WO2016096322A1

WO2016096322A1 - Optical encoder system, encoder head and lithographic apparatus

Info

Publication number: WO2016096322A1
Application number: PCT/EP2015/077232
Authority: WO
Inventors: Teunis Ikkink; Leon MERKX; Jan VAN DER PUT; Tom Van Zutphen; Olaf VREEDE
Original assignee: Asml Netherlands B.V.
Priority date: 2014-12-19
Filing date: 2015-11-20
Publication date: 2016-06-23
Also published as: NL2015826A

Abstract

An optical encoder system (200) comprises a radiation source (20), an encoder head (22), a scale (24) and an optical fiber (26). The radiation source is arranged to generate a radiation beam (28). The encoder head has a splitting element for splitting the radiation beam into split radiation beams (210a, 210b). The scale is arranged to receive at least one of the split radiation beams. The optical fiber is arranged to propagate the radiation beam at least partly between the radiation source and the splitting element. The optical fiber is a single-polarization fiber.

Description

OPTICAL ENCODER SYSTEM, ENCODER HEAD AND LITHOGRAPHIC APPARATUS

CROSS REFERENCE TO RELATED APPLICATIONS

[001] This application claims priority of EP application 14199247.9 which was filed on 2014- Dec-19 and of EP application 15170508.4 which was filed on 2015-Jun-03 and which are incorporated herein in their entirety by reference

FIELD OF THE INVENTION

[002] The invention relates to an optical encoder system, an encoder head for use in the optical encoder system, and a lithographic apparatus.

BACKGROUND ART

[003] A lithographic apparatus is an apparatus that can be used in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred by a radiation beam via a projection system onto a target portion on a substrate, such as a silicon wafer. Transfer of the pattern is typically performed via imaging onto a layer of radiation- sensitive material provided on the substrate. The location on which the radiation beam is incident on the target portion is referred to as the exposure location.

[004] The cross-section of the radiation beam is typically much smaller than the surface of the substrate. So in order to expose all the target portions on the surface of the substrate, the substrate is moved relative to the projection system. The lithographic apparatus has a stage system to move the substrate relative to the projection system. The stage system is able to move the substrate in such a way that the target portions are placed consecutively in the path of the radiation beam.

[005] To place each of the target portions in the path of the radiation beam correctly, the lithographic apparatus is provided with a position measurement system. The position

measurement system measures a position of the stage system. The position measurement system may comprise an encoder head and a scale. The scale has a grating surface. The encoder is arranged to receive a radiation beam from the grating surface of the grating. The encoder head is able to detect a change in the radiation beam when the grating surface moves relative to the encoder. In dependence of the radiation beam, the encoder head is able to generate a position signal representative of the position of the grating surface relative to the encoder head.

SUMMARY OF THE INVENTION

[006] The encoder head makes use of the polarization of the radiation beam to determine the position of the encoder head relative to the scale. The radiation beam propagates to the encoder head via an optical fiber. To maintain the correct polarization, the optical fiber typically is a polarization-maintaining fiber. A radiation beam will maintain a particular linear polarization while propagating from entrance to exit of a polarization maintaining fiber, provided that this particular linear polarization is aligned to the first of two principal birefringence axes of the polarization maintaining fiber at the entrance of this fiber.

[007] Unfortunately, if the radiation beam entering the polarization maintaining fiber does not have perfectly linear polarization, or if its linear polarization is not perfectly aligned to either one of the two principal birefringence axes of the polarization maintaining fiber, the polarization of the propagating radiation beam will not be maintained perfectly. In this case the radiation beam will have two non-zero linear polarization components. Of the two, one is intended and is aligned to the first of the two principal birefringence axes of the polarization maintaining fiber. The other one of the two is unintended and is aligned to the second of the two principal birefringence axes of the polarization maintaining fiber. The intended and unintended linear polarization components of the radiation beam will propagate through the polarization maintaining fiber at distinctly different velocities. They will therefore acquire a mutual phase difference, which depends on their velocity difference, on the fiber length and on the wavelength of the radiation beam. In the encoder head the unintended linear polarization component will interfere with the intended linear polarization component, which deteriorates the measurement accuracy of the encoder system, depending on the acquired mutual phase difference. To avoid this accuracy deterioration, the unintended linear polarization component must be attenuated considerably. A linear polarizer is commonly applied in the encoder head to achieve this attenuation. A disadvantage of the linear polarizer in the encoder head is that it increases the complexity of the encoder head and that it requires additional manufacturing steps for mounting and accurate alignment.

[008] It is an objective of the invention to improve the accuracy of the encoder head. [009] In a first embodiment of the invention, there is provided an optical encoder system comprising a radiation source, an encoder head, a scale and an optical fiber. The radiation source is arranged to generate a radiation beam. The encoder head has a splitting element for splitting the radiation beam into split radiation beams. The scale is arranged to receive at least one of the split radiation beams. The optical fiber is arranged to propagate the radiation beam at least partly between the radiation source and the splitting element. The optical fiber is a single-polarization fiber.

[010] According to the first embodiment, only light with the proper polarization exits the optical fiber. As a result, the encoder head uses a radiation beam with the proper polarization, which increases the accuracy with which the encoder head can determine the position relative to the scale. Additional polarizers may be omitted to achieve this increase in accuracy.

[011] In a second embodiment of the invention, the splitting element is arranged to split the radiation beam based on a polarization of the radiation beam.

[012] According to the second embodiment, the splitting element receives the radiation beam with the proper polarization, which increases the accuracy with which the encoder head can determine the position of the encoder head relative to the scale.

[013] In a third embodiment of the invention, the splitting element comprises a beam splitter for splitting the radiation beam into the split radiation beams.

[014] In a fourth embodiment of the invention, the optical fiber is connected to the splitting element.

[015] According to the fourth embodiment, the radiation beam exiting the optical fiber with the correct polarization is received by the splitting element.

[016] In a fifth embodiment of the invention, the optical encoder system comprises a coupling for optically coupling the optical fiber and the radiation source to each other.

[017] In a sixth embodiment of the invention, the optical encoder system comprises a further optical fiber. The coupling is arranged to optically couple the optical fiber and the further optical fiber to each other. The further optical fiber is arranged to propagate the radiation beam at least partly from the radiation source to the coupling.

[018] According to the sixth embodiment, any type of optical fiber, such as any type of single- mode optical fiber may be used between the radiation source and the coupling. [019] In a seventh embodiment of the invention, the coupling comprises a first part and a second part. The first part is fixedly connected to the optical fiber. The second part is fixedly connected to the further optical fiber. The first part and the second part are detachably connectable with each other.

[020] According to the seventh embodiment, the encoder head can be easily connected and detached from the radiation source.

[021] In an eighth embodiment of the invention, there is provided an encoder head for use in the optical encoder system described above. The encoder head comprises the optical fiber.

[022] In a ninth embodiment of the invention, there is provided a lithographic apparatus comprising a body, a reference and the optical encoder system described above. One of the encoder head and the scale is connected to the body. The other of the encoder head and the scale is connected to the reference. The optical encoder system is arranged to provide a signal representative of a position of the body relative to the reference.

[023] According to the ninth embodiment, the position of the body relative to the reference can be determined with more accuracy.

[024] In a tenth embodiment of the invention, the body comprises at least part of a projection system for projecting an image on a substrate.

[025] According to the tenth embodiment, a position of at least part of the projection system can be determined with more accuracy.

[026] In an eleventh embodiment of the invention, the lithographic apparatus comprises a projection system. The projection system is arranged to project an image on a substrate. The body comprises a detection system arranged to detect a property of the substrate.

[027] According to the eleventh embodiment, a position of the detection system can be determined with more accuracy.

[028] In a twelfth embodiment of the invention, the lithographic apparatus comprises a projection system, a support structure and a substrate table. The projection system is arranged to project an image of a pattern on a substrate. The support structure is arranged to support a patterning device having the pattern. The substrate table is arranged to support the substrate. The body comprises one of the substrate table and the support structure.

[029] According to the twelfth embodiment, a position of the support structure or the substrate table can be determined with more accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which:

Figure 1 depicts a lithographic apparatus according to the invention.

Figure 2 depicts an optical encoder system according to an embodiment of the invention.

Figure 3 depicts part of an encoder head according to a further embodiment of the invention.

DETAILED DESCRIPTION

[030] Figure 1 schematically depicts a lithographic apparatus with an optical encoder system according to the invention. The apparatus may comprise an illumination system IL, a support structure MT, a substrate table WT and a projection system PS.

[031] The illumination system IL is configured to condition a radiation beam B. The illumination system IL may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic or other types of optical components, or any combination thereof, for directing, shaping, or controlling radiation.

[032] The illumination system IL receives a radiation beam from a radiation source SO. The radiation source SO and the lithographic apparatus may be separate entities, for example when the radiation source SO is an excimer laser. In such cases, the radiation source SO is not considered to form part of the lithographic apparatus and the radiation beam B is passed from the radiation source SO to the illumination system IL with the aid of a beam delivery system BD comprising, for example, suitable directing mirrors and/or a beam expander. In other cases the radiation source SO may be an integral part of the lithographic apparatus, for example when the radiation source SO is a mercury lamp. The radiation source SO and the illumination system IL, together with the beam delivery system BD if required, may be referred to as a radiation system.

[033] The illumination system IL may comprise an adjuster AD for adjusting the angular intensity distribution of the radiation beam. In addition, the illumination system IL may comprise various other components, such as an integrator IN and a condenser CO. The illumination system IL may be used to condition the radiation beam B, to have a desired uniformity and intensity distribution in its cross section.

[034] The term "radiation beam B" used herein encompasses all types of electromagnetic radiation, including ultraviolet (UV) radiation (e.g. having a wavelength of or about 365, 355, 248, 193, 157 or 126 nm) and extreme ultra-violet (EUV) radiation (e.g. having a wavelength in the range of 5-20 nm), as well as particle beams, such as ion beams or electron beams.

[035] The support structure (e.g. a mask table) MT is for supporting a patterning device (e.g. a mask or reticle) MA. The support structure MT is connected to a first stage system PM configured to accurately position the patterning device MA in accordance with certain parameters.

[036] The support structure MT supports, i.e. bears the weight of the patterning device MA. The support structure MT holds the patterning device MA in a manner that depends on the orientation of the patterning device MA, the design of the lithographic apparatus, and other conditions, such as for example whether or not the patterning device MA is held in a vacuum environment. The support structure MT can use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device MA. The support structure MT may be a frame or a table, for example, which may be fixed or movable as required. 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.

[037] The term "patterning device MA" used herein should be broadly interpreted as referring to any device that can be used to impart a radiation beam B with a pattern in its cross-section such as to create a pattern in a target portion C of the substrate W. It should be noted that the pattern imparted to the radiation beam B may not exactly correspond to the desired pattern in the target portion C of the substrate W, for example if the pattern includes phase- shifting features or so called assist features. Generally, the pattern imparted to the radiation beam B will correspond to a particular functional layer in a device being created in the target portion C, such as an integrated circuit.

[038] The patterning device MA may be transmissive or reflective. Examples of a patterning device MA include masks, programmable mirror arrays, and programmable LCD panels. Masks are well known in lithography, and include mask types such as binary, alternating phase-shift, and attenuated phase-shift, as well as various hybrid mask types. An example of a programmable mirror array employs 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 in a radiation beam which is reflected by the mirror matrix. As here depicted, the apparatus is of a transmissive type, which employs a transmissive mask.

[039] The substrate table WT, e.g. a wafer table, is for holding a substrate W, e.g. a resist coated wafer. The substrate table WT is connected to a second stage system PW configured to accurately position the substrate W in accordance with certain parameters.

[040] The projection system PS is configured to project a pattern imparted to the radiation beam B by patterning device MA onto a target portion C of the substrate W.

[041] The term "projection system PS" used herein should be broadly interpreted as encompassing any type of projection system PS, including refractive, reflective, magnetic, electromagnetic and electrostatic optical systems, or any combination thereof, as appropriate for the exposure radiation being used, or for other factors such as the use of an immersion liquid or the use of a vacuum. The projection system PS may comprise at least one mirror to reflect EUV radiation.

[042] The radiation beam B is incident on the patterning device MA and is patterned by the patterning device MA. Having traversed the patterning device MA, the radiation beam B passes through the projection system PS which focuses the radiation beam B onto a target portion C of the substrate W. The location on the substrate W on which the radiation beam B is focused is referred to as the exposure location. With the aid of the second positioning system PW and position measurement system IF (e.g. an interferometric device, encoder or capacitive sensor), the substrate table WT can be moved accurately, e.g., so as to position different target portions C in the path of the radiation beam B. Similarly, the first stage system PM and another position sensor (which is not depicted in Figure 1) can be used to accurately position the patterning device MA with respect to the path of the radiation beam B. In general, movement of the support structure MT may be realized with the aid of a long-stroke module and a short-stroke module. The long-stroke module provides coarse positioning of the short-stroke module relative to the projection system PS over a long range. The short-stroke module provides fine positioning of the patterning device MA relative to the long-stroke module over a small range. Similarly, movement of the substrate table WT may be realized using a long-stroke module and a short- stroke module, which form part of the second stage system PW. In the case of a stepper (as opposed to a scanner) the support structure MT may be connected to a short-stroke actuator only, or may be fixed.

[043] Patterning device MA and substrate W may be aligned using mask alignment marks Ml, M2 and substrate alignment marks PI, P2. Although the substrate alignment marks PI, P2 as illustrated occupy dedicated target portions, they may be located in spaces between target portions C. Similarly, in situations in which more than one die is provided on the patterning device MA, the mask alignment marks Ml, M2 may be located between the dies.

[044] The lithographic apparatus may be of a type having two or more substrate tables WT and/or two or more support structures MT. In addition to the at least one substrate table WT, the lithographic apparatus may comprise a measurement table, which is arranged to perform measurements but is not arranged to hold a substrate W.

[045] The lithographic apparatus may also be of a type wherein at least a portion of the substrate W 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 PS and the substrate W. An immersion liquid may also be applied to other spaces in the lithographic apparatus, for example, between the patterning device MA and the projection system PS. 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 a substrate W, must be submerged in liquid, but rather only means that liquid is located between the projection system PS and the substrate W during exposure.

[046] The depicted lithographic apparatus could be used in at least one of the following three modes:

[047] In the first mode, the so-called step mode, the support structure MT and the substrate table WT are kept essentially stationary, while an entire pattern imparted to the radiation beam B is projected onto a target portion C at one time. The substrate table WT is then shifted in the X and/or Y direction by the second positioning system PW so that a different target portion C can be exposed.

[048] In the second mode, the so-called scan mode, the support structure 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. The velocity and direction of the substrate table WT relative to the support structure MT may be determined by the (de-)magnification and image reversal characteristics of the projection system PS.

[049] In the third mode, the support structure MT is kept essentially stationary holding a programmable patterning device MA. The substrate table WT is moved or scanned while a pattern imparted to the radiation beam B is projected onto a target portion C. In this mode, generally a pulsed radiation source is employed and the programmable patterning device is updated as required after each movement of the substrate table WT or in between successive radiation pulses during a scan. This mode of operation can be readily applied to maskless lithography that utilizes programmable patterning device MA, such as a programmable mirror array of a type as referred to above.

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

[051] Figure 2 depicts an optical encoder system 200 according to a first embodiment of the invention. The optical encoder system 200 may be part of the position measurement system IF. The optical encoder system 200 comprises a radiation source 20, an encoder head 22, a scale 24 and an optical fiber 26. The radiation source 20 is arranged to generate a radiation beam 28. The encoder head 22 has a splitting element 30, which is shown in Figure 3. The splitting element 30 is arranged to split the radiation beam 28 into split radiation beams 210a and 210b. The scale 24 is arranged to receive at least one of the split radiation beams 210a, 210b. The optical fiber 26 is arranged to propagate the radiation beam 28 at least partly between the radiation source 20 and the splitting element 30. The optical fiber is a single-polarization fiber. A single polarization fiber may comprise an optical fiber comprising a polarizing structure.

[052] The scale 24 has a pattern. The at least one split radiation beam 210a, 210b diffracts as a result of the pattern on the scale 24. The diffracted split radiation beam 210a, 210b is received by the encoder head 22. After the encoder head 22 receives the diffracted split radiation beam 210a, 210b from the scale 24, the encoder head 22 is able to interfere the two split radiation beams 210, 210b with each other, to create a combined radiation beam 36, see Figure 3. The combined radiation beam 36 is incident on a detector (not shown). The detector generates a signal, such as an electrical signal, based on the combined radiation beam 36. The signal is representative of the position of the encoder head 22 relative to the scale 24. [053] The encoder head 22, the scale 24 and the detector may be arranged at least partly as described in US-patent US 8,390,820 B2, published on March 5, 2013, hereby incorporated by reference.

[054] The splitting element 30 may be any type of element suitable for splitting the radiation beam 28 into the split radiation beams 210a, 210b. The splitting element 30 splits the radiation beam 28 into the split radiation beams 210a, 210b, which have a high mutual correlation. The high mutual correlation allows the split radiation beams 210a, 210b to interfere with each other after at least one of the split radiation beams 210a, 210b is diffracted by the scale 24. The splitting element 30 may comprise a grating or a beam splitter. The splitting element 30 may comprise a polarizing beam splitter. A polarizing beam splitter is a beam splitter that splits the radiation beam 28 into a split radiation beam 210a with a first polarization and into a split radiation beam 210b with a second polarization. The first polarization and the second

polarization may be substantially orthogonal to each other. For example, the split radiation beams 210a and 210b are each linearly polarized in mutually orthogonal directions.

[055] The optical fiber is a single-polarization fiber, which may comprise an optical fiber containing a polarizing structure. Single-polarization fibers are special optical fibers which can transmit light with a certain linear polarization direction, whereas light with the orthogonal linear polarization direction is either not guided or at least experiences strong optical losses. Such fibers should not be confused with polarization-maintaining fibers, which guide light of both orthogonal linear polarization states, and which can preserve a linear polarization state when the polarization direction is properly aligned to either one of the two orthogonal principal birefringence axes of the fiber. More about single-polarization fibers is disclosed on

http://www.rp-photonics.com/single polarization fibers, tml.

[056] The optical fiber 26 may be connected to the splitting element 30. For example, one end of the optical fiber 26 is physically connected to the splitting element 30. The one end is the end at which the radiation beam 28 exits the optical fiber 26. Alternatively, there is an open space or another optical component, such as a collimating lens, between the splitting element 30 and the optical fiber 26.

[057] As shown in Figure 2, the optical encoder system 200 may be provided with a coupling 212. The coupling 212 may be arranged for optically coupling the optical fiber 26 and the radiation source 20 to each other. The coupling 212 may either be part of the encoder head 22 or be part of the radiation source 20. The coupling 212 transfers the radiation beam 28 from the radiation source 20 to the encoder head 22.

[058] The optical encoder system 200 may be provided with a further optical fiber 214. The coupling 212 may be arranged to optically couple the optical fiber 26 and the further optical fiber 214 to each other. The further optical fiber 214 is arranged to propagate the radiation beam 28 at least partly from the radiation source 20 to the coupling 212. The further optical fiber 214 may be any type of suitable optical fiber, such as a polarization-maintaining fiber. Ideally, in an embodiment in which the further optical fiber 214 is a polarization-maintaining fiber, the radiation beam 28 emitted by the radiation source 20 is linearly polarized and the polarization direction of the radiation beam 28 is aligned to the intended one of the two principal

birefringence axes of the further optical fiber 214. However, manufacturing tolerances may result in a non-zero radiation beam component having a linear polarization direction aligned to the undesired one of the two principal birefringence axes of the further optical fiber 214. However, since the optical fiber 26 only propagates the intended linear polarization component, the unintended polarization component of the radiation beam 28 is blocked from entering the encoder head 22 by the optical fiber 26.

[059] The coupling 212 may be a permanent coupling, in which an endface of the optical fiber 26 and an endface of the further optical fiber 214 are permanently coupled together. Such a permanent coupling may be made by splicing the endfaces together, for example by fusion splicing or dry splicing. As an alternative to a permanent coupling, the coupling 212 may be a detachable connector. In this case the coupling 212 may comprise a first part and a second part. The first part is fixedly connected to the optical fiber 26. The second part is fixedly connected to the further optical fiber 214. The first part and the second part are detachably connectable with each other. The term "detachably connectable" means that the first part and the second part are connectable in such a way that the radiation beam 20 may propagate from the second part to the first part. The first part and the second part are detachable such that the first part and the second part can be separated from each other without damaging the first part and/or the second part. For example, no tools are needed to separate the first part and the second part from each other.

[060] The pattern on the scale 24 may be any type of line pattern or grating suitable to diffract the at least one of the split radiation beams 210a, 210b. The pattern may have lines that extend in one or two directions. The pattern may be a 2D-pattern allowing diffraction of the split radiation beams 210a, 210b in multiple directions. The pattern may diffract the split radiation beams 210a, 210b into a +/-l^st diffraction order or in one or more higher diffraction orders.

[061] Figure 3 schematically depicts a detailed view on the encoder head 22. The radiation beam 28 propagates from the radiation source 20 via the optical fiber 26 to the splitting element 30. Via the splitting element 30, the radiation beam 28 is split into split radiation beams 210a and 210b. Each of split radiation beams 210a and 210b propagates via a mirror 32a, 32b to the scale 24. The scale 24 diffracts split radiation beams 210a and 210b. Via two additional mirrors 34a, 34b, the split radiation beam 210a and 210b are redirected back to the scale 24, diffract a second time on the scale 24, and are reflected back to the splitting element 30. The splitting element 30 recombines split radiation beams 210a and 210b into a combined radiation beam 36. The combined radiation beam 36 propagates via a detection channel to the detector.

[062] The splitting element 30 may split the radiation beam 28 into the split radiation beams 210a, 210b based on the polarization of the radiation beam 28. For example, the radiation beam 28 may be linearly polarized at an angle of 45 degrees to either of the polarizing axes of the splitting element 30. Radiation with a linear polarization at an angle of 45 degrees may be decomposed into two orthogonal components at respective angles of 0 degrees and 90 degrees. One of the two components is reflected by the splitting element 30 to create the split radiation beam 210b. The other of the two components is transmitted by the splitting element 30 to create the split radiation beam 210a. To obtain maximum interference contrast, the intensity of each of the split radiation beams 210a, 210b may be substantially the same. For example, each intensity is 50% of the intensity of the radiation beam 28.

[063] In Figure 3 a single radiation beam 28 is split into two split radiation beams 210a, 210b. In an embodiment, multiple radiation beams 28 are provided by the radiation source 20. The radiation beam 28 may pass a plurality of splitting elements 30, which causes the radiation beam 28 to split into more than 2 split radiation beams 210a, 210b. The more than two split radiation beams 210a, 210b may propagate in a single plane or may in multiple planes, for example two planes perpendicular to each other.

[064] The optical encoder system 200 described above may be used in the lithographic apparatus. One of the scale 24 and the encoder head 22 may be provided on a body. The other of the scale 24 and the encoder head 22 may be provided on a reference. The optical encoder system 200 is arranged to provide a signal representative of a position of the body relative to the reference.

[065] The optical encoder system 200 described above can be used in the projection system PS, for example to determine a position of an optical component of the projection system PS relative to a reference. The optical component may comprise a lens or a mirror. The mirror may be arranged to reflect EUV radiation. A plurality of optical encoder systems 200 may be used in the projection system PS. The plurality of optical encoders systems 200 may share some

components. For example, one radiation source 20 may provide a radiation beam to multiple encoder heads 22. In addition or alternatively, the optical encoder system 200 may be used in the illumination system IL to determine a position of a optical component in the illumination system IL relative to a reference.

[066] The optical encoder system 200 described above may be used to determine the position of a detection system to detect a property of the substrate W. Such a detection system may be an alignment sensor arranged to determine the location of the substrate alignment marks PI, P2. The alignment sensor may be arranged to determine the position of the substrate W relative to the substrate table WT. The detection system may be a level sensor arranged to determine a height profile of the substrate W when on the substrate table WT.

[067] The reference described above may be a metrology frame. The metrology frame may be arranged to support the projection system PS. The metrology frame may comprise a thermal conditioning system to maintain a substantially constant temperature.

[068] The optical encoder system 200 described above may be used to determine the position of the support structure MT or the substrate table WT relative to a reference. For example, a plurality of encoder heads 22 are arranged on metrology frame. A plurality of scales 24 are arranged on the support structure MT or the substrate table WT.

[069] The optical encoder system 200 described above may be used in any type of arrangement in which a position of an encoder head 22 relative to a scale 24 is to be determined. Such an arrangement may be in a metrology apparatus arranged to measure features on the substrate W. Such features may be created by exposing the substrate W in the lithographic apparatus.

[070] Although specific reference may be made in this text to the use of a 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, micro electromechanical systems (MEMS), flat-panel displays, liquid-crystal displays (LCDs), thin film magnetic heads, etc. The substrate W may be processed, before or after the transfer of the pattern onto the substrate W, in for example a track, a metrology tool and/or an inspection tool. A track is a tool that typically applies a layer of resist to a substrate W and develops the resist that has been exposed to the radiation beam B. Further, the substrate W may be processed more than once, for example in order to create a multi-layer IC, so that the term substrate W used herein may also refer to a substrate W that already contains multiple processed layers.

[071] While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described.

[072] The descriptions above are intended to be illustrative, not limiting. Thus, it will be apparent to one skilled in the art that modifications may be made to the invention as described without departing from the scope of the claims set out below.

Claims

WHAT IS CLAIMED IS:

1. An optical encoder system, comprising:

a radiation source, an encoder head, a scale and an optical fiber,

wherein the radiation source is arranged to generate a radiation beam,

wherein the encoder head has a splitting element for splitting the radiation beam into split radiation beams,

wherein the scale is arranged to receive at least one of the split radiation beams,

wherein the optical fiber is arranged to propagate the radiation beam at least partly between the radiation source and the splitting element,

wherein the optical fiber is a single-polarization fiber.

2. The optical encoder system of claim 1, wherein the splitting element is arranged to split the radiation beam based on a polarization of the radiation beam.

3. The optical encoder system of one of the preceding claims, wherein the splitting element comprises a beam splitter for splitting the radiation beam into the split radiation beams.

4. The optical encoder system of one of the preceding claims, wherein the optical fiber is connected to the splitting element.

5. The optical encoder system of one of the preceding claims, comprising a coupling for optically coupling the optical fiber and the radiation source to each other.

6. The optical encoder system of claim 5, comprising a further optical fiber, wherein the coupling is arranged to optically couple the optical fiber and the further optical fiber to each other, wherein the further optical fiber is arranged to propagate the radiation beam at least partly from the radiation source to the coupling.

7. The optical encoder system of claim 6, wherein the coupling comprises a first part and a second part,

wherein the first part is fixedly connected to the optical fiber, wherein the second part is fixedly connected to the further optical fiber,

wherein the first part and the second part are detachably connectable with each other.

8. The optical encoder system of claim 6, wherein the coupling comprising an endface of the optical fiber and an endface of the further optical fiber coupled together by splicing.

9. An encoder head for use in the optical encoder system of one of the preceding claims, wherein the encoder head comprises the optical fiber.

10. A lithographic apparatus comprising a body, a reference and the optical encoder system of one of claims 1-9,

wherein one of the encoder head and the scale is connected to the body,

wherein the other of the encoder head and the scale is connected to the reference,

wherein the optical encoder system is arranged to provide a signal representative of a position of the body relative to the reference.

11. The lithographic apparatus of claim 10, wherein the body comprises at least part of a projection system for projecting an image on a substrate.

12. The lithographic apparatus of claim 10, comprising a projection system,

wherein the projection system is arranged to project an image on a substrate,

wherein the body comprises a detection system arranged to detect a property of the substrate.

13. The lithographic apparatus of claim 10, comprising a projection system, a support structure and a substrate table,

wherein the projection system is arranged to project an image of a pattern on a substrate, wherein the support structure is arranged to support a patterning device having the pattern, wherein the substrate table is arranged to support the substrate,

wherein the body comprises one of the substrate table and the support structure.