Abstract:
The invention provides a mask blank for EUV exposure wherein a substrate is provided at its flank with an electrically conductive film unlikely to peel off in EUV exposure mask fabrication process steps, etc. and its fabrication process, and provide a mask for EUV exposure which is readily attachable to or detachable from an electrostatic chuck, thereby foreclosing the possibility of the mask remaining clinging firmly to the electrostatic chuck after EUV exposure and being hard to detach from it. A mask blank for EUV exposure is provided, in which on one major surface of a substrate, a reflective layer adapted to reflect EUV light and an absorptive layer located on said reflective layer for absorption of said EUV light are at least provided as a pattern-formation layer. An electrically conductive layer is formed on another major surface of the substrate, and the pattern-formation layer and the conductive layer on the opposite major surfaces of the substrate are in conduction with each other via one or more flank conductive films provided at the flank of the substrate.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates generally to a mask blank for lithography in the fabrication of semiconductor devices, etc. and its fabrication process as well as a mask for lithography, and more particularly to a mask blank for EUV exposure (EUV is an acronym of extreme ultraviolet) for the fabrication of the mask to transfer a mask pattern onto a wafer using EUV and its fabrication process as well as a mask for EUV exposure.  
         [0002]     As semiconductor devices are now much finer, there is an exposure technique available, in which patterns are transferred onto wafers under photomasks, employing optical projection aligners using KrF or ArF excimer lasers. Before long, however, exposure techniques relying on such optical projection aligners would reach their own resolution limits; so there are new transfer techniques proposed such as direct lithography by electron beam lithography systems, electron beam projection lithography: EPL), low energy electron beam projection lithography: LEEPL), and EUV lithography.  
         [0003]     Among new such lithography techniques, EUV exposure now attracts much attention as a lithography technique capable of being applied to semiconductor devices over two or more generations. This is because EUV exposure makes use of extreme ultraviolet light (EUV light having a wavelength of 13.5 nm) much shorter in wavelength than excimer lasers so that exposure can be implemented on a size usually reduced down to about ¼; it is thought of as limits of making the wavelength of ultraviolet exposure shortest.  
         [0004]     For EUV exposure, because of being unable to use a dioptric system due to short wavelengths, it is proposed to use a catoptric system and employ a reflection type mask as the mask (for instance, see patent publications 1 and 2).  
         [0005]      FIG. 9  is illustrative of one example of such a prior art EUV exposure mask blank and EUV exposure mask. An EUV exposure mask blank depicted in  FIG. 9 ( a ) have a structure such that a reflective layer  92  having a multilayer structure and adapted to reflect EUV light is located on a substrate  91 , an etching stopper layer  93  is provided on the reflective layer  92 , and an absorptive layer  94  for absorption of EUV light is formed on that etching stopper layer. An EUV exposure mask depicted in  FIG. 9 ( b ), on the other hand, is formed by patterning the absorptive layer of the above mask blank, and removing off the etching stopper layer  93  on the basis of the patterned absorptive layer. Upon incidence on the EUV exposure mask, the EUV light is reflected at the reflective layer  92  while absorbed in the absorptive layer  94 , so that the reflected EUV light produces a reduced transfer pattern on a wafer.  
         [0006]     With a mask attached to an aligner for implementing EUV exposure, as the mask sags even a bit due to its own weight, it brings on a misalignment in the post-transfer pattern. To prevent this, an electrostatic chuck is used to hold the mask in place. To this end, an electrically conductive layer must be provided facing away from the surface with an EUV exposure mask pattern formed on it to keep the mask in place.  
         [0007]     However, the EUV exposure mask having an electrically conductive layer is often likely to remain clinging firmly to the electrostatic chuck after EUV exposure, rendering its removal hard; there are problems arising in connection with the time taken for detachment operation, and contamination of the surface of the mask.  
         [0008]     There is one possible approach to obviating such problems, wherein, to bring both major surfaces of an EUV exposure mask blank in conduction with each other thereby facilitating removal of charges on the back surface, an electrically conductive layer is formed all around the flank of a blank substrate at the time of mask blank fabrication, for instance, the formation of films on both major surfaces of the blank substrate by sputtering. 
    Patent Publication 1: JP-B7-27198     Patent Publication 2: JP-A8-213303    
 
         [0011]     During mask fabrication using a mask blank with an electrically conductive film formed all around the flank of the substrate, however, the flank of the mask comes in contact with a pin of a mask holder chuck at a mask fabrication process step such as a washing or drying step or when the mask is washed to clear out it from stains resulting from exposure. This in turn causes the conductive film at the flank of the substrate to be mechanically rubbed due to the high speed rotation of the chuck, etc., ending up with a peel of the conductive film at the flank of the substrate and, hence, leading to contamination of the system or re-deposition of the once peeled film onto the mask, which are otherwise responsible for mask defects or other problem.  
       SUMMARY OF THE INVENTION  
       [0012]     In view of such problems as mentioned above, an object of the present invention is to provide a mask blank for EUV exposure wherein a substrate is provided at its flank with an electrically conductive film unlikely to peel off in EUV exposure mask fabrication process steps, etc. and its fabrication process, and provide a mask for EUV exposure which is readily attachable to or detachable from an electrostatic chuck, thereby foreclosing the possibility of the mask remaining clinging firmly to the electrostatic chuck after EUV exposure and being hard to detach from it.  
         [0013]     The invention of claim  1  is directed to a mask blank for EUV exposure in which on one major surface of a substrate, a reflective layer adapted to reflect EUV light and an absorptive layer located on said reflective layer for absorption of said EUV light are at least provided as a pattern-formation layer, characterized in that an electrically conductive layer is formed on another major surface of said substrate, and said pattern-formation layer and said conductive layer on the opposite major surfaces of said substrate are in conduction with each other via one or more flank conductive films provided at a flank of said substrate.  
         [0014]     In the invention of claim  2 , the mask blank for EUV exposure according to claim  1  is further characterized in that said flank conductive film is composed of the same material as that of said conductive layer.  
         [0015]     In the invention of claim  3 , the mask blank for EUV exposure according to claim  1  is further characterized in that said flank conductive film is composed of the same material as that of said pattern-formation layer.  
         [0016]     In the invention of claim  4 , the mask blank for EUV exposure according to claim  1  is further characterized in that said flank conductive film is composed of a material contained in said conductive layer and said pattern-formation layer.  
         [0017]     The invention of claim  5  is directed to a mask for EUV exposure, characterized in that it is fabricated using the mask blank for EUV exposure according to any one of claims  1 - 4 .  
         [0018]     The invention of claim  6  is directed to a process for fabrication of a mask blank for EUV exposure in which on one major surface of a substrate, a reflective layer adapted to reflect EUV light and an absorptive layer located on said reflective layer for absorption of said EUV light are at least provided as a pattern-formation layer, characterized by involving steps of (1) forming said reflective layer on one major surface of said substrate, (2) forming said absorptive layer on said reflective layer, (3) forming an electrically conductive layer on another major surface of said substrate, and (4) forming one or more flank conductive films at a flank portion of said substrate.  
         [0019]     In the invention of claim  7 , the process for fabrication of a mask blank for EUV exposure according to claim  6  is further characterized in that said conductive layer and said flank conductive film are simultaneously formed.  
         [0020]     In the invention of claim  8 , the process for fabrication of a mask blank for EUV exposure according to claim  6  is further characterized in that said pattern-formation layer and said flank conductive film are simultaneously formed.  
         [0021]     In the invention of claim  9 , the process for fabrication of a mask blank for EUV exposure according to claim  6  is further characterized in that said flank conductive film is formed by formation of said conductive layer and formation of said pattern-formation layer.  
         [0022]     In the invention of claim  10 , the process for fabrication of a mask blank for EUV exposure according to claim  6  is further characterized in that said flank conductive film is formed separately from formation of said conductive layer or formation of said pattern-formation layer.  
         [0023]     In the invention of claim  11 , the process for fabrication of a mask blank for EUV exposure according to any one of claims  6 - 10  is further characterized in that said flank conductive film is formed by a vacuum film-formation technique using a mask holder having a cutout space at a site with said flank conductive film formed thereon.  
         [0024]     According to the EUV exposure mask blank of the invention, the formation of an electrically conductive film at the flank of the mask blank at a site in mechanical contact with a mask jig is beforehand avoided, so that there is no peel of the flank conductive film, which prevents contamination of a mask and a mask fabrication system, resulting in much fewer mask defects count.  
         [0025]     According to the inventive process for the fabrication of a mask blank for EUV exposure, an electrically conductive film is formed at any desired position of the flank of the substrate at the time of forming a mask blank-formation thin film, so that the mask blank can be easily fabricated.  
         [0026]     The EUV exposure mask of the invention has another advantage that, since it is capable of ready attachment to, or ready detachment from, an electrostatic chuck, there is no contamination of a mask or a mask fabrication system due to a peel of the flank conductive film, ensuring much fewer mask defects count.  
         [0027]     Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.  
         [0028]     The invention accordingly comprises the features of construction, combinations of elements, and arrangement of parts which will be exemplified in the construction hereinafter set forth, and the scope of the invention will be indicated in the claims. 
     
    
     BRIEF ESCRIPTION OF THE DRAWINGS  
       [0029]      FIG. 1  is schematically illustrative in section of one exemplary mask blank for EUV exposure according to the invention.  
         [0030]      FIG. 2  is illustrative in schematic of one embodiment of the mask blank for EUV exposure according to the invention.  
         [0031]      FIG. 3  is illustrative in schematic of another embodiment of the mask blank for EUV exposure according to the invention.  
         [0032]      FIG. 4  is illustrative in schematic of yet another embodiment of the mask blank for EUV exposure according to the invention.  
         [0033]      FIG. 5  is illustrative in schematic of the steps of one fabrication process for the inventive mask blank for EUV exposure, shown in  FIG. 2 .  
         [0034]      FIG. 6  is schematically illustrative in section of the steps of another fabrication process for the inventive mask blank for EUV exposure.  
         [0035]      FIG. 7  is schematically illustrative in section of the steps of yet another fabrication process for the inventive mask blank for EUV exposure.  
         [0036]      FIG. 8  is schematically illustrative in section of one exemplary structure of the inventive mask for EUV exposure.  
         [0037]      FIG. 9  is illustrative in schematic of sectional structures of a prior art mask blank and mask for EUV exposure. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0038]     Some embodiments of the inventive mask blank for EUV exposure and its fabrication process as well as of the inventive mask for EUV exposure are now explained with reference to the accompanying drawings.  
         [0039]      FIG. 1  is schematically illustrative in section of one example of the inventive mask blank for EUV exposure, and  FIGS. 2, 3  and  4  are illustrative in schematic of embodiments of the inventive mask blank for EUV exposure. In  FIGS. 2, 3  and  4 , the same references as in  FIG. 1  are indicative of the same sites and materials.  
         [0040]      FIG. 5  is illustrative in schematic of the steps of the fabrication process for the inventive mask blank for EUV exposure, depicted in  FIG. 3 .  FIGS. 6 and 7  are schematically illustrative in section of the steps of other fabrication processes for the inventive mask blank for EUV exposure.  FIG. 8  is schematically illustrative in section of one exemplary structure of the inventive mask for EUV exposure.  
       Mask Blank for EUV Exposure  
       [0041]     As depicted in  FIG. 1 , the inventive mask blank  10  for EUV exposure comprises a pattern-formation layer  12  formed on one major surface of a substrate  11  and an electrically conductive layer  13  formed on another major surface of the substrate  11 , wherein the pattern-formation layer  12  and the conductive layer  13  on the opposite major surfaces of the substrate  11  are in conduction with each other via at least one flank conductive film  14  located at the flank of the substrate  11 .  
         [0042]     The pattern-formation layer  12  at least comprises a reflective layer  15  that reflects EUV light and an absorptive layer  18  located on that reflective layer for absorption of EUV light; however, the absorptive layer  18  is not necessarily in direct contact with the reflective layer  15 . Usually, the pattern-formation layer  12  is provided with an etching stopper layer  17  (also called a buffer layer) between the reflective layer  15  and the absorptive layer  18  for the purpose of preventing damages to the underlying reflective layer  15  at the time of dry etching the absorptive layer  18  in a pattern form.  
         [0043]     Optionally or if required, the pattern-formation layer  12  may be provided with a capping layer  16  on the reflective layer  15  for the purpose of prevention of oxidation of the reflective layer, or the like. Sometimes, to enhance the reflection contrast of inspection light (250 nm) at the time of mask inspection, a low-reflection layer such as TaO may be provided on the absorptive layer  18  (not shown).  
         [0044]     Each component of the mask blank for EUV exposure is now explained.  
       Substrate  
       [0045]     For the substrate  11  of the inventive mask blank  10  for EUV exposure, it is preferable to use a material that has a low coefficient of thermal expansion so as to keep pattern alignment accuracy high, possesses high smoothness and flatness so as to obtain high reflectivity and high transfer accuracy, and has high resistance to a washing fluid used for washing, etc. in a mask fabrication process. For instance, low thermal expansion glasses such as quartz glass and SiO 2 —TiO 2  glass, glass substrates such as crystallized glass resulting from precipitation of β-quartz solid solutions, and metal substrates such as silicon and Fe-Ni inver alloys may be used. The flatness of the mask blank, for instance, must be 50 nm or lower in a pattern area.  
       Pattern-Formation Layer  
       [0046]     For the reflective layer  15  that forms a part of the pattern-formation layer  12 , a material capable of reflecting EUV light used for EUV exposure with high reflectivity is used. To this end a multilayer film comprising molybdenum and silicon is frequently used. For instance, a reflective layer formed of a multilayer comprising 40 Mo layers, each being 2.74 nm thick, and 40 Si layers, each being 4.11 nm thick, is used. Besides, Ru/Si, Mo/Be, Mo compound/Si compound, Si/Nb periodic multilayer film, Si/Mo/Ru periodic multilayer film, Si/Mo/Ru/Mo periodic multilayer film, Si/Ru/Mo/Ru periodic multilayer film, etc., too, may be used as the material having high reflectivity in a specific wavelength range. However, the optimum film thickness varies from material to material.  
         [0047]     The multilayer film comprising Mo and Si may be prepared by a DC magnetron sputtering technique wherein a silicon target is first used to form a silicon film in an argon gas atmosphere, and a molybdenum target is then used to form a molybdenum film in an argon gas atmosphere, thereby forming one period of film. Then, 30 to 60, preferably 40, such periods of films are stacked together. Finally, the formation of a silicon film gives a reflective film comprising a multilayer film.  
       Capping Layer  
       [0048]     As the layer that forms a part of the pattern-formation layer  12 , the capping layer  16  may optionally be provided on the reflective layer  15  by formation of a silicon or ruthenium film by sputtering or the like for the purposes of preventing oxidation of the reflective layer and protecting the reflective layer against mask washing.  
       Etching Stopper Layer  
       [0049]     As the layer that forms a part of the pattern-formation layer  12 , usually, the etching stopper layer (also called the buffer layer)  17  is provided between the reflective layer  15  and the absorptive layer  18  so as to prevent damages to the underlying layer  15  at the time when the absorptive layer  18  for absorption of EUV light used for EUV exposure is pattern etched as by dry etching.  
         [0050]     In most cases, SiO 2  is used as the material for the etching stopper layer  17 ; however, it is acceptable to make use of Al 2 O 3 , Cr, CrN, etc. as the material of high etching resistance, although dependent on absorptive layer-etching conditions.  
         [0051]     When SiO 2  is used, it is preferable that a SiO 2  film is formed on the reflective layer comprising the above multilayer film by an RF magnetron sputtering technique wherein a SiO 2  target is used in an argon atmosphere.  
       Absorptive Layer  
       [0052]     For the material for the absorptive layer  18  that forms a part of the pattern-formation layer  12  and is adapted to absorb EUV light, for instance, Ta, TaN, a material comprising Ta as a major component, Cr, and a material that comprises Cr as a major component and at least one component selected from N, O and C may be used. Besides, materials such as TaSi, TaSiN, TaGe, TaGeN, WN, and TiN may also be used.  
       Conductive Layer  
       [0053]     In the invention, the electrically conductive layer  13  is formed on another major surface of the substrate  11  opposite to the pattern-formation layer  12  formed on one major surface of the substrate  11 . As already noted, the conductive layer  13  is for attachment to the electrostatic chuck of a mask for EUV exposure, and is made up of a metal or metal compound thin film that has an electrical conductivity and a thickness of about 80 to 150 nm, for instance, a Cr or CrN thin film.  
       Flank Conductive Film  
       [0054]     In the mask blank of the present invention, the pattern-formation layer  12  and the conductive layer  13  on the opposite major surfaces of the above substrate are in conduction with each other via at least one flank conductive film  14  located at the flank of the substrate. The flank conductive film  14  may be made up of the same material as that of the conductive layer  13 , the same material as that of the pattern-formation layer  12 , or both the materials for the conductive layer  13  and the pattern-formation layer  12 . Note here that it is not always necessary to use all the layers that form the pattern-formation layer. For instance, the flank conductive film may be formed of the material for the electrically conductive, reflective or absorptive layer. For the material for the flank conductive film  14 , for instance, use may be made of a metal or metal compound thin film exhibiting electrical conductivity such as Cr, and CrN, or a multilayer film comprising Mo, Si, and Mo and Si, all having preferably a thickness of about 80 nm to about 150 nm.  
         [0055]     The flank conductive film  14  is preferably formed simultaneously with the formation of the pattern-formation layer  12  and/or the conductive layer  13 , because the fabrication process can be cut back on the same vacuum system.  
         [0056]     Alternatively, only the flank conductive film  14  may be formed in any separate step.  
         [0057]     The flank conductive film  14  is located at a position with a width such that in the mask blank fabrication step, the mask fabrication step and the EUV exposure step, the flank is not in mechanical contact with the jig, etc. How many flank conductive films  14  are located may be optionally determined.  
         [0058]     In the way as described above, the inventive mask blank for EUV exposure such as one shown in  FIG. 1  is obtained.  
         [0059]     Several embodiments of the flank conductive film  14  are now explained.  
       First Embodiment  
       [0060]      FIG. 2 ( a ) is a top view of the mask blank  20  for EUV exposure that is one example of the present invention;  FIG. 2 ( b ) is a side view as taken from an arrow A direction; and  FIG. 2 ( c ) is a side view as taken from an arrow B direction.  
         [0061]     As depicted in  FIG. 2 , in the inventive mask blank  20  for EUV exposure, a reflective layer that reflects EUV light and an absorptive layer located on that reflective layer for absorption of EUV light are at least provided as the pattern-formation layer  12  on one major surface of the substrate  11 , and the electrically conductive layer  13  is formed on another major surface of the substrate  11 . And then, the pattern-formation layer  12  and the conductive layer  13  on the opposite major surfaces of the substrate  11  are in conduction with each other via at least one flank conductive film  24  provided at the flank of the substrate  11 . The conductive film  24  depicted in  FIG. 2  are made up of materials contained in both the pattern-formation layer  12  and the conductive layer  13 , and near the middle of the flank conductive film  24  the materials contained in both overlap.  
         [0062]     The flank conductive film  24  may be formed simultaneously with the formation of the pattern-formation layer  12  and the conductive layer  13  as by sputtering.  
       Second Embodiment  
       [0063]     In the inventive mask blank  30  for EUV exposure depicted in  FIG. 3 , a reflective layer that reflects EUV light and an absorptive layer located on that reflective layer for absorption of EUV light are at least provided as the pattern-formation layer  12  on one major surface of the substrate  11 , and the electrically conductive layer  13  is formed on another major surface of the substrate  11 . And then, the pattern-formation layer  12  and the conductive layer  13  on the opposite major surfaces of the substrate  11  are in conduction with each other via at least one flank conductive film  34  provided at the flank of the substrate  11 . The flank conductive film  34  is made up of the same material as that for the conductive layer  13 .  
         [0064]     The flank conductive film  34  may be formed simultaneously with the formation of the conductive layer  13  as by sputtering.  
       Third Embodiment  
       [0065]     In the inventive mask blank  40  for EUV exposure depicted in  FIG. 4 , a reflective layer that reflects EUV light and an absorptive layer located on that reflective layer for absorption of EUV light are provided as the pattern-formation layer  12  on one major surface of the substrate  11 , and the electrically conductive layer  13  is formed on another major surface of the substrate  11 . And then, the pattern-formation layer  12  and the conductive layer  13  on the opposite major surfaces of the substrate  11  are in conduction with each other via at least one flank conductive film  44  provided at the flank of the substrate  11 . The flank conductive film  44  is made up of the same material as that for the pattern-formation layer  12 .  
         [0066]     The flank conductive film  44  may be formed simultaneously with the formation of the pattern-formation layer  12  as by sputtering.  
       Fabrication Process of the Mask Blank for EUV Exposure  
       [0067]     The fabrication process of the inventive mask blank for EUV exposure involves the steps of forming a reflective layer that reflects EUV light on one major surface of a substrate, forming on that reflective layer an absorptive layer for absorption of EUV light, forming an electrically conductive layer on another major surface of the substrate, and forming at least one flank conductive film at the flank of the substrate.  
         [0068]     Several embodiments of the fabrication process of the inventive mask blank for EUV exposure are now explained primarily with reference to how to form the flank conductive film.  
       First Embodiment  
       [0069]     The first embodiment is directed to the EUV exposure mask blank fabrication process wherein a thin-film layer that forms a mask blank is formed by a vacuum film-formation technique using a mask holder having a cutout space at a site where a flank conductive film is to be formed and, at the same time, the flank conductive film is formed.  
         [0070]     With the EUV exposure mask blank of  FIG. 3  in mind, reference is made to  FIG. 5 .  
         [0071]     The pattern-formation layer  12  is formed on one major surface of the substrate  11  at a given thickness as by sputtering, and then placed in a mask holder  51  having a cutout space  52 , as depicted in  FIG. 5 ( a ).  FIG. 5 ( b ) is a sectional view as taken on A-A line in  FIG. 5 ( a ).  
         [0072]     Then, as depicted in  FIG. 5 ( c ), the electrically conductive layer  13  is formed on another major surface of the substrate  11  at a given thickness as by sputtering.  FIG. 5 ( d ) is a sectional view as taken on B-B line in  FIG. 5 ( c ). Simultaneously with this, the flank conductive film  34  is formed at the flank of the substrate  11  in the mask holder  51  with the cutout space  52  located, giving the inventive mask blank for EUV exposure.  
       Second Embodiment  
       [0073]     The second embodiment is directed to a process of fabricating an EUV exposure mask blank having a flank conductive film by a liftoff technique, which process is well fit for where, upon formation of films on both major surfaces of the substrate, the sputtered films do not fully come down to the flank.  
         [0074]     As depicted in  FIG. 6 ( a ), the pattern-formation layer  12  is provided on one major surface of the substrate  11  at a given thickness as by sputtering, and the electrically conductive layer  13  is formed on another major surface of the substrate  11  at a given thickness as by sputtering.  
         [0075]     Then, a liftoff material is coated or laminated on the conductive layer  13  to form a liftoff layer  65  of about 0.1 to 1 μm in thickness. For the liftoff layer  65 , for instance, a layer obtained by coating of a photosensitive resin solution or a dry film is used.  
         [0076]     Then, as depicted in  FIG. 6 ( b ), the above substrate is placed in a mask holder  61  having a cutout space  62 .  
         [0077]     Then, as depicted in  FIG. 6 ( c ), an electrically conductive material is formed as by sputtering on the liftoff layer  65  on another major surface of the substrate  11 , and at the flank of the substrate  11  in the holder  61  having a cutout space  62 , thereby forming an electrically conductive layer  66  and a flank conductive film  64 .  
         [0078]     Then, the above substrate is detached from the mask holder ( FIG. 6 ( d )), and the liftoff layer  65  is lifted off with a solvent in which the liftoff layer  65  is dissolvable, thereby allowing the conductive film  66  on the liftoff layer  65  to peel off together with the liftoff layer  65 . In this way, the inventive EUV exposure mask blank having the flank conductive film  64  is obtained ( FIG. 6 ( e )). In this embodiment, the flank conductive film  64  material may be the same as, or different other than, that of the pattern-formation layer  12  and the conductive layer  13 .  
       Third Embodiment  
       [0079]     The third embodiment is directed to a process of fabricating an EUV exposure mask blank having a flank conductive film by masking using a blocking plate, which process is well fit for where, upon formation of films on both major surfaces of the substrate, the sputtered films do not fully come down to the flank.  
         [0080]     As depicted in  FIG. 7 ( a ), the pattern-formation layer  12  is provided on one major surface of the substrate  11  at a given thickness as by sputtering, and the electrically conductive layer  13  is formed on another major surface of the substrate  11  at a given thickness as by sputtering.  
         [0081]     Then, as depicted in  FIG. 7 ( b ), the above substrate is placed in a mask holder  71  having a cutout space  72 . Then, the flank of the substrate and the conductive layer  13  are covered up with a blocking plate  75  except the position to be provided with the desired conductive film.  
         [0082]     Then, as depicted in  FIG. 7 ( c ), an electrically conductive material is sputtered or otherwise formed on the blocking plate  75  and the portion of the flank of the substrate  11  that is not covered up with the blocking plate to form an electrically conductive film  76  and a flank conductive film  74 .  
         [0083]     Then, the substrate  11  is removed out of the mask holder  71 , thereby obtaining the inventive EUV exposure mask blank having the flank conductive film  74  ( FIG. 7 ( d )). In this embodiment, the flank conductive film  74  material may be the same as, or different other than, that of the pattern-formation layer  12  and the conductive layer  13 .  
       Mask for EUV Exposure  
       [0084]      FIG. 8  is schematically illustrative in section of the inventive mask  80  for EUV exposure that has been fabricated using the inventive EUV exposure mask blank depicted typically in  FIG. 1 .  
         [0085]     The reference numerals given in  FIG. 8  stand for the same sites as in  FIG. 1 , and the explanation of each layer in the EUV exposure mask is not given because it has been explained with reference to the mask blank.  
         [0086]     The present invention is now explained in further details with reference to some examples.  
       EXAMPLE  
     Example 1  
       [0087]     A 4.11 nm thick silicon film was formed on one major surface of an optically polished synthetic quartz substrate of  6  inches square (0.25 inch in thickness) by a DC magnetron sputtering technique using a silicon target in an argon atmosphere, subsequently followed by formation of a 2.74 nm thick molybdenum film using a molybdenum target, thereby forming one period of film. Forty such films were stacked one upon another. Finally, a silicon film was capped to form a reflective layer comprising a multilayer film of Mo and Si and adapted to reflect EUV light.  
         [0088]     Then, a 50 nm thick SiO 2  film was formed on the above reflective layer by an RF magnetron sputtering technique using an SiO 2  target in an argon gas atmosphere, thereby obtaining an etching stopper layer.  
         [0089]     Subsequently, a 0.1 μm thick TaN film was formed on the above SiO 2  film by a DC magnetron sputtering technique, thereby forming an absorptive layer capable of absorbing EUV light.  
         [0090]     A substrate with the above reflective layer, etching stopper layer and absorptive layer provided as a pattern-formation layer on its one major surface was placed in a mask holder having a single cutout space.  
         [0091]     Then, a 0.1 μm thick chromium film was formed on another major surface of the substrate facing away from the pattern-formation layer by an RF sputtering technique, thereby providing an electrically conductive layer. Simultaneously with the formation of the conductive chromium film, a 20 nm thick, 20 mm wide chromium film was formed as a flank conductive film on the portion of the flank of the substrate corresponding to the site provided with the cutout space, thereby obtaining a flank conductive film. In this way, there was an EUV exposure mask blank obtained, wherein the pattern-formation layer and the conductive layer were in conduction with each other via that chromium flank conductive film.  
         [0092]     Then, an EB resist was coated on this EUV exposure mask blank to form a resist pattern by EB lithography. Then, a TaN layer was dry etched using Cl 2  gas, and the resist pattern was stripped off, after which the SiO 2  film was removed off with dilute fluoric acid to obtain an EUV exposure mask.  
         [0093]     At each step of the above EUV exposure mask fabrication process, there was no peel of the flank Cr conductive film at all; attachment or detachment of the mask to or from the electrostatic chuck in the EUV aligner was readily done, so that high-accuracy transfer patterns could be obtained.  
       Example 2  
       [0094]     On one major surface of an optically polished SiO 2 —TiO 2  substrate of 6 inches square, there was a pattern-formation layer formed, which was made up of a multilayer film layer consisting of 40 molybdenum films of 2.74 nm in thickness and 40 silicon films of 4.11 nm in thickness, a 0.01 μm chromium etching stopper layer and a 0.1 nm thick TaN absorptive layer, and on another major surface of the substrate there was a 0.1 μm thick CrN film formed.  
         [0095]     Then, the above substrate was placed in a mask holder having two cutout spaces. While the site of the substrate with no flank conductive film formed was blocked off by a stainless blocking plate, a Ta film was formed by sputtering, thereby obtaining an EUV exposure mask blank which had two flank conductive films of 20 nm in thickness and 15 mm in width at the middles of the opposite substrate flanks and in which the pattern-formation layer and the conductive layer were in conduction with each other via the Ta flank conductive films.  
         [0096]     Using the above EUV exposure mask blank, the absorptive layer and the etching stopper layer were pattern etched to obtain an EUV exposure mask. As in Example 1, the present EUV exposure mask was free of any peel of the flank conductive films at each fabrication process step; attachment or detachment of the mask to or from the electrostatic chuck in the EUV aligner was readily done, so that high-accuracy transfer patterns could be obtained.