System and method for discharging patterning device

Abstract

Disclosed herein is a light source arranged to illuminate a non-patterned surface of a patterning device in a lithographic apparatus, where the light source is configured such that in response to illumination from the light source, the non-patterned surface emits electrons due to a photoelectric effect. Advantageously, when the non-patterned surface is charged, the non-patterned surface may be discharged before the non-patterned surface is unloaded.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority from European application No. 23151475.3 filed on January 13, 2023, and the entire contents of this European application are incorporated herein by reference. Technical Field

[0003] The present invention relates to discharging a charged surface of a patterning device in a lithographic apparatus. Embodiments provide a system and method for discharging a charged surface of a patterning device using the photovoltaic effect. Background Art

[0004] A lithographic apparatus is a machine that applies a desired pattern to a substrate (typically onto a target portion of the substrate). A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In this case, a patterning device (alternatively referred to as a mask or reticle) can be used to generate the circuit pattern to be formed on a separate layer of the IC. This pattern can be transferred to a target portion (e.g., a portion comprising one or several die) on a substrate (e.g., a silicon wafer). The pattern is typically transferred by imaging onto a layer of radiation-sensitive material (resist) disposed on the substrate. Typically, a single substrate will include a network of continuously patterned adjacent target portions.

[0005] Photolithography is widely considered to be one of the key steps in manufacturing ICs and other devices and / or structures. However, as the size of features made using photolithography becomes smaller and smaller, photolithography is becoming a more critical factor for enabling the manufacture of small ICs or other devices and / or structures.

[0006] A theoretical estimate of the limit of pattern printing can be given by the Rayleigh criterion for resolution, as shown in equation (1):

[0007]

[0008] where λ is the wavelength of the 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), it can be seen that a 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 reducing the value of k1.

[0009] In order to shorten the exposure wavelength and thus reduce the minimum printable dimensions, it has been proposed to use extreme ultraviolet (EUV) radiation sources. EUV radiation is electromagnetic radiation with a wavelength in the range of 10 nm to 20 nm, for example, in the range of 13 nm to 14 nm. It has further been proposed that EUV radiation with a wavelength less than 10 nm (for example, in the range of 5 nm to 10 nm, such as 6.7 nm or 6.8 nm) could be used. This radiation is known as extreme ultraviolet radiation or soft x-ray radiation. Possible sources include, for example, laser-generated plasma sources, discharge plasma sources, or sources based on synchrotron radiation provided by electron storage rings.

[0010] Once the EUV radiation has been generated, it is directed through the lithographic apparatus by a plurality of mirrors to a patterned surface of a patterning device, which imparts a desired pattern to the EUV radiation.

[0011] The performance and reliability of patterning devices are crucial to the effectiveness and efficiency of lithographic processes. Any damage to the patterning device or related features of the patterning device can increase downtime of the lithographic apparatus and significantly reduce the yield of the manufacturing process. There is a general need to improve the performance and reliability of patterning devices in lithographic apparatuses. Summary of the Invention

[0012] According to a first aspect of the present invention, there is provided a light source arranged to illuminate a non-patterned surface of a patterning device in a lithographic apparatus, wherein the light source is configured such that in response to illumination from the light source, the non-patterned surface emits electrons due to a photoelectric effect.

[0013] According to a second aspect of the present invention, there is provided a pattern forming device discharge system for use in a lithographic apparatus, the system comprising: a pattern forming device; a support structure for holding the pattern forming device in the lithographic apparatus; and one or more light sources according to the first aspect.

[0014] According to a third aspect of the invention there is provided a lithographic apparatus comprising: a system according to the second aspect; and a controller arranged to control illumination of a patterning device of the system by one or more light sources of the system.

[0015] According to a fourth aspect of the present invention, there is provided a method of reducing the charge of a charged non-patterned surface of a patterning device in a lithographic apparatus, the method comprising irradiating the non-patterned surface with light such that the non-patterned surface emits electrons due to a photoelectric effect.

[0016] According to a fifth aspect of the present invention, there is provided a method for manufacturing a device, the method comprising the method of the fourth aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference characters indicate corresponding parts.

[0018] Figure 1 A lithographic apparatus is schematically depicted.

[0019] Figure 2 A more detailed view of a lithographic apparatus is schematically depicted.

[0020] Figure 3 A patterning device is schematically depicted being secured to a support structure.

[0021] Figure 4 A patterning device discharge system according to an embodiment is schematically depicted.

[0022] The features shown in the various figures are not necessarily drawn to scale, and the sizes and / or arrangements depicted are not limiting. It will be understood that the various figures include optional features that may not be essential to the present invention. Furthermore, not all features of the device are depicted in each of the various figures, and the various figures may only show some of the components that are relevant for describing a particular feature. DETAILED DESCRIPTION

[0023] Figure 1 A lithographic apparatus 100 comprising a source collector module SO according to an embodiment of the present invention is schematically depicted. The apparatus 100 comprises:

[0024] - an illumination system (or illuminator) IL configured to condition a radiation beam B (e.g. EUV radiation);

[0025] a support structure (eg, mask table) MT configured to support a patterning device (eg, mask or reticle) MA and connected to a first positioner PM configured to accurately position the patterning device;

[0026] a substrate table (e.g., wafer stage) WT configured to hold a substrate (e.g., a resist-coated wafer) W and connected to a second positioner PW configured to accurately position the substrate; and

[0027] - a projection system (eg, a reflective projection system) PS configured to project the pattern imparted to the radiation beam B by the patterning device MA onto a target portion C of the substrate W (eg, comprising one or more dies).

[0028] The illumination system IL may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic or other types of optical components, or any combination thereof, to direct, shape or control the radiation.

[0029] The support structure MT holds the patterning device MA in a manner that depends on the orientation of the patterning device, the design of the lithographic apparatus, and other conditions, such as, for example, whether the patterning device is held in a vacuum environment. The support structure MT may use mechanical, vacuum, electrostatic, or other clamping techniques to hold the patterning device MA. The support structure MT may be, for example, a frame or table that may be fixed or movable as desired. The support structure MT may ensure that the patterning device MA is in a desired position, for example, relative to the projection system PS.

[0030] The term “patterning device” should be broadly interpreted as referring to any device that can be used to impart a radiation beam B with a pattern in its cross-section so as to create a pattern in a target portion C of the substrate W. The pattern imparted to the radiation beam B may correspond to a specific functional layer in a device (such as an integrated circuit) created in the target portion C.

[0031] Examples of patterning devices include masks, programmable mirror arrays, and programmable liquid crystal display (LCD) panels. Masks are well known in photolithography and include types such as binary, alternating phase-shift, and attenuated phase-shift, as well as various hybrid mask types. An example of a programmable mirror array uses a matrix arrangement of small mirrors, each of which can be individually tilted to reflect an incident radiation beam in different directions. The tilted mirrors impart a pattern in the radiation beam that is reflected by the mirror matrix.

[0032] Similar to illumination system IL, projection system PS can include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic, or other types of optical components, or any combination thereof, appropriate for the exposure radiation used or for other factors such as the use of a vacuum. It may be desirable to use a vacuum for EUV radiation since other gases may absorb too much radiation. Therefore, a vacuum environment can be provided throughout the beam path with the aid of vacuum walls and a vacuum pump.

[0033] As depicted here, the lithographic apparatus 100 is of a reflective type (eg, using a reflective mask).

[0034] The lithographic apparatus 100 may be of a type having two (dual stage) or more substrate tables WT (and / or two or more supports MT). In such a "multi-stage" lithographic apparatus, additional substrate tables WT (and / or additional supports MT) may be used in parallel, or preparatory steps may be performed on one or more substrate tables WT (and / or one or more supports MT) while one or more other substrate tables WT (and / or one or more other supports MT) are being used for exposure.

[0035] refer to Figure 1 The illumination system IL receives an extreme ultraviolet radiation beam from a source collector module SO. Methods for generating EUV light include, but are not necessarily limited to, converting a material having at least one element (e.g., xenon, lithium, or tin) into a plasma state by utilizing one or more emission lines in the EUV range. In one such method, often referred to as laser produced plasma ("LPP"), the desired plasma can be generated by irradiating a fuel (such as a droplet, stream, or cluster of a material having the desired line-emitting element) with a laser beam. The source collector module SO may be a laser ( Figure 1 The laser is used as part of an EUV radiation system (not shown) to provide a laser beam for excitation of the fuel. The resulting plasma emits output radiation (e.g., EUV radiation), which is collected using a radiation collector disposed in a source collector module. For example, when a CO2 laser is used to provide the laser beam for fuel excitation, the laser and source collector module SO may be separate entities.

[0036] In such cases, the laser is not considered to form part of the lithographic apparatus 100, and the radiation beam B is delivered from the laser to the source collector module SO by means of a beam delivery system comprising, for example, suitable directing mirrors and / or a beam expander. In other cases, such as when the source is a discharge produced plasma EUV generator (commonly referred to as a DPP source), the source may be an integral part of the source collector module SO.

[0037] The illumination system IL can include an adjuster for adjusting the angular intensity distribution of the radiation beam. Typically, at least the outer radial extent and / or the inner radial extent (commonly referred to as σ-outer and σ-inner, respectively) of the intensity distribution in a pupil plane of the illumination system IL can be adjusted. In addition, the illumination system IL can include various other components, such as a faceted field mirror arrangement and a faceted pupil mirror arrangement. The illumination system IL can be used to condition the radiation beam B to have a desired uniformity and intensity distribution in its cross-section.

[0038] A radiation beam B is incident on a patterning device (e.g., a mask) MA, which is held on a support structure (e.g., a mask table) MT, and is patterned by the patterning device MA. After reflecting from the patterning device (e.g., mask) MA, the radiation beam B passes through a projection system PS, which focuses the radiation beam B onto a target portion C of a substrate W. With the aid of a second positioner PW and a position sensor PS2 (e.g., an interferometer device, a linear encoder, or a capacitive sensor), the substrate table WT can be accurately moved, for example, to position a different target portion C in the path of the radiation beam B. Similarly, a first positioner PM and another position sensor PS1 can be used to accurately position the patterning device (e.g., mask) MA relative to the path of the radiation beam B. Mask alignment marks M1, M2 and substrate alignment marks P1, P2 can be used to align the patterning device (e.g., mask) MA and substrate W.

[0039] The controller 500 controls the overall operation of the lithographic apparatus 100 and, in particular, executes the operational processes described further below. The controller 500 can be embodied as a suitably programmed general-purpose computer including a central processing unit, volatile and non-volatile storage components, one or more input and output devices (such as a keyboard and screen), one or more network connections to various components of the lithographic apparatus 100, and one or more interfaces. It will be appreciated that a one-to-one correspondence between the control computer and the lithographic apparatus 100 is not necessary. In embodiments of the present invention, a single computer can control multiple lithographic apparatuses 100. In embodiments of the present invention, multiple networked computers can be used to control a single lithographic apparatus 100. The controller 500 can also be configured to control one or more associated process devices and substrate handling devices of a lithocell or litho cluster of which the lithocell 100 forms a part. The controller 500 can also be configured to be subordinate to the management control system of the lithocell or litho cluster and / or the overall control system of the factory.

[0040] Figure 2 The lithographic apparatus 100 is shown in greater detail and includes a source collector module SO, an illumination system IL, and a projection system PS. An EUV radiation-emitting plasma 210 can be formed by a plasma source. The EUV radiation can be generated by a gas or vapor (e.g., Xe gas, Li vapor, or Sn vapor), wherein the radiation-emitting plasma 210 is generated to emit radiation in the EUV range of the electromagnetic spectrum. In one embodiment, an excited tin (Sn) plasma is provided to generate EUV radiation.

[0041] Radiation emitted by radiation emitting plasma 210 passes from source chamber 211 into collector chamber 212 .

[0042] The collector chamber 212 may include a radiation collector CO. Radiation traversing the radiation collector CO may be focused into a virtual source point IF. The virtual source point IF is often referred to as an intermediate focus, and the source collector module SO is arranged such that the virtual source point IF is located at or near an opening 221 in the enclosure 220. The virtual source point IF is an image of the radiation emitting plasma 210.

[0043] The radiation then traverses an illumination system IL, which may include a faceted field mirror arrangement 22 and a faceted pupil mirror arrangement 24 arranged to provide a desired angular distribution of the unpatterned beam 21 at the patterning device MA, and a desired uniformity of radiation intensity at the patterning device MA. The unpatterned beam 21 forms a patterned beam 26 after reflection at the patterning device MA, which is held by the support structure MT, and is imaged by the projection system PS via reflective elements 28, 30 onto a substrate W held by a substrate table WT.

[0044] More elements than shown may typically be present in the illumination system IL and the projection system PS. Also, there may be more mirrors than shown in the various figures, for example more than Figure 2 From 1 to 6 additional reflective elements than those shown may be present in projection system PS.

[0045] Alternatively, the source collector module SO may be part of an LPP radiation system.

[0046] like Figure 1 As depicted in FIG, in an embodiment, a lithographic apparatus 100 comprises an illumination system IL and a projection system PS. The illumination system IL is configured to emit a radiation beam B. The projection system PS is separated from a substrate table WT by an intervening space. The projection system PS is configured to project a pattern imparted to the radiation beam B onto a substrate W. The pattern is for EUV radiation of the radiation beam B.

[0047] The space intervening between the projection system PS and the substrate table WT may be at least partially evacuated.The intervening space may be defined at the location of the projection system PS by a solid surface from which the employed radiation is directed towards the substrate table WT.

[0048] Figure 3A schematic representation of the patterning device MA clamped to the support structure MT is depicted. As described above, the support structure MT may use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device MA. The support structure MT may include a plurality of burls (conical protrusions) on a support surface 42 of the support structure MT that faces a non-patterned surface 41 of the patterning device MA. When the patterning device MA is clamped to the support structure MT, the non-patterned surface 41 faces the support structure MT and contacts the distal ends of the plurality of burls. It is not necessary for each of the plurality of burls to contact the non-patterned surface 41. The burls are not necessarily in contact with the non-patterned surface 41. Figure 3 The non-patterned surface 41 may be referred to as the back side of the patterning device MA. The patterned surface 40 may be referred to as the front side of the patterning device MA.

[0049] Both the patterning device MA and the support structure MT may be housed within a patterning device environment 90. The patterning device environment 90 may be separated from an external environment surrounding the lithographic apparatus 100 and / or other elements within the lithographic apparatus such that gases and contaminant particles P are substantially prevented from entering the patterning device environment 90.

[0050] The patterning device environment 90 may be partially evacuated of gas. That is, the pressure within the patterning device environment 90 may be less than the ambient pressure. This is to limit the attenuation of EUV radiation as it travels through the patterning device environment 90.

[0051] like Figure 2 As shown, but Figure 3 Not shown in FIG, 5 , a pellicle 80 may at least partially cover the patterning device MA. The purpose of the pellicle 80 is to substantially prevent any contaminant particles in the environment 90 of the patterning device MA from reaching the surface of the patterned surface 40.

[0052] One problem that can arise in EUV systems is that the patterning device MA can become charged by EUV-induced plasma generated near the patterning device MA by EUV radiation. Specifically, charge can accumulate on the unpatterned surface 41 of the patterning device MA. When the charged patterning device MA is unloaded from its support structure MT, a large potential difference can develop between the patterning device MA and the support structure MT due to losses in capacitive coupling with the support structure MT. This generated potential difference can cause damage to the patterning device MA and / or the pellicle 80 used for the patterning device MA.

[0053] A known technique for addressing the problem of charging of the patterning device MA is to generate a plasma around the patterning device MA by irradiating the patterning device MA with EUV light. When the patterning device MA is removed from its support structure MT, the plasma can reach the non-patterned surface 41 of the patterning device MA. The electrical conduction through the plasma can discharge the patterning device MA and thereby reduce the possibility of damage due to charging of the patterning device MA.

[0054] The known techniques described above present several problems. The additional use of EUV light to discharge the patterning device MA significantly increases energy requirements and also reduces the lifetime of the EUV source. Most of the charge accumulation may occur on the non-patterned surface 41, and the EUV plasma cannot discharge this surface until the patterning device MA is removed from its support structure MT. While the EUV plasma may reduce the magnitude and / or duration of the potential difference, potential difference accumulation may still occur when the patterning device MA is removed from its support structure MT.

[0055] Embodiments provide a new technique for discharging charged surfaces of a patterning device MA that reduces or avoids one or more of the problems described above.

[0056] Embodiments provide a light source within the lithographic apparatus for illuminating at least a portion of the patterning device MA. Illumination from the light source is arranged to cause the patterning device MA to emit electrons due to the photoelectric effect. This may allow the patterning device MA to discharge sufficiently and thereby prevent or reduce problems with voltage buildup when the patterning device MA is unloaded from its support structure MT.

[0057] Figure 4 The arrangement of a patterning device discharge system according to an embodiment is schematically shown. A light source 43 is arranged to illuminate the patterning device MA with photons 44.

[0058] The irradiated surface of the patterning device MA may be a surface of the patterning device MA on which a substantial charge accumulation has occurred. In particular, the irradiated surface may be the non-patterned surface 41 of the patterning device MA.

[0059] The material of the irradiated surface is a known property of the patterning device MA. The irradiated surface may be made of the same material as the body of the patterning device MA. Alternatively, the patterning device MA may be at least partially coated such that the irradiated surface comprises a different material than the body of the patterning device MA.

[0060] The light source 43 is configured such that the emitted photons 44 are suitable for generating a photoelectric effect in the illuminated surface.Thus, the power and wavelength of the light emitted from the light source 43 may be determined depending on the requirements for inducing a photoelectric effect in the particular material of the illuminated surface.

[0061] The light source 43 can also be configured so that the emitted light does not cause plasma generation near the patterning device MA. Hydrogen gas may be present near the patterning device MA, and the light source 43 can be configured so that full ionization of the hydrogen gas does not occur. Advantageously, this avoids the risk of hydrogen ionization causing electrical breakdown and / or plasma-related effects.

[0062] Hydrogen ionization typically occurs in the energy spectrum around 13.6 eV, which corresponds to light with a wavelength of 91 nm. Therefore, by emitting photons 44 with energies below 13.6 eV (i.e., photons 44 with wavelengths longer than 91 nm), hydrogen ionization can be substantially avoided. Consequently, the maximum energy of photons 44 emitted by light source 43 can be 11 eV or less, which corresponds to photons 44 with wavelengths of 113 nm or longer.

[0063] The required power of light source 43 can be determined based on the required charge reduction of the irradiated surface so that the irradiated surface is sufficiently discharged. This can be determined based on a determination or estimation of how much charge needs to be extracted, the voltage at the irradiated surface, and the light yield of the irradiated surface. The light yield is the number of electrons emitted from the irradiated surface in response to the number of incident photons 44. A light yield of 1 indicates that one electron is emitted for each single incident photon 44. The light yield depends on the type of irradiated material and the energy of the incident photons 44.

[0064] If the desired current for discharging the irradiated surface is, for example, 50 nA, and the voltage across the irradiated surface is, for example, 150 V, the power required to cause electron generation of photons 44 would be 7.5 µW. The material of the irradiated surface could be, for example, chromium. When irradiated with electrons having an energy of 11 eV (corresponding to a wavelength of 113 nm), the light yield of chromium is approximately 0.01. Therefore, the power required for the light source 43 to emit photons 44 having a wavelength of 113 nm would need to be approximately 0.75 mW. If a longer discharge time is acceptable, a lower light source power can be used. Thus, the light source power could, for example, be in the range of approximately 0.07 mW to 0.75 mW.

[0065] The irradiated surface can be made of a variety of different materials and is not limited to pure chromium. When using different materials for the irradiated surface, the same photon energy can still be used, and these photon energies can be 11 eV or less to avoid any hydrogen ionization. However, due to the different light yields of the irradiated surface, different light source powers can be used. For example, the irradiated surface can include nickel and / or tantalum. For these materials, the light yield increases to about 0.08. Therefore, the required light source power can be reduced to a power in the range of about 8 μW to 94 μW.

[0066] The required light source power may depend on one or more of the material of the irradiated surface, the charge of the irradiated surface, and the desired discharge rate of the irradiated surface. The required light source power may be in the range of, for example, about 5 μW to 1 mW.

[0067] The power of the light emitted from the light source 43 may be tunable. The appropriate power of the emitted light may be determined depending on the material of the surface of the patterning device MA that the light source 43 is arranged to illuminate. The light source 43 may then be configured such that the light source 43 emits light having the determined power.

[0068] The wavelength of the emitted light from light source 43 may be tunable. The appropriate wavelength of the emitted light may be determined depending on the material of the surface of patterning device MA that light source 43 is arranged to illuminate. Light source 43 may then be configured such that light source 43 emits light having the determined wavelength.

[0069] The illuminated surface may be an alloy comprising two or more of chromium, nickel, tantalum and / or other materials.The required light source power may be determined depending on the light yield of the illuminated surface.

[0070] The light source 43 may be any of a number of different commercially available light sources. The light source 43 may be a laser or another type of light source 43. The light source 43 may be, for example, a krypton or xenon based lamp suitable for use in a vacuum. The light source 43 may be, for example, a https: / / resonance.on.ca / high-power-vuv-light-source / One of the ultraviolet (UV) light sources shown at (as viewed on January 5, 2023). Light source 43 can emit light with an appropriate wavelength according to the technical requirements of the embodiment. Light source 43 can also emit light with an appropriate power according to the technical requirements of the embodiment.

[0071] Embodiments provide a patterning device discharge system within a lithographic apparatus. The patterning device discharge system includes a patterning device arrangement and one or more light sources 43. The patterning device arrangement may include a patterning device MA and a support structure MT for the patterning device MA. The patterning device MA may be arranged and operated according to known techniques. Each light source 43 may be one of the light sources 43 described above. Each light source 43 may be arranged such that each light source 43 can illuminate at least one surface of the patterning device MA. Each light source 43 may be configured such that, in response to illumination of a surface of the patterning device MA by the light source 43, the illuminated surface emits electrons due to the occurrence of a photoelectric effect.

[0072] Embodiments include a number of different implementations of each light source 43 of the patterning device discharge system.

[0073] In a first embodiment of the patterning device discharge system, the light source 43 can be integrated into or located behind the support structure MT of the patterning device MA. The support structure MT can include an aperture. The light source 43 can be arranged so that the light source 43 emits light through the aperture and onto the non-patterned surface 41 of the patterning device MA. Advantageously, the patterning device MA can be illuminated by the light source 43 before being removed from its support structure MT. Thus, the patterning device MA can be fully discharged before being removed from its support structure MT. This can effectively prevent any potential difference from accumulating between the patterning device MA and its support structure MT when the patterning device MA is removed from its support structure MT.

[0074] The embodiment includes a method of operating the first embodiment of the patterning device discharge system. The patterning device MA can be irradiated during EUV lithography. During the irradiation process, charge can accumulate on the non-patterned surface 41 of the patterning device MA. After the irradiation process is completed, the light source 43 can begin to emit light, which illuminates the non-patterned surface 41 of the patterning device MA. Due to the photoelectric effect, electrons can be emitted from the non-patterned surface 41, and the non-patterned surface 41 is thereby fully discharged. The light source 43 can then stop emitting light so that the photoelectric effect no longer occurs. The patterning device MA can then be removed from the support structure MT of the patterning device MA.

[0075] In a second embodiment of the patterning device discharge system, the light source 43 can be a structure that is separate from the support structure MT of the patterning device MA. The light source 43 can be located at a position away from the support structure MT, for example, on the side of the support structure MT. The light source 43 can be located, for example, on an arm of a transport device used to exchange the patterning device MA. The patterning device MA can be removed from its support structure MT and positioned so that the light source 43 can illuminate the non-patterned surface 41 of the patterning device MA. When the patterning device MA is charged, the second embodiment may require the patterning device MA to be removed from its support structure MT. This may cause an initial potential difference to accumulate between the patterning device MA and its support structure MT. However, an advantage of the second embodiment is that the second embodiment may not require any modification to the existing design of the support structure MT for the patterning device MA.

[0076] Embodiments include methods of operating the second embodiment of the patterning device discharge system. The patterning device MA can be irradiated during EUV lithography. During the irradiation process, charge can accumulate on the non-patterned surface 41 of the patterning device MA. After the irradiation process has been completed, the patterning device MA can be removed from its support structure MT and positioned so that its non-patterned surface 41 can be irradiated by the light source 43. The light source 43 can begin to emit light, which illuminates the non-patterned surface 41 of the patterning device MA. Due to the photoelectric effect, electrons can be emitted from the non-patterned surface 41, and the non-patterned surface 41 is thereby fully discharged. The light source 43 can then stop emitting light so that the photoelectric effect no longer occurs. The reduction in charge due to the photoelectric effect can reduce the magnitude and / or duration of any potential difference accumulation that occurs between the patterning device MA and its support structure MT.

[0077] Embodiments provide a number of advantages over known techniques. In particular, charge accumulation on the surface of the patterning device MA can be neutralized without the need to use an EUV source. This increases the lifetime of the EUV source. In embodiments, the power required to discharge the patterning device MA can be much lower than when an EUV source is used. Thus, embodiments can provide overall energy savings. Embodiments can also cause the patterning device MA to heat up less than when known techniques for discharging the patterning device MA are performed. In embodiments, each light source 43 can be operated independently of the EUV source, and this can allow the patterning device MA to be exchanged more quickly. In a first embodiment of the patterning device discharging system, the patterning device MA can be discharged before being unloaded from its support structure MT, and this can prevent any initial potential difference from accumulating.

[0078] Embodiments include numerous modifications and variations of the techniques described above.

[0079] Although the technology of the embodiment has been described as being applied to an EUV lithography system, the technology of the embodiment can be applied to any type of lithography system. For example, the technology of the embodiment can be applied to a DUV lithography system.

[0080] Embodiments include patterning device discharge systems comprising more than one light source 43 for illuminating the patterning device MA. For example, the first light source 43 can be integrated into or located behind the support structure MT of the patterning device MA, as described above for the first embodiment of the patterning device discharge system. The second light source 43 can be located remote from the support structure MT, for example, to the side of the support structure MT, as described above for the second embodiment of the patterning device discharge system. The first and / or second light sources 43 can be used to discharge the patterning device MA.

[0081] In embodiments, the light source 43 is not limited to illuminating the non-patterned surface 41 of the patterning device MA. Embodiments include light sources 43 arranged to illuminate any surface of the patterning device MA. For example, the light source 43 and the transport device of the patterning device MA may be configured such that all surfaces of the patterning device MA on which significant charge accumulation may occur may be illuminated.

[0082] In the first embodiment of the patterning device discharge system described above, the light source 43 can be used to discharge the patterning device MA before each process in which the patterning device MA is unloaded from its support structure MT. The process of discharging the patterning device MA can be performed once after all lithography processes using the patterning device MA have been completed. Alternatively, the process of discharging the patterning device MA can be performed more than once while the patterning device MA is loaded on its support structure MT. This can reduce the maximum amount of charge accumulation that occurs during use of the patterning device MA. The light source 43 can discharge the patterning device MA between lithography processes performed using the patterning device MA. Embodiments also include a light source 43 that discharges the patterning device MA while a lithography process is being performed using the patterning device.

[0083] The one or more light sources 43 for discharging the patterning device may be incorporated into a lithographic apparatus.Such a lithographic apparatus may be used to manufacture ICs.

[0084] Although specific reference may be made herein to the use of lithographic apparatus in IC fabrication, it should be understood that the lithographic apparatus described herein may have other applications. Possible other applications include the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat panel displays, liquid crystal displays (LCDs), thin film magnetic heads, and the like.

[0085] Where context permits, embodiments of the present invention may be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the present invention may also be implemented by instructions stored on a machine-readable medium, which can be read and executed by one or more processors. A machine-readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, machine-readable media may include read-only memory (ROM); random-access memory (RAM); magnetic storage media; optical storage media; flash memory devices; electrical, optical, acoustic, or other forms of propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.). Furthermore, firmware, software, routines, and instructions may be described herein as performing certain actions. However, it should be understood that such descriptions are for convenience only and that these actions are actually caused by a computing device, processor, controller, or other device executing the firmware, software, routines, instructions, etc., and that, when performing such actions, they may cause actuators or other devices to interact with the physical world.

[0086] Although specific reference may be made herein to embodiments of the present invention in the context of a lithographic apparatus, embodiments of the present invention may be used with other apparatus. Embodiments of the present invention may form part of a mask inspection apparatus, a metrology apparatus, or any apparatus that measures or processes an object such as a wafer (or other substrate) or a mask (or other patterning device). These apparatuses may generally be referred to as lithographic tools.

[0087] Although the above may have made specific reference to the use of embodiments of the invention in the context of photolithography, it will be appreciated that the invention is not limited to photolithography, where the context permits.

[0088] Aspects of the invention are described in the following numbered aspects:

[0089] 1. A light source arranged to illuminate a non-patterned surface of a patterning device in a lithographic apparatus, wherein the light source is configured such that, in response to illumination from the light source, the non-patterned surface emits electrons due to a photoelectric effect.

[0090] 2. Light source according to aspect 1, wherein the light source is arranged to emit light having a wavelength greater than 91 nm, preferably at least 113 nm.

[0091] 3. The light source according to aspect 1 or 2, wherein the power of the light emitted by the light source is less than 1 mW.

[0092] 4. A light source according to any preceding aspect, wherein the power of light emitted by the light source is greater than 5 μW.

[0093] 5. A light source according to any preceding aspect, wherein the light source is tunable such that the wavelength and / or power of the emitted light can be varied.

[0094] 6. The light source of any preceding aspect, wherein the non-patterned surface of the patterning device is located on an opposite side of the patterning device to the patterned surface of the patterning device.

[0095] 7. The light source according to any preceding aspect, wherein the lithographic apparatus is an EUV lithographic apparatus or a DUV lithographic apparatus.

[0096] 8. A patterning device discharge system for use in a lithographic apparatus, the system comprising:

[0097] a patterning device;

[0098] a support structure for holding the patterning device in the lithographic apparatus; and

[0099] One or more light sources according to any preceding aspect.

[0100] 9. The system of clause 8, wherein the support structure is arranged such that when the patterning device is held by the support structure, the non-patterned surface of the patterning device faces the support structure; and

[0101] The at least one light source is arranged to illuminate a non-patterned surface of the patterning device while the patterning device is held by the support structure.

[0102] 10. The system of aspect 9, wherein the support structure comprises one or more openings; and

[0103] At least one light source arranged to illuminate the non-patterned surface of the patterning device when the patterning device is held by the support structure is arranged to illuminate light through the one or more openings.

[0104] 11. A system according to aspect 9 or 10, wherein at least one light source arranged to illuminate the non-patterned surface of the patterning device when the patterning device is held by the support structure is arranged in the support structure.

[0105] 12. The system according to any one of aspects 8 to 11, further comprising:

[0106] a conveyor device for the patterning device;

[0107] wherein the transport device is arranged to move the patterning device away from the support structure toward the irradiation site; and

[0108] When the patterning device is in the illumination site, the at least one light source is arranged to illuminate the patterning device.

[0109] 13. The system of any one of clauses 8 to 12, wherein the lithographic apparatus is an EUV lithographic apparatus or a DUV lithographic apparatus.

[0110] 14. A lithographic apparatus comprising:

[0111] A system according to any one of aspects 8 to 13; and

[0112] A controller is arranged to control illumination imparted to a patterning device of the system by one or more light sources of the system.

[0113] 15. A lithographic apparatus according to clause 14, wherein when a patterning device of the system is charged, the controller is arranged to control illumination of the patterning device by the one or more light sources of the system such that the patterning device is substantially discharged.

[0114] 16. The lithographic apparatus according to clause 14 or 15, wherein the lithographic apparatus is an EUV lithographic apparatus or a DUV lithographic apparatus.

[0115] 17. A method of reducing the charge of a charged non-patterned surface of a patterning device in a lithographic apparatus, the method comprising: illuminating the non-patterned surface with light such that the non-patterned surface emits electrons due to a photoelectric effect.

[0116] 18. The method of clause 17, wherein the lithographic apparatus is the lithographic apparatus of any one of clauses 14 to 16.

[0117] 19. A method for manufacturing a device, the method comprising the method according to clause 17 or 18.

[0118] Although specific embodiments of the present invention have been described above, it will be appreciated that the present invention may be practiced in other ways than those described. The above description is intended to be illustrative, not restrictive. Therefore, it will be understood by those skilled in the art that modifications may be made to the present invention as described without departing from the scope of the claims set forth below.

Claims

1. A light source arranged to illuminate a non-patterned surface of a patterning device in a lithographic apparatus, wherein The light source is configured such that, in response to illumination from the light source, the non-patterned surface emits electrons due to a photoelectric effect.

2. The light source according to claim 1, wherein The light source is arranged to emit light having a wavelength greater than 91 nm, preferably at least 113 nm.

3. The light source according to claim 1 or 2, wherein The power of the light emitted by the light source is less than 1 mW.

4. A light source according to any preceding claim, wherein The power of the light emitted by the light source is greater than 5 μW.

5. A light source according to any preceding claim, wherein The light source is tunable such that the wavelength and / or power of the emitted light can be varied.

6. A light source according to any preceding claim, wherein The non-patterned surface of the patterning device is located on an opposite side of the patterning device from the patterning surface of the patterning device.

7. A light source according to any preceding claim, wherein The lithography equipment is an EUV lithography equipment or a DUV lithography equipment.

8. A patterning device discharge system for use in a lithographic apparatus, the system comprising: a patterning device; a support structure for holding the patterning device in the lithographic apparatus; as well as One or more light sources according to any preceding claim.

9. The system according to claim 8, wherein: the support structure being arranged such that when the patterning device is held by the support structure, a non-patterned surface of the patterning device faces the support structure; and At least one light source is arranged to illuminate a non-patterned surface of the patterning device when the patterning device is held by the support structure.

10. The system according to claim 9, wherein: The support structure includes one or more openings; and The at least one light source arranged to illuminate a non-patterned surface of the patterning device when the patterning device is held by the support structure is arranged to illuminate light through the one or more openings.

11. The system according to claim 9 or 10, wherein: The at least one light source arranged to illuminate the non-patterned surface of the patterning device when the patterning device is held by the support structure is arranged in the support structure.

12. The system according to any one of claims 8 to 11, further comprising: a conveying device for the pattern forming device; wherein the transport device is arranged to move the pattern forming device away from the support structure toward the irradiation site; and At least one light source is arranged to illuminate the patterning device when the patterning device is in the illumination location.

13. The system according to any one of claims 8 to 12, wherein: The lithography equipment is an EUV lithography equipment or a DUV lithography equipment.

14. A lithographic apparatus comprising: A system according to any one of claims 8 to 13; and A controller is arranged to control illumination of a patterning device of the system by the one or more light sources of the system.

15. The lithographic apparatus of claim 14, wherein: When a patterning device of the system is charged, the controller is arranged to control illumination of the patterning device by the one or more light sources of the system such that the patterning device is substantially discharged.

16. The lithographic apparatus according to claim 14 or 15, wherein: The lithography equipment is an EUV lithography equipment or a DUV lithography equipment.

17. A method of reducing charge on a charged non-patterned surface of a patterning device in a lithographic apparatus, the method comprising: The non-patterned surface is illuminated with light, causing the non-patterned surface to emit electrons due to the photoelectric effect.

18. The method according to claim 17, wherein The lithographic apparatus is a lithographic apparatus according to any one of claims 14 to 16.

19. A method for manufacturing a device, comprising the method according to claim 17 or 18.

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