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    • 专利摘要:
    The invention provides a position control system configured to control a position of a movable object, wherein the position control system is configured to determine cross talk of an encoder system, by: determining a first position of the movable object with each of the encoder measurement system and the reference position measurement system; moving the movable object in a second direction other than the measurement direction; determining the second position of the movable object with each of the encoder system and the reference position measurement system, and determining cross talk between the second direction and the measurement direction by comparison of the position measurements of the first position and the second position of both the encoder system and the reference position measurement system.
    公开号:NL2018131A
    申请号:NL2018131
    申请日:2017-01-05
    公开日:2017-08-04
    发明作者:De Jongh Robertus；Butler Hans；Antonius Fransiscus Van Der Pasch Engelbertus
    申请人:Asml Netherlands Bv；
    IPC主号:
    专利说明:

    POSITION MEASUREMENT SYSTEM, LITHOGRAPHIC EQUIPMENT AND METHOD OR DETERMINING CROSS TALK OR AN ENCODER SYSTEM
    BACKGROUND
    Field gF the Invention
    The present invention relates to a position measurement system, a lithographic apparatus, and a method of determining cross talk or an encoder system.
    Description of the Related Art 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 cart is transferred onto a target portion ( e, g. including part or. one, or several dies) on a substrate (eg, a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that arc successively patterned. Conventional lithographic apparatus include so-called steppers, in which each target 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 beaut in a given direction (the “scanning” direction) while synchronously scanning tire 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.
    In order to accurately transfer the pattern from the patterning device to the substrate, the position of different movable objects, such as substrate table and a support for the patterning device have to be ...... controlled with high accuracy, In order to contrei the position of these movable objects a position control system is provided to control the position of the movable objects, usually in six degrees of freedom.
    With increasing demands on the accuracy of the transfer of the pattern from the patterning device to the substrate, also one or more mirror devices of the projection system are provided with a position control system to control the position of the one or more mirror devices with high accuracy in six degrees of freedom.
    Such position control system may include a position measurement system, configured to determine a position of the movable object with respect to a reference object, a controller to provide a control signal on the basis of the determined position, and at least one actuator to actuate the movable object to a desired position.
    In a known embodiment, the position measurement system comprises an encoder system including at least one encoder head and an encoder scale. The encoder head is mounted on the movable object and the encoder scale is mounted on the reference object. In an alternative embodiment, the encoder head is mounted on the reference object and the encoder scale is mounted on the movable object.
    The encoder head is configured to measure a relative movement of the encoder head with respect to the encoder scale in the measurement direction, When a start position of the encoder head with respect to the encoder scale is known, the current position of the encoder head with respect to the encoder scale can be determined by measuring the relative movement between the encoder head and the encoder scale and addirtg this to the known start position.
    To determine art absolute reference position of the movable object with respect to tits reference object, the position measurement system may include a reference position measurement system. The reference position measurement system comprises an absolute reference position sensor, for example mounted on the movable object, and an absolute reference position mark, for example mounted on the reference object.
    The reference position measurement system can be used to determine an absolute position of the movable object with respect to the reference object. This absolute position can typically be determined when the absolute reference position sensor is aligned with the absolute reference position marks. This absolute position can be used as the start position with which, in combination with the relative movement measured by the encoder system, the position of the movable object and be determined.
    The known encoder system used in position measurement systems for controlling the position of the mirrors or the projection system usually suffers from cross talk. This means that a movement in a non-measurement direction may result in a disturbance in the relative movement measured by the encoder system in the measurement direction, Also other position measurement systems may show cross talk between a measurement direction and another direction.
    The cross talk leading to disturbance in the position determined by the position measurement system, avoiding the position control system can be used for position control or the mirror device with a high position accuracy.
    SUMMARY
    It is desirable to provide a position control system that allows to more accurately determine the position of a movable object, in particular a mirror device or a projection system or a lithographic apparatus, with respect to a reference object using an encoder system., Further, it is desirable to provide a lithographic apparatus incorporating such a position control system and to provide a method of determining cross talk or an encoder system.
    According to an embodiment of the invention, there is provided a position measurement system configured to determine a position of the movable object with respect to a reference object, including an encoder system including at. least one encoder head and an encoder scale; and a reference position measurement system including art absolute reference position sensor and an absolute reference position mark, where, when the movable object Is at a first position, the encoder system is arranged to provide a first encoder signal representative of the first position along a measurement direction, and the reference position measurement system is arranged to provide a first reference signal representative of the first position along the measurement direction, when, the movable object is at a second position, the encoder system is arranged to provide a second encoder signal representative or the second position along the measurement direction, and thereference position measurement system is arranged to provide a second reference signal representative of the- second position along the measurement direction, the position measurement system is arranged to determine a difference between the first encoder signal and the second encoder signal caused by a difference between the first position and the second position along a second direction other than the measurement direction, based on the first encoder signal, the second encoder signal, the. first reference signal and the second reference signal. According to an embodiment of the invention, there is provided a lithographic apparatus including: a support structure constructed to support a patterning device, the patterning device being capable of imparting a 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, the position measurement system or one of the clauses 1-9. a position control system including a controller and an actuator, the controller is arranged to provide a control signal on a basis or at least one of the. first encoder signal and the second encoder signal, the actuator is arranged to actuate the movable object based on the control signal.
    According to art embodiment of the invention, there is provided a method of determining cross talk or an encoder system, the encoder system being configured to determine a relative movement or a movable object with respect to a reference object in a measurement direction, according to the method comprises using a reference position measurement system including an absolute reference position sensor and an absolute reference position mark, the method including the steps of: determining a first position of the movable object with each of the encoder measurement system and the reference position measurement system; moving the movable object in a second direction other than the measurement direction; determining the second position of the movable object with each of the encoder system and the reference position measurement system, and determining cross talk between the second direction and the measurement direction by comparison of the position measurements of the first position and the second position of both the encoder system and the reference position measurement system,
    LETTER DESCRIPTION OF THE DRAWINGS
    Embodiments of the invention will now be described, by -way or example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which:
    Figure 1 schematically depicts a lithographic apparatus including a substrate stage according to an embodiment of the invention;
    Figure 2 schematically depicts a first embodiment of a position control system for a movable object positioned in a first position;
    Figure 3 schematically depicts the embodiment of the position control system or Figure 2 with the movable object positioned in a second position;
    Figures 4 and 5 schematically depict a possible cause of cross talk in an encoder position measurement system;
    Figure 6 shows a control scheme of an embodiment or a position control system according to the invention in which a cross talk compensation device is incorporated; and
    Figure 7 shows a control scheme of an alternative embodiment or a position control system according to the invention in which a cross talk compensation device is Incorporated.
    DETAILED DESCRIPTION
    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 mask 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 (eg, 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 (eg 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 (eg including one or more dies) or the substrate W,
    Tire illumination system IL may include various types of optical components, soch as refractive, reflective, magnetic, electromagnetic, electrostatic or other types of optical components, or any combination of, for directing, shaping, or controlling radiation.
    The mask support structure MT supports, i.e, bears the weight of, the patterning device MA. It holds the patterning device MA 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 a hero in a vacuum environment. The mask support structure can use mechanical, vacuum, electrostatic or oiler damping techniques to hold the patterning device. The mask support structure may be a frame or a table, for example, which may be fixed or movable as required. The mask support structure mayensure that the patterning device is at a desired postdon, for example with respect to the projection system PS. Any use of the. terms "reticle" or "mask" may be considered synonymous with the more general term "patterning device."
    The term “patterning device *” used should be broadly interpreted as referring to any device that can be used to impart a radiation beam with a patient in its cross-section so as to create a pattern in a target portion of the substrate W, it should be noted that the pattern transmitted 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.
    The patterning device spay 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, ss 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 tilled mirrors impart a pattern in a radiation beam which is reflected by the .matrix mirror.
    The term "projection system" used should be broadly interpreted as encompassing any type of projection system, including refractive, reflective, eatadiopirie, magnetic, electromagnetic and electrostatic optical systems, or any combination thereof, as appropriate for the exposure radiation being used, or for other factors suds as the use of an immersion liquid or the use of a vacuum. Any use of the term "projection lens *" may be considered as synonymous with the more general term "projection system".
    Tim terms “radiation” and “beam” used and compassed all types of electromagnetic radiation, including ultraviolet (UY) radiation (eg having a wavelength or about 365,248, 193, 15 Or 126 nm) and extreme ultra-violet (EtiV) radiation (eg having a wavelength in the range of 5-20 nm), as well as particle beams, such as ion beams or electron beams.
    As here depicted, the apparatus is of a transmissive type (ie, employing a transmissive mask). Alternatively, the apparatus may be of a reflective type (e.g., employing a programmable mirror array or a type referred to above, or employing a reflective mask).
    The lithographic apparatus may be of a type having two (dual stage) or more substrate fables or "substrate supports" (and / or two or more mask tables or "mask supports"). In sssch "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 used for exposure. In addition to one or more substrate supports, the lithographic apparatus may have a measurement stage provided with at least one sensor to measure a property of the substrate support or a property of the radiation beaut exiting the projection system. The measurement stage may be arranged not to hold a substrate.
    The lithographic apparatus may also be a type of at least a portion of the substrate W may be covered by a liquid having a relatively high refractive index, eg water, so as to fill a space between the projection system PS arid the substrate W. An immersion liquid may also be applied to other spaces in the lithographic apparatus, for example, between the patterning device MA and the projection system PS. Immersion techniques can be used to Increase the numerical aperture of projection systems. The term "immersion" as used 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.
    Referring to figure S, 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 radiation source SO is not considered to be part of the lithographic apparatus and foe radiation beam is passed from the radiation 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 fit of the lithographic apparatus, for example when the source is a mercury lamp. The radiation source SO and the illuminator IL, together with the beam delivery system BD if required, may be referred to as a radiation system.
    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-irrer, respectively) or the intensity distribution in a pupil plane or the illuminator IL can be adjusted. In addition, die.iHuminator .EL..may include various other components, such as an integrator IN and a condenser CO. The illuminator may be used to condition the radiation to have a desired uniformity and intensity distribution in its cross-section.
    The radiation beam B is incident on the patterning device MA, which is hero on the mask support structure MT, and is patterned by the patterning device MA, Having traversed the patterning device MA, the radiation beam B passes through the projection system PS, which vary the beam onto a target portion C of the substrate W. With the aid of the second'p0 ^ tit ^ nf'deivi £ te''PW'aiïd''ixKttion sensor IF (eg an interferometric device, linear encoder or capacitive sensor ), the substrate table WT can be moved accurately, eg so as to position different target portions € 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 MA with respect to the path of the radiation beam B, eg, after mechanical retrieval from a mask library, or during a scan. Its general, movement of the mask support structure MT may be realized with the aid of a long-stroke module (coarse positioning) and a short-stroke module (fine positioning), which form pan of the first positioning device PM, Similarly, movement of the substrate table WT may be realized using a long-stroke module or a short-stroke module, which form part of the second positioner PW, in the ease of a stepper (as opposed to a scanner) the, mask support structure MT may be connected to a short · actuator only, or may be fixed. Patterning device MA and substrate May be aligned using mask 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 that is provided on the patterning device MA, the mask alignment marks may be located between the dies.
    The depicted apparatus could be used in at least one of the following modes: 1. In step mode, the mask support structure MT and the substrate table WT or "substrate support" are kept essentially stationary, while an entire pattern is imparted to the radiation beam is projected onto a target portion C at one time (ie 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 can be exposed. In step mode, the maximum size of the exposure field limits the size of the target portion € imaged in a single static exposure. 2. In scan mode, the mask support structure MT and the substrate table WT or "substrate support" are scanned synchronously while a pattern beamed 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 support structure MT 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) or the target portion in a single dynamic exposure, whereas the length of the scanning motion has the height (in the scanning direction) of the large! portion. 3. In another mode, the mask support structure MT 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 or a type as referred to above.
    Combinations and / or variations on the modes described above or use or entirely different modes or use may also be employed,
    As shown in Figure 1, the projection system PS comprises a number of minor devices MD configured to reflect the patterned beam B within the projection system PS. To optimize the accuracy, i.e, focus and overlay, or the lithographic apparatus, the mirror devices MD are provided as movable objects. A position control system is provided to control the position of the movable object in six degrees of freedom.
    Figures 2 and 3 show such a position control system to control the position of a movable object MO, for example a mirror device MD or the projections system PS shown in Figure 1, in six degrees of freedom.
    The position control system consists of position measurement system PMS, a controller CONT and an actuator ACT.
    The position measurement system PMS is configured to determine a position of the movable object MG with respect to a reference object RO in six degrees of treedon. The determined position is fed into a controller CONT to provide a control signal that is used by the actuator ACT to actuate the movable object MO to move to a desired position.
    The position measurement system comprises an encoder system and a reference position measurement system. The encoder system comprises art encoder bead EH mounted on the movable object MO, and an encoder scale ES, for example a grid plate., Mounted on the reference object RO.
    The encoder scale ES comprises a known patient or indices, for example lines, with a known spacing between them. These indices can be seen by the encoder head EH when it moves along the encoder scale ES. By counting the number of indices that are passed by the encoder head EH, the relative movement of the encoder head EH with respect to the encoder settle ES can be measured.
    To determine a position of the movable object MO with respect to the reference object RO, a start position must be known since; the encoder system is only configured to measure a relative movement between the encoder head EH and the encoder scale ES. When the start, position is known, the current position can be calculated by adding the relative movement to the start position.
    It is remarkably remarked that some encoder systems are capable of measuring the absolute position of the movable object within a measurement period, e.g. between two indices. In such an encoder system, the position of the movable object MO with respect to the reference object RO may be determined as the start position plus the relative movement plus the position measured within the measurement period.
    Since the encoder system is not equipped to measure an absolute position of the movable object MO with respect to the reference object RO, the position measurement system comprises a reference position measurement system including an absolute reference position sensor ARPS and an absolute reference position mark ARPM. The reference position measurement system is configured to measure an absolute reference position, e, g. a start position or zero position, or the movable object MO with respect to the reference object RO. 'The absolute reference position sensor ARPS is configured to determine the position of the absolute reference position mark ARPM so that the starting position of the movable object MO with respect to the reference object RO can be determined. The absolute reference position mark ARPM is therefore a unique mark in the. y-direction so that the start position can be unambiguously determined by the position limesÉurement syÉereiiiiiijjj
    In prior art position measurement systems, the accuracy of the absolute reference position sensor ARPS has only to be efficient to determine the position of the movable object MO with respect to one measurement period, i, e, between two Indices, since the encoder system will only determine relative movement when the encoder head measures a movement passing one of the indices. il is remarked that m Figures 2 and 3 only the encoder bead EH and the encoder scale BS and the absolute reference position sensor ARPS and the absolute reference position mark ARPM for measurement of the position in one measurement direction, in particular the y direction, are shown. The position measurement system; may include further encoder heads and encoder scales to determine a position of the movable object MO in other measurement directions. For each measurement direction also an absolute reference position sensor and an absolute reference position mark ARPM may be provided to determine a start position of the movable object in the respective measurement direction.
    Preferably, the position measurement system comprises suficient encoder heads, encoder scales, absolute reference, position sensors and absolute reference position marks to determine the. position of the movable object MO in six degrees of freedom. However, in other alternative the position measurement system may be configured to determine the position in less than six degrees of freedom. ft is also possible to provide measurement systems or a different type for one or more of the other measurement directions and / or for different degrees of freedom.
    In practice, the known encoder system may staffer from cross talk, in the shown embodiment of Figure 2, this means that a movement in the z-direction, may lead to a disturbance in the relative movement measured by the encoder system in the measurement direction , ie y-direction. You will be clear that this is generally undesirable.
    More generally stated, an encoder system suffers from cross talk when an encoder signal from the encoder system representative of a position of the moveable object in a measurement direction is affected by a movement of the movable object in a direction other than the measurement direction. The movement in the direction other than the measurement direction may include a translation, a rotation or any combination thereof.
    For example, this cross talk may have the consequence that the position measurement of the mirror device shown in Figure 1 is insufficiently accurate, which in practice results in the need of verification of the position of the mirror device after a movement of the mirror device MD. Such a verification may for example be carried out by a TIS or ILIAS sensor. The need of this verification measurement using the position control system or one or more of the mirror devices MD, can be actively used during the projection process or a patterned beaut Beautifull substrate W. For example, repositioning the mirror device MD during projection or a pattern on a target portion € or between two subsequent projections or pattern of wo target porticos C, cannot be carried out due to the cross talk in the encoder system.
    One of the possible causes of cross talk will now be explained, while reference is made to Figures 4 and 5, In figure 4, the encoder head EH is shown in a first position with respect to the encoder scale ES. It can be seen that the laser beam that is emitted by the encoder head EH towards the encoder scale ES to measure a relative movement of the encoder head EH with respect to the encoder scale ES, has a small angle with respect to the direction perpendicular to the encoder scale ES, This small angle of the laser beam has the advantage that reflections and other optical effects have no or less influence on the quality of the measurement. As a result of this small angle, she reflected laser beam at the location received by the encoder head EH a small offset with respect to the emitted laser beam.
    In Figure 5, the encoder head EH has been moved with respect to the encoder scale ES to a second position in the zirection. This z-direction is perpendicular to the measurement direction. The position of the encoder scale of Figure 4 and the associated reflected laser beam are indicated in Figure 5 by dashed lines.
    It can be seen that due to the small angle of the emitted laser beam the offset O 'between the reflected laser beam has at the location received by the encoder head EH with respect to the emitted laser beam has been changed. It is remarked that in practice this small angle may be considerably narrower than shown in Figures 4 and 3, but the cross talk effect may still occur.
    Thus, movement of She encoder head EH with respect to the encoder scale ES in a direction perpendicular to the measurement direction may result in the encoder system judged that the encoder head EH has moved in the measurement direction with respect to the encoder scale ES, As discussed above, this effect is referred to as cross talk, it is noted that other causes for cross talk may also be present in the encoder system.
    The present invention provides a position control system and a method to determine the crossbill between the movement in a second direction, for example z-direction. and the resulting measurement in the measurement direction, for example the y-direction. When this cross talk is determined, the cross talk may be tasks into account. The determined cross talk may for instance be tasks into an account in a compensation device to compensate for the cross talk determined by the position control system. As ait alternative, or in addition, the determined cross talk can be used as measurement data without using this directly in a position control system, for instance for use in aTIS measurement. The method may be part of a calibration and / or compensation method to calibrate and / or compensate cross talk in an encoder system.
    In the method and system, the reference position measurement system is used to determine the cross talk. This is based on the insight that the reference position measurement system does not suffer from cross talk, or suffers from a different cross talk than the encoder position measurement system. For example, the absolute reference position sensor ARPS uses a laser beam that is perpendicular to the measurement direction, ie, the y-direction. The cross talk of the encoder system as described with reference to Figures 4 and 5 will not occur in this embodiment of the reference position measurement system.
    Furthermore, it may be advantageous that the measurement, accuracy of the reference position measurement system is substantially the same as the measurement accuracy of the encoder system, including an absolute position measurement of the encoder system within a measurement period.
    The method to determine cross talk is based on the following steps.
    In a first step, a first position, shown in Figure 2, or the movable object MO is determined with each of the encoder system and the reference position measurement system. This means that the movable object MO is arranged in tire start position of the measurement direction, ie the y-direction, to determine this statt position by using the encoder head EH and the encoder scale ES and by using the absolute reference position sensor ARPS to measure the position of the absolute reference position mark ARPM.
    In a second step, the movable object MO is moved in at least one direction perpendicular to the measurement direction to a second position. Figure 3 shows the position control system after the movable object MO has been moved, in the ^ .- direction, from the first position, shown in Figure 2, to a second position. In respect of the measurement direction, the movable object MÖ is still in the same position. 1st a third step, the second position, shown in Figure 3, or the movable object MO is determined with each of the encoder system and the reference position measurement system. This means that the movable object MO is still arranged in the start position, with respect to the measurement direction, ie the y-direction, to measure the start position both by using the encoder head EH and the encoder scale ES, and by using the absolute reference position sensor ARPS to measure the position of the absolute reference position mark ARPM.
    When during the movement from the first position to the second position substantial cross talk was present in the encoder system, there will be a difference between the y-position determined by the encoder system and the y-position determined by the reference position measurement system. Typically, the encoder system will determine a relative movement of the encoder head EH with respect to the scale encoder ES in the y-direction, while the reference, position measurement system wants to still measure the same y-position.
    As a fourth step, cross talk of the encoder system between the z-directior, and the y-direction can be determined by comparison of the position measurements of the first position and the second position of both the encoder system and the reference position measurement system . When this cross talk is known,
    the cross talk can be tasks into account in the position control system, also in positions of the movable object, where the absolute reference position sensor ARPS is no longer aligned with the absolute reference position marlk ARPM
    The above steps for determining cross talk between movement in the z-di motion and measuring in the y-direction may also be perforated in all other measurement directions, translations and rotations, in combination with all non-measurement directions of the respective encoder heads EH and encoder scales ES of the encoder system in order to determine cross talk in the encoder system in all measurement directions in combination with all non-measurement directions associated with that measurement direction, Titos, the movement from the first position to the second position its the second direction, i, e, he non-measurement direction, may be a translation and / or a rotation.
    It's remarked that for one set of encoder head EH and encoder scale ES, a certain direction may be a measurement direction while for another set of encoder head EH and encoder scale ES, the same direction may be a non-measurement direction.
    Further, it is remarked that the determination of the cross talk may require iteratively repeat the above steps to improve the correct determination of cross talk in all measurement directions. In particular, the accuracy of the determination of the cross talk can be improved by averaging multiple measurement samples that are determined at the same location (s) or by making small scans with data fit in order to average out dynamics and other measurement errors, such as noise and non-linearities.
    Also, the movement from the first position to the second position does not have to be strictly in the non-measurement direction, in this case the ^ -direction. The movement may also be partly in the measurement direction and / or in other directions, in particular when the cross talk is determined in iterative steps for one or more measurement directions.
    The determined cross talk data associated with each encoder head EH and / or, more generally, with the encoder system may be stored in an electronic data sheet of the encoder heads EH and / or the encoder system. This etsables the user of that encoder system to quickly obiaiat insight into the cross talk associated with the encoder system.
    Figure 6 shows an embodiment of a control scheme of a position control system of the invention in which a cross talk compensation device CTCD is incorporated, in the control scheme, a comparator is provided to compare the actual position P of the movable object MO with a desired position Fd. The difference is fed into the CONT controller. On the basis of the difference between the current post ten P and the desired position Pd. the controller CONT provides a cot troll signal cs to the movable object MO, in particular to the actuator ACT 'to actuate the movable object MO to move to the desired position Pd.
    The position of the movable object MO is measured by the encoder system EMS. Since the output of the encoder system EMS may suffer from cross talk, the output is fed into the cross talk compensation device CTCD in which use is jmade of the cross talk determined by the steps as described above. In the cross talk compensation device CTCD, the measurements of the encoder system for measurement direction are. compensated for the cross talk resuiting from movements in other directions, Therefore, the current position P of the movable object MO is fed into the cross talk compensation device CTCD so that, for example, the measurement in the y-direction can be adapted by tasks into account the movement in the z-dsrecUon and the cross talk resulting from this movement in the z-direction.
    When the outputs of the encoder system are compensated for cross talk in the cross talk compensation device CTCD, the compensated outputs of the encoder system are fed into a position measurement block PMB. In the position measurement block, the compensated outputs or the encoder system are used to calculate the position of the movable object MO in six degrees of freedom.
    Figure 7 shows an alternative control scheme of a position control system of the invention in which a cross talk compensation device CTCD is incorporated, in this control scheme, the cross talk compensation device CTCD is arranged before the desired position is fed into the comparator.
    Before the desired position Pd, provided by a desired position generator, is compared to the current position P, the desired position is compensated for the cross talk or the encoder system. The resulting compensated desired position Pdc is fed into the comparator, where it is compared to the current position P,
    Similarly, to the embodiment of Figure 6, the difference between the compensated desired position Fdcand the actual position P is fed into the controller CONT. The CONT controller provides a control signal to the movable object MO, in particular to the actuator ACT to the movable object MO to move to the desired position Pd. The position of the movable object MO is measured by the encoder system EMS aud the outputs of the encoder system are fed into a position measurement block PMB to calculate the position P of the movable object MO in si x degree * of freedom.
    The placement of the cross talk compensation device CTCD before the comparator has the advantage that it can be calculated upfront and the calculation of the compensation Is no longer a part of the calculations to be done in one sample.
    Hereinabove, a position measurement system has been described in which the encoder head EH and the absolute reference position sensor ARPS are arranged on the movable object MO and the encoder scale ES and the absolute reference position mark ARPM are arranged on the reference object RO. In an alternative embodiment the encoder head EH and / or the absolute reference position sensor ARPS may be arranged on the reference object RO and the encoder scale ES and the absolute reference position mark ARPM may be arranged on the movable object MO,
    Although specific reference may be made in this lest to the use of lithographic apparatus in the manufacture of ICs, it should be understood that the lithographic apparatus described 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 suets alternative applications, any use of the terms '' wafer "or "That" may be considered as synonymous with the more general terms "substrate" or "target portion", respectively. The substrate referred to may be processed before or after exposure, in a track example (a tool that typically applies) a layer of resist to a substrate and develops the exposed resist), a metrology too! and / or an inspection tool Where applicable, the disclosure 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 the term substrate used may also refer to a substrate that already contains multiple processed layers.
    Although specific reference may have been made above to the use 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 the pattern created on a substrate. The topography of the patterning device may be pressed into a layer or 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.
    While specific expired or the invention have been described above, it wri! be appreciated that the invention may be practiced otherwise than as described.
    The descriptions above are intended to be illustrative, not limiting. Thus, it will be apparent to one skilled in the tut that modifications may be made to the Invention as described without departing from the scope or the clauses set out below. Other aspects of the invention are set out as in the following numbered clauses: 1. A position measurement system configured to determine a position of the movable object with respect to a reference object, including an encoder system including at least one encoder head and an encoder scale; and a reference position measurement system including an absolute reference position sensor and an absolute reference position mark, where, when the movable object is at a first position, the encoder system is arranged to provide a first encoder signal representative of the first position along a measurement direction, and the reference position measurement system Is arranged to provide a first reference signal representative of the first position along the measurement direction, when, the movable object is at a second position, the encoder system is arranged to provide a second encoder signal representative or the second position along the measurement direction, and the reference position measurement system is arranged to provide a second reference signal representative of the second position along the measurement direction, the position measurement system is arranged to determine a difference between the ftrst encoder signal and the second encoder signal caused b y a difference between the first position and the second position along a second direction other than the measurement direction, based on the first encoder signal, the second encoder signal, the first reference signal and the second reference signal. 2. The position measurement system as clause I in clause I, the encoder head is arranged on the movable object and the encoder scale is arranged on the reference object, or the encoder scale is arranged on the movable object and the encoder head is arranged on the reference object. 3. The position measurement system as clause clause 1 or 2. the absolute reference position sensor is arranged including the movable object and the absolute reference position mark is arranged on the reference object, or the absolute reference position mark is arranged on the movable object and absolute reference position sensor is arranged on the reference object. 4. The position measurement system as negotiated in one of the preceding clauses, including a cross talk compensation device configured to compensate for the difference. 5. The position measurement system as claused in clause 4, configured to determine the position of the movable object with respect to a reference object in six degrees of freedom, and the cross talk compensation device is configured to compensate for the difference in six degrees of freedom. 6. The position measurement system as clause-clause. where the position measurement system is configured to determine the difference of the encoder system for each measurement direction. 7, Tin position measurement system as clauseed in clause 5, configured to determine the difference of the encoder system in each measurement direction by iteratively repeating, for each measurement direction, the steps of: determining the first position of the movable object with each of the encoder system and the reference position measurement system in a measurement direetion; moving the movable object in one or more non-measurement directions to the second position; determining the second position of the movable object with each of the encoder system and the reference, position measurement system in the measurement direction, and determining the. difference between the one or more non-measurement directions and the measurement direction by comparison of the position measurements of the first position and the second position of both the encoder system and the reference position measurement system. 8, The position measurement system as eluseed in one of the preceding clauses, the movable object comprises a mirror device or a projection system or a lithographic apparatus, 9, The. position measurement system as eluseed in one of the clauses 1-7, the movable object comprises a substrate table or support or a patterning device or a lithographic apparatus. SO. A lithographic apparatus including: a support structure constructed to support a patterning device, the patterning device being capable of imparting a 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 on a target portion of the substrate, the position measurement system or one of the preceding clauses, a position control system including a controller and an actuator, the controller is arranged to provide a control signal on basis or at least one of the first encoder signal and the second encoder signal, the actuator is arranged to actuate the movable object feas * id on the control signal. 3 i. Tire lithographic apparatus of clause 10, the movable object comprises one of the support structure, the substrate support and an optical component of the projection system. 12. A method of determining cross talk or as encoder system, the encoder system being configured to determine a relative movement of a movable object with respect to a reference object in a measurement direction, the method comprises using a reference position measurement system including an absolute reference position sensor and an absolute reference position mark, the method including the steps of: determining a first position of the movable object with each of the encoder measurement system and the reference position measurement system, moving the movable object in a second direction other than the measurement direction; determining the second position of the movable object with each of the encoder system and the reference position measurement system, and determining cross talk between the second direction and the measurement direction by comparison of the position measurements of the first position and the second position of both the encoder system and the reference position measurement system, 13. The method of disuse i 2, further including: using the determined cross talk to compensate the encoder system. 14, The method of clause 12 or 13, the method comprises iteratively repeating the steps of: determining the first position of the movable object with each of the encoder system and the reference position measurement system; moving the movable object in at least the second direction to the second position; determining the second position of the movable object with each of the encoder system and the reference position measurement system; and determining cross talk between tits second direction and the measurement direction by comparison of the position measurements of the first position and the second position of both the encoder -.ystem and the reference position measurement system. 15, The method of any of the clauses 12-14, the method comprising, for each measurement direction, the steps of: determining the first position of the movable object with each of the encoder system and reference position measurement system in the measurement direction ; moving the movable object in one or more non-measurement directions to a second position; determining tbc- second position of the movable object with each of she encoder system and the reference position measurement system in the measurement direction, and determining cross talk between the one or more non-measurement directions and the measurement direction by comparison of the position measurements of the first position and the second position of both the encoder system and the reference position measurement system, 16. The method of any of the clauses 12-15, the method comprises the steps of determining cross talk or the encoder system for each measurement direction and with respect to all non-measurement directions associated with that measurement direction.
    权利要求:
    Claims (1)
    [1]
    A lithography device comprising: an illumination 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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    EP16153624|2016-02-01|
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