Lithographic pattern representation using curvilinear elements.

Abstract

Methods, systems, and computer software are disclosed for determining a mask pattern for use in a lithography process. One method includes assigning locations of two-dimensional elements based on a target pattern, associating the two-dimensional elements based on an association criterion to form clusters that represent mask features, and adjusting the two-dimensional elements of the clusters to vary the mask features.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Application No. 63 / 322,517, filed March 22, 2022, which is incorporated by reference in its entirety into this specification. [Background technology]

[0002]

[0002] The description herein relates generally to lithographic manufacturing and patterning processes. More specifically, the description herein relates to mask pattern determination.

[0003] Lithographic projection apparatus may be used, for example, in the manufacture of integrated circuits (ICs). In such cases, a patterning device (e.g. a mask) may contain or be provided with a pattern (a "design layout") corresponding to an individual layer of the IC, which may be transferred onto a target portion (e.g. comprising one or more dies) on a substrate (e.g. a silicon wafer) that is coated with a layer of radiation-sensitive material ("resist"), such as by irradiating the target portion through the pattern on the patterning device. Typically, a single substrate will contain several adjacent target portions (one target portion at a time), onto which the pattern is successively transferred by the lithographic projection apparatus. In one type of lithographic projection apparatus, the pattern on the entire patterning device is transferred onto one target portion in one go, and such an apparatus is commonly referred to as a stepper. In an alternative apparatus, a step-and-scan apparatus, the projection beam is synchronized with scanning the patterning device in a given reference direction (the "scan" direction) and the substrate is moved parallel or anti-parallel to this reference direction. Different parts of a pattern on the patterning device are progressively transferred onto one target portion. Typically, a lithographic projection apparatus has a demagnification ratio M (e.g. 4), so that the speed F at which the substrate is moved is 1 / M times the speed at which the projection beam scans the patterning device. More information on lithographic devices can be found, for example, in U.S. Pat. No. 6,046,792, which is incorporated herein by reference.

[0004]

[0004] Before transferring the pattern from the patterning device to the substrate, the substrate may undergo various procedures such as priming, resist coating, and a soft bake. After exposure, the substrate may undergo other procedures ("post-exposure procedures") such as a post-baking (PEB), developing, a hard bake, and measurement / inspection of the transferred pattern. This series of procedures is used as a basis for creating the individual layers of a device (e.g., an IC). The substrate may then undergo various processes such as etching, ion implantation (doping), metallization, oxidation, deposition, chemical-mechanical polishing, etc., all intended to finish off the individual layers of the device. If several layers are required for a device, the entire procedure, or a variation thereof, is repeated for each layer. Eventually, a device is present on each target portion on the substrate. The devices are then separated from each other by techniques such as dicing or sawing so that the individual devices can be mounted on a carrier, connected to pins, etc.

[0005]

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

[0006]

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

[0007]

[0007] As semiconductor manufacturing processes continue to advance, the dimensions of functional elements are continually decreasing, while the amount of functional elements, such as transistors, per device has been steadily increasing for decades, following a trend known as "Moore's Law". In the current state of the art, layers of devices are fabricated using lithographic projection apparatus that uses illumination from a deep ultraviolet illumination source to project a design layout onto a substrate, producing individual functional elements with dimensions well below 100 nm (i.e., less than half the wavelength of the radiation from the illumination source (e.g., a 193 nm illumination source)).

[0008]

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

[0009]

[0009] Methods, systems and computer software are disclosed for determining a mask pattern for use in a lithography process. In one aspect, the method may include assigning locations of two-dimensional elements based on a target pattern, associating the two-dimensional elements based on an association criterion to form a cluster representing a mask feature, and adjusting the two-dimensional elements of the cluster to vary the mask feature.

[0010] In some variations, the adjusting can be based on simulations related to the lithographic process or based on geometric properties of the mask pattern and on rules defined for OPC.

[0011]

[0011] In another variation, the method may include generating a contour of the cluster based on the two-dimensional elements. The contour may be an outer contour of the cluster corresponding to an outer edge of the mask feature, or an inner contour of the cluster corresponding to an inner edge of the mask feature. The method may also include generating subareas of the contour by applying a polygon offset operation to pairs of associated two-dimensional elements, and calculating an aggregate of the subareas, the contour being the aggregate of the subareas. The method may also include manufacturing a mask from a mask pattern including the contour generated from the adjusted two-dimensional elements.

[0012] In yet another variation, the contour may be at least partially a predetermined distance from the location of the two-dimensional element, or may be entirely at least a predetermined distance from the location of the two-dimensional element. The predetermined distance may be based on an MRC rule for a minimum width of a mask feature. In some embodiments, at least a portion of the contour may violate an MRC rule. The geometry of the two-dimensional element may also be defined based on one or more Mask Rule Compliance (MRC) rules. A dimensional parameter of the two-dimensional element may be selected to be a minimum width specified by the MRC rule. The one or more MRC rules may include a minimum space requirement, and the association criteria may include connecting the second two-dimensional element into the cluster if the distance between a second contour of the second two-dimensional element and a contour of a two-dimensional element in the cluster is less than the minimum space requirement.

[0013]

[0013] In some variations, the method may include modifying a cluster of two-dimensional elements into one or more modified clusters. The modified clusters may be formed based on an MRC rule. The method may also include modifying the cluster by separating one of the two-dimensional elements from the cluster and modifying the contour based on the modified cluster. The method may also include modifying the cluster by associating a two-dimensional element from another cluster to the cluster and modifying the contour based on the modified cluster.

[0014]

[0014] In other variations, adjusting can include optimizing the mask pattern by moving the location of one or more of the two-dimensional elements, or adjusting can include optimizing the mask pattern by adjusting the size or shape of one or more of the two-dimensional elements. Associating can include associating two-dimensional elements that are within a predetermined distance from other two-dimensional elements. Associating or adjusting can also include separating a two-dimensional element from a two-dimensional element of a cluster and associating the two-dimensional element with a two-dimensional element in a second cluster.

[0015] In yet another variation, the method can include calculating a cost function that quantifies an evaluation of the mask pattern, and adjusting the two-dimensional element is based on the cost function. The cost function may not include a term based on the MRC rule.

[0016]

[0016] In some variations, each of the two-dimensional elements may be circular, elliptical, the same size, may define a non-zero area, may be polygonal, or may define a closed or semi-closed area.

[0017]

[0017] In another variation, the method may include performing corner rounding on the outer contour. The corner rounding may include performing a spline interpolation between two points on either side of the corner.

[0018]

[0018] In yet another variation, the method may include generating a homogeneous cluster by replicating the cluster in the mask pattern and adjusting the corresponding two-dimensional elements in the homogeneous cluster. Adjusting the homogeneous cluster may include identifying a boundary two-dimensional element that crosses a boundary between the first mask patch and the second mask patch, and adjusting the two-dimensional element excludes adjusting the boundary two-dimensional element. Adjusting the homogeneous cluster may also include designating a two-dimensional element within a threshold boundary of the boundary between the first mask patch and the second mask patch as a preferred two-dimensional element, and adjusting the two-dimensional element excludes adjusting the preferred two-dimensional element. The method may include storing the preferred two-dimensional element in a computer memory for later recall. The method may also include replacing one or more of the two-dimensional elements within a threshold distance to the boundary with the preferred two-dimensional element.

[0019]

[0019] In some variations, the method may include receiving a mask pattern; generating a homogeneous cluster by replicating the cluster in the mask pattern, where the adjusting includes adjusting corresponding two-dimensional elements in the homogeneous cluster; designating two-dimensional elements within a threshold distance of a boundary between the first mask patch and the second mask patch as preferred two-dimensional elements; replacing one or more of the two-dimensional elements near the boundary with the preferred two-dimensional element recalled from computer memory; and generating an adjusted mask pattern based on the two-dimensional elements in the homogeneous cluster, where the adjusting the two-dimensional elements excludes adjusting the preferred two-dimensional element.

[0020]

[0020] In some embodiments, there may be a non-transitory computer-readable medium having instructions recorded thereon for determining a mask pattern for use in a lithography process, which, when executed by a computer having at least one programmable processor, causes operations to be performed including any of the operations in the method embodiments described above.

[0021]

[0021] In some embodiments, there may be a system for determining a mask pattern for use in a lithography process, the system including at least one programmable processor and a non-transitory computer-readable medium having instructions recorded thereon, which when executed by a computer having at least one programmable processor cause operations to be performed including any of the operations in the method embodiments described above. [Brief description of the drawings]

[0022]

[0022] The accompanying drawings, which are incorporated in and form a part of this specification, illustrate certain aspects of the subject matter disclosed in this specification and, together with the following description, help to explain some of the principles associated with the disclosed implementations. [Figure 1]

[0023] FIG. 2 shows a block diagram of various subsystems of a lithographic projection apparatus, according to an embodiment of the present disclosure; [Diagram 2]

[0024] 1 shows an exemplary flowchart for simulating lithography in a lithographic projection apparatus, according to an embodiment of the present disclosure. [Diagram 3]

[0025] 1 illustrates an exemplary mask pattern and mask features. [Figure 4]

[0026] 1 shows a conventional mask feature generated with OPC that violates MRC rules. [Diagram 5]

[0027] 1 illustrates an exemplary process for placing, associating, and adjusting two-dimensional elements that form a mask feature, according to one embodiment of the present disclosure. [Figure 6]

[0028] 1 illustrates an exemplary process for obtaining a contour line of a mask feature based on two-dimensional elements according to an embodiment of the present disclosure. [Figure 7]

[0029] 1 illustrates an example mask feature contour made of two-dimensional elements that respects MRC rules, and an example contour made of two-dimensional elements that allows flexibility with respect to the MRC rules, according to various embodiments of the present disclosure. [Figure 8A]

[0030] 1 illustrates an exemplary cluster of two-dimensional elements arranged tip-to-tip and spaced according to the MRC rule, according to one embodiment of the present disclosure. [Figure 8B]

[0031] 1 illustrates an exemplary cluster of two-dimensional elements arranged tip-to-side and spaced according to the MRC rule, according to one embodiment of the present disclosure. [Figure 9]

[0032] 1 illustrates an example merging of clusters of two-dimensional elements based on the MRC rule, according to one embodiment of the present disclosure. [Figure 10A]

[0033] 1 illustrates replicating a cluster of two-dimensional elements at symmetrical locations on a mask pattern to ensure homogeneity of the OPC pattern, according to one embodiment of the present disclosure. [Figure 10B]

[0034] 1 illustrates adjusting corresponding two-dimensional elements in homogeneous clusters according to one embodiment of the present disclosure. [Figure 11A]

[0035] 1 illustrates a preferred two-dimensional element near a mask boundary according to one embodiment of the present disclosure. [Figure 11B]

[0036] 13 illustrates preferred 2D elements near a mask boundary that are excluded from adjustment according to one embodiment of the present disclosure. [Figure 12]

[0037] FIG. 1 is a process flow diagram illustrating an exemplary method for utilizing a preferred two-dimensional shape to improve mask homogeneity near a mask boundary, according to an embodiment of the present disclosure. [Figure 13]

[0038] FIG. 1 is a block diagram of an exemplary computer system according to one embodiment of the present disclosure. [Figure 14]

[0039] 1 is a schematic diagram of a lithographic projection apparatus according to an embodiment of the present disclosure; [Figure 15]

[0040] 2 is a schematic diagram of another lithographic projection apparatus, in accordance with an embodiment of the present disclosure; [Figure 16]

[0041] FIG. 1 depicts a detailed view of a lithographic projection apparatus according to an embodiment of the present disclosure; [Figure 17]

[0042] FIG. 2 illustrates a detailed view of a source collector module of a lithographic projection apparatus according to an embodiment of the present disclosure; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023]

[0043] Although specific reference may be made herein to the manufacture of integrated circuits (ICs), it should be expressly understood that the description herein has many other possible applications. For example, it may be used in the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, liquid crystal display panels, thin film magnetic heads, etc. Those skilled in the art will recognize that, in the context of such alternative applications, any use of the terms "reticle," "wafer," or "die" herein should be considered as interchangeable with the more general terms "mask," "substrate," and "target portion," respectively.

[0024]

[0044] In this document, the terms "radiation" and "beam" are used to encompass all types of electromagnetic radiation, including ultraviolet (e.g., having wavelengths of 365, 248, 193, 157 or 126 nm) and EUV (extreme ultraviolet, e.g., having a wavelength in the range of about 5 to 100 nm).

[0025]

[0045] A patterning device may include or form one or more design layouts. A design layout may be generated utilizing a CAD (Computer Aided Design) program, a process often referred to as EDA (Electronic Design Automation). Most CAD programs follow a predefined set of design rules to generate a functional design layout / patterning device. These rules are set by process and design limitations. For example, design rules define the space tolerance between devices (such as gates, capacitors, etc.) or interconnect lines to ensure that the devices or lines do not interact with each other in an undesirable way. One or more of the design rule limitations may be referred to as a "critical dimension" (CD). A critical dimension of a device may be defined as the smallest width of a line or hole, or the smallest space between two lines or two holes. Thus, the CD determines the overall size and density of the designed device. Of course, one of the goals in device fabrication is to faithfully reproduce the original device design (with the patterning device) on the substrate.

[0026]

[0046] The terms "mask" or "patterning device" as used herein can be broadly interpreted as referring to any general-purpose patterning device that can be used to impart an incident radiation beam with a patterned cross-section that corresponds to the pattern to be produced in a target portion of a substrate, and the term "light valve" may also be used in this context. In addition to the classic mask (transmissive or reflective; binary, phase-shifting, hybrid, etc.), examples of other such patterning devices include programmable mirror arrays and programmable LCD arrays.

[0027]

[0047] An example of a programmable mirror array would be a matrix-addressable surface having a viscoelastic control layer and a reflective surface. The basic principle behind such a device is that (for example) addressed areas of the reflective surface will reflect incident radiation as diffracted radiation, whereas unaddressed areas will reflect the incident radiation as undiffracted radiation. Using appropriate filters, the undiffracted radiation can be filtered out of the reflected beam, leaving only the diffracted radiation behind, and in this way the beam is patterned according to the addressing pattern of the matrix-addressable surface. The required matrix addressing can be performed using suitable electronic methods.

[0028]

[0048] An example of a programmable LCD array is given in US Pat. No. 5,229,872, which is incorporated herein by reference.

[0029]

[0049] 1 shows a block diagram of various subsystems of a lithographic projection apparatus 10A, according to one embodiment. The main components are a radiation source 12A, which may be a deep ultraviolet excimer laser source or other type of radiation source including an extreme ultraviolet (EUV) source (as mentioned above, the lithographic projection apparatus itself does not have to have a radiation source), illumination optics, which may include, for example, optics 14A, 16Aa and 16Ab that define the partial coherence (denoted by sigma) and shape the radiation from the radiation source 12A, a patterning device 18A, and a transmission optics 16Ac that projects an image of the patterning device pattern onto a substrate surface 22A. An adjustable filter or aperture 20A in a pupil plane of the projection optics may limit the range of beam angles impinging on the substrate surface 22A, with the maximum possible angle being determined by the numerical aperture NA=nsin(Θ) of the projection optics. max ), where n is the refractive index of the medium between the substrate and the last element of the projection optical system, and Θ max is the maximum angle of the beam exiting the projection optics that can still impinge on the substrate surface 22A.

[0030]

[0050] In a lithographic projection apparatus, a radiation source provides illumination (i.e., radiation) to a patterning device, and a projection optics system directs and shapes the illumination through the patterning device onto a substrate. The projection optics system may include at least some of the components 14A, 16Aa, 16Ab, and 16Ac. The aerial image (AI) is the radiation intensity distribution at the substrate level. A resist model can be used to calculate the resist image from the aerial image, an example of which can be found in US Patent Application Publication No. 2009-0157360, the disclosure of which is incorporated herein by reference in its entirety. The resist model is only related to the properties of the resist layer (e.g., the effects of chemical processes occurring during exposure, post-exposure bake (PEB), and development). The optical properties of the lithographic projection apparatus (e.g., the properties of the illumination, the patterning device, and the projection optics system) dictate the aerial image and can be defined in the optical model. Since the patterning device used in the lithographic apparatus may be varied, it may be 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 radiation source and the projection optics. Details of the techniques and models used to convert the design layout into various lithographic images (e.g., aerial images, resist images, etc.), to apply OPC using techniques and models, and to evaluate performance (e.g., in terms of process window) are described in U.S. Patent Application Publication Nos. 2008-0301620, 2007-0050749, 2007-0031745, 2008-0309897, 2010-0162197, and 2010-0180251, the disclosures of each of which are incorporated herein by reference in their entirety.

[0031]

[0051] One aspect of understanding the lithographic process is to understand the interaction of radiation with a patterning device. The electromagnetic field of the radiation after it has passed through the patterning device can be determined from the electromagnetic field of the radiation before it reaches the patterning device and a function that characterizes the interaction. This function is sometimes called the mask transmission function (this function can be used to describe interactions through transmissive and / or reflective patterning devices).

[0032]

[0052] The mask transmission function may have a variety of different forms. One form is binary. A binary mask transmission function has one of two values ​​(e.g., zero and a positive constant) at a given location on the patterning device. A mask transmission function in binary form may be referred to as a binary mask. Another form is continuous. That is, the transmittance (or reflectance) of the patterning device is a continuous function of the location of the patterning device. The phase of the transmittance (or reflectance) may also be a continuous function of the location of the patterning device. A mask transmission function in continuous form may be referred to as a continuous tone mask or continuous transmission mask (CTM). For example, a CTM may be represented as a pixelated image, where each pixel may be assigned a value between 0 and 1 (e.g., 0.1, 0.2, 0.3, etc.) instead of a binary value of either 0 or 1. In one embodiment, the CTM may be a pixelated grayscale image, where each pixel has a value (e.g., a value in the range [-255,255], a value normalized to the range [0,1] or [-1,1], or other suitable range).

[0033]

[0053] To simplify the determination of the interaction of radiation with the patterning device, the thin mask approximation, also called the Kirchhoff boundary condition, is widely used. In the thin mask approximation, it is assumed that the thickness of the structures on the patterning device is very small compared to the wavelength, and the width of the structures on the mask is very large compared to the wavelength. Thus, the thin mask approximation assumes that the electromagnetic field after the patterning device is a multiplication of the incident electromagnetic field and the mask transmission function. However, as lithography processes use radiation of shorter and shorter wavelengths, and the structures on the patterning device are becoming smaller and smaller, the assumptions in the thin mask approximation may break down. For example, due to the finite thickness, the interaction of the radiation with the structures (e.g., the edges between the top surface and the sidewalls) ("mask 3D effect" or "M3D") may become significant. Including this scattering in the mask transmission function may allow 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 the transmission function of the thin mask. A mask transmission function that encompasses M3D is sometimes called an M3D mask transmission function.

[0034]

[0054] According to an embodiment of the present disclosure, one or more images may be generated. The images include various types of signals that may be characterized by a pixel value or intensity value of each pixel. As may be understood by one of ordinary skill in the art, a signal may be referred to as, for example, a weak signal or a strong signal depending on the relative value of the pixel in the image. The terms "strong" and "weak" are relative terms based on the intensity value of the pixel in the image, and a particular intensity value does not limit the scope of the present disclosure. In an embodiment, strong and weak signals may be identified based on a selected threshold. In an embodiment, the threshold may be fixed (e.g., at the midpoint between the highest and lowest intensity of the pixels in the image). In an embodiment, a strong signal may refer to a signal having a value equal to or greater than the average signal value across the image, and a weak signal may refer to a signal having a value less than the average signal value across the image. In an embodiment, the relative intensity values ​​may be based on a percentage. For example, a weak signal may be a signal having an intensity less than 50% of the highest intensity of the pixels in the image (e.g., a pixel corresponding to a design layout may be considered as the pixel having the highest intensity). Furthermore, each pixel in the image may be considered as a variable. According to this embodiment, a derivative or partial derivative can be determined for each pixel in the image, and the value of each pixel can be determined or modified according to a cost-function based evaluation and / or a gradient based calculation of the cost function. For example, a CTM image can include pixels, where each pixel is a variable that can take on any real value.

[0035]

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

[0036]

[0056] More specifically, it should be noted that the source model 31 may represent the optical characteristics of the source, including, but not limited to, the illumination sigma (σ) setting and any particular illumination geometry (e.g., off-axis sources such as annular sources, quadrupole sources, dipole sources, etc.). The projection optics model 32 may represent the optical characteristics of the projection optics, including aberrations, distortion, one or more refractive indices, one or more physical sizes, one or more physical dimensions, etc. The design layout model 35 may represent one or more physical characteristics of a physical patterning device, for example, as described in U.S. Pat. No. 7,587,704, which is incorporated by reference in its entirety. The goal of the simulation is to accurately predict, for example, edge placement, aerial image intensity gradient, and / or CD, which can then be compared to the intended design. The intended design is generally defined as a pre-OPC design layout and may be provided in a standardized digital file format, such as GDSII or OASIS or other file format.

[0037]

[0057] From this design layout, one or more portions can be identified, which are called "clips." In one embodiment, a set of clips is extracted that represents complex patterns in the design layout (typically about 50-1000 clips, although any number of clips can be used). These patterns or clips represent small portions of the design (i.e., circuits, cells, or patterns), and in particular clips typically represent small portions that require specific attention and / or validation. In other words, clips can be portions of the design layout, or critical features may be similar or have similar behavior to portions of the design layout identified by experience (including customer-provided clips), by trial and error, or by running full-chip simulations. Clips can include one or more test or gauge patterns.

[0038]

[0058] The initial set of larger clips may be provided a priori by a customer based on known critical feature areas within the design layout that require specific image optimization. Alternatively, in another embodiment, the initial set of larger clips may be extracted from the overall design layout by using some type of automated (e.g., machine vision) or manual algorithm that identifies one or more critical feature areas.

[0039]

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

number

[0040]

[0060] Here, (z1, z2, …, z N ) are N design variables or their values. p (z1, z2, …, z N ) is the design variable (z1, z2, …, z N), such as the difference between the actual and intended values ​​of a feature for a set of values ​​of the design variables (z1, z2, …, z N ) may be a function of w p f p (z1, z2, …, z N ) is a weighting constant related to the feature size. For example, a feature may be the position of an edge of a pattern, measured at a given point on the edge of the pattern. p (z1, z2, …, z N ) are weighted by different weights w p For example, if the range of allowable positions for a particular edge is narrow, then f may be used to represent the difference between the actual position of that edge and its intended position. p (z1, z2, …, z N ) weight w p can be given a higher value. p (z1, z2, …, z N ) can also be a function of the inter-layer features, which is the design variables (z1, z2, …, z N ) function. Of course, CF(z1, z2, ..., z N CF(z1, z2, ..., z) is not limited to the form of formula 1. N ) may be in any other suitable form.

[0041]

[0061] The cost function may represent any one or more suitable characteristics of the lithographic projection apparatus, the lithographic process, or the substrate (e.g., focus, CD, image shift, image distortion, image rotation, stochastic variation, throughput, local CD variation, process window, inter-layer features, or a combination thereof). N ) may include one or more selected from dose, global bias of the patterning device, and / or geometry of the illumination. Since the resist image often dictates the pattern on the substrate, the cost function may include a function that represents one or more characteristics of the resist image. For example, f p (z1, z2, …, z N ) is simply the distance between a point in the resist image and its intended location (i.e., the edge placement error EPE p (z1, z2, …, z N)) The design variables may include any adjustable parameters, such as adjustable parameters of the radiation source, the patterning device, the projection optics, the dose, the focus, etc.

[0042]

[0062] Lithographic projection apparatuses may include components collectively referred to as "wavefront manipulators" that may be used to adjust the shape of the wavefront as well as the intensity distribution and / or phase shift of the radiation beam. In an embodiment, the lithographic projection apparatus may adjust the wavefront and intensity distribution anywhere along the optical path of the lithographic projection apparatus, such as in front of a patterning device, near a pupil plane, near an image plane, and / or near a focal plane. The wavefront manipulators may be used to correct or compensate for certain distortions of the wavefront and the intensity distribution and / or phase shift caused, for example, by the radiation source, the patterning device, temperature variations within the lithographic projection apparatus, thermal expansion of components of the lithographic projection apparatus, etc. By adjusting the wavefront and the intensity distribution and / or phase shift, the value of the characteristic represented by the objective function may be changed. Such changes may be simulated from a model or may be measured in practice. The design variables may include parameters of the wavefront manipulator.

[0043]

[0063] The design variables are (z1, z2, …, z N)∈Z, where Z is a set of possible values ​​for the design variables. One possible constraint on the design variables may be imposed by the desired throughput of the lithographic projection apparatus. Without such constraints imposed by the desired throughput, optimization may produce an unrealistic set of design variable values. For example, if dose is a design variable without such constraints, optimization may result in dose values ​​that make the throughput economically unfeasible. However, the usefulness of a constraint should not be interpreted as a necessity. For example, throughput may be affected by pupil fill factor. For some illumination designs, a low pupil fill factor may waste radiation, leading to a lower throughput. Throughput may also be affected by the chemistry of the resist. A slower resist (e.g., a resist that requires a larger amount of light to be exposed adequately) leads to a lower throughput.

[0044]

[0064] As used herein, the term "patterning process" refers to the process of creating an etched substrate by applying light in a specified pattern as part of a lithography process.

[0045]

[0065] As used herein, the term "design layout" means the ideal pattern to be formed on a substrate.

[0046]

[0066] The term "printed pattern" as used herein means a physical pattern on a substrate formed based on a design layout. The printed pattern may include, for example, vias, contact holes, troughs, channels, recesses, edges, or other 2-3 dimensional features resulting from a lithography process.

[0047]

[0067] The term "process model" as used herein means a model that includes one or more models that simulate a patterning process. For example, a process model can include any combination of a light model (e.g., modeling a lens system / projection system used to deliver light in a lithography process and modeling the final optical image of the light traveling onto a photoresist), a mask model, a resist model (e.g., modeling physical effects of the resist such as chemical effects caused by light), an OPC model (e.g., can be used to create a design layout and can include sub-resolution resist features (SRAFs), etc.), an imaging device model (e.g., modeling what an imaging device can image from a printed pattern).

[0048]

[0068] As used herein, the term "imaging device" refers to any number of devices, associated computer hardware and software, and any combination thereof that can be configured to generate images of a target, such as a printed pattern or portions thereof. Non-limiting examples of imaging devices can include scanning electron microscopes (SEMs), x-ray machines, etc.

[0049]

[0069] As used herein, the term "calibrate" means to modify (eg, improve or adjust) and / or verify a process model or the like.

[0050]

[0070] FIG. 3 illustrates an exemplary mask pattern and mask features. Mask pattern 310 in FIG. 3 illustrates a complex pattern of mask features such as vias, troughs, channels, etc. In some embodiments, the mask pattern can be divided into sections, which are referred to herein as mask patches. Mask pattern 310 is illustrated with four mask patches 310a, 310b, 310c, and 310d, but any number or arrangement of mask patches is possible. The mask patches can be divided by boundaries, for example boundary 312 and boundary 314. An enlarged portion of mask pattern 310 is shown as inset 320. At this scale, the shape of mask feature 330 can be clearly seen. As shown in the inset, some mask features 330 can extend across boundary 312.

[0051]

[0071] FIG. 4 shows a conventional OPC generated mask feature that violates the MRC rules. OPC can be utilized during mask design to optimize the mask so that it ultimately delivers light to the substrate, resulting in a desired design layout. An example of a mask feature 410 (e.g., what would be present on a fully optimized mask) is depicted in the top 400A of FIG. 4, with a grid shown as dots for reference. The example mask feature 410 has some portions that are curved in shape and can be optimized through simulation to result in a desired feature on the printed pattern. Conventional mask optimization can include starting with a target pattern polygon (e.g., representing the desired pattern to be manufactured) and extracting such polygon to serve as the basis for the mask. Then, points or line segments representing the boundary of the mask feature (or pixel values ​​in the mask pattern representing transmission in the case of CTM) are iteratively adjusted until an optimized mask pattern is obtained that results in the closest printed pattern (e.g., as simulated in SMO or other process simulators). However, such conventional mask feature optimization can be computationally expensive due to the large number of elements that need to be adjusted to form the optimized mask feature. At the bottom 400B of FIG. 4, straight mask features 420 can be utilized to approximate any shape of a mask feature (e.g., mask feature 410), and can also be optimized using conventional OPC in a simpler manner than curvilinear mask features, since only line segments need to be adjusted instead of points on a continuous curve.

[0052]

[0072] Optimization resulting from conventional OPC may often result in mask features that violate Mask Rule Check (MRC) rules. As an example, MRC rules may require that mask features have a certain minimum width to prevent unacceptably small mask features that are impossible to build or likely to be fabricated with errors. As shown in the example of FIG. 4, optimized straight mask feature 420 has a portion 422 (shown in bold) that is significantly narrower than the corresponding location of mask feature 410. In this example, because the optimization was not constrained to follow the MRC rules, a mask feature 430 (e.g., a mask feature that would result on a physical mask if built) was generated that has a similarly narrow portion that may not be suitable for actual mask manufacturing.

[0053]

[0073] The present disclosure provides, for example, efficient methods for constructing and optimizing mask features so that MRC rules can be more easily observed (and in some embodiments automatically), facilitates optimization through homogeneous modification of similar mask features, and provides embodiments that improve homogeneity of mask feature geometries across boundaries between mask patches.

[0054]

[0074] According to an embodiment of the present disclosure, in an OPC process, a mask feature representation is constructed by using an array of two-dimensional elements defined based on MRC rules. FIG. 5 illustrates an exemplary process for locating, associating, and adjusting two-dimensional elements forming a mask feature, according to an embodiment of the present disclosure. In some embodiments, determining a mask pattern (or portions thereof) for use in a lithography process may include assigning locations of two-dimensional elements 510 based on a target pattern. As shown in the first (top) portion 500A of FIG. 5, the shape of a mask feature 410 can be represented by a collection of two-dimensional elements 510 (shown as circles in this example) as opposed to straight line segments in conventional OPC (as shown in FIG. 4). Four of the two-dimensional elements are numbered as 510a-d. As will be explained further herein, it will be appreciated that a contour line formed around a two-dimensional element (e.g., a circle having a diameter that is at least the minimum width specified by the MRC rules) can inherently and automatically satisfy the MRC rules, regardless of the location of the two-dimensional element.

[0055]

[0075] The next panel 500B of FIG. 5 illustrates an example of associating two-dimensional elements based on association criteria to form a cluster 530 that represents a mask feature. The associations 520 are depicted as line segments between the two-dimensional elements. As described further herein, the associated two-dimensional elements can then be utilized to form a cluster 530 having a shape corresponding to the mask feature 410. In FIG. 5, all of the illustrated two-dimensional elements are part of the example cluster. Not all two-dimensional elements in a cluster need to be associated with each other, as the elements that are associated depend on the optimization of the mask feature. For example, the top left two-dimensional element 510a is not associated with the bottom right 510d, but through associations with other two-dimensional elements, they are part of the same cluster 530.

[0056]

[0076] The middle panel 500C of Figure 5 illustrates an example contour 540 and cluster 530. As described in more detail herein, such as with reference to Figure 6, the contour 540 can be generated to encompass the area formed by the two-dimensional elements and the regions between the two-dimensional elements. Thus, the contour can be an outer contour of the cluster that corresponds to the outer edge of the mask feature. Similarly, for a mask feature that has an inner edge, such as a donut-shaped mask feature, the contour can be an inner contour of the cluster that corresponds to the inner edge of the mask feature.

[0057]

[0077] The next panel 500D again shows 2D elements 510, associations 520, clusters 530, and contour lines 540, similar to the middle panel, but does not show the lines forming the regions between the 2D elements or mask features 410. Here, the contour lines 540 are more clearly visible and surround the clusters of 2D elements.

[0058]

[0078] The bottom panel 500E in FIG. 5 illustrates adjusting two-dimensional elements of a cluster to change the mask feature formed by the cluster. In some embodiments, adjusting the mask feature can be based on simulations, OPC models, etc. related to the lithography process. In other embodiments, adjusting the mask feature can be based on geometric properties of the mask pattern (e.g., width, separation, etc.) and also based on rules prescribed for OPC (e.g., adding serifs, bias, hammerheads, SRAFs, etc. to the main feature). In some embodiments where the adjustment is based on simulation, the mask generation process, such as in SMO or OPC, can optimize the mask feature by adjusting any combination of two-dimensional elements of any cluster formed for the simulated mask. In this example, two-dimensional element 550a is shown in a slightly different position and two-dimensional element 550b has been added (with the nearby two-dimensional elements also moving slightly). As used herein, "adjusting" a two-dimensional element means moving the two-dimensional element, changing the shape of the two-dimensional element, or adding / removing a two-dimensional element. For example, the center of a circular two-dimensional element can be moved in a manner required to optimize the mask. In other implementations, the radius of the circular two-dimensional elements can be varied as part of the optimization process.When using these methods of determining / adjusting the contours of mask features, any of the disclosed methods can include manufacturing a mask from a mask pattern that includes contours generated from the adjusted two-dimensional elements.

[0059]

[0079] The present disclosure contemplates that many types of two-dimensional elements may be utilized. Since two-dimensional elements may be utilized to define at least certain dimensions (e.g., CD, minimum gap between mask features, etc.) and possibly certain areas (minimum area allowed by the mask features), the two-dimensional elements may define non-zero areas (e.g., as opposed to points). For example, the two-dimensional elements may be circular, or more generally elliptical. The two-dimensional elements may be of the same size or may vary in size within or between clusters. Two-dimensional elements need not be circular / elliptical. For example, the two-dimensional elements may be polygonal (e.g., square, triangle, rectangle, hexagon, etc.) or any suitable shape. In such implementations, contour lines may be drawn around the vertices or against the sides. Such two-dimensional elements may define closed or semi-closed areas (e.g., the area of ​​a circle as illustrated). Although circles, polygons, and other shapes are examples of closed areas, in some embodiments, the two-dimensional elements may be effectively represented by arcs or other similar structures. For example, the same contour line in the bottom panel of Figure 5 can be produced by positioning an arc segment having the same center as the circle, oriented appropriately, and of sufficient length to produce the contour line shown. Accordingly, substantial equivalents of the exemplary two-dimensional elements illustrated herein are considered to be within the scope of this disclosure.

[0060]

[0080] The present disclosure is not limited to a particular mechanism for determining a contour from a cluster of two-dimensional elements. For example, FIG. 6 illustrates an exemplary process for obtaining a contour of a mask feature based on two-dimensional elements, according to one embodiment of the present disclosure. A cluster of two-dimensional elements can be contoured in any suitable manner without departing from the scope of the present disclosure, and one implementation is illustrated in FIG. 6. The upper portion 600A of FIG. 6 illustrates two exemplary associated two-dimensional elements 610a and 610b. A virtual line segment 520 can connect the centers of the two-dimensional elements. The system is not required to generate the virtual line segment 620, which is provided herein for illustrative purposes. For a contour around a two-dimensional element, the virtual line 520 can be offset to either side by a distance equal to the radius of the two-dimensional element. This can then form what is referred to herein as a "subarea" (the area of ​​the two-dimensional element and the area between them based on the offset line), one of which is illustrated as subarea 622a. In implementations where the two-dimensional elements are not of the same size, the offsetting can be done such that the offset distance goes from one radius to the other. However, it will be understood that this discussion is merely exemplary. The offset distance or subarea may be defined in any other suitable manner, and a mask feature may have multiple such subareas. The area enclosed by the contour line may be the area occupied by the subarea and any corresponding area inside the connected collection of subareas (e.g., the area of ​​the subareas around the perimeter of the mask feature, and the area that such perimeter may occupy).

[0061]

[0081] The next portion 600B of FIG. 6 extends the above example to include a two-dimensional element 610c. Another imaginary line segment 620a is shown between 610b and 610c, with a corresponding offset line segment forming part of the contour 630b. Thus, in various embodiments, a process similar to that described above may include generating subareas of the contour (e.g., 622a and 622b) by applying a polygon offset operation to the pair of associated two-dimensional elements (e.g., 610a / b and 610b / c). The process then includes calculating the totality of the subareas, with the contour 630b defining the totality of the subareas. Since the illustrated two-dimensional elements may form a cluster, the system may thereby generate a contour of the cluster based on the two-dimensional elements. In this example, the contour corresponds to the outer contour of all the subareas in the cluster that form the periphery of the cluster. This process can be extended to any number and configuration of two-dimensional elements, as shown by the lower portion 600C of FIG. 6, showing contour line 630c, also illustrated by contour line 540 in FIG.

[0062]

[0082] 6 in panels 610A-C has been provided to provide an exemplary step-by-step method of contouring, in some implementations, contouring can be performed in substantially fewer steps. For example, once the two-dimensional elements that form the basis of the mask shape have been determined, such two-dimensional elements can then form a single shape (which may include any combination of polygons and line segments). This shape can then be treated as a polygon (again, not strictly a polygon, as it may have parts that are line segments), and this "polygon" can then be contoured by performing polygon offset operations according to any of the examples herein, including some described below.

[0063]

[0083] In some embodiments, a "polygon offset" operation may be performed in which a contoured polygon is defined by selecting locations (e.g., centers) of two-dimensional elements that correspond to a desired mask feature. An example of such a polygon 640 is shown in bold in 600C, with various line segments connecting particular centers of the two-dimensional elements. The polygon 640 (including an example additional line segment 650) may then be offset (e.g., by the radius of the two-dimensional element) to form the illustrated contour 630c. Although not shown in the example of FIG. 6, any interior regions (e.g., as in a "doughnut-shaped" mask feature) may similarly be defined, contoured, and shaped as described herein.

[0064]

[0084] The defined outer contour may be further processed with any suitable technique. As can be seen from the example of the circular two-dimensional element in Fig. 5 and Fig. 6, some parts of the determined contour are naturally rounded based on the radius of the two-dimensional element. However, in some places, such as the concave portion of the contour 630, the disclosed method may also include performing corner rounding or any other type of smoothing operation on the outer contour. One method of corner rounding may also include performing spline interpolation between two points on either side of the corner. In some embodiments, the spline interpolation may modify the contour to be smooth, but not touch the two-dimensional element. Such deviations are acceptable because they may further enforce compliance with the minimum width MRC rule.

[0065]

[0085] In some embodiments, as shown in panel 600D, the system generates "square corners" 670, rather than rounded corners 660, around the vertices of the contoured polygon, so that intersecting sections that would normally create sharp vertices can instead meet with a third line segment (e.g., similar to a chamfer). Another option could be for the line segments to meet to form a "miter corner" 680, but in certain embodiments this may cause an undesired extension of the contour line (e.g., beyond a predetermined distance limit from the associated vertex). In such cases, the system can square off the miter corner 680 into another square corner 680a, so that the contour line does not extend beyond the predetermined limit.

[0066]

[0086] FIG. 7 illustrates an example mask feature contour made of two-dimensional elements that respects the MRC rules and allows flexibility with respect to the MRC rules, according to various embodiments. In some embodiments, as shown in FIG. 7, the contour can be at least partially a predetermined distance from the location (e.g., center) of the two-dimensional element, so that the mask feature can naturally meet the minimum width requirement. The upper part 700A of FIG. 7 illustrates an embodiment in which the contour (e.g., contour 710) is generally at least a predetermined distance (e.g., predetermined distance 720) from the location (e.g., center 730a) of the two-dimensional element (e.g., two-dimensional element 730). The predetermined distance can be arbitrarily set by the user or otherwise manipulated by the system, but in some embodiments, the predetermined distance can be based on the MRC rules for the minimum width of the mask feature. Two-dimensional elements, particularly circular two-dimensional elements, can also meet other MRC rules, such as minimum curvature (e.g., by having a minimum radius of the two-dimensional element).

[0067]

[0087] In other embodiments, at least a portion 740 of the contour 710 may be allowed to violate the MRC rules, such as to allow more flexibility in calculating an optimal or converged solution for the mask. For example, as shown in the lower portion of FIG. 7, while most of the mask features are shown as complying with the MRC rules, there is one portion (shown in bold) that may violate the MRC minimum width rule. This may occur, for example, when a two-dimensional element 750 has a different size than other two-dimensional elements, which is an option that can be implemented in some embodiments. Such flexibility may be beneficial, for example, by allowing some violation of the MRC rules in certain parts of the mask design if such violations improve the overall convergence of the mask or allow compliance in more critical places of the mask.

[0068]

[0088] The geometry of the two-dimensional elements can be defined based on one or more MRC rules. For example, the dimensional parameters of the two-dimensional elements (e.g., diameter, distance to a vertex or face of a polygon, etc.) can be selected to be the minimum width specified by the MRC rules. One technical benefit of the present disclosure is that any optimized mask feature automatically adheres to such MRC rules by forming part or all of the mask feature by drawing a contour around a two-dimensional element that is at least the size of the minimum allowed. This capability allows the mask simulator / optimizer to determine a mask pattern that can be efficiently optimized (e.g., by moving the two-dimensional elements in the required manner). Thus, automatic adherence to such MRC rules results in the resulting mask being simulated more quickly and manufactured with reduced errors.

[0069]

[0089] 8A and 8B show an example cluster of two-dimensional elements arranged tip-to-tip and separated based on the MRC rule, according to one embodiment.

[0070]

[0090] The MRC rules may include minimum space requirements. For example, in FIG. 8A, a contour line 810 may have a cluster 810a of two-dimensional elements (only a few of which are shown in the figure). Similarly, a second contour line 820 may have a second cluster 820b of two-dimensional elements. As shown by the example of FIG. 8A, if the tips of two contour lines 810 and 820 are closer than the minimum space requirement 830, mask features formed from such contour lines may have a substantial risk of merging when constructing the mask. A similar example is shown in FIG. 8B, where the tip of contour line 810 is close to the side of contour line 840. According to an embodiment of the present disclosure, two clusters (e.g., clusters 810a and 840a) and the resulting contour line may merge if the two-dimensional elements of either cluster violate the minimum space requirement.

[0071]

[0091] FIG. 9 illustrates an exemplary merging of clusters of two-dimensional elements based on MRC rules, according to one embodiment. To provide an MRC-compliant mask solution, some embodiments may merge contours when two-dimensional elements violate a minimum space requirement, thereby restoring the mask solution to compliance without the need for a subsequent MRC violation detection and calculation procedure. In other words, such merging may force the resulting non-merged contours to be at least a minimum distance apart (because otherwise the contours would merge). As illustrated by the example of FIG. 9 (based on FIG. 8B), the association criteria may include connecting (e.g., as illustrated by association 920) a second two-dimensional element (e.g., a two-dimensional element at the tip of the second cluster 820a) into a cluster (e.g., 810a) if the distance between the second contour (e.g., contour 820) of the second two-dimensional element and the contour (e.g., contour 810) of a two-dimensional element in the cluster is less than the minimum space requirement. The same condition can also be expressed in terms of the distance between two-dimensional elements (e.g., the minimum spacing requirement can be violated by two-dimensional elements whose centers are at the minimum spacing requirement plus the sum of their respective radii).

[0072]

[0092] The present disclosure provides a method that may include modifying a cluster of two-dimensional elements into one or more modified clusters. In the example of FIG. 9, adjusting two of the two-dimensional elements causes clusters 810a and 840a to become part of the same cluster (due to being within a minimum space requirement). The resulting contour 910 reflects the modified cluster. Modifications to the cluster may include, for example, adding or removing two-dimensional elements, changing gaps between the two-dimensional elements (which may cause separation or merging of the cluster and its resulting contour), etc. Such modified clusters may be formed based on MRC rules similar to the examples given above. In some embodiments, modifying the cluster may include modifying the cluster by separating (e.g., removing) one of the two-dimensional elements from the cluster and modifying the contour based on the modified cluster. In other embodiments, a particular method may include modifying the cluster by associating a two-dimensional element from another cluster with the cluster and modifying the contour based on the modified cluster, as shown in FIG. 9.

[0073]

[0093] As described herein, adjustments to two-dimensional elements can be utilized in mask optimization. For example, in an optimization process, adjusting two-dimensional elements can include optimizing a mask pattern by moving the location of one or more of the two-dimensional elements, adjusting the size or shape of one or more of the two-dimensional elements, etc. Associating two-dimensional elements as part of the optimization can also include associating two-dimensional elements that are within a predetermined distance from other two-dimensional elements, in other words, adding two-dimensional elements to a cluster if they are close enough (as illustrated by the example of FIG. 9). Certain embodiments can also include separating a two-dimensional element from a two-dimensional element of a cluster and associating the two-dimensional element with a two-dimensional element in a second cluster. This can be described as moving a two-dimensional element from one cluster to another.

[0074]

[0094] As described herein, some embodiments may use a cost function to optimize a simulated pattern (e.g., for a mask, resist layer, etc.). For example, a cost function, such as that shown in the example of Equation 1, may include terms such as EPE (e.g., z1, z2, etc.), which may be minimized as part of the optimization. Because the disclosed methods for mask generation (e.g., moving two-dimensional elements to optimize mask features) affect the calculated cost for the resulting mask, some embodiments may include calculating a cost function that quantifies an evaluation of the mask pattern, and adjusting the two-dimensional elements is based on the cost function. In other words, the two-dimensional elements may be moved, resized, etc., to reduce the calculated cost, and may be based on rule-based OPC or model-based OPC. In some cases, the cost function may include terms related to MRC rules (e.g., determining whether an MRC rule is violated and assigning a cost based thereon). Because these determinations are computationally expensive, another technical benefit of the present disclosure is that some embodiments include cost functions that do not include terms based on MRC rules. In these embodiments, two-dimensional elements do not require consideration in the cost function, since they can automatically satisfy one or more MRC rules.

[0075]

[0095] FIG. 10A illustrates replicating a cluster of two-dimensional elements at symmetrical locations on a mask pattern to ensure homogeneity of the OPC pattern, according to one embodiment of the present disclosure. In some cases, the pattern layout may have a large number of features that are replicated throughout the pattern (e.g., using standard vias, troughs, etc.). Replication of such features may thereby be reflected in the mask and the respective mask features. FIG. 10A illustrates an example portion 1010 of a mask with several mask features, where a mask feature 1020 is replicated in several locations. The mask feature 1020 is shown in an expanded view similar to that described above with two-dimensional elements 1030 and contour lines 1040.

[0076]

[0096] FIG. 10B illustrates adjusting corresponding two-dimensional elements in a homogeneous cluster according to one embodiment. In some embodiments, generating a "homogeneous cluster" (associated two-dimensional elements in a replicated mask feature 1020) may be done by replicating a cluster in a mask pattern, as shown in FIG. 10A. Such homogeneous clusters can then be homogeneously adjusted by adjusting corresponding two-dimensional elements in the homogeneous cluster. In this example, corresponding two-dimensional elements 1050 are shown as being adjusted, for example, as part of an optimization process. In the illustrated example mask portion 1010, the same adjustment is made to all corresponding two-dimensional elements 1050 in corresponding clusters in the mask pattern. In this manner, replicated homogeneous clusters can facilitate fast and homogeneous adjustments to features used throughout the mask, allowing many adjustments to be made with a single (or relatively few) instructions.

[0077]

[0097] FIG. 11A illustrates preferred 2-dimensional elements near a mask boundary, according to one embodiment. To improve homogeneity of mask features across patch boundaries, some embodiments include adjusting homogeneous clusters by identifying boundary 2-dimensional elements that cross the boundary between a first mask patch and a second mask patch, where adjusting the 2-dimensional elements excludes adjusting the boundary 2-dimensional elements. In some embodiments, this includes designating certain 2-dimensional elements as preferred 2-dimensional elements. Such elements may have priority in the sense that they may be excluded from adjustment by a process that would otherwise adjust them as described herein (e.g., belong to a homogeneous cluster). For example, if patches are processed sequentially, the first patch may be optimized first, and mask features at the boundary may be adjusted. To ensure homogeneity across boundaries, when the second patch is optimized, some or all of the 2-dimensional elements in the mask features from the first mask may be designated as "preferred" in the second patch, meaning that they will not be adjusted with the rest of the second patch.

[0078]

[0098] The example shown in FIG. 11A shows a first mask patch 1110 and a second mask patch 1120 separated by a boundary 1130. Mask features 1140 and 1140a are shown as mask features replicated in four places, and the two instances (1140a) that cross the boundary may be treated differently from the other two instances (1140). Corresponding two-dimensional elements 1150 (at the edge of the mask feature) are shown with single cross-hatching, similar to what was described with reference to FIG. 10A / B. Corresponding two-dimensional elements 1150 of the second mask patch 1120 may be adjusted in the manner described for similar corresponding two-dimensional elements 1050 of FIG. 10A / B. However, similar two-dimensional elements (at the edge of mask feature 1140a) may be treated differently. In some embodiments, to improve homogeneity of mask features across the boundary, two-dimensional elements that are within a threshold distance to the boundary 1130 of the first mask patch 1110 and the second mask patch 1120 are designated as preferred two-dimensional elements 1170, illustrated with double cross-hatching. The threshold distance can be defined by parameters set by the system or the user, and an exemplary illustration of such a region is illustrated by a dashed line. The threshold distance for designating a two-dimensional element as a preferred two-dimensional element need not be the same on either side of the boundary 1130. For example, as illustrated, the second threshold distance 1160 in the second patch and the corresponding first threshold distance 1160a in the first patch are illustrated as being farther away from the boundary 1130 than the second threshold distance 1160, thereby encompassing all of the illustrated two-dimensional elements in the first patch 1110. Thus, in some embodiments, some or all of the two-dimensional elements in mask feature 1140a that straddle boundary 1160 may be designated as preferred two-dimensional elements 1170, such that the two-dimensional elements of mask feature 1140a may not be adjusted along with other two-dimensional elements of second patch 1120 (e.g., two-dimensional element 1150) even though they could be adjusted as corresponding two-dimensional elements in a manner similar to that shown in FIGS. 10A / B if the boundary were not in place.

[0079]

[0099] FIG. 11B illustrates preferred 2-D elements near the mask boundary that are excluded from adjustment, according to one embodiment. FIG. 11B illustrates that in some embodiments, adjusting the 2-D elements can exclude adjusting the preferred 2-D elements. In this way, certain applications can benefit from having a more consistent homogeneity of mask features across the mask boundary, even during the optimization process where 2-D elements are moved, resized, etc. This can include, for example, regrouping some 2-D elements near the boundary (e.g., regrouping the 2-D element 1170 as its own cluster, and optionally doing the same for similar 2-D elements of other mask features 1140a). As shown in FIG. 11B and described above, in some embodiments, the preferred 2-D element 1170 includes the entire mask feature 1140a that extends beyond the boundary 1130. In such an embodiment, the mask feature 1140a that extends beyond the boundary 1130 may be adjusted as part of optimizing the first patch 1110 (on one side of the boundary), but is not adjusted when optimizing the second patch 1120, even though the mask feature 1140a has some two-dimensional elements on the second patch 1120. This can further ensure that such boundary-extending mask features are not adjusted in a way that would modify the optimization of the first patch 1110. In some embodiments, two-dimensional elements of the second patch 1120 near the patch boundary 1130 can be regrouped. For example, two elements such as 1150 in FIG. 11A can be regrouped to belong to two different groups 1180 and 1190. For example, the two groups can be treated separately when adjusting the two-dimensional elements as a result of group 1180 being closer to the boundary 1130 and the preferred two-dimensional element 1170 in the mask feature 1140a.

[0080]

[0100] In some embodiments, the preferred two-dimensional element can be stored in computer memory for later recall. For example, this facilitates some embodiments to replace one or more of the two-dimensional elements within a threshold distance to a boundary with the preferred two-dimensional element. Such a two-dimensional element can thereby both improve computational performance by not having to recalculate or optimize the contours of the boundary area, and improve the homogeneity of such mask features across the boundary.

[0081]

[0101] FIG. 12 is a process flow diagram illustrating an exemplary method of utilizing preferred 2D shapes to improve mask homogeneity near the mask boundary in accordance with an embodiment of the present disclosure.

[0082]

[0102] The method may include, at 1210, receiving a mask pattern. The mask pattern may be an initial mask pattern, a partially optimized mask pattern, a mask pattern that needs to be re-optimized based on changes to a source, MRC rules, an updated design layout, etc.

[0083]

[0103] At 1220, the method may include generating a homogeneous cluster by replicating the cluster in the mask pattern. The adjusting may include adjusting corresponding two-dimensional elements in the homogeneous cluster.

[0084]

[0104] At 1220, the method may include designating two-dimensional elements within a threshold distance of a boundary between the first mask patch and the second mask patch as preferred two-dimensional elements.

[0085]

[0105] At 1230, the method may include replacing one or more of the two-dimensional elements near the boundary with a preferred two-dimensional element recalled from computer memory.

[0086]

[0106] At 1240, the method may include generating an adjusted mask pattern based on the two-dimensional elements in the homogeneous cluster. Adjusting the two-dimensional elements may exclude adjusting the preferred two-dimensional elements.

[0087]

[0107] FIG. 13 is a block diagram of an exemplary computer system CS according to one embodiment of the present disclosure.

[0088]

[0108] The computer system CS includes a bus BS or other communication mechanism for communicating information, and also includes a processor PRO (or multiple processors) coupled to the bus BS for processing information. The computer system CS also includes a main memory MM, such as a random access memory (RAM) or other dynamic storage device, coupled to the bus BS for storing information and instructions executed by the processor PRO. The main memory MM may also be used to store temporary variables or other intermediate information during execution of instructions executed by the processor PRO. The computer system CS further includes a read only memory (ROM) ROM or other static storage device coupled to the bus BS for storing static information and instructions for the processor PRO. A storage device SD, such as a magnetic or optical disk, is provided and coupled to the bus BS for storing information and instructions.

[0089]

[0109] The computer system CS may be coupled via a bus BS to a display DS, such as a cathode ray tube (CRT) or flat panel display or a touch panel display, for displaying information to a computer user. An input device ID, including alphanumeric and other keys for communicating information and command selections to the processor PRO, is coupled to the bus BS. Another type of user input device is a cursor control CC, such as a mouse, a trackball, or cursor direction keys, for communicating directional information and command selections to the processor PRO, as well as for controlling cursor movement on the display DS. This input device typically has two degrees of freedom in two axes, i.e., a first axis (e.g., x) and a second axis (e.g., y), allowing the device to specify a position in a plane. A touch panel (screen) display may also be used as an input device.

[0090]

[0110] According to one embodiment, parts of one or more methods described herein can be executed by the computer system CS in response to the processor PRO executing one or more sequences of one or more instructions contained in the main memory MM. Such instructions can be read into the main memory MM from another computer-readable medium, such as a storage device SD. Execution of the sequences of instructions contained in the main memory MM causes the processor PRO to perform the process steps described herein. Also, one or more processors of a multi-processing arrangement may be used to execute the sequences of instructions contained in the main memory MM. In alternative embodiments, hardwired circuitry can be used in place of or in combination with software instructions. Thus, the description herein is not limited to any particular combination of hardware circuitry and software.

[0091]

[0111] The term "computer-readable medium" as used herein refers to any medium that participates in providing instructions to the processor PRO for execution. Such media may take many forms, including but not limited to non-volatile media, volatile media, and transmission media. Non-volatile media include, for example, optical or magnetic disks, such as the storage device SD. Volatile media include dynamic memory, such as the main memory MM. Transmission media include coaxial cables, copper wire, and optical fibers, including the wires that make up the bus BS. Transmission media may also take the form of acoustic or light waves, such as those generated during radio frequency (RF) and infrared (IR) data communications. Computer-readable media may be non-transitory, such as, for example, a floppy disk, a flexible disk, a hard disk, a magnetic tape, any other magnetic medium, a CD-ROM, a DVD, any other optical medium, punch cards, paper tape, any other physical medium with a pattern of holes, a RAM, a PROM, an EPROM, a FLASH-EPROM, any other memory chip or cartridge. A non-transitory computer-readable medium may have instructions recorded thereon. The instructions, when executed by a computer, can perform any of the features described herein. The transitory computer-readable medium may include a carrier wave or other propagating electromagnetic signal.

[0092]

[0112] Various forms of computer readable media may be involved in carrying one or more sequences of one or more instructions to the processor PRO for execution. For example, the instructions may initially be carried on a magnetic disk of a remote computer. The remote computer may load the instructions into its dynamic memory and send the instructions over a telephone line using a modem. A modem local to the computer system CS may receive the data on the telephone line and convert the data to an infrared signal using an infrared transmitter. An infrared detector coupled 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 instructions. The instructions received by the main memory MM may optionally be stored in a storage device SD either before or after execution by the processor PRO.

[0093]

[0113] The computer system CS may also include a communications interface CI coupled to the bus BS. The communications interface CI provides a bidirectional data communications coupling to a network link NDL connected to a local network LAN. For example, the communications interface CI may be an integrated services digital network (ISDN) card or a modem for providing a data communications connection to a corresponding type of telephone line. As another example, the communications interface CI may be a local area network (LAN) card for providing a data communications connection to a compatible LAN. A wireless link may also be implemented. In any such implementation, the communications interface CI sends and receives electrical, electromagnetic or optical signals that carry digital data streams representing various types of information.

[0094]

[0114] The network link NDL typically provides data communication to other data devices via one or more networks. For example, the network link NDL may provide a connection to a host computer HC via a local network LAN. This may include data communication services provided via a worldwide packet data communication network, nowadays commonly referred to as the "Internet" INT. Both local networks LAN (Internet) use electrical, electromagnetic or optical signals that carry digital data streams. The signals through the various networks and the signals on the network data link NDL via the communication interface CI that carry digital data to and from the computer system CS are exemplary forms of carrier waves transporting information.

[0095]

[0115] The computer system CS can send messages and receive data including program code via the network, the network data link NDL and the communication interface CI. In the Internet example, the host computer HC can send requested code for an application program via the Internet INT, the network data link NDL, the local network LAN and the communication interface CI. One such downloaded application can provide, for example, all or part of the method described herein. The received code can be executed by the processor PRO as 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.

[0096]

[0116] FIG. 16 depicts a schematic diagram of a lithographic projection apparatus according to one embodiment of the present disclosure.

[0097]

[0117] The lithographic projection apparatus may include an illumination system IL, a first object table MT, a second object table WT, and a projection system PS.

[0098]

[0118] The illumination system IL is capable of conditioning the radiation beam B. In this particular case, the illumination system also comprises a radiation source SO.

[0099]

[0119] The first object table (e.g., patterning device table) MT may be provided with a patterning device holder for holding a patterning device MA (e.g., a reticle) and may be connected to a first positioner for accurately positioning the patterning device relative to an item PS.

[0100]

[0120] A second object table (substrate table) WT may comprise a substrate holder for holding a substrate W (eg a resist-coated silicon wafer) and may be connected to a second positioner for accurately positioning the substrate relative to the component PS.

[0101]

[0121] A projection system ("lens") PS (e.g., a refractive optical system, a reflective optical system, or a catadioptric optical system) can image the irradiated portion of the patterning device MA onto a target portion C of the substrate W (e.g., comprising one or more dies).

[0102]

[0122] As depicted herein, the apparatus can be of a transmissive type (i.e. having a transmissive patterning device). In general, however, the apparatus can also be of a reflective type (e.g. having a reflective patterning device). The apparatus can employ different kinds of patterning devices in a conventional mask; examples include a programmable mirror array or an LCD matrix.

[0103]

[0123] A radiation source SO (e.g. a mercury lamp or excimer laser, LPP (Laser Produced Plasma) EUV source) produces a beam of radiation. This beam is fed into an illumination system (illuminator) IL, either directly or after having traversed an adjusting device, such as a beam expander Ex. The illuminator IL may comprise adjusting devices AD for setting the outer and / or inner radial extent (commonly referred to as σ-outer and σ-inner, respectively) of the intensity distribution in the beam. Furthermore, the illuminator IL generally comprises various other components, such as an integrator IN and a condenser CO. In this way, the beam B impinging on the patterning device MA has a desired uniformity and intensity distribution in its cross-section.

[0104]

[0124] In some embodiments, the source SO may be within the housing of the lithographic projection apparatus (this is often the case when the source SO is a mercury lamp, for example), but it is also possible that the source SO is located remote from the lithographic projection apparatus and the beam of radiation that it generates is directed into the apparatus (for example by the use of suitable directing mirrors). This latter situation is often the case when the source SO is an excimer laser (for example based on KrF, ArF or F2 lasing).

[0105]

[0125] The beam PB may subsequently intercept the patterning device MA, which is held on a patterning device table MT. Having traversed the patterning device MA, the beam B passes through a lens PL, which focuses the beam B onto a target portion C of the substrate W. Using the second positioning device (and the interferometric measurement device IF), the substrate table WT may be precisely moved, for example to position various target portions C in the path of the beam PB. Similarly, the first positioning device may be used to precisely position the patterning device MA with respect to the path of the beam B, for example after mechanical retrieval of the patterning device MA from a patterning device library or during a scan. In general, movement of the object tables MT, WT may be realised using 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 to a short-stroke actuator only, or may be fixed.

[0106]

[0126] The depicted tool can be used in two different modes: step mode and scan mode. In step mode, the patterning device table MT is kept essentially stationary and the entire patterning device image is projected onto the target portion C in one go (i.e. in a single "flash"). The substrate table WT can be moved in the x and / or y directions so that a different target portion C can be irradiated by the beam PB.

[0107]

[0127] In scan mode, essentially the same situation applies, with the difference that a given target portion C is not exposed in a single "flash". Instead, the patterning device table MT is movable in a given direction (the so-called "scan direction", e.g. the y direction) with a speed v, so that the patterning device image is scanned by the projection beam B while simultaneously moving the substrate table WT in the same or opposite direction with a speed V = Mv, in which 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 compromising on resolution.

[0108]

[0128] FIG. 15 is a schematic diagram of another lithographic projection apparatus (LPA), according to an embodiment of the present disclosure.

[0109]

[0129] The LPA may include a source collector module SO, an illumination system (illuminator) IL configured to condition a radiation beam B (e.g., EUV radiation), a support structure MT, a substrate table WT, and a projection system PS.

[0110]

[0130] A support structure (eg, patterning device table) MT may be constructed to support a patterning device (eg, mask or reticle) MA and connected to a first positioner PM configured to accurately position the patterning device.

[0111]

[0131] A substrate table (eg, a wafer table) WT may be constructed to support a substrate (eg, a resist-coated wafer) W and connected to a second positioner PW configured to accurately position the substrate.

[0112]

[0132] The projection system (eg, a reflection projection system) PS may be configured to project a pattern imparted to a radiation beam B by a patterning device MA onto a target portion C of a substrate W (eg comprising one or more dies).

[0113]

[0133] As shown here, the LPA may be reflective (e.g., using a reflective patterning device). Note that since most materials are absorptive in the EUV wavelength range, the patterning device may have a multi-layer reflector, including, for example, a multi-stack of molybdenum and silicon. In one example, the multi-stack reflector has 40 layers of molybdenum and silicon pairs, each layer being a quarter wavelength thick. Even shorter wavelengths can be produced using x-ray lithography. Since most materials are absorptive at EUV and x-ray wavelengths, thin pieces of absorbing material patterned on the patterning device topography (e.g., TaN absorber on top of a multi-layer reflector) define where features will be printed (positive resist) or not printed (negative resist).

[0114]

[0134] The illuminator IL can receive a beam of extreme ultraviolet radiation from the source collector module SO. Methods of generating EUV radiation include, but are not necessarily limited to, converting a material having at least one element with one or more emission lines in the EUV range, such as xenon, lithium, or tin, into a plasma state. In one such method, often referred to as laser-produced plasma ("LPP"), a fuel, such as a droplet, stream, or cluster of a material having a line-emitting element, can be irradiated with a laser beam to generate a plasma. The source collector module SO can be part of an EUV radiation system that includes a laser for providing a laser beam to excite the fuel. The resulting plasma emits output radiation (e.g., EUV radiation), which is collected using a radiation collector disposed in the source collector module. For example, when a CO2 laser is used to provide the laser beam for fuel excitation, the laser and the source collector module can be separate components.

[0115]

[0135] In such cases, the laser may not be considered to form part of the lithographic apparatus, and the radiation beam may be passed from the laser to the source collector module using a beam delivery system including, for example, suitable directing mirrors and / or beam expanders. In other cases, the source may be an integral part of the source collector module, for example when the source is a discharge produced plasma EUV generator, often referred to as a DPP source.

[0116]

[0136] The illuminator IL may comprise an adjuster for adjusting the angular intensity distribution of the radiation beam. Generally, at least the outer and / or inner radial extent (commonly referred to as σ-outer and σ-inner, respectively) of the intensity distribution in a pupil plane of the illuminator may be adjusted. In addition, the illuminator IL may also include various other components, such as facetted field mirror devices and facetted pupil mirror devices. The illuminator may be used to adjust the radiation beam to have a desired uniformity and intensity distribution in its cross-section.

[0117]

[0137] The radiation beam B may be incident on a patterning device (e.g. mask) MA held on a support structure (e.g. patterning device table) MT and is patterned by the patterning device. After reflecting from the patterning device (e.g. mask) MA, the radiation beam B passes through a projection system PS, which focuses the beam onto a target portion C of a substrate W. Using a second positioner PW and a position sensor PS2 (e.g. an interferometric device, a linear encoder or a capacitive sensor), the substrate table WT may be accurately moved, for example to position various target portions C in the path of the radiation beam B. Similarly, using a first positioner PM and another position sensor PS1, the patterning device (e.g. mask) MA may be accurately positioned relative to the path of the radiation beam B. The patterning device (e.g. mask) MA and substrate W may be aligned using patterning device alignment marks M1, M2 and substrate alignment marks P1, P2.

[0118]

[0138] The depicted apparatus LPA can be used in at least one of a step mode, a scan mode and a stationary mode.

[0119]

[0139] In step mode, the support structure (e.g. patterning device table) MT and substrate table WT are kept essentially stationary, while an entire pattern imparted to the radiation beam is projected onto the target portion C in one go (i.e. a single static exposure), and the substrate table WT is then moved in the X and / or Y direction so that a different target portion C can be exposed.

[0120]

[0140] In scan mode, the support structure (e.g. patterning device table) MT and the substrate table WT are scanned synchronously while a pattern imparted to the radiation beam is projected onto a target portion C (i.e. a single dynamic exposure). The velocity and direction of the substrate table WT relative to the support structure (e.g. patterning device table) MT can be determined by the (de-)magnification and image reversal characteristics of the projection system PS.

[0121]

[0141] In a stationary mode, the support structure (e.g. patterning device table) MT holds a programmable patterning device and is kept essentially stationary while the substrate table WT is moved or scanned while projecting a pattern imparted to the radiation beam onto a target portion C. In this mode, a pulsed radiation source is generally used, and the programmable patterning device is updated as required after each movement of the substrate table WT, or between successive radiation pulses during a scan. This mode of operation is readily applicable to maskless lithography using a programmable patterning device, such as a programmable mirror array.

[0122]

[0142] FIG. 16 depicts a detailed view of a lithographic projection apparatus, according to one embodiment of the present disclosure.

[0123]

[0143] As shown, the LPA can include a source collector module SO, an illumination system IL, and a projection system PS. The source collector module SO is constructed and arranged to maintain a vacuum environment within the closed structure ES of the source collector module SO. The EUV radiation emitting high temperature plasma HP can be formed by a discharge-produced plasma source. The EUV radiation can be generated by a gas or vapor (e.g., Xe gas, Li vapor, or Sn vapor) in which a high temperature plasma HP is generated to emit radiation in the EUV range of the electromagnetic spectrum. The high temperature plasma HP is generated, for example, by generating an at least partially ionized plasma by an electric discharge. For efficient radiation generation, for example, a partial pressure of 10 Pa of Xe, Li, Sn vapor, or any other suitable gas or vapor may be required. In one embodiment, an excited tin (Sn) plasma is provided to generate EUV radiation.

[0124]

[0144] The radiation emitted by the high temperature plasma HP is delivered from the source chamber SC into the collector chamber CC through an optional gas barrier or contaminant trap CT (sometimes also referred to as a contaminant barrier or foil trap) positioned in or behind the opening of the source chamber SC. The contaminant trap CT may include a channel structure. The contaminant trap CT may also include a gas barrier or a combination of a gas barrier and a channel structure. The contaminant trap or contaminant barrier CT further indicated herein includes at least a channel structure known in the art.

[0125]

[0145] The collector chamber CC may include a radiation collector CO, which may be a so-called grazing incidence collector. The radiation collector CO has an upstream radiation collector side US and a downstream radiation collector side DS. Radiation that traverses the collector CO may be reflected off a grating spectral filter SF and focused along an optical axis indicated by dashed line "O" to a virtual source point IF. The virtual source point IF may be referred to as an intermediate focus, and the source collector module may be positioned such that the intermediate focus IF is located at or near an aperture OP of the enclosure structure ES. The virtual source point IF is an image of the radiation emitting plasma HP.

[0126]

[0146] The radiation subsequently traverses an illumination system IL, which may include a faceted field mirror device FM and a faceted pupil mirror device pm arranged to provide a desired angular distribution of the radiation beam B at the patterning device MA and a desired radiation amplitude uniformity at the patterning device MA. Reflection of the radiation beam B off the patterning device MA, held by the support structure MT, forms a patterned beam PB which is imaged by the projection system PS via a reflective element RE onto a substrate W held by a substrate table WT.

[0127]

[0147] In general, there may be more elements in the illumination optics unit IL and projection system PS than shown. A grating spectral filter SF may optionally be present depending on the type of lithographic apparatus. Further, there may be more mirrors than shown, for example there may be 1-6 additional reflective elements in the projection system PS.

[0128]

[0148] The collector optic CO may be a nested collector with a grazing incidence reflector GR, just as one example of a collector (or collector mirror), arranged axially symmetrically about the optical axis O, and this type of collector optic CO may be used in combination with a discharge produced plasma source, often referred to as a DPP source.

[0129]

[0149] FIG. 17 shows a detailed view of a source collector module SO of lithographic projection apparatus LPA according to an embodiment of the present disclosure.

[0130]

[0150] The source collector module SO can be part of an LPA radiation system. The laser LA can be arranged to deposit laser energy into a fuel such as xenon (Xe), tin (Sn) or lithium (Li) to generate a highly ionized plasma HP with an electron temperature of tens of eV. Energetic radiation produced during de-excitation and recombination of these ions is emitted from the plasma and collected by a near-normal incidence collector optic CO and focused into an aperture OP of a closed structure ES.

[0131]

[0151] The concepts disclosed herein can be simulated or mathematically modeled on any general purpose imaging system for imaging sub-wavelength features and can be particularly useful for use with new imaging technologies that can produce increasingly shorter wavelengths. New technologies already in use include EUV (extreme ultraviolet), DUV lithography, which can produce 193 nm wavelengths using ArF lasers and even 157 nm wavelengths using fluorine lasers. Furthermore, EUV lithography can produce wavelengths in this range by using synchrotrons or by bombarding materials (either solids or plasmas) with high energy electrons to produce photons in the 20-50 nm range.

[0132]

[0152] Embodiments of the present disclosure can be further described using the following clauses. 1. A method for determining a mask pattern for use in a lithography process, comprising: assigning locations of the two-dimensional elements based on the target pattern; associating the two-dimensional elements based on an association criterion to form clusters representative of the mask features; adjusting two-dimensional elements of the cluster to vary the mask features; A method comprising: 2. The method according to clause 1, wherein the adjusting is based on a simulation related to a lithography process. 3. The method of claim 1, wherein the adjusting is based on geometric characteristics of the mask pattern and on rules prescribed for OPC. 4. The method of claim 1, further comprising generating cluster contours based on two-dimensional elements. 5. The method of claim 4, wherein the contour is an outer contour of the cluster corresponding to an outer edge of the mask feature. 6. The method of claim 4, wherein the contour is an inner contour of the cluster corresponding to an inner edge of the mask feature. 7. Generating subareas of the contour by applying a polygon offset operation to pairs of associated 2D elements; calculating the total number of sub-areas; 5. The method according to claim 4, wherein the contour line is the aggregate of the sub-areas. 8. The method of claim 4, further comprising manufacturing a mask from a mask pattern including contour lines generated from the adjusted two-dimensional elements. 9. The method of claim 4, wherein the contour line is at least in part a predetermined distance from the location of the two-dimensional element. 10. The method of claim 9, wherein the contour line is generally at least a predetermined distance from the location of the two-dimensional element. 11. The method of clause 9, wherein the predetermined distance is based on MRC rules for minimum width of mask features. 12. The method of claim 9, wherein at least a portion of the contour line violates MRC rules. 13. The method of clause 1, wherein the geometry of the two-dimensional elements is defined based on one or more Mask Rule Compliance (MRC) rules. 14. The method according to clause 13, in which the dimensional parameters of two-dimensional elements are selected to be the minimum widths specified by the MRC rules. 15. One or more MRC regulations contain minimum space requirements, 14. The method of claim 13, wherein the association criteria includes connecting the second two-dimensional element into the cluster if a distance between a second contour of the second two-dimensional element and a contour of a two-dimensional element in the cluster is less than a minimum space requirement. 16. The method of claim 1, further comprising modifying the clusters of two-dimensional elements into one or more modified clusters. 17. One or more modified clusters are based on the MRC Rules and are processed as described in clause 16. 18. Operation: modifying the cluster by separating one of the two-dimensional elements from the cluster; modifying the contours based on the modified clusters; 17. The method of claim 16, further comprising: 19. Operation: modifying the cluster by associating a two-dimensional element from another cluster with the cluster; modifying the contours based on the modified clusters; 17. The method of claim 16, further comprising: 20. The method of clause 1, wherein adjusting includes optimizing the mask pattern by moving the location of one or more of the two-dimensional elements. 21. The method of clause 1, wherein adjusting includes optimizing the mask pattern by adjusting a size or shape of one or more of the two-dimensional elements. 22. The method of clause 1, wherein associating further comprises associating two-dimensional elements that are within a predetermined distance from other two-dimensional elements. 23. The method of claim 22, wherein the relating or adjusting further comprises: separating a two-dimensional element from a two-dimensional element of a cluster; and relating the two-dimensional element to a two-dimensional element in a second cluster. 24. The method of claim 1, further comprising calculating a cost function that quantifies an evaluation of the mask pattern, and wherein adjusting the two-dimensional element is based on the cost function. 25. A method as set forth in clause 24, in which the cost function does not include a term based on MRC rules. 26. The method of claim 1, wherein each of the two-dimensional elements is circular. 27. The method of claim 1, wherein each of the two-dimensional elements is an ellipse. 28. The method of claim 1, wherein each of the two-dimensional elements is the same size. 29. The method of claim 1, wherein each of the two-dimensional elements defines a non-zero area. 30. The method of claim 1, wherein each of the two-dimensional elements is a polygon. 31. The method of clause 1, wherein each of the two-dimensional elements defines a closed or semi-closed area. 32. The method of claim 5, further comprising performing corner rounding on the outer contour. 33. The method of claim 32, wherein corner rounding comprises performing spline interpolation between two points on either side of the corner. 34. Operation: generating homogeneous clusters by replicating the clusters in a mask pattern; adjusting corresponding two-dimensional elements in the homogeneous clusters; 2. The method of claim 1, further comprising: 35. Refining the homogeneous clusters includes identifying boundary two-dimensional elements that cross a boundary between the first mask patch and the second mask patch; 35. The method of claim 34, wherein adjusting the two-dimensional element excludes adjusting a boundary two-dimensional element. 36. Adjusting the homogeneous cluster includes designating a two-dimensional element within a threshold distance of a boundary between the first mask patch and the second mask patch as a preferred two-dimensional element; 35. The method of claim 34, wherein adjusting the two-dimensional element excludes adjusting a preferred two-dimensional element. 37. The method of clause 35, further comprising storing the preferred two-dimensional elements in a computer memory for later recall. 38. The method of claim 35, further comprising replacing one or more of the two-dimensional elements within a threshold distance to the boundary with a preferred two-dimensional element. 39. Receiving a mask pattern; generating a homogeneous cluster by replicating the cluster in a mask pattern, where adjusting includes adjusting corresponding two-dimensional elements in the homogeneous cluster; designating a two-dimensional element within a threshold distance of a boundary between the first mask patch and the second mask patch as a priority two-dimensional element; replacing one or more of the two-dimensional elements near the boundary with a preferred two-dimensional element retrieved from a computer memory; generating an adjusted mask pattern based on the two-dimensional elements in the homogeneous cluster, where adjusting the two-dimensional elements excludes adjusting the preferred two-dimensional elements; 2. The method of claim 1, further comprising: 40. A non-transitory computer-readable medium having instructions recorded thereon for determining a mask pattern for use in a lithography process, comprising: A non-transitory computer-readable medium having instructions that, when executed by a computer having at least one programmable processor, cause the computer to perform operations including those recited in any one of clauses 1-39. 41. A system for determining a mask pattern for use in a lithography process, comprising: at least one programmable processor; a non-transitory computer readable medium having instructions recorded thereon; The instructions, when executed by a computer having at least one programmable processor, cause the system to perform the operations recited in any one of clauses 1 to 39.

[0133]

[0153] The concepts disclosed herein may be used for imaging on substrates such as silicon wafers, although it should be understood that the disclosed concepts may be used with any type of lithographic imaging system (e.g., one used for imaging on substrates other than silicon wafers).

[0134]

[0154] Combinations and subcombinations of the elements disclosed herein constitute separate embodiments and are provided for illustrative purposes only. Also, the above description is intended to be illustrative and not limiting. Thus, it will be apparent to one skilled in the art that modifications may be made as described above without departing from the scope of the claims set forth below.

Claims

1. 1. A computer-implemented method for determining a mask pattern for use in a lithography process, comprising: assigning locations of the two-dimensional elements based on the target pattern; associating the two-dimensional elements based on an association criterion to form clusters representative of mask features; adjusting the two-dimensional elements of the cluster to vary the mask feature; 4. A computer-implemented method comprising:

2. The computer-implemented method of claim 1 , wherein the adjusting is based on a simulation of the lithography process to optimize the mask pattern.

3. generating a contour of the cluster based on the two-dimensional elements; The computer-implemented method of claim 1 , wherein the contour is one of an outer contour of the cluster corresponding to an outer edge of the mask feature and an inner contour of the cluster corresponding to an inner edge of the mask feature.

4. generating sub-areas of the contour by applying a polygon offset operation to the associated pairs of two-dimensional elements; calculating an aggregate of the sub-areas; The computer-implemented method of claim 3 , wherein the contour line defines the totality of the sub-area.

5. The computer-implemented method of claim 2 , wherein the contour line is at least partially set at a predetermined distance from the location of the two-dimensional element.

6. The computer-implemented method of claim 1 , wherein the geometry of the two-dimensional elements is defined based on one or more Mask Rule Compliance (MRC) rules.

7. the one or more MRC rules include a minimum space requirement; 7. The computer-implemented method of claim 6, wherein the association criteria includes connecting a second two-dimensional element into the cluster if a distance between a second contour of the second two-dimensional element and the contour of the two-dimensional element in the cluster is less than the minimum space requirement.

8. The computer-implemented method of claim 1 , further comprising: modifying the clusters of the two-dimensional elements into one or more modified clusters.

9. The computer-implemented method of claim 8 , wherein the one or more modified clusters are formed based on MRC rules and / or the simulation associated with the lithography process.

10. 9. The computer-implemented method of claim 8, wherein modifying the cluster comprises modifying the cluster by separating one of the two-dimensional elements from the cluster or by associating a two-dimensional element from another cluster to the cluster, and further comprising modifying the contour line based on the modified cluster.

11. The computer-implemented method of claim 1 , wherein the adjusting comprises optimizing the mask pattern by adjusting a size or shape of one or more of the two-dimensional elements.

12. each of said two-dimensional elements defines a closed or semi-closed area; The computer-implemented method of claim 1 , wherein each of the two-dimensional elements is a circle, an ellipse, or a polygon.

13. generating homogeneous clusters for repeating features by replicating the clusters in the mask pattern; adjusting corresponding two-dimensional elements in the homogenous clusters; The computer-implemented method of claim 1 , further comprising:

14. said adjusting said homogeneous clusters includes identifying boundary two-dimensional elements that cross a boundary between a first mask patch and a second mask patch; The computer-implemented method of claim 13 , wherein adjusting the two-dimensional elements excludes adjusting the boundary two-dimensional elements.

15. adjusting the homogeneous cluster includes designating the two-dimensional elements within a threshold distance of a boundary between a first mask patch and a second mask patch as preferred two-dimensional elements; The computer-implemented method of claim 13 , wherein adjusting the two-dimensional elements excludes adjusting a preferred two-dimensional element.

16. The computer-implemented method of claim 14 , further comprising replacing one or more of the two-dimensional elements within the threshold distance to the boundary with a preferred two-dimensional element.

Images