Patent Publication Number: US-11640109-B2

Title: Extreme ultraviolet mask absorber materials

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Application No. 62/966,183, filed Jan. 27, 2020, and U.S. Provisional Application No. 63/011,683, filed Apr. 17, 2020, the entire disclosures of which are hereby incorporated by reference herein. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates generally to extreme ultraviolet lithography, and more particularly extreme ultraviolet mask blanks with an antimony nitride absorber and methods of manufacture. 
     BACKGROUND 
     Extreme ultraviolet (EUV) lithography, also known as soft x-ray projection lithography, is used for the manufacture of 0.0135 micron and smaller minimum feature size semiconductor devices. However, extreme ultraviolet light, which is generally in the 5 to 100 nanometer wavelength range, is strongly absorbed in virtually all materials. For that reason, extreme ultraviolet systems work by reflection rather than by transmission of light. Through the use of a series of mirrors, or lens elements, and a reflective element, or mask blank, coated with a non-reflective absorber mask pattern, the patterned actinic light is reflected onto a resist-coated semiconductor substrate. 
     The lens elements and mask blanks of extreme ultraviolet lithography systems are coated with reflective multilayer coatings of materials such as molybdenum and silicon. Reflection values of approximately 65% per lens element, or mask blank, have been obtained by using substrates that are coated with multilayer coatings that strongly reflect light within an extremely narrow ultraviolet bandpass, for example, 12.5 to 14.5 nanometer bandpass for 13.5 nanometer ultraviolet light. 
       FIG.  1    shows a conventional EUV reflective mask  10 , which is formed from an EUV mask blank, which includes a reflective multilayer stack  12  on a substrate  14 , which reflects EUV radiation at unmasked portions by Bragg interference. Masked (non-reflective) areas  16  of the conventional EUV reflective mask  10  are formed by etching buffer layer  18  and absorbing layer  20 . The absorbing layer typically has a thickness in a range of 51 nm to 77 nm. A capping layer  22  is formed over the reflective multilayer stack  12  and protects the reflective multilayer stack  12  during the etching process. As will be discussed further below, EUV mask blanks are made of on a low thermal expansion material substrate coated with multilayers, a capping layer and an absorbing layer, which is then etched to provide the masked (non-reflective) areas  16  and reflective areas  24 . 
     The International Technology Roadmap for Semiconductors (ITRS) specifies a node&#39;s overlay requirement as some percentage of a technology&#39;s minimum half-pitch feature size. Due to the impact on image placement and overlay errors inherent in all reflective lithography systems, EUV reflective masks will need to adhere to more precise flatness specifications for future production. Additionally, EUV blanks have a very low tolerance to defects on the working area of the blank. Furthermore, while the absorbing layer&#39;s role is to absorb light, there is also a phase shift effect due to the difference between the absorber layer&#39;s index of refraction and vacuum&#39;s index of refraction (n=1), and this phase shift that accounts for the 3D mask effects. There is a need to provide EUV mask blanks having a thinner absorber to mitigate 3D mask effects. 
     SUMMARY 
     One or more embodiments of the disclosure are directed to a method of manufacturing an extreme ultraviolet (EUV) mask blank comprising forming on a substrate a multilayer stack which reflects EUV radiation, the multilayer stack comprising a plurality of reflective layer pairs; forming a capping layer on the multilayer stack; and forming an absorber layer on the capping layer, the absorber layer comprising a compound of antimony and nitrogen. 
     Additional embodiments of the disclosure are directed to an EUV mask blank comprising a substrate; a multilayer stack which reflects EUV radiation, the multilayer stack comprising a plurality of reflective layer pairs; a capping layer on the multilayer stack of reflecting layers; and an absorber layer comprising a compound of antimony and nitrogen. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the above recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this disclosure and are therefore not to be considered limiting of its scope, for the disclosure may admit to other equally effective embodiments. 
         FIG.  1    schematically illustrates a background art EUV reflective mask employing a conventional absorber. 
         FIG.  2    schematically illustrates an embodiment of an extreme ultraviolet lithography system; 
         FIG.  3    illustrates an embodiment of an extreme ultraviolet reflective element production system. 
         FIG.  4    illustrates an embodiment of an extreme ultraviolet reflective element such as an EUV mask blank; 
         FIG.  5    illustrates an embodiment of an extreme ultraviolet reflective element such as an EUV mask blank; and 
         FIG.  6    illustrates an embodiment of a multi-cathode physical deposition chamber. 
     
    
    
     DETAILED DESCRIPTION 
     Before describing several exemplary embodiments of the disclosure, it is to be understood that the disclosure is not limited to the details of construction or process steps set forth in the following description. The disclosure is capable of other embodiments and of being practiced or being carried out in various ways. 
     The term “horizontal” as used herein is defined as a plane parallel to the plane or surface of a mask blank, regardless of its orientation. The term “vertical” refers to a direction perpendicular to the horizontal as just defined. Terms, such as “above”, “below”, “bottom”, “top”, “side” (as in “sidewall”), “higher”, “lower”, “upper”, “over”, and “under”, are defined with respect to the horizontal plane, as shown in the figures. 
     The term “on” indicates that there is direct contact between elements. The term “directly on” indicates that there is direct contact between elements with no intervening elements. 
     Those skilled in the art will understand that the use of ordinals such as “first” and “second” to describe process regions do not imply a specific location within the processing chamber, or order of exposure within the processing chamber. 
     As used in this specification and the appended claims, the term “substrate” refers to a surface, or portion of a surface, upon which a process acts. It will also be understood by those skilled in the art that reference to a substrate refers to only a portion of the substrate, unless the context clearly indicates otherwise. Additionally, reference to depositing on a substrate means both a bare substrate and a substrate with one or more films or features deposited or formed thereon. 
     Referring now to  FIG.  2   , an exemplary embodiment of an extreme ultraviolet lithography system  100  is shown. The extreme ultraviolet lithography system  100  includes an extreme ultraviolet light source  102  for producing extreme ultraviolet light  112 , a set of reflective elements, and a target wafer  110 . The reflective elements include a condenser  104 , an EUV reflective mask  106 , an optical reduction assembly  108 , a mask blank, a mirror, or a combination thereof. 
     The extreme ultraviolet light source  102  generates the extreme ultraviolet light  112 . The extreme ultraviolet light  112  is electromagnetic radiation having a wavelength in a range of 5 to 50 nanometers (nm). For example, the extreme ultraviolet light source  102  includes a laser, a laser produced plasma, a discharge produced plasma, a free-electron laser, synchrotron radiation, or a combination thereof. 
     The extreme ultraviolet light source  102  generates the extreme ultraviolet light  112  having a variety of characteristics. The extreme ultraviolet light source  102  produces broadband extreme ultraviolet radiation over a range of wavelengths. For example, the extreme ultraviolet light source  102  generates the extreme ultraviolet light  112  having wavelengths ranging from 5 to 50 nm. 
     In one or more embodiments, the extreme ultraviolet light source  102  produces the extreme ultraviolet light  112  having a narrow bandwidth. For example, the extreme ultraviolet light source  102  generates the extreme ultraviolet light  112  at 13.5 nm. The center of the wavelength peak is 13.5 nm. 
     The condenser  104  is an optical unit for reflecting and focusing the extreme ultraviolet light  112 . The condenser  104  reflects and concentrates the extreme ultraviolet light  112  from the extreme ultraviolet light source  102  to illuminate the EUV reflective mask  106 . 
     Although the condenser  104  is shown as a single element, it is understood that the condenser  104  in some embodiments includes one or more reflective elements such as concave mirrors, convex mirrors, flat mirrors, or a combination thereof, for reflecting and concentrating the extreme ultraviolet light  112 . For example, the condenser  104  in some embodiments is a single concave mirror or an optical assembly having convex, concave, and flat optical elements. 
     The EUV reflective mask  106  is an extreme ultraviolet reflective element having a mask pattern  114 . The EUV reflective mask  106  creates a lithographic pattern to form a circuitry layout to be formed on the target wafer  110 . The EUV reflective mask  106  reflects the extreme ultraviolet light  112 . The mask pattern  114  defines a portion of a circuitry layout. 
     The optical reduction assembly  108  is an optical unit for reducing the image of the mask pattern  114 . The reflection of the extreme ultraviolet light  112  from the EUV reflective mask  106  is reduced by the optical reduction assembly  108  and reflected on to the target wafer  110 . The optical reduction assembly  108  in some embodiments includes mirrors and other optical elements to reduce the size of the image of the mask pattern  114 . For example, the optical reduction assembly  108  in some embodiments includes concave mirrors for reflecting and focusing the extreme ultraviolet light  112 . 
     The optical reduction assembly  108  reduces the size of the image of the mask pattern  114  on the target wafer  110 . For example, the mask pattern  114  in some embodiments is imaged at a 4:1 ratio by the optical reduction assembly  108  on the target wafer  110  to form the circuitry represented by the mask pattern  114  on the target wafer  110 . The extreme ultraviolet light  112  in some embodiments scans the EUV reflective mask  106  synchronously with the target wafer  110  to form the mask pattern  114  on the target wafer  110 . 
     Referring now to  FIG.  3   , an embodiment of an extreme ultraviolet reflective element production system  200  is shown. The extreme ultraviolet reflective element includes a EUV mask blank  204 , an extreme ultraviolet mirror  205 , or other reflective element such as an EUV reflective mask  106 . 
     The extreme ultraviolet reflective element production system  200  in some embodiments produces mask blanks, mirrors, or other elements that reflect the extreme ultraviolet light  112  of  FIG.  2   . The extreme ultraviolet reflective element production system  200  fabricates the reflective elements by applying thin coatings to source substrates  203 . 
     The EUV mask blank  204  is a multilayered structure for forming the EUV reflective mask  106  of  FIG.  2   . The EUV mask blank  204  in some embodiments is formed using semiconductor fabrication techniques. The EUV reflective mask  106  in some embodiments has the mask pattern  114  of  FIG.  2    formed on the EUV mask blank  204  by etching and other processes. 
     The extreme ultraviolet mirror  205  is a multilayered structure reflective in a range of extreme ultraviolet light. The extreme ultraviolet mirror  205  in some embodiments is formed using semiconductor fabrication techniques. The EUV mask blank  204  and the extreme ultraviolet mirror  205  in some embodiments are similar structures with respect to the layers formed on each element, however, the extreme ultraviolet mirror  205  does not have the mask pattern  114 . 
     The reflective elements are efficient reflectors of the extreme ultraviolet light  112 . In an embodiment, the EUV mask blank  204  and the extreme ultraviolet mirror  205  has an extreme ultraviolet reflectivity of greater than 60%. The reflective elements are efficient if they reflect more than 60% of the extreme ultraviolet light  112 . 
     The extreme ultraviolet reflective element production system  200  includes a wafer loading and carrier handling system  202  into which the source substrates  203  are loaded and from which the reflective elements are unloaded. An atmospheric handling system  206  provides access to a wafer handling vacuum chamber  208 . The wafer loading and carrier handling system  202  in some embodiments includes substrate transport boxes, loadlocks, and other components to transfer a substrate from atmosphere to vacuum inside the system. Because the EUV mask blank  204  is used to form devices at a very small scale, the source substrates  203  and the EUV mask blank  204  are processed in a vacuum system to prevent contamination and other defects. 
     The wafer handling vacuum chamber  208  in some embodiments contains two vacuum chambers, a first vacuum chamber  210  and a second vacuum chamber  212 . The first vacuum chamber  210  includes a first wafer handling system  214  and the second vacuum chamber  212  includes a second wafer handling system  216 . Although the wafer handling vacuum chamber  208  is described with two vacuum chambers, it is understood that the system in some embodiments has any number of vacuum chambers. 
     The wafer handling vacuum chamber  208  in some embodiments has a plurality of ports around its periphery for attachment of various other systems. The first vacuum chamber  210  has a degas system  218 , a first physical vapor deposition system  220 , a second physical vapor deposition system  222 , and a pre-clean system  224 . The degas system  218  is for thermally desorbing moisture from the substrates. The pre-clean system  224  is for cleaning the surfaces of the wafers, mask blanks, mirrors, or other optical components. 
     The physical vapor deposition systems, such as the first physical vapor deposition system  220  and the second physical vapor deposition system  222 , in some embodiments are used to form thin films of conductive materials on the source substrates  203 . For example, the physical vapor deposition systems in some embodiments includes vacuum deposition system such as magnetron sputtering systems, ion sputtering systems, pulsed laser deposition, cathode arc deposition, or a combination thereof. The physical vapor deposition systems, such as the magnetron sputtering system, form thin layers on the source substrates  203  including the layers of silicon, metals, alloys, compounds, or a combination thereof. 
     The physical vapor deposition system forms reflective layers, capping layers, and absorber layers. For example, the physical vapor deposition systems in some embodiments forms layers of silicon, molybdenum, titanium oxide, titanium dioxide, ruthenium oxide, niobium oxide, ruthenium tungsten, ruthenium molybdenum, ruthenium niobium, chromium, antimony, iron, copper, boron, nickel, bismuth, tellurium, hafnium, tantalum, antimony, nitrides, compounds, or a combination thereof. Although some compounds are described as an oxide, it is understood that the compounds in some embodiments include oxides, dioxides, atomic mixtures having oxygen atoms, or a combination thereof. 
     The second vacuum chamber  212  has a first multi-cathode source  226 , a chemical vapor deposition system  228 , a cure chamber  230 , and an ultra-smooth deposition chamber  232  connected to it. For example, the chemical vapor deposition system  228  in some embodiments includes a flowable chemical vapor deposition system (FCVD), a plasma assisted chemical vapor deposition system (CVD), an aerosol assisted CVD system, a hot filament CVD system, or a similar system. In another example, the chemical vapor deposition system  228 , the cure chamber  230 , and the ultra-smooth deposition chamber  232  in some embodiments are in a separate system from the extreme ultraviolet reflective element production system  200 . 
     The chemical vapor deposition system  228  in some embodiments forms thin films of material on the source substrates  203 . For example, the chemical vapor deposition system  228  in some embodiments is used to form layers of materials on the source substrates  203  including mono-crystalline layers, polycrystalline layers, amorphous layers, epitaxial layers, or a combination thereof. The chemical vapor deposition system  228  in some embodiments forms layers of silicon, silicon oxides, silicon oxycarbide, tantalum, tellurium, antimony, hafnium, iron, copper, boron, nickel, tungsten, bismuth silicon carbide, silicon nitride, titanium nitride, metals, alloys, and other materials suitable for chemical vapor deposition. For example, the chemical vapor deposition system in some embodiments forms planarization layers. 
     The first wafer handling system  214  is capable of moving the source substrates  203  between the atmospheric handling system  206  and the various systems around the periphery of the first vacuum chamber  210  in a continuous vacuum. The second wafer handling system  216  is capable of moving the source substrates  203  around the second vacuum chamber  212  while maintaining the source substrates  203  in a continuous vacuum. The extreme ultraviolet reflective element production system  200  in some embodiments transfers the source substrates  203  and the EUV mask blank  204  between the first wafer handling system  214 , the second wafer handling system  216  in a continuous vacuum. 
     Referring now to  FIG.  4   , an embodiment of an extreme ultraviolet reflective element  302  is shown. In one or more embodiments, the extreme ultraviolet reflective element  302  is the EUV mask blank  204  of  FIG.  3    or the extreme ultraviolet mirror  205  of  FIG.  3   . The EUV mask blank  204  and the extreme ultraviolet mirror  205  are structures for reflecting the extreme ultraviolet light  112  of  FIG.  2   . The EUV mask blank  204  in some embodiments is used to form the EUV reflective mask  106  shown in  FIG.  2   . 
     The extreme ultraviolet reflective element  302  includes a substrate  304 , a multilayer stack  306  of reflective layers, and a capping layer  308 . In one or more embodiments, the extreme ultraviolet mirror  205  is used to form reflecting structures for use in the condenser  104  of  FIG.  2    or the optical reduction assembly  108  of  FIG.  2   . 
     The extreme ultraviolet reflective element  302 , which in some embodiments is a EUV mask blank  204 , includes the substrate  304 , the multilayer stack  306  of reflective layers, the capping layer  308 , and an absorber layer  310 . The extreme ultraviolet reflective element  302  in some embodiments is a EUV mask blank  204 , which is used to form the EUV reflective mask  106  of  FIG.  2    by patterning the absorber layer  310  with the layout of the circuitry required. 
     In the following sections, the term for the EUV mask blank  204  is used interchangeably with the term of the extreme ultraviolet mirror  205  for simplicity. In one or more embodiments, the EUV mask blank  204  includes the components of the extreme ultraviolet mirror  205  with the absorber layer  310  added in addition to form the mask pattern  114  of  FIG.  2   . 
     The EUV mask blank  204  is an optically flat structure used for forming the EUV reflective mask  106  having the mask pattern  114 . In one or more embodiments, the reflective surface of the EUV mask blank  204  forms a flat focal plane for reflecting the incident light, such as the extreme ultraviolet light  112  of  FIG.  2   . 
     The substrate  304  is an element for providing structural support to the extreme ultraviolet reflective element  302 . In one or more embodiments, the substrate  304  is made from a material having a low coefficient of thermal expansion (CTE) to provide stability during temperature changes. In one or more embodiments, the substrate  304  has properties such as stability against mechanical cycling, thermal cycling, crystal formation, or a combination thereof. The substrate  304  according to one or more embodiments is formed from a material such as silicon, glass, oxides, ceramics, glass ceramics, or a combination thereof. 
     The multilayer stack  306  is a structure that is reflective to the extreme ultraviolet light  112 . The multilayer stack  306  includes alternating reflective layers of a first reflective layer  312  and a second reflective layer  314 . 
     The first reflective layer  312  and the second reflective layer  314  form a reflective pair  316  of  FIG.  4   . In a non-limiting embodiment, the multilayer stack  306  includes a range of 20-60 of the reflective pairs  316  for a total of up to 120 reflective layers. 
     The first reflective layer  312  and the second reflective layer  314  in some embodiments are formed from a variety of materials. In an embodiment, the first reflective layer  312  and the second reflective layer  314  are formed from silicon and molybdenum, respectively. Although the layers are shown as silicon and molybdenum, it is understood that the alternating layers in some embodiments are formed from other materials or have other internal structures. 
     The first reflective layer  312  and the second reflective layer  314  in some embodiments have a variety of structures. In an embodiment, both the first reflective layer  312  and the second reflective layer  314  are formed with a single layer, multiple layers, a divided layer structure, non-uniform structures, or a combination thereof. 
     Because most materials absorb light at extreme ultraviolet wavelengths, the optical elements used are reflective instead of the transmissive as used in other lithography systems. The multilayer stack  306  forms a reflective structure by having alternating thin layers of materials with different optical properties to create a Bragg reflector or mirror. 
     In an embodiment, each of the alternating layers has dissimilar optical constants for the extreme ultraviolet light  112 . The alternating layers provide a resonant reflectivity when the period of the thickness of the alternating layers is one half the wavelength of the extreme ultraviolet light  112 . In an embodiment, for the extreme ultraviolet light  112  at a wavelength of 13 nm, the alternating layers are about 6.5 nm thick. It is understood that the sizes and dimensions provided are within normal engineering tolerances for typical elements. 
     The multilayer stack  306  in some embodiments is formed in a variety of ways. In an embodiment, the first reflective layer  312  and the second reflective layer  314  are formed with magnetron sputtering, ion sputtering systems, pulsed laser deposition, cathode arc deposition, or a combination thereof. 
     In an illustrative embodiment, the multilayer stack  306  is formed using a physical vapor deposition technique, such as magnetron sputtering. In an embodiment, the first reflective layer  312  and the second reflective layer  314  of the multilayer stack  306  have the characteristics of being formed by the magnetron sputtering technique including precise thickness, low roughness, and clean interfaces between the layers. In an embodiment, the first reflective layer  312  and the second reflective layer  314  of the multilayer stack  306  have the characteristics of being formed by the physical vapor deposition including precise thickness, low roughness, and clean interfaces between the layers. 
     The physical dimensions of the layers of the multilayer stack  306  formed using the physical vapor deposition technique in some embodiments is precisely controlled to increase reflectivity. In an embodiment, the first reflective layer  312 , such as a layer of silicon, has a thickness of 4.1 nm. The second reflective layer  314 , such as a layer of molybdenum, has a thickness of 2.8 nm. The thickness of the layers dictates the peak reflectivity wavelength of the extreme ultraviolet reflective element. If the thickness of the layers is incorrect, the reflectivity at the desired wavelength 13.5 nm in some embodiments is reduced. 
     In an embodiment, the multilayer stack  306  has a reflectivity of greater than 60%. In an embodiment, the multilayer stack  306  formed using physical vapor deposition has a reflectivity in a range of 66%-67%. In one or more embodiments, forming the capping layer  308  over the multilayer stack  306  formed with harder materials improves reflectivity. In some embodiments, reflectivity greater than 70% is achieved using low roughness layers, clean interfaces between layers, improved layer materials, or a combination thereof. 
     In one or more embodiments, the capping layer  308  is a protective layer allowing the transmission of the extreme ultraviolet light  112 . In an embodiment, the capping layer  308  is formed directly on the multilayer stack  306 . In one or more embodiments, the capping layer  308  protects the multilayer stack  306  from contaminants and mechanical damage. In one embodiment, the multilayer stack  306  is sensitive to contamination by oxygen, tantalum, hydrotantalums, or a combination thereof. The capping layer  308  according to an embodiment interacts with the contaminants to neutralize them. 
     In one or more embodiments, the capping layer  308  is an optically uniform structure that is transparent to the extreme ultraviolet light  112 . The extreme ultraviolet light  112  passes through the capping layer  308  to reflect off of the multilayer stack  306 . In one or more embodiments, the capping layer  308  has a total reflectivity loss of 1% to 2%. In one or more embodiments, each of the different materials has a different reflectivity loss depending on thickness, but all of them will be in a range of 1% to 2%. 
     In one or more embodiments, the capping layer  308  has a smooth surface. For example, the surface of the capping layer  308  in some embodiments has a roughness of less than 0.2 nm RMS (root mean square measure). In another example, the surface of the capping layer  308  has a roughness of 0.08 nm RMS for a length in a range of 1/100 nm and 1/1 μm. The RMS roughness will vary depending on the range it is measured over. For the specific range of 100 nm to 1 micron that roughness is 0.08 nm or less. Over a larger range the roughness will be higher. 
     The capping layer  308  in some embodiments is formed in a variety of methods. In an embodiment, the capping layer  308  is formed on or directly on the multilayer stack  306  with magnetron sputtering, ion sputtering systems, ion beam deposition, electron beam evaporation, radio frequency (RF) sputtering, atomic layer deposition (ALD), pulsed laser deposition, cathode arc deposition, or a combination thereof. In one or more embodiments, the capping layer  308  has the physical characteristics of being formed by the magnetron sputtering technique including precise thickness, low roughness, and clean interfaces between the layers. In an embodiment, the capping layer  308  has the physical characteristics of being formed by the physical vapor deposition including precise thickness, low roughness, and clean interfaces between the layers. 
     In one or more embodiments, the capping layer  308  is formed from a variety of materials having a hardness sufficient to resist erosion during cleaning. In one embodiment, ruthenium is used as a capping layer material because it is a good etch stop and is relatively inert under the operating conditions. However, it is understood that other materials in some embodiments are used to form the capping layer  308 . In specific embodiments, the capping layer  308  has a thickness in a range of 2.5 and 5.0 nm. 
     In one or more embodiments, the absorber layer  310  is a layer that absorbs the extreme ultraviolet light  112 . In an embodiment, the absorber layer  310  is used to form the pattern on the EUV reflective mask  106  by providing areas that do not reflect the extreme ultraviolet light  112 . The absorber layer  310 , according to one or more embodiments, comprises a material having a high absorption coefficient for a particular frequency of the extreme ultraviolet light  112 , such as about 13.5 nm. In an embodiment, the absorber layer  310  is formed directly on the capping layer  308 , and the absorber layer  310  is etched using a photolithography process to form the pattern of the EUV reflective mask  106 . 
     According to one or more embodiments, the extreme ultraviolet reflective element  302 , such as the extreme ultraviolet mirror  205 , is formed with the substrate  304 , the multilayer stack  306 , and the capping layer  308 . The extreme ultraviolet mirror  205  has an optically flat surface and in some embodiments efficiently and uniformly reflects the extreme ultraviolet light  112 . 
     According to one or more embodiments, the extreme ultraviolet reflective element  302 , such as the EUV mask blank  204 , is formed with the substrate  304 , the multilayer stack  306 , the capping layer  308 , and the absorber layer  310 . The mask blank  204  has an optically flat surface and in some embodiments efficiently and uniformly reflects the extreme ultraviolet light  112 . In an embodiment, the mask pattern  114  is formed with the absorber layer  310  of the EUV mask blank  204 . 
     According to one or more embodiments, forming the absorber layer  310  over the capping layer  308  increases reliability of the EUV reflective mask  106 . The capping layer  308  acts as an etch stop layer for the absorber layer  310 . When the mask pattern  114  of  FIG.  2    is etched into the absorber layer  310 , the capping layer  308  beneath the absorber layer  310  stops the etching action to protect the multilayer stack  306 . In one or more embodiments, the absorber layer  310  is etch selective to the capping layer  308 . In some embodiments, the capping layer  308  comprises ruthenium, and the absorber layer  310  is etch selective to ruthenium. 
     In an embodiment, the absorber layer  310  comprises a compound of antimony and nitrogen. In some embodiments the absorber has a thickness of less than about 45 nm. In some embodiments, the absorber layer has a thickness of less than about 45 nm, including less than about 40 nm, less than about 35 nm, less than about 30 nm, less than about 25 nm, less than about 20 nm, less than about 15 nm, less than about 10 nm, less than about 5 nm, less than about 1 nm, or less than about 0.5 nm. In other embodiments, the absorber layer  310  has a thickness in a range of about 0.5 nm to about 45 nm, including a range of about 1 nm to about 44 nm, 1 nm to about 40 nm, and 15 nm to about 40 nm. 
     Without intending to be bound by theory, it is thought that an absorber layer  310  having a thickness of less than about 45 nm advantageously results in an absorber layer having a reflectively of less than about 2%, reducing and mitigating 3D mask effects in the extreme ultraviolet (EUV) mask blank. 
     In an embodiment, the absorber layer  310  is made from a compound of antimony and nitrogen. In one or more embodiments, the compound of antimony and nitrogen comprises from about 78.8 wt. % to about 99.8 wt. % antimony and from about 0.2 wt. % to about 21.2 wt. % nitrogen based upon the total weight of the compound. In one or more embodiments, the compound of antimony and nitrogen comprises from about 83.8 wt. % to about 94.8 wt. % antimony and from about 5.2 wt. % to about 16.2 wt. % nitrogen based upon the total weight of the compound. In one or more embodiments, the compound of antimony and nitrogen comprises from about 86.8 wt. % to about 91.8 wt. % antimony and from about 8.2 wt. % to about 13.2 wt. % nitrogen based upon the total weight of the compound. In one or more embodiments, the compound of antimony and nitrogen is amorphous. In one or more embodiments, the compound is a single-phase compound. 
     In a specific embodiment, the compound of antimony and nitrogen is a nitrogen rich compound. As used herein, the term “nitrogen rich” means that there is more nitrogen in the compound than antimony. In one or more embodiments, the compound of antimony and nitrogen is amorphous. In one or more embodiments, the compound is a single phase compound. 
     In one or more embodiments, the compound of antimony and nitrogen comprises a dopant. In an embodiment, the dopant comprises oxygen. In an embodiment, the dopant is present in the compound in an amount in the range of about 0.1 wt. % to about 10 wt. %, based on the weight of the compound. In other embodiments, the dopant is present in the compound in an amount of about 0.1 wt. %, 0.2 wt. %, 0.3 wt. %, 0.4 wt. %, 0.5 wt. %, 0.6 wt. %, 0.7 wt. %. 0.8 wt. %, 0.9 wt. %, 1.0 wt. %, 1.1 wt. %, 1.2 wt. %, 1.3 wt. %, 1.4 wt. %, 1.5 wt. %, 1.6 wt. %, 1.7 wt. %. 1.8 wt. %, 1.9 wt. %, 2.0 wt. % 2.1 wt. %, 2.2 wt. %, 2.3 wt. %, 2.4 wt. %, 2.5 wt. %, 2.6 wt. %, 2.7 wt. %. 2.8 wt. %, 2.9 wt. %, 3.0 wt. %, 3.1 wt. %, 3.2 wt. %, 3.3 wt. %, 3.4 wt. %, 3.5 wt. %, 3.6 wt. %, 3.7 wt. %. 3.8 wt. %, 3.9 wt. %, 4.0 wt. %, 4.1 wt. %, 4.2 wt. %, 4.3 wt. %, 4.4 wt. %, 4.5 wt. %, 4.6 wt. %, 4.7 wt. %. 4.8 wt. %, 4.9 wt. %, or 5.0 wt. %. 
     In one or more embodiments, the compound of the absorber layer is a sputtered compound absorber material formed in a physical deposition chamber, which in some embodiments provides much thinner absorber layer thickness (less than 45 nm or less than 30 nm) while achieving less than 2% reflectivity and suitable etch properties. In one or more embodiments, the compound of the absorber layer in some embodiments is sputtered by gases selected from one or more of argon (Ar), oxygen (O 2 ), or nitrogen (N 2 ). In an embodiment, the compound of the absorber layer in some embodiments is sputtered by a mixture of argon and oxygen gases (Ar+O 2 ). In some embodiments, sputtering by a mixture of argon and oxygen forms an oxide of antimony and/or an oxide of nitrogen. In other embodiments, sputtering by a mixture of argon and oxygen does not form an oxide of antimony or nitrogen. In an embodiment, the compound of the absorber layer in some embodiments is sputtered by a mixture of argon and nitrogen gases (Ar+N 2 ). In some embodiments, sputtering by a mixture of argon and nitrogen forms a nitride of antimony and/or a nitride of nitrogen. In other embodiments, sputtering by a mixture of argon and nitrogen does not form a nitride of antimony or nitrogen. In an embodiment, the compound of the absorber layer in some embodiments is sputtered by a mixture of argon and oxygen and nitrogen gases (Ar+O 2 +N 2 ). In some embodiments, sputtering by a mixture of argon and oxygen and nitrogen forms an oxide and/or nitride of nitrogen and/or an oxide and/or nitride of antimony. In other embodiments, sputtering by a mixture of argon and oxygen and nitrogen does not form an oxide or a nitride of antimony or nitrogen. In an embodiment, the etch properties and/or other properties of the absorber layer in some embodiments is tailored to specification by controlling the compound percentage(s), as discussed above. In an embodiment, the compound percentage(s) in some embodiments is precisely controlled by operating parameters such voltage, pressure, flow, etc., of the physical vapor deposition chamber. In an embodiment, a process gas is used to further modify the material properties, for example, N 2  gas is used to form nitrides of antimony and nitrogen. 
     In other embodiments, the compound of antimony and nitrogen in some embodiments is deposited layer by layer as a laminate of antimony and nitrogen layers by forming a layer of antimony by sputtering, wherein the layer of antimony has a thickness in a range of from 1 nm to 10 nm (e.g., 1-2 nm, 1-3 nm, 1-4 nm, 1-5 nm, 1-6 nm, 1-7 nm, 1-8, nm, 1-9 nm, 2-3 nm, 2-4 nm, 2-5 nm, 2-6 nm, 2-7 nm, 2-8 nm, 2-9 nm, 2-10 nm, 3-4 nm, 3-5 nm, 3-6 nm, 3-7 nm, 3-8 nm, 3-9 nm, 3-10 nm, 4-5 nm, 4-6 nm, 4-7 nm, 4-8 nm, 4-9 nm, 4-10 nm, 5-6 nm, 5-7 nm, 5-8 nm, 5-9 nm or 5-10 nm). After deposition of the layer of antimony, the power the PVD chamber is turned off, and a flow of nitrogen gas or nitrogen and oxygen gas at a pressure of from 1-10 mT (e.g., 2 mT) for a period of time ranging from 1-10 s (e.g., 5 s) for one cycle. This process is referred to as gas phase nitridation of antimony. The cycle of antimony deposition by sputtering followed by nitrogen layer formation is repeated until the desired SbN thickness is achieved. 
     In one or more embodiments, bulk targets of the antimony nitride compounds described herein may be made by reactive sputtering using gases selected from one or more of argon (Ar), oxygen (O 2 ), or nitrogen (N 2 ). In one or more embodiments, the compound is deposited using a bulk target having the same composition of the compound and is sputtered using a gas selected from one or more of argon (Ar), oxygen (O 2 ), or nitrogen (N 2 ) to form the absorber layer. In an embodiment, the compound of the absorber layer in some embodiments is deposited using a bulk target having the same composition of the compound and is sputtered using a mixture of argon and oxygen gases (Ar+O 2 ). In some embodiments, bulk target deposition using a mixture of argon and oxygen forms an oxide of antimony and/or an oxide of nitrogen. In other embodiments, bulk target deposition using a mixture of argon and oxygen does not form an oxide of antimony or nitrogen. In an embodiment, the compound of the absorber layer in some embodiments is deposited using a bulk target having the same composition of the compound and is sputtered using a mixture of argon and nitrogen gases (Ar+N 2 ). In some embodiments, bulk target deposition using a mixture of argon and nitrogen forms a nitride of antimony and/or a nitride of nitrogen. In other embodiments, bulk target deposition using a mixture of argon and nitrogen does not form a nitride of antimony or nitrogen. In an embodiment, the compound of the absorber layer in some embodiments is deposited using a bulk target having the same composition of the compound and is sputtered using a mixture of argon and oxygen and nitrogen gases (Ar+O 2 +N 2 ). In some embodiments, bulk target depositing using a mixture of argon and oxygen and nitrogen forms an oxide and/or nitride of nitrogen and/or an oxide and/or nitride of antimony. In other embodiments, bulk target deposition using a mixture of argon and oxygen and nitrogen does not form an oxide or a nitride of antimony or nitrogen. In some embodiments, the compound of antimony and nitrogen is doped with oxygen in a range of from 0.1 wt. % to 10 wt. %. 
     The EUV mask blank in some embodiments is made in a physical deposition chamber having a first cathode comprising a first absorber material, a second cathode comprising a second absorber material, a third cathode comprising a third absorber material, a fourth cathode comprising a fourth absorber material, and a fifth cathode comprising a fifth absorber material, wherein the first absorber material, second absorber material, third absorber material, fourth absorber material and fifth absorber materials are different from each other, and each of the absorber materials have an extinction coefficient that is different from the other materials, and each of the absorber materials have an index of refraction that is different from the other absorber materials. 
     Referring now to  FIG.  5   , an extreme ultraviolet mask blank  400  is shown as comprising a substrate  414 , a multilayer stack of reflective layers  412  on the substrate  414 , the multilayer stack of reflective layers  412  including a plurality of reflective layer pairs. In one or more embodiments, the plurality of reflective layer pairs is made from a material selected from a molybdenum (Mo) containing material and silicon (Si) containing material. In some embodiments, the plurality of reflective layer pairs comprises alternating layers of molybdenum and silicon. The extreme ultraviolet mask blank  400  further includes a capping layer  422  on the multilayer stack of reflective layers  412 , and there is a multilayer stack  420  of absorber layers on the capping layer  422 . In one or more embodiment, the plurality of reflective layers  412  are selected from molybdenum (Mo) containing material and silicon (Si) containing material and the capping layer  422  comprises nitrogen. 
     The multilayer stack  420  of absorber layers including a plurality of absorber layer pairs  420   a ,  420   b ,  420   c ,  420   d ,  420   e ,  420   f , each pair ( 420   a / 420   b ,  420   c / 420   d ,  420   e / 420   f ) comprising a compound of antimony and nitrogen. In some embodiments, the compound of antimony and nitrogen comprises about 78.8 wt. % to about 99.8 wt. % antimony and about 0.2 wt. % to about 21.2 wt. % nitrogen based upon the total weight of the compound. In one or more embodiments, the compound of antimony and nitrogen comprises about 83.8 wt. % to about 94.8 wt. % antimony and from about 5.2 wt. % to about 16.2 wt. % nitrogen based upon the total weight of the compound. 
     In one or more embodiments, the compound of antimony and nitrogen comprises from about 86.8 wt. % to about 91.8 wt. % antimony and from about 8.2 wt. % to about 13.2 wt. % nitrogen based upon the total weight of the compound. In one or more embodiments, the compound of antimony and nitrogen is amorphous. In one or more embodiments, the compound is a single phase compound. In one example, absorber layer  420   a  is made from antimony and the material that forms absorber layer  420   b  is nitrogen. Likewise, absorber layer  420   c  is made from antimony and the material that forms absorber layer  420   d  is nitrogen, and absorber layer  420   e  is made from antimony material and the material that forms absorber layer  420   f  that is nitrogen. 
     In one embodiment, the extreme ultraviolet mask blank  400  includes the plurality of reflective layers  412  selected from molybdenum (Mo) containing material and silicon (Si) containing material, for example, molybdenum (Mo) and silicon (Si). The absorber materials that are used to form the absorber layers  420   a ,  420   b ,  420   c ,  420   d ,  420   e  and  420   f  are a compound of antimony and nitrogen. In some embodiments, the compound of antimony and nitrogen comprises from about 78.8 wt. % to about 99.8 wt. % antimony and from about 0.2 wt. % to about 21.2 wt. % nitrogen based upon the total weight of the compound. In one or more embodiments, the compound of antimony and nitrogen comprises from about 83.8 wt. % to about 94.8 wt. % antimony and from about 5.2 wt. % to about 16.2 wt. % nitrogen based upon the total weight of the compound. In one or more embodiments, the compound of antimony and nitrogen comprises from about 86.8 wt. % to about 91.8 wt. % antimony and from about 8.2 wt. % to about 13.2 wt. % nitrogen based upon the total weight of the compound. In one or more embodiments, the compound of antimony and nitrogen is amorphous. In one or more embodiments, the compound is a single phase compound. 
     In one or more embodiments, the absorber layer pairs  420   a / 420   b ,  420   c / 420   d ,  420   e / 420   f  comprise a first layer ( 420   a ,  420   c ,  420   e ) including an absorber material comprising a compound of antimony and nitrogen and a second absorber layer ( 420   b ,  420   d ,  420   f ) including an absorber material including a compound of antimony and nitrogen. In specific embodiments, the absorber layer pairs comprise a first layer ( 420   a ,  420   c ,  420   e ) including a compound of antimony and nitrogen and a second absorber layer ( 420   b ,  420   d ,  420   f ) including an absorber material including a compound of antimony and nitrogen. 
     According to one or more embodiments, the absorber layer pairs comprise a first layer ( 420   a ,  420   c ,  420   e ) and a second absorber layer ( 420   b ,  420   d ,  420   f ) each of the first absorber layers ( 420   a ,  420   c ,  420   e ) and second absorber layer ( 420   b ,  420   d ,  420   f ) have a thickness in a range of 0.1 nm and 10 nm, for example in a range of 1 nm and 5 nm, or in a range of 1 nm and 3 nm. In one or more specific embodiments, the thickness of the first layer  420   a  is 0.5 nm, 0.6 nm, 0.7 nm, 0.8 nm, 0.9 nm, 1 nm, 1.1 nm, 1.2 nm, 1.3 nm, 1.4 nm, 1.5 nm, 1.6 nm, 1.7 nm, 1.8 nm, 1.9 nm, 2 nm, 2.1 nm, 2.2 nm, 2.3 nm, 2.4 nm, 2.5 nm, 2.6 nm, 2.7 nm, 2.8 nm, 2.9 nm, 3 nm, 3.1 nm, 3.2 nm, 3.3 nm, 3.4 nm, 3.5 nm, 3.6 nm, 3.7 nm, 3.8 nm, 3.9 nm, 4 nm, 4.1 nm, 4.2 nm, 4.3 nm, 4.4 nm, 4.5 nm, 4.6 nm, 4.7 nm, 4.8 nm, 4.9 nm, and 5 nm. In one or more embodiments, the thickness of the first absorber layer and second absorber layer of each pair is the same or different. For example, the first absorber layer and second absorber layer have a thickness such that there is a ratio of the first absorber layer thickness to second absorber layer thickness of 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 11:1, 12:1, 13:1, 14:1, 15:1, 16:1, 17:1, 18:1, 19:1, or 20:1, which results in the first absorber layer having a thickness that is equal to or greater than the second absorber layer thickness in each pair. Alternatively, the first absorber layer and second absorber layer have a thickness such that there is a ratio of the second absorber layer thickness to first absorber layer thickness of 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 11:1, 12:1, 13:1, 14:1, 15:1, 16:1, 17:1, 18:1, 19:1, or 20:1 which results in the second absorber layer having a thickness that is equal to or greater than the first absorber layer thickness in each pair. 
     According to one or more embodiments, the different absorber materials and thickness of the absorber layers are selected so that extreme ultraviolet light is absorbed due to absorbance and due to a phase change caused by destructive interfere with light from the multilayer stack of reflective layers. While the embodiment shown in  FIG.  5    shows three absorber layer pairs,  420   a / 420   b ,  420   c / 420   d  and  420   e / 420   f , the claims should not be limited to a particular number of absorber layer pairs. According to one or more embodiments, the EUV mask blank  400  in some embodiments includes in a range of 5 and 60 absorber layer pairs or in a range of 10 and 40 absorber layer pairs. 
     According to one or more embodiments, the absorber layers have a thickness which provides less than 2% reflectivity and other etch properties. A supply gas in some embodiments is used to further modify the material properties of the absorber layers, for example, nitrogen (N 2 ) gas in some embodiments is used to form nitrides of the materials provided above. The multilayer stack of absorber layers according to one or more embodiments is a repetitive pattern of individual thickness of different materials so that the EUV light not only gets absorbed due to absorbance but by the phase change caused by multilayer absorber stack, which will destructively interfere with light from multilayer stack of reflective materials beneath to provide better contrast. 
     Another aspect of the disclosure pertains to a method of manufacturing an extreme ultraviolet (EUV) mask blank comprising forming on a substrate a multilayer stack of reflective layers on the substrate, the multilayer stack including a plurality of reflective layer pairs, forming a capping layer on the multilayer stack of reflective layers, and forming absorber layer on the capping layer, the absorber layer comprising a compound of antimony and nitrogen, wherein the compound of antimony and nitrogen comprises from about 78.8 wt. % to about 99.8 wt. % antimony and from about 0.2 wt. % to about 21.2 wt. % nitrogen based upon the total weight of the compound. In one or more embodiments, the compound of antimony and nitrogen comprises from about 83.8 wt. % to about 94.8 wt. % antimony and from about 5.2 wt. % to about 16.2 wt. % nitrogen based upon the total weight of the compound. In one or more embodiments, the compound of antimony and nitrogen comprises from about 86.8 wt. % to about 91.8 wt. % antimony and from about 8.2 wt. % to about 13.2 wt. % nitrogen based upon the total weight of the compound. In one or more embodiments, the compound of antimony and nitrogen is amorphous. In one or more embodiments, the compound is a single phase compound. 
     The EUV mask blank in some embodiments has any of the characteristics of the embodiments described above with respect to  FIG.  4    and  FIG.  5   , and the method in some embodiments is performed in the system described with respect to  FIG.  3   . 
     Thus, in an embodiment, the plurality of reflective layers is selected from molybdenum (Mo) containing material and silicon (Si) containing material and the absorber layer is a compound of antimony and nitrogen, wherein the compound of antimony and nitrogen comprises from about 78.8 wt. % to about 99.8 wt. % antimony and from about 0.2 wt. % to about 21.2 wt. % nitrogen based upon the total weight of the compound. In one or more embodiments, the compound of antimony and nitrogen comprises from about 83.8 wt. % to about 94.8 wt. % antimony and from about 5.2 wt. % to about 16.2 wt. % nitrogen based upon the total weight of the compound. In one or more embodiments, the compound of antimony and nitrogen comprises from about 86.8 wt. % to about 91.8 wt. % antimony and from about 8.2 wt. % to about 13.2 wt. % nitrogen based upon the total weight of the compound. In one or more embodiments, the compound of antimony and nitrogen is amorphous. In one or more embodiments, the compound is a single phase compound. 
     In another specific method embodiment, the different absorber layers are formed in a physical deposition chamber having a first cathode comprising a first absorber material and a second cathode comprising a second absorber material. Referring now to  FIG.  6    an upper portion of a multi-cathode chamber  500  is shown in accordance with an embodiment. The multi-cathode chamber  500  includes a base structure  501  with a cylindrical body portion  502  capped by a top adapter  504 . The top adapter  504  has provisions for a number of cathode sources, such as cathode sources  506 ,  508 ,  510 ,  512 , and  514 , positioned around the top adapter  504 . 
     In one or more embodiments, the method forms an absorber layer that has a thickness in a range of 5 nm and 60 nm. In one or more embodiments, the absorber layer has a thickness in a range of 51 nm and 57 nm. In one or more embodiments, the materials used to form the absorber layer are selected to effect etch properties of the absorber layer. In one or more embodiments, the compound of the absorber layer is formed by sputtering a compound absorber material formed in a physical deposition chamber, which in some embodiments provides much thinner absorber layer thickness (less than 45 nm or less than 30 nm) and achieving less than 2% reflectivity and desired etch properties. In an embodiment, the etch properties and other desired properties of the absorber layer in some embodiments are tailored to specification by controlling the compound percentage of each absorber material. In an embodiment, the compound percentage in some embodiments is precisely controlled by operating parameters such voltage, pressure, flow etc., of the physical vapor deposition chamber. In an embodiment, a process gas is used to further modify the material properties, for example, N 2  gas is used to form nitrides of antimony and nitrogen. The compound absorber material in some embodiments comprises a compound of antimony and nitrogen which comprises from about 78.8 wt. % to about 99.8 wt. % antimony and from about 0.2 wt. % to about 21.2 wt. % nitrogen based upon the total weight of the compound. In one or more embodiments, the compound of antimony and nitrogen comprises from about 83.8 wt. % to about 94.8 wt. % antimony and from about 5.2 wt. % to about 16.2 wt. % nitrogen based upon the total weight of the compound. In one or more embodiments, the compound of antimony and nitrogen comprises from about 86.8 wt. % to about 91.8 wt. % antimony and from about 8.2 wt. % to about 13.2 wt. % nitrogen based upon the total weight of the compound. In one or more embodiments, the compound of antimony and nitrogen is amorphous. In one or more embodiments, the compound is a single phase compound. 
     The multi-cathode source chamber  500  in some embodiments is part of the system shown in  FIG.  3   . In an embodiment, an extreme ultraviolet (EUV) mask blank production system comprises a substrate handling vacuum chamber for creating a vacuum, a substrate handling platform, in the vacuum, for transporting a substrate loaded in the substrate handling vacuum chamber, and multiple sub-chambers, accessed by the substrate handling platform, for forming an EUV mask blank, including a multilayer stack of reflective layers on the substrate, the multilayer stack including a plurality of reflective layer pairs, a capping layer on the multilayer stack of reflective layers, and an absorber layer on the capping layer, the absorber layer made from a compound of antimony and nitrogen. The system in some embodiments is used to make the EUV mask blanks shown with respect to  FIG.  4    or  FIG.  5    and have any of the properties described with respect to the EUV mask blanks described with respect to  FIG.  4    or  FIG.  5    above. 
     Processes may generally be stored in the memory as a software routine that, when executed by the processor, causes the process chamber to perform processes of the present disclosure. The software routine may also be stored and/or executed by a second processor (not shown) that is remotely located from the hardware being controlled by the processor. Some or all of the method of the present disclosure may also be performed in hardware. As such, the process may be implemented in software and executed using a computer system, in hardware as, e.g., an application specific integrated circuit or other type of hardware implementation, or as a combination of software and hardware. The software routine, when executed by the processor, transforms the general purpose computer into a specific purpose computer (controller) that controls the chamber operation such that the processes are performed. 
     Reference throughout this specification to “one embodiment,” “certain embodiments,” “one or more embodiments” or “an embodiment” means that a particular feature, structure, material, or characteristic described in connection with the embodiment is included in at least one embodiment of the disclosure. Thus, the appearances of the phrases such as “in one or more embodiments,” “in certain embodiments,” “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily referring to the same embodiment of the disclosure. Furthermore, the particular features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments. 
     Although the disclosure herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present disclosure. It will be apparent to those skilled in the art that various modifications and variations can be made to the method and apparatus of the present disclosure without departing from the spirit and scope of the disclosure. Thus, it is intended that the present disclosure include modifications and variations that are within the scope of the appended claims and their equivalents.