Method and apparatus for measuring the topography of an object's surface

Abstract

A method for determining a correction value for the height profile of a substrate comprises: fixing the substrate to a substrate holder; creating a first measurement of a first height profile; rotating the substrate around the global normal of its surface; creating a second measurement of a second height profile; correcting the first and second measurements for the shape of the substrate holder to determine first and second corrected measurements, respectively; and combining the first and second corrected measurements to determine a correction value for the height profile. Creating first and second measurements of the first height profile each comprises: projecting a patterned radiation beam onto a beam spot region; moving the substrate relative to the beam spot region while it is in its current orientation; receiving a portion of the patterned radiation beam reflected from the substrate and determining a first measurement of the first height profile from there.

Description

[Technical Field]

[0001] (Cross-reference of related applications)

[0001] This application claims priority to European Application No. 23173024.3, filed on 12 May 2023, which is incorporated herein by reference in its entirety.

[0002]

[0002] The present invention relates to a method for determining a correction value for the height profile of a substrate surface. The present invention also relates to a method for measuring the topography of a substrate surface. The present invention also relates to a corresponding apparatus for measuring the topography of a substrate surface. The present invention has particular applications in the field of lithography. The substrate may be a substrate in a lithography apparatus. Such a substrate may comprise a silicon wafer coated with photoresist. The apparatus may be referred to as a level sensor and may form part of a lithography apparatus. The present invention also relates to a lithographic exposure method using a method or apparatus for measuring the topography of a substrate surface. [Background technology]

[0003]

[0003] A lithography apparatus is a machine built to apply a desired pattern to a substrate. Lithography apparatus can be used, for example, in the manufacture of integrated circuits (ICs). A lithography apparatus can project, for example, a pattern of a patterning device (e.g., a mask) (often referred to as a "design layout" or "design") onto a radiative-sensitive material (resist) layer provided on a substrate (e.g., a wafer).

[0004]

[0004] As semiconductor manufacturing processes continue to advance, the dimensions of circuit elements have continuously decreased, while the amount of functional elements such as transistors per device has steadily increased over decades, following a trend commonly known as "Moore's Law." To keep up with Moore's Law, the semiconductor industry is pursuing technologies that enable the creation of increasingly smaller features. To project patterns onto a substrate, lithography equipment can use electromagnetic radiation. The wavelength of this radiation determines the minimum size of the feature that can be patterned on the substrate. Typical wavelengths currently in use are 365 nm (i-line), 248 nm, 193 nm, and 13.5 nm. To form features smaller on a substrate than those produced by a lithography equipment using radiation with a wavelength of 193 nm, for example, a lithography equipment using extreme ultraviolet (EUV) radiation with wavelengths in the range of 4 nm to 20 nm, for example, 6.7 nm or 13.5 nm, can be used.

[0005]

[0005] Before exposing a wafer to patterned radiation in a lithography apparatus, the wafer's topography may be determined using a device sometimes referred to as a level sensor. This measurement of the wafer's topography may be performed within the lithography apparatus, for example, when the wafer is clamped to the wafer stage. This information can be used during subsequent exposures of the wafer to keep the exposed portion of the wafer within the best-focus plane.

[0006]

[0006] It would be desirable to provide a new method and / or apparatus for determining the topography of a wafer that can at least partially address one or more problems relating to existing configurations, whether or not they are specified herein. [Overview of the Initiative]

[0007]

[0007] According to a first aspect of the present disclosure, a method is provided for determining a correction value for the surface height profile of a substrate, the method comprising: fixing the substrate to a substrate holder; creating a first measurement of a first height profile by projecting a patterned radiant beam onto a beam spot region; moving the substrate relative to the beam spot region while it is in a first orientation; receiving a portion of the patterned radiant beam reflected from the substrate and determining a first measurement of the first height profile therefrom; rotating the substrate to a second orientation around the global normal of the surface; creating a second measurement of a second height profile by projecting a patterned radiant beam onto a beam spot region; moving the substrate relative to the beam spot region while it is in a second orientation; receiving a portion of the patterned radiant beam reflected from the substrate and determining a second measurement of the second height profile therefrom; correcting the first and second measurements for the shape of the substrate holder to determine first and second corrected measurements, respectively; and combining the first corrected measurement and the second corrected measurement to determine a correction value for the height profile.

[0008]

[0008] The method according to the first embodiment is advantageous as follows.

[0009]

[0009] A substrate may be referred to as an object. A substrate may be a substrate in a lithography apparatus. Such a substrate may comprise a silicon wafer coated with photoresist. It will be understood that such a substrate comprises a relatively thin, flat disk of material having two opposing, generally circular surfaces. It will also be understood that the surface of the substrate is not perfectly flat, and therefore there is some variation in the local normal to the surface of the substrate. However, the global normal of the substrate is the normal to the global plane or mean plane of the surface of the substrate. A lithography apparatus may be used to expose a substrate to radiation patterned by a reticle or mask. The topology of the surface of the substrate may be determined before the substrate is exposed to the patterned radiation. For example, a height map of the surface of the substrate may be determined, for example, using a level sensor. The measured topography of the surface of the substrate can then be used to control the height of the substrate while the substrate is exposed to the patterned radiation, for example, to keep the substrate within the best-focus plane of the image of a patterning device.

[0010]

[0010] A certain type of level sensor can be used to measure the height profile of a substrate surface by projecting a patterned radiation beam onto a beam spot area, moving the substrate relative to the beam spot area, and receiving a portion of the patterned radiation beam reflected from an object to determine a first measurement of height from there. As the height of the substrate changes, the position of the pattern of the reflected radiation may change, for example, with respect to a splitting optical system arranged to divide the reflected radiation into a first portion and a second portion.

[0011]

[0011] The inventors of the present invention have recognized that the height map thus determined will generally have contributions from both (a) the shape of the substrate holder (e.g., clamp) on which the substrate is clamped (because when clamped, the substrate conforms to the shape of the clamp) and (b) process layers formed on the surface. A silicon wafer may have one or more layers previously formed using, for example, a lithography process. Generally, various different materials and / or features of different densities will be present across the surface of such a wafer. Furthermore, the inventors have recognized that features on process layers can introduce some errors in height measurement, and that the layers depend on the orientation of the substrate when scanned through the beam spot region. For example, some errors in height measurements due to features on process layers will change sign if the substrate is rotated 180° around its global normal (and thus may be referred to herein as antisymmetry errors). In contrast, the (actual) contribution to height measurement from the shape of the clamp is not antisymmetry. By correcting the first and second height measurements for the clamp shape to determine the first and second corrected height measurements of the surface, the data becomes independent of the clamp shape. The first and second corrected height measurements are then combined to accurately determine the antisymmetry process-dependent error. For example, if the two orientations are opposite (i.e., the substrate rotates 180° around its global normal between the two measurements), the first and second corrected height profiles can be determined by h0+Δh and h0-Δh, respectively, where Δh is the antisymmetry error. The antisymmetry error can be determined as half the difference between the first and second corrected height measurements.

[0012]

[0012] Since different materials can absorb different proportions of incident radiation, and features of different densities can result in different amounts of scattering of incident radiation, the reflectivity across the wafer surface can vary. For example, a 3D-NAND wafer may contain features that can reduce the amount of specular reflection of radiation by up to 50%. Due to the change in substrate reflectivity, there is a change in the measured height profile Δh in the transition region.

[0013]

[0013] Determining the height profile of an object will be understood to involve determining the height profile of an object with respect to a reference height or reference position.

[0014]

[0014] Correcting the height profile measurement with respect to the shape of the substrate holder to determine the corrected measurement may involve fixing a reference substrate to the substrate holder, creating a reference measurement of the height profile of the reference substrate by projecting a patterned radiation beam onto a beam spot area, moving the substrate relative to the beam spot area while the substrate holder is in the same orientation as when the corrected measurement was determined, receiving a portion of the patterned radiation beam reflected from the substrate and determining the reference measurement of the height profile from there, and determining the corrected measurement of the height profile as the difference between the measurement and the reference measurement.

[0015]

[0015] The reference substrate is sometimes referred to as the reference object. The reference substrate may be a bare wafer. That is, the reference object may be a silicon wafer to which no process layers have been applied.

[0016]

[0016] The step of rotating the substrate to a second orientation around the global normal of the surface may include rotating the substrate 180° around the global normal of the surface.

[0017]

[0017] For such embodiments, much of the error in the height measurement due to features on the process layer contributes to the first and second measurements with the same magnitude but opposite signs (i.e., anti-symmetry error). For example, for such embodiments, the anti-symmetry error can be determined as half of the difference between the first corrected measurement of height and the second corrected measurement of height.

[0018]

[0018] The correction value can be determined as half of the difference between the first corrected measurement of the height profile and the second corrected measurement of the height profile.

[0019]

[0019] Creating each of the first and second measurements of the height profile can comprise measuring the height of the surface at a plurality of positions on the object.

[0020]

[0020] It will be understood that determining the correction value of the height profile of the surface of the object by combining the first corrected measurement and the second corrected measurement of the height profile can comprise combining the measurements from the first and second corrected measurements of the height profile corresponding to the same position on the object.

[0021]

[0021] Creating each of the first and second measurements of the height profile of the surface can comprise measuring the height map of the surface for substantially the entire surface of the substrate. That is, the height map (and thus the correction value) can be determined for substantially the entire object (wafer).

[0022]

[0022] Alternatively, creating each of the first and second measurements of the height profile can comprise measuring the height map of the surface for one or more of a plurality of regions of the surface of the object to which the same pattern is applied.

[0023]

[0023] That is, the height map (and therefore the correction value) may be determined for one or more fields or dies of the substrate (wafer). In some embodiments, the height map (and therefore the correction value) may be determined for only one (or a relatively small proportion) of multiple areas of the substrate surface to which the same pattern is applied.

[0024]

[0024] The method may further comprise correcting the first and second measurements of the height profile for local variations in the inclination of the substrate surface before correcting the first and second measurements of the height profile for the shape of the substrate holder. The method may further comprise correcting the first and second reference measurements of the height profile for local variations in the inclination of the reference substrate surface before correcting the first and second measurements of the height profile for the shape of the substrate holder.

[0025]

[0025] Variations in the slope of the substrate surface generally affect the focusing of the patterned radiated beam onto the beam spot region. This, in turn, results in height measurement errors that depend on the slope or gradient of the substrate surface. One important factor of local variations in the slope of the substrate surface can be the shape of the substrate holder (or clamp) to which the substrate is fixed / clamped. Such errors are typically antisymmetric errors (and thus can form part of the correction value determined using the method according to the first embodiment). However, such errors can generally be subject to significant local variations across the substrate surface. For example, a substrate (which may be a resist-coated silicon wafer) may have several roughly rectangular regions (which may be called fields or dies) to which substantially the same pattern is applied (and has already been applied in the formation of a previous process layer). Local variations in the slope of the substrate surface can result in significant variations in the error per field (or per die). This is in contrast to some other antisymmetric errors, which may depend primarily on the features of the process layer on the substrate and therefore may be substantially the same for all fields or dies.

[0026]

[0026] This method may further include storing the correction value in memory.

[0027]

[0027] The inventors have also recognized that the correction values ​​determined by the method according to the first aspect of the present disclosure depend primarily on (a) the substrate holder (or clamp) and (b) the lithography process (i.e., the layer recipe). If, as is typical, multiple wafers are processed by the same lithography process using a given lithography apparatus, the correction values ​​will be substantially the same for all such wafers. Thus, in some embodiments, the correction values ​​can be determined once and then used for all subsequent wafers processed on the same clamp with the same lithography process. Furthermore, the method according to the first aspect includes correcting the first and second measurements for the shape of the substrate holder to determine the first and second corrected measurements, respectively, before these are combined to determine the correction value for the height profile, so that the correction values ​​determined by this method are substantially independent of the substrate holder or clamp. Therefore, in some embodiments, the correction value may be determined once in one lithography apparatus (with clamps) and then used for all subsequent wafers processed in the same lithography process, even on different clamps or in different lithography apparatuses. Furthermore, in some embodiments, the correction value may be determined once for a single field or die of a wafer and then used for all fields or dies of all subsequent wafers processed in the same lithography process.

[0028]

[0028] A second aspect of the present disclosure provides a method for measuring the topography of the surface of a substrate, the method comprising: creating a measurement of the surface height profile by projecting a patterned radiation beam onto a beam spot area; moving an object relative to the beam spot area while in a first orientation; receiving a portion of the patterned radiation beam reflected from the object and determining a height profile therefrom; and determining a corrected measurement of the height profile by combining the measurement of the height profile with a correction value of the substrate height profile determined using the method of any of the preceding claims.

[0029]

[0029] The method according to the second embodiment is advantageous because it provides a corrected measurement value that has been corrected using the correction value determined by the method according to the first embodiment. For example, this allows antisymmetry errors to be accurately corrected.

[0030]

[0030] The corrected measurement of the height profile can be determined by subtracting the correction value from the measurement of the height profile.

[0031]

[0031] This method may further comprise determining a correction value for the height profile using the method of the first aspect of the present disclosure.

[0032]

[0032] With respect to at least some wafers, the method may comprise first determining a correction value (using the method according to the first embodiment) and then correcting the height measurement using this value (using the method according to the second embodiment). For example, the correction value may be determined for at least a first wafer processed using a given lithography process or recipe.

[0033]

[0033] This method may include retrieving a correction value from memory.

[0034]

[0034] Combining the height profile measurement with the correction value of the substrate height profile may involve combining the measurement with the correction value at substantially the same location on the substrate.

[0035]

[0035] For example, in some embodiments, the correction value for the surface height of an object may be determined substantially over the entire object (wafer). Similarly, the surface height measurement may be determined substantially over the entire object (wafer) and may be combined with the correction value to determine the corrected surface height measurement.

[0036]

[0036] The substrate may have multiple regions to which the same pattern is applied, and combining the height profile measurement with the correction value of the substrate height profile may involve combining the measurement of each of the multiple regions with the correction value of one of the multiple regions.

[0037]

[0037] In other words, in some embodiments, the correction value may be determined for only one (or a relatively small proportion) of several areas of the surface of the object to which the same pattern is applied. The correction value for that single area of ​​the object may be used to correct the height measurements of each of the several areas of the object.

[0038]

[0038] In any one of the first and second embodiments of the present disclosure, determining a height profile measurement from a portion of a patterned radiation beam reflected from a substrate may include receiving a portion of the radiation beam reflected from the substrate, dividing the reflected radiation into a first portion and a second portion, determining the intensity of the first and second portions of the radiation, and determining the height of the substrate by combining the intensity of the first portion of the radiation and the intensity of the second portion of the radiation.

[0039]

[0039] Advantageously, by dividing the reflected radiation into a first part and a second part, and determining the height of the substrate by combining the intensity of the first part and the intensity of the second part, the determination of the height may be substantially independent of the intensity of the radiation beam. For example, the height may be determined as a difference measurement.

[0040]

[0040] Dividing the reflected radiation into a first part and a second part may involve forming a pattern image on a splitting optical system and using the splitting optical system to induce radiation from the first and second parts of the second image and spatially separate them.

[0041]

[0041] The position of the second image relative to the split optical system can determine how much of the reflected radiation is directed to the first and second parts, respectively.

[0042]

[0042] The height of the substrate may be proportional to the difference between the first strength and the second strength.

[0043]

[0043] For example, the height of an object may be determined as being proportional to the difference between the first strength and the second strength divided by the sum of the first strength and the second strength.

[0044]

[0044] A third aspect of the present disclosure provides a lithography exposure method comprising measuring the topography of the surface of a substrate using the method of the second aspect of the present disclosure, patterning a radiation beam using a patterning device, and projecting the patterned radiation onto the substrate to form an image of the patterning device onto the substrate, wherein the position of the substrate while the patterned radiation is projected onto the substrate is controlled depending on the measured topography of the surface of the substrate.

[0045]

[0045] Advantageously, the measured topography of the substrate surface can be used to control the height of the substrate while it is exposed to patterned radiation, for example, to keep the substrate within the best-focus plane of the patterning device image. It will be understood that the image of the patterning device formed on the substrate may be a diffraction-limited image.

[0046]

[0046] Lithography exposure may also be scanning exposure, and therefore, patterning the radiation beam using a patterning device comprises moving the patterning device through the radiation beam, and projecting the patterned radiation onto the substrate to form an image of the patterning device on the substrate comprises moving the substrate so that the image of the patterning device is substantially stationary relative to the substrate.

[0047]

[0047] That is, in order to image a pattern onto a target area on the substrate, the patterning device is moved or scanned in the scanning direction through the illumination area. It will be understood that the substrate is also scanned with respect to the illumination area in the plane of the substrate. The movement of the substrate is such that the spatial image of the patterning device is stationary relative to the substrate, and it will be understood that the direction and / or speed of the substrate may generally differ from that of the patterning device (for example, if the image is inverted and / or if a reduction factor is applied by the projection system).

[0048]

[0048] According to a fourth aspect of the present disclosure, an apparatus is provided for measuring the topography of the surface of a substrate, the apparatus comprising: a support for supporting the substrate; a projection optical system operable to form a first image of a pattern on a beam spot region using a radiation beam; a movement mechanism operable to cause relative movement between the support and the beam spot region; a detection optical system operable to receive a portion of the radiation beam reflected from the substrate; and a controller operable to determine the height of the substrate from the radiation beam reflected from the substrate and further operable to implement any one of the first, second, and third aspects of the present disclosure.

[0049]

[0049] This device may be referred to as a level sensor. This device may form part of a lithography apparatus. The support supporting the substrate may include a substrate holder that is operable to secure the substrate. For example, the support may include a clamp for clamping the substrate to the support. The apparatus according to the fourth embodiment is advantageous because it takes into account a corrected measurement of height corrected using a correction value determined by the method according to the first embodiment. For example, this may allow antisymmetry errors in height measurement to be accurately corrected.

[0050]

[0050] The moving mechanism may be operable to move the support relative to the beam spot region. Additionally or alternatively, the moving mechanism may be operable to move the beam spot region relative to the support. For example, movement of the beam spot region can be achieved by moving the projection optical system. In such embodiments, the moving mechanism may also be operable to move the detection optical system.

[0051]

[0051] The detection optical system may be operable to receive a portion of the radiation beam reflected from the substrate and to divide the reflected radiation into a first portion and a second portion, so that the first portion of the radiation corresponding to the first portion of the first image is spatially separated from the second portion of the radiation corresponding to the second portion of the first image. The device may further include a first detector positioned to determine the intensity of the first portion of the radiation and a second detector positioned to determine the intensity of the second portion of the radiation, and the controller may be operable to determine the height profile of the substrate by combining the intensity of the first portion of the radiation and the intensity of the second portion of the radiation.

[0052]

[0052] Advantageously, the detection optics can be operated to split the reflected radiation into a first part and a second part, and the controller can be operated to determine the height of the substrate by combining the intensity of the first part and the intensity of the second part, so that the determination of the height may be substantially independent of the intensity of the radiation beam. For example, the height may be determined as a difference measurement.

[0053]

[0053] The projection optical system may include a projection patterning device and a first imaging optical system positioned to form an image of the projection patterning device on a beam spot region.

[0054]

[0054] The projection patterning device may include a grid. The grid may include a plurality of lines. The lines may be of uniform thickness. The grid may have a duty cycle of 50%.

[0055]

[0055] The detection optical system may include a splitting optical system arranged to divide the reflected radiation into a first part and a second part, and a second imaging optical system arranged to receive the radiation reflected from an object supported by a support and to form a second image of the pattern on the splitting optical system.

[0056]

[0056] The first imaging optical system may be substantially equivalent to the second imaging optical system.

[0057]

[0057] The segmented optical system, beam spot region, and projection patterning device are all located in optically conjugate planes. The two planes are optically conjugate if all radiation passing through each distinct point in the first plane is imaged onto a distinct point in the second plane.

[0058]

[0058] The image of the projection patterning device is formed on the splitting optical system, and the position of the image indicates the height of the object. Specifically, the position of the image relative to the splitting optical system indicates the height of the object. As described above, the projection patterning device may include a grating with multiple lines. The splitting optical system may include multiple prisms, and the image of each line may be formed on one of several roughly triangular prisms, so that a first portion of the line is incident on a first surface of the prism and a second portion of the line is incident on a second surface of the prism. The first portion of the line is guided to a first detector and the second portion of the line is guided to a second detector. As the line moves relative to the prism (as a result of the change in the height of the object), the amount of radiation guided to each detector changes.

[0059]

[0059] The device may further include a radiation source that is operable to generate a radiation beam.

[0060]

[0060] According to a fifth aspect of the present disclosure, a lithography apparatus is provided which comprises the apparatus of a fourth aspect of the present disclosure.

[0061]

[0061] The lithography apparatus may further include: an illumination system capable of operating to illuminate an illumination area; a support structure configured to support a patterning device so that the patterning device can be positioned within the illumination area; a substrate table configured to support a substrate; and a projection system capable of operating to form an image of the patterning device supported by the support structure onto a substrate supported by the substrate table. [Brief explanation of the drawing]

[0062]

[0062] Embodiments of the present invention will be described below as merely illustrative examples with reference to the attached schematic diagrams.

[0063] [Figure 1] A schematic diagram of a lithography apparatus is shown. [Figure 2]Figure 1 is a schematic diagram of a level or height sensor that may form part of the lithography apparatus shown. [Figure 3] This is a schematic representation of a method for determining a correction value for the surface height profile of a substrate according to one embodiment of the present disclosure. [Figure 4] This is a schematic representation of a method for determining corrected measurements by correcting the height profile measurements for the shape of a substrate holder, which can form part of the method shown in Figure 3. [Figure 5] This is a schematic representation of a method for determining height profile measurements from a portion of a patterned radiation beam reflected from a substrate (or reference substrate), which may form part of the method shown in Figures 3 and 4. [Figure 6] This is a schematic diagram of a portion of the substrate, showing the beam spot area or measurement location, a first image of a projection grid pattern with two lines, and a first feature on the substrate having a different reflectivity than the rest of the substrate. [Figure 7A] The first intensity I1 and the second intensity I2 (determined using the method shown in Figure 5), comprising radiation from the first and second portions of the first image shown in Figure 6, are expressed as functions of the position of the substrate in the y-direction. [Figure 7B] Figure 7A shows the height determined by combining the first intensity I1 and the second intensity I2. [Figure 8] This is a schematic representation of a method for measuring the surface topography of a substrate according to one embodiment of the present disclosure. [Figure 9] This is a schematic representation of a lithography exposure method according to one embodiment of the present disclosure. [Figure 10] This is a schematic representation of an apparatus for measuring the topography of an object's surface according to one embodiment of the present disclosure, which may form part of the lithography apparatus shown in Figure 1 and implement the methods shown in Figures 3, 4, 5, and 8. [Figure 11] This diagram illustrates the three types of level sensor height measurement errors that depend on the substrate orientation when measuring the surface height on a wafer. [Modes for carrying out the invention]

[0064]

[0063] In this document, the terms “radiation” and “beam” are used to encompass all types of electromagnetic radiation, including ultraviolet radiation (e.g., having wavelengths of 365 nm, 248 nm, 193 nm, 157 nm, or 126 nm) and EUV (extreme ultraviolet radiation, e.g., having wavelengths in the range of about 5 to 100 nm).

[0065]

[0064] The terms “reticle,” “mask,” or “patterning device,” as used herein, may be broadly interpreted to refer to a general-purpose patterning device that can be used to give an incoming radiation beam a patterned cross-section corresponding to a pattern created on a target portion of a substrate. The term “light bulb” can also be used in this context. In addition to classic masks (transmissive or reflective masks, binary masks, phase-shift masks, hybrid masks, etc.), other examples of such patterning devices include programmable mirror arrays and programmable LCD arrays.

[0066]

[0065] Figure 1 schematically illustrates a lithography apparatus LA. The lithography apparatus LA includes an illumination system (also called an illuminator) IL configured to adjust a radiation beam B (e.g., UV radiation, DUV radiation, or EUV radiation), a mask support (e.g., a mask table) MT connected to a first positioner PM, which is constructed to support a patterning device (e.g., a mask) MA and configured to precisely position the patterning device MA according to specific parameters, a substrate support (e.g., a wafer table) WT connected to a second positioner PW, which is constructed to hold a substrate (e.g., a resist-coated wafer) W and configured to precisely position the substrate support according to specific parameters, and a projection system (e.g., a refractive projection lens system) PS configured to project the pattern applied to the radiation beam B by the patterning device MA onto a target portion C of the substrate W (e.g., comprising one or more dies).

[0067]

[0066] During operation, the illumination system IL receives the radiated beam from the radiation source SO, for example, via the beam delivery system BD. The illumination system IL may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic, and / or other types of optical components, or any combination thereof, for inducing, shaping, and / or controlling the radiation. The illuminator IL may be used to adjust the radiated beam B so that its cross-section has a desired spatial and angular intensity distribution in the plane of the patterning device MA.

[0068]

[0067] As used herein, the term “projection system” PS should be interpreted broadly to encompass a variety of projection systems, including refractive optical systems, reflective optical systems, reflective refractive optical systems, anamorphic optical systems, magneto-optical systems, electromagnetic optical systems, and / or electrostatic optical systems, or any combination thereof, as appropriate in accordance with the exposure radiation used and / or other factors such as the use of immersion liquid or vacuum. Where the term “projection lens” is used herein, it can be considered synonymous with the more general term “projection system” PS.

[0069]

[0068] The lithography apparatus LA may be of a type that can cover at least a portion of the substrate with a liquid having a relatively high refractive index, such as water, to fill the space between the projection system PS and the substrate W. This is also known as immersion lithography. Further information relating to immersion technology is given in U.S. Patent No. 6,952,253, which is incorporated herein by reference.

[0070]

[0069] The lithography apparatus LA may be of a type having two or more substrate support WTs (also called a “dual-stage”). In such a “multi-stage” machine, the substrate support WTs may be used in parallel, and / or, while a substrate W on one substrate support WT is being used to expose a pattern on this substrate W, a preparation step for subsequent exposure of the substrate W located on the other substrate support WT may be performed on the substrate W.

[0071]

[0070] In addition to the substrate support WT, the lithography apparatus LA may include a measurement stage. The measurement stage is arranged to hold sensors and / or cleaning devices. The sensors may be arranged to measure the characteristics of the projection system PS or the characteristics of the radiation beam B. The measurement stage may hold multiple sensors. The cleaning devices may be arranged to clean a part of the lithography apparatus, for example, a part of the projection system PS or a part of the system that provides the immersion fluid. The measurement stage may move below the projection system PS when the substrate support WT is away from the projection system PS.

[0072]

[0071] During operation, the radiating beam B is incident on a patterning device MA, such as a mask, which is held on a mask support MT, and is patterned by the pattern (design layout) present on the patterning device MA. The radiating beam B, having crossed the mask MA, passes through a projection system PS, which focuses the beam onto a target portion C of the substrate W. Utilizing a second positioner PW and a position measuring system IF, the substrate support WT can be precisely moved to position various target portions C, for example, in a focused and aligned position within the path of the radiating beam B. Similarly, the patterning device MA can be precisely positioned relative to the path of the radiating beam B using a first positioner PM and optionally another position sensor (not explicitly shown in Figure 1). The patterning device MA and the substrate W can be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. Although the substrate alignment marks P1, P2 occupy dedicated target portions in the illustration, they may be located in the space between target portions C. When substrate alignment marks P1 and P2 are located between target portions C, they are known as scribe line alignment marks.

[0073]

[0072] To clarify the present invention, the Cartesian coordinate system is used. The Cartesian coordinate system has three axes, namely the x-axis, y-axis, and z-axis. Each of the three axes is orthogonal to the other two axes. A rotation about the x-axis is called an Rx rotation. A rotation about the y-axis is called a Ry rotation. A rotation about the z-axis is called an Rz rotation. The x-axis and y-axis define the horizontal plane, while the z-axis is perpendicular. The Cartesian coordinate system is not limiting to the present invention and is used only for clarification. Alternatively, another coordinate system, such as a cylindrical coordinate system, may be used to clarify the present invention. The orientation of the Cartesian coordinate system may be different, for example, such that the z-axis has a component along the horizontal plane.

[0074]

[0073] The topography measurement system is a level sensor or height sensor, which may be integrated into a lithography apparatus, and is positioned to measure the topography of the top surface of a substrate (or wafer). From these measurements, which show the height of the substrate as a function of the position on the substrate, a topographic map of the substrate, also called a height map, can be generated. This height map can then be used to correct the position of the substrate when transferring a pattern to the substrate in order to provide an aerial image of a patterning device focused on the substrate. In this context, it will be understood that “height” broadly refers to the out-of-plane dimension (also called the Z-axis) relative to the substrate. Typically, the level or height sensor performs measurements at a fixed location (relative to its optical system), and the relative movement between the substrate and the optical system of the level or height sensor results in height measurements at each location on the entire substrate.

[0075]

[0074] An example of a level or height sensor LS known in the art is schematically shown in Figure 2. The figure illustrates only the principle of operation. In this example, the level sensor LS comprises an optical system including a projection unit LSP and a detection unit LSD. The projection unit LSP comprises a radiation source LSO that provides a radiation beam LSB patterned by the projection grating PGR of the projection unit LSP. The projection grating PGR may alternatively be called a patterning device PGR. The radiation source LSO may be a narrowband or broadband radiation source, such as a supercontinuum light source, and may be polarized or unpolarized, such as a polarized or unpolarized laser beam, and may be intermittent or continuous. The radiation source LSO may include multiple radiation sources having different color or wavelength ranges, such as multiple LEDs. The radiation source LSO of the level sensor LS is not limited to visible radiation and may additionally or alternatively include UV and / or infrared radiation and any range of wavelengths suitable for reflection from the surface of the substrate.

[0076]

[0075] The projection grating PGR is a periodic grating having a periodic structure that produces a radiation beam BE1 having a periodically fluctuating intensity. The radiation beam BE1, whose intensity fluctuates periodically, is guided toward the measurement location MLO on the substrate W with an incident angle ANG of 0 to 90 degrees, typically 70 to 80 degrees, with respect to an axis perpendicular to the incident substrate surface (Z axis). The measurement location MLO may alternatively be referred to as the beam spot region MLO. At the measurement location MLO, the patterned radiation beam BE1 is reflected by the substrate W (indicated by arrow BE2) and guided toward the detection unit LSD.

[0077]

[0076] To determine the height level at the measurement location MLO, the level sensor further comprises a detection system comprising a detection grid DGR, a detector DET, and a processing unit (not shown) for processing the output signal of the detector DET. The detection grid DGR may be the same as the projection grid PGR. The detector DET generates a detector output signal that indicates the received light, for example, the intensity of the received light as can be output by a photodetector, or the spatial distribution of the received intensity as can be output by a camera or sensor array. The detector DET may comprise any combination of one or more detector types.

[0078]

[0077] The height level at the measurement location MLO can be determined by triangulation techniques. The detected height level is typically related to the signal intensity measured by the detector DET, which has a periodicity that depends, in particular, on the design of the projection grid PGR and the (oblique) incidence angle ANG.

[0079]

[0078] The projection unit LSP and / or detection unit LSD may include further optical elements, such as lenses and / or mirrors, along the path of the patterned radiation beam between the projection grid PGR and the detection grid DGR (not shown).

[0080]

[0079] In one embodiment, the detection grid DGR may be omitted, and a detector DET may be installed in the position where the detection grid DGR is located. Such a configuration provides a more direct detection of the image of the projection grid PGR.

[0081]

[0080] In order to effectively cover the surface of the substrate W, the level sensor LS may be configured to project an array of measurement beams BE1 onto the surface of the substrate W, thereby generating a measurement area MLO or an array of spots that cover a larger measurement range.

[0082]

[0081] Various types of height sensors are disclosed, for example, in U.S. Patent No. 7,265,364 and U.S. Patent No. 7,646,471, both incorporated by reference. A height sensor that uses UV radiation instead of visible or infrared radiation is disclosed in U.S. Patent Application Publication No. 2010233600A1, incorporated by reference. International Publication No. 2016102127A1 describes a small height sensor that detects and recognizes the position of a grid image using a multi-element detector without requiring a detection grid.

[0083]

[0082] Generally, the detection unit LSD can be arranged such that the reflected radiation BE2 is divided into a first part and a second part, and the height of the substrate W is determined by combining the intensity of the first part and the intensity of the second part. For example, the height may be determined as a difference measurement. Advantageously, in such an arrangement, the determination of the height of the substrate W may be substantially independent of the intensity of the radiation beam BE1. In practice, dividing the radiation into a first part and a second part can be achieved by several different methods.

[0084]

[0083] For example, in some known configurations, a polarizer and a Shear plate (e.g., in the form of a Wollaston prism) are used to form two laterally shifted images of a projection grating PGR (each having a different polarization state) on the detection grating DGR. An example of such a configuration is schematically shown in Figure 5 of U.S. Patent Application Publication No. 2010233600A1. For example, the projection grating PGR may have a pitch P and a duty cycle of 50%, thereby providing a radiation beam BE1 having a periodically fluctuating intensity with multiple lines having a thickness of P / 2, and adjacent lines being separated by P / 2. The polarizer and Shear plate are positioned on the detection grating DGR to form two images of the projection grating PGR (each having a different polarization state), with one image laterally shifted by P / 2 relative to the other. Downstream of the detection grating DGR, the two separate polarization states are each induced to different detectors. The height of the substrate W is determined as being proportional to the difference in intensity between the two separate polarization states.

[0085]

[0084] In some other known configurations, instead of splitting the reflected radiation BE2 using two images of a projection grating PGR having different polarization states, a single image of the projection grating PGR is formed on a splitting optical system arranged to split that single image into a first and a second part. Examples of such configurations are schematically shown in Figure 6 of U.S. Patent Application Publication No. 2010233600A1 and Figure 2 of International Publication No. 2016102127A1. For example, such configurations generally include a splitting optical system arranged to split the reflected radiation into a first and a second part. The splitting optical system may be a serrated grating having a triangular grating profile, which acts as a series of wedges or prisms to redirect the reflected radiation BE2 (according to Snell's law). Such a split optical system can be thought of as comprising multiple prisms, and the image of each line of the projection grating PGR can be imaged onto one of several roughly triangular prisms such that a first portion of the line is incident on a first surface of the prism and a second portion of the line is incident on a second surface of the prism. The first portion of the line is guided to a first detector and the second portion of the line is guided to a second detector. As the line moves relative to the prism (as a result of a change in the height of the substrate W), the amount of radiation guided to each detector changes. Embodiments of this disclosure are particularly applicable to level sensors using this type of split optical system.

[0086]

[0085] Some embodiments of the present disclosure relate to a method for determining a correction value for the height profile of the surface of a substrate W, which is described below with reference to Figure 3. As used herein, the surface of a substrate may refer to the surface of a bare (untreated) substrate or the surface of a treated substrate having one or more layers of material deposition and / or resist.

[0087]

[0086] Figure 3 is a schematic representation of method 100 for determining the correction value of the surface height profile of a substrate (e.g., substrate W). Method 100 can be performed, for example, using a level sensor LS in the form generally shown in Figure 2.

[0088]

[0087] Method 100 comprises step 110 of fixing the substrate W to a substrate holder. For example, the substrate holder may include a clamp (e.g., an electrostatic clamp). The clamp may be operable to clamp the substrate W to a support such as a wafer stage WT in a lithography apparatus LA.

[0089]

[0088] Method 100 further comprises step 120 of creating a first measurement of a first height profile while the substrate W is in a first orientation.

[0090]

[0089] Method 100 further comprises step 130 of rotating the substrate W to a second orientation about the global normal of the surface. The substrate W may be a substrate in a lithography apparatus LA. Such a substrate W may comprise a silicon wafer coated with photoresist. It will be understood that such a substrate W comprises a relatively thin, flat disk of material having two opposing, generally circular surfaces. It will also be understood that the surface of the substrate W is not perfectly flat, and therefore there is some variation in the local normal to the surface of the substrate W. However, the global normal of the substrate W is the normal to the global or mean plane of the surface of the substrate W.

[0091]

[0090] Method 100 further comprises step 140 of creating a second measurement of the second height profile while the substrate W is in a second orientation.

[0092]

[0091] Method 100 further comprises step 150 of correcting the first and second measurements (determined in steps 120 and 140) for the shape of the substrate holder to determine the first and second corrected measurements, respectively.

[0093]

[0092] Method 100 further comprises step 160 of determining a correction value for the height profile by combining a first corrected measurement and a second corrected measurement.

[0094]

[0093] Step 120 comprises creating a first measurement of a first height profile, and step 140 comprises creating a second measurement of a second height profile. Such measurement of a height profile comprises a substep 170a of projecting a patterned radiant beam onto a beam spot area, a substep 170b of moving the substrate W relative to the beam spot area while it is in a current orientation (either a first orientation for the first measurement 120 or a second orientation for the second measurement 140), a substep 170c of receiving a portion of the patterned radiant beam reflected from the substrate W, and a substep 170d of determining a measurement of the height profile from the portion of the patterned radiant beam reflected from the substrate W.

[0095]

[0094] Step 170a, which projects a patterned radiation beam onto a beam spot region, may comprise forming a first image of the pattern onto the beam spot region using the radiation beam. Forming a first image of the pattern onto the beam spot region MLO may comprise providing a radiation beam LSB, patterning the radiation beam LSB using a patterning device (e.g., a projection grating PGR), and projecting the patterned radiation BE1 onto the beam spot MLO region using a projection optical system. For example, a projection unit LSP may be used to form a first image of a projection grating PGR (pattern) onto the measurement location MLO (beam spot region) using the radiation beam LSB.

[0096]

[0095] Step 170b, which moves the substrate W with respect to the beam spot region (e.g., measurement location MLO) while it is in the first orientation, is described here as moving the substrate with respect to the beam spot region, but it will be understood that in alternative embodiments, the beam spot region may be moved with respect to the substrate W (for example, by moving the projection unit LSP and the detection unit LSD while the object W remains stationary).

[0097]

[0096] Moving the substrate W relative to the beam spot region MLO may comprise scanning the substrate W relative to the beam spot region MLO. Such scanning may be at a constant speed or velocity, or at a variable speed. As used herein, scanning the substrate W is intended to mean continuous movement of the substrate W. Alternatively, moving the substrate W relative to the beam spot region MLO may comprise stepping the substrate W relative to the beam spot region MLO. As used herein, stepping the substrate W is intended to mean movement of the substrate W in a number of consecutive (temporarily separated) steps.

[0098]

[0097] The substrate W is fixed to a substrate holder such as a wafer stage WT in the lithography apparatus LA (see step 110). Therefore, moving the substrate W relative to the beam spot region MLO may involve moving the substrate holder WT.

[0099]

[0098] Step 170c, which involves receiving a portion of the patterned radiation beam reflected from the substrate W, may include receiving the reflected radiation BE2 with the detection unit LSD of the level sensor LS.

[0100]

[0099] The method 100 for determining the correction value of the surface height profile of the substrate (e.g., substrate W) shown in Figure 3 is advantageous as follows.

[0101]

[0100] The substrate W may be a substrate W in a lithography apparatus LA. Such a substrate W may comprise a silicon wafer coated with photoresist. The lithography apparatus LA may be used to expose the substrate W to radiation B patterned by a reticle or mask MA. Before the substrate W is exposed to the patterned radiation, the topology of the surface of the substrate W may be determined. For example, a height map of the surface of the substrate W may be determined using, for example, a level sensor LS. The measured topography of the surface of the substrate W can then be used to control the height of the substrate W while the substrate W is exposed to the patterned radiation, for example, to keep the substrate W within the best-focus plane of the image of the patterning device MA.

[0102]

[0101] A certain type of level sensor LS can be used to measure the surface height profile of a substrate W by projecting a patterned radiation beam BE1 onto a beam spot region MLO, moving the substrate W relative to the beam spot region MLO, and receiving a portion of the patterned radiation beam BE2 reflected from the substrate W to determine the height of the substrate W. As the height of the substrate W changes, the position of the pattern in the reflected radiation BE2 may change, for example, with respect to a splitting optical system DGR arranged to split the reflected radiation into a first part and a second part.

[0103]

[0102] The inventors of the present invention have recognized that the height map thus determined will generally have contributions from both (a) the shape of the substrate holder (e.g., a clamp or wafer stage WT) on which the substrate W is clamped (because when clamped, the substrate W conforms to the shape of the clamp) and (b) process layers formed on the surface. A silicon wafer W may have one or more layers previously formed using, for example, a lithography process. Generally, various different materials and / or features of different densities will be present across the surface of such a wafer. Furthermore, the inventors have recognized that features on process layers can cause some errors in height measurement, and that the layers depend on the orientation of the substrate W when the substrate W is scanned through the beam spot region MLO. For example, some errors in height measurements due to features on process layers will change sign when the substrate W is rotated 180° around its global normal (and thus may be called antisymmetry errors in this specification). In contrast, the (actual) contribution to height measurement from the shape of the clamp is not antisymmetry. (In step 150) the data becomes independent of the clamp shape by correcting the first and second height measurements for the clamp shape to determine the first and second corrected height measurements for the surface, respectively. The first and second corrected height measurements are then combined to make an accurate determination of the antisymmetry process-dependent error. For example, if the two orientations are opposite (i.e., the substrate W rotates 180° around its global normal between the two measurements in steps 120 and 140), the first and second corrected height measurements can be obtained by h0 + Δh and h0 - Δh, respectively, where Δh is the antisymmetry error. The antisymmetry error can be determined as half the difference between the first and second corrected height measurements.

[0104]

[0103] Since different materials can absorb different proportions of incident radiation, and features of different densities can result in different amounts of scattering of incident radiation, the reflectivity across the surface of the wafer W can vary. For example, a 3D-NAND wafer W may contain features that can reduce the amount of specular reflection of radiation by up to 50%. Due to the change in substrate reflectivity, there is a change in the measured height profile Δh in the transition region.

[0105]

[0104] As is known in the art, determining the height profile of the substrate W is understood to involve determining the height profile of the substrate W with respect to a reference height or reference position.

[0106]

[0105] Although Method 100 is shown in Figure 3 as six separate steps 110, 120, 130, 140, 150, and 160, this is simply for ease of understanding, and it should be understood that the steps can be performed in any order. In some embodiments, Method 100 is performed over an extended measurement period, and therefore these steps can be performed simultaneously.

[0107]

[0106] There are three types of level sensor height measurement errors that depend on the orientation of the substrate W when measuring a wafer at height Z. These three errors each depend on the orientation of the wafer W (0° vs 180°) as follows, as explained with reference to Figure 11.

[0108]

[0107] The first error is the phase step error (see Figure 11(a)). This error is due to the actual height steps encountered during measurement. In such height steps, the height does not simply step up from one level (left side of Figure 11(a)) to another level (right side of Figure 11(a)), but rather the raw height measurement has two features. Due to these features, the height measurement drops below the height on the left side of Figure 11(a) and peaks above the height on the left side of Figure 11(b). The magnitude of these two features is the rotationally symmetric component E pand the rotation anti-symmetric components ±dE p can be expressed as. It should be noted that the anti-symmetric component is non-zero (i.e., ±dE p ≠0) when the surface tilt error (see Fig. 11(c) described later) is non-zero.

[0109]

[0108] The second error is the reflectance step error (or reflectance error) (see Fig. 11(b)). This error is caused by the step of the reflectance (there is no change in the height of the wafer W). This reflectance error will be further described later by referring to Figs. 6 to 7B. The reflectance error (±E R ) has rotational anti-symmetry. Therefore, the error is +E R at 0°, and the error is -E R at 180°.

[0110]

[0109] The third error is the surface tilt error (see Fig. 11(c)). This error is caused by the local variation of the tilt of the surface of the wafer W. The variation of the tilt of the surface of the substrate W generally affects the focusing of the patterned radiation beam onto the beam spot region MLO. This will result in a height measurement error (±E T ) that depends on the tilt or gradient of the surface of the substrate. This surface tilt error is proportional to the local wafer tilt and has rotational anti-symmetry. Therefore, the error is +E T at 0°, and the error is -E T at 180°.

[0111]

[0110] In addition to these anti-symmetry errors, the contribution to the height measurement value from the shape of the substrate holder or clamp depends on the orientation of the wafer W, but is not anti-symmetric.

[0112]

[0111] The two measured values Z W and Z 0 of the height of the wafer W with the actual height Z 180 determined at the orientations of 0° and 180° of the wafer W, respectively, can be described as follows and are obtained by the following formula.

[0113]

number

[0114] Here, the antisymmetric term ΔZ can be found by the following equation.

[0115]

number

[0116] The main error contributing to the antisymmetric term ΔZ is the reflection step error E. R The two measured values ​​Z 0 and Z 180 The antisymmetric term ΔZ can be found by the following equation.

[0117]

number

[0118]

[0112] Method 100 shown in Figure 3 can be used to determine any combination of antisymmetry errors. For example, in some embodiments, Method 100 shown in Figure 3 can be used to determine ΔZ obtained by equation (3) as a correction value for the surface height profile of the substrate W. For example, the first measurement of the first height profile created while the substrate W is in the first orientation (in step 120) is Z 0 It is possible. Similarly, the second measurement of the second height profile created while the substrate W is in the second orientation (in step 140) is Z 180 This is possible. The first and second corrected measurements are, respectively,

[0119]

number

[0120] It can be determined by this method.

[0121]

[0113] Alternatively, as described below, in some embodiments, the method 100 shown in Figure 3 is used to reduce surface tilt error ±E T This can be used to determine a correction value for rotational antisymmetry error that excludes the following. That is, using method 100 in Figure 3, the following antisymmetry term ΔZ' obtained by the following equation can be determined as a correction value for the height profile of the surface of the substrate W.

[0122]

number

[0123] Two measurement values ​​Z 0 and Z 180 Regarding this, the antisymmetric correction term ΔZ' can be obtained by the following equation.

[0124]

number

[0125]

[0114] In such embodiments, the first and second measurements of the height profile may be considered to have been corrected for local variations in the inclination of the surface of the substrate W.

[0126]

[0115] In some embodiments, correcting the height profile measurement for the shape of the substrate holder to determine the corrected measurement (for example in step 150) may be done using a reference substrate (e.g., a bare wafer), as described below with reference to Figure 4.

[0127]

[0116] As schematically shown in Figure 4, the method 200 for determining a corrected measurement by correcting the height profile measurement with respect to the shape of the substrate holder (for example in step 150) may include the steps of fixing a reference substrate to the substrate holder (step 210), creating a reference measurement of the height profile of the reference substrate (step 220), and determining the corrected measurement of the height profile as the difference between the measurement and the reference measurement (step 230).

[0128]

[0117] Step 220 comprises creating a reference measurement of the height profile of a reference substrate. Similar to steps 120 and 140 of method 100 shown in Figure 3 and described above, such measurement of the height profile comprises substep 170a of projecting a patterned radiant beam onto a beam spot area, substep 170b of moving the reference substrate relative to the beam spot area while it is in its current orientation, substep 170c of receiving a portion of the patterned radiant beam reflected from the reference substrate, and substep 170d of determining a first measurement of the reference height profile from the portion of the patterned radiant beam reflected from the reference substrate.

[0129]

[0118] When using Method 200, it should be noted that in step 220, the substrate holder should be in the same orientation as when the height profile measurement, which is corrected for the shape of the substrate holder, was determined. For example, when using Method 200 in Figure 4 to correct the first measurement to determine a first corrected measurement for the shape of the substrate holder, in step 220, the substrate holder should be in the same orientation as when the first measurement was determined (i.e., the first orientation used in step 120). Similarly, when using Method 200 in Figure 4 to correct the second measurement to determine a second corrected measurement for the shape of the substrate holder, in step 220, the substrate holder should be in the same orientation as when the second measurement was determined (i.e., the second orientation used in step 140).

[0130]

[0119] Step 150 of method 100 shown in Figure 3 can be achieved by performing method 200 shown in Figure 4 twice (once to correct the first measurement value for the shape of the substrate holder to determine the first corrected measurement value, and once to correct the second measurement value for the shape of the substrate holder to determine the second corrected measurement value).

[0131]

[0120] The reference substrate is sometimes referred to as the reference object. The reference substrate may be a bare wafer. That is, the reference substrate may be a silicon wafer to which no process layers have been applied.

[0132]

[0121] This process using a reference substrate or bare wafer can function as follows: To compensate for the shape of the substrate holder (clamp), the bare wafer is measured at the same location as the process wafer for both rotations. In the case of a (flat) bare wafer, there are no phase step errors and reflectance step errors. Therefore, the process wafer height measurement can be corrected by subtracting the bare wafer measurement. Thus, the corrected measurement can be written as follows:

[0133]

number

[0134] The correction term can be determined as follows:

[0135]

number

[0136]

[0122] In some embodiments, step 170d, which determines a height profile measurement from a portion of the patterned radiation beam reflected from the substrate (or reference substrate), may comprise the following steps, as schematically shown in Figure 5.

[0137]

[0123] Specifically, step 170d may include step 310 of receiving a portion of the radiation beam reflected from the substrate W (e.g., reflected radiation BE2) and dividing the reflected radiation into a first portion and a second portion. Specifically, the reflected radiation BE2 may be divided such that the first portion of radiation BE2 corresponding to the first portion of the first image (formed at measurement location MLO) is spatially separated from the second portion of radiation corresponding to the second portion of the first image.

[0138]

[0124] Step 170d may further comprise step 320 of determining the intensities I1 and I2 of the first and second portions of the radiation, respectively. For example, step 320 may be carried out by a detector DET which may comprise at least two parts, each part operable to determine the intensity of one of the first and second portions of the reflected radiation BE2.

[0139]

[0125] Step 170d may further comprise step 330, which determines the height h of the substrate W by combining the intensity I1 of the first part of the radiated BE2 and the intensity I2 of the second part of the radiated BE2.

[0140]

[0126] As is known in the art, determining the height of an object W will be understood to involve determining the height of the object relative to a reference height or position. The height h of object W may be proportional to the difference between a first intensity I1 and a second intensity I2. For example, the height h of object W may be determined as being proportional to the difference between the first intensity I1 and the second intensity I2 divided by the sum of the first intensity I1 and the second intensity I2. That is, the height h may be calculated by the following equation.

[0141]

number

[0142] Here, α is the gain. Any measurement of the wafer W height mentioned herein (e.g., the measurement Z described above) 0 and Z 180 ) can be determined according to equation (10).

[0143]

[0127] As the height of object W changes, the position of at least a portion of the second image of pattern PGR formed on the detection grating DGR also changes, which in turn results in a change in the relative values ​​of the first and second intensities I1 and I2. For example, as the height of object W changes, the position of at least a portion of the second image of pattern PGR may change with respect to the splitting optical system (or detector array) arranged to split the reflected radiation into a first and a second portion.

[0144]

[0128] Advantageously, by dividing the reflected radiation BE2 into a first part and a second part, and determining the height of the substrate W by combining the intensity of the first part and the intensity of the second part, the determination of the height may be substantially independent of the intensity of the radiation beam LSB. For example, the height may be determined as a difference measurement (e.g., according to equation (10)).

[0145]

[0129] The method 170d shown in Figure 5 is of the type in which the reflected light BE2 is divided into two parts corresponding to different parts of the first image (formed on the substrate W). The first image is formed in the beam spot region or measurement location MLO. Generally, there may be a spatial offset between the first and second parts of the first image (however, the first and second parts may partially overlap spatially). The object W being measured may have some variation in reflectance across its surface. For example, the object W may have localized areas or features that have a different reflectance from the surrounding parts of its surface. In such a configuration, as the feature moves in (or out) the beam spot region MLO (for example, due to relative movement in step 120), any spatial offset between the first and second parts of the first image will result in a difference between the first and second intensities due to the change in reflectance (not the height of the object W). As will be further discussed with reference to Figures 6 to 7B, such features may result in height measurement errors due to any change in the reflectance of the surface of the object W. This is because the first and second parts of the radiation are reflected from different areas of the surface of object W.

[0146]

[0130] In some embodiments, splitting the reflected radiation BE2 into a first and a second part (in step 310) may involve forming a second image of the pattern on a splitting optical system (which may generally be located where the detection grating DGR is shown in Figure 2), and using the splitting optical system to induce and spatially separate the radiation from the first and second parts of the second image. The position of the second image relative to the splitting optical system may determine how much of the reflected radiation is induced into each of the first and second parts.

[0147]

[0131] Alternatively, in some embodiments, dividing the reflected radiation BE2 into a first and a second part (in step 310) may involve forming a second image of the pattern on a detector array comprising a plurality of sensing elements. The detector array may be referred to as a camera, and the individual sensing elements may be referred to as pixels. In such an arrangement, the intensity of the first part of the radiation can be determined using a first subset of the sensing elements (in step 320), and the intensity of the second part of the radiation can be determined using a second subset of the sensing elements (also in step 320).

[0148]

[0132] In some embodiments of the method 100 shown in Figure 3, step 130 of rotating the substrate W to a second orientation around the global normal of the surface may comprise rotating the substrate 180° around the global normal of the surface.

[0149]

[0133] In such embodiments, much of the error in the height measurement due to features on the process layer contributes to the first and second measurements by the same magnitude but with opposite signs (i.e., antisymmetry error). For example, in such embodiments, the antisymmetry error can be determined as half the difference between the first corrected measurement of height and the second corrected measurement.

[0150]

[0134] In some embodiments of the method 100 shown in Figure 3, the correction value (determined in step 160) may be determined as half the difference between the first corrected measurement and the second corrected measurement of the height profile (for example, according to any of equations 4, 6, 9, or 13).

[0151]

[0135] In some embodiments of the method 100 shown in Figure 3, creating each of the first and second measurements of the height profile (in steps 120 and 140) may involve measuring the surface height at multiple locations on the object.

[0152]

[0136] (In step 160) it will be understood that determining the correction value of the height profile on the surface of the substrate W by combining the first and second corrected measurements of the height profile may involve combining the measurements from the first and second corrected measurements of the height profile corresponding to the same position on the substrate W.

[0153]

[0137] In some embodiments of the method 100 shown in Figure 3, creating each of the first and second measurements of the surface height profile (in steps 120 and 140) comprises measuring a surface height map over substantially the entire surface of the substrate W. That is, the height map (and therefore the correction value) can be determined over substantially the entire substrate (wafer W).

[0154]

[0138] In some embodiments of the method 100 shown in Figure 3, creating each of the first and second measurements of the height profile (in steps 120 and 140) may involve measuring a surface height map for one or more of several regions C of the surface W of an object to which the same pattern is applied.

[0155]

[0139] That is, the height map (and therefore the correction value) may be determined for one or more fields or dies C of the substrate (wafer W). In some embodiments, the height map (and therefore the correction value) may be determined for only one (or a relatively small proportion) of multiple regions C of the surface of the substrate W to which the same pattern is applied.

[0156]

[0140] In some embodiments of method 100 shown in Figure 3, method 100 may further comprise correcting the first and second measurements of the height profile for local variations in the inclination of the substrate surface W. Also, with respect to embodiments of method 100 shown in Figure 3, step 150 of method 100 comprises method 200 shown in Figure 4, in which the first and second reference measurements of the height profile may be corrected for local variations in the inclination of the substrate surface before the first and second measurements of the height profile are corrected for the shape of the substrate holder.

[0157]

[0141] Variations in the tilt of the substrate W surface generally affect the focusing of the patterned radiated beam onto the beam spot region MLO. This, in turn, results in height measurement errors that depend on the tilt or gradient of the substrate W surface. One important factor in local variations in the tilt of the substrate W surface may be the shape of the substrate holder (or clamp) to which the substrate W is fixed / clamped. Such errors are typically antisymmetric errors (and thus may form part of the correction value determined using method 100 shown in Figure 3). However, such errors can generally be subject to significant local variations across the surface of the substrate W. For example, the substrate W (which may be a resist-coated silicon wafer) may have several roughly rectangular regions C (which may be called fields or dies) to which substantially the same pattern is applied (and has already been applied in the formation of previous process layers). Local variations in the tilt of the substrate W surface may result in significant variations in error for each field C (or die). This is in contrast to some other antisymmetry errors, which may depend primarily on the features of the process layer on the substrate W and therefore may be substantially the same for all fields C or die C.

[0158]

[0142] In such embodiments of Method 100, (a) first and second measurements of the height profile and (b) first and second reference measurements of the height profile are corrected for local variations in the inclination of the surface of the substrate W, the corrected measurements can be described as follows:

[0159]

number

[0160] Here, E T,ref This is the surface tilt error (E) of the reference substrate. T (It may be equal to or not equal to Z) W ' is the height profile of the substrate W corrected for local variations in the slope of the substrate W surface, Z reference ' is the height profile of the reference substrate corrected for local variations in the surface inclination of the reference substrate. The correction term ΔZ' can be determined as follows:

[0161]

number

[0162]

[0143] Optionally, in some embodiments of method 100 shown in Figure 3, method 100 may further include a step 180 of storing the correction value in memory.

[0163]

[0144] The inventors also recognized that the correction value determined by method 100 shown in Figure 3 depends primarily on (a) the substrate holder (or clamp MT) and (b) the lithography process (i.e., the layer recipe). If, as is typical, multiple wafers W are processed by a given lithography apparatus LA using the same lithography process, then the correction value will be substantially the same for all such wafers W. Thus, in some embodiments, the correction value can be determined once and then used for all subsequent wafers W processed on the same clamp WT using the same lithography process. Furthermore, method 100 shown in Figure 3 includes correcting the first and second measurements (determined in steps 120 and 140) for the shape of the substrate holder (in step 150) to determine the first and second corrected measurements, respectively, before these are combined (in step 160) to determine the correction value for the height profile, so that the correction value determined in step 160 is substantially independent of the substrate holder or clamp. Therefore, in some embodiments, the correction value may be determined once in one lithography apparatus LA (with clamp WT) and then used for all subsequent wafers W processed in the same lithography process, even on different clamps or in different lithography apparatus LA. Furthermore, in some embodiments, the correction value may be determined once for a single field C or die of wafer W and then used for all fields C or dies of all subsequent wafers W processed in the same lithography process.

[0164]

[0145] Figure 6 is a schematic diagram of a portion of the substrate W, showing the beam spot region or measurement location MLO. A first image of the pattern of the projection grating PGR having two lines L1 and L2 is also shown. In addition, each of the two lines has two parts (the upper and lower halves of each line L1 and L2 in Figure 6, respectively). The first image of the projection grating PGR can be considered to have a first part 210 (having the upper part of the two lines L1 and L2) and a second part 220 (having the lower part of the two lines L1 and L2).

[0165]

[0146] The first and second portions 210, 220 of the first image correspond to the first and second portions of radiation reflected by the substrate W, which are divided, for example, by a splitting optical system (see 648 in Figure 10, described later). That is, the first and second portions 210, 220 shown in Figure 6 may be considered as the back projection onto the substrate W of the division performed by the splitting optical system (shown here only to illustrate the advantages of the method of the embodiments of this disclosure). As described above (see equation (10)), the intensities of the reflected radiation from the first and second portions 210, 220 of the first image, which may be called the first intensity I1 and the second intensity I2, can be used (in step 170d) to determine a measurement of the height profile from the portion of the patterned radiation beam reflected from the substrate. Specifically, the division of the first image shown in Figure 6 into a first portion 210 and a second portion 220 represents a situation where the height of the substrate W is zero (relative to the reference height), because the first portion 210 and the second portion 220 are substantially equal in size.

[0166]

[0147] As indicated by arrow 230, during method 100 (in step 120), the substrate W is moved in the scan direction (y direction in Figure 6) relative to the beam spot area (measurement location MLO). Note that in step 140, the substrate W may be moved in the same scan direction (y direction in Figure 6) relative to the beam spot area (measurement location MLO), but with a different orientation. The x and y directions shown in Figure 6 represent the sides of the target portion C (e.g., comprising one or more dies) of the substrate W (see Figure 1), and generally, features formed on the substrate W tend to be aligned in the x and / or y directions. Note that the lines L1, L2 of the projection grid PGR are positioned at non-zero angles with respect to both the x and y directions in Figure 6. This is to minimize the effect of scattering of the incident radiation beam BE1 from features on the substrate W (other than specular reflection) on the height measurement.

[0167]

[0148] Each of the two lines L1 and L2 has a thickness t in the direction in which the substrate W is moved relative to the beam spot region MLO (i.e., the y-direction). Note that the thickness t of each of the lines L1 and L2 in the first image (formed on the substrate W) is generally (by 1 / cos(ANG) times) greater than the thickness of each of the corresponding lines on the projection grating PGR. The distance between the two lines in the y-direction is also t, and therefore the pitch p (in the y-direction) of the first image is 2t. Between the first part 210 and the second part 220 of the first image there is a spatial offset equal to t / 2 in the y-direction (where t is the thickness t of the lines L1 and L2).

[0168]

[0149] Figure 6 also shows a feature 240 on wafer W having a different reflectivity from the rest of the substrate W. Specifically, the feature 240 on wafer W may have 80% of the reflectivity of the rest of the substrate W. In this example, the reduced reflectivity feature 240 has a range in the x-direction that is greater than the range of the beam spot region MLO. Thus, the feature 240 can be thought of as providing a one-dimensional step in reflectivity (in the y-direction). As the substrate is scanned or stepped in the y-direction, the feature 240 moves into the beam spot region MLO and then out of the beam spot region MLO.

[0169]

[0150] As feature 240 moves in (or out) the beam spot region MLO (for example, due to relative movement in step 120), the y-direction spatial offset between the first portion 210 and the second portion 220 of the first image results in a difference between the first and second intensities due to a change in reflectivity between feature 240 and the rest of the substrate W (rather than due to the height of the substrate W). This can be seen from Figures 7A and 7B.

[0170]

[0151] Figure 7A shows the first intensity I1 and the second intensity I2, which are the radiations from the first portion 210 and the second portion 220 of the first image, respectively, as a function of the position of the substrate in the y direction. From Figure 7A (moving from left to right in Figure 7A), it can be seen that as feature 240 moves into the beam spot region MLO, the first intensity I1 decreases (due to a decrease in the reflectivity of feature 240) before the second intensity I2 decreases. When feature 240 is completely inside the beam spot region MLO, both the first intensity I1 and the second intensity I2 decrease due to a decrease in the reflectivity of feature 240. Also, as feature 240 moves out of the beam spot region MLO, the first intensity I1 increases back to its nominal value before the second intensity I2.

[0171]

[0152] Figure 7B shows the height determined by combining a first intensity I1 and a second intensity I2, which are determined at any given time. Specifically, the height is proportional to the difference I2-I1. It should be noted that this example shown in Figure 6 represents a situation where the height of the substrate W is zero (relative to the reference height) because the first portion 210 and the second portion 220 are substantially equal in size. As a result, when feature 240 is not within the beam spot region MLO (left and right sides of Figures 7A and 7B), the height is zero. Also, when feature 240 is completely within the beam spot region MLO (central parts of Figures 7A and 7B), the height is close to zero. However, due to the change in reflectivity caused as feature 240 moves in or out of the beam spot region 240, the substrate is at a height of zero, but as feature 240 moves in (or out) the beam spot region MLO (for example, due to relative movement in step 120), combining the two simultaneously determined intensities will result in a significant error in determining the height of the substrate W. This is because the first portion 210 and the second portion 220 of the radiation are reflected from different areas on the surface of the substrate W.

[0172]

[0153] Some embodiments of the present disclosure relate to methods for measuring the topography of the surface of a substrate W, as described below with reference to Figure 8. Figure 8 is a schematic representation of method 400 for measuring the topography of the surface of a substrate W.

[0173]

[0154] Method 400 in Figure 8 comprises a step 410 of creating a measurement of the surface height profile of the substrate W. Similar to steps 120 and 140 of Method 100 shown in Figure 3 and described above (and step 220 of Method 200 shown in Figure 4), such measurement of the height profile of the substrate W comprises a substep 170a of projecting a patterned radiation beam onto a beam spot area, a substep 170b of moving a reference substrate relative to the beam spot area while in its current orientation, a substep 170c of receiving a portion of the patterned radiation beam reflected from the reference substrate, and a substep 170d of determining a first measurement of the reference height profile from the portion of the patterned radiation beam reflected from the reference substrate.

[0174]

[0155] Method 400 in Figure 8 further comprises step 410 of determining a corrected measurement of the height profile by combining the measured height profile with a corrected value of the substrate height profile determined using Method 100 in Figure 3.

[0175]

[0156] Method 400 shown in Figure 8 is advantageous because it provides a corrected measurement value that has been corrected using the correction value determined by Method 100 shown in Figure 3. For example, this may allow antisymmetry errors to be accurately corrected. In some embodiments of Method 400 shown in Figure 8, the corrected measurement value of the height profile is determined by subtracting the correction value from the measurement value of the height profile. That is,

[0176]

number

[0177] Here, the correction value Δ can be, for example, ΔZ or ΔZ' as described above.

[0178]

[0157] In some embodiments, the method 400 shown in Figure 8 may further comprise determining the correction value of the height profile using the method 100 shown in Figure 3.

[0179]

[0158] For at least some wafers W, the method 400 in Figure 8 may comprise first determining a correction value (using the method 100 in Figure 3) and then correcting the height measurement using this value (using the method 400 in Figure 8). For example, the correction value may be determined for at least a first wafer W processed using a given lithography process or recipe.

[0180]

[0159] In some embodiments, the method 400 in Figure 8 may include retrieving the correction value from memory. For example, if the method 100 in Figure 3 has been previously implemented and includes a step 180 of storing the correction value in memory, the stored correction value may be retrieved from memory.

[0181]

[0160] In some embodiments of the method 400 in Figure 8, step 420 of combining the height profile measurement with a correction value for the height profile of the substrate W may include combining the measurement with a correction value at substantially the same location on the substrate W.

[0182]

[0161] For example, in some embodiments, the correction value for the surface height of the substrate W may be determined substantially over the entire substrate (wafer W). Similarly, the surface height measurement may be determined substantially over the entire substrate (wafer W) and may be combined with the correction value to determine the corrected measurement of the surface height of the substrate W.

[0183]

[0162] In some embodiments of the method 400 in Figure 8, the substrate W may comprise multiple regions C to which the same pattern is applied. In such embodiments, combining the height profile measurement with a correction value for the substrate height profile may comprise combining the measurement of each of the multiple regions C with a correction value for one of the multiple regions C.

[0184]

[0163] In other words, in some embodiments, the correction value may be determined for only one (or a relatively small proportion) of a plurality of regions C on the surface of the substrate W to which the same pattern is applied. The correction value for that single region C of the substrate W may be used to correct each of the height measurements of the plurality of regions C of the substrate.

[0185]

[0164] Some embodiments of the present disclosure relate to lithography exposure methods. An example of such a lithography exposure method 500 is schematically shown in Figure 9. The lithography exposure method 500 comprises measuring the topography of the surface of a substrate W using the method 400 of Figure 8. The lithography exposure method 500 further comprises the steps of: patterning a radiation beam B using a patterning device MA; and projecting the patterned radiation onto the substrate W to form an image of the patterning device MA onto the substrate W. The position of the substrate W while the patterned radiation is projected onto the substrate W (in step 520) is controlled depending on the measured topography of the surface of the substrate W (measured in step 400).

[0186]

[0165] Advantageously, the measured topography of the substrate surface can be used to control the height of the substrate W while the substrate W is exposed to patterned radiation, for example, to keep the substrate W within the best-focus plane of the patterning device MA image. It will be understood that the image of the patterning device MA formed on the substrate W may be a diffraction-limited image.

[0187]

[0166] In some embodiments, the lithography exposure method 500 comprises scan exposure, and thus patterning the radiation beam using a patterning device MA comprises moving the patterning device MA through the radiation beam B and projecting the patterned radiation onto the substrate W to form an image of the patterning device MA on the substrate W, and moving the substrate W such that the image of the patterning device MA is stationary with respect to the substrate W. That is, in order to image a pattern onto a target region C of the substrate W, the patterning device MA is moved or scanned in the scan direction through the illumination region. It will be understood that the substrate W is also scanned with respect to the illumination region 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 with respect to the substrate W, and it will be understood that the direction and / or speed of the substrate W may generally differ from that of the patterning device MA (e.g., when the image is inverted and / or when reduction is applied by the projection system PS).

[0188]

[0167] Some embodiments of the present disclosure relate to an apparatus for measuring the topography of the surface of an object W. One embodiment of such an apparatus 600 is shown in Figure 10. The apparatus 600 may be referred to as a level sensor. The apparatus 600 may form part of a lithography apparatus LA of the type shown in Figure 1 and described above. The apparatus 600 is generally in the form of a level sensor LS shown in Figure 2.

[0189]

[0168] The apparatus 600 comprises a support 610, a projection optical system 620, a moving mechanism 630, a detection optical system 640, a first detector 650, a second detector 660, and a controller 670.

[0190]

[0169] The support 610 is suitable for supporting an object W, such as a substrate W. The support 610 may include, for example, a substrate table WT. The support 610 may include, for example, a substrate holder such as a clamp.

[0191]

[0170] The projection optics system 620 is operable to form a first image of the pattern on the beam spot region 680 using the radiation beam 622. The projection optics system 620 is generally equivalent to the projection unit LSP shown in Figure 2 and described above, and the beam spot region 680 may be generally equivalent to the measurement location MLO shown in Figure 2 and described above. The projection optics system 620 may comprise, for example, a projection patterning device 624 and a first imaging optics system 626 positioned to form an image of the projection patterning device 624 on the beam spot region 680. The projection patterning device 624 may comprise a grating. The grating may comprise a plurality of lines. The lines may be of uniform thickness. The grating may have a duty cycle of 50%. The projection patterning device 624 may be generally equivalent to the projection grating PGR shown in Figure 2 and described above.

[0192]

[0171] The moving mechanism 630 is operable to move the support 610 to move the object supported by the support 610 (e.g., the substrate W) through the beam spot region 680. This movement is schematically shown by arrow 632.

[0193]

[0172] The detection optical system 640 is operable to receive a portion 642 of the radiation beam reflected from the object W, and to divide the reflected radiation 642 into a first portion 644 and a second portion 646, so that the first portion 644 of the radiation corresponding to the first portion of the first image is spatially separated from the second portion 646 of the radiation corresponding to the second portion of the first image. The detection optical system 640 is substantially equivalent to the detection unit LSD shown in Figure 2 and described above.

[0194]

[0173] The first detector 650 is positioned to determine the intensity of the first portion 644 of the reflected radiation. The second detector 660 is positioned to determine the intensity of the second portion 646 of the reflected radiation.

[0195]

[0174] The detection optical system may include a splitting optical system 648 arranged to split the reflected radiation 642 into a first portion 644 and a second portion 646, and a second imaging optical system 649 arranged to receive the radiation 642 reflected from an object W supported by a support 610 and to form a second image of the pattern on the splitting optical system 648. The first imaging optical system 626 may be substantially equivalent to the second imaging optical system 649.

[0196]

[0175] The segmented optical system 648, the beam spot region 680, and the projection patterning device 624 all lie in optically conjugate planes. The two planes are optically conjugate if all radiation passing through each distinct point in the first plane is imaged onto a distinct point in the second plane.

[0197]

[0176] The image of the projection patterning device 624 is formed on the splitting optical system 648, and the position of the image indicates the height of the object W. Specifically, the position of the image relative to the splitting optical system 648 indicates the height of the object W. As described above, the projection patterning device 624 may have a grid with multiple lines. The splitting optical system 648 may have multiple prisms, and the image of each line may be formed on one of multiple roughly triangular prisms, so that a first portion of the line is incident on a first surface of the prism and a second portion of the line is incident on a second surface of the prism. The first portion of the line is guided to a first detector 650, and the second portion of the line is guided to a second detector 660. As the line moves relative to the prism (as a result of the change in the height of the object W), the amount of radiation guided to each detector 650, 660 changes.

[0198]

[0177] Alternatively, in some embodiments, dividing the reflected radiation 642 into a first portion 644 and a second portion 646 may involve forming a second image of the pattern on a detector array comprising a plurality of sensing elements (for example, using a second imaging optical system 649). The detector array may be referred to as a camera, and the individual sensing elements may be referred to as pixels. In such an arrangement, the intensity of the first portion of the radiation can be determined using a first subset of the sensing elements (in step 320), and the intensity of the second portion of the radiation can be determined using a second subset of the sensing elements (also in step 320). It should be noted that in such an arrangement (where the splitting optical system 648, the first detector 650, and the second detector 660 are replaced by a detector array), the detection optical system 640 may be configured to receive a portion 642 of the radiation beam reflected from the object W, and to split the reflected radiation 642 into a first portion 644 and a second portion 646, so that the first portion 644 of the radiation corresponding to the first portion of the first image is spatially separated from the second portion 646 of the radiation corresponding to the second portion of the first image by forming a second image of the pattern (for example, using a second imaging optical system 649).

[0199]

[0178] The controller 670 is configured to receive a first signal s1 indicating a first intensity from the first detector 450 and a second signal s2 indicating a second intensity from the second detector 460.

[0200]

[0179] The controller 670 is operable to determine the height of object W by combining the intensity of the first portion 644 of the reflected radiation and the intensity of the second portion 646 of the reflected radiation.

[0201]

[0180] The apparatus 600 shown in Figure 10 has the following advantages. The detection optical system 640 is operable to divide the reflected radiation into a first portion 644 and a second portion 646, and the controller 670 is operable to determine the height of the substrate W by combining the intensity of the first portion 644 and the intensity of the second portion 646, so that the determination of the height may be substantially independent of the intensity of the radiation beam 622. For example, the height may be determined as a difference measurement (for example, according to equation (10)).

[0202]

[0181] The controller 670 may be operable to implement any one of the methods shown in Figures 3, 4, 5, and 8, as described above.

[0203]

[0182] In some embodiments, the first and second detectors 650, 660 are arranged to determine the intensity of the first portion 644 and the second portion 646 multiple times at a sampling frequency f, respectively. That is, the first detector 650 and the second detector 660 may be arranged so that the intensity of the first portion 644 and the second portion 646 of the radiation is determined multiple times, and each determination is temporally separated from the previous determination and the next determination. The sampling frequency f may be the reciprocal of the temporal separation between the start of one determination and the start of the next determination.

[0204]

[0183] In some embodiments, the apparatus 600 may further include a radiation source 690 that is operable to generate a radiation beam 622.

[0205]

[0184] Some embodiments of the present disclosure relate to a lithography apparatus comprising an apparatus 600 of the type shown in Figure 10. The lithography apparatus may be of the type shown in Figure 1. The lithography apparatus LA may further comprise: an illumination system IL operable to illuminate an illumination area; a support structure MT configured to support a patterning device MA such that the patterning device MA can be positioned within the illumination area; a substrate table WT configured to support a substrate W; and a projection system PS operable to form an image of the patterning device MA supported by the support structure MT onto a substrate W supported by the substrate table WT.

[0206]

[0185] Some examples of methods 100, 300 shown in Figures 3 and 8 are described herein using two measurements (in steps 120 and 140), each of which is corrected for the shape of the substrate holder (in step 150) and then combined (in step 160) to determine the corrected value. However, alternative embodiments may use additional measurements that can be performed using substrates W and substrate holders of different orientations. For example, some of the examples described above use two measurements at angles of 0° and 180° (i.e., a 180° substrate rotation between measurements). However, in an alternative embodiment, method 100 in Figure 3 may use four measurements with a 90° substrate rotation between measurements (i.e., measurements at 0°, 90°, 180°, and 270°). Embodiments using more measurements may yield more accurate corrected values.

[0207]

[0186] Although this text specifically refers to the use of lithography equipment in the manufacture of ICs, it should be understood that lithography equipment described herein may have other applications. Possible other applications include the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memory, flat panel displays, liquid crystal displays (LCDs), thin-film magnetic heads, and the like.

[0208]

[0187] Although embodiments of the present invention are specifically referred to in the context of lithography apparatus in this text, embodiments of the present invention may be used in other apparatuses. Embodiments of the present invention may form part of a mask inspection apparatus, a metrology apparatus, or any apparatus for measuring or processing objects such as wafers (or other substrates) or masks (or other patterning devices). These apparatuses are sometimes commonly referred to as lithography tools. Such lithography tools may operate under vacuum conditions or ambient (non-vacuum) conditions.

[0209]

[0188] The above has particularly referred to the use of embodiments of the present invention in the context of optical lithography, but it will be understood that the present invention is not limited to optical lithography and may be used in other applications, such as imprint lithography, where permitted in the context.

[0210]

[0189] Where permitted by context, 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 in a machine-readable medium that can 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, propagating signals of electrical, optical, acoustic or other forms (e.g., carrier waves, infrared signals, digital signals, etc.), and others. Furthermore, firmware, software, routines, and instructions are described herein as performing specific actions. However, such descriptions are merely for convenience, and it should be understood that such actions actually originate from a computing device, processor, controller, or other device that executes the firmware, software, routines, instructions, etc., and that in execution, actuators or other devices may interact with the material world.

[0211]

[0190] Although specific embodiments of the present invention have been described above, it will be understood that the present invention can be practiced in ways other than those described. The above description is for illustrative purposes only and is not limiting. Accordingly, it will be obvious to those skilled in the art that modifications to the described invention can be made without departing from the claims described below. Other aspects of the present invention are described in the following numbered clauses. 1. A method for determining the correction value of the height profile of the surface of a substrate, To fix the circuit board to the circuit board holder, A first measurement of the first height profile is created by projecting a patterned radiant beam onto a beam spot region, moving the substrate relative to the beam spot region while it is in a first orientation, and receiving a portion of the patterned radiant beam reflected from the substrate and determining the first measurement of the first height profile from there. Rotating the substrate to a second orientation around the global normal of the surface, The second measurement of the second height profile is created by projecting a patterned radiant beam onto a beam spot region, moving the substrate relative to the beam spot region while it is in a second orientation, and receiving a portion of the patterned radiant beam reflected from the substrate to determine the second measurement of the second height profile. The first and second measured values ​​are corrected for the shape of the substrate holder to determine the first and second corrected measured values, and The correction value for the height profile is determined by combining the first corrected measurement value and the second corrected measurement value. A method for providing this. 2. Correcting the height profile measurement for the shape of the substrate holder to determine the corrected measurement is: To fix the reference substrate to the substrate holder, The reference measurement of the height profile of a reference substrate is created by projecting a patterned radiant beam onto the beam spot area, moving the substrate relative to the beam spot area while the substrate holder is in the same orientation as when the corrected measurement was determined, receiving a portion of the patterned radiant beam reflected from the substrate, and determining the reference measurement of the height profile from there, and The corrected height profile measurement is determined as the difference between the measured value and the reference measured value. The method of Clause 1, comprising: 3. The step of rotating the substrate to a second orientation about the global normal of the surface comprises rotating the substrate 180° about the global normal of the surface, according to any method of Clause 1 to 2. 4. The correction value is determined by any of the methods in clauses 1 to 3, as half the difference between the first corrected measurement and the second corrected measurement of the height profile. 5. Creating each of the first and second measurements of the height profile is any method of Clauses 1 to 4, comprising measuring the height of the surface at multiple locations on the object. 6. The method of any of the clauses 1 to 5, wherein each of the first and second measurements of the surface height profile comprises measuring a surface height map over substantially the entire surface of the substrate. 7. The method of any one of the clauses 1 to 5, wherein creating each of the first and second measurements of the height profile comprises measuring a surface height map for one or more of several areas of the surface of an object to which the same pattern is applied. 8. Correcting the first and second measurements of the height profile for local variations in the inclination of the substrate surface, and, when subject to Clause 2, correcting the first and second reference measurements of the height profile for local variations in the inclination of the reference substrate surface before correcting the first and second measurements of the height profile for the shape of the substrate holder, The method of further comprising any of clauses 1 through 7. 9. Any method of clauses 1 to 8, further comprising storing the correction value in memory. 10. A method for measuring the topography of the surface of a substrate, The surface height profile is created by projecting a patterned radiation beam onto a beam spot area, moving the object relative to the beam spot area while it is in a first orientation, receiving a portion of the patterned radiation beam reflected from the object, and determining the height profile from there, and The height profile measurement is combined with the corrected height profile measurement of the substrate, determined using one of the methods described in clauses 1 through 9, to determine the corrected height profile measurement. A method for providing this. 11. The corrected measurement of the height profile is determined by subtracting the correction value from the measurement of the height profile, as per the method of Clause 10. 12. The method of Clause 10 or Clause 11, further comprising determining the correction value for the height profile using the method of any one of Clauses 1 to 9. 13. A method comprising retrieving a correction value from memory, the method of any one of the provisions of provisions 10 to 12, which is directly or indirectly dependent on provision 9. 14. Combining a height profile measurement with a correction value for the substrate height profile is a method of any one of the clauses 10 to 13, comprising combining the measurement with a correction value at substantially the same location on the substrate. 15. The method of any one of the clauses 10 to 14, wherein the substrate comprises multiple regions to which the same pattern is applied, and combining a measurement of the height profile with a correction value for the height profile of the substrate comprises combining a measurement of each of the multiple regions with a correction value for one of the multiple regions. 16. Determining height profile measurements from a portion of the patterned radiation beam reflected from the substrate is possible. Receiving a portion of the radiation beam reflected from the substrate and dividing the reflected radiation into a first part and a second part, Determining the intensity of the first and second parts of the radiation, and The height of the substrate is determined by combining the intensity of the first part of the radiation and the intensity of the second part of the radiation. A method comprising any of clauses 1 to 15. 17. The method of Clause 16, wherein the reflected radiation is divided into a first part and a second part, comprising forming an image of a pattern on a splitting optical system and using the splitting optical system to induce radiation from the first and second parts of the second image and spatially separate them. 18. The height of the substrate is proportional to the difference between the first strength and the second strength, according to the method of Clause 16 or Clause 17. 19. A lithography exposure method, Measuring the topography of the substrate surface using any of the methods described in Clauses 1 to 18, when directly or indirectly dependent on Clause 10. Patterning the radiation beam using a patterning device, and Projecting patterned radiation onto a substrate to form an image of a patterning device on the substrate. Equipped with, A method in which the position of the substrate while patterned radiation is projected onto the substrate is controlled by the measured topography of the substrate surface. 20. Lithography exposure is a scanning exposure, and therefore, the lithography exposure method of Clause 19 comprises: using a patterning device to impart a pattern to a radiation beam, moving the patterning device through the radiation beam; and projecting the patterned radiation onto a substrate to form an image of the patterning device on the substrate, moving the substrate so that the image of the patterning device is substantially stationary relative to the substrate. 21. Apparatus for measuring the topography of the surface of a substrate, Supports for supporting the circuit board, A projection optical system capable of operating to form a first image of a pattern on a beam spot region using a radiation beam, A movable mechanism that can operate to cause relative movement between the support and the beam spot region, A detection optical system capable of receiving a portion of the radiation beam reflected from the substrate, A controller that is operable to determine the height of a substrate from a radiation beam reflected from the substrate, and is further operable to implement any one of the methods described in clauses 1 to 18, A device equipped with the following features. 22. The detection optical system is operable to receive a portion of the radiation beam reflected from the substrate, and to divide the reflected radiation into a first part and a second part, so that the first part of the radiation corresponding to the first part of the first image is spatially separated from the second part of the radiation corresponding to the second part of the first image, and the device is, A first detector positioned to determine the intensity of a first portion of the radiation, and A second detector positioned to determine the intensity of the second portion of the radiation. Furthermore, The apparatus of Clause 21, wherein the controller is operable to determine the height profile of the substrate by combining the intensity of a first part of the radiation and the intensity of a second part of the radiation. 23. The projection optical system is, Projection patterning device, A first imaging optical system arranged to form an image of a projection patterning device on a beam spot region, The apparatus of Clause 21 or Clause 22, comprising: 24. The detection optical system is, A splitting optical system arranged to divide the reflected radiation into a first part and a second part, A second imaging optical system is arranged to receive radiation reflected from an object supported by a support and to form a second image of the pattern on the splitting optical system, An apparatus comprising any one of the clauses 21 to 23. 25. The apparatus of any one of the clauses 21 to 24, further comprising a radiation source capable of generating a radiation beam. 26. A lithography apparatus equipped with the apparatus specified in any one of the clauses 21 to 25.

Claims

1. A method for determining a correction value for the height profile of the surface of a substrate, To fix the aforementioned substrate to the substrate holder, A first measurement of the first height profile is created by projecting a patterned radiation beam onto a beam spot region, moving the substrate relative to the beam spot region while it is in a first orientation, and receiving a portion of the patterned radiation beam reflected from the substrate and determining the first measurement of the first height profile from there. Rotating the substrate to a second orientation around the global normal of the surface, A second measurement of the second height profile is created by projecting a patterned radiation beam onto the beam spot region, moving the substrate relative to the beam spot region while it is in the second orientation, and receiving a portion of the patterned radiation beam reflected from the substrate and determining the second measurement of the second height profile from there. The first and second measured values ​​are corrected with respect to the shape of the substrate holder to determine the first and second corrected measured values, and The correction value of the height profile is determined by combining the first corrected measurement value and the second corrected measurement value. A method for providing this.

2. Correcting the height profile measurement with respect to the shape of the substrate holder to determine the corrected measurement is, To fix the reference substrate to the substrate holder, The reference measurement of the height profile of the reference substrate is created by projecting a patterned radiation beam onto a beam spot area, moving the substrate relative to the beam spot area while the substrate holder is in the same orientation as when the corrected measurement was determined, receiving a portion of the patterned radiation beam reflected from the substrate, and determining the reference measurement of the height profile from there, and The corrected measurement value of the height profile is determined as the difference between the measurement value and the reference measurement value. The method according to claim 1, comprising:

3. The method according to any one of claims 1 to 2, wherein the step of rotating the substrate to a second orientation about the global normal of the surface comprises rotating the substrate 180° about the global normal of the surface.

4. The method according to any one of claims 1 to 3, wherein the correction value is determined as half the difference between the first corrected measurement value and the second corrected measurement value of the height profile.

5. A method of any one of claims 1 to 4, wherein creating each of the first and second measurements of the height profile comprises measuring the height of the surface at a plurality of locations on the object.

6. A method of any one of claims 1 to 5, wherein creating each of the first and second measurements of the height profile of the surface comprises measuring a surface height map for substantially the entire surface of the substrate.

7. The method according to any one of claims 1 to 5, wherein creating each of the first and second measurements of the height profile comprises measuring a height map of the surface for one or more of a plurality of regions of the surface of the object to which the same pattern is applied.

8. Correcting the first and second measured values ​​of the height profile for local variations in the inclination of the surface of the substrate, and, in accordance with claim 2, correcting the first and second reference measured values ​​of the height profile for local variations in the inclination of the surface of the reference substrate before correcting the first and second measured values ​​of the height profile for the shape of the substrate holder, A method according to any one of claims 1 to 7, further comprising:

9. A method for measuring the topography of the surface of a substrate, The measurement of the surface height profile is created by projecting a patterned radiation beam onto a beam spot area, moving the object relative to the beam spot area while it is in a first orientation, receiving a portion of the patterned radiation beam reflected from the object, and determining the height profile from there, and The measured value of the height profile is combined with a correction value of the substrate height profile determined using any of the methods from claims 1 to 8 to determine the corrected measured value of the height profile. A method for providing this.

10. Determining the height profile measurement from a portion of the patterned radiation beam reflected from the aforementioned substrate is: Receiving a portion of the radiation beam reflected from the substrate, and dividing the reflected radiation into a first portion and a second portion. Determining the intensity of the first and second portions of the radiation, and The height of the substrate is determined by combining the intensity of the first portion of the radiation and the intensity of the second portion of the radiation. A method comprising any one of claims 1 to 9.

11. The method of claim 10, wherein dividing the reflected radiation into a first part and a second part comprises forming an image of the pattern on a dividing optical system and using the dividing optical system to induce radiation from the first and second parts of the second image and spatially separate them.

12. A lithography exposure method, Measuring the topography of the substrate surface using any of the methods of claims 1 to 8, in cases directly or indirectly dependent on claim 9. Patterning the radiation beam using a patterning device, and Projecting the patterned radiation onto the substrate to form an image of the patterning device on the substrate. Equipped with, A method wherein the position of the substrate while the patterned radiation is projected onto the substrate is controlled depending on the measured topography of the surface of the substrate.

13. A device for measuring the topography of the surface of a substrate, Supports for supporting the circuit board, A projection optical system capable of operating to form a first image of a pattern on a beam spot region using a radiation beam, A moving mechanism that is operable to cause relative movement between the support and the beam spot region, A detection optical system capable of receiving a portion of the radiation beam reflected from the substrate, A controller that is operable to determine the height of the substrate from the radiation beam reflected from the substrate, and is further operable to implement the method of any one of claims 1 to 11, A device equipped with the following features.

14. The detection optical system is operable to receive a portion of the radiation beam reflected from the substrate, and to divide the reflected radiation into a first portion and a second portion, so that the first portion of the radiation corresponding to the first portion of the first image is spatially separated from the second portion of the radiation corresponding to the second portion of the first image, and the device is A first detector arranged to determine the intensity of the first portion of the radiation, and A second detector arranged to determine the intensity of the second portion of the radiation. Furthermore, The apparatus of claim 13, wherein the controller is operable to determine the height profile of the substrate by combining the intensity of the first portion of the radiation and the intensity of the second portion of the radiation.

15. A lithography apparatus comprising the apparatus according to any one of claims 13 or 14.

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