Mask assembly and associated method

Abstract

Mask assemblies and associated methods are disclosed. A method includes the steps of receiving a mask assembly including a mask and a removable EUV transparent pellicle held by a pellicle frame, removing the pellicle frame and the EUV transparent pellicle from the mask, inspecting a mask pattern on the mask using an inspection tool, and subsequently attaching the EUV transparent pellicle held by the pellicle frame to the mask. The method may further include the steps of: after removing the pellicle frame and the EUV transparent pellicle from the mask, attaching an alternative pellicle frame holding an alternative pellicle to the mask, the alternative pellicle being formed of a material that is substantially transparent to an inspection beam of the inspection tool; and after inspecting the mask pattern on the mask using the inspection tool, removing the alternative pellicle held by the alternative pellicle frame from the mask in order to attach the EUV transparent pellicle held by the pellicle frame to the mask.

Description

[0001] This application is a divisional application of the Chinese patent application with international application number PCT / EP / 2016 / 052055, international application date February 1, 2016, national application number 201680008470.X, and invention name “MASK ASSEMBLY AND ASSOCIATED METHODS”. Technical Field

[0002] The present invention relates to a mask assembly and particularly, but not exclusively, to a method of using a mask assembly. The mask assembly may include a mask and a pellicle. The present invention has particular, but not exclusive, use in connection with EUV lithography apparatus and EUV lithography tools. Background Art

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

[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 the substrate. A lithographic apparatus using EUV radiation, which is electromagnetic radiation having a wavelength in the range 4 nm to 20 nm, can be used to form smaller features on a substrate than a conventional lithographic apparatus (which may, for example, use electromagnetic radiation having a wavelength of 193 nm).

[0005] A mask used to impart a pattern to a radiation beam in a lithographic apparatus may form part of a mask assembly. The mask assembly may include a pellicle to protect the mask from damage by particle contaminants. The pellicle may be supported by a pellicle frame.

[0006] The use of pellicles in lithography is well known and well established. A typical pellicle in an EUV lithography apparatus is a pellicle that is located away from the mask and outside the focal plane of the lithography apparatus during use. Because the pellicle is outside the focal plane of the lithography apparatus, contaminant particles that land on the pellicle are out of focus in the lithography apparatus. As a result, the image of the contaminant particles is not projected onto the substrate. If the pellicle were not present, then the contaminant particles that landed on the mask would be projected onto the substrate and would introduce defects into the projected pattern.

[0007] It may be desirable to use a pellicle in an EUV lithography apparatus. EUV lithography differs from DUV lithography in that it is typically performed in a vacuum and the mask is typically reflective rather than transmissive. Challenges may arise with the use of a pellicle for EUV lithography that are not present when the pellicle is used for DUV lithography.

[0008] It may be desirable to provide mask assemblies and associated methods that overcome or mitigate the problems associated with the prior art. Summary of the invention

[0009] According to a first aspect of the present invention, a method is provided, comprising the steps of: receiving a mask assembly comprising a mask and a removable EUV transparent pellicle held by a pellicle frame; removing the pellicle frame and the EUV transparent pellicle from the mask; inspecting a mask pattern on the mask using an inspection tool; and subsequently attaching the EUV transparent pellicle held by the pellicle frame to the mask.

[0010] The method is advantageous because it allows inspection of the mask without interference from an EUV transparent pellicle (which may be opaque to the beam used by the mask inspection tool).

[0011] The method may further include: attaching an alternative pellicle frame holding an alternative pellicle to the mask after removing the pellicle frame and the EUV transparent pellicle from the mask, the alternative pellicle being formed of a material that is substantially transparent to an inspection beam of an inspection tool; and after inspecting a mask pattern on the mask using the inspection tool, removing the alternative pellicle held by the alternative pellicle frame from the mask so as to attach the EUV transparent pellicle held by the pellicle frame to the mask.

[0012] Removing the pellicle frame from the mask may include disengaging the attachment mechanism from the attachment feature, and attaching the pellicle frame to the mask may include engaging the attachment mechanism to the attachment feature. The attachment feature may be coupled to the mask, and the attachment mechanism may be coupled to the pellicle frame. After the pellicle frame and EUV transparent pellicle are removed from the mask by disengaging the attachment mechanism from the attachment feature, the attachment feature may be coupled to the mask so that the attachment feature can be used for subsequent attachment of the EUV transparent pellicle held by the pellicle frame after inspecting the mask pattern on the mask. An alternative pellicle may be attached to the mask so that the attachment feature of the EUV transparent pellicle does not touch the alternative pellicle.

[0013] The attachment mechanism may include a locking member configured to engage with an attachment feature including a protrusion.

[0014] The EUV transparent pellicle and pellicle frame that are subsequently attached to the mask may be the same EUV transparent pellicle and pellicle frame that were removed from the mask.

[0015] An alternative pellicle may be substantially transparent to the non-EUV radiation beam used by the mask inspection tool.

[0016] The non-EUV radiation beam used by the mask inspection tool may be a DUV radiation beam.

[0017] An alternative pellicle may be substantially transparent to the particle beam used by the mask inspection tool.

[0018] The particle beam used by the mask inspection tool may be an electron beam.

[0019] The alternative pellicle may be attached to the mask using an attachment mechanism that is used solely for the alternative pellicle and not for attachment of the EUV transparent pellicle.

[0020] The mask can be kept in a clean environment throughout the process.

[0021] The method may further include transferring the mask assembly within the sealed container from the lithographic apparatus to a pellicle removal and attachment tool.

[0022] The method may further include transferring one or more selected from the mask, the pellicle assembly, or the mask assembly within the sealed container from the pellicle removal and attachment tool to the mask inspection tool.

[0023] The mask inspection tool can be integrated with the pellicle removal and attachment tool so that the mask assembly remains in the same environment.

[0024] The method may further include cleaning the mask or pellicle.

[0025] The sealed container may have a depending recessed portion configured to accommodate the skin film.

[0026] The spacing between the recessed portion of the container and the plane of the pellicle of the mask assembly may be between 0.5 mm and 1 mm.

[0027] According to a second aspect of the invention, there is provided a method comprising the steps of: receiving a mask assembly comprising a mask and an EUV transparent pellicle held by a pellicle frame arranged to be removably attached to the mask;

[0028] Removing the pellicle frame and the EUV transparent pellicle from the mask; attaching an alternative pellicle held by an alternative pellicle frame arranged to be removably attached to the mask to the mask, wherein the alternative pellicle is formed of a material different from a material used to form the EUV transparent pellicle, the material forming the alternative pellicle being substantially transparent to an inspection beam of an inspection tool; inspecting a mask pattern on the mask using the inspection beam in the inspection tool; removing the alternative pellicle from the mask; and subsequently attaching the EUV transparent pellicle held by the pellicle frame to the mask.

[0029] The method is advantageous because it allows inspection of the mask without interference from an EUV transparent pellicle (which may be opaque to the beam used by the mask inspection tool).

[0030] The alternative pellicle frame may be attached to the mask at a different location than the EUV transparent pellicle frame.

[0031] According to a third aspect of the present invention, there is provided a mask assembly container, comprising: an opening through which a mask assembly can be placed in the container; and a seal which seals the opening when the mask assembly is in the container, wherein the container has an outwardly drooping bottom plate configured to accommodate a surface film.

[0032] Accommodating sagging of the membrane in this manner is advantageous because it prevents the membrane from contacting the container, which could easily damage the membrane.

[0033] When the mask assembly is held in a sealed container, the base plate may be between 0.5 mm and 1 mm or more from the plane of the pellicle.

[0034] According to a fourth aspect of the present invention, a mask is provided, which is provided with a protrusion configured to receive a pellicle frame attachment mechanism, wherein the bottom surface of the protrusion has a lip defining a recess in the surface of the base, and wherein the protrusion is attached to the mask by glue in the recess.

[0035] Attaching the protrusions in this way is advantageous as it reduces the risk of unwanted outgassing from the glue.

[0036] The volume of the glue may be smaller than the volume of the recess.

[0037] The glue may pull the protrusions toward the mask so that the recesses and the mask form a substantially closed space that retains the glue.

[0038] The protrusion may include an opening in the lip so that the recess and the mask form a space that is partially open for glue outgassing.

[0039] The protrusions may be attached to the substrate material of the mask.

[0040] According to a fifth aspect of the present invention, a diaphragm assembly container is provided, comprising: an opening through which the diaphragm assembly can be placed in the container; and a seal that seals the opening when the diaphragm assembly is located in the container, wherein the container has an outwardly drooping bottom plate configured to accommodate the diaphragm.

[0041] Accommodating sagging of the membrane in this manner is advantageous because it prevents the membrane from contacting the container, which could easily damage the membrane.

[0042] According to a sixth aspect of the present invention, there is provided a mask provided with at least three protrusions configured to receive a pellicle frame attachment mechanism, wherein the protrusions are removably attached to the mask.

[0043] Having the protrusions removably attachable is advantageous because it allows the mask to be cleaned in a straightforward manner without the protrusions present, after which the protrusions can be attached to the mask.

[0044] The protrusions may be attached to the substrate material of the mask.

[0045] According to a seventh aspect of the present invention, a method for manufacturing a pellicle assembly is provided, the method comprising: forming a thin film on a substrate and etching away the substrate material to expose the thin film, and thereby providing a pellicle film supported by the periphery of the substrate; attaching a support frame to a portion of the substrate that interfaces with the thin film; providing a first cover on one side of the substrate and a second cover on the opposite side of the substrate, and clamping the first cover and the second cover together to form a sealed environment containing the pellicle film.

[0046] This approach is advantageous because the substrate provides support for the membrane and keeps the membrane taut, while the cover serves to protect the membrane.

[0047] The first cover may be clamped against the substrate.

[0048] The second cover may be clamped against the substrate.

[0049] The method may further include cutting away portions of the substrate that protrude beyond the first cover and the second cover.

[0050] The substrate may be a silicon wafer.

[0051] The second cover may cover the support frame such that the support frame is located within a sealed environment.

[0052] The first cover may include a depending recess configured to receive the pellicle membrane.

[0053] The method of manufacturing a pellicle assembly may be performed at a pellicle manufacturing location.

[0054] According to the eighth aspect of the present invention, a method is provided, comprising the above method for manufacturing a pellicle assembly, and further comprising forming a mask assembly by the following steps: attaching a pellicle positioning tool to a support frame; removing the second cover from the pellicle assembly; attaching the support frame to the mask; and removing the first cover from the pellicle assembly using the pellicle positioning tool.

[0055] The pellicle locating tool may include an arm received in a blind hole provided in the support frame.

[0056] The method of forming a mask assembly may be performed at a mask shop.

[0057] The method may further include placing the mask assembly within a container and sealing the container.

[0058] According to the ninth aspect of the present invention, a pellicle assembly is provided, comprising a pellicle film extending from a boundary portion of a substrate, a support frame attached to the boundary portion of the substrate, a first cover, and a second cover, wherein the first cover and the second cover are arranged on opposite sides of the boundary portion of the substrate and form a sealed environment containing the pellicle film.

[0059] A sealed environment is beneficial because it prevents contaminants from entering the environment and contaminating the pellicle membrane.

[0060] The second cover may cover the support frame such that the support frame is located within a sealed environment.

[0061] The first and second covers may be clamped against the substrate boundary portion.

[0062] According to a tenth aspect of the present invention, there is provided a method for monitoring a pellicle of a mask assembly, the mask assembly comprising a pellicle assembly and a mask, the method comprising: measuring properties of the pellicle and monitoring changes in the properties associated with an increased risk of rupture of the pellicle, and when such changes are encountered, removing the pellicle assembly from the mask and replacing the pellicle assembly with a new pellicle assembly.

[0063] The properties of the pellicle may be measured while the mask assembly is in situ in a lithographic apparatus.

[0064] The property may be the infrared emission of the pellicle and / or may be the deflection of the pellicle during movement of the scanning mask assembly.

[0065] The method may include transferring the mask assembly to a mask assembly inspection tool and then measuring a property of the pellicle using the mask assembly inspection tool.

[0066] One or more properties of the pellicle may be measured using one or more of the following measurement techniques: EUV reflectometry, EUV transmittance measurement, ellipsometry, Raman spectroscopy, X-ray reflectometry, microscopy, resonance measurement, scanning heat load measurement, pellicle deflection during pumping or exhaust.

[0067] The method may include removing the pellicle assembly from the mask, transferring the pellicle assembly to a pellicle assembly inspection tool, and then measuring a property of the pellicle using the pellicle assembly inspection tool.

[0068] One or more properties of the pellicle may be measured using one or more of the following measurement techniques: EUV transmission measurement (pellicle assembly removed from mask), EUV reflection measurement, birefringence measurement, ellipsometry, Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray reflection measurement, microscopy, resonance measurement, measurement of pellicle displacement due to pressure difference, deflection during pumping or exhaust, scanning heat load measurement, frame deformation measurement.

[0069] Features of different aspects of the invention may be combined with features of other aspects of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0071] Figure 1 is a schematic illustration of a lithographic system including a lithographic apparatus and a radiation source;

[0072] Figure 2 is a schematic illustration of a mask assembly according to an embodiment of the present invention;

[0073] Figure 3 is formed Figure 2 A schematic illustration of a protrusion of a portion of a mask assembly shown in;

[0074] Figure 4 is a process flow diagram depicting a method according to an embodiment of the present invention;

[0075] Figure 5 is a schematic illustration of a mask assembly and a container according to an embodiment of the present invention;

[0076] Figure 6 is a process flow diagram depicting a method according to an embodiment of the present invention;

[0077] Figure 7 is a process flow depicting a method according to an embodiment of the present invention; and

[0078] Figure 8 is a process flow diagram depicting a method according to an embodiment of the present invention;

[0079] 9A to 9D schematically depicts a method of making a pellicle assembly; and

[0080] FIG. 10A to FIG. 10C A method of forming a mask assembly using a pellicle assembly is schematically depicted; and

[0081] Fig.11 is a process flow depicting a method according to an embodiment of the present invention. DETAILED DESCRIPTION

[0082] Figure 1A lithography system including a mask assembly according to an embodiment of the present invention is shown. The lithography system includes a radiation source SO and a lithography apparatus LA. The radiation source SO is configured to generate an extreme ultraviolet (EUV) radiation beam B. The lithography apparatus LA includes an illumination system IL, a support structure MT configured to support a mask assembly 15 including a mask 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 the radiation beam B is incident on the mask MA. The projection system is configured to project the radiation beam B (now patterned by the mask MA) onto the substrate W. The substrate W may include a previously formed pattern. In this case, the lithography apparatus aligns the patterned radiation beam B with the pattern previously formed on the substrate W.

[0083] The radiation source SO, the illumination system IL and the projection system PS may all be constructed and arranged so that they may be isolated from the external environment. A gas (e.g., hydrogen) at a pressure below atmospheric pressure may be provided in the radiation source SO. A vacuum may be provided in the illumination system IL and / or the projection system PS. A small amount of gas (e.g., hydrogen) at a pressure much below atmospheric pressure may be provided in the illumination system IL and / or the projection system PS.

[0084] Figure 1 The radiation source SO shown in is of a type that may be referred to as a laser produced plasma (LPP) source. A laser 1, which may be, for example, a CO2 laser, is arranged to deposit energy via a laser beam 2 into a fuel such as tin (Sn) provided by a fuel emitter 3. Although tin is mentioned in the following description, any suitable fuel may be used. The fuel may, for example, be in liquid form and may, for example, be a metal or an alloy. The fuel emitter 3 may include a nozzle configured to direct tin, for example in the form of droplets, along a trajectory toward a plasma formation region 4. The laser beam 2 is incident on the tin at the plasma formation region 4. The deposition of laser energy into the tin creates a plasma 7 at the plasma formation region 4. During de-excitation and recombination of ions of the plasma, radiation including EUV radiation is emitted from the plasma 7.

[0085] 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). The collector 5 may have a multilayer structure arranged to reflect EUV radiation (e.g., EUV radiation having a desired wavelength such as 13.5 nm). The 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.

[0086] In other embodiments of the laser produced plasma (LPP) source, the collector 5 may be a so-called grazing incidence collector configured to receive EUV radiation at a grazing incidence angle and to focus the EUV radiation at an intermediate focus. The grazing incidence collector may, for example, be a nested collector comprising a plurality of grazing incidence reflectors. The grazing incidence reflectors may be arranged axially symmetrically around the optical axis O.

[0087] 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 be, for example, a rotating foil trap, or may be any other suitable form of contamination trap.

[0088] 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 with the aid of a beam delivery system (not shown) comprising, for example, suitable guiding mirrors and / or a beam expander and / or other optical devices. The laser 1 and the radiation source SO may together be considered a radiation system.

[0089] The radiation reflected by the collector 5 forms a radiation beam B. The radiation beam B is focused at a point 6 to form an image of the plasma formation region 4, which acts as a virtual radiation source for illuminating the system IL. The point 6 at which the radiation beam B is focused may be referred to as an intermediate focus. The radiation source SO is arranged such that the intermediate focus 6 is located at or near an opening 8 in an enclosure structure 9 of the radiation source.

[0090] A radiation beam B is transmitted from a radiation source SO to an illumination system IL configured to condition the radiation beam. The illumination system IL may include a faceted field mirror device 10 and a faceted pupil mirror device 11. The faceted field mirror device 10 and the faceted pupil mirror device 11 together provide the radiation beam B with a desired cross-sectional shape and a desired angular distribution. The radiation beam B is transmitted from the illumination system IL and is incident on a mask assembly 15 held by a support structure MT. The mask assembly 15 includes a mask MA and a pellicle 19 held in place by a pellicle frame 17. The mask MA reflects and patterns the radiation beam B. The illumination system IL may include other mirrors or devices in addition to or in place of the faceted field mirror device 10 and the faceted pupil mirror device 11.

[0091] After reflection from the mask MA, the patterned radiation beam B enters the projection system PS. The projection system comprises a plurality of mirrors configured to project the radiation beam B onto a substrate W supported by a substrate table WT. The projection system PS may apply a reduction factor to the radiation beam, thereby forming an image having features that are smaller than corresponding features on the mask MA. A reduction factor of 4 may be applied, for example. Although the projection system PS is Figure 1There are two mirrors in the embodiment, but the projection system may include any number of mirrors (e.g., six mirrors).

[0092] The lithographic apparatus may, for example, be used in a scanning 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 speed and direction of the substrate table WT relative to the support structure (e.g., mask table) MT may be determined by the reduction ratio and image reversal characteristics of the projection system PS. The patterned radiation beam incident on the substrate W may include a frequency band of radiation. The frequency band of radiation may be referred to as an exposure slit. During scanning exposure, movement of the substrate table WT and the support structure MT may cause the exposure slit to travel across an exposure field of the substrate W.

[0093] Figure 1 The radiation source SO and / or the lithographic apparatus shown in the figure may include components not shown. For example, a spectral filter may be provided in the radiation source SO. The spectral filter may be substantially transmissive for EUV radiation, but substantially blocking radiation of other wavelengths such as infrared radiation.

[0094] In other embodiments of the lithography system, the radiation source SO may take other forms. For example, in alternative embodiments, the radiation source SO may include one or more free electron lasers. The one or more free electron lasers may be configured to emit EUV radiation, which may be provided to one or more lithography devices.

[0095] As briefly described above, mask assembly 15 includes a pellicle 19 disposed adjacent to mask MA. Pellicle 19 is disposed in the path of radiation beam B so that radiation beam B passes through pellicle 19 as it approaches mask MA from illumination system IL and as it is reflected by mask MA toward projection system PS. Pellicle 19 comprises a thin film that is substantially transparent to EUV radiation (although it will absorb a small amount of EUV radiation). Pellicle 19 serves to protect mask MA from being damaged by particle contaminants. Pellicle 19 may be referred to herein as an EUV transparent pellicle.

[0096] Although efforts may be made to maintain a clean environment within the lithographic apparatus LA, particles may still be present within the lithographic apparatus LA. In the absence of the pellicle 19, particles may be deposited onto the mask MA. Particles on the mask MA may adversely affect the pattern imparted to the radiation beam B and the pattern transferred to the substrate W. The pellicle 19 advantageously provides a barrier between the mask MA and the environment in the lithographic apparatus LA so as to prevent particles from being deposited on the mask MA.

[0097] The pellicle 19 is positioned at a distance from the mask MA sufficient that any particles incident on the surface of the pellicle 19 are not in the focal plane of the radiation beam B. This spacing between the pellicle 19 and the mask MA serves to reduce the extent to which any particles on the surface of the pellicle 19 impart a pattern to the radiation beam B. It will be appreciated that where a particle is present in the beam B of radiation, but at a position that is not in the focal plane of the beam B of radiation (i.e., not at the surface of the mask MA), then any image of the particle will not be in focus at the surface of the substrate W. In some embodiments, the spacing between the pellicle 19 and the mask MA may be, for example, between 2 mm and 3 mm (e.g., approximately 2.5 mm).

[0098] Figure 2 The mask assembly 15 is depicted in cross section and in more detail. The mask MA has a patterned surface 24. The pellicle frame 17 supporting the pellicle 19 is provided with an attachment mechanism 22. The attachment mechanism 22 can be configured to allow the pellicle frame to be removably attached to the mask MA (i.e., to allow the pellicle frame to be attached to the mask and detachable from the mask). The attachment mechanism 22 is configured to engage with an attachment feature (not shown) provided on the mask MA. The attachment feature can be, for example, a protrusion extending from the mask MA. The attachment mechanism 22 can, for example, include a locking member that engages with the protrusion and securely fixes the pellicle frame 17 to the mask MA.

[0099] Multiple attachment mechanisms and associated attachment features may be provided. The attachment mechanisms may be distributed around the pellicle frame 17 (eg, two on one side of the frame, and two on the opposite side of the frame). The associated attachment features may be distributed around the perimeter of the mask MA.

[0100] The attachment mechanism 22 can suspend the pellicle frame 17 relative to the mask MA. That is, there can be a spacing between the pellicle frame 17 and the mask MA so that there is a gap between them, through which gas can flow into and out of the space between the pellicle 19 and the mask. The gap can be in the form of a slit extending around the perimeter of the pellicle frame 17, the slit being interrupted by the attachment mechanism that connects the pellicle frame to the mask MA. The spacing between the pellicle frame 17 and the mask MA can be, for example, between 200 microns and 300 microns. Because the spacing is relatively narrow, the flow of gas into and out of the space between the pellicle 19 and the mask MA is restricted.

[0101] In alternative embodiments, the attachment mechanism may bring the pellicle frame 17 into contact with the mask MA.

[0102] As noted above, a plurality of attachment mechanisms and associated attachment features may be provided. Each attachment mechanism may, for example, include a locking member, and each associated attachment feature may include a protrusion (which may be referred to as a post). The locking member and the protrusion may form a kinematic connection between the pellicle frame and the mask. This may allow the pellicle frame to be mounted on the mask without causing significant distortion of the mask.

[0103] The attachment mechanism can be configured to avoid lateral sliding movement between the attachment mechanism and the attachment features when attaching the mask frame to the mask, including during subsequent pellicle attachment after mask inspection has occurred. Avoiding such sliding movement provides the advantage of avoiding contaminant particles that might otherwise be generated.

[0104] exist Figure 3 In the embodiment depicted in FIG, protrusion 27 extends from mask MA and includes a distal head 28. The locking member can be configured to engage protrusion 27 (post) below the distal head 28 and thereby securely fix the pellicle frame to the mask. The attachment mechanism can include a resilient feature configured to bias the locking member against the post. The locking member can be disengaged from the post by applying a force resisting the resilient bias.

[0105] although Figure 3 Protrusions 27 are depicted extending from the face of the mask MA, but in embodiments the protrusions may instead be provided on the sides of the mask.In embodiments, some protrusions may be provided on the sides of the mask and some protrusions may be provided on the face of the mask.

[0106] If you can Figure 3 As can be seen, in an embodiment, the protrusion includes a base 29 fixed to the mask MA. A lip 31 is provided on the bottom surface of the base, the lip defining a recess 33 in the surface of the base. Glue is provided in the recess 33 to firmly fix the base 29 to the mask MA. The volume of glue provided in the recess is smaller than the volume of the recess, and the glue is completely retained in the recess when the base is pressed against the mask MA. The lip 31 is held against the mask MA by the glue because the glue shrinks when drying and thus pulls the base 28 toward the mask MA. As a result, the recess and the mask MA together define a substantially closed space for holding glue. This is advantageous because outgassing of the glue into a clean environment is substantially avoided.

[0107] However, the gluing of the protrusions to the mask MA can be achieved in any other suitable way. In another embodiment, a groove (e.g. a substantially U-shaped groove) can be provided for venting in the base of the protrusion. In such a case, the U-shaped groove (together with the mask MA) defines an island in the base surface of the protrusion. The glue will be sucked into the groove by capillary action and firmly fix the protrusion to the mask MA, while the groove is still partially open for some glue outgassing.

[0108] In yet another embodiment in which the protrusion has a lip 31 defining a recess 33, for venting it is sufficient to have one or more openings in the lip 31 so that the recess 33 is partially open for some glue outgassing.

[0109] In the above embodiments, the grooves in the base of the protrusions or the openings in the protrusion lip 31 are arranged so as to prevent outgassing of the glue from directly entering the space between the pellicle and the mask. Thus, although some outgassing of the glue may occur over time, the outgassing will occur toward the outside of the pellicle frame and will therefore not cause significant contamination of the pellicle or patterned mask areas that may be sensitive to contaminants, thereby preventing haze on the mask.

[0110] The volume of glue used may be, for example, about 50 microns. The glue may be, for example, Glue from Huntsman Advanced Materials. Type, such as Epoxy adhesive or any other EUV suitable soft or hard adhesive.

[0111] In embodiments where the protrusions 27 extend from the face of the mask MA, the protrusions may be located a few millimeters away from the patterned surface of the mask. In such embodiments, material outgassing from the base 29 of the protrusions 27 may impinge on the patterned surface of the mask MA and may cause defects in the projected pattern. In such circumstances, it is particularly advantageous to avoid outgassing of the glue that securely secures the protrusions 27 to the mask MA. Providing the glue in a substantially enclosed space that retains the glue (as described above) provides this advantage.

[0112] The engagement between the protrusion 27 and the mask may be permanent or temporary. The protrusion may be fixed to the mask MA, for example, with an adhesive (e.g., as described above) or by using other means. For example, the protrusion may be fixed to the mask MA using mechanical attachment such as screws or clamps, by electrostatic or magnetic forces induced to attract the protrusion to the mask, by optical engagement (using van der Waals adhesion), or any other suitable means. Preferably, the attachment of the protrusion to the mask is accomplished in a manner that allows the protrusion to be easily and cleanly removed (e.g., so that particles or outgassing molecules and species that may be deposited on the mask MA are substantially not released). In an alternative embodiment, the protrusion may be an integral part of the mask MA (i.e., non-removable).

[0113] A multilayer stack of materials may be provided across the mask MA to provide EUV reflectivity. The multilayer stack may be partially covered with an EUV absorbing layer, which partially covers the mask and provides a pattern to be projected onto the substrate by the lithographic apparatus. The outer boundaries of the mask may be provided with other patterns that are not projected onto the substrate but have other uses. For example, these patterns may include alignment marks and may indicate the identity of the mask.

[0114] In an embodiment (which may be combined with any other embodiment described in this document), the portion of the surface of the mask MA to which the protrusion 27 is attached does not include a multilayer stack of materials or an EUV absorbing layer. Instead, the multilayer stack of materials or the EUV absorbing layer is removed from that portion of the surface of the mask MA (or never existed at that portion of the surface of the mask). As a result, the protrusion is directly attached to the material forming the mask. This may be referred to as attaching the protrusion to the substrate material of the mask (or equivalently, attaching the protrusion to the mask substrate). The mask substrate may, for example, be formed of glass. The mask substrate may, for example, be formed of a low thermal expansion material (LTEM).

[0115] Attaching the protrusions in this manner is advantageous because the strength of the connection between the protrusions 27 and the mask MA is not affected by the material properties of the multilayer stack or the absorber layer. Instead, the connection is determined solely by the material of the mask substrate. A further advantage is that, because the protrusions 27 are not attached to the multilayer stack or the absorber layer, damage to these layers and the resulting generation of contaminant particles when attaching the protrusions is avoided.

[0116] An additional advantage is that it is easier to remove the protrusions 27 and the glue from the mask MA at a later time, if this becomes necessary. In particular, any glue removal process does not risk damaging the multilayer stack or the absorber layer, because there is no multilayer stack or absorber layer where the glue was located. Again, this avoids the subsequent generation of contaminant particles.

[0117] In alternative embodiments, the attachment mechanism may be provided on the mask and the attachment features may be provided on the pellicle frame.

[0118] exist Figure 2 A contaminant particle 26 is schematically shown in FIG. 2. The contaminant particle 26 is incident on and held by the pellicle 19. The pellicle 19 holds the contaminant particle sufficiently away from the patterned surface 24 of the mask MA that the contaminant particle is not imaged onto the substrate by the lithographic apparatus LA.

[0119] The pellicle 19 may be formed, for example, of a material such as a polycrystalline silicon (pSi) film. The polycrystalline silicon (pSi) film is substantially transparent to EUV radiation. The pellicle 19 may alternatively be formed of some other material that is substantially transparent to EUV radiation, such as graphene, silane, and the like. With respect to an EUV transparent pellicle or a film that is substantially transparent to EUV radiation herein is meant that the pellicle 19 transmits at least 65% of the incident EUV radiation, preferably at least 80% of the incident EUV radiation, and more preferably at least 90%. A coating layer may be provided that may help reduce the effects of trace amounts of hydrogen radicals, plasma, and oxygen on the pellicle 19. The coating layer may be provided on both the pellicle and the pellicle frame.

[0120] A mask assembly according to an embodiment of the present invention can provide a mask pattern that remains substantially free of defects during use (the mask pattern is protected from damage by contaminants by the pellicle). As noted above, a space (e.g., in the form of a slit) can be provided between the pellicle frame and the mask that allows some gas to flow into and out of the space between the pellicle and the mask. This allows suction and exhaust of the mask assembly to be performed without damaging the mask assembly.

[0121] Figure 4 is a process flow illustrating processing of a mask assembly to allow inspection of a mask pattern by a mask inspection tool. Although the pellicle 19 is substantially transparent to EUV radiation, it may be substantially opaque to an inspection beam used by the mask inspection tool (or at least not sufficiently transparent to allow the mask inspection tool to properly inspect the mask pattern). The process flow addresses this issue. The mask inspection tool may, for example, use a radiation beam at a non-EUV wavelength (e.g., DUV, VIS, or IR radiation) as the inspection beam. The mask inspection tool may, for example, use a particle beam such as an electron beam (e-beam) as the inspection beam.

[0122] The mask assembly is transferred from the lithographic apparatus to the pellicle removal and attachment tool. A controlled clean environment is provided within the pellicle removal and attachment tool. The pellicle removal and attachment tool includes an attachment mechanism actuator configured to cause the attachment mechanism 22 (see Figure 2 ) is detached from the mask MA. These actuators are used to detach the attachment mechanism 22 and then remove the pellicle frame 17 (with the EUV transparent pellicle 19) from the mask MA.

[0123] The alternative pellicle is then attached to the mask MA. The alternative pellicle is formed of a material different from the EUV transparent pellicle. The alternative pellicle can be formed of a material such as an amorphous fluoropolymer (e.g., Teflon AF or Cytop) and is substantially transparent to the inspection beam (e.g., EUV radiation beam or e-beam) used by the mask inspection tool. The term "substantially transparent to the inspection beam" is intended to mean that the alternative pellicle transmits the inspection beam sufficiently to allow inspection of the mask to be performed. The alternative pellicle can, for example, transmit at least 80% of the inspection beam, more preferably at least 90% of the inspection beam.

[0124] The alternative pellicle may be attached to the same attachment features as are used to attach the EUV transparent pellicle to the mask MA. In another arrangement, the alternative pellicle may be attached to the mask MA using alternative attachment features that are solely used to receive the alternative pellicle and are not used for the EUV transparent pellicle. The alternative attachment features may be set further away from the patterned area of ​​the mask than the attachment features used for the EUV transparent pellicle. The use of alternative attachment features is advantageous because the possibility of the EUV transparent pellicle attachment features being damaged when attaching the alternative pellicle is avoided (the EUV transparent pellicle attachment features are not touched when attaching the alternative pellicle). It is advantageous to set the alternative attachment features further away from the patterned area of ​​the mask because the risk of contaminant particles traveling from the attachment features to the patterned area is reduced. The alternative attachment features may, for example, be set on the side of the mask MA.

[0125] The alternative pellicle may be provided with an attachment mechanism configured to engage with an alternative attachment feature provided on the mask MA. The alternative attachment mechanism may, for example, be provided on a frame supporting the alternative pellicle.

[0126] Since the alternative pellicle is in place during inspection of the mask by the mask inspection tool, the alternative pellicle may be referred to as an inspection compatible pellicle (since it is substantially transparent to the inspection beam). The alternative pellicle may also be referred to as a temporary pellicle.

[0127] The mask assembly, now including the mask and the alternative pellicle, is then transferred to a mask inspection tool. The mask inspection tool inspects contaminants on the mask pattern. If contaminants are found, cleaning of the mask MA can be performed to remove the contaminants. The alternative pellicle can be removed to allow the mask to be cleaned (e.g., using a pellicle removal and attachment tool). Attachment features (e.g., protrusions) can remain in place on the mask MA during the cleaning of the mask. This includes attachment features for receiving an EUV transparent pellicle, and may also include attachment features for receiving an alternative pellicle (if such attachment features exist). After cleaning, the alternative pellicle can be reattached to the mask MA (e.g., using a pellicle removal and attachment tool). The mask assembly is returned to the mask inspection tool, where further inspection is performed to check whether the contaminants have been removed.

[0128] The mask assembly is then transferred from the mask inspection tool to the pellicle removal and attachment tool. The pellicle removal and attachment tool then removes the alternative pellicle from the mask MA.

[0129] The pellicle frame and EUV transparent pellicle are then attached to the mask MA. This can be the same pellicle frame and pellicle that were previously removed from the mask MA, or it can be a new pellicle frame and pellicle. If the same pellicle frame and pellicle are reused, the pellicle can be cleaned before reattaching to the mask MA.

[0130] Next, the mask assembly 15, which now includes the mask MA, the pellicle frame 17 and the EUV transparent pellicle 19, is transferred to a lithographic apparatus. The lithographic apparatus is used to project a pattern from the mask MA onto a substrate.

[0131] The mask inspection tool and the pellicle removal and attachment tool may be integrated with each other to minimize the transfer of the mask assembly.

[0132] The alternative pellicle may be a DUV transparent pellicle, or any suitable pellicle (ie, inspection compatible or temporary pellicle) for use in place of an EUV transparent pellicle. The alternative pellicle may be substantially transparent to a radiation beam or particle beam (eg, e-beam) used by a mask inspection tool.

[0133] In an alternative approach, the pellicle frame 17 and the EUV transparent pellicle 19 can be removed from the mask MA using a pellicle removal and attachment tool and then transferred to the mask inspection tool without attaching the alternative pellicle to the mask. After inspection of the mask MA by the mask inspection tool, the pellicle frame 17 and the EUV transparent pellicle 19 can be reattached to the mask (or a new pellicle frame 17 and EUV transparent pellicle 19 can be attached) by the pellicle removal and attachment tool. Although this approach allows inspection of the mask, it includes the following disadvantages: the mask is not protected by the pellicle during inspection of the mask or during transfer to or from the mask inspection tool. The mask inspection tool may, for example, have a less tightly controlled clean environment than the environment of the pellicle removal and attachment tool or the environment of the lithography equipment. Contaminant particles may, for example, attach to the mask MA after inspection and before the pellicle frame 17 and the EUV transparent pellicle 19 are attached to the mask. Since this occurs after mask inspection, contaminant particles are not detected and may cause defects in the pattern projected on the substrate. Figure 4 The method shown in is avoided because the mask MA is protected by the pellicle during mask inspection and during transfer to or from the mask inspection tool. The mask MA is only unprotected during the exchange between the EUV transparent pellicle and the alternative (e.g., DUV transparent) pellicle as a small part of the process. The environment provided in the pellicle removal and attachment tool can be tightly controlled (e.g., more tightly controlled than other environments), considering that this is the only environment where the mask MA is unprotected.

[0134] In an embodiment, the mask MA may be equipped with an alternative pellicle instead of an EUV transparent pellicle during periods of non-use. The alternative pellicle may, for example, include a DUV transparent pellicle. The DUV transparent pellicle material may be subject to less outgassing than the EUV transparent pellicle material, and therefore less contamination due to outgassing over time may be expected when using storage of mask assemblies with a DUV transparent pellicle.

[0135] Although described above in the context of removing a pellicle frame from a mask and subsequently reattaching the pellicle frame, the pellicle removal and attachment tool may also be used to attach a pellicle frame to a mask that has not previously been provided with a pellicle.

[0136] exist Figure 4During the process depicted in , the mask assembly is always maintained in a clean environment. Like the interior of the mask inspection tool, the interior of the pellicle removal and attachment tool is a controlled clean environment. Transfer of the mask assembly between the pellicle removal and attachment tool and the mask inspection tool can be achieved in one of two ways. The pellicle removal and attachment tool can be connected to the mask inspection tool via a port that connects them directly together. The port is sealed relative to the external environment. The port can connect the controlled clean environments of the two tools together, thereby allowing the mask assembly to travel directly from the pellicle removal and attachment tool to the mask inspection tool without leaving the controlled clean environment.

[0137] In an alternative approach, the mask assembly can be placed in a container that provides a clean environment, and can then be transferred from the pellicle removal and attachment tool to the mask inspection tool within the container. The interior of the container can be connected to the controlled clean environment of the pellicle removal and attachment tool so that the mask assembly can be placed into the container without leaving the controlled clean environment (e.g., using a suitable operator). The container is then sealed so that a clean environment is maintained within the container. The container is then brought to the mask inspection tool. At the mask inspection tool, the clean environment within the container is connected to the controlled clean environment within the mask inspection tool, and the mask assembly is then transferred to the mask inspection tool. The above steps are reversed to transfer the mask assembly back to the pellicle removal and attachment tool.

[0138] The container can also be used to provide a clean environment for the transfer of the pellicle assembly including the pellicle and the pellicle frame. For example, the pellicle assembly can be transferred to the pellicle removal and attachment tool using the container.

[0139] In an embodiment, a container with a replaceable window is provided, which is arranged to be assembled into a mask assembly (or a pellicle assembly) together with a mask in a lithographic apparatus. By providing a replaceable film (replaceable window) for a container to be transferred to a scanner or an inspection tool, the mask will be continuously protected. In such a case, when the mask is exchanged between containers, the main exposure to particles occurs in a controlled environment. The protective replaceable film can be selected to be transparent to EUV during the exposure time, and is exchanged to be transparent for inspection when provided to the inspection equipment. The bottom side of the container near the replaceable film can be closed to protect the fragile film. During the inspection, the mask with the protective film is loaded onto the mask platform, and the replaceable film is selected to be compatible with the light source used during the inspection. Then the mask is changed from container A (with a film suitable for inspection) to container B (with a film suitable for exposure) in a clean environment to minimize particles. During exposure, the mask with the protective film is loaded onto the reticle stage and the exchangeable film is chosen to be compatible with the light source used during exposure.

[0140] exist Figure 5 An example of a container that can be used to transfer a mask assembly (or pellicle assembly) between controlled clean environments is schematically shown in . The container 30 has a shape that generally corresponds to the shape of the mask assembly 15. The container 30 includes a plate 32, which includes a recessed portion 33. The recessed portion 33 is spaced apart from the pellicle 19 to accommodate some sagging of the pellicle. The spacing between the recessed portion 33 and the plane of the pellicle can be, for example, between about 0.5 mm and about 1 mm (e.g., about 0.7 mm or greater). The term "plane of the pellicle" can be interpreted as referring to a plane that corresponds to the edge of the pellicle and in which the pellicle is located if it is not subjected to sagging.

[0141] If the pressure in the space between the diaphragm 19 and the mask MA is greater than the pressure on the side of the space, outward drooping of the diaphragm 19 may occur. This may also occur if the pressure in the controlled clean environment of the container 30 is reduced, because although there may be slits between the diaphragm frame 17 and the mask MA, these slits may be relatively small and may restrict the flow of gas. Outward drooping of the diaphragm 19 may also occur due to gravity.

[0142] Container 30 may generally correspond to known containers configured to transport EUV masks without a pellicle, except that known containers do not include recess 33. The depth of recess 33 may be, for example, about 3 mm. The recess accommodates pellicle frame 17 and pellicle 19 and provides space to accommodate outward droop of the pellicle, as noted above, pellicle frame 17 and pellicle 19 may have a height between about 2 mm and about 2.5 mm.

[0143] The container 30 further includes a cover 34 that can be placed on the mask assembly 15. The cover has the form of an open box (i.e., a box without a cover). The plate 32 acts as a bottom plate, which together with the cover 34 forms the container 30 surrounding the mask assembly 15. A seal 36 is provided between the plate 34 and the cover 34, the seal being used to isolate the interior of the container from the external environment. The seal 36 can have any suitable form (the black disk depicted is merely illustrative).

[0144] Any suitable opening in the form of an opening may be used to allow the mask assembly 15 to be placed within the container 30 .

[0145] The container 30 can be used to transfer the mask assembly 15 (or pellicle assembly) between a location in a vacuum state and a location not in a vacuum state. The vacuum and non-vacuum locations can both be controlled clean environments. For example, the pellicle removal and attachment tool may not be in a vacuum state, and the mask inspection tool may not be in a vacuum state. In this case, the container can bring the mask assembly 15 (or pellicle assembly) from a vacuum environment (e.g., within a lithography apparatus) to a non-vacuum environment, and vice versa.

[0146] The container 30 may include a port (not shown) through which gas may be introduced to bring the interior of the container from a vacuum to atmospheric pressure. As further noted above, although there may be slits between the diaphragm frame 17 and the mask MA, these slits may be relatively small and may limit the flow of gas into the space between the diaphragm 19 and the mask MA. When gas is introduced into the container 30, sagging of the diaphragm 19 toward the mask MA may occur. However, the spacing between the plane of the diaphragm 19 and the mask MA is arranged to be sufficiently large so that the diaphragm does not contact the mask. The flow of gas into the container 30 can be controlled to ensure that the difference between the pressures on both sides of the diaphragm 19 remains below a desired threshold level (which may be sufficiently low to avoid the possibility of the diaphragm touching the mask MA and to avoid breaking the diaphragm).

[0147] Gas may be pumped out of the port as desired to provide a vacuum within the container 30 prior to transferring the mask assembly 15 to the lithographic apparatus. The gas may be pumped out at a rate sufficiently low that the difference in pressure on either side of the diaphragm 19 remains below a desired threshold level (the threshold may be sufficiently low to avoid the possibility of the diaphragm touching the container 30 and to avoid rupturing the diaphragm).

[0148] In embodiments where the pellicle assembly is transported without the mask MA, pressure buildup on one side of the pellicle does not occur. Nevertheless, sagging of the pellicle 19 may still occur, for example due to gravity. The recess 33 of the container 30 may have a depth greater than the extent to which the pellicle would sag. This prevents the pellicle from touching the container and causing potential damage to the pellicle. The depth of the recess 33 may be, for example, about 3 mm.

[0149] Figure 6 1 is a process flow illustrated in high-level steps of a method according to an embodiment of the present invention. Figure 6 As depicted in , some of these steps may be performed at a pellicle manufacturing location, some may be performed at a mask manufacturing location (which may be referred to as a mask shop), and some may be performed at a lithography FAB (where integrated circuits may be fabricated).

[0150] At the pellicle manufacturing site, the pellicle is formed from a suitable material such as polysilicon and bonded (e.g., glued) to a pellicle frame. The pellicle and pellicle frame are then inspected for contaminants. If contaminants are found, the pellicle and pellicle frame are cleaned to remove the contaminants. The pellicle and pellicle frame are then transferred to a container that provides a clean environment for the mask shop. The container can be, for example, combined with the above Figure 5 The container described corresponds to the

[0151] The mask is manufactured in a mask shop. This includes providing a pattern on the mask, which is then projected onto the substrate by a lithography apparatus. The pellicle frame is securely fixed to the mask to form a mask assembly including the pellicle, pellicle frame and mask. The mask assembly is then inspected for contaminants. If contaminants are found, the mask assembly is cleaned to remove the contaminants (e.g., the pellicle is removed, the mask is cleaned and the same or a new pellicle is reattached). The mask assembly is then placed in a container that provides a clean, controlled environment and is transported to the lithography FAB. The container can be, for example, combined with the above Figure 5 The container described corresponds to the

[0152] The mask assembly is transferred from the container to the lithographic apparatus at the lithography FAB. The lithographic apparatus projects the pattern from the mask onto the substrate in a conventional manner. The mask assembly is periodically inspected for pellicle contaminants and / or mask contaminants. Inspection for pellicle contaminants can be performed, for example, within the lithographic apparatus (however, it can also be done in a separate tool outside the lithographic apparatus). Inspection of the mask pattern can be performed, for example, using a mask inspection tool. The mask assembly can be cleaned as needed and then used again to project the pattern onto the substrate.

[0153] Figure 7 The steps of manufacturing a mask assembly that can be performed at a mask shop are shown in more detail. The mask is manufactured in a conventional manner. The mask is a reflective mask for use in an EUV lithography device. After manufacturing, the mask is cleaned to remove contaminants that may have been generated during the manufacture of the mask. The back surface of the mask is then inspected for contaminants (contaminant particles on the back surface of the mask may cause undesirable local distortion of the mask during use). The patterned surface of the mask is then inspected for contaminants (as noted above, such contaminants may introduce defects into the projected pattern). In an embodiment, the order of the inspections may be reversed, i.e., the patterned surface is first inspected and then the back surface is inspected. In an embodiment, one of the inspections may be skipped (e.g., the back surface is not inspected).

[0154] A pellicle mounted on a pellicle frame is received from a pellicle manufacturer. The pellicle is attached to a mask to form a mask assembly. Attaching the pellicle frame to the mask may include engaging an attachment mechanism to an attachment feature (although any other engagement / attachment form is possible). The attachment mechanism may include a locking member configured to engage with a protrusion. In an embodiment, a plurality of protrusions (e.g., posts) may extend from the mask. The pellicle frame may be provided with a locking member that engages with the protrusions and securely secures the pellicle frame to the mask. The protrusions may be provided on the front and / or sides of the mask.

[0155] The pellicle of the mask assembly is inspected for contaminants. Attaching / removing the pellicle frame to / from the mask and inspecting the pellicle for contaminants can be performed by the same tool. Although mentioned here with respect to a mask shop, this can also be the case in a lithography FAB.

[0156] If contamination is found, the pellicle can be removed and cleaned. Inspection of the mask pattern may be required. If such inspection is not required, the mask assembly is placed in a container for transfer to the lithography FAB. The container can be combined with the above Figure 5 The container described corresponds to the

[0157] If inspection of the mask pattern is required, this inspection can be done using Figure 4 The method described above can be performed in a method corresponding to the method described above. That is, the pellicle and pellicle frame (which is EUV transparent) can be removed and replaced with an alternative pellicle. This will allow inspection of the mask pattern using a mask inspection tool (as further described above). The inspection can be performed without removing the protrusions from the mask. After inspection of the mask pattern, the alternative pellicle is replaced with an EUV transparent pellicle. The resulting mask assembly can then be transported in a container to a lithography FAB.

[0158] like Figure 7 As noted in , and as further described above, inspection of the mask pattern can be performed in the absence of a pellicle (i.e., neither an EUV transparent pellicle nor an alternative pellicle). A disadvantage of this approach is that contaminants may be introduced onto the mask pattern when the mask is not present. Inspection can be performed without removing the protrusions from the mask.

[0159] If contaminants are found, the mask is cleaned to remove the contaminants. Cleaning of the mask may be performed in the absence of a pellicle. The protrusions may remain on the mask during cleaning of the mask. The protrusions may be permanently bonded to the mask (ie, the protrusions are a non-removable portion of the mask).

[0160] In some cases it may be desirable to remove the protrusions from the mask as part of the mask cleaning process. If the protrusions have been attached to the mask by glue, the process for removing the protrusions may depend on the form of glue used to attach the protrusions. If the glue is a soft glue (i.e., a soluble glue), the protrusions can be removed from the mask by dissolving the glue. This also removes the glue from the mask. If the glue is a hard glue (i.e., it will not dissolve in a solvent compatible with the mask), the protrusions are removed from the mask mechanically. The hard glue is then removed from the mask mechanically. In alternative embodiments, as mentioned above, other forms of attachment of the protrusions are conceivable, such as magnetic or electrostatic attachment, optical attachment, or mechanical clamping. In the case of using these forms, appropriate techniques are used to remove the protrusions (e.g., removing the voltage used to provide attachment when electrostatic attachment is used).

[0161] Once the protrusions and glue have been removed from the mask, mask cleaning of the mask is performed. A replacement protrusion may then be glued to the mask to receive the pellicle frame and pellicle. Inspection of the mask pattern for contaminants may be performed before and / or after the protrusions have been glued to the mask. The pellicle may be inspected for contaminants before and / or after the pellicle is attached to the mask.

[0162] Figure 8 The processes performed in the lithography FAB are depicted in more detail. A portion of the process performed within the lithography apparatus is identified with dashed lines.

[0163] The lithographic apparatus receives a device held in a container (which may be combined with the above Figure 5 The mask assembly is placed in a container (corresponding to the container described above). The container is placed in a load lock of a lithographic apparatus and evacuated to a vacuum. The mask assembly is then removed from the container. The back surface of the mask is inspected for contaminants using an inspection tool located within the lithographic apparatus. The surface film is inspected for contaminants using an inspection tool located within the lithographic apparatus. If no contaminants are found, the pattern is projected onto a substrate using the mask by the lithographic apparatus.

[0164] Once exposure of the substrate is complete, the mask assembly is returned to the container in the load lock chamber. Gas is introduced into the container and load lock chamber, and the container and mask assembly are removed from the lithographic apparatus.

[0165] If contaminants are found, the mask assembly is removed from the lithographic apparatus. This involves placing the mask assembly back into the container in the load lock cabin, followed by the introduction of gas into the container and load lock cabin. The mask assembly and container are then removed from the load lock cabin. The next steps then depend on the nature of the contaminants found. If contaminants are found only on the pellicle, the pellicle (and pellicle frame) can be replaced with a new pellicle. This can be performed in the pellicle removal and attachment tool as further described above.

[0166] If it is suspected or found that there are contaminants on the mask pattern (or contaminants on the back surface of the mask), then an inspection of the mask using a mask inspection tool can be performed. This can be followed by cleaning of the mask to remove the contaminants. The cleaning of the mask can be performed while the protrusions remain in place on the mask. After the cleaning of the mask, a further inspection of the mask can then be performed using a mask inspection tool. If the mask is found to be free of contaminants, then the pellicle and frame are attached to the mask and then the mask is transferred to the lithography equipment in a container.

[0167] If cleaning does not remove the contaminants, the mask is returned to the mask shop for further cleaning. This further cleaning can be performed with the protrusions remaining in place. Alternatively, the protrusions can be removed before further cleaning.

[0168] The tool that removes and attaches the pellicle from the mask can be separate from the pellicle inspection tool. Alternatively, a single tool can be provided that removes and attaches the pellicle from the mask and also inspects the pellicle.

[0169] FIG9 schematically shows a method for making a surface film assembly according to an embodiment of the present invention. Fig.9A , forming a pellicle on the silicon wafer 50. Polycrystalline silicon is deposited onto the wafer 50 using chemical vapor deposition (CVD). A coating material may be deposited on top of the polycrystalline silicon. A rectangular area of ​​the silicon wafer 50 is then etched away, leaving a thin layer of polycrystalline silicon supported by the perimeter of the silicon wafer. The thin layer of polycrystalline silicon, which may be referred to as a thin film, forms a pellicle 52. The thin layer of polycrystalline silicon may, for example, have a thickness of less than 100 nm, and may, for example, have a thickness of approximately 50 nm. In an embodiment, the pellicle may measure approximately 80 mm×80 mm.

[0170] The presence of the silicon wafer 50 around the perimeter of the pellicle 52 is advantageous because it provides a rigid frame that keeps the pellicle 52 taut. The pellicle 52 is taut when created due to the way it is formed. The crystalline nature of the polysilicon causes some contraction of the polysilicon. This contraction removes wrinkles from the pellicle 52 and gives it tension (which can be considered as a prestress of the pellicle). If the wafer 50 does not provide a rigid frame to support the pellicle 52, but instead provides a frame with flexibility, the tension of the pellicle 52 will cause the frame to bend inward. As a result of this inward bending, the tension of the pellicle 52 will be lost. The remaining steps of the method allow the outer portion of the wafer 50 to be removed without losing the tension of the pellicle 52. If the tension of the pellicle 52 is lost, uncontrolled sagging of the pellicle will occur and wrinkles will be encountered in the pellicle.

[0171] The portion of wafer 50 that extends around the outer edge of the thin film of pellicle 52 may be referred to as a boundary portion 55 of the pellicle (the outer edge of the boundary portion is indicated by a dashed line).

[0172] Fig. 9B The lid is schematically shown clamped to the wafer 50 . Fig. 9B The figure on the left hand side of shows the top side cover 54 and wafer 50 as viewed from above. Fig. 9B The figure on the right hand side of shows the top side cover 54, the wafer 50 and other components viewed in cross section. The top side cover 54 is pressed against a border portion 55 on the side of the pellicle which is furthest from the mask in use.

[0173] Fig. 9B The dotted line on the right hand side of indicates the location of the thin film of pellicle 52. In this embodiment, the thin film of pellicle 52 is on the bottom side of wafer 50. This is because the etching used to remove the rectangular area of ​​the wafer is applied to the top side of the wafer. In such an embodiment, there is a gap between the thin film of pellicle 52 and the top side cover 54. The top side cover 54 can therefore have a flat inner surface. In an alternative embodiment, the thin film of pellicle 52 is on the top side of wafer 50 (etching is applied to the bottom side of the wafer). In such an embodiment, there is no gap between the thin film of pellicle 52 and the top side cover 54, and the top side cover will therefore include a recess to accommodate the droop of the pellicle.

[0174] Frame 58 and bottom cover 56 are disposed on opposite sides of wafer 50. Frame 58 is secured to border portion 55. Frame 58 is sufficiently rigid so that it can resist inward bending and thus can maintain tension on pellicle 52. Glue or any other suitable means may be used to secure frame 58 to border portion 55. Bottom cover 56 is pressed against wafer 50 and covers both the bottom side of pellicle film 52 and frame 58.

[0175] from Fig. 9B It can be seen that the top side cover 54 covers the pellicle film 52 on the top side, and the bottom side cover 56 covers the pellicle film on the bottom side. Thus, between them, the covers 54, 56 form a sealed enclosure containing the pellicle film 52. The top side cover 54 and the bottom side cover 56 are assembled to the wafer 50 under clean conditions in order to minimize the possibility of contaminants being introduced into the environment of the pellicle film 52 when they are attached to the wafer 50. Indeed, the entire process of making the pellicle and then assembling the frame 58 and the covers 54, 56 can be performed under clean conditions.

[0176] like Fig. 9C As schematically depicted in FIG. 5 , a cutting tool (e.g., a milling machine) is used to trim away portions of the wafer 50 that extend beyond the bottom side cover 56. Fig. 9C6, the right hand portion of wafer 50 has been removed. The top portion of wafer 50 will be removed by cutting in the direction indicated by arrow 60. The remaining portion of wafer 50 will then be removed. Because pellicle film 52 is contained within a sealed environment, this cutting away of the wafer does not risk introducing contaminants onto the pellicle film.

[0177] Once the edges of the wafer 50 have been trimmed, the remaining assembly is as follows Fig.9D The membrane assembly 62 is shown. The membrane assembly includes the membrane film 52, the substrate boundary portion 55, the frame 58, the top cover 54 and the bottom cover 56. The membrane assembly 62 holds the membrane film 52 in a sealed environment where contaminants cannot enter. The frame 58 supports the membrane and keeps it taut.

[0178] In the illustrated embodiment, the bottom cover 56 covers the frame 58. This is advantageous in embodiments where holes are provided in the frame. Such holes are intended to allow the passage of gas during use of the pellicle, but at other times contaminants may pass through the holes to the pellicle film 52. The bottom cover 56 prevents this from happening by providing a seal between the bottom cover and the substrate boundary portion 55 that isolates the hole from the external environment.

[0179] The top side cover 54 and the bottom side cover 56 are pressed against the substrate boundary portion 55 by one or more clamps. The one or more clamps may be of conventional construction.

[0180] The steps described and illustrated in conjunction with FIG. 9 provide a membrane assembly 62 that maintains membrane tension and prevents membrane contaminants. The membrane assembly 62 can be manufactured, for example, at a single location. This is advantageous over, for example, manufacturing the membrane at a first manufacturing location and then transporting the membrane to a second location to be assembled on a support frame (where contaminants may be introduced during transport to the second location).

[0181] The pellicle assembly 62 can be transported, for example, from a pellicle manufacturing location to a mask shop where the pellicle is assembled onto a mask for use by a lithographic apparatus. Figure 10 schematically illustrates a process for attaching a pellicle to a mask. The process is performed, for example, in a mask shop (i.e., a factory that creates patterned masks).

[0182] In a first step (not shown), the pellicle assembly 62 is cleaned to remove contaminants from the outside of the pellicle assembly. After cleaning, the pellicle assembly 62 is maintained in a clean environment to avoid contaminants from being incident on the pellicle assembly. Within the clean environment, a pellicle placement tool 64 is attached to the frame 58. The pellicle placement tool 64 includes an arm 66 that is received in a blind hole (i.e., an opening on the outer surface of the frame that does not completely pass through the frame) provided in the frame 58. The pellicle placement tool 64 securely holds the frame 58 and presses the top side cover 54 against the substrate boundary portion 55 (thereby holding the top side cover 54 in place). Once the pellicle placement tool has been attached to the frame 58, the one or more clamps pressing the covers 54, 56 against the boundary portion 55 are removed. The pellicle placement tool 64 may then be attached as shown. Fig. 10A The bottom cover 56 is depicted removed from the frame 58. As depicted, the bottom surface of the pellicle membrane 52 is thereby exposed. The frame 58 is also exposed.

[0183] See also Fig. 10B , use the pellicle placement tool 64 to position the pellicle film 52 and the frame 58 relative to the mask MA, and press the frame 58 onto the mask. The frame 58 can be securely fixed to the mask MA in any suitable manner. This can, for example, include attaching the frame to an attachment feature provided on the mask MA (as further described above). The pellicle placement tool 64 is then removed. This takes the pellicle placement tool away with the top side cover 54.

[0184] exist Fig. 10C The resulting assembly 70, which may be referred to as a mask assembly, is shown in FIG. The mask assembly 70 includes a pellicle frame 58 and a mask MA to which the pellicle 52 is securely fixed. The mask assembly 70 may be stored and / or transported in a suitable container (which may correspond, for example, to the mask assembly container further described above).

[0185] Although FIGS. 9 and 10 describe embodiments of the present invention with respect to a silicon wafer 50 , other suitable substrates may be used.

[0186] Fig.11 A method of monitoring pellicle according to an embodiment of the invention is schematically depicted.The method starts with a mask assembly being used in a lithographic apparatus to expose a substrate.

[0187] The first step of the method is the in situ measurement of a property of the pellicle (or more than one property of the pellicle). Figure 1 In-situ measurements of the properties of the pellicle mean measurements performed while the mask assembly 15 is held by the support structure MT. If a change in the property is encountered that is associated with an increased risk of pellicle rupture, the pellicle assembly is removed from the mask and replaced with a new one.

[0188] In an embodiment, in-situ measurement of the pellicle may be performed using an infrared sensor. During exposure of the substrate, the pellicle is heated by EUV radiation absorbed by the pellicle. As a result, the pellicle will emit infrared radiation, wherein the wavelength of the radiation is correlated to the temperature of the pellicle. If the wavelength of the infrared radiation shifts to a shorter wavelength, then this indicates that the temperature of the pellicle has increased. A significant temperature increase of the pellicle may indicate damage to the pellicle, which increases the risk of the pellicle being broken. Therefore, the mask assembly is removed from the lithographic apparatus and the pellicle assembly is replaced with a new pellicle assembly.

[0189] In an embodiment, a deformation of the pellicle that may occur during a scanning movement of the mask assembly may be measured. The deformation may, for example, be a deflection of the pellicle towards the mask and may, for example, be determined by measuring a wavefront aberration in EUV radiation that has passed through the pellicle using a lateral shearing interferometer. An increase or decrease in the deformation, for example compared to the deformation observed when the mask assembly was first subjected to the scanning movement, indicates a change in the stress of the pellicle. If an increase or decrease in the stress of the pellicle corresponds to an increased risk of rupture of the pellicle, the mask assembly is removed from the lithographic apparatus and the pellicle assembly is replaced with a new pellicle assembly.

[0190] The next step of the method is to determine whether a predetermined period of time has elapsed since the last offline inspection. The term "offline" may be interpreted to mean an inspection performed when the pellicle assembly is not in situ in the lithographic apparatus (i.e., when the mask assembly is not held by a support structure). The predetermined period of time may be based on a statistical likelihood of the pellicle becoming damaged over time.

[0191] When the predetermined period of time has elapsed, the mask assembly is transferred to a mask assembly inspection tool. This may include removing the mask assembly from the lithographic apparatus. The mask assembly may be placed in a container (e.g., with Figure 5 30 depicted in the figure), for transfer from the lithography equipment to the mask assembly inspection tool.

[0192] The mask assembly inspection tool inspects the mask assembly to monitor for damage to the pellicle. The mask assembly inspection tool measures a property (or more than one property) of the pellicle. If a change in a property that is associated with an increased risk of pellicle rupture is encountered during operation of the lithographic apparatus (e.g., the pellicle is found to be damaged), the pellicle assembly is removed from the mask assembly and replaced with a new pellicle assembly.

[0193] If the pellicle is not found to be damaged by the mask assembly inspection tool, the pellicle assembly (i.e., the pellicle and pellicle frame) can be removed from the mask using the pellicle frame removal tool (e.g., as further described above). After this removal, the pellicle assembly is handled separately from the mask. The pellicle assembly is transferred to the pellicle inspection tool. The pellicle assembly can be located in a sealed container during this transfer. The mask is transferred to the mask inspection tool. The mask can be maintained in a sealed container during this transfer. Inspection of the pellicle assembly by the pellicle inspection tool can be performed in parallel with inspection of the mask by the mask inspection tool.

[0194] The pellicle inspection tool measures a property (or more than one property) of the pellicle. If a change in the property is encountered during operation of the lithographic apparatus that is associated with an increased risk of pellicle rupture (e.g., the pellicle is found to be damaged), the pellicle assembly is removed from the mask assembly and replaced with a new pellicle assembly. For example, if the pellicle is found to be damaged, the pellicle assembly may be replaced with a new pellicle assembly.

[0195] If the mask is found to be contaminated, the mask is cleaned to remove the contaminants. If the cleaning of the mask does not remove the contaminants, the mask is replaced with a new mask.

[0196] Once the pellicle has been confirmed to be undamaged (or replaced with a new pellicle), the mask and pellicle assembly is transferred to an installation / removal tool (e.g., using a sealed container), where the pellicle assembly is installed on the mask. The pellicle assembly is then transferred back to the lithography apparatus (e.g., in a sealed container). Exposure of the substrate using the mask assembly can then be performed by the lithography apparatus.

[0197] Embodiments of the present invention monitor the pellicle for damage that may cause an increased risk of pellicle rupture (which may be referred to as a pellicle failure) during subsequent operation of the lithographic apparatus. When such damage is discovered, the pellicle assembly is removed and replaced with a different pellicle assembly. This is advantageous because it minimizes the risk of the pellicle failing during operation of the lithographic apparatus. A pellicle failure during operation of the lithographic apparatus is undesirable because it may cause contamination of the mask and / or the lithographic apparatus.

[0198] In the embodiment ( Fig.11 In the case of a lithographic apparatus LA, inspection of the mask assembly (e.g., inspection of the pellicle in situ on the mask) may be performed more frequently than separate inspection of the pellicle assembly. In this case, if inspection of the mask assembly does not reveal pellicle damage associated with an increased risk of pellicle rupture, the mask assembly may be returned to the lithographic apparatus LA without separation of the mask and pellicle assembly and additional inspection thereof.

[0199] The mask assembly inspection tool may measure one or more properties of the pellicle using one or more of the following measurement techniques: EUV reflectometry, EUV transmittance measurement, ellipsometry, Raman spectroscopy, X-ray reflectometry, microscopy, resonance measurement, scanning heat load measurement, pellicle deflection during pump down or exhaust. Each of these is described below:

[0200] EUV reflectometry—EUV radiation is directed onto the pellicle and a sensor monitors local changes in the reflection of the pellicle. Local changes in the EUV reflection indicate degradation (or other changes) of the cladding material on the pellicle. This degradation or change in the cladding material indicates a risk of rupture of the pellicle. If such degradation or other changes are found, the pellicle assembly is removed from the mask and replaced. EUV reflectometry can also monitor global changes in the reflection of the pellicle. Again, changes in the EUV reflection (compared to a reference value of the reflection, which can be a previously measured value) indicate degradation or other changes of the cladding material on the pellicle. Again, if such changes are encountered, the pellicle assembly is removed from the mask and replaced.

[0201] EUV transmission measurement (pellicle in situ on mask)—EUV radiation is directed onto the pellicle. EUV radiation that passes through the pellicle is reflected by the mask and returns through the pellicle. The reflected EUV radiation is monitored. Monitoring can be accomplished by measuring the EUV radiation before using the mask assembly and plotting it and then comparing the subsequently measured plot to the initial plot. Differences between the plots indicate either a change in the pellicle or a change in the mask. The nature of the difference can be used to distinguish changes in the pellicle from changes in the mask. If significant changes in the pellicle are encountered, then the pellicle assembly can be replaced. If significant changes in the mask are encountered, then the mask can be cleaned.

[0202] Ellipsometry - This technique measures changes in the reflectance of a pellicle over a range of wavelengths. If the measured spectrum of the reflected radiation changes (e.g., compared to a previously performed reference measurement), then this indicates changes in the material properties of the pellicle (e.g., oxidation). These changes may indicate an increased risk of pellicle rupture. Additionally, changes in material properties may affect the optical performance of the pellicle during lithographic exposure. Therefore, when changes in material properties of a pellicle are determined by ellipsometery, the pellicle assembly is replaced.

[0203] Raman Spectroscopy—This technique measures local changes in stress in the pellicle. Raman spectroscopy is a spectroscopic technique based on inelastic scattering of monochromatic light. The monochromatic light may be provided by a laser source. When photons undergo inelastic scattering from the pellicle, the frequency of these photons changes. The change in the frequency of the photons depends on the stress in the pellicle. Therefore, changes in stress in the pellicle may be observed using Raman spectroscopy. Changes in stress in the pellicle may indicate an increased risk of pellicle rupture. Changes in stress in the pellicle may be global changes or may be local changes. Local changes in stress may be referred to as stress concentrations. If changes in stress in the pellicle are encountered that indicate an increased risk of pellicle rupture, replace the pellicle assembly.

[0204] X-ray reflectometry - This technique directs a beam of x-rays onto the pellicle at a grazing incidence angle and measures the intensity of the specular reflection of the x-rays from the pellicle. The intensity of the reflected x-rays is analyzed to determine one or more of the density, thickness, or roughness of the pellicle. The roughness can be the surface roughness of the pellicle or the roughness of the interface between the material layers of the pellicle. A significant deviation of any of the density, thickness, or roughness from the value expected from an undamaged pellicle can indicate an increased risk of pellicle rupture. In this case, the pellicle assembly is removed and replaced with a new one.

[0205] Microscope inspection - A microscope can be used to inspect the pellicle for local defects. Inspection can be manual or automated, for example using image analysis software to monitor for defects in the pellicle. Inspection can determine the number and / or size and / or shape of particles and / or holes in the pellicle. If particles are found or holes are found (holes create an increased risk of pellicle rupture), then the pellicle assembly is removed and replaced with a new one. For example, if holes are found in the pellicle, this may create an unacceptable risk of pellicle rupture when the mask assembly is pumped to a vacuum or vented (significant pressure differentials on both sides of the pellicle may occur during pumping or venting). Replacing the pellicle assembly prevents such rupture from occurring.

[0206] Resonance Measurement—A vibration is applied to the diaphragm assembly and the frequency of the vibration is adjusted until a resonant frequency is found. This can be done prior to using the mask assembly when the diaphragm is known to be undamaged. During a subsequent inspection of the diaphragm assembly, the vibration is again applied to the diaphragm assembly. A deviation in the resonant frequency from a previously observed resonant frequency indicates a global change in stress in the diaphragm and / or a change in stress in some other portion of the mask assembly. If a change in the resonant frequency is observed that indicates damage associated with an increased risk of diaphragm failure, the diaphragm assembly is replaced.

[0207] Scanning Heat Load Measurement - In this technique, a heat source, such as a laser beam, is scanned across the diaphragm. At the same time, the temperature of the diaphragm is measured, for example using a pyrometer. The pyrometer can be used to identify localized hot areas on the diaphragm (i.e., areas that are hotter than the rest of the diaphragm). If localized hot areas, which may be referred to as hot spots, are encountered, then this may indicate an increased risk of diaphragm failure. In this case, the diaphragm assembly is removed and replaced. The heat transferred to the diaphragm will cause a wrinkle pattern to be generated on the diaphragm. The period (or other characteristics) of the wrinkle pattern are associated with the stress of the diaphragm. Therefore, the wrinkle pattern can be analyzed to determine if the stress of the diaphragm is such that there is an increased risk of diaphragm failure. If there is an increased risk of failure, then the diaphragm assembly is removed and replaced.

[0208] Deflection of the membrane during pumping or exhausting - The mask assembly can be transferred to a chamber that can be pumped to a vacuum or can be exhausted to atmospheric pressure. The chamber can be initially at atmospheric pressure when it receives the mask assembly. The chamber is then pumped to a vacuum in a controlled manner. As described above in conjunction with Figure 2 As further described, there is a gap between the diaphragm frame and the mask, but the gap is relatively narrow and restricts the flow of gas. As a result, when the chamber is evacuated to a vacuum, the pressure between the diaphragm and the mask will be higher than the pressure in the chamber. This pressure difference will cause an outward deflection of the diaphragm, which is measured using a suitable sensor (e.g., a camera). The chamber can then be vented to atmospheric pressure in a controlled manner. This will cause an inward deflection of the diaphragm, which again can be measured using a suitable sensor (e.g., a camera). The degree of deflection of the diaphragm depends on the stress of the diaphragm. A deflection that falls outside a predetermined threshold can indicate an increased risk of diaphragm failure.

[0209] Inspection of the pellicle when the pellicle assembly has been removed from the mask may include one or more of the following methods: EUV transmission measurement, EUV reflection measurement, birefringence measurement, ellipsometry, Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray reflection measurement, microscopy, resonance measurement, pellicle displacement measurement due to pressure difference, pellicle deflection during suction or exhaust, scanning heat load measurement, frame deformation measurement. Most of these methods are as described above. Those not described above or that may take a different form when the mask assembly has been removed from the mask are described as follows:

[0210] EUV Transmission Measurement (pellicle assembly removed from mask)—A beam of EUV radiation is directed onto the pellicle, and the amount of EUV radiation transmitted by the pellicle is measured using a sensor located on the opposite side of the pellicle. This allows local changes in the transmission of the pellicle to be measured. For example, the test criteria for the pellicle may be a transmission of 85% plus or minus 2%. If the transmission of the pellicle is above this (e.g., 87% or higher), then this may indicate that a loss of material from the pellicle (e.g., cladding material) has occurred. In this condition, an increased risk of pellicle failure may occur, and thus the pellicle assembly may be replaced with a new one. If the transmission of the pellicle is below the test criteria (e.g., 83% or lower), then this may indicate that oxidation of the pellicle (e.g., oxidation of the cladding) has occurred. An increased risk of pellicle failure may occur from oxidation, and thus the pellicle assembly may be replaced with a new one.

[0211] Birefringence Measurements—Birefringence measurements (which may also be referred to as photoelastic measurements) can be used to measure local changes in stress of a pellicle membrane. Birefringence can be measured, for example, by directing a radiation beam through the pellicle and measuring changes in the polarization of the radiation beam. Measurements of birefringence of a pellicle can be used to discover changes in stress and / or local stress concentrations in the pellicle. When stress changes or local stress concentrations are encountered that indicate an increased risk of pellicle failure, the pellicle assembly can be replaced with a new pellicle assembly.

[0212] Fourier Transform Infrared Spectroscopy - Infrared radiation (e.g., over a range of wavelengths) is directed toward the pellicle and the absorption of the infrared radiation is measured. This can be used to monitor local changes in the infrared absorption of the pellicle film. The technique can be used to monitor local changes in the emissivity of the pellicle. For example, the minimum emissivity value of the pellicle can be set to 0.3. If the emissivity (e.g., the local emissivity) is below 0.3, then this can indicate damage to the pellicle. The lower emissivity may cause the local temperature of the pellicle to increase during use in the lithographic equipment, which in turn creates an increased risk of rupture of the pellicle. The pellicle assembly is therefore replaced with a new pellicle assembly.

[0213] Measurement of diaphragm displacement due to pressure differential - This involves applying a pressure on one side of the diaphragm that is different from the pressure on the other side of the diaphragm. The diaphragm will deflect toward the lower pressure side. The extent of the deflection depends on the stress of the diaphragm, and a deflection that falls outside a predetermined threshold can indicate an increased risk of diaphragm failure. In one example, a maximum threshold deflection of 500 μm can be set for a pressure differential of 2 Pascals. If the deflection is greater than 500 μm, then this indicates a significant risk of diaphragm rupture (e.g., during suction or exhaust), and therefore the diaphragm assembly is replaced with a new one. In another example, if the deflection is less than 400 μm, then this can indicate that the stress in the diaphragm is significantly higher than the stress in the membrane when it was originally manufactured (i.e., when attached to the diaphragm frame, but before use in the lithographic apparatus). A significant increase in stress in the diaphragm can mean an increased risk of diaphragm rupture during use by the lithographic apparatus. Therefore, the diaphragm assembly is replaced with a new one.

[0214] Frame deformation measurement - This involves applying a force to the diaphragm frame to cause deformation of the diaphragm frame, and then monitoring the wrinkles in the diaphragm that appear during the deformation of the diaphragm frame. The location of the wrinkles in the diaphragm is indicative of the stress in the diaphragm. An initial measurement of the location of the wrinkles can be performed before the diaphragm is used in order to provide a reference measurement. After use, a change in the location of the wrinkles compared to that encountered in the reference measurement indicates a change in the stress of the diaphragm. If a significant change in the stress of the diaphragm is encountered that is associated with an increased risk of diaphragm rupture, then the diaphragm assembly is replaced with a new diaphragm assembly.

[0215] As mentioned further above, inspection of the pellicle after removal from the mask may be performed in parallel with inspection and / or cleaning of the mask.

[0216] Monitoring the pellicle, for example using one or more of the above techniques, allows for early identification of pellicle damage and therefore allows replacement of the pellicle assembly before failure of the pellicle occurs. If failure of the pellicle occurs in the lithographic apparatus, for example during exposure of a substrate, this may cause problematic contamination of the lithographic apparatus. This problem is avoided by monitoring the pellicle for damage that is associated with an increased risk of pellicle failure and replacing the pellicle as needed when such damage is discovered.

[0217] Inspection of the pellicle for contaminants may be performed simultaneously with inspection of the pellicle for damage.

[0218] Embodiments of the invention relating to monitoring damage to a pellicle may be combined with other embodiments of the invention described elsewhere in this document.

[0219] Various inventive aspects of the mask assembly have been described above and shown in the accompanying drawings in the context of specific embodiments of the invention. Various aspects of various methods have been described above. It should be appreciated that any of the described and / or illustrated aspects may be combined in a single embodiment. For example, one or more features of one embodiment may be combined with one or more features of another embodiment. It should be further appreciated that, although some embodiments including more than one inventive aspect have been described, embodiments including only a single inventive aspect are also contemplated herein. In general, any of the features of any of the embodiments described may be used in isolation or in any combination with any of the other features of the embodiments described.

[0220] Although specific reference may be made in this text to embodiments of the invention in the context of lithographic equipment, embodiments of the invention may be used in other equipment. Embodiments of the invention may form part of mask inspection equipment, metrology equipment, or any equipment that measures or processes objects such as wafers (or other substrates) or masks (or other masks). These equipment may be generally referred to as lithographic tools. Such lithographic tools may use vacuum conditions or ambient (non-vacuum) conditions.

[0221] The term "EUV radiation" may be taken to encompass electromagnetic radiation having a wavelength in the range of 4 nm to 20 nm, for example in the range of 13 nm to 14 nm. EUV radiation may have a wavelength less than 10 nm, for example in the range of 4 nm to 10 nm, such as 6.7 nm or 6.8 nm.

[0222] Although specific reference may be made in this text to the use of lithographic apparatus in the manufacture of ICs, it should be understood that the lithographic apparatus described herein may have other applications. Possible other applications include the manufacture of integrated optical systems, guidance and detection diagrams for magnetic domain memories, flat panel displays, liquid crystal displays (LCDs), thin film magnetic heads.

[0223] Although specific embodiments of the present invention are described above, it should be appreciated that the present invention may be practiced in other ways than those described above. The above description is intended to be illustrative, not restrictive. It is therefore apparent to those skilled in the art that various modifications may be made to the present invention as described above without departing from the scope of the claims and clauses set forth below.

[0224] 1. A method comprising the following steps:

[0225] receiving a mask assembly comprising a mask and a removable EUV transparent pellicle held by a pellicle frame;

[0226] removing the pellicle frame and the EUV transparent pellicle from the mask;

[0227] inspecting a mask pattern on the mask using an inspection tool; and

[0228] An EUV transparent pellicle held by a pellicle frame is then attached to the mask.

[0229] 2. The method according to clause 1, further comprising:

[0230] attaching an alternative pellicle frame holding an alternative pellicle to the mask after removing the pellicle frame and the EUV transparent pellicle from the mask, the alternative pellicle formed of a material that is substantially transparent to an inspection beam of the inspection tool; and

[0231] After inspecting the mask pattern on the mask using an inspection tool, the candidate pellicle held by the candidate pellicle frame is removed from the mask so that the EUV transparent pellicle held by the pellicle frame is attached to the mask.

[0232] 3. The method of clause 1 or 2, wherein removing the pellicle frame from the mask comprises disengaging an attachment mechanism from an attachment feature, and attaching the pellicle frame to the mask comprises engaging the attachment mechanism to an attachment feature.

[0233] 4. The method of clause 3, wherein the attachment feature is coupled to the mask, and wherein the attachment mechanism is coupled to the pellicle frame.

[0234] 5. A method according to clause 3 or 4, wherein after the pellicle frame and the EUV transparent pellicle are removed from the mask by disengaging the attachment mechanism from the attachment feature, the attachment feature is also connected to the mask so that after inspecting the mask pattern on the mask, the attachment feature can be used for subsequent attachment of the EUV transparent pellicle held by the pellicle frame.

[0235] 6. A method according to any of clauses 3 to 5, wherein the attachment mechanism comprises a locking member configured to engage with an attachment feature comprising a protrusion.

[0236] 7. The method according to any of the preceding clauses, wherein the EUV transparent pellicle and the pellicle frame subsequently attached to the mask are the same EUV transparent pellicle and pellicle frame removed from the mask.

[0237] 8. The method of any of the preceding clauses, wherein the candidate pellicle is substantially transparent to a non-EUV radiation beam used by the mask inspection tool.

[0238] 9. The method of clause 8, wherein the non-EUV radiation beam used by the mask inspection tool is a DUV radiation beam.

[0239] 10. The method of any of clauses 2 to 7, wherein the candidate pellicle is substantially transparent to a particle beam used by the mask inspection tool.

[0240] 11. The method of clause 10, wherein the particle beam used by the mask inspection tool is an electron beam.

[0241] 12. The method of any one of clauses 2 to 11, wherein the alternative pellicle is attached to the mask using an attachment mechanism that is used solely for the alternative pellicle and not used for attachment of the EUV transparent pellicle.

[0242] 13. The method of clause 12, wherein the alternative pellicle is attached to the mask such that the attachment features of the EUV transparent pellicle do not touch the alternative pellicle.

[0243] 14. A method according to any one of the preceding clauses, wherein the mask is in a clean environment throughout the method.

[0244] 15. The method of any of the preceding clauses, wherein the method further comprises transferring the mask assembly within the sealed container from a lithographic apparatus to a pellicle removal and attachment tool.

[0245] 16. A method according to any of the preceding clauses, wherein the method further comprises: transferring one or more selected from the mask, the pellicle assembly or the mask assembly in a sealed container from a pellicle removal and attachment tool to a mask inspection tool.

[0246] 17. The method of any of clauses 1 to 14, wherein the mask inspection tool is integrated with the pellicle removal and attachment tool such that the mask assembly remains in the same environment.

[0247] 18. The method of any of the preceding clauses, wherein the method further comprises cleaning the mask or the pellicle.

[0248] 19. The method of clause 18, wherein the attachment feature remains coupled to the mask during cleaning.

[0249] 20. The method of clause 18, wherein the attachment features are removed from the mask prior to cleaning.

[0250] 21. The method of clause 15 or clause 16, wherein the sealed container has a depending recessed portion configured to accommodate the skin film.

[0251] 22. The method of clause 21, wherein the spacing between the recessed portion of the container and the plane of the pellicle of the mask assembly is between 0.5 mm and 2 mm.

[0252] 23. The method of clause 22, wherein the spacing between the recessed portion of the container and the plane of the pellicle of the mask assembly is between 0.5 mm and 1 mm.

[0253] 24. A method comprising the steps of:

[0254] receiving a mask assembly comprising a mask and an EUV transparent pellicle held by a pellicle frame arranged to be removably attached to the mask;

[0255] removing the pellicle frame and the EUV transparent pellicle from the mask;

[0256] attaching to the mask an alternative pellicle held by an alternative pellicle frame arranged to be removably attached to the mask, wherein the alternative pellicle is formed of a material different from a material used to form the EUV transparent pellicle, the material forming the alternative pellicle being substantially transparent to an inspection beam of an inspection tool;

[0257] inspecting a mask pattern on the mask using the inspection beam in the inspection tool;

[0258] removing the alternative pellicle from the mask; and

[0259] An EUV transparent pellicle held by a pellicle frame is then attached to the mask.

[0260] 25. The method of clause 24, wherein the alternative pellicle frame is attached to the mask at a different location than the EUV transparent pellicle frame.

[0261] 26. A mask assembly container, comprising: an opening through which a mask assembly can be placed in the container; and a seal that seals the opening when the mask assembly is located in the container, wherein the container has an outwardly drooping bottom plate configured to accommodate the surface film.

[0262] 27. The mask assembly container according to clause 26, wherein when the mask assembly is held in the sealed container, the distance between the bottom plate and the pellicle plane is between 0.5 mm and 1 mm or more.

[0263] 28. A mask provided with a protrusion configured to receive a pellicle frame attachment mechanism, wherein a bottom surface of the protrusion has a lip defining a recess in a surface of a base, and wherein the protrusion is attached to the mask by glue in the recess.

[0264] 29. The mask of clause 28, wherein the volume of the glue is smaller than the volume of the recess.

[0265] 30. The mask according to clause 28 or clause 29, wherein the glue pulls the protrusion towards the mask so that the recess and the mask form a substantially closed space that retains the glue.

[0266] 31. A mask according to clause 28 or 29, wherein the protrusion comprises an opening in the lip, such that the recess and the mask form a space that is partially open for glue outgassing.

[0267] 32. A mask according to any of clauses 28 to 31, wherein the protrusions are attached to a substrate material of the mask.

[0268] 33. A diaphragm assembly container, comprising: an opening through which the diaphragm assembly can be placed in the container; and a seal that seals the opening when the diaphragm assembly is located in the container, wherein the container has an outwardly drooping bottom plate configured to accommodate the diaphragm.

[0269] 34. A mask provided with at least three protrusions configured to receive a pellicle frame attachment mechanism, wherein the protrusions are removably attached to the mask.

[0270] 35. The mask of clause 33, wherein the protrusions are attached to a substrate material of the mask.

[0271] 36. A method for manufacturing a pellicle assembly, the method comprising:

[0272] forming a thin film on a substrate and etching away substrate material to expose the thin film and thereby provide a pellicle thin film supported by the perimeter of the substrate;

[0273] attaching a support frame to a portion of the substrate that interfaces with the film;

[0274] A first cover is provided on one side of the substrate and a second cover is provided on an opposite side of the substrate, and the first cover and the second cover are clamped together to form a sealed environment containing the pellicle membrane.

[0275] 37. The method of clause 36, wherein the first cover is clamped against the substrate.

[0276] 38. The method of clause 36 or clause 37, wherein the second cover is clamped against the substrate.

[0277] 39. The method of any of clauses 36 to 38, wherein the method further comprises cutting away portions of the substrate that protrude beyond the first cover and the second cover.

[0278] 40. A method according to any one of clauses 36 to 39, wherein the substrate is a silicon wafer.

[0279] 41. The method of any of clauses 36 to 40, wherein the second cover covers the support frame such that the support frame is located within the sealed environment.

[0280] 42. The method of any one of clauses 36 to 41, wherein the first cover comprises a depending recess configured to accommodate the pellicle membrane.

[0281] 43. A method according to any one of clauses 36 to 42, wherein the method is performed at a pellicle manufacturing location.

[0282] 44. A method comprising the method according to any one of clauses 36 to 43, and further comprising forming a mask assembly by the steps of:

[0283] attaching a pellicle positioning tool to the support frame;

[0284] removing the second cover from the diaphragm assembly;

[0285] attaching the support frame to a mask; and

[0286] The first cover is removed from the diaphragm assembly using the diaphragm positioning tool.

[0287] 45. The method of clause 44, wherein the pellicle locating tool comprises an arm received in a blind hole provided in the support frame.

[0288] 46. ​​The method of clause 44 or clause 45, wherein the method is performed at a mask shop.

[0289] 47. The method of any of clauses 44 to 46, further comprising placing the mask assembly within a container and sealing the container.

[0290] 48. A pellicle assembly, comprising a pellicle film extending from a substrate boundary portion, a support frame attached to the substrate boundary portion, a first cover, and a second cover, wherein the first cover and the second cover are arranged on opposite sides of the substrate boundary portion and form a sealed environment containing the pellicle film.

[0291] 49. The pellicle assembly of clause 48, wherein the second cover covers the support frame such that the support frame is located within the sealed environment.

[0292] 50. The pellicle assembly of clause 48 or clause 49, wherein the first cover and the second cover are clamped against the substrate boundary portion.

[0293] 51. A mask having a protrusion configured to receive a film frame attachment mechanism, wherein the base surface of the protrusion has a groove so that glue is drawn into the volume surrounded by the groove and the mask by capillary action so that the protrusion is attached to the mask by the glue and the groove is partially open for glue degassing.

[0294] 52. A method for monitoring a pellicle of a mask assembly, the mask assembly comprising a pellicle assembly and a mask, the method comprising:

[0295] measuring a property of the pellicle and monitoring changes in the property associated with an increased risk of pellicle rupture, and

[0296] When such a change is encountered, the pellicle assembly is removed from the mask and replaced with a new pellicle assembly.

[0297] 53. The method of clause 52, wherein the property of the pellicle is measured while the mask assembly is in situ in a lithographic apparatus.

[0298] 54. A method according to clause 53, wherein the property is infrared emission of the pellicle and / or deflection of the pellicle during scanning movement of the mask assembly.

[0299] 55. The method of any one of clauses 52 to 54, wherein the method comprises transferring the mask assembly to a mask assembly inspection tool and subsequently measuring the property of the pellicle using the mask assembly inspection tool.

[0300] 56. A method according to clause 55, wherein one or more properties of the surface film are measured using one or more of the following measurement techniques: EUV reflectometry, EUV transmittance measurement, ellipsometry, Raman spectroscopy, X-ray reflectometry, microscopy, resonance measurement, scanning heat load measurement, surface film deflection during pumping or exhaust.

[0301] 57. A method according to any one of clauses 52 to 56, wherein the method comprises: removing the pellicle assembly from the mask, transferring the pellicle assembly to a pellicle assembly inspection tool, and then measuring the property of the pellicle using the pellicle assembly inspection tool.

[0302] 58. A method according to claim 57, wherein one or more properties of the pellicle are measured using one or more of the following measurement techniques: EUV transmission measurement (pellicle component removed from the mask), EUV reflection measurement, birefringence measurement, ellipsometry, Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray reflection measurement, microscopy, resonance measurement, measurement of pellicle displacement due to pressure difference, deflection during suction or exhaust, scanning heat load measurement, frame deformation measurement.

Claims

1. A pellicle inspection tool for EUV transparent pellicle, the pellicle inspection tool comprising: Support structure for supporting: (a) a pellicle, the pellicle comprising the EUV transparent pellicle film supported by a substrate perimeter, the substrate perimeter intersecting the film; or (b) a pellicle assembly comprising the EUV transparent pellicle film and a pellicle frame attached to the perimeter of the substrate interfacing with the pellicle; or (c) a mask assembly comprising the EUV transparent pellicle film, a pellicle frame attached to the perimeter of the substrate interfacing with the pellicle, and a mask attached to the pellicle frame; as well as Measuring device for measuring the displacement of the diaphragm due to pressure difference and the deflection of the diaphragm during suction or exhaust. 2 . The pellicle inspection tool of claim 1 , wherein the EUV transparent pellicle has a thickness of less than 100 nm and is configured to transmit at least 65% of incident EUV radiation.

3. The diaphragm inspection tool of claim 1, further comprising means for applying pressure on one side of the diaphragm, the pressure being different from the pressure on the other side of the diaphragm such that a maximum threshold deflection for a pressure differential of 2 Pascals is 500 μm.

4. The pellicle inspection tool of claim 1, wherein the measuring device is used to monitor changes associated with an increased risk of pellicle rupture.

5. The diaphragm inspection tool of claim 1, wherein the measuring device is a sensor arranged to measure the degree of deflection of the diaphragm due to a pressure differential.

6. The pellicle inspection tool of claim 1, further comprising a source of an x-ray beam arranged to direct a beam of x-rays onto the pellicle at a grazing angle of incidence.

7. The pellicle inspection tool of claim 1, wherein the measuring device is arranged to measure changes in polarization of a radiation beam to determine global or local changes in stress of the pellicle.

8. The pellicle inspection tool of claim 1, wherein the measuring device is arranged to measure the intensity of specular reflection of x-rays from the pellicle.

9. The pellicle inspection tool of claim 1, wherein the measuring device is arranged to measure a change in a resonant frequency of the pellicle assembly or the mask assembly.

10. A mask provided with a protrusion configured to receive a pellicle frame attachment mechanism, wherein the bottom surface of the protrusion has a base and a lip, the lip defining a recess in the surface of the base, and wherein the protrusions are attached to the mask by glue in the recesses.

11. The mask of claim 10, wherein the protrusion comprises an opening in the lip such that the recess and the mask form a space that is partially open for glue outgassing. The mask according to claim 10 , wherein a volume of the glue is smaller than a volume of the recess.

13. The mask of claim 10, wherein the glue pulls the protrusion toward the mask so that the recess and the mask form a substantially closed space, the substantially closed space retaining the glue.

14. A mask provided with at least three protrusions configured to receive a pellicle frame attachment mechanism, wherein the bottom surface of each of the protrusions has a base and a recess in the surface of the base, and wherein the protrusions are removably attached to the mask by glue in the recesses.

15. A mask provided with a protrusion configured to receive a pellicle frame attachment mechanism, The base surface of the protrusion has a groove so that glue is drawn into the volume enclosed by the groove and the mask by capillary action so that the protrusion is attached to the mask by the glue and the groove is partially open for glue degassing.

16. A surface film assembly comprising: a pellicle film extending from a boundary portion of the substrate; a support frame attached to a boundary portion of the substrate; A first cover and a second cover; The first cover and the second cover are disposed on opposite sides of the boundary portion of the substrate and form a sealed environment containing the pellicle film.

17. The diaphragm assembly of claim 16, wherein the second cover covers the support frame such that the support frame is located within the sealed environment.

18. A mask assembly container, comprising: an opening through which a mask assembly can be placed within the container; as well as a sealing member, wherein when the mask assembly is located in the container, the sealing member seals the opening, The container has a bottom plate configured to accommodate outward sagging of the membrane.

19. The mask assembly container according to claim 18, wherein when the mask assembly is held in the sealed container, the distance between the bottom plate and the surface film plane is between 0.5 mm and 1 mm or more.

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