Abstract:
An EUV photolithographic mask device and a method of fabricating the same. The EUV photolithographic mask comprises a multi-layer over an EUV masking substrate and a patterned light absorbing layer formed on the multi-layer. The method comprises the steps of forming a multi-layer on an EUV mask substrate, forming a light absorbing layer on the multi-layer, and etching an opening through the light absorbing layer to the multi-layer. The light absorbing layer includes a metal selected from the group comprising nickel, chromium, cobalt, and alloys thereof, and is preferably nickel.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    Extreme ultraviolet is the most commonly accepted solution for next generation lithography (NGL). The mask is a reflective system having up to 50 pairs of multi-layer materials and the absorber layer patterned with low temperature processes. The current two basic EUV mask patterning approaches (Direct Metal Patterning and Damascene Process) involves multi-steps of etching/film deposition/chemical mechanical polishing (CMP) process.  
           [0002]    U.S. Pat. No. 5,958,629 to Yan et al. describes a method of fabricating EUV masks by forming an etch stop layer over the surface of a mask to create a more controllable etch profile for etching patterns into the material above the etch stop layer.  
           [0003]    U.S. Pat. No. 5,935,737 to Yan describes a method of fabricating EUV masks using dual defect-absorbing layers to ensure that through two steps of repair, the repair stains are eliminated on that section of the mask which must cleanly reflect light in the case of a reflective mask, or transmit light in the case of a transmissive mask.  
           [0004]    U.S. Pat. No. 5,521,031 to Tenant et al. describes a method of fabricating EUV masks by incorporating the operating principle of the attenuated phase mask in a reflecting structure. The apparatus serves as an alternative, or supplement, to a surface-activated resist to permit projection-reduction lithography with improved image edge definition.  
         SUMMARY OF THE INVENTION  
         [0005]    Accordingly, it is an object of the present invention to provide EUV masks and a method of fabricating the EUV masks using less processing steps.  
           [0006]    Another object of the present invention is to provide EUV masks and a method of fabricating the EUV masks using low processing temperatures.  
           [0007]    Yet another object of the present invention is to provide EUV masks and a method of fabricating the EUV masks with minimum sub-layer damage.  
           [0008]    A further object of the present invention is to provide an easier and more economic method of fabricating EUV masks.  
           [0009]    Another object of the present invention is to use nickel (Ni) as an absorber layer instead of chromium (Cr) allowing for a relatively low temperature etch.  
           [0010]    Other objects will appear hereinafter.  
           [0011]    It has now been discovered that the above and other objects of the present invention may be accomplished in the following manner. The EUV photolithographic mask comprises a multi-layer over an EUV masking substrate and a patterned light absorbing layer formed on the multi-layer. The method comprises the steps of forming a multi-layer on an EUV mask substrate, forming a light absorbing layer on the multi-layer, and etching an opening through the light absorbing layer to the multi-layer. The light absorbing layer includes a metal selected from the group comprising nickel, chromium and cobalt and is preferably nickel.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    The features and advantages of the method of fabricating EUV masks according to the present invention will be more clearly understood from the following description taken in conjunction with the accompanying drawings in which like reference numerals designate similar or corresponding elements, regions and portions and in which:  
         [0013]    [0013]FIGS. 1 and 2 schematically illustrate in cross-sectional representation a Direct Metal Patterning Process of forming EUV masks known to the inventors.  
         [0014]    [0014]FIGS. 3 and 4 schematically illustrate in cross-sectional representation a Damascene Process of forming EUV masks known to the inventors.  
         [0015]    [0015]FIGS. 5 through 8 schematically illustrate in cross-sectional representation a preferred embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0016]    Unless otherwise specified, all structures, layers, etc. may be formed or accomplished by conventional methods known in the prior art. While not limited to a particular application, the invention is particularly useful for extreme ultraviolet lithography (EUVL) that is preferably conducted at wavelength of between 3 and 50 nanometers (nm) and is intended for use in chip fabrication where minimum line widths of ≦0.07 micron are required.  
         [0017]    Two Processes Known to the Inventors  
       Process One  
       [0018]    [0018]FIGS. 1 and 2 illustrate a Direct Metal Patterning Process of forming EUV masks known to the inventors.  
         [0019]    As shown in FIG. 1, reflector layer  202  is formed over mask blank  200 . Buffer layer  204 , that may be comprised of SiO 2 , is then deposited over reflector layer  202 . Metal layer  206 , that may be comprised of Al, TaSi, Cr, SiON, Ti, of TiN, is deposited over buffer layer  204 .  
         [0020]    As shown in FIG. 2, metal layer  206  is then patterned by, for example, depositing and patterning a photoresist layer (not shown) over metal layer  206 , then etching metal layer  206  to form metal layer trench  208  exposing a portion of underlying buffer layer  204 . The exposed portion of buffer layer  204  is then etched to form buffer layer trench  210  beneath metal layer trench  208 .  
         [0021]    Optionally (not shown) a layer of silicon (Si) may be deposited and chemically mechanically polished (CMP) to complete formation of the Direct Metal Patterning photolithographic mask.  
       Process Two  
       [0022]    [0022]FIGS. 3 and 4 illustrate a Damascene Process of forming EUV masks known to the inventors.  
         [0023]    As shown in FIG. 3, a multi-layer reflector layer  302  is formed over mask blank  300 . Silicon cap layer  304  is then formed over reflector layer  302 . Silicon cap layer  304  is then etched to form trench  306  leaving bottom portion  308  of silicon cap layer beneath trench  306 .  
         [0024]    The structure is then inspected for defects and any necessary repairs are effected.  
         [0025]    A metal layer (not shown) is deposited over the structure, filling trench  306 , and planarized by chemical mechanical polishing (CMP) to form planarized metal portion  310  over silicon cap layer portion  308 .  
         [0026]    Optionally (not shown) a layer of silicon (Si) may be deposited and chemically mechanically polished (CMP) to complete formation of the Damascene photolithographic mask.  
         [0027]    However, both the Direct Metal Patterning Process of FIGS. 1 and 2 and the Damascene Process of FIGS. 3 and 4 in forming photolithographic masks involve multiple steps of (at least) etching, stripping of a patterned photoresist layer (not shown), deposition of a film, and planarization of the film by chemical mechanical polishing.  
         [0028]    Further, it is a great challenge to make EUV masks with low temperature, low defects, and no multi-layer reflector layer damage.  
       PREFERRED EMBODIMENT OF THE PRESENT INVENTION  
       [0029]    Accordingly as shown in FIGS.  5 - 8 , multi-reflector layer  12  is formed over mask blank  10  to form a mask substrate. Mask blank  10  is any material suitable for the type of photolithography wavelength regime to be used. For extreme ultraviolet lithography (EUVL), mask blank  10  is preferably either silicon or fused silica with a highly polished surface.  
         [0030]    Reflector layer  12  preferably consists of multiple layers of alternating reflecting material and transmissive material. Various combinations of reflective and transmissive materials may be used such as Mo/Si, Ru/C, Ru/B 4 C, Mo/Be, etc. The reflector layer is preferably comprised of molybdenum (Mo) and silicon (Si) layers (Mo/Si), each layer with a thickness of about (lambda/2) (sin) (theta). Where lambda is the wavelength of the light, and theta is the incident angle. The reflector layer  12  has preferably from about 40 to 50 paired layers.  
         [0031]    Light absorbing layer  14  is deposited over reflector layer  12  preferably to a thickness of from about 200 to 500 Å, and more preferably from about 250 to 350 Å. Light absorbing layer  14  is comprised of a material selected for its characteristics of being absorptive to the wavelength of light to be used and for its ease in mask fabrication.  
         [0032]    Specifically, light absorbing layer  14  may be comprised of a metal selected from the group nickel (Ni), chromium (Cr), and cobalt (Co) and alloys thereof.  
         [0033]    In a key step of the invention, light absorbing layer  14  is most preferably comprised of nickel (Ni) as will be used hereafter for the purposes of example. The use of a nickel light absorbing layer  14  permits a low temperature etch.  
         [0034]    Light absorbing layer  14  is then patterned, for example, as shown in FIG. 5, by deposited a suitable photoresist (PR) layer  16  over Ni layer  14  to an appropriate thickness.  
         [0035]    As shown in FIG. 6, PR layer  16  is patterned forming PR trench  18 , and exposing portion  20  of Ni layer  14 . PR layer  16  is split into portions  16   a ,  16   b . The photoresist is exposed and developed using conventional processes.  
         [0036]    As shown in FIG. 7, in an important step in the present invention, light absorbing layer  14  is etched by a highly selective, low temperature, low power and with no bias power to minimize to the bombardment. The etch splits layer  14  into portions  14   a ,  14   b  and forming light absorbing layer trench  22 . That is, the temperature is lower that about 40° C. and preferably between about 0 to 39° C.; the inductive coil power is less than about 350 watts (W) and preferably between about 100 to 200 watts; preferably at a CO gas flow between about 50 and 400 sccm, more preferably between about 200 and 350 sccm, and most preferably about 300 sccm; preferably from about 8 to 12 milli torr and more preferably about 10 milli torr, and with no bias power being applied to minimize the bombardment.  
         [0037]    This etch is conducted by a reactive ion etching (RIE) plasma etcher, such as the IPS, IEM, DRM, or TCP etcher and preferably the Lam transformer-coupled plasma source TCP9100 PTX. The etching conditions depend upon the specific plasma etcher selected.  
         [0038]    This etch does not create a side-wall polymer because the etch products are very volatile at the low temperature at which the etch is possible because nickel is selected as comprising light absorbing layer  14 .  
         [0039]    The reaction during the Ni layer etch is:  
                         
 
         [0040]    As shown in FIG. 8, remaining PR layer portions  16   a ,  16   b  are stripped and removed. The PR strip may be accomplished by ozone (O 3 ) injected into hot water, that is by the Hydrozone Process by Fluorowave System Inc. (FSI) with the water at 85° C. Alternatively, the PR strip can be accomplished by a SO 3  strip process developed by Anon Inc. at ≦50° C.  
         [0041]    The structure is then subject to defect inspection and repair by any standard technique using any standard tool. Any defects are identified visually by type, clear or opaque, and by location. An ion beam is used, usually in a focused gallium ion beam system, to either create patches in the structure or remove unwanted material arising from any such defects.  
         [0042]    The ability to use the low temperature, low power and minimum bombardment etch of nickel light absorbing layer  14  allows one to retain the reflecting properties of the mirror (mask) due to the absence of thermal interdiffusion between the layers, thus permitting fabrication of quality EUV photolithographic masks.  
         [0043]    While particular embodiments of the present invention have been illustrated and described, it is not intended to limit the invention, except as defined by the following claims.