Abstract:
A method of fabricating a photomask includes includes forming a light blocking layer over a transparent substrate, and forming a hard mask pattern over the light blocking layer. The hard mask pattern exposes a portion of the light blocking layer. The method also includes depositing a self assembly molecule (SAM) layer over the hard mask pattern. The SAM layer covers the hard mask pattern and a portion of the exposed light blocking layer. The method also includes forming a resist layer pattern over an exposed portion of the light blocking layer that is not covered by the deposited SAM layer. The method further includes removing the SAM layer to expose the hard mask pattern and the light blocking layer, and etching the light blocking layer with the hard mask pattern and the resist layer pattern to form the photomask. Still further, the method includes removing the hard mask pattern and the resist layer pattern. The disclosed method permits one to manufacture fine patterns in semiconductor devices utilizing conventional apparatus and materials.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The priority of Korean patent application No. 10-2008-0034223 filed Apr. 14, 2008, the disclosure of which is incorporated by reference in its entirety, is claimed. 
       BACKGROUND OF THE INVENTION 
       [0002]    The invention generally relates generally to a method of fabricating a photomask, and more particularly, to a method of fabricating a photomask using a Self Assembly Molecule (SAM). 
         [0003]    Generally, a semiconductor device is formed of numerous patterns. These patterns are made by a photolithography process that includes exposure, development, and etch processes, using a photoresist layer pattern as an etch mask. More specifically, the exposure process is one in which the pattern on a photomask is transferred to a photoresist layer on a wafer. Therefore, when the pattern on the photomask is not accurately formed, it is impossible to obtain the desired photoresist layer pattern. 
         [0004]    Recently, as degree of semiconductor device integration has increased, the size of the pattern has decreased and and become finer. Presently, an electron beam lithography method or a laser beam method are typically used as a method of forming patterns on the photomask. In a phase shift mask, for example, a phase shift layer, a chrome layer, and a resist layer are sequentially formed on a transparent substrate. Next, a resist layer pattern is formed by performing exposure and development by an electron beam lithography or a laser beam lithography on the resist layer. A phase shift layer pattern and a chrome layer pattern that expose a light transmitting region of the transparent substrate are formed by sequentially removing the exposed portions of the chrome layer and the phase shift layer, using the resist layer pattern as an etch mask. Then, the resist layer pattern is removed, and the chrome layer pattern in the rest portion except for a frame region is subsequently removed. 
         [0005]    Although exposure by the electron lithography method or a laser beam lithography method makes it easy to form fine patterns, compared to an exposure by a photolithography method, there are various problems in forming ultra fine patterns due to the rapid increase in the integration degree of semiconductor devices. For example, the lithography apparatus, the exposure apparatus, development apparatus, and the etching apparatus should be continuously improved to obtain and ensure more fine patterns. Also, development of a resist layer material required in the electron beam lithography process or a laser beam lithography process should be performed together. However, now, the improvement of the apparatus and development of the material cannot keep up with required increase in the integration degree. 
       SUMMARY OF THE INVENTION 
       [0006]    Embodiments of the present invention are directed to a method of fabricating a photomask (e.g., a binary photomask, a phase shift mask) using self assembly molecules. The method is capable of forming fine patterns and can be carried out using conventional exposure apparatus and resist layer material. 
         [0007]    According to one embodiment, the method includes forming a light blocking layer over a transparent substrate, and forming a hard mask pattern over the light blocking layer. The hard mask pattern exposes a portion of the light blocking layer. The method also includes depositing a self assembly molecule (SAM) layer over the hard mask pattern. The SAM layer covers the hard mask pattern and a portion of the exposed light blocking layer. The method also includes forming a resist layer pattern over an exposed portion of the light blocking layer that is not covered by the deposited SAM layer. The method further includes removing the SAM layer to expose the hard mask pattern and the light blocking layer, and etching the light blocking layer with the hard mask pattern and the resist layer pattern to form the photomask. Still further, the method includes removing the hard mask pattern and the resist layer pattern. 
         [0008]    According to another embodiment, a method of fabricating a phase shift includes forming a phase shift layer and a light blocking layer over a transparent substrate and forming a hard mask pattern over the light blocking layer. The hard mask pattern exposes a portion of the light blocking layer. The method also includes depositing a self assembly molecule (SAM) layer over the hard mask pattern. The SAM layer covers the hard mask pattern and a portion of the exposed light blocking layer. The method also includes forming a resist layer pattern over an exposed portion of the light blocking layer that is not covered by the SAM layer. The method further includes removing the SAM layer to expose the hard mask pattern and the light blocking layer, and etching the light blocking layer with the hard mask pattern and the resist layer pattern to form the photomask. Still further, the method includes removing the phase shift layer exposed by the photomask, the hard mask pattern, and the resist layer pattern. The method also includes removing the hard mask pattern, the photomask, and the resist layer pattern. 
         [0009]    In these various embodiments, the hard mask pattern may be made of or include a gold (Au) material. 
         [0010]    Formation of the hard mask pattern can include forming a resist layer over the hard mask layer, and exposing the resist layer and developing the exposed resist layer to form a resist layer pattern. The resist layer pattern can have an opening that exposes a portion of the hard mask layer. The exposed portion of the hard mask layer can be etched, using the resist layer pattern as an etch mask, to form the hard mask pattern, and the resist layer pattern can be removed. The hard mask pattern preferably has an opening that exposes a portion of the light blocking layer. 
         [0011]    The hard mask pattern opening preferably has a width that is three times that of the hard mask pattern. 
         [0012]    Deposition of the SAM layer preferably includes dipping the substrate in a SAM solution. 
         [0013]    Preferably, in the SAM solution, an end of each self assembly molecule is substituted with a sulfur (S) atom, which atom is preferably also connected to the self assembly molecule by an alkyl group. 
         [0014]    The exposed portion of the light blocking layer not covered by the SAM layer preferably has a width that is controllable by controlling the length of the alkyl group. 
         [0015]    Preferably the resist layer is a negative type resist layer. 
         [0016]    Preferably, removal of the SAM layer can be accomplished by and/or include performing an ammonia treatment method. 
         [0017]    According to the present invention, spontaneous reaction of self assembly molecules with the hard mask pattern makes it possible to form accurately fine patterns, compared to existing lithography methods. Therefore, it is possible to easily form the fine patterns only using currently conventionally used exposure apparatus and resist layer material. 
         [0018]    Additional features of the disclosed invention may become apparent to those skilled in the art from a review of the following detailed description, taken in conjunction with the drawings and the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    For a more complete understanding of the disclosure, reference should be made to the following detailed description and accompanying drawings wherein: 
           [0020]      FIGS. 1 through 6  are cross-sectional views illustrating a method of fabricating a binary photomask according to an embodiment of the present invention; 
           [0021]      FIG. 7  is a view illustrating a process of forming a self assembly molecule layer; and, 
           [0022]      FIGS. 8 through 13  are cross-sectional views illustrating a method of fabricating a phase shift mask according to another embodiment of the present invention. 
       
    
    
       [0023]    While the disclosed methods are susceptible of embodiments in various forms, there are illustrated in the drawings (and will hereafter be described) specific embodiments of the invention, with the understanding that the disclosure is intended to be illustrative, and is not intended to limit the invention to the specific embodiments described and illustrated herein. 
       DETAILED DESCRIPTION 
       [0024]      FIGS. 1 through 6  are cross-sectional views illustrating a method of fabricating a (binary) photomask according to an embodiment of the present invention.  FIG. 7  is a view illustrating a process of forming a self assembly molecule layer. Referring now to  FIG. 1 , a light blocking layer  110  is formed over a transparent substrate  100 . The substrate  100  preferably has a first region  101  and a second region  102 . The first region  101  preferably is a light blocking region on which a light blocking pattern is disposed, and the second region  102  preferably is a light transmitting region in which the transparent substrate  100  is exposed. Quartz may be used, for example, as the transparent substrate  100 , and a chrome (Cr) layer may be used for the light blocking layer  110 . Next, a hard mask layer  120  is formed over the light blocking layer  110 . The hard mask layer  120  is formed of a material capable of inducing an absorption reaction with a self assembly molecule (SAM) layer to be subsequently formed. For example, the hard mask layer  120  preferably is formed of a gold (Au) material. Next, a resist layer  130  is formed over the hard mask layer  120 , and an electron beam exposure to the resist layer  130  is performed, as shown by arrows. In some cases, a laser beam exposure may be performed instead of the electron beam exposure. 
         [0025]    Next, referring to  FIG. 2 , a resist layer pattern  132  is formed by developing those portions of the resist layer ( 130  in  FIG. 1 ) that were exposed to the electron beam. The resist layer pattern  132  has an opening  134  that exposes a portion of the hard mask layer  120 . The resist layer pattern  132  has a first width L and the opening  134  has a second width  3 L that is as about three times as the first width L. Thus, the exposed portion of the hard mask layer  120  similarly has the same second width  3 L. Control of these widths can be performed upon the electron beam exposure. Next, the exposed portion of the hard mask layer  120  is etched using the resist layer pattern  132  as an etch mask to form a hard mask pattern  122  shown in  FIG. 3 . 
         [0026]    Next, a SAM layer  140  is deposited (formed) over the upper and side surfaces of the hard mask pattern  122 . The SAM layer  140  covers the hard mask pattern  122  and a portion of the exposed light blocking layer  110 . In order to form the SAM layer  140 , as shown in  FIG. 7 , the transparent substrate  100  formed with the hard mask layer pattern  122  is dipped in a solution  710  (shown in more detail in the exploded view denoted by reference number  720 ) of self assembly molecules  712 . Ends of the self assembly molecules  712  in the SAM solution  710  are substituted with sulfur (S) atoms  714 . These sulfur (S) atoms  714  are connected to a molecule of an alkyl group (e.g. (CH 2 ) n X, wherein, X is CH 3 , COOH, NH 3 ). When the transparent substrate formed with the hard mask layer pattern  122  is dipped in the SAM solution  710 , the sulfur (S) atoms  714  of the SAM  712  in the SAM solution  710  are absorbed to the gold material of the hard mask pattern  122  and, as a result, the unit SAMs are absorbed to the hard mask pattern  122  as shown by a reference numeral “ 730 ” and the SAM layer  140  is formed. The deposited SAM layer  140  covers the hard mask pattern  122  and a portion of the exposed light blocking layer. As shown, the deposited SAM layer  140  leaves an opening  142  that exposes the first region  101  (i.e. the light blocking region of the exposed portion of the light blocking layer  110 ). The width of the opening  142  (and, therefore, the portion of the exposed light blocking pattern not covered by the deposited SAM layer  140 ) can be adjusted by controlling a length of the alkyl group of the SAM that constitutes the SAM layer  140 . 
         [0027]    Next, referring to  FIG. 4 , a resist layer pattern  150  is formed in the opening  142  by the SAM layer  140 . To this end, a negative type resist layer is preferably coated over an entire surface, and is then exposed and developed to form the resist layer pattern  150 . Light is restrictively irradiated to the opening ( 142  in  FIG. 3 ) upon the exposure, and the portion irradiated by the light thus remains upon the development. Therefore, the resist layer pattern  150  that is restricted in the opening  142  is formed. After that, surfaces of the SAM layer  140  and the resist layer pattern  150  are planarized by performing planarization such as Chemical Mechanical Polishing (CMP). 
         [0028]    Next, as shown in  FIG. 5 , the SAM layer ( 140  in  FIG. 4 ) is removed. The removal of the SAM layer  140  may be performed using an ammonia treatment method. As the SAM layer  140  is removed, the hard mask pattern  122  is exposed. Next, the light blocking layer ( 110  in  FIG. 4 ) is etched, using the hard mask pattern  122  and the resist layer pattern  150  as an etch mask, to form a light blocking layer pattern (i.e., a photomask)  112 . The formed photomask  112  exposes the surface of the second region  102  (i.e. the light transmitting region) of the transparent substrate  100 . Next, as shown in  FIG. 6 , the hard mask pattern ( 122  in  FIG. 5 ), and the resist layer pattern ( 150  in  FIG. 5 ) are removed, thereby fabricating a (binary) photomask in which the photomask  112  is disposed in the first region  101  (i.e., the light blocking region) and the transparent substrate  100  is exposed in the second region  102  (i.e., the light transmitting region). 
         [0029]      FIGS. 8 through 13  are cross-sectional views illustrating a method of fabricating a phase shift mask according to another embodiment of the present invention. First, as shown in  FIG. 8 , a phase shift layer  805  and a light blocking layer  810  are sequentially formed over a transparent substrate  800 . The substrate  800  is shown having a first region  801  and a second region  802 . The first region  801  preferably is a phase shift region on which a phase shift layer pattern is disposed, and the second region  802  preferably is a light transmitting region in which the transparent substrate is exposed. Quartz may be used, for example, as the transparent substrate  800 , a molybdenum silicon layer may be used for the phase shift layer  805 , and a chrome (Cr) layer may be used for the light blocking layer  810 . Next, a hard mask layer  820  is formed over the light blocking layer  810 . The hard mask layer  820  is formed of a material capable of inducing an absorption reaction with a SAM layer to be subsequently formed. For example, the hard mask layer  820  preferably is formed of a gold (Au) material. Next, a resist layer  830  is formed over the hard mask layer  820 , and an electron beam exposure to the resist layer  830  is performed, as shown by arrows. In some cases, a laser beam exposure may be performed instead of the electron beam exposure. 
         [0030]    Next, referring to  FIG. 9 , a resist layer pattern  832  is formed by developing those portions of the resist layer ( 830  in  FIG. 8 ) that were exposed to the electron beam. The resist layer pattern  832  has an opening  834  that exposes a portion of the hard mask layer  820  between the resist layer patterns  832 . The resist layer pattern  832  has a first width L and the opening  834  has a second width  3 L that is as about three times as the first width L. Thus, the exposed portion of the hard mask layer  820  similarly has the same second width  3 L. Control of these widths can be performed upon the electron beam exposure. Next, the exposed portion of the hard mask layer  820  is etched using the resist layer pattern  832  as an etch mask to form a hard mask pattern  822  shown in  FIG. 10 . 
         [0031]    Next, a SAM layer  840  is deposited (formed) over the upper and side surfaces of the hard mask pattern  822 . The SAM layer  840  covers the hard mask pattern  822  and a portion of the exposed light blocking layer  810 . The method of forming the SAM layer  840  is the same as that described with reference to  FIG. 7 . That is to say, the transparent substrate formed with the hard mask layer pattern  822  is dipped in the SAM solution. Ends of the self assembly molecules  712  in the SAM solution  710  are substituted by sulfur (S) atoms  714 . These sulfur (S) atoms  714  are connected to a molecule of an alkyl group (e.g., (CH 2 ) n X, wherein, X is CH 3 , COOH, NH 3 ). Therefore, when the transparent substrate formed with the hard mask pattern  822  is dipped in the SAM solution, the sulfur (S) atoms  714  of the SAM  712  in the SAM solution  710  are absorbed to the gold material of the hard mask pattern  822  and, as a result, the unit SAMs are absorbed to the hard mask pattern  822  and the SAM layer  840  is formed. The deposited SAM layer  840  covers the hard mask pattern  822  and a portion of the exposed light blocking layer. As shown, the deposited SAM layer  840  leaves an opening  842  that exposes the first region  801  (i.e., the light blocking region of the exposed portion of the light blocking layer  810 ). 
         [0032]    Next, as shown in  FIG. 11 , a resist layer pattern  850  is formed in the opening  842  by the SAM layer  840 . To this end, a negative type resist layer preferably is coated over an entire surface, and is then exposed and developed to form the resist layer pattern  850 . Light is restrictively irradiated to the opening ( 842  in  FIG. 10 ) upon the exposure, and the portion irradiated by the light thus remains upon the development. Therefore, the resist layer pattern  850  that is restricted in the opening  842  is formed. After that, surfaces of the SAM layer  840  and the resist layer pattern  850  are planarized by performing planarization such as CMP. 
         [0033]    Next, as shown in  FIG. 12 , the SAM layer ( 840  in  FIG. 11 ) is removed. The removal of the SAM layer  840  may be performed using an ammonia treatment method. As the SAM layer  840  is removed, the hard mask pattern  822  is exposed. Next, the light blocking layer ( 810  in  FIG. 11 ) is etched, using the hard mask pattern  822  and the resist layer pattern  850  as an etch mask, to form a light blocking layer pattern (i.e., a photomask)  812 . The formed photomask  812  exposes the surface of the phase shift layer  805  in the light transmitting region. Next, as shown in  FIG. 13 , a phase shift layer pattern  807  that exposes the transparent substrate  800  in the second region  802  (i.e., the light transmitting region) is etched to the exposed portion of the phase shift layer ( 805  in  FIG. 12 ). Then, the hard mask pattern ( 822  in  FIG. 12 ), the resist layer pattern ( 850  in  FIG. 12 ), and the photomask ( 812  in  FIG. 12 ) are removed, thereby fabricating a phase shift layer pattern (i.e., phase shift mask)  807  that is disposed in the first region  801  (i.e. the light blocking region) and the transparent substrate  100  is exposed in the second region  802  (i.e. the light transmitting region). 
         [0034]    While the present invention has been described with respect to the specific embodiments, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the following claims.