Patent Publication Number: US-2020286732-A1

Title: Method of pre-treating substrate and method of directly forming graphene using the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of Korean Patent Application Nos. 10-2019-0024851, filed on Mar. 4, 2019, and 10-2020-0026762, filed on Mar. 3, 2020, in the Korean Intellectual Property Office, the entire disclosures of which are incorporated herein by reference. 
     BACKGROUND 
     1. Field 
     The present disclosure relates to methods of forming a material on a substrate, and more particularly, to methods of pre-treating a substrate in a process of forming graphene and methods of directly forming graphene by using the methods of pre-treating a substrate. 
     2. Description of Related Art 
     The usage of graphene has gradually increased due to its high physical, electrical, and optical characteristics, and, in particular, graphene has drawn attention as a new material in semiconductor fields. In order to apply graphene in a semiconductor process, research has been actively conducted into methods of directly forming graphene on a non-catalyst substrate. 
     As a widely known method of forming graphene, after forming graphene on a metal substrate by using a chemical vapor deposition (CVD) method, the formed graphene is transferred onto another desired substrate. 
     SUMMARY 
     Provided are methods of pre-treating a substrate to minimize a physical change of the substrate in a process of forming graphene. 
     Provided are methods of directly forming graphene by using the methods of pre-treating a substrate. 
     Additional aspects will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the presented embodiments. 
     In the method of substrate pre-treatment in a method of directly forming graphene according to an embodiment, the substrate may be pre-treated using a pre-treatment gas including at least a carbon source and hydrogen. 
     In some embodiments, the pre-treatment gas may include the carbon source and the hydrogen, and the pre-treatment gas may further include N 2 , a noble gas, or both N 2  and a noble gas. 
     In some embodiments, the pre-treating the substrate may include discontinuously suppling the at least one of the carbon source and the hydrogen of the pre-treatment gas to the substrate. 
     In some embodiments, the pre-treating the substrate may include preparing a mixed pre-treatment gas, based on mixing the carbon source and the hydrogen outside a chamber before the graphene is directly formed on the substrate, and supplying the mixed pre-treatment gas to the chamber while the substrate is placed in the chamber. 
     In some embodiments, the pre-treating the substrate may include supplying the carbon source and the hydrogen individually supplied to a chamber where the substrate is placed, and the carbon source and the hydrogen may be mixed in the chamber during the pre-treating the substrate. 
     In some embodiments, the carbon source may be represented by the formula C x H y , where x may be in a range from 1 to 12, and y may be in a range from 2 to 26. 
     In some embodiments, the pre-treating the substrate may include continuously supplying the carbon source and the hydrogen in the pre-treatment gas during the pre-treating the substrate. 
     In some embodiments, a supply rate of the carbon source to the substrate and a supply rate of the hydrogen to the substrate may be maintained constant during the pre-treating the substrate. 
     In some embodiments, a supply rate of the carbon source to the substrate, a supply rate of the hydrogen to the substrate, or both the supply rate of the carbon source to the substrate and the supply rate of the hydrogen to the substrate may be changed during the pretreating the substrate. 
     In some embodiments, the supply rate of the carbon source to the substrate may be changed according to time during the pre-treating the substrate. 
     In some embodiments, the supply rate of the hydrogen to the substrate may be changed according to time during the pre-treating the substrate. 
     In some embodiments, both the supply rate of the carbon source to the substrate and the supply rate of the hydrogen to the substrate may be changed according to time during the pre-treating the substrate. 
     In some embodiments, the the pre-treating the substrate may include discontinuously supplying the carbon source in the pre-treatment gas to the substrate, discontinuously supplying the hydrogen in the pre-treatment gas to the substrate, or discontinuously suppling both the carbon source and the hydrogen gas in the pretreatment gas to the substrate. 
     In some embodiments, the carbon source may be continuously supplied to the substrate and the hydrogen may be discontinuously supplied to the substrate during the pre-treating the substrate. 
     In some embodiments, the carbon source may be discontinuously supplied to the substrate and the hydrogen may be continuously supplied to the substrate during the pre-treating the substrate. 
     In some embodiments, both of the carbon source and the hydrogen may be discontinuously supplied to the substrate during the pre-treating the substrate. 
     In some embodiments, the pre-treating the substrate may include preparing a mixed pre-treatment gas, based on mixing the carbon source and the hydrogen outside of a chamber, and supplying the mixed pre-treatment gas to the chamber while the substrate is placed in the chamber. 
     In some embodiments, a supply rate of the mixed pre-treatment gas may change over time during the supplying the mixed pre-treatment gas to the chamber while substrate is placed in the chamber. 
     In some embodiments, the pre-treating the substrate may include supplying the carbon source and the hydrogen individually supplied to a chamber where the substrate is placed, and the carbon source and the hydrogen may be mixed in the chamber during the pre-treating the substrate. 
     In some embodiments, the method may further include forming the carbon source using a liquid source or a solid source before the pre-treating the substrate. 
     In some embodiments, the pre-treating the substrate may include forming a plasma from the pre-treatment gas and exposing the substrate to the plasma. 
     In some embodiments, the substrate may be a non-metal substrate. 
     In some embodiments, the non-metal substrate may include a semiconductor substrate or a dielectric substrate. 
     In some embodiments, the method of pre-treating the substrate may not include pre-treating the substrate using an other pre-treatment gas that only includes hydrogen. 
     According to some embodiments, a method of forming graphene may include preparing a pre-treated substrate by performing one of the above-described methods to pretreat the substrate and directly growing graphene on the pre-treated substrate. 
     In some embodiments, the directly growing the graphene using a source of carbon that may be formed using a liquid source or a solid source. 
     In some embodiments, the liquid source includes an aromatic hydrocarbon benzene having at least one of a benzene ring, a toluene, a xylene, or anisole, or a derivative of these materials. 
     In some embodiments, the liquid source may include an aliphatic hydrocarbon hexane having a C—C single bond, an octane, or an ethanol. 
     In some embodiments, the directly growing graphene may include a doping process. 
     In some embodiments, the doping process may use a doping gas, and the doping gas may include NH 3 , NO 2 , BH 3 , B 2 H 6 , or a combination thereof. 
     In some embodiments, the pre-treating the substrate may increase a k-value of the substrate to a value that is greater than 2.70 and less than about 2.80. 
     In some embodiments, the pre-treating the substrate may decrease an absorbance of the substrate, measured at a wavenumber corresponding to a D band of graphene, to a value that is about 0.26 
     In some embodiments, the substrate may have an absorbance peak corresponding to a G band of graphene after the pre-treating the substrate. 
     In some embodiments, the pre-treating the substrate may increase a k-value of the substrate to a value that is greater than 2.70 and less than about 2.80. 
     According to some embodiments, a pre-treated substrate may be prepared by one of the foregoing methods of a pre-treating a substrate. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other aspects will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings in which: 
         FIGS. 1 through 4  are cross-sectional views showing steps of a method of forming graphene according to an embodiment. 
         FIG. 5  is a cross-sectional view showing a case in which a carbon source and hydrogen, among gas components of a pre-treatment gas in a method of directly forming graphene, are independently supplied into a chamber and mixed in the chamber. 
         FIG. 6A  is a table showing an example of supply methods of a carbon source and hydrogen included in the pre-treatment gas in the case of  FIG. 5 . 
         FIG. 6B  is a timing diagram showing an example of the first supply method of  FIG. 5 . 
         FIG. 6C  is a timing diagram showing an example of the second supply method of  FIG. 5 . 
         FIG. 7  is a cross-sectional view showing a case in which a carbon source and hydrogen, among gas components of a pre-treatment gas in a method of directly forming graphene, are supplied into a chamber after mixing the carbon source and the hydrogen outside the chamber. 
         FIG. 8  is a graph showing a test result of measuring the change of a Si—CHs bond in an Inter-Metal Dielectric (IMD) substrate when the IMD substrate is pre-treated according to a pre-treating method applied to a method of directly forming graphene according to an embodiment and when the IMD substrate is pre-treated according to a pre-treating method applied to a method of directly forming graphene of the related art. 
         FIG. 9  is a magnified graph of a first peak P 1  that shows the presence of a Si—CH 3  bond in  FIG. 8 . 
         FIG. 10  is a graph showing a measurement result of Raman intensities with respect to graphene obtained by using a method of directly forming graphene according to an embodiment, the method including a process of pre-treating a substrate with a pre-treatment gas that includes both a carbon source and a hydrogen source, and graphene obtained by using a method of directly forming graphene of the related art, the method including a process of pre-treating a substrate with a pre-treatment gas that includes only one of a carbon source and a hydrogen source. 
         FIG. 11  is a cross-sectional view of an apparatus for forming graphene according to some example embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to embodiments, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. In this regard, the present embodiments may have different forms and should not be construed as being limited to the descriptions set forth herein. Accordingly, the embodiments are merely described below, by referring to the figures, to explain aspects. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. Expressions such as “at least one of,” when preceding a list of elements, modify the entire list of elements and do not modify the individual elements of the list. 
     In order to apply graphene to a semiconductor process, the graphene should be able to directly grow on a non-catalyst substrate or a non-metal substrate at a relatively low temperature (for example, 1000° C. or less). In order to directly grow graphene on a non-catalyst substrate at a low temperature, a plasma process may be used to activate a carbon source gas. The plasma process may change physical properties of the non-catalyst substrate, and thus, the use of the plasma process may be limited. 
     A pre-treating process with respect to the non-catalyst substrate may be performed before directly forming graphene on the non-catalyst substrate, and thus, residues and oxides may be removed from a surface of the non-catalyst substrate. In the pre-treating process, hydrogen plasma may be used. However, the physical properties of the non-catalyst substrate exposed to the hydrogen plasma may be changed. As a result, a k value (dielectric constant) of the non-catalyst substrate may be increased, and the amount of CH 3  may be reduced on a surface of the non-catalyst substrate. 
     Thus, as a method of pre-treating a substrate, by which the efficiency of forming graphene may be increased by reducing and/or minimizing the change of the physical properties of the substrate in a method of directly forming graphene on a non-catalyst substrate at a low temperature, a case in which a pre-treatment gas including hydrogen and carbon is used is introduced. 
     Hereinafter, methods of pre-treating a substrate and methods of directly forming graphene by using the methods of pre-treating according to an embodiment will be described in detail with reference to the accompanying drawings. In the drawings, thicknesses of layers or regions are exaggerated for clarity of the specification. 
       FIGS. 1 through 4  are cross-sectional views showing steps of a method of forming graphene according to an embodiment. 
     Referring to  FIG. 1 , in the method of forming graphene according to an embodiment, a surface  20 A of a substrate  20  on which graphene will be formed is pre-treated in advance. The surface  20 A on which the graphene will be formed may be, for example, an upper surface of the substrate  20 . Through pre-treatment of the substrate  20 , residues (for example, oxides) that may be obstacles for growing graphene may be removed from the surface  20 A of the substrate  20  on which the graphene will be formed. Also, as depicted in  FIG. 2 , graphene seeds  24  may be formed on some regions of the surface  20 A of the substrate  20  by the pre-treatment process. The graphene seeds  24  include carbon. In a subsequent process for forming graphene, graphene may grow from the graphene seeds  24 . 
     The pre-treatment may be a process of exposing the surface  20 A of the substrate  20  on which graphene will be formed to plasma of a pre-treatment gas. The plasma of a pre-treatment gas may denote plasma including a pre-treatment gas. A pre-treatment gas used in the pre-treatment process may include at least a carbon source and a hydrogen gas H 2 , and the carbon source may be a carbon precursor gas including carbon. The pre-treatment gas may further include other components besides the carbon source and hydrogen, for example, at least one of nitrogen N 2  and a noble gas. Here, the noble gas may denote an inert gas, an inactive gas, or a rare gas, that is, elements of Group 18 in the Periodic Table, the outermost shell of which is completely filled with electrons, and thus, it is difficult to form a chemical bond. As a result, the pre-treatment gas may be a gas mixture including at least a carbon source and hydrogen among a carbon source, hydrogen, nitrogen, and noble gas. 
     In the pre-treatment gas, the carbon source may exist as a precursor type. For example, the carbon source may be included in the pre-treatment gas as a C x H y (x: 1 ˜ 12 , y: 2 ˜ 26 ) type. In C x H y , x may be in a range of 1 to 12 and y may be in a range of 2 to 26. C x H y  may be, for example, CH 4 , C 2 H 2 , C 2 H 4 , C 2 H 6 , C 3 H 8 , C 5 H 12 , etc. If the carbon source of the pre-treatment gas is obtained from a liquid source or a solid source, the carbon source may be a type different from C x H y , for example, CHO type. The noble gas may include one or more of He, Ne, Ar, Kr, Xe, etc. The substrate  20  may include a non-metal substrate or a non-catalyst substrate. The non-metal substrate may include a semiconductor substrate, such as a Si substrate, a Ge substrate, a SiGe substrate, and a GaAs substrate and/or the non-metal substrate may be a dielectric substrate, but the non-metal substrate is not limited thereto. The dielectric substrate may be a SiO 2  substrate, a Si 3 N 4  substrate, or a SiC x O y H z  (0&lt;x&lt;2, 1&lt;y&lt;2.5, 0&lt;z&lt;6) substrate, but is not limited thereto. 
     The pre-treatment process may be performed under various process conditions. As an example, in the pre-treatment process, the substrate  20  may be maintained at a temperature lower than 1,000° C., for example, in a range from about 200° C. to about 700° C. The pre-treatment process may be performed under a pressure in a range from about 0.01 torr to about 5.0 torr together with the temperature described above. In the pre-treatment process, a microwave (MW) plasma frequency band for forming plasma of a pre-treatment gas may be in a range from about 0.7 GHz to about 2.5 GHz, and/or a radio frequency (RF) plasma frequency band may be in a range from about 3 MHz to about 100 MHz. In the pre-treatment process, power for forming plasma of a pre-treatment gas may be in a range from about 10 W to about 4,000 W. The process conditions for the pre-treatment process may be applied to a main process, that is, a process of directly growing graphene after the pre-treatment process, but the process condition of the main process may be different from the process condition of the pre-treatment process. As an example, the rate of carbon supply for growing graphene in the main process may be greater than that in the pre-treatment process. Also, the rate of hydrogen supply in the main process may be lower than that in the pre-treatment process. Also, the temperature of the substrate  20  in the main process may be maintained at a greater temperature than that in the pre-treatment process. Also, power for forming plasma in the main process may be less than that in the pre-treatment process. 
     In the process of the pre-treatment process, the surface  20 A of the substrate  20  on which graphene will be formed is exposed to plasma of a pre-treatment gas. Accordingly, the pre-treatment process may be referred to as a process of exposing the substrate  20  to the plasma of a pre-treatment gas. As a result of the process of the pre-treatment process, residues (for example, oxides) may be removed from the surface  20 A of the substrate  20  on which graphene will be formed. Also, carbon in the pre-treatment gas that is activated while the pre-treatment gas is converted into plasma may be adsorbed on the surface  20 A of the substrate  20  on which graphene will be formed. As a result, after the pre-treatment process is completed, as depicted in  FIG. 2 , carbons may be distributed in places to places on the surface  20 A of the substrate  20  on which graphene will be formed. The distributed carbons may act as graphene seeds  24  and may become nuclei for graphene growth. In the subsequent main process, the graphene-grow starts from the graphene seeds  24 . 
     Considering that the graphene seeds  24  are formed on the surface  20 A of the substrate  20  on which graphene will be formed by the pre-treatment process, the pre-treatment process may be referred to as a process of forming graphene seeds. 
     After the graphene seeds  24  are formed on the surface  20 A of the substrate  20  on which graphene will be formed by the pre-treatment process, as depicted in  FIG. 3 , a carbon source  26  is supplied onto the surface  20 A to form graphene on the surface  20 A of the substrate  20 . The carbon source  26  may be supplied in a plasma type. Carbons included in the carbon source  26  may be adsorbed onto the substrate  20  around the graphene seeds  24 . In this way, graphene may grow in a lateral direction around the graphene seeds  24  on the surface  20 A of the substrate  20 , and as a result, as depicted in  FIG. 4 , a graphene layer  28  may be formed on the surface  20 A of the substrate  20 . In the process of forming the graphene layer  28 , a doping with respect to the graphene layer  28  may be performed according to the use of the graphene. A gas for doping may be, for example, one of NH 3 , NO 2 , BH 3 , and B 2 H 6  or at least one of these materials. The carbon source  26  may be, for example, an aliphatic carbon material including CH 4  and/or C 2 H 2  and/or an aromatic carbon material. 
     The carbon source  26  may be supplied in a plasma type. When the carbon source  26  is supplied onto the substrate  20 , carbons included in the carbon source  26  are supplied by dividing into individual carbons. For this purpose, plasma may be irradiated to the carbon source  26 . At this point, the plasma may include at least one of H 2 , Ar, and N 2 . Energy of the plasma may be controlled according to the kind of the carbon source  26 . A plurality of carbons include in the carbon source  26  may be separated by the plasma process and are supplied onto the substrate  20 . When the carbon source  26  is an aromatic carbon material, the plasma irradiation may be performed to remove materials (for example, hydrogen) attached to rings of the aromatic carbon material like branches while the hexagonal ring shape of the aromatic carbon material is maintained instead of individually separating the carbons in the carbon source  26 . The energy intensity of plasma irradiated onto the carbon source  22  may be controlled according to the kind of the carbon source  26 . 
     When the carbon source  26  is supplied, a gas source may be used, but a liquid source or a solid source may also be used. When a liquid source is used in supplying the carbon source  26 , a gas state carbon source may be supplied by generating bubbles in a container in which the liquid source is contained. When a solid source is used in supplying the carbon source  26 , a carbon source in a gas state may be supplied by heating the solid source. Both the liquid source and the solid source may include a carbon compound including the carbon source  26 . As an example, the liquid source may include one of aromatic hydrocarbon benzene having at least one benzene ring, toluene, xylene, anisole, and a derivative of these materials. As another embodiment, the liquid source may include one of aliphatic hydrocarbon hexane having a C—C single bond, octane, and ethanol. 
     In the method of directly forming graphene as depicted in  FIGS. 1 through 4 , the substrate  20  is loaded in a chamber before starting the pre-treatment process, and an inner state of the chamber is set suitable for the pre-treatment process. A pre-treatment gas may be supplied into the chamber through individual supply lines or a common supply line. 
       FIG. 5  is a cross-sectional view showing a case in which a carbon source and hydrogen, among gas components of a pre-treatment gas in a method of directly forming graphene are independently supplied into a chamber and mixed in the chamber. 
     Referring to  FIG. 5 , first through third gas lines L 1 , L 2 , and L 3  through which gases are supplied to or discharged from a chamber  50  are connected to the chamber  50  in which a process of directly growing graphene is performed. A carbon source, that is, a carbon precursor may be supplied through the first gas line L 1 , and hydrogen may be supplied through the second gas line L 2 . Residue gases in the chamber  50  may be discharged through the third gas line L 3  during a process of directly growing graphene or after the process is completed. 
     When a mixed pre-treatment gas is formed in the chamber  50  by individually supplying a carbon source and hydrogen of the gas components of the pre-treatment gas, the supply rates of gas components of pre-treatment gas may be controlled. As an example, the supply rates of the gas components of pre-treatment gas may be equal or different according to time. 
       FIG. 6A  is a Table showing an example of supply methods of the carbon source and the hydrogen included in the pre-treatment gas in the case of  FIG. 5 . 
     Referring to  FIG. 6A , as a first supply method, a carbon source and hydrogen may be continuously supplied into the chamber  50 . As a second supply method, hydrogen may be continuously supplied and a carbon source may be discontinuously supplied. As a third supply method, a carbon source may be continuously supplied and hydrogen may be discontinuously supplied. As a fourth supply method, both a carbon source and hydrogen may be discontinuously supplied. In the methods of  FIG. 6A , the discontinuously supplying method is a method of repeating the gas supply and stopping the gas supply by using a time division method. In the time division method, the gas supply time may be constant or changed in the repeating operation, but the gas supply rate may be changed even though the gas supply time is maintained as constant in the repeating operation. 
     In the first supply method, the gas supply rate may be constant or changed according to time. As an example,  FIG. 6B  shows the supply rates of a carbon source and hydrogen in the first supply method respectively may be constant. However, at least one of the supply rates of the carbon source and the hydrogen in the first supply method may be changed while maintaining continuity of gas supply.  FIG. 6C  shows an example of the second supply method. Referring to  FIG. 6C , hydrogen is continuously supplied and a carbon source is discontinuously supply by using the time division method. 
       FIG. 7  shows a case in which a carbon source and hydrogen are supplied into the chamber  50  after mixing the carbon source and the hydrogen source outside the chamber  50  in a method of directly forming graphene. 
     Referring to  FIG. 7 , the third gas line L 3  and a sixth gas line L 6  are connected to the chamber  50 . An end of the sixth gas line L 6  is connected to the chamber  50  and the other end is connected to a mixing container or a mixer  56 . A pre-treatment gas mixture is formed in the mixer  56 , and a carbon source and hydrogen respectively are supplied to the mixer  56  through fourth and fifth gas lines L 4  and L 5  that are connected to the mixer  56 . The pre-treatment gas mixture formed in the mixer  56  is supplied to the chamber  50  through the sixth gas line L 6 . 
     In this way, in the method in which the pre-treatment gas is supplied to the chamber  50  after the pre-treatment gas is mixed outside the chamber  50 , the mixed pre-treatment gas may be continuously supplied to the chamber  50  at a constant rate or supplied to the chamber  50  by using a time division method. When the mixed pre-treatment gas is supplied to the chamber  50  by using a time division method, the mixed pre-treatment gas may be supplied for a certain period of time and may be stopped for a certain period of time. In the case of the time division method, the time for supplying and the time for stopping the supply of the mixed pre-treatment gas may be equal to or different from each other, and may be controlled in a direction to improve and/or maximize the pre-treatment efficiency. 
     In both cases when the mixed pre-treatment gas is continuously supplied and is supplied by using a time division method, the supply of the mixed pre-treatment gas may be performed in various ways according to a gas supply rate and pressure. For example, when the mixed pre-treatment gas is continuously supplied, the supply rate of the mixed pre-treatment gas supplied to the chamber  50  may be changed. In other words, the mixed pre-treatment gas may be supplied to the chamber  50  at a first supply rate for a first set time, and the mixed pre-treatment gas may be supplied to the chamber  50  at a second supply rate for a second set time. 
     When the mixed pre-treatment gas is supplied to the chamber  50  by using a time division method, in every operation of supplying the mixed pre-treatment gas, the supply rates of the mixed pre-treatment gas supplied to the chamber  50  may be controlled equal to or different from each other. In the time division method, a single supply time and a single stopping time may constitute a unit supply cycle, and the unit supply cycle may be repeated greater than twice. In this case, the supply time and the stopping time of the unit supply cycle may be equal to or different from each other. As an example of the case in which the supply time and the stopping time of each unit supply cycle are different, a supply time in a first unit supply cycle may be greater or less than a supply time in a second unit supply cycle. 
       FIG. 8  shows a test result of measuring the change of a Si—CHs bond in an Inter-Metal Dielectric (IMD) substrate (for example, SiO 2  substrate) when the IMD substrate is pre-treated according to the pre-treating method applied to a method of directly forming graphene according to an embodiment and when the IMD substrate is pre-treated according to a pre-treating method applied to a method of directly forming graphene of the related art. The substrate pre-treatment method applied to the method of directly forming graphene of the related art may denote a case of substrate pre-treatment by using a pre-treatment gas that includes hydrogen but does not include a carbon source. 
       FIG. 9  is a magnified graph of a first peak P 1  that shows the presence of Si-CH 3  bond in  FIG. 8 . In  FIGS. 8 and 9 , the horizontal axis represents wavenumber and the vertical axis represents absorbance. The absorbance may be measured by using a Fourier Transform Infra-Red (FTIR) spectroscopy method. 
     In  FIG. 9 , a first graph G 1  shows a result with respect to a substrate that is not pre-treated, a second graph G 2  shows a result with respect to a substrate that is pre-treated according to the substrate pre-treatment method applied to the method of directly forming graphene according to an embodiment. A third graph G 3  shows a result with respect to a substrate that is pre-treated according to the substrate pre-treatment method applied to the method of directly forming graphene of the related art. 
     When a first peak P 1  of the first through third graphs G 1 , G 2 , and G 3  in  FIG. 9  is observed, the absorbance is the highest in the substrate that is not pre-treated, and is the lowest in the substrate that is pre-treated according to the substrate pre-treatment method applied to the method of directly forming graphene of the related art. The absorbance of the substrate that is pre-treated according to the substrate pre-treatment method applied to the method of directly forming graphene according to an embodiment is in a medium level. The result denotes that the amount of Si—CH 3  bonds is the largest in the substrate that is not pre-treated, and is the least in the substrate that is pre-treated according to the substrate pre-treatment method applied to the method of directly forming graphene of the related art. The result also denotes that the amount of Si—CH 3  bonds is in a medium level in the substrate that is pre-treated according to the substrate pre-treatment method applied to the method of directly forming graphene according to an embodiment. The result may denote that the amount of the Si—CH 3  bonds present in the substrate that is pre-treated according to the substrate pre-treatment method applied to the method of directly forming graphene according to an embodiment is greater than that in the substrate that is pre-treated according to the substrate pre-treatment method applied to the method of directly forming graphene of the related art. In other words, when a substrate is pre-treated according to the substrate pre-treatment method applied to the method of directly forming graphene according to an embodiment, the reduction of CH 3  on a surface of the substrate may be reduced than in a substrate that is pre-treated according to the substrate pre-treatment method applied to the method of directly forming graphene of the related art. 
     The result indicates that, when a substrate is pre-treated according to the substrate pre-treatment method applied to the method of directly forming graphene according to an embodiment, the absorbance of carbon is advantageous when growing graphene, and thus, the growing of graphene is promoted. 
     Table 1 shows the quantification of the results of  FIG. 8  and the variation of k value in a method of directly forming graphene according to an embodiment and a method of directly forming graphene of the related art. 
     
       
         
           
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Substrate pre-treatment method 
                 Si—CH 3   
                 k(C—V) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 Bare 
                 0.275 
                 2.70 
               
               
                 Hydrogen plasma pre-treatment 
                 0.249 
                 2.85 
               
               
                 Carbon + Hydrogen plasma pre-treatment 
                 0.262 
                 2.78 
               
               
                   
               
            
           
         
       
     
     In Table 1, “Bare” indicates a substrate that is not pre-treated The “Hydrogen plasma pre-treatment” indicates a case in which a substrate is pre-treated according to the substrate pre-treatment method applied to the method of directly forming graphene of the related art. Also, the “Carbon+Hydrogen plasma pre-treatment” indicates a case in which a substrate is pre-treated according to the substrate pre-treatment method applied to the method of directly forming graphene according to an embodiment. “Si—CH 3 ” indicates Si—CH 3  bonds. 
     Referring to  FIG. 9  and Table 1, in the substrate that is pre-treated according to the substrate pre-treatment method applied to the method of directly forming graphene according to an embodiment, a figure that indicates the presence of Si—CH 3  bonds is 0.262. On the other hand, in the substrate that is pre-treated according to the substrate pre-treatment method of the related art, a figure that indicates the presence of Si—CH 3  bonds is 0.249 which is the lowest, and, in the substrate that is not pre-treated, a figure that indicates the presence of Si—CH 3  bonds is 0.275 which is the highest. In the case of k values, the k value is the lowest (2.7) in the substrate that is not pre-treated, the k value is the highest (2.85) in the substrate that is pre-treated according to the substrate pre-treatment method of the related art, and the k value (2.78) of the substrate that is pre-treated according to the substrate pre-treatment method applied to the method of directly forming graphene according to an embodiment is greater than that of the substrate that is not pre-treated and is less than that of the substrate that is pre-treated according to the substrate pre-treatment method of the related art. 
       FIG. 10  is a graph showing a measurement result of Raman intensities with respect to graphene obtained by using a method of directly forming graphene according to an embodiment, the method including a process of pre-treating a substrate with a pre-treatment gas that includes both a carbon source and a hydrogen source, and graphene obtained by using a method of directly forming graphene of the related art, the method including a process of pre-treating a substrate with a pre-treatment gas that includes only a hydrogen source. These two methods were performed at a temperature lower than 1,000° C., for example, 400° C., and a silicon substrate is used as a substrate for directly growing graphene. 
     In  FIG. 10 , the horizontal axis represents Raman shift, and the vertical axis represents Raman intensity. A first graph G 11  indicates a measurement result with respect to a substrate before forming graphene and immediately after a pre-treatment by using the substrate pre-treatment method applied to the method of directly forming graphene according to an embodiment. A second graph G 22  indicates a measurement result with respect to graphene obtained by using the method of directly forming graphene of the related art. A third graph G 33  indicates a measurement result with respect to graphene obtained by using the method of directly forming graphene according to an embodiment. 
     Referring to  FIG. 10 , a meaningful peak is not seen on the first graph G 11 , and this is regarded as a natural result since graphene is not present on the substrate immediately after the pre-treatment. 
     In second and third graphs G 22  and G 33 , second peaks P 2  and P 2 ′ are present on the same locations and third peaks P 3  and P 3 ′ are also present on the same locations. The second peaks P 2  and P 2 ′ indicate a D band, and the third peaks P 3  and P 3 ′ indicate a G band. The second peaks P 2  and P 2 ′ and the third peaks P 3  and P 3 ′ indicate the presence of graphene. That is, the second peaks P 2  and P 2 ′ and the third peaks P 3  and P 3 ′ appeared on the second and third graphs G 22  and G 33  denote that graphene is grown on the substrate that is pre-treated. The locations of the second and third peaks P 2  and P 3  appeared on the second graph G 22  are the same as the locations of the second and third peaks P 2 ′ and P 3 ′ appeared on the third graph G 33 . However, heights of the second and third peaks P 2 ′ and P 3 ′ appeared on the third graph G 33  are higher than those of the second and third peaks P 2  and P 3  appeared on the second graph G 22 . The result indicates that a greater amount of graphene may be formed when the graphene is formed by using the method of directly forming graphene according to an embodiment than the method of directly forming graphene of the related art. 
     In the substrate pre-treatment method according to an embodiment and the method of directly forming graphene using the substrate pre-treatment method, a pre-treatment gas including together a carbon source and hydrogen is used as a pre-treatment gas. The increase in the k value (dielectric constant) of the non-catalyst substrate may be suppressed when a pre-treatment gas including both a carbon source and hydrogen is used than when a pre-treatment gas including only hydrogen of the related art is used. 
     Also, the reduction rate of CH 3  on a surface of the substrate may be reduced by pre-treating a substrate with plasma of a pre-treatment gas including together a carbon source and hydrogen than when a substrate is pre-treated with plasma of a pre-treatment gas including only hydrogen of the related art. Accordingly, a greater amount of CH 3  may be present on a surface of a substrate than when the substrate is pre-treated with plasma of a pre-treatment gas including only hydrogen of the related art. The CH 3  present on the surface of the substrate may advantageously induce the absorbance of carbon during growing graphene, and thus, the growing of the graphene may be promoted. 
       FIG. 11  a cross-sectional view of an apparatus for forming graphene according to some example embodiments. 
     Referring to  FIG. 11 , the apparatus  1100  may be configured to form a graphene product according to any one of the embodiments in  FIGS. 1 to 5 and 7  of the present application. 
     The apparatus  1100  may include a gas supply  1110 , a process chamber  1160 , a plasma generation unit  1170  (e.g., RF generator), microwave generator  1190  (e.g., magnetron), a substrate transporter  1172 , a pumping system  1174 , a heater  1176 , a power supply  1178 , and an operation station  1180 . The process chamber  1160  may include a chamber housing  1120 , an upper electrode  1130  in the chamber housing  1120 , and a substrate support  1150  in the chamber housing  1120 . The upper electrode  1130  may be connected to a gas supply  1110  with conduits and gas flow controllers for providing reaction gases into the process chamber  1160 . The substrate support  1310  may be an electrostatic chuck, but is not limited thereto. 
     Although not illustrated in  FIG. 11 , the gases (e.g., gases for pretreatment gas, gases for reaction gas) may be mixed outside the process chamber  1160 , like the arrangement in  FIG. 7 , or individually delivered to the process chamber  1160  like the arrangement in  FIG. 5 . 
     A substrate transporter  1172 , such as a robot arm, may transport a substrate  1140  into and out of the process chamber  1160 . The process chamber  1160  may include a gate valve that opens when the substrate transporter  1172  transports the substrate  1140  into or out of the process chamber  1160  and closes when the process chamber  1160  performs operations (e.g., vacuum processes). A heater  1176  may control the temperature of the substrate support  1150 , inner wall of process chamber  1160 , and upper electrode  1130 . An RF power generator  1170 , may be connected to the substrate support  1150  and may be used to generate a plasma P of a reaction gas in the process chamber  1160 . Alternatively, or in addition, the microwave generator  1190  may be used to generate the plasma P in the process chamber  1160 . A pumping system  1174  connected to the process chamber  1160  may create a vacuum in the process chamber  1160 . A power supply  1178  may provide electrical power to the apparatus  1100 . 
     The operation station  1180  may control operations of the apparatus  1100 . The operation station  1180  may include a controller  1182 , a memory  1184 , a display  1186  (e.g., monitor), and an input and output device  1188 . The memory  1184  may include a nonvolatile memory, such as a flash memory, a phase-change random access memory (PRAM), a magneto-resistive RAM (MRAM), a resistive RAM (ReRAM), or a ferro-electric RAM (FRAM), and/or a volatile memory, such as a static RAM (SRAM), a dynamic RAM (DRAM), or a synchronous DRAM (SDRAM). The input and output device  1188  may be a keyboard or a touch screen. 
     The memory  1184  may store an operating system and may store recipe instructions that include settings (e.g., gas flow rates, temperature, time, power, pressure, etc.) for different manufacturing processes performed by the apparatus  1100 . The memory  1184  may store recipe instructions for pre-treating the substrate  1140  and/or forming graphene directly on the substrate  1140  after the substrate  1140  has been pre-treated according to one or more of the embodiments in  FIGS. 1 to 5 and/or 7  of the present application. 
     The controller  1182  may be, a central processing unit (CPU), a controller, or an application-specific integrated circuit (ASIC), that when, executing recipe instructions stored in the memory  1184  (for one or more of the embodiments in  FIGS. 1 to 5 and/or 7 ) configures the controller  1182  as a special purpose controller that operates apparatus  1100  for performing operations on the substrate  1140  (e.g., pre-treating the substrate, forming graphene directly on the substrate) according to example embodiments. 
     It should be understood that embodiments described herein should be considered in a descriptive sense only and not for purposes of limitation. Descriptions of features or aspects within each embodiment should typically be considered as available for other similar features or aspects in other embodiments. While one or more embodiments have been described with reference to the figures, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope as defined by the following claims.