Patent Publication Number: US-2007102117-A1

Title: Substrate processing system and substrate processing method

Description:
CROSS REFERENCE TO RELATED APPLICATION  
      This application is a division of U.S. application Ser. No. 10/602,041 filed on Jun. 23, 2003, the entire contents of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a substrate processing system and a substrate processing method for processing substrates, such as semiconductor wafers or glass substrates for LCDs (liquid crystal displays).  
      2. Description of the Related Art  
      For example, a known resist film removing process for removing a resist film coating a surface of a semiconductor wafer (hereinafter referred to simply as “wafer”) included in semiconductor device fabricating processes exposes a wafer placed in a processing chamber to a mixed processing fluid prepared by mixing ozone and steam to alter the resist film into a water-soluble film by oxidation, and then removes the water-soluble film with pure water. A general substrate processing system that performs such a resist film removing process is provided with a plurality of processing chambers, and ozone generated by a single ozone generator is distributed through ozone supply pipes to those processing chambers. The ozone generator generates ozone by discharging electricity in an oxygen-containing gas prepared by mixing oxygen gas and nitrogen gas.  
      In a general substrate processing system that distributes a processing fluid generated by a single source through branch lines to a plurality of processing chambers, there is the possibility that a wafer loading and unloading operations performed at one of the processing chambers affects on the processing condition of the process being performed in the other processing chambers. For example, in a substrate processing system in which a single processing fluid source supplies a processing fluid through branch lines to two processing chambers, the pressure and flow rate of the processing fluid being supplied to one of the processing chamber vary when a wafer is carried into or carried out of the other processing chamber and thereby the uniformity of a resist-solubilizing process is reduced. Consequently, the uniformity and reliability of the effects of the subsequent processes, such as a resist film removing process and etching process, are deteriorated.  
     SUMMARY OF THE INVENTION  
      Accordingly, it is an object of the present invention to provide a substrate processing system and a substrate processing method capable of supplying ozone gas (ozone-containing gas) having a stable ozone concentration into each processing chamber at a stable flow rate even if the processing system is configured so that a common ozone gas source supplies the ozone gas to a plurality of processing chambers.  
      In order to attain the objective, the present invention provides a substrate processing system, which includes: an ozone generator provided with electrodes and configured to generate an ozone-containing gas by applying an electric discharge produced by the electrodes to an oxygen-containing gas supplied to the ozone generator; a plurality of processing chambers each adapted to process therein a substrate with the ozone-containing gas generated by the ozone generator; a plurality of ozone-containing gas supply lines each connecting the ozone generator to each of the processing chambers; a flow regulator adapted to regulate a flow rate of the oxygen-containing gas supplied to the ozone generator; and a controller configured to determine an ozone-containing gas demand of processes to be carried out in the processing chambers, and configured to control the flow regulator to regulate a flow rate of the oxygen-containing gas being supplied to the ozone generator so that a flow rate of the ozone-containing gas being discharged from the ozone generator to be supplied to the processing chamber or chambers complies with the ozone-containing gas demand.  
      The present invention further provides a substrate processing system, which includes: an ozone generator provided with electrodes and configured to generate an ozone-containing gas by applying an electric discharge produced by the electrodes to an oxygen-containing gas supplied to the ozone generator; a plurality of processing chambers each adapted to process therein a substrate with the ozone-containing gas generated by the ozone generator; a plurality of ozone-containing gas supply lines each connecting the ozone generator to each of the processing chambers; a plurality of blow-off lines, connected to each of the ozone-containing gas supply lines, adapted to discharge the ozone-containing gas from each of the ozone supply lines before the ozone-containing gas reaches each of the processing chambers; and a plurality of valves each adapted to connect or disconnect each of the blow-off lines to or from each of the ozone-containing gas supply lines.  
      The present invention further provides a substrate processing system, which includes: a plurality of first gas passages; a plurality of ozone generators each interposed in each of the first gas passages, each of the ozone generators being provided with electrodes and configured to generate an ozone-containing gas by applying an electric discharge produced by the electrodes to an oxygen-containing gas fed from an upstream side of each of the first gas passages to each of the ozone generator in order to discharge the ozone-containing gas therefrom toward a downstream side of each of the first gas passages; a second gas passage connected to the first gas passages; a plurality of processing chambers each adapted to process therein a substrate with the ozone-containing gas generated by the ozone generators; a plurality of third gas passages branched from the second gas passage and connected respectively to the processing chambers to supply the ozone-containing gas to the processing chambers; and a controller configured to determine an ozone-containing gas demand of processes to be carried out in the processing chambers, and configured to control a state of at least one of the ozone generators between a first state in which said at least one of the ozone generators is generating the ozone-containing gas and a second state in which said at least one of the ozone generator stops generating the ozone-containing gas so that a sum of flow rates being discharged from the ozone generators toward the downstream sides of the first gas passages complies with the ozone gas demand.  
      According to another aspect of the present invention, a substrate processing method is provided, the method including the steps of: providing a processing system including an ozone generator having electrodes, and a plurality of processing chambers each adapted to process a substrate therein by using an ozone-containing gas generated by the ozone generator; determining an ozone-containing gas demand of processes to be carried out in the processing chambers; feeding an oxygen-containing gas to the ozone generator at a flow rate that enables the ozone generator to discharge an ozone-containing gas at a flow rate that complies with the ozone-containing gas demand; applying a voltage across the electrodes of the ozone generator to produce an electric discharge, thereby producing an ozone-containing gas by applying the electric discharge to the oxygen-containing gas fed to the ozone generator; supplying the ozone-containing gas thus generated by the ozone generator and discharged therefrom to the processing chamber or chambers, thereby processing a substrate accommodated in each of the processing chamber or chambers with the ozone-containing gas; and changing the flow rate of the oxygen-containing gas being fed to the ozone generator, if the ozone-containing gas demand changes.  
      The present invention further provides a substrate processing method including the steps of: providing a processing system including an ozone generator having electrodes, and a plurality of processing chambers each adapted to process a substrate therein by using an ozone-containing gas supplied by the ozone generator; determining whether or not each of the processing chambers requires the ozone-containing gas; feeding an oxygen-containing gas to the ozone generator; applying a voltage across the electrodes of the ozone generator to produce an electric discharge, thereby producing an ozone-containing gas by applying the electric discharge to the oxygen-containing gas fed to the ozone generator; supplying the ozone-containing gas thus generated by the ozone generator only to the chamber or chambers that are requiring the ozone-containing gas, thereby processing a substrate accommodated in each of the processing chamber or chambers with the ozone-containing gas; and discarding a part of the ozone-containing gas generated by the ozone generator without supplying it to any one of the processing chambers.  
      The present invention further provides a substrate processing method including the steps of: providing a processing system including a plurality of ozone generators each having electrodes, and a plurality of processing chambers each adapted to process a substrate therein by using an ozone-containing gas supplied by the ozone generator; determining an ozone-containing gas demand of processes to be carried out in the processing chambers; determining the number of the ozone generators to be operated to generate an ozone-containing gas based on the ozone-containing gas demand; feeding an oxygen-containing gas to the ozone generator or generators determined to be operated; applying a voltage across the electrodes of the ozone generator or generators determined to be operated to produce an electric discharge, thereby producing an ozone-containing gas by applying the electric discharge to the oxygen-containing gas fed to the ozone generator or generators; supplying the ozone-containing gas thus generated by the ozone generator or generators to the processing chamber or chambers, thereby processing a substrate accommodated in each of the processing chamber or chambers with the ozone-containing gas; changing the number of the ozone generators to be operated, if the ozone-containing gas demand is increased or decreased. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a schematic plan view of a substrate processing system according to the present invention;  
       FIG. 2  is a schematic side elevation of the substrate processing system shown in  FIG. 1 ;  
       FIG. 3  is a piping diagram of a piping system included in the substrate processing system shown in  FIG. 1 ;  
       FIG. 4  is a longitudinal sectional view of a processing vessel included in the substrate processing system shown in  FIG. 1 ;  
       FIG. 5  is a detailed piping diagram of a piping system relating to an ozone supply, which is extracted from the entire piping system of the processing system shown in  FIG. 3 ;  
       FIG. 5A  schematically shows a structure of an ozone generator shown in  FIG. 5 ;  
       FIG. 6  is a piping diagram of a piping system relating to a mist trap shown in  FIG. 3 ;  
       FIG. 7  is a cross-sectional view of the mist trap shown in  FIG. 6 ;  
       FIG. 8  is a piping diagram of a piping system, provided with an additional ozone generator and additional processing vessels, modified based on the system shown in  FIG. 5 ;  
       FIG. 9  is a piping diagram of a piping system, provided with blow-off lines, modified based on the system shown in  FIG. 5 ; and  
       FIG. 10  is a piping diagram of a piping system, provided with a carbon dioxide gas supply, modified based on the system shown in  FIG. 5 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       FIGS. 1 and 2  show a substrate processing system  1  according to the present invention for carrying out a resist-solubilizing process and a resist film removing process. The substrate processing system  1  includes a substrate processing section  2  for processing a wafer W (i.e., a substrate) by a cleaning process and a resist-solubilizing process, and a wafer transfer section  3  for carrying a wafer W into the substrate processing section  2  and vice versa.  
      The wafer transfer section  3  includes an in/out port  4  provided with a table  6  for supporting wafer carriers C each capable of holding, for example, twenty-five disk-shaped wafers W, thereon, and a wafer carrying area  5  provided with a wafer conveyer  7  for transferring wafers W from the wafer carrier C placed on the table  6  to the substrate processing section  2  and vice versa.  
      The wafer carrier C has one side provided with an opening covered with a cover. The cover of the wafer carrier C is opened to take out wafers W from and to put wafers W into the wafer carrier C. Shelves are supported on the inner surfaces of walls of the wafer carrier C to support wafers W at predetermined intervals. The shelves define, for example, twenty-five slots for accommodating wafers W. One wafer W is inserted in each of the slots with its major surface (on which semiconductor devices are formed) facing up.  
      For example, three wafer carriers C can be arranged along the Y-axis in a horizontal plane at predetermined positions on the table  6  of the in/out port  4 . The wafer carrier C is placed on the table  6  with its side provided with the cover faced toward a partition wall  8  separating the in/out port  4  and the wafer carrying area  5 . Windows  9  are formed in the partition wall  8  at positions corresponding to the positions where the wafer carriers C are placed on the table  6 . Shutters (not shown) are installed on the side of the wafer carrying area  5  with respect to the windows  9 , and the shutters are operated by shutter operating mechanisms  10  to open and close the windows  9 .  
      Each of the shutter operating mechanisms  10  is also capable of opening and closing the cover of the wafer carrier C. The shutter operating mechanism opens and closes the shutter covering the window  9  and the cover of the wafer carrier C simultaneously. After the window  9  and the open side of the wafer carrier C have been opened, the wafer conveyer  7  arranged in the wafer carrying area  5  is able to access the wafer carrier C to carry a wafer W.  
      The wafer conveyer  7  placed in the wafer carrying area  5  is horizontally movable along the Y-axis, is vertically movable along the Z-axis, and is turnable in the θ-direction in a horizontal plane, i.e., XY-plane. The wafer conveyer  7  has a wafer transfer arm  11  capable of holding and carrying a wafer W. The wafer transfer arm  11  is horizontally movable along the X-axis. Thus, the wafer conveyer  7  is capable of accessing every one of the slots, at different levels, of the wafer carrier C placed on the table  6  and each of two vertically arranged wafer delivery units  16  and  17 . Accordingly, the wafer conveyer  7  is capable of transferring the wafer from the in/out port  4  to the substrate processing section  2  and vice versa.  
      The substrate processing section  2  includes a main wafer conveyer  18 , the wafer delivery units  16  and  17  for temporarily holding a wafer W before delivery, four substrate cleaning units  12 ,  13 ,  14  and  15 , and substrate processing units  23   a  to  23   f  for subjecting wafers W to a resist-solubilizing process for altering resist films into a water-soluble condition.  
      The substrate processing section  2  is provided with an ozone producing unit  24  including an ozone generator  42 , and a chemical liquid storage unit  25  storing a processing liquid to be supplied to the substrate cleaning units  12 ,  13 ,  14  and  15 . An ozone-containing gas produced by the ozone producing unit  24  is supplied to the substrate processing units  23   a  to  23   f.    
      A fan filter unit (FFU)  26  is installed on the top wall of the substrate processing section  2  to supply clean air to those units and the main wafer conveyer  18 . Part of clean air blown downward by the FFU  26  flows through the wafer transfer units  16  and  17  and a space extending over the wafer transfer units  16  and  17  into the wafer carrying area  5 . Thus, contaminants, such as particles, are prevented from migrating from the wafer carrying area  5  into the substrate processing section  2  to keep the interior of the substrate processing section  2  clean.  
      Each of the wafer delivery units  16  and  17  (i.e., wafer relay units  16 ,  17 ) is capable of holding temporarily a wafer W received from the wafer conveyer  7  and a wafer to be delivered to the wafer conveyer  7 . The wafer transfer units  16  and  17  are stacked vertically. The upper wafer transfer unit  16  may be used for transferring a wafer W from the substrate processing section  2  to the in/out port  4 , and the lower wafer transfer unit  17  may be used for transferring a wafer W from the in/out port  4  to the substrate processing section  2 .  
      The main wafer conveyer  18  is has a base movable in directions parallel to the X-axis and the Z axis and is turnable in the θ-direction in an XY-plane. The main wafer conveyer  18  has a carrying arm  18   a  mounted to the base thereof and capable of holding a wafer W. The carrying arm  18   a  is capable of moving in directions parallel to the Y-axis when the base of the wafer conveyer  18  is in an angular position shown in  FIG. 1 . Thus, the main wafer conveyer  18  is able to access the wafer delivery units  16  and  17 , the substrate cleaning units  12  to  15  and the substrate processing units  23   a  to  23   f.    
      The substrate cleaning units  12 ,  13 ,  14  and  15  perform a cleaning process and a drying process to clean and dry wafers W processed by the resist-solubilizing process by the substrate processing units  23   a  to  23   f . The two wafer cleaning units  12  and  13  are stacked, and the two wafer cleaning units  14  and  15  are stacked. The wafer cleaning units  12  to  15  are substantially similar in construction, except that the two wafer cleaning units  12 ,  13  and the two wafer cleaning units  14 ,  15  are symmetrical with respect to a wall  27  separating the two wafer cleaning units  12 ,  13  and the two wafer cleaning units  14 ,  15  as shown in  FIG. 1 .  
      The substrate processing units  23   a  to  23   f  perform the resist-solubilizing process for making resist films formed on the surfaces of wafers W water-soluble. As shown in  FIG. 2 , the substrate processing units  23   a  to  23   f  are stacked in two stacks; the substrate processing units  23   e ,  23   c  and  23   a  are stacked up in that order in the left stack, and the substrate processing units  23   f ,  23   d  and  23   b  are stacked up in that order in the right stack. The substrate processing units  23   a  to  23   f  are virtually similar in construction, except that the substrate processing units  23   a  and  23   b , the substrate processing units  23   c  and  23   d , and the substrate processing units  23   e  and  23   f  are symmetrical, respectively, with respect to a wall  28  separating the right and the left stack as shown in  FIG. 1 . A piping system for the substrate processing units  23   a  and  23   b , a piping system for the substrate processing units  23   c  and  23   d , and a piping system for the substrate processing units  23   e  and  23   f  are similar. The substrate processing units  23   a  and  23   b , and the piping system for the substrate processing units  23   a  and  23   b  will be described by way of example.  
       FIG. 3  shows the piping system for the substrate processing units  23   a  and  23   b . The substrate processing units  23   a  and  23   b  are provided with processing vessels (i.e., processing chambers)  30 A and  30 B, respectively. Each of the processing vessels  30 A and  30 B is adapted to hold a wafer W therein. The processing vessels  30 A and  30 B are connected respectively by steam supply pipes  38   a  and  38   b  (hereinafter referred to as “main supply pipes  38   a  and  38   b ”) to a steam generator  40 .  
      The ozone generator  42  and a nitrogen gas source  43  are connected to the main supply pipe  38   a  through a supply selector  41   a , and are connected to the main supply pipe  38   b  through a supply selector  41   b . The ozone generator  42  is included in the ozone producing unit  24 . The supply selectors  41   a  and  41   b  include flow regulating valves  50   a  and  50   b , flow regulating valves  52   a  and  52   b , and stop valves  54   a  and  54   b , respectively.  
      The flow regulating valve  50   a  ( 50   b ) is capable of connecting and disconnecting the corresponding processing vessel  30 A ( 30 B) to and from the steam generator  40 , and also capable of regulating the flow rate of wafer vapor (steam) to be supplied to the corresponding processing vessel  30 A ( 30 B) from the steam generator  40 .  
      The flow regulating valve  52   a  ( 52   b ) is capable of connecting and disconnecting the corresponding processing vessel  30 A ( 30 B) to and from the ozone generator  42 , and also capable of regulating the flow rate of the ozone-containing gas to be supplied to the corresponding processing vessel  30 A ( 30 B) from the ozone generator  42 .  
      The stop valve  54   a  ( 54   b ) is capable of connecting and disconnecting the processing vessel  30 A ( 30 B) to and from a nitrogen gas source  43 .  
      Connected to the ozone generator  42  is an ozone-containing gas supply main pipe  60 , which is divided into two ozone-containing gas supply branch pipes  61   a  and  61   b . The branch pipes  61   a  and  61   b  are connected through the flow regulating valves  52   a  and  52   b  to the main supply pipes  38   a  and  38   b , respectively. Thus, the main supply pipe  60 , the branch pipes  61   a ,  61   b , and the main supply pipes  38   a ,  38   b  constitute ozone-containing gas supply lines that carry an ozone-containing gas generated by the ozone generator  42  to the processing vessels  30 A,  30 B, respectively. A filter  64  and an ozone concentration measuring device  65  for measuring the ozone concentration of the ozone-containing gas produced by the ozone generator  42  are placed in that order from the side of the ozone generator  42  in the ozone-containing gas supply main pipe  60 . Flow meters  66   a  and  66   b  and the flow regulating valves  52   a  and  52   b  are placed in that order from the side of the ozone generator  42  in the ozone-containing gas supply branch pipes  61   a  and  61   b , respectively. The flow meters  66   a  and  66   b  measure respective flow rates of the ozone-containing gas being supplied to the processing vessels  30 A and  30 B.  
      The respective flow regulating characteristics of the flow regulating valves  52   a  and  52   b  are adjusted beforehand such that the flow rates measured by the flow meters  66   a  and  66   b  are equal, when the flow regulating valves  52   a  and  52   b  are opened. When both the flow regulating valves  52   a  and  52   b  are opened, the ozone-containing gas carried by the ozone-containing gas supply main pipe  60  is distributed equally to the branch ozone-containing gas supply pipes  61   a  and  61   b , flows at the same flow rates into the processing vessels  30 A and  30 B. Supposing the ozone-containing gas is supplied into the ozone-containing gas supply main pipe  60  at about 8 l/min, the ozone-containing gas flows through each of the ozone-containing gas supply branch pipes  61   a  and  61   b  at about 4 l/min.  
      Connected to the nitrogen gas source  43  is a nitrogen gas supply pipe  53 , which is divided into two nitrogen gas supply branch pipes  53   a  and  53   b . The branch pipes  53   a  and  53   b  are connected, through flow selector valves  68 ,  68  and to the stop valves  54   a  and  54   b  of the supply selectors  41   a  and  41   b  in that order from the side of the nitrogen gas source  43 , to the main supply pipes  38   a  and  38   b , respectively. Each of the flow selector valves  68  has a high-flow position and a low-flow position.  
      The flow regulating valves  50   a  and  50   b  can be adjusted such that steam generated by the steam generator  40  is supplied through the main supply pipes  38   a  and  38   b  into the processing vessels  30 A and  30 B at equal flow rates. Nitrogen gas can be supplied, from the nitrogen gas source  43  through the nitrogen gas supply branch pipes  53   a  and  53   b  and the main supply pipes  38   a  and  38   b , into the processing vessels  30 A and  30 B at equal flow rates, if the positions (high-flow position or low-flow position) of the flow selector valves  68  are the same.  
      Discharge pipes  70   a  and  70   b  are connected to parts of the processing vessels  30 A and  30 B respectively diametrically opposite to parts of the processing vessels  30 A and  30 B to which the main supply pipes  38   a  and  38   b  are connected. The discharge pipes  70   a  and  70   b  are joined to a discharge pipe  70   c  connected to a mist trap  71 . Discharge selectors  72  serving as pressure regulators for the processing vessels  30 A and  30 B are provided in the discharge pipes  70   a  and  70   b , respectively.  
      Each of the discharge pipes  70   a  and  70   b  are divided into three branch pipes  76 ,  77  and  85 , respectively. The branch pipe  76  is provided with a first switch valve  81 . The branch pipe  77  is provided with a second switch valve  82 . The branch pipe  85  is provided with a third switch valve  86 . The first switch valve  81  has a restrictor therein and allows a fluid to flow therethrough at a relatively low flow rate, when opened. The second switch valve  82  allows a fluid to flow therethrough at a relatively high flow rate, when opened. Normally, the third switch valve  86  is closed. The third switch valve  86  opens in a state of emergency, such as a state where the internal pressure of the processing vessel  30 A ( 30 B) becomes excessively high. The downstream ends of the branch pipes  76 ,  77  and  85  are joined together into a single discharge pipe  70   a  ( 70   b ) again. Each of the discharge selectors  72  are composed of the branch pipes  76  and  77  and the first and the second switch valves  81  and  82 .  
      The mist trap  71  cools a processing fluid discharged from the processing vessels  30 A and  30 B, separates the liquid contained in the discharged processing fluid from the ozone-containing gas contained in the discharged processing fluid, and drains the liquid through a drain pipe  90 . A discharge pipe  91  carries the ozone-containing gas thus extracted from the discharged processing fluid to an ozone killer  92 . The ozone killer  92  decomposes ozone contained in the ozone-containing gas into oxygen by thermal decomposition, cools the oxygen and discharges the cooled oxygen through a discharge pipe  94 .  
      As mentioned above, the flow regulating valves  50   a  and  50   b  regulate the flow rates of steam supplied to the processing vessels  30 A and  30 B, respectively. The flow regulating valves  52   a  and  25   b  regulates the flow rates of the oxygen-containing gas supplied to the processing vessels  30 A and  30 B, respectively. The discharge selector  72  regulate, by selectively opening the first or second switch valve  81 ,  82 , the rates of discharge of fluids from the processing vessels  30 A and  30 B to control the pressures of steam, ozone-containing gas or the processing fluid containing steam and the ozone-containing gas in the processing vessels  30 A and  30 B, respectively.  
      Leak detectors  95  are connected respectively to the processing vessels  30 A and  30 B to monitor the leakage of the processing fluid from the processing vessels  30 A and  30 B.  
      The processing vessels  30 A and  30 B are the same in construction and hence only the processing vessel  30 A will be described by way of example. Referring to  FIG. 4 , the processing vessel  30 A has, as principal components, a vessel body  100  for holding a wafer W therein, and a cover  101  for transferring a wafer W from the main wafer conveyer  18  to the vessel body  100  and vice versa. A cover lifting mechanism (not shown) including a cylinder actuator (not shown) separates the cover  101  from the vessel body  100  when the cover  101  receives a wafer W from the main wafer conveyer  18 , and joins the cover  101  closely to the vessel body  100  while a wafer W is processed in the processing vessel  30 A. A sealed processing space S 1  is formed by closely joining the vessel body  100  and the cover  101  together.  
      The vessel body  100  has a disk-shaped base  100   a , and an annular circumferential wall  100   b  rising from a peripheral part of the base  100   a . The base  100   a  is internally provided with a heater  105 . A circular land  110  of a diameter smaller than that of a wafer W is formed on an upper surface of the base  100   a . The upper surface of the circular land  110  is at a level below that of the upper surface of the circumferential wall  100   b . An annular groove  100   c  is formed between the circumferential wall  100   b  and the circular land  110 .  
      Four support members  111 , for supporting a wafer W placed in the vessel body  100 , are disposed at four positions in a peripheral part of the circular land  110 . The four support members  111  support a wafer W placed thereon stably in place. A gap G of about 1 mm is formed between the lower surface of a wafer W supported in place by the support members  111  and the upper surface of the circular land  110 . The support members  111  are formed of a resin, such as a PTFE resin.  
      Two concentric circular grooves are formed in the upper surface of the circumferential wall  100   b . Two O-rings  115   a  and  115   b  are fitted in the circular grooves to seal gaps between the upper surface of the circumferential wall  100   b  and the lower surface of the cover  101  so that the processing space S 1  may be sealed when the vessel body  100  and the cover  101  are joined together.  
      A supply port  120  is formed in the circumferential wall  100   b . The processing fluid is supplied through the supply port  120  into the processing vessel  30 A. A discharge port  121  is formed in the circumferential wall  110   b  at a position diametrically opposite to the supply port  120 . The main supply pipe  38   a  and the discharge pipe  70   a  are connected, respectively, to the supply port  120  and the discharge port  121 .  
      The supply port  120  and the discharge port  121  open into an upper part and a lower part, respectively, of the annular groove  100   c . The arrangement of the ports  120  and  121  enables the processing fluid to be supplied smoothly through the supply port  120  into the processing space S 1  so that the processing fluid may not stagnate, and also prevents the processing fluid from remaining in the processing vessel  30 A when the processing fluid is discharged from the processing vessel  30 A.  
      In fact, the supply port  120  opens into a space between the two adjacent support members  111 , and the discharge port  121  opens into a space between the other two adjacent support members  111 , so that the processing fluid is smoothly supplied into and discharged from the processing vessel  30 A without being obstructed by the support members. However, in  FIG. 4 , the support members  111  are shown as being diametrically aligned with the supply and discharge ports  120  and  121  to the contrary, for simplicity of the drawing.  
      The cover  101  has a body  101   a  internally provided with a heater  125 , and a pair of holding members  112  projecting downward from diametrically opposite parts of the lower surface of the cover  101 . Each of the holding members  112  have a substantially L-shaped section, and has a tip portion bent radially inward, on which a wafer W is placed. When a cover lifting mechanism lowers the cover  101  toward the vessel body  100 , the holding members  112  holding a wafer W advance into the annular groove  100   c  to place the wafer W on the support members  111  of the vessel body  100 .  
      The steam generator  40  has a tank (not shown), into which pure water is supplied from a pure water (DIW) source  141 . The steam generator  40  generates steam, or a water vapor, by heating the pure water contained in the tank with a heater. The interior space of the tank is kept at temperature of about 120° C. and in a pressurized state. Referring to  FIG. 3 , parts, extending between the steam generator  40  and the supply selector  41   a  and  41   b , of the main supply pipes  38   a  and  38   b  are covered with tubular temperature regulators  136 . The regulators  136  regulate the temperature of steam flowing from the steam generator  40  to the supply selector  41   a  and  41   b.    
      A flow regulating valve V 2  is placed in a pure water supply pipe  140 , which carries pure water from the pure water source  141  to the steam generator  40 . A branch pipe  142  branched from the nitrogen gas supply branch pipe  53   b  connected to the nitrogen gas source  43  is connected to a part, between the flow regulating valve V 2  and the steam generator  40 , of the pure water supply pipe  140 . The branch pipe  142  is provided therein with a flow regulating valve V 3 . The flow regulating valves V 2  and V 3  are capable of not only regulating the flow rates of the fluids flowing through the pipes  140  and  142 , but also opening and shutting-off the pipes  140  and  142 , respectively.  
      A drain pipe  145  is connected to the not-shown tank of the steam generator  40  to drain pure water therefrom. The drain pipe  145  is provided with a drain valve DV interlocked with the flow regulating valve V 3  in the branch pipe  142 . The drain pipe  145  has a downstream end connected to a mist trap  148 . A pressure-relief pipe  150  is connected to the not-shown tank of the steam generator  40  to discharge steam therefrom to prevent the internal pressure of the tank of the steam generator  40  from increasing beyond a specified limit. The pressure-relief pipe  150  is also used for controlling the flow rates of steam to be supplied to the processing vessels  30 A and  30 B, as mentioned later. The downstream end of the pressure-relief pipe  150  is connected to a part, on the downstream side of the drain valve DV, of the drain pipe  145 . The pressure-relief pipe  150  is provided with a flow regulating valve V 4  and a stop valve V 5 . A branch pipe  153  is connected to the pressure-relief pipe  150 . One end the branch pipe  153  is connected to a part, on the upstream side of the flow regulating valve V 4 , of the pressure-relief pipe  150 , and the other end of the branch pipe  153  is connected to a part, on the downstream side of the stop valve V 5 , of the pressure-relief pipe  150 . The branch pipe is provided with a pressure-relief valve RV 1 . The mist trap  148  cools pure water drained through the drain pipe  145  and steam discharged through the pressure-relief pipe  150 , and drains therefrom cooled pure water and condensed steam through a drain pipe  154 .  
      The heater of the steam generator  40  is supplied with a fixed electric power in order to keep the steam generating rate of the steam generator  40  constant. As mentioned above, the flow regulating characteristics of the flow regulating valves  50   a  and  50   b  are adjusted beforehand such that steam generated by the steam generator  40  is supplied to the processing vessels  30 A and  30 B at equal flow rates, respectively.  
      Now, it is supposed that the steam generator generates five units of steam per unit time.  
      In the event that steam needs to be supplied to both the processing vessels  30 A and  30 B simultaneously, two units of steam are supplied per unit time to the processing vessel  30 A, two units of steam are supplied per unit time to the processing vessel  30 B, and one unit of steam is discharged per unit time from the steam generator  40  through the pressure-relief pipe  150 . In this case, the flow regulating valve V 4  is adjusted so that one unit of steam flows per unit time through the pressure-relief pipe  150 , and the flow regulating valves  50   a  and  50   b  and the stop valve V 5  of the pressure-relief pipe  150  are opened.  
      In a case where steam needs to be supplied only to the processing vessel  30 A or the processing vessel  30 B, such as a case where a wafer W is carried into the processing vessel  30 A (or  30 B) and, at the same time, a resist water-solubilizing process using steam and the ozone-containing gas is carried out in the processing vessel  30 B (or  30 A), two units of steam per unit time out of five units of steam generated per unit time by the steam generator  40  are supplied only to the processing vessel  30 B (or  30 A), and three units of steam are discharged per unit time through the pressure-relief pipe  150 . Therefore, the flow regulating valve V 4  is adjusted so that three units of steam out of five units of steam are discharged per unit time through the pressure-relief pipe  150 , the flow regulating valve  50   a  (or  50   b ) is closed and the stop valve V 5  is opened when steam needs to be supplied only to the processing vessel  30 B (or  30 A).  
      When neither the processing vessel  30 A nor the processing vessel  30 B needs steam, all the steam generated by the steam generator  40  is discharged through the pressure-relief pipe  150  by closing both the flow regulating valves  50   a  and  50   b  and opening the stop valve V 5  and the flow regulating valve V 4 .  
      In order to perform the above operation effectively, each of the flow regulating valves  50   a  and  50   b  is provided therein with a variable throttle capable of being adjusted beforehand, and a shut-off valve capable of adopting only a fully-opened position and a closed position. The openings of the variable throttles of the flow regulating valves  50   a  and  50   b  are adjusted beforehand such that the stem generated by the steam generator  40  is evenly distributed to the main supply pipes  38   a  and  38   b  and to the processing chambers  30 A and  30 B, when both the shut-off valves of the flow regulating valves  50   a  and  50   b  are opened.  
      The flow regulating valves  52   a  and  52   b  for regulating ozone-containing gas have the same structure as that of the flow regulating valves  50   a  and  50   b . Thus, each of the flow regulating valves  52   a  and  52   b  includes a variable throttle and a shut-off valve.  
      Steam discharged from the steam generator  40  through the pressure-relief pipe  150  is carried to the mist trap  148  by the drain pipe  145 . The pressure-relief valve RV 1  opens when the internal pressure of the tank  130  increases beyond a specified limit to discharge steam from the tank  130  through the pressure-relief pipe  150 , the branch pipe  153 , the pressure-relief pipe  150  and the drain pipe  145 .  
      The flow rates of steam supplied to the processing vessels  30 A and  30 B can be adjusted by discharging steam generated by the steam generator  40  at a proper discharge rate regulated by the flow regulating valve V 4 . Even if the steam demand of the processes to be carried out by the processing vessels (in other words, the number of the processing vessels simultaneously needing steam, for example) is changed, the flow regulating characteristics (the openings of the variable throttles) of the flow regulating valves  50   a  and  50   b  adjusted beforehand do not need to be changed, and only the shut-off valves of the flow regulating valve  50   a  and/or the flow regulating valve  50   b  need to be opened and/or closed. The aforementioned method of regulating the flow rates of steam flowing into the processing vessels  30 A and  30 B using the flow regulating valve V 4  is easier than a flow regulating method that controls the openings of the flow regulating valves  50   a  and  50   b  or a flow regulating method that controls the output of a heater to control the steam generating rate of the steam generator  40 . Thus, the flow rates of steam being supplied to the processing vessels  30 A and  30 B can accurately be regulated according to processes to be carried out in the processing vessels  30 A and  30 B, which improves the uniformity of the effect and the reliability of the resist-solubilizing process.  
       FIG. 5  shows a piping diagram of a piping system relating to the ozone supply, which is extracted from the entire piping system of the processing system shown in  FIG. 3  for the purpose of detailed explanation. An oxygen gas source  181  is connected to the ozone generator  42  by an oxygen gas supply pipe  180 . A nitrogen gas supply pipe  182  has one end connected to a nitrogen gas source  183  and the other end connected to the oxygen gas supply pipe  180 . A stop valve  185 , and a mass flow controller  188 , i.e., a flow regulating device for regulating the flow of oxygen gas to the ozone generator  42  are arranged in that order from the side of the oxygen gas source  181  in the oxygen gas supply pipe  180 . The nitrogen gas supply pipe  182  is connected to a part, on the downstream side of the mass flow controller  188 , of the oxygen gas supply pipe  180 . A stop valve  190 , and a mass flow controller  191 , i.e., a flow regulating device for regulating the flow of nitrogen gas supplied to the ozone generator  42 , are arranged in that order from the side of the nitrogen gas source  183  in the nitrogen gas supply pipe  182 . Oxygen gas supplied from the oxygen gas source  181  and nitrogen gas supplied from the nitrogen gas source  183  flow at flow rates regulated by the mass flow controllers  188  and  191 , respectively. Then, the oxygen gas and the nitrogen gas mix to produce an oxygen-containing gas. The oxygen gas supply pipe  180  carries the oxygen-containing gas into the ozone generator  42 .  
      Referring to  FIG. 5A , the ozone generator  42  has discharge electrodes  42   a ,  42   b  between which the oxygen-containing gas passes. At least one of the discharge electrodes  42   a  and  42   b  is covered with a dielectric member, not shown. An ac power source  42   c , typically a high-frequency power source, applies a voltage across the discharge electrodes  42   a  and  42   b  to produce a corona discharge, i.e., an electric discharge, between the discharge electrodes  42   a  and  42   b . The oxygen-containing gas passing between the discharge electrodes  42   a  and  42   b  is subjected to the corona discharge, thereby part of oxygen molecules contained in the oxygen-containing gas are ionized to be converted into ozone. The ozone thus produced is discharged together with other gases (such as nitrogen and non-reacted oxygen), as an ozone-containing gas, from the ozone generator  42 . The ac power source  42   c  includes a power regulator capable of varying the voltage applied across the discharge electrodes  42   a  and  42   b  to control the ozone concentration of the ozone-containing gas. Referring again to  FIG. 5 , the ozone-containing gas discharged from the ozone generator  42  can be supplied to the processing chambers  30 A and  30 B, through the ozone-containing gas supply pipe  60  and the ozone-containing gas supply branch pipes  61   a  and  61   b , respectively.  
      A unit controlling CPU  200 , which processes information on processes to be performed by the substrate processing units  23   a  and  23   b , is capable of detecting the respective states of the flow regulating valves  52   a  and  52   b , namely, whether or not each of the flow regulating valves  52   a  and  52   b  is opened. The unit controlling CPU  200  sends information on the processes to be performed by the substrate processing units  23   a  and  23   b , and aforesaid information on the respective states of the flow regulating valves  52   a  and  52   b  to a CPU  201 , i.e., a controller for controlling the mass flow controllers  188  and  191  and the ozone generator  42 .  
      The CPU  201  determines a sum of the flow rates of the ozone-containing gas to be supplied into the processing vessels  30 A and  30 B on the basis of the information on the respective states of the flow regulating valves  52   a  and  52   b  given thereto by the unit controlling CPU  200 . In other words, the CPU  201  determines the ozone-containing gas demand of processes to be performed in the processing vessels  30 A and  30 B. The CPU  201  controls the mass flow controllers  188  and  191  to supply oxygen gas and nitrogen gas to the ozone generator  42  at a supply rate (flow rate) that enables the ozone generator  42  to discharge the ozone-containing gas at an discharging rate (flow rate) that complies with or coincides with the aforementioned sum of the flow rates of the ozone-containing gas to be supplied into the processing vessels  30 A and  30 B. The CPU  201  controls the mass-flow controllers  188  and  191  so that nitrogen-oxygen ratio of the oxygen-containing gas supplied to the ozone generator  42  is kept substantially constant regardless of the flow rate of the oxygen-containing gas supplied to the ozone generator  42 .  
      If only one of the processing vessels  30 A and  30 B needs the ozone-containing gas, the ozone generator  42  produces the ozone-containing gas at a rate of, for example, about 4 l/min.  
      When both the processing vessels  30 A and  30 B need the ozone-containing gas, the ozone generator  42  produces the ozone-containing gas at a rate of, for example about 8 l /min. In this case, since the flow regulating characteristics of the flow regulating valves  52   a  and  52   b  are adjusted beforehand, the ozone-containing gas is supplied at equal flow rates, such as about 4 l/min, to the processing vessels  30 A and  30 B, respectively.  
      In the above explanation, the CPU  201  determines the ozone-containing gas demand based on the conditions of the flow regulating valves  52   a  and  52   b . Alternatively, the CPU  201  may determine the ozone-containing gas demand with reference to the process recipe defining the time sequence of the processes to be performed by the processing units and pre-installed in a system controller (not shown) that controls the CPU  200  and the CPU  201 .  
      The CPU  201  is capable of detecting an ozone concentration measured by an ozone-concentration measuring device  165  and of controlling the discharge voltage of the ozone generator  42 , in other words, the voltage applied across the electrodes  42   a  and  42   b . The measured ozone concentration is used as a control signal for the feedback control of the discharge voltage of the ozone generator  42 . Thus, the ozone concentration of the ozone-containing gas is controlled in a feedback control mode. Consequently, the ozone-containing gas having a stable ozone concentration can be produced by appropriately adjusting the discharge voltage, even if the flow rate of the oxygen-containing gas flowing into the ozone generator  42 , the oxygen-nitrogen ratio of the oxygen-containing gas, or pressure in the ozone generator  42  is changed.  
      The ozone-containing gas of a desired pressure having a stable ozone concentration can be supplied at desired flow rates to the processing vessels  30 A and  30 B by the control operations of the CPU  201 . Therefore, wafers W processed by supplying the ozone-containing gas only one of the processing vessels  30 A and  30 B, and those processed by supplying the ozone-containing gas simultaneously to both the processing vessels  30 A and  30 B can be subjected to the resist-solubilizing processes of the same process conditions.  
      In the illustrated embodiment, the processing system has two separated CPU&#39;s  200  and  201 , however, these CPU&#39;s may be integrated into a single processing unit.  
      Referring to  FIGS. 6 and 7 , the mist trap  71  has a cooling unit  210  for cooling a discharge fluid discharged from the processing vessels  30 A and  30 B and containing steam and the ozone-containing gas, and a tank  211  for storing liquefied ozone-containing water produced by cooling the discharge fluid by the cooling unit  210 .  
      The cooling unit  210  has a cooling coil formed by coiling a double pipe  215  consisting of an inner pipe  213  and an outer pipe  214  surrounding the inner pipe  213  in, for example, six coils. Cooling water is passed through an annular space between the inner pipe  213  and the outer pipe  314  to cool the discharge fluid flowing through the inner pipe  213 . An upper end part of the inner pipe  213  projecting from the upper end of the coiled double pipe  215  is connected to the discharge pipe  70   c . A cooling water discharge pipe  221  is connected to the upper end, from which the upper end part of the inner pipe  213  projects from the double pipe  215 , of the outer pipe  214  of the double pipe  215 . Cooling water flows upward through the annular space and is discharged through the cooling water discharge pipe  221 . A lower end part of the inner pipe  213  projecting from the lower end of the coiled double pipe  215  is extended through the top wall of the tank  211  into the tank  211 . A cooling water supply pipe  222  is connected to the lower end, from which the lower end part of the inner pipe  213  projects from the double pipe  215 , of the outer pipe  214 . Cooling water is supplied into the annular space between the inner pipe  213  and the outer pipe  214  through the cooling water supply pipe  222 .  
      The cooling water discharge pipe  221  and the cooling water supply pipe  222  are connected to a cooling water recovery means  232  and a cooling water supply means  231 , respectively, as shown in  FIG. 6 . Cooling water flows through the annular space between the inner pipe  213  and the outer pipe  214 . The cooling water supply means  231  and the cooling water recovery means  232  are connected to a cooling device  93  to circulate cooling water through the cooling unit  93 .  
      The discharged processing fluid containing the ozone-containing gas, steam and nitrogen gas, and discharged through the discharge pipe  70   c , flows through the inner pipe  213 , and is cooled by cooling water flowing through the annular space between the inner and outer pipes  213  and  214 . Consequently, steam contained in the discharged processing fluid condenses into water. Thus, the discharged processing fluid is reduced into water and the ozone-containing gas containing oxygen gas, nitrogen gas and ozone. Actually, the discharged processing fluid is reduced into ozone-containing water and an ozone-containing gas by cooling because part of ozone dissolves in pure water produced by the transformation of steam.  
      The lower end part of the inner pipe  213  and the discharge pipe  91  are extended through the top wall of the tank  211  into the tank  211 . The drain pipe  90  and a gas supply port  230  are extended through the bottom wall of the tank  211 . A gas source  232  is connected to the gas supply port  230 . A level indicator  233  connected to the tank  211  indicates liquid level in the tank  211 . The discharge pipe  91  is extended upward through a space surrounded by the coils of the double pipe  215 , is projected upward from the cooling unit  210  and is connected to the ozone killer  92 .  
      The inner pipe  213  delivers the ozone-containing water and the ozone-containing gas into the tank  211 . The ozone-containing gas filling an upper space in the tank  211  is discharged from the tank  211  through the discharge pipe  91  to the ozone killer  92 . A gas, such as air, is introduced into the ozone-containing water stored in a lower space of the tank  211  through the gas supply port  230  to remove ozone from the ozone-containing water by bubbling. Bubbling can reduce the ozone concentration of the ozone-containing water from about 15 ppm to a value not higher than an effluent standard ozone concentration of 5 ppm. The ozone-containing water is drained through the drain pipe  90  after thus reducing the ozone concentration of the ozone-containing water below the effluent standard ozone concentration. This ozone concentration reducing method is capable of reducing the harmfulness of effluents at a running cost lower than that is necessary for reducing the ozone concentration of the ozone-containing water by a method that dilutes the ozone-containing water with pure water or uses an ozone decomposing chemical.  
      A processing method of processing a wafer W by the aforementioned substrate processing system  1  will be described. The wafer transfer arm  11  takes out one wafer W at a time from the wafer carrier C placed on the table  6  of the in/out port  4  and carries the wafer W to the wafer delivery unit  17 . Then, the main wafer conveyer  18  receives the wafer W from the wafer delivery unit  17 . The main wafer conveyer  18  carries the wafers W one by one successively to the substrate processing units  23   a  to  23   f . The substrate processing units  23   a  to  23   f  subject the wafers W to the resist-solubilizing process to make the resist films formed on the wafers W water-soluble. Then, the carrying arm  18   a  carries out the wafers W successively from the substrate processing units  23   a  to  23   f , and delivers the wafers W to the substrate cleaning units  12  to  15 . Then, the substrate cleaning units  12  to  15  subject the wafers W to the cleaning process to remove the water-soluble resist films from the wafers W, subject the wafers W, when necessary, to a metal removing process to remove particles from the wafers W with a chemical liquid, and subject the cleaned wafers W to the drying process. Then, the carrying arm  18   a  carries the dried wafers W to the wafer delivery unit  17 . The wafer transfer arm  11  transfers the thus cleaned wafers W from the wafer delivery unit  17  to the wafer carrier C.  
      The operation of the substrate processing unit  23   a  (i.e., the processes to be performed by unit  23   a ) will be described as a representative example of those of the substrate processing units  23   a  to  23   f.    
      At first, a wafer loading process is performed. Referring to  FIG. 4 , the cover  101  is separated from the vessel body  100 . The carrying arm  18   a , holding a wafer W, of the main wafer conveyer  18  is moved to a position under the body  101   a  of the cover  101 . The holding members  112  of the cover  101  receive the wafer W from the carrying arm  18   a . Then, the cylinder lifting mechanism, not shown, lowers the cover  101  toward the vessel body  100  to advance the holding members  112  into the annular groove  100   c  of the vessel body  100  and to place the wafer W on the support members  111  arranged on the circular land  110  of the vessel body  100 . The gap G is formed between the lower surface of the wafer W supported on the support members, and the upper surface of the circular land  110 . The cover  101  is lowered further after the wafer W has been supported on the support members  111 . The cover  101  is joined to the upper surface of the circumferential wall  100   b  of the vessel body  100  so as to compress the O-rings  115   a  and  115   b  to seal the processing vessel  30 A. Thus, the loading of the wafer W into the processing vessel  30 A is completed.  
      After the completion of the wafer loading process, a heating process is performed. The heaters  105  and  125  are energized to heat the interior of the processing vessel  30 A and the wafer W. The heating process promotes the effect of a resist-solubilizing process.  
      After the completion of the heating process, an ozone-containing gas filling process is performed. After the interior of the processing vessel  30 A and the wafer W have been heated at a predetermined temperature, the unit controlling CPU  200  gives a signal, representing that the interior of the processing vessel  30 A and the wafer W have been heated at the predetermined temperature, to the CPU  201 . Then, the CPU  201  decides to start supplying an ozone-containing gas into the processing vessel  30 A. The unit controlling CPU  200  gives a control signal to the flow regulating valve  52   a  to open the flow regulating valve  52   a . Then, an ozone-containing gas having a predetermined ozone concentration is supplied from the ozone generator  42  through the ozone-containing gas supply main pipe  60 , the ozone-containing gas supply branch pipes  61   a , the flow regulating valve  52   a  and the main supply pipe  38   a  into the processing vessel  30 A at a flow rate according to the opening of the variable throttle of the flow regulating valve  52   a  adjusted beforehand. As previously mentioned, the openings of the variable throttles of the flow regulating valves  52   a  and  52   b  are adjusted beforehand so that the ozone-containing gas is supplied into both the processing vessels  30 A and  30   b  at equal flow rates when both the flow regulating valves  52   a  and  52   b  are opened.  
      The first switch valve  81  of the discharge selector  72  is opened and regulates the flow of the processing fluid discharged from the processing vessel  30 A so that the discharged processing fluid flows at a predetermined flow rate through the discharge pipe  70   a . Thus, the ozone-containing gas is supplied into the processing vessel  30 A while the processing fluid is thus discharged through the discharge pipe  70   a  to create an ozone-containing gas atmosphere of a fixed pressure in the processing vessel  30 A. The internal pressure of the processing vessel  30 A is kept at a positive pressure higher than the atmospheric pressure by, for example, a gage pressure of about 0.2 MPa. The heaters  105  and  125  keep heating the internal temperature of the processing vessel  30 A and the wafer W at the predetermined temperature. The processing fluid is discharged from the processing vessel  30 A through the discharge pipe  70   a  into the mist trap  71 . Thus, the processing vessel  30 A is filled with the ozone-containing gas having the predetermined ozone concentration.  
      The CPU  201  controls the mass flow controllers  188  and  191  and the ozone generator  42  to control the flow rate and the ozone concentration of the ozone-containing gas being supplied to the processing vessel  30 A. The CPU  201  controls the mass flow controllers  188  and  191  on the basis of the respective conditions of the flow regulating valves  52   a  and  52   b  (opened or closed) represented by signals provided by the unit controlling CPU  200  to control the flow rate of the oxygen-containing gas flowing into the ozone generator  42 , and thereby the flow rate of the ozone-containing gas produced by the ozone generator  42  and discharged therefrom is controlled.  
      A feedback control system including the CPU  201 , the ozone generator  42  and the ozone-concentration measuring device  165  controls the ozone concentration of the ozone-containing gas by a feedback control mode. The ozone-containing gas flows through the flow regulating valve  52   a , being opened, and the ozone-containing gas supply branch pipes  61   a  into the processing vessel  30 A. Since the flow regulating valve  52   b  is closed, the ozone-containing gas is unable to flow through the ozone-containing gas supply branch pipes  61   b  into the processing chamber  30 B. The ozone-containing gas having the desired ozone concentration is supplied at a desired flow rate of, for example, 4 l/min, into the processing vessel  30 A irrespective of the condition of the processing vessel  30 B.  
      After the completion of the ozone-containing gas filling process, a resist-solubilizing process is performed. Steam is supplied into the processing vessel  30 A together with the ozone-containing gas. Steam and the ozone-containing gas are supplied simultaneously into the processing vessel  30 A with the first switch valve  81  of the discharge selector  72  opened to discharge the processing fluid from the processing vessel  30 A. The temperature of steam generated by the steam generator  40  and flowing through the main supply pipe  38   a  is regulated at, for example about 115° C. The steam and the ozone-containing gas are mixed at the supply selector  41   a  to produce a processing fluid, and the processing fluid is supplied into the processing vessel  30 A. The internal pressure of the processing vessel  30 A is still kept at a positive pressure higher than the atmospheric pressure by, for example, a gage pressure of about 0.2 MPa. The heaters  105  and  125  keep heating the internal temperature of the processing vessel  30 A and the wafer W at the predetermined temperature. The processing fluid oxidizes the resist film formed on the surface of the wafer W for the resist-slubilizing process.  
      During the resist-solubilizing process, the ozone-containing gas is supplied through the main supply pipe  38   a  at the flow rate determined by the opening of the variable throttle the flow regulating valve  52   a  adjusted beforehand, and steam is supplied through the main supply pipe  38   a  at the flow rate determined by the opening of the variable throttle of the flow regulating valve  50   a  adjusted beforehand. The first switch valve  81  of the discharge selector  72  is opened to control the flow rate of the discharged processing fluid discharged from the processing vessel  30 A and flowing through the discharge pipe  70   a  by the first switch valve  81 . Thus, the ozone-containing gas and steam are supplied respectively at the predetermined flow rates into the processing vessel  30 A while the processing fluid is thus discharged through the discharge pipe  70   a  to create a processing fluid atmosphere of a fixed pressure containing steam and the ozone-containing gas in the processing vessel  30 A.  
      During the resist-solubilizing process is performed, the processing fluid is continuously supplied through the main supply pipe  38   a  into the processing vessel  30 A, and the processing fluid is continuously discharged from the processing vessel  30 A through the discharge pipe  70   a . The processing fluid flows along the upper and the lower surface (gap G) of the wafer W toward the discharge port  121  connected to the discharge pipe  70   a . At least part of the time period of the resist-solubilizing process, the supply of the processing fluid through the main supply pipe  83   a  and the discharge of the processing fluid through the discharge pipe  70   a  may be stopped during the resist-solubilizing process to process the resist film by the processing fluid held in the processing vessel  30 A.  
      During the resist-solubilizing process, the CPU  201  also controls the mass flow controllers  188  and  191  and the ozone generator  42  to control the flow rate and the ozone concentration of the ozone-containing gas to be supplied into the processing vessel  30 A. Consequently, the ozone-containing gas having the desired ozone concentration is supplied at the desired flow rate into the processing vessel  30 A irrespective of the operating condition of the processing vessel  30 B. Supply of the ozone-containing gas at the fixed flow rate keeps the internal pressure of the processing vessel  30 A constant. Thus, the internal pressure of the processing vessel  30 A, the flow of the processing fluid around the wafer W and the ozone concentration of the processing fluid can be kept at the desired values, respectively, irrespective of the operating condition of the processing vessel  30 B. Wafers W simultaneously subjected to the resist-solubilizing process by the processing vessels  30 A and  30 B, and wafers W processed by the resist-solubilizing process in a processing mode in which the processing vessel  30 A (or  30 B) performs the resist-solubilizing process while the processing vessel  30 B (or  30 A) performs the wafer loading process are processed equally by the resist-solubilizing process. After the completion of the resist-solubilizing process, the purging process is performed. The flow regulating valves  50   a  and  52   b  are closed, the stop valve  54   a  is opened, the flow selector valve  68  is set to the high-flow position to supply nitrogen gas at a high flow rate from the nitrogen gas source  43  into the processing vessel  30 A, and the second discharge regulating valve  82  of the discharge selector  72  connected to the discharge pipe  70   a  is opened. Thus, nitrogen gas is supplied from the nitrogen gas source into the processing chamber  30 A while the processing fluid is thus discharged from the processing vessel  30 A to purge the main supply pipe  38   a , the processing vessel  30 A and the discharge pipe  70   a  by the nitrogen gas. The discharged processing fluid is carried by the discharge pipe  70   a  into the mist trap  71 . Thus, the processing fluid containing the ozone-containing gas and steam is discharged from the processing vessel  30 A.  
      After the completion of the purging process, a wafer unloading process is performed. The cover lifting mechanism is actuated to raise the cover  101  so as to separate the cover  101  from the vessel body  100  and to transfer the wafer W from the support members  111  of the vessel body  100  to the diametrically opposite holding members  112  of the cover  101 . Then, the carrying arm  18   a  of the main conveyer  18  advances into a space under the body  101   a  of the cover  101 , receives the wafer W from the holding members  112  of the cover  101 , and carries the wafer W out of the processing vessel  30 A.  
      There is a case where the substrate processing unit  23   b  performs the ozone-containing gas supplying process or the resist-solubilizing process that needs the ozone-containing gas while the substrate processing unit  23   a  performs the ozone-containing gas supplying process or the resist-solubilizing process, and a case where the substrate processing unit  23   b  performs the ozone-containing gas supplying process of the resist-solubilizing process while the substrate processing unit  23   a  performs the wafer loading process, the processing fluid discharging process or the wafer unloading process that does not need the ozone-containing gas. In the former case, the ozone-containing gas is supplied simultaneously to both the processing vessels  30 A and  30 B. In the latter case, the ozone-containing gas is supplied only to the processing vessel  30 A or the processing vessel  30 B.  
      In a case where the substrate processing unit  23   b  performs the wafer loading process while the substrate processing unit  23   a  performs the ozone-containing gas supplying process to supply the ozone-containing gas into the processing vessel  30 A, the flow regulating valve  52   a  is opened and the flow regulating valve  52   b  is closed, and the ozone generator  42  produces the ozone-containing gas at a rate sufficient for supplying the ozone-containing gas only to the processing vessel  30 A. The ozone-containing gas flows through the ozone-containing gas supply branch pipe  61   a  at a flow rate on the order of 4 l/min, and flows through the main supply pipe  38   a  into the processing vessel  30 A.  
      In a case where the substrate processing unit  23   b  starts the ozone-containing gas supplying process while the substrate processing unit  23   a  is performing the resist-solubilizing process and the ozone-containing gas and steam is supplied into the processing vessel  30 A, the flow regulating valve  52   b  is opened, the unit controlling CPU  200  gives a signal indicating that both the flow regulating valves  52   a  and  52   b  are open to the CPU  201 , and the CPU  201  controls the mass flow controllers  188  and  191  to supply the oxygen-containing gas to the ozone generator  42  at a flow rate twice the flow rate at which the oxygen-containing gas is supplied to the ozone generator  42  when the ozone-containing gas needs to be supplied only to the processing vessel  30 A or the processing vessel  30 B. Then, the ozone-containing gas flows through the main supply pipe  60  at a flow rate on the order of 8 l/min and through each of the ozone-containing gas supply branch pipes  61   a  and  61   b  at a flow rate on the order of 4 l/min because both the flow regulating valves  52   a  and  52   b  are open, and is supplied through the main supply pipes  38   a  and  38   b  at the same flow rates into the processing vessels  30 A and  30 B. Thus, an ozone-containing gas supply mode for supplying the ozone-containing gas only to the processing vessel  30 A for an ozone-containing gas supply mode for supplying the ozone-containing gas to both the processing vessels  30 A and  30 B.  
      When the substrate processing unit  23   a  starts the processing fluid discharging process after the completion of the resist-solubilizing process, the flow regulating valve  52   a  is closed and the unit controlling CPU  200  gives a signal to the CPU  201  to the effect that flow regulating valve  52   a  has been closed. Then, the CPU  201  controls the mass flow controllers  188  and  191  so that the flow rate of the oxygen-containing gas for supplying the oxygen-containing gas necessary for supplying the ozone-containing gas to the two processing vessels  30 A and  30 B is reduced by half. The ozone-containing gas flows through the main supply pipe  60  at a flow rate on the order of 4 l/min, and flows only through the ozone-containing gas supply branch pipe  61   b  at a flow rate on the order of 4 l/min because the flow regulating valve  52   a  is closed. The ozone-containing gas flows through the main supply pipe  38   b  into the processing vessel  30 B. Thus, the ozone-containing gas is supplied only to the processing vessel  30 B.  
      An ozone-containing gas having a predetermined ozone concentration can be produced even if the flow rate of the oxygen-containing gas is changed or the oxygen concentration of the ozone-containing gas is changed because the ozone-concentration measuring device  165  measures the ozone concentration and the CPU  201  controls the discharge voltage of the ozone generator  42  according to the measured ozone concentration.  
      As mentioned above, the ozone-containing gas having the desired ozone concentration can be supplied at the desired flow rate into the processing vessels  30 A and  30 B, regardless of the number (one or two) of the processing vessels  30 A and  30 B being supplied with the ozone-containing gas.  
      The substrate processing system  1  is able to generate the ozone-containing gas having a stable ozone concentration according to the demands of the processing vessels  30 A and  30 B for the ozone-containing gas. Since the pressure of the ozone-containing gas in the processing vessels  30 A and  30 B, flow rates at which the ozone-containing gas is supplied to the processing vessels  30 A and  30 B, and the ozone concentration of the ozone-containing gas are stabilized, the uniformity of the effect of the resist-solubilizing process in the processing vessels  30 A and  30 B is improved, and thereby the uniformity and reliability of the effect of the subsequent cleaning process to be carried out by the substrate cleaning units  12  to  15  to remove the resist films, and the uniformity of the effect and the reliability of an etching process including the processes to be carried out by the substrate processing system are improved.  
      Although the invention has been described in its preferred embodiment as applied to processing semiconductor wafers, substrates that can be processed by the present invention is not limited thereto; the present invention is applicable to processing substrates including glass substrates for LCDs, printed circuit boards, ceramic substrates and the like.  
      The oxygen-containing gas is not limited to a mixed gas of oxygen gas and nitrogen gas, but may be any suitable mixed gas provided that the mixed gas contains oxygen gas. For example, the oxygen-containing gas may be a mixture of oxygen gas and air.  
      The control means for controlling the discharge voltage of the ozone generator  42  is not limited to the feedback control system including the CPU  201 , the ozone generator  42  and the ozone-concentration measuring device  165 . For example, when the flow rate of the oxygen-containing gas is changed suddenly and if the ozone concentration varies in a wide range or the stabilization of the ozone concentration takes time, operations for changing the flow control setting of the mass flow controllers  188  and  191 , opening or closing the flow regulating valves  52   a  and  52   b , and changing the discharge voltage may be timed so as to perform those operations at different times so that the ozone concentration may not vary in a wide range.  
      The steam distribution ratio, i.e., the ratio of the units of steam generated by the steam generator per unit time to the units of steam supplied per unit time to the processing vessel  30 A or the processing vessel  30 B, is not limited to five-to-two. For example, if steam generated by the steam generator  40  needs to be distributed to three of more processing vessels, the steam generating rate of the steam generator  40  is increased according to the number of processing vessels demanding steam and the steam may be distributed at a proper distribution ratio to the processing vessels.  
      Although two processing vessels ( 30 A,  30 B) of two substrate processing unit ( 23   a ,  23   b ) is connected to single ozone generator  42  in this embodiment, three or more processing chambers of three or more processing units may be connected to single ozone generator  42 .  
      In the event that a large number of the processing vessels are connected to a common ozone supply means, the processing system may be constituted as including one or more additional ozone generator.  FIG. 8  shows another embodiment of the present invention. In the system shown  FIG. 8 , there are provided two ozone generators  240  and  241 , and only one ( 240 ) of the ozone generators or both the ozone generators are used for supplying the ozone-containing gas, depending on the number of the processing vessels  30 A to  30 F demanding the ozone-containing gas.  
      As is similar to  FIG. 5 ,  FIG. 8  shows a piping diagram of a piping system relating to the ozone supply, which is extracted from the entire piping system of the processing system for the purpose of detailed explanation. The members in  FIG. 8  designated by the reference numerals, which are the same as or similar to those shown in  FIG. 5 , are the same or similar to the members shown in  FIG. 5 . Of course, the processing system having the piping system of  FIG. 8  has a steam supply system and the processing fluid discharge system similar to those shown in  FIG. 3 , however, being modified according to the change in the number of the processing vessels.  
      In the substrate processing system of  FIG. 8 , two branch pipes  180   a  and  180   b  branched off from the downstream end of the oxygen gas supply pipe  180  are connected to the ozone generators  240  and  241 , respectively. The branch pipe  180   b  is provided with a stop valve  242 . Each of the ozone generators  240  and  421  has an ozone generating capacity capable of simultaneously supplying the ozone-containing gas to the three processing vessels.  
      An ozone-containing gas supply passage means  51  includes an ozone-containing gas supply main pipe  60 , and ozone-containing gas supply branch pipes  61   a ,  61   b ,  61   c ,  61   d ,  61   e  and  61   f  branched from the main pipe  60 . The upstream end of the main pipe  60  is branched into two branch pipes, which are connected to the ozone generators  240  and  241 , respectively. The ozone-containing gas supply branch pipes  61  are provided with flowmeters  66   a  to  66   f , flow regulating valves  52   a  to  52   f  for regulating the flow rates of the ozone-containing gas flowing into processing vessels  30 A to  30 F, respectively. The flowmeters  66   a  to  66   f  and the flow regulating valves  52   a  to  52   f  are arranged in that order from the side of the ozone generators  240  and  241 . The flow regulating characteristics of the flow regulating valves  52  to  52   f  are adjusted beforehand such that, when two or more than two of the flow regulating valves  52   a  to  52   f  are opened, the flow rates measured by the flowmeters ( 66   a  to  66   f ) corresponding to the opened flow regulating valves are equal.  
      The ozone-containing gas supply branch pipes  61   a  to  61   f  are connected to main supply pipes  38   a  to  38   f , at the supply selectors (which are of the same structure as the supply selectors  41   a  and  41   b  shown in  FIG. 3 , however, are not shown in  FIG. 8 ) respectively including the flow regulating valves  52  to  52   f , so that the ozone-containing gas can be supplied into the processing vessels  30 A to  30 F solely or together with water vapor.  
      A CPU  201 , similarly to the case where the CPU  201  controls the single ozone generator  42 , controls the discharge voltages of the ozone generators  240  and  241  on the basis of a measured ozone concentration measured by the ozone-concentration measuring device  65 . The CPU  201  controls the set position of the stop valve  242 , and the operation of the additional ozone generator  241  according to the number of the processing vessels needing the supply of the ozone-containing gas. When the ozone-containing gas needs to be supplied to the three or less processing vessels, stop valve  242  is closed, the ozone generator  241  is stopped, and only the ozone generator  240  is operated.  
      When the ozone-containing gas needs to be supplied to the four or more processing vessels, the stop valve  242  is opened and both the ozone generators  240  and  241  are operated for ozone generation. Thus, only the ozone generator  240  or both the ozone generators  240  and  241  are used selectively depending on the number of the processing vessels needing the ozone-containing gas. Thus the ozone-containing gas can be produced at a sufficiently high production rate even if the ozone-containing gas demand of the processing vessels exceeds the ozone-containing gas producing capacity of one of the ozone generators  240  and  241 .  
       FIG. 9  shows another embodiment of the present invention. As is similar to  FIG. 5 ,  FIG. 9  shows a piping diagram of a piping system relating to the ozone supply, which is extracted from the entire piping system of the processing system for the purpose of detailed explanation. The members in  FIG. 9  designated by the reference numerals, which are the same as or similar to those shown in  FIG. 5 , are the same or similar to the members shown in  FIG. 5 . Of course, the processing system having the piping system of  FIG. 9  has a steam supply system and the processing fluid discharge system similar to those shown in  FIG. 3 . However, the discharge system is modified according to the provision of the blow-off lines, mentioned below. The discharge system has discharge selectors ( 72 , see  FIG. 3 ), which are not shown in  FIG. 9 .  
      Referring to  FIG. 9 , the substrate processing system is provided with blow-off pipes  245   a  and  245   b  for discharging part of an ozone-containing gas produced by an ozone generator  42  without supplying that part to processing vessels  30 A and  30 B to supply ozone-containing gases respectively having a desired ozone concentrations at desired flow rates to the processing vessels  30 A and  30 B depending on processes being performed in the processing vessels  30 A and  30 B. The blow-off pipe  245   a  is connected to a selector valve  246   a  connected to an ozone-containing gas supply branch pipe  61   a . The blow-off pipe  245   b  is connected to a selector valve  246   b  connected to an ozone-containing gas supply branch pipe  61   b.    
      A unit controlling CPU  200  controls each of the selector valves  246   a  and  246   b  to set a state where the blow-off pipe  245   a  (or  245   b ) is disconnected from the corresponding ozone gas supply branch pipe  61   a  (or  61   b ) to supply the ozone-containing gas to the corresponding processing chamber  30 A (or  30 B), or to set a state where the blow-off pipe  245   a  (or  245   b ) is connected to the corresponding ozone-containing gas supply branch pipe  61   a  (or  61   b ) to discharge the ozone-containing gas therefrom so that the ozone-containing gas is not supplied to the corresponding processing chamber  30 A (or  30 B).  
      The blow-off pipes  245   a  and  245   b  are provided with flow regulating valves  248   a  and  248   b , and flowmeters  250   a  and  250   b , respectively. The downstream ends of the blow-off pipes  245   a  and  245   b  are connected to a pipe connected to an ozone killer  92 . Preferably, the blow-off pipes  245   a  and  245   b  are formed of a fluorocarbon resin.  
      In the system shown in  FIG. 9 , the mass-flow controllers  188  and  191  keep the flow rates of oxygen gas and nitrogen gas being supplied to the ozone generator  42  constant regardless of the sorts of the processes being performed at the processing chambers. Thus, the ozone generator  42  discharges the ozone-containing gas at a fixed flow rate, for example 8 l/min.  
      The openings of the variable throttles included in the flow regulating valves  52   a ,  52   b ,  248   a  and  248   b  are adjusted beforehand so that: when the ozone-containing gas is supplied to both the processing vessels  30 A and  30 B, the ozone-containing gas is supplied to the processing vessels  30 A and  30 B at specific flow rates identical to each other, for example 4 l/min, respectively; and when the ozone-containing gas is supplied to one of the processing vessels ( 30 A or  30 B), the ozone-containing gas is supplied to said one of the processing vessels ( 30 A or  30 B) at said specific flow rate, for example 4 l/min, and is flown through the blow-off pipe ( 248   b  or  248   a ) corresponding to the other processing vessel ( 30 B or  30 A) at said specific flow rates, for example 4 l/min. The adjustment of the flow regulating valves  52   a ,  52   b ,  248   a  and  248   b  is performed based on the measurement of the flow rates by using the flowmeters  66   a ,  66   b ,  250   a  and  250   b.    
      The flow regulating valves  52   a ,  52   b ,  248   a  and  248   b  are opened during a usual operation of the system. Thus, variable throttles without having shut-off function may be used instead of the flow regulating valves  52   a ,  52   b ,  248   a  and  248   b.    
      The operation of the system shown in  FIG. 9  is as follows.  
      The unit controlling CPU  200  controls the selector valves  246   a  and  246   b  according to the ozone-containing gas demand of processes performed in the processing vessels  30 A and  30 B.  
      When processes needing the ozone-containing gas are being carried out in both the processing vessels  30 A and  30 B, the selector valves  246   a  and  246   b  are opened to the ozone-containing gas supply branch pipes  61   a  and  61   b . Due to the aforementioned adjustment of the flow regulating valves, the ozone-containing gas is supplied through the ozone-containing gas supply branch pipes  61   a  and  61   b  and the flow regulating valves  52   a  and  52   b  at said specific flow rates identical to each other into the processing vessels  30 A and  30 B, respectively.  
      If the processing vessel  30 B is performing a process that does not need the ozone-containing gas, such as the wafer loading process, and the processing vessel  30 A is performing a process that needs the ozone-containing gas, such as the ozone-containing gas supplying process, the selector valve  246   a  opens into the ozone-containing gas supply branch pipe  61   a  and the selector valve  246   b  is opened into the blow-off pipe  245   b . Due to the aforementioned adjustment of the flow regulating valves, the ozone-containing gas flown into the ozone-containing gas supply branch pipe  61   a  is supplied into the processing vessel  30 A at said specific flow rate, for example 4 l/min, and the ozone-containing gas ozone-containing gas supply branch pipe  61   b  is discharged therefrom through the blow-off pipe  245   b  at said specific flow rate, for example 4 l/min, and is not supplied to the processing chamber  30 B. Thus, the ozone-containing gas is supplied at the desired flow rate into the processing vessel  30 A whether or not the ozone-containing gas is supplied to the processing vessel  30 B. The ozone-containing gas can be supplied only into the processing vessel  30 B in the same manner as mentioned above in connection with the processing vessel  30 A.  
      The ozone concentration of the ozone-containing gas is adjusted to a predetermined value by a feedback control system including the CPU  201 , the ozone generator  42  and the ozone-concentration measuring device  165 . Thus, the ozone-containing gas having the desired ozone concentration can always be supplied to the processing vessels  30 A and  30 B at the desired flow rate, such as 4 l/min.  
      According to the embodiment shown in  FIG. 9 , since the ozone generator  42  operates in a stable condition, the ozone-containing gas has a stable quality, resulting in the stable processing of the wafers W.  
      The flow rate of the ozone-containing gas may be controlled by using, in combination, the flow rate control method that controls the respective flow rates of oxygen gas and nitrogen gas, and the flow rate control method that controls the discharge of the ozone-containing gas through the blow-off pipes  245   a  and  245   b.    
      Preferably, ozone-containing gas further includes carbon dioxide gas, and has a composition of about 0.008 vol % of nitrogen gas, and about 0.1 vol % of carbon dioxide gas, and the remainder being oxygen gas. In this case, the system shown in  FIG. 5  is modified so that it further include a carbon dioxide gas source, a carbon dioxide gas supply pipe connected to the oxygen gas supply pipe  180 , and a stop valve and a mass-flow controller placed in the carbon dioxide gas supply pipe, as shown in  FIG. 10 . The system shown in  FIG. 8  may also include the carbon dioxide supply system as shown in  FIG. 10 .  
      As apparent from the foregoing description, the substrate processing system and the substrate processing method of the present invention are capable of producing an ozone-containing gas having a stable ozone concentration and of supplying the ozone-containing gas to the processing vessels at flow rates corresponding to the ozone-containing gas demands of the processes being carried out by the processing vessels. Consequently, the uniformity and reliability of effects of the resist removing process and the etching process are improved.  
      Although the invention has been described in its preferred embodiments with a certain degree of particularity, obviously many changes and variations are possible therein. It is therefore to be understood that the present invention may be practiced otherwise than as specifically described herein without departing from the scope and spirit hereof.