Patent Publication Number: US-2011073490-A1

Title: Cleaning method, cleaning system, and method for manufacturing microstructure

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2009-220127, filed on Sep. 25, 2009; the entire contents of which are incorporated herein by reference. 
     FIELD 
     Embodiments described herein relate generally to a cleaning method, a cleaning system, and a method for manufacturing a microstructure. 
     BACKGROUND 
     Microstructures having fine wall bodies are manufactured on a surface using lithography technology in fields such as semiconductor devices and MEMS (Micro Electro Mechanical Systems). Resists that are formed during manufacturing processes and then become unnecessary are peeled using an SPM (sulfuric acid hydrogen peroxide mixture) solution, i.e., a mixed liquid of concentrated sulfuric acid solution and aqueous hydrogen peroxide (for example, refer to JP-A 2007-123330 (Kokai)). 
     Here, it is necessary to repeatedly replenish the aqueous hydrogen peroxide because mixing the concentrated sulfuric acid solution and the aqueous hydrogen peroxide produces oxidizing substances (e.g., peroxomonosulfuric acid) that react with water and decompose; and the decomposed amounts must be replenished. Therefore, it is difficult to maintain the solution mixing rate at a constant value. Moreover, the concentration of the sulfuric acid decreases due to the increase of the mixture amount of the aqueous hydrogen peroxide, and recycling unfortunately can no longer be performed. 
     Therefore, technology has been proposed to peel the resist adhered to a silicon wafer and the like using oxidizing substances produced by electrolyzing an aqueous solution of sulfuric acid (refer to JP-A 2006-111943 (Kokai)). According to the technology discussed in JP-A 2006-111943 (Kokai), the solution mixing rate can be stabilized by producing the oxidizing substances from the aqueous solution of the sulfuric acid. However, the processing time unfortunately is longer than that of the case where the resist is peeled using an SPM solution. Also, even in the case where the resist is peeled using an SPM solution, the need to increase productivity even more makes it necessary to shorten the processing time. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of a cleaning system according to an embodiment; 
         FIGS. 2A and 2B  are schematic views of the production mechanism of an oxidizing substance; 
         FIG. 3  is a graph of effects of the concentration of oxidizing substances and the concentration of inorganic acid on a peeling time; 
         FIG. 4  is a graph of temperature increase due to heat of reaction; 
         FIG. 5  is a graph of the relationship between a peeling time and the number of times being supplied sequentially; 
         FIG. 6  is a graph of effects of a processing temperature (a solution temperature); 
         FIG. 7  is a flowchart of a cleaning method; 
         FIG. 8  is a flowchart of a cleaning method according to another embodiment; and 
         FIG. 9  is a schematic view of a cleaning system according to another embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     According to one embodiment, a cleaning method is disclosed. The method can produce an oxidizing solution including an oxidizing substance by electrolyzing a dilute sulfuric acid solution. In addition, the method can supply a highly concentrated inorganic acid solution individually, sequentially, or substantially simultaneously with the oxidizing solution to a surface of an object to be cleaned. 
     According to another embodiment, a cleaning system includes a sulfuric acid electrolysis unit, a dilute sulfuric acid supply unit, a cleaning processing unit, an inorganic acid supply unit, and an oxidizing solution supply unit. The sulfuric acid electrolysis unit includes an anode, a cathode, a partitioning membrane provided between the anode and the cathode, an anode chamber provided between the anode and the partitioning membrane, and a cathode chamber provided between the anode and the partitioning membrane. The sulfuric acid electrolysis unit produces an oxidizing substance in the anode chamber by electrolyzing a dilute sulfuric acid solution. The dilute sulfuric acid supply unit supplies a dilute sulfuric acid solution to the anode chamber and the cathode chamber. The cleaning processing unit performs a cleaning processing of an object to be cleaned. The inorganic acid supply unit supplies a highly concentrated inorganic acid solution to the cleaning processing unit. The oxidizing solution supply unit supplies an oxidizing solution including the oxidizing substance to the cleaning processing unit. The highly concentrated inorganic acid solution is supplied to the cleaning processing unit by the inorganic acid supply unit individually, sequentially, or substantially simultaneously with the oxidizing solution supplied by the oxidizing solution supply unit. 
     According to still another embodiment, a method is disclosed for forming a microstructure. The method can clean an object to be cleaned by the cleaning method described above and form a microstructure. 
     Embodiments will now be described with reference to the drawings. Similar components in the drawings are marked with like reference numerals, and a detailed description is omitted as appropriate. 
       FIG. 1  is a schematic view illustrating a cleaning system according to this embodiment. 
     As illustrated in  FIG. 1 , a cleaning system  5  includes a sulfuric acid electrolysis unit  10 , an inorganic acid supply unit  50 , a cleaning processing unit  12 , a solution circulation unit  14 , and a dilute sulfuric acid supply unit  15 . 
     The sulfuric acid electrolysis unit  10  has a function of electrolyzing a sulfuric acid solution and producing an oxidizing substance in an anode chamber  30 . Although the oxidizing capability of a solution including oxidizing substances decreases when the solution including oxidizing substances is used to remove contaminants adhered to an object to be cleaned, the sulfuric acid electrolysis unit  10  also has a function of recovering the reduced oxidizing capability. 
     The sulfuric acid electrolysis unit  10  includes an anode  32 , a cathode  42 , a partitioning membrane  20  provided between the anode  32  and the cathode  42 , the anode chamber  30  provided between the anode  32  and the partitioning membrane  20 , and a cathode chamber  40  provided between the cathode  42  and the partitioning membrane  20 . 
     An upper end sealing unit  22  is provided at the upper end of the partitioning membrane  20 , the anode chamber  30 , and the cathode chamber  40 ; and a lower end sealing unit  23  is provided at the lower end of the partitioning membrane  20 , the anode chamber  30 , and the cathode chamber  40 . The anode  32  opposes the cathode  42  with the partitioning membrane  20  interposed therebetween. The anode  32  is supported by an anode support body  33 ; and the cathode  42  is supported by a cathode support body  43 . A direct-current power source  26  is connected between the anode  32  and the cathode  42 . 
     The anode  32  is made of a conductive anode base member  34  and an anode conductive film  35  formed on a surface of the anode base member  34 . The anode base member  34  is supported by the inner face of the anode support body  33 ; and the anode conductive film  35  faces the anode chamber  30 . 
     The cathode  42  is made of a conductive cathode base member  44  and a cathode conductive film  45  formed on a surface of the cathode base member  44 . The cathode base member  44  is supported by the inner face of the cathode support body  43 ; and the cathode conductive film  45  faces the cathode chamber  40 . 
     An anode inlet  19  is formed on the lower end side of the anode chamber  30 ; and an anode outlet  17  is formed on the upper end side. The anode inlet  19  and the anode outlet  17  communicate with the anode chamber  30 . A cathode inlet  18  is formed on the lower end side of the cathode chamber  40 ; and a cathode outlet  16  is formed on the upper end side. The cathode inlet  18  and the cathode outlet  16  communicate with the cathode chamber  40 . 
     The inorganic acid supply unit  50  includes a tank  51  which retains a highly concentrated inorganic acid solution, a pump  52 , and an open/shut valve  71 . The tank  51 , the pump  52 , and the open/shut valve  71  are connected to a dispense unit  61  via a piping line  53 . The highly concentrated inorganic acid solution retained in the tank  51  can be supplied to the dispense unit  61  via the piping line  53  by the operation of the pump  52 . In other words, the inorganic acid supply unit  50  has a function of supplying the highly concentrated inorganic acid solution retained in the tank  51  to the dispense unit  61  of the cleaning processing unit  12 ; and the highly concentrated inorganic acid solution supplied to the dispense unit  61  can be supplied to the surface of an object W to be cleaned. It is favorable for the highly concentrated inorganic acid solution to be a solution having a dehydrating action. Examples of such include, for example, a concentrated sulfuric acid solution having a sulfuric acid concentration not less than 90 weight percent. Temperature control of the highly concentrated inorganic acid solution can be performed by providing the tank  51  with a heater. 
     A highly concentrated inorganic acid solution also can be supplied to the object W to be cleaned from a piping system separate from that of the solution including oxidizing substances (the oxidizing solution) by providing a not-illustrated piping line and dispense unit separate from a piping line  74  and the dispense unit  61 . 
     The cleaning processing unit  12  has a function of cleaning the object W to be cleaned using the solution including oxidizing substances (the oxidizing solution) obtained in the sulfuric acid electrolysis unit  10  and the highly concentrated inorganic acid solution supplied by the inorganic acid supply unit  50 . 
     The oxidizing solution obtained in the sulfuric acid electrolysis unit  10  is supplied to the dispense unit  61  provided in the cleaning processing unit  12  via the solution circulation unit  14 . The highly concentrated inorganic acid solution is supplied by the inorganic acid supply unit  50  to the dispense unit  61  provided in the cleaning processing unit  12 . The oxidizing solution and the highly concentrated inorganic acid solution may be supplied sequentially; and the oxidizing solution and the highly concentrated inorganic acid solution may be supplied substantially simultaneously. 
     The oxidizing solution and the highly concentrated inorganic acid solution may be mixed; and the mixed liquid (the cleaning liquid) may be supplied. In the case where the highly concentrated inorganic acid solution supplied by the inorganic acid supply unit  50  and the oxidizing solution supplied by the sulfuric acid electrolysis unit  10  are supplied substantially simultaneously to the piping line  74 , the piping line  74  forms a mixing unit mixing both solutions. 
     Also, a not-illustrated tank may be provided to mix the oxidizing solution and the highly concentrated inorganic acid solution. In such a case, the not-illustrated tank is a mixing unit. By providing the not-illustrated tank, the flow rate fluctuation of the mixed liquid (the cleaning liquid) can be buffered, the mixing rate can be adjusted, etc. Temperature control of the mixed liquid (the cleaning liquid) can be performed by providing the not-illustrated tank and the piping line  74  with a heater. 
     The dispense unit  61  has a dispensing nozzle for dispensing the oxidizing solution, the highly concentrated inorganic acid solution, and the mixed liquid (the cleaning liquid) of the oxidizing solution and the highly concentrated inorganic acid solution onto the object W to be cleaned. A rotating table  62  is provided on which the object W to be cleaned is placed to oppose the dispensing nozzle. The rotating table  62  is provided in the interior of a cover  29 . By dispensing the oxidizing solution, the highly concentrated inorganic acid solution, and the mixed liquid (the cleaning liquid) of the oxidizing solution and the highly concentrated inorganic acid solution from the dispense unit  61  toward the object W to be cleaned, the contaminants and unnecessary substances (e.g., the resist, etc.) can be removed from the top of the object W to be cleaned in a short length of time. The removing of the contaminants and unnecessary substances (e.g., the resist, etc.) in a short length of time from the top of the object W to be cleaned is described below. 
     Although so-called single wafer processing is used in the cleaning processing unit  12  illustrated in  FIG. 1 , batch processing also may be used. 
     The oxidizing solution produced in the sulfuric acid electrolysis unit  10  is supplied from the anode outlet  17  to the cleaning processing unit  12  via the solution circulation unit  14 . As a solution maintaining unit, the anode outlet  17  is connected to a tank  28  via a piping line  73  in which an open/shut valve  73   a  is provided. The tank  28  is connected to the dispense unit  61  via the piping line  74 . The oxidizing solution retained in the tank  28  is supplied to the dispense unit  61  via the piping line  74  by the operation of a pump  81 . An open/shut valve  74   a  is provided in the piping line  74  on the dispensing side of the pump  81 . In this embodiment, the tank  28 , the pump  81 , etc., form an oxidizing solution supply unit that supplies the oxidizing solution including oxidizing substances to the cleaning processing unit  12 . In such a case, the flow rate fluctuation of the oxidizing solution produced in the sulfuric acid electrolysis unit  10  can be buffered by retaining and maintaining the oxidizing solution in the tank  28 . Temperature control of the oxidizing solution can be performed by providing the tank  28  with a heater. 
     The oxidizing solution discharged from the cleaning processing unit  12  is recoverable by the solution circulation unit  14  and resuppliable to the cleaning processing unit  12 . For example, the oxidizing solution discharged from the cleaning processing unit  12  is suppliable to the anode inlet  19  of the sulfuric acid electrolysis unit  10  by passing through a returning tank  63 , a filter  64 , a pump  82 , and an open/shut valve  76  in this order. In other words, the oxidizing solution can be circulated between the sulfuric acid electrolysis unit  10  and the cleaning processing unit  12 . In such a case, as necessary, the oxidizing solution used during the cleaning processing can be supplied to the sulfuric acid electrolysis unit  10 ; subsequently, the oxidizing solution including oxidizing substances obtained by performing electrolysis in the sulfuric acid electrolysis unit  10  can be passed through the tank  28 , etc.; and the oxidizing solution can be supplied to the cleaning processing unit  12 . 
     Here, as necessary, the oxidizing solution can be produced by supplying diluted sulfuric acid from the dilute sulfuric acid supply unit  15  to the sulfuric acid electrolysis unit  10  as well as supplying the used oxidizing solution to the sulfuric acid electrolysis unit  10 , and then performing electrolysis. The oxidizing solution obtained here can be passed through the tank  28 , etc., and supplied to the cleaning processing unit  12 . By repeating such re-utilization of the oxidizing solution as much as possible, it is possible to reduce the amount of the materials (chemical solutions, etc.) necessary to produce the oxidizing solution and the amount of the waste fluid during the cleaning processing of the object W to be cleaned. 
     Alternatively, the oxidizing solution discharged from the cleaning processing unit  12  is suppliable to the tank  28  by passing through the returning tank  63 , the filter  64 , the pump  82 , and an open/shut valve  91  in this order, that is, without passing through the sulfuric acid electrolysis unit  10 . Here, continuing, cleaning processing of the object W to be cleaned can be performed by supplying the oxidizing solution from the tank  28  to the cleaning processing unit  12 . In such a case, the used oxidizing solution can be re-utilized during the cleaning processing. By repeating such re-utilization of the oxidizing solution as much as possible, it is possible to reduce the amount of the materials (chemical solutions, etc.) necessary to produce the oxidizing solution and the amount of the waste fluid. 
     Similarly, the highly concentrated inorganic acid solution and the mixed liquid (the cleaning liquid) of the oxidizing solution and the highly concentrated inorganic acid solution discharged from the cleaning processing unit  12  can be circulated and re-utilized. In particular, in the case where the inorganic acid is sulfuric acid, the amount of the dilute sulfuric acid supplied by the dilute sulfuric acid supply unit  15  (a tank  60 ) can be reduced because the inorganic acid is a source material liquid of the oxidizing solution. In the case where problems occur when re-utilizing a mixture of the inorganic acid solution and the oxidizing solution, a not-illustrated returning tank, open/shut valve, etc., can be connected to the cleaning processing unit  12  for the inorganic acid solution to separate and recover the inorganic acid solution and the oxidizing solution. In such a case, by supplying the inorganic acid solution and the oxidizing solution sequentially, the separation and recovery can be performed during each supplying thereof. Separate re-utilization is possible by separate reprocessing, etc. 
     The returning tank  63  is provided with a discharge piping line  75  and a discharge valve  75   a  having a function of discharging the contaminants and unnecessary substances (e.g., the resist, etc.) cleaned and removed in the cleaning processing unit  12  to the outside of the system. The filter  64  has a function of filtering the contaminants and unnecessary substances (e.g., the resist, etc.) included in the oxidizing solution, the inorganic acid solution, and the mixed liquid (the cleaning liquid) discharged from the cleaning processing unit  12 . 
     The dilute sulfuric acid supply unit  15  has a function of supplying a dilute sulfuric acid solution to the sulfuric acid electrolysis unit  10  (the anode chamber  30  and the cathode chamber  40 ). The dilute sulfuric acid supply unit  15  includes a pump  80  which supplies the dilute sulfuric acid solution to the anode chamber  30  and the cathode chamber  40 , the tank  60  which retains the dilute sulfuric acid, and open/shut valves  70  and  72 . 
     A dilute sulfuric acid solution having a sulfuric acid concentration not less than 30 weight percent and not more than 70 weight percent is retained in the tank  60 . The pump  80  is driven such that the dilute sulfuric acid solution in the tank  60  passes through the open/shut valve  70  and is supplied to the anode chamber  30  via the piping line on the downstream side of the open/shut valve  76  and the anode inlet  19 . Also, the pump  80  is driven such that the dilute sulfuric acid solution in the tank  60  passes through the open/shut valve  72  and is supplied to the cathode chamber  40  via a piping line  86  on the downstream side of the open/shut valve  72  and the cathode inlet  18 . 
     In this embodiment, damage of the partitioning membrane  20  due to the electrolysis of the sulfuric acid can be suppressed because the sulfuric acid concentration of the solution supplied to the cathode side is low. In other words, water on the cathode side moves to the anode side during the electrolysis reaction of the sulfuric acid; the sulfuric acid concentration of the solution on the cathode side increases; and the partitioning membrane  20  easily deteriorates. Moreover, in the case where an ion exchange membrane is used as the partitioning membrane  20 , the resistance of the ion exchange membrane increases as the water content decreases in the concentrated sulfuric acid solution; and the container voltage undesirably increases. Therefore, to mitigate such problems as well, the resistance increase can be suppressed by supplying dilute sulfuric acid to the cathode side to supply water to the ion exchange membrane. 
     By reducing the concentration of the sulfuric acid supplied to the sulfuric acid electrolysis unit  10 , the production efficiency of the oxidizing substance (e.g., peroxomonosulfuric acid and peroxodisulfuric acid) included in the oxidizing solution can be increased. Increasing the production efficiency of the oxidizing substance is described below. 
     The open/shut valves  70 ,  71 ,  72 ,  73   a ,  74   a ,  75   a ,  76 , and  91  described above also have a function of controlling the flow rate of the various solutions. The pumps  80 ,  81 , and  82  also have a function of controlling the flow velocities of the various solutions. 
     From the aspect of chemical resistance, the material of the anode support body  33 , the cathode support body  43 , the cathode outlet  16 , the anode outlet  17 , the cathode inlet  18 , the anode inlet  19 , and the cover  29  of the cleaning processing unit  12 , may favorably include, for example, a fluorocarbon resin such as polytetrafluoroethylene. 
     The piping that supplies the oxidizing solution, the highly concentrated inorganic acid solution, and the mixed liquid (the cleaning liquid) of the oxidizing solution and the highly concentrated inorganic acid solution to the cleaning processing unit  12  may include a fluorocarbon resin tube wound with insulation, etc. Such piping also may be provided with in-line heaters made of fluorocarbon resin. The pumps that pump the oxidizing solution, the highly concentrated inorganic acid solution, and the mixed liquid (the cleaning liquid) of the oxidizing solution and the highly concentrated inorganic acid solution may include a bellows pump made of fluorocarbon resin having heat resistance and chemical resistance. 
     The material of the tanks that retain the sulfuric acid solution may include, for example, quartz. Each of the tanks may include an overflow control device, temperature control device, etc., as appropriate. 
     The partitioning membrane  20  may include, for example, a neutral film (albeit having undergone hydrophilizing processing) including a PTFE porous partitioning membrane such as that having the product name Poreflon, etc., and a positive ion exchange membrane such as those having the product names Nafion, Aciplex, Flemion, etc. The dimensions of the partitioning membrane  20  are, for example, about 50 square centimeters. It is suitable for the upper end sealing unit  22  and the lower end sealing unit  23  to include, for example, an O ring coated with fluorocarbon resin. 
     The material of the anode conductive base member  34  may include, for example, p-type silicon and valve metal such as niobium. Herein, “valve metal” refers to a metal having the metal surface thereof uniformly covered with an oxide film by anode oxidation and having excellent corrosion resistance. The cathode conductive base member  44  may include, for example, n-type silicon. 
     The material of the anode conductive film  35  and the cathode conductive film  45  may include, for example, glassy carbon. From the aspect of durability, it is suitable to use a conductive diamond film in the case where a solution having a relatively high sulfuric acid concentration is supplied. 
     For both the anode and the cathode, the conductive film and the base member may be formed of the same material. For example, in the case where glassy carbon is used as the cathode base member and in the case where a conductive diamond self-supporting film is used as the anode base member, the base member itself forms a conductive film having electrocatalytic properties which can contribute to the electrolyzing reaction. 
     Although diamond has stable chemical, mechanical, and thermal properties, it has been difficult to use diamond in an electrochemical system because of poor conductivity. However, a conductive diamond film can be obtained by forming while supplying boron gas and nitrogen gas using hot filament chemical vapor deposition (HF-CVD). The conductive diamond film has a wide “potential window” of, for example, 3 to 5 volts and an electrical resistance of, for example, 5 to 100 milli-ohm-centimeters. 
     Herein, the “potential window” is the minimum potential (not less than 1.2 volts) necessary for the electrolysis of water. The “potential window” differs by material quality. In the case where a material having a wide “potential window” is used and electrolysis is performed at a potential in the “potential window,” an electrolyzing reaction having an oxidation-reduction potential inside the “potential window” may progress preferentially to the electrolysis of water; and there are cases where the oxidation reaction or reduction reaction of a substance which does not easily undergo electrolysis can progress preferentially. Accordingly, decomposing and synthesizing is possible by using such a conductive diamond for substances which cannot undergo conventional electrochemical reactions. 
     In HF-CVD, decomposition is performed by supplying the source-material gas to the tungsten filament in a high-temperature state. The radicals necessary for forming the film are formed. Subsequently, the radicals diffused into the substrate surface react with other reactive gases to form the film on the desired substrate. 
     The production mechanism of the oxidizing substance in the sulfuric acid electrolysis unit  10  will now be described. 
       FIGS. 2A and 2B  are schematic views illustrating the production mechanism of the oxidizing substance.  FIG. 2A  is a schematic side cross-sectional view of the sulfuric acid electrolysis unit.  FIG. 2B  is a schematic view illustrating the cross section along line A-A of  FIG. 2A . 
     As illustrated in  FIGS. 2A and 2B , the anode  32  and the cathode  42  are provided to oppose each other with the partitioning membrane  20  interposed therebetween. The anode  32  is supported by the anode support body  33  with the anode conductive film  35  of the anode  32  facing the anode chamber  30 . The cathode  42  is supported by the cathode support body  43  with the cathode conductive film  45  of the cathode  42  facing the cathode chamber  40 . Electrolysis unit housings  24  are provided on both end portions of each of the partitioning membrane  20 , the anode support body  33 , and the cathode support body  43 . 
     A sulfuric acid solution (a dilute sulfuric acid solution) of 70 weight percent, for example, is supplied from the tank  60  to the anode chamber  30  via the anode inlet  19 . The 70 weight percent sulfuric acid solution (the dilute sulfuric acid solution), for example, is supplied from the tank  60  also to the cathode chamber  40  via the cathode inlet  18 . 
     By applying a positive voltage to the anode  32  and a negative voltage to the cathode  42 , an electrolysis reaction occurs in each of the anode chamber  30  and the cathode chamber  40 . The reactions of chemical formula 1, chemical formula 2, and chemical formula 3 occur in the anode chamber  30 . 
       2HSO 4   − →S 2 O 8   2− +2H + +2 e   −   Chemical formula 1
 
       HSO 4   − +H 2 O→HSO 5   − +2H + +2 e   −   Chemical formula 2
 
       2H 2 O→4H + +4 e   − +O 2 ↑  Chemical formula 3
 
     Here, the water (H 2 O) in chemical formula 2 and chemical formula 3 is the water included as 30 percent of the 70 weight percent sulfuric acid solution. In the anode chamber  30 , the reaction of chemical formula 2 produces peroxomonosulfuric acid ions (HSO 5   − ). The overall reaction of chemical formula 4 occurs by the elementary reactions of chemical formula 1 and chemical formula 3 to also produce peroxomonosulfuric acid ions (HSO 5   − ) and sulfuric acid. Peroxomonosulfuric acid has a cleaning capability higher than that of sulfuric acid. 
       S 2 O 8   2− +H + +H 2 O→HSO 5   − +H 2 SO 4   Chemical formula 4
 
     Alternatively, in some cases, the peroxomonosulfuric acid ions (HSO 5   − ) of chemical formula 4 are produced after hydrogen peroxide (H 2 O 2 ) is produced as illustrated by chemical formula 5 from the elementary reactions of chemical formula 1 and chemical formula 3. In some cases, peroxodisulfuric acid (H 2 S 2 O 8 ) is produced by the reaction of chemical formula 1. Chemical formula 4 and chemical formula 5 are second order reactions from chemical formula 1. 
       S 2 O 8   2− +H + +H 2 O→H 2 O 2 +H 2 SO 4   Chemical formula 5
 
     Hydrogen gas is produced in the cathode chamber  40  as illustrated by chemical formula 6. This occurs because hydrogen ions (H + ) produced at the anode move to the cathode via the partitioning membrane  20  and an electrolysis reaction occurs. The hydrogen gas is discharged from the cathode chamber  40  via the cathode outlet  16 . 
         2 H + +2 e   − →H 2 ↑  Chemical formula 6
 
     In this embodiment as illustrated by chemical formula 7, oxidizing substances such as, for example, peroxomonosulfuric acid (H 2 SO 5 ), peroxodisulfuric acid (H 2 S 2 O 8 ), etc., can be obtained by electrolyzing the sulfuric acid solution; and an oxidizing solution including these oxidizing substances can be obtained. Although hydrogen gas is produced as a by-product, the hydrogen gas does not affect the peeling of the resist, etc. 
       H 2 SO 4 +H 2 O→oxidizing substances+H 2   Chemical formula 7
 
     In the case where peroxomonosulfuric acid is used, the reaction rate with organic substances such as the resist is high. Therefore, even the resist peeling, in which the amount to be removed is relatively large, can be completed in a short length of time. Also, in the case where peroxomonosulfuric acid is used, peeling is possible at a low temperature. Therefore, the fine-tuning time for temperature ramp-up and the like is unnecessary. Moreover, peroxomonosulfuric acid can be produced stably in large amounts. Therefore, the reaction rate with the object of removal can be increased even at low temperatures. 
     Here, to increase the production efficiency by shortening the processing time, it is sufficient to increase the amount of the oxidizing substance. In such a case, the amount of oxidizing substances produced can be increased by increasing the apparatus size, increasing the applied power, increasing the amount of the dilute sulfuric acid solution, etc. However, such actions lead to higher production costs and environmental impacts. Therefore, it is necessary to efficiently produce the oxidizing substance by increasing the electrolysis efficiency. 
     According to knowledge obtained by the inventors, in the case of constant electrolysis parameters (e.g., the amount of electricity, flow rate, temperature, etc.), more oxidizing substances can be produced by reducing the sulfuric acid concentration during the electrolyzing. Therefore, the production efficiency of the oxidizing substances (e.g., peroxomonosulfuric acid and peroxodisulfuric acid) included in the oxidizing solution can be increased by reducing the sulfuric acid concentration supplied to the sulfuric acid electrolysis unit  10 . 
     However, according to other knowledge obtained by the inventors, the processing time for peeling and removing an organic substance such as a resist lengthens as the concentration of the inorganic acid such as sulfuric acid decreases. 
       FIG. 3  is a graph illustrating the effects of the concentration of the oxidizing substances and the concentration of the inorganic acid on the peeling time. The oxidizing substance concentration is plotted on the horizontal axis. The peeling time is plotted on the vertical axis. In  FIG. 3 , B 1  is the case where the sulfuric acid concentration is 70 weight percent; B 2  is the case where the sulfuric acid concentration is 80 weight percent; B 3  is the case where the sulfuric acid concentration is 85 weight percent; B 4  is the case where the sulfuric acid concentration is 90 weight percent; and B 5  is the case where the sulfuric acid concentration is 95 weight percent. 
       FIG. 3  shows that as the sulfuric acid concentration decreases, more oxidizing substances are produced; and the concentration of the oxidizing substances therefore increases. Also, for the same sulfuric acid concentration, the peeling time shortens as the concentration of the oxidizing substances increases (as the amount of the oxidizing substances increases). 
     However, when comparing different sulfuric acid concentrations, the peeling time shortens as the sulfuric acid concentration increases. 
     In other words, while more oxidizing substances can be produced as the sulfuric acid concentration decreases during the production stage of the oxidizing substances, the peeling time can be shortened by increasing the sulfuric acid concentration during the peeling stage even while the amount of the oxidizing substances is the same. 
     Therefore, in this embodiment, a dilute sulfuric acid solution having a sulfuric acid concentration not less than 30 weight percent and not more than 70 weight percent is supplied to the sulfuric acid electrolysis unit  10 . The highly concentrated inorganic acid solution (e.g., a concentrated sulfuric acid solution having a sulfuric acid concentration not less than 90 weight percent) is supplied to the surface of the object W to be cleaned without passing through the sulfuric acid electrolysis unit  10 . 
     Therefore, more oxidizing substances can be produced by increasing the electrolysis efficiency of the sulfuric acid electrolysis unit  10 . Also, the highly concentrated inorganic acid can be supplied to the surface of the object W to be cleaned without affecting the electrolysis efficiency of the sulfuric acid electrolysis unit  10 . As a result, a solution having a high concentration of an inorganic acid such as sulfuric acid and including a large amount of oxidizing substances can be supplied to the surface of the object W to be cleaned. Therefore, the processing time can be shortened drastically. 
     Here, according to experiments performed by the inventors, the peeling time of a resist was about 120 seconds when a dilute sulfuric acid solution having a sulfuric acid concentration of 70 weight percent was supplied to the sulfuric acid electrolysis unit  10 , an oxidizing solution was produced, and peeling of the resist was performed by supplying the oxidizing solution to the surface of the object W to be cleaned. On the other hand, the peeling time was shortened drastically to about 20 seconds when the dilute sulfuric acid solution having a sulfuric acid concentration of 70 weight percent was supplied to the sulfuric acid electrolysis unit  10 , the oxidizing solution was produced, and a concentrated sulfuric acid solution having a sulfuric acid concentration of 98 weight percent was added to the oxidizing solution to supply an oxidizing solution having a sulfuric acid concentration of 82 weight percent to the surface of the object W to be cleaned. 
     While a high-speed operation semiconductor device is manufactured by implanting an impurity with a high dose, an altered layer is formed in the surface of the resist by the implanting of the impurity with the high dose. The resist having such an altered layer does not peel easily; and the desired peeling margin unfortunately cannot be obtained. 
     According to this embodiment, a highly concentrated inorganic acid and an oxidizing solution including a large amount of oxidizing substances can be supplied to the surface of the object W to be cleaned. Therefore, the peelability of a resist can be increased even in the case where an altered layer is formed in the resist. 
     The heat of reaction can be utilized when a highly concentrated inorganic acid solution is mixed with an oxidizing solution which also is a low-concentration inorganic acid solution. As the temperature increases, the reactivity of the oxidizing substances included in the oxidizing solution can be increased. Therefore, the processing time can be shortened. 
     However, increasing the solution temperature of the sulfuric acid electrolysis unit  10  and the inorganic acid supply unit  50  may cause problems regarding the allowable temperature and strength of the components (e.g., the piping lines, open/shut valves, pumps, and tanks of each unit, the cleaning processing unit cover, etc.). The components often are formed of, for example, fluorocarbon resin, etc., to increase the chemical resistance of the portions in contact with the highly concentrated inorganic acid solution and the oxidizing solution. In such a case, the necessary strength may not be possible in the case where the temperature is too high. 
     According to this embodiment, a heat of reaction can be generated by mixing the highly concentrated inorganic acid solution and the oxidizing solution, which also is a low-concentration inorganic acid solution, prior to supplying to the object W to be cleaned or on the object W to be cleaned. Therefore, the temperature increase of the components can be suppressed; and the reactivity of the oxidizing substance can be increased by increasing the temperature of the mixed liquid. 
       FIG. 4  is a graph illustrating the temperature increase due to the heat of reaction. The temperature of the mixed liquid is plotted on the vertical axis. The concentration of the mixed liquid is plotted on the horizontal axis. The temperature of each of the highly concentrated inorganic acid solution and the low-concentration inorganic acid solution (the solution illustrated in  FIG. 4  is of a concentrated sulfuric acid solution and a dilute sulfuric acid solution) prior to the mixing is 88° C. C 1  of  FIG. 4  illustrates the case where a dilute sulfuric acid solution having a sulfuric acid concentration of 30 weight percent is mixed with a concentrated sulfuric acid solution having a sulfuric acid concentration of 98 weight percent. C 2  of  FIG. 4  illustrates the case where a dilute sulfuric acid solution having a sulfuric acid concentration of 50 weight percent is mixed with a concentrated sulfuric acid solution having a sulfuric acid concentration of 98 weight percent. C 3  of  FIG. 4  illustrates the case where a dilute sulfuric acid solution having a sulfuric acid concentration of 70 weight percent is mixed with a concentrated sulfuric acid solution having a sulfuric acid concentration of 98 weight percent. 
       FIG. 4  shows that a heat of reaction can be generated by mixing inorganic acids (sulfuric acids) of different concentrations; and the heat of reaction can be utilized to increase the temperature of the mixed liquid. As the difference is increased between the concentrations of the liquids to be mixed, or as the mixing ratio is set to dilute the mixed liquid (as the mixing ratio is set to reduce the concentration of the mixed liquid), the temperature increase can be greater. 
     Therefore, it is possible to adjust conditions to perform optimal peeling by appropriately selecting the concentrations of the liquids to be mixed, the mixing ratio, the amount and reactivity of the oxidizing substances, the temperatures of the solutions prior to mixing, etc. 
     Although the case is described above where the highly concentrated inorganic acid solution is mixed with the oxidizing solution which also is a low-concentration inorganic acid solution, the case will now be described where the highly concentrated inorganic acid solution and the oxidizing solution are supplied sequentially. 
     Table 1 illustrates a comparison of the times to peel a resist in the case where a test piece having the resist formed on the surface thereof is immersed in a highly concentrated inorganic acid solution and subsequently immersed in an oxidizing solution. The highly concentrated inorganic acid solution was a concentrated sulfuric acid solution having a sulfuric acid concentration of 98 weight percent. The oxidizing solution was a dilute sulfuric acid solution having a sulfuric acid concentration of 70 weight percent produced by electrolysis. The temperature of each of the highly concentrated inorganic acid solution and the oxidizing solution was, as an example, about 100 to 110° C. 
     
       
         
           
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                 IMMERSION TIME 
                 TIME TO PEELING 
               
               
                 SAMPLE 
                 IN CONCENTRATED 
                 AFTER IMMERSING IN 
               
               
                 NO. 
                 SULFURIC ACID 
                 OXIDIZING SOLUTION 
               
               
                   
               
             
            
               
                 1 
                 0 sec 
                 120 sec  
               
               
                 2 
                 10 sec  
                 20 sec 
               
               
                 3 
                 5 sec 
                 15 sec 
               
               
                 4 
                 1 sec 
                 15 sec 
               
               
                   
               
            
           
         
       
     
     As illustrated in table  1 , in the case where immersion in the highly concentrated inorganic acid solution (the concentrated sulfuric acid solution having a sulfuric acid concentration of 98 weight percent) was not performed (the case of Sample No. 1), it took 120 seconds for the resist to peel. Conversely, it was shown that in the cases where the immersion in the highly concentrated inorganic acid solution (the concentrated sulfuric acid solution having the sulfuric acid concentration of 98 weight percent) was performed (the cases of Samples Nos. 2 to 4), it took only about 20 seconds for the resist to peel; and the processing time (the peeling time) was shortened drastically. Moreover, it was shown that even in the case where the time of the immersion in the highly concentrated inorganic acid solution (the concentrated sulfuric acid solution having the sulfuric acid concentration of 98 weight percent) was short, the time for the resist to peel was not affected greatly. 
       FIG. 5  is a graph illustrating the relationship between the peeling time and the number of times being supplied sequentially. The sample numbers are plotted on the vertical axis. The time for a resist formed on the test piece surface to peel (the peeling time) is plotted on the horizontal axis. D 1  of  FIG. 5  illustrates the case of immersion in a concentrated sulfuric acid solution having a sulfuric acid concentration of 98 weight percent; and D 2  illustrates the case of immersing in an oxidizing solution produced by electrolyzing a dilute sulfuric acid solution having a sulfuric acid concentration of 70 weight percent. The temperature of each of the concentrated sulfuric acid solution having the sulfuric acid concentration of 98 weight percent and the oxidizing solution was, as an example, about 100 to 110° C. 
     Sample No. 10 is the case of immersion once in the concentrated sulfuric acid solution having the sulfuric acid concentration of 98 weight percent for 1 second (the D 1  portion). It was shown that in this case, it took about 16 seconds for the resist to peel. 
     Sample No. 11 is the case where the immersion in the concentrated sulfuric acid solution having the sulfuric acid concentration of 98 weight percent for 1 second (the D 1  portion) and an immersion in the oxidizing solution for 4 seconds (the D 2  portion) were performed sequentially. In this case, the resist had peeled when the immersion in the concentrated sulfuric acid solution having the sulfuric acid concentration of 98 weight percent was performed twice and the immersion in the oxidizing solution was performed twice. It was shown that the time for the resist to peel was 10 seconds, and the processing time was shortened. 
     Sample No. 12 is the case where the immersion in the concentrated sulfuric acid solution having the sulfuric acid concentration of 98 weight percent for 1 second (the D 1  portion) and the immersion in the oxidizing solution for 1 second (the D 2  portion) were performed sequentially. In this case, the resist had peeled when the immersion in the 98 weight percent concentrated sulfuric acid solution was performed four times and the immersion in the oxidizing solution was performed four times. It was shown that the time for the resist to peel was 8 seconds, and the processing time was shortened even more. 
     Thus, the processing time can be shortened by increasing the number of immersions and repeating sequentially. As illustrated in table  1 , even in the case where the immersion time in the concentrated sulfuric acid solution was short, the time for the resist to peel was not affected greatly. Therefore, the processing time can be shortened by repeatedly performing immersions for somewhat short times. 
       FIG. 6  is a graph illustrating effects of the processing temperature (the solution temperature). The sample numbers are plotted on the vertical axis. The time for a resist formed on the test piece surface to peel (the peeling time) is plotted on the horizontal axis. E 1  of  FIG. 6  illustrates the case of immersion in a concentrated sulfuric acid solution having a sulfuric acid concentration of 98 weight percent; and E 2  illustrates the case of immersion in an oxidizing solution produced by electrolyzing a dilute sulfuric acid solution having a sulfuric acid concentration of 70 weight percent. 
     Sample No. 20 is the case where the temperature of the concentrated sulfuric acid solution having the sulfuric acid concentration of 98 weight percent was room temperature and the temperature of the oxidizing solution was 75° C.; and the resist was peeled by immersing in the concentrated sulfuric acid solution having the sulfuric acid concentration of 98 weight percent for 5 seconds and then immersing in the oxidizing solution. In this case, the time for the resist to peel was 520 seconds. 
     Sample No. 21 is the case where the temperature of the concentrated sulfuric acid solution having the sulfuric acid concentration of 98 weight percent was 75° C.; the temperature of the oxidizing solution was 75° C.; and the resist was peeled by immersing in the concentrated sulfuric acid solution having the sulfuric acid concentration of 98 weight percent for 5 seconds and then immersing in the oxidizing solution. In this case, the time for the resist to peel was 360 seconds. 
     Sample No. 22 is the case where the temperature of the concentrated sulfuric acid solution having the sulfuric acid concentration of 98 weight percent was 100° C.; the temperature of the oxidizing solution was 75° C.; and the resist was peeled by immersing in the concentrated sulfuric acid solution having the sulfuric acid concentration of 98 weight percent for 5 seconds and then immersing in the oxidizing solution. In this case, the time for the resist to peel was 80 seconds. 
     Sample No. 23 is the case where the temperature of the concentrated sulfuric acid solution having the sulfuric acid concentration of 98 weight percent was 100° C.; the temperature of the oxidizing solution was 100° C.; and the resist was peeled by immersing in the concentrated sulfuric acid solution having the sulfuric acid concentration of 98 weight percent for 5 seconds and then immersing in the oxidizing solution. In this case, the time for the resist to peel was 20 seconds. 
     Thus, although the processing time shortens as the processing temperature (the solution temperature) is increased, increasing the temperature too high may cause problems regarding the allowable temperature and strength of the components of the cleaning system (e.g., the piping lines, open/shut valves, pumps, and tanks of each unit, the cleaning processing unit cover, etc.). The components often are formed of, for example, fluorocarbon resin, etc., to increase the chemical resistance of the portions in contact with the highly concentrated inorganic acid solution and the oxidizing solution. In such a case, the necessary strength may not be possible in the case where the temperature is too high. 
     Therefore, considering shortening the processing time and the allowable temperature, strength, etc., of the cleaning system, it is favorable for the temperatures of the highly concentrated inorganic acid solution and the oxidizing solution to be not less than 100° C. and not more than 110° C. In such a case, the processing temperature (the solution temperature) can be increased even more while reducing the thermal load on the cleaning system by utilizing the heat of reaction described above. In the case where the heat of reaction is utilized, the processing temperature (the solution temperature) can be not less than 100° C. and not more than 150° C. 
     A cleaning method according to this embodiment will now be described. 
       FIG. 7  is a flowchart illustrating the cleaning method. 
     First, an oxidizing solution including oxidizing substances (e.g., peroxomonosulfuric acid and peroxodisulfuric acid) is produced by electrolyzing a dilute sulfuric acid solution (step S 1 - 1 ). In such a case, the oxidizing substances can be produced efficiently by making the sulfuric acid concentration of the dilute sulfuric acid solution not less than 30 weight percent and not more than 70 weight percent. 
     Then, the temperature of the produced oxidizing solution is adjusted (step S 1 - 2 ). Although such a temperature adjustment is not always necessary, it is favorable for the temperatures of the solutions to be adjusted to be not less than 100° C. and not more than 110° C. as described above. The temperature adjustment can be performed on any of the produced oxidizing solution, the oxidizing solution during production (during the electrolysis), and the dilute sulfuric acid solution supplied for the electrolysis. 
     The temperature of the highly concentrated inorganic acid solution is adjusted (step S 2 ). Examples of a highly concentrated inorganic acid solution include, for example, an inorganic acid solution having an inorganic acid concentration not less than 90 weight percent. For example, a concentrated sulfuric acid solution having a sulfuric acid concentration not less than 90 weight percent, etc., may be used. Although such a temperature adjustment is not always necessary, it is favorable for the temperatures to be adjusted to be not less than 100° C. and not more than 110° C. as described above. 
     Then, the highly concentrated inorganic acid solution is supplied individually, sequentially, or substantially simultaneously with the oxidizing solution to the surface of the object W to be cleaned (step S 3 ). The supplying may be performed from a dispense unit and the like for each of the objects W to be cleaned and by sequentially immersing in the highly concentrated inorganic acid solution and the oxidizing solution. Also, for example, the supplying may be performed individually, sequentially, or substantially simultaneously from separate piping systems for the highly concentrated inorganic acid solution and the oxidizing solution. So-called single wafer processing, batch processing, and the like may be used. 
     The processing time (the peeling time) can be shortened even more by repeatedly performing the processing of supplying the highly concentrated inorganic acid solution (e.g., the concentrated sulfuric acid solution) and the processing of supplying the oxidizing solution including the oxidizing substances (e.g., electrolyzed sulfuric acid produced by electrolyzing dilute sulfuric acid) a prescribed number of times to the surface of the object W to be cleaned. 
     In such a case, it is unnecessary to provide a process to supply a rinsing fluid to the surface of the object W to be cleaned between the supplying of the highly concentrated inorganic acid solution and the supplying of the oxidizing solution. Therefore, the manufacturing processes can be simplified and the processing time (the peeling time) can be shortened. 
       FIG. 8  is a flowchart illustrating a cleaning method according to another embodiment. 
     In this embodiment, the oxidizing solution and the highly concentrated inorganic acid solution are mixed; and the mixture is supplied to the surface of the object W to be cleaned. 
     First, an oxidizing solution including oxidizing substances (e.g., peroxomonosulfuric acid and peroxodisulfuric acid) is produced by electrolyzing a dilute sulfuric acid solution (step S 10 ). In such a case, the oxidizing substances can be produced efficiently by making the sulfuric acid concentration of the dilute sulfuric acid not less than 30 weight percent and not more than 70 weight percent. 
     Then, the oxidizing solution and the highly concentrated inorganic acid solution are mixed to produce a cleaning liquid (step S 11 ). At this time, the inorganic acid concentration and the amount of the oxidizing substances in the cleaning liquid are appropriately adjusted. Examples of the highly concentrated inorganic acid solution include an inorganic acid solution having, for example, an inorganic acid concentration not less than 90 weight percent. For example, a concentrated sulfuric acid solution having a sulfuric acid concentration not less than 90 weight percent, etc., may be used. 
     Continuing, the temperature of the produced cleaning liquid is adjusted (step S 12 ). Although such a temperature adjustment is not always necessary, it is favorable for the temperature of the cleaning liquid to be adjusted to be not less than 100° C. and not more than 110° C. as described above. The temperature adjustment can be performed on the oxidizing solution and the highly concentrated inorganic acid solution prior to mixing. 
     Then, the cleaning liquid (the mixed liquid of the highly concentrated inorganic acid solution and the oxidizing solution) is supplied to the surface of the object W to be cleaned (step S 13 ). The supplying may be performed from a dispense unit and the like for each of the objects W to be cleaned and by immersing in the cleaning liquid. So-called single wafer processing, batch processing, and the like may be used. 
     In this embodiment as illustrated in  FIG. 7  and  FIG. 8 , dilute sulfuric acid solution is electrolyzed. Therefore, the electrolysis efficiency is high and more oxidizing substances can be produced efficiently. In such a case, the highly concentrated inorganic acid solution and the oxidizing solution are mixed after the oxidizing substances are produced (after the electrolysis). Therefore, the electrolysis efficiency is not affected. 
     Also, processing using a cleaning liquid having a high concentration of inorganic acid is possible by using the highly concentrated inorganic acid solution, or processing on the surface of the object W to be cleaned is possible with a high-concentration inorganic acid. 
     Therefore, the processing time (the peeling time) can be shortened drastically because processing (cleaning) can be performed with a high concentration of an inorganic acid such as sulfuric acid and a large amount of oxidizing substances. 
     While a high-speed operation semiconductor device is manufactured by implanting an impurity with a high dose, an altered layer is formed in the surface of the resist by the implanting of the impurity with the high dose. The resist having such an altered layer does not peel easily; and the desired peeling margin unfortunately cannot be obtained. 
     According to this embodiment, a solution including a highly concentrated inorganic acid and a large amount of oxidizing substances can be supplied to the surface of the object W to be cleaned. Therefore, the peelability of a resist can be increased even in the case where an altered layer is formed in the resist. 
     A heat of reaction can be generated by mixing the highly concentrated inorganic acid solution with an oxidizing solution, which also is a low-concentration inorganic acid solution, prior to supplying to the object W to be cleaned or on the object W to be cleaned. Therefore, the temperature increase of the components of the cleaning system can be suppressed; and the reactivity of the oxidizing substances can be increased by increasing the temperature of the mixed liquid. As a result, the processing time (the peeling time) can be shortened even more. 
     A method for manufacturing a microstructure according to this embodiment will now be described. 
     Examples of a method for manufacturing a microstructure include, for example, a method for manufacturing a semiconductor device. Here, the manufacturing processes of the semiconductor device include the so-called front-end processes such as the processes that form a pattern on a substrate (wafer) surface by film formation, resist coating, exposing, developing, etching, resist removal, etc., the inspection processes, cleaning processes, heat treatment processes, impurity introduction processes, diffusion processes, planarizing processes, etc. The so-called back-end processes include the assembly processes of dicing, mounting, bonding, encapsulation, etc., the functional and reliability inspection processes, etc. 
     In such a case, the resist removal (peeling) can be performed rapidly by using, for example, the cleaning method and the cleaning system described above in the resist removal process. Known technology may be applied for the processes other than those of the cleaning method and the cleaning system according to this embodiment described above, and therefore a detailed description thereof is omitted. 
     Although a method for manufacturing a semiconductor device is illustrated as one example of the method for manufacturing the microstructure, the method for manufacturing the microstructure is not limited thereto. For example, applications are possible in fields such as liquid crystal display devices, phase shift masks, micromachines in MEMS fields, precision optical components, etc. 
     In the cleaning system described above, it is not always necessary to provide a configuration to circulate the solution. As illustrated in  FIG. 9 , the solution used in the cleaning processing unit  12  may be recovered by the returning tank  63  with contaminants and the like and then subsequently discharged outside the system via the discharge piping line  75 . 
     Such processing may be used not only to remove a resist made of an organic substance, but also to similarly remove metal impurities, particles, and dry etching residue. 
     A robot may be provided to transfer the objects to be cleaned. Each of the tank  60  retaining the dilute sulfuric acid solution and the tank  51  retaining the highly concentrated inorganic acid solution may be connected to a line of a factory to automatically replenish the solution. A rinse bath may be provided for rinsing of the object to be cleaned after removing the contaminants. Such a rinse bath may include an overflow control device and a temperature control device using an in-line heater. It is suitable to use quartz as the material quality of the rinse bath. 
     However, it is unnecessary to provide a process to supply a rinsing fluid to the surface of the object to be cleaned between the supplying of the highly concentrated inorganic acid solution (e.g., the concentrated sulfuric acid solution) and the supplying of the oxidizing solution (e.g., the electrolyzed sulfuric acid produced by electrolyzing dilute sulfuric acid). It is sufficient to repeatedly perform the processing of supplying the highly concentrated inorganic acid solution (e.g., the concentrated sulfuric acid solution) to the object W to be cleaned and the processing of supplying the oxidizing solution including the oxidizing substances (e.g., the electrolyzed sulfuric acid produced by electrolyzing dilute sulfuric acid) to the object W to be cleaned a prescribed number of times. Therefore, the manufacturing processes can be simplified and the processing time (the peeling time) can be shortened. 
     Hereinabove, embodiments are illustrated. However, the invention is not limited to the descriptions thereof. 
     Design modifications appropriately made by one skilled in the art in regard to the embodiments described above also are included in the scope of the invention to the extent that features of the invention are included. 
     For example, the configurations, dimensions, material qualities, dispositions, etc., of the components of the cleaning systems described above are not limited to those illustrated herein and may be appropriately modified. 
     Further, the components of the embodiments described above may be combined within the extent of feasibility; and such combinations also are included in the scope of the invention to the extent that the features of the invention are included. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modification as would fall within the scope and spirit of the inventions.