Optical system

Abstract

An optical system includes at least one position sensor and adjustable optics and is arranged to receive a radiation beam and direct the radiation beam to an illumination area. The at least one position sensor is operable to determine a position of a portion of the optical system. The adjustable optic is configured to control the optical path of the received radiation beam depending on the determined position of the portion of the optical system. The adjustable optics may be configured to at least partially correct for any change in the spatial and / or angular distribution of radiation at the illumination region due to any deviation of the determined position from the nominal position. The optical system may include an illumination system for an imaging apparatus, such as a lithographic apparatus. A corresponding method of providing radiation to an illumination area via an optical system is also claimed.

Description

[0001] Cross - reference to related applications

[0002] This application claims priority to EP application 22216652.2, filed on December 23, 2022, which is hereby incorporated by reference in its entirety. Technical field

[0003] The present invention relates to an optical system for delivering a radiation beam to an illumination area. The optical system can be an illumination system within a lithographic apparatus. The present invention also relates to a corresponding method of providing radiation to an illumination area via the optical system. The method can form part of a lithographic exposure method. Background art

[0004] A lithographic apparatus is a machine configured to apply a desired pattern onto a substrate. For example, a lithographic apparatus can be used to manufacture integrated circuits (ICs). For example, a lithographic apparatus projects a pattern (commonly also referred to as a “design layout” or “design”) of a patterning device (e.g., a mask) onto a layer of radiation - sensitive material (resist) provided on a substrate (e.g., a wafer).

[0005] With the continuous progress of the semiconductor manufacturing process, the dimensions of circuit elements have been continuously decreasing, and the number of functional elements (such as transistors) per device has been steadily increasing for decades, following a trend commonly known as ‘Moore's Law’. To keep up with Moore's Law, the semiconductor industry has been pursuing technologies that can create increasingly smaller features. To project a pattern onto a substrate, a lithographic apparatus can use electromagnetic radiation. The wavelength of this radiation determines the minimum size 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. Compared to a lithographic apparatus using radiation with a wavelength of, for example, 193 nm, a lithographic apparatus using extreme ultraviolet (EUV) radiation with a wavelength in the range of 4 nm to 20 nm (e.g., 6.7 nm or 13.5 nm) can be used to form smaller features on a substrate.

[0006] Within a lithographic apparatus, the radiation is delivered to the patterning device by an optical system, which can be referred to as an illumination system. The illumination system can be arranged to condition the radiation beam such that the radiation beam is delivered to the patterning device with a desired spatial and angular distribution. It may be desirable to provide alternative devices and methods for delivering radiation to an exposure area or patterning device that at least partially address one or more problems in the prior - art arrangements, whether identified herein or elsewhere. Summary of the invention

[0007] 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 direct the radiation beam via an optical path to an illumination region, the optical system comprising: at least one position sensor operable to determine the position and / or orientation of at least a part of the optical system; and an adjustable optical device configured to control the optical path of the received radiation beam depending on the determined position and / or orientation of the part of the optical system.

[0008] During use, if at least a part of the optical system moves, then the spatial and / or angular distribution of the radiation transmitted to the illumination region may change, which may be undesirable. The optical system according to the first aspect is advantageous because this allows any movement (or change in position and / or orientation) of at least a part of the optical system to be corrected so that the radiation is accurately transmitted to the illumination region.

[0009] The optical system may be suitable for use in a lithographic apparatus. The optical system may comprise an illumination system for use in an imaging device (such as a lithographic apparatus). Such an illumination system may be operable to condition the received radiation beam (e.g. from a radiation source or a laser) and transmit the received radiation to the illumination region (where a mask or reticle may be provided) with a desired or required spatial and angular distribution.

[0010] As now discussed, the optical system according to the first aspect is particularly beneficial for use in the illumination system of a lithographic apparatus.

[0011] For a precision imaging device such as a lithographic apparatus, it may be very important to irradiate a patterning device (also known as a mask or reticle) with radiation having a well-defined spatial and angular distribution. For example, it is generally desirable to irradiate the patterning device with a substantially uniform spatial distribution to ensure that the radiation dose transmitted to a substrate (such as a silicon wafer coated with a resist) is well controlled. This may in turn lead to better critical dimension (CD) control. The angular distribution of the radiation at the illumination region (where the patterning device is provided) may also be referred to as the illumination pattern or pupil. The angular distribution of the radiation at the illumination region (where the patterning device is provided) describes how the radiation cones filling each part of the illumination patterning device are shaped. This may be described by the radiation intensity in the entrance pupil of a projection optical device arranged to image the patterning device onto the substrate. It is well known that irradiating the patterning device with an illumination pattern (such as an annular illumination pattern and a dipole illumination pattern) in which the peripheral part of the entrance pupil is illuminated and the central part of the entrance pupil is not illuminated can generally improve the contrast on a series of different features of the image formed on the substrate (e.g. relative to full pupil filling illumination).

[0012] Any variation 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 area can lead to an asymmetric numerical aperture (NA) clipping, especially for illumination patterns where the outermost part of the entrance pupil is illuminated (such as extreme dipole). In turn, this will have an adverse effect on the imaging of the patterning device, which is undesirable. It is to be understood that the projection system of a lithographic apparatus typically provides NA clipping of the radiation beam patterned by the mask or patterning device. In practice, a lithographic apparatus is used to image features that are small compared to the wavelength of the radiation beam, so the image of the pattern formed on the wafer is typically diffraction limited and is formed by only a very small number of diffraction orders of the radiation interacting with the mask. However, any asymmetric NA clipping of the radiation beam by the projection system can lead to alignment errors. A slow change in the NA clipping (symmetry) will result in a position error (i.e., a moving average) of the image formed on the wafer, while a rapid change in the clipping will be smeared out, resulting in a blurring of the features formed on the wafer (an increase in the standard deviation of the average). It is to be understood that, as used herein, "slow" may mean a time scale that is large compared to the exposure time of the wafer, while "rapid" may mean a time scale that is small compared to the exposure time of the wafer.

[0013] The adjustable optical device can be configured to control the optical path of the received radiation beam depending on the determined position and / or orientation of a part of the optical system, to at least partially correct for any change in the spatial and / or angular distribution of the radiation at the illumination area due to any deviation of the determined position and / or orientation from the nominal position.

[0014] For example, the optical system can have a nominal position. When set at the nominal position, the position and direction of the radiation delivered to the illumination area may be optimal. In use, the optical system may be subject to vibrations. For example, for an embodiment where the optical system is the illumination system of a lithographic apparatus or forms part thereof, the movement of other parts of the lithographic apparatus during use may cause some vibrations of the optical system.

[0015] Any deviation of the determined position and / or orientation from the nominal position can lead to sub-optimal irradiation of the illumination area, and thus, for such an embodiment, the adjustable optical device is used to at least partially correct for any change.

[0016] To the extent possible, the adjustable optical device can be configured such that the spatial and / or angular distribution of the radiation at the illumination area is generally independent of the determined position of the part of the optical system.

[0017] The optical system may further include a radiation beam measurement sensor operable to determine the position and / or orientation of a received radiation beam relative to at least a portion of the optical system. The adjustable optical device may be operable to control the optical path of the received radiation beam depending on the determined position and / or orientation of the received radiation beam relative to the at least portion of the optical system.

[0018] That is, the radiation beam measurement sensor may be used to align the received radiation beam with the optical system (using the adjustable optical device). This may correct any alignment and / or pointing errors of the radiation beam received by the optical system. However, with such an arrangement, if the optical system itself moves, then the radiation beam will also move, and thus the radiation beam will not be accurately aligned with the illumination area. However, since the adjustable optical device is configured to control the optical path of the received radiation beam depending on the determined position of a portion of the optical system, any misalignment between the radiation beam and the illumination area can be corrected.

[0019] At least a portion of the optical system with respect to which the radiation beam measurement sensor of the optical system is operable to determine the position and / or orientation of a received radiation beam may be the same portion of the optical system as at least one position sensor operable to determine its position and / or orientation.

[0020] Alternatively, in some embodiments, at least a portion of the optical system with respect to which the radiation beam measurement sensor of the optical system is operable to determine the position and / or orientation of a received radiation beam may be a portion of the optical system different from the portion of the optical system where 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 orientation of a received radiation beam relative to a portion of the optical system near the entrance, and at least one position sensor may be operable to determine the position and / or orientation of a portion of the optical system near the illumination area.

[0021] Note that the same actuatable or adjustable optical device may be used for: (a) controlling the optical path of the received radiation beam depending on the determined position and / or orientation of a portion of the optical system; and (b) controlling the optical path of the received radiation beam depending on the determined position and / or orientation 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 depending on the determined position and / or orientation of a portion of the optical system, and a second set of optical elements may be provided to control the optical path of the received radiation beam depending on the determined position and / or orientation of the received radiation beam. For such an embodiment, the adjustable optical device may be considered to include the first set of optical elements and the second set of optical elements.

[0022] The optical system may include a plurality of position sensors, and the adjustable optical device may be operable to control the optical path of the received radiation beam depending on the position and / or orientation of the part of the optical system determined by each of the plurality of position sensors.

[0023] This may allow for correction of more complex distortions of the optical system. For example, if the optical system not only oscillates as a whole, but is also affected by vibration or oscillation modes corresponding to the distortion of the optical system.

[0024] At least one position sensor is operable to determine the position and / or orientation of at least a part 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 (such as acceleration), from which the position and / or orientation may be determined. Any suitable type of position sensor may be used. Generally, each position sensor determines the position and / or orientation of the part of the optical system relative to a reference frame. The reference frame may be any frame in which the illumination area (also referred to in the art as the illumination slit or simply the slit) is stationary.

[0025] In some embodiments, at least one position sensor is operable to determine the position and / or orientation of at least a part of the optical system in all six degrees of freedom.

[0026] The position sensor or each position sensor may include one or more accelerometers.

[0027] Such embodiments determine the position and / or orientation of the part of the optical system relative to an inertial frame.

[0028] In one embodiment, the position sensor or each position sensor may include at least two accelerometers arranged to determine the acceleration of the part of the optical system in at least two directions, which two directions are generally orthogonal to the optical path. This allows for determination of the position of the optical part in the two directions generally orthogonal to the optical path. In one embodiment, the position sensor or each position sensor may include at least three accelerometers arranged to determine the acceleration of the part of the optical system in three linearly independent directions. This allows for determination of the position of the optical part in the three linearly independent directions.

[0029] In some embodiments, the accelerometer or each accelerometer is operable to determine acceleration and / or position and has three degrees of freedom. In one embodiment, the position sensor includes two or three accelerometers, each accelerometer being arranged to determine three degrees of freedom. Advantageously, this may allow the position sensor to determine the position and / or orientation of at least a part of the optical system in all six degrees of freedom.

[0030] The alternative position sensor may comprise an interferometric sensor. For example, such an interferometric sensor may be of the type for monitoring the position of a mask table or a wafer table in a lithographic apparatus.

[0031] At least one position sensor may be optically located downstream of the adjustable optics.

[0032] Advantageously, this may allow the at least one position sensor to be as close as possible to the irradiation area. In turn, this may result in a more accurate control of the spatial and angular distribution of the radiation at the irradiation area.

[0033] The optical system may further comprise a controller operable to: receive a first signal from the position sensor or each position sensor, indicative of the position and / or orientation of a part of the optical system; and generate a control signal and send it to the adjustable optics, the control signal being dependent on the first signal.

[0034] The controller may further be operable to receive a second signal from a radiation beam measurement sensor, indicative of the position and / or direction of the received radiation beam relative to the optical system; and the control signal may be dependent on the first signal and the second signal.

[0035] The optical system may further comprise beam steering optics arranged to direct the radiation along an adjustable optical path.

[0036] The beam steering optics may receive a radiation beam (e.g. from a radiation source). For example, the beam steering optics may 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.

[0037] The adjustable optics may comprise the beam steering optics.

[0038] The optical system may comprise pupil shaping optics operable to control the angular distribution of the radiation transmitted to the irradiation area.

[0039] That is, by selecting one or more configurations of the pupil shaping optics, different irradiation patterns or pupils may be used to irradiate the irradiation area.

[0040] The pupil shaping optics may comprise an array of mirrors, the array of mirrors comprising a plurality of independently adjustable mirrors.

[0041] The adjustable optics may comprise the pupil shaping optics.

[0042] 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 direct at least part of the received radiation to an illumination area; a support structure configured to support a patterning device such that the patterning device can be positioned in 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 on the substrate supported by the substrate table.

[0043] The lithographic apparatus according to the second aspect is advantageous because this allows correction of any movement (or change in position) of at least part of the optical system, such that the radiation is more accurately delivered to the illumination area (where the patterning device is positioned in use). In turn, as explained above, any change in the position and / or angle of the radiation delivered to the patterning device can affect the imaging of the patterning device on the substrate. In particular, any pointing error of the radiation delivered to the illumination area can lead to an asymmetric numerical aperture (NA) clipping, especially for illumination patterns where the outermost part of the entrance pupil is illuminated (such as extreme dipole). In turn, this will have an adverse effect on the imaging of the patterning device, which is undesirable. The lithographic apparatus according to the second aspect allows the use of a wider range of illumination patterns without such problems (such as asymmetric NA clipping). Additionally or alternatively, the lithographic apparatus according to the second aspect allows for greater movement or vibration of parts of the lithographic apparatus without such problems (such as asymmetric NA clipping). In turn, tolerating greater movement or vibration can advantageously allow an increase in the throughput of the lithographic apparatus and, associated therewith, a reduction in the manufacturing cost per wafer.

[0044] According to a third aspect of the present disclosure, there is provided a method of providing radiation to an illumination area via an optical system, the method comprising: determining the position and / or orientation of at least part of the optical system; and adjusting at least one optical element in the optical system depending on the determined position of the part of the optical system.

[0045] The method according to the third aspect can be carried out using the optical system according to the first aspect. The method according to the third aspect is advantageous because this allows correction of any movement (or change in position and / or orientation) of at least part of the optical system, such that the radiation is accurately delivered to the illumination area.

[0046] The method according to the third aspect is particularly beneficial for use in irradiating a patterning device (also known as a reticle or mask) as part of a lithographic exposure process. For example, any variation in the position and / or angle of the radiation transmitted to the patterning device can affect the imaging of the patterning device on the substrate. In particular, any pointing error of the radiation transmitted to the illumination region can lead to an asymmetric numerical aperture (NA) clipping, especially for illumination patterns (such as extreme dipole) where the outermost part of the entrance pupil is illuminated. In turn, this will have an adverse effect on the imaging of the patterning device, which is undesirable.

[0047] Adjusting at least one optical element in the optical system depending on a determined position and / or orientation of a part of the optical system can include: at least partially correcting any variation in the spatial and / or angular distribution of the radiation at the illumination region resulting from any deviation of the determined position and / or orientation from a nominal position.

[0048] For example, the optical system can have a nominal position. When set at the nominal position, the position and direction of the radiation transmitted to the illumination region may be optimal. In use, the optical system may be subject to vibrations. For example, for an embodiment in which the optical system is an illumination system of a lithographic apparatus or forms part thereof, the movement of other parts of the lithographic apparatus during use may cause some vibrations of the optical system.

[0049] Any deviation of the determined position and / or orientation from the nominal position can lead to sub-optimal irradiation of the illumination region, and thus, for such an embodiment, at least one optical element (which can be referred to as an adjustable optical device) is used to at least partially correct any variation.

[0050] To the extent possible, adjusting at least one optical element in the optical system depending on a determined position and / or orientation of a part of the optical system can be performed such that the spatial and / or angular distribution of the radiation at the illumination region is generally independent of the determined position of this part of the optical system.

[0051] The method can further include: providing a radiation beam; determining the position and / or direction of the provided radiation beam relative to at least a part of the optical system; and adjusting at least one optical element in the optical system depending on the determined position and / or direction of the provided radiation beam relative to the said at least a part of the optical system.

[0052] The method can include: determining the positions and / or orientations of a plurality of parts of the optical system; and adjusting at least one optical element in the optical system depending on the determined position and / or orientation of each part of the plurality of parts of the optical system.

[0053] This can allow for the correction of more complex distortions of the optical system. For example, if the optical system not only oscillates as a whole, but is also affected by vibration or oscillation modes corresponding to the distortion of the optical system.

[0054] At least part of the optical system for which the position and / or orientation is determined can be optically downstream of at least one optical element depending on its adjustment.

[0055] Advantageously, this can allow at least part of the optical system for which the position and / or orientation is determined to be as close as possible to the irradiation area. In turn, this may result in a more accurate control of the spatial and angular distribution of the radiation at the irradiation area.

[0056] The method can also include adjusting the radiation beam to control the spatial and / or angular distribution of the radiation delivered to the irradiation area.

[0057] According to a fourth aspect of the present disclosure, there is provided a lithographic exposure method, the method comprising: providing a patterning device in an irradiation area; providing radiation to the irradiation area via an optical system using the method of the third aspect of the present disclosure 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.

[0058] The lithographic exposure method according to the fourth aspect is advantageous because this allows for the correction of any movement (or change in position and / or orientation) of at least part of the optical system, such that the radiation is delivered more accurately to the irradiation area (where the patterning device is provided). In turn, as explained above, any change in the position and / or angle of the radiation delivered to the patterning device can affect the imaging of the patterning device on the substrate. In particular, any pointing error of the radiation delivered to the irradiation area can lead to an asymmetric numerical aperture (NA) clipping (in the step of collecting the patterned radiation beam), especially for irradiation modes where the outermost part of the entrance pupil is illuminated (such as extreme dipole). In turn, this will have an adverse effect on the imaging of the patterning device, which is undesirable. The lithographic exposure method according to the fourth aspect allows for the use of a wider range of irradiation modes without such problems (such as asymmetric NA clipping). Additionally or alternatively, the lithographic exposure method according to the fourth aspect allows for a greater movement or vibration of parts of the lithographic apparatus without such problems (such as asymmetric NA clipping). In turn, tolerating a larger movement or vibration can advantageously allow for an increase in the throughput of the lithographic apparatus and, associated therewith, a reduction in the manufacturing cost per wafer.

[0059] The exposure may be a scanning exposure such that providing the patterning device in the exposure area may include moving the patterning device through the exposure area, and forming an image of the patterning device on the substrate may include moving the substrate such that the image of the patterning device is substantially stationary relative to the substrate. Description of the Drawings

[0060] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which:

[0061] Figure 1 A first schematic overview of a lithographic apparatus is depicted;

[0062] Figure 2 A second schematic overview of a lithographic apparatus is depicted;

[0063] Figure 3 is a schematic diagram of an optical system according to an embodiment of the present disclosure, the optical system being capable of forming Figure 1 and / or Figure 2 a part of the lithographic apparatus as shown, the optical system being shown in a first nominal position and / or configuration;

[0064] Figure 4A shows Figure 3 the optical system as shown in a second non-nominal or distorted position and / or configuration;

[0065] Figure 4B shows Figure 3 the optical system as shown in a second non-nominal or distorted position and / or configuration (also as Figure 4A shown), and wherein adjustable optics have been used to at least partially correct for the effects that changes in the first nominal position and / or configuration (see Figure 3 ) may have on the spatial and / or angular distribution of the radiation at the exposure area;

[0066] Figure 5 is a schematic illustration of a first method of providing radiation to an exposure area via an optical system according to an embodiment of the present disclosure;

[0067] Figure 6 is a schematic illustration of a second method of providing radiation to an exposure area via an optical system according to an embodiment of the present disclosure; and

[0068] Figure 7 is a schematic illustration of a lithographic exposure method according to an embodiment of the present disclosure, which may include Figure 5 and / or Figure 6 the methods of. Detailed Description

[0069] In this document, the terms "radiation" and "beam" are used to encompass all types of electromagnetic radiation, including ultraviolet radiation (e.g., having a wavelength of 365, 248, 193, 157, or 126 nm) and EUV (extreme ultraviolet radiation, e.g., having a wavelength in the range of approximately 5 to 100 nm).

[0070] The terms "reticle", "mask", or "patterning device" as used in this document can be broadly interpreted to refer to a general patterning device that can be used to endow an incoming radiation beam with a patterned cross-section corresponding to a pattern to be created in a target portion of a substrate. The term "light valve" can also be used in this context. Examples of other such patterning devices include programmable mirror arrays and programmable LCD arrays in addition to classical masks (transmission or reflection masks, binary masks, phase-shift masks, hybrid masks, etc.).

[0071] Figure 1 A lithographic apparatus LA is schematically depicted. The lithographic apparatus LA includes an illumination system (also referred to as 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 connected 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 wafer coated with resist) W and connected 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 the pattern imparted to the radiation beam B by the patterning device MA onto a target portion C (e.g., including one or more dies) of the substrate W.

[0072] In operation, the illumination system IL receives the radiation beam from a radiation source SO (e.g., via a beam delivery system BD). The illumination system IL can 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 can be used to condition the radiation beam B to have a desired spatial and angular intensity distribution in the plane of the patterning device MA in its cross-section.

[0073] The term "projection system" PS as used in this document should be broadly interpreted to encompass various types of projection systems, including refractive, reflective, refractive-reflective, anamorphic, magnetic, electromagnetic, and / or electrostatic optical systems or any combination thereof, depending as appropriate on the exposure radiation used and / or other factors, such as the use of an immersion liquid or the use of a vacuum. Any use of the term "projection lens" in this document can be considered synonymous with the more general term "projection system" PS.

[0074] The lithographic apparatus LA can be of the type in which at least part of the substrate can be covered by a liquid (e.g. water) having a relatively high refractive index to fill the space between the projection system PS and the substrate W, which is also known as immersion lithography. More information on immersion techniques is given in US6952253, which is incorporated herein by reference.

[0075] The lithographic apparatus LA can also be of the type having two or more substrate supports WT (also referred to as "dual stage"). In such a "multi-stage" machine, the substrate supports WT can be used in parallel, and / or steps for preparing a subsequent exposure of a substrate W located on one of the substrate supports WT can be carried out while another substrate W on another substrate support WT is being used for exposing a pattern on another substrate W.

[0076] In addition to the substrate support WT, the lithographic apparatus LA can include a measurement stage. The measurement stage is arranged to hold a sensor and / or a cleaning device. The sensor can be arranged to measure a property of the projection system PS or of the radiation beam B. The cleaning device can be arranged to clean parts of the lithographic apparatus, such as parts of the projection system PS or parts of the system providing the immersion liquid. The measurement stage can move under the projection system PS when the substrate support WT is moved away from the projection system PS.

[0077] In operation, the radiation beam B is incident on a patterning device (e.g. a mask) MA held on a mask support MT and is patterned by the pattern (design layout) present on the patterning device MA. After traversing 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. By means of a second positioner PW and a position measurement system IF, the substrate support WT can be accurately moved, for example in order to position different target portions C in the path of the radiation beam B in a focused and aligned position. Similarly, a first positioner PM and possibly another position sensor (not explicitly depicted in Figure 1 can be used to accurately position the patterning device MA relative to the path of the radiation beam B. Mask alignment marks M1, M2 and substrate alignment marks P1, P2 can be used to align the patterning device MA and the substrate W. Although the illustrated substrate alignment marks P1, P2 occupy dedicated target portions, the substrate alignment marks P1, P2 can be located in the space between the target portions. When the substrate alignment marks P1, P2 are located between the target portions C, the substrate alignment marks P1, P2 are referred to as scribe alignment marks.

[0078] To illustrate the present invention, a Cartesian coordinate system is used. The Cartesian coordinate system has three axes, namely, the x-axis, the y-axis, and the z-axis. Each of the three axes is orthogonal to the other two axes. A rotation about the x-axis is referred to as an Rx rotation. A rotation about the y-axis is referred to as an Ry rotation. A rotation about the z-axis is referred to as an Rz rotation. The x-axis and the y-axis define a horizontal plane, while the z-axis is in the vertical direction. The Cartesian coordinate system does not limit the present invention but is only used for illustration. Instead, another coordinate system (such as a cylindrical coordinate system) can be used to illustrate the present invention. The orientation of the Cartesian coordinate system can be different, for example, such that the z-axis has a component along the horizontal plane.

[0079] Figure 2 is a second schematic depiction of the lithographic apparatus LA. Figure 2 The illustrated lithographic apparatus LA is generally Figure 1 of the form of the illustrated lithographic apparatus LA. In particular, Figure 2 the illustrated lithographic apparatus LA further 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. Figure 2 The illustrated lithographic apparatus LA may include any of the features discussed above in connection with Figure 1 the illustrated lithographic apparatus LA.

[0080] In use, the illumination system IL receives the radiation beam B from a radiation source SO via a beam steering unit BSU. Figure 1 The illustrated beam delivery system BD generally may correspond to Figure 2 the illustrated beam steering unit BSU.

[0081] The beam steering unit BSU is operable to receive the 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 change 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.

[0082] In use, two beam measurement sensors BM1, BM2 and two beam steering mirrors BS1, BS2 can be used as a feedback loop, as follows. The beam measurement sensors BM1, BM2 can be used to determine any deviation of the optical path OP of the radiation beam B from the optimal or nominal optical path when the radiation beam B leaves the beam steering unit and enters the illumination system IL. These measurements can 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 the optimal or nominal optical path of the radiation beam B when the radiation beam B leaves the beam steering unit and enters the illumination device IL. This can be achieved by using a control loop algorithm, for example executed by a controller that can be operable to receive signals from the beam measurement sensors BM1, BM2 and send control signals to the beam steering mirrors BS1, BS2. In this way, the beam steering unit BSU can be operable to maintain the position and orientation of the radiation beam B when the radiation beam B leaves the beam steering unit BSU (and enters the illumination system IL), substantially independently of the position and orientation when the radiation beam B enters the beam steering unit BSU.

[0083] In addition to the optical components mentioned above, the beam steering unit BSU further includes a mirror M, which also forms part of the optical path OP. It is to be understood that in other embodiments, such a mirror M may not be present, and further, in other embodiments, the beam steering unit BSU may further include one or more additional optical components.

[0084] In this embodiment, the illumination system IL includes: pupil shaping optics PSO; a masking device MD; and relay optics RL.

[0085] The pupil shaping optics PSO is operable to control the angular distribution of the radiation delivered to the illuminated area in the plane of the patterning device MA. That is, by selecting one or more configurations of the pupil shaping optics PSO, different illumination modes or pupils can be used to irradiate the illuminated area. For example, the pupil shaping optics PSO can include a mirror array that includes 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.

[0086] The masking device MD is operable to control the extent of the illumination area in the plane of the patterning device MA. For example, the masking device SD may include two pairs of masking blades, each pair of masking blades being arranged to define the extent of the illumination area in a different one of two directions in the plane of the patterning device MA. Accordingly, the masking device MD may include: a pair of x-masking blades arranged to define the extent of the illumination area 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 area in a second direction in the plane of the patterning device MA. The masking device MD may be arranged such that during the exposure of a target area of the substrate W, an adjacent target area of the substrate W does not receive radiation.

[0087] In some embodiments, the lithographic apparatus LA may be a scanning lithographic apparatus LA (also referred to simply as a scanner). In a scanner, the extent of the pattern on the patterning device MA in the scan direction may be greater than the extent of the illumination area 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 area in the scan direction. It will be appreciated that the substrate W is also scanned relative to the illumination area in the plane of the substrate W. The movement of the substrate W is such that the spatial image of the patterning device MA is stationary relative to the substrate W, and it will be appreciated that typically the direction and speed of the substrate W may be different from the direction and speed of the patterning device MA (e.g. if the image is inverted and / or if the projection system PS applies a reduction factor).

[0088] In embodiments in which the lithographic apparatus LA is a scanning lithographic apparatus, the masking blade (which may be a y-masking blade) that defines the extent of the illumination area in the scan direction may be moved during the scanned exposure of a target area of the substrate W such that an adjacent target area of the substrate W does not receive radiation.

[0089] The relay optics RL is arranged to image the masking device MD (or its masking blades) 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 blades) is conjugate to the plane of the patterning device MA (and the substrate W). Such a plane conjugate to the plane of the patterning device MA (and the substrate W) may be referred to as the field plane. This ensures that the masking device MD is imaged sharply onto the substrate, which minimizes the amount of radiation received by adjacent target areas when any given target area is exposed to the radiation beam B.

[0090] Some known lithographic apparatuses LA use Figure 2A beam steering unit BSU of the type shown and described above is used 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 can be considered to be arranged to align the received radiation beam B with the nominal optical path of the illumination system IL.

[0091] Now refer to Figures 3 to 4B Describe an optical system 100 according to an embodiment of the present disclosure. The optical system 100 is for use in an imaging device, such as, for example, the lithography apparatus LA referred to above Figure 1 and 2 described. For example, the optical system 100 can be, include the illumination system IL of the lithography apparatus LA referred to above Figure 1 and 2 described or form part thereof.

[0092] The optical system 100 is arranged to receive a radiation beam 102 at an entrance 104 and direct the radiation beam 102 via an optical path to an illumination area 106, as described further below. In use, the patterning device MA of the lithography apparatus LA can be disposed in the illumination area 106. The optical system 100 includes a position sensor 108 and an adjustable optical device 110.

[0093] The position sensor 108 is operable to determine the position and / or orientation of at least a part of the optical system 100. For example, the position sensor 108 can be operable to determine the position and / or orientation of the part of the optical system 100 to which it is attached.

[0094] In this example, the adjustable optical device 110 includes two mirrors 112, 114. The adjustable optical device 110 is configured to control the optical path of the received radiation beam 102. In particular, the adjustable optical device 110 is configured to control the optical path of the received radiation beam 102 depending on the determined position and / or orientation of the part of the optical system 100 (as determined by the position sensor 108).

[0095] The optical system 100 further includes a controller 116. The controller 116 is operable to receive a first signal s1 from the position sensor 108 indicating the position and / or orientation of the part of the optical system 100. The controller 116 is also operable to generate a control signal s C and send it to the adjustable optical device 110, the control signal depending on the (one or more) first signals s1.

[0096] The adjustable optical device 110 may be configured to control the optical path of the received radiation beam 102 depending on the determined position and / or orientation of a part of the optical system 100, to at least partially correct any change in the spatial and / or angular distribution of the radiation at the illumination area 106 due to any deviation of the determined position and / or orientation from a nominal position, as now referenced Figures 4A to 4B discussed.

[0097] The radiation beam 102 may leave the optical system 100 at the exit 118. After leaving the exit 118, the radiation beam 102 may propagate to the illumination area 106. The radiation beam may be aligned with the optical system 100 at the exit 118. This is schematically indicated in Figures 3 to 4B as the radiation beam 102 being aligned with the exit axis 120 of the optical system 100.

[0098] In use, the optical system 100 may have a nominal position. When set in the nominal position, the position and direction of the radiation transmitted to the illumination area 106 may be optimal. The optical system 100 is shown in Figure 3 in the nominal position and configuration. In this nominal position, as very schematically shown in Figure 3 the exit axis 120 of the optical system 100 is aligned with the axis 122 of the illumination area 106.

[0099] However, in use, the optical system 100 may be subject to vibrations. For example, for embodiments in which the optical system comprises, is the illumination system IL of a lithographic apparatus LA or forms part thereof, movement of other parts of the lithographic apparatus LA (such as the mask support MT and / or the substrate support WT) during use may cause some vibrations of the optical system 100. In turn, this may lead to a deviation in the position and / or orientation of the optical system 100 relative to the illumination area 106, as determined by the position sensor 108.

[0100] Any such deviation of the determined position and / or orientation (e.g., of the position sensor 108) from the nominal position may result in sub-optimal irradiation of the illumination area 106 (see Figure 4A ), and the adjustable optical device 110 may be used to at least partially correct any such change (see Figure 4B ).

[0101] For example, the optical system 100 may be subject to vibrations that cause the position sensor 108 to move up and down in the plane of Figure 3 Any deviation of the position sensor 108 (and thus the part of the optical system 100 to which it is attached) may cause the exit axis 120 of the optical system 100 to be misaligned with the axis 122 of the illumination area 106. For example, as in Figure 4AAs shown, if the optical system 100 is moved such that the position sensor 108 moves upward, the output axis 120 of the optical system 100 may make a non-zero angle with the axis 122 of the illumination area 106. If the radiation beam 102 is aligned with the output axis 120 of the optical system 100, it will no longer be aligned with the axis 122 of the illumination area 106. As a result, the angular distribution of the radiation at the illumination area 106 will change (relative to the angular distribution of the radiation at the illumination area 106 when the optical system 100 is at Figure 3 its nominal position), which is undesirable. However, as Figure 4B shown, the optical system 100 is arranged to correct this using the adjustable optical device 110.

[0102] In particular, by appropriate rotation of the two mirrors 112, 114 of the adjustable optical device (under the control of the control signal s C ), the radiation beam 102 can be aligned with the axis 122 of the illumination area 106.

[0103] In Figure 4A and 4B the example shown, the optical system 100 is illustrated as using the adjustable optical device 110 to correct any up and down movement of the position sensor 108. It should be understood that this is a simplified example as shown in Figure 4A and 4B shown, only for illustrating the correction principle applied by the adjustable optical device 110. Note that in practice, the adjustable optical device 110 is operable to correct any movement (i.e., changes in position and / or orientation) of the position sensor 108 in all six degrees of freedom.

[0104] To the extent possible, the adjustable optical device 110 can be configured such that the spatial and / or angular distribution of the radiation 102 at the illumination area 106 is generally independent of the determined position and / or orientation (as determined by the position sensor 108) of the parts of the optical system 100. That is, the position sensor 108 and the adjustable optical device 110 form a feedback loop that automatically corrects for the movement of the optical system 100 (as Figure 4B shown).

[0105] Unlike known arrangements for illumination systems IL of lithographic apparatuses in which a radiation beam is generally aligned with the illumination system IL (e.g., using a beam steering unit BSU), Figures 3 to 4B the optical system 100 shown is arranged to create a misalignment between the radiation beam 102 and the optical system 100. In particular, this misalignment automatically corrects for the movement of the optical system 100 (as Figure 4B shown).

[0106] During use, if at least 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. Figures 3 to 4B The optical system 100 shown is advantageous because this allows correction of any movement (or change in position and / or orientation) of at least part of the optical system 100 such that the radiation 102 is accurately delivered to the illumination area 106.

[0107] The optical system 100 may be adapted for use in a lithographic apparatus LA. The optical system may comprise or be part of an illumination system IL used in an imaging device (such as a lithographic apparatus LA). Such an illumination system IL may be operable to condition a received radiation beam (such as from a radiation source or a laser) and to deliver the received radiation to an illumination area (where a mask or reticle MA may be provided) with a desired or required spatial and angular distribution.

[0108] As now discussed, the optical system 100 is particularly beneficial for use in the illumination system IL of a lithographic apparatus LA.

[0109] For a precision imaging device such as a lithographic apparatus LA, it may be very important to illuminate a patterning device MA (also referred to as a mask or reticle) with radiation having a well-defined spatial and angular distribution. For example, it is often desirable to illuminate the patterning device MA with a substantially uniform spatial distribution to ensure good control of the radiation dose delivered to a substrate W (such as a silicon wafer coated with resist). In turn, this may result in better critical dimension (CD) control. The angular distribution of the radiation at the illumination area (where the patterning device MA is provided) may also be referred to as the illumination mode or pupil. The angular distribution of the radiation at the illumination area (where the patterning device MA is provided) describes how the radiation cones that fill each part of the patterning device MA are filled. This may be described by the radiation intensity in the entrance pupil of a projection optical device PS that is arranged to image the patterning device MA onto the substrate W. It is well known that illuminating the patterning device MA with an illumination mode in which the peripheral part of the entrance pupil is illuminated and the central part of the entrance pupil is not illuminated (such as an annular illumination mode and a dipole illumination mode) can generally improve the contrast of the image formed on the substrate in a range of different features (such as relative to full-pupil filling illumination).

[0110] Any variation 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 error of the radiation delivered to the illumination area can result in an asymmetric numerical aperture (NA) clipping, especially for illumination patterns where the outermost part of the entrance pupil is illuminated (such as the extreme dipole). In turn, this will have an adverse effect on the imaging of the patterning device MA, which is undesirable. It is to be understood that the projection system PS typically provides an NA clipping of the radiation beam B patterned by the mask MA. In fact, the lithographic apparatus LA is used to image features that are small compared to the wavelength of the radiation beam B, so the image of the pattern formed on the wafer W is typically diffraction limited and is formed by only a very small number of diffraction orders of the radiation interacting with the mask MA. However, any asymmetric NA clipping of the radiation beam by the projection system PS can lead to alignment errors. A slow variation in the NA clipping (symmetry) will result in a position error (i.e., a moving average) of the image formed on the wafer W, while a rapid variation in the NA clipping will be smeared out, resulting in a blurring of the features formed on the wafer W (an increase in the standard deviation of the average). It is to be understood that, as used herein, "slow" may mean a time scale that is large compared to the exposure time of the wafer, while "fast" may mean a time scale that is small compared to the exposure time of the wafer.

[0111] As described above, in the absence of the feedback loop provided by the position sensor 108 and the adjustable optics (via the controller 116), near the exit 118, the radiation beam 102 can be aligned with the exit axis 120 of the optical system 100. This can be achieved by providing the radiation beam 102 to the optical system 100 such that when the optical system 100 is in its nominal position or configuration, the radiation beam 102 is aligned with the exit axis 120 of the optical system 100. Alternatively, in some embodiments, this can also be achieved using the adjustable optics 110, as now discussed.

[0112] Figure 3 The illustrated optical system 100 also includes a radiation beam measurement sensor 124. The radiation beam measurement sensor 124 is operable to determine the position and / or orientation of the received radiation beam 102 relative to at least a portion of the optical system 100. The adjustable optics 110 is operable to control the optical path of the received radiation beam 102 depending on the determined position and / or orientation of the received radiation beam 102 relative to the said at least portion of the optical system 100 (as determined by the radiation beam measurement sensor 124).

[0113] The controller 116 is also operable to receive a second signal s2 from the radiation beam measurement sensor 124, the second signal s2 indicating the position and / or orientation of the received radiation beam 102 relative to the optical system 100. Additionally, for such an embodiment, the control signal s Cdepending on the first signal s1, the second signal s2, or both the first signal s1 and the second signal s2.

[0114] That is, the radiation beam measurement sensor 124 can be used to align the received radiation beam 102 with the optical system 100 (using the adjustable optics 110) such that when the optical system 100 is in its nominal position or configuration, the radiation beam 102 is aligned with the exit axis 120 of the optical system 100. This can correct any alignment and / or pointing errors of the radiation beam 102 received by the optical system 100. That is, this can correct any misalignment between the radiation beam 102 received by the optical system 110 and the incident axis 126 of the optical system 100.

[0115] However, in the absence of such an arrangement of the above feedback loop using the position sensor 108 and the adjustable optics, if the optical system 100 itself moves, then the radiation beam 102 will also move, and thus the radiation beam 102 will not be accurately aligned with the irradiation area 106 (as Figure 4A shown and described above). However, since the adjustable optics 110 is configured to control the optical path of the received radiation beam 102 depending on the determined position and / or orientation of a part of the optical system 100, any such misalignment between the radiation beam 102 and the irradiation area 106 can be corrected.

[0116] In this embodiment, at least a part of the optical system 100 that operates the radiation beam measurement sensor 124 to determine the position and / or direction of the received radiation beam 102 relative to it is a part of the optical system 100 different from the part of the optical system 100 that 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 part of the optical system 100 near the entrance 104, and the position sensor 108 is operable to determine the position and / or orientation of the part of the optical system 100 near the irradiation area 106. In other embodiments, the part of the optical system 100 that operates the radiation beam measurement sensor 124 to determine the position and / or direction of the received radiation beam 102 relative to it can be the same part of the optical system 100 that operates the position sensor 108 to determine its position and / or orientation.

[0117] Furthermore, in this embodiment, the position sensor 108 is optically located downstream of the adjustable optics 110. Advantageously, this can allow the position sensor 108 to be as close as possible to the irradiation area 106. In turn, this may result in more accurate control of the spatial and angular distribution of the radiation at the irradiation area 106.

[0118] Note that the same actuatable or adjustable optical elements (e.g., mirrors 112, 114 of the adjustable optical device 110) can be used to: (a) control the optical path of the received radiation beam 102 depending on the determined position and / or orientation of a part of the optical system (as determined by the position sensor 108); and (b) control the optical path of the received radiation beam 102 depending on the determined position and / or direction of the received radiation beam 102 (as determined by the radiation beam measurement sensor 124). Alternatively, a first set of optical elements can be provided to control the optical path of the received radiation beam 102 depending on the determined position and / or orientation of a part of the optical system 100 (as determined by the position sensor 108), and a second set of optical elements can be provided to control the optical path of the received radiation beam depending on the determined position and / or direction of the received radiation beam (as determined by the radiation beam measurement sensor 124). For such an embodiment, the adjustable optical device 110 can be considered to include the first set of optical elements and the second set of optical elements.

[0119] In some alternative embodiments, the optical system 100 can include a plurality of position sensors 108, each position sensor operable to determine the position and / or orientation of at least a part of the optical system 100. For example, each position sensor 108 can be operable to determine the position and / or orientation of the part of the optical system 100 to which it is attached. The plurality of position sensors 108 can be disposed at different parts of the optical system 100, such as, but not limited to, at the relay lens RL or the masking device MD. For such an embodiment with a plurality of position sensors 108, the adjustable optical device 110 can be operable to control the optical path of the received radiation beam 102 depending on the position and / or orientation of the part of the optical system 100 determined by each of the plurality of position sensors 108.

[0120] This can allow for the correction of more complex distortions of the optical system 100. For example, if the optical system 100 not only oscillates as a whole, but is also affected by vibration or oscillation modes corresponding to the distortion of the optical system 100, then the plurality of position sensors can allow for at least partial correction of the effect of such oscillation modes on the spatial and / or angular distribution of the radiation transmitted to the illumination area 106.

[0121] At least one position sensor 108 is operable to determine the position and / or orientation of at least part of the optical system 100. Such determination can be a direct measurement of position and / or orientation. Alternatively, the determination can be indirect. For example, the position sensor 108 can measure another quantity (such as acceleration) from which the position can be determined. Any suitable type of position sensor 108 can be used. Generally, each position sensor determines the position and / or orientation of a part of the optical system 100 relative to a reference frame. The reference frame can be any frame in which the illumination area 106 (also known as the illumination slit or just the slit in the art) is stationary.

[0122] In some embodiments, at least one position sensor 108 is operable to determine the position and / or orientation of at least part of the optical system in all six degrees of freedom. These degrees of freedom can be, for example, x position, y position, z position, Rx rotation, Ry rotation, and Rz rotation.

[0123] In some embodiments, the (plural) position sensors 108 include one or more accelerometers. Such embodiments determine the position and / or orientation of a part of the optical system 100 relative to an inertial frame.

[0124] In one embodiment, the position sensor 108 or each position sensor 108 can include at least two accelerometers arranged to determine the acceleration of a part of the optical system 100 in at least two directions, which two directions are generally orthogonal to the optical path of the radiation beam 102. This allows determination of the position of the part of the optics 100 in the two directions that are generally orthogonal to the optical path. In one embodiment, the position sensor 108 or each position sensor 108 can include at least three accelerometers arranged to determine the acceleration of a part of the optical system 100 in three linearly independent directions. This allows determination of the position of the part of the optics 100 in the three linearly independent directions.

[0125] In some embodiments, the accelerometer or each accelerometer is operable to determine acceleration and / or position and has three degrees of freedom. In one embodiment, the position sensor 108 includes two or three accelerometers, each arranged to determine three degrees of freedom. Advantageously, this can allow the position sensor 108 to determine the position and / or orientation of at least part of the optical system in all six degrees of freedom.

[0126] Alternative position sensors can include interferometric sensors. For example, such interferometric sensors can be of the type used to monitor the position of the mask table MT or the wafer table WT in a lithographic apparatus LA.

[0127] In some embodiments, the optical system 100 can include beam steering optics (such as Figure 2The beam steering unit BSU (of the type provided), arranged to direct radiation 102 along an adjustable optical path.

[0128] The beam steering optics can receive a radiation beam B (e.g., from a radiation source SO). For example, the beam steering optics can include 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. For such an embodiment, the adjustable optics 110 of the optical system 100 can include the beam steering optics BSU.

[0129] Additionally or alternatively, in some embodiments, the optical system 100 can include pupil shaping optics PSO (e.g., Figure 2 of the type shown and described above), operable to control the angular distribution of the radiation delivered to the illumination area 106. That is, by selecting one or more configurations of the pupil shaping optics, different illumination patterns or pupils can be used to irradiate the illumination area 106. For such an embodiment, the adjustable optics 110 can include the pupil shaping optics PSO. Those skilled in the art will appreciate that an array of mirrors disposed in the pupil shaping optics PSO can be used to control the radiation beam depending on the position and / or direction of the radiation beam measured by the sensors 108, 124.

[0130] Some embodiments of the present disclosure relate to a new lithography apparatus LA, which is generally Figure 1 and 2 of the type shown and described above, the lithography apparatus LA comprising: Figures 3 to 4BAn optical system 100 of the type shown and described above, wherein a support structure MT (mask table) is configured to support a patterning device MA such that the patterning device MA can be positioned in an illumination region 106. This new type of lithographic apparatus LA is advantageous because this allows correction of any movement (or change in position and / or orientation) of at least part of the optical system 100, such that radiation B is more accurately delivered to the illumination region 106 (in use, the patterning device MA is positioned in this illumination region 106). In turn, as explained above, any change in the position and / or angle of the radiation B delivered to the patterning device MA can affect the imaging of the patterning device ME on the substrate W. In particular, any pointing error of the radiation B delivered to the illumination region 106 can lead to an asymmetric numerical aperture (NA) clip, especially for illumination patterns where the outermost part of the entrance pupil is illuminated (such as extreme dipole). In turn, this will have an adverse effect on the imaging of the patterning device MA, which is not desirable. The new lithographic apparatus LA allows the use of a wider range of illumination patterns without such problems (such as asymmetric NA clip). Additionally or alternatively, the new lithographic apparatus LA allows greater movement or vibration of parts of the lithographic apparatus LA without such problems (such as asymmetric NA clip). In turn, tolerating greater movement or vibration can advantageously allow an increase in the throughput of the lithographic apparatus LA and, associated therewith, a reduction in the manufacturing cost per wafer W.

[0131] Some embodiments of the present disclosure relate to a method 200 of providing radiation 102 to an illumination region 106 via an optical system 100, as now referenced Figure 5 and 6 discussed.

[0132] Method 200 includes a step 202 of determining the position and / or orientation of at least part of the optical system 100. Method 200 further includes a step 204 of adjusting at least one optical element 112, 114 in the optical system 100 depending on the determined position and / or orientation of the part of the optical system 100.

[0133] Figure 5 The method 200 shown can be performed using Figures 3 to 4B the optical system 100 shown. Figure 5 The method 200 shown is advantageous because this allows correction of any movement (or any change in position and / or orientation) of at least part of the optical system 100, such that the radiation 102 is accurately delivered to the illumination region 106.

[0134] Figure 5The method 200 shown is particularly beneficial for irradiating a patterning device MA (also known as a reticle or mask) as part of a lithographic exposure process. For example, any variation in the position and / or angle of the radiation delivered to the patterning device MA can affect the imaging of the patterning device MA on the substrate W. In particular, any pointing error of the radiation delivered to the illumination area 106 can lead to an asymmetric numerical aperture (NA) clipping, especially for illumination patterns (such as extreme dipole) where the outermost part of the entrance pupil of the projection system PS is illuminated. In turn, this will have an adverse effect on the imaging of the patterning device MA, which is undesirable.

[0135] Depending on the determined position and / or orientation of a part of the optical system 100, adjusting at least one optical element 112, 114 in the optical system 100 can include at least partially correcting any variation in the spatial and / or angular distribution of the radiation at the illumination area 106 due to any deviation of the determined position and / or orientation from the nominal position.

[0136] For example, the optical system 100 can have a nominal position. When set at the nominal position, the position and direction of the radiation 102 delivered to the illumination area 106 may be optimal. In use, the optical system 100 may be subject to vibrations. For example, for an embodiment in which the optical system 100 comprises, is the illumination system IL of a lithographic apparatus LA or forms part thereof, movement of other parts of the lithographic apparatus LA during use may cause some vibrations of the optical system 100.

[0137] Any deviation of the determined position and / or orientation of the optical system 100 from the nominal position can lead to sub-optimal irradiation of the illumination area 106, and thus, for such an embodiment, at least one optical element 112, 114 (which may be referred to as an adjustable optical device 110) is used to at least partially correct any variation.

[0138] To the extent possible, adjusting at least one optical element 112, 114 in the optical system 100 depending on the determined position and / or orientation of a part of the optical system 100 can be performed such that the spatial and / or angular distribution of the radiation at the illumination area 106 is generally independent of the determined position and / or orientation of that part of the optical system 100.

[0139] In Figure 6 Another method 300 of providing radiation 102 to the illumination area 106 via the optical system 100 is schematically shown. Figure 6 The method 300 shown includes Figure 5 Steps 202, 204 of the method 200 shown and described above.

[0140] Figure 6The method 300 shown further includes step 302 of providing a radiation beam 102.

[0141] Figure 6 The method 300 shown further includes step 304 of determining the position and / or orientation of the provided radiation beam 102 relative to at least a portion of the optical system 100.

[0142] Figure 6 The method 300 shown further includes step 306 of adjusting at least one optical element 112, 114 in the optical system 100 depending on the determined position and / or orientation of the provided radiation beam 102 relative to the at least a portion of the optical system 100.

[0143] Thus, in this embodiment, the method 300 may include step 308 of adjusting at least one optical element 112, 114 in the optical system 100 depending on both: (a) the determined position and / or orientation of a portion of the optical system 110; and (b) the determined position and / or orientation of the received radiation beam 102.

[0144] Figure 5 and 6 Any of the methods 200, 300 shown may include determining the position and / or orientation of a plurality of portions of the optical system 100; and adjusting at least one optical element 112, 114 in the optical system 100 depending on the determined position and / or orientation of each of the plurality of portions of the optical system 100. This may allow for correction of more complex distortions of the optical system 100. For example, if the optical system 100 not only oscillates as a whole, but is also affected by vibration or oscillation modes corresponding to the distortion of the optical system 100.

[0145] Using Figure 5 and 6 Any of the methods 200, 300 shown, at least a portion of the optical system 100 whose position and / or orientation is determined is optically downstream of at least one optical element 112, 114 depending on its adjustment. Advantageously, this may allow at least a portion of the optical system 100 whose position and / or orientation is determined to be as close as possible to the irradiation area 106. In turn, this may result in more accurate control of the spatial and angular distribution of the radiation 102 at the irradiation area 106.

[0146] Figure 5 and 6 Any of the methods 200, 300 shown may further include adjusting the radiation beam 102 to control the spatial and / or angular distribution of the radiation delivered to the irradiation area 106.

[0147] Some embodiments of the present disclosure relate to a lithographic exposure method 400, as now referencedFigure 7 discussed

[0148] The lithographic exposure method 400 includes a step 402 of providing a patterning device MA in an illumination region 106.

[0149] The lithographic exposure method 400 further includes using Figure 5 or the method 200, 300 shown in FIG. 6 to provide radiation to the illumination region 106 via an optical system 100 to form a patterned radiation beam in step 404.

[0150] The lithographic exposure method 400 further includes a step 406 of collecting the patterned radiation beam and using it to form an image of the patterning device MA on a substrate W.

[0151] Figure 7 The lithographic exposure method shown is advantageous because this allows correction of any movement (or change in position and / or orientation) of at least part of the optical system 100 such that the radiation 102 is more accurately delivered to the illumination region 106 (which provides the patterning device MA in use). In turn, as explained above, any change in the position and / or angle of the radiation 102 delivered to the patterning device MA can affect the imaging of the patterning device MA on the substrate W. In particular, any pointing error of the radiation delivered to the illumination region 106 can lead to an asymmetric numerical aperture (NA) clipping (in step 406 of collecting the patterned radiation beam), especially for illumination patterns (such as extreme dipoles) where the outermost part of the entrance pupil of the projection system PS is illuminated. In turn, this will have an adverse effect on the imaging of the patterning device MA, which is undesirable. Figure 7 The lithographic exposure method 400 shown allows the use of a wider range of illumination patterns without this problem (such as asymmetric NA clipping). Additionally or alternatively, Figure 7 The lithographic exposure method 400 shown allows greater movement or vibration of parts of the lithographic apparatus LA without this problem (such as asymmetric NA clipping). In turn, tolerating greater movement or vibration can advantageously allow an increase in the throughput of the lithographic apparatus LA and, associated therewith, a reduction in the manufacturing cost per wafer W.

[0152] In Figure 7 some embodiments of the lithographic exposure method 400 shown, the exposure can be a scanning exposure such that: (a) the step 402 of providing the patterning device MA in the illumination region 106 can include moving the patterning device MA through the illumination region 106; and (b) the step 406 of forming an image of the patterning device MA on the substrate W can include moving the substrate W such that the image of the patterning device MA is substantially stationary relative to the substrate W.

[0153] Although specific reference may be made in this text to the use of lithographic equipment in IC manufacture, it should be understood that the lithographic equipment described herein may have other applications. Possible other applications include the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat panel displays, liquid crystal displays (LCDs), thin film magnetic heads, and the like.

[0154] Although embodiments of the invention may be specifically recited herein in the context of lithographic equipment, embodiments of the invention may be used in other apparatuses. Embodiments of the invention may form part of a mask inspection apparatus, a metrology apparatus, or any apparatus for measuring or processing an object such as a wafer (or other substrate) or a mask (or other patterning device). Such apparatuses may generally be referred to as lithographic tools. Such lithographic tools may operate under vacuum conditions or ambient (non-vacuum) conditions.

[0155] Although the use of embodiments of the invention may have been specifically recited above in the context of optical lithography, it should be appreciated that, where the context allows, the invention is not limited to optical lithography and may be used in other applications, such as imprint lithography.

[0156] Where the context allows, embodiments of the invention may be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the invention may also be implemented as instructions stored on a machine-readable medium, which may be read and executed by one or more processors. The 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, the machine-readable medium 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. Further, firmware, software, routines, instructions may be described herein as performing certain actions. However, it should be appreciated that such description is merely for convenience and that such actions are in fact caused by computing devices, processors, controllers, or other devices executing the firmware, software, routines, instructions, etc., and that this causes actuators or other devices to interact with the physical world.

[0157] Aspects of the invention are set out in the following clauses.

[0158] 1. 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 direct the radiation beam via an optical path to an illumination area, the optical system comprising: at least one position sensor operable to determine the position and / or orientation of at least part of the optical system; and an adjustable optical device configured to control the optical path of the received radiation beam depending on the determined position and / or orientation of the part of the optical system.

[0159] 2. The optical system according to item 1, wherein the adjustable optical device is configured to control the optical path of the received radiation beam depending on the determined position and / or orientation of the part of the optical system to at least partially correct any change in the spatial and / or angular distribution of the radiation at the illumination area due to any deviation of the determined position and / or orientation from a nominal position.

[0160] 3. The optical system according to item 1 or antenna 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 part of the optical system, and wherein the adjustable optical device is operable to control the optical path of the received radiation beam depending on the determined position and / or direction of the received radiation beam relative to the said at least part of the optical system.

[0161] 4. The optical system according to any one of the preceding items, comprising a plurality of position sensors, and wherein the adjustable optical device is operable to control the optical path of the received radiation beam depending on the position and / or orientation of the part of the optical system determined by each of the plurality of position sensors.

[0162] 5. The optical system according to any one of the preceding items, wherein the position sensor or each position sensor comprises one or more accelerometers.

[0163] 6. The optical system according to any one of the preceding items, wherein at least one position sensor is optically located downstream of the adjustable optical device.

[0164] 7. The optical system according to any one of the preceding items, further comprising a controller operable to:

[0165] receive a first signal from the position sensor or each position sensor, the first signal indicating the position and / or orientation of the part of the optical system; and generate a control signal and send it to the adjustable optical device, the control signal being dependent on the first signal.

[0166] 8. An optical system according to claim 7 when directly or indirectly dependent on claim 3, wherein the controller is further operable to receive a second signal from the radiation beam measurement sensor or each radiation beam measurement sensor, the second signal indicating the position and / or orientation of the received radiation beam relative to the optical system; and wherein the control signal is dependent on the first signal and the second signal.

[0167] 9. An optical system according to any of the preceding claims, comprising beam steering optics arranged to direct radiation along an adjustable optical path.

[0168] 10. An optical system according to claim 9, wherein the adjustable optics comprise beam steering optics.

[0169] 11. An optical system according to any of the preceding claims, comprising pupil shaping optics operable to control the angular distribution of the radiation transmitted to the illumination area.

[0170] 12. An optical system according to claim 11, wherein the pupil shaping optics comprise a mirror array including a plurality of independently adjustable mirrors.

[0171] 13. An optical system according to claim 11 or claim 12, wherein the adjustable optics comprise pupil shaping optics.

[0172] 14. A lithographic apparatus comprising: an optical system according to any of the preceding claims, the optical system operable to receive radiation and direct at least part of the received radiation to an illumination area; a support structure configured to support a patterning device such that the patterning device can be positioned in 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 on the substrate supported by the substrate table.

[0173] 15. A method of providing radiation to an illumination area via an optical system, the method comprising: determining the position and / or orientation of at least part of the optical system; and

[0174] adjusting at least one optical element in the optical system depending on the determined position of the part of the optical system.

[0175] 16. The method according to claim 15, wherein adjusting at least one optical element in the optical system depending on the determined position and / or orientation of the part of the optical system comprises: at least partially correcting any change in the spatial and / or angular distribution of the radiation at the illumination area due to any deviation of the determined position and / or orientation from a nominal position.

[0176] 17. The method according to item 15 or item 16 further comprises: providing a radiation beam; determining the position and / or orientation of the provided radiation beam relative to at least a part of the optical system; and adjusting at least one optical element in the optical system depending on the determined position and / or orientation of the provided radiation beam relative to the at least a part of the optical system.

[0177] 18. The method according to any one of items 15 to 17 comprises: determining the position and / or orientation of a plurality of parts of the optical system; and adjusting at least one optical element in the optical system depending on the determined position and / or orientation of each part of the plurality of parts of the optical system.

[0178] 19. The method according to any one of items 15 to 18, wherein at least a part of the optical system whose position and / or orientation is determined is optically downstream of at least one optical element that is adjusted depending on the determined position and / or orientation.

[0179] 20. The method according to any one of items 15 to 19 further comprises: adjusting the radiation beam to control the spatial and / or angular distribution of the radiation transmitted to the irradiation area.

[0180] 21. A lithographic exposure method, the method comprising: providing a patterning device in an irradiation area; using the method according to any one of items 15 to 20 to provide radiation to the irradiation 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.

[0181] 22. The lithographic exposure method according to item 21, wherein the exposure is a scanning exposure, such that providing the patterning device in the irradiation area comprises: moving the patterning device through the irradiation area, and forming an image of the patterning device on the substrate comprises: moving the substrate such that the image of the patterning device is substantially stationary relative to the substrate.

[0182] 23. A lithographic apparatus comprising an optical system according to any one of items 1 to 13.

[0183] 24. The optical system according to any one of items 1 to 13 and 23, wherein at least one position sensor is provided at a shielding device of a relay lens and / or an imaging device.

[0184] Although specific embodiments of the present invention have been described above, it is to be understood that the present invention may be practiced in other ways different from the described manner. The above description is intended to be illustrative, not restrictive. Thus, it will be apparent to those skilled in the art that the described present invention may be modified without departing from the scope of the claims set forth below.

Claims

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

2. The optical system according to claim 1, wherein the adjustable optical device is configured to control the optical path of the received radiation beam depending on the determined position and / or orientation of the part of the optical system to at least partially correct any change in the spatial and / or angular distribution of the radiation at the illumination area due to any deviation of the determined position and / or orientation from a nominal position.

3. The optical system according to claim 1 or 2, comprising a plurality of position sensors, and wherein the adjustable optical device is operable to control the optical path of the received radiation beam depending on the position and / or orientation of the part of the optical system determined by each of the plurality of position sensors.

4. The optical system according to any one of the preceding claims, wherein the position sensor or each position sensor comprises one or more accelerometers.

5. The optical system according to any one of the preceding claims, wherein at least one position sensor is optically located downstream of the adjustable optical device.

6. The optical system according to any one of the preceding claims, further comprising a controller operable to: receive a first signal from the position sensor or each position sensor, the first signal indicating the position and / or orientation of the part of the optical system; and generate a control signal and send the control signal to the adjustable optical device, the control signal depending on the first signal.

7. The optical system according to claim 6, wherein the controller is further operable to receive a second signal from the radiation beam measurement sensor or each radiation beam measurement sensor, the second signal indicating the position and / or direction of the received radiation beam relative to the optical system; and wherein the control signal depends on the first signal and the second signal.

8. The optical system according to any one of the preceding claims, comprising beam steering optics arranged to direct the radiation along an adjustable optical path.

9. The optical system according to any one of the preceding claims, comprising pupil shaping optics operable to control the angular distribution of the radiation transmitted to the illumination area.

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

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

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

13. The method according to claim 11 or 12, comprising: determining the position and / or orientation of a plurality of parts of the optical system; and adjusting at least one optical element in the optical system depending on the determined position and / or orientation of each part of the plurality of parts of the optical system.

14. The method according to any one of claims 11 to 13, wherein at least a part of the optical system whose position and / or orientation is determined is optically downstream of the at least one optical element adjusted depending on the determined position and / or orientation.

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

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