Patent Publication Number: US-2023161241-A1

Title: Extreme ultraviolet mask with capping layer

Description:
PRIORITY CLAIM AND CROSS-REFERENCE 
     This application claims the benefit of U.S. Provisional Patent Application No. 63/282,289 filed Nov. 23, 2021, which is incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     The semiconductor industry has experienced exponential growth. Technological advances in materials and design have produced generations of integrated circuits (ICs), where each generation has smaller and more complex circuits than the previous generation. In the course of IC evolution, functional density (i.e., the number of interconnected devices per chip area) has generally increased while geometry size (i.e., the smallest component or line that can be created using a fabrication process) has decreased. This scaling down process generally provides benefits by increasing production efficiency and lowering associated costs. 
     Photolithography may be used to form the components or lines on a semiconductor wafer. One example of a photolithographic technique utilizes extreme ultraviolet (EUV) energy and a patterned absorber layer of an EUV mask. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is noted that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion. 
         FIG.  1    is a cross-sectional view of an extreme ultraviolet (EUV) mask, in accordance with a first embodiment. 
         FIG.  2    is a flowchart of a method for fabricating the EUV mask of  FIG.  1   , in accordance with some embodiments. 
         FIGS.  3 A- 3 J  are cross-sectional views of an EUV mask at various stages of the fabrication process of  FIG.  2   , in accordance with some embodiments. 
         FIG.  4    is a cross-sectional view of an extreme ultraviolet (EUV) mask, in accordance with a second embodiment. 
         FIG.  5    is a flowchart of a method for fabricating the EUV mask of  FIG.  4   , in accordance with some embodiments. 
         FIGS.  6 A- 6 L  are cross-sectional views of an EUV mask at various stages of the fabrication process of  FIG.  5   , in accordance with some embodiments. 
         FIG.  7    is a flowchart of a method of using an EUV mask in accordance with some embodiments. 
         FIG.  8    is a flowchart of a method of using an EUV mask in accordance with some embodiments. 
         FIG.  9    is an illustration of the results of an assessment of the thickness of carbon contamination on a capping layer in accordance with embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The following disclosure provides many different embodiments, or examples, for implementing different features of the provided subject matter. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed. 
     Further, spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly. 
     In the manufacture of integrated circuits (ICs), patterns representing different layers of the ICs are fabricated using a series of reusable photomasks (also referred to herein as photolithography masks or masks) in order to transfer the design of each layer of the ICs onto a semiconductor substrate during the semiconductor device fabrication process. 
     With the shrinkage in IC size, extreme ultraviolet (EUV) light, for example, with a wavelength of 13.5 nm is employed in a lithographic process to enable transfer of very small patterns (e.g., nanometer-scale patterns) from a mask to a semiconductor wafer. Because most materials are highly absorbing at the wavelength of 13.5 nm, EUV lithography utilizes a reflective-type EUV mask having a reflective multilayer to reflect the incident EUV light and an absorber layer on top of the reflective multilayer to absorb radiation in areas where light is not intended to be reflected by the mask. The reflective multilayer and absorber layer are on a low thermal expansion material substrate. The reflective multilayer reflects the incident EUV light and the patterned absorber layer on top of the reflective multilayer absorbs light in areas where light is not intended to be reflected by the mask. The mask pattern is defined by the absorber layer and is transferred to a semiconductor wafer by reflecting EUV light off portions of a reflective surface of the EUV mask. 
     An ongoing desire to have more densely packed integrated devices has resulted in changes to the photolithography process in order to form smaller individual feature sizes. The minimum feature size or “critical dimension” (CD) obtainable by a process is determined approximately by the formula CD=k 1 *λ/NA, where k 1  is a process-specific coefficient, λ is the wavelength of applied light/energy, and NA is the numerical aperture of the optical lens as seen from the substrate or wafer. 
     The present disclosure describes various embodiments of an EUV mask that exhibits a resistance to carbon contamination and utilizes durable capping features that protect the underlying reflective multilayer stack from oxidants even after being exposed to etching or cleaning processes during the manufacture of the mask. Carbon contamination can negatively affect the critical dimension of features formed in an absorber layer and a capping feature of the EUV mask. For example, some materials used as a capping layer may have many free radicals that can react with carbon atoms near the EUV mask surface during exposure to EUV energy. During exposure, hydrocarbon molecules near the surface of the EUV mask can be cracked when exposed to high energy and deposit onto exposed surfaces (e.g., sidewalls and bottoms or trenches in the absorber material) of the EUV mask. Cracking of the hydrocarbon molecules can produce carbon atoms that can react with the free radicals. It has been observed that carbon deposits to greater thicknesses on exposed surfaces of the mask that are near the center of the mask compared to exposed surfaces of the mask that are near edges of the mask. In some embodiments, the amount of carbon that forms on the exposed surfaces near the center of the mask is three times as thick as the carbon that forms on exposed surfaces near the edges of the mask. The hydrocarbons may originate from numerous sources, including outgassing from materials within the EUV tool, such as structures of the tool, photoresists or hard masks used in the tool. The resulting carbon atoms or carbon containing molecules react with or are absorbed by materials they come in contact with and build up on surfaces of the EUV mask. The buildup of carbon on surfaces of the EUV mask, e.g., surfaces of the capping layer or sidewalls of features in the absorber material, can negatively affect the ability of the EUV mask to pattern features on a substrate that meet critical dimension criteria, such as critical dimension uniformity (CDU). For example, carbon absorbs EUV wavelengths to a greater degree than other materials making up an EUV mask. Thus, when unwanted carbon is present on an EUV mask, the exposure energy or amount of incident EUV energy needed to achieve a desired level of EUV radiation reflected from the mask is greater than when the unwanted carbon is not present. In some embodiments, depending on the critical dimension of the features on the wafer and the critical dimensions of the features on the mask, the exposure energy needed when carbon is present on the EUV mask can be 10% or more than when carbon is not present on the EUV mask. This need for increased exposure energy will increase the cost of the energy required to effectively expose the wafer or will increase the length of time needed to achieve a desired level of exposure. 
     Some embodiments of EUV masks of the present disclosure exhibit improved strength and/or resistance to etching and cleaning processes to which the materials of the EUV mask are exposed during manufacturing of the mask. The strength and/or resistance to etching and cleaning processes to which the materials of the EUV mask exposed during manufacturing of the mask is important because a weak or damaged layer of the mask is susceptible to infiltration by oxidants, such as oxygen. Oxygen that infiltrates a damaged or weak layer of the mask can react with materials of the reflective multilayer and form unwanted oxide layers on a top surface of the reflective multilayer. 
     Embodiments in accordance with the present disclosure broadly provide a photolithography mask that includes a capping feature over the reflective multilayer stack of the mask. In some embodiments, the capping feature includes a single layer of capping material and in other embodiments, the capping feature includes multiple capping layers of capping material. In some embodiments, the capping feature includes a first capping layer that includes material having an amorphous structure. This first capping layer can be combined with a second capping layer that includes materials having an amorphous structure. In some embodiments, the material of the first capping layer includes an element having a solid carbon solubility at the eutectic point, of a system containing the element and carbon, that is less than 3 atomic %. Examples of elements useful in a capping layer of a capping feature in accordance with embodiments of the present disclosure include Rh, Ir, Pt, Au and Zr or alloys thereof. In other embodiments, a capping layer of a capping feature in accordance with embodiments of the present disclosure includes Hf, Nb or N. In other embodiments, a capping layer of a capping feature in accordance with the present disclosure includes Ag or Cu. In other embodiments, a capping layer of a capping feature in accordance with the present disclosure includes Pd. In accordance with embodiments of the present disclosure, a single layered capping feature is employed to reduce carbon buildup or contamination on surfaces of the EUV mask. The materials of a capping layer formed in accordance with the present disclosure reduce the susceptibility of the capping feature to contamination with hydrocarbon molecules or carbon atoms. The materials of a capping feature formed in accordance with the present disclosure also protect an underlying reflective multilayer from exposure to oxidants and formation of unwanted oxide layers. 
     In examples of the present disclosure directed to a multilayered capping feature, the material used for one capping layer of the multilayered capping feature is different in composition from the material used for another capping layer of the multilayered capping feature. Such materials can be in accordance with the description in the previous paragraph regarding the materials for use in a capping feature that includes only a single capping layer. In some embodiments, the material of one capping layer exhibits a solid carbon solubility property that is different from a solid carbon solubility property of the material of another capping layer of the multilayered capping feature. For example, in some embodiments, a multilayered capping feature is provided that includes a first capping layer formed of a material including an element having a first carbon solubility property. The multilayered capping feature includes at least another capping layer formed of a material including an element having a second carbon solubility property that is different from the first carbon solubility property of the element of the material of the first capping layer. In some embodiments the, the solid carbon solubility of the elements of the material of the first capping layer and the second capping layer at an eutectic point, of a system containing the element and carbon, is less than 3 atomic %. The solid carbon solubility property refers to the maximum carbon solubility in a solid phase, of a system containing the element and carbon, which is in equilibrium with a liquid phase of the system at an eutectic point of the system. Solid carbon solubility of an element of the material of a capping layer is an indication of the propensity of an element of a capping layer to react with, retain, attract or absorb carbon atoms or carbon containing molecules. When the carbon atoms are attracted to and retained or absorbed by or react with the material of the capping layer, they build up and contaminate the capping layer. In some situations, the carbon build up or contamination completely covers exposed portions of the capping layer. In other situations, the carbon build up or contamination partially covers the capping layer. In other situations, the carbon buildup contamination at least partially covers portions of sidewalls of the absorber material of the mask. The presence of a layer of carbon contamination changes dimensions and EUV transmission properties of the mask. Such changes in dimension and/or changes in the incident EUV energy needed to produce a desired intensity of reflected EUV energy causes the negative issues described in the previous paragraph. In accordance with embodiments of the present disclosure, a multi-layered capping feature including multiple individual capping layers is employed to protect EUV masks from carbon buildup or contamination on surfaces of the EUV mask. The materials of the capping layers formed in accordance with the present disclosure reduce the susceptibility of the multilayered capping feature to contamination with hydrocarbon molecules or carbon atoms. The materials of a capping feature formed in accordance with the present disclosure also protect an underlying reflective multilayer from exposure to oxidants and formation of unwanted oxide layers. 
     In embodiments of the present disclosure, an EUV mask includes a multilayered capping feature that includes at least one capping layer that includes a material containing an element having a low solid carbon solubility. An element that has a low solid carbon solubility is characterized by a maximum carbon solubility in a solid phase, of a system of the element and carbon, in equilibrium with a liquid phase of the system at the eutectic point of the system. An example of an element that has a low solid carbon solubility is an element having a solid carbon solubility that is less than about 3 atomic percent. Examples of elements having a low atomic percent solid carbon solubility include, but are not limited to, materials that have a solid carbon solubility that is less than about 3 atomic % and in some embodiments less than 2 atomic %. For example, in some embodiments, materials of a capping layer do not have a solid carbon solubility that is less than about 3 atomic %, yet still provide a resistance to carbon buildup or contamination on the surface of the material. Elements having low solid carbon solubility that are useful in embodiments of the present disclosure are alternatively characterized by an effective solid carbon solubility in the element at 1000° C. of less than 1.6. The effective solid carbon solubility in the element at 1000° C. is obtained by multiplying the eutectic point solid carbon solubility value by 1000° C./the eutectic point of the element and carbon system. In accordance with some embodiments of multilayered capping features of the present disclosure, the element(s) of the material of one capping layer has a solid carbon solubility that is different from the solid carbon solubility of element(s) of the material of another capping layer forming the multilayered capping feature. In some embodiments, the material of at least one layer of the multilayered capping feature includes an element that has an EUV extinction coefficient for EUV radiation having a wavelength of 13.5 nm that is greater than or less than an EUV extinction coefficient for EUV radiation having a wavelength of 13.5 nm of an element of another layer of the multilayered capping feature. When the individual capping layers of the multilayered capping feature include materials that include elements having differing EUV extinction coefficients for EUV radiation having a wavelength of 13.5 nm, the amount of incident EUV energy absorbed in one capping layer is different from the EUV energy absorbed in another capping layer of the multilayered capping feature. For example, in some embodiments, an element of the material of one capping layer has an EUV extinction coefficient for EUV radiation having a wavelength of 13.5 nm between 0 and 0.1 and an element of the material of another capping layer has an EUV extinction coefficient for EUV radiation having a wavelength of 13.5 nm different from the EUV extinction coefficient of the element of the one capping layer. In other embodiments, the material of the first capping layer includes an element having an EUV extinction coefficient for EUV radiation having a wavelength of 13.5 nm between 0 and 0.08, between 0 and 0.06, between 0 and 0.04 or between 0 and 0.04. Materials that include an element having an EUV extinction coefficient for EUV radiation having a wavelength of 13.5 nm within the ranges described above do not reduce the transmission of EUV energy by an amount that requires that the level of incident EUV energy be increased by an undesirable amount. The materials for use in capping layers of the multilayered capping features in accordance with the present embodiments, should not absorb so much EUV energy that the amount of EUV energy incident on the EUV mask needs to be increased or the exposure time needs to be increased an undesirable amount. In addition, the materials for use in an individual capping layer of a capping feature or in capping layers of the multilayered capping features in accordance with disclosed embodiments exhibit good adhesion to each other as well as materials upon which the capping layer(s) are deposited or with materials that are deposited onto the capping layer(s). Elements that are suitable as a material for a capping layer in accordance with embodiments of the present disclosure include elements that exhibit a binding energy for carbon that is less than about 285 electronvolts (eV). Examples of elements that have a binding energy for carbon that is less than about 285 eV include Rh, Ir and Pt. Elements that have a binding energy for carbon that is less than about 285 eV are not limited to Rh, Ir and Pt. Other elements that have a binding energy for carbon that is less than about 285 eV are also useful as an element of a material used for in capping layers in accordance with the present disclosure. 
     In some embodiments, the capping feature includes at least one capping layer including rhodium (Rh), iridium (Ir), platinum (Pt), gold (Au) and/or zirconium (Zr) or alloys thereof. Examples of alloys of Rh, Ir, Pt, Au or Zr include RuZr, IrZr, RhZr, HfZr, NbZr and ZnZr. Additional examples of alloys of Rh, Ir, Pt, Au or Zr in accordance with the present disclosure include RuRh, RuIr, RuPt, PtIr, RuIrPt, NbIr, NbPt, NbRh, RhN, IrN, RuRhN, RuIrN, RuPtN, PtIrN, RuIrPtN, NbIrN, NbPtN and NbRhN. For example, a capping layer in accordance with the present disclosure can include an alloy such as RuRh (5 at %˜100 at % Rh), RuIr (5 at %˜100 at % Ir), RuPt (5 at %˜100 at % Pt), PtIr (5 at %˜100 at % Ir), RuIrPt (5 at %˜100 at % Ir), RuIrPt (5 at %˜100 at % Pt), NbIr (5 at %˜100 at % Ir), NbPt (5 at %˜100 at % Pt), NbRh (5 at %˜100 at % Rh), RhN (5 at %˜100 at % Rh), IrN, (5 at %˜100 at % Ir), RuRhN (5 at %˜100 at % Rh), RuRhN (5 at %˜100 at % N), RuIrN (5 at %˜100 at % Ir), RuIrN (5 at %˜100 at % N), RuPtN (5 at %˜100 at % Pt), RuPtN (5 at %˜100 at % N), PtIrN (5 at %˜100 at % Ir), PtIrN (5 at %˜100 at % N), RuIrPtN (5 at %˜100 at % Ir), RuIrPtN (5 at %˜100 at % Pt), RuIrPtN (5 at %˜100 at % N), NbIrN (5 at %˜100 at % Ir), NbPtN (5 at %˜100 at % Pt) or NbRhN (5 at %˜100 at % Rh). In other embodiments, a capping layer in accordance with the present disclosure can include an alloy that contains Hf, Nb or N. In other embodiments, a capping layer in accordance with the present disclosure can include an alloy that contains Ag or Cu. In other embodiments, a capping layer in accordance with the present disclosure can include an alloy that contains Pd. 
     In some embodiments, the single or multilayered capping feature includes at least one layer that includes a material containing an element having an index of refraction of greater than 0.87 and less than 0.97. Examples of materials having an index of refraction of greater than 0.87 and less than 0.97 include, but are not limited to the materials described above. 
       FIG.  1    is a cross-sectional view of an EUV mask  100 , in accordance with a first embodiment of the present disclosure. Referring to  FIG.  1   , the EUV mask  100  includes a substrate  102 , a reflective multilayer stack  110  over a front surface of the substrate  102 , a capping feature  125  over the reflective multilayer stack  110  that includes a first patterned capping layer  120 P and a patterned absorber layer  140 P over the capping feature  125 . The EUV mask  100  further includes a conductive layer  104  over a back surface of the substrate  102  opposite the front surface. 
     The patterned absorber layer  140 P contains a pattern of openings  152  that correspond to patterns of conductive or non-conductive features to be formed on or in a semiconductor wafer. The pattern of openings  152  is located in a pattern region  100 A of the EUV mask  100 , exposing a surface of the first capping layer  120 P. The pattern region  100 A is surrounded by a peripheral region  100 B of the EUV mask  100 . The peripheral region  100 B corresponds to a non-patterned region of the EUV mask  100  that is not used in an exposing process during IC fabrication. In some embodiments, the pattern region  100 A of EUV mask  100  is located at a central region of the substrate  102 , and the peripheral region  100 B is located at an edge portion of the substrate  102 . The pattern region  100 A is separated from the peripheral region  100 B by trenches  154 . The trenches  154  extend through the patterned absorber layer  140 P, the first capping layer  120 P, and the reflective multilayer stack  110 , exposing the front surface of the substrate  102 . 
     In accordance with some embodiments of the present disclosure, patterned absorber layer  140 P is a layer of absorber material that is an alloy of a transition metal, e.g., tantalum (Ta), ruthenium (Ru), chromium (Cr), platinum (Pt), gold (Au), iridium (Ir), titanium (Ti), niobium (Nb), rhodium (Rh), molybdenum (Mo), tungsten (W), or palladium (Pd), and at least one alloying element selected from ruthenium (Ru), chromium (Cr), tantalum (Ta), platinum (Pt), palladium (Pd), tungsten (W), gold (Au), iridium (Ir), titanium (Ti), niobium (Nb), rhodium (Rh), molybdenum (Mo), hafnium (Hf), boron (B), nitrogen (N), oxygen (O), silicon (Si), zirconium (Zr), or vanadium (V). 
       FIG.  2    is a flowchart of a method  200  for fabricating an EUV mask in accordance with an embodiment of the present disclosure, for example, EUV mask  100 .  FIG.  3 A  through  FIG.  3 L  are cross-sectional views of the EUV mask  100  at various stages of the fabrication process, in accordance with some embodiments. The method  200  is discussed in detail below, with reference to the EUV mask  100 . In some embodiments, additional operations are performed before, during, and/or after the method  200 , or some of the operations described are replaced and/or eliminated. In some embodiments, some of the features described below are replaced or eliminated. One of ordinary skill in the art would understand that although some embodiments are discussed with operations performed in a particular order, these operations may be performed in another logical order. 
     Referring to  FIGS.  2  and  3 A , the method  200  includes operation  202 , in which a reflective multilayer stack  110  is formed over a substrate  102 , in accordance with some embodiments.  FIG.  3 A  is a cross-sectional view of an initial structure of an EUV mask  100  after forming the reflective multilayer stack  110  over the substrate  102 , in accordance with some embodiments. 
     Referring to  FIG.  3 A , the initial structure of the EUV mask  100  includes a substrate  102  made of glass, silicon, quartz, or other low thermal expansion materials. The low thermal expansion material helps to minimize image distortion due to mask heating during use of the EUV mask  100 . In some embodiments, the substrate  102  includes fused silica, fused quartz, calcium fluoride, silicon carbide, black diamond, or titanium oxide doped silicon oxide (SiO 2 /TiO 2 ). In some embodiments, the substrate  102  has a thickness ranging from about 1 mm to about 7 mm. If the thickness of the substrate  102  is too small, a risk of breakage or warping of the EUV mask  100  increases, in some instances. On the other hand, if the thickness of the substrate is too great, a weight and cost of the EUV mask  100  is needlessly increased, in some instances. 
     In some embodiments, a conductive layer  104  is disposed on a back surface of the substrate  102 . In some embodiments, the conductive layer  104  is in direct contact with the back surface of the substrate  102 . The conductive layer  104  is adapted to provide for electrostatically coupling of the EUV mask  100  to an electrostatic mask chuck (not shown) during fabrication and use of the EUV mask  100 . In some embodiments, the conductive layer  104  includes chromium nitride (CrN) or tantalum boride (TaB). In some embodiments, the conductive layer  104  is formed by a deposition process such as, for example, chemical vapor deposition (CVD), plasma-enhanced chemical vapor deposition (PECVD), or physical vapor deposition (PVD). The thickness of the conductive layer  104  is controlled such that the conductive layer  104  is optically transparent. 
     The reflective multilayer stack  110  is disposed over a front surface of the substrate  102  opposite the back surface. In some embodiments, the reflective multilayer stack  110  is in direct contact with the front surface of the substrate  102 . The reflective multilayer stack  110  provides a high reflectivity to the EUV light. In some embodiments, the reflective multilayer stack  110  is configured to achieve about 60% to about 75% reflectivity at the peak EUV illumination wavelength, e.g., the EUV illumination at 13.5 nm. Specifically, when the EUV light is applied at an incident angle of 6° to the surface of the reflective multilayer stack  110 , the maximum reflectivity of light in the vicinity of a wavelength of 13.5 nm is about 60%, about 62%, about 65%, about 68%, about 70%, about 72%, or about 75%. 
     In some embodiments, the reflective multilayer stack  110  includes alternatively stacked layers of a high refractive index material and a low refractive index material. A material having a high refractive index has a tendency to scatter EUV light on the one hand, and a material having a low refractive index has a tendency to transmit EUV light on the other hand. Pairing these two type materials together provides a resonant reflectivity. In some embodiments, the reflective multilayer stack  110  includes alternatively stacked layers of molybdenum (Mo) and silicon (Si). In some embodiments, the reflective multilayer stack  110  includes alternatively stacked Mo and Si layers with Si being in the topmost layer. In some embodiments, a molybdenum layer is in direct contact with the front surface of the substrate  102 . In some other embodiments, a silicon layer is in direct contact with the front surface of the substrate  102 . Alternatively, the reflective multilayer stack  110  includes alternatively stacked layers of Mo and beryllium (Be). 
     The thickness of each layer in the reflective multilayer stack  110  depends on the EUV wavelength and the incident angle of the EUV light. The thickness of alternating layers in the reflective multilayer stack  110  is tuned to maximize the constructive interference of the EUV light reflected at each interface and to minimize the overall absorption of the EUV light. In some embodiments, the reflective multilayer stack  110  includes from 30 to 60 pairs of alternating layers of Mo and Si. Each Mo/Si pair has a thickness ranging from about 2 nm to about 7 nm, with a total thickness ranging from about 100 nm to about 300 nm. In some embodiments, the thickness of the alternating layers in the reflective multilayer stack  110  are different. 
     In some embodiments, each layer in the reflective multilayer stack  110  is deposited over the substrate  102  and underlying layer using ion beam deposition (IBD) or DC magnetron sputtering. The deposition method used helps to ensure that the thickness uniformity of the reflective multilayer stack  110  is better than about 0.85 across the substrate  102 . For example, to form a Mo/Si reflective multilayer stack  110 , a Mo layer is deposited using a Mo target as the sputtering target and an argon (Ar) gas (having a gas pressure of from 1.3×10 −2  Pa to 2.7×10 −2  Pa) as the sputtering gas with an ion acceleration voltage of from 300 V to 1,500 V at a deposition rate of from 0.03 to 0.30 nm/sec and then a Si layer is deposited using a Si target as the sputtering target and an Ar gas (having a gas pressure of 1.3×10 −2  Pa to 2.7×10 −2  Pa) as the sputtering gas, with an ion acceleration voltage of from 300 V to 1,500 V at a deposition rate of from 0.03 to 0.30 nm/sec. By stacking Si layers and Mo layers in 40 to 50 cycles, each of the cycles comprising the above steps, the Mo/Si reflective multilayer stack is deposited. 
     Referring to  FIGS.  2  and  3 B , the method  200  proceeds to operation  204 , in which a first capping layer  120  is deposited over the reflective multilayer stack  110 , in accordance with some embodiments.  FIG.  3 B  is a cross-sectional view of the structure of  FIG.  3 A  after depositing the first capping layer  120  over the reflective multilayer stack  110 , in accordance with some embodiments. 
     Referring to  FIG.  3 B , the first capping layer  120  (of the capping feature  125  in  FIGS.  1  and  3 C ) is disposed over the topmost surface of the reflective multilayer stack  110 . As described herein, the first capping layer  120  includes a material in an amorphous state. In some embodiments, the material has a with low solid carbon solubility which serves to prevent or reduce the amount of carbon contamination of the mask. 
     Materials in an amorphous state include materials that are solid and lack the long-range order that is characteristic of a crystal. Materials in an amorphous state are sometimes referred to as being in a glass or glassy state. A “glassy solid” or “amorphous solid” is considered to be the overarching concept, with glass being a special case, where glass is an amorphous solid stabilized below its glass transition temperature. Polymers are often amorphous. Other types of amorphous solids include gels, thin films and nanostructured materials. Materials in an amorphous state have an internal structure made of interconnected structural blocks. These blocks can be similar to the basic structural units found in the corresponding crystalline phase of the same material. Nano-crystalline materials are examples of materials in an amorphous state and in the present disclosure are characterized by a grain size of less than 5 nm, less than 4 nm, less than 3 nm or less than 2 nm. Materials that are in an amorphous state and useful as a material of a capping layer in accordance with the present disclosure include the materials for a capping layer described above. 
     In some embodiments, the first capping layer  120  includes a material that is less susceptible to carbon contamination compared to conventional materials used as capping layers. Such materials have been described above. As described above, such materials include elements that have a low effective solid carbon solubility in the element of the material at 1000° C., e.g., an effective solid carbon solubility of less than 1.6 atomic % at 1000° C. Other examples of materials including elements having a low atomic percent effective solid carbon solubility at 1000° C. include, but are not limited to materials including elements that have an effective solid carbon solubility at 1000° C. that is less than about 1.3 atomic percent. In some embodiments, materials of a capping layer include elements that do not have an effective solid carbon solubility that is less than about 1.6 atomic percent or less than about 1.3 atomic percent, yet still provide a resistance to carbon buildup or contamination on the surface of the material. In some embodiments in accordance with  FIG.  1   , the material of the first capping layer  120  includes an element that has an EUV extinction coefficient for EUV radiation having a wavelength of 13.5 nm between 0 and 0.1, 0 and 0.08, 0 and 0.06, 0 and 0.04 or between 0 and 0.02. Materials that include elements having an EUV extinction coefficient for EUV radiation having a wavelength of 13.5 nm with the foregoing ranges do not reduce the transmission of EUV energy by an amount that requires that the level of incident EUV energy be increased by an undesirable amount. The materials for use in capping layers of the capping features in accordance with the present embodiments, should not absorb so much EUV energy that the amount of EUV energy incident on the EUV mask needs to be increased or the exposure time needs to be increased an undesirable amount. In addition, the materials for use in capping layers of the capping features in accordance with the present embodiment exhibit good adhesion to materials upon which the capping layers are deposited or with materials that are deposited onto the capping layer. In accordance with embodiments of the present disclosure, carbides of the elements described above are undesirable for use as a material for first capping layer  120  because carbon atoms from the carbide can diffuse into a lower layer during heat treatment thereof. In some embodiments the multilayered capping feature  125  includes at least one layer  120  that includes a material containing an element having an index of refraction for EUV radiation having a wavelength of 13.5 nm of less than 0.97. In some embodiments the multilayered capping feature  125  includes at least one layer  120  that includes a material containing an element having an index of refraction for EUV radiation having a wavelength of 13.5 nm that is greater than 0.87. Examples of materials including elements having an index of refraction for EUV radiation having a wavelength of 13.5 nm of less than 0.97 or greater than 0.87 include, but are not limited to the materials described above. In some embodiments, the first capping layer  120  has a thickness ranging from about 0.5 to 5 nm. First capping layer  120  having a thickness ranging from about 0.5 to 5 nm has a thickness that is sufficient to prevent or reduce carbon contamination while not being so thick as to reduce EUV transmission by an undesired amount. Embodiments in accordance with the present disclosure are not limited to EUV masks that include a first capping layer  120  that has a thickness from 0.5 to about 5 nm. Embodiments in accordance with the present disclosure include EUV masks that include a first capping layer  120  that has a thickness less than 0.5 nm and EUV masks that have a first capping layer 120 that has a thickness greater than about 5 nm. 
     In some embodiments, the first capping layer  120  is formed using a deposition process such as, for example, IBD, chemical vapor deposition (CVD), physical vapor deposition (PVD), atomic layer deposition (ALD), thermal ALD, PE-ALD, PECVD, E-beam evaporation, thermal evaporation, ion beam induced deposition, sputtering, electrodeposition, or electroless deposition. 
     Referring to  FIGS.  2  and  3 C , the method  200  proceeds to operation  208 , in which an absorber layer  140  is deposited over the first capping layer  120 , in accordance with various embodiments.  FIG.  3 C  is a cross-sectional view of the structure of  FIG.  3 B  after depositing the absorber layer  140  over the first capping layer  120 , in accordance with some embodiments. 
     Referring to  FIG.  3 C , the absorber layer  140  is disposed in direct contact with the first capping layer  120 . The absorber layer  140  is usable to absorb radiation in the EUV wavelength projected onto the EUV mask  100 . 
     The absorber layer  140  includes an absorber material having a high extinction coefficient κ and a low refractive index n for EUV wavelengths. In some embodiments, the absorber layer  140  includes an absorber material having a high extinction coefficient and a low refractive index at 13.5 nm wavelength. In other embodiments, the absorber layer includes an absorber material having a low extinction coefficient and a high index of refraction for EUV radiation having a wavelength of 13.5 nm. In accordance with some embodiments of the present disclosure, the index of refraction and the extinction coefficient of the material of the absorber layer  140  are in relation to light having a wavelength of about 13.5 nm. In accordance with some embodiments, the thickness of absorber layer  140  is less than about 80 nm. In accordance with other embodiments, the thickness of absorber layer  140  is less than about 60 nm. Other embodiments utilize an absorber layer  140  that is less than about 50 nm. 
     In some embodiments, the absorber material is in a polycrystalline state characterized by grains, grain boundaries and different phases of formation. In other embodiments, the absorber material is in an amorphous state, e.g., characterized by grains on the order of less than 5 nanometers, less than 3 nanometers, less than 2 nanometers or no grain boundaries, and a single phase. In accordance with some embodiments of the present disclosure, the absorber material includes interstitial elements selected from nitrogen (N), oxygen (O), boron (B), carbon (C), or combinations thereof. As used herein, interstitial elements refer to elements which are located at interstices between materials comprising a main alloy and an alloying element of absorber materials formed in accordance with the present disclosure. 
     The absorber layer  140  is formed by deposition techniques such as PVD, CVD, ALD, RF magnetron sputtering, DC magnetron sputtering, or IBD. The deposition process can be carried out in the presence of elements described as interstitial elements, such as B or N. Carrying out the deposition in the presence of the interstitial elements results in the interstitial elements being incorporated into the material of the absorber layer  140 . 
     In accordance with embodiments of the present disclosure, multiple combinations of different families of alloy materials are useful as absorber materials. Each of the different families of different alloys includes a main alloy element selected from a transition metal and at least one alloying element. In accordance with some embodiments, the main alloy element comprises up to 90 atomic percent of the alloy used as an absorber material. In some embodiments, the main alloy element comprises more than 50 atomic percent of the alloy used as an absorber material. In some embodiments, the main alloy element comprises about 50 to 90 atomic percent of the alloy used as an absorber material. 
     In accordance with some embodiments, the main alloy element is a transition metal selected from ruthenium (Ru), chromium (Cr), tantalum (Ta), platinum (Pt), gold (Au), iridium (Ir), titanium (Ti), niobium (Nb), rhodium (Rh), molybdenum (Mo), tungsten (W), and palladium (Pd). In accordance with some embodiments, the at least one alloying element is a transition metal, metalloid, or reactive nonmetal. Examples of the at least one alloying element that is a transition metal include ruthenium (Ru), chromium (Cr), tantalum (Ta), platinum (Pt), palladium (Pd), tungsten (W), gold (Au), iridium (Ir), titanium (Ti), niobium (Nb), rhodium (Rh), molybdenum (Mo), hafnium (Hf), zirconium (Zr), and vanadium (V). Examples of the at least one alloying element that is a metalloid include boron (B) and silicon (Si). Examples of the at least one alloying element that is a reactive nonmetal includes nitrogen (N) or oxygen (O). 
     Different materials may be used to etch the different absorber materials of the present disclosure and different materials may be used as a hard mask layer with the different absorber materials. For example, in some embodiments, the absorber layer  140  is dry etched with a gas that contains chlorine, such as Cl 2  or BCl 3 , or with a gas that contains fluorine, such as NF 3 . Ar may be used as a carrier gas. In some embodiments, oxygen (O 2 ) may also be included as the carrier gas. For example, a chlorine-based etchant, chlorine-based plus oxygen etchant, or a mixture of a chlorine-based and fluorine-based (e.g., carbon tetrafluoride and carbon tetrachloride) etchant will etch the alloys that include a main alloy element comprising ruthenium (Ru), chromium (Cr), tantalum (Ta), platinum (Pt) or gold (Au), and at least one alloying element selected from ruthenium (Ru), chromium (Cr), tantalum (Ta), platinum (Pt), palladium (Pd), tungsten (W), gold (Au), iridium (Ir), niobium (Nb), rhodium (Rh), molybdenum (Mo), hafnium (Hf) or vanadium (V). In with some embodiments, a fluorine-based etchant is suitable to etch the alloys that include a main alloy element comprising iridium (Ir), titanium (Ti), niobium (Ni) or rhodium (Rh) and at least one alloying element selected from boron (B), nitrogen (N), oxygen (O), silicon (Si), tantalum (Ta), zirconium (Zr), niobium (Ni), molybdenum (Mo), rhodium (Rh), titanium (Ti) or ruthenium (Ru). In some embodiments, a fluorine-based or a fluorine-based plus oxygen etchant is suitable to etch the alloys that include a main alloy element comprising molybdenum (Mo), tungsten (W) or palladium (Pd) and at least one alloying element selected from ruthenium (Ru), palladium (Pd), tungsten (W), iridium (Ir), titanium (Ti), niobium (Nb), rhodium (Rh), molybdenum (Mo), silicon (Si) or zirconium (Zr). 
     In accordance with some embodiments, SiN, TaBO, TaO, SiO, SiON, and SiOB are examples of materials useful as hard mask layer  160  for absorber layer  140  utilizing alloys that include a main alloy element comprising ruthenium (Ru), chromium (Cr), tantalum (Ta), platinum (Pt) or gold (Au), and at least one alloying element selected from ruthenium (Ru), chromium (Cr), tantalum (Ta), platinum (Pt), palladium (Pd), tungsten (W), gold (Au), iridium (Ir), niobium (Nb), rhodium (Rh), molybdenum (Mo), hafnium (Hf) or vanadium (V). CrO and CrON are examples of materials useful for hard mask layer  160  for an absorber layer  140  that utilizes alloys that include a main alloy element comprising iridium (Ir), titanium (Ti), niobium (Ni) or rhodium (Rh) and at least one alloying element selected from boron (B), nitrogen (N), oxygen (O), silicon (Si), tantalum (Ta), zirconium (Zr), niobium (Ni), molybdenum (Mo), rhodium (Rh), titanium (Ti) or ruthenium (Ru). SiN, TaBO, TaO, CrO, and CrON are examples of materials useful for hard mask layer  160  for an absorber layer  140  that utilizes alloys that include a main alloy element comprising molybdenum (Mo), tungsten (W) or palladium (Pd) and at least one alloying element selected from ruthenium (Ru), palladium (Pd), tungsten (W), iridium (Ir), titanium (Ti), niobium (Nb), rhodium (Rh), molybdenum (Mo), silicon (Si) or zirconium (Zr). In other embodiments, there may be a buffer layer (not shown) similar in composition to the hard mask layer between the capping feature  125  and the layer  140  of absorber material. In some embodiments, the material of the hard mask layer  160  is the same or different from the material of the buffer layer. Embodiments in accordance with the present invention are not limited to the foregoing types of materials for hard mask layer  160  or the buffer layer. 
     In some embodiments, the absorber layer  140  is deposited as an amorphous layer. By maintaining an amorphous phase, the overall roughness of the absorber layer  140  is improved. The thickness of the absorber layer  140  is controlled to provide between 95% and 99.5% absorption of the EUV light at 13.5 nm. In some embodiments, the absorber layer  140  may have a thickness ranging from about 30 to 70 nm. Embodiments in accordance with the present disclosure include absorber layers having a thickness less than 30 nm and a thickness greater than 70 nm. If the thickness of the absorber layer  140  is too small, the absorber layer  140  is not able to absorb a sufficient amount of the EUV light to generate contrast between the reflective areas and non-reflective areas. On the other hand, if the thickness of the absorber layer  140  is too great, the precision of a pattern to be formed in the absorber layer  140  tends to be low. 
     Referring to  FIGS.  2  and  3 D , the method  200  proceeds to operation  210 , in which a resist stack including a hard mask layer  160  and a photoresist layer  170  are deposited over the absorber layer  140 , in accordance with some embodiments.  FIG.  3 E  is a cross-sectional view of the structure of  FIG.  3 C  after sequentially depositing the hard mask layer  160  and the photoresist layer  170  over the absorber layer  140 , in accordance with some embodiments. 
     Referring to  FIG.  3 D , the hard mask layer  160  is disposed over the absorber layer  140 . In some embodiments, the hard mask layer  160  is in direct contact with the absorber layer  140 . In some embodiments, the hard mask layer  160  includes a dielectric oxide such as silicon dioxide or a dielectric nitride such as silicon nitride. In some embodiments, the hard mask layer  160  is formed using a deposition process such as, for example, CVD, PECVD, or PVD. In some embodiments, the hard mask layer  160  has a thickness ranging from about 2 to 10 nm. Embodiments in accordance with the present disclosure are not limited to hard mask layer  160  having a thickness ranging from about 2 to 10 nm. 
     The photoresist layer  170  is disposed over the hard mask layer  160 . The photoresist layer  170  includes a photosensitive material operable to be patterned by radiation. In some embodiments, the photoresist layer  170  includes a positive-tone photoresist material, a negative-tone photoresist material or a hybrid-tone photoresist material. In some embodiments, the photoresist layer  170  is applied to the surface of the hard mask layer  160 , for example, by spin coating. 
     Referring to  FIGS.  2  and  3 E , the method  200  proceeds to operation  212 , in which the photoresist layer  170  is lithographically patterned to form a patterned photoresist layer  170 P, in accordance with some embodiments.  FIG.  3 F  is a cross-sectional view of the structure of  FIG.  3 D  after lithographically patterning the photoresist layer  170  to form the patterned photoresist layer  170 P, in accordance with some embodiments. 
     Referring to  FIG.  3 E , the photoresist layer  170  is patterned by first subjecting the photoresist layer  170  to a pattern of irradiation. Next, the exposed or unexposed portions of the photoresist layer  170  are removed, depending on whether a positive-tone or negative-tone resist is used in the photoresist layer  170 , with a resist developer, thereby forming the patterned photoresist layer  170 P having a pattern of openings  172  formed therein. The openings  172  expose portions of the hard mask layer  160 . The openings  172  are located in the pattern region  100 A and correspond to locations where the pattern of openings  152  are present in the EUV mask  100  ( FIG.  1   ). 
     Referring to  FIGS.  2  and  3 F , the method  200  proceeds to operation  214 , in which the hard mask layer  160  is etched using the patterned photoresist layer  170 P as an etch mask to form a patterned hard mask layer  160 P, in accordance with some embodiments.  FIG.  3 F  is a cross-sectional view of the structure of  FIG.  3 E  after etching the hard mask layer  160  to form the patterned hard mask layer  160 P, in accordance with some embodiments. 
     Referring to  FIG.  3 F , portions of the hard mask layer  160  that are exposed by the openings  172  are etched to form openings  162  extending through the hard mask layer  160 . The openings  162  expose portions of the underlying absorber layer  140 . In some embodiments, the hard mask layer  160  is etched using an anisotropic etch using fluorine containing or chlorine containing gases such as CF 4 , SF 6  or Cl 2 . In some embodiments, the anisotropic etch is a dry etch such as, for example, reactive ion etch (RIE), a wet etch, or a combination thereof. The etch removes the material providing the hard mask layer  160  selective to the material providing the absorber layer  140 . The remaining portions of the hard mask layer  160  constitute the patterned hard mask layer  160 P. If not completely consumed during the etching of the hard mask layer  160 , after etching the hard mask layer  160 , the patterned photoresist layer  170 P is removed from the surfaces of the patterned hard mask layer  160 P, for example, using wet stripping or plasma ashing followed by a wet cleaning. 
     Referring to  FIGS.  2  and  3 G , the method  200  proceeds to operation  216 , in which the absorber layer  140  is etched using the patterned hard mask layer  160 P as an etch mask to form a patterned absorber layer  140 P, in accordance with some embodiments.  FIG.  3 G  is a cross-sectional view of the structure of  FIG.  3 F  after etching the absorber layer  140  to form the patterned absorber layer  140 P, in accordance with some embodiments. 
     Referring to  FIG.  3 G , portions of the absorber layer  140  that are exposed by the openings  162  are etched to form openings  142  extending through the absorber layer  140 . The openings  142  expose portions of the first capping layer  120 . In some embodiments, the absorber layer  140  is etched using an anisotropic etching process. In some embodiments, the anisotropic etch is a dry etch such as, for example, RIE, a wet etch, or a combination thereof that removes the material providing the absorber layer  140  selective to the material providing the underlying first capping layer  120 . For example, in some embodiments, the absorber layer  140  is dry etched with a gas that contains chlorine, such as Cl 2  or BCl 3 , or with a gas that contains fluorine, such as CF 4 , SF 3  or NF 3 . Ar may be used as a carrier gas. In some embodiments, oxygen (O 2 ) may also be included as the carrier gas. The etch rate and the etch selectivity depend on the etchant gas, etchant flow rate, power, pressure, and substrate temperature. After etching, the remaining portions of the absorber layer  140  constitute the patterned absorber layer  140 P. In accordance with embodiments of the present disclosure, when absorber layer  140  includes multiple layers of absorber material, when the individual layers of absorber material have differential etching properties, the individual layers of absorber material may be etched individually using different etchants. When the individual layers of absorber material do not have differential etching properties, the individual layers of absorber for material may be etched simultaneously. 
     In some embodiments, etching of absorber layer  140  also removes a portion of the first capping layer  120 . In other embodiments, etching of absorber layer  140  does not remove any of the first capping layer  120 . The openings  142  expose portions of the underlying first capping layer  120  at the bottom of trenches formed in the absorber layer  140 . After etching the absorber layer  140 , the patterned hard mask layer  160 P is removed from the surfaces of the patterned absorber layer  140 P, for example, using oxygen plasma or a wet etch. 
     The openings  142  in the patterned absorber layer  140 P define the pattern of openings  152  in the EUV mask  100 . In accordance with embodiments of the present disclosure, the portions of patterned first capping layer  120  that are exposed through patterned absorber layer  140  exhibit a reduced susceptibility to deposition or contamination with carbon. In addition, owing to the amorphous structure of the material of first capping layer  120 , first capping layer  120  resists weakening by etchants, cleaners or processes using such etchants or cleaners that are carried out during the manufacture of the EUV mask  100 . Such resistance to weakening by etchants, cleaners or processes using such etchants or cleaners not only increases the lifetime of the mask, but also increases the ability of the first capping layer  120  to resist infiltration by oxidants which can react with the underlying reflective multilayer stack to form unwanted oxides. 
     Referring to  FIGS.  2  and  3 H , the method  200  proceeds to operation  220 , in which a patterned photoresist layer  180 P comprising a pattern of openings  182  is formed over the patterned absorber layer  140 P and the first capping layer  120 , in accordance with some embodiments.  FIG.  3 H  is a cross-sectional view of the structure of  FIG.  3 G  after forming the patterned photoresist layer  180 P comprising openings  182  over the patterned absorber layer  140 P and the first capping layer  120 , in accordance with some embodiments. 
     Referring to  FIG.  3 H , the openings  182  expose portions of the patterned absorber layer  140 P at the periphery of the patterned absorber layer  140 P. The openings  182  correspond to the trenches  154  in the peripheral region  100 B of the EUV mask  100  that are to be formed. To form the patterned photoresist layer  180 P, a photoresist layer (not shown) is applied over the first capping layer  120  and the patterned absorber layer  140 P. The photoresist layer fills the openings  142  in the patterned absorber layer  140 P, respectively. In some embodiments, the photoresist layer includes a positive-tone photoresist material, a negative-tone photoresist material, or a hybrid-tone photoresist material. In some embodiments, the photoresist layer includes a same material as the photoresist layer  170  described above in  FIG.  3 D . In some embodiments, the photoresist layer includes a different material from the photoresist layer  170 . In some embodiments, the photoresist layer is formed, for example, by spin coating. A photoresist layer is subsequently patterned by exposing the photoresist layer to a pattern of radiation, and removing the exposed or unexposed portions of the photoresist layer using a resist developer depending on whether a positive or negative resist is used. The remaining portions of the photoresist layer constitute the patterned photoresist layer  180 P. 
     Referring to  FIGS.  2  and  3 I , the method  200  proceeds to operation  222 , in which the patterned absorber layer  140 P, the first capping layer  120 , and the reflective multilayer stack  110  are etched using the patterned photoresist layer  180 P as an etch mask to form trenches  154  in the peripheral region  100 B of the substrate  102 , in accordance with some embodiments.  FIG.  3 I  is a cross-sectional view of the structure of  FIG.  3 H  after etching the patterned absorber layer  140 P, the first capping layer  120 , and the reflective multilayer stack  110 , to form the trenches  154  in the peripheral region  100 B of the substrate  102 , in accordance with some embodiments. 
     Referring to  FIG.  3 I , the trenches  154  extend through the patterned absorber layer  140 P, the first capping layer  120 , and the reflective multilayer stack  110  to expose the surface of the substrate  102 . The trenches  154  surround the pattern region  100 A of the EUV mask  100 , separating the pattern region  100 A from the peripheral region  100 B. 
     In some embodiments, the patterned absorber layer  140 P, the first capping layer  120 , and the reflective multilayer stack  110  are etched using a single anisotropic etching process. The anisotropic etch can be a dry etch such as, for example, RIE, a wet etch, or a combination thereof that removes materials of the respective patterned absorber layer  140 P, the first capping layer  120 , and the reflective multilayer stack  110 , selective to the material providing the substrate  102 . In some embodiments, the patterned absorber layer  140 P, the first capping layer  120 , and the reflective multilayer stack  110  are etched using multiple distinct anisotropic etching processes. Each anisotropic etch can be a dry etch such as, for example, RIE, a wet etch, or a combination thereof. 
     Referring to  FIGS.  2  and  3 J , the method  200  proceeds to operation  224 , in which the patterned photoresist layer  180 P is removed, in accordance with some embodiments.  FIG.  3 J  is a cross-sectional view of the structure of  FIG.  3 I  after removing the patterned photoresist layer  180 P, in accordance with some embodiments. 
     Referring to  FIG.  3 J , the patterned photoresist layer  180 P is removed from the pattern region  100 A and the peripheral region  100 B of the substrate  102 , for example, by wet stripping or plasma ashing. The removal of the patterned photoresist layer  180 P from the openings  142  in the patterned absorber layer  140 P re-exposes the surfaces of the first capping layer  120  in the pattern region  100 A. 
     An EUV mask  100  is thus formed. The EUV mask  100  includes a substrate  102 , a reflective multilayer stack  110  over a front surface of the substrate  102 , a first capping layer  120 P over the reflective multilayer stack  110  and a patterned absorber layer  140 P over the first capping layer  120 . The EUV mask  100  further includes a conductive layer  104  over a back surface of the substrate  102  opposite the front surface. In accordance with embodiments of the present disclosure, the first capping layer  120  protects the EUV mask from carbon contamination by reducing or preventing deposition, formation or absorption of carbon onto exposed surfaces of the first capping layer  120 . As a result, the detrimental effects (e.g., need for increased EUV energy or negative effects on CDU) from carbon formation on or carbon contamination of an EUV mask are reduced or prevented and a pattern on the EUV mask  100  can be projected precisely onto a silicon wafer. Owing to the amorphous structure of the material of first capping layer  120 , first capping layer  120  resists weakening by etchants, cleaners or processes using such etchants or cleaners that are carried out during the manufacture of the EUV mask  100 . Such resistance to weakening by actions, cleaners or processes using such actions or cleaners increases the ability of the first capping layer  120  resist infiltration by oxidants which can react with the underlying reflective multilayer stack to form unwanted oxides. 
     After removal of the patterned photoresist layer  180 P, the EUV mask  100  is cleaned to remove any contaminants therefrom. In some embodiments, the EUV mask  100  is cleaned by submerging the EUV mask  100  into an ammonium hydroxide (NH 4 OH) solution. In some embodiments, the EUV mask  100  is cleaned by submerging the EUV mask  100  into a diluted hydrofluoric acid (HF) solution. 
     The EUV mask  100  is subsequently radiated with, for example, a UV light with a wavelength of 193 nm, for inspection of any defects in the patterned region  100 A. The foreign matters may be detected from diffusely reflected light. If defects are detected, the EUV mask  100  is further cleaned using suitable cleaning processes. 
       FIG.  4    is a cross-sectional view of an EUV mask  400 , in accordance with a second embodiment of the present disclosure. EUV mask  400  is similar in some regards to EUV mask  100  described above with respect to  FIGS.  1 - 3   . EUV mask  400  differs from EUV mask  100  in that EUV mask  400  includes a multilayer capping feature that includes two or more capping layers as described below in more detail. Structures and features which are common between EUV mask  400  and EUV mask  100  are identified by the same reference numerals and the description above applies to those features. Referring to  FIG.  4   , the EUV mask  400  includes a substrate  102 , a reflective multilayer stack  110  over a front surface of the substrate  102 , a patterned first capping layer  120 P′ over the reflective multilayer stack  110 , a patterned second capping layer  130 P′ and a patterned absorber layer  140 P over the second patterned capping layer  130 P′. The composition of patterned first capping  120 P′ of EUV mask  400  differs from the composition of patterned second capping layer  130 P′. In accordance with embodiments of the present disclosure relative to  FIG.  4   , the description above regarding the composition or material of the first capping layer  120  applies to the patterned first capping layer  120 P′ and the patterned second capping layer  130 P′. In other words, the materials of first capping layer  120 P′ and second capping layer  130 P′ can be selected from the materials described above for use in the first capping layer  120  of the embodiments of  FIGS.  1 - 3   . The EUV mask  400  further includes a conductive layer  104  over a back surface of the substrate  102  opposite the front surface. While the embodiment of  FIG.  4    is illustrated and described with reference to a multilayered capping feature  125  that includes two capping layers, embodiments of the present disclosure include EUV masks that include a multilayered capping feature including more than two capping layers, e.g., three, four or more capping layers. 
       FIG.  5    is a flowchart of a method  500  for fabricating an EUV mask, for example, EUV mask  400 , in accordance with some embodiments.  FIG.  6 A  through  FIG.  6 L  are cross-sectional views of the EUV mask  400  at various stages of the fabrication process, in accordance with some embodiments. The method  500  is discussed in detail below, with reference to the EUV mask  400 . In some embodiments, additional operations are performed before, during, and/or after the method  500 , or some of the operations described are replaced and/or eliminated. In some embodiments, some of the features described below are replaced or eliminated. One of ordinary skill in the art would understand that although some embodiments are discussed with operations performed in a particular order, these operations may be performed in another logical order. 
     Referring to  FIGS.  5  and  6 A , the method  500  includes operation  502 , in which a reflective multilayer stack  110  is formed over a substrate  102 , in accordance with some embodiments.  FIG.  6 A  is a cross-sectional view of an initial structure of an EUV mask  400  after forming the reflective multilayer stack  110  over the substrate  102 , in accordance with some embodiments. The materials and formation processes for the reflective multilayer stack  110  are similar to those described above in  FIG.  3 A , and hence are not described in detail herein. 
     Referring to  FIGS.  5  and  6 B , the method  500  proceeds to operation  504 , in which a first capping layer  120 ′ is deposited over the reflective multilayer stack  110 , in accordance with some embodiments.  FIG.  6 B  is a cross-sectional view of the structure of  FIG.  6 A  after depositing the first capping layer  120 ′ over the reflective multilayer stack  110 , in accordance with some embodiments. The materials and formation processes for the first capping layer  120 ′ are similar to those described above with respect to the materials and formation of first capping layer  120  in  FIG.  3 B , and hence are not described in detail herein. 
     Referring to  FIGS.  5  and  6 C , the method  500  proceeds to operation  506 , in which a second capping layer  130 ′ is deposited over the first capping layer  120 ′, in accordance with some embodiments.  FIG.  6 C  is a cross-sectional view of the structure of  FIG.  6 B  after depositing the second capping layer  130 ′ over the first capping layer  120 ′, in accordance with some embodiments. In the embodiment of  FIG.  6 C , first capping layer  120 ′ and second capping layer  130 ′ comprise the multilayered capping feature  125 ′. 
     Referring to  FIG.  6 C , the second capping layer  130 ′ is disposed on the first capping layer  120 ′. In some embodiments, the second capping layer  130 ′ possesses different etching characteristics from an absorber layer subsequently formed thereon, and thereby may serve as an etch stop layer to prevent damages to the capping layer  120 ′ during patterning of an absorber layer. Further, the second capping layer  130 ′ may also serve later as a sacrificial layer for focused ion beam repair of defects in the absorber layer. In some embodiments the second capping layer  130 ′ is selected from one of the materials described above as being useful as a material for first capping layer  120  in the embodiments of  FIGS.  1 - 3   . For example, the material of the second capping layer  130 ′ includes an element having an extinction coefficient κ ranging between 0 and 0.1 and a refractive index n between 0.87 and 0.97 relative to EUV wavelengths. With a material having an extinction coefficient κ and a refractive index n in these ranges, the material of the second capping layer  130 ′ is able to transmit a desired level of incident EUV light and not affect the phase of the incident EUV light in an undesirable way. 
     In some embodiments, the second capping layer  130 ′ is deposited by thermal ALD, PE-ALD, CVD, PECVD, PVD E-beam evaporation, thermal evaporation, ion beam induced deposition, sputtering, electrodeposition, or electroless deposition. In some embodiments, the second capping layer has a thickness ranging from about 0.5 to 5 nm. Second capping layer  130 ′ having a thickness ranging from about 0.5 to 5 nm has a thickness that is sufficient to protect the underlying first capping layer  120 ′ and/or multilayer stack  110  from oxidants or chemical etchants during the mask formation process or semiconductor process using the mask. When second capping layer  130 ′ is 0.5 to 5 nm thick it is not so thick as to reduce EUV transmission by an undesired amount. Embodiments in accordance with the present disclosure are not limited to EUV masks that include a second capping layer  130 ′ that has a thickness from 0.5 to about 5 nm. Embodiments in accordance with the present disclosure include EUV masks that include a second capping layer  130 ′ that has a thickness less than 0.5 nm and EUV masks that have a second capping layer  130 ′ that has a thickness greater than about 5 nm. 
     In some embodiments, the material of the second capping layer  130 ′ includes elements that have a solid carbon solubility that is different from elements in the material of the first capping layer  120 ′. For example in some embodiments, the solid carbon solubility of the element of the material of the second capping layer  130 ′ is greater than or less than the solid carbon solubility of the material of the first capping layer  120 ′. In accordance with some embodiments of  FIG.  4   , the material of the second capping layer  130 ′ includes an element that has an EUV extinction coefficient that is less than an EUV extinction coefficient of an element in the material of another layer, e.g., first capping layer  120 ′ of the multilayered capping feature  125 ′. In other embodiments of  FIG.  4   , the element of the material of the second capping layer  130 ′ has an EUV extinction coefficient for EUV radiation having a wavelength of 13.5 nm that is greater than an EUV extinction coefficient for EUV radiation having a wavelength of 13.5 nm of an element of the material of the first capping layer  120 ′ of the multilayered capping feature  125 ′. In addition, the materials for use in second capping layer  130 ′ of the multilayered capping features in accordance with the present embodiment exhibit good adhesion to first capping layer  120 ′, as well as materials which are deposited onto the second capping layer  130 ′. 
     The formation processes for the second capping layer  130 ′ are similar to those described above with respect to the formation of first capping layer  120  in  FIG.  3 C , and hence are not described in detail here. 
     Referring to  FIGS.  5  and  6 D , the method  500  proceeds to operation  508 , in which an absorber layer  140  is deposited over the second capping layer  130 ′, in accordance with various embodiments.  FIG.  6 D  is a cross-sectional view of the structure of  FIG.  6 C  after depositing the absorber layer  140  over the second capping layer  130 ′, in accordance with some embodiments. The materials and formation processes for the absorber layer  140  are similar to those described above in  FIG.  3 C , and hence are not described in detail herein. 
     Referring to  FIGS.  5  and  6 E , the method  500  proceeds to operation  509 , in which a resist stack including a hard mask layer  160  and a photoresist layer  170  is deposited over the absorber layer  140 , in accordance with some embodiments.  FIG.  6 E  is a cross-sectional view of the structure of  FIG.  6 D  after sequentially depositing the hard mask layer  160  and the photoresist layer  170  over the absorber layer  140 , in accordance with some embodiments. Materials and formation processes for respective hard mask layer  160  and photoresist layer  170  are similar to those described in  FIG.  3 D , and hence are not described in detail herein. 
     Referring to  FIGS.  5  and  6 F , the method  500  proceeds to operation  510 , in which the photoresist layer  170  is lithographically patterned to form a patterned photoresist layer  170 P, in accordance with some embodiments.  FIG.  6 F  is a cross-sectional view of the structure of  FIG.  6 E  after lithographically patterning the photoresist layer  170  to form the patterned photoresist layer  170 P, in accordance with some embodiments. Etching processes for the photoresist layer  170  are similar to those described in  FIG.  3 E , and hence are not described in detail herein. 
     Referring to  FIGS.  5  and  6 G , the method  500  proceeds to operation  512 , in which the hard mask layer  160  is etched using the patterned photoresist layer  170 P as an etch mask to form a patterned hard mask layer  160 P, in accordance with some embodiments.  FIG.  6 G  is a cross-sectional view of the structure of  FIG.  6 F  after etching the hard mask layer  160  to form the patterned hard mask layer  160 P, in accordance with some embodiments. Etching processes for the hard mask layer  160  are similar to those described in  FIG.  3 F , and hence are not described in detail herein. 
     Referring to  FIGS.  5  and  6 H , the method  500  proceeds to operation  514 , in which the absorber layer  140  is etched using the patterned hard mask layer  160 P as an etch mask to form a patterned absorber layer  140 P, in accordance with some embodiments.  FIG.  6 H  is a cross-sectional view of the structure of  FIG.  6 G  after etching the absorber layer  140  to form the patterned absorber layer  140 P, in accordance with some embodiments. Etching processes for the absorber layer  140  are similar to those described in  FIG.  3 G , and hence are not described in detail herein. The patterned absorber layer  140 P includes a plurality of openings  142  that expose the underlying second capping layer  130 ′. After etching the absorber layer  140 , the patterned hard mask layer  160 P is removed from the surfaces of the patterned absorber layer  140 P, for example, using oxygen plasma or a wet etch. The resulting structure is illustrated in  FIG.  6 I . 
     In some embodiments in accordance with  FIGS.  4 - 6   , the steps of etching absorber layer  140  to form patterned absorber layer  140 P and/or the step of removing the photoresist layer  170  and/or patterned hard mask layer  160 P can remove portions of an upper surface of second capping layer  130 ′. Such embodiments are illustrated in  FIG.  4    by reference number  131  where a portion of patterned second capping layer  130 P′ is removed by the step of etching absorber layer  140  or the step of removing the photoresist layer  170  and/or patterned hard mask layer  160 P. In accordance with embodiments where a portion of an upper surface of patterned second capping layer  130 P′ is removed, an amount of the upper surface of patterned second capping layer  130 P′ remains, e.g., at least a few nanometers of patterned second capping layer  130 P′ remains. Examples of a few nanometers includes 1 to 2 nm. In other embodiments in accordance with  FIGS.  4 - 6   , the steps of etching absorber layer  140  to form patterned absorber layer  140 P and/or the step of removing the photoresist layer  170  and/or patterned hard mask layer  160 P do not remove portions of second capping layer  130 ′. Such embodiments are illustrated in  FIG.  4    by reference number  133 .  FIG.  6 I  illustrates an embodiment wherein none of second capping layer  130 ′ has been removed by the absorber layer, photoresist or hard mask removal steps. 
     Referring to  FIGS.  5  and  6 J , the method  500  proceeds to operation  516 , in which a patterned photoresist layer  180 P comprising a pattern of openings  182  is formed over the patterned absorber layer  140 P and second capping layer  130 ′, in accordance with some embodiments.  FIG.  6 J  is a cross-sectional view of the structure of  FIG.  6 I  after forming the patterned photoresist layer  180 P comprising openings  182  over the patterned absorber layer  140 P and second capping layer  130 ′, in accordance with some embodiments. Materials and fabrication processes for the patterned photoresist layer  180 P are similar to those described in  FIG.  3 H , and hence are not described in detail herein. 
     Referring to  FIGS.  5  and  6 K , the method  500  proceeds to operation  518 , in which the patterned absorber layer  140 P, the second capping layer  130 ′, the first capping layer  120 ′, and the reflective multilayer stack  110  are etched using the patterned photoresist layer  180 P as an etch mask to form trenches  154  in the peripheral region  100 B of the substrate  102 , in accordance with some embodiments.  FIG.  6 K  is a cross-sectional view of the structure of  FIG.  6 J  after etching the patterned absorber layer  140 P, the second capping layer  130 ′, the first capping layer  120 ′ and the reflective multilayer stack  110 , to form the trenches  154  in the peripheral region  100 B of the substrate  102 , in accordance with some embodiments. 
     Referring to  FIG.  6 K , the trenches  154  extend through the patterned absorber layer  140 P, the second capping layer  130 ′, the first capping layer  120 ′ and the reflective multilayer stack  110  to expose the surface of the substrate  102 . The trenches  154  surround the pattern region  100 A of the EUV mask  100 , separating the pattern region  100 A from the peripheral region  100 B. 
     In some embodiments, the patterned absorber layer  140 P, the second capping layer  130 ′, the first capping layer  120 ′, and the reflective multilayer stack  110  are etched using a single anisotropic etching process. The anisotropic etch can be a dry etch such as, for example, RIE, a wet etch, or a combination thereof that removes materials of the respective patterned absorber layer  140 P, the second capping layer  130 ′, the first capping layer  120 ′ and the reflective multilayer stack  110 , selective to the material providing the substrate  102 . In some embodiments, the patterned absorber layer  140 P, the second capping layer  130 ′, the first capping layer  120 ′ and the reflective multilayer stack  110  are etched using multiple distinct anisotropic etching processes. Each anisotropic etch can be a dry etch such as, for example, RIE, a wet etch, or a combination thereof. 
     Referring to  FIGS.  5  and  6 L , the method  500  proceeds to operation  520 , in which the patterned photoresist layer  180 P is removed, in accordance with some embodiments.  FIG.  6 L  is a cross-sectional view of the structure of  FIG.  6 K  after removing the patterned photoresist layer  180 P, in accordance with some embodiments. 
     Referring to  FIG.  6 L , the patterned photoresist layer  180 P is removed from the pattern region  100 A and the peripheral region  100 B of the substrate  102 , for example, by wet stripping or plasma ashing. The removal of the patterned photoresist layer  180 P from the openings  142  in the patterned absorber layer  140 P re-exposes the surfaces of the second capping layer  130 ′ in the pattern region  100 A. The openings  142  in the patterned absorber layer  140 P define the pattern of openings in the EUV mask  400  that correspond to circuit patterns to be formed on a semiconductor wafer. 
     An EUV mask  400  is thus formed. The EUV mask  400  includes a substrate  102 , a reflective multilayer stack  110  over a front surface of the substrate  102 , a first patterned capping layer  120 P′ over the reflective multilayer stack  110 , a second patterned capping layer  130 P′ over the first patterned capping layer  120 P′ and a patterned absorber layer  140 P over the second patterned capping layer  130 P′. The EUV mask  400  further includes a conductive layer  104  over a back surface of the substrate  102  opposite the front surface. In accordance with embodiments of  FIGS.  4 - 6   , the second capping layer  130 ′ is resistant to carbon contamination and thereby protects the underlying first capping layer  120 ′ and reflective multilayer stack  110  from carbon contamination by reducing or preventing deposition, formation or absorption of carbon onto exposed surfaces of the second capping layer  130 ′. As a result, the detrimental effects (e.g., need for increased EUV energy or negative effects on CDU) from carbon formation on or carbon contamination of an EUV mask are reduced or prevented and a pattern on the EUV mask  100  can be projected precisely onto a silicon wafer. Owing to the amorphous structure of the material of first capping layer  120 ′ and/or second capping layer  130 ′, first capping layer  120 ′ and/or second capping layer  130 ′ resist weakening by etchants, cleaners or processes using such etchants or cleaners that are carried out during the manufacture of the EUV mask  400 . Such resistance to weakening by etchants, cleaners or processes using such etchants or cleaners increases the ability of the first capping layer  120 ′ and second capping layer  130 ′ to resist infiltration by oxidants which can react with the underlying reflective multilayer stack to form unwanted oxides. 
     After removal of the patterned photoresist layer  180 P, the EUV mask  400  is cleaned to remove any contaminants therefrom. In some embodiments, the EUV mask  400  is cleaned by submerging the EUV mask  400  into an ammonium hydroxide (NH 4 OH) solution. In some embodiments, the EUV mask  400  is cleaned by submerging the EUV mask  400  into a diluted hydrofluoric acid (HF) solution. 
     The EUV mask  400  is subsequently radiated with, for example, a UV light with a wavelength of 193 nm, for inspection of any defects in the patterned region  100 A. The foreign matters may be detected from diffusely reflected light. If defects are detected, the EUV mask  400  is further cleaned using suitable cleaning processes. 
       FIG.  7    illustrates a method  1200  of using an EUV mask in accordance with embodiments of the present disclosure. Method  1200  includes step  1202  of exposing an EUV mask to an incident radiation, e.g., EUV radiation. An example of an EUV mask useful in step  1202  includes the EUV masks  100  or  400  described above. At step  1204 , a portion of the incident radiation is absorbed in a patterned absorber layer of the EUV mask. At step  1206 , a portion of the incident radiation is transmitted through a capping layer having an amorphous structure. An example of a capping layer having an amorphous structure includes the first capping layer  120  described with reference to  FIGS.  1 - 3   . At optional step  1208  which relates to a method employing a multilayer capping feature in accordance with embodiments of the present disclosure, a portion of the incident radiation is transmitted through a second capping layer having a second solid carbon solubility or second EUV extinction property that is different from the first carbon solubility or first EUV extinction property of the first capping layer. Examples of capping layers having a second solid carbon solubility or second EUV extinction property include the first capping layer  120 ′ or the second capping layer  130 ′ described above. At step  1209 , a portion of the incident radiation is reflected from the reflective multilayer stack. A portion of the incident radiation that is reflected by the reflective multilayer stack is directed to a material to be patterned in step  1210 . In the embodiment that omits optional step  1208 , the reflected incident radiation will be transmitted back through the first capping layer having an amorphous structure. In the embodiment that includes optional step  1208 , the reflected incident radiation will be transmitted back through the first capping layer and the second capping layer on its path to the material to be patterned. After the material to be patterned has been exposed to the radiation reflected from the EUV mask, portions of the material exposed or not exposed to the radiation reflected from the EUV mask are removed at step  1212 . 
       FIG.  8    illustrates a method  800  of using an EUV mask in accordance with embodiments of the present disclosure. Method  800  includes step  802  of exposing an EUV mask to an incident radiation, e.g., EUV radiation. An example of an EUV mask useful in step  802  includes the EUV masks  400  described above. At step  804 , a portion of the incident radiation is absorbed in a patterned absorber layer of the EUV mask. At step  806 , an amount of a first portion of the incident radiation is absorbed in the first capping layer including an element having a first solid carbon solubility and a first EUV extinction coefficient. An example of a capping layer having a first carbon solubility and a first EUV extinction property includes the second capping layers  130 ′ described above. At step  808 , an amount of a second portion of the incident radiation is absorbed by a second capping layer including an element having a second solid carbon solubility and/or a second EUV extinction coefficient different from the first solid carbon solubility and/or the first EUV extinction coefficient. In some embodiments, the amount of the first portion of incident radiation absorbed by the first capping layer is different from the amount of incident radiation absorbed by the second capping layer. Examples of second capping layer include the first capping layers  120 ′ described above. At step  809 , a portion of the incident radiation is reflected from the reflective multilayer stack. A portion of the incident radiation that is reflected by the reflective multilayer stack is directed to a material to be patterned in step  810 . The reflected incident radiation will be transmitted back through the first capping layer and the second capping layer on its path to the material to be patterned. After the material to be patterned has been exposed to the radiation reflected from the EUV mask, portions of the material exposed or not exposed to the radiation reflected from the EUV mask are removed at step  812 . 
       FIG.  9    illustrates the results of an analysis of thickness of carbon contamination on a capping feature containing an Rh containing alloy, e.g., RuRh in accordance with embodiments of the present disclosure. As illustrated in  FIG.  9   , the thickness of the carbon contamination is on the order of 6.5 nm. In contrast, thickness of carbon contamination on a capping feature not formed in accordance with the present disclosure and exposed to the same lithography conditions as the capping feature of  FIG.  9   , was observed to be greater, e.g., on the order of 11.7 nm. This is approximately a 40% decrease in thickness of carbon contamination achieved by capping layers in accordance with the present disclosure. 
     One aspect of this description relates to an EUV mask. The EUV mask includes a substrate, a reflective multilayer stack on the substrate, and a capping feature on the reflective multilayer stack. The capping feature includes a first capping layer including material having an amorphous structure. In some embodiments, the amorphous structure includes a nano-crystalline structure having grain size less than 2 nm. The EUV mask also includes a patterned absorber layer on the multilayer capping feature. In some embodiments, the first capping layer includes a material including an element having a solid carbon solubility, at an eutectic point of a system containing the element and carbon, that is less than 3 atomic %. Such EUV masks exhibit a reduced propensity to carbon build up or contamination which can negatively affect the ability of the mask to produce patterns that satisfy critical dimension criteria. In addition, such EUV capping features exhibit a resistance to weakening by etchants or cleaners that the capping layer is exposed to during manufacturing of the EUV mask. 
     Another aspect of this description relates to a method of using an EUV mask. The method includes exposing an EUV mask to an incident radiation. The EUV mask includes a substrate, a reflective multi-stack on the substrate and a multilayer capping feature on the reflective multilayer stack. The multilayer capping feature includes a first capping layer including a Rh, Ir, Pt, Au or Zr containing first alloy and a second capping layer including a Rh, Ir, Pt, Au or Zr containing second alloy different from the first alloy. The EUV mask includes a patterned absorber layer on the multilayer capping feature. The method includes absorbing a portion of the incident radiation in the patterned absorber layer. A portion of the incident radiation is transmitted through the first capping layer and the second capping layer. A portion of the incident radiation is reflected from the reflective multilayer stack and directed to a material to be patterned. In some embodiments, the first alloy and the second alloy are selected from RuZr, IrZr, RhZr, HfZr and NbZr, wherein the Zr content of the first alloy and the second alloy is at least 5 atomic %. 
     Still another aspect of this description relates to another method of using an EUV mask. The method includes exposing the EUV mask to an incident radiation. The EUV mask includes a substrate, a reflective multi-stack layer on the substrate, a capping feature and a patterned absorber layer on the capping feature. The capping feature includes a material including an element having a solid carbon solubility, at an eutectic point of a system of the element and carbon, that is less than three atomic percent. The method further includes absorbing a portion of incident radiation in the patterned absorber layer. In the method, a portion of the incident radiation is absorbed in the capping layer. The method proceeds with reflecting a portion of the incident radiation from the reflective multi-stack layer and directing it to a material to be patterned. 
     The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure.