Abstract:
Photomask blanks are provided. One of the photomask blanks includes a light transmission substrate, a light blocking layer disposed on a top surface of the light transmission substrate, and a heat radiation layer disposed on sidewalls and a bottom surface of the light transmission substrate. Related photomasks and fabrication methods of the photomasks are also provided.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority under 35 U.S.C. 119(a) to Korean Application No. 10-2015-0024490, filed on Feb. 17, 2015, in the Korean intellectual property Office, which is incorporated herein by reference in its entirety as set forth in full. 
     BACKGROUND 
     1. Technical Field 
     Various embodiments of the present disclosure relate to photomasks used in lithography processes and, more particularly, to photomask blanks, photomasks fabricated using the same, and methods of fabricating photomasks using the same. 
     2. Related Art 
     In general, a semiconductor device may include a plurality of patterns disposed on a semiconductor substrate. The patterns may be formed using a photolithography process and an etch process to realize active elements and/or passive elements. The photolithography process may be used to form photoresist patterns. More specifically, the photolithography process may be performed by coating a photoresist material on a target layer to form a photoresist layer, by selectively exposing portions of the photoresist layer to light with a photomask, and by developing the exposed photoresist layer to form the photoresist patterns. The photoresist patterns may be used as etch masks for patterning the target layer. As such, the photomask may be used to transfer predetermined pattern images onto the photoresist layer and may be generally comprised of a transparent substrate and a plurality of transfer patterns. 
     In the photolithography process, light having a specific wavelength may irradiate a photoresist layer on a wafer through a photomask. In such a case, regions on which light blocking patterns are disposed on the photomask may prevent the light from irradiating the wafer, and only light transmitting regions of the photomask may allow the light to reach the wafer. During the photolithography process, the light blocking patterns may absorb a large amount of optical energy of the light irradiating the photomask, thereby generating heat. The heat may be conducted to the transparent substrate of the photomask, and the transparent substrate may be expanded and deformed due to the heat. The thermal deformation of the transparent substrate may cause a position change of overlay patterns of the photomask. As a result, the thermal deformation of the transparent substrate may lead to an overlay error between the photomask and the wafer. 
     SUMMARY 
     Various embodiments are directed to photomask blanks, photomasks fabricated using the same, and methods of fabricating photomasks using the same. 
     According to an embodiment, a photomask blank includes a light transmission substrate, a light blocking layer disposed on a top surface of the light transmission substrate, and a heat radiation layer disposed on sidewalls and a bottom surface of the light transmission substrate. 
     According to another embodiment, a photomask blank includes a light transmission substrate, a phase shift layer disposed on a top surface of the light transmission substrate, a light blocking layer disposed on the phase shift layer, and a heat radiation layer disposed on sidewalls and a bottom surface of the light transmission substrate. 
     According to another embodiment, a photomask blank includes a light transmission substrate, a light blocking layer disposed on a top surface of the light transmission substrate, and a high strength support layer disposed on sidewalls and a bottom surface of the light transmission substrate. 
     According to another embodiment, a photomask blank includes a light transmission substrate, a phase shift layer disposed on a top surface of the light transmission substrate, a light blocking layer disposed on the phase shift layer, and a high strength support layer disposed on sidewalls and a bottom surface of the light transmission substrate. 
     According to another embodiment, a photomask includes a light transmission substrate having a transfer region and a frame region that surrounds the transfer region, a first light blocking pattern disposed on a top surface of the light transmission substrate in the transfer region, a second light blocking pattern disposed on a top surface of the light transmission substrate in the frame region, and a heat radiation pattern disposed on sidewalls and a portion of a bottom surface of the light transmission substrate. 
     According to another embodiment, a photomask includes a light transmission substrate having a transfer region and a frame region that surrounds the transfer region, a first phase shift pattern disposed on a top surface of the light transmission substrate in the transfer region, a second phase shift pattern and a light blocking pattern sequentially stacked on a top surface of the light transmission substrate in the frame region, and a heat radiation pattern disposed on sidewalls and a portion of a bottom surface of the light transmission substrate. 
     According to another embodiment, a photomask includes a light transmission substrate having a transfer region and a frame region that surrounds the transfer region, a first light blocking pattern disposed on a top surface of the light transmission substrate in the transfer region, a second light blocking pattern disposed on a top surface of the light transmission substrate in the frame region, and a high strength support pattern disposed on sidewalls of the light transmission substrate. 
     According to another embodiment, a photomask includes a light transmission substrate having a transfer region and a frame region that surrounds the transfer region, a first phase shift pattern disposed on a top surface of the light transmission substrate in the transfer region, a second phase shift pattern and a light blocking pattern sequentially stacked on a top surface of the light transmission substrate in the frame region, and a high strength support pattern disposed on sidewalls of the light transmission substrate. 
     According to another embodiment, a method of fabricating a photomask includes providing a photomask blank. The photomask blank includes a light transmission substrate that has a transfer region and a frame region surrounding the transfer region, a light blocking layer disposed on a top surface of the light transmission substrate, and a heat radiation layer disposed on sidewalls and a bottom surface of the light transmission substrate. The light blocking layer is patterned to form a light blocking pattern that exposes a portion of the light transmission substrate in the transfer region. A mask pattern is formed to expose a portion of the heat radiation layer below the transfer region. The exposed portion of the heat radiation layer is removed to form a heat radiation pattern. The mask pattern is removed after the heat radiation pattern is formed. 
     According to another embodiment, a method of fabricating a photomask includes providing a photomask blank. The photomask blank includes a light transmission substrate that has a transfer region and a frame region surrounding the transfer region, a phase shift layer disposed on a top surface of the light transmission substrate, a light blocking layer disposed on the phase shift layer, and a heat radiation layer disposed on sidewalls and a bottom surface of the light transmission substrate. The light blocking layer and the phase shift layer are patterned to form light blocking patterns and phase shift patterns that expose a portion of the light transmission substrate in the transfer region. The light blocking patterns located above the transfer region are selectively removed. A mask pattern is formed to expose a portion of the heat radiation layer below the transfer region. The exposed portion of the heat radiation layer is removed to form a heat radiation pattern. The mask pattern is removed after the heat radiation pattern is formed. 
     According to another embodiment, a method of fabricating a photomask includes providing a photomask blank. The photomask blank includes a light transmission substrate that has a transfer region and a frame region surrounding the transfer region, a light blocking layer disposed on a top surface of the light transmission substrate, and a high strength support layer disposed on sidewalls and a bottom surface of the light transmission substrate. The light blocking layer is patterned to form a light blocking pattern that exposes a portion of the light transmission substrate above the transfer region. A mask pattern is formed to expose a portion of the high strength support layer below the transfer region. The exposed portion of the high strength support layer is removed to form a high strength support pattern. The mask pattern is removed after the high strength support pattern is formed. 
     According to another embodiment, a method of fabricating a photomask includes providing a photomask blank. The photomask blank includes a light transmission substrate that has a transfer region and a frame region surrounding the transfer region, a phase shift layer disposed on a top surface of the light transmission substrate, a light blocking layer disposed on the phase shift layer, and a high strength support layer disposed on sidewalls and a bottom surface of the light transmission substrate. The light blocking layer and the phase shift layer are patterned to form light blocking patterns and phase shift patterns that expose a portion of the light transmission substrate in the transfer region. The light blocking patterns located above the transfer region are selectively removed. A mask pattern is formed to expose a portion of the high strength support layer below the transfer region. The exposed portion of the high strength support layer is removed to form a high strength support pattern. The mask pattern is removed after the high strength support pattern is formed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various embodiments of the present disclosure will become more apparent in view of the attached drawings and accompanying detailed description, in which: 
         FIG. 1  is a perspective view illustrating a photomask blank according to an embodiment; 
         FIG. 2  is a cross-sectional view taken along a line I-I′ of  FIG. 1 ; 
         FIG. 3  is a perspective view illustrating a photomask blank according to another embodiment; 
         FIG. 4  is a cross-sectional view taken along a line II-II′ of  FIG. 3 ; 
         FIG. 5  is a perspective view illustrating a photomask blank according to yet another embodiment; 
         FIG. 6  is a cross-sectional view taken along a line III-III′ of  FIG. 5 ; 
         FIG. 7  is a perspective view illustrating a photomask blank according to still another embodiment; 
         FIG. 8  is a cross-sectional view taken along a line IV-IV′ of  FIG. 7 ; 
         FIG. 9  is a plan view illustrating a photomask according to an embodiment; 
         FIG. 10  is a cross-sectional view taken along a line V-V′ of  FIG. 9 ; 
         FIG. 11  is a plan view illustrating a photomask according to another embodiment; 
         FIG. 12  is a cross-sectional view taken along a line VI-VI′ of  FIG. 11 ; 
         FIG. 13  is a plan view illustrating a photomask according to yet another embodiment; 
         FIG. 14  is a cross-sectional view taken along a line VII-VII′ of  FIG. 13 ; 
         FIG. 15  is a plan view illustrating a photomask according to still another embodiment; 
         FIG. 16  is a cross-sectional view taken along a line VIII-VIII′ of  FIG. 15 ; 
         FIGS. 17 to 20  are cross-sectional views illustrating a method of fabricating a photomask according to an embodiment; 
         FIGS. 21 to 26  are cross-sectional views illustrating a method of fabricating a photomask according to another embodiment; 
         FIGS. 27 to 30  are cross-sectional views illustrating a method of fabricating a photomask according to yet another embodiment; and 
         FIGS. 31 to 36  are cross-sectional views illustrating a method of fabricating a photomask according to still another embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     It will be understood that although the terms first, second, third etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another element. Thus, a first element in some embodiments could be termed a second element in other embodiments without departing from the teachings of the present disclosure. 
     It will also be understood that when an element is referred to as being located “on”, “over”, “above”, “under”, “beneath” or “below” another element, it may directly contact the other element, or at least one intervening element may be present therebetween. Accordingly, the terms such as “on”, “over”, “above”, “under”, “beneath”, “below” and the like that are used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the present disclosure. 
     It will be further understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. 
       FIG. 1  is a perspective view illustrating a photomask blank  110  according to an embodiment, and  FIG. 2  is a cross-sectional view taken along a line I-I′ of  FIG. 1 . Referring to  FIGS. 1 and 2 , the photomask blank  110  may be provided to fabricate a binary photomask. The photomask blank  110  may include a light transmission substrate  111 , a light blocking layer  113  disposed on the light transmission substrate  111 , and a resist layer  114  disposed on the light blocking layer  113 . In some embodiments, the resist layer  114  may be absent. The light blocking layer  113  may cover an entire top surface of the light transmission substrate  111 . The resist layer  114  may cover an entire top surface of the light blocking layer  113 . In some embodiments, the light transmission substrate  111  may be a quartz substrate, and the light blocking layer  113  may be a chromium (Cr) layer. 
     A heat radiation layer  115  may be disposed on sidewalls and a bottom surface of the light transmission substrate  111 . In some embodiments, the heat radiation layer  115  may cover the bottom surface and each sidewall of the light transmission substrate  111 . The heat radiation layer  115  may include a material having a heat conductivity that is higher than a heat conductivity of the light transmission substrate  111 . In some embodiments, when the light transmission substrate  111  is a quartz substrate, the heat radiation layer  115  may include a metal material such as an aluminum (Al) material, a copper (Cu) material, a gold (Au) material or a silver (Ag) material. 
       FIG. 3  is a perspective view illustrating a photomask blank  120  according to another embodiment, and  FIG. 4  is a cross-sectional view taken along a line II-II′ of  FIG. 3 . Referring to  FIGS. 3 and 4 , the photomask blank  120  may be provided to fabricate a phase shift mask (PSM). The photomask blank  120  may include a light transmission substrate  121 , a phase shift layer  122  disposed on the light transmission substrate  121 , a light blocking layer  123  disposed on the phase shift layer  122 , and a resist layer  124  disposed on the light blocking layer  123 . In some embodiments, the resist layer  124  may be absent. The phase shift layer  122  may cover an entire top surface of the light transmission substrate  121 . The light blocking layer  123  may cover an entire top surface of the phase shift layer  122 . The resist layer  124  may cover an entire top surface of the light blocking layer  123 . In some embodiments, the light transmission substrate  121  may be a quartz substrate, and the phase shift layer  122  may be a molybdenum silicon (MoSi) layer. The light blocking layer  123  may be a chromium (Cr) layer. 
     A heat radiation layer  125  may be disposed on sidewalls and a bottom surface of the light transmission substrate  121 . In some embodiments, the heat radiation layer  125  may cover the bottom surface and each sidewall of the light transmission substrate  121 . The heat radiation layer  125  may include a material having a heat conductivity that is higher than a heat conductivity of the light transmission substrate  121 . In some embodiments, when the light transmission substrate  121  is a quartz substrate, the heat radiation layer  125  may include a metal material such as an aluminum (Al) material, a copper (Cu) material, a gold (Au) material or a silver (Ag) material. 
       FIG. 5  is a perspective view illustrating a photomask blank  130  according to yet another embodiment,  FIG. 6  is a cross-sectional view taken along a line III-III′ of  FIG. 5 . Referring to  FIGS. 5 and 6 , the photomask blank  130  may be provided to fabricate a binary photomask. The photomask blank  130  may include a light transmission substrate  131 , a light blocking layer  133  disposed on the light transmission substrate  131 , and a resist layer  134  disposed on the light blocking layer  133 . In some embodiments, the resist layer  134  may be absent. The light blocking layer  133  may cover an entire top surface of the light transmission substrate  131 . The resist layer  134  may cover an entire top surface of the light blocking layer  133 . In some embodiments, the light transmission substrate  131  may be a quartz substrate, and the light blocking layer  133  may be a chromium (Cr) layer. 
     A high strength support layer  135  may be disposed on sidewalls and a bottom surface of the light transmission substrate  131 . In some embodiments, the high strength support layer  135  may cover the bottom surface and each sidewall of the light transmission substrate  131 . The high strength support layer  135  may include a material having a coefficient of thermal expansion that is lower than a coefficient of thermal expansion of the light transmission substrate  131 . In some embodiments, when the light transmission substrate  131  is a quartz substrate, the high strength support layer  135  may include a reinforced quartz material containing titanium (Ti). While a general quartz material has a coefficient of thermal expansion of about 0.55×10 −6 °C −1 , the reinforced quartz material containing titanium (Ti) may have a coefficient of thermal expansion of about 0.01×10 −6 °C −1 . 
       FIG. 7  is a perspective view illustrating a photomask blank  140  according to still another embodiment, and  FIG. 8  is a cross-sectional view taken along a line IV-IV′ of  FIG. 7 . Referring to  FIGS. 7 and 8 , the photomask blank  140  may be provided to fabricate a phase shift mask (PSM). The photomask blank  140  may include a light transmission substrate  141 , a phase shift layer  142  disposed on the light transmission substrate  141 , a light blocking layer  143  disposed on the phase shift layer  142 , and a resist layer  144  disposed on the light blocking layer  143 . In some embodiments, the resist layer  144  may be absent. The phase shift layer  142  may cover an entire top surface of the light transmission substrate  141 . The light blocking layer  143  may cover an entire top surface of the phase shift layer  142 . The resist layer  144  may cover an entire top surface of the light blocking layer  143 . In some embodiments, the light transmission substrate  141  may be a quartz substrate, and the phase shift layer  142  may be a molybdenum silicon (MoSi) layer. The light blocking layer  143  may be a chromium (Cr) layer. 
     A high strength support layer  145  may be disposed on sidewalls and a bottom surface of the light transmission substrate  141 . In some embodiments, the high strength support layer  145  may cover the bottom surface and each sidewall of the light transmission substrate  141 . The high strength support layer  145  may include a material having a coefficient of thermal expansion that is lower than a coefficient of thermal expansion of the light transmission substrate  141 . In some embodiments, when the light transmission substrate  141  is a quartz substrate, the high strength support layer  145  may include a reinforced quartz material containing titanium (Ti). While a general quartz material has a coefficient of thermal expansion of about 0.55×10 −6 °C −1 , the reinforced quartz material containing titanium (Ti) may have a coefficient of thermal expansion of about 0.01×10 −6 °C −1 . 
       FIG. 9  is a plan view illustrating a photomask  210  according to an embodiment, and  FIG. 10  is a cross-sectional view taken along a line V-V′ of  FIG. 9 . Referring to  FIGS. 9 and 10 , the photomask  210  may correspond to a binary photomask and may include a plurality of first light blocking patterns  213 - 1  and a second light blocking pattern  213 - 2  which are disposed on a top surface of a light transmission substrate  211 . The light transmission substrate  211  may be a quartz substrate. The light transmission substrate  211  may have a transfer region  211 A and a frame region  211 B. The transfer region  211 A may be an inner region of the light transmission substrate  211 , and the frame region  211 B may be edge portions of the light transmission substrate  211  that surround the transfer region  211 A. Here, the term “surround” in the context of the relationship between the transfer region  211 A and the frame region  211 B means that the frame region  211 B wraps around sides of the central transfer region  211 A so that the central transfer region  211 A is enclosed by the frame region  211 B in two dimensions. In other words, the frame region  211 B surrounds the transfer region in a manner similar to the way a picture frame surrounds a picture. 
     The transfer region  211 A may be divided into a light blocking region covered with the first light blocking patterns  213 - 1  and a light transmitting region that is not covered with the first light blocking patterns  213 - 1 . Although  FIGS. 9 and 10  illustrate an example in which each of the first light blocking patterns  213 - 1  is a line pattern, the present disclosure is not limited thereto. For example, the first light blocking patterns  213 - 1  may have various planar shapes, which are transferred onto a wafer. The second light blocking pattern  213 - 2  may be disposed on the light transmission substrate  211  in the frame region  211 B. Although not shown in  FIGS. 9 and 10 , the second light blocking pattern  213 - 2  may include overlay patterns having various shapes. In some embodiments, the first light blocking patterns  213 - 1  and the second light blocking pattern  213 - 2  may be formed of a chromium (Cr) layer. 
     A heat radiation pattern  215  may be disposed on sidewalls and a portion of a bottom surface of the light transmission substrate  211 . The heat radiation pattern  215  may include a material having a heat conductivity that is higher than a heat conductivity of the light transmission substrate  211 . In some embodiments, when the light transmission substrate  211  is a quartz substrate, the heat radiation pattern  215  may include a metal material such as an aluminum (Al) material, a copper (Cu) material, a gold (Au) material or a silver (Ag) material. The heat radiation pattern  215  may cover each sidewall of the light transmission substrate  211 . In addition, the heat radiation pattern  215  may cover edge portions of the bottom surface of the light transmission substrate  211 , which is vertically aligned with the frame region  211 B. A central portion of the bottom surface of the light transmission substrate  211 , which is vertically aligned with the transfer region  211 A, may be exposed by an opening  215 A of the heat radiation pattern  215 . The photomask  210  may be a light permeable photomask. During an exposure step, light irradiating a bottom surface of the light transmission substrate  211  may penetrate the light transmission substrate  211  to reach a wafer. The bottom surface of the light transmission substrate  211  irradiated by the light may be exposed by the opening  215 A of the heat radiation pattern  215 . Accordingly, the heat radiation pattern  215  may not interfere with the exposure step. 
     The first light blocking patterns  213 - 1  disposed above the transfer region  211 A may be transferred to a wafer during the exposure step. The exposure step may be repeatedly performed to expose a plurality of chip regions included in a single wafer. Thus, exposure energy may be accumulated in the light transmission substrate  211  during the exposure steps, and the accumulated exposure energy may act as a heat source that increases a temperature of the light transmission substrate  211 . When the temperature of the light transmission substrate  211  increases, the light transmission substrate  211  may expand to deform the overlay patterns. According to the present embodiment, the photomask  210  may include the heat radiation pattern  215  having a heat conductivity that is higher than a heat conductivity of the light transmission substrate  211 . Thus, the heat of the light transmission substrate  211  may be readily emitted into an external space through the heat radiation pattern  215 , as indicated by arrows  219 . Accordingly, deformation of the overlay patterns may be suppressed. 
       FIG. 11  is a plan view illustrating a photomask  220  according to another embodiment, and  FIG. 12  is a cross-sectional view taken along a line VI-VI′ of  FIG. 11 . Referring to  FIGS. 11 and 12 , the photomask  220  may correspond to a phase shift mask (PSM) and may include a plurality of first phase shift patterns  222 - 1  and a second phase shift pattern  222 - 2  which are disposed on a top surface of a light transmission substrate  221 . The photomask  220  may further include a light blocking pattern  223  disposed on the second phase shift pattern  222 - 2 . The light transmission substrate  221  may be a quartz substrate. The light transmission substrate  221  may have a transfer region  221 A and a frame region  221 B. The transfer region  221 A may be an inner region of the light transmission substrate  221 , and the frame region  221 B may be edge portions of the light transmission substrate  221  that surround the transfer region  221 A. The transfer region  221 A may be divided into a phase shift region covered with the first phase shift patterns  222 - 1  and a light transmitting region that is not covered with the first phase shift patterns  222 - 1 . 
     Although  FIGS. 11 and 12  illustrate an example in which each of the first phase shift patterns  222 - 1  is a line pattern, the present disclosure is not limited thereto. For example, the first phase shift patterns  222 - 1  may have various planar shapes, which are transferred onto a wafer. The second phase shift pattern  222 - 2  and the light blocking pattern  223  may be sequentially stacked on the light transmission substrate  221  in the frame region  221 B. Although not shown in  FIGS. 11 and 12 , the light blocking pattern  223  may include overlay patterns having various shapes. In some embodiments, the first phase shift patterns  222 - 1  and the second phase shift pattern  222 - 2  may be formed of a molybdenum silicon (MoSi) layer. In some embodiments, the light blocking pattern  223  may be formed of a chromium (Cr) layer. 
     A heat radiation pattern  225  may be disposed on sidewalls and a portion of a bottom surface of the light transmission substrate  221 . The heat radiation pattern  225  may include a material having a heat conductivity that is higher than a heat conductivity of the light transmission substrate  221 . In some embodiments, when the light transmission substrate  221  is a quartz substrate, the heat radiation pattern  225  may include a metal material such as an aluminum (Al) material, a copper (Cu) material, a gold (Au) material or a silver (Ag) material. The heat radiation pattern  225  may cover each sidewall of the light transmission substrate  221 . In addition, the heat radiation pattern  225  may cover edge portions of the bottom surface of the light transmission substrate  221 , which are vertically aligned with the frame region  221 B. 
     A central portion of the bottom surface of the light transmission substrate  221 , which is vertically aligned with the transfer region  221 A, may be exposed by an opening  225 A of the heat radiation pattern  225 . The photomask  220  may be a light permeable PSM. During an exposure step, light irradiating a bottom surface of the light transmission substrate  221  may penetrate the light transmission substrate  221  to reach a wafer. The bottom surface of the light transmission substrate  221  irradiated by the light may be exposed by the opening  225 A of the heat radiation pattern  225 . Accordingly, the heat radiation pattern  225  may not interfere with the exposure step. 
     The first phase shift patterns  222 - 1  disposed above the transfer region  221 A may be transferred to a wafer during the exposure step. The exposure step may be repeatedly performed to expose a plurality of chip regions included in a single wafer. Thus, exposure energy may be accumulated in the light transmission substrate  221  during the exposure steps, and the accumulated exposure energy may act as a heat source that increases a temperature of the light transmission substrate  221 . When the temperature of the light transmission substrate  221  increases, the light transmission substrate  221  may expand to deform the overlay patterns. According to the present embodiment, the photomask  220  may include the heat radiation pattern  225  having a heat conductivity that is higher than a heat conductivity of the light transmission substrate  221 . Thus, the heat of the light transmission substrate  221  may be readily emitted into an external space through the heat radiation pattern  225 , as indicated by arrows  229 . Accordingly, deformation of the overlay patterns may be suppressed. 
       FIG. 13  is a plan view illustrating a photomask  230  according to yet another embodiment, and  FIG. 14  is a cross-sectional view taken along a line VII-VII′ of  FIG. 13 . Referring to  FIGS. 13 and 14 , the photomask  230  may correspond to a binary photomask and may include a plurality of first light blocking patterns  233 - 1  and a second light blocking pattern  233 - 2  which are disposed on a top surface of a light transmission substrate  231 . The light transmission substrate  231  may be a quartz substrate. The light transmission substrate  231  may have a transfer region  231 A and a frame region  231 B. The transfer region  231 A may be an inner region of the light transmission substrate  231 , and the frame region  231 B may be edge portions of the light transmission substrate  231  that surround the transfer region  231 A. The transfer region  231 A may be divided into a light blocking region covered with the first light blocking patterns  233 - 1  and a light transmitting region that is not covered with the first light blocking patterns  233 - 1 . 
     Although  FIGS. 13 and 14  illustrate an example in which each of the first light blocking patterns  233 - 1  is a line pattern, the present disclosure is not limited thereto. For example, the first light blocking patterns  233 - 1  may have various planar shapes, which are transferred onto a wafer. The second light blocking pattern  233 - 2  may be disposed on the light transmission substrate  231  in the frame region  231 B. Although not shown in  FIGS. 13 and 14 , the second light blocking pattern  233 - 2  may include overlay patterns having various shapes. In some embodiments, the first light blocking patterns  233 - 1  and the second light blocking pattern  233 - 2  may be formed of a chromium (Cr) layer. 
     A high strength support pattern  235  may be disposed on sidewalls of the light transmission substrate  231 . Although not shown in  FIGS. 13 and 14 , an adhesive layer may be disposed between the light transmission substrate  231  and the high strength support pattern  235 . The high strength support pattern  235  may cover a portion of a bottom surface of the light transmission substrate  231 . In such a case, an adhesive strength between the light transmission substrate  231  and the high strength support pattern  235  may increase. The high strength support pattern  235  may include a material having a coefficient of thermal expansion that is lower than a coefficient of thermal expansion of the light transmission substrate  231 . In some embodiments, when the light transmission substrate  231  is a quartz substrate, the high strength support pattern  235  may include a reinforced quartz material containing titanium (Ti). While a general quartz material has a coefficient of thermal expansion of about 0.55×10 −6 °C −1 , the reinforced quartz material containing titanium (Ti) may have a coefficient of thermal expansion of about 0.01×10 −6 °C −1 . 
     When the high strength support pattern  235  extends onto the bottom surface of the light transmission substrate  231 , the high strength support pattern  235  may cover edge portions of the bottom surface of the light transmission substrate  231 , which are vertically aligned with the frame region  231 B. A central portion of the bottom surface of the light transmission substrate  231 , which is vertically aligned with the transfer region  231 A, may be exposed by an opening  235 A of the high strength support pattern  235 . The photomask  230  may be a light permeable binary photomask. During an exposure step, light irradiating a bottom surface of the light transmission substrate  231  may penetrate the light transmission substrate  231  to reach a wafer. The bottom surface of the light transmission substrate  231  irradiated by the light may be exposed by the opening  235 A of the high strength support pattern  235 . Accordingly, the high strength support pattern  235  may not interfere with the exposure step. 
     The first light blocking patterns  233 - 1  disposed above the transfer region  231 A may be transferred to a wafer during the exposure step. The exposure step may be repeatedly performed to expose a plurality of chip regions included in a single wafer. Thus, exposure energy may be accumulated in the light transmission substrate  231  during the exposure steps, and the accumulated exposure energy may act as a heat source that increases a temperature of the light transmission substrate  231 . When the temperature of the light transmission substrate  231  increases, the light transmission substrate  231  may expand to deform the overlay patterns. According to the present embodiment, the photomask  230  may include the high strength support pattern  235  having a coefficient of thermal expansion that is lower than a coefficient of thermal expansion of the light transmission substrate  231 . Thus, the high strength support pattern  235  may suppress the lateral expansion, depicted by arrows  239  in  FIG. 14 , of the light transmission substrate  231 . Accordingly, deformation of the overlay patterns may be suppressed. 
       FIG. 15  is a plan view illustrating a photomask  240  according to still another embodiment, and  FIG. 16  is a cross-sectional view taken along a line VII-VII′ of  FIG. 15 . Referring to  FIGS. 15 and 16 , the photomask  240  may correspond to a PSM and may include a plurality of first phase shift patterns  242 - 1  and a second phase shift pattern  242 - 2  which are disposed on a top surface of a light transmission substrate  241 . The photomask  240  may further include a light blocking pattern  243  disposed on the second phase shift pattern  242 - 2 . The light transmission substrate  241  may be a quartz substrate. The light transmission substrate  241  may have a transfer region  241 A and a frame region  241 B. The transfer region  241 A may be an inner region of the light transmission substrate  241 , and the frame region  241 B may be edge portions of the light transmission substrate  241  that surround the transfer region  241 A. The transfer region  241 A may be divided into a phase shift region covered with the first phase shift patterns  242 - 1  and a light transmitting region that is not covered with the first phase shift patterns  242 - 1 . 
     Although  FIGS. 15 and 16  illustrate an example in which each of the first phase shift patterns  242 - 1  is a line pattern, the present disclosure is not limited thereto. For example, the first phase shift patterns  242 - 1  may have various planar shapes, which are transferred onto a wafer. The second phase shift pattern  242 - 2  and the light blocking pattern  243  may be sequentially stacked on the light transmission substrate  241  in the frame region  241 B. Although not shown in  FIGS. 15 and 16 , the light blocking pattern  243  may include overlay patterns having various shapes. In some embodiments, the first phase shift patterns  242 - 1  and the second phase shift pattern  242 - 2  may be formed of a molybdenum silicon (MoSi) layer. In some embodiments, the light blocking pattern  243  may be formed of a chromium (Cr) layer. 
     A high strength support pattern  245  may be disposed on sidewalls of the light transmission substrate  241 . Although not shown in  FIGS. 15 and 16 , an adhesive layer may be disposed between the light transmission substrate  241  and the high strength support pattern  245 . The high strength support pattern  245  may cover a portion of a bottom surface of the light transmission substrate  241 . In such a case, an adhesive strength between the light transmission substrate  241  and the high strength support pattern  245  may increase. The high strength support pattern  245  may include a material having a coefficient of thermal expansion that is lower than a coefficient of thermal expansion of the light transmission substrate  241 . In some embodiments, when the light transmission substrate  241  is a quartz substrate, the high strength support pattern  245  may include a reinforced quartz material containing titanium (Ti). While a general quartz material has a coefficient of thermal expansion of about 0.55×10 −6 °C −1 , the reinforced quartz material containing titanium (Ti) may have a coefficient of thermal expansion of about 0.01×10 −6 °C −1 . 
     When the high strength support pattern  245  extends onto the bottom surface of the light transmission substrate  241 , the high strength support pattern  245  may cover edge portions of the bottom surface of the light transmission substrate  241 , which are vertically aligned with the frame region  241 B. A central portion of the bottom surface of the light transmission substrate  241 , which is vertically aligned with the transfer region  241 A, may be exposed by an opening  245 A of the high strength support pattern  245 . The photomask  240  may be a light permeable PSM. During an exposure step, light irradiating a bottom surface of the light transmission substrate  241  may penetrate the light transmission substrate  241  to reach a wafer. The bottom surface of the light transmission substrate  241  irradiated by the light may be exposed by the opening  245 A of the high strength support pattern  245 . Accordingly, the high strength support pattern  245  may not interfere with the exposure step. 
     The first phase shift patterns  242 - 1  disposed above the transfer region  241 A may be transferred to a wafer during the exposure step. The exposure step may be repeatedly performed to expose a plurality of chip regions included in a single wafer. Thus, exposure energy may be accumulated in the light transmission substrate  241  during the exposure steps, and the accumulated exposure energy may act as a heat source that increases a temperature of the light transmission substrate  241 . When the temperature of the light transmission substrate  241  increases, the light transmission substrate  241  may expand to deform the overlay patterns. According to the present embodiment, the photomask  240  may include the high strength support pattern  245  having a coefficient of thermal expansion that is lower than a coefficient of thermal expansion of the light transmission substrate  241 . Thus, the high strength support pattern  245  may suppress the lateral expansion, depicted by arrows  249  in  FIG. 16 , of the light transmission substrate  241 . Accordingly, deformation of the overlay patterns may be suppressed. 
       FIGS. 17 to 20  are cross-sectional views illustrating a method of fabricating a photomask according to an embodiment. As illustrated in  FIG. 17 , a photomask blank  310  including a light blocking layer  313  and a resist layer  314 ′ stacked on a top surface of a light transmission substrate  311  may be provided. The photomask blank  310  may further include a heat radiation layer  315 ′ disposed on sidewalls and a bottom surface of the light transmission substrate  311 . The light transmission substrate  311  may have a transfer region  311 A and a frame region  311 B surrounding the transfer region  311 A. The photomask blank  310  may have the same structure and configuration as the photomask blank  110  described with reference to  FIGS. 1 and 2 . 
     As illustrated in  FIGS. 17 and 18 , portions of the resist layer  314 ′ may be selectively exposed and developed to form a resist pattern  314 . In some embodiments, the resist layer  314 ′ may be exposed using an electron beam exposure technique. The resist pattern  314  may cover the frame region  311 B of a top surface of the light blocking layer  313  and cover portions of a top surface of the light blocking layer  313  above the transfer region  311 A. 
     As illustrated in  FIG. 19 , the light blocking layer  313  may be etched using the resist pattern  314  as an etch mask, thereby forming first light blocking patterns  313 - 1  and a second light blocking pattern  313 - 2 . The first light blocking patterns  313 - 1  may expose a portion of the light transmission substrate  311  in the transfer region  311 A. The second light blocking pattern  313 - 2  may cover the frame region  311 B of the light transmission substrate  311 . Subsequently, a mask pattern  318  may be formed on a bottom surface of the heat radiation layer  315 ′ opposite to the light transmission substrate  311 . The mask pattern  318  may have an opening  319  that exposes the heat radiation layer  315 ′ below the transfer region  311 A. 
     As illustrated in  FIGS. 19 and 20 , the heat radiation layer  315 ′ on the bottom surface of the light transmission substrate  311  may be etched using the mask pattern  318  as an etch mask, thereby forming a heat radiation pattern  315 . As a result, the heat radiation pattern  315  may cover edge portions of the bottom surface and each sidewall of the light transmission substrate  311 . The heat radiation pattern  315  may have an opening  315 A that exposes the bottom surface of the light transmission substrate  311  in the transfer region  311 A. After forming the heat radiation pattern  315 , the resist pattern  314  and the mask pattern  318  may be removed. 
       FIGS. 21 to 26  are cross-sectional views illustrating a method of fabricating a photomask according to another embodiment. As illustrated in  FIG. 21 , a photomask blank  320  including a phase shift layer  322 , a light blocking layer  323  and a resist layer  324 ′ stacked on a top surface of a light transmission substrate  321  may be provided. The photomask blank  320  may further include a heat radiation layer  325 ′ disposed on sidewalls and a bottom surface of the light transmission substrate  321 . The light transmission substrate  321  may have a transfer region  321 A and a frame region  321 B surrounding the transfer region  321 A. The photomask blank  320  may have the same structure and configuration as the photomask blank  120  described with reference to  FIGS. 3 and 4 . 
     As illustrated in  FIGS. 21 and 22 , portions of the resist layer  324 ′ may be selectively exposed and developed to form a first resist pattern  324 . In some embodiments, the resist layer  324 ′ may be exposed using an electron beam exposure technique. The first resist pattern  324  may cover an entire top surface of the light blocking layer  323  above the frame region  321 B and cover portions of a top surface of the light blocking layer  323  above the transfer region  321 A. 
     As illustrated in  FIGS. 22 and 23 , the light blocking layer  323  and the phase shift layer  322  may be etched using the first resist pattern  324  as an etch mask, thereby forming first phase shift patterns  322 - 1 , a second phase shift pattern  322 - 2 , first light blocking patterns  323 - 1  and a second light blocking pattern  323 - 2 . The first phase shift patterns  322 - 1  and the first light blocking patterns  323 - 1  may expose a portion of the light transmission substrate  321  in the transfer region  321 A. The second phase shift pattern  322 - 2  and the second light blocking pattern  323 - 2  may cover the frame region  321 B of the light transmission substrate  321 . After forming the first phase shift patterns  322 - 1 , the second phase shift pattern  322 - 2 , the first light blocking patterns  323 - 1  and the second light blocking pattern  323 - 2 , the first resist pattern  324  may be removed. 
     As illustrated in  FIG. 24 , a second resist pattern  327  may be formed on the second light blocking pattern  323 - 2 , such that a portion of the transfer region  321 A is exposed. More specifically, the second resist pattern  327  may be formed by coating an entire surface of the substrate including the first and second light blocking patterns  323 - 1  and  323 - 2  with a second resist layer after the first resist pattern  324  is removed and by selectively removing a portion of the second resist layer with an electron beam exposure technique and a development technique to expose the first light blocking patterns  323 - 1  above the transfer region  321 A. 
     As illustrated in  FIGS. 24 and 25 , all of the first light blocking patterns  323 - 1  above the transfer region  321 A may be removed using the second resist pattern  327  as an etch mask to expose the first phase shift patterns  322 - 1 . Accordingly, the transfer region  321 A may be divided into a phase shift region covered with the first phase shift patterns  322 - 1  and a light transmitting region that is not covered with the first phase shift patterns  322 - 1 , and the frame region  321 B may be covered with the second phase shift pattern  322 - 2  and the second light blocking pattern  323 - 2 . Subsequently, the second resist pattern  327  may be removed, and a mask pattern  328  may be formed on a bottom surface of the heat radiation layer  325 ′ opposite to the light transmission substrate  321 . The mask pattern  328  may have an opening  329  that exposes the heat radiation layer  325 ′ below the transfer region  321 A. 
     As illustrated in  FIG. 26 , the heat radiation layer  325 ′ on the bottom surface of the light transmission substrate  321  may be etched using the mask pattern  328  as an etch mask, thereby forming a heat radiation pattern  325 . As a result, the heat radiation pattern  325  may cover edge portions of the bottom surface and each sidewall of the light transmission substrate  321 . The heat radiation pattern  325  may have an opening  325 A that exposes the bottom surface of the light transmission substrate  321  in the transfer region  321 A. After forming the heat radiation pattern  325 , the mask pattern  328  may be removed. 
       FIGS. 27 to 30  are cross-sectional views illustrating a method of fabricating a photomask according to yet another embodiment. As illustrated in  FIG. 27 , a photomask blank  330  including a light blocking layer  333  and a resist layer  334 ′ stacked on a top surface of a light transmission substrate  331  may be provided. The photomask blank  330  may further include a high strength support layer  335 ′ disposed on sidewalls and a bottom surface of the light transmission substrate  331 . The light transmission substrate  331  may have a transfer region  331 A and a frame region  331 B surrounding the transfer region  331 A. The photomask blank  330  may have the same structure and configuration as the photomask blank  130  described with reference to  FIGS. 5 and 6 . 
     As illustrated in  FIGS. 27 and 28 , portions of the resist layer  334 ′ may be selectively exposed and developed to form a resist pattern  334 . In some embodiments, the resist layer  334 ′ may be exposed using an electron beam exposure technique. The resist pattern  334  may cover the frame region  331 B of a top surface of the light blocking layer  333  and cover portions of a top surface of the light blocking layer  333  above the transfer region  331 A. 
     As illustrated in  FIG. 29 , the light blocking layer  333  may be etched using the resist pattern  334  as an etch mask, thereby forming first light blocking patterns  333 - 1  and a second light blocking pattern  333 - 2 . The first light blocking patterns  333 - 1  may expose a portion of the light transmission substrate  331  in the transfer region  331 A. The second light blocking pattern  333 - 2  may cover the frame region  331 B of the light transmission substrate  331 . Subsequently, a mask pattern  338  may be formed on a bottom surface of the high strength support layer  335 ′ opposite to the light transmission substrate  331 . The mask pattern  338  may have an opening  339  that exposes the high strength support layer  335 ′ below the transfer region  331 A. 
     As illustrated in  FIG. 30 , the high strength support layer  335 ′ on the bottom surface of the light transmission substrate  331  may be etched using the mask pattern  338  as an etch mask, thereby forming a high strength support pattern  335 . As a result, the high strength support pattern  335  may cover edge portions of the bottom surface and each sidewall of the light transmission substrate  331 . The high strength support pattern  335  may have an opening  335 A that exposes the bottom surface of the light transmission substrate  331  in the transfer region  331 A. After forming the high strength support pattern  335 , the resist pattern  334  and the mask pattern  338  may be removed. 
       FIGS. 31 to 36  are cross-sectional views illustrating a method of fabricating a photomask according to still another embodiment. As illustrated in  FIG. 31 , a photomask blank  340  including a phase shift layer  342 , a light blocking layer  343  and a resist layer  344 ′ stacked on a top surface of a light transmission substrate  341  may be provided. The photomask blank  340  may further include a high strength support layer  345 ′ disposed on sidewalls and a bottom surface of the light transmission substrate  341 . The light transmission substrate  341  may have a transfer region  341 A and a frame region  341 B surrounding the transfer region  341 A. The photomask blank  340  may have the same structure and configuration as the photomask blank  140  described with reference to  FIGS. 7 and 8 . 
     As illustrated in  FIGS. 31 and 32 , portions of the resist layer  344 ′ of may be selectively exposed and developed to form a first resist pattern  344 . In some embodiments, the resist layer  344 ′ may be exposed using an electron beam exposure technique. The first resist pattern  344  may cover the frame region  341 B of a top surface of the light blocking layer  343  and cover portions of a top surface of the light blocking layer  343  above the transfer region  341 A. 
     As illustrated in  FIGS. 32 and 33 , the light blocking layer  343  and the phase shift layer  342  may be etched using the first resist pattern  344  as an etch mask, thereby forming first phase shift patterns  342 - 1 , a second phase shift pattern  342 - 2 , first light blocking patterns  343 - 1  and a second light blocking pattern  343 - 2 . The first phase shift patterns  342 - 1  and the first light blocking patterns  343 - 1  may expose a portion of the light transmission substrate  341  in the transfer region  341 A. The second phase shift pattern  342 - 2  and the second light blocking pattern  343 - 2  may cover the frame region  341 B of the light transmission substrate  341 . After forming the first phase shift patterns  342 - 1 , the second phase shift pattern  342 - 2 , the first light blocking patterns  343 - 1  and the second light blocking pattern  343 - 2 , the first resist pattern  344  may be removed. 
     As illustrated in  FIG. 34 , a second resist pattern  347  may be formed on the second light blocking pattern  343 - 2 , the transfer region  341 A is exposed. More specifically, the second resist pattern  347  may be formed by coating an entire surface of the substrate including the first and second light blocking patterns  343 - 1  and  343 - 2  with a second resist layer after the first resist pattern  344  is removed and by selectively removing a portion of the second resist layer with an electron beam exposure technique and a development technique to expose the first light blocking patterns  343 - 1  in the transfer region  341 A. 
     As illustrated in  FIGS. 34 and 35 , all of the first light blocking patterns  343 - 1  above the transfer region  341 A may be removed using the second resist pattern  347  as an etch mask to expose the first phase shift patterns  342 - 1 . Accordingly, the transfer region  341 A may be divided into a phase shift region covered with the first phase shift patterns  342 - 1  and a light transmitting region that is not covered with the first phase shift patterns  342 - 1 , and the frame region  341 B may be covered with the second phase shift pattern  342 - 2  and the second light blocking pattern  343 - 2 . Subsequently, the second resist pattern  347  may be removed, and a mask pattern  348  may be formed on a bottom surface of the high strength support layer  345 ′ opposite to the light transmission substrate  341 . The mask pattern  348  may have an opening  349  that exposes the high strength support layer  345 ′ below the transfer region  341 A. 
     As illustrated in  FIG. 36 , the high strength support layer  345 ′ on the bottom surface of the light transmission substrate  341  may be etched using the mask pattern  348  as an etch mask, thereby forming a high strength support pattern  345 . As a result, the high strength support pattern  345  may cover edge portions of the bottom surface and each sidewall of the light transmission substrate  341 . The high strength support pattern  345  may have an opening  345 A that exposes the bottom surface of the light transmission substrate  341  in the transfer region  341 A. After forming the high strength support pattern  345 , the mask pattern  348  may be removed. 
     The embodiments of the present disclosure have been disclosed above for illustrative purposes. Those of ordinary skill in the art will appreciate that various modifications, additions, and substitutions are possible, without departing from the scope and spirit of the present disclosure as claimed below.