Patent Publication Number: US-2019172813-A1

Title: Substrate joining method

Description:
TECHNICAL FIELD 
     The present invention relates to a substrate bonding method of bonding a first substrate and a second substrate by sputter-etching. 
     BACKGROUND ART 
     For example, in the case where substrates made of a semiconductor material such as Si and Ge, a compound semiconductor material such as a Ga-based material and an In-based material, or a metal material such as Au, Cu, and Al are bonded to each other at room temperature; in conventional methods, the surface of each substrate is irradiated with a beam of ion particles in a vacuum environment to activate the surface of the substrate by sputter-etching, and these substrates are bonded to each other by bringing these surfaces into contact with each other. 
     CITATION LIST 
     Patent Literature 
     Patent literature 1: International Publication No. WO2012/105474 
     Summary Of Invention 
     Technical Problem 
     However, for example, for substrates made of an amorphous oxide material such as amorphous SiO 2 , an amorphous nitride material such as amorphous SiN, or the like, even when the surfaces of the substrates are sputter-etched by irradiating the surfaces with a beam of ion particles, the activity of the surfaces decreases rapidly. Thus, it is difficult to bond the substrates with a sufficient strength. 
     Solution to Problem 
     A substrate bonding method according to a first aspect of the invention to solve the above problem is a substrate bonding method of bonding a first substrate and a second substrate by sputter-etching, characterized in that the first substrate is made of at least one of a semiconductor material, a compound semiconductor material, and a metal material, and the substrate bonding method comprises: an activation step of sputter-etching a surface of the first substrate by irradiating the surface of the first substrate with a beam of ion particles, to deposit spattered particles of the first substrate on a surface of the second substrate; and a bonding step of bonding the second substrate and the first substrate by bringing the surface of the second substrate on which the sputtered particles of the first substrate have been deposited and the surface of the first substrate that have been sputter-etched into contact with each other. 
     A substrate bonding method according to a second aspect of the invention is the substrate bonding method according to the first aspect of the invention, characterized in that the substrate bonding method further comprises, before the activation step, a cleaning step of sputter-etching the surface of the second substrate by irradiating the surface of the second substrate with a beam of ion particles to clean the surface of the second substrate. 
     A substrate bonding method according to a third aspect of the invention is the substrate bonding method according to the first or second aspect of the invention, characterized in that the second substrate is made of at least one of an oxide material, a nitride material, a carbide material, a fluoride material, a semiconductor material, a compound semiconductor material, and a metal material. 
     Advantageous Effects of Invention 
     In the substrate bonding method according to the present invention, the first substrate is mads of at least one of a semiconductor material, a compound semiconductor material, and metal material. A surface of the first substrate is sputter-etched by irradiating the surface of the first substrate with a beam of ion particles, to deposit the sputtered particles of the first substrate on a surface of the second substrate. Then, the second substrate and the first substrate are bonded to each other by bringing the surface of the second substrate on which the sputtered particles of the first substrate has been deposited and the surface of the first substrate that has been sputter-etched into contact with each other. Consequently, for example, even though the second substrate is made of a material the activity of which tends to decrease, the second substrate can be bonded to the first substrate at room temperature with a high strength. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram illustrating a schematic configuration of a substrate bonding apparatus used for explaining and implementing a procedure of a first embodiment of a substrate bonding method according to the present invention. 
         FIG. 2  is a diagram for explaining a procedure subsequent to  FIG. 1 . 
         FIG. 3  is a diagram for explaining a procedure subsequent to  FIG. 2 , 
         FIG. 4  is a diagram for explaining a procedure subsequent to  FIG 3 . 
         FIG. 5  is a diagram illustrating a schematic configuration of a substrate bonding apparatus used for explaining and implementing a procedure of a second embodiment of a substrate bonding method, according to the present invention. 
         FIG. 6  is a diagram for explaining a procedure subsequent to  FIG. 5 . 
         FIG. 7  is a diagram for explaining a procedure subsequent to  FIG. 6 . 
         FIG. 8  is a diagram for explaining a procedure subsequent to  FIG. 7 . 
         FIG. 9  is a diagram for explaining a procedure subsequent to  FIG. 8 . 
         FIG. 10A  is a diagram for explaining the action in  FIG. 1  and  FIG. 6 . 
         FIG. 10B  is a diagram for explaining the action in  FIG. 3  and  FIG. 8 . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Embodiments of substrate bonding methods according to the present invention will be described based on the drawings; however, the present invention is not limited only to the following embodiments described based on the drawings. 
     First Embodiments 
     A first embodiment of a substrate bonding method according to the present invention will be described based on  FIGS. 1 to 4 . 
     As illustrated in  FIG. 1 , at a lower center portion inside a chamber  111  is placed a support base  112 . On the support base  112 , a lower stage  113  is arranged so as to attachably and detachably hold a first substrate  11  on its upper surface. To the upper center portion of the ceiling of the chamber  111  is attached the distal end of a lifting cylinder  114  with its axial direction oriented in the up-down direction. The lifting cylinder  114  is configured to move the distal end of a rod  114   a  upward and downward inside the chamber  111 . To the lower-surface of the distal end of the rod  114   a  of the lifting cylinder  114  is attached an upper stage  115 , which attachably and detachably holds a second substrate  12  under its lower surface. 
     To the chamber  111  is connected an exhaust pump  116  which evacuates the chamber  111  to make the inside a high vacuum environment. Inside the chamber  111  is arranged an ion gun  118 , such as a FAB, to be oriented with its delivery port directed to a surface (upper surface) of the first substrate  11  held on the lower stage  113 . The ion gun  118  is connected to a gas source  117  which supplies the ion gun  118  with gas  1 , such as argon, as feedstock gas. 
     The first substrate  11  is made of at least one of a semicondcutor material such as Si and Ge; a compound semiconductor material including a Ga based material such as GaN, GaAs, and GaP, and an In based material such as InP and InSb; and a metal material such as Au, Cu, and Al. On the other hand, the second substrate  12  is made of at least one of an amorphous oxide material such as amorphous SiO 2 ; an amorphous nitride material such as amorphous SiN; an amorphous carbide material such as amorphous SiC, and an amorphous fluoride material such as amorphous CaF 2 . 
     Next, description will be provided for a substrate bonding method using the substrate bonding apparatus  100  according to this embodiment described above. 
     First, the first substrate  11  is attached to the lower stage  113 , and the second substrate  12  is attached to the upper stage  115  (a substrate holding step). Then, the exhaust pump  116  is operated to evacuate the chamber  111  to make the inside a high vacuum environment (an exhaust step). 
     Next, when the gas  1  is supplied for the ion gun  118  from the gas source  117  and the ion gun  118  is turned on, the ion gun  118  radiates a beam  2  of ion particles of the gas  1  toward the surface (upper surface) of the first substrate  11  on the lower stage  113  (see  FIG. 1 ) . 
     With this operation, the surface (upper surface) of the first substrate  11  made of a material described above is sputter-etched to be activated, and at the same time, sputtered particles Ms of a foregoing material of the first substrate  11  are attached to the surface (lower surface) of the second substrate  12  (see  FIG. 10A ). Thus, an active layer  11   a  composed of the sputtered particles Ms of the foregoing material is formed so as to adhere to the surface (lower surface) of the second substrate  12  (see  FIG. 2 ) (an activation step). 
     After the active layer  11   a  composed of the sputtered particles Ms of the material of the first substrate  11  is formed so to adhere to the surface (lower surface) of the second substrate  12  in this way, the operation of the ion gun  118  is stopped. Then, the lifting cylinder  114  is operated to extend the rod  114   a  and lower the upper stage  115 , so that the lower stage  113  and the upper stage  115  are brought relatively close to each other in the opposing direction. The active layer  11   a  of the surface (lower surface) of the second substrate  12  held by the upper stage  115  is pressed against the activated surface (upper surface) of the first substrate  11  held by the lower stage  113  with these surfaces in contact with each other (see  FIG. 3 ). Thus, the first substrate  11  and the second substrate  12  are bonded to each other via the active layer  11   a  (see  FIG. 10B ) (a bonding step). 
     After the surface (upper surface) of the first substrate  11  is bonded to the surface (lower surface) of the second substrate  12  via the active layer  11   a  as described above, the upper stage  115  releases the holding of the second substrate  12 . Then, the lifting cylinder  114  is operated to shorten the rod  114   a  to move the upper stage  115  upward, so that the lower stage  113  and the upper stage  115  relatively move apart from each other in the opposing direction. Thus, the upper stage  115  is disengaged from the second substrate  12  (see  FIG. 4 ). 
     The operation of the exhaust pump  116  is stopped, and the pressure inside the chamber  111  is returned to the atmospheric pressure. Then, the lower stage  113  releases the holding of the first substrate  11 . A bonded material  10  is obtained by taking it out from the position on the lower stage  113  to the outside of the chamber  111 . 
     In summary, as described earlier, the beam  2  is radiated to the first substrate  11  made of the foregoing material to activate the surface of the first substrate  11  and also deposit the sputtered particles Ms of the first substrate  11  on the surface of the second substrate  12 . Thus, the active layer  11   a  of the sputtered particles Ms is formed on the surface of the second substrate  12  made of a material the activity of which tends to decrease so as to adhere to it (the activation step). The activated surface of the first substrate  11  and the active layer  11   a  are pressed and bonded to each other (the bonding step). With these steps, the first substrate  11  is bonded to the second substrate  12  made of a material the activity of which tends to decrease in this embodiment. 
     As a result, in this embodiment, the second substrate  12  made of a material the activity of which tends to decrease can be bonded to the first substrate  11  at room temperature with high strength. 
     Thus, according to this embodiment, a bonded material  10  with a sufficient joint strength can be produced at room temperature a sing the second substrate  12  even made of a material the activity of which tends to decrease. 
     In addition, since radiating the beam  2  to the first substrate  11  activates the surface of the first substrate  11  and also attaches the sputtered particles Ms that occur from the first substrate  11  to the surface of the second substrate  12  so that the active layer  11   a  is formed so as to adhere to the surface of the second substrate  12 , this eliminates the need for the dedicated material and process to form the active layer  11   a  and suppresses the increase in cost and time to produce the bonded material  10 . 
     Here, Table 1 shows results of experiments conducted to confirm effects of the substrate bonding method according to this embodiment. Note that Table 1 also shows results of a conventional method which was conducted for comparison. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 This embodiment 
                 Conventional method 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                   
                 First substrate 
                 Si 
                 Si 
               
               
                   
                 Second substrate 
                 Amorphous SiO 2   
                 Amorphous SiO 2   
               
               
                   
                 Gas 
                 Ar 
                 Ar 
               
               
                   
                 Beam radiation 
                 To only 
                 To both 
               
               
                   
                   
                 the first 
                 the first and second 
               
               
                   
                   
                 substrate 
                 substrates 
               
               
                   
                   
                 for 2.5 minutes 
                 for 2.5 minutes 
               
               
                   
                 Surface energy 
                 1.3 
                 0.3 
               
               
                   
                 (J/mm 2 ) 
               
               
                   
                   
               
            
           
         
       
     
     As can be seen from the above Table 1, the surface energy of the bonded surface between the first substrate and the second substrate by the conventional method was only 0.3 J/m 2 . On the other hand, it was confirmed that the surface energy in this embodiment was as much as 1.3 J/m 2 , which is a practical value (1.0 J/m 2  or more). 
     Second Embodiment 
     A second embodiment of a substrate bonding method according to the present invention will be described based on  FIGS. 5 to 9 . Here, for the same parts as in the foregoing embodiment, the same reference signs as have been used in the description for the foregoing embodiment are used to omit explanation overlapped with the description for the foregoing embodiment. 
     As illustrated in  FIG. 5 , inside the chamber  111  is arranged an ion gun  218 , such as a FAB, to be oriented with its delivery port directed to the surface (lower surface) of the second substrate  12  held by the upper stage  115 . The ion gun  218  is connected to a gas source  217  which supplies the ion gun  218  with gas  1 , such as argon. 
     Specifically, although in the foregoing embodiment, the ion gun  118  or other parts are arranged substrate  11  held by the lower stage  113 ; in this embodiment, the ion gun  218  and other parts are also arranged such that the beam  2  can be radiated to the second substrate  12  held by the upper stage  115 . 
     Next, description will be provided for a substrate bonding method using the substrate bonding apparatus  200  according to the embodiment described above. 
     First, as in the foregoing embodiment, a first substrate  11  is attached to the lower stage  113 , and also a second substrate  12  is attached to the upper stage  115  (the substrate holding step). Then, the exhaust pump  116  is turned on to evacuate the chamber  111  and make the inside a high vacuum environment (the exhaust step). 
     Next, when the gas  1  is supplied to the ion gun  218  from the gas source  217 , and the ion gun  218  is turned on, the ion gun  218  radiates a beam  2  of ion particles of the gas I toward the surface (lower surface) of the second substrate  12  under the upper stage  115  (see  FIG. 5 ). With this operation, the surface (lower surface) of the second substrate  12  is sputter-etched and cleaned (a cleaning step). 
     After the surface (lower surface) of the second substrate  12  is cleaned in this way, the operation of the ion gun  218  is stopped. Then, as in the foregoing embodiment, the gas source  117  supplies the gas  1  to the ion gun  118 , and the ion gun  118  is turned on, so that the ion gun  118  radiates the beam  2  of ion particles of the gas  1  toward the surface (upper surface) of the first substrate  11  on the lower stage  113  (see  FIG. 6 ). As in the foregoing embodiment, the surface of the first substrate  11  (upper surface) is sputter-etched and activated, and at the same time, the sputtered particles Ms of the first substrate  11  are deposited on the surface (lower surface) of the second substrate  12  (see  FIG. 10A ). With this operation, an active layer  11   a  composed of the sputtered particles Ms is formed on the surface (lower surface) of the second substrate  12  so as to adhere to it (see  FIG. 7 ) (the activation step). 
     Next, as in the foregoing embodiment, after the operation of the ion gun  118  is stopped, the lifting cylinder  114  is operated so that the lower stage  113  and the upper stage  115  are brought relatively close to each other in the opposing direction. Then, the active layer  11   a  of the surface (lower surface) of the second substrate  12  held by the upper stage  115  is pressed against the activated surface (upper surface) of the first substrate  11  held by the lower stage  113  with these surfaces in contact with each other (see  FIG. 8 ). Thus, the first substrate  11  and the second substrate  12  are bonded to each other via the active layer  11   a  (see  FIG. 10B ) (the bonding step). 
     Next, as in the foregoing embodiment, the upper stage  115  releases the holding of the second substrate  12 . Then, the lifting cylinder  114  is operated to move the upper stage  115  upward, so that the lower stage  113  and the upper stage  115  relatively move apart from each other in the opposing direction (see  FIG. 9 ). After that, the operation of the exhaust pump  116  is stopped, and the pressure inside the chamber  111  is returned to the atmospheric pressure. Then, the lower stage  113  releases the holding of the first substrate  11 . A bonded material  10  is taken out from the position on the lower stage  113  to the outside of the chamber  111 . 
     In summary, in this embodiment, the surface of the second substrate  12  is cleaned in advance by irradiating the second substrate  12  with the beam  2  and sputter-etching it, before the foregoing activation step in the foregoing embodiment is performed. 
     As result, in this embodiment, the adhesion of the active layer  11   a  to the surface (lower surface) of the second substrate  12  can be further increased, compared to the case in the foregoing embodiment. 
     Thus, this embodiment not only provides the same effect as in the foregoing embodiment as a matter of course but also provides a bonded material  10  with a bonding strength higher than the cases in the foregoing embodiment. 
     Note that in the activation step, in order to form an active layer  11   a  with a necessary and sufficient thickness (about 0.5 nm) on the surface of the second substrate  12  with the sputtered particles Ms from the first substrate  11 , the first substrate  11  is irradiated with the beam  2  for necessary and sufficient time (for example, about 1 minute). On the other hand, in the cleaning step, the second subs trace  12  is irradiated with the beam  2  for necessary and sufficient time (for example, about 30 seconds) to remove contamination such as natural oxide film formed on the surface of the second substrate  12 . Accordingly, this cleaning step does not activate the surface of the second substrate  12 , unlike the activation 
     In addition, it is preferable that the distance between the first substrate  11  and the second substrate  12  in the opposing direction be large in the cleaning step so that the contamination such as natural oxide film removed from the surface of the second substrate  12  is less likely to be attached to the surface of the first substrate  11 . In contrast, it is preferable that the distance between the first substrate  11  and the second substrate  12  in the opposing direction be small in the activation step to the extent where the radiation of the beam  2  to the first substrate  11  is not hindered substrate  11  can be deposited on the surface of the second substrate  12  efficiently. 
     Other Embodiments 
     Note that although in the foregoing first embodiment, the lower stage  113  holds the first substrate  11 , while the upper stage  115  holds the second substrate  12 , and the ion gun  118  is arranged such that the delivery port is directed to the first substrate  11  held by the lower stage  113 ; in another embodiment, the same effect as in the foregoing first embodiment can be obtained, for example, with the configuration in which the upper stage  115  holds the first substrate  11 , while the lower stage  113  holds the second substrate  12 , and the ion gun is arranged such that the delivery port is directed to the first substrate  11  held by the upper stage  115 . 
     In addition, although the foregoing second embodiment includes two ion guns, the ion gun  118  oriented such that the delivery port is directed to the first substrate  11  held by the lower stage  113  and the ion gun  218  oriented such that the delivery port is directed to the second: substrate  12  held by the upper stage  115 ; in another embodiment, the same effect as in the foregoing second embodiment can be obtained, for example, with the configuration including a single ion port between to the first substrate  11  held by the lower stage  113  and to the second substrate  11  held by the lower stage  113  and to the second substrate  12  held by the upper stage  115 . 
     In addition, although in the foregoing second substrate  11 , while the upper stage  115  holds the second substrate  12 ; in another embodiment, the same effect as in the foregoing second embodiment can be obtained, for example, with the configuration in which the upper stage  115  holds the first substrate  11 , and the lower stage  113  holds the second substrate  12 . 
     In addition, the foregoing embodiments have the configuration in which the lower stage  113  is arranged on the floor side of the chamber  111  via the support base  112 , while the upper stage  115  is arranged on the ceiling side of the chamber  111  via the lifting cylinder  114 , and the lower stage  113  and the upper stage  115  can be moved relatively close to or apart from each other in the opposing direction by the operation of the lifting cylinder  114 . However, another embodiment can employ, for example, a configuration in which the lower stage  113  is arranged on the floor side of the chamber  111  via moving means capable of lifting up and down the lower stage  113 , while the upper stage  115  is arranged on the ceiling side of the chamber  111  via a support member, and the lower stage  113  and the upper stage  115  can move relatively close to or apart from each other in the opposing direction by operating the moving means. Alternatively, another embodiment can employ, for example, a configuration in which the lowest stage  113  is arranged on the floor side of the chamber  111  via first moving means capable of lifting up and down the lower stage  113 , while the upper stage  115  is arranged on the ceiling side of the chamber  111  via second moving means capable of lifting up and down the upper stage  115 , and the lower stage  113  and the upper stage  115  can move relatively close to or apart from the each other in the opposing direction by operating the first and second moving means. 
     In addition, although in the foregoing embodiments, description has been provided for the cases where the second substrate  12  is made of at least one of an amorphous oxide material such as amorphous SiO 2 , an amorphous nitride material such as amorphous SiN, an amorphous carbide material such as amorphous SiC, and an amorphous fluoride material such as amorphous CaF 2 , the present invention is not limited to these materials. For example, the second substrate can be used in the same way as in the foregoing embodiments if the second substrate is made of at least one of materials including a crystalline oxide material such as crystalline SiO 2 , a crystalline nitride materials such as crystalline SiC, and a crystals me fluoride material such as crystalline CaF 2 , and further including, in the same way as for the first substrate  11 , a semiconductor material such as Si and Ge, a compound semiconductor material including a Ga based material such as GaN, GaAs, and GaP and an In based material such as InP and InSb, and a metal material such as Au, Cu, and Al. 
     However, it is much preferable that the second substrate  12  be made of at least one of an amorphous oxide material such as amorphous SiO 2 , an amorphous nitride material such as amorphous SiN, an amorphous carbide material such as amorphous SiC, and an amorphous fluoride material such as amorphous CaF 2  as in the foregoing embodiments, because the substrate bonding method according to the present invention can utilized most effectively in these cases. 
     INDUSTRIAL APPLICABILITY 
     The substrate bonding method according to the present invention can be utilized very usefully from the industrial point of view because the second substrate can be bonded to the first substrate at room temperature with a high strength, for example, even if the second substrate is made of a material the activity of which tends to decrease. 
     REFERENCE SIGNS LIST 
     
         
           1  gas 
           2  beam 
           10  bonded material 
           11  first substrate 
           11   a  active layer 
           100 ,  200  substrate bonding apparatus 
           112  support base 
           113  lower stage 
           114  lifting cylinder 
           114   a  rod 
           115  upper stage 
           116  exhaust pump 
           117 ,  217  gas source 
           118 ,  218  ion gun