Lithographic apparatus and method

Abstract

The lithographic apparatus includes a reflector for reflecting radiation, the reflector including a body, a reflective surface disposed on the body, and a channel formed in the body for conveying a fluid, and a controller configured to adjust a pressure of the fluid in the channel to control deformation of the reflective surface and thereby control overlay of the lithographic apparatus.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to European Patent Application No. 22202403.6, filed October 19, 2022, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to a lithographic apparatus and method for controlling overlay. [Background technology]

[0003] A lithographic apparatus is a machine constructed to apply a desired pattern onto a substrate. Lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). A lithographic apparatus can, for example, project a pattern 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. To form smaller features on a substrate than lithographic apparatuses that use radiation having a wavelength of, for example, 193 nm, lithographic apparatuses that use extreme ultraviolet (EUV) radiation having a wavelength in the range of 4 nm to 20 nm, for example, 6.7 nm or 13.5 nm, may be used.

[0005]

[0005] Typically, a lithography process involves performing multiple exposures across multiple successive substrate layers to form a desired structure. In the art, the accuracy with which a newly generated pattern is aligned with a previously generated pattern is referred to as overlay. Throughout the device manufacturing process, overlay errors can arise from many different factors. A first known method for controlling overlay involves changing the position of one or more reflectors in a lithography apparatus. However, the first known method for controlling overlay can only reduce lower-order overlay errors (e.g., overlay errors corresponding to lower-order field dependencies, such as offset or tilt). That is, the first known method cannot reduce higher-order overlay errors (e.g., overlay errors corresponding to higher-order field dependencies, such as higher-order polynomial deformation profiles). A second known method for controlling overlay involves heating one or more reflectors in a lithography apparatus to cause controlled thermal deformation of the one or more reflectors. However, reflectors, especially EUV reflectors, can be relatively large, and bulky objects that take a relatively long time to thermally deform in response to temperature changes. Therefore, the second known method of controlling overlay cannot perform fast and efficient overlay correction due to the relatively long thermal curing time of the reflector.

[0006]

[0006] Known lithographic apparatus and methods may have limited ability to correct for overlay. It would be desirable to provide a lithographic apparatus and method that avoids or mitigates one or more of the problems of the prior art, whether or not identified herein. Summary of the Invention

[0007] According to a first aspect of the present disclosure, there is provided a lithographic apparatus comprising a reflector for reflecting radiation, the reflector comprising a body, a reflective surface disposed on the body, and a channel formed in the body for conveying a fluid, the lithographic apparatus comprising a controller configured to adjust a pressure of the fluid in the channel to control a deformation of the reflective surface, thereby controlling an overlay of the lithographic apparatus.

[0008] The lithographic apparatus of the present disclosure can reduce higher order optical errors (e.g., overlay errors corresponding to higher order field dependencies, such as higher order polynomial deformation profiles). The lithographic apparatus of the present disclosure has the advantage of being able to perform high speed, high spatial frequency deformations on the reflective surface, thereby producing high speed, high spatial frequency overlay corrections. The high spatial frequency deformations on the reflective surface may refer to at least a fourth order polynomial deformation profile applied to the reflective surface by adjusting the pressure of a fluid. The high spatial frequency overlay corrections may refer to at least a third order polynomial overlay shape or error.

[0009]

[0009] The reflective surface and the body may be integrally formed.

[0010]

[0010] The reflective surface and the body may be formed separately. The body may be configured to support the reflective surface. The body may form part of a clamp configured to secure the reflective surface.

[0011]

[0011] The channel may form part of a cooling system configured to cool the reflective surface. The controller may be integrated into an existing cooling system. This has the advantage of increasing the practicality of the cooling system: the cooling system may cool the reflective surface (thereby reducing undesired thermal deformations) while controlling pressure-based deformations of the reflective surface (thereby imparting desired characteristics to radiation upon reflection from the reflective surface).

[0012]

[0012] Adjusting the pressure of the fluid may include adjusting the flow rate of the fluid.

[0013]

[0013] The depth of the channel relative to the reflecting surface may vary along the length of the channel.

[0014]

[0014] Varying the depth of the channel has the advantage of varying the stiffness profile of the body between the channel and the reflective surface, thereby allowing a greater variety of reflective surface deformations to be applied.

[0015] The reflector body may include a plurality of channels, wherein the depth of a first channel relative to the reflective surface may vary along the length of the first channel in a manner different from the manner in which the depth of a second channel relative to the reflective surface varies along the length of the second channel, i.e., different channels may have different depth profiles relative to the reflective surface.

[0016] The channel may be one of a plurality of channels formed in the body for transporting a fluid. At least two of the plurality of channels may have different cross-sectional shapes. The cross-sectional shapes of at least two of the plurality of channels may have different orientations relative to the reflective surface.

[0017]

[0017] Using channels with different cross-sectional shapes and / or orientations has the advantage of providing a varying force profile on the reflective surface that is applied to the reflective surface by the pressure of the fluid flowing through the first and second channels, thereby allowing a greater variety of reflective surface deformations to be applied. Using channels with different cross-sectional shapes and / or orientations has the advantage of allowing the flow rate and restriction of the fluid in the first and second channels to be maintained at a desired level, while allowing the force profile applied to the reflective surface to be varied by the pressure of the fluid flowing through the first and second channels.

[0018]

[0018] The depth of the channel relative to the reflective surface along the length of the channel and the cross-sectional shape of the channel can be designed so that the controller is operable to adjust the pressure of the fluid within the channel to apply a deformation profile of at least a fourth-order polynomial to the reflective surface.

[0019]

[0019] Applying a fourth-order polynomial deformation profile to the reflective surface has the advantage that the controller can reduce higher-order optical errors (e.g., overlay errors corresponding to higher-order field dependencies such as higher-order polynomial deformation profiles (e.g., third-order polynomial overlay errors)).

[0020]

[0020] The controller may be configured to separately adjust the pressure of the fluid in at least two of the plurality of channels to control the deformation of the reflective surface.

[0021]

[0021] Separately adjusting the fluid pressure in at least two of the multiple channels has the advantage of allowing different deformation profiles to be applied to the reflective surface, thereby enabling better control of the overlay of the lithographic apparatus.

[0022]

[0022] The controller may comprise multiple sub-controllers, where different sub-controllers may be configured to regulate the pressure of the fluid in different channels or different groups of channels.

[0023]

[0023] The lithographic apparatus may include an inlet conduit configured to provide a fluid to the channel. The lithographic apparatus may include an outlet conduit configured to receive a fluid from the channel. The lithographic apparatus may include a flow restrictor disposed on the outlet conduit.

[0024]

[0024] The controller may be configured to adjust the flow rate of the fluid, and the pressure of the fluid in the channel may be adjusted by the action of the flow restrictor.

[0025]

[0025] The lithographic apparatus may comprise a pressure sensor configured to detect a pressure of the fluid in the channel, and the controller may be configured to control the pressure of the fluid in the channel using data provided by the pressure sensor.

[0026]

[0026] The flow restrictor may comprise a pressure valve. The controller may be configured to control the pressure valve to regulate the pressure of the fluid in the channel.

[0027]

[0027] The pressure valve has the advantage that it allows the controller to provide rapid changes in pressure and therefore rapid changes in deformation of the reflective surface.

[0028]

[0028] The pressure valve may comprise a piezoelectric element configured to grip the outlet conduit.

[0029]

[0029] The lithographic apparatus may comprise an optical sensor configured to detect at least a portion of the radiation reflected by the reflective surface, and the controller may be configured to receive optical measurement data from the optical sensor and to use the optical measurement data to control the deformation of the reflective surface.

[0030]

[0030] Optical sensors have the advantage of allowing feedback control of the radiation so that the radiation is given desired characteristics when reflected from the reflective surface despite changes in operating conditions. Optical sensors have the advantage of allowing calibrations to be performed in which the effect that pressure adjustments by the controller have on the characteristics of the radiation reflected from the reflective surface (e.g. the wavefront of the radiation) is determined and / or modeled. The optical sensors may comprise one or more interferometric wavefront sensors.

[0031] The lithographic apparatus may comprise an actuator configured to adjust the position and / or orientation of the reflector.

[0032]

[0032] Actuators have the advantage of providing additional control in imparting desired characteristics to radiation upon reflection from a reflective surface.

[0033] The actuators may be configured to provide movement of the reflector in six rigid body degrees of freedom (eg, three linear degrees of freedom and three rotational degrees of freedom).

[0034]

[0034] The reflecting surface may be partially spherical.

[0035]

[0035] The lithographic apparatus may also include a heater configured to heat the reflector and cause controlled thermal deformation of the reflective surface, thereby providing further control in imparting desired characteristics to the radiation upon reflection from the reflective surface.

[0036]

[0036] The lithographic apparatus may comprise an illumination system configured to condition the radiation beam. The lithographic apparatus may comprise a support structure constructed to support a patterning device, the patterning device being capable of imparting the radiation beam with a pattern in its cross-section to form a patterned radiation beam. The lithographic apparatus may comprise a substrate table constructed to hold a substrate. The lithographic apparatus may comprise a projection system configured to project the patterned radiation beam onto the substrate. The reflector may be a mirror in the projection system.

[0037]

[0037] The lithographic apparatus may comprise an illumination system configured to condition the radiation beam. The lithographic apparatus may comprise a support structure constructed to support a patterning device, the patterning device being capable of imparting the radiation beam with a pattern in its cross-section to form a patterned radiation beam. The lithographic apparatus may comprise a substrate table constructed to hold a substrate. The lithographic apparatus may comprise a projection system configured to project the patterned radiation beam onto the substrate. The reflective surface may form part of the patterning device. The body may form part of the support structure.

[0038] According to a second aspect of the present disclosure, there is provided a method comprising providing a flow of a fluid through a channel formed in a body of a lithographic apparatus in which a reflective surface is disposed, the method comprising adjusting a pressure of the fluid to control a deformation of the reflective surface and thereby controlling overlay of the lithographic apparatus, the method comprising reflecting radiation from the reflective surface. A method comprising:

[0039]

[0039] The depth of the channel may vary along the length of the channel and relative to the reflective surface.

[0040] The channel may be one of a plurality of channels formed in the body for conveying a fluid. The method may include providing a flow of the fluid through at least two channels having different cross-sectional shapes. The method may include providing a flow of the fluid through at least two channels having cross-sectional shapes with different orientations relative to the reflective surface.

[0041] The method may include adjusting the pressure of the fluid in the channel to apply a deformation profile of at least a fourth order polynomial to the reflective surface.

[0042] The method may include separately adjusting the pressure of the fluid in at least two of the plurality of channels to control the deformation of the reflective surface.

[0043] The method may include adjusting the position and / or orientation of the reflective surface.

[0044]

[0044] According to a third aspect of the present disclosure, there is provided a method for manufacturing a body of a reflector of a lithographic apparatus according to the first aspect, the method comprising performing laser ablation to form a channel.

[0045] Laser ablation has the advantage of providing precise control over the depth profile and cross-sectional shape of the channels, thereby allowing a greater variety of depth profiles and cross-sectional shapes to be formed.

[0046]

[0046] Performing laser ablation to form the channel may include varying the depth of the channel relative to the reflective surface along the length of the channel.

[0047]

[0047] The method of manufacturing the reflector body may include performing laser ablation to form at least two channels having different cross-sectional shapes.

[0048]

[0048] A method of manufacturing the body of the reflector may include performing laser ablation to form at least two channels having cross-sectional shapes with different orientations relative to the reflective surface. [Brief explanation of the drawings]

[0049]

[0049] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which:

[0050] [Figure 1] 1 illustrates schematically a lithography system comprising a lithographic apparatus, a radiation source, a reflector, and a controller according to the present disclosure; [Figure 2] 1 shows a schematic cross-sectional view of a reflector according to the present disclosure; [Figure 3] 1A and 1B show schematic cross-sectional views of a multi-channel reflector according to the present disclosure; [Figure 4] 10 shows a graph comparing the ability of the reflector and controller of the present disclosure to control third-order field plane variations in overlay with known methods. [Figure 5] 1 shows a flowchart of a method according to the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0051] 1 shows a lithography system comprising a radiation source SO, a lithographic apparatus LA, reflectors MA, MT, 13, 14, and a controller 100 according to the present disclosure. The radiation source SO is configured to generate a beam of EUV radiation B and to provide this beam of EUV radiation B to the lithographic apparatus LA. The lithographic apparatus LA comprises 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.

[0052] The illumination system IL is configured to condition the EUV radiation beam B before it is incident on the patterning device MA. To this end, the illumination system IL may comprise 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 impart a desired cross-sectional shape and a desired intensity distribution to the EUV radiation beam B. The illumination system IL may comprise other mirrors or devices in addition to or instead of the facetted field mirror device 10 and the facetted pupil mirror device 11.

[0053] After being conditioned in this way, 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 this end, the projection system PS may comprise a plurality of mirrors 13, 14 configured to project the patterned radiation beam B' onto the substrate W held on a substrate table WT. The projection system PS can apply a demagnification factor to the patterned EUV radiation beam B' to form 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 Figure 1 the projection system PS is illustrated as having only two mirrors 13, 14, the projection system PS may include a different number of mirrors (for example 6 or 8 mirrors).

[0054]

[0053] The substrate W may include a pre-formed pattern, in which case the lithographic apparatus LA aligns the image formed by the patterned radiation beam B' with a previously formed pattern on the substrate W.

[0055] A relative vacuum, ie a small amount of gas (eg hydrogen) at a pressure well below atmospheric pressure, may be provided in the source SO, in the illumination system IL and / or in the projection system PS.

[0056]

[0055] 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.

[0057] The lithographic apparatus LA includes reflectors MA-MT, 13, 14 for reflecting radiation B, B'. The reflectors may be a patterning device MA and a support structure MT. The reflector may also be one of the mirrors 13, 14 in the projection system PS. According to the present disclosure, the lithographic apparatus LA may include multiple reflectors. In the example of FIG. 1, the lithographic apparatus LA includes three reflectors MA-MT, 13, 14 according to the present disclosure. Each reflector includes a body, a reflective surface disposed on the body, and a channel for transporting a fluid formed in the body. Components of the reflectors 13, 14 according to the present disclosure are shown in more detail in FIGS. 2 and 3. In the example of the patterning device MA and the support structure MT, the reflective surface forms part of the patterning device MA, and the body forms part of the support structure MT. For example, the body may form part of an electrostatic clamp of the support structure MT configured to clamp the patterning device MA. In the example of the patterning device MA and support structure MT, the reflective surface and body may be considered to be separately formed components, or the reflective surface and body may be integrally formed, for example as in one or more of the mirrors 13, 14 in the projection system PS.

[0058] The lithographic apparatus LA further comprises a controller 100 configured to adjust the pressure of the fluid in the channels of the reflectors MA-MT, 13, 14 to control deformation of the reflective surfaces and thereby control overlay of the lithographic apparatus LA. The deformation of the reflective surfaces may be due to a pressure difference between the pressure of the fluid in the channels and the pressure in the vacuum environment in which the reflective surfaces are located. For example, the pressure of the fluid in the channels may be about 300 mbar, while the pressure in the environment in which the reflective surfaces are located may be about 5 Pa. In the example of FIG. 1 , the channels (not shown) form part of a cooling system 110 configured to cool the reflective surfaces of the reflectors MA-MT, 13, 14. The controller 100 may be integrated into an existing cooling system of the lithographic apparatus LA.

[0059]

[0058] Figure 2 shows a schematic cross-sectional view of a reflector 14 according to the present disclosure. Cartesian coordinates X, Y, and Z are provided in Figures 2 and 3 to facilitate understanding of the reflectors 13, 14. In the example of Figure 2, the reflector 14 corresponds to the second illustrated mirror 14 of the projection system PS of the lithographic apparatus LA in Figure 1. The reflector 14 comprises a body 200, a reflective surface 210 disposed on the body 200, and channels 220 for transporting a fluid formed within the body 200. The reflective surface 210 may be configured to reflect EUV radiation. The reflector 14 may comprise a material having a relatively low coefficient of thermal expansion, such as titania silicate glass (e.g., ULE™ from Corning), Zerodur™, or cordierite.

[0060] The reflective surface 210 may have a reflectivity of approximately 70% or less. Therefore, the reflective surface 210 absorbs a significant amount of energy from the radiation beam B′ during operation of the lithographic apparatus LA. The reflective surface 210 experiences a non-uniform temperature increase across the area of ​​the reflective surface 210, especially when the illumination mode (e.g., dipole illumination) of the illumination system IL is set such that the radiation beam B′ is non-uniformly distributed across various regions of the reflective surface 210. Such a non-uniform temperature increase in the reflector 14 may cause significant deformation of the reflective surface 210. Although the deformation of the reflective surface 210 may be very small in absolute terms, such deformation may cause imaging errors due to the extremely high precision required to manufacture devices with small feature sizes. Therefore, the lithographic apparatus LA is provided with a cooling system 110 configured to remove thermal energy from the reflectors MA-MT, 13, 14, thereby reducing undesired thermal deformation of the reflectors MA-MT, 13, 14.

[0061] The cooling system 110 includes channels 220 passing through the body 200 of the reflectors MA-MT, 13, 14. In the example of FIG. 2, the channels 220 are connected to inlet conduits 230 configured to provide a fluid to the channels 220 and outlet conduits 240 configured to receive a fluid from the channels 220. The inlet conduits 230 can form part of an input manifold configured to provide a fluid to the multiple channels 220 in the body 200, and the outlet conduits 240 can form part of an output manifold configured to receive a fluid from the multiple channels 220 in the body 220. The channels 220 can be positioned to increase heat transfer between the body 200 and the fluid flowing within the channels 220. The channels 220 can be formed directly within the material of the body 200 using laser ablation. The cooling system 110 can include a temperature regulation system to ensure that the fluid supplied to the channels 220 is at a desired temperature. The fluid can be, for example, water. Using water can be advantageous because water has a relatively high heat capacity, thereby providing a relatively large heat transfer capacity at a relatively low mass flow rate. As another example, the fluid can be carbon dioxide. Using carbon dioxide can be advantageous because it can be supplied as a liquid (under pressure) so that it evaporates in the higher temperature regions of the channel 220. The latent heat of evaporation therefore increases the heat transfer capacity of the fluid. For a given heat load, the required mass flow rate is much lower than for water, which can reduce vibration of the reflective surface 210 due to the fluid flow.

[0062] The depth of the channel 220 relative to the reflective surface 210 varies along the length of the channel 220. That is, at a first location along the length of the channel 220, the channel 220 has a first depth 221 relative to the reflective surface 210, and at a second location along the length of the channel 220, the channel 220 has a second depth 222 relative to the reflective surface 210. The first depth 221 and the second depth 222 are different. In the example of FIG. 2, the depth of the channel 220 relative to the reflective surface 210 varies along the length of the channel 220 such that the channel 220 forms an umbrella-like shape. That is, the depth of the channel 220 relative to the reflective surface 210 increases with distance from the center of the length of the channel 220. The depth of the channel 220 may vary in other manners to form other shapes. In the example of FIG. 2, only a single channel 220 is shown. However, the reflector 14 may include multiple channels 220, with different channels having different depth profiles. In general, the depth profile of the channels 220 may be selected to create a desired stiffness profile within the portion of the body 220 located between the channels 220 and the reflective surface 210. The depths 221, 222 of the channels 220 relative to the reflective surface 210 may be approximately 0.5 mm or greater. The depths 221, 222 of the channels 220 relative to the reflective surface 210 may be approximately 30 mm or less.

[0063] FIG. 3 schematically illustrates a cross-sectional view of a reflector 13 including a plurality of channels 320-324 according to the present disclosure. In the example of FIG. 3, the reflector 13 corresponds to the first illustrated mirror 13 of the projection system PS of the lithographic apparatus LA in FIG. 1. The viewing direction of the cross-sectional view of FIG. 3 corresponds to a direction rotated 90° from the viewing direction of the cross-sectional view of FIG. 2, in that FIG. 2 illustrates a side view of the channel 220, while FIG. 3 illustrates a front view of the channels 320-324. The number of channels 320-324 may depend, at least in part, on the size of the reflector 13 and / or the spacing between adjacent channels 320-324. For example, 10-100 channels 320-324 may be provided within the body 300. For example, 20-60 channels 320-324 may be provided within the body 300. For example, approximately 40 channels may be provided within the body 300.

[0064] At least two of the channels 320-324 may have different cross-sectional shapes. In the example of FIG. 3, three of the channels 320, 322, and 324 have elliptical cross-sectional shapes, and two of the channels 321 and 323 have circular cross-sectional shapes. The channels 320-324 may have other cross-sectional shapes. For example, the channels 320-324 may have square, rectangular, triangular, or other cross-sectional shapes. If the cross-sectional shape of the channels 320-324 is not circular, the diameter of the channel may be selected to be the maximum dimension of the cross-sectional shape. If the diameter of the channels 320-324 is relatively small, the flow resistance will be relatively large, requiring a larger pressure difference to achieve a sufficient mass flow rate of the fluid. If the diameter of the channels 320-324 is too large, it may be difficult to achieve uniform cooling of the reflective surface 310. The diameter of the channels 220, 320-324 may be approximately 0.1 mm or greater. The diameter of the channels 220, 320-324 may be about 10 mm or less.

[0065] The cross-sectional shapes of at least two of the channels 320-324 may have different orientations relative to the reflective surface 310. In the example of Figure 3, two of the elliptical channels 320, 324 are oriented with their major axes 325, 326 substantially perpendicular to the reflective surface 310, while elliptical channel 322 is oriented with its major axis 327 substantially parallel to the reflective surface 310. That is, elliptical channel 320, 324 is oriented at 90° relative to the other elliptical channel 322. The cross-sectional shapes of channels 320, 322, 324 may have other orientations relative to the reflective surface and / or each other.

[0066] In general, the cross-sectional shapes and / or orientations of the channels 320-324 may be selected to create a desired force profile that can be exerted by adjusting the pressure of the fluid within the channels 320-324 and / or to create a desired fluid flow restriction through the channels 320-324. For example, the aspect ratios of the cross-sectional shapes of the channels 320-324 may be selected to create a desired force profile that can be exerted by adjusting the pressure of the fluid within the channels 320-324 and / or to create a desired fluid flow restriction through the channels 320-324. In the example of FIG. 3 , the first diameters 327 of the cross-sectional shapes of the channels 320-324 along a first direction X are selected to at least partially determine the desired force profile that can be exerted by adjusting the pressure of the fluid within the channels 320-324. The first direction X is substantially parallel to the reflective surface 210. Increasing the first diameter 327 can increase the force applied to the reflective surface 210 by the pressure of the fluid within the channels 320-324. The cross-sectional shapes of the channels 320-324 have second diameters 325, 326 along a second direction Z substantially perpendicular to the first direction X, selected to at least partially determine the desired fluid flow restriction by the channels 320-324. The second direction Z is substantially perpendicular to the reflective surface 210. Referring to FIGS. 1-3 , in general, the depth profiles 221, 222 and / or cross-sectional shapes and / or orientations of the cross-sectional shapes of the channels 320-324 can be selected to at least partially determine the deformation profile of the reflective surface 310 (and thus the overlay of the lithographic apparatus LA) while maintaining a desired cooling capacity of the cooling system 110. The depths 221, 222 of the channels 220 relative to the reflective surface 210 can be approximately 2 mm or greater. The depth 221, 222 of the channel 220 relative to the reflective surface 210 may be about 10 mm or less.

[0067] 1 and 2, the lithographic apparatus LA includes a flow restrictor 250 disposed on the outlet conduit 240. In the case of a simple flow restrictor, the controller 100 adjusts the flow rate of the fluid, and the action of the flow restrictor 250 can adjust the pressure of the fluid in the channel. The lithographic apparatus LA may also include a pressure sensor (not shown) configured to detect the pressure of the fluid in the channels 220, 320-324. The controller 100 can be configured to control the pressure in the channels 220, 320-324 using data provided by the pressure sensor. In the example of FIG. 2, the flow restrictor is a pressure valve 250. The controller 100 is configured to control the pressure valve 250 to adjust the pressure of the fluid in the channel 220. The pressure valve 250 can include a piezoelectric element configured to apply an adjustable grip or "knob" to the outlet conduit 240. The pressure valve 250 has the advantage of providing rapid changes in pressure through the controller 100, thereby providing rapid changes in deformation of the reflective surface 210 and correspondingly rapid control of the overlay of the lithographic apparatus LA. The controller 100 and pressure valve 250 may be able to change the overlay of the lithographic apparatus LA in less than one second (e.g., about 100 ms, 200 ms, or 500 ms). For example, the controller 100 and pressure valve 250 may be able to change the overlay of the lithographic apparatus LA between multiple substrates W, such that overlay corrections can be applied to already printed layers of multiple substrates W.

[0068] The lithographic apparatus LA comprises an optical sensor 120 configured to detect at least a portion of the radiation B′ reflected by the reflective surfaces MA-MT, 13, 14. The optical sensor 120 may comprise one or more interferometric wavefront sensors. The controller 100 is configured to receive optical measurement data from the optical sensor 120 and use the optical measurement data to control the deformation of the reflective surfaces MA-MT, 13, 14. The optical sensor 120 has the advantage of providing feedback control of the overlay of the lithographic apparatus LA. That is, the optical measurement data may be used by the controller 100 to control the deformation of the reflective surfaces MA-MT, 13, 14 such that the radiation B′ is imparted with desired characteristics (e.g., a desired wavefront) upon reflection from the reflective surfaces MA-MT, 13, 14, despite changes in operating conditions. The optical sensor 120 has the advantage of enabling calibration to be performed in which the effect that pressure adjustment by the controller 100 has on the characteristics of the radiation B' reflected by the reflecting surfaces MA-MT, 13, 14 (e.g., the wavefront of the radiation) is determined and / or modeled.

[0069] 1 and 3, the lithographic apparatus LA includes an actuator 130 configured to adjust the position and / or orientation of the reflector 13. The actuator 130 may be configured to move the reflector 13 such that the relative positioning between the reflective surface 310 and the radiation B′ is changed. That is, after the reflector 13 is moved by the actuator 130, different portions of the radiation B′ may be reflected by different portions of the reflective surface 310. The controller 100 may be configured to control the actuator 130, thereby providing further control of the overlay of the lithographic apparatus LA. As shown in FIGS. 1 and 3, the reflective surface 310 of the first illustrated reflector 13 in the projection system PS is at least partially spherical. The partially spherical shape of the reflective surface 310, combined with the pressure-induced deformation of that shape, provides an additional degree of freedom in controlling the overlay of the lithographic apparatus LA compared to simply moving the reflectors 13, 14 relative to the radiation B′.

[0070]

[0069] The reflector 13 has the advantage that, in imparting desired characteristics (eg, a desired wavefront adjustment) to the radiation B' upon reflection from the reflective surface 310, it allows for further control of the overlay of the lithographic apparatus LA.

[0071] The controller 100 is configured to adjust the pressure of the fluid in the channels 320-324 to control the deformation of the reflective surface 310, and thereby control the overlay of the lithographic apparatus LA. The shape of the wavefront of the radiation B' reflected from the reflective surface 310 can be adjusted via the deformation of the reflective surface 310. The wavefront can be adjusted such that overlay errors are reduced. The alignment of an image with respect to an intended position on the substrate W can be referred to as overlay. An imprecision in the alignment of an image with respect to an intended position on the substrate can be referred to as an overlay error. The wavefront of the radiation B' can be adjusted by the reflective surface 310 such that overlay errors are reduced.

[0072] The knowledge of overlay of lithographic apparatus LA may be determined by direct measurement (e.g., using a detector system such as optical sensor 120 of FIG. 1), indirect measurement (e.g., by performing lithographic exposures in resist and analyzing the resist), and / or prediction (e.g., by inputting data into a computer model and running the computer model). For example, data regarding overlay may be measured and input into the computer model. The computer model may be configured to receive the data and perform calculations using this data to predict the overlay performance of lithographic apparatus LA.

[0073] The overlay of the lithographic apparatus LA can be understood as a combination of different polynomials. The projection system PS of the lithographic apparatus LA includes intrinsic optical aberrations due to imperfections in its optical components. Information about the optical aberrations can be expressed as a wavefront shape at the pupil plane of the lithographic apparatus LA. This wavefront shape can be expressed as a combination of polynomials, such as Zernike polynomials for an optical system with a circular pupil. Different polynomials can represent different types of optical aberrations. For example, a first Zernike polynomial can represent tilt aberrations, while a second Zernike polynomial can represent defocus aberrations. Zernike polynomials are often classified as either odd (i.e., asymmetric) or even (i.e., symmetric). Different categories of Zernike polynomials can correspond to different characteristics of the projection system PS. For example, even Zernike polynomials can correspond to focus errors, and odd Zernike polynomials can correspond to overlay errors. In general, Zernike polynomials can be classified in any desired manner. The following discussion of Zernike polynomials uses the dual-index American National Standards Institute (ANSI) Zernike numbering method.

[0074]

[0073] Radiation B' arriving at different positions on the field plane of the lithographic apparatus LA (e.g. the surface of the substrate W) travels through different parts of the projection system PS and is subjected to different aberrations. This means that the wavefront shape at the pupil plane varies from position to position in the field plane. The variation of overlay across the field plane and / or wavefront can be represented by a combination of polynomials of different orders. For example, the field plane variation of lower order Zernikes (e.g. Z[1,1], a Zernike representing the horizontal slope of the wavefront shape) can be represented by a combination of different polynomials. Considering the field plane variation of higher order polynomials can provide more information about the overlay and / or optical aberrations present in the lithographic apparatus LA and / or what corrections can be caused in the lithographic apparatus LA by adjustments made to optical elements present in the lithographic apparatus LA. Field plane variations of overlay and / or wavefront described by higher order polynomials may be more difficult to compensate than field plane variations described by lower order polynomials.

[0075] The reflectors MA-MT, 13, 14 and controller 100 of the present disclosure may be capable of performing fine adjustment of the wavefront incident on the reflective surface (e.g., providing nanometer-scale deformation of the reflective surface 210, 310). The fine adjustment of the wavefront enabled by the reflectors MA-MT, 13, 14 and controller 100 of the present disclosure may enable a reduction in lithography errors, particularly overlay errors corresponding to higher-order field plane variations than known lithography error reduction methods. For example, the reflectors MA-MT, 13, 14 and controller 100 of the present disclosure may be used to apply correction profiles that compensate for at least third-order field plane variations in overlay. For example, the reflectors MA-MT, 13, 14 and controller 100 of the present disclosure may be used to apply correction profiles that compensate for at least fourth-order field plane variations in overlay. The reflectors MA-MT, 13, 14 and controller 100 of the present disclosure may be used to apply correction profiles that compensate for Zernike field plane variations. The reflectors MA-MT, 13, 14 and controller 100 of the present disclosure can be used to apply correction profiles that reduce overlay errors associated with at least third-order field plane variations of the Zernike. The reflectors MA-MT, 13, 14 and controller 100 of the present disclosure can be used to apply correction profiles that reduce overlay errors associated with at least fourth-order field plane variations of the Zernike. Of course, in general, the higher the order of the field plane variations of the polynomials (e.g., Zernike polynomials) that the reflectors MA-MT, 13, 14 and controller 100 of the present disclosure can compensate for, the more complex the construction and operation of the reflectors MA-MT, 13, 14 can be. A balance between the complexity of the reflectors MA-MT, 13, 14 and the correction performance of the controller 100 can be selected as desired.

[0076] A correction profile for the patterned radiation beam B' may be determined based on knowledge of the overlay error. The correction profile is configured to reduce the overlay error when the correction profile is applied to the patterned radiation beam B' by the reflective surfaces 210, 310 of the reflectors MA-MT, 13, 14. The correction profile may include wavefront modifications necessary to reduce the overlay error. The reflectors MA-MT, 13, 14 may be manufactured such that the reflective surfaces 210, 310 achieve the desired correction profile when the controller 100 adjusts the pressure of the fluid in the channels 220, 320-324. That is, the reflectors MA-MT, 13, 14 may be designed to compensate for field plane variations of a particular polynomial shape. For example, third-order field-plane variations in overlay can be compensated for by designing the reflectors MA-MT, 13, 14 such that adjusting the pressure of the fluid in the channels 220, 320-324 induces a fourth-order polynomial deformation profile in the reflective surface 210, 310. As previously mentioned, in general, the depth profiles 221, 222 and / or cross-sectional shapes and / or cross-sectional shape orientations of the channels 220, 320-324 can be selected to at least partially determine the deformation profile of the reflective surface 210, 310 (and thus the overlay of the lithography apparatus LA). The deformation profile of the reflective surface 210, 310 can have a surface variation of about 100 pm or less. For example, for a channel having a diameter of about 2 mm located at a depth of about 10 mm relative to the reflective surface, this corresponds to a fluid pressure adjustment of about 1000 Pa. At smaller depths, a smaller pressure change is required for the desired deformation of the reflective surface 210, 310.

[0077] The controller 100 may be configured to adjust the pressure of the fluid to about 10 Pa or more. The controller 100 may be configured to adjust the pressure of the fluid to about 1 bar or less. The controller 100 may be configured to separately adjust the pressure of the fluid in at least two of the plurality of channels 320-324 to control the deformation of the reflective surface 310. That is, the controller 100 may apply a first pressure adjustment in a first channel or a first group of channels and a different pressure adjustment in a second channel or a second group of channels. This allows different deformation profiles to be applied to the reflective surface 310, thereby enabling better overlay control of the lithographic apparatus LA. The controller 100 may include multiple sub-controllers (not shown). Different sub-controllers may be configured to adjust the pressure of the fluid in different channels or different groups of channels 320-324. For example, pressure valve 250 may include sub-valves (not shown) configured to act on different channels 320-324 to separately control the pressure within the different channels 320-324.

[0078]

[0077] The deformation profile applied to the reflective surface 210, 310 by adjusting the pressure of the fluid in the channels 220, 320-324 can be designed using the channel depth profile as a sensitivity parameter. This is because the mechanical stiffness of the portion of the body 200 located between the channels 220, 320-324 and the reflective surface 210, 310 can be proportional to the cube of the depth 221, 222 of the channels 220, 320-324 based on the area moment of inertia (i.e., the area moment of inertia). That is, referring to FIG. 2, the material of the body 200 located between the channel 220 and the reflective surface 210 can be likened to a rectangular simply supported beam 260 supported by the channel 220. The rectangular simply supported beam 260 has a uniformly distributed load applied by the pressure of the fluid in the channel 220. It is known in mechanical engineering that the stiffness of a rectangular simply supported beam with a uniformly distributed load is linearly proportional to the moment of inertia, which in turn is proportional to the cube of the height of the rectangular beam 260 (i.e., the depths 221, 222 of the channels 220 in this example). The diameter profile of the channels 220, 320-324 can be considered an independent design parameter in designing the deformation profile of the reflective surfaces 210, 310 while ensuring that the cooling capacity of the fluid remains sufficiently uniform.

[0079] The correction profile can compensate for overlay errors having field plane variations of third order or higher, for example, in the x-direction of the field plane. The depth of the channel 220, 320-324 along its length relative to the reflective surface 210, 310 and the cross-sectional shape of the channel can be designed such that the controller 100 is operable to adjust the pressure of the fluid in the channel to apply a deformation profile to the reflective surface that is at least a fourth order polynomial.

[0080] The dependence between the magnitude of the optical correction applied by the reflective surface 210, 310 and the pressure of the fluid in the channels 220, 320-324 may be assumed to be linear. Alternatively, the dependence between the magnitude of the optical correction applied by the reflective surface 210, 310 and the pressure of the fluid in the channels 220, 320-324 may be numerically modeled and calibrated in the lithographic apparatus LA by adjusting the pressure of the fluid in the channels using the controller 100 and measuring the effect on the wavefront of the reflected radiation B' using an optical sensor 120 (e.g., an interferometric wavefront sensor). The controller 100 may be configured to determine the pressure adjustment required to achieve the deformation of the reflective surface 210, 310 required to apply a correction profile of a desired magnitude to the patterned radiation beam B'. In general, increasing the pressure of the fluid in the channels 220, 320-324 can increase the magnitude of the correction profile applied by the reflective surface 210, 310 to the patterned radiation beam B'.

[0081] The deformation of the reflective surfaces 210, 310 by the controller 100 may occur during the projection of the patterned radiation beam B′. Distorting the reflective surfaces 210, 310 during the projection of the patterned radiation beam B′ has the advantage that overlay errors within a single target portion of the substrate W and / or between different target portions of the substrate W may be reduced while a pattern is projected onto the substrate W. Alternatively, the deformation of the reflective surfaces 210, 310 by the controller 100 may occur prior to the projection of the patterned radiation beam B′, with the reflective surfaces being held in their new shape during the projection of the patterned radiation beam B′. The reflectors MA-MT, 13, 14 and controller 100 of the present disclosure may be used in combination with other optical element manipulations present in the projection system PS to control overlay in the lithographic apparatus LA.

[0082]

[0081] Specific overlay errors and corresponding applications of the reflectors MA-MT, 13, 14 and controller 100 of the present disclosure are described below.

[0083] The reflectors MA-MT, 13, 14 and controller 100 of the present disclosure can be used to apply correction profiles that correct overlay errors that are not attributable to optical aberrations of the projection system PS (e.g. overlay errors that are attributable to deformations of the reticle MA and / or substrate W, temperature changes of the reticle MA and / or substrate W, substrate processing effects, etc.) and overlay errors that are attributable to optical aberrations of the lithographic apparatus LA. As already mentioned, overlay errors can be expressed in terms of field plane variations of the overlay error having different polynomial orders. A correction profile that adjusts the wavefront of the radiation B′ reflected from the reflective surface 210, 310 can be applied to correct at least third order field plane variations of the overlay error in the x-direction of the field plane, for example by applying a correction profile that adjusts the Zernike of the wavefront reflected from the reflective surface 210, 310.

[0084] The correction profile to be applied to the wavefront can be determined by determining the overlay error, determining a correction for the overlay error, and converting the correction to a desired wavefront adjustment. Of course, the steps of determining the overlay error, determining the correction, and converting the correction to a desired wavefront adjustment can be performed by any of a number of suitable methods. The correction profile (i.e., the correction to the wavefront that reduces the overlay error) can then be determined, for example, by determining the value of a polynomial (e.g., a Zernike) that induces a wavefront adjustment that reduces the overlay error. The correction profile can then be converted into the deformation of the reflecting surface 210, 310 required to apply the correction profile to the wavefront reflected from the reflecting surface. The effect of gradually adjusting the pressure of the fluid in the channels 220, 320-324 on the wavefront of radiation B' at different field plane positions can be measured and stored in memory. The information stored in memory can be referred to as reflector MA-MT, 13, 14 dependence.

[0085] The reflector MA-MT, 13, 14 dependence can be used to convert the correction profile into a deformation of the reflecting surface 210, 310. For example, the correction profile and the reflector MA-MT, 13, 14 dependence can be provided to an algorithm configured to determine an adjustment of the pressure of the fluid in the channel 220, 324 by the controller 100 that best applies the correction profile to the wavefront. The algorithm can be configured to reduce or minimize the residual wavefront (i.e., to reduce the difference between the desired "setpoint" wavefront and the actual "realized" wavefront). The algorithm can be, for example, a least-squares algorithm. FIG. 4 shows a graph comparing the ability 420 of the disclosed reflector and controller to control third-order field plane variations 400 of the overlay 400 with known methods. As can be seen from the graph, the setpoint overlay variation with field position takes the form of a third-order polynomial 400. Known methods 410 rely solely on the rigid mechanical action of the reflective surface relative to the radiation beam, and have poor compatibility with the setpoint overlay 400. The performance 420 of the disclosed reflectors MA-MT, 13, 14 and controller 100 combined with the rigid mechanical action of the reflective surfaces 210, 310 provides better compatibility with the overlay setpoint 400. Other types of algorithms may also be used, such as algorithms that take into account the limits of deformation of the reflecting surface 210, 310. In that case, the pressure of the fluid within the channels 220, 320-324 may be adjusted so that portions of the reflecting surface 210, 310 are in the relative positions required to apply the correction profile to the wavefront. A wavefront incident on the deformed reflecting surface 210, 310 is adjusted upon reflection from the reflecting surface to reduce the specified overlay error.

[0086] In some device manufacturing methods, the substrate W may be processed between different lithography exposures. That is, one layer of the substrate W is exposed to patterned radiation B′, after which the substrate W is removed from the lithography apparatus LA and subjected to substrate processing, such as polishing, etching, baking, etc. After substrate processing, the substrate W may be inserted into the same lithography apparatus LA (or a different lithography apparatus) and another layer of the substrate W may be exposed to patterned radiation B′. Substrate processing may result in overlay errors. Overlay errors resulting from substrate processing may be referred to as substrate processing effects. For example, etching a layer of the substrate W may change the stresses acting in the substrate (e.g., the stress across the scribe lines of the substrate), and as a result of the changed stresses in the substrate, the positions of features present on the substrate may change from their intended positions. As another example, baking the substrate W may cause thermal deformation of the substrate, which may cause the positions of features present on the substrate to change from their intended positions.

[0087] The correction profile can correct for the effects of substrate processing. For example, a first layer of substrate W may be exposed in a first lithographic exposure. The substrate W may be removed from the lithographic apparatus LA and subjected to substrate processing. The substrate W may then be reinserted into the lithographic apparatus LA and a next layer of the substrate may be subjected to a second lithographic exposure. For example, an overlay error between the first and second layers may be measured by performing a lithographic exposure in resist on the substrate W and measuring the overlay error of projected features, such as product features and / or alignment features, present on the substrate W. The controller 100 may determine a correction profile, via deformation of the reflective surfaces 210, 310 of the reflectors MA-MT, 13, 14, that, when applied to the radiation beam B′, reduces the measured overlay error. This correction profile is then applied to the radiation beam B′ in future exposures to reduce the overlay error. Different correction profiles may be determined for different combinations of lithographic apparatus LA and substrate processing.

[0088] The lithographic apparatus LA may include a support structure MT configured to support the reticle MA. By supporting the reticle MA, the support structure MT may induce undesired deformations of the reticle. For example, the reticle MA may be clamped to the support structure MT, for example by vacuum clamping or electrostatic clamping. The act of clamping the reticle MA to the support structure MT may deform the reticle from its rest shape. Deformations of the reticle MA may result in overlay errors. The correction profile may correct for deformations of the reticle MA caused by the support structure MT supporting the reticle.

[0089] During lithographic exposure, the temperature of the reticle MA may change. As a result of the change in reticle temperature, the reticle MA may undergo thermal deformation. For example, the reticle MA may absorb energy from the radiation beam B incident on the reticle, causing the temperature of the reticle to increase. As the temperature increases, the reticle MA may undergo thermal expansion. Thermal deformation of the reticle MA may cause overlay errors. A correction profile can correct for changes in the temperature of the reticle MA. For example, a computer model can be used to predict the overlay error due to changes in the temperature of the reticle MA. The computer model can be calibrated by comparing the results of the model with the results of lithographic exposure of a substrate W with resist. The results of the computer model can be used to determine a correction profile configured to reduce the overlay error. Alternatively, wavefront aberrations can be measured using known alignment sensors, such as, for example, one or more interferometric wavefront sensors. The measured wavefront aberrations can then be used to determine the correction profile. The correction profile can be applied to the patterned radiation B' by the controller 100 via deformation of the reflective surfaces 210, 310. The reflectors MA-MT, 13, 14 and controller 100 of the present disclosure can be used to reduce overlay errors caused by changes in the temperature of the reticle MA.

[0090] The lithographic apparatus LA may comprise a substrate table WT configured to hold a substrate W. For example, the substrate table WT may comprise burls configured to support the substrate W. The burls may apply forces to the substrate W that cause the substrate to deform. The deformation of the substrate W may induce overlay errors. Different substrate tables WT may cause different deformations of the substrate W. The deformation caused by the substrate table WT holding the substrate W may change over the lifetime of the substrate table. For example, the burls may deteriorate over time and, as a result, the force that the burls exert on the substrate W may also change over time.

[0091] The correction profile may correct for deformation of the substrate W caused by the substrate table WT holding the substrate. For example, a topography measurement system may be used to measure the topography of the substrate W while the substrate is held by the substrate table WT. The measured topography of the substrate W may be provided to a computer model configured to convert the measured topography into a predicted overlay error. The predicted overlay error may be used to determine the correction profile. Alternatively, the overlay error caused by deformation of the substrate W may be determined by performing a lithographic exposure in resist on the substrate and measuring the overlay error of projected features, such as product features and / or alignment features, present on the substrate. The measured overlay error may be used to determine the correction profile. The reflective surfaces 210, 310 may be deformed by the controller 100 to reduce the overlay error caused by deformation of the substrate W caused by the substrate table WT holding the substrate.

[0092] During lithographic exposure, the temperature of the substrate W may change. The substrate W may undergo thermal deformation as a result of the temperature change of the substrate. For example, the substrate W may absorb energy from the patterned radiation B′ incident on the substrate, causing the temperature of the substrate to increase. As the temperature of the substrate W increases, it may undergo thermal expansion and deformation. The thermal deformation of the substrate W may cause overlay errors. A correction profile may correct for the change in temperature of the substrate W. The reflectors MA-MT, 13, 14 and controller 100 of the present disclosure may be used to reduce the overlay errors caused by the change in temperature of the substrate W.

[0093] 5 shows a flowchart of a method according to the present disclosure, which comprises a first step 301 of providing a fluid flow through channels 220, 320-324 formed in a body 200, 300 in which a reflective surface 210, 310 of a lithographic apparatus LA is arranged.

[0094]

[0093] The method includes a second step 402 of adjusting the pressure of the fluid to control the deformation of the reflective surfaces 210, 310 and thereby the overlay of the lithographic apparatus LA.

[0095]

[0094] The method includes a third step 403 of reflecting radiation B' from the reflecting surface 210,310.

[0096] The depth of the channel 220, 320-324 can vary along the length of the channel relative to the reflective surface 210, 310. The channel 220, 320-324 can be one of a plurality of channels formed within the body 200, 300 for conveying a fluid. The method includes providing a fluid flow through at least two channels 220, 320-324 having different cross-sectional shapes. The method may include providing a fluid flow through at least two channels 220, 320-324 having cross-sectional shapes with different orientations relative to the reflective surface 210, 310. The method may include adjusting the pressure of the fluid within the channel 220, 320-324 to impart a deformation profile of at least a fourth-order polynomial to the reflective surface 210, 310. The reflective surface 210, 310 can be at least partially spherical. The method may include adjusting the position of the reflective surface 210, 310.

[0097] A method for fabricating the body 200, 300 of the reflector MA-MT, 13, 14 of the lithography apparatus LA can include performing laser ablation to form channels 220, 320-324 in the body of the reflector. Forming the channels 220, 320-324 using laser ablation has the advantage of providing precise control over the channel depth profile and cross-sectional shape, thereby allowing for a greater variety of depth profiles and cross-sectional shapes to be formed. For example, channels 220, 320-324 having more "free-form" shapes, such as fourth-order polynomial shapes, can be accurately formed using laser ablation compared to known methods of forming channels (e.g., by mechanically drilling channels into the body 200). Performing laser ablation to form the channels 220, 320-324 can include varying the depth of the channels 220, 320-324 relative to the reflective surface along the length of the channels 220, 320-324. A method of manufacturing the body 200, 300 of the reflector MA-MT, 13, 14 may include performing laser ablation to form at least two channels 220, 320-324 having different cross-sectional shapes. A method of manufacturing the body 200, 300 of the reflector MA-MT, 13, 14 may include performing laser ablation to form at least two channels 220, 320-324 having cross-sectional shapes with different orientations relative to the reflective surface.

[0098] The method for correcting overlay errors using the reflectors MA-MT, 13, 14 and controller 100 described herein can be incorporated into existing lithographic apparatus LA without requiring significant redesign of the lithographic apparatus. For example, the reflectors MA-MT, 13, 14 according to the present disclosure can replace the previous reflectors, and the controller 100 of the lithographic apparatus LA can be reconfigured to apply pressure adjustments to the fluids in the channels 220, 320-324 of the reflectors MA-MT, 13, 14. The reflectors MA-MT, 13, 14 and controller 100 can then be used to perform the method for correcting overlay errors described herein. The reflective surfaces 210, 310 can be modified by the controller to apply different correction profiles at any desired frequency. For example, the correction profile can be applied to the reflective surfaces 210, 310 for each lot of substrates W, for each substrate, for each target portion of a substrate, or during exposure of one target portion of a substrate. In general, the overlay error reduced by using reflectors MA-MT, 13, 14 and controller 100 can be determined by direct measurement (e.g., using detector system 120), indirect measurement (e.g., by performing a lithographic exposure in resist and analyzing the resist), and / or prediction (e.g., by inputting data into a computer model and running the computer model).

[0099]

[0098] Although specific reference is made in this specification to the use of lithographic apparatus LA in IC manufacturing, it should be understood that the lithographic apparatus described herein may have other applications, including the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat panel displays, liquid crystal displays (LCDs), thin film magnetic heads, etc.

[0100]

[0099] Depending on the circumstances, embodiments of the present invention may be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the present invention may also be implemented as instructions stored on a machine-readable medium and readable and executable by one or more processors. A machine-readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, a machine-readable medium may include read-only memory (ROM), random-access memory (RAM), magnetic storage media, optical storage media, flash memory devices, or electrical, optical, acoustic, or other forms of propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.). Also, firmware, software, routines, or instructions may be described herein as performing certain actions. However, it should be understood that such description is for convenience only, and that such actions are actually due to a computing device, processor, controller, or other device executing the firmware, software, routines, instructions, etc., thereby enabling an actuator or other device to interact with the physical world.

[0101]

[0100] While specific embodiments of the present invention have been described above, it will be apparent that the present invention can be practiced in other ways than those described above. The foregoing description is intended to be illustrative and not limiting. Thus, it will be apparent to those skilled in the art that modifications may be made to the invention as described herein without departing from the scope of the claims set forth below.

[0102] Further embodiments are disclosed in the following list of numbered clauses: 1. A lithographic apparatus comprising: a reflector for reflecting radiation, the reflector comprising a body, a reflective surface disposed on the body, and a channel formed in the body for conveying a fluid; a controller configured to adjust the pressure of the fluid in the channel to control the deformation of the reflective surface and thereby control the overlay of the lithographic apparatus; 1. A lithographic apparatus comprising: 2. A lithographic apparatus according to clause 1, wherein the depth of the channel relative to the reflective surface varies along the length of the channel. 3. the channel is one of a plurality of channels formed in the body for conveying a fluid, at least two of the plurality of channels having different cross-sectional shapes; and / or At least two of the plurality of channels have cross-sectional shapes with different orientations relative to the reflective surface. 3. A lithographic apparatus according to any of clauses 1 and 2. 4. A lithographic apparatus as described in clauses 2 and 3, wherein the depth of the channel relative to the reflective surface along the length of the channel and the cross-sectional shape of the channel are designed such that the controller is operable to adjust the pressure of the fluid in the channel to apply a deformation profile to the reflective surface that is at least a fourth-order polynomial. 5. The lithographic apparatus of clause 3 or 4, wherein the controller is configured to separately adjust the pressure of the fluid in at least two of the plurality of channels to control the deformation of the reflective surface. 6. An inlet conduit configured to provide a fluid to the channel; an outlet conduit configured to receive fluid from the channel; a flow restrictor disposed on the outlet conduit; 6. The lithographic apparatus of any of clauses 1 to 5, comprising: 7. The lithographic apparatus of clause 6, wherein the flow restrictor comprises a pressure valve, and wherein the controller is configured to control the pressure valve to regulate the pressure of the fluid in the channel. 8. A lithographic apparatus as described in any of clauses 1 to 7, comprising an optical sensor configured to detect at least a portion of radiation reflected by the reflective surface, and wherein the controller is configured to receive optical measurement data from the optical sensor and use the optical measurement data to control deformation of the reflective surface. 9. A lithographic apparatus according to any of clauses 1 to 8, comprising an actuator configured to adjust the position and / or orientation of the reflector. 10. An illumination system configured to condition a radiation beam; a support structure constructed to support a patterning device, the patterning device being capable of imparting the radiation beam with a pattern in its cross-section to form a patterned radiation beam; and a substrate table constructed to hold a substrate; a projection system configured to project the patterned beam of radiation onto a substrate; A reflector is a mirror in a projection system. 10. A lithographic apparatus according to any one of clauses 1 to 9. 11. An illumination system configured to condition a radiation beam; a support structure constructed to support a patterning device, the patterning device being capable of imparting the radiation beam with a pattern in its cross-section to form a patterned radiation beam; and a substrate table constructed to hold a substrate; a projection system configured to project the patterned beam of radiation onto a substrate; the reflective surface forms part of a patterning device and the body forms part of a support structure; 10. A lithographic apparatus according to any one of clauses 1 to 9. 12. Providing a fluid flow through a channel formed in a body of a lithographic apparatus in which a reflective surface is disposed; adjusting the pressure of the fluid to control the deformation of the reflective surface and thereby control the overlay of the lithographic apparatus; reflecting radiation from a reflective surface; A method comprising: 13. The method of clause 12, wherein the depth of the channel relative to the reflecting surface varies along the length of the channel. 14. The channel is one of a plurality of channels formed in the body for transporting a fluid; the method comprises providing a flow of fluid through at least two channels having different cross-sectional shapes; and / or The method includes providing a flow of fluid through at least two channels having cross-sectional shapes with different orientations relative to the reflective surface. 14. The method according to clause 12 or 13. 15. The method of clauses 13 and 14, comprising adjusting the pressure of the fluid in the channel to apply a deformation profile to the reflective surface that is at least a fourth order polynomial. 16. The method of clause 14 or 15, comprising separately adjusting the pressure of the fluid in at least two of the plurality of channels to control the deformation of the reflective surface. 17. A method according to any of clauses 12-1, comprising adjusting the position and / or orientation of the reflective surface. 18. A method of manufacturing a body of a reflector of a lithographic apparatus according to any one of clauses 1 to 12, the method comprising performing laser ablation to form channels. 19. The method of clause 18, wherein performing laser ablation to form the channel includes varying the depth of the channel relative to the reflective surface along the length of the channel. 20. Performing laser ablation to form at least two channels with different cross-sectional shapes; and / or performing laser ablation to form at least two channels having cross-sectional shapes with different orientations relative to the reflective surface; 19. The method of claim 18 or 19, comprising:

Claims

1. 1. A lithographic apparatus comprising: a reflector for reflecting radiation, the reflector comprising a body, a reflective surface disposed on the body, and a channel formed in the body for conveying a fluid; a controller configured to adjust the pressure of the fluid in the channel to control deformation of the reflective surface and thereby control overlay of the lithographic apparatus; 1. A lithographic apparatus comprising:

2. The lithographic apparatus of claim 1 , wherein a depth of the channel relative to the reflective surface varies along a length of the channel.

3. the channel is one of a plurality of channels formed in the body for conveying the fluid, at least two of the plurality of channels having different cross-sectional shapes; and / or At least two of the channels have cross-sectional shapes with different orientations relative to the reflecting surface.

3. A lithographic apparatus according to claim 1 or 2.

4. 4. The lithographic apparatus of claim 2, wherein a depth of the channel relative to the reflective surface along a length of the channel and a cross-sectional shape of the channel are designed such that the controller is operable to adjust a pressure of the fluid in the channel to apply a deformation profile to the reflective surface that is at least a fourth order polynomial.

5. 5. A lithographic apparatus according to claim 3 or 4, wherein the controller is configured to separately adjust the pressure of the fluid in at least two of the plurality of channels to control the deformation of the reflective surface.

6. an inlet conduit configured to provide the fluid to the channel; an outlet conduit configured to receive the fluid from the channel; a flow restrictor disposed on the outlet conduit; A lithographic apparatus according to any one of claims 1 to 5, comprising:

7. The lithographic apparatus of claim 6 , wherein the flow restrictor comprises a pressure valve, and the controller is configured to control the pressure valve to regulate the pressure of the fluid in the channel.

8. 8. A lithographic apparatus according to any preceding claim, comprising an optical sensor configured to detect at least a portion of the radiation reflected by the reflective surface, wherein the controller is configured to receive optical measurement data from the optical sensor and to control the deformation of the reflective surface using the optical measurement data.

9. A lithographic apparatus according to any preceding claim, comprising an actuator configured to adjust the position and / or orientation of the reflector.

10. an illumination system configured to condition a radiation beam; a support structure constructed to support a patterning device, the patterning device being capable of imparting the radiation beam with a pattern in its cross-section to form a patterned radiation beam; and a substrate table constructed to hold a substrate; a projection system configured to project the patterned beam of radiation onto the substrate; the reflector is a mirror in the projection system; A lithographic apparatus according to any one of claims 1 to 9.

11. an illumination system configured to condition a radiation beam; a support structure constructed to support a patterning device, the patterning device being capable of imparting the radiation beam with a pattern in its cross-section to form a patterned radiation beam; and a substrate table constructed to hold a substrate; a projection system configured to project the patterned beam of radiation onto the substrate; the reflective surface forms part of the patterning device and the body forms part of the support structure. A lithographic apparatus according to any one of claims 1 to 9.

12. providing a flow of fluid through a channel formed in a body of a lithographic apparatus in which a reflective surface is disposed; adjusting the pressure of the fluid to control deformation of the reflective surface and thereby control overlay of the lithographic apparatus; reflecting radiation from said reflective surface; A method comprising:

13. A method for manufacturing the body of the reflector of a lithographic apparatus according to any one of claims 1 to 11, comprising performing laser ablation to form the channels.

14. The method of claim 13 , wherein performing laser ablation to form the channel includes varying a depth of the channel relative to the reflective surface along a length of the channel.

15. performing laser ablation to form at least two channels having different cross-sectional shapes; and / or performing laser ablation to form at least two channels having cross-sectional shapes with different orientations relative to the reflective surface; 15. The method of claim 13 or 14, comprising:

Images