Lithographic apparatus and method

Abstract

A lithographic apparatus includes a reflector for reflecting radiation. The reflector includes a body, a reflective surface disposed on the body, and a channel formed in the body for conveying a fluid. The lithographic apparatus includes 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

[0001] Cross - Reference to Related Applications

[0002] This application claims priority to EP application 22202403.6, which was filed on October 19, 2022 and the entire content of which is incorporated herein by reference. Field of the Invention

[0003] The present invention relates to a lithographic apparatus and a method for controlling overlay. Background Art

[0004] A lithographic apparatus is a machine configured to apply a desired pattern onto a substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). A lithographic apparatus can project a pattern present on a patterning device (e.g., a mask) onto a layer of radiation-sensitive material (resist) provided on a substrate, for example.

[0005] To project a pattern onto a substrate, a lithographic apparatus can use electromagnetic radiation. The wavelength of this radiation determines the minimum feature size that can be formed on the substrate. A lithographic apparatus using extreme ultraviolet (EUV) radiation having a wavelength in the range of 4 - 20 nm (e.g., 6.7 nm or 13.5 nm) can be used to form smaller features on a substrate than a lithographic apparatus using, for example, radiation having a wavelength of 193 nm.

[0006] Lithographic processing typically involves performing multiple exposures across successive substrate layers to form a desired structure. The accuracy with which a newly projected pattern is aligned with a previously projected pattern is known in the art as overlay. During an entire device manufacturing process, overlay errors can arise from several different sources. A first known method of controlling overlay involves varying the position of one or more reflectors within the lithographic apparatus. However, the first known method of 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 distributions)). A second known method of controlling overlay involves heating one or more reflectors of the lithographic apparatus to introduce a controlled thermal deformation of the one or more reflectors. However, reflectors, especially EUV reflectors, can be relatively large and bulky objects, and they thermally deform relatively slowly in response to temperature changes. Therefore, due to the relatively long thermal curing time of the reflectors, the second known method of controlling overlay cannot perform fast, high-frequency overlay corrections.

[0007] Known lithographic apparatuses and methods may be limited in their ability to correct overlay errors. It is desirable to provide a lithographic apparatus and method that eliminates or alleviates one or more of the problems in the prior art, whether indicated herein or elsewhere. Summary of the Invention

[0008] According to a first aspect of the present disclosure, a lithographic apparatus is provided, including a reflector for reflecting radiation. The reflector includes a body, a reflective surface disposed on the body, and a channel formed in the body for conveying a fluid. The lithographic apparatus includes 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.

[0009] The lithographic apparatus of the present disclosure is capable of reducing higher-order optical errors (e.g., overlay errors corresponding to higher-order field dependencies such as higher-order polynomial deformation distributions). The lithographic apparatus of the present disclosure advantageously enables rapid, high-spatial-frequency deformation of the reflective surface, thereby allowing for rapid, high-spatial-frequency overlay correction. High-spatial-frequency deformation of the reflective surface may refer to at least a fourth-order polynomial deformation distribution applied to the reflective surface by adjusting the pressure of the fluid. High-spatial-frequency overlay correction may refer to at least a third-order polynomial overlay shape or error.

[0010] The reflective surface and the body may be integrally formed.

[0011] The reflective surface and the body may be separately formed. The body may be configured to support the reflective surface. The body may form part of a fixture configured to fix the reflective surface.

[0012] The channel may form part of a cooling system configured to cool the reflective surface. The controller may be retrofitted to an existing cooling system. This advantageously increases the utility of the cooling system. That is, the cooling system can cool the reflective surface (thereby reducing unwanted thermal deformation) while also controlling the pressure-based deformation of the reflective surface (thereby imparting desired characteristics to the radiation after reflection from the reflective surface).

[0013] Adjusting the pressure of the fluid may include adjusting the flow rate of the fluid.

[0014] The depth of the channel relative to the reflective surface may vary along the length of the channel.

[0015] The varying depth of the channel advantageously introduces a varying stiffness distribution of the body between the channel and the reflective surface, thereby allowing for a greater variety of reflective surface deformations to be applied.

[0016] The body of the reflector may include a plurality of channels. The depth of the first channel relative to the reflective surface may vary along the length of the first channel in a manner different from the way the depth of the second channel relative to the reflective surface varies along the length of the second channel. That is, different channels may have different depth distributions relative to the reflective surface.

[0017] The channel can be one of a plurality of channels formed in the body for conveying fluid. At least two of the channels can have different cross-sectional shapes. The cross-sectional shapes of at least two of the channels can have different orientations relative to the reflective surface.

[0018] Using channels with different cross-sectional shapes and / or orientations advantageously introduces a varying force distribution applied by the pressure of the fluid flowing through the first and second channels to the reflective surface, thereby allowing a greater variety of deformations of the reflective surface to be applied. Using channels with different cross-sectional shapes and / or orientations advantageously allows the flow rates and restrictions of the fluid in the first and second channels to be maintained at desired levels while enabling the force distribution applied by the pressure of the fluid flowing through the first and second channels to the reflective surface to vary.

[0019] The depth of the channel along its length relative to the reflective surface and the cross-sectional shape of the channel can be designed such that the controller can operate to adjust the pressure of the fluid in the channel to apply at least a fourth-order polynomial deformation distribution to the reflective surface.

[0020] Applying a fourth-order polynomial deformation distribution to the reflective surface advantageously allows the controller to reduce higher-order optical errors (e.g., registration errors corresponding to higher-order field dependencies (such as higher-order polynomial deformation distributions (e.g., third-order polynomial registration errors))).

[0021] The controller can be configured to independently adjust the pressure of the fluid in at least two of the plurality of channels to control the deformation of the reflective surface.

[0022] Independently adjusting the pressure of the fluid in at least two of the plurality of channels advantageously allows different deformation distributions to be applied to the reflective surface, thereby allowing better control of the registration of the lithographic apparatus.

[0023] The controller can include a plurality of sub-controllers. Different sub-controllers can be configured to adjust the pressure of the fluid in different channels or different groups of channels.

[0024] The lithographic apparatus can include an inlet conduit configured to supply fluid to the channels. The lithographic apparatus can include an outlet conduit configured to receive fluid from the channels. The lithographic apparatus can include a flow restrictor disposed on the outlet conduit.

[0025] The controller can be configured to adjust the flow rate of the fluid, and the action of the flow restrictor can adjust the pressure of the fluid in the channel.

[0026] The lithographic apparatus can include a pressure sensor configured to detect the pressure of the fluid in the channel. The controller can be configured to use the data provided by the pressure sensor to control the pressure of the fluid in the channel.

[0027] The flow limiter may include a pressure valve. The controller may be configured to control the pressure valve to adjust the pressure of the fluid in the channel.

[0028] The pressure valve advantageously provides a rapid change in pressure via the controller, thereby providing a rapid change in the deformation of the reflective surface.

[0029] The pressure valve may include a piezoelectric element configured to clamp the outlet pipe.

[0030] The lithographic apparatus may include an optical sensor configured to detect at least a portion of the radiation reflected by the reflective surface. The controller may be configured to receive optical measurement data from the optical sensor and use the optical measurement data to control the deformation of the reflective surface.

[0031] The optical sensor advantageously allows feedback control of the radiation such that, despite changes in the operating conditions, the radiation is given the desired characteristics after being reflected from the reflective surface. The optical sensor advantageously allows calibration to be performed, wherein the effect of the pressure adjustment by the controller on the characteristics of the radiation reflected by the reflective surface (e.g., the wavefront of the radiation) is determined and / or modeled. The optical sensor may include one or more interferometric wavefront sensors.

[0032] The lithographic apparatus may include an actuator configured to adjust the position and / or orientation of the reflector.

[0033] The actuator advantageously provides additional control when giving the desired characteristics to the radiation after being reflected from the reflective surface.

[0034] The actuator may be configured to provide movement of the reflector within six rigid body degrees of freedom (e.g., three linear degrees of freedom and three rotational degrees of freedom).

[0035] The reflective surface may be partially spherical.

[0036] The lithographic apparatus may include a heater configured to heat the reflector and introduce a controlled thermal deformation of the reflective surface, and thereby provide additional control when giving the desired characteristics to the radiation after being reflected from the reflective surface.

[0037] The lithographic apparatus may include an illumination system configured to condition a radiation beam. The lithographic apparatus may include a support structure configured to support a patterning device capable of imparting a pattern to the radiation beam in a cross-section thereof to form a patterned radiation beam. The lithographic apparatus may include a substrate table configured to hold a substrate. The lithographic apparatus may include a projection system configured to project the patterned radiation beam onto the substrate. The reflector may be a mirror in the projection system.

[0038] A lithographic apparatus may include an illumination system configured to condition a radiation beam. The lithographic apparatus may include a support structure configured to support a patterning device that is capable of imparting a pattern in a cross-section of the radiation beam to form a patterned radiation beam. The lithographic apparatus may include a substrate table configured to hold a substrate. The lithographic apparatus may include a projection system configured to project the patterned radiation beam onto the substrate. A reflective surface may form part of the patterning device. A body may form part of the support structure.

[0039] According to a second aspect of the present disclosure, there is provided a method including providing a flow of fluid through a channel formed in a body on which a reflective surface of a lithographic apparatus is disposed. The method includes adjusting a pressure of the fluid to control a deformation of the reflective surface and thereby control overlay of the lithographic apparatus. The method includes reflecting radiation from the reflective surface.

[0040] A depth of the channel may vary along a length of the channel relative to the reflective surface.

[0041] The channel may be one of a plurality of channels formed in the body for conveying fluid. The method may include providing a flow of fluid through at least two channels having different cross-sectional shapes. The method may include providing a flow of fluid through at least two channels having cross-sectional shapes with different orientations relative to the reflective surface.

[0042] The method may include adjusting a pressure of the fluid in the channel to apply at least a fourth-order polynomial deformation profile to the reflective surface.

[0043] The method may include independently adjusting a pressure of the fluid in at least two of the plurality of channels to control a deformation of the reflective surface.

[0044] The method may include adjusting a position and / or an orientation of the reflective surface.

[0045] According to a third aspect of the present disclosure, there is provided a method of manufacturing a body of a reflector of the lithographic apparatus of the first aspect, including performing laser ablation to form the channel.

[0046] Laser ablation advantageously provides fine control over a depth profile and a cross-sectional shape of the channel, thereby allowing for the formation of a greater variety of depth profiles and cross-sectional shapes.

[0047] Performing laser ablation to form the channel may include varying a depth of the channel relative to the reflective surface along a length of the channel.

[0048] The method of manufacturing the body of the reflector may include performing laser ablation to form at least two channels having different cross-sectional shapes.

[0049] A method of manufacturing a body of a reflector may include performing laser ablation to form at least two channels, wherein cross-sectional shapes of the at least two channels have different orientations relative to a reflective surface. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which:

[0051] Figure 1 A lithography system according to the present disclosure is schematically depicted, which includes a lithography apparatus, a radiation source, a reflector, and a controller.

[0052] Figure 2 A cross-sectional view of a reflector according to the present disclosure is schematically depicted.

[0053] Figure 3 A cross-sectional view of a reflector including a plurality of channels according to the present disclosure is schematically depicted.

[0054] Figure 4 A graph showing the ability of the reflector and the controller according to the present disclosure to control third-order field plane overlay variations as compared with known methods is shown.

[0055] Figure 5 A flowchart of a method according to the present disclosure is shown. DETAILED DESCRIPTION

[0056] Figure 1 A lithography system according to the present disclosure is shown, which includes a radiation source SO, a lithography apparatus LA, reflectors MA, MT, 13, 14, and a controller 100. The radiation source SO is configured to generate an EUV radiation beam B and supply the EUV radiation beam B to the lithography apparatus LA. The lithography 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 stage WT configured to support a substrate W.

[0057] The illumination system IL is configured to condition the EUV radiation beam B before the EUV radiation beam B is incident on the patterning device MA. In addition, the illumination system IL may include a multi-faceted field mirror device 10 and a multi-faceted pupil mirror device 11. The multi-faceted field mirror device 10 and the multi-faceted pupil mirror device 11 together provide a desired cross-sectional shape and a desired intensity distribution for the EUV radiation beam B. The illumination system IL may also include other mirrors or devices in addition to the multi-faceted field mirror device 10 and the multi-faceted pupil mirror device 11, or include other mirrors or devices in place of the multi-faceted field mirror device 10 and the multi-faceted pupil mirror device 11.

[0058] After such adjustment, the EUV radiation beam B interacts with the patterning device MA. As a result of this interaction, a patterned EUV radiation beam B' is generated. The projection system PS is configured to project the patterned EUV radiation beam B' onto the substrate W. For this purpose, the projection system PS may include a plurality of mirrors 13, 14 configured to project the patterned EUV radiation beam B' onto the substrate W held by the substrate table WT. The projection system PS may apply a reduction factor to the patterned EUV radiation beam B', thereby forming an image with features smaller than the corresponding features on the patterning device MA. For example, a reduction factor of 4 or 8 may be applied. Although the projection system PS is Figure 1 illustrated in [the figure] as having only two mirrors 13, 14, the projection system PS may include a different number of mirrors (e.g., six or eight mirrors).

[0059] The substrate W may include a previously formed pattern. In this case, the lithographic apparatus LA aligns the image formed by the patterned EUV radiation beam B' with the pattern previously formed on the substrate W.

[0060] A relative vacuum, i.e., a small amount of gas (e.g., hydrogen gas) at a pressure far lower than atmospheric pressure, may be provided in the radiation source SO, the illumination system IL, and / or the projection system PS.

[0061] The radiation source SO may be a laser-produced plasma (LPP) source, a discharge-produced plasma (DPP) source, a free electron laser (FEL), or any other radiation source capable of generating EUV radiation.

[0062] The lithographic apparatus LA includes reflectors MA-MT, 13, 14 for reflecting the radiation B, B'. The reflectors may be the patterning device MA and the support structure MT. The reflectors may be one of the mirrors 13, 14 in the projection system PS. The lithographic apparatus LA may include a plurality of reflectors according to the present disclosure. In Figure 1 an example, 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 formed in the body for conveying fluid. In Figure 2 and Figure 3The components of the reflectors 13, 14 according to the present disclosure are shown in more detail in []. In an 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 chuck of the support structure MT, which is configured to hold the patterning device MA. In an example of the patterning device MA and the support structure MT, the reflective surface and the body may be considered as separately shaped components. Alternatively, the reflective surface and the body may be integrally shaped, such as one or more of the mirrors 13, 14 in the projection system PS for example.

[0063] The lithographic apparatus LA further includes a controller 100, which is configured to adjust the pressure of the fluid in the channels of the reflectors MA-MT, 13, 14 to control the deformation of the reflective surface, and thereby control the overlay of the lithographic apparatus LA. The deformation of the reflective surface may be caused by the pressure difference between the pressure of the fluid in the channel and the pressure of the vacuum environment in which the reflective surface is located. For example, the pressure of the fluid in the channel may be about 300 mbar, while the pressure of the environment in which the reflective surface is located may be about 5 Pa. In Figure 1 the example of [], the channels (not shown) form part of a cooling system 110, which is configured to cool the reflective surfaces of the reflectors MA-MT, 13, 14. The controller 100 may be retrofitted to an existing cooling system of the lithographic apparatus LA.

[0064] Figure 2 A cross-sectional view of the reflector 14 according to the present disclosure is schematically depicted. Figure 2 and Figure 3 Cartesian coordinates X, Y, Z are provided in [] to facilitate the understanding of the reflectors 13, 14. In Figure 2 the example of [], the reflector 14 corresponds to the second mirror 14 shown in the projection system PS of the lithographic apparatus LA of Figure 1 []. The reflector 14 includes a body 200, a reflective surface 210 disposed on the body 200, and channels 220 formed in the body 200 for conveying fluid. The reflective surface 210 may be configured to reflect EUV radiation. The reflector 14 may include a material having a relatively low coefficient of thermal expansion (such as, for example, titania silicate glass (e.g., ULE TM ) manufactured by Corning Incorporated), Zerodur TM or cordierite).

[0065] The reflective surface 210 may have a reflectivity of about 70% or lower. Thus, when the lithographic apparatus LA is operating, the reflective surface 210 absorbs a significant amount of energy from the radiation beam B'. The reflective surface 210 may experience a non-uniform temperature rise across the area of the reflective surface 210, especially if the illumination pattern of the illumination system IL (e.g., dipole illumination) is set such that the radiation beam B' is non-uniformly distributed across different areas of the reflective surface 210. The non-uniform temperature rise 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 an absolute sense, since manufacturing devices with small feature sizes requires extremely high precision, such deformation may cause imaging errors. Therefore, a cooling system 110 is provided to the lithographic apparatus LA, which cooling system 110 is configured to remove thermal energy from the reflectors MA-MT, 13, 14, thereby reducing unwanted thermal deformation of the reflectors MA-MT, 13, 14.

[0066] The cooling system 110 includes channels 220 that pass through the body 200 of the reflectors MA-MT, 13, 14. In Figure 2 the example, the channels 220 are connected to an inlet pipe 230 and an outlet pipe 240, the inlet pipe 230 being configured to supply fluid to the channels 220 and the outlet pipe 240 being configured to receive fluid from the channels 220. The inlet pipe 230 may form part of an input manifold configured to supply fluid to a plurality of channels 220 in the body 200, and the outlet pipe 240 may form part of an output manifold configured to receive fluid from a plurality of channels 220 in the body 200. The channels 220 may be arranged to increase heat transfer between the body 200 and the fluid flowing through the channels 220. The channels 220 may be formed directly in the material of the body 200 using laser ablation. The cooling system 110 may include a temperature regulation system to ensure that the fluid supplied to the channels 220 is at a desired temperature. The fluid may be, for example, water. Using water may be advantageous because water has a relatively high heat capacity, so a relatively low mass flow rate can provide a relatively large heat transfer capacity. As another example, the fluid may be carbon dioxide. Using carbon dioxide may be advantageous because carbon dioxide can be supplied as a liquid (under pressure) such that it evaporates within the channels 220 in the higher temperature regions. Thus, the latent heat of evaporation increases the heat transfer capacity of the fluid. For a given heat load, the required mass flow can be much lower than for water, thereby reducing vibrations caused by the flow of the reflective surface 210.

[0067] 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 position 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 position 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 Figure 2 the example of, 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 shape. That is, the farther away from the center of the length of the channel 220, the greater the depth of the channel 220 relative to the reflective surface 210. The depth of the channel 220 can vary in other ways to form other shapes. In Figure 2 the example of, only a single channel 220 is shown. However, the reflector 14 can include a plurality of channels 220, and different channels 220 within the plurality of channels 220 can have different depth distributions. Generally, the depth distribution of the channels 220 can be selected to create a desired stiffness distribution within a portion of the body 200 located between the channels 220 and the reflective surface 210. The depths 221, 222 of the channel 220 relative to the reflective surface 210 can be about 0.5 mm or more. The depths 221, 222 of the channel 220 relative to the reflective surface 210 can be about 30 mm or less.

[0068] Figure 3 A cross-sectional view of a reflector 13 including a plurality of channels 320 - 324 according to the present disclosure is schematically depicted. In Figure 3 the example of, the reflector 13 corresponds to the shown first mirror 13 of the projection system PS of the lithographic apparatus LA of Figure 1 . The cross-sectional view of Figure 3 corresponds to a 90° rotation of the viewing direction of the cross-sectional view of Figure 2 , where Figure 2 shows a side view of the channel 220, while Figure 3 shows a front view of the channels 320 - 324. The number of channels 320 - 324 can depend at least in part on the size of the reflector 13 and / or the separation between adjacent channels 320 - 324. For example, 10 to 100 channels 320 - 324 can be provided in the body 300. For example, 20 to 60 channels 320 - 324 can be provided in the body 300. For example, about 40 channels can be provided in the body 300.

[0069] At least two of the channels 320 - 324 can have different cross-sectional shapes. In Figure 3In the example, three of the channels in the channel have oval cross-sectional shapes 320, 322, 324, and two of the channels in the channel have circular cross-sectional shapes 321, 323. The channels 320-324 may have other cross-sectional shapes. For example, the channels 320-324 may have cross-sectional shapes such as square, rectangular, triangular, etc. If the cross-sectional shape of the channels 320-324 is not circular, then the diameter of the channel can be taken as the maximum dimension of the cross-sectional shape. If the diameter of the channels 320-324 is relatively small, then the flow resistance may be relatively high, so that a larger pressure difference is required 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 can be about 0.1 mm or greater. The diameter of the channels 220, 320-324 can be about 10 mm or less.

[0070] The cross-sectional shapes of at least two of the channels 320-324 can have different orientations with respect to the reflective surface 310. In Figure 3 the example, two of the oval channels, 320 and 324, are oriented such that their major axes 325, 326 are substantially perpendicular to the reflective surface 310, while one of the oval channels, 322, is oriented such that its major axis 327 is substantially parallel to the reflective surface 310. That is, the two channels 320, 324 in the oval channel are oriented 90° with respect to the other oval channel 322. The cross-sectional shapes of the channels 320, 322, 324 can have other orientations with respect to the reflective surface 310 and / or each other.

[0071] Generally speaking, the cross-sectional shape and / or the orientation of the cross-sectional shape of the channels 320-324 can be selected to create a desired force distribution that can be actuated by adjusting the pressure of the fluid in the channels 320-324 and / or to create a desired fluid flow restriction by the channels 320-324. For example, the aspect ratio of the cross-sectional shape of the channels 320-324 can be selected to create a desired force distribution that can be actuated by adjusting the pressure of the fluid in the channels 320-324 and / or to create a desired fluid flow restriction by the channels 320-324. In Figure 3In the example, the first diameter 327 of the cross-sectional shape of channels 320 - 324 along the first direction X is selected to at least partially determine the desired force distribution that can be actuated by adjusting the pressure of the fluid in channels 320 - 324. The first direction X is substantially parallel to the reflective surface 210. Increasing the first diameter 327 can increase the force exerted on the reflective surface 210 by the pressure of the fluid in channels 320 - 324. The second diameters 325, 326 of the cross-sectional shape of channels 320 - 324 along the second direction Z, which is substantially perpendicular to the first direction X, are selected to at least partially determine the desired fluid flow restriction through channels 320 - 324. The second direction Z is substantially perpendicular to the reflective surface 210. Refer to Figures 1 - 3 , generally speaking, the depth distribution 221, 222 and / or the cross-sectional shape and / or the orientation of the cross-sectional shape of channels 320 - 324 can be selected to at least partially determine the deformation distribution of the reflective surface 310 (and thus determine the overlay of the lithographic apparatus LA), while also maintaining the desired cooling power of the cooling system 110. The depths 221, 222 of channel 220 relative to the reflective surface 210 can be about 2 mm or more. The depths 221, 222 of channel 220 relative to the reflective surface 210 can be about 10 mm or less.

[0072] See Figure 1 and Figure 2 , the lithographic apparatus LA includes a flow restrictor 250 disposed on the outlet pipe 240. In the case of a simple flow restrictor, the controller 100 can adjust the flow rate of the fluid, and the operation of the flow restrictor 250 can adjust the pressure of the fluid in the channels. The lithographic apparatus LA can include a pressure sensor (not shown) configured to detect the pressure of the fluid in channels 220, 320 - 324. The controller 100 can be configured to use the data provided by the pressure sensor to control the pressure of the fluid in channels 220, 320 - 324. In Figure 2 the example, 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 channel 220. The pressure valve 250 can include a piezoelectric element configured to apply an adjustable clamping or "grasping" to the outlet pipe 240. The pressure valve 250 advantageously provides a rapid change in pressure through the controller 100, thereby providing a rapid change in the deformation of the reflective surface 210 and a corresponding rapid control of the overlay of the lithographic apparatus LA. The controller 100 and the pressure valve 250 can 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 the pressure valve 250 can be capable of changing the overlay of the lithographic apparatus LA between multiple substrates W such that overlay correction can be applied to the previously printed layers of the substrate W.

[0073] The lithographic apparatus LA includes an optical sensor 120 which is configured to detect at least a part of the radiation B' reflected by the reflective surfaces MA-MT, 13, 14. The optical sensor 120 may include one or more interferometric wavefront sensors. A controller 100 is configured to receive optical measurement data from the optical sensor 120 and to use the optical measurement data to control the deformation of the reflective surfaces MA-MT, 13, 14. The optical sensor 120 advantageously provides feedback control of the overlay of the lithographic apparatus LA. That is, the controller 100 may use the optical measurement data to control the deformation of the reflective surfaces MA-MT, 13, 14 such that, despite changes in the operating conditions, the radiation B' is given a desired characteristic (e.g., a desired wavefront) after reflection from the reflective surfaces MA-MT, 13, 14. The optical sensor 120 advantageously allows calibration to be performed, in which the effect of the pressure adjustment made by the controller 100 on the characteristic of the radiation B' (e.g., the wavefront of the radiation) reflected by the reflective surfaces MA-MT, 13, 14 is determined and / or modeled.

[0074] See Figure 1 and Figure 3 , the lithographic apparatus LA includes an actuator 130 which is 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 position between the reflective surface 310 and the radiation B' is changed. That is, after the reflector 13 has been moved by the actuator 130, different parts of the radiation B' may be reflected by different parts of the reflective surface 310. The controller 100 may be configured to control the actuator 130 and thereby provide further control of the overlay of the lithographic apparatus LA. As Figure 1 and Figure 3 shown in, the reflective surface 310 of the first reflector 13 shown in the projection system PS is at least partially spherical. The combination of the partially spherical shape of the reflective surface 310 and the pressure-induced deformation of said shape may provide additional degrees of freedom in controlling the overlay of the lithographic apparatus LA compared to merely moving the reflectors 13, 14 relative to the radiation beam B'.

[0075] The reflector 13 advantageously allows additional control of the overlay of the lithographic apparatus LA when imparting a desired characteristic (e.g., a desired wavefront adjustment) to the radiation B' after reflection from the reflective surface 310.

[0076] The controller 100 is configured to adjust the pressure of the fluid in channels 320 - 324 to control the deformation of the reflective surface 310, and thereby control the alignment of the lithographic apparatus LA. The wavefront shape 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 so as to reduce the alignment error. The alignment of an image with its intended position on the substrate W can be referred to as alignment. The inaccuracy of the alignment of an image with its intended position on the substrate W can be referred to as alignment error. The wavefront of the radiation B’ can be adjusted by the reflective surface 310 so as to reduce the alignment error.

[0077] Knowledge of the alignment of the lithographic apparatus LA can be determined via direct measurement (e.g., using a detector system such as Figure 1 the optical sensor 120), indirect measurement (e.g., performing a lithographic exposure in a photoresist and analyzing the photoresist), and / or prediction (e.g., by inputting data into a computer model and running the computer model). For example, data related to alignment can be measured and input into a computer model. The computer model can be configured to receive the data and perform calculations using the data in order to predict the alignment performance of the lithographic apparatus LA.

[0078] The alignment 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 defects in its optical components. Information related to the optical aberrations can be represented as the wavefront shape in the pupil plane of the lithographic apparatus LA. The wavefront shape can be represented as a combination of polynomials. For example, for an optical system including a circular pupil, the wavefront shape can be represented as Zernike polynomials. Different polynomials can represent different types of optical aberrations. For example, the first Zernike polynomial can represent tilt aberration, while the second Zernike polynomial can represent defocus aberration. Zernike polynomials are generally classified as odd (i.e., asymmetric) or even (i.e., symmetric). Different classes of Zernike polynomials can correspond to different projection system PS characteristics. For example, even Zernike polynomials can correspond to focus error, while odd Zernike polynomials can correspond to alignment error. In general, the Zernike polynomials can be classified in any desired manner. In the following discussion of Zernike, the double-index American National Standards Institute (ANSI) Zernike numbering scheme will be used.

[0079] The 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 undergoes different aberrations. That is, the shape of the wavefront at the pupil plane varies with each position in the field plane. The variation of the field plane across the overlay and / or the wavefront can be expressed as a combination of polynomials of different orders. For example, the variation of the field plane of lower-order Zernike (e.g., Z[1,1], which represents the horizontal tilt of the wavefront shape) can be expressed as a combination of different polynomials. Considering the variation of the field plane of higher-order polynomials can provide more information about the overlay and / or optical aberrations present in the lithographic apparatus LA, and / or more information about how to induce corrections within the lithographic apparatus LA via adjustments made to the optical elements present within the lithographic apparatus LA. The variation of the field plane of the overlay and / or the wavefront described by higher-order polynomials may be more difficult to compensate than the variation of the field plane described by lower-order polynomials.

[0080] The reflectors MA-MT, 13, 14 and the controller 100 of the present disclosure may be capable of performing fine adjustments on the wavefront incident on the reflective surface (e.g., providing nanoscale deformations of the reflective surfaces 210, 310). The reflectors MA-MT, 13, 14 and the controller 100 of the present disclosure may perform fine adjustments on the wavefront, which allows for reducing lithography errors, particularly overlay errors, that correspond to field plane variations of higher orders than known methods of reducing lithography errors. For example, the reflectors MA-MT, 13, 14 and the controller 100 of the present disclosure may be used to apply a correction distribution that compensates for at least the 3rd order field plane variation of the overlay. For example, the reflectors MA-MT, 13, 14 and the controller 100 of the present disclosure may be used to apply a correction distribution that compensates for at least the 4th order field plane variation of the overlay. The reflectors MA-MT, 13, 14 and the controller 100 of the present disclosure may be used to apply a correction distribution that compensates for the field plane variation of Zernike. The reflectors MA-MT, 13, 14 and the controller 100 of the present disclosure may be used to apply a correction distribution that reduces the overlay error associated with at least the 3rd order field plane variation of Zernike. The reflectors MA-MT, 13, 14 and the controller 100 of the present disclosure may be used to apply a correction distribution that reduces the overlay error associated with at least the 4th order field plane variation of Zernike. Generally speaking, it should be understood that the higher the order of the polynomial of the field plane variation (e.g., Zernike polynomial) that the reflectors MA-MT, 13, 14 and the controller 100 of the present disclosure can compensate for, the more complex the construction and operation of the reflectors MA-MT, 13, 14. The balance between the complexity of the reflectors MA-MT, 13, 14 and the correction ability of the controller 100 can be selected as needed.

[0081] A correction distribution for patterning the radiation beam B’ can be determined based on knowledge of the overlay error. The correction distribution is configured to reduce the overlay error when the reflective surfaces 210, 310 of the reflectors MA-MT, 13, 14 apply the correction distribution to the patterning radiation beam B’. The correction distribution can include wavefront modifications required to reduce the overlay error. The reflectors MA-MT, 13, 14 can be fabricated such that the reflective surfaces 210, 310 obtain a desired correction distribution after adjusting the pressure of the fluid in the channels 220, 320-324 by the controller 100. That is, the reflectors MA-MT, 13, 14 can be designed to compensate for field plane variations of a particular polynomial shape. For example, the reflectors MA-MT, 13, 14 can be designed to compensate for third-order field plane variations in overlay such that pressure adjustment of the fluid in the channels 220, 320-324 induces a fourth-order polynomial deformation distribution in the reflective surfaces 210, 310. As previously discussed, in general, the depth distribution 221, 222 and / or the cross-sectional shape and / or the orientation of the cross-sectional shape of the channels 220, 320-324 can be selected to at least partially determine the deformation distribution of the reflective surfaces 210, 310 (and thus the overlay of the lithographic apparatus LA). The deformation distribution of the reflective surfaces 210, 310 can have a surface variation of about 100 pm or less. For example, channels with a diameter of about 2 mm are located at a depth of about 10 mm relative to the reflective surface, which corresponds to a pressure adjustment of the fluid of about 1000 Pa. At lower depths, the pressure change required for the desired deformation of the reflective surfaces 210, 310 will be lower.

[0082] The controller 100 can be configured to adjust the pressure of the fluid by about 10 Pa or more. The controller 100 can be configured to adjust the pressure of the fluid by about 1 bar or less. The controller 100 can be configured to independently 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 can 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 distributions to be applied to the reflective surface 310, thereby allowing better control of the overlay of the lithographic apparatus LA. The controller 100 can include a plurality of sub-controllers (not shown). Different sub-controllers can be configured to adjust the pressure of the fluid in different channels or different groups of channels 320-324. For example, the pressure valve 250 can include a plurality of sub-valves (not shown) that are configured to act on different channels 320-324 and thus independently control the pressure within different channels 320-324.

[0083] The deformation distribution applied to the reflective surfaces 210, 310 by adjusting the pressure of the fluid in the channels 220, 320 - 324 can be designed using the depth distribution of the channels as a sensitive parameter, because the mechanical stiffness of the portion of the body 200 located between the channels 220, 320 - 324 and the reflective surfaces 210, 310 is proportional to the cube of the depth 221, 222 of the channels 220, 320 - 324 based on the second moment of area (i.e., the moment of inertia of area). That is, referring to Figure 2 , the material of the body 200 located between the channel 220 and the reflective surface 210 can be likened to a simply supported rectangular beam 260 supported by the channel 220. The simply supported rectangular beam 260 has a uniformly distributed load applied to it by the pressure of the fluid in the channel 220. In the field of mechanical engineering, it is known that the stiffness of a simply supported rectangular beam with a uniformly distributed load is linearly proportional to the second moment of area, and the second moment of area is proportional to the cube of the height of the rectangular beam 260 (i.e., in this case, the depth 221, 222 of the channel 220). The diameter distribution of the channels 220, 320 - 324 can be regarded as an independent design parameter in designing the deformation distribution of the reflective surfaces 210, 310 while ensuring that the cooling power of the fluid remains sufficiently uniform.

[0084] The correction distribution can compensate for overlay errors having a field plane variation of third order or higher, for example, in the x - direction of the field plane. The depth of the channels 220, 320 - 324 relative to the reflective surfaces 210, 310 along the length of the channels and the cross - sectional shape of the channels can be designed such that the controller 100 can operate to adjust the pressure of the fluid in the channels to apply at least a fourth - order polynomial deformation distribution to the reflective surface.

[0085] The dependence between the magnitude of the optical correction applied by the reflective surfaces 210, 310 and the pressure of the fluid in the channels 220, 320 - 324 can be assumed to be linear. Alternatively, by using the controller 100 to adjust the pressure of the fluid in the channels and using an optical sensor 120 (such as an interferometric wavefront sensor) to measure the effect on the wavefront of the reflected radiation B’, the dependence between the magnitude of the optical correction applied by the reflective surfaces 210, 310 and the pressure of the fluid in the channels 220, 320 - 324 can be modeled and calibrated numerically in the lithographic apparatus LA. The controller 100 can be configured to determine the pressure adjustment required to achieve the deformation of the reflective surfaces 210, 310, and the deformation of the reflective surfaces 210, 310 is required to apply a correction distribution of a desired magnitude to the patterned radiation beam B’. Generally speaking, increasing the pressure of the fluid in the channels 220, 320 - 324 can increase the magnitude of the correction distribution applied by the reflective surfaces 210, 310 to the patterned radiation beam B’.

[0086] The deformation of the reflective surfaces 210, 310 by the controller 100 can occur during the projection of the patterned radiation beam B'. The deformation of the reflective surfaces 210, 310 during the projection of the patterned radiation beam B' advantageously allows for reducing the registration error present within a single target portion of the substrate W and / or the registration error present between different target portions of the substrate W while the pattern is being projected onto the substrate W. Alternatively, the deformation of the reflective surfaces 210, 310 by the controller 100 can occur prior to the projection of the patterned radiation beam B', and the reflective surfaces can be held in their new shape during the projection of the patterned radiation beam B'. The reflectors MA-MT, 13, 14 and the controller 100 of the present disclosure can be used in combination with other optical element manipulators present in the projection system PS to control the registration of the lithographic apparatus LA.

[0087] The specific registration errors and corresponding applications of the reflectors MA-MT, 13, 14 and the controller 100 of the present disclosure are discussed below.

[0088] The reflectors MA-MT, 13, 14 and the controller 100 of the present disclosure can be used to apply a correction distribution that compensates for registration errors not caused by the optical aberrations of the projection system PS (e.g., registration errors caused by deformation of the mask MA and / or the substrate W, temperature variations of the mask MA and / or the substrate W, substrate processing effects, etc.) and registration errors caused by the optical aberrations of the lithographic apparatus LA. As previously discussed, the registration error can be expressed in the form of a field plane variation of the registration error having different polynomial orders. A correction distribution can be applied to adjust the wavefront of the radiation B' reflected from the reflective surfaces 210, 310 such that the correction distribution compensates for at least a third-order field plane variation of the registration error in the x direction of the field plane, for example, by applying a Zernike correction distribution that adjusts the wavefront reflected from the reflective surfaces 210, 310.

[0089] The correction distribution to be applied to the wavefront can be determined by determining the registration error, determining the correction to the registration error, and converting the correction to a desired wavefront adjustment. It should be understood that each of the steps of determining the registration error, determining the correction, and converting the correction to a desired wavefront adjustment can be performed in any of several suitable ways. The correction distribution (i.e., the adjustment to the wavefront that reduces the registration error) can then be determined, for example, by determining the values of a polynomial (e.g., Zernike) that induces a wavefront adjustment to reduce the registration error. The correction distribution can then be converted into the deformation of the reflective surfaces 210, 310 required to apply the correction distribution to the wavefront reflected from the reflective surfaces. The effect of an incremental adjustment of the pressure of the fluid in the channels 220, 320 - 324 on the wavefront of the radiation B' at different field plane positions can be measured and stored in a memory. The information stored in the memory can be referred to as reflector MA-MT, 13, 14 dependence.

[0090] When performing the transformation of the correction distribution into the deformation of the reflective surfaces 210, 310, the reflector MA-MT, 13, 14 dependencies can be used. For example, the correction distribution and the reflector MA-MT, 13, 14 dependencies can be provided to an algorithm that is configured to determine the pressure adjustment of the fluid in channels 220, 320 - 324 by the controller 100 so as to optimally apply the correction distribution to the wavefront. The algorithm can be configured to reduce or minimize the residual wavefront (i.e., reduce the difference between the desired "setpoint" wavefront and the actual "achieved" wavefront). The algorithm can be, for example, a least squares algorithm. Figure 4 A graph is shown that demonstrates the ability 420 of the reflector and controller of the present disclosure to control the third-order field plane variation of the overlay 400 compared to a known method 410. As can be seen, the setpoint overlay varies with the field position in the form of a third-order polynomial 400. The known method 410 relies only on the rigid mechanical movement of the reflective surface relative to the radiation beam and provides a poor fit to the setpoint overlay 400. The performance 420 of the reflector MA-MT-13, 14 and the controller 100 of the present disclosure, in combination with the rigid mechanical movement of the reflective surfaces 210, 310, provides a much better fit to the overlay setpoint 400.

[0091] Other types of algorithms can be used (such as algorithms that take into account the limitations of the deformation of the reflective surfaces 210, 310). Then the pressure of the fluid in channels 220, 320 - 324 can be adjusted such that the various parts of the reflective surfaces 210, 310 are in the relative positions required to apply the correction distribution to the wavefront. The wavefront incident on the deformed reflective surfaces 210, 310 is adjusted upon reflection from the reflective surface so as to reduce the determined overlay error.

[0092] In some device manufacturing methods, the substrate W can be processed between different lithographic exposures. That is, a layer of the substrate W can be exposed to patterned radiation B', and then the substrate W can be removed from the lithographic apparatus LA for substrate processing (such as polishing, etching, baking, etc.). After substrate processing, the substrate W can be inserted into the same lithographic apparatus LA (or a different lithographic apparatus), and another layer of the substrate W can be exposed to the patterned radiation beam B'. Substrate processing may result in overlay errors. The overlay errors caused by substrate processing can be referred to as substrate processing effects. For example, etching a layer of the substrate W may change the stress acting within the substrate (e.g., the stress at both ends of the scribe lanes of the substrate), and due to the change in the stress within the substrate, the position of the features present on the substrate may change from their intended positions. As another example, baking of the substrate W may cause thermal deformation of the substrate, which may cause the position of the features present on the substrate to change from their intended positions.

[0093] A correction distribution can correct substrate processing effects. For example, a first layer of substrate W can be exposed in a first lithographic exposure. The substrate W can be removed from the lithographic apparatus LA and subjected to substrate processing. The substrate W can then be reinserted into the lithographic apparatus LA, and a next layer of the substrate can be subjected to a second lithographic exposure. The overlay error between the first layer and the second layer can be measured, for example, by performing a lithographic exposure in a photoresist 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, for example). When a correction distribution is applied to the radiation beam B' by deforming the reflective surfaces 210, 310 of the reflectors MA-MT, 13, 14 via the controller 100, a correction distribution that reduces the measured overlay error can be determined. The correction distribution can then be applied to the radiation beam B' in future exposures to reduce the overlay error. Different correction distributions can be determined for different combinations of the lithographic apparatus LA and substrate processing.

[0094] The lithographic apparatus LA can include a support structure MT configured to support a mask MA. By supporting the mask MA, the support structure MT may induce an unwanted deformation of the mask. For example, the mask MA can be clamped (e.g., via vacuum clamping or electrostatic clamping) to the support structure MT. The act of clamping the mask MA to the support structure MT may deform the mask from its rest shape. The deformation of the mask MA may introduce an overlay error. A correction distribution can correct the deformation of the mask MA caused by the support structure MT supporting the mask.

[0095] During a lithographic exposure, the temperature of the mask MA may change. As a result of the mask temperature change, the mask MA may undergo thermal deformation. For example, the mask MA may absorb energy from the radiation beam B incident on the mask, and the temperature of the mask may increase. When the temperature of the mask increases, the mask MA may undergo thermal expansion. The thermal deformation of the mask MA may introduce an overlay error. A correction distribution can correct for the temperature change of the mask MA. For example, a computer model can be used to predict the overlay error caused by the temperature change of the mask MA. The computer model can be calibrated by comparing its results with the results of a lithographic exposure of a substrate W including a photoresist. The results of the computer model can be used to determine a correction distribution configured to reduce the overlay error. Alternatively, known alignment sensors (such as one or more interferometric wavefront sensors) can be used to measure the wavefront aberration. The measured wavefront aberration can then be used to determine the correction distribution. The correction distribution can be applied to the patterned radiation beam B' by deforming the reflective surfaces 210, 310 via the controller 100. The reflectors MA-MT, 13, 14 and the controller 100 of the present disclosure can be used to reduce the overlay error caused by the temperature change of the mask MA.

[0096] The lithographic apparatus LA may include a substrate table WT configured to hold a substrate W. For example, the substrate table WT may include protrusions configured to support the substrate W. The protrusions may apply a force on the substrate W, which causes the substrate to deform. The deformation of the substrate W may introduce 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 during the service life of the substrate table. For example, the protrusions may deteriorate over time, and thus the force applied by the protrusions to the substrate W may change over time.

[0097] The correction distribution may correct the deformation of the substrate W caused by the substrate table WT holding the substrate. For example, when the substrate is held by the substrate table WT, a topography measurement system may be used to measure the topography of the substrate W. 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 distribution. Alternatively, the overlay error caused by the deformation of the substrate W may be determined by performing a lithographic exposure in the photoresist on the substrate and measuring the overlay error of the 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 distribution. The reflective surfaces 210, 310 may be deformed by the controller 100 to reduce the overlay error caused by the deformation of the substrate W due to holding the substrate by the substrate table WT.

[0098] During the lithographic exposure, the temperature of the substrate W may change. Due to the substrate temperature change, the substrate W may undergo thermal deformation. For example, the substrate W may absorb energy from the patterned radiation beam B’ incident on the substrate, and the temperature of the substrate may increase. When the temperature of the substrate increases, the substrate W may undergo thermal expansion and deformation. The deformation of the substrate W may cause overlay errors. The correction distribution may correct the temperature change of the substrate W. The reflectors MA-MT, 13, 14 of the present disclosure and the controller 100 may be used to reduce the overlay error caused by the temperature change of the substrate W.

[0099] Figure 5 A flowchart of a method according to the present disclosure is shown. The method includes a first step 401 of providing a flow of fluid through channels 220, 320 - 324 formed in bodies 200, 300, on which the reflective surfaces 210, 310 of the lithographic apparatus LA are disposed.

[0100] 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 control the overlay of the lithographic apparatus LA.

[0101] The method includes a third step 403 of reflecting radiation B’ from the reflective surfaces 210, 310.

[0102] The depths of channels 220, 320 - 324 relative to the reflective surfaces 210, 310 can vary along the lengths of the channels. Channels 220, 320 - 324 can be one of a plurality of channels formed in bodies 200, 300 for conveying fluid. The method can include providing for the flow of fluid through at least two channels 220, 320 - 324 having different cross-sectional shapes. The method can include providing for the flow of fluid through at least two channels 220, 320 - 324, the cross-sectional shapes of the at least two channels 220, 320 - 324 having different orientations relative to the reflective surfaces 210, 310. The method can include adjusting the pressure of the fluid in channels 220, 320 - 324 to apply at least a fourth-order polynomial deformation distribution to the reflective surfaces 210, 310. The reflective surfaces 210, 310 can be at least partially spherical. The method can include adjusting the position of the reflective surfaces 210, 310.

[0103] A method of fabricating bodies 200, 300 of reflectors MA - MT, 13, 14 of a lithographic apparatus LA can include performing laser ablation to form channels 220, 320 - 324 in the bodies of the reflectors. Forming channels 220, 320 - 324 using laser ablation advantageously provides fine control over the depth profile and cross-sectional shape of the channels, thereby allowing for the formation of a greater variety of depth profiles and cross-sectional shapes. For example, compared to known channel formation methods (such as mechanical drilling in bodies 200, 300), using laser ablation can accurately profile channels 220, 320 - 324 into more “free-form” shapes (such as fourth-order polynomial shapes). Performing laser ablation to form channels 220, 320 - 324 can include varying the depth of channels 220, 320 - 324 relative to the reflective surface along the lengths of the channels 220, 320 - 324. A method of fabricating bodies 200, 300 of reflectors MA - MT, 13, 14 can include performing laser ablation to form at least two channels 220, 320 - 324 having different cross-sectional shapes. A method of fabricating bodies 200, 300 of reflectors MA - MT, 13, 14 can include performing laser ablation to form at least two channels 220, 320 - 324, the cross-sectional shapes of the at least two channels 220, 320 - 324 having different orientations relative to the reflective surface.

[0104] The method of using the reflectors MA-MT, 13, 14 described herein and the controller 100 to correct overlay errors can be retrofitted to exist in an existing lithographic apparatus LA without significant re-design of the lithographic apparatus. For example, the reflectors MA-MT, 13, 14 according to the present disclosure can replace previous reflectors, and the controller 100 of the lithographic apparatus LA can be reconfigured to apply a pressure adjustment to the fluid in the channels 220, 320-324 of the reflectors MA-MT, 13, 14. The method of correcting overlay errors described herein can then be performed using the reflectors MA-MT, 13, 14 and the controller 100. The controller can deform the reflective surfaces 210, 310 to apply different correction distributions at any desired frequency. For example, the correction distribution can be applied to the reflective surfaces 210, 310 during each batch of substrates W, each substrate, each target portion of the substrate, or during the exposure of a single target portion of the substrate. In general, the overlay error reduction achieved by using the reflectors MA-MT, 13, 14 and the controller 100 can be determined via direct measurement (e.g., using the detector system 120), indirect measurement (e.g., performing a lithographic exposure in the photoresist and analyzing the photoresist), and / or prediction (e.g., by inputting data into a computer model and executing the computer model).

[0105] Although the present text may specifically refer to the use of the lithographic apparatus LA in IC manufacturing, it should be understood that the lithographic apparatus described herein can have other applications. Possible other applications include manufacturing integrated optical systems, guiding and detecting patterns for magnetic domain memories, flat panel displays, liquid crystal displays (LCDs), thin film magnetic heads, and the like.

[0106] Where context permits, embodiments of the invention can be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the invention can also be implemented as instructions stored on a machine-readable medium that can be read and executed by one or more processors. A machine-readable medium can 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 can include read-only memory (ROM); random access memory (RAM); magnetic storage media; optical storage media; flash memory devices; electrical, optical, acoustic, or other forms of propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.). Additionally, firmware, software, routines, instructions can be described herein as performing certain actions. However, it should be understood that such descriptions are merely for convenience, and such actions are actually caused by a computing device, processor, controller, or other device executing the firmware, software, routines, instructions, etc., and in doing so may cause an actuator or other device to interact with the physical world.

[0107] Although specific embodiments of the present invention have been described above, it should be understood that the present invention can be practiced in other ways than those described. The above description is intended to be illustrative, not restrictive. Thus, those skilled in the art will appreciate that the described present invention can be modified without departing from the scope of the claims set forth below.

[0108] Additional embodiments are disclosed in the following numbered list of clauses:

[0109] 1. A lithographic apparatus, comprising:

[0110] 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; and,

[0111] 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.

[0112] 2. The lithographic apparatus according to clause 1, wherein the depth of the channel relative to the reflective surface varies along the length of the channel.

[0113] 3. The lithographic apparatus according to any one of the preceding clauses, wherein the channel is one of a plurality of channels formed in the body for conveying a fluid, and wherein at least two of the channels have different cross-sectional shapes,

[0114] and / or

[0115] wherein the cross-sectional shapes of at least two of the channels have different orientations relative to the reflective surface.

[0116] 4. The lithographic apparatus according to 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 can operate to adjust the pressure of the fluid in the channel to apply at least a fourth-order polynomial deformation distribution to the reflective surface.

[0117] 5. The lithographic apparatus according to clause 3 or 4, wherein the controller is configured to independently adjust the pressure of the fluid in at least two of the plurality of channels to control the deformation of the reflective surface.

[0118] 6. The lithographic apparatus according to any one of the preceding clauses, comprising:

[0119] An inlet pipe configured to supply fluid to the channel;

[0120] An outlet pipe configured to receive fluid from the channel; and,

[0121] A flow restrictor disposed on the outlet pipe.

[0122] 7. The lithographic apparatus according to clause 6, wherein the flow limiter comprises a pressure valve, and the controller is configured to control the pressure valve to adjust the pressure of the fluid in the channel.

[0123] 8. The lithographic apparatus according to any one of the preceding clauses, 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 use the optical measurement data to control the deformation of the reflective surface.

[0124] 9. The lithographic apparatus according to any one of the preceding clauses, comprising an actuator configured to adjust the position and / or orientation of the reflector.

[0125] 10. The lithographic apparatus according to any one of the preceding clauses, comprising:

[0126] An illumination system configured to condition a radiation beam;

[0127] A support structure configured to support a patterning device capable of imparting a pattern to the radiation beam in a cross-section thereof to form a patterned radiation beam;

[0128] A substrate table configured to hold a substrate; and,

[0129] A projection system configured to project the patterned radiation beam onto the substrate,

[0130] wherein the reflector is a mirror in the projection system.

[0131] 11. The lithographic apparatus according to any one of clauses 1 - 9, comprising:

[0132] An illumination system configured to condition a radiation beam;

[0133] A support structure configured to support a patterning device capable of imparting a pattern to the radiation beam in a cross-section thereof to form a patterned radiation beam;

[0134] A substrate table configured to hold a substrate; and,

[0135] A projection system configured to project the patterned radiation beam onto the substrate,

[0136] wherein the reflective surface forms part of the patterning device and the body forms part of the support structure.

[0137] 12. A method, comprising:

[0138] Providing a flow of fluid through a channel formed in a body, a reflective surface of a lithographic apparatus being disposed on the body;

[0139] Adjusting the pressure of the fluid to control deformation of the reflective surface and thereby control overlay of the lithographic apparatus; and,

[0140] Reflecting radiation from the reflective surface.

[0141] 13. The method according to clause 12, wherein a depth of the channel relative to the reflective surface varies along a length of the channel.

[0142] 14. The method according to clause 12 or 13, wherein the channel is one of a plurality of channels formed in the body for conveying fluid,

[0143] wherein the method includes providing a flow of fluid through at least two channels having different cross-sectional shapes,

[0144] and / or

[0145] wherein the method includes providing a flow of fluid through at least two channels, cross-sectional shapes of the at least two channels having different orientations relative to the reflective surface.

[0146] 15. The method according to clauses 13 and 14, including adjusting the pressure of the fluid in the channel to apply at least a fourth-order polynomial deformation profile to the reflective surface.

[0147] 16. The method according to clause 14 or 15, including independently adjusting the pressure of the fluid in at least two of the plurality of channels to control deformation of the reflective surface.

[0148] 17. The method according to any one of clauses 12 to 16, including adjusting a position and / or an orientation of the reflective surface.

[0149] 18. A method of manufacturing a body of a reflector of a lithographic apparatus according to any one of clauses 1 to 11, including performing laser ablation to form the channel.

[0150] 19. The method according to clause 18, 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.

[0151] 20. The method according to clause 18 or 19, including performing laser ablation to form at least two channels having different cross-sectional shapes,

[0152] and / or

[0153] performing laser ablation to form at least two channels, cross-sectional shapes of the at least two channels having different orientations relative to the reflective surface.

Claims

1. A lithographic apparatus, comprising: 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 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.

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

3. The lithographic apparatus according to any one of the preceding claims, wherein the channel is one of a plurality of channels formed in the body for conveying the fluid, and wherein at least two of the channels have different cross-sectional shapes, and / or wherein the cross-sectional shapes of at least two of the channels have different orientations relative to the reflective surface.

4. The lithographic apparatus according to claims 2 and 3, wherein the depth of the channel along the length of the channel relative to the reflective surface and the cross-sectional shape of the channel are designed such that the controller can operate to adjust the pressure of the fluid in the channel to apply at least a fourth-order polynomial deformation distribution to the reflective surface.

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

6. The lithographic apparatus according to any one of the preceding claims, comprising: an inlet pipe configured to supply the fluid to the channel; an outlet pipe configured to receive the fluid from the channel; and a flow limiter disposed on the outlet pipe.

7. The lithographic apparatus according to claim 6, wherein the flow limiter includes a pressure valve, and the controller is configured to control the pressure valve to adjust the pressure of the fluid in the channel.

8. The lithographic apparatus according to any one of the preceding claims, including 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 use the optical measurement data to control the deformation of the reflective surface.

9. The lithographic apparatus according to any one of the preceding claims, including an actuator configured to adjust the position and / or orientation of the reflector.

10. The lithographic apparatus according to any one of the preceding claims, comprising: an illumination system configured to condition the radiation beam; a support structure configured to support a patterning device that can impart a pattern to the radiation beam in a cross-section of the radiation beam to form a patterned radiation beam; a substrate table configured to hold a substrate; and, a projection system configured to project the patterned radiation beam onto the substrate, wherein the reflector is a mirror in the projection system.

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

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

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

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

15. The method according to claim 13 or claim 14, comprising 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 different orientations of cross - sectional shape relative to the reflective surface.

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