Laser roughing: roughness of engineered burst top

Abstract

Methods, computer program products, and apparatus for reducing adhesion during a lithographic process are disclosed. An exemplary method of reducing adhesion of an object to a modified surface for supporting the object in a lithographic process may include controlling a light source to deliver light to a native surface, thereby causing ablation of at least a portion of the native surface to increase roughness of the native surface, thereby forming the modified surface. The increased roughness reduces the ability of the object to adhere to the modified surface.

Description

[0001] This application is a divisional application of the invention application with application number 202080013587.3, which entered the Chinese national phase on August 10, 2021, and is a divisional application of international application PCT / EP2020 / 052551.

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS

[0003] This application claims priority to U.S. Provisional Patent Application No. 62 / 807,361, filed on February 19, 2019, which is incorporated herein by reference in its entirety. Background Art

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

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

[0006] Therefore, manufacturing devices such as semiconductor devices typically involves processing a substrate (e.g., a semiconductor wafer) using a variety of manufacturing processes to form various features and multiple 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 can be manufactured on multiple dies on a substrate and then separated into individual devices. The device manufacturing process can be considered a patterning process. The patterning process involves a patterning step, such as optical and / or nanoimprint lithography using a pattern forming device in a lithographic apparatus to transfer the pattern on the pattern forming device to the substrate, and typically but optionally involves one or more related pattern processing steps, such as resist development by a developing apparatus, baking the substrate using a baking tool, etching using a pattern using an etching apparatus, and the like.

[0007] As mentioned above, photolithography is a core 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 photolithography techniques are also used to form flat panel displays, microelectromechanical systems (MEMS), and other devices.

[0008] As semiconductor manufacturing processes continue to advance, the size of functional elements continues to decrease, while the number 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 technology, multiple layers of a device are fabricated using a lithography projection device that projects a design layout onto a substrate using illumination from a deep ultraviolet illumination source, resulting in individual functional elements with dimensions well below 100 nm (i.e., less than half the wavelength of the radiation from the illumination source (e.g., a 193 nm illumination source)).

[0009] According to the resolution formula CD=k1×λ / NA, this process of printing features with a size smaller than the classical resolution limit of the lithographic projection apparatus can be referred to as low-k1 lithography, where λ is the wavelength of the radiation employed (e.g., 248nm or 193nm), NA is the numerical aperture of the projection optical element in the lithographic projection apparatus, CD is the "critical dimension", usually the minimum feature size printed, and k1 is an empirical resolution factor. In general, the smaller the k1, the more difficult it is to replicate a pattern on a substrate that is similar in shape and size to the designer's plan to achieve specific electrical functions and performance. To overcome these difficulties, complex fine-tuning steps are applied to the lithographic projection apparatus, the design layout, or the patterning device. These include, for example, but are not limited to, optimization of NA and optical coherence settings, customized illumination schemes, the use of phase-shifting pattern devices, optical proximity correction (OPC, sometimes also called "optical and process correction") in the design layout, or other methods generally defined as "resolution enhancement technology" (RET). The term "projection optical element" as used herein should be broadly interpreted to cover various types of optical systems, including, for example, refractive optical elements, reflective optical elements, apertures, and reflective-refractive optical elements. The term "projection optics" may also include components that operate according to any of these design types for collectively or individually directing, shaping or controlling 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 in the optical path of the lithographic projection apparatus. Projection optics may include optical components for shaping, conditioning and / or projecting radiation from a source before the radiation passes through a patterning device, and / or optical components for shaping, conditioning and / or projecting radiation after the radiation passes through a patterning device. Projection optics typically do not include a source and a patterning device. Summary of the invention

[0010] A method for reducing adhesion of an object to a modified surface for supporting the object during a photolithography process is disclosed. The method includes controlling a light source to deliver light to a native surface, thereby causing ablation of at least a portion of the native surface to increase the roughness of the native surface, thereby forming a modified surface. The increased roughness reduces the ability of the object to adhere to the modified surface.

[0011] In some variations, the light source can be a laser and the native surface can include a top surface of a burl. Control of the light source can include setting an energy density of the light source to generate light having a fluence at the native surface, the light causing selective ablation of the native surface based on the atomic structure of the native surface when delivered to the surface, the selective ablation reducing the surface area for contacting the object. The native surface can have grains separated by grain boundaries, wherein the selective ablation removes material from the grain boundaries and does not substantially cause ablation of the grains. In addition, the control can include adjusting one or more of the intensity and / or focus of the light source to set the energy density based on the desired roughness of the modified surface.

[0012] In other variations, the controlling may include delivering light at discrete locations on the native surface to cause ablation of a portion of a grain boundary, the delivery causing the modified surface to include roughened regions with spacing between the roughened regions. The spacing may be greater than the spot size of the light source. Additionally, the spacing between the light delivery locations may be less than the spot size of the light source. The delivery of light may also span vertices on the top surface of a section that forms part of the reticle holder.

[0013] In a related aspect, a non-transitory machine-readable medium stores instructions that, when executed by at least one programmable processor, cause the programmable processor to perform operations including controlling a light source to deliver light to a native surface, thereby causing ablation of at least a portion of the native surface to increase the roughness of the native surface, thereby forming a modified surface, wherein the increased roughness reduces the ability of an object to adhere to the modified surface.

[0014] In some variations, controlling may include setting an energy density of the light source to generate light having a fluence at the native surface that, when delivered to the surface, causes selective ablation of the native surface based on the atomic structure of the native surface, the selective ablation reducing the surface area available to contact the object.

[0015] In addition, in other variations, the controlling may include adjusting one or more of the intensity and / or focus of the light source to set the energy density based on the desired roughness of the modified surface. The controlling may also include delivering light at discrete locations on the native surface to cause ablation of a portion of the grain boundary, the delivering causing the modified surface to include roughened regions with spaces between the roughened regions.

[0016] In yet another related aspect, an apparatus may have a modified surface configured to contact an object, the modified surface formed of a material including a grain structure, the grain structure including grains and grain boundaries, wherein the modified surface has a roughness based at least on grain peaks and grain boundary valleys located below the grain peaks.

[0017] In some variations, the roughness can be the root mean square of the height of the modified surface. The roughness can be between 3 and 35 nm, between 20 and 35 nm, or greater than 2 nm. In addition, the roughness of the native surface can be less than 3 nm. The apparatus can remove between 2 nm and 30 nm of grain boundary material from the native surface at at least one location on the modified surface.

[0018] In other variations, the apparatus may include a burl extending from a substrate, wherein the modified surface is on a top surface of the burl. The substrate may be a reticle holder, a wafer holder, or a wafer stage. The apparatus may include a coating on the top surface of the burl, and the modified surface is formed in the coating. The coating may be a TiN, CrN, or DLC coating. The burl may include a plurality of hillocks and the modified surface is on the plurality of hillocks, and the modified surface may include a plurality of roughened regions formed across the hillock.

[0019] In other variations, the modified surface may include roughened regions with spacing between the roughened regions. The distance between the roughened regions may be about 10 microns, about 15 microns, or about 20 microns. The modified surface may have an arithmetic mean height (Sa) between 0.4 nm and 19 nm. The modified surface includes a roughened region in which about 5 nm of material is removed from at least one of the grain boundaries. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0021] Figure 1 is a block diagram of various subsystems of a lithographic projection apparatus according to one embodiment.

[0022] Figure 2 is an exemplary flow chart for simulating lithography in a lithographic projection apparatus according to one embodiment.

[0023] Figure 3 is a simplified top view of a wafer positioned on a burl surface of a wafer stage according to one embodiment.

[0024] Figure 4 is a simplified side view of an exemplary burl having a coating according to one embodiment.

[0025] Figure 5 is a simplified illustration of a side cross-sectional view of an exemplary burl having grains and grain boundaries according to one embodiment.

[0026] Figure 6is a simplified illustration of an exemplary cross-sectional view of a burl receiving light at a native surface formed by grains and grain boundaries according to one embodiment.

[0027] Figure 7 According to an embodiment Figure 6 Simplified illustration of a burl being roughened by ablating a portion of the grain boundary to form a modified surface.

[0028] Figure 8 is a simplified diagram illustrating an exemplary burl having discrete roughened region vertices formed on the burl according to one embodiment.

[0029] Fig. 9 is a simplified diagram showing a roughness map according to one embodiment.

[0030] Fig.10 is a process flow diagram for controlling a tool to form grooves and ridges according to one embodiment.

[0031] Fig.11 is a block diagram of an example computer system according to one embodiment.

[0032] Fig.12 is a schematic diagram of a lithographic projection apparatus according to an embodiment.

[0033] Fig.13 is a schematic diagram of another lithographic projection apparatus according to an embodiment.

[0034] Fig.14 is a detailed view of a lithographic projection apparatus according to one embodiment.

[0035] Fig.15 is a detailed view of a source collector module of a lithographic projection apparatus according to one embodiment. DETAILED DESCRIPTION

[0036] Although specific reference may be made herein to the manufacture of ICs, it should be clearly understood that the description herein has many other possible applications. For example, it can be used to manufacture integrated optical systems, guidance and detection patterns for magnetic domain memories, liquid crystal display panels, thin film magnetic heads, etc. The skilled person will understand that in the context of such alternative applications, any use of the terms "reticle", "wafer" or "chip" herein should be considered interchangeable with the more general terms "mask", "substrate" and "target portion", respectively.

[0037] In this document, the terms "radiation" and "beam" are used to cover all types of electromagnetic radiation, including UV radiation (e.g., having a wavelength of 365, 248, 193, 157 or 126 nm) and EUV (extreme ultraviolet radiation, e.g., having a wavelength in the range of about 5-100 nm).

[0038] The patterning device may include or may form one or more design layouts. The design layout may be generated using a CAD (computer-aided design) program, a process often referred to as EDA (electronic design automation). Most CAD programs follow a set of predetermined design rules to produce a functional design layout / patterning device. These rules are set by process and design constraints. For example, the design rules define the spatial tolerances between devices (such as gates, capacitors, etc.) or interconnects to ensure that the devices or lines do not interact with each other in an undesirable manner. One or more design rule constraints may be referred to as "critical dimensions" (CDs). The critical dimension of a device may be defined as the minimum width of a line or hole or the minimum spacing 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 of device fabrication is to faithfully reproduce the original design intent on the substrate (via the patterning device).

[0039] The terms "mask" or "patterning device" as used herein may be broadly interpreted as referring to a generic patterning device that can be used to impart to an incoming radiation beam a patterned cross-section corresponding to the pattern to be produced in a target portion of the substrate; the term "light valve" may also be used in this context. In addition to classical masks (transmissive or reflective; binary, phase-shifting, hybrid, etc.), other examples of such patterning devices include programmable mirror arrays and programmable LCD arrays.

[0040] An example of a programmable mirror array may be a matrix-addressable surface having a viscoelastic control layer and a reflective surface. The basic principle behind such a device is that (for example) addressed areas of the reflective surface reflect incident radiation as diffracted radiation, while unaddressed areas reflect incident radiation as undiffracted radiation. Using suitable filters, the above-mentioned undiffracted radiation can be filtered out of the reflected beam, leaving only the diffracted radiation; in this way, the beam becomes patterned according to the addressing pattern of the matrix-addressable surface. The required matrix addressing can be performed using suitable electronic methods.

[0041] An example of a programmable LCD array is given in US Pat. No. 5,229,872 (incorporated herein by reference).

[0042] Figure 1A block diagram of various subsystems of a lithographic projection apparatus 10A according to one embodiment is shown. The main components are a radiation source 12A, which may be a deep ultraviolet excimer laser source or other types of sources, including extreme ultraviolet (EUV) sources (as described above, the lithographic projection apparatus itself need not have a radiation source), illumination optics, for example, that define partial coherence (expressed as sigma) and may include optical elements 14A, 16Aa, and 16Ab that shape the radiation from source 12A; a patterning device 18A; and a transmission optical element 16Ac that projects an image of the patterning device pattern onto a substrate plane 22A. An adjustable filter or aperture 20A at a pupil plane of the projection optics may limit the range of beam angles that impinge on the substrate plane 22A, with the maximum possible angle defining the numerical aperture of the projection optics. , where n is the refractive index of the medium between the substrate and the last element of the projection optics, is the maximum angle of the beam emerging from the projection optics that can still impinge on the substrate plane 22A.

[0043] In a lithographic projection apparatus, a source provides illumination (i.e., radiation) to a pattern forming device, and a projection optical element directs and shapes the illumination onto a substrate via the pattern forming device. The projection optical element may include at least some of components 14A, 16Aa, 16Ab, and 16Ac. An aerial image (AI) is a radiation intensity distribution at the substrate level. A resist model may be used to calculate a resist image from an aerial image, an example of which may be found in U.S. Patent Application Publication No. US 2009-0157630 (the disclosure of which is incorporated herein by reference in its entirety). The resist model is only related to the properties of the resist layer (e.g., the effects of chemical processes occurring during exposure, post-exposure baking (PEB), and development). The optical properties of the lithographic projection apparatus (e.g., the properties of the illumination, pattern forming device, and projection optical element) determine the aerial image and may be defined in an optical model. Since the pattern forming device used in the lithographic projection apparatus may be changed, it is desirable to separate the optical properties of the pattern forming device from the optical properties of the rest of the lithographic projection apparatus including at least the source and projection optical element. Detailed information on techniques and models for converting a design layout into various lithographic images (e.g., aerial images, resist images, etc.), applying OPC using these techniques and models, and evaluating performance (e.g., in terms of process windows) are described in U.S. Patent Application Publication Nos. 2008-0301620, 2007-0050749, 2007-0031745, 2008-0309897, 2010-0162197, and 2010-0180251 (the entire disclosures of which are incorporated herein by reference).

[0044] One aspect of understanding the lithography process is understanding the interaction of radiation and patterning devices. After the radiation passes through the patterning device, the electromagnetic field of the radiation can be determined based on the electromagnetic field of the radiation before the radiation reaches the patterning device and a function that characterizes the interaction. This function can be called a mask transfer function (which can be used to describe the interaction of transmissive patterning devices and / or reflective patterning devices).

[0045] The mask transfer function can have a variety of different forms. One form is binary. A binary mask transfer function has either of two values ​​(e.g., zero and a positive constant) at any given location on the patterning device. A mask transfer function in binary form may be referred to as a binary mask. Another form is continuous. That is, the modulus of the transmittance (or reflectance) of the patterning device is a continuous function of the location on the patterning device. The phase of the transmittance (or reflectance) may also be a continuous function of the location on the patterning device. A mask transfer function in continuous form may be referred to as a continuous tone mask or a 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.), rather than a binary value of 0 or 1. In one embodiment, the CTM may be a pixelated grayscale image, where each pixel has a value (e.g., in the range [-255, 255], a normalized value in the range [0, 1] or [-1, 1], or other appropriate range).

[0046] The thin mask approximation (also known as Kirchhoff boundary conditions) is widely used to simplify the determination of the interaction of radiation and the patterning device. The thin mask approximation assumes that the thickness of the structures on the patterning device is very small compared to the wavelength, and the width of the structures on the mask is very large compared to the wavelength. Therefore, the thin mask approximation assumes that the electromagnetic field after the patterning device is the product of the incident electromagnetic field and the mask transfer function. However, as the lithography process uses radiation with shorter and shorter wavelengths, and the structures on the patterning device become smaller and smaller, the assumption of the thin mask approximation may fail. For example, the interaction of radiation with the structure (e.g., the edge between the top surface and the sidewall) may become significant due to the finite thickness of the structure ("mask 3D effect" or "M3D"). Including this scattering in the mask transfer function can enable the mask transfer function to better capture the interaction of radiation with the patterning device. The mask transfer function under the thin mask approximation can be referred to as a thin mask transfer function. The mask transfer function that includes M3D can be referred to as an M3D mask transfer function.

[0047] According to an embodiment of the present disclosure, one or more images may be generated. The image includes various types of signals that may be characterized by a pixel value or an intensity value of each pixel. It will be appreciated by a person skilled in the art that, depending on the relative value of the pixel within the image, the signal may be referred to as, for example, a weak signal or a strong signal. The terms "strong" and "weak" are relative terms based on the intensity value of the pixel within the image, and the specific value of the intensity does not limit the scope of the present disclosure. In one embodiment, a strong signal and a weak signal may be identified based on a selected threshold. In one embodiment, the threshold may be fixed (e.g., the midpoint of the highest intensity and the lowest intensity of the pixel within the image). In one embodiment, a strong signal may refer to a signal whose value is greater than or equal to the average signal value over the entire image, and a weak signal may refer to a signal whose value is less than the average signal value. In one embodiment, the relative intensity value may be based on a percentage. For example, a weak signal may be a signal whose intensity is less than 50% of the highest intensity of the pixel within the image (e.g., the pixel corresponding to the target pattern may be regarded as the pixel with the highest intensity). In addition, each pixel within the image may be regarded as a variable. According to this embodiment, a derivative or a partial derivative may be determined for each pixel within the image, and the value of each pixel may be determined or modified based on an evaluation based on a cost function and / or a gradient-based calculation of a cost function. For example, a CTM image may include pixels, where each pixel is a variable that can take any real value.

[0048] Figure 2 An exemplary flow chart for simulating lithography in a lithographic projection apparatus according to one embodiment is shown. A source model 31 represents the optical properties of a source (including radiation intensity distribution and / or phase distribution). A projection optical element model 32 represents the optical properties of the projection optical element (including changes in radiation intensity distribution and / or phase distribution caused by the projection optical element). A design layout model 35 represents the optical properties of a design layout (including changes in radiation intensity distribution and / or phase distribution caused by a design layout 33), which is a representation of a feature arrangement formed on or by a pattern forming device. An aerial image 36 can be simulated from the design layout model 35, the projection optical model 32, and the design layout model 35. A resist image 38 can be simulated from the aerial image 36 using a resist model 37. The simulation of lithography can, for example, predict the profile and CD in the resist image.

[0049] More specifically, note that the source model 31 can represent the optical properties of the source, including but not limited to numerical aperture settings, illumination sigma (σ) settings, and any specific illumination shapes (e.g., off-axis radiation sources such as toroidal, quadrupole, dipole, etc.). The projection optical model 32 can represent the optical properties of the projection optical elements, including aberrations, distortions, one or more refractive indices, one or more physical sizes, one or more physical dimensions, etc. The design layout model 35 can represent one or more physical properties of the physical pattern forming device, such as described in U.S. Patent No. 7,587,704 (incorporated herein by reference in its entirety). The purpose of the simulation is to accurately predict, for example, edge location, spatial image intensity slope, and / or CD, which can then be compared to the intended design. The intended design is typically defined as a pre-OPC design layout, which can be provided in a standardized digital file format (such as GDSII or OASIS) or other file format.

[0050] From this design layout, one or more portions, referred to as "clips," may be identified. In one embodiment, a set of clips is extracted that represent complex patterns in the design layout (typically about 50 to 1000 clips, although any number of clips may be used). These patterns or clips represent small portions of the design (i.e., circuits, cells, or patterns), and more specifically, clips typically represent small portions that require special attention and / or verification. In other words, a clip may be a portion of the design layout, or may be similar or have similar behavior to a portion of the design layout, where one or more key features are identified through experience (including clips provided by customers), through trial and error, or by running full-chip simulations. A clip may contain one or more test patterns or instrumentation patterns.

[0051] The customer may a priori provide an initial larger set of clips based on one or more known key feature areas in the design layout that require specific image optimization. Alternatively, in another embodiment, the initial larger set of clips may be extracted from the entire design layout using some automatic (such as machine vision) or manual algorithm that identifies the one or more key feature areas.

[0052] In a lithographic projection apparatus, as an example, the cost function can be expressed as

[0053] (Equation 1)

[0054] in are N design variables or their values. Can be a design variable Functions such as The difference between the actual and expected values ​​of a property for a set of values ​​of a design variable. is with The characteristic may be, for example, the position of the pattern edge measured at a given point on the pattern edge. Can have different weights For example, if a particular edge has a narrower set of predetermined locations, then the difference between the actual location of the edge and the expected location Weight Can be assigned higher values. It can also be a function of the interlayer characteristics, which are in turn design variables Of course, It is not limited to the form in Equation 1. It may be in any other suitable form.

[0055] The cost function may represent any one or more suitable characteristics of the lithographic projection apparatus, the lithographic process, or the substrate, such as focus, CD, image shift, image distortion, image rotation, random variation, yield, local CD variation, process window, inter-layer characteristics, or a combination thereof. In one embodiment, the design variables The cost function may include one or more selected from dose, global bias of the pattern forming device, and / or irradiation shape. Since it is usually the resist image that determines the pattern on the substrate, the cost function may include a function representing one or more characteristics of the resist image. For example, can simply be the distance between a point in the resist image and the expected position of that point (i.e., edge placement error The design variables may include any adjustable parameters, such as adjustable parameters of the source, patterning device, projection optics, dose, focus, etc.

[0056] The lithographic apparatus may include components collectively referred to as "wavefront manipulators", which may be used to adjust the shape of the wavefront and the intensity distribution and / or phase shift of the radiation beam. In one embodiment, the lithographic apparatus may adjust the wavefront and intensity distribution at any position along the optical path of the lithographic projection apparatus, such as before the pattern forming device, near the pupil plane, near the image plane, and / or near the focal plane. The wavefront manipulator may be used to correct or compensate for certain distortions of the wavefront and intensity distribution and / or phase shift caused by, for example, temperature changes in the source, pattern forming device, lithographic projection apparatus, thermal expansion of components of the lithographic projection apparatus, and the like. Adjusting the wavefront and intensity distribution and / or phase shift may change the value of the characteristic represented by the cost function. Such changes may be simulated from a model or actually measured. The design variables may include parameters of the wavefront manipulator.

[0057] Design variables can have constraints, which can be expressed as ,in is a set of possible values ​​for the design variables. One possible constraint on the design variables may be imposed by the desired yield of the lithographic projection apparatus. Without such a constraint imposed by the desired yield, the optimization may produce an unrealistic set of values ​​for the design variables. For example, if dose is a design variable, without such a constraint, the optimization may produce a dose value that makes the yield economically impossible. However, the usefulness of a constraint should not be interpreted as a necessity. For example, yield may be affected by pupil fill rate. For certain illumination designs, a low pupil fill rate may discard radiation, resulting in reduced yield. Yield may also be affected by the resist chemistry. Slower resists (e.g., resists that require more radiation to be properly exposed) produce lower yields.

[0058] As used herein, the term "patterning process" refers to a process that produces an etched substrate by applying a specified light pattern as part of a photolithography process.

[0059] As used herein, the term "imaging device" refers to any number or combination of devices and associated computer hardware and software that can be configured to generate an image of a target, such as a printed pattern or portion thereof, or to generate an image of any surface and feature, as described throughout the specification. Non-limiting examples of imaging devices may include: scanning electron microscope (SEM), atomic force microscope (AFM), X-ray machine, optical microscope, etc.

[0060] Some photolithography processes include, for example, using a reticle (or mask) to provide a specific pattern of light at the photoresist to produce a pattern for etching onto a wafer. In order to hold the reticle and wafer in place, a clamping device may be used. Because it is important for the manufacturing process that the surfaces involved are very flat, an undesirable result may be that the reticle may adhere to the reticle fixture, the wafer may adhere to the wafer fixture or the wafer stage on which the wafer is placed, etc. Such adhesion may cause damage to the wafer, reticle, fixture, etc. The adhesion mechanism may include the formation of van der Waals bonds between components along the contact surfaces. Therefore, embodiments of the disclosed subject matter solve the adhesion problem by, for example, reducing the contact area between the components to reduce the total van der Waals forces between the objects, etc., so that adhesion is not easy to occur.

[0061] One way to reduce the contact surface area is to make the contact surface rougher so that only the higher portion of the rough surface is in contact with the wafer or mask. As further described below, the surface to be roughened can be made of a combination of crystalline and amorphous materials. As an example, a laser can be used to deliver a specific amount of energy to the surface so that the amorphous material is ablated while the crystalline material is not ablated or is ablated significantly less. This selective ablation reduces the contact surface area by only allowing the wafer or mask to contact the remaining crystalline material. By varying the delivery of the laser energy and the laser pattern to the surface, different degrees of roughness and roughness patterns can be formed.

[0062] Figure 3 A simplified top view of a wafer 310 positioned on a burl surface 340 of a wafer stage 320 is shown according to one embodiment.

[0063] Wafer stage 320 is shown as having a plurality of burls 330 that combine to form burl surface 340. Example wafer 310 may be positioned on burl surface 340. Figure 4 As further shown, a burl as used herein may include any material feature extending from a substrate, such as a wafer stage 320, a wafer chuck, a reticle chuck, etc., to support a wafer 310 or a reticle.

[0064] The burls may provide some nominal spacing (and reduction in contact surface area) between the wafer 310 and the wafer stage 320. For example, by supporting the wafer 310 on the burl surface 340 (which may be made of a plurality of burls 330 with spacing therebetween), the aforementioned van der Waals forces may be reduced as well as vacuums, cavitation, etc. avoided.

[0065] The embodiments described herein generally refer to a wafer on a wafer stage. However, such description is not intended to be limiting. For example, in addition to a wafer and a wafer stage, aspects of the present disclosure may also be applied to other components (e.g., a reticle in contact with a reticle holder), and to a wafer on burls having any type, number, and geometry of associated burl surfaces.

[0066] Figure 4 A simplified side view of burl 330 with coating 420 is shown according to one embodiment.

[0067] Figure 4The side view shown shows a plurality of exemplary burls 330 extending from a substrate 410. In some embodiments, as shown, the burls 330 may include a coating 420 disposed on at least a top surface of the burls 330, and the coating 420 may be a hard ceramic coating. The coating 420 may include, for example, titanium nitride (TiN), chromium nitride (CrN), diamond-like carbon (DLC), tantalum (Ta), tantalum boride (TaB), tungsten (W), tungsten carbide (WC), boronitride (BN), etc. Such coatings may be added to the burls 330 to protect the underlying burl structure. As used herein, the term "burl surface" (e.g., Figure 4 The burl surface 430 in FIG. 4 may refer to the top surface of the burl 330 when there is no coating 420 , or the top surface of the coating 420 when such a coating 420 is present on the burl 330 .

[0068] As discussed throughout this disclosure, surfaces that are candidates for roughening may include the tops of burls (eg, the substrate of the burls themselves), coatings, or any other suitable surface that may exhibit adhesion during use. Figure 5 A side view of the top of an example burl is shown. An expanded portion of a cross-section of the burl is shown in the upper left corner. As described herein, some materials may have portions that are easier to remove (such as by laser ablation) than others. For example, the burl coating shown may have a semi-crystalline structure that may include grains 510 and softer material between the grains (referred to herein as grain boundaries 520). Figure 5 In the figure, the light vertical bands are a simplified representation of the hard grains, while the dark vertical bands are a simplified representation of the softer grain boundaries.

[0069] A further enlarged view of a portion of the burl is shown in Figure 5 An example transmission electron microscope image is shown in the upper right portion of to show vertical grains 510 (light colored) and grain boundaries 520 (dark colored and located between the grains 510 ).

[0070] As used herein, the term "native surface" refers to the surface as it exists prior to a given roughening process (resulting in a "modified surface" discussed below). A simplified example of native surface 530 is shown by the dashed lines in the simplified cross-sectional view of the burl top.

[0071] Figure 6 and 7 A method for reducing the roughness of an object (e.g., a mask) and a modified surface (e.g., a mask holder, such as Figure 7 In some cases, this can be a modified surface used to support objects during photolithography. Figure 6As shown, one example method of reducing adhesion may include controlling a light source (e.g., a laser) to deliver light 620 to a native surface 610 (e.g., a portion of a top surface of a burl), thereby causing ablation of at least a portion of the native surface to increase the roughness of the native surface, thereby forming a modified surface (e.g., as Figure 7 Because ablating a portion of the surface that can come into contact with an object can reduce the contact surface area, increased roughness reduces the ability of the object to adhere to the modified surface.

[0072] As used herein, the term "modified surface" refers to a surface that has been roughened relative to a previous state by any of the methods disclosed herein. For simplicity, the present disclosure generally refers to a "native surface" that is roughened to become a modified surface. However, a modified surface can also be produced by any surface that has been treated by the disclosed method or by other methods. For example, multiple applications of the roughening process described herein can produce a modified surface, wherein the surface is first modified (roughened), and then roughened again to form another further modified surface. In addition, as another example, the surface can be cut, polished, ground, etc. before any of the disclosed methods of "modifying" the initial or "native" surface.

[0073] Since the native surface may include grains separated by grain boundaries by selecting an energy density of the light source that rounds the grain boundaries but is insufficient to ablate the grains, selective ablation of the native surface may be performed with the effect of roughening the native surface.

[0074] Thus, some embodiments may include setting the energy density of the light source to generate light with a fluence at the native surface that, when delivered to the surface, causes selective ablation of the native surface based on the atomic structure of the native surface. In this way, selective ablation can reduce the surface area for contacting an object and thereby reduce adhesion between the object and the modified surface.

[0075] This can be performed, for example, by removing material from the grain boundaries while not substantially causing ablation of the grains. As used herein, when describing "substantially" no ablation of the grains, this is intended to mean that the ablation of the grains is significantly less than the ablation of the grain boundaries. For example, the amount of completion of the grains may be less than 10% or 1% of the corresponding ablation of the grain boundaries receiving light of the same energy density.

[0076] The present disclosure contemplates different ways in which the energy density for ablation can be set. For example, the light source can be controlled to adjust one or more of the intensity and / or focus of the light source to set the energy density based on the desired roughness of the modified surface. The adjustment and intensity of the light source can include turning up the power of the light source, adding additional light sources to combine light at the modified surface.

[0077] like Figure 6 As shown, the focus 630 of the light source can be adjusted (e.g., increased or decreased) so that the light spot formed by the light source changes, thereby increasing or decreasing the energy density. As used herein, the term "focus" refers to the degree to which the light source is focused at the native surface. Generally, the energy density is greatest when the light from the light source is most focused at the surface. Figure 6 In the example of , where the position of the surface is moved relative to the light source (either by moving the burl / burl surface or by moving the lens 612), the focus will change. In addition, as shown, the light source is slightly out of focus, resulting in an energy density that is less than the maximum density when the surface is at the focal point shown. Focus is also related to spot size, because generally speaking, the spot size on the surface is smallest when the light source is focused on the surface.

[0078] Furthermore, as used herein, when referring to a "light source", it should be understood that this includes not only the laser source itself, but also any intermediate optical elements between the laser source and the surface. These optical elements may include, for example, mirrors, filters, lenses, etc.

[0079] Figure 7 A simplified example of a modified surface 710 resulting from the roughening methods described herein is shown. Figure 7 Similar to Figure 6 , and shows an exemplary portion of the light source 610 and the burl top. However, the illustrated example illustrates ablated crystalline boundary material 520 so that the modified surface 710 has some portions that are lower than the original native surface 530.

[0080] The surfaces described herein may be formed on objects or devices used in photolithography processes, but may also be formed on any other object or device for use in applications that may benefit from the disclosed methods. Thus, the modified surface may be part of a device in which the modified surface may be configured to contact an object. The modified surface of such a device may be formed of a material having a grain structure including grains and grain boundaries. Figure 7 As shown, the modified surface may have a roughness based at least on the peaks of the grains and the valleys of the grain boundaries located below the peaks of the grains. Figure 6 In the particular example shown, prior to roughening, native surface 530 has regions that include both grains and grain boundaries (although shown from the side and indicated by dashed lines). Figure 7 , after roughening, some grain boundary material has been ablated to form grain peaks 720 and grain boundary valleys 730. Thus, the modified surface 710 that will contact the object (again indicated by the dashed lines) does not include grain boundary material (e.g., grain boundary valleys 730). Thus, in general, the contact surface area at the modified surface can be less than the contact surface area before the roughening process.

[0081] Figure 7 The lower part shows the Figure 7 An example of a TEM image corresponding to the simplified diagram in the upper portion. Here, the lighter colored material represents the grains 510 (having a columnar structure in this example). It can be seen that some material (e.g., grain boundary material) has been removed from between the grains. Therefore, the increase in roughness and the reduction in contact surface area of ​​the modified surface are evident in this image.

[0082] In some embodiments, in at least one location on the modified surface, between 2nm and 30nm of grain boundary material has been removed from the native surface. In addition, in other embodiments, the modified surface may include a roughened region in which approximately 5nm of material in at least one grain boundary has been removed. In other embodiments, the modified surface may have an arithmetic mean height (Sa) between 0.4nm and 19nm. As used herein, "roughness" may refer to the arithmetic mean height or RMS roughness of a portion of the modified surface.

[0083] In some embodiments, the roughness can be the root mean square of the height of the modified surface and can be between 3 and 35 nm, or between 20 and 35 nm. Thus, in various embodiments, the roughness of the modified surface can be greater than 2 nm and the roughness of the native surface can be less than 3 nm.

[0084] Since ablation of grain boundary material can be a function of the energy density of the light delivered at the surface, the surface roughness can be expressed in terms of a ratio of energy densities. Specifically, in some examples, an energy density ratio of 1.0 (for a given light source output, spot size, etc.) can result in a surface roughness of about 20 nm, an energy density ratio of 1.05 results in a surface roughness of about 25 nm, and an energy density ratio of 1.15 results in a surface roughness of about 30 nm.

[0085] The roughening process described herein can produce a number of useful devices that exhibit reduced adhesion. For example, the device can include a plurality of burls extending from a substrate (e.g., a reticle holder, a wafer holder, or a wafer stage) with the modified surface on the top surface of the burls. In such an embodiment, the burls can be, for example, Si or SiC, and can optionally have a coating (e.g., Ti, Cr, or DLC) applied to the top surface of the burls so that the modified surface can be formed in the coating to reflect the roughened burls beneath the coating.

[0086] In other embodiments of the present disclosure, roughening can be applied in a variety of patterns at a macroscopic scale. This can be considered "low frequency roughening" rather than "high frequency roughening," which better describes the small-scale ablation regions resulting from the removal of grain boundary material. Low frequency roughening can be performed by controlling a light source to deliver light at discrete locations 810 on the native surface to cause ablation of a portion of the grain boundary. In this manner, the delivery of light can cause the modified surface to include roughened regions with spaces 820 between them. These discrete roughened regions (at Figure 8 The separation position (shown by a grey band in FIG. 1 ) may take the form of, for example, a series of parallel lines, intersecting lines (e.g., similar to a checkerboard pattern), a spiral pattern, etc. An example of such a separation position is Figure 8 The example shown is shown on a burl.

[0087] In some embodiments, the burl 330 may (e.g., which is part of a mask holder) include hillocks 830 formed on the burl 330 or the burl coating. The hillocks formed in the burl may be, for example, approximately 10 μm wide, spaced 10 μm apart from each other, and have a height between 80 and 120 nm. In this example, the light source may be controlled to deliver light across the apex of the hillock formed on the top surface of the burl, thereby forming a modified surface on the hillock. When used to deliver light across the apex (or any other feature of the burl), the term "across" means approximately perpendicular to the hillock direction. However, in other embodiments, the approximate angle of the light path may be, for example, 90 degrees, 80 degrees, 60 degrees, 45 degrees, 30 degrees, 15 degrees, etc. In this way, the light path across the apex formed in the surface may intersect with multiple vertices to form secondary roughening features. In other embodiments, roughening may be performed on the apex (e.g., approximately parallel to the apex) to add a roughened area as described herein.

[0088] The spacing between the roughened regions can vary. In some embodiments, the spacing between the roughened regions on the modified surface can be approximately 2, 5, 10, 15, 20, or 30 μm. Figure 8 As shown, the spacing 820 can be larger than the spot size of the light source (represented by the width of the gray band) so that the roughened areas do not overlap. In other embodiments, the spacing between the light delivery locations can be smaller than the spot size of the light source, which can cause the locations receiving light to overlap to some extent. In such embodiments, there may be additional roughening in the overlapping areas, for example due to multiple applications of energy to the grain boundary material in those overlapping areas.

[0089] Although the embodiments of the present disclosure are discussed with reference to materials having a crystalline structure with soft grain boundaries suitable for ablation, the methods and resulting devices described herein can be used with other materials in other applications. For example, the material does not have to have a strict crystalline structure. Instead, any suitable material that allows certain areas to be preferentially or selectively ablated when exposed to light can be used or be a recipient of the disclosed methods.

[0090] By applying the methods described herein, the roughness of a surface (e.g., the top of a burl) can be engineered by controlled application of light to the native surface. As previously described, this can be a function of a) the spacing or line spacing between the locations where the light is delivered, and b) the energy density of the light at the native surface. This can essentially provide a roughness map that can be delivered when specific programming instructions are executed to the light source. A simplified example of such a roughness map is shown in Fig. 9 . Roughness is represented schematically by shading, and in this example, ranges from 2 to 15 nm Sa. As shown, the roughness increases as the line spacing decreases (as the gaps between the roughened areas are smaller). In addition, the roughness increases as the energy density increases (as more grain boundaries are removed). In this manner, consistent with certain aspects of the present disclosure, the roughness can be selected by the user, and the spacing between the roughened areas and the energy density delivered by the light source can be specified. Similar roughness maps can be generated for different burl materials, different coatings, and the like. Therefore, variations in the example roughness maps are contemplated, and the spacing between specific roughness values ​​and indicated light delivery locations should not be considered limiting.

[0091] An example method of reducing adhesion of an object to a modified surface (e.g., used to support the object during a photolithography process) is described in Fig.10 In this embodiment, the method includes controlling a light source to deliver light to a native surface, thereby causing ablation of at least a portion of the native surface to increase the roughness of the native surface, thereby forming a modified surface, wherein the increased roughness reduces the ability of an object to adhere to the modified surface.

[0092] Fig.11is a block diagram of an example computer system CS according to one embodiment. The computer system CS includes a bus BS or other communication mechanism for transmitting information, and a processor PRO (or multiple processors) coupled to the bus BS to process 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 to store information and instructions to be executed by the processor PRO. The main memory MM can also be used to store temporary variables or other intermediate information during the execution of instructions to be executed by the processor PRO. The computer system CS also includes a read-only memory (ROM) ROM or other static storage device coupled to the bus BS to store static information and instructions for the processor PRO. A storage device SD (such as a magnetic disk or optical disk) is provided and coupled to the bus BS to store information and instructions.

[0093] The computer system CS can be coupled to a display DS (such as a cathode ray tube (CRT) or a flat panel or touch panel display) via a bus BS to display information to a computer user. An input device ID including alphanumeric and other keys is coupled to the bus BS to communicate information and command selections to the processor PRO. Another type of user input device is a cursor control CC, such as a mouse, trackball, or cursor direction keys, which is used to communicate direction information and command selections to the processor PRO and to control cursor movement on the display DS. The input device typically has two degrees of freedom in two axes, a first axis (e.g., x) and a second axis (e.g., y) to allow the device to specify a position in a plane. A touch panel (screen) display can also be used as an input device.

[0094] According to one embodiment, in response to the processor PRO executing one or more sequences of one or more instructions contained in the main memory MM, the computer system CS can perform part of one or more methods described herein. Such instructions can be read into the main memory MM from another computer-readable medium (such as a storage device SD). The execution of the instruction sequence contained in the main memory MM causes the processor PRO to perform the processing steps described herein. It is also possible to use one or more processors in a multi-processing arrangement to execute the instruction sequence contained in the main memory MM. In an alternative embodiment, a hard-wired circuit system can replace software instructions or be used in combination with software instructions. Therefore, the description herein is not limited to any specific combination of hardware circuits and software.

[0095] The term "computer-readable medium" as used herein refers to any medium that participates in providing instructions to the processor PRO for execution. Such a medium may take a variety of 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 storage devices SD. Volatile media include dynamic memory, such as main memory MM. Transmission media include coaxial cables, copper wires, and optical fibers, including wires that constitute the bus BS. Transmission media may also take the form of sound waves or light waves, such as those generated during radio frequency (RF) and infrared (IR) data communications. Computer-readable media may be non-transient, such as floppy disks, flexible disks, hard disks, tapes, any other magnetic media, CD-ROMs, DVDs, any other optical media, punch cards, paper tapes, any other physical media with hole patterns, RAMs, PROMs and EPROMs, FLASH-EPROMs, any other memory chips, or cassettes. Non-transient computer-readable media may have instructions recorded thereon. Instructions may implement any of the features described herein when executed by a computer. Transient computer-readable media may include carrier waves or other propagating electromagnetic signals.

[0096] Various forms of computer-readable media may be involved when 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 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. The modem local to the computer system CS may receive data over a telephone line and convert the data into 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 transfers 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 on a storage device SD before or after being executed by the processor PRO.

[0097] The computer system CS may also include a communication interface CI coupled to the bus BS. The communication interface CI provides a bidirectional data communication coupling with a network link NDL connected to a local network LAN. For example, the communication interface CI may be an integrated services digital network (ISDN) card or a modem for providing a data communication connection with a corresponding type of telephone line. As another example, the communication interface CI may be a local area network (LAN) card for providing a data communication connection with a compatible LAN. A wireless link may also be implemented. In any such implementation, the communication interface CI sends and receives electrical, electromagnetic or optical signals carrying digital data streams representing various types of information.

[0098] The network link NDL usually provides data communication to other data devices through one or more networks. For example, the network link NDL can provide a connection to a host computer HC through a local network LAN. This can include data communication services provided through the global packet data communication network (now generally called the "Internet" INT). Both the local network 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 and the signals through the communication interface CI (these signals carry the digital data to and from the computer system CS) are example forms of carrier waves that transport information.

[0099] The computer system CS can send messages and receive data, including program code, through the network, the network data link NDL and the communication interface CI. In the Internet example, the host HC can transmit the request code of the application program through the Internet INT, the network data link NDL, the local network LAN and the communication interface CI. For example, such a download application can provide all or part of the method described in this article. The received code can be executed by the processor PRO when 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.

[0100] Fig.12 is a schematic diagram of a lithographic projection apparatus according to an embodiment.

[0101] The lithographic projection apparatus may include an illumination system IL, a first stage MT, a second stage WT and a projection system PS.

[0102] The illumination system IL may condition the radiation beam B. In this particular case, the illumination system also includes a radiation source SO.

[0103] A first stage (eg, patterning device table) MT may be provided with a patterning device holder to hold a patterning device MA (eg, a reticle) and connected to a first positioner to accurately position the patterning device relative to the article PS.

[0104] A second worktable (substrate table) WT may be provided with a substrate holder to hold a substrate W (eg a silicon wafer coated with resist) and connected to a second positioner to accurately position the substrate relative to the item PS.

[0105] A projection system ("lens") PS (eg, a refractive, reflective, or catadioptric optical system) may image the illuminated portion of the patterning device MA onto a target portion C (eg, comprising one or more dies) of the substrate.

[0106] As described herein, the device may be transmissive (i.e., having a transmissive patterning device). However, in general, it may also be reflective, for example (having a reflective patterning device). The device may employ a patterning device other than a conventional mask; examples include a programmable mirror array or an LCD matrix.

[0107] A source SO (e.g. a mercury lamp or an excimer laser, an LPP (laser produced plasma) EUV source) generates a radiation beam. This beam is fed into an illumination system (illuminator) IL, either directly or after passing through a conditioning device such as a beam expander Ex. The illuminator IL may include an adjustment device AD ​​for setting the outer and / or inner radial extent (commonly referred to as outer σ and inner σ, respectively) of the intensity distribution in the beam. In addition, it typically includes various other components, such as an integrator IN and a condenser CO. In this way, the beam B impinging on the patterning device MA has a desired uniformity and intensity distribution in its cross section.

[0108] In some embodiments, the source SO may be within the housing of the lithographic projection apparatus (e.g., this is often the case when the source SO is a mercury lamp), but it may also be remote from the lithographic projection apparatus, into which the radiation beam it generates is introduced (e.g., with the aid of suitable directing mirrors); the latter may be the case when the source SO is an excimer laser (e.g., based on KrF, ArF or F2 lasers).

[0109] The beam PB may then intercept the patterning device MA held on the patterning device table MT. After passing the patterning device MA, the beam B may pass through a lens PL which focuses the beam B onto a target portion C of the substrate W. With the aid of the second positioning device (and the interferometric measurement device IF), the substrate table WT may be accurately moved, for example in order to position a different target portion C in the path of the beam PB. Similarly, the first positioning device may be used to accurately position the patterning device MA relative to the path of the beam B, for example after mechanical retrieval of the patterning device MA from a patterning device library, or during scanning. Typically, movement of the stage MT, WT may be achieved with the aid of a long-stroke module (coarse positioning) and a short-stroke module (fine positioning). However, in the case of a stepper (as opposed to a step-and-scan tool), the patterning device table MT may be connected to a short-stroke actuator only, or may be fixed.

[0110] The depicted tool can be used in two different modes: a step mode and a scan mode. In the step mode, the patterning device table MT remains essentially stationary and the entire patterning device image is projected at once (i.e. a single "flash") onto a target portion C. The substrate table WT can be moved in the x and / or y direction so that a different target portion C can be illuminated by the beam PB.

[0111] In scan mode, essentially the same scenario applies, except that a given target portion C is not exposed in a single "flash". Instead, the patterning device table MT can be moved at a speed v in a given direction (the so-called "scanning direction", e.g. the y-direction) so that the projection beam B is caused to scan the patterning device image; while the substrate table WT is simultaneously moved in the same or opposite direction at a speed V=Mv, where M is the magnification of the lens PL (typically M=1 / 4 or 1 / 5). In this way, a relatively large target portion C can be exposed without having to sacrifice resolution.

[0112] Fig.13 is a schematic diagram of another lithographic projection apparatus (LPA) according to an embodiment.

[0113] The LPA may comprise a source collector module SO, an illumination system (illuminator) IL configured to condition a radiation beam B (eg EUV radiation), a support structure MT, a substrate table WT and a projection system PS.

[0114] The support structure (eg, patterning device table) MT may be configured to support a patterning device (eg, mask or reticle) MA and connected to a first positioner PM configured to accurately position the patterning device;

[0115] The substrate table (eg, wafer stage) WT may be configured to hold a substrate (eg, a resist-coated wafer) W and connected to a second positioner PW configured to accurately position the substrate.

[0116] The projection system (eg, a reflective projection system) PS may be configured to project the pattern imparted to the radiation beam B by the patterning device MA onto a target portion C of the substrate W (eg, comprising one or more dies).

[0117] As depicted here, the LPA can be reflective (e.g., employing a reflective patterning device). It should be noted that because most materials are absorptive in the EUV wavelength range, the patterning device can have a multilayer reflector including multiple stacks of, for example, molybdenum and silicon. In one example, the multilayer reflector has 40 layers of molybdenum and silicon pairs, where each layer is a quarter wavelength thick. Even smaller wavelengths can be produced by X-ray lithography. Since most materials are absorptive at EUV and X-ray wavelengths, a patterned sheet of absorbing material on the patterning device topography (e.g., a TaN absorber above a multilayer reflector) defines where features will print (positive resist) or not print (negative resist).

[0118] The illuminator IL may receive an extreme ultraviolet radiation beam from a source collector module SO. Methods for generating EUV radiation include, but are not necessarily limited to, converting a material into a plasma state having at least one element, such as xenon, lithium, or tin, wherein one or more emission lines are in the EUV range. In one such method, a plasma, generally referred to as a laser produced plasma ("LPP"), may be generated by irradiating a fuel, such as a droplet, stream, or cluster of a material having a line emitting element, with a laser beam. The source collector module SO may 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, such as EUV radiation, which is collected using a radiation collector disposed in the source collector module. The laser and the source collector module may be separate entities, such as when a CO2 laser is used to provide a laser beam for fuel excitation.

[0119] In this case, the laser may be considered not to form part of the lithographic apparatus, and the radiation beam may be delivered from the laser to the source collector module with the aid of a beam delivery system comprising, for example, suitable directing mirrors and / or a beam expander. 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 (commonly referred to as a DPP source).

[0120] The illuminator IL may include an adjuster for adjusting the angular intensity distribution of the radiation beam. Typically, at least the outer and / or inner radial extent of the intensity distribution in a pupil plane of the illuminator (commonly referred to as outer σ and inner σ, respectively) may be adjusted. Furthermore, the illuminator IL may include various other components, such as a facet field and pupil mirror means. The illuminator may be used to adjust the radiation beam to have a desired uniformity and intensity distribution in its cross section.

[0121] A radiation beam B may be incident on a patterning device (e.g. a mask) MA, which is held on a support structure (e.g. a patterning device table) MT, and patterned by the patterning device. After reflection from the patterning device (e.g. a mask) MA, the radiation beam B passes through a projection system PS, which focuses the beam onto a target portion C of a substrate W. With the help of a second positioner PW and a position sensor PS2 (e.g. an interferometric device, a linear encoder or a capacitive sensor), the substrate table WT may be accurately moved, for example in order to position a different target portion C in the path of the radiation beam B. Similarly, a first positioner PM and a further position sensor PS1 may be used to accurately position the patterning device (e.g. a mask) MA relative to the path of the radiation beam B. The patterning device (e.g. a mask) MA and the substrate W may be aligned using patterning device alignment marks M1, M2 and substrate alignment marks P1, P2.

[0122] The depicted device LPA can be used in at least one of the following modes: a stepping mode, a scanning mode and a stationary mode.

[0123] In step mode, the support structure (e.g. patterning device table) MT and the substrate table WT remain essentially stationary, and an entire pattern imparted to the radiation beam is projected at one time onto a target portion C (i.e. a single static exposure). The substrate table WT is then moved in the X and / or Y direction so that a different target portion C can be exposed.

[0124] 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 speed and direction of the substrate table WT relative to the support structure (e.g. patterning device table) MT may be determined by the (de-)magnification and image reversal properties of the projection system PS.

[0125] In stationary mode, the support structure (e.g. patterning device table) MT is held substantially stationary to hold the programmable patterning device, and the substrate table WT is moved or scanned while a pattern imparted to the radiation beam is projected onto a target portion C. In this mode, typically a pulsed radiation source is employed and the programmable patterning device is updated as required after each movement of the substrate table WT or between successive radiation pulses during a scan. This mode of operation can be readily applied to maskless lithography utilizing a programmable patterning device, such as a programmable mirror array.

[0126] Fig.14 is a detailed view of a lithographic projection apparatus according to one embodiment.

[0127] As shown, the LPA may include a source collector module SO, an illumination system IL, and a projection system PS. The source collector module SO is constructed and arranged so that a vacuum environment can be maintained in the closed structure ES of the source collector module SO. EUV radiation emitting a hot plasma HP may be formed by a discharge-generated plasma source. EUV radiation may be generated by a gas or vapor, such as Xe gas, Li vapor, or Sn vapor, wherein a hot plasma HP is generated to emit radiation in the EUV range of the electromagnetic spectrum. The hot plasma HP is generated, for example, by a discharge that causes at least partially ionized plasma. In order to effectively generate radiation, a partial pressure of, for example, 10 Pa of Xe, Li, Sn vapor, or any other suitable gas or vapor may be required. In one embodiment, an excited tin (Sn) plasma is provided to generate EUV radiation.

[0128] The radiation emitted by the hot plasma HP is transferred from the source chamber SC to the collector chamber CC through an optional gas barrier or contaminant trap CT (also referred to as a contaminant barrier or foil trap in some cases) in or behind an opening in the source chamber SC. The contaminant trap CT may include a channel structure. The contaminant trap CT may also include a gas barrier or a combination of a gas barrier and a channel structure. As known in the art, the contaminant trap or contaminant barrier CT further referred to herein includes at least a channel structure.

[0129] 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 passing through the radiation collector CO may be reflected by a grating spectral filter SF to be focused in a virtual source point IF along an optical axis indicated by a dash-dot line "O". The virtual source point IF may be referred to as an intermediate focus, and the source collector module may be arranged such that the intermediate focus IF is located at or near an opening OP in the enclosed structure ES. The virtual source point IF is an image of the radiation emitting plasma HP.

[0130] The radiation then passes through an illumination system IL which may include a faceted field mirror arrangement FM and a faceted pupil mirror arrangement pm arranged to provide a desired angular distribution of the radiation beam B at the patterning device MA and to provide a desired uniformity of radiation amplitude at the patterning device MA. When the radiation beam B is reflected at the patterning device MA held by the support structure MT a patterned beam PB is formed and the patterned beam PB is imaged by the projection system PS via a reflective element RE onto a substrate W held by a substrate table WT.

[0131] There may typically be more elements than shown in the illumination optics unit IL and the projection system PS. Depending on the type of lithographic apparatus, a grating spectral filter SF may optionally be present. Furthermore, there may be more mirrors than shown in the figures, for example, 1-6 additional reflective elements may be present in the projection system PS.

[0132] The collector optic CO may be a nested collector with a grazing incidence reflector GR, as an example of a collector (or collector mirror). The grazing incidence reflector GR is arranged axisymmetrically around the optical axis O, and this type of collector optic CO may be used in conjunction with a discharge produced plasma source (commonly referred to as a DPP source).

[0133] Fig.15 is a detailed view of a source collector module SO of a lithographic projection apparatus LPA according to an embodiment.

[0134] The source collector module SO can be part of the LPA radiation system. The laser LA can be arranged to deposit laser energy into a fuel, such as xenon (Xe), tin (Sn) or lithium (Li), thereby producing a highly ionized plasma HP with an electron temperature of tens of eV. The high-energy radiation generated during the de-excitation and recombination of these ions is emitted from the plasma, collected by the near-normal incidence collector optical element CO and focused onto an opening OP in the closed structure ES.

[0135] The embodiments may be further described using the following terms:

[0136] 1. A method for reducing adhesion of an object to a modified surface, the modified surface being used to support the object during a photolithography process, the method comprising:

[0137] A light source is controlled to deliver light to a native surface, thereby causing ablation of at least a portion of the native surface to increase the roughness of the native surface, thereby forming the modified surface, wherein the increased roughness reduces the ability of the object to adhere to the modified surface.

[0138] 2. A method according to claim 1, wherein the light source is a laser.

[0139] 3. A method according to clause 1, wherein the native surface includes a top surface of the burl.

[0140] 4. The method according to clause 1, wherein the controlling comprises:

[0141] An energy density of the light source is set to generate light having a fluence at the native surface that, when delivered to the surface, causes selective ablation of the native surface based on the atomic structure of the native surface, the selective ablation reducing the surface area available to contact the object.

[0142] 5. The method of clause 4, the native surface comprising grains separated by grain boundaries, wherein the selective ablation removes material from the grain boundaries without substantially causing ablation of the grains.

[0143] 6. The method according to clause 4, wherein the controlling further comprises:

[0144] One or more of the intensity and / or focus of the light source is adjusted to set the energy density based on a desired roughness of the modified surface.

[0145] 7. The method according to clause 1, wherein the controlling further comprises:

[0146] Light is delivered at discrete locations on the native surface to cause ablation of a portion of the grain boundaries, the delivery causing the modified surface to include roughened regions having spaces therebetween.

[0147] 8. A method according to clause 7, wherein the spacing is larger than the spot size of the light source.

[0148] 9. A method according to clause 1, wherein the spacing between the light delivery locations can be smaller than the spot size of the light source.

[0149] 10. The method of clause 1, wherein the light delivery spans across a plurality of vertices on a top surface of a burl forming part of a reticle holder.

[0150] 11. A non-transitory machine-readable medium storing instructions that, when executed by at least one programmable processor, cause the at least one programmable processor to perform operations comprising:

[0151] A light source is controlled to deliver light to a native surface, thereby causing ablation of at least a portion of the native surface to increase the roughness of the native surface, thereby forming the modified surface, wherein the increased roughness reduces the ability of the object to adhere to the modified surface.

[0152] 12. The non-transitory machine-readable medium of clause 11, wherein the controlling comprises:

[0153] An energy density of the light source is set to generate light having a fluence at the native surface that, when delivered to the surface, causes selective ablation of the native surface based on the atomic structure of the native surface, the selective ablation reducing the surface area available to contact the object.

[0154] 13. The non-transitory machine-readable medium of clause 12, wherein the controlling further comprises:

[0155] One or more of the intensity and / or focus of the light source is adjusted to set the energy density based on a desired roughness of the modified surface.

[0156] 14. The non-transitory machine-readable medium of clause 11, wherein the controlling further comprises:

[0157] Light is delivered at discrete locations on the native surface to cause ablation of a portion of the grain boundaries, the delivery causing the modified surface to include roughened regions having spaces therebetween.

[0158] 15. A device comprising:

[0159] A modified surface is configured to contact an object, the modified surface being formed of a material including a grain structure including grains and grain boundaries, wherein the modified surface has a roughness based at least on a plurality of grain peaks and a plurality of grain boundary valleys located below the grain peaks.

[0160] 16. An apparatus according to claim 15, wherein the roughness is the root mean square of the height of the modified surface.

[0161] 17. An apparatus according to claim 16, wherein the roughness is between 3 and 35 nm.

[0162] 18. An apparatus according to claim 16, wherein the roughness is between 20 and 35 nm.

[0163] 19. An apparatus according to claim 16, wherein the roughness of the modified surface is greater than 2 nm.

[0164] 20. An apparatus according to clause 16, wherein the roughness of the native surface is less than 3 nm.

[0165] 21. The apparatus of clause 15, wherein at least one location on the modified surface between 2 nm and 30 nm of grain boundary material is removed from the native surface.

[0166] 22. The apparatus of clause 15, further comprising a plurality of burls extending from the substrate, wherein the modified surface is on top surfaces of the plurality of burls.

[0167] 23. The apparatus of clause 22, wherein the substrate is a mask holder, a wafer holder, or a wafer stage.

[0168] 24. The apparatus of clause 22, further comprising a coating on the top surface of the burl, and the modified surface is formed in the coating.

[0169] 25. An apparatus according to claim 24, wherein the coating is a TiN, CrN or DLC coating.

[0170] 26. The apparatus of clause 22, wherein the plurality of burls comprises a plurality of hillocks and the modified surface is on the plurality of hillocks.

[0171] 27. An apparatus according to clause 26, wherein the modified surface comprises a plurality of roughened regions formed throughout the hillock.

[0172] 28. An apparatus according to claim 15, wherein the modified surface includes roughened regions having spaces therebetween.

[0173] 29. An apparatus according to claim 28, wherein the spacing between the roughened areas is approximately 10 microns.

[0174] 30. An apparatus according to claim 28, wherein the spacing between the roughened areas is approximately 15 microns.

[0175] 31. An apparatus according to claim 28, wherein the spacing between the roughened areas is approximately 20 microns.

[0176] 32. The apparatus of clause 28, wherein the modified surface has an arithmetic mean height (Sa) between 0.4 nm and 19 nm.

[0177] 33. The apparatus of clause 15, wherein the modified surface comprises a roughened region in which approximately 5 nm of material in at least one of the grain boundaries has been removed.

[0178] The concepts disclosed herein can simulate or mathematically model any general imaging system for imaging sub-wavelength features, and are particularly useful for emerging imaging technologies that can produce shorter and shorter wavelengths. Emerging technologies already in use include EUV (extreme ultraviolet), DUV lithography that can produce 193nm wavelengths using ArF lasers, and even 157nm wavelengths using fluorine lasers. In addition, EUV lithography can produce wavelengths in the 20-50nm range by using a synchrotron or by bombarding materials (solid or plasma) with high-energy electrons to transmit photons in the 20-50nm range.

[0179] Although the concepts disclosed herein may be used for imaging on substrates such as silicon wafers, it should be understood that the disclosed concepts may be used with any type of photolithography imaging system, such as those used for imaging on substrates other than silicon wafers.

[0180] The above description is intended to be illustrative rather than limiting. It will therefore be apparent to one skilled in the art that modifications described may be made without departing from the scope of the claims set forth below.

Claims

1. A device comprising: a modified surface configured to contact an object, the modified surface being formed of a material including a grain structure including grains and grain boundaries, wherein the modified surface includes roughened regions having spaces therebetween, each of the roughened regions having a roughness based at least on a plurality of grain peaks and a plurality of grain boundary valleys located below the grain peaks; and A plurality of burls extend from a substrate, wherein the modified surface is on top surfaces of the plurality of burls.

2. The apparatus of claim 1, wherein the roughness of each roughened region is the root mean square of the height of the modified surface.

3. The device according to claim 2, wherein the roughness is between 3 and 35 nm. The device according to claim 2 , wherein the roughness is between 20 and 35 nm. The device of claim 2 , wherein the roughness is greater than 2 nm.

6. The apparatus of claim 2, wherein the roughness of the native surface is less than 3 nm.

7. The apparatus of claim 1, wherein at least one location on the modified surface between 2 nm and 30 nm of grain boundary material is removed from the native surface.

8. The apparatus of claim 1, wherein the substrate is a reticle holder, a wafer holder, or a wafer stage.

9. The apparatus of claim 1, further comprising a coating on a top surface of the burl, and the modified surface is formed in the coating.

10. The device according to claim 9, wherein the coating is a TiN, CrN or DLC coating.

11. The apparatus of claim 1, wherein the plurality of burls comprises a plurality of hillocks and the modified surface is on the plurality of hillocks.

12. The apparatus according to claim 11, wherein the roughened area is formed all over the hillock.

13. The apparatus of claim 1, wherein the spacing between the roughened areas is between 10 microns and 20 microns.

14. The apparatus of claim 1, wherein the modified surface has an arithmetic mean height (Sa) between 0.4 nm and 19 nm.

15. The apparatus of claim 1, wherein in at least one of the roughened regions, approximately 5 nm of material in at least one of the grain boundaries has been removed.

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