Patent Publication Number: US-8980189-B2

Title: Ozone gas supply system

Description:
TECHNICAL FIELD 
     The present invention relates to an ozone gas supply system that includes an ozone generation unit and supplies a stable ozone gas to a plurality of ozone treatment apparatuses, the ozone generation unit having a nitrogen-free ozone generator to which a high purity oxygen gas containing added nitrogen of less than several thousands ppm is supplied as a raw material gas, the ozone generation unit having a function with a plurality of means for outputting an ozone gas. 
     BACKGROUND ART 
     Conventionally, various techniques have been developed, as follows. A raw material gas obtained by adding a nitrogen gas of several thousands ppm or more to an oxygen gas is supplied to an ozone generator to generate a high concentration ozone gas, and this high concentration ozone gas is often used in an ozone treatment process such as formation of an ozone oxide insulating film and ozone washing in the field of semiconductor fabrication. In the field of semiconductor fabrication and the like, in a case of supplying an ozone gas to a multiple ozone treatment apparatus including a plurality of ozone treatment apparatuses, it is generally conceivable to build an ozone gas supply system in which a plurality of ozone generation mechanisms (means) each including an ozone generator, an ozone power source, a flow rate controller (MFC), and the like, are provided corresponding to the plurality of ozone treatment apparatuses, respectively, so that the ozone generation mechanisms independently supply an ozone gas to the corresponding ozone treatment apparatuses. 
     Conventionally, as shown in  FIG. 26 , in order that an ozone generator  71  that includes electrodes  71   a  and  71   b , a dielectric material  71   c , and the like, and that is supplied with power from an ozone power source  72  can generate an ozone gas with an increased efficiency, an ordinary oxygen gas contains a nitrogen gas of about 50 to several thousands ppm, and in a case of a high purity oxygen gas containing less nitrogen (less than 50 ppm), a small amount of a N 2  gas (500 ppm or more) as well as the high purity oxygen gas is added to the interior of the ozone generator. 
     Accordingly, in a case of a N 2  gas of 500 ppm or more is contained in a raw material oxygen gas, high concentration ozone is generated due to a catalytic reaction of a small amount of NO 2  that is generated as a result of a discharge reaction shown in  FIG. 27 . Particularly, adding a nitrogen gas of 500 to 20000 ppm allows ozone to be generated efficiently due to a catalytic reaction of a small amount of nitrogen dioxide that is generated as a result of the discharge. This consequently generates ozone having the highest concentration. It has been verified from experiments that a raw material gas in which the amount of added nitrogen is 500 to 20000 ppm is the optimal condition in terms of ozone generation performance. 
     As shown in (1) to (3) below, the discharge reaction shown in  FIG. 27  achieves generation of high concentration ozone by using raw material oxygen O 2 , photoelectric discharge light, and a catalytic gas of a small amount of NO 2 . 
     (1) Reaction for generating a small amount of NO 2  gas by discharge
         Reaction for ionizing nitrogen molecule
 
N 2   +e→ 2N + 
   Reaction for generating NO 2  
 
2N + +O 2 +M→NO 2  
           (generate a NO 2  gas of several ppm to several tens ppm)   
               

     (2) Generation of an oxygen atom O by a catalytic effect of NO 2  caused by discharge light
         Photodissociation reaction of NO 2  
 
NO 2   +hν→NO+O  
   Oxidation reaction of NO
 
NO+O 2  (raw material oxygen)→NO 2 +O
       

     * In these two reactions, NO 2  acts as a catalyst to generate an oxygen atom. 
     A large amount of oxygen atoms O generated by the reaction (2) react with oxygen gas molecules O 2 , to generate ozone O 3 . 
     (3) Generation of ozone O 3  (three-body collision)
 
R2;O+O 2 +M→O 3 +M
 
     Through (1) to (3) described above, high concentration ozone is generated. 
     However, when a large amount of N 2  gas is contained in the raw material oxygen gas, not only an ozone gas but also NO x  by-product gases, such as a N 2 O 5  gas and N 2 O gas, and nitric acid, are generated as a result of a silent discharge in the ozone generator. Specific formulas of generation of the NO x  by-product gases and nitric acid are as follows.
 
N 2   +e→N   2   *+e→N   2   +hν( 310,316,337,358 nm)
 
     N 2   * ; excitation of nitrogen 
     ultraviolet light by nitrogen gas
 
H 2 O+ e →H+OH+ e  (dissociation of water vapor)
 
N 2   +e→ 2N −   +e  (dissociation of nitrogen molecule)
 
NO 2   +h ν(295 to 400 nm)→NO+O( 3 P)
 
H+O 2 +M→HO 2 +M
 
HO 2 +NO→OH+NO 2  
 
N 2 O 5 ±H 2 O→2HNO 3  
 
OH+NO 2 +M→HNO 3 +M
 
     In this manner, not only the ozone gas but also NO X  by-product gases and nitric acid are generated. 
     When a large amount of NO X  by-product is generated, a NO X  gas component reacts with moisture contained in the raw material gas, to generate a nitric acid (HNO 3 ) cluster (vapor). Thus, an ozonized gas is extracted under a state where a small amount of NO X  gas and nitric acid cluster, together with oxygen and the ozone gas, are mixed. When the small amount of nitric acid cluster is several hundred ppm or more, the following problems are caused. That is, rust of chromium oxide or the like resulting from nitric acid is deposited on an inner surface of a stainless pipe that is an ozone gas outlet pipe. As a result, a metal impurity is mixed into a clean ozone gas. In a reaction gas for a semiconductor manufacturing apparatus, the metal impurity adversely affects fabrication of a semiconductor. Additionally, the small amount of nitric acid cluster thus generated acts as a reaction poisonous substance and adversely affects “an etching process on a silicon oxide film by using ozone” and “washing of a wafer or the like by using ozone water”, which are performed in the semiconductor manufacturing apparatus. 
     In a ozone gas supply system including an ozone generator, an ozone power source, and the like, it is generally conceivable that an ozone generator, an ozone power source, a raw material gas pipe system line, an output gas pipe system line, and the like, are provided, and the number of each of them is equal to the number of system lines included in a multiple ozone treatment apparatus. The raw material gas pipe system line supplies an ozone gas or a raw material gas to the ozone generator via a flow rate adjuster such as an MFC for controlling the flow rate of the ozone gas or the raw material gas. The output gas pipe system line includes an ozone concentration detector and an ozone flow meter. The ozone concentration detector has pressure adjuster, such as an APC, for controlling gas atmosphere pressure in the ozone generator. The ozone concentration detector detects a concentration of the ozone gas outputted from the ozone generator. 
     However, it is impossible to supply high concentration ozonized oxygen with a very small amount of NO X  by-product though the amount of NO X  is large. Additionally, a very large space is required for building an ozone generation system compatible with such a multiple ozone treatment apparatus, and moreover, a still larger system configuration is required for building a system that supplies an ozone gas while coordinately controlling the multiple ozone treatment apparatus. Thus, there are problems of costs, an installation space, and the like, which causes many disadvantages in a practical use. 
     Accordingly, an attempt was made to generate ozone by using only a high purity oxygen gas without any nitrogen gas being contained in the conventional ozone generator. As a result, however, only a small amount ozone was generated. The reason therefor is considered as follows. The oxygen molecule, which constitutes the raw material gas, has a light absorption spectrum (ultraviolet wavelength of 130 to 200 nm) of a continuous spectrum at wavelengths of an ultraviolet light of 245 nm or less. By absorbing excimer light of ultraviolet light of 245 nm or less, the oxygen molecule is dissociated into oxygen atoms, and ozone is generated by three-body collision among the oxygen atom resulting from the dissociation, the oxygen molecule, and a third material, which is known in an excimer lamp or the like that emits ultraviolet rays. However, in a silent discharge under high pressure of one atmospheric pressure or higher, which is used in, for example, an ozone generator based on an oxygen gas, there is no emission of excimer light of ultraviolet light of 245 nm or less. Thus, dissociation into oxygen atoms caused by the silent discharge light and a reaction constant during a reaction process in ozone generation are very small. Therefore, it cannot be considered as a reaction that generates a high concentration ozone gas having a high concentration of several % or higher. 
     Therefore, for supplying ozone to a multiple ozone treatment apparatus, the following ozone gas supply system has been conventionally adopted as disclosed in Patent Document 1, for example. That is, a raw material gas that is a raw material oxygen gas containing a nitrogen gas of several thousands ppm or more, or a raw material gas obtained by forcibly adding a nitrogen gas of several thousands ppm or more to a raw material oxygen gas, is supplied to an ozone generator, to generate high concentration ozone. Additionally, in order to supply an ozone gas to a plurality of ozone treatment apparatuses, the volume of one ozone generator is increased, and a pipe system line that outputs an ozone gas is divided into a plurality of pipes. Thereby, ozone gases each having a predetermined flow rate and a predetermined concentration are stepwisely outputted to a multiple ozone treatment apparatus. 
       FIG. 28  is a block diagram showing an internal configuration of a conventional ozone gas supply system  70 , which can be simulated based on the disclosure of the Patent Document 1. 
     In  FIG. 28 , the ozone gas supply system  70  includes one ozone generator  71 , one ozone power source  72 , one ozone control unit  77 , and one system collective management unit  80 . The ozone control unit  77  has a raw material gas pipe system line that supplies a raw material gas to the ozone generator  71  via a flow rate controller (MFC)  73   a , a flow rate controller (MFC)  73   b , and a pressure meter  62 . The flow rate controller (MFC)  73   a  controls the flow rate of a raw material gas that is supplied from a raw material gas supply port  64   a . The flow rate controller (MFC)  73   b  controls the flow rate of a nitrogen gas that is supplied from a nitrogen gas supply port  64   b  such that the nitrogen gas having a predetermined flow rate is added to the raw material oxygen gas. The pressure meter  62  monitors the pressure of the generator. Additionally, the ozone control unit  77  includes a valve switch  61  and an ozone concentration meter  75 . The valve switch  61  adjusts opening/closing of a valve depending on a pressure fluctuation in the ozone generator  71 . A part of the output gas pipe system line located subsequent to an output pipe in which an ozone flow meter  67  is provided is divided into a plurality of pipes. Furthermore, in the ozone gas supply system  70 , individual ozone gas flow rate controllers (MFC)  68 - 1  to  68 -n are provided to the divided parts of the output gas pipe system line, respectively, so that the ozone gas is independently supplied to a plurality of ozone treatment apparatuses  12 - 1  to  12 -n that are provided corresponding to the individual MFCs  68 - 1  to  68 -n, respectively. An amount of ozone gas exceeding the amount that can be supplied through the individual MFCs  68 - 1  to  68 -n is discharged by a flow rate discharge unit  69 . 
     In an ozone generator disclosed in Patent Document 2, light having a wavelength of the visible light region (visible light of 428 nm to 620 nm) can be emitted (discharged) in a silent discharge caused by an oxygen gas in the ozone generator. A photocatalytic material that absorbs the light having a wavelength of the visible light region which is emitted in the discharge, is applied to a discharge surface of the generator. This causes a raw material oxygen gas to be dissociated due to a photocatalytic effect. A chemical reaction between an oxygen atom resulting from the dissociation and an oxygen molecule of a raw material oxygen generates an ozone gas. 
     PRIOR-ART DOCUMENTS 
     Patent Documents 
     Patent Document 1: Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2009-500855( FIGS. 2 ,  3 , and  5 ) 
     Patent Document 2: International Publication No. WO2005/080263( FIGS. 1 ,  3 ,  4 , and  5 ; Tables 2-(a), (b), and (c)) 
     SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
     The conventional ozone gas supply system for supplying ozone to a multiple ozone treatment apparatus, which is disclosed in the Patent Document 1, has the above-described configuration. In the configuration, a raw material oxygen gas containing nitrogen and moisture is supplied, and an ozone gas is outputted from a single ozone generator  71 , and a pipe system line for the output is divided into distribution pipes. As a result, an active gas containing a by-product substance of a nitrogen oxide, a nitric acid cluster, and an OH radical substance is supplied as the outputted ozone gas. This involves a problem that the supplied ozone gas contains a large amount of metal contamination caused by abnormal heating and corrosion which occur due to a chemical decomposition and a oxidation reaction between the material of the output pipe and the by-product substance of the nitrogen oxidation, the nitric acid cluster, and the OH radical substance. Moreover, in an ozone apparatus including the ozone generator disclosed in the Patent Document 1, it is necessary that an ozone gas is supplied to the multiple ozone treatment apparatus (ozone treatment apparatuses  12 - 1  to  12 -n) with a constant flow rate and at a constant ozone concentration. Only a single ozone supply condition is commonly adopted for supplying ozone to the respective ozone treatment apparatuses. This involves a problem that the flow rate and concentration of the ozone gas cannot be independently controlled and changed for the plurality of ozone treatment apparatuses. 
     Additionally, there is also a problem that the reliability of the supply of the ozone gas is low, because the ozone gas is supplied from the single ozone generator to the multiple ozone treatment apparatus, and therefore if the ozone generator breaks down, the supply of the ozone gas to all the ozone treatment apparatuses is stopped. 
     Moreover, as shown in  FIG. 28 , the ozone generator  71 , the ozone power source  72 , and the gas pipe system are separate. Therefore, an ozone generation part including the ozone generator  71 , the ozone power source  72 , and the gas pipe system occupies a large space. This arises a problem that it is very difficult in practical use to build an ozone gas supply system having a plurality of such ozone generation parts, and also a problem that the maintainability of the ozone generation part is poor. 
     The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a downsized nitrogen-free ozone generation unit and an ozone gas supply system including a plurality of such nitrogen-free ozone generation units, the nitrogen-free ozone generation unit having various functions concerning a process from supply of a raw material gas to generation of ozone, such as an ozone generator, an ozone power source, and a gas pipe system, and also having a function for outputting an ozone gas with an extremely increased quality which is generated by the ozone generator capable of generating an ozone gas having a high purity and a high concentration by using only a high purity oxygen gas in which no nitrogen gas is added to a raw material gas. 
     An object of the present invention is to solve the above-described problems, and provide an ozone gas supply system that includes a nitrogen-free ozone generator in which a photocatalytic material for generating ozone is applied to a discharge surface and that is able to supply an ozone gas to ozone treatment apparatuses with a high reliability. 
     Means for Solving the Problems 
     An ozone gas supply system according to the present invention is an ozone gas supply system that supplies an ozone gas to each of a plurality of ozone treatment apparatuses while controlling the flow rate and concentration of the gas, the ozone gas supply system comprising: a plurality of nitrogen-free ozone generation units, each of the plurality of nitrogen-free ozone generation units including a nitrogen-free ozone generator for generating an ozone gas, in which a photocatalytic material for generating ozone is applied to a discharge surface, an ozone power source for controlling power that is supplied to the nitrogen-free ozone generator, a mass flow controller (MFC) for controlling a flow rate of a raw material gas that is inputted to the nitrogen-free ozone generator, an automatic pressure controller (APC) for automatically controlling internal pressure that is pressure within the nitrogen-free ozone generator, an ozone concentration meter for detecting an ozone concentration value of the ozone gas outputted from the nitrogen-free ozone generator, and an ozone control part for performing an initial operation in which the ozone power source is driven with a predetermined set power amount, and after the elapse of a predetermined time period, performing a PID control on power supplied by the ozone power source based on comparison between an ozone concentration detected by the ozone concentration meter and an ozone concentration that has been set; an ozone gas output flow rate management unit configured to receive a plurality of ozone gas outputs from a plurality of the nitrogen-free ozone generators in the plurality of nitrogen-free ozone generation units, and capable of performing an ozone gas output flow rate control for selectively outputting one or a combination of two or more of the plurality of ozone gas outputs to any of the plurality of ozone treatment apparatuses by performing an opening/closing operation on a plurality of ozone gas control valves provided in the ozone gas output flow rate management unit; and an ozone gas output flow rate management unit control part for, based on a process ozone gas event signal supplied from the plurality of ozone treatment apparatuses, controlling the ozone gas output of each of the plurality of nitrogen-free ozone generation units and causing the ozone gas output flow rate management unit to perform the ozone gas output flow rate control. 
     Effects of the Invention 
     The ozone gas supply system according to the present invention includes the ozone gas output flow rate management unit capable of performing the ozone gas output flow rate control for selectively outputting one or a combination of two or more of the plurality of ozone gas outputs to any of the plurality of ozone treatment apparatuses by performing the opening/closing operation on the plurality of ozone gas control valves. 
     Accordingly, by supplying each of the plurality of ozone gas outputs to each corresponding ozone treatment apparatus among the plurality of ozone treatment apparatuses, the gas flow rate and the concentration of the ozone gas supplied to the plurality of ozone treatment apparatuses can be independently controlled. 
     Additionally, by supplying a combination of two or more ozone gas outputs to one ozone treatment apparatus, the ozone gas can be supplied with various gas flow rates and various concentrations. 
     Moreover, even when a trouble occurs in a part of the plurality of nitrogen-free ozone generation units, the other ozone generation units that are normally operating are able to supply the ozone gas to any of the plurality of ozone treatment apparatuses. Therefore, an ozone gas supply with a high reliability is achieved. 
     These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       [ FIG. 1 ] A block diagram showing a configuration of a nitrogen-free ozone generator employed in embodiments of the present invention. 
       [ FIG. 2 ] A graph showing output ozone concentration characteristics of ozone obtained by the nitrogen-free ozone generator shown in  FIG. 1 . 
       [ FIG. 3 ] A diagram schematically showing a mechanism of dissociation of an oxygen molecule into oxygen atoms caused by an oxygen molecule and a photocatalyst during ozone generation. 
       [ FIG. 4 ] A diagram schematically showing a mechanism of generation of ozone caused by three-body collision among an oxygen atom and an oxygen molecule. 
       [ FIG. 5 ] A block diagram showing a configuration of an ozone gas supply system including a nitrogen-free ozone generator according to an embodiment 1 of the present invention. 
       [ FIG. 6 ] An explanatory diagram showing an internal configuration of an ozone gas output flow rate management unit of the ozone gas supply system shown in  FIG. 5 . 
       [ FIG. 7 ] An explanatory diagram schematically showing a display state of a main control panel of the ozone gas supply system according to the embodiment 1. 
       [ FIG. 8 ] A block diagram showing a configuration of an ozone control part included in a nitrogen-free ozone generation unit shown in  FIG. 5 . 
       [ FIG. 9 ] An explanatory diagram schematically showing memory contents of a data memory included in the nitrogen-free ozone generation unit shown in  FIG. 5 . 
       [ FIG. 10 ] A graph showing an output concentration control waveform obtained in a case where an output concentration control is performed on the nitrogen-free ozone generation unit shown in  FIG. 5 . 
       [ FIG. 11 ] A graph showing received power of an ozone power source included in one nitrogen-free ozone generation unit, and ozone concentration characteristics of ozone generated in an ozone generator. 
       [ FIG. 12 ] A circuit diagram showing details of an internal configuration of an ozone power source provided in a nitrogen-free ozone generation unit according to an embodiment 2. 
       [ FIG. 13 ] A perspective view schematically showing a combined structure of the nitrogen-free ozone generation unit according to the embodiment 2. 
       [ FIG. 14 ] An explanatory diagram showing an internal configuration of an ozone gas output flow rate management unit according to an embodiment 3, which is included in the ozone gas supply system shown in  FIG. 5 . 
       [ FIG. 15 ] A perspective view schematically showing a combined structure of a nitrogen-free ozone generation unit according to the embodiment 3. 
       [ FIG. 16 ] A block diagram showing a configuration of an ozone gas supply system according to an embodiment 4 of the present invention. 
       [ FIG. 17 ] A perspective view schematically showing a combined structure of a nitrogen-free ozone generation unit according to the embodiment 4. 
       [ FIG. 18 ] A block diagram showing a configuration of an ozone gas supply system according to an embodiment 5 of the present invention. 
       [ FIG. 19 ] A perspective view schematically showing a combined structure of a nitrogen-free ozone generation unit according to the embodiment 5. 
       [ FIG. 20 ] A block diagram showing a configuration of an ozone gas supply system according to an embodiment 6 of the present invention. 
       [ FIG. 21 ] A perspective view schematically showing a combined structure of a nitrogen-free ozone generation unit according to the embodiment 6. 
       [ FIG. 22 ] A block diagram showing a configuration of an ozone gas supply system according to an embodiment 7 of the present invention. 
       [ FIG. 23 ] A perspective view schematically showing a combined structure of a nitrogen-free ozone generation unit according to the embodiment 7. 
       [ FIG. 24 ] An explanatory diagram schematically showing a conventional configuration corresponding to the ozone generation unit according to the embodiment 2. 
       [ FIG. 25 ] An explanatory diagram showing the relationship between a dew point of a raw material gas and a moisture content in the raw material gas. 
       [ FIG. 26 ] A diagram showing a configuration of a conventional ozone generator, which is illustrated as a reference example. 
       [ FIG. 27 ] An explanatory diagram schematically showing, as a reference example, details of ozone generation that is achieved by a conventional ozone generator in combination with a raw material oxygen gas containing added nitrogen. 
       [ FIG. 28 ] A block diagram showing an internal configuration of a conventional ozone gas supply system. 
     
    
    
     EMBODIMENT FOR CARRYING OUT THE INVENTION 
     &lt;Nitrogen-Free Ozone Generator&gt; 
     A nitrogen-free ozone generator employed in an ozone gas supply system according to embodiments of the present invention will be described with reference to  FIGS. 1 to 4 .  FIG. 1  is a block diagram showing a configuration of a gas system line including a nitrogen-free ozone generator as a main part thereof. 
     In a narrow sense, an ozone generator using a high purity oxygen raw material gas in which the amount of added nitrogen is 10 ppm or more and 1000 ppm or less is called “nitrogen-suppressed ozone generator”, while an ozone generator using a high purity oxygen raw material gas in which the amount of added nitrogen is less than 10 ppm is called “nitrogen-free ozone generator”. In this specification, ozone generators using a high purity oxygen raw material gas in which the amount of added nitrogen is 1000 ppm or less, including the “nitrogen-suppressed ozone generator”, are collectively called the “nitrogen-free ozone generator” in a broad sense. 
       FIG. 2  is a diagram showing ozone concentration characteristics of ozone obtained by the nitrogen-free ozone generator  1  shown in  FIG. 1 .  FIG. 3  is a diagram schematically showing a mechanism of dissociation of an oxygen molecule into oxygen atoms caused by an oxygen molecule and a photocatalyst. 
       FIG. 4  is a diagram schematically showing a mechanism of generation of ozone caused by three-body collision among an oxygen atom and an oxygen molecule, which occurs in the nitrogen-free ozone generator  1 . In this specification and the drawings, the same reference sign denotes the same or similar part. 
     The nitrogen-free ozone generator according to the present invention is effective in a case where there is a need for a high concentration ozone gas having a concentration of 200 g/m 3  or higher, a clean ozone gas for use in a semiconductor manufacturing apparatus, a washing apparatus, or the like, a nitrogen-free ozone gas from which a by-product such as NO X  or an OH radical substance is eliminated, and an apparatus having a high efficiency of ozone generation. 
     In  FIG. 1 , a raw material supply system  99  that supplies oxygen (raw material gas) having a purity of 99.99% or higher includes a high purity oxygen cylinder  991 , a pressure reducing valve  992 , and an open/close valve  993 . The raw material supply system  99  supplies an oxygen gas  994  to the outside. The oxygen gas  994 , serving as a raw material gas  995 , is supplied to the nitrogen-free ozone generator  1  via an MFC  3 . In the nitrogen-free ozone generator  1 , electrodes  1   a  and  1   b , a dielectric material  1   c , and a photocatalyst  1   d  are provided. The two electrodes  1   a  and  1   b  are opposed to each other. The dielectric material  1   c  is provided on a surface of the electrode  1   a  opposed to the electrode  1   b . The photocatalyst  1   d  is applied to each of the surfaces of the dielectric material  1   c  and the electrode  1   b  opposed to each other. 
     A gas filter for removing moisture is provided, by which a moisture content in high purity oxygen that is supplied from the cylinder is reduced to 0.1 ppm or less, though not shown in  FIG. 1 . The oxygen gas  994  serving as the raw material gas  995  is supplied to the nitrogen-free ozone generator  1 , through the flow rate adjuster (MFC)  3  that adjusts the amount of nitrogen-free and moisture-free raw material gas in which a nitrogen content and a moisture content are suppressed as low as possible. 
     Here, even when oxygen having a purity of 99.99% or higher and more specifically high purity oxygen having a purity of 99.995% is adopted as the oxygen gas, N 2  of 151×10 2  ppb (that is, 15 ppm) is contained and thus N 2  is unavoidablly mixed. However, in order to obtain an ozone gas having a high purity, it is desirable to use a raw material oxygen gas having a smaller amount of mixed N 2 . 
       FIG. 3  schematically shows an electronic configuration structure of a solid of a photocatalyst in accordance with the solid state electron theory (band gap theory) in a silent discharge, and a mechanism of dissociation of an oxygen molecule. A description will be given to the operation and action of the function of a photocatalytic reaction caused by a photocatalytic material with discharge light. A photocatalyst is applied to a wall surface of an electrode or the like in a silent discharge space, and the electronic configuration structure of a band gap of the photocatalyst optically absorbs silent discharge light having energy equal to or greater than the band gap, as shown in  FIG. 3 . As a result, in the photocatalyst, an electron is jumped out from a valence band and transferred (pumped) to a conduction band. 
     In the valence band from which the electron is transferred, the positive hole (hole) occurs. The electron having been transferred into the conduction band moves to the periphery, or the electron is discharged to a discharge region. Thus, the lifetime of the electron ends. That is, the lifetime of the electron having been transferred into the conduction band is very short, several tens psec. Since the positive hole in the valence band continuously exists unless the electron having been transferred into the conduction band reruns due to recombination, the lifetime of the positive hole is long, 200 to 300 nsec. When the photocatalyst in the excited state where the positive hole exists is brought into quantum contact with an oxygen molecule, the electron shared with the oxygen molecule is stolen, thus physically dissociating the oxygen molecule (phenomenon of adsorption and dissociation of oxygen by the photocatalyst [oxidation reaction]). 
     On the other hand, in a photocatalyst with a band gap of 2.0 eV to 2.9 eV, the light absorption wavelength is 428 nm to 620 nm, which is visible light. In either of a case of oxygen containing no nitrogen and a case of oxygen and an argon gas, light having a light wavelength within the visible light region can be emitted (discharged) in a silent discharge. Therefore, it has been revealed that when the photocatalyst with a band gap of 2.0 eV to 2.9 eV is applied to an electrode surface (wall surface) of an ozone generator, the photocatalyst absorbs discharge light emitted in the silent discharge in either of a case of oxygen containing no nitrogen and a case of oxygen and an argon gas. As a result, the photocatalyst is excited, and oxygen can be dissociated due to the adsorption and dissociation caused between the excited photocatalyst and the oxygen gas. Moreover, as shown in the schematic diagram of  FIG. 4 , due to the three-body collision among the oxygen atom resulting from the dissociation, the supplied oxygen molecule (raw material oxygen gas), and a third material, the binding action is accelerated on the photocatalyst ld (wall M). Thus, ozone is generated. 
     In a silent discharge in the ozone generator with use of a nitrogen gas, light having a light wavelength in the ultraviolet region (ultraviolet light of 413 nm to 344 nm) can be emitted (discharged). 
     Therefore, in the nitrogen-free ozone generator  1  of the present application in which a photocatalytic material is applied to a discharge surface, a photocatalyst with a band gap of 3.0 eV to 3.6 eV can be optically excited. The photocatalyst thus excited is able to dissociate an oxygen molecule, and thereby an ozone gas can be generated in a silent discharge including nitrogen. 
     In the silent discharge including nitrogen, the photocatalyst with a band gap of 3.0 eV to 3.6 eV can be optically excited. In the silent discharge with oxygen, the photocatalyst with a band gap of 2.0 eV to 2.9 eV can be optically excited. Therefore, by adding a small amount of nitrogen (a suppressed amount of nitrogen) to oxygen, the photocatalyst provided on a dielectric material or an electrode in the discharge region acquires an allowable band gap ranging from 2.0 eV to 3.6 eV. This enables the reaction of ozone generation to be accelerated using discharge light (ultraviolet light) with not only oxygen but also nitrogen. That is, containing a N 2  gas can enhance the effect of an ozone generation function obtained by the invention of the present application. 
     The photocatalytic material applied to the discharge surface of the ozone generator is regarded as one kind of semiconductor. The photocatalytic material is a substance having a band gap unique to the semiconductor. The band gap has a greater value than a band gap of an ordinary semiconductor substance. Normally, the photocatalytic material is a metal oxide substance in which a metal is bound to an oxygen atom. Among such metal oxide substances, a metal oxide substance having a crystal structure with an oxygen defect in which a metal atom and an oxygen atom are not completely bound, is considered as a substance having a semiconductor effect and a photocatalytic effect. 
     For example, as for iron oxide (Fe 2 O 3 ) which is a photocatalytic material disclosed in the Patent Document 2, to be exact, the iron oxide serving as a photocatalytic material is Fe 2 O X . The iron oxide in which the number X of bound oxygen is less than three (X&lt;3) has a crystal structure that serves as a photocatalytic material. That is, although at most three oxygen atoms can be bound to two iron atoms, a crystal structure that can serve as a photocatalytic material is a structure having an oxygen defect portion. 
     In the nitrogen-free ozone generator employed in the ozone gas supply system according to the present invention, the photocatalytic material is applied to the discharge surface, and in order to enhance the photocatalytic effect and thereby generate high concentration ozone, the discharge surface through which the oxygen gas in the discharge passes is designed such that the surface area of the photocatalytic material applied to the discharge surface is considerably increased. 
     Therefore, in the nitrogen-free ozone generator  1 , even though a small amount of (several ppm or less) moisture is contained in the raw material gas, the moisture is likely to be adsorbed onto a surface of the photocatalytic material applied to the discharge surface, because the photocatalytic material has an increased surface area. Causing a discharge under a state where the moisture is adsorbed dissociates the moisture into an H atom and an OH molecule. The H atom and OH molecule resulting from the dissociation are bound to an oxygen defect portion of the photocatalytic material. In the photocatalytic material to which the H atom and OH molecule are bound, the photocatalytic effect is deteriorated or lost. This results in a considerable loss of the ozone generation ability. 
     As described above, in the nitrogen-free ozone generator  1  employed in the ozone gas supply system according to the present invention, even a small amount of (several ppm or less) moisture contained in the raw material oxygen causes a deterioration in the performance of the nitrogen-free ozone generator  1 . Desirably, therefore, as means for removing a small amount of moisture contained in the raw material oxygen, a moisture removal filter for removing a small amount of moisture and thereby suppressing a moisture content to 300 ppb (0.3 ppm) or less is provided in a raw material oxygen gas supply port. 
     &lt;Embodiment 1&gt; 
     Hereinafter, an embodiment 1 of the present invention will be described with reference to  FIGS. 5 to 10 . The outline of  FIGS. 5 to 10  is as follows.  FIG. 5  is a block diagram showing a configuration of an ozone gas supply system according to the embodiment 1 of the present invention.  FIG. 6  is an explanatory diagram showing an internal configuration of an ozone gas output flow rate management unit of the ozone gas supply system shown in  FIG. 5 .  FIG. 7  is an explanatory diagram schematically showing a display state of a main control panel of the ozone gas supply system according to the embodiment 1.  FIG. 8  is a block diagram showing a configuration of an ozone control part included in a nitrogen-free ozone generation unit shown in  FIG. 5 .  FIG. 9  is an explanatory diagram schematically showing memory contents (for example, initial conditions for the ozone generation unit to control the concentration and flow rate) of a data memory included in the ozone generation unit shown in  FIG. 5 .  FIG. 10  is a graph showing an output concentration control waveform obtained in a case where an output concentration control is performed on the nitrogen-free ozone generation unit  7  shown in  FIG. 5 . 
     (Overall Configuration) 
     As shown in  FIG. 5 , an ozone gas supply system  10  has n (≧2) nitrogen-free ozone generation units  7 - 1  to  7 -n included therein. In the following, among the nitrogen-free ozone generation units  7 - 1  to  7 -n, the nitrogen-free ozone generation unit  7 - 2  will be taken as a representative, and an internal configuration thereof will be described mainly with reference to  FIG. 5 . 
     The interior of the nitrogen-free ozone generator  1  included in the nitrogen-free ozone generation unit  7 - 2  is filled with a gas containing an oxygen gas. An ozone power source  2  provided in the nitrogen-free ozone generation unit  7 - 2  applies high frequency high voltages HV and LV across the electrodes in the nitrogen-free ozone generator  1 , thus causing a dielectric-barrier discharge (silent discharge) between these electrodes. Thereby, due to the discharge, a gas existing in the discharge space produces an ozone gas. The ozone power source  2  includes a converter  2   a , an inverter  2   b , and a high voltage circuit part  2   c , which will be detailed later. 
     In this embodiment, as a structure of the nitrogen-free ozone generator  1 , an ozone generator having a structure that employs the silent discharge has been described as a representative. Here, as a function for generating ozone, there may be also adopted an ozone generator having a structure that employs a creeping discharge or a glow discharge without addition of any nitrogen, or an ozone generator having a structure that employs a super-high frequency or a microwave discharge. 
     In order to obtain a stable output of ozone, it is important to limit gas types of the raw material gas that is supplied to the ozone generator, and to provide a function for constantly adjusting environmental conditions such as a flow rate value, the gas pressure in the ozone generator, the temperature of water for cooling the electrodes, the amount of water, and the like. 
     Desirably, a high purity oxygen gas for generating an ozone gas such as an oxygen gas or a high purity oxygen raw material gas containing a small amount of nitrogen gas less than 10 ppm (these high purity oxygen raw material gases are collectively called “nitrogen-free oxygen raw material gas” in a narrow sense) is supplied to the raw material gas supply port  14 . These raw material gases contain a small amount of impurities, an impure gas, and moisture which are unnecessary for generating the ozone gas. The moisture and the impurities contained in the raw material gas are adsorbed to the discharge surface of the nitrogen-free ozone generator  1 , to deteriorate the performance of the photocatalytic material of the nitrogen-free ozone generator  1 . Accordingly, in order to remove a small amount of the impurities, the impure gas, and the moisture contained in the raw material gas, it is desirable that, for example, a gas filter and a moisture removal filter for removing moisture contained in a gas are provided in an inlet for the raw material gas. 
     A raw material gas having a predetermined raw material gas flow rate Q is obtained through a raw material gas supply port  14  of the ozone gas supply system  10  and a raw material gas supply port  14 - 2  of the nitrogen-free ozone generation unit  7 - 2 , and supplied to the nitrogen-free ozone generator  1  with a constant flow rate through the gas flow rate controller (MFC)  3 . 
     An ozone generator system is equipped with, as means for keeping the pressure in the nitrogen-free ozone generator  1  constant, means for detecting a gas pressure in the generator and a function for finely adjusting the amount of ozone gas outputted by the generator thus detected and thereby keeping the pressure in the nitrogen-free ozone generator  1  constant. One of methods therefor is implemented by an automatic pressure adjuster (APC)  4  for automatically adjusting the pressure in the generator to a predetermined pressure. The automatic pressure adjuster (APC)  4  is provided in an ozone gas output pipe gas line of the ozone generator. 
     A specific configuration of the ozone gas output pipe gas line is as follows. An ozone gas generated in the nitrogen-free ozone generator  1  passes through a gas filter  51  for removing impurities and foreign substances therefrom, and then through an ozone concentration meter  5  and the automatic pressure adjuster (APC)  4 . Thereby, the ozone (ozonized oxygen) gas having a predetermined ozone concentration C is continuously outputted from an ozone gas output port  15 - 2  to the outside of the nitrogen-free ozone generation unit  7 - 2 . 
     Sometimes, an ozone gas flow rate controller (MFC) for keeping the flow rate of the output ozone gas constant is provided in the ozone gas output pipe gas line. In this embodiment, no ozone-gas flow rate controller (MFC) is provided. 
     Accordingly, a flow rate Qx of the output ozone gas is the sum of an ozone flow rate Qc and a flow rate Qn. The ozone flow rate Qc is for the ozone obtained as a result of conversion from the raw material gas having the flow rate Q. The flow rate Qn is for raw material oxygen that has not been converted from the raw material gas having the flow rate Q. That is, the flow rate Qx of the ozone (ozonized oxygen) gas is determined by the formula (1): {Qx=F(Q,C) . . . (1)}, which is based on the flow rate Q and the ozone concentration C of a raw material (oxygen) gas. By the gas flow rate controller (MFC)  3 , the flow rate of the raw material gas supplied to the ozone generator is controlled to a constant value. 
     The APC  4  controls the pressure of the ozone gas flowing in an output pipe path for the ozone gas of the nitrogen-free ozone generator  1 , and thereby automatically controls the gas pressure of the nitrogen-free ozone generator  1  to a constant value. 
     The nitrogen-free ozone generation unit  7 - 2  is configured as a package unit that consitutes one unit in which a plurality of function means are assembled together. The plurality of function means include, for example, the nitrogen-free ozone generator  1  having means for generating the ozone gas, the ozone power source  2  having means for supplying predetermined power to the ozone gas, the MFC  3  having means for controlling the flow rate of the supplied raw material gas to a constant value, the APC  4  having means for controlling a pressure value of the pressure in the nitrogen-free ozone generator  1  to a constant value, the gas filter  51  having means for trapping the impurity gas in the output ozone gas, and the ozone concentration meter  5  having means for detecting an output ozone concentration value. All the ozone generation units  7 - 1  to  7 -n have identical configurations (only the configuration of  7 - 2  is shown), and have the internal configuration that has been described with regard to the ozone generation unit  7 - 2  as a representative. 
     Each of the nitrogen-free ozone generation units  7  (ozone generation units  7 - 1  to  7 -n) has a water leakage sensor  6  provided on a bottom surface thereof, to monitor presence or absence of water leakage in each ozone generation unit  7 . More specifically, information obtained from the water leakage sensor  6  is supplied to an EMO circuit (emergency stop circuit)  81  in an system collective management unit  8 , so that the monitoring can be made under control of a system management control part  84 . 
     The system collective management unit  8  provided in the ozone gas supply system  10  receives detection information from each of an exhaust gas sensor  23  and an ozone leak sensor  24 . The exhaust gas sensor  23  monitors and keeps a negative pressure state of the interior of the apparatus by vacuuming the interior through an exhaust duct  11 . When the system collective management unit  8  receives an abnormal exhaust or an abnormal leakage from the exhaust gas sensor  23  or the ozone leakage sensor  24 , the system collective management unit  8  causes the system management control part  84  to supply nitrogen-free ozone generation unit control signals  86 - 1  to  86 -n that are stop instructions to all the nitrogen-free ozone generation units  7 - 1  to  7 -n, to thereby stop operations of the nitrogen-free ozone generation units  7 - 1  to  7 -n. 
     Also, the system management control part  84  provided in the system collective management unit  8  receives process ozone gas event signals  16 - 1  to  16 -n from ozone treatment apparatuses  12 - 1  to  12 -n through a user information I/F  83 . The process ozone gas event signals  16 - 1  to  16 -n include a request ozone flow rate Qs 12  and a request ozone concentration Cs 12 . 
     Based on instructions indicated by the process ozone gas event signals  16 - 1  to  16 -n, the system management control part  84  outputs the nitrogen-free ozone generation unit control signals  86 - 1  to  86 -n to the nitrogen-free ozone generation units  7 - 1  to  7 -n, and also outputs a control signal S 8  to an ozone gas output flow rate management unit  9 . 
     As a result, the flow rate and concentration of an ozone gas outputted from each of the nitrogen-free ozone generation units  7 - 1  to  7 -n are controlled, and additionally the opening/closing of an ozone gas control valve  9 a and the like provided in the ozone gas output flow rate management unit  9  is controlled. Thereby, an ozone gas having a gas flow rate and a gas concentration in accordance with the instructions of the process ozone gas event signals  16 - 1  to  16 -n can be supplied to the ozone treatment apparatuses  12 - 1  to  12 -n. In the following, the system collective management unit  8  will be described in more detail. 
     The system collective management unit  8  includes the EMO circuit  81  for stopping the apparatus in emergency, a unit information I/F  82 , the user information I/F  83 , the system management control part  84 , and a main control panel  85 . 
     As described above, the EMO circuit  81  is a circuit for monitoring a system error signal obtained from the water leakage sensor  6  of each nitrogen-free ozone generation unit  7 . To be more specific, when the EMO circuit  81  receives detection information indicating detection of abnormal water leakage from the water leakage sensor  6 , the EMO circuit  81  transmits this information to the system management control part  84 . Then, the system management control part  84  supplies the ozone generation unit control signal  86  (any one of the ozone generation unit control signals  86 - 1  to  86 -n) to the nitrogen-free ozone generation unit  7  corresponding to the water leakage sensor  6  that has detected the abnormal water leakage. Thus, the nitrogen-free ozone generation unit  7  is stopped. 
     The unit information I/F  82  receives unit information signals  17 - 1  to  17 -n from the nitrogen-free ozone generation units  7 - 1  to  7 -n. 
     As described above, the user information I/F  83  receives the process ozone gas event signals  16 - 1  to  16 -n (indicating the request ozone flow rate Qs 12 , the request ozone concentration Cs 12 , operation information Y, an apparatus No., and the like), which are command signals, from the ozone treatment apparatuses  12 - 1  to  12 -n. 
     The system management control part  84  outputs the control signal S 8  which is a command for controlling the opening/closing of the ozone gas control valves ( 9   a ,  9   b ,  9   c ,  9   ab ,  9   bc ,  9   ca ) provided in the ozone gas output flow rate management unit  9 , and thereby collectively controls the parts within the ozone gas output flow rate management unit  9 . The system management control part  84  also receives information from the main control panel  85 . 
     As shown in  FIG. 5 , the ozone gas supply system  10  includes a cooling water inlet port  13 A and a cooling water outlet port  13 B. Cooling water is introduced from an external cooling system (not shown) through the cooling water inlet port  13 A and cooling water inlet ports  13   a - 1  to  13   a -n into the nitrogen-free ozone generation units  7 - 1  to  7 -n. The water having served for the cooling is outputted from the nitrogen-free ozone generation units  7 - 1  to  7 -n to the outside through cooling water outlet ports  13   b - 1  to  13   b -n and the cooling water outlet port  13 B. 
     The amount and temperature of cooling water supplied from the external cooling system is controlled at constant values, though not illustrated herein. 
     The ozone gas supply system  10  has the raw material gas supply port  14 . The raw material gas is introduced from the outside into the nitrogen-free ozone generation units  7 - 1  to  7 -n through the raw material gas supply port  14  and the raw material gas supply ports  14 - 1  to  14 -n. At an external inlet for the raw material gas, a gas filter for removing a small amount of impurities, an impure gas, and moisture contained in the raw material gas is provided, though not illustrated herein, to thereby control and stabilize the purity of the raw material gas. 
     The ozone gas output ports  15 - 1  to  15 -n of the nitrogen-free ozone generation units  7 - 1  to  7 -n are connected to the ozone gas output flow rate management unit  9  in the ozone gas supply system  10 , and the ozone gas is outputted from the ozone gas output flow rate management unit  9  through ozone gas output ports  25 - 1  to  25 -n to the outside of the ozone gas supply system  10 . 
     The process ozone gas event signals  16 - 1  to  16 -n outputted from the n ozone treatment apparatuses  12 - 1  to  12 -n are inputted to the system management control part  84  via the user information I/F  83 . The process ozone gas event signal  16  ( 16 - 1  to  16 -n) indicates the request ozone flow rate Qs 12 , the raw material gas set concentration Cs 12 , the operation information Y, and the like. The system management control part  84  outputs the nitrogen-free ozone generation unit control signals  86 - 1  to  86 -n for controlling the nitrogen-free ozone generation units  7 - 1  to  7 -n based on the process ozone gas event signals  16 - 1  to  16 -n. 
     The nitrogen-free ozone generation units  7 - 1  to  7 -n include nitrogen-free ozone generation unit control panels  85 - 1  to  85 -n. The unit information signals  17 - 1  to  17 -n are transmitted from the nitrogen-free ozone generation units  7 - 1  to  7 -n to the system management control part  84  via the unit information I/F  82  of the system collective management unit  8 . The unit information signal  17  ( 17 - 1  to  17 -n) is an information signal indicating the breakdown and an operating/stopping state of the ozone generator  1  included in each nitrogen-free ozone generation unit  7 . 
     The operation information Y included in the process ozone gas event signal  16  corresponds to a user information signal indicating the breakdown and an operating/stopping state of each ozone treatment apparatus  12  ( 12 - 1  to  12 -n) and, as described above, is outputted to the user information I/F  83  of the system collective management unit  8 . 
     Each of the nitrogen-free ozone generation units  7 - 1  to  7 -n includes an ozone control part  19 . The ozone control part  19  is a control part, as will be detailed later, that receives a set flow rate Qs and a detected flow rate Q for the flow rate of the raw material gas, a set pressure Ps and a detected pressure P for the pressure of the ozone generator  1 , and the ozone concentration C of the ozone outputted from each nitrogen-free ozone generation unit  7 , and that controls the ozone power source  2  to thereby control the ozone concentration, the gas flow rate, and the like, of the ozone gas generated in the nitrogen-free ozone generator  1 . The ozone control part  19  communicates signals with the ozone concentration meter  5 , the MFC  3 , the APC  4 , and the ozone power source  2 . 
     (Control of Ozone Gas Output Flow Rate Management Unit) 
     As shown in  FIG. 6 , the ozone gas output flow rate management unit  9  has ozone gas input ports  29 - 1  to  29 -n corresponding to output parts of the nitrogen-free ozone generation units  7 - 1  to  7 -n, respectively, and ozone gas output ports  39 - 1  to  39 -n corresponding to input parts of the ozone treatment apparatuses  12 - 1  to  12 -n, respectively. Ozone gas on/off valves  22 - 1  to  22 -n are interposed between the ozone gas output ports  39 - 1  to  39 -n (ozone gas output ports  25 - 1  to  25 -n) and the ozone treatment apparatuses  12 - 1  to  12 -n. At a time of supplying the ozone gas, the ozone treatment apparatuses  12 - 1  to  12 -n open the ozone gas on/off valves  22 - 1  to  22 -n. This ozone gas supply system  10  is configured as a system including n ozone gas output ports, namely, the ozone gas output ports  39 - 1  to  39 -n. However, if the number of ozone treatment apparatuses at the user side is less than n, a pipe fitting of the ozone gas output port  39  not serving for the output may be capped so that an output of gas is plugged. 
     The ozone gas output flow rate management unit  9  is provided therein with the ozone gas control valves  9   a ,  9   b ,  9   c ,  9   bc ,  9   ab , and  9   ca . The ozone gas control valves  9   a ,  9   b , and  9   c  are normally open (NO), and the ozone gas control valves  9   bc ,  9   ab , and  9   ca  are normally close (NC). For convenience of the description,  FIG. 2  shows a specific case of n=3. As the ozone gas control valves  9   a ,  9   b ,  9   c ,  9   bc ,  9   ab , and  9   ca , electrically-operated valves or pneumatic valves which are openable and closable by means of electricity or air pressure are conceivable. 
     The ozone gas control valves  9   a  to  9   c  are interposed between the ozone gas input ports  29 - 1  to  29 -n for the input of the ozone gas from the nitrogen-free ozone generation units  7 - 1  to  7 -n, and the ozone gas output ports  39 - 1  to  39 -n. The ozone gas control valve  9   ab  is provided between the outputs of the ozone gas control valves  9   a  and  9   b . The ozone gas control valve  9   bc  is provided between the outputs of the ozone gas control valves  9   b  and  9   c . The ozone gas control valve  9   ca  is provided between the outputs of the ozone gas control valves  9   c  and  9   a.    
     An open state and a closed state of each of the ozone gas control valves  9   a ,  9   b ,  9   c ,  9   bc ,  9   ab , and  9   ca  are controlled based on the control signal S 8  supplied from the system management control part  84  of the system collective management unit  8 . 
     In  FIG. 6 , among the ozone treatment apparatuses  12 - 1  to  12 -n, only one ozone treatment apparatus  12 - 2  is operated, and the ozone gas on/off valve  22 - 2  thereof is in the open state (blacked out).  FIG. 2  shows a state of the ozone gas output flow rate management unit  9  in a case where the flow rate of the ozone gas supplied to the ozone treatment apparatus  12 - 2  is 30 SLM (L/min). In other words, the ozone treatment apparatus  12 - 2  instructs that the ozone flow rate be 30 SLM based on the request ozone flow rate Qs 12  included in the process ozone gas event signal  16 - 2 . 
     The system management control part  84  provided in the system collective management unit  8  controls, by the nitrogen-free ozone generation unit control signals  86 - 1  to  86 -n, the nitrogen-free ozone generation units  7 - 1  to  7 -n such that the ozone gas can be supplied at 10 SLM from each of the nitrogen-free ozone generation units  7 - 1  to  7 -n. 
     Furthermore, the system management control part  84  controls, by the control signal S 8 , the opening/closing state of each of the ozone gas control valves  9   a ,  9   b ,  9   c ,  9   bc ,  9   ab , and  9   ca  in the ozone gas output flow rate management unit  9 . More specifically, the system management control part  84  outputs, to the ozone gas output flow rate management unit  9 , the control signal S 8  for bringing the ozone gas control valves  9   a ,  9   b ,  9   c ,  9   bc , and  9   ab  into the open state (blacked out) while bringing the ozone gas control valve  9   ca  into the closed state (shown in white). 
     As mentioned above, among the ozone gas on/off valves  22 - 1  to  22 -n, only the ozone gas on/off valve  22 - 2  is in the open state, and the ozone gas on/off valves  22 - 1  and  22 -n are in the closed state. In the description given herein, the ozone treatment apparatus  12  that is not in use is brought into the closed state by means of the ozone gas on/off valves  22 - 1  to  22 -n. Alternatively, it may be acceptable that the ozone treatment apparatus that is not in use is forcibly capped by a pipe fitting at the portion  25 - 1  to  25 -n in order to block the supply of the ozone gas. 
     In this manner, the system management control part  84  causes each of the nitrogen-free ozone generation units  7 - 1  to  7 -n to supply the ozone gas with a flow rate of 10 SLM by the nitrogen-free ozone generation unit control signals  86 - 1  to  86 -n, and also controls the ozone gas output flow rate management unit  9  based on the control signal S 8 . Thereby, the system management control part  84  is able to supply the ozone gas to the ozone treatment apparatus  12 - 2  with a gas flow rate of 30 SLM (10 SLM×3). 
     (Main Control Panel) 
     As shown in  FIG. 7 , the main control panel  85  of the ozone gas supply system  10  displays, on a display surface thereof, the opening/closing state of the ozone gas control valves  9   a ,  9   b ,  9   c ,  9   bc ,  9   ab , and  9   ca  in association with the nitrogen-free ozone generation units  7 - 1  to  7 -n and the ozone treatment apparatuses  12 - 1  to  12 -n. The request ozone flow rate Qs 12  (SLM) and the request ozone concentration Cs 12 (g/m 3 ) of the ozone treatment apparatuses  12 - 1  to  12 -n are also displayed. 
     In an example shown in  FIG. 7 , only the ozone treatment apparatus  12 - 2  requests the request ozone flow rate Qs 12 =30 SLM and the request ozone concentration Cs 12 =280 (g/m 3 ). 
     Thereby, each of the nitrogen-free ozone generation units  7 - 1  to  7 -n is caused to output the ozone gas with an ozone flow rate of 10 (SLM) and an ozone concentration of 280 (g/m 3 ), and the ozone gas control valves  9   a ,  9   b ,  9   c ,  9   bc , and  9   ab  are brought into the open state while the ozone gas control valve  9   ca  is brought into the closed state. Thus, the ozone gas can be supplied to the ozone treatment apparatus  12 - 2  with an ozone flow rate of 30 (SLM) and an ozone concentration of 280 (g/m 3 ). 
     (Ozone Control Part) 
     As shown in  FIG. 8 , the ozone control part  19  provided in each nitrogen-free ozone generation unit  7  controls the ozone power source  2  to thereby control the ozone generation (the gas flow rate and the ozone gas concentration) in the nitrogen-free ozone generator  1 . 
     The ozone power source  2  includes a converter  2   a , an inverter  2   b , a high voltage circuit part  2   c , and a current sensor  2   d . The converter  2   a  rectifies commercial AC voltages AC 1 φ to AC 3 φ. The inverter  2   b  converts a DC voltage into a frequency most suitable for the nitrogen-free ozone generator  1 , and controls an output voltage to supply predetermined power to the nitrogen-free ozone generator  1 . The high voltage circuit part  2   c  raises the voltage outputted from the inverter  2   b  into a high voltage capable of producing a discharge that causes the ozone generation in the nitrogen-free ozone generator  1 . The converter  2   a , the inverter  2   b , and the high voltage circuit part  2   c  are connected in series in the mentioned order. The current sensor  2   d  is interposed between the converter  2   a  and the inverter  2   b.    
     In order to control the ozone gas generation (the gas flow rate Q and the ozone concentration C) in the nitrogen-free ozone generator  1 , the ozone control part  19  applies the high frequency high voltages HV and LV, which are outputted by the high voltage circuit part  2   c , to the nitrogen-free ozone generator  1 , and causes a discharge phenomenon to thereby generate an ozone gas containing a predetermined amount of ozone from the oxygen gas which is the raw material gas. 
     The ozone control part  19  includes a raw material gas flow rate setter  1 S 1 , a selector  1 S 2 , an ozone concentration setter  1 S 3 , analog switches  1 S 4 -A to  1 S 4 -F for controlling ON/OFF of the respective control signals, and inverter devices  1 S 5 - 1 ,  1 S 5 - 2  for inverting the respective control signals. 
     The ozone control part  19  further includes a data memory  1 S 6  and a current signal converter  1 S 7 . The data memory  1 S 6  stores a set power Ws necessary for generating an optimum amount of ozone in response to the raw material gas set flow rate Qs, the set concentration Cs, and a signal including the set pressure Ps of the nitrogen-free ozone generator  1 . The current signal converter  1 S 7  converts the set power Ws into a current signal for applying a necessary current to the ozone power source. 
     Additionally, the ozone control part  19  includes a timer  1 S 8  and a PID control circuit  1 S 9 . The timer  1 S 8  drives the inverter  2   b  based on an initial current command, and switches to a PID control in response to the flow rate Q of the actually flowing raw material gas and the ozone concentration C of the generated ozone obtained by the MFC  3  and the ozone concentration meter  5 . The PID control circuit  1 S 9  performs the PID control based on a result of comparison between the ozone concentration C and the gas set concentration Cs. 
     Moreover, the ozone control part  19  includes an event adjuster  1 S 10  for, in response to the ozone generation unit control signal  86  received from the system management control part  84 , adjusting the signal including the set flow rate Qs and the set ozone concentration Cs based on the request ozone flow rate Qs 8 , the request ozone concentration Cs 8 , and the operation information Y 8  indicated by the ozone generation unit control signal  86 . 
     Furthermore, the ozone control part  19  includes a pressure setter  1 S 11 , an initial pulse width setter  1 S 12 , and a current converter  1 S 13 . The initial pulse width setter  1 S 12  sets, based on the output current of the current signal converter  1 S 7 , an initial pulse width in which the inverter  2   b  is turned ON, for controlling the applied power. The current converter  1 S 13  receives the ozone concentration C detected by the ozone concentration meter  5  and the set ozone concentration Cs, and, based on a result of comparison between the ozone concentration C and the raw material gas set concentration Cs, outputs a current signal for controlling the power applied to the inverter  2   b.    
     (Data Memory  1 S 6 ) 
     As shown in  FIG. 9 , the data memory  1 S 6 , which stores initial conditions for controlling the ozone concentration and the ozone flow rate in the nitrogen-free ozone generation unit  7 , includes a plurality of memory banks BK 1  to BK 4  (four memory banks are shown in  FIG. 9  for convenience of the description), with the set pressure Ps of the nitrogen-free ozone generator  1  serving as a parameter. If the set pressure Ps of the nitrogen-free ozone generator  1  is determined, accordingly the memory bank BKx (any one of 1 to 4) corresponding to the set pressure Ps is selected. 
     As shown in  FIG. 9 , the one memory bank BK selected is divided into a plurality of areas each corresponding to ΔQ along a horizontal axis (X-axis) that represents an address of the set flow rate Qs for the ozone-gas flow rate, while the one memory bank BK selected is divided into a plurality of areas each corresponding to AC along a vertical axis (Y-axis) that represents an address of the set concentration Cs for the ozone concentration. 
     The data memory  1 S 6  receives the signal including the set flow rate Qs and the set concentration Cs functioning as the address on the horizontal axis (X-axis) and the vertical axis (Y-axis). In the data memory  1 S 6 , a set power amount W (A 11  to A 17 , . . . , A 61  to A 67 ) required for generating a predetermined amount of ozone is written into a memory address which is determined by the address on the X-axis and the Y-axis. The data memory  1 S 6  outputs the set power amount Ws to the current signal converter  1 S 7  provided in the ozone control part  19 . As a result, the current signal converter  1 S 7  converts the set power amount Ws into a current signal. The current signal is supplied through the analog switch  1 S 4 -E to the initial pulse width setter  1 S 12 . The initial pulse width setter  1 S 12  outputs a pulse signal Tw to the inverter  2   b . The pulse signal Tw has a predetermined frequency and a predetermined pulse width, and is for achieving the set power amount Ws. 
     As shown in  FIG. 10 , the output concentration control waveform obtained in a case where the output concentration control is performed on the nitrogen-free ozone generation unit  7  corresponds to an operation command signal (included in the operation information Y 8 ) supplied to the nitrogen-free ozone generation unit  7 , and, in an initial state defined by a set time period To, sets the power applied to the inverter  2   b  based on the set power amount Ws supplied from the data memory  1 S 6 . 
     After the elapse of the set time period To, the timer  1 S 8  performs a time control so that the control is switched to the PID control performed by the PID control circuit  1 S 9 . The PID control circuit  1 S 9  slightly varies a pulse width ΔTw of the pulse signal Tw based on the current signal (the signal determined based on the result of comparison between the ozone gas concentration C (detected by the ozone concentration meter  5 ) and the gas set concentration Cs) supplied from the current converter  1 S 13 . Thereby, the PID control circuit  1 S 9  performs the PID control on the power applied to the inverter  2   b . As a result, the ozone concentration (C) of the ozone generated in the nitrogen-free ozone generator  1  exhibits a control responsiveness waveform shown in part (a) of  FIG. 10 . 
     Hereinafter, a concentration control shown in  FIG. 10  will be described in detail. Firstly, a description will be given to an operation of the nitrogen-free ozone generation unit  7  alone, which is not based on the ozone generation unit control signal  86 . 
     Triggered by an input of an operation command (not shown), the event adjuster  1 S 10  activates the timer  1 S 8 . At this time, the event adjuster  1 S 10  controls a raw material gas flow rate comparator  1 S 2  so as to select the raw material gas set flow rate Qs of the raw material gas flow rate setter  1 S  1 , and brings the analog switches  1 S 4 -A and  1 S 4 -D into the ON state while bringing the analog switches  1 S 4 -B and  1 S 4 -C into the OFF state. On the other hand, the timer  1 S 8 , immediately after being activated, brings the analog switch  1 S 4 -E into the ON state while bringing the analog switch  1 S 4 -F into the OFF state. 
     Thus, the data memory  1 S 6  obtains the set pressure Ps from the pressure setter  1 S 11 , the raw material gas set flow rate Qs from the raw material gas flow rate setter  1 S 1 , and the raw material gas set concentration Cs from the ozone concentration setter  1 S 3 . Consequently, as described above, the data memory  1 S 6  outputs the set power amount Ws to the current signal converter  1 S 7 . As a result, the initial pulse width setter  1 S 12  generates the pulse signal Tw having the initial pulse width. The ON/OFF of the inverter  2   b  is controlled in accordance with “H” or “L” of the pulse signal Tw. 
     In this manner, within the set time period To during which the timer  1 S 8  is in an operation state, an initial control is performed based on the set power amount Ws supplied from the data memory  1 S 6 . 
     Then, when the set time period To has elapsed since the timer  1 S 8  was activated, the initial state ends, and the analog switch  1 S 4 -E is switched to the OFF state while the analog switch  1 S 4 -F is switched to the ON state. 
     Thus, the PID control circuit  1 S 9  performs the PID control on the ozone power source  2 . The PID control is mainly for, based on the current signal supplied from the current converter  1 S 13 , causing a slight displacement (ΔTw) of the pulse width of the pulse signal Tw so as to reflect the result of comparison between the ozone concentration C obtained by the ozone concentration meter  5  and the gas set concentration Cs. Here, also based on a current I detected by the current sensor  2   d , the PID control circuit  1 S 9  causes the slight displacement ΔTw. In this manner, the control is switched to the PID control (W) after the set time period To has elapsed since the operation command. 
     Next, a description will be given to an operation of the nitrogen-free ozone generation unit  7  alone, which is based on the ozone generation unit control signal  86 . 
     Triggered by an input of the ozone generation unit control signal  86  indicating the request ozone flow rate Qs 8 , the request ozone concentration Cs 8 , and the operation information Y 8 , the event adjuster  1 S 10  activates the timer  1 S 8 . At this time, the analog switches  1 S 4 -A and  1 S 4 -D are brought into the OFF state, and the analog switches  1 S 4 -B and  1 S 4 -C are brought into the ON state. On the other hand, the timer  1 S 8 , immediately after being activated, brings the analog switch  1 S 4 -E into the ON state while bringing the analog switch  1 S 4 -F into the OFF state. 
     The request ozone flow rate Qs 8  and the request ozone concentration Cs 8  are determined by the system management control part  84  based on the request ozone flow rate Qs 12  and the request ozone concentration Cs 12  that are indicated by the process ozone gas event signals  16 - 1  to  16 -n supplied from the ozone treatment apparatuses  12 - 1  to  12 -n. 
     Thus, the data memory  1 S 6  obtains the set pressure Ps from the pressure setter  1 S 11 , and the request ozone flow rate Qs 8  and the request ozone concentration Cs 8  indicated by the ozone generation unit control signal  86  which serve as the set flow rate Qs and the set concentration Cs. Consequently, as described above, the data memory  1 S 6  outputs the set power amount Ws to the current signal converter  1 S 7 . As a result, the initial pulse width setter  1 S 12  generates the pulse signal Tw having the initial pulse width. 
     In this manner, also by the input of the ozone generation unit control signal  86 , the initial control is performed based on the set power amount Ws supplied from the data memory  1 S 6  within the set time period To during which the timer  1 S 8  is in the operation state. 
     Then, after the set time period To has elapsed since the timer  1 S 8  was activated, the initial state ends, and the analog switch  1 S 4 -E is switched to the OFF state while the analog switch  1 S 4 -F is switched to the ON state. 
     Thus, the PID control circuit  1 S 9  performs the PID control on the ozone power source  2 . The PID control is mainly for, based on the current signal supplied from the current converter  1 S 13 , causing a slight displacement (ΔTw) of the pulse width of the pulse signal Tw. 
     As thus far described, the ozone control part  19  performs the initial control and the PID control on the ozone power source  2 .  FIG. 11  is a graph showing received power of the ozone power source  2  of 2.5 KW provided in one nitrogen-free ozone generation unit  7 , and ozone concentration characteristics of ozone occurring in the nitrogen-free ozone generator  1 . 
     In  FIG. 11 , ozone concentration characteristics L 11  represent the ozone concentration characteristics obtained when the flow rate Q of the ozone gas supply is 1.25 L/min (=1.25 SLM). In this case, by making the received power variable in a range of 100 W to 1.0 kW, the ozone concentration of the generated ozone can be variably set in a range of about 0 g/m 3  to 360 g/m 3 . 
     In the same manner, ozone concentration characteristics L 12  represent the ozone concentration characteristics obtained when the flow rate Q of the ozone gas supply is 2.5 SLM. In this case, by making the received power variable in a range of 100 W to 2.0 kW, the ozone concentration of the generated ozone can be variably set in a range of about 0 g/m 3  to 360 g/m 3 . 
     Ozone concentration characteristics L 13  represent the ozone concentration characteristics obtained when the flow rate Q of the ozone gas supply is 5.0 SLM. Ozone concentration characteristics L 14  represent the ozone concentration characteristics obtained when the flow rate Q of the ozone gas supply is 7.5 SLM. Ozone concentration characteristics L 15  represent the ozone concentration characteristics obtained obtained when the flow rate Q of the ozone gas supply is 10 SLM. Ozone concentration characteristics L 16  represent the ozone concentration characteristics obtained when the flow rate Q of the ozone gas supply is 20 SLM. Ozone concentration characteristics L 17  represent the ozone concentration characteristics obtained when the flow rate Q of the ozone gas supply is 30 SLM. 
     In a case where the ozone gas is supplied from one ozone generation unit  7  with a flow rate Q of 5 SLM, the maximum ozone concentration generated with the received power 2.5 kW is 350 g/m 3  (see the ozone concentration characteristics L 13 ). In a case where the ozone gas is supplied with a flow rate Q of 7.5 SLM, the maximum ozone concentration generated with the received power 2.5 kW is 300 g/m 3  (see the ozone concentration characteristics L 14 ). 
     In a case where the ozone gas is supplied with a flow rate Q of 10 SLM, the maximum ozone concentration generated with the received power 2.5 kW is only 280 g/m 3  (see the ozone concentration characteristics L 15 ). In a case where the ozone gas is supplied with a flow rate Q of 20 SLM, the maximum ozone concentration generated with the received power 2.5 kW is only 180 g/m 3  (see the ozone concentration characteristics L 16 ). In a case where the ozone gas is supplied with a flow rate Q of 30 SLM, the maximum ozone concentration generated with the received power 2.5 kW is only 140 g/m 3  (see the ozone concentration characteristics L 17 ). 
     In order to maintain an ozone concentration of 280 g/m 3  in the nitrogen-free ozone generation unit  7  including the ozone power source  2  with a received power of 2.5 kW, the highest flow rate that can be supplied by one nitrogen-free ozone generator  1  is 10 SLM. In other words, in order to satisfy an ozone concentration of 280 g/m 3  by using one nitrogen-free ozone generator  1 , it is impossible to supply the ozone gas with a flow rate equal to or higher than 10 SLM. 
     On the other hand, the ozone gas supply system  10  of this embodiment adopts an output ozone gas output control method in which the ozone gas output flow rate management unit  9  is able to selectively output one or more of n ozone gas outputs supplied from the n nitrogen-free ozone generation units  7 - 1  to  7 -n to any ozone treatment apparatus  12  among the ozone treatment apparatuses  12 - 1  to  12 -n. 
     Therefore, in the ozone gas supply system  10  of the embodiment 1, by controlling the opening/closing of the ozone gas control valves  9   ab ,  9   bc , and  9   ca  each provided between the units within the ozone gas output flow rate management unit  9  in the manner as shown in  FIGS. 6 and 7 , all of the ozone gases generated by the n nitrogen-free ozone generation units  7 - 1  to  7 -n can be supplied to only one ozone treatment apparatus  12 - 2 . Accordingly, by causing each of the nitrogen-free ozone generation units  7 - 1  to  7 -n to output the ozone gas with a flow rate of 10 SLM and an ozone gas concentration of 280 g/m 3 , an ozone A gas can be supplied to the ozone treatment apparatus  12 - 2  with a gas flow rate of 30 SLM, and at that time, the ozone concentration can be made as high as 280 g/m 3 . This provides an effect that the treatment capacity of the ozone treatment apparatus, such as a processing speed and the performance, can be considerably improved while the existing ozone generator is used. 
     Additionally, if the flow rate of the raw material gas is 10 SLM in the nitrogen-free ozone generation unit  7 , the maximum outputtable ozone concentration is 280 g/m 3 . However, the ozone concentration can be increased by using the control of opening/closing of the ozone gas control valves  9   ab ,  9   bc , and  9   ca  each provided between the units in the ozone gas output flow rate management unit  9 . 
     For example, in a case where the opening/closing of the ozone gas control valves  9   a ,  9   b ,  9   c ,  9   bc ,  9   ab , and  9   ca  is controlled as shown in  FIGS. 6 and 7  such that each of the three ozone generation units  7  supplies the gas with a flow rate of 3.3 SLM, the output concentration can be increased to the maximum value of the ozone concentration corresponding to 3.3 SLM. Thus, as indicated by an imaginary point P 3 , the ozone gas can be supplied with a total flow rate of 10 SLM and with an ozone concentration of about 330 g/m 3 . This provides an effect that an ozone treatment capacity of the ozone treatment apparatus  12 - 2  that receives the ozone gas supply can be increased. 
     In the ozone gas supply system  10  of this embodiment that includes the n nitrogen-free ozone generation units  7  and that adopts the output ozone gas output control method implemented by the ozone gas output flow rate management unit  9 , breakdown of any of the nitrogen-free ozone generation units  7 - 1  to  7 -n does not make the corresponding ozone treatment apparatus  12  unusable. The ozone gas outputted from the nitrogen-free ozone generation unit  7  that is not broken down can be supplied by opening/closing the ozone gas control valves  9   ab ,  9   bc , and  9   ca . This can provide an ozone gas supply system with a higher reliability of ozone gas supply. 
     For example, in a case where the nitrogen-free ozone generation unit  7 - 2  corresponding to the ozone treatment apparatus  12 - 2  is broken down, the ozone gas supplied from the nitrogen-free ozone generation unit  7 - 1  can be supplied to the ozone treatment apparatus  12 - 2  by opening the ozone gas control valves  9   a ,  9   ab  and the ozone gas on/off valve  22 - 2  into the open state. 
     Furthermore, even though any of the n ozone treatment apparatuses  12 - 1  to  12 -n is broken down or stops its operation, the operation information Y of the process ozone gas event signal  16  is introduced and thereby the operation of the nitrogen-free ozone generation unit  7  that is supplying the ozone gas to the broken-down ozone treatment apparatus  12  can be promptly stopped by the ozone generation unit control signal  86 . 
     (Effects, etc.) 
     In the above-described embodiment  1 , one ozone gas supply system  10  includes the plurality of nitrogen-free ozone generation units  7 - 1  to  7 -n, and each nitrogen-free ozone generation unit  7  includes the nitrogen-free ozone generator  1  having the means for generating the ozone gas, the ozone power source  2  having the means for controlling power to be supplied for ozone generation, the MFC  3  having the means for controlling the flow rate Q of the raw material gas to be a constant value, the APC  4  having the means for automatically controlling the pressure P in the nitrogen-free ozone generator  1 , and the ozone concentration meter  5  having the means for detecting the concentration value C of the output ozone gas. 
     In the nitrogen-free ozone generator  1 , the raw material gas is the oxygen gas alone, and an MFC for adding a nitrogen gas of several thousands f or more is not necessary. An ozone gas having a higher purity and a higher concentration, in which no by-product such as NO X  and an OH radical substance is contained, can be independently supplied to a plurality of ozone treatment apparatuses, with separate amounts of ozone gas and separate ozone concentrations. 
     In the ozone gas supply system  10 , the ozone gas output flow rate management unit  9  is provided in which the open/close valve (ozone gas control valves  9   a  to  9   c ) is arranged corresponding to the output ozone gas pipe of each nitrogen-free ozone generator  1 , and additionally the open/close valve ( 9   bc ,  9   ab ,  9   ca ) is arranged between the output ozone gas pipes of the respective nitrogen-free ozone generators  1 . 
     The ozone gas supply system  10  of the embodiment 1 includes the system collective management unit  8  (ozone gas output flow rate management unit control part) that can control the ozone gas output flow rate so that one or a combination of two or more of the plurality of ozone gas outputs from the nitrogen-free ozone generation units  7 - 1  to  7 -n can be selectively outputted to any of the ozone treatment apparatuses  12 - 1  to  12 -n by the opening/closing operation of the ozone gas control valves  9   a ,  9   b ,  9   c ,  9   bc ,  9   ab , and  9   ca  provided in the ozone gas output flow rate management unit  9 . 
     Accordingly, by bringing the ozone gas control valves  9   a ,  9   b , and  9   c  into the open state, bringing the ozone gas control valves  9   ab ,  9   bc , and  9   ca  into the closed state, and bringing the ozone gas on/off valves  22 - 1  to  22 -n into the open state so that the ozone gas can be supplied from the nitrogen-free ozone generation units  7 - 1  to  7 -n to the ozone treatment apparatuses  12 - 1  to  12 -n that are in one-to-one correspondence with each other, the gas flow rate and the ozone gas concentration of the ozone gas supplied to the ozone treatment apparatuses  12 - 1  to  12 -n can be independently controlled. 
     Additionally, as shown in  FIGS. 6 and 7 , supplying a combination of two or more ozone gas outputs to one ozone treatment apparatus (ozone treatment apparatus  12 - 2 ) makes it possible to suuply the ozone gas with various gas flow rates and various concentrations. 
     Moreover, even when a trouble occurs in a part of the nitrogen-free ozone generation units  7 - 1  to  7 -n, the other nitrogen-free ozone generation units  7  that are normally operating are able to supply the ozone gas to any of the ozone treatment apparatuses  12 - 1  to  12 -n. Therefore, an ozone gas supply with a high reliability is achieved. 
     In this manner, the ozone gas supply system  10  controls the ozone gas output flow rate management unit  9  based on the control signal S 8  supplied from the system management control part  84 , to perform a combination/selection process for combining and selecting ozone gas outputs from the nitrogen-free ozone generation units  7 - 1  to  7 -n, so that the ozone gas can be outputted to the ozone treatment apparatus  12  with a desired gas flow rate and a desired ozone gas concentration. 
     In the ozone gas supply system  10  of the embodiment 1, electrically-operated valves or pneumatic valves that are openable and closable by means of electricity or air pressure are adoptable as the ozone gas control valves  9   a ,  9   b ,  9   c ,  9   bc ,  9   ab , and  9   ca  provided in the ozone gas output flow rate management unit  9 . Thereby, the gas flow rate and the ozone gas concentration of the ozone gas outputted from the nitrogen-free ozone generator  1  of each nitrogen-free ozone generation unit  7  to the outside can be centrally managed under control of the control signal S 8 . 
     The system collective management unit  8  includes the water leakage sensor  6 , the EMO circuit  81 , the unit information I/F  82 , the system management control part  84 , and the like. Thereby, in a case where an emergency stop or water leakage is detected in any of the nitrogen-free ozone generation units  7 - 1  to  7 -n, the corresponding the nitrogen-free ozone generation unit can be stopped. 
     Furthermore, the exhaust gas sensor  23 , the ozone leakage sensor  24 , the system management control part  84 , and the like, are provided. Thereby, in a case where an abnormal exhaust or an abnormal ozone leakage is detected in the system as a whole, all the nitrogen-free ozone generation units  7 - 1  to  7 -n can be stopped. 
     In this manner, the ozone gas supply system  10  of the embodiment 1 has a function for safety shutdown which is exerted in a case where a trouble of each nitrogen-free ozone generation unit  7 , a trouble of the entire ozone gas supply system  10 , and the like. Thus, a system with a high security is achieved. 
     Furthermore, in the ozone gas supply system  10  of the embodiment 1, an ozone gas having a higher purity and a higher concentration, in which no by-product such as NO X  and an OH radical substance is contained, can be independently supplied to a plurality of ozone treatment apparatuses, with separate amounts of ozone gas and separate ozone concentrations. Thus, this apparatus is able to collectively manage the amount of ozone gas and the ozone concentration in a plurality of ozone treatment processes in the field of semiconductor fabrication. This is effective for labor-saving in an ozone treatment facility. 
     &lt;Embodiment 2&gt; 
     An embodiment 2 is characterized by focusing on the nitrogen-free ozone generation unit  7  as one unit corresponding to each of the nitrogen-free ozone generation units  7 - 1  to  7 -n in the ozone gas supply system  10 , and achieving downsizing of the nitrogen-free ozone generation unit  7 . 
       FIG. 12  is a circuit diagram showing details of an internal configuration of the ozone power source  2 .  FIG. 13  is a perspective view schematically showing a combined structure of a nitrogen-free ozone generation unit  7 X according to the embodiment 2. 
     Hereinafter, downsizing of the nitrogen-free ozone generation unit  7 X will be described with reference to  FIGS. 12 and 13 . The nitrogen-free ozone generation unit  7 X means an ozone generation unit as one unit that is configured as each of the nitrogen-free ozone generation units  7 - 1  to  7 -n according to the embodiment 1. 
     In the nitrogen-free ozone generation unit  7 X shown in  FIG. 13 , each of the ozone power source  2  and the nitrogen-free ozone generator  1  is downsized. Not only the compactified ozone power source  2  configured to supply power and having the means for controlling the amount of power, and the compactified nitrogen-free ozone generator  1  having the means for generating an ozone gas, but also the MFC  3  having means for controlling the flow rate of the raw material gas, the gas filter  51  having the means for removing impurities from the ozone gas, the ozone concentration meter  5  having the means for detecting the ozone gas concentration of the outputted ozone gas, and the APC  4  having the means for controlling the gas pressure in the ozone generator to a constant value, are assembled together into a package, thereby achieving the nitrogen-free ozone generation unit  7 X serving as one unit in a structural sense, too. 
     Additionally, a raw material gas pipe (raw material gas supply port  14 ) and an output gas pipe system (ozone gas output port  15 ) are integrated into a gas pipe integrated block  30  as a gas pipe integrated block structure. Thereby, the nitrogen-free ozone generator  1 , the ozone power source  2 , and the gas pipe system are packaged, and thus the nitrogen-free ozone generation unit  7 X is further downsized. 
     Therefore, even if, as in the ozone gas supply system  10  of the embodiment 1, a plurality of nitrogen-free ozone generation units  7 X are mounted as the nitrogen-free ozone generation units  7 - 1  to  7 -n, an ozone gas supply system having improved functionality and improved reliability is achieved without increasing the size of the apparatus as a whole. 
     (Compactification of Ozone Power Source  2 ) 
       FIG. 12  shows a compactified circuit configuration achieved by integrating main components of the nitrogen-free ozone generator  1  and the ozone power source  2  with each other. 
     In order to obtain a desired amount of ozone generation, the nitrogen-free ozone generator  1  requires an area as a discharge area for generation of ozone. Therefore, to reduce an area occupied by the generator, a thin electrode cell is formed and moreover a cross-sectional area of one electrode cell is reduced. Thereby, the nitrogen-free ozone generator  1  of multi-layered electrode cell type is formed. This achieves the nitrogen-free ozone generator  1  that occupies a very small area. 
     The ozone power source  2  includes the converter  2   a  for rectifying the commercial AC voltage, the inverter  2   b  for converting the DC voltage into a high frequency most suitable for the nitrogen-free ozone generator and controlling the output voltage to supply predetermined power to the ozone generator, and the high voltage circuit part  2   c  for raising the voltage outputted from the inverter  2   b  into a high voltage capable of producing the discharge that causes the ozone generation in the nitrogen-free ozone generator  1 . The ozone control part  19  controls applied power of the ozone power source. 
     The converter  2   a  is made up of a rectifier circuit  2   a   1 , a capacitor bank  2   a   2 , a smoothing reactor  2   a   3 , a chopper circuit part  2   a   4 , and a chopper control circuit part  2   a   5  that are connected in series. The inverter  2   b  is made up of an inverter circuit  2   b   1  and an inverter control circuit  2   b   2 . Each component of the converter  2   a  and the inverter  2   b  of the ozone power source  2  is sorted and formed into a module. Thus, the circuit configuration is downsized. 
     To be specific, the rectifier circuit  2   a   1 , the capacitor bank  2   a   2 , and the smoothing reactor  2   a   3  are integrated into a DC/smoothing circuit part  2   ax  as a module. Thus, the circuit configuration is downsized, and the quality of the component is increased. 
     The chopper circuit part  2   a   4  forming the converter  2   a  and the inverter circuit  2   b   1  forming the inverter  2   b  are made of power semiconductors such as an FET device or an IGBT device, and need to be cooled by a cooling fin. Therefore, by forming the chopper circuit part  2   a   4  and the inverter circuit  2   b   1  into a single semiconductor module, an effectively downsized power device part  2   p  is achieved. By forming the chopper control circuit  2   a   5  of the converter  2   a  and the inverter control circuit  2   b   2  of the inverter  2   b  on a single substrate or as an integrated circuit IC, an extremely downsized power supply control substrate  2   q  is achieved. 
     The high voltage circuit part  2   c  is made up of a series reactor L 0  for limiting an inverter output current, a high voltage transformer Tr for raising the voltage, and a parallel reactor Lb for improving power factor. Each of the components is large and heavy in weight. However, a special transformer is formed by which the series reactor L 0  and the parallel reactor Lb can be integrated and functions thereof can be incorporated into the high voltage transformer Tr. That is, a transformer is designed such that the series reactor L 0  can be integrated by using a primary leakage inductance of the high voltage transformer. The parallel reactor Lb is designed such that a large excitation inductance of the transformer can be obtained. Thus, the function of the parallel reactor Lb can be incorporated into the transformer. 
     Furthermore, the high voltage transformer Tr is adapted to a high frequency of several tens kHz. Thereby, the transformer can be formed using a ferrite core having a light weight and good high frequency characteristics. To reduce an installation area of the transformer Tr and to ensure a predetermined capacity of the transformer, a plurality of small transformers are connected in parallel. The plurality of (in the drawing, three) transformers are vertically installed, thus achieving the very small high voltage circuit part  2   c . However, the series reactor L 0  for limiting the output current of the inverter may not be integrated into the transformer, but may be independently formed as a small reactor L 0 . 
     (Combined Structure of Ozone Generation Unit) 
       FIG. 13  shows the nitrogen-free ozone generation unit  7 X as one unit in which the nitrogen-free ozone generator  1 , the ozone power source  2 , the MFC  3 , the gas filter  51 , the ozone concentration meter  5 , the APC  4 , and the gas pipe integrated block  30  are assembled together. 
     In  FIG. 13 , a control panel  85 -i (i indicates any of one to n) is provided on a front surface (at the left side in  FIG. 13 ), and the integrated ozone control part  19  (not shown) is provided at the rear side thereof. The ozone control part  19  is connected via electrical signals to the nitrogen-free ozone generator  1 , the ozone power source  2  (blocks BL 1  and BL 2 ), the MFC  3 , the ozone concentration meter  5 , and the APC  4  that are assembled together. Hereinafter, a description will be given on the assumption that a side where the control panel  85 -i exists is defined as the front surface of the nitrogen-free ozone generation unit  7 X. 
     As shown in  FIG. 8 , in the nitrogen-free ozone generator  1  and the ozone power source  2 , for example, each of the components is formed into a module, so that the number of components is reduced, thus compactifying each component and reducing the installation area thereof. As shown in  FIG. 9 , in one nitrogen-free ozone generation unit  7 X, the nitrogen-free ozone generator  1  is provided at the center, and the DC/smoothing circuit part  1 Ax, the power device part  2   p , and the power supply control substrate of the ozone power source  2  are formed into the single block BL 1  which is arranged at the front surface, while a plurality of small transformers laminated in the vertical direction are formed into the high voltage circuit part  2   c  as the block BL 2 . By such a distributed arrangement, the integration is achieved. 
     The gas supply pipe system including the MFC  3  for supplying the raw material gas, the ozone gas output pipe system for outputting the ozone gas to the outside via the gas filter  51 , the ozone concentration meter  5 , and the APC  4 , and a cooling pipe system (the cooling water inlet port  13 A, the cooling water outlet port  13 B) for cooling the electrodes of the nitrogen-free ozone generator  1 , are necessary for the nitrogen-free ozone generator  1 . These pipe systems have to be arranged three-dimensionally. Therefore, if the components are connected by existing gas pipes, cooling pipes, and the like, the number of connection joints for connecting the pipes and the components is increased. This makes it necessary to ensure a connection space for connecting the joints. Thus, in order to connecting these pipe systems, a very large space is required. 
     Conventionally, a pipe unit separate from the nitrogen-free ozone generation unit (nitrogen-free ozone generator) is provided, for example, at the rear side, and the generator unit and the pipes are connected at the rear side. Therefore, it has been difficult to integrate the nitrogen-free ozone generation unit with the gas supply pipe system, the ozone gas output pipe system, and the cooling pipe system  13 A,  13 B. 
     In the embodiment 2, these pipe systems are assembled together into the single gas pipe integrated block  30 , and pipe paths for the gas supply pipe, the ozone gas output pipe, and the cooling pipe are incorporated in the gas pipe integrated block  30 . This gas pipe integrated block  30  has a three-dimensional structure, and at respective surfaces thereof, the nitrogen-free ozone generator  1 , the MFC  3 , the gas filter  51 , the ozone monitor  5 , and the APC  4  (hereinafter, these may be collectively referred to as “nitrogen-free ozone generator  1  and the like”) are adjacently arranged. A connecting portion between the nitrogen-free ozone generator  1  and the like and the gas pipe integrated block  30  is, for example, screwed via an O-ring, thereby keeping air-tightness to ensure highly accurate pipe paths. As a result, the nitrogen-free ozone generator  1  and the like can be arranged integrally with the gas pipe integrated block  30 . Additionally, the components of the ozone generator  1  and the like can be mounted and dismounted easily, thus improving maintainability. 
     In this manner, in the nitrogen-free ozone generation unit  7 X of the embodiment 2, the nitrogen-free ozone generator  1  and the like are mounted in close contact with the gas pipe integrated block  30 . In the following, a description will be given to the pipe paths in the nitrogen-free ozone generation unit  7 X which utilizes the gas pipe integrated block  30  shown in  FIG. 13 . In the gas pipe integrated block  30 , pipe paths R 30   a  to R 30   f  are provided. The cooling water inlet port  13 A, the cooling water outlet port  13 B, the raw material gas supply port  14 , and the ozone gas output port  15  are mounted to the side surfaces of the gas pipe integrated block  30 . The nitrogen-free ozone generator  1  is mounted to the gas pipe integrated block  30  using ozone generator mounting bolts Bt 1  to Bt 4 . 
     The MFC  3  is interposed between MFC mounting blocks  33 ,  33  and thereby mounted to the gas pipe integrated block  30 . The APC  4  is interposed between APC mounting blocks  34 ,  34  and thereby mounted to the gas pipe integrated block  30 . The ozone concentration meter  5  is interposed between ozone concentration meter mounting blocks  35 ,  35  and thereby mounted. In these mounting blocks  33  to  35 , in-block passages B 3  to B 5  for ensuring the pipe paths are formed. The gas filter  51  is mounted to the gas pipe integrated block  30  by using a gas filter mounting block  31 . 
     A raw material gas input pipe path for a raw material gas Gm to be supplied from the raw material gas supply port  14  through the MFC  3  to an ozone generator input part ET 1  of the nitrogen-free ozone generator  1  is a path constituted of the raw material gas supply port  14 , the pipe path R 30   a , the in-block passage B 3 , the MFC  3 , the in-block passage B 3 , the pipe path R 30   b , and the ozone generator input part ET 1  arranged in the mentioned order. At this time, a portion of the nitrogen-free ozone generator  1  around the ozone generator input part ET 1  is mounted to the gas pipe integrated block  30  by the ozone generator mounting bolt Bt 1 . In this manner, the input pipe path for the raw material gas Gm is formed using the gas pipe integrated block  30 . 
     An ozone gas output pipe for an ozone gas outputted from the nitrogen-free ozone generator  1  and received by an ozone generator output part EX 1  to be outputted from the ozone gas output port  15  through the gas filter  51 , the ozone concentration meter  5 , and the APC  4  is a path constituted of the nitrogen-free ozone generator output part EX 1 , the pipe path R 30   c , the inside of the gas filter mounting block  31 , the gas filter  51 , the inside of the gas filter mounting block  31 , the pipe path R 30   d , the in-block passage B 5 , the ozone concentration meter  5 , the in-block passage B 5 , the pipe path R 30   e , the in-block passage B 4 , the APC  4 , the in-block passage B 4 , the pipe path R 30   f , and the ozone gas output port  15  arranged in the mentioned order. At this time, a portion of the nitrogen-free ozone generator  1  around the ozone generator output part EX 1  is mounted to the gas pipe integrated block  30  by the ozone generator mounting bolt Bt 2 . In this manner, the output pipe path for the ozone gas is formed using the gas pipe integrated block  30 . 
       FIG. 24  is an explanatory diagram schematically showing a conventional configuration corresponding to the nitrogen-free ozone generation unit  7 X. As shown in  FIG. 24 , conventionally, the configuration corresponding to the nitrogen-free ozone generation unit  7 X generally has a gas control unit  400 , an inverter control unit  500 , and an ozone generation unit  600  that are divided from one another. 
     The gas control unit  400  is provided therein with an MFC  73 , an APC  74 , an ozone concentration meter  75 , and a gas filter  91 . The inverter control unit  500  is provided therein with a converter  2   a , an inverter  2   b , an ozone control part  79 , an control panel  85 -i, a series reactor L 0 , and the like. The nitrogen-free ozone generation unit  600  includes an ozone generator  71 , and a high voltage transformer Tr and a parallel reactor Lb. 
     The inside of the converter  2   a  includes a rectifier circuit  2   a   1 , a capacitor bank  2   a   2 , a smoothing reactor  2   a   3 , a chopper circuit part  2   a   4 , and a chopper control circuit part  2   a   5 . The inverter  2   b  includes an inverter circuit  2   b   1  and an inverter control circuit  2   b   2 . Herein, a description of the connection relationship and details of the operation is omitted. 
     In a conventional ozone gas supply system or a conventional ozone generation apparatus, as shown in  FIG. 24 , merely an electrical connection or a gas pipe connection is allowed between three divided blocks of the gas control unit  400 , the inverter control unit  500  corresponding to the ozone power source, and the ozone generation unit  600 . Thus, the structure shown in  FIG. 13  cannot be achieved. 
     As shown in  FIG. 13 , in the nitrogen-free ozone generation unit  7 X, these three units ( 400 ,  500 ,  600 ) are assembled together, to achieve considerable downsizing as compared with the configuration shown in  FIG. 24 . 
     Thus, the nitrogen-free ozone generation unit  7 X of the embodiment 2 is formed as an integrated structure in which the nitrogen-free ozone generator  1 , the ozone power source  2 , the MFC  3 , the gas filter  51 , the APC  4 , the ozone concentration meter  5 , the raw material gas supply port  14 , the ozone gas output port  15 , the cooling water inlet port  13 A, and the cooling water outlet port  13 B are assembled together. This can achieve considerable downsizing as compared with the similar, conventional configuration. 
     Additionally, the gas pipe integrated block  30  of the nitrogen-free ozone generation unit  7 X has the pipe paths R 30   a  to R 30   f  that are a plurality of internal pipe paths. Therefore, by connecting the pipe paths R 30   a  to R 30   f  to the ozone generator  1 , the MFC  3 , the gas filter  51 , the APC  4 , the ozone concentration meter  5 , the raw material gas supply port  14 , the ozone gas output port  15 , and each of the cooling water inlet/outlet ports  13 A and  13 B, the input pipe path for the raw material gas Gm described above and the output pipe path for the ozone gas described above are formed. Accordingly, downsizing of the part including these pipe paths can be effectively achieved. 
     In this manner, by downsizing each of the nitrogen-free ozone generation units  7 - 1  to  7 -n as the nitrogen-free ozone generation unit  7 X of the embodiment 2, the ozone gas supply system  10  shown in the embodiment 1 can be achieved at a practical use level. 
     As a result, in the ozone gas supply system of the embodiment 2, similarly to in the ozone gas supply system  10  of the embodiment 1, it is possible that a plurality of the nitrogen-free ozone generation units  7 X are installed. By connecting the output pipes of the nitrogen-free ozone generation units  7 X by the gas control valve  9 , the supply of the ozone gas can be distributed among the respective ozone treatment apparatuses  12  including the ozone treatment apparatuses  12 - 1  to  12 -n or a large amount of ozone gas or an ozone gas having a high concentration can be selectively supplied to one ozone treatment apparatus  12 , as described in the embodiment 1. 
     Moreover, in the ozone gas supply system of the embodiment 2, a part corresponding to the nitrogen-free ozone generation system is configured as an integrated nitrogen-free ozone generation unit. This enables the ozone gas having a high purity and a high concentration to be independently supplied to a plurality of ozone treatment apparatuses under separate amount parameter conditions, which is an effect of the embodiment 2. Therefore, not only the effect that “this apparatus is able to collectively manage the amount of ozone gas and the ozone concentration in a plurality of ozone treatment processes in the field of semiconductor fabrication, so that labor-saving in an ozone treatment facility is achieved”, but also an effect that the ozone gas supply system itself can be made compact and inexpensive, is exerted. 
     &lt;Embodiment 3&gt; 
     An embodiment 3 is, similarly to the embodiment 2, characterized by focusing on the nitrogen-free ozone generation unit  7  as one unit, and achieving downsizing of the nitrogen-free ozone generation unit  7  in combination with the ozone gas output flow rate management unit  9 . 
     (Control of Ozone Gas Output Flow Rate Management Unit) 
       FIG. 14  is an explanatory diagram showing an internal configuration of an ozone gas output flow rate management unit based on an ozone gas supply system  20  of the embodiment 3 that corresponds to the ozone gas supply system  10  shown in  FIG. 5 . 
     As shown in  FIG. 14 , in an ozone gas output flow rate management unit  9 Y of the embodiment 3 corresponding to the ozone gas output flow rate management unit  9  of the embodiment 1, portions corresponding to the respective nitrogen-free ozone generation units  7 - 1  to  7 -n are formed integral with one another. In the following, for convenience of the description, a case of n=3 will be described as an example with reference to  FIG. 14 . 
     The ozone gas control valves  9   a  to  9   c  are integrally provided corresponding to the nitrogen-free ozone generation units  7 - 1  to  7 -n. Mounting blocks  93   a  to  93   c  are provided in close contact with the ozone gas control valves  9   a  to  9   c . The ozone gas control valve  9   ab , the ozone gas control valve  9   bc , and the ozone gas control valve  9   ca  are provided at one path side (at the upper side in  FIG. 14 ) of the mounting blocks  93   a ,  93   b , and  93   c.    
     The ozone gas control valve  9   ab  provided at the one path side of the mounting block  93   a  is connected to the other path side (the lower side in  FIG. 14 ) of the mounting block  93   ab  via a pipe fitting  98   u , an inter-unit ozone gas pipe  95   ab , and a pipe fitting  98   d . In the same manner, the ozone gas control valve  9   ab  provided at the one path side of the mounting block  93   ab  is connected to the other path side of the mounting block  93   ac  via a pipe fitting  98   u , an inter-unit ozone gas pipe  95   bc , and a pipe fitting  98   d . The ozone gas control valve  9   ca  provided at the one path side of the mounting block  93   ac  is connected to the other path side of the mounting block  93   a  via a pipe fitting  98   u , an inter-unit ozone gas pipe  95   ca , and a pipe fitting  98   d.    
     Furthermore, the output is made from output parts (at the right side in  FIG. 14 ) of the mounting blocks  93   a  to  93   c  through the ozone gas output ports  25 - 1  to  25 -n to the outside of the ozone gas supply system  20  of the embodiment 3. 
     Accordingly, the ozone gas output flow rate management unit  9 Y has the ozone gas control valves  9   a ,  9   b ,  9   c ,  9   bc ,  9   ab , and  9   ca  as a circuit configuration similar to the ozone gas output flow rate management unit  9 . 
     The ozone gas on/off valves  22 - 1  to  22 -n are interposed between the ozone gas output ports  25 - 1  to  25 -n and the ozone treatment apparatuses  12 - 1  to  12 -n. 
     In the ozone gas control valves  9   a ,  9   b ,  9   c ,  9   bc ,  9   ab , and  9   ca  that form the ozone gas output flow rate management unit  9 Y, the ozone gas control valves  9   a ,  9   b , and  9   c  are of the normally open type (NO), and the ozone gas control valves  9   bc ,  9   ab , and  9   ca  are of the normally close type (NC). 
     A control signal S 8   a  supplied from the system management control part  84  of the system collective management unit  8  is given to the ozone gas control valve  9   a  and the ozone gas control valve  9   ab , and a control signal S 8   b  is given to the ozone gas control valve  9   b  and the ozone gas control valve  9   bc , and a control signal S 8   c  is given to the ozone gas control valve  9   c  and the ozone gas control valve  9   ca.    
     In this manner, the open state and the closed state of the ozone gas control valves  9   a ,  9   b ,  9   c ,  9   bc ,  9   ab , and  9   ca  of the ozone gas output flow rate management unit  9 Y are controlled based on the control signal S 8  (S 8   a  to S 8   c ) supplied from the system management control part  84  of the system collective management unit  8 . 
     In  FIG. 14 , among the ozone treatment apparatuses  12 - 1  to  12 -n, only one ozone treatment apparatus  12 - 2  is operated (the ozone gas on/off valve  22 - 2  is in the open state).  FIG. 14  shows a state of the ozone gas output flow rate management unit  9 Y in a case where the flow rate of the ozone gas supplied to the ozone treatment apparatus  12 - 2  is 30 SLM. 
     In other words, based on the ozone generation unit control signals  86 - 1  to  86 -n supplied from the system management control part  84 , the ozone gas with a flow rate of 10 SLM is outputted from each of the ozone generation units  7 - 1  to  7 -n, and the ozone gas control valves  9   a ,  9   b ,  9   c ,  9   bc , and  9   ab  are brought into the open state (blacked out) while the ozone gas control valve  9   ca  is brought into the closed state (shown in white). 
     On the other hand, among the ozone gas on/off valves  22 - 1  to  22 -n, only the ozone gas on/off valve  22 - 2  is in the open state, while the ozone gas on/off valves  22 - 1  and  22 -n are in the closed state, as described above. In a case where only the ozone treatment apparatus  12 - 2  is used and the other ozone treatment apparatuses  12  are not used, the ozone gas on/off valve  22  is closed. Here, in a case where there is no ozone treatment apparatus, pipe portions of the ozone gas outlet ports  25 - 1  and  25 -n, which are non-used ozone gas outlets, may be forcibly capped with pipe cap fittings. Moreover, needless to say, in a case where any of the connection pipes  95   ab ,  95   bc , and  95   ca  connecting the ozone generation units is not provided in the ozone gas supply system  10 , any of the pipe fittings  98   u  and  98   d  is formed as a pipe cap fitting and capped so that the output ozone gas is blocked. 
     In this manner, the nitrogen-free ozone generation units  7 - 1  to  7 -n and the ozone gas output flow rate management unit  9 Y are controlled so that each of the nitrogen-free ozone generation units  7 - 1  to  7 -n supplies the ozone gas with a flow rate of 10 SLM. This enables the ozone gas to be supplied through the ozone gas output flow rate management unit  9  to the ozone treatment apparatus  12 - 2  with a gas flow rate of 30 SLM. 
     (Combined Structure of Ozone Generation Unit) 
       FIG. 15  is a perspective view schematically showing a combined structure of one unit of the nitrogen-free ozone generation unit according to the embodiment 3. As shown in  FIG. 15 , in the nitrogen-free ozone generation unit  7 Y of the embodiment 3, not only the nitrogen-free ozone generator  1 , the ozone power source  2 , the MFC  3 , the gas filter  51 , the ozone concentration meter  5 , the APC  4 , and the gas pipe integrated block  30 , but also component parts of the ozone gas output flow rate management unit  9  are assembled together. 
     As shown in  FIG. 15 , in order to mount the component parts of the ozone gas output flow rate management unit  9  to the gas pipe integrated block  30 , ozone gas control valve accommodation parts  931  and  932 , an ozone gas output part  933 , and ozone gas branching parts  934  and  935  are provided around block main bodies  930   a  and  930   b  (corresponding to any of the mounting blocks  93   a  to  93   c  shown in  FIG. 10 ). 
     In the ozone gas control valve accommodation part  931 , an ozone gas control valve  90   x (corresponding to any of the ozone gas control valves  9   a  to  9   c ) is accommodated. In the ozone gas control valve accommodation part  932 , an ozone gas control valve  90   xy  (corresponding to any of the ozone gas control valves  9   ab ,  9   bc , and  9   ca ) is accommodated. The ozone gas output part  933  corresponds to the ozone gas output port  15  of the ozone generation unit  7 X of the embodiment 2 shown in  FIG. 13 , and is connected to the ozone gas output port  25  shown in  FIG. 14 . The ozone gas branching part  934  functions as a branching part (inter-unit ozone gas pneumatic valve pipe connection port) at the one path side connected to the pipe fitting  98   u  shown in  FIG. 14 . The ozone gas branching part  935  functions as a branching part (inter-unit ozone gas pneumatic valve pipe connection port) at the other path side connected to the pipe fitting  98   d  shown in  FIG. 14 . 
     In the embodiment 3, similarly to the embodiment 2, all of the gas supply pipe system, the ozone gas output pipe system, and the cooling pipe systems  13 A and  13 B are assembled together into the single gas pipe integrated block  30 . The component parts of the ozone gas output flow rate management unit  9 Y are combined so that pipe paths for a gas supply pipe, an ozone gas output pipe, and a cooling pipe are incorporated in the gas pipe integrated block  30 . 
     Substantially in the same manner as in the ozone generation unit  7 X of the embodiment 2, the raw material gas input pipe path for the raw material gas Gm to be supplied from the raw material gas supply port  14  through the MFC  3  to the ozone generator input part ET 1  of the nitrogen-free ozone generator  1  is a path constituted of the raw material gas supply port  14 , the pipe path R 30   a , the in-block passage B 3 , the MFC  3 , the in-block passage B 3 , the pipe path R 30   b , and the ozone generator input part ET 1  arranged in the mentioned order. 
     The ozone gas output pipe extending from the ozone generator output part EX 1  of the nitrogen-free ozone generator  1  through the gas filter  51 , the ozone concentration meter  5 , and the APC  4  to the block main body  930   b  is a path constituted of the ozone generator output part EX 1 , the pipe path R 30   c , the inside of the gas filter mounting block  31 , the gas filter  51 , the inside of the gas filter mounting block  31 , the pipe path R 30   d , the in-block passage B 5 , the ozone concentration meter  5 , the in-block passage B 5 , the pipe path R 30   e , the in-block passage B 4 , the APC  4 , the in-block passage B 4 , the pipe path R 30   f , the block main body  930   a  (inner portion), the ozone gas control valve  90   x , the pipe path R 30   g , and the block main body  930   b  (outer portion) arranged in the mentioned order. Here, the block main bodies  930   a  and  930   b  may be formed integral with each other and formed through the gas pipe integrated block  30 . 
     In the block main body  930   b , there are formed one branch path connected to the ozone gas branching part  934  through the ozone gas control valve  90   xy , the other branch path connected to the ozone gas branching part  935 , and a joint path in which the one and the other branch paths and the above-mentioned ozone gas output pipe are joined to form an output from the ozone gas output part  933 . 
     The other parts, pipe paths, and the like, of the configuration are identical to those of the nitrogen-free ozone generation unit  7 X shown in  FIG. 13 , and therefore a description thereof is omitted. 
     In the ozone gas supply system  20  of the embodiment 3, the plurality of ozone gas control valve accommodation parts  931  and  932  accommodating the ozone gas control valves  90   x  and  90   xy  therein are mounted in tight contact to the gas pipe integrated block  30  in the corresponding nitrogen-free ozone generation unit  7 Y, and interposed on the output pipe path for the ozone gas described above. 
     This exerts an effect that, in the ozone gas supply system  20 , the combined structure of the ozone gas output flow rate management unit  9 Y and the nitrogen-free ozone generation units  7 - 1  to  7 -n can be downsized. 
     In this manner, in the nitrogen-free ozone generation unit  7 Y of the embodiment 3 has, the features of the nitrogen-free ozone generation unit  7 X of the embodiment 2 are provided, and in addition, most part of the component parts of the ozone gas output flow rate management unit  9  and the gas pipe integrated block  30  are integrated to thereby achieve further downsizing as compared with a case where the nitrogen-free ozone generation unit  7 X and the ozone gas output flow rate management unit  9  of the embodiment 2 are separately provided. 
     &lt;Embodiment 4&gt; 
     In an embodiment 4, in the configuration of the ozone gas supply system of the embodiment 2, a super-high purity moisture remover which is a gas filter for trapping moisture contained in the raw material gas is mounted to the raw material gas supply part, to thereby increase the purity of the raw material gas that is supplied into the apparatus. Thereby, an active gas that is generated together with the ozone gas within the apparatus can be suppressed. 
     Particularly, similarly to the embodiment 2, a super-high purity moisture remover for trapping moisture contained in the gas is mounted to the raw material gas inlet portion of one unit of the nitrogen-free ozone generation unit  7 . Thus, by the combined structure, downsizing of the nitrogen-free ozone generation unit  7  and an increase in the performance and quality of the nitrogen-free ozone generator itself are achieved. 
     (Management of Gas Purity of Raw Material Gas) 
     In the conventional ozone generator in which nitrogen of several thousands ppm or more is added, a catalytic action of nitrogen dioxide NO 2  generated in the generator accelerates dissociation of the oxygen molecule. As a result, three bodies of an oxygen molecule and an oxygen atom produced as a result of the dissociation are bound, thus generating an ozonized gas having a high concentration. In this case, nitrogen dioxide NO 2  is in the form of a gas, and therefore there is little influence that deteriorates the ozone concentration as long as the moisture dew point of the raw material gas is equal to or lower than −50° C. (the moisture content is about 100 ppm). Accordingly, in the conventional ozone generator, a simple moisture remover that is able to ensure a moisture dew point of −50° C. or lower suffices in order to remove the moisture contained in the raw material gas (see  FIG. 28 ). 
     On the other hand, the nitrogen-free ozone generator according to the invention of the present application is an apparatus that adopts a photocatalytic action as a catalytic action for generating the ozone gas, and a photocatalytic material is applied to the discharge surface so that ozone having a high purity and a high concentration is generated from a high purity oxygen gas. Accordingly, even though moisture contained in the raw material gas is a small amount of moisture of several tens ppm, the moisture contained in the gas is adsorbed by the photocatalytic material applied to the discharge surface, so that the moisture is accumulated. On the discharge surface where the moisture has been accumulated, the moisture is dissociated into a hydrogen H atom and an OH molecule due to a silent discharge. As a result, a chemical reaction of binding with the applied photocatalytic material causes reforming of the photocatalytic material itself. This deteriorates the ozone generation ability of the nitrogen-free ozone generator and accelerates the deterioration. This fact is being found out. Furthermore, when moisture is contained in the nitrogen-free ozone generator, the ozone gas containing an OH molecule and a hydrogen H atom produced as a result of dissociation is supplied to the ozone treatment apparatus. This causes a deterioration in the film formation quality in the semiconductor manufacturing process. 
     Therefore, in the nitrogen-free ozone generator according to the invention of the present application, the super-high purity moisture remover is mounted that removes moisture from the raw material gas that contains a small amount of moisture of 3000 ppb or more such that the moisture content is reduced to several hundred ppb or less (desirably 300 ppb or less). 
     Providing this super-high purity moisture remover can remove not only moisture but also CO 2 , CO, and an extremely small amount of impurities, thus exerting an effect that an ozone gas having a higher purity can be obtained. 
       FIG. 16  is an explanatory diagram showing an internal configuration for suppressing a small amount of moisture contained in the raw material gas supplied from an ozone gas supply system  101  of the embodiment 4, which corresponds to the ozone gas supply system  10  shown in  FIG. 5 . 
       FIG. 17  is a perspective view schematically showing a combined structure of a nitrogen-free ozone generation unit as one unit according to the embodiment 4. 
     As shown in  FIGS. 16 and 17 , in the raw material gas inlet ports  14 - 1  to  14 -n of the nitrogen-free ozone generation units  7 - 1  to  7 -n, super-high purity moisture removers (gas filters)  59 - 1  to  59 -n are mounted at positions that allow easy replacement, and integrally formed. In the following, for convenience of the description, a case of n=3 will be described as an example, with reference to  FIG. 16 . 
     As shown in  FIG. 17 , a raw material gas pipe (the raw material gas supply port  14  + the super-high purity moisture remover  59 ) and an output gas pipe system (the ozone gas output port  15 ) are integrated into a gas pipe integrated block  30  as a gas pipe integrated block structure. Thereby, the ozone generator  1 , the ozone power source  2 , and the gas pipe system are packaged, and thus the ozone generation unit  7 X 2  is further downsized. Here, the raw material gas supply port  14  and the super-high purity moisture remover  59  are coupled to each other. 
     As the raw material gas that is supplied to the ozone gas supply system  10 , in general, a raw material gas having a high purity of 99.99% or higher is used. This high-purity raw material gas contains, in addition to the raw material gas, an impurity gas of about 0.1 to several ppm. Examples of the impurity gas include a nitrogen-based gas, a carbon-based gas, and a sulfide gas. The high-purity raw material gas also contains moisture of one to several ppm. Additionally, these impurity gas and moisture are contained in the air, too. Therefore, when a part of the pipes in the raw material gas pipe path is opened to the air, the moisture and the impurity gas such as a nitrogen gas are immediately adsorbed to a pipe surface. If the raw material gas flows in the raw material gas pipe to which the impurity gas is adsorbed, not only the impurity gas and the moisture contained in the high-purity raw material gas but also the impurity gas adhering to the pipe are separated by the gas flow, which may lower the purity of the supplied raw material gas. 
     If a small amount of moisture or an impurity gas such as a nitrogen-based gas, a carbon-based gas, or a sulfide gas is contained in the raw material gas, not only the ozone gas but also N radical and OH radical gases are generated by discharging. These radical gases are combined with the moisture, thus outputting the ozone gas that contains cluster molecule gases of nitric acid and hydrogen peroxide water. Since these cluster molecule gases of nitric acid and hydrogen peroxide water are very active gases, a chemical reaction occurs on a metal surface of the ozone-gas output gas pipe, the valve, or the like, to cause corrosion of the pipe surface. This may cause a corroded-metal impurity (metal contamination) to be contained in the output ozone gas. 
     An increase in the amount of the metal impurity (metal contamination) contained in the output ozone gas causes a deterioration in the performance of formation of, for example, an oxide film that is formed on a semiconductor by an oxide film process using the ozone gas. 
     From the above, it has been confirmed from tests that the quality of an output ozone gas is deteriorated if an impurity gas or a small amount of moisture is contained in the raw material gas. Accordingly, the super-high purity moisture removers (gas filters) for the purpose of trapping the impurity gas and removing a small amount of moisture are mounted to a raw material gas supply part. Particularly, in the embodiment 4, in the raw material gas inlet ports  14 - 1  to  14 -n of the nitrogen-free ozone generation units  7 - 1  to  7 -n, the super-high purity moisture removers  59 - 1  to  59 -n are mounted at positions that allow easy replacement, so that the impurity gas and a small amount of moisture are removed. 
     To be specific, when the raw material gas supplied from the raw material gas supply port  14  contains moisture of 3000 ppb or more before the raw material gas passes through the super-high purity moisture removers  59 - 1  to  59 -n, the super-high purity moisture removers  59 - 1  to  59 -n have a moisture removal ability to reduce the moisture contained in the raw material gas to 300 ppb or less. 
     In this manner, in the ozone gas supply system  101  of the embodiment 4, the super-high purity moisture removers  59 - 1  to  59 -n are provided in the raw material gas inlet ports  14 - 1  to  14 -n of the respective ozone generation units  7 - 1  to  7 -n. Thereby, ozone having a high quality in which no impurity is contained can be obtained with a high concentration. 
     In this configuration, the super-high purity moisture removers  59 - 1  to  59 -n are provided in one-to-one correspondence with the nitrogen-free ozone generation units  7 - 1  to  7 -n. However, depending on a type of the impurity gas, a plurality of gas filters may be provided in series and at multiple stages, or a gas filter for trapping a small amount of moisture may be configured. 
     The other parts, pipe paths, and the like, of the configuration are substantially identical to those of the nitrogen-free ozone generation unit  7 X shown in  FIG. 13 . Therefore, a description thereof is omitted. 
     In the embodiment 4, at the raw material gas supply port  14  provided at a rear surface of the nitrogen-free ozone generation units  7 - 1  to  7 -n, the super-high purity moisture remover is mounted at a position that allows easy replacement. As a result, the ozone gas having a higher purity is provided, and additionally, the mounted super-high purity moisture remover can remove a small amount of moisture. This exerts an effect that a time during which a purge gas is flowed prior to generation of the ozone gas can be considerably shortened. 
     In the embodiment 4, the super-high purity moisture removers  59 - 1  to  59 -n are provided corresponding to the nitrogen-free ozone generation units  7 - 1  to  7 -n. Instead, one super-high purity moisture remover  59  having a function for trapping a small amount of moisture contained in the raw material gas supplied from the raw material gas supply port  14  may be additionally provided such that the one super-high purity moisture remover  59  is shared among the nitrogen-free ozone generation units  7 - 1  to  7 -n. In such a case, when the raw material gas supplied from the raw material gas supply port  14  contains moisture of 3000 ppb or more before the raw material gas passes through the one super-high purity moisture remover  59 , the super-high purity moisture remover  59  has a moisture removal ability to reduce the moisture contained in the raw material gas to 300 ppb or less. 
     &gt;Embodiment 5&gt; 
     An embodiment 5 illustrates another embodiment, “focusing on the nitrogen-free ozone generation unit  7  as one unit corresponding to each of the nitrogen-free ozone generation units  7 - 1  to  7 -n, and achieving downsizing of the nitrogen-free ozone generation unit  7 ” of the embodiment 2. Particularly, instead of the MFC  3  of the embodiment 2 that is the means for controlling the flow rate of the raw material gas, an MFC  53  serving as flow-rate controller is arranged at the ozone gas output part for the output of the generated ozone gas, thus achieving downsizing of the nitrogen-free ozone generation unit  7 . 
     (Ozone-Gas Flow-Rate Control) 
       FIG. 18  is an explanatory diagram showing an internal configuration for controlling the flow rate of the ozone gas by means of an ozone gas supply system  102  according to the embodiment  5 , which corresponds to the ozone gas supply system  10  shown in  FIG. 5 .  FIG. 19  is a perspective view schematically showing a combined structure of a nitrogen-free ozone generation unit as one unit according to the embodiment 5. 
     As shown in  FIGS. 18 and 19 , the embodiment 5 is an embodiment in which, in terms of the function, the MFC  3  serving as the gas-flow-rate controller provided in the raw material gas supply part in the embodiments 1 and 2 is displaced into the pipe system for the generated ozone gas. Since the operation, and the like, of the apparatus is identical to that of the embodiments 1 and 2, a description thereof is omitted. 
     In the embodiment 5, the amount of the generated output ozone gas itself is controlled by the MFC  53 . This exerts an effect that the ozone-gas flow rate can be controlled so as to achieve an accurate output so that the amount of output ozone is accurately controlled. 
     It suffices that the raw material gas pipe system is directly piped, without the need of any pipe peripheral component. In the ozone gas output pipe part, the gas filter  51 , the MFC  53 , the ozone concentration meter  5 , and the APC  4  are collectively mounted to the gas pipe component. Therefore, an integrated pipe configuration is allowed only in the output gas pipe system. As a result, the pipe can be made more compact, and the number of components of the integrated pipe configuration can be reduced, which makes it easier to replace components. 
     &lt;Embodiment 6&gt; 
       FIG. 20  is a block diagram showing a configuration of an ozone gas supply system according to an embodiment 6 of the present invention. As shown in  FIG. 17 , an ozone gas supply system  103  is additionally provided with one super-high purity moisture remover  59  such that the one super-high purity moisture remover  59  is shared among the nitrogen-free ozone generation units  7 - 1  to  7 -n. The one super-high purity moisture remover  59  has a function for trapping, with a super-high purity, a small amount of moisture contained in the raw material gas supplied from the raw material gas supply port  14   
     Additionally, similarly to the embodiment 4 shown in  FIG. 16 , a configuration (not shown) in which the super-high purity moisture removers  59 - 1  to  59 -n are provided near the raw material gas supply ports  14 - 1  to  14 -n of the ozone generation units  7 - 1  to  7 -n may be adopted. 
     In this case, as shown in  FIG. 21 , the raw material gas supply port  14  and the super-high purity moisture remover  59  (any of the super-high purity moisture removers  59 - 1  to  59 -n) are provided in series in the ozone generator input part ET 1 . That is, as shown in  FIG. 21 , there is obtained an ozone generation unit  7 X 4  having a gas pipe integrated block structure in which the raw material gas pipe (the raw material gas supply port  14 +the moisture removal filter  59 ) and the output gas pipe system (ozone gas output port  15 ) are integrated into the gas pipe integrated block  30 . 
     &lt;Embodiment 7&gt; 
       FIG. 22  is a block diagram showing a configuration of an ozone gas supply system according to an embodiment 7 of the present invention. 
     In an ozone gas supply system  104  of an embodiment 7, gas filters  52 - 1  to  52 -n (for the raw material gas) are provided for the purpose of trapping impurities, an impurity gas, or moisture contained in the raw material gas that is supplied through the raw material gas supply port  14 . However, the gas filters  52 - 1  to  52 -n are provided in one-to-one correspondence with the ozone generation units  7 - 1  to  7 -n, and provided near the inlet portions of the raw material gas supply parts of the ozone generation units  7 - 1  to  7 -n. Each of the gas filters  52 - 1  to  52 -n increases the purity of the raw material gas supplied to each of the ozone generation units  7 - 1  to  7 -n, so that the purity of the ozone gas generated in the ozone gas supply system  105  is increased. 
     Particularly, in the ozone generation units  7 - 1  to  7 -n of the embodiment 7, similarly to the embodiment 2, the gas filter  52  for trapping impurities, an impurity gas, or moisture contained in the gas is mounted to the raw material gas inlet portion of one unit of the ozone generation unit  7 , and thus downsizing of the ozone generation unit  7  is achieved by the combined structure. 
     (Management of Gas Purity of Raw Material Gas) 
       FIG. 23  is a perspective view schematically showing a combined structure of an ozone generation unit  7 X 5  as one unit according to the embodiment 7. 
     As shown in  FIGS. 22 and 23 , the gas filter  52  ( 52 - 1  to  52 -n) is mounted at a position that allows easy replacement and in connection with the raw material gas inlet ports  14 - 1  to  14 -n of the ozone generation units  7 - 1  to  7 -n, and integrally formed. In the following, for convenience of the description, a case of n=3 will be described as an example, with reference to  FIG. 20 . 
       FIG. 25  is an explanatory diagram showing the relationship between the dew point of the raw material gas and the moisture content in the raw material gas. As the raw material gas that is supplied to the ozone gas supply system  10 , in general, a raw material gas having a high purity of 99.99% or higher is used. This high-purity raw material gas contains, in addition to the raw material gas, an impurity gas of about 0.1 to several ppm. Examples of the impurity gas include a nitrogen-based gas, a carbon-based gas, and a sulfide gas. The high-purity raw material gas also contains moisture of one to several ppm (see  FIG. 25 ). 
     Additionally, these impurity gas and moisture are contained in the air, too. Therefore, when a part of the pipes in the raw material gas pipe path is opened to the air, the moisture and the impurity gas such as a nitrogen gas are immediately adsorbed to a pipe surface. If the raw material gas flows in the raw material gas pipe to which the impurity gas is adsorbed, not only the impurity gas and the moisture contained in the high-purity raw material gas but also the impurity gas adhering to the pipe are separated by the gas flow, which may lower the purity of the supplied raw material gas. 
     If moisture or an impurity gas such as a nitrogen-based gas, a carbon-based gas, or a sulfide gas is contained in the raw material gas, not only the ozone gas but also N radical and OH radical gases are generated by discharging. These radical gases are combined with the moisture, thus outputting the ozone gas that contains cluster molecule gases of nitric acid and hydrogen peroxide water. 
     Since these cluster molecule gases of nitric acid and hydrogen peroxide water are very active gases, a chemical reaction occurs on a metal surface of the ozone-gas output gas pipe, the valve, or the like, to cause corrosion of the pipe surface. This may cause a corroded-metal impurity (metal contamination) to be contained in the output ozone gas. 
     An increase in the amount of the metal impurity (metal contamination) contained in the output ozone gas causes a deterioration in the performance of formation of, for example, an oxide film that is formed on a semiconductor by an oxide film process using the ozone gas. 
     From the above, it has been confirmed from tests that the quality of an output ozone gas is deteriorated if an impurity gas or moisture is contained in the raw material gas. Accordingly, the gas filters for the purpose of trapping the impurity gas or moisture are mounted to a raw material gas supply part. Particularly, in the embodiment 7, in the raw material gas inlet ports  14 - 1  to  14 -n of the ozone generation units  7 - 1  to  7 -n, the gas filters  52 - 1  to  52 -n are mounted at positions that allow easy replacement, so that the impurity gas or moisture are removed. 
     In this configuration, one gas filter  52 - 1  to  52 -n is provided. However, depending on a type of the impurity gas, a plurality of gas filters may be provided in series and at multiple stages, or an impurity gas filter and a moisture trapping gas filter may be provided in series and at multiple stages. 
     The other parts, pipe paths, and the like, of the configuration are identical to those of the ozone generation unit  7 X 2  shown in  FIG. 14 , except that the gas filter  52  replaces the super-high purity moisture remover  59 . Therefore, a description thereof is omitted. 
     As shown in  FIG. 23 , a raw material gas pipe (the raw material gas supply port  14 +the gas filter  52 ) and an output gas pipe system (ozone gas output port  15 ) are integrated into a gas pipe integrated block  30  as a gas pipe integrated block structure. Thereby, the ozone generator  1 , the ozone power source  2 , and the gas pipe system are packaged, and thus the ozone generation unit  7 X 5  can be further downsized. The raw material gas supply port  14  and the gas filter  52  are coupled to each other. 
     Similarly to the embodiment 7, at the raw material gas supply port  14  provided at a rear surface of the nitrogen-free ozone generation units  7 - 1  to  7 -n, the gas filter  52  (gas filters  52 - 1  to  52 -n) is mounted at a position that allows easy replacement. As a result, the ozone gas having a higher purity is provided, and additionally, the mounted gas filter  52  can remove the impurity gas. This exerts an effect that a time during which a purge gas is flowed prior to generation of the ozone gas can be considerably shortened. 
     &lt;Others&gt; 
     In the embodiments 1 to 7 above, the description has been give to the system for supplying the ozone gas with a predetermined ozone flow rate and a predetermined ozone concentration in an ozone-gas multi-processing apparatus for use in a semiconductor manufacturing apparatus that requires an ozone treatment apparatus capable of generating about several tens to 500 g/h ozone. 
     Instead of the ozone treatment apparatus  12  described above, an ozone-bleaching apparatus for pulp, an ozone treatment apparatus for pool water, an ozone treatment apparatus for clean and sewage water, and an ozone treatment apparatus for a chemical plant, which require a larger amount of ozone gas, may be adopted. For example, in a case of a processing apparatus that requires one to several kg/h ozone gas, a plurality of nitrogen-free ozone generation units  7 - 1  to  7 -n are installed in the ozone gas supply system  10  ( 101  to  104 ) described above, and output ozone gases of the nitrogen-free ozone generation units  7 - 1  to  7 -n are collectively supplied to one ozone treatment apparatus. This exerts an effect that the process can be easily performed at a relatively low cost and excellent maintainability is obtained. Therefore, the field of application of the ozone gas supply system is expanded. 
     While the invention has been shown and described in detail, the foregoing description is in all aspects illustrative and not restrictive. It is therefore understood that numerous modifications and variations can be devised without departing from the scope of the invention. 
     Industrial Applicability 
     The present invention relates to a nitrogen-free ozone generation unit provided with a function having a plurality of means for supplying an ozone gas, and an ozone gas supply system for supplying the ozone gas to a plurality of ozone treatment apparatuses. An object of the present invention is to achieve downsizing of the nitrogen-free ozone generation unit provided with a function having a plurality of means for outputting an ozone gas. However, obviously, also in a gas generation unit for a gas other than the ozone gas and a gas supply system for supplying the generated gas other than the ozone gas to a plurality of gas processing apparatuses, it is preferable to integrate and downsize a gas generator unit provided with a function having a plurality of means for outputting a gas, and build a gas generation system having a plurality of gas generation units installed therein.