Abstract:
An exemplary embodiment relates to a mask for integrated circuit fabrication equipment. The mask includes a multilayer film and an amorphous carbon layer above the multilayer film. The multilayer film is at least partially relatively reflective to radiation having a wavelength of less than 70 nanometers.

Description:
This application claims priority to provisional application 60/399,816, filed Jul. 31, 2002, which is incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to integrated circuit (IC) fabrication equipment. More particularly, the present invention relates to an EUV reflective mask-having a low temperature buffer and absorber film and a method of making such a mask. 
     BACKGROUND OF THE INVENTION 
     Semiconductor fabrication techniques often utilize a mask or reticle. Radiation is provided through or reflected off the mask or reticle to form an image on a semiconductor wafer. The wafer is positioned to receive the radiation transmitted through or reflected off the mask or reticle. The image on the wafer corresponds to the pattern on the mask or reticle. The radiation can be light, such as ultraviolet light, vacuum ultraviolet (VUV) light, extreme ultraviolet light (EUV) and deep ultraviolet light. The radiation can also be x-ray radiation, e-beam radiation, etc. 
     One advanced form of lithography is extreme ultraviolet (EUV) light lithography. A conventional EUV system (e.g., an optical reduction camera or stepper) utilizes an EUV radiation source, an EUV lens assembly (e.g., a condenser lens), an EUV reticle, and another EUV lens assembly (e.g., an objective lens). EUV radiation can be created at the radiation source and projected onto the reticle. The EUV reticle is typically a resonant-reflective medium including an IC pattern of absorbing material. The resonant reflective medium reflects a substantial portion of the EUV radiation in accordance with the IC pattern to the second EUV lens assembly. The lens assemblies can be an all resonant-reflective imaging system including aspheric optics at 4:1 magnification factor (e.g., a series of high precision mirrors). EUV radiation reflected off the EUV reticle is provided from the second EUV lens assembly to a photoresist coated wafer. 
     EUV lithography utilizes radiation in a wavelength of 5 to 70 nanometers (e.g., 11-14 nanometers). A conventional EUV lithographic system or EUV stepper provides the EUV reticle as a multilayer coated reflective mask or reticle which has an absorber pattern across its surface. The multilayer coated reflective reticle (i.e., the resonant reflective medium) can utilize molybdenum/silicon (Mo—Si) layers or molybdenum/beryllium layers (Mo—Be). 
     EUV lithography can employ a reflective mask consisting of a patterned absorber on a multilayer coated substrate (mask blank) that reflects a narrow band of EUV wavelengths near 13.4 nm. Such masks have the advantage of being thick and dimensionally stable; however, the use of such masks presents some challenges. 
     Current EUV reflective masks use silicon oxide (SiO 2 ) as buffer layers to protect delicate multilayer reflectors. Metal layers are used as absorbers. While the silicon oxide buffer layers and metal layer absorbers are effective, the high temperature processing required by these layers can degrade the reflector (e.g., the Mo—Si or Mo—Be layers). 
     Conventional EUV multilayer reflectors can also be very delicate due to the need for precise interface properties to achieve high reflectance. Depositing metal absorbers and glass (SiO 2 ) buffers add unwanted thermal cycles that can blur the interfaces and reduce reflectance. 
     Thus, there is a need for a low temperature layer in an EUV reflective mask. Further, there is a need to use amorphous carbon layers as absorbers or buffers or both. Even further, there is a need to make an EUV mask with high reflectance. 
     SUMMARY OF THE INVENTION 
     An exemplary embodiment relates to a mask for integrated circuit fabrication equipment. The mask includes a multilayer film and an amorphous carbon layer above the multilayer film. The multilayer film is at least partially relatively reflective to radiation having a wavelength of less than 70 nanometers. 
     Another exemplary embodiment relates to an lithographic mask for fabrication equipment. The mask can include means for reflecting radiation and means for absorbing the radiation. The means for absorbing the radiation includes an amorphous carbon layer located above the means for reflecting radiation. 
     Another exemplary embodiment relates to a method of manufacturing a mask. The method includes providing a multilayer film on a substrate, providing an amorphous carbon mask over the multilayer film, and etching the amorphous carbon mask selectively to form a pattern. 
     Other principle features and advantages of the invention will become apparent to those skilled in the art upon review of the following drawings, the detailed description, and the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments will hereafter be described with reference to the accompanying drawings, wherein like numerals denote like elements, and: 
         FIG. 1  is a schematic cross-sectional view of an lithographic mask in accordance with an exemplary embodiment; 
         FIG. 2  is a schematic cross-sectional view of the lithographic mask illustrated in  FIG. 1 , showing a multilayer film formation step; 
         FIG. 3  is a schematic cross-sectional view of the lithographic mask illustrated in  FIG. 2 , showing a barrier layer deposition step; 
         FIG. 4  is a schematic cross-sectional view of the lithographic mask illustrated in  FIG. 3 , showing a reflective layer deposition step; 
         FIG. 5  is a schematic cross-sectional view of the lithographic mask illustrated in  FIG. 4 , showing a photoresist deposition step; and 
         FIG. 6  is a schematic cross-sectional view of the lithographic mask illustrated in  FIG. 5 , showing a selective etching step. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     With reference to  FIG. 1 , a binary mask  10  is provided for use with semiconductor fabrication equipment. Mask  10  can be utilized in extreme ultraviolet (EUV) lithography in which radiation has a wavelength of less than 70 nm is utilized (preferably between 5 and 14 nm). For example, radiation or ultraviolet light at a wavelength of 13.5 nm can be reflected off mask  10  to a semiconductor wafer coated with a photoresist. Alternatively, mask  10  can be employed at other locations with respect to the EUV or advanced lithographic system. 
     Binary mask  10  includes a substrate  12 , a multilayer  14 , a buffer or barrier layer  16 , and an absorbing layer  18 . Substrate  12  can be a low thermal expansion material (LTEM), such as, ultra low expansion (ULE) glass manufactured by Corning. Alternatively, substrate  12  can be a silicon oxynitride (SiON) material. Layer  14  includes individual films or thin layers  20  of various materials. 
     Multilayer  14  is provided above substrate  12 . Layers  20  of multilayer  14  can be molybdenum/beryllium (Mo—Be) film pairs (i.e., a layer of molybdenum above or below a layer of beryllium in each film pair). Each film pair is configured for maximum reflectance in the EUV band. Alternatively, layers  20  can be molybdenum/silicon (Mo—Si) film pairs configured for maximum reflectance in the EUV band. Each Mo—Si or Mo—Be film pair can be 5-7 nm thick. Multilayer  14  can include as many as forty pairs or more of layers  20  and have a total thickness of 300 nm. 
     Multilayer  14  is configured for reflectance at the actinic wavelength associated with the advanced lithographic or EUV lithographic system. The actinic wavelength is the wavelength which causes photochemical reactions to take place in the photoresist material on the wafer. Multilayer  14  can be manufactured by Osmic. 
     Alternative materials for multilayer  14  can also be used depending upon design parameters and system requirements. Any material highly reflective at EUV wavelengths (i.e., an EUV mirror) can be utilized for multilayer  14 . 
     Barrier layer  16  is disposed above multilayer  14 . Barrier layer  16  preferably has different etch characteristics than multilayer  14  (more particularly, different etch characteristics than the closest of layers  20  to layer  16 ). In an exemplary embodiment, barrier layer  16  includes amorphous carbon material. Contrary to conventional masks which utilize silicon dioxide as a barrier material, mask  10  preferably utilizes amorphous carbon. The amorphous carbon may contain other variations in its crystallographic structure. 
     Amorphous carbon can be deposited at a lower temperature than SiO 2 . For example, amorphous carbon can be deposited at a temperature of 100° C. Layer  16  includes an undercut  22  associated with an etching of aperture  26  discussed below with reference to FIG.  6 . 
     An absorptive layer  18  is disposed above layer  16  and preferably has different etch characteristics than layer  16 . Layer  18  can have similar etch characteristics to those of multilayer  14  (e.g., those of the closest of layers  20  to layer  16 ). Alternatively, layer  18  can have different etch characteristics than those of the closest of layers  20  to layer  16 . Layers  16  and  18  are preferably materials which can be easily deposited and etched in accordance with conventional fabrication techniques. 
     Layer  16  can be a 10-200 nm thick film or layer of amorphous carbon. Layer  18  is preferably an absorptive metal layer at the actinic wavelength. Layer  18  can be a 30 nm-100 nm thick layer or film of chromium, chromium oxide, titanium nitride or tantalum nitride. Alternatively, layer  18  is an amorphous carbon layer or layer  18  and layer  16  are replaced by layer  16  including amorphous carbon. Advantageously, amorphous carbon protects multilayer  14  and absorbs EUV radiation. 
     With reference to  FIGS. 1-6 , an exemplary method for fabricating binary mask  10  is described below as follows. As discussed above, mask  10  is manufactured without relying upon conventional phase shifting layers. 
     In  FIG. 2 , mask  10  is provided as a mask blank and includes substrate  12  and multilayer  14 . Substrate  12  can be an industry standard thickness. Substrate  12  and multilayer  14  can be a variety of shapes including squares, circles, ovals, rectangles, etc. 
     Layers  20  of multilayer  14  are preferably alternating layers of molybdenum and silicon, each 2-7 nm thick. Multilayer  14  is preferably formed on a top surface  60  of substrate  12 . Multilayer  14  can include any number of layers  20  of various sizes depending upon the desired reflective properties for mask  10 . As shown in  FIG. 2 , mask  10  does not yet include a pattern for reflecting an image to photoresist material on a semiconductor wafer. 
     In  FIG. 3 , film or repair buffer layer  16  is provided above a top surface  62  of multilayer  14 . Layer  16  can be a 10-200 nm thick amorphous carbon layer. Layer  16  can be deposited by a variety of processes including sputter deposition or chemical vapor deposition. 
     In  FIG. 4 , a film or reflective layer  18  is provided above a top surface  66  of layer  16 . Layer  18  is preferably an absorbing layer with respect to the radiation provided in the lithographic system and a reflective or blocking layer with respect to the radiation used in the heat treatment step described below with reference to FIG.  7 . Layer  18  can be a 30-300 nm thick layer of metal, such as, chromium. Layers  16  and  18  preferably have different etch characteristics. Alternatively, layer  18  is a 10-300 nm thick layer of amorphous carbon. As described above with reference to  FIG. 1 , layer  18  and layer  16  can be combined into one amorphous carbon layer. A variety of processes can be utilized to deposit layer  18  on surface  66  including sputter deposition. 
     With reference to  FIG. 5 , a photoresist layer  70  is provided above a top surface  68  of layer  18 . Photoresist layer  70  can be a positive photoresist material having a thickness of 500 nm. Layer  70  is preferably spin-coated onto layer  18 . 
     In  FIG. 6 , a conventional lithographic process can be utilized to provide apertures  72 ,  74  and  76  in photoresist layer  70 . An exemplary lithographic process for forming apertures is a consists of exposure using an e-beam writer followed by development of the resist pattern. 
     Apertures  72 ,  74  and  76  in photoresist layer  70  are utilized to etch layer  18  and layer  16 . Preferably, a chemical etch selective to layer  18  is utilized to extend aperture  72 ,  74  and  76  into layer  18  followed by a chemical etch selective to layer  16  to extend apertures  72 ,  74  and  76  through layer  16 . Apertures  72 ,  74  and  76  expose top surface  44  of multilayer  14 . Undercut  22  can be formed when layer  16  is etched. 
     Apertures  72 ,  74  and  76  form a pattern in layers  18  and  16  above multilayer  14 . The pattern includes an island  82  between recesses  72  and  74  and an island  84  between recesses  74  and  76 . Islands  82  and  84  can be a variety of dimensions depending upon the particular image to be transferred to the semiconductor wafer. 
     Referring again to  FIG. 1 , photoresist layer  70  can be stripped using a conventional photoresist removal process. Islands  82  and  84  can be removed in a selective etching process. The selective etching process can utilize another photoresist material. 
     According to one process, if layer  18  has different etch characteristics than the closest of layers  20  to layer  16 , the photoresist material can cover layer  18  and be exclusive of recesses  72 ,  74  and  76  and islands  82  and  84 . In this process, a two step etching process is utilized to remove layer  18  associated with islands  82  and  84  and layer  16  associated with islands  82  and  84 . 
     Advantageously, use of amorphous carbon as layer  16  or layer  18  avoids high temperature deposition processes of SiO 2 , metals, and other buffer and metal layers. The low temperature deposition of amorphous carbon can be 100° C. In contrast, high temperature deposition processes of conventional materials, such as, SiO 2  can be &gt;300° C. Other negative effects or multilayer reflector films can also be avoided. Advantageously, amorphous carbon can be etched in an oxygen plasma, thereby achieving higher selectivity to the multilayer compared to SiO 2  etching in halogen plasmas. 
     It is understood that although the detailed drawings, specific examples, and particular values given provide exemplary embodiments of the present invention, the exemplary embodiments are for the purpose of illustration only. The method and apparatus in the aforementioned embodiments are not limited to the precise details and descriptions disclosed. For example, although particular films, barrier layers, and substrates are described, other materials can be utilized. Various changes may be made to the details disclosed without departing from the spirit of the invention which is defined by the following claims.