Abstract:
An electronic device cleaning method includes the steps of: placing, on a processing face, a semiconductor substrate having an obverse face portion in which an electronic device is formed so that the processing face faces a reverse face of the semiconductor substrate; diselectrifying at least the reverse face of the semiconductor substrate by irradiating light to the semiconductor substrate by a light source provided at the processing face; and supplying a chemical solution to an obverse face of the semiconductor substrate after the diselectrifying step starts. Whereby, static electricity present on the processing face is removed reliably.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This Non-provisional application claims priority under 35 U.S.C. §119(a) on Patent Application No. 2005-276095 filed in Japan on Sep. 22, 2005, the entire contents of which are hereby incorporated by reference. 
     BACKGROUND ART 
     The present invention relates to electronic device cleaning equipment and an electronic device cleaning method, and particularly relates to single-wafer electronic device cleaning equipment and a single-wafer electronic device cleaning method. 
     Recently, demands for high speed and highly integrated electronic devices are increasing, and miniaturization of electronic devices is being promoted for realizing the demand. In association, cleaning methods for miniaturized electronic devices are in transition from batch cleaning to single-wafer cleaning for enhancing controllability in a region subjected to cleaning. 
     In a conventional single-wafer cleaning method, as shown in  FIG. 10A , after a wafer  1  is placed on a processing face of a cleaning stage  114  located inside a cup  113  with a chuck pin  115  interposed, the obverse face of the wafer  1  is etched in such a manner that a chemical solution is discharged onto the obverse face of the wafer  1  from a chemical solution nozzle  111  while the wafer  1  supported on the cleaning stage  114  is rotated by a rotary table  116 . Subsequently, as shown in  FIG. 10B , the obverse face of the wafer  1  is cleaned with water by discharging water onto the obverse face of the wafer  1  from a water cleaning nozzle  112 . Then, as shown in  FIG. 10C , the obverse face of the wafer  1  is dried in such a manner that the wafer  1  supported on the cleaning stage  114  is rotated by the rotary table  116  to shake off water remaining on the obverse face of the wafer  1 . 
     In the above conventional electronic device cleaning method, however, involves the following problems. 
     Rotation of the cleaning stage  114  supporting the wafer  1  by the rotary table  116  causes friction with air, thereby charging static electricity on the obverse face of the cleaning stage  114 . Therefore, the static electricity is present on the processing face of the cleaning stage  114 . For this reason, when the wafer  1  having an obverse face on which an insulating film is formed is cleaned, for example, the static electricity present on the processing face of the cleaning stage  114  is induced to the obverse face of the wafer  1  placed on the processing face of the cleaning stage  114  to cause discharge of the static electricity between the insulating film and the chemical solution discharged from the chemical solution nozzle  111 . 
     Accordingly, the discharge of the static electricity forms a hole-like flaw at the obverse face of the wafer  1  (particularly, part of the insulating film where the chemical solution is supplied). As a result, the conventional electronic device cleaning method may lower yield of the electronic device. 
     For tackling this problem, a method for preventing flaws from being formed at the obverse face of a wafer (particularly, a circuit part of the wafer) is proposed as an electronic device cleaning method (a first conventional example). In this method, after a chemical solution is discharged onto a non-circuit part of a wafer with the use of a chemical solution nozzle capable of moving over the wafer, the chemical solution is discharged onto the circuit part of the wafer (see, for example, Japanese Patent Application Laid Open Publication No. 11-233473A). 
     According to this method, though a hole-like flaw may be formed by the static electricity discharge in part of the wafer where the chemical solution is supplied first, that is, the non-circuit part at the edge portion of the wafer, it is not formed in the circuit part of the wafer, attaining electronic device cleaning with no lowering of the yield of the electronic device. 
     Further, there is an electronic device cleaning method using cleaning equipment (see  FIG. 11 ) (a second conventional example) which is aimed at removing the static electricity present on the processing face of the cleaning stage. As shown in  FIG. 11 , the electronic device cleaning equipment in the second conventional example includes, as main elements, a chamber  210 , a chemical solution nozzle  211 , a water nozzle  212   a , a cap  213 , a cleaning stage  214 , a chuck pin  215 , a rotary table  216 , holding means  217 , an FFU (fan filter unit)  218 , a solution supply line  230 , and a valve  231 . 
     In the electronic device cleaning method of the second conventional example, a chemical solution is discharged onto the obverse face of the wafer  1  from the chemical solution nozzle  211  while a solution (a chemical solution, a soda water, or the like, for example) is discharged onto the central part of the reverse face of the wafer  1  from a solution nozzle  230   a  provided at the solution supply line  230  arranged in the cleaning stage  214 . The solution supply to the reverse face of the wafer  1  removes the static electricity present on the processing face of the cleaning stage  214 . 
     The electronic device cleaning method of the first conventional example, however, involves the following problems. 
     In the electronic device cleaning method of the first conventional example, the chemical solution must be discharged onto the non-circuit part at the edge portion of the wafer from the chemical solution nozzle  211 . The selective discharge onto the non-circuit part is difficult, and therefore, the chemical solution is discharged onto part other than the non-circuit part at the edge portion of the wafer  1 , that is, the circuit part of the wafer  1 , to form a hole-like flaw by the static electricity discharge at the part of the circuit part of the wafer  1  where the chemical solution is discharged. Further, particles may adhere to the obverse face of the wafer  1  by the static electricity discharge. 
     In addition, in the electronic device cleaning method of the first conventional example, the chemical solution collides with the edge of the wafer  1  and is scattered in discharging the chemical solution, so that the chemical solution cannot be recovered to the cap  213  and the scattered chemical solution adheres to the obverse face of the wafer, resulting in contamination of the obverse face of the wafer  1 . 
     As well, the electronic device cleaning method of the second conventional example involves the following problems. 
     In the electronic device cleaning method of the second conventional example, as shown in  FIG. 11 , the solution (a chemical solution, a soda water, or the like, for example) is supplied to the reverse face of the wafer  1  from the solution nozzle  230   a  provided at the solution supply line  230  arranged at the central part of the processing face of the cleaning stage  214 . The solution supply to the edge portion of the reverse face of the wafer  1  is rather difficult. 
     Accordingly, the static electricity present on the processing face of the cleaning stage  214  (particularly, a range of the processing face of the cleaning stage  214  in the vicinity of the edge of the wafer  1 ) is removed insufficiently. As a result, the remaining static electricity is induced to the obverse face of the wafer  1  to cause the static electricity discharge between the obverse face of the wafer  1  and the chemical solution discharged from the chemical solution nozzle  211 , thereby forming a hole-like flaw at the part of the obverse face of the wafer  1  where the chemical solution is discharged. Further, particles may adhere to the obverse face of the wafer  1  by the static electricity discharge. 
     As described above, in the electronic device cleaning methods of the first and second conventional examples, the static electricity discharge caused between the obverse face of the wafer and the chemical solution discharged from the chemical solution nozzle causes defects (specifically, flaws and particles), lowering the yield of the electronic device. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing, the present invention has its object of providing electronic device cleaning equipment and an electronic device cleaning method in which static electricity discharge between the obverse face of a wafer and a chemical solution discharged from a chemical solution nozzle is prevented in chemical solution discharge by reliably removing the static electricity present on a processing face of a cleaning stage. 
     To attain the above object, electronic device cleaning equipment according to a first aspect of the present invention includes: a cleaning stage having a processing face on which a semiconductor substrate having an obverse face portion in which an electronic device is formed is to be placed so that the processing face faces a reverse face of the semiconductor substrate; a light source provided at the processing face for irradiating light to the semiconductor substrate; and chemical solution supply means for supplying a chemical solution to an obverse face of the semiconductor substrate. 
     In the electronic device cleaning equipment according to the first aspect of the present invention, the light source provided at the processing face irradiates light to the semiconductor substrate to generate ionized air in a region where the light is irradiated. This removes the static electricity present on the processing face, attaining effective prevention of induction of the static electricity to the obverse face of the semiconductor substrate. 
     Accordingly, the static electricity discharge between the obverse face of the semiconductor substrate and the supplied chemical solution is prevented. Whereby, a flaw, which would be formed by the static electricity discharge, is prevented from being formed at the obverse face of the semiconductor substrate (particularly, part of the obverse face of the semiconductor substrate where the chemical solution is supplied), and particles are prevented from adhering to the obverse face of the semiconductor substrate. 
     Hence, the electronic device cleaning equipment according to the first aspect of the present invention cleans the electronic device well without causing any defects (specifically, flaws and particles) at the obverse face of the semiconductor substrate, increasing yield of the electronic device. 
     In the electronic device cleaning equipment according to the first aspect of the present invention, the light is preferably a soft X ray. 
     With the above structure, the ionized air can be generated in a region where the soft X ray is irradiated to remove the static electricity present on the processing face. Further, even if the static electricity present on the processing face would be induced to the obverse face of the semiconductor substrate, and therefore, would be present thereon, the ionized air generated on the obverse face of the semiconductor substrate by the soft X ray transmitted through the semiconductor substrate would remove the static electricity present thereon. 
     Accordingly, the static electricity discharge is further prevented from being caused between the obverse face of the semiconductor substrate and the supplied chemical solution, so that a flaw, which would be formed by the static electricity discharge, is further prevented from being formed at the obverse face of the semiconductor substrate (particularly, part of the obverse face of the semiconductor substrate where the chemical solution is supplied), and particles are further prevented from adhering to the obverse face of the semiconductor substrate. 
     The electronic device cleaning equipment according to the first aspect of the present invention preferably includes oxygen gas supply means provided at the processing face for supplying an oxygen gas to the reverse face of the semiconductor substrate. 
     With the above structure, the oxygen gas can be supplied to the soft X ray irradiation region. The oxygen gas promotes a reaction of generating ionized air through the soft X ray irradiation, increasing the density of the ionized air on the processing face. This promotes neutralization of the static electricity by the ionized air, so that the static electricity present on the processing face can be further removed in a shorter period of time. Moreover, the soft X ray transmitted through the semiconductor substrate generates ionized air on the obverse face of the semiconductor substrate, removing the static electricity which would be present on the obverse face of the semiconductor substrate by induction from the processing face. 
     Hence, the static electricity discharge can be reliably prevented from being caused between the obverse face of the semiconductor substrate and the supplied chemical solution, and therefore, a flaw, which would be formed by the static electricity discharge, is prevented from being formed at the obverse face of the semiconductor substrate (particularly, part of the obverse face of the semiconductor substrate where the chemical solution is supplied), and particles are prevented from adhering to the obverse face of the semiconductor substrate. 
     Electronic device cleaning equipment according to a second aspect of the present invention includes: a cleaning stage having a processing face on which a semiconductor substrate having an obverse face portion in which an electronic device is formed is to be placed so that the processing face faces a reverse face of the semiconductor substrate; solution supply means which is provided at the processing face and in which a plurality of first discharge ports for discharging a solution onto the reverse face of the semiconductor substrate are formed dispersedly; and chemical solution supply means for supplying a chemical solution to an obverse face of the semiconductor substrate. 
     In the electronic device cleaning equipment according to the second aspect of the present invention, the solution supply means in which the plurality of first discharge ports are formed dispersedly enables uniform supply of the solution (a chemical solution, a soda water, or the like, for example) to the reverse face of the semiconductor substrate. This leads to effective removal of the static electricity present on the processing face, effectively preventing induction of the static electricity to the obverse face of the semiconductor substrate. 
     Hence, the static electricity discharge can be prevented from being caused between the obverse face of the semiconductor substrate and the supplied chemical solution, and therefore, a flaw, which would be formed by the static electricity discharge, is prevented from being formed at the obverse face of the semiconductor substrate (particularly, part of the obverse face of the semiconductor substrate where the chemical solution is supplied), and particles are prevented from adhering to the obverse face of the semiconductor substrate. 
     In turn, the electronic device cleaning equipment according to the second aspect of the present invention cleans the electronic device well without generating any defects (specifically, flaws and particles) at the obverse face of the semiconductor substrate, increasing the yield of the electronic device. 
     The electronic device cleaning equipment according to the second aspect of the present invention preferably includes first control means for allowing the plurality of first discharge ports of the solution supply means to discharge the solution onto the reverse face of the semiconductor substrate before the chemical solution supply means supplies the chemical solution to the obverse face of the semiconductor substrate. 
     In this structure, the solution is supplied to the reverse face of the semiconductor substrate prior to supply of the chemical solution to the obverse face of the semiconductor substrate. Accordingly, the static electricity present on the processing face is removed in advance, effectively preventing induction of the static electricity to the obverse face of the semiconductor substrate. 
     Hence, the static electricity discharge can be effectively prevented from being caused between the obverse face of the semiconductor substrate and the supplied chemical solution, and therefore, a flaw, which would be formed by the static electricity discharge, is prevented from being formed at the obverse face of the semiconductor substrate (particularly, part of the obverse face of the semiconductor substrate where the chemical solution is supplied), and particles are effectively prevented from adhering to the obverse face of the semiconductor substrate. 
     In the electronic device cleaning equipment according to the second aspect of the present invention, it is preferable that a second discharge port is formed in the chemical solution supply means and the equipment further includes second control means for allowing a first discharge port located correspondingly to the second discharge port of the chemical solution supply means out of the plurality of first discharge ports to discharge the solution onto the reverse face of the semiconductor substrate. 
     With the above structure, the solution can be discharged onto the reverse face of the semiconductor substrate from a first discharge port located correspondingly to the second discharge port out of the plurality of first discharge ports. This enables solution discharge from the first discharge port onto a region of the reverse face of the semiconductor substrate where it corresponds to a region of the obverse face of the semiconductor substrate where the chemical solution is supplied, reliably preventing induction of the static electricity to the obverse face of the semiconductor substrate (particularly, the chemical solution supply region of the obverse face of the semiconductor substrate). 
     Hence, the static electricity discharge can be reliably prevented from being caused between the obverse face of the semiconductor substrate and the chemical solution discharged from the second discharge port, and therefore, a flaw, which would be formed by the static electricity discharge, is reliably prevented from being formed at the obverse face of the semiconductor substrate (particularly, part of the obverse face of the semiconductor substrate where the chemical solution is supplied), and particles are reliably prevented from adhering to the obverse face of the semiconductor substrate. 
     In the electronic device cleaning equipment according to the second aspect of the present invention, the solution is preferably a chemical solution or soda water. 
     Whereby, the static electricity preset on the processing face can be removed. 
     An electronic device cleaning method according to the first aspect of the present invention includes the steps of: (a) placing, on a processing face, a semiconductor substrate having an obverse face portion in which an electronic device is formed so that the processing face faces a reverse face of the semiconductor substrate; (b) diselectrifying at least the reverse face of the semiconductor substrate by irradiating light to the semiconductor substrate by a light source provided at the processing face; and (c) supplying a chemical solution to an obverse face of the semiconductor substrate after the step (b) starts. 
     In the electronic device cleaning method according to the first aspect of the present invention, the light is irradiated to the semiconductor substrate with the use of the light source provided at the processing face to generate ionized air in the light irradiation region, thereby removing the static electricity present on the processing face. Accordingly, the static electricity is effectively prevented from being induced to the obverse face of the semiconductor substrate. 
     Hence, the static electricity discharge can be prevented from being caused between the obverse face of the semiconductor substrate and the supplied chemical solution, and therefore, a flaw, which would be formed by the static electricity discharge, is prevented from being formed at the obverse face of the semiconductor substrate (particularly, part of the obverse face of the semiconductor substrate where the chemical solution is supplied), and particles are prevented from adhering to the obverse face of the semiconductor substrate. 
     Therefore, the electronic device cleaning method according to the first aspect of the present invention attains excellent cleaning of the electronic device without generating any defects (specifically, flaws and particles) at the obverse face of the semiconductor substrate, increasing the yield of the electronic device. 
     In the electronic device cleaning method according to the first aspect of the present invention, it is preferable that in the step (b), a soft X ray is irradiated as the light irradiated to the semiconductor substrate. 
     With the above arrangement, ionized air can be generated in the soft X ray irradiation region to remove the static electricity present on the processing face. Further, even if the static electricity present on the processing face would be induced to the obverse face of the semiconductor substrate, and therefore, would be present thereon, the ionized air generated on the obverse face of the semiconductor substrate by the soft X ray transmitted through the semiconductor substrate would remove the static electricity present thereon. 
     Accordingly, the static electricity discharge is further prevented from being caused between the obverse face of the semiconductor substrate and the supplied chemical solution, so that a flaw, which would be formed by the static electricity discharge, is further prevented from being formed at the obverse face of the semiconductor substrate (particularly, part of the obverse face of the semiconductor substrate where the chemical solution is supplied), and particles are further prevented from adhering to the obverse face of the semiconductor substrate. 
     In the electronic device cleaning method according to the first aspect of the present invention, the step (b) is preferably performed while an oxygen is supplied to the reverse face of the semiconductor substrate. 
     In the above arrangement, the oxygen gas is supplied to the soft X ray irradiation region. The oxygen gas promotes a reaction of generating ionized air through the soft X ray irradiation, increasing the density of the ionized air on the processing face. This promotes neutralization of the static electricity by the ionized air, so that the static electricity present on the processing face can be further removed in a shorter period of time. Moreover, the soft X ray transmitted through the semiconductor substrate generates the ionized air on the obverse face of the semiconductor substrate, removing the static electricity which would be present on the obverse face of the semiconductor substrate by induction from the processing face. 
     Hence, the static electricity discharge can be reliably prevented from being caused between the obverse face of the semiconductor substrate and the supplied chemical solution, and therefore, a flaw, which would be formed by the static electricity discharge, is reliably prevented from being formed at the obverse face of the semiconductor substrate (particularly, part of the obverse face of the semiconductor substrate where the chemical solution is supplied), and particles are reliably prevented from adhering to the obverse face of the semiconductor substrate. 
     Moreover, with the above arrangement, the static electricity present on the processing face can be removed within a shorter period of time. This means shortening of diselectrification time, that is, shortening time required for a diselectrification step, resulting in an increase in productivity. 
     An electronic device cleaning method according to the second aspect of the present invention includes the steps of: (a) placing, on a processing face, a semiconductor substrate having an obverse face portion in which an electronic device is formed so that the processing face faces a reverse face of the semiconductor substrate; (b) diselectrifying the reverse face of the semiconductor substrate by supplying a solution to the reverse face of the semiconductor substrate from a plurality of first discharge ports formed dispersedly at the processing face; and (c) supplying a chemical solution to an obverse face of the semiconductor substrate from a second discharge port after the step (b) starts. 
     In the electronic device cleaning method according to the second aspect of the present invention, the plurality of first discharge ports formed dispersedly at the processing face enables uniform supply of the solution (a chemical solution, a soda water, or the like, for example) to the reverse face of the semiconductor substrate. This attains effective removal of the static electricity present on the processing face, effectively preventing induction of the static electricity to the obverse face of the semiconductor substrate. 
     Further, in the electronic device cleaning method according to the second aspect of the present invention, the chemical solution is supplied to the obverse face of the semiconductor substrate after supply of the solution to the reverse face of the semiconductor substrate starts, rather than simultaneous supply of the solution to the reverse face of the semiconductor substrate and of the chemical solution to the obverse face thereof. Therefore, the static electricity present on the processing face can be removed in advance, effectively preventing induction of the static electricity to the obverse face of the semiconductor substrate. 
     Hence, the static electricity discharge can be effectively prevented from being caused between the obverse face of the semiconductor substrate and the chemical solution discharged from the second discharge port, and therefore, a flaw, which would be formed by the static electricity discharge, is effectively prevented from being formed at the obverse face of the semiconductor substrate (particularly, part of the obverse face of the semiconductor substrate where the chemical solution is supplied), and particles are effectively prevented from adhering to the obverse face of the semiconductor substrate. 
     In turn, the electronic device cleaning method according to the second aspect of the present invention attains excellent cleaning of the electronic device without generating any defects (specifically, flaws and particles) at the obverse face of the semiconductor substrate, increasing the yield of the electronic device. 
     In the electronic device cleaning method according to the second aspect of the present invention, it is preferable that in the step (b), the solution is supplied to the reverse face of the semiconductor substrate from a first discharge port located correspondingly to the second discharge port out of the plurality of first discharge ports. 
     By this method, the solution is discharged in advance onto the reverse face of the semiconductor substrate from a first discharge port located correspondingly to the second discharger port out of the plurality of discharge ports. This enables advance solution discharge from the first discharge port onto the region of the reverse face of the semiconductor substrate where it corresponds to the chemical solution supply region of the obverse face of the semiconductor substrate, reliably preventing induction of the static electricity to the obverse face of the semiconductor substrate (particularly, the chemical solution supply region of the obverse face of the semiconductor substrate). 
     Advance removal of the static electricity present on the processing face under the second discharge port surely prevents induction of the static electricity to the obverse face of the semiconductor substrate (particularly, the obverse face of the semiconductor substrate under the second discharge port). 
     Hence, the static electricity discharge can be reliably prevented from being caused between the obverse face of the semiconductor substrate and the chemical solution discharged from the second discharge port, and therefore, a flaw, which would be formed by the static electricity discharge, is reliably prevented from being formed at the obverse face of the semiconductor substrate (particularly, part of the obverse face of the semiconductor substrate where the chemical solution is supplied), and particles are reliably prevented from adhering to the obverse face of the semiconductor substrate. 
     In the electronic device cleaning method according to the second aspect of the present invention, it is preferable that in the step (b), a chemical solution or a soda water is supplied as the solution supplied to the reverse face of the semiconductor substrate. 
     By this method, the static electricity present on the processing face can be removed. 
     As described above, in the electronic device cleaning equipment and the electronic device cleaning methods according to the first and second aspects of the present invention, the static electricity discharge in chemical solution discharge is prevented from being caused between the obverse face of the wafer and the chemical solution discharged from the chemical nozzle, increasing the yield of the electronic device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a section showing a construction of electronic device cleaning equipment according to Embodiment 1 of the present invention. 
         FIG. 2A  to  FIG. 2D  are sections showing main steps of an electronic device cleaning method according to Embodiment 1 of the present invention. 
         FIG. 3A  and  FIG. 3B  are sections showing the structures of wafers subjected to cleaning by respective electronic device cleaning methods. 
         FIG. 4  is a section showing a construction of electronic device cleaning equipment according to Embodiment 2 of the present invention. 
         FIG. 5  is a section showing a construction of electronic device cleaning equipment according to Embodiment 3 of the present invention. 
         FIG. 6A  to  FIG. 6C  are sections showing main steps of an electronic device cleaning method according to a second conventional example. 
         FIG. 7A  to  FIG. 7C  are sections showing main steps of a second electronic device cleaning method. 
         FIG. 8A  to  FIG. 8D  are sections showing main steps of an electronic device cleaning method according to Embodiment 3 of the present invention. 
         FIG. 9A  to  FIG. 9C  are sections showing the structures of wafers subjected to cleaning by first to third electronic device cleaning methods, respectively. 
         FIG. 10A  to  FIG. 10C  are sections showing main steps of a conventional electronic device cleaning method. 
         FIG. 11  is a section showing a construction of electronic device cleaning equipment according to the second conventional example. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Each embodiment of the present invention will be described below with reference to the accompanying drawings. 
     Embodiment 1 
     The construction of electronic device cleaning equipment according to Embodiment 1 of the present invention will be described below with reference to  FIG. 1 .  FIG. 1  is a section showing the construction of the electronic device cleaning equipment according to Embodiment 1 of the present invention. 
     As shown in  FIG. 1 , the electronic device cleaning equipment in the present embodiment includes, as main elements, a cleaning chamber  10 , a chemical solution nozzle  11  for discharging a chemical solution onto the obverse face of a wafer  1 , a water nozzle  12  for discharging water onto the obverse face of the wafer  1 , a cap  13  for recovering the chemical solution and the water, a cleaning stage  14  having a processing face on which the wafer  1  is to be placed, a chuck pin  15  for holding the wafer  1 , a rotary table  16  for rotating the wafer  1 , holding means  17  for holding the cap  13 , the cleaning stage  14 , and the rotary table  16 , an FFU (fan filter unit)  18  provided at the upper part of the cleaning chamber  10 , and a soft X ray irradiation system  19  provided at the processing face of the cleaning stage  14  so as to face the reverse face of the wafer  1 . 
     An electronic device cleaning method using the electronic device cleaning equipment according to Embodiment 1 of the present invention will be described below with reference to  FIG. 2A  to  FIG. 2D .  FIG. 2A  to  FIG. 2D  are sections showing main steps of the electronic device cleaning method according to Embodiment 1 of the present invention. 
     First, as shown in  FIG. 2A , a wafer  1  having an obverse face portion in which, for example, an electronic device (not shown) is formed is placed on the processing face of the cleaning stage  14  with the chuck pin  15  interposed. Then, a soft X ray is irradiated to the reverse face of the waver  1  by the soft X ray irradiation system  19  provided at the processing face of the cleaning stage  14  for a predetermined time period for diselectrification of the wafer  1 . 
     Next, as shown in  FIG. 2B , the obverse face of the wafer  1  is subjected to etching in such a manner that a chemical solution is discharged onto the obverse face of the wafer  1  from the chemical solution nozzle  11  for a predetermined time period for etching while the wafer  1  supported on the cleaning stage  14  is rotated by the rotary table  16 . 
     Subsequently, as shown in  FIG. 2C , the obverse face of the wafer  1  is water cleaned in such a manner that water is discharged onto the obverse face of the wafer  1  from the water nozzle  12  while the wafer  1  supported on the cleaning stage  14  is rotated by the rotary table  16 . Then, as shown in  FIG. 2D , the obverse face of the wafer  1  is dried in such a manner that the wafer  1  supported on the cleaning stage  14  is rotated by the rotary table  16  to shake off water remaining on the obverse face of the wafer  1 . 
     Herein, in order to effectively explain the effects of the present embodiment, the following evaluation is performed on a wafer subjected to cleaning by a conventional electronic device cleaning method and a wafer subjected to cleaning by the electronic device cleaning method according to the present embodiment. 
     First, a wafer is cleaned by the conventional electronic device cleaning method under the cleaning condition indicated below. 
     Specifically, etching is performed on a thermal oxide film (not shown) formed on the wafer  1  and having a film thickness of 100 nm with the use of the conventional electronic device cleaning equipment, as described with reference to  FIG. 10A , in such a manner that a DHF solution (diluted hydrofluoric acid: a mixed solution having a volume ratio of HF:H 2 O=1:10) is discharged onto the central part of the obverse face of the thermal oxide film from the chemical solution nozzle  111  for 10 seconds in an atmosphere at room temperature (23° C.) while the wafer  1  supported on the cleaning stage  114  is rotated by the rotary table  116 . Then, after the obverse face of the wafer  1  is water cleaned as described with reference to in  FIG. 10B , the obverse face of the wafer  1  is dried as describe with reference to  FIG. 10C . 
     Meanwhile, a wafer is cleaned by the electronic device cleaning method according to the present embodiment under the following cleaning conditions. 
     Specifically, the wafer  1  is subjected to diselectrification using the electronic device cleaning equipment according to the present embodiment, as shown in  FIG. 2A , in such a manner that the soft X ray is irradiated to the reverse face of the wafer  1  for a predetermined time period for diselectrification (10 seconds) by the soft X ray irradiation system  19  provided at the processing face of the cleaning stage  14 . 
     Subsequently, etching is performed on a thermal oxide film (not shown) formed on the wafer  1  and having a film thickness of 100 nm, as shown in  FIG. 2B , in such a manner that the DHF solution (the mixed solution having a volume ratio of HF:H 2 O=1:10) is discharged onto the central part of the obverse face of the thermal oxide film from the chemical solution nozzle  111  for 10 seconds in an atmosphere at room temperature (23° C.) while the wafer  1  supported on the cleaning stage  14  is rotated by the rotary table  16 . Then, after the obverse face of the wafer  1  is water cleaned as shown in  FIG. 2C , the obverse face of the wafer  1  is dried as shown in  FIG. 2D . 
     Particles of 0.16 μm or larger adhering to the respective wafers subjected to cleaning by the conventional electronic device cleaning method or to cleaning by the electronic device cleaning method according to the present embodiment under the aforementioned cleaning condition (etching condition: at 23° C., for 10 seconds, HF:H 2 O=1:10) were counted as defects by a particle counter for evaluating the defects at the respective wafers. The defects at the wafers will be described below with reference to Table 1,  FIG. 3A , and  FIG. 3B . Table 1 indicates each number of defects at the wafers and defect types thereof.  FIG. 3A  and  FIG. 3B  are sections showing the structures of the wafers subjected to cleaning by the respective electronic device cleaning methods. 
     
       
         
               
               
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
             
             
               
                   
                   
               
               
                   
                 Number of defects 
                 Defect type 
               
             
          
           
               
                   
                 Before 
                 After 
                 Increased 
                 Damage due to 
                   
               
               
                   
                 processing 
                 processing 
                 number 
                 static electricity 
                 Particle 
               
               
                   
                   
               
             
          
           
               
                 Conven- 
                 3 
                 7 
                 4 
                 1 
                 3 
               
               
                 tional 
               
               
                 example 
               
               
                 Embod- 
                 4 
                 4 
                 0 
                 0 
                 0 
               
               
                 iment 1 
               
               
                   
               
             
          
         
       
     
     Table 1 indicates that the number of defects of the wafer subjected to cleaning by the conventional electronic device cleaning method is three before the processing and seven after the processing, which means an increase in the number of defects after the processing compared with those before the processing (specifically, four defects increased). Detailed evaluation of the defects observed after the processing (specifically, the four defects) was carried out using SEM defect inspection equipment. The wafer defects observed after the processing will be described below with reference to  FIG. 3A .  FIG. 3A  is a section showing the structure of the wafer subjected to cleaning by the conventional electronic device cleaning method. 
     As shown in  FIG. 3A , a hole D having a diameter d of approximately 1 μm was formed at the central part of the thermal oxide film  2  formed on the wafer  1 . It was confirmed that the hole D, which was one of the four defects observed after the processing, was formed in such a way that the thermal oxide film  2  was damaged by static electricity discharge caused at the space between the obverse face of the wafer  1  and the DHF solution discharged from the chemical solution nozzle  111 . The defects other than the hole D, that is, three defects out of the four defects (not shown) observed after the processing were recognized as particles. 
     On the other hand, Table 1 indicates that each number of defects before and after the processing is four in the wafer subjected to cleaning by the electronic device cleaning method according to the present embodiment, which means no increase in the number of defects after the processing compared with those before the processing.  FIG. 3B  is a section showing the structure of the wafer subjected to cleaning by the electronic device cleaning method according to the present embodiment and indicates that no damage by the static electricity discharge was observed at the obverse face of the wafer  1 . 
     In sum, the number of defects after the cleaning processing increased compared with that before the cleaning processing in the wafer subjected to the conventional electronic device cleaning under the aforementioned cleaning condition (etching condition: at 23° C., for 10 seconds, HF:H 2 O=1:10). While, no increase in the number of defects was observed after the cleaning processing compared with those before the cleaning processing in the wafer subjected to cleaning by the electronic device cleaning method according to the present embodiment. From this, it was understood that the static electricity present on the processing face of the cleaning stage  14  was removed by irradiating the soft X ray to the reverse face of the wafer  1  before the cleaning processing. 
     As described above, in the electronic device cleaning method according to the present embodiment, as shown in  FIG. 2A , the soft X ray is irradiated to the reverse face of the wafer  1  by the soft X ray irradiation system  19  provided at the processing face of the cleaning stage  14  before the cleaning processing (see  FIG. 2B  to  FIG. 2D ). 
     The soft X ray irradiation generates ionized are in a region where the soft X ray is irradiated to remove the static electricity present on the processing face of the cleaning stage  14 , preventing induction of the static electricity to the obverse face of the wafer  1 . 
     Further, even if the static electricity present on the processing face of the cleaning stage  14  would be induced to the obverse face of the wafer  1 , and therefore, would be present on the obverse face of the wafer  1 , the static electricity thereon could be removed by the ionized air generated on the obverse face of the wafer  1  through irradiation of the soft X ray, which is transmitted through the wafer  1 . 
     Accordingly, in supplying the chemical solution in the cleaning processing (see  FIG. 2B ), the static electricity discharge is prevented from being causing between the obverse face of the wafer  1  and the chemical solution discharged from the chemical solution nozzle  11 , preventing a hole-like flaw D, which would be formed by the static electricity discharge, from being formed at the obverse face of the wafer  1  (particularly, part of the obverse face of the wafer  1  where the chemical solution is supplied) and preventing adhesion of particles to the obverse face of the wafer  1 . 
     Hence, according to the electronic device cleaning method in the present embodiment, the electronic device can be cleaned well without generating defects (specifically, flaws and particles) at the obverse face of the wafer  1 , increasing the yield of the electronic device. 
     Moreover, the electronic device cleaning equipment in the present embodiment includes the soft X ray irradiation system  19  as shown in  FIG. 1 , rather than the conventional one including the solution supply line (see the reference numeral  230  in  FIG. 11 ). The soft X ray irradiation system  19  is not so cumbersome compared with the solution supply line, resulting in reduction in size of the electronic device cleaning equipment. 
     Embodiment 2 
     The construction of electronic device cleaning equipment according to Embodiment 2 of the present invention will be described below with reference to  FIG. 4 .  FIG. 4  is a section showing the construction of the electronic device cleaning equipment according to Embodiment 2 of the present invention. In  FIG. 4 , the same reference numerals are assigned to the same elements as those in the electronic device cleaning equipment according to Embodiment 1 of the present invention. Therefore, the same description as that of the electronic device cleaning equipment according to Embodiment 1 of the present invention is not repeated. 
     The soft X ray is irradiated on the reverse face of the wafer  1  for a predetermined time period for diselectrification by the soft X ray irradiation system  19  provided at the processing face of the cleaning stage  14  in Embodiment 1. While in Embodiment 2, the soft X ray is irradiated on the reverse face of the wafer  1  for a predetermined time period for diselectrification by the soft X ray irradiation system  19  provided at the processing face of the cleaning stage  14  with an oxygen gas supplied to the reverse face of the wafer  1  by an oxygen gas supply line  20  provided at the processing face of the cleaning stage  14 . 
     As shown in  FIG. 4 , the electronic device cleaning device according to the present embodiment includes not only the soft X ray irradiation system  19  as in the electronic device cleaning equipment according to Embodiment 1 of the present invention but also the oxygen gas supply line  20  provided at the processing face of the cleaning stage  14 . 
     An electronic device cleaning method using the electronic device cleaning equipment according to Embodiment 2 of the present invention will be described below briefly. 
     First, a wafer  1  having an obverse face portion in which, for example, an electronic device (not shown) is formed is placed on the processing face of the cleaning stage  14  with the chuck pin  15  interposed. Then, the wafer  1  is subjected to diselectrification in such a manner that a soft X ray is irradiated to the reverse face of the waver  1  for a predetermined time period for diselectrification by the soft X ray irradiation system  19  provided at the processing face of the cleaning stage  14  while the oxygen gas is supplied to the reverse face of the wafer  1  by the oxygen gas supply line  20  provided at the processing face of the cleaning stage  14 . 
     Next, similarly to the step shown in  FIG. 2B , the obverse face of the wafer  1  is subjected to etching in such a manner that a chemical solution is discharged onto the obverse face of the wafer  1  from the chemical solution nozzle  11  for a predetermined time period for etching while the wafer  1  supported on the cleaning stage  14  is rotated by the rotary table  16 . Then, after the obverse face of the wafer  1  is water cleaned similarly to the step shown in  FIG. 2C , the obverse face of the wafer  1  is dried similarly to the step shown in  FIG. 2D . 
     As described above, in the electronic device cleaning method according to the present embodiment, the soft X ray is irradiated to the reverse face of the wafer  1  while the oxygen gas is supplied to the reverse face of the wafer  1 . In general, it is known that supply of an oxygen gas to a region where a soft X ray is irradiated promotes a reaction of generating ionized air through the soft X ray irradiation. Accordingly, the soft X ray irradiation to the reverse face of the wafer  1  with the oxygen gas supplied to the reverse face thereof increases the density of the ionized air generated from the oxygen gas in the soft X ray irradiation region, resulting in effective removal of the static electricity present on the processing face of the cleaning stage  14 . 
     Herein, in order to effectively explain the effects of the present embodiment, the following evaluation was performed on a wafer subjected to cleaning by the electronic device cleaning method according to Embodiment 1 of the present invention and a wafer subjected to cleaning by the electronic device cleaning method according to the present embodiment. 
     First, the relationship between the time periods for diselectrification and the numbers of defects at the wafers was evaluated in the wafers subjected to cleaning by the electronic device cleaning method according to Embodiment 1 of the present invention. 
     In this evaluation, the wafers  1  were subjected to diselectrification for respective predetermined time periods for diselectrification (specifically, 2.5 seconds, 5 seconds, and 10 seconds), as shown in  FIG. 2A , in such a manner that the soft X ray was irradiated to the reverse faces of the wafers  1  by the soft X ray irradiation system  19  provided at the processing face of the cleaning stage  14 . Then, etching was performed on the thermal oxide films (not shown) formed on the respective wafers  1  and having a film thickness of 100 nm, as shown in  FIG. 2B , in such a manner that a DHF solution (a mixed solution of HF:H 2 O=1:10 in volume ratio) was discharged onto the obverse faces of the thermal oxide films from the chemical solution nozzle  11  for 10 seconds in an atmosphere at room temperature (23° C.) while the wafers  1  supported on the cleaning stage  14  were rotated by the rotary table  16 . Next, after the obverse faces of the wafers  1  were water cleaned as shown in  FIG. 2C , the obverse faces of the wafers  1  were dried as shown in  FIG. 2D . 
     In the wafers subjected to cleaning by the electronic device cleaning method according to Embodiment 1 under the aforementioned cleaning condition (etching condition: at 23° C., for 10 seconds, HF:H 2 O=1:10) for the respective predetermined time periods for diselectrification, defects generated at the wafers were evaluated by counting particles having a size of 0.16 μm or larger by a particle counter. The relationship between the time periods for diselectrification and the numbers of defects at the wafers will be described with reference to Table 2. Table 2 shows the relationship between the time periods for diselectrification and the numbers of defects generated at the wafers subjected to cleaning by the electronic device cleaning method according to Embodiment 1 of the present invention. 
     
       
         
               
               
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                   
                 TABLE 2 
               
             
             
               
                   
                   
               
               
                   
                 Number of defects 
                 Defect type 
               
             
          
           
               
                   
                 Before 
                 After 
                   
                 Damage due 
                   
               
               
                 Diselectrification 
                 pro- 
                 pro- 
                 Increased 
                 to static 
                   
               
               
                 period (sec.) 
                 cessing 
                 cessing 
                 number 
                 electricity 
                 particle 
               
               
                   
               
             
          
           
               
                 2.5 
                 4 
                 11 
                 7 
                 1 
                 6 
               
               
                 5 
                 5 
                 9 
                 4 
                 1 
                 3 
               
               
                 10 
                 4 
                 4 
                 0 
                 0 
                 0 
               
               
                   
               
             
          
         
       
     
     Table 2 indicates that of the wafers subjected to cleaning by the electronic device cleaning method according to Embodiment 1, the number of defects before the processing and that after the processing are four and 11, respectively, in the wafer subjected to diselectrification for 2.5 seconds, which means an increase in the number of defects after the processing compared with those before the processing (specifically, seven defects increased). Detailed evaluation of the defects observed at the wafer after the processing (specifically, the seven defects) was carried out using SEM defect inspection equipment. This evaluation confirmed that one of the seven defects observed after the processing was a hole-like flaw and six defects out of the seven defects observed after the processing were particles. 
     Further, as indicated in Table 2, the number of defects before the processing and that after the processing are five and nine, respectively, in the wafer subjected to diselectrification for 5 seconds, which means an increase in the number of defects after the processing compared with those before the processing (specifically, four defects increased). Detailed evaluation of the defects observed at the wafer after the processing (specifically, the four defects) was carried using SEM defect inspection equipment. This evaluation confirmed that one of the four defects observed after the processing was a hole-like flaw and three defects out of the four defects observed after the processing were particles. 
     In contrast, as indicated in Table 2, each number of defects before the processing and after the processing was four in the wafer subjected to diselectrification for 10 seconds, which means no increase in the number of defects after the processing compared with those before the processing. 
     Next, the relationship between the time periods for diselectrification and the numbers of defects at the wafers was evaluated in the wafers subjected to cleaning by the electronic device cleaning according to the present embodiment. 
     In this evaluation, the wafers  1  were subjected to diselectrification for respective predetermined time periods for diselectrification (specifically, 2.5 seconds, 5 seconds, and 10 seconds) in such a manner that the soft X ray was irradiated to the reverse faces of the wafers  1  by the soft X ray irradiation system  19  provided at the processing face of the cleaning stage  14  while the oxygen gas was supplied to the reverse faces of the wafers  1  by the oxygen gas supply line  20  provided at the processing face of the cleaning stage  14 . Then, etching was performed on the thermal oxide films (not shown) formed on the wafers  1  and having a film thickness of 100 nm, similarly to the step shown in  FIG. 2B , in such a manner that the DHF solution (the mixed solution of HF:H 2 O=1:10 in volume ratio) was discharged onto the obverse faces of the thermal oxide films from the chemical solution nozzle  11  for 10 seconds under an atmosphere at room temperature (23° C.) while the wafers  1  supported on the cleaning stage  14  were rotated by the rotary table  16 . Next, after the obverse faces of the wafers  1  were water cleaned similarly to the step shown in  FIG. 2C , the obverse faces of the wafers  1  were dried similarly to the step shown in  FIG. 2D . 
     In the wafers subjected to cleaning by the electronic device cleaning method according to the present embodiment under the aforementioned cleaning condition (etching condition: at 23° C., for 10 seconds, HF:H 2 O=1:10) for the respective predetermined time periods for diselectrification, defects generated at the wafers were evaluated by counting particles having a size of 0.16 μm or larger as defects by a particle counter. The relationship between the time periods for diselectrification and the numbers of defects at the wafers will be described with reference to Table 3. Table 3 indicates the relationship between the time periods for diselectrification and the numbers of defects generated at the wafers subjected to cleaning by the electronic device cleaning method according to Embodiment 2 of the present invention. 
     
       
         
               
               
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                   
                 TABLE 3 
               
             
             
               
                   
                   
               
               
                   
                 Number of defects 
                 Defect type 
               
             
          
           
               
                   
                 Before 
                 After 
                   
                 Damage due 
                   
               
               
                 Diselectrification 
                 pro- 
                 pro- 
                 Increased 
                 to static 
               
               
                 period (sec.) 
                 cessing 
                 cessing 
                 number 
                 electricity 
                 particle 
               
               
                   
               
             
          
           
               
                 2.5 
                 1 
                 1 
                 0 
                 0 
                 0 
               
               
                 5 
                 4 
                 4 
                 0 
                 0 
                 0 
               
               
                 10 
                 2 
                 2 
                 0 
                 0 
                 0 
               
               
                   
               
             
          
         
       
     
     Table 3 indicates that each number of defects before the processing and after the processing is one in the wafer subjected to diselectrification for 2.5 seconds, which means no increase in the number of defects after the processing compared with those before the processing. Also, each number of defects before the processing and after the processing is four in the wafer subjected to diselectrification for 5 seconds, which means no increase in the number of defects after the processing compared with those before the processing. In addition, each number of defects before the processing and those after the processing is two in the wafer subjected to diselectrification for 10 seconds, which means no increase in the number of defects after the processing compared with those before the processing. 
     As described above, in the electronic device cleaning method according to Embodiment 1 of the present invention, as indicated in Table 2, mere soft X ray irradiation for 2.5 seconds or 5 seconds to the reverse face of the wafer  1  under the aforementioned cleaning condition (etching condition: at 23° C., for 10 seconds, HF:H 2 O=1:10) leads to insufficient removal of the static electricity present on the processing face of the cleaning stage  14 . As a result, defects (specifically, flaws and particles) are formed at the wafer  1  in discharging chemical solution in the cleaning processing by the static electricity remaining even after the diselectrification step. 
     In contrast, in the electronic device cleaning method according to the present embodiment, as indicated in Table 3, no increase in the number of defects after the processing is observed in any of the wafers subjected to diselectrification for 2.5 seconds, 5 seconds, or 10 seconds under the cleaning condition (etching condition: at 23° C., for 10 seconds, HF:H 2 O=1:10), compared with the respective numbers of defects before the processing. This proves that the soft X ray irradiation to the reverse face of the wafer  1  with the oxygen gas supplied to the reverse face of the wafer attains excellent removal of the static electricity present on the processing face of the cleaning stage  14  within a shorter period of time. 
     As described above, in the electronic device cleaning method according to the present embodiment, the soft X ray is irradiated to the reverse face of the wafer  1  while the oxygen gas is supplied to the reverse face of the wafer  1 . 
     The irradiation of the soft X ray to the reverse face of the wafer  1  generates ionized air in a region where the soft X ray is irradiated. The ionized air removes the static electricity present on the processing face of the cleaning stage  14 . 
     Further, the supply of the oxygen gas to the soft X ray irradiation region promotes a reaction of generating ionized air through the soft X ray irradiation, resulting in an increase in density of the ionized air on the processing face of the cleaning stage  14 . Accordingly, the ionized air of increased density promotes neutralization of the static electricity. Hence, the static electricity present on the processing face of the cleaning stage  14  can be further removed within a shorter period of time, compared with that in Embodiment 1. 
     Further, even if the static electricity present on the processing face of the cleaning stage  14  would be induced to the obverse face of the wafer  1 , and therefore, would be present on the obverse face of the wafer  1 , the static electricity present thereon could be removed by the ionized air generated on the obverse face of the wafer  1  through irradiation of the soft X ray, which is transmitted through the wafer  1 . 
     Accordingly, the static electricity discharge is reliably prevented from being caused between the obverse face of the wafer  1  and the chemical solution discharged from the chemical solution nozzle  11 , preventing a hole-like flaw, which would be formed by the static electricity discharge, from being formed at the obverse face of the wafer  1  (particularly, part of the obverse face of the wafer  1  where the chemical solution is supplied) and preventing adhesion of particles to the obverse face of the wafer  1 . 
     In addition, in the electronic device cleaning method according to the present embodiment, the static electricity present on the processing face of the cleaning stage  14  can be removed within a shorter period of time compared with that in Embodiment 1. This means shortening of diselectrification time, that is, shortening of time required for the diselectrification step, resulting in an increase in productivity. 
     Embodiment 3 
     The construction of electronic device cleaning equipment according to Embodiment 3 of the present invention will be described below with reference to  FIG. 5 .  FIG. 5  is a section showing the construction of the electronic device cleaning equipment according to Embodiment 3 of the present invention. In  FIG. 5 , the same reference numerals are assigned to the same elements as those in the electronic device cleaning equipment according to Embodiment 1 of the present invention. Therefore, the same description as that of the electronic device cleaning equipment according to Embodiment 1 of the present invention is not repeated. 
     One of significant features of the present embodiment lies in that in a wafer diselectrification step, a solution (for example, a chemical solution, a soda water, or the like) is discharged onto the reverse face of the wafer in advance from a solution nozzle located correspondingly to the chemical solution nozzle out of a plurality of solution nozzles provided at a solution supply line arranged at the processing face of the cleaning stage before the chemical solution is discharged from the chemical solution nozzle onto the obverse face of the wafer. 
     Referring to the electronic device cleaning equipment according to the second conventional example, the solution (for example, a chemical solution, a soda water, or the like) must be supplied to the reverse face of the wafer  1  from the solution nozzle  230   a  provided at the solution supply line  230  arranged at the central part of the processing face of the cleaning state  214 , as shown in  FIG. 11 , causing difficulty in solution supply to the vicinity of the edge of the wafer  1 . 
     Under the circumstances, in the electronic device cleaning equipment according to the present embodiment, a plurality of solution nozzles  30   a  to  30   i  are formed dispersedly in the solution supply line  30  provided in the cleaning stage  14 , wherein a valve  31  is provided in each of the plurality of solution nozzles  30   a  to  30   .    
     Accordingly, in the electronic device cleaning equipment according to the present embodiment, as shown in  FIG. 5 , the solution (for example, a chemical solution, a soda water, or the like) can be supplied to the entirety of the reverse face of the wafer  1  from the plurality of solution nozzles  30   a  to  30   i  dispersedly formed in the solution supply line  30  at the processing face of the cleaning stage  14 , attaining uniform solution supply to the reverse face of the wafer  1 . 
     Recent single-wafer electronic device cleaning methods employ a method of supplying an APM solution (Ammonia Hydrogen Peroxide Mixture, a mixed solution of NH 4 OH:H 2 O 2 :H 2 O=1:1:40 in volume ratio) to the obverse face of the wafer for a short period of time (30 second, for example) in an atmosphere at high temperature (approximately 70° C., for example), and the chemical solution nozzle performs scanning in general in order to ensure etching uniformity. Further, in view of particle removal, in many recent single-wafer electronic device cleaning methods, a chemical solution is discharged onto the obverse face of a wafer from the chemical solution nozzle from the edge of the obverse face of the wafer as a starting point by allowing the chemical solution nozzle to perform scanning. 
     Under the circumstances, the following evaluation was performed on wafers subjected to cleaning by first to third electronic device cleaning methods under the aforementioned cleaning conditions (etching condition: at 70° C., for 30 seconds, NH 4 OH:H 2 O 2 :H 2 O=1:1:40). Specifically, wafers on which thermal oxide films having a thickness of 100 nm are formed were subjected to etching under an atmosphere at 70° C. for 30 seconds by supplying the APM solution (a mixed solution of NH 4 OH:H 2 O 2 :H 2 O=1:1:40 in volume ratio), and then, defects at the wafers were evaluated using a particle counter. 
     The first to third electronic device cleaning methods will be described first in detail. 
     Referring to the first electronic device cleaning method, a wafer is cleaned by the electronic device cleaning method according to the second conventional example under the aforementioned cleaning condition (etching condition: at 70° C., for 30 seconds, NH 4 OH:H 2 O 2 :H 2 O=1:1:40) with the use of the electronic device cleaning equipment according to the second conventional example. The electronic device cleaning method according to the second conventional example will be described below with reference to  FIG. 6A  to  FIG. 6C . 
     First, as shown in  FIG. 6A , the thermal oxide film is subjected to etching (see the aforementioned etching conditions) in such a manner that the APM solution is discharged onto the obverse face of the wafer  1  from the chemical solution nozzle  211  with the chemical solution nozzle  211  allowed to perform scanning from a point approximately 1 cm apart from one of edges of the wafer  1  as a starting point towards the other edge of the wafer  1  while the wafer  1  supported on the cleaning stage  214  is rotated at a rotation speed of 300 rpm by the rotary table  216 . 
     In this etching, as shown in  FIG. 6A , in order to diselectrify the reverse face of the wafer  1 , the APM solution is discharged onto the reveres face of the wafer  1  (particularly, the central part of the reverse face of the wafer  1 ) from the solution nozzle  230   a  provided at the solution supply line  230  for a second time period for diselectrification (30 seconds) at the same time when the APM solution is discharged onto the obverse face of the wafer  1  from the chemical solution nozzle  211 . Then, after the obverse face of the wafer  1  is water cleaned as shown in  FIG. 6B , the obverse face of the wafer  1  is dried as shown in  FIG. 6C . 
     In the second electronic device cleaning method, the wafer  1  is cleaned under the aforementioned cleaning condition (etching condition: at 70° C., for 30 seconds, NH 4 OH:H 2 O 2 :H 2 O=1:1:40) with the use of the electronic device cleaning equipment according to the second conventional example. The electronic device cleaning method using the electronic device cleaning equipment according to the second conventional example will be described below with reference to  FIG. 7A  to  FIG. 7D . 
     First, as shown in  FIG. 7A , the reverse face of the wafer  1  is subjected to diselectrification in such a manner that the APM solution is discharged onto the reverse face of the wafer  1  (particularly, the central part of the reverse face of the wafer  1 ) from the solution nozzle  230   a  provided at the solution supply line  230  for a first time period for diselectrification (30 seconds) while the wafer  1  supported on the cleaning stage  214  is rotated at a rotation speed of 300 rpm by the rotary table  216 . 
     Subsequently, as shown in  FIG. 7B , the thermal oxide film is subjected to etching (see the aforementioned etching conditions) in such a manner that the APM solution is discharged onto the obverse face of the wafer  1  from the chemical solution nozzle  211  with the chemical solution nozzle  211  allowed to perform scanning from a point approximately 1 cm apart from one of edges as a starting point towards the other edge of the wafer  1  while the APM solution is discharged onto the reverse face of the wafer  1  from the solution nozzle  230   a  for the second time period for diselectrification (30 seconds). Then, after the obverse face of the wafer  1  is water cleaned as shown in  FIG. 7C , the obverse face of the wafer  1  is dried as shown in  FIG. 7D . 
     Referring to the third electronic device cleaning method, a wafer is cleaned by the electronic device cleaning method under the aforementioned cleaning conditions (etching condition: at 70° C., for 30 seconds, NH 4 OH:H 2 O 2 :H 2 O=1:1:40) with the use of the electronic device cleaning equipment according to the present embodiment. The electronic device cleaning method according to the present embodiment will be described below with reference to  FIG. 8A  to  FIG. 8D . 
     First, as shown in  FIG. 8A , the reverse faces of the wafers  1  are subjected to diselectrification in such a manner that the APM solution is discharged onto the reverse face of the wafers  1  from the plurality of solution nozzles  30   a  to  30   i  provided at the solution supply line  30  for respective first predetermined time periods for diselectrification (specifically, 10 seconds and 30 seconds) while the wafer  1  supported on the cleaning stage  14  is rotated at a rotation speed of 300 rpm by the rotary table  16 . 
     Subsequently, as shown in  FIG. 8B , each thermal oxide film is subjected to etching (see the aforementioned etching conditions) in such a manner that the APM solution is discharged onto the obverse face of the wafer  1  from the chemical solution nozzle  211  with the chemical solution nozzle  211  allowed to perform scanning from a point approximately 1 cm apart from one of edges as a starting point towards the other edge of the wafer  1  while the APM solution is discharged onto the reverse face of the wafer  1  from a solution nozzle located correspondingly to the chemical solution nozzle  11  for the second time period for diselectrification (30 seconds). 
     In this etching, the APM solution is supplied to the reverse face of the wafer  1  from a solution nozzle (solution nozzle  30   b , for example) located correspondingly to the chemical solution nozzle  11  out of the plurality of solution nozzles  30   a  to  30   i  so that the static electricity present on the processing face of the cleaning stage  14  is not induced to the obverse face of the wafer  1  (particularly, part of the obverse face of the wafer  1  where the chemical solution is supplied) in the cleaning processing. 
     Next, after the obverse face of the wafer  1  is water cleaned as shown in  FIG. 8C , the obverse face of the wafer  1  is dried as shown in  FIG. 8D . 
     As described above, in the electronic device cleaning method according to the present embodiment, the solution (the APM solution, for example) is discharged in advance onto the reverse face of the wafer  1  from the plurality of solution nozzles  30   a  to  30   i  provided at the solution supply line  30  with the use of, for example, a first controller (not shown), as shown in  FIG. 8A , before, the chemical solution is discharged onto the obverse face of the wafer  1  from the chemical solution nozzle  11  (see  FIG. 8B ). Then, the chemical solution is discharged onto the obverse face of the wafer  1  from the chemical solution nozzle  11  movable over the obverse face of the waver  1  while the solution is discharged onto the reverse face of the wafer  1  from a solution nozzle (the solution nozzle  30   b,  for example) located correspondingly to the chemical solution nozzle  11  out of the plurality of solution nozzles  30  with the use of a second controller (not shown), as shown in  FIG. 8B . 
     The respective wafers subjected to cleaning by the first to third electronic device cleaning methods under the aforementioned cleaning conditions (etching condition: at 70° C., for 30 seconds, NH 4 OH:H 2 O 2 :H 2 O=1:1:40) were evaluated by counting particles of 0.16 μm or larger as defects at the respective wafers by a particle counter. The defects at each wafer will be described below with reference to Table 4 and  FIG. 9A  to  FIG. 9C . Table 4 indicates each number of defects at the wafers and defect types thereof.  FIG. 9A  to  FIG. 9C  are sections showing the structures of the respective wafers subjected to cleaning by the first to third electronic device cleaning methods. 
     
       
         
               
               
               
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE 4 
               
             
             
               
                   
                   
               
               
                   
                 First 
                 Number of defects 
                 Defect type 
               
             
          
           
               
                   
                 diselectrification 
                 Before 
                 After 
                 Increased 
                 Damage due to 
                   
               
               
                   
                 period (sec.) 
                 processing 
                 processing 
                 number 
                 static electricity 
                 particle 
               
               
                   
                   
               
             
          
           
               
                 1st 
                  0 
                 2 
                 8 
                 6 
                 1 
                 5 
               
               
                 2nd 
                 30 
                 1 
                 3 
                 2 
                 1 
                 1 
               
               
                 3rd 
                 10 
                 2 
                 2 
                 0 
                 0 
                 0 
               
               
                   
                 30 
                 4 
                 4 
                 0 
                 0 
                 0 
               
               
                   
               
             
          
         
       
     
     Referring to the wafer  1  subjected to cleaning by the first electronic device cleaning method, that is, the electronic device cleaning method according to the second conventional example, Table 4 indicates that the numbers of defects before the processing and after the processing are two and eight, respectively, which means an increase in the number of defects after the processing compared with those before the processing (specifically, six defects increased). Detailed evaluation of the defects after the processing (specifically, the six defects) was carried out by SEM defect inspection equipment. The wafer defects after the processing will be described below with reference to  FIG. 9A .  FIG. 9A  is a section showing the structure of the wafer subjected to cleaning by the first electronic device cleaning method. 
     As shown in  FIG. 9A , a hole Da having a diameter da of approximately 1 μm was formed at part approximately 1 cm apart from the edge of the wafer  1  having an obverse face on which the thermal oxide film  2  is formed, that is, part of the obverse face of the wafer  1  where the APM solution is discharged first. The hole Da, which is one of the six defects observed after the processing, was formed in such a way that the thermal oxide film  2  was damaged by the static electricity discharge caused in the space between the obverse face of the wafer  1  and the APM solution discharged from the chemical solution nozzle  211 . Further, the defects other than the hole Da, that is, five defects out of the six defects after the processing were recognized as particles (not shown). 
     Referring to the wafer  1  subjected to cleaning by the second electronic device cleaning method, Table 4 indicates that the numbers of defects before the processing and after the processing are one and three, respectively, which means an increase in the number of defects after the processing compared with those before the processing (specifically, two defects increased). Detailed evaluation of the defects after the processing (specifically, the two defects) was carried out by SEM defect inspection equipment. The wafer defects after the processing will be described below with reference to  FIG. 9B .  FIG. 9B  is a section showing the structure of the wafer subjected to cleaning by the second electronic device cleaning method. 
     As shown in  FIG. 9B , a hole Db having a diameter db of approximately 0.5 μm was formed at part approximately 1 cm apart from the edge of the wafer  1  having an obverse face on which the thermal oxide film  2  is formed, that is, part of the obverse face of the wafer  1  where the APM solution is discharged first. The hole Da, which is one of the two defects observed after the processing, was formed in such a way that the thermal oxide film  2  was damaged by static electricity discharge caused in the space between the obverse face of the wafer  1  and the APM solution discharged from the chemical solution nozzle  211 . Further, the defect other than the hole Db, that is, one defect out of the two defects after the processing was recognized as a particle (not shown). 
     In contrast, referring to the wafer  1  subjected to cleaning by the third electronic device cleaning method, Table 4 indicates that each number of defects before the processing and after the processing is four in the case where the first time period for diselectrification is 30 seconds, which means no increase in the number of defects after the processing compared with those before the processing. Also, as indicated in Table 4, each number of defects before the processing and after the processing is two in the case where the first time period for diselectrification is 10 seconds, which means no increase in the number of defects after the processing compared with those before the processing.  FIG. 9C  is a section showing the structure of the wafer subjected to cleaning by the third electronic device cleaning method, wherein the first time period for diselectrification is 10 seconds. As shown in  FIG. 9C , no damage by the static electricity discharge is observed at the obverse face of the wafer  1 . 
     As described above, the static electricity present on the processing face of the cleaning stage  14  can be removed in advance by supplying the solution to the reverse face of the wafer  1  before the chemical solution is supplied to the obverse face of the wafer  1 , attaining effective prevention of induction of the static electricity to the obverse face of the wafer  1 . Further, the solution can be discharged onto the reverse face of the wafer  1  from a solution nozzle located correspondingly to the chemical solution nozzle  11  out of the plurality of solution nozzles  30   a  to  30   i  provided at the solution supply line  30 , so that the static electricity present on the processing face of the cleaning stage  14  under the chemical solution nozzle  11  can be removed. Thus, induction of the static electricity to a region of the obverse face of the wafer  1  under the chemical solution nozzle, that is, the chemical solution supply region of the obverse face of the wafer  1  can be prevented reliably. 
     Accordingly, the static electricity discharge can be prevented from being caused in the space between the obverse face of the wafer  1  and the chemical solution discharged from the chemical solution nozzle  11 , reliably preventing formation of a hole-like flaw at the obverse face of the wafer  1  (particularly, part of the obverse face of the wafer  1  where the chemical solution is supplied) and reliably preventing adhesion of particles to the obverse face of the wafer  1 , which would be caused due to the static electricity discharge. 
     Hence, by the electronic device cleaning method according to the present embodiment, the electronic device can be cleaned excellently without causing defects (specifically, flaws and particles) at the wafer  1 , improving the yield of the electronic device. 
     Further, in the electronic device cleaning method according to the present embodiment, diselectrification of the wafer  1  is performed using the solution supply line  30  as shown in  FIG. 8A , which is different from the first and second embodiments in which the wafer  1  is diselectrified with the use of the soft X ray irradiation system (see the reference numeral  19  in  FIG. 2A ), achieving electronic device cleaning at low cost compared with the first and second embodiments. 
     It is noted that the APM solution is used as the solution to be supplied to the reverse face of the wafer  1  in the electronic device cleaning method according to the present embodiment but the present invention is not limited thereto, and the same effects can be obtained even when a soda water, an inorganic chemical solution, an organic chemical solution, or the like is used as the solution to be supplied to the reverse face of the wafer  1 . 
     Moreover, in the electronic device cleaning method according to the present embodiment, the solution is discharged onto the reverse face of the wafer  1  from the plurality of solution nozzles  30   a  to  30   i  provided at the solution supply line  30  for the first time period for diselectrification as shown in  FIG. 8A , and the solution is discharged onto the reverse face of the wafer  1  from a solution nozzle (for example, the solution nozzle  30   b ) located correspondingly to the chemical solution nozzle  11  out of the plurality of solution nozzles for the second time period for diselectrification, as shown in  FIG. 8B . However, the present invention is not limited to this specific example. The same effects as in the electronic device cleaning method according to the present embodiment can be obtained in the case where the solution is discharged onto the reverse face of the wafer  1  from the plurality of solution nozzles for the first time period for diselectrification and for the second time period for diselectrification or in the case where the solution is discharged onto the reverse face of the wafer  1  from a solution nozzle located correspondingly to the chemical solution nozzle  11  out of the plurality of solution nozzles for the first time period for diselectrification and for the second time period for diselectrification. 
     As described above, the present invention is useful for electronic device cleaning equipment and electronic device cleaning methods, particularly, for single-wafer electronic device cleaning equipment and single-wafer electronic device cleaning methods.