Diffraction-based pupil determination for lithography process optimization

Abstract

Methods, apparatuses, and software for optimizing a radiation source and / or mask used in a lithography manufacturing and patterning process are disclosed. One method includes determining a first pupil having a central obscuration (CO), determining a diffraction order (DO) based on a target design and a mask model, determining a first diffraction pattern (DP) based on the DO and the first pupil, wherein the first DP includes overlapping regions of diffracted light, determining a second DP based on the DO and the first pupil, and determining an initial pupil based on the first DP and the second DP, wherein the initial pupil includes at least some of the overlapping regions.

Description

Technical Field

[0001] Cross - reference to related applications

[0001] This application claims priority to U.S. Patent Application No. 63 / 343,041, filed May 17, 2022, the entire disclosure of which is incorporated herein by reference.

[0002]

[0002] This specification generally relates to determining pupils for the optimization of radiation sources and masks used in lithography manufacturing and patterning processes. More particularly, the disclosure includes apparatus, methods, and computer programs for determining pupils, including taking into account diffraction effects.

Background Art

[0003]

[0003] A lithographic projection apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In such a case, a patterning device (e.g., a mask) can contain, or provide, a pattern (the “design layout”) corresponding to an individual layer of the IC, and this pattern can be transferred onto a target portion (e.g., including one or more dies) on a substrate (e.g., a silicon wafer) coated with a layer of radiation-sensitive material (the “resist”) by, for example, irradiating the target portion through the pattern on the patterning device. In general, a single substrate includes a plurality of adjacent target portions (one target portion at a time) onto which the pattern is successively transferred by the lithographic projection apparatus. In one type of lithographic projection apparatus, the pattern over the entire patterning device is transferred onto one target portion at a time, and such an apparatus can also be called a stepper. In an alternative apparatus, a step-and-scan apparatus can move the substrate in a direction parallel or anti-parallel to a given reference direction (the “scan” direction) in synchronization with the projection beam scanning the patterning device in this reference direction. Different parts of the pattern on the patterning device are progressively transferred onto one target portion. In general, since the lithographic projection apparatus has a reduction ratio M (e.g., 4), the speed F at which the substrate is moved is the speed at which the projection beam scans the patterning device × 1 / M. Further information regarding lithographic devices can be found, for example, in U.S. Patent No. 6,046,792, which is incorporated herein by reference.

[0004]

[0004] Before transferring a pattern from a patterning device to a substrate, the substrate may undergo various procedures such as priming, resist coating, and soft baking. After exposure, the substrate may undergo other procedures (the "post procedures") such as post-exposure bake (PEB), development, hard bake, and measurement / inspection of the transferred pattern. This number of procedures is used as a basis for creating individual layers of a device, such as an IC. The substrate may then undergo various processes such as etching, ion implantation (doping), metallization, oxidation, chemical mechanical polishing, etc. (all intended to finish individual layers of the device). If several layers are required for the device, the entire procedure or a variant thereof is repeated for each layer. Finally, there are devices present at each target portion on the substrate. These devices are then separated from each other by techniques such as dicing or sawing, and as a result, it is possible to attach individual devices onto a carrier, connect them to pins, etc.

[0005]

[0005] Thus, manufacturing a device such as a semiconductor device typically involves processing a substrate (e.g., a semiconductor wafer) using several manufacturing processes to form various features and multiple layers of the device. Such layers and features are typically fabricated and processed using, for example, deposition, lithography, etching, chemical mechanical polishing, and ion implantation. Multiple devices can be fabricated on multiple dies on the substrate and then separated into individual devices. This device manufacturing process can be regarded as a patterning process. The patterning process includes a patterning step of transferring a pattern on a patterning device to a substrate, such as optical lithography and / or nanoimprint lithography using the patterning device in a lithography apparatus, and typically, but optionally, includes one or more related pattern processing steps such as resist development by a development device, baking of the substrate using a baking tool, etching using the pattern using an etching device, etc.

[0006] As described above, lithography is a central step in the manufacture of devices such as ICs, where the patterns formed on a substrate define the functional elements of devices such as microprocessors, memory chips, etc. Similar lithography techniques are also used in the formation of flat panel displays, microelectromechanical systems (MEMS), and other devices.

[0007]

[0007] As semiconductor manufacturing processes continue to advance, while the dimensions of functional elements are continuously decreasing, the amount of functional elements such as transistors per device has been steadily increasing over the decades according to a trend called "Moore's Law". In the current state of the art, the layers of a device are manufactured using a lithography projection apparatus that projects a design layout onto a substrate using illumination from a deep ultraviolet light source to create individual functional elements having dimensions far below 100 nm (i.e., less than half the wavelength of the radiation from the illumination source (e.g., a 193 nm illumination source)).

[0008]

[0008] This process, in which features having dimensions below the classical limit resolution of a lithographic projection apparatus are printed, may be referred to as low-k1 lithography according to the resolution formula CD = k1×λ / NA, where λ is the wavelength of the radiation used (e.g., 248 nm or 193 nm), NA is the numerical aperture of the projection optics in the lithographic projection apparatus, CD is the "critical dimension" (generally, the smallest feature size printed), and k1 is an empirical resolution coefficient. Generally, the smaller k1 is, the more difficult it becomes to reproduce on the substrate a pattern that closely resembles the shape and dimensions planned by the designer to achieve a particular electrical functionality and performance. To overcome these difficulties, state-of-the-art fine-tuning steps are applied to the lithographic projection apparatus, the design layout, or the patterning device. These include, for example, but are not limited to, optimization of the NA and the optical coherence setting, customized illumination schemes, use of phase-shifting patterning devices, optical proximity effect correction (OPC, sometimes also referred to as "optical and process correction") in the design layout, or other methods generally defined as "resolution enhancement techniques" (RET). As used herein, the term "projection optics" is to be broadly construed to encompass various types of optical systems, including, for example, refractive optical systems, reflective optical systems, apertures, and catadioptric optical systems. The term "projection optics" may include components that operate according to any of these design types, either collectively or individually, to direct, shape, or control the projection beam of radiation. The term "projection optics" may include any optical component within the lithographic projection apparatus, regardless of where the optical component is located on the optical path of the lithographic projection apparatus. The projection optics may include optical components for shaping, conditioning, and / or projecting the radiation before the radiation from the source passes through the patterning device and / or optical components for shaping, conditioning, and / or projecting the radiation after the radiation has passed through the patterning device. The projection optics generally excludes the source and the patterning device.

Summary of the Invention

[0009]

[0009] Methods, apparatuses, and software for determining a pupil for optimizing a radiation source and / or mask used in a lithography manufacturing and patterning process are disclosed. In one aspect, determining a first pupil having a central obscuration (CO), determining a diffraction order (DO) based on a target design and a mask model, determining a first diffraction pattern (DP) based on the DO and the first pupil, wherein the first DP includes overlapping regions of diffracted light, determining a second DP based on the DO and the first pupil, and determining an initial pupil based on the first DP and the second DP, wherein the initial pupil includes at least some of the overlapping regions, are included in a method for determining a radiation source for a lithography process.

[0010]

[0010] In some variations, the method may include performing a radiation source-mask optimization (SMO) initialized with the initial pupil. The initial pupil may not be able to include all of the diffracted light in the CO. The SMO may be performed under the constraint that any pupil obtained as a result of the SMO does not include the CO.

[0011]

[0011] In other variations, the first pupil may be determined for a lithography system having a numerical aperture of at least 0.45 for an isotropic system with a chief ray angle (CRAO) of 9 or less. The first pupil may be determined for a lithography system having a numerical aperture of at least 0.5 for an anamorphic (4×8) lithography system.

[0012]

[0012] In still other variations, the central obscuration may be circular, oval, or rectangular. The mask model may be a thick film mask model.

[0013]

[0013] In some variants, the DO may include the first-order diffracted light at the DO peak position closest to the zero-order DO peak position. The DO may include the closest first-order diffracted light at the DO peak position orthogonal to the zero-order DO peak position. The method may include determining the DO peak position based on local peaks of the DO array, where the DO is determined based on the DO peak position. The amplitude of the DO may be based on the sum of all amplitudes in the corresponding local DO area. In other variants, the initial pupil may be included within the sigma of -NA to +NA.

[0014]

[0014] In other variants, the method may include discretizing the DO and using a first pupil with discrete amplitudes to generate a second DP with discretized amplitudes. The discrete amplitudes of the DO and the first pupil may each be set to 1. The first DP may indicate the number of overlapping diffraction beams. The initial pupil may be determined based on the degree of overlap in the overlapping region of the first DP.

[0015]

[0015] In yet other variants, the method may also include generating a normalized DP based on the degree of overlap exceeding a threshold, where the overlapping region exceeding the threshold of the degree of overlap is set to have a value of 1 and all other regions in the normalized DP are set to have a value of 0, and multiplying the normalized DP by the second DP to generate the initial pupil.

[0016]

[0016] In some variants, the initial pupil may be determined based on the highest degree of overlap in the overlapping region of the first DP. The method may include determining the DO amplitude of the DO, where the initial pupil is filled when the sum of the amplitudes of the first DP exceeds the threshold of the overlapping diffraction pattern.

[0017]

[0017] In other variations, the method may include determining an overlapping region of the initial pupil and, if the region with the most overlap alone meets or exceeds the pupil filling rate threshold, generating an initial pupil that includes only the region with the most overlap, and, if the initial pupil does not meet or exceed the pupil filling rate threshold, repeatedly adding the next most overlapping region to the initial pupil.

[0018]

[0018] In some embodiments, there may be a non - transitory computer - readable medium storing instructions for determining a pupil for the optimization of a radiation source and / or mask used in a lithography manufacturing and patterning process, wherein when the instructions are executed by a computer having at least one programmable processor, the instructions cause an operation including any of the operations in the above - described method embodiments.

[0019]

[0019] In some embodiments, there may be a system for determining a pupil for the optimization of a radiation source and / or mask used in a lithography manufacturing and patterning process, the system comprising at least one programmable processor and a non - transitory computer - readable medium storing instructions that, when executed by a computer having at least one programmable processor, cause an operation including any of the operations in the above - described method embodiments.

[0020]

[0020] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate specific aspects of the subject matter disclosed herein and, together with the description, help to explain some of the principles associated with the disclosed implementations. The drawings are as follows.

Brief Description of the Drawings

[0021]

Figure 1

[0021] A block diagram of various subsystems of a lithography projection apparatus according to an embodiment of the present disclosure is shown.

Figure 2

[0022] An exemplary flowchart for simulating lithography in a lithographic projection apparatus, according to one embodiment of the present disclosure, is shown.

Figure 3

[0023] An exemplary portion of a lithographic projection apparatus having an unobscured pupil, according to one embodiment of the present disclosure, is shown.

Figure 4

[0024] An exemplary portion of a lithographic projection apparatus having a pupil with central obscuration, according to one embodiment of the present disclosure, is shown.

Figure 5A

[0025] An exemplary process flow diagram for determining a radiation source for a lithography process, according to one embodiment of the present disclosure, is shown.

Figure 5B

[0026] An exemplary process flow diagram for utilizing a diffraction pattern when initializing SMO, according to one embodiment of the present disclosure, is shown.

Figure 6

[0027] An exemplary first pupil having central obscuration, according to one embodiment of the present disclosure, is shown.

Figure 7

[0028] An exemplary diffraction order map, according to one embodiment of the present disclosure, is shown.

Figure 8

[0029] An exemplary second diffraction pattern, according to one embodiment of the present disclosure, is shown.

Figure 9

[0030] An exemplary first diffraction pattern in a region of interest, according to one embodiment of the present disclosure, is shown.

Figure 10

[0031] Determining an exemplary initial pupil based on an overlapping region in a first diffraction pattern, according to one embodiment of the present disclosure, is shown.

Figure 11

[0032] Determining an exemplary initial pupil based on pupil fill factor, according to one embodiment of the present disclosure, is shown.

Figure 12

[0033] An exemplary division of a radiation source and an initial pupil based on the angle of incidence of light on a mask, according to one embodiment of the present disclosure, is shown.

Figure 13

[0034] A block diagram of an example computer system according to an embodiment of the present disclosure.

Figure 14

[0035] A schematic diagram of a lithographic projection apparatus according to an embodiment of the present disclosure.

Figure 15

[0036] A schematic diagram of another lithographic projection apparatus according to an embodiment of the present disclosure.

Figure 16

[0037] A detailed view of a lithographic projection apparatus according to an embodiment of the present disclosure.

Figure 17

[0038] A detailed view of a source collector module of a lithographic projection apparatus according to an embodiment of the present disclosure.

DETAILED DESCRIPTION OF THE INVENTION

[0022]

[0039] Although specific reference may be made in this specification to the manufacture of integrated circuits, it should be clearly understood that the description herein has many other possible applications. For example, it may be used in the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, liquid crystal display panels, thin film magnetic heads, and the like. Those skilled in the art will recognize that in the context of such alternative applications, the use of the terms "reticle", "wafer", or "die" in this specification should be considered synonymous with the more general terms "mask", "substrate", and "target portion", respectively.

[0023]

[0040] In this specification, the terms "radiation" and "beam" are used to encompass all types of electromagnetic radiation including ultraviolet light (e.g., having a wavelength of 365, 248, 193, 157, or 126 nm) and EUV (extreme ultraviolet light, e.g., having a wavelength in the range of about 5 - 100 nm).

[0024]

[0041] The patterning device can include or form one or more design layouts. The design layout can be generated using a CAD (Computer-Aided Design) program, and this process is often referred to as EDA (Electronic Design Automation). Most CAD programs follow a set of predefined design rules to generate the functional design layout / patterning device. These rules are set by the processing and design limitations. For example, the design rules define the space tolerances between devices (such as gates, capacitors, etc.) or interconnect lines, which is done to ensure that those devices or lines do not interact with each other in an undesirable manner. One or more of the limits of the design rules can be referred to as the "critical dimension" (CD). The critical dimension of a device can be defined as the minimum width of a line or hole, or the minimum space between two lines or two holes. Thus, the CD determines the overall size and density of the device being designed. Naturally, one of the goals of device manufacturing is to faithfully reproduce the original design intent on the substrate (through the patterning device).

[0025]

[0042] As used herein, the terms "mask" or "patterning device" can be broadly interpreted to refer to a general patterning device that can be used to provide a patterned cross-section corresponding to the pattern that will be generated on the target portion of the substrate for an incoming radiation beam, and the term "light valve" may also be used in this context. In addition to conventional masks (transmission or reflection; binary, phase shift, hybrid, etc.), examples of other such patterning devices include programmable mirror arrays and programmable LCD arrays.

[0026]

[0043] An example of a programmable mirror array can be a matrix addressable surface having a viscoelastic control layer and a reflective surface. The basic principle behind such an apparatus is that the addressed areas of the reflective surface, for example, reflect the incident radiation as diffracted radiation, and the non-addressed areas reflect the incident radiation as non-diffracted radiation. Using an appropriate filter, the non-diffracted radiation can be removed from the reflected beam, leaving only the diffracted radiation, and in this way, the beam is patterned according to the addressing pattern of the matrix addressable surface. The required matrix addressing can be performed using appropriate electronic means.

[0027]

[0044] An example of a programmable LCD array is given in U.S. Patent No. 5,229,872, which is incorporated herein by reference.

[0028]

[0045] FIG. 1 shows a block diagram of various subsystems of a lithographic projection apparatus 10A according to an embodiment of the present disclosure. The main components are a radiation source 12A, which may be a deep ultraviolet excimer laser source or another type of source such as an extreme ultraviolet (EUV) source (as described above, the lithographic projection apparatus itself need not have a radiation source), and an illumination optical system that may include, for example, optical systems 14A, 16Aa, and 16Ab that define partial coherence (represented by sigma) and shape the radiation from the source 12A, a patterning device 18A, and a projection optical system 16Ac that projects an image of the patterning device pattern onto a substrate plane 22A. An adjustable filter or aperture 20A in the pupil plane of the projection optical system can limit the range of beam angles that impinge on the substrate plane 22A, where the maximum possible angle is defined by the numerical aperture NA = nsin(Θ max ), where n is the refractive index of the medium between the substrate and the last element of the projection optical system, and Θ max is the maximum angle of the beam emerging from the projection optical system that can still impinge on the substrate plane 22A.

[0029]

[0046] In a lithographic projection apparatus, a source provides illumination (i.e., radiation) to a patterning device, and a projection optical system guides and shapes the illumination onto a substrate via the patterning device. The projection optical system may include at least some of components 14A, 16Aa, 16Ab, and 16Ac. A spatial image (AI) is the radiation intensity distribution at the substrate level. A resist image can be calculated from the spatial image using a resist model, an example of which can be found in US Patent Application Publication No. 2009-0157630, the disclosure of which is incorporated herein by reference in its entirety. The resist model relates only to the characteristics of the resist layer (e.g., the effects of exposure, post-exposure bake (PEB), and chemical processes occurring during development). The optical characteristics of the lithographic projection apparatus (e.g., the characteristics of the illumination, patterning device, and projection optical system) determine the spatial image and can be defined by an optical model. Since the patterning device used in the lithographic projection apparatus can be changed, it is desirable to decouple the optical characteristics of the patterning device from the optical characteristics of the remainder of the lithographic projection apparatus, including at least the source and the projection optical system. Details of techniques and models used to convert a design layout into various lithographic images (e.g., spatial images, resist images, etc.), apply OPC using these techniques and models, and evaluate performance (e.g., from the perspective of the process window) are described in US Patent Application Publication Nos. 2008-0301620, 2007-0050749, 2007-0031745, 2008-0309897, 2010-0162197, and 2010-0180251, the disclosures of each of which are incorporated herein by reference in their entireties.

[0030]

[0047] One way to understand the lithography process is to understand the interaction between radiation and the patterning device. The electromagnetic field of the radiation after it passes through the patterning device can be determined from the electromagnetic field of the radiation before it reaches the patterning device and a function that characterizes the interaction. This function can be called the mask transmission function (the mask transmission function can be used to describe the interaction by a transmissive patterning device and / or a reflective patterning device).

[0031]

[0048] The mask transmission function can have various different forms. One form is binary. The binary mask transmission function has either of two values (e.g., zero and a positive constant) at any position on the patterning device. The mask transmission function in binary form can be called a binary mask. Another form is continuous. That is, the transmittance (or reflectance) of the patterning device is a continuous function of the position on the patterning device. The phase of the transmission (or reflection) can also be a continuous function of the position on the patterning device. The mask transmission function in continuous form can be called a continuous tone mask or a continuous transmission mask (CTM). For example, a CTM may be represented as a pixelated image, and each pixel can be assigned a value that is not one of the two values 0 or 1, but a value between 0 and 1 (e.g., 0.1, 0.2, 0.3, etc.). In one embodiment, the CTM may be a pixelated grayscale image, and each pixel has a value (e.g., a value within the range [-255, 255], a normalized value within the range [0, 1] or [-1, 1], or a value within another suitable range).

[0032]

[0049] To simplify the determination of the interaction between radiation and a patterning device, the thin-film mask approximation, also known as Kirchhoff's boundary condition, is widely used. In the thin-film mask approximation, it is assumed that the thickness of the structures on the patterning device is very small compared to the wavelength, and the width of the structures on the mask is very large compared to the wavelength. Thus, in the thin-film mask approximation, it is assumed that the electromagnetic field after the patterning device is the multiplication of the incident electromagnetic field and the mask transmission function. However, since the lithography process uses radiation with an increasingly shorter wavelength and the structures on the patterning device are getting smaller, the assumptions in the thin-film mask approximation may break down. For example, the interaction between radiation and the structures (e.g., the edges between the top surface and the sidewalls) may become significant due to the finite thickness (the "mask 3D effect" or "M3D"). By including this scattering in the mask transmission function, the mask transmission function may be able to better capture the interaction between radiation and the patterning device. The mask transmission function under the thin-film mask approximation may be referred to as the thin-film mask transmission function. The mask transmission function including M3D may be referred to as the M3D mask transmission function.

[0033]

[0050] According to one embodiment of the present disclosure, one or more images can be generated. The image includes various types of signals that can be characterized by pixel values or intensity values of each pixel. As can be understood by those skilled in the art, depending on the relative values of the pixels within the image, the signals can be referred to as, for example, weak signals or strong signals. The terms "strong" and "weak" are relative terms based on the intensity values of the pixels within the image, and the specific values of the intensity do not limit the scope of the present disclosure. In one embodiment, strong signals and weak signals can be identified based on a selected threshold value. In one embodiment, the threshold value can be fixed (e.g., the midpoint between the highest intensity and the lowest intensity of the pixels within the image). In one embodiment, a strong signal can refer to a signal having a value greater than the average signal value of the entire image, and a weak signal can refer to a signal having a value less than the average signal value. In one embodiment, the relative intensity value can be based on a percentage. For example, a weak signal can be a signal having an intensity less than 50% of the highest intensity of the pixels within the image (e.g., the pixels corresponding to the target pattern can be regarded as the pixels having the highest intensity). Further, each pixel within the image can be regarded as a variable. According to this embodiment, a derivative or partial derivative can be determined for each pixel within the image, and the value of each pixel can be determined or changed according to an evaluation based on a cost function and / or a calculation of the cost function based on a gradient. For example, a CTM image can include pixels, and each pixel is a variable that can take any real value.

[0034]

[0051] Figure 2 shows an exemplary flowchart for simulating lithography in a lithographic projection apparatus according to an embodiment of the present disclosure. The radiation source model 31 represents the optical characteristics of the radiation source (including the radiation intensity distribution and / or phase distribution). The projection optical system model 32 represents the optical characteristics of the projection optical system (including changes to the radiation intensity distribution and / or phase distribution produced by the projection optical system). The design layout model 35 represents the optical characteristics of the design layout (which is a representation of the arrangement of features on or formed by the patterning device) (including changes to the radiation intensity distribution and / or phase distribution produced by the design layout 33). The aerial image 36 can be simulated using the design layout model 35, the projection optical system model 32, and the design layout model 35. The resist image 38 can be simulated from the aerial image 36 using the resist model 37. For example, the simulation of lithography can predict the contours and CDs of the resist image.

[0035]

[0052] More specifically, it should be noted that the radiation source model 31 can represent the optical characteristics of the radiation source, including, but not limited to, numerical aperture setting, illumination sigma (σ) setting, and any particular illumination shape (e.g., off-axis radiation sources such as annular, quadrupole, dipole, etc.). The projection optical system model 32 can represent the optical characteristics of the projection optical system, including aberration, distortion, one or more refractive indices, one or more physical sizes, one or more physical dimensions, etc. The design layout model 35 can represent one or more physical characteristics of a physical patterning device, such as that described in U.S. Patent No. 7,587,704, which is incorporated herein by reference in its entirety. The purpose of the simulation is, for example, to accurately predict edge placement, aerial image intensity gradients, and / or CDs, which can then be compared to the intended design. The intended design is generally defined as a pre-OPC design layout that can be provided in a standard digital file format such as GDSII, or OASIS, or other file formats.

[0036]

[0053] One or more portions (which are referred to as "clips") can be identified from this design layout. In one embodiment, a set of clips representing complex patterns within the design layout is extracted (any number of clips can be used, but typically about 50 to 1000 clips). These patterns or clips represent small portions of the design (i.e., circuits, cells, or patterns), and more specifically, clips typically represent small portions that require special attention and / or verification. That is, a clip can be a portion of the design layout, or can be similar, or can have similar behavior to a portion of the design layout where one or more critical features are identified by experience (including clips provided by customers), by trial and error, or by performing full-chip simulations. A clip can include one or more test patterns or gauge patterns.

[0037]

[0054] An initial set of larger clips may be provided empirically by a customer based on one or more known critical feature areas within a design layout that require specific image optimization. Alternatively, in another embodiment, the initial set of larger clips may be extracted from the entire design layout by using some kind of automated (such as machine vision) or manual algorithm that identifies one or more critical feature areas.

[0038]

[0055] In a lithographic projection apparatus, as an example, the cost function can be expressed as follows.

Number

[0039]

[0056] The cost function can represent any one or more suitable characteristics of the lithographic projection apparatus, the lithographic process, or the substrate, such as focus, CD, image shift, image distortion, image rotation, stochastic variation, throughput, local CD variation, process window, interlayer characteristics, or a combination thereof. In one embodiment, the design variables (z 1 , z 2 , …, z N) includes one or more selected from the dose amount, the global bias of the patterning device, and / or the shape of the illumination. Since it is often the resist image that determines the pattern on the substrate, the cost function may include a function representing one or more characteristics of the resist image. For example, f p (z 1 、z 2 、…、z N ) may simply be the distance between a point in the resist image and the intended position of that point (i.e., the edge placement error EPE p (z 1 、z 2 、…、z N ). The design variables may include any adjustable parameters such as adjustable parameters of the radiation source, patterning device, projection optical system, dose amount, focus, etc.

[0040]

[0057] The lithographic apparatus may include components collectively referred to as "wavefront manipulators" that can be used to adjust the shape and intensity distribution and / or phase shift of the radiation beam. In one embodiment, the lithographic apparatus can adjust the wavefront and intensity distribution at any location along the optical path of the lithographic projection apparatus, such as in front of the patterning device, near the pupil plane, near the image plane, and / or near the focal plane. The wavefront manipulator can be used to correct or compensate for specific distortions of the wavefront and intensity distribution and / or phase shift caused, for example, by temperature variations of the radiation source, patterning device, lithographic projection apparatus, and thermal expansion of components of the lithographic projection apparatus. By adjusting the wavefront and intensity distribution and / or phase shift, the value of the characteristic represented by the cost function can be changed. Such changes can be simulated from the model or actually measured. The design variables may include the parameters of the wavefront manipulator.

[0041]

[0058] There may be constraints on the design variables, which are (z 1 、z 2 、…、z N) can be expressed as ∈Z, where Z is a set of possible values of the design variables. One of the possible constraints on the design variables may be imposed by the desired throughput of the lithographic projection apparatus. Without such a constraint imposed by the desired throughput, optimization may generate a set of unrealistic design variable values. For example, if the dose amount is a design variable, without such a constraint, optimization may generate a dose amount value that makes the throughput economically impossible. However, the usefulness of the constraint should not be misinterpreted. For example, the throughput may be affected by the pupil fill factor. Depending on the illumination design, a low pupil fill factor may result in wasted radiation and a decrease in throughput. The throughput may also be affected by the chemical properties of the resist. A more time-consuming resist (e.g., a resist that requires more radiation to be properly exposed) will result in a decrease in throughput.

[0042]

[0059] As used herein, the term "patterning process" means a process of creating an etched substrate by applying a specified pattern of light as part of a lithography process.

[0043]

[0060] As used herein, the term "target pattern" means the ideal pattern to be etched on the substrate.

[0044]

[0061] As used herein, the term "printed pattern" means the physical pattern on the substrate formed based on the design layout. The printed pattern can include, for example, vias, contact holes, troughs, channels, depressions, edges, or other two-dimensional and three-dimensional features generated from the lithography process.

[0045]

[0062] As used herein, the term "process model" means a model that includes one or more models that simulate a patterning process. For example, a process model can include an optical model (e.g., one that models a lens system / projection system used for light delivery in a lithography process and models the final optical image of light reaching a photoresist), a mask model, a resist model (e.g., one that models the physical effects of a resist, such as chemical effects due to light), an OPC model (e.g., one that can be used in creating a design layout and can include sub-resolution assist features (SRAFs), etc.), and an imaging device model (e.g., one that models what an imaging device can image from a printed pattern), and can include any combination thereof.

[0046]

[0063] As used herein, the term "imaging device" means any number or combination of devices, associated computer hardware, and software that can be configured to generate an image of a target, such as a printed pattern or a portion thereof. Non-limiting examples of imaging devices include a scanning electron microscope (SEM), an X-ray device, and the like.

[0047]

[0064] FIG. 3 shows an exemplary portion of a lithography projection apparatus having an unshaded pupil, according to one embodiment of the present disclosure.

[0048]

[0065] In a patterning process, light from a lithography radiation source (e.g., UV, EUV, etc.) can be directed to and / or through a number of optical components such as lenses, masks, mirrors, etc., and ultimately reach the substrate (e.g., wafer) to be processed. FIG. 3 shows a portion of a lithography system comprising a mask 310 that receives light 320 from a radiation source (not shown; however, radiation source 12A of FIG. 1 is an example). The light 320 is directed through a series of optical elements such as a mirror 330 and ultimately reaches the substrate 340. The enlarged view 350 on the right shows one embodiment showing the angle 360 between the incident light rays filling two of the mirrors 330 and the last mirror 332. Such an angle can be related to the numerical aperture (NA) of the system. Also shown are the pupil plane 370 and the simply depicted pupil 380. As is understood in the art, the pupil represents the pattern of light at a particular position along the optical axis. This pattern can be at the physical pupil position if a pupil exists in a given system, but generally can be at any position.

[0049]

[0066] In the illustrated example, since the pupil 380 is not blocked, in theory, light can enter any part of the pupil. Such an unblocked pupil can function in a relatively low NA system, but a different pupil may be required in a higher NA system. When referring to high NA systems and low NA systems in the present disclosure, this is merely for the purpose of distinguishing between them. Thus, such designations do not imply or require any particular value of NA. In some embodiments, a low NA system can have an NA of about 0.33 and a high NA system can have an NA of about 0.5.

[0050]

[0067] FIG. 4 shows an exemplary portion of a lithography projection apparatus having a pupil with central obscuration according to an embodiment of the present disclosure.

[0051]

[0068] High-NA systems, such as the example shown in FIG. 4, can provide numerous technical advantages, including enhancing the resolution of the light pattern reaching the substrate. Such high-NA systems can have optical components (e.g., mirror 430) and configurations that are quite different from those of low-NA systems. This can be seen in the example of FIG. 4, where, for example, the last mirror 432 is larger than the corresponding last mirror 332 in the low-NA system shown in FIG. 3. A technical challenge of EUV lithography is that EUV mirror coatings can accurately reflect light only at relatively small angles, and high-NA systems can exceed this. One solution is shown in FIG. 4, which is by the system having a central obscuration (CO) 482 in the pupil 480. One effect of the CO can be to reduce the angle of the light reaching the EUV mirror, thereby enabling the light to be accurately reflected. Thus, the disclosed high-NA projection optical system can enable a pupil having a CO that increases the system's transmittance due to the reduced angle.

[0052]

[0069] In some embodiments, the pupil can be determined for a lithography system having a numerical aperture of at least 0.45 for an isotropic system with a chief ray angle (CRAO) of 9 or less. In other embodiments, the pupil can be determined for a lithography system having a numerical aperture of at least 0.5 for an anamorphic (4×8) lithography system.

[0053]

[0070] FIG. 5A shows an exemplary process flow diagram for determining a radiation source for a lithography process according to one embodiment of the present disclosure.

[0054]

[0071] To determine an optimized system that can supply light to a substrate as needed, the system can be computationally optimized to determine an optimal combination of a radiation source, a mask, and optionally other aspects of the lithography system. Thereby, such a radiation source-mask optimization (SMO) can determine an optimal combination of the radiation source and the mask design, taking into account physical constraints of the optical system, the desired process window, etc. The pupil can be a factor in SMO, and the light in the pupil can include diffracted light of various orders that can be combined at the substrate. Accordingly, the present disclosure provides a method for determining an optimized aspect of a radiation source, a mask, or other aspects of the system for a lithography process. Although various aspects of the following method and other features of the present disclosure are discussed in more detail herein, in one embodiment shown by the diagram of FIG. 5A, the method may include, at 510, determining a first pupil having a central obscuration, as shown, for example, by the exemplary pupil 480 of FIG. 4. The method may include, at 520, determining a diffraction order (DO) based on a target design and a mask model. The DO can be used to determine how the pattern of diffracted light overlaps the first pupil 510. Next, the method is, at 530, determining a first diffraction pattern (DP) based on the DO and the first pupil, wherein the first DP includes an overlapping region of diffracted light, i.e., a region where the DO overlaps. Since the pupil represents the pattern of light at a position along the optical axis, the diffraction patterns described herein can represent the overlapping light that forms the pupil. At 540, the method may include determining a second DP based on the DO and the first pupil. The second DP may include information regarding the amplitude of the region of the second DP (e.g., the amplitude of the zero-order peak, the amplitude of the first-order peak, etc.). The method may also be, at 550, determining an initial pupil based on the first DP and the second DP, wherein the initial pupil includes at least some of the overlapping regions. The initial pupil can be generated by multiplying the first DP and the second DP.However, in other embodiments, some specific overlapping regions of the first DP can be extracted and normalized to form a normalized DP, and the second DP can be multiplied by the normalized DP to generate an initial pupil. In some embodiments, the initial pupil does not include any diffracted light in the central obscuration. As described in more detail herein, some embodiments may include requiring regions that overlap sufficiently to supply the necessary light. Also, some embodiments can benefit by forcing no light to be determined to be in the CO (e.g., by an SMO process).

[0055]

[0072] As used herein, the term "first" pupil refers to the pupil determined by the disclosed method but before being utilized by an SMO system. The term "initial" pupil refers to the pupil that can be provided to an SMO system and, in some embodiments, is used to initiate SMO. Such an "initial pupil" is generally determined from the "first pupil" as described herein.

[0056]

[0073] Also, as further described herein, some embodiments of the method may include performing source-mask optimization (SMO) initialized with the initial pupil at 552. Some optimizers find solutions where there is light in the CO, which may not be desirable for at least the reasons above, so in certain embodiments, SMO can be performed under the constraint that all pupils resulting from SMO do not include the CO.

[0057]

[0074] FIG. 5B shows an exemplary process flow diagram for utilizing a diffraction pattern when initializing SMO according to one embodiment of the present disclosure.

[0058]

[0075] In one embodiment, the flow for utilizing a diffraction pattern when determining the initial pupil of SMO can include the following, the details of which are further provided herein according to some of the above examples.

[0059]

[0076] The flow shown in FIG. 5B can start, for example, from a device pattern 560 having a predetermined pitch, CD, I. A mask model can be applied to the device pattern to generate a DO570 (see also FIG. 7, for example). Only the position of the central zero-order diffraction region and the first-order diffraction peak are shown in the DO570. The DO570 can be determined to have continuous (i.e., not discrete) amplitudes at various diffraction order peak positions. See also 520 in FIG. 5A.

[0060]

[0077] A first DP572 can be generated to show regions of overlapping diffraction orders. The first DP572 can be based on diffraction caused by a first pupil 576 having a CO. The amplitude of the first DP572 can be set to have discrete values such as integers as shown (see also FIG. 8, for example) to directly show the overlapping regions, but in some embodiments, the amplitude can be set to continuous values based on the determined amplitude (see also FIG. 7, for example). In some embodiments, a particular overlapping region can serve as the region utilized for the initial pupil in the SMO process. In such embodiments, a normalized DP574 can then be generated having, for example, a region with light normalized to a value of 1 and other regions to which a value of 0 is assigned (see also 1120 in FIG. 11), as will be described in more detail below. See also 530 in FIG. 5A.

[0061]

[0078] A second DP578 can be generated by convolving the DO570 with the first pupil 576 (see also FIGS. 6 and 8). In this embodiment, the second DP578 can be continuous (i.e., having a continuous amplitude from the continuous DO570 peak amplitudes). See also 510 and 540 in FIG. 5A.

[0062]

[0079] In one embodiment, the initial pupil 580 can be determined from a first DP 572 (used to generate a normalized DP 574) and a second DP 578. See also 550 in FIG. 5A. In some embodiments, this involves generating a normalized DP 574 based on a degree of overlap exceeding a threshold, where overlapping regions exceeding the threshold of the degree of overlap can be set to have a value of 1, and all other regions in the normalized DP 574 can be set to have a value of 0. Next, the normalized DP 574 can be multiplied by the second DP 578 to generate the initial pupil 580.

[0063]

[0080] Thus, the initial pupil 580 can have regions determined based on the discretization of the amplitude of the diffraction order, although the amplitude can be continuous. In other embodiments, such as those described in FIG. 8, the amplitude of the second DP 578 can also be discretized to provide an initial pupil with a discrete amplitude. Next, the initial pupil 580 is provided and the SMO process 590 can be initiated. See also 552 in FIG. 5A.

[0064]

[0081] In some embodiments, such as to satisfy the pupil filling ratio constraint during SMO, other regions of the second DP 578, such as the most overlapping regions, can be included (see also 1150 in FIG. 11 for example). This is shown by an exemplary second normalized DP 582, depicting a more filled pupil (compared to the normalized DP 574).

[0065]

[0082] FIG. 6 shows an exemplary first pupil with a central obscuration, according to one embodiment of the present disclosure.

[0066]

[0083] The above exemplary method (and throughout the present disclosure, e.g., at 510 of the method shown in FIG. 5A) may determine a pupil 610 that includes a central obscuration 620. Next, the pupil 610 may serve as a basis for pupil determination based on the diffraction orders described herein. The pupil 610 may be a pupil from a library of pupils or a pupil generated from a pupil design input by a user. In general, the central obscuration can be of any shape. In the examples shown herein, embodiments are shown where the central obscuration is circular. In other embodiments, the central obscuration can be, for example, oval, rectangular, elliptical, polygonal, or irregular in shape.

[0067]

[0084] FIG. 7 shows an exemplary diffraction order map according to one embodiment of the present disclosure.

[0068]

[0085] The above method describes determining a diffraction order (DO) 700 at 520 based on a target design and a mask model. In some embodiments, the mask model can also be a thick film mask model, such as one that can account for light interacting at various depths in the mask. Since light diffracts from different depths and positions in the mask, the position of the diffraction order in the pupil can be different. FIG. 7 shows the position of the diffraction order as a function of σ.

Num

[0069]

[0086] A zero-order diffracted light 710 (solid circle) having a zero-order DO peak position 712 is shown at the center of the plot. Additionally, other diffraction orders and their respective positions can be considered when determining the diffraction pattern contributing to the light in the pupil. The DO can also include a first-order diffracted light 720 (dashed circle) at a first-order DO peak position 722 that is closest to the zero-order DO peak position 712. The DO can also include a first-order diffracted light 720 that is closest at a DO peak position 732 that is orthogonal to the zero-order DO peak position. As further discussed herein, it can be seen that the light within σ = 1 can include overlapping patterns of diffracted light.

[0070]

[0087] In some embodiments, various methods may also include determining the DO peak position based on local peaks of the DO array, where the DO is determined based on the DO peak position in the local DO area 740. The DO array is any data representation of the diffraction pattern described herein and can be, for example, a 2D array of values stored in a computer memory. A portion of an exemplary DO array is depicted in the inset figure, where, for example, the grayscale levels represent the amplitudes of the diffraction peaks, which can have a complex 2D pattern. The pixel representation of the diffraction amplitude can be used to assign a specific amplitude to a specific pixel in the DO representation. Thus, a pixel 742 having the maximum DO (depicted by the darkest pixel shown in the inset figure) can be selected to be the DO peak position (indicated by the white crosshairs). The local DO area utilized can include any range around the position where the DO peak position is expected. In some embodiments, the amplitude of the DO can be based on the sum of all amplitudes in the corresponding local DO area, the amplitude of the local DO peak, etc. For example, in various embodiments, the local DO area can include ±0.03s, ±0.05s, etc. centered on the DO peak position D.

[0071]

[0088] FIG. 8 shows an exemplary second diffraction pattern according to an embodiment of the present disclosure.

[0072]

[0089] In some embodiments, the disclosed method may include convolving the initial pupil 610 with the DO 700 to determine the second DP 800 shown in the figure. Throughout the second DP 800, the zero-order diffraction 710 and a number of first-order diffractions 720 overlap in many places to generate a second DP 800 having various amplitudes. As an example, the amplitude of the light in the second DP 800 is most overlapping at position 810. In the area immediately adjacent to position 810, three diffraction patterns overlap, for example.

[0073]

[0090] As shown in the exemplary embodiment of FIG. 8, some of the disclosed methods may include discretizing the DO700 and using a first pupil 610 with discrete amplitudes to generate a second DP800 having a discretized amplitude. As an example, the discrete amplitudes of the DO and the first pupil may each be set to 1. This is depicted on a scale, with the arrows indicating that some regions of the second DP800 have the full amplitude. The act of discretizing the amplitudes of the first pupil 610 and the DO700 may provide several technical advantages. For example, thanks to such an act, the system can be made to perform integer operations instead of floating-point operations, thereby shortening the calculation time. Also, since the DO has a discrete nature (the DO can be regarded as discrete points well separated in sigma space), the discretization of the DO image is easy and convenient. Once the discretized DO is obtained, the discretized second DP800 can be formed accordingly and used, for example, for accurate calculation of the radiation source in the region of interest without relying on discovery threshold binarization and dilation, such as those disclosed in International Application PCT / EP2020 / 054545. This can be synergistically combined with an implementation where the SMO process converges more quickly to an accurate solution and reduces the computational overhead compared to conventional methods, due to the fact that the pupil design is not an arbitrary design but is derived by diffraction effects. Thus, in some embodiments, various methods may include determining a discretized DO by discretizing the DO amplitude for the DO700. The method may also include determining an initial pupil discretized by setting the pupil amplitude of the first pupil to a discrete value. Next, using the discretized DO and the discretized first pupil, the second DP800 can be determined. Setting the amplitude to 1 is one example of discretization, but any value can be selected, such as 0.5, 1.5, 2, etc.

[0074]

[0091] FIG. 9 shows an exemplary second diffraction pattern in a region of interest according to an embodiment of the present disclosure.

[0075]

[0092] In the previous drawing (e.g., FIG. 8), overlapping second DPs 800 covering a range of ±2NA in the sigma space were shown. In some embodiments, the region of interest 900 of the initial pupil may be included within the sigma of -NA to +NA. In other embodiments, the second DP may be determined over any other range that can be utilized by the SMO system, such as ±1.5NA, ±0.5NA, etc.

[0076]

[0093] FIG. 10 shows determining an exemplary pupil based on the overlapping regions of the DO in the first diffraction pattern, according to one embodiment of the present disclosure.

[0077]

[0094] As shown in the region of interest 900, the first DP (e.g., the first DP 572) can indicate the number of overlapping diffraction beams, which can serve as a measure of the light available for use in the pupil. In particular, the initial pupil can be determined based on the degree of overlap in the overlapping region of the first DP. The "degree of overlap" can be a numerical value (e.g., 4, 3, 2, etc.) as described above, or a relative value (e.g., the highest, the next highest, etc.). In some embodiments, the initial pupil can be determined based on the highest degree of overlap in the overlapping region of the first DP. In this example, based on the region of interest 900, the pupil obtains light only in the region where the amplitude is 4, i.e., the region with the highest degree of overlap in the discretized example.

[0078]

[0095] Another embodiment is shown in FIG. 10, where the pupil 1000 includes regions having a degree of overlap exceeding a threshold. For example, such a method can include determining the DO amplitude of the DO, and when the sum of the amplitudes of the first DP exceeds the threshold of the overlapping diffraction pattern, the initial pupil can be filled. In this example, the pupil 1000 can include not only the position 810 (having an amplitude of 4) but also the adjacent region 1010 (having an amplitude of 3).

[0079]

[0096] FIG. 11 shows determining an exemplary initial pupil based on the pupil filling rate, according to one embodiment of the present disclosure.

[0080]

[0097] In related embodiments, the determination of the area included in the pupil can be based, in this specification, on the pupil filling rate defined as the integral intensity of the fill light divided by the maximum pupil intensity and then multiplied by the total number of pixels of the pupil. When all of the amplitudes of the points of the filled pupil are the same, the pupil filling rate is generally the ratio of the pupil that is filled with light.

[0081]

[0098] A method for such an embodiment is shown as a process flow diagram in FIG. 11. At 1110, the method can start with a pupil, for example, a first pupil 610.

[0082]

[0099] At 1120, the method can include determining an overlapping region of the initial pupil based on the first DP. Next, the method can include generating an initial pupil to include only the most overlapping region if including only the most overlapping region meets or exceeds a pupil filling rate threshold. Determining the pupil filling rate can include calculating the area or sub - area covered by the pupil and comparing this to a desired pupil filling rate (pupil filling rate threshold).

[0083]

[0100] At 1130, a comparison can be performed to check whether the initial pupil has a pupil filling rate that meets or exceeds the pupil filling rate threshold. If so, at 1140, an initial pupil can be generated using a selected portion of the second DP.

[0084]

[0101] As shown at 1150, the method can repeatedly add the next most overlapping region to the pupil if the initial pupil does not meet or exceed the pupil filling rate threshold (e.g., adding the adjacent region 1010 of amplitude 3 as shown in the inset). A subsequent comparison is shown at 1160, and further regions of the first DP are added to the pupil until the pupil filling rate threshold is met or exceeded.

[0085]

[0102] FIG. 12 shows an exemplary division of a radiation source and a pupil based on the angle of incidence of light on a mask according to an embodiment of the present disclosure.

[0086]

[0103] Since the radiation source is not a point radiation source (i.e., it has a finite size), the light reaching the mask from the radiation source reaches at different incident angles. Therefore, during SMO, the accuracy of the spatial image obtained from the mask and a given pupil can be improved by utilizing the small incident angles obtained from the division. When dividing the radiation source light into different incident angles, this can be represented by dividing the pupil into corresponding sections in the sigma space. One example of this is shown in FIG. 12, where it is shown that the pupil 1200 is divided into four sections 1210a, 1210b, 1210c, and 1210d. Each of the sections can have some light therein based on the determined pupil as described by any of the embodiments herein. As shown in FIG. 12, each region of the pupil can be decomposed into individual pupils (1220a - d) having only the light present in a specific section (1210a - d) (at 1220). Next, the divided pupils can be processed individually by the SMO process.

[0087]

[0104] Using the mask 1230 at stages 1230a - d having the corresponding pupils 1210a - d, the corresponding mask transmission images 1240 can be generated. Using the divided radiation source model (e.g., a model that simulates the light from the radiation source divided as described above), an appropriate projection optical system model 32, and an appropriate design layout model 35 (e.g., see FIG. 2), a partial spatial image 1250 can be simulated. Next, the partial spatial images can be incoherently added at 1260 to obtain the spatial image 1270 generated by the entire radiation source pupil (i.e., the intensity of the partial spatial images added without interference effects). A similar process is described in U.S. Patent Application Publication No. 2018 - 0120709A1, the content of which is incorporated herein by reference in its entirety.

[0088]

[0105] FIG. 13 is a block diagram of an exemplary computer system CS according to an embodiment of the present disclosure.

[0089]

[0106] Computer system CS includes a bus BS or other communication mechanism for communicating information, and a processor PRO (or multiple processors) coupled to the bus BS for processing information. The computer system CS also includes a main memory MM coupled to the bus BS for storing information and instructions executed by the processor PRO, such as random access memory (RAM) or other dynamic storage devices. The main memory MM may also be used to store temporary variables or other intermediate information during the execution of instructions executed by the processor PRO. The computer system CS further includes a read-only memory (ROM) or other static storage device coupled to the bus BS for storing static information and instructions for the processor PRO. A storage device SD, such as a magnetic disk or optical disk for storing information and instructions, is provided and coupled to the bus BS.

[0090]

[0107] The computer system CS may be coupled via the bus BS to a display DS, such as a cathode ray tube (CRT), flat panel, or touch panel display, for displaying information to a computer user. An input device ID including alphanumeric and other keys is coupled to the bus BS for communicating information and command selections to the processor PRO. Another type of user input device is a cursor control unit CC, such as a mouse, trackball, or cursor direction keys, for communicating direction information and command selections to the processor PRO and for controlling the movement of a cursor on the display DS. This input device generally has two degrees of freedom that enable the device to specify a position within a plane in two axes (a first axis (e.g., x) and a second axis (e.g., y)). A touch panel (screen) display may be used as the input device.

[0091]

[0108] According to one embodiment, portions of one or more of the methods described herein may be performed by a computer system CS in response to a processor PRO executing one or more sequences of one or more instructions included in a main memory MM. Such instructions may be read into the main memory MM from another computer-readable medium, such as a storage device SD. Execution of the sequence of instructions included in the main memory MM causes the processor PRO to perform the process steps described herein. One or more processors in a multiprocessing configuration may be used to execute the sequence of instructions included in the main memory MM. In an alternative embodiment, instead of software instructions, or in combination with software instructions, hard-wired circuitry may be used. Accordingly, the description herein is not limited to a particular combination of hardware circuitry and software.

[0092]

[0109] As used herein, the term "computer-readable medium" refers to any medium that participates in providing instructions to processor PRO for execution. Such a medium can take many forms, including but not limited to non-volatile media, volatile media, and transmission media. Non-volatile media includes, for example, optical or magnetic disks such as storage device SD. Volatile media includes dynamic memory such as main memory MM. Transmission media includes coaxial cables, copper wire, and fiber optics (including wires that include bus BS). Transmission media can also take the form of acoustic or light waves, such as those generated during radio frequency (RF) and infrared (IR) data communications. A computer-readable medium can be non-transitory and can be, for example, a floppy disk, flexible disk, hard disk, magnetic tape, other magnetic media, CD-ROM, DVD, other optical media, punch cards, paper tape, other physical media with patterns of holes, RAM, PROM, and EPROM, FLASH-EPROM, other memory chips or cartridges. Instructions can be recorded on a non-transitory computer-readable medium. When executed by a computer, the instructions can implement any of the features described herein. A transitory computer-readable medium can include a carrier wave or a propagating electromagnetic signal.

[0093]

[0110] Various forms of computer-readable media may be involved in carrying one or more sequences of one or more instructions to processor PRO for execution. For example, the instructions may initially be on the magnetic disk of a remote computer. The remote computer can load the instructions into its dynamic memory and send the instructions over a telephone line using a modem. A modem local to computer system CS can receive the data on the telephone line and convert the data into an infrared signal using an infrared transmitter. An infrared detector coupled to bus BS can receive the data carried by the infrared signal and place the data on bus BS. Bus BS carries the data to main memory MM, from where processor PRO reads and executes the instructions. The instructions received by main memory MM may optionally be stored in storage device SD before or after execution by processor PRO.

[0094]

[0111] Computer system CS may also include a communication interface CI coupled to bus BS. Communication interface CI also provides bi-directional data communication coupling to network link NDL connected to local network LAN. For example, communication interface CI may be a digital integrated services network (ISDN) card or modem that provides a data communication connection to a corresponding type of telephone line. As another example, communication interface CI may be a local area network (LAN) card that provides a data communication connection to a compatible LAN. A wireless link may be implemented. In such an implementation, communication interface CI transmits and receives electrical, electromagnetic, or optical signals that carry digital data streams representing various types of information.

[0095]

[0112] A network link NDL generally provides data communication to other data devices through one or more networks. For example, the network link NDL can provide a connection to a host computer HC through a local area network LAN. This includes data communication services provided by the worldwide packet data communication network (currently generally referred to as the "Internet" INT). Both the local area network LAN (Internet) use electrical, electromagnetic, or optical signals to carry digital data streams. Signals passing through various networks, on the network data link NDL, and through the communication interface CI, to and from the computer system CS, are examples of forms of carrier waves that carry information.

[0096]

[0113] The computer system CS can send messages and receive data including program code through one or more networks, network data links NDL, and communication interfaces CI. In the Internet example, the host computer HC may send request code for an application program through the Internet INT, network data link NDL, local area network LAN, and communication interface CI. One such downloaded application can provide, for example, all or part of the methods described herein. The received code is executed by the processor PRO upon receipt and / or may be stored in a storage device SD or other non-volatile storage for later execution. In this way, the computer system CS can obtain application code in the form of a carrier wave.

[0097]

[0114] FIG. 14 is a schematic diagram of a lithographic projection apparatus according to an embodiment of the present disclosure.

[0098]

[0115] A lithographic projection apparatus may comprise an illumination system IL, a first object table MT, a second object table WT, and a projection system PS.

[0099]

[0116] The illumination system IL may condition a beam of radiation B. In this particular case, the illumination system also includes a radiation source SO.

[0100]

[0117] The first object table (e.g., a patterning device table) MT may be provided with a patterning device holder for holding a patterning device MA (e.g., a reticle) and may be connected to a first positioner to accurately position the patterning device relative to item PS.

[0101]

[0118] The second object table (e.g., a substrate table) WT may be provided with a substrate holder for holding a substrate W (e.g., a resist-coated silicon wafer) and may be connected to a second positioner to accurately position the substrate relative to item PS.

[0102]

[0119] The projection system (the "lens") PS (e.g., a refractive, reflective, or catadioptric optical system) may image an irradiated portion of the patterning device MA onto a target portion C (e.g., one or more dies) of the substrate W.

[0103]

[0120] As shown herein, the apparatus may be of the transmissive type (i.e., having a transmissive patterning device). However, in general, the apparatus may be, for example, of the reflective type (comprising a reflective patterning device). The apparatus may utilize different types of patterning devices in a typical mask. Examples include a programmable mirror array or an LCD matrix.

[0104]

[0121] A source SO (for example, a mercury lamp or an excimer laser, an LPP (laser-produced plasma) EUV source) generates a radiation beam. This beam is supplied to an illumination system (illuminator) IL, either directly or after passing through conditioning devices such as, for example, a beam expander Ex. The illuminator IL may include a conditioning device AD for setting the outer and / or inner radial ranges (generally referred to as σ-outer and σ-inner, respectively) of the intensity distribution of the beam. Furthermore, it generally includes various other components such as an integrator IN and a condenser CO. In this way, the beam B impinging on the patterning device MA has a desired uniformity and intensity distribution in cross-section.

[0105]

[0122] In some embodiments, the source SO may be located within the housing of the lithographic projection apparatus (in most cases, when the source SO is, for example, a mercury lamp), but may be located remotely from the lithographic projection apparatus and the radiation beam it generates may be introduced into the apparatus (for example, using suitable guiding mirrors). This latter scenario is the case when the source SO is an excimer laser (for example, based on KrF, ArF, or F2 laser).

[0106]

[0123] Subsequently, the beam PB can intersect the patterning device MA held on the patterning device table MT. After the beam B crosses the patterning device MA, the beam B can pass through a lens PL that aligns the focus of the beam B with the target portion C of the substrate W. Using the second positioning device (and the interferometric measuring device IF), the substrate table WT can be accurately moved, for example, to position different target portions C within the path of the beam PB. Similarly, for example, after a mechanical search for the patterning device MA from a patterning device library or during scanning, the patterning device MA can be accurately positioned with respect to the path of the beam B using the first positioning device. Generally, the movement of the object tables MT, WT can be realized using a long stroke module (coarse positioning) and a short stroke module (fine positioning). However, in the case of a stepper (in contrast to a step and scan tool), the patterning device table MT may be connected only to a short stroke actuator or may be fixed.

[0107]

[0124] The depicted tool can be used in two different modes, namely, the step mode and the scan mode. In the step mode, the patterning device table MT remains essentially stationary, and the entire patterning device image is projected onto the target portion C in one go (i.e., a single "flash"). The substrate table WT can be shifted in the x and / or y directions so that different target portions C can be irradiated by the beam PB.

[0108]

[0125] In the scanning mode, basically the same scenario applies, except that a predetermined target portion C is not exposed with a single "flash". Instead, the patterning device table MT is movable at a speed v in a predetermined direction (so-called "scanning direction", e.g., the y direction) such that the projection beam B is scanned over the patterning device image. In parallel, the substrate table WT is moved simultaneously in the same or opposite direction at a speed V = Mv (M is the magnification of the lens PL (generally, M = 1 / 4 or 1 / 5)). In this way, a relatively large target portion C can be exposed without the need to compromise the resolution.

[0109]

[0126] Figure 15 is a schematic view of another lithographic projection apparatus (LPA) according to an embodiment of the present disclosure.

[0110]

[0127] The LPA may include a source collector module SO, an illumination system (illuminator) IL configured to condition a radiation beam B (e.g., EUV radiation), a support structure MT, a substrate table WT, and a projection system PS.

[0111]

[0128] The support structure (e.g., patterning device table) MT may be constructed to support a patterning device (e.g., a mask or reticle) MA and may be connected to a first positioner PM configured to accurately position the patterning device.

[0112]

[0129] The substrate table (e.g., wafer table) WT may be constructed to hold a substrate (e.g., a resist-coated wafer) W and may be connected to a second positioner PW configured to accurately position the substrate.

[0113]

[0130] The projection system (e.g., a reflective projection system) PS may be configured to project the pattern imparted to the radiation beam B by the patterning device MA onto a target portion C (e.g., one or more dies) of the substrate W.

[0114]

[0131] As depicted herein, the LPA can be reflective (e.g., using a reflective patterning device). Note that since most materials are absorptive within the EUV wavelength range, the patterning device can have a multilayer reflector that includes, for example, a multi-stack of molybdenum and silicon. In one example, the multi-stack reflector has 40 pairs of molybdenum and silicon with each layer having a thickness of a quarter wavelength. Even smaller wavelengths can be generated using x-ray lithography. Since most materials are absorptive at EUV and x-ray wavelengths, a thin patch of patterned absorptive material (e.g., a TaN absorber on a multilayer reflector) on the patterning device topography defines where features are printed (positive resist) or not printed (negative resist).

[0115]

[0132] Illuminator IL can receive an extreme ultraviolet radiation beam from source collector module SO. The method of generating EUV radiation is not necessarily limited, but includes converting a material to a plasma state having at least one element (e.g., xenon, lithium, or tin) with one or more emission lines in the EUV range. In one such method, often referred to as laser-produced plasma (“LPP”), the plasma can be generated by irradiating a fuel such as a droplet, stream, or cluster of material having a line-emitting element with a laser beam. Source collector module SO can be part of an EUV radiation system that includes a laser that provides a laser beam for exciting the fuel. The resulting plasma emits output radiation (e.g., EUV radiation), which is collected using a radiation collector disposed in the source collector module. The laser and the source collector module can be separate entities, for example, when a CO2 laser is used to provide a laser beam for fuel excitation.

[0116]

[0133] In such cases, the laser is not considered to form part of the lithographic apparatus, and the radiation beam can be passed from the laser to the source collector module using a beam delivery system, for example, including suitable guiding mirrors and / or beam expanders. In other cases, for example, when the source is a discharge-produced plasma EUV generator, often called a DPP source, the source may be an integrated part of the source collector module.

[0117]

[0134] The illuminator IL may include adjusters for adjusting the angular intensity distribution of the radiation beam. In general, at least the outer and / or inner radius ranges of the intensity distribution of the pupil plane of the illuminator (generally referred to as σ-outer and σ-inner, respectively) can be adjusted. Further, the illuminator IL may include various other components such as a facet field and a pupil mirror device. The illuminator can be used to adjust the radiation beam to have a desired uniformity and intensity distribution in the cross-section.

[0118]

[0135] The radiation beam B can be incident on a patterning device (e.g., a mask) MA held on a support structure (e.g., a patterning device table) MT and be patterned by the patterning device. After being reflected from the patterning device (e.g., a mask) MA, the radiation beam B passes through a projection system PS that focuses the beam onto a target portion C of the substrate W. A second positioner PW and a position sensor PS2 (e.g., an interferometric device, a linear encoder, or a capacitance sensor) can be used to accurately move the substrate table WT, for example, to position different target portions C within the path of the radiation beam B. Similarly, a first positioner PM and another position sensor PS1 can be used to accurately position the patterning device (e.g., a mask) MA with respect to the path of the radiation beam B. The patterning device (e.g., a mask) MA and the substrate W may be aligned using patterning device alignment marks M1, M2 and substrate alignment marks P1, P2.

[0119]

[0136] The depicted apparatus LPA can be used in at least one of a step mode, a scan mode, and a stationary mode.

[0120]

[0137] In the step mode, while the entire pattern imparted to the radiation beam is projected onto the target portion C in one go, the support structure (e.g., the patterning device table) MT and the substrate table WT remain substantially stationary (i.e., single static exposure). Then, the substrate table WT is shifted in the X and / or Y directions so that different target portions C can be exposed.

[0121]

[0138] In the scan mode, while the pattern imparted to the radiation beam is projected onto the target portion C, the support structure (e.g., the patterning device table) MT and the substrate table WT are scanned synchronously (i.e., single dynamic exposure). The speed and direction of the substrate table WT relative to the support structure (e.g., the patterning device table) MT can be determined by the reduction and image inversion characteristics of the projection system PS.

[0122]

[0139] In the stationary mode, while the pattern imparted to the radiation beam is projected onto the target portion C, the support structure (e.g., the patterning device table) MT holds the programmable patterning device and remains substantially stationary, and the substrate table WT is moved or scanned. In this mode, generally a pulsed radiation source is used, and the programmable patterning device is updated as necessary after each movement of the substrate table WT or between successive radiation pulses during the scan. This mode of operation can be easily applied to maskless lithography that utilizes a programmable patterning device such as a programmable mirror array.

[0123]

[0140] FIG. 16 is a detailed view of a lithographic projection apparatus according to an embodiment of the present disclosure.

[0124]

[0141] As shown in the illustration, the LPA may include a source collector module SO, an illumination system IL, and a projection system PS. The source collector module SO is constructed and arranged such that a vacuum environment can be maintained within the closed structure ES of the source collector module SO. The EUV radiation-emitting high-temperature plasma HP can be formed by a discharge-generating plasma source. The EUV radiation can be generated by a gas or vapor (e.g., Xe gas, Li vapor, or Sn vapor in which a high-temperature plasma HP is created to emit radiation within the EUV range of the electromagnetic spectrum). The high-temperature plasma HP is created, for example, by a discharge that produces at least a partially ionized plasma. A partial pressure of, for example, 10 Pa of Xe, Li, Sn vapor or any other suitable gas or vapor may be required for the efficient generation of radiation. In certain embodiments, a plasma of excited tin (Sn) is provided to generate EUV radiation.

[0125]

[0142] The radiation emitted by the high-temperature plasma HP passes from the source chamber SC, through an optional gas barrier or contaminant trap CT (which may also be referred to as a contaminant barrier or foil trap in some cases) located within or behind the opening of the source chamber SC, into the collector chamber CC. The contaminant trap CT may include a channel structure. The contaminant trap CT may also include a gas barrier, or a combination of a gas barrier and a channel structure. The contaminant trap or contaminant barrier CT shown further herein includes at least a channel structure, as is known in the art.

[0126]

[0143] The collector chamber CC may include a radiation collector CLO, which may be a so-called oblique incidence type collector. The radiation collector CLO has an upstream radiation collector side US and a downstream radiation collector side DS. Radiation traversing the radiation collector CO is reflected by the grating spectral filter SF and focused on a virtual light source point IF along the optical axis indicated by the dashed line “O”. The virtual light source point IF may be referred to as an intermediate focus, and the source collector module can be arranged such that the intermediate focus IF is located at or near the opening OP of the closed structure ES. The virtual light source point IF is an image of the radiation emitting plasma HP.

[0127]

[0144] Subsequently, the radiation traverses an illumination system IL that may include a facet field mirror device FM and a facet pupil mirror device pm arranged to provide a desired angular distribution of the radiation beam B and a desired uniformity of the radiation amplitude in the patterning device MA. When the radiation beam B is reflected in the patterning device MA held by the support structure MT, a patterned beam PB is formed, and the patterned beam PB is imaged onto a substrate W held by the substrate table WT by the projection system PS via the reflection element RE.

[0128]

[0145] In general, more elements than shown may be present within the illumination optical system unit IL and the projection system PS. The grating spectral filter SF may optionally be present depending on the type of lithographic apparatus. Furthermore, more mirrors than those shown in the drawing may be present, for example, 1 to 6 additional reflection elements may be present in the projection system PS.

[0129]

[0146] The collector system CLO can be a nested collector with an oblique incidence reflector GR as just one example of a collector (or collector mirror). The oblique incidence reflector GR is arranged axially symmetrically with respect to the optical axis O, and this type of collector system CLO may be used in combination with a discharge generating plasma source, often called a DPP source.

[0130]

[0147] Figure 17 is a detailed view of a source collector module SO of a lithographic projection apparatus LPA according to an embodiment of the present disclosure.

[0131]

[0148] The source collector module SO may be part of the LPA radiation system. The laser LA may be arranged to deposit laser energy onto a fuel such as xenon (Xe), tin (Sn), or lithium (Li) to generate a highly ionized plasma HP with an electron temperature of several tens of eV. The energy radiation generated during the de-excitation and recombination of these ions is emitted from the plasma, collected by the near-normal incidence collector system CLO, and focused onto the aperture OP of the closed structure ES.

[0132]

[0149] The concepts disclosed herein can perform simulations or mathematical modeling of general imaging systems for imaging sub-wavelength features and can be useful, in particular, for new imaging techniques capable of generating increasingly shorter wavelengths. New techniques already in use include EUV (extreme ultraviolet), DUV lithography capable of generating wavelengths of 193 nm using an ArF laser, and even 157 nm using a fluorine laser. Also, EUV lithography can generate wavelengths within this range by using a synchrotron or by bombarding a material (solid or plasma) with high-energy electrons to generate photons within the range of 20 - 50 nm.

[0133]

[0150] Embodiments of the present disclosure may be further described by the following clauses. 1. A method for determining a radiation source for a lithography process, comprising: determining a first pupil having a central obscuration (CO); determining a diffraction order (DO) based on a target design and a mask model; determining a first diffraction pattern (DP) based on the DO and the first pupil, wherein the first DP includes an overlapping region of diffracted light. Determining a second DP based on the DO and the first pupil, and determining an initial pupil based on the first DP and the second DP, wherein the initial pupil includes at least some of the overlapping regions, and A method comprising. 2. The method according to clause 1, further comprising performing source-mask optimization (SMO) initialized with the initial pupil. 3. The method according to clause 1, wherein the initial pupil does not include any diffracted light from the CO. 4. The method according to clause 3, further comprising performing SMO under the constraint that any pupil obtained as a result of SMO does not include the CO. 5. The method according to clause 1, wherein the first pupil is determined for a lithography system having a numerical aperture of at least 0.45 for an isotropic system with a chief ray angle (CRAO) of 9 or less. 6. The method according to clause 1, wherein the first pupil is determined for a lithography system having a numerical aperture of at least 0.5 for an anamorphic (4×8) lithography system. 7. The method according to clause 1, wherein the central obscuration is circular. 8. The method according to clause 1, wherein the central obscuration is elliptical. 9. The method according to clause 1, wherein the central obscuration is rectangular. 10. The method according to clause 1, wherein the mask model is a thick film mask model. 11. The method according to clause 1, wherein the DO includes the first-order diffracted light at the DO peak position closest to the zero-order DO peak position. 12. The method according to clause 1, wherein the DO includes the first-order diffracted light closest to the DO peak position orthogonal to the zero-order DO peak position. 13. The method according to clause 1, further comprising determining the DO peak position based on local peaks of the DO array, wherein the DO is determined based on the DO peak position. 14. The method according to clause 8, wherein the amplitude of the DO is based on the sum of all amplitudes in the corresponding local DO area. 15. The method according to clause 1, wherein the initial pupil is included within the sigma of -NA to +NA. 16. The method according to clause 1, further comprising discretizing the DO and generating a second DP to have a discretized amplitude using a first pupil having a discrete amplitude. 17. The method according to clause 10, wherein the discrete amplitudes of the DO and the first pupil are each set to 1. 18. The method according to clause 1, wherein the first DP indicates the number of overlapping diffraction beams. 19. The method according to clause 1, wherein the initial pupil is determined based on the degree of overlap in the overlapping region of the first DP. 20. Generating a normalized DP based on a degree of overlap exceeding a threshold, wherein the overlapping region exceeding the threshold of the degree of overlap is set to have a value of 1, and all other regions in the normalized DP are set to have a value of 0, and multiplying the normalized DP by a second DP to generate an initial pupil. The method according to clause 12, further comprising the above. 21. The method according to clause 1, wherein the initial pupil is determined based on the highest degree of overlap in the overlapping region of the first DP. 22. The method according to clause 1, further comprising determining the DO amplitude of the DO, wherein when the sum of the amplitudes of the first DP exceeds the threshold of the overlapping diffraction pattern, the initial pupil is filled. 23. Determining the overlapping region of the initial pupil, and generating the initial pupil to include only the most overlapping region when including only the most overlapping region satisfies or exceeds the pupil filling rate threshold, and repeatedly adding the next most overlapping region to the initial pupil when the initial pupil does not satisfy or exceed the pupil filling rate threshold. The method according to clause 1, further comprising the above. ​​​A non-transitory computer-readable medium storing instructions for determining a radiation source for use in a lithography process, the instructions, when executed by a computer comprising at least one programmable processor, causing the computer to perform operations including the operations recited in any one of clauses 1 to 23. 25. A system for determining a radiation source for use in a lithography process, the system comprising: at least one programmable processor; a non-transitory computer-readable medium storing instructions that, when executed by a computer comprising at least one programmable processor, cause the computer to perform the operations recited in any one of clauses 1 to 23; and the system comprising the same.

[0134]

[0151] The concepts disclosed herein may be used for imaging on a substrate such as a silicon wafer, but it is understood that the disclosed concepts may be used in any type of lithographic imaging system (e.g., those used for imaging on substrates other than silicon wafers).

[0135]

[0152] The combinations and sub-combinations of elements disclosed herein constitute separate embodiments and are provided by way of example only. Also, the above description is intended to be illustrative and not limiting. Accordingly, it should be apparent to those skilled in the art that modifications can be made as described without departing from the scope of the claims set forth below.

Claims

1. A non-transitory computer-readable medium storing instructions that, when executed by one or more processors, cause the one or more processors to perform a method for determining a radiation source for a lithography process, the method comprising: Determining a first pupil having a central obscuration (CO); Determining a diffraction order (DO) based on a target design and a mask model; Determining a first diffraction pattern (DP) based on the DO and the first pupil, the first DP including an overlapping region of diffraction patterns; Determining a second DP based on the DO and the first pupil; Determining an initial pupil based on the first DP and the second DP, the initial pupil including at least some of the overlapping region; Executing a method including the above steps.

2. The medium of claim 1, wherein the method further comprises performing source-mask optimization (SMO) using the initial pupil.

3. The medium of claim 1, wherein the initial pupil does not include any diffracted light at the CO.

4. The medium of claim 1, wherein the first pupil is determined for a lithography system having a numerical aperture of at least 0.45 for an isotropic system with a chief ray angle (CRAO) of 9 or less, or for a lithography system having a numerical aperture of at least 0.5 for an anamorphic (4×8) lithography system.

5. The medium of claim 1, wherein the mask model is a thick film mask model.

6. The medium of claim 1, wherein the DO includes a first-order diffracted light at a DO peak position closest to the zero-order DO peak position.

7. The medium of claim 1, wherein the DO includes a first-order diffracted light at a DO peak position orthogonal to the zero-order DO peak position and closest thereto.

8. The method further comprises determining a DO peak position based on local peaks of a DO array, and the DO is determined based on the DO peak position. In addition, The amplitude of the DO is based on the sum of all amplitudes in the corresponding local DO area. The medium of claim 1.

9. The medium of claim 1, wherein the initial pupil is included within a sigma of -NA to +NA.

10. The medium according to claim 1, wherein the method further comprises discretizing the DO and generating the second DP to have a discretized amplitude using the first pupil having a discrete amplitude.

11. The medium according to claim 1, wherein the first DP indicates the number of overlapping diffraction beams.

12. The medium according to claim 1, wherein the initial pupil is determined based on the degree of overlap in the overlapping region of the first DP.

13. The method is generating a normalized DP based on the degree of overlap exceeding a threshold, wherein the overlapping region exceeding the threshold of the degree of overlap is set to have a value of 1 and all other regions in the normalized DP are set to have a value of 0, multiplying the second DP by the normalized DP to generate the initial pupil The medium according to claim 12, further comprising.

14. The method according to claim 1, further comprising determining the DO amplitude of the DO, wherein when the sum of the amplitudes of the first DP exceeds a threshold of an overlapping diffraction pattern, the initial pupil is filled.

15. The method is to determine the overlapping region of the initial pupil, generating the initial pupil to include only the most overlapping region when including only the most overlapping region meets or exceeds a pupil filling rate threshold, iteratively adding the next most overlapping region to the initial pupil when the initial pupil does not meet or exceed the pupil filling rate threshold The medium according to claim 1, further comprising.

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