Electrostatic clamp used in lithography, lithography apparatus, and method for controlling the electrostatic clamp for clamping components in a lithography apparatus.

Abstract

The lithography apparatus includes an electrostatic clamping system comprising: a plurality of electrodes configured to exert an electrostatic clamping force on a component; a power supply connected to the plurality of electrodes; and a controller configured to alternately switch the potential applied to the plurality of electrodes between a first mode and a second mode in synchronization with the generation of radiation pulses in the lithography apparatus, wherein in the first mode, the average potential of the plurality of electrodes is the first potential, and in the second mode, the average potential of the plurality of electrodes is the second potential, with the first potential being higher than the second potential.

Description

[Technical Field]

[0001] Cross-reference of related applications This application claims priority to European Application No. 23168046.3, filed on 14 April 2023, which is incorporated herein by reference in its entirety.

[0002] The present invention relates to a lithography apparatus having an electrostatic clamping system, a method for controlling an electrostatic clamp for clamping a component in the lithography apparatus, a device manufacturing method including a method for controlling an electrostatic clamp for clamping a component in the lithography apparatus, and a computer program that, when executed by the control system of the lithography apparatus, provides instructions to cause the lithography apparatus to execute a method for controlling an electrostatic clamp for clamping a component in the lithography apparatus. [Background technology]

[0003] A lithography apparatus is a machine that imparts a desired pattern to a substrate, typically a target area on the substrate. Lithography apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In this case, a patterning device, also called a mask or reticle, may be used to generate the circuit pattern to be formed on individual layers of the IC. This pattern can be transferred to a target area on a substrate (e.g., a silicon wafer) (e.g., a part of a die, one die, or several dies). The transfer of the pattern is typically performed by imaging onto a radiative-sensitive material (resist) layer provided on the substrate. Generally, a single substrate contains a network of adjacent target areas that are patterned in sequence.

[0004] Lithography is widely recognized as a crucial process in the manufacturing of ICs and other devices and / or structures. However, as the dimensions of features manufactured using lithography decrease, lithography is becoming an even more critical element in enabling the production of smaller ICs and other devices and / or structures.

[0005] A theoretical estimate of the limits of pattern printing can be given by the Rayleigh criterion for resolution, as shown in equation (1). CD = k1 * (λ / NA) (1) Here, λ is the wavelength of radiation used, NA is the numerical aperture of the projection system used to print the pattern, k1 is a process-dependent adjustment factor also known as the Rayleigh constant, and CD is the feature size (or critical dimension) of the printed feature. From equation (1), we can see that the reduction in the minimum printable size of a feature can be achieved in three ways: by shortening the exposure wavelength λ, by increasing the numerical aperture NA, or by decreasing the value of k1.

[0006] To shorten the exposure wavelength and thereby reduce the minimum printable size, it has been proposed to use an extreme ultraviolet (EUV) radiation source. EUV radiation is electromagnetic radiation with wavelengths in the range of 10–20 nm, for example, in the range of 13–14 nm. Furthermore, it has been proposed that EUV radiation with wavelengths less than 10 nm, in the range of 5–10 nm, such as 6.7 nm or 6.8 nm, may be used. Such radiation is called extreme ultraviolet radiation or soft X-ray radiation. Possible radiation sources include, for example, radiation sources based on synchrotron radiation supplied from laser-generated plasma sources, discharge plasma sources, or electron storage rings.

[0007] Once EUV radiation is generated, it is guided through a lithography apparatus via multiple mirrors to the patterning surface of a patterning device, thereby imparting the desired pattern to the EUV radiation.

[0008] During operation of the lithography apparatus, the patterning device may be clamped using a high-voltage electrostatic clamp. The environment surrounding the patterning device and the electrostatic clamp may be maintained at a low voltage. This environment may be non-conductive. Therefore, charge may accumulate on dielectric surfaces or ungrounded surfaces such as the patterning surface of the patterning device.

[0009] EUV radiation irradiated onto a patterning surface can cause electrons to be emitted from the patterning surface as a result of the photoelectric effect and flow into the environment surrounding the patterning device. This can cause the patterning surface to become positively charged. EUV radiation can excite hydrogen molecules in the environment surrounding the patterning device, forming a plasma. Electrons emitted from the patterning surface can also contribute to this plasma. Free negative charges in the plasma can cause contaminant particles in the environment surrounding the patterning device to become negatively charged. Negatively charged contaminant particles can be attracted to the positively charged patterning surface. As a result, contaminant particles can accumulate on the patterning surface. Contaminant particles accumulated on the patterning surface can absorb and / or scatter EUV radiation incident on the patterning surface. Consequently, contaminant particles can cause defects in the pattern projected onto the substrate, potentially leading to substrate defects.

[0010] EUV radiation may be generated in pulses. During the intervals between pulses, the patterning surface may be discharged by free negative charges in the plasma (i.e., the positive charge may decrease).

[0011] When a pellicle is placed in front of a patterning device, EUV radiation can cause both the patterning device and the pellicle to become positively charged. During the intervals between pulses, negative charges in the plasma may decrease the positive charge of the pellicle or cause it to become negatively charged. On the other hand, the patterning surface may not be discharged by the negative charges and may retain its positive charge. Therefore, an electric field can be generated between the negatively charged pellicle and the positively charged patterning surface. This electric field can cause electrostatic discharge and potentially lead to the rupture of the pellicle. [Overview of the Initiative]

[0012] One object of the present invention is to provide a lithography apparatus having an electrostatic clamping system that solves or improves the aforementioned problems, and a method for controlling the electrostatic clamp in the lithography apparatus. That is, this object of the present invention is to provide a lithography apparatus having an electrostatic clamping system that reduces defects on the patterning surface of a patterning device and reduces the risk of pellicle fracture, and a method for controlling the electrostatic clamp in the lithography apparatus.

[0013] According to the present invention, a lithography apparatus is provided, comprising an electrostatic clamp system including a plurality of electrodes configured to exert an electrostatic clamping force on a component, a power supply connected to the plurality of electrodes, and a controller configured to alternately switch the potential applied to the plurality of electrodes between a first mode and a second mode in synchronization with the generation of radiation pulses in the lithography apparatus, wherein in the first mode, the average potential of the plurality of electrodes is a first potential, and in the second mode, the average potential of the plurality of electrodes is a second potential, and the first potential is higher than the second potential.

[0014] Furthermore, according to the present invention, there is a method for controlling an electrostatic clamp for clamping a component in a lithography apparatus, comprising: applying a clamping force to the component by a plurality of electrodes arranged in the electrostatic clamp; and controlling the potential applied to the plurality of electrodes such that the average potential of the plurality of electrodes alternates between a first potential and a second potential, wherein the first potential is higher than the second potential, and the alternating switching between the first potential and the second potential is synchronized with the generation of radiation pulses in the lithography apparatus. [Brief explanation of the drawing]

[0015] Hereinafter, several embodiments of the present invention will be described for illustrative purposes only with reference to the accompanying schematic drawings. In the drawings, corresponding reference numerals indicate corresponding parts.

[0016] [Figure 1] It is a diagram schematically showing a lithographic apparatus. [Figure 2] It is a schematic diagram showing the lithographic apparatus in more detail. [Figure 3] A schematic view showing an electrostatic clamp (which can be part of the lithographic apparatus according to the present invention) and a patterning device is shown. [Figure 4] A plot of the potential (V) of the first surface of the patterning device during the period in which two EUV radiation pulses are generated by the lithographic apparatus is shown. [Figure 5] A schematic view showing an electrostatic clamp (which can be part of the lithographic apparatus according to the present invention) and a patterning device covered with a pellicle is shown. [Figure 6A] A plot of the potential (V) of the first surface of the patterning device and the potential of the pellicle during and after the period in which one EUV radiation pulse is generated by the lithographic apparatus is shown. [Figure 6B] A plot of the charge (Q) on the first surface of the patterning device and the charge on the pellicle during and after the period in which one EUV radiation pulse is generated by the lithographic apparatus is shown. [Figure 7] Figures 7A and 7B schematically show an electrostatic clamp (which can be part of the lithographic apparatus according to the present invention) and a patterning device covered with a pellicle. [Figure 8A] A plot of the EUV radiation intensity (I) against time for several EUV radiation pulses is shown. [Figure 8B] A plot of the average potential (V) of a plurality of electrodes in the electrostatic clamp against time for several EUV radiation pulses is shown. [Figure 8C] A plot of the potential (V) applied to the first electrode group and the potential (V) applied to the second electrode group against time for several EUV radiation pulses is shown.

[0017] Features shown in each drawing are not necessarily to scale, and the depicted size and / or arrangement are not limiting. It should be understood that each drawing may contain optional features that are not essential to the present invention. Furthermore, not all features of the apparatus are depicted in each drawing, and each drawing may show only a portion of the relevant components to illustrate a particular feature. [Modes for carrying out the invention]

[0018] Figure 1 schematically shows a lithography apparatus 100 including a radiation source SO according to one embodiment of the present invention. Apparatus 100 is - An illumination system (or illuminator) IL configured to adjust the radiation beam B (e.g., EUV radiation), - A support structure (e.g., a mask table) MT constructed to support a patterning device (e.g., a mask or reticle), the support structure being connected to a first positioner PM configured to precisely position the patterning device, - A substrate table (e.g., wafer table) WT constructed to hold a substrate (e.g., a wafer covered with resist) W, the substrate table being connected to a second positioner PW configured to precisely position the substrate, - A projection system (e.g., a reflection projection system) PS configured to project a pattern applied to a radiation beam B by a patterning device MA onto a target portion C of a substrate W (e.g., comprising one or more dies).

[0019] The lighting system IL may include various optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic, or other types of optical components, or any combination thereof, to direct, shape, or control radiation.

[0020] The support structure MT holds the patterning device MA in a manner that depends on the orientation of the patterning device MA, the design of the lithography apparatus, and other conditions such as whether the patterning device is held in a vacuum environment. The support structure MT can hold the patterning device MA using mechanical, vacuum, electrostatic, or other clamping techniques. The support structure MT may be a frame or a table, which may be fixed or movable as needed. The support structure MT can ensure that the patterning device MA is in a desired position, for example, relative to the projection system PS.

[0021] The term "patterning device" should be broadly interpreted to refer to any device that can be used to impart a pattern to the cross-section of a radiation beam B in order to form a pattern on a target portion C of a substrate W. The pattern imparted to the radiation beam B may correspond to a specific functional layer of a device to be created on the target portion C, such as an integrated circuit.

[0022] Examples of patterning devices include masks, programmable mirror arrays, and programmable liquid crystal display (LCD) panels. Masks are well-known in lithography and include various mask types such as binary, alternating phase shift, or attenuating phase shift, as well as various hybrid mask types. An example of a programmable mirror array is a matrix of small mirrors, each of which can be individually tilted to reflect an incident radiation beam in a different direction. The radiation beam B reflected by the matrix of small mirrors is then patterned by the tilted mirrors.

[0023] The projection system PS, like the illumination system IL, may include various optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic, or other types of optical components, or any combination thereof, as long as it is appropriate depending on the exposure radiation used or other factors such as the use of vacuum. For EUV radiation, the use of vacuum may be desirable because the radiation can be absorbed too much by the gas. Therefore, a vacuum environment may be provided throughout the beam path using a vacuum wall and a vacuum pump.

[0024] As shown in the figure, the lithography apparatus 100 is reflective (for example, a reflective mask is used).

[0025] The lithography apparatus 100 may be of a type having two or more substrate tables WT (and / or two or more support structures MT). In such a "multi-stage" lithography apparatus, additional substrate tables WT (and / or additional support structures MT) can be used in parallel, or preparation steps can be performed on one or more other substrate tables WT (and / or one or more other support structures MT) while one or more substrate tables WT (and / or one or more support structures MT) is being used for exposure.

[0026] Referring to Figure 1, the illumination system IL receives an extreme ultraviolet radiation beam from the radiation source SO. The radiation source SO may be a laser-generated plasma (LPP) source, a discharge-generated plasma (DPP) source, a free-electron laser (FEL), or other radiation source capable of generating EUV radiation. Methods for generating EUV light include, but are not limited to, converting a material into a plasma state having at least one element having one or more emission lines in the EUV range, such as xenon, lithium, or tin. In a laser-generated plasma ("LPP"), the required plasma can be generated by irradiating a fuel, such as droplets, streams, or clusters of material having the required emission-emitting elements, with a laser beam. The radiation source SO may be part of an EUV radiation system that includes a laser (not shown in Figure 1) for supplying the laser beam that excites the fuel. The resulting plasma emits output radiation, such as EUV radiation. This radiation is collected using a radiation collector located at the radiation source SO. The laser and the radiation source SO may be separate entities, for example, if a CO2 laser is used to supply the laser beam for fuel excitation.

[0027] In such cases, the laser is not considered to form part of the lithography apparatus 100, and the radiation beam B passes from the laser to the radiation source SO using, for example, a beam delivery system equipped with appropriate directional mirrors and / or beam expanders. In other embodiments, the source can be an integral part of the radiation source SO, for example, if the source is a discharge-generated plasma EUV generator (also called a DPP source).

[0028] The illumination system IL may include adjusters for adjusting the angular intensity distribution of the radiated beam. Generally, the radial range of at least the outer and / or inner (generally referred to as "σ outer" and "σ inner") of the intensity distribution at the pupil plane of the illumination system IL can be adjusted. Furthermore, the illumination system IL may include various other components such as faceted field mirror devices and faceted pupil mirror devices. The illumination system IL can be used to adjust the radiated beam B to have desired uniformity and intensity distribution in its cross-section.

[0029] A radiant beam B is incident on a patterning device (e.g., a mask) MA held on a support structure (e.g., a mask table) MT, and is patterned by the patterning device MA. After being reflected from the patterning device (e.g., a mask) MA, the radiant beam B passes through a projection system PS, which focuses the radiant beam B onto a target portion C of the substrate W. A second positioner PW and a position sensor PS2 (e.g., an interferometer device, a linear encoder, or a capacitance sensor) can be used to precisely move the substrate table WT to position various target portions C within the path of the radiant beam B, for example. Similarly, a first positioner PM and another position sensor PS1 can be used to precisely position the patterning device (e.g., a mask) MA relative to the path of the radiant beam B. The patterning device (e.g., a mask) MA and the substrate W can be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2.

[0030] The controller 500 controls the overall operation of the lithography apparatus 100 and, in particular, performs the operational processes described further below. The controller 500 can be embodied as a well-programmed general-purpose computer comprising a central processing unit, volatile and non-volatile storage means, one or more input / output devices such as a keyboard and a screen, one or more network connections, and one or more interfaces to various parts of the lithography apparatus 100. It will be understood that a one-to-one relationship between the controlling computer and the lithography apparatus 100 is not required. In one embodiment of the present invention, one computer can control multiple lithography apparatuses 100. In one embodiment of the present invention, multiple networked computers can be used to control one lithography apparatus 100. The controller 500 may also be configured to control one or more associated process devices and substrate handling devices within a lithocell or cluster in which the lithography apparatus 100 forms part. The controller 500 may also be configured to be subordinate to a higher-level control system of the lithocell or cluster and / or to the overall control system of the factory.

[0031] Figure 2 shows a lithography apparatus 100 in more detail, including a radiation source SO, an illumination system IL, and a projection system PS. 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 comprises an illumination system IL, a support structure MT configured to support a patterning device MA (e.g., a mask), a projection system PS, and a substrate table WT configured to support a substrate W.

[0032] The illumination system IL is configured to adjust the EUV radiation beam B before it is incident on the patterning device MA. Therefore, the illumination system IL may include a faceted field mirror device 10 and a faceted pupil mirror device 11. Both the faceted field mirror device 10 and the faceted pupil mirror device 11 provide the EUV radiation beam B with a desired cross-sectional shape and intensity distribution. In addition to, or instead of, the illumination system IL may include other mirrors or devices.

[0033] After this adjustment, the EUV radiation beam B interacts with the patterning device MA. This interaction results in the production of a patterned EUV radiation beam B'. 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 number of mirrors 13, 14 configured to project the patterned EUV radiation beam B' onto the substrate W, which is held by a substrate table WT. The projection system PS may apply a reduction factor to the patterned EUV radiation beam B', thereby forming an image with features smaller than the corresponding features on the patterning device MA. For example, a reduction factor of 4 or 8 may be applied. Although Figure 1 shows the projection system PS having only two mirrors 13, 14, the projection system PS may include a different number of mirrors (e.g., 6 or 8 mirrors).

[0034] The substrate W may contain a pre-formed pattern. In this case, the lithography apparatus LA aligns the image formed by the patterned EUV radiation beam B' with the pre-formed pattern on the substrate W.

[0035] Within the radiation source SO, the illumination system IL, and / or the projection system PS, a relative vacuum, i.e., a trace amount of gas (e.g., hydrogen) at a pressure significantly below atmospheric pressure, may be supplied.

[0036] The radiation source SO may 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.

[0037] Figure 3 schematically shows a cross-sectional view of a portion of a support structure MT that may be part of a lithography apparatus according to the present invention. This cross-section extends in a vertical plane (i.e., parallel to the z-direction). This portion of the support structure MT may be the radially outer portion of the support structure MT. That is, the support structure MT may be continuous radially inward (to the right in Figure 3). The support structure MT clamps the patterning device MA during lithography operation. According to the present invention, the support structure MT is an electrostatic clamp 100. The electrostatic clamp 100 may be considered as part of a lithography apparatus, or as part of an apparatus separate from the lithography apparatus.

[0038] The patterning device MA, clamped by the electrostatic clamp 100, may comprise a first surface 110 and a second surface 111. The first surface 110 and the second surface 111 may be substantially parallel. The first surface 110 is a patterning surface and may comprise a patterning region. The patterning region may be configured to impart a pattern to be projected onto the substrate W. The patterning region may be configured to reflect a radiation beam, and the reflected radiation beam may become a patterned radiation beam. The second surface 111 is on the opposite side from the first surface 110.

[0039] Both the electrostatic clamp 100 and the patterning device MA may be housed within the patterning device environment 90. The patterning device environment 90 may be isolated from the external environment surrounding the lithography apparatus and / or other components within the lithography apparatus to substantially prevent gases and contaminating particles from entering the patterning device environment 90. The patterning device environment 90 may be partially evacuated of gases; that is, the pressure within the patterning device environment 90 may be lower than the ambient pressure. This is to limit the attenuation that occurs as EUV radiation travels through the patterning device environment 90. Although the pressure within the patterning device environment 90 is lower than the ambient pressure, it is not a perfect vacuum, and therefore gas particles are present within the patterning device environment 90.

[0040] The electrostatic clamp 100 may have a clamping surface 102. When the patterning device MA is clamped to the electrostatic clamp 100, the clamping surface 102 faces the second surface 111 of the patterning device MA. When the patterning device MA is clamped to the electrostatic clamp 100, the first surface 110 of the patterning device MA faces away from the clamping surface 102. The clamping surface 102 may be generally planar. The electrostatic clamp 100 may be configured such that when the patterning device MA is clamped to the electrostatic clamp 100, the clamping surface 102 of the electrostatic clamp 100 is substantially parallel to the second surface 111 of the patterning device MA.

[0041] The electrostatic clamp 100 may be equipped with a plurality of electrodes 104A to 104D. The plurality of electrodes 104A to 104D may be embedded within the body of the electrostatic clamp 100. For example, the plurality of electrodes 104A to 104D may be embedded below the clamping surface 102 of the electrostatic clamp 100. Each of the plurality of electrodes 104A to 104D may be connected to a power source so that a potential can be applied to each of the plurality of electrodes 104A to 104D.

[0042] The electrostatic clamp 100 may have a plurality of protrusions 106. The plurality of protrusions may project from the clamping surface 102 of the electrostatic clamp 100. The electrostatic clamp 100 may be configured such that the distal ends of the plurality of protrusions 106 (i.e., the ends furthest from the clamping surface 102 of the electrostatic clamp 100) form a single plane. When the patterning device MA is clamped to the electrostatic clamp 100, the second surface 111 of the patterning device MA comes into contact with the distal ends of the plurality of protrusions 106. As a result, the clamping surface 102 of the electrostatic clamp 100, and electrodes 104A to 104D that may be embedded below the clamping surface 102 of the electrostatic clamp, can be separated from the second surface 111 of the patterning device MA.

[0043] The clamping surface 102 of the electrostatic clamp 100, and the multiple electrodes 104A to 104D that may be embedded beneath the clamping surface 102 of the electrostatic clamp 100, may also be separated from the second surface 111 of the patterning device MA by the dielectric coating 105.

[0044] The electrodes 104A to 104D may each be rectangular in shape. However, this is not essential to the present invention, and the shape of the electrodes 104A to 104D is not particularly limited. The electrodes 104A to 104D may be uniformly distributed on the clamping surface 102 of the electrostatic clamp 100. However, the specific arrangement of the electrodes 104A to 104D on the clamping surface 102 of the electrostatic clamp is not particularly limited. As shown in Figure 3, there are four electrodes 104A to 104D on the radially outer portion of the electrostatic clamp 100. However, the number of electrodes 104A to 104D in the electrostatic clamp is not particularly limited and can be any number, such as 2, 3, 4, 5, 10, 20, or more.

[0045] The patterning device MA, clamped by the electrostatic clamp 100, may have a first conductive coating 112 on a first surface 110 and a second conductive coating 113 on a second surface 111. The first and second conductive coatings 112 and 113 can each cover a large portion of the first surface 110 and the second surface 111. The first conductive coating 112 and the second conductive coating 113 may be substantially electrically insulated. That is, the first conductive coating 112 may be electrically insulated from the second conductive coating 113, and both the first conductive coating 112 and the second conductive coating 113 may be substantially electrically insulated from other components in the lithography apparatus. As a result, charge may accumulate on the first surface 110 and the second surface 111.

[0046] Each of the electrodes 104A to 104D may be connected to a power source (not shown). This makes it possible to apply a potential to each of the electrodes 104A to 104D. The controller 500 may control the potential applied to each of the electrodes 104A to 104D.

[0047] The multiple electrodes 104A to 104D may comprise a first electrode group 104A, 104C and a second electrode group 104B, 104D. The first electrode groups 104A, 104C may be connected to one or more first voltage sources, and the second electrode groups 104B, 104D may be connected to one or more second voltage sources. The potential applied to the first electrode groups 104A, 104C may differ from the potential applied to the second electrode groups 104B, 104D. For example, the potential applied to the second electrode groups 104B, 104D may be similar in magnitude to the potential applied to the first electrode groups 104A, 104C, but with opposite polarity.

[0048] The first electrode groups 104A and 104C and the second electrode groups 104B and 104D may be uniformly arranged on the clamping surface 102 of the clamping device 100. For example, the first electrode groups 104A and 104C and the second electrode groups 104B and 104D can be arranged in a two-dimensional checkerboard configuration. In the checkerboard configuration, the electrodes 104A to 104D may be arranged alternately in the first and second directions, with those belonging to the first electrode groups 104A and 104C and those belonging to the second electrode groups 104B and 104D alternating. Here, the first and second directions are orthogonal to each other and lie in the plane of the clamping surface 102.

[0049] When a potential is applied to the multiple electrodes 104A to 104D, a high electric field is formed between the multiple electrodes 104A to 104D and the patterning device MA, and the patterning device MA is attracted to the multiple electrodes 104A to 104D. In particular, the potential applied to the multiple electrodes 104A to 104D causes charge separation within the second conductive coating 113. The displacement of charges within the second conductive coating 113 means that an attractive force can be established between the multiple electrodes 104A to 104D and the second conductive coating 113. As a result, the electrostatic clamp 100 can exert a clamping force on the patterning device MA.

[0050] The potential applied to the multiple electrodes 104A to 104D may be sufficiently large so that the clamping force exerted on the patterning device MA by the electrostatic clamp exceeds the gravitational force acting on the patterning device MA. The required potential may depend on the mass of the patterning device MA and the quality of the first conductive coating 112 and the second conductive coating 113. The absolute value of the potential applied to the multiple electrodes 104A to 104D may be on the order of several kV. For example, the absolute value of the potential applied to the multiple electrodes 104A to 104D may be greater than 100V, preferably greater than 300V, and more preferably greater than 1kV. The absolute value of the potential applied to the multiple electrodes 104A to 104D may be less than 100kV, preferably less than 50kV, and more preferably less than 25kV.

[0051] The masking blade 120 may be provided within the lithography apparatus adjacent to the first surface 110 of the patterning device MA. For example, the masking blade 120 may be positioned at a distance from the first surface 110 in the z direction. If a pellicle 131 is provided in front of the patterning device MA, the masking blade 120 may be positioned at a distance from the first surface 110 in the z direction. The masking blade 120 may be configured to selectively shield the patterning device MA from the radiation beam during exposure. The lithography apparatus may be configured so that the masking blade 120 is movable in the horizontal plane to provide different levels of shielding to the patterning device MA.

[0052] Contaminating particles may be present within the patterning device environment 90. Even though the patterning device environment 90 is isolated from the external environment and / or other components within the lithography apparatus, contaminating particles may enter the patterning device environment 90 from the external environment and / or other locations within the lithography apparatus. Furthermore, contaminating particles may be generated within the patterning device environment 90 through mechanisms such as wear that occurs when relative motion occurs between contact surfaces.

[0053] The lithography apparatus may be an EUV lithography apparatus. That is, the lithography apparatus may be configured to project an EUV radiation beam onto the substrate W. During exposure, the EUV radiation beam may be incident on the patterning region of the first surface 110 of the patterning device MA. As a result, electrons may be emitted from the first surface 110 as a result of the photoelectric effect. Consequently, the first surface 110 may become positively charged.

[0054] EUV radiation within the patterning device environment 90 can negatively charge contaminating particles. This is because the presence of EUV radiation within the patterning device environment 90 generates plasma from gas molecules within it. Since photons in the EUV radiation beam ionize hydrogen molecules to produce free electrons, plasma can be generated within the patterning device environment 90. In an example using 13.5 nm EUV radiation, the energy of each photon is approximately 92 eV, and the ionization energy of a hydrogen molecule can be approximately 15 eV. Therefore, the generated free electrons have sufficient energy (e.g., 75 eV or more) and range to generate secondary plasma relatively far from the initial ionization event. These emitted electrons (i.e., electrons with an energy of approximately 75 eV) can further ionize one, two, or even three hydrogen molecules. Therefore, even if primary plasma is generated only at the site where the EUV photons are incident, secondary plasma can be generated throughout the entire clamp environment 90, for example, around the patterning device MA. Furthermore, electrons emitted from the first surface 110 as a result of the photoelectric effect may contribute to the plasma within the patterning device environment 90. Electrons may also be emitted from other surfaces to which EUV radiation is incident. Grounded surfaces to which EUV radiation is incident can continue to supply electrons to the plasma throughout the period during which EUV radiation pulses are generated. Free electrons in the plasma may be absorbed by contaminating particles, resulting in those particles becoming negatively charged.

[0055] As a result of the first surface 110 being positively charged and the contaminating particles P being negatively charged, an electrostatic attraction may act between the first surface 110 and the contaminating particles. This may accelerate the contaminating particles toward the first surface 110. Consequently, the contaminating particles in the lithography apparatus may accumulate on the first surface 110. The contaminating particles accumulated on the first surface 110 may absorb and / or scatter EUV radiation incident on the patterning area of ​​the first surface 110. As a result, the contaminating particles may cause defects in the pattern projected onto the substrate W, potentially leading to defects on the substrate W.

[0056] In EUV lithography systems, EUV radiation may be generated in pulses; that is, there are periods when EUV radiation is generated and periods when it is not. EUV radiation pulses are typically generated at high speed. This frequency can be, for example, about 50 kHz, 60 kHz, or 100 kHz. In a typical EUV pulse cycle (for example, the period starting from when the first EUV radiation pulse is generated and ending just before the next EUV radiation pulse is generated), the EUV radiation pulse may be generated for only a very short time. For example, the EUV radiation pulse may be generated for only about 1% of the time of a typical EUV pulse cycle.

[0057] Figure 4 shows, on the same axis, (1) a plot of EUV intensity (I) against time (solid line) and (2) a plot of the potential (V) of the first surface 110 of the patterning device MA against time (dashed line). Figure 4 shows the time at which two EUV radiation pulses are generated by the lithography apparatus. The illustrated situation may be one in which the pellicle 131 is not provided in front of the first surface 110 of the patterning device MA. As described above, at the start of the EUV radiation pulse, the EUV radiation incident on the first surface 110 can cause electron emission from the first surface 110, causing the first surface 110 to become positively charged. This results in the first surface 110 having a positive potential. After the EUV pulse ends, the first surface 110 is discharged. That is, the magnitude of the positive charge on the first surface 110 decreases. This can make the first surface 110 nearly neutral. Discharge of the patterning surface 40 can be caused by free negative charges in the plasma formed within the patterning device environment 90. This means that during the EUV lithography process, the first surface 110 can periodically change between a positively charged state and a nearly neutral state at high frequencies.

[0058] During exposure, the second surface 111 is not exposed to EUV radiation and therefore does not become positively charged. Rather, the second surface 111 may become negatively charged as a result of the free negative charge of the plasma in the patterning device environment 90.

[0059] Figure 5 schematically shows an electrostatic clamp 100 and a patterning device covered with a pellicle 131, which may be part of a lithography apparatus according to the present invention. The pellicle 131 may be positioned opposite the first surface 110. For example, the pellicle 131 may be positioned spaced apart in the z direction from the first surface 110. The pellicle may be a film assembly configured to protect the patterning device MA from contaminating particles in the patterning device environment 90. To minimize the absorption of EUV radiation by the pellicle, the pellicle is very thin and consequently very fragile. The pellicle 131 may be supported by a pellicle frame 132. The pellicle 131 may be stretched over the pellicle frame 132. The pellicle 131 may be substantially electrically insulated. That is, the pellicle 131 may be substantially electrically insulated from the patterning device MA and substantially electrically insulated from other components in the lithography apparatus. As a result, static charge may accumulate on the pellicle 131.

[0060] When the pellicle 131 is located in front of the first surface 110, an electric field may be formed between the pellicle 131 and the first surface 110 due to the difference in charge discharge rates between them. Figure 6A shows a plot of the potential (V) (dashed line) of the first surface 110 of the patterning device MA and the potential (V) (solid line) of the pellicle 131 against time (t). Figure 6B shows a plot of the charge (Q) (dashed line) (dashed line) on the first surface 110 of the patterning device MA and the charge (Q) (solid line) on the pellicle 131 against time (t). The charge can be measured in nanocoulombs (nC). The times shown in Figures 6A and 6B include the time during which the lithography apparatus generates EUV radiation pulses and the time after the lithography apparatus generates EUV radiation pulses. The time can be measured in microseconds (μs).

[0061] In the time following the generation of an EUV radiation pulse by the lithography apparatus, the positively charged first surface 110 can attract free negative charges in the plasma. As these free negative charges are attracted to the first surface 110, they may land on the pellicle 131. As a result, the charge on the pellicle 131 may become more negative. For example, as shown in Figure 6B, the magnitude of the positive charge on the pellicle 131 may decrease and then become negative (although it may not necessarily have a negative potential relative to the clamp). On the other hand, the pellicle 131 can substantially prevent free negative charges from reaching the first surface 110. As a result, the first surface 110 can maintain its positively charged state.

[0062] The fact that the first surface 110 is positively charged and the pellicle 131 is negatively charged during the period following the EUV radiation pulse may lead to the presence of an electric field between the first surface 110 and the pellicle 131. Due to the close proximity of the first surface 110 and the presence of an electric field between them, electrostatic discharge can occur. As the electric field strength increases, the likelihood of electrostatic discharge increases. Electrostatic discharge can cause a large current to flow through the pellicle 131, which may damage the pellicle 131. For example, if the pellicle 131 comprises a thin film of metal, a large current flowing through the pellicle 131 may cause the thin film of metal to rupture.

[0063] Pellicle 131 fracture can also be caused by other mechanisms. For example, if an electric field exists between the first surface 110 and other components near the patterning device MA, a discharge may occur from the patterning device to the other components. The current and heat resulting from such a discharge may cause pellicle fracture.

[0064] The potential applied to the multiple electrodes 104A to 104D may be controlled to change the average potential of the multiple electrodes 104A to 104D. That is, the potential applied to the multiple electrodes 104A to 104D may be controlled to make the average potential of the multiple electrodes positive, negative, or neutral.

[0065] In the electrostatic clamp 100 shown in Figure 3, the multiple electrodes 104A to 104D may be divided into a first electrode group 104A and 104C and a second electrode group 104B and 104D. The potential applied to the first electrode group 104A and 104C may be substantially equal in magnitude to the potential applied to the second electrode group 104B and 104D, and may have opposite polarity. The number of electrodes in the first electrode group 104A and 104C may be substantially the same as the number of electrodes in the second electrode group 104B and 104D. As a result, the average potential of the multiple electrodes 104A to 104D may be approximately 0V.

[0066] Figures 7A and 7B show schematic diagrams of an electrostatic clamp 100 and a patterning device MA, which may be part of a lithography apparatus according to the present invention. In Figures 7A and 7B, the first surface 110 of the patterning device MA is covered with a pellicle 131. However, this is not essential to the present invention, nor is it essential for the operation of the electrostatic clamp 100 in the first and second modes described later.

[0067] In the electrostatic clamp 100 shown in Figure 7A, the absolute value of the positive potential applied to the first electrode group 104A, 104C may be greater than the absolute value of the negative potential applied to the second electrode group 104B, 104D. When the number of electrodes in the first electrode group 104A, 104C is approximately equal to the number of electrodes in the second electrode group 104B, 104D, the average potential of the multiple electrodes 104A to 104D may be positive.

[0068] In the electrostatic clamp 100 shown in Figure 7B, the absolute value of the positive potential applied to the first electrode group 104A, 104C may be smaller than the absolute value of the negative potential applied to the second electrode group 104B, 104D. When the number of electrodes in the first electrode group 104A, 104C is approximately equal to the number of electrodes in the second electrode group 104B, 104D, the average potential of the multiple electrodes 104A to 104D may be negative.

[0069] In general, the absolute value and polarity of the average potential of multiple electrodes 104A to 104D may be controlled by adjusting the difference between the absolute value of the potential applied to the first electrode group 104A and 104C and the absolute value of the potential applied to the second electrode group 104B and 104D.

[0070] This method is not limited to the above technique of controlling multiple electrodes 104A to 104D to have a positive or negative average potential. Alternatively, the first electrode group 104A, 104C may be negative, and the second electrode group 104B, 104D may be positive. Furthermore, there may be more than two electrode groups 104A to 104D. For example, there may be three, four, five, or more electrode groups 104A to 104D. The electrostatic clamp 100 may be configured to apply different potentials to each electrode group 104A to 104D. That is, the potential applied to each electrode group may be independently controllable. Even further alternatively, each electrode 104A to 104D may be independently controllable so that different potentials can be applied to each electrode 104A to 104D. As those skilled in the art will understand, there are various ways to control the multiple electrodes 104A to 104D in order to make the average potential of the multiple electrodes 104A to 104D positive or negative.

[0071] In a lithography apparatus, some components, such as the masking blade 120, may be grounded. That is, some components, such as the masking blade 120, may be at a potential of approximately 0V. Near the electrostatic clamp 100 and the patterning device MA, there may be other relatively large conductive components at ground potential. If the average potential of the multiple electrodes 104A to 104D is not 0V, an electric field may be formed between the electrostatic clamp 100 and other grounded components in the lithography apparatus. For example, an electric field may be formed between the electrostatic clamp 100 and the masking blade 120. As a result, if the average potential of the multiple electrodes in the electrostatic clamp is not 0V, a potential may be capacitively induced in the first conductive coating 112 on the first surface 110 of the patterning device MA, and a potential may be capacitively induced in the second conductive coating 113 on the second surface 111 of the patterning device MA.

[0072] When the first conductive coating 112 and the second conductive coating 113 are substantially uncharged, the potentials induced in the first conductive coating 112 and the second conductive coating 113 may have the same polarity as the average potential of the multiple electrodes 104A to 104D. That is, if the average potential of the multiple electrodes 104A to 104D is negative, the potentials induced in the first conductive coating 112 and the second conductive coating 113 may also be negative. On the other hand, if the average potential of the multiple electrodes 104A to 104D is positive, the potentials induced in the first conductive coating 112 and the second conductive coating 113 may be positive. When the average potential of the multiple electrodes 104A to 104D is approximately 0V, it is possible that no potential will be induced in the first conductive coating 112 or the second conductive coating 113 by the electrostatic clamp 100. Generally, when the first conductive coating 112 and the second conductive coating 113 are substantially charge-free, the potential induced in the first conductive coating 112 and the second conductive coating 113 may be controlled by controlling the average potential of the multiple electrodes 104A to 104D.

[0073] In this context, the average potential of the multiple electrodes 104A to 104D may be an average calculated by taking into account (i.e., weighting) the potentials capacitively induced in the first conductive coating 112 and the second conductive coating 113. The potential capacitively induced in the first conductive coating 112 and the second conductive coating 113 by a given electrode is proportional to the surface area of ​​that electrode and the dielectric constant of the region between the electrode and the first and second conductive coatings 112 and 113, and inversely proportional to the distance between the electrode and the first and second conductive coatings 112 and 113. When multiple electrodes 104A to 104D are arranged in a plane parallel to the first and second conductive coatings 112 and 113 (i.e., the distance between the multiple electrodes 104A to 104D and the first and second conductive coatings 112 and 113 is substantially uniform), and the dielectric constant is uniform throughout the region between the multiple electrodes 104A to 104D and the first and second conductive coatings 112 and 113, the contribution of a particular electrode to the average potential may depend on the potential and surface area of ​​that electrode. Therefore, the average potential of the multiple electrodes 104A to 104D may be a weighted average based on the surface area of ​​each electrode.

[0074] The capacitive induction of potential in the first conductive coating 112 and the second conductive coating 113 has been described with reference to the masking blade 120, but this is not essential to the present invention. That is, even in the absence of the masking blade 120, the electrostatic clamp can capacitively induce potential in the first conductive coating 112 and the second conductive coating 113 of the patterning device MA. In some embodiments, other components of the lithography apparatus may perform the function of the masking blade 120 described above.

[0075] In the present invention, the potential applied to the multiple electrodes may be controlled such that the average potential of the multiple electrodes 104A to 104D alternately switches between a first mode and a second mode. In the first mode, a potential may be applied to the multiple electrodes 104A to 104D such that the average potential of the multiple electrodes 104A to 104D becomes the first potential. In the second mode, a potential may be applied to the multiple electrodes 104A to 104D such that the average potential of the multiple electrodes 104A to 104D becomes the second potential. The operating state in which the average potential of the multiple electrodes 104A to 104D alternately switches between the first potential and the second potential may be referred to as the exposure state.

[0076] Furthermore, the first potential may be higher than the second potential. For example, if the second potential is negative, the first potential may also be negative and have a smaller absolute value than the second potential, or the first potential may be positive. If the second potential is positive, the first potential may be positive and have a larger absolute value than the second potential. The difference between the first and second potentials may be greater than 10V, preferably greater than 50V, and more preferably greater than 75V. The difference between the first and second potentials may be less than 1000V, preferably less than 700V, and more preferably less than 500V. For example, the first potential may be about 100V and the second potential may be about -100V. Alternatively, the first potential may be about -5V and the second potential may be about -100V.

[0077] During exposure, the alternating switching between the first and second average potentials of the multiple electrodes 104A to 104D may be synchronized with the generation of radiation pulses in the lithography apparatus.

[0078] In an exposure cycle, the period during which radiation pulses are generated may be called the on period, and the period during which no radiation pulses are generated may be called the off period. The lithography apparatus may operate in a first mode (i.e., a mode in which the average potential of the multiple electrodes 104A to 104D is the first potential) during the on period, or for most of the on period. The lithography apparatus may operate in a second mode (i.e., a mode in which the average potential of the multiple electrodes 104A to 104D is the second potential) during the off period, or for most of the off period.

[0079] In the context of the present invention, "synchronously" may mean that the generation of radiation pulses and the alternating switching between the first and second modes occur at the same frequency and with a stable phase relationship. However, this does not necessarily mean that the switching from the first mode to the second mode (or vice versa) occurs simultaneously with the end (or start) of the radiation pulse in the lithography apparatus.

[0080] For example, the transition from the second mode to the first mode may be initiated before the start time of the radiation pulse (i.e., the point at which the radiation pulse begins). This can be beneficial when there is a delay between the point at which the transition from the second mode to the first mode is initiated and the point at which the first mode is achieved (i.e., the point at which the average potential of the multiple electrodes 104A to 104D becomes the first potential). In other words, this can be beneficial when the transition of the average potential of the multiple electrodes 104A to 104D from the second potential to the first potential involves a rise time. By initiating the switch from the second mode to the first mode before the start of the radiation pulse, it is possible to ensure that the average potential of the multiple electrodes 104A to 104D becomes the first potential at the start time of the radiation pulse. Also, the transition from the first mode to the second mode may be initiated after the end time of the radiation pulse (i.e., the point at which the radiation pulse ends). This can ensure that the electrostatic clamp 100 operates in the first mode throughout the entire ON period.

[0081] The frequency at which the electrostatic clamp 100 completes one cycle in the exposure state may be the same as the frequency of EUV radiation. For example, the electrostatic clamp may alternately switch between the first mode and the second mode at a frequency greater than 19 kHz, preferably greater than 49 kHz, more preferably greater than 59 kHz, and even more preferably greater than 99 kHz.

[0082] The second potential may be negative. As a result, if the second surface 111 of the patterning device MA is substantially uncharged, a negative potential may be induced on the second surface 111 of the patterning device MA during the off period. By inducing a negative potential on the second surface 111 of the patterning device MA during the off period, negative charges in the patterning device environment 90 originating from the plasma generated by EUV radiation may be repelled from the second surface 111 of the patterning device MA. As a result, the degree to which the second surface 111 of the patterning device MA becomes negatively charged can be reduced. Furthermore, if the first surface 110 of the patterning device MA is substantially uncharged, a negative potential may be induced on the first surface 110 of the patterning device MA during the off period. By inducing a negative potential on the first surface 110 of the patterning device MA during the off period, contaminating particles in the patterning device environment that have become negatively charged by negative charges in the plasma may be repelled from the first surface 110. As a result, defects caused by the deposition of contaminating particles on the first surface 110 can be reduced.

[0083] By changing the average potential of multiple electrodes 104A to 104D to a first potential (a potential higher than the second potential, i.e., negative but with a smaller absolute value, or positive), the degree of negativity of the potential induced on the first surface 110 is reduced. This means that the degree of photoelectron emission generated from the first surface 110 while it is irradiated with EUV radiation can be reduced.

[0084] The first potential may be positive. If the first potential is positive and the first conductive coating 112 and the second conductive coating 113 are not significantly negatively charged, a positive potential may be induced on the first conductive coating 112 and the second conductive coating 113 (i.e., the first surface 110 and the second surface 111 of the patterning device MA). That is, the electrostatic clamp may be configured such that a positive potential is induced on the first surface 110 and the second surface 111 during the ON period, and a negative potential is induced on the first surface 110 and the second surface 111 during the OFF period. By inducing a positive potential on the first surface 110 during the ON period, electron emission from the first surface 110 can be reduced. As a result, the degree to which the first surface is positively charged is reduced, which can reduce the supply of electrons to the plasma in the patterning device environment 90.

[0085] The absolute value of the first positive potential may be determined such that the positive potential induced on the first surface 110 of the patterning device is sufficient to prevent electron emission due to the photoelectric effect. That is, the absolute value of the first positive potential is such that the positive potential induced on the first surface 110 is sufficient to prevent electron emission due to the photoelectric effect. stop It may be set to be greater than ). The maximum kinetic energy of electrons emitted by photoemission is given by equation (2), where h is Planck's constant (4.14 × 10⁻¹⁴). -15 Here, eVs is the frequency of the radiation, f is the energy required to emit electrons from the surface, and φ is the work function of the material (i.e., the minimum energy required to emit electrons from the surface). The work function is a characteristic of the material on the surface from which the electrons are emitted. E kmax =hf-φ (2)

[0086] If the energy supplied to the electrons by the electric field generated from the positive potential induced on the first surface 110 is greater than the maximum possible kinetic energy of the emitted electrons, then photoemission does not occur. Therefore, the stopping potential can be defined by equation (3). eV stop =hf-φ (3)

[0087] In EUV lithography, the wavelength of radiation can be approximately 13.5 nm. Therefore, the photon energy of photons in the EUV radiation beam can be approximately 92 eV. The work function of the first surface 110 can depend on the material forming the first surface 110. Generally, the work function can be between 2 eV and 7 eV. When the work function is 7 eV or less, it is preferable that the potential induced on the first surface 110 is approximately 85 V or higher in order to substantially suppress photoemission. When the work function is 2 eV or less, it is preferable that the potential induced on the first surface 110 is approximately 90 V or higher in order to substantially suppress photoemission. To ensure that photoemission is substantially suppressed regardless of the work function of the material, it is preferable that the potential induced on the first surface 110 is approximately 92 V or higher. To ensure that photoemission is substantially suppressed despite the inaccuracy of the electrostatic clamp 100, it is preferable that the potential induced on the first surface is approximately 99 V or higher. The first potential may be less than 2000V, preferably less than 1000V, and more preferably less than 500V. This is to prevent the time required to transition the electrostatic clamp 100 from the first mode to the second mode (and vice versa) from being excessive. This may be to ensure that the electrostatic clamp 100 is alternately switched between the first mode and the second mode at the frequency at which radiation pulses are generated in the lithography apparatus.

[0088] The means for synchronizing the alternating switching between the first and second modes with the radiation pulses generated by the lithography apparatus are not particularly limited. In one embodiment, a signal responsible for the start of the radiation pulse may also be transmitted to the electrostatic clamp 100, thereby controlling the electrostatic clamp 100 to switch from the second mode to the first mode simultaneously with the start of the radiation pulse. Similarly, a signal responsible for the end of the radiation pulse may also be transmitted to the electrostatic clamp 100, thereby controlling the electrostatic clamp 100 to switch from the first mode to the second mode simultaneously with the end of the radiation pulse. Alternatively, the electrostatic clamp 100 may determine the timing of radiation pulse generation by the lithography apparatus using a sensor (not shown) that is built into the electrostatic clamp 100 itself or a sensor in an electrostatic clamp system equipped with an electrostatic clamp. An example of this will be described later. As yet another method, the generation of radiation pulses and the alternating switching between the first and second modes may be performed independently. In this case, the generation of radiation pulses and the alternating switching between the first and second modes may be performed synchronously by starting at a predetermined same time and proceeding at a predetermined same frequency.

[0089] Figures 8A-8C illustrate the synchronization between the generation of radiated pulses and the alternating switching between the first and second modes.

[0090] Figure 8A shows plots of EUV radiation intensity (I) against time for several EUV radiation pulses. The durations shown in Figures 8A-C include three radiation pulses. Specifically, the first radiation pulse starts at t=t1 and ends at t=t2, the second radiation pulse starts at t=t3 and ends at t=t4, and the third radiation pulse starts at t=t5 and ends at t=t6. The period from t1 to t3 can be considered one cycle of the radiation pulse.

[0091] Figure 8B shows a plot of the average potential (V) of multiple electrodes 104A to 104D in the electrostatic clamp 100 against time (t) for three radiation pulses. As shown in Figure 8B, the average potential of multiple electrodes 104A to 104D before the start time (t1) of the first radiation pulse is the second potential (V2). As mentioned above, the second potential is negative. Immediately before the start time (t=t1) of the first radiation pulse, the electrostatic clamp 100 starts switching from the second mode to the first mode. During a relatively short switching phase, the average potential of the multiple electrodes increases. By the start time (t1) of the first radiation pulse, the average potential of multiple electrodes 104A to 104D may have reached the first potential (V1). The average potential of multiple electrodes 104A to 104D during the time this radiation pulse is generated (i.e., from t=t1 to t=t2) is the first potential (V1). At or immediately after the end of the radiation pulse (t2), the electrostatic clamp 100 begins switching from the first mode to the second mode. During a relatively short switching phase, the average potential of the multiple electrodes 104A to 104D may decrease until its average potential reaches the second potential (V2). The cycle may then be repeated. A complete cycle of alternating switching between the first and second modes can be considered to be from t=t1 to t=t3.

[0092] Figure 8C shows an example of a method for controlling the average potential of multiple electrodes 104A to 104D. Figure 8C shows a plot of the potential (V) applied to the first electrode group 104A and 104C and the potential applied to the second electrode group 104B and 104D against time (t) for several EUV radiation pulses. The number of electrodes in the first electrode group 104A and 104C may be approximately the same as the number of electrodes in the second electrode group 104B and 104D. Therefore, the average potential of multiple electrodes 104A to 104D is the average of the potentials applied to the first electrode group 104A and 104C and the potentials applied to the second electrode group 104B and 104D.

[0093] As shown in FIG. 8C, the potentials applied to the first electrode groups 104A and 104C are maintained positive through three pulse cycles. The potentials applied to the second electrode groups 104B and 104D are maintained negative through three pulse cycles. Before the start time (t = t1) of the first radiation pulse, a potential V = V A2 is applied to the first electrode groups 104A and 104C, and a potential V = V B2 is applied to the second electrode groups 104B and 104D. The absolute value of V B2 is larger than the absolute value of V A2 . As a result, as shown in FIG. 8B, the average potential of the plurality of electrodes 104A to 104D becomes negative. During the time when the radiation pulse is generated (i.e., from t = t1 to t = t2), a potential V = V A1 is applied to the first electrode groups 104A and 104C, and a potential V = V B1 is applied to the second electrode groups 104B and 104D. When transitioning from V A2 to V A1 , the potential applied to the first electrode groups 104A and 104C is increased, and when transitioning from V B2 to V B1 , the potential applied to the second electrode groups 104B and 104D is increased (i.e., the absolute value of the negative potential applied to the second electrode group becomes smaller). During the time when the radiation pulse is generated (i.e., from t = t1 to t = t2), since the absolute value of V A1 is larger than the absolute value of V B1 , the average potential of the plurality of electrodes 104A to 104D becomes positive.

[0094] <000034२>The method of applying potentials to the first electrode groups 104A and 104C and the second electrode groups 104B and 104D is not essential to the essence of the present invention. Alternatively, the potential applied to either one of the first electrode groups 104A and 104C or the second electrode groups 104B and 104D may be made constant. For example, the potential applied to the first electrode groups 104A and 104C may be maintained constant. In this case, the potential applied to the second electrode groups 104B and 104D, as shown in FIG. 8C, is V B1 and V B2 in accordance with the generation of the radiation pulse in the lithographic apparatus.They may be switched alternately between. In this case, V B2 The absolute value of is greater than the absolute value of the constant potential applied to the first electrode group 104A, 104C, and V B1 If the absolute value of is smaller than the absolute value of the constant potential applied to the first electrode group 104A, 104C, the average potential of the multiple electrodes 104A-104D can alternate between negative and positive, as shown in Figure 8B. As can be understood, other possible methods of applying potential to the first and second electrode groups 104A-104D may be employed to generate the average potential pattern of the multiple electrodes 104A-104D shown in Figure 8B.

[0095] When a radiation pulse is irradiated onto the first surface 110 of the patterning device MA, the amount of positive charge accumulated on the first surface 110 is reduced or suppressed by reducing or suppressing electron emission from the first surface 110 of the patterning device MA, thereby reducing or eliminating any positive charge. This means that when the average potential of the multiple electrodes 104A to 104D becomes negative (i.e., when the electrostatic clamp 100 transitions to the second mode), the potential of the first surface 110 can be rapidly reduced. This is because the discharge of the first surface 110 by the plasma in the patterning device environment 90 is required to a lesser extent or not at all. As a result, the average potential of the first surface 110 decreases over time. This means that the degree to which negatively charged contaminant particles are attracted to the first surface 110 is reduced. Therefore, the amount of contaminant particles deposited on the first surface 110 can be reduced. This can improve the defect rate of the substrate because the number of defects in the pattern projected onto the substrate is reduced. By ensuring that the electrostatic clamp 100 operates in the first mode throughout the entire ON period, emission due to the photoelectric effect can be reduced or prevented throughout the entire ON period.

[0096] Furthermore, suppressing electron emission from the first surface 110 of the patterning device MA can reduce the plasma density within the patterning device environment 90. The presence of plasma within the patterning device environment 90 contributes to particle emission from the surface. The presence of plasma within the patterning device environment 90 can also cause contaminating particles to become negatively charged. Therefore, reducing the plasma density within the patterning device environment 90 can further improve the defect rate of the first surface 110.

[0097] A further advantage of suppressing electron emission from the first surface 110 of the patterning device MA when a radiation pulse is irradiated onto the first surface 110 of the patterning device MA is realized when the pellicle 131 is located in front of the first surface 110. Specifically, the first surface 110 may not be positively charged, and no electric field (e.g., the electric field described in relation to Figures 6A and 6B) may be generated between the first surface 110 and the pellicle 131. This means that the risk of fracture of the pellicle 131 may be reduced.

[0098] Capacitance exists between components within a lithography apparatus. In particular, the capacitance between the clamp surface 102 and the second surface 111 of the patterning device MA can be considered a variable capacitance that changes as a function of the gap between the clamp surface 102 and the second surface 111.

[0099] In a closed system, where charge cannot move in or out of the system, and given a predetermined initial charge state, a change in the isolation distance between the electrostatic clamp 100 and the patterning device MA results in a change in their respective variable capacitances. Furthermore, this change in capacitance also causes (sometimes significantly) a change in the potential across the capacitances in accordance with the change in isolation distance. In particular, the relationship Q=CV must always be maintained for each capacitance (unless charge is injected). Therefore, if a capacitance C changes while the amount of charge Q contained in that capacitance remains the same, the potential V must change inversely proportional to the changing capacitance C. This can lead to significant potential amplification.

[0100] As described above, charge can accumulate on the insulating surfaces of the patterning device MA, for example, the first surface 110 and the second surface 111. The clamped patterning device MA may retain residual charge even after being released from the electrostatic clamp 100. As the unclamped patterning device MA moves away from the clamp surface, the distance between the clamp surface and the patterning device surface increases, which can decrease the capacitance and amplify the potential. That is, considering the proportional relationship between charge and potential in a closed system (Q=CV), when the capacitance changes (inversely proportional to the distance between parallel plates), a decrease in capacitance results in a proportional increase in potential. Therefore, as the patterning device MA and the clamp 100 are separated, the potential of the patterning device may rise sufficiently to cause electrical breakdown of the hydrogen gas. Such a discharge can cause damage to the patterning device MA, the electrostatic clamp 100, and / or particle generation, which can lead to subsequent defects. Therefore, it is desirable that the residual charge on the patterning device is small or absent before the patterning device is unclamped from the electrostatic clamp 100.

[0101] Any residual charge that may exist on the patterning device before it is released from the electrostatic clamp is a negative electrostatic charge on the second surface 111. This negative electrostatic charge can arise from free charges in the plasma being attracted to the second surface 111.

[0102] To repel negative charges from the second surface 111, the lithography apparatus may operate in an alternate state. In the alternate state, the average potential of the multiple electrodes 104A to 104D does not need to be alternately switched between the first potential and the second potential. Rather, the average potential of the multiple electrodes may be maintained at a constant negative potential.

[0103] The lithography apparatus may operate in an alternate state for a predetermined period before the patterning device MA is removed from the electrostatic clamp. For example, the lithography apparatus may operate in an alternate state for a predetermined number of pulses before the end of the exposure cycle. By operating the apparatus to make the average potential of the multiple electrodes 104A to 104D negative, the second surface 111 of the electrostatic clamp 100 becomes capacitively negative. This causes negative charges to be repelled from the second surface 111. As a result, the accumulation of negative charges on the second surface 111 can be prevented during the period before the patterning device is unloaded from the electrostatic clamp 100. Thus, damage to the patterning device caused by discharge when the patterning device MA is released from the electrostatic clamp 100 can be avoided. In this context, "unclamping" refers not only to the time when the clamping force between the electrostatic clamp 100 and the patterning device MA is removed, but also to the period after which the electrostatic clamp 100 is separated from the patterning device MA (i.e., the period during which the distance between the electrostatic clamp 100 and the patterning device MA increases).

[0104] In the alternative state, the electrostatic clamp may always operate in the second mode. That is, in the alternative state, the average potential of the multiple electrodes 104A to 104D may be the second potential. Alternatively, the absolute value of the average potential of the multiple electrodes 104A to 104D in the alternative state may be larger than that in the second mode. For example, while the average potential of the multiple electrodes in the second mode is approximately -5V, the average potential of the multiple electrodes 104A to 104D in the alternative state may be approximately -20V. In the second mode, it is desirable that the absolute value of the (negative) average potential of the multiple electrodes 104A to 104D be sufficient to reduce the degree to which the second surface 111 becomes negatively charged. However, it is desirable that the absolute value of the (negative) average potential of the multiple electrodes 104A to 104D is not excessively large to the extent that positive charges in the patterning device environment 90 are attracted to the first surface 110. This could result in the first surface 110 becoming positively charged and requiring compensation by negative charges during the on period. In the alternative state (i.e., during clamp release), the accumulation of positive charge on the first surface 110 is of less importance, while the reduction of charge accumulation on the second surface 111 becomes more important. Therefore, the absolute value of the average potential of the multiple electrodes 104A to 104D may be larger in the alternative state compared to the second mode.

[0105] In response to the generation of radiation pulses in the lithography apparatus, the average potential of multiple electrodes 104A to 104D is alternately switched between a first potential (when the first potential is positive) and a second potential (when the second potential is negative), thereby realizing the advantages of applying positive and negative potentials to the patterning device MA. That is, for most of the exposure time, negative charges can be repelled from the second surface 111 of the patterning device MA, and contaminating particles can be repelled from the first surface 110 of the patterning device MA. In addition, when radiation pulses are generated, electron emission from the first surface 110 of the patterning device MA can be reduced or prevented. By reducing or preventing electron emission from the first surface 110 of the patterning device MA when radiation pulses are generated, the amount of positive charge accumulation on the first surface 110 is reduced. This means that the amount of contaminating particles attracted to the first surface 110 is reduced. As a result, the deposition of contaminating particles on the first surface 110 of the patterning device MA can be effectively reduced, and the accumulation of negative charge on the second surface 111 of the patterning device MA can be effectively avoided. This reduces the defect rate of the substrate. At the same time, it reduces the risk when removing the charged patterning device MA from the electrostatic clamp 100.

[0106] In one embodiment, when the patterning device MA is clamped to an electrostatic clamp, the second surface 111 of the patterning device MA may be connected to an electrical circuit (not shown). The electrical circuit may be connected to the second surface 111 of the patterning device by contacts.

[0107] The electrical circuit may include a power supply to provide a predetermined potential to the second surface 111 via a contact. During the exposure cycle, a net charge may accumulate on the second surface 111 of the patterning device MA. This may impair the potential induced on the first surface 110 of the patterning device MA. This can be avoided by providing an electrical connection to the second surface 111 and supplying the necessary potential to the second surface 111. This is particularly beneficial when the charging of the second surface 111 of the patterning device MA by plasma in the patterning device environment 90 occurs only when the lithography apparatus generates radiation pulses.

[0108] Alternatively, or additionally, the electrical circuit connected to the second surface 111 of the patterning device MA may include a sensor. The sensor may be configured to detect a photoelectric current induced on the second surface 111 of the patterning device MA. The sensor may also be an ammeter. When electrons are emitted by radiation irradiated onto the first surface 110, and the first surface 110 becomes positively charged, a charge mirror image of the charge on the first surface 110 may be induced on the second surface 111. As a result, the sensor in the electrical circuit connected to the second surface 111 may be able to detect that the first surface 110 is being irradiated. That is, the sensor in the electrical circuit connected to the second surface 111 may be able to detect when a radiation pulse is generated by the lithography apparatus. The alternating switching between the first and second modes may be controlled depending on whether or not a radiation pulse is being generated in the lithography apparatus as detected by the sensor in the electrical circuit. In this way, a closed system incorporated into the electrostatic clamp 100, or an electrostatic clamp system comprising the electrostatic clamp 100, may be capable of controlling the alternating switching between the first mode and the second mode in response to the generation of radiation pulses in the lithography apparatus.

[0109] Additionally, or alternatively, the second surface 111 may be electrically connected to the first surface 110. For example, the second surface 111 may be electrically connected to the first surface 110 via the side surface of the patterning device MA. For example, a conductive material (not shown) in contact with the first conductive coating 112 and the second conductive coating 113 may be provided on the side surface of the patterning device.

[0110] The system and method of the present invention may be implementable in existing electrostatic clamp models without requiring hardware modifications. As a result, the system and method can be implemented quickly and easily.

[0111] The lithography apparatus according to the present invention may be used in the manufacture of ICs.

[0112] While this specification may specifically refer to the use of lithography equipment in IC manufacturing, it should be understood that the lithography equipment described herein can also be used for other applications. Possible other applications include the manufacture of integrated optical systems, guide and detection patterns for magnetic domain memory, flat panel displays, liquid crystal displays (LCDs), and thin-film magnetic heads.

[0113] To the extent permitted by context, embodiments of the present invention may be implemented in hardware, firmware, software, or any combination thereof. Alternatively, embodiments of the present invention may be implemented as instructions stored in a machine-readable medium that can be read and executed by one or more processors. The machine-readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computer device). Examples of machine-readable mediums include read-only memory (ROM), random-access memory (RAM), magnetic storage media, optical storage media, flash memory devices, and propagating signals of electrical, optical, acoustic, or other forms (e.g., carrier waves, infrared signals, digital signals, etc.). Furthermore, firmware, software, routines, and instructions may be described herein as performing specific operations. However, such descriptions are merely for convenience; in practice, such operations occur when a computer device, processor, controller, or other device executes firmware, software, routines, instructions, etc., thereby enabling actuators or other devices to interact with the physical world.

[0114] While embodiments of the present invention may be specifically referenced in the context of lithography apparatus, embodiments of the present invention may be used in other apparatuses. Embodiments of the present invention may form part of a mask inspection apparatus, a measuring apparatus, or any apparatus for measuring or processing objects such as wafers (or other substrates) or masks (or other patterning devices). These apparatuses are sometimes commonly referred to as lithography tools.

[0115] While this specification may contain specific references to using embodiments of the present invention in the context of photolithography, it will be understood that the present invention is not limited to photolithography, to the extent permitted by the context.

Claims

1. Lithography apparatus, Multiple electrodes configured to exert an electrostatic clamping force on the component, A power supply connected to the aforementioned plurality of electrodes, The electrostatic clamp system comprises a controller configured to alternately switch the potential applied to the plurality of electrodes between a first mode and a second mode in synchronization with the generation of radiation pulses in the lithography apparatus, In the first mode, the average potential of the plurality of electrodes is the first potential. In the second mode, the average potential of the plurality of electrodes is the second potential. A lithography apparatus in which the first potential is higher than the second potential.

2. The lithography apparatus according to claim 1, wherein the controller is configured to operate the electrostatic clamp in the first mode during the time when radiation pulses are being generated by the lithography apparatus, and to operate the electrostatic clamp in the second mode during the time when radiation pulses are not being generated by the lithography apparatus.

3. The lithography apparatus according to any of the preceding claims, wherein the controller is configured to initiate a switch from the second mode to the first mode before the start time of the radiation pulse and to initiate a switch from the first mode to the second mode after the end time of the radiation pulse.

4. The lithography apparatus according to any of the preceding claims, wherein the second potential is negative.

5. The lithography apparatus according to any of the preceding claims, wherein the first potential is positive.

6. The lithography apparatus according to claim 5, wherein the component comprises a first surface and a second surface opposite to the first surface, and the lithography apparatus is configured such that a positive potential is induced on the first surface and the second surface when the electrostatic clamp operates in the first mode, and a negative potential is induced on the first surface and the second surface when the electrostatic clamp operates in the second mode.

7. The lithography apparatus according to claim 5 or 6, wherein the first potential is determined such that the positive potential induced on the first surface is greater than or equal to the stopping potential of the material forming the first surface, with respect to the wavelength of the radiation pulse generated by the lithography apparatus.

8. The lithography apparatus according to any one of claims 5 to 7, wherein the average potential of the electrode in the first mode is determined such that the positive potential induced on the first surface is greater than 85V, preferably greater than 90V, more preferably greater than 92V, even more preferably greater than 99V, and less than 2000V, preferably less than 1000V, and even more preferably less than 500V.

9. The lithography apparatus according to any of the preceding claims, wherein the plurality of electrodes include a first electrode group and a second electrode group, and in both the first mode and the second mode, a positive potential is applied to the first electrode group and a negative potential is applied to the second electrode group.

10. The lithography apparatus according to claim 9, wherein in the first mode, the absolute value of the potential applied to the first electrode group is greater than the absolute value of the potential applied to the second electrode group, and in the second mode, the absolute value of the potential applied to the first electrode group is smaller than the absolute value of the potential applied to the second electrode group.

11. The lithography apparatus according to claim 9 or 10, wherein the first electrode group and the second electrode group are uniformly distributed on the surface of an electrostatic clamp configured to face a second surface of the component when the component is clamped to the electrostatic clamp.

12. The lithography apparatus according to any of the preceding claims, wherein when the component is supported by an electrostatic clamp, the plurality of electrodes are separated from the second surface of the component by a dielectric coating and / or a plurality of protrusions such that the component is substantially electrically insulated.

13. The lithography apparatus according to any of the preceding claims, wherein the controller is configured to alternately switch the electrostatic clamp between the first mode and the second mode at a frequency greater than 19 kHz, preferably greater than 49 kHz, more preferably greater than 59 kHz, and even more preferably greater than 99 kHz.

14. The lithography apparatus according to any prior claim, further comprising a contact portion and an electrical circuit configured such that an electrical connection is formed between the second surface of the component and the electrical circuit when the component is clamped by an electrostatic clamp.

15. The lithography apparatus according to claim 14, wherein the electrical circuit and the contact portion are configured to apply a predetermined potential to the second surface of the component.

16. The lithography apparatus according to claim 14 or 15, wherein the electrical circuit includes a sensor configured to detect a current induced on the second surface of the component, in order to determine whether or not the lithography apparatus is generating a radiation pulse.

17. The lithography apparatus according to any of the preceding claims, wherein the controller is configured to alternately switch between the first mode and the second mode in the exposure state, and to control the potential applied to the plurality of electrodes such that the average potential is constant and negative in the alternative state.

18. The lithography apparatus according to claim 17, wherein the lithography apparatus is configured to operate in the alternative state for a predetermined period before the component is released from the electrostatic clamp.

19. The lithography apparatus according to claim 17 or 18, wherein the controller is configured to control the potential applied to the plurality of electrodes so that it always operates in the second mode in the alternative state.

20. The lithography apparatus according to any of the preceding claims, wherein the component is a patterning device, the first surface being a patterning surface having a patterning region configured to impart a pattern to the radiation pulses generated by the lithography apparatus, and the second surface being a clamping surface to which an electrostatic clamp exerts an attractive force.

21. A lithography apparatus according to any of the prior claims, further comprising a radiation source configured to generate EUV radiation pulses.

22. A method for controlling an electrostatic clamp for clamping a component in a lithography apparatus, A clamping force is applied to the component by a plurality of electrodes arranged in the electrostatic clamp, The method includes controlling the potential applied to the plurality of electrodes such that the average potential of the plurality of electrodes alternates between a first potential and a second potential, The first potential is higher than the second potential, A method wherein the alternating switching between the first potential and the second potential is synchronized with the generation of radiation pulses in the lithography apparatus.

23. The method according to claim 22, wherein the average potential of the plurality of electrodes is the first potential during the time when radiation pulses are being generated by the lithography apparatus, and the second potential during the time when radiation pulses are not being generated by the lithography apparatus.

24. The method according to claim 22 or 23, wherein the switching of the potential from the second potential to the first potential is initiated before the start time of the radiation pulse, and the switching of the potential from the first potential to the second potential is initiated after the end time of the radiation pulse.

25. The method according to claim 23 or 24, wherein the second potential is negative.

26. The method according to any one of claims 22 to 25, wherein the first potential is positive.

27. The method according to claim 26, wherein the component comprises a first surface and a second surface opposite to the first surface, and when the average potential of the plurality of electrodes is the first potential, a positive potential is induced on the first surface and the second surface, and when the average potential of the plurality of electrodes is the second potential, a negative potential is induced on the first surface and the second surface.

28. The method according to claim 27, wherein the first potential is determined such that, with respect to the wavelength of the radiation pulse generated by the lithography apparatus, the positive potential induced on the first surface is greater than the stopping potential of the material forming the first surface.

29. The method according to any one of claims 26 to 28, wherein the first potential is determined such that the positive potential induced on the first surface is greater than 85V, preferably greater than 90V, more preferably greater than 92V, even more preferably greater than 99V, and less than 2000V, preferably less than 1000V, and even more preferably less than 500V.

30. The method according to any one of claims 26 to 29, wherein the plurality of electrodes include a first electrode group and a second electrode group, a positive potential is applied to the first electrode group and a negative potential is applied to the second electrode group.

31. The method according to claim 30, wherein, in order to generate the first potential, the absolute value of the potential applied to the first electrode group is greater than the absolute value of the potential applied to the second electrode group, and in order to generate the second potential, the absolute value of the potential applied to the first electrode group is smaller than the absolute value of the potential applied to the second electrode group.

32. The method according to any one of claims 23 to 31, wherein the frequency for alternately switching between the first potential and the second potential is greater than 19 kHz, preferably greater than 49 kHz, more preferably greater than 59 kHz, and even more preferably greater than 99 kHz.

33. The method according to any one of claims 22 to 32, further comprising applying a predetermined potential to the second surface of the component via a physical connection.

34. The method according to any one of claims 23 to 33, further comprising: detecting a current induced on the second surface of the component; determining whether or not the lithography apparatus is generating a radiation pulse based on the detected current; and controlling the alternating switching of the average potential of the plurality of electrodes between the first potential and the second potential based on whether or not it has been determined that a radiation pulse is being generated.

35. The method according to any one of claims 23 to 34, further comprising controlling the potential applied to the plurality of electrodes such that the average potential of the plurality of electrodes becomes negative during a predetermined period before the component is released from the electrostatic clamp.

36. The method according to any one of claims 23 to 35, further comprising controlling the potential applied to the plurality of electrodes such that the average potential of the plurality of electrodes is always the second potential during a predetermined period before the component is released from the electrostatic clamp.

37. A device manufacturing method comprising the method according to any one of claims 22 to 36, for controlling an electrostatic clamp for clamping a component in a lithography apparatus.

38. A computer program comprising an instruction, when executed by the control system of a lithography apparatus, that causes the lithography apparatus to perform the method according to any one of claims 22 to 37.

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