Method and apparatus for imaging using narrowed bandwidth

Abstract

Systems, methods, and computer programs for increasing the contrast of a lithography system are disclosed. In one aspect, the method includes a method for optimizing a method of imaging a feature onto a substrate using a lithography system, the optimization method including: obtaining a spectrum of a beam used for the imaging, wherein the beam includes pulses having a plurality of different wavelengths; narrowing the spectrum of pulses of the beam used for the imaging to improve a quality index of the imaging.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. Application No. 62 / 813,079, filed on March 3, 2019, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The description herein relates generally to improving and optimizing photolithography processes. More specifically, the present disclosure includes apparatus, methods, and computer programs for narrowing the bandwidth of laser light used for imaging to improve contrast. Background Art

[0004] A lithographic projection apparatus may be used, for example, in the manufacture of integrated circuits (ICs). In this case, 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 this pattern may be transferred to a target portion (e.g., including one or more dies) on a substrate (e.g., a silicon wafer) that has been coated with a layer of radiation-sensitive material ("resist") by methods such as irradiating the target portion through the pattern on the patterning device. Typically, a single substrate includes a plurality of adjacent target portions to which the pattern is transferred successively, one target portion at a time, by the lithographic projection apparatus. In one type of lithographic projection apparatus, the pattern on the entire patterning device is transferred to one target portion at a time; such an apparatus may also be referred to as a stepper. In an alternative apparatus, a step-and-scan apparatus is capable of causing a projection beam to be scanned over the patterning device in a given reference direction (the "scanning" direction) while synchronously moving the substrate in a direction parallel or antiparallel to the reference direction. Different portions of the pattern on the patterning device are gradually transferred to one target portion. Since typically a lithographic projection apparatus will have a reduction ratio M (eg 4), the rate F at which the substrate is moved will be 1 / M times the rate at which the projection beam scans the patterning device.More information on lithographic apparatus can be found, for example, in 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 primer coating, 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 series 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 ultimately complete a single layer of the device. If the device requires multiple layers, the entire process or its variation is repeated for each layer. Ultimately, the device will be set in each target portion on the substrate. These devices are then separated from each other by techniques such as slicing or cutting, whereby individual devices can be mounted on a carrier, connected to pins, etc.

[0006] Thus, manufacturing devices (such as semiconductor devices) typically involves using multiple 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 typically manufactured and processed using, for example, deposition, lithography, etching, chemical mechanical polishing, and ion implantation. Multiple devices can be manufactured on multiple dies on a substrate and then separated into separate devices. This device manufacturing process can be considered a patterning process. The patterning process involves a patterning step, such as optical and / or nanoimprint lithography using a patterning device in a lithographic apparatus to transfer the pattern on the patterning device to the substrate, and typically but optionally involves one or more related pattern processing steps, such as resist development by a developing apparatus, substrate baking using a baking tool, etching using a pattern using an etching apparatus, etc.

[0007] As mentioned, photolithography is a core step in the manufacture 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, over the decades, the size of functional elements has continued to decrease 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, multiple layers of a device are fabricated using a lithography projection apparatus that projects a design layout onto a substrate using illumination from a deep ultraviolet illumination source, thereby forming a single functional element having a size 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] Such a process in which features having dimensions smaller than the classical resolution limit of a lithographic projection apparatus are printed may be referred to as low-k 1 Photolithography, which is based on the resolution formula CD = k 1 × 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 smallest feature size printed), and k 1 is the empirical resolution factor. Usually, k 1 The smaller it is, the more difficult it becomes to reproduce a pattern on a substrate that is similar to the shape and size planned by the designer to achieve specific electrical functionality and performance. In order to overcome these difficulties, complex fine adjustment steps are applied to the lithographic projection equipment, design layout or pattern forming device. These steps include, for example, but not limited to: optimization of NA and optical coherence settings, customized illumination schemes, use of phase-shifted pattern forming devices, optical proximity correction (OPC, sometimes also referred to as "optical and process correction") in the design layout, or other methods generally defined as "resolution enhancement technology" (RET). The term "projection optical element" as used in this article should be broadly interpreted as covering various types of optical systems, including, for example, refractive optical devices, reflective optical devices, apertures and reflective refractive optical devices. The term "projection optical element" may also include components that operate according to any of these design types for guiding, shaping or controlling the projection radiation beam collectively or individually. The term "projection optical element" may include any optical component in the lithographic projection equipment, regardless of where the optical component is located on the optical path of the lithographic projection equipment. Projection optics may include optical components for shaping, conditioning and / or projecting radiation from a source before it passes through a patterning device, or optical components for shaping, conditioning and / or projecting radiation after it passes through a patterning device. Projection optics typically do not include a source and a patterning device. Summary of the invention

[0010] Systems, methods, and computer programs for improving contrast in imaging operations are described.

[0011] In an embodiment, a method for optimizing a method for imaging features onto a substrate using a photolithography system comprises: obtaining a spectrum of a light beam used for the imaging, wherein the light beam comprises pulses having a plurality of different wavelengths; and narrowing the spectrum of pulses of the light beam used for the imaging to improve a quality indicator of the imaging.

[0012] In an embodiment, the method may include: obtaining a design of a pattern forming device configured to produce the features on the substrate; obtaining a light source design for the imaging; and simultaneously iteratively changing the spectrum of the light beam, the mask design, and the light source design to provide an optimized spectrum, an optimized mask design, and an optimized light source design.

[0013] In an embodiment, a method of improving contrast in a lithography system includes imaging a pattern onto a substrate using pulses of light having multiple different wavelengths, narrowing a bandwidth of the light pulses.

[0014] In an embodiment, a method of imaging a feature onto a substrate using a lithography system comprises: directing a pulsed beam of light toward a patterning device along a propagation direction, the pulsed beam of light comprising a plurality of light pulses; patterning a set of light pulses in the pulsed beam of light using the patterning device to produce a patterned beam of light; directing the patterned beam of light toward a substrate during a single exposure pass; generating at least a first aerial image and a second aerial image on the substrate during the single exposure pass, the first aerial image being located at a first plane on the substrate and the second aerial image being located at a second plane on the substrate, the first plane and the second plane being spatially different from each other and separated from each other by a separation distance along the propagation direction; and forming a three-dimensional semiconductor component based on an interaction between light in the first aerial image and a material in a first portion of the substrate and an interaction between light in the second aerial image and a material in a second portion of the substrate, wherein at least one of the pulses in the set of pulses has a first wavelength and at least one of the other pulses in the set of pulses has a second wavelength different from the first wavelength, such that the separation distance is formed during the single exposure pass based on a difference between the first wavelength and the second wavelength, and wherein a bandwidth of the set of pulses is narrowed.

[0015] In an embodiment, the bandwidth of the pulses is between 50 fm (femtometers) and 275 fm (femtometers).

[0016] In an embodiment, the pulsed beam is generated in a laser having a nominal bandwidth of 300 fm (femtometers) and the line narrowing module of the laser is adjusted to produce a bandwidth of 50 fm (femtometers) to 275 fm (femtometers).

[0017] In an embodiment, the method comprises selecting the bandwidth to produce an improvement in a quality indicator of the imaging process.

[0018] In an embodiment, the quality indicator is selected from contrast, imaging light intensity logarithmic slope, exposure latitude, and / or normalized imaging light intensity logarithmic slope.

[0019] In an embodiment, the method comprises optimizing the light source design and / or the mask design based at least in part on the bandwidth of the pulses prior to the imaging. The optimization may comprise simultaneously iteratively changing the spectrum of the light beam, the mask design, and the light source design to provide an optimized spectrum, an optimized mask design, and an optimized light source design.

[0020] In an embodiment, a lithography system is configured to perform any of the methods described above.

[0021] Furthermore, according to an embodiment, a computer program product is provided, which includes a non-transitory computer-readable medium having instructions recorded thereon, and the machine-executable instructions implement the above-listed methods when executed by a computer. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] 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 embodiments, help explain some principles associated with the disclosed embodiments. In the drawings,

[0023] Figure 1 A block diagram illustrating various subsystems of a lithographic projection apparatus according to an embodiment.

[0024] Figure 2 An exemplary flow chart for simulating lithography in a lithographic projection apparatus according to an embodiment is illustrated.

[0025] Figure 3 is a graph illustrating an exemplary application of multiple wavelengths of light according to an embodiment.

[0026] Figure 4 is a graph illustrating an exemplary pupil design for forming a light pattern according to an embodiment.

[0027] Figure 5 is a graph illustrating an exemplary mask pattern according to an embodiment.

[0028] Figure 6 A graph illustrating an exemplary effect of using dichroic light according to an embodiment.

[0029] Figure 7 is a graph illustrating exemplary spacing of spectral based sub-resolution assist features in accordance with an embodiment.

[0030] Figure 8 is a graph illustrating a first example of simultaneously or concurrently optimizing the spectrum, mask pattern, and pupil design according to an embodiment.

[0031] Fig. 9is a graph illustrating a second example of simultaneously or concurrently optimizing the spectrum, mask pattern, and pupil design according to an embodiment.

[0032] Fig.10 is a graph illustrating changes to the mask pattern and pupil design based on changes to the bandwidth in the spectrum according to an embodiment.

[0033] Fig.11 is a process flow diagram illustrating an exemplary method for increasing depth of focus according to an embodiment.

[0034] Fig.12 is a process flow diagram illustrating an exemplary method for increasing depth of focus based on a modified spectrum and a modified mask pattern in accordance with an embodiment.

[0035] Fig.13 is a process flow diagram illustrating an exemplary iterative method for increasing depth of focus in accordance with an embodiment.

[0036] Fig.14 is a diagram illustrating a method corresponding to Fig.13 An example graph of the mask pattern and pupil design of the process is shown in FIG.

[0037] Fig.15 is a graph illustrating simulated improvement in Normalized Imaging Light Intensity Log Slope (NILS) produced by using a narrow bandwidth light source according to an embodiment.

[0038] Fig.16 is a graph illustrating simulated improvement in NILS produced by using a narrow bandwidth light source according to an embodiment.

[0039] Fig.17 is a graph illustrating a simulated improvement in exposure latitude (EL) produced by using a narrow bandwidth light source according to an embodiment.

[0040] Fig.18 is a block diagram of an example computer system according to an embodiment.

[0041] Fig.19 is a schematic diagram of a lithographic projection apparatus according to an embodiment. DETAILED DESCRIPTION

[0042] 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 herein 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.

[0043] 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, 248, 193, 157 or 126 nm) and EUV (i.e., extreme ultraviolet radiation, e.g., having a wavelength in the range of about 5 to 100 nm).

[0044] The pattern forming device may include or may form one or more design layouts. The design layout may be generated using a CAD (i.e., computer-aided design) process. This process is often referred to as EDA (i.e., electronic design automation). Most CAD programs follow a set of predetermined 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 restrictions in 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 / gap between two lines or two holes. Thus, CD determines the total size and density of the designed device. Of course, one of the goals in device manufacturing is to faithfully reproduce the original design intent (via a pattern forming device) on a substrate.

[0045] 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.), examples of other such patterning devices include programmable mirror arrays and / or programmable LCD arrays.

[0046] 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 on which such a device is based is that (for example) addressed areas of the reflective surface reflect incident radiation as diffracted radiation, while unaddressed areas reflect incident radiation as non-diffracted radiation. Using suitable filters, the non-diffracted radiation can be filtered out of the reflected beam, so that only the diffracted radiation remains; in this way, the beam is patterned according to the addressing pattern of the matrix-addressable surface. The required matrix addressing can be performed by using suitable electronic methods.

[0047] An example of a programmable LCD array is given in US Pat. No. 5,229,872, which is incorporated herein by reference.

[0048] Figure 1 A block diagram of various subsystems of a lithographic projection apparatus 10A according to an embodiment is illustrated. The main components 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 need not have a radiation source itself); an illumination optical device, which, for example, defines partial coherence (expressed as a standard deviation) and may include optical devices 14A, 16Aa and 16Ab that shape the radiation from source 12A; a patterning device (or mask) 18A; and a transmission optical device 16Ac, which projects an image of the patterning device pattern onto a substrate plane 22A.

[0049] Pupil 20A may be included in transmission optics 16Ac. In some embodiments, one or more pupils may be present before and / or after mask 18A. As described in further detail herein, pupil 20A may provide patterning of light that ultimately reaches substrate plane 22A. An adjustable filter or aperture at the pupil plane of the projection optics may constrain the range of beam angles impinging on substrate plane 22A, where the maximum possible angle defines the numerical aperture NA=n sin(θ max ), where n is the refractive index of the medium between the substrate and the last element of the projection optics, and θ max is the maximum angle of the beam emerging from the projection optics that can still impinge on the substrate plane 22A.

[0050] In a lithographic projection apparatus, a source providing illumination (i.e., radiation) to a pattern forming device and projection optics directs and shapes the illumination onto a substrate via the pattern forming device. The projection optics may include at least some of components 14A, 16Aa, 16Ab, and 16Ac. An aerial image (AI) is a distribution of radiation intensity at the substrate level. A resist model may be used to calculate a resist image based on the aerial image, and an example of this situation may be found in U.S. Patent Application Publication No. US 2009-0157630, the entire disclosure of which is hereby incorporated by reference. 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, pattern forming device, and projection optics) specify the aerial image and may be defined in an optical model. Since the patterning device used in a lithographic projection apparatus can be varied, it is desirable to decouple 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 the projection optics. Techniques and models for transforming a design layout into various lithographic images (e.g., aerial images, resist images, etc.), using which OPC is applied and performance (e.g., in terms of process windows) is evaluated, are described in U.S. Patent Application Publication Nos. US2008-0301620, 2007-0050749, 2007-0031745, 2008-0309897, 2010-0162197, and 2010-0180251, the disclosure of each of which is hereby incorporated by reference in its entirety.

[0051] One aspect of understanding the lithography process is understanding the interaction of the radiation with the patterning device. The electromagnetic field of the radiation after the radiation passes through the patterning device can be determined based on the electromagnetic field of the radiation before it reaches the patterning device and a function that characterizes the interaction. Such a function can be called a mask transmission function (which can be used to describe the interaction by the transmission patterning device and / or the reflection patterning device).

[0052] The mask transmission function can have a variety of different forms. One form is binary. A binary mask transmission function has any of two values ​​(e.g., zero and a positive constant) at any given location on the pattern forming device. A mask transmission function in binary form can 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 location on the pattern forming device. The phase of the transmittance (or reflectance) can also be a continuous function of the location on the pattern forming device. A mask transmission function in continuous form can be referred to as a continuous tone mask or a continuous transmission mask (CTM). For example, a CTM can be represented as a pixelated image, in which each pixel can be assigned, that is, 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 multiple values ​​(eg, in the range [-255, 255], normalized values ​​in the range [0, 1] or [-1, 1] or other suitable range).

[0053] The thin mask approximation, also known as the Kirchhoff boundary condition, is widely used to simplify the determination of the interaction of the 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 multiplication of the incident electromagnetic field and the mask transmission function. However, as lithography processes use radiation with shorter and shorter wavelengths, and the structures on the patterning device become smaller and smaller, the assumption or assumption of the thin mask approximation breaks down. For example, the interaction of radiation with structures (such as the edge between the top surface and the sidewalls) can become significant due to the finite thickness of the structures ("mask 3D effect" or "M3D"). Including this scattering in the mask transmission function may enable the mask transmission function to better capture the interaction of the radiation with the patterning device. The mask transmission function under the thin mask approximation may be referred to as a thin mask transmission function. A mask transmission function covering M3D may be referred to as an M3D mask transmission function.

[0054] 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, which 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 or recognized 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 an 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, a relative intensity value may be based on a percentage. For example, the weak signal may be a signal having an intensity less than 50% of the highest intensity of the pixels 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 may be considered as a variable. According to this 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 the cost function. For example, a CTM image may include pixels, where each pixel is a variable that may take any real value.

[0055] Figure 2 An exemplary flow chart for simulating lithography in a lithographic projection apparatus according to an embodiment is illustrated. A source model 31 represents the optical properties of the source (including radiation intensity distribution and / or phase distribution). A projection optics model 32 represents the optical properties of the projection optics (including changes to the 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 to the radiation intensity distribution and / or phase distribution caused by the design layout 33), which is a representation of the arrangement of features on or formed by a pattern forming device. An aerial image 36 can be simulated based on the design layout model 35, the projection optics model 32, and the design layout model 35. A resist image 38 can be simulated based on the aerial image 36 using a resist model 37. The simulation of lithography can, for example, predict the contour and CD in the resist image.

[0056] More particularly, it should be noted that the source model 31 can represent the optical properties of the source, including but not limited to numerical aperture settings, illumination mean square deviation or standard deviation (σ) settings, and any specific illumination shape (e.g., off-axis radiation sources such as toroidal, quadrupole, dipole, etc.). The projection optics model 32 can represent the optical properties 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, for example, 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 an intended design. An intended 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.

[0057] From this design layout, one or more portions referred to as "clips" may be identified. In an embodiment, a set of clips are extracted that 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 / checking. In other words, a clip may be a portion of the design layout, or may be similar or have similar behavior of multiple portions of the 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 contain one or more test patterns or gauge patterns.

[0058] An initial larger set of 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, an initial larger set of segments may be extracted from the entire design layout using some automated (such as machine vision) or manual algorithm that identifies one or more critical feature areas.

[0059] In a lithographic projection apparatus, as an example, the cost function can be expressed as

[0060]

[0061] Among them (z 1 ,z 2 ,…,z N ) are N design variables or their values. p (z1 ,z 2 ,…,z N ) can be a design variable (z 1 ,z 2 , …, z N ), such as for (z 1 , z 2 , …, z N ) is the difference between the actual and expected values ​​of a characteristic for a set of values ​​of a design variable. p is with f p (z 1 , z 2 , …, z N ) is associated with a weight constant. For example, the characteristic may be the position of the edge of the pattern measured at a given point on the edge. Different f p (z 1 , z 2 , …, z N ) can have different weights w p For example, if a particular edge has a narrow range of allowed positions, then the value for f that represents the difference between the actual position of the edge and the expected position is p (z 1 ,z 2 ,…,z N )’s weight w p can be given a higher value. p (z 1 ,z 2 ,…,z N ) may also be a function of interlayer characteristics, which in turn are the design variables (z 1 ,z 2 ,…,z N ) function. Of course, CF(z 1 ,z 2 ,…,z N ) is not limited to the form in equation 1. CF(z 1 ,z 2 ,…,z N ) may be in any other suitable form.

[0062] The cost function may represent any one or more suitable characteristics of the lithographic projection apparatus, the lithographic process, or the substrate, such as focus, CD, image shift, image deformation, image rotation, random variation, throughput, local CD variation, process window, inter-layer characteristics, or a combination thereof. In one embodiment, the design variable (z 1 ,z 2 ,…,z N) includes one or more selected from dose, global bias of the patterning device, and / or shape of the irradiation. 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, f p (z 1 ,z 2 ,…,z N ) may simply be the distance between a point in the resist image and the expected position of that point (i.e., the edge placement error EPE p (z 1 ,z 2 ,…,z N )). The design variables may include any adjustable parameters, such as adjustable parameters of the source, the patterning device, the projection optics, dose, focus, etc.

[0063] The lithographic apparatus may include components commonly 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, the source, the pattern forming device, temperature changes in the lithographic projection apparatus, thermal expansion of components 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. Such changes can be simulated according to a model, or actually measured. The design variables may include parameters of the wavefront manipulator.

[0064] The design variables may have constraints, which may be expressed as (z 1 ,z 2 ,…,z N)∈Z, where Z is a set of possible values ​​for the design variables. A possible constraint on the design variables may be imposed by the required throughput of the lithographic projection apparatus. In the absence of such a constraint imposed by the required throughput, the optimization may result in a set of values ​​for the design variables that are impractical. For example, if dose is a design variable, then in the absence of such a constraint, the optimization may result in dose values ​​that make throughput economically impossible. However, the usefulness of a constraint should not be interpreted as necessity. For example, the throughput may be affected by the pupil fill ratio. For some illumination designs, a low pupil fill ratio may discard radiation, resulting in lower throughput. 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.

[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., a lens system / projection system used to transmit light during a lithography process, and may include modeling the final optical image of the light reaching the resist), a resist model (e.g., a physical effect of the resist, such as due to chemical effects of light), an optical proximity correction (OPC) model (e.g., which may be used to manufacture a mask or reticle, and may include sub-resolution resist features (SRAF), etc.).

[0066] As used herein, the term "simultaneously" (or "concurrently"), for example when referring to "changing simultaneously or concurrently," means that two or more things occur at substantially, but not necessarily exactly, the same time. For example, changing a pupil design simultaneously or concurrently using a mask pattern may mean making a small modification to the pupil design, followed by a small adjustment to the mask pattern, and then making another modification to the pupil design, and so on. However, the present disclosure contemplates that in some parallel processing applications, simultaneously may refer to multiple operations occurring at the same time or with some overlap in time.

[0067] As an introduction, the present disclosure provides systems, methods and computer program products that are particularly related to modifying or optimizing features of a lithography system to improve performance and manufacturing efficiency. Features that can be modified can include spectra of light used in lithography processes, masks, pupils, etc. Any combination of these features (and possible other features) can be implemented to improve, for example, the depth of focus, process window, contrast, etc. of the lithography system. Of particular importance is the fact that, in some embodiments, the modification of a feature affects other features. In this way, multiple features can be modified / changed simultaneously to achieve the desired improvement, as described below.

[0068] Figure 3 is a graph illustrating an exemplary application of multiple wavelengths of light according to an embodiment.

[0069] In an embodiment, a laser or plasma emission having a single wavelength of light (i.e., having a central wavelength) may be used for a photolithography process. An example of such a single wavelength spectrum 310 is represented by Figure 3 Here we see that a simplified representation of a single wavelength of light can include amplitude 320, center wavelength, and bandwidth 330 (the shape of spectrum 310 is shown relative to the center wavelength, which can be any value). Any of the example spectra (or portions thereof) described herein can be roughly Lorentzian, Gaussian, or other such profiles of a light beam.

[0070] In another embodiment, light having a multi-wavelength spectrum 340 (also referred to herein as a polychromatic spectrum) may be used. An example of this is shown in FIG. Figure 3 340 is illustrated by the middle figure, which shows two peaks representing two different light beams having a first center wavelength 342 and a second center wavelength 344 different from the first center wavelength 342. In this way, the spectrum 340 can be a polychromatic spectrum, wherein the polychromatic spectrum includes at least two different peaks with a peak spacing 346. Although light is generally discussed herein as having two center wavelengths, this should not be considered limiting. For example, light having any number of center wavelengths (four, five, ten, etc.) can be implemented in a manner similar to that described for the two-color light discussed throughout the present disclosure. Similarly, more complex patterns or waveforms of light can be combined to approximately reproduce the desired primary light peaks.

[0071] Figure 3 The bottom portion of illustrates that the light corresponding to the polychromatic spectrum 340 can come from a light source, where the light of multiple colors is transmitted at different times. For example, the two different light wavelengths can be transmitted in bursts 350, wherein the center wavelength of the light alternates between bursts. In other embodiments, the two light wavelengths can be transmitted approximately simultaneously (e.g., emitted by multiple laser systems or multi-wavelength plasmas, combined to form a two-color light pattern). The transmission of light can be at any part of the photolithography system. In some embodiments, the light can be transmitted to components such as lenses or pupils. In addition, the light can be transmitted to other components such as apertures, masks, reticles, substrates, etc. Figure 1 An example of the optical path of light through an example lithography system is illustrated in FIG.

[0072] In some embodiments, the light may be delivered with further changes in the central wavelength (other than just making the spectrum "bichromatic"). This has the effect of "blurring" the delivered light, and may also result in the beneficial effect of increasing exposure latitude at the expense of only slightly reducing the depth of focus. For example, any central wavelength of the peak of the spectrum may be changed (e.g., increased or decreased) by approximately 1 fm (i.e., femtometer), 10 fm, 50 fm, 100 fm, 200 fm, 500 fm, 1000 fm, etc. The changes may be set to specific values, or may be selected so that the increase in exposure latitude is maximized relative to the reduction in depth of focus. Furthermore, in some embodiments, the changes may be applied to every other pulse (i.e., alternating), but may also be applied to every third pulse, every fourth pulse, etc. In this way, the spectrum may be provided as a series of pulses, wherein the central wavelength in at least one peak in the spectrum is further changed in every other pulse to shift by approximately 500 fm.

[0073] Figure 4 is a graph illustrating an exemplary pupil design 410 for forming a light pattern according to an embodiment.

[0074] In an embodiment, a lithography system may include one or more pupils. As part of the lithography process, the light may be converted into a specified pattern (e.g., having a specific spatial distribution of intensity and / or phase) before it passes through the mask. As used herein, the term "pupil design" refers to the pattern of light produced by the physical construction or configuration of the pupil. Throughout this disclosure, a pupil design is referred to together with an image of light representing the pupil design, and the intensity of the light of the pupil design. Figure 4 An example of a pupil design 410 is illustrated in the top portion of FIG. Here, the circular area represents light of varying intensity shown by different colors. Such pupil designs as illustrated herein are intended only as examples and should not be considered limiting in any respect.

[0075] In an embodiment, the pupil may be a glass disk, referred to herein as a diffractive optical element (DOE) 420. The material structure of the DOE 420 may cause the light to be deflected and combined to form a specific pupil design. Because the pupil design is set by the structure of the DOE 420, a different DOE 420 may be required for each desired pupil design.

[0076] In another embodiment, the pupil may be a mirror array 430, which is composed of many small mirrors that can be individually controlled to produce the pupil design. Examples of DOE 420 and mirror array 430 are shown in FIG. Figure 44 is illustrated in the bottom portion of FIG. 4. DOE 420 is shown on the left side as receiving a light beam and then emitting the illustrated pupil design 410. On the right side is an example mirror array 430, where light is incident on a collection of mirrors. By the specific configuration of the mirror array 430, the pupil design 410 (shown here as equivalent to the pupil design formed by the DOE 420) can also be formed.

[0077] Figure 5 is a graph illustrating an exemplary mask pattern according to an embodiment.

[0078] In many photolithography processes, it is desirable to use a mask to perform selective blocking of light to affect a specific pattern on a photoresist or substrate. As used herein, "mask" refers to the actual physical mask itself. In contrast, as used herein, "mask pattern" refers to the shape of the features of the mask. Such features may include, for example, channels, slots, holes, ridges, areas of variation of different light transmission (e.g., in a continuous transmission mask), and the like. Figure 5 An ideal mask pattern 510 is illustrated in the top portion of . Here, the ideal mask pattern 510 consists of perfect horizontal and vertical lines, and these are referred to herein as main features 512. However, in actual lithography processes, diffraction effects and limitations in the resolution of the transmitted light do not allow such an ideal mask pattern 510 to be reproduced at the substrate. In order to compensate for these limitations, a process known as optical proximity correction (OPC) can be implemented. OPC adds small features (known as auxiliary features 520) to the mask, which when combined with the pattern of light incident on the mask create an improved pattern (also known as an aerial image) at the substrate. In Figure 5 In the illustration of FIG. 5 , these auxiliary features 520 are added to the main features 512 and can be seen as a slight deviation from the ideal mask pattern 510. In addition, in some cases, entirely new features can be added to further compensate for (or exploit) diffraction effects. These features, referred to herein as sub-resolution auxiliary features (SRAFs) 522, are also shown in FIG. Figure 5 510 by a heavier weight line that is not present in the ideal mask pattern 510. As used herein, the general term "assist feature" may refer to the assist feature 520 shown as a modification to the main feature 512, or may refer to the SRAF 522.

[0079] Figure 6 A graph illustrating an exemplary effect of using dichroic light according to an embodiment.

[0080] The present disclosure provides, among other things, a method for increasing the depth of focus of a lithography system. The method may include providing a spectrum, a mask pattern, and a pupil design, wherein the spectrum, the mask pattern, and the pupil design are configured together to provide the lithography system with a depth of focus. The method may also include iteratively changing the configuration of the spectrum and one or more reflectors in a reflector array to provide a modified spectrum and a modified pupil design that increases the depth of focus. One or more of the multiple reflectors in the reflector array may then be configured based on the modified pupil design and the modified mask pattern that increases the depth of focus. As used herein, "depth of focus" means the distance at which light at a desired location (e.g., at the substrate, at the photoresist, etc.) is considered to be "in focus". The specific number corresponding to whether the light is in focus can be automatically defined by the user and can be changed as requested for a given application, and this can be referred to as a "specification".

[0081] exist Figure 6 , a graph of exposure latitude versus depth of focus is shown for a monochromatic spectrum 610 (circle symbols) and a bichromatic spectrum 620 (triangle symbols). Here, by changing the spectrum from monochromatic to bichromatic (e.g., in a simulation performed according to one or more of the models described herein, such as OPC, resist, source, etc.), an increased depth of focus is produced, as well as a change in exposure latitude.

[0082] The modified spectrum (or any "modified" feature) need not be a final or optimized feature, but it can be. For example, a modified spectrum can be an intermediate step, where the initial spectrum has been modified but may not be a final solution. However, as described herein, a modified feature can be an optimization or best solution for a particular aspect involved (e.g., a modified spectrum, a modified mask pattern, or a modified pupil design). Reference Fig.13 Discuss this situation further.

[0083] In some embodiments of the present disclosure, simultaneous changes can be implemented by a computer-implemented process collectively referred to herein as an optimization module. The optimization module can jointly optimize and analyze any number of aspects of the lithography system, for example, the spectrum, mask pattern, pupil design, main features, SRAF, and the like. The optimization module can include any number of computer programs distributed across any number of computing systems. Predictive modeling and machine learning techniques (e.g., trained models as part of the optimization module) can also be included. The optimization module can provide improved solutions in the form of graphical displays, data files, and the like. For example, these solutions can include mask patterns, photoresist parameters, light source settings, pupil configurations, and the like.

[0084] In some embodiments, the optimization module may modify and / or optimize the spectrum, for example to increase or maximize the depth of focus. Thus, in an embodiment, iterative changes may include changing the bandwidth of the peaks in the spectrum 340. Similarly, in another embodiment, iterative changes may also include changing the peak spacing 346 between two (or more) peaks in the spectrum 340.

[0085] Due to the interdependencies between some components of the lithography system, and when considered for joint optimization by the optimization module, changing one aspect of the lithography system may affect another aspect. For example, when increasing the depth of focus, changing the spectrum 340 can cause the pupil design 410 to change so that (for example) the contrast loss may be reduced. As used herein, the illustrations showing the spectrum, pupil design, and mask pattern can also refer to the initial or modified version, and for simplicity, they are all referred to herein by similar reference numerals. The modified pupil design 410 can be implemented as a data file containing programming instructions or operation sequences of the mirror array. For example, the modified pupil design can specify the angle or orientation of the mirrors in the mirror array 430 so that the desired modified pupil design 410 is created.

[0086] Figure 7 is a diagram illustrating exemplary spacing of sub-resolution assist features based on the spectrum according to an embodiment.

[0087] exist Figure 7 A simplified example of a portion of a mask pattern 710 is shown in the top panel of Here, the mask pattern 710 shows a main feature 720, a critical dimension 730, a mask offset 740, and two SRAFs 750 separated from the center of the main feature by a SRAF spacer 760.

[0088] Similar to the embodiments described above, in which a change in the spectrum can result in a change in the pupil design, the method can include providing a spectrum, a mask pattern 710, and a pupil design, the spectrum, the mask pattern, and the pupil design together being configured to provide a depth of focus to the lithography system. The method can also include iteratively changing the spectrum and the auxiliary features in the mask pattern to provide a modified spectrum and a modified mask pattern that increases the depth of focus. The components of the lithography system can then be configured based on the modified spectrum and the modified mask pattern 710 that increases the depth of focus. For example, the components can include any combination of the mask, the light source, the pupil, or other components of the lithography system. In general, the process of optimizing the illumination spectrum, the pupil, and the mask is referred to as source-mask optimization (SMO).

[0089] The mask pattern 710 can be iteratively changed simultaneously with the spectrum to provide a modified spectrum and a modified mask pattern 710. The iterative change can also include changing the main feature 720 in the mask pattern 710 to increase the depth of focus. The main feature 720 can include an edge portion and / or a mask bias 740, and the iterative change can also change at least one of the edge portion or the mask bias portion. In some embodiments, two mask bias portions can be changed symmetrically around the center 735 of the main feature 720. As used in these embodiments, symmetrically changing means making corresponding changes in the mask bias portions on either side of the center 735 of the main feature 720 so that a plurality of the mask bias portions have the same distance from the center 735 of the main feature 720.

[0090] The modified mask pattern 710 may include a modification of the mask pattern 710 by applying a Figure 5 The features added by OPC or changes to SRAF are performed on the mask shown in FIG. Figure 7 As shown in , the iterative changes may include changing the sub-resolution assist features in the mask pattern 710 to increase the depth of focus. In some embodiments, the iterative changes may include changing the sub-resolution assist features 750 by changing at least one of the position or width of the sub-resolution assist features 750. Figure 7 As shown in the bottom figure of FIG, the Normalized Imaging Light Intensity Log Slope (NILS), which is a measure of aerial image quality, is maximized by different SRAF spacings 760 when comparing the monochromatic spectrum (circles) 770 to the bichromatic spectrum (triangles) 780. In the given example, the spacing 760 is changed from 125 nm (in the case of monochromatic spectrum) to 130 nm (in the case of bichromatic spectrum) for peak NILS. In this way, the optimization module can determine the spacing 760, location, etc. of the SRAF 750 that increases the quality of the aerial image.

[0091] Figure 8 is a graph illustrating a first example of simultaneously optimizing the spectrum, mask pattern, and pupil design according to an embodiment.

[0092] Optimization of the combination of aspects of the lithography system as described herein can be as follows Figure 8 The benefits to the performance of the lithography system are shown in FIG. 8. Shown is a simulated monochromatic spectrum 810 (with an arbitrarily small bandwidth) and also a simulated dichroic spectrum 850. Examples of modified pupil designs 812 and 852 are shown for the monochromatic spectrum 810 and the dichroic spectrum 850, respectively. For the monochromatic spectrum 810, Figure 8A simulated continuous transmission mask (CTM) 814, mask 816 (e.g., a representation of a mask with slots corresponding to the primary features and the secondary features), and a resulting aerial image 818 are shown. Similarly, for the two-color spectrum 852, CTM 854, mask 856, and aerial image 858 are also shown. While generally similar in appearance, there are differences between the two solutions (most easily seen by the changes in the spacing of the SRAFs in masks 816 and 856). The results of the solutions are shown in Figure 8 , wherein the optimization increases the process window (PW). The process window is illustrated by the area between the curves and is a function of the provided dose at a given focal length. The dose-focus curve corresponding to the two-color spectrum is shown by a plurality of triangular points 820, and the dose-focus curve corresponding to the monochromatic spectrum is shown by a plurality of circle points 860. The two ovals 822 and 862 that touch their respective curves correspond to the ideal PW. It can be seen that in the lower right figure, when the two-color spectrum is implemented together with the optimization of the mask pattern and the pupil design, the process window is increased. Similarly, in this example, the two-color focal depth 864 (shown by a plurality of triangles on the lower right figure) increases from about 144nm to 320nm compared to the monochromatic focal depth 824, and only slightly reduces the exposure latitude.

[0093] Any classification or number of indicators may be increased or optimized by the methods disclosed herein. While there may be a trade-off or trade-off between some parameters that are increased and other parameters that are decreased due to the changes (e.g., DOF compared to EF), in some embodiments, the iterative changes may include performing the changes at least until the product of the depth of focus and the exposure latitude increases. Similarly, the iterative changes may include performing the iterative changes at least until the process window is increased based on a region defined at least in part by dose and exposure latitude.

[0094] Fig. 9 is a graph illustrating a third example of simultaneously optimizing the spectrum, mask pattern, and pupil design according to an embodiment.

[0095] Fig. 9 The embodiment illustrated in FIG. 1 may include iteratively varying spectrum 910, mask pattern 914, and pupil design 912 simultaneously to provide modified spectrum 950, modified mask pattern 954, and modified pupil design 952. Although similar to Figure 8 ,but Fig. 9 The mask pattern 914 and the modified mask pattern 954 are shown where not only are there small features along the main features that have been changed, but also entirely new SRAFs have emerged (or disappeared) as part of the improved solution. These areas of significant change are indicated by dashed lines. Similar to Figure 8As an example, the depth of focus of the two-color spectrum is significantly increased when using a monochromatic spectrum with only a moderate reduction in exposure latitude.

[0096] Fig.10 is a graph illustrating changes to mask pattern and pupil design based on changes to bandwidth in the spectrum according to an embodiment.

[0097] In addition to changing the central wavelength of the two-color spectrum, the bandwidth of one or more peaks of the spectrum can also be changed as part of the optimization process. As a simplified example, Fig.10 Four pupil designs 1010 are shown in which the bandwidth of the monochromatic spectrum is varied (e.g., 300 fm, 900 fm, 1300 fm, 2000 fm). It can be seen that the optimization module can generate modified mask patterns 1010 and modified pupil designs 1020 in an attempt to maintain or increase the contrast at the aerial image. Therefore, in some embodiments, the iterative changes can include constraining the changes to increase the contrast at the aerial image when the changes in the spectrum result in an increase in the bandwidth of the peaks in the spectrum. Although shown for a monochromatic spectrum, a similar process can be applied using a two-color spectrum.

[0098] As is apparent from this disclosure, there are many possible optimizations that can be caused by simultaneously changing multiple aspects of the lithography system. Although each arrangement or permutation is not described in detail, all such arrangements or permutations are considered to be within the scope of this disclosure. For example, the spectrum, bandwidth, peak spacing, mask pattern, main features, auxiliary features, pupil design, process model (OPC, resist, etc.) can be changed in any combination to improve the lithography system. Similarly, changes can be performed to improve any combination of depth of focus, exposure latitude, dose, focal length, contrast, NILS, process window, etc. In addition, changes can be performed to reduce any combination of edge placement error, mask error enhancement factor (MEEF), etc.

[0099] As described herein, embodiments of the present disclosure may be used to provide prescriptions for configurations of lithography systems. Thus, based on the solutions provided by the optimization process, the components of the optical system may be constructed and / or configured to achieve the determined benefits. For example, in an embodiment, the component may be a laser configured to provide light based on a modified spectrum. In an embodiment, the component may be a mask manufactured based on a modified mask pattern. In an embodiment, the component may be a pupil in the form of a diffractive optical element manufactured based on a modified pupil design. In another embodiment, the pupil may be a mirror array configured based on a modified pupil design. Another embodiment may include configuring a mirror array based on a modified pupil design and also manufacturing a mask based on a modified mask pattern.

[0100] Fig.11 is a process flow diagram illustrating an exemplary method for increasing depth of focus according to an embodiment.

[0101] In an embodiment, a method for increasing the depth of focus of a lithography system may include providing a spectrum, a mask pattern, and a pupil design, the spectrum, the mask pattern, and the pupil design together configured to provide a depth of focus to the lithography system at step 1110. The method may iteratively change the spectrum and assist features in the mask pattern to provide a modified spectrum and a modified mask pattern that increases the depth of focus at step 1120. At step 1120, components of the lithography system may be based on the modified spectrum and the modified mask pattern that increases the depth of focus.

[0102] Fig.12 is a process flow diagram illustrating an exemplary method for increasing depth of focus based on a modified spectrum and a modified mask pattern in accordance with an embodiment.

[0103] In an embodiment, a method for increasing the depth of focus of a lithography system may include providing a spectrum, a mask pattern, and a pupil design, the spectrum, the mask pattern, and the pupil design together configured to provide a depth of focus to the lithography system at step 1210. The method may iteratively change the spectrum and the configuration of one or more mirrors in a mirror array to provide a modified spectrum and a modified pupil design that increases the depth of focus at step 1220. At step 1220, one or more mirrors of the mirror array may be configured based on the modified spectrum and the modified pupil design that increases the depth of focus.

[0104] Fig.13 is a process flow diagram illustrating an exemplary iterative method for increasing depth of focus in accordance with an embodiment. Fig.14 is a diagram illustrating a method according to an embodiment Fig.13 Graphs of examples of pupil designs and mask patterns corresponding to the process shown in .

[0105] Performing a co-optimization (or a concurrent optimization process) involving changing two or more features of a spectrum, pupil design, or mask pattern can be iteratively performed to produce, for example, a modified spectrum, a modified pupil design, or a modified mask pattern that will result in an increased depth of focus. For example, when a desired metric is not met (e.g., 150nm DOF at 5% EL), the spacing between two or more peaks of the plurality of peaks in the spectrum can be changed to determine the spacing that achieves the desired metric. In addition, constraints can be applied so that the spectrum, pupil design, and mask pattern meet certain process requirements, such as a mask with a specific transmittance or a pupil with specific physical properties. An example implementation of a co-optimization of a spectrum, pupil design, and mask pattern including examples of these constraints is described below.

[0106] At step 1310, setup parameters specifying aspects of the lithography system may be obtained / set for computational simulation as described herein (e.g., to perform a co-optimization process). The setup parameters may include any combination of imaging conditions, including polarization of light from the light source, configuration of the film stack on which the photoresist is coated, mask rule check (MRC) parameters, photoresist, photoresist thickness, film stack on which the photoresist is coated, capabilities of a scanner (e.g., numerical aperture, polarization, Zernike coefficients), etc. These parameters may be received from another computer and in the form of a data file, and may also include default setup parameters including default values ​​for any of the above. Alternatively, the setup parameters may be defined by a user and stored as a data file or in a temporary computer memory.

[0107] At step 1320, a spectrum may be generated (e.g., as determined by Figure 3 310 or 340 in FIG. 3 ). Initially, the spectrum may include a single wavelength (meaning having a single center wavelength / peak). In other embodiments, as described herein, a multi-wavelength spectrum (e.g., two, three, or more center wavelengths / peaks) may be generated. In some embodiments, the bandwidth of any of the spectra (single or multiple) may be initially set to, for example, 200 fm, 300 fm, 400 fm, etc., and subsequently changed throughout the iterative process.

[0108] At step 1330, a process window based on a point source model may be generated. This may model the light source as a point source, but in some embodiments may include a more complex source model, such as a finite size source approximation. The process window conditions may be defined, such as optimizing to achieve a process window with a 150nm depth of focus at a 5% exposure latitude, or approaching such a target process window until optimal convergence is achieved based on other constraints of the simulation. Such numbers are intended only as examples, for example, the process window may be based on any combination of process windows with a depth of focus greater than 1nm, 5nm, 10nm, 20nm, 50nm, 75nm, 150nm, 200nm, 300nm, 500nm, or 1000nm. Similarly, the exposure latitude may be defined as less than 1%, 3%, 8%, 10%, 15%, 20%, 30%, or 50%.

[0109] At step 1340, an unrestricted pupil design 1440 (such as Fig.14 1440 for incorporation into the iterative process. An unrestricted pupil design 1440 allows light of any intensity at any pixel of the pupil. Because the unrestricted pupil can have any value and (at this stage in the iteration) no mask constraints have been applied, a mask pattern can be generated that has continuous (or smoothly changing) transmission properties (similar to those found in a continuous transmission mask (CTM)). An example is shown by a grayscale CTM pattern 1445.

[0110] At step 1350, a pupil map may be applied to the unrestricted pupil design 1440. The pupil map may define the characteristics of the current unrestricted pupil (see examples below). Two examples of pupil maps are a freeform pupil map 1450 or a parametric pupil map 1455, the application of which may result in a restricted pupil design.

[0111] Freeform optimization may include applying a freeform pupil map 1450 to, for example, specify a pupil resolution (e.g., as set by the resolution of a diffractive optical element, which may be comprised of hundreds or thousands of mirrors, each mirror corresponding to a pixel in the pupil map). This is illustrated by comparing an example of a coarse unconstrained pupil design 1440 with a freeform pupil map 1450. Here, we see that the freeform optimization does not change the general light pattern at the pupil, but increases resolution.

[0112] Parametric optimization may include constraining features of the pupil as illustrated by parametric pupil map 1455. An example of a feature that may be specified as a constraint is the mean squared deviation, i.e., standard deviation (sigma), or the value of the pupil filling factor. Various regions (also referred to as poles 1457) of the parametric pupil map 1455 are shown with mean squared deviations expressed in terms of, for example, pole intensity (i.e., the value of the mean squared deviation in the region), pole angle (i.e., the angle at the center of the region), "pole width (i.e., the angular extent of the region), sigma_in (i.e., the inner radius), and sigma_out (i.e., the outer radius). It will be appreciated that Fig.14 The examples shown in are examples only, and any pupil pattern (whether a free-form pupil pattern or a parametric pupil pattern) may be used. In other embodiments, the constraints on the pupil shown may also be based on physical features of the diffractive optical element shown and may include, for example, specular reflectivity, resolution, mirror position, etc.

[0113] Mask and / or physical pupil constraints may also be generated and applied in conjunction with freeform or parameter optimization. The mask constraints shown may be used to generate modified mask patterns as described herein. For example, mask constraints may include mask transmittance, phase effects on the mask, locations for SRAF seeding, OPC features, and the like.

[0114] At step 1360 (when the free-form source is defined at 1350), simultaneous modification (or optimization) of the constrained pupil design with the applied mask constraints may produce a modified pupil design and a modified mask pattern. Fig.14 Also shown is an example of a resulting co-optimized pupil 1460 and mask pattern 1465. At this stage, the mask pattern shown may optionally be binarized (having discrete transmittance values ​​on the mask pattern shown instead of the initial CTM pattern before co-optimization).

[0115] Similarly, at step 1370 (when the free source is defined at 1350), the simultaneous modification (or optimization) of the constrained pupil design with the applied mask constraints can produce a modified pupil design and a modified mask pattern. An example of the resulting modified pupil and modified mask pattern is shown. It can be seen that the resulting pupils (1460 and 1470) and mask patterns (1465 and 1475) are different due to the differences in the selected common optimization modes.

[0116] At step 1380, the process window and / or optional MEEF can be calculated based on the modified mask pattern and pupil design. As mentioned above with respect to the required indicators (e.g., process window) of the example, if the process window does not meet the process window conditions initially defined at step 1320, the spectrum can be modified, for example, by changing the bandwidth, peak interval, number of peaks, etc. The modified spectrum can be an input for the setup parameters for the process for repetition, so that a closer consistency with the required process window is achieved. Any of the other setup parameters can also be optionally changed. In this way, after step 1380, the iterative process can be restored to any previous step described above, such as step 1310 or step 1320.

[0117] When the process window is satisfied, the results of the modified spectrum, mask pattern, and / or pupil design can be provided as data output to one or more computing systems. In some implementations, the process can terminate after a predefined number of iterations at optimal convergence toward a specified process window.

[0118] When using the above-described multi-color or dual-color imaging process, there may be a certain degree of image blurring due to the difference in the focal plane between the two different wavelengths of light. In addition, since the projection optical system shown is optimized for a specific wavelength, deviations from the optimal wavelength may introduce lens errors that further cause blurring. This may result in a loss of contrast in the resulting imaging features.

[0119] To some extent, the methods described above in connection with source-mask optimization can be used to compensate for these image quality losses. Likewise, optical proximity correction techniques can be used to assist in imaging the features as designed. Figure 8 The large improvement in depth of focus resulting from the use of two-color imaging is shown, and the loss of contrast that comes with it is also shown.

[0120] Two metrics related to contrast are the image log slope (ILS) or the normalized image log slope (NILS). The higher the NILS, the better the image contrast, which directly translates into improved exposure latitude.

[0121] Contrast can be thought of as the ratio between the dark and light portions of an image. On the other hand, the imaging intensity log slope can be thought of as being related to the rate of change of brightness at the edge between dark and light areas of the image. Thus, both are related to the contrast between light and dark, but ILS is more particularly related to transition regions, and therefore more specifically to line edge locations, and thus to line widths and other image qualities other than contrast. Defocus and blur (such as can be caused by using two-color imaging) can have a detrimental effect on ILS.

[0122] Since ILS is proportional to the inverse of a critical dimension (such as line width), the normalization of ILS can be calculated by multiplying by the critical dimension, so that NILS = ILS*x = dI / dx*1 / x*x = dI / dx. ILS and NILS can then be related to exposure latitude through simulation and / or experimental methods in a manner understood by those skilled in the art.

[0123] Fig.15 The simulated effect of the application of bandwidth narrowing according to an embodiment is illustrated. Specifically, the graph shows the NILS of a 100nm line with a 400nm pitch, which is plotted against the deviation from best focus in both positive and negative directions. The grey line represents the simulated NILS curve using a light source with a 300fm bandwidth (E95), while the black line represents the effect of using a 200fm bandwidth. As can be seen from the figure, the NILS is slightly higher across the entire range of defocus.

[0124] Similarly, Fig.16 The simulated effect of bandwidth narrowing according to the application of the embodiment is illustrated. This graph shows the NILS of the 38nm line in the case of 90nm pitch. That is, compared with Fig.15 , the second graph is associated with finer features at a finer pitch. Again, bandwidth narrowing produces improved values ​​of NILS across the entire range of defocus as shown.

[0125] Fig.17 A simulated graph of exposure latitude (EL) versus depth of focus in a two-tone image using normal (300 fm bandwidth shown in black) and narrowed (200 fm bandwidth shown in grey) illumination light is illustrated. As can be seen, due to the narrowed bandwidth, the EL is improved across the entire depth of focus range.

[0126] In a typical laser source for a DUV lithography system, the laser includes a line narrowing module operable to perform a narrowing of the laser bandwidth. In an embodiment, the bandwidth may be reduced from a typical 300 fm to within a range of 50 fm to 275 fm, more particularly to within a range of 100 fm to 250 fm, and more particularly to within a range of 150 fm to 225 fm. In an embodiment, the bandwidth is selected to be 200 fm.

[0127] In an embodiment, according to known principles, the laser may include a grating and one or more actuatable prisms. The actuator may be, for example, a stepper motor and / or a PZT, which is configured to rotate at least one prism so as to adjust the beam width and thereby change the bandwidth of the laser source. Similarly, one or other prisms may also be installed for rotational motion with the actuator to allow fine adjustment of the central wavelength of each pulse, such adjustment being able to be performed, for example, in the order of tens of femtometers, i.e., tens of millimeter. In an embodiment, the line narrowing module may include a bandwidth measurement module to allow feedback and / or feedforward control of the bandwidth of the source. In some cases, differential ignition time may be used to implement fine control, while the actuator is used to provide overall control. Other details of such a system may be found, for example, in U.S. Patent Publication No. 20080253413, which is incorporated herein by reference in its entirety.

[0128] In applications, the method used to image features is relative to Fig.16 The method is performed as described below. The method includes directing a pulsed light beam toward a mask, the mask being configured to impart a pattern to the pulsed light beam. As described in more detail above, the pulses have different wavelengths to allow two-color printing in a single exposure stroke, which produces two aerial images in the resist on the wafer. The depth of focus can be selected and the selected depth of focus can be used to select the difference between the two wavelengths. As will be appreciated, more than two colors can be used to produce more than two aerial images without departing from the principles of the disclosed method.

[0129] Two (or more) aerial images located in the focal plane are separated by a distance along the optical axis, the distance being determined by the difference in wavelength between several pulses. The bandwidth of the pulses is controlled to be between 50 fm and 275 fm. In addition, the bandwidth is selected to improve the quality index of the imaging process.

[0130] In particular, the quality indicator may be, for example, a contrast, an ILS, a NILS, an EL and / or an indicator describing the process window.

[0131] In an embodiment, source mask optimization as described in detail above can be used after selecting the narrowed bandwidth. Thus, the narrowed bandwidth becomes an input variable to the SMO process and can be selected as a constant, or can vary with other parameters when performing the optimization. That is, when the spectrum 340 is narrowed, the method of iteratively simulating and adjusting the pupil design, spectrum, mask pattern 710 is performed in the same manner as previously described. The method may also include iteratively changing the auxiliary features in the spectrum and the mask pattern to provide a modified spectrum and a modified mask pattern that increases the depth of focus. The components of the lithography system can then be configured based on the modified spectrum and the modified mask pattern 710 that increases the depth of focus. For example, components may include any combination of masks, light sources, pupils, or other components of the lithography system.

[0132] Fig.15 is a block diagram of an example computer system CS according to an embodiment.

[0133] 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.

[0134] The computer system CS can be connected to a display DS for displaying information to a computer user via a bus BS, such as a cathode ray tube (CRT) or a flat panel display or a touch panel display. An input device ID including alphanumeric keys 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 controller 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. Such an input device typically has two degrees of freedom on two axes (a first axis (e.g., x) and a second axis (e.g., y)), which allows the device to specify a position in a plane. A touch panel (screen) display can also be used as an input device.

[0135] According to one embodiment, the 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 contained in main memory MM. Such instructions can be read in main memory MM from another computer readable medium (such as storage device SD). The execution of the sequence of instructions contained in main memory MM makes processor PRO perform process steps described herein. One or more processors in a multi-processing arrangement can also be used to execute the sequence of instructions contained in main memory MM. In an alternative embodiment, hard-wired circuits can be used to replace software instructions or be combined with software instructions. Therefore, the description herein is not limited to any specific combination of hardware circuits and software.

[0136] The term "computer-readable medium" used herein refers to any medium that participates in providing instructions to the processor PRO for execution. Such a medium can take many forms, including but not limited to non-volatile media, volatile media and transmission media. Non-volatile media include, for example, optical disks or disks, such as storage devices SD. Volatile media include dynamic memory, such as main memory MM. Transmission media include coaxial cables, copper wires and optical fibers, including wires containing bus BS. Transmission media can also take 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. Common forms of computer-readable media include, for example, floppy disks, flexible disks, hard disks, tapes, any other magnetic media, CD-ROMs, DVDs, any other optical media, punch cards, paper tapes, any other physical media with hole patterns, RAM, PROMs and EPROMs, FLASH-EPROMs, any other memory chips or thyristors. Instructions can be recorded on non-temporary computer-readable media. The machine executable instructions can implement any of the features described herein when executed by a computer. Temporary computer-readable media can include carriers or other propagating electromagnetic signals.

[0137] Various forms of computer-readable media may involve one or more sequences of one or more instructions being transmitted to the processor PRO for execution. For example, the instruction may initially be carried on a disk of a remote computer. The remote computer may load the instruction into its dynamic memory and send the instruction via a telephone line using a modem. The modem local to the computer system CS may receive data on the telephone line and convert the data into an infrared signal using an infrared transmitter. An infrared detector connected to the bus BS may receive the data carried in the infrared signal and place the data on the bus BS. The bus BS transmits the data to the main memory MM, from which the processor PRO retrieves and executes the instruction. The instruction received by the main memory MM may optionally be stored on a storage device SD before or after being executed by the processor PRO.

[0138] 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 connected to 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 for providing a data communication connection to a telephone line of a corresponding type. As another example, the communication interface CI may be a local area network (LAN) card for providing a data communication connection to 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.

[0139] The network link NDL typically provides data communication to other data devices through one or more networks. For example, the network link NDL can provide a connection to the host computer HC through a local area network LAN. This can include data communication services provided through the global packet data communication network now commonly referred to as the "Internet" INT. Both the local area network LAN (Internet) and the local area network LAN use electrical signals, electromagnetic signals or optical signals that carry digital data streams. The signals through the various networks and the signals on the network data link NDL and through the communication interface CI (which transmits digital data to and from the computer system CS) are exemplary forms of carrier waves that transport information.

[0140] The computer system CS can send messages and receive data, including program code, through the network, the network data link NDL and the communication interface CI. In the Internet example, the host computer HC can transmit the requested code for the application program through the Internet INT, the network data link NDL, the local area network LAN and the communication interface CI. For example, one such downloaded application can provide all parts of the method described herein. The received 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.

[0141] Fig.16 is a schematic diagram of a lithographic projection apparatus according to an embodiment.

[0142] The lithographic projection apparatus may comprise an illumination system IL, a first object table MT, a second object table WT and a projection system PS.

[0143] The illumination system IL may condition the radiation beam B. In this particular case, the illumination system also comprises a radiation source SO.

[0144] A first object table (eg patterning device table) MT may have a patterning device holder for holding a patterning device MA (eg mask table) and be connected to a first positioner for accurately positioning the patterning device relative to the item PS.

[0145] A second object table (substrate table) 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 item PS.

[0146] 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).

[0147] As described herein, the apparatus may be of the transmissive type (e.g., employing a transmissive patterning device). However, in general, it may be of the reflective type (e.g., employing a reflective patterning device). The apparatus may employ a different kind of patterning device than a classical mask; examples include a programmable mirror array or an LCD matrix.

[0148] A source SO (e.g. a mercury lamp or an excimer laser, 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 comprise an adjustment device AD ​​for setting 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 the beam. In addition, the illuminator IL will typically comprise various other components, such as an integrator IN and a condenser CO. In this way, the beam B impinging on the pattern forming device MA has the desired uniformity and intensity distribution in its cross section.

[0149] In some embodiments, the source SO may be within the housing of the lithographic projection device (this is often the case when the source SO is, for example, a mercury lamp), but it may also be remote from the lithographic projection device, into which the radiation beam it generates is directed (for example, with the aid of appropriate directional mirrors); the latter may be the case when the source SO is an excimer laser (for example, based on KrF, ArF or F2 laser action).

[0150] 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 PB may pass through a lens PL which focuses the beam B onto a target portion C of the substrate W. With the aid of a second positioning device (and the interferometric measurement device IF), the substrate table WT may be accurately moved, for example, in order to position different target portions 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 mechanically retrieving the patterning device MA from a patterning device library or during scanning. Typically, movement of the object tables 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 a short-stroke actuator, or may be fixed.

[0151] 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 can be shifted in the x and / or y direction so that a different target portion C can be illuminated by the beam PB.

[0152] In scan mode, essentially the same situation applies, except that a given target portion C is not exposed in a single "flash". Alternatively, the patterning device table MT can be moved in a given direction (the so-called "scanning direction", e.g. the y-direction) at a velocity v, so that the projection beam B is scanned across the patterning device image; while the substrate table WT is simultaneously moved in the same or opposite direction at a velocity 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.

[0153] The embodiments may also be described using the following aspects:

[0154] 1. A method for optimizing a method of imaging a feature onto a substrate using a lithography system, the method comprising:

[0155] obtaining a spectrum of a light beam used for said imaging, wherein said light beam comprises pulses having a plurality of different wavelengths; and

[0156] The spectrum of the pulses of the light beam used for the imaging is narrowed to improve a quality indicator of the imaging.

[0157] 2. The method according to aspect 1 further comprises:

[0158] obtaining a design of a patterning device configured to produce the features on the substrate;

[0159] obtaining a light source design for said imaging; and

[0160] The spectrum of the light beam, the mask design, and the light source design are simultaneously and iteratively varied to provide an optimized spectrum, an optimized mask design, and an optimized light source design.

[0161] 3. A method according to any one of the preceding aspects, wherein the bandwidth of each pulse is between 50 fm and 275 fm.

[0162] 4. The method according to any of the preceding clauses, wherein the beam is generated in a laser having a nominal bandwidth of 300 fm, and wherein a line narrowing module of the laser is tuned to produce a bandwidth of 50 fm to 275 fm.

[0163] 5. A method according to any one of the preceding aspects, wherein the method comprises selecting the bandwidth to produce an improvement in a quality indicator of the imaging process.

[0164] 6. The method of clause 5, wherein the quality indicator is contrast.

[0165] 7. The method according to clause 5, wherein the quality indicator is the imaging light intensity logarithmic slope or the normalized imaging light intensity logarithmic slope.

[0166] 8. The method of clause 5, wherein the quality indicator is exposure latitude.

[0167] 9. The method according to any of the preceding aspects, further comprising optimizing a light source design and / or a mask design based at least in part on the bandwidth of the pulses.

[0168] 10. The method of clause 9, wherein the optimizing comprises simultaneously iteratively varying the spectrum of the light beam, the mask design, and the light source design to provide an optimized spectrum, an optimized mask design, and an optimized light source design.

[0169] 11. The method according to any of the preceding aspects, further comprising selecting a difference between the first wavelength and the second wavelength according to the selected depth of focus.

[0170] 12. The method according to any of the preceding aspects, further comprising imaging the feature onto the substrate.

[0171] 13. A method of imaging a feature onto a substrate using a photolithography system, the method comprising:

[0172] directing a pulsed light beam in a propagation direction toward a patterning device, the pulsed light beam comprising a plurality of light pulses;

[0173] patterning a collection of light pulses in the pulsed light beam using the pattern forming device to produce a patterned light beam;

[0174] directing the patterned beam toward a substrate during a single exposure pass;

[0175] During the single exposure pass, at least a first aerial image and a second aerial image are generated on the substrate, the first aerial image being located at a first plane on the substrate and the second aerial image being located at a second plane on the substrate, the first plane and the second plane being spatially distinct from each other and separated from each other by a spacing distance in a propagation direction; and

[0176] A three-dimensional semiconductor component is formed based on interaction between light in the first aerial image and material in a first portion of the substrate, and interaction between light in the second aerial image and material in a second portion of the substrate, wherein at least one of the pulses in the set of pulses has a first wavelength, and at least one of the other pulses in the set of pulses has a second wavelength different from the first wavelength, so that the separation distance is formed during the single exposure pass based on a difference between the first wavelength and the second wavelength, and wherein a bandwidth of the set of pulses is narrowed.

[0177] 14. A lithography system, comprising:

[0178] a light source configured and arranged to generate light pulses having a plurality of different wavelengths; and

[0179] A bandwidth narrowing module is configured and arranged to narrow the bandwidth of the optical pulse.

[0180] 15. The lithography system according to claim 14, further comprising:

[0181] a substrate table configured to hold a substrate; and

[0182] A projection system is configured to project a patterned radiation beam including the light pulses onto a target area of ​​the substrate to form an image on the substrate.

[0183] 16. A lithography system according to clause 15, wherein the system is further configured and arranged to generate at least a first aerial image and a second aerial image on the substrate during a single exposure pass, the first aerial image being located at a first plane on the substrate and the second aerial image being located at a second plane on the wafer, the first plane and the second plane being spatially distinct from each other and separated from each other by a spacing distance along a propagation direction of the patterned radiation beam; and

[0184] A semiconductor component is formed based on an interaction between light in the first aerial image and a material in a first portion of the substrate and an interaction between light in the second aerial image and a material in a second portion of the substrate, wherein

[0185] At least one of the pulses in the set of pulses has a first wavelength, and at least one of the other pulses in the set of pulses has a second wavelength different from the first wavelength, so that during the single exposure stroke, the spacing distance is formed based on the difference between the first wavelength and the second wavelength, and wherein the bandwidth of the set of pulses is narrowed.

[0186] 17. The lithography system according to any one of clauses 14 to 16, further comprising a line narrowing module configured and arranged to adjust the bandwidth of the light pulses.

[0187] 18. The lithographic apparatus of any of clauses 14 to 17, wherein the line narrowing module of the laser is tuned to produce a bandwidth of 50 fm to 275 fm.

[0188] 19. A computer program product, comprising a non-transitory computer readable medium having machine executable instructions recorded thereon, the machine executable instructions implementing the method according to any one of aspects 1 to 13 when executed.

[0189] 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 193nm wavelengths by using ArF lasers and even 157nm wavelengths by using fluorine lasers. In addition, EUV lithography can produce wavelengths in the range of 5nm to 20nm by using synchrotrons or by using high energy electrons to bombard materials (solid or plasma) to produce photons in this range.

[0190] 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 applicable with any type of lithography imaging system, for example, a lithography imaging system for imaging on substrates other than silicon wafers.

[0191] The above description is intended to be illustrative rather than limiting. Accordingly, those skilled in the art will appreciate that modifications may be made to the described invention without departing from the scope of the claims set forth below.

Claims

1. A method for optimizing a method of illuminating a patterning device with a photolithography system to image a feature onto a substrate, the method comprising: obtaining a spectrum of the light beam used to illuminate the patterning device for imaging, wherein the light beam comprises pulses having a plurality of different wavelengths; selecting a difference in value between a first wavelength and a second wavelength of the plurality of different wavelengths of the light beam used to illuminate the patterning device to increase depth of focus; and The spectra of pulses of the light beam used to illuminate the patterning device, respectively associated with the first wavelength and / or the second wavelength, are narrowed to improve a quality indicator of the imaging.

2. The method according to claim 1, further comprising: obtaining a design of the patterning device configured to produce the features on the substrate; obtaining a light source design for said imaging; and The spectrum of the light beam, the mask design, and the light source design are simultaneously and iteratively varied to provide an optimized spectrum, an optimized mask design, and an optimized light source design.

3. The method according to any one of claims 1 to 2, wherein the bandwidth of each pulse is between 50 fm and 275 fm.

4. The method according to any one of claims 1 to 2, wherein the beam is generated in a laser having a nominal bandwidth of 300 fm, and wherein a line narrowing module of the laser is tuned to produce a bandwidth of 50 fm to 275 fm.

5. The method of any one of claims 1 to 2, wherein the method comprises selecting a bandwidth to produce an improvement in a quality indicator of the imaging process. The method according to claim 5 , wherein the quality indicator is contrast. 7 . The method according to claim 5 , wherein the quality indicator is a logarithmic slope of imaging light intensity or a normalized logarithmic slope of imaging light intensity. The method according to claim 5 , wherein the quality indicator is exposure latitude.

9. The method of any preceding claim, further comprising optimizing a light source design and / or a mask design based at least in part on the bandwidth of the pulses.

10. The method of claim 9, wherein the optimizing comprises simultaneously iteratively varying the spectrum of the light beam, the mask design, and the light source design to provide an optimized spectrum, an optimized mask design, and an optimized light source design.

11. The method of any preceding claim, further comprising selecting a difference between the first wavelength and the second wavelength in dependence on the selected depth of focus.

12. The method of any preceding claim, further comprising imaging the feature onto the substrate.

13. A method of imaging a feature onto a substrate using a photolithography system, the method comprising: directing a pulsed light beam in a propagation direction toward a patterning device, the pulsed light beam comprising a plurality of light pulses; patterning a collection of light pulses in the pulsed light beam using the pattern forming device to produce a patterned light beam; directing the patterned beam toward a substrate during a single exposure pass; During the single exposure pass, at least a first aerial image and a second aerial image are generated on the substrate, the first aerial image being located at a first plane on the substrate and the second aerial image being located at a second plane on the substrate, the first plane and the second plane being spatially distinct from each other and separated from each other by a spacing distance in a propagation direction; and forming a three-dimensional semiconductor component based on an interaction between light in the first aerial image and a material in a first portion of the substrate and an interaction between light in the second aerial image and a material in a second portion of the substrate, wherein at least one of the pulses in the set of pulses has a first wavelength, and at least one of the other pulses in the set of pulses has a second wavelength different from the first wavelength, so that the spacing distance is formed during the single exposure stroke based on the difference between the first wavelength and the second wavelength, and wherein the bandwidth of the set of pulses is narrowed.

14. A lithography system, comprising: a light source configured and arranged to generate light pulses having a plurality of different wavelengths for illuminating a patterning device, at least one of the plurality of light pulses having a first wavelength and at least one of the plurality of light pulses having a second wavelength different from the first wavelength; and a bandwidth narrowing module, the bandwidth narrowing module being configured and arranged to narrow the spectrum of the light pulses respectively associated with the first wavelength and / or the second wavelength for illuminating the pattern forming device so as to narrow the bandwidth of the light pulses; Therein, the lithography system is configured and arranged to select a difference in value between the first wavelength and the second wavelength to increase depth of focus.

15. The lithography system according to claim 14, further comprising: a substrate stage configured to hold a substrate; and A projection system is configured to project a patterned radiation beam including the light pulses onto a target area of ​​the substrate to form an image on the substrate.

16. The lithography system of claim 15, wherein the system is further configured and arranged to generate at least a first aerial image and a second aerial image on the substrate during a single exposure pass, the first aerial image being located at a first plane on the substrate and the second aerial image being located at a second plane on the wafer, the first plane and the second plane being spatially distinct from each other and separated from each other by a spacing distance along a propagation direction of the patterned radiation beam; and A semiconductor component is formed based on an interaction between light in the first aerial image and a material in a first portion of the substrate and an interaction between light in the second aerial image and a material in a second portion of the substrate, wherein During the single exposure pass, the separation distance is formed based on a difference between the first wavelength and the second wavelength, and wherein a bandwidth of the set of pulses is narrowed.

17. The lithography system according to any one of claims 14 to 16, further comprising a line narrowing module configured and arranged to adjust the bandwidth of the light pulses.

18. The lithography system of claim 17, wherein the line narrowing module of the laser is tuned to produce a bandwidth of 50 fm to 275 fm.

19. A computer program product, comprising a non-transitory computer-readable medium having machine-executable instructions recorded thereon, the machine-executable instructions implementing the method according to any one of claims 1 to 13 when executed.

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