CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority of U.S. Provisional Patent Application Number

62/845,351, which was filed on May 9, 2019, and which is incorporated herein in its entirety by reference.

FIELD

[0002] The present disclosure relates to bumpers, for example, bumper apparatuses for protecting a crashing reticle that has disengaged from a reticle stage in lithography apparatuses and systems.

BACKGROUND

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

[0004] To project a pattern on a substrate a lithographic apparatus may use electromagnetic radiation. The wavelength of this radiation determines the minimum size of features which can be formed on the substrate. A lithographic apparatus, which uses extreme ultraviolet (EUV) radiation, having a wavelength within the range 4-20 nm, for example 6.7 nm or 13.5 nm, may be used to form smaller features on a substrate than a lithographic apparatus which uses, for example, radiation with a wavelength of 193 nm.

[0005] Bumper apparatuses protect interchangeable detachable elements (e.g., a reticle in a reticle exchange system) that are held in place on a stage using a clamping mechanism. If the clamping mechanism fails or loses power while the stage undergoes acceleration, a bumper apparatus receives the reticle and absorb its kinetic energy (e.g., a reticle crash). Current bumper apparatuses are susceptible to damaging the reticle. Thus, there is a need to improve bumper apparatuses to reduce damage to the reticle during a crash in a reliable and repeatable manner. SUMMARY

[0006] In some embodiments, a bumper apparatus for protecting a reticle comprises a base structure, first and second elongate elements, a contact piece, and a restoring element. The first and second elongate elements each comprise a distal end and a proximal end. The proximal ends of the first and second elements are attached to the base structure. The contact piece is disposed at the end of the distal ends of the first and second elongate elements. The first and second elongate elements are configured to deform in response to a contact force caused by the reticle. The restoring element is attached to the first and second elongate elements. The restoring element is configured to generate a restoring force that opposes the deforming of the first and second elongate elements.

[0007] In some embodiments, a bumper apparatus for protecting a reticle comprises a base structure and a flexible segment. The flexible segment has opposing ends attached to the base structure. The flexible segment comprises a curve and a contact area. The flexible segment is configured to deform in response to a contact force caused by the reticle. The deforming comprises forming new contact areas on the flexible segment to redistribute the contact force of the reticle on the flexible segment among two or more contact areas.

[0008] In some embodiments, a bumper apparatus for protecting a reticle comprises a base structure and a compressible system attached to the base structure. The compressible system is configured to deform in response to a contact force caused by the reticle and then self-restore to a nominal shape. The compressible system absorbs kinetic energy of the reticle by applying a non linear force on the reticle for a given stopping distance. The non-linear force comprises a maximum magnitude that is less than a maximum magnitude that a substantially linear restoring element would require to absorb the kinetic energy for the given stopping distance, and/or a force redistributed among two or more contact areas of the compressible system, wherein the two or more contact areas are configured to form sequentially during the deforming.

[0009] Further features and advantages of the invention, as well as the structure and operation of various embodiments of the invention, are described in detail below with reference to the accompanying drawings. It is noted that the invention is not limited to the specific embodiments described herein. Such embodiments are presented herein for illustrative purposes only. Additional embodiments will be apparent to persons skilled in the relevant art(s) based on the teachings contained herein. BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES

[0010] The accompanying drawings, which are incorporated herein and form part of the specification, illustrate the present invention and, together with the description, further serve to explain the principles of the invention and to enable a person skilled in the relevant art(s) to make and use the invention. Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which:

[0011] FIG. 1 shows a schematic illustration of a lithographic apparatus, according to some embodiments.

[0012] FIG. 2 shows a perspective schematic illustration of a reticle stage, according to some embodiments.

[0013] FIG. 3 shows a top plan view of the reticle stage of Figure 2.

[0014] FIG. 4 shows a perspective schematic illustration of a reticle exchange apparatus, according to some embodiments.

[0015] FIG. 5 shows a partial cross-sectional view of the reticle exchange apparatus of

Figure 4.

[0016] FIG. 6A shows a partial schematic illustration of a reticle exchange apparatus in an approach configuration, according to some embodiments.

[0017] FIG. 6B shows a partial schematic illustration of a reticle exchange apparatus in a first contact configuration, according to some embodiments.

[0018] FIG. 6C shows a partial schematic illustration of a reticle exchange apparatus in a full contact configuration, according to some embodiments.

[0019] FIG. 7 shows a schematic illustration of a reticle stage, according to some embodiments.

[0020] FIG. 8 shows a schematic illustration of a bumper apparatus, according to some embodiments.

[0021] FIG. 9 shows a graph of force behaviors as a function of displacement for different impact absorbers, according to some embodiments.

[0022] FIGS. 10 and 11 show schematic illustrations of bumper apparatuses, according to some embodiments.

[0023] The features and advantages of the present invention will become more apparent from the detailed description set forth below when taken in conjunction with the drawings, in which like reference characters identify corresponding elements throughout. In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements. Additionally, generally, the left-most digit(s) of a reference number identifies the drawing in which the reference number first appears. Unless otherwise indicated, the drawings provided throughout the disclosure should not be interpreted as to-scale drawings.

DETAILED DESCRIPTION

[0024] This specification discloses one or more embodiments that incorporate the features of this invention. The disclosed embodiment(s) merely exemplify the invention. The scope of the invention is not limited to the disclosed embodiment(s). The invention is defined by the claims appended hereto.

[0025] The embodiment(s) described, and references in the specification to “one embodiment,”“an embodiment,”“an example embodiment,” etc., indicate that the embodiment(s) described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is understood that it is within the knowledge of one skilled in the art to effect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

[0026] Spatially relative terms, such as “beneath,” “below,”“lower,” “above,”“on,”

“upper” and the like, may be used herein for ease of description to describe one element or feature’s relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly.

[0027] The term“about” as used herein indicates the value of a given quantity that can vary based on a particular technology. Based on the particular technology, the term“about” can indicate a value of a given quantity that varies within, for example, 10-30% of the value (e.g., ±10%, ±20%, or ±30% of the value). [0028] Embodiments of the disclosure may be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the disclosure may also be implemented as instructions stored on a machine-readable medium, which may be read and executed by one or more processors. A machine-readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, a machine-readable medium may include read only memory (ROM); random access memory (RAM); magnetic disk storage media; optical storage media; flash memory devices; electrical, optical, acoustical or other forms of propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.), and others. Further, firmware, software, routines, and/or instructions may be described herein as performing certain actions. However, it should be appreciated that such descriptions are merely for convenience and that such actions in fact result from computing devices, processors, controllers, or other devices executing the firmware, software, routines, instructions, etc., and in doing that may cause actuators or other devices to interact with the physical world.

[0029] Before describing such embodiments in more detail, however, it is instructive to present an example environment in which embodiments of the present disclosure may be implemented.

[0030] Exemplary Lithographic System

[0031] FIG. 1 shows a lithographic system comprising a radiation source SO and a lithographic apparatus FA. The radiation source SO is configured to generate an EUV radiation beam B and to supply the EUV radiation beam B to the lithographic apparatus FA. The lithographic apparatus FA comprises an illumination system IF, a support structure MT configured to support a patterning device MA (e.g., a mask), a projection system PS, and a substrate table WT configured to support a substrate W.

[0032] The illumination system IF is configured to condition the EUV radiation beam B before the EUV radiation beam B is incident upon the patterning device MA. Thereto, the illumination system IF can include a faceted field mirror device 10 and a faceted pupil mirror device 11. The faceted field mirror device 10 and faceted pupil mirror device 11 together provide the EUV radiation beam B with a desired cross-sectional shape and a desired intensity distribution. The illumination system IF can include other mirrors or devices in addition to, or instead of, the faceted field mirror device 10 and faceted pupil mirror device 11. [0033] After being thus conditioned, the EUV radiation beam B interacts with the patterning device MA. As a result of this interaction, a patterned EUV radiation beam B’ is generated. The projection system PS is configured to project the patterned EUV radiation beam B’ onto the substrate W. For that purpose, the projection system PS can comprise a plurality of mirrors 13, 14 that are configured to project the patterned EUV radiation beam B’ onto the substrate W held by the substrate table WT. The projection system PS can apply a reduction factor to the patterned EUV radiation beam B’, thus forming an image with features that are smaller than corresponding features on the patterning device MA. For example, a reduction factor of 4 or 8 can be applied. Although the projection system PS is illustrated as having only two mirrors 13, 14 in FIG. 1, the projection system PS can include a different number of mirrors (e.g. six or eight mirrors).

[0034] The substrate W can include previously formed patterns. Where this is the case, the lithographic apparatus LA aligns the image, formed by the patterned EUV radiation beam B’, with a pattern previously formed on the substrate W.

[0035] A relative vacuum, i.e. a small amount of gas (e.g. hydrogen) at a pressure well below atmospheric pressure, can be provided in the radiation source SO, in the illumination system IL, and/or in the projection system PS.

[0036] The radiation source SO can be a laser produced plasma (LPP) source, a discharge produced plasma (DPP) source, a hydrogen plasma source, a free electron laser (FEL), or any other radiation source that is capable of generating EUV radiation.

[0037] Exemplary Reticle Stage

[0038] FIGS. 2 and 3 show schematic illustrations of an exemplary reticle stage 200, according to some embodiments. Reticle stage 200 can include top stage surface 202, bottom stage surface 204, side stage surfaces 206, and clamp 300. In some embodiments, reticle stage 200 with clamp 300 can be implemented in lithographic apparatus LA. For example, reticle stage 200 can be support structure MT in lithographic apparatus LA. In some embodiments, clamp 300 can be disposed on top stage surface 202. For example, as shown in FIG. 2, clamp 300 can be disposed at a center of top stage surface 202 with clamp frontside 302 facing perpendicularly away from top stage surface 202.

[0039] In some lithographic apparatuses, for example, lithographic apparatus LA, a reticle stage 200 with a clamp 300 can be used to hold and position a reticle 408 for scanning or patterning operations. In one example, the reticle stage 200 can require powerful drives, large balance masses, and heavy frames to support it. In one example, the reticle stage 200 can have a large inertia and can weigh over 500 kg to propel and position a reticle 408 weighing about 0.5 kg. To accomplish reciprocating motions of the reticle 408, which are typically found in lithographic scanning or patterning operations, accelerating and decelerating forces can be provided by linear motors that drive the reticle stage 200.

[0040] In some embodiments, as shown in FIGS. 2 and 3, reticle stage 200 can include first encoder 212 and second encoder 214 for positioning operations. For example, first and second encoders 212, 214 can be interferometers. First encoder 212 can be attached along a first direction, for example, a transverse direction (i.e., X-direction) of reticle stage 200. And second encoder 214 can be attached along a second direction, for example, a longitudinal direction (i.e., Y-direction) of reticle stage 200. In some embodiments, as shown in FIGS. 2 and 3, first encoder 212 can be orthogonal to second encoder 214.

[0041] As shown in FIGS. 2 and 3, reticle stage 200 can include clamp 300. Clamp 300 is configured to hold reticle 408 in a fixed plane on reticle stage 200. Clamp 300 includes clamp frontside 302 and can be disposed on top stage surface 202. In some embodiments, clamp 300 can use mechanical, vacuum, electrostatic, or other suitable clamping techniques to hold and secure an object. In some embodiments, clamp 300 can be an electrostatic clamp, which can be configured to electrostatically clamp (i.e., hold) an object, for example, reticle 408 in a vacuum environment. Due to the requirement for EUV radiation to perform in a vacuum environment, vacuum clamps cannot be used to clamp a mask or reticle and instead electrostatic clamps can be used. For example, clamp 300 can include an electrode, a resistive layer on the electrode, a dielectric layer on the resistive layer, and burls projecting from the dielectric layer. In use, a voltage can be applied to clamp 300, for example, several kV. And current can flow through the resistive layer, such that the voltage at an upper surface of the resistive layer will substantially be the same as the voltage of the electrode and generate an electric field. Also, a Coulomb force, attractive force between electrically opposite charged particles, will attract an object to clamp 300 and hold the object in place. In some embodiments, clamp 300 can be a rigid material, for example, a metal, a dielectric, a ceramic, or a combination thereof.

[0042] Exemplary Reticle Exchange Apparatus [0043] FIGS. 4 through 6 show schematic illustrations of an exemplary reticle exchange apparatus 100, according to some embodiments. Reticle exchange apparatus 100 can be configured to minimize reticle exchange time, particle generation, and contact forces or stresses from clamp 300 and/or reticle 408 to reduce damage to clamp 300 and reticle 408 and increase overall throughput in a reticle exchange process, for example, in a lithographic apparatus LA.

[0044] As shown in FIGS. 4 and 5, reticle exchange apparatus 100 can include reticle stage

200, clamp 300, and in-vacuum robot 400. In-vacuum robot 400 can include reticle handler 402.

[0045] In some embodiments, reticle handler 402 can be a rapid exchange device (RED), which is configured to efficiently rotate and minimize reticle exchange time. For example, reticle handler 402 can save time by moving multiple reticles from one position to another substantially simultaneously, instead of serially.

[0046] In some embodiments, as shown in FIG. 4, reticle handler 402 can include one or more reticle handler arms 404. Reticle handler arm 404 can include reticle baseplate 406. Reticle baseplate 406 can be configured to hold an object, for example, reticle 408.

[0047] In some embodiments, reticle baseplate 406 can be an extreme ultraviolet inner pod

(EIP) for a reticle. In some embodiment, reticle baseplate 406 includes reticle baseplate frontside 407, and reticle 408 includes reticle backside 409.

[0048] In some embodiments, as shown in FIGS. 4 and 5, reticle baseplate 406 can hold reticle 408 such that reticle baseplate frontside 407 and reticle backside 409 each face top stage surface 202 and clamp frontside 302. For example, reticle baseplate frontside 407 and reticle backside 409 can be facing perpendicularly away from top stage surface 202 and clamp frontside 302.

[0049] As shown in FIG. 5, reticle exchange apparatus 100 can include reticle exchange area 410, which is the cross-sectional area between clamp 300, reticle 408, reticle baseplate 406, and reticle handler arm 404 during a reticle exchange process.

[0050] In some embodiments, as shown in FIG. 4, reticle handler arms 404 can be arranged symmetrically about reticle handler 402. For example, reticle handler arms 404 can be spaced from each other by about 90 degrees, 120 degrees, or 180 degrees. In some embodiments, reticle handler arms 404 can be arranged asymmetrically about reticle handler 402. For example, two reticle handler arms 404 can be spaced from each other by about 135 degrees, while another two reticle handler arms 404 can be spaced from each other by about 90 degrees. [0051] In one example, during a reticle exchange process, reticle handler arm 404 of reticle handler 402 positions reticle 408 on reticle baseplate 406 towards clamp 300 in reticle exchange area 410. As described above, a reticle handoff from reticle handler 402 to clamp 300 includes an unknown reticle position offset, which includes a reticle vertical distance offset (i.e., Z-direction offset) and a reticle tilt offset (i.e., Rx offset and Ry offset). Tilt or excessive non-alignment between clamp 300 and reticle 408 can be a source of particle generation and can damage reticle 408 or clamp 300 over time. Reticle backside 409 and clamp frontside 302 should be in coplanar alignment for a final handoff. Despite calibration, variations still exist due to reticle mechanical and positioning tolerances, which can lead to high corner impacts and unpredictable first contact points between clamp 300 and reticle 408.

[0052] In one example, the reticle exchange process can involve lowering reticle stage 200 with clamp 300, which starts far away from reticle handler 402, as close to reticle 408 as possible until clamp 300 contacts reticle 408 to account for all possible offsets and/or tilts. During a reticle exchange process, reticle stage 200 with clamp 300 can be adjusted in a multi-stage movement.

[0053] As shown in FIGS. 6A through 6C, reticle exchange apparatus 100 can include clamp 300, reticle 408, and reticle baseplate 406. The multi-stage movement can occur in four stages: (1) approach; (2) first contact; (3) full contact; and (4) voltage applied to clamp.

[0054] First, as shown in FIG. 6A, reticle exchange apparatus 100 can be in an approach configuration 20 and clamp 300 can be adjusted in a substantially vertical direction (i.e., Z- direction) toward reticle backside 409. In approach configuration 20, clamp 300 is turned off (i.e., no applied voltage) and reticle handler 402 deactivates the vertical direction (i.e., Z-direction) and tilt (i.e., Rx and Ry, rotation about X-direction and rotation about Y-direction, respectively) servo motors of reticle handler arm 404 in reticle exchange area 410. The motors (i.e., Z, Rx, and Ry) brake and rotation about Z-direction (i.e., Rz) activates.

[0055] Second, as shown in FIG. 6B, reticle exchange apparatus 100 can be in a first contact configuration 30 and clamp 300 can be adjusted in a substantially vertical direction (i.e., Z-direction) toward reticle backside 409 until clamp 300 makes contact with reticle backside 409. In first contact configuration 30, clamp 300 is turned off and clamp 300 makes contact with reticle backside 409, for example, a comer of reticle 408, and then rotates or tilts about the contact (i.e., Rx and Ry). [0056] Third, as shown in FIG. 6C, reticle exchange apparatus 100 can be in a full contact configuration 40 and clamp 300 can be rotationally adjusted about the contact (i.e., Rx and Ry) toward reticle backside 409 until clamp 300 makes full contact with reticle backside 409. In full contact configuration 40, clamp 300 is turned off and clamp 300 makes full contact with reticle backside 409, for example, all four corners of reticle 408, and is coplanar with reticle backside 409.

[0057] In some embodiments, in full contact configuration 40, clamp 300 makes contact with all four corners of reticle 408 and continues to move in a substantially vertical direction (i.e., Z-direction) until a mechanical force of at least 5 N is achieved.

[0058] Fourth, with clamp frontside 302 and reticle backside 409 aligned and coplanar, clamp 300 is turned on (i.e., a voltage is applied to clamp 300) and reticle 408 is held in a fixed plane on clamp 300.

[0059] In some embodiments, as shown in FIG. 5, reticle exchange apparatus 100 can include clamp controller 360. Clamp controller 360 can be coupled to clamp 300 and be configured to control a position of clamp 300. For example, clamp controller 360 can be configured to control reticle stage 200 to allow compliant movement of clamp 300. In some embodiments, clamp controller 360 can be coupled to servo motors or servo actuators (i.e., X-direction, Y-direction, Z- direction, Rx, Ry, Rz) of reticle stage 200 and/or clamp 300. For example, clamp controller 360 can control translations of reticle stage 200 with clamp 300 along an x-axis, y-axis, and z-axis (i.e., X-direction, Y-direction, Z-direction) and rotations about the x-axis, y-axis, and z-axis (i.e., Rx, Ry, Rz), where the x-axis, y-axis, and z-axis are orthogonal coordinates.

[0060] Exemplary Bumper Apparatuses

[0061] A reticle is a critical and sensitive component for imparting patterns on a substrate.

Damage to the reticle, however light, often necessitates costly production downtime and maintenance when replacing the damaged reticle. A reticle can be damage during a crash, for example, when the clamp affixing the reticle to its host reticle stage ceases its clamping function (e.g., electrostatic clamp losing power) and the reticle stage undergoes acceleration. The reticle will stop moving relative to the reticle stage when it encounters one or more affixed structures on a reticle stage (e.g., a bumper). A bumper is designed to absorb the kinetic energy of the reticle.

[0062] FIG. 7 shows a schematic illustration of a reticle stage 700, according to some embodiments. The view in FIG. 7 is one that is analogous to, for example, top stage surface 202 in FIGS. 2 and 3. In some embodiments, reticle stage 700 comprises a clamp 702, latches 704, and bumper apparatuses 706. Reticle stage 700 is configured to support a reticle 708. Latches 704 and bumper apparatuses 706 are attached to reticle stage 700 outside of an area where reticle 708 is to be disposed. In some embodiments, clamp 702 is configured to engage (e.g., affix) reticle 708 to reticle stage 700 when reticle stage 700 supports reticle 708. In some embodiments, clamp 702 comprises an electrostatic clamp that uses a Coulomb potential to attract and engage reticle 708.

[0063] Latches 704 and bumper apparatuses 706 are particularly helpful in scenarios where reticle 708 unexpectedly disengages from reticle stage 700. In some embodiments, latches 704 are configured to pivot so as to overlap reticle 708. Latches 704 are further configured to limit a motion of the stage in the Z-direction (e.g., out of the page in FIG. 7). Bumper apparatuses 706 are configured to receive and contact reticle 708 when reticle 708 moves relative to reticle stage 700 in the X and Y directions (e.g., in the plane of the page in FIG. 7). Bumper apparatuses 706 are further configured to absorb a kinetic energy of the reticle 708 in a controlled manner so as to reduce impact forces imparted on reticle 708. Reticle 708 is brought to rest by dissipative forces (e.g., drag, friction, acoustic dissipation, etc.).

[0064] FIG. 8 shows a schematic illustration of a bumper apparatus 800, according to some embodiments. In some embodiments, bumper apparatus 800 comprises a base structure 802 and an elongate element 804 (e.g., a flexure). Elongate element 804 comprises a contact piece 806. In some embodiments, bumper apparatus 800 comprises an elongate element 808. Elongate element 808 comprises a contact piece 810. Elongate element 804 and elongate element 808 each comprise a proximal end and a distal end. The proximal ends of elongate element 804 and elongate element 808 are attached to base structure 802. Contact piece 806 is disposed at the distal end of elongate element 804. Contact piece 810 is disposed at the distal end of elongate element 808. Elongate element 804 is a straight elongate element. Elongate element 808 is a bent elongate element (e.g., has an elbow). Bumper apparatus 800 can be implemented on a reticle stage, for example, in place of bumper apparatuses 706 on reticle stage 700 (FIG. 7).

[0065] In some embodiments, bumper apparatus 800 is configured to protect a reticle 812.

When reticle 812 becomes disengaged while its host stage is in motion, reticle 812 can collide with either or both of contact piece 806 and contact piece 810. Elongate element 804 and/or elongate element 808 deform (e.g., bend) in response to a contact force caused by reticle 812. The deformation is of a flexure variety for absorbing and softening the impact on reticle 812. Elongate element 804 and elongate element 808 are oriented to receive perpendicular components (e.g., X/Y directions) of the momentum of reticle 812. A skilled artisan will appreciate the various configurations of bumper apparatus 800 are possible beyond the one shown in FIG. 8. For example, in order to absorb X/Y momenta of the reticle, bumper apparatus 800 may be arranged with only elbowed elongate elements, only straight elongate elements, two base structures each with one elongate element, etc.

[0066] Flexure impact absorbers (e.g., bumper apparatuses) can have compression-force relationships similar to springs (e.g., F = kAx, where F is force, k is spring constant, and Dc is displacement by compression or bending). Since the energy absorbed by this type of impact absorber is proportional to kAx ² , the force-energy relationship of a flexure/spring style absorber is E oc F Ax. One simple method to absorb a large amount of energy would be to increase the range Dc that a flexure or spring can displace. However, on a reticle stage in a lithographic apparatus, the range of Dc can be considered to be relatively limited because the amount of free space in the vicinity of the bumper apparatus is very limited. Since Dc is difficult to adjust, the absorption of kinetic energy of a reticle is dominated by the force, F . And herein lies a challenge— risk of damage to the reticle increases with higher force. Another challenge is that the risk of permanent deformation of a flexure impact absorber increases with higher force, which often lead to costly repairs. Embodiments of the present disclosure provide structures and operations to overcome these challenges.

[0067] FIG. 9 shows a graph 900 of force behaviors as a function of displacement for different impact absorbers, according to some embodiments. In graph 900, the vertical axis represents the force exerted by a displaced impact absorber and the horizontal axis represents a displacement of an impact absorber by compression or bending. In some embodiments, plot line 902 represents a force response of a spring or flexure impact absorber. Plot line 904 represents a force response of a buckling impact absorber. Inset 906, inset 908, and inset 910 depict modes of operation of spring, flexure, and buckling elements, respectively. In inset 906, inset 908, and inset 910, the dashed-line structures represent the deflection of the respective impact absorber and black arrows represent a direction of an applied force. In the labels of graph 900, the subscripts s, f, and b respectively denote spring, flexure, and buckling.

[0068] In some embodiments, the force response of a spring or flexure element is linear

(e.g., substantially direct proportionality to displacement) as shown by plot line 902. The force response of a buckling element is non-linear (e.g., substantially different from a direct proportionality to displacement, force response transitions between differing regimes of behavior), as shown by plot line 904. The behavior of plot line 904 can be described as having at least a fast rising region 912 and a flatter region 916. Fast-rising region 912 is characterized with a high slope (i.e., fast-rising force) as compared to other regions of plot line 904. Flatter region 916 has a slope that is substantially smaller than the slope in fast-rising region 912. In other words, a rate of increase of the non-linear force with respect to the displacement of the non-linear absorber is substantially reduced for displacements larger than a threshold displacement. The threshold displacement can be a single value (e.g., x ₀ in FIG. 9) or a threshold region 914.

[0069] In graph 900, the area under a curve represents the energy stored in the impact absorber. In other words, the area under the curve can represent kinetic energy (absorbed by an impact absorber) of a reticle that collides with the impact absorber. Therefore, a reticle impacting a linear impact absorber (e.g., as in plot line 902) with a given energy will produce a maximum force F _S f _Tnax and displace the linear impact absorber by a maximum of x _S f,max Conversely, a non-linear impact absorber (e.g., as in plot line 904) produces a maximum force F _{b max} and displaces the non-linear impact absorber by a maximum of x _b ,max f° ^r the same given energy of a reticle (i.e., assuming areas under both curves are equal). As shown in graph 900, using a non linear impact absorber can reduce the maximum force imparted on the reticle while also stopping the reticle in a shorter distance, as compared to a linear impact absorber (F _{b max} < F _s ^ _max and ^X b,max < ^X sf,max)· Thus, non-linear impact absorbers are adequate for force reduction and volume reduction of parts.

[0070] FIG. 10 shows a schematic illustration of a bumper apparatus 1000, according to some embodiments. In some embodiments, bumper apparatus 1000 comprises a base structure 1002, an elongate element 1004, an elongate element 1006, a contact piece 1008, and a restoring element 1010. Elongate element 1004 and elongate element 1006 each comprise a proximal end, a middle section, a distal end. In some embodiments, elongate element 1004 and elongate element 1006 are buckling elements (i.e., they have non-linear force response). In some embodiments, restoring element 1010 is a spring. In some embodiments, restoring element 1010 is a flexure. In some embodiments, restoring element 1010 is a clip.

[0071] A well-performing bumper apparatus can be achieved by, for example, appropriate choice of material, fabrication process, and structure dimensions while observing other constraints (e.g., volume restriction, chemical stability). It was shown in FIG. 1 that a support table MT can be disposed close to illumination system IL. In this, and other configurations, it is possible for the support table MT (and any bumper apparatuses implemented on it) to be exposed to the plasma that generates the radiation for illuminating a reticle. Therefore, in some embodiments, bumper apparatus 1000 (and comprising parts) can comprise stainless steel (e.g., 304, 316, 316L, 420, and the like) to better resist chemical interaction with a reticle and/or ions in a nearby plasma. Stainless steel presents suitable hardness and elasticity to perform the deforming, buckling, and self restoring that is desirable for bumper apparatuses. Stainless steel is also suitable for a host of fabrication processes. For example, bumper apparatus 1000 comprising stainless steel can be fabricated using monolithic fabrication (e.g., from a single starting block), piecewise fabrication, electrical discharge machining (EDM), computer numerical control (CNC) machining, and/or electropolishing, among others. In some embodiments, processes such as electropolishing remove surface defects from stainless steel surfaces of bumper apparatus 1000 (e.g., reduce roughness, cracks, sharp edges, projections, etc.). Removal of surface defects helps prevent bumper apparatus 1000 from chemically interacting with ions from a nearby plasma.

[0072] In some embodiments, a length of elongate element 1004 is between approximately

20-40 mm (e.g., the longer dimension in the plane of the page, X, in FIG. 10). A thickness of elongate element 1004 is between approximately 50-1000 microns (e.g., the narrower dimension in the plane of the page, Y, in FIG. 10). A height of contact piece 1008 and/or elongate element 1004 is between approximately 1-10 mm (e.g., dimension out of the page, Z, in FIG. 10). For the height, it is desirable for contact piece 1008 to be able to contact the full height of a reticle 1108 in order to maximize a spreading of a contact force (i.e., reduce pressure). In some embodiments, a height of reticle 1012 is approximately 6.5 mm. Thus, the 1-10 mm specified range for the height of contact piece 1008 is identified with such cognizance. Therefore, in some embodiments, a height of contact piece 1008 and/or elongate element 1004 substantially matches the height of reticle 1012, which may be outside of the 1-10 mm range given earlier. In some embodiments, dimensions of elongate element 1006 are the same or substantially similar to dimensions of elongate element 1004. The dimensions of elongate element 1004 and elongate element 1006, coupled with mechanical properties of stainless steel, are suitable for producing the impact absorption, buckling, and self-restoring qualities desired in bumper apparatuses. [0073] In some embodiments, elongate element 1004 and elongate element 1006 are straight elongate elements. The proximal ends of elongate element 1004 and elongate element 1006 are attached to base structure 1002. Elongate element 1004 and elongate element 1006 can be attached to base structure 1002 using, for example, monolithic fabrication, press fitting, or welding. Contact piece 1008 is disposed at the distal ends of elongate element 1004 and elongate element 1006. Contact piece 1008 can be attached to elongate element 1004 and elongate element 1006 using, for example, monolithic fabrication, press fitting, or welding. Restoring element 1010 is attached to the middle sections of elongate element 1004 and elongate element 1006. Restoring element 1010 can be attached to elongate element 1004 and elongate element 1006 using, for example, monolithic fabrication, press fitting, or welding. Bumper apparatus 1000 can be implemented on a reticle stage, for example, in place of bumper apparatuses 706 on reticle stage 700 (FIG. 7).

[0074] In some embodiments, bumper apparatus 1000 is configured to protect a reticle

1012. When reticle 1012 becomes disengaged while its host stage is in motion, reticle 1012 can collide with contact piece 1008 (e.g., during a change in movement of the stage). Elongate element 1004 and elongate element 1006 are configured to deform (e.g., buckle) in response to a contact force caused by reticle 1012. Buckling mechanics of elongate element 1004 and elongate element 1006 incorporate the features and advantages described in reference to FIG. 9 (e.g., reduce maximum force and damage imparted on the reticle). For example, bumper apparatus 1000 is configured to apply a non-linear force on reticle 1012 in response to the contact force caused by reticle 1012. A skilled artisan will appreciate other functions of bumper apparatus 1000 in reference to descriptions of FIG. 9.

[0075] Since buckling elements have a risk of becoming permanently deformed, in some embodiments, restoring element 1010 is configured to generate a restoring force that opposes the deforming of elongate element 1004 and elongate element 1006 so as to oppose permanent deformation (i.e., bumper apparatus 1000 self-restores to a nominal shape). In some embodiments, elongate element 1004 is configured to bow away from elongate element 1006, and vice versa for elongate element 1006 (indicated by arrows 1014). This can be achieved by, for example, having restoring element 1010 apply a small force to elongate element 1004 and elongate element 1006 in directions indicated by arrows 1014. In this scenario, restoring element 1010 is configured to revert the direction of the applied force (e.g., to a restoring force) when elongate element 1004 and elongate element 1006 are deforming. In some embodiments, elongate element 1004 and elongate element 1006 is substantially straight but also slightly curved or bowed outward in the direction of arrows 1014. The slightly bowed shape can promote a preferred direction of deformation when bumper apparatus 1000 receives an impact from reticle 1012.

[0076] A skilled artisan will appreciate that bumper apparatus 1000 can be conceived in various configurations for receiving reticle 1012 moving in two dimensions. For example, in some embodiments, multiple iterations of bumper apparatus 1000 can be used for receiving reticle 1012— one for the X component and another one for the Y component (e.g., placed at position box 1016). In some embodiments, multiple iterations of bumper apparatus 1000 can have a shared, single base structure.

[0077] Until now, reducing damage on a reticle has been discussed in the context of force reduction of a bumper apparatus on the reticle. In another perspective, a cause of damage to a crashing reticle is the stress (e.g., local pressure at impact points) a bumper apparatus imparts on the reticle. Since pressure is a force over an area, a pressure on the reticle can be reduced by reducing the force, increasing a contact area, or both. We have already discussed embodiments that can reduce the maximum force on a reticle. Embodiments of the present disclosure also provide structures and methods to increase a contact area at a reticle/bumper interface.

[0078] FIG. 11 shows a schematic illustration of a bumper apparatus 1100 at different stages of deformation, according to some embodiments. In some embodiments, bumper apparatus 1100 comprises a base structure 1102 and a flexible segment 1104. Flexible segment 1104 comprises opposing ends attached to base structure 1102. Flexible segment 1104 is curved. Flexible segment 1104 further comprises a contact area 1106. Flexible segment 1104 comprises a leaf spring.

[0079] Similar to deformable components in bumper apparatus 1000, flexible segment

1104 has a construction that is designed to deform as well as self-restore. To achieve this, bumper apparatus 1000 (and comprising parts) can comprise stainless steel (e.g., 304, 316, 316L, 420, and the like) to better resist chemical interaction with a reticle and/or ions in a nearby plasma. Bumper apparatus 1100 can be fabricated using monolithic fabrication, piecewise fabrication, EDM, CNC machining, and/or electropolishing, among others. In some embodiments, electropolishing is used remove surface defects from stainless steel surfaces of bumper apparatus 1000 (e.g., reduce roughness, cracks, sharp edges, projections, etc.). [0080] In some embodiments, length of flexible segment 1104 is between approximately

20-50 mm (e.g., the longer dimension in the plane of the page, Y, in FIG. 11). A thickness of flexible segment 1104 is between approximately 50-1000 microns (e.g., the narrower dimension in the plane of the page, X, in FIG. 10). A height of flexible segment 1104 is between approximately 1-10 mm (e.g., dimension out of the page, Z, in FIG. 10). For the height, it is desirable for contact area 1106 to be able to contact the full height of a reticle 1108 in order to maximize a spreading of a contact force (i.e., reduce pressure). In some embodiments, a height of reticle 1108 is approximately 6.5 mm. Thus, the 1-10 mm specified range for the height of flexible segment 1104 is identified with such cognizance. Therefore, in some embodiments, a height of flexible segment 1104 substantially matches the height of reticle 1108, which may be outside of the 1-10 mm range given earlier. The curve of flexible segment 1104 has a radius of curvature that is between 50-150 mm. The range of the radius of curvature is identified by considering a reduction of Hertzian stress on reticle 1108 and available volume (e.g., too large of a radius may be difficult to accommodate on a reticle stage). The dimensions of flexible segment 1104, coupled with mechanical properties of stainless steel, are suitable for producing the impact absorption, buckling, and self-restoring qualities desired in bumper apparatuses.

[0081] In some embodiments, flexible segment 1104 can be attached to base structure 1102 using, for example, monolithic fabrication, press fitting, or welding. Bumper apparatus 1100 can be implemented on a reticle stage, for example, in place of bumper apparatuses 706 on reticle stage 700 (FIG. 7).

[0082] In some embodiments, bumper apparatus 1100 is configured to protect reticle 1108.

When reticle 1108 becomes disengaged while its host stage is in motion, reticle 1108 can collide with contact area 1106 (e.g., during a change in movement of the stage). Flexible segment 1104 is configured to deform in response to a contact force caused by reticle 1108. Inset 1110 and inset 1112 show sequential stages of deformation of flexible segment 1104. As bumper apparatus 1100 absorbs the impact from reticle 1108, inset 1110 shows two new contact areas 1114 formed in sequence from nominal a nominal shape. The nominal shape is the shape of flexible segment 1104 corresponding to being at rest prior to coming into contact with reticle 1108 (e.g., only contact area 1106 is present). As bumper apparatus 1100 further absorbs the impact from reticle 1108, inset 1112 shows three new contact areas 1116 formed in sequence from the state shown in inset 1110. In other words, the deforming of flexible segment 1104 comprises forming new contact areas sequentially. In some embodiments, the deformation of flexible segment 1104 and the sequential formation of new contact areas resemble a shape of standing wave harmonics. In some embodiments, bumper apparatus 1100 is configured to self-restore to a nominal shape.

[0083] In some embodiments, the contact force caused by the reticle is redistributed among two or more contact areas (e.g., the newly formed contact areas). A redistribution of the contact force is also a form of non-linearity because the contact force is redistributed in response to each of the sequentially forming new contact areas. The redistributing reduces a pressure exerted on the reticle for each redistribution of the contact force. The force that opposes the contact force from reticle 1108 can be said to be a non-linear force.

[0084] In some embodiments, a total stopping distance of reticle 1108 after coming into contact with bumper apparatus 1100 is between approximately 0-2 mm. When at rest, the shortest distance between contact area 1106 and base structure 1102 is between approximately 1-20 mm. A displacement of flexible segment 1104, during deformation, can refer to a difference between (a) the shortest distance between contact area 1106 and base structure 1102 and (b) the shortest distance between contact areas 1114 (or contact areas 1116) and base structure 1102. Tuning the amount of maximum displacement can be achieved by adjusting the stiffness of flexible element 1104 (e.g., by adjusting its thickness). Tuning the amount displacement is also applicable to the displacement undergone by contact piece 1008 of bumper apparatus 1000, for example, by adjusting a thickness of elongate element 1004 and elongate element 1006 (FIG. 10).

[0085] A skilled artisan will appreciate that bumper apparatus 1100 can be conceived in various configurations for receiving reticle 1108 moving in two dimensions. For example, in some embodiments, multiple iterations of bumper apparatus 1100 can be used for receiving reticle 1108— one for the X component and another one for the Y component (e.g., placed at position box 1118). In some embodiments, multiple iterations of bumper apparatus 1100 can have a shared, single base structure.

[0086] In some embodiments, embodiments in reference to FIGS. 10 and 11 can be combined. For example, Bumper apparatus 1100 (FIG. 11) can replace contact piece 1008 of bumper apparatus 1000 (FIG. 10).

[0087] The embodiments may further be described using the following clauses:

1. A bumper apparatus for protecting a reticle, the bumper apparatus comprising:

a base structure; first and second elongate elements, each element comprising a distal end and a proximal end, the proximal ends of the first and second elements being attached to the base structure; a contact piece disposed at the distal ends of the first and second elongate elements, wherein the first and second elongate elements are configured to deform in response to a contact force caused by the reticle; and

a restoring element attached to the first and second elongate elements, wherein the restoring element is configured to generate a restoring force that opposes the deforming of the first and second elongate elements.

2. The bumper apparatus of clause 1, wherein:

the bumper apparatus absorbs an amount of kinetic energy of the reticle by applying a non linear force on the reticle for a given stopping distance; and

the non-linear force has a maximum magnitude that is less than a maximum magnitude that a substantially linear restoring element would require to absorb the amount of kinetic energy for the given stopping distance.

3. The bumper apparatus of clause 1, wherein:

the bumper apparatus is configured to apply a non-linear force on the reticle in response to the contact force; and

a rate of increase of the non-linear force with respect to a displacement of the contact piece is substantially reduced for displacements larger than a threshold displacement.

4. The bumper apparatus of clause 1, wherein the bumper apparatus is configured to self restore to a nominal shape.

5. The bumper apparatus of clause 1, wherein:

the bumper apparatus is attached to a stage that is configured to engage the reticle, wherein the stage is further configured to move; and

the bumper apparatus is configured to protect the reticle during a change in movement of the stage with the reticle disengaged.

6. The bumper apparatus of clause 1, wherein the bumper apparatus comprises stainless steel.

7. The bumper apparatus of clause 1, wherein the bumper apparatus comprises electropolished surfaces.

8. The bumper apparatus of clause 1, wherein the bumper apparatus is further configured such that the deforming comprises buckling. 9. The bumper apparatus of clause 1, wherein the restoring element comprises a spring or a flexure.

10. The bumper apparatus of clause 1, wherein the bumper apparatus comprises a monolithic structure including at least the base structure, the first and second elongate elements, and the contact piece.

11. A bumper apparatus for protecting a reticle, the bumper apparatus comprising:

a base structure; and

a flexible segment having opposing ends attached to the base structure, the flexible segment comprising a curve and a contact area, wherein the flexible segment is configured to deform in response to a contact force caused by the reticle,

wherein the deforming comprises forming new contact areas on the flexible segment to redistribute the contact force of the reticle on the flexible segment among two or more contact areas.

12. The bumper apparatus of clause 11, wherein:

the bumper apparatus absorbs kinetic energy of the reticle by applying a non-linear force on the reticle; and

wherein the new contact areas are configured to sequentially form during the deforming.

13. The bumper apparatus of clause 12, wherein the redistributing occurs in response to each of the sequentially forming of the new contact areas so as to reduce a pressure exerted on the reticle for each redistribution of the contact force.

14. The bumper apparatus of clause 11, wherein the bumper apparatus is configured to self restore to a nominal shape.

15. The bumper apparatus of clause 11, wherein:

the bumper apparatus is attached to a stage that is configured to engage the reticle, wherein the stage is further configured to move; and

the bumper apparatus is configured to protect the reticle during a change in movement of the stage with the reticle disengaged.

16. The bumper apparatus of clause 11, wherein the bumper apparatus comprises stainless steel.

17. The bumper apparatus of clause 11, wherein the bumper apparatus comprise electropolished surfaces. 18. The bumper apparatus of clause 1, wherein the bumper apparatus comprises a monolithic structure including the base structure and the flexible segment.

19. A bumper apparatus for protecting a reticle, the bumper apparatus comprising:

a base structure; and

a compressible system attached to the base structure, wherein the compressible system is configured to deform in response to a contact force caused by the reticle and then self-restore to a nominal shape, and wherein the compressible system absorbs kinetic energy of the reticle by applying a non-linear force on the reticle for a given stopping distance,

wherein the non-linear force comprises:

a maximum magnitude that is less than a maximum magnitude that a substantially linear restoring element would require to absorb the kinetic energy for the given stopping distance; and/or a force redistributed among two or more contact areas of the compressible system, wherein the two or more contact areas are configured to form sequentially during the deforming.

20. The bumper apparatus of clause 19, wherein:

the bumper apparatus is attached to a stage that is configured to engage the reticle and move; and

the bumper apparatus is configured to protect the reticle during a change in movement of the stage with the reticle disengaged.

[0088] The term“compressible system” and the like can be used herein to describe bumper apparatuses or a grouping of one or more elements within a bumper apparatus, due to the compressible nature of bumper apparatuses or the grouping of the elements.

[0089] Embodiments of the present disclosure are not limited to protecting reticles or exclusive implementation on reticle stages. Moving components described in the present disclosure may benefit from one or more embodiments herein. For example, embodiments can be directed at wafers and wafer stages.

[0090] The term“non-linear” and the like can be used herein to impart qualities of non linearity on other terms (e.g., a non-linear element, component, apparatus, system, force, pressure, response, etc.). Likewise, the term“linear” and the like can be used herein to impart qualities of linearity on other terms.

[0091] 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 patterns for magnetic domain memories, flat- panel displays, liquid-crystal displays (LCDs), thin film magnetic heads, etc.

[0092] Although specific reference may be made in this text to embodiments of the disclosure in the context of a lithographic apparatus, embodiments of the disclosure may be used in other apparatuses. Embodiments of the disclosure may form part of a mask inspection apparatus, a metrology apparatus, or any apparatus that measures or processes an object such as a wafer (or other substrate) or mask (or other patterning device). These apparatuses may be generally referred to as lithographic tools. Such lithographic tools may use vacuum conditions or ambient (non vacuum) conditions.

[0093] Although specific reference may have been made above to the use of embodiments of the disclosure in the context of optical lithography, it will be appreciated that the disclosure, where the context allows, is not limited to optical lithography and may be used in other applications, for example imprint lithography. In another example, embodiments of the present disclosure may be used in general applications where a sensitive component is moved while needing impact protection.

[0094] It is to be understood that the phraseology or terminology herein is for the purpose of description and not of limitation, such that the terminology or phraseology of the present specification is to be interpreted by those skilled in relevant art(s) in light of the teachings herein.

[0095] The above examples are illustrative, but not limiting, of the embodiments of this disclosure. Other suitable modifications and adaptations of the variety of conditions and parameters normally encountered in the field, and which would be apparent to those skilled in the relevant art(s), are within the spirit and scope of the disclosure.

[0096] While specific embodiments of the disclosure have been described above, it will be appreciated that the disclosure may be practiced otherwise than as described. The descriptions above are intended to be illustrative, not limiting. Thus it will be apparent to one skilled in the art that modifications may be made to the disclosure as described without departing from the scope of the claims set out below.

[0097] It is to be appreciated that the Detailed Description section, and not the Summary and Abstract sections, is intended to be used to interpret the claims. The Summary and Abstract sections may set forth one or more but not all exemplary embodiments of the present invention as contemplated by the inventor(s), and thus, are not intended to limit the present invention and the appended claims in any way.

[0098] The present invention has been described above with the aid of functional building blocks illustrating the implementation of specified functions and relationships thereof. The boundaries of these functional building blocks have been arbitrarily defined herein for the convenience of the description. Alternate boundaries can be defined so long as the specified functions and relationships thereof are appropriately performed.

[0099] The foregoing description of the specific embodiments will so fully reveal the general nature of the invention that others can, by applying knowledge within the skill of the art, readily modify and/or adapt for various applications such specific embodiments, without undue experimentation, without departing from the general concept of the present invention. Therefore, such adaptations and modifications are intended to be within the meaning and range of equivalents of the disclosed embodiments, based on the teaching and guidance presented herein.

[0100] The breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.