Projection system characterization system and method

Abstract

Disclosed herein is a computing system configured to perform a method for determining an aberration of an optical system in response to patterned light, the method comprising: determining a combination of test features, the combination of test features substantially corresponding to an arrangement of product features on a patterning device, the product feature is arranged to pattern the light before it passes through the optical system; and determining an aberration caused by a response of the optical system to the patterned light, the response of the optical system to the patterned light depending on the known response of each test feature in the determined combination.

Description

Cross Reference to Related Applications

[0001] This application claims priority to EP application 23199147.2, filed on September 22, 2023, which is incorporated herein in its entirety by reference. TECHNICAL FIELD

[0002] The present invention relates to a method of characterizing a projection system of a lithographic apparatus. During a lithographic exposure, a patterned light illuminates the projection system. The method of characterizing the projection system according to embodiments allows determining a thermal response of the projection system for any pattern of light. BACKGROUND

[0003] A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually a target portion of the substrate. The lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that situation, a patterned device, which is also called a mask or a reticle, can be used to generate the circuit pattern to be formed on individual layers of the IC. This pattern can be transferred onto a target portion (e.g., including part of, one, or several dies) of the substrate (e.g., a silicon wafer) by imaging it onto a layer of radiation-sensitive material (resist) provided on the substrate. Typically, a single substrate will contain a network of adjacent target portions to be patterned simultaneously, which are commonly referred to as “fields” or “shots”.

[0004] A lithographic apparatus includes a projection system. The projection system includes optical elements such as, for example, lenses. Optical aberrations can arise due to defects in the optical elements. Optical aberrations can also arise due to projection effects such as, for example, heating of the optical elements that occurs during a lithographic exposure. A projection system model is used to determine one or more adjustments that can be made to the optical elements of the projection system. The determined adjustments can have the effect of reducing optical aberrations within the projection system.

[0005] It can be desirable to provide, for example, aspects that improve calibration, tuning, and / or use of a projection system modeling method that can eliminate or mitigate one or more of the problems identified in the prior art, whether in this document or elsewhere. SUMMARY

[0006] According to a first aspect of the invention, a computing system is provided, configured to perform a method for determining aberrations of an optical system in response to patterned light, the method comprising: determining a combination of test features substantially corresponding to an arrangement of product features on a patterning device, the product features being arranged to pattern the light before it passes through the optical system; and determining aberrations resulting from the response of the optical system to the patterned light, the response of the optical system to the patterned light depending on a known response of each test feature in the determined combination.

[0007] According to a second aspect of the invention, a characterization system for characterizing an optical system is provided, the characterization system comprising: an illumination device configured to perform a plurality of illumination processes; a wavefront sensor configured to measure, in each of the plurality of illumination processes, the wavefront of light after the light has traveled through the optical system; and a computing system; wherein: each illumination process comprises: patterning the light with a different one of the test features in a set comprising a plurality of test features; each test feature in the set having a single pitch; each test feature in the set having a single pitch different from the other test features in the set; each test feature in the set having a single orientation; and the computing system being configured to generate data characterizing the optical system, the data characterizing the optical system depending on a determined change in the wavefront measured in the plurality of illumination processes.

[0008] According to a third aspect of the invention, a computer-implemented method is provided for determining aberrations in response of an optical system to patterned light, the method comprising: determining a combination of test features substantially corresponding to product features on a patterning device, the product features being arranged to pattern the light prior to its passage through the optical system; and determining aberrations resulting from the response of the optical system to the patterned light, the response of the optical system to the patterned light depending on a known response of each test feature in the determined combination.

[0009] According to a fourth aspect of the invention, a method for characterizing an optical system is provided, the method comprising: performing a plurality of illumination processes; wherein each illumination process comprises: patterning light with a different one of the test features in a set comprising a plurality of test features; and measuring a wavefront change of the patterned light after the patterned light has traveled through the optical system; wherein: each test feature in the set has a single pitch; each test feature in the set has a single pitch different from the other test features in the set; and each test feature in the set has a single orientation. Attached Figure Description

[0010] Embodiments of the invention will now be described by way of example only with reference to the accompanying schematic diagrams, in which: Figure 1 A schematic overview of the photolithography apparatus is described; and Figure 2A and Figure 2B The diffraction order and diffraction angle of the patterned light are schematically shown. Detailed Implementation

[0011] In this document, the terms “radiation” and “beam” are used to cover all types of electromagnetic radiation, including ultraviolet radiation (e.g., with wavelengths of 365 nm, 248 nm, 193 nm, 157 nm, or 126 nm) and EUV (extreme ultraviolet radiation, e.g., with wavelengths in the range of about 5 nm to 100 nm).

[0012] The terms “mask,” “mask,” or “patterning apparatus” as used herein can be broadly understood to refer to a general patterning apparatus that can be used to impart a patterned cross-section to an incoming radiation beam, the patterned cross-section corresponding to a pattern to be created in a target portion of a substrate. The term “optical valve” may also be used in this context. Examples of such patterning apparatuses, in addition to classic masks (transmissive or reflective, binary, phase-shifting, hybrid, etc.), include programmable mirror arrays and programmable LCD arrays.

[0013] For the purpose of illustrating this invention, the Cartesian coordinate system is used. The Cartesian coordinate system has three axes: the x-axis, the y-axis, and the z-axis. Each of the three axes is orthogonal to the other two axes. Rotation about the x-axis is called Rx rotation. Rotation about the y-axis is called Ry rotation. Rotation about the z-axis is called Rz rotation. The Cartesian coordinate system is not intended to limit the invention and is merely used for illustration.

[0014] Figure 1 A lithography apparatus LA is schematically depicted. The lithography apparatus LA includes: an irradiation system (also referred to as an irradiator) IL configured to modulate a radiation beam or beam B (e.g., UV radiation, DUV radiation, or EUV radiation); a mask support (e.g., a mask stage) MT configured to support a patterning apparatus (e.g., a mask) MA and connected to a first positioner configured to accurately position the patterning apparatus MA according to specific parameters; and a substrate support (e.g., a wafer stage) WT configured to hold a substrate (e.g., a resist-coated wafer) W. A second positioner PW may be arranged and configured to accurately position the substrate support according to specific parameters. A projection lens system (e.g., a refractive projection lens system) PS is configured to project a pattern, imparted by the radiation beam B by the patterning apparatus MA, onto a target portion (e.g., comprising one or more dies) of the substrate W.

[0015] In operation, the irradiation system IL receives a radiation beam from the radiation source SR, for example, via a beam delivery system. The irradiation system IL may include various types of optical components for guiding, shaping, and / or controlling the radiation, such as refractive, reflective, magnetic, electromagnetic, electrostatic, and / or other types of optical components or any combination thereof. The irradiator IL can be used to modulate the radiation beam B to have a desired spatial and angular intensity distribution in a cross-section of the radiation beam B at the plane of the patterning device MA.

[0016] Depending on the exposure radiation used and / or other factors (such as the use of immersion liquid or vacuum), the term "projection lens system" PS as used herein should be interpreted broadly to encompass all types of projection systems, including refractive, reflective, catadioptric, distorting, magnetic, electromagnetic, and / or electrostatic optical systems, or any combination thereof. Any use of the term "projection lens" herein may be considered synonymous with the more general term "projection system" PS.

[0017] A lithography apparatus LA can be of the type in which at least a portion 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; this is also known as immersion lithography. Further information on immersion techniques is given in US6952253, which is incorporated herein by reference.

[0018] The lithography apparatus LA can also be of the type with two or more substrate supports WT (also known as "dual platforms"). In such a "multi-platform" machine, the substrate supports WT can be used in parallel, and / or the step of preparing the substrate W for subsequent exposure can be performed on the substrate W located on one of the substrate supports WT, while another substrate W on the other substrate support WT is used to expose a pattern on the other substrate W.

[0019] In addition to the substrate support WT, the lithography apparatus LA may also include a measurement platform. The measurement platform is arranged to hold sensors and / or cleaning equipment. The sensors may be arranged to measure characteristics of the projection system PS or the radiation beam B. The measurement platform may hold multiple sensors. The cleaning equipment may be arranged to clean portions of the lithography apparatus LA, such as portions of the projection system PS or portions of the system providing the immersion solution. The measurement platform may move below the projection system PS as the substrate support WT moves away from the projection system PS.

[0020] In operation, a radiation beam B is incident on a patterning apparatus (e.g., a mask MA held on a mask support MT) and patterned by a pattern (design layout) present on the patterning apparatus MA. After passing through the mask MA, the radiation beam B passes through a projection system PS, which focuses the beam onto a target portion of the substrate W. With the aid of a second positioner and a position measurement system, the substrate support WT can be moved precisely, for example, to position different target portions in the path of the radiation beam B at a focused and aligned location. Similarly, a first positioner and possibly another position sensor (which...) Figure 1 (Not explicitly depicted) can be used to accurately position the patterning apparatus MA relative to the path of the radiation beam B. The patterning apparatus MA and the substrate W can be aligned using mask alignment marks and substrate alignment marks. Although the substrate alignment marks occupy dedicated target portions, they can be located in the space between the target portions. When the substrate alignment marks are located between the target portions, the substrate alignment marks are called scribing alignment marks.

[0021] A shielding device MD is provided for selectively shielding portions of the pattern forming device MA from radiation beam B. Figure 1 In other embodiments not illustrated, the masking device MD can be provided for selectively blocking portions of the patterned projection beam. For example... Figure 1 As shown, a relay optics (or relay lens) RL is provided for projecting radiation passing through the shielding device onto the pattern forming device MA.

[0022] Among the factors affecting overlay and focus drift, especially for commonly used, very localized illumination sources such as dipole illumination, lens heating is a major contributor to image quality degradation. These localized heat distributions on the lens can lead to undesirable effects on the imaging wavefront. Aberration drift during batch exposures is unavoidable due to lens heating during exposure. Accumulated light absorption within the lens can ultimately result in imaging defects, a direct consequence of wavefront errors induced by lens heating. Lens heating control is crucial for maintaining image quality. A key step in lens heating control is accurately predicting the lens's heating capability.

[0023] The lithography apparatus LA may also include one or more wavefront sensors, for example, on the substrate support WT. The wavefront sensor can measure the quality of the wavefront image and any aberrations, and thus enables (e.g., in parallel) measurement of optical aberrations through the projection slit, thereby enabling, for example, more accurate alignment, improved heating correction of the patterning apparatus MA, and heating correction of flying lenses. The wavefront sensor may include an interferometric wavefront measurement system and can perform static measurements of up to high-order lens aberrations. It can be implemented as an integrated measurement system for system initialization and calibration. Alternatively, it can be used for “on-demand” monitoring and recalibration. Therefore, the wavefront sensor may be able to measure lens aberrations on a batch-by-batch or per-wafer basis, depending on its design.

[0024] Wavefront sensors are known to be used to measure wavefront errors, or aberrations. These are typically described as coefficients in a series of two-dimensional (2D) mathematical functions known as Zernike polynomials. These can be recombinated to describe some well-known optical aberrations, such as spherical aberration, coma, and astigmatism.

[0025] As referenced above Figure 1 As described, during operation of the photolithography apparatus LA, light (i.e., radiation beam B) is patterned by a pattern (design layout) present on a patterning apparatus MA. The patterning apparatus MA includes an arrangement of product features. The arrangement of product features (i.e., the pattern) imparts the pattern to the light. During the exposure process, the patterned light is projected onto the substrate W via a lens.

[0026] The wavefront of the light used during the exposure process depends on how the light is patterned by the patterning equipment MA. Specifically, the wavefront depends on the type and arrangement of the product features on the patterning equipment MA.

[0027] It is known that for a lens that has been heated through the exposure process, the wavefront signal will carry the "memory" or "ghost" of the exposed product feature (a wavefront contribution specific to the patterning apparatus MA, irradiation, and dose). This is because the lens (i.e., the projection system PS) heats up when the product feature is exposed. The heated area is determined by the diffraction pattern induced by the combination of the irradiation mode and the product feature on the patterning apparatus MA. Immediately after exposure, the wavefront data can be determined using a wavefront sensor. The wavefront sensor will determine the change in the wavefront relative to its state before the lens was heated. This change is generated by and describes the shape of the product feature and the irradiation settings. As heat diffuses within the lens material, this change will gradually disappear.

[0028] US2023 / 0084130 A1 discloses a technique for using such wavefront data to improve lens heating control and to reduce adverse effects caused by lens heating. In US2023 / 0084130 A1, aberrations induced by lens heating effects are determined for a specific arrangement of product features.

[0029] Actual products will typically consist of numerous layers, each with a different arrangement of product features. The arrangement of product features within each layer may also vary.

[0030] The limitation of the technology disclosed in US2023 / 0084130 A1 is that wavefront data requires a large arrangement of product features. The time required to obtain the required wavefront data can be daunting. Furthermore, additional wavefront data measurements may be necessary whenever a new arrangement of product features is used.

[0031] The embodiments provide a new technique for characterizing the heating and / or cooling effects of a lens. The lens may be a projection system (PS) of a photolithography apparatus. Therefore, the embodiments provide a new technique for characterizing the heating and / or cooling effects of the projection system (PS).

[0032] The embodiments determine the lens heating and / or cooling response for each of a plurality of specific pitches of a test feature on the patterning apparatus MA. The combination of lens heating responses can be used to determine the overall lens heating response for an arrangement of the test feature. Advantageously, the embodiments can model the lens heating response for any arrangement of test features without measuring the lens heating response for a specific arrangement.

[0033] The embodiments are described in more detail below.

[0034] Light is used to pattern a test feature on a patterning device MA under predetermined illumination conditions. The test feature may have a critical size and a single orientation. The test feature may be, for example, a linear line pattern, wherein the pattern has a constant pitch. It may be a dense linear line pattern.

[0035] Patterned light passes through a lens, which can be an objective lens (i.e., a projection system PS). The light is diffracted by the pattern as it enters the lens, and this diffraction causes the light to illuminate different parts of the lens.

[0036] Figure 2A The diffraction order of patterned light is schematically shown. The light may have been patterned by a patterning device, such as a patterning device MA provided by an illumination system IL. The patterned light can thus be placed in front of a lens. Figure 2B The diffraction angle is schematically shown in the side view. For σ in / σ outThe different orders are shown, where σ in and σ out These refer to the interior and exterior angles of the light cone distribution provided by the illumination system IL, respectively. σ in value and σ out The value is normalized to the numerical aperture of the optical arrangement, such as the numerical aperture of the projection system PS.

[0037] The wavefront of light after passing through the lens can be measured by one or more wavefront sensors. Each wavefront sensor can be as described above. Accordingly, the wavefront sensor can be on the substrate support WT and can include an interferometric wavefront measurement system.

[0038] A wavefront sensor may include a camera that captures pixelated images. The pixelated images are converted into wavefront sensor signals. In this example, the wavefront sensor signal carries specific wavefront information contributed to or induced by test features. Such a wavefront sensor signal may be a mapped representation of the wavefront error across the exit pupil plane of the lens. Alternatively or additionally, processing may be performed to determine the Zernike polynomial corresponding to the wavefront sensor signal according to known techniques.

[0039] In an embodiment, wavefront data (or information) for specific test characteristics and irradiation conditions may include wavefront sensor signals and / or corresponding Zernike polynomials for the wavefront sensor signals.

[0040] The embodiments repeatedly use the above process to determine wavefront data for multiple test features at different pitches and illumination conditions. The wavefront data characterizes the lens heating response of the lens (i.e., the projection system PS). The characterization process can determine the full-angle response of the lens (i.e., the projection system PS).

[0041] The characterization of the lens heating response according to the embodiments may include the following irradiation process.

[0042] In the first illumination process, the lens can be illuminated by light with low energy. The light used in the first illumination process is preferably unpatterned light. The purpose of the first illumination process is to fill the pupil to enable interferometric wavefront measurements. While patterned light can alternatively be used in the first illumination process, by using unpatterned light, the pupil will be filled uniformly, and full wavefront characterization becomes possible. The lens can be an objective lens, such as a projection system PS. The first illumination process can be performed while the lens is cold. If the lens is at ambient temperature, it is cold because it has not recently been heated by an exposure process, etc. By using illumination light at low intensity, the light will not significantly heat the lens. The light that has passed through the lens can be used to illuminate the substrate W, and a wavefront sensor can be used to measure the wavefront data of the light after passing through the lens. This wavefront data is an initial characterization of the cold-state lens using light.

[0043] The first set of multiple illumination processes can then be performed using light patterned with the same test feature on a patterning device MA. The test feature may have a critical size and a single orientation. The test feature may be, for example, a first linear line pattern, wherein the pattern has a first constant pitch. The first constant pitch may be referred to as the first pitch P1.

[0044] Light patterned with a pattern having a first pitch P1 can be used to irradiate the substrate W, causing the lens to heat up. Wavefront data can be measured at the beginning and end of the irradiation process. The change (i.e., difference) in the wavefront data is a measure of the lens heating effect during irradiation of the substrate W using light patterned with a first pitch P1.

[0045] Light patterned with a pattern having a first pitch P1 can then be used to irradiate one or more other substrates W. This further heats the lens. Given the number of substrates that have been irradiated, the expected amount of lens heating can be determined. For each substrate W, wavefront data can be measured at the beginning and end of the irradiation process. The change in wavefront data is a measure of the effect of lens heating during the irradiation of each substrate W. The process of heating the substrates W and thus determining the change in wavefront data can be repeated until there is no substantial change in the wavefront data when the substrate is irradiated. This indicates that the thermal behavior of the lens has saturated for light patterned with a pattern having a first pitch P1.

[0046] The lens can then be allowed to cool, allowing it to return to a cooled state. The cooling time of the lens can be measured to determine its cooling characteristics. The factors defining the cooling characteristics of the lens are expected to be the same as those defining its heating characteristics. Therefore, the heating and cooling responses of the lens are related to each other.

[0047] A second set of processes involving irradiating multiple substrates W and measuring wavefront data can then be performed using light patterned with different test features on a patterning apparatus MA. The test features may have a critical size and a single orientation. The test feature may be, for example, a second linear line pattern having a second constant pitch. It may be a second dense linear line pattern. The second constant pitch may be referred to as the second pitch P2. The second pitch P2 may have a pitch different from the first pitch P1. For example, the second pitch P2 may be a larger pitch than the first pitch P1. The second pitch P2 may be a smaller pitch than the first pitch P1. The orientation of the second linear line pattern may be the same as the first linear line pattern. The orientation of the second linear line pattern may be different from the orientation of the first linear line pattern.

[0048] The process of irradiating a substrate with light patterned through a pattern having a second pitch P2 can be performed until no significant change is observed in the wavefront data when the substrate is irradiated. This indicates that the thermal behavior of the lens is saturated for light patterned through a pattern having a second pitch P2.

[0049] The lens can then be allowed to cool, returning it to a cooled state. As described above, the cooling characteristics of the lens can be determined.

[0050] One or more other sets of irradiation processes can then be performed on the lens, wherein the lens is allowed to be cooled to a cooled state between each set of irradiation processes. In each set of irradiation processes, as described above for a first line pattern and a second line pattern having a first pitch P1 and a second pitch P2 respectively, multiple substrates W are irradiated and wavefront data are measured.

[0051] Furthermore, the irradiation process set can be performed using test features with a critical size (i.e., pitch) and the same single orientation. The pitch used in any set of irradiation processes can be different from the pitch used in all other sets of irradiation processes. Therefore, the total number of sets of irradiation processes performed can be the same as the total number of pitches used. When the number of sets of irradiation processes performed is N, the corresponding pitches used can be referred to as P1, P2, …, PN. The first pitch P1 can be the smallest pitch used, and the pitch size can be increased sequentially, such that the Nth pitch PN is the largest pitch used.

[0052] Different pitches P1, P2, …, PN can cover the full range of pitches that can be used with a lens. Therefore, the pitch can cover the full angular response of the lens.

[0053] To pattern light at different pitches P1, P2, …, PN, a single pattern forming device MA can be used to provide each pitch and / or pattern orientation. Each of the N pattern forming devices MA (or 2N for different pattern orientations) can include a line pattern with a constant pitch, which is one of P1, P2, …, PN. A different pattern forming device among the N pattern forming devices MA can be used in each set of the irradiation process.

[0054] Alternatively, a single pattern forming device MA comprising N individual regions can be used. Each region may comprise a (dense) line pattern with a constant pitch, the constant pitch being one of P1, P2, …, PN. In the case of considering two regions with the same pitch but different pattern orientations for each pitch, more than twice the number of regions can be provided at the pattern forming device MA. The different regions of the pattern forming device MA can be used in each set of the irradiation process.

[0055] The above set of irradiation processes provides a dataset of wavefront data characterizing the lens heating effect on light patterned using pitches P1 to PN. Examples include using this dataset to model the lens heating response for any arrangement of product features on a patterning apparatus MA.

[0056] Product features are features used in the fabrication of features on the substrate W during the manufacturing of the actual product, on the patterning equipment MA. Test features differ from product features in that they are used to characterize the thermal properties of the lens. Test features are not used in the fabrication of features in the actual product.

[0057] Lens heating is a linear effect, and therefore different individual heating responses can be combined to determine the overall response. An embodiment includes analyzing the arrangement of product features on a patterning apparatus MA. Product features can have any arrangement and include a mixture of patterns with different pitches. The analysis determines a combination of one or more patterns, each pattern having pitches P1 to PN and orientations that completely or approximately correspond to the arrangement of the product features. Any arrangement of product features on the patterning apparatus MA can therefore be substantially modeled as a combination of one or more patterns, each individual pattern having pitches P1 to PN and orientations.

[0058] The embodiment models the overall lens heating response for an arrangement of product features, which depends on the individual heating responses for combinations of patterns selected from a set of patterns determined through analysis. This set of patterns covers a pitch range from a first pitch P1 to an Nth pitch PN. The model can combine (e.g., sum) the heating responses for the determined combinations of patterns with different pitches (and / or orientations). The heating responses for all patterns among those with different pitches P1 to PN and orientations are known based on a dataset of determined wavefront data characterizing the lens heating effect on light patterned using patterns with different pitches P1 to PN (and orientations).

[0059] During a series of exposures using a lens, the lens can be illuminated by light, which patterns different arrangements of product features on one or more pattern forming devices MA. For each arrangement of product features used, the arrangement of product features can be analyzed to determine substantially corresponding combinations of selected patterns, the selected patterns being a set of patterns including pitches P1 to PN. For each determined combination of patterns, the model can combine (e.g., sum) the heating responses to the patterns (pitches) to model the overall effect of lens heating.

[0060] The embodiments can therefore model overall lens heating for lenses illuminated by light patterned using different arrangements of product features on one or more pattern forming devices MA. A dataset of wavefront data characterizing the lens heating effect can be used to model lens heating caused by any arrangement of product features.

[0061] The embodiments also include modeling the overall lens heating response, which depends on any other factors that may affect lens heating. For example, the model can use timing data about when each exposure process is performed to determine the lens cooling effect.

[0062] Any arrangement of product features can be analyzed to determine how the arrangement of product features substantially corresponds to combinations of different line patterns. Examples use such analysis to determine the lens heating response. This is clearly advantageous compared to techniques that require wavefront measurements for every arrangement of product features used.

[0063] Examples can be used for process correction to reduce errors caused by lens heating. For example, examples can be used to predict the evolution of lens heating behavior. The predicted lens heating behavior can then be corrected using one or more of a number of available lens heating correction options, such as, for example, image tuner lens adjustment control. For example, a lens heating feedforward (LHFF) dataset can be generated at the end of a calibration procedure for a device layer on a scanner. This LHFF dataset can be applied to the target device and layer to correct for wavefront drift induced by lens heating.

[0064] The embodiments can also be used to improve lens selection and / or design. Specifically, the embodiments can be used to determine the conditions that lead to the strongest lens heating response. Options for mitigating the heating response of large lenses can therefore be considered during lens design.

[0065] The following describes a process for characterizing a lens according to an embodiment.

[0066] The process includes performing multiple illumination procedures. Each illumination procedure includes: patterning the light with a different test feature from a set of test features comprising multiple test features; and measuring the wavefront change of the patterned light after it has traveled through the lens. Each test feature in the set has a single pitch. Each test feature in the set has a different pitch. Each test feature in the set has a single orientation.

[0067] The following describes a computer-implemented method for determining the heating response of a lens to patterned light, according to an embodiment.

[0068] The computer-implemented method determines a combination of test features that substantially corresponds to a combination of test features arranged on a patterning device to pattern light before it passes through a lens. The computer-implemented method then determines the lens's heating response to the patterned light, which depends on a known combination of heating responses of the test features.

[0069] The embodiments include several modifications and variations of the above-described technology.

[0070] The embodiments include a set of illumination processes performed for each of a plurality of different orientations of the test features. That is, the test features can consist of multiple sets of test features. Each set of test features may include multiple test features with different pitches P1 to PN but with the same orientation. The orientations of the test features in each set may be different. Wavefront data is generated by using multiple sets of test features, characterizing the lens heating effect for light patterned with each of the plurality of different pitches P1 to PN. This allows for more accurate modeling of any lens heating effect that depends on the orientation of the product feature.

[0071] The embodiments have been described primarily with reference to determining the heating response of the lens. More generally, the embodiments include determining the thermal response of the lens. Accordingly, the embodiments may determine the heating and / or cooling response of the lens. The lens may be a projection system PS or any other type of optical system.

[0072] The embodiments generally involve determining aberrations in an optical system. Aberrations are caused by the thermal effects that depend on the pattern of the patterned light.

[0073] While this article provides specific examples of the use of lithography apparatuses (LA) in IC manufacturing, it should be understood that the LA lithography apparatuses described herein can have other applications. Possible other applications include manufacturing integrated optical systems, guiding and detecting patterns for magnetic domain memory, flat panel displays, liquid crystal displays (LCDs), thin-film magnetic heads, etc.

[0074] Although specific reference to embodiments of the invention may be made herein in the context of a lithography apparatus (LA), embodiments of the invention may be used in other apparatuses. Embodiments of the invention may form part of a mask inspection apparatus, a measurement apparatus, or any apparatus for measuring or processing objects such as wafers (or other substrates) or masks (or other patterning devices). These apparatuses may be collectively referred to as lithography tools. Such lithography tools may use vacuum conditions or ambient (non-vacuum) conditions.

[0075] Where the context permits, embodiments of the present invention may be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the present invention may also be implemented as instructions stored on a machine-readable medium, which may be read and executed by one or more processors. A machine-readable medium may include any mechanism for storing or transmitting information in a machine-readable (e.g., computing device) form. For example, a machine-readable medium may include read-only memory (ROM); random access memory (RAM); magnetic storage media; optical storage media; flash memory devices; electrical, optical, acoustic, or other forms of propagation signals (e.g., carrier waves, infrared signals, digital signals, etc.). Furthermore, firmware, software, programs, and instructions may be described herein as performing specific actions. However, it should be understood that such descriptions are for convenience only, and such actions are actually generated by a computing device, processor, controller, or other device executing firmware, software, programs, instructions, etc., and may result in actuators or other devices interacting with the physical world in the performance of these actions.

[0076] The embodiments include the following numbered clauses: 1. A computing system configured to perform a method for determining aberrations of an optical system in response to patterned light, the method comprising: determining a combination of test features, the combination of test features substantially corresponding to an arrangement of product features on a patterning device, the product features being arranged to pattern the light before it passes through the optical system; and determining aberrations resulting from the response of the optical system to the patterned light, the response of the optical system to the patterned light depending on a known response of each test feature in the determined combination. 2. The calculation system according to Clause 1, wherein each test feature is a linear line pattern. 3. The computing system according to Clause 1 or 2, wherein: the test feature is selected from a set of test features; each test feature in the set has a single pitch; each test feature in the set has a single pitch different from the other test features in the set; and each test feature in the set has a single orientation. 4. The computing system according to Clause 3, wherein: the test features are selected from a plurality of sets of test features; each set of test features includes a plurality of test features with different pitches and the same orientation; and the orientations of the test features in each set are different. 5. The computing system according to Clause 3 or 4, wherein the pitch of the test features in each set covers the angular response for which the optical system is designed. 6. The computing system according to any one of the preceding clauses, wherein the method further comprises: determining the aberrations of the optical system, the aberrations of the optical system depending on the illumination conditions of the patterned light. 7. The computing system according to any one of the preceding clauses, wherein the optical system is the projection system of a photolithography apparatus. 8. The computing system according to Clause 7, wherein the method further comprises: Identify potential aberrations that may result from the thermal response of the optical system to the patterned light; and determine changes to one or more processes performed by the photolithography apparatus to reduce the aberrations caused by the thermal response. 9. The computing system according to any one of the preceding clauses, wherein determining the aberration comprises: determining the heating response of the optical system to patterned light, the heating response of the optical system to patterned light depending on the known heating response of each test feature in the determined combination. 10. A characterization system for characterizing an optical system, the characterization system comprising: an illumination device configured to perform a plurality of illumination processes; a wavefront sensor configured to measure, in each of the plurality of illumination processes, the wavefront of light after the light has traveled through the optical system; and A computational system; wherein: each illumination process includes patterning light with a different test feature from a set of test features, the set including multiple test features; each test feature in the set has a single pitch; each test feature in the set has a single pitch different from the other test features in the set; each test feature in the set has a single orientation; and the computational system is configured to generate data characterizing the optical system, the data depending on determined changes in the wavefront measured during the multiple illumination processes. 11. The characterization system according to Clause 10, wherein each illumination process includes patterning light with a different test feature from one of a plurality of sets of test features; each set of test features includes a plurality of test features with different pitches and the same orientation; and the orientation of the test features in each set is different. 12. The characterization system according to clause 10 or 11, wherein the irradiation device is further configured to perform the irradiation process with low-intensity unpatterned light. 13. A computer-implemented method for determining aberrations in response of an optical system to patterned light, the method comprising: determining a combination of test features, the combination of test features substantially corresponding to product features on a patterning device, the product features being arranged to pattern the light before it passes through the optical system; and determining aberrations resulting from the response of the optical system to the patterned light, the response of the optical system to the patterned light depending on a known response of each test feature in the determined combination. 14. The computer-implemented method according to Clause 13, wherein each test feature is a linear line pattern. 15. The computer-implemented method according to clause 13 or 14, wherein: The test features are selected from a set of test features; each test feature in the set has a single pitch; each test feature in the set has a single pitch that is different from the other test features in the set; and each test feature in the set has a single orientation. 16. A computer-implemented method according to any one of clauses 13 to 15, wherein the test feature is selected from a plurality of sets of test features; each set of test features includes a plurality of test features with different pitches and the same orientation; and the orientation of the test features in each set is different. 17. The computer-implemented method according to Clause 16, wherein the pitch of the test features in the set covers the angular response for which the optical system is designed. 18. A computer-implemented method according to any one of clauses 13 to 17, wherein the method further comprises: determining the aberrations of the optical system, the aberrations of the optical system depending on the illumination conditions of the patterned light. 19. The computer-implemented method according to any one of Clauses 13 to 18, wherein the optical system is a projection system of a photolithography apparatus. 20. A computer-implemented method according to any one of claims 13 to 19, wherein the method further comprises: determining potential aberrations that may result from the thermal response of the optical system to patterned light; and determining changes to one or more processes performed by a photolithography apparatus to reduce the aberrations resulting from the thermal response. 21. A computer-implemented method according to any one of claims 13 to 20, wherein determining the aberration comprises: determining the heating response of the optical system to patterned light, the heating response of the optical system to patterned light depending on the known heating response of each test feature in the determined combination. 22. A method for characterizing an optical system, the method comprising: performing a plurality of illumination processes; wherein each illumination process comprises: patterning light with a different one of the test features from a set comprising a plurality of test features; and The wavefront change of patterned light after the patterned light has traveled through an optical system is measured; wherein: each test feature in the set has a single pitch; each test feature in the set has a single pitch different from the other test features in the set; and each test feature in the set has a single orientation. 23. The method according to Clause 22, wherein: each irradiation process includes patterning light with a different test feature from one of a plurality of sets of test features; each set of test features includes a plurality of test features with different pitches and the same orientation; and the orientation of the test features in each set is different. 24. The method described in accordance with Clause 22 or 23 further includes: performing the irradiation process with low-intensity, unpatterned light. 25. A method for determining aberrations in an optical system, comprising: illuminating a plurality of diffraction targets provided at a patterning apparatus with at least one illumination setting to generate a plurality of diffraction orders, the patterning apparatus being arranged at an object plane of the optical system; measuring a spatial image of the diffraction orders at an image side of the optical system; and calculating aberrations based on each spatial image for each diffraction order. The calculated aberrations are stored in a database; and based on the stored calculated aberrations, aberrations for features having a desired diffraction order pattern are determined.

[0077] While specific embodiments of the invention have been described above, it should be understood that the invention can be practiced in ways different from those described. The foregoing description is intended to be illustrative and not limiting. Therefore, it will be apparent to those skilled in the art that modifications can be made to the described invention without departing from the scope of the set forth claims.

Claims

1. A computing system configured to perform a method for determining aberrations of an optical system in response to a patterned light, the method comprising: determining a combination of test features, the combination of test features corresponding substantially to an arrangement of product features on a patterning device, the product features arranged to pattern light before the light passes through the optical system; and determining aberrations resulting from a response of the optical system to the patterned light, the response of the optical system to the patterned light dependent on a known response of each test feature in the determined combination.

2. The computing system of claim 1, wherein each test feature is a linear line pattern.

3. The computing system of claim 1 or 2, wherein: the test features are selected from a set of test features; each test feature in the set has a single pitch; each test feature in the set has a single pitch that is different from other test features in the set; and each test feature in the set has a single orientation.

4. The computing system of claim 3, wherein: the test features are selected from a plurality of sets of test features; each set of test features includes a plurality of test features having different pitches and a same orientation; and the orientation of the test features in each set is different. determining the aberrations of the optical system, the aberrations of the optical system dependent on an illumination condition of the patterned light.

5. The computing system of any of the preceding claims, wherein the method further comprises:

6. The computing system of any preceding claim, wherein the method further comprises: determining potential aberrations that can result from a thermal response of the optical system to the patterned light, wherein the optical system is a projection system of a lithographic apparatus; and determining changes to one or more processes performed by the lithographic apparatus to reduce the aberrations resulting from the thermal response. determining a heating response of the optical system to the patterned light, the heating response of the optical system to the patterned light dependent on a known heating response of each test feature in the determined combination.

7. The computing system of any of the preceding claims, wherein determining the aberration comprises:

8. A characterization system for characterizing an optical system, the characterization system comprising: an illumination device configured to perform a plurality of illumination processes; a wavefront sensor configured to measure a wavefront of light after the light has travelled through an optical system in each of the plurality of illumination processes; and a computing system; wherein: each illumination process comprises patterning light with a different one of test features in a set of test features; each test feature in the set has a single pitch; each test feature in the set has a single pitch that is different from other test features in the set; each test feature in the set has a single orientation; and the computing system is configured to generate data characterizing the optical system, the data dependent on determined changes to the wavefronts measured in the plurality of illumination processes.

9. The characterization system of claim 8, wherein: ​ ​ Each illumination process comprises patterning light with a different one of the test features in one of a plurality of sets of test features; Each set of test features comprises a plurality of test features having different pitches and the same orientation; and The orientation of the test features in each set is different.

10. The characterization system of claim 8 or 9, wherein the illumination device is further configured to perform an illumination process with low intensity unpatterned light.

11. A computer-implemented method of determining aberrations of an optical system in response to patterned light, the method comprising: determining a combination of test features, the combination of test features corresponding substantially to product features on a patterning device, the product features arranged to pattern light before the light passes through the optical system; and determining aberrations resulting from a response of the optical system to the patterned light, the response of the optical system to the patterned light dependent on a known response of each test feature in the determined combination.

12. The computer-implemented method of claim 11, wherein each test feature is a linear line pattern.

13. The computer-implemented method of claim 11 or 12, wherein: the test features are selected from a set of test features; each test feature in the set has a single pitch; each test feature in the set has a single pitch that is different from other test features in the set; and each test feature in the set has a single orientation.

14. The computer-implemented method of any one of claims 11 to 13, wherein the method further comprises: determining the aberrations of the optical system, the aberrations of the optical system dependent on illumination conditions of the patterned light.

15. A method of characterizing an optical system, the method comprising: performing a plurality of illumination processes; wherein each illumination process comprises: patterning light with a different one of the test features in a set of test features; and measuring a wavefront change of the patterned light after the patterned light has travelled through an optical system; wherein: each test feature in the set has a single pitch; each test feature in the set has a single pitch that is different from other test features in the set; and each test feature in the set has a single orientation.

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