Method for reducing the effect of cyclic errors in a lithographic process, projection system and lithographic apparatus including a projection system - Patents.com

Abstract

The present invention provides a method for reducing the effect of cyclic errors in a lithography process having a projection phase and an idling phase, the method comprising controlling a first position of a first module in a first control loop, the first module being a position controlled mirror of a projection system, the first control loop having a first bandwidth and including a first position measurement system having a first cyclic error, and controlling the first position comprises continuously moving the first module at least during the projection phase such that a first dominant frequency of the first cyclic error exceeds a first bandwidth of the first control loop.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to European Application No. 21217454.4, filed December 23, 2021, the entire contents of which are incorporated by reference into this specification.

[0002] The present invention relates to a method for reducing the effects of cyclic errors in a lithographic process, and further to a projection system and a lithographic apparatus including such a projection system. [Background technology]

[0003]

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

[0004]

[0004] To project a pattern onto a substrate, a lithographic apparatus may use electromagnetic radiation. The wavelength of this radiation determines the minimum size of features that can be formed on the substrate. Lithographic apparatus using extreme ultraviolet (EUV) radiation having a wavelength in the range of 4-20 nm, for example 6.7 nm or 13.5 nm, can be used to form smaller features on a substrate than lithographic apparatus using radiation with a wavelength of, for example, 193 nm.

[0005]

[0005] In known embodiments of a lithographic apparatus, a projection system with one or more mirrors may be provided. These mirrors may be accurately positioned so that their positions can be controlled, for example to counter vibrations. Such position-controlled mirrors may be actively controlled by a feedback controller based on the actual position of the mirror measured by a position measurement system, such as an interferometer or encoder measurement system.

[0006]

[0006] The principle of interferometry is based on the interference of two beams originating from the same source, where one beam travels between the transmitter, the target (e.g. a mirror) and back to the receiver, while the other travels a fixed distance. This interference pattern is due to the approximation of a sinusoidal signal as a function of the displacement of the target. There may be periodic deviations about this sinusoidal signal, these deviations being higher order deviations that also depend on the distance of the target, the so-called periodic errors.

[0007]

[0007] Since cyclic errors have a negative effect on the accuracy of position measurements, it is desirable to compensate for the cyclic errors. To achieve this compensation, the cyclic errors can be calibrated and compensated for using software. However, this is only possible if the cyclic errors are stable over time. However, the cyclic errors may change over time, for example due to thermal drift, so that the calibration is no longer accurate and the drift effect may substantially reduce the measurement accuracy.

[0008]

[0008] This can lead to position-dependent offsets in the measurement error, for example when the mirror is not moved. This can interfere with the measurement of the position of the optical substrate table because adjustments after the optical measurement do not move the mirror to the correct position. It can also lead to dynamic disturbances when the mirror is scanned during exposure, which has a direct impact on performance.

[0009]

[0009] Other position measurement systems, such as encoder measurement systems, can also suffer from unstable periodic errors over time. Summary of the Invention

[0010]

[0010] It is an object of the present invention to provide a method for reducing the effect of cyclic errors in a lithographic process. It is also an object of the present invention to provide a projection system arranged to reduce the effect of cyclic errors, and a lithographic apparatus including such a projection system.

[0011]

[0011] According to one aspect of the present invention, there is provided a method for reducing the effect of periodic errors in a lithography process having a projection phase and an idle phase, the method comprising controlling a first position of a first module in a first control loop, the first module being a position controlled mirror of a projection system, the first control loop having a first bandwidth and including a first position measurement system having a first periodic error, and controlling the first position comprises continuously moving the first module at least during the projection phase such that a first dominant frequency of the first periodic error exceeds the first bandwidth of the first control loop.

[0012]

[0012] According to one aspect of the present invention, there is provided a projection system for projecting a beam, comprising: a first module having a first range of movement, the first module being a position control mirror of the projection system arranged to reflect the beam; a first position measurement system for measuring a first position of the first module; and a control system including a first control loop for controlling the first position of the first module, the first control loop having a first bandwidth, wherein the control system is arranged to move the first module continuously at least during a projection phase of a lithography process, such that a first dominant frequency of a first periodic error of the first position measurement system exceeds the first bandwidth of the first control loop.

[0013] According to an aspect of the invention, there is provided a lithographic apparatus including a projection system as defined in any one of claims 15 to 28. [Brief description of the drawings]

[0014]

[0014] Some embodiments of the present invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which: [Figure 1] 1 depicts a lithography system comprising a lithographic apparatus and a radiation source. [Diagram 2] 2 illustrates a portion of the lithography system of FIG. 1 in more detail. [Diagram 3] 2 illustrates a control system for a projection system according to an embodiment of the present invention; [Figure 4] 4 shows an example of moving a mirror in a projection system to reduce the effect of cyclic errors. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015]

[0015] A lithographic system including a radiation source SO and a lithographic apparatus LA is shown in Figure 1. The radiation source SO is configured to generate a beam of EUV radiation B and to provide the EUV radiation beam B to the lithographic apparatus LA. The lithographic apparatus LA includes an illumination system IL, a support structure MT configured to support a patterning device MA (e.g. a mask), a projection system PS, and a substrate table WT configured to support a substrate W.

[0016]

[0016] A substrate table positioning system WTP is provided for positioning the substrate table WT at a desired position. The substrate positioning system WTP includes a position measurement system for measuring the position of the substrate table WT and an actuation system for moving the substrate table WT to the desired position. A patterning device support positioning system MTP is provided for positioning the support structure MT at a desired position. The patterning device support positioning system MTP also includes a position measurement system for measuring the position of the support structure MT and an actuation system for moving the support structure MT to the desired position.

[0017]

[0017] The illumination system IL is configured to condition the EUV radiation beam B before it is incident on the patterning device MA. Furthermore, the illumination system IL may include a facetted field mirror device 10 and a facetted pupil mirror device 11. Together the facetted field mirror device 10 and the facetted pupil mirror device 11 provide the EUV radiation beam B with a desired cross-sectional shape and a desired intensity distribution. The illumination system IL may include other mirrors or devices in addition to or instead of the facetted field mirror device 10 and the facetted pupil mirror device 11.

[0018] After being conditioned as described above, the EUV radiation beam B interacts with the patterning device MA. This interaction results in a patterned EUV radiation beam B'. The projection system PS is configured to project the patterned EUV radiation beam B' onto the substrate W. To that end, the projection system PS may include a number of mirrors 13, 14 configured to project the patterned EUV radiation beam B' onto the substrate W held by a substrate table WT. The projection system PS may apply a demagnification factor to the patterned EUV radiation beam B', thereby forming an image having smaller features than corresponding features on the patterning device MA. For example, a demagnification factor of 4 or 8 may be applied. Although in FIG. 1 the projection system PS is depicted as having only two mirrors 13, 14, the projection system PS may include a different number of mirrors (for example 6 or 8 mirrors).

[0019]

[0019] The substrate W may include a previously formed pattern, in which case the lithographic apparatus LA aligns the image formed by the patterned EUV radiation beam B' with the previously formed pattern on the substrate W.

[0020] A relative vacuum may be provided within the source SO, the illumination system IL and / or the projection system PS, ie a small amount of gas (eg hydrogen) at a pressure well below atmospheric pressure.

[0021]

[0021] The source SO may be a laser-produced plasma (LPP) source, a discharge-produced plasma (DPP) source, a free-electron laser (FEL) or any other source capable of producing EUV radiation.

[0022]

[0022] The lithographic process includes a series of projection stages (wherein a patterned EUV radiation beam B' is projected onto the substrate W (exposure stage) and / or the substrate W is aligned with the patterned EUV radiation beam B' (alignment stage)) and idling stages (wherein the patterned EUV radiation beam B' is not projected onto the substrate W or onto irrelevant parts of the substrate W and the positioning accuracy of the substrate W relative to the patterned EUV radiation beam B' is less important). During the projection stages, the patterning device and the substrate may be moved in a scanning movement at a constant scanning velocity. The idling stages may be used to decelerate and (re)accelerate the patterning device MT and the substrate W to a desired scanning velocity and to a desired alignment relative to the EUV radiation beam B and the patterned EUV radiation beam B', respectively. The constant scanning velocity of the patterning device MT is typically different from the constant scanning velocity of the substrate W.

[0023]

[0023] The projection system PS of the lithographic apparatus of Fig. 1 is shown in more detail in Fig. 2. The projection system comprises mirrors 13, 14, hereinafter referred to as the first mirror 13 and the second mirror 14. The first mirror 13 and the second mirror 14 are position-controlled mirrors. This means that the position of the first mirror 13 is controlled within a first range of movement and the position of the second mirror 14 is controlled within a second range of movement.

[0024]

[0024] A first position measuring system 15 is provided for measuring the actual position of the first mirror 13. A second position measuring system 16 is provided for measuring the actual position of the second mirror 14. A control unit CON is provided for controlling the positions of the first mirror 13 and the second mirror 14. The control unit CON includes a first control loop for controlling the position of the first mirror 13 and a second control loop for controlling the position of the second mirror 14. Based on a first output signal of the control unit CON, a first actuator 17 is actuated to position the first mirror 13 at a desired position. Based on a second output signal of the control unit CON, a second actuator 18 is actuated to position the second mirror 14 at a desired position.

[0025]

[0025] If the projection system PS is provided with more than two position controlled mirrors, additional position measurements may be provided for the additional mirrors to measure the position of each additional mirror. The control unit CON may include an additional control loop for each additional mirror to control the position of the additional mirror. The control unit CON may provide additional output signals of the control unit CON to actuators to position the additional mirrors at desired positions.

[0026]

[0026] The positions of the first mirror 13, the second mirror 14 and any additional mirrors can be controlled in six degrees of freedom. The control unit CON is shown as a single unit for controlling the positions of the first mirror 13, the second mirror 14 and any additional mirrors. This control unit CON may for example be integrated in a central processing unit of the lithographic apparatus LA or in a separate control unit of the projection system PS. It is also possible to provide separate control processors for each control loop.

[0027]

[0027] The first and second position measuring systems 15, 16 may be interferometer measuring systems. In the measurements of these position measuring systems 15, 16, periodic deviations, so-called cyclic errors, may occur. Since the cyclic errors have a negative effect on the accuracy of the position measurements of the first mirror 13 and the second mirror 14, it is desirable to compensate for the cyclic errors. To achieve this compensation, a calibration and compensation of the cyclic errors can be performed in software. However, this is only possible if the cyclic errors are stable over time. However, the cyclic errors may change over time, for example due to thermal drift, so that the calibration is no longer accurate and the measurement accuracy may be significantly reduced due to the effects of the drift.

[0028]

[0028] Therefore, in the projection system PS, a first periodic error may occur in the first position measuring system 15 and a second periodic error may occur in the second position measuring system 16, and these first and second periodic errors may only be partially reduced by calibration.

[0029]

[0029] The projection system PS shown in Fig. 2 is configured to substantially reduce the influence of the first and second cyclic errors by continuously moving the first mirror 13 and the second mirror 14 during at least the projection phase, e.g. the exposure phase and / or the alignment phase, of the lithographic process, when the positioning of the substrate W is critical for the optical performance of the lithographic process. This continuous movement of the first mirror 13 and the second mirror 14 causes the first and second cyclic errors to become high-frequency disturbances. By selecting a suitable speed of the continuous movement of the first mirror 13 and the second mirror 14, the first main frequency of the first cyclic error can be shifted above the first bandwidth of the first control loop, and the second main frequency of the second cyclic error can be shifted above the second bandwidth of the second control loop. As a result, the first control loop can no longer follow the first cyclic error, and the second control loop can no longer follow the second cyclic error. Therefore, by continuously moving the first mirror 13 and the second mirror 14, the adverse effects of the first and second cyclic errors can be effectively reduced.

[0030]

[0030] At the same time, the irregular movements of the first mirror 13 and the second mirror 14 adversely affect the optical performance of the projection system PS. Therefore, the projection system PS is further configured to match the movements of the first mirror 13 and the second mirror 14 with each other to reduce alignment errors between the first mirror 13 and the second mirror 14 caused by moving the first mirror 13 and the second mirror 14 continuously.

[0031]

[0031] The continuous movement of the first mirror 13 and the second mirror 14 during the projection phase may have a constant non-zero velocity and may be in a constant direction.

[0032]

[0032] In one embodiment, the continuous movement of the first mirror 13 and the continuous movement of the second mirror 14 are arranged such that one of the first mirror 13 and the second mirror 14 follows the other of the first mirror 13 and the second mirror 14. In such an embodiment, there is one so-called leading mirror and one or more trailing mirrors. In the embodiment of Fig. 2, the first mirror 13, being the heaviest mirror, is selected as the leading mirror and the second mirror 14 is the trailing mirror.

[0033] The first control loop CL-1 and the second control loop CL-2 are shown diagrammatically in FIG.

[0034]

[0034] A set point generator SPG is provided. The set point generator SPG outputs a desired position R1 of the first mirror 13. This desired position R1 follows a desired movement profile of the first mirror 13 with continuous movement at a constant speed during the projection phase of the lithography process. A first measured position MP1 of the first mirror 13 is subtracted from the desired position R1 to determine a first position error E1 of the first mirror 13. The first measured position MP1 includes a periodic error CE1 caused by the first position measurement system 15. The first position error E1 is input to a first feedback controller FBC1. The first feedback controller FBC1 provides an output signal O1 that is provided as a first actuation signal input to a first actuator 17 that is part of the block P-M1 in the first control loop. The first control loop CL-1 may include a first feed forward controller FFC1 that provides a feed forward output signal based on the desired position R1 that is added to the output signal O1 of the first feedback controller FBC1.

[0035]

[0035] In response, the set point generator SPG outputs a desired position R2 of the second mirror 14. This desired position R2 follows a desired movement profile similar to the desired position R1 of the first mirror 13. A second measured position MP2 of the second mirror 14 is subtracted from the desired position R2 to determine a second position error E2 of the second mirror 14. The second measured position MP2 includes a cyclic error CE2 caused by the second position measurement system 16. The first position error E1 of the first control loop CL-1 is subtracted from the second position error E2 to determine an adapted second position error AE2 before the second position error E2 is input to the second feedback controller FBC2, which provides an output signal O2 that is provided as a second actuation signal to the second actuator 18, which is part of the block P-M2 of the second control loop CL-2.

[0036]

[0036] The second control loop CL-2 may include a second feedforward controller FFC2 that provides a feedforward output signal based on the desired position R2 that is added to the output signal O2 of the second feedback controller FBC2.

[0037]

[0037] By introducing the first position error E1, i.e. the position error of the first mirror 13, into the second control loop CL-2, the feedback controller FBC2 tries to correct the first position error E1 of the first mirror 13. The first position error E1 has a low frequency component (i.e. within the first bandwidth), because the first control loop CL-1 cannot follow the precise trajectory and the high frequency errors due to periodic errors. The second control loop CL-2 will follow the low frequency components, which are within the second bandwidth of the second feedback controller FBC2, which means that the second mirror 14 remains properly aligned with the first mirror 13. In other words, the first mirror 13 and the second mirror 14 form the same or similar deviations from the desired trajectory. Similar deviations may also occur if a coordinate transformation is applied between the movements of the first mirror 13 and the second mirror 14. The same coordinate transformation is also applied to the error E1 before being introduced into the second control loop CL-2.

[0038]

[0038] The adapted second position error AE2 of the second mirror 14 has three components. a) A small positioning error due to the need to correct a first position error E1 of the first mirror 13. This is a low frequency error and therefore a relatively small error. b) A large contribution at high frequencies due to the first cyclic error CE1 of the first position measuring system 15 of the first mirror 13. c) A similar high frequency contribution due to a second cyclic error CE2 of the second position measuring system 16 of the second mirror 14.

[0039]

[0039] Only element a) will be added to the alignment error AE, which is shown diagrammatically in Fig. 3 as the difference between the actual position P1 of the first mirror 13 and the actual position P2 of the second mirror 14. Elements b) and c) do not substantially affect the alignment error AE, since they are based on the first cyclic error CE1 and the second cyclic error CE2, which are measurement errors that the second feedback controller FBC2 cannot follow.

[0040]

[0040] It should be noted that in the embodiment of Fig. 3, the first position error E1 is subtracted from the second position error E2 to obtain an adapted second position error AE2. In another embodiment, the first position error E1 may be introduced into the second control loop CL-2 by adding the first position error E1 to the second measured position MP2. The adapted second position error AE2 would then be obtained by subtracting the combination of the second measured position MP2 and the first position error E1 from the second desired position R2. It is also possible to first subtract the first position error E1 from the second desired position R2 and then subtract the second measured position MP2 to obtain the adapted second position error AE2.

[0041]

[0041] When more than two position-controlled mirrors are provided in the projection system PS, each position-controlled mirror may be controlled as a trailing mirror, in which case the first position error of the leading mirror, in this embodiment the first position error E1 of the first mirror 13, is input to each additional control loop to determine an adapted additional position error, based on which the feedback controller of the additional control loop can provide an additional output signal to the actuator to position the additional mirror at a desired position. By inputting this first position error of the leading mirror to each additional control loop, the additional mirror will form a deviation similar to that of the first mirror 13 from the desired trajectory.

[0042]

[0042] In practice, it is advantageous for each mirror of the projection system PS to be a position-controlled mirror controlled as a following mirror following one leading mirror. The leading mirror can be any suitable mirror, such as the heaviest mirror and / or the mirror that dominates the optical performance of the projection system PS. Furthermore, it may be advantageous to also input the first position error E1 of the first control loop CL1, i.e. the position error of the leading mirror, into a control loop for positioning the patterning device support structure MT and / or the substrate table WT, to improve the alignment of the patterning device support structure MT and / or the substrate table WT relative to the first mirror 13.

[0043]

[0043] As an example, the movement profile of the desired position R1 of the first mirror 13 is shown in Fig. 4. The upper graph shows the position in time and the lower graph shows the velocity over time. It can be seen that the first mirror moves with a constant velocity of about 400 μm / s over a first movement range of about 100 μm. This constant velocity movement is performed during the projection phase of the lithography process. During the idling phases between the projection phases, the movement direction can be changed by decelerating and accelerating the first mirror 13 in opposite directions.

[0044]

[0044] The movement profile of the desired position R2 of the second mirror 14 may be the same as the desired position R1 of the first mirror 13. However, in practice, the movement profile of the trailing mirror, e.g., the second mirror 14, may include a position transformation relative to the movement of the leading mirror, e.g., the first mirror 13.

[0045]

[0045] The first cyclic error CE1 and the second cyclic error CE2 may have a periodicity of, for example, 160 nm. When the first mirror 13 and the second mirror 14 are moved at a constant speed of about 400 μm / s, the first main frequency of the first cyclic error of the first control loop CL-1 is about 2.5 kHz, which is much larger than the first bandwidth of the first control loop CL-1 and the second bandwidth of the second control loop CL-2. As a result, the first control loop CL-1 cannot follow the first cyclic error CE1, and the second control loop CL-2 cannot follow the second cyclic error CE2.

[0046]

[0046] For the projection system PS of a lithographic apparatus, it is important that the successive movements of the mirrors 13, 14 have a relatively small adverse effect on the optical performance of the projection system PS. Therefore, rather than selecting the movement profile of the desired position of the mirrors to be substantially the same movement or movement profile, it may be advantageous to select it to have a small adverse effect on the optical performance.

[0047]

[0047] The optical sensitivity of the projection system PS to the relative positions of the mirrors in the projection system can be described by an optical sensitivity matrix. If the movement profile of a mirror is selected to be in the null space of the optical sensitivity matrix, its movement may have a relatively small effect on the optical performance of the projection system PS. Therefore, the optical sensitivity matrix can be used to design the desired movement profile of the leading and trailing mirrors. The inventors have found that in a projection system PS with three or more position-controlled mirrors, it may be beneficial to keep at least one of the other mirrors stationary. Furthermore, the inventors have found that it may be beneficial to limit the total movement of each position-controlled mirror to within a predetermined range.

[0048]

[0048] Since the periodicity of the cyclic errors of the first position measuring system 15 and the second position measuring system 16 can be accurately measured and the moving speeds of the first mirror 13 and the second mirror 14 can be accurately controlled, the respective dominant frequencies of the first and second cyclic errors can be accurately predicted. In order to further reduce possible adverse effects due to the presence of cyclic errors, the first control loop CL-1 can be provided with a first filter, such as a first notch filter, having a first filter frequency corresponding to the first dominant frequency of the first cyclic error caused by moving the first mirror 13. Similarly, the second control loop CL-2 can be provided with a second filter, such as a second notch filter, having a second filter frequency corresponding to the second dominant frequency of the second cyclic error caused by moving the second mirror 14.

[0049]

[0049] Although specific reference is made in this specification to the use of lithographic apparatus in IC manufacture, it should be understood that the lithographic apparatus described herein may have other applications. Other possible applications include 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.

[0050]

[0050] Although specific reference is made herein to embodiments of the invention in the context of lithographic apparatus, embodiments of the invention may be used in other apparatus. Embodiments of the invention may form part of a mask inspection apparatus, a metrology apparatus, or any apparatus that measures or processes objects such as wafers (or other substrates) or masks (or other patterning devices). These apparatus may be commonly referred to as lithography tools. Such lithography tools may use vacuum or ambient (non-vacuum) conditions.

[0051]

[0051] Although specific reference has been made above to the use of embodiments of the present invention in the context of optical lithography, it will be apparent that the invention is not limited to optical lithography and may, where circumstances permit, be used in other applications, for example imprint lithography.

[0052]

[0052] Although specific embodiments of the present invention have been described above, it is clear that the present invention can be implemented in other ways than those described above. The above description is intended to be illustrative and not limiting. Therefore, it will be clear to those skilled in the art that modifications can be made to the present invention as described above without departing from the scope of the claims set forth below.

Claims

1. 1. A method for reducing the effect of cyclic errors in a lithography process having a projection phase and an idle phase, the method comprising: controlling a first position of a first module in a first control loop, the first module being a position controlled mirror of a projection system, the first control loop including a first position measurement system having a first bandwidth and having a first cyclic error; controlling the first position includes continuously moving the first module during at least the projection phase such that a first dominant frequency of the first cyclic error exceeds the first bandwidth of the first control loop.

2. The method includes controlling a second position of a second module in a second control loop; 2. The method of claim 1, wherein controlling the first position and the second position includes matching a movement of the first module and a movement of the second module with respect to one another to reduce alignment errors between the first module and the second module caused by continuously moving the first module.

3. the second control loop includes a second position measurement system having a second bandwidth and having a second cyclic error; Controlling the first position and the second position includes: continuously moving the second module during at least the projection stage such that a second dominant frequency of the second cyclic error exceeds the second bandwidth of the second control loop; 3. The method of claim 2, further comprising: matching the movement of the first module and the movement of the second module with respect to one another to reduce alignment errors between the first module and the second module caused by sequentially moving the first module and the second module.

4. 4. The method of claim 2 or 3, wherein adapting the movement of the first module and the movement of the second module to each other comprises adapting the movement of the second module to the movement of the first module such that the second module follows the first module.

5. inputting a first position error in the first control loop between a first actual position of the first module and a first reference position of the first module into the second control loop; determining an adapted second position error based on a second actual position of the second module, a second reference position of the second module, and the first position error; using the adapted second position error as an input to a feedback controller of the second control loop; The method according to any one of claims 2 to 4, comprising:

6. The method according to any of claims 2 to 5, wherein the second module is a second position control mirror, a patterning device support, or a substrate support.

7. The method according to any of claims 2 to 6, wherein the movements of the first module and the movements of the second module are adapted to be in a null space of an optical sensitivity matrix of the projection system.

8. The method comprises: controlling a position of an additional module in an additional control loop, the additional control loop having a bandwidth and including a position measurement system having a cyclic error; Controlling the position of the additional module comprises: continuously moving the additional module at least during the projection phase such that a dominant frequency of the cyclic error exceeds the bandwidth of the additional control loop; The method of any one of claims 2 to 7, wherein the movement of the additional module is adapted to the movement of the first module to reduce alignment errors between the first module and the additional module caused by continuously moving the first module.

9. The method of claim 8 , wherein the additional module is a position controlled mirror, a patterning device support, or a substrate support.

10. The method according to any of the preceding claims, wherein moving the first module at least during the projection stage comprises moving the first module at a constant, non-zero velocity and in a constant direction.

11. The method according to claim 10, wherein the idling phase is used to adapt the direction and / or speed of movement of the first module.

12. The method according to any of the preceding claims, wherein the first position measuring system and / or the second position measuring system are interferometers.

13. 13. The method according to any one of claims 1 to 12, wherein the first control loop includes a first notch filter having a first filter frequency corresponding to the first dominant frequency of the first cyclic error resulting from moving the first module.

14. The method according to any one of claims 3 to 13, wherein the second control loop includes a second notch filter having a second filter frequency corresponding to the second dominant frequency of the second cyclic error resulting from moving the second module.

15. 1. A projection system for projecting a beam, comprising: a first module having a first range of movement, the first module being a position controlled mirror of the projection system arranged to reflect the beam; a first position measurement system for measuring a first position of the first module; a control system including a first control loop for controlling the first position of the first module, the first control loop having a first bandwidth; 1. A projection system, comprising: a control system arranged to continuously move the first module during at least a projection phase of a lithographic process, such that a first dominant frequency of a first periodic error of the first position measurement system exceeds the first bandwidth of the first control loop.

16. the projection system comprising: a second module having a second range of motion; a second position measurement system for measuring a second position of the second module; the control system includes a second control loop for controlling the second position of the second module; 16. The projection system of claim 15, wherein the control system is arranged to match the movement of the first module and the movement of the second module with respect to one another to reduce alignment errors between the first module and the second module caused by continuously moving the first module.

17. the second control loop has a second bandwidth; the control system is arranged to continuously move the second module at least during a projection phase of the projection system such that a second dominant frequency of a second cyclic error of the second position measurement system exceeds the second bandwidth of the second control loop; 17. The projection system of claim 16, wherein the control system is arranged to coordinate the movement of the first module and the movement of the second module with respect to one another to reduce alignment errors between the first module and the second module caused by moving the first module and the second module sequentially.

18. 18. Projection system according to claim 16 or 17, wherein the control system is arranged to adapt a movement of the second module to a movement of the first module such that the second module follows the first module.

19. The control system includes: inputting a first position error in the first control loop between a first actual position of the first module and a first reference position of the first module into the second control loop; determining an adapted second position error based on a second actual position of the second module, a second reference position of the second module, and the first position error; using the adapted second position error as an input to a feedback controller of the second control loop; A projection system according to any of claims 16 to 18, arranged to:

20. The projection system of any of claims 16 to 19, wherein the second module is a second positionally controlled mirror, a patterning device support, or a substrate support.

21. The projection system of any of claims 16 to 20, wherein the movements of the first module and the movements of the second module are adapted to be in a null space of an optical sensitivity matrix of the projection system.

22. the projection system comprising: an additional module having a range of motion; an additional position measurement system for measuring the position of said additional module; 22. The projection system of any one of claims 16 to 21, wherein the control system comprises an additional control loop for controlling the position of the additional module, the additional control loop comprising a band, and the control system is further arranged to: continuously move the additional module at least during the projection phase of the projection system such that a dominant frequency of a periodic error of the additional position measurement system exceeds the bandwidth of the additional control loop; and to adapt the movement of the additional module to the movement of the first module to reduce alignment errors between the first module and the additional module caused by continuously moving the first module and the additional module.

23. 23. The projection system of claim 22, wherein the additional module is a position controlled mirror, a patterning device support, or a substrate support.

24. A projection system according to any of claims 15 to 23, wherein the control system is arranged to move the first module at a constant, non-zero velocity and in a constant direction at least during the projection phase.

25. 25. Projection system according to claim 24, wherein the control system is arranged to adapt a direction and / or a speed of movement of the first module during the idling phase.

26. The projection system according to any of claims 15 to 25, wherein the first position measuring system and / or the second position measuring system are interferometers.

27. 27. The projection system of any one of claims 15 to 26, wherein the first control loop includes a first notch filter having a first filter frequency corresponding to the first dominant frequency of the first cyclic error resulting from moving the first module.

28. 28. The projection system of any one of claims 17 to 27, wherein the second control loop includes a second notch filter having a second filter frequency corresponding to the second dominant frequency of the second cyclic error resulting from moving the second module.

29. A lithographic apparatus comprising a projection system according to any one of claims 15 to 28.

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