Lithography exposure system and methods

Abstract

The lithography system includes a light source, a substrate stage, and a mask stage located between the light source and the substrate stage along a light path from the light source to the substrate stage. The lithography system further includes a reflector along the light path. The reflector includes: a first layer having a first material and a first thickness; a second layer having the first material and a second thickness different from the first thickness; and a third layer located between the first and second layers, having a second material different from the first material.

Description

[Technical Field]

[0001] This disclosure relates to a photolithography system and method. [Previous Technology]

[0002] The integrated circuit (IC) industry has experienced exponential growth. Technological advancements in IC materials and design have resulted in several generations of ICs, each with smaller and more complex circuitry than its predecessors. Throughout IC development, functional density (i.e., the number of interconnects per wafer area) has generally increased, while geometric dimensions (i.e., the smallest components (or lines) that can be manufactured using a manufacturing process) have decreased. This reduction in size has generally benefited from increased manufacturing efficiency and lower associated costs. However, this reduction in size has also increased the complexity of handling and manufacturing ICs. [Summary of the Invention]

[0003] One aspect of this disclosure provides a lithography exposure system, which includes a light source, a substrate stage, and a mask stage, the mask stage being located between the light source and the substrate stage and along an optical path from the light source to the substrate stage. The lithography exposure system further includes a reflector along the optical path. The reflector includes: a first layer having a first material and a first thickness; a second layer having the first material and a second thickness different from the first thickness; and a third layer located between the first layer and the second layer, having a second material different from the first material.

[0004] Another aspect of this disclosure provides a lithography exposure system comprising an optical path and a first reflector. The optical path is located between a light source and a substrate stage. The first reflector is along the optical path having a first incident angle and comprises at least three first material layers. The first material layers have a first number of layer materials, a second number of layer thicknesses, and a first order of the first material layers. The lithography exposure system further comprises a second reflector along the optical path having a second incident angle different from the first incident angle. The second reflector comprises at least three second material layers. The second material layers have a third number of layer materials, a fourth number of layer thicknesses, and a second order of the second material layers. At least one of the following conditions is satisfied: the third number is different from the first number; the fourth number is different from the second number; or the second order is different from the first order.

[0005] One aspect of this disclosure provides a method for photolithography, comprising: forming a plurality of intermediate reflective multilayer structure configurations by executing a reverse engineering algorithm; and forming a reflective multilayer based on a reflective multilayer structure configuration selected from the plurality of intermediate reflective multilayer structure configurations. The reflective multilayer is formed by the following steps: forming a first material layer having a first material and a first thickness; forming a second material layer on the first material layer, each of the second material layers having a second material and a second thickness different from the first material and the first thickness; and forming a third material layer on the second material layer, the third material layer having a first material and a third thickness different from the first thickness. [Simplified Explanation of the Diagram]

[0111] The form of this disclosure can be best understood through the following detailed description when read in conjunction with the accompanying drawings. It should be noted that, according to standard industry practice, the various features are not drawn to scale. In fact, the dimensions of the various features can be arbitrarily increased or decreased for clarity of explanation.

[0112] Figures 1A to 1E are views of portions of a lithography scanner according to an embodiment of the present disclosure.

[0113] Figures 2A to 3D are views of various embodiments of the mirror structure of the lithography scanner according to various forms of the present disclosure.

[0114] Figures 4 to 6B are views illustrating the manufacturing methods of various mirror structures according to this disclosure.

[0115] Figure 7 is a view illustrating a method for manufacturing various types of semiconductor devices according to this disclosure.

[0116] Figures 8 to 9 are views illustrating the method of creating mirror structures by means of machine learning process according to various states of this disclosure.

Implementation Method

[0006] The following disclosure provides numerous different embodiments or examples for implementing various features of the provided subject matter. To simplify this disclosure, specific examples of components and arrangements are described below. Of course, these are merely examples and are not intended to be limiting. For instance, in the following description, forming a first feature above or on a second feature may include embodiments where the first and second features are in direct contact, or embodiments where an additional feature is formed between the first and second features such that the first and second features are not in direct contact. Furthermore, element symbols and / or letters may be repeated in various examples of this disclosure. Such repetition is for the purpose of brevity and clarity and does not inherently imply a relationship between the various embodiments and / or arrangements discussed.

[0007] Additionally, for ease of description, this document may use spatially relative terms such as "below," "below," "lower part," "above," "upper part," and similar terms to describe the relationship between one element or feature as shown in the figures and another element or feature. Besides the orientations depicted in the figures, the spatially relative terms are intended to cover different orientations of elements in use or operation. Devices may be oriented in other ways (rotated 90 degrees or otherwise), and therefore the spatially relative descriptive terms used herein may be interpreted in the same way.

[0008] For ease of description, terms such as "approximately," "roughly," "substantially," and similar terms may be used herein. Those skilled in the art will understand and derive the meaning of such terms. For example, "approximately" may indicate a variation within the range of 20%, 10%, 5%, or similar, but other values ​​may be used where appropriate. Large features, such as the longest dimension of a semiconductor fin, may have variations of less than 5%, while very small features, such as the thickness of an interface layer, may have variations of up to 50%, and the term "approximately" can indicate both types of variation. "Substantially" is generally more stringent than "approximately," so variations of 10%, 5%, or less are appropriate and without limitation. A feature that is "substantially planar" may differ from a straight line by 10% or less. The concentration of a material having a "substantially constant concentration" may have variations of 5% or less along one or more dimensions. Furthermore, those skilled in the art will be able to understand and derive the appropriate meaning of such terms based on industry knowledge, current manufacturing techniques, and the like.

[0009] This disclosure generally relates to lithography equipment for manufacturing semiconductor devices, and more particularly to field facet mirrors, pupil facet mirrors, masks / masks, projection mirrors, and similar reflective multilayers. At advanced technology nodes, size reduction becomes increasingly difficult. To ensure accurate patterning within reduced dimensions, lithography uses shorter exposure wavelengths, including deep ultraviolet (DUV, approximately 193-248 nm), extreme ultraviolet (EUV, approximately 10-100 nm, particularly 13.5 nm), and X-rays (approximately 0.01-10 nm).

[0010] A typical EUV scanner is a type of lithography apparatus that contains approximately 10 reflectors, such as the various mirrors and masks listed above. Each mirror generally has a reflectivity of less than approximately 70% (see Figure 1B for example), for example, approximately 67%. Thus, the total reflectivity along the path containing 10 reflectors can be less than approximately 2% (R10 = 0.67 × 101.8%), which corresponds to an EUV energy loss of over 98%. Some of this EUV energy loss due to reflectivity is observed to be a result of two effects. First, the multilayer mirror structure uses only two materials, typically molybdenum and silicon. Second, only one or two thicknesses are used, such that the overlapping material layers (e.g., Si, Mo, Si, Mo) exhibit a high level of periodicity at the depth of the ML mirror structure.

[0011] In embodiments of this disclosure, a significantly increased reflectivity in the reflective multilayer can be achieved by eliminating the two limitations described above. The number of materials can be increased to three (plus ruthenium), four (plus ruthenium and strontium), or more than four. A greater number of materials can be used, taking into account the arbitrary ordering / placement of each layer relative to adjacent layers. The thickness of the overlapping layers can be non-periodic, allowing each layer in the reflective multilayer to have an arbitrary thickness relative to the other layers. With a greater number of design tools (layer materials, thicknesses, layer ordering), the reflectivity of the reflective multilayer can be further increased by intelligently using algorithms, such as random "pathfinding" algorithms for searching for local and / or global maximum reflectivity, or various machine learning techniques based on massive data and neural networks. In the diagram, the reflective multilayer is illustrated as planar for simplicity. In some embodiments, some or all of the reflective multilayers can be further curved, such that the curvature of the reflective multilayer is further considered when increasing the reflectivity of individual reflectors.

[0012] This disclosure further describes a method for manufacturing semiconductor devices using a reflector comprising an ML mirror structure having increased reflectivity in a lithography operation. In general, this method comprises the following operations: depositing a mask layer over a substrate; patterning the mask layer using an ML mirror structure having increased reflectivity; and removing material from the layer beneath the mask layer exposed by openings in the mask layer formed in the patterning operation.

[0013] Figure 1A is a schematic and illustrated view of a lithography system 10 according to some embodiments. In some embodiments, the lithography system 10 is an extreme ultraviolet (EUV) lithography system designed to expose a resist layer by EUV radiation, and may also be referred to as EUV system 10. According to some embodiments, the lithography system 10 includes a light source 120, an illuminator 140, a mask stage 16, a projection optics module (or projection optics box (POB)) 30, and a substrate stage 24. Components of the lithography system 10 may be added or omitted, and the embodiments should not limit this disclosure.

[0014] In some embodiments, the light source 120 is configured to generate light radiation with wavelengths between about 1 nm and about 100 nm. In a particular example, the light source 120 generates EUV radiation with wavelengths concentrated at about 13.5 nm. Therefore, the light source 120 is also referred to as an EUV radiation source. However, it should be understood that the light source 120 is not limited to emitting EUV radiation. The light source 120 can be used for any high-intensity photon emission of self-excited target fuels.

[0015] In various embodiments, the illuminator 140 includes various refractive optical elements, such as a single lens or a lens system having multiple reflectors 100, such as a lens (zone plate) or alternative reflective optical elements (for EUV lithography systems), such as a single mirror or a mirror system having multiple mirrors, to guide light from the light source 120 onto the mask stage 16, particularly onto the mask 18 fixed to the mask stage 16. In this embodiment where the light source 120 generates light in the EUV wavelength range, reflective optical elements are used. In some embodiments, the illuminator 140 includes at least three lenses.

[0016] A mask stage 16 is configured to hold the mask 18. In some embodiments, the mask stage 16 includes an electrostatic chuck (e-chuck) to hold the mask 18. This is because gas molecules absorb EUV radiation, and the lithography exposure system used for EUV lithography patterning is kept in a vacuum environment to avoid EUV intensity loss. In this disclosure, the terms mask, photomask, and screen are used interchangeably. In this embodiment, the mask 18 is a reflective mask. An exemplary structure of the mask 18 includes a substrate made of a suitable material, such as a low thermal expansion material (LTEM) or fused silica. In various examples, the LTM comprises TiO2 doped with SiO2, or other suitable materials having low thermal expansion. The mask 18 includes a reflective multilayer deposited on the substrate.

[0017] A projection optics box (POB) 30 is configured to image the pattern of the mask 18 onto a semiconductor wafer 22, which is fixed to a substrate stage 24 of the lithography system 10. In some embodiments, the POB 30 has refractive optics (e.g., for a UV lithography system) or alternative refractive optics (e.g., for an EUV lithography system). The POB 30 collects light directed from the mask 18, carrying the pattern defined on the mask. The illuminator 140 and the POB 30 are collectively referred to as the optical module of the lithography system 10. In some embodiments, the POB 30 includes at least six reflective optics.

[0018] In this embodiment, the semiconductor wafer 22 may be made of silicon or other semiconductor materials. Alternatively or additionally, the semiconductor wafer 22 may comprise other elemental semiconductor materials, such as germanium (Ge). In some embodiments, the semiconductor wafer 22 is made of compound semiconductors, such as silicon carbide (SiC), gallium arsenide (GaAs), indium arsenide (InAs), or indium phosphide (InP). In some embodiments, the semiconductor wafer 22 is made of alloy semiconductors, such as silicon germanium (SiGe), silicon germanium carbide (SiGeC), gallium arsenide phosphide (GaAsP), or gallium indium phosphide (GaInP). In some other embodiments, the semiconductor wafer 22 may be a silicon-on-insulator (SOI) or germanium-on-insulator (GOI) substrate.

[0019] Additionally, the semiconductor wafer 22 may have various device elements. Examples of device elements formed on the semiconductor wafer 22 include transistors (e.g., metal oxide semiconductor field effect transistors (MOSFETs), complementary metal oxide semiconductor (CMOS) transistors, bipolar junction transistors (BJTs), high voltage transistors, high frequency transistors, p-channel and / or n-channel field-effect transistors (PFETs / NFETs), etc.), diodes, and / or other suitable elements. To form the device elements, various processes are performed, such as deposition, etching, implantation, photolithography, annealing, and / or other suitable processes. In some embodiments, the semiconductor wafer 22 is coated with a resist layer sensitive to EUV radiation in this embodiment. Integrating the various components including the components described above allows for the execution of lithography processes.

[0020] The lithography system 10 may further include or be integrated with (or coupled to) other modules, such as a cleaning module designed to supply hydrogen to the light source 120. Hydrogen helps reduce contamination in the light source 120.

[0021] Figure 1B is a partial view of reflector 100, which may be included in illuminator 140, shield 18, and / or POB 30. Reflector 100 is configured to reflect incident light 85 having incident energy Ei at an incident angle θ. Reflector 100 absorbs some of the incident energy Ei and reflects reflected light 86 having reflected energy Er from the incident surface of reflector 100. In some embodiments, the reflectivity of reflector 100 is at least 75%. In some embodiments, the reflectivity is at least 77%. The greater reflectivity of reflector 100 can increase the total output of EUV system 10. For example, for an EUV system 10 containing ten reflectors 100, a total reflectivity of 75% (0.7510 = 5.6%) is greater than 5.5% (0.7510 = 5.6%), more than three times greater than that of a reflector 100 having 67% reflectivity. With a reflectivity of 77%, the total reflectivity of the EUV system 10 containing ten reflectors 100 is greater than 7% (0.7710 = 7.3%), which is about four times higher than that of the reflector 100 with a reflectivity of 67%.

[0022] The reflector 100 includes a reflective multilayer comprising: first material layers 11A to 11E, collectively referred to as "first material layer 11" or "reflector layer 11"; and second material layers 12A to 12E, collectively referred to as "second material layer 12" or "spacer layer 12". The first and second material layers 11 and 12 may be further collectively referred to as "material layers 11 and 12". Although Figure 1B shows five of each of the first and second material layers 11 and 12, the reflector 100 may include more of the first and second material layers 11 and 12, for example, 50 of each material layer, but fewer or more may be present in various embodiments. In some embodiments, the first material layer 11 is molybdenum or contains molybdenum, and the second material layer 12 is silicon or contains silicon. The reflective multilayer includes a plurality of film pairs, such as molybdenum-silicon (Mo / Si) film pairs (e.g., in each film pair, the molybdenum layer 11B is above or below the silicon layer 12B or 12A). Alternatively, the reflective multilayer may comprise a molybdenum-beryllium (Mo / Be) film pair, or other suitable materials configured to reflect EUV radiation. Reflector 100 may further comprise a capping layer (not specifically illustrated for simplicity), such as ruthenium (Ru), disposed on the reflective multilayer for protection. When reflector 100 is a shield 18, reflector 100 may further comprise an absorbing layer, such as a tantalum boron nitride (TaBN) layer, deposited over the reflective multilayer. The absorbing layer is patterned to correspond to an integrated circuit (IC) layer. Alternatively, another reflective layer may be deposited over the reflective multilayer and patterned to correspond to an integrated circuit layer, thereby forming an EUV phase-shifting shield.

[0023] Figure 1C is a detailed view of the reflection of light in the reflector 100 according to various embodiments. In Figure 1B, for the purpose of illustrative simplicity, a single arrow represents incident light 85, and a second single arrow represents reflected light 86. As depicted in Figure 1C, for a reflective multilayer having a total of up to one hundred layers, light reflection is a complex process involving reflection and transmission at each material interface. For example, incident light 85 is partially reflected at the upper surface 111U of the first material layer 11A to form a first reflected light 86A, the uppermost first material layer being the closest to the light source (e.g., reflector 100 or light source 120). The transmitted light 87A of the incident light 85 passes through the first material layer 11A before reaching the lower surface 111L of the first material layer 11A, which is substantially in contact with the upper surface 112U of the second material layer 12A immediately below the first material layer 11A.

[0024] At the interface between the first material layer 11A and the second material layer 12A, the transmitted light 87A is further reflected and transmitted to form internally reflected light 88A and transmitted light 87B, respectively. Figure 1C further illustrates the internally reflected light 88B and 88C. The internally reflected light 88A to 88C can be collectively referred to as internally reflected light 88. The internally reflected light 88B is reflected by the transmitted light 87B incident at the interface between the second material layer 12A and the first material layer 11B via the first material layer 11B. In some embodiments, a composite light 89 is formed, which includes the internally reflected light from the internally reflected light 88C, i.e., the transmitted light from the internally reflected light 88B.

[0025] Transmitted light 86E is the light that escapes from reflector 100 when composite light 89 is incident on the interface between the reflective multilayer and the covering layer or the external atmosphere (e.g., environment). Generally speaking, reflected light 86, including reflected light 86A to 86J, includes a combination of reflected light (e.g., first reflected light 86A), transmitted light (e.g., transmitted light 86B, 86C), and composite light (e.g., composite light 86D to 86J).

[0026] Based on the above, a rigorous calculation of all transmissions and reflections in the reflective multilayer can be performed to calculate the reflectivity of the reflective multilayer. The calculation can be based on several parameters, including but not limited to the incident light wavelength, incident light intensity, incident angle, material properties of each layer (e.g., the extinction coefficient and / or refractive index of each first and second multilayer 11, 12), the thickness of each layer, and the layer order.

[0027] Figure 1D is a graph illustrating the material properties of various materials along the refractive index n-axis (horizontal axis) and extinction coefficient K-axis (vertical axis). In some embodiments, based on the material of each layer, the reflectivity at the interface between two materials can be approximated as the difference in refractive index. For example, for the interface between a first material with a refractive index n1 and a second material with a refractive index n2, the reflectivity at the interface can be approximated as |n1-n2|. Overall, to maximize the reflectivity at each interface in a reflective multilayer, it is observed that the difference between the refractive indices n1 and n2 of adjacent layers should be large, and all materials should have a low extinction coefficient K.

[0028] Thus, as shown by the horizontal dashed line in Figure 1D, in some embodiments, it may be necessary to select a material having an extinction coefficient K < 0.02. Generally, materials with an extinction coefficient K greater than 0.02 do not provide a significant benefit to the total reflectivity of the reflective multilayer. Materials below the horizontal dashed line have an extinction coefficient K < 0.02 and may include Ru, Tc, Mo, Nb, Ti, Zr, Y, Sc, and the like. Furthermore, to achieve good reflection at the interface between each pair of adjacent layers, the materials of adjacent layers preferably exhibit significant separation along the horizontal axis. As shown by the circles around the corresponding points on the graph in Figure 1D, in some embodiments, the reflective multilayer comprises layers of ruthenium, molybdenum, strontium, and / or silicon. In some embodiments, the reflective multilayer may further comprise a niobium layer, or another suitable material.

[0029] Based on the calculation of the reflectivity of the reflective multilayer, high reflectivity can be achieved through a stochastic reverse design methodology. This methodology seeks increasingly higher reflectivity by combining material layers (materials and thicknesses with arbitrary, non-periodic ordering). The thickness can be at a lower limit due to the constraints of actual manufacturing of thin films for each material type. Therefore, the lower limit for using ruthenium may differ from the lower limit for using molybdenum, and may differ from the lower limit for using strontium and silicon. Figures 4 through 6B illustrate various stochastic reverse design processes.

[0030] Figure 1E illustrates a portion of the optical path of the lithography exposure system 10 in Figure 1A, which includes a mask stage 16, two reflectors 100A and 100B before the mask stage, and a reflector 100C after the mask stage 16. Reflectors 100A and 100B may be part of an illuminator 140, and reflector 100C may be part of a projection optical module 30.

[0031] Partial light path illustration in Figure 1E: After reflection by reflectors 100A, 100B, the mask stage 16, and reflector 100C, incident light 84 becomes reflected light 88. More specifically, incident light 84 with incident energy Ei0 is incident on reflector 100A at an incident angle θ0 (illustrated in Figure 1E by a dashed line perpendicular to the main surface of reflector 100A, measured relative to the normal of reflector 100A). Reflector 100A partially reflects and partially attenuates incident light 84. Reflected light 85 with energy Er0 is a portion of incident light 84 reflected by reflector 100A. Relative to reflector 100B, reflected light 85 is also incident light 85 with an incident energy Ei1 equal to energy Er0. Incident light 85 is incident on reflector 100B at an incident angle θ1. Incident light 85 is reflected to form reflected / incident light 86, which has energy Er1 / Ei2. Incident light 86 is incident on the mask stage 16 at an incident angle θ2 and is reflected to form reflected / incident light 87 with energy Er2 / Ei3. Incident light 87 is incident on reflector 100C at an incident angle θ3 and is reflected to form reflected / incident light 88 with energy Er3 / Ei4.

[0032] As shown in Figure 1E but not specifically labeled, although the reflective multilayers of each of reflectors 100A to 100C and the masking stage 16 may be the same, in general, each of reflectors 100A to 100C and the reflective multilayers of the masking stage 16 may have different designs. For example, reflector 100B may have more, fewer, or the same number of layers 11 to 14 than reflector 100A (as shown in Figures 2A to 2F, first, second, third, and / or fourth layers 11 to 14), and more, fewer, or the same number of layers 11 to 14 than reflector 100C. In some embodiments, reflector 100B has more, fewer, or the same number of layers of the same type as reflector 100A, or the same number of layers of the same type as reflector 100C. In some embodiments, some of reflectors 100A to 100C and the masking stage 16 have the same reflective multilayer design, while others have different designs. Therefore, each of the reflectors 100A to 100C and the shielding stage 16 can be individually designed to achieve high reflectivity based on the relative position and / or incident angle θ0-θ3 before or after the reflector or shielding stage. In some embodiments, some of the reflectors 100A to 100C and the shielding stage 16 include aperiodic and non-alternating reflective multilayers. In some embodiments, some of the reflectors 100A to 100C or the shielding stage 16 include aperiodic and alternating reflective multilayers. In some embodiments, some of the reflectors 100A to 100C or the shielding stage 16 include periodic and alternating reflective multilayers.

[0033] From a system perspective, considering the distance between reflectors, the angle of incidence, the curvature of the reflectors and the like, individual reflectors 100A to 100C and / or the mask stage 16 are designed for high reflectivity, and the overall optical path is also designed for high reflectivity.

[0034] Figures 2A, 2C, and 2E are partial cross-sectional views of the reflective multilayers 20A, 20B, and 20C according to various embodiments. Figures 2B, 2D, and 2F are enlarged views of regions 200A, 200B, and 200C of the reflective multilayers 20A, 20B, and 20C, respectively. As described above, the design of the reflective multilayers 20A, 20B, and 20C can depend on many factors. Therefore, although the views in Figures 2A to 2F illustrate various features related to a particular embodiment, these views should not be construed as limiting to any particular design or configuration.

[0035] In Figure 2A, a reflective multilayer 20A is shown, comprising two types of material layers 11 and 12. In some embodiments, the first material layer 11 is a molybdenum layer, and the second material layer 12 is a silicon layer. The thickness of each material layer 11 and 12, measured along the Z direction, can be substantially constant along a horizontal plane, for example, along the X direction as shown in Figure 2A, and further along the Y direction (not specifically labeled), which is orthogonal to both the X and Z directions. Each material layer 11A to 11I can have any thickness within process constraints, and each material layer 12A to 12I can have any thickness within process constraints. In some embodiments, the thicknesses T11A-T12I of the first and second material layers 11 and 12 can each be at least about 5 angstroms, and the material layers 11 and 12 are deposited by an ALD process. In some embodiments, thicknesses less than 5 angstroms indicate voids or other non-uniformities that reduce yield. In some embodiments, the first material layer 11 has a thickness in the range of about 20 angstroms to about 40 angstroms. In some embodiments, the second material layer 12 has a thickness ranging from about 30 angstroms to about 45 angstroms. Further description of the thickness and variations of the reflective multilayer 20A is provided with reference to Figure 3A.

[0036] As shown in Figures 2A and 2B, in the configuration of the reflective multilayer 20A containing only two types of material layers 11 and 12, material layers 11 and 12 alternate along the Z direction. Thus, material layer 12C is below material layer 11C, material layer 11C is below material layer 12B, material layer 12B is below material layer 11B, and so on. Except for the top and bottom layers of the reflective multilayer 20A, each intermediate first material layer 11 directly contacts the upper and lower second material layers 12. For example, first material layer 11B directly contacts second material layers 12A and 12B. Similarly, second material layer 12B directly contacts first material layers 11B and 11C. Therefore, it can be said that the reflective multilayer 20A is alternating and periodic in terms of materials.

[0037] In Figure 2B, since it contains only two types of material layers 11 and 12, it can be said that the reflective multilayer 20A contains a plurality of double layers with arbitrary periods PA, PB, PC, ..., PI. Each period (e.g., period PB) is the sum of the thicknesses of two layers, such as the thickness T11B of the first material layer 11B and the thickness T12B of the second material layer 12B. Since the thicknesses T11A-T12A are arbitrary, the periods PA, PB, PC, ..., PI are arbitrary, and the period of each double layer can be greater than, less than, or equal to the period of the overlying or underlying (adjacent) double layer. For example, as shown in Figure 2B, the period PB corresponding to the double layer containing the first material layer 11B and the second material layer 12B is less than the period PC corresponding to the double layer containing the first material layer 11C and the second material layer 12C. In some embodiments, the periods PA and PC are the same, but the first material layers 11A and 11C have different thicknesses, and the second material layers 12A and 12C have different thicknesses. It can be said that the reflective multilayer 20A is non-alternating with respect to thickness. Generally, the reflective multilayer 20A has at least one double layer, which has a period different from some or all of the remaining layers of the reflective multilayer 20A. Therefore, it can also be said that the reflective multilayer 20A is aperiodic with respect to thickness. In some embodiments, the degree of aperiodicity of the double layers can be calculated as the deviation of the period of each double layer from the average value. A more detailed description of the degree of aperiodicity of the double layers is provided with reference to Figure 3D.

[0038] In Figures 2C and 2D, the reflective multilayer 20B is illustrated in cross-sectional views, and region 200B is shown in magnified views. The reflective multilayer 20B contains three different materials in material layers 11, 12, and 13. The first material layer 11 and the second material layer 12 have been described in detail above with reference to Figures 2A and 2B. In some embodiments, the third material layer 13 is a ruthenium layer. The thickness of the third material layer 13, measured along the Z direction, can be substantially constant along a horizontal plane, for example, along the X direction as shown in Figure 2C and further along the Y direction (not specifically labeled), which is orthogonal to both the X and Z directions. Each material layer 13A to 13I can have any thickness within process constraints. In some embodiments, the thicknesses T13A-T13I (not specifically labeled) of the third material layer 13 are each at least about 5 angstroms, and the third material layer 13 is deposited by an ALD process. In some embodiments, thicknesses T13A-T13I less than 5 angstroms indicate voids or other non-uniformities that reduce yield. In some embodiments, in the reflective multilayer 20B, the first material layer 11 has a thickness ranging from about 5 angstroms to about 35 angstroms. In some embodiments, the second material layer 12 has a thickness ranging from about 25 angstroms to about 50 angstroms. In some embodiments, the third material layer 13 has a thickness ranging from about 5 angstroms to about 50 angstroms. A further description of the thickness and variations of the reflective multilayer 20B is provided with reference to Figure 3B.

[0039] Further referring to Figure 2D, as shown in region 200B, the reflective multilayer 20B can be understood as being aperiodic and alternating in terms of thickness and material. As shown, the third material layer 13A contacts the first material layer 11A and the second material layer 12A. In some embodiments, the third material layer 13A can be said to be intermediate between the first material layer 11A and the second material layer 12A. Turning to the first material layer 11B and the second material layer 12B, there is no third material layer intermediate between the first material layer 11B and the second material layer 12B. The first material layer 11B contacts the second material layer 12A and the second material layer 12B. Thus, the reflective multilayer 20B is non-alternating in terms of material. Similarly, the reflective multilayer 20B is aperiodic in terms of material.

[0040] Referring to the diagram in Figure 1D, molybdenum and ruthenium are relatively close to each other, on the lower left side of the diagram. Therefore, referring here to Figure 2D, at least one of the first material layer 11 (e.g., molybdenum) or the third material layer 13 (e.g., ruthenium) may be in the middle between every two second material layers 12 (e.g., silicon). For example, a single first material layer 11B may be in the middle between second material layers 12A and 12B. A first material layer 11C and a third material layer 13B may be in the middle between second material layers 12B and 12C. In some embodiments, although not specifically shown in Figure 2D, a single third material layer 13 may be in the middle between two adjacent second material layers 12, such that the third material layer 13 contacts the upper and lower second material layers 12. Thus, the reflective multilayer 20B in Figure 2D can be considered as a stack of two layers, each double layer comprising a second material layer 12 (or "spacer layer 12") and at least one first or third material layer 11, 13 (or "reflector layers 11, 13"). Due to the material variation in each double-layered reflector layer 11 and / or 13, the reflective multilayer 20B is non-periodic in terms of material.

[0041] In Figures 2E and 2F, the reflective multilayer 20C is illustrated in cross-sectional views, and the region 200C is shown in magnified views. The reflective multilayer 20C contains four different materials in material layers 11, 12, 13, and 14. The first, second, and third material layers 11, 12, and 13 are described in detail above with reference to Figures 2A to 2D. In some embodiments, the fourth material layer 14, also referred to as "spacer layer 14," is a strontium layer. The thickness of the fourth material layer 14, measured along the Z direction, can be substantially constant along a horizontal plane, for example, along the X direction as shown in Figure 2E and further along the Y direction (not specifically labeled), which is orthogonal to both the X and Z directions. Each material layer 14A to 14I can have any thickness within process constraints. In some embodiments, the thicknesses T14A-T14I (not specifically labeled) of the fourth material layers 14 are each at least about 5 angstroms, and the fourth material layers 14 are deposited by an ALD process. In some embodiments, thicknesses T14A-T14I less than 5 angstroms indicate voids or other non-uniformities that reduce yield. In some embodiments, in the reflective multilayer 20C, a first material layer 11 has a thickness ranging from about 5 angstroms to about 35 angstroms. In some embodiments, a second material layer 12 has a thickness ranging from about 15 angstroms to about 50 angstroms. In some embodiments, a third material layer 13 has a thickness ranging from about 5 angstroms to about 50 angstroms. In some embodiments, a fourth material layer 14 has a thickness ranging from about 5 angstroms to about 40 angstroms. A further description of the thickness and variations of the reflective multilayer 20C is provided with reference to Figure 3C.

[0042] Referring to the diagram in Figure 1D, silicon and strontium are relatively close to each other, on the lower right side of the diagram. Thus, referring again to Figure 2F, the reflective multilayer 20C can be viewed as a stack of two layers, each double layer comprising at least one second or fourth material layer 12, 14 (or "spacer layers 12, 14") and at least one first or third material layer 11, 13 (or "reflector layers 11, 13"). Figures 2G to 2L illustrate examples of double layers 30A to 30F according to various embodiments. Referring again to Figure 2F, at least one of the first material layer 11 (e.g., molybdenum) or the third material layer 13 (e.g., ruthenium) may be located between at least two spacer layers 12, 14 (e.g., silicon, strontium). For example, a single third material layer 13A may be located between spacer layers 12C, 14C and spacer layers 12D, 14D. Due to the material variations in each double-layered reflector layer 11 and / or 13 and septum layer 12 and / or 14, the reflective multilayer 20C is non-periodic in terms of material.

[0043] Figures 3A to 3D are diagrams illustrating the design of the reflective multilayers 20A to 20C, and in particular, figures 300A to 300C showing the relative thicknesses and order of the first, second, third, and / or fourth material layers 11 to 14 in the reflective multilayers 20A to 20C. In some embodiments, the first material layer 11 is molybdenum, the second material layer 12 is silicon, the third material layer 13 is ruthenium, and the fourth material layer 14 is strontium. As described above, the order and thickness of the material layers 11 to 14 are arbitrary and may depend on various factors, including the wavelength of the incident light, the angle of incidence of the incident light, the distance to the preceding reflector, the distance to the following reflector, and other suitable factors. Therefore, each of the settings illustrated in Figures 3A to 3D represents a single solution that is optimal overall or locally for high reflectivity based on the only factor of the reflective multilayers 20A to 20C. However, even if one of these factors is significantly changed (e.g., by about 1% in any direction), this solution is not optimal overall or locally.

[0044] Generally, the reflective multilayers 20A to 20C may comprise at least one region, for example, a region along the Z-axis (see, for example, Figure 2E) from a first depth to a second depth. In each region, each of the material layers 11 to 14 may exhibit one or more of several trends. For example, in a single region comprising 10 layers of material layers 11 to 14, the trends may include at least a large slope trend and a changing trend. In some embodiments, the large slope trend may be upward, downward, or lateral, wherein the average thickness of any of the material layers 11 to 14 may substantially increase (e.g., slope > 0.1 Å / layer), decrease (e.g., slope < -0.1 Å / layer), or remain substantially constant (e.g., -0.1 Å / layer < slope < 0.1 Å / layer) above the region. In some embodiments, the changing trend may be large or small, such that the variation in thickness is high or low near the average thickness in this region.

[0045] In Figure 3A, the first line 311A ​​illustrates the average thickness of the first material layer 11 sequentially from the first material layer 11A to the first material layer 11N (see Figure 2A), which may be the first material layer 11 at the farthest point of the incident light from the reflective multilayer 20A. The second line 312A illustrates the average thickness of the second material layer 12 sequentially from the second material layer 12A to the second material layer 12N (see Figure 2A), which may be the second material layer 12 at the farthest point of the incident light from the reflective multilayer 20A. The upper lines 311A_U and 312A_U respectively illustrate the deviation of the upper thickness from the average thickness illustrated by the first and second lines 311A ​​and 312A. In some embodiments, the upper thickness deviation is a maximum deviation, a first deviation, or another deviation therebetween. The lower lines 311A_L and 312A_L respectively illustrate the deviation of the lower thickness from the average thickness illustrated by the first and second lines 311A ​​and 312A. In some embodiments, the lower thickness deviation is the maximum deviation, the first deviation, or another deviation in between.

[0046] In some embodiments, the first material layer 11 and the second material layer 12 alternate, and each of the first and second material layers 11, 12 has an arbitrary thickness. In some embodiments, the first material layer 11 is substantially thinner than the second material layer 12. For example, more than 90% of the second material layer 12 may be thicker than the thickest first material layer 11. In some embodiments, more than 90% of the second material layer 12 is thicker than the average thickness of the first material layer 11. In some embodiments, making the spacer layer 12 substantially thicker than the reflector layer 11 can provide a better overall reflectivity for the reflector 100 comprising the reflective multilayer 20A.

[0047] As further illustrated in Figure 3A, the reflective multilayer 20A, comprising only a first material layer 11 and a second material layer 12, may include at least two distinct regions 301A and 302A. In the embodiment shown in Figure 3A, the first region 301A of the reflective multilayer 20A may include the first and second material layers 11 and 12 to the left of the dividing line 350A. The second region 302A includes the material layers 11 and 12 to the right of the dividing line 350A. In the first region 301A to the left of the dividing line 350A, the steep slope of material layer 11 may be slightly downward, and the thickness of material layer 11 may have a significant variation. The steep slope of material layer 12 may be slightly upward, and the thickness of material layer 12 may have a significant variation. In the second region 302A, the steep slope of material layers 11 and 12 may be substantially lateral (slightly downward or slightly upward), and the variation in the thickness of material layers 11 and 12 may be small.

[0048] In some embodiments, the variation (or "variance coefficient (CV)") can be quantified as the standard deviation divided by the average. By way of example, the average thickness of the first material layer 11 in the first region 310A may be about 31 nm, and the standard deviation of the thickness of the first material layer 11 in the first region 301A may be about 2.3 nm, resulting in a variation of about 7.4% for the first material layer 11 in the first region 301A. In the second region 302A, the average thickness of the first material layer 11 is about 27 nm, and the standard deviation is about 0.2 nm, resulting in a variation of about 0.74% for the first material layer 11 in the second region 302A, or one-tenth of the variation in the first region 301A. For the second material layer 12, the variation in the first region 301A may be about 4.8%, and the variation in the second region 302A may be about 1.7%, or one-third of the variation in the first region 301A. In some embodiments, the thickness variation of material layers 11, 12 in the first region 301A is in the range of about 2% to about 20%, and the thickness variation of material layers 11, 12 in the second region 302A is in the range of about a minimum process variation (e.g., 0.01%) to about 10%. A thickness variation of less than about 2% in material layers 11, 12 may result in insufficient increase in reflectivity.

[0049] Figure 3D illustrates a histogram 390A corresponding to graph 300A of Figure 3A, which further helps to describe the thickness variation of all layers in the reflective multilayer 20A. Histogram 390 of the reflective multilayer 20A includes several non-overlapping thickness ranges R1 to R9. Each thickness range R1 to R9 may be, for example, about 1 angstrom wide, without excluding other suitable widths greater than or less than about 1 angstrom. Line 350D illustrates the average thickness of material layers 11 and 12. Lines 351D and 352D represent a standard deviation that is respectively below or above the average thickness. As a non-limiting example, the average thickness represented by line 350 may be about 69.5 nm, and the standard deviation may be about 1.5 nm, corresponding to a thickness variation of about 2.2%.

[0050] In Figure 3B, graphic 300B depicts a first line 311B, a second line 312B, and a third line 313B, which respectively correspond to the average thickness of the first material layer 11, the second material layer 12, and the third material layer 13 of the reflective multilayer 20B in Figures 2C to 2D. Upper lines 311B_U, 312B_U, and 313B_U respectively illustrate the deviation of the upper thickness from the average thickness illustrated by the first, second, and third lines 311B, 312B, and 313B. In some embodiments, the upper thickness deviation is a maximum deviation, a first deviation, or another deviation therebetween. Lower lines 311B_L, 312B_L, and 313B_L respectively illustrate the deviation of the lower thickness from the average thickness illustrated by the first, second, and third lines 311B, 312B, and 313B. In some embodiments, the lower thickness deviation is a maximum deviation, a first deviation, or another deviation therebetween.

[0051] In some embodiments, the first material layer 11 is not necessarily alternated with the second material layer 12 and / or the third material layer 13, and each of the first, second, and third material layers 11, 12, and 13 has an arbitrary thickness. In some embodiments, the first material layer 11 is substantially thinner than the second material layer 12. For example, more than 90% of the second material layer 12 may be thicker than the thickest first material layer 11. In some embodiments, more than 90% of the second material layer 12 is thicker than the average thickness of the first material layer 11. In some embodiments, the first material layer 13 is substantially thinner than the second material layer 12. For example, more than 90% of the second material layer 12 may be thicker than the thickest third material layer 13 (this is not specifically illustrated in Figure 3B). In some embodiments, more than 90% of the second material layer 12 is thicker than the average thickness of the third material layer 13. Overall, as understood from Figure 3B, the reflector layers 11 and 13 illustrated by lines 311B and 313B are not thicker than the spacer layer 12. However, a small portion (e.g., <10%) of the reflector layers 11 and 13 may have a thickness greater than the average thickness of the spacer layer 12.

[0052] Referring further to Figure 3B, five distinct regions 301B to 305B are depicted, highlighting certain characteristics of the composition of the reflective multilayer 20B in terms of the order and relative thickness of the first, second, and third material layers 11 to 13. In the first region 301B to the left of line 350B, only the third material layer 13 and the second material layer 12 are present. The intermediate layer of the first material layer 11 is absent in the first region 301B. In some embodiments, the first region 301B may contain only the first and second material layers 11 and 12, without the intermediate layer of the third material layer 13. Further, in the first region 301B, the average thicknesses of the second and third material layers 12 and 13 are approximately similar (e.g., within about 20% of each other).

[0053] In the second region 302B between line 350B and line 351B, the first material layer 11 is first present in the reflective multilayer 20B. The thickness of the third material layer 13 has a large downward slope tendency, and the thicknesses of the first and second material layers 11 and 12 each have a large upward slope tendency in the second region 302B.

[0054] In the third region 303B between line 351B and line 352B, a majority (e.g., >90%) of the reflector layers 11, 13 has a thickness substantially smaller than that of the spacer layer 12. In some embodiments, the average thickness of either reflector layer 11, 13 is at least about 20% thinner than the average thickness of spacer layer 12. In some embodiments, the first material layer 11 is substantially thicker than the third material layer 13 in the third region 303B, such that the average thickness of the first material layer 11 is at least about 10% greater than the average thickness of the third material layer 13.

[0055] In the fourth region 304B between line 352B and line 353B, the second and third material layers 12 and 13 have a generally large lateral slope tendency and small thickness variation. The first material layer 11 has a large thickness variation and a large lateral slope tendency. The average thickness of the second material layer 12 is greater than the average thickness of the first material layer 11, and the average thickness of the first material layer 11 is greater than the average thickness of the third material layer 13.

[0056] In the fifth region 305B to the right of line 353B, the first, second, and third material layers 11 to 13 all exhibit a large, substantially lateral slope tendency and small thickness variations. In some embodiments, the reflective multilayer 20B has minimal thickness variation in the region furthest from the surface from which light is incident (e.g., the fifth region 305B).

[0057] In Figure 3C, graphic 300C depicts a first line 311C, a second line 312C, a third line 313C, and a fourth line 314C, which respectively correspond to the average thickness of the first material layer 11, the second material layer 12, the third material layer 13, and the fourth material layer 14 of the reflective multilayer 20C in Figures 2E to 2F. Upper lines 311C_U, 312C_U, 313C_U, and 314C_U respectively illustrate the deviation of the upper thickness from the average thickness illustrated by the first, second, third, and fourth lines 311C, 312C, 313C, and 314C. In some embodiments, the upper thickness deviation is a maximum deviation, a first deviation, or another deviation somewhere in between. The lower lines 311C_L, 312C_L, 313C_L, and 314C_L respectively illustrate the deviation of the lower thickness from the average thickness illustrated by the first, second, third, and fourth lines 311C, 312C, 313C, and 314C. In some embodiments, the lower thickness deviation is the maximum deviation, the first deviation, or another deviation somewhere in between.

[0058] Since each of the material layers 11 to 14 can have arbitrary thickness and arrangement in the reflective multilayer 20C, pattern 300C can be similar in many respects to any or both of patterns 300A and 300B. For illustrative purposes, region 301C of the reflective multilayer 20C, which may be an intermediate region, is highlighted in Figure 3C. In some embodiments, intermediate region 301C may comprise a very small portion of at least one of the intermediate layers 11 to 14. As illustrated in Figure 3C, in some embodiments, the reflective multilayer 20C includes an intermediate layer 301C having a sparse layer of a third material layer 13 (denoted by point 313I), which is a reflector layer. In some embodiments, this may result from the intelligent recombination of adjacent reflector layers of different materials into a single reflector layer of a single material (further described with reference to Figures 6A to 6B), such as the first material layer 11, which may be a molybdenum layer. This further highlights the non-periodic nature of the reflective multilayer 20C, where some reflector / spacer double layers may contain all four material layers 11 to 14, while others may contain only three material layers, such as material layers 11, 12, and 14. In some embodiments, in at least one region of the reflective multilayer 20C, at least one of the material layers (e.g., material layer 13) may be present in the range of approximately 1% to approximately 15% of all layers in the region. The presence of at least one material layer within the aforementioned range can improve manufacturing yield and cost while maintaining the high reflectivity of the reflector 100 containing the reflective multilayer 20C. In some embodiments, the total number of layers in the region ranges from approximately 20 to approximately 100 layers.

[0059] Figures 4 through 6B are various views illustrating a process 40 for forming a reflective multilayer according to some embodiments. Figure 4 is a flowchart of process 40, Figure 5 illustrates a diagram corresponding to operation 412 of Figure 4, and Figures 6A through 6B are diagrams illustrating the reorganization of the first, second, third, and / or fourth material layers 11 to 14 corresponding to operation 414 of Figure 4. Process 40 can be executed by a computing system, which may include a processor, such as a general-purpose central processing unit (CPU), a graphics processing unit (GPU), or an application-specific integrated circuit (ASIC), random access memory (RAM), and a communication bus configured to provide bidirectional signal transmission between the processor and the RAM.

[0060] In Figure 4, process 40 begins at operation 400, where a reflective multilayer structure M, also referred to as the "initial reflective multilayer structure M," is provided. In some embodiments, the reflective multilayer structure M is provided by creating data objects, the data objects comprising an array or list of data structures representing individual material layers. In some embodiments, each data structure includes at least the location (e.g., an integer from 0 to 99), material (e.g., molybdenum, silicon, etc.), and thickness (e.g., 30 nm) of the represented material layer. In some embodiments, each data structure includes a depth (e.g., from 0.00 nm to 50000.00 nm), which may be recorded instead of the location, or the depth may be recorded in addition to the location.

[0061] In some embodiments, the reflective multilayer structure M is further provided in operation 400 by establishing design constraints (or rules) related to the location, depth, material, and thickness of the material layers. For example, a minimum and / or maximum thickness may be set for each material based on manufacturing capabilities, and / or a maximum total number of layers may be set, and / or material selection exclusions may be set based on materials immediately following previously specified material layers. Material selection exclusions may be established rules that reduce the available material library for layers during randomization. For example, if the material of the first material layer 11 is randomly selected for the first layer, material selection exclusions may remove the material of the first material layer 11 after considering the immediately following second layer, so that the material of the second layer can be randomly selected only from the materials corresponding to the second, third, or fourth material layers 12 to 14. In another instance, removal may be based on the first layer being reflector layers 11, 13 or spacer layers 12, 14, so that the second layer may be individually spacer layers 12, 14 or reflector layers 11, 13.

[0062] In some embodiments, the reflective multilayer structure M is further provided by assigning a random value to at least one of the material or thickness at each location. For example, the material layer at location 0 can be randomly assigned to be molybdenum, and the thickness can be randomly assigned to be 22 nm. The material layer at location 1 can be randomly assigned to be silicon, and the thickness can be assigned to be a fixed thickness of 40 nm. The material layer at location 2 can be randomly assigned to be molybdenum with a thickness of 25 nm. This assignment operation can continue until a fixed number of layers is reached, or until a random number (e.g., 75) of layers is reached between a minimum number (e.g., 60) and a maximum number (e.g., 100).

[0063] In some embodiments, the layers of the reflective multilayer structure M may be specified with a periodic, alternating arrangement. For example, the arrangement may include a fixed number of alternating layers of first, second, third, and fourth material layers 11 to 14, each having the same thickness. Selecting this arrangement can significantly reduce the processing load of operation 400.

[0064] In operation 410, at least one technique is used to find the optimal intermediate reflective multilayer structure M' (or "intermediate reflective multilayer structure configuration M'"). Technique 412 may include reverse engineering techniques, such as local maximum path search algorithms, global maximum path search algorithms, and / or machine learning algorithms. As described above, technique 412 may be subject to manufacturability constraints 414, which may include at least minimum thickness constraints and layer number constraints. Manufacturability constraints 414 may influence other techniques, such as intralayer recombining and / or interlayer recombining, as described more fully with reference to Figures 6A to 6B.

[0065] Figure 5 illustrates the local and global maximum path search algorithms corresponding to operations 420, 430, 440, and 450 in Figure 4. In Figure 5, the vertical axis represents reflectivity, and the horizontal axis represents candidates. Each of the initial reflective multilayer structure M and the subsequent intermediate reflective multilayer structure M' is a candidate.

[0066] In some embodiments, the local maximum path search algorithm may receive an initial reflective multilayer structure M or an intermediate reflective multilayer structure M', change at least one parameter (position, depth, material, thickness) of at least one of the material layers, and calculate the reflectivity R by means of the technique corresponding to operation 410 in Figure 4, as described with reference to Figure 1C. Each cycle of changing the initial or intermediate reflective multilayer structures M, M' and the corresponding calculated reflectivity R may be referred to as a path search cycle. In some embodiments, the number of path search cycles may be set, such as 1000 cycles, 10000 cycles, or another suitable number of path search cycles. After a path search cycle, the path search algorithm may be terminated, and the optimal reflective multilayer structure M* for all path search cycles may be determined and saved for use in manufacturing the reflector 100. In some embodiments, after performing a certain number of path search cycles, such as 100 cycles, 10 cycles, or another suitable number of cycles, if no significant improvement is found, the path search algorithm terminates. This may correspond to the transition from operation 420 to operation 430 in Figure 4.

[0067] In some embodiments, changes may be applied to a single layer, altering the layer's material, location, depth, or thickness. In some embodiments, changes may be applied to multiple layers. In some embodiments, the changes are random. For example, a change may affect a random number of layers and / or the material, location, depth, and / or thickness of each of the layers. In some embodiments, the change may include swapping layers. For example, a first layer at position 0 and a second layer at position 50 may be swapped, such that the changed first layer occupies position 50 and the second layer occupies position 0. In some embodiments, the change is subject to manufacturability constraint 414. In some embodiments, the change includes adding or removing layers. For example, a second layer at position 50 may be removed, such that a third layer initially at position 51 occupies position 50 after the change, reducing the total number of intermediate reflective multilayer structures M' by one.

[0068] Some changes increase reflectivity, while others decrease it, which may correspond to operation 420 in Figure 4. For example, as shown in Figure 5, one or more changes are performed on the initial reflective multilayer structure M, increasing reflectivity (corresponding to the transition from operation 420 to operation 430 in Figure 4), and a first local maximum value 520 is found to have a reflectivity Rmax_local(0), which is greater than the initial reflectivity R0 of the initial reflective multilayer structure M. In some embodiments, several changes (or change / computation loops, e.g., >100 loops) occur before a change that decreases the reflectivity of the intermediate reflective multilayer structure M' is reached. The first local maximum value 520 may correspond to the final optimal intermediate reflective multilayer structure M' before the subsequent decreasing change. Each intermediate reflective multilayer structure M' may be stored in RAM, containing parameters of all layers and the calculated reflectivity.

[0069] Figure 5 further illustrates the global maximum path search algorithm. After identifying the first local maximum 520, several path search loops may initially lead to a decrease in reflectivity R, followed by several more path search loops leading to an increase in reflectivity R. After one or more path search loops that increase reflectivity R, a second local maximum 521 can be identified, which has a reflectivity Rmax_local(1), Rmax_local(1) being greater than the reflectivity Rmax_local(0) corresponding to the first local maximum 520. Here, several path search loops may be performed, which decrease reflectivity R, followed by several more path search loops ending with the identification of the global maximum 530 corresponding to reflectivity Rmax_global, Rmax_global being greater than any other local maximum 520, 521 in Figure 500. Identification and recording / storing of the optimal reflective multilayer structure M* respectively correspond to operations 420 and 440 in Figure 4. Once the optimal reflective multilayer structure M* is identified and recorded / stored, process 40 can terminate at operation 450.

[0070] In some embodiments, if several path-searching cycles are performed and changing the layers of the intermediate reflective multilayer structure M' does not significantly improve the reflectivity R, it may be necessary to avoid local maxima, such as a first local maxima 520. To avoid local maxima, strong changes can be applied, where strong changes affect many layers. For example, a strong change may include at least 10% of the synchronously random positions, materials, and / or thicknesses of the layers in the intermediate reflective multilayer structure M'. Applying a strong change may initially result in a significant decrease in reflectivity R, followed by subsequent path-searching cycles resulting in a significant increase in reflectivity R.

[0071] In some embodiments, after the operation 450 of recording / storing the optimal reflective multilayer structure M*, a reflective multilayer, such as one of reflective multilayers 20A to 20C, is manufactured, and then the recorded / stored optimal reflective multilayer structure M* is designed, corresponding to operation 460 of Figure 4. For example, the optimal reflective multilayer structure M* may be a digital file containing information on the location, material, and thickness of material layers 11 to 14, as shown graphically in Figure 3B.

[0072] In some embodiments, operation 460 includes depositing a first material layer having a first material and a first thickness, depositing a second material layer having a second material and a second thickness, and so on, until all material layers 11 to 12, 11 to 13, and 11 to 14 of the reflective multilayers 20A to 20C are deposited individually. Further manufacturing operations may be performed on the completed reflective multilayers 20A to 20C, such as adding a cover layer or encapsulating the reflective multilayers 20A to 20C in, for example, a protective package.

[0073] Turning to Figures 6A and 6B, in some embodiments, as part of operation 410, at least two layers (typically adjacent or neighboring layers) of the intermediate reflective multilayer structure M' are recombined. Recombination can achieve several benefits, including restoring the layer number budget when the intermediate reflective multilayer structure M' is at or near a layer number constraint. In some embodiments, the layer number is limited to a maximum number of layers, corresponding to the optimal reflective multilayer structure M* of reflective multilayers 20A to 20C containing the maximum number of layers. Recombination can also improve manufacturing yield, for example by combining one layer at a minimum thickness constraint with another layer to obtain a single, thicker layer, which is generally easier to manufacture with high uniformity.

[0074] Figure 6A illustrates an in-layer recombination 600A according to various embodiments. As shown, the reflective multilayer 20C includes three periods P1, P2, and P3, each period containing two layers. The first period P1 includes a third material layer 13A, which covers the first material layer 11A. The second period P2 includes a fourth material layer 14A, which is placed below the first material layer 11A and covers the second material layer 12A. The third period P3 includes a third material layer 13B, which is placed below the second material layer 12A and covers the first material layer 11B. The fourth and second material layers 14A and 12A of the second period P2 are both spacer layers 12 and 14, but are made of different materials and have different thicknesses. The first thickness of the fourth material layer 14A may be at or near a minimum thickness constraint, and the second thickness of the second material layer 12A may be significantly thicker than the first thickness. Thus, the fourth material layer 14A can be combined with the second material layer 12A to form a reconstituted second material layer 12A' having a thickness substantially equal to the sum of the first and second thicknesses. In some embodiments, the intralayer recombination 600A includes removing one layer (e.g., the fourth material layer 14A) and increasing the thickness of another layer (e.g., the second material layer 12A). In some embodiments, the intralayer recombination 600A includes changing the material of one layer (e.g., changing the fourth material layer 14A from strontium to silicon) and merging one layer with another (e.g., the second material layer 12A). The intralayer recombination 600A results in the reconstituted second material layer 12A' eliminating a manufacturing operation (one layer instead of two layers), removing a relatively difficult-to-manufacture layer, and thickening a relatively easy-to-manufacture layer, making it even easier to manufacture.

[0075] Figure 6B illustrates interlayer recombination 600B according to various embodiments. As shown, the reflective multilayer 20C includes four periods P1, P2, P3, and P4, each period including one or two layers. The first period P1 includes a fourth material layer 14A, which overlays a second material layer 12A. The second period P2 includes a third material layer 13A, which is placed below the second material layer 12A. The third period P3 includes a second material layer 12B, which is placed below the third material layer 13A. The fourth period P4 includes a third material layer 13B, which is placed below the second material layer 12B and overlays a first material layer 11A. The third and second material layers 13A and 12B may be at or near minimum thickness constraints. Thus, it may be necessary to recombine the relatively thin second and third material layers 12B and 13A with the relatively thick second and third material layers 12A and 13B respectively from a manufacturing perspective.

[0076] Following interlayer recombination 600B, the reflective multilayer 20C' comprises two shorter periods: a first period P1' and a fourth period P4'. The first period P1' may comprise an initial fourth material layer 14A and a recombined second material layer 12A', the recombined second material layer 12A' having a thickness substantially equal to the sum of the thicknesses of the second material layers 12A and 12B. The fourth period P4' may comprise an initial first material layer 11A and a recombined third material layer 13B', the recombined third material layer 13B' having a thickness substantially equal to the sum of the thicknesses of the third material layers 13A and 13B. In some embodiments, interlayer recombination 600B comprises removing the thickness of two layers (e.g., the third material layer 13A and the second material layer 12B) and adding the thickness of two layers (e.g., the second material layer 12A and the third material layer 13B). In some embodiments, interlayer reconfiguration 600B includes changing the positions of two layers (e.g., swapping the positions of the third material layer 13A and the second material layer 12B) and merging the swapped layers with two other layers (e.g., the third material layer 13B and the second material layer 12A), respectively. Interlayer reconfiguration 600B results in the removal of two manufacturing operations (two layers instead of four layers) for reconfiguring the second material layer 12A' and reconfiguring the third material layer 13B', the removal of two relatively difficult-to-manufacture layers, and the thickening of two relatively easy-to-manufacture layers, making them even easier to manufacture.

[0077] In some embodiments, recombination of 600A and 600B results in a small but measurable reduction in the reflectivity of the reflective multilayers 20A to 20C. Thus, recombination of 600A and 600B can be maintained when the resulting reduction in reflectivity of the reflective multilayers 20A to 20C is less than about 0.01%. For a lithography system 10 comprising at least ten reflectors 100, and assuming ten recombinations per reflector 100, the reduction in the optical path is about 1%. In some embodiments, a recombination budget can be established such that the total reduction in reflectivity of the reflectors 100 does not exceed a critical value, such as about 0.1%, such that the reduction in the optical path comprising the ten reflectors 100 does not exceed 1%. In some embodiments, recombination is discarded when the reduction due to recombination is greater than about 0.01%.

[0078] Figure 7 is a flowchart of process 70 for manufacturing a semiconductor device using a lithography system 10, which includes at least one of reflective multilayers 20A to 20C. In operation 700, a mask layer is deposited over a substrate. The mask layer may include a hard mask (e.g., SiN) and one or more photoresist layers, which may include anti-reflective layers. The semiconductor device generally comprises a patterned layer of semiconductor, dielectric, and conductor materials on and within the substrate. The mask layer may be deposited over the material layers prior to patterning by, for example, an etching system. Deposition may include any suitable deposition process, such as chemical vapor deposition, physical vapor deposition, spin coating, or the like.

[0079] After depositing the mask layer, in operation 710, an opening is formed in the mask layer by means of a lithography exposure system 10, the lithography exposure system 10 including at least one reflective multilayer 20A, 20B, 20C, which has at least three layers with substantially different thicknesses. As described with reference to Figures 2F to 2L, the position, depth, material, and thickness of the first, second, third, and fourth material layers 11 to 14 may be non-periodic and non-alternating. The opening is formed by exposing the mask layer to a pattern on the mask stage 16, and then removing the exposed or unexposed portions of the mask layer. After removing the exposed or unexposed portions, the remaining portion of the mask layer contains the opening.

[0080] After the opening is formed, in operation 720, the material exposed by the opening is removed. The material may be the material of the hard mask exposed by the opening in the photoresist layer. The material may be the material of a semiconductor, dielectric, or conductor exposed by the opening in the photoresist layer. Process 70 may be repeated multiple times to form a single layer, and multiple layers of a semiconductor device may also be repeated multiple times.

[0081] Figure 8 is a block diagram of a system 3224 according to an embodiment, which may be a control system for performing the process 40 of Figure 4. The control system 3224 uses machine learning to adjust the parameters of the intermediate reflective multilayer structure M'.

[0082] In one embodiment, the memory system 3224 includes an analysis model 3302 and a training module 3304. The training module 3304 trains the analysis model 3302 using a machine learning process. The machine learning process trains the analysis model 3302 to select parameters for operation 410, which will cause the intermediate reflective multilayer structure M' to have selected characteristics such as high reflectivity R. Although the training module 3304 is shown as separate from the analysis model 3302, in practice, the training module 3304 is part of the analysis model 3302.

[0083] The control system 3224 includes or stores training set data 3306. The training set data 3306 includes historical reflector data 3308 and historical environmental condition data 3310. The historical reflector data 3308 includes data related to the intermediate reflection multilayer structure M' obtained from operation 410. The historical environmental condition data 3310 includes data related to the simulation environment in which the intermediate reflection multilayer structure M' will be operated. As will be explained in more detail below, the training module 3304 uses the historical reflector data 3308 and the historical environmental condition data 3310 to train the analysis model 3302 using a machine learning process.

[0084] In one embodiment, the historical reflector data 3308 includes data related to the location, depth, material, and / or thickness of the material layers. For example, thousands or millions of intermediate reflective multilayer structures M' may be generated (initialized or modified) over several hours or days. Each of the intermediate reflective multilayer structures M' may contain material layers with different thicknesses, materials, and locations and / or depths. After each generation, the reflectivity of the intermediate reflective multilayer structure M' is calculated. The historical reflector data 3308 includes parameters for each of the layers in each of the intermediate reflective multilayer structures M' generated by, for example, operation 410. Therefore, the historical reflector data 3308 may contain thickness, material, depth, and location data for a large number of intermediate reflective multilayer structures M' generated by operation 410.

[0085] In one embodiment, the historical reflector data 3308 may also include data related to material layer reorganization in operation 410. For example, the modification process may include a large number of reorganizations, during which material layers of the intermediate reflective multilayer structure M' are merged and / or rearranged. After an individual path-searching cycle or a group of path-searching cycles, the historical reflector data 3308 may include reflectivity data of the intermediate reflective multilayer structure M'. Thus, the historical reflector data 3308 may include not only data related to the total reflectivity of the intermediate reflective multilayer structure M' after the path-searching process is completed, but also data related to the reflectivity of the intermediate reflective multilayer structure M' at each stage of the path-searching process.

[0086] In one embodiment, historical environmental condition data 3310 includes various environmental conditions or parameters during the operation of the intermediate reflective multilayer structure M' associated with historical reflector data 3308. For each intermediate reflective multilayer structure M' having data in historical reflector data 3308, historical environmental condition data 3310 may include environmental conditions or parameters present during the calculation of reflectivity. For example, historical environmental condition data 3310 may include data related to the ambient atmosphere, the angle of incidence of incident light, the wavelength of incident light, the position in the optical path of the intermediate reflective multilayer structure M', and the like.

[0087] In one embodiment, training set data 3306 connects historical reflector data 3308 with historical environmental condition data 3310. In other words, the material layer thickness, material composition, layer depth, or location associated with the intermediate reflective multilayer structure M' in the historical reflector data 3308 is connected (e.g., by labeling) to the environmental condition data 3310 and reflectivity data associated with that intermediate reflective multilayer structure M'. As will be described in more detail below, the labeled training set data can be used during the machine learning process to train the analysis model 3302 to predict the material layer conditions that will result in the high reflectivity reflector 100.

[0088] In one embodiment, the control system 3324 includes processing resources 3312, memory resources 3314, and communication resources 3316. Processing resources 3312 may include one or more controllers or processors. Processing resources 3312 are configured to execute software instructions, process data, make thin-film etching control decisions, perform signal processing, read data from memory, write data to memory, and perform other processing operations. Processing resources 3312 may include physical processing resources 3312 and / or virtual processing resources 3312. Processing resources 3312 may include cloud processing resources, which include processors and servers accessed via one or more cloud computing platforms.

[0089] In one embodiment, memory resource 3314 may include one or more computer-readable memories. Memory resource 3314 is configured to store software instructions associated with the functionality of the control system and its components (including, but not limited to, the analysis model 3302). Memory resource 3314 may store data associated with the functionality of the control system 3224 and its components. The data may include training set data 3306, current process condition data, and any other data associated with the operation of the control system 3224 and any of its components. Memory resource 3314 may include physical memory resources and / or virtual memory resources. Memory resource 3314 may include cloud memory resources accessed via one or more cloud computing platforms.

[0090] In one embodiment, the communication resources may include wired or wireless communication resources that facilitate communication via one or more networks such as wired networks, wireless networks, the Internet, or intranets. Communication resources 3316 enable components of the control system 3224 to communicate with each other.

[0091] Figure 9 is a block diagram illustrating the operational and training states of the analysis model 3302 of Figure 8 according to an embodiment. As described above, the training set data 3306 includes data related to the previously generated plurality of intermediate reflective multilayer structures M'. Each previously generated intermediate reflective multilayer structure M' is generated under specific environmental conditions and has a specific reflectivity. The material layer position, depth, material, and thickness parameters of each previously generated intermediate reflective multilayer structure M' are formatted into a separate reflector condition matrix 3352. The reflector condition matrix 3352 contains a plurality of data vectors 3354. Each data vector 3354 corresponds to a specific layer and contains at least four data quanta 3354A to 3354D, which may include a position quanta 3354A, a depth quanta 3354B, a material quanta 3354C, and a thickness quanta 3354D.

[0092] The example illustration in Figure 9 will be passed to the single reflector condition matrix 3352 of the analysis model 3302 during the training process. In the example of Figure 9, the reflector condition matrix 3352 contains nine data vectors 3354, each data vector corresponding to an individual material layer of the intermediate reflective multilayer structure M'. Each data scalar 3354A to 3354D is numerically represented in the corresponding data vectors 3354. For condition types that are not naturally represented by numbers (e.g., material 3354C), numbers can be specified for each possible material.

[0093] The analysis model 3302 comprises a plurality of neural layers 3356a to e. Each neural layer comprises a plurality of nodes 3358. Each node 3358 may also be referred to as a neuron. Each node 3358 from the first neural layer 3356a receives the data value of each data field from the reflector condition matrix 3352. Therefore, in the example of Figure 23, since the reflector condition matrix 3352 has 36 data scalars (9*4=36), each node 3358 from the first neural layer 3356a receives 36 data values. Each neuron 3358 contains a separate internal mathematical function labeled F(x) in Figure 9. Each node 3358 of each neural layer 3356a produces a scalar value by applying the internal mathematical function F(x) to the data value of the data field 3354 from the reflector condition matrix 3352. Further details about the internal mathematical function F(x) are provided below.

[0094] Each node 3358 of the second neural layer 3356b receives scalar values ​​generated by each node 3358 of the first neural layer 3356a. Therefore, in the example of Figure 9, since there are four nodes 3358 in the first neural layer 3356a, each node of the second neural layer 3356b receives four scalar values. Each node 3358 of the second neural layer 3356b generates scalar values ​​by applying a separate internal mathematical function F(x) to the scalar values ​​from the first neural layer 3356a.

[0095] Each node 3358 of the third neural layer 3356c receives scalar values ​​generated by each node 3358 of the second neural layer 3356b. Therefore, in the example of Figure 9, since there are five nodes 3358 in the second neural layer 3356b, each node of the third neural layer 3356c receives five scalar values. Each node 3358 of the third neural layer 3356c generates scalar values ​​by applying a separate internal mathematical function F(x) to the scalar values ​​from the nodes 3358 of the second neural layer 3356b.

[0096] Each node 3358 of neural layer 3356d receives scalar values ​​generated by each node 3358 of the previous neural layer (not shown). Each node 3358 of neural layer 3356d generates scalar values ​​by applying a separate internal mathematical function F(x) to the scalar values ​​of nodes 3358 from the second neural layer 3356b.

[0097] The final neural layer contains only a single node 3358. The final neural layer receives scalar values ​​generated by each node 3358 of the previous neural layer 3356d. The nodes 3358 of the final neural layer 3356e generate data values ​​3368 by applying individual mathematical functions F(x) to the scalar values ​​received from the nodes 3358 of the neural layer 3356d.

[0098] In the example of Figure 9, data value 3368 corresponds to the predicted reflectivity of an intermediate reflective multilayer structure M', which is generated by reflector values ​​corresponding to those contained in the reflector condition matrix 3352. In other embodiments, the final neural layer 3356e may generate multiple data values, each corresponding to a specific reflective multilayer characteristic (e.g., reflectivity) or other characteristics of the reflective multilayer. The final neural layer 3356e will contain individual nodes 3358 for generating each output data value. For the predicted reflectivity, in one instance, the engineer may provide a constraint that the predicted reflectivity 3368 must be within a selected range, for example, greater than 70%. The analysis model 3302 will adjust the internal function F(x) to ensure that the data value 3368 corresponding to the predicted reflectivity will be within the specified range.

[0099] During the machine learning process, the analysis model compares the predicted reflectance in data value 3368 with the actual or rigorously calculated reflectance of the intermediate reflective multilayer structure M' indicated by data value 3370. As explained above, for each set of historical environmental condition data, training set data 3306 contains historical reflector data indicating the characteristics of the intermediate reflective multilayer structure M' obtained by the historical generation process (e.g., operation 410). Therefore, data field 3370 contains the actual reflectance of the intermediate reflective multilayer structure M' obtained by the reflection generation process in reflector condition matrix 3352. Analysis model 3302 compares the predicted reflectance from data value 3368 with the actual reflectance from data value 3370. Analysis model 3302 generates an error value 3372, which indicates the error or difference between the predicted reflectance from data value 3368 and the actual reflectance from data value 3370. Analysis model 3302 is trained using error value 3372.

[0100] The training of the analysis model 3302 can be more fully understood by discussing the internal mathematical function F(x). Although all nodes 3358 are labeled with the internal mathematical function F(x), the mathematical function F(x) for each node is unique. In one instance, each internal mathematical function has the following form: F(x) = x1*w1 + x2*w2 + ... + xn*w1 + b.

[0101] In the above equations, each value x1 to xn corresponds to a data value received from node 3358 in the previous neural layer, or for the first neural layer 3356a, each value x1 to xn corresponds to a data value from data field 3354 of the reflector condition matrix 3352. Therefore, n for each node is equal to the number of nodes in the previous neural layer. Values ​​w1 to wn are scalar weights associated with the corresponding values ​​in the previous layer. The analysis model 3302 selects the values ​​of weights w1 to wn. The constant b is a scalar bias value, which may also be multiplied by the weights. The values ​​generated by node 3358 are based on weights w1 to wn. Therefore, each node 3358 has n weights w1 to wn. Although not shown above, each function F(x) may also contain an activation function. The sum described in the above equations is multiplied by the activation function. Instances of activation functions may include rectified linear unit (ReLU) functions, sigmoid functions, hyperbolic tension functions, or other types of activation functions.

[0102] After calculating the error value 3372, the analysis model 3302 adjusts the weights w1 to wn for multiple nodes in multiple neural layers 3356a to 3356e. After adjusting the weights w1 to wn, the analysis model 3302 again provides the reflector condition matrix 3352 to the input neural layer 3356a. Since the weights for each node 3358 of the analysis model 3302 are different, the predicted reflectivity 3368 will be different from that in the previous iteration. The analysis model 3302 generates the error value 3372 again by comparing the actual reflectivity 3370 with the predicted reflectivity 3368.

[0103] The analysis model 3302 readjusts the weights w1 to wn associated with each node 3358. The analysis model 3302 then processes the reflector condition matrix 3352 again, generating the predicted reflectivity 3368 and the associated error value 3372. The training process involves adjusting the weights w1 to wn in the iterations until the error value 3372 is minimized.

[0104] Figure 9 illustrates a single reflector condition matrix 3352 transmitted to the analysis model 3302. In practice, the training process involves transmitting a large number of reflector condition matrices 3352 through the analysis model 3302, generating a predicted reflectance 3368 for each reflector condition matrix 3352, and generating an associated error value 3372 for each predicted reflectance. The training process may also include generating an ensemble error value, which indicates the average error of all predicted reflectances for a batch of reflector condition matrices 3352. After processing each batch of reflector condition matrices 3352, the analysis model 3302 adjusts the weights w1 to wn. The training process continues until the average error of all reflector condition matrices 3352 is less than a selected critical tolerance. When the average error is less than the selected critical tolerance, the analysis model 3302 is trained to accurately predict the reflectance of the intermediate reflective multilayer structure M' based on environmental conditions. The analysis model 3302 can then be used to predict reflectance, and the reflector conditions that will yield the desired reflectance can be selected. During the use of the trained model 3302, an environmental condition vector or matrix is ​​provided to the trained analysis model 3302. This environmental condition vector or matrix represents the current environmental conditions of the current intermediate reflective multilayer structure M' and has a format similar to the reflector condition matrix 3352. The subsequently trained analysis model 3302 can then predict the reflectivity of the intermediate reflective multilayer structure M' derived from these environmental conditions.

[0105] A specific example of the neural network-based analysis model 3302 has been described with reference to Figure 9. However, other types of neural network-based analysis models, as well as analysis models other than neural networks, may be used without departing from the scope of this disclosure. Furthermore, without departing from the scope of this disclosure, the neural network may have a different number of neural layers, and each neural layer may have a different number of nodes.

[0106] The embodiments offer advantages. Due to the inclusion of various techniques, such as non-periodic layer sequencing, free-form variable layer thickness, reverse random design, and / or addable layer materials, reflective multilayers 20A to 20C exhibit improved reflectivity. By combining these techniques, the reflectivity improvement of a lithography system comprising ten reflective multilayers 20A to 20C is set to at least 15% for two materials and at least 50% for using four or more materials. This increased reflectivity allows for higher wafer throughput per hour in EUV lithography, enabling the mass production of semiconductor electronic components with greater cost-effectiveness.

[0107] According to at least one embodiment, a lithography system includes a light source, a substrate stage, and a mask stage, the mask stage being located between the light source and the substrate stage and along an optical path from the light source to the substrate stage. The lithography system further includes a reflector along the optical path. The reflector includes: a first layer having a first material and a first thickness; a second layer having the first material and a second thickness different from the first thickness; and a third layer located between the first and second layers and having a second material different from the first material. In some embodiments, the reflector further includes a fourth layer having a third material different from the first and second materials. In some embodiments, the reflector further includes: a fifth layer having a fourth material different from the first, second, and third materials. In some embodiments, the first material, the second material, the third material, and the fourth material are each different materials having an extinction coefficient of less than about 0.02. In some embodiments, the first material, the second material, the third material, and the fourth material are each different from one of silicon, molybdenum, strontium, beryllium, or ruthenium. In some embodiments, the reflector further includes a sixth layer having a first material; and a fourth layer located between the second and sixth layers. In some embodiments, the lithography system further includes an illuminator and a projection optics box. The illuminator includes at least two first reflectors located along the light path between the light source and the mask stage. The projection optics box includes at least two second reflectors located along the light path between the mask stage and the substrate stage; wherein the reflector is one of at least two first reflectors or one of at least two second reflectors; the light source is an extreme ultraviolet light source.

[0108] According to at least one embodiment, a lithography system includes a light path and a first reflector. The light path is located between a light source and a substrate stage. The first reflector is along the light path having a first incident angle and includes at least three first material layers. The first material layers have a first number of layer materials, a second number of layer thicknesses, and a first order of the first material layers. The lithography system further includes a second reflector along the light path, which has a second incident angle different from the first incident angle. The second reflector includes at least three second material layers. The second material layers have a third number of layer materials, a fourth number of layer thicknesses, and a second order of the second material layers. At least one of the following conditions is satisfied: the third number is different from the first number; the fourth number is different from the second number; or the second order is different from the first order. In some embodiments, the number of first materials is at least four, and the number of second materials is less than four. In some embodiments, the first reflector includes: a first region and a second region. The first region extends from a first depth of the first reflector to a second depth. The second region extends from a third depth of the first reflector to a fourth depth, and the second region does not overlap the first region along the depth of the first reflector and has a first material layer arrangement different from the first region. In some embodiments, the thickness variation of the first material layer in the first region is greater than the thickness variation of the first material layer in the second region. In some embodiments, the amount of first material in the first region differs from the amount of first material in the second region by at least 1. In some embodiments, the first material layer in the first region comprises a third material layer and a fourth material layer. The third material layer comprises a first material. The fourth material layer comprises a second material different from the first material. The third material layer has a different thickness variation than the fourth material layer.

[0109] According to at least one embodiment, a method of lithography includes: forming a plurality of intermediate reflective multilayer structure configurations by performing a reverse engineering algorithm; and forming a reflective multilayer based on a reflective multilayer structure configuration selected from the plurality of intermediate reflective multilayer structure configurations. The reflective multilayer is formed by the following steps: forming a first material layer having a first material and a first thickness; forming a second material layer on the first material layer, each of the second material layers having a second material and a second thickness different from the first material and the first thickness; and forming a third material layer on the second material layer, the third material layer having a first material and a third thickness different from the first thickness. In some embodiments, forming an intermediate reflective multilayer structure configuration includes: forming a second intermediate reflective multilayer structure configuration by changing at least one parameter of at least one layer in a first intermediate reflective multilayer structure configuration. In some embodiments, changing at least one parameter includes changing a position of at least one layer. In some embodiments, changing at least one parameter includes changing the material of the at least one layer. In some embodiments, changing at least one parameter includes changing the thickness of the at least one layer. In some embodiments, forming an intermediate reflective multilayer structure configuration includes: recombining the first and second layers of the first intermediate reflective multilayer structure configuration. In some embodiments, the first layer has a first reflector material; the second layer has a second reflector material and is directly adjacent to the first layer; and the reorganization includes changing the second layer from the second reflector material to the first reflector material.

[0110] The foregoing summary outlines the features of several embodiments, enabling those skilled in the art to better understand the nature of this disclosure. Those skilled in the art should understand that they can easily design or modify other processes or structures based on this disclosure to achieve the same purpose and / or obtain the same advantages of the embodiments described herein. Those skilled in the art should also recognize that such equivalent constructions do not depart from the spirit and scope of this disclosure, and that various changes, substitutions, and modifications can be made without departing from the spirit and scope of this disclosure.

Claims

1. A lithography system comprising: a light source; a substrate stage; a mask stage located between the light source and the substrate stage and along an optical path from the light source to the substrate stage; and a reflector along the optical path comprising: a first layer having a first material and a first thickness; a second layer having the first material and a second thickness different from the first thickness; a third layer located between the first layer and the second layer and having a second material different from the first material; a fourth layer having a third material different from the first material and the second material; and a fifth layer having a fourth material different from the first material, the second material, and the third material, wherein the first material comprises silicon, the second material comprises molybdenum, the third material comprises ruthenium, and the fourth material comprises strontium or beryllium.

2. The lithography system as claimed in claim 1, wherein the reflector further comprises: a sixth layer having the first material, the fourth layer being located between the second layer and the sixth layer.

3. The lithography exposure system as claimed in claim 1, further comprising: an illuminator including at least two first reflectors and located along the light path between the light source and the mask stage; and a projection optics box including at least two second reflectors and located along the light path between the mask stage and the substrate stage; wherein the reflector is one of the at least two first reflectors or one of the at least two second reflectors; wherein the light source is an extreme ultraviolet light source.

4. The lithography system as claimed in claim 1, wherein the first material, the second material, the third material and the fourth material each have an extinction coefficient of less than about 0.

02.

5. The lithography system as claimed in claim 1, wherein the reflector includes: a first region extending from a first depth of the reflector to a second depth; and a second region extending from a third depth of the reflector to a fourth depth, the second region not covering the first region along the depth of the reflector, and having a first material layer disposed different from the first region.

6. A lithography system comprising: a light path located between a light source and a substrate stage; a first reflector along the light path having a first incident angle, and comprising: at least four first material layers having at least four different layer materials, a second number of layer thicknesses, and a first order of the first material layers, wherein each of the at least four different layer materials has an extinction coefficient of less than about 0.02; and a second reflector along the light path having a second incident angle different from the first incident angle, and comprising: at least three second material layers having fewer than four different layer materials, a fourth number of layer thicknesses, and a second order of the second material layers.

7. The lithography system as claimed in claim 6, wherein the first reflector includes: a first region extending from a first depth of the first reflector to a second depth; and a second region extending from a third depth of the first reflector to a fourth depth, the second region not covering the first region along the depth of the first reflector, and having a first material layer disposed different from the first region.

8. The lithography system as claimed in claim 7, wherein the thickness variation of the first material layers in the first region is greater than the thickness variation of the first material layers in the second region.

9. A method for photolithography, comprising: forming a plurality of intermediate reflective multilayer configurations by executing a reverse engineering algorithm; and forming a reflective multilayer by means of the following steps based on a reflective multilayer configuration selected from the intermediate reflective multilayer configurations: forming a first material layer having a first material and a first thickness; forming a second material layer on the first material layer having a second thickness different from the first thickness; forming a third material layer on the second material layer having the first material and a third thickness different from the first thickness; forming a fourth material layer on the third material layer having a third material; and forming a fifth material layer on the fourth material layer having a fourth material, wherein the first material, the second material, the third material, and the fourth material are different from each other, and each of the first material, the second material, the third material, and the fourth material has an extinction coefficient less than or equal to ruthenium.

10. The method as described in claim 9, wherein forming the intermediate reflection multilayer configuration comprises: forming a second intermediate reflection multilayer configuration by changing at least one parameter of at least one layer in a first intermediate reflection multilayer configuration.

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