Stacked confocal pulse stretcher series for speckle reduction

Abstract

The invention relates to a series of stacked confocal pulse stretcher for speckle reduction. An extended optical pulse stretcher is provided that combines confocal pulse stretchers to generate, for example, four reflections, four reflections, twelve reflections, and twelve reflections in each optical path configuration. The combination including different mirror partitions and delay path lengths may result in very long pulse broadening, long optical delay, and minimal efficiency loss. Moreover, in the expanded optical pulse stretcher, at least one beam splitter may be positioned relative to the center of curvature of the mirror to "flatten" each optical path to enable the beam to propagate in the same plane (e.g., parallel to the floor). Moreover, the curvature and size of each mirror can be designed to position the beam splitter closer to one of the mirrors in the set of mirrors to allow the optical pulse stretcher to properly fit at a distribution position in the laser system.

Description

[0001] This application is a divisional application of an invention patent application with an international filing date of October 14, 2020 (priority date of October 16, 2019), which entered the Chinese national stage on April 15, 2022, and has a Chinese national application number of 202080072817.3 and is named “Stacked confocal pulse stretcher series for speckle reduction”. Technical Field

[0002] The present disclosure relates to optical pulse stretchers for extending the pulse of the output of a laser source, such as a high power gas discharge laser system, to reduce the peak power of the pulse while delivering substantially the same dose, for use as a pulsed light source in, for example, a lithographic apparatus. Background Art

[0003] A lithographic apparatus is a machine that applies a desired pattern to a substrate, usually to a target portion of the substrate. A lithographic apparatus can be used, for example, to manufacture integrated circuits (ICs). In this case, a pattern forming device (or mask or intermediate mask) can be used to generate a circuit pattern to be formed on a single layer of the IC. This pattern can be transferred to a target portion (e.g., a portion including one or more dies) on a substrate (e.g., a silicon wafer). The transfer of the pattern is usually by imaging onto a layer of radiation-sensitive material (resist) disposed on the substrate. Typically, a single substrate will contain a network of adjacent target portions that are patterned continuously. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing the entire pattern to the target portion at once; and so-called scanners, in which each target portion is irradiated by scanning the pattern by a radiation beam in a given direction (the "scanning" direction) while scanning the target portion parallel or antiparallel to the scanning direction. The pattern can also be transferred from the pattern forming device to the substrate by imprinting the pattern onto the substrate.

[0004] A laser source may be used with a lithographic apparatus, for example to generate illumination radiation for illuminating a patterning device. The laser source may include an optical pulse stretcher for extending the output pulse of a high power gas discharge laser system. However, prior art techniques do not provide sufficient pulse stretching with sufficient optical efficiency, nor are they suitable for the available volume of the laser source. Summary of the invention

[0005] Embodiments of stacked confocal pulse stretchers designed to achieve very long pulse stretching and the ability to fit within the available laser volume are described in this disclosure.

[0006] One aspect of the present disclosure provides an optical pulse stretcher configured to receive a laser beam and generate an output pulse-stretched laser beam. The optical pulse stretcher includes a first-stage optical pulse stretcher, which includes two or more mirrors and is configured to receive a portion of the laser beam and generate a first pulse-stretched laser beam. The optical pulse stretcher also includes a second-stage optical pulse stretcher, which includes four or more mirrors and is configured to receive a portion of the first pulse-stretched laser beam and generate a second pulse-stretched laser beam. The optical pulse stretcher also includes a third-stage optical pulse stretcher, which includes four or more mirrors and is configured to receive a portion of the second pulse-stretched laser beam and generate an output pulse-stretched laser beam.

[0007] In some embodiments, the two or more mirrors of the first stage optical pulse stretcher, the four or more mirrors of the second stage optical pulse stretcher, and the four or more mirrors of the third stage optical pulse stretcher include concave mirrors.

[0008] In some embodiments, the two mirrors of the first stage optical pulse stretcher, the four mirrors of the second stage optical pulse stretcher, and the four mirrors of the third stage optical pulse stretcher include rectangular concave mirrors.

[0009] In some embodiments, the first stage optical pulse stretcher is configured to generate a first pulse-stretched laser beam by reflecting a portion of the laser beam four times using two or more mirrors of the first stage optical pulse stretcher. In addition, in some embodiments, the second stage optical pulse stretcher is configured to generate a second pulse-stretched laser beam by reflecting a portion of the first pulse-stretched laser beam twelve times using four or more mirrors of the second stage optical pulse stretcher. In addition, in some embodiments, the third stage optical pulse stretcher is configured to generate an output pulse-stretched laser beam by reflecting a portion of the second pulse-stretched laser beam twelve times using four or more mirrors of the third stage optical pulse stretcher.

[0010] In some embodiments, the optical pulse stretcher further comprises a first beam splitter corresponding to the first-stage optical pulse stretcher and configured to receive the laser beam and direct portions of the laser beam to two or more mirrors of the first-stage optical pulse stretcher. In some embodiments, the first beam splitter may be positioned closer to a first mirror of the two or more mirrors of the first optical pulse stretcher, and the first beam splitter may be a D-shaped beam splitter. In some embodiments, the first beam splitter is positioned relative to a center of curvature of the two or more mirrors to flatten the first-stage optical pulse stretcher and enable portions of the laser beam to propagate in the same plane in the first-stage optical pulse stretcher.

[0011] In some embodiments, the optical pulse stretcher further comprises a second beam splitter corresponding to the second-stage optical pulse stretcher and configured to receive the first pulse-stretched laser beam and direct a portion of the first pulse-stretched laser beam to the four or more mirrors of the second-stage optical pulse stretcher. According to some embodiments, the second beam splitter is positioned relative to the center of curvature of the four or more mirrors of the second-stage optical pulse stretcher to flatten the second-stage optical pulse stretcher and enable a portion of the first pulse-stretched laser beam to propagate in the same plane in the second-stage optical pulse stretcher.

[0012] In some embodiments, the optical pulse stretcher may further include a third beam splitter corresponding to the third-stage optical pulse stretcher and configured to receive the second pulse-stretched laser beam and direct a portion of the second pulse-stretched laser beam to four or more mirrors of the third-stage optical pulse stretcher. In some embodiments, the third beam splitter is positioned relative to the center of curvature of the four or more mirrors of the third-stage optical pulse stretcher to flatten the third-stage optical pulse stretcher and enable a portion of the second pulse-stretched laser beam to propagate in the same plane in the third-stage optical pulse stretcher.

[0013] In some embodiments, the second beam splitter is positioned closer to the first pair of mirrors among the four or more mirrors of the second optical pulse stretcher, and the second beam splitter can be a D-shaped beam splitter. In some embodiments, the third beam splitter is positioned closer to the first pair of mirrors among the four or more mirrors of the third optical pulse stretcher, and the third beam splitter can be a D-shaped beam splitter.

[0014] In some embodiments, the laser beam received by the first stage optical pulse stretcher is a pulse-stretched laser beam generated by an orthogonal stage optical pulse stretcher, wherein the orthogonal stage optical pulse stretcher is positioned outside of the optical pulse stretcher and perpendicular or approximately perpendicular to the optical pulse stretcher. In some embodiments, the orthogonal stage optical pulse stretcher is configured to reflect a portion of the laser beam four times.

[0015] Another aspect of the present disclosure provides a laser source. The laser source includes an optical pulse stretcher configured to receive a laser beam and generate an output pulse-stretched laser beam. The optical pulse stretcher includes a first-stage optical pulse stretcher, which includes two mirrors and is configured to receive a portion of the laser beam and generate a first pulse-stretched laser beam. The optical pulse stretcher also includes a second-stage optical pulse stretcher, which includes four or more mirrors and is configured to receive a portion of the first pulse-stretched laser beam and generate a second pulse-stretched laser beam. The optical pulse stretcher also includes a third-stage optical pulse stretcher, which includes four or more mirrors and is configured to receive a portion of the second pulse-stretched laser beam and generate an output pulse-stretched laser beam.

[0016] Another aspect of the present disclosure provides a lithographic apparatus, the lithographic apparatus comprising: an illumination system configured to condition a radiation beam; a support structure configured to support a pattern forming device; a substrate table configured to hold a substrate; and a projection system configured to project a pattern imparted to the radiation beam by the pattern forming device onto a target portion of the substrate. The illumination system comprises a laser source. The laser source comprises an optical pulse stretcher configured to receive the laser beam and generate an output pulse-stretched laser beam. The optical pulse stretcher comprises a first-stage optical pulse stretcher comprising a plurality of first confocal resonators and configured to receive a portion of the laser beam and generate a first pulse-stretched laser beam. The optical pulse stretcher also comprises a second-stage optical pulse stretcher comprising a plurality of second confocal resonators and configured to receive a portion of the first pulse-stretched laser beam and generate a second pulse-stretched laser beam. The optical pulse stretcher also includes a third stage optical pulse stretcher including a plurality of third confocal resonators and configured to receive a portion of the second pulse-stretched laser beam and generate an output pulse-stretched laser beam.

[0017] In some embodiments, the first stage optical pulse stretcher has a first optical delay. The second stage optical pulse stretcher has a second optical delay, which is equal to or greater than the first optical delay. The third stage optical pulse stretcher has a third optical delay, which is equal to or greater than the second optical delay.

[0018] Another aspect of the present disclosure provides an optical pulse stretcher configured to receive a laser beam and generate an output pulse-stretched laser beam. The optical pulse stretcher includes two or more confocal optical pulse stretchers stacked in the optical pulse stretcher. A first confocal optical pulse stretcher of the two or more confocal optical pulse stretchers is configured to receive a portion of the laser beam and generate a first pulse-stretched laser beam by reflecting the portion of the laser beam four times. A second confocal optical pulse stretcher of the two or more confocal optical pulse stretchers is configured to receive a portion of the first pulse-stretched laser beam and generate a second pulse-stretched laser beam by reflecting the portion of the first pulse-stretched laser beam twelve times.

[0019] Another aspect of the present disclosure provides an extended optical pulse stretcher. The extended optical pulse stretcher includes a first-stage optical pulse stretcher, which includes a plurality of first confocal resonators and is configured to receive a laser beam and generate a first pulse-stretched laser beam. The extended optical pulse stretcher also includes a stacked confocal pulse stretcher. The stacked confocal pulse stretcher includes a second-stage optical pulse stretcher, which includes a plurality of second confocal resonators and is configured to receive a portion of the first pulse-stretched laser beam and generate a second pulse-stretched laser beam. The stacked confocal pulse stretcher includes a third-stage optical pulse stretcher, which includes a plurality of third confocal resonators and is configured to receive a portion of the second pulse-stretched laser beam and generate a third pulse-stretched laser beam. The stacked confocal pulse stretcher includes a fourth-stage optical pulse stretcher, which includes a plurality of fourth confocal resonators and is configured to receive a portion of the third pulse-stretched laser beam and generate an output pulse-stretched laser beam. The first stage optical pulse stretcher is positioned perpendicular or approximately perpendicular to the stacked confocal pulse stretcher.

[0020] In some embodiments, the first stage optical pulse stretcher has a first optical delay. The second stage optical pulse stretcher has a second optical delay, which is equal to or greater than the first optical delay. The third stage optical pulse stretcher has a third optical delay, which is equal to or greater than the second optical delay. The fourth stage optical pulse stretcher has a fourth optical delay, which is equal to or greater than the second optical delay.

[0021] Another aspect of the present disclosure provides a method for generating a laser beam and directing the laser beam through an optical pulse stretcher. The optical pulse stretcher includes a first stage optical pulse stretcher, the first stage optical pulse stretcher includes a plurality of first confocal resonators, and is configured to receive a portion of the laser beam and generate a first pulse-stretched laser beam. The optical pulse stretcher also includes a second stage optical pulse stretcher, the second stage optical pulse stretcher includes a plurality of second confocal resonators, and is configured to receive a portion of the first pulse-stretched laser beam and generate a second pulse-stretched laser beam. The optical pulse stretcher also includes a third stage optical pulse stretcher, the third stage optical pulse stretcher includes a plurality of third confocal resonators, and is configured to receive a portion of the second pulse-stretched laser beam and generate an output pulse-stretched laser beam.

[0022] The structure and operation of other features and various embodiments are described in detail below with reference to the accompanying drawings. It should be noted that the present disclosure is not limited to the specific embodiments described herein. These embodiments presented herein are for illustrative purposes only. Based on the teachings contained herein, additional embodiments will be apparent to those skilled in the relevant art. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The accompanying drawings, which are incorporated herein and form a part of the specification, illustrate the present disclosure and, together with the description, further serve to explain the principles of the embodiments of the present disclosure and to enable those skilled in the relevant art to make and use the embodiments of the present disclosure.

[0024] Figure 1 is a schematic diagram of a reflective lithography apparatus according to an exemplary embodiment.

[0025] Figure 2 is a schematic diagram of a transmissive lithography apparatus according to an exemplary embodiment.

[0026] Figure 3 is a schematic diagram of a lithography cell according to an exemplary embodiment.

[0027] Figure 4 A schematic diagram of a laser source with an extended optical pulse stretcher according to some embodiments of the present disclosure is shown.

[0028] Figure 5A A schematic front view of an expanded optical pulse stretcher having a first optical pulse stretcher and a second optical pulse stretcher according to some embodiments of the present disclosure is shown.

[0029] Figure 5B A schematic top view of a second optical pulse stretcher according to some embodiments of the present disclosure is shown.

[0030] Figure 5CA schematic side view of an expanded optical pulse stretcher having a first optical pulse stretcher and a second optical pulse stretcher according to some embodiments of the present disclosure is shown.

[0031] Fig. 6A A schematic diagram showing a portion of the path of a laser beam in a second optical pulse stretcher according to some embodiments of the present disclosure.

[0032] Figure 6B A schematic diagram showing a portion of the path of a laser beam in a second optical pulse stretcher and a portion of a mirror used in the second optical pulse stretcher according to some embodiments of the present disclosure.

[0033] Fig. 7A A schematic top view of a first stage in a second optical pulse stretcher according to some embodiments of the present disclosure is shown.

[0034] Figure 7B A schematic top view of a second stage or a third stage in a second optical pulse stretcher according to some embodiments of the present disclosure is shown.

[0035] Figure 8 A schematic diagram showing a portion of the path of a laser beam in a first optical pulse stretcher according to some embodiments of the present disclosure.

[0036] Features of the present disclosure will become more apparent from the detailed description set forth below in conjunction with the accompanying drawings, in which the same reference numerals identify corresponding elements throughout. In the drawings, unless otherwise indicated, the same reference numerals generally indicate identical, functionally similar, and / or structurally similar elements. In addition, generally, the leftmost (multiple) digits in a reference numeral identify the drawing in which the reference numeral first appears. Unless otherwise indicated, the drawings provided throughout the disclosure should not be construed as drawings drawn to scale. DETAILED DESCRIPTION

[0037] This specification discloses one or more embodiments that include features of the present invention. The disclosed (multiple) embodiments are merely illustrative of the present invention. The scope of the present disclosure is not limited to the disclosed (multiple) embodiments. The breadth and scope of the present disclosure are defined by the appended claims and their equivalents.

[0038] The described embodiment(s) and references in the specification to "one embodiment," "an embodiment," "an example embodiment," etc. indicate that the described embodiment(s) may include a particular feature, structure, or characteristic, but each embodiment may not necessarily include the particular feature, structure, or characteristic. In addition, these terms do not necessarily refer to the same embodiment. Furthermore, when a particular feature, structure, or characteristic is described in conjunction with an embodiment, it should be understood that it is within the knowledge of those skilled in the art to affect such feature, structure, or characteristic in conjunction with other embodiments, whether or not explicitly described.

[0039] Spatially relative terms (such as "below," "below," "below," "above," "above," "on," etc.) may be used herein for convenience of description to describe the relationship of one element or feature to another element(s) or feature(s) as shown in the figures. 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 device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly.

[0040] The term "about" may be used herein to indicate a value of a given amount that may vary based on a particular technology. Based on a particular technology, the term "about" may indicate a value of a given amount that varies within, for example, 10% to 30% (e.g., ±10%, ±20%, or ±30% of a value).

[0041] However, before describing such embodiments in further detail, it is helpful to present an example environment in which embodiments of the present disclosure may be implemented.

[0042] Example Lithography System

[0043] Figure 1 and Figure 2Schematic diagrams of a lithographic apparatus 100 and a lithographic apparatus 100', respectively, in which embodiments of the present disclosure may be implemented. The lithographic apparatus 100 and the lithographic apparatus 100' each include the following: an illumination system (illuminator) IL configured to condition a radiation beam B (e.g., deep ultraviolet (DUV) radiation); a support structure (e.g., a mask stage) MT configured to support a pattern forming device (e.g., a mask, a reticle, or a dynamic pattern forming device) MA, and connected to a first positioner PM configured to precisely position the pattern forming device MA; and a substrate stage (e.g., a wafer stage) WT configured to hold a substrate (e.g., a resist-coated wafer) W, and connected to a second positioner PW configured to precisely position the substrate W. The lithographic apparatus 100 and 100' also have a projection system PS configured to project a pattern imparted to the radiation beam B onto a target portion (e.g., including one or more dies) C of the substrate W through the pattern forming device MA. In lithographic apparatus 100, patterning device MA and projection system PS are reflective. In lithographic apparatus 100', patterning device MA and projection system PS are transmissive.

[0044] The illumination system IL may include various types of optical components for directing, shaping or controlling the radiation beam B, such as refractive, reflective, catadioptric, magnetic, electromagnetic, electrostatic or other types of optical components, or any combination thereof.

[0045] The support structure MT holds the patterning device MA in a manner that depends on the orientation of the patterning device MA relative to the reference frame, the design of at least one of the lithographic apparatuses 100 and 100', and other conditions (such as whether the patterning device MA is held in a vacuum environment). The support structure MT may use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device MA. The support structure MT may be, for example, a frame or table that may be fixed or movable as required. By using sensors, the support structure MT may ensure that the patterning device MA is in a desired position (e.g. relative to the projection system PS).

[0046] The term “patterning device” MA should be broadly interpreted as any device that can be used to impart a pattern to the cross-section of the radiation beam B, such as a device for producing a pattern in a target portion C of the substrate W. The pattern imparted to the radiation beam B may correspond to a specific functional layer in a device being created in the target portion C to form an integrated circuit.

[0047] The pattern forming device MA can be a transmissive type (such as Figure 2 lithographic apparatus 100') or a reflective type (such as Figure 1100 in the lithographic apparatus). Examples of pattern forming devices MA include reticles, masks, programmable mirror arrays, and programmable LCD panels. Masks are known in lithography and include mask types such as binary, alternating phase shift, and attenuated phase shift, as well as various hybrid mask types. Examples of programmable mirror arrays employ a matrix arrangement of small mirrors, each of which can be individually tilted to reflect an incoming radiation beam in different directions. The tilted mirrors impart a pattern in a radiation beam B that is reflected by the matrix of small mirrors.

[0048] The term "projection system" PS may cover any type of projection system, including refractive, reflective, catadioptric, magnetic, electromagnetic and electrostatic optical systems, or any combination thereof, depending on the exposure radiation used or other factors such as the use of immersion liquid on the substrate W or the use of a vacuum.

[0049] The lithographic apparatus 100 and / or the lithographic apparatus 100' may be of a type having two (dual stage) or more substrate tables WT (and / or two or more mask tables). In such a "multi-stage" machine, the additional substrate tables WT may be used in parallel, or preparation steps may be performed on one or more tables while one or more other substrate tables WT are being used for exposure. In some cases the additional tables may not be substrate tables WT.

[0050] The lithographic apparatus may also be of a type in which at least a portion of the substrate may be covered by a liquid having a relatively high refractive index, such as water, so as to fill the space between the projection system and the substrate. Immersion liquid may also be applied to other spaces in the lithographic apparatus, for example, between the mask and the projection system. Immersion techniques for increasing the numerical aperture of the projection system are known in the art. The term "immersion" as used herein does not mean that structures such as the substrate must be immersed in the liquid, but only means that the liquid is located between the projection system and the substrate during exposure.

[0051] Reference Figure 1 and Figure 2 , the illuminator IL receives a radiation beam from a radiation source SO. For example, when the source SO is an excimer laser, the source SO and the lithographic apparatus 100, 100' may be separate physical entities. In this case, the source SO is not considered to form part of the lithographic apparatus 100 or 100', and the radiation beam B is delivered to the lithographic apparatus 100 or 100' by the beam delivery system BD (in Figure 2 The beam is transferred from the source SO to the illuminator IL with the help of a beam delivery system BD, which includes, for example, suitable pointing mirrors and / or a beam expander. In other cases, the source SO may be an integral part of the lithographic apparatus 100, 100' - for example when the source SO is a mercury lamp. If desired, the source SO and the illuminator IL together with the beam delivery system BD may be referred to as a radiation system.

[0052] The illuminator IL may comprise an adjuster AD (at Figure 2 Typically, at least the outer and / or inner diameter extent of the intensity distribution in a pupil plane of the illuminator (commonly referred to as "σ-outer" and "σ-inner", respectively) can be adjusted. In addition, the illuminator IL may include various other components (in Figure 2 In the embodiment of the present invention, an integrator IN and a condenser CO are provided, such as an illuminator IL. The illuminator IL can be used to condition the radiation beam B to have a desired uniformity and intensity distribution in its cross-section.

[0053] Reference Figure 1 , a radiation beam B is incident on a patterning device (e.g., a mask) MA, which is held on a support structure (e.g., a mask table) MT, and the radiation beam B is patterned by the patterning device MA. In the lithographic apparatus 100, the radiation beam B is reflected from the patterning device (e.g., a mask) MA. After being reflected from the patterning device (e.g., a mask) MA, the radiation beam B passes through a projection system PS, which focuses the radiation beam B onto a target portion C of a substrate W. With the help of a second positioner PW and a position sensor IF2 (e.g., an interferometric measurement device, a linear encoder, or a capacitive sensor), the substrate table WT can be precisely moved (e.g., so as to position a different target portion C into the path of the radiation beam B). Similarly, a first positioner PM and a further position sensor IF1 can be used to precisely position the patterning device (e.g., a mask) MA relative to the path of the radiation beam B. The patterning device (e.g., a mask) MA and the substrate W can be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2.

[0054] Reference Figure 2 , the radiation beam B is incident on a patterning device (e.g., mask MA), which is held on a support structure (e.g., mask table MT), and the radiation beam B is patterned by the patterning device. After passing through the mask MA, the radiation beam B passes through a projection system PS, which focuses the beam onto a target portion C of the substrate W. The projection system has a pupil PPU conjugate to the illumination system pupil IPU. Portions of the radiation emanate from the intensity distribution at the illumination system pupil IPU and pass through the mask pattern without being affected by diffraction at the mask pattern, and produce an image of the intensity distribution at the illumination system pupil IPU.

[0055] The projection system PS projects an image MP' of the mask pattern MP onto a photoresist layer coated on a substrate W, wherein the image MP' is formed by a diffraction beam generated by radiation from the mask pattern MP according to an intensity distribution. For example, the mask pattern MP may include an array of lines and spaces. The diffraction of the radiation at the array is different from the zero-order diffraction, generating a diffraction beam deflected in a direction perpendicular to the line, and the deflected diffraction beam has a change in direction. The undiffracted beam (the so-called zero-order diffraction beam) passes through the pattern without any change in the propagation direction. The zero-order diffraction beam passes through the upper lens or upper lens group of the projection system PS upstream of the pupil conjugate PPU of the projection system PS to reach the pupil conjugate PPU. The portion of the intensity distribution in the plane of the pupil conjugate PPU and associated with the zero-order diffraction beam is an image of the intensity distribution in the illumination system pupil IPU of the illumination system IL. For example, the aperture device PD is arranged or substantially arranged at a plane including the pupil conjugate PPU of the projection system PS.

[0056] The projection system PS is arranged to capture not only the zeroth order diffraction beam, but also the first order or first and higher order diffraction beams (not shown) by means of a lens or lens group L. In some embodiments, dipole illumination for imaging a line pattern extending in a direction perpendicular to the line can be used to exploit the resolution enhancement effect of dipole illumination. For example, a first order diffraction beam interferes with the corresponding zeroth order diffraction beam at the level of the wafer W to produce an image of the line pattern MP at the highest possible resolution and process window (i.e., the available focal depth combined with a tolerable exposure dose deviation).

[0057] With the aid of a second positioner PW and a position sensor IF (e.g. an interferometric device, a linear encoder or a capacitive sensor), the substrate table WT can be accurately moved (e.g. in order to position a different target portion C into the path B of the radiation beam). Similarly, the first positioner PM and another position sensor ( Figure 2 ) can be used to accurately position the mask MA relative to the path of the radiation beam B (for example, after mechanical retrieval from a mask library or during scanning).

[0058] Movement of the mask table MT can be achieved with the help of a long-stroke module (rough positioning) and a short-stroke module (fine positioning), which form part of the first positioner PM. Similarly, the long-stroke module and the short-stroke module, which form part of the second positioner PW, can be used to achieve movement of the substrate table WT. In the case of a stepper (as opposed to a scanner), the mask table MT may be connected only to a short-stroke actuator or may be fixed. The mask MA and the substrate W may be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. Although the substrate alignment marks (as shown) occupy dedicated target portions, they can be located in the space between the target portions (called scribe alignment marks). Similarly, in the case where more than one die is provided on the mask MA, the mask alignment marks may be located between the dies.

[0059] The mask table MT and the patterning device MA can be in a vacuum chamber, wherein an in-vacuum robot IVR can be used to move the patterning device (such as a mask) into and out of the vacuum chamber. Alternatively, when the mask table MT and the patterning device MA are outside the vacuum chamber, various transport operations can be performed using an out-of-vacuum robot, similar to the in-vacuum robot IVR. Both the in-vacuum robot and the out-of-vacuum robot need to be calibrated for smooth transfer of any payload (e.g., a mask) to the fixed kinematic support of the transfer station.

[0060] The lithographic apparatus 100 and 100' may be used in at least one of the following modes:

[0061] 1. In step mode, the support structure (e.g. mask table) MT and the substrate table WT remain substantially stationary while an entire pattern imparted to the radiation beam B is projected at one time onto a target portion C (i.e. a single static exposure). The substrate table WT is then shifted in the X and / or Y direction so that a different target portion C can be exposed.

[0062] 2. In scan mode, the support structure (e.g. mask table) MT and the substrate table WT are scanned synchronously while a pattern imparted to the radiation beam B is projected onto a target portion C (i.e. a single 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 (de)magnification and image reversal characteristics of the projection system PS.

[0063] 3. In another mode, the support structure (e.g. mask table) MT is maintained substantially stationary to hold the programmable patterning device, and the substrate table WT is moved or scanned whilst a pattern imparted to the radiation beam B is projected onto a target portion C. A pulsed radiation source SO may be employed, and the programmable patterning device may be updated as required after each movement of the substrate table WT or between successive radiation pulses during a scan. This mode of operation may be readily applied to maskless lithography using a programmable patterning device, such as a programmable mirror array.

[0064] Combinations and / or variations of the described modes of use or entirely different modes of use may also be employed.

[0065] Exemplary Lithography Cell

[0066] Figure 3 A lithographic unit 300 is shown, sometimes also referred to as a lithocell or cluster. The lithographic apparatus 100 or 100' may form part of the lithographic unit 300. The lithographic unit 300 may also include equipment for performing pre-exposure and post-exposure processes on a substrate. Typically these devices include a spin coater SC for depositing a resist layer, a developer DE for developing the exposed resist, a cooling plate CH and a baking plate BK. A substrate handler or robot RO picks up substrates from input / output ports I / O1, I / O2, moves them between different processing devices, and delivers them to a feed station LB of the lithographic apparatus 100 or 100'. These devices (generally referred to as tracks) are under the control of a track control unit TCU, which itself is controlled by a management control system SCS, which also controls the lithographic apparatus via a lithographic control unit LACU. Therefore, different devices may be operated to maximize throughput and processing efficiency.

[0067] Exemplary stacked confocal pulse stretcher series

[0068] According to some embodiments, a laser source is provided with one or more extended optical pulse stretchers comprising a stacked series of optical pulse stretchers. According to some embodiments, the laser source may be used as part of or in addition to a source SO of a lithographic apparatus 100 or 100'. Additionally or alternatively, the laser source may be used to generate DUV radiation to be used in the lithographic apparatus 100 or 100' or other DUV lithographic apparatus.

[0069] According to some embodiments, the laser source may be a gas discharge laser source, such as a KrF or ArF or a molecular fluorine gas discharge laser. In some examples, an extended optical pulse stretcher including the stacked optical pulse stretcher series of the present disclosure may have a long optical delay, but is constrained to have a practical physical length for being mounted on an existing laser frame or contained within a beam delivery unit and adapted, for example, in a manufacturing facility clean room floor chamber. According to some embodiments, the extended optical pulse stretcher of the present disclosure combines confocal pulse stretchers to produce 4 reflections, 4 reflections, 12 reflections, and 12 reflections for each optical path configuration in combination. According to some embodiments, a combination including different reflector separations and delay path lengths (e.g., 4 reflection and 12 reflection delay lengths) may result in very long pulse stretching, long optical delay, and minimal efficiency loss. Embodiments of the present disclosure may also minimize the number of adjustments required for the alignment system and may allow for a considerable amount of misalignment. According to some embodiments, the extended optical pulse stretcher of the present disclosure may use different combinations of mirrors in different optical paths to produce 4 reflections, 4 reflections, 12 reflections, and 12 reflections, but other numbers of reflections may be used in other embodiments. Additionally or alternatively, in the extended optical pulse stretcher of the present disclosure, one or more beam splitters are positioned relative to the center of curvature of the mirrors to "flatten" each of the optical paths so that the beams can propagate in the same plane (e.g., parallel to the floor). Additionally or alternatively, the curvature and size of the individual mirrors can be designed to position one or more beam splitters closer to one of the mirrors in the mirror group to allow the upper beam splitter to be placed after the excimer laser cavity to allow the pulse stretcher to fit correctly at the assigned position in the laser system.

[0070] According to some embodiments, the extended optical pulse stretcher of the present disclosure may be implemented in a nitrogen purge environment. Alternatively, the extended optical pulse stretcher of the present disclosure may be implemented in a vacuum environment.

[0071] Figure 4 Schematic diagram of a laser source 400 with an extended optical pulse stretcher 401 according to some embodiments of the present disclosure is shown. In some embodiments, the laser source 400 may be used as part of a source SO of a lithographic apparatus 100 or 100' or as a source in addition to the source SO. Additionally or alternatively, the laser source 400 may be provided at Figure 2 Additionally or alternatively, the laser source 400 may be used to generate DUV radiation to be used in the lithographic apparatus 100 or 100 ′ or other DUV lithographic apparatus.

[0072] like Figure 4As shown, the laser source 400 may include a dual-chamber laser source. For example, the laser source 400 may include a first laser chamber 403a and a second laser chamber 403b. In an exemplary embodiment, the first laser chamber 403a may include a master oscillator or a portion of a master oscillator. For example, the laser source 400 may include a master oscillator, wherein the master source includes the first laser chamber 403a. In this example, the second laser chamber 403b may include a power amplifier or a portion of a power amplifier. For example, the laser source may include a power amplifier, wherein the power amplifier includes the second laser chamber 403b. Although some embodiments are discussed for a dual-chamber laser source, embodiments of the present disclosure are not limited to these examples. Embodiments of the present disclosure may be applied to a laser source having one chamber or a laser source having multiple laser chambers.

[0073] According to some embodiments, the first chamber 403a generates a first laser beam 409, which is transferred to the second laser chamber 403b, where the first laser beam 409 is amplified to generate a second laser beam 411. The second laser beam 411 is input to the extended optical pulse stretcher 401, where copies of the second laser beam 411 are delayed and recombined to reduce speckle. A third laser beam 413 is output from the extended optical pulse stretcher to a lithography apparatus (e.g., lithography apparatus 100 and / or 110').

[0074] According to some embodiments, each laser chamber 403a and 403b contains a gas mixture. For example, in an excimer laser source, the first laser chamber 403a and the second laser chamber 403b may contain halogens (e.g., fluorine and other gases, such as argon, neon), and possible other gases at different partial pressures (total pressure). The laser chambers 403a and 403b may include other gases for generating and amplifying the laser beam. Additionally or alternatively, the laser chambers 403a and 403b may include the same or different gas mixtures.

[0075] In some embodiments, the laser source 400 may include (or may be coupled to) gas sources (e.g., gas cylinders) 420a and 420b. For example, the gas source 420a may be coupled to the first laser chamber 403a to provide a gas mixture for generating the first laser beam 409. In addition, the gas source 420b may be coupled to the second laser chamber 403b to provide a gas mixture for generating the second laser beam 411. In some examples, the gas sources 420a and 420b may be coupled to the laser chambers 403a and 403b, respectively, via valves (not shown). A control system (not shown) may be used to control the valves for sending gas from the gas sources 420a and 420b to the laser chambers 403a and 403b.

[0076] In some embodiments, gas source 420a may include a gas mixture including, but not limited to, fluorine, argon, and neon. According to some embodiments, gas source 420b may include a mixture of argon, neon, and / or other gases, but not fluorine. However, other gas mixtures may be used in gas sources 420a and 420b.

[0077] According to some embodiments, and as discussed above, the extended optical pulse stretcher 401 is configured to receive the second laser beam 411 and delay and recombine a copy of the second laser beam 411 to reduce speckle. In some examples, the speckle contrast may be defined using an intensity pattern of bright and dark spots generated by interference of coherent light. The intensity contrast of bright and dark areas in the speckle pattern may be a measure of coherence. In some examples, temporal coherence and spatial coherence may contribute to the overall coherence. The speckle contrast may be defined as the standard deviation of the intensity variation divided by the mean intensity. In some examples, the speckle contrast may be estimated based on laser parameters.

[0078] According to some embodiments, the extended optical pulse stretcher 401 may include two parts - a first optical pulse stretcher 401a and a second optical pulse stretcher 401b. For example, the first optical pulse stretcher 401a receives the second laser beam 411 and delays and recombine the copies of the second laser beam 411 to generate a first output laser beam. The first output laser beam is input to the second optical pulse stretcher 401b. The second optical pulse stretcher 401b receives the first output laser beam and delays and recombine the copies of the first output laser beam to generate a second output laser beam. The second output laser beam is input to the first optical pulse stretcher 401a, where the second output laser beam is redirected into a third laser beam 413.

[0079] According to some embodiments, the second optical pulse stretcher 401b includes a stacked series of optical pulse stretchers. In other words, a plurality of optical pulse stretchers are stacked in the second optical pulse stretcher 401b. Each level of optical pulse stretcher in the optical pulse stretcher level (e.g., a level optical pulse stretcher) includes a plurality of confocal resonators. For example, the optical pulse stretcher 401b may include a first-level optical pulse stretcher, which includes a plurality of first confocal resonators. The optical pulse stretcher 401b also includes a second-level optical pulse stretcher, which includes a plurality of second confocal resonators. The optical pulse stretcher 401b also includes a third-level optical pulse stretcher, which includes a plurality of third confocal resonators. According to some examples, a plurality of first confocal resonators include two rectangular concave mirrors, a plurality of second confocal resonators include four rectangular concave mirrors, and a plurality of third confocal resonators include four rectangular concave mirrors. However, embodiments of the present disclosure may include other numbers of optical pulse stretchers in the optical pulse stretcher 401b, and each optical pulse stretcher may include other numbers of confocal resonators. In addition, embodiments of the present disclosure may include other types of mirrors as confocal resonators. Figure 4 The relative orientation of the first optical pulse stretcher 401a and the second optical pulse stretcher 401b in the orthogonal arrangement is provided by way of example only, and other relative configurations and orientations may be used in other embodiments.

[0080] Figure 5A A schematic front view of an extended optical pulse stretcher 401 having a first optical pulse stretcher 401a and a second optical pulse stretcher 401b is shown according to some embodiments of the present disclosure.

[0081] According to some embodiments, and as discussed in more detail below, the first optical pulse stretcher 401a may include a first-order optical pulse stretcher 507 having an optical design that includes four mirrors (a first mirror pair 509 and a second mirror pair 510) that generate four reflections of the laser beam between them. Although this example is discussed using four mirrors, the first-order optical pulse stretcher 507 may include other numbers of mirrors. These mirrors may be positioned to generate four reflections of the laser beam. In some embodiments, the two mirror pairs 509 and 510 of the first-order optical pulse stretcher 507 of the first optical pulse stretcher 401a may be separated from each other by a physical distance of about 1m-3m. For example, the physical distance may be about 1.5m to 2.5m. These distances are provided as examples only, and other distances may be used in other embodiments. In some examples, the first-order optical pulse stretcher 507 of the first optical pulse stretcher 401a is capable of performing optical pulse stretching, for example, with an optical delay of about 30ns-50ns. For example, an optical delay of about 35ns-45ns. For example, an optical delay of about 40ns-44ns. It should be noted that the example physical distance and example optical delay between the two reflectors provided do not limit the embodiments of the present disclosure. The first optical pulse stretcher 401a can be designed to achieve various other physical distances and / or various optical delays.

[0082] According to some embodiments, each of the mirrors in the two mirror pairs 509 and 510 of the first-stage optical pulse stretcher 507 of the first optical pulse stretcher 401a may include a circular concave mirror.

[0083] According to some embodiments, the first optical pulse stretcher 401a may include additional optical elements. In one example, the primary optical pulse stretcher 507 of the first optical pulse stretcher 401a may include a beam splitter 511 for separating the laser beam 411 and generating a copy of the laser beam 411. The beam splitter 511 of the first optical pulse stretcher 401a may have a reflectivity of, for example, about 50%-70%. In some examples, the beam splitter 511 may have a reflectivity of about 55%-65%. However, the embodiments of the present disclosure are not limited to these examples, and various other reflectivity values ​​may be used. In some examples, the reflectivity of the beam splitter 511 may depend on the reflectivity of the mirror used in the first optical pulse stretcher 401a and / or be calculated based on the reflectivity of the mirror used in the first optical pulse stretcher 401a.

[0084] Additionally, the first optical pulse stretcher 401a may include beam tuning, beam relaying, and / or alignment features.

[0085] According to some embodiments, and as discussed in more detail below, the second optical pulse stretcher 401b can include two or more (e.g., three) levels of confocal optical pulse stretchers. In some examples, the three levels of confocal optical pulse stretchers can be positioned approximately parallel to each other in the second optical pulse stretcher 401b. In some embodiments, the second optical pulse stretcher 401b can be positioned perpendicular or approximately perpendicular to the first optical pulse stretcher 401a. In other words, in some embodiments, the first optical pulse stretcher 401a (e.g., an orthogonal optical pulse stretcher that can be positioned vertically) is positioned perpendicular or approximately perpendicular to the two or more (e.g., three) levels of confocal optical pulse stretchers of the second optical pulse stretcher 401b. According to some embodiments, the second optical pulse stretcher 401b is designed such that it provides additional optical delay, enables very long pulse stretching, is stable, may not require additional adjustments for alignment, and may be mounted on an existing laser frame or contained within a beam delivery unit and fit into the available laser volume (e.g., fits into a manufacturing facility clean room floor chamber). For example, the second optical pulse stretcher 401b may fit into a small space, such as above the first laser chamber 403a.

[0086] According to some embodiments, the extended optical pulse stretcher 401 combines two or more confocal optical pulse stretchers. For example, the extended optical pulse stretcher 401 combines confocal optical pulse stretchers in a combination of 4 reflections, 4 reflections, 12 reflections, and 12 reflections per optical path configuration. According to some embodiments, combinations including different reflector separations and delay path lengths (e.g., 4 reflection and 12 reflection delay lengths) can result in very long pulse stretching with minimal efficiency loss.

[0087] According to some embodiments, the second optical pulse stretcher 401b may include a three-stage confocal optical pulse stretcher. However, the embodiments of the present disclosure are not limited to these examples, and the second optical pulse stretcher 401b may include confocal optical pulse stretchers of other numbers of levels. In some examples, the first-stage second optical pulse stretcher 401b is discussed as having two mirrors. However, the embodiments of the present disclosure are not limited to these examples, and the first-stage second optical pulse stretcher 401b may include other numbers (e.g., two or more) and / or configurations of mirrors. In some examples, the multiple mirrors used in the first-stage second optical pulse stretcher 401b are configured to generate four reflections of the laser beam between them.

[0088] In some examples, the second-stage second optical pulse stretcher 401b is discussed as having four mirrors. However, embodiments of the present disclosure are not limited to these examples, and the second-stage second optical pulse stretcher 401b may include other numbers (e.g., four or more) and / or configurations of mirrors. In some examples, the plurality of mirrors used in the second-stage second optical pulse stretcher 401b are configured to generate twelve reflections of the laser beam between them.

[0089] In some examples, the third-stage second optical pulse stretcher 401b is discussed as having four mirrors. However, embodiments of the present disclosure are not limited to these examples, and the third-stage second optical pulse stretcher 401b may include other numbers (e.g., four or more) and / or configurations of mirrors. In some examples, the plurality of mirrors used in the third-stage second optical pulse stretcher 401b are configured to generate twelve reflections of the laser beam between them.

[0090] According to some embodiments, the first optical pulse stretcher 401a and the second optical pulse stretcher 401b are designed so that the optical delay from the first optical pulse stretcher 401a to the second optical pulse stretcher 401b increases. Moreover, the optical delay of each second optical pulse stretcher 401b from the first stage to the third stage increases. For example, the first optical pulse stretcher 401a (e.g., an orthogonal optical pulse stretcher) may have an optical delay. The first-stage second optical pulse stretcher 401b may have a first optical delay, which is equal to or greater than the optical delay of the first optical pulse stretcher 401a. The second-stage second optical pulse stretcher 401b may have a second optical delay, which is equal to or greater than the first optical delay. The third-stage second optical pulse stretcher 401b may have a third optical delay, which is equal to or greater than the second optical delay. According to some embodiments, the optical delay may be determined based on the distance traveled by the light beam in the optical pulse stretcher.

[0091] According to some embodiments, the first-stage second optical pulse stretcher 401b may have a structure including two mirrors (eg, Figure 5AThe optical design of the first-stage second optical pulse stretcher 401b is a reflector 501 in the first stage and two lower reflectors in 502, which generate four reflections of the laser beam between them. Although this example is discussed using two reflectors, the first-stage second optical pulse stretcher 401b may include other numbers of reflectors (e.g., two or more reflectors). These reflectors may be positioned to generate four reflections of the laser beam between them. In some embodiments, the two reflectors in the first-stage second optical pulse stretcher 401b may be separated from each other by a physical distance of about 2m-4m. For example, the physical distance may be about 2.5m to 3.5m. These distances are provided only as examples, and other distances may be used in other embodiments. In some examples, the first-stage second optical pulse stretcher 401b is capable of optical pulse stretching, which optical pulse stretching has, for example, an optical delay of about 60ns-80ns. For example, an optical delay of about 65ns-75ns. For example, an optical delay of about 70ns-75ns. It should be noted that the example physical distance and example optical delay between the two mirrors provided do not limit the embodiments of the present disclosure. The first-stage second optical pulse stretcher 401b can be designed to achieve various other physical distances and / or various optical delays.

[0092] According to some embodiments, the reflectors in the first-stage second optical pulse stretcher 401b (e.g., the two lower reflectors in the reflectors 501 and 502) may include rectangular concave reflectors. For example, two large rectangular concave reflectors may be used, but other shapes may be used in other embodiments. According to some embodiments, the reflective surface of the reflector may be spherically concave, so that the distance between the two reflectors in the first-stage second optical pulse stretcher 401b (e.g., the surfaces of the two lower reflectors in the reflectors 501 and 502) is equal to (or approximately equal to) the radius of curvature of each of the two reflectors. For example, the reflectors may be designed and positioned based on a telecentric design. According to some embodiments, the concave reflector may be designed using orthogonal tilt-dump adjustments and Z-axis (e.g., beam propagation direction) adjustments.

[0093] According to some embodiments, the first-stage second optical pulse stretcher 401b may include additional optical elements. In one example, the first-stage second optical pulse stretcher 401b may include a beam splitter ( Figure 5AThe lower beam splitter in the beam splitter 503 of the first-stage second optical pulse stretcher 401b) is used to separate the laser beam and generate a copy of the laser beam. The beam splitter in the first-stage second optical pulse stretcher 401b can have a reflectivity of, for example, approximately 45%-65%. In some examples, the beam splitter can have a reflectivity of approximately 50%-60%. However, the embodiments of the present disclosure are not limited to these examples, and various other reflectivity values ​​can be used. In some examples, the reflectivity of the beam splitter can depend on the reflectivity of the mirror used in the first-stage second optical pulse stretcher 401b and / or be calculated based on the reflectivity of the mirror used in the first-stage second optical pulse stretcher 401b.

[0094] According to some embodiments, the second-stage second optical pulse stretcher 401b may have a structure including four mirrors (eg, Figure 5A The optical design of the second-stage second optical pulse stretcher 401b (reflector 501 in the second stage and four intermediate reflectors in 502) produces twelve reflections of the laser beam between them. Although this example is discussed using four reflectors, the second-stage second optical pulse stretcher 401b may include other numbers of reflectors (e.g., four or more reflectors). These reflectors may be positioned to generate twelve reflections of the laser beam between them. In some embodiments, the two reflector pairs in the second-stage second optical pulse stretcher 401b may be separated from each other by a physical distance of about 2m-4m. For example, the physical distance may be about 2.5m to 3.5m. These distances are provided only as examples, and other distances may be used in other embodiments. In some examples, the second-stage second optical pulse stretcher 401b is capable of optical pulse stretching, which, for example, has an optical delay of about 170ns-210ns. For example, an optical delay of about 180ns-190ns. For example, an optical delay of about 185ns-195ns. It should be noted that the exemplary physical distance and exemplary optical delay between the two mirror pairs provided do not limit the embodiments of the present disclosure. The second stage second optical pulse stretcher 401b can be designed to achieve various other physical distances and / or various optical delays.

[0095] According to some embodiments, the reflectors in the second-stage second optical pulse stretcher 401b (e.g., four intermediate reflectors in reflectors 501 and 502) may include rectangular concave reflectors. For example, four large rectangular concave reflectors may be used, but other shapes may be used in other embodiments. According to some embodiments, the reflective surface of the reflector may be spherically concave, so that the distance between two reflector pairs in the second-stage second optical pulse stretcher 401b (e.g., the surfaces of two intermediate reflector pairs in reflectors 501 and 502) is equal to (or approximately equal to) the radius of curvature of each of the four reflectors. For example, the reflectors may be designed and positioned based on a telecentric design. According to some embodiments, the concave reflectors may be designed using orthogonal tilt-dump adjustments.

[0096] According to some embodiments, the second stage second optical pulse stretcher 401b may include additional optical elements. In one example, the second stage second optical pulse stretcher 401b may include a beam splitter ( Figure 5A The beam splitter 503 of the second-stage second optical pulse stretcher 401b is used to separate the laser beam and generate a copy of the laser beam. The beam splitter in the second-stage second optical pulse stretcher 401b can have a reflectivity of, for example, approximately 45%-65%. In some examples, the beam splitter can have a reflectivity of approximately 50%-60%. However, the embodiments of the present disclosure are not limited to these examples, and various other reflectivity values ​​can be used. In some examples, the reflectivity of the beam splitter can depend on the reflectivity of the mirror used in the second-stage second optical pulse stretcher 401b and / or be calculated based on the reflectivity of the mirror used in the second-stage second optical pulse stretcher 401b.

[0097] According to some embodiments, the third-stage second optical pulse stretcher 401b may be similar to or identical to the second-stage second optical pulse stretcher 401b. For example, the third-stage second optical pulse stretcher 401b may have a structure including four mirrors (e.g., Figure 5AThe optical design of the second optical pulse stretcher 401b of the third stage 401b (reflectors 501 in the third stage 401b and four top reflectors in 502) produces twelve reflections of the laser beam between them. Although this example is discussed using four reflectors, the third stage second optical pulse stretcher 401b may include other numbers of reflectors (e.g., four or more reflectors). These reflectors may be positioned to generate twelve reflections of the laser beam between them. In some embodiments, the two reflector pairs in the third stage second optical pulse stretcher 401b may be separated from each other by a physical distance of approximately 2m-4m. For example, the physical distance may be approximately 2.5m to 3.5m. These distances are provided as examples only, and other distances may be used in other embodiments. According to some examples, the distances between the reflectors in the second optical pulse stretchers 401b of different stages may be similar or identical.

[0098] In some examples, the second stage second optical pulse stretcher 401b is capable of optical pulse stretching, for example, the optical pulse stretching has an optical delay of about 150ns-190ns. For example, an optical delay of about 160ns-180ns. For example, an optical delay of about 165ns-175ns. It should be noted that the exemplary physical distance and exemplary optical delay between the two mirror pairs provided do not limit the embodiments of the present disclosure. The third stage second optical pulse stretcher 401b can be designed to achieve various other physical distances and / or various optical delays.

[0099] According to some embodiments, the reflectors in the third-stage second optical pulse stretcher 401b (e.g., the four top reflectors in the reflectors 501 and 502) may include rectangular concave reflectors. For example, four large rectangular concave reflectors may be used, but other shapes may be used in other embodiments. According to some embodiments, the reflective surface of the reflector may be spherically concave, so that the distance between two reflector pairs in the third-stage second optical pulse stretcher 401b (e.g., the surfaces of the two top reflector pairs in the reflectors 501 and 502) is equal to (or approximately equal to) the radius of curvature of each of the four reflectors. For example, the reflectors may be designed and positioned based on a telecentric design. According to some embodiments, the concave reflectors may be designed using an orthogonal tilt-dump adjustment.

[0100] According to some embodiments, the third-stage second optical pulse stretcher 401b may include additional optical elements. In one example, the third-stage second optical pulse stretcher 401b may include a beam splitter ( Figure 5AThe top beam splitter in the beam splitter 503 of the third-stage second optical pulse stretcher 401b is used to separate the laser beam and generate a copy of the laser beam. The beam splitter of the third-stage second optical pulse stretcher 401b can have a reflectivity of, for example, approximately 45%-65%. In some examples, the beam splitter can have a reflectivity of approximately 50%-60%. However, the embodiments of the present disclosure are not limited to these examples, and various other reflectivity values ​​can be used. In some examples, the reflectivity of the beam splitter can depend on the reflectivity of the mirror used in the third-stage second optical pulse stretcher 401b and / or be calculated based on the reflectivity of the mirror used in the third-stage second optical pulse stretcher 401b.

[0101] The second optical pulse stretcher 401b may include additional optical elements. For example, the second optical pulse stretcher 401b may include mirrors 505a and 505b. The mirrors 505a and 505b may be used to direct the optically stretched laser beam back to the first optical pulse stretcher 401a, where the optically stretched laser beam may be output from the laser source 400 as the third laser beam 413. It should be noted that according to some embodiments, the optically stretched laser beam redirected toward the first optical pulse stretcher 401a does not pass through the stage 507 of the first optical pulse stretcher 401a, but is redirected as the third laser beam 413 of the output laser source 400.

[0102] According to some embodiments, reflectors 505a and 505b may include s-polarizing mirrors mounted at approximately 45 degrees (to provide an angle of incidence of approximately 45 degrees). However, other examples and / or orientations of reflectors 505a and 505b may be used with embodiments of the present disclosure.

[0103] Figure 5B A schematic top view of a second optical pulse stretcher 401b is shown according to some embodiments of the present disclosure. Figure 5C A schematic side view of an extended optical pulse stretcher 401 having a first optical pulse stretcher 401a and a second optical pulse stretcher 401b is shown according to some embodiments of the present disclosure.

[0104] exist Figure 5B In the top view of the second optical pulse stretcher 401b, four mirrors in the third-stage second optical pulse stretcher 401b are shown, for example. The four mirrors may include two mirror pairs - mirrors 501d and 501e and mirrors 502d and 502e. Figure 5B The top view also shows the beam splitter 503. Figure 7B The reflection and propagation of the laser beam between the four mirrors of the second optical pulse stretcher 401b of the second and third stages are further discussed.

[0105] exist Figure 5CIn the side view of the first optical pulse stretcher 401a and the second optical pulse stretcher 401b, five mirrors on one side of the second optical pulse stretcher 401b are shown. In this example, the reflector 502a in the first-stage second optical pulse stretcher 401b is shown. The reflector (e.g., the reflector 501a) is on the other side of the first-stage second optical pulse stretcher 401b, which is not shown in this view. In this example, a reflector pair 502b and 502c in the second-stage second optical pulse stretcher 401b is shown. Another reflector pair (e.g., the reflector pair 501b and 501c) is located on the other side of the second-stage second optical pulse stretcher 401b, which is not shown in this view. In addition, in this example, a reflector pair 502d and 502e in the third-stage second optical pulse stretcher 401b is shown. Another mirror pair (eg, mirror pair 501d and 501e) is located on the other side of the third stage second optical pulse stretcher 401b, which is not shown in this view.

[0106] Fig. 6A A schematic diagram showing a portion of the path of a laser beam in a second optical pulse stretcher 401b according to some embodiments of the present disclosure.

[0107] like Fig. 6A As shown, laser beam 601 optically stretched using the first stage optical pulse stretcher 401a enters second optical pulse stretcher 401b. Laser beam 601 is split into laser beam 603 and laser beam 605 using first beam splitter 503a. Laser beam 605 enters second stage second optical pulse stretcher 401b. Laser beam 603 enters first stage second optical pulse stretcher 401b including two mirrors. After four reflections from two mirrors in first stage second optical pulse stretcher 401b (e.g., as shown in FIG. 5 ), laser beam 603 enters first stage second optical pulse stretcher 401b including two mirrors. Fig. 7A As shown), the laser beam enters the second-stage second optical pulse stretcher 401b using a beam splitter 503a.

[0108] Laser beam 605 (and / or laser beam from first-stage second optical pulse stretcher 401b) is split into laser beam 607 and laser beam 609. Laser beam 609 enters third-stage second optical pulse stretcher 401b. Laser beam 607 enters second-stage second optical pulse stretcher 401b, which includes four mirrors. After twelve reflections from four mirrors in second-stage second optical pulse stretcher 401b (e.g., Figure 7B As shown), the laser beam enters the third-stage second optical pulse stretcher 401b using a beam splitter 503b.

[0109] Laser beam 609 (and / or the laser beam from the second-stage second optical pulse stretcher 401b) is split into laser beam 611 and laser beam 613. Laser beam 613 is reflected back to first optical pulse stretcher 401a using mirrors 505a and 505b. Laser beam 611 enters third-stage second optical pulse stretcher 401b including four mirrors. After twelve reflections from four mirrors in third-stage second optical pulse stretcher 401b (e.g., Figure 7B As shown), the laser beam is reflected back to the first optical pulse stretcher 401a using a beam splitter 503c and mirrors 505a and 505b.

[0110] Figure 6B A schematic diagram showing a portion of the path of a laser beam in a second optical pulse stretcher 401b and a portion of a mirror used in the second optical pulse stretcher 401b according to some embodiments of the present disclosure.

[0111] exist Figure 6B , five reflectors on one side of the second optical pulse stretcher 401b are shown. In this example, the reflector 502a in the first-stage second optical pulse stretcher 401b is shown. The reflector (e.g., the reflector 501a) is on the other side of the first-stage second optical pulse stretcher 401b, which is not shown in this view. In this example, a reflector pair 502b and 502c in the second-stage second optical pulse stretcher 401b is shown. Another reflector pair (e.g., the reflector pair 501b and 501c) is located on the other side of the second-stage second optical pulse stretcher 401b, which is not shown in this view. In addition, in this example, a reflector pair 502d and 502e in the third-stage second optical pulse stretcher 401b is shown. Another reflector pair (e.g., the reflector pair 501d and 501e) is located on the other side of the third-stage second optical pulse stretcher 401b, which is not shown in this view.

[0112] Fig. 7A FIG. 4 shows a schematic top view of a first-stage second optical pulse stretcher 401b according to some embodiments of the present disclosure. Fig. 7A As shown, the first-stage second optical pulse stretcher 401 b may include two mirrors 501 a and 502 a , a beam splitter 503 a and an optional compensator 701 .

[0113] According to some embodiments, the reflectors 501a and 502a in the first-stage second optical pulse stretcher 401b may include rectangular concave reflectors. For example, two large rectangular concave reflectors may be used, but other shapes may be used in other embodiments. According to some embodiments, the reflective surfaces of the reflectors 501a and 502a may be spherically concave, so that the distance between the reflectors 501a and 502a is equal to (or approximately equal to) the radius of curvature of each of the reflectors 501a and 502a. For example, the reflectors 501a and 502a may be designed and positioned based on a telecentric design. According to some embodiments, the concave reflectors may be designed using orthogonal tilt-dump adjustments. According to some embodiments, and compared to, for example, circular reflectors, the reflectors 501a and 502a may be relatively insensitive to reflector misalignment, may have a smaller number of parts, may simplify their mounting design, and / or may be easier to align, with reduced components and degrees of freedom.

[0114] According to some embodiments, the respective curvatures and dimensions of the mirrors 501a and 502a can be designed to position the beam splitter 503a closer to one of the mirrors in the mirror group (e.g., closer to the mirror 501a) to allow an upper beam splitter (e.g., a beam splitter in the upper second optical pulse stretcher 401b) to be placed after the excimer laser chamber to allow the pulse stretcher to be properly fitted at the assigned position in the laser system. For example, the beam splitter 503a can be a "D" shaped beam splitter. However, the embodiments of the present disclosure are not limited to these examples, and various other types of beam splitters and / or various other configurations of beam splitters and mirrors may also be used.

[0115] According to some embodiments, beam splitter 503a is positioned relative to the center of curvature of mirrors 501a and / or 502a to "flatten" each of the optical paths so that the laser beams propagate in the same plane (eg, parallel to the floor).

[0116] In accordance with some embodiments, the optional compensator 701 may include a compensator plate configured to compensate for the laser beam exiting the finite thickness of the beam splitter 503a and reduce the degrees of freedom (DOF) in the mirror adjustment (e.g., 4 DOF in a large mirror design compared to 8 DOF in a small mirror design).

[0117] According to some embodiments, the distance between mirrors 501a and 502a may be adjusted during manufacturing, and tilt / tilt adjustments of the mirrors may be performed in the field.

[0118] Figure 7B FIG. 4 shows a schematic top view of a second-stage second optical pulse stretcher 401 b or a third-stage second optical pulse stretcher 401 b according to some embodiments of the present disclosure. Figure 7B As shown, the second-stage second optical pulse stretcher 401b or the third-stage second optical pulse stretcher 401b may include four mirrors 501b, 501c, 502b and 502c and a beam splitter 503b.

[0119] Figure 7B The second optical pulse stretcher 401b of the second stage is discussed. However, the third second optical pulse stretcher 401b can be the same or similar. According to some embodiments, the reflectors 501b, 501c, 502b and 502c in the second second optical pulse stretcher 401b can include rectangular concave reflectors. For example, two large rectangular concave reflectors can be used, but other shapes can be used in other embodiments.

[0120] According to some embodiments, the reflective surfaces of reflectors 501b, 501c, 502b, and 502c may be spherically concave, such that the distance between reflectors 501b and 502b (or reflectors 501c and 502c) is equal to (or approximately equal to) the radius of curvature of each of reflectors 501b, 501c, 502b, and 502c. For example, reflectors 501b, 501c, 502b, and 502c may be designed and positioned based on a telecentric design. According to some embodiments, concave reflectors may be designed using orthogonal tilt-tilt adjustments. According to some embodiments, and compared to, for example, circular reflectors, reflectors 501b, 501c, 502b, and 502c may be relatively insensitive to reflector misalignment, may have a lower number of components, may simplify their mounting design, and / or may be easier to align, having reduced components and degrees of freedom.

[0121] According to some embodiments, the respective curvatures and dimensions of the mirrors 501b, 501c, 502b, and 502c may be designed to position the beam splitter 503b closer to one of the mirrors in the mirror group (e.g., closer to the mirrors 501b and 501c) to allow an upper beam splitter (e.g., a beam splitter in the upper second optical pulse stretcher 401b) to be placed after the excimer laser chamber to allow the pulse stretcher to fit correctly in the allocated laser volume. For example, the beam splitter 503b may be a "D" shaped beam splitter. However, embodiments of the present disclosure are not limited to these examples, and various other types of beam splitters and / or various other configurations of beam splitters and mirrors may also be used.

[0122] According to some embodiments, beam splitter 503b is positioned relative to the center of curvature of mirrors 501b, 501c, 502b and / or 502c to "flatten" each of the optical paths so that the laser beams propagate in the same plane (e.g., parallel to the floor).

[0123] According to some embodiments, an optional compensator (not shown - similar to Fig. 7A Compensator 701). An optional compensator may include a compensator plate configured to compensate for the laser beam exiting the finite thickness of the beam splitter 503b and reduce the degrees of freedom (DOF) in the mirror adjustment (e.g., 4 DOF in a large mirror design compared to 8 DOF in a small mirror design).

[0124] According to some embodiments, the distances between the mirrors 501b, 501c, 502b, and 502c may be adjusted during manufacturing, and the tilt / tilt adjustment of the mirrors may be performed in the field.

[0125] According to some embodiments, the propagation path of the laser beam within the second-stage (and / or third-stage) second optical pulse stretcher 401b may be similar to the propagation path of the laser beam discussed in US Pat. No. 7,415,065, the entire contents of which are incorporated herein by reference.

[0126] In this example, the laser beam is caused to enter the second-stage second optical pulse stretcher 401b using, for example, a beam splitter 503b. According to some embodiments, the incoming laser beam may be the laser beam output of the first-stage second optical pulse stretcher 401b. The laser beam is incident at a first point 1 on the reflector 501b. The reflected beam is incident from point 1 on the reflector 501b to point 2 on the reflector 502c. The reflected beam is incident from point 2 on the reflector 502c to point 3 on the reflector 501b. The reflected beam is incident from point 3 on the reflector 501b to point 4 on the reflector 502b. The reflected beam is incident from point 4 on the reflector 502b to point 5 on the reflector 501c. The reflected beam is incident from point 5 on the reflector 501c to point 6 on the reflector 502b.

[0127] The reflected beam is incident from point 5 on the reflector 502b to point 7 on the reflector 501b. The reflected beam is incident from point 7 on the reflector 501b to point 8 on the reflector 502c. The reflected beam is incident from point 8 on the reflector 502c to point 9 on the reflector 501b. The reflected beam is incident from point 9 on the reflector 501b to point 10 on the reflector 502b. The reflected beam is incident from point 10 on the reflector 502b to point 11 on the reflector 501c. The reflected beam is incident from point 11 on the reflector 501c to point 12 on the reflector 502b. The reflected beam is incident from point 12 on the reflector 502b to the beam splitter 503b.

[0128] Using the beam splitter 503b, the reflected beam from the point 12 on the mirror 502b may be reflected toward the third-stage second optical pulse stretcher 401b. Similar twelve reflections and beam propagation may occur in the third-stage second optical pulse stretcher 401b.

[0129] According to some embodiments, the first, second and third stage second optical pulse stretcher 401b (and / or optical pulse stretcher stages of first optical pulse stretcher 401a) may be designed such that their design may not be affected by initial misalignment and / or vibration issues during operation.

[0130] According to some embodiments, and as discussed above, the laser beam output of the second optical pulse stretcher 401b is reflected back toward the first optical pulse stretcher 401a to be reflected and emitted from the laser source 400. According to some examples, because of the distance between the second optical pulse stretcher 401b and the output laser source 400, the first optical pulse stretcher 401a may include a beam repeater. The beam repeater in the first optical pulse stretcher 401a is configured to receive Figure 4 The output of the second optical pulse stretcher 401b and the output laser beam 413. In some examples, the beam relay may include two or more lenses configured in a telescopic configuration. Additionally or alternatively, the beam relay may include one or more apertures.

[0131] Figure 8 Schematic diagram showing a portion of the path of a laser beam in a first optical pulse stretcher 401a according to some embodiments of the present disclosure. According to some embodiments, Figure 4 The second laser beam 411 is input to the first optical pulse stretcher 401a. The second laser beam 411 can pass through an optional beam splitter 802 and an optional alignment optical device 804 (e.g., an alignment prism). For example, when assembling the first optical pulse stretcher 401a for aligning optical elements and / or beams, the alignment optical device 804 can be used for alignment. The alignment optical device 804 can be removed during operation of the second optical pulse stretcher 401b and the laser source 400.

[0132] The second laser beam 411 can further be incident on a beam splitter of the optical pulse stretcher stage 507 of the first optical pulse stretcher 401a. A portion 807 of the second laser beam 411 can enter the optical pulse stretcher stage 507 of the first optical pulse stretcher 401 to be optically stretched. The output of the optical pulse stretcher stage 507 of the first optical pulse stretcher 401a can be reflected 809 toward the second optical pulse stretcher 401b using a mirror 808a. The output of the second optical pulse stretcher 401b (e.g., laser beam 811) is sent back to the first optical pulse stretcher 401a.

[0133] Optical element 812 may be an optional optical element of the optional beam repeater described above. The output of second optical pulse stretcher 401b (e.g., laser beam 811) is reflected using mirror 808b. The reflected laser beam may pass through one or more optional system apertures 814 and / or beam splitters 816. Figure 4 ) The third laser beam 413 is the output of the laser source 400.

[0134] Although specific reference may be made herein 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, such as the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat panel displays, LCDs, thin film heads, etc. Those skilled in the art will understand that in the context of these alternative applications, any use of the term "wafer" or "die" herein may be considered synonymous with the more general term "substrate" or "target portion", respectively. Before or after exposure, the substrate referred to herein may be processed in, for example, a tracking unit (a tool that typically applies a resist layer to a substrate and develops the exposed resist), a measurement unit, and / or an inspection unit. Where applicable, the disclosure herein may be applied to such and other substrate processing tools. In addition, for example, in order to generate a multi-layer IC, the substrate may be processed more than once, so that the term substrate used herein may also refer to a substrate that already contains multiple processed layers.

[0135] It should be understood that the phraseology or terminology herein is for the purpose of description rather than limitation, so that the phraseology or terminology of this specification should be interpreted by those skilled in the relevant art based on the teachings herein.

[0136] The term "substrate" as used herein describes a material on which a layer of material is added. In some embodiments, the substrate itself may be patterned, and the material added on top of it may also be patterned, or may remain unpatterned.

[0137] The above and following examples are illustrative of embodiments of the present disclosure rather than limiting. Other suitable modifications and adaptations of the various conditions and parameters normally encountered in the art (which will be apparent to those skilled in the relevant art) are within the spirit and scope of the present disclosure.

[0138] Although specific reference may be made herein to the use of the apparatus and / or system according to the embodiments in IC manufacturing, it should be clearly understood that such an apparatus and / or system has many other possible applications. For example, it can be used in the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, LCD panels, thin film magnetic heads, etc. Those skilled in the art will understand that in the context of these alternative applications, any use of the terms "mask", "wafer" or "die" herein should be considered to be replaced by the more general terms "mask", "substrate" and "target portion", respectively.

[0139] While specific embodiments of the present disclosure have been described above, it will be appreciated that these embodiments may be practiced otherwise than as described. This description is not intended to limit these embodiments.

[0140] It should be understood that the Detailed Description section, rather than 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 contemplated by the inventors, and thus are not intended to limit the present embodiments and the appended claims in any way.

[0141] Some embodiments have been described above by means of functional building blocks that illustrate the implementation of specific functions and their relationships. For ease of description, the boundaries of these functional building blocks are arbitrarily defined in this article. As long as the specified functions and their relationships are properly performed, alternative boundaries can be defined.

[0142] The above description of specific embodiments will fully reveal the general nature of the embodiments, so that others can easily modify and / or adapt various applications of such specific embodiments by applying knowledge within the art without excessive experimentation, without departing from the general concepts of the present disclosure. Therefore, based on the teachings and guidance presented herein, such adjustments and modifications are intended to be within the meaning and scope of the equivalents of the disclosed embodiments.

[0143] Further aspects of the invention are set out in the following numbered clauses.

[0144] 1. An optical pulse stretcher, the optical pulse stretcher being configured to receive a laser beam and generate an output pulse-stretched laser beam, the optical pulse stretcher comprising:

[0145] a first stage optical pulse stretcher including two or more mirrors and configured to receive a portion of the laser beam and generate a first pulse stretched laser beam;

[0146] a second stage optical pulse stretcher comprising four or more mirrors and configured to receive a portion of the first pulse stretched laser beam and generate a second pulse stretched laser beam; and

[0147] A third stage optical pulse stretcher includes four or more mirrors and is configured to receive a portion of the second pulse-stretched laser beam and generate an output pulse-stretched laser beam.

[0148] 2. An optical pulse stretcher according to clause 1, wherein the two or more mirrors of the first stage optical pulse stretcher, the four or more mirrors of the second stage optical pulse stretcher, and the four or more mirrors of the third stage optical pulse stretcher comprise concave mirrors.

[0149] 3. The optical pulse stretcher according to clause 1, wherein the first stage optical pulse stretcher is configured to generate the first pulse stretched laser beam by reflecting a portion of the laser beam four times using two or more mirrors of the first stage optical pulse stretcher.

[0150] 4. An optical pulse stretcher according to claim 3, wherein the second-stage optical pulse stretcher is configured to generate a second pulse-stretched laser beam by reflecting a portion of the first pulse-stretched laser beam twelve times, and the third-stage optical pulse stretcher is configured to generate an output pulse-stretched laser beam by reflecting a portion of the second pulse-stretched laser beam twelve times.

[0151] 5. The optical pulse stretcher according to clause 1, wherein the second stage optical pulse stretcher is configured to generate the second pulse stretched laser beam by reflecting a portion of the first pulse stretched laser beam twelve times using four or more mirrors of the second stage optical pulse stretcher.

[0152] 6. The optical pulse stretcher according to clause 1, wherein the third stage optical pulse stretcher is configured to generate the output pulse stretched laser beam by reflecting the portion of the second pulse stretched laser beam twelve times using four or more mirrors of the third stage optical pulse stretcher.

[0153] 7. An optical pulse stretcher according to clause 1, further comprising:

[0154] The first beam splitter corresponds to the first-stage optical pulse stretcher and is configured to receive the laser beam and direct a portion of the laser beam to two or more mirrors of the first-stage optical pulse stretcher.

[0155] 8. An optical pulse stretcher according to clause 7, wherein the first beam splitter is positioned closer to a first mirror of the two or more mirrors of the first optical pulse stretcher, and wherein the first beam splitter is a D-shaped beam splitter.

[0156] 9. An optical pulse stretcher according to clause 7, wherein the first beam splitter is positioned relative to the center of curvature of the two or more mirrors to flatten the first stage optical pulse stretcher and enable parts of the laser beam to propagate in the same plane in the first stage optical pulse stretcher.

[0157] 10. An optical pulse stretcher according to clause 7, further comprising:

[0158] The second beam splitter corresponds to the second-stage optical pulse stretcher and is configured to receive the first pulse-stretched laser beam and direct a portion of the first pulse-stretched laser beam to the four or more mirrors of the second-stage optical pulse stretcher.

[0159] 11. An optical pulse stretcher according to claim 10, wherein the second beam splitter is positioned relative to the center of curvature of the four or more mirrors of the second-stage optical pulse stretcher to flatten the second-stage optical pulse stretcher and enable portions of the first pulse stretched laser beam to propagate in the same plane in the second-stage optical pulse stretcher.

[0160] 12. An optical pulse stretcher according to clause 10, further comprising:

[0161] The third beam splitter corresponds to the third-stage optical pulse stretcher and is configured to receive the second pulse-stretched laser beam and direct a portion of the second pulse-stretched laser beam to the four or more mirrors of the third-stage optical pulse stretcher.

[0162] 13. An optical pulse stretcher according to claim 12, wherein the third beam splitter is positioned relative to the center of curvature of the four or more mirrors of the third-stage optical pulse stretcher to flatten the third-stage optical pulse stretcher and enable a portion of the second pulse stretched laser beam to propagate in the same plane in the third-stage optical pulse stretcher.

[0163] 14. An optical pulse stretcher according to clause 12, wherein:

[0164] The second beam splitter is positioned closer to the first mirror pair of the four or more mirrors of the second optical pulse stretcher,

[0165] The second beam splitter is a D-shaped beam splitter,

[0166] The third beam splitter is positioned closer to the first pair of mirrors of the four or more mirrors of the third optical pulse stretcher, and

[0167] The third beam splitter is a D-shaped beam splitter.

[0168] 15. An optical pulse stretcher according to clause 1, wherein:

[0169] The laser beam received by the first stage optical pulse stretcher includes a pulse-stretched laser beam generated by an orthogonal stage optical pulse stretcher,

[0170] The orthogonal-stage optical pulse stretcher is located outside the optical pulse stretcher and is approximately perpendicular to the optical pulse stretcher.

[0171] 16. An optical pulse stretcher according to clause 15, wherein the orthogonal stage optical pulse stretcher is configured to reflect the portion of the laser beam four times.

[0172] 17. A laser source, comprising:

[0173] An optical pulse stretcher configured to receive a laser beam and generate an output pulse-stretched laser beam, the optical pulse stretcher comprising:

[0174] a first stage optical pulse stretcher including two or more mirrors and configured to receive a portion of the laser beam and generate a first pulse stretched laser beam;

[0175] a second stage optical pulse stretcher comprising four or more mirrors and configured to receive a portion of the first pulse stretched laser beam and generate a second pulse stretched laser beam; and

[0176] A third stage optical pulse stretcher includes four or more mirrors and is configured to receive a portion of the second pulse-stretched laser beam and generate an output pulse-stretched laser beam.

[0177] 18. A lithographic apparatus comprising:

[0178] an irradiation system configured to condition the radiation beam;

[0179] a support structure configured to support a patterning device;

[0180] a substrate stage configured to hold a substrate; and

[0181] a projection system configured to project the pattern imparted to the radiation beam by the patterning device onto a target portion of the substrate,

[0182] Wherein the illumination system comprises a laser source, the laser source comprises an optical pulse stretcher, the optical pulse stretcher is configured to receive a laser beam and generate an output pulse-stretched laser beam, the optical pulse stretcher comprising:

[0183] a first stage optical pulse stretcher including a plurality of first confocal resonators and configured to receive a portion of the laser beam and generate a first pulse stretched laser beam;

[0184] a second stage optical pulse stretcher comprising a plurality of second confocal resonators and configured to receive a portion of the first pulse stretched laser beam and generate a second pulse stretched laser beam; and

[0185] A third stage optical pulse stretcher includes a plurality of third confocal resonators and is configured to receive a portion of the second pulse-stretched laser beam and generate an output pulse-stretched laser beam.

[0186] 19. A lithographic apparatus according to clause 18, wherein:

[0187] The plurality of first confocal resonators include two or more concave mirrors,

[0188] The plurality of second confocal resonators include four or more concave mirrors, and

[0189] The plurality of third confocal resonators includes four or more concave mirrors.

[0190] 20. A lithographic apparatus according to clause 18, wherein:

[0191] The first-stage optical pulse stretcher has a first optical delay,

[0192] The second stage optical pulse stretcher has a second optical delay that is equal to or greater than the first optical delay, and

[0193] The third-stage optical pulse stretcher has a third optical delay that is equal to or greater than the second optical delay.

[0194] 21. A lithographic apparatus according to clause 18, wherein:

[0195] The first stage optical pulse stretcher is configured to generate a first pulse stretched laser beam by reflecting a portion of the laser beam four times,

[0196] The second stage optical pulse stretcher is configured to generate a second pulse stretched laser beam by reflecting a portion of the first pulse stretched laser beam twelve times, and

[0197] The third stage optical pulse stretcher is configured to generate an output pulse stretched laser beam by reflecting a portion of the second pulse stretched laser beam twelve times.

[0198] 22. The lithographic apparatus according to clause 18, wherein the laser source further comprises:

[0199] The orthogonal-stage optical pulse stretcher is configured to guide the laser beam to the optical pulse stretcher, and the orthogonal-stage optical pulse stretcher is located outside the optical pulse stretcher and approximately perpendicular to the optical pulse stretcher.

[0200] 23. The lithographic apparatus according to clause 22, wherein the orthogonal order optical pulse stretcher comprises four circular concave mirrors.

[0201] 24. A lithographic apparatus according to clause 22, further comprising:

[0202] The beam repeater is configured to receive the output pulse-stretched laser beam and output the output pulse-stretched laser beam from the laser source.

[0203] 25. An optical pulse stretcher, the optical pulse stretcher being configured to receive a laser beam and generate an output pulse-stretched laser beam, the optical pulse stretcher comprising:

[0204] Two or more confocal optical pulse stretchers stacked in an optical pulse stretcher,

[0205] wherein a first confocal optical pulse stretcher of the two or more confocal optical pulse stretchers is configured to receive a portion of the laser beam and generate a first pulse-stretched laser beam by reflecting the portion of the laser beam four times, and

[0206] A second confocal optical pulse stretcher of the two or more confocal optical pulse stretchers is configured to receive a portion of the first pulse-stretched laser beam and generate a second pulse-stretched laser beam by reflecting the portion of the first pulse-stretched laser beam twelve times.

[0207] 26. An optical pulse stretcher according to clause 25, wherein

[0208] A first confocal optical pulse stretcher of the two or more confocal optical pulse stretchers has a first optical delay, and

[0209] A second confocal optical pulse stretcher of the two or more confocal optical pulse stretchers has a second optical delay that is equal to or greater than the first optical delay.

[0210] 27. An extended optical pulse stretcher, comprising:

[0211] a first stage optical pulse stretcher including a plurality of first confocal resonators and configured to receive the laser beam and generate a first pulse stretched laser beam;

[0212] Stacked confocal pulse stretcher, including:

[0213] a second stage optical pulse stretcher including a plurality of second confocal resonators and configured to receive a portion of the first pulse stretched laser beam and generate a second pulse stretched laser beam;

[0214] a third stage optical pulse stretcher including a plurality of third confocal resonators and configured to receive a portion of the second pulse-stretched laser beam and generate a third pulse-stretched laser beam;

[0215] a fourth stage optical pulse stretcher comprising a plurality of fourth confocal resonators and configured to receive a portion of the third pulse-stretched laser beam and generate an output pulse-stretched laser beam,

[0216] The first stage optical pulse stretcher is positioned approximately perpendicular to the stacked confocal pulse stretcher.

[0217] 28. An extended optical pulse stretcher according to clause 27, wherein:

[0218] The first-stage optical pulse stretcher has a first optical delay,

[0219] The second stage optical pulse stretcher has a second optical delay which is equal to or greater than the first optical delay,

[0220] The third stage optical pulse stretcher has a third optical delay that is equal to or greater than the second optical delay, and

[0221] The fourth-stage optical pulse stretcher has a fourth optical delay that is equal to or greater than the second optical delay.

[0222] 29. An extended optical pulse stretcher according to clause 27, wherein:

[0223] The first stage optical pulse stretcher is configured to receive a portion of the laser beam and generate a first pulse stretched laser beam by reflecting the portion of the laser beam four times.

[0224] The second stage optical pulse stretcher is configured to receive the portion of the laser beam and generate a second pulse stretched laser beam by reflecting the portion of the laser beam four times.

[0225] The third stage optical pulse stretcher is configured to: receive the portion of the laser beam and generate a third pulse stretched laser beam by reflecting the portion of the laser beam twelve times, and

[0226] The fourth stage optical pulse stretcher is configured to receive the portion of the laser beam and generate a fourth pulse stretched laser beam by reflecting the portion of the laser beam twelve times.

[0227] 30. A method comprising:

[0228] generating a laser beam; and

[0229] The laser beam is directed through an optical pulse stretcher comprising:

[0230] a first stage optical pulse stretcher including a plurality of first confocal resonators and configured to receive a portion of the laser beam and generate a first pulse stretched laser beam;

[0231] a second stage optical pulse stretcher comprising a plurality of second confocal resonators and configured to receive a portion of the first pulse stretched laser beam and generate a second pulse stretched laser beam; and

[0232] A third stage optical pulse stretcher includes a plurality of third confocal resonators and is configured to receive a portion of the second pulse-stretched laser beam and generate an output pulse-stretched laser beam.

[0233] 31. A method according to clause 30, wherein the optical pulse stretcher also includes an orthogonal stage optical pulse stretcher, which is configured to guide the laser beam to the first stage optical pulse stretcher, and the orthogonal stage optical pulse stretcher is positioned approximately perpendicular to the first stage optical pulse stretcher, the second stage optical pulse stretcher and the third stage optical pulse stretcher.

[0234] The breadth and scope of the present disclosure should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.

Claims

1. An optical pulse stretcher, the optical pulse stretcher being configured to receive a laser beam and generate an output pulse-stretched laser beam, the optical pulse stretcher comprising: a first stage optical pulse stretcher comprising two or more mirrors and configured to receive the portion of the laser beam and generate a first pulse stretched laser beam; a second stage optical pulse stretcher including four or more mirrors and configured to receive a portion of the first pulse stretched laser beam and generate a second pulse stretched laser beam; as well as A third stage optical pulse stretcher includes four or more mirrors and is configured to receive a portion of the second pulse-stretched laser beam and generate an output pulse-stretched laser beam.

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