Lithography method, extreme ultraviolet mask and fabrication method thereof

Abstract

An extreme ultraviolet (EUV) mask and a method for forming an EUV mask are provided. The method includes forming a mask layer on a semiconductor wafer; generating extreme ultraviolet (EUV) light using a lithography system; patterning the EUV light using a mask containing an absorber to form patterned EUV light, wherein the absorber has an extinction coefficient at EUV wavelength exceeding that of TaBN and TaN at EUV wavelength; and exposing the mask layer using the patterned EUV light.

Description

Prior Art

[0001] The semiconductor integrated circuit (IC) industry has experienced exponential growth. Technological advancements in IC materials and design have produced generation after generation of ICs, with each generation having smaller and more complex circuits than the previous one. During the evolution of ICs, the functional density (i.e., the number of interconnected devices per chip area) generally increases, while the geometric size (i.e., the smallest component (or wiring) that can be created using a manufacturing process) decreases. This scaling process typically provides benefits by increasing production efficiency and reducing related costs. This scaling also increases the complexity of processing and manufacturing ICs. Brief Description of the Drawings

[0002] Aspects of the present disclosure are best understood from the following detailed description when read in conjunction with the accompanying drawings. It should be noted that various features are not drawn to scale according to standard practice in the industry. In practice, for clarity of discussion, the dimensions of various features may be arbitrarily increased or decreased. FIG. 1A and FIG. 1B are views of portions of a lithography scanner according to an embodiment of the present disclosure. FIGS. 2 to 9B are views of various embodiments of a system including a lithography apparatus and a fuel cell according to various aspects of the present disclosure. FIGS. 10 and 11 are flowcharts of methods of forming a mask according to various aspects of the present disclosure. Embodiments

[0003] The following disclosure provides many different embodiments or examples for implementing different features of the provided subject matter. Specific examples of components and configurations are described below to simplify the present disclosure. Of course, these specific embodiments or examples are merely examples and are not intended to be limiting. For example, in the following description, the formation of a first feature above or on a second feature may include embodiments in which the first feature and the second feature are formed in direct contact, and may also include embodiments in which additional features may be formed between the first feature and the second feature such that the first feature and the second feature may not be in direct contact. Additionally, the present disclosure may repeat reference numerals and / or letters in various examples. This repetition is for simplicity and clarity purposes and does not itself indicate a relationship between the various embodiments and / or configurations discussed.

[0004] In addition, for ease of description, spatial relative terms (such as "under", "below", "bottom", "above", "upper" and the like) may be used herein to describe the relationship of one component or feature to another component or feature as illustrated in the drawings. In addition to the orientation depicted in the drawings, the spatial relative terms are also intended to encompass different orientations of the device during use or operation. The device may be oriented in other ways (rotated 90 degrees or in other orientations), and thus the spatial relative descriptors used herein may be interpreted accordingly.

[0005] When describing a numerical value or a numerical range with terms such as "about", "approximate", "substantially", "essentially" and the like, the terms are intended to cover numerical values within a reasonable range, including the described numerical value, such as within + / - 10% of the described numerical value, or other values understood by those skilled in the art as non-limiting examples. For example, the term "about 5 nm" covers a size range from 4.5 nm to 5.5 nm.

[0006] The present disclosure is generally related to a lithography apparatus for manufacturing semiconductor devices, and more particularly, to a mask including a high-K absorber that improves the exposure quality associated with the use of extreme ultraviolet (EUV) lithography apparatus. It should be understood that in the context of the embodiments, "high-K" generally refers to a high extinction coefficient.

[0007] An EUV mask blank having a thick absorber layer may suffer from high M3D (Mask 3-Dimensional) effects, such as light shielding. The absorber material of the EUV mask blank affects the high-volume manufacturing of extreme ultraviolet (EUV) lithography. The EUV production efficiency difficulties that the absorber material of the EUV mask may introduce are the M3D effect and the increased exposure energy consumption due to the relatively thick absorber material in some methods.

[0008] In an embodiment of the present disclosure, a high-K material is used as an EUV mask blank, such as a Ru-based material absorber. For example, the mask blank material according to various embodiments may include a single layer or a double layer of a Ru-based alloy, and the Ru-based alloy may be PtRu, IrRu, OsRu, HfRu, RhRu, PtRuN, IrRuN, OsRuN, HfRuN, RhRuN, PtRuO, IrRuO, OsRuO, HfRuO, RhRuO, PtRuON, IrRuON, OsRuON, HfRuON, RhRuON, or the like. Different types of hard mask layers and buffer layers may be included above the absorber to achieve improved patterning through dry etching. The hard mask layer may include 2, 3, or 4 layers in combination with the buffer layer. The materials of the hard mask layer and the buffer layer may be Ta-based materials, Si-based materials, or the like. As a non-limiting example, the hard mask layer and / or the buffer layer may include TaBO, TaBN, TaN, Ta2O5, TaO2, TaO, Ta2O, MoSi, MoSiN, MoSiO, SiN, SiON, SiO2, SiCON, SiC, SiCN, CrN, Cr2N, or GaN.

[0009] The high-K material of the EUV mask blank described herein can reduce the M3D (Mask 3-Dimensional) effect. In an embodiment, a high-K material is used as the absorber layer of the EUV mask blank to reduce the thickness of the absorber film, which in turn reduces the M3D (Mask 3-Dimensional) effect, the exposure energy, and improves the image quality. For example, the high-K material of the EUV mask blank can reduce the exposure energy and increase the spatial image contrast through the normalized image log slope (NILS) and the low mask error enhancement factor (MEEF). The image log slope (ILS) may refer to a method for evaluating the spatial image quality. The larger the logarithmic slope value of the imaging, the higher the contrast of the spatial imaging may be, and the better the quality of the imaging may be.

[0010] FIG. 1A is a schematic and illustrative view of a lithography exposure system or apparatus 10 according to some embodiments. The lithography exposure system 10 is described in detail to provide context for understanding the mask 18, the formation of which is described with reference to FIGS. 2 to 9B.

[0011] In some embodiments, the lithography exposure system 10 is an extreme ultraviolet (EUV) lithography system operable to expose a photoresist layer using EUV radiation, and may also be referred to as the EUV system 10. The EUV system 10 may also be referred to as an EUV scanner or a lithography scanner. According to some embodiments, the lithography exposure system 10 includes a light source 120, an illuminator 140, a mask stage 16, a projection optical module (or projection optics box (POB)) 180, and a substrate stage 24. Components of the lithography exposure system 10 may be added or omitted, and the present disclosure should not be limited by the embodiments.

[0012] In certain embodiments, the light source 120 is configured to generate optical radiation having a wavelength in a range between about 1 nm and about 300 nm. In one particular example, the light source 120 generates EUV radiation having a wavelength centered at about or substantially 13.5 nm. Accordingly, the light source 120 is also referred to as an EUV radiation source. However, it should be understood that the light source 120 is not limited to emitting EUV radiation. The light source 120 can be used to perform any high-intensity photon emission from an excited target fuel.

[0013] In various embodiments, the illuminator 140 includes various reflective optical elements, such as the reflective optical element 100, which includes a single mirror or a mirror system having multiple mirrors, to direct light from the light source 120 onto the mask stage 16, specifically onto the mask 18 fixed on the mask stage 16. In embodiments where the light source 120 generates light in the EUV wavelength range, reflective optical elements are employed. In some embodiments, the illuminator 140 includes at least two reflectors, at least three reflectors, or more.

[0014] The mask stage 16 is operable to hold the mask 18. In the present disclosure, the terms mask, photomask, and reticle may be used interchangeably. In the present embodiment, the mask 18 is a reflective mask. An exemplary structure of the mask 18 includes a substrate having a suitable material such as a low thermal expansion material (LTEM) or fused silica. In various examples, the LTEM includes SiO2 doped with TiO2 or other suitable materials having low thermal expansion. The mask 18 includes a reflective multilayer deposited on the substrate. In some embodiments, the mask stage 16 includes an electrostatic chuck (e-chuck) capable of holding the mask 18. One reason the electron beam is beneficial is that gas molecules absorb EUV radiation, and the electrostatic chuck can operate in a lithography exposure system for EUV lithography patterning maintained in a vacuum environment to avoid EUV intensity loss. The mask stage 16 is operable to translate in two horizontal directions such as the X-axis direction and the Y-axis direction so as to expose multiple different regions of the semiconductor wafer 22 to light having a pattern generated by the mask 18. A mask layer 26 may be provided on the semiconductor wafer 22, and the mask layer 26 may be a photoresist layer sensitive to light carrying the pattern of the mask 18.

[0015] The projection optical module (or projection optics box (POB)) 180 is operable to image the pattern of the mask 18 onto the semiconductor wafer 22 fixed on the substrate or wafer stage 24 of the lithography exposure system 10. In some embodiments, the POB 180 has reflective optics. The light guided from the mask 18 and carrying the image of the pattern on the mask is collected by the POB 180. The illuminator 140 and the POB 180 may be collectively referred to as the optical module of the lithography exposure system 10. In some embodiments, the POB 180 includes at least six reflective optics, although four are depicted in FIG. 1A.

[0016] In some embodiments, the semiconductor wafer 22 can be made of silicon or other semiconductor materials. Alternatively or additionally, the semiconductor wafer 22 can include other elemental semiconductor materials such as germanium (Ge). In some embodiments, the semiconductor wafer 22 is made of a compound semiconductor such as silicon carbide (SiC), gallium arsenide (GaAs), indium arsenide (InAs), or indium phosphide (InP). In some embodiments, the semiconductor wafer 22 is made of an alloy semiconductor such as silicon germanium (SiGe), silicon germanium carbide (SiGeC), gallium arsenide phosphide (GaAsP), or gallium indium phosphide (GaInP). In some other embodiments, the semiconductor wafer 22 can be a silicon-on-insulator (SOI) or germanium-on-insulator (GOI) substrate.

[0017] In addition, the semiconductor wafer 22 can have various device components. Examples of device components formed in the semiconductor wafer 22 include transistors (e.g., metal oxide semiconductor field effect transistors (MOSFETs), complementary metal oxide semiconductor (CMOS) transistors, bipolar junction transistors (BJTs), high-voltage transistors, high-frequency transistors, p-channel and / or n-channel field-effect transistors (PFET / NFET), etc.), capacitors, inductors, diodes, and / or other suitable components. Various processes are performed to form the device components, such as deposition, etching, implantation, lithography, annealing, and / or other suitable processes. In some embodiments, the semiconductor wafer 22 is coated with a photoresist layer sensitive to EUV radiation. Various components including the above elements are integrated together and operable to perform a lithography process.

[0018] In FIG. 1B, according to some embodiments, the light source 120 is shown in a schematic view. In some embodiments, the light source 120 employs a dual-pulse laser produced plasma (LPP) mechanism to generate plasma 88 and further generate EUV radiation from the plasma. The light source 120 includes a droplet generator 30, a droplet receiver 35, a laser generator 50, a laser produced plasma (LPP) collector 60, a monitoring device 70, and a controller 90. Some or all of the above components of the light source 120 may be held under vacuum. It should be understood that components of the light source 120 may be added or omitted and should not be limited by the embodiments.

[0019] The droplet generator 30 is operable to generate a plurality of droplets 82 of a target fuel 80 (the droplets 82 may be elongated) into an excitation region where at least one laser pulse 51 from the laser generator 50 impinges on the droplets 82, as shown in FIG. 1B. In an embodiment, the target fuel 80 includes tin (Sn). In an embodiment, the droplets 82 may be formed in an elliptical shape. In an embodiment, the droplets 82 are generated at a rate of about 50 kilohertz (kHz) and introduced into the excitation region in the light source 120 at a speed of about 70 meters per second (m / s). Other materials may also be used for the target fuel 80, for example, a tin-containing liquid material such as a eutectic alloy containing tin, lithium (Li), and xenon (Xe). The target fuel 80 in the droplet generator 30 may be in a liquid phase.

[0020] The laser generator 50 is operable to generate at least one laser pulse to allow the droplets 82 to be converted into plasma 88. In some embodiments, the laser generator 50 is operable to generate a laser pulse 51 that reaches an illumination point 52 to convert the droplets 82 into plasma 88, and the plasma 88 generates EUV radiation 84. The laser pulse 51 is guided through a window (or lens) 55 and irradiates the droplets 82 at the illumination point 52. The window 55 is formed in the collector 60 and is made of a suitable material that is substantially transparent to the laser pulse 51. The droplet receiver 35 captures and collects unused droplets 82 and / or scattered materials of the droplets 82 generated due to the impingement of the laser pulse 51 on the droplets 82. Some of the scattered materials may land on various components of the lithography exposure system 10, such as on the collector 60 of the light source 120, which is closest to the tin droplets 82 when the tin droplets 82 are impinged by the laser pulse 51.

[0021] Plasma emits EUV radiation 84, and the EUV radiation 84 is collected by the collector 60. The collector 60 further reflects and focuses the EUV radiation 84 for the lithography process performed by the exposure tool. In some embodiments, the collector 60 has an optical axis 61 parallel to the z-axis and perpendicular to the x-axis. The collector 60 may comprise a single part, as shown in the figure, or at least two parts offset from each other in the z-axis direction.

[0022] The lithography exposure system 10 may include other modules or be integrated (or coupled) with other modules, such as a cleaning module or device or system 62 operable to supply hydrogen gas to the light source 120 and a tin supply system operable to supply liquid tin to the light source 120. Hydrogen gas is beneficial for reducing contamination in the light source 120. The cleaning system 62 may clean the collector 60 of the light source 120, but is not limited thereto. For example, tin debris 82A may fall on various components of the lithography exposure system 10, and the cleaning system 62 may discharge hydrogen gas towards the various components to remove the tin debris 82A.

[0023] The collector 60 may further include a container wall 65, and the container wall 65 has a cleaning system 62 and a first pump 66 and a second pump 68 attached thereto. The cleaning system 62 may include one or more nozzles that may be directed towards areas of the lithography exposure system 10, such as the collector 60, to discharge hydrogen gas at high pressure, thereby removing debris 82A from the surface of the collector 60. Cleaning by the cleaning system 62 is beneficial for maintaining the mirror surface of the collector 60, which increases the light output power of the light source 120 and improves wafer throughput.

[0024] In an embodiment, the laser generator 50 is a carbon dioxide (CO2) laser source. In some embodiments, the laser generator 50 is operable to generate laser pulses 51 having a single wavelength. The laser pulses 51 are transmitted through the optical components for focusing and determining the incident angle of the laser pulses 51. In some embodiments, the laser pulses 51 have a spot size of about 200 μm to 300 μm, such as 225 μm. The laser pulses 51 are generated with a selected drive power to meet wafer production goals, such as a throughput of 125 wafers per hour (WPH). For example, the laser pulses 51 are equipped with a drive power of about 23 kW. In various embodiments, the drive power of the laser pulses 51 is at least 20 kW, such as 27 kW.

[0025] The monitoring device 70 is operable to monitor one or more conditions in the light source 120, thereby generating data for controlling selectable parameters of the light source 120. In some embodiments, the monitoring device 70 includes a metrology tool 71 and an analyzer 73. In the case where the metrology tool 71 is operable to monitor the condition of the droplets 82 supplied by the droplet generator 30, the metrology tool 71 may include an image sensor, such as a charge coupled device (CCD), a complementary metal oxide semiconductor sensor (CMOS) sensor, or the like. The metrology tool 71 generates a monitoring image including an image or video of the droplets 82, and transmits the monitoring image to the analyzer 73. In the case where the metrology tool 71 is used to detect the energy or intensity of the EUV light 84 generated by the droplets 82 in the light source 120, the metrology tool 71 may include a plurality of energy sensors. The energy sensors can be any suitable sensors operable to observe and measure the energy of electromagnetic radiation in the ultraviolet region.

[0026] The analyzer 73 is operable to analyze the signals generated by the metrology tool 71, and outputs a detection signal to the controller 90 according to the analysis result. For example, the analyzer 73 includes an image analyzer. The analyzer 73 receives data associated with the image transmitted from the metrology tool 71, and performs an image analysis process on the image of the droplets 82 in the excitation region. Then, the analyzer 73 sends the data related to the analysis to the controller 90. The analysis may include flow path error or position error.

[0027] In some embodiments, two or more metrology tools 71 are operable to monitor different conditions of the light source 120. One metrology tool 71 is operable to monitor the condition of the droplets 82 supplied by the droplet generator 30, while another metrology tool 71 is operable to detect the energy or intensity of the EUV light 84 generated by the droplets 82 in the light source 120. In some embodiments, the metrology tool 71 is a final focus module (FFM), and is positioned in the laser source 50 to detect the light reflected from the droplets 82.

[0028] The controller 90 is operable to control one or more components of the light source 120, for example, by selecting one or more parameters or variables of the components. In some embodiments, the controller 90 is operable to drive the droplet generator 30 to generate droplets 82. Additionally, the controller 90 is operable to drive the laser generator 50 to emit laser pulses 51. The controller 90 can be utilized to control the generation of the laser pulses 51 to be associated with the generation of the droplets 82, such that the laser pulses 51 sequentially strike each target 80. The controller 90 is operable to control the delivery of hydrogen gas and the discharge of waste hydrogen gas by means of pumps 66, 68.

[0029] In some embodiments, the droplet generator 30 includes a reservoir 31 and a nozzle assembly 32. The reservoir 31 is configured to hold the target material 80. In some embodiments, a gas pipeline 41 is connected to the reservoir 31 for introducing a pumping gas, such as argon, from a gas source 40 into the reservoir 31. By controlling the airflow in the gas pipeline 41, the pressure in the reservoir 31 can be manipulated. For example, when gas is continuously supplied into the reservoir 31 via the gas pipeline 41, the pressure in the reservoir 31 increases. Thus, the target material 80 in the reservoir 31 can be extruded from the reservoir 31 in the form of droplets 82. The reservoir 31 receives the target material 80, such as liquid tin, from a target supply system, which may include one or more low-pressure reservoirs and one or more high-pressure reservoirs.

[0030] Figures 2 to 9B are illustrative views of the mask 20 in intermediate stages of formation according to various embodiments. The mask 20 may include a high-K absorber layer or layers 220 having a reduced thickness and being advantageous for improving imaging quality.

[0031] FIG. 10 and FIG. 11 depict flowcharts of processes 1000, 2000 according to various embodiments. In some embodiments, process 1000 for forming a mask includes multiple operations (1010, 1020, 1030, 1040, 1050, 1060, and 1070). In some embodiments, process 2000 for patterning a wafer layer via a mask with a high-K absorber includes operations (2010, 2020, and 2030). Processes 1000, 2000 will be further described according to one or more embodiments. It should be noted that the operations of processes 1000, 2000 can be reconfigured or otherwise modified within the scope of various aspects. It should be further noted that additional processes can be provided before, during, and after processes 1000, 2000, and some other processes may be briefly described herein only. In some embodiments, process 2000 is performed by system 10 described in FIGS. 1A and 1B. Embodiments of process 2000 are described with reference to the structural components described in FIGS. 1A and 1B, but process 2000 can be performed by a system having one or more structural components different from the structural components of system 10.

[0032] FIG. 2 depicts an unpatterned mask 20 (or simply referred to as "mask 20") having a hard mask structure 230 and a photoresist layer 240 thereon according to various embodiments.

[0033] Mask 20 includes an absorber structure 220 on a reflective multilayer 270. Absorber structure 220 is operable to absorb incident EUV light, and reflective multilayer 270 is operable to reflect incident EUV light. By patterning absorber structure 220 to selectively expose regions of reflective multilayer 270 according to a selected pattern, a pattern can be transferred using mask 20 when exposed to light (such as EUV light 84 described with reference to FIGS. 1A and 1B). In some embodiments, the microstructure of one or more layers 200, 210, 222, 224 of mask 20 is in the polycrystalline range (e.g., grain size less than about 5 nm) or the amorphous range.

[0034] The reflective multilayer 270 may include alternating layers of materials such as molybdenum and silicon. In some embodiments, the reflective multilayer 270 includes one or more layers of materials having an extinction coefficient K < 0.02, such as Ru, Tc, Mo, Nb, Ti, Zr, Y, Sc, and the like. For example, the reflective multilayer 270 may include a stack of layers of molybdenum, silicon, ruthenium, and strontium. The silicon layer and the strontium layer may be referred to as spacer layers, and the molybdenum layer and the ruthenium layer may be referred to as reflector layers. The reflective multilayer 270 may include dozens or hundreds of spacer / reflector layer pairs (or "bilayers") stacked on top of each other. The thickness of the individual layers may be uniform throughout the stack or may vary throughout the stack (e.g., non-periodically). The individual thickness of each of the layers may range from about 5 angstroms to about 50 angstroms. The configuration of the bilayers may be uniform or non-uniform throughout the stack.

[0035] The absorber structure 220 is on the reflective multilayer 270 and may be or include a single layer or multiple layers. For example, as depicted in FIG. 2, the absorber structure 220 may be multilayered, the multilayer including a first absorber layer 222 and a second absorber layer 224 on the first absorber layer 222. The first absorber layer 222 may have a thickness in the range of about 5 nm to about 30 nm and may have a grain size in the polycrystalline or amorphous range, such as less than about 5 nm. The second absorber layer 224 may have a thickness in the range of about 10 nm to about 40 nm or in the range of about 20 nm to about 50 nm and may have a grain size similar to that described for the first absorber layer 222. The total thickness of the absorber structure 220 may range from about 15 nm to about 80 nm. Generally, the total thickness of the absorber structure 220 is less than about 80 nm, less than about 60 nm, or less than about 50 nm. Below about 50 nm, the benefits of reducing the M3D effect, reducing the exposure energy, and improving NILS are achieved. The described thicknesses may be measured along the second or vertical direction D2 depicted in FIG. 2. The absorber structure 220 may extend along a first or horizontal direction D1 that is transverse to (e.g., perpendicular to) the second direction D2.

[0036] The first absorber layer 222 may be or include a ruthenium-based high-K material, which may be one or more of PtRu, IrRu, OsRu, HfRu, RhRu, PtRuN, IrRuN, OsRuN, HfRuN, RhRuN, RuTa, RuTaO, RuTa / RuTaO bilayer, or the like. In some embodiments, the material may include ruthenium at an atomic concentration ("at%") in the range of about 40% to about 70% and may include nitrogen in the range of about 2 at% to about 20 at%.

[0037] The second absorber layer 224 can be or include a ruthenium-based high-k material, and the ruthenium-based high-k material can be one or more of PtRuO, IrRuO, OsRuO, HfRuO, RhRuO, PtRuON, IrRuON, OsRuON, HfRuON, RhRuON, RuTa, RuTaO, RuTa / RuTaO bilayer, or the like. In some embodiments, the material of the second absorber layer 224 includes ruthenium in the range of about 40 at% to about 70 at%, oxygen in the range of about 2 at% to about 20 at%, and nitrogen in the range of about 2 at% to about 20 at%.

[0038] In some embodiments, the first absorber layer 222 or the second absorber layer 224 is omitted. That is, the absorber structure 220 can include the first absorber layer 222, the second absorber layer 224, or both. In some embodiments, additional absorber layers similar to the first absorber layer 222 and / or the second absorber layer 224 are included in the absorber structure 220. That is, the absorber structure 220 can include three or more absorber layers, and the absorber layers include, for example, the first absorber layer 222 and / or the second absorber layer 224 just described and additional absorber layers similar to the first absorber layer 222 and / or the second absorber layer 224.

[0039] The first absorber layer 222 and the second absorber layer 224 include Ru-based high extinction coefficient materials as described above. The extinction coefficients of the first absorber layer 222 and the second absorber layer 224 can be associated with an EUV wavelength such as 13.5 nm. The Ru-based material can be selected due to having an extinction coefficient exceeding the extinction coefficients of TaBN and TaN at the EUV wavelength at the EUV wavelength. In some embodiments, when other materials without ruthenium have an extinction coefficient exceeding the extinction coefficients of TaBN and TaN at the EUV wavelength, other materials are included.

[0040] In some embodiments, a capping layer 200 is present on the upper surface of the reflective multilayer 270. The capping layer 200 covering the reflective multilayer 270 is present to protect the reflective multilayer 270 from oxidation and other environmental damages. The capping layer 200 can be a ruthenium-based thin layer of one or more of the following materials: such as Ru, RuO, RuNb, RuNbO, RuZr, RuZrN, RuRh, RuON, RuNbN, RuRhN, RuVO, RuV, RuVN, or the like. Ruthenium can be selected due to its beneficial stability and compatibility with the EUV wavelength. The capping layer 200 can have a thickness in the range of about 2 nm to about 5 nm.

[0041] In some embodiments, a buffer layer or a barrier layer 210 is present between the cover layer 200 and the absorber structure 220. The buffer layer 210 can be included between the reflective multilayer 270 and the absorber structure 220 to prevent damage to the cover layer 200 during the etching of the absorber structure 220. The buffer layer 210 can be or include CrN, Cr2N, or both. The thickness of the buffer layer 210 can range from about 2 nm to about 20 nm. In some embodiments, the buffer layer 210 is omitted. The cover layer 200 can also act as an etch stop layer during the removal of the buffer layer 210.

[0042] The multilayer reflector 270 is formed on or attached to the substrate 260, which can be or include a low thermal expansion material (LTEM), such as SiO2 doped with TiO2, or other suitable materials. The LTEM substrate 260 facilitates maintaining the structural integrity and optical performance of the multilayer reflector 270 under the intense thermal loads experienced during EUV lithography.

[0043] A conductive layer or multilayer 250 can be present on the lower side of the substrate 260. The conductive layer 250 present on the lower side of the substrate 260 can be used to attach the mask 20 to the mask stage via an electrostatic chuck. The conductive layer 250 can also, for example, improve the dissipation of heat generated by the electrostatic chuck and / or improve the thermal conductivity of the mask 20 during the operation of the mask 20.

[0044] Briefly, the formation of the mask 20 may include: providing a substrate 260; forming a conductive layer 250 on the lower side of the substrate 260; forming a multilayer reflector 270 on the top side of the substrate 260; forming a covering layer 200 on the multilayer reflector 270; forming an optionally selected buffer layer 210 on the covering layer 200; and forming an absorber structure 220 on the buffer layer 210 or the covering layer 200. Each of the structures formed on the substrate 260 (e.g., the conductive layer 250, the multilayer reflector 270, the covering layer 200, the optionally selected buffer layer 210, and the absorber structure 220) may be formed using one or more suitable forming operations, and the suitable forming operations may include physical vapor deposition (PVD), chemical vapor deposition (CVD), atomic layer deposition (ALD), or the like. The formation of the conductive layer 250 may include any of the methods just mentioned or other methods, such as electroplating, electroless plating, or the like.

[0045] The formation of the absorber structure 220 corresponds to operation 1010 in FIG. 10. In some embodiments, the absorber structure 220 is or includes a PtRu layer, and the PtRu layer may be formed using sputtering, thermal evaporation, metal-organic chemical vapor deposition (MOCVD), atomic layer deposition, electroplating, electrophoretic deposition, chemical solution deposition, nanoparticle deposition, a combination thereof, or the like. As mentioned before, the absorber structure 220 may be or include a high extinction coefficient material, and the high extinction coefficient material may reduce the thickness of the absorber 220. The absorber structure 220 may be formed to have a thickness in the range of about 20 nm to about 50 nm.

[0046] After forming the unpatterned mask 20, a hard mask structure 230 is formed on the unpatterned mask 20, corresponding to operations 1020, 1030, 1040, 1050 of FIG. 10. FIG. 2 depicts four separate hard mask layers 232, 234, 236, 238 included in the hard mask structure 230 on the unpatterned mask 20. According to various embodiments, the hard mask structure 230 may include fewer or additional hard mask layers than the hard mask layers shown in FIG. 2. For example, the hard mask structure 230 may include only the third hard mask layer 236 and the fourth hard mask layer 238, while omitting the first hard mask layer 232 and the second hard mask layer 234. In another example, the hard mask structure 230 may include the second hard mask layer 234, the third hard mask layer 236, and the fourth hard mask layer 238, while omitting the first hard mask layer 232. Generally, the bottommost hard mask layer of the hard mask structure 230 (e.g., the first hard mask layer 232) is in direct contact with the upper surface of the uppermost absorber layer of the absorber structure 220 (e.g., the second absorber layer 224). In some embodiments, one or more additional material layers not separately depicted in FIG. 2 may be interposed between the absorber structure 220 and the hard mask structure 230. The total thickness of the hard mask structure 230 may range from about 4 nm to about 80 nm in the vertical (e.g., Z-axis) direction.

[0047] The first hard mask layer 232 may be formed on the absorber 220, corresponding to operation 1020 of FIG. 10. The first hard mask layer 232 may be or include one or more of CrN, Cr2N, or the like, and may have a thickness ranging from about 2 nm to about 20 nm in the vertical direction. The first hard mask layer 232 may be formed using reactive sputtering, cathodic arc deposition, thermal CVD, plasma-enhanced CVD (PECVD), ALD, pulsed laser deposition (PLD), or another suitable process.

[0048] The second hard mask layer 234 may be formed on the first hard mask layer 232, corresponding to operation 1030 of FIG. 10. The second hard mask layer 234 may be or include one or more of TaBN, TaN, MoSi, MoSiN, SiN, SiC, SiCN, combinations thereof, or the like, and may have a thickness ranging from about 2 nm to about 20 nm in the vertical direction. In some embodiments, the second hard mask layer 234 is formed using sputtering, electron beam evaporation, thermal CVD, PECVD, MOCVD, ALD, electrochemical deposition, or another suitable process.

[0049] The third hard mask layer 236 may be formed on the second hard mask layer 234, corresponding to operation 1040 of FIG. 10. The third hard mask layer 236 may be or include one or more of TaBO, Ta2O5, TaO2, TaO, Ta2O, MoSiO, SiON, SiO2, SiCON, combinations thereof, or the like, and may have a thickness in the range of from about 2 nm to about 20 nm in the vertical direction. In some embodiments, the third hard mask layer 236 is formed using sputtering, electron beam evaporation, thermal CVD, PECVD, MOCVD, ALD, electrochemical deposition, or another suitable process.

[0050] The fourth hard mask layer 238 may be formed on the third hard mask layer 236, corresponding to operation 1050 of FIG. 10. The fourth hard mask layer 238 may be or include one or more of CrON, CrCON, GaN, SiO, SiCO, Y2O3, SiCN, SiCON, combinations thereof, or the like, and may have a thickness in the range of from about 2 nm to about 20 nm in the vertical direction. In some embodiments, the fourth hard mask layer 238 is formed using sputtering, electron beam evaporation, thermal CVD, PECVD, MOCVD, ALD, electrochemical deposition, or another suitable process.

[0051] In some embodiments, one or more of the hard mask layers 232, 234, 236, 238 just described may be exchanged with another of the hard mask layers 232, 234, 236, 238. For example, the positions of the second hard mask layer 234 and the third hard mask layer 236 may be interchanged such that the third hard mask layer 236 is between the second hard mask layer 234 and the first hard mask layer 232. In another example, the first hard mask layer 232 and the fourth hard mask layer 238 may be exchanged such that the fourth hard mask layer is directly adjacent to or in direct contact with the absorber structure 220. In some embodiments, one or more of the hard mask layers 232, 234, 236, 238 are omitted. For example, as described with reference to FIGS. 4B and 4C, in some embodiments, the first hard mask layer 232, the second hard mask layer 234, or both are omitted.

[0052] After the hard mask structure 230 is formed, a photoresist layer 240 is formed on the hard mask structure 230. The photoresist layer 240 can be or include one or more of a photoresist layer, a bottom antireflective coating (BARC) layer, a combination thereof, or the like. The choice of photoresist material and its components can facilitate achieving high resolution and pattern fidelity at the nanoscale. Two types of photoresists include positive photoresists and negative photoresists, and the components of each photoresist are selected according to specific application and manufacturing requirements. After exposure to light, positive photoresists become more soluble in developer solutions. This property allows the removal of the exposed areas, leaving a pattern where light modifies the solubility of the photoresist. The components of positive photoresists can include a photoactive compound (PAC), which can be a component that undergoes a chemical change when exposed to light, typically producing a soluble product in the exposed areas. Positive photoresists can include a resin, which can form the bulk of the photoresist and provide its mechanical properties. The photoresist can include a solvent, which can be used to adjust the viscosity of the photoresist for application purposes. The solvent can be selected based on its ability to dissolve the resin and PAC and can evaporate during the pre-baking process. After exposure to light, negative photoresists become less soluble in developer solutions, such that the exposed areas remain after the development process, creating a negative of the exposure pattern. The components of negative photoresists typically include PAC, which, unlike positive photoresists, crosslinks polymer chains in the exposed areas, making the polymer chains insoluble in the developer. Negative photoresists can include a polymer that provides the structural framework of the photoresist, such as an epoxy polymer or other polymers that can crosslink when exposed to light. Like positive photoresists, negative photoresists can include a solvent that adjusts the viscosity of the photoresist for the coating process and can be selected based on its ability to dissolve the polymer and PAC. As the semiconductor industry moves towards nanoscale dimensions, photoresists are being developed to provide the benefits of extreme ultraviolet (EUV) lithography, electron beam lithography, and immersion lithography. Such “advanced” photoresists can provide higher resolution, lower line edge roughness (LER), and increased sensitivity and can include chemically amplified resist (CAR) and / or inorganic photoresists. CAR can be a subclass of both positive and negative photoresists, and positive and negative photoresists use chemical amplification mechanisms to increase the sensitivity of the photoresist. This can be achieved using exposure-induced catalytic reactions, which allow for the generation of finer patterns. In some embodiments, inorganic photoresists can be included in the photoresist layer 240.Inorganic photoresists can include hafnium-based compounds for EUV lithography, due to their smaller molecular size and higher etch resistance, which are advantageous for higher-resolution patterning.

[0053] In FIG. 3, a pattern including at least one opening 56 is formed in the photoresist layer 240. The opening 56 can be formed by electron beam (or “e-beam”) writing and can include one or more baking operations and a developing operation. During electron beam writing, a focused electron beam is scanned over the surface of the photoresist layer 240. The photoresist layer 240 can be selected to be sensitive to electron beam exposure. The interaction of the electron beam with the photoresist layer 240 changes its solubility in a subsequent developing stage. For an EUV mask, the pattern written by the electron beam corresponds to the mask design, which can include complex features that will be transferred onto a semiconductor wafer during EUV lithography. Electron beam lithography can achieve high resolution and high precision, which are beneficial for the manufacture of EUV masks, and EUV masks benefit from nanoscale patterning features. The resolution can be determined by factors such as beam size, photoresist sensitivity, and proximity effects (e.g., the phenomenon of exposing the nearby area by scattered electrons, which may cause accidental exposure).

[0054] Before electron beam exposure, the photoresist layer 240 can undergo pre-exposure baking to remove any solvents and improve the adhesion of the photoresist 240 to the substrate (e.g., absorber 220). This step can be beneficial for increasing photoresist thickness uniformity and reducing defects. After electron beam exposure, post-exposure baking can be performed, which can promote chemical reactions initiated by electron beam exposure within the photoresist layer 240. For a chemically amplified resist (CAR), the baking step can activate the acid catalyst generated during exposure, enabling the acid catalyst to decompose or crosslink the polymer of the photoresist layer 240, depending on whether the photoresist layer 240 is a positive photoresist or a negative photoresist.

[0055] After post-exposure baking, the developing stage can remove the exposed or unexposed areas of the photoresist layer 240, depending on whether the photoresist layer 240 is a positive tone or a negative tone. In a positive-tone photoresist, the exposed areas become more soluble and are removed, leaving a patterned photoresist in the unexposed areas of the photoresist layer 240. In a negative-tone photoresist, the exposed areas become insoluble, and the unexposed areas of the photoresist layer 240 are washed away. After development, the patterned photoresist of the photoresist layer 240 reveals a complex pattern that will be used in a subsequent etching process to transfer the pattern onto the absorber 220.

[0056] The opening 56 in the intermediate manufacturing stage depicted in FIG. 3 may expose the hard mask structure 230. For example, when there is a fourth hard mask layer 238, the opening 56 may expose the upper surface of the fourth hard mask layer 238. In some embodiments, the opening 56 formed only in the photoresist layer 240 after the initial patterning of the photoresist layer 240 may expose the upper surface of the fourth hard mask layer 238, the third hard mask layer 236, the second hard mask layer 234, or the first hard mask layer 232.

[0057] In FIGS. 4A to 7C, the hard mask structure 230 is patterned according to various embodiments, corresponding to operation 1060 of FIG. 10.

[0058] In FIGS. 4A to 4C, according to various embodiments, by removing portions of one or more of the hard mask layers 232, 234, 236, 238 exposed by the opening 56 in the photoresist layer 240, the opening 56 extends partially through the hard mask structure 230. FIG. 4A depicts the hard mask structure 230 including four hard mask layers 232, 234, 236, 238. FIG. 4B depicts the hard mask structure 230 including three hard mask layers 234, 236, 238, wherein the hard mask layer 232 is omitted. FIG. 4C depicts the hard mask structure 230 including two hard mask layers 236, 238, wherein the hard mask layers 232, 234 are omitted. The hard mask structure 230 can be used to select the minimum feature size (the "critical dimension" or "CD") of the mask 20. The minimum feature size can refer to the width or length in the horizontal plane of the mask 20, which is perpendicular to the second direction D2 and does not exceed any other width or length in the mask 20. Generally, the hard mask structure 230 includes at least two hard mask layers, such as the hard mask layers 236, 238 and optionally the hard mask layers 232, 234, which is beneficial for improving the pattern profile when patterning one or more absorber layers of the absorber 220. The ruthenium-based material of the absorber 220 may be relatively more difficult to pattern, which results in an increased number of hard mask layers (e.g., two to four layers) being beneficial for generating the selected pattern profile when etching the absorber layers 222, 224. For example, the ruthenium-based material may have a relatively high etch resistance to many etching chemicals and / or plasmas, which may increase the difficulty of selectively removing the ruthenium-based material while substantially not affecting adjacent materials, such as the materials of the hard mask layers 232, 234, 236, 238.

[0059] In FIG. 4A, the hard mask structure 230 includes all four hard mask layers 232, 234, 236, 238, and an extended opening 56' is formed by extending the opening 56 through the second hard mask layer 234, the third hard mask layer 236, and the fourth hard mask layer 238, such that the first hard mask layer 232 is exposed by the extended opening 56'. The extended opening 56 may include removing portions of the hard mask layers 234, 236, 238 exposed by the opening 56 in the photoresist layer 240. The removing may include one or more suitable etching operations for removing the material of the hard mask layers 234, 236, 238.

[0060] A first etching operation for removing the material of the fourth hard mask layer 238 may be performed using the photoresist layer 240 as a mask. As previously described with reference to FIG. 2, the fourth hard mask layer 238 may be or include CrON, CrCON, GaN, SiO, SiCO, Y2O3, SiCN, SiCON, or the like, and may have a thickness in the range of from about 2 nm to about 20 nm. The first etching operation may be an anisotropic etching, such as dry etching (e.g., reactive ion etching or "RIE" or inductively coupled plasma etching or "ICP"), and the dry etching may be fluorine-based dry etching or chlorine-based dry etching. The first etching operation may be high-density plasma (HDP) etching, atomic layer etch (ALE), or the like. In some embodiments, the fourth hard mask layer 238 is a CrON layer, and the first etching operation is performed using Cl2 and O2 gases. The first etching operation may have a directionality in a second direction D2, and the second direction D2 may be a vertical direction perpendicular to the main surface of the fourth hard mask layer 238. The first etching operation may etch completely through the fourth hard mask layer 238 and may terminate on the third hard mask layer 236. In some embodiments, the first etching operation slightly continues into the third hard mask layer 236. The upper surface of the third hard mask layer 236 may be exposed after the first etching operation is completed.

[0061] The photoresist layer 240 and the fourth hard mask layer 238 can be used as masks to perform a second etching operation to remove the material of the third hard mask layer 236. As previously described with reference to FIG. 2, the third hard mask layer 236 can be or include TaBO, Ta2O5, TaO2, TaO, Ta2O, MoSiO, SiON, SiO2, SiCON, or the like, and can have a thickness in the range of about 2 nm to about 20 nm. In FIGS. 4A and 4B, the third hard mask layer 236 includes a material having an etching selectivity different from that of the fourth hard mask layer 238 and the second hard mask layer 234, such that the second etching operation can terminate on the second hard mask layer 234. In FIG. 4C, the third mask layer 236 includes a material having an etching selectivity different from that of the fourth hard mask layer 238 and the absorber 220, such that the second etching operation can terminate on the absorber 220. The second etching operation can be an anisotropic etching, such as dry etching (e.g., reactive ion etching or "RIE" or inductively coupled plasma etching or "ICP"), and the dry etching can be fluorine-based dry etching or chlorine-based dry etching. The second etching operation can be high-density plasma (HDP) etching, atomic layer etching (ALE), or the like. Generally, the second etching operation will have parameters different from those of the first etching operation (e.g., reactant type and / or ratio, RF and / or bias power level, pressure, gas flow rate, temperature, substrate bias voltage, plasma composition, and the like), such that the second etching operation removes the material of the third hard mask layer 236 while substantially not attacking the fourth hard mask layer 238 or underlying layers, such as the first hard mask layer 232 or the second hard mask layer 234 or the absorber 220. For example, the third hard mask layer 236 can be a TaBO layer, and the second etching operation can use Cl2 and CF4 gases. The second etching operation can have a directionality in a second direction D2, and the second direction D2 can be a vertical direction perpendicular to the main surface of the third hard mask layer 236. In the embodiments depicted in FIGS. 4A and 4B, the second etching operation can etch completely through the third hard mask layer 236 and can terminate on the second hard mask layer 234. In FIG. 4C, the second etching operation can etch completely through the third hard mask layer 236 and can terminate on the absorber 220, or can continue slightly into the absorber 220. The upper surface of the second hard mask layer 234 or the absorber 220 can be exposed after the second etching operation is completed.

[0062] In FIGS. 4A and 4B, a photoresist layer 240, a third hard mask layer 236, and a fourth hard mask layer 238 can be used as masks to perform a third etching operation to remove the material of the second hard mask layer 234. As previously described with reference to FIG. 2, the second hard mask layer 234 can be or include TaBN, TaN, MoSi, MoSiN, SiN, SiC, SiCN, or the like, and can have a thickness in the range of about 2 nm to about 20 nm. In FIG. 4A, the second hard mask layer 234 includes a material having an etching selectivity different from that of the first hard mask layer 232, the third hard mask layer 236, and the fourth hard mask layer 238, such that the third etching operation can terminate on the first hard mask layer 232 without substantially attacking the first hard mask layer 232, the third hard mask layer 236, and the fourth hard mask layer 238. In FIG. 4B, the second hard mask layer 234 includes a material having an etching selectivity different from that of the absorber 220, the third hard mask layer 236, and the fourth hard mask layer 238, such that the third etching operation can terminate on the absorber 220 without substantially attacking the absorber 220, the third hard mask layer 236, and the fourth hard mask layer 238. The third etching operation can be an anisotropic etching, such as dry etching (e.g., reactive ion etching or "RIE" or inductively coupled plasma etching or "ICP"), and the dry etching can be fluorine-based dry etching or chlorine-based dry etching. The third etching operation can be high-density plasma (HDP) etching, atomic layer etch (ALE), or the like. Generally, the third etching operation will have parameters different from those of the first etching operation and / or the second etching operation (e.g., reactant type and / or ratio, RF and / or bias power level, pressure, gas flow rate, temperature, substrate bias voltage, plasma composition, and the like), such that the third etching operation removes the material of the second hard mask layer 234 without substantially attacking the third hard mask layer 236 and the fourth hard mask layer 238 or the underlying layer, such as the first hard mask layer 232 (FIG. 4A) or the absorber 220 (FIG. 4B). For example, the second hard mask layer 234 can be a TaBN layer, and the third etching process can use Cl 2 gas. The third etching operation can have a directionality in a second direction D2, and the second direction D2 can be a vertical direction perpendicular to the main surface of the second hard mask layer 234. In the embodiment depicted in FIG. 4A, the third etching operation can etch completely through the second hard mask layer 236 and can terminate on the first hard mask layer 232. In FIG. 4B, the third etching operation can terminate on the absorber 220 or can continue slightly into the absorber 220. The upper surface of the first hard mask layer 232 or the absorber 220 can be exposed after completion of the third etching operation.

[0063] In FIGS. 5A, 5B, and 5C, for example, the photoresist layer 240 is removed by lift-off. FIG. 5A depicts an embodiment in which the hard mask structure 230 includes hard mask layers 232, 234, 236, 238 and the photoresist layer 240 is removed. FIG. 5B depicts an embodiment in which the hard mask structure 230 includes hard mask layers 234, 236, 238 and the photoresist layer 240 is removed. FIG. 5C depicts an embodiment in which the hard mask structure 230 includes hard mask layers 236, 238 and the photoresist layer 240 is removed.

[0064] As described with reference to FIGS. 4A to 4C, the absorber 220 is exposed by the extended opening 56' in FIGS. 4B and 4C, where the first hard mask layer 232 and the optionally selected second hard mask layer 234 are omitted.

[0065] In FIG. 6, after removing the photoresist layer 240 in FIG. 5A (where the first hard mask layer 232 and the second hard mask layer 234 are present in FIG. 5A), the exposed portion of the first hard mask layer 232 is removed to form an opening 56'' that exposes the absorber 220. As described with reference to FIG. 2, the absorber 220 may include a single layer 222 or 224 or a multi-layer including at least two layers 222, 224. The opening 56'' may expose a single layer 222 or 224 or the uppermost layer of the multi-layer 220, such as the absorber layer 224.

[0066] The opening 56’’ can be formed by performing one or more suitable etching operations to remove portions of the first hard mask layer 232 exposed by the extended opening 56’’. As previously described with reference to FIG. 2, the first hard mask layer 232 can be or include CrN, Cr₂N, or the like, and can have a thickness in the range of about 2 nm to about 20 nm. The fifth etching operation can be an anisotropic etching, such as dry etching (e.g., reactive ion etching or "RIE" or inductively coupled plasma etching or "ICP"), and the dry etching can be fluorine-based dry etching or chlorine-based dry etching. The fifth etching operation can be high-density plasma (HDP) etching, atomic layer etch (ALE), or the like. For example, the second hard mask layer 234, the third hard mask layer 236, and the fourth hard mask layer 238 can be used as masks to perform the fifth etching operation to remove the exposed portions of the first hard mask layer 232. In some embodiments, the first hard mask layer 232 is or includes CrN, and the fifth etching operation uses Cl₂ and O₂ gases as reactive gases in the anisotropic etching. The fifth etching operation can have a directionality in the second direction D2, and the second direction D2 can be a vertical direction perpendicular to the main surface of the first hard mask layer 232. The fifth etching operation can etch completely through the first hard mask layer 232 and can terminate on the absorber 220. In some embodiments, the fifth etching operation slightly continues into the absorber 220. The upper surface of the absorber 220 can be exposed after the fifth etching operation is completed. As described above, one or more other hard masks disposed above the first hard mask layer can be used to pattern the first hard mask layer 232. This feature can provide more fine-tuning of the minimum feature size ("critical dimension" or "CD") in preparation for patterning the absorber 220.

[0067] In the embodiments described with reference to FIGS. 4B, 4C, 5B, and 5C, the fifth etching operation can be omitted, where the extended opening 56’ directly exposes the absorber 220.

[0068] In some embodiments, as depicted in FIG. 6, the fifth etching operation removes the fourth hard mask layer 238.

[0069] FIGS. 7A, 7B, and 7C depict the removal of any remaining hard mask layers other than the bottommost hard mask layer of the hard mask structure 230 closest to (e.g., in direct contact with) the absorber 220.

[0070] In FIG. 7A, the second hard mask layer 234 and the third hard mask layer 236 are removed, and the first hard mask layer 232 is left in place on the absorber 220. The upper portion of the opening 56'' is removed, leaving an opening 57 in the first hard mask layer 232, and the opening 57 exposes a portion of the absorber 220. The second hard mask layer 234 and the third hard mask layer 236 can be removed using one or more suitable removal operations such as a stripping operation, followed by a cleaning operation. For example, a wet chemical stripping, dry etching, or other suitable process can be performed to remove the second hard mask layer 234 and the third hard mask layer 236 with substantially no change or damage to underlying structures such as the first hard mask layer 232 and the absorber 220.

[0071] In FIG. 7B, the third hard mask layer 236 and the fourth hard mask layer 238 are removed, and the second hard mask layer 234 is left in place on the absorber 220. The upper portion of the opening 56'' is removed, leaving an opening 57 in the second hard mask layer 234, and the opening 57 exposes a portion of the absorber 220. The third hard mask layer 236 and the fourth hard mask layer 238 can be removed using one or more suitable removal operations such as a stripping operation, followed by a cleaning operation. For example, a wet chemical stripping, dry etching, or other suitable process can be performed to remove the third hard mask layer 236 and the fourth hard mask layer 238 with substantially no change or damage to underlying structures such as the second hard mask layer 234 and the absorber 220.

[0072] In FIG. 7C, the fourth hard mask layer 238 is removed, and the third hard mask layer 236 is left in place on the absorber 220. The upper portion of the opening 56'' is removed, leaving an opening 57 in the third hard mask layer 236, and the opening 57 exposes a portion of the absorber 220. The fourth hard mask layer 238 can be removed using a suitable removal operation such as a stripping operation, followed by a cleaning operation. For example, a wet chemical stripping, dry etching, or other suitable process can be performed to remove the fourth hard mask layer 238 with substantially no change or damage to underlying structures such as the third hard mask layer 236 and the absorber 220.

[0073] In FIGS. 8A, 8B, and 8C, as described with reference to FIGS. 7A to 7C, after removing the upper hard mask layer, the absorber 220 is patterned, corresponding to operation 1070 of FIG. 10. The absorber 220 can be patterned by using the hard mask structure 230 (e.g., the first hard mask layer 232, the second hard mask layer 234, or the third hard mask layer 236) as a mask to remove the exposed portion of the absorber 220. As described with reference to FIG. 2, the absorber 220 can include a single layer 222 or 224 or can be a multilayer including at least two layers 222, 224. For example, the absorber 220 can include PtRuO, IrRuO, OsRuO, HfRuO, RhRuO, PtRuON, IrRuON, OsRuON, HfRuON, RhRuON, RuTa, RuTaO, PtRu, IrRu, OsRu, HfRu, RhRu, PtRuN, IrRuN, OsRuN, HfRuN, RhRuN, or the like. An opening 57' is formed extending through the layers of the absorber 220 to expose the buffer layer 210.

[0074] In FIG. 8A, the exposed portion of the absorber 220 can be etched via a sixth etching operation and / or a seventh etching operation that use the first hard mask layer 232 as a mask to form an extended opening 57' that exposes the buffer layer 210. In an embodiment where the absorber 220 is a single layer, the sixth etching operation can be used to etch the single layer. In an embodiment where the absorber 220 includes a bilayer or a multilayer, the sixth etching operation and the seventh etching operation and optionally additional etching operations can be used to etch the bilayer or the multilayer. The sixth etching operation and / or the seventh etching operation can each be an anisotropic etching, such as dry etching (e.g., reactive ion etching or "RIE" or inductively coupled plasma etching or "ICP"), and the dry etching can be fluorine-based dry etching or chlorine-based dry etching. The sixth etching operation and / or the seventh etching operation can each be a high-density plasma (HDP) etching, an atomic layer etch (ALE), or the like. In some embodiments, the absorber 220 includes a single PtRu layer, and the sixth etching operation uses CF4 and O2 as reactive gases.

[0075] In FIG. 8B, the exposed portion of absorber 220 can be etched via a sixth operation and / or a seventh operation that uses the second hard mask layer 234 as a mask to form an extended opening 57' in the exposed buffer layer 210. The etching can be similar to the etching described with reference to FIG. 8A. The sixth operation and / or the seventh operation can be an anisotropic etching, such as dry etching (e.g., reactive ion etching or "RIE" or inductively coupled plasma etching or "ICP"), and the dry etching can be fluorine-based dry etching or chlorine-based dry etching. The sixth operation and / or the seventh operation can be high-density plasma (HDP) etching, atomic layer etching (ALE), or the like. In some embodiments, absorber 220 includes a single PtRu layer, and the sixth etching operation uses CF4 and O2 as reaction gases.

[0076] In FIG. 8C, the exposed portion of absorber 220 can be etched via a sixth operation and / or a seventh operation that uses the third hard mask layer 236 as a mask to form an extended opening 57' in the exposed buffer layer 210. The etching can be similar to the etching described with reference to FIG. 8A. The sixth operation and / or the seventh operation can be an anisotropic etching, such as dry etching (e.g., reactive ion etching or "RIE" or inductively coupled plasma etching or "ICP"), and the dry etching can be fluorine-based dry etching or chlorine-based dry etching. The sixth operation and / or the seventh operation can be high-density plasma (HDP) etching, atomic layer etching (ALE), or the like. In some embodiments, absorber 220 includes a single PtRu layer, and the sixth etching operation uses CF4 and O2 as reaction gases.

[0077] FIGS. 9A and 9B depict the formation of an opening 58 that exposes the cover layer 200 overlying the reflective multilayer 270. The opening 58 can be one of a plurality of openings 58 disposed in absorber 220 according to a pattern. The pattern including the opening 58 allows incident light to be absorbed by the absorber 220 outside the opening 58 and allows the incident light to be reflected by the reflective multilayer 270 via the opening 58. In FIG. 9A, absorber 220 includes a single layer, which can be absorber layer 222 or absorber layer 224 described with reference to FIG. 2. In FIG. 9B, absorber 220 includes multiple layers, such as a bilayer including absorber layer 222 and absorber layer 224.

[0078] In FIGS. 9A and 9B, after forming the extended opening 57' that exposes the buffer layer 210 in FIGS. 8A to 8C, an opening 58 that exposes the cover layer 200 is formed by removing the portion of the buffer layer 210 exposed by the extended opening 57'. The buffer layer 210 can be or include a layer of CrN or Cr2N. The opening 58 can be formed by an operation that selectively removes the material of the buffer layer 210. In some embodiments, the first hard mask layer 232 is in place and has a material similar to or the same as the material of the buffer layer 210. As a non-limiting example, the hard mask layer 232 and the buffer layer 210 can each be formed of the same material as each other, the material including TaBO, TaBN, TaN, Ta2O5, TaO2, TaO, Ta2O, MoSi, MoSiN, MoSiO, SiN, SiON, SiO2, SiCON, SiC, SiCN, CrN, Cr2N, or GaN. In such embodiments, the removal operation can be a stripping operation that simultaneously removes the exposed portions of the first hard mask layer 232 and the buffer layer 210. The removal operation can include wet chemical etching, dry etching (e.g., RIE, ICP), or another suitable process. In embodiments where the removal operation is performed with the second hard mask layer 234 or the third hard mask layer 236 in place, the second hard mask layer 234 or the third hard mask layer 236 can be removed separately from the removal of the exposed portion of the buffer layer 210. For example, the second hard mask layer 234 or the third hard mask layer 236 can be removed after removing the exposed portion of the buffer layer 210.

[0079] The mask 20 depicted in FIGS. 9A and 9B includes an absorber 220 having a high-K material, which can reduce the thickness of the absorber film 220, which in turn reduces the M3D effect and the exposure energy, and improves the image quality. The absorber layer 220 including the high-K material can be a single layer, a double layer, or a multi-layer. A Ru-based alloy can be included in the absorber layer 220, such as PtRu, IrRu, OsRu, HfRu, RhRu, PtRuN, IrRuN, OsRuN, HfRuN, RhRuN, PtRuO, IrRuO, OsRuO, HfRuO, RhRuO, PtRuON, IrRuON, OsRuON, HfRuON, RhRuON, and the like. The hard mask structure 230 and the buffer layer 210 provide improved patterning through dry etching.

[0080] FIG. 11 is a flowchart of a process 2000 for forming an integrated circuit die using a mask including an absorber having a high extinction coefficient in accordance with various embodiments. In some embodiments, process 2000 includes multiple operations (2010, 2020, 2030). In some embodiments, process 2000 can be used to pattern a wafer layer as an intermediate step in forming an integrated circuit die via a mask having a high-K absorber. Process 2000 is described in accordance with one or more embodiments. The operations of process 2000 can be reconfigured or otherwise modified within the scope of various aspects. Additional processes can be provided before, during, and after process 2000, and some other processes can be described only briefly herein. In some embodiments, process 2000 is performed by system 10 described with reference to FIGS. 1A and 1B using mask 20 described with reference to FIGS. 2 to 9B. Embodiments of process 2000 are described with reference to the structural components described in FIGS. 1A and 1B and FIGS. 9A and 9B, but process 2000 can be performed using a system having one or more structural components different from the structural components of system 10 and a mask having one or more structural components different from the structural components of mask 20. The process 2000 of FIG. 11 can be combined with system 10 and mask 20 described with reference to FIGS. 1A and 1B and FIGS. 2 to 9B.

[0081] In operation 2010, EUV radiation is generated. The EUV radiation can be similar to light 84 described with reference to FIGS. 1A and 1B.

[0082] In operation 2020, the EUV radiation is patterned using a mask having a high-K absorber. The mask can be similar to mask 20 described with reference to FIGS. 2 to 9B. The high-K absorber can reduce the thickness of the absorber, thereby reducing the M3D effect and exposure energy and improving image quality. The absorber including the high-K material can be a single layer, a double layer, or a multi-layer. A Ru-based alloy can be included in the high-K absorber, such as PtRu, IrRu, OsRu, HfRu, RhRu, PtRuN, IrRuN, OsRuN, HfRuN, RhRuN, PtRuO, IrRuO, OsRuO, HfRuO, RhRuO, PtRuON, IrRuON, OsRuON, HfRuON, RhRuON, and the like.

[0083] In operation 2030, patterned EUV radiation from a reflective multilayer reflection having a portion exposed by an opening in a high-K absorber can be directed toward a layer of a wafer to expose the wafer layer according to the pattern of a mask. For example, EUV radiation 84 can be reflected by a reflective multilayer 270 of a mask 20 having a pattern of an opening 58 in an absorber 220. The patterned EUV radiation can be directed via a projection optical cell 180 described with reference to FIG. 1A to a layer 26 on a wafer 22. In some embodiments, layer 26 is a photosensitive photoresist layer. Although not necessarily the same as the photoresist layer 240 described with reference to FIG. 2, patterning of layer 26 can be similar in most respects to the patterning described in FIG. 2. For example, layer 26 can include a positive-tone or negative-tone photoresist, and the photoresist can be patterned by exposure to the patterned EUV light to increase or decrease the solubility of the exposed regions of layer 26, followed by a development process that removes the exposed or unexposed regions of layer 26 to form openings in layer 26. Layer 26 can be used as a mask to pattern (e.g., etch via a suitable etching operation) an underlying layer located below layer 26. The etching operation, although not necessarily the same as the operations described with reference to FIGS. 3 to 9B, can be similar in many respects to the described operations, such as being an anisotropic etching, and the anisotropic etching can be a dry etching.

[0084] Embodiments can provide advantages. The absorber 220 with a high extinction coefficient includes one or more Ru-based alloy materials, which allows reducing the thickness of the absorber 220, which can reduce the M3D effect and exposure energy while improving image quality. The hard mask structure 230 and the buffer layer 210 allow for improved patterning by dry etching.

[0085] According to at least one embodiment, a method includes: forming a mask layer on a semiconductor wafer; generating extreme ultraviolet (EUV) light using a lithography exposure system; patterning the EUV light using a mask including an absorber having an extinction coefficient at an EUV wavelength that exceeds the extinction coefficients of TaBN and TaN at the EUV wavelength; and exposing the mask layer using the patterned EUV light.

[0086] According to at least one embodiment, a method includes: forming a reflective multilayer on a substrate, the reflective multilayer operable to reflect extreme ultraviolet (EUV) light; forming an absorber layer above the reflective multilayer, the absorber layer including ruthenium; forming a hard mask structure above the absorber layer; forming an opening in the hard mask structure; and forming an absorber by removing a portion of the absorber layer exposed by the opening in the hard mask structure.

[0087] According to at least one embodiment, an extreme ultraviolet (EUV) mask includes: a substrate; a reflective multilayer disposed above the substrate; and an absorber disposed above the reflective multilayer, the absorber including a ruthenium-based material.

[0088] The foregoing outlines features of several embodiments so that those skilled in the art may better understand aspects of the present disclosure. Those skilled in the art should understand that they can readily use the present disclosure as a basis for designing or modifying other processes and structures for the same purposes and / or achieving the same advantages as the embodiments introduced herein. Those skilled in the art should also recognize that such equivalent structures do not depart from the spirit and scope of the present disclosure, and that various changes, substitutions, and alterations can be made by those skilled in the art without departing from the spirit and scope of the present disclosure.

[0089] 10: Lithography exposure system or equipment 16: Mask stage 18: Mask 22: Semiconductor wafer 24: Substrate stage 26: Mask layer 20: Mask 30: Droplet generator 31: Reservoir 32: Nozzle assembly 35: Droplet receiver 40: Gas source 41: Gas pipeline 50: Laser generator 51: Laser pulse 52: Illumination point 55: Window 56, 56'', 57, 57', 58: Aperture 56': Extended aperture 60: Collector 61: Optical axis 62: Cleaning system 65: Container wall 66: First pump 68: Second pump 70: Monitoring device 71: Metrology tool 73: Analyzer 80: Target fuel 82: Droplet 82A: Tin debris 84: EUV radiation 88: Plasma 90: Controller 100: Reflective optics 120: Light source 140: Illuminator 180: Projection optical module 200, 210, 222, 224: Layer 220: Absorber structure 250: Conductive layer 230: Hard mask structure 232, 234, 236, 238: Hard mask layer 240: Photoresist layer 260: Substrate 270: Reflective multilayer 1000, 2000: Process 1010, 1020, 1030, 1040, 1050, 1060, 1070, 2010, 2020, 2030: Operation D1: First direction D2: Second direction

[0090] Domestic deposit information (Please note in the order of deposit institution, date, and number) None Foreign deposit information (Please note in the order of deposit country, institution, date, and number) None

Claims

1. A lithography method comprising the following steps: forming a mask layer on a semiconductor wafer; generating extreme ultraviolet (EUV) light using a lithography exposure system; patterning the EUV light using a mask comprising an absorber to form patterned EUV light, the absorber having an extinction coefficient at an EUV wavelength exceeding that of TaBN and TaN at the EUV wavelength, wherein the absorber comprises a first absorber layer and the oxygen content of the first absorber layer is in the range of about 2 at% to about 20 at%, the first absorber layer having nitrogen content in the range of about 2 at% to about 20 at%; and exposing the mask layer using the patterned EUV light.

2. The method as described in claim 1, wherein the step of forming patterned extreme ultraviolet light comprises the step of forming the patterned extreme ultraviolet light using a mask comprising an absorber having a ruthenium-based alloy.

3. The method as described in claim 1, wherein the grain size of the first absorber layer is less than 5 nm.

4. The method as claimed in claim 1, wherein the step of forming patterned extreme ultraviolet light comprises the steps of forming the patterned extreme ultraviolet light using a mask comprising: a reflective multilayer; a buffer layer on the reflective multilayer; and an absorber on the buffer layer.

5. A method for fabricating an extreme ultraviolet (EUV) shield, comprising the following steps: forming a reflective multilayer on a substrate, the reflective multilayer being operable to reflect extreme ultraviolet light; forming an absorber layer above the reflective multilayer, the absorber layer comprising ruthenium, wherein the absorber layer comprises a first absorber layer and the oxygen content of the first absorber layer is in the range of about 2 at% to about 20 at%, the first absorber layer having nitrogen content in the range of about 2 at% to about 20 at%; forming a hard shield structure above the absorber layer; forming an opening in the hard shield structure; and forming an absorber by removing a portion of the absorber layer exposed by the opening in the hard shield structure.

6. The method as described in claim 5, wherein the step of forming a hard mask structure comprises the following steps: forming a first hard mask layer on the absorber layer, the first hard mask layer comprising a first material; and forming a second hard mask layer on the first hard mask layer, the second hard mask layer comprising a second material different from the first material.

7. The method as described in claim 6, wherein the step of forming a hard mask structure comprises the following steps: forming a third hard mask layer on the second hard mask layer, the third hard mask layer comprising a third material different from the first material and the second material.

8. An extreme ultraviolet (EUV) shield, comprising: One substrate; A multilayer reflector is positioned above the substrate; An absorber is located above the reflective multilayer, the absorber comprising a ruthenium-based material, wherein the absorber comprises a first absorber layer and the oxygen content of the first absorber layer is in the range of about 2 at% to about 20 at%, and the nitrogen content of the first absorber layer is in the range of about 2 at% to about 20 at%.

9. The extreme ultraviolet shield as described in claim 8, further comprising: A covering layer is placed above the reflective multilayer; A buffer layer is placed between the cover layer and the absorber.

10. An extreme ultraviolet shield as described in claim 9, wherein the buffer layer comprises TaBN, TaN, MoSi, MoSiN, SiN, SiC, or SiCN.

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