Diffraction-based pupil determination for optimizing lithographic processes

Abstract

Methods, apparatus, and software are disclosed for optimizing sources and / or masks used in lithographic manufacturing and patterning processes. A method includes determining a first pupil having a central occlusion region (CO); determining a diffraction order (DO) based on the target design and the mask model; determining a first diffraction pattern (DP) based on the DO and the first pupil, the first DP including an overlap 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, the initial pupil comprising at least some of the overlap regions.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. application No. 63 / 343,041, filed on May 17, 2022, and the entire contents of that U.S. application are incorporated herein by reference. Technical Field

[0003] The description herein generally relates to determining a pupil for optimizing sources and masks used in photolithographic manufacturing and patterning processes. More particularly, the present disclosure includes apparatus, methods, and computer programs for determining a pupil including accounting for diffraction effects. Background Art

[0004] Lithographic projection apparatus may be used, for example, in the manufacture of integrated circuits (ICs). In such cases, a patterning device (e.g., a mask) may include or provide a pattern corresponding to a single layer of the IC (a "design layout"), and such pattern may be transferred to a target portion (e.g., comprising one or more dies) on a substrate (e.g., a silicon wafer) coated with a layer of radiation-sensitive material ("resist") by methods such as irradiating the target portion via the pattern on the patterning device. Typically, a single substrate comprises a plurality of adjacent target portions to which the pattern is transferred successively, one at a time, by the lithographic projection apparatus. In this type of lithographic projection apparatus, the pattern on the entire patterning device is transferred to one target portion in one operation; such an apparatus may also be referred to as a stepper. In an alternative apparatus, a step-and-scan apparatus may cause the projection beam to be scanned across the patterning device in a given reference direction (the "scanning" direction) while synchronously moving the substrate parallel or antiparallel to such reference direction. Different portions of the pattern on the patterning device are transferred stepwise to one target portion. Since typically the lithographic projection apparatus will have a reduction ratio M (eg 4), the movement speed F of the substrate will be 1 / M the time the projection beam scans the patterning device.More information on lithographic apparatus can be found in, for example, US 6,046,792, which is incorporated herein by reference.

[0005] Before the pattern is transferred from the pattern forming device to the substrate, the substrate may undergo various processes, such as priming, resist coating, and soft baking. After exposure, the substrate may undergo other processes ("post-exposure processes"), such as post-exposure baking (PEB), development, hard baking, and measurement / inspection of the transferred pattern. This array of processes is used as the basis for manufacturing a single layer of a device (e.g., IC). The substrate may then undergo various processes, such as etching, ion implantation (doping), metallization, oxidation, chemical mechanical polishing, etc., all of which are intended to refine a single layer of the device. If several layers are required in the device, the entire process or a variation thereof is repeated for each layer. Ultimately, there will be a device in each target portion on the substrate. These devices are then separated from each other by techniques such as cutting or sawing, whereby individual devices can be mounted on a carrier, connected to pins, etc.

[0006] Therefore, manufacturing devices (such as semiconductor devices) generally involves using a certain number of manufacturing processes to process a substrate (e.g., a semiconductor wafer) to form various features and multiple layers of the device. These layers and features are generally manufactured and processed using, for example, deposition, photolithography, etching, chemical mechanical polishing, and ion implantation. Multiple devices can be made on multiple dies on a substrate, and then the devices are separated into separate devices. This device manufacturing process can be considered a patterning process. The patterning process involves using a pattern forming device in a lithographic device to perform a patterning step (such as optical and / or nanoimprint lithography) to transfer the pattern on the pattern forming device to the substrate, and the patterning process generally but optionally involves one or more related pattern processing steps, such as resist development by a developing device, baking the substrate using a baking tool, etching using a pattern using an etching device, etc.

[0007] As mentioned, photolithography is a central step in the fabrication of devices such as ICs, where patterns formed on a substrate define the functional elements of the device, such as microprocessors, memory chips, etc. Similar photolithography techniques are also used to form flat panel displays, microelectromechanical systems (MEMS), and other devices.

[0008] As semiconductor manufacturing processes continue to advance, the size of functional elements has continued to decrease over the decades, while the number of functional elements, such as transistors, per device has steadily increased, following a trend known as "Moore's Law." In the current state of the art, the layers of a device are fabricated using a lithographic projection apparatus that projects a design layout onto a substrate using illumination from a deep ultraviolet illumination source, thereby producing individual functional elements with dimensions well below 100 nm (i.e., less than half the wavelength of the radiation from the illumination source (e.g., a 193 nm illumination source)).

[0009] This process for printing features with dimensions smaller than the classical resolution limit of a lithographic projection apparatus 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 employed (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" (usually the minimum feature size printed), and k1 is an empirical resolution factor. In general, the smaller k1 is, the more difficult it becomes to reproduce a pattern on a substrate that resembles the shape and dimensions planned by the designer in order to achieve specific electrical functionality and performance. To overcome these difficulties, complex fine-tuning steps are applied to the lithographic projection apparatus, the design layout, or the patterning device. These steps include, for example, but are not limited to, optimization of NA and optical coherence settings, customized illumination schemes, use of phase-shifted patterning devices, optical proximity correction (OPC, sometimes also called "optical and process correction") in the design layout, or other methods generally defined as "resolution enhancement techniques" (RET). The term "projection optics" as used herein should be broadly interpreted to cover various types of optical systems, including, for example, refractive optics, reflective optics, apertures, and reflective-refractive optics. The term "projection optics" may also include elements that operate according to any of these design types for guiding, shaping, or controlling a projection radiation beam, either collectively or individually. The term "projection optics" may include any optical element in a lithographic projection apparatus, regardless of where the optical element is positioned on the optical path of the lithographic projection apparatus. Projection optics may include optical elements for shaping, adjusting, and / or projecting radiation from a source before the radiation passes through a patterning device, and / or optical elements for shaping, adjusting, and / or projecting the radiation after the radiation passes through a patterning device. Projection optics typically do not include a source and a patterning device. Summary of the invention

[0010] Methods, apparatus, and software for determining a pupil for optimizing a source and / or mask used in a lithography manufacturing and patterning process are disclosed. In one aspect, a method for determining a source for a lithography process includes: determining a first pupil having a central obscuration region (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 overlap 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, the initial pupil including at least some of the overlap regions.

[0011] In some variations, the method may include performing a source mask optimization (SMO) initialized with an initial pupil. The initial pupil may not include any diffracted light in the CO. The SMO may be performed under the constraint that any pupil generated by the SMO does not include the CO.

[0012] In other variations, the first pupil of the lithography system having a numerical aperture of at least 0.45 may be determined for a homogeneous system having a chief ray angle (CRAO) less than or equal to 9. The first pupil of the lithography system having a numerical aperture of at least 0.5 may be determined for an anamorphic (4×8) lithography system.

[0013] In other variations, the central masking area may be circular, oval or rectangular.The mask pattern may be a thick mask pattern.

[0014] In some variations, the DO may include a first-order diffracted light at a DO peak position closest to a zero-order DO peak position. The DO may include a closest first-order diffracted light at a DO peak position orthogonal to the zero-order DO peak position. The method may include determining a DO peak position based on a local peak of a DO array, wherein 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 a corresponding local DO region. In other variations, the initial pupil may be contained within a standard deviation between -NA and +NA.

[0015] In other variations, the method may include discretizing the DO and using the first pupil having a discrete amplitude to generate the second DP having a discretized amplitude. The discrete amplitudes of the first pupil and the DO may each be set to 1. The first DP may indicate the number of overlapped diffracted beams. The initial pupil may be determined based on the degree of overlap in the overlap region of the first DP.

[0016] In other variations, the method may also include: generating a normalized DP based on the degree of overlap exceeding a threshold, wherein the overlap area exceeding the threshold of the degree of overlap is set to have a value of 1, and all other areas 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.

[0017] In some variations, the initial pupil may be determined based on a highest degree of overlap in an overlap region of the first DPs. The method may include determining a DO amplitude of the DO, wherein the initial pupil is filled if the sum amplitude of the first DPs exceeds a threshold for diffraction pattern overlap.

[0018] In other variations, the method may include determining an overlapping region of the initial pupil; generating the initial pupil to include only the region with the most overlap when only the region with the most overlap reaches or exceeds a pupil filling ratio threshold; and iteratively adding subsequent regions with the most overlap to the initial pupil when the initial pupil does not reach or exceed the pupil filling ratio threshold.

[0019] In some embodiments, there may be a non-transitory computer-readable medium having instructions recorded thereon for determining a pupil for optimizing a source and / or mask used in a lithography manufacturing and patterning process, the instructions, when executed by a computer having at least one programmable processor, causing operations including any of the operations in the above method embodiments.

[0020] In some embodiments, there may be a system for determining a pupil for optimizing a source and / or mask used in a lithography manufacturing and patterning process, the system comprising: a non-transitory computer-readable medium having instructions recorded thereon, the instructions, when executed by a computer having at least one programmable processor, causing operations including any of the operations in the above method embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate certain aspects of the subject matter disclosed herein and, together with the description, help explain some principles associated with the disclosed embodiments. In the drawings:

[0022] Figure 1 A block diagram illustrating various subsystems of a lithographic projection apparatus according to an embodiment of the present disclosure.

[0023] Figure 2 An exemplary flow chart for simulating lithography in a lithographic projection apparatus according to an embodiment of the present disclosure is illustrated.

[0024] Figure 3 An exemplary portion of a lithographic projection apparatus with an unobstructed pupil is illustrated according to an embodiment of the present disclosure.

[0025] Figure 4 An exemplary portion of a lithographic projection apparatus having a pupil provided with a central obscuration region according to an embodiment of the present disclosure is illustrated.

[0026] Figure 5A An exemplary process flow diagram for determining a source for a photolithography process according to an embodiment of the present disclosure is illustrated.

[0027] Figure 5BAn exemplary process flow diagram for utilizing a diffraction pattern when initializing a SMO according to an embodiment of the present disclosure is illustrated.

[0028] Figure 6 An exemplary first pupil with a central obscured region is illustrated according to an embodiment of the present disclosure.

[0029] Figure 7 An exemplary mapping of diffraction orders according to an embodiment of the present disclosure is illustrated.

[0030] Figure 8 An exemplary second diffraction pattern according to an embodiment of the present disclosure is illustrated.

[0031] Fig. 9 An exemplary first diffraction pattern in a region of interest according to an embodiment of the present disclosure is illustrated.

[0032] Fig.10 An exemplary initial pupil is determined based on an overlap region in a first diffraction pattern according to an embodiment of the present disclosure.

[0033] Fig.11 FIG. 2 illustrates determining an exemplary initial pupil based on a pupil filling ratio according to an embodiment of the present disclosure.

[0034] Fig.12 An exemplary segmentation of a source and an initial pupil based on incident light angle relative to a mask is illustrated in accordance with an embodiment of the present disclosure.

[0035] Fig.13 is a block diagram of an example computer system according to an embodiment of the present disclosure.

[0036] Fig.14 is a schematic diagram of a lithography projection apparatus according to an embodiment of the present disclosure.

[0037] Fig.15 is a schematic diagram of another lithography projection apparatus according to an embodiment of the present disclosure.

[0038] Fig.16 is a detailed view of a lithographic projection apparatus according to an embodiment of the present disclosure.

[0039] Fig.17 is a detailed view of a source collector module of a lithographic projection apparatus according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0040] Although specific reference may be made herein to the manufacture of ICs, it should be clearly understood that the description herein has many other possible applications. For example, the description may be used to manufacture integrated optical systems, guidance and detection patterns for magnetic domain memories, liquid crystal display panels, thin film magnetic heads, etc. Those skilled in the art will appreciate that in the context of such alternative applications, any use of the terms "reticle", "wafer" or "die" herein should be considered interchangeable with the more general terms "mask", "substrate" and "target portion", respectively.

[0041] In this document, the terms "radiation" and "beam" are used to cover all types of electromagnetic radiation, including ultraviolet radiation (e.g., having a wavelength of 365 nm, 248 nm, 193 nm, 157 nm, or 126 nm) and extreme ultraviolet radiation (EUV, e.g., having a wavelength in the range of about 5 nm to 100 nm).

[0042] The pattern forming device may include or may form one or more design layouts. The design layout may be generated using a computer-aided design (CAD) process, which is often referred to as electronic design automation (EDA). Most CAD processes follow a predetermined set of design rules to generate a functional design layout / pattern forming device. These rules are set by processing and design restrictions. For example, the design rules define the spatial tolerance between devices (such as gates, capacitors, etc.) or interconnects to ensure that the devices or lines do not interact with each other in an undesirable manner. One or more of the design rule restrictions may be referred to as a "critical dimension" (CD). The critical dimension of a device may be defined as the minimum width of a line or hole or the minimum space between two lines or two holes. Therefore, CD determines the overall size and density of the designed device. Of course, one of the goals of device fabrication is to faithfully reproduce the original design on a substrate (via a pattern forming device).

[0043] The term "mask" or "patterning device" as used herein may be broadly interpreted as referring to a general patterning device that can be used to impart a patterned cross-section to an incident radiation beam, the patterned cross-section corresponding to the pattern to be produced in a target portion of the substrate; the term "light valve" may also be used in this context. In addition to classical masks (transmissive or reflective; binary, phase-shifting, hybrid, etc.), other examples of such patterning devices include programmable mirror arrays and programmable LCD arrays.

[0044] An example of a programmable mirror array may be a matrix-addressable surface having a viscoelastic control layer and a reflective surface. The basic principle underlying such an arrangement is, for example, that the addressed areas of the reflective surface reflect the incident radiation as diffracted radiation, while the unaddressed areas reflect the incident radiation as undiffracted radiation. Using an appropriate filter, the undiffracted radiation can be filtered out from the reflected beam, so that only the diffracted radiation remains; in this way, the beam becomes patterned according to the addressing pattern of the matrix-addressable surface. Suitable electronic methods may be used to perform the desired matrix addressing.

[0045] An example of a programmable LCD array is given in US Pat. No. 5,229,872, which is incorporated herein by reference.

[0046] Figure 1 A block diagram of various subsystems of a lithographic projection apparatus 10A according to an embodiment of the present disclosure is illustrated. The main elements are: a radiation source 12A, which may be a deep ultraviolet excimer laser source or other type of source including an extreme ultraviolet (EUV) source (as discussed above, the lithographic projection apparatus itself need not have a radiation source); an illumination optical device, which, for example, defines partial coherence (expressed as sigma, i.e., standard deviation) and may include optical devices 14A, 16Aa, and 16Ab that shape the radiation from source 12A; a patterning device 18A; and a transmissive optical device 16Ac that projects an image of the patterning device pattern onto a substrate plane 22A. The adjustable filter or hole 20A at the pupil plane of the projection optics can limit the range of beam angles that impinge on the substrate plane 22A, where the maximum possible angle defines the numerical aperture NA = n sin(Θmax) of the projection optics, where n is the refractive index of the medium between the substrate and the final element of the projection optics, and Θmax is the maximum angle of the beam emerging from the projection optics that can still impinge on the substrate plane 22A.

[0047] In a lithographic projection apparatus, a source provides illumination (i.e., radiation) to a patterning device, and projection optics direct the illumination onto a substrate via the patterning device and shape the illumination. The projection optics may include at least some of the elements 14A, 16Aa, 16Ab, and 16Ac. The aerial image (AI) is the radiation intensity distribution at the substrate level. A resist model may be used to calculate a resist image from an aerial image, an example of which may be found in U.S. Patent Application Publication No. US 2009-0157630, the disclosure of which is incorporated herein by reference in its entirety. The resist model is only related to the properties of the resist layer (e.g., the effects of chemical processes occurring during exposure, post-exposure baking (PEB), and development). The optical properties of the lithographic projection apparatus (e.g., the properties of the illumination, patterning device, and projection optics) specify the aerial image and may be defined in the optical model. Since the patterning device used in the lithographic projection apparatus may be changed, it is necessary to separate the optical properties of the patterning device from the optical properties of the rest of the lithographic projection apparatus including at least the source and projection optics. Details of techniques and models for transforming a design layout to various lithography images (e.g., aerial images, resist images, etc.), applying OPC using those techniques and models, and evaluating performance (e.g., in terms of process windows) are described in U.S. patent application publications US 2008-0301620, 2007-0050749, 2007-0031745, 2008-0309897, 2010-0162197, and 2010-0180251, the disclosures of each of the foregoing being incorporated herein by reference in their entirety.

[0048] One aspect of understanding the lithography process is understanding the interaction of radiation with 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. Such a function may be referred to as the mask transmission function (which may be used to describe the interaction of a transmission patterning device and / or a reflective patterning device).

[0049] The mask transmission function can have a variety of different forms. One form is binary. A binary mask transmission function has either of two values ​​(e.g., zero and a positive constant) at any given position on the pattern forming device. A mask transmission function in binary form may be referred to as a binary mask. Another form is continuous. That is, the modulus of the transmittance (or reflectance) of the pattern forming device is a continuous function of the position on the pattern forming device. The phase of the transmittance (or reflectance) may also be a continuous function of the position on the pattern forming device. A mask transmission function in continuous form may be referred to as a continuous tone mask or a continuous transmission type mask (CTM). For example, a CTM may be represented as a pixelated image, where each pixel may be assigned a value between 0 and 1 (e.g., 0.1, 0.2, 0.3, etc.) instead of a binary value of 0 or 1. In an embodiment, the CTM may be a pixelated grayscale image, where each pixel has a value (eg, a normalized value in the range [-255, 255], in the range [0, 1] or [-1, 1] or other suitable range).

[0050] The thin mask approximation (also known as the Kirchhoff boundary condition) is widely used to simplify the determination of the interaction of radiation with the patterning device. The thin mask approximation assumes 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. Therefore, the thin mask approximation assumes that the electromagnetic field after the patterning device is the product of the incident electromagnetic field and the mask transmission function. However, as the lithography process uses radiation with shorter and shorter wavelengths, and the structures on the patterning device become smaller and smaller, the assumption of the thin mask approximation can break down. For example, due to the finite thickness of the structure (e.g., the edge between the top surface and the sidewall), the interaction of radiation with the structure ("mask 3D effect" or "M3D") can become important. Including this scattering in the mask transmission function can enable the mask transmission function to preferably capture the interaction of radiation with the patterning device. The mask transmission function under the thin mask approximation can be referred to as a thin mask transmission function. The mask transmission function that includes M3D can be referred to as an M3D mask transmission function.

[0051] According to an embodiment of the present disclosure, one or more images may be generated. The image includes various types of signals that may be characterized by a pixel value or an intensity value of each pixel. Depending on the relative value of the pixels within the image, the signal may be referred to as, for example, a weak signal or a strong signal, as may be understood by a person of ordinary skill in the art. The terms "strong" and "weak" are relative terms based on the intensity values ​​of the pixels within the image, and the specific value of the intensity may not limit the scope of the present disclosure. In an embodiment, a strong signal and a weak signal may be identified based on a selected threshold. In an embodiment, the threshold may be fixed (e.g., the midpoint between the highest intensity and the lowest intensity of the pixels within the image). In an embodiment, a strong signal may refer to a signal having a value greater than or equal to the average signal value across the image, and a weak signal may refer to a signal having a value less than the average signal value. In an embodiment, the relative intensity value may be based on a percentage. For example, a weak signal may be a signal having an intensity less than 50% of the highest intensity of a pixel within the image (e.g., a pixel corresponding to a target pattern may be considered as a pixel having the highest intensity). In addition, each pixel within the image is considered a variable. According to the present embodiment, a derivative or partial derivative may be determined with respect to each pixel within the image, and the value of each pixel may be determined or modified based on an evaluation based on a cost function and / or a gradient-based calculation of a cost function. For example, a CTM image may include pixels, where each pixel is a variable that may take any real value.

[0052] Figure 2 An exemplary flow chart for simulating lithography in a lithographic projection apparatus according to an embodiment of the present disclosure is illustrated. A source model 31 represents the optical properties of a source (including radiation intensity distribution and / or phase distribution). A projection optics model 32 represents the optical properties of the projection optics (including changes in radiation intensity distribution and / or phase distribution caused by the projection optics). A design layout model 35 represents the optical properties of a design layout (including changes in radiation intensity distribution and / or phase distribution caused by a design layout 33), which is a representation of a feature arrangement formed on or by a pattern forming device. An aerial image 36 can be simulated from the design layout model 35, the projection optics model 32, and the design layout model 35. A resist image 38 can be simulated from the aerial image 36 using a resist model 37. The simulation of lithography can, for example, predict the profile and CD in the resist image.

[0053] More specifically, it should be noted that the source model 31 can represent the optical characteristics of the source, including but not limited to the numerical aperture setting, the illumination standard deviation (σ) setting, and any specific illumination shape (e.g., off-axis radiation source, such as a toroidal, quadrupole, dipole, etc.). The projection optics model 32 can represent the optical characteristics of the projection optics, including aberrations, deformations, 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 properties of a physical pattern forming device, such as described in U.S. Patent No. 7,587,704, which is incorporated herein by reference in its entirety. The goal of the simulation is to accurately predict, for example, edge placement, aerial image intensity slope, and / or CD, which can then be compared to the expected design. The expected design is typically defined as a pre-OPC design layout that can be provided in a standardized digital file format such as GDSII or OASIS or other file formats.

[0054] From this design layout, one or more portions, referred to as "clip", may be identified. In an embodiment, a set of clips is extracted, which represent complex patterns in the design layout (typically about 50 to 1000 clips, but any number of clips may be used). These patterns or clips represent small portions of the design (i.e., circuits, cells, or patterns), and more specifically, the clips typically represent small portions that require special attention and / or verification. In other words, a clip may be a portion of a design layout, or may be similar or have similar behavior to a portion of a design layout, where one or more critical features are identified through experience (including clips provided by customers), through trial and error, or by running full-chip simulations. A clip may include one or more test patterns or gauge patterns.

[0055] The initial set of larger segments may be provided a priori by the customer based on one or more known critical feature areas in the design layout that require specific image optimization. Alternatively, in another embodiment, the initial set of larger segments may be extracted from the entire design layout by using some automatic (such as machine vision) or manual algorithm that identifies the one or more critical feature areas.

[0056] In a lithographic projection apparatus, as an example, the cost function can be expressed as

[0057] (Equation 1)

[0058] in are N design variables or their values. Can be a design variable Functions such as The difference between the actual and expected values ​​of a characteristic for a set of values ​​of a design variable. For The associated weight constant. For example, a characteristic may be the location of the edge of a pattern measured at a given point on the edge. Can have different weights For example, if a particular edge has a narrow allowed positioning range, then the difference between the actual position of the edge and the expected position may be expressed as Weight Can be given a higher value. It can also be a function of interlayer characteristics, which are design variables Of course, It is not limited to the form in Equation 1. Any other suitable form may be used.

[0059] The cost function may represent any one or more suitable characteristics of the lithographic projection apparatus, the lithographic process, or the substrate, such as focal length, CD, image shift, image deformation, image rotation, random variation, throughput, local CD variation, process window, inter-layer characteristics, or a combination thereof. In one embodiment, the design variables The cost function may include one or more selected from dose, global bias of the patterning device, and / or illumination shape. Since the resist image often dictates the pattern on the substrate, the cost function may include a function representing one or more characteristics of the resist image. For example, It can be simply the distance between a point in the resist image and the expected position of that point (i.e., the edge placement error ). Design variables may include any adjustable parameters, such as adjustable parameters of the source, patterning device, projection optics, dose, focal length, etc.

[0060] The lithographic apparatus may include elements collectively referred to as "wavefront manipulators" that can be used to adjust the shape of the wavefront and intensity distribution and / or the phase shift of the radiation beam. In an embodiment, the lithographic apparatus can adjust the wavefront and intensity distribution at any position along the optical path of the lithographic projection apparatus, such as before the pattern forming 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 certain deformations of the wavefront and intensity distribution and / or phase shift caused by, for example, temperature changes in the source, pattern forming device, lithographic projection apparatus, thermal expansion of elements of the lithographic projection apparatus, etc. Adjusting the wavefront and intensity distribution and / or phase shift can change the value of the characteristic represented by the cost function. These changes can be simulated from a model or actually measured. The design variables may include parameters of the wavefront manipulator.

[0061] Design variables can have constraints, which can be expressed as ,in, is a set of possible values ​​for the design variables. A possible constraint on the design variables may be imposed by the desired throughput of the lithographic projection apparatus. In the absence of such a constraint imposed by the desired throughput, the optimization may result in an unrealistic set of values ​​for the design variables. For example, if the dose is a design variable, then in the absence of such a constraint, the optimization may result in a dose value that makes the throughput economically impossible. However, the usefulness of a constraint should not be interpreted as a necessity. For example, the throughput may be affected by the pupil fill ratio. For some irradiation designs, a low pupil fill ratio may discard radiation, resulting in a lower throughput. The throughput may also be affected by the chemical reaction of the resist. Slower resists (e.g., resists that require a higher amount of radiation to be properly exposed) result in lower throughput.

[0062] As used herein, the term "patterning process" means a process that produces an etched substrate by applying a specific pattern of light as part of a photolithography process.

[0063] As used herein, the term "target pattern" means an idealized pattern to be etched on a substrate.

[0064] As used herein, the term "printed pattern" means a physical pattern on a substrate formed based on a design layout. The printed pattern may include, for example, vias, contact holes, grooves, channels, recesses, edges, or other two-dimensional and three-dimensional features produced by a lithography process.

[0065] 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 may include any combination of an optical model (e.g., it models the lens system / projection system used to deliver light during the lithography process and may include modeling the final optical image of the light onto the resist), a mask model, a resist model (e.g., it models the physical effects of the resist, such as the chemical effects due to light), an OPC model (e.g., it may be used to make a design layout and may include sub-resolution resist features (SRAFs), etc.), an imaging device model (e.g., it models what an imaging device may image from a printed pattern).

[0066] As used herein, the term "imaging device" means any number of devices and associated computer hardware and software or a combination thereof that can be configured to produce an image of a target (such as a printed pattern or portion thereof). Non-limiting examples of imaging devices may include: scanning electron microscopes (SEMs), x-ray machines, etc.

[0067] Figure 3An exemplary portion of a lithographic projection apparatus with an unobstructed pupil is illustrated according to an embodiment of the present disclosure.

[0068] During the patterning process, light from a photolithography source (eg, UV, EUV, etc.) may be directed and / or guided via a number of optical elements such as lenses, masks, mirrors, etc. to ultimately reach a substrate (eg, wafer) undergoing processing. Figure 3 A portion of a lithography system is shown, which includes receiving a source (not shown, but Figure 1 12A is an example). The light 320 is directed via a series of optical elements such as mirrors 330 to ultimately reach a substrate 340. The expanded view 350 on the right depicts an embodiment showing angles 360 between two of the mirrors 330 and the rays of incident light filling the final mirror 332. These angles can be related to the numerical aperture (NA) of the system. A pupil plane 370 is also shown, as well as a simplified depiction of a pupil 380. As understood in the art, a pupil represents a pattern of light at a particular location along the optical axis. While such a pattern can be at the location of a physical pupil, if a pattern exists in a given system, it can generally be at any arbitrary location.

[0069] In the example shown, pupil 380 is unobstructed, and thus theoretically can have light at any part of the pupil. While these unobstructed pupils can work for relatively low NA systems, higher NA systems may require different pupils. The disclosure refers to high NA and low NA systems simply to distinguish one from the other. Therefore, such designated names do not imply or require any specific value of NA. In some embodiments, a low NA system may have a NA of approximately 0.33, while a high NA system may have a NA of approximately 0.5.

[0070] Figure 4 An exemplary portion of a lithographic projection apparatus having a pupil provided with a central obscuration region according to an embodiment of the present disclosure is illustrated.

[0071] High NA systems (such as Figure 4 ) can provide a number of technical advantages, including increasing the resolution of the light pattern reaching the substrate. Such high NA systems can have very different optical elements (e.g., mirror 430) and configurations than their low NA counterparts. This is in Figure 4 As can be seen in the example, by for example the final reflector 432 is larger than Figure 3 The corresponding final mirror 332 in the low NA system depicted in . A technical challenge in EUV lithography is that EUV mirror coatings can accurately reflect light only over relatively small angles, while high NA systems may exceed said angles. Figure 44, the system causes a central obscuration region (CO) 482 to appear at the pupil 480. One effect of the CO can be that the light reaching the EUV mirror is at a smaller angle and can thus be accurately reflected. Therefore, the disclosed high NA projection optics can allow a pupil with a CO, which increases the transmission of the system due to the reduced angle.

[0072] In some embodiments, a pupil of a lithography system having a numerical aperture of at least 0.45 may be determined for a homogeneous system having a chief ray angle (CRAO) less than or equal to 9. In other embodiments, a pupil of a lithography system having a numerical aperture of at least 0.5 may be determined for an anamorphic (4×8) lithography system.

[0073] Figure 5A An exemplary process flow diagram for determining a source for a photolithography process according to an embodiment of the present disclosure is illustrated.

[0074] In order to determine an optimized system that can deliver light to the substrate as desired, the system can be computationally optimized to determine the optimal combination of source, mask, and optionally other aspects of the lithography system. Such source mask optimization (SMO) can thereby determine the optimal combination of light source and mask design and take into account physical constraints of the optical system, desired process window, etc. The pupil can be a factor in the SMO, and the light at the pupil can include diffracted light of different orders that can be combined at the substrate. Therefore, the present disclosure provides a method of determining a source, mask, or other optimized aspects of a system for a lithography process. Although various aspects of the following methods and other features of the present disclosure are discussed in more detail herein, in one embodiment, by Figure 5A As shown in the figure, a method may include determining a first pupil having a central obscured area at 510, for example, by Figure 4, as depicted by the example pupil 480 in . At 520, the method may include determining a diffraction order (DO) based on the target design and the mask model. The DO can be used to determine how the pattern of diffracted light overlaps across the first pupil 510. The method may then include determining a first diffraction pattern (DP) based on the DO and the first pupil at 530, the first DP including an overlapping region of diffracted light or a DO overlapping region. Since the pupil represents a pattern of light at a position along the optical axis, the diffraction pattern described herein may then 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 about the amplitude of a region of the second DP (e.g., the amplitude of a zero-order peak, a first-order peak, etc.). The method may also include determining an initial pupil based on the first DP and the second DP at 550, the initial pupil including at least some of the overlapping regions. The first DP and the second DP may be multiplied to produce the initial pupil. However, in other embodiments, some specific overlap regions of the first DP may be extracted and normalized to form a normalized DP, wherein the normalized DP is multiplied by the second DP to produce the initial pupil. In some embodiments, the initial pupil does not include any diffracted light in the central obscured region. As described in more detail herein, some embodiments may include a need for sufficient overlap regions to deliver the desired light. Likewise, some embodiments may benefit by forcing (e.g., through a SMO process) the determination that there is no light in the CO.

[0075] As used herein, the term "first" pupil refers to a pupil determined by the disclosed method but before being utilized by the SMO system. The term "initial" pupil refers to a pupil that may be provided to the SMO system and, in some embodiments, is used to begin SMO. As described herein, such an "initial pupil" has generally been determined based on a "first pupil".

[0076] Also, as further described herein, some embodiments of the method may include performing a source mask optimization (SMO) initialized with an initial pupil at 552. Since some optimizers will find solutions that utilize light in the CO, which may not be desirable for at least the reasons given above, certain embodiments may perform the SMO under the constraint that any pupil produced by the SMO does not include the CO.

[0077] Figure 5B An exemplary process flow diagram for utilizing a diffraction pattern when initializing a SMO according to an embodiment of the present disclosure is illustrated.

[0078] In an embodiment, a procedure for utilizing a diffraction pattern in determining an initial pupil of a SMO may include the following, with details being further provided herein according to some of the mentioned examples.

[0079] Figure 5B The process depicted in can start with a device pattern 560, for example with a given pitch, CD, I. The mask model can be applied to the device pattern to generate DO 570 (see also, for example, Figure 7 ). DO 570 is shown as having only the zero-order diffraction region at the center and the location of the first-order diffraction peak. It can be determined that DO 570 has continuous (ie, non-discrete) amplitudes at the various diffraction order peak locations. See also Figure 5A Of the 520.

[0080] A first DP 572 may be generated to indicate a region of overlapping diffraction orders. The first DP 572 may be based on diffraction due to a first pupil 576 having CO. The amplitude in the first DP 572 may be set to have discrete values ​​such as integers (as shown) to directly indicate overlapping regions (see also, e.g. Figure 8 ), but in some embodiments the amplitude may be set to a continuous value based on the determined amplitude (see also e.g. Figure 7 ). In some embodiments, certain overlapping regions may be used as regions of the initial pupil used for the SMO process. In such embodiments, as described in more detail below, a normalized DP 574 may then be generated (see also Fig.11 1120 in FIG. 1120 ), for example, regions of light having a value normalized to 1 and regions of light not being assigned a value of 0. See also Figure 5A Of which 530.

[0081] A second DP 578 may be generated by convolving the DO 570 with the first pupil 576 (see also, e.g. Figure 6 and Figure 8 ). In such an embodiment, the second DP 578 may be continuous (ie, have a continuous amplitude from the continuous DO 570 peak amplitude). See also Figure 5A 510 and 540.

[0082] In one embodiment, the initial pupil 580 may be determined from the first DP 572 (used to generate the normalized DP 574) and the second DP 578. Figure 5A550 in the normalized DP 574. In some embodiments, this may include generating a normalized DP 574 based on a degree of overlap exceeding a threshold, wherein an overlap region exceeding the threshold degree of overlap may be set to have a value of 1, and all other regions in the normalized DP 574 may be set to have a value of 0. Next, to generate the initial pupil 580, the second DP 578 may be multiplied by the normalized DP 574.

[0083] The initial pupil 580 may thus be continuous in amplitude, but may have multiple regions determined based on a discretization of the diffraction order amplitudes. Figure 8 In other embodiments described in , the amplitude of the second DP 578 can be discretized to provide an initial pupil with discrete amplitudes. The initial pupil 580 can then be provided to start the SMO process 590. See also Figure 5A Of which 552.

[0084] In some embodiments, to satisfy pupil fill ratio constraints during SMO, other regions of the second DP 578 may be included, such as the region with the most subsequent overlap (see also, e.g. Fig.11 This is illustrated by the second normalized DP 582 of the example and depicts a more filled pupil (compared to the normalized DP 574).

[0085] Figure 6 An exemplary first pupil with a central obscured region is illustrated according to an embodiment of the present disclosure.

[0086] The exemplary methods described above (and throughout this disclosure, e.g., in Figure 5A 510 in the method described in the above) can determine a pupil 610 including a central shielded area 620. The pupil 610 can then be used as the basis for the pupil determination based on the diffraction order described herein. The pupil 610 can be a pupil generated from a pupil library or a user input pupil design. Generally, the central shielded area can be of any shape. In the examples described herein, an embodiment in which the central shielded area is circular is described. In other embodiments, the central shielded area can be, for example, oval, rectangular, elliptical, polygonal, or irregularly shaped.

[0087] Figure 7 An exemplary mapping of diffraction orders according to an embodiment of the present disclosure is illustrated.

[0088] The above method describes determining diffraction orders (DO) 700 based on the target design and mask model at 520. In some embodiments, the mask model can be a thick mask model, such as a mask model that can account for light interacting with various depths in the mask. As light diffracts from different depths and locations in the mask, the location of the diffraction orders at the pupil can vary. Figure 7 Describe The changing diffraction order position:

[0089] (Equation 2).

[0090] Zero-order diffracted light 710 (solid circle) having a zero-order DO peak position 712 is shown in the center of the drawing. In addition, other diffraction orders and their corresponding positions may be considered when determining the diffraction pattern that contributes light to the pupil. DO may also include first-order diffracted light 720 (dashed circle) at a DO peak position 722 that is closest to the zero-order DO peak position 712. DO may also include the closest first-order diffracted light 720 at a DO peak position 732 that is orthogonal to the zero-order DO peak position. As will be discussed further herein, it can be seen that = 1 can include overlapping patterns of diffracted light.

[0091] In some embodiments, various methods may also include determining a DO peak position based on a local peak of a DO array, wherein the DO is determined based on the DO peak position in a local DO region 740. The DO array may be a data representation of any of the multiple diffraction patterns described herein, such as a 2D array of values ​​stored in a computer memory. A portion of an exemplary DO array is depicted in the illustration, wherein, for example, grayscale tones represent the amplitude of a diffraction peak, which may have a complex 2D pattern. The pixelated representation of the diffraction amplitude may be used to assign a specific amplitude to a specific pixel in the DO representation. Therefore, the pixel 742 with the maximum DO (depicted by the darkest pixel shown in the illustration) may be selected as the DO peak position (shown by a white crosshair). The local DO region utilized may include any range around the position as the expected DO peak position. In some embodiments, the amplitude of the DO may be based on the amplitude of the local DO peak, the sum of all amplitudes in the corresponding local DO region, etc. For example, in various embodiments, the local DO region may include ± 0.03s, ± 0.05s, etc. around the DO peak position.

[0092] Figure 8 An exemplary second diffraction pattern according to an embodiment of the present disclosure is illustrated.

[0093] In some embodiments, the disclosed method may include convolving the initial pupil 610 with the DO 700 to determine the depicted second DP 800. Throughout the second DP 800, the zero-order diffraction 710 and the many first-order diffraction 720 overlap at many locations to produce a second DP 800 with a certain amplitude range. As an example, the amplitude of the light in the second DP 800 overlaps the most in the location 810. The area immediately adjacent to the location 810 causes the three diffraction patterns to overlap, and so on.

[0094] like Figure 8 As shown in the exemplary embodiments of , some disclosed methods may include discretizing the DO 700 and generating a second DP 800 having a discretized amplitude using the first pupil 610 having a discrete amplitude. As an example, the discrete amplitudes of the first pupil 610 and the DO may each be set to 1. This is depicted by a scale with arrows indicating some regions of the second DP 800 having the total amplitude shown. The act of discretizing the amplitudes of the first pupil 610 and the DO 700 may provide several technical advantages. For example, this may reduce computation time by allowing the system to perform integer operations rather than floating point operations. Similarly, due to the discrete nature of the DO (the DO may be considered as discrete points that are well separated in the standard deviation space), it is easy and convenient to discretize the DO image. Once the discretized DO is achieved, the discretized second DP 800 may be formed accordingly and used, for example, for accurate source region calculation of interest without having to resort to heuristic threshold binarization and dilation or expansion such as disclosed in PCT / EP2020 / 054545. This can be combined synergistically with an embodiment in which the SMO process may converge to an accurate solution more quickly because the pupil design is guided by diffraction effects rather than an arbitrary design, thereby reducing the computational overhead compared to previous methods. Therefore, in some embodiments, various methods may include determining a discretized DO by discretizing the DO amplitude of DO 700. The method may also include determining a discretized initial pupil by setting the pupil amplitude of the first pupil to discrete values. Then, the determination of the second DP 800 may be performed using the discretized DO and the discretized first pupil. Although setting the amplitude to 1 is an example of discretization, any value may be selected, such as 0.5, 1.5, 2, etc.

[0095] Fig. 9 An exemplary second diffraction pattern in a region of interest according to an embodiment of the present disclosure is illustrated.

[0096] Previous figures (e.g., Figure 8 ) depicts an overlapping second DP 800 covering a range of ± 2NA in standard deviation space. In some embodiments, the region of interest 900 of the initial pupil may be contained within the standard deviation between -NA and +NA. In other embodiments, the second DP may be determined within any other range that may be utilized by the SMO system (e.g., ± 1.5NA, ± 0.5NA, etc.).

[0097] Fig.10 FIG. 2 illustrates an exemplary pupil determined based on an overlapping region of DOs in a first diffraction pattern according to an embodiment of the present disclosure.

[0098] As shown in the area of ​​interest 900, the first DP (e.g., first DP 572) can indicate the number of overlapped diffraction beams, and this can be used as a measure of the light that can be used in the pupil. In particular, the initial pupil can be determined based on the degree of overlap in the overlap zone of the first DP. The "degree of overlap" can be a numerical value as previously described (e.g., 4, 3, 2, etc.) or can be a relative value (e.g., highest, next highest, etc.). In some embodiments, the initial pupil can be determined based on the highest degree of overlap in the overlap zone of the first DP. In this example, based on the area of ​​interest 900, the pupil will have light only in the area with an amplitude of 4 (the highest degree of overlap in the discretized example).

[0099] Another embodiment is Fig.10 , where pupil 1000 includes multiple zones with a degree of overlap exceeding a threshold. For example, such a method may include determining a DO amplitude of a DO, where the initial pupil may be filled if the amplitude of the sum of the first DPs exceeds a threshold for diffraction pattern overlap. In this example, pupil 1000 may include not only position 810 (with amplitude 4), but also adjacent zone 1010 (with amplitude 3).

[0100] Fig.11 FIG. 2 illustrates determining an exemplary initial pupil based on a pupil filling ratio according to an embodiment of the present disclosure.

[0101] In a related embodiment, the determination of the area included in the illustrated pupil can be based on a pupil fill ratio, which is defined herein as the integrated intensity of the filled light divided by the maximum pupil intensity multiplied by the total number of pixels in the pupil. In the case where all amplitudes of the filled pupil points are the same, the illustrated pupil fill ratio is approximately the percentage of the pupil that is filled with light.

[0102] The method for this embodiment is Fig.11 At 1110 , the method can begin with a pupil, such as the first pupil 610 .

[0103] At 1120, the method may include determining an overlap region of the initial pupil based on the first DP. The method may then include generating the initial pupil to include only the region with the most overlap when only the region with the most overlap meets or exceeds a pupil filling ratio threshold. Determining the pupil filling ratio may include calculating an area or fractional area covered by the pupil and comparing it to a desired pupil filling ratio (the pupil filling ratio threshold).

[0104] At 1130, a comparison can be performed to check whether the initial pupil has a pupil filling ratio that reaches or exceeds the pupil filling ratio threshold. If so, at 1140, the initial pupil can be generated using a selected portion of the second DP.

[0105] As shown at 1150, the method may iteratively add subsequent most overlapping zones to the pupil when the initial pupil does not reach or exceed the pupil fill ratio threshold (e.g., adding adjacent zone 1010 with amplitude 3 as shown in the inset). A subsequent comparison is shown at 1160, where additional zones of the first DP are added to the pupil until the pupil fill ratio threshold is reached or exceeded.

[0106] Fig.12 An exemplary segmentation of the source and pupil based on the incident light angle relative to the mask is illustrated in accordance with an embodiment of the present disclosure.

[0107] Because the source is not a point source (i.e., has a finite size), the light from the source that reaches the mask arrives at different angles of incidence. Therefore, during SMO, the accuracy of the aerial image produced by the mask and a given pupil can be improved by utilizing the smaller angles of incidence produced by segmentation. When the source light is segmented into different angles of incidence, this can be expressed as dividing the pupil into corresponding partitions in the standard deviation space. Fig.12 An example of this is depicted in , which shows a pupil 1200 divided into four partitions 1210a, 1210b, 1210c, and 1210d. Based on the pupil determined as described by any of the embodiments herein, each of the partitions may have some light in it. Fig.12 As shown in , each region of the pupil may be decomposed (at 1220) into multiple separate pupils (1220a-1220d) having only light present in a particular partition (1210a-1210d). The segmented pupils may then be processed individually by the SMO process.

[0108] Utilizing mask 1230 through corresponding pupils 1210a to 1210d at stages 1230a to 1230d, a corresponding mask transmittance image 1240 may be generated. Using a segmented source model (e.g., a model simulating light from a source segmented as described above), a suitable projection optics model 32, and a suitable design layout model 35 (see, e.g., Figure 2), a partial aerial image 1250 may be simulated. The partial aerial images may then be added in an incoherent manner at 1260 (i.e., the intensities of the partial aerial images are added without any interference effects) to obtain the aerial image 1270 produced by the entire source pupil 1200. A similar process is described in U.S. 2018-0120709 A1, which is incorporated herein by reference in its entirety.

[0109] Fig.13 is a block diagram of an example computer system CS according to an embodiment of the present disclosure.

[0110] The computer system CS comprises a bus BS or other communication mechanism for communicating information and a processor PRO (or multiple processors) connected to the bus BS for processing information. The computer system CS also comprises a main memory MM, such as a random access memory (RAM) or other dynamic storage device, connected to the bus BS for storing information and instructions to be executed by the processor PRO. The main memory MM can also be used to store temporary variables or other intermediate information during the execution of the instructions to be executed by the processor PRO. The computer system CS also comprises a read-only memory (ROM) ROM or other static storage device connected 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, is provided and connected to the bus BS for storing information and instructions.

[0111] The computer system CS can be connected by a bus BS to a display DS for displaying information to a computer user, such as a cathode ray tube (CRT), or a flat panel or touch panel display. An input device ID including alphanumeric and other keys is connected to the bus BS for communicating information and command selections to the processor PRO. Another type of user input device is a cursor control CC, such as a mouse, trackball, or cursor direction keys, for communicating direction information and command selections to the processor PRO and for controlling cursor movement on the display DS. This input device typically has two degrees of freedom on two axes, a first axis (e.g., x) and a second axis (e.g., y), allowing the device to be positioned in a specified plane. A touch panel (screen) display can also be used as an input device.

[0112] According to one embodiment, part of one or more methods described herein can be executed by computer system CS in response to processor PRO executing one or more sequences of one or more instructions included in main memory MM. These instructions can be read into main memory MM from another computer readable medium (such as storage device SD). The execution of the instruction sequence included in main memory MM causes processor PRO to execute the process steps described herein. One or more processors in a multi-processing arrangement can also be used to execute the instruction sequence included in main memory MM. In an alternative embodiment, hard-wired circuits can be used instead of or in combination with software instructions. Therefore, the description herein is not limited to any specific combination of hardware circuits and software.

[0113] As used herein, the term "computer-readable medium" refers to any medium that participates in providing instructions to the processor PRO for execution. This medium can take many forms, including but not limited to non-volatile media, volatile media and transmission media. Non-volatile media include, for example, optical disks or disks, such as storage devices SD. Volatile media include volatile memories, such as main memory MM. Transmission media include coaxial cables, copper wires and optical fibers, including wires containing bus BS. Transmission media can also be in the form of sound waves or light waves, such as sound waves or light waves generated during radio frequency (RF) and infrared (IR) data communication. Computer-readable media can be non-temporary, such as floppy disks, flexible disks, hard disks, magnetic tapes, any other magnetic media, CD-ROMs, DVDs, any other optical media, punch cards, paper tapes, any other physical media with hole patterns, RAMs, PROMs and EPROMs, FLASH-EPROMs, any other memory chips or cassettes. Non-temporary computer-readable media can have instructions recorded thereon. When executed by a computer, instructions can implement any of the features described herein. Transitory computer readable media may include carrier waves or other propagated electromagnetic signals.

[0114] Various forms of computer-readable media can be involved when one or more sequences of one or more instructions are carried to the processor PRO for execution. For example, the instructions can be initially carried on the disk of a remote computer. The remote computer can load the instructions into its volatile memory and send the instructions via a telephone line using a modem. The modem local to the computer system CS can receive the data on the telephone line and convert the data into infrared signals using an infrared transmitter. The infrared detector connected to the bus BS can receive the data carried in the infrared signal and place the data on the bus BS. The bus BS carries the data to the main memory MM, and the processor PRO obtains the instructions from the main memory MM and executes the instructions. The instructions received by the main memory MM can be optionally stored on the storage device SD before or after being executed by the processor PRO.

[0115] The computer system CS may also include a communication interface CI connected to the bus BS. The communication interface CI provides a bidirectional data communication connection with a network link NDL, which is connected to a local area network LAN. For example, the communication interface CI may be an integrated services digital network (ISDN) card or a modem to provide a data communication connection with a corresponding type of telephone line. As another example, the communication interface CI may be a local area network (LAN) card to provide a data communication connection with a compatible LAN. A wireless link may also be implemented. In any such implementation, the communication interface CI sends and receives electrical, electromagnetic or optical signals carrying digital data streams representing various types of information.

[0116] The network link NDL usually provides data communication with other data devices via one or more networks. For example, the network link NDL can provide a connection to the host computer HC by a local area network LAN. This can include providing data communication services via the global packet data communication network (now generally referred to as the "Internet" INT). Local area networks LAN (Internet) all use electrical signals, electromagnetic signals or optical signals that carry digital data streams. The signals passing through the various networks and the signals on the network data link NDL and passing through the communication interface CI are exemplary carrier forms for conveying information, which carry digital data to and from the computer system CS.

[0117] The computer system CS can send messages and receive data (including program code) by the network, the network data link NDL and the communication interface CI. In the Internet example, the host computer HC can transmit the requested program code for the application program by the Internet INT, the network data link NDL, the local area network LAN and the communication interface CI. For example, one such downloaded application program can provide all or part of the method described herein. The received program code can be executed by the processor PRO when it is received, and / or stored in the storage device SD or other non-volatile storage for later execution. In this way, the computer system CS can obtain the application code in the form of a carrier wave.

[0118] Fig.14 is a schematic diagram of a lithography projection apparatus according to an embodiment of the present disclosure.

[0119] The lithographic projection apparatus may include an illumination system IL, a first stage MT, a second stage WT and a projection system PS.

[0120] The illumination system IL may condition the radiation beam B. In such a particular case, the illumination system also comprises a radiation source SO.

[0121] A first stage (eg, patterning device table) MT may have a patterning device holder for holding a patterning device MA (eg, a reticle) and be connected to a first positioner for accurately positioning the patterning device relative to the article PS.

[0122] A second stage (substrate stage) WT may have a substrate holder for holding a substrate W (eg, a silicon wafer coated with resist), and is connected to a second positioner for accurately positioning the substrate relative to the article PS.

[0123] A projection system ("lens") PS (eg, a refractive, reflective or catadioptric optical system) may image the irradiated portion of the patterning device MA onto a target portion C of the substrate W (eg, comprising one or more dies).

[0124] As depicted herein, the device may be of the transmissive type (i.e., have a transmissive patterning device). However, in general, it may also be of, for example, the reflective type (have a reflective patterning device). The device may employ a different kind of patterning device than a classical mask; examples include a programmable mirror array or an LCD matrix.

[0125] A source SO (e.g. a mercury lamp or an excimer laser, a laser produced plasma (LPP) EUV source) generates a radiation beam. This beam is fed into an illumination system (illuminator) IL, for example directly or after having traversed a conditioning device such as a beam expander Ex. The illuminator IL may include an adjustment device AD ​​for setting the outer radial extent and / or the inner radial extent of the intensity distribution in the beam (commonly referred to as σ-outer and σ-inner, respectively). In addition, it will typically include various other elements, such as an integrator IN and a condenser CO. In this way, the beam B incident on the patterning device MA has a desired uniformity and intensity distribution in its cross-section.

[0126] In some embodiments, the source SO may be within the housing of the lithographic projection apparatus (as is often the case when the source SO is, for example, a mercury lamp), but it may also be remote from the lithographic projection apparatus, the radiation beam generated by the source SO being directed into the apparatus (for example, with the aid of suitable directional reflectors); this latter case may be the case when the source SO is an excimer laser (for example, lasing based on KrF, ArF or F2).

[0127] The beam PB may then intercept the patterning device MA held on the patterning device table MT. Having traversed the patterning device MA, the beam B may pass through a lens PL which focuses the beam B onto a target portion C of the substrate W. With the aid of the second positioning device (and the interferometric measurement device IF), the substrate table WT may be accurately moved, for example in order to position a different target portion C in the path of the beam PB. Similarly, the first positioning device may be used to accurately position the patterning device MA relative to the path of the beam B, for example after mechanical acquisition of the patterning device MA from a patterning device library or during scanning. Typically, movement of the stage MT, WT may be achieved with the aid of a long-stroke module (coarse positioning) and a short-stroke module (fine positioning). However, in the case of a stepper (as opposed to a step-and-scan tool), the patterning device table MT may be connected only to the short-stroke actuator, or may be fixed.

[0128] The depicted tool can be used in two different modes, a step mode and a scan mode. In the step mode, the patterning device table MT is held substantially stationary and the entire patterning device image is projected at once (i.e. a single "flash") onto a target portion C. The substrate table WT is shifted in the x and / or y direction so that a different target portion C can be irradiated by the beam PB.

[0129] In scan mode, essentially the same situation applies, except that a given target portion C is not exposed in a single "flash". Instead, the patterning device table MT can be moved at a speed v in a given direction (the so-called "scanning direction", e.g. the y-direction) so that the projection beam B is scanned over the patterning device image; while the substrate table WT is simultaneously moved in the same or opposite direction at a speed V=Mv, where M is the magnification of the lens PL (typically M=1 / 4 or 1 / 5). In this way, a relatively large target portion C can be exposed without having to compromise resolution.

[0130] Fig.15 is a schematic diagram of another lithographic projection apparatus (LPA) according to an embodiment of the present disclosure.

[0131] The LPA may comprise a source collector module SO, an illumination system (illuminator) IL configured to condition a radiation beam B (eg EUV radiation), a support structure MT, a substrate table WT and a projection system PS.

[0132] The support structure (eg, patterning device table) MT may be configured to support a patterning device (eg, mask or reticle) MA and be connected to a first positioner PM configured to accurately position the patterning device.

[0133] The substrate table (eg, wafer stage) WT may be configured to hold a substrate (eg, a resist-coated wafer) W and connected to a second positioner PW configured to accurately position the substrate.

[0134] The projection system (eg, 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 of the substrate W (eg, comprising one or more dies).

[0135] As depicted in this, the LPA can be of a reflective type (e.g., using a reflective patterning device). It should be noted that because most materials are absorptive in the EUV wavelength range, the patterning device can have a multilayer reflector including, for example, multiple overlapping layers of molybdenum and silicon. In one example, the multiple overlapping layer reflectometry instrument has 40 layer pairs of molybdenum and silicon, where each layer is a quarter wavelength thick. Even smaller wavelengths can be produced using x-ray lithography. Since most materials are absorptive at EUV and x-ray wavelengths, a patterned thin segment of absorbing material on the patterning device topography (e.g., a TaN absorber on top of a multilayer reflector) defines where features will be printed (positive resist) or not (negative resist).

[0136] The illuminator IL receives an extreme ultraviolet radiation beam from the source collector module SO. Methods for generating EUV radiation include, but are not necessarily limited to, converting a material having at least one element (e.g., xenon, lithium, or tin) into a plasma state using one or more emission lines in the EUV range. In one such method, often referred to as laser produced plasma ("LPP"), a plasma can be generated by irradiating a fuel (such as a droplet, stream, or cluster of a material having a line emitting element) with a laser beam. The source collector module SO can be part of an EUV radiation system including a laser that is used to provide a laser beam that excites 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. For example, when a CO2 laser is used to provide a laser beam for fuel excitation, the laser and the source collector module can be separate entities.

[0137] In these cases, the laser may not be considered to form part of the lithographic apparatus, and the radiation beam may be delivered from the laser to the source collector module by means of a beam delivery system comprising, for example, suitable directing mirrors and / or a beam expander. In other cases, for example, when the source is a discharge produced plasma EUV generator (often referred to as a DPP source), the source may be an integral part of the source collector module.

[0138] The illuminator IL may include an adjuster for adjusting the angular intensity distribution of the radiation beam. Typically, at least the outer radial extent and / or the inner radial extent (commonly referred to as σ-outer and σ-inner, respectively) of the intensity distribution in a pupil plane of the illuminator may be adjusted. In addition, the illuminator IL may include various other elements, such as a faceted field mirror arrangement and a faceted pupil mirror arrangement. The illuminator may be used to adjust the radiation beam to have a desired uniformity and intensity distribution in its cross-section.

[0139] The radiation beam B may be incident on a patterning device (e.g. a mask) MA held on a support structure (e.g. a patterning device table) MT and patterned by the patterning device. After reflection from the patterning device (e.g. a mask) MA, the radiation beam B passes through a projection system PS which focuses the radiation beam B onto a target portion C of a substrate W. With the aid of a second positioner PW and a position sensor PS2 (e.g. an interferometric device, a linear encoder or a capacitive sensor), the substrate table WT may be accurately moved, for example in order to position a different target portion C in the path of the radiation beam B. Similarly, a first positioner PM and a further position sensor PS1 may be used to accurately position the patterning device (e.g. a mask) MA relative 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.

[0140] The depicted apparatus LPA can be used in at least one of the following modes: a stepping mode, a scanning mode and a stationary mode.

[0141] In step mode, the support structure (e.g. patterning device table) MT and the substrate table WT are kept substantially stationary while the entire pattern imparted to the radiation beam is projected at one time (i.e. a single static exposure) onto a target portion C. Subsequently, the substrate table WT is shifted in the X and / or Y direction so that a different target portion C can be exposed.

[0142] In scan mode, the support structure (e.g. patterning device table) MT and substrate table WT are scanned synchronously (i.e. single dynamic exposure) as a pattern imparted to the radiation beam is projected onto a target portion C. The speed and direction of the substrate table WT relative to the support structure (e.g. patterning device table) MT may be determined by the (de-)magnification and image reversal characteristics of the projection system PS.

[0143] In stationary mode, the support structure (e.g. patterning device table) MT is kept substantially stationary, thereby holding the programmable patterning device, and the substrate table WT is moved or scanned while a pattern imparted to the radiation beam is projected onto a target portion C. In this mode, a pulsed radiation source is typically employed, and the programmable patterning device is updated as required after each movement of the substrate table WT or between successive radiation pulses during a scan. This mode of operation may be readily applied in maskless lithography using a programmable patterning device, such as a programmable mirror array.

[0144] Fig.16 is a detailed view of a lithographic projection apparatus according to an embodiment of the present disclosure.

[0145] As shown, 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 so that a vacuum environment can be maintained in the enclosure structure ES of the source collector module SO. A plasma source may be generated by discharge to form EUV radiation emitting a thermal plasma HP. EUV radiation may be generated by a gas or vapor (e.g., Xe gas, Li vapor, or Sn vapor), wherein a thermal plasma HP is established to emit radiation in the EUV range of the electromagnetic spectrum. For example, a thermal plasma HP is established by a discharge that generates an at least partially ionized plasma. For efficient generation of radiation, a partial pressure of, for example, 10 Pa of Xe, Li, Sn vapor, or any other suitable gas or vapor may be required. In an embodiment, an excited tin (Sn) plasma is provided to generate EUV radiation.

[0146] The radiation emitted by the hot plasma HP is transferred from the source chamber SC to the collector chamber CC via an optional gas barrier or contaminant trap CT (also referred to as a contaminant barrier or fin trap in some cases) positioned in or behind an opening in the source chamber SC. 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. It is known in the art that a contaminant trap or contaminant barrier CT further indicated herein includes at least a channel structure.

[0147] The collector chamber CC may include a radiation collector CLO which may be a so-called grazing incidence 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 may be reflected from the grating spectral filter SF to be focused in a virtual source point IF along the optical axis indicated by the dotted line "O". The virtual source point IF may be referred to as an intermediate focus, and the source collector module is arranged such that the intermediate focus IF is located at or near an opening OP in the enclosing structure ES. The virtual source point IF is an image of the radiation emitting plasma HP.

[0148] The radiation then traverses an illumination system IL which may include a faceted field mirror arrangement FM and a faceted pupil mirror arrangement PM which are arranged to provide a desired angular distribution of the radiation beam B at the patterning device MA and a desired uniformity of the amplitude of the radiation at the patterning device MA. After reflection of the radiation beam B at the patterning device MA held by the support structure MT, a patterned beam PB is formed and is imaged by the projection system PS via a reflective element RE onto a substrate W held by a substrate table WT.

[0149] In general, there may be more elements than shown in the illumination optics unit IL and the projection system PS. Depending on the type of lithographic apparatus, a grating spectral filter SF may optionally be present. In addition, there may be more mirrors than shown in the figures, for example, there may be 1 to 6 additional reflective elements present in the projection system PS.

[0150] The collector optics CLO may be a nested collector with a grazing incidence reflector GR as just one example of a collector (or collector mirror). The grazing incidence reflector GR is arranged axially symmetrically around the optical axis O, and this type of collector optics CLO may be used in conjunction with a discharge produced plasma source (often referred to as a DPP source).

[0151] Fig.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.

[0152] The source collector module SO can be part of the LPA radiation system. The laser LA can be arranged to deposit laser energy into a fuel such as xenon (Xe), tin (Sn) or lithium (Li), thereby producing a highly ionized plasma HP with an electron temperature of tens of electron volts (eV). The high-energy radiation produced during the deexcitation and recombination of these ions is emitted from the plasma, collected by the near normal incidence collector optical device CLO, and focused onto an opening OP in the enclosure structure ES.

[0153] The concepts disclosed herein can simulate or mathematically model any general imaging system for imaging sub-wavelength features, and can be used in particular with emerging imaging technologies that can produce shorter and shorter wavelengths. Emerging technologies already in use include extreme ultraviolet (EUV), DUV lithography that can produce 193 nm wavelengths by using ArF lasers and even 157 nm wavelengths by using fluorine lasers. In addition, EUV lithography can produce wavelengths in the range of 20 to 50 nm by using a synchrotron or by using high energy electrons to impinge on a material (solid or plasma) in order to produce photons in this range.

[0154] The embodiments of the present disclosure can be further described in the following aspects.

[0155] 1. A method for determining a source for a photolithography process, comprising:

[0156] determining a first pupil having a central obscuration region (CO);

[0157] Determine the diffraction order (DO) based on the target design and mask model;

[0158] determining a first diffraction pattern (DP) based on the DO and the first pupil, the first DP comprising an overlapping region of diffracted light;

[0159] determining a second DP based on the DO and the first pupil; and

[0160] An initial pupil is determined based on the first DP and the second DP, the initial pupil including at least some of the overlap regions.

[0161] 2. The method of clause 1, further comprising performing a source mask optimization (SMO) using initial pupil initialization.

[0162] 3. The method of clause 1, wherein the initial pupil does not include any diffracted light in the CO.

[0163] 4. The method of clause 3, further comprising performing the SMO under the constraint that any pupil produced by the SMO does not include a CO.

[0164] 5. The method of clause 1, wherein the first pupil of a lithography system having a numerical aperture of at least 0.45 is determined for a homogeneous system having a chief ray angle (CRAO) less than or equal to 9.

[0165] 6. The method of clause 1, wherein the first pupil of a lithography system having a numerical aperture of at least 0.5 is determined for an anamorphic (4x8) lithography system.

[0166] 7. The method of clause 1, wherein the central shaded area is circular.

[0167] 8. The method of clause 1, wherein the central shaded region is oval in shape.

[0168] 9. The method of clause 1, wherein the central masking region is rectangular.

[0169] 10. The method of clause 1, wherein the mask pattern is a thick mask pattern.

[0170] 11. The method according to clause 1, wherein the DO includes first-order diffraction light at a DO peak position closest to a zero-order DO peak position.

[0171] 12. The method according to clause 1, wherein the DO comprises a closest first-order diffracted light at a DO peak position orthogonal to the zero-order DO peak position.

[0172] 13. The method of aspect 1, further comprising determining a DO peak position based on a local peak of a DO array, wherein the DO is determined based on the DO peak position.

[0173] 14. The method of aspect 8, wherein the amplitude of the DO is based on the sum of all amplitudes in the corresponding local DO region.

[0174] 15. The method of clause 1, wherein the initial pupil is contained within a standard deviation between -NA and +NA.

[0175] 16. The method of clause 1, further comprising discretizing the DO and utilizing the first pupil having a discrete amplitude to generate the second DP having a discretized amplitude.

[0176] 17. The method of clause 10, wherein the discrete amplitudes of the first pupil and the DO are each set to 1.

[0177] 18. The method of clause 1, wherein the first DP indicates a number of overlapping diffraction beams.

[0178] 19. A method according to aspect 1, wherein the initial pupil is determined based on the degree of overlap in the overlap region of the first DP.

[0179] 20. The method according to aspect 12, further comprising:

[0180] generating a normalized DP based on the degree of overlap exceeding a threshold, wherein the overlap 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

[0181] The normalized DP is multiplied by the second DP to produce the initial pupil.

[0182] 21. A method according to aspect 1, wherein the initial pupil is determined based on a highest degree of overlap in an overlap region of the first DP.

[0183] 22. The method of aspect 1, further comprising determining a DO amplitude of the DO, wherein the initial pupil is filled if a sum amplitude of the first DP exceeds a threshold for diffraction pattern overlap.

[0184] 23. The method according to aspect 1, further comprising:

[0185] determining an overlap region of the initial pupils;

[0186] generating the initial pupil to include only the region with the most overlap when the pupil filling ratio threshold is reached or exceeded by including only the region with the most overlap; and

[0187] Subsequent most overlapping regions are iteratively added to the initial pupil when the initial pupil does not reach or exceed the pupil filling ratio threshold.

[0188] 24. A non-transitory computer-readable medium having recorded thereon instructions for determining a source for use in a photolithography process, the instructions, when executed by a computer having at least one programmable processor, causing operations including those according to any one of aspects 1 to 23.

[0189] 25. A system for determining a source for use with a photolithography process, the system comprising:

[0190] at least one programmable processor; and

[0191] A non-transitory computer-readable medium having recorded thereon instructions that, when executed by a computer having at least one programmable processor, cause the operations of any one of aspects 1 to 23.

[0192] Although the concepts disclosed herein may be used for imaging on substrates such as silicon wafers, it should be understood that the disclosed concepts may be used with any type of lithography imaging system, for example, a lithography imaging system for imaging on substrates other than silicon wafers.

[0193] The combinations and sub-combinations of the elements disclosed herein constitute separate embodiments and are provided only as examples. Likewise, the above description is intended to be illustrative, not restrictive. Therefore, it will be appreciated by those skilled in the art that modifications may be made as described without departing from the scope of the claims set forth below.

Claims

1. A non-transitory computer-readable medium having instructions recorded thereon, wherein: The instructions, when executed by one or more processors, cause the one or more processors to perform a method of determining a source for a photolithography process, the method comprising: determining a first pupil having a central obscuration region (CO); Determine the diffraction order (DO) based on the target design and mask model; determining a first diffraction pattern (DP) based on the DO and the first pupil, the first DP comprising an overlapping region of diffraction patterns; determining a second DP based on the DO and the first pupil; and An initial pupil is determined based on the first DP and the second DP, the initial pupil including at least some of the overlap regions.

2. The non-transitory computer-readable medium of claim 1, wherein: The method also includes performing a source mask optimization (SMO) using the initial pupil.

3. The non-transitory computer-readable medium of claim 1, wherein: The initial pupil does not include any diffracted light in the CO.

4. The non-transitory computer-readable medium of claim 1, wherein: The first pupil of the lithography system is determined to have a numerical aperture of at least 0.45 for a homogeneous system with a chief ray angle (CRAO) less than or equal to 9, or to have a numerical aperture of at least 0.5 for an anamorphic (4×8) lithography system.

5. The non-transitory computer readable medium of claim 1, wherein: The mask model is a thick mask model.

6. The non-transitory computer-readable medium of claim 1, wherein: The DO includes first-order diffraction light at a DO peak position closest to a zero-order DO peak position.

7. The non-transitory computer-readable medium of claim 1, wherein: The DO includes the most proximal first-order diffracted light at a DO peak position orthogonal to the zeroth-order DO peak position.

8. The non-transitory computer readable medium of claim 1, wherein: The method further includes determining a DO peak position based on a local peak of the DO array, wherein the DO is determined based on the DO peak position, The amplitude of the DO is based on the sum of all amplitudes in the corresponding local DO area.

9. The non-transitory computer readable medium of claim 1, wherein: The initial pupil is contained within a standard deviation between -NA and +NA.

10. The non-transitory computer readable medium of claim 1, wherein: The method also includes discretizing the DO and utilizing the first pupil having a discrete amplitude to generate the second DP having a discretized amplitude.

11. The non-transitory computer readable medium of claim 1, wherein: The first DP indicates the number of overlapping diffraction beams.

12. The non-transitory computer readable medium of claim 1, wherein: The initial pupil is determined based on the degree of overlap in the overlap region of the first DP.

13. The non-transitory computer readable medium of claim 121, wherein: The method further comprises: generating a normalized DP based on the degree of overlap exceeding a threshold, wherein the overlap 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 The normalized DP is multiplied by the second DP to produce the initial pupil.

14. The non-transitory computer readable medium of claim 1, wherein: The method further comprises determining a DO amplitude of the DO, wherein the initial pupil is filled if a sum amplitude of the first DP exceeds a threshold for diffraction pattern overlap.

15. The non-transitory computer readable medium of claim 1, wherein: The method further comprises determining an overlap region of the initial pupils; generating the initial pupil to include only the region with the most overlap when the pupil filling ratio threshold is reached or exceeded by including only the region with the most overlap; as well as Subsequent most overlapping regions are iteratively added to the initial pupil when the initial pupil does not reach or exceed the pupil filling ratio threshold.

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