Position measurement system and lithographic apparatus

Abstract

In the integrated displacement sensor, a source beam is directed along a plane, and at least a portion of the beam is received by an emission grating and diffracted in an emission direction away from the plane to form an emission beam. A target grating positioned on the object of interest receives the emission beam, and the emission beam is diffracted on the object of interest to form zeroth-order, first-order, and minus-first-order diffraction beams. Two first-order couplers form the planar first-order and minus-first-order diffraction beams. The zeroth-order coupler forms the planar zeroth-order diffraction beam, and first-order and minus-first-order combining devices generate at least one first-order diffraction order interference optical signal, and the zeroth-order combining device generates a zeroth-order diffraction order interference optical signal using the planar zeroth-order diffraction beam and a reference portion of the source beam. An optical sensor receives the diffraction order interference optical signal and generates an output signal.

Description

[Technical Field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS)

[0001] This application claims priority to European Application No. 22206565.8 filed on November 10, 2022 and European Application No. 22214508.8 filed on December 19, 2022, which applications are incorporated by reference in their entirety into this specification.

[0002] The present invention relates to a position measurement system, a lithographic apparatus, and a projection system of an optical lithography system. [Background technology]

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

[0004] As semiconductor manufacturing processes continue to advance, the dimensions of circuit elements have continually decreased, while the amount of functional elements, such as transistors, per device has steadily increased for decades, following a trend commonly referred to as "Moore's Law." To accommodate Moore's Law, the semiconductor industry pursues technologies that enable the creation of smaller and smaller features. To project a pattern onto a substrate, a lithography apparatus may use electromagnetic radiation. The wavelength of this radiation determines the minimum size of the features patterned on the substrate. Typical wavelengths currently in use are 365 nm (i-line), 248 nm, 193 nm, and 13.5 nm. To form smaller features on a substrate than lithography apparatuses using radiation having a wavelength of, for example, 193 nm, lithography apparatuses using extreme ultraviolet (EUV) radiation, having wavelengths in the range of 4 nm to 20 nm, e.g., 6.7 nm or 13.5 nm, may be used.

[0005]

[0005] In a semiconductor manufacturing process, multiple layers are provided on a substrate. In addition, a pattern is projected onto the substrate, followed by processing of the substrate with the projected pattern. The process of projecting a pattern onto a substrate and processing the projected pattern may be repeated multiple times, for example, using different patterns and / or different processes. In order to realize small features on the substrate, the substrate should be accurately positioned each time a pattern is projected onto the substrate, thereby ensuring that successive patterns are accurately aligned with each other. A lithographic apparatus includes a substrate table for holding the substrate. When projecting a pattern onto the substrate, the substrate table may, for example, perform a scanning movement, whereby portions of the substrate are successively irradiated. In order to accurately position the substrate, an accurate determination of the position of the substrate table is desired.

[0006] The position of the substrate table can be measured using one or more interferometers, whereby an optically reflective surface of the substrate table is illuminated with a measurement beam, the measurement beam is reflected by the reflective surface, and an interferometric measurement is performed. A Michelson interferometer may be applied. The position of the reflective surface, and therefore the position of the substrate table, can be derived from the interferometric measurement.

[0007]

[0007] To measure the position of the substrate table in multiple degrees of freedom, multiple interferometers may be used, for example to perform measurements in different directions. Measurements in different directions may involve interferometer beams reflecting off different parts of the substrate table, for example different sides of the substrate table. For example, to perform X and Y measurements in a horizontal plane, dual interferometers may be used, each emitting an interferometer beam in a mutually perpendicular direction and reflecting off a mutually perpendicular surface of the substrate table. In order to accurately correlate the measurements from the different interferometers with each other, and therefrom determine the position of the substrate table in multiple degrees of freedom, a rigid body behavior of the substrate table would be desirable.

[0008]

[0008] High throughput requirements for lithographic apparatus tend to necessitate increased acceleration and movement speed of the substrate table. To meet such high throughput requirements, a reduction in the mass of the substrate table is desirable. However, such a reduction in the mass of the substrate table may adversely affect the rigid body behavior of the substrate table, which may affect the accuracy of position measurements of the substrate table. Summary of the Invention

[0009]

[0009] In view of the above, it is an object of the present invention to provide accurate position measurement of an object that facilitates weight reduction of the object.

[0010]

[0010] According to one embodiment of the present invention, a light guide configured to provide a light path along a plane for directing a light source beam from a light source; an emission grating configured to receive at least a portion of the source beam and to diffract the source beam in an emission direction away from the plane to form an emission beam; a target grating configured to be placed on the object of interest to receive the emitted beam, the target grating configured to diffract the emitted beam to form a zeroth order diffraction beam, a first order diffraction beam, and a minus first order diffraction beam; at least two first-order couplers arranged in a plane and configured to receive the first and minus first-order diffracted beams and diffract the first and minus first-order diffracted beams into the plane to form planar first and minus first-order diffracted beams; a zero-order coupler disposed in the plane and configured to receive the zero-order diffracted beam and to diffract the zero-order diffracted beam into the plane to form a planar zero-order diffracted beam; a first and minus first combining device configured to receive the planar first and minus first diffracted beams and to generate at least one first diffraction order interference light signal using the planar first and minus first diffracted beams; a zero-order combining device configured to receive the planar zero-order diffracted beam and a reference portion of the source beam, and to generate a zero-order diffraction order interference light signal using the planar zero-order diffracted beam and the reference portion of the source beam; a primary optical sensor positioned to receive at least one first diffraction order interference optical signal and to generate a first diffraction order output signal in response thereto; a zero order optical sensor positioned to receive the zeroth diffraction order interference optical signal and to generate a zero order output signal in response thereto; An integrated displacement sensor is provided comprising:

[0011]

[0011] According to a further embodiment of the present invention, there is provided a position measurement system comprising one or more integrated displacement sensors according to the present invention and a processor configured to derive position data of an object in a first direction parallel to the light guide plane from the first order interference signal, and to derive position data of the object in a direction perpendicular to the light guide plane from the zero order interference signal.

[0012] According to a further embodiment of the invention there is provided a lithographic apparatus comprising a position measurement system according to the invention.

[0013] According to a further embodiment of the invention there is provided a projection system of an optical lithography system comprising a position measurement system according to the invention. [Brief explanation of the drawings]

[0014]

[0014] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which:

[0015] [Figure 1] 1 shows a schematic overview of a lithographic apparatus according to one embodiment of the invention; [Figure 2] 2 illustrates a detailed view of a portion of the lithographic apparatus of FIG. 1; [Figure 3] 1 illustrates a schematic representation of a position control system as part of a positioning system according to an embodiment of the present invention; [Figure 4] 1A and 1B schematically illustrate a perspective view of a measurement system according to an embodiment of the present invention; [Figure 5] 5 schematically illustrates a side view of the measurement system according to FIG. 4. [Figure 6] FIG. 6 shows a schematic top view of the measurement system according to FIGS. 4 and 5. [Figure 7] 10A and 10B schematically illustrate a top view of a measurement system according to another embodiment of the present invention. [Figure 8] 10A and 10B schematically illustrate a top view of a measurement system according to yet another embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0016]

[0015] In this document, the terms "radiation" and "beam" are used to encompass all types of electromagnetic radiation, including ultraviolet (e.g., having a wavelength of 365 nm, 248 nm, 193 nm, 157 nm, or 126 nm) and EUV (extreme ultraviolet, e.g., having a wavelength in the range of about 5 to 100 nm).

[0017] The terms "reticle," "mask," or "patterning device," as used herein, may be broadly interpreted as referring to a general-purpose patterning device that can be used to impart a patterned cross-section to an incoming radiation beam, corresponding to the pattern to be created in a target portion of a substrate. The term "light valve" can also be used in this context. Besides the classic mask (transmissive or reflective mask, binary mask, phase-shifting mask, hybrid mask, etc.), examples of other such patterning devices include programmable mirror arrays and programmable LCD arrays.

[0018] 1 schematically depicts a lithographic apparatus LA. The lithographic apparatus LA includes an illumination system (also called an illuminator) IL configured to condition a radiation beam B (e.g. UV radiation, DUV radiation, or EUV radiation), a mask support (e.g. a mask table) MT constructed to support a patterning device (e.g. a mask) MA and coupled to a first positioner PM configured to accurately position the patterning device MA according to certain parameters, a substrate support (e.g. a wafer table) WT constructed to hold a substrate (e.g. a resist-coated wafer) W and coupled to a second positioner PW configured to accurately position the substrate support according to certain parameters, and a projection system (e.g. a refractive projection lens system) PS configured to project a pattern imparted to the radiation beam B by the patterning device MA onto a target portion C (e.g. comprising one or more dies) of the substrate W.

[0019]

[0018] In operation, the illumination system IL receives a radiation beam from the radiation source SO, for example via the beam delivery system BD. The illumination system IL may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic and / or other types of optical components, or any combination thereof, for directing, shaping and / or controlling the radiation. The illuminator IL may be used to condition the radiation beam B, so that it has a desired spatial and angular intensity distribution across its cross-section in the plane of the patterning device MA.

[0020]

[0019] The term "projection system" PS as used herein should be interpreted broadly as encompassing various types of projection systems, including refractive optical systems, catadioptric optical systems, anamorphic optical systems, magnetic optical systems, electromagnetic optical systems, and / or electrostatic optical systems, or any combination thereof, as appropriate to the exposure radiation used and / or other factors such as the use of an immersion liquid or a vacuum. Where the term "projection lens" is used herein, this may be considered as synonymous with the more general term "projection system" PS.

[0021]

[0020] The lithographic apparatus LA may be of a type in which at least a portion of the substrate W is covered by a liquid having a relatively high refractive index, such as water, so as to fill a space between the projection system PS and the substrate W. This is also known as immersion lithography. More information about immersion techniques is given in US Patent No. 6,952,253, which is incorporated herein by reference.

[0022] The lithographic apparatus LA may be of a type having two or more substrate supports WT (also referred to as "dual stage"). In such a "multi-stage" machine, the substrate supports WT may be used in parallel, and / or a substrate W on one substrate support WT may be used to expose a pattern thereon while a preparation step for a subsequent exposure of the substrate W is performed on a substrate W located on another substrate support WT.

[0023] In addition to the substrate support WT, the lithographic apparatus LA may include a measurement stage. The measurement stage is arranged to hold a sensor and / or a cleaning device. The sensor may be arranged to measure a property of the projection system PS or a property of the radiation beam B. The measurement stage may hold multiple sensors. The cleaning device may be arranged to clean part of the lithographic apparatus, for example part of the projection system PS or part of a system for providing immersion liquid. When the substrate support WT is away from the projection system PS, the measurement stage may move below the projection system PS.

[0024] In operation, a radiation beam B is incident on a patterning device MA, e.g., a mask, which is held on a mask support MT, and is patterned according to a pattern (design layout) present on the patterning device MA. Having traversed the patterning device MA, the radiation beam B passes through the projection system PS, which focuses the beam onto a target portion C of a substrate W. With the aid of the second positioner PW and the position measurement system IF, the substrate support WT can be precisely moved, for example, to position various target portions C at focused and aligned positions in the path of the radiation beam B. Similarly, the first positioner PM, and possibly further position sensors (not explicitly shown in FIG. 1 ), can be used to precisely position the patterning device MA with respect to the path of the radiation beam B. The patterning device MA and substrate W may be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. Although the illustrated substrate alignment marks P1, P2 occupy dedicated target portions, the substrate alignment marks may be located in spaces between the target portions. When the substrate alignment marks P1, P2 are located between target portions C, they are known as scribe-lane alignment marks.

[0025] To clarify the invention, a Cartesian coordinate system is used. The Cartesian coordinate system has three axes: x, y, and z. Each of the three axes is orthogonal to the other two. Rotation about the x-axis is called Rx rotation. Rotation about the y-axis is called Ry rotation. Rotation about the z-axis is called Rz rotation. The x-axis and y-axis define a horizontal plane, while the z-axis is vertical. The Cartesian coordinate system is not a limitation of the invention and is used for clarity only. Alternatively, another coordinate system, such as a cylindrical coordinate system, may be used to clarify the invention. The orientation of the Cartesian coordinate system may be different, for example, the z-axis may have a component along the horizontal plane.

[0026]

[0025] Figure 2 shows a more detailed view of part of the lithographic apparatus LA of Figure 1. The lithographic apparatus LA may comprise a base frame BF, a balance mass BM, a metrology frame MF, and a vibration isolation system IS. The metrology frame MF supports the projection system PS. The metrology frame MF may also support part of the position measurement system PMS. The metrology frame MF is supported by the base frame BF via the vibration isolation system IS. The vibration isolation system IS is arranged to prevent or reduce vibrations from propagating from the base frame BF to the metrology frame MF.

[0027]

[0026] The second positioner PW is arranged to accelerate the substrate support WT by providing a driving force between the substrate support WT and the balance mass BM. The driving force accelerates the substrate support WT in a desired direction. Due to conservation of momentum, the driving force is also applied to the balance mass BM with the same magnitude but in a direction opposite to the desired direction. Typically, the mass of the balance mass BM is significantly greater than the mass of the second positioner PW and the moving parts of the substrate support WT.

[0028] In one embodiment, the second positioner PW is supported by the balance mass BM. For example, the second positioner PW then comprises a planar motor for levitating the substrate support WT above the balance mass BM. In another embodiment, the second positioner PW is supported by the base frame BF. For example, the second positioner PW then comprises a linear motor, and the second positioner PW then comprises a bearing, such as a gas bearing, for levitating the substrate support WT above the base frame BF.

[0029] The position measurement system PMS may comprise any type of sensor suitable for determining the position of the substrate support WT. The position measurement system PMS may comprise any type of sensor suitable for determining the position of the mask support MT. The sensor may be an optical sensor, such as an interferometer or an encoder. The position measurement system PMS may comprise a combined interferometer and encoder system. The sensor may be another type of sensor, such as a magnetic sensor, a capacitive sensor or an inductive sensor. The position measurement system PMS may determine the position relative to a reference, for example the metrology frame MF or the projection system PS. The position measurement system PMS may determine the position of the substrate table WT and / or the mask support MT by measuring the position or a time derivative of the position, such as the velocity or acceleration. Optionally, the position measurement system PMS may comprise any type of sensor suitable for determining the position of optical elements of a lithographic apparatus, in particular the position of the projection system of a lithographic apparatus.

[0030] The position measurement system PMS may comprise an encoder system. Encoder systems are known, for example, from US Patent Application No. 2007 / 0058173 A1, filed September 7, 2006, which is incorporated herein by reference. The encoder system comprises an encoder head, a grating, and a sensor. The encoder system may receive a primary radiation beam and a secondary radiation beam. Both the primary radiation beam and the secondary radiation beam may originate from the same radiation beam, i.e., an original radiation beam. At least one of the primary radiation beam and the secondary radiation beam is generated by diffracting the original radiation beam with a grating. If both the primary radiation beam and the secondary radiation beam are generated by diffracting the original radiation beam with a grating, the primary radiation beam must have a different diffraction order from the secondary radiation beams. The different diffraction orders are, for example, +1, −1, +2, and −2. The encoder system optically combines the primary radiation beam and the secondary radiation beam into a combined radiation beam. A sensor in the encoder head determines the phase or phase difference of the combined radiation beam. The sensor generates a signal based on the phase or phase difference. The signal indicates the position of the encoder head relative to the grating. One of the encoder head or the grating may be located on the substrate structure WT. The other of the encoder head or the grating may be located on the metrology frame MF or the base frame BF. For example, multiple encoder heads are located on the metrology frame MF, while one grating is located on the top surface of the substrate support WT. In another example, one grating is located on the bottom surface of the substrate support WT, and one encoder head is located below the substrate support WT.

[0031] The position measurement system PMS may comprise an interferometer system. Interferometer systems are known, for example, from U.S. Pat. No. 6,020,964, filed July 13, 1998, which is incorporated herein by reference. The interferometer system may comprise a beam splitter, a mirror, a reference mirror, and a sensor. The beam splitter splits the radiation beam into a reference beam and a measurement beam. The measurement beam propagates to the mirror and is reflected by the mirror back to the beam splitter. The reference beam propagates to the reference mirror and is reflected by the reference mirror back to the beam splitter. At the beam splitter, the measurement beam and the reference beam combine into a combined radiation beam. The combined radiation beam is incident on a sensor. The sensor determines the phase or frequency of the combined radiation beam. The sensor generates a signal based on the phase or frequency. The signal represents the displacement of the mirror. In one embodiment, the mirror is coupled to the substrate support WT. The reference mirror may be coupled to the metrology frame MF. In one embodiment, the measurement and reference beams are combined into a combined radiation beam by an additional optical component rather than a beam splitter.

[0032] The first positioner PM may comprise a long-stroke module and a short-stroke module. The short-stroke module is arranged to move the mask support MT over a small range of movement with high accuracy relative to the long-stroke module. The long-stroke module is arranged to move the short-stroke module over a large range of movement with relatively low accuracy relative to the projection system PS. By combining the long-stroke module and the short-stroke module, the first positioner PM can move the mask support MT over a large range of movement with high accuracy relative to the projection system PS. Similarly, the second positioner PW may comprise a long-stroke module and a short-stroke module. The short-stroke module is arranged to move the substrate support WT over a small range of movement with high accuracy relative to the long-stroke module. The long-stroke module is arranged to move the short-stroke module over a large range of movement with relatively low accuracy relative to the projection system PS. By combining the long-stroke module and the short-stroke module, the second positioner PW can move the substrate support WT over a large range of movement with high accuracy relative to the projection system PS.

[0033] The first positioner PM and the second positioner PW each include an actuator for moving the mask support MT and the substrate support WT, respectively. The actuator may be a linear actuator for providing a driving force along a single axis, for example, the y-axis. Multiple linear actuators may be applied to provide driving forces along multiple axes. The actuator may be a planar actuator for providing driving forces along multiple axes. For example, the planar actuator may be arranged to move the substrate support WT with six degrees of freedom. The actuator may be an electromagnetic actuator including at least one coil and at least one magnet. The actuator is arranged to move the at least one coil relative to the at least one magnet by applying a current to the at least one coil. The actuator may be a moving magnet actuator, which has at least one magnet coupled to the substrate support WT or the mask support MT. The actuator may be a moving coil actuator, which has at least one coil coupled to the substrate support WT or the mask support MT. The actuator may be a voice coil actuator, a reluctance actuator, a Lorentz actuator, a piezoelectric actuator, or any other suitable actuator.

[0034] The lithographic apparatus LA includes a position control system PCS, as shown schematically in FIG. 3. The position control system PCS includes a setpoint generator SP, a feedforward controller FF, and a feedback controller FB. The position control system PCS provides drive signals to actuators ACT. The actuators ACT may be actuators of the first positioner PM or may be actuators of the second positioner PW. The actuators ACT drive a plant P, which may include a substrate support WT or a mask support MT. The output of the plant P is a position quantity, such as a position, velocity, or acceleration. The position quantity is measured by a position measurement system PMS. The position measurement system PMS generates a signal, which is a position signal representing the position quantity of the plant P. The setpoint generator SP generates a signal, which is a reference signal representing a desired position quantity of the plant P. For example, the reference signal represents a desired trajectory of the substrate support WT. The difference between the reference signal and the position signal forms the input of the feedback controller FB. Based on the input, the feedback controller FB provides at least a portion of the drive signal for the actuator ACT. The reference signal may form the input of a feedforward controller FF, based on which the feedforward controller FF provides at least a portion of the drive signal for the actuator ACT. The feedforward FF may utilize information about the mechanical properties of the plant P, such as mass, stiffness, resonant modes, and natural frequencies.

[0035] In FIGS. 4 to 8, identical or similar items are designated by identical or similar reference numerals.

[0036]

[0035] Figure 4 shows a perspective view of a position measurement system PMS according to an embodiment of the present invention. The position measurement system comprises an integrated displacement sensor IDS for measuring the position of an object OBJ, and a processor PRC.

[0037]

[0036] The integrated displacement sensor IDS comprises the following components, most of which are located in the plane PL of the integrated displacement sensor:

[0038]

[0037] The light guide LGD provides a light path along a plane for directing the light source beam LSB from the light source to the emission grid EGR.

[0039]

[0038] The emission grating EGR receives at least a portion of the source beam from the light source and diffracts the source beam in an emission direction away from the plane to form an emission beam EMB.

[0040]

[0039] A target grating TGR is positioned to receive the emitted beam EMB. The target grating is a reflective grating and may be positioned on the object OBJ whose position is to be determined. The target grating forms a diffraction grating to diffract the emitted beam EMB, forming a zeroth-order diffracted beam ZOD, a first-order diffracted beam FOD, and a minus-first-order diffracted beam MOD. Higher-order diffracted beams may also be formed. The zeroth-order, first-order, and minus-first-order diffracted beams propagate back to the plane of the integrated displacement sensor IDS.

[0041] At the plane PL, a coupler receives the zeroth, first and minus first order diffracted beams and diffracts each beam into a planar beam oriented parallel to the plane as follows:

[0042]

[0041] Two first-order couplers FOC are positioned in the plane PL to receive the first-order and minus-first-order diffracted beams. The first-order couplers FOC include gratings positioned to diffract the first-order and minus-first-order diffracted beams into the plane. The first-order diffracted beams diffracted into the plane are identified as plane first-order diffracted beams. The minus-first-order diffracted beams diffracted into the plane are identified as plane minus-first-order diffracted beams.

[0043]

[0042] Similar to the first-order coupler, a zero-order coupler ZOC is positioned in the plane to receive the zero-order diffraction beam. The zero-order coupler includes a grating for diffracting the zero-order diffraction beam into the plane. The zero-order diffraction beam diffracted into the plane is identified as the plane zero-order diffraction beam.

[0044]

[0043] The emission grating and the coupler may each comprise a computer-generated hologram.

[0045]

[0044] The source beam may be split by one or more splitters SPR. In this example, a first splitter SPR splits the source beam into one portion directed to the emission grating and two portions directed to respective further splitters SPR, each splitting a respective portion of the source beam into two portions. In the embodiment illustrated in Figure 4, the emission grating also forms a splitter in that it comprises a leaky grating, whereby a portion of the source beam is diffracted toward the target grating and a portion of the source beam propagates in the plane of the emission grating. In this specification, the portion of the source beam that propagates to the emission grating may be identified as the source beam. The portion of the source beam split by the splitter may also be identified as the split portion of the source beam.

[0046]

[0045] The planar zero-order beam interferes with a portion of the source beam LSB, which portion remains on the planar surface due to leakage of the emission grating. The planar first and minus first diffracted beams interfere with each other or each with a respective portion of the source beam provided by at least one splitter. In the latter case, the double interfering beams obtained by interference can be electronically combined, as will be explained in more detail below. In general, an integrated displacement sensor comprises:

[0046] It is provided with a first and minus first order combining device FCD which receives the planar first order and minus first order diffraction beams and generates at least one first order diffraction order interference optical signal therefrom, i.e., generates a first order diffraction order interferometer optical signal using the planar first order and minus first order diffraction beams.

[0047]

[0047] Typically, the integrated displacement sensor further comprises a zero-order combining device that receives the planar zero-order diffraction beam and a reference portion of the source beam, and that uses the planar zero-order diffraction beam and the reference portion of the source beam to generate a zero-order diffraction order interference optical signal.

[0048]

[0048] The first diffraction order interference optical signal and the zeroth diffraction order interference optical signal are provided to respective optical sensors for generating respective electrical output signals. Accordingly, the integrated displacement sensor IDS further comprises a first order optical sensor FOS, which receives the at least one first diffraction order interference optical signal and generates a first diffraction order output signal in response thereto (in the electrical domain). Similarly, the integrated displacement sensor IDS further comprises a zeroth order optical sensor ZOS, arranged to receive the zeroth diffraction order interference optical signal and to generate a zeroth order output signal in response thereto (in the electrical domain).

[0049]

[0049] The position measurement system further comprises a processor PRC, such as a microprocessor or controller. The processor derives position data of the object in a first direction parallel to the light guide plane from the first-order interference signal and derives position data of the object in a direction perpendicular to the light guide plane from the zero-order interference signal. The zero-order interference signal and the first-order interference signal are provided to the processor.

[0050]

[0050] To determine displacement in the horizontal direction, i.e., the direction parallel to the plane PL, the first and minus first diffracted beams captured by the primary coupler and returned to the integrated displacement sensor IDS can be combined in one of two ways: either the first and minus first diffracted beams can be combined together, or each of the first and minus first diffracted beams can be combined with the output of a continuous wave laser. When combining the first and minus first diffracted beams according to the latter of these approaches, a proportion can be split off from the source beam by a splitter, or the output of said continuous wave laser can be emitted from a separate (second) light source coupled to or in communication with the integrated displacement sensor.

[0051]

[0051] The optical interference signal resulting from the combined first and minus first diffraction beams, i.e., the first diffraction order interference optical signal, is then incident on a detector, such as a photodiode, integrated on the integrated displacement sensor IDS, where it is converted into the electronic domain and the downconverted beat frequency can be detected. The electronic beat signals of the waves of the first and minus first diffraction beams can then be combined according to techniques well known to those skilled in the art. As a result, a wave can be obtained whose signal intensity varies as the cosine of a function of the grating displacement in the X or Y direction and has a period Λ. The pitch of the grating determines the high displacement resolution.

[0052] To determine displacement in a substantially vertical direction, i.e., a direction substantially perpendicular to the plane PL, the zero-order diffracted beam ZOD reflected from the target grating TGR is guided back to the plane PL, where it interferes with a portion of the input source beam (LSB), thereby forming a Mach-Zehnder interferometer. The change in frequency is due to the variation in the position of the target grating in the vertical direction. By measuring the phase, the change in displacement in the in-plane and out-of-plane directions (x and z) can be determined.

[0053]

[0053] The position of an object in two dimensions can be measured using a single integrated displacement sensor.

[0054]

[0054] The planar first and minus first diffracted beams can be interfered in various ways, two possible embodiments are identified below.

[0055]

[0055] In one embodiment, the first-order and minus-first-order combining device is configured to optically interfere the planar first-order and minus-first-order diffracted beams to generate at least one first-order diffraction order interference optical signal. On the one hand, this embodiment can make it possible to directly derive the displacement in the in-plane direction from the optical interference signal. On the other hand, these planar first-order diffracted beams need to be optically combined by respective planar optical guides in the plane, which may impose layout restrictions on other gratings or combining devices in the plane.

[0056]

[0056] In another embodiment, the first and minus first-order combining device is configured to optically interfere the planar first-order diffracted beam with a further reference portion of the light source beam and to interfere the minus first-order diffracted beam with a further reference portion of the light source beam to generate two first-order diffraction order interference light signals, the first-order optical sensor is configured to receive the two first-order diffraction order interference light signals and to generate two first-order diffraction order output signals in the electrical domain in response thereto, and the processor is configured to derive position data of the object in a first direction parallel to the light guide plane from the two first-order interference signals. This embodiment may provide greater flexibility in layout in the plane in that the planar first-order diffracted beams are optically combined by respective planar optical guides in the plane, which may impose layout restrictions on other gratings or combining devices in the plane.

[0057]

[0057] In one embodiment, the processor is configured to derive position data from the phase difference of each interference signal. As explained above, the interference signal may provide a wave whose signal intensity varies as the cosine of a function of the grating displacement in the X or Y direction and has a period Λ. The pitch of the grating determines the high displacement resolution. Thus, phase information can be accurately converted into displacement information.

[0058] In one embodiment, the target grating comprises a first target grating portion and a second target grating portion, the first target grating portion configured to diffract the emitted beam to form a zeroth order diffraction beam, a first order diffraction beam, and a minus first order diffraction beam, and the second target grating portion configured to diffract the emitted beam to form a zeroth order diffraction beam, a further first order diffraction beam, and a further minus first order diffraction beam. In this embodiment, the displacement sensor further comprises a further coupler, a further first order combining device, and a further first order optical sensor, as follows: at least two further couplers FFOC arranged in the plane of the light guide and configured to receive the further first and further minus first diffracted beams and to diffract the further first and minus first diffracted beams into the plane of the light guide to form further plane first and minus first diffracted beams; a further first and minus first order combining device FFCD configured to receive the further planar first and minus first order diffracted beams and to generate at least one further first diffraction order interference light signal using the further planar first and minus first order diffracted beams; a further first order light sensor FFOS arranged to receive at least one further first diffraction order interference light signal and to generate a further first diffraction order output signal in response thereto, in this embodiment the processor is further configured to derive position data of the object in a second direction parallel to the light guide plane and perpendicular to the first direction from the further first order interference signal.

[0059] The position in a second direction parallel to the light guide plane can be determined in the same manner as the position in the first direction parallel to the light guide plane. Thus, the position can be determined in three mutually perpendicular directions. This development makes it possible to provide a photonic integrated sensor capable of measuring the relative displacement between a surface and a target grating in three translational degrees of freedom. The sensor combines two types of optical interferometers: a Mach-Zehnder interferometer with an "effective" Fabry-Perot interferometer in one arm to measure the out-of-plane displacement of the target grating, and an optical interferometric encoder to measure the in-plane displacement. In this way, both the first-order diffracted light and the reflected light perpendicular to the plane of the target surface, generated when light is incident on the grating, are used.

[0060]

[0060] The use of photonic integrated devices is expected to miniaturize existing sensors in terms of size, weight, and power consumption, thereby enabling on-stage sensing opportunities. By utilizing reflected and diffracted beams, a single illuminated point can be used to interfere with changes in the position of a target grating in the x, y, and z directions, instead of the three illuminated points required by a line-of-sight interferometer on three different planes. This can reduce the footprint and mass on the stage. Also, placing the light source on the stage can significantly reduce the sensor's standoff, which can relax the requirements for frequency stability of the measurement light. To measure to an accuracy of 500 pm with a 5 mm imbalance, a 20 MHz frequency-stable laser would be required for a 1550 nm laser beam wavelength.

[0061]

[0061] In one embodiment, the first and second target grating portions are arranged substantially perpendicular to each other, whereby these target grating portions are arranged in the same plane, but the structure of the grating, for example the grating lines of the grating, are perpendicular. As a result, when viewed in the light guide plane, the first and minus first diffracted beams propagate in a direction perpendicular to the further first and minus first diffracted beams because the target grating portions are perpendicular to each other. Therefore, the first direction derived from the first and minus first diffracted beams and the second direction derived from the further first and minus first diffracted beams are essentially perpendicular to each other.

[0062]

[0062] For miniaturization, the light guide, emission grating, coupler, combining device, and light sensor may be disposed on a dielectric or semiconductor substrate.

[0063]

[0063] To facilitate orthogonal measurement directions, the emission grating is configured so that the emission direction is substantially perpendicular to the light guide plane.

[0064]

[0064] The position measurement system further comprises a light source configured to emit a source beam into the light guide. The source beam emitted by the light source may be a monochromatic beam.

[0065]

[0065] Additional degrees of freedom of the object may be measured in that the position measurement system comprises at least two integrated displacement sensors, and target gratings are placed on the object. More specifically, the target gratings of each of the at least two integrated displacement sensors may be spaced apart from one another on the object, and the processor is configured to determine the position of the object in six degrees of freedom. Using two of these integrated displacement sensors would allow measurement of three rotational DoFs.

[0066] For example, two such sensors can be used to determine the rotational degree of freedom. Rz can be determined from the quotient of (yy1-yy2) divided by (xx1-xx2). Ry can be determined from the quotient of (zz1-zz2) divided by (xx1-xx2). Ry can be determined from the quotient of (zz1-zz2) divided by (yy1-yy2). Here, (xx1, yy1, zz1) and (xx2, yy2, zz2) are the measurement positions of integrated displacement sensor 1 and integrated displacement sensor 2.

[0067] According to the above example, six degrees of freedom can be measured with two integrated displacement sensors. As a result of incorporating fewer sensors, one for three degrees of freedom and two for six degrees of freedom, the position measurement system can reduce the sensor footprint in terms of size, weight, and power consumption.

[0068]

[0068] Using multiple integrated displacement sensors not only makes it possible to determine position in multiple degrees of freedom. Alternatively, or in addition, non-rigid behavior can be determined. For example, non-rigid behavior can be determined by providing at least two integrated displacement sensors, the target gratings of each of the at least two integrated displacement sensors being spaced apart from one another on the object, and a processor configured to determine deformation of the object, for example, by comparing position measurements from the at least two integrated displacement sensors.

[0069]

[0069] In one embodiment illustrated in Figure 4, the emission grating is a zero-order coupler, allowing the emission beam and the zero-order diffraction beam to propagate perpendicular to the plane, thus facilitating the derivation of the position in the direction perpendicular to the plane.

[0070]

[0070] In one embodiment, as further described below with reference to Figure 8, two integrated displacement sensors may be arranged on a plane, for example on the same chip, and the processor is further configured to derive the rotation of the object about a second direction parallel to the light guide plane and perpendicular to the first direction from the position data of the object in a direction perpendicular to the light guide plane derived for the two integrated displacement sensors.

[0071] As described above, a position measurement system can be used to measure a position of an object in a lithographic apparatus. According to an aspect of the present invention, there is provided a lithographic apparatus comprising a position measurement system as described herein. The lithographic apparatus may comprise a substrate table configured to support a substrate, the object comprising the substrate table. For example, the position measurement system may be configured to measure a position of a short stroke of the substrate table with respect to a long stroke of the substrate table. At least one target grating of the at least one integrated displacement sensor may be arranged on the short stroke, and at least one remaining component of the at least one integrated displacement sensor may be arranged on the long stroke. Optionally, the object may be an optical element of the lithographic apparatus, in particular a projection system of the lithographic apparatus, such as a mirror or a lens.

[0072]

[0072] Figure 5 illustrates a highly schematic cross-sectional side view of an integrated displacement sensor. Figure 5 illustrates an object OBJ to which a target grating TRG is attached. The remaining part of the integrated displacement sensor, the in-plane sensor, is illustrated as PL and shows the emission grating EGR, and the first and minus first order diffraction gratings FOG, MOG. The emission beam EMB from the emission grating is diffracted by the target grating to provide a zero order diffraction beam ZOD, and first and minus first order diffraction beams FOD, MOD, which are then diffracted by the first and minus first order diffraction gratings FOG, MOG as described above with reference to Figure 4.

[0073] FIG. 6 illustrates a highly schematic top view of an integrated displacement sensor according to one embodiment of the present invention, as described above with reference to FIGS. 4 and 5. The emission grating, which also acts as a zero-order coupler, the first-order and minus-first-order couplers, and the further first-order and minus-first-order couplers have been described above. Similarly, the combining device and the optical sensor (photodetector) have been described above. A source beam is provided to the emission grating and to the combining device as follows: The source beam coupled to the integrated displacement sensor is first split into three parts by the optical splitter SPR. One part of this light travels to the emission grating. Part of this part is diffracted perpendicularly by the emission grating, such as a computer-generated hologram (CGH), toward a target grating (attached to the object whose position is to be measured), while another part of that part of the light is transmitted through a weak emission grating to form part of the source beam for the zero-order coupling device. The light reflected from the target grating is captured by the same emission grating (acting as a zero-order coupler) and interferes with the light transmitted through it. The signal is detected by a photodetector on the integrated displacement sensor. The other portion of the source beam split by the optical splitter is directed to a further optical splitter SPR, which provides sub-portions of the source beam to each of the primary combining device (X+ coupler), the minus primary combining device (X- coupler), the further primary combining device (Y+ coupler), and the further minus primary combining device (Y- coupler). Thus, the other two portions of the light coupled into the integrated displacement sensor are each subdivided into two and, using optical combiners, interfere with one of the four first-order diffractions (+Y, -Y, -X, +X) captured by the four CGHs shown at the corners of the integrated displacement sensor. The interference pattern is detected by a photodetector on the integrated displacement sensor.

[0074]

[0074] Figure 7 illustrates a highly schematic top view of an integrated displacement sensor according to one embodiment of the present invention. The integrated displacement sensor illustrated in Figure 7 largely corresponds to the integrated displacement sensor illustrated in Figure 6. However, the integrated displacement sensor according to the embodiment illustrated in Figure 7 comprises separate emission grids EGR and zero-order coupler ZOC grids instead of a combined emitter coupler.

[0075]

[0075] The measurement in Figure 7 is similar to that in the embodiment shown in Figure 6. More specifically, the XY measurement remains the same, but the Z measurement has changed. In Figure 7, the source beam coupled to the integrated displacement sensor is split into four parts. One part propagates to the emission grating, which diffracts the emission beam perpendicularly toward the target grating. The resulting reflected beam, i.e., the zero-order diffraction beam, is coupled to the integrated displacement sensor by the zero-order coupler ZOC to form a planar zero-order diffraction beam. Another part of the source beam propagates through the waveguide. This part of the source beam and the planar zero-order diffraction beam are combined using the zero-order combining device ZCD, which is an optical combiner, and the interference signal detected on the zero-order optical sensor ZOS, which is a photodiode.

[0076] FIG. 8 illustrates a highly schematic top view of an integrated displacement sensor according to one embodiment of the present invention.

[0077] 8 measures three degrees of freedom, namely X, Z of two closely spaced illumination points and, through these two measurements, rotation Ry about the Y axis. The integrated displacement sensor has a line of symmetry in the plane of the drawing, and one side will be described below.

[0078]

[0078] The source beam from the light source is coupled into the waveguide of the integrated displacement sensor. This signal is split into four parts. The z emitter receives one part. This light passes through a taper that increases the size of the mode and is then diffracted at an angle by the emission grating to form an emission beam, and the corresponding reflected zeroth-order diffraction beam is collected by the zeroth-order coupler to provide a planar zeroth-order diffraction beam. The combined planar zeroth-order diffraction beam then passes through a taper to reduce the size of the mode to the size of the waveguide and then interferes with a part of the source beam in the combiner. The resulting interference signal is then sent to a photodiode. The diffraction orders, i.e., the first and minus first-order diffraction beams, captured by the first and minus first-order couplers X- and X+ to form planar first and minus first-order diffraction beams, are similarly combined with one of the other two parts of the source beam. Therefore, the respective arrangements of the left and right parts of Figure 8 measure position in both the X and Z directions. The processor can derive the rotation Ry about the y-axis from the quotient of (zz1-zz2) divided by (xx1-xx2), where zz1 and zz2 are the z measurements of the first and second sensors, and xx1 and xx2 are the x measurements of the first and second sensors.

[0079] Although specific reference may be made in this text to the use of lithographic apparatus in the manufacture of ICs, it will be appreciated that the lithographic apparatus described herein may have other applications, including the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat panel displays, liquid crystal displays (LCDs), thin film magnetic heads, etc.

[0080] Although specific reference may be made in this text to embodiments of the invention in the context of a lithography apparatus, embodiments of the invention may also be used in other apparatus. Embodiments of the invention may form part of a mask inspection apparatus, a metrology apparatus, or any apparatus that measures or processes objects such as wafers (or other substrates) or masks (or other patterning devices). These apparatus may be generally referred to as lithography tools. Such lithography tools may use vacuum conditions or ambient (non-vacuum) conditions.

[0081]

[0081] While the above may specifically refer to the use of embodiments of the present invention in the context of optical lithography, it will be understood that the present invention is not limited to optical lithography and may be used in other applications, such as imprint lithography, where the context permits.

[0082] Where the context permits, embodiments of the present invention may be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the present invention may also be implemented as instructions stored on a machine-readable medium, which may be read and executed by one or more processors. A machine-readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, machine-readable media may include read-only memory (ROM), random-access memory (RAM), magnetic storage media, optical storage media, flash memory devices, electrical, optical, acoustic, or other forms of propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.), and others. Furthermore, firmware, software, routines, and instructions may be described herein as performing particular actions. However, it should be understood that such description is merely for convenience and that such actions actually result from computing devices, processors, controllers, or other devices executing the firmware, software, routines, instructions, etc., and that in performing these actions, actuators or other devices may interact with the physical world.

[0083] While specific embodiments of the present invention have been described above, it will be understood that the invention may be practiced otherwise than as described. The foregoing description is intended to be illustrative, not limiting. Thus, it will be apparent to those skilled in the art that modifications to the invention as described may be made without departing from the scope of the claims set forth below.

[0084] Other aspects of the invention are described in the following numbered clauses: 1. A light guide configured to provide a light path along a plane for directing a light source beam from a light source; an emission grating configured to receive at least a portion of the source beam and to diffract the source beam in an emission direction away from the plane to form an emission beam; a target grating configured to be placed on the object of interest to receive the emitted beam, the target grating configured to diffract the emitted beam to form a zeroth order diffraction beam, a first order diffraction beam, and a minus first order diffraction beam; at least two first-order couplers arranged in a plane and configured to receive the first and minus first-order diffracted beams and diffract the first and minus first-order diffracted beams into the plane to form planar first and minus first-order diffracted beams; a zero-order coupler disposed in the plane and configured to receive the zero-order diffracted beam and to diffract the zero-order diffracted beam into the plane to form a planar zero-order diffracted beam; a first and minus first combining device configured to receive the planar first and minus first diffracted beams and to generate at least one first diffraction order interference light signal using the planar first and minus first diffracted beams; a zero-order combining device configured to receive the planar zero-order diffracted beam and a reference portion of the source beam, and to generate a zero-order diffraction order interference light signal using the planar zero-order diffracted beam and the reference portion of the source beam; a primary optical sensor positioned to receive at least one first diffraction order interference optical signal and to generate a first diffraction order output signal in response thereto; a zero order optical sensor positioned to receive the zeroth diffraction order interference optical signal and to generate a zero order output signal in response thereto; 1. An integrated displacement sensor comprising: 2. A position measurement system comprising one or more integrated displacement sensors as described in clause 1 and a processor configured to derive position data of an object in a first direction parallel to the light guide plane from the first order interference signal and to derive position data of the object in a direction perpendicular to the light guide plane from the zero order interference signal. 3. The target grating comprises a first target grating portion and a second target grating portion, the first target grating portion configured to diffract the emitted beam to form a zeroth order diffraction beam, a first order diffraction beam, and a minus first order diffraction beam, and the second target grating portion configured to diffract the emitted beam to form a zeroth order diffraction beam, a further first order diffraction beam, and a further minus first order diffraction beam, and the displacement sensor further comprises: at least two further couplers arranged in the light guide plane and configured to receive the further first and further minus first diffracted beams and to diffract the further first and further minus first diffracted beams into the light guide plane to form further planar first and minus first diffracted beams; a further first and minus first combining device configured to receive the further planar first and minus first diffracted beams and to generate at least one further first diffraction order interference light signal using the further planar first and minus first diffracted beams; a further first order optical sensor arranged to receive at least one further first diffraction order interference optical signal and to generate a further first diffraction order output signal in response thereto; Equipped with A position measurement system as described in clause 2, wherein the processor is configured to derive position data of the object in a second direction parallel to the light guide plane and perpendicular to the first direction from the further first-order interference signal. 4. A position measurement system as described in clause 3, wherein the first and second target grating portions are arranged substantially perpendicular to each other. 5. A position measurement system as described in any one of clauses 2 to 4, wherein the processor is configured to derive position data from the phase difference of the respective interference signals. 6. A position measurement system as described in any one of clauses 2 to 5, wherein the first and minus first order combining device is configured to optically interfere the planar first and minus first order diffracted beams to generate at least one first order diffraction order interference optical signal. 7. A position measurement system described in any one of clauses 2 to 6, wherein the first and minus first combining device is configured to optically interfere with the plane first diffraction beam with a further reference portion of the light source beam and to interfere with the minus first diffraction beam with a further reference portion of the light source beam to generate two first diffraction order interference light signals, the first light sensor is configured to receive the two first diffraction order interference light signals and to generate two first diffraction order output signals in response thereto, and the processor is configured to derive position data of the object in a first direction parallel to the light guide plane from the two first diffraction order interference signals. 8. A position measurement system as described in any one of clauses 2 to 7, further comprising a splitter configured to split a reference portion of the light source beam and optionally a further reference portion of the light source beam from the light source beam. 9. A position measurement system according to any one of clauses 2 to 8, wherein the light guide, emission grating, coupler, combining device, and light sensor are arranged on a semiconductor substrate. 10. A position measurement system according to any one of clauses 2 to 9, wherein the emission grating is configured such that the emission direction is substantially perpendicular to the plane of the light guide. 11. A position measurement system according to any one of clauses 2 to 10, further comprising a light source configured to emit a light source beam into the light guide. 12. A position measurement system as described in clause 10, wherein the light source beam is a monochromatic beam. 13. A position measurement system according to any one of clauses 2 to 12, comprising at least two integrated displacement sensors and a target grating arranged on the object. 14. A position measurement system as described in clause 12, wherein the target gratings of each of the at least two integrated displacement sensors are spaced apart from one another on the object, and the processor is configured to determine the position of the object in six degrees of freedom. 15. A position measurement system as described in clause 12 or 13, wherein the target gratings of each of the at least two integrated displacement sensors are spaced apart from one another on the object, and the processor is configured to determine deformation of the object. 16. A position measurement system according to any one of clauses 2 to 15, wherein the emission grating is a zero-order coupler. 17. A position measurement system as described in any one of clauses 2 to 16, comprising two integrated displacement sensors arranged in a plane, and wherein the processor is further configured to derive a rotation of the object about a second direction parallel to the light guide plane and perpendicular to the first direction from position data of the object in a direction perpendicular to the light guide plane derived for the two integrated displacement sensors. 18. A lithographic apparatus comprising a position measurement system according to any one of clauses 2 to 17. 19. A lithographic apparatus according to clause 17, comprising a substrate table configured to support a substrate, the object comprising the substrate table. 20. A projection system of an optical lithography system comprising a position measurement system according to any one of clauses 2 to 17.

Claims

1. a light guide configured to provide a light path along a plane for directing a light source beam from a light source; an emission grating configured to receive at least a portion of the source beam and to diffract the source beam in an emission direction away from the plane to form an emission beam; a target grating configured to be placed on an object of interest to receive the emitted beam, the target grating configured to diffract the emitted beam to form a zeroth order diffraction beam, a first order diffraction beam, and a minus first order diffraction beam; at least two first-order couplers disposed in the plane and configured to receive the first and minus first-order diffracted beams and diffract the first and minus first-order diffracted beams into the plane to form planar first and minus first-order diffracted beams; a zero-order coupler disposed in the plane and configured to receive the zero-order diffracted beam and to diffract the zero-order diffracted beam into the plane to form a planar zero-order diffracted beam; a first and minus first combining device configured to receive the planar first and minus first diffracted beams and to generate at least one first diffraction order interference light signal using the planar first and minus first diffracted beams; a zero-order combining device configured to receive the planar zero-order diffracted beam and a reference portion of the source beam, and to generate a zero-order diffraction order interference light signal using the planar zero-order diffracted beam and the reference portion of the source beam; a primary optical sensor positioned to receive the at least one first diffraction order interference optical signal and to generate a first diffraction order output signal in response thereto; a zero order optical sensor positioned to receive the zeroth diffraction order interference optical signal and to generate a zero order output signal in response thereto; 1. An integrated displacement sensor comprising:

2. 10. A position measurement system comprising one or more integrated displacement sensors according to claim 1; and a processor configured to derive position data of the object in a first direction parallel to the light guide plane from the first order interference signal and to derive position data of the object in a direction perpendicular to the light guide plane from the zero order interference signal.

3. the target grating comprises a first target grating portion and a second target grating portion, the first target grating portion configured to diffract the emission beam to form the zeroth order diffraction beam, the first order diffraction beam, and the minus first order diffraction beam, and the second target grating portion configured to diffract the emission beam to form the zeroth order diffraction beam, a further first order diffraction beam, and a further minus first order diffraction beam, and the displacement sensor further comprises: at least two further couplers arranged in the light guide plane and configured to receive the further first and further minus first diffracted beams and to diffract the further first and further minus first diffracted beams into the light guide plane to form further planar first and minus first diffracted beams; a further first and minus first order combining device configured to receive the further planar first and minus first order diffracted beams and to generate at least one further first diffraction order interference light signal using the further planar first and minus first order diffracted beams; a further first order optical sensor arranged to receive at least one further first diffraction order interference optical signal and to generate a further first diffraction order output signal in response thereto; Equipped with 3. The position measurement system of claim 2, wherein the processor is configured to derive position data of the object in a second direction parallel to the light guide plane and perpendicular to the first direction from the further first-order interference signal.

4. The position measurement system of claim 3 , wherein the first and second target grating portions are disposed substantially perpendicular to one another.

5. 5. A position measurement system according to claim 2, wherein the processor is configured to derive the position data from a phase difference between the respective interference signals.

6. 6. The position measurement system of claim 2, wherein the first and minus first order combining device is configured to optically interfere the planar first and minus first order diffracted beams to generate the at least one first order diffraction order interference optical signal.

7. 7. The position measurement system of claim 2, wherein the first and minus first-order combining device is configured to optically interfere the plane first-order diffracted beam with a further reference portion of the light source beam and to interfere the minus first-order diffracted beam with the further reference portion of the light source beam to generate two first-order diffraction order interference light signals, the first-order optical sensor is configured to receive the two first-order diffraction order interference light signals and to generate two first-order diffraction order output signals in response thereto, and the processor is configured to derive the position data of the object in the first direction parallel to the light guide plane from the two first-order interference signals.

8. 8. A position measurement system according to claim 2, further comprising a splitter configured to split the reference portion of the source beam and optionally the further reference portion of the source beam from the source beam.

9. The position measurement system according to claim 2 , wherein the light guide, emission grating, coupler, combining device, and light sensor are arranged on a semiconductor substrate.

10. 10. A position measurement system according to claim 2, wherein the emission grating is configured such that the emission direction is substantially perpendicular to the plane of the light guide.

11. 11. A position measurement system according to claim 2, further comprising a light source configured to emit the light source beam into the light guide.

12. The position measurement system of claim 10 , wherein the source beam is a monochromatic beam.

13. 13. A position measurement system according to claim 2, comprising at least two integrated displacement sensors, the target grating being arranged on the object.

14. 13. The position measurement system of claim 12, wherein the respective target gratings of the at least two integrated displacement sensors are spaced apart from one another on the object, and the processor is configured to determine the position of the object in six degrees of freedom.

15. 14. A position measurement system according to claim 12 or 13, wherein the respective target gratings of the at least two integrated displacement sensors are spaced apart from one another on the object, and the processor is configured to determine deformation of the object.

16. 16. A position measurement system according to claim 2, wherein the emission grating is a zero-order coupler.

17. 17. The position measurement system of claim 2, comprising two integrated displacement sensors arranged in the same plane, wherein the processor is further configured to derive a rotation of the object about the second direction parallel to the light guide plane and perpendicular to the first direction from the position data of the object in the direction perpendicular to the light guide plane derived for the two integrated displacement sensors.

18. A lithographic apparatus comprising a position measurement system according to any one of claims 2 to 17.

19. 18. A lithographic apparatus according to claim 17, comprising a substrate table configured to support a substrate, wherein the object comprises the substrate table.

20. A projection system of an optical lithography system comprising a position measurement system according to any one of claims 2 to 17.

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