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    公开号:NL2006180A
    申请号:NL2006180
    申请日:2011-02-11
    公开日:2011-09-13
    发明作者:Arie Boef；Johannes Jacobs；Mirvais Yousefi；Michael Engelmann；Peter Harmsma
    申请人:Asml Netherlands Bv；
    IPC主号:
    专利说明:

    MEASUREMENT SYSTEM, STAGE, AND LITHOGRAPHIC APPARATUS
    FIELD
    [0001] The present invention relates to a measurement system, a stage, and a lithographic apparatus.
    BACKGROUND
    [0002] A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In such a case, 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 onto a target portion (e.g. including part of, one, or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Conventional lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at once, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning’-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.
    [0003] In order to provide an accurate patterning, an accurate temperature conditioning of the lithographic apparatus is desired. As such, at several locations in a lithography system the temperature of an object is measured with electrical temperature sensors. As an example, of such an object, a substrate or lens element can be mentioned. The temperature signal is in most cases used as an input signal for a control loop to control the temperature of the object. Because system performance depends on temperature it is desirable to control temperature.
    [0004] At present, an electrical temperature sensor is mostly used, such as an NTC or sometimes a platinum element. The electrical resistance of these devices is a function of temperature. By measuring the electrical resistance, the temperature can be deduced. The electrical resistance of an NTC is stronger influenced by temperature than that of platinum. In order to obtain the required temperature resolution, the electrical signal from the temperature sensor is very small and susceptible to external electro magnetic influences. Examples of these external influences are changing motor currents or the magnetic field of e.g. a planar or linear motor.
    Furthermore, in order to obtain the electrical signal, a current needs to be provided to the NTC or platinum element which results in dissipation in the element and thus affects the temperature that is sensed.
    SUMMARY
    [0005] It is desirable to provide an improved measurement system.
    [0006] According to a first aspect of the invention, there is provided a measurement system for determining a characteristic of an object of interest, the system including: an interrogation system including a detector and a radiation source configured to provide a beam, and a sensor including a radiation guide, optically coupled to the radiation source and the detector, to guide at least part of the beam and provide, in response to the beam, an output beam to the detector; the detector being arranged to: determine a wavelength shift of the output beam as received from the radiation guide, and determine a characteristic associated with the sensor based on the wavelength shift.
    [0007] In an embodiment, the characteristic is temperature.
    [0008] According to a second aspect of the invention, there is provide a stage for positioning an object in a lithographic apparatus including a measurement system according to the first aspect of the invention wherein the sensor is mounted to a support of the stage.
    [0009] Such a stage may e.g. be applied in a lithographical apparatus for positioning a substrate or a patterning device. In such an arrangement, the measurement device according to the first aspect of the invention enables a temperature measurement or estimate of the substrate or patterning device substantially without being affected by electrical or magnetic influences.
    [0010] According to a third aspect of the invention, there is provided a lithographic apparatus including an illumination system configured to condition a radiation beam; a support constructed to support a patterning device, the patterning device being capable of imparting the radiation beam with a pattern in its cross-section to form a patterned radiation beam; a substrate table constructed to hold a substrate; and a projection system configured to project the patterned radiation beam onto a target portion of the substrate, a measurement system for determining a temperature of lithographic apparatus, the system including: an interrogation system including a detector and a radiation source configured to provide a beam, and a sensor including a radiation guide, optically coupled to the radiation source and the detector, to guide at least part of the beam and provide, in response to the beam, an output beam to the detector; the detector being arranged to: determine a wavelength shift of the output beam as received from the radiation guide and determine a temperature associated with the sensor based on the wavelength shift.
    BRIEF DESCRIPTION OF THE DRAWINGS
    [0011] Embodiments of the invention will now be described, byway of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which:
    [0012] Figure 1 depicts a lithographic apparatus according to an embodiment of the invention;
    [0013] Figures 2a-2c depict measurement systems according to embodiments of the invention;
    [0014] Figures 3a-3h depict sensors as can be applied in a measurement system, a stage or a lithographic apparatus according to embodiments of the invention;
    [0015] Figures 4a-4c depict measurement systems, as can be applied in, a stage or a lithographic apparatus according to embodiments of the invention;
    [0016] Figure 5 depicts an interrogation system as can be applied in a measurement system, a stage or a lithographic apparatus according to an embodiment of the invention;
    [0017] Figure 6 depicts an interrogation system as can be applied in a measurement system, a stage or a lithographic apparatus according to an embodiment of the invention;
    [0018] Figure 7 schematically depicts a stage according to an embodiment of the present invention;
    [0019] Figure 8 schematically depicts a 3D view of a stage according to an embodiment of the invention.
    DETAILED DESCRIPTION
    [0020] Figure 1 schematically depicts a lithographic apparatus according to one embodiment of the invention. The apparatus includes an illumination system (illuminator) IL configured to condition a radiation beam B (e.g. UV radiation or any other suitable radiation), a patterning device support or support structure (e.g. a mask table) MT constructed to support a patterning device (e.g. a mask) MA and connected to a first positioning device PM configured to accurately position the patterning device in accordance with certain parameters. The apparatus also includes a substrate table (e.g. a wafer table) WT or "substrate support" constructed to hold a substrate (e.g. a resist-coated wafer) W and connected to a second positioning device PW configured to accurately position the substrate in accordance with certain parameters. The apparatus further includes a projection system (e.g. a refractive projection lens system) PS configured to project a pattern imparted to the radiation beam B by patterning device MA onto a target portion C (e.g. including one or more dies) of the substrate W.
    [0021] The illumination system may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic or other types of optical components, or any combination thereof, to direct, shape, or control radiation.
    [0022] The patterning device support holds the patterning device in a manner that depends on the orientation of the patterning device, the design of the lithographic apparatus, and other conditions, such as for example whether or not the patterning device is held in a vacuum environment. The patterning device support can use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device. The patterning device support may be a frame or a table, for example, which may be fixed or movable as required. The patterning device support may ensure that the patterning device is at a desired position, for example with respect to the projection system. Any use of the terms “reticle” or “mask” herein may be considered synonymous with the more general term “patterning device.”
    [0023] The term “patterning device” used herein should be broadly interpreted as referring to any device that can be used to impart a radiation beam with a pattern in its cross-section so as to create a pattern in a target portion of the substrate. It should be noted that the pattern imparted to the radiation beam may not exactly correspond to the desired pattern in the target portion of the substrate, for example if the pattern includes phase-shifting features or so called assist features. Generally, the pattern imparted to the radiation beam will correspond to a particular functional layer in a device being created in the target portion, such as an integrated circuit.
    [0024] The patterning device may be transmissive or reflective. Examples of patterning devices 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.
    [0025] The term “projection system” used herein should be broadly interpreted as encompassing any type of projection system, including refractive, reflective, catadioptric, 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. Any use of the term “projection lens” herein may be considered as synonymous with the more general term “projection system”.
    [0026] As here depicted, the apparatus is of a transmissive type (e.g. employing a transmissive mask). Alternatively, the apparatus may be of a reflective type (e.g. employing a programmable mirror array of a type as referred to above, or employing a reflective mask).
    [0027] The lithographic apparatus may be of a type having two (dual stage) or more substrate tables or "substrate supports" (and/or two or more mask tables or "mask supports"). In such “multiple stage” machines the additional tables or supports may be used in parallel, or preparatory steps may be carried out on one or more tables or supports while one or more other tables or supports are being used for exposure.
    [0028] The lithographic apparatus may also be of a type wherein at least a portion of the substrate may be covered by a liquid having a relatively high refractive index, e.g. water, so as to fill a space between the projection system and the substrate. An immersion liquid may also be applied to other spaces in the lithographic apparatus, for example, between the mask and the projection system. Immersion techniques can be used to increase the numerical aperture of projection systems. The term “immersion” as used herein does not mean that a structure, such as a substrate, must be submerged in liquid, but rather only means that a liquid is located between the projection system and the substrate during exposure.
    [0029] Referring to Figure 1, the illuminator IL receives a radiation beam from a radiation source SO. The source and the lithographic apparatus may be separate entities, for example when the source is an excimer laser. In such cases, the source is not considered to form part of the lithographic apparatus and the radiation beam is passed from the source SO to the illuminator IL with the aid of a beam delivery system BD including, for example, suitable directing mirrors and/or a beam expander. In other cases the source may be an integral part of the lithographic apparatus, for example when the source is a mercury lamp. The source SO and the illuminator IL, together with the beam delivery system BD if required, may be referred to as a radiation system.
    [0030] The illuminator IL may include an adjuster AD configured to adjust the angular intensity distribution of the radiation beam. Generally, at least the outer and/or inner radial extent (commonly referred to as σ-outer and σ-inner, respectively) of the intensity distribution in a pupil plane of the illuminator can be adjusted. In addition, the illuminator IL may include various other components, such as an integrator IN and a condenser CO. The illuminator may be used to condition the radiation beam, to have a desired uniformity and intensity distribution in its cross-section.
    [0031] The radiation beam B is incident on the patterning device (e.g., mask) MA, which is held on the patterning device support (e.g., mask table) MT, and is patterned by the patterning device. Having traversed the patterning device (e.g. mask) MA, the radiation beam B passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W. With the aid of the second positioning device PW and position sensor IF (e.g. an interferometric device, linear 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 positioning device PM and another position sensor (which is not explicitly depicted in Figure 1) can be used to accurately position the patterning device (e.g. mask) MA with respect to the path of the radiation beam B, e.g. after mechanical retrieval from a mask library, or during a scan. In general, movement of the patterning device support (e.g. mask table) MT may be realized with the aid of a long-stroke module (coarse positioning) and a short-stroke module (fine positioning), which form part of the first positioning device PM. Similarly, movement of the substrate table WT or "substrate support" may be realized using a long-stroke module and a short-stroke module, which form part of the second positioner PW. In the case of a stepper (as opposed to a scanner) the patterning device support (e.g. mask table) MT may be connected to a short-stroke actuator only, or may be fixed. Patterning device (e.g. mask) MA and substrate W may be aligned using patterning device alignment marks M1, M2 and substrate alignment marks P1, P2. Although the substrate alignment marks as illustrated occupy dedicated target portions, they may be located in spaces between target portions (these are known as scribe-lane alignment marks). Similarly, in situations in which more than one die is provided on the patterning device (e.g. mask) MA, the patterning device alignment marks may be located between the dies.
    [0032] Referring to Figure 1, the apparatus as shown further includes a measurement system including a sensing structure (broadly termed sensor) SE which is mounted to the substrate table WT in order to determine a temperature of the table (and as such, provide an estimate of the temperature of the substrate W when provided on the table). The measurement system further includes a light source (broadly termed radiation source) LS configured to provide a beam to the sensor SE. In an embodiment, the radiation source can e.g. be a laser or laser diode, the sensor can e.g. include a waveguide or a fiber arranged to receive the beam. The measurement system can further include an interconnect configured to provide the beam from the radiation source to the sensor. As will be explained in more detail below, such an interconnect can include one or more fibers but may also include a guiding mechanism configured to guide the beam from the radiation source towards a capturing element e.g. including a parabolic mirror mounted to the substrate table WT or the second positioner PW arranged to receive the beam and provide the beam to the sensing structure.
    [0033] The depicted apparatus could be used in at least one of the following modes: 1. In step mode, the patterning device support (e.g. mask table) MT or "mask support" and the substrate table WT or "substrate support" are kept essentially stationary, while an entire pattern imparted to the radiation beam is projected onto a target portion C at one time (i.e. a single static exposure). The substrate table WT or "substrate support" is then shifted in the X and/or Y direction so that a different target portion C can be exposed. In step mode, the maximum size of the exposure field limits the size of the target portion C imaged in a single static exposure.
    2. In scan mode, the patterning device support (e.g. mask table) MT or "mask support" and the substrate table WT or "substrate support" are scanned synchronously while a pattern imparted to the radiation beam is projected onto a target portion C (i.e. a single dynamic exposure). The velocity and direction of the substrate table WT or "substrate support" relative to the mask table MT or "mask support" may be determined by the (de-)magnification and image reversal characteristics of the projection system PS. In scan mode, the maximum size of the exposure field limits the width (in the non-scanning direction) of the target portion in a single dynamic exposure, whereas the length of the scanning motion determines the height (in the scanning direction) of the target portion.
    3. In another mode, the patterning device support (e.g. mask table) MT or "mask support" is kept essentially stationary holding a programmable patterning device, and the substrate table WT or "substrate support" is moved or scanned while a pattern imparted to the radiation beam 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 "substrate support" 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, such as a programmable mirror array of a type as referred to above.
    [0034] Combinations and/or variations on the above described modes of use or entirely different modes of use may also be employed.
    [0035] In accordance with the first aspect of the invention, a measurement system is provided that enables a characteristic of an object (e.g. a temperature or a mechanical strain) to be determined based on an optical signal obtained from a sensing structure.
    [0036] In Figure 2a, a general set-up of an embodiment of the measurement system according to the first aspect of the invention is schematically depicted. The embodiment as shown applies a transmissive type sensor or sensing structure SE. As shown, the measurement system includes an interrogation system IS
    which includes a light source (broadly termed radiation source) LS and a detector. The radiation source LS (e.g. a scanning laser or a wide band light source) is arranged to, in use, provide a beam 100 (e.g. a laser beam), optionally via an interconnect IC, to a sensor SE. Various embodiments of the sensor SE are explained in more detail below. In general, the sensor includes a light guide (broadly termed radiation guide) LG (e.g. a fiber or waveguide) which receives the beam from the radiation source and provides an output beam 110 to a detector DE of the interrogation system IS. As the radiation guide will, in general, undergo an, albeit small, transformation, due to thermal or mechanical effects, the wavelength of the beam of the radiation source, will undergo a transformation which can e.g. manifest itself as a wavelength shift. In the embodiment as shown, the beam from the radiation source enters the radiation guide LG at one end 102 and leaves the radiation guide at an opposite end 112. Such a wavelength shift of the output beam can subsequently be determined by the detector DE whereupon the detector can determine a characteristic of the sensor associated with the wavelength shift. As such, the wavelength shift as determined can e.g. be associated with a temperature of the sensing structure or a mechanical strain the structure is subject to. In Figure 2b, an embodiment of the measurement system according to the invention is shown having a reflective type sensor or sensor SE. In such an arrangement, the radiation beam enters and leaves the sensor SE at the same end 122.
    [0037] In an embodiment, the elements inside the dotted line FW can be positioned on the fixed world (FW) whereas the elements indicated by MS can e.g. be mounted to a moving stage MS.
    [0038] When using a transmissive sensor, as can be seen from Figure 2a, two connections are needed between the sensor or sensing structure SE and the interrogator system IS whereas, when a reflective sensor is used, the number of connections can be reduced to one, by using a circulator as shown in Figure 2b. As will be known the skilled person, an optical circulator as shown directs light a —> b and b —> c, but not c —» a.
    [0039] For completeness, a way to connect a transmissive sensor by means of only a single fiber is shown in Figure 2c, using a coupler 140 and two isolators 142,144 for providing an output light beam leaving the sensor via the same connection as the input radiation beam. It is worth noting that this implementation may have one or more of the following drawbacks: 1 Two additional components are needed (2 x isolator) which may add to the cost of goods.
    2 The lower isolator may remove approximately 50% of the input radiation, which is an inefficient use of optical power, and causes heating of the isolator.
    3 50% of the usable output may be lost at the coupler, resulting again in an inefficient use of power.
    [0040] The measurement system according to the first aspect of the invention as schematically shown in Figures 2a-2c can e.g. be applied to determine an object’s temperature based on a wavelength shift determined from an output beam received from a light guide.
    [0041] Compared to conventional temperature sensors such as NTCs or platinum elements, the measurement system according to the first aspect of the invention can provide various benefits.
    [0042] Conventional electrical temperature sensors for high resolution applications (< 1 mK) may require a NTC with a dedicated in house designed electronics. To prevent self heating of such a temperature sensor, the measurement current needs to be kept small, typically < 1 .e-5 A. As a result small voltage changes need to be detected typically order 1e-3 V as an electrical measurement signal. In order to maintain a desired accuracy, current designs aim to amplify the electrical measurement signal as close a possible to the sensor location. However, there will always be a certain length of unamplified signal between the sensor and the pre-amp, e.g. due to volume or area restrictions. Typically, in case of the WT temperature sensors mounted to a substrate table WT, this is about 50 cm. Other drawbacks of the amplified signals are local power dissipation and therefore heating of the object, construction volume requirements and a reduction of the reliability of the introduction of additional components. In the measurement system according to the first aspect of the invention, one or more of these drawbacks are mitigated. The measurement system does not rely on electric or magnetic characteristic of a sensing element but rather on an optical characteristic. In an embodiment, environmental parameters such as strain or temperature can be sensed at high resolutions by trapping radiation in miniscule optical sensors. Examples of such sensors are provided below in more detail.
    [0043] In an embodiment, the measurement system includes a plurality of sensors, also referred to as a sensing array enabling the measurement of e.g. temperature or strain at different locations on an object. By applying multiplexing techniques, a single radiation source LS and/or a single detector DE may suffice to provide the radiation beam to a plurality of sensors and/or providing a read out of the output beams of the various sensors.
    [0044] With respect to the application of such a sensor or sensing array, it is worth mentioning that such a sensor or array of structures is not susceptible to external electrical and magnetic influences. Further benefits which can be achieved include an improved resolution compared to conventional electrical sensors. In addition, when e.g. applied on a stage of a lithographic apparatus (in order to determine a temperature on a substrate or mask table), it is worth mentioning that the measurement system according to an embodiment of the invention requires less functionality and components on object that is sensed. As in the case of a substrate or mask table, the dynamic behavior of such a table is critical to obtain an accurate positioning of the mask or substrate, any reduction of components required on the table will facilitate in obtaining the desired dynamic performance. A further benefit of the measurement system according to an embodiment of the invention is that the number of sensors can easily be increased with only a small increase in overall cost of the system. This can e.g. be contributed to the use of a common interrogator system for multiple sensing structures.
    [0045] In Figures 3a-3h, some embodiments of sensors are schematically depicted.
    [0046] As a first example of a sensor, a so-called fiber Bragg grating can be applied. In Figure 3a, a radiation beam 100 (e.g. a laser beam from a laser source) is provided via an optical circulator to a fiber Bragg grating 200. In such a grating, a portion is provided with a modulated index, e.g. with a period Δ. A reflected beam 110 of the grating is subsequently provided, via the circulator, to a detector which can e.g. include a spectrum analyzer. A benefit of such a fiber Bragg grating is that it can generate a precise reflection peak, enabling a comparatively high resolution.
    [0047] A Fiber Bragg Grating (FBG) is an optical fiber (typical diameter 125 pm) with a periodic modulation (Bragg grating) of the refractive index of the fiber core. In a long fiber, this modulation is generated locally, so that the sensor and the connecting fiber can form a monolithic unit. The Bragg grating can be as short as about 2 mm. It reflects a narrow wavelength band of radiation while it transmits all other wavelengths. The reflection peaks of multiple cascaded FBGs can be individually identified due to the wavelength selection property of the FBG, so this brings a huge potential for distributed sensing using FBGs. As schematically shown in Figure 3b, an array of FBG’s (1,2,3) can be provided with a radiation beam of a broadband radiation source LS having an input light spectrum (ISP). The transmitted spectrum (TSP) of the array of FBG’s is equally shown and the reflected spectrum (RSP) as received by a detector DE, via a coupler. The FBG sensor principle relies on the fact that the measurement changes the grating period, which in turn shifts the FBG reflection wavelength. An interrogator detects the wavelength shift and translates that to a measurement value, for example temperature. Typically, a glass-based FBG has a temperature sensitivity of 10 pm/K. Benefits of FBGs are the small size, and its cascadability to have multiple sensors connected to a single fiber, and modest price.
    [0048] A next sensor which can be used in a measurement system according to an embodiment of the invention is a FIBER BRAGG LASER (FBL). Such a laser is schematically depicted in Figure 3c.
    [0049] A Fiber Bragg Laser (FBL) consists of 2 FBGs with an Erbium doped fiber (EBF) in between. An optical pump signal 160 (980 nm or 1480 nm laser light), input via a coupler 150,excites the Erbium ions to a higher energy stage, so that they can participate in a process of stimulated emission, providing optical gain at 1550 nm, output 170. The FBGS at both ends of the Erbium doped section have their peak reflection at the same wavelength, resulting in a very narrow laser line radiating from the FBL.
    [0050] The sensor principle is based upon length variations of the FBGs, in our case due to temperature changes, resulting in a wavelength shift. The FWFIM (Full Width at Half Maximum) of the emitted spectrum is much less than that of an FBG, and a superior resolution can be achieved.
    [0051] As yet another embodiment, a so-called Fabry-Perot (FP) interferometer can be applied as a sensor.
    [0052] A schematic layout of a first example of such an interferometer is given in Figure 3d. It consists of two mirrors with reflection coefficients R1 and R2, which form a cavity of length L. To explain the principle, the figure shows the configuration where radiation enters the cavity at an angle from the left. (Input light “in” entering from the left) is partly reflected back to the left by mirror R1, and partly transmitted to the right where it can either be reflected or transmitted by the mirror R2. Radiation can reflect multiple times between the mirrors before being transmitted by either of the two mirrors. The transmitted and reflected radiation is focused onto single spots by means of lenses 175. All the contributions add up coherently, and depending on the mutual phase shifts the interference varies between constructive or destructive. As the phase shift depends on the wavelength, so is the total reflected or transmitted power. Such an interferometer may also be implemented in fiber as schematically shown in Figure 3e. In Figure 3e, a Fabry-Perot interferometer 220 is schematically depicted including a fiber segment (indicated as a cavity) enclosed by two high-reflective (FIR) ends. Instead of a fiber, a waveguide could be considered as well which would result in a compact and robust design. By using the appropriate coatings providing the reflections, a comparatively sharp resonance of the reflected or transmitted power can be obtained. The FP can be used as a temperature sensor because the resonances of the reflected or transmitted power shift as the temperature changes. This is due to thermal expansion of the cavity, and due to the temperature dependence of the cavity refractive index.
    [0053] In Figures 3f-3h, some further, fiber based arrangements of sensors are schematically depicted.
    [0054] The embodiment in figure 3f is a so-called Mach Zehnder arrangement which can be used to determine small wavelength shifts in one of two beams by providing an input beam (input), separating the beam in to two beams and directing both beams along a different path towards to provide an output beam (output). The small wavelength shift can e.g. be caused by a change in length of one of the paths, e.g. cause by a change in temperature in one of the fibers forming the paths. The embodiment as shown in Figure 3g is a so-called Sagnac or ring resonator. In the resonator as shown, an input beam (input) is provided to a fiber 300 coupled to a ring shaped fiber 310 via a first coupler A, the ring shaped fiber further being coupled to an output fiber 320 via a second coupler B. In such an arrangement, two output signals (referred to as through output and drop output) can be used for determining a wavelength shift. The benefit of such a ring resonator as shown is that it can provide sharper resonances.
    [0055] With respect to the application of a ring resonator as a sensing structure, it is worth mentioning that such a resonator can be implemented as a waveguide as well, compared to an implementation using fiber. In such an arrangement, the waveguide could be implemented as Silicon on Insulator or using dielectrics such as oxinitrides or triplex.
    [0056] In Figure 3h, the embodiment schematically shows two further ring resonators implemented by use of fibers. In the embodiments, an input radiation beam is reflected by a high reflective (HR) end or an anti reflective (AR) end towards the input, thus forming an output beam. Input and output are thus shared in those arrangements. In the upper arrangement, the through signal is applied as an output, whereas in the lower arrangement of Figure 3h, the drop signal can be applied.
    [0057] With respect to the interrogation system including the radiation source and the detector, equally various optics exist. As an example, a scanning laser or multiple lasers can be applied as a radiation source. When a scanning laser is used, it is desirable that such a laser scans across at least one FSR (free spectral range), preferable more.
    [0058] In Figure 4a, a set-up with a scanning laser and a plurality of sensors (indicated as sensor 1 to sensor N) is schematically shown. In the arrangement, an input beam 100 (from a scanning laser) is provided via a circulator and an optical multiplexer to the various sensing structures. The output beams of the various sensors are subsequently provided via the optical multiplexer and the circulator as an output beam 110 to the detector. In such a set-up, also referred to as Wavelength Division Multiplexing (WDM), all sensors can communicate via a single fiber. A dedicated wavelength band (spectral width in the order of a few nm) can be allocated for each sensor. These sensor-specific bands are selected from a broad-band source (total spectral width 10 nm or more) by means of a wavelength filter, for example an Arrayed Waveguide Grating (AWG). The sensor-specific wavelength bands can be recombined to the single optical fiber by means of the same AWG. The interrogator system will contain a similar WDM filter, or has knowledge of the wavelength (scanning laser system).
    [0059] Various other options exist in order to accommodate for multiple sensors.
    [0060] In the set-up as shown in Figure 4b, each sensor has its own optical connection to its individual detector. As will be understood by the skilled person, this may make the connection quite complex and affect the robustness. Also, the power may need to be split over the different sensors.
    [0061] In Figure 4c, yet another set-up is schematically depicted using Time division Multiplexing (TDM). In such an arrangement, all sensors communicate via a single fiber, and are interrogated one by one. In the arrangement as shown in the upper part of Figure 4c, an optical switch is located on the stage, this can be for example a MEMs switch. A potential drawback of this set-up may be that the switch consumes power and so it generates heat. Note that no continuous link exists to each sensor at all times.
    [0062] As an alternative, the lower part of Figure 4c schematically shows a kind of cross-over between TDM with an on-stage switch and individually connected sensors by locating the switch off-stage. In this way, no splitter is needed and a large number of circulators and detectors can be saved.
    [0063] In Figure 5, another embodiment of the interrogation system is schematically depicted using a wide band optical source. In the arrangement, the transmission / reflection of the sensor is measured in series with a reference sensor resulting in a signal that can indicate the alignment between the sensing structure and the reference sensor. Such an arrangement can also be implemented using Wavelength Division Multiplexing (WDM). In an embodiment, the reference sensor is slightly different from the sensor. As a detector, a commercially available spectrometer can be used.
    [0064] As a third example of an interrogator system (see Figure 6), a 3x3 interferometer system can be used as a sensor. Such an interferometer system includes a Mach Zehnder interferometer (MZI), a beam splitter, two fiber arms of different length and a 3x3 coupler, as schematically indicated by reference number 400. The interrogator system is applied, as shown in Figure 6, in combination with a ring resonator as shown in Figure 3c. As a radiation source, a wide band source is applied. As further shown, a filter is applied to the output beam 110 prior to being applied to the 3x3 interferometer 400.
    [0065] In case the measurement system according to an embodiment of the invention is e.g. applied to measure or estimate the temperature of an object mounted to a support of a stage which requires accurate positioning, it may be desirable (as shown in more detail below), to provide only part of the measurement system on the stage. In an embodiment, only the sensor or sensors are provided on the stage or support of the object of interest. As such, the interrogator system (i.e. including the light source and detector) can e.g. be provided on a separate frame or even outside the apparatus including the stage, e.g. in an electronics cabinet. When the sensor or sensors are thus remotely optically connected to the interrogation system, an interconnect (such as interconnect 1C as shown in Figure 2) can be applied. Various options exist for providing such an interconnect between the interrogation system and the sensing structure.
    [0066] In a first embodiment, the interconnect can include a fiber connection, e.g. including glass or plastic fibers. In case the interconnect connects an interrogation system mounted on a fixed position and a sensor mounted on a movable structure, e.g. a stage in a lithographic apparatus, care should be taken with respect to bending conditions of the fiber. Life expectance of such fiber should considered during the design, e.g. by performing endurance fatigue tests on the fiber.
    [0067] As an alternative to a ‘wired’ fiber connection, in a second embodiment, a so-called free-space connection is applied. In such an interconnect, a beam originating from a radiation source such as a laser is directed without use of a solid medium such as a fiber is directed, e.g. using an aiming or tracking device, towards a collector mounted to the movable component including the sensing structure.
    [0068] Such an aiming device (e.g. a laser gun) can direct (e.g. based on positional information of the stage where the sensing structure is mounted to) a laser beam to a particular position on the stage where a collector (e.g. including a parabolic mirror) collects the incoming beam whereupon the beam is guided, e.g. via a fiber, to the sensing structure or structures.
    [0069] In Figure 7, the various components of a stage according to an embodiment of the present invention are schematically shown. Such a stage can e.g. include a long stroke assembly or positioning system (e.g. including a linear or planar motor) configured to displace an object (e.g. a wafer or patterning device) over comparatively large distances, and a short-stroke assembly to provide a more accurate positioning of the object. In general, the object to be positioned is mounted to an encoder or mirror block (depending whether an encoder based measurement system or an interferometer based measurement system is applied) which is used to determine a position of the object relative to a position reference, e.g. a metrology frame or a projection system using a position measurement system schematically indicated by the arrows 450.
    [0070] In accordance with an embodiment of the present invention, a measurement system is included in the stage whereby the sensor or sensors can e.g. be mounted to the encoder block in order to determine an accurate temperature or temperature distribution of the encoder block. The interrogator system can e.g. be mounted to the long stroke assembly or baseframe or can be placed separate from the stage, e.g. in an electronics cabinet. An interconnect (e.g. including a parabolic mirror) capable of receiving and outputting light beams of the measurement system can e.g. be mounted to the short stroke assembly whereas the light transmitting device can be mounted on a fixed component such as the base frame. As such, the measurement system does not require a wired connection to the short stroke assembly, improving the dynamical performance of the stage.
    [0071] In Figure 8, a 3D view on an encoder block and short stroke assembly including a measurement system according to the invention is shown. As schematically shown, the interrogation system (or interrogator) of the measurement system is mounted in an electronics cabinet whereby a fiber is used (which can e.g. be 10 - 50 m in length) to provide radiation beams to and from the stage. An auto-focus system (e.g. mounted to a metrology frame MF or at an other fixed position) can be arranged to provide the radiation beam through free space to a collector operating as an I/O port for the radiation beam and which can be mounted to the short stroke assembly. The I/O port can e.g. include a thin glass plate of approx. 100 gr. From the I/O port, the radiation beam received can be guided towards a plurality of sensors (e.g. from 10 -100 sensing structures) mounted on the encoder block 500.
    [0072] Although specific reference may be made in this text to the use of lithographic apparatus in the manufacture of ICs, it should be understood that the lithographic apparatus described herein may have other applications, such as 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. The skilled artisan will appreciate that, in the context of such alternative applications, any use of the terms “wafer” or “die” herein may be considered as synonymous with the more general terms “substrate” or “target portion", respectively. The substrate referred to herein may be processed, before or after exposure, in for example a track (a tool that typically applies a layer of resist to a substrate and develops the exposed resist), a metrology tool and/or an inspection tool. Where applicable, the disclosure herein may be applied to such and other substrate processing tools. Further, the substrate may be processed more than once, for example in order to create a multi-layer IC, so that the term substrate used herein may also refer to a substrate that already contains multiple processed layers.
    [0073] Although specific reference may have been made above to the use of embodiments of the invention in the context of optical lithography, it will be appreciated that the invention may be used in other applications, for example imprint lithography, and where the context allows, is not limited to optical lithography. In imprint lithography a topography in a patterning device defines the pattern created on a substrate. The topography of the patterning device may be pressed into a layer of resist supplied to the substrate whereupon the resist is cured by applying electromagnetic radiation, heat, pressure or a combination thereof. The patterning device is moved out of the resist leaving a pattern in it after the resist is cured.
    [0074] The terms “radiation” and “beam” used herein encompass all types of electromagnetic radiation, including ultraviolet (UV) radiation (e.g. having a wavelength of or about 365,248,193,157 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.
    [0075] The term “lens”, where the context allows, may refer to any one or combination of various types of optical components, including refractive, reflective, magnetic, electromagnetic and electrostatic optical components.
    [0076] While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. For example, the invention may take the form of a computer program containing one or more sequences of machine-readable instructions describing a method as disclosed above, or a data storage medium (e.g. semiconductor memory, magnetic or optical disk) having such a computer program stored therein.
    [0077] 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 clauses set out below. Other aspects of the invention are set out as in the following numbered clauses: 1. A measurement system for determining a characteristic of an object, the system comprising: an interrogation system comprising a detector and a radiation source configured to provide a beam; and a sensor comprising a radiation guide, optically coupled to the radiation source and the detector, to guide at least part of the beam and provide, in response to the beam, an output beam to the detector, the detector being arranged to: determine a wavelength shift of the output beam as received from the radiation guide, and determine a characteristic associated with the sensor based on the wavelength shift.
    2. The measurement system of clause 1, wherein the characteristic is a temperature.
    3. The measurement system of clause 1 or 2, wherein the radiation guide comprises a ring resonator.
    4. The measurement system of clause 3, wherein the ring resonator comprises a waveguide or a fiber.
    5. The measurement system according to clause 3, wherein the radiation guide comprises a fiber Bragg grating.
    6. The measurement system of any of the preceding clauses, wherein the radiation source comprises a laser.
    7. A stage for positioning an object in a lithographic apparatus comprising a measurement system according to any of the preceding clauses, wherein the sensor is mounted to a support of the stage.
    8. The stage of clause 7, further comprising a positioning device configured to displace the support.
    9. The lithographic apparatus comprising a stage according to clause 7 or 8 to position a patterning device or a substrate.
    10. A lithographic apparatus comprising: an illumination system configured to condition a radiation beam; a support constructed to support a patterning device, the patterning device being capable of imparting the radiation beam with a pattern in its cross-section to form a patterned radiation beam; a substrate table constructed to hold a substrate; a projection system configured to project the patterned radiation beam onto a target portion of the substrate; and a measurement system configured to determine a temperature of lithographic apparatus, the system comprising: an interrogation system comprising a detector and a radiation source configured to provide a beam, and a sensor comprising a radiation guide, optically coupled to the radiation source and the detector, to guide at least part of the beam and provide, in response to the beam, an output beam to the detector, the detector being arranged to determine a wavelength shift of the output beam as received from the radiation guide, and determine a temperature associated with the sensor based on the wavelength shift.
    权利要求:
    Claims (1)
    [1]
    A lithography device comprising: an exposure device adapted to provide a radiation beam; a carrier constructed to support a patterning device, the patterning device being capable of applying a pattern in a section of the radiation beam to form a patterned radiation beam; a substrate table constructed to support a substrate; and a projection device adapted to project the patterned radiation beam onto a target area of the substrate, characterized in that the substrate table is adapted to position the target area of the substrate in a focal plane of the projection device.
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    公开号 | 申请日 | 公开日 | 申请人 | 专利标题
    法律状态:
    2015-06-10| WDAP| Patent application withdrawn|Effective date: 20120604 |
    优先权:
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    US31300510P| true| 2010-03-11|2010-03-11|
    US31300510|2010-03-11|
    US35782410P| true| 2010-06-23|2010-06-23|
    US35782410|2010-06-23|
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