Optical measurement marks

Abstract

An optical measurement mark for an imaging system includes a reflective region and a substructure configured to reduce an intensity of an image of the optical measurement mark formed by the imaging system. The substructure can effectively reduce the rate of carbon contamination that may occur when measuring using the optical measurement mark.

Description

Cross-references to related applications

[0001] This application claims priority to European patent application 23180307.3, filed on 20 June 2023, which is incorporated herein by reference in its entirety. Technical Field

[0002] This invention relates to an optical measurement mark and method for an imaging system. The optical measurement mark and method are applicable to use in lithography equipment or processes. This invention is particularly useful in conjunction with EUV lithography equipment, EUV lithography tools, and EUV lithography processes. Background Technology

[0003] A lithography apparatus is a machine configured to apply a desired pattern onto a substrate. For example, a lithography apparatus can be used in the manufacture of integrated circuits (ICs). For example, a lithography apparatus can project a pattern at a patterning device (e.g., a mask) onto a radiation-sensitive material layer (photoresist) provided on a substrate.

[0004] To project patterns onto a substrate, a photolithography apparatus can use electromagnetic radiation. The wavelength of this radiation at least partially determines the minimum size of the feature that can be formed on the substrate. For example, a photolithography apparatus using EUV (EUV) radiation in the wavelength range of 4–20 nm (e.g., 6.7 nm or 13.5 nm) can form smaller features on a substrate compared to a photolithography apparatus using radiation with wavelengths such as 193 nm, 248 nm, or 365 nm.

[0005] A lithography apparatus may include an optical alignment system that can be used to determine and improve the alignment between a patterning device and a substrate. The patterning device may include optical measurement marks that can be imaged by a projection system of the lithography apparatus. The optical measurement marks may impart radiation beam markings, which can then be measured after imaging by the projection system to derive one or more properties of the lithography apparatus. The optical alignment system may include a sensor device configured to detect the image of the optical measurement marks to determine information, such as the position of the substrate relative to the patterning device and / or one or more optical aberrations associated with the projection system.

[0006] The aim is to provide an optical measurement mark and method that overcomes or mitigates one or more problems associated with the prior art. The embodiments of the invention described herein can be used in EUV lithography equipment. Summary of the Invention

[0007] According to a first aspect of this disclosure, an optical measurement mark for an imaging system is provided. The optical measurement mark includes a reflective region and a substructure configured to reduce the intensity of an image of the optical measurement mark formed by the imaging system.

[0008] Radiation reflected by an optical measurement marker and collected by an imaging system can cause the breaking of one or more chemical bonds in one or more gases present in the imaging system. This generates contamination particles that can negatively impact the performance of the imaging system and / or require maintenance (e.g., cleaning and / or replacement of one or more components). Reducing the intensity of the image of the optical measurement marker formed by the imaging system can advantageously reduce the rate of contamination that may occur during measurements performed using the optical measurement marker. This, in turn, advantageously reduces the frequency of maintenance (e.g., cleaning and / or replacement) of one or more components of the imaging system (e.g., the sensor device of the imaging system), thereby improving the availability of the imaging system.

[0009] The optical measurement mark may include multiple reflective regions configured to preferentially reflect the radiation beam. The optical measurement mark may also include multiple absorptive regions configured to preferentially absorb the radiation beam. The reflective and absorptive regions may be arranged to form a periodic reflective structure, such as a line-spaced pattern. The reflective regions may be configured to reflect the incident radiation so that an imaging system can form an image of the optical measurement mark.

[0010] The reference in this document to a reflective region configured to preferentially reflect radiation of a given wavelength should be interpreted as meaning that the reflective region is configured such that its reflectivity at that given wavelength is higher than its reflectivity at other wavelengths. Additionally, the reflective region may also reflect radiation whose wavelength differs from the given wavelength.

[0011] For example, a reflective region can have a multilayer structure comprising layers of two or more materials with different refractive indices. Radiation can be reflected from the interfaces between the different layers. These layers can be arranged to provide separation between the interfaces, thereby causing constructive interference between the radiation reflected at the different interfaces. The separation between the interfaces that causes constructive interference between the radiation reflected at the different interfaces depends on the wavelength of the radiation. Therefore, by providing separation between the interlayer interfaces, a multilayer reflective region can preferentially reflect radiation of a given wavelength, which causes constructive interference between radiation of a given wavelength reflected from the different interfaces.

[0012] The reflective region can be disposed on the absorption layer, and the absorption layer can include absorption layer regions thereon where no reflective region is disposed. Alternatively, the reflective layer can be disposed on a substrate (which may be referred to in the art as a "blank mask"), and then the absorption layer can be disposed on the reflective layer. The absorption layer can then be etched to expose the underlying reflective region.

[0013] The radiation beam can include EUV radiation.

[0014] Substructures can include subresolution features. Subresolution features can be considered features small enough that they do not form significant features on their own after the photolithography steps of development and etching. In embodiments, subresolution features may still be large enough to affect the imaging of adjacent features. Therefore, the size and shape of subresolution features can depend at least in part on the process used and can be related to the substrate layer. Generally, features small enough that they do not form an image on the image plane of the imaging system (e.g., the substrate W layer of a photolithography apparatus) can be considered “subresolution”.

[0015] The reflective area can be a pinhole. The reflective area can be rectangular. The reflective area can be square.

[0016] The reflective zone can form part of a periodic structure.

[0017] The periodic structure can be one-dimensional. The periodic structure can include a line grating. The periodic structure can also include a line-spaced pattern.

[0018] The periodic structure can be two-dimensional. This periodic structure can include a checkerboard pattern. This periodic structure can also include a binary square pattern.

[0019] The reflective region can be configured to reflect extreme ultraviolet radiation. The reflective region may include multiple layers configured to introduce constructive interference of the reflected EUV radiation.

[0020] Substructures may include diffraction substructures. Diffraction substructures can be configured to diffract incident radiation to form zero-order and first-order diffraction orders. Diffraction substructures can be configured to guide the first-order diffraction order at an angle outside the numerical aperture of the imaging system.

[0021] First-order diffraction orders (e.g., positive and negative first-order diffraction orders) are not collected by the imaging system and do not contribute to the image of the optical measurement marks formed by the imaging system, thereby reducing the intensity of the image of the optical measurement marks formed by the imaging system. This, in turn, reduces the contamination rate of one or more components of the imaging system.

[0022] The diffraction substructure may include a periodic substructure having a pitch whose size is designed relative to the wavelength of the incident radiation and the numerical aperture of the imaging system, such that the first-order diffraction stage is guided at an angle outside the numerical aperture of the imaging system.

[0023] Diffraction substructures can form part of the reflection region.

[0024] Diffraction substructures can form part of the absorption region of optical measurement markers.

[0025] The diffraction substructure can form part of the reflection phase-shift region of the optical measurement mark. The reflection phase-shift region can include a reflection phase-shift structure configured to introduce destructive interference to the incident radiation.

[0026] The reflection region can form part of a periodic structure. The diffraction substructures can be arranged to be substantially orthogonal to the periodic structure.

[0027] Diffraction substructures can be arranged in other orientations relative to the periodic structure. Diffraction substructures can also be arranged substantially parallel to the periodic structure.

[0028] Orthogonal arrangement is particularly advantageous because, compared to non-orthogonal arrangement, the diffraction substructure can guide the first-order diffraction order outside the numerical aperture of the imaging system at a smaller angle (i.e., the required scattering level may be smaller). Orthogonal arrangement can also advantageously reduce the risk of the diffraction substructure interfering with the expected measurements of the optical measurement markers.

[0029] The pitch of periodic substructures can satisfy the following relationship:

[0030] in It is the pitch of the periodic substructure. It is the refractive index of the imaging system. It is the wavelength of the incident radiation. It is the numerical aperture of the imaging system. It is the magnification factor of the imaging system.

[0031] At the image plane of the imaging system, the pitch of the diffraction substructure can be approximately 12 nm or larger. At the image plane of the imaging system, the pitch of the diffraction substructure can be approximately 32 nm or smaller. At the object plane of the imaging system, the pitch of the diffraction substructure can be represented by the pitch of the diffraction substructure at the image plane multiplied by the magnification factor of the imaging system.

[0032] The critical size of a diffraction substructure can be approximately 3 nm or larger. The critical size of a diffraction substructure can be approximately 10 nm or smaller.

[0033] The substructure may include a diffuse substructure configured to introduce destructive interference to the incident radiation.

[0034] This diffuse substructure can form part of the reflective zone.

[0035] This diffuse substructure can form part of the absorption region of an optical measurement marker.

[0036] The diffuse substructure can form part of the reflection phase-shift region of the optical measurement mark. This reflection phase-shift region can include a reflection phase-shift structure configured to introduce destructive interference to the incident radiation.

[0037] The diffuse substructure can be configured to introduce multiple different phase shifts to the incident radiation.

[0038] The diffuse substructure can include random phase patterns.

[0039] Random phase patterns can include QR code patterns.

[0040] Random phase patterns can include random square patterns.

[0041] In a random square pattern, the square components do not merge with each other (coalesce).

[0042] Random square patterns can include squares of different sizes.

[0043] Optical measurement markers may include reflective phase-shifting materials configured to introduce destructive interference to incident EUV radiation.

[0044] Reflective phase-shifting materials can form part of the reflective region.

[0045] Reflective phase-shifting materials can form part of the absorption region of optical measurement markers.

[0046] Reflective phase-shifting materials can form part of the reflective phase-shifting region of optical measurement markers.

[0047] Reflective phase-shifting materials may include ruthenium. Reflective phase-shifting materials may include ruthenium-based alloys. Reflective phase-shifting materials may include alloys with a refractive index of about 0.87 or higher. Reflective phase-shifting materials may include alloys with a refractive index of about 0.93 or lower.

[0048] According to a second aspect of this disclosure, an optical measurement system is provided, comprising the optical measurement mark described in the first aspect. The optical measurement system includes an imaging system configured to collect at least a portion of radiation reflected by a reflective region and form an image of the optical measurement mark. The optical measurement system includes a sensor device configured to detect the image of the optical measurement mark.

[0049] This optical measurement system can be applied to photolithography equipment. Radiation reflected from the optical measurement mark can enter the projection system of the photolithography equipment. The radiation reflected from the optical measurement mark can then be projected by the projection system onto a sensor placed on or near the plane of the projection system image.

[0050] This optical measurement system can be configured to determine the alignment between the marker and the sensor device.

[0051] This optical measurement system can be configured to determine the optical aberrations of an imaging system.

[0052] The imaging system may include reflective optical elements configured to form an image of optical measurement marks.

[0053] Sensor devices may include periodic structures that are similar to or substantially match the periodic structures of optical measurement markers.

[0054] Sensor devices may include photodetectors. Photodetectors can be configured to detect radiation following interaction with periodic structures of the sensor device.

[0055] According to a third aspect of this disclosure, a photolithography apparatus is provided, arranged to project a pattern from a patterning device onto a substrate. The photolithography apparatus includes a support structure for supporting the patterning device. The patterning device is capable of imparting a pattern to incident radiation across a cross-section of the incident radiation to form a patterned radiation beam. The photolithography apparatus includes a substrate stage configured to hold the substrate. The photolithography apparatus includes the optical measurement system described in the second aspect.

[0056] Optical measurement markers can form part of the supporting structure.

[0057] Optical measurement marks can be incorporated into a patterned device.

[0058] According to a fourth aspect of this disclosure, a fiducial for a photolithography apparatus is provided, the fiducial comprising: - Optical measurement markers, and - Patterned areas, including sub-resolution features arranged at or near optical measurement marks.

[0059] The patterning device can be a low-n decay phase shift patterning device.

[0060] The sensor device can be incorporated into the substrate platform. The imaging system can be configured to project patterned radiation beams onto the substrate.

[0061] According to a fourth aspect of this disclosure, a patterning apparatus for a photolithography device is provided, including the optical measurement mark described in the first aspect.

[0062] The patterning device can be a low-n decay phase shift patterning device.

[0063] According to a fifth aspect of this disclosure, a method for forming an image of an optical measurement mark is provided. The method includes: using a reflective region of the optical measurement mark to reflect incident radiation. The method also includes using substructures of the optical measurement mark to reduce the intensity of the image of the optical measurement mark.

[0064] According to a sixth aspect of this disclosure, a method for projecting a patterned radiation beam onto a substrate is provided, the method comprising the method according to the fifth aspect.

[0065] The features of different aspects of this disclosure can be combined with features of other aspects. Attached Figure Description

[0066] The accompanying schematic diagrams illustrate embodiments of the invention by way of example only, wherein: - Figure 1 A lithography system according to the present disclosure is schematically depicted, the system including lithography equipment, a radiation source, and optical measurement markers. - Figure 2 A known optical measurement mark is schematically depicted, which includes a line-spaced pattern. - Figure 3 It schematically depicts the composition of Figure 2 The individual reflective area of ​​the known optical measurement mark relative to Figure 1 The diffraction order of the reflection zone is formed by the pupil surface of the projection system of the lithography system. - Figure 4 An optical measurement mark according to the present disclosure is schematically depicted, the mark including a diffraction substructure formed in the reflective region of the optical measurement mark. - Figure 5 It schematically depicts the composition of Figure 4 The diffraction order of the individual reflective region formed by the optical measurement mark and the diffraction substructure forming the individual reflective region relative to Figure 1 The zero-order and first-order substructure diffraction orders are formed by the pupil surface of the projection system PS. - Figure 6A A known optical measurement mark is schematically depicted, which includes a square reflective area. - Figure 6B An optical measurement mark comprising a substructure according to the present disclosure is schematically depicted, the substructure including a square reflective area. - Figure 7An optical measurement mark according to the present disclosure is schematically depicted, the mark including a diffraction substructure formed in the absorption region of the optical measurement mark. - Figure 8 A schematic depiction of from Figure 7 A cross-sectional view of a portion of the reflective phase-shift region of the optical measurement marker, viewed from the side. - Figure 9A A schematic depiction of an example pupil view of a bipolar illumination mode. - Figure 9B schematically depicted Figure 8 The diffraction substructure of the optical measurement marker in being Figure 9A The zero-order diffraction order and the positive and negative first-order diffraction orders formed during bipolar irradiation. - Figure 10A A portion of an optical measurement mark according to this disclosure is schematically depicted, the portion including a diffuse substructure. - Figure 10B A schematic depiction of from Figure 10A A cross-sectional view of a portion of the optical measurement markers shown, viewed from the side. - Figure 11 A diffuse substructure according to this disclosure is schematically depicted, the structure comprising a random square pattern. - Figure 12 A schematic cross-sectional view of the reference section is depicted, which includes a cap layer and an absorbent layer. - Figure 13 A schematic top view of a reference section according to this disclosure is depicted, the reference section including optical measurement marks and patterned areas. - Figure 14 A cross-sectional view of a patterned area of ​​the reference section according to the invention is schematically depicted. The same reference numerals indicate the same features. Detailed Implementation

[0067] Figure 1 A lithography system including a radiation source SO and a lithography apparatus LA is shown. The radiation source SO is configured to generate an EUV radiation beam B and to supply the EUV radiation beam B to the lithography apparatus LA. The lithography apparatus LA includes an irradiation system IL, a support structure MT configured to support a patterning device MA (e.g., a mask), a projection system PS, and a substrate stage WT configured to support a substrate W.

[0068] The illumination system IL is configured to adjust the EUV radiation beam B before it is incident on the patterning device MA. Relatedly, the illumination system IL may include a faceted field mirror device 10 and a faceted pupil mirror device 11. The faceted field mirror device 10 and the faceted pupil mirror device 11 together provide the EUV radiation beam B with the desired cross-sectional shape and the desired intensity distribution. Additional mirrors or devices may be included in or as alternatives to the faceted field mirror device 10 and the faceted pupil mirror device 11.

[0069] After such adjustment, the EUV radiation beam B interacts with the patterning device MA. As a result of this interaction, a patterned EUV radiation beam B' is generated. A projection system PS is configured to project the patterned EUV radiation beam B' onto a substrate W. For this purpose, the projection system PS may include a plurality of mirrors 13, 14 configured to project the patterned EUV radiation beam B' onto the substrate W held by the substrate stage WT. The projection system PS may apply a reduction factor to the patterned EUV radiation beam B', thereby forming an image whose features are smaller than the corresponding features on the patterning device MA. For example, a reduction factor of 1 / 4 or 1 / 8 may be applied. Although... Figure 1 The projection system PS is illustrated as having only two reflectors 13 and 14, but the projection system PS may include a different number of reflectors (e.g., six or eight reflectors).

[0070] The substrate W may include a previously formed pattern. In this case, the photolithography apparatus LA aligns the image formed by the patterned EUV radiation beam B' with the pattern previously formed on the substrate W.

[0071] A relative vacuum can be provided in the radiation source SO, the irradiation system IL, and / or the projection system PS, i.e., a small amount of gas (e.g., hydrogen) at a pressure far below atmospheric pressure.

[0072] The radiation source SO can be a laser plasma (LPP) source, a discharge plasma (DPP) source, a free electron laser (FEL) or any other radiation source capable of generating EUV radiation.

[0073] A lithography apparatus LA can be used to expose portions of a substrate W to form a pattern on the substrate W. To improve the accuracy of transferring the desired pattern onto the substrate W, one or more properties of the lithography apparatus LA can be measured. These properties can be measured periodically, for example, before and / or after each exposure of the substrate W, or infrequently, for example, as part of a calibration process. Examples of properties that can be measured on the lithography apparatus LA include the relative alignment of the components of the lithography apparatus LA and / or optical aberrations associated with the components of the lithography apparatus (e.g., the projection system PS). For example, measurements can be performed to determine the relative alignment of a support structure MT for supporting a patterning device MA and a substrate platform WT for supporting the substrate W. Determining the relative alignment of the support structure MT and the substrate platform WT helps to project a patterned radiation beam B' onto the desired portion of the substrate W. This is particularly important when projecting a patterned radiation beam B' onto the substrate W, including portions of the substrate W that have been exposed to that radiation, as this improves the alignment of the patterned radiation beam B' with previously exposed areas.

[0074] Measurements such as the alignment measurements described above can be performed by irradiating optical measurement markers 17 (e.g.) Figure 1 (Illustrated in the diagram) to perform the measurement. Optical measurement mark 17 is a reflective feature, which is used when placed in an imaging system (such as...) Figure 1 When the radiation from the projection system (PS) of the lithography apparatus LA appears in the field of view, it will appear in the image generated by the imaging system. The reflective optical measurement markers described herein are suitable for use as reference points and / or for measuring the properties of the image formed by the imaging system. For example, radiation reflected from the reflective optical measurement marker 17 can be used to determine the alignment of one or more components of the imaging system and / or the optical aberrations associated with one or more components of the imaging system.

[0075] exist Figure 1In the illustrated embodiment, optical measurement marks 17 form part of a patterning apparatus MA. The patterning apparatus MA can be referred to as a mask. One or more optical measurement marks 17 may be provided on the patterning apparatus MA used to perform photolithographic exposure. The optical measurement marks 17 may be positioned outside a patterned area of ​​the patterning apparatus MA that is irradiated with radiation during photolithographic exposure. In some embodiments, one or more optical measurement marks 17 may be additionally or alternatively provided on a support structure MT. For example, dedicated hardware, generally referred to as a reference section, may be provided on the support structure MT. The reference section may include one or more optical measurement marks 17. For the purposes of this description, the reference section is considered as an example of a patterning apparatus MA. In some embodiments, a patterning apparatus MA specifically designed for measuring one or more properties of a photolithography apparatus LA may be placed on the support structure MT to perform a measurement process. The patterning apparatus MA may include one or more optical measurement marks 17 for irradiation as part of the measurement process.

[0076] exist Figure 1 In the illustrated embodiment, the lithography apparatus LA is an EUV lithography apparatus, and therefore a reflective patterning apparatus MA is used. The optical measurement mark 17 is therefore a reflective mark 17. The configuration of the optical measurement mark 17 can depend on the nature of the measurement performed using the optical measurement mark 17. Known optical measurement marks include one or more reflective pinhole features (including a reflective area surrounded by an absorption area), reflective line features, arrangements of multiple reflective line features and absorption features, reflective square features, etc.

[0077] To measure one or more properties of the lithography equipment LA, a sensor device 19 (such as...) is provided. Figure 1 (Illustrated in the diagram) to measure the radiation output from the projection system PS. For example, sensor device 19 can be used as follows: Figure 1 The image shows a substrate stage WT. To perform the measurement process, a support structure MT can be positioned to illuminate the optical measurement marker 17 on the patterning device MA with radiation. The substrate stage WT can be positioned so that radiation reflected from the reflective area of ​​the optical measurement marker 17 is projected onto the sensor device 19 via a projection system PS. The sensor device 19 communicates with a controller CN, which can determine one or more properties of the lithography apparatus LA from the measurement results of the sensor device 19. In some embodiments, multiple optical measurement markers 17 and / or sensor devices 19 can be provided, and the properties of the lithography apparatus LA can be measured at multiple different field points (i.e., positions on the field plane or object plane of the projection system PS).

[0078] As described above, in some embodiments, the relative alignment of components of the lithography apparatus LA can be determined using radiation reflected from the reflective area of ​​the optical measurement mark 17. In such embodiments, the reflective area may serve as an alignment feature, or may form part of a periodic structure that serves as an alignment feature.

[0079] The alignment features in the radiation beam B can be positioned on the substrate W layer (e.g., in a layer such as...). Figure 1 The sensor device 19 (on the substrate stage WT shown) is used for measurement. The sensor device 19 is operable to detect the position of alignment features in the radiation incident upon it. This allows the alignment of the substrate stage WT with respect to the optical measurement mark 17 on the patterning device MA to be determined. After determining the relative alignment of the patterning device MA and the substrate stage WT, the patterning device MA and the substrate stage WT can be moved relative to each other to form a pattern at the desired location on the substrate W (using the patterned radiation beam B' reflected from the patterning device MA). The position of the substrate W on the substrate stage WT can be determined using a separate measurement process.

[0080] For example, sensor device 19 may be a device referred to in the art as an image alignment sensor. For example, sensor device 19 may be a transmission image sensor (TIS). A TIS is a sensor that can be used to measure the position of a projected aerial image of an optical measurement mark 17 at a mask (i.e., a mask plate) MA layer at a substrate layer. The TIS is configured to use a transmission pattern to measure the image of the optical measurement mark 17, with a radiation sensor located below the transmission pattern. The measurement data generated by sensor device 19 can be used to measure the position of the mask MA relative to the substrate platform WT with six degrees of freedom (three translational degrees of freedom and three rotational degrees of freedom). Additionally, the magnification and scaling of the projected image of the optical measurement mark 17 can be measured. Sensor device 19 may be another form of sensor. For example, sensor device 19 may include an interferometric sensing system configured to determine the position relative to an imaging system (e.g., Figure 1 The projection system (PS) is associated with one or more optical aberrations. For example, sensor device 19 may be an integrated lens interferometer scanner (ILIAS) sensor or a parallel ILIAS sensor (PARIS).

[0081] Figure 1 The illumination system IS, optical measurement marker 17, projection system PS, and sensor device 19 can collectively function as an optical measurement system. This optical measurement system can be configured to determine and improve the alignment between the patterning device MA and the substrate W prior to performing dual-lithography exposure. The optical measurement system can also be configured to determine and improve image quality at the substrate W layer level.

[0082] Hydrocarbon gases escape from the photoresist of substrate W and accumulate near the upper surface of substrate W and / or substrate stage WT. When EUV radiation propagates through the hydrocarbon gases, HC molecules decompose, releasing carbon contaminants that deposit on substrate W and / or substrate stage WT. Because EUV radiation is patterned, the carbon contaminants tend to deposit on substrate W and / or substrate stage WT in a pattern corresponding to the pattern carried by the EUV radiation. Thus, whenever... Figure 1 When the optical measurement system, consisting of the irradiation system IS, optical measurement marker 17, projection system PS, and sensor device 19, is active, carbon contaminants are typically deposited on the sensor device 19 in a pattern corresponding to the optical measurement marker 17. The carbon contamination rate depends at least in part on the dose (i.e., power) of the EUV radiation. The carbon contamination rate increases linearly with increasing EUV radiation dose. Over time, the carbon contamination of the sensor device 19 increases until it must be replaced or cleaned. Replacing or cleaning the sensor device 19 requires taking the lithography equipment LA offline, which negatively impacts the productivity of the lithography equipment LA. Therefore, it is desirable to reduce the carbon contamination rate of the sensor device 19.

[0083] Figure 2 A known optical measurement mark 100 is schematically depicted. The known optical measurement mark 100 comprises a periodic structure consisting of a plurality of reflective regions 110 and a plurality of absorptive regions 120 arranged in a line-spaced pattern. Figure 2 In the example, only five reflection zones 110 are shown. In reality, known optical measurement marks 100 may include hundreds of reflection zones 110. Known optical measurement marks 100 are configured for use in optical alignment measurements. The orientation of the reflection zones 110 relative to an optical measurement system configured to use the optical measurement marks 100 can determine the alignment direction determined by the optical alignment measurement. For example, Figure 2 The reflective area 110 can extend along the Y-axis and is configured to determine alignment along the orthogonal X-direction; and is arranged to be with Figure 2 The substantially orthogonal reflective regions shown (i.e., along the X-axis) can be used to determine alignment along the orthogonal Y-direction. Known optical measurement markers 100 are configured for use with EUV radiation. For example, reflective region 110 may have a linewidth 130 of approximately 200 nm, and the periodic structure formed by reflective region 110 and absorption region 120 may have a pitch 140 of approximately 4 µm (i.e., periodicity).

[0084] When EUV radiation is projected onto a known optical measurement marker 100, the image of the optical measurement marker 100 reflected in the far field by each individual reflective region 110 is decomposed into multiple diffraction orders, with the intensity peak along the X-axis at angle α. m The following relationship is satisfied: in It can be an integer (e.g., 0, 1, 2, etc.). The wavelength of EUV radiation (e.g., approximately 13.5 nm), while The pitch 140 of the periodic structure formed by the reflective region 110 and the absorptive region 120 of the optical measurement mark 100.

[0085] Figure 3 It schematically depicts the composition of Figure 2 The known optical measurement mark 100 of the individual reflective zone 110 relative to Figure 1 The diffraction order 300 of the reflection zone is formed by the pupil plane 330 of the projection system PS. Typically, the pupil plane 330 can be defined by the numerical aperture (NA) of the projection system PS. That is, the pupil plane 330 can be defined by the maximum radiation angle distribution received by the projection system PS. The numerical aperture can be expressed as the radius 340 of the pupil plane 330. The pupil plane 330 can be the Fourier transform plane of a plane in which a substrate W is disposed (which may be called the image plane) or a plane in which a patterning device MA is disposed (which may be called the object plane). Therefore, the electric field intensity distribution radiated in the pupil plane 330 may be related to the object disposed in the object plane (e.g., an optical measurement mark 17, which...). Figure 3 The example is Figure 2 The Fourier transform of the known optical measurement mark 100 is related. In particular, the electric field intensity distribution of radiation in the pupil surface 330 (i.e., the angular distribution of radiation scattered by an object such as the optical measurement mark 17) can be given by the convolution of the following two items: (a) the electric field intensity distribution of radiation illuminating the pupil surface (i.e., the angular distribution of radiation illuminating the object (e.g., the optical measurement mark 17); and (b) the Fourier transform of the object.

[0086] The intensity of the diffraction order in the far field (e.g., at sensor device 19) varies along the X-axis as a function of the X-position, following the relationship: in This represents the position along the X-axis.

[0087] The intensity of the zeroth order diffraction order may be proportional to the duty cycle of the reflection region 110 and the absorption region 120. In, for example... Figure 2In an example of a line-and-space grating like the one shown, the duty cycle of the periodic structure formed by the reflective region 110 and the absorptive region 120 can be defined by the following relationship: in The linewidth of the reflection zone 110 is 130. The pitch is 140 for the periodic structure. The combined effect of EUV radiation reflected from all reflective zones 110 is the superposition of EUV radiation reflected from each individual reflective zone 110.

[0088] To reduce the total dose of EUV radiation received by sensor device 19 during optical measurements, thereby reducing the associated carbon pollution rate, a substructure can be introduced into optical measurement marker 100.

[0089] Figure 4 A first optical measuring mark 200 according to this disclosure is schematically depicted. (With) Figure 2 Similar to a known optical measurement mark 100, the first optical measurement mark 200 includes a plurality of reflective regions 110 and an absorption region 120 surrounding the reflective regions 110. The reflective regions 110 are arranged to form a periodic structure. Figure 4 In the example, the periodic structure is a line-spaced grating pattern. Other periodic structures can be formed depending on the shape and arrangement of the reflective areas 110. However, compared to... Figure 2 Unlike known optical measurement markers 100, the first optical measurement marker 200 includes a substructure 250, which is configured to reduce the signal to be measured by an imaging system (e.g., Figure 1 The image intensity of the first optical measurement mark 200 is formed by the projection system PS. For ease of observation, in Figure 4 The image shows an enlarged portion 260 of substructure 250. Figure 4 In the example, substructure 250 is a diffraction substructure. Diffraction substructure 250 includes a periodic substructure configured to diffract incident radiation. Figure 4 In the example, the diffraction substructure 250 is arranged substantially orthogonal to the periodic structure formed by the reflection region 110 of the first optical measurement mark 200. For example, the pitch 270 of the diffraction substructure 250 is along the Y direction and substantially orthogonal to the pitch 140 of the periodic structure of the optical measurement mark 200 along the X direction. Other orientations can be used. For example, the diffraction substructure 250 can be arranged substantially parallel to the periodic structure formed by the reflection region 110 of the first optical measurement mark 200. In an example configured to determine an alternative optical measurement mark aligned along the Y direction (i.e., instead of...) Figure 4 (Optical measurement markers in the X direction), the diffraction substructure 250 can be arranged along the X direction.

[0090] Figure 5 It schematically depicts the composition of Figure 4 The diffraction order 300 of the reflection zone formed by the individual reflection zone 110 of the first optical measurement mark 200, and the diffraction substructure 250 formed by the individual reflection zone 110 relative to Figure 1 The zero-order and first-order substructure diffraction orders 300, 310, and 320 are formed by the pupil plane 330 of the projection system PS. The zero-order diffraction order formed by the diffraction substructure 250 coincides with the reflection region diffraction order 300 and is therefore within the numerical aperture 340. However, the positive first-order diffraction order 310 and the negative first-order diffraction order 320 formed by the diffraction substructure 250 are outside the numerical aperture 330 of the projection system PS. That is, the diffraction substructure 250 is configured to diffract the incident radiation into the zero-order diffraction order 300 and the first-order diffraction orders 310 and 320, and guide the first-order diffraction orders 310 and 320 at an angle 350 outside the numerical aperture 330 of the projection system PS. Figure 5 In the example, the diffraction substructure 250 is configured to guide the first-order diffraction stages 310 and 320 at an angle 350, which is twice the maximum angle 340 of the numerical aperture of the projection system PS. Angles other than the numerical aperture 330 can also be used. Figure 5 In the example, angle 350 is represented as the distance on the pupil plane 330.

[0091] exist Figure 4 In the example, the periodic substructure includes multiple reflective regions 112 surrounded by an absorption region 120 and arranged to form a line-spaced grating pattern. Each reflective region 110 of the periodic substructure includes a diffraction substructure 250. The reflective region 112 of each diffraction substructure 250 forms a portion of the corresponding reflective region 110. The size of the reflective region 112 of the diffraction substructure 250 can be determined to be smaller than the resolution limit of the imaging system. That is, the imaging system still “treats” each reflective region 110 as a complete (i.e., undivided) region (e.g., like...). Figure 2 (The reflective region 110 of the known optical measurement mark 100 is the same). In this sense, the substructure 250 of the optical measurement mark 200 can be considered a subresolution feature. A subresolution feature can be considered small enough that it does not form a significant feature after the photolithography steps of development and etching, while being large enough to affect adjacent features. Therefore, the size and shape of the subresolution feature depend at least in part on the process used and may be related to the substrate layer. Generally, features that are small enough not to form an image at the substrate W layer can be considered "subresolution" features.

[0092] exist Figure 5In the example, the directions (e.g., along the Y-axis) in which the first-order diffraction orders 310, 320 formed by the diffraction substructure are guided are substantially orthogonal to the directions (e.g., along the X-axis) in which the first-order diffraction orders 300 of the reflection region formed by the individual reflection region 110 of the first optical measurement mark 200 are guided. This is because, in Figure 4 In the example, the diffraction substructure 250 is arranged substantially orthogonal to the periodic structure formed by the reflection region 110 and the absorption region 120 of the first optical measurement mark 200.

[0093] The periodic substructure has a pitch of 270, the size of which is relative to the wavelength of the incident radiation (e.g., EUV radiation) and the imaging system (e.g., Figure 1 The numerical aperture 330 of the projection system (PS) is designed to guide the first-order diffraction stages 310 and 320 at an angle 350 outside the numerical aperture 330 of the imaging system. For example, the diffraction substructure 250 can be arranged to satisfy the following relationship in the image plane (i.e., the substrate W layer or the sensor device 19 layer): in The numerical aperture of the imaging system is 330. The refractive index of the imaging system, The maximum acceptable radiation angle for the imaging system. It is an integer. Where is the wavelength of the incident radiation, and Let be the pitch of the diffraction substructure 250. The coefficient 2 on the left-hand side of the above equation ensures that both positive and negative diffraction orders 310 and 320 are guided at an angle 350 beyond the numerical aperture 340. That is, even if the irradiation is incident at different angles, the positive and negative first-order diffraction orders 310 and 320 are always guided beyond the numerical aperture 340. For example, Figure 1 The LA lithography equipment has a numerical aperture of approximately 0.33 nm (330), a refractive index between approximately 0.87 and 1, and receives EUV radiation with a wavelength of approximately 13.5 nm, thereby forming a diffraction substructure 250 with a pitch of 270 nm on the image plane. The pitch of 270 nm is approximately:

[0094] The pitch 270 of the diffraction substructure 250 can be customized according to any given imaging system. The imaging system can be configured to receive EUV radiation at wavelengths of about 4 nm or longer. The imaging system can be configured to receive EUV radiation at wavelengths of about 20 nm or shorter. For example, the imaging system can be configured to receive EUV radiation at wavelengths of about 13.5 nm. The imaging system can have a refractive index of about 0.87 or higher. The refractive index of the imaging system can be about 1 or lower. The refractive index of the imaging system can be about 0.93 or lower. The numerical aperture of the imaging system can be about 0.33 or higher. The numerical aperture of the imaging system can be about 0.55 or higher. For example, the imaging system can have a numerical aperture within a closed interval of about 0.7 to about 0.75. For the case where the numerical aperture is about 0.33, the pitch 270 of the diffraction substructure 250 on the image plane can be about 16 nm or greater. For the case where the numerical aperture is about 0.33, the pitch 270 of the diffraction substructure 250 on the image plane can be about 32 nm or less. For a numerical aperture of approximately 0.55, the pitch 270 of the diffraction substructure 250 on the image plane can be approximately 12 nm or larger. For a numerical aperture of approximately 0.55, the pitch 270 of the diffraction substructure 250 on the image plane can be approximately 22 nm or smaller. The critical size of the diffraction substructure 250 (e.g., in...) Figure 4 The linewidth (in the example) can be approximately 3 nm or larger. The critical size of the diffraction substructure 250 can be approximately 10 nm or smaller.

[0095] The pitch calculation above does not take into account any magnification or reduction that the imaging system may perform. For imaging systems involving reduction, the imaging system (e.g., Figure 1 The reduction factor of the projection system (PS) is used to determine the pitch of the diffraction substructure 250 at the object plane (e.g., the MA level of the mask or the 17th level of the optical measurement marker). The calculated pitch 270 of the diffraction substructure 250 on the image plane W can be multiplied by the reduction factor of the imaging system. Continuing the example above, if Figure 1 If the reduction factor of the projection system PS is 4, then the pitch of the required diffraction substructure 17 on the object plane MA can be approximated as follows: in This is the magnification factor of the imaging system; in this example, the imaging system is... Figure 1 The projection system of the LA lithography equipment PS.

[0096] Generally speaking, the pitch 270 of the diffraction substructure 250 can satisfy the following relationship: in The pitch is 270 for the diffraction substructure 250. The refractive index of the imaging system, Where is the wavelength of the incident radiation. The numerical aperture of the imaging system PS is 330. This is the magnification factor of the imaging system. For example, in... Figure 5 As can be seen, when this relationship is satisfied, all the intensity carried by the first-order diffraction orders 310, 320 and above is directed beyond the numerical aperture 340 of the projection system PS and therefore does not propagate to the sensor device 19. This advantageously reduces the rate of carbon contamination during measurements using the first optical measurement mark 200, thereby reducing the frequency of cleaning and / or replacement of the sensor device 19 and improving the availability of the lithography equipment LA.

[0097] The distance 350 between the zeroth order diffraction order 300 and the first order diffraction orders 310 and 320 in the pupil plane 330 can be determined by the following formula: in Where is the wavelength of the incident radiation. The numerical aperture of the imaging system, Let 350 be the pitch of the diffraction substructure 250 at the image plane. The distance is equal to one, corresponding to the numerical aperture size of the imaging system. Thus, the pitch of the diffraction substructure is chosen such that the distance 350 is greater than one, thereby guiding the first-order diffraction orders 310 and 320 outside the numerical aperture of the imaging system. For example, for EUV radiation with a wavelength of approximately 13.5 nm and an imaging system with a numerical aperture of approximately 0.33, the pitch 270 of the diffraction substructure 250 can be set to 24 nm, such that the spacing between the zeroth and first-order diffraction orders on the pupil plane is as follows: This guides the first-order diffraction stages 310 and 320 beyond the numerical aperture of the imaging system.

[0098] The intensity of the zero-order diffraction order (coinciding with the diffraction order 300 in the reflection region) formed by the diffraction substructure 250 can be at least partially determined by the duty cycle (DC) of the diffraction substructure 250. That is, the effective reflectivity of the diffraction substructure 250 can be controlled by selecting the duty cycle. For example, the intensity of the zero-order diffraction order formed by the diffraction substructure 250 can be inversely proportional to the duty cycle. In other words, by reducing the critical size 230 of the reflection region 112 of the diffraction substructure 250 relative to the pitch 270 of the diffraction substructure 250, the intensity of the zero-order diffraction order formed by the diffraction substructure 250 can be reduced. This advantageously further reduces the intensity of EUV radiation reaching the sensor device 19, thereby further reducing the carbon pollution rate. The ratio of the critical size to the duty cycle of the diffraction substructure 250 can be approximately 1 / 6 or greater. The ratio of the critical size to the duty cycle of the diffraction substructure 250 can be approximately 1 / 2 or less. For example, the ratio of the critical size to the duty cycle of the diffraction substructure 250 can be approximately 1 / 4. This diffraction substructure 250 has been shown to reduce the intensity of radiation reaching the sensor device 19 by approximately 50% or more, thereby reducing the carbon pollution rate by approximately two times or more. No need to... Figure 1 The aforementioned objective can be achieved by modifying the macroscopic geometry of the optical measurement mark 200 using a known optical measurement mark 100. For example, the pitch 140 and linewidth 130 of the periodic structure formed by the reflective region 110 and the absorptive region 120 of the first optical measurement mark 200 can be identical to the corresponding parameters of the known optical measurement mark 100. This means that the measurement performance of the first optical measurement mark 200 matches that of the known optical measurement mark 100, while ensuring a reduced carbon pollution rate.

[0099] As previously discussed, optical measurement markings are not limited to line-spaced gratings but can take other forms. The substructures disclosed herein can be applied to any given pattern. For example, Figure 6A Another known optical measurement mark 400 is schematically depicted, which is square in shape. That is, Figure 6A The known optical measurement mark 400 has a square reflective area 410 surrounded by an absorption area.

[0100] Figure 6B A second optical measurement mark 500 according to this disclosure is schematically depicted, the mark including substructures 510 and 520. The second optical measurement mark 500 is based on... Figure 6BThe known optical measurement mark 400 is used, but it is modified to introduce a substructure corresponding to the shape of the reflective region 410. That is, the square reflective region 410 is divided into multiple smaller squares 510, which are spaced apart by absorption regions 520. The smaller reflective regions 510 and the absorption regions 520 located between them form a binary grid pattern. Other patterns can also be used, such as a checkerboard pattern. In general, a reflective region of any given shape can be divided to introduce a diffraction substructure comprising reflective regions corresponding to smaller versions of the shape of the original reflective region.

[0101] exist Figure 6B In the example, the substructures are diffraction substructures 510 and 520, and like the diffraction substructure 250 of the first optical measurement mark 200, these substructures are configured to diffract the incident radiation to form zero-order and first-order diffraction orders, and to guide the first-order diffraction order at an angle outside the numerical aperture of the imaging system that will image the optical measurement mark 500. Thus, the relationships between the pitch of the diffraction substructures 510 and 520, the refractive index of the imaging system, the wavelength of the incident radiation, the numerical aperture PS of the imaging system, and (if necessary) the magnification factor of the imaging system described above apply to checkerboard patterns rather than line-spaced grating patterns. For example, the diffraction substructures 510 and 520 may have a pitch of approximately 84 nm and a critical dimension of approximately 42 nm (i.e., the length of the smaller individual squares).

[0102] The macroscopic geometry of the second optical measurement mark 500 and Figure 6A The macroscopic geometry of the known optical measurement mark 400 is the same. That is, for example, the length 530 of the entire checkerboard pattern is the same as the length 430 of the square reflective area 410. This means that the measurement performance of the second optical measurement mark 500 is the same as... Figure 6B The measurement performance is matched by the known optical measurement marker 400, while ensuring a reduced rate of carbon pollution.

[0103] For example, the reflective regions 110, 510 of the optical measurement marks 200, 500 according to this disclosure may comprise a multilayer structure composed of two or more layers of materials with different refractive indices. For example, the multilayer structure may comprise molybdenum and silicon, or molybdenum and ruthenium. Radiation can be reflected from the interfaces between different layers of the multilayer structure. These layers may be arranged to provide a pitch between the interfaces, which causes constructive interference between the radiation reflected at different interfaces of the multilayer structure. The interface pitch that causes constructive interference between the radiation reflected at different interfaces depends on the wavelength of the radiation. Thus, the multilayer reflective regions 110, 510 may preferentially reflect radiation of a given wavelength (e.g., EUV radiation) by providing a spacing between the layer interfaces, which causes constructive interference between the radiation of a given wavelength reflected from different interfaces. The reflective regions 110, 510 may be disposed on an absorbing layer comprising one or more materials configured to absorb incident radiation. Alternatively, the multilayer structure may be disposed on a substrate (which may be referred to in the art as a “blank mask”), and then the absorbing layer may be disposed on the multilayer structure. The absorption layer can then be etched to expose the reflective regions (i.e., the multilayer structure visible beneath the etched portion of the absorption layer). For example, for EUV radiation, the absorption layer may include one or more tantalum, ruthenium-based alloys, and other alloys with refractive indices in a closed range of about 0.87 to about 0.93. For example, these alloys may include one or more of molybdenum, chromium, nitrogen, and / or other elements. For high-k (i.e., high extinction coefficient) masks MA or mask plates with refractive indices between about 0.94 and about 1 and extinction coefficients greater than about 0.031, the absorption layer may include, for example, one or more of nickel, tantalum, and cobalt. The absorption regions 120, 520 of the optical measurement marks 200, 500 of this disclosure may include absorption layer regions in which reflective regions 110, 510 are not provided. Alternatively, the absorption regions 120, 520 of the optical measurement marks 200, 500 of this disclosure may include absorption layer regions that are not etched away to expose the underlying reflective regions 110, 510.

[0104] exist Figure 4 and Figure 6B In the example, substructure 250 forms part of reflective regions 110 and 520. Alternatively, substructure 250 may form part of absorption region 120. In alternative embodiments, such as Figure 7 In the embodiments shown, the absorption layers (and therefore absorption regions 120 and 520) of the optical measurement marks 200 and 500 according to this disclosure can be replaced by reflective phase-shifting regions. These reflective phase-shifting regions may include reflective phase-shifting structures configured to introduce destructive interference to the incident radiation. The reflective phase-shifting regions may be of the type used in low-n attenuation phase-shifting patterning devices.

[0105] Figure 7A third optical measurement mark 600 according to this disclosure is schematically depicted. Similar to... Figure 2 The known optical measurement mark 100 and the third optical measurement mark 600 also include multiple reflection regions 110. However, unlike the absorption region 120 of the known optical measurement mark 100, the third optical measurement mark 600 includes a reflection phase-shifting region 610 surrounding the multiple reflection regions 110.

[0106] Figure 8 A schematic depiction of from Figure 7 A cross-sectional view taken from the side of a portion of the reflection phase-shifting region 610. Figure 8 The diffraction substructure is omitted. The reflection phase-shifting region 610 includes a reflection phase-shifting structure configured to introduce destructive interference to the incident radiation. This reflection phase-shifting structure includes a stepped arrangement of multiple reflectors 620 forming a series of sills 622 and troughs 624 resembling a square wave pattern. The incident radiation is reflected from both the sills 622 and troughs 624. However, the height 625 of the sills 622 relative to the troughs 624 is chosen to introduce a phase difference of approximately π between the radiation reflected from the sills 622 and the radiation reflected from the troughs 624. Thus, the height 625 of the sills 622 can be selected based on the wavelength of the radiation reflected by the reflection phase-shifting region 610. In the case of EUV radiation, the height 625 of the sills 622 can be approximately 40 nm or higher. In the case of EUV radiation, the height 625 of the sills 622 can be approximately 70 nm or lower. The phase difference introduced by the reflection phase shift structures 622 and 624 causes destructive interference in the radiation reflected by the reflection phase shift region 610. Thus, compared to the "bright" region formed by the reflection region 110, the radiation reflected by the reflection phase shift region 610 exhibits greater interference in the imaging system (e.g., Figure 1 A "dark" area is formed in the image of the optical measurement mark 600 formed by the projection system (PS). The reflective phase-shifting region 610 may include one or more reflective phase-shifting materials configured to introduce destructive interference to the incident EUV radiation. For example, the reflective phase-shifting region 610 may include one or more of ruthenium, ruthenium-based alloys, and other alloys with a refractive index between about 0.87 and about 0.93. These alloys may include one or more of molybdenum, chromium, nitrogen, or other elements. See also Figure 1 A patterning device MA comprising one or more reflective phase shift regions can be referred to as a low-n (i.e., low-refractive-index) attenuated phase shift patterning device. Low refractive index can be considered as a closed interval of refractive index from about 0.87 to about 0.97.

[0107] See you again Figure 7 Multiple reflection zones 110 and reflection phase-shifting zones 610 form a periodic structure, which in Figure 7The example shown is a line-spaced grating pattern. Depending on the shape and arrangement of the reflective areas 110, other periodic structures can be formed. Unlike the known optical measurement mark 100, the third optical measurement mark 600 includes a substructure 650 configured to reduce the impact of the imaging system (e.g., Figure 1 The intensity of the image formed by the projection system PS in the third optical measurement mark 600. (Image) Figure 4 The first optical measurement mark 200 is the same as in the middle. Figure 7 In the example, substructure 650 is a diffraction substructure. However, unlike the first optical measurement mark 200, the diffraction substructure 650 forms part of the reflection phase-shift region 610, rather than part of the reflection region 110.

[0108] Similar to Figure 4 The first optical measurement marker 200, the diffraction substructure 650, includes a periodic substructure. This periodic substructure includes a plurality of reflective regions 112 surrounded by a reflective phase-shifting region 610 and arranged to form a line-spaced grating pattern. Other periodic patterns may also be used. The reflective regions 112 of the diffraction substructure may be formed from the same material and structure (e.g., a multilayer structure) as the reflective regions 110 of the periodic structure. The size of the reflective regions 112 of the diffraction substructure 650 can be designed to be smaller than the resolution limit of the imaging system. The critical size (e.g., linewidth) of the reflective regions 112 of the diffraction substructure 650 can be larger than the minimum size that can be manufactured by a given mask process (this may be referred to in the art as a "mask rule check" or "MRC"). For example, the critical size of the reflective regions 112 of the diffraction substructure 650 may be within a closed interval of about 6 nm to 10 nm on the imaging plane. The distance between the end of the reflection region 122 of the diffraction substructure 650 and the side of the periodic structure reflection region 110 can be greater than MRC.

[0109] The pitch of the diffraction substructure 650 required to guide the first-order diffraction order beyond the numerical aperture of the imaging system can depend at least in part on the illumination mode provided to the imaging system. For example, reference Figure 1 The irradiation system IL can be configured to adjust the radiation beam B to form different irradiation patterns for irradiating the patterning device MA and / or the optical measurement mark 17. This irradiation pattern can be defined by the number of areas in the pupil plane of the lithography device LA irradiated by the radiation beam B. Figure 9A An example pupil view of a bipolar illumination mode is schematically depicted. Other illumination modes can also be used to illuminate the optical measurement marks of this disclosure. For example, a quadrupole illumination mode may include four regions of the pupil surface illuminated by radiation, etc. A bipolar illumination mode includes two opposing portions 331 and 332 of the pupil surface 330 illuminated by radiation.

[0110] Figure 9B It schematically depicts, when through Figure 9A When irradiated by bipolar illumination modes 331 and 332, the diffraction substructure 650 of the third optical measurement mark 600 forms a zero-order diffraction order 700 and positive and negative first-order diffraction orders 710 and 720. Similar to... Figure 5 For example, the zeroth-order diffraction order 700 remains within the numerical aperture 330 of the imaging system, while the positive and negative first-order diffraction orders 710 and 720 are directed outside the numerical aperture 330 of the imaging system.

[0111] Generally, the relative orientation between the illumination mode and the diffraction substructure 650 at least partially determines the pitch of the diffraction substructure 650 required to guide the first-order diffraction orders 710, 720 beyond the numerical aperture of the imaging system. Figure 9A In the example, the bipolar illumination patterns are orthogonally oriented relative to the diffraction substructure 650 of the third optical measurement mark 600. This arrangement may require a relatively large pitch of the diffraction substructure 650 to guide the first-order diffraction orders 710 and 720 outside the numerical aperture 330 of the imaging system. If the relative orientation of illumination patterns 331 and 332 to the diffraction substructure 650 is not orthogonal (e.g., parallel), a smaller pitch may be required to increase the spacing between the diffraction orders, thereby guiding the first-order diffraction orders 710 and 720 outside the numerical aperture 330 of the imaging system. With this in mind, it may be desirable to choose a smaller pitch of the diffraction substructure 650 such that all planned illumination patterns diffract to guide the first-order diffraction orders 710, 720 outside the numerical aperture 330 of the imaging system. For example, using the formula for D provided above, for EUV radiation with a numerical aperture of approximately 0.33 and a wavelength of approximately 13.5 nm, a pitch of approximately 22 nm on the imaging plane will produce a spacing of approximately 1.9 nm between the zeroth and first-order diffraction orders on the pupil plane 330. This can be applied to illumination modes in all directions.

[0112] This substructure can take other forms and be added to or used as a substitute for diffraction. It can also be used for other optical functions to reduce the intensity of the image of the optical measurement mark formed by the imaging system.

[0113] Figure 10A A portion of the fourth optical measurement mark 800 according to this disclosure is schematically depicted. Like the previous embodiments, the fourth optical measurement mark 800 includes a plurality of reflective areas 110 ( Figure 8 Only a portion of one of the reflective regions 110 is shown in the image, along with an absorption layer 120 that surrounds the reflective region 110 and forms a periodic structure including the reflective region 110 and the absorption region 120. The reflective layer 810 may include multiple layers (in... Figure 10B (Visible in the cross-section of the layer), the multilayer is configured to introduce constructive interference for radiation (e.g., EUV radiation) reflected from different interfaces of the multilayer. The absorbing layer 820 may include one or more materials for absorbing incident radiation. The reflecting region 110 (i.e., the multilayer) and the absorbing region 120 may include the structures and materials described above with respect to other optical measurement marks 200 and 500.

[0114] The substructure of the fourth optical measurement marker 800 includes a diffuse substructure 880, which is configured to introduce destructive interference with the incident radiation. The destructive interference introduced by the diffuse substructure 880 reduces the effective reflectivity of the reflection region 110, thereby reducing the imaging system's (e.g., Figure 1 The projection system (PS) in the optical measurement mark 800 forms an image of the intensity of the image. This advantageously reduces the rate of carbon contamination that occurs during measurements performed using the optical measurement mark 800, thereby reducing the frequency of cleaning and / or replacement of the sensor device 19 and improving the availability of the lithography device LA. No need for relative to Figure 1 The aforementioned objective can be achieved by modifying the macroscopic geometry of the optical measurement mark 800 using the known optical measurement mark 100. For example, by... Figure 10A The pitch 140 and linewidth 130 of the periodic structure formed by the reflective region 110 and the absorptive region 120 of the optical measurement mark 800 can be... Figure 2 The corresponding parameters of the known optical measurement mark 100 are the same. This means that... Figure 10A The measurement performance of the optical measurement mark 800 is matched with that of the known optical measurement mark 100, while ensuring a reduced rate of carbon pollution.

[0115] exist Figure 10A In the example, the diffuse substructure 880 forms part of the reflection region 110. Alternatively or additionally, the diffuse substructure 880 may form part of the absorption region 820. The diffuse substructure 880 may also be applied to the reflection phase-shifting region (e.g., Figure 7 The optical measurement mark 600 has a reflective phase-shifting region 610. The diffuse substructure 880 can be applied to any type of optical measurement mark, for example, Figure 6B The binary checkered pattern marking 500 has a reflective area 510 and / or an absorptive area 520.

[0116] Figure 10B A schematic depiction of from Figure 10AA cross-sectional view of a portion 890 of an optical measurement mark 800, viewed from the side. The optical measurement mark 800 includes a multilayer reflective region 110. A cap layer 830 is formed on the reflective region 110. The cap layer 830 can be configured to act as a passivation layer and protect the reflective region 110 from the influence of the external environment. For example, the cap layer 830 may include ruthenium. For example, the thickness of the cap layer 830 may be in a closed range of about 1 nm to about 5 nm, for example, about 3 nm. A diffuse substructure 880 may be formed on the cap layer 830. The diffuse substructure 880 may be formed of an EUV phase-shifting material, such as ruthenium, a ruthenium-based alloy, or other alloys with a refractive index in a closed range of about 0.87 to about 0.93. For example, the alloy may be composed of materials such as Mo, Cr, and N. An EUV phase-shifting material 840 may be formed (e.g., deposited) on top of the cap layer 830.

[0117] The diffuse substructure 880 includes a reflective phase-shifting structure configured to introduce destructive interference to the incident radiation. This reflective phase-shifting structure comprises a stepped arrangement of EUV phase-shifting material 840 forming a series of tiers 822 and troughs 824 resembling a square wave pattern with a pseudo-random duty cycle. The incident radiation is reflected from the tiers 822 and troughs 824. However, the height 825 of the tiers 822 relative to the troughs 824 is chosen to introduce a phase difference of approximately π between the radiation reflected from the tiers 822 and troughs 824. The tiers 822 and troughs 824 can be considered as a binary phase-shifting structure, generating a "0" phase shift or a "1" phase shift, respectively, from the reflection from the tiers 822 or troughs 824. Alternatively, the tiers 822 and troughs 824 can be configured to introduce different phase shift distributions within a desired range, for example, from approximately 0.7 π to approximately 1.5 π. The pseudo-random duty cycle of the diffuse substructure 880 also contributes to introducing a phase shift distribution into the incident radiation. The selected phase shift can depend at least in part on the numerical aperture of the imaging system and / or the material of the optical measurement marker 800, etc. Thus, the height 825 of the platform 822 can be selected based on the wavelength of the radiation to be reflected through the diffuse substructure 880. In the case of EUV radiation, the height 825 of the platform 822 can be approximately 40 nm or higher. In the case of EUV radiation, the height 825 of the platform 822 can be approximately 70 nm or lower. The phase difference (or phase shift) of the reflected radiation introduced by the reflection phase shift structures 822, 824 causes destructive interference in the radiation reflected through the diffuse substructure 880. Thus, the intensity of the image of the reflection region 110 formed by the imaging system is reduced due to the presence of the diffuse substructure 880. That is, the effective reflectivity of the diffuse substructure 880 is lower than the nominal reflectivity of the reflection region 110 (e.g., multilayer), resulting in a reduction in the intensity of the reflected radiation.

[0118] The diffuse substructure 880 can be configured to introduce multiple different phase shifts into the incident radiation. To achieve this, the diffuse substructure 880 can include a random phase pattern. That is, different regions of the diffuse substructure 880 can impart different phase shifts (or phase delays) to the reflected radiation, thereby introducing destructive interference into the radiation reflected through the diffuse substructure 880. Figure 10A In the example, the random phase pattern is a QR code pattern. This QR code pattern consists of multiple squares (viewed from the front). As in... Figure 10B As can be seen, these squares are actually columnar structures formed in the EUV phase-shifting material 840. Other shapes besides squares can also be used. The dimensions of the squares are designed and arranged to introduce different, pseudo-randomly distributed phase delays into the radiation reflected through the diffuse substructure 880. For example, the length of the squares can be approximately 30 nm or longer. Alternatively, the length of the squares can be approximately 200 nm or shorter. Figure 10A As can be seen, some of the squares merge (i.e., connect) to form different, larger shapes. The phase tuning effect of the columnar structure at a height of 825 and the random phase patterns (e.g., Figure 10A The pseudo-random structure of the pixel map formed by the QR code pattern causes destructive interference of combined radiation reflected by the diffuse substructure 880 over long distances, thus acting as an optical diffuser in the case of EUV wavelengths.

[0119] Other patterns can be used to form diffuse substructures. Figure 11 An alternative diffuse substructure 980 comprising a random square pattern according to this disclosure is schematically depicted. The random square pattern comprises a distribution of squares 991, 992 of different sizes. Figure 11 The example shows only two different square sizes, but more square sizes can be used. For example, the side length of the square can vary within a closed range of approximately 30 nm to approximately 200 nm. Each square 991, 992 can correspond to a columnar structure formed in EUV phase-shifting material 840, in a manner similar to... Figure 10B Similar. With Figure 10A The QR code patterns are different. Figure 11 The squares in the random square pattern do not merge with each other.

[0120] Forming optical measurement marks according to this disclosure may include: coating a substrate with layers comprising one or more materials to form a reflective layer for reflecting EUV radiation. To create the desired periodic structure, one or more materials configured to absorb EUV radiation may be deposited on the reflective layer to form an absorbing layer with the desired pattern. The periodic structure and the reflective regions of the substructures effectively correspond to the reflective regions in the reflective layer not covered by the absorbing material. Forming the diffuse substructure may include depositing a thickness-controllable EUV phase-shifting material (e.g., ruthenium) to provide the desired phase-shifting effect.

[0121] A method for forming an image of an optical measurement mark according to this disclosure may include: using a reflective region of the optical measurement mark to reflect incident radiation. For example, Figure 4 , Figure 6B , Figure 7 and Figure 10A The reflective areas 110 and 510 of the optical measurement marker can be illuminated by EUV radiation and reflect the EUV radiation. The method may include using the substructure of the optical measurement marker to reduce the intensity of the image of the optical measurement marker. For example, Figure 4 , Figure 6B or Figure 7 Diffraction substructure 250 and / or Figure 10A or Figure 11 The diffuse substructure 880 can use diffraction and / or diffusion, as previously described, to reduce the intensity of the image of the optical measurement mark. The method of projecting a patterned radiation beam onto a substrate according to this disclosure may include a method of forming an image of the optical measurement mark. For example, refer to... Figure 1 The optical measurement mark 17 can be adopted Figure 4 , Figure 6B , Figure 7 and Figure 10A The shape of any optical measurement mark. The illumination system IL can be in a given illumination mode (e.g., Figure 9A The optical measurement mark 17 is illuminated using EUV radiation in a bipolar illumination mode. The projection system PS can form an image of the optical measurement mark 17, and the sensor device 19 can detect the image of the optical measurement mark 17 to determine the alignment between the patterning device MA and the substrate W, and / or the optical aberrations of the lithography device LA. The determined alignment information and / or optical aberration information can be used to at least partially control the lithographic exposure performed by the lithography device LA.

[0122] According to another aspect of the invention, a reference portion for a photolithography apparatus is provided. For example, the reference portion may include a multilayer structure as discussed above and one or more optical measurement marks. For example, these marks may be optical measurement marks according to a first aspect of the invention. For example, the reference portion may be mounted to a support structure configured to support or hold a patterning device. A reference portion having a multilayer structure may also be referred to as a multilayer reference portion.

[0123] In an embodiment, the reference portion may be provided with optical measurement marks, which include a reflective area and an absorption area, such as reflective features, an arrangement of multiple reflective features and absorption features, a reflective square feature, etc. Figure 12 A schematic cross-sectional view of a portion of a reference section 1200 having such optical measurement markings is shown. As shown, the reference section 1200 includes a multilayer structure 1210 (e.g., a Mo / Si multilayer), a capping layer 1220, and an absorption layer 1230. The absorption layer 1230 can absorb EUV radiation during use. Regions where the absorption layer 1230 is absent can reflect the incident EUV radiation beam. During the use of this reference section, damage such as delamination may occur. In particular, delamination may occur between the absorption layer 1230 and the capping layer 1220. It is believed that this delamination (also known as blistering) may be caused by hydrogen gas (H2) present near the reference section 1200 and incident on the absorption layer 1230. The incident EUV radiation beam ionizes the hydrogen gas. Hydrogen radicals and ions (via...) H + H2 + H3 + The hydrogen bladder 1240 may be formed at the interface between the absorber layer 1230 and the capping layer, as indicated by the hydrogen bladder 1250. For example, the capping layer 1220 may be made of ruthenium, which is less permeable to hydrogen than tantalum. It can be noted that delamination may also occur between the capping layer 1220 and the underlying multilayer structure 1210, as indicated by the hydrogen bladder 1250.

[0124] To mitigate the bubbling effect, the present invention proposes patterning the absorber layer 1230 to prevent or reduce hydrogen accumulation between the absorber layer 1230 and the capping layer 1220. Patterning the absorber layer 1230 creates channels through which generated hydrogen can escape without causing delamination of the absorber layer 1230. In known reference sections, the area surrounding the optical mark on the reference section is typically completely covered by an absorber layer (such as absorber layer 1230). Therefore, when this area is exposed to EUV radiation in the presence of hydrogen, delamination or bubbling is likely to occur. According to an aspect of the invention, the area around or near the optical mark is at least partially patterned to mitigate the bubbling effect. Figure 13 A schematic plan view of a portion of a reference portion 1300 according to the invention is shown, the reference portion 1300 including optical measurement marks 1310. In the illustrated embodiment, the optical measurement marks 1310 include a line pattern. Therefore, the area indicating the line 1310.1 can be considered as an area where no absorption layer exists. Therefore, the area surrounding the line 1310.1 and the area between the lines 1310.1 are covered by an absorption layer. According to an embodiment of the invention, a patterned area 1320 is provided near the optical mark 1310, the patterned area 1320 being separated from the optical mark 1310 by a narrow gap 1330. As an alternative, one or more patterned areas can be provided around the optical measurement marks, the patterned areas being located where the reference portion is known to be prone to bubbling or delamination. Generally, for example, it can be achieved that, according to an embodiment of the invention, there should be a minimum distance between the irradiated absorption area and the patterned area on the reference portion. For example, the minimum distance could be 50 micrometers. It should be noted that the patterned area 1320 can also completely surround the optical mark 1310. According to the invention, the patterned region 1320 includes areas extending through the absorption layer (e.g., Figure 12 The protrusions or pores in the absorber layer 1230 shown. Figure 14 The diagram schematically shows a cross-sectional view of such a patterned region 1450 of the reference portion 1400 according to the invention. Figure 14 A portion of the optical mark 1410 is schematically shown; the etched absorption region 1410.1 of the optical mark can be considered as... Figure 13The line 1310.1 shown corresponds to this. As shown, the reference portion 1400 includes a multilayer structure 1420 (e.g., a Mo / Si multilayer), a capping layer 1430, and an absorption layer 1440. The absorption layer 1440 can absorb EUV radiation during use. Areas where the absorption layer 1440 is missing can reflect incident EUV radiation beams. A patterned region 1450 exists near the optical mark 1410. As shown, the patterned region 1450 includes apertures or protrusions 1450 protruding from the absorption layer 1440. The lateral dimensions of the protrusions 1450 are much smaller than the protrusions 1410.1 of the optical mark 1410, thereby reducing or eliminating their impact on the imaging performance of the optical mark 1410. Due to the presence of the protrusions 1450.1 near the optical mark 1410, hydrogen buildup at the interface between the absorption layer 1440 and the capping layer 1430 can be mitigated. According to the invention, the size of this protrusion or aperture is designed to function as a sub-resolution feature as described above. Therefore, the features of the patterned region 1450 are small enough that they do not form an image on the image plane of the imaging system. The density of the features (i.e., bumps or apertures) of the patterned region 1450 is chosen to provide mitigation against delamination or bubbling, while having minimal impact on the performance of the optical measurement markers. A typical size of aperture 1450.1 is a 30 nm aperture size and a 1 μm pitch (i.e., the distance between adjacent apertures 1450.1).

[0125] In embodiments of the invention, the features used to form patterned layers or regions at or near reference optical marks can have different sizes and shapes. For example, these features can be linear, or they can have circular, square, or rectangular cross-sections. These features can form arrays with regular or irregular pitches, wherein irregular arrays have less impact on imaging performance.

[0126] In embodiments of the invention, a narrow border is provided between the optical measurement mark and the patterned area, for example, Figure 13 The border shown is 1330. An appropriate border size can be selected to prevent sub-resolution features from interfering with optical measurement marks. A typical value for this border is 1 micrometer.

[0127] In embodiments of the invention, the absorption region is subdivided using a sub-resolution trench grid to mitigate the additional compressive stress generated by hydrogen absorption in the absorption region and the pattern displacement caused by this compressive stress. Typical dimensions are a trench width of 30 nanometers and a pitch of approximately tens of micrometers.

[0128] In embodiments of the invention, the absorption region is subdivided using a sub-resolution trench mesh to mitigate the effects of thermal stress. Typical dimensions include a trench width of 30 nanometers and a pitch of approximately tens of micrometers.

[0129] In embodiments, the multilayer reference section according to the invention may include a phase-rotated patterned layer, or a combination of an absorption layer and a phase-rotated patterned layer, wherein the pattern comprises lines or squares. Such a layer may be placed on top of a capping layer (e.g., Ru). This layer may be patterned, i.e., the capping layer is exposed in some areas. As long as... If the permeation properties are similar, then larger patches, similar to absorption (e.g., Ta), may exhibit bubbling. In such cases, a similar approach can be used to mitigate or delay bubbling, i.e., introducing sub-resolution features within relatively large patches of the phase-rotation layer or a combination of absorption and phase rotation. These features facilitate the lateral expulsion of accumulated hydrogen and prevent bubbling expansion. The composition of the absorption layer, phase-rotation layer, or combination of absorption and phase rotation within the reference layer can be homogeneous or heterogeneous. In one example, the patterned reference layer may include portions containing additional oxygen, nitrogen, boron, or other elements. In another example, the top or bottom surface of the patterned layer, or the surface facing a protrusion (as associated with marking patterns or hydrogen expulsion features), may include such portions. Such portions contribute to improved optical performance or help control the hydrogen gas as H2 or... Infiltrating in the form of...

[0130] While this article may specifically mention the application of photolithography equipment in IC manufacturing, it should be understood that the photolithography equipment described herein can have other applications. Other possible applications include manufacturing integrated optical systems, guiding and detecting patterns for magnetic domain memories, flat panel displays, liquid crystal displays (LCDs), thin-film magnetic heads, etc.

[0131] While specific embodiments of the invention in lithography equipment may be mentioned herein, these embodiments can also be used in other equipment. Embodiments of the invention can form part of mask inspection equipment, metrology equipment, or any equipment used to measure or process objects such as wafers (or other substrates) or masks (or other patterning devices). These devices are commonly referred to as lithography tools. Such lithography tools can be used under vacuum conditions or ambient (non-vacuum) conditions.

[0132] Where the context permits, embodiments of the present invention may be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the present invention may also be implemented in the form of instructions stored on a machine-readable medium, which can be read and executed by one or more processors. A machine-readable medium may include any mechanism for storing or transmitting information in a machine-readable (e.g., computing device) form. For example, a machine-readable medium may include read-only memory (ROM), random access memory (RAM), magnetic storage media, optical storage media, flash memory devices, electrical signals, optical signals, acoustic signals, or other forms of propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.). Furthermore, firmware, software, routines, and instructions may be described herein as performing specific operations. However, it should be understood that such descriptions are merely for convenience, and such actions are actually caused by a computing device, processor, controller, or other means of executing firmware, software, routines, instructions, etc., and may result in interaction between the actuator or other means and the physical world.

[0133] This invention can also be characterized by the following terms: 1. An optical measurement mark for use in an imaging system, the optical measurement mark comprising: Reflective area; and, The substructure is configured to reduce the intensity of the image of the optical measurement mark formed by the imaging system. 2. According to the optical measurement markings of Clause 2, wherein the substructure includes a diffraction substructure, the diffraction substructure being configured as follows: The incident radiation is diffracted to form the zeroth-order and first-order diffraction orders; and, The first diffraction stage is guided at an angle outside the numerical aperture of the imaging system. 3. The optical measurement mark according to Clause 2, wherein the diffraction substructure includes a periodic substructure having a pitch whose size is designed relative to the wavelength of the incident radiation and the numerical aperture of the imaging system to guide the first-order diffraction order at an angle outside the numerical aperture of the imaging system. 4. The optical measurement mark according to Clause 2 or Clause 3, wherein the diffraction substructure forms part of the reflection region. 5. An optical measurement mark according to any one of Clauses 2 to 4, wherein the diffraction substructure forms part of the absorption region of the optical measurement mark. 6. An optical measurement mark according to any one of Clauses 2 to 5, wherein the diffraction substructure forms part of a reflection phase-shift region of the optical measurement mark, the reflection phase-shift region including a reflection phase-shift structure configured to introduce destructive interference to the incident radiation. 7. An optical measurement mark according to any one of Clauses 2 to 6, wherein the reflective region forms part of a periodic structure, and wherein the diffraction substructure is arranged substantially orthogonal to the periodic structure. 8. An optical measurement mark according to any one of Clauses 3 to 7, wherein the pitch of the periodic substructure satisfies the following relationship: in It is the pitch of the periodic substructure. It is the refractive index of the imaging system. It is the wavelength of the incident radiation. It is the numerical aperture of the imaging system, and It is the magnification factor of the imaging system. 9. The optical measurement mark according to any one of Clauses 3 to 8, wherein the pitch of the diffraction substructure is within a closed interval of about 12 nm to about 32 nm on the image plane of the imaging system. 10. An optical measurement mark according to any one of Clauses 2 to 9, wherein the critical size of the diffraction substructure is in a closed interval of about 3 nm to about 10 nm. 11. The optical measurement mark according to any one of the preceding clauses, wherein the substructure includes a diffuse substructure configured to introduce destructive interference to the incident radiation. 12. The optical measurement mark as described in Clause 11, wherein the diffuse substructure forms part of the reflective region. 13. The optical measurement mark according to Clause 11 or Clause 12, wherein the diffuse substructure forms part of the absorption region of the optical measurement mark. 14. An optical measurement mark according to any one of clauses 11 to 13, wherein the diffuse substructure forms part of a reflection phase-shifting region of the optical measurement mark, the reflection phase-shifting region including a reflection phase-shifting structure configured to introduce destructive interference to incident radiation. 15. An optical measurement mark according to any one of clauses 11 to 14, wherein the diffuse substructure is configured to introduce multiple different phase shifts to the incident radiation. 16. The optical measurement mark according to any one of Clauses 11 to 15, wherein the diffuse substructure comprises a random phase pattern. 17. The optical measurement mark as described in Clause 16, wherein the random phase pattern includes a QR code pattern. 18. The optical measurement mark as described in Clause 16, wherein the random phase pattern comprises a random square pattern. 19. The optical measurement mark as described in Clause 18, wherein the squares do not merge with each other. 20. The optical measurement mark as described in Clause 18 or Clause 19, wherein the random square pattern comprises squares of different sizes. 21. An optical measurement mark according to any one of the preceding clauses, wherein the optical measurement mark comprises a reflective phase-shifting material configured to introduce destructive interference to incident EUV radiation. 22. The optical measurement mark according to Clause 21, wherein the reflective phase-shifting material comprises one or more of ruthenium, ruthenium-based alloys, and other alloys with a refractive index in a closed range of about 0.87 to about 0.93. 23. A reference section for a photolithography apparatus, the reference section comprising: - Optical measurement marks according to any one of the foregoing clauses, and - Patterned areas, including sub-resolution features arranged at or near the optical measurement marks. 24. A reference section for a photolithography apparatus, the reference section comprising: - Optical measurement markers, and - Patterned areas, including sub-resolution features arranged at or near the optical measurement marks. 25. The reference section as described in Clause 23 or Clause 24, wherein the patterned area substantially surrounds the optical measurement mark. 26. The reference portion according to any one of Clauses 23 to 25, wherein the distance between the optical measurement mark and the patterned area is less than 50 micrometers. 27. An optical measurement system, comprising: Optical measurement marks according to any one of the foregoing clauses; An imaging system is configured to collect at least a portion of the radiation reflected by the reflective area and form the image of the optical measurement mark. A sensor device is configured to detect the image of the optical measurement mark. 28. A photolithography apparatus arranged to project a pattern from a patterning device onto a substrate, the photolithography apparatus comprising: The support structure is configured to support a patterning device, which is capable of applying a pattern to the incident radiation on the cross-section of the incident radiation to form a patterned radiation beam. A substrate stage, configured to hold the substrate; and The optical measurement system as described in Clause 27. 29. The lithography apparatus according to Clause 28, wherein the optical measurement mark forms part of the support structure. 30. The lithography apparatus according to Clause 28, wherein the optical measurement mark forms part of the patterning apparatus. 31. The lithography apparatus according to Clause 30, wherein the patterning apparatus is a low-n attenuation phase-shift patterning apparatus. 32. The lithography apparatus according to any one of Clauses 28 to 31, wherein the sensor device forms part of the substrate stage, and wherein the imaging system is configured to project the patterned radiation beam onto the substrate. 33. A patterning apparatus for a photolithography device, the patterning apparatus comprising optical measurement marks as described in Clauses 1 to 22. 34. The patterning apparatus according to Clause 33, wherein the patterning apparatus is a low-n attenuation phase-shift patterning apparatus. 35. A method for forming an image of an optical measurement mark, comprising: The incident radiation is reflected using a reflective area marked by optical measurement; and, The intensity of the image of the optical measurement mark is reduced by using the substructure of the optical measurement mark. 36. A method for projecting a patterned radiation beam onto a substrate, comprising the method described in accordance with Clause 35. Although specific embodiments of the invention have been described above, it should be understood that the invention can be practiced in ways different from those described above. The above description is intended to illustrate, not limit, the invention. Therefore, it will be apparent to those skilled in the art that modifications can be made to the invention without departing from the scope of the following claims.

Claims

1. An optical measurement mark for use in an imaging system, the optical measurement mark comprising: Reflection zone; as well as, The substructure is configured to reduce the intensity of the image of the optical measurement mark formed by the imaging system.

2. The optical measurement mark according to claim 1, wherein the substructure includes a diffraction substructure, the diffraction substructure being configured as follows: The incident radiation is diffracted to form the zeroth-order and first-order diffraction orders; and, The first-order diffraction stage is guided at an angle outside the numerical aperture of the imaging system.

3. The optical measurement mark of claim 2, wherein the diffraction substructure comprises a periodic substructure having a pitch whose dimensions are designed relative to the wavelength of the incident radiation and the numerical aperture of the imaging system to guide the first-order diffraction order at an angle outside the numerical aperture of the imaging system.

4. The optical measurement mark according to claim 2 or 3, wherein the diffraction substructure forms part of the reflection region.

5. The optical measurement mark according to any one of claims 2 to 4, wherein the diffraction substructure forms part of the absorption region of the optical measurement mark.

6. The optical measurement mark according to any one of claims 2 to 5, wherein the diffraction substructure forms part of a reflection phase-shift region of the optical measurement mark, the reflection phase-shift region comprising a reflection phase-shift structure configured to introduce destructive interference to incident radiation.

7. The optical measurement mark according to any one of claims 2 to 6, wherein the reflective region forms part of a periodic structure, and wherein the diffraction substructure is arranged substantially orthogonal to the periodic structure.

8. The optical measurement mark according to any one of claims 3 to 7, wherein the pitch of the periodic substructure satisfies the following relationship: in It is the pitch of the periodic substructure. It is the refractive index of the imaging system. It is the wavelength of the incident radiation. It is the numerical aperture of the imaging system. It is the magnification factor of the imaging system.

9. The optical measurement mark according to any one of the preceding claims, wherein the substructure includes a diffuse substructure configured to introduce destructive interference to the incident radiation.

10. The optical measurement mark according to any one of the preceding claims, wherein the optical measurement mark comprises a reflective phase-shifting material configured to introduce destructive interference to incident EUV radiation.

11. An optical measurement system, comprising: Optical measurement mark according to any one of the preceding claims; An imaging system is configured to collect at least a portion of the radiation reflected by the reflective area and form an image of the optical measurement mark; and, A sensor device configured to detect the image of the optical measurement mark.

12. A photolithography apparatus arranged to project a pattern from a patterning device onto a substrate, the photolithography apparatus comprising: A support structure is configured to support the patterning device, which is capable of imparting a pattern to the incident radiation in the cross-section of the incident radiation to form a patterned radiation beam. A substrate stage, configured to hold the substrate; and, The optical measurement system according to claim 11.

13. The lithography apparatus of claim 12, wherein the optical measurement mark forms part of the support structure.

14. The lithography apparatus of claim 12, wherein the optical measurement mark forms part of the patterning apparatus.

15. The lithography apparatus of claim 14, wherein the patterning device is a low-n attenuation phase-shift patterning device.

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