated neutralization of residual charge during unloading of the mask MA. This acceleration is achieved by using electrodes 104A to 104D as an additional E-field source to provide a higher plasma flux toward the surface of the mask MA. That is, the voltages of the electrodes 104A to 104D of the electrostatic clamp 100 are set such that the net positive charge from the plasma will be attracted to the (primary) rear surface 124 and (secondary) front surface 122 of the mask MA.

[0126] Therefore, it can enhance the compensation of residual charge on the mask MA by the plasma induced by EUV during the unloading / loading operation of the mask MA.

[0127] Other advantages include: no hardware changes are required, saving on commodity costs and shortening development time. Implementations can be carried out on any lithography equipment (LA). Furthermore, embodiments can be customized for specific and unusual mask (MA) cases (such as the use of modified back-side coated mask MAs). Additionally, the contactless grounding scheme can increase the lifespan of the fixture 100 / mask MA.

[0128] Figures 3a to 3c Another embodiment of the electrostatic clamp 100 operating in a third mode is shown, wherein the general relative values ​​of the polarity and potential of the four electrodes 104A to 104D are identified.

[0129] exist Figure 3a In this embodiment, each of electrodes 104A to 104D has a negative potential, wherein the magnitude of the potential of electrodes 104B to 104D is greater than the magnitude of the potential of electrode 104A (edge ​​electrode). This means that the average potential of all electrodes 104A to 104D is still negative. Edge electrode 104A is negative, but the average potential of all electrodes has an even greater negative value compared to edge electrode 104A. This electrode arrangement provides increased throughput to the second surface 124 of the mask MA while simultaneously suppressing throughput to the fixture surface 102.

[0130] Therefore, a similar method can be applied to achieve a <0 (negative) capacitively induced potential on the mask MA by applying a net additional negative bias to electrodes 104B to 104D and combinations thereof. The arrangement of electrodes 104A to 104D provides a near-field at the mask edge 128, which has less negative value compared to the rest of the second surface 124 of the mask MA, and provides an additional negative bias to the second surface 124 of the mask MA (i.e., the surface adjacent to the fixture 100), which increases the positive ion flux toward the mask MA. This can also be achieved through a potential imbalance on the positive electrode.

[0131] Figure 3b and Figure 3c The electrostatic clamp 100 is shown operating in a third mode, having a similar electrode arrangement with negative edge electrodes 104A and the average potential of electrodes 104A to 104D having more negative values. However, in Figure 3b In this electrode, electrodes 104B and 104D have positive potentials, while electrode 104C has a negative potential and a much larger potential value compared to the other electrodes. Figure 3c Implementation examples and Figure 3b The embodiments are the same, except that the potentials of electrodes 104B and 104C have been swapped.

[0132] When the clamping of the mask MA is released and while the mask MA is still held by the clamp 100, an unbalanced / unequalized electrode potential can be applied before the EUV radiation beam B is "turned on". Therefore, the embodiment enables the mask MA to be grounded while it is still on the electrostatic clamp 100, which allows the mask MA to be grounded before the release action begins, and thus minimizes the risk of damage to the mask MA due to discharge. When the mask MA is still close to the clamp 100, or even still physically connected to the clamp 100, the residual charge on the mask MA can be reduced to zero. Therefore, the risk of damage to the mask MA due to discharge is significantly minimized when the gap between the mask MA and the clamp 100 becomes too large during unloading (in the presence of a fixed charge, the voltage increases when the capacitance is reduced by increasing the gap).

[0133] Figures 4a to 4c Another embodiment of the electrostatic clamp 100 operating in a third mode is shown, wherein the general relative values ​​of the polarity and potential of the four electrodes 104A to 104D are identified.

[0134] exist Figure 4a In the embodiment, the edge electrode 104A is positive, and in Figures 2a to 2cSimilar to the previous example, but the other electrodes 104B to 104D have potentials and potential values ​​such that the average potential of all electrodes 104A to 104D is approximately 0V. More specifically, electrodes 104A and 104D have positive potentials (+) and electrodes 104B and 104C have negative potentials (-), wherein the potential values ​​of each of the electrodes 104A to 104D are approximately the same.

[0135] Therefore, the capacitively induced potential on the mask MA (particularly on the second surface 124) remains constant. The edge electrode 104A (which has a positive potential in this case) protects the jig 100 from attracting positive ions and thus increases the positive ion flux to the second surface 124 of the mask MA, as well as protecting the jig protrusions (not shown) from sputtering. This helps maintain a relatively long lifetime of jig functionality. Even in this embodiment, where the capacitively induced potential on the mask MA is approximately 0V, the positive ion flux to the mask MA increases as positive ions are directed away from the jig 100 by the positive edge electrode 104A.

[0136] The arrangement of electrodes 104A to 104D provides a positive near field at the edge 128 of the mask, thereby increasing the positive ion flux toward the mask MA while maintaining an additional zero bias voltage to the second surface 124 of the mask MA.

[0137] Figure 4b and Figure 4c The electrostatic clamp 100 is shown operating in a third mode, having a similar electrode arrangement with a positive edge electrode 104A and an average potential of approximately 0V for electrodes 104A to 104D. However, in Figure 4b In the diagram, electrodes 104B and 104D have negative potentials, while electrode 104C is positive. The magnitude of the potential of each of electrodes 104A to 104D is related to the potential in... Figure 4a They are roughly the same. Figure 4c Implementation examples and Figure 4b The embodiments are the same, except that the potentials of electrodes 104B and 104C have been swapped.

[0138] Figures 4a to 4c The embodiments create conditions for plasma flux (positive ions) primarily directed toward the second surface 124 of the mask MA, while simultaneously suppressing the positive ion flux toward the clamp 100. This primarily helps to minimize damage to the clamping surface 102 (and other clamping surfaces).

[0139] It should be understood that the above description Figures 2a to 4cThe exact configuration of electrodes 104A to 104D is merely exemplary, and in other embodiments, they may have different polarities and magnitudes, as long as they provide the described advantages. For example, in Figure 4c In this configuration, the polarities of electrodes 104B and 104C can be interchanged, and the potential values ​​of both electrodes 104B and 104C can be increased to approximately larger values ​​compared to electrodes 104A and 104D, provided that the values ​​are roughly matched. Even in this case, there will still be an edge electrode 104A with a positive potential, and the overall average potential of the electrodes will be approximately 0V.

[0140] Modeling the plasma flux to the mask MA allows for the representation of the positive ion flux to the second surface 124 of the mask MA, enabling charge compensation within a fraction of a second (e.g., approximately 0.1 s). This facilitates the achievement of throughput neutralization for a soft grounded mask MA.

[0141] The embodiment may result in approximately 10 times higher neutralization of residual charge on the second surface 124 of the mask MA, thereby enabling throughput neutralization of the soft mask ground during unloading (and loading) of the mask MA.

[0142] Another embodiment involves configuring the electrostatic fixture 100 to operate in a third mode such that electrodes 104A to 104D have an average negative potential before exposure by the patterning apparatus (mask) MA (i.e., when the radiation beam B is incident on the patterning apparatus MA to provide the reflected patterned EUV radiation beam B' onto the substrate). For example, electrodes 104A to 104D can be configured to have an average negative potential similar to that in... Figures 2a to 2c or Figures 3a to 3c Another configuration where the same potential is present, or where the average potential of electrodes 104A to 104D is negative.

[0143] This method aims to induce a positive charge on the mask MA (specifically, the second surface 124 of the mask MA) so that the neutralization of the residual charge on the mask MA upon unloading will be achieved by electrons (rather than by positive ions as in the previous embodiment). This utilizes the higher electron mobility compared to ions, thus achieving neutralization much faster (several orders of magnitude faster, i.e., neutralization can be achieved in just 0.1 s instead of 10 s). This method can also achieve rapid neutralization of a back-side trimmed mask MA. This is because the neutralization of a back-side trimmed mask is slower due to the removal of approximately 1 mm of metallic coating on the back side of the mask at the edge. The ion flux to this trimmed back-side coating needs to pass through a narrow slit—i.e., the space / gap between the fixture and the back side of the mask. The chance of ions penetrating into such a slit is relatively very low, which is not a problem for electrons. For example, a 2 mm coating retraction would result in back-side neutralization by ions for an indefinite time, but by electrons, it would still be completed in just a few seconds.

[0144] For example, to induce a positive charge on the mask MA during exposure, the fixture electrodes 104A to 104D are configured to provide a negative mask MA offset potential of approximately -1 to -100V before exposure. Once exposure stops, i.e., once the EUV radiation beam B is no longer incident on the pattern forming apparatus MA, the mask MA will have a positive charge (instead of the negative charge described above). To achieve this, one or more negative electrodes are set to a higher potential than the positive electrodes. For example, two positive electrodes are set to +1kV and two negative electrodes are set to -1.1kV. Due to this, electrons will be repelled from the mask MA and positive ions will be attracted to the mask MA, thus establishing a positive charge on the mask MA after exposure.

[0145] When the mask MA is still close to or even physically connected to the fixture 100, the residual charge on the mask MA can be reduced to zero. This significantly minimizes the risk of damage to the mask MA due to discharge when the gap between the mask MA and the fixture 100 becomes too large during unloading.

[0146] The conditions described above, namely that the average potential of electrodes 104A to 104D is set to negative, can be maintained for the entire exposure duration or for only a portion of the time prior to the mask MA unloading operation. In some embodiments, the electrodes may be set to a certain state (e.g., configuration and / or specific potential) for only a portion of the exposure time. The electrodes do not necessarily need to be configured the same for the entire exposure duration. It may be necessary to set the electrodes to a balanced state (i.e., averaging zero) to ensure the mask becomes neutral.

[0147] Another embodiment aims to prevent the mask MA from becoming charged during exposure. Again, this embodiment involves setting the electrostatic clamp 100 in a third mode such that electrodes 104A to 104D have an average negative potential before exposure of the patterning apparatus (mask) MA (i.e., when the radiation beam B is incident on the patterning apparatus MA to provide the reflected patterned EUV radiation beam B' to the substrate). However, in this embodiment, the potentials of electrodes 104A to 104D are set to provide a negative offset within a specific potential value. This specific value can be calibrated to a specific mask MA and exposure conditions, such as the EUV dose. This specific value can be measured from a previous exposure and then fed forward. For example, for one mask, the specific value can be set such that it provides a potential of -2V on the mask and for another mask MA, the potential could be -10V. Setting the mask MA to a calibration value (i.e., -2V) means that throughout the exposure, the potential of the mask MA will not increase or decrease significantly overall because the charge transfer caused by electrons and ions will be offset / balanced. Therefore, at the end of the exposure, the mask MA will have the same or similar charge (e.g., -2V) as the previous exposure. In other embodiments, specific values ​​can be set such that they provide a potential on the mask in the range of 0V to -20V.

[0148] The specific values ​​of the negative potentials of electrodes 104A to 104D can be selected such that the mask MA is substantially uncharged, i.e., approximately zero-charged, after exposure. This means that during unloading (i.e., when the mask MA is removed from the fixture 100), the potential difference between the second surface 124 of the mask MA and the clamping surface 102 of the fixture 100 will not increase significantly, as seen when the mask MA remains charged after exposure. The near-zero residual charge of the mask MA while it remains close to, or even physically connected to, the fixture 100 significantly minimizes the risk of damage to the mask MA due to discharge should the gap between the mask MA and the fixture 100 become too large during unloading. In other embodiments, the specific value may be selected such that the potential on the mask MA matches the potential on the fixture 100, so that the potential difference between the second surface 124 of the mask MA and the clamping surface 102 of the fixture 100 will not increase relatively.

[0149] The conditions described above can be maintained for the entire duration of exposure, or for only a portion of the time before the mask MA unloading action, i.e., the average potential of electrodes 104A to 104D is set to a specific negative value.

[0150] It should be understood that embodiments can be implemented by changing the software process without changing the hardware. This means that lithography equipment (LA) in the art can be implemented relatively quickly with little impact on production. Furthermore, embodiments can be reversible and flexible. They can be used as temporary mitigation strategies (i.e., turned on and off as needed or to be tuned).

[0151] Because this embodiment does not require additional hardware, it can save on commodity costs compared to other methods of grounding the mask (e.g., during unloading). This embodiment can be directly applied to all EUV lithography equipment (LA) and may result in improved reliability and availability of the LA. Additionally, this embodiment can be implemented using throughput neutralization of the mask grounding. This embodiment may lead to higher yields.

[0152] Figure 5 An embodiment of an electrostatic clamp 200 in which the polarities of four electrodes 204A to 204D are identified is shown. The components of the electrostatic clamp 200 are similar to those of the electrostatic clamp 100 of the previous embodiment, and similar components will be provided with similar reference numerals increased by 100.

[0153] exist Figure 5 In the embodiments, electrodes 204A to 204D and Figure 4a Electrodes 104A to 104D are identical. Therefore, the potential induced by capacitance on the mask MA (particularly on the second surface 224) remains constant (i.e., approximately 0V in this embodiment). However, this is merely an example, and electrodes 204A to 204D can have different polarities and magnitudes, such as those shown in the previous embodiments. In any case, electrodes 204A to 204D provide clamping for the pattern forming apparatus (mask) MA.

[0154] exist Figure 5 In one embodiment, there is an additional (or fifth) electrode 204E. This additional electrode 204E does not participate in clamping the mask MA. The additional electrode 204E is located in the same plane as electrodes 204A to 204D. The additional electrode 204E is located in a different plane from the mask MA. In this embodiment, the additional electrode 204E is above the mask MA, such as... Figure 5 As shown.

[0155] The additional electrode 204E is positioned at least partially around a (hypothetical) volume 230 that extends from the second surface 224 (back side) (i.e., the z-direction) of the mask MA in the direction of the electrostatic clamp 200. In other words, the additional electrode 204E is positioned around a space / spacing above the second surface 224 of the mask MA. The second surface 224 may be referred to as the surface of the mask MA adjacent to the electrostatic clamp 200.

[0156] Volume 230 is shown as a dashed line extending from the edge (or end) 228 of the mask MA and the opposite ends of the mask MA. It should be understood that... Figure 5 The right-hand side is not shown in its entirety for the mask MA, and volume 230 can be considered to extend on both sides to the edges of the mask MA. In this embodiment, the edges 228 are closest to the EUV radiation beam B and therefore closest to the EUV-induced plasma.

[0157] Figure 6 The additional electrode 204E and the pattern forming apparatus MA are shown from above (i.e., in plan view)—electrodes 204A to 204D and the middle portion of the electrostatic jig 200 are not shown for clarity. The additional electrode 204E is shown as extending entirely (i.e., completely) around volume 230. The additional electrode 204E may be coated onto the dielectric of the electrostatic jig 200. In fact, the area around the mask MA is coated with electrode 204E. The additional electrode 204E may be a thin metal coating.

[0158] The additional electrode 204E can be made of any suitable conductive material. For example, a material that is compatible with plasma and does not present any problems. As an example, chromium nitride can be used as the material for the additional electrode 204E.

[0159] A mask can collect electrical charge. Unloading a charged mask will cause an increase in the mask voltage. This may lead to discharge and the generation of particles or damage.

[0160] The voltage on the additional electrode 204E can be controlled. For example, in this embodiment, the potential on the additional electrode 204E is set to negative. This establishes an electric field around the mask MA. This means that electrons (i.e., free charges) generated by the mechanism can be repelled away from the second surface 224 of the mask MA. This means that the number of electrons reaching the mask MA is reduced. Thus, the mask can be prevented or at least its charge can be reduced. This can prevent electrical breakdown that could damage the mask surface (e.g., during mask unloading). The magnitude of the potential of the additional electrode 204E may not be comparable to that of electrodes 204A to 204D; for example, it may be much smaller.

[0161] It should be understood that in other embodiments, the additional electrode 204E can be set to positive. This establishes an electric field around the mask MA. This means that positive ions (i.e., free charges) generated by the mechanism can be repelled away from the second surface 224 of the mask MA. This means that the number of positive ions reaching the mask MA will be reduced. Thus, the mask will be prevented or at least its charge will be reduced. This can prevent electrical breakdown that could damage the mask surface (e.g., during mask unloading).

[0162] More typically, the device can be configured such that the additional electrode 204E is positioned such that the flux of free charge to the second surface 224 generated by the mechanism is reduced. This flux of free charge can be considered reduced when there are no electrodes around the mask, or when the additional electrode has a potential of 0 volts.

[0163] It should be understood that any size of the additional 204E electrode will provide some benefits. However, the larger the electrode (e.g., in the y-direction), the more it repels charged particles, because a larger electrode can generate a larger electric field.

[0164] It should be understood that any combination of negative (or positive) voltages on the additional electrode 204E will provide some benefit. However, a larger voltage will repel charged particles more strongly, because a larger voltage can generate a larger electric field. For example, the voltage could be 10, 20, or 50 volts.

[0165] The surface of the additional electrode 204E may be flat. However, in other embodiments, the surface may not be flat. For example, in one embodiment, the additional electrode 204E may have rounded corners in the region corresponding to the corner of the mask MA. This can increase the electric field. More typically, at least one or more edges of the additional electrode 204E (i.e., the edges of the surface adjacent to the mask MA) may be rounded.

[0166] In an embodiment, an additional electrode 204E may be in electrical contact with the mask MA (e.g., the second surface 224 of the mask MA). This allows for direct control of the potential of the second surface 224 of the mask MA. This allows for greater repulsion of charged particles (e.g., electrons). The electrical contact may be achieved through one or more protrusions. The one or more protrusions may be located within volume 230.

[0167] In some embodiments, an electrical conductor (e.g., an existing grounding wire) can be used as an additional electrode 204E. In such cases, an electrical supply device can be connected to the grounding wire and voltage can be supplied to the grounding wire.

[0168] The potential of the additional electrode 204E can be set to persist for at least a portion or all of the time during which the mechanism generates free charge (e.g., during the exposure of the mask MA). The potential of the additional electrode 204E can also be set to persist for a period of time before the mask MA moves from being held by the electrostatic clamp to being separated from the electrostatic clamp (e.g., just before the clamping of the mask MA is released).

[0169] Figure 6a Another embodiment of the electrostatic clamp 200 is shown. This embodiment is similar to... Figure 5 The embodiments are similar, except that the additional electrode 204E is located on the other side of the clamping surface 202 and includes multiple walls. That is, the walls can be considered to extend upward (i.e., in the z-direction) from the additional electrode 204E to partially surround the sidewall electrode 204F of the electrostatic clamp 200, and to extend downward (i.e., in the opposite direction to the sidewall electrode 204F) from the additional electrode 204E to partially surround the wall electrode 204G that implements the mask MA. The walls can be metal plates. It should be understood that in some embodiments, both the sidewall electrode 204F and the wall electrode 204G are not required. Furthermore, in some embodiments, one or both of the sidewall electrode 204F and the wall electrode 204G can be included in electrode 204E or replace the additional electrode 204E. In other embodiments, the additional electrode 204E may also be located as... Figure 5 In the positions shown, and the sidewall electrode 204F and / or wall electrode 204G can be in the positions shown, as Figure 6a The location shown in the image.

[0170] In some embodiments, the additional electrode 204E may also be set to a voltage that depletes the free charge in the volume surrounding the MA. This can have the advantage of preventing free charge from reaching the mask MA (and charging the mask MA). This may only be possible if the additional electrode 204E is not coated with an insulating surface. For example, this may be possible if the coating is as follows: Figure 6a It is possible to have sidewall electrodes 204F and wall electrodes 204G as described above.

[0171] Figure 7 Another embodiment of the electrostatic clamp 200 is shown. This embodiment is similar to... Figure 6 The embodiment is the same, except that there is a space (gap) 232 between volume 230 and the other electrode 204E. That is, the other electrode does not need to be precisely around volume 230.

[0172] Figure 8 Another embodiment of the electrostatic clamp 200 is shown. This embodiment is similar to... Figure 6The embodiment is the same, except that the additional electrode 204E is located only on one side of the mask MA. Therefore, the additional electrode 204E can be considered to at least partially surround the volume 230.

[0173] In this embodiment, the additional electrode 204E is positioned adjacent to the edge 228, which is closest to the EUV radiation beam B and thus closest to the EUV-induced plasma. This side corresponds to the principal direction of charged particles, and therefore, it is preferable to have the additional electrode 204E on this side compared to having it on only one of the other sides. It should be understood that in other embodiments, the additional electrode 204E may extend more or less in the x-direction. It should be understood that in other embodiments, the additional electrode 204E may be on a different side from the edge 228.

[0174] Figure 9 Another embodiment of the electrostatic clamp 200 is shown. This embodiment is similar to... Figure 6 The embodiment is the same, except that there are four additional electrodes 204E. That is, the additional electrodes 204E are located on each side of the mask MA. In this embodiment, there are gaps between the additional electrodes 204E. Thus, the four additional electrodes 204E can be considered to at least partially surround the volume 230. In other embodiments, where there are no or substantially no gaps between the additional electrodes 204E, the plurality of electrodes can be considered to completely surround the volume 230. It should be understood that in the embodiments, there may be more or fewer additional electrodes than four, such as two, three, five, or six, etc. For example, if there are two additional electrodes, they may be located on two different sides, such as adjacent or opposite sides, or they may be located on the same side.

[0175] In embodiments, the additional electrodes 204E may operate independently, in pairs, or in any other configuration. For example, one of the additional electrodes 204E may be positively charged, the other electrode may be negatively charged, and the other additional electrode 204E may be configured such that the flux of free charge generated by the mechanism to the second surface 224 is reduced.

[0176] refer to Figure 4c Now, another embodiment will be described. Figure 4c In this embodiment, the average potential of all electrodes 104A to 104D is approximately 0V. More specifically, electrodes 104A and 104B have positive potentials (+) and electrodes 104C and 104D have negative potentials (-), wherein the magnitude of the potential of each of the electrodes 104A to 104D is approximately the same. It should be understood that Figure 4cThe settings for electrodes 104A to 104D are merely examples and other settings can be used, such as in Figure 2a , Figure 3a or Figure 4a It should be understood that embodiments may exist in which the potential of the electrodes, or each potential of each electrode, is not set such that the flux of free charge generated by the mechanism to the surface of the component adjacent to the electrostatic clamp is increased.

[0177] exist Figure 4c In this embodiment, the mask (patterning apparatus) MA is electrostatically held by two pairs of electrodes 104A to 104D, wherein the conductive second surface 124 (back side) of the mask MA serves as a counter electrode or reverse electrode. The capacitance of each electrode 104A to 104D in each pair is approximately equal. As a result, the potential of the second surface 124 remains close to ground. Therefore, the potential induced by capacitance on the mask MA (particularly on the second surface 124) remains constant.

[0178] As previously mentioned, charging on the front and back sides of the mask can lead to defects. Specifically, during release of the clamp, the distance d between the back side of the mask and the electrodes increases. This reduces the total electrode-mask capacitance C(∝1 / d) and thus increases the potential V = Q / C, where Q is the amount of charge on the mask. The charge on the back or front side of the mask remains constant until discharge occurs, which can potentially lead to defects and / or film breakage.

[0179] One method of charging the mask is through EUV-induced plasma. In the most likely scenario, high-energy (photo)electrons arrive at the back side of the mask and induce a negative charge. During this process, the potential on the back side of the mask becomes increasingly negative. As the charging begins at ground potential, it is a rapid "uphill" process, requiring ever-increasing numbers of high-energy electrons to overcome the increasing negative potential. This process can saturate at approximately -10V.

[0180] As mentioned, since the capacitance of each of the electrodes 104A to 104D in the pair of electrodes is approximately equal, the potential of the second surface 124 remains close to ground. However, even though the average potential of all electrodes 104A to 104D is approximately 0V, a capacitively induced potential can exist on the second surface 124 of the mask MA. This can be due to small imbalances in the capacitance of the electrostatic clamp 100 (more specifically, the individual capacitances of electrodes 104A to 104D). This imbalance can induce a positive (or negative) potential in the second surface 124 of the mask MA.

[0181] In some examples, the clamping surface 102 of the electrostatic clamp 100 is almost perfectly flat, but the control of the mask-electrode spacing is imprecise. That is, the spacing between electrodes 104A to 104D and the second surface 124 of the mask MA can be slightly different for some or all of the electrodes 104A to 104D. This can be, for example, because the clamping surface 102 is tilted relative to the second surface 124 of the mask MA. As a result, each clamp 100 will have a slightly different electrode capacitance. In addition, the electrode capacitance may vary depending on which mask MA is clamped.

[0182] The positive residual potential on the back side of the mask can accelerate (negative) mask back-side charging and may result in a larger potential (and discharge) during unloading. Furthermore, the lack of control over mask back-side charging may make controlled unbalanced clamping leading to a negative mask back-side potential (no charge) impractical.

[0183] Achieving reliable control over the mask back-side potential, which is at least 10V below approximately, presents a problem. This level of control is required to prevent discharge during mask unloading. The issue is not the control of the (high) voltage applied to the mask fixture, but rather the uncertainty in the fixture electrode-mask back-side capacitance.

[0184] Figure 10 A schematic circuit diagram is shown of the back side (second surface 124) of the mask (pattern forming apparatus) MA, electrodes 104A to 104D, and a high-voltage supply device. The capacitance of each of electrodes 104A to 104D (in conjunction with the back side of the mask) is depicted as C1 to C4, respectively. Each of electrodes 104A to 104D is powered by a high-voltage supply device, which has a voltage depicted as V1 to V4, respectively.

[0185] Multiple charge measuring devices 300A to 300D are provided, one charge measuring device for each electrode 104A to 104D. The charge measuring devices 300A to 300D measure the charge from the voltage supply device to the electrodes 104A to 104D.

[0186] It should be understood that this is only one embodiment and different electronic device arrangements may exist in other embodiments. For example, there may be only two electrodes (e.g., electrodes 104A and 104C) or a single charge measuring device configured to measure the charge of each of the electrodes.

[0187] Charge measuring devices 300A to 300D are used to measure the capacitance of a fixture-mask. The measurement is relatively complex, i.e., relatively straightforward, because the second surface 124 of the mask MA does not have a contact portion; that is, it is floating.

[0188] At the level of a high-voltage power amplifier, it may not be possible to directly measure the capacitance of individual electrodes 104A to 104D. For example, when V1 is changed via step dV1, the change in charge leading to electrode 104A (i.e., dQ1) is:

[0189] dQ1=dV1*(1 / C1+1 / (C2+C3+C4)) -1 .

[0190] That is, the series capacitance of C1 and C2+C3+C4 is measured. However, with charge measuring devices 300A to 300D (one charge measuring device for each high voltage source of the fixture 100), the capacitance or capacitance ratio can be determined.

[0191] When, for example, the potential of electrode 104A changes by an amount dV1, the potential of the second surface 124 of the mask MA will change by a substantially unknown amount dVb. This, in turn, causes a change in the charge leading to electrodes 104A through 104D:

[0192] dQ1=C1*(dV b –dV1)

[0193] dQ2=C2*dVb

[0194] dQ3=C3*dVb

[0195] dQ4=C4*dVb

[0196] (dQ1+dQ2+dQ3+dQ4)=0 (because no net charge reaches the second surface 124 of the mask MA).

[0197] The measured charge is given by the following equation:

[0198] Q n =(V n -V b )·C n

[0199] Where n = 1...4, C n The unknown capacitance and Q of electrodes 104A to 104D n The charge and V measured by charge measuring devices 300A to 300D b It is the potential of the second surface (back side) 124 of the mask MA, and V n It is the potential applied to electrodes 104A to 104D.

[0200] In this embodiment, by applying a first set of sufficiently high potentials V n,1 For example, V n,1=(-1) n φ1 is used to clamp the mask MA, and the mask MA is flattened against the protrusion. This produces four equations and five unknowns (C). 1-4 and V b,1 Next, change the MA potential of the mask, that is, change the potential of electrodes 104A to 104D, for example, change it to V. n,2 =(-1) n φ2. This produces eight equations and six unknowns (C). 1-4 and V b,1 V b,2 Having more equations than unknowns allows for the application of C. n V b,1 and V b,2 The equations are solved. Therefore, the capacitance of electrodes 104A to 104D, and the first set of high potentials V are determined. n,1 The potential (V) of the second surface 124 b,1 ) and having a second set of high potentials V n,2 The potential (V) of the second surface 124 b,2 ).

[0201] Since the potential V of the second surface has been determined b,2 Then this equation can be used to apply the currently known C n To adjust the potential of electrodes 104A to 104D to achieve the desired backside potential (V). b ):

[0202] V b =sum(V n ·C n ) / sum(C n )

[0203] For example, when a zero backside potential is required, V can be selected. n =φ2·C1 / C n .

[0204] Preferably, the potential of one or more electrodes 104A to 104D is set such that the potential of the second surface 124 is negative before or at least relatively shortly after the mechanism for generating free charge is turned on (e.g., the mask MA is exposed to EUV radiation). This potential can be maintained for the entire duration of free charge generation. This minimizes the number of negative charges attracted to the second surface 124. However, in embodiments, the potential can be set such that the potential of the second surface 124 is negative for a portion of the EUV exposure time and / or for a period of time before the mask MA is moved from being held by the electrostatic clamp 100 to being spaced apart from the electrostatic clamp 100.

[0205] Preferably, the potentials of one or more electrodes 104A to 104D are set such that the potential of the second surface 124 is approximately zero before the time when the mechanism generates free charge (e.g., before exposure of the mask MA). This minimizes the number of negative charges attracted to the second surface 124. This is because if the electrode potentials are set only at some point after EUV exposure has begun, the second surface 124 may already have a negative charge due to the rapid movement of negative electrons, which may then not be able to be reduced before the clamp 100 is released.

[0206] It should be understood that the described measurement and potential setting steps can be used in conjunction with, for example, EUV-induced plasma to remove charge from the back side of the mask. It should also be understood that the measurement and potential setting steps can be used in conjunction with the methods described above for increasing the flux of free charge generated by the EUV source.

[0207] Variations to the above scheme are possible. For example, the first potential step from zero to φ1 will actually be larger than the second step from φ1 to φ2, where |φ1-φ2| is typically less than 10% of |φ1|. As a result, the charge measuring devices 300A to 300D may need to have a high dynamic range. It may be advantageous to first clamp the mask MA at a high potential and then consider the change in charge to change the clamp potential:

[0208] ΔQ n =(ΔV) n -ΔV b )·C n

[0209] In a similar manner, C can be determined n And thus, it can be achieved by applying two sets of potential steps ΔV with similar values. n,1 and ΔV n,2 To determine the potential of the second surface 124 of the mask MA.

[0210] In the example, the electrode arrangement of the clamp 100 can be considered as, for example, Figure 2a The setup shown is similar. It should be understood that this is merely an example and other electrode setups may be used.

[0211] In addition to maintaining the potential of the second surface 124 of the mask MA at approximately zero volts (i.e., grounded), the potential of the second surface 124 can also be maintained at a (approximately) specific negative (or positive) predetermined value. That is, the potential of the second surface 124 of the mask MA can be maintained at an approximately controlled potential. In other words, the potential of one or more electrodes 104A to 104D can be set such that the potential of the second surface 124 is approximately a predetermined value. Preferably, the potential of one or more electrodes 104A to 104D is set such that the potential of the second surface 124 is negative, thereby repelling (or at least preventing) high-energy (photo) electrons from (or from being attracted to) the second surface 124 of the mask MA.

[0212] The potential of the second surface 124 of the mask MA can be determined using the one or more charges measured by one or more charge measuring devices 300A to 300D, and the capacitances C1 to C4 of the electrodes 104A to 104D. Determining the potential can be considered, for example, measuring, calculating, or setting the potential of the second surface 124.

[0213] The capacitance of electrodes 104A to 104B can vary only within a certain percentage (e.g., + / - 10%). For the nominal clamp capacitance, an unbalanced electrode 104A of -100V may result in a back-side potential of -25V. Then, by correcting the measured capacitance of the electrodes, a potential of -25V + / - to 10% can be applied to the second surface 124 to, for example, mitigate electron charging.

[0214] Since capacitance can vary by only + / - to 10%, a back-side potential of >-10V (using nominal clamp capacitance) is sufficient to ensure a negative potential on the second surface 124. In the example above, a -25V back-side potential could be intended to ensure some margin that the second surface 124 will definitely eventually become negative to mitigate electron charging. More generally, the potential of at least one of the electrodes 104A to 104D can be set based on the variance of the capacitance of one or more of the electrodes 104A to 104D.

[0215] In other embodiments, the electrodes can be changed to have more positive values ​​(e.g., +100V), which may result in, for example, a back-side potential of +25V. This can be applicable where it is necessary to mitigate the positive ion charging of the second surface 124.

[0216] Besides determining the capacitances C1 to C4 as described above, other methods can be used to determine the individual capacitances C1 to C4 of electrodes 104A to 104D. This can be done by applying a voltage step to the different electrodes 104A to 104D and then measuring the charge transfer. In other words, the potential of electrodes 104A to 104D is changed by a predetermined amount in a stepwise manner, and after each potential change, the charge from the voltage supply device to electrodes 104A to 104D is measured using charge measuring devices 300A to 300D.

[0217] This results in a (over)constrained set of equations that can be solved for individual capacitors C1 to C4. Sufficient information exists to individually determine C1 to C4 by progressively changing the four voltages V1, V2, V3, V4, along with the measured charge from each of the charge measuring devices 300A to 300D. In this embodiment, the charge leading to each electrode 104A to 104D can be measured. However, it should be understood that this is merely an example and a wide range of variations in the measurement is possible.

[0218] As an example, at least two voltage steps can be applied, such as dV1 and dV2. This then generates eight equations and six unknowns (C). 1-4 ,dV b1 ,dV b2 This set can be solved. The absolute values ​​of C1 to C4 can then be obtained. This allows the second surface 124 of the mask MA to be set to 0V by adhering to, for example, V4 / V3 = -C3 / C4 and V2 / V1 = -C1 / C2. Therefore, in an embodiment, the potentials of electrodes 104A to 104D can be based on the ratio of the capacitances of electrodes 104A to 104D. Alternatively, instead of setting the second surface 124 of the mask MA to 0V, any arbitrary potential can be set.

[0219] Alternatively, in other embodiments, the two electrodes can be floated and the series capacitance of the other two electrodes can be determined using a single charge measuring device. For example, the capacitance of C1 to C2 can be measured in series (C 12 And then C can be measured similarly. 13 C 14 C 23 C 24 and C 34 Six unique combinations are used to provide another set of overconstrained equations that can be used to derive the individual capacitors C1 through C4. It should be understood that many variations are possible and can be optimized in conjunction with hardware development.

[0220] The above derivation neglects stray capacitances, such as the 50 to 100 pF / m cable-to-ground capacitance. In practical implementation, these capacitances should be included and calibrated. This is possible, for example, by applying a potential to the mask fixture without a mask. In this case, the fixture-to-mask capacitance is practically zero, and stray capacitance can be measured.

[0221] While the foregoing generally pertains to one or more charge measuring devices 300A to 300D for measuring the amount of charge Q leading to electrodes 104A to 104D, it should be understood that other measuring devices may be used in other embodiments. For example, in embodiments, one or more current measuring devices for measuring the current leading to the electrodes may be used instead of charge measuring devices 300A to 300D, or in addition to charge measuring devices 300A to 300D. In embodiments, an oscillating electrode potential V may be applied. n =V n0 +V a *sin(Ω*t). The AC portion of the current entering the electrostatic clamp can then be measured. Therefore, instead of measuring Q or ΔQ, dQ / dt (=I) can then be measured.

[0222] It should be understood that using one or more of the aforementioned current measuring devices to determine the potential of the second surface 124 of the mask MA (by calculating the capacitance of one or more electrodes 104A to 104D using the measured currents leading to one or more electrodes 104A to 104D) can function in a similar manner to using charge measuring devices 300A to 300D. As mentioned in the embodiments for charge measurement above, Q versus V or dQ versus dV is measured. However, dQ / dt = I versus dV / dt can also be measured. The equivalence will be understood because: Q = C*V, dQ = C*dV, dQ / dt = I = C*dV / dt.

[0223] It should be understood that calculations can be performed in a device and / or in a separate system (such as a computer device).

[0224] While specific references can be made to the use of lithography equipment in IC manufacturing within this document, it should be understood that the lithography equipment described herein can have other applications. Possible other applications include manufacturing integrated optical systems, guiding and detecting patterns for magnetic domain memories, flat panel displays, liquid crystal displays (LCDs), thin-film magnetic heads, and more.

[0225] While specific reference is made herein to embodiments of the invention within the context of a photolithography apparatus, these embodiments can be used in other apparatuses. Embodiments of the invention can form components of mask inspection apparatus, metrology apparatus, or any apparatus that measures or processes objects such as wafers (or other substrates) or masks (or other patterning devices). These apparatuses are generally referred to as photolithography tools. Such photolithography tools can be used under vacuum conditions or ambient (non-vacuum) conditions.

[0226] While reference may be specifically made to the use of embodiments of the invention in the context of optical lithography, it should be understood that the invention can be used in other applications (e.g., imprint lithography) and is not limited to optical lithography where circumstances permit.

[0227] Where circumstances permit, embodiments of the invention may be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the invention may also be implemented as instructions stored on a machine-readable medium, which may be read and executed by one or more processors. A machine-readable medium may include any means for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, a machine-readable medium may include read-only memory (ROM); random access memory (RAM); magnetic storage media; optical storage media; flash memory devices; propagated signals in electrical, optical, acoustic, or other forms (e.g., carrier waves, infrared signals, digital signals, etc.), and so on. Furthermore, firmware, software, routines, and instructions may be described herein as performing certain actions. However, it should be understood that such descriptions are for convenience only, and these actions actually originate from a computing device, processor, controller, or other device that executes firmware, software, routines, instructions, etc., and, in performing such operations, enables actuators or other devices to interact with the physical world.

[0228] While specific embodiments of the invention have been described above, it should be understood that the invention can be practiced in other ways than those described. The above description is illustrative and not restrictive. Therefore, those skilled in the art will understand that modifications can be made to the described invention without departing from the scope of the claims set forth below.

Claims

1. A clamping device, comprising: An electrostatic clamp, the electrostatic clamp being used to hold components; and a mechanism for generating free charges adjacent to the electrostatic clamp: The electrostatic clamp includes one or more electrodes. The device is configured such that the potential of the electrodes, or each potential of each electrode, is set such that the flux of free charge generated by the mechanism to the surface of the component adjacent to the electrostatic clamp changes; as well as The device is configured to: In a first mode of operation, the electrodes, or each electrode, are positioned at a potential such that a clamping electric field is generated between the electrostatic clamp and the component to clamp the component. In a second mode of operation, the potential of the electrodes, or each potential of each electrode, is set such that the clamping of the component is released, and In a third mode of operation, the potential of the electrodes or each potential of each electrode is set such that, compared with operation in the first or second mode, the flux of free charge generated by the mechanism to the surface of the component adjacent to the electrostatic clamp is increased. as well as in, The electrostatic clamp includes the plurality of electrodes, and wherein, in the third mode, the device is configured such that the potential of the edge electrode closest to the edge of the electrostatic clamp is set to positive, or In the third mode, the device is configured such that the potential of the electrodes, or each potential of each electrode, is set such that the potential of the electrodes, or the average potential of the plurality of electrodes, is negative. The electrostatic clamp includes the plurality of electrodes, and in the third mode, the device is configured such that the potential of the edge electrode closest to the edge of the electrostatic clamp is set to negative, and the potentials of the remaining portions of the plurality of electrodes are set such that the average potential of the plurality of electrodes has a smaller negative value compared to the potential of the edge electrode.

2. The device of claim 1, wherein in the third mode, the device is configured such that the potentials of the plurality of electrodes are set such that the average potential of the plurality of electrodes is approximately 0 V.

3. The device of claim 1, wherein in the third mode, the device is configured such that the potential of the electrodes or each potential of each electrode is set such that the surface of the component adjacent to the electrostatic clamp has a positive potential before the component moves from being held by the electrostatic clamp to being spaced apart from the electrostatic clamp.

4. The device according to claim 1, wherein in the third mode, the potential of the electrode or the average potential of the electrode is set to a predetermined negative value such that during the period when the component moves from being held by the electrostatic clamp to being spaced apart from the electrostatic clamp, the surface of the component has a potential that is substantially the same as the potential of the electrode or the average potential of the electrode.

5. The device of claim 4, wherein in the third mode, the potential of the electrode or the average potential of the electrode is set to the predetermined negative value such that the component has approximately zero charge after exposure of the component.

6. The device of claim 1, wherein in the third mode, the potential of the electrode or each potential of each electrode is set to last for at least one of the following times: a period of time before the component is moved from being held by the electrostatic clamp to being spaced apart from the electrostatic clamp; a portion or all of the time spent moving the component from being held by the electrostatic clamp to being spaced apart from the electrostatic clamp; and a portion or all of the time spent moving the component from being spaced apart from the electrostatic clamp to being held by the electrostatic clamp.

7. The device according to claim 1, wherein in the third mode, the potential of the electrode or the average potential of the electrode is set to sustain the generation of free charge by the mechanism for at least a portion or all of the time.

8. The device according to claim 1, wherein the mechanism for generating free charge adjacent to the electrostatic clamp comprises: Gas source; and an ionizing radiation source, the ionizing radiation source being configured to ionize the gas supplied by the gas source.

9. The device according to claim 8, wherein the ionizing radiation source comprises at least one of an EUV source, a VUV source, a soft X-ray source, and a radiation source.

10. The device of claim 1, wherein the electrostatic clamp includes additional electrodes or a plurality of additional electrodes, wherein the additional electrodes or the plurality of additional electrodes are positioned at least partially around a volume extending in a direction away from the surface of the electrostatic clamp adjacent to the component, wherein the device is configured such that the potential of the additional electrodes or each potential of each additional electrode is set such that the flux of free charge generated by the mechanism toward the surface of the component adjacent to the electrostatic clamp is reduced.

11. The device of claim 1, wherein the device is configured to: measure the charge or current from the voltage supply device to the electrode or each electrode using at least one charge or current measuring device; calculate the capacitance of the electrode or each electrode using the measured charge or current to the electrode or each electrode; and determine the potential of the surface of the component adjacent to the electrostatic clamp using the calculated capacitance of the electrode or each electrode.

12. A photolithography apparatus arranged to project a pattern from a pattern forming apparatus onto a substrate, wherein the photolithography apparatus includes an irradiation system configured to adjust a radiation beam and an apparatus according to any one of the preceding claims, wherein the irradiation system is configured to project the radiation beam onto the pattern forming apparatus, and wherein the pattern forming apparatus includes a component to be clamped.

13. A method of operating a device, the device comprising: Static electricity clamps; The method includes a mechanism for generating free charges adjacent to the electrostatic clamp, the electrostatic clamp comprising one or more electrodes, and the method comprising: A component is disposed adjacent to the electrostatic clamp; The mechanism for generating free charges is controlled to generate free charges adjacent to the electrostatic clamp. The device is operated in a first mode, in which the electrodes, or each electrode, are positioned at a potential such that a clamping electric field is generated between the electrostatic clamp and the component to clamp the component. The device is operated in a second mode, in which the potential of the electrodes, or each potential of each electrode, is set such that the clamping of the component is released, and The device is operated in a third mode in which the potential of the electrodes, or each potential of each electrode, is set such that the flux of free charge to the surface of the component adjacent to the electrostatic clamp increases compared to operation in the first or second mode.

14. The method of claim 13, wherein the electrostatic clamp comprises a plurality of electrodes, and the method further comprises: In the third mode, the potential of the edge electrode closest to the edge of the electrostatic clamp is set to positive.

15. The method of claim 14, further comprising: In the third mode, the potential of the electrode or each potential of each electrode is set such that the potential of the electrode or the average potential of the plurality of electrodes is negative.

16. The method of claim 14, further comprising: In the third mode, the potentials of the plurality of electrodes are set such that the average potential of the plurality of electrodes is approximately 0 V.

17. The method of claim 13, wherein the electrostatic clamp includes additional electrodes or a plurality of additional electrodes, said additional electrodes or the plurality of additional electrodes being positioned at least partially around a volume extending in a direction away from the component and adjacent to the electrostatic clamp, the method further comprising: The potential of the additional electrodes, or each potential of each additional electrode, is set such that the flux of free charge to the surface of the component adjacent to the electrostatic clamp is reduced.

18. The method according to any one of claims 13 to 17, further comprising: The charge or current from the voltage supply device to the electrode or each electrode is measured using at least one charge or current measuring device; the capacitance of the electrode or each electrode is calculated using the measured charge or current to the electrode or each electrode. The potential of the surface of the component adjacent to the electrostatic clamp is determined using the electrodes or the calculated capacitance of each electrode.

19. A computer program comprising computer-readable instructions configured to cause a processor to execute the method according to any one of claims 13 to 18.

20. A computer-readable medium carrying a computer program according to claim 19.

21. A computer device for operating a device, comprising: Memory, which stores processor-readable instructions; and a processor, the processor being arranged to read and execute instructions stored in the memory; The processor-readable instructions include instructions arranged to control the computer to perform the method according to any one of claims 13 to 18.

22. A clamping device, comprising: An electrostatic clamp, the electrostatic clamp being used to hold components; and a mechanism for generating free charges adjacent to the electrostatic clamp: The electrostatic clamp includes one or more electrodes. The electrode or the plurality of electrodes is positioned at least partially around a volume that extends in a direction away from the surface of the electrostatic clamp adjacent to the component. The device is configured such that the potential of the electrodes, or each potential of each electrode, is set such that the flux of free charge generated by the mechanism to the surface of the component adjacent to the electrostatic clamp changes; as well as The device is configured such that the potential of the electrodes, or each electrode or each potential, is set such that the flux of free charge generated by the mechanism to the surface of the component adjacent to the electrostatic clamp is also changed to a reduction.

23. The device of claim 22, wherein the electrode or the plurality of electrodes is located on one side of the component.

24. The device of claim 22 or 23, wherein the electrode or the plurality of electrodes extends throughout the volume.

25. The device of claim 22, wherein the potential of the electrode or each potential of each electrode is set to negative.

26. The device of claim 22, wherein the potential of the electrode or each potential of each electrode is set to positive.

27. The device of claim 22, wherein the electrode or each electrode is in electrical contact with the surface of the component adjacent to the electrostatic clamp.

28. The device of claim 22, wherein at least one or more edges of the surface of the electrode or each electrode adjacent to the component are rounded.

29. The device of claim 28, wherein the electrode or each electrode is rounded at a region corresponding to the corner of the component.

30. The device of claim 22, wherein the potential of the electrode or each potential of each electrode is set to last for at least one of the following times: at least a portion or all of the time during which the mechanism generates free charge, and the time period before the component moves from being held by the electrostatic clamp to being spaced apart from the electrostatic clamp.

31. The device of claim 22, wherein the mechanism for generating free charge adjacent to the electrostatic clamp comprises: Gas source; and an ionizing radiation source, the ionizing radiation source being configured to ionize the gas supplied by the gas source.

32. The device of claim 31, wherein the ionizing radiation source comprises at least one of an EUV source, a VUV source, a soft X-ray source, and a radiation source.

33. A lithography apparatus arranged to project a pattern from a pattern forming apparatus onto a substrate, wherein the lithography apparatus includes an irradiation system configured to adjust a radiation beam and an apparatus according to any one of claims 22 to 32, wherein the irradiation system is configured to project the radiation beam onto the pattern forming apparatus, and wherein the pattern forming apparatus includes a component to be clamped.

34. A method of operating a device, the device comprising: Static electricity clamps; The method includes a mechanism for generating free charges adjacent to the electrostatic clamp, the electrostatic clamp comprising one or more electrodes positioned at least partially around a volume extending in a direction away from a surface of the electrostatic clamp from a component adjacent to the electrostatic clamp. The component is disposed adjacent to the electrostatic clamp; The mechanism for generating free charges is controlled to generate free charges adjacent to the electrostatic clamp. The potential of the electrodes, or each potential of each electrode, is set such that the flux of free charge to the surface of the component adjacent to the electrostatic clamp is reduced.

35. The method of claim 34, further comprising setting the potential of the electrodes or each potential of each electrode to be negative.

36. The method of claim 34, further comprising setting the potential of the electrodes or each potential of each electrode to positive.

37. The method according to any one of claims 34 to 36, further comprising controlling the potential of the surface of the component adjacent to the electrostatic clamp via an electrical connection between the electrode or each electrode and the surface of the component adjacent to the electrostatic clamp.

38. A computer program comprising computer-readable instructions configured to cause a processor to execute the method according to any one of claims 34 to 37.

39. A computer-readable medium carrying a computer program according to claim 38.

40. A computer device for operating a device, comprising: Memory, which stores processor-readable instructions; and a processor, the processor being arranged to read and execute instructions stored in the memory; The processor-readable instructions include instructions arranged to control the computer to perform the method according to any one of claims 34 to 37.

41. A clamping device comprising an electrostatic clamp for clamping a component; and a mechanism for generating a free charge adjacent to the electrostatic clamp: The electrostatic clamp includes one or more electrodes. The device is configured such that: the potential of the electrodes, or each potential of each electrode, is set such that the flux of free charge generated by the mechanism to the surface of the component adjacent to the electrostatic clamp changes; and The device is configured to: The charge or current from the voltage supply device to the electrode or each electrode is measured using at least one charge or current measuring device; The capacitance of the electrode or each electrode is calculated using the measured charge or current flowing to the electrode or each electrode; and The potential of the surface of the component adjacent to the electrostatic clamp is determined using the electrodes or the calculated capacitance of each electrode.

42. The device of claim 41, wherein the device is configured such that the potential of one of the plurality of electrodes or each electrode is set such that the potential of the surface of the component adjacent to the electrostatic clamp is approximately a predetermined value.

43. The device of claim 42, wherein the predetermined value of the potential of the surface of the component adjacent to the electrostatic clamp is at least one of positive, negative, and approximately zero.

44. The apparatus of claim 42, wherein the apparatus is configured to measure the ratio of the capacitances of the plurality of electrodes.

45. The device of claim 44, wherein the device is configured to set the potential of at least one of the plurality of electrodes based on the ratio of the capacitances of the plurality of electrodes.

46. ​​The device of claim 41, wherein the device is configured to set the potential of at least one of the plurality of electrodes based on the variance of the capacitance of the electrodes or each electrode.

47. The device of claim 41, wherein the device is configured to change the potential of the plurality of electrodes by a predetermined amount in a stepwise manner, and after each potential change, to use the at least one charge or current measuring device to measure the charge or current from the voltage supply device to the electrode or each electrode to determine the individual capacitance of the plurality of electrodes.

48. The device of claim 41, wherein the potential of the electrode or each electrode is set to last for at least one of the following times: before at least a portion or all of the time during which the mechanism generates free charge; and before the component moves from being held by the electrostatic clamp to being spaced apart from the electrostatic clamp.

49. The device of claim 41, wherein the mechanism for generating free charge at the adjacent location of the electrostatic clamp comprises: Gas source; and an ionizing radiation source, the ionizing radiation source being configured to ionize the gas supplied by the gas source.

50. The device of claim 49, wherein the ionizing radiation source comprises at least one of an EUV source, a VUV source, a soft X-ray source, and a radiation source.

51. A photolithography apparatus arranged to project a pattern from a pattern forming apparatus onto a substrate, wherein the photolithography apparatus includes an irradiation system configured to adjust a radiation beam and an apparatus according to any one of claims 41 to 50, wherein the irradiation system is configured to project the radiation beam onto the pattern forming apparatus, and wherein the pattern forming apparatus includes a component to be clamped.

52. A method of operating a device, the device comprising: Static electricity clamps; The method includes a mechanism for generating free charges adjacent to the electrostatic clamp, the electrostatic clamp comprising one or more electrodes, and the method comprising: A component is disposed adjacent to the electrostatic clamp; The mechanism for generating free charges is controlled to generate free charges adjacent to the electrostatic clamp. The charge or current from the voltage supply device to the electrode or each electrode is measured using at least one charge or current measuring device. The capacitance of the electrode or each electrode is calculated using the measured charge or current leading to the electrode or each electrode. The potential of the surface of the component adjacent to the electrostatic clamp is determined using the electrodes or the calculated capacitance of each electrode.

53. The method of claim 52, further comprising setting the potential of one or each of the plurality of electrodes such that the potential of the surface of the component adjacent to the electrostatic clamp is approximately a predetermined value.

54. The method of claim 53, further comprising setting the potential of one or each of the plurality of electrodes such that the predetermined value of the potential of the surface of the component adjacent to the electrostatic clamp is at least one of positive, negative, and approximately zero.

55. The method of claim 52, further comprising setting the potential of at least one of the plurality of electrodes based on the ratio of the capacitances of the plurality of electrodes.

56. The method of claim 52, further comprising setting the potential of at least one of the plurality of electrodes based on the variance of the capacitance of the electrodes or each electrode.

57. A computer program comprising computer-readable instructions configured to cause a processor to execute the method according to any one of claims 52 to 56.

58. A computer-readable medium carrying a computer program according to claim 57.

59. A computer device for operating a device, comprising: Memory, which stores processor-readable instructions; and a processor, the processor being arranged to read and execute instructions stored in the memory; The processor-readable instructions include instructions arranged to control the computer to perform the method according to any one of claims 52 to 56.

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