Pellicle and pellicle assembly

Abstract

To provide a pellicle and a pellicle assembly which overcome or mitigate a problem associated with the prior art.SOLUTION: The invention provides a pellicle suitable for use with a patterning device for a lithographic apparatus. The pellicle comprises at least one breakage region which is configured to preferentially break, during normal use in the lithographic apparatus, prior to breakage of remaining regions of the pellicle. At least one breakage region comprises a region of the pellicle thinner than surrounding regions of the pellicle.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to European application 15200767.0, filed December 17, 2015, U.S. application 62 / 328,291, filed April 27, 2016, and U.S. application 62 / 365,524, filed July 22, 2016, each of which is incorporated by reference in its entirety herein.

[0002]

[0002] The present invention relates to a pellicle and a pellicle assembly. The pellicle assembly may comprise a pellicle and a frame supporting the pellicle. The pellicle may be suitable for use in a patterning device of a lithographic apparatus. The present invention finds particular, but not exclusive, use in the context of EUV lithographic apparatus and tools. [Background technology]

[0003]

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

[0004]

[0004] The wavelength of radiation used by a lithographic apparatus to project a pattern onto a substrate determines the minimum size of features that can be formed on that substrate. Lithographic apparatus using EUV radiation, which is electromagnetic radiation having a wavelength in the range of 4-20 nm, can be used to form smaller features on a substrate than conventional lithographic apparatus (which may use electromagnetic radiation having a wavelength of 193 nm, for example).

[0005]

[0005] A pattern can be imparted to a radiation beam of a lithographic apparatus using a patterning device. The patterning device can be protected from particle contamination by a pellicle. The pellicle can be supported by a pellicle frame.

[0006]

[0006] The use of pellicles in lithography is well known and established. A typical pellicle in a DUV lithography tool is a thin membrane located away from the patterning device and outside the focal plane of the lithography tool when in use. Because the pellicle is outside the focal plane of the lithography tool, any contaminant particles that land on the pellicle are out of focus of the lithography tool. As a result, no image of the contaminant particles is projected onto the substrate. If the pellicle were not present, contaminant particles that land on the patterning device would be projected onto the substrate and introduce defects into the projected pattern.

[0007]

[0007] It is desirable to use a pellicle in an EUV lithography tool. EUV lithography differs from DUV lithography in that it is typically performed in a vacuum and the patterning device is typically reflective rather than transmissive.

[0008]

[0008] It is desired to provide a pellicle and pellicle assembly that overcomes or mitigates problems associated with the prior art. The embodiments of the invention described herein may be used in an EUV lithography apparatus. The embodiments of the invention may also be used in a DUV lithography apparatus or in another form of lithography apparatus. Summary of the Invention

[0009]

[0009] According to a first aspect of the present invention, there is provided a pellicle suitable for use with a patterning device of a lithographic apparatus, the pellicle having at least one damage area configured to preferentially damage before the remaining areas of the pellicle damage during normal use in the lithographic apparatus.

[0010]

[0010] Advantageously, the provision of a failure region on the pellicle allows for a pre-determined location on the pellicle where failure will occur first. The failure region of the pellicle may be structurally weaker than the surrounding portions of the pellicle. The failure region may be configured to cause the pellicle to fail in a controlled manner that limits contamination of the surrounding environment by pellicle debris. Additionally or alternatively, the failure region provides an area of ​​the pellicle that can be monitored for signs of impending pellicle failure. Failure in the failure region may indicate that the remainder of the pellicle is about to fail and, if detected, may act to remove the pellicle from operation.

[0011]

[0011] At least one damaged area may include an area of ​​the pellicle that is of reduced thickness compared to a surrounding area of ​​the pellicle.

[0012]

[0012] The at least one damaged region may include an area of ​​the pellicle that is exposed to radiation to structurally weaken the damaged region compared to the remaining areas of the pellicle.

[0013] The at least one damaged area may include an area of ​​the pellicle where one or more holes and / or cracks have formed.

[0014]

[0014] At least one damaged region may include an area of ​​the pellicle exposed to a substance configured to structurally weaken the damaged region compared to the remaining areas of the pellicle.

[0015]

[0015] The pellicle further includes a reinforced region disposed adjacent the damaged region, the reinforced region having a greater thickness compared to the remaining region of the pellicle.

[0016]

[0016] The reinforced region can be curved in shape on the pellicle.

[0017]

[0017] At least one failure region may include a fracture line configured to preferentially fail before the remaining regions of the pellicle fail, such that a crack is formed in the pellicle along the fracture line.

[0018]

[0018] The pellicle may further comprise a sensor configured to monitor the at least one damaged area and detect damage in the at least one damaged area.

[0019]

[0019] According to a second aspect of the present invention, there is provided a pellicle assembly comprising a pellicle according to the first aspect and a frame configured to support the pellicle, the pellicle including a peripheral portion supported by the frame and an unsupported portion surrounded by the peripheral portion.

[0020]

[0020] The fracture line may extend between sections of the outer periphery supported by the frame of the pellicle.

[0021]

[0021] The fracture line may surround a portion located at the edge of the unsupported portion of the pellicle.

[0022]

[0022] A portion of the reinforced portion of the pellicle may be in contact with the frame.

[0023]

[0023] Increasing the thickness of the reinforced portion allows the reinforced portion to be heated to a higher temperature than the rest of the pellicle. Contact between the reinforced portion of the pellicle and the frame provides a thermal connection between the reinforced portion and the frame that allows for heat transfer from the pellicle and to the frame.

[0024]

[0024] The at least one damaged area may form part of a perimeter supported by a frame of the pellicle.

[0025]

[0025] According to a third aspect of the present invention, there is provided a pellicle assembly suitable for use with a patterning device of a lithographic apparatus, comprising a frame configured to support the pellicle, and a pellicle mounted to the frame, the pellicle including at least a first layer having a first tension and a second layer having a second tension, the first tension being higher than the second tension such that in the event of pellicle damage the difference between the first tension and the second tension causes the pellicle to roll up.

[0026]

[0026] Advantageously, the pellicle rolls up on itself when it breaks, containing the pellicle debris therein, thereby reducing contamination of the surrounding environment by pellicle debris.

[0027]

[0027] The pellicle can include at least one break region configured to preferentially break before the remaining areas of the pellicle break during normal use in the lithographic apparatus, and the at least one break region is positioned such that breakage in the at least one break region of the pellicle ensures that the pellicle rolls up.

[0028]

[0028] According to a fourth aspect of the present invention, there is provided a pellicle suitable for use with a patterning device of a lithographic apparatus, comprising at least one conductive layer and a plurality of electrical contacts capable of establishing an electrical connection with the conductive layer, thereby enabling the electrical resistance between contacts of the conductive layer to be measured.

[0029]

[0029] According to a fifth aspect of the present invention, there is provided a pellicle fault detection device comprising a pellicle according to the fourth aspect and a sensor connected to at least two of the electrical contacts on the pellicle and configured to measure resistance between the electrical contacts.

[0030]

[0030] The conductive layer of the pellicle can be configured to release thermal energy from the pellicle to regulate the temperature of the pellicle. The conductive layer can oxidize over time. Oxidation of the conductive layer reduces the emissivity of the layer, which in turn reduces the efficiency of releasing thermal energy from the pellicle. Oxidation of the conductive layer also increases the electrical resistance of the layer. The sensor can detect an increase in the electrical resistance of the conductive layer and a decrease in the emissivity of the layer, indicative of oxidation of the layer. If the electrical resistance of the conductive layer increases beyond a threshold, the pellicle may no longer be suitable for use and can be replaced.

[0031]

[0031] An increase in the electrical resistance of the conductive layer may additionally or alternatively indicate a crack in the pellicle, and therefore, by monitoring the resistance of the conductive layer with a sensor, cracks in the pellicle may be identified.

[0032]

[0032] According to a sixth aspect of the present invention, there is provided a pellicle failure detection apparatus comprising a sensor assembly arranged to detect a change in a characteristic associated with a pellicle located on a pellicle frame, wherein the change in the characteristic associated with the pellicle indicates damage to the pellicle.

[0033]

[0033] The sensor assembly may be configured to detect changes in the optical transmission or reflection of radiation by the pellicle.

[0034]

[0034] The sensor assembly may include a radiation source configured to couple a beam of radiation into the pellicle so that the radiation is transmitted along the pellicle, and a radiation sensor configured to receive radiation that is reflected back through the pellicle or that is transmitted through the pellicle, wherein a change in the reflected or transmitted radiation received by the sensor indicates damage to the pellicle.

[0035]

[0035] The sensor assembly can be configured to detect changes in acoustic transmission or acoustic reflection of sound waves by the pellicle.

[0036]

[0036] The sensor assembly can include a transducer configured to generate acoustic waves in the pellicle and a sensor configured to receive the acoustic waves that are reflected back through the pellicle or that are transmitted through the pellicle, wherein a change in the reflected or transmitted acoustic waves received by the sensor indicates damage to the pellicle.

[0037]

[0037] The sensor assembly may include a stress sensor configured to measure the stress experienced by the pellicle.

[0038]

[0038] The sensor may include a strain gauge configured to measure the strain experienced by the pellicle.

[0039]

[0039] According to a seventh aspect of the present invention, there is provided a pellicle suitable for use with a patterning device of a lithographic apparatus, the pellicle comprising a first layer having a first ductility, a second layer having a second ductility, and a third layer having a third ductility, the third layer being located between the first and second layers, the third ductility being less than the first ductility and less than the second ductility.

[0040]

[0040] The third layer has a ductility less than that of the first and second layers. Thus, the third layer is relatively brittle compared to the first and second layers. When the pellicle is placed under tensile stress, the third layer will break before the first and second layers break. The breakage of the third layer dissipates energy before the pellicle is catastrophically broken. The first and second layers may undergo further strain after the breakage of the third layer, which leads to further dissipation of energy. Because the third layer is located between the first and second layers, advantageously, the debris of the third layer is contained by the first and second layers and therefore does not contaminate the surrounding environment.

[0041]

[0041] According to an eighth aspect of the present invention, there is provided a debris mitigation apparatus comprising a debris steering device arranged in proximity to a pellicle of a lithographic apparatus, the debris steering device being configured to guide debris resulting from breakage of the pellicle in a preferred direction.

[0042]

[0042] The debris mitigation apparatus further includes a sensor configured to monitor the pellicle and detect pellicle breakage, and the debris steering device is configured to respond to detection of pellicle breakage and to guide debris resulting from the pellicle breakage in a preferred direction.

[0043]

[0043] The debris steering device can include a closed chamber positioned adjacent to the pellicle, the interior of which is maintained at a pressure lower than the pressure at which the pellicle is maintained, and an actuator configured to open the chamber in response to detection of pellicle breakage, thereby causing debris from the broken pellicle to be sucked into the chamber.

[0044]

[0044] The debris steering device can include a closed chamber positioned adjacent to the pellicle, the interior of which is maintained at a pressure higher than the pressure at which the pellicle is held, and an actuator configured to open the chamber in response to detection of pellicle breakage, thereby causing debris resulting from the broken pellicle to be blown out of the chamber in a preferred direction.

[0045]

[0045] The debris steering device may include a charged surface positioned adjacent to the pellicle such that in the event of pellicle damage, debris from the pellicle is guided towards the charged surface by electrostatic attraction.

[0046]

[0046] According to a ninth aspect of the present invention, there is provided a debris reduction apparatus comprising a sensor configured to monitor a pellicle held by a frame and detect damage to the pellicle, and a tension control device configured to reduce the tension in the pellicle in response to detection of damage to the pellicle, thereby inhibiting further damage to the pellicle.

[0047]

[0047] The tension control device can include a plurality of actuators configured to reduce the tension of the pellicle held by the frame by compressing the frame holding the pellicle.

[0048]

[0048] The tension control device may include a temperature control device configured to reduce the tension of the pellicle by increasing the temperature of the pellicle.

[0049]

[0049] The temperature control device can be configured to increase the temperature of the pellicle by resistive heating.

[0050]

[0050] The temperature control device may include a radiation source configured to illuminate all or part of the pellicle to increase the temperature of the pellicle.

[0051]

[0051] According to a tenth aspect of the present invention, there is provided a pellicle frame configured to support a pellicle at an outer periphery of the pellicle so as to surround a suspension region of the pellicle, the pellicle frame comprising a first pair of sides arranged on opposing edges of the suspension region of the pellicle and extending in a first direction along the edges of the suspension region of the pellicle, and a second pair of sides arranged on opposing edges of the suspension region of the pellicle and extending in a second direction substantially perpendicular to the first direction along the edges of the suspension region of the pellicle, the first pair of sides being configured to have a compliance in a second direction that is greater than the compliance in the first direction of the second pair of sides, such that a pellicle supported by the pellicle frame has an initial tension in the second direction that is less than the initial tension of the pellicle in the first direction.

[0052]

[0052] The first pair of sides may each have a thickness in a second direction that is less than a thickness in the first direction of the second pair of sides.

[0053]

[0053] The first pair of sides may each include a slit extending in a first direction along the first pair of sides.

[0054]

[0054] According to a twelfth aspect of the present invention, there is provided a pellicle failure detection apparatus comprising a radiation source configured to illuminate with a radiation beam a portion of a pellicle arranged to protect a patterning device, a sensor arranged to detect a portion of the radiation beam reflected from the pellicle, and a controller communicating with the sensor and configured to detect a pellicle failure from detection of the reflected radiation by the sensor.

[0055]

[0055] Advantageously, the pellicle failure detection device can be used to remotely monitor pellicle failures. The radiation source can be separate from the radiation source provided in the lithographic apparatus and used to perform the lithographic exposure. The radiation source can include, for example, a laser. The radiation source can emit a radiation beam having a wavelength longer than that associated with ultraviolet radiation.

[0056]

[0056] The radiation source may be configured so that the radiation beam is incident on the pellicle at a non-normal angle of incidence.

[0057]

[0057] By illuminating the pellicle with radiation at a non-normal incidence angle, the position of the reflected radiation depends on whether the radiation is reflected from the pellicle or from a patterning device located behind the pellicle. Thus, radiation reflected from the pellicle can be distinguished from radiation reflected from the patterning device (based on the position of the reflected radiation). Thus, radiation reflected from the pellicle can be measured independently from radiation reflected from the patterning device. Such measurements may allow pellicle failures to be detected from measurements of radiation reflected from the pellicle.

[0058]

[0058] The sensor may be positioned to detect diffuse reflection of the radiation beam from the pellicle.

[0059]

[0059] The sensor may be positioned to detect specular reflection of the radiation beam from the pellicle.

[0060]

[0060] The controller may be configured to detect a failure of the pellicle when a measure produced by the sensor of the intensity of a portion of the radiation beam reflected from the pellicle falls below a threshold value.

[0061]

[0061] The sensor may be further configured to detect a portion of the radiation beam reflected from the patterning device that is incident at a different position to the portion of the radiation beam reflected from the pellicle on the sensor.

[0062]

[0062] The sensor may include a first sensor area configured to detect radiation reflected from the pellicle and a second sensor area configured to detect radiation reflected from the patterning device.

[0063]

[0063] According to a thirteenth aspect of the present invention, there is provided a pellicle failure detection apparatus comprising a radiation source configured to illuminate a portion of a patterning device protected by the pellicle with a radiation beam that passes through the pellicle, a sensor apparatus arranged to receive and measure at least a portion of the radiation beam that has passed through the pellicle, and a controller in communication with the sensor apparatus and configured to detect a pellicle failure when a measure of the intensity of the radiation received by the sensor apparatus increases.

[0064]

[0064] The radiation source may emit, for example, EUV radiation. The radiation source may form part of a lithographic apparatus or may be used in other ways for performing lithographic exposures. The radiation provided by the radiation source may be directed to impinge on the patterning device by one or more other components, which may be considered to form an illumination system.

[0065]

[0065] The patterning device may be provided with a reflective fiducial and the sensor apparatus may be configured to measure a portion of the radiation beam reflected from the fiducial.

[0066]

[0066] The sensor arrangement and controller may be further configured to measure the alignment of a feature formed in a portion of the radiation beam reflected from the fiducial.

[0067]

[0067] The sensor arrangement and controller may be further configured to measure wavefront aberration of a portion of the radiation beam reflected from the fiducial.

[0068]

[0068] According to a fourteenth aspect of the present invention, there is provided a pellicle suitable for use with a patterning device of a lithographic apparatus, the pellicle comprising a plurality of termination features, the termination features being configured such that when a crack in the pellicle having a crack tip propagates into the termination feature, the crack tip experiences a reduction in stress at the crack tip.

[0069]

[0069] Advantageously, the termination feature can terminate the propagation of the crack within the pellicle. This can prevent the crack from damaging further portions of the pellicle and can prevent complete failure of the pellicle (i.e., the crack from extending substantially through the entire pellicle). By terminating the crack using the termination feature, the generation of pellicle debris can be suppressed. Thus, advantageously, the termination feature reduces contamination of the surrounding compound by pellicle debris in the event of pellicle failure.

[0070]

[0070] The termination features can be configured such that when the pellicle is placed under tension, stress induced in the termination features is less than stress induced in areas of the pellicle outside the termination features.

[0071]

[0071] The termination features may be arranged in a substantially regular pattern.

[0072]

[0072] The termination feature may include a hole formed in the pellicle.

[0073]

[0073] The holes may be substantially circular holes.

[0074] The pores can have lateral dimensions greater than about 10 nanometers.

[0075]

[0075] The lateral dimension may be, for example, the radius of the hole.

[0076] The pores can have lateral dimensions greater than about 20 nanometers.

[0077]

[0077] The termination feature may include a doped region of the pellicle that is doped with a doping material.

[0078] In some embodiments, the doping material may be a p-type dopant. In some embodiments, the doping material may be an s-type dopant.

[0079] In some embodiments, the pellicle can include silicon (e.g., a polysilicon film). In such embodiments, the doping material can be a p-type dopant, such as a dopant including one or more of boron, aluminum, nitrogen, gallium, and / or indium. Additionally or alternatively, the doping material can be an n-type dopant, such as a dopant including phosphorus, arsenic, antimony, bismuth, and / or lithium.

[0080]

[0080] In some embodiments, the pellicle can include graphene. In such embodiments, the doping material can include one or more of boron, nitrogen, titanium, chromium, platinum, cobalt, indium, and / or sulfur. Additionally or alternatively, the doping material can include one or more of an organic molecule, an acid, a base, and / or a halide. In some embodiments, the doping material can include a transition metal, such as, for example, copper, nickel, ruthenium, molybdenum, and / or platinum.

[0081] The doping material may include boron.

[0082]

[0082] The doped region may be substantially circular.

[0083]

[0083] The termination feature may comprise multiple stripes of doped regions doped with a doping material.

[0084]

[0084] The stripes of doped regions may be arranged substantially parallel to one another.

[0085] The doped regions can have lateral dimensions greater than about 10 nanometers.

[0086] The doped regions can have lateral dimensions greater than about 20 nanometers.

[0087]

[0087] The pellicle can have a termination feature including a boundary portion of the pellicle doped with a doping material, the boundary portion being positioned at the periphery of a suspension region of the pellicle, which is an area configured to be suspended on the pellicle frame.

[0088]

[0088] According to a fifteenth aspect of the present invention, there is provided a load stage of a lithographic apparatus comprising a chamber configured to accommodate a patterning device protected by a pellicle, a sensor device configured to measure the position of at least a portion of the pellicle located in the chamber, and a pressure change device configured to change the pressure inside the chamber, wherein the pressure change device is configured to control a rate at which the pressure inside the chamber is changed in response to a measurement of the position of at least a portion of the pellicle.

[0089]

[0089] The pressure change device can be configured to reduce the rate at which the pressure inside the chamber is changed in response to measurements indicating that the pellicle position is outside of a desired range of pellicle positions.

[0090]

[0090] A desired range of pellicle positions may be between a minimum distance from the patterning device and a maximum distance from the patterning device.

[0091]

[0091] The sensor apparatus may include a radiation source configured to illuminate at least a portion of the pellicle with radiation, and a radiation sensor positioned to receive and measure radiation reflected from the pellicle.

[0092]

[0092] The radiation source can be configured to illuminate the pellicle at a non-normal angle of incidence, and the radiation sensor is configured to measure the position at which the reflected radiation is incident on the radiation sensor.

[0093]

[0093] The sensor device may comprise a confocal imaging sensor.

[0094]

[0094] The sensor device is positioned outside the chamber, and the chamber may be provided with a window configured to allow radiation to propagate into and out of the chamber.

[0095]

[0095] The pressure change apparatus may be configured to pump the chamber to a vacuum pressure when loading the patterning device into the lithographic apparatus.

[0096]

[0096] The pressure change apparatus may be configured to vent the chamber to atmospheric pressure when unloading the patterning device from the lithographic apparatus.

[0097]

[0097] The load stage may further comprise a controller configured to record changes in the position of the pellicle as a function of the pressure inside the chamber.

[0098]

[0098] The controller may be further configured to detect fatigue of the pellicle from changes in the position of the pellicle recorded as a function of pressure inside the chamber.

[0099]

[0099] According to a sixteenth aspect of the present invention, there is provided a method of treating a pellicle, the method comprising heating at least a portion of the pellicle to a temperature higher than the ductile-to-brittle transition temperature of the pellicle, and placing the pellicle under tension sufficient to plastically deform at least a portion of the heated portion of the pellicle.

[0100]

[0100] Heating at least a portion of the pellicle may include locally heating only a portion of the pellicle.

[0101]

[0101] Heating at least a portion of the pellicle may include heating a pellicle frame to which the pellicle is mounted.

[0102]

[0102] Heating at least a portion of the pellicle may include illuminating at least a portion of the pellicle with radiation.

[0103]

[0103] Heating at least a portion of the pellicle may include illuminating at least a portion of the pellicle with a laser beam.

[0104]

[0104] Placing the pellicle under tension can include suspending the pellicle in a pellicle frame.

[0105]

[0105] Placing the pellicle under tension further includes creating a pressure differential across the pellicle.

[0106]

[0106] According to a 17th aspect of the present invention, there is provided a pellicle assembly suitable for use with a patterning device of a lithographic apparatus, comprising a frame configured to support a pellicle, a pellicle mounted on the frame and having at least one conductive layer, and a current source connected to the at least one conductive layer and configured to generate a current in the at least one conductive layer, wherein the current source is configured to generate a current that heats the pellicle by resistive heating such that the temperature of the pellicle is above a threshold temperature.

[0107]

[0107] The threshold temperature may be approximately 120 degrees Celsius.

[0108]

[0108] The current source may be configured to generate a substantially direct current in the at least one conductive layer.

[0109]

[0109] According to an 18th aspect of the present invention, there is provided a pellicle assembly suitable for use with a patterning device of a lithographic apparatus, the pellicle assembly comprising a frame configured to support a pellicle, a pellicle mounted on the frame, and a tension control device configured to adjust the tension of the pellicle.

[0110]

[0110] The tension control device can include at least one heater configured to heat a component of the pellicle assembly, where heating the component of the pellicle assembly increases the tension in the pellicle.

[0111]

[0111] At least one heater can be configured to heat at least a portion of the pellicle frame. A heater can be provided on each side of the pellicle frame.

[0112]

[0112] The pellicle frame can include a first layer having a first Young's modulus and a first thermal expansion coefficient, and a second layer having a second Young's modulus higher than the first Young's modulus and a second thermal expansion coefficient higher than the first thermal expansion coefficient, the second layer positioned closer to the pellicle than the first layer.

[0113]

[0113] The at least one heater can be configured to heat at least a portion of the pellicle.

[0114]

[0114] The pellicle can comprise a first layer having a first Young's modulus and a first thermal expansion coefficient, and a second layer having a second Young's modulus higher than the first Young's modulus and a second thermal expansion coefficient higher than the first thermal expansion coefficient, the first layer being positioned closer to the pellicle frame than the second layer.

[0115]

[0115] The pellicle may include at least one region in which the thickness of the pellicle is greater than the thickness of the remainder of the pellicle.

[0116]

[0116] At least one region may be proximate to an edge of the pellicle.

[0117]

[0117] In at least one region, the thickness of the second layer may be greater than the thickness of the second layer in the remainder of the pellicle.

[0118]

[0118] The at least one heater may be configured to locally heat at least one region of the pellicle having a thickness greater than a thickness of the remainder of the pellicle.

[0119]

[0119] The heater may be configured to heat at least one component of the pellicle assembly by resistive heating.

[0120]

[0120] The tension control device can include at least one actuator configured to apply a force to the pellicle frame to stretch the pellicle frame and increase the tension in the pellicle.

[0121]

[0121] According to a nineteenth aspect of the present invention there is provided a method of strengthening a pellicle comprising temporarily exposing the pellicle to tension.

[0122]

[0122] The pellicle can be exposed to tension for less than 1 second.

[0123]

[0123] The tension can be applied as an impact load.

[0124]

[0124] Features of different aspects of the invention may be combined with features of other aspects of the invention. [Brief description of the drawings]

[0125]

[0125] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying schematic drawings.

[0126] [Figure 1] 1 depicts a schematic diagram of a lithography system comprising a lithographic apparatus and a radiation source; [Diagram 2] 1 is a schematic diagram of a patterning device and a pellicle assembly. [Diagram 3] FIG. 1 is a schematic diagram of a pellicle according to an embodiment of the present invention. [Figure 4A] 1A-1D are schematic diagrams illustrating stages in a process for forming a pellicle according to an embodiment of the present invention. [Figure 4B] 1A-1D are schematic diagrams illustrating stages in a process for forming a pellicle according to an embodiment of the present invention. [Figure 4C] 1A-1D are schematic diagrams illustrating stages in a process for forming a pellicle according to an embodiment of the present invention. [Figure 4D] 1A-1D are schematic diagrams illustrating stages in a process for forming a pellicle according to an embodiment of the present invention. [Diagram 5] 1 is a schematic diagram of a pellicle assembly and a patterning device. [Figure 6] FIG. 1 is a schematic diagram of a pellicle assembly according to an embodiment of the present invention. [Figure 7] 7 illustrates a schematic diagram of a portion of the pellicle assembly of FIG. 6 after a pellicle of the pellicle assembly has been broken. [Figure 8] 1 illustrates a schematic diagram of a portion of a pellicle assembly according to an alternative embodiment of the present invention. [Figure 9] FIG. 13 is a schematic diagram of a pellicle assembly according to another alternative embodiment of the present invention. [Figure 10] FIG. 13 is a schematic diagram of a pellicle assembly in accordance with yet another alternative embodiment of the present invention. [Figure 11] FIG. 13 is a schematic diagram of a pellicle assembly in accordance with yet another alternative embodiment of the present invention. [Figure 12A] 1 is a schematic diagram of a pellicle failure detection device according to an embodiment of the present invention. [Figure 12B] 1 is a schematic diagram of a pellicle failure detection device according to an embodiment of the present invention. [Figure 12C] 1 is a schematic diagram of a pellicle failure detection device according to an embodiment of the present invention. [Figure 12D] 1 is a schematic diagram of a pellicle failure detection device according to an embodiment of the present invention. [Figure 13A] FIG. 1 is a schematic diagram of a pellicle according to an embodiment of the present invention. [Figure 13B] 13B illustrates a stress-strain curve that the pellicle of FIG. 13A may experience. [Figure 14] 1 is a schematic diagram of a debris mitigation device according to an embodiment of the present invention; [Figure 15] 2 is a schematic diagram of a debris mitigation apparatus according to an alternative embodiment of the present invention; [Figure 16] 4 is a schematic diagram of a debris mitigation apparatus according to another alternative embodiment of the present invention. [Figure 17A] 1 is a schematic diagram of a pellicle frame according to an embodiment of the present invention. [Figure 17B]1 is a schematic diagram of a pellicle frame according to an embodiment of the present invention. [Figure 18] FIG. 1 is a schematic diagram of a pellicle fault detection apparatus according to an embodiment of the present invention. [Figure 19] 2 is a schematic diagram of a patterning device and pellicle assembly located within a protective case and monitored by a pellicle failure detection apparatus according to an embodiment of the present invention. [Figure 20] 1 is a schematic illustration of a lithographic apparatus comprising a pellicle fault detection apparatus according to an embodiment of the present invention; [Figure 21] FIG. 2 is a schematic diagram of a pellicle including termination features in accordance with one embodiment of the present invention. [Figure 22] FIG. 1 is a schematic diagram of a crack in a pellicle. [Figure 23] 1 shows a schematic representation of the stress at the tip of a crack in a pellicle as a function of the crack length. [Figure 24A] 1 illustrates diagrammatically the stages of crack propagation in a pellicle. [Figure 24B] 1 illustrates diagrammatically the stages of crack propagation in a pellicle. [Diagram 25] FIG. 2 is a schematic diagram of a pellicle including stripe-shaped termination features of doped regions in accordance with an embodiment of the present invention. [Figure 26] FIG. 1 is a schematic diagram of a pellicle assembly including a pellicle having a doped boundary. [Figure 27] FIG. 1 is a schematic diagram of a pellicle assembly including a heater configured to heat a pellicle frame. [Figure 28A] 1A-1C are schematic diagrams illustrating portions of a pellicle assembly prior to heating a portion of the pellicle frame. [Figure 28B] 13A-13C are schematic diagrams illustrating portions of a pellicle assembly after a portion of the pellicle frame has been heated. [Figure 29A] FIG. 2 is a schematic diagram of a pellicle assembly prior to heating the pellicle. [Figure 29B] FIG. 2 is a schematic diagram of the pellicle assembly after heating the pellicle. [Diagram 30] FIG. 13 is a schematic diagram of a pellicle assembly according to an alternative embodiment after heating the pellicle. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0127]

[0126] Figure 1 shows a lithographic system including a pellicle assembly 15 according to an embodiment of the invention. The lithographic system comprises a radiation source SO and a lithographic apparatus LA. The radiation source SO is configured to generate an extreme ultraviolet (EUV) radiation beam B. The lithographic apparatus LA comprises an illumination system IL, a support structure MT configured to support a patterning device MA, a projection system PS, and a substrate table WT configured to support a substrate W. The illumination system IL is configured to condition the radiation beam B before it is incident on the patterning device MA. The projection system is configured to project the radiation beam B (patterned by the patterning device MA) onto the substrate W. The substrate W may include a preformed pattern. In this case, the lithographic apparatus aligns the patterned radiation beam B with respect to the preformed pattern on the substrate W.

[0128]

[0127] The source SO, illumination system IL and projection system PS may all be constructed and arranged such that they can be isolated from the external environment. A gas (e.g. hydrogen) at a pressure below atmospheric pressure may be provided in the source SO. A vacuum may be provided in the illumination system IL and / or projection system PS. A small amount of gas (e.g. hydrogen) at a pressure well below atmospheric pressure may be provided in the illumination system IL and / or projection system PS.

[0129]

[0128] The radiation source SO shown in Figure 1 is of a type sometimes referred to as a laser-produced plasma (LPP) source. A laser 1, which may be, for example, a CO2 laser, is arranged to impart energy via a laser beam 2 to a fuel, such as tin (Sn), provided from a fuel emitter 3. Although the following description refers to tin, any suitable fuel may be used. The fuel may be, for example, in liquid form and may be, for example, a metal or an alloy. The fuel emitter 3 may comprise a nozzle configured to direct the tin, for example in the form of droplets, along a trajectory towards the plasma formation region 4. The laser beam 2 is incident on the tin in the plasma formation region 4. By imparting laser energy to the tin, a plasma 7 is generated in the plasma formation region 4. Radiation, including EUV radiation, is emitted from the plasma 7 during de-excitation and recombination of the ions of the plasma.

[0130]

[0129] The EUV radiation is collected and focused by a near-normal incidence radiation collector 5 (sometimes more generally referred to as a normal incidence radiation collector). Collector 5 may have a multi-layer structure arranged to reflect EUV radiation (e.g. EUV radiation having a desired wavelength such as 13.5 nm). Collector 5 may have an elliptical configuration with two elliptical foci. The first focus may be at the plasma formation region 4 and the second focus may be at an intermediate focus 6, as discussed below.

[0131]

[0130] In another embodiment of the laser produced plasma (LPP) source, the collector 5 may be a so-called grazing incidence collector configured to receive the EUV radiation at a grazing incidence angle and to focus the EUV radiation to an intermediate focus. The grazing incidence collector may for example be a nested collector with multiple grazing incidence reflectors. The grazing incidence reflectors may be arranged axially symmetrically about the optical axis O.

[0132]

[0131] The radiation source SO may include one or more contamination traps (not shown). For example the contamination trap may be located between the plasma formation region 4 and the radiation collector 5. The contamination trap may for example be a rotating foil trap or any other suitable form of contamination trap.

[0133]

[0132] The laser 1 may be separate from the radiation source SO. In this case, the laser beam 2 may be delivered from the laser 1 to the radiation source SO using a beam delivery system (not shown) including, for example, suitable directing mirrors and / or beam expanders and / or other optics. The laser 1 and the radiation source SO together may be considered as a radiation system.

[0134]

[0133] The radiation reflected by the collector 5 forms a radiation beam B. The radiation beam B is focused at a point 6 and forms an image of the plasma formation region 4. This image acts as a virtual source of the illumination system IL. The point 6 at which the radiation beam B is focused is sometimes called the intermediate focus. The radiation source SO is arranged such that the intermediate focus 6 is located at or near an opening 8 of a closure structure 9 of the radiation source.

[0135]

[0134] The radiation beam B passes from the radiation source SO into an illumination system IL configured to condition the radiation beam. The illumination system IL may comprise a facetted field mirror device 10 and a facetted pupil mirror device 11. Together the facetted field mirror device 10 and the facetted pupil mirror device 11 provide the radiation beam B with a desired cross-sectional shape and a desired angular distribution. The radiation beam B passes through the illumination system IL and is incident on a patterning device MA held by a support structure MT. The patterning device MA is protected by a pellicle 19 which is held in place by a pellicle frame 17. The pellicle 19 and the pellicle frame 17 together form a pellicle assembly 15. The patterning device MA (which may for example be a mask) reflects and patterns the radiation beam B into the radiation beam B. The illumination system IL may comprise other mirrors or devices in addition to or instead of the facetted field mirror device 10 and the facetted pupil mirror device 11.

[0136]

[0135] After reflecting from the patterning device MA, the patterned radiation beam B is incident on a projection system PS. The projection system comprises a number of mirrors arranged to project the radiation beam B onto a substrate W held on a substrate table WT. The projection system PS may apply a demagnification factor to the radiation beam to form an image having smaller features than corresponding features on the patterning device MA. For example a demagnification factor of 4 may be applied. Although in Figure 1 the projection system PS has two mirrors, the projection system may comprise any number of mirrors (for example six mirrors).

[0137]

[0136] The lithographic apparatus can, for example, be used in a scan mode, in which the support structure (e.g. mask table) MT and the substrate table WT are scanned synchronously while a pattern imparted to the radiation beam is projected onto the substrate W (i.e. dynamic exposure). The velocity and direction of the substrate table WT relative to the support structure (e.g. mask table) MT may be determined by the demagnification and image reversal characteristics of the projection system PS. The patterned radiation beam incident on the substrate W may include a band of radiation. This band of radiation may be referred to as an exposure slit. During a scanning exposure, the substrate table WT and the support structure MT may be moved such that the exposure slit progresses over an exposure field of the substrate W.

[0138]

[0137] The source SO and / or the lithographic apparatus depicted in Figure 1 may comprise components not shown. For example, the source SO may be provided with a spectral filter. The spectral filter may be substantially transparent for EUV radiation but substantially block other radiation wavelengths, such as infrared radiation.

[0139]

[0138] In other embodiments of the lithography system, the source SO may take other forms. For example, in alternative embodiments, the source SO may include one or more free electron lasers. The one or more free electron lasers may be configured to emit EUV radiation that may be supplied to one or more lithography apparatus.

[0140]

[0139] As briefly described above, the pellicle assembly 15 comprises a pellicle 19 disposed adjacent to the patterning device MA. The pellicle 19 is disposed in the path of the radiation beam B such that the radiation beam B passes through the pellicle 19 both as it approaches the patterning device MA from the illumination system IL and as it is reflected by the patterning device MA to the projection system PS. The pellicle 19 comprises a thin film that is substantially transparent to EUV radiation (although it absorbs small amounts of EUV radiation). The pellicle 19 serves to protect the patterning device MA from particle contamination. The pellicle 19 may be referred to herein as an EUV transparent pellicle.

[0141]

[0140] Despite efforts to maintain a clean environment inside the lithographic apparatus LA, particles may be present inside the lithographic apparatus LA. Without the pellicle 19, particles may deposit on the patterning device MA. Particles on the patterning device MA may adversely affect the pattern imparted to the radiation beam B and the pattern transferred to the substrate W. Advantageously, the pellicle 19 provides a barrier between the patterning device MA and the environment within the lithographic apparatus LA to prevent particles from depositing on the patterning device MA.

[0142]

[0141] The pellicle 19 is positioned sufficiently far from the patterning device MA such that particles incident on the surface of the pellicle 19 are not in the focal plane of the radiation beam B. Separating the pellicle 19 and the patterning device MA in this manner serves to reduce the extent to which particles on the surface of the pellicle 19 will impart a pattern to the radiation beam B. It will be appreciated that if a particle is present in the radiation beam B but not in the focal plane of the radiation beam B (i.e. not on the surface of the patterning device MA), then the image of the particle will not be focused at the surface of the substrate W. In some embodiments the spacing between the pellicle 19 and the patterning device MA may be, for example, 2mm to 3mm (e.g. around 2.5mm).

[0143]

[0142] Figure 2 shows the pellicle assembly 15 and the patterning device MA in more detail and schematic in cross-section. The patterning device MA has a pattern-forming surface 24. The pellicle frame 17 supports the pellicle 19 at a peripheral portion of the pellicle 19. The pellicle frame 17 may comprise a mounting structure 22 configured to allow releasable mounting of the pellicle frame to the patterning device MA (i.e. to allow mounting and removal of the pellicle frame from the patterning device MA). The mounting structure 22 is configured to engage with a mounting mechanism (not shown) provided on the patterning device MA. The mounting mechanism may be, for example, a protrusion extending from the patterning device MA. The mounting structure 22 may include, for example, a locking member that engages with the protrusion and secures the pellicle frame 17 to the patterning device MA.

[0144]

[0143] A plurality of mounting structures and corresponding mounting mechanisms may be provided. The mounting structures may be distributed around the pellicle frame 17 (e.g. two on one side of the frame and two on the opposite side of the frame). The corresponding mounting mechanisms may be distributed around the periphery of the patterning device MA.

[0145]

[0144] A contamination particle 26 is shown diagrammatically in Figure 2. The contamination particle 26 is retained by the pellicle 19 after impacting with the pellicle 19. The pellicle 19 retains the contamination particle sufficiently away from the patterned surface 24 of the mask MA so that the contamination particle is not imaged onto the substrate by the lithographic apparatus LA.

[0146]

[0145] A pellicle assembly according to an embodiment of the present invention may be capable of providing a mask pattern (on a patterning device) that remains substantially defect-free during use (the mask pattern is protected by the pellicle). In some embodiments, a gap (e.g., in the form of a slit) may be provided between the pellicle frame and the mask to allow gas to flow in and out of the space between the pellicle and the mask. This allows for pumping down and venting of the mask assembly without damaging the pellicle 19.

[0147]

[0146] Figure 3 shows a cross-section of the pellicle 19 in more detail and in schematic form. The pellicle 19 comprises a thin film formed from a plurality of layers 31a-31d. In the embodiment shown in Figure 3, the pellicle comprises four layers 31a-31d. However, in other embodiments, the pellicle 19 may comprise more or less than four layers. For ease of illustration, the thicknesses of the layers 31a-31d shown in Figure 3 are exaggerated relative to the width of the pellicle 19. Thus, the layers 31a-31d shown in Figure 3 are not to scale.

[0148]

[0147] The pellicle 19 includes a main membrane layer 31c. The thickness of the main membrane layer is greater than the thickness of each of the other layers 31a, 31b, 31d forming the pellicle 19 (as shown diagrammatically in FIG. 3). The main membrane layer 31c may include a material such as a polysilicon (pSi) membrane. A polysilicon (pSi) membrane is substantially transparent to EUV radiation and is therefore suitable for use in an EUV lithography apparatus. The main membrane layer 31c may have a thickness on the order of approximately 40 nm.

[0149]

[0148] The main membrane layer 31c may alternatively be formed from some other material that is substantially transparent to EUV radiation, such as graphene, silicene, etc. References herein to a pellicle or pellicle layer being substantially transparent to EUV radiation are intended to mean that the pellicle or pellicle layer transmits at least 65% of the incident EUV radiation, preferably at least 80% of the incident EUV radiation, and more preferably at least 90%.

[0150]

[0149] The pellicle 19 further includes a first capping layer 31b and a second capping layer 31d. The first and second capping layers 31b, 31d are located on either side of the main membrane layer 31c to encapsulate the main membrane layer 31c. The capping layers 31b, 31d serve to protect the main membrane layer 31c from substances to which the pellicle 19 is exposed and which may damage the main membrane layer 31c if it contacts the main membrane layer 31c. For example, the capping layers 31b, 31d may serve to protect the main membrane layer 31c from exposure to hydrogen radicals, plasma, and traces of oxygen, which may damage the main membrane layer 31c if it contacts the main membrane layer 31c. Thus, the capping layers 31b, 31d may serve to reduce damage caused to the pellicle 19 by exposure to damaging substances. The first and / or second capping layers 31b, 31c may have a thickness, for example, on the order of approximately 5 nm. For example, the first and / or second capping layers 31b, 31c may have a thickness greater than approximately 3 nm. The thickness of the first and / or second capping layers 31b, 31c may be less than approximately 7 nm.

[0151]

[0150] The pellicle 19 further includes an emissive layer 31a. The emissive layer may be formed from a material having a relatively high thermal emissivity. For example, the emissive layer 31a may be formed from a metal (e.g., a transition metal such as ruthenium). In some embodiments, the emissive layer 31a may be formed from graphene. The emissive layer 31a may be conductive in some embodiments of the present invention and may alternatively be referred to as a conductive layer. The conductive emissive layer 31a may be electrically connected to the emissive layer 31a, for example to measure the electrical resistance of the emissive layer 31a.

[0152]

[0151] During use of the pellicle 19 in the lithographic apparatus LA, the pellicle is exposed to radiation (e.g. EUV radiation). The pellicle 19 is configured to be substantially transparent to the radiation to which it is exposed (e.g. EUV radiation), but some of the radiation is absorbed by the pellicle and serves to heat it up. It is desirable for the temperature of the pellicle to not reach a temperature that may cause damage to the pellicle. The relatively high thermal emissivity of the emissive layer 31a facilitates the release of thermal energy from the pellicle 19, thereby regulating the temperature of the pellicle 19. The emissive layer 31a allows the pellicle 19 to be exposed to high power radiation (compared to a pellicle not including an emissive layer) without the temperature of the pellicle 19 reaching a temperature that may cause significant damage to the pellicle 19.

[0153]

[0152] The layers 31a-31d of the pellicle 19 can be formed by a deposition process. For example, a first layer can be deposited on a substrate and the remaining layers can be sequentially deposited on top of the first layer. A suitable deposition process by which the layers can be deposited can be a chemical vapor deposition (CVD) process.

[0154]

[0153] Figure 4 illustrates generally a method of manufacturing the pellicle assembly 15. Referring first to Figure 4A, a pellicle 19 is formed on a substrate 50 (e.g., a silicon wafer). For example, chemical vapor deposition (CVD) may be used to deposit layers (e.g., layers 31a-31d described above with reference to Figure 3) on the substrate 50. A rectangular region of the substrate 50 is then etched away leaving the pellicle 19 supported by the remaining substrate 50 at a peripheral portion 55 of the pellicle 19.

[0155]

[0154] The presence of the substrate 50 around the outer periphery 55 of the pellicle 19 is advantageous because it provides a rigid frame that keeps the pellicle 19 taut. That is, the pellicle 19 is stretched by the rigid frame so that the pellicle 19 is in tension. The pellicle 19 is taut when it is made (e.g., during a CVD process) because of the way it is formed. If the substrate 50 did not provide a rigid frame to support the pellicle 19, but instead a flexible frame was provided, the tension of the pellicle 19 would cause the frame to bend inwards. As a result of this inward bending, the tension of the pellicle 19 would be lost. The remaining steps of the method allow the outer portion of the substrate 50 to be removed without the pellicle 19 losing tension. If the tension of the pellicle 19 were to be lost, uncontrolled sagging of the pellicle 19 would occur and wrinkles would be observed in the pellicle 19.

[0156] The portion of the pellicle supported by substrate 50 that extends around the outer edge of the membrane of pellicle 19 may be referred to as the outer periphery portion 55 of the pellicle. The outer edge of outer periphery portion 55 is shown in dashed lines. The inner edge of outer periphery portion 55 is defined by the inner portion of substrate 50 that supports pellicle 19 and is shown in solid lines in FIG. 4A.

[0157]

[0156] Figure 4B shows a schematic of a cover that may be clamped to a substrate 50. The left-hand view of Figure 4B shows the top cover 54 and substrate 50 from above. The right-hand view of Figure 4B shows the top cover 54, substrate 50 and other components in cross-section. The top cover 54 is pressed against the substrate 50 on the side of the pellicle 19 that is furthest from the patterning device MA in use.

[0158]

[0157] The dashed line on the right side of Figure 4B indicates the location of the pellicle 19. In this embodiment, the pellicle 19 is on the bottom surface of the substrate 50. This is because the etch used to remove the rectangular area of ​​the substrate 50 was applied to the top surface of the wafer. In such an embodiment, there is a gap between the pellicle 19 and the top cover 54. Thus, the top cover 54 can have a flat inner surface. In an alternative embodiment, the pellicle 19 is on the top surface of the substrate 50 (the etch was applied to the bottom surface of the substrate). In such an embodiment, there is no gap between the pellicle 19 and the top cover 54, and therefore the top cover will include a recess to accommodate the sagging of the pellicle.

[0159]

[0158] On the opposite side of the substrate 50, a pellicle frame 17 and a bottom cover 56 are provided. The pellicle frame 17 is fixed to the outer perimeter portion 55 of the pellicle 19. The frame 17 is capable of resisting inward bending and is therefore sufficiently rigid to maintain tension on the pellicle 19. The frame 17 can be fixed to the outer perimeter portion 55 using an adhesive or any other suitable means. The bottom cover 56 is pressed against the substrate 50 and covers both the bottom surface of the pellicle 19 and the frame 17. The portion of the pellicle 19 that is not in contact with the frame 17 may be referred to as the unsupported portion.

[0160] 4B, it can be seen that the top cover 54 covers the top surface of the pellicle 19, and the bottom cover 56 covers the bottom surface of the pellicle 19. Thus, the covers 54, 56 form a sealed space between them that contains the pellicle 19 attached to the pellicle frame 17. The top cover 54, bottom cover 56 and frame 17 are attached to the substrate 50 in a clean state to minimize the possibility of introducing contaminants into the surroundings of the pellicle 19 when it is attached to the substrate 50. In fact, the entire process of making the pellicle 19 and then attaching the frame 17 and covers 54, 56 can be performed in a clean state.

[0161]

[0160] As shown diagrammatically in Figure 4C, a cutting tool (e.g., a milling machine) is used to trim the portion of substrate 50 that extends beyond bottom cover 56. In Figure 4C, the right-hand portion of substrate 50 has already been removed. The top portion of substrate 50 is now to be removed by cutting in the direction indicated by arrow 60. The other portion of substrate 50 is then removed. Such cutting of substrate 50 does not risk introducing contaminants to pellicle 19, since pellicle 19 is contained within a sealed environment.

[0162] Once the edges of the substrate 50 have been trimmed, the remaining assembly is the pellicle transport assembly 62 shown in Figure 4D. The pellicle transport assembly 62 includes the pellicle membrane 19, a portion of the substrate 50, the pellicle frame 17, the top cover 54, and the bottom cover 56. The pellicle transport assembly 62 holds the pellicle 19 in a sealed environment that cannot be penetrated by contaminants. The frame 17 supports the pellicle and maintains tension on the pellicle 19.

[0163] 4 provides a pellicle transport assembly 62 that maintains tension in the pellicle and prevents contamination of the pellicle. The pellicle transport assembly 62 can be manufactured, for example, at a single location. This is advantageous compared to, for example, manufacturing the pellicle at a first manufacturing location and then transporting it to a second location and mounting it on a support frame, where contaminants may be introduced during transport to the second location.

[0164]

[0163] The pellicle transport assembly 62 can be transported, for example, from a pellicle manufacturing site to a mask shop where the pellicle is attached to a patterning device MA (e.g. a mask) for use by a lithographic apparatus. The pellicle 19 and pellicle frame 17 can be removed from the remainder of the pellicle transport assembly 62 and attached to the patterning device MA. The rigidity of the pellicle frame 17 maintains tension in the pellicle 19, keeping it taut when placed in close proximity to the patterning device MA (e.g. as seen in Figure 2).

[0165]

[0164] As explained above with reference to Figure 4, the pellicle 19 is formed such that the pellicle 19 is in tension. The tension of each layer of the pellicle 19 is established during deposition of each layer on the substrate 50 and is maintained by the pellicle frame 17 that is later attached to the pellicle 19. The tension of each layer of the pellicle 19 can be determined, for example, by the characteristics of the deposition process. For example, the temperature and / or pressure at which the deposition (e.g., by CVD) of the layers of the pellicle 19 is performed can determine the tension of the deposited layers. Thus, the tension of each layer can be controlled by controlling one or more characteristics (e.g., temperature and / or pressure) of the deposition process by which the layers are deposited.

[0166]

[0165] The tension of each layer of the pellicle 19 also depends on the composition of the layer with respect to the material on which the layer is deposited. For example, a layer containing ruthenium deposited on a polysilicon layer will have a different tension than a layer containing ruthenium deposited on a silicon nitride layer under the same deposition conditions (e.g., the temperature and pressure at which the deposition is performed). Thus, the tension of each layer of the pellicle 19 can additionally or alternatively be controlled by selecting the materials that form the different layers of the pellicle 19.

[0167]

[0166] During use in the lithographic apparatus LA, the pellicle 19 may be subjected to forces and / or conditions that cause wear to the pellicle 19, which may result in damage to the pellicle 19. For example, the pellicle 19 and / or the pellicle frame 17 may be subjected to temperature changes (e.g. due to exposure to radiation) that cause expansion and / or contraction of the pellicle 19 and / or the pellicle frame 17. The expansion and / or contraction of the pellicle 19 and / or the pellicle frame may place additional stresses on the pellicle 19, which may result in wear to the pellicle 19 and ultimately damage to the pellicle 19.

[0168]

[0167] The pellicle 19 may also be exposed to substances and / or conditions that may chemically alter the pellicle 19. For example, the emissive layer 31a of the pellicle 19 may undergo oxidation over time. Oxidation of the emissive layer 31a may reduce the emissivity of the emissive layer 31a and reduce its effectiveness in regulating the temperature of the pellicle 19, resulting in further damage to the pellicle 19. In the lithographic apparatus LA, the pellicle 19 may be exposed to substances such as hydrogen radicals that may chemically alter and structurally weaken the pellicle 19.

[0169]

[0168] The pellicle 19 may be subject to pressure changes during the life of the pellicle 19. For example, the pellicle 19 may experience atmospheric pressure conditions outside the lithographic apparatus LA, and may be pumped down to vacuum pressure conditions for use in the lithographic apparatus LA. The changes in pressure conditions experienced by the pellicle 19 may cause the pellicle 19 to experience a pressure differential across it. The pressure differential across the pellicle 19 may apply additional stress to the pellicle 19, acting to curve the pellicle 19 towards or away from the patterning device MA.

[0170] The processes described above and / or other processes not described herein will gradually weaken the pellicle 19 until it breaks. For example, one or more cracks may develop in the pellicle 19 that may cause the pellicle 19 to rupture. The broken pellicle may break into several pieces. The pellicle pieces may contaminate the surrounding environment. For example, the broken pellicle may contaminate the patterning device MA, rendering the patterning device unusable.

[0171]

[0170] To limit contamination caused by a broken pellicle 19, it may be desirable to monitor the pellicle 19 to detect whether the pellicle 19 is about to break and / or to detect that the pellicle 19 has broken, so that steps can be taken to remove the pellicle 19 from use and / or to mitigate potential contamination that the pellicle 19 may cause. Additionally or alternatively, it may be desirable to configure the pellicle 19 so that, when it does break, the break occurs in a controlled manner that results in little or no contamination.

[0172]

[0171] Embodiments of the invention contemplated herein include features of the pellicle 19 and / or pellicle frame that allow for detection of impending pellicle failure and / or failure of the pellicle 19. Also contemplated are embodiments in which the pellicle 19 is configured to fail in a controlled manner. Another embodiment comprises an apparatus configured to mitigate contamination resulting from a failed pellicle 19.

[0173]

[0172] Figure 5 is a schematic diagram of a pellicle assembly 15 comprising a pellicle 19 and a pellicle frame 17, attached to a patterning device MA. The pellicle 55 includes a perimeter portion 55 attached to the frame 17. The patterning device MA includes a patterning region 71 in which a pattern to be transferred to the substrate W is formed. An exposure field 73 of the patterning device MA is exposed to radiation (e.g. EUV radiation) during a lithographic exposure. The exposure field 73 may be exposed to radiation by scanning an exposure slit 75 of radiation across the exposure field 73. The exposure slit may be scanned in a y direction (sometimes referred to as the scanning direction), indicated in the figure by a double arrow 77. An x direction perpendicular to the y direction is also shown in Figure 5. The x direction may be referred to as the non-scanning direction. The exposure slit 75 may be scanned over the exposure field 73 through a movement of the patterning device MA relative to the exposure slit 75.

[0174] 5, the pellicle 19 includes an area 79 that is within the exposure field 73 but does not cover the patterned region 71. This area 79 of the pellicle 19 is therefore exposed to the same conditions (including heating from exposure to radiation) as the pellicle 19 that covers the patterned region 71. However, modifications to this area 79 of the pellicle 19 do not affect the radiation incident on the patterned region 71 or the patterned radiation beam reflected from the patterned region 71. The area 79 of the pellicle 19 that is within the exposure field 73 but does not cover the patterned region 71 is sometimes referred to as the available area 79. Modifications to the available area 79 of the pellicle 19 can be made without affecting the radiation incident on the patterned region 71 or the patterned radiation beam reflected from the patterned region 71. Modifications that can be made to the available area 79 of the pellicle 19 can include features that can be monitored for indications that the pellicle 19 may be on the verge of failure. Alterations that can be made to the usable area 79 of the pellicle 19 can include features that cause the pellicle 19 to break in a controlled manner.

[0175] The patterning device MA may include a marker (e.g., a fiducial) 81. The marker 81 may be used for alignment measurements, for example to measure the alignment of the patterning device MA. The marker 81 may be located within the usable area 79 of the pellicle. It is desirable that any alterations to the usable area 81 of the pellicle 19 do not interfere with any alignment measurements using the marker 81.

[0176]

[0175] Figure 6 is a schematic diagram of a pellicle assembly 15 and patterning device MA in which the pellicle 19 of the pellicle assembly 15 includes a damaged region 83. Many of the features of the pellicle assembly 15 and patterning device MA of Figure 6 are the same as the pellicle assembly 15 and patterning device MA described with reference to Figure 5 and will not be described in further detail herein. For ease of illustration, some of the features shown in Figure 5 have been omitted in Figure 6 (e.g. exposure slit 75 and marker 81 are not shown in Figure 6).

[0177]

[0176] The damaged region 83 of the pellicle 19 is located within the available area 79 and therefore does not affect radiation incident on the patterned region 71 or the patterned radiation beam reflected from the patterned region 71. The damaged region 83 is configured to preferentially fail before the remaining regions of the pellicle fail during normal use of the pellicle 19 in the lithographic apparatus LA. The damaged region 83 may comprise a region of reduced thickness of the pellicle 19, for example, compared to the surrounding region of the pellicle 19. For example, during manufacture of the pellicle 19, less material may be deposited in the damaged region 83 such that the thickness of the damaged region 83 is less than the thickness of the surrounding region of the pellicle 19. Thus, the damaged region 83 is structurally weaker than the surrounding region of the pellicle 19 and will preferentially fail before the remaining regions of the pellicle 19 fail.

[0178] Additionally or alternatively, the damaged region 83 may comprise an area of ​​the pellicle 19 that has been exposed to different conditions than the remainder of the pellicle 19. The different conditions to which the damaged region is exposed renders the damaged region 83 structurally weaker than the surrounding areas of the pellicle 19. For example, prior to use of the pellicle 19 in the lithographic apparatus LA, the damaged region 83 may be exposed to radiation that does not expose the remaining areas of the pellicle 19. That is, the damaged region 83 may be selectively exposed to radiation that serves to structurally weaken the pellicle 19 (e.g., EUV radiation), while the remaining areas of the pellicle 19 are not exposed to the radiation. Thus, the damaged region 83 is structurally weaker than the surrounding areas of the pellicle 19 and will preferentially fail before the remaining areas of the pellicle 19 fail.

[0179] In some embodiments, the damaged region 83 may include a region of the pellicle 19 that is exposed to a different substance than the remainder of the pellicle is exposed to. For example, prior to use of the pellicle 19 in the lithographic apparatus LA, the damaged region 83 may be exposed to a substance configured to structurally weaken the damaged region compared to the remainder of the pellicle 19. The damaged region 83 may be exposed to, for example, hydrogen radicals, which may act to chemically alter the damaged region 83 to structurally weaken it. Thus, the damaged region 83 will preferentially fail before the remainder of the pellicle 19 fails.

[0180] Additionally or alternatively, the damaged region 83 may include a region of the pellicle 19 in which one or more holes and / or cracks are intentionally formed in the pellicle 19 prior to use of the pellicle 19 in a lithographic apparatus. The one or more holes and / or cracks in the pellicle 19 cause the damaged region 83 to be structurally weaker than the surrounding regions of the pellicle 19. Thus, the damaged region 83 will preferentially fail before the remaining regions of the pellicle 19 fail.

[0181]

[0180] Once failure region 83 breaks, the break in pellicle 19 may propagate to other regions of pellicle 19. For example, pellicle 19 may fracture along fracture line 85 such that cracks in pellicle 19 form along fracture line 85. In some embodiments, fracture line 85 may be configured to be structurally weaker than surrounding regions of pellicle 19 and may include other examples of failure regions as described above. Thus, fracture line 85 may have any of the characteristics described above with reference to failure region 83 and / or may be formed using any of the methods described above with reference to failure region 83.

[0182]

[0181] Alternatively, the fracture line 85 can be configured to be structurally stronger than the surrounding area of ​​the pellicle 19. For example, the fracture line can include a reinforced area of ​​the pellicle having a greater thickness than the surrounding area of ​​the pellicle 19. If the pellicle 19 were to break at the failure area 83, the cracks in the pellicle would be prevented from propagating through the pellicle 19 by the reinforced fracture line 85. In general, cracks tend to follow the weakest path available. Thus, by providing a reinforced fracture line 85, the cracks would follow a path between the fracture line 85 and the frame 17.

[0183]

[0182] In embodiments in which the pellicle 19 includes a reinforced region and a broken region 83, it is desirable to locate the broken region 83 between the reinforced region and the frame 17. As a result, any cracks that result from failure of the broken region 83 in the pellicle 19 will be confined to the region of the pellicle 19 that is between the frame 17 and the reinforced region.

[0184] In other embodiments, fracture line 85 can be configured to be no structurally stronger or weaker than the surrounding regions of pellicle 19, and can result inevitably from the pellicle failing at failure region 83. Failure region 83 can be positioned such that subsequent pellicle 19 failure occurs at a preferential location, such as along fracture line 85.

[0185]

[0184] In some embodiments, the pellicle 19 can be configured such that the pellicle 19 rolls up in a controlled manner after it breaks. For example, when the pellicle 19 breaks along the fracture line 85, the pellicle 19 can roll up on itself in a controlled manner. FIG. 7 is a schematic diagram of the pellicle 19 after it has rolled up on itself. Also shown in FIG. 7 is a portion of the pellicle frame 17 to which a section of the outer periphery 55 of the pellicle 19 remains attached. In the configuration shown in FIG. 7, the majority of the pellicle remains intact and attached to the pellicle frame 17. The broken pellicle 19 is contained within a small area, preventing the pellicle 19 from contacting the patterning device MA. Thus, the breakage of the pellicle 19 results in little or no contamination of the surrounding environment. The patterning device MA is in an operational state and can be used again. In such a case, the broken pellicle 19 can be simply removed from the patterning device MA and replaced with a new pellicle 19.

[0186]

[0185] The pellicle 19 can be configured to roll up by introducing different tensions in different layers of the pellicle 19. For example, the pellicle can include at least a first layer having a first tension and a second layer having a second tension. The first tension can be higher than the second tension. The difference in tension between the first and second layers can allow the first layer to pull on the second layer in case of pellicle breakage, so that the pellicle 19 rolls up on itself as shown in FIG. 7. In the embodiment shown in FIG. 7, the first layer of the pellicle, which has a higher tension, is located further from the pellicle frame 17 than the second layer of the pellicle 19, which has a lower tension. This causes the pellicle to roll up on the side of the pellicle opposite to where the patterning device MA is located. Advantageously, this can avoid the pellicle 19 coming into contact with the patterning device MA when rolled up.

[0187] In an alternative embodiment, a first layer of the pellicle having a high tension can be located closer to the pellicle frame 17 than a second layer of the pellicle 19 having a low tension. This allows the pellicle 19 to roll up on the same side of the pellicle 19 on which the patterning device MA is located.

[0188]

[0187] The radius r of the rolled up pellicle 19 (labeled in Figure 7) depends at least in part on the difference in tension between the first and second layers. In general, the greater the difference between the tensions of the first and second layers, the smaller the radius r of the resulting rolled up pellicle 19.

[0189] As described above with reference to Figure 3, the pellicle 19 can include three or more layers. The pellicle 19 can be configured to roll up on itself if any two layers of the pellicle are tensioned differently. In some embodiments, all layers forming the pellicle can be tensioned differently.

[0190]

[0189] As explained above, the tension of each layer of the pellicle can be determined by the characteristics of the deposition process (e.g., CVD) used to form each layer. Different layers can be deposited using different characteristics of the deposition process to provide layers with different tensions. For example, a first layer can be deposited using a first temperature and a first pressure, and a second layer can be deposited using a temperature and / or pressure different from the first temperature and the first pressure. Thus, the first layer is provided with a tension different from that of the second layer. Additionally or alternatively, the materials used to form the different layers of the pellicle 19 can be selected to provide layers with different tensions.

[0191]

[0190] In embodiments where the pellicle 19 is configured to roll up on itself, the pellicle 19 can include at least one failure region 83. The failure region 83 can be positioned to ensure that the pellicle 19 rolls up on itself when the failure region 83 breaks. For example, the failure region 83 shown in FIG. 6 is in a position that allows the failure of the failure region 83 to ensure that the pellicle rolls up on itself. As explained above, the fracture line 85 can also constitute a failure region where the pellicle 19 will preferentially break. Breaking the pellicle along the fracture line 85 can ensure that the pellicle rolls up on itself in a controlled manner.

[0192]

[0191] In the embodiment shown in Figure 6, at least one failure point 83 is provided where the pellicle 19 fails in a controlled manner that reduces any contamination of the surrounding environment from debris generated during failure of the pellicle 19. In some embodiments, the failure area 83 can be configured such that failure of the failure area 83 does not cause catastrophic failure of the entire pellicle. In such an embodiment, the failure area 83 can be monitored and failure of the failure point 83 can be detected. Detection of failure of the failure area 83 can indicate that the remainder of the pellicle is on the verge of failure, such that the pellicle 19 can be removed from operation prior to catastrophic failure of the entire pellicle (which could contaminate the surrounding environment).

[0193]

[0192] Figure 8 is a schematic diagram of a portion of a pellicle assembly 15 with a pellicle 19 held by a pellicle frame 17. The pellicle assembly 15 may include any of the features described herein with reference to other embodiments. The pellicle 19 includes an available area 79 that is within the exposure field 73 but does not cover a patterning area of ​​the patterning device MA (not shown in Figure 8). The pellicle 19 further includes a failure area 83. The failure area 83 includes a portion of the pellicle 19 that is configured to preferentially fail before the remaining area of ​​the pellicle 19 fails during normal use. At least a portion of the failure area 83 is located within the available area 79 of the pellicle 19. The failure area 83 may be structurally weakened relative to the surrounding portions of the pellicle 19. The failure area 83 of Figure 8 may be similar to the failure area described above with reference to Figure 6 and may include any of the features of other failure areas described herein. The failure area 83 of Figure 8 may be formed using any of the methods of forming a failure area described herein.

[0194]

[0193] The pellicle 19 further includes a reinforced region 87 disposed adjacent the failure region 83. The reinforced region has a greater thickness compared to the remaining region of the pellicle 19. Thus, the reinforced region 87 is structurally stronger than the failure region 83 and is configured to resist further failure of the pellicle 19 if the failure region 83 fails. The failure region 83 can fail, for example, along a fracture line 85 adjacent the reinforced region 87.

[0195] In the embodiment shown in FIG. 8, the reinforced region 87 follows a contoured curve on the pellicle 19. This increases the strength of the reinforced region 87 and allows the reinforced region 87 to resist further breakage of the pellicle 19. The reinforced region 87 and fracture line 85 extend between sections of the perimeter portion 55 of the pellicle 19 that are supported by the frame 17. The fracture line 85 and reinforced region 87 surround a portion of the pellicle 19 that is located at the edge of the unsupported portion of the pellicle 19 (the portion that is not in contact with the frame 17). Thus, the broken area of ​​the pellicle 19 is a small containment area, and the remainder of the pellicle remains intact, with little or no debris being generated.

[0196]

[0195] During normal use, the damaged area is subjected to the same forces and conditions as the rest of the pellicle 19. Failure of the damaged area 83 can indicate that other areas of the pellicle are on the verge of failure. The damaged area 83 can be monitored, and if it is detected that the damaged area 83 has failed, the pellicle can be taken out of operation and replaced. Advantageously, the pellicle is taken out of operation prior to catastrophic failure of the pellicle. This avoids significant debris generation and contamination of the surrounding environment.

[0197]

[0196] The damaged area 83 can be monitored using any form of sensor configured to detect damage in the damaged area 83. For example, the damaged area can be illuminated with radiation and reflection and / or transmission of the radiation from the damaged area can be detected. A change in reflectance or transmittance of the damaged area can indicate that the damaged area 83 is damaged.

[0198] At least a portion of the damaged region 83 receives radiation (e.g. EUV radiation) during the lithographic exposure process, and a portion of the radiation reflected from the patterning device MA and subsequently incident on the substrate W will pass through the damaged region. When the damaged region is damaged, the transmittance of the damaged region 83 will change. This can be detected by a change in intensity of the radiation at the substrate W in the region of the substrate receiving the radiation that has passed through the substrate W. Such a change in intensity can be detected and can indicate that the damaged region 83 has been damaged. The change in radiation intensity at the substrate W can be detected directly. Alternatively, the change in radiation intensity at the substrate W can be detected by monitoring the substrate W after exposure to radiation. The substrate W can comprise a photoresist that undergoes a state change upon exposure to radiation. A change in intensity of the radiation exposing the photoresist can be detectable in the photoresist and can indicate damage to the damaged region 83. The region of the substrate W receiving the radiation that has passed through the damaged region 83 is outside the region of the substrate W where the patterned features are formed (as the damaged region 83 is located outside the patterning region of the patterning device MA). Therefore, damage in the damaged area does not affect the pattern formed on the substrate.

[0199] In some embodiments, the damaged region 83 (or another feature of a pellicle as described herein) may be located outside of an image field that displays the portion of the patterning device that is imaged onto the substrate W. Thus, the damaged region 83 (or another feature of a pellicle as described herein) may not affect the radiation that exposes the substrate W.

[0200]

[0199] In some embodiments, the pellicle can include multiple damaged areas 83 similar to damaged area 83 of Figure 8. Each of the multiple damaged areas 83 can be monitored to detect damage to the damaged areas.

[0201]

[0200] As explained above, the reinforced region 87 has a greater thickness compared to the remaining regions of the pellicle 19. By increasing the thickness of the pellicle 19, the reinforced region 87 can be heated to a higher temperature than other parts of the pellicle (e.g., due to greater absorption of radiation). The reinforced region 87 is in contact with the frame 17 to provide a thermal connection between the reinforced region 87 and the frame. Thus, heat from the reinforced region 87 can be conducted to the frame 17, which can act as a heat sink and regulate the temperature of the reinforced region 87.

[0202] 5-8, at least the damaged regions 83 are provided in an available area 79 of the pellicle 19 that is within the exposure field 73 but does not cover the patterning area of ​​the patterning device MA. In some embodiments, the pellicle frame 17 may be at least partially positioned within the exposure field 73 such that at least a portion of a peripheral portion 55 of the pellicle receives the exposure radiation. This allows one or more damaged regions 83 or other areas of modification to the pellicle to be located in the peripheral portion 55 of the pellicle 19 that is supported by the frame 17.

[0203]

[0202] Figure 9 is a schematic diagram of a pellicle assembly 15 and patterning device MA with a portion of the pellicle frame 17 located within the exposure field 73. The embodiment shown in Figure 9 has many of the same features as the embodiment shown in Figure 5. The same reference numbers have been used to indicate corresponding features in Figures 5 and 9, and many of these features will not be described in detail again with reference to Figure 9.

[0204] In the embodiment shown in Figure 9, the pellicle frame 17 includes a portion that is located inside the exposure field 73 and thus receives radiation (e.g. EUV radiation) during the lithographic exposure process. The available portion 79 of the pellicle 19 that is within the exposure field 73 but does not cover the patterning area of ​​the patterning device MA thus includes part of the periphery 55 supported by the frame 17. This allows one or more damaged areas 83 to be located on the periphery 55 supported by the frame 17. Multiple damaged areas 83 located on the periphery of the pellicle 19 are shown in Figure 9.

[0205]

[0204] Because the damaged area 83 shown in Figure 9 is supported by the frame 17, any damage to the damaged area does little to affect the unsupported areas of the pellicle 19 that are not in contact with the frame 17. Thus, the remainder of the pellicle 19 advantageously remains intact, thereby avoiding the generation of a significant amount of debris.

[0206]

[0205] As described above with reference to Figure 8, the damaged area 83 can be monitored to detect damage thereto. Damage in the damaged area 83 can indicate that other areas of the pellicle 19 are on the verge of failure. If the damaged area 83 is detected to be damaged, the pellicle 19 can be taken out of operation and replaced. Advantageously, the pellicle is taken out of operation prior to catastrophic failure of the pellicle 19. This can avoid significant debris generation and contamination of the surrounding environment.

[0207]

[0206] In the embodiment of Figure 9, the available space on the patterning device MA that is not occupied by the pellicle frame 17 is smaller, for example compared to the embodiment of Figure 5. This may provide limited or no available space on the patterning device MA in which the markers 81 can be provided. In the embodiment of Figure 9, the pellicle frame 17 is provided with a window 82 through which the markers 81 on the patterning device MA are visible. This allows access to the markers 81, for example during alignment of the patterning device MA.

[0208] As explained above with reference to Figure 3, the pellicle 19 may include at least one layer that is electrically conductive. For example, the pellicle 19 may include an emissive layer 31a, which may also be electrically conductive. The electrically conductive layer of the pellicle 19 may be formed, for example, from a metal (e.g., a transition metal such as ruthenium). Alternatively, the electrically conductive layer of the pellicle 19 may be formed from graphene.

[0209]

[0208] The electrical conductivity of the pellicle 19 allows the electrical resistance of each part of the pellicle 19 to be monitored. As described above, the emissive layer 31a of the pellicle may undergo chemical changes over time. For example, the emissive layer 31a of the pellicle 19 may oxidize. The oxidation of the emissive layer 31a may reduce the emissivity of the emissive layer 31a, which may reduce the effect of the emissive layer 31a in regulating the temperature of the pellicle 19. Thus, the oxidation of the emissive layer 31a may increase the possibility that the pellicle 19 may be damaged by overheating of the pellicle 19.

[0210]

[0209] Oxidation of the emissive layer 31a will also increase the electrical resistance of the emissive layer 31a. Thus, oxidation of the emissive layer 31a can be detected by monitoring the electrical resistance of all or part of the pellicle 19. The pellicle 19 can include, for example, electrical contacts that allow electrical connection with a conductive layer (e.g., the emissive layer 31a) of the pellicle 19. The electrical connection established with the conductive layer allows the resistance of the conductive layer and the resistance between the electrical contacts to be measured. An increase in the measured resistance can indicate oxidation of the conductive layer (e.g., the emissive layer 31a). If the measured resistance is above a threshold value, the pellicle 19 can cease operation to avoid failure of the pellicle 19 due to overheating.

[0211]

[0210] The electrical contacts on the pellicle can be located, for example, on the outer periphery portion 55 of the pellicle 19 supported by the frame 17. Figure 10 is a schematic diagram of a portion of a pellicle assembly 15 including a pellicle frame 17 and a pellicle 19 supported by the pellicle frame 17 at the outer periphery portion 55 of the pellicle 19. The pellicle 19 includes electrical contacts 89 that allow an electrical connection to be established with the conductive layer of the pellicle 19. The electrical contacts 89 are located at the outer periphery portion 55 of the pellicle 19. Because the outer periphery portion 55 of the pellicle 19 is directly supported by the frame 17, any damage to the outer periphery portion 55 of the pellicle (e.g., as may result from an electrical connection with the pellicle) is unlikely to cause damage to the unsupported portion of the pellicle 19 that is not in contact with the frame 17.

[0212]

[0211] A sensor 91 is connected between the two electrical contacts 89 and configured to measure the resistance between the electrical contacts. The sensor 91 may be in any form of sensor capable of measuring the resistance between the two contacts.

[0213]

[0212] The electrical contacts 89 are located in the available areas 79 of the pellicle 19 that are within the exposure field 73 but do not cover the patterned areas of the patterning device MA (not shown in Figure 10). Thus, the areas of the pellicle 19 between the electrical contacts 89 will be exposed to similar conditions as the unsupported portions of the pellicle 19. Thus, oxidation of the areas of the pellicle 19 between the electrical contacts 89 that causes an increase in the resistance measured by the sensor 91 can be indicative of oxidation of other areas of the pellicle 19. As explained above, if the resistance measured by the sensor 91 exceeds a threshold value, the pellicle 19 can cease operation to avoid failure of the pellicle 19 due to overheating.

[0214]

[0213] The electrical resistance of the pellicle 19 can additionally or alternatively be monitored to detect cracks in the pellicle 19. In some instances, one or more cracks may occur in the pellicle 19 that do not cause a catastrophic failure of the pellicle 19. A cracked pellicle 19 may indicate that a catastrophic failure of the pellicle 19 is imminent. It is therefore desirable to detect cracks in the pellicle 19 before a catastrophic failure of the pellicle 19 occurs so that the pellicle 19 can be taken out of operation prior to the catastrophic failure (thereby reducing the generation of significant debris and contamination of the surrounding environment).

[0215]

[0214] Cracks in the pellicle 19 can be detected by measuring the electrical resistance across the pellicle 19. Figure 11 is a schematic diagram of a pellicle assembly 15 comprising a pellicle 19 and a pellicle frame 17 supporting a peripheral portion 55 of the pellicle. The pellicle 19 comprises electrical contacts 89 that allow an electrical connection to be established with the conductive layer of the pellicle 19. In the embodiment of Figure 11, the electrical contacts 89 are located at the peripheral portion 55 of the pellicle 19.

[0216]

[0215] A sensor 91 is connected between each pair of electrical contacts 89 and configured to measure the electrical resistance of the pellicle 19 and the electrical resistance between the electrical contacts 89. An increase in the resistance measured by one or more of the sensors 91 can indicate the occurrence of a crack in the pellicle 19. If an increase in the resistance measured by the one or more sensors 91 is detected, the pellicle 19 can cease operation to avoid further damage to the pellicle 19 and the risk of catastrophic failure of the pellicle 19.

[0217] 11, four electrical contacts 89 and two sensors 91 are shown. However, in other embodiments, the pellicle 19 may include fewer or more than four electrical contacts 89. In some embodiments, several electrical contacts 89 may be distributed around the outer periphery 55 of the pellicle, and multiple sensors 91 may be used to measure the resistance of multiple different electrical paths across the pellicle. This allows cracks occurring anywhere in the pellicle 19 to be detected.

[0218] In some embodiments, the electrical path between the electrical contacts 89 can be electrically isolated from other portions of the pellicle 19. For example, the pellicle 19 can include a conductive path between two electrical contacts 89 that is electrically isolated from other regions of the pellicle 19 (e.g., due to the absence of conductive material in the other regions). In such an embodiment, a potential can be applied to a particular region of the pellicle 19 as opposed to exposing the entire pellicle 19 to a potential. Any current flowing along the isolated electrical path can be measured to derive the electrical resistance of the path. A change in any resistance of the path can indicate possible damage to the pellicle and / or impending failure of the pellicle 19.

[0219]

[0218] In some embodiments, the pellicle assembly can include a sensor assembly configured to detect a change in a property associated with the pellicle 19. The change in the property associated with the pellicle 19 can be indicative of damage to the pellicle 19. For example, the sensor assembly can be configured to detect a change in the transmittance or reflectance of the pellicle to radiation and / or sound waves. If the pellicle is damaged, for example due to a crack in the pellicle, the reflectance of the damaged area may increase. Thus, detecting an increase in the reflectance of the pellicle can be indicative of damage to the pellicle 19.

[0220]

[0219] Figures 12A-12D are schematic diagrams of components of a pellicle failure detection apparatus according to an embodiment of the present invention. Figure 12A shows a portion of a pellicle assembly 15 and components of an embodiment of a sensor assembly. The pellicle assembly 15 comprises a frame 17 and a pellicle 19 supported by the frame at a perimeter portion 55 of the pellicle 19. The pellicle frame 17 is attached to the patterning device MA. The pellicle failure detection apparatus comprises a sensor assembly comprising a radiation source 93 and a radiation sensor (not shown in Figure 12A). The radiation source 93 is configured to emit a radiation beam 97 that is input into a waveguide 98. The waveguide 98 is connected to the pellicle 19 and configured to couple the radiation beam 97 to the pellicle 19 such that the radiation beam 97 is transmitted through the pellicle 19. The pellicle 19 acts as a waveguide and supports the transmission of the radiation beam 97 along the pellicle 19.

[0221]

[0220] Figure 12B illustrates a portion of the pellicle assembly 15 and components of an alternative embodiment of the sensor assembly. The embodiment illustrated in Figure 12B includes a transducer 94 (e.g., a piezo transducer) disposed in contact with the pellicle 19. The transducer 94 excites an acoustic wave 96 in the pellicle 19 that is transmitted along the pellicle 19.

[0222]

[0221] Figure 12C shows a schematic of a wave propagating within a pellicle 19 held at its outer periphery 55 by a frame 17. A waveform is input to the pellicle 19 at an input point 100. In Figure 12C, the wavefront is represented by a line 102. The wave may be an electromagnetic wave (e.g., when a beam of radiation is coupled into the pellicle 19 as shown in Figure 12A) or an acoustic wave (e.g., when a transducer generates an acoustic wave within the pellicle as shown in Figure 12B). The pellicle 19 acts as a waveguide and supports the propagation of the wave across the pellicle 19. The wave propagates in a direction substantially parallel to the surface of the pellicle 19.

[0223] In some embodiments, the transmission and / or reflection of the wave by the pellicle 19 can be measured. For example, a sensor can be placed near the input point 100 and can measure the wave reflected back towards the input point. The sensor can measure, for example, the return time from when the waveform is input to the pellicle 19 to when the corresponding reflection is measured by the sensor. In the case of an undamaged pellicle 19, the wave may be reflected at the frame 17 on the opposite side of the pellicle 19 from the input point 100 (as shown in FIG. 12C).

[0224]

[0223] Figure 12D shows a pellicle 19 in which a crack 104 has developed. The crack 104 acts to reflect the incoming wave, thereby providing a source of reflection closer to the input point 100 than the frame 17 on the opposite end side of the pellicle 19. Thus, the crack 104 in the pellicle 19 may reduce the return time from when the waveform is input to the pellicle 19 until the corresponding reflection is measured by the sensor. Thus, a change in the signal detected by the sensor may indicate damage to the pellicle 19. In some embodiments, one or more sensors may be positioned to detect the intensity of the wave transmitted and / or reflected by the pellicle 19. A change in the intensity of the wave transmitted and / or reflected by the pellicle 19 may indicate damage to the pellicle 19.

[0225]

[0224] In some embodiments, a sensor assembly that may form part of the pellicle failure detection apparatus may comprise a sensor configured to measure a stress experienced by the pellicle 19. For example, a stress sensor may be disposed on a peripheral portion 55 of the pellicle 19 supported by the pellicle frame 17. The stress sensor may be configured to measure a compressive stress experienced by the pellicle 19. Additionally or alternatively, the stress sensor may be configured to measure a tensile stress experienced by the pellicle 19.

[0226]

[0225] A suitable stress sensor may include, for example, a microbridge stress sensor that includes a thin bridge extending between two elements. If the microbridge is subjected to a compressive stress, the thin bridge may bend or break under the stress, thereby indicating the stress experienced by the pellicle 19 in which the stress sensor is located.

[0227]

[0226] In some embodiments, suitable stress sensors may include, for example, one or more Guckel rings. The Guckel ring has a ring-like structure and one or more beams that span the ring-like structure. The Guckel ring is configured to convert tensile stress into compressive stress. When the Guckel ring is subjected to tensile stress, the one or more beams that span the ring may bend under this stress, thereby indicating the stress experienced by the pellicle 19 on which the Guckel ring is placed.

[0228] In some embodiments, two or more stress sensors can be disposed on the pellicle 19. Different stress sensors disposed on the pellicle 19 can be configured to measure stresses at different locations, stresses acting in different directions, and / or stresses of different magnitudes.

[0229]

[0228] A pellicle 19 that is subjected to a high level of stress may be damaged by the stress. By disposing one or more stress sensors on the pellicle 19, it is possible to monitor the stress to which the pellicle 19 is subjected. If the stress to which the pellicle 19 is subjected is large enough that damage to the pellicle 19 may occur, the pellicle 19 may cease operation to avoid damage to the pellicle 19 and catastrophic failure.

[0230] Additionally or alternatively, one or more strain gauges can be disposed on the pellicle 19. For example, one or more strain gauges can be disposed on the outer periphery portion 55 of the pellicle 19. The one or more strain gauges can monitor the strain experienced by the pellicle. If the strain experienced by the pellicle 19 is large enough that damage to the pellicle 19 may occur, the pellicle 19 can cease operation to avoid damage to the pellicle 19 and catastrophic failure.

[0231]

[0230] In some embodiments, the pellicle 19 can be configured to contain debris therein if a portion of the pellicle 19 is broken. FIG. 13A is a schematic cross-sectional view of a pellicle 19 according to an embodiment of the present invention. The pellicle 19 includes a first layer 101, a second layer 103, and a third layer 105. As shown in FIG. 13A, the third layer 105 is located between the first layer 101 and the second layer 103. The first layer 101 has a first ductility, the second layer 103 has a second ductility, and the third layer 105 has a third ductility. The third ductility is less than the first ductility and less than the second ductility.

[0232]

[0231] Ductility is a measure of a material's ability to deform plastically under stress. For example, when a material is subjected to tensile stress, the material will deform and elongate under the tensile stress. Ductility is a measure of how much plastic deformation / elongation a material can undergo before it breaks. For example, a material with relatively high ductility will undergo a large deformation before the material breaks. A material with low ductility may not be able to deform as easily under tensile stress and may only undergo a small deformation before breaking.

[0233] 13A, each of the three layers 101, 103, 105 of the pellicle 19 will be subjected to the same stress during use. The third layer 105 has a lower ductility than the first and second layers 101, 103 and is therefore relatively brittle compared to the first and second layers 101, 103.

[0234]

[0233] Figure 13B shows a schematic of the stress-strain curves that the pellicle shown in Figure 13A may experience. If all layers 101, 103, 105 are intact, the strain experienced by the pellicle 19 is determined by the total stiffness of the pellicle 19, which is dominated by the stiffest layer of the pellicle. The stiffest layer of the pellicle 19 is the third layer 105. Thus, under initial stress, the strain of the pellicle 19 will approximately follow the stress-strain curve of the third layer 105 (shown as 105 in Figure 3B). At a first critical strain 108, the third layer 105 will break. Breaking of the third layer will dissipate energy in the pellicle 19, for example, by crack formation and / or sound wave generation in the third layer 105.

[0235] After the third layer 105 fails, the overall stress strain curve of the pellicle 19 will show the combined stress strain curve of the first and second layers 101, 103 (shown as 101, 103 in FIG. 13B). The first and second layers 101, 103 have a higher ductility than the third layer 105 and therefore may undergo further deformation after the third layer 105 fails. The further deformation of the first and second layers 101, 103 after the third layer 105 fails further dissipates potential energy within the pellicle 19 before catastrophic fracture of the pellicle 19.

[0236]

[0235] At the second critical strain 110, the first and second layers 101, 103 break, causing catastrophic fracture of the pellicle 19. As explained above, the strain experienced by the first and second layers 101, 103 after the third layer 105 breaks serves to dissipate potential energy. Thus, less potential energy is available when the first and second layers 101, 103 break, causing catastrophic fracture of the pellicle 19. As a result, less energy is dissipated during catastrophic fracture. The presence of the first and second layers 101, 103 having relatively high ductility serves to increase the amount of energy that the pellicle 19 can dissipate before catastrophic failure of the pellicle 19.

[0237] As explained above with reference to FIG. 13B, if the pellicle 19 is subjected to a stress large enough to break the third layer 105, the third relatively brittle layer 105 will break before the first and second relatively ductile layers 101, 103 (due to the lower ductility of the third layer 105). As shown in FIG. 13A, the third layer 105 is located between the first and second layers 101, 103. Thus, when the third layer 105 breaks, the fragments of the third layer are contained by the first and second layers 101, 103. Thus, the fragments of the third layer 105 do not contaminate the surrounding environment, and the pellicle 19 can be cleanly removed and / or replaced without causing substantial contamination. Even after the third layer 105 breaks, the first and second layers 101, 103 are able to withstand additional stress (due to their relatively high ductility) and safely contain the broken third layer 105.

[0238]

[0237] The first and second relatively ductile layers 101, 103 may form capping layers as described above with reference to Figure 3. The first and second layers 101, 103 may be formed, for example, from a metal and / or metal alloy. For example, the first and second layers 101, 103 may include, for example, a titanium, niobium and / or zirconium alloy.

[0239]

[0238] In some embodiments, the pellicle 19 can include four or more layers. For example, in addition to the three layers described above with reference to FIG. 13A, the pellicle 19 can also include an emissive layer (e.g., an emissive layer similar to the emissive layer 31a described with reference to FIG. 3). In general, the pellicle 19, which serves to contain the pellicle debris therein, can include any number of layers, at least one of which has a lower ductility than the ductility of two other layers located on either side of the less ductile layer. The relatively more ductile layers (i.e., the first and second ductile layers 101, 103) do not need to be in direct contact with the relatively less ductile layer (i.e., the third ductile layer 105). That is, one or more intermediate layers can be disposed between these layers. In such an embodiment, the third relatively less ductile layer is considered to be located between the first and second relatively more ductile layers, even if there is no direct contact between the layers.

[0240]

[0239] Figure 14 is a schematic diagram of a debris reduction device 107 according to an embodiment of the present invention. The debris reduction device 107 is arranged near the pellicle 19. In the embodiment shown in Figure 14, the debris reduction device 107 is arranged adjacent to a pellicle assembly 15 comprising a pellicle frame 17 and a pellicle held by the pellicle frame 17 at a peripheral portion 55 of the pellicle 19. The debris reduction device 107 comprises a debris steering device configured to guide debris resulting from a break in the pellicle 19 in a preferred direction. In the embodiment shown in Figure 14, the debris reduction device 107 further comprises a sensor 112 configured to monitor the pellicle 19 and detect break in the pellicle 19. The debris steering device is configured to guide debris resulting from a break in the pellicle in a preferred direction in response to detection of a break in the pellicle 19 (detected by the sensor 112).

[0241]

[0240] In the embodiment shown in Fig. 14, the debris steering device comprises a closed chamber 109 and an actuator 111. The interior of the chamber 109 is held at a pressure lower than the pressure holding the pellicle 19. For example, the interior of the chamber 109 can be pumped down to a very low pressure by using a vacuum pump. The actuator 111 is configured to open the chamber 109 in response to detection of a break in the pellicle 19. For example, when a break in the pellicle 19 is detected by the sensor 112, the sensor 112 can send a signal 113 to the actuator 111. The actuator 111 responds to the signal 113 by opening the chamber 109. The actuator 111 can open a door (not shown) of the chamber 109, for example to expose the interior of the chamber 109. When the chamber 109 is opened by the actuator 111, the low initial pressure inside the chamber 109 will cause material to be sucked into the chamber 109. For example, debris resulting from the broken pellicle 19 can be directed into the chamber 109 (which may be considered an example of a preferred direction) by the broken pellicle 19 being sucked into the chamber 109. The debris can be safely contained within the chamber 109, avoiding contamination of the surrounding environment (e.g. contamination of the patterning device MA).

[0242]

[0241] In some embodiments, the debris mitigation device may comprise two or more chambers 109. For example, multiple chambers 109 may be arranged around the pellicle 109, each having an actuator configured to open the chamber 109 upon detecting a break in the pellicle 109.

[0243]

[0242] The sensor 112 may be any sensor capable of detecting damage to the pellicle 109. For example, the sensor 112 may include any of the sensors described above in connection with other embodiments of the invention. In general, any sensing method, whether or not described herein, may be used to detect damage to the pellicle 109.

[0244] In an alternative embodiment, a chamber 109 located near the pellicle 19 (as shown in FIG. 14) can be held at a higher pressure than the pressure holding the pellicle 19. For example, a vacuum pumping mechanism can be configured to pump down the environment holding the pellicle 19 to a pressure lower than the pressure inside the chamber 109. When the sensor 112 detects a break in the pellicle 109 and the actuator 111 opens the chamber 109, the pressure difference will cause gas to be evacuated from the chamber 109. As a result, debris resulting from the broken pellicle 19 is blown out of the chamber 109 in a preferred direction. For example, the debris can be blown away from the patterning device MA, reducing any contamination of the patterning device MA.

[0245]

[0244] Figure 15 is a schematic diagram of a debris reduction device 107' according to an alternative embodiment of the present invention. The debris reduction device 107' is arranged near the pellicle 19. In the embodiment shown in Figure 15, the debris reduction device 107 is arranged adjacent to a pellicle assembly 15 comprising a pellicle frame 17 and a pellicle held by the pellicle frame 17 at a peripheral portion 55 of the pellicle 19. The debris reduction device 107' comprises a debris steering device configured to steer debris resulting from a break in the pellicle 19 in a preferred direction. The debris steering device comprises a charged surface 115 arranged near the pellicle 19. The charged surface 115 may include, for example, a charged plate. The charged surface may be charged, for example, using a voltage source 117. In the event of a break in the pellicle 19, debris resulting from the pellicle is guided towards the charged surface by electrostatic attraction. Advantageously, by directing pellicle debris towards the charged surface 115, contamination of other components (eg, patterning device MA) is reduced.

[0246] In some embodiments, the charged surface 115 can be used in conjunction with a sensor (e.g., sensor 112) configured to detect breakage of the pellicle 19. For example, the surface 115 can be charged (e.g., by turning on the voltage source 117) only in response to detection of breakage of the pellicle 19 by the sensor.

[0247]

[0246] Figure 16 is a schematic diagram of a debris mitigation device 121 according to an embodiment of the present invention. The debris mitigation device 121 comprises a sensor 123 configured to monitor a pellicle 19 held by a frame 17 to detect damage to the pellicle 19. For example, the sensor may be configured to detect the formation of one or more cracks in the pellicle 19. Additionally or alternatively, the sensor may be configured to detect damage to one or more damaged areas that the pellicle 19 may contain. In general, any sensing method, whether described herein or not, may be used to detect damage to the pellicle 19.

[0248]

[0247] The debris mitigation device 121 further comprises a tension control device configured to, in response to detection (by the sensor 123) of damage to the pellicle 19, reduce the tension in the pellicle, thereby inhibiting further damage to the pellicle 19.

[0249]

[0248] In the embodiment shown in Figure 16, the tension control device takes the form of a number of actuators 125 configured to compress the frame 17 holding the pellicle 19. The actuators may be responsive to a signal 126 sent from a sensor 123 to the actuators 125, for example upon detection of damage to the pellicle 19. The actuators 125 compress the frame 17 by applying opposing forces to two sides of the frame 17 as shown by the arrows in Figure 16. By compressing the frame 17 as shown in Figure 16, the distance 127 between the opposing sections of the perimeter portion 55 of the pellicle 19 held by the frame 17 is slightly shortened, which reduces the tension in the unsupported portion of the pellicle 19 (suspended between the opposing portions of the frame 17).

[0250]

[0249] Reducing the tension in the pellicle 19 reduces the stress experienced by the pellicle 19, reducing the likelihood of further damage and catastrophic failure of the pellicle 19. This allows the pellicle 19 to be removed from operation and / or replaced prior to catastrophic failure of the pellicle 19.

[0251]

[0250] In other embodiments, the tension control device can take other forms. For example, the tension control device can include a temperature control device configured to increase the temperature of the pellicle 19 in response to detecting damage to the pellicle 19. Increasing the temperature of the pellicle 19 causes the pellicle 19 to expand, which reduces the tension in the pellicle 19.

[0252]

[0251] The temperature control device can be configured to increase the temperature of the pellicle 19, for example, by resistive heating. For example, a current can be passed through a resistive element placed in contact with the pellicle 19. The resistance of the resistive element causes heating of the element which can result in the transfer of thermal energy to the pellicle 19, thereby increasing the temperature of the pellicle 19. Additionally or alternatively, a current can be passed through the pellicle 19 itself, causing the pellicle 19 to be heated directly due to its resistance.

[0253]

[0252] In other embodiments, the temperature control device can include a radiation source configured to illuminate all or a portion of the pellicle 19. The pellicle 19 can absorb a portion of the illumination radiation, thereby radiatively heating the pellicle 19.

[0254]

[0253] In some embodiments, measures other than those described above can be taken to reduce contamination of components of the lithographic apparatus. For example, in some embodiments, one or more shutters can be positioned in proximity to the pellicle 19. The one or more shutters can be configured to close in response to detection of damage to the pellicle 19. The one or more shutters can serve to limit an area of ​​the lithographic apparatus LA through which debris resulting from a damaged pellicle 19 is permitted to reach, thereby limiting the degree of contamination of the lithographic apparatus LA.

[0255]

[0254] The lithographic apparatus may comprise a masking blade arranged near the patterning device MA. The masking blade may be used, for example, to limit the spatial extent of radiation incident on the patterning device MA. In some embodiments, the masking blades may be configured to move closer together in response to detection of a break in the pellicle 19. This may prevent debris resulting from a broken pellicle 19 from entering the illumination system IL, and thus advantageously prevent contamination of the illumination system IL.

[0256]

[0255] Some embodiments may include an apparatus configured to intentionally break the pellicle in a controlled manner. For example, if damage to the pellicle 19 is detected, the pellicle 19 may be broken in a controlled manner to avoid uncontrolled catastrophic fracturing of the pellicle 19, which may generate a significant amount of debris. In some embodiments, one or more actuators may be provided that may break the pellicle in a controlled manner. In other embodiments, one or more radiation sources may be provided that are operable to form cracks in the pellicle. For example, one or more lasers may be arranged to illuminate the pellicle with a high-power laser beam that may fracturize the pellicle. The laser beam may be passed through the pellicle in a controlled manner to form a controlled crack in the pellicle.

[0257] As explained above with reference to Figure 5, the pellicle 19 may, during use in the lithographic apparatus LA, be exposed to a slit of radiation 75 that is scanned across the pellicle 19 in a scan direction (usually indicated as the y direction). The radiation exposure may cause localized heating of the pellicle 19 which may reduce the tension in the pellicle 19. As can be seen for example from Figure 5, the exposure slit of radiation 75 has different dimensions in the x and y directions.

[0258]

[0257] In particular, the dimensions of the exposure slit 75 are greater in the x direction than in the y direction. As a result, the greater portion of the pellicle in the x direction is heated by the radiation in the slit 75 and expands, thereby reducing tension in the x direction. Meanwhile, at a given position of the exposure slit 75 on the pellicle 19, only the smaller portion of the pellicle 19 in the y direction is heated by the radiation in the exposure slit. As a result, the reduction in tension of the pellicle 19 in the y direction is less than the reduction in tension of the pellicle 19 in the x direction. It is desirable to provide a mechanism to compensate for the difference in tension reduction in the x and y directions so that the pellicle 19 has approximately the same tension in the x and y directions.

[0259]

[0258] Figures 17a and 17b are schematic diagrams of alternative embodiments of a pellicle frame 17. Each embodiment of a pellicle frame 17 shown in Figures 17a and 17b is configured to have different compliance in the x and y directions. Each pellicle frame 17 shown in Figures 17a and 17b is configured to support a pellicle 19 at a peripheral portion 55 of the pellicle 19. The pellicle frame 17 surrounds a suspended (i.e., unsupported) region 131 of the pellicle. The pellicle frame 17 includes a first pair of sides 133a, 133b disposed at either end of the suspended region 131 of the pellicle 19 and extending in the x direction (sometimes referred to as the first direction) along the edge of the suspended region 131 of the pellicle 19. The pellicle frame 17 further includes a second pair of sides 135a, 135b disposed at either end of the suspended region 131 of the pellicle 19 and extending in the y direction (sometimes referred to as the second direction) along the edge of the suspended region 131 of the pellicle 19.

[0260] The first pair of sides 133a, 133b is configured to have a greater compliance in the y direction than the second pair of sides 135a, 135b in the x direction. The greater compliance of the frame 17 in the y direction means that the pellicle 19 supported by the pellicle frame 17 has an initial tension in the y direction that is less than the initial tension of the pellicle in the x direction. The initial tension can be thought of as the tension of the pellicle 19 before the pellicle is used in the lithographic apparatus LA. In the same way, the initial tension of the pellicle 19 can be thought of as the tension of the pellicle 19 when it is in thermal equilibrium (i.e. all areas of the pellicle 19 are at substantially the same temperature).

[0261]

[0260] As explained above, the pellicle 19 can be heated differently in different directions while it is exposed to an exposure slit of radiation. In particular, the decrease in tension of the pellicle in the x-direction due to heating can be greater than the decrease in tension of the pellicle in the y-direction due to heating. Because the initial tension in the x-direction is greater than the initial tension in the y-direction, after heating the pellicle by exposure to an exposure slit of radiation, the pellicle 19 can advantageously have a tension in the x-direction that is approximately equal to the tension in the y-direction.

[0262] In both embodiments shown in Figures 17a and 17b, the thickness of the first pair of sides 133a, 133b of the pellicle frame in the y direction is smaller than the thickness of the second pair of sides 135a, 135b in the x direction. As a result, the compliance of the frame 17 in the y direction is greater than the compliance of the frame 17 in the x direction. In the embodiment shown in Figure 17b, the thickness of the first pair of sides 133a, 133b is reduced compared to the thickness of the second pair of sides 135a, 135b by forming a slit 137 in the first pair of sides 133a, 133b. The slit 137 extends along the first pair of sides 133a, 133b in the x direction. The thickness of the first pair of sides 133a is considered to be the total thickness excluding the slit 137 which constitutes the portion of the frame 17 where no material is present.

[0263]

[0262] In some embodiments, it is advantageous to monitor the presence and integrity of the pellicle. A pellicle integrity detector can be operated based on the reflection of a light beam (radiation beam 142) from a detection surface. Pellicle integrity is monitored by detection of the radiation beam 142 reflected from the pellicle surface. The beam emitter and receiver can be positioned so that the reflected beam can reach the receiver. The receiver detects a signal if the pellicle membrane is present and does not detect a signal if the pellicle membrane is not present or intact (i.e., if the pellicle is damaged).

[0264]

[0263] In the embodiment shown in Figures 18 and 19, the signal at the receiver sensor is sensitive to the distance of the pellicle from the transmitter. When the pellicle membrane moves up and down, the amplitude and position of the reflected radiation beam 142 will change on the receiver. The receiver is sensitive to one or both of these parameters to allow monitoring of the dynamic response of the pellicle membrane to any external factors such as ambient air pressure fluctuations and vibrations. For example, a position sensitive detector that is sensitive to the position of the reflected radiation beam 142 can be used as the receiver.

[0265]

[0264] A frame presence detector is also desired and can operate based on the reflected radiation beam 142. A multiple light beam frame detector can be used to detect the frame condition, the presence or absence of the frame, delamination or distortion, or any thermal effects from the EUV radiation that may be distorting the frame.

[0266]

[0265] Thus, both the pellicle membrane and the pellicle frame detector can comprise a radiation beam emitter and a receiver. The radiation beam 142 can be provided by a single laser diode or a diode array. However, it can also be provided by any other radiation beam source. An optical fiber can be used to remote the emitter and the receiver. The radiation beam 142 is selected to have a wavelength that gives a good reflection coefficient from the pellicle material to the reticle material and the pellicle (and mask) protective case cover surface. It is also desirable to have a low absorption of the beam in the pellicle to reduce undesirable thermal effects. Although the above detectors are described as operating on the reflection of a light (radiation) beam, this is for illustrative purposes only. Other types of emitted beams, for example based on acoustic waves, or any other suitable detectors can be used for this purpose.

[0267]

[0266] The detectors described above can use mixed optical fiber bundles with different receiving fiber numerical apertures (NA), which allows for reflectance compensation and makes detection insensitive to reflectance changes at the sensing surface.

[0268]

[0267] Detectors using the optical (radiation) beam approach will detect the pellicle motion and its motion frequency. The resonant frequency is indicative of the pellicle condition, for example. Any change in the motion frequency can indicate changes related to impending pellicle failure, thermal effects, or changes / degradation of the pellicle due to use. For such purposes, both normal and non-normal incidence beam scans can be used. Optimal angles of incidence allow fewer detectors in a smaller space. The condition of the pellicle membrane can be measured at an initial stage and then monitored to detect changes over time.

[0269]

[0268] Optical emitter / receiver arrays (e.g. laser diodes, one or two dimensional arrays) can be used to detect multiple areas of the pellicle. The radiation beam can be adjusted to a different angle for each emitter, effectively checking multiple areas from a small footprint. Examples of emitter / detector pair configurations can be a row of three sensors, five or nine sensors forming a cross array, or a 3x3 sensor array with at least one frame sensor at the edge of the array and at least one pellicle sensor in the center of the array.

[0270]

[0269] It is also possible to use a scanning beam concept to scan the pellicle surface to detect changes in pellicle integrity, which entails providing a radiation beam with the ability to rotate in 1D or 2D space (e.g. coupled with a rotation stage).

[0271]

[0270] Pellicle and frame detection devices can be positioned at various locations inside and outside of a lithographic apparatus or other device (e.g., a carrying case, a reticle inspection tool, etc.) to detect pellicle condition during storage, transport, etc. Pellicle integrity can also be monitored during reticle inspection, for example during use of a scatterometry apparatus used to detect particle contamination on the reticle through the pellicle.

[0272]

[0271] Figure 18 is a schematic diagram of a pellicle fault detection apparatus 140 according to an embodiment of the present invention. The pellicle fault detection apparatus 140 comprises a radiation source 141 and a radiation sensor 143. The radiation source 141 is configured to emit a radiation beam 142. The radiation sensor 143 is positioned to receive and detect reflected light of the radiation beam 142.

[0273]

[0272] Also shown in Figure 18 is the patterning device MA and a pellicle assembly 15. The pellicle assembly 15 comprises a pellicle 19 and a pellicle frame 17 which holds the pellicle 19 in a suitable position to protect the patterning device MA from particle contamination. A radiation source 141 is arranged to illuminate a portion of the pellicle 19 and (through the pellicle 19) the patterning device MA with a radiation beam 142. A radiation sensor 143 is arranged to receive and measure reflections of the radiation beam 142 from the pellicle 19 and from the patterning device MA. The radiation sensor is arranged to illuminate a portion of the pellicle 19 at a non-normal angle of incidence, i.e. the angle of incidence θ of the radiation beam 142 at the pellicle 19 is greater than zero. Typically the pellicle 19 is approximately parallel to the patterned surface 24 of the patterning device MA. Thus, the angle of incidence at which radiation beam 142 strikes patterned surface 24 of patterning device MA is typically approximately equal to the angle of incidence θ of radiation beam 142 at pellicle 19 .

[0274]

[0273] Due to the non-normal angle of incidence θ of the radiation beam 142 at the pellicle 19 and the patterned surface 24, the position of the reflected beam 142a reflected from the pellicle 19 is different to the position of the reflected beam 142b reflected from the patterning device MA. Thus, the reflected beam 142a from the pellicle 19 is incident on the radiation sensor 143 at a different position than the reflected beam 142b from the patterning device MA. The radiation sensor 143 may be configured to determine the position at which the radiation is incident. Thus, the radiation sensor 143 may be able to distinguish between radiation reflected from the pellicle 19 and radiation reflected from the patterning device MA.

[0275]

[0274] The pellicle detection apparatus 140 further comprises a controller 145 in communication with the sensor 143. The controller 145 is configured to detect a pellicle failure from the detection of the reflected radiation by the sensor. For example, the controller 145 may infer that the pellicle 19 is not present or that the pellicle 19 is damaged (and therefore not present in the optical path of the radiation beam 142) if there is no substantial reflection of radiation from the pellicle 19. In some embodiments, the controller may be configured to detect a pellicle failure if a measure of the intensity of the portion 142a of the radiation beam 142 reflected from the pellicle 19 falls below a threshold. The measure of the intensity of the reflected portion 142a is made by the sensor 143 and may, for example, include the power and / or intensity of the reflected radiation incident on the sensor 143.

[0276] 18, the radiation sensor 143 includes a first detector area 143a and a second detector area 143b. The first detector area is positioned to receive radiation 142a reflected from the pellicle 19, and the second detector area 143b is positioned to receive radiation 142b reflected from the patterning device MA.

[0277] If the first detector area 143a detects substantial reflected light from the pellicle 19 (e.g., radiation having an intensity or power above a threshold is measured), the controller 145 can determine that the pellicle 19 is in place and not faulty. If the first detector area 143a does not detect substantial reflected light from the pellicle (e.g., the intensity or power measured at the first detector area 143a is below a threshold), the controller 145 can determine that the pellicle is not present or that the pellicle is damaged (and therefore not in the path of the radiation beam 142).

[0278]

[0277] Radiation may also be measured at the second detector area 143b for comparison with the radiation measured at the first detector area 143a. The radiation measured at the second detector area 143b may be used, for example, to confirm the presence of the patterning device MA and / or to confirm that the patterning device MA and / or pellicle are correctly aligned for purposes of detecting the presence or absence of a pellicle 19. For example, if no substantial reflection of radiation from the patterning device MA is measured at the second detector area 143b, this may indicate that the pellicle fault detection apparatus 140 is not correctly positioned and / or aligned to detect the presence or absence of a pellicle.

[0279]

[0278] If the pellicle failure detection device 140 is correctly positioned and aligned to detect the presence or absence of a pellicle 19, and the pellicle breaks, the power and / or intensity of the radiation measured at the second detector area 143b may decrease. If the pellicle 19 is present in the path of the radiation 142b reflected from the patterned surface 24, a portion of the radiation may be absorbed by the pellicle 19 (in addition to being reflected by the pellicle 19), thereby reducing the power of the radiation incident on the second detector area 143b. For example, approximately 10-20% of the EUV radiation incident on the pellicle 19 may be absorbed by the pellicle 19 each time it passes through it. If the pellicle 19 breaks and is no longer present in the path of the radiation beam 142, the radiation will no longer be absorbed by the pellicle 19. Thus, the power of the radiation incident on the second detector area 143b will increase. In some embodiments, the controller 145 can use a reduction in the power of the radiation incident on the second detector area 143b to detect that the pellicle 19 has failed.

[0280] 18, the radiation sensor 143 includes a first detector area 143a configured to detect radiation 142a reflected from the pellicle 19, and a second detector area 143b configured to detect radiation 142b reflected from the patterning device MA. In other embodiments, the radiation sensor 143 may take other forms. For example, in some embodiments, the second detector area 143b may be omitted. In such embodiments, the results of the measurements by the first detector area 142a alone may be used to determine whether the pellicle 19 is present or not, or whether it has failed.

[0281]

[0280] In general, any sensor arranged to detect the portion 142a of the radiation beam 142 reflected from the pellicle 19 can be used. As shown in the embodiment of Figure 18, the radiation sensor 143 can further be configured to detect the portion 142b of the radiation beam 142 reflected from the patterning device MA. Because the radiation beam is incident on the pellicle at a non-normal angle of incidence, the portion 142b of the radiation beam 142 reflected from the patterning device MA is incident on the radiation sensor 143 at a different position to the portion 142a of the radiation beam 142 reflected from the patterning device MA.

[0282]

[0281] As described above, the pellicle 19 is placed on the pellicle frame 17 so that an initial tension is generated in the pellicle 19. If the pellicle 19 is broken, the initial tension of the pellicle can remove the pellicle from almost the entire area surrounded by the pellicle frame 17. For example, the pellicle 19 may roll up on itself after the breakage and / or be cut off from the pellicle frame 17. Therefore, the breakage of the pellicle 19 can be detected by monitoring the pellicle 19 at any location on the pellicle 19. In some embodiments, a single pellicle failure detection device can be used to determine the failure of the pellicle 19 at any location on the pellicle 19. In other embodiments, multiple pellicle failure detection devices can be provided to monitor different parts of the pellicle 19.

[0283] 18, the controller 145 is shown as a separate component from the sensor 143. In other embodiments, the controller 145 may form part of the sensor 143 or may form part of another component.

[0284] 18, the sensor 143 is positioned to detect the specular reflection of the radiation beam 142 from the pellicle 19. As a result, the radiation source 141 is positioned to illuminate the pellicle 19 at a non-normal angle of incidence such that the specular reflection 142a from the pellicle 19 is at a different position to the specular reflection from the patterning device MA.

[0285] In some embodiments, the sensor 143 can be arranged to detect diffuse reflection from the pellicle 19. Similar to the methods described above, detection of diffuse reflection can be used to detect whether the pellicle 19 has failed. In such an embodiment, the radiation source 141 can be arranged to illuminate the pellicle 19 at a non-normal incidence angle, or can be arranged to illuminate the pellicle at normal incidence. The angular profile of the diffuse reflection from the pellicle 19 can be different from the angular profile of the diffuse reflection from the patterning device. As a result, in an embodiment in which the radiation source SO illuminates the pellicle 19 at a normal incidence angle, the measurement of the diffuse reflection can be used to distinguish between reflections from the pellicle 19 and reflections from the patterning device MA.

[0286]

[0285] The pellicle fault detection apparatus 140 (such as the pellicle detection apparatus described above with reference to Figure 18) may be used at any stage of a process in which a patterning device MA protected by a pellicle 19 is handled and used. For example, the pellicle fault detection apparatus 140 may be used in a load lock stage of a lithographic apparatus. The load lock stage may be used to transfer the patterning device MA protected by a pellicle 19 into or out of the lithographic apparatus. For example, the patterning device MA may be moved from atmospheric pressure outside the lithographic apparatus and placed in a load lock. The load lock may be pumped down to a vacuum pressure with the patterning device MA in the load lock in preparation for use of the patterning device MA in the lithographic apparatus. The patterning device MA may then be transferred from the load lock to the lithographic apparatus for use in a lithographic process.

[0287] In some embodiments, the pellicle failure detection device 140 may be located in a load lock stage of the lithographic apparatus. The pellicle failure detection device 140 may be used to check the pellicle prior to loading the patterning device MA and the pellicle into the lithographic apparatus for use. If the pellicle failure detection device 140 detects that the pellicle is faulty, the patterning device MA may not be loaded into the lithographic apparatus and may not be used in the lithographic apparatus. Checking the pellicle before loading the patterning device MA into the lithographic apparatus may prevent a damaged pellicle from entering the lithographic apparatus. Advantageously, this may prevent pellicle debris from entering the lithographic apparatus and contaminating the lithographic apparatus.

[0288]

[0287] The patterning device MA and the pellicle 19 protecting the patterning device MA can be transferred to a protective pod (sometimes called a reticle pod). For example, the patterning device can be loaded into the lithographic apparatus (e.g. via a load lock) while still located in the protective case. The patterning device MA can then be removed from the protective case for use in a lithographic process. The protective case can comprise inner and outer compartments, sometimes called, for example, an inner pod and an outer pod, with the inner pod being located within the outer pod.

[0289]

[0288] Figure 19 is a schematic diagram of a portion of a protective case 147 within which the patterning device MA and pellicle assembly 15 reside. The pellicle assembly 15 comprises a pellicle 19 and a pellicle frame 17. Also shown in Figure 19 is a pellicle fault detection apparatus 140 that may be used to monitor the pellicle 19 for faults whilst the patterning device MA and pellicle assembly are within the protective case 147. To facilitate monitoring of the pellicle 19 within the protective case 147, the protective case 147 comprises a first transparent window 149a. The first transparent window 149a transmits at least a portion of the radiation beam 142 and the reflected portions 142a, 142b of the radiation beam 142.

[0290] 19, the protective case 147 further comprises a second transparent window 149b. The second transparent window 149b can be used to monitor further features of the pellicle assembly 15 and / or the patterning device MA. For example, in the embodiment shown in FIG. 19, a monitoring device 240 is arranged to monitor the presence of the pellicle frame 17.

[0291]

[0290] The monitoring device 240 utilizes a similar principle to the pellicle failure detection apparatus 140, and includes a radiation source 241 and a radiation sensor 243. The radiation source is configured to illuminate the pellicle frame 17 with a radiation beam 242 at a non-normal incidence angle. The radiation sensor 243 is configured to receive and measure a portion 242a of the radiation beam 242 reflected from the pellicle frame 17. The radiation sensor 243 can determine whether the pellicle frame 17 is present or not based on the result of the measurement of the reflected radiation 242a by the sensor 243. For example, if the power or intensity of the radiation measured by the radiation sensor 243 is above a threshold value, it can be determined that the pellicle frame 17 is present. If the power or intensity of the radiation measured by the radiation sensor 243 is below a threshold value, it can be determined that the pellicle frame 17 is not present.

[0292]

[0291] The monitoring device 240 can be used to distinguish between a patterning device MA that is intended to be protected by a pellicle and a patterning device MA that is not intended to be protected by a pellicle. For example, if the monitoring device 240 determines that a pellicle frame 17 is present on the patterning device, it can be inferred that the patterning device is intended to be protected by a pellicle. If the monitoring device 240 determines that the pellicle frame 17 is not in a proper position, it can be inferred that the patterning device MA is not intended to be protected by a pellicle. As explained above, the pellicle failure detection apparatus 140 can determine whether an intact pellicle 19 is protecting the patterning device MA.

[0293]

[0292] In some embodiments, whether a patterning device is intended to be protected by a pellicle can be detected by other means. For example, the protective case 147 in which the patterning device MA is located may differ depending on whether the patterning device is intended to be protected by a pellicle. To determine whether the patterning device MA is intended to be protected by a pellicle, one or more features of the protective case may be monitored. For example, in some embodiments, a protective case 147 designed for use with a patterning device MA protected by a pellicle 19 may include a recess to accommodate the pellicle frame 17 and the pellicle 19. A protective case 147 designed for use with a patterning device MA not protected by a pellicle 19 may not include a recess to accommodate the pellicle frame 17 and the pellicle. In such an embodiment, the monitoring device 240 may be configured to detect the presence or absence of a recess in the protective case 147. The presence or absence of a recess in protective case 147 can indicate whether the protective case is carrying a patterning device MA that is intended to be protected by pellicle 19, or whether it is carrying a patterning device MA that is not intended to be protected by pellicle 19.

[0294]

[0293] Although the pellicle fault detection apparatus 140 and / or monitoring device 240 have been described above as being used in a load lock stage, the pellicle fault detection apparatus 140 and / or monitoring device may also be used in other locations. For example, they may be used in a patterning device MA handling stage of a lithographic apparatus, where the patterning device MA is prepared for use in a lithographic process. In some embodiments, multiple pellicle fault detection apparatus 140 and / or monitoring device 240 may be used in multiple different locations.

[0295]

[0294] Embodiments have been described above in which a pellicle failure detection device is used to detect pellicle failure. In some embodiments, an optical device can be used to measure the position of one or more regions of the pellicle while the pellicle is exposed to a pressure difference. As described above, as part of the process of loading a patterning device into a lithographic apparatus, the patterning device and pellicle can be pumped down to a vacuum pressure (e.g., in a load lock stage). As part of the process of unloading a patterning device from a lithographic apparatus, the patterning device and pellicle can be exposed to an increased pressure. For example, the patterning device can be placed in a load lock stage that is vented to atmospheric pressure before the patterning device is unloaded from the load lock stage.

[0296]

[0295] As the patterning device and pellicle are exposed to changing pressure conditions, a pressure differential may develop across the pellicle. For example, the pressure in the volume between the patterning device and the pellicle may change at a slower rate than the pressure outside of this volume, which may create a pressure differential across the pellicle. The pressure differential across the pellicle may exert a force on the pellicle that serves to bend the pellicle. For example, the pellicle may bend toward the patterning device or away from the patterning device. Bending of the pellicle may cause damage to the pellicle and / or breakage of the pellicle. For example, the pellicle may bend enough to contact the patterning device and / or a protective case that may contain the patterning device and pellicle (such as protective case 147 shown in FIG. 19). Contact between the pellicle and another component may cause damage to the pellicle and may result in breakage of the pellicle.

[0297]

[0296] To avoid damaging the pellicle, the rate at which the pressure state is changed (e.g. during a pump-down or vent procedure) can be limited to ensure that any pressure difference across the pellicle is maintained within a safe threshold that will not damage the pellicle. This can be achieved, for example, by measuring the position of one or more regions of the pellicle during the pressure change and adjusting the rate at which the pressure is changed depending on the measurement. For example, the position of a substantially central portion of the pellicle can be measured. If it is detected that the central portion of the pellicle is too close to and / or too far from the patterning device, the rate of change in pressure to which the patterning device is exposed can be reduced. If it is detected that the position of the pellicle is sufficiently within a safe range (i.e., not too close to or too far from the patterning device), the rate of change in pressure can be increased to reduce the time required to complete the pump-down and / or vent procedure.

[0298]

[0297] In general, a lithographic apparatus may comprise a load stage for the lithographic apparatus, comprising a chamber configured to accommodate a patterning device protected by a pellicle, a sensor device configured to measure a position of at least a portion of the pellicle located in the chamber, and a pressure change device configured to change a pressure inside the chamber. The pressure change device may be configured to control a rate of changing the pressure inside the chamber in response to a measurement of the position of at least a portion of the pellicle. The pressure change device may for example be configured to reduce a rate of changing the pressure inside the chamber in response to a measurement indicating that the position of the pellicle is outside a desired range of pellicle positions. The desired range of pellicle positions may for example be between a minimum distance from the patterning device and a maximum distance from the patterning device. That is, the rate of pressure change may be reduced if the pellicle is too close to the patterning device or too far away from the patterning device.

[0299]

[0298] Advantageously, by controlling the rate of pressure change to which the patterning device and pellicle are exposed in response to measurements of the position of the pellicle, the time required for pump-down and / or venting procedures can be reduced while ensuring that the rate of pressure change remains within safe limits.

[0300] In an alternative embodiment, the rate of pressure change to which the patterning device and pellicle may be exposed during the pump down and / or venting procedures may be modeled. For example, the response of the pellicle during the pump down and / or venting procedures may be modeled at a number of different rates of pressure change. This allows for the determination of a safe rate of pressure change that will not damage the pellicle. For example, the maximum rate of pressure change to which the patterning device and pellicle may be exposed without damaging the pellicle may be determined by modeling.

[0301]

[0300] However, modeling results have associated uncertainties and may not accurately predict the behavior of the pellicle. For example, the mechanical properties of the pellicle may vary from one pellicle to another and may differ from the mechanical properties actually input into the model. Thus, the behavior of the pellicle may differ from the modeling results. To resolve the modeling uncertainties, the rate of pressure change actually used may be substantially less than the maximum safe rate of pressure change determined using the modeling process. That is, the rate of pressure change used in the pump-down and / or venting process may be reduced below the theoretically safe rate of pressure change (determined as a result of the modeling process) to reduce the risk of damaging the pellicle.

[0302]

[0301] Thus, one result of the modeling uncertainties may be that the rate of pressure change actually used may be less than the maximum rate of pressure change that may be used without substantially damaging the pellicle. As a result, the time taken to perform pump-down and / or venting processes may increase. As a result, the speed at which patterning devices can be loaded and removed from the lithographic apparatus may decrease, potentially reducing the throughput of the lithographic apparatus.

[0303]

[0302] As explained above, in some embodiments, the rate of pressure change to which the patterning device and pellicle are subjected can be controlled in response to measurements of the position of the pellicle. By controlling the rate of pressure change in response to measurements of the pellicle (as opposed to modeling), the rate of pressure change can be increased without risking damage to the pellicle. That is, a higher rate of pressure change can be used when relying on real-time measurements than when relying on modeling. As a result, the patterning device can be loaded into and / or out of the lithographic apparatus at a faster rate by controlling the pump-down and / or venting process in response to measurements of the pellicle. Advantageously, this allows for an increased throughput of the lithographic apparatus.

[0304]

[0303] The pump-down and / or venting procedures may be performed while the patterning device and pellicle are within a protective case (such as protective case 147 shown in Figure 19). As described above with reference to Figure 19, protective case 147 may include one or more transparent windows 149a, 149b.

[0305]

[0304] The transparent windows 149a, 149b of the protective case allow optical measurement of the pellicle to determine its position. For example, a sensor similar to the pellicle fault detection device 140 shown in Fig. 19 can be used to determine the position of a region of the pellicle. The pellicle fault detection device 140 shown in Fig. 19 comprises a radiation source 141, a radiation sensor 143 and a controller 145. The radiation source 141 illuminates a portion of the pellicle 19 with a radiation beam 142 at a non-normal incidence angle. As a result, the position of the portion 142a of the radiation beam 142 reflected from the pellicle 19 depends on the position of the illuminated portion of the pellicle 19. For example, if the illuminated portion of the pellicle 19 moves closer to or further away from the patterning device MA, the position at which the reflected portion 142a is incident on the radiation sensor 143 may change.

[0306]

[0305] The radiation sensor 143 may be operable to detect the position at which the reflected portion 142a is incident on the radiation sensor 143. For example, the radiation sensor 143 may include a number of different detector areas located at different positions on the radiation sensor 143. The multiple detector areas may for example be arranged as a detector area array (for example a CCD array or a CMOS array). The controller 145 may receive the results of the measurements by the radiation sensor 143 and determine the position of the reflected portion 142a on the radiation sensor 143 from the measurements. The controller 145 may further determine the position of the illuminated portion of the pellicle from the measurements. For example, the controller 145 may measure the distance of the illuminated portion of the pellicle 19 from the patterning device MA.

[0307]

[0306] Radiation sensor 143 may also measure the reflection of radiation beam 142 from transparent window 149a and / or the patterning device. The position of the reflected light from transparent window 149a and / or the patterning device on radiation sensor 143 may act as a reference measurement to which the position of the reflected light from the pellicle may be compared. For example, by comparing the position of the reflected light from the pellicle with the position of the reflected light from transparent window 149a and / or the patterning device MA, the distance of the pellicle from transparent window 149a and / or the patterning device MA may be measured.

[0308]

[0307] In some embodiments, a confocal imaging sensor can be used to determine the position of a portion of a pellicle. The confocal imaging sensor can include a radiation source configured to form a series of monochromatic images along the optical axis of the confocal imaging sensor. Reflected light of the emitted radiation is imaged through a pinhole. The sensor can determine a wavelength of the imaged reflected radiation that depends on the position on the optical axis that reflects the imaged radiation. The wavelength of the imaged radiation is therefore indicative of the position of a reflective surface, such as a pellicle. Using this principle, a confocal imaging sensor can be used to measure the position of an illuminated area of ​​a pellicle.

[0309] In some embodiments, a confocal imaging sensor can be used to determine the positions of multiple reflective surfaces simultaneously. For example, a confocal imaging sensor can be used to determine the position of the illuminated portion of the pellicle while determining the position of the transparent window 149a and / or the patterning device MA. The determined position of the pellicle can be compared to the determined position of the patterning device and / or transparent window, for example to measure the distance of the pellicle from the transparent window and / or the patterning device MA. Other methods can also be used to measure the position of the pellicle and the position of the patterning device and / or transparent window simultaneously. For example, triangulation can be used to measure the position of the pellicle and the position of the patterning device and / or transparent window together simultaneously. These positions can be monitored simultaneously as shown above in relation to FIG. 19.

[0310]

[0309] As described above, measurements of the position of a portion of the pellicle can be used to control the rate of pressure change to which the pellicle is exposed. The portion of the pellicle being measured can be, for example, substantially a central portion of the pellicle. In some embodiments, the position of multiple portions of the pellicle can be measured (e.g., using multiple sensors). In some embodiments, an optical sensor (e.g., a sensor of the type described above with reference to FIG. 19) can be used to measure the position of a portion of the pellicle. In general, any form of sensor can be used to measure the position of one or more portions of the pellicle.

[0311]

[0310] The number of sensors and their locations in Figures 18 and 19 are shown for illustrative purposes only. Additional sensors and locations with appropriate wavelength selection can be used to add functionality as desired or needed.

[0312]

[0311] In some embodiments, additionally or alternatively, measurements of the position of one or more portions of the pellicle can be used as an indication of pellicle fatigue. For example, the change in the position of the pellicle as a function of pressure can be measured during a number of different pump-down and / or vent procedures. If the position of the pellicle as a function of pressure is significantly different for different pump-down and / or vent procedures, this may indicate that the mechanical properties of the pellicle have changed. This may indicate, for example, pellicle fatigue and may be used as a warning that the pellicle may be susceptible to further damage and breakage. Such pellicles may then be removed from use to avoid further damage to the pellicle.

[0313]

[0312] In some embodiments, a fault in the pellicle 19 can be detected through a measurement of radiation propagating in the pellicle 19. Such a measurement may already be performed for other purposes in the lithographic apparatus. For example, a measurement of radiation propagated in the pellicle 19 can be performed for alignment purposes and / or to measure wavefront aberrations. Figure 20 is a schematic illustration of a lithographic apparatus LA that can be used to measure the alignment and / or wavefront aberrations of a component. The lithographic apparatus LA shown in Figure 20 is similar to the lithographic apparatus LA shown in Figure 1. The same reference numbers are used in Figure 20 to indicate the same features described above with reference to Figure 1. These features will not be described in further detail with reference to Figure 20.

[0314] In the embodiment shown in Figure 20, the patterning device MA comprises a fiducial 150. The fiducial 150 may be similar to the marker 81 shown in Figure 5. The fiducial 150 may be patterned into a portion of the radiation beam B for measurement purposes. For example, the fiducial 150 may comprise a reflective diffraction grating that, when illuminated by the radiation beam B, results in the formation of multiple diffraction orders. In other embodiments, the fiducial 150 may not form part of the patterning device MA, but may be located adjacent to the patterning device MA (e.g. on the support structure MT). Radiation reflected from the fiducial 150 passes through the pellicle 19.

[0315]

[0314] Also shown in Figure 20 is a sensor arrangement 151. The sensor arrangement 151 is configured to measure one or more properties of the radiation beam B output from the projection system PS. The sensor arrangement 151 may for example measure one or more properties of the radiation reflected from the fiducial 150 (e.g. diffraction orders formed at the fiducial). Measurements made by the sensor arrangement 151 may be used to determine the alignment of the substrate table WT relative to the alignment of the patterning device MA and / or the support structure MT. For example, the sensor arrangement 151 may be used to determine the position of one or more features of the radiation beam B (e.g. one or more diffraction orders) formed by the fiducial 150. This allows the alignment of the sensor arrangement 151 relative to the fiducial 150 to be determined.

[0316]

[0315] In some embodiments, the fiducial 150 and the sensor arrangement 151 may additionally or alternatively be used to measure wavefront aberrations introduced by the projection system PS. For example, the sensor arrangement 151 may be configured to perform a shearing interferometric measurement. In such an embodiment, the sensor arrangement 151 may include a transmission grating and a radiation sensor arranged behind the transmission grating. The radiation sensor may be configured to measure the interaction of the diffraction orders formed on the fiducial 150 and the diffraction orders formed on the transmission grating of the sensor arrangement 151. The fiducial 150 and / or the sensor arrangement 151 may be moved relative to each other. For example, the sensor arrangement 151 may be stepped relative to the radiation beam B and a measurement may be taken at each step position. The results of the measurements by the sensor arrangement 151 may be fitted to a set of polynomials, such as Zernike polynomials. Such a set of polynomials may characterize the wavefront aberrations introduced by the projection system PS and may be used to tune the projection system (e.g. to suppress the wavefront aberrations introduced by the projection system PS).

[0317]

[0316] As explained above, measurements used to determine the alignment and / or wavefront aberrations of the components may include measuring radiation transmitted through the pellicle 19. As explained further above, the pellicle 19 may absorb and / or reflect a portion of the radiation incident thereon. For example, the power of the EUV radiation beam B may be absorbed by the pellicle 19 by approximately 10% each time it passes through the pellicle 19. Because the radiation beam B passes through the pellicle 19 twice before reaching the radiation sensor 151, the power of the EUV radiation beam B may be absorbed by the pellicle 19 by approximately 20%. As a result, the radiation intensity measured by the sensor arrangement 151 is reduced by the presence of the pellicle 19. If the pellicle 19 is about to break, it may be removed from the optical path of the radiation beam B. For example, the pellicle 19 may shatter and / or roll up, such that it is no longer held by the pellicle frame 17 on the patterning device MA. If the pellicle 19 is removed from the path of the radiation beam B, the intensity of the radiation reaching the sensor arrangement 151 will increase. This can be detected by an increase in the signal measured by the sensor arrangement 151. Such an increase can be used to detect a failure of the pellicle 19.

[0318]

[0317] In the embodiment shown in Figure 20, the lithographic apparatus LA further comprises a controller 153 in communication with the sensor arrangement 151. The controller 153 may receive a signal from the sensor arrangement 151 indicative of a measure of radiation intensity measured by the sensor arrangement 151. The controller 153 may detect an increase in the measure of radiation intensity measured by the sensor arrangement 151 and may determine from the detected increase that the pellicle 19 is damaged. The controller 153 may, for example, issue a signal and / or an alarm indicating that a failure of the pellicle 19 has been detected.

[0319] In the embodiment shown in Figure 20, the radiation source SO, the sensor arrangement 151 and the controller 153 can be considered to form an example of a pellicle failure detection arrangement. The radiation source SO is configured to illuminate a portion of the patterning device MA protected by the pellicle 19 with a radiation beam B. The radiation beam B is transmitted through the pellicle 19. The sensor arrangement 151 is arranged to receive and measure at least a portion of the radiation beam B that has been transmitted through the pellicle 19. The controller 153 is in communication with the sensor arrangement 151 and is configured to detect a failure of the pellicle 19 when a measure of the intensity of the radiation received by the sensor arrangement increases. The measure of the radiation intensity can for example be the power of the radiation.

[0320]

[0319] Embodiments for controlling and / or detecting pellicle failure have been described above. In the above embodiments, it is generally assumed that once the pellicle begins to fail, cracks in the pellicle continue to propagate throughout the pellicle. However, in some embodiments, the pellicle may include features configured to limit the propagation of cracks in the pellicle. FIG. 21 is a schematic diagram of a pellicle 19 including multiple termination features 301. For ease of illustration, the termination features 301 are shown as relatively large compared to the size of the pellicle 19. In practice, the termination features 301 may be smaller than shown in FIG. 21 compared to the size of the pellicle 19. The pellicle 19 may also include more termination features 301 than shown in FIG. 21.

[0321]

[0320] The termination feature 301 can be configured such that when the pellicle 19 is placed under tension (e.g., suspended from a pellicle frame), the stress induced in the termination feature is less than the stress induced in an area of ​​the pellicle outside the termination feature. As described in more detail below, the termination feature 301 can include, for example, a hole in the pellicle 19 (and thus has no stress within the termination feature itself). Alternatively, the termination feature can include an area of ​​the pellicle that is doped with a doping material.

[0322]

[0321] Figure 22 is a schematic diagram of a crack 303 formed in a pellicle 19. The crack 303 has a length a. The crack 303 has a tip 305 having a radius R. References herein to the crack tip 305 should be interpreted as referring to the region of the pellicle material abutting the end of the crack 303, as shown by the bold line labeled 305 in Figure 22. References herein to stress at the crack tip should be interpreted as meaning the stress experienced by the region of the pellicle material abutting the end of the crack 303.

[0323]

[0322] First, once a crack 303 forms in the pellicle 19, the crack will continue to grow if the following conditions are met.

[0324]

[0323]

number

[0325]

[0324] where σ is the stress at the crack tip, a is the crack length, and KIC is the critical stress intensity factor, or toughness, of the pellicle material. The expression on the left side of the condition given in (1) is approximately equal to the stress intensity factor, KI, at the crack tip. The critical stress intensity factor, KIC, is a constant characteristic of the pellicle material.

[0326]

[0325] Typically, the stress σ at the tip of a crack in the pellicle material is initially (i.e., when the crack first initiates) similar to the stress caused by the pretensioning force experienced when the pellicle is attached to the pellicle frame. When a crack begins to propagate in a conventional pellicle, the stress σ at the crack tip typically does not decrease. Instead, the stress σ at the crack tip increases as the crack length a increases. As a result, condition (1) continues to be satisfied and the crack will continue to propagate until it reaches the edge of the suspended region of the pellicle 19 (i.e., until it reaches the pellicle frame).

[0327] In the embodiment of the pellicle shown in Figure 21, the pellicle 19 includes a termination feature 301. The termination feature 301 is configured such that when a crack tip 305 propagates into the termination feature, the crack tip experiences a reduction in stress σ at the crack tip. The reduction in stress σ at the crack tip is reduced by such an amount that the condition given in (1) no longer holds. As a result, the propagation of the crack can be terminated and the crack will not continue to grow any further.

[0328]

[0327] Figure 23 shows a schematic of the stress σ at the crack tip as a function of crack length a as the crack propagates towards and into the termination feature 301. The stresses shown in Figure 22 are von Mises stresses in Newtons per square meter. As the crack grows, the crack tip radius R remains substantially constant while the crack length a increases. As a result, the ratio a / R of the crack length a to the crack tip radius R increases and, as a result, the stress σ at the crack tip also increases with increasing crack length a.

[0329]

[0328] The initial increase in stress σ with increasing crack length a can be seen in Figure 22. As the crack approaches the termination feature 301, the rate of increase in stress σ increases until it reaches infinity. This is because in the area immediately surrounding the termination feature 301, the stress is higher than in the rest of the pellicle 19, and higher than the termination feature 301 itself. The high stress area surrounding the termination feature can cause the crack to be pulled into the termination feature 301.

[0330] The termination feature 301 can have a radius that is larger than the crack tip radius R. As the crack enters the termination feature 301, the crack tip radius R increases to the radius of the termination feature 301. As a result, the ratio a / R decreases and the stress σ at the crack tip also decreases. The large reduction in stress σ occurs at approximately 0.985×10 -7 This can be seen for crack lengths a greater than m. The reduction in stress σ means that condition (1) is no longer satisfied and therefore the crack propagation terminates at the termination feature 301. In this way, the crack is prevented from propagating further and the size of the crack is limited before it propagates through the entire pellicle 19.

[0331]

[0330] As explained above, the radius of the termination feature 301 can be greater than the radius R of the propagating crack tip. The crack tip propagating in the pellicle 19 can have a radius R on the order of about 1-10 nanometers. Thus, the termination feature 301 can have a radius greater than about 10 nanometers. In some embodiments, the radius of the termination feature 301 can be greater than this, for example the radius can be greater than about 20 nanometers, about 50 nanometers, or even about 100 nanometers. Advantageously, having the termination feature 301 have a radius greater than the radius R of the propagating crack tip ensures that the ratio a / R decreases as the crack tip enters the termination feature 301, with a corresponding decrease in the stress σ at the crack tip.

[0332] 21, each termination feature 301 is substantially circular. In other embodiments, the termination features 301 can have a shape other than substantially circular. In general, the termination features 301 can have a lateral dimension that is greater than the radius R of the crack tip. The lateral dimension can be, for example, a radius. The lateral dimension can be a width of the termination feature 301. The lateral dimension can be greater than about 10 nanometers, about 20 nanometers, about 50 nanometers, or even about 100 nanometers.

[0333]

[0332] As shown in the embodiment of Figure 21, the termination features 301 can be arranged in a substantially regular pattern. That is, the spacing between adjacent termination features 301 can be substantially the same for several different sets of adjacent termination features 301. Advantageously, arranging the termination features 301 in a substantially regular pattern can increase the likelihood that a crack will propagate between two termination features and then terminate at both ends of the pellicle 19 before reaching its edges. This can serve to limit the extent of the crack, and advantageously can prevent the crack from generating a significant amount of debris that could result in contamination. Thus, advantageously, the termination features 301 reduce contamination of surrounding components that could result from a failure of the pellicle 19.

[0334]

[0333] In some embodiments, some or all of the termination features 301 may include holes in the pellicle 19. The holes may be, for example, substantially circular holes. A circular hole is a relatively stable discontinuity in the material and may therefore reduce the change that causes the pellicle 19 to fail (compared to holes having other shapes). In general, a hole in the pellicle 19 creates a greater stress in the area of ​​the pellicle 19 that borders the hole than elsewhere in the pellicle 19. For example, the stress in the area of ​​the pellicle 19 that borders the hole may be approximately twice as large as the stress elsewhere in the pellicle 19. However, the stress in the area of ​​the pellicle 19 that borders the hole is typically less than the stress σ at the tip of the propagating crack.

[0335] 24A is a schematic diagram of a crack 303 propagating towards a termination feature 301 that includes a hole in a pellicle 19. Before the crack 303 reaches the termination feature 301, it has a crack tip 305 with a radius R that is smaller than the radius of the termination feature 301. The stress σ at the crack tip is such that condition (1) is satisfied and the crack tip continues to propagate within the pellicle 19.

[0336]

[0335] Figure 24B is a schematic diagram of crack 303 after it has reached termination feature 305. Once crack tip 305 enters termination region 305, the radius R of crack tip 305 becomes the radius of termination feature 301, and the stress σ at the crack tip becomes the stress at the region of pellicle 19 that interfaces with termination feature 301. As explained above, the stress at the region of pellicle 19 that interfaces with termination feature 301 is typically greater than elsewhere in the pellicle (e.g., twice the stress elsewhere in the pellicle), but is typically less than the stress at crack tip 305 as it propagates toward termination feature 301 (as shown in Figure 24A). Thus, upon entering the termination feature, the stress σ at the crack tip decreases as explained above with reference to Figure 22, and propagation of crack 303 ceases.

[0337] In embodiments comprising a termination feature 301 comprising a hole in the pellicle 19, the diameter of the hole (or other lateral dimension of the hole) may be smaller than the size of a contaminant particle that the pellicle 19 is configured to prevent contact with the patterning device MA. A termination feature 301 comprising a hole in the pellicle 19 may be formed, for example, by isotropically etching a layer of the pellicle 19 to form a hole in the pellicle 19. The size and / or shape of the hole may be controlled by controlling the etching process.

[0338] In some embodiments, some or all of the termination features 301 may include doped regions of the pellicle 19. The doped regions of the pellicle 19 are doped with a doping material. A doping material such as boron may be used to dope each region of the pellicle. In some embodiments, a doping material other than boron may be used. In some embodiments, the doping material may be a p-type dopant. Additionally or alternatively, the doping material may be an s-type dopant.

[0339] In some embodiments, the pellicle can include silicon (e.g., a polysilicon film). In such embodiments, the doping material can be a p-type dopant, such as a dopant including one or more of boron, aluminum, nitrogen, gallium, and / or indium. Additionally or alternatively, the doping material can be an n-type dopant, such as a dopant including phosphorus, arsenic, antimony, bismuth, and / or lithium.

[0340] In some embodiments, the pellicle can include graphene. In such embodiments, the doping material can include one or more of boron, nitrogen, titanium, chromium, platinum, cobalt, indium, and / or sulfur. Additionally or alternatively, the doping material can include one or more of an organic molecule, an acid, a base, and / or a halide. In some embodiments, the doping material can include a transition metal, such as, for example, copper, nickel, ruthenium, molybdenum, and / or platinum.

[0341]

[0340] The doped regions of the pellicle 19 may be subject to less stress than other non-doped regions of the pellicle. For example, when a pellicle 19 including a doped region is placed under tension (e.g., suspended from a pellicle frame), the stress induced in the doped region may be less than the stress induced in regions of the pellicle 19 outside the doped region. In some embodiments, a compressive stress may be introduced into the pellicle 19 by the doped region of the pellicle 19.

[0342]

[0341] Because the stress in the doped regions of the pellicle 19 is less than the other undoped regions of the pellicle, when the tip of a propagating crack enters the doped region, the stress σ at the crack tip decreases as it enters the doped region. The decrease in stress σ at the crack tip may be sufficient that condition (1) above is no longer satisfied. As a result, the propagation of the crack will terminate in the doped region.

[0343]

[0342] Regions of the pellicle can be selectively doped, for example, by first applying a mask to the pellicle 19. The mask can cover areas of the pellicle 19 other than the areas to be doped, such that only the areas to be doped remain exposed. The exposed areas can then be doped with a doping material. After doping has occurred, the mask can be removed to expose the pellicle 19 including the doped areas. Because only portions of the pellicle 19 are doped, the mechanical properties of the entire pellicle 19 are substantially unaffected by the doped areas.

[0344] In some embodiments, the doped region can have a substantially circular shape. The mechanical properties of the substantially circular doped region can be similar to those discussed above with reference to the holes formed in the pellicle 19. By forming the termination region by doping, the doping process can be controlled to control the mechanical properties of the termination region (e.g., the stress distribution resulting from tensioning the pellicle).

[0345]

[0344] In some embodiments, the doped regions can be formed in other than a regular pattern of circular doped regions. Figure 25 is a schematic diagram of a pellicle 19 including multiple stripes of doped regions 301. In the embodiment of Figure 25, the stripes extend the entire extent of the pellicle 19 in the x direction shown in Figure 25. In the embodiment of Figure 25, the stripes of doped regions are substantially parallel to each other. By aligning the doped regions so that they are approximately or substantially parallel to each other, any cracks that start to propagate from a component in a direction perpendicular to the stripes (i.e., in the y direction shown in Figure 25) will reach and terminate in the doped region 301. Furthermore, the stress distribution in the pellicle 19 caused by the stripe doped regions 301 generally means that cracks will only grow and propagate approximately in the y direction (or at least from components that are larger in the y direction than in the x direction). Thus, the stripe doped regions arranged as shown in Figure 25 can ensure that substantially all cracks that occur in the pellicle will enter the doped region 301.

[0346] The stripe of doped region 301 can have a lateral dimension that is greater than the radius R of the crack tip that terminates in doped region 301. The lateral dimension can be the width (in the y direction shown in FIG. 25) of doped region 301. The width of doped region 301 can be, for example, greater than about 10 nanometers, about 20 nanometers, about 50 nanometers, or even about 100 nanometers.

[0347]

[0346] In some embodiments, the doped region can be provided around the suspension region of the pellicle. FIG. 26 is a schematic diagram of an embodiment of a pellicle assembly including a doped region provided around the suspension region of the pellicle. The pellicle assembly comprises a pellicle 19 and a pellicle frame 17. The pellicle 19 is held by the pellicle frame 17. The pellicle frame 17 surrounds the suspended (i.e. unsupported) region 131 of the pellicle 19. The suspended region 131 of the pellicle 19 includes a boundary portion 311 disposed around the suspension region 131 of the pellicle 19. In the embodiment of FIG. 26, the boundary portion 311 is doped with a doping material (e.g., boron). As explained above, the doped region of the pellicle may be subjected to less stress than other regions outside the doped region of the pellicle 19. The boundary portion can function as a termination feature similar to the termination feature described above.

[0348]

[0347] Advantageously, providing a doped region in the form of interface 311 allows stresses in different directions on the pellicle to be controlled by controlling the doping of interface 311. For example, to control the stresses on the pellicle in the x and y directions shown in Figure 26, different amounts of doping material can be provided at different locations on interface 311.

[0349]

[0348] In some embodiments, different forms of termination features as described above with reference to Figures 21-27 may be combined in a single embodiment. For example, in some embodiments, the doped interface shown in Figure 26 may be combined with other termination features, such as circular doped regions and / or hole patterns in a pellicle. In general, any of the different forms of termination features described herein may be combined in a single embodiment.

[0350] In some embodiments, the pellicle can be subjected to a treatment process to increase the toughness of the pellicle before it is used. For example, the whole or a part of the pellicle can be heated to a temperature higher than the ductile-brittle transition temperature (DBTT) of the pellicle while being held in tension. As described in more detail below, heating the whole or a part of the pellicle to a temperature higher than the DBTT of the pellicle while being held in tension can cause plastic deformation in some areas of the pellicle. The plastic deformation can introduce compressive stresses in defective areas in the pellicle. As described above, the presence of compressive stresses in the pellicle can slow down or stop crack propagation in the pellicle.

[0351]

[0350] As explained above, a pellicle can be formed from layers of different materials. For example, different layers can be deposited on top of each other to form a pellicle. During the manufacture of a pellicle, due to imperfections in the deposition process, one or more layers may be deposited with defects therein. The presence of defects in one or more layers may result in locally weak areas of the pellicle. Additionally or alternatively, small cracks (e.g., having a size on the order of a few nanometers) may occur in one or more layers of the pellicle. Such defects in the pellicle may cause local stress concentrations in the pellicle that may later cause the pellicle to fatigue and / or fail. It is therefore desirable to strengthen such defective areas of the pellicle to reduce the likelihood of causing pellicle failure.

[0352]

[0351] In some circumstances, ductile materials can be strengthened by temporarily exposing them to tension. Tension can result in a persistent strengthened state that is more resistant to crack growth in the material. For example, if a ductile pellicle containing a small crack is held in tension, the entire material can elastically deform. However, in the region proximate to the tip of the crack, the pellicle can plastically deform, which can introduce compressive stress at the tip of the crack. The compressive stress at the tip of the crack can slow down or prevent further crack propagation, thus strengthening the pellicle against further damage. Thus, the fatigue recovery of the pellicle is increased. Such fatigue recovery of the pellicle remains after the tension is removed. For example, tension can be applied for a short period of time, for example, less than one second. Tension can be applied, for example, as an impact load.

[0353]

[0352] Generally, a pellicle is formed of at least some layers that are relatively brittle. Thus, at normal operating temperatures, the pellicle may not be sufficiently ductile to introduce the compressive stresses described above. Therefore, the pellicle may first be heated to a temperature above the DBTT of the pellicle before tensioning it. Heating the pellicle to a temperature above the DBTT increases the ductility of the pellicle. While the pellicle is highly ductile, the pellicle may be subjected to high tension such that the area of ​​the pellicle adjacent to the defect in the pellicle is plastically deformed. As explained above, the plastic deformation may introduce areas of compressive stress into the pellicle that may strengthen the pellicle against further crack growth.

[0354]

[0353] The plastic deformation of each region of the pellicle should be kept smaller than the critical plastic deformation. In other words, the pellicle should not be subjected to a tension that causes the stress at the tip of the crack in the pellicle to exceed the tensile strength of the pellicle. This is because the plastic deformation is caused by the crack This ensures that if a crack does occur at the tip, it will not propagate into the pellicle.

[0355]

[0354] When the pellicle is heated to a temperature above the DBTT of the pellicle, tension can be applied to the pellicle, for example, by exposing the pellicle to a pressure difference across the pellicle. As explained above, when the patterning device and the pellicle are exposed to changing pressure conditions, a pressure difference can be established across the pellicle. For example, the pressure in the volume between the patterning device and the pellicle can change at a slower rate than the pressure outside the volume, which can result in a pressure difference across the pellicle. The pressure difference across the pellicle can exert a force on the pellicle that acts to bend the pellicle. For example, the pellicle can bend toward the patterning device or away from the patterning device. The force acting to bend the pellicle can increase the tension of the pellicle. As explained above, increasing the tension of the pellicle while the temperature of the pellicle is above the DBTT can cause regions of the pellicle to plastically deform. The plastic deformation can serve to introduce compressive stresses into the pellicle.

[0356]

[0355] In some embodiments, the tension of the pellicle supported by the pellicle frame can heat the pellicle to a temperature high enough to cause plastic deformation in some areas of the pellicle. Thus, in such embodiments, it may not be necessary to further increase the tension of the pellicle (e.g., by introducing a pressure difference across the pellicle). However, disadvantageously, increasing the temperature of the entire pellicle to a point where no further increase in tension is required to cause plastic deformation may serve to reduce the tension of the entire pellicle. Thus, such heating can be performed locally and only in limited areas of the pellicle.

[0357] In some embodiments, the corners of the suspended portion of the pellicle can be locally heated to reduce stress at the corners of the pellicle. The corners of the suspended portion of the pellicle where the pellicle contacts the pellicle frame can typically be locations where relatively high stress concentrations occur. By locally heating the corners to a temperature higher than the DBTT of the pellicle, creep can be induced in the corner area. Creep can serve to locally reduce the stress of the pellicle in the heated area.

[0358]

[0357] The pellicle can be locally heated, for example, by illuminating one or more portions of the pellicle with radiation. For example, a laser can be used to illuminate one or more portions of the pellicle with a laser beam to heat the illuminated areas. Additionally or alternatively, the pellicle can be locally heated by heating a pellicle frame that holds the pellicle in place. By heating the pellicle frame, the area of ​​the pellicle that is in contact with or adjacent to the pellicle frame will be heated. This can include the corners of the suspension area of ​​the pellicle. The remaining portions of the pellicle may receive only limited or no heating and may remain below the DBTT of the pellicle. As a result, the tension throughout the pellicle will not be reduced.

[0359]

[0358] As discussed above, one or more regions of the pellicle can be heated to a temperature above the DBTT of the pellicle. Heating of the pellicle can be performed such that the temperature of the pellicle does not exceed the melting point of the pellicle. For example, a pellicle comprising a polysilicon material can be heated to a temperature of about 1000°C or higher.

[0360] In some embodiments, the pellicle may be continuously heated during operation in the lithographic apparatus. For example, the pellicle may be continuously heated such that the temperature of the pellicle is kept above a threshold temperature. During a lithographic exposure, each portion of the pellicle may be cyclically exposed to radiation (e.g., EUV radiation) as the radiation is scanned over the patterning device. The pellicle may absorb a portion of the incident radiation, which increases the temperature of the pellicle. Due to the cyclic nature of exposing the pellicle to radiation, the temperature of the pellicle may undergo cyclic heating. That is, the pellicle is heated during exposure to radiation and cooled between exposures to radiation.

[0361]

[0360] In the environment of the lithographic apparatus, the patterning device and the pellicle are typically pumped to a vacuum pressure. However, the environment may still contain gases, such as water vapor. The water vapor may condense on the pellicle, resulting in the presence of water on the pellicle. Contact between the pellicle and water may cause the pellicle to oxidize. Oxygen has a low transmittance for EUV radiation. Thus, oxidation of the pellicle reduces the transmittance of the pellicle at EUV wavelengths.

[0362]

[0361] Water can condense on the pellicle only when the temperature of the pellicle falls below a threshold temperature. For example, water can condense on a pellicle that is subjected to periodic heating when the pellicle is not exposed to radiation (and is heated by radiation). When the pellicle is exposed to radiation, the temperature of the pellicle may be sufficient to prevent substantial condensation of water on the pellicle. Thus, condensation of water on the pellicle can be inhibited and / or prevented by heating the pellicle between exposures to radiation so that the temperature of the pellicle does not fall to a temperature at which substantial condensation of water can occur. For example, the pellicle can be continuously heated during use so that the temperature of the pellicle does not fall below the threshold temperature. The threshold temperature can be a temperature at which substantial condensation of water does not occur on the pellicle. The threshold temperature can be, for example, about 120°C.

[0363]

[0362] Reducing and / or preventing water condensation on the pellicle by heating the pellicle reduces oxidation of the pellicle (due to the absence of water on the pellicle). Advantageously, reducing oxidation of the pellicle reduces degradation of the EUV transmittance of the pellicle due to oxidation.

[0364]

[0363] The pellicle can be heated, for example, by resistive heating. As described above, the pellicle can include at least one layer that is electrically conductive. Electrical connection is made with one or more conductive layers, and a current can be passed through the conductive layer to cause resistive heating of the layer.

[0365]

[0364] In general, heating the pellicle can shorten the life of the pellicle (e.g., by causing pellicle fatigue). However, by resistively heating the pellicle to reduce oxidation of the pellicle, the pellicle can absorb a relatively small amount of power compared to the power absorbed by exposure to EUV radiation. For example, in some embodiments, the pellicle can absorb approximately 4 W / cm2 of power by exposure to EUV radiation. 2 In contrast, resistive heating of the pellicle, which ensures that the pellicle remains above a threshold temperature of about 120°C, can absorb approximately 0.1 W / cm 2 Therefore, resistive heating can contribute a relatively small amount of additional absorbed power and may not significantly increase pellicle fatigue.

[0366]

[0365] As described above, the pellicle can be heated by resistive heating. A current source can be provided as part of the pellicle assembly to heat the pellicle. According to some embodiments of the present invention, the pellicle assembly can include a frame configured to support the pellicle, and a pellicle attached to the frame and including at least one conductive layer. The pellicle assembly can further include a current source connected to the at least one conductive layer and configured to generate a current in the at least one conductive layer. The current source can be configured to generate a current that heats the pellicle by resistive heating such that the temperature of the pellicle is above a threshold temperature. The threshold temperature can be about 120 degrees Celsius or higher. The current source can be configured to generate a substantially direct current in the at least one conductive layer.

[0367]

[0366] It will be appreciated that the current required to heat a pellicle to a threshold temperature may vary depending on the material. For example, the current required to heat a pellicle to a threshold temperature may depend on the resistivity of the conductive material of the pellicle and the thermal mass of the pellicle. The current required to heat a given pellicle to a threshold temperature can be easily calculated and / or established through experimentation by one of ordinary skill in the art.

[0368]

[0367] As described in detail above, the pellicle is typically placed on the pellicle frame such that the pellicle is held in an initial tension state. The initial tension of the pellicle serves to suppress the curvature and deflection of the pellicle when a pressure difference is established across the pellicle. For example, during loading and unloading of a patterning device from a lithographic apparatus, the patterning device and the pellicle may be subjected to changing pressure conditions. The changing pressure conditions may cause a pressure difference to be established across the pellicle. Holding the pellicle in an initial tension state suppresses the curvature and deflection of the pellicle caused by the pressure difference. For example, it is desirable to place the pellicle under initial tension such that the pellicle does not deflect more than about 500 μm when exposed to a pressure difference of up to about 2 Pascals. Thus, a high initial tension of the pellicle can provide an advantageous effect when the pellicle is exposed to changing pressure conditions (e.g., during loading and / or unloading of a patterning device from a lithographic apparatus).

[0369]

[0368] During the lithography exposure process, the pressure to which the pellicle is exposed can be substantially constant. Thus, the pressure on both sides of the pellicle can be substantially the same, and there may be no substantial pressure difference across the pellicle. Thus, there may be less need to place the pellicle under tension while undergoing the lithography exposure process.

[0370]

[0369] During the lithographic exposure process, a given portion of the pellicle can be subjected to cyclic heating as EUV radiation is scanned through the pellicle. Cyclic heating of each portion of the pellicle increases stress in some portions of the pellicle and decreases stress in other portions of the pellicle. Changes in pellicle stress due to cyclic heating have been shown to cause fatigue in the pellicle; that is, the tensile strength of the pellicle decreases over time. The rate at which the pellicle fatigues increases with increasing initial tension of the pellicle. Thus, the initial tension of the pellicle can act to increase the rate at which pellicle fatigue occurs and shorten the life of the pellicle. Thus, high initial tension of the pellicle can have adverse effects during the lithographic exposure process.

[0371]

[0370] As described above, a relatively high initial tension in the pellicle may be advantageous during loading and / or unloading of the patterning device, but may be disadvantageous during lithographic exposure. Therefore, methods and apparatus are proposed that serve to increase and / or decrease the tension in the pellicle. This allows the tension to be controlled based on the state of the pellicle. For example, the tension in the pellicle may be increased before loading and / or unloading the pellicle into the lithographic apparatus. The tension in the pellicle may be decreased before exposing the pellicle to EUV radiation in a lithographic exposure process.

[0372]

[0371] Figure 27 is a schematic diagram of a pellicle assembly 15 configured to adjust the tension of a pellicle. The pellicle assembly 15 includes a pellicle 19 and a pellicle frame 17 configured to support the pellicle 19. The pellicle assembly 15 further includes a heater 501. The heater 501 is configured to heat the pellicle frame 17. The heater can be configured to heat the pellicle frame 17, for example, by resistive heating. The heater 501 shown in Figure 27 is a thin film resistive heater 501 disposed on the pellicle frame 17. Heating the pellicle frame 17 causes the pellicle frame to expand, which elongates the frame and the pellicle 19 on the frame 17. Stretching the pellicle 19 serves to increase the tension of the pellicle 19.

[0373]

[0372] In the embodiment shown in FIG. 27, the heaters 501 are disposed only on two opposing sides of the pellicle frame 17. Thus, the heaters 501 are configured to increase the tension of the pellicle 19 only in the y direction shown in FIG. 27. As shown in FIG. 27, the pellicle 19 is longer in the y direction than in the x direction. Thus, the tension in the y direction may be the dominant factor in determining how much the pellicle deflects when exposed to a pressure difference. In other embodiments, the heaters 501 may be disposed on other sides of the pellicle frame 17. For example, the heaters 501 may be disposed to elongate the pellicle 19 in the x direction.

[0374] In one embodiment (not shown), a heater can be provided on each side of the pellicle frame 17. When a heater is provided on each side of the pellicle frame, the pellicle expands isotropically. This is advantageous because it can reduce stress in the pellicle 19.

[0375] In some embodiments, the pellicle 19 can be placed on the pellicle frame 17 at an initial tension that is less than the tension desired for loading and unloading the patterning device into the lithographic apparatus. Prior to loading the patterning device into the lithographic apparatus, the heater 501 can be switched on to heat the pellicle frame 17 and increase the tension in the pellicle 19. The tension in the pellicle 19 can be increased, for example, to a tension that resists bending and curvature of the pellicle when a pressure differential is established across the pellicle 19. The patterning device and pellicle assembly 15 can then be pumped down to a vacuum pressure and loaded into the lithographic apparatus.

[0376] After being loaded into the lithographic apparatus, the heater 501 can be switched off and the pellicle frame 17 can be allowed to cool. As the pellicle frame 17 cools, the tension in the pellicle 19 is reduced. The patterning device and pellicle can then be exposed to EUV radiation as part of a lithographic exposure process. Because the tension in the pellicle has been reduced prior to exposure to EUV radiation, advantageously fatigue resulting from exposure to EUV radiation is reduced.

[0377] Prior to unloading the patterning device and pellicle assembly from the lithographic apparatus, heater 501 can be powered on to heat the pellicle frame 17. Heating the pellicle frame 17 stretches the pellicle frame and pellicle 19 to increase the tension in the pellicle 19. Increasing the tension in the pellicle 19 allows the pellicle to resist bowing and curvature when the pellicle 19 is vented to atmospheric pressure during the unloading process.

[0378] In some embodiments, the pellicle frame 17 can be heated using methods other than resistive heating. For example, the pellicle frame 17 can be exposed to radiation that is absorbed by the pellicle frame 17 and heats the pellicle frame 17. In some embodiments, the pellicle frame 17 can be stretched using methods other than heating the pellicle frame 17. For example, one or more actuators (e.g., piezo actuators) can be configured to apply a force to the pellicle frame 17 to stretch the frame.

[0379] In some embodiments, the tension of the pellicle 19 can be adjusted by bending the pellicle frame 17 as opposed to stretching it. Figures 28A and 28B are schematic diagrams of a portion of a pellicle assembly after (Figure 28B) and before (Figure 28A) bending the pellicle frame 17 to increase the tension of the pellicle 19. The pellicle frame 17 includes a first layer 17a and a second layer 17b disposed on the first layer 17a. The pellicle 19 is attached to the second layer 17b.

[0380]

[0379] The second layer 17b of the pellicle frame 17 has a higher Young's modulus and thermal expansion coefficient than the first layer 17a of the pellicle frame 17. The second layer 17b may include, for example, ruthenium. When the pellicle frame 17 is heated, the second layer 17b expands at a faster rate than the first layer 17a. As a result, the frame 17 bends as shown in FIG. 28B. The bending of the frame 17 acts to pull the pellicle 19 to increase the tension in the pellicle 19.

[0381]

[0380] The pellicle frame 17 can be heated, for example, by resistive heating, to bend the pellicle frame 17. For example, the second layer 17b can be electrically conductive, and a current can be passed through the second layer 17b to heat the second layer 17b by resistive heating. Alternatively, the pellicle frame 17 can include a third conductive layer through which a current can be passed to heat the pellicle frame 17 by resistive heating. The third layer can be disposed, for example, between the first layer 17a and the second layer 17b. It is desirable to electrically insulate the pellicle 19 from the pellicle frame 17 so that the current does not reach the pellicle 19. The pellicle 19 can be electrically insulated from the conductive layer, for example, by fabricating etch lines on the top surface of the conductive layer.

[0382] 28A and 28B, the amount that the pellicle frame bends when subjected to a certain amount of heat can depend on the relative thicknesses of the first and second layers 17a, 17b. Thus, the thicknesses of the first and second layers 17a, 17b can be selected to provide a desired amount of bending for a certain amount of heat.

[0383]

[0382] In some embodiments, the tension of the pellicle can be changed by bending the pellicle 19 itself, rather than bending the pellicle frame 17. For example, the multi-layer structure described above with reference to Figures 28A and 28B can be used for the pellicle itself. Figures 29A and 29B are schematic diagrams of a pellicle assembly 15 according to an embodiment of the present invention. The pellicle assembly 15 comprises a pellicle 19 supported by a pellicle frame 17. The pellicle 19 includes at least a first layer 19a having a first Young's modulus and a first thermal expansion coefficient, and a second layer 19b having a second Young's modulus and a second thermal expansion coefficient. The second Young's modulus is higher than the first Young's modulus, and the second thermal expansion coefficient is higher than the first thermal expansion coefficient.

[0384]

[0383] The second layer 19b can be located further from the patterning device than the first layer 19a. The pellicle 19 can include further layers than the first and second layers 19a, 19b. For ease of illustration, the further layers are not shown in Figures 29A and 29B.

[0385]

[0384] Figure 29A shows the pellicle 19 in an initial tension state. The initial tension can be used, for example, during a lithographic exposure process. The tension of the pellicle 19 can be increased before loading and / or unloading the patterning device and pellicle assembly into and / or from the lithographic apparatus. To increase the tension of the pellicle 19, the pellicle 19 can be heated. For example, to heat the pellicle by resistive heating, a current can be passed through a conductive layer of the pellicle (not shown in Figures 29A and 29B). Additionally or alternatively, the pellicle 19 can be exposed to radiation that is absorbed by the pellicle and thus serves to heat the pellicle.

[0386]

[0385] Figure 29B shows the pellicle assembly 15 after the pellicle 19 has been heated. By heating the pellicle 19, the second layer 19b expands more than the first layer 19a. This has the effect of bending the pellicle and increasing the tension in the pellicle. As a result, the pellicle is able to adequately resist further bending when subjected to a pressure differential across the pellicle 19. To reduce the tension in the pellicle 19 (e.g., for use in lithography exposure), the pellicle 19 is allowed to cool so that it relaxes back to the position shown in Figure 29A.

[0387]

[0386] In some embodiments, the pellicle 19 can be configured such that the stiffness of the pellicle is not uniform across the pellicle. Figure 30 is a schematic diagram of a pellicle assembly 15 in which the stiffness of the pellicle is higher in regions closer to the edge of the pellicle 19. The pellicle assembly 15 shown in Figure 30 is similar to the pellicle assembly 15 shown in Figures 29A and 29B, and similar components will not be described in detail again. In the embodiment of Figure 30, the second layer 19b has a greater thickness in regions closer to the edge of the pellicle 19. The thicker regions of the pellicle 19 may not cover the exposure field on the patterning device. Therefore, increasing the thickness of the pellicle 19 does not affect the imaging performance of the pellicle.

[0388]

[0387] In the embodiment of Figure 30, the thicker region of the pellicle 19 can be locally heated. By locally heating the thicker region, most of the curvature of the pellicle 19 occurs in the thicker region (as shown in Figure 30). The body of the pellicle is stretched by the curvature of the thicker region, which results in an increase in tension in the pellicle. The thicker region of the pellicle 19 is also stiffer. Therefore, this region is well suited to withstand the stresses induced in the region by the curvature of the pellicle 19.

[0389]

[0388] The areas of greater thickness can be locally heated, for example, by placing a heater on the pellicle frame 17. The heater would serve to locally heat the area of ​​the pellicle near the edge of the pellicle 19. The heater could be, for example, a resistive heater.

[0390]

[0389] In some embodiments, localized heating of the pellicle can be configured to create a desired stress distribution in the pellicle. This can create a non-uniform stress field in the pellicle. For example, localized heating can be configured to reduce stress in one direction while maintaining stress in another direction. In general, localized heating can be used to control the stress distribution in the pellicle. This can be used to balance stress, for example, to reduce wrinkling of the pellicle.

[0391]

[0390] In the embodiment of Figure 30, one region of the suspended portion of the pellicle 19 has a greater thickness. The greater thickness serves to increase the stiffness of that region. Increasing the stiffness of the pellicle results in a decrease in the tension in the pellicle required to withstand a pressure differential across the pellicle 19. Thus, advantageously, the tension in the pellicle can be increased to a lesser tension than would be used in the absence of the greater thickness region.

[0392]

[0391] In some embodiments, the transition between the thicker region of the pellicle and the body of the pellicle can be configured such that the thickness of the pellicle transitions smoothly between the regions (as opposed to the step change in thickness shown in FIG. 30). Such a transition can be formed, for example, by isotropically etching the pellicle during manufacture of the pellicle. A smooth transition between regions of different thickness can result in lower stress concentrations in the transition region.

[0393]

[0392] Using the method and apparatus for increasing the stress tension of a pellicle described above, tension can be introduced into a pellicle of a material in which it is difficult to introduce an inherent tension. For example, in some embodiments, the pellicle can include graphene. In general, it is difficult to introduce tension into a pellicle that includes graphene. The method and apparatus described above advantageously allow tension to be introduced into a pellicle that includes graphene.

[0394]

[0393] Various embodiments for controlling the tension of a pellicle have been described above. A device configured to control the tension of a pellicle may be referred to as a tension controller. The tension controller may include a heater configured to heat a component of the pellicle assembly (e.g., the pellicle frame and / or the pellicle). The tension controller may include one or more actuators configured to exert a force on the pellicle frame.

[0395]

[0394] Various inventive aspects of the pellicles and pellicle assemblies have been described above and illustrated in the figures with reference to specific embodiments of the invention. It will be understood that any of the aspects described and / or illustrated may be combined into a single embodiment. For example, one or more features of one embodiment may be combined with one or more features of another embodiment. It will be further understood that although some embodiments have been described that include more than one inventive aspect, embodiments that include only a single inventive aspect are also contemplated herein. In general, any feature of the described embodiments may be used alone or in any combination with any other feature of the described embodiments.

[0396]

[0395] Although particular reference is made in this text to embodiments of the invention in the context of lithographic apparatus, embodiments of the invention can be used in other apparatus. Embodiments of the invention can form part of a mask inspection apparatus, a metrology apparatus or any apparatus that measures or processes objects such as wafers (or other substrates) or masks (or other patterning devices). These apparatus can be generally referred to as lithography tools. Such lithography tools can use vacuum or atmospheric (non-vacuum) conditions.

[0397] The term "EUV radiation" may be taken to encompass electromagnetic radiation having a wavelength in the range of 4 to 20 nm, for example in the range of 13 to 14 nm. EUV radiation may have a wavelength of less than 10 nm, for example in the range of 4 to 10 nm, such as 6.7 nm or 6.8 nm.

[0398]

[0397] Although specific reference is made in this text to the use of lithographic apparatus in IC manufacture, it should be understood that the lithographic apparatus described herein may have other applications, including the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat panel displays, liquid crystal displays (LCDs), thin film magnetic heads, etc.

[0399]

[0398] Although specific embodiments of the present invention have been described above, it is clear that the present invention can be implemented in other ways. The above description is intended to be illustrative and not limiting. Thus, it will be apparent to one skilled in the art that modifications can be made to the present invention without departing from the scope of the following claims.

[0400]

[0399] This specification discloses one or more embodiments incorporating the features of the present invention. The disclosed embodiments are merely exemplary of the present invention. The scope of the present invention is not limited to the disclosed embodiments. The present invention is defined by the appended claims.

[0401]

[0400] References to a described embodiment(s), "one embodiment," "an embodiment," "an exemplary embodiment," and the like in the specification indicate that the described embodiment may include a particular feature, structure, or characteristic, but not all embodiments may include that particular feature, structure, or characteristic. Furthermore, such phrases do not necessarily refer to the same embodiment. Furthermore, when a particular feature, structure, or characteristic is described in connection with one embodiment, it is understood that it is within the knowledge of one of ordinary skill in the art to bring such feature, structure, or characteristic into connection with other embodiments, whether or not it is explicitly described.

[0402]

[0401] It should be understood that the Detailed Description section is intended to be used to interpret the claims, and not the Summary and Abstract sections. The Summary and Abstract sections may describe one or more exemplary embodiments of the invention as contemplated by the inventor(s), but are not exhaustive and therefore are not intended to limit the scope of the invention and the appended claims in any manner.

[0403]

[0402] Up to now, the present invention has been described using functional building blocks that show the implementation of specific functions and their relationships. The boundaries of these functional building blocks have been arbitrarily defined in this specification for the convenience of description. Other boundaries can be defined as long as the specific functions and their relationships are appropriately performed.

[0404]

[0403] The above description of the specific embodiments fully discloses the general nature of the present invention, so that others, applying knowledge within the skill of the art, may easily modify and / or adapt such specific embodiments to various applications without departing from the basic concept of the present invention and without the need for undue experimentation. Such adaptations and modifications are therefore intended to be within the meaning and range of equivalents of the disclosed embodiments, based on the teaching and guidance presented herein. It should be understood that the phrases or terms used herein are for the purpose of description and not limitation, and that the terms or terms used herein should be interpreted in light of the above teaching and guidance by those of skill in the art.

[0405]

[0404] The breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.

Claims

1. A pellicle failure detection device, comprising: a sensor arranged to detect a portion of the radiation beam reflected from a portion of a pellicle arranged to protect the patterning device; a controller in communication with the sensor and configured to detect a fault in the pellicle from the detection of reflected radiation performed by the sensor; the failure of the pellicle is breakage or damage to the pellicle; the sensor is configured to detect a portion of the radiation beam reflected from the patterning device, the sensor having a first sensor area configured to detect radiation reflected from the pellicle and a second sensor area configured to detect radiation reflected from the patterning device; The pellicle failure detection device, wherein the controller is configured to determine that the pellicle failure detection device is correctly positioned and / or aligned to detect the presence or absence of the pellicle.

2. 10. The apparatus of claim 1, further comprising a radiation output configured to illuminate the portion of the pellicle with the radiation beam such that the radiation beam is incident on the pellicle at a non-normal angle of incidence.

3. The apparatus of claim 1 , wherein the sensor is positioned to detect diffuse reflection of the radiation beam from the pellicle.

4. 2. The apparatus of claim 1, wherein the controller is configured to detect a failure of the pellicle when a measure produced by the sensor of an intensity of the portion of the radiation beam reflected from the pellicle falls below a threshold value.

5. a radiation output configured to illuminate a portion of a pellicle protecting a patterning device with a radiation beam that is transmitted through said pellicle; and a sensor positioned to receive and measure at least a portion of the radiation beam that is transmitted through the pellicle; a controller in communication with the sensor and configured to detect a failure of the pellicle when a measure of the intensity of the radiation received by the sensor increases; The failure of the pellicle is breakage or damage to the pellicle. Pellicle failure detection device.

6. the patterning device includes a reflective fiducial; The apparatus of claim 5 , wherein the sensor is configured to measure a portion of the radiation beam that is reflected from the fiducial.

7. The apparatus of claim 6 , wherein the sensor and the controller are further configured to measure an alignment of a feature formed on the portion of the radiation beam reflected from the fiducial.

8. The apparatus of claim 6 , wherein the sensor and the controller are further configured to measure a wavefront aberration of the portion of the radiation beam reflected from the fiducial.

9. The apparatus of claim 6 , wherein the fiducial is located within an available area of ​​the pellicle.

10. The apparatus of claim 6 , wherein the fiducial is patterned into a portion of the radiation beam for measurement purposes.

11. The apparatus of claim 10 , wherein the fiducial comprises a reflective diffraction grating that, when illuminated by the radiation beam, results in the formation of multiple diffraction orders.

12. 7. The apparatus of claim 6, wherein the sensor is used to determine the position of one or more features of the radiation beam formed by the fiducial, thereby enabling an alignment of the sensor relative to the fiducial to be determined.

13. 7. The apparatus of claim 6, wherein the sensor is disposed after a transmission grating and configured to measure an interaction between a diffraction order formed at the fiducial and a diffraction order formed at the transmission grating.

14. The apparatus of claim 6 , wherein the fiducial and / or the sensor are movable relative to each other.

15. a fiducial positioned adjacent to the patterning device; The apparatus of claim 5 , wherein radiation reflected from the fiducial passes through the pellicle.

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