NL2006843A - Control system, lithographic apparatus, and method to control a position of a movable object. - Google Patents

Description

CONTROL SYSTEM, LITHOGRAPHIC APPARATUS, AND METHOD TO CONTROL

A POSITION OF A MOVABLE OBJECT

FIELD

[0001] The present invention relates to a lithographic apparatus, and a method to control a position of a movable object.

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] A conventional lithographic apparatus includes a position control system configured to control the position of the substrate support. This position control system includes a position measurement system which is configured to measure a position of a number of sensors or sensor targets mounted on the substrate support. On the basis of the measured positioned of the sensor or sensor targets the position of another location of the substrate support, for instance a target portion on a substrate for a patterned beam of radiation, may be determined.

[0004] Important factors for the performance of a lithographic apparatus are the throughput, i.e. the number of wafers that is produced within a certain period, and the overlay, i.e. the accuracy with which one layer of the chip is positioned with respect to another layer. In industry, there is a continuous demand to improve the throughput and overlay of the lithographic apparatus.

[0005] In a conventional lithographic apparatus, the substrate stage accuracy, which is measured in 6 degrees of freedom and is important for overlay, is controlled. Generally the two requirements of a higher throughput and a better overlay performance contradict each other, as higher accelerations used for higher throughput cause larger internal dynamic vibrations (or deformations) of the stages, which may result in a deterioration of the substrate stage positioning accuracy.

[0006] In view thereof, there is need for a position control system which is capable of controlling a stage with high speed and position accuracy.

SUMMARY

[0007] It is desirable to provide a position control system for a movable object of a lithographic apparatus which increases the accuracy and/or speed of position control of the movable object. Also, it is desirable to provide a method to control a position of a movable object of a lithographic apparatus which increases the accuracy and/or speed of position control of the movable object.

[0008] According to an embodiment of the invention, there is provided a lithographic apparatus including: an illumination system configured to condition a radiation beam; a patterning device support configured to support a patterning device being capable of imparting the radiation beam with a pattern in its cross-section to form a patterned radiation beam; a substrate support constmcted to hold a substrate; and a projection system configured to project the patterned radiation beam onto a target portion of the substrate, wherein the lithographic apparatus includes a position control system to control a position of a movable object of the lithographic apparatus, including: a position measurement system configured to determine an actual position of the movable object; a set-point generator to provide a desired position of the movable object; a comparator configured to provide an error signal on the basis of a comparison of the actual position and the desired position, a controller to provide a control signal on the basis of the error signal, and one or more actuators to act on the movable object on the basis of the control signal, wherein the controller includes: a derivative controller part including a differentiator to differentiate the error signal to obtain a differential error signal, and a sector-bounded non-linear gain device, wherein an output signal of the derivative controller part is based on the differential error signal multiplied with a gain of the gain device, and the output signal is at least part of the control signal.

[0009] According to an embodiment of the invention, there is provided a lithographic apparatus including: an illumination system configured to condition a radiation beam; a patterning device support configured to support a patterning device being capable of imparting the radiation beam with a pattern in its cross-section to form a patterned radiation beam; a substrate support constmcted to hold a substrate; and a projection system configured to project the patterned radiation beam onto a target portion of the substrate, wherein the lithographic apparatus includes a position control system to control the position of a movable object of the lithographic apparatus, including: a position measurement system configured to determine an actual position of the movable object; a set-point generator to provide a desired position of the movable object; a comparator configured to provide an error signal on the basis of a comparison of the actual position and the desired position, a controller to provide a control signal on the basis of the error signal, and one or more actuators to act on the movable object on the basis of the control signal, wherein the controller includes a differentiator to differentiate the error signal to obtain a differential error signal, wherein the control system includes a differential frequency, a bandwidth frequency and a low-pass filter frequency, wherein a ratio between the low-pass filter frequency and the bandwidth frequency and/or a ratio between the bandwidth frequency and the differential frequency is adaptable to the differential error signal.

[0010] According to an embodiment of the invention, there is provided a method of controlling a position of a movable object, including: determining with a position measurement system a position of the movable object, comparing with a comparator a measured position and a set-point signal provided by a set-point generator to obtain an error signal, providing a control signal by a controller on the basis of the error signal, and actuating one or more actuators on the basis of the control signal, wherein the controller includes a derivative controller part including a differentiator to differentiate the error signal to obtain a differential error signal, and a sector-bounded non-linear gain device, and wherein the providing includes differentiating the error signal to obtain a differential error signal, and calculating an output signal of the derivative controller part on the basis of the differential error signal multiplied with a gain of the non-linear gain device, and using the output signal as a part of the control signal.

[0011] According to an embodiment of the invention, there is provided a method of controlling a position of a movable object, including: determining with a position measurement system a position of the movable object, comparing with a comparator a measured position and a set-point signal provided by a set-point generator to obtain an error signal, providing a control signal by a controller on the basis of the error signal, and actuating one or more actuators on the basis of the control signal, wherein the control system includes a differential frequency, a bandwidth frequency and a low-pass filter frequency, wherein a ratio between the differential frequency and the bandwidth frequency and/or a ratio between the bandwidth frequency and the low-pass filter frequency is adaptable to the differential error signal, wherein the providing includes differentiating the error signal to obtain a differential error signal, and adapting the ratio between the differential frequency and the bandwidth frequency and/or the ratio between the bandwidth frequency and the low-pass filter frequency in dependence of the differential error signal.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which:

[0013] Figure 1 depicts a lithographic apparatus according to an embodiment of the invention;

[0014] Figure 2 depicts a typical time response of a stage of a lithographic apparatus;

[0015] Figure 3 shows a controller structure of a position control system according to an embodiment of the invention;

[0016] Figure 4 and 5 show Bode plots indicating the effect of changing a ratio a between the differential frequency and the bandwidth frequency and between the bandwidth frequency and the low-pass filter frequency; and

[0017] Figure 6 depicts a possible embodiment of adapting ratio according to the invention.

DETAILED DESCRIPTION

[0018] 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.

[0019] 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.

[0020] 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.”

[0021] 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.

[0022] 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.

[0023] 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”.

[0024] 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).

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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 Ml, M2 and substrate alignment marks PI, 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.

[0030] 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 patterning device support (e.g. 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.

[0031] Combinations and/or variations on the above described modes of use or entirely different modes of use may also be employed.

[0032] In the lithographic apparatus according to the invention a control device (broadly termed “controller”) CD is provided to control the position of the substrate support WT in six degrees of freedom. A set-point generator SG is provided to provide a set-point signal SP to the control device or controller CD. On the basis of the difference between the set-point SP and the measured position MP of the substrate support WT, an actuation signal AS is provided by the controller CD. The actuation signal AS is fed to one or more actuators PWA of the second positioner PW to actuate the substrate support WT and the substrate W supported thereon to the desired position.

[0033] The controller CD may include a PID control device (broadly termed “PID controller”) including a proportional, a derivative and an integral controller part.

[0034] Similar controllers may be used to control the position of other movable objects of the lithographic apparatus. Stages and other movable objects of a lithographic apparatus will generally behave as second order systems. A typical time response of the error signal e and the velocity error e’ in the control system of such second order system is shown in Figure 2. The error signal e and velocity error signal e’ are sinusoidal signals with decreasing amplitude. These errors signals are shifted 90 degrees in phase with respect to each other.

[0035] In a conventional prior art position control system a non-linear gain device including a dead zone around a zero error signal is provided in the control scheme before the PID

controller. An output of this non linear gain device is added to the error signal before the signal enters the PID controller. In Figure 2, the boundaries of the dead zone are indicated by DZB. For an error signal e having a value outside the boundaries of the dead zone the non linear gain device provides an increasing gain with an increasing value of the error signal.

[0036] When the error signal is between the boundaries of the dead zone, i.e. between the dashed lines in Figure 2, the gain of the control action will be at nominal level. However, when the error signal is outside the dead zone, i.e. above or below the boundaries shown in Figure 2, the gain of the control action of the PID controller will be above the nominal value as a result of the non-linear gain device. By this increased gain the movable object will be more quickly driven towards the zero error position.

[0037] An embodiment of the present invention provides an alternative controller embodiment which further improves the control behavior of a position control system (broadly termed “position controller”) according to an embodiment of the invention. Figure 3 shows this controller in schematic form.

[0038] The controller includes a proportional controller part 1, a derivative controller part 2, and an integral controller part 3.

[0039] The proportional controller part 1 includes a proportional controller part gain device 4 providing a nominal gain Kp for the proportional control action, and a sector-bounded non-linear gain device 5 including a dead zone having the error signal e as an input, and a first filter unit 6 including a filter to filter the output of the non-linear gain device 5. The filtered output signal of the first filter unit 6 is added to the error signal e as an input of the proportional controller part gain device 4. The output of the proportional controller part gain device 4 is also output of the proportional controller part 1. This output signal is basis for the control signal and is fed to the addition device 7.

[0040] A benefit of the provision of the non-linear gain device 5 in the side loop of the proportional controller part 1 results in an extra gain when the error signal is relative large, i.e. when the error signal lies outside the boundaries of the dead zone of the non-linear gain device 5. This extra gain is large when the error, i.e. the difference between set-point position and the actual measured position is relative large. The increased gain results in improved control behavior.

[0041] The first filter unit 6 may include a filter, for instance a notch filter, to limit the extra gain provided by the non-linear gain device 4 to certain frequencies. In this way extra gain may be avoided at those frequency intervals that would otherwise associate with small closed-loop stability margins.

[0042] Furthermore, the non-linear gain device 4 with as an input a sinusoidal signal may provide higher harmonic signals in the output of the non-linear gain device 4. The filter unit 6 may include a filter, for instance a low-pass filter, to take these harmonic noise signals out of the output signal of the non-linear gain device 4.

[0043] The derivative controller part 2 includes a differentiator 8 to provide a derivative error signal e’ by differentiating the error signal, and a derivative controller part gain device 9 providing a nominal gain Kd for the derivative control action based on the derivative error signal e’. In a side loop of the derivative controller part 2, a sector-bounded non-linear gain device 10 including a dead zone having the derivative error signal e’ as an input, and a second filter unit 11 including a filter to filter the output of the non-linear gain device 10 are provided. The filtered output signal of the second filter unit 11 is added to the derivative error signal e’ as an input of the derivative controller part gain device 9. The output of the derivative controller part gain device 4 is also an output signal of the derivative controller part 2 and is basis for the control signal. This output of the derivative controller part 2 is fed to the addition device 7.

[0044] The provision of the non-linear gain device 9 in the side loop of the derivative controller part 2 results in an extra gain when the derivative error signal is relative large, i.e. when the derivative error signal lies outside the boundaries of the dead zone of the non-linear gain device 10. Typically, the derivative error signal, i.e. the velocity error will be large when the error signal itself will be small, as shown in Figure 2. Thus, the provision of a non-linear gain device 10 within the derivative controller part 2 may further improve the controller behavior by extra damping action when the derivative error signal is relative large, i.e. lies outside the boundaries of the dead zone of the non-linear gain device 9.

[0045] The second filter unit 11 may, similar to the first filter unit 6, include a filter to limit the extra gain provided by the non-linear gain device 10 to certain frequencies or to take harmonic noise signals out of the output signal of the non-linear gain device 10.

[0046] The integral controller part 3 includes an integrator 12 to provide an integral error signal by integrating the error signal, and an integral controller part gain device 13 providing a nominal gain Ki for the integral control action based on the integral error signal.

[0047] Similar to the proportional controller part 1 and the derivative controller part 2, the integral controller part 3 includes in a side loop a sector-bounded non-linear gain device 14 including a dead zone having the integral error signal as an input, and a second filter unit 15 to filter an output of the non-linear gain device 13.

[0048] In the addition device 7 the output signals of the proportional controller part 1, the derivative controller part 2, and the integral controller part 3 are added to provide a combined output signal which is filtered in the PID filter unit 16, for instance a low-pass filter. The filtered output signal of the PID filter unit 16 is the control signal to be fed to the actuators of the control system, for instance actuators PWA of the second positioner PW of the lithographic apparatus of Figure 1.

[0049] It is remarked that due to the provision of a non-linear gain device 4, 9, 14 in the respective controller parts the control action resulting from these controller parts 1, 2, 3 can be adequately adapted to the respective input signals of the controller parts, i.e. the error signal, the differential error signal and the integral error signal. As a result extra gain can be created in the proportional controller part 1 when the error signal is relative large, and extra gain can be created in the derivative controller part 2 when the derivative error signal is relative large.

[0050] In the above embodiments the magnitude of a gain provided by the non-linear gain devices 4, 9, 14, is based on the magnitude of the input signal. For instance, the magnitude of a gain provided by the non-linear gain device 9 is based on the magnitude of the differential error signal. In alternative embodiments the magnitude of the gain of the non-linear gain devices 4, 9, 14, may also be based on other signals. For instance, magnitude of a gain provided by the non-linear gain device 9 may be based on the magnitude of the differential error signal and the error signal.

[0051] In the above embodiment, instead of the non-linear gain device 4, 9, 14 including a dead zone, any non-linear gain device which increases the gain of the respective controller part, when the respective error signal is large, may also be used. In an embodiment, preferably, the non-linear gain device is a sector-bounded non-linear gain device.

[0052] According to another embodiment of the invention a ratio between the low-pass filter frequency and the bandwidth frequency of the controller and/or a ratio between the bandwidth frequency and the differential frequency of the controller is adaptable to influence the controller behavior. Normally, in a position control system the low-pass filter frequency is chosen a factor “a” larger than the bandwidth frequency, while the bandwidth frequency is chosen the same factor “a” larger than the differential frequency. The present embodiment is based on the insight that this ratio a can be adapted in dependence of the error signal and/or the differential error signal to obtain the desired controller behavior.

[0053] For instance, a small value of ratio “a” results in a small phase margin but a high low-frequency error rejection, and hence can be beneficially used when the position error is large, i.e. the proportional error signal is large. A large value of “a” increases the phase margin giving more damping, but reduces the low-frequency disturbance rejection. This can be used if the velocity error, i.e. the differential error signal is relatively large.

[0054] As an example, Figure 4 shows open-loop Bode plots for values of a between 2 and 5, and Figure 5 the corresponding sensitivity plots of a typical position control system for a movable object such as a stage.

[0055] On the basis of this insight, the ratio a may be selected dependent on the values of the error signal and the differential error signal. For instance, when the error signal and the differential error signal are relative small value a is chosen at a nominal level, for instance 3. When the error signal is relatively large and the differential error signal is relatively small (i.e. the velocity error is small but position error is large), a value of a is chosen at a level below nominal level, for instance 2, and when the error signal is relatively small and the differential error signal is relatively large a value a is chosen at a level above nominal level, for instance 4 or 5. Again, the controller provides more damping when the velocity error is relatively large compared to the position error, while low-frequency error rejection is made large for the reverse case.

[0056] Figure 6 shows an example of such selection criterion. On the axes the error signal and differential error signal are used as input for the selection. Within circle I the nominal value is selected. Within sections II the value of a is chosen below the nominal level and within the sections III the value of a is chosen above the nominal level, at the lines between sections II and III, the value of a can be selected at nominal level. On the basis of this selection criterion, the controller behavior can be properly adapted to the actual values of both the error signal and the differential error signal.

[0057] Hereinabove embodiments of controllers have been described. It is remarked that these controllers can be separate controller units, but also may be integrated as software on a processing unit, for instance a dedicated control processing unit or as a part of the central processing unit of the lithographic apparatus.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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 lithographic apparatus comprising: an illumination system configured to condition a radiation beam; a patterning device support configured to support a patterning device being capable of imparting the radiation beam with a pattern in its cross-section to form a patterned radiation beam; a substrate support constructed to hold a substrate; a projection system configured to project the patterned radiation beam onto a target portion of the substrate; and a position control system to control a position of a movable object of the lithographic apparatus, the position control system comprising a position measurement system configured to determine an actual position of the movable object; a set-point generator to provide a desired position of the movable object; a comparator configured to provide an error signal on the basis of a comparison of the actual position and the desired position, a controller to provide a control signal on the basis of the error signal, and an actuator to act on the movable object on the basis of the control signal, wherein the controller comprises a derivative controller part comprising a differentiator configured to differentiate the error signal to obtain a differential error signal, and a non-linear gain device, wherein an output signal of the derivative controller part is based on the differential error signal multiplied with a gain of the gain device, and the output signal is at least part of the control signal.

2. The control system of clause 1, wherein the non-linear gain device comprises a dead zone around a zero value of the differential error signal.

3. The control system of clause 1, wherein the non-linear gain device provides a small gain for small differential error signal and a large gain for a large differential error signal.

4. The control system of clause 1, wherein a sum of an output signal of the non-linear gain device and the differential error signal is fed into a derivative controller gain device to multiply the sum with a derivative control gain to obtain the output signal of the derivative controller part.

5. The control system of clause 1, wherein the derivative controller part comprises a filter unit configured to filter the output signal of the non-linear gain device.

6. The control system of clause 1, wherein the gain provided by the non-linear gain device is dependent on the differential error signal.

7. The control system of clause 1, wherein the gain provided by the non-linear gain device is dependent on the error signal.

8. The control system of clause 1, wherein the controller comprises a proportional controller part comprising a second sector-bounded non-linear gain device, wherein an output signal of the proportional controller part is based on the error signal multiplied with a gain of the second gain device, and the output signal of the proportional controller part is part of the control signal.

9. The control system of clause 1, wherein the controller comprises an integral controller part comprising an integrator configured to integrate the error signal to obtain an integral error signal, and a third sector-bounded non-linear gain device, wherein an output signal of the integral controller part is based on the integral error signal multiplied with a gain of the third gain device, and the output signal of the proportional controller part is part of the control signal.

10. The control system of clause 1, wherein the movable object is the substrate support and/or the patterning device support.

11. A lithographic apparatus comprising: an illumination system configured to condition a radiation beam; a patterning device support configured to support a patterning device being capable of imparting the radiation beam with a pattern in its cross-section to form a patterned radiation beam; a substrate support constructed to hold a substrate; a projection system configured to project the patterned radiation beam onto a target portion of the substrate; and a position control system configured to control the position of a movable object of the lithographic apparatus, the position control system comprising a position measurement system configured to determine an actual position of the movable object; a set-point generator configured to provide a desired position of the movable object; a comparator configured to provide an error signal on the basis of a comparison of the actual position and the desired position; a controller to provide a control signal on the basis of the error signal, and an actuator configured to act on the movable object on the basis of the control signal, wherein the controller comprises a differential frequency, a bandwidth frequency and a low-pass filter frequency, wherein a ratio between the low-pass filter frequency and the bandwidth frequency and/or a ratio between the bandwidth frequency and the differential frequency is adaptable to the error signal or to a signal based on the error signal.

12. The lithographic apparatus of clause 11, wherein the controller comprises a differentiator to differentiate the error signal to obtain a differential error signal, and wherein the controller is configured to set the ratio between the low-pass filter frequency and the bandwidth frequency and the ratio between the bandwidth frequency and the differential frequency on the basis of the error signal and the differential error signal, at a nominal level when the error signal and the differential error signal are relative small, at a level below nominal level when the error signal is large and the differential error signal is small, and at a level above nominal level when the error signal is small and the differential error signal is large.

13. The lithographic apparatus of clause 11, wherein the movable object is the substrate support or the patterning device support.

14. A method of controlling a position of a movable object, comprising: determining with a position measurement system a position of the movable object; comparing with a comparator a measured position and a set-point signal provided by a set-point generator to obtain an error signal; providing a control signal by a controller on the basis of the error signal; and actuating an actuator on the basis of the control signal, wherein the controller comprises a derivative controller part comprising a differentiator to differentiate the error signal to obtain a differential error signal, and a non-linear gain device, and wherein the providing comprises differentiating the error signal to obtain a differential error signal, and calculating an output signal of the derivative controller part on the basis of the differential error signal multiplied with a gain of the non-linear gain device, and using the output signal as a part of the control signal.

15. A method of controlling a position of a movable object, comprising: determining with a position measurement system a position of the movable object; comparing with a comparator a measured position and a set-point signal provided by a set-point generator to obtain an error signal; providing a control signal by a controller on the basis of the error signal; and actuating an actuator on the basis of the control signal; wherein the controller comprises a differential frequency, a bandwidth frequency and a low-pass filter frequency, wherein a ratio between the differential frequency and the bandwidth frequency and/or a ratio between the bandwidth frequency and the low-pass filter frequency is adaptable to the differential error signal, and wherein the providing comprises differentiating the error signal to obtain a differential error signal, and adapting the ratio between the differential frequency and the bandwidth frequency and/or the ratio between the bandwidth frequency and the low-pass filter frequency in dependence of the differential error signal.

Claims (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 cross-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.