Optical System

Abstract

The optical system comprises at least one position sensor and an adjustable optical component, and is arranged to receive the radiation beam and to direct the radiation beam to the illumination area. The at least one position sensor is operable to determine a position of a part of the optical system. The adjustable optical component is configured to control an optical path of the received radiation beam in response to the determined position of the part of the optical system. The adjustable optical component may be configured to at least partially correct any variations in the spatial and / or angular distribution of the radiation in the illumination area due to any deviation of the determined position from a nominal position. The optical system may comprise an illumination system of an imaging apparatus (e.g., a lithography apparatus). Corresponding methods of providing radiation to the illumination area via the optical system are also claimed.

Description

[Technical Field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS)

[0001] This application claims priority to European Application No. 22216652.2, filed December 23, 2022, which is incorporated herein by reference in its entirety.

[0002] The present invention relates to an optical system for delivering a radiation beam to an illumination area. This optical system may be an illumination system in a lithographic apparatus. The present invention also relates to a corresponding method of providing radiation to an illumination area via an optical system. This method may form part of a lithographic exposure method. [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 may, for example, project a pattern (often referred to as a "design layout" or "design") in a patterning device (e.g., mask) onto a layer of radiation-sensitive material (resist) provided on a substrate (e.g., wafer).

[0004] As semiconductor manufacturing processes continue to advance, the dimensions of circuit elements have continually decreased, while the amount of functional elements, such as transistors, per device has steadily increased for decades, following a trend commonly referred to as "Moore's Law." To accommodate Moore's Law, the semiconductor industry pursues technologies that enable the creation of smaller and smaller features. To project a pattern onto a substrate, a lithography apparatus may use electromagnetic radiation. The wavelength of this radiation determines the minimum dimensions of the features patterned on the substrate. Typical wavelengths currently in use are 365 nm (i-line), 248 nm, 193 nm, and 13.5 nm. To form smaller features on a substrate than lithography apparatuses using radiation having a wavelength of, for example, 193 nm, lithography apparatuses using extreme ultraviolet (EUV) radiation, having wavelengths in the range of 4 nm to 20 nm, e.g., 6.7 nm or 13.5 nm, may be used.

[0005]

[0005] In a lithographic apparatus, radiation is delivered to the patterning device by an optical system that may be referred to as an illumination system. The illumination system may be arranged to condition the radiation beam so that it is delivered to the patterning device with a desired spatial and angular distribution. It would be desirable to provide alternative apparatus and methods for delivering radiation to an exposure region or patterning device that at least partially address one or more problems of prior art arrangements, whether or not identified herein. Summary of the Invention

[0006]

[0006] According to a first aspect of the present disclosure, there is provided an optical system for use in an imaging device, the optical system being arranged to receive a radiation beam (provided by a radiation source) at an entrance and to direct the radiation beam via an optical path to an illumination area, the optical system comprising at least one position sensor operable to determine a position and / or orientation of at least a part of the optical system, and an adjustable optical component configured to control the optical path of the received radiation beam in response to the determined position and / or orientation of the part of the optical system.

[0007]

[0007] During use, when at least part of the optical system moves, the spatial and / or angular distribution of radiation delivered to the illumination area may change, which may be undesirable. The optical system according to the first aspect is advantageous because it allows any movement (or variation in position and / or orientation) of at least part of the optical system to be corrected so that radiation is accurately delivered to the illumination area.

[0008] The optical system may be suitable for use in a lithographic apparatus. The optical system may comprise an illumination system of an imaging apparatus (e.g., a lithographic apparatus). Such an illumination system may be operable to condition a received radiation beam (e.g., from a radiation source or laser) and to deliver the received radiation to an illumination area (wherein a mask or reticle may be disposed) with a desired or required spatial and angular distribution.

[0009]

[0009] The optical system according to the first aspect is particularly useful for use in an illumination system of a lithographic apparatus, as will be described below.

[0010]

[0010] For precision imaging apparatus such as lithography apparatus, it can be crucial to illuminate a patterning device (also called a mask or reticle) with radiation having a well-defined spatial and angular distribution. For example, it is generally desirable to illuminate a patterning device with a generally uniform spatial distribution to ensure that the radiation dose delivered to a substrate (e.g., a resist-coated silicon wafer) is well controlled. This, in turn, can result in better critical dimension (CD) control. The angular distribution of radiation in an illumination area (where the patterning device is disposed) can also be referred to as the illumination mode or pupil. The angular distribution radiation in an illumination area (where the patterning device is disposed) describes how the cone of radiation illuminating each part of the patterning device is filled. This can be described by the intensity of radiation at the entrance pupil of projection optics arranged to image the patterning device onto the substrate. It is generally known that illuminating a patterning device with an illumination mode in which the periphery of the entrance pupil is illuminated but the center of the entrance pupil is not (e.g., annular illumination mode and dipole illumination mode) can generally improve the contrast of the image formed on the substrate for a wide range of different features (e.g., compared to full pupil-fill illumination).

[0011]

[0011] Any variations in the position and / or angle of the radiation delivered to the patterning device can affect the imaging of the patterning device onto the substrate. In particular, any pointing error of the radiation delivered to the illumination field can result in asymmetric numerical aperture (NA) clipping, especially for illumination modes in which the outermost part of the entrance pupil is illuminated (e.g. extreme dipole). This in turn will have a negative effect on the imaging of the patterning device, which is undesirable. It will be appreciated that the projection system of a lithographic apparatus generally provides numerical aperture clipping of the radiation beam patterned by a mask or patterning device. In practice, lithographic apparatus are used to image features that are small compared to the wavelength of the radiation beam, and therefore the image of the pattern formed on the wafer is usually diffraction limited, being formed only from very small diffraction orders of the radiation that has interacted with the mask. However, any asymmetric numerical aperture clipping of the radiation beam by the projection system may result in alignment errors. Slow changes in NA clipping (symmetry) result in position errors (i.e., moving averages) in the image formed on the wafer, while fast changes in clipping smear and contribute to blurring (increased mean standard deviation) of features formed on the wafer. It will be understood that "slow," as used herein, can mean over a time scale that is large compared to the wafer exposure time, and "fast" can mean over a time scale that is smaller than the wafer exposure time.

[0012]

[0012] The adjustable optical component may be configured to control the optical path of the received radiation beam in accordance with a determined position and / or orientation of a part of the optical system to at least partially correct any variations in the spatial and / or angular distribution of the radiation in the illumination area due to any deviation of the determined position and / or orientation from a nominal position.

[0013] For example, the optical system may have a nominal position. When disposed in the nominal position, the position and direction of radiation delivered to the illumination area may be optimal. During use, the optical system may be subjected to vibrations. For example, for embodiments in which the optical system is or forms part of an illumination system of a lithographic apparatus, movements of other parts of the lithographic apparatus during use may cause some vibrations of the optical system.

[0014]

[0014] Any deviation of the determined position and / or orientation from the nominal position may result in less than optimal illumination of the illumination area, and therefore, for such embodiments, adjustable optical components are used to at least partially correct any variations.

[0015]

[0015] As far as possible, the adjustable optical components may be configured so that the spatial and / or angular distribution of the radiation in the illumination area is largely independent of the determined position of the part of the optical system.

[0016]

[0016] The optical system may further comprise a radiation beam measurement sensor operable to determine a position and / or direction of the received radiation beam relative to at least part of the optical system. The adjustable optical component may be operable to control the optical path of the received radiation beam in response to the determined position and / or direction of the received radiation beam relative to at least part of the optical system.

[0017]

[0017] That is, the radiation beam measurement sensor can be used to align the received radiation beam with the optical system (using adjustable optics). This allows for correction of any alignment and / or pointing errors of the radiation beam received by the optical system. However, in such an arrangement, when the optical system itself moves, the radiation beam will also move and therefore the radiation beam will not be precisely aligned with the illumination area. However, since the adjustable optics is configured to control the optical path of the received radiation beam depending on a determined position of part of the optical system, any misalignment between the radiation beam and the illumination area can be corrected.

[0018]

[0018] At least a part of the optical system that is operable for the radiation beam measurement sensor to determine the position and / or direction of the radiation beam received therefrom may also be the same part of the optical system that is operable for at least one position sensor to determine its position and / or orientation.

[0019] Alternatively, in some embodiments, at least the part of the optical system for which the radiation beam measurement sensor is operable to determine the position and / or direction of the received radiation beam may be a different part of the optical system to the part of the optical system for which the at least one position sensor is operable to determine its position and / or orientation. For example, in one embodiment the radiation beam measurement sensor may be operable to determine the position and / or direction of the received radiation beam relative to a part of the optical system proximate the entrance, and the at least one position sensor may be operable to determine the position and / or orientation of a part of the optical system proximate the illumination area.

[0020]

[0020] It should be noted that the same actuatable or adjustable optical elements may be used both (a) to control the optical path of the received radiation beam in response to a determined position and / or orientation of a part of the optical system, and (b) to control the optical path of the received radiation beam in response to a determined position and / or direction of the received radiation beam. Alternatively, a first set of optical elements may be provided to control the optical path of the received radiation beam in response to a determined position and / or orientation of a part of the optical system, and a second set of optical elements may be provided to control the optical path of the received radiation beam in response to the determined position and / or direction of the received radiation beam. For such embodiments, the adjustable optical component may be considered to comprise both the first set of optical elements and the second set of optical elements.

[0021]

[0021] The optical system may include a plurality of position sensors, and the adjustable optical component may be operable to control the optical path of the received radiation beam in response to the position and / or orientation of a portion of the optical system determined by each of the plurality of position sensors.

[0022] This may allow more complex distortions of the optical system to be corrected, for example when the optical system is not simply vibrating as a whole, but is instead subjected to vibrations or vibration modes that correspond to the distortions of the optical system.

[0023]

[0023] At least one position sensor is operable to determine the position and / or orientation of at least a portion of the optical system. Such determination may be a direct measurement of the position and / or orientation. Alternatively, the determination may be indirect. For example, the position sensor may measure another quantity (e.g., acceleration) from which the position and / or orientation can be determined. Any suitable type of position sensor may be used. Generally, each position sensor determines the position and / or orientation of a portion of the optical system relative to a reference frame. The reference frame may be any frame in which the illumination field (also referred to in the art as an illumination slit or simply a slit) is stationary.

[0024] In some embodiments, the at least one position sensor is operable to determine the position and / or orientation of at least a portion of the optical system in all six degrees of freedom.

[0025]

[0025] The or each position sensor may comprise one or more accelerometers.

[0026] Such an embodiment determines the position and / or orientation of multiple parts of the optical system relative to an inertial coordinate system.

[0027] In one embodiment, the or each position sensor may comprise at least two accelerometers arranged to determine the acceleration of a portion of the optical system in at least two directions generally orthogonal to the optical path. This allows the position of the portion of the optics to be determined in two directions generally orthogonal to the optical path. In one embodiment, the or each position sensor may comprise at least three accelerometers arranged to determine the acceleration of a portion of the optical system in three linearly independent directions. This allows the position of the portion of the optics to be determined in three linearly independent directions.

[0028] In some embodiments, the or each accelerometer is operable to determine acceleration and / or position, and has three degrees of freedom. In one embodiment, the position sensor comprises two or three accelerometers, each arranged to determine three degrees of freedom. Advantageously, this may enable the position sensor to determine the position and / or orientation of at least part of the optical system in all six degrees of freedom.

[0029]

[0029] Alternative position sensors may include interferometric sensors, which may be, for example, of the type used to monitor the position of a reticle stage or wafer stage in a lithographic apparatus.

[0030]

[0030] The at least one position sensor may be optically downstream of the adjustable optical component.

[0031] Advantageously, this may allow the at least one position sensor to be as close as possible to the illumination area, which in turn may result in more precise control of the spatial and angular distribution of radiation in the illumination area.

[0032]

[0032] The optical system may further comprise a controller operable to receive a first signal from the position sensor or each position sensor indicating the position and / or orientation of a portion of the optical system, and to generate and send a control signal to the adjustable optical component, the control signal being dependent on one or more first signals.

[0033]

[0033] The controller may further be operable to receive a second signal from the radiation beam measurement sensor indicating the position and / or direction of the received radiation beam relative to the optical system, and the control signal may depend on one or more of the first signals and the second signal.

[0034]

[0034] The optical system may further comprise beam steering optics arranged to direct the radiation along an adjustable optical path.

[0035]

[0035] The beam steering optics may receive a radiation beam (e.g. from a radiation source). The beam steering optics may, for example, comprise two rotatable mirrors. By rotating the mirrors, the position and direction of the radiation beam downstream of the beam steering optics can be controlled.

[0036]

[0036] The adjustable optical component may comprise a beam steering optical component.

[0037]

[0037] The optical system may comprise pupil shaping optics operable to control the angular distribution of radiation delivered to the illumination area.

[0038]

[0038] That is, the illumination area can be illuminated using different illumination modes or pupils by selecting one or more configurations of the pupil-shaping optics.

[0039]

[0039] The pupil shaping optics may comprise a mirror array comprising a plurality of independently adjustable mirrors.

[0040]

[0040] The adjustable optics may comprise a pupil shaping optic.

[0041]

[0041] According to a second aspect of the present disclosure, there is provided a lithographic apparatus comprising an optical system according to the first aspect of the present disclosure operable to receive radiation and to direct at least a portion of the received radiation to an illumination area, a support structure configured to support a patterning device such that the patterning device is positionable within the illumination area, a substrate table configured to support a substrate, and a projection system operable to form an image of the patterning device supported by the support structure onto a substrate supported by the substrate table.

[0042] The lithographic apparatus according to the second aspect is advantageous because it allows any movement (or positional variation) of at least part of the optical system to be corrected so that radiation is more accurately delivered to the illumination field (where the patterning device is positioned in use). And, as explained above, any variation in the position and / or angle of radiation delivered to the patterning device can affect the imaging of the patterning device onto the substrate. In particular, any pointing error of the radiation delivered to the illumination field can result in asymmetric numerical aperture (NA) clipping, especially for illumination modes in which the outermost part of the entrance pupil is illuminated (e.g., extreme dipole). This in turn will adversely affect the imaging of the patterning device, which is undesirable. The lithographic apparatus according to the second aspect allows a wider range of illumination modes to be used without suffering from such problems (e.g., asymmetric NA clipping). Additionally or alternatively, a lithographic apparatus according to the second aspect allows for larger movements or vibrations of parts of the lithographic apparatus without suffering from such problems (e.g. asymmetric NA clipping), and allowing for larger movements or vibrations advantageously allows for an increase in throughput of the lithographic apparatus and an associated reduction in manufacturing cost per wafer.

[0043]

[0043] According to a third aspect of the present disclosure, there is provided a method for providing radiation to an illumination area via an optical system, the method comprising determining a position and / or orientation of at least a portion of the optical system and adjusting at least one optical element of the optical system in accordance with the determined position of the portion of the optical system.

[0044] The method according to the third aspect may be carried out using the optical system according to the first aspect. The method according to the third aspect is advantageous because it allows any movement (or variation in position and / or orientation) of at least part of the optical system to be corrected so that radiation is accurately delivered to the illumination area.

[0045] The method according to the third aspect is particularly beneficial for use in illuminating a patterning device (also called a reticle or mask) as part of a lithographic exposure process. For example, any variations in the position and / or angle of radiation delivered to the patterning device can affect the imaging of the patterning device onto the substrate. In particular, any pointing error of the radiation delivered to the illumination field can result in asymmetric numerical aperture (NA) clipping, especially for illumination modes where the outermost part of the entrance pupil is illuminated (e.g., extreme dipole). This in turn will adversely affect the imaging of the patterning device, which is undesirable.

[0046]

[0046] Adjusting at least one optical element of the optical system in accordance with the determined position and / or orientation of a part of the optical system may comprise at least partially correcting any variations in the spatial and / or angular distribution of radiation in the illumination area due to any deviation of the determined position and / or orientation from a nominal position.

[0047] For example, the optical system may have a nominal position. When disposed in the nominal position, the position and direction of radiation delivered to the illumination area may be optimal. During use, the optical system may be subjected to vibrations. For example, for embodiments in which the optical system is or forms part of an illumination system of a lithographic apparatus, movements of other parts of the lithographic apparatus during use may cause some vibrations of the optical system.

[0048]

[0048] Any deviation of the determined position and / or orientation from the nominal position may result in less than optimal illumination of the illumination area, and therefore, for such embodiments, at least one optical element (which may be referred to as an adjustable optical component) is used to at least partially correct any variations.

[0049]

[0049] As far as possible, adjusting at least one optical element of the optical system in accordance with the determined position and / or orientation of a part of the optical system can be carried out so that the spatial and / or angular distribution of radiation in the illumination area is generally independent of the determined position of the part of the optical system.

[0050]

[0050] The method may further comprise providing a radiation beam, determining a position and / or direction of the provided radiation beam relative to at least a portion of the optical system, and adjusting at least one optical element of the optical system in accordance with the determined position and / or direction of the provided radiation beam relative to at least a portion of the optical system.

[0051]

[0051] The method may comprise determining the positions and / or orientations of multiple parts of the optical system and adjusting at least one optical element of the optical system in accordance with the determined positions and / or orientations of each of the multiple parts of the optical system.

[0052] This may allow more complex distortions of the optical system to be corrected, for example when the optical system is not simply vibrating as a whole, but is instead subjected to vibrations or vibration modes that correspond to distortions of the optical system.

[0053]

[0053] At least one part of the optical system whose position and / or orientation is determined may be optically downstream of at least one optical element that is adjusted accordingly.

[0054] Advantageously, this may allow at least one part of the optical system, the position and / or orientation of which is determined, to be as close as possible to the illumination area, which in turn may result in more precise control of the spatial and angular distribution of radiation in the illumination area.

[0055]

[0055] The method may further comprise adjusting the radiation beam to control the spatial and / or angular distribution of the radiation delivered to the illumination area.

[0056]

[0056] According to a fourth aspect of the present disclosure, there is provided a lithographic exposure method, the method comprising providing a patterning device within an illumination area, using the method of the third aspect of the present disclosure, providing radiation to the illumination area via an optical system to form a patterned radiation beam, and collecting the patterned radiation beam and using it to form an image of the patterning device on a substrate.

[0057] The lithographic exposure method according to the fourth aspect is advantageous because it allows any movement (or variation in position and / or orientation) of at least part of the optical system to be corrected so that radiation is more accurately delivered to the illumination field (where the patterning device is provided). And, as explained above, any variation in the position and / or angle of the radiation delivered to the patterning device may affect the imaging of the patterning device onto the substrate. In particular, any pointing error of the radiation delivered to the illumination field may result in asymmetric numerical aperture (NA) clipping (in the step of collecting the patterned radiation beam), especially for illumination modes in which the outermost part of the entrance pupil is illuminated (e.g. extreme dipole). This in turn will adversely affect the imaging of the patterning device, which is undesirable. The lithographic exposure method according to the fourth aspect allows a wider range of illumination modes to be used without suffering from such problems (e.g. asymmetric NA clipping). Additionally or alternatively, the lithographic exposure method according to the fourth aspect allows for larger movements or vibrations of parts of the lithographic apparatus without suffering from such problems (e.g. asymmetric NA clipping), and allowing for larger movements or vibrations advantageously allows for an increase in throughput of the lithographic apparatus and an associated reduction in manufacturing cost per wafer.

[0058]

[0058] The exposure may be a scanning exposure, such that providing a patterning device within the illumination area may comprise moving the patterning device through the illumination area, and forming an image of the patterning device on the substrate may comprise moving the substrate so that the image of the patterning device is generally stationary relative to the substrate. [Brief explanation of the drawings]

[0059]

[0059] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which:

[0060] [Figure 1] 1 shows a first schematic overview of a lithographic apparatus; [Figure 2] 2 shows a second schematic view of a lithographic apparatus; [Figure 3] 3 is a schematic diagram of an optical system according to an embodiment of the present disclosure that may form part of the lithographic apparatus shown in Figures 1 and / or 2, the optical system being shown in a first, nominal position and / or configuration. [Figure 4A] The optical system shown in FIG. 3 is shown in a second, non-nominal or distorted position and / or configuration. [Figure 4B] 4A shows the optical system shown in FIG. 3 in a second, non-nominal or distorted position and / or configuration (also shown in FIG. 4A), in which adjustable optical components are used to at least partially correct for the effects that variations from the first, nominal position and / or configuration (see FIG. 3) may have on the spatial and / or angular distribution of radiation in the illumination area. [Figure 5] 1 is a schematic diagram of a first method of providing radiation to an illumination area via an optical system according to an embodiment of the present disclosure. FIG. [Figure 6] FIG. 10 is a schematic diagram of a second method of providing radiation to an illumination area via an optical system according to an embodiment of the present disclosure. [Figure 7] FIG. 7 is a schematic diagram of a lithographic exposure method according to an embodiment of the present disclosure, which may comprise the method of FIGS. 5 and / or 6. DETAILED DESCRIPTION OF THE INVENTION

[0061]

[0060] In this document, the terms "radiation" and "beam" are used to encompass all types of electromagnetic radiation, including ultraviolet (e.g., having a wavelength of 365 nm, 248 nm, 193 nm, 157 nm, or 126 nm) and EUV (extreme ultraviolet, e.g., having a wavelength in the range of about 5 nm to 100 nm).

[0062]

[0061] As used herein, the terms "reticle," "mask," or "patterning device" may be broadly interpreted as referring to a general-purpose patterning device that can be used to impart a patterned cross section to an incoming radiation beam that corresponds to the pattern to be created in a target portion of a substrate. The term "light valve" may also be used in this context. Besides the classic mask (transmissive or reflective mask, binary mask, phase-shifting mask, hybrid mask, etc.), examples of other such patterning devices include programmable mirror arrays and programmable LCD arrays.

[0063] 1 schematically illustrates a lithographic apparatus LA. The lithographic apparatus LA includes an illumination system (also called an illuminator) IL configured to condition a radiation beam B (e.g. UV radiation, DUV radiation, or EUV radiation), a mask support (e.g. a mask table) MT constructed to support a patterning device (e.g. a mask) MA and coupled to a first positioner PM configured to accurately position the patterning device MA according to certain parameters, a substrate support (e.g. a wafer table) WT constructed to hold a substrate (e.g. a resist-coated wafer) W and coupled to a second positioner PW configured to accurately position the substrate support according to certain parameters, and a projection system (e.g. a refractive projection lens system) PS configured to project a pattern imparted to the radiation beam B by the patterning device MA onto a target portion C (e.g. comprising one or more dies) of the substrate W.

[0064]

[0063] In operation, the illumination system IL receives a radiation beam from the radiation source SO, for example via the beam delivery system BD. The illumination system IL may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic and / or other types of optical components, or any combination thereof, for directing, shaping and / or controlling the radiation. The illuminator IL may be used to condition the radiation beam B so that it has a desired spatial and angular intensity distribution in its cross-section in the plane of the patterning device MA.

[0065]

[0064] The term "projection system" PS as used herein should be interpreted broadly as covering various types of projection systems including refractive optical systems, reflective optical systems, catadioptric optical systems, anamorphic optical systems, magnetic optical systems, electromagnetic optical systems and / or electrostatic optical systems, or any combination thereof, as appropriate depending on, for example, the exposure radiation used and / or other factors such as the use of an immersion liquid or the use of a vacuum. Where the term "projection lens" is used herein, this may be considered as synonymous with the more general term "projection system" PS.

[0066]

[0065] The lithographic apparatus LA may be of a type in which at least a portion of the substrate may be covered by a liquid having a relatively high refractive index, for example water, so as to fill a space between the projection system PS and the substrate W. This is also known as immersion lithography. Further information about immersion techniques is given in US Patent No. 6,952,253, which is incorporated herein by reference.

[0067] The lithographic apparatus LA may be of a type having two or more substrate supports WT (also known as "dual stage"). In such a "multi-stage" machine, the substrate supports WT may be used in parallel, and / or a substrate W on one substrate support WT may be used to expose a pattern on this substrate W while a preparation step for a subsequent exposure of the substrate W is performed on a substrate W located on another substrate support WT.

[0068] In addition to the substrate support WT, the lithographic apparatus LA may comprise a measurement stage. The measurement stage is arranged to hold a sensor and / or a cleaning device. The sensor may be arranged to measure a property of the projection system PS or a property of the radiation beam B. The measurement stage may hold a plurality of sensors. The cleaning device may be arranged to clean part of the lithographic apparatus, for example part of the projection system PS or part of a system for providing immersion liquid. The measurement stage may be movable below the projection system PS when the substrate support WT is spaced apart from the projection system PS.

[0069] In operation, the radiation beam B is incident on a patterning device, for example a mask MA, which is held on the mask support MT, and is patterned according to a pattern (design layout) present on the patterning device MA. Having traversed the mask MA, the radiation beam B passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W. With the aid of the second positioner PW and the position measurement system IF, the substrate support WT can be accurately moved, for example to position different target portions C at focused and aligned positions in the path of the radiation beam B. Similarly, the first positioner PM, and possibly further position sensors (not explicitly shown in FIG. 1 ), can be used to accurately position the patterning device MA with respect to the path of the radiation beam B. The patterning device MA and substrate W may be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. Although the substrate alignment marks P1, P2 are shown occupying dedicated target portions, they may be located in spaces between the target portions. When the substrate alignment marks P1, P2 are located between target portions C, they are known as scribe-lane alignment marks.

[0070] To clarify the invention, a Cartesian coordinate system is used. The Cartesian coordinate system has three axes: x, y, and z. Each of the three axes is orthogonal to the other two. Rotation about the x-axis is called Rx rotation. Rotation about the y-axis is called Ry rotation. Rotation about the z-axis is called Rz rotation. The x- and y-axes define a horizontal plane, while the z-axis is vertical. The Cartesian coordinate system is not a limitation of the invention and is used for clarity only. Alternatively, another coordinate system, such as a cylindrical coordinate system, may be used to clarify the invention. The orientation of the Cartesian coordinate system may be different, for example, the z-axis may have a component along the horizontal plane.

[0071] Figure 2 is a second schematic illustration of a lithographic apparatus LA. The lithographic apparatus LA shown in Figure 2 is generally in the form of the lithographic apparatus LA shown in Figure 1. In particular, the lithographic apparatus LA shown in Figure 2 also comprises an illumination system IL configured to condition a radiation beam B, a mask support MT constructed to support a patterning device MA, a substrate support WT constructed to hold a substrate W, and a projection system PS configured to project a pattern imparted to the radiation beam B by the patterning device MA onto a target portion of the substrate W. The lithographic apparatus LA shown in Figure 2 may comprise any of the features discussed above in relation to the lithographic apparatus LA shown in Figure 1.

[0072]

[0071] In use, the illumination system IL receives a radiation beam B from a radiation source SO via a beam steering unit BSU. The beam delivery system BD shown in Figure 1 may be generally equivalent to the beam steering unit BSU shown in Figure 2.

[0073] The beam steering unit BSU is operable to receive a radiation beam from the radiation source SO and to deliver the radiation beam to the illumination system IL via an adjustable optical path OP. The adjustability of the optical path OP is achieved by (at least) two beam steering mirrors BS1, BS2 which form part of the optical path OP. Each of the beam steering mirrors BS1, BS2 can be rotated to vary the optical path OP. The beam steering unit BSU further comprises (at least) two beam measurement sensors BM1, BM2. Each of the beam measurement sensors BM1, BM2 is operable to measure the position of the radiation beam B (relative to the beam steering unit BSU) as it propagates along the optical path OP.

[0074]

[0073] In use, the two beam measurement sensors BM1, BM2 and the two beam steering mirrors BS1, BS2 may be used as a feedback loop as follows: The beam measurement sensors BM1, BM2 may be used to determine any deviation of the optical path OP of the radiation beam B from an optimal or nominal optical path of the radiation beam B as it leaves the beam steering unit and enters the illumination system IL. These measurements may be used to control the orientation of the two beam steering mirrors BS1, BS2 to reduce any such deviation of the optical path OP of the radiation beam B from an optimal or nominal optical path of the radiation beam B as it leaves the beam steering unit and enters the illumination system IL. This may be achieved using, for example, a control loop algorithm executed by a controller which may be operable to receive signals from the beam measurement sensors BM1, BM2 and to send control signals to the beam steering mirrors BS1, BS2. In this manner, the beam steering unit BSU may be operable to maintain the position and orientation of the radiation beam B as it exits the beam steering unit BSU (and enters the illumination system IL) substantially independently of the position and orientation of the radiation beam B as it enters the beam steering unit BSU.

[0075] In addition to the optical components described above, the beam steering unit BSU further comprises a mirror M, which also forms part of the optical path OP. It will be understood that in other embodiments such a mirror M may not be present and that in other embodiments the beam steering unit BSU may further comprise one or more additional optical components.

[0076] In this embodiment, the illumination system IL comprises pupil shaping optics PSO, a masking device MD and relay optics RL.

[0077] The pupil shaping optics PSO are operable to control the angular distribution of radiation delivered to an illumination area in the plane of the patterning device MA. That is, the illumination area can be illuminated using different illumination modes or pupils by selecting one or more configurations of the pupil shaping optics PSO. The pupil shaping optics PSO may, for example, comprise a mirror array comprising a plurality of independently adjustable mirrors. By controlling the orientation of the plurality of independently adjustable mirrors, the illumination mode (or pupil shape) of the radiation beam at the patterning device MA can be controlled.

[0078] The masking device MD is operable to control the extent of the illumination field in the plane of the patterning device MA. For example, the masking device MD may comprise two pairs of masking blades, each pair of masking blades arranged to define the extent of the illumination field in a different one of two directions in the plane of the patterning device MA. For example, the masking device MD may comprise a pair of x masking blades arranged to define the extent of the illumination field in a first direction in the plane of the patterning device MA, and a pair of y masking blades arranged to define the extent of the illumination field in a second direction in the plane of the patterning device MA. The masking device MD may be arranged such that during exposure of one target area of ​​the substrate W, an adjacent target area of ​​the substrate W does not receive radiation.

[0079] In some embodiments, the lithographic apparatus LA may be a scanning lithographic apparatus LA (also known simply as a scanner). In a scanner, the extent of the pattern on the patterning device MA in the scan direction may be larger than the extent of the illumination field in the plane of the patterning device MA. To image the pattern onto a target area of ​​the substrate W, the patterning device is moved or scanned through the illumination field in the scan direction. It will be appreciated that the substrate W is also scanned relative to the illumination field in the plane of the substrate W. It will be appreciated that the movement of the substrate W is such that the aerial image of the patterning device MA is stationary relative to the substrate W, and that the direction and speed of the substrate W may generally differ from that of the patterning device MA (for example, if the image is inverted and / or if a demagnification is applied by the projection system PS).

[0080]

[0079] In an embodiment in which the lithographic apparatus LA is a scanning lithographic apparatus, a masking blade (which may be a y masking blade) that defines the extent of the illumination area in the scanning direction may move during scanning exposure of one target area of ​​the substrate W so that adjacent target areas of the substrate W do not receive radiation.

[0081] The relay optics RL are positioned to image the masking device MD (or its masking blade) onto the plane of the patterning device MA. That is, the relay optics RL may ensure that the plane of the masking device MD (or its masking blade) is conjugate to the plane of the patterning device MA (and substrate W). Such a plane that is conjugate to the plane of the patterning device MA (and substrate W) may be called the field plane. This ensures that the masking device MD is sharply imaged onto the substrate, thereby minimizing the amount of radiation received by adjacent target areas when any given target area is exposed to the radiation beam B.

[0082] Some known lithographic apparatus LA use a beam steering unit BSU of the type shown in Figure 2 and described above to at least partially correct any position or pointing error of the radiation beam B received from the radiation source SO. In other words, the beam steering unit BSU may be considered to be arranged to align the received radiation beam B with a nominal optical path through the illumination system IL.

[0083] An optical system 100 according to an embodiment of the present disclosure will now be described with reference to Figures 3 to 4B. The optical system 100 is for use in an imaging apparatus such as the lithographic apparatus LA described above with reference to Figures 1 and 2. For example, the optical system 100 may be, comprise, or form part of the illumination system IL of the lithographic apparatus LA described above with reference to Figures 1 and 2.

[0084]

[0083] Optical system 100 is arranged to receive a radiation beam 102 at an entrance 104 and to direct the radiation beam 102 via an optical path to an illumination region 106, as will be described further below. In use, a patterning device MA of lithographic apparatus LA may be disposed within illumination region 106. Optical system 100 comprises a position sensor 108 and an adjustable optical component 110.

[0085] Position sensor 108 is operable to determine the position and / or orientation of at least a portion of optical system 100. For example, position sensor 108 may be operable to determine the position and / or orientation of the portion of optical system 100 to which it is attached.

[0086]

[0085] The adjustable optical component 110, in this example, comprises two mirrors 112, 114. The adjustable optical component 110 is configured to control the optical path of the received radiation beam 102. In particular, the adjustable optical component 110 is configured to control the optical path of the received radiation beam 102 in response to a determined position and / or orientation of a part of the optical system 100 (as determined by the position sensor 108).

[0087]

[0086] The optical system 100 further comprises a controller 116. The controller 116 is operable to receive a first signal s1 indicative of a position and / or orientation of a portion of the optical system 100 from the position sensor 108. The controller 116 is further operable to receive a control signal s1. C and transmitting to the tunable optical component 110, the control signal being dependent on the one or more first signals s1.

[0088]

[0087] The adjustable optical component 110 may be configured to control the optical path of the received radiation beam 102 in response to a determined position and / or orientation of a portion of the optical system 100, as will now be described with reference to Figures 4A to 4B, to at least partially correct any variations in the spatial and / or angular distribution of radiation in the illumination area 106 due to any deviation of the determined position and / or orientation from a nominal position.

[0089] The radiation beam 102 may exit the optical system 100 at an outlet 118. After leaving the outlet 118, the radiation beam 102 may propagate to the illumination region 106. The radiation beam may be aligned with the optical system 100 at the outlet 118. This is shown schematically in Figures 3 to 4B as the radiation beam 102 being aligned with an exit axis 120 of the optical system 100.

[0090] In use, the optical system 100 may have a nominal position. When disposed in the nominal position, the position and direction of radiation delivered to the illumination area 106 may be optimal. The optical system 100 is shown in the nominal position and configuration in FIG. 3. In this nominal position, the output axis 120 of the optical system 100 is aligned with the axis 122 of the illumination area 106, as shown very diagrammatically in FIG. 3.

[0091] However, during use, optical system 100 may be subjected to vibrations. For example, for embodiments in which the optical system comprises, is, or forms part of an illumination system IL of lithographic apparatus LA, movements of other parts of lithographic apparatus LA (e.g., mask support MT and / or substrate support WT) during use may cause some vibrations of optical system 100. This may in turn lead to deviations in the position and / or orientation of optical system 100 relative to illumination field 106, as determined by position sensor 108.

[0092]

[0091] Any such deviation of the determined position and / or orientation (e.g., of the position sensor 108) from a nominal position may result in less than optimal illumination of the illumination area 106 (see FIG. 4A), and the adjustable optical component 110 can be used to at least partially correct any such variations (see FIG. 4B).

[0093] For example, the optical system 100 may be subjected to vibrations that cause the position sensor 108 to move up and down within the plane of FIG. 3 . Any deviation of the position sensor 108 (and therefore the part of the optical system 100 to which it is mounted) may result in misalignment of the output axis 120 of the optical system 100 with respect to the axis 122 of the illumination field 106. For example, as shown in FIG. 4A , if the optical system 100 moves such that the position sensor 108 moves up, the output axis 120 of the optical system 100 may be at a non-zero angle with respect to the axis 122 of the illumination field 106. When the radiation beam 102 is aligned with the output axis 120 of the optical system 100, it is no longer aligned with the axis 122 of the illumination field 106. This results in an undesirable change in the angular distribution of radiation in the illumination field 106 (relative to the angular distribution of radiation in the illumination field 106 when the optical system 100 is in the nominal position of FIG. 3 ). However, as shown in FIG. 4B, optical system 100 is arranged to compensate for this using adjustable optical component 110.

[0094] Specifically, (control signal s C By appropriate rotation of the two mirrors 112, 114 of the adjustable optical element (under the control of ), the radiation beam 102 can be aligned with the axis 122 of the illumination area 106.

[0095] 4A and 4B, the optical system 100 is described as being arranged to correct for any up and down movement of the position sensor 108 using the adjustable optical component 110. It will be understood that this is a simplified example shown in FIGS. 4A and 4B merely to illustrate the principles of the correction applied by the adjustable optical component 110. It should be noted that in practice, the adjustable optical component 110 is operable to correct for any movement (i.e., change in position and / or orientation) of one or more position sensors 108 in all six degrees of freedom.

[0096] To the extent possible, the adjustable optical component 110 may be configured such that the spatial and / or angular distribution of radiation 102 in the illumination field 106 is substantially independent of the determined position and / or orientation of parts of the optical system 100 (as determined by the position sensor 108). That is, the position sensor 108 and the adjustable optical component 110 form a feedback loop that automatically corrects for movements of the optical system 100 (as shown in FIG. 4B ).

[0097] In contrast to known arrangements of an illumination system IL of a lithographic apparatus, in which the radiation beam is generally aligned with the illumination system IL (for example using a beam steering unit BSU), the optical system 100 shown in Figures 3 to 4B is arranged to create a misalignment between the radiation beam 102 and the optical system 100. In particular, this misalignment is arranged to automatically compensate for movements of the optical system 100 (as shown in Figure 4B).

[0098] During use, if at least a part of the optical system 100 moves, the spatial and / or angular distribution of the radiation 102 delivered to the illumination area 106 may change, which may be undesirable. The optical system 100 shown in Figures 3 to 4B is advantageous because it allows any movement (or variation in position and / or orientation) of at least a part of the optical system 100 to be corrected so that the radiation 102 is accurately delivered to the illumination area 106.

[0099] The optical system 100 may be suitable for use in a lithographic apparatus LA. The optical system may comprise, be, or form part of an illumination system IL of an imaging apparatus (e.g. lithographic apparatus LA). Such an illumination system IL may be operable to condition a received radiation beam (e.g. from a radiation source or laser) and to deliver the received radiation to an illumination area (on which a mask or reticle MA may be arranged) with a desired or required spatial and angular distribution.

[0100]

[0099] The optical system 100 is particularly useful for use in an illumination system IL of a lithographic apparatus LA, as will now be described.

[0101] For precision imaging apparatus such as lithographic apparatus LA, it can be crucial to illuminate the patterning device MA (also called a mask or reticle) with radiation having a well-defined spatial and angular distribution. For example, it is generally desirable to illuminate the patterning device MA with a generally uniform spatial distribution to ensure that the radiation dose delivered to the substrate W (e.g., a resist-coated silicon wafer) is well controlled. This, in turn, can result in better critical dimension (CD) control. The angular distribution of radiation in the illumination area (where the patterning device MA is disposed) can also be referred to as the illumination mode or pupil. The angular distribution radiation in the illumination area (where the patterning device MA is disposed) describes how the cone of radiation illuminating each part of the patterning device MA is filled. This can be described by the intensity of radiation at the entrance pupil of projection optics PS, which is arranged to image the patterning device MA onto the substrate W. It is generally known that illuminating the patterning device MA with an illumination mode in which the periphery of the entrance pupil is illuminated and the center of the entrance pupil is not illuminated (e.g., annular illumination mode and dipole illumination mode) can generally improve the contrast of the image formed on the substrate for a wide range of different features (e.g., compared to full pupil-fill illumination).

[0102] Variations in the position and / or angle of the radiation delivered to the patterning device MA can affect the imaging of the patterning device MA onto the substrate W. In particular, any pointing errors of the radiation delivered to the illumination field can result in asymmetric numerical aperture (NA) clipping, especially for illumination modes in which the outermost part of the entrance pupil is illuminated (e.g. extreme dipole). This in turn will have a negative effect on the imaging of the patterning device MA, which is undesirable. It will be appreciated that the projection system PS typically provides numerical aperture clipping of the radiation beam B patterned by the mask MA. In practice, lithographic apparatus LA are used to image features that are small compared to the wavelength of the radiation beam B, and therefore the image of the pattern formed on the wafer W is typically diffraction limited, being formed only from very small diffraction orders of the radiation that has interacted with the mask MA. However, any asymmetric numerical aperture clipping of the radiation beam by the projection system PS may result in alignment errors. Slow changes in NA clipping (symmetry) result in position errors (i.e., moving averages) in the image formed on the wafer W, whereas fast changes in NA clipping smear and contribute to blurring (increased mean standard deviation) of features formed on the wafer W. It will be understood that "slow" as used herein can mean over a time scale that is large compared to the wafer exposure time, and "fast" can mean over a time scale that is smaller than the wafer exposure time.

[0103] As mentioned above, in the absence of the feedback loop provided by the position sensor 108 and adjustable optics (via the controller 116), near the outlet 118 the radiation beam 102 may be aligned with the output axis 120 of the optical system 100. This may be achieved by providing the radiation beam 102 to the optical system 100 such that the radiation beam 102 is aligned with the output axis 120 of the optical system 100 when the optical system 100 is in a nominal position or configuration. Alternatively, in some embodiments this may be achieved using the adjustable optics 110, as will now be described.

[0104] 3 further comprises a radiation beam measurement sensor 124. The radiation beam measurement sensor 124 is operable to determine a position and / or direction of the received radiation beam 102 relative to at least a portion of the optical system 100. The adjustable optical component 110 is operable to control the optical path of the received radiation beam 102 in response to the determined position and / or direction of the received radiation beam 102 (as determined by the radiation beam measurement sensor 124) relative to at least a portion of the optical system 100.

[0105] The controller 116 is further operable to receive a second signal s2 from the radiation beam measurement sensor 124 indicative of the position and / or direction of the received radiation beam 102 relative to the optical system 100. Furthermore, in such an embodiment, the control signal s C depends on the first signal s1, the second signal s2, or both the first signal s1 and the second signal s2.

[0106] That is, the radiation beam measurement sensor 124 may be used to align the received radiation beam 102 with the optical system 100 (using the adjustable optics 110) such that the radiation beam 102 is aligned with the exit axis 120 of the optical system 100 when the optical system 100 is in a nominal position or configuration. This may correct for any alignment and / or pointing errors of the radiation beam 102 received by the optical system 100. This may correct for any misalignment between the radiation beam 102 received by the optical system 110 and the entrance axis 126 of the optical system 100.

[0107] However, in such an arrangement without the above-mentioned feedback loop using position sensor 108 and adjustable optics, movement of the optical system 100 itself will cause movement of the radiation beam 102, and therefore (as shown in Figure 4A and described above) the radiation beam 102 will not be precisely aligned with the illumination area 106. However, because the adjustable optics 110 is configured to control the optical path of the received radiation beam 102 in response to determined positions and / or orientations of parts of the optical system 100, any such misalignment between the radiation beam 102 and the illumination area 106 can be corrected.

[0108] In this embodiment, at least the portion of the optical system 100 for which the radiation beam measurement sensor 124 is operable to determine the position and / or direction of the received radiation beam 102 is a different portion of the optical system 100 to the portion of the optical system 100 for which the position sensor 108 is operable to determine its position and / or orientation. For example, in this embodiment the radiation beam measurement sensor 124 is operable to determine the position and / or direction of the received radiation beam 102 relative to the portion of the optical system 100 proximate the entrance 104, and the position sensor 108 is operable to determine the position and / or orientation of the portion of the optical system 100 proximate the illumination area 106. In other embodiments, the portion of the optical system 100 for which the radiation beam measurement sensor 124 is operable to determine the position and / or direction of the received radiation beam 102 may be the same portion of the optical system 100 for which the position sensor 108 is operable to determine its position and / or orientation.

[0109] Furthermore, in this embodiment, the position sensor 108 is optically downstream of the adjustable optics 110. Advantageously, this may allow the position sensor 108 to be as close as possible to the illumination area 106. This may in turn result in more precise control of the spatial and angular distribution of the radiation 102 in the illumination area 106.

[0110] It should be noted that the same actuable or adjustable optical elements (e.g. mirrors 112, 114 of adjustable optical component 110) may be used both (a) to control the optical path of the received radiation beam 102 in response to a determined position and / or orientation of a part of the optical system (determined by position sensor 108), and (b) to control the optical path of the received radiation beam 102 in response to a determined position and / or direction of the received radiation beam 102 (determined by radiation beam measurement sensor 124). Alternatively, a first set of optical elements may be provided to control the optical path of the received radiation beam 102 in response to a determined position and / or orientation of a part of the optical system 100 (determined by position sensor 108), and a second set of optical elements may be provided to control the optical path of the received radiation beam in response to the determined position and / or direction of the received radiation beam (determined by radiation beam measurement sensor 124). For such embodiments, adjustable optic 110 may be considered to comprise both the first set of optical elements and the second set of optical elements.

[0111] In some alternative embodiments, the optical system 100 may comprise a plurality of position sensors 108, each operable to determine the position and / or orientation of at least a portion of the optical system 100. For example, each position sensor 108 may be operable to determine the position and / or orientation of the portion of the optical system 100 to which it is attached. The multiple position sensors 108 may be disposed in different portions of the optical system 100, for example, but not limited to, in the relay lens RL or in the masking device MD. For such embodiments having multiple position sensors 108, the adjustable optics 110 may be operable to control the optical path of the received radiation beam 102 in response to the position and / or orientation of the portion of the optical system 100 determined by each of the multiple position sensors 108.

[0112] This may allow more complex distortions of the optical system 100 to be corrected. For example, if the optical system 100 does not simply vibrate as a whole, but is instead subjected to vibrations or vibration modes that correspond to distortions of the optical system 100, multiple position sensors may allow the effects of such vibration modes on the spatial and / or angular distribution of radiation delivered to the illumination field 106 to be at least partially corrected.

[0113] At least one position sensor 108 is operable to determine the position and / or orientation of at least a portion of the optical system 100. Such a determination may be a direct measurement of the position and / or orientation. Alternatively, the determination may be indirect. For example, the position sensor 108 may measure another quantity (e.g., acceleration) from which the position can be determined. Any suitable type of position sensor 108 may be used. Generally, each position sensor determines the position and / or orientation of a portion of the optical system 100 relative to a reference frame. The reference frame may be any frame in which the illumination field 106 (also referred to in the art as an illumination slit or simply a slit) is stationary.

[0114] In some embodiments, the at least one position sensor 108 is operable to determine the position and / or orientation of at least a portion of the optical system in all six degrees of freedom, which may be, for example, x position, y position, z position, Rx rotation, Ry rotation, and Rz rotation.

[0115] In some embodiments, the one or more position sensors 108 comprise one or more accelerometers. Such embodiments determine the position and / or orientation of portions of the optical system 100 relative to an inertial coordinate system.

[0116] In an embodiment, the or each position sensor 108 may comprise at least two accelerometers arranged to determine the acceleration of the part of the optical system 100 in at least two directions generally orthogonal to the optical path of the radiation beam 102. This allows the position of the part of the optics 100 to be determined in two directions generally orthogonal to the optical path. In an embodiment, the or each position sensor 108 may comprise at least three accelerometers arranged to determine the acceleration of the part of the optical system 100 in three linearly independent directions. This allows the position of the part of the optics 100 to be determined in three linearly independent directions.

[0117] In some embodiments, the or each accelerometer is operable to determine acceleration and / or position, and has three degrees of freedom. In one embodiment, position sensor 108 comprises two or three accelerometers, each arranged to determine three degrees of freedom. Advantageously, this may enable position sensor 108 to determine the position and / or orientation of at least a portion of the optical system in all six degrees of freedom.

[0118]

[0117] Alternative position sensors may include interferometric sensors, for example of the type used to monitor the position of the reticle stage MT or wafer stage WT of the lithographic apparatus LA.

[0119]

[0118] In some embodiments, the optical system 100 may include beam steering optics (e.g., of the type provided by the beam steering unit BSU of Figure 2) arranged to direct the radiation 102 along an adjustable optical path.

[0120] The beam steering optics may receive the radiation beam B (e.g. from the radiation source SO). The beam steering optics may, for example, comprise two rotatable mirrors BS1, BS2. By rotating the mirrors BS1, BS2, the position and direction of the radiation beam B downstream of the beam steering optics BSU can be controlled. In such an embodiment, the adjustable optics 110 of the optical system 100 may comprise the beam steering optics BSU.

[0121] Additionally or alternatively, in some embodiments, optical system 100 may comprise pupil shaping optics PSO (e.g., of the type shown in FIG. 2 and described above) operable to control the angular distribution of radiation delivered to illumination region 106. That is, illumination region 106 may be illuminated using different illumination modes or pupils by selecting one or more configurations of pupil shaping optics. In such embodiments, adjustable optics 110 may comprise pupil shaping optics PSO. Those skilled in the art will appreciate that a mirror array disposed within pupil shaping optics PSO may be used to control the radiation beam in response to the position and / or direction of the radiation beam measured by sensors 108, 124.

[0122] Some embodiments of the present disclosure generally relate to a novel lithographic apparatus LA of the type shown in Figures 1 and 2 and described above, comprising an optical system 100 of the type shown in Figures 3 to 4B and described above, where a support structure MT (reticle stage) is configured to support a patterning device MA such that the patterning device MA is positionable within an illumination field 106. Such a novel lithographic apparatus LA is advantageous because it allows any movement (or variations in position and / or orientation) of at least part of the optical system 100 to be corrected so that radiation B is more accurately delivered to the illumination field 106 (where the patterning device MA is positioned in use). And, as explained above, any variations in the position and / or angle of radiation B delivered to the patterning device MA may affect the imaging of the patterning device ME onto a substrate W. In particular, any pointing error of the radiation B delivered to the illumination region 106 can result in asymmetric numerical aperture (NA) clipping, especially for illumination modes in which the outermost portion of the entrance pupil is illuminated (e.g., extreme dipole). This, in turn, can adversely affect imaging of the patterning device MA, which is undesirable. The new lithographic apparatus LA allows a wider range of illumination modes to be used without suffering from such problems (e.g., asymmetric NA clipping). Additionally or alternatively, the new lithographic apparatus LA allows for greater movement or vibration of parts of the lithographic apparatus LA without suffering from such problems (e.g., asymmetric NA clipping). And allowing for greater movement or vibration advantageously allows for increased throughput of the lithographic apparatus LA and an associated reduction in manufacturing costs per wafer W.

[0123] Some embodiments of the present disclosure relate to a method 200 of providing radiation 102 to an illumination area 106 via an optical system 100, as will now be described with reference to FIGS.

[0124] The method 200 comprises determining 202 a position and / or orientation of at least a portion of the optical system 100. The method 200 further comprises adjusting 204 at least one optical element 112, 114 of the optical system 100 in response to the determined position and / or orientation of the portion of the optical system 100.

[0125] The method 200 shown in Figure 5 may be performed using the optical system 100 shown in Figures 3 to 4B. The method 200 shown in Figure 5 is advantageous because it allows any movement (or variations in position and / or orientation) of at least part of the optical system 100 to be corrected so that the radiation 102 is accurately delivered to the illumination area 106.

[0126] 5 is particularly beneficial for use in illuminating a patterning device MA (also called a reticle or mask) as part of a lithographic exposure process. For example, any variations in the position and / or angle of radiation delivered to the patterning device MA can affect the imaging of the patterning device MA onto the substrate W. In particular, any pointing error of the radiation delivered to the illumination field 106 can result in asymmetric numerical aperture (NA) clipping, especially for illumination modes in which the outermost part of the entrance pupil of the projection system PS is illuminated (e.g., extreme dipole). This in turn will adversely affect the imaging of the patterning device MA, which is undesirable.

[0127]

[0126] Adjusting at least one optical element 112, 114 of the optical system 100 in accordance with the determined position and / or orientation of a part of the optical system 100 may comprise at least partially correcting any variations in the spatial and / or angular distribution of radiation in the illumination area 106 due to any deviation of the determined position and / or orientation from a nominal position.

[0128] For example, optical system 100 may have a nominal position. When disposed in the nominal position, the position and direction of radiation 102 delivered to illumination field 106 may be optimal. During use, optical system 100 may be subjected to vibrations. For example, for embodiments in which optical system 100 comprises, is, or forms part of an illumination system IL of lithographic apparatus LA, movements of other parts of lithographic apparatus LA during use may cause some vibrations of optical system 100.

[0129]

[0128] Any deviation of the determined position and / or orientation of the optical system 100 from the nominal position may result in less than optimal illumination of the illumination area 106, and therefore, for such embodiments, at least one optical element 112, 114 (which may be referred to as an adjustable optical component 110) is used to at least partially correct any variations.

[0130]

[0129] As far as possible, adjusting at least one optical element 112, 114 of the optical system 100 in accordance with the determined position and / or orientation of a portion of the optical system 100 can be performed so that the spatial and / or angular distribution of radiation in the illumination region 106 is generally independent of the determined position and / or orientation of the portion of the optical system 100.

[0131] Another method 300 of providing radiation 102 to an illumination area 106 via an optical system 100 is shown schematically in Figure 6. The method 300 shown in Figure 6 comprises steps 202, 204 of the method 200 shown in Figure 5 and described above.

[0132]

[0131] The method 300 shown in Figure 6 further comprises the step 302 of providing a radiation beam 102.

[0133] The method 300 shown in FIG. 6 further comprises determining 304 the position and / or direction of the provided radiation beam 102 relative to at least a part of the optical system 100.

[0134]

[0133] The method 300 shown in Figure 6 further comprises a step 306 of adjusting at least one optical element 112, 114 of the optical system 100 in accordance with the determined position and / or direction of the provided radiation beam 102 relative to at least a portion of the optical system 100.

[0135]

[0134] Thus, in this embodiment, the method 300 may further comprise a step 308 of adjusting at least one optical element 112, 114 of the optical system 100 in accordance with both (a) the determined position and / or orientation of a portion of the optical system 110 and (b) the determined position and / or direction of the received radiation beam 102.

[0136] 5 and 6 may comprise determining the position and / or orientation of multiple portions of the optical system 100 and adjusting at least one optical element 112, 114 of the optical system 100 in response to the determined position and / or orientation of each of the multiple portions of the optical system 100. This may allow more complex distortions of the optical system 100 to be corrected, such as when the optical system 100 is subjected to vibrations or vibration modes that correspond to distortions of the optical system 100, rather than simply vibrating as a whole.

[0137] 5 and 6, at least one part of the optical system 100, the position and / or orientation of which is determined, is optically downstream of at least one optical element 112, 114 that is adjusted accordingly. Advantageously, this may allow the at least one part of the optical system 100, the position and / or orientation of which is determined, to be as close as possible to the illumination region 106. This may in turn result in more precise control of the spatial and angular distribution of the radiation 102 in the illumination region 106.

[0138]

[0137] Either of the methods 200, 300 shown in Figures 5 and 6 may further comprise adjusting the radiation beam 102 to control the spatial and / or angular distribution of the radiation delivered to the illumination area 106.

[0139] Some embodiments of the present disclosure relate to a lithographic exposure method 400, as will now be described with reference to FIG.

[0140] The lithographic exposure method 400 comprises the step 402 of providing a patterning device MA within the illumination field 106.

[0141] The lithographic exposure method 400 further comprises the step 404 of providing radiation to the illumination area 106 via the optical system 100 to form a patterned radiation beam using the method 200, 300 shown in FIG. 5 or FIG.

[0142] The lithographic exposure method 400 further comprises a step 406 of collecting a patterned beam of radiation and using it to form an image of the patterning device MA on the substrate W.

[0143] 7 is advantageous because it allows any movement (or variation in position and / or orientation) of at least part of the optical system 100 to be corrected so that radiation 102 is more accurately delivered to the illumination region 106 (wherein the patterning device MA is provided in use). And, as explained above, any variation in the position and / or angle of the radiation 102 delivered to the patterning device MA may affect the imaging of the patterning device MA onto the substrate W. In particular, any pointing error of the radiation delivered to the illumination region 106 may result in asymmetric numerical aperture (NA) clipping (in step 406 of collecting the patterned radiation beam), especially for illumination modes in which the outermost part of the entrance pupil of the projection system PS is illuminated (e.g., extreme dipole). This, in turn, will adversely affect the imaging of the patterning device MA, which is undesirable. The lithography exposure method 400 shown in Figure 7 allows a wider range of illumination modes to be used without suffering from such problems (e.g., asymmetric NA clipping). Additionally or alternatively, the lithography exposure method 400 shown in Figure 7 allows for greater movement or vibration of parts of the lithography apparatus LA without suffering from such problems (e.g., asymmetric NA clipping). And, allowing for greater movement or vibration advantageously allows for an increase in the throughput of the lithography apparatus LA and an associated reduction in manufacturing cost per wafer W.

[0144]

[0143] In some embodiments of the lithographic exposure method 400 shown in Figure 7, the exposure may be a scanning exposure, such that (a) step 402 of providing a patterning device MA within the illumination area 106 may comprise moving the patterning device MA through the illumination area 106, and (b) step 406 of forming an image of the patterning device MA on the substrate W may comprise moving the substrate W so that the image of the patterning device MA is generally stationary relative to the substrate W.

[0145]

[0144] Although specific reference may be made in this text to the use of lithographic apparatus in the manufacture of ICs, it will be appreciated 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.

[0146] Although specific reference may be made in this text to embodiments of the invention in the context of a lithography apparatus, embodiments of the invention may also be used in other apparatus. Embodiments of the invention may form part of a mask inspection apparatus, a metrology apparatus, or any apparatus that measures or processes objects such as wafers (or other substrates) or masks (or other patterning devices). These apparatus may be generally referred to as lithography tools. Such lithography tools may utilize vacuum or atmospheric (non-vacuum) conditions.

[0147]

[0146] While the above may specifically refer to the use of embodiments of the present invention in the context of optical lithography, it will be understood that the present invention is not limited to optical lithography and may be used in other applications, for example imprint lithography, where the context permits.

[0148] Where the context permits, 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, which may be read and executed 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, machine-readable media may 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.), and others. Furthermore, firmware, software, routines, and instructions may be described herein as performing particular actions. However, it should be understood that such description is merely for convenience and that such actions actually result from a computing device, processor, controller, or other device executing the firmware, software, routines, instructions, etc., and, in doing so, may cause actuators or other devices to interact with the physical world.

[0149]

[0148] Aspects of the present invention are described in the following clauses. 1. An optical system for use in an imaging device, arranged to receive a radiation beam (provided by a radiation source) at an entrance and to direct the radiation beam via an optical path to an illumination area, the optical system comprising at least one position sensor operable to determine a position and / or orientation of at least a part of the optical system, and an adjustable optical component configured to control the optical path of the received radiation beam in response to the determined position and / or orientation of the part of the optical system. 2. An optical system according to clause 1, wherein the adjustable optical component is configured to control the optical path of the received radiation beam in response to a determined position and / or orientation of a part of the optical system to at least partially compensate for any variations in the spatial and / or angular distribution of the radiation in the illumination area resulting from any deviation of the determined position and / or orientation from a nominal position. 3. An optical system of clause 1 or clause 2, further comprising at least one radiation beam measurement sensor operable to determine the position and / or direction of the received radiation beam relative to at least a portion of the optical system, and the adjustable optical component operable to control the optical path of the received radiation beam in response to the determined position and / or direction of the received radiation beam relative to at least a portion of the optical system. 4. An optical system according to any of clauses 1 to 3, comprising a plurality of position sensors, wherein the adjustable optical component is operable to control the optical path of the received radiation beam in response to a position and / or orientation of a portion of the optical system determined by each of the plurality of position sensors. 5. The optical system of any of clauses 1 to 4, wherein the or each position sensor comprises one or more accelerometers. 6. The optical system of any of clauses 1 to 5, wherein at least one position sensor is optically downstream of the adjustable optical component. 7. The optical system of any of clauses 1 to 6, further comprising a controller operable to receive a first signal from the or each position sensor indicative of a position and / or orientation of a portion of the optical system, and to generate and send a control signal to the adjustable optical component, the control signal being dependent on the one or more first signals. 8. The optical system of clause 7 when directly or indirectly dependent on clause 3, wherein the controller is further operable to receive from the or each radiation beam measurement sensor a second signal indicative of the position and / or direction of the received radiation beam relative to the optical system, the control signal being dependent on the one or more first signals and the second signal. 9. An optical system according to any of clauses 1 to 8, comprising beam steering optics arranged to direct radiation along an adjustable optical path. 10. The optical system of clause 9, wherein the adjustable optical component comprises a beam steering optical component. 11. The optical system of any of clauses 1 to 10, comprising a pupil-shaping optic operable to control the angular distribution of radiation delivered to the illumination region. 12. The optical system of clause 11, wherein the pupil shaping optics comprises a mirror array comprising a plurality of independently adjustable mirrors. 13. The optical system of clause 11 or clause 12, wherein the adjustable optic comprises a pupil-shaping optic. 14. A lithographic apparatus comprising an optical system according to any of clauses 1 to 13 operable to receive radiation and to direct at least a portion of the received radiation to an illumination region; a support structure configured to support a patterning device such that the patterning device is positionable within the illumination region; a substrate table configured to support a substrate; and a projection system operable to form an image of the patterning device supported by the support structure onto a substrate supported by the substrate table. 15. A method of providing radiation to an illumination area via an optical system, the method comprising: determining a position and / or orientation of at least a portion of the optical system; and adjusting at least one optical element of the optical system in response to the determined position of the portion of the optical system. 16. The method of clause 15, wherein adjusting at least one optical element of the optical system in response to the determined position and / or orientation of the part of the optical system comprises at least partially correcting any variations in the spatial and / or angular distribution of radiation in the illumination area due to any deviation of the determined position and / or orientation from a nominal position. 17. The method of clause 15 or clause 16, further comprising providing a radiation beam, determining a position and / or direction of the provided radiation beam relative to at least a portion of the optical system, and adjusting at least one optical element of the optical system in response to the determined position and / or direction of the provided radiation beam relative to at least a portion of the optical system. 18. The method of any one of clauses 15 to 17, comprising determining positions and / or orientations of a plurality of portions of the optical system, and adjusting at least one optical element of the optical system in response to the determined positions and / or orientations of each of the plurality of portions of the optical system. 19. The method of any one of clauses 15 to 18, wherein at least one part of the optical system whose position and / or orientation is determined is optically downstream of at least one optical element that is adjusted accordingly. 20. The method of any one of clauses 15 to 19, further comprising adjusting the radiation beam to control the spatial and / or angular distribution of the radiation delivered to the illumination area. 21. A lithographic exposure method comprising providing a patterning device within an illumination area, and using the method of any one of clauses 15 to 20, providing radiation to the illumination area via an optical system to form a patterned radiation beam, and collecting the patterned radiation beam and using it to form an image of the patterning device on a substrate. 22. The lithographic exposure method of clause 21, wherein the exposure is a scanning exposure, such that providing a patterning device within the illumination field comprises moving the patterning device through the illumination field, and such that forming an image of the patterning device on the substrate comprises moving the substrate such that the image of the patterning device is generally stationary relative to the substrate. 23. A lithographic apparatus comprising an optical system according to any one of clauses 1 to 13. 24. An optical system according to any of clauses 1 to 13 and 23, wherein at least one position sensor is provided in a relay lens of the imaging device and / or in a masking device.

[0150]

[0149] While specific embodiments of the present invention have been described above, it will be understood that the present invention may be practiced otherwise than as described. The above 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 without departing from the scope of the following claims.

Claims

1. 1. An optical system for use in an imaging apparatus, the optical system being arranged to receive a radiation beam at an entrance and to direct the radiation beam via an optical path to an illumination area, the optical system comprising: at least one position sensor operable to determine a position and / or orientation of at least a portion of the optical system; an optical system comprising: an adjustable optical component configured to control the optical path of the received radiation beam in response to a determined position and / or orientation of the part of the optical system; and at least one radiation beam measurement sensor operable to determine the position and / or direction of the received radiation beam relative to at least a part of the optical system, wherein the adjustable optical component is operable to control the optical path of the received radiation beam in response to the determined position and / or direction of the received radiation beam relative to the at least a part of the optical system.

2. 2. The optical system of claim 1, wherein the adjustable optical component is configured to control the optical path of the received radiation beam in response to the determined position and / or orientation of the part of the optical system to at least partially compensate for any variations in the spatial and / or angular distribution of the radiation in the illumination area due to any deviation of the determined position and / or orientation from a nominal position.

3. 3. The optical system of claim 1 or 2, comprising a plurality of position sensors, the adjustable optical component being operable to control the optical path of the received radiation beam in response to a position and / or orientation of a part of the optical system determined by each of the plurality of position sensors.

4. 4. An optical system according to claim 1, wherein the or each position sensor comprises one or more accelerometers.

5. 5. The optical system of claim 1, wherein at least one position sensor is optically downstream of the adjustable optical component.

6. receiving a first signal from the or each position sensor indicative of a position and / or orientation of a portion of the optical system; and 6. The optical system of claim 1, further comprising a controller operable to generate and send a control signal to the adjustable optical component, the control signal being dependent on the one or more first signals.

7. 7. The optical system of claim 6, wherein the controller is further operable to receive a second signal from the or each radiation beam measurement sensor indicative of a position and / or direction of the received radiation beam relative to the optical system, the control signal being dependent on the one or more first signals and the one or more second signals.

8. 8. An optical system according to claim 1, comprising beam steering optics arranged to direct the radiation along an adjustable optical path.

9. 9. The optical system of claim 1, comprising pupil shaping optics operable to control the angular distribution of radiation delivered to the illumination area.

10. The optical system of claim 9 , wherein the pupil shaping optics comprises a mirror array comprising a plurality of independently adjustable mirrors.

11. 1. A method of providing radiation to an illumination area via an optical system, comprising: determining a position and / or orientation of at least a portion of the optical system; providing a beam of radiation; determining a position and / or direction of the provided radiation beam relative to at least a portion of the optical system; adjusting at least one optical element of the optical system in response to the determined position of the portion of the optical system; adjusting at least one optical element of the optical system in response to the determined position and / or direction of the provided radiation beam relative to the at least part of the optical system; A method for providing the above.

12. 12. The method of claim 11, wherein adjusting at least one optical element of the optical system in response to the determined position and / or orientation of a part of the optical system comprises at least partially correcting any variations in the spatial and / or angular distribution of the radiation in the illumination area due to any deviation of the determined position and / or orientation from a nominal position.

13. determining positions and / or orientations of portions of the optical system; adjusting at least one optical element of the optical system in response to the determined positions and / or orientations of each of the plurality of portions of the optical system; 13. The method of claim 11 or 12, comprising:

14. 14. The method of any one of claims 11 to 13, wherein at least one part of the optical system, the position and / or orientation of which is determined, is optically downstream of the at least one optical element that is adjusted accordingly.

15. 15. The method of any one of claims 11 to 14, further comprising adjusting the radiation beam to control the spatial and / or angular distribution of radiation delivered to the illumination area.

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