Patent Publication Number: US-2010119958-A1

Title: Mask blank, mask formed from the blank, and method of forming a mask

Description:
FIELD OF THE INVENTION 
     The present invention relates to masks and mask blanks for semiconductor fabrication processes. 
     BACKGROUND 
     Decreases in integrated circuit (IC) device dimensions are accompanied by decreases in dimensions of circuit pattern elements which connect the IC devices. If the wavelength of coherent light employed in a photolithographic fabrication process is not substantially smaller than the minimum dimension within the reticle through which those integrated circuit devices and conductor elements are printed, the resolution, exposure latitude and depth of focus of the printed device or element decreases. This is due to aberrational effects of coherent light passing through openings of width similar to the wavelength of the coherent light. 
     Phase shift masks (PSMs) have been used in projection lithography systems to expose a layer of photoresist formed on a semiconductor substrate as the requirements of image definition and depth of focus have become more stringent. 
     PSMs typically incorporate an additional layer, usually patterned, within the conventional chrome metal-on-glass reticle construction. The additional layer, which is commonly referred to as a shifter layer, has a thickness related to the wavelength of coherent light passing through the PSM. Coherent light rays passing through the transparent substrate and the shifter layer have different optical path lengths and thus emerge from those surfaces with different phases. The interference effects of the coherent light rays of different phase provided by a Phase Shift Mask (PSM) form a higher resolution image when projected onto a semiconductor substrate. 
     U.S. Pat. No. 5,045,417 describes a PSM as shown in  FIG. 1  of the present disclosure. The mask has light shield regions, A and transmission regions B for transferring a given pattern at least by irradiation of coherent light locally. A transparent film  4   a  is formed above a substrate  2  in a pattern slightly wider than that of the pattern of metal layer  3 . Thus, a phase shifting portion  4   a  is formed in a part of the transmission region B for shifting a phase of transmitted light. A phase contrast is generated between the light transmitted through the phase shifting portion  4   a  and the light transmitted through the remaining portion  5  of transmission region B where the phase shifting portion  4   a  is not formed. The phase shifting portion  4   a  is arranged so that the interfering light is weakened in the boundary area of the transmission region B and light shield region A. 
     SUMMARY OF THE INVENTION 
     In some embodiments, a mask for manufacturing a semiconductor device comprises a transparent substrate. A metal-containing layer overlies the transparent substrate in a first region. A capping layer overlies and is coextensive with the metal-containing layer without wrapping around side edges of the metal-containing layer. The capping layer is substantially free of nitride. The transparent substrate has a second region separate from the first region. The transparent substrate is exposed in the second region. 
     In some embodiments, a mask blank for manufacturing a semiconductor mask or reticle comprises a transparent substrate. A metal layer overlies the transparent substrate. A planar capping layer overlies the metal layer without wrapping around side edges thereof. The capping layer is substantially free of nitride. 
     In some embodiments, a method of forming a mask comprises forming a metal-containing layer above a transparent substrate in a first region on a first surface of the transparent substrate. A capping layer is formed overlying and coextensive with the metal-containing layer, such that the capping layer is substantially free of nitride. The first surface of the transparent substrate is exposed in a second region separate from the first region, so that the metal-containing layer includes at least two patterns in the first region, with the second region occupying an entire distance between the at least two patterns, and the second region is free of the capping layer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross section of a prior art phase shift mask. 
         FIG. 2A  is a cross section of an example of a phase shift mask blank. 
         FIG. 2B  is a cross section of a phase shift mask formed from the blank of  FIG. 2A . 
         FIG. 3A  is a cross section of an example of a binary mask blank. 
         FIG. 3B  is a cross section of a binary mask formed from the blank of  FIG. 3A . 
     
    
    
     DETAILED DESCRIPTION 
     This description of the exemplary embodiments is intended to be read in connection with the accompanying drawings, which are to be considered part of the entire written description. In the description, relative terms such as “lower,” “upper,” “horizontal,” “vertical,”, “above,” “below,” “up,” “down,” “top” and “bottom” as well as derivative thereof (e.g., “horizontally,” “downwardly,” “upwardly,” etc.) should be construed to refer to the orientation as then described or as shown in the drawing under discussion. These relative terms are for convenience of description and do not require that the apparatus be constructed or operated in a particular orientation. 
     The inventors have determined that phase shift masks (PSMs) are subject to a mask haze problem. Haze is a complicated precipitate, induced by ammonia, sulfured ion components and the like. Two common ways to address the mask haze problems are: to use less chemical mask cleaning; and chemical controlled mask storage with N 2  gas purge. 
     However, in a PSM including a nitride material in the transparent layer of the mask blank (overlying the metal regions), the inclusion of nitrogen in the mask blank film can generate ammonia to induce haze problems. From the composition of a transparent layer, the PSM may include a large amount of nitrogen capable of serving as a source of ammonia NH 4 + after exposure to light from an ArF excimer laser light source (wavelength: 193 nm). 
       FIG. 2A  is a cross sectional diagram of a phase shift mask blank  200  for manufacturing a phase shift mask (PSM)  201  (shown in  FIG. 2B ) for a semiconductor device. In some embodiments, as shown in  FIG. 2A , a mask blank  200  for manufacturing a semiconductor mask or reticle comprises: a transparent substrate  202 ; a metal layer  204  overlying the transparent substrate  202 ; and a planar capping layer  206  overlying the metal layer  204  without wrapping around side edges thereof, wherein the capping layer  206  is substantially free of nitride. 
     By providing a capping layer  206  without nitrogen on the PSM blank  200 , a substantial ammonia generator is eliminated as a source of haze. 
     The mask blank  200  comprises a transparent substrate  202 , formed of a material such as a quartz, CaF 2  or other material that is transparent to the exposure light. 
     A metal-containing phase shift layer  204  is formed overlying the transparent substrate  202 . In some embodiments, the metal of which the phase shift function film  204  is constructed may include any element selected from among transition metals, lanthanoids and combinations thereof. Examples include, Mo, Zr, Ta, Cr and Hf. In more specific examples, metal containing layer  204  may be a material such as MoSi, ToSi 2 , iron oxide, inorganic material, Mo, Nb 2 O 5 , Ti, Ta, CrN, MoO 3 , MoN, Cr 2 O 3 , TiN, ZrN, TiO 2 , TaN, Ta 2 O 5 , SiO 2 , NbN, Si 3 N 4 , ZrN, Al 2 O 3 N, or combinations thereof. In one example, the metal containing layer is formed of either MoSi, MoSiON or Cr. 
     The metal-containing layer  204  may be about 700 Å thick for technology nodes beyond 0.13 μm technology, for example, but other thicknesses may be used as appropriate for various other technology nodes. For example, the thickness of metal-containing layer  204  may range from 400 to 1500 Å thick. 
     A capping layer  206  is formed overlying and coextensive with the metal-containing layer  204 , without wrapping around side edges thereof. The capping layer  206  is substantially free of nitride. In some embodiments, the capping layer  206  is an oxide, such as SiO or SiO 2 . The capping layer  206  may be about 50 Å thick, for example. 
     In some embodiments, as shown in  FIG. 2A , the phase shift mask blank  200  further includes a second metal containing layer  208  formed on the capping layer  206 . The second metal containing layer  208  may comprise Cr, for example. The second metal containing layer  208  may be a chromium-based light shielding or antireflection film  208  formed on the capping layer  206  for reducing reflection from the metal film  204 . The chromium-based light-shielding film or chromium-based antireflection film  208  may be made of chromium oxycarbide (CrOC), chromium oxynitride carbide (CrONC) or a multilayer combination of both. The second metal containing layer  210  may be about 590 Å thick, for example. 
     In some embodiments, the film  208  is a CrOC film consisting essentially of 20 to 95 at % Cr, 1 to 30 at % C and 1 to 60 at % O. In other embodiments, the film  208  is a CrONC film consisting essentially of 20 to 95 at % Cr, 1 to 20 at % C,  1  to  60  at % O, and 1 to 30 N. 
     The chromium-based light-shielding film or chromium-based antiroflection film  208  can be formed by reactive sputtering. For example, the target may be chromium or chromium having oxygen, nitrogen, carbon or a combination thereof added. The sputtering gas is an inert gas such as neon, argon or krypton to which a gas containing carbon, oxygen or nitrogen may be added, depending on the desired final composition of the layer  208 . 
     A layer  210  of photoresist is formed on the second metal containing layer  208 . A variety of photoresists may be used. For example, layer  210  may comprise NEB-22 negative photoresist sold by Sumitomo Chemical Co., Ltd., Tokyo, Japan, with a thickness of about 3000 Å. The photoresist is used during a photolithographic process for selectively etching material from the mask blank  200  to form the PSM  201  shown in  FIG. 2B . 
     The layer  210  of photoresist may be applied by spin coating, for example, following deposition of the Cr layer  208 . Alternatively, the photoresist  208  may be formed by chemical vapor deposition (CVD), physical vapor deposition (PVD), atomic layer deposition (ALD), remote plasma enhanced chemical vapor deposition (RPECVD), liquid source misted chemical deposition (LSMCD), coating, or another process that is adapted to form a thin film layer over the Cr layer  208 . 
     In one embodiment of a PSM blank as shown in  FIG. 2A , the substrate  202  comprises quartz, the metal containing layer  204  comprises MoSiON, the capping layer  206  comprises SiO 2 , and the mask blank  200  further comprises a layer  208  of Cr overlying the capping layer  206 . A layer  210  of NEB-22 photoresist is applied over the Cr layer  208 . This is only one example, and any combination of the various constituent layers described above may be used. 
       FIG. 2B  is a cross sectional diagram of an attenuated phase shift mask  201 , made from PSM blank  200 , for manufacturing a semiconductor device. The mask  201  comprises a transparent substrate  202 , formed of a material such as a quartz, CaF 2  or other material that is transparent to the exposure light. 
     A metal-containing layer  204   a ,  204   b  is formed from the layer  204 , overlying the transparent substrate  202  in a first region. In some embodiments, metal-containing layer  204   a ,  204   b  may include any element selected from among transition metals, lanthanoids and combinations thereof. Examples include, Mo, Zr, Ta, Cr and Hf. In more specific examples, metal containing layer  204  may be a material such as ToSi 2 , iron oxide, inorganic material, Mo, Nb 2 O 5 , Ti, Ta, CrN, MoO 3 , MoN, Cr 2 O 3 , TiN, ZrN, TiO 2 , TaN, Ta 2 O 5 , SiO 2 , NbN, Si 3 N 4 , ZrN, Al 2 O 3 N, or combinations thereof. In one example, the metal containing layer is formed of either MoSi, MoSiON or Cr. 
     A capping layer  206   a ,  206   b  is formed overlying and coextensive with the metal-containing layer  204   a ,  204   b  without wrapping around side edges thereof. The capping layer  206   a ,  206   b  is substantially free of nitride. In some embodiments, the capping layer is an oxide, such as SiO or SiO 2 . 
     In some embodiments, the step of forming a capping layer  206  includes plasma vapor deposition. Preferably, the step of forming a capping layer  206  includes sputtering. For example, an SiO 2  target may be used for sputtering the capping layer  206 . 
     The transparent substrate  202  has a second region  207  separate from the first region  204   a ,  204   b . The transparent substrate  202  is exposed in the second region  207 , without having the capping layer  206   a  or  206   b  extending over the second region. The second region  207  occupies an entire distance between the at least two patterns  204   a ,  204   b . The second region  207  is also free of the capping layer  206   a ,  206   b.    
     The resulting PSM  201  has a transparent substrate  202 . A metal-containing layer  204   a ,  204   b  overlies the transparent substrate  202  in a first region. A capping layer  206   a ,  206   b  overlies and is coextensive with the metal-containing layer  204   a ,  204   b  without wrapping around side edges of the metal-containing layer. The capping layer  206   a ,  206   b  is substantially free of nitride. The transparent substrate  202  has a second region  207  separate from the first region containing metal layer  204   a ,  204   b . The transparent substrate  202  is exposed in the second region  207 . 
     In one example, the transparent substrate  202  is quartz, the phase shifting regions  204   a ,  204   b  are MoSiON, and the capping layer is SiO 2 . Samples of a PSM  201  as shown in  FIG. 2B  were fabricated, and the yield was compared with that of standard (STD) masks formed with a nitride capping layer over the phase shifting layer thereof. The process capability index Cp for the mask having a capping layer without nitride compares favorably to that of a mask formed with a nitride capping layer, as shown in Table 1. 
     
       
         
           
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Cp Yield 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 STD 
                 71.03 
               
               
                   
                 Mask w/o nitride 
                 72.01 
               
               
                   
                 in capping layer 
               
               
                   
                 Bias 
                 0.98 
               
               
                   
                   
               
            
           
         
       
     
     A sample was tested and haze check performed by 172 nm vacuum ultra violet (VUV) exposure. The PSM  201  having the capping layer  206   a ,  206   b  without nitride was exposed to the 172 nm light for 15 minutes. A subsequent scanning electron microscope inspection showed no noticeable haze defects. 
       FIG. 4  shows a process apparatus for depositing the layers  204 ,  206 ,  208  on the substrate  202 . The metal-containing layer  204  may be formed by sputtering, as described below with reference to apparatus  400  shown in  FIG. 4 . The substrate  202  and a target (or targets)  404  in a chamber  406 , feeding a sputtering gas  408  or gases to the chamber  406 , and applying power to the target  404  to create a discharge for depositing a film  204  on the substrate  202 . The sputtering gas  408  may be an inert gas such as neon, argon or krypton, optionally mixed with a reactive gas which such as oxygen-containing gases, nitrogen-containing gases or carbon-containing gases, depending on the desired type of light elements including oxygen, nitrogen and carbon, of which the metal-containing phase shift layer  204  is formed. 
     For example, the target or targets  404  may contain molybdenum and silicon, and the sputtering gas  408  may include an inert gas plus oxygen and nitrogen. The target(s)  404  contains a metal (corresponding to the metal contained in the metal-containing phase shift layer  204  to be formed) and/or silicon. The metal element (e.g., Mo) and silicon may be formed using a metal target and a silicon target separate from each other, or a metal silicide (e.g., MoSi) target and a silicon target, or a metal silicide (e.g., MoSi) target alone. Similarly, in place of an Mo target, an alloy target including an additional metal may optionally be used. Alternatively, two separate metal targets and a silicon target may be used. In other embodiments, the oxygen for forming MoSiON may be provided using an SiO 2  target. 
     In one embodiment, the sputtering gas  408  is argon. When only an inert gas is used as the sputtering gas  408 , a metal containing layer  204  composed of a metal and silicon (e.g., MoSi) can be formed. 
     In one embodiment, the capping layer is applied using an Si or SiO 2  target, a sputtering gas containing O 2  and Ar gas, and RF power of 500 to 1000 W. 
       FIG. 3  is a cross section of a binary mask blank  300  according to another embodiment. The binary mask blank  300  comprises a transparent substrate  302 ; a metal layer  304  overlying the transparent substrate  302 ; and a planar capping layer  306  overlying the metal layer  304  without wrapping around side edges thereof, wherein the capping layer  306  is substantially free of nitride. A layer of photoresist  308  is formed over the capping layer  306 . The capping layer  306  can also prevent haze formation in a binary mask blank  300 , in a manner analogous to haze prevention in the PSM described above. 
     The mask blank  300  is used to malce a mask  301  ( FIG. 3B ). In some embodiments, mask  301  is an extreme ultraviolet mask. The mask blank  300  comprises a transparent substrate  302 , formed of a material such as a quartz, CaF 2  or other material that is transparent to the exposure light. 
     A metal-containing phase shift layer  304  is formed overlying the transparent substrate  302 . In some embodiments, the metal of which the phase shift function film  204  is constructed may include any element selected from among transition metals, lanthanoids and combinations thereof. Examples include, Mo, Zr, Ta, Cr and Hf. In more specific examples, metal containing layer  304  may be a material such as MoSi, ToSi 2 , iron oxide, inorganic material, Mo, Nb 2 O 5 , Ti, Ta, CrN, MoO 3 , MoN, Cr 2 O 3 , TiN, ZrN, TiO 2 , TaN, Ta 2 O 5 , SiO 2 , NbN, Si 3 N 4 , ZrN, Al 2 O 3 N, or combinations thereof. In one example, the metal containing layer comprises Cr. 
     The metal-containing layer  304  may be about 700 Å thick, for example, but other thicknesses may be used as appropriate for various other technology nodes. For example, the thickness of metal-containing layer  304  may range from 400 to 1500 Å thick. 
     A capping layer  306  is formed overlying and coextensive with the metal-containing layer  304 , without wrapping around side edges thereof. The capping layer  306  is substantially free of nitride. In some embodiments, the capping layer  306  is an oxide, such as SiO or SiO 2 . The capping layer  306  may be about 50 Å thick, for example. 
     A layer  308  of photoresist is formed on the capping layer  306 . A variety of photoresists may be used. For example, layer  308  may comprise NEB-22 negative photoresist, with a thickness of about 3000 Å. The photoresist  308  is used during a photolithographic process for selectively etching material from the mask blank  300  to form the mask  301  shown in  FIG. 3B . 
       FIG. 3B  shows the completed binary mask  301 , formed from the blank  300  by photo-patterning the photoresist layer  308  and removing the undesired patterns. The binary mask  301  has a transparent substrate  302 ; a metal layer  304   a ,  304   b  overlying the transparent substrate  302  in a first region; and a planar capping layer  306   a ,  306   b  overlying the metal layer  304   a ,  304   b  without wrapping around side edges thereof. The capping layer  306   a ,  306   b  is substantially free of nitride. The top surface of the transparent substrate  302  is exposed in a second region  307  separate from the first region containing the metal layer patterns  304   a ,  304   b , so that the metal-containing layer includes at least two patterns  304   a ,  304   b  in the first region, with the second region  307  occupying an entire distance between the at least two patterns  304   a ,  304   b , and the second region  307  is free of the capping layer  306   a ,  306   b . The capping layer  306   a ,  306   b  can also prevent haze formation in a binary mask  301 , in a manner analogous to haze prevention in the PSM described above. 
     Although the invention has been described in terms of exemplary embodiments, it is not limited thereto. Rather, the appended claims should be construed broadly, to include other variants and embodiments of the invention, which may be made by those skilled in the art without departing from the scope and range of equivalents of the invention.