Patent Publication Number: US-2022219209-A1

Title: Substrate processing device and substrate processing method

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is a continuation of U.S. patent application Ser. No. 17/273,123, filed Mar. 3, 2021, which is a U.S.C. § 371 national phase conversion of PCT/JP2019/028345, filed Jul. 18, 2019, which claims priority of JP 2018-176394, filed Sep. 20, 2018. Applicant claims priority to each of the foregoing patent applications. The PCT International Application was published in the English language. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a substrate processing apparatus, and a substrate processing method. Exemplary substrates to be processed include semiconductor wafers, substrates for liquid crystal display devices, substrates for FPDs (Flat Panel Displays) such as organic EL (electroluminescence) display devices, substrates for optical disks, substrates for magnetic disks, substrates for magneto-optical disks, substrates for photomasks, ceramic substrates, and substrates for solar cells. 
     BACKGROUND ART 
     In production processes for semiconductor devices and liquid crystal display devices, substrate processing apparatuses are used for processing substrates such as semiconductor wafers and liquid crystal display glass substrates. 
     The following PTL 1 discloses a substrate processing apparatus of single-substrate processing type, which is adapted to process substrates one by one. The substrate processing apparatus includes a spin chuck which horizontally holds and rotates a substrate, and a nozzle which spouts SPM (a liquid mixture of sulfuric acid and hydrogen peroxide water) toward the substrate held by the spin chuck. PTL 1 also discloses an arrangement for recovering SPM used for treatment of the substrate and reusing the recovered SPM for the subsequent treatment. 
     CITATION LIST 
     Patent Literature 
     PTL 1: JP2006-024793A 
     SUMMARY OF INVENTION 
     Problem to be Solved by Invention 
     In PTL 1, the SPM is recovered from a treatment chamber in which the spin chuck is provided, and is collected in a recovery tank through a recovery line. After foreign matter is removed from the SPM collected in the recovery tank by a filter, the resulting SPM is supplied to a circulation tank. An SPM supply pipe extending to the SPM nozzle is connected to the circulation tank. A pump is provided in an intermediate portion of the SPM supply pipe. Further, a filter, a heater, and an outlet valve are provided downstream of the pump in the SPM supply pipe. An SPM return pipe is branched from the SPM supply pipe at a position between the heater and the outlet valve. A distal portion of the SPM return pipe extends to the circulation tank. 
     During the operation of the substrate processing apparatus, the pump and a temperature controller are constantly driven. By opening a return valve with the outlet valve closed, the SPM is pumped out from the circulation tank, flows through the SPM supply pipe to the branch position at which the SPM return pipe is branched, and flows back into the circulation tank from the branch position through the SPM return pipe. During a period in which the SPM is not spouted from the SPM nozzle, the SPM is circulated through the circulation tank, the SPM supply pipe, and the SPM return pipe. The temperature of the SPM is adjusted at a predetermined temperature by the circulation of the SPM, and the temperature-adjusted SPM is stored in the circulation tank. When the SPM is spouted from the SPM nozzle, the SPM temperature-adjusted at the predetermined temperature is pumped out from the circulation tank, and supplied to the SPM nozzle through the SPM supply pipe. Then, the SPM spouted from the SPM nozzle is supplied to the substrate. 
     According to PTL 1, however, if the SPM is repeatedly recovered and reused, the concentrations of sulfuric acid and hydrogen peroxide water contained in the SPM are reduced to levels inappropriate for the reuse. 
     Particularly, the hydrogen peroxide concentration is remarkably reduced. That is, it is desirable to use the SPM at a higher temperature, because the removal capability of the SPM (the resist removing capability of the SPM) is increased as the temperature of the SPM is increased. However, hydrogen peroxide is liable to decompose into water and oxygen at a higher temperature. For this reason, the hydrogen peroxide concentration is liable to decrease to a level inappropriate for the reuse at a relatively early stage if the SPM is repeatedly recovered and reused. 
     In any case, the concentrations of sulfuric acid and hydrogen peroxide water contained in the SPM are reduced in the art disclosed in PTL 1. This makes it impossible to efficiently remove the resist from the substrate. 
     It is therefore an object of the present invention to provide a substrate processing apparatus and a substrate processing method, which can efficiently remove a resist from a substrate by using SPM prepared from a recovered sulfuric acid-containing liquid. 
     Solution to Problem 
     The present invention provides a substrate processing apparatus for removing a resist from a substrate with SPM that is a liquid mixture of sulfuric acid and hydrogen peroxide water, the apparatus including: a substrate holding unit which holds a substrate at least partly covered with the resist; a nozzle having a spout and adapted to spout SPM from the spout toward the substrate held by the substrate holding unit; a mixing portion communicating with the spout; a sulfuric acid-containing liquid supply device which recovers liquid supplied to and expelled from the substrate held by the substrate holding unit, prepares a sulfuric acid-containing liquid from the recovered liquid, and supplies the prepared sulfuric acid-containing liquid to the mixing portion; a hydrogen peroxide water supply unit which supplies hydrogen peroxide water to the mixing portion; and a control device which controls the sulfuric acid-containing liquid supply device and the hydrogen peroxide water supply unit; wherein the control device performs a sulfuric acid-containing liquid preparing step of recovering SPM supplied to and expelled from the substrate and preparing the sulfuric acid-containing liquid, and an SPM spouting step of supplying the prepared sulfuric acid-containing liquid and hydrogen peroxide water to the mixing portion, mixing the sulfuric acid-containing liquid and hydrogen peroxide water together in the mixing portion to prepare SPM, and spouting the prepared SPM from the spout. 
     In the present disclosure, the sulfuric acid-containing liquid is a liquid containing sulfuric acid, and may contain a component other than sulfuric acid. The sulfuric acid-containing liquid contains sulfuric acid at a weight percent concentration of not less than 50%. 
     With this arrangement, the sulfuric acid-containing liquid, but not the SPM itself, is prepared from the SPM expelled and recovered from the substrate. The prepared sulfuric acid-containing liquid is mixed with hydrogen peroxide water to be thereby reused for the SPM. 
     In order to increase the removal capability of the SPM, the sulfuric acid concentration of the prepared sulfuric acid-containing liquid is required to fall within a predetermined concentration range. Similarly, the temperature of the prepared sulfuric acid-containing liquid is required to fall within a predetermined temperature range. 
     By particularly considering sulfuric acid contained in the recovered SPM separately from hydrogen peroxide, the sulfuric acid concentration and the temperature of the sulfuric acid-containing liquid are adjusted and, therefore, the sulfuric acid-containing liquid can be properly prepared as having a sulfuric acid concentration and a temperature falling within the required concentration range and temperature range. Then, the prepared sulfuric acid-containing liquid is mixed with hydrogen peroxide water. Thus, the resist can be efficiently removed from the substrate with the use of the SPM prepared from the recovered sulfuric acid-containing liquid. 
     In one embodiment of the present invention, the sulfuric acid-containing liquid supply device includes a first liquid storage, and a second liquid storage. The first liquid storage includes a first tank which stores the recovered liquid, and a sulfuric acid adding unit which adds sulfuric acid to the first tank. The second liquid storage includes a second tank which stores liquid supplied from the first tank, a first pipe having opposite ends connected to the second tank so that the liquid stored in the second tank is circulated therethrough, and a first heater which heats the liquid circulated through the second tank and the first pipe. In the sulfuric acid-containing liquid preparing step, the control device performs: a first storing step of recovering the SPM expelled from the substrate and storing the recovered SPM as the sulfuric acid-containing liquid in the first tank; a sulfuric acid adding step of causing the sulfuric acid adding unit to add sulfuric acid to the first tank; a second storing step of storing the sulfuric acid-containing liquid supplied from the first tank in the second tank; and a first heating step of causing the first heater to heat the sulfuric acid-containing liquid circulated through the second tank and the first pipe. In the SPM spouting step, the control device performs the step of supplying the sulfuric acid-containing liquid circulated through the second tank and the first pipe into the mixing portion. 
     With this arrangement, the SPM expelled and recovered from the substrate is stored as the sulfuric acid-containing liquid in the first tank of the first liquid storage. Further, sulfuric acid from the sulfuric acid adding unit is added to the first tank. Thus, the sulfuric acid concentration of the sulfuric acid-containing liquid stored in the first tank can be accurately adjusted within the required concentration range. 
     Further, the sulfuric acid-containing liquid supplied from the first liquid storage is circulated through the second tank and the first pipe in the second liquid storage. The sulfuric acid-containing liquid circulated through the second tank and the first pipe is heated by the first heater. Thus, the temperature of the sulfuric acid-containing liquid circulated through the second tank and the first pipe is accurately adjusted within the required temperature range. 
     The second liquid storage which is solely adapted for the temperature adjustment of the sulfuric acid-containing liquid is provided separately from the first liquid storage in which sulfuric acid can be added to the sulfuric acid-containing liquid (the sulfuric acid concentration of the sulfuric acid-containing liquid can be adjusted). The temperature of sulfuric acid to be added is a room temperature. If the temperature of the sulfuric acid-containing liquid is adjusted in a storage adapted for the temperature adjustment of the sulfuric acid-containing liquid while sulfuric acid is added to the sulfuric acid-containing liquid in the storage, therefore, the temperature of the sulfuric acid-containing liquid will become unstable in the storage. Since the second liquid storage which is solely adapted for the temperature adjustment of the sulfuric acid-containing liquid is provided separately from the first liquid storage in which sulfuric acid can be added to the sulfuric acid-containing liquid, the temperature of the sulfuric acid-containing liquid is stabilized in the second liquid storage. Thus, the temperature of the sulfuric acid-containing liquid to be supplied to the mixing portion can be adjusted within the desired temperature range. 
     In one embodiment of the present invention, the second liquid storage further includes a sulfuric acid concentration meter which measures the sulfuric acid concentration of the sulfuric acid-containing liquid circulated through the second tank and the first pipe. The control device performs the sulfuric acid adding step if a value of the sulfuric acid concentration measured by the sulfuric acid concentration meter is less than a predetermined threshold. 
     With this arrangement, the sulfuric acid concentration of the sulfuric acid-containing liquid circulated through the second tank and the first pipe is measured by the concentration meter. Therefore, the sulfuric acid concentration of the sulfuric acid-containing liquid circulated through the second tank and the first pipe can be accurately measured. Thus, the sulfuric acid concentration of the sulfuric acid-containing liquid to be supplied to the mixing portion can be accurately adjusted within the desired concentration range. 
     In one embodiment of the present invention, the first liquid storage further includes a second pipe having opposite ends connected to the first tank so that the sulfuric acid-containing liquid stored in the first tank is circulated therethrough, and a second heater which heats the sulfuric acid-containing liquid circulated through the first tank and the second pipe. In the sulfuric acid-containing liquid preparing step, the control device further performs a second heating step of causing the second heater to heat the sulfuric acid-containing liquid circulated through the first tank and the second pipe. 
     With this arrangement, the sulfuric acid-containing liquid is circulated through the first tank and the second pipe in the first liquid storage. The sulfuric acid-containing liquid circulated through the first tank and the second pipe is heated by the second heater. In the first and second liquid storages, the sulfuric acid-containing liquid is heated by the second and first heaters, respectively. Thus, a greater amount of heat can be applied to the sulfuric acid-containing liquid. This makes it possible to increase the temperature of the sulfuric acid-containing liquid to a higher temperature in the second liquid storage. 
     Since the sulfuric acid-containing liquid is heated by using both of the first and second heaters, a load to be exerted on one of the heaters (i.e., the first heater) can be reduced. 
     In one embodiment of the present invention, the first liquid storage further includes a second pipe having opposite ends connected to the first tank so that the sulfuric acid-containing liquid stored in the first tank is circulated therethrough. In the first liquid storage, no heating unit is provided for heating the sulfuric acid-containing liquid circulated through the first tank and the second pipe. 
     With this arrangement, the heating unit for heating the sulfuric acid-containing liquid circulated through the first tank and the second pipe is not provided in the first liquid storage. That is, the sulfuric acid-containing liquid is not heated in the first liquid storage. Therefore, the sulfuric acid-containing liquid circulated through the first tank and the second pipe has a relatively low temperature. 
     In one embodiment of the present invention, the first liquid storage further includes a filter provided in the second pipe for capturing foreign matter contained in the sulfuric acid-containing liquid flowing through the second pipe. 
     With this arrangement, the sulfuric acid-containing liquid flowing through the second pipe is filtered by the filter. The sulfuric acid-containing liquid filtered by the filter has a relatively low temperature. 
     If the sulfuric acid-containing liquid flowing through the first tank and the second pipe has a higher temperature, the higher-temperature sulfuric acid-containing liquid continuously flows through the filter and, therefore, the filter is liable to expand to thereby have a greater pore diameter. If the pores of the filter each have a greater diameter, the diameter of the foreign matter capturable by the filter is increased. This reduces the filtering capability of the filter, making it impossible to properly capture the foreign matter contained in the sulfuric acid-containing liquid in the first liquid storage. 
     The inventive arrangement suppresses the reduction of the filtering capability of the filter, because the sulfuric acid-containing liquid flowing through the filter has a relatively low temperature. Therefore, the foreign matter contained in the sulfuric acid-containing liquid can be advantageously captured in the first liquid storage. This makes it possible to supply the sulfuric acid-containing liquid in a clean state to the mixing portion. 
     In one embodiment of the present invention, the sulfuric acid-containing liquid supply device further includes a third liquid storage. The third liquid storage includes a third tank which stores the liquid supplied from the first tank, a third pipe having opposite ends connected to the third tank so that the liquid stored in the third tank is circulated therethrough, and a second heater which heats the liquid circulated through the third tank and the third pipe. In the sulfuric acid-containing liquid preparing step, the control device further performs: a third storing step of storing the sulfuric acid-containing liquid supplied from the first tank in the third tank; and a second heating step of causing the second heater to heat the sulfuric acid-containing liquid circulated through the third tank and the third pipe. In the SPM spouting step, the control device further performs the step of supplying the sulfuric acid-containing liquid circulated through the third tank and the third pipe to the second tank. 
     With this arrangement, the sulfuric acid-containing liquid supplied from the first liquid storage is circulated through the third tank and the third pipe. The sulfuric acid-containing liquid circulated through the third tank and the third pipe is heated by the second heater. In the third and second liquid storages, the sulfuric acid-containing liquid is heated by the second and first heaters, respectively. Thus, a greater amount of heat can be applied to the sulfuric acid-containing liquid. This makes it possible to heat the sulfuric acid-containing liquid to a higher temperature in the second liquid storage. 
     Since the sulfuric acid-containing liquid is heated by using both of the first and second heaters, a load to be exerted on the first heater can be reduced. 
     In one embodiment of the present invention, the first liquid storage further includes a cooler which cools the sulfuric acid-containing liquid circulated through the first tank and the second pipe. In the sulfuric acid-containing liquid preparing step, the control device further performs a cooling step of causing the cooler to cool the sulfuric acid-containing liquid circulated through the first tank and the second pipe. 
     With this arrangement, the sulfuric acid-containing liquid circulated through the first tank and the second pipe is cooled by the cooler. Therefore, the temperature of the sulfuric acid-containing liquid circulated through the first tank and the second pipe can be reduced to a room temperature or lower than the room temperature. 
     In this case, the first liquid storage preferably further includes the filter. 
     With this arrangement, the temperature of the sulfuric acid-containing liquid passing through the filter can be reduced to the room temperature or lower than the room temperature, thereby more effectively suppressing the reduction of the filtering capability. Therefore, the foreign matter contained in the sulfuric acid-containing liquid can be more advantageously captured in the first liquid storage. This makes it possible to supply the sulfuric acid-containing liquid in a cleaner state to the mixing portion. 
     In one embodiment of the present invention, the sulfuric acid-containing liquid circulated through the first tank and the second pipe is cooled only through natural cooling. 
     With this arrangement, the sulfuric acid-containing liquid can be cooled without increase in costs. 
     In one embodiment of the present invention, a first heating temperature to be achieved through the heating by the first heater is higher than a second heating temperature to be achieved through the heating by the second heater. 
     With this arrangement, the sulfuric acid-containing liquid heated to the second heating temperature in the first liquid storage (or the third liquid storage) is supplied to the second liquid storage. Then, the sulfuric acid-containing liquid is heated to the first heating temperature in the second liquid storage. That is, the sulfuric acid-containing liquid is heated stepwise. This makes it possible to heat the sulfuric acid-containing liquid to a higher temperature in the second liquid storage. Even if the temperature (first heating temperature) of the sulfuric acid-containing liquid to be supplied to the mixing portion is set to an extremely high temperature, the high-temperature sulfuric acid-containing liquid can be properly prepared. 
     In one embodiment of the present invention, the substrate processing apparatus further includes a sulfuric acid-containing liquid supply pipe which connects the second tank or the first pipe to the mixing portion, and a third heater which heats the sulfuric acid-containing liquid flowing through the sulfuric acid-containing liquid supply pipe. In the sulfuric acid-containing liquid preparing step, the control device performs a third heating step of causing the third heater to heat the sulfuric acid-containing liquid flowing through the sulfuric acid-containing liquid supply pipe. 
     With this arrangement, the sulfuric acid-containing liquid circulated through the second tank and the first pipe is guided to the sulfuric acid-containing liquid supply pipe. Then, the sulfuric acid-containing liquid flowing through the sulfuric acid-containing liquid supply pipe is heated by the third heater. Through the heating by the third heater, the temperature of the sulfuric acid-containing liquid can be further increased to a higher level than when the sulfuric acid-containing liquid is circulated through the second tank and the first pipe. 
     In one embodiment of the present invention, the substrate processing apparatus further includes: a mixing ratio changing unit which changes the ratio of the sulfuric acid-containing liquid to hydrogen peroxide water in the mixing portion; a recovery pipe through which the liquid supplied to and expelled from the substrate held by the substrate holding unit is recovered to be supplied to the sulfuric acid-containing liquid supply device; a liquid drain pipe into which the liquid supplied to and expelled from the substrate held by the substrate holding unit flows; and a switching unit which switches, between the liquid drain pipe and the recovery pipe, a pipe into which the liquid expelled from the substrate held by the substrate holding unit flows. The control device further performs: a first SPM supplying step of controlling the mixing ratio changing unit so that a first SPM is prepared by mixing the sulfuric acid-containing liquid and hydrogen peroxide water in a first mixing ratio of the sulfuric acid-containing liquid to hydrogen peroxide water, and supplying the prepared first SPM to the substrate held by the substrate holding unit; a second SPM supplying step of controlling the mixing ratio changing unit so that a second SPM is prepared by mixing the sulfuric acid-containing liquid and hydrogen peroxide water in a second mixing ratio of the sulfuric acid-containing liquid to hydrogen peroxide water that is greater than the first mixing ratio and, after the supply of the first SPM is stopped in the first SPM supplying step, supplying the prepared second SPM to the substrate held by the substrate holding unit; a liquid draining step of controlling the switching unit so that the first SPM supplied to and expelled from the substrate in the first SPM supplying step flows into the liquid drain pipe; and a recovering step of controlling the switching unit so that the second SPM supplied to and expelled from the substrate in the second SPM supplying step flows into the recovery pipe. 
     With this arrangement, the sulfuric acid-containing liquid and hydrogen peroxide water are mixed in the first mixing ratio for the preparation of the first SPM. The sulfuric acid-containing liquid and hydrogen peroxide water are mixed in the second mixing ratio for the preparation of the second SPM. The first mixing ratio and the second mixing ratio are each defined as the ratio of the volume of the sulfuric acid-containing liquid before the mixing to the volume of hydrogen peroxide water before the mixing. The first mixing ratio is smaller than the second mixing ratio. Therefore, the concentration of hydrogen peroxide contained in the first SPM is higher than the concentration of hydrogen peroxide contained in the second SPM. 
     The first SPM has a higher hydrogen peroxide concentration and, hence, a higher removal capability than the second SPM. Therefore, the resist can be efficiently removed from the substrate. After the first SPM is supplied to the substrate, the second SPM is supplied to the substrate. The second SPM has a lower removal capability than the first SPM. However, almost all the resist is removed from the substrate by the supply of the first SPM, so that only an easily removable part of the resist remains on the substrate. Therefore, even the second SPM having a lower removal capability can reliably remove the remaining resist from the substrate. 
     The first SPM supplied to and expelled from the substrate flows into the liquid drain pipe but not into the recovery pipe. The first SPM expelled from the substrate has a relatively high hydrogen peroxide concentration and a relatively low sulfuric acid concentration. In addition, the first SPM expelled from the substrate contains a greater amount of contaminants (carbides of the resist and the like) occurring due to reaction between the first SPM and the resist. Therefore, the first SPM expelled from the substrate is inappropriate for the recovery. 
     On the other hand, the second SPM expelled from the substrate has a relatively high sulfuric acid concentration. Further, the amount of contaminants contained in the second SPM expelled from the substrate is smaller than the amount of the contaminants contained in the first SPM expelled from the substrate. Therefore, the second SPM having a relatively high sulfuric acid concentration and a smaller contaminant amount is guided into the recovery pipe, and used for the preparation of the sulfuric acid-containing liquid. The prepared sulfuric acid-containing liquid is mixed with hydrogen peroxide water. Thus, sulfuric acid contained in the sulfuric acid-containing liquid reacts with hydrogen peroxide, whereby the SPM is newly prepared. This reduces the amount of the SPM to be discarded. 
     The SPM is recovered, when the sulfuric acid concentration is higher, i.e., when the ratio of the volume of sulfuric acid before the mixing to the total volume of sulfuric acid and hydrogen peroxide water before the mixing is higher. Therefore, the SPM having a higher sulfuric acid concentration can be recovered. The sulfuric acid concentration is not maintained at a higher level, but the SPM having a higher hydrogen peroxide concentration and a sufficient removal capability is supplied to the substrate before the recovery of the SPM is started. Therefore, the resist can be efficiently removed from the substrate. This makes it possible to recover the SPM having a higher sulfuric acid concentration, while efficiently removing the resist from the substrate. 
     In one embodiment of the present invention, the substrate processing apparatus further includes: a first guard which is connected to the liquid drain pipe and surrounds the substrate held by the substrate holding unit; and a second guard which is connected to the recovery pipe and surrounds the substrate held by the substrate holding unit. The switching unit includes a guard switching unit which switches the first guard and the second guard between a first state such that the liquid expelled from the substrate is received by the first guard and a second state such that the liquid expelled from the substrate is received by the second guard. The control device further performs: a first SPM capturing step of controlling the guard switching unit to cause the first guard to receive the first SPM expelled from the substrate in the first SPM supplying step; and a second SPM capturing step of controlling the guard switching unit to cause the second guard to receive the second SPM expelled from the substrate in the second SPM supplying step. 
     With this arrangement, the first SPM expelled from the substrate is received by the first guard surrounding the substrate. The second SPM expelled from the substrate is received by the second guard surrounding the substrate. The first SPM received by the first guard flows into the liquid drain pipe connected to the first guard. The second SPM received by the second guard flows into the recovery pipe connected to the second guard. 
     The first SPM expelled from the substrate contains a greater amount of contaminants. Therefore, the contaminants are liable to remain on the inner wall of the first guard after the first SPM is received by the first guard. When the second SPM expelled from the substrate is received and recovered by the first guard, the second SPM is liable to be contaminated with the contaminants adhering to the first guard. Therefore, the second SPM is received by the second guard different from the first guard, whereby the amount of the contaminants to be contained in the recovered SPM can be reduced. 
     The present invention provides a substrate processing method to be performed by a substrate processing apparatus including a nozzle which spouts SPM that is a liquid mixture of sulfuric acid and hydrogen peroxide water from its spout toward a substrate held by a substrate holding unit, and a mixing portion communicating with the spout, the method including: a sulfuric acid-containing liquid preparing step of preparing a sulfuric acid-containing liquid by recovering SPM supplied to and expelled from the substrate held by the substrate holding unit, the substrate being at least partly covered with a resist; and an SPM spouting step of supplying the prepared sulfuric acid-containing liquid and hydrogen peroxide water to the mixing portion, mixing the sulfuric acid-containing liquid and hydrogen peroxide water in the mixing portion to prepare SPM, and spouting the prepared SPM from the spout. 
     According to this method, the sulfuric acid-containing liquid, but not the SPM itself, is prepared from the SPM expelled and recovered from the substrate. The prepared sulfuric acid-containing liquid is mixed with hydrogen peroxide water to be thereby reused for the SPM. 
     In order to increase the removal capability of the SPM, the sulfuric acid concentration of the prepared sulfuric acid-containing liquid is required to fall within a predetermined concentration range. Similarly, the temperature of the prepared sulfuric acid-containing liquid is required to fall within a predetermined temperature range. 
     By particularly considering sulfuric acid contained in the recovered SPM separately from hydrogen peroxide, the sulfuric acid concentration and the temperature of the sulfuric acid-containing liquid are adjusted and, therefore, the sulfuric acid-containing liquid can be properly prepared as having a sulfuric acid concentration and a temperature falling within the required concentration range and temperature range. Then, the prepared sulfuric acid-containing liquid is mixed with hydrogen peroxide water. Thus, the resist can be efficiently removed from the substrate with the use of the SPM prepared from the recovered sulfuric acid-containing liquid. 
     In one embodiment of the present invention, the sulfuric acid-containing liquid preparing step includes: the step of recovering the SPM expelled from the substrate and storing the recovered SPM as the sulfuric acid-containing liquid in a first tank of a first liquid storage; a sulfuric acid adding step of adding sulfuric acid to the first tank; the step of storing the sulfuric acid-containing liquid from the first tank in a second tank of a second liquid storage different from the first tank; and a heating step of heating a sulfuric acid-containing liquid circulated through the second tank and a first pipe having opposite ends connected to the second tank by a first heater of the second liquid storage. The SPM spouting step includes the step of supplying the sulfuric acid-containing liquid circulated through the second tank and the first pipe to the mixing portion. 
     According to this method, the SPM expelled and recovered from the substrate is stored as the sulfuric acid-containing liquid in the first tank of the first liquid storage. Further, sulfuric acid from a sulfuric acid adding unit is added to the first tank. Thus, the sulfuric acid concentration of the sulfuric acid-containing liquid stored in the first tank can be accurately adjusted within the required concentration range. 
     Further, the sulfuric acid-containing liquid supplied from the first liquid storage is circulated through the second tank and the first pipe in the second liquid storage. The sulfuric acid-containing liquid circulated through the second tank and the first pipe is heated by the first heater. Thus, the temperature of the sulfuric acid-containing liquid circulated through the second tank and the first pipe can be accurately adjusted within the required temperature range. 
     The second liquid storage which is solely adapted for the temperature adjustment of the sulfuric acid-containing liquid is provided separately from the first liquid storage in which sulfuric acid can be added to the sulfuric acid-containing liquid (the sulfuric acid concentration of the sulfuric acid-containing liquid can be adjusted). The temperature of sulfuric acid to be added is a room temperature. If the temperature of the sulfuric acid-containing liquid is adjusted in a storage adapted for the temperature adjustment of the sulfuric acid-containing liquid while sulfuric acid is added to the sulfuric acid-containing liquid in the storage, therefore, the temperature of the sulfuric acid-containing liquid will become unstable in the storage. Since the second liquid storage which is solely adapted for the temperature adjustment of the sulfuric acid-containing liquid is provided separately from the first liquid storage in which sulfuric acid can be added to the sulfuric acid-containing liquid, the temperature of the sulfuric acid-containing liquid is stabilized in the second liquid storage. Thus, the temperature of the sulfuric acid-containing liquid to be supplied to the mixing portion can be adjusted within the desired temperature range. 
     In one embodiment of the present invention, the substrate processing method further includes: a first SPM supplying step of changing the ratio of the sulfuric acid-containing liquid to hydrogen peroxide water in the mixing portion, mixing the sulfuric acid-containing liquid and hydrogen peroxide water in a first mixing ratio of the sulfuric acid-containing liquid to hydrogen peroxide water to prepare a first SPM, and supplying the prepared first SPM to the substrate held by the substrate holding unit; a second SPM supplying step of changing the ratio of the sulfuric acid-containing liquid to hydrogen peroxide water in the mixing portion, mixing the sulfuric acid-containing liquid and hydrogen peroxide water in a second mixing ratio of the sulfuric acid-containing liquid to hydrogen peroxide water that is greater than the first mixing ratio to prepare a second SPM and, after the supply of the first SPM is stopped in the first SPM supplying step, supplying the prepared second SPM to the substrate held by the substrate holding unit; a liquid draining step of causing the first SPM supplied to and expelled from the substrate in the first SPM supplying step to flow into a liquid drain pipe different from a recovery pipe through which the liquid supplied to and expelled from the substrate held by the substrate holding unit is recovered to be supplied to the sulfuric acid-containing liquid supply device; and a recovering step of causing the second SPM supplied to and expelled from the substrate in the second SPM supplying step to flow into the recovery pipe. 
     According to this method, the sulfuric acid-containing liquid and hydrogen peroxide water are mixed in the first mixing ratio for the preparation of the first SPM. The sulfuric acid-containing liquid and hydrogen peroxide water are mixed in the second mixing ratio for the preparation of the second SPM. The first mixing ratio and the second mixing ratio are each defined as the ratio of the volume of the sulfuric acid-containing liquid before the mixing to the volume of hydrogen peroxide water before the mixing. The first mixing ratio is smaller than the second mixing ratio. Therefore, the concentration of hydrogen peroxide contained in the first SPM is higher than the concentration of hydrogen peroxide contained in the second SPM. 
     The first SPM has a higher hydrogen peroxide concentration and, hence, a higher removal capability than the second SPM. Therefore, the resist can be efficiently removed from the substrate. After the first SPM is supplied to the substrate, the second SPM is supplied to the substrate. The second SPM has a lower removal capability than the first SPM. However, almost all the resist is removed from the substrate by the supply of the first SPM, so that only an easily removable part of the resist remains on the substrate. Therefore, even the second SPM having a lower removal capability can reliably remove the remaining resist. 
     The first SPM supplied to and expelled from the substrate flows into the liquid drain pipe but not into the recovery pipe. The first SPM expelled from the substrate has a relatively high hydrogen peroxide concentration and a relatively low sulfuric acid concentration. In addition, the first SPM expelled from the substrate contains a greater amount of contaminants (carbides of the resist and the like) occurring due to reaction between the first SPM and the resist. Therefore, the first SPM expelled from the substrate is inappropriate for the recovery. 
     On the other hand, the second SPM expelled from the substrate has a relatively high sulfuric acid concentration. Further, the amount of contaminants contained in the second SPM expelled from the substrate is smaller than the amount of the contaminants contained in the first SPM expelled from the substrate. Therefore, the second SPM having a relatively high sulfuric acid concentration and a smaller contaminant amount is guided into the recovery pipe, and used for the preparation of the sulfuric acid-containing liquid. The prepared sulfuric acid-containing liquid is mixed with hydrogen peroxide water. Thus, sulfuric acid contained in the sulfuric acid-containing liquid reacts with hydrogen peroxide, whereby the SPM is newly prepared. This reduces the amount of the SPM to be discarded. 
     The SPM is recovered, when the sulfuric acid concentration is higher, i.e., when the ratio of the volume of sulfuric acid before the mixing to the total volume of sulfuric acid and hydrogen peroxide water before the mixing is higher. Therefore, the SPM having a higher sulfuric acid concentration can be recovered. The sulfuric acid concentration is not maintained at a higher level, but the SPM having a higher hydrogen peroxide concentration and a sufficient removal capability is supplied to the substrate before the recovery of the SPM is started. Therefore, the resist can be efficiently removed. This makes it possible to recover the SPM having a higher sulfuric acid concentration, while efficiently removing the resist from the substrate. 
     In one embodiment of the present invention, the substrate processing method further includes: a first SPM capturing step of receiving the first SPM expelled from the substrate in the first SPM supplying step by a first guard surrounding the substrate and connected to the liquid drain pipe; and a second SPM capturing step of receiving the second SPM expelled from the substrate in the second SPM supplying step by a second guard surrounding the substrate and connected to the recovery pipe. 
     According to this method, the first SPM expelled from the substrate is received by the first guard surrounding the substrate. The second SPM expelled from the substrate is received by the second guard surrounding the substrate. The first SPM received by the first guard flows into the liquid drain pipe connected to the first guard. The second SPM received by the second guard flows into the recovery pipe connected to the second guard. 
     The first SPM expelled from the substrate contains a greater amount of contaminants. Therefore, the contaminants are liable to remain on the inner wall of the first guard after the first SPM is received by the first guard. When the second SPM expelled from the substrate is received and recovered by the first guard, the second SPM is liable to be contaminated with the contaminants adhering to the first guard. Therefore, the second SPM is received by the second guard different from the first guard, whereby the amount of the contaminants to be contained in the recovered SPM can be reduced. 
     The foregoing and other objects, features, and effects of the present invention will become more apparent from the following description of embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic diagram of a substrate processing apparatus according to a first embodiment of the present invention as seen from the top. 
         FIG. 2  is a diagram of a first sulfuric acid-containing liquid supply device and an apparatus main body shown in  FIG. 1  as seen in a horizontal direction. 
         FIG. 3  is a sectional view showing the structure of a third capturing filter shown in  FIG. 2  on an enlarged scale. 
         FIG. 4  is a diagram of a second sulfuric acid-containing liquid supply device and the apparatus main body shown in  FIG. 1  as seen in a horizontal direction. 
         FIG. 5  is a schematic sectional view for describing the structure of a treatment unit shown in  FIG. 1  by way of example. 
         FIG. 6  is a block diagram for describing the electrical configuration of the substrate processing apparatus. 
         FIG. 7  is a flowchart for describing an exemplary substrate processing process to be performed by the substrate processing apparatus. 
         FIG. 8  is a timing chart showing a change in the mixing ratio between the sulfuric acid-containing liquid and hydrogen peroxide water, the operations of a first guard and a second guard, and the like in an SPM step (S 3  in  FIG. 7 ). 
         FIG. 9  is a flowchart showing a process to be performed when the sulfuric acid-containing liquid and hydrogen peroxide water are mixed together for preparation of SPM, and SPM recovered from a substrate is supplied to another substrate. 
         FIG. 10  is a graph showing a change in the sulfuric acid concentration of the recovered sulfuric acid-containing liquid. 
         FIG. 11  is a diagram of a first sulfuric acid-containing liquid supply device according to a second embodiment of the present invention as seen in a horizontal direction. 
         FIG. 12  is a diagram of a first sulfuric acid-containing liquid supply device according to a third embodiment of the present invention as seen in a horizontal direction. 
         FIG. 13  is a diagram for describing a change in the filtering capability of a capturing filter due to thermal influence. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
       FIG. 1  is a schematic diagram of a substrate processing apparatus  1  according to a first embodiment of the present invention as seen from the top. 
     The substrate processing apparatus  1  is an apparatus of a single-substrate processing type for processing disk-shaped substrates W such as semiconductor wafers one by one. The substrate processing apparatus  1  includes an apparatus main body  2  disposed in a clean room, an indexer unit  3  connected to the apparatus main body  2 , a treatment liquid supply device, and a control device  4  which controls the substrate processing apparatus  1 . 
     The indexer unit  3  includes a plurality of load ports LP which respectively hold a plurality of carriers C each containing substrates W, and an indexer robot IR which transports a substrate W with respect to each of the carriers C. 
     The apparatus main body  2  includes a transport chamber  5 , and a plurality of treatment units  6  in which the substrates W transported from the plurality of load ports LP are treated with a treatment fluid such as a treatment liquid or a treatment gas. The plurality of treatment units  6  define six towers, which are disposed at six positions horizontally spaced from each other. The towers each include a plurality of treatment units  6  (e.g., three treatment units  6 ) vertically stacked one on another. The six towers are disposed three by three on opposite sides of the transport chamber  5 . The treatment units  6  are located inside an outer wall  7  of the apparatus main body  2 , i.e., are surrounded by the outer wall  7 . 
     The substrate processing apparatus  1  includes a first substrate transport robot CR 1  and a second substrate transport robot CR 2  in addition to the indexer robot IR as transport robots. The first substrate transport robot CR 1  and the second substrate transport robot CR 2  are disposed in the transport chamber  5 . The indexer robot IR transports substrates W between the load ports LP and the first substrate transport robot CR 1 . The indexer robot IR includes a hand which supports a substrate W. The first substrate transport robot CR 1  transports substrates W between the indexer robot IR and the treatment units  6  of two of the towers located closest to the load ports LP, and transports substrates W between the indexer robot IR and the second substrate transport robot CR 2 . The second substrate transport robot CR 2  transports substrates W between the transport units  6  of the other four towers located opposite from the load ports LP and the indexer robot IR. The first substrate transport robot CR 1  and the second substrate transport robot CR 2  each include a hand which supports a substrate W. 
     The treatment liquid supply device supplies the treatment liquid (a sulfuric acid-containing liquid (an etching liquid or a cleaning liquid) to the treatment units  6 . The treatment liquid supply device includes sulfuric acid-containing liquid supply devices  8  which supply the sulfuric acid-containing liquid containing sulfuric acid to the treatment units  6 . The sulfuric acid-containing liquid supply devices  8  recover the sulfuric acid-containing liquid from the treatment units  6 , then condition the recovered liquid as the sulfuric acid-containing liquid, and supply the conditioned sulfuric acid-containing liquid to the treatment units  6 . The sulfuric acid-containing liquid supply devices  8  each include a first sulfuric acid-containing liquid supply device  9  disposed outside the clean room, and a second sulfuric acid-containing liquid supply device  10  disposed outside the outer wall  7  in the clean room. 
     In this embodiment, the substrate processing apparatus  1  includes two first sulfuric acid-containing liquid supply devices  9 . The two first sulfuric acid-containing liquid supply devices  9  are disposed in a so-called Sub-Fab which is a space beneath the clean room. The first sulfuric acid-containing liquid supply devices  9  are each associated with the three towers disposed on each side of the transport chamber  5 . The first sulfuric acid-containing liquid supply devices  9  are each supplied with SPM drained from the treatment units  6  of the three towers associated therewith. The first sulfuric acid-containing liquid supply devices  9  each include a first liquid storage  11  which recovers the SPM drained from the treatment units  6  and then stores the recovered SPM as the sulfuric acid-containing liquid to condition the sulfuric acid-containing liquid in a predetermined state. 
     A second sulfuric acid-containing liquid supply device  10  is provided in association with each of the first sulfuric acid-containing liquid supply devices  9 . That is, the substrate processing apparatus  1  includes two second sulfuric acid-containing liquid supply devices  10 . 
     The second sulfuric acid-containing liquid supply devices  10  are supplied with the sulfuric acid-containing liquid from the first sulfuric acid-containing liquid supply devices  9  associated therewith. The second sulfuric acid-containing liquid supply devices  10  each include a second liquid storage  12  which stores the sulfuric acid-containing liquid supplied from the first liquid storage  11  and conditions the sulfuric acid-containing liquid at a predetermined sulfuric acid concentration and a predetermined temperature. The sulfuric acid-containing liquid conditioned by the second liquid storage  12  is supplied to an SPM nozzle (nozzle)  13  (see  FIGS. 2 and 4 ) of each of the treatment units  6 . To the SPM nozzle  13 , hydrogen peroxide water is supplied from a hydrogen peroxide water supply unit  122  (see  FIG. 4 ). The sulfuric acid-containing liquid and hydrogen peroxide water supplied to the SPM nozzle  13  are mixed together in the SPM nozzle  13  (mixing portion), whereby SPM is prepared. The SPM is spouted from a spout  13   a  (see  FIG. 5 ) provided at a lower portion of the SPM nozzle  13 . The spout  13   a  communicates with the inside of the SPM nozzle  13 . In the treatment unit  6 , the SPM spouted from the spout  13   a  is supplied to the substrate W. Thus, a resist is removed from the substrate W. 
     In the sulfuric acid-containing liquid supply device  8 , the sulfuric acid-containing liquid, but not the SPM itself, is prepared from the SPM expelled and recovered from the substrate W (sulfuric acid-containing liquid preparing step). The prepared sulfuric acid-containing liquid is reused to be mixed with hydrogen peroxide water for use as the SPM. 
     In order to increase the removal capability of the SPM, the sulfuric acid concentration of the prepared sulfuric acid-containing liquid is required to fall within a predetermined concentration range. Similarly, the temperature of the prepared sulfuric acid-containing liquid is required to fall within a predetermined temperature range. 
     In the sulfuric acid-containing liquid supply device  8 , the sulfuric acid concentration and the temperature of the sulfuric acid-containing liquid are adjusted by particularly considering sulfuric acid contained in the recovered SPM separately from hydrogen peroxide and, therefore, the sulfuric acid-containing liquid can be properly prepared as having a sulfuric acid concentration and a temperature falling within the required concentration range and temperature range. 
     Then, the prepared sulfuric acid-containing liquid is mixed with hydrogen peroxide water in the SPM nozzle  13 , whereby the SPM is prepared. The prepared SPM is spouted from the SPM nozzle  13  to be supplied to the substrate W (SPM spouting step). Thus, the resist can be efficiently removed from the substrate W with the use of the SPM prepared from the recovered sulfuric acid-containing liquid. 
       FIG. 2  is a diagram of the first sulfuric acid-containing liquid supply device  9  and the apparatus main body  2  shown in  FIG. 1  as seen in a horizontal direction.  FIG. 3  is a sectional view showing the structure of a third capturing filter  37  shown in  FIG. 2  on an enlarged scale. 
     As shown in  FIG. 2 , the first liquid storage  11  of the first sulfuric acid-containing liquid supply device  9  includes a reclaim tank  21 , a first circulation tank (first tank)  22 , a first circulation pipe (second pipe)  23 , a first circulation heater (second heater)  24 , and a sulfuric acid adding unit  25 . 
     As shown in  FIG. 2 , the SPM recovered from a total of nine treatment units  6  of the associated three towers is stored as the sulfuric acid-containing liquid in the reclaim tank  21 . Specifically, a downstream end of a recovery outlet pipe  26  connected to recovery pipes  156  to be described later is connected to the reclaim tank  21 . SPM recovered in treatment cups  111  of the respective treatment units  6  is guided to the reclaim tank  21  through the respective recovery pipes  156  and the recovery outlet pipe  26 , and stored as the sulfuric acid-containing liquid in the reclaim tank  21 . A first capturing filter  27  which captures and removes foreign matter from the SPM flowing through the recovery outlet pipe  26  is provided in the recovery outlet pipe  26 . The first capturing filter  27  is a filter for capturing relatively large foreign matter contained in the SPM. The first capturing filter  27  has substantially the same structure as a third capturing filter  37  to be described later. The first capturing filter  27  has pores  71  (to be described later with reference to  FIG. 3 ) each having a greater diameter than a second capturing filter  30  (to be described later) and the third capturing filter (filter)  37 . The recovery outlet pipe  26  vertically extends, so that the SPM flowing through the recovery outlet pipe  26  is forced against the first capturing filter  27  by the gravity of the SPM. Thus, the first capturing filter  27  captures relatively large foreign matter. Then, the SPM removed of the relatively large foreign matter is stored as the sulfuric acid-containing liquid in the reclaim tank  21 . 
     Downstream ends of three recovery outlet pipes  26  respectively associated with the three towers are connected to the reclaim tank  21 . In  FIG. 2 , an arrangement for only one tower is shown in detail. The other two towers are not described in detail, but each designated simply as “another tower” in  FIG. 2 . 
     As shown in  FIG. 2 , a transport pipe  28  is connected at its upstream end to the reclaim tank  21 , and connected at its downstream end to the first circulation tank  22 . A first liquid pumping device  29  such as a pump for pumping out the sulfuric acid-containing liquid from the reclaim tank  21 , and a second capturing filter  30  for capturing and removing relatively small foreign matter from the sulfuric acid-containing liquid flowing through the transport pipe are provided in the transport pipe  28 . The second capturing filter  30  has substantially the same structure as the third capturing filter  37  to be described layer. The second capturing filter  30  has substantially the same pore diameter as the diameter of each of the pores  71  (see  FIG. 3 ) of the third capturing filter  37 . As shown in  FIG. 2 , the first liquid pumping device  29  and the second capturing filter  30  are disposed in this order from the side of the reclaim tank  21 . Therefore, the sulfuric acid-containing liquid flowing through the transport pipe  28  is forced against the second capturing filter  30  by the pumping force of the first liquid pumping device  29 . Thus, the foreign matter can be captured by the second capturing filter  30 . The sulfuric acid-containing liquid is supplied from the reclaim tank  21  to the first circulation tank  22  through the transport pipe  28 , and stored in the first circulation tank  22  (first storing step). 
     As shown in  FIG. 2 , a first liquid guide pipe  31  extending toward the second sulfuric acid-containing liquid supply device  10  (toward the second liquid storage  12 ) is connected to the first circulation tank  22 . A second liquid pumping device  32  such as a pump for pumping out the sulfuric acid-containing liquid from the first circulation tank  22  is provided in the first liquid guide pipe  31 . The third capturing filter  37  and an on/off valve  38  are provided downstream of the second liquid pumping device  32  in the first liquid guide pipe  31 . The third capturing filter  37  is a filter for capturing and removing relatively small foreign matter from the sulfuric acid-containing liquid flowing through the first liquid guide pipe  31 . The third capturing filter  37  removes foreign matter that cannot be removed by the second capturing filter  30 . 
     As shown in  FIG. 3 , the third capturing filter  37  is, for example, a tubular filter having a blocked downstream end, e.g., a filter of standard blocking type. A plurality of pores  71  are provided in the entire third capturing filter  37  as each extending thicknesswise through the third capturing filter  37 . The pores  71  of the third capturing filter  37  each have, for example, a square shape, but may otherwise be a polygonal shape, a round shape, or an oval shape, as seen thicknesswise of the third capturing filter  37 . 
     As shown in  FIG. 3 , the third capturing filter  37  is removably attached to a housing  72  which holds the third capturing filter  37  therein. The housing  72  includes an inlet portion  73  connected to a downstream end of a pipe portion (of the first liquid guide pipe  31 ) upstream of the third capturing filter  37 , and an outlet portion  74  connected to an upstream end of a pipe portion (of the first liquid guide pipe  31 ) downstream of the third capturing filter  37 . 
     As shown in  FIG. 3 , the third capturing filter  37  partitions an inside space of the housing  72  into an upstream space B 1  of the third capturing filter  37  through which the sulfuric acid-containing liquid to be filtered flows, and a downstream space B 2  of the third capturing filter  37  through which the filtered sulfuric acid-containing liquid flows. The sulfuric acid-containing liquid flowing through the first liquid guide pipe  31  is forced against the third capturing filter  37  by the pumping force of the second liquid pumping device  32 . Thus, the sulfuric acid-containing liquid flows from the upstream space B 1  to the downstream space B 2  to pass through the pores  71  of the third capturing filter  37 . Thus, the sulfuric acid-containing liquid is filtered by the third capturing filter  37 . The foreign matter contained in the sulfuric acid-containing liquid present in the upstream space B 1  is adsorbed on a wall surface of the third capturing filter  37  having the pores  71  defined therein to be thereby captured in the pores  71 . Thus, the foreign matter is removed by the third capturing filter  37 . 
     As shown in  FIG. 2 , the on/off valve  38  is a valve for controlling the on and off of the flow of the sulfuric acid-containing liquid in the first liquid guide pipe  31 . 
     As shown in  FIG. 2 , a return pipe  40  is branched from the first liquid guide pipe  31  at a position between the on/off valve  38  and the third capturing filter  37 . A downstream portion of the return pipe  40  extends to the first circulation tank  22 . A return valve  41  is provided in the return pipe  40 . The first circulation pipe  23  is constituted by the return pipe  40  and a portion of the first liquid guide pipe  31  upstream of the branch position  42  at which the return pipe  40  is branched. 
     As shown in  FIG. 2 , the sulfuric acid adding unit  25  is a unit which supplies fresh sulfuric acid (sulfuric acid yet to be used for the treatment of the substrates W) to the first circulation tank  22 . The sulfuric acid adding unit  25  includes a sulfuric acid addition pipe  44  through which sulfuric acid is added to the first circulation tank  22 , and a sulfuric acid addition valve  45  which opens and closes the sulfuric acid addition pipe  44 . Sulfuric acid to be added is unused sulfuric acid (e.g., concentrated sulfuric acid) having a sulfuric acid concentration that is higher than the sulfuric acid concentration of the sulfuric acid-containing liquid in the first circulation tank  22 . The temperature of sulfuric acid to be added is a room temperature (about 23° C. to about 25° C.) 
     During the operation of the substrate processing apparatus  1  (including a period in which the treatment of the substrates W is halted), the second liquid pumping device  32  and the first circulation heater  24  are constantly driven. With the on/off valve  38  closed and with the return valve  41  open, therefore, the sulfuric acid-containing liquid pumped out from the first circulation tank  22  flows to the branch position  42  through the first liquid guide pipe  31 , and then flows back to the first circulation tank  22  from the branch position  42  through the return pipe  40 . That is, the sulfuric acid-containing liquid is circulated through the first circulation tank  22  and the first circulation pipe  23  during a period in which the sulfuric acid-containing liquid is not supplied to the second liquid storage  12 . When the sulfuric acid-containing liquid is supplied to the second liquid storage  12 , the sulfuric acid-containing liquid pumped out from the first circulation tank  22  is supplied to the second liquid storage through the first liquid guide pipe  31  by opening the on/off valve  38  and closing the return valve  41 . 
     As shown in  FIG. 2 , the first circulation heater  24  is provided upstream of the second liquid pumping device  32  in the first liquid guide pipe  31 . The first circulation heater  24  heats the sulfuric acid-containing liquid circulated through the first circulation tank  22  and the first circulation pipe  23  (second heating step). The heating temperature of the first circulation heater  24  is set to a predetermined first temperature (second heating temperature, e.g., about 120° C. to about 130° C.). The sulfuric acid-containing liquid is circulated through the first circulation tank  22  and the first circulation pipe  23 , whereby the sulfuric acid-containing liquid is conditioned at the first temperature. During the period in which the sulfuric acid-containing liquid is not supplied to the second liquid storage  12 , the sulfuric acid-containing liquid conditioned at the first temperature can be stored in the first circulation tank  22  by the circulation of the sulfuric acid-containing liquid. After the on/off valve  38  is opened, the sulfuric acid-containing liquid conditioned at the first temperature can be supplied to the second liquid storage  12 . 
     As shown in  FIG. 2 , the first liquid storage  11  further includes a liquid drain tank  50 . A liquid drain pipe  46  extending to the liquid drain tank  50  is connected to the first circulation tank  22 . A liquid drain valve  47  which opens and closes the liquid drain pipe  46  is provided in the liquid drain pipe  46 . Where the sulfuric acid-containing liquid stored in the first circulation tank  22  is no longer used for the treatment of the substrates W, the liquid drain valve  47  is opened, whereby the sulfuric acid-containing liquid stored in the first circulation tank  22  is drained from the first circulation tank  22  and guided to the liquid drain tank  50  to be stored in the liquid drain tank  50 . 
     As shown in  FIG. 2 , an outlet pipe  48  extends from the liquid drain tank  50 , and a downstream end of the outlet pipe  48  is connected to a cooling unit (not shown). A third liquid pumping device  49  such as a pump is provided in the outlet pipe  48 . With the third liquid pumping device  49  driven, the sulfuric acid-containing liquid stored in the liquid drain tank  50  is pumped out into the outlet pipe  48  to be supplied to the cooling unit. The sulfuric acid-containing liquid is cooled by the cooling unit, and then guided to a waste liquid disposal device (not shown) provided outside the apparatus to be treated in the waste liquid disposal device. 
     The first liquid storage  11  has thus been described. In the first liquid storage  11 , the SPM recovered from the treatment units  6  is stored as the sulfuric acid-containing liquid in the first circulation tank  22 . The sulfuric acid-containing liquid stored in the first circulation tank  22  is circulated through the first circulation pipe  23 . Further, sulfuric acid from the sulfuric acid adding unit  25  is added to the first circulation tank  22 . With the provision of the sulfuric acid adding unit  25 , the first liquid storage  11  may be regarded as a storage adapted for the adjustment of the sulfuric acid concentration. 
       FIG. 4  is a diagram of the second sulfuric acid-containing liquid supply device  10  and the apparatus main body  2  shown in  FIG. 1  as seen in a horizontal direction. 
     The second liquid storage  12  of the second sulfuric acid-containing liquid supply device  10  includes a second circulation tank (second tank)  51 , a second circulation heater (first heater)  52 , second circulation pipes  53 , and heaters (third heater)  54 . 
     A downstream end of the first liquid guide pipe  31  is connected to the second circulation tank  51 . The sulfuric acid-containing liquid conditioned at the first temperature (e.g., about 120° C. to about 130° C.) in the first liquid storage  11  is guided into the second circulation tank  51 . Then, the guided sulfuric acid-containing liquid is stored in the second circulation tank  51  (second storing step). 
     A liquid amount meter  65  having a plurality of sensors located at different height positions is attached to the second circulation tank  51 . The liquid amount meter  65  detects the liquid surface height of the sulfuric acid-containing liquid stored in the second circulation tank  51 . 
     A common pipe  51 A is connected to the second circulation tank  51 . The second circulation heater  52  is provided in the common pipe  51 A. 
     Three sulfuric acid-containing liquid flowing pipes  51 B are connected to the second circulation tank  51  through the common pipe  51 A. Specifically, upstream ends of the three sulfuric acid-containing liquid flowing pipes  51 B for supplying the sulfuric acid-containing liquid to the corresponding towers are connected to a downstream end portion of the common pipe  51 A. Downstream ends of the three sulfuric acid-containing liquid flowing pipes  51 B are connected to the second circulation tank  51 . The second circulation pipes  53  are constituted by the common pipe  51 A and the respective sulfuric acid-containing liquid flowing pipes  51 B. Fourth liquid pumping devices  56  for pumping out the sulfuric acid-containing liquid from the common pipe  51 A are respectively provided in the sulfuric acid-containing liquid flowing pipes  51 B. The sulfuric acid-containing liquid pumped out into the second circulation pipes  53  by the fourth liquid pumping devices  56  flows from the upstream ends to the downstream ends of the sulfuric acid-containing liquid flowing pipes  51 B back into the second circulation tank  51 . Thus, the sulfuric acid-containing liquid is circulated through the second circulation tank  51  and the second circulation pipes  53  (the common pipe  51 A and the sulfuric acid-containing liquid flowing pipes  51 B). 
     In  FIG. 4 , an arrangement for only one tower is shown in detail. The other two towers are not described in detail, but each designated simply as “another towers” in  FIG. 4 . 
     The second circulation heater  52  heats the sulfuric acid-containing liquid circulated through the second circulation tank  51  and the second circulation pipes  53  (the common pipe  51 A and the sulfuric acid-containing liquid flowing pipes  51 B) (first heating step). The heating temperature of the second circulation heater  52  is set to a predetermined second temperature (first heating temperature) (which is higher than the first temperature, e.g., about 160° C.). The sulfuric acid-containing liquid is circulated through the second circulation tank  51  and the second circulation pipes  53  (the common pipe  51 A and the sulfuric acid-containing liquid flowing pipes  51 B), whereby the sulfuric acid-containing liquid is conditioned at the second temperature from the previous first temperature. 
     The second liquid storage  12  includes the same number of sulfuric acid-containing liquid supply pipes  57  as the number of the treatment units  6  included in each of the towers, and the sulfuric acid-containing liquid supply pipes  57  are branched from the second circulation pipe  53  and adapted to supply the sulfuric acid-containing liquid to the plural treatment units  6  (three treatment units  6 ) of the corresponding tower. 
     The heaters (third heater)  54  are respectively provided in the sulfuric acid-containing liquid supply pipes  57 . A flow rate meter  58 , a sulfuric acid-containing liquid flow rate control valve (mixing ratio changing unit)  59 , and a sulfuric acid-containing liquid valve  60  are provided in this order from the side of the heater  54  downstream of the heater  54  in each of the sulfuric acid-containing liquid supply pipes  57 . 
     The flow rate meter  58  is a flow rate meter which detects the flow rate of the sulfuric acid-containing liquid flowing through the sulfuric acid-containing liquid supply pipe  57 . 
     The sulfuric acid-containing liquid flow rate control valve  59  is a valve which adjusts the opening degree of the sulfuric acid-containing liquid supply pipe  57  to control the flow rate of the sulfuric acid-containing liquid to be supplied to the SPM nozzle  13 . The sulfuric acid-containing liquid flow rate control valve  59  may be configured to include a valve body having a valve seat therein, a valve element which opens and closes the valve seat, and an actuator which moves the valve element between an open position and a closed position. 
     The sulfuric acid-containing liquid valve  60  is a valve which controls the on and off of the supply of the sulfuric acid-containing liquid to the SPM nozzle  13 . 
     A return pipe  61  is branched from the sulfuric acid-containing liquid supply pipe  57  at a position between the sulfuric acid-containing liquid valve  60  and the sulfuric acid-containing liquid flow rate control valve  59 . A downstream end of the return pipe  61  is connected to the sulfuric acid-containing liquid flowing pipe  51 B. A pressure loss in a portion of the sulfuric acid-containing liquid supply pipe  57  upstream of the branch position  63  is greater than a pressure loss in the return pipe  61 . 
     When the sulfuric acid-containing liquid is to be supplied to the SPM nozzle  13 , the control device  4  opens the sulfuric acid-containing liquid valve  60 . Thus, the pressure loss in the return pipe  61  increases to a level greater than the pressure loss in the portion of the sulfuric acid-containing liquid supply pipe  57  downstream of the branch position  63 . Therefore, the sulfuric acid-containing liquid in the portion of the sulfuric acid-containing liquid supply pipe  57  upstream of the branch position  63  is supplied to the portion of the sulfuric acid-containing liquid supply pipe  57  downstream of the branch position  63 , and supplied from the downstream portion to the SPM nozzle  13 . 
     When the supply of the sulfuric acid-containing liquid to the SPM nozzle  13  is to be stopped, the control device  4  closes the sulfuric acid-containing liquid valve  60 . Thus, the pressure loss in the return pipe  61  decreases to a level smaller than the pressure loss in the portion of the sulfuric acid-containing liquid supply pipe  57  downstream of the branch position  63 . Therefore, the sulfuric acid-containing liquid reaching the branch position  63  does not flow back to the portion of the sulfuric acid-containing liquid supply pipe  57  upstream of the branch position  63 , but is guided to the return pipe  61 . The sulfuric acid-containing liquid guided to the return pipe  61  flows back to the sulfuric acid-containing liquid flowing pipe  51 B, and is circulated again through the second circulation tank  51  and the second circulation pipe  53  (the common pipe  51 A and the sulfuric acid-containing liquid flowing pipe  51 B). 
     The heater  54  heats the sulfuric acid-containing liquid flowing through the sulfuric acid-containing liquid supply pipe  57 . The heating temperature of the heater  54  is set to a predetermined third temperature (which is higher than the second temperature, e.g., about 165° C.). The sulfuric acid-containing liquid flows through the sulfuric acid-containing liquid supply pipe  57 , whereby the temperature of the sulfuric acid-containing liquid conditioned at the second temperature is increased to the third temperature from the previous second temperature. 
     During the operation of the substrate processing apparatus  1  (including the period in which the treatment of the substrates W is halted), the fourth liquid pumping device  56  and the second circulation heater  52  are constantly driven. During the operation of the substrate processing apparatus  1 , therefore, the sulfuric acid-containing liquid conditioned at the second temperature is circulated through the second circulation tank  51  and the second circulation pipe  53  (the common pipe  51 A and the sulfuric acid-containing liquid flowing pipe  51 B). 
     With the sulfuric acid-containing liquid valves  60  closed, the sulfuric acid-containing liquid flowing through the second circulation pipe  53  flows from the second circulation pipe  53  to the sulfuric acid-containing liquid supply pipes  57 , and further flows into the return pipes  61  through the branch positions  63  and then back to the sulfuric acid-containing liquid flowing pipe  51 B. Thus, the sulfuric acid-containing liquid is circulated through the second circulation tank  51  and the second circulation pipe  53 . 
     With the sulfuric acid-containing liquid valves  60  open, on the other hand, the sulfuric acid-containing liquid flowing through the sulfuric acid-containing liquid flowing pipe  51 B flows from the second circulation pipe  53  to the sulfuric acid-containing liquid supply pipes  57  to be supplied to the SPM nozzles  13 . That is, the sulfuric acid-containing liquid conditioned at the third temperature is supplied to the SPM nozzles  13 . 
     With reference to the output of the liquid amount meter  65 , the amount of the sulfuric acid-containing liquid stored in the second circulation tank  51  is constantly monitored by the control device  4 . When the amount of the sulfuric acid-containing liquid stored in the second circulation tank  51  is reduced below a lower limit liquid amount, the on/off valve  38  is opened to supply the sulfuric acid-containing liquid from the first liquid storage  11  through the first liquid guide pipe  31 . 
     In one of the three sulfuric acid-containing liquid flowing pipes  51 B, a sulfuric acid concentration meter  64  which measures the sulfuric acid concentration of the sulfuric acid-containing liquid flowing through the sulfuric acid-containing liquid flowing pipe  51 B (i.e., the sulfuric acid-containing liquid circulated through the second circulation tank  51  and the second circulation pipe  53 ) is provided downstream of the fourth liquid pumping device  56 . Since it is considered that the sulfuric acid-containing liquid flowing through the three second circulation pipes  53  has the same sulfuric acid concentration, it is sufficient to provide the single sulfuric acid concentration meter  64  in one of the three second circulation pipes  53 . 
     With reference to the output of the sulfuric acid concentration meter  64 , the sulfuric acid concentration of the sulfuric acid-containing liquid circulated through the second circulation tank  51  and the second circulation pipes (the sulfuric acid concentration of the sulfuric acid-containing liquid stored in the second circulation tank  51 ) is constantly monitored by the control device  4 . When the sulfuric acid concentration of the sulfuric acid-containing liquid circulated through the second circulation tank  51  and the second circulation pipes  53  is reduced below a lower limit concentration, the sulfuric acid addition valve  45  which opens and closes the sulfuric acid addition pipe  44  is opened to supply sulfuric acid to the first circulation tank  22  (sulfuric acid adding step). Thus, the sulfuric acid concentration of the sulfuric acid-containing liquid circulated through the first circulation tank  22  and the first circulation pipe  23  is increased and, after a while, the sulfuric acid concentration of the sulfuric acid-containing liquid circulated through the second circulation tank  51  and the second circulation pipes  53  is correspondingly increased. 
     The second liquid storage  12  has thus been described. The sulfuric acid-containing liquid supplied from the first liquid storage  11  is stored in the second circulation tank  51  of the second liquid storage  12 . The sulfuric acid-containing liquid stored in the second circulation tank  51  is heated. Thus, the temperature of the sulfuric acid-containing liquid in the second liquid storage  12  can be increased to a temperature suitable for the treatment. Therefore, the second liquid storage  12  may be regarded as a storage adapted for the temperature adjustment of the sulfuric acid-containing liquid. 
       FIG. 5  is a schematic sectional view for describing the structure of the treatment unit  6  by way of example. 
     The treatment units  6  each include a box-shaped chamber  107  having an inside space, a spin chuck (substrate holding unit)  108  which horizontally holds a single substrate W and rotates the substrate W about a vertical rotation axis A 1  extending through the center of the substrate W in the chamber  107 , the SPM nozzle  13 , a rinse liquid supply unit  110  which supplies a rinse liquid to an upper surface of the substrate W held by the spin chuck  108 , and a tubular treatment cup  111  surrounding the spin chuck  108 . 
     The chamber  107  includes a box-shaped partition wall  112 , a FFU (fan filter unit)  114  as an air supply unit which supplies clean air to the inside of the partition wall  112  (into the chamber  107 ) from an upper portion of the partition wall  112 , and an exhaust device (not shown) which expels gas from the chamber  107  through a lower portion of the partition wall  112 . The FFU  114  is disposed above the partition wall  112 , and attached to a ceiling of the partition wall  112 . The FFU  114  supplies clean air into the chamber  107  from the ceiling of the partition wall  112 . The exhaust device (not shown) is connected to a bottom portion of the treatment cup  111  through an exhaust duct  113  connected to the treatment cup  111 , and sucks gas from the inside of the treatment cup  111  through the bottom portion of the treatment cup  111 . A down flow (downward stream) is formed in the chamber  107  by the FFU  114  and the exhaust device (not shown). 
     A chuck of clamp type which horizontally clamps the substrate W to horizontally hold the substrate W is used as the spin chuck  108 . Specifically, the spin chuck  108  includes a spin motor (rotation unit) M, a spin shaft  115  unitary with the driving shaft of the spin motor M, and a disk-shaped spin base  116  generally horizontally attached to an upper end of the spin shaft  115 . 
     The spin base  116  has a horizontal round upper surface  116   a  having an outer diameter that is greater than the outer diameter of the substrate W. A plurality of clamp members  117  (not less than three clamp members  117 , e.g., six clamp members  117 ) are disposed on a peripheral portion of the upper surface  116   a . The plural clamp members  117  are spaced a proper distance from each other circumferentially of the substrate W on the upper surface peripheral portion of the spin base  116 . 
     The SPM nozzle  13  is, for example, a straight nozzle which spouts the SPM in the form of continuous stream. The SPM nozzle  13  is attached to a distal end of a nozzle arm  119 . The SPM nozzle  13  is, for example, attached to the nozzle arm  119  in a vertical posture for spouting the treatment liquid (SPM) perpendicularly to the upper surface of the substrate W. The nozzle arm  119  extends horizontally. A nozzle moving unit  120  which moves the nozzle arm  119  to move the SPM nozzle  13  is connected to the nozzle arm  119 . The nozzle moving unit  120  includes an electric motor. 
     The nozzle moving unit  120  horizontally moves the nozzle arm  119  about a vertical pivot axis defined adjacent to the treatment cup  111  to horizontally move the SPM nozzle  13 . The nozzle moving unit  120  horizontally moves the SPM nozzle  13  between a treatment position defined such that the SPM spouted from the SPM nozzle  13  is applied to the upper surface of the substrate W and a retracted position defined such that the SPM nozzle  13  is located outside the spin chuck  108  as seen in plan. In this embodiment, the treatment position is, for example, a center position defined such that the SPM spouted from the SPM nozzle  13  is applied to an upper surface center portion of the substrate W. 
     The treatment liquid supply device includes a hydrogen peroxide water supply unit  122  which supplies hydrogen peroxide water (H 2 O 2 ) to the SPM nozzle  13 . The hydrogen peroxide water supply unit  122  includes a hydrogen peroxide water pipe  135  connected to the SPM nozzle  13 , a hydrogen peroxide water valve  136  which opens and closes the hydrogen peroxide water pipe  135 , and a hydrogen peroxide water flow rate control valve (mixing ratio changing unit)  137  which controls the opening degree of the hydrogen peroxide water valve  136  to control the flow rate of hydrogen peroxide water flowing through the hydrogen peroxide water valve  136 . The hydrogen peroxide water flow rate control valve  137  may be configured to include a valve body having a valve seat therein, a valve element which opens and closes the valve seat, and an actuator which moves the valve element between an open position and a closed position. Hydrogen peroxide water, which is temperature-uncontrolled and has an ordinary temperature (about 20° C. to about 40° C.), is supplied from a hydrogen peroxide water supply source (not shown) to the hydrogen peroxide water pipe  135 . 
     With the sulfuric acid-containing liquid valve  60  and the hydrogen peroxide water valve  136  open, the sulfuric acid-containing liquid supplied at a higher temperature (165° C.) through the sulfuric acid-containing liquid supply pipe  57  and hydrogen peroxide water supplied through the hydrogen peroxide water pipe  135  are supplied into a casing (not shown) of the SPM nozzle  13 , and sufficiently mixed (stirred) together in the casing. Thus, the sulfuric acid-containing liquid and hydrogen peroxide water are homogeneously mixed together, whereby a liquid mixture (SPM) of sulfuric acid and hydrogen peroxide water is prepared by a reaction between sulfuric acid contained in the sulfuric acid-containing liquid and hydrogen peroxide water. The SPM contains peroxosulfuric acid (peroxomonosulfuric acid, H 2 SO 5 ) having a higher oxidation power, and is heated to a temperature (e.g., about 190° C. to about 220° C.) that is higher than the temperature of the sulfuric acid-containing liquid (e.g., about 165° C.) and the temperature of hydrogen peroxide water before the mixing. The prepared higher-temperature SPM is spouted from the spout that opens at a distal end (e.g., lower end) of the casing of the SPM nozzle  13 . 
     The flow rate of the sulfuric acid-containing liquid to be supplied to the SPM nozzle  13  is changed by the sulfuric acid-containing liquid flow rate control valve  59 . The flow rate of hydrogen peroxide water to be supplied to the SPM nozzle  13  is changed by the hydrogen peroxide water flow rate control valve  137 . Therefore, the mixing ratio between the sulfuric acid-containing liquid and hydrogen peroxide water is changed by the sulfuric acid-containing liquid flow rate control valve  59  and the hydrogen peroxide water flow rate control valve  137 . The mixing ratio between the sulfuric acid-containing liquid and hydrogen peroxide water (the flow rate ratio between the sulfuric acid-containing liquid and hydrogen peroxide water) is controlled, for example, within a range of 30:1 ((sulfuric acid-containing liquid):(hydrogen peroxide water)) to 2:1 ((sulfuric acid-containing liquid):(hydrogen peroxide water)). 
     The rinse liquid supply unit  110  includes a rinse liquid nozzle  147  which spouts a rinse liquid toward the upper surface of the substrate W. The rinse liquid nozzle  147  is, for example, a straight nozzle which spouts the liquid in the form of continuous stream. The rinse liquid nozzle  147  is a stationary nozzle fixed to the partition wall  112  of the chamber  107 . The spout of the rinse liquid nozzle  147  is directed toward the upper surface center portion of the substrate W. The rinse liquid nozzle  147  may be a scan nozzle which is movable within the chamber  107 . That is, the rinse liquid supply unit  110  may include a nozzle moving unit which moves the rinse liquid nozzle  147  so that a rinse liquid application position with respect to the upper surface of the substrate W is moved within the upper surface of the substrate W. 
     The rinse liquid nozzle  147  is connected to a rinse liquid pipe  148  which guides the rinse liquid from a rinse liquid supply source. A rinse liquid valve  149  for switching the on and off of the supply of the rinse liquid from the rinse liquid nozzle  147  is provided in the rinse liquid pipe  148 . With the rinse liquid valve  149  open, the rinse liquid is supplied from the rinse liquid pipe  148  to the rinse liquid nozzle  147  to be spouted from a spout provided at a lower end of the rinse liquid nozzle  147 . 
     With the rinse liquid valve  149  closed, the supply of the rinse liquid from the rinse liquid pipe  148  to the rinse liquid nozzle  147  is stopped. The rinse liquid is, for example, deionized water (DIW), but not limited to the DIW. The rinse liquid may be carbonated water, electrolytic ion water, hydrogen water, ozone water, ammonia water, and hydrochloric acid water having a dilute concentration (e.g., about 10 ppm to about 100 ppm). The rinse liquid may be at an ordinary temperature (20° C. to 40° C.), or may be heated before being supplied to the substrate W. 
     The treatment cup  111  is disposed outward of the substrate W held by the spin chuck  108  (apart from the rotation axis A 1 ). The treatment cup  111  laterally surrounds the spin base  116 . When the treatment liquid is supplied to the substrate W being rotated by the spin chuck  108 , the treatment liquid supplied to the substrate W is spun out around the substrate W. When the treatment liquid is supplied to the substrate W, an upper edge  111   a  of the treatment cup  111  which opens upward is located at a higher level than the spin base  116 . Therefore, the treatment liquid such as the chemical liquid and water is expelled around the substrate W to be received by the treatment cup  111 . Then, the treatment liquid received by the treatment cup  111  is supplied to the reclaim tank  21  of the first liquid storage  11 , or is supplied to the waste liquid disposal device (not shown) via the cooling unit (not shown). 
     The treatment cup  111  includes a plurality of tubular guards (a first guard  143 , a second guard  144 , and a third guard  145 ) which receive the treatment liquid (the chemical liquid or the rinse liquid) scattered around the substrate W, and a plurality of annular cups (a first cup  141  and a second cup  142 ) which receive the treatment liquid guided by the plurality of guards, and a hollow cylindrical member  140  which surrounds the plurality of guards and the plurality of cups. 
     The treatment cup  111  further includes a guard lift unit  146  which independently moves up and down the respective guards (the first guard  143 , the second guard  144 , and the third guard  145 ). The guard lift unit  146  includes, for example, an electric motor which generates power, a ball screw mechanism which transmits the power of the electric motor to any of the guards. When the guard lift unit  146  moves up and down at least one of the three guards, the state of the treatment cup  111  is changed. 
     As will be described later, the state of the treatment cup  111  is switched among a retracted state in which the upper edges of all the guards are located at a lower level than the substrate W (as shown in  FIG. 5 ), a first opposed state in which the first guard  143  is opposed to the peripheral surface of the substrate W, a second opposed state in which the second guard  144  is opposed to the peripheral surface of the substrate W, and a third opposed state in which the third guard  145  is opposed to the peripheral surface of the substrate W. 
     The first cup  141  surrounds the spin chuck  108  inside the hollow cylindrical member  140 . The first cup  141  defines an annular first channel  150  into which the treatment liquid used for the treatment of the substrate W flows. A liquid drain port  151  is provided in the lowermost portion of the bottom of the first channel  150 , and a first liquid drain pipe  152  is connected to the liquid drain port  151 . The treatment liquid introduced into the first liquid drain pipe  152  is supplied to a liquid drain device, and treated in the liquid drain device. 
     The second cup  142  surrounds the first cup  141  inside the hollow cylindrical member  140 . The second cup  142  defines an annular second channel  153  into which the treatment liquid used for the treatment of the substrate W flows. A liquid drain/recovery port  154  is provided in the lowermost portion of the bottom of the second channel  153 , and a common pipe  155  is connected to the liquid drain/recovery port  154 . The recovery pipe  156  and a second liquid drain pipe  157  are branched from the common pipe  155 . An upstream end of the recovery pipe  156  is connected to the common pipe  155 , and a downstream end of the recovery pipe  156  is connected to the reclaim tank  21  of the first liquid storage  11 . 
     A recovery valve  158  is provided in the recovery pipe  156 , and a liquid drain valve  159  is provided in the second liquid drain pipe  157 . With the liquid drain valve  159  closed and with the recovery valve  158  open, the liquid flowing through the common pipe  155  is guided to the recovery pipe  156 . With the liquid drain valve  159  open and with the recovery valve  158  closed, the liquid flowing through the common pipe  155  is guided to the second liquid drain pipe  157 . The recovery valve  158  and the liquid drain valve  159  are included in a recovery/drain switching unit which switches, between the recovery pipe  156  and the second liquid drain pipe  157 , the pipe into which the liquid expelled from the substrate W flows. 
     The innermost first guard  143  surrounds the spin chuck  108  inside the hollow cylindrical member  140 . The first guard  143  includes a hollow cylindrical lower portion  163  which surrounds the periphery of the spin chuck  108 , a tubular portion  164  extending outward from an upper edge of the lower portion  163  (apart from the rotation axis A 1  of the substrate W), a hollow cylindrical middle portion  165  extending vertically upward from an upper edge of the tubular portion  164 , and an annular upper portion  166  extending obliquely upward inward from an upper edge of the middle portion  165  (toward the rotation axis A 1  of the substrate W). 
     The lower portion  163  of the first guard  143  is located above the first channel  150  of the first cup  141 . An inner peripheral edge of the upper portion  166  of the first guard  143  has a round shape having a greater diameter than the substrate W held by the spin chuck  108  as seen in plan. As shown in  FIG. 5 , the upper portion  166  of the first guard  143  has a linear sectional shape. The sectional shape of the upper portion  166  may be a nonlinear shape such as an arcuate shape. 
     The second guard  144  located at the second position from the inner side surrounds the first guard  143  inside the hollow cylindrical member  140 . The second guard  144  includes a hollow cylindrical portion  167  which surrounds the first guard  143 , and an annular upper portion  168  extending obliquely upward from an upper edge of the hollow cylindrical portion  167  toward the center thereof (toward the rotation axis A 1  of the substrate W). The hollow cylindrical portion  167  of the second guard  144  is located above the second channel  153  of the second cup  142 . 
     An inner peripheral edge of the upper portion  168  of the second guard  144  has a round shape having a greater diameter than the substrate W held by the spin chuck  108  as seen in plan. The upper portion  168  of the second guard  144  has a linear sectional shape. The sectional shape of the upper portion  168  may be a nonlinear shape such as an arcuate shape. The upper portion  168  of the second guard  144  vertically overlaps with the upper portion  166  of the first guard  143 . The upper portion  168  of the second guard  144  is configured so as to be spaced a minute distance from the upper portion  166  of the first guard  143  when the first guard  143  and the second guard  144  are located closest to each other. 
     The third guard  145  located at the third position from the inner side surrounds the second guard  144  inside the hollow cylindrical member  140 . The third guard  145  includes a hollow cylindrical portion  170  which surrounds the second guard  144 , and an annular upper portion  171  extending obliquely upward from an upper edge of the hollow cylindrical portion  170  toward the center thereof (toward the rotation axis A 1  of the substrate W). An inner peripheral edge of the upper portion  171  has a round shape having a greater diameter than the substrate W held by the spin chuck  108  as seen in plan. The upper portion  171  has a linear sectional shape. The sectional shape of the upper portion  171  may be a nonlinear shape such as an arcuate shape. 
     The first channel  150  of the first cup  141 , an inner wall  143   a  of the first guard  143 , and the casing outer periphery of the spin chuck  108  define a first flow space (i.e., liquid drain space) SP 1  into which the chemical liquid used for the treatment of the substrate W is guided. The second channel  153  of the second cup  142 , an outer wall  143   b  of the first guard  143 , and an inner wall  144   a  of the second guard  144  define a second flow space (i.e., recovery space) SP 2  into which the chemical liquid used for the treatment of the substrate W is guided. The first flow space SP 1  and the second flow space SP 2  are separated from each other by the first guard  143 . 
     The guard lift unit  146  moves up and down each of the guards (the first guard  143 , the second guard  144 , and the third guard  145 ) between an upper position defined such that the upper edge of the guard is located at a higher level than the substrate W and a lower position defined such that the upper edge of the guard is located at a lower level than the substrate W. The guard lift unit  146  is capable of holding each of the guards at any position between the upper position and the lower position. The treatment liquid is supplied to the substrate W with any of the guards in opposed relation to the peripheral surface of the substrate W. 
     Where the treatment cup  111  is in the first opposed state in which the innermost first guard  143  is opposed to the peripheral surface of the substrate W, the first guard  143 , the second guard  144 , and the third guard  145  are all located at the upper position (treatment height position). Where the treatment cup  111  is in the second opposed state in which the second guard  144  located at the second position from the inner side is opposed to the peripheral surface of the substrate W, the second and third guards  144 ,  145  are each located at the upper position, and the first guard  143  is located at the lower position. Where the treatment cup  111  is in the third opposed state in which the outermost third guard  145  is opposed to the peripheral surface of the substrate W, the third guard  145  is located at the upper position, and the first guard  143  and the second guard  144  are each located at the lower position. In the retracted state (see  FIG. 5 ) in which all the guards are retracted from the peripheral surface of the substrate W, the first guard  143 , the second guard  144 , and the third guard  145  are all located at the lower position. 
     As will be described later, when the treatment cup  111  is switched from the first opposed state to the second opposed state, the first guard  143  is located at a cleaning height position between the upper position and the lower position with the second guard  144  and the third guard  145  each located at the upper position. This state is a transition state in which the treatment cup  111  is switched from the first opposed state to the second opposed state. The treatment cup  111  is switched to any of the plural states including the first to third opposed states, the retracted state, and the transition state. The transition state is such that the first guard  143  is opposed to the peripheral surface of the substrate W. 
       FIG. 6  is a block diagram for describing the electrical configuration of the substrate processing apparatus  1 . 
     The control device  4  is, for example, a computer. The control device  4  includes an arithmetic unit such as CPU, storage units such as a fixed memory device and a hard disk drive, and an input/output unit for inputting and outputting information. The storage units include computer-readable recording media which store computer programs to be executed by the arithmetic unit. Process steps to be executed by the control device  4  for the resist removal treatment to be described later are incorporated in the storage media. 
     The control device  4  controls the operations of the spin motors M, the nozzle moving units  120 , the guard lift units  146 , the first liquid pumping devices  29 , the second liquid pumping devices  32 , the third liquid pumping devices  49 , the fourth liquid pumping devices  56 , the first circulation heaters  24 , the second circulation heaters  52 , the heaters  54 , and the like according to a predetermined program. Further, the control device  4  controls the on/off operations of the on/off valves  38 , the return valves  41 , the sulfuric acid addition valves  45 , the liquid drain valves  47 , the sulfuric acid-containing liquid valves  60 , the hydrogen peroxide water valves  136 , the rinse liquid valves  149 , the recovery valves  158 , the liquid drain valves  159 , and the like according to a predetermined program. The control device  4  controls the opening degrees of the sulfuric acid-containing liquid flow rate control valves  59 , and the hydrogen peroxide water flow rate control valves  137  according to a predetermined program. The measurement values of the sulfuric acid concentration meters  64  and the liquid amount meters  65  are inputted to the control device  4 . 
       FIG. 7  is a flowchart for describing an exemplary treatment to be performed on the substrate W by the substrate processing apparatus  1 . 
     With reference to  FIGS. 1 to 7 , the treatment of the substrate W will hereinafter be described by way of example. The exemplary treatment of the substrate W is a resist removal treatment for removing a resist from the upper surface (major surface) of the substrate W. The resist is, for example, a photoresist of a carbon-containing compound. 
     When a substrate W with its front surface (device formation surface) at least partly covered with the resist is to be treated by the substrate processing apparatus  1 , the control device  4  retracts all the nozzles from above the spin chuck  108  and locates all the guards  143  to  145  at the lower position and, in this state, inserts the hand of the substrate transport robot (the first substrate transport robot CR 1  or the second substrate transport robot CR 2  (see  FIG. 1 ) into the chamber  107  with the substrate W held thereon. Thus, the substrate W is transferred to the spin chuck  108  and held by the spin chuck  108  with its front surface facing up. 
     With the substrate W held by the spin chuck  108 , the control device  4  starts rotating the spin motor M. Thus, the rotation of the substrate W is started (S 2  in  FIG. 7 ). The rotation speed of the substrate W is increased to a predetermined liquid treatment speed (within a range of 300 to 1500 rpm, e.g., 500 rpm), and kept at the liquid treatment speed. After the rotation speed of the substrate W reaches the liquid treatment speed, the control device  4  performs an SPM step S 3 . 
     Specifically, the control device  4  controls the nozzle moving unit  120  to move the SPM nozzle  13  from the retracted position to the treatment position. Further, the control device  4  opens the sulfuric acid-containing liquid valve  60  and the hydrogen peroxide water valve  136  simultaneously. Thus, the sulfuric acid-containing liquid flowing through the sulfuric acid-containing liquid supply pipe  57  is supplied to the SPM nozzle  13  and, at the same time, hydrogen peroxide water flowing through the hydrogen peroxide water pipe  135  is supplied to the SPM nozzle  13 . Inside the SPM nozzle  13 , the sulfuric acid-containing liquid and hydrogen peroxide water are mixed together, whereby the SPM is prepared at a higher temperature (e.g., 190° C. to 220° C.). The SPM is spouted from the spout of the SPM nozzle  13  to be applied to the upper surface center portion of the substrate W. 
     After the SPM spouted from the SPM nozzle  13  is applied to the upper surface of the substrate W, the SPM flows outward on the upper surface of the substrate W by centrifugal force. Therefore, the SPM is supplied over the entire upper surface of the substrate W, whereby a liquid film of the SPM is formed on the substrate W as covering the entire upper surface of the substrate W. Thus, the resist chemically reacts with the SPM to be thereby removed from the substrate W by the SPM. The SPM is moved to the periphery of the substrate W to be scattered laterally of the substrate W from the periphery of the substrate W. 
     In the SPM step S 3 , the control device  4  may control the nozzle moving unit  120  to move the SPM nozzle  13  between a peripheral position at which the SPM nozzle  13  is opposed to an upper surface peripheral portion of the substrate W and a center position at which the SPM nozzle  13  is opposed to the upper surface center portion of the substrate W. In this case, the SPM application position on the upper surface of the substrate W is moved over the entire upper surface of the substrate W, whereby the entire upper surface of the substrate W is scanned with the SPM application position. Thus, the entire upper surface of the substrate W is evenly treated. 
     After a lapse of a predetermined period from the start of the spouting of the SPM, the control device  4  closes the sulfuric acid-containing liquid valve  60  and the hydrogen peroxide water valve  136  to stop spouting the SPM from the SPM nozzle  13 . Thus, the SPM step S 3  ends. Thereafter, the control device  4  controls the nozzle moving unit  120  (see  FIG. 6 ) to move the SPM nozzle  13  back to the retracted position. 
     Then, a rinsing step of supplying the rinse liquid to the substrate W (S 4  in  FIG. 7 ) is performed. Specifically, the control device  4  opens the rinse liquid valve  149  to spout the rinse liquid from the rinse liquid nozzle  147  toward the upper surface center portion of the substrate W. The rinse liquid spouted from the rinse liquid nozzle  147  is applied to the upper surface center portion of the substrate W covered with the SPM. The rinse liquid applied to the upper surface center portion of the substrate W receives centrifugal force generated by the rotation of the substrate W to flow toward the periphery of the substrate W on the upper surface of the substrate W. Thus, the SPM on the substrate W is forced to flow outward to be expelled around the substrate W by the rinse liquid. As a result, the SPM and the resist (residual resist) are washed away from the entire upper surface of the substrate W. After a lapse of a predetermined period from the start of the rinsing step S 4 , the control device  4  closes the rinse liquid valve  149  to stop spouting the rinse liquid from the rinse liquid nozzle  147 . 
     Then, a drying step of drying the substrate W (S 5  in  FIG. 7 ) is performed. Specifically, the control device  4  controls the spin motor M to accelerate the substrate W to a drying rotation speed (e.g., several thousands rpm) that is higher than the rotation speed employed in the SPM step S 3  and the rinsing step S 4  and rotate the substrate W at the drying rotation speed. Thus, greater centrifugal force is applied to the liquid adhering to the substrate W to spin out the liquid around the substrate W. In this manner, the liquid is removed from the substrate W, whereby the substrate W is dried. After a lapse of a predetermined period from the start of the high-speed rotation of the substrate W, the control device  4  stops the spin motor M to stop the rotation of the substrate W by the spin chuck  108  (S 6  in  FIG. 7 ). 
     Then, the substrate W is unloaded from the chamber  107  (S 7  in  FIG. 7 ). Specifically, the control device  4  inserts the hand of the substrate transport robot (the first substrate transport robot CR 1  or the second substrate transport robot CR 2  (see  FIG. 1 )) into the chamber  107  with all the guards  143  to  145  located at the lower position. Then, the control device  4  causes the hand of the substrate transport robot to hold the substrate W held on the spin chuck  108 . Thereafter, the control device  4  retracts the hand of the substrate transport robot from the chamber  107 . Thus, the substrate W with its front surface (device formation surface) removed of the resist is unloaded from the chamber  107 . 
     Next, the change in the mixing ratio between the sulfuric acid-containing liquid and hydrogen peroxide water in the SPM step (S 3  in  FIG. 7 ), the operations of the first guard  143  and the second guard  144 , and the like will be described. 
       FIG. 8  is a timing chart showing the change in the mixing ratio between the sulfuric acid-containing liquid and hydrogen peroxide water, the operations of the first guard  143  and the second guard  144 , and the like in the SPM step (S 3  in  FIG. 7 ). In  FIG. 8 , “RECOVERY ON” means that the SPM expelled from the substrate W flows into the recovery pipe  156  through the second guard  144 , and “RECOVERY OFF” means that the flow of the SPM into the recovery pipe  156  is stopped. In  FIG. 8 , “LIQUID DRAIN ON” means that the SPM expelled from the substrate W flows into the first liquid drain pipe  152  through the first guard  143 , and “LIQUID DRAIN OFF” means that the flow of the SPM into the first liquid drain pipe  152  is stopped. In the following description, reference will be made to  FIGS. 5 and 8 . The control device  4  controls the substrate processing apparatus  1  to perform the following process. In other words, the control device  4  is programmed so as to perform the following process. 
     When the sulfuric acid-containing liquid valve  60  and the hydrogen peroxide water valve  136  are opened at time T 1  in  FIG. 8 , the sulfuric acid-containing liquid is supplied at a first sulfuric acid-containing liquid flow rate to the SPM nozzle  13 , and hydrogen peroxide water is supplied at a first H 2 O 2  flow rate to the SPM nozzle  13 . Therefore, the sulfuric acid-containing liquid and hydrogen peroxide water are mixed in a first mixing ratio ((first sulfuric acid-containing liquid flow rate)/(first H 2 O 2  flow rate) within the SPM nozzle  13 . Thus, a first SPM is prepared within the SPM nozzle  13 , and spouted from the SPM nozzle  13  toward the upper surface of the substrate W (first SPM supplying step). As a result, a film of the first SPM is formed, which covers the entire upper surface of the substrate W. 
     After a lapse of a predetermined period from the opening of the sulfuric acid-containing liquid valve  60  and the hydrogen peroxide water valve  136 , at least one of the opening degree of the sulfuric acid-containing liquid flow rate control valve  59  and the opening degree of the hydrogen peroxide water flow rate control valve  137  is changed at time T 2  shown in  FIG. 8 , and the sulfuric acid-containing liquid and hydrogen peroxide water are mixed in a second mixing ratio ((second sulfuric acid-containing liquid flow rate)/(second H 2 O 2  flow rate)) that is greater than the first mixing ratio within the SPM nozzle  13 . In  FIG. 8 , both the opening degree of the sulfuric acid-containing liquid flow rate control valve  59  and the opening degree of the hydrogen peroxide water flow rate control valve  137  are changed by way of example. Thus, a second SPM is prepared within the SPM nozzle  13 , and spouted from the SPM nozzle  13  toward the upper surface of the substrate W (second SPM supplying step). As a result, the first SPM film covering the entire upper surface of the substrate W is replaced with a film of the second SPM which covers the entire upper surface of the substrate W. 
     In the example shown in  FIG. 8 , the sulfuric acid-containing liquid is supplied at the second sulfuric acid-containing liquid flow rate greater than the first sulfuric acid-containing liquid flow rate to the SPM nozzle  13 , and hydrogen peroxide water is supplied at the second H 2 O 2  flow rate smaller than the first H 2 O 2  flow rate to the SPM nozzle  13 . The second sulfuric acid-containing liquid flow rate and the second H 2 O 2  flow rate may be set so that the flow rate of the SPM to be spouted from the SPM nozzle  13  is kept constant even if the mixing ratio (the ratio of the sulfuric acid-containing liquid to hydrogen peroxide water) is changed, or may be set so that the flow rate of the SPM to be spouted from the SPM nozzle  13  is increased or reduced. The mixing ratio is continuously changed from the first mixing ratio to the second mixing ratio. Therefore, the SPM to be supplied to the upper surface of the substrate W is continuously changed from a state in which the hydrogen peroxide concentration is higher to a state in which the sulfuric acid-containing liquid concentration is higher. 
     After a lapse of a predetermined period from the time at which the mixing ratio for the SPM is changed to the second mixing ratio, the sulfuric acid-containing liquid valve  60  and the hydrogen peroxide water valve  136  are closed to stop spouting the SPM from the SPM nozzle  13  at time T 5  shown in  FIG. 8 . 
     As shown in  FIG. 8 , the treatment cup  111  is set in the first opposed state in which the innermost first guard  143  out of the three guards  143  to  145  is opposed to the peripheral surface of the substrate W before the SPM nozzle  13  starts spouting the first SPM (before time T 1  shown in  FIG. 8 ). Therefore, the first SPM expelled from the substrate W is received by the inner wall  143   a  of the first guard  143  to be guided to the first cup  141  (first SPM capturing step). Then, the first SPM in the first cup  141  is drained into the first liquid drain pipe  152  (“LIQUID DRAIN ON” shown in  FIG. 8 , liquid draining step). 
     As shown in  FIG. 8 , when the mixing ratio for the SPM is changed to the second mixing ratio (at time T 2  shown in  FIG. 8 ), the first guard  143  is located at the upper position. Therefore, the second SPM expelled from the substrate W is received by the inner wall  143   a  of the first guard  143 , and guided to the first cup  141 . After the mixing ratio for the SPM is changed to the second mixing ratio, the guard lift unit  146  moves down the first guard  143  to the cleaning height position between the upper position and the lower position at time T 3  shown in  FIG. 8 . Thus, an SPM hitting position at which the second SPM directly hits the inner wall  143   a  of the first guard  143  is moved up with respect to the first guard  143 . 
     After the first guard  143  is maintained at the cleaning height position for a predetermined period, for example, the guard lift unit  146  moves down the first guard  143  to the lower position at time T 4  shown in  FIG. 8 . In a state such that the second SPM is spouted from the SPM nozzle  13  and the entire upper surface of the substrate W is covered with the second SPM film, therefore, the treatment cup  111  is switched to the second opposed state such that the second guard  144  is opposed to the peripheral surface of the substrate W. The second SPM expelled from the substrate W is received by the inner wall  144   a  of the second guard  144 , and guided to the second cup  142  (second SPM capturing step). Then, the second SPM in the second cup  142  is supplied to the reclaim tank  21  of the first liquid storage  11  through the common pipe  155  and the recovery pipe  156 . Thus, the second SPM supplied to the substrate W is recovered (recovering step, “RECOVERY ON” shown in  FIG. 8 ). 
     After the spouting of the SPM from the SPM nozzle  13  is stopped at time T 5  shown in  FIG. 8 , the guard lift unit  146  moves up the first guard  143  from the lower position to the upper position at time T 6  shown in  FIG. 8 . In a state such that the spouting of the SPM from the SPM nozzle  13  is stopped and the entire upper surface of the substrate W is covered with the SPM film, the treatment cup  111  is thus switched to the first opposed state such that the first guard  143  is opposed to the peripheral surface of the substrate W. In this state, a rinsing step of supplying the rinse liquid to the substrate W (S 4  in  FIG. 7 ) is performed. A drying step of drying the substrate W (S 5  in  FIG. 7 ) is performed with the treatment cup  111  set in the third opposed state such that the third guard  145  is opposed to the peripheral surface of the substrate W. 
       FIG. 9  is a flowchart showing a process to be performed when the sulfuric acid-containing liquid and hydrogen peroxide water are mixed together to prepare the SPM and the SPM recovered from the substrate W is supplied to another substrate W. In the following description, reference will be made to  FIGS. 5 and 9 . The control device  4  controls the substrate processing apparatus  1  to perform the following process. In other words, the control device  4  is programmed so as to perform the following process. 
     As described above, when the SPM step (S 3  in  FIG. 7 ) is started, as shown in  FIG. 9 , the sulfuric acid-containing liquid and hydrogen peroxide water are mixed in the first mixing ratio, whereby the first SPM is prepared (S 11  in  FIG. 9 ). The first SPM is spouted from the SPM nozzle  13  to be supplied to the substrate W (S 12  in  FIG. 9 ). Then, the first SPM expelled from the substrate W is guided to the first liquid drain pipe  152  through the first guard  143  and the first cup  141 . 
     After a lapse of a predetermined period from the start of the spouting of the first SPM, the mixing ratio between the sulfuric acid-containing liquid and hydrogen peroxide water (the ratio of the flow rate of the sulfuric acid-containing liquid before the mixing to the flow rate of hydrogen peroxide water before the mixing) is increased from the first mixing ratio to the second mixing ratio (S 13  in  FIG. 9 ). Thus, the sulfuric acid-containing liquid and hydrogen peroxide water are mixed in the second mixing ratio, whereby the second SPM is prepared. Thereafter, the second SPM is supplied to the substrate W (S 14  in  FIG. 9 ) and expelled from the substrate W. The second SPM expelled from the substrate W is recovered as the sulfuric acid-containing liquid in the reclaim tank  21  of the first liquid storage  11  through the second guard  144 , the second cup  142 , the common pipe  155 , and the recovery pipe  156  (S 15  in  FIG. 9 ). 
     The sulfuric acid-containing liquid recovered in the reclaim tank  21  is supplied to the second circulation tank  51  of the second liquid storage  12  through the first circulation tank  22  of the first liquid storage  11 . Since hydrogen peroxide is easily decomposed into water and oxygen at a higher temperature, the second SPM (sulfuric acid-containing liquid) recovered in the reclaim tank  21  contains water. However, the second SPM (sulfuric acid-containing liquid) contains sulfuric acid in not less than 50%. The second SPM (sulfuric acid-containing liquid) recovered in the reclaim tank  21  is mixed with the sulfuric acid-containing liquid in the first circulation tank  22  and with the sulfuric acid-containing liquid in the second circulation tank  51 , and circulated through the second circulation tank  51  and the second circulation pipes  53  (through the common pipe  51 A and the sulfuric acid-containing liquid flowing pipes  51 B). The sulfuric acid concentration of the sulfuric acid-containing liquid thus circulated is measured by the sulfuric acid concentration meter  64  (S 16  in  FIG. 9 ). The control device  4  monitors the sulfuric acid concentration of the sulfuric acid-containing liquid circulated through the second circulation tank  51  and the second circulation pipes  53  based on the measurement value of the sulfuric acid concentration meter  64  (S 17  in  FIG. 9 ). 
     If the sulfuric acid concentration of the sulfuric acid-containing liquid measured by the sulfuric acid concentration meter  64  is the lower limit value or higher (YES in S 17  in  FIG. 9 ), the control device  4  opens the sulfuric acid-containing liquid valve  60 . Thus, the sulfuric acid-containing liquid flowing through the sulfuric acid-containing liquid flowing pipe  51 B flows through the sulfuric acid-containing liquid supply pipe  57  to be supplied to the SPM nozzle  13 . Thus, the sulfuric acid-containing liquid prepared from the second SPM expelled from the substrate W is mixed with hydrogen peroxide water, whereby the SPM is newly prepared. The newly prepared SPM is supplied to the subsequent substrate W. Since the SPM expelled from the substrate W is reused, the amount of the SPM to be discarded can be reduced. 
     If the sulfuric acid concentration of the sulfuric acid-containing liquid measured by the sulfuric acid concentration meter  64  is less than the lower limit value (NO in S 17  in  FIG. 9 ), on the other hand, the control device  4  opens the sulfuric acid addition valve  45  provided in the sulfuric acid addition pipe  44  to add sulfuric acid into the first circulation tank  22  (S 18  in  FIG. 9 ). Since fresh sulfuric acid is added into the first circulation tank  22 , the sulfuric acid concentration of the sulfuric acid-containing liquid circulated through the first circulation tank  22  and the first circulation pipe  23  is increased. Thereafter, the sulfuric acid-containing liquid circulated through the first circulation tank  22  and the first circulation pipe  23  is supplied to the second circulation tank  51  through the first liquid guide pipe  31 , whereby the sulfuric acid concentration of the sulfuric acid-containing liquid circulated through the second circulation tank  51  and the second circulation pipes  53  (the common pipe  51 A and the sulfuric acid-containing liquid flowing pipes  51 B) is increased. Accordingly, the sulfuric acid concentration of the sulfuric acid-containing liquid thus circulated is maintained at a higher level. 
     In the exemplary substrate treatment described with reference to  FIGS. 7 to 9 , the sulfuric acid-containing liquid and hydrogen peroxide water are mixed together to prepare the first SPM, and the prepared first SPM is supplied to the substrate W. After the supply of the first SPM is stopped, the sulfuric acid-containing liquid and hydrogen peroxide water are mixed together to prepare the second SPM, and the prepared second SPM is supplied to the substrate W. Thus, the first SPM and the second SPM are supplied to the substrate W, whereby the resist is removed from the substrate W. 
     When the first SPM is prepared, the sulfuric acid-containing liquid and hydrogen peroxide water are mixed in the first mixing ratio. When the second SPM is prepared, the sulfuric acid-containing liquid and hydrogen peroxide water are mixed in the second mixing ratio. The first mixing ratio and the second mixing ratio are each defined as the ratio of the volume of the sulfuric acid-containing liquid before the mixing to the volume of hydrogen peroxide water before the mixing. The first mixing ratio is smaller than the second mixing ratio. Therefore, the concentration of hydrogen peroxide contained in the first SPM is higher than the concentration of hydrogen peroxide contained in the second SPM. 
     Since the hydrogen peroxide concentration is relatively high, the first SPM has a higher removal capability than the second SPM. Therefore, the resist can be efficiently removed from the substrate W. After the first SPM is supplied to the substrate, the second SPM is supplied to the substrate W. The second SPM has a lower removal capability than the first SPM. Since almost all the resist is removed from the substrate W by supplying the first SPM to the substrate W, only an easily removable part of the resist remains on the substrate W. Further, the temperature of the SPM (second SPM) to be supplied to the substrate W is adjusted at a very high level (about 190° C. to about 220° C.) and, therefore, the removal capability of the second SPM is high though being poorer than that of the first SPM. Therefore, even the second SPM having a lower removal capability can reliably remove the remaining resist from the substrate W. 
     The first SPM expelled from the substrate W flows into the first liquid drain pipe  152  but not into the recovery pipe  156 . The first SPM expelled from the substrate W has a relatively high hydrogen peroxide concentration and a relatively low sulfuric acid concentration. In addition, the first SPM expelled from the substrate W contains a greater amount of contaminants (carbides of the resist and the like) generated by a reaction between the first SPM and the resist. Therefore, the first SPM expelled from the substrate W is inappropriate for the recovery. 
     On the other hand, the second SPM expelled from the substrate W has a relatively high sulfuric acid concentration. Further, the second SPM expelled from the substrate W contains the contaminants in a smaller amount than the first SPM expelled from the substrate W. Therefore, the second SPM having a relatively high sulfuric acid concentration and a smaller contaminant amount is guided to the recovery pipe  156 , and mixed again with hydrogen peroxide water. Thus, sulfuric acid contained in the second SPM reacts with hydrogen peroxide water, whereby SPM is newly prepared. Accordingly, the amount of the SPM to be discarded can be reduced. 
     Thus, the SPM is recovered when the sulfuric acid concentration, i.e., the ratio of the volume of sulfuric acid before the mixing to the total volume of sulfuric acid and hydrogen peroxide water before the mixing, is high. Therefore, the SPM having a higher sulfuric acid concentration can be recovered. Further, the SPM having a higher hydrogen peroxide concentration and a sufficient removal capability is supplied to the substrate W before the recovery of the SPM is started without maintaining the sulfuric acid concentration at a higher level. Therefore, the resist can be efficiently removed from the substrate W. This makes it possible to recover the SPM having a higher sulfuric acid concentration while efficiently removing the resist from the substrate W. 
     In this exemplary substrate treatment, the first SPM expelled from the substrate W is received by the first guard  143  surrounding the substrate W. The second SPM expelled from the substrate W is received by the second guard  144  surrounding the substrate W. The first SPM received by the first guard  143  flows into the first liquid drain pipe  152  connected to the first guard  143 . The second SPM received by the second guard  144  flows into the recovery pipe  156  connected to the second guard  144 . 
     The first SPM expelled from the substrate W contains a greater amount of contaminants. After the first guard  143  receives the first SPM, therefore, the contaminants are liable to remain on the inner peripheral surface of the first guard  143 . If the second SPM expelled from the substrate W is received by the first guard  143  to be recovered, the second SPM is liable to be contaminated with the contaminants adhering to the first guard  143 . Therefore, the second SPM is received by the second guard  144  different from the first guard  143 , whereby the amount of the contaminants contained in the recovered SPM can be reduced. 
     In this exemplary substrate treatment, the first SPM expelled from the substrate W when the supply of the first SPM is stopped is received by the first guard  143 . Thereafter, the first guard  143  and the second guard  144  are switched from the first opposed state to the second opposed state, whereby the second SPM expelled from the substrate W is received by the second guard  144 . That is, after the expelling of the first SPM having a greater contaminant amount is completed, the state in which the first guard  143  is directly opposed to the substrate W is switched to the state in which the second guard  144  is directly opposed to the substrate W. Thus, the second guard  144  is prevented from being contaminated with the first SPM having a greater contaminant amount. 
       FIG. 10  is a graph showing a change in the sulfuric acid concentration of the recovered sulfuric acid-containing liquid. The ordinate in  FIG. 10  indicates the sulfuric acid concentration of the recovered sulfuric acid-containing liquid, and the abscissa in  FIG. 10  indicates the number of substrates W treated by the substrate processing apparatus  1 . In  FIG. 10 , the ratio X, the ratio Y, and the ratio Z each indicate the ratio of the flow rate of the sulfuric acid-containing liquid with respect to the flow rate of hydrogen peroxide water regarded as 1. The ratio X is greater than the ratio Y, and the ratio Y is greater than the ratio Z ((ratio X)&gt;(ratio Y)&gt;(ratio Z)). 
     As can be understood from  FIG. 10 , for any of the sulfuric acid-containing liquid ratios X, Y, Z, the sulfuric acid concentration of the sulfuric acid-containing liquid is reduced, as the number of the treated substrates W increases. The reduction rate of the sulfuric acid concentration is increased, as the sulfuric acid-containing liquid ratio decreases. That is, where the sulfuric acid-containing liquid ratio is the ratio Z, the reduction rate of the sulfuric acid concentration of the sulfuric acid-containing liquid is the greatest. Where the sulfuric acid-containing liquid ratio is the ratio Y, the reduction rate of the sulfuric acid concentration of the sulfuric acid-containing liquid is the second greatest. In other words, the sulfuric acid concentration of the sulfuric acid-containing liquid is unlikely to decrease, if the sulfuric acid-containing liquid ratio is high. It was confirmed that, even if 100 or more substrates W are treated while the SPM is supplied to and recovered from the substrates W with the sulfuric acid-containing liquid ratio set to the ratio X, the sulfuric acid concentration of the sulfuric acid-containing liquid is only reduced to about 90%. 
     In this embodiment, as described above, the SPM containing the sulfuric acid-containing liquid having a higher sulfuric acid concentration is recovered in the sulfuric acid-containing liquid supply device  8 , and the recovered SPM is reused as the sulfuric acid-containing liquid. As can be understood from  FIG. 10 , the reduction rate of the sulfuric acid concentration is increased, as the sulfuric acid-containing liquid ratio decreases. Therefore, the sulfuric acid concentration of the sulfuric acid-containing liquid is unlikely to decrease even when a greater number of substrates W are treated, if the ratio of the sulfuric acid-containing liquid recovered in the sulfuric acid-containing liquid supply device  8  is greater. Therefore, the sulfuric acid concentration of the sulfuric acid-containing liquid recovered in the sulfuric acid-containing liquid supply device  8  can be maintained at a level suitable for the reuse. This makes it possible to reduce the frequency of replacing the sulfuric acid-containing liquid with fresh sulfuric acid in the first circulation tank  22  and the second circulation tank  51 , and the frequency of adding fresh sulfuric acid to the first circulation tank  22 . Therefore, the consumption of sulfuric acid (i.e., the amount of sulfuric acid to be discarded) can be reduced. 
     According to this embodiment, as described above, the storage for the adjustment of the sulfuric acid concentration (first liquid storage  11 ) and the storage for the temperature adjustment (second liquid storage  12 ) are separately provided in the sulfuric acid-containing liquid supply device  8 . If the temperature of the sulfuric acid-containing liquid is adjusted in the second liquid storage  12  adapted for the temperature adjustment while sulfuric acid is added to the second liquid storage  12 , the temperature of the sulfuric acid-containing liquid will become unstable in the storage because the temperature of sulfuric acid to be added is a room temperature. In this embodiment, the first liquid storage  11  for the adjustment of the sulfuric acid concentration and the second liquid storage  12  for the temperature adjustment are separately provided, so that the temperature of the sulfuric acid-containing liquid in the second liquid storage  12  is stabilized. Thus, the sulfuric acid-containing liquid to be supplied to the SPM nozzles  13  can be adjusted at the desired high temperature. 
     In this embodiment, the sulfuric acid-containing liquid is heated by the second and first circulation heaters  52  and  24  in the first liquid storage  11  and the second liquid storage  12 , respectively. Therefore, a greater heat amount can be applied to the sulfuric acid-containing liquid. Further, the sulfuric acid-containing liquid temperature-adjusted at the first temperature (about 120° C. to about 130° C.) in the first liquid storage  11  is supplied to the second liquid storage  12 . Then, the sulfuric acid-containing liquid is heated to the second temperature (about 160° C.) in the second liquid storage  12 . That is, the sulfuric acid-containing liquid is heated stepwise. Therefore, the temperature of the sulfuric acid-containing liquid can be increased to a higher temperature in the second liquid storage  12 . 
     Further, the sulfuric acid-containing liquid circulated through the second circulation tank  51  and the second circulation pipes  53  is guided to the sulfuric acid-containing liquid supply pipes  57 . Then, the sulfuric acid-containing liquid flowing through the sulfuric acid-containing liquid supply pipes  57  is heated by the heaters  54 . The sulfuric acid-containing liquid can be heated by the heaters  54  to the third temperature (about 165° C.) that is still higher than when being circulated through the second circulation tank  51  and the second circulation pipes  53 . 
     The second SPM having the second mixing ratio has a lower removal capability than the first SPM. However, the removal capability of the SPM depends not only on the hydrogen peroxide concentration but also on the temperature of the SPM. That is, the removal capability of the SPM is increased, as the temperature of the SPM is increased. The temperature of the SPM after the mixing is increased, as the temperature of the sulfuric acid-containing liquid is increased. Even if the mixing ratio is the second mixing ratio, therefore, the removal capability of the SPM can be kept at a higher level by increasing the temperature of the sulfuric acid-containing liquid before the mixing. Thus, the resist can be efficiently removed from the substrate W even with the use of the SPM having the second mixing ratio. 
     In this embodiment, the sulfuric acid concentration of the sulfuric acid-containing liquid circulated through the second circulation tank  51  and the second circulation pipes  53  is measured by the sulfuric acid concentration meter  64 . Therefore, the sulfuric acid concentration of the sulfuric acid-containing liquid circulated through the second circulation tank  51  and the second circulation pipes can be accurately determined. If the sulfuric acid concentration measured by the sulfuric acid concentration meter  64  is reduced below the lower limit value, sulfuric acid is supplied to the first circulation tank  22  by the sulfuric acid adding unit  25 . Thus, the sulfuric acid concentration of the sulfuric acid-containing liquid to be supplied to the SPM nozzles  13  can be adjusted at the desired higher concentration. 
     In this embodiment, both the first circulation heater  24  and the second circulation heater  52  are used to heat the sulfuric acid-containing liquid. Therefore, the load to be exerted on the second circulation heater  52  can be reduced as compared with a case in which the sulfuric acid-containing liquid is heated only by the second circulation heater  52 . 
       FIG. 11  is a diagram of a first sulfuric acid-containing liquid supply device  209  according to a second embodiment of the present invention as seen in a horizontal direction. In  FIG. 11 , the same components as in  FIGS. 1 to 10  will be denoted by the same reference characters as in  FIG. 1  and the like, and the description thereof will be omitted. 
     The first sulfuric acid-containing liquid supply device  209  according to the second embodiment is different from the first sulfuric acid-containing liquid supply device  9  according to the first embodiment in that a third liquid storage  213  is provided in addition to the first liquid storage. The sulfuric acid-containing liquid is supplied to the third liquid storage  213  from the first liquid storage, and the sulfuric acid-containing liquid stored in the third liquid storage  213  is supplied to the second liquid storage  12 . 
     Further, the first liquid storage  211  is different from the first liquid storage  11  according to the first embodiment in that the first circulation heater  24  is not provided. Further, the first liquid storage  211  does not include the liquid drain tank  50 . That is, the first liquid storage  211  does not include the unit which heats the sulfuric acid-containing liquid circulated through the first circulation tank  22  and the first circulation pipe  23 . 
     The SPM recovered in the reclaim tank  21  is stored as the sulfuric acid-containing liquid in the reclaim tank  21 . The SPM expelled from the substrate W flows through the treatment cup  111 , the recovery pipe  156 , and the recovery outlet pipe  26  to be thereby cooled, and is recovered in the reclaim tank  21 . Therefore, the temperature of the SPM recovered in the reclaim tank  21  is much lower than the temperature of the SPM to be supplied to the substrate W (about 190° C. to about 220° C.), but is still relatively high (about 80° C. to about 90° C.) 
     The sulfuric acid-containing liquid stored in the reclaim tank  21  is supplied to the first circulation tank  22  through the transport pipe  28  by driving the first liquid pumping device  29 . Then, the sulfuric acid-containing liquid is circulated through the first circulation tank  22  and the first circulation pipe  23 . The temperature of the sulfuric acid-containing liquid is lowered, because the sulfuric acid-containing liquid is deprived of heat by the pipe wall of the transport pipe  28  and the pipe wall of the first circulation pipe  23  when flowing through the transport pipe  28  and the first circulation pipe  23 . The temperature of the sulfuric acid-containing liquid circulated through the first circulation tank  22  and the first circulation pipe  23  is higher than the room temperature (about 23° C. to about 25° C.) but maintained at a fourth temperature (about 40° C. to about 60° C.) that is lower than the sulfuric acid-containing liquid stored in the reclaim tank  21  due to thermal equilibrium with respect to the pipe wall of the first circulation pipe  23 . 
     The third liquid storage  213  of the first sulfuric acid-containing liquid supply device  209  includes a third circulation tank (third tank)  222 , a third circulation pipe (third pipe)  223 , and a third circulation heater (second heater)  224 . 
     A downstream end of the first liquid guide pipe  31  is connected to the third circulation tank  222 . The sulfuric acid-containing liquid having the fourth temperature (e.g., about 40° C. to about 60° C.) in the first liquid storage  211  is guided to the third circulation tank  222 . Then, the guided sulfuric acid-containing liquid is stored in the third circulation tank  222  (third storing step). 
     A second liquid guide pipe  231  extending to the second sulfuric acid-containing liquid supply device  10  (second liquid storage  12 ) is connected to the third circulation tank  222 . A downstream end of the second liquid guide pipe  231  is connected to the second circulation tank  51  of the second liquid storage  12 . A fifth liquid pumping device  232  such as a pump for pumping out the sulfuric acid-containing liquid from the third circulation tank  222  is provided in the second liquid guide pipe  231 . A fourth capturing filter  237  and an on/off valve  238  are provided downstream of the fifth liquid pumping device  232  in the second liquid guide pipe  231 . The fourth capturing filter  237  is a filter adapted to capture and remove relatively small foreign matter from the sulfuric acid-containing liquid flowing through the second liquid guide pipe  231 . The fourth capturing filter  237  removes foreign matter which cannot be completely removed by the third capturing filter  37 . 
     The on/off valve  238  is a valve for controlling the on and off of the flow of the sulfuric acid-containing liquid in the second liquid guide pipe  231 . 
     A return pipe  240  is branched from the second liquid guide pipe  231  at a position between the on/off valve  238  and the fourth capturing filter  237 . A downstream portion of the return pipe  240  extends to the third circulation tank  222 . A return valve  241  is provided in the return pipe  240 . The third circulation pipe  223  is constituted by the return pipe  240  and a portion of the second liquid guide pipe  231  upstream of the branch position  242  at which the return pipe  240  is branched. 
     During the operation of the substrate processing apparatus (including a period in which the treatment of the substrate W is halted), the fifth liquid pumping device  232  and the third circulation heater  224  are constantly driven. With the on/off valve  238  closed and with the return valve  241  open, therefore, the sulfuric acid-containing liquid pumped out from the third circulation tank  222  flows to the branch position  242  through the second liquid guide pipe  231 , and flows back to the third circulation tank  222  from the branch position  242  through the return pipe  240 . That is, the sulfuric acid-containing liquid is circulated through the third circulation tank  222  and the third circulation pipe  223  during a period in which the sulfuric acid-containing liquid is not supplied to the second liquid storage  12 . When the sulfuric acid-containing liquid is to be supplied to the second liquid storage  12 , the on/off valve  238  is opened and the return valve  241  is closed, whereby the sulfuric acid-containing liquid pumped out from the third circulation tank  222  is supplied to the second liquid storage  12  through the second liquid guide pipe  231 . 
     The third circulation heater  224  is provided in the second liquid guide pipe  231  upstream of the fifth liquid pumping device  232 . The third circulation heater  224  heats the sulfuric acid-containing liquid circulated through the third circulation tank  222  and the third circulation pipe  223  (third heating step). The heating temperature of the third circulation heater  224  is set to a predetermined first temperature (second heating temperature), e.g., about 120° C. to about 130° C. The sulfuric acid-containing liquid is conditioned at the first temperature by the circulation of the sulfuric acid-containing liquid through the third circulation tank  222  and the third circulation pipe  223 . During the period in which the sulfuric acid-containing liquid is not supplied to the second liquid storage  12 , the sulfuric acid-containing liquid conditioned at the first temperature can be stored in the third circulation tank  222  by the circulation of the sulfuric acid-containing liquid. After the on/off valve  238  is opened, the sulfuric acid-containing liquid conditioned at the first temperature is supplied to the second liquid storage  12 . 
     The third liquid storage  213  includes a liquid drain pipe  246 , a liquid drain valve  247 , an outlet pipe  248 , a sixth liquid pumping device  249 , and a liquid drain tank  250 . The liquid drain pipe  246 , the liquid drain valve  247 , the outlet pipe  248 , the sixth liquid pumping device  249 , and the liquid drain tank  250  respectively have the same structures and the same functions as the liquid drain pipe  46 , the liquid drain valve  47 , the outlet pipe  48 , the third liquid pumping device  49 , and the liquid drain tank  50 . 
     The second embodiment has the following effects in addition to the effects provided by the first embodiment described above. 
     More specifically, a unit for heating the sulfuric acid-containing liquid circulated through the first circulation tank  22  and the first circulation pipe  23  is not provided in the first liquid storage  211 . That is, the sulfuric acid-containing liquid is not heated in the first liquid storage  211 . Therefore, the temperature of the sulfuric acid-containing liquid circulated through the first circulation tank  22  and the first circulation pipe  23  is relatively low (about 40° C. to about 60° C.). Therefore, the temperature of the sulfuric acid-containing liquid passing through the third capturing filter  37  is relatively low. 
     If the sulfuric acid-containing liquid having a higher temperature (about 120° C. to about 130° C.) is circulated through the first circulation tank  22  and the first circulation pipe  23  as in the first embodiment, the sulfuric acid-containing liquid having a higher temperature (about 120° C. to about 130° C.) continuously flows through the third capturing filter  37  to expand the filter, whereby the diameter of each of the pores  71  (see  FIG. 3 ) is liable to be increased. If the diameter of each of the pores  71  (see  FIG. 3 ) is increased, the diameter of foreign matter capturable by the third capturing filter  37  is increased. Therefore, the filtering capability of the third capturing filter  37  is liable to be reduced, so that the foreign matter contained in the sulfuric acid-containing liquid cannot be properly captured in the first liquid storage. 
     In the second embodiment, the temperature of the sulfuric acid-containing liquid passing through the third capturing filter  37  is relatively low (about 40° C. to about 60° C.), so that the reduction in the filtering capability of the third capturing filter  37  can be suppressed. Therefore, the foreign matter contained in the sulfuric acid-containing liquid can be properly captured in the first liquid storage  211 . Thus, the sulfuric acid-containing liquid can be supplied in a clean state to the SPM nozzles  13 . 
     In the second embodiment, the sulfuric acid-containing liquid supplied from the first liquid storage  211  is circulated through the third circulation tank  222  and the third circulation pipe  223  in the third liquid storage  213 . The sulfuric acid-containing liquid circulated through the third circulation tank  222  and the third circulation pipe  223  is heated by the third circulation heater  224 . In the third liquid storage  213  and the second liquid storage  12 , the sulfuric acid-containing liquid is heated by the third circulation heater  224  and the second circulation heater  52 , respectively. Since a greater amount of heat can be applied to the sulfuric acid-containing liquid, the temperature of the sulfuric acid-containing liquid can be increased to a higher level in the second liquid storage  12 . 
     Further, both the third circulation heater  224  and the second circulation heater  52  are used for heating the sulfuric acid-containing liquid. Therefore, the load to be exerted on one of the heaters (i.e., the second circulation heater  52 ) can be reduced. 
       FIG. 12  is a diagram of a first sulfuric acid-containing liquid supply device  309  according to a third embodiment of the present invention as seen in a horizontal direction. In  FIG. 12 , the same components as in  FIGS. 1 to 10  will be denoted by the same reference characters as in  FIG. 1  and the like, and the description thereof will be omitted. 
     A first liquid storage  311  of the first sulfuric acid-containing liquid supply device  309  according to the third embodiment is different from the first liquid storage of the first sulfuric acid-containing liquid supply device  9  according to the first embodiment in that the first circulation heater  24  is not provided. Except for that, the first liquid storage  311  has substantially the same structure as the first liquid storage  11 . 
     As described above, the temperature of the SPM recovered in the reclaim tank  21  is much lower than the temperature of the SPM to be supplied to the substrate W (about 190° C. to about 220° C.), but is still relatively high, i.e., about 80° C. to about 90° C. As described above, the temperature of the sulfuric acid-containing liquid circulated through the first circulation tank  22  and the first circulation pipe  23  is higher than the room temperature (about 23° C. to about 25° C.) but is maintained at the fourth temperature (about 40° C. to about 60° C.) that is lower than the temperature of the sulfuric acid-containing liquid stored in the reclaim tank  21  due to thermal equilibrium with respect to the pipe wall of the first circulation pipe  23 . Then, the sulfuric acid-containing liquid circulated through the first circulation tank  22  and the first circulation pipe  23  is supplied to the second liquid storage  12  of the second sulfuric acid-containing liquid supply device  10 . 
     In the second liquid storage  12 , the sulfuric acid-containing liquid circulated through the second circulation tank  51  and the second circulation pipes  53  is heated by the second circulation heater  52 , whereby the temperature of the circulated sulfuric acid-containing liquid is increased to the second temperature. 
     In the third embodiment, the temperature of the sulfuric acid-containing liquid passing through the third capturing filter  37  is relatively low (about 40° C. to about 60° C.), so that the reduction in the filtering capability of the third capturing filter  37  can be suppressed. Therefore, the foreign matter contained in the sulfuric acid-containing liquid can be properly captured in the first liquid storage  311 . Thus, the sulfuric acid-containing liquid can be supplied in a clean state to the SPM nozzles  13 . 
     While the three embodiments of the present invention have thus been described, the present invention may be embodiment in other ways. 
     In the second and third embodiments described above, for example, as indicated by broken lines in  FIGS. 11 and 12 , the first liquid storages  211 ,  311  may each further include a cooler  401  for cooling the sulfuric acid-containing liquid circulated through the first circulation tank  22  and the first circulation pipe  23 . The cooler  401  is disposed, for example, in the first liquid guide pipe  31  upstream of the second liquid pumping device  32 . In this case, the sulfuric acid-containing liquid is cooled by the circulation of the sulfuric acid-containing liquid through the first circulation tank  22  and the first circulation pipe  23 . Depending on the setting of the cooling temperature of the cooler  401 , the temperature of the sulfuric acid-containing liquid circulated through the first circulation tank  22  and the first circulation pipe  23  can be reduced to the room temperature (about 23° C. to about 25° C.) or a temperature lower than the room temperature. 
       FIG. 13  is a diagram for describing a change in the filtering capability of a capturing filter (third capturing filter  37 ) due to thermal influence. As shown in  FIG. 13 , the filtering capability of the capturing filter is improved (i.e., relatively small foreign matter (fine particles) can be more advantageously captured), as the temperature (circulation temperature) of the sulfuric acid-containing liquid passing through the capturing filter (third capturing filter  37 ) is reduced. It is herein assumed that the passage rate of the fine particles observed when the temperature of the sulfuric acid-containing liquid passing through the capturing filter is set to a level (temperature A) lower than the temperature of the sulfuric acid-containing liquid stored in the reclaim tank is a reference passage rate (100%). Where the temperature of the sulfuric acid-containing liquid flowing through the capturing filter is reduced to an ordinary temperature (temperature B), the passage rate of the fine particles is reduced to 40%, further improving the filtering capability. On the other hand, though not shown, where the temperature of the sulfuric acid-containing liquid is 80° C. or higher, the passage rate of the fine particles is significantly increased as compared with the reference passage rate (100%), deteriorating the filtering capability. With the provision of the cooler  401 , therefore, the relatively small foreign matter contained in the sulfuric acid-containing liquid can be more advantageously captured in the first liquid storage  211 ,  311 . This makes it possible to supply the sulfuric acid-containing liquid in a cleaner state to the SPM nozzles  13 . 
     As indicated by broken lines in  FIG. 4 , the second liquid storage  12  may include a sulfuric acid supply unit  402  which supplies fresh sulfuric acid (sulfuric acid yet to be used for the treatment of the substrate W) to the second circulation tank  51 . The sulfuric acid supply unit  402  includes a sulfuric acid supply pipe  403  through which sulfuric acid is supplied to the second circulation tank  51 , and a sulfuric acid supply valve  404  which opens and closes the sulfuric acid supply pipe  403 . Sulfuric acid to be supplied to the sulfuric acid supply pipe  403  is unused sulfuric acid (e.g., concentrated sulfuric acid). 
     The supply of sulfuric acid from the sulfuric acid supply unit  402  is not intended to increase the sulfuric acid concentration of the sulfuric acid-containing liquid circulated through the second circulation tank  51  and the second circulation pipes  53  by the addition of sulfuric acid, but is solely intended to store the sulfuric acid-containing liquid in the second circulation tank  51  at the startup of the substrate processing apparatus  1 . 
     The in-nozzle mixing method is employed in which the sulfuric acid-containing liquid and hydrogen peroxide water are mixed together in the SPM nozzle  13 , as described above, but an in-pipe mixing method may be employed in which the sulfuric acid-containing liquid and hydrogen peroxide water are mixed together in a treatment liquid pipe connected to the nozzle or in a mixing pipe connected to the treatment liquid pipe. 
     In the first liquid storage  11 ,  211 ,  311 , as described above, the SPM from the recovery outlet pipe  26  is once recovered in the reclaim tank  21  and then stored in the first circulation tank  22 , but the SPM may be stored directly in the first circulation tank  22  without the recovery in the reclaim tank  21 . In this case, the reclaim tank  21  may be eliminated. 
     Further, the sulfuric acid concentration meter  64  may be provided in each of the sulfuric acid-containing liquid flowing pipes  51 B, but not in one of the sulfuric acid-containing liquid flowing pipes  51 B, associated with the respective towers. The sulfuric acid concentration meter  64  may be provided in the second circulation tank  51  and/or the common pipe  51 A, but not in the sulfuric acid-containing liquid flowing pipe  51 B. The sulfuric acid concentration of the sulfuric acid-containing liquid prepared in the sulfuric acid-containing liquid supply device  8  may be determined by measurement of the sulfuric acid concentration of the sulfuric acid-containing liquid circulated through the first circulation tank  22  and the first circulation pipe  23  instead of or in addition to the measurement of the sulfuric acid concentration of the sulfuric acid-containing liquid circulated through the second circulation tank  51  and the second circulation pipe  53 . 
     Further, the single sulfuric acid-containing liquid supply device including the single first sulfuric acid-containing liquid supply device  9  and the single second sulfuric acid-containing liquid supply device  10  may be adapted to supply the sulfuric acid-containing liquid only to the treatment units  6  of the single tower rather than to supply the sulfuric acid-containing liquid to the treatment units  6  of the plurality of towers (three towers). That is, the first circulation tank  22  and the second circulation tank  51  may be provided in pair for each of the towers of the treatment units  6 . In this case, the opposite ends of the sulfuric acid-containing liquid flowing pipe  51 B are connected to the second circulation tank  51  without the provision of the common pipe  51 A. That is, the second circulation pipe  53  can be constituted only by the sulfuric acid-containing liquid flowing pipe  51 B. 
     In this embodiment, the first liquid storage  11 ,  211 ,  311  and/or the third liquid storage  213  may be provided together in the clean room (on the same floor as the second liquid storage  12 ) rather than on a floor different from the floor on which the second liquid storage  12  is provided. In this case, the first liquid storage  11 ,  211 ,  311  and/or the third liquid storage  213  and the second liquid storage  12  may be disposed in a common frame rather than in different frames. 
     In the embodiments described above, the substrate processing apparatus  1  is adapted to treat semiconductor wafers as the substrates W, but the substrate processing apparatus may be adapted to treat substrates for liquid crystal display devices, substrates for FPDs (Flat Panel Displays) such as organic EL (electroluminescence) display devices, substrates for optical disks, substrates for magnetic disks, substrates for magneto-optical disks, substrates for photomasks, ceramic substrates, and substrates for solar cells. 
     Various modifications may be made within the scope of the following claims. 
     This application corresponds to Japanese Patent Application No. 2018-176394 filed on Sep. 20, 2018, the disclosure of which is incorporated herein by reference in its entirety. 
     REFERENCE SIGNS LIST 
     
         
           1 : SUBSTRATE PROCESSING APPARATUS 
           4 : CONTROL DEVICE 
           6 : TREATMENT UNIT 
           8 : SULFURIC ACID-CONTAINING LIQUID SUPPLY DEVICE 
           11 : FIRST LIQUID STORAGE 
           12 : SECOND LIQUID STORAGE 
           13 : SPM NOZZLE (NOZZLE) 
           13   a : INSIDE OF SPM NOZZLE (MIXING PORTION) 
           22 : FIRST CIRCULATION TANK (FIRST TANK) 
           23 : FIRST CIRCULATION PIPE (SECOND PIPE) 
           24 : FIRST CIRCULATION HEATER (SECOND HEATER) 
           25 : SULFURIC ACID ADDING UNIT 
           37 : THIRD CAPTURING FILTER (FILTER) 
           51 : SECOND CIRCULATION TANK (SECOND TANK) 
           52 : SECOND CIRCULATION HEATER (FIRST HEATER) 
           53 : SECOND CIRCULATION PIPE (FIRST PIPE) 
           54 : HEATER (THIRD HEATER) 
           59 : SULFURIC ACID-CONTAINING LIQUID FLOW RATE CONTROL VALVE (MIXING RATIO CHANGING UNIT) 
           64 : SULFURIC ACID CONCENTRATION METER 
           108 : SPIN CHUCK (SUBSTRATE HOLDING UNIT) 
           122 : HYDROGEN PEROXIDE WATER SUPPLY UNIT 
           137 : HYDROGEN PEROXIDE WATER FLOW RATE CONTROL VALVE (MIXING RATIO CHANGING UNIT) 
           143 : FIRST GUARD 
           144 : SECOND GUARD 
           146 : GUARD LIFT UNIT (GUARD SWITCHING UNIT) 
           156 : RECOVERY PIPE 
           157 : SECOND LIQUID DRAIN PIPE (LIQUID DRAIN PIPE) 
           209 : FIRST SULFURIC ACID-CONTAINING LIQUID SUPPLY DEVICE 
           211 : FIRST LIQUID STORAGE 
           213 : THIRD LIQUID STORAGE 
           222 : THIRD CIRCULATION TANK (THIRD TANK) 
           223 : THIRD CIRCULATION PIPE (THIRD PIPE) 
           224 : THIRD CIRCULATION HEATER (THIRD HEATER) 
           248 : OUTLET PIPE 
           309 : FIRST SULFURIC ACID-CONTAINING LIQUID SUPPLY DEVICE 
           311 : FIRST LIQUID STORAGE 
           401 : COOLER 
         W: SUBSTRATE