Abstract:
The present invention is a treatment solution supply method for supplying a treatment solution on a substrate by a pump through a supply path, which connects a treatment solution supply source and a discharge nozzle, wherein a storage portion for storing the treatment solution temporarily is disposed in the supply path between the treatment solution supply source and the pump. In the present invention another pump is further disposed in the supply path between the storage portion and the treatment solution supply source for supplying the treatment solution to the storage portion. The present invention comprises the step of maintaining the level height of the treatment solution in the storage portion at a predetermined height by supplying the treatment solution to the storage portion by the said another pump. 
     According to the present invention, the pressure of a primary side of the pump is constantly maintained the same. As a result, a force feed pressure of a secondary side of the pump is also kept steady, thereby keeping the discharge pressure of the treatment solution from the discharge nozzle steady. Therefore, the treatment solution with a predetermined discharge pressure is discharged on the substrate, and a substrate processing is performed in a preferable way.

Description:
This application is a Continuation of application Ser. No. 09/783,596 filed on Feb. 15, 2001, and has now issued as U.S. Pat. No. 6,340,643. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a treatment solution supply method and a treatment solution supply unit for a substrate. 
     2. Description of the Related Art 
     In a photolithography process in semiconductor device fabrication processes, for example, resist coating treatment for applying a resist solution to the surface of a wafer to form a resist film, exposure treatment for exposing the wafer in a pattern, developing treatment for performing development treatment for the exposed wafer, and so on are performed in respective processing units to form a predetermined circuit pattern on the wafer by a series of these treatments. 
     To describe a conventional resist solution supply system of a resist coating unit for performing resist coating treatment referring to FIG. 12, from a gallon bottle  131 , for example, which works as a resist solution supply source, through a pipeline  134 , which connects the gallon bottle  131  with a resist solution discharge nozzle  133 , to the resist solution discharge nozzle  133 , a resist solution in the gallon bottle is forcibly fed by a pump  132 , so that the resist solution is supplied on a wafer W to the discharge nozzle  133  to perform resist coating treatment. When there are plural gallon bottles, they are sometimes disposed in two tiers up and down due to space restriction. 
     However, when the level height in the gallon bottle  131  becomes lower as the supply to the resist solution discharge nozzle  133  proceeds, the pressure given on a primary side of the pump  132  changes, which changes a force feed pressure on a secondary side of the pump  132  delicately, and thus, there is a fear that the supply pressure to the resist solution discharge nozzle  133  changes. Then, as a result, since the discharge pressure from the resist solution discharge nozzle  133  changes, and a discharge amount of the resist solution on the wafer W and an impact on the surface of the wafer W fluctuates, there is a fear that a uniform predetermined resist film is not formed. 
     When the gallon bottles are disposed in two tiers up and down, the level height of the resist solution of the gallon bottle in an upper tier differs greatly from that of the gallon bottle in a lower tier. Therefore, when the resist solution is forcibly fed to the resist solution discharge nozzle  133  selectively from either of the gallon bottles by the above-mentioned pump  132 , since from the first the pressure of the primary side of the pump  132  differs in case the resist solution in the upper gallon bottle is selected from in case the lower gallon bottle is selected, the force feed pressure of the secondary side also differs. Consequently, the discharge pressure from the resist discharge nozzle  133  also differs as described above, and the same resist film is not formed on the wafer W when the resist solution is supplied from the upper gallon bottle as when the resist solution is supplied from the lower gallon bottle. 
     In recent years, especially, since there is a tendency to save a resist solution and so on and make a discharging port small to reduce a discharge amount therefrom, it is feared that even a delicate fluctuation of the discharge pressure may give a great influence on the resist film formed on the wafer. 
     SUMMARY OF THE INVENTION 
     The present invention is made in consideration of the above-described points, and its object is to maintain the discharge pressure of a treatment solution discharged on a substrate such as a wafer and so on within a predetermined range to perform a substrate processing in a preferable way when the treatment solution is supplied by a pump from a solution supply source to a discharge nozzle such as a nozzle. 
     Considering the above object, the present invention, from a first viewpoint of the present invention, is a treatment solution supply method for supplying, with a treatment solution in a treatment solution supply source forcibly fed by a pump, the treatment solution on a substrate through a supply path connecting the treatment solution supply source and a discharge nozzle, wherein a storage portion for storing the treatment solution temporarily is disposed in the supply path between the treatment solution supply source and the pump, and another pump for supplying the treatment solution to the storage portion is disposed in the supply path between the storage portion and the treatment solution supply source, and comprising the step of maintaining the level height of the treatment solution in the storage portion at a predetermined height by supplying the treatment solution to the storage portion by the said another pump. 
     From another viewpoint of the present invention, the present invention is a treatment solution supply method for supplying, with a treatment solution in a treatment solution supply source forcibly fed by a pump, the treatment solution on a substrate through a supply path connecting the treatment solution supply source and a discharge nozzle, wherein a storage portion for storing the treatment solution temporarily is disposed in the supply path between the treatment solution supply source and the pump, and another pump for supplying the treatment solution to the storage portion is disposed in said supply path between said storage portion and said treatment solution supply source, and comprising the step of maintaining the level height of the treatment solution in the storage portion at a predetermined height by operating the pump in association with the said another pump. 
     From still another viewpoint of the present invention, the present invention is a treatment solution supply method for supplying, with a treatment solution in a treatment solution supply source forcibly fed by a pump, the treatment solution on a substrate through a supply path connecting the treatment solution supply source and a discharge nozzle, wherein a storage portion for storing the treatment solution temporarily is disposed in the supply path between the treatment solution supply source and the pump, and another pump for supplying the treatment solution to the storage portion is disposed in the supply path between the storage portion and the treatment solution supply source, and comprising the step of detecting the level height in the storage portion, and the step of maintaining the level height of the treatment solution in the storage portion at a predetermined height by supplying the treatment solution to the storage portion from the said another pump only when the level height becomes lower than a predetermined value. 
     From yet another viewpoint of the present invention, the present invention is a treatment solution supply method for supplying, with a treatment solution in a treatment solution supply source forcibly fed by a pump, a predetermined amount of the treatment solution each time on a substrate through a supply path connecting the treatment solution supply source and a discharge nozzle, wherein a storage portion for storing the treatment solution temporarily is disposed in the supply path between the treatment solution supply source and the pump, and another pump for supplying the treatment solution to the storage portion is disposed in the supply path between the storage portion and the treatment solution supply source, and comprising the step of measuring the number of times the predetermined amount is supplied, and the step of maintaining the level height of the treatment solution in the storage portion at a predetermined height by supplying the treatment solution to the storage portion by the said another pump only when the number of supply times exceeds a predetermined number of times. 
     A treatment solution supply unit of the present invention is a treatment solution supply unit for supplying, with a treatment solution in a treatment solution supply source forcibly fed by a pump, the treatment solution on a substrate through a supply path connecting the treatment solution supply source and a discharge nozzle, comprising a storage portion, disposed in the supply path between said treatment solution supply source and said pump, for storing the treatment solution temporarily, and another pump, disposed in the supply path between the storage portion and the treatment solution supply source, for supplying the treatment solution to the storage portion. 
     A treatment solution supply unit from another viewpoint of the present invention is a treatment solution supply unit for supplying, with a treatment solution in a treatment solution supply source forcibly fed by a pump, a predetermined amount of the treatment solution on a substrate each time through a supply path connecting the treatment solution supply source and a discharge nozzle, comprising a storage portion, disposed in the supply path between the treatment solution supply source and the pump, for storing the treatment solution temporarily, another pump, disposed in the supply path between the storage portion and the treatment solution supply source, for supplying the treatment solution to the storage portion, a counter for measuring the number of times said predetermined amount is supplied, and a pump controller for controlling the said another pump based on the result measure by the counter. 
     According to the present invention, the pressure on a primary side of the pump is constantly maintained at the same pressure by disposing the storage portion between the discharge nozzle and the treatment solution supply source, and further by maintaining the level height in the storage portion by the said another pump. Consequently, the force feed pressure on a secondary side of the pump is also kept steady, which keeps the discharge pressure of the treatment solution from the discharge nozzle steady. As a result, the treatment solution with a predetermined discharge pressure is discharged on the substrate, and a substrate processing is performed in a preferable way. 
     When the level height of the treatment solution in the storage portion is maintained at a predetermined height by operating the pump in association with the said another pump, the same amount of the treatment solution as that supplied on the substrate by the pump can be supplied to the storage portion by the said another pump. Thus, since the level height in the storage portion is maintained at a predetermined height, the discharge pressure of the treatment solution discharged on the substrate from the discharge nozzle is kept steady to perform a substrate processing in a preferable way. 
     The level height in the storage portion may be maintained at the predetermined height by measuring the number of supplying times by the pump and supplying the treatment solution to the storage pump by the said another pump only when the number of supplying times exceeds a predetermined times, for example, the number of supplying times corresponding to the level fluctuation in the storage portion causing a fluctuation of the discharge pressure to the degree in which a substrate processing is performed without any problem. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a plan view showing a schematic structure of a coating and developing system, having a coating solution supply unit according to a first embodiment of the present invention; 
     FIG. 2 is a front view of the coating and developing system in FIG. 1; 
     FIG. 3 is a rear view of the coating and developing system in FIG. 1; 
     FIG. 4 is an explanatory view of a vertical cross section of a resist coating unit to which a resist solution is supplied by the coating solution supply unit according to the first embodiment; 
     FIG. 5 is an explanatory view of the coating solution supply unit according to the first embodiment; 
     FIG. 6 is an explanatory view of a coating solution supply unit according to a second embodiment; 
     FIG. 7 is an explanatory view of a coating solution supply unit according to a third embodiment; 
     FIG. 8 is an explanatory view of the coating solution supply unit in another embodiment according to the third embodiment; 
     FIG. 9 is an explanatory view showing a rough view of a coating solution supply unit schematically when the resist coating unit has plural discharge nozzles; 
     FIG. 10 is an explanatory view of a treatment solution supply unit having a pipeline for air bubble venting; 
     FIG. 11 is an explanatory view of another treatment solution supply unit omitting a second pump; and 
     FIG. 12 is an explanatory view showing a rough view of a conventional treatment solution supply unit. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention will be described below. FIG. 1 is a plan view of a coating and developing system  1  having a coating solution supply unit according to the present embodiment, FIG. 2 is a front view of the coating and developing system  1 , and FIG. 3 is a rear view of the coating and developing system  1 . 
     As shown in FIG. 1, the coating and developing system  1  has a structure in which a cassette station  2  for carrying, for example, 25 wafers W from/to the outside to/from the coating and developing system  1  in the unit of cassette and for carrying the wafers W into/from a cassette C, a processing station  3  with various kinds of processing units disposed in multi-tiers for performing predetermined processing one by one in the coating and developing process, and an interface section  4  provided adjacent to the processing station  3 , for receiving and delivering the wafer W from/to an aligner which is not shown, are integrally connected. 
     In the cassette station  2 , a plurality of the cassettes C are mountable at predetermined positions on a cassette mounting table  5  serving as a mounting section in a line in an X-direction (a perpendicular direction in FIG.  1 ). Further, a wafer carrier  7 , which is transferable in the direction of the alignment of the cassettes (an X-direction) and in the direction of the alignment of the wafers W housed in the cassette C (a Z-direction; a perpendicular direction), is provided to be movable along a carrier guide  8  and is selectively accessible to the respective cassettes C. Below the cassette station  2 , a gallon bottle  81 , for example, is disposed serving as a treatment solution supply source. 
     The wafer carrier  7  has an alignment function for aligning the wafer W. The wafer carrier  7  is structured so as to be also accessible to an extension unit  32  included in a third processing unit group G 3  on the side of the processing station  3  as will be described later. 
     In the processing station  3 , a main carrier unit  13  is provided in a center part thereof, and various kinds of processing units are multi-tiered on the periphery of the main carrier unit  13  to compose processing unit groups. In the coating and developing system  1 , there are four processing unit groups G 1 , G 2 , G 3  and G 4 , and a first and a second processing unit groups G 1  and G 2  are disposed on the front side of the coating and developing system  1 , the third processing unit group G 3  is disposed adjacent to the cassette station  2 , and a fourth processing unit group G 4  is disposed adjacent to the interface section  4 . Further, as an option, a fifth processing unit group G 5  depicted by broken lines can be additionally arranged on the rear side of the coating and developing system  1 . The main carrier unit  13  can carry the wafer W into/from various kinds of processing units described later disposed in these processing unit groups G 1  to G 5 . 
     In the first processing unit group G 1 , for example, as shown in FIG. 2, a resist coating unit  17 , to which a resist solution is supplied from the coating solution supply unit according to the present embodiment, and a developing unit  18  for performing treatment on the wafer W with a developing solution supplied are two-tiered in the order from the bottom. As for the second processing unit group G 2 , a resist coating unit  19  and a developing unit  20  are similarly two-tiered in the order from the bottom. 
     In the third processing unit group G 3 , for example, as shown in FIG. 3, a cooling unit  30  for cooling the wafer W, an adhesion unit  31  for increasing the fixability between the resist solution and the wafer W, the extension unit  32  for keeping the wafer W waiting, pre-baking units  33  and  34  for drying a solvent in the resist solution, and post-baking units  35  and  36  for performing heating processing after developing treatment, and so on are, for example, seven-tiered in the order from the bottom. 
     In the fourth processing unit group G 4 , for example, a cooling unit  40 , an extension and cooling unit  41  for spontaneously cooling the placed wafer W, an extension unit  42 , a cooling unit  43 , post-exposure baking units  44  and  45  for performing heat treatment after exposure processing, post-baking units  46  and  47  and so on are, for example, eight-tiered in the order from the bottom. 
     In the center part of the interface section  4 , a wafer carrier  50  is provided. The wafer carrier  50  is structured so as to be movable in the direction X (the up-and-down direction in FIG. 1) and the direction Z (the perpendicular direction), and to be rotatable in a direction θ (a rotational direction about an axis Z), so that it can access the extension and cooling unit  41 , the extension unit  42  which are included in the fourth processing unit group G 4 , a peripheral aligner  51 , and an aligner which is not shown. 
     As described above, the embodiment of the present invention is materialized as the coating solution supply unit for supplying the resist solution to the resist coating unit  17 . 
     First, the structure of the resist coating unit  17  will be described. As shown in FIG. 4, in a casing  17   a  of the resist coating unit  17 , a spin chuck  61  is disposed for holding the wafer W horizontally by suction. On a bottom side of the spin chuck  61  a drive mechanism  62  having, for example, a motor and so on, for rotating the spin chuck  61  is attached. Therefore, when resist solution coating on the wafer W is performed, the wafer W is held on the spin chuck  61  by suction, and undergoes resist solution coating while the wafer W is rotated. Furthermore, the drive mechanism, having a function for moving the spin chuck  61  freely up and down, moves the spin chuck  61  up and down when the wafer W is carried in/out so that the wafer W is delivered to/from a main carrier unit  13 . 
     In an outer periphery of the spin chuck  61 , a cup  63  with its upper face open is provided to surround the spin chuck  61 . The cup  63  surrounds a side part and a lower part of the spin chuck to be formed to house the wafer W undergoing the treatment. Therefore, it can collect the resist solution scattering around from the wafer W due to the rotation of the wafer W during coating treatment and prevent peripheral units to be contaminated by the scattering resist solution. In addition, in a bottom portion of the cup  63 , a drainpipe  65  communicated with it for discharging the solution is provided, and the resist solution collected as described above is discharged from the drainpipe  65 . 
     A discharge nozzle  67  for discharging the resist solution on, for example, the wafer W and a solvent discharge nozzle  68  for discharging a solvent of the resist solution on the wafer W move above a center of the spin chuck  61 . Therefore, the discharge nozzle  67  is movable above the center of the wafer W. When the resist solution is discharged from the discharge nozzle  67  on the center of the wafer W rotated by the drive mechanism  62 , a predetermined resist film is formed on the wafer by a so-called spin coating method. 
     Next, the coating solution supply unit  80  for supplying the resist solution to the resist coating unit  17  will be described. As shown in FIG. 5, the resist solution is usually stored in the gallon bottle  81  disposed below the cassette station  2 , which serves as the treatment solution supply source. To the gallon bottle  81  an auxiliary pipeline  82  for supplying the resist solution to the gallon bottle  81  is provided, through which the resist solution is forcibly fed by nitrogen gas, which is inactive gas, at the time of supplying. 
     The gallon bottle  81  is communicated with an intermediate buffer tank  83 , which serves as a storage portion, by a first pipeline  84 . To the first pipeline  84  a first pump  89  serving as another pump is attached, and it is so structured to supply the resist solution in the gallon bottle  81  to the intermediate buffer tank  83 . The first pump  89  is controlled by a pump controller  87 , and by the order from the pump controller  87  the first pump  89  is put into operation so that the resist solution in the gallon bottle  81  is supplied in the intermediate buffer tank  83 . There is a case where a plurality of the gallon bottles  81  are disposed, and in this case the first pipeline  84  with the first pump  89  attached thereto as described above is disposed to each of the respective gallon bottles  81 , and is communicated with the single intermediate buffer tank  83 . 
     To the intermediate buffer tank  83  a low-level level sensor  90 , which serves as a sensor, for detecting that the level height of the resist solution in the intermediate buffer tank  83  lowers to the minimum allowable height L, and a high-level level sensor  91  for detecting that the said level rises to the maximum allowable height H are attached. 
     Signals from the low-level level sensor  90  and the high-level level sensor  91  are inputted to the pump controller  87 . Therefore, when the level height in the intermediate buffer tank  83  lowers to reach the minimum allowable height L after the resist solution is discharged on the wafer W from the discharge nozzle  67 , the low-level level sensor  90  detects it and the signal is sent to the pump controller  87 . Then, from the pump controller  87  an operation order is given to the first pump  89 , so that the resist solution in the gallon bottle  81  is supplied to the intermediate buffer  83 . 
     When the level rises to the maximum allowable height H after the resist solution is supplied in the intermediate buffer tank  83  in this way, the high-level level sensor  91  detects it, and according to the signal from the high-level level sensor  91  the pump controller  87  stops the operation of the first pump  89 . 
     The intermediate buffer tank  83  is communicated with the discharge nozzle  67  in the resist coating unit  17  by a second pipeline  95 . To the second pipeline  95 , a second pump  96  in a bellows type for forcibly feeding the resist solution in the intermediate buffer tank  83  to the discharge nozzle  67  is provided. At a discharge nozzle  67  side of the second pump  96  in the second pipeline  95 , that is a downstream side, the filter  97  is attached for removing impurities and air bubbles in the resist solution, and further downstream a valve  98  for finally controlling a discharge timing to the wafer W in accordance with an operation signal of the second pump is disposed. The second pump  96  and the valve  98  are controlled by a controller which is not shown. 
     The operations of the resist coating unit  17  and the coating solution supply unit  80  as structured above will be described together with a photolithography process performed in the coating and developing system  1 . 
     First, an unprocessed wafer W is taken out of the cassette C by the wafer carrier  7 , and then carried into the adhesion unit  31  included in the third processing unit group G 3 , and is coated with, for example, HMDS for improving the adhesion of the resist solution on its surface. Next, the wafer W is carried to the cooling unit  30  by the main carrier unit  13  and cooled to a predetermined temperature. Thereafter, the wafer W is carried to the resist coating unit  17  or  19 . 
     In the resist coating unit  17  or  19 , the wafer W coated with the resist solution is then carried to the pre-baking unit  33  or  34  and to the cooling unit  40  in sequence by the main carrier unit  13 . After that, the wafer W undergoes predetermined treatment such as exposure treatment, developing treatment and so on in the respective processing units, and a series of the coating and developing treatment is finished. 
     Detailing the operation in the above resist coating unit  17 , the wafer W after undergoing the above-described treatment is first carried into the resist coating unit  17  by the main carrier unit  13 . Then, the wafer W is held by suction by the spin chuck  61 , which has been raised by the drive mechanism  62  and has been waiting in advance, and after that, the spin chuck  61  is lowered by the drive mechanism  62  to stop in a predetermined position in the cup  63 . Next, the wafer W on the spin chuck  61  is rotated at a predetermined rotation speed by a rotation mechanism of the drive mechanism  62 . Then, a predetermined solvent is supplied on the wafer W from the solvent supply nozzle  68  first. After that, the resist solution supplied by the coating solution supply unit  80  is discharged on the rotating wafer W from the discharge nozzle  67  to perform resist coating treatment. Then, the wafer W, on which a predetermined resist film has been formed after undergoing the coating treatment, is raised again by the drive mechanism  62 , and transferred to the main carrier unit to be carried out from the resist coating unit  17 . 
     Next, the process of the coating solution supply unit  80  for supplying the resist solution to the resist coating unit  17  will be described. 
     First, when the wafer W is mounted on the spin chuck  61  and rotated in the resist coating unit  17  as described above, the second pump  96  is put into operation, and the resist solution in the intermediate buffer tank  83  is discharged from the discharge nozzle  67  through the second pipeline  95 . Incidentally, since the discharge pressure of the resist solution at this time is dependent on the pressure given to an admission port of the second pump  96 , if the level height of the resist solution in the intermediate buffer tank  83  fluctuates to change its potential energy, the pressure given to the admission port of the second pump  96  also changes and as a result, the discharge pressure fluctuates. Therefore, in order to keep the discharge pressure steady, it is necessary to store the resist solution in the intermediate buffer tank  83  temporarily and control the fluctuation of the level in the intermediate buffer tank  83  to the minimum so that the installation condition of the gallon bottle  81  can be neglected. 
     When the resist solution is discharged from the discharge nozzle  67 , the level height in the intermediate buffer tank  83  lowers, and when it reaches the minimum allowable height L, the low-level level sensor  90  detects it and transmits a predetermined signal to the pump controller  87 . The pump controller  87  which receives this signal orders the first pump  89  to operate, and the resist solution in the gallon bottle  81  is supplied in the intermediate buffer tank  83 . 
     This supply raises the level in the intermediate buffer tank  83 , and when it reaches the maximum allowable height H, the high-level level sensor  91  detects it and stops the operation of the first pump  89  via the pump controller  87 . In this way, the resist solution is supplied from the gallon bottle  81  each time the level of the resist solution in the intermediate buffer tank  83  reaches the minimum allowable height L after the resist solution is discharged on the wafer W, so that the level height in the intermediate buffer tank  83  is constantly maintained at the height between the maximum allowable height H and the minimum allowable height L. 
     Therefore, since the level height in the intermediate buffer tank  83  is maintained within a predetermined range, the pressure given to a primary side of the second pump  96 , that is, an upstream side, is maintained at a predetermined value, to maintain the discharge pressure at a predetermined pressure, so that a predetermined amount of the resist film is formed on the wafer W. Incidentally, though the low-level level sensor  90  and the high-level level sensor  91  are used as sensors to detect the level height in the intermediate buffer tank  83  in this embodiment, other means for detecting the level height, such as a float level gauge, may be used. 
     Though in the above embodiment, the level height of the resist solution in the intermediate buffer tank  83  is maintained by using the level sensors  90  and  91 , the level height may be maintained by associating the operations of the first pump  89  and the second pump  96  with each other. This will be detailed below as a second embodiment. 
     First, though the structure of a coating solution supply unit  100  according to the second embodiment is substantially the same as that of the coating solution supply unit  80  in the first embodiment, the second pump  96  is controlled by a pump controller  101  which also controls the first pump  89  as shown in FIG.  6 . The pump controller  101  controls the first pump  89  and the second pump  96  associating the operations of them with each other. To be more concrete, the first pump  89  is put into operation in accordance with the operation timing of the second pump  96 . 
     Next, to describe the process of the coating solution supply unit  100  as structured above, first, when the wafer W is held by the spin chuck  61  in the resist coating unit  17  and rotated by the drive mechanism  62  in the same way as in the above-described first embodiment, the second pump  96  is put into operation, so that the resist solution is discharged on the wafer W. Then, the first pump  89  is put into operation by the pump controller  101  with the operation of the second pump  96  working as a trigger, so that the resist solution is supplied in the intermediate buffer tank  83  from the gallon bottle  81 . The amount of the resist solution supplied at this time is made to match the amount discharged on the wafer W by the second pump  96  as described above. 
     By controlling the second pump  96  in this way, the level height of the resist solution in the intermediate buffer tank  83  is maintained at a predetermined height. Accordingly, the discharge pressure of the resist solution discharged from the discharge nozzle  67  is maintained within a predetermined range, and as a result, the discharge pressure from the discharge nozzle  67  is maintained steady, so that the resist film of a predetermined thickness is formed on the wafer W. Incidentally, the operation timings of the second pump  96  and the first pump  89  may be the same, or the first pump  89  may be put into operation after some time lag, for example, after a predetermined time passes from the operation of the second pump  96  on the condition that the level of the resist solution in the intermediate buffer tank  83  is maintained at a predetermined height. 
     Next, a third embodiment will be described. A coating solution supply unit  105  in the third embodiment is so structured that the number of times the second pump  96  in a so-called bellows type is pushed in is measured, and when the number of measured push-in times reaches a predetermined number, the first pump  89  is put into operation to maintain the level height in the intermediate buffer tank  83 . 
     In the third embodiment, a counter  106  for measuring the number of times the second pump  96  is pushed in is provided as shown in FIG.  7 . The counter  106  is structured to be able to set a predetermined number of the push-in times. In addition, the counter  106  is so structured to send the signal to the pump controller  107  when a measured value for the number of the push-in times reaches a predetermined number of times. The pump controller  107  also has a function for controlling the operation of the first pump  89  based on this signal. 
     Incidentally, a predetermined number of times for the number of times the second pump  96  is pushed in means the number of times within a range where the accumulated amount of a discharge amount discharged by pushing in a bellows portion can maintain the level height in the intermediate buffer tank  83  at a predetermined height, so it may be once or a plurality of times, and this predetermined number of times is set in advance to, for example, the counter  106 . 
     Therefore, in the process bv the coating solution supply unit  105 , the second pump  96  in a push-in type, for example, in a bellows type, operates first, and then the resist solution is supplied on the wafer W from the discharge nozzle  67 . At this time, the counter  106  measures the number of times the second pump  96  is pushed in. Then, when the number of the push-in times reaches a predetermined number of times, the counter  106  sends the signal to the pump controller  107 . 
     The pump controller  107  puts the first pump  89  into operation with this signal working as a trigger. Then, the same amount of the resist solution as that of the resist solution forcibly fed by the second pump  96  to the discharge nozzle  67 , for example, the amount of the resist solution forcibly fed by one push-in operation multiplied by a predetermined number of times, is supplied from the gallon bottle  81  to the intermediate buffer tank  83 . 
     As a result, the level height of the resist solution in the intermediate buffer tank  83  is maintained at a predetermined height. Thus, the discharge pressure of the resist solution discharged from the discharge nozzle  67  at the time of coating treatment is maintained within a predetermined range to form a predetermined amount of the resist film on the wafer W. 
     Though the second pump  96  as described above is a bellows type pump, other types, for example, a diaphragm type pump, may be used as long as it is a push-in type pump. Even if such a pump is not used, it is possible in a coating solution supply unit that a predetermined amount of the resist solution could be supplied on the wafer W each time by using a valve. For example, as shown in FIG. 8, when a valve  115  is provided in the second pipeline  95 , and the supply and the supply stop of the resist solution is controlled by the opening and closing of the valve  115 , the first pump  89  may be put into operation in the same way as in the third embodiment by counting the number of opening and closing times of the valve  115 . 
     Furthermore, as in the third embodiment, the second pump  96  in another embodiment may be a pump in types other than a push-in type, for example, a rotation type. 
     The above-described embodiments, where a single gallon bottle  81  is provided, may be applicable when a plurality of gallon bottles  81  are provided if necessary. In this case, since supply sources of a coating solution are different from each other, level heights may sometimes differ greatly from each other due to the difference of the positions where the gallon bottles are placed and their remaining amount. 
     In this case, too, the resist solution is stored in the intermediate buffer tank  83  for common use temporarily, and its level is maintained within a predetermined range as described above, so that the resist solution can be discharged on the wafer W with the same discharge pressure no matter which of the gallon bottles the resist solution is supplied from. Particularly, since level heights in the respective gallon bottles are greatly different from each other when two or more gallon bottles are disposed in a vertical tier, the intermediate buffer tank is provided as described above to improve the uniformity of the discharge pressures to a great extent by maintaining its level height. 
     The above-described embodiments, where the resist solution is supplied to the single discharge nozzle  67  from the intermediate buffer tank  83 , are also applicable when the resist solution is supplied to a plurality of discharge nozzles. 
     In a coating solution supply unit  120  having discharge nozzles  67   a,    67   b,  and  67   c,  for example as shown in FIG. 9, respective second pipelines  95   a,    95   b  and  95   c,  which communicate the intermediate buffer tank  83  with respective discharge nozzles  67   a,    67   b,  and  67   c,  are disposed. To the second pipelines  95   a,    95   b,  and  95   c  respective second pumps  96   a,    96   b,  and  96   c  are attached. Then, for the respective supply paths, the mechanisms described in the first, second, or third embodiments, for maintaining the level height in the buffer tank  83  at a predetermined height are provided to maintain the discharge pressures of the resist solutions discharged from all of the discharge nozzles  67   a,    67   b,  and  67   c  within a predetermined range. Therefore, when a plurality of discharge nozzles  67  are provided, a predetermined discharge pressure is also maintained for all of the discharge nozzles  67   a,    67   b,  and  67   c,  so that a predetermined resist film is formed on the wafer W in all of the resist coating units. 
     Still another embodiment will be described. In an example as shown in FIG. 10, a pipeline for air bubble venting  141  is laid between the filter  97  and the intermediate buffer tank  83 , and to this pipeline  141  a valve  142  for air bubble venting is provided. Therefore, air bubbles collected in the filter  97  are returned to the intermediate buffer tank  83  through the pipeline  141  by opening the valve  142 . 
     Usually, air bubbles collected by the filter  97  of this kind are disposed as drains, but according to the example in FIG. 10, they are returned to the intermediate buffer tank  83  to be usable again, so that an effective use of the resist solution can be realized. 
     Yet another embodiment is described. In an example shown in FIG. 11, the second pump  96  is omitted when an intake port  95   a  of the second pipeline  95  in the intermediate buffer tank  83 , that is, an intake port  95   a  for taking in the resist solution in the intermediate buffer tank  83  into the second pipeline  95 , is positioned higher than the discharge nozzle  67 . In other words, the resist solution in the intermediate buffer tank  83  is discharged from the discharge nozzle  67  by a pressure difference caused by a height difference. A discharge amount is controlled by the opening and closing operation of the valve  98 . Thus the whole unit is simplified. 
     In an example shown in FIG. 11, the filter  97  is provided at a downstream side of the first pump  89  in the first pipeline  84 . The pipeline for air bubble venting  141  is laid between the filter  97  and the gallon bottle  81 . Therefore, in an example shown in FIG. 11, the air bubbles of the resist solution collected by the filter are returned to the gallon bottle  81  by the opening of the valve  142 . Thus, in an example in FIG. 11 an effective use of the resist solution can also be realized. 
     The above described embodiments are materialized as a coating solution supply unit for supplying the resist solution to the resist coating unit, but may, of course, be materialized as other treatment solution supply units such as a development solution supply unit and so on. Furthermore, though a substrate is a wafer, they are applicable to a coating unit for other substrates, for example, an LCD substrate. 
     As described above, according to the present invention, since the level height of the treatment solution in the storage portion is maintained at a predetermined height, the fluctuation of the discharge pressure to the substrate caused by the fluctuation of the level height of the treatment solution as in a conventional treatment solution supply source is reduced, this discharge pressure is maintained within a predetermined range. Consequently, owing to the stable discharge of the treatment solution a substrate processing is performed in a preferable way to improve a yield. 
     Operating the pump for supplying the treatment solution from the storage portion to the discharge nozzle in association with the said another pump for supplying the treatment solution to the storage portion from the treatment solution supply source can reduce the fluctuation of the level height in the storage portion to a smaller level, and maintain the discharge pressure of the treatment solution within a narrower predetermined range. 
     When a plurality of the nozzles are provided, the discharge pressure is also maintained within a predetermined range, and the same discharge pressure of the treatment solution, in addition, is also maintained for these discharge nozzles, so that the same treatments are performed simultaneously, which improves a throughput. 
     Furthermore, as the air bubbles of the treatment solution, which are conventionally disposed as drains, can be utilized again, an effective use of the treatment solution can be realized.