Lithographic apparatus, inspection system, and detector having a square core fiber - Patents.com

Abstract

The apparatus includes an illumination system, a projection system, and an inspection system. The illumination system illuminates a pattern of a patterning device. The projection system projects an image of the pattern onto a substrate. The inspection system includes a radiation source, an optical element, and a detector. The radiation source generates radiation. The optical element directs the radiation towards a target on the substrate. The detector includes a photosensitive device and a square core optical fiber. The photosensitive device receives at least a portion of the radiation scattered by the target and generates a measurement signal based on the received portion of the radiation. The square core optical fiber is coupled to the photosensitive device and directs the portion of the radiation to the photosensitive device and homogenizes the directed portion of the radiation such that an intensity cross-section of the received portion of the radiation at the photosensitive device is substantially uniform.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Application No. 63 / 331,759, filed April 15, 2022, and is incorporated by reference in its entirety into this specification.

[0002]

[0002] The present disclosure relates to detectors, for example in inspection systems used for wafer alignment measurements in lithography apparatus and systems. [Background technology]

[0003]

[0003] A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. Lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). A patterning device, also called a mask or reticle, can then be used to generate a circuit pattern that is formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. comprising part of a die, or one or more dies) on the substrate (e.g. a silicon wafer). Typically, the transfer of the pattern is by imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing the entire pattern onto the target portion at once, and so-called scanners, in which each target portion is irradiated by scanning the pattern with a radiation beam in a given direction (the "scan" direction) and simultaneously scanning the target portion parallel or anti-parallel to this scan direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.

[0004]

[0004] During lithography operations, different processing steps may require different layers to be formed sequentially on a substrate. It may therefore be necessary to position the substrate with high precision relative to a previous pattern formed thereon. Generally, alignment marks are placed on the substrate to be aligned and positioned with reference to a second object. The lithography apparatus may use an alignment device to detect the position of the alignment marks and to use the alignment marks to align the substrate to ensure accurate exposure from the mask. The misalignment between the respective alignment marks in two different layers is measured as an overlay error.

[0005]

[0005] To monitor the lithographic process, parameters of the patterned substrate are measured. The parameters may include, for example, the overlay error between successive layers formed in or on the patterned substrate, and the critical linewidth of the developed photosensitive resist. The measurements may be made on the product substrate and / or on a dedicated metrology target. Various techniques exist for making measurements of the microstructures formed in the lithographic process, including the use of scanning electron microscopes and various specialized inspection tools. A fast and non-invasive form of specialized inspection tool is a scatterometer, in which a beam of radiation is directed at a target on the surface of the substrate and the properties of the scattered or reflected beam are measured. By comparing the properties of the beam before and after it is reflected or scattered by the substrate, the properties of the substrate can be determined. This can be done, for example, by comparing the reflected beam to data stored in a library of known measurements associated with known substrate properties. A spectroscopic scatterometer directs a broadband beam of radiation onto the substrate and measures the spectrum (intensity as a function of wavelength) of the radiation scattered into a specific narrow angular range. In contrast, an angularly resolved scatterometer uses a monochromatic radiation beam and measures the intensity of the scattered radiation as a function of angle.

[0006]

[0006] Ideally, a detector in an inspection system would exhibit a stable and predictable response to photons incident on its surface (e.g., a signal that is linearly proportional to the number of incident photons). However, in reality, detectors exhibit a nonlinear response to incident radiation. The nonlinear response can be due to microscopic imperfections resulting from the detector manufacturing process and / or absorption nonlinearities of the detector material. Intensity variations due to detector nonlinearities can contribute to uncertainties in measurements made by the inspection system. Summary of the Invention

[0007]

[0007] Thus, the embodiments described herein address measurement uncertainties arising from the non-linear response of the detector.

[0008]

[0008] In some embodiments, the apparatus may include an illumination system, a projection system, and an inspection system. The illumination system may be configured to illuminate a pattern of a patterning device. The projection system may be configured to project an image of the pattern onto the substrate. The inspection system may include a radiation source, an optical element, and a detector. The radiation source may be configured to generate radiation. The optical element may be configured to direct the radiation towards a target on the substrate. The detector may include a photosensitive device and a square core optical fiber. The photosensitive device may be configured to receive at least a portion of the radiation scattered by the target and to generate a measurement signal based on the received portion of the radiation. The square core optical fiber may be coupled to the photosensitive device and configured to direct the portion of the radiation to the photosensitive device and homogenize the directed portion of the radiation such that an intensity cross-section of the received portion of the radiation at the photosensitive device is approximately uniform.

[0009]

[0009] In some embodiments, the inspection system may include a radiation source, an optical element, and a detector. The radiation source may be configured to generate radiation. The optical element may be configured to direct the radiation towards the target. The detector may include a photosensitive device and a square core optical fiber. The photosensitive device may be configured to receive at least a portion of the radiation scattered by the target and to generate a measurement signal based on the received portion of the radiation. The square core optical fiber may be coupled to the photosensitive device and configured to direct the portion of the radiation to the photosensitive device and homogenize the directed portion of the radiation such that an intensity cross-section of the received portion of the radiation at the photosensitive device is approximately uniform.

[0010]

[0010] In some embodiments, the detector may include a photosensitive device and a square core optical fiber. The photosensitive device may be configured to receive radiation and generate a measurement signal based on the received radiation. The square core optical fiber may be coupled to the photosensitive device and configured to guide radiation to the photosensitive device and homogenize the guided radiation such that an intensity cross-section of the received radiation at the photosensitive device is approximately uniform.

[0011]

[0011] Further features of the present disclosure, as well as the structure and operation of 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. Such embodiments are shown herein for illustrative purposes only. Based on the teachings herein, additional embodiments will be apparent to those skilled in the art. [Brief description of the drawings]

[0012]

[0012] The accompanying drawings, which are incorporated in and form a part of this specification, illustrate the present disclosure and, together with the description, serve to explain the principles of the present disclosure and to enable those skilled in the art to make and use the embodiments described in this specification.

[0013] [Figure 1A]

[0013] FIG. 1 shows a schematic diagram of a reflective lithographic apparatus according to some embodiments. [Figure 1B]

[0014] 1 depicts a schematic diagram of a transmissive lithographic apparatus according to some embodiments; [Diagram 2]

[0015] 1 shows a more detailed schematic diagram of a reflective lithographic apparatus according to some embodiments; [Diagram 3]

[0016] 1 shows a schematic diagram of a lithographic cell according to some embodiments. [Figure 4A]

[0017] 1 shows a schematic diagram of an inspection apparatus according to some embodiments. [Figure 4B]

[0017] A schematic diagram of an inspection apparatus according to some embodiments is shown. [Diagram 5]

[0018] 1 illustrates a detection portion of an inspection system according to some embodiments. [Figure 6A]

[0019] 1 illustrates a radiation spot having a speckle pattern according to some embodiments. [Figure 6B]

[0020] 7 illustrates a graph of intensity data of the speckle pattern of FIG. 6 according to some embodiments. [Figure 7A]

[0021] 1 illustrates an output face of a rectangular core optical fiber according to some embodiments. [Figure 7B]

[0022] 7B illustrates a two-dimensional intensity map of the radiative output from the surface of FIG. 7A according to some embodiments.

[0014]

[0023] Features of the present disclosure will become more apparent from the detailed description set forth below when considered in conjunction with the drawings, in which like reference numbers identify corresponding elements throughout. In the drawings, like reference numbers generally indicate identical, functionally similar, and / or structurally similar elements. Also, the leftmost digit(s) of a reference number generally identifies the figure in which that reference number first appears. The drawings provided throughout this disclosure should not be construed as drawings to scale unless otherwise indicated. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015]

[0024] This specification discloses one or more embodiments incorporating features of the present disclosure. The disclosed embodiments are presented as examples. The scope of the present disclosure is not limited to the disclosed embodiments. The claimed features are defined by the claims appended hereto.

[0016]

[0025] References to a described embodiment(s), "one embodiment," "an embodiment," "an exemplary embodiment," etc. in the specification indicate that the described embodiment may include a particular feature, structure, or characteristic, but not all embodiments may include that particular feature, structure, or characteristic. Furthermore, such phrases do not necessarily refer to the same embodiment. Furthermore, when a particular feature, structure, or characteristic is described in connection with one embodiment, it will be understood that it is within the knowledge of one of ordinary skill in the art that such feature, structure, or characteristic may be provided in connection with other embodiments, whether or not expressly stated.

[0017]

[0026] Spatially relative terms such as "below," "below," "lower," "above," "on," "higher," and the like are used herein for ease of description and may describe the relationship of one element or feature as illustrated in the figures to another element or feature(s). Spatially relative terms are intended to encompass various orientations of the device in use or operation in addition to the orientation depicted. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may be similarly interpreted accordingly.

[0018]

[0027] The term "about" as used herein refers to a given quantity value that may vary based on a particular technique. Based on a particular technique, the term "about" may refer to a given quantity value that varies, for example, within 10% to 30% of the value (e.g., ±10%, ±20%, or ±30% of the value).

[0019]

[0028] The embodiments of the present disclosure may be implemented in hardware, firmware, software, or any combination thereof. The embodiments of the present disclosure may also be implemented as instructions that can be stored on a machine-readable medium and read and executed by one or more processors. A machine-readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, a machine-readable medium may include a read-only memory (ROM), a random access memory (RAM), a magnetic disk storage medium, an optical storage medium, a flash memory device, an electrical, optical, acoustic, or other form of propagated signal (e.g., carrier wave, infrared signal, digital signal, etc.), and the like. Also, firmware, software, routines, and / or instructions may be described herein as performing certain operations. However, it should be understood that such description is merely for convenience and that such operations are in fact performed by a computing device, processor, controller, or other device executing the firmware, software, routines, instructions, etc.

[0020]

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

[0021]

[0030] Exemplary Lithography System

[0031] 1A and 1B show schematic diagrams of lithographic apparatus 100 and lithographic apparatus 100', respectively, in which embodiments of the present disclosure may be implemented. Lithographic apparatus 100 and lithographic apparatus 100' each include the following: an illumination system (illuminator) IL configured to condition a radiation beam B (e.g., deep ultraviolet or extreme ultraviolet), a support structure (e.g., mask table) MT configured to support a patterning device (e.g., mask, reticle, or dynamic patterning device) MA and connected to a first positioner PM configured to accurately position the patterning device MA, and a substrate table (e.g., wafer table) W configured to hold a substrate (e.g., resist coated wafer) W and connected to a second positioner PW configured to accurately position the substrate W. Lithographic apparatus 100 and 100' also include a projection system PS configured to project a pattern imparted to radiation beam B by patterning device MA onto a target portion C of substrate W (e.g., comprising one or more dies). In lithographic apparatus 100, the patterning device MA and the projection system PS are reflective. In lithographic apparatus 100', the patterning device MA and the projection system PS are transmissive.

[0022]

[0032] The illumination system IL may include various types of optical components, such as refractive, reflective, catadioptric, magnetic, electromagnetic, electrostatic or other types of optical components, or any combination thereof, for directing, shaping or controlling the radiation beam B.

[0023]

[0033] The support structure MT holds the patterning device MA in a manner that depends on the orientation of the patterning device MA relative to a 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 or not. 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 a table, which may be fixed or movable as required. By using sensors, the support structure MT may ensure that the patterning device MA is at a desired position, for example with respect to the projection system PS.

[0024]

[0034] The term "patterning device" MA should be interpreted broadly as referring to any device that can be used to impart a radiation beam B with a pattern in its cross-section so as to create a pattern in a target portion C of a substrate W. The pattern imparted to the radiation beam B may correspond to a particular functional layer in a device being created in the target portion C to form an integrated circuit.

[0025]

[0035] As used herein, terms such as "inspection apparatus", "metrology system", etc. may be used to refer to devices or systems (e.g., alignment apparatus) used, for example, to measure characteristics of structures (e.g., overlay error, critical dimension parameters) or used within a lithographic apparatus to inspect the alignment of a wafer.

[0026]

[0036] The patterning device MA may be transmissive (as in lithographic apparatus 100' of FIG. 1B) or reflective (as in lithographic apparatus 100 of FIG. 1A). Examples of patterning devices MA include reticles, masks, programmable mirror arrays, or programmable LCD panels. Masks are well known in lithography and include mask types such as binary, alternating phase-shift, or attenuated phase-shift, as well as various hybrid mask types. An example of a programmable mirror array uses a matrix arrangement of small mirrors, each of which can be individually tilted so as to reflect an incoming radiation beam in different directions. The tilted mirrors impart a pattern to a radiation beam B that is reflected by the matrix of small mirrors.

[0027]

[0037] The term "projection system" PS may encompass any type of projection system, including refractive, reflective, catadioptric, magnetic, electromagnetic and electrostatic optics, or any combination thereof, appropriate for the exposure radiation being used, or other factors such as the use of an immersion liquid or the use of a vacuum on the substrate W. A vacuum environment may be used for EUV or electron beam radiation, as other gases may absorb too much radiation or electrons. Therefore, a vacuum environment may be provided throughout the beam path using a vacuum wall and vacuum pumps.

[0028]

[0038] Lithographic apparatus 100 and / or 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 preliminary steps may be carried out on one or more tables while one or more other tables WT are used for exposure. In some situations the additional tables may not be substrate tables WT.

[0029]

[0039] 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 (e.g. water) so as to fill a space between the projection system and the substrate. Immersion liquid may also be applied to other spaces in the lithographic apparatus (e.g. between the mask and the projection system). Immersion techniques are well known in the art for increasing the numerical aperture of projection systems. The term "immersion" as used herein does not mean that a structure such as the substrate must be submerged in liquid, but simply that there is a liquid between the projection system and the substrate during exposure.

[0030]

[0040] 1A and 1B, the illuminator IL receives radiation from a radiation source SO. The source SO and the lithographic apparatus 100, 100' may be separate entities, for example if the source SO is an excimer laser. In such a case, the source SO is not considered to form part of the lithographic apparatus 100 or 100', and the radiation beam B is delivered from the source SO to the illuminator IL by means of a beam delivery system BD (of FIG. 1B) including, for example, suitable directing mirrors and / or beam expanders. In other cases, the source SO may be an integral part of the lithographic apparatus 100, 100', for example if the source SO is a mercury lamp. The source SO and the illuminator IL, together with the beam delivery system BD if required, may be referred to as a radiation system.

[0031]

[0041] The illuminator IL may include an adjuster AD (of Figure 1B) for adjusting the angular intensity distribution of the radiation beam. Generally, at least the outer and / or inner radial extent (commonly referred to as σ-outer and σ-inner, respectively) of the intensity distribution in a pupil plane of the illuminator may be adjusted. In addition, the illuminator IL may include various other components (of Figure 1B), such as an integrator IN and a condenser CO. The illuminator IL can be used to condition the radiation beam B so that it has a desired uniformity and intensity distribution in its cross-section.

[0032]

[0042] Referring to FIG. 1A, a 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 is patterned by the patterning device MA. In the lithographic apparatus 100, the radiation beam B is reflected from the patterning device (e.g., mask) MA. After being reflected from the patterning device (e.g., mask) MA, the radiation beam B passes through a projection system PS, which focuses the radiation beam B onto a target portion C of a substrate W. The substrate table WT can be accurately moved (e.g. to position a different target portion C in the path of the radiation beam B) using a second positioner PW and a position sensor IF2 (e.g., an interferometer device, a linear encoder, or a capacitive sensor). Similarly, the patterning device (e.g., mask) MA can also be accurately positioned with respect to the path of the radiation beam B using a first positioner PM and another position sensor IF1. Patterning device (eg mask) MA and substrate W may be aligned using mask alignment marks M1 and M2 and substrate alignment marks P1 and P2.

[0033]

[0043] Referring to Figure 1B, a 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 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 a substrate W. The projection system has a pupil PPU that is conjugate with the illumination system pupil IPU. Portions of radiation arise from the intensity distribution in the illumination system pupil IPU and traverse the mask pattern without being affected by diffraction at the mask pattern to create an image of the intensity distribution in the illumination system pupil IPU.

[0034]

[0044] The projection system PS projects an image of the mask pattern MP, where the image is formed on a photoresist layer coated on the substrate W by diffracted beams generated from the mask pattern MP by radiation from the intensity distribution. For example, the mask pattern MP may include an array of lines and spaces. Diffraction of the radiation at the array, but not the zeroth order, generates stimulated diffracted beams redirected perpendicular to the lines. The non-diffracted beams (i.e. the so-called zeroth order diffracted beams) traverse the pattern without changing their propagation direction. The zeroth order diffracted beams traverse the upper lens or upper lens group of the projection system PS, which is upstream of the conjugate pupil PPU of the projection system PS, to reach the conjugate pupil PPU. The part of the intensity distribution that lies in the plane of the conjugate pupil PPU and is associated with the zeroth order diffracted beam is an image of the intensity distribution of the illumination system pupil IPU of the illumination system IL. The aperture device PD is for example arranged in a plane that includes the conjugate pupil PPU of the projection system PS, or is arranged substantially in this plane.

[0035]

[0045] The projection system PS is arranged to capture not only the zeroth order diffracted beam but also the first or higher order diffracted beams (not shown) by means of a lens or lens group L. In some embodiments, the resolution enhancing effect of dipole illumination can be exploited by using dipole illumination for imaging a line pattern extending in a direction perpendicular to the line. For example, a first order diffracted beam interferes with a corresponding zeroth order diffracted beam at the level of the wafer W to generate an image of the line pattern MP with the highest possible resolution and process window (i.e. usable depth of focus combined with an acceptable exposure dose deviation). In some embodiments, astigmatism can be reduced by providing poles (not shown) in opposing quadrants of the illumination system pupil IPU. Furthermore, in some embodiments, astigmatism can be reduced by blocking the zeroth order beam in a conjugate pupil PPU of the projection system associated with the poles in the opposing quadrants. This is explained in more detail in U.S. Pat. No. 7,511,799, issued Mar. 31, 2009, which is incorporated herein by reference in its entirety.

[0036]

[0046] The substrate table WT may be accurately moved (e.g. to position different target portions C in the path of the radiation beam B) using the second positioner PW and a position sensor IFD (e.g. an interferometer device, a linear encoder or a capacitive sensor). Similarly, the first positioner PM and a further position sensor (not shown in FIG. 1B) may be used to accurately position the mask MA with respect to the path of the radiation beam B (e.g. after mechanical retrieval from a mask library or during a scan).

[0037]

[0047] Typically, movement of the mask table MT may be achieved with the aid of a long-stroke module (coarse positioning) and a short-stroke module (fine positioning), which form part of the first positioner PM. Similarly, movement of the substrate table WT may be achieved with the aid of a long-stroke module and a short-stroke module, which form part of the second positioner PW. In the case of a stepper (as opposed to a scanner) the mask table MT may be connected to a short-stroke actuator only, or may be fixed. The mask MA and substrate W may be aligned using mask alignment marks M1 and M2 and substrate alignment marks P1 and P2. The (exemplary) substrate alignment marks occupy dedicated target portions, although the substrate alignment marks may also be located in spaces between the target portions (these are known as scribe-lane alignment marks). Similarly, in a situation in which more than one die is provided on the mask MA, the mask alignment marks may be located between the dies.

[0038]

[0048] The mask table MT and patterning device MA may be in a vacuum chamber V, where an in-vacuum robot IVR can be used to move a patterning device such as a mask in and out of the vacuum chamber. Alternatively, if the mask table MT and patterning device MA are outside the vacuum chamber, an ex-vacuum robot can be used for various transfer operations, similar to the in-vacuum robot IVR. Both in-vacuum and ex-vacuum robots need to be calibrated for smooth transfer of any payload (e.g. a mask) to the fixed kinematic mount of the transfer station.

[0039]

[0049] Lithographic apparatus 100 and 100' can be used in at least one of the following modes:

[0040]

[0050] 1. In step mode, the support structure (e.g. mask table) MT and substrate table WT are kept essentially stationary, and the entire pattern imparted to the radiation beam B is projected onto the target portion C in one go (i.e. a single static exposure), while the substrate table WT is then shifted in the X and / or Y direction so that a different target portion C can be exposed.

[0041]

[0051] 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 can be determined by the (de-)magnification and image reversal characteristics of the projection system PS.

[0042]

[0052] 3. In another mode, the support structure (e.g. mask table) MT is kept essentially stationary, holding a programmable patterning device, and the substrate table WT is moved or scanned while a pattern imparted to the radiation beam B is projected onto a target portion C. A pulsed radiation source SO can be used, and the programmable patterning device is updated as required after each movement of the substrate table WT, or between successive radiation pulses during a scan. This mode of operation can readily be applied to maskless lithography employing a programmable patterning device, such as a programmable mirror array.

[0043]

[0053] Combinations and / or variations on the above described modes of use or entirely different modes of use may also be used.

[0044]

[0054] In a further embodiment, the lithographic apparatus 100 includes an extreme ultraviolet (EUV) source configured to generate a beam of EUV radiation for EUV lithography. Typically, the EUV source is configured in a radiation system, and a corresponding illumination system is configured to condition the EUV radiation beam of the EUV source.

[0045]

[0055] FIG. 2 shows the lithographic apparatus 100 in more detail, including a source collector apparatus SO, an illumination system IL, and a projection system PS. The source collector apparatus SO is constructed and arranged such that a vacuum environment can be maintained within an enclosure 220 of the source collector apparatus SO. The EUV radiation emitting plasma 210 can be formed by a discharge-produced plasma source. The EUV radiation can be produced by a gas or vapor (e.g., Xe gas, Li vapor, or Sn vapor), where a very hot plasma 210 is produced that emits radiation in the EUV range of the electromagnetic spectrum. The very hot plasma 210 is produced, for example, by a discharge resulting in an at least partially ionized plasma. A partial pressure of, for example, 10 Pa of Xe, Li, Sn vapor, or other suitable gas or vapor may be required to generate radiation efficiently. In some embodiments, a plasma of excited tin (Sn) is provided to generate the EUV radiation.

[0046]

[0056] Radiation emitted by the hot plasma 210 is directed from the source chamber 211 into the collector chamber 212 through an optional gas barrier or contaminant trap 230 (sometimes also referred to as a contaminant barrier or foil trap) positioned in or behind an opening in the source chamber 211. The contaminant trap 230 may include a channel structure. The contaminant trap 230 may also include a gas barrier or a combination of a gas barrier and a channel structure. The contaminant trap or contaminant barrier 230 further illustrated herein includes at least a channel structure.

[0047]

[0057] The collector chamber 212 may include a radiation collector CO, which may be a so-called grazing incidence collector. The radiation collector CO has an upstream radiation collector side 251 and a downstream radiation collector side 252. Radiation traversing the collector CO may be reflected by a grating spectral filter 240 and focused into a virtual source point INTF. The virtual source point INTF is commonly called an intermediate focus, and the source collector arrangement is positioned such that the intermediate focus INTF is located at or near an opening 219 in the enclosure structure 220. The virtual source point INTF is an image of the radiation emitting plasma 210. The grating spectral filter 240 is used, inter alia, to suppress infrared (IR) radiation.

[0048]

[0058] The radiation then traverses the illumination system IL, which may include a faceted field mirror device 222 and a faceted pupil mirror device 224 arranged to give a desired angular distribution of the radiation beam 221 at the patterning device MA and a desired uniformity of the radiation intensity at the patterning device MA. Upon reflection of the radiation beam 221 off the patterning device MA, which is held by the support structure MT, a patterned beam 226 is formed which is imaged by the projection system PS via reflective elements 228, 229 onto the substrate W held by a wafer stage or substrate table WT.

[0049]

[0059] In general, more elements than shown may be present in the illumination optics unit IL and projection system PS. A grating spectral filter 240 may optionally be present depending on the type of lithographic apparatus. Furthermore, more mirrors may be present than shown in Figure 2. For example, there may be an additional one to six reflective elements in the projection system PS compared to what is shown in Figure 2.

[0050]

[0060] 2 is depicted as a nested collector with grazing incidence reflectors 253, 254 and 255 as just one example of a collector (or collector mirror). Grazing incidence reflectors 253, 254 and 255 are arranged axially symmetrically about optical axis O, and this type of collector optic CO is preferably used in combination with a discharge produced plasma source, often referred to as a DPP source.

[0051]

[0061] Exemplary Lithographic Cell

[0062] FIG. 3 shows a lithographic cell 300, sometimes called a lithocell or lithocluster, according to some embodiments. The lithographic apparatus 100 or 100′ may form part of the lithographic cell 300. The lithographic cell 300 may also include one or more apparatuses for performing pre-exposure and post-exposure processes on a substrate. Conventionally, these apparatuses include a spin coater SC for depositing a resist layer, a developer DE for developing the exposed resist, a chill plate CH, and a bake plate BK. A substrate handler or robot RO picks up the substrate from input / output ports I / O1, I / O2, moves the substrate between the different processing devices, and delivers the substrate to a loading bay LB of the lithographic apparatus 100 or 100′. These devices, often collectively referred to as a track, are under the control of a track control unit TCU, which is itself controlled by a supervisory control system SCS, which also controls the lithographic apparatus via a lithography control unit LACU. In this way, different devices can be operated to maximize throughput and processing efficiency.

[0052]

[0063] Exemplary Inspection Equipment

[0064] To control the lithographic process and accurately place device features on the substrate, alignment marks are usually provided on the substrate and the lithographic apparatus includes one or more inspection devices for accurately positioning the marks on the substrate. These alignment devices are actually position measurement devices. Various types of marks and various types of alignment devices and / or systems are known from different times and from different manufacturers. A type of system that is widely used in current lithographic apparatus is based on a self-referencing interferometer as described in U.S. Pat. No. 6,961,116 (den Boef et al.). Usually, the marks are measured separately to obtain the positions in the X and Y directions. However, a combined measurement in the X and Y directions can be performed using the technique described in U.S. Patent Application Publication No. 2009 / 195768 (Bijnen et al.). The entire contents of both of the above disclosures are incorporated herein by reference.

[0053]

[0065]

[0066] 4A shows a schematic cross-sectional view of an inspection apparatus 400 that may be implemented as part of lithographic apparatus 100 or 100' according to some embodiments. In some embodiments, inspection apparatus 400 may be configured to align a substrate (e.g., substrate W) relative to a patterning device (e.g., patterning device MA). Inspection apparatus 400 may be further configured to detect positions of alignment marks on the substrate and use the detected positions of the alignment marks to align the substrate relative to the patterning device or other components of lithographic apparatus 100 or 100'. Such alignment of the substrate may ensure accurate exposure of one or more patterns on the substrate.

[0054]

[0067] In some embodiments, the inspection apparatus 400 may include an illumination system 412, a beam splitter 414, an interferometer 426, a detector 428, a beam analyzer 430, and a processor 432. The illumination system 412 may be configured to provide an electromagnetic narrowband radiation beam 413 having one or more passbands. In one example, the one or more passbands may fall within a spectral range of wavelengths between about 500 nm and about 900 nm. In another example, the one or more passbands may be discrete narrow passbands within a spectral range of wavelengths between about 500 nm and about 900 nm. The illumination system 412 may be further configured to provide one or more passbands having a substantially constant central wavelength (CWL) value over an extended period of time (e.g., over the lifetime of the illumination system 412). Such a configuration of the illumination system 412 may help prevent deviations of the actual CWL value from the desired CWL value in current alignment systems, as discussed above. And, as a result, the use of a constant CWL value may improve the long-term stability and accuracy of an alignment system (eg, inspection tool 400) compared to current alignment tools.

[0055]

[0068] In some embodiments, the beam splitter 414 may be configured to receive the radiation beam 413 and split the radiation beam 413 into at least two radiation sub-beams. For example, as shown in FIG. 4A, the radiation beam 413 may be split into radiation sub-beams 415 and 417. The beam splitter 414 may be further configured to direct the radiation sub-beam 415 onto a substrate 420 mounted on a stage 422. In one example, the stage 422 is movable along a direction 424. The radiation sub-beam 415 may be configured to illuminate an alignment mark or target 418 located on the substrate 420. The alignment mark or target 418 may be coated with a radiation sensitive film. In some embodiments, the alignment mark or target 418 may have one hundred eighty degree (i.e., 180°) symmetry. That is, when the alignment mark or target 418 is rotated 180° about an axis of symmetry perpendicular to the plane of the alignment mark or target 418, the rotated alignment mark or target 418 may be substantially identical to the non-rotated alignment mark or target 418. The target 418 on the substrate 420 may be (a) a resist layer grating including bars formed from solid resist lines, or (b) a product layer grating, or (c) a composite grating stack in an overlay target structure including a resist grating superimposed or interleaved on a product layer grating. Alternatively, the bars may be etched into the substrate. This pattern is sensitive to chromatic aberrations in the lithographic projection apparatus, in particular the projection system PL, and the illumination symmetry and the presence of such aberrations will manifest themselves in variations in the printed grating.

[0056]

[0069] In some embodiments, beam splitter 414 may be further configured to receive diffracted radiation beam 419 and split diffracted radiation beam 419 into at least two radiation sub-beams, according to one embodiment diffracted radiation beam 419 may be split into diffracted radiation sub-beams 429 and 439, as shown in Figure 4A.

[0057]

[0070] It should be noted that, although beam splitter 414 is shown directing radiation sub-beam 415 towards alignment mark or target 418 and directing diffracted radiation sub-beam 429 towards interferometer 426, this disclosure is not so limited. It will be apparent to one skilled in the relevant art that other optical arrangements can be used to achieve similar results of illuminating alignment mark or target 418 on substrate 420 and detecting an image of alignment mark or target 418.

[0058]

[0071] As shown in Figure 4A, the interferometer 426 may be configured to receive the radiation sub-beam 417 and the diffracted radiation sub-beam 429 through the beam splitter 414. In an example embodiment, the diffracted radiation sub-beam 429 may be at least a portion of the radiation sub-beam 415 that may be reflected from the alignment mark or target 418. In one example of this embodiment, the interferometer 426 includes any suitable set of optical elements, such as a combination of prisms that may be configured to form two images of the alignment mark or target 418 based on the received diffracted radiation sub-beam 429. It should be understood that a good quality image need not be formed, but features of the alignment mark 418 must be resolved. The interferometer 426 may be further configured to rotate one of the two images by 180 degrees relative to the other of the two images, and to interferometrically recombine the rotated and non-rotated images.

[0059]

[0072] In some embodiments, the detector 428 may be configured to receive the recombined image via the interferometer signal 427 and detect interference as a result of the recombined image when the alignment axis 421 of the inspection apparatus 400 passes through the center of symmetry (not shown) of the alignment mark or target 418. According to an example embodiment, such interference may be due to the alignment mark or target 418 being 180° symmetrical and the recombined image constructively or destructively interfering. Based on the detected interference, the detector 428 may be further configured to determine the position of the center of symmetry of the alignment mark or target 418 and thus detect the position of the substrate 420. According to an example, the alignment axis 421 may be aligned with a light beam perpendicular to the substrate 420 and passing through the center of the image rotation interferometer 426. The detector 428 may be further configured to estimate the position of the alignment mark or target 418 by implementing sensor features and interacting with wafer mark process variations.

[0060]

[0073] In a further embodiment, the detector 428 determines the location of the center of symmetry of the alignment mark or target 418 by performing one or more of the following measurements: 1. Measurement of position change for various wavelengths (registration mismatch between colors) 2. Measurement of the position change for various orders (positional deviation between diffraction orders) 3. Measurement of the position change for various polarizations (position shift between polarizations)

[0061]

[0074] This data can be obtained using any type of alignment sensor, such as, for example, a SMASH (SMart Alignment Sensor Hybrid) sensor as described in U.S. Pat. No. 6,961,116, which uses a self-referencing interferometer with a single detector and four different wavelengths to derive the alignment signal in software, or ATHENA (Advanced Technology using High order ENhancement of Alignment) as described in U.S. Pat. No. 6,297,876, which directs each of seven different diffraction orders to a dedicated detector, both of which are incorporated by reference in their entireties.

[0062]

[0075] In some embodiments, the beam analyzer 430 may be configured to receive and determine an optical state of the diffracted radiation sub-beam 439. The optical state may be a measure of the beam wavelength, polarization, or beam profile. The beam analyzer 430 may be further configured to determine the position of the stage 422 and correlate the position of the stage 422 with the position of the center of symmetry of the alignment mark or target 418. Thus, the position of the alignment mark or target 418, and therefore the position of the substrate 420, may be precisely known relative to the stage 422. Alternatively, the beam analyzer 430 may be configured to determine the position of the inspection apparatus 400 or any other reference element such that the center of symmetry of the alignment mark or target 418 may be known relative to the inspection apparatus 400 or any other reference element. The beam analyzer 430 may be a point or imaging polarimeter with some form of wavelength band selectivity. In some embodiments, the beam analyzer 430 may be directly integrated into the inspection apparatus 400. Alternatively, the beam analyzer 430 may be connected via some type of fiber, such as polarization-preserving single mode, multimode, or imaging, according to other embodiments.

[0063]

[0076] In some embodiments, an array of detectors (not shown) may be connected to the beam analyzer 430, allowing for accurate stack profile detection, as described below. For example, the detector 428 may be an array of detectors. For the array of detectors, several options are possible: a bundle of multimode fibers, a discrete pin detector per channel, or a CCD or CMOS (linear) array. Using a bundle of multimode fibers allows for the discrete elements to be positioned far apart for stability reasons. Discrete PIN detectors offer a large dynamic range, but each requires a separate preamplifier. Therefore, the number of elements is limited. A CCD linear array offers a large number of elements that can be read out at high speed, and is of particular interest when phase stepping detection is used.

[0064]

[0077] In some embodiments, the second beam analyzer 430' may be configured to receive and determine the optical state of the diffracted radiation sub-beam 429, as shown in FIG. 4B. The optical state may be a measure of the beam wavelength, polarization, or beam profile. The second beam analyzer 430' may be identical to the beam analyzer 430. Alternatively, the second beam analyzer 430' may be configured to perform at least all of the functions of the beam analyzer 430, such as determining the position of the stage 422 and correlating the position of the stage 422 with the position of the center of symmetry of the alignment mark or target 418. Thus, the position of the alignment mark or target 418, and therefore the position of the substrate 420, may be accurately known with respect to the stage 422. The second beam analyzer 430' may also be configured to determine the position of the inspection apparatus 400 or any other reference element, such that the center of symmetry of the alignment mark or target 418 may be known with respect to the inspection apparatus 400 or any other reference element. The second beam analyzer 430' may be further configured to determine overlay data between the two patterns and a model of the product stack profile of the substrate 420. The second beam analyzer 430' may also be configured to measure the overlay, critical dimensions, and focus of the target 418 in a single measurement.

[0065]

[0078] In some embodiments, the second beam detector 430' may be directly integrated into the inspection apparatus 400. Alternatively, the second beam detector 430' may be connected via some type of optical fiber, polarization-preserving single mode, multimode, or imaging, according to other embodiments. Alternatively, the second beam detector 430' and the beam detector 430 may be combined to form a single analyzer (not shown) configured to receive and determine the optical state of both diffracted radiation sub-beams 429 and 439.

[0066]

[0079] Exemplary square-core fiber-equipped detector

[0080] It is useful to first consider some of the problems in current technology. Advances in nanofabrication technology have allowed printed devices to be scaled to extremely small sizes. Traditionally, micron-scale devices required alignment accuracy on the order of microns. For example, alignment devices with uncertainties in the range of tens of nanometers were negligible for the purposes of micron-scale manufacturing. However, devices have now reached the sub-nanometer scale, where even small variations in the signal from a detector can result in errors (e.g., picometer-range errors) that significantly increase the failure rate of sub-nanometer printed devices. The embodiments described herein reduce the nonlinear variations in the measurement signal, thus increasing the accuracy of lithographic pattern transfer and reducing the number of instances of manufacturing failure.

[0067]

[0081] We now briefly describe how measurement signals can be analyzed when performing alignment measurements. In some embodiments, the target 418 can be illuminated with illumination radiation to generate scattered radiation. The scattered radiation can have one or more diffraction orders (e.g., ±1, ±2, etc.). The diffraction orders are collected and sent to a detector 428 (or multiple detectors). The detector 428 can generate measurement information in the form of a signal (e.g., a measurement signal). The measurement signal can be analyzed by a processor to determine the relative position of the target 418 (e.g., wafer alignment position), overlay offset, etc. For alignment measurements, the detector 428 can be a single cell detector (i.e., a single pixel detector), a multi-pixel detector capable of resolving an image (e.g., a camera), etc. By analyzing the total intensity on the detector, without analyzing the intensity of individual pixels, the alignment position can be inferred. For example, an alignment measurement can include modulating the illumination (e.g., the intensity of a sine wave versus time) and then analyzing the characteristics (e.g., amplitude, phase, etc.) of the AC signal generated by the detector. The alignment position of the target 418 can be derived from the characteristics of the AC signal, and this analysis can be accomplished using either a single pixel detector or a camera.

[0068]

[0082] In some embodiments, an optical fiber may be used to collect radiation scattered from the target 418 and direct the radiation directly to the photosensitive element of the detector 428. An optical fiber implementation may maximize the number of photons collected. Optical fibers may be more compact and convenient than free-space optics using lenses and / or mirrors. The output end of the optical fiber may be affixed to the photosensitive element of the detector 428.

[0069]

[0083] FIG. 5 illustrates a detection portion of an inspection system 500 according to some embodiments. In some embodiments, the inspection system 500 may include a detector 502. The detector 502 may be used as the detector 428 of FIGS. 4A and 4B. The detector 502 may be disposed on a board 508 (e.g., a circuit board, a digital board, etc.). The detector 502 may include a photosensitive device 504 and an optical fiber 506. The optical fiber 506 may be coupled to the photosensitive device 504 using, for example, an index matching adhesive, a fiber connector (e.g., a pigtail connector), etc. The board 508 may include a corresponding optical fiber connector such that the optical fiber 506 may be coupled to a connector on the board 508 to achieve optical coupling between the optical fiber 506 and the photosensitive device 504. The optical fiber 506 may receive radiation 510. The radiation 510 may be radiation scattered by a target (e.g., radiation scattered by target 418, diffracted radiation beam 419, diffracted sub-beam 429, etc. (FIG. 4)), which may be directed to the photosensitive device 504. The photosensitive device 504 may generate a measurement signal 512 according to the radiation incident on a face 514 of the photosensitive device 504. The measurement signal 512 may be an electrical signal (e.g., a voltage signal, a current signal, etc.).

[0070]

[0084] In some embodiments, the optical fiber 506 may be a step index fiber or a graded index fiber. In some embodiments, the optical fiber 506 includes a rectangular core optical fiber, which will be described in more detail with reference to FIG. 7. The optical fiber 506 may enable substantially lossless transmission of multiple wavelengths of received radiation. With respect to the inspection system, the wavelength may include two or more wavelengths. The selected wavelengths may include any combination of red, green, near infrared (NIR), and far infrared (FIR) wavelengths. The red wavelengths may be understood to be in the range of approximately 620-770 nm. The green wavelengths may be understood to be in the range of approximately 490-570 nm. The NIR wavelengths may be understood to be in the range of approximately 780 nm to 2500 nm. The FIR wavelengths may be understood to range beyond the NIR to approximately 1 mm.

[0071]

[0085] In some embodiments, a single photosensitive device 504 and optical fiber 506 combination as shown in FIG. 5 is provided as a non-limiting example. Additional detectors 502 are envisioned (e.g., a second detector, a third detector, etc.) (additional detectors are not shown for clarity of illustration). In one example, an inspection system 500 with multiple detectors 502 may dedicate each detector to a particular wavelength. In another example, multiple detectors 502 may be dedicated to different diffraction orders from the target 418 (FIGS. 4A and 4B). The wavelengths and / or diffraction orders may be separated using optical devices such as beam splitters, demultiplexers, filters, refraction, etc., as would be apparent to one skilled in the art.

[0072]

[0086] It should be understood that in some embodiments, enumerated adjectives (e.g., "first," "second," "third," etc.) may be used as a naming convention and are not intended to indicate order or hierarchy (unless otherwise specified). For example, the terms "first detector" and "second detector" may distinguish two detectors, but need not specify whether the detectors have a particular order or hierarchy. Furthermore, the elements in the drawings are not limited to specific enumerated adjectives. For example, detector 502 may be referred to as a second detector when other detectors use appropriately distinguishing enumerated adjectives.

[0073]

[0087] In some embodiments, the photosensitive device 504 may exhibit a stable and predictable response to photons incident on its surface (e.g., a signal that is linearly proportional to the number of incident photons). However, in some embodiments, the photosensitive device 504 may exhibit a non-linear response to incident radiation. In one example, a radiation spot 516 incident on the surface 514 may have a diameter of 100 microns (non-limiting example). Despite a manufacturer's best efforts to provide a device with a uniform response, a region 518 of the photosensitive device 504 within the illumination spot 516 may exhibit an optical response that is different from the optical response of another region 520 of the photosensitive device 504. Microscopic defects are often found in the manufacture of photosensitive devices.

[0074]

[0088] In some embodiments, the problem of nonlinear optical behavior of the photosensitive device 504 is less detrimental if the radiation spot 516 has a uniform intensity over its entire area. However, because the alignment measurement is a dynamic process (e.g., scanning a radiation beam over a grating of the target 418 to generate an AC signal), the radiation spot 516 may not be perfectly uniform over the entire measurement. The problem may be exacerbated when using coherent radiation as the source of the radiation beam, since self-interfering coherent radiation can generate a speckle pattern in the illumination cross-section.

[0075]

[0089] FIG 6A illustrates a radiation spot 616 according to some embodiments. In some embodiments, FIG 6A is a two-dimensional intensity map of the radiation spot 616, with the intensity ranging from darker / black (low intensity) to brighter / white (high intensity). The intensity map shows that the radiation spot 616 has a speckle pattern. The line 622 corresponds to a "slice" of the intensity data shown in FIG 6B. A type of optical fiber that may generate the intensity pattern of FIG 6 may be, for example, a standard circular core optical fiber.

[0076]

[0090] FIG. 6B shows a graph 624 of the speckle pattern in line 622 according to some embodiments. The circle highlighting corresponds to the intensity of radiation spot 616. The intensity fluctuation corresponds to the speckle pattern in line 622 of the intensity cross section. Considering the average intensity of radiation spot 616, it can be easily estimated that 3σ (i.e., 3 standard deviation (sigma) rule) is very high. Dividing 3σ by the mean value gives a quantity similar to the coefficient of variation (CV) (e.g., CV=σ / mean value). For the data shown in FIG. 6, 3σ / mean value is about 0.7, indicating a large relative variance (i.e., the intensity distribution is not flat). Separate sensitivity regions 518 and 520 (FIG. 5) receiving such unpredictable radiation will correspondingly generate noisy measurement signals that may affect the accuracy in determining the alignment position.

[0077]

[0091] In some embodiments, the measurement (e.g., alignment measurement) may generate a measurement signal that behaves according to a modulation of the intensity of the radiation spot 616 (e.g., light to dark, dark to light, sinusoidal modulation, etc.). A characteristic of the modulation (e.g., phase) may be used to infer the position of the target 418 (FIG. 4). If the phase is noisy due to speckle in the detected radiation, the determined position will also have high uncertainty. Excessive phase noise may be caused by the conversion of optical intensity noise to electrical phase noise due to the phase nonlinearity of the photosensitive device 504, which is characterized by a power-to-phase conversion factor (e.g., which may be expressed in units of degrees of phase per unit power). Additional information regarding the power-to-phase conversion factor may be found, for example, in Joshi, A., Datta, S. (2009), “Dual InGaAs photodiodes having high phase linearity for precise timing applications”, IEEE Photonics Technology Letters, 21(19), 1360-1362, which is incorporated by reference in its entirety.

[0078]

[0092] In some embodiments, detector 502 with step index fiber can have a power-to-phase conversion factor of about 1-15 rad / W (e.g., 5 rad / W). Assuming a power-to-phase conversion factor of 5 rad / W and a grating pitch of target 418 (FIG. 4) of 1.6-3.2 microns leads to a measured position of target 418 (FIG. 4) with an uncertainty of about 0.15-0.29 nm, which is not negligible when fabricating sub-nanometer devices.

[0079]

[0093] In some embodiments, the above problem of position uncertainty can be solved by redesigning the detector 502 or modifying its operating principle, but such a solution has the drawback of being costly and potentially lacking backward compatibility with existing systems. Another solution involves making changes to the optics to reduce speckle.

[0080]

[0094] The inventors have overcome these shortcomings by employing a square core optical fiber. Figure 7A shows an output face 714 of a square core optical fiber 706, according to some embodiments. Figure 7B shows a two-dimensional intensity map 726 of the radiation output at the face 714. The intensity ranges from darker / black (low intensity) to brighter / white (high intensity). The intensity map 726 shows that the face 714 can output a much more uniform radiation compared to the speckle of the radiation spot 616 (Figure 6) from a standard circular core optical fiber.

[0081]

[0095] In some embodiments, the nonlinear response may be suppressed by providing a more uniform intensity cross-section incident on the photosensitive element 504 (FIG. 5). Rather than the speckle pattern being incident on separate sensitive regions 518 and 520 (FIG. 5), the radiation incident on these regions is relatively constant, mitigating unpredictable differences in response.

[0082]

[0096] In embodiments implementing a square core fiber 706, the power to phase conversion factor of the detector 502 (FIG. 5) may be reduced to less than about 1 rad / W, 0.8 rad / W, 0.5 rad / W, or 0.3 rad / W. Implementations using a square core fiber 706 may be compatible with standard connector schemes (e.g., pigtails). The square core fiber 706 may save on redesign costs and space usage (device footprint), as well as being more viable for retrofitting existing systems.

[0083]

[0097] In some embodiments, providing a long square core fiber can enhance the homogenization effect. The square core fiber 706 can have a length of about 1-100 m, 1-50 m, 1-20 m, 1-10 m, 1-5 m, 1 m, 5 m, or 10 m. The square core fiber 706 can have a core size (e.g., diameter) of about 10-600 microns. The core of the square core fiber 706 can be made of pure silica. The silica can include one or more dopants (e.g., fluorine, germanium, etc.). The numerical aperture (NA) of the square core fiber 706 can be about 0.15 or more (e.g., 0.16-0.39).

[0084]

[0098] The embodiments can be further described using the following clauses. 1. An apparatus comprising: an illumination system configured to illuminate a pattern on a patterning device; a projection system configured to project an image of the pattern onto the substrate; 1. An inspection system comprising: a radiation source configured to generate radiation; an optical element configured to direct the radiation towards a target on the substrate; A detector comprising: a photosensitive device configured to receive at least a portion of the radiation scattered by the target and to generate a measurement signal based on the received portion of the radiation; a detector including a square core optical fiber coupled to the photosensitive device, the square core optical fiber configured to guide the portion of the radiation to the photosensitive device and to homogenize the guided portion of the radiation such that an intensity cross-section of a received portion of the radiation at the photosensitive device is substantially uniform; and 13. An apparatus comprising: 2. The apparatus of claim 1, wherein the rectangular core optical fiber is further configured to enable substantially lossless transmission of multiple wavelengths of the received portion of the radiation. 3.The inspection system includes a digital board, 2. The apparatus of claim 1, wherein the detector is disposed on a digital board. 4. The digital board includes a fiber optic connector; The rectangular core optical fiber includes a fiber optic connector; 4. The apparatus of claim 3, wherein the optical fiber connector of the digital board and the square core optical fiber are configured to mate to provide coupling between the square core optical fiber and the photosensitive device. 5. The inspection system includes a second detector, a second photosensitive device configured to receive a second portion of the radiation scattered by the target and to generate a measurement signal based on the received second portion of the radiation; The apparatus described in clause 1, including a second detector including a square core optical fiber coupled to the photosensitive device, the square core optical fiber configured to guide a second portion of the radiation to the photosensitive device and to homogenize the guided second portion of the radiation so that the intensity cross-section of the received second portion of the radiation at the second photosensitive device is approximately uniform. 6. The apparatus of claim 1, wherein the power to phase conversion coefficient of the detector is less than about 1 rad / W. 7. The apparatus of claim 1, wherein the rectangular core optical fiber has a length of about 1-100 m, 1-50 m, 1-20 m, 1-10 m, 1-5 m, 1 m, 5 m, or 10 m. 8. An inspection system comprising: a radiation source configured to generate radiation; an optical element configured to direct the radiation towards the target; A detector comprising: a photosensitive device configured to receive at least a portion of the radiation scattered by the target and to generate a measurement signal based on the received portion of the radiation; a square core optical fiber coupled to the photosensitive device, the square core optical fiber configured to guide the portion of the radiation to the photosensitive device and to homogenize the guided portion of the radiation such that an intensity cross-section of a received portion of the radiation at the photosensitive device is substantially uniform; and 2. An inspection system comprising: 9. The inspection system of claim 8, wherein the rectangular core optical fiber is further configured to enable substantially lossless transmission of multiple wavelengths of the received portion of the radiation. 10. The inspection system includes a digital board; 9. The inspection system of claim 8, wherein the detector is disposed on a digital board. 11. The board includes a fiber optic connector; The rectangular core optical fiber includes a fiber optic connector; 11. The inspection system of claim 10, wherein the optical fiber connector of the board and the square core optical fiber are configured to mate to provide coupling between the square core optical fiber and the photosensitive device. 12. A second detector, comprising: a second photosensitive device configured to receive a second portion of the radiation scattered by the target and to generate a measurement signal based on the received second portion of the radiation; The inspection system of clause 8, further comprising a second detector including a square core optical fiber coupled to the photosensitive device, the square core optical fiber configured to guide a second portion of the radiation to the photosensitive device and to homogenize the guided second portion of the radiation so that the intensity cross-section of the received second portion of the radiation at the second photosensitive device is approximately uniform. 13. The inspection system of claim 8, wherein the power to phase conversion factor of the detector is less than about 1 rad / W. 14. The inspection system of clause 8, wherein the rectangular core optical fiber has a length of about 1-100m, 1-50m, 1-20m, 1-10m, 1-5m, 1m, 5m, or 10m. 15. A detector comprising: a photosensitive device configured to receive radiation and generate a measurement signal based on the received radiation; and a square core optical fiber coupled to the photosensitive device, the square core optical fiber configured to guide radiation scattered by a target to the photosensitive device and to homogenize the directed radiation such that an intensity cross-section of the received radiation at the photosensitive device is substantially uniform. 16. The detector of clause 15, wherein the rectangular core optical fiber is further configured to enable substantially lossless transmission of multiple wavelengths of the received radiation. 17. A detector as described in clause 15, wherein the detector is disposed on a digital board. 18. The detector of clause 17, wherein the digital board includes an optical fiber connector, and the square core optical fiber includes an optical fiber connector, and the optical fiber connector of the digital board and the square core optical fiber are configured to mate to provide coupling between the square core optical fiber and the photosensitive device. 19. A detector as described in clause 15, wherein the power to phase conversion coefficient of the detector is less than about 1 rad / W. 20. The detector of clause 15, wherein the rectangular core optical fiber has a length of about 1-100m, 1-50m, 1-20m, 1-10m, 1-5m, 1m, 5m, or 10m.

[0085]

[0099] Although specific reference is 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 magnetic heads, and the like. In such other applications, as will be appreciated by those skilled in the art, any term "wafer" or "die" used herein may be considered as a specific example of the more general term "substrate" or "target portion", respectively. The substrates described herein may be processed, either before or after exposure, for example in a track unit (a tool that typically applies a layer of resist to the substrate and develops the exposed resist) and / or a metrology unit. Where applicable, the disclosure herein may be applied to such and other substrate processing tools. Furthermore, a substrate may be processed multiple times, for example to create a multi-layer IC, and therefore the term substrate as used herein may refer to a substrate that already includes multiple processed layers.

[0086]

[0100] Although specific reference has been made above to the use of embodiments of the present disclosure in the context of optical lithography, it will be appreciated that the present disclosure may be used in other applications, for example imprint lithography, and is not limited to optical lithography where the context permits. In imprint lithography, a topography in a patterning device defines a pattern to be created on a substrate. The topography of the patterning device is pressed into a layer of resist supplied to the substrate where the resist is cured by applying electromagnetic radiation, heat, pressure or a combination thereof. The patterning device is moved out of the resist after the resist has been cured, leaving a pattern in the resist.

[0087]

[0101] It is to be understood that the phrases or terms used herein are for purposes of description and not of limitation, and that the terms or terms of the present disclosure should be interpreted by one of ordinary skill in the art in light of the teachings herein.

[0088]

[0102] As used herein, terms such as "radiation", "beam of radiation" and the like may encompass all types of electromagnetic radiation, including, for example, ultraviolet (UV) radiation (e.g., with wavelengths λ of 365 nm, 248 nm, 193 nm, 157 nm, or 126 nm), extreme ultraviolet (EUV or soft x-ray) radiation (e.g., with wavelengths in the range of 5 nm to 20 nm, such as 13.5 nm), or hard x-ray radiation operating below 5 nm, as well as matter beams such as ion beams or electron beams. Terms such as "light", "illumination", and the like may refer to non-material radiation (e.g., photons, UV, x-ray, etc.). In general, radiation with wavelengths between about 400 nm and about 700 nm is considered to be visible radiation, and radiation with wavelengths between about 780 nm and 3000 nm (or greater) is considered to be infrared (IR). Infrared radiation may be further sub-classified into short wavelength portions (near infrared (NIR)) and long wavelength portions (far infrared (FIR)). UV refers to radiation with wavelengths between about 100 nm and 400 nm. In lithography, the term "UV" also applies to wavelengths that can be produced by mercury discharge lamps, namely G-line 436 nm, H-line 405 nm, and / or I-line 365 nm. Vacuum UV or VUV (i.e. UV absorbed by gases) refers to radiation with wavelengths between about 100 nm and 200 nm. Deep UV (DUV) generally refers to radiation with wavelengths in the range of 126 nm to 428 nm, and in some embodiments, excimer lasers may generate DUV radiation for use in lithography equipment. It is to be understood that radiation with wavelengths in the range of, for example, 5 nm to 20 nm, refers to radiation having a particular wavelength band, at least a portion of which is in the range of 5 nm to 20 nm.

[0089]

[0103] It is understood that the Detailed Description section is intended to be used to interpret the claims, and not the Summary and Abstract sections. The Summary and Abstract sections may describe one or more exemplary embodiments of the disclosure as contemplated by the inventors, but may not describe all exemplary embodiments, and thus are not intended to limit the scope of the disclosure and the appended claims in any way.

[0090]

[0104] The present disclosure is made using functional building blocks that illustrate the implementation of specific functions and relationships between these functional building blocks. The boundaries of these functional building blocks are arbitrarily defined herein for the convenience of description. Alternative boundaries can be defined as long as the specific functions and relationships between these functions are appropriately implemented.

[0091]

[0105] Although specific embodiments of the present disclosure have been described, it will be understood that the embodiments of the present disclosure may be practiced otherwise than as described. The above description is intended to be illustrative and not limiting. Thus, it will be apparent to one skilled in the art that modifications may be made to the present disclosure as described without departing from the scope of the appended claims.

[0092]

[0106] The above description of specific embodiments sufficiently reveals the general nature of the present disclosure so that others, by applying knowledge within the art, can easily modify and / or adapt such specific embodiments for various applications without undue experimentation and without departing from the general concept of the present disclosure. Such adaptations and modifications are therefore intended to be within the meaning and range of equivalents of the disclosed embodiments, based on the teaching and guidance presented herein.

[0093]

[0107] The breadth and scope of protected subject matter 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 apparatus comprising: an illumination system configured to illuminate a pattern on a patterning device; a projection system configured to project an image of the pattern onto a substrate; 1. An inspection system comprising: a radiation source configured to generate radiation; an optical element configured to direct the radiation towards a target on the substrate; A detector comprising: a photosensitive device configured to receive at least a portion of the radiation scattered by the target and to generate a measurement signal based on the received portion of the radiation; a detector including a square core optical fiber coupled to the photosensitive device, the square core optical fiber configured to guide the portion of the radiation to the photosensitive device and to homogenize the guided portion of the radiation such that an intensity cross-section of the received portion of the radiation at the photosensitive device is substantially uniform; and 13. An apparatus comprising:

2. 10. The apparatus of claim 1, wherein the rectangular core optical fiber is further configured to allow substantially lossless transmission of multiple wavelengths of the received portion of the radiation.

3. The inspection system includes a digital board; The apparatus of claim 1 , wherein the detector is disposed on the digital board.

4. the digital board includes a fiber optic connector; the rectangular core optical fiber includes an optical fiber connector; The apparatus of claim 3 , wherein the fiber optic connector of the digital board and the square core optical fiber are configured to mate to provide a coupling between the square core optical fiber and the photosensitive device.

5. The inspection system includes a second detector, a second photosensitive device configured to receive a second portion of the radiation scattered by the target and to generate a measurement signal based on the received second portion of the radiation; and 2. The apparatus of claim 1, further comprising: a second detector comprising: a square core optical fiber coupled to the photosensitive device, the square core optical fiber configured to guide the second portion of the radiation to the photosensitive device and to homogenize the guided second portion of the radiation such that an intensity cross-section of the received second portion of the radiation at the second photosensitive device is approximately uniform.

6. 10. The apparatus of claim 1, wherein the detector has a power-to-phase conversion factor of less than about 1 rad / W.

7. 10. The apparatus of claim 1, wherein the rectangular core optical fiber has a length of about 1-100 m, 1-50 m, 1-20 m, 1-10 m, 1-5 m, 1 m, 5 m, or 10 m.

8. 1. An inspection system comprising: a radiation source configured to generate radiation; an optical element configured to direct the radiation towards a target; A detector comprising: a photosensitive device configured to receive at least a portion of the radiation scattered by the target and to generate a measurement signal based on the received portion of the radiation; a square core optical fiber coupled to the photosensitive device, the square core optical fiber configured to guide the portion of the radiation to the photosensitive device and to homogenize the guided portion of the radiation such that an intensity cross-section of the received portion of the radiation at the photosensitive device is substantially uniform; and 2. An inspection system comprising:

9. The inspection system of claim 8 , wherein the rectangular core optical fiber is further configured to allow substantially lossless transmission of multiple wavelengths of the received portion of the radiation.

10. The inspection system includes a digital board; The inspection system of claim 8 , wherein the detector is disposed on the digital board.

11. the board includes a fiber optic connector; the rectangular core optical fiber includes an optical fiber connector; The inspection system of claim 10 , wherein the fiber optic connector of the board and the rectangular core optical fiber are configured to mate to provide a connection between the rectangular core optical fiber and the photosensitive device.

12. a second detector, a second photosensitive device configured to receive a second portion of the radiation scattered by the target and to generate a measurement signal based on the received second portion of the radiation; and 10. The inspection system of claim 8, further comprising: a second detector comprising: a square core optical fiber coupled to the photosensitive device, the square core optical fiber configured to guide the second portion of the radiation to the photosensitive device and to homogenize the guided second portion of the radiation such that an intensity cross-section of the received second portion of the radiation at the second photosensitive device is approximately uniform.

13. A detector comprising: a photosensitive device configured to receive radiation and generate a measurement signal based on the received radiation; a rectangular core optical fiber coupled to the photosensitive device, the rectangular core optical fiber configured to guide the radiation scattered by the target to the photosensitive device and to homogenize the guided radiation such that an intensity cross-section of the received radiation at the photosensitive device is substantially uniform; a detector.

14. The detector of claim 13 , wherein the rectangular core optical fiber is further configured to allow substantially lossless transmission of multiple wavelengths of the received radiation.

15. the digital board includes a fiber optic connector; the rectangular core optical fiber includes an optical fiber connector; 15. The detector of claim 14, wherein the fiber optic connector of the digital board and the square core optical fiber are configured to mate to provide coupling between the square core optical fiber and the photosensitive device.

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