Abstract:
A liquid processing method includes: placing a plate adjacently to at least one of surfaces of a target substrate, and supplying a process liquid into a gap between the plate and the target substrate, thereby forming a liquid film of the process liquid; subjecting the target substrate to a process using a state with the liquid film of the process liquid thus formed; and supplying a gas to the liquid film, thereby breaking the liquid film, after finishing the process.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a liquid processing method and liquid processing apparatus for performing a liquid process, such as cleaning, on a target substrate, such as a semiconductor wafer or a glass substrate for a flat panel display (FPD), representative of which is a liquid crystal display (LCD). The present invention also relates to a control program and computer readable storage medium for executing a liquid processing method of this kind.  
         [0003]     2. Description of the Related Art  
         [0004]     In the process of manufacturing semiconductor devices, a cleaning process is performed by supplying a predetermined chemical liquid (cleaning liquid) to clean a semiconductor wafer (which will be simply referred to as “wafer”, hereinafter), so that contaminants, such as particles, organic contaminants, and metal impurities, and polymers remaining after an etching process are removed from the wafer.  
         [0005]     As a wafer cleaning apparatus for performing such a cleaning process, a wafer cleaning apparatus of the single-wafer type is known, as follows. Specifically, at first, a chemical liquid is supplied onto the front and back surfaces of a wafer held on a spin chuck, while the wafer is set in a stationary state or in a rotated state, to perform a chemical liquid process. Then, a rinsing liquid, such as purified water, is supplied onto the wafer, while the wafer is rotated at a predetermined rotation number, to wash away the chemical liquid. Then, the wafer is rotated to perform a drying process.  
         [0006]     Jpn. Pat. Appln. KOKAI Publication No. 2003-224100 discloses a technique in light of economical efficiency for a wafer cleaning apparatus of the single-wafer type, in which a cleaning process is performed while a chemical liquid puddle (liquid film) is formed on the cleaning target surface of a wafer, so that the chemical liquid consumption can be as little as possible. Specifically, for example, a plate for forming a chemical liquid puddle is disposed to face the back surface of a wafer. Then, while this plate is set to be adjacent to the back surface of the wafer, a chemical liquid is supplied into the gap between the wafer and plate from a nozzle disposed on the plate to form a puddle. The plate is arranged to be movable up and down, so that the plate is moved down, after the chemical liquid cleaning, to expand the gap between the plate and wafer. In this state, a rinsing process and a drying process are performed, while the wafer is rotated at a high speed. During the chemical liquid process, the gap between the plate and wafer is set to be as small as possible to decrease the chemical liquid consumption per wafer.  
         [0007]     However, when the plate is moved down to separate it from the wafer, or when the wafer is rotated at a high speed thereafter, the liquid volume within the gap becomes smaller than the gap volume. Consequently, the gap falls into a vacuum state, and the wafer is thereby stuck on the plate and may suffer warp and/or crack generation.  
       BRIEF SUMMARY OF THE INVENTION  
       [0008]     An object of the present invention is to provide a liquid processing method and liquid processing apparatus, which can prevent a target substrate from suffering warp and/or crack generation when a liquid process is performed while using a plate to form a liquid film on the target substrate.  
         [0009]     Another object of the present invention is to provide a control program and computer readable storage medium for executing a method of this kind.  
         [0010]     A according to a first aspect of the present invention, there is provided a liquid processing method comprising: placing a plate adjacently to at least one of surfaces of a target substrate, and supplying a process liquid into a gap between the plate and the target substrate, thereby forming a liquid film of the process liquid; subjecting the target substrate to a process using a state with the liquid film thus formed; and supplying a gas to the liquid film of the process liquid, thereby breaking the liquid film, after finishing the process.  
         [0011]     In the liquid processing method according to the first aspect, the process liquid may be supplied into the gap between the plate and the target substrate from a nozzle disposed at a central portion of the plate. The process liquid of the liquid film may be a chemical liquid at least when the liquid film is formed. In this case, after forming the liquid film from the chemical liquid used as the process liquid and before breaking the liquid film, the method may further comprise supplying a rinsing liquid into the gap between the plate and the target substrate, thereby replacing the chemical liquid of the liquid film partly or entirely with the rinsing liquid. The method may further comprise releasing pressure inside a gas line for supplying the gas to the liquid film before breaking the liquid film. The method may further comprise: expanding the gap between the plate and the target substrate while rotating the target substrate at a first rotation number that defines a relatively lower speed; and then increasing the rotation number of the target substrate to a second rotation number that defines a higher speed than the speed defined by the first rotation number. In this case, the first rotation number may be set to be 10 to 100 rpm, and the second rotation number may be set to be 100 to 1,000 rpm. The method may further comprise: supplying a rinsing liquid onto the target substrate while rotating the target substrate; and rotating the target substrate, thereby performing throwing-off and drying.  
         [0012]     A according to a second aspect of the present invention, there is provided a liquid processing method comprising: placing a plate adjacently to at least one of surfaces of a target substrate, and supplying a process liquid into a gap between the plate and the target substrate, thereby forming a liquid film of the process liquid; subjecting the target substrate to a process using a state with the liquid film thus formed; supplying a gas to the liquid film, thereby breaking the liquid film, after finishing the process; expanding the gap between the plate and the target substrate; removing the liquid film from the target substrate; performing rinsing on a surface of the target substrate facing the plate; and performing throwing-off and drying on the target substrate.  
         [0013]     A according to a third aspect of the present invention, there is provided a liquid processing method comprising: placing a plate adjacently to a back surface of a target substrate, and supplying a process liquid into a gap between the plate and the target substrate, thereby forming a liquid film of the process liquid; subjecting the target substrate to a process using a state with the liquid film thus formed; supplying a gas to the liquid film, thereby breaking the liquid film, after finishing the process; expanding the gap between the plate and the target substrate while rotating the target substrate at a first rotation number that defines a relatively lower speed; increasing the rotation number of the target substrate to a second rotation number that defines a relatively higher speed, thereby removing the liquid film from the back surface of the target substrate; supplying a rinsing liquid onto the back surface of the target substrate while rotating the target substrate, thereby performing rinsing thereon; supplying a process liquid onto a front surface of the target substrate, thereby subjecting the front surface to a process, while the process on the back surface of the target substrate is proceeding; supplying a rinsing liquid onto the front surface of the target substrate, thereby performing rinsing thereon, after finishing the process on the front surface of the target substrate; and switching the rinsing liquid supplied onto the front surface of the target substrate to a two-fluid spray comprising purified water atomized by a gas, at timing when the first rotation number is increased to the second rotation number.  
         [0014]     In the liquid processing method according to the third aspect, the first rotation number may be set to be 10 to 100 rpm, and the second rotation number may be set to be 100 to 1,000 rpm. The method may further comprise rotating the target substrate at a high speed, thereby performing throwing-off and drying.  
         [0015]     A according to a fourth aspect of the present invention, there is provided a liquid processing method comprising: placing a plate to face at least one of surfaces of a target substrate with a first distance therebetween, and supplying a liquid into a gap between the plate and the target substrate, thereby performing a liquid process; stopping supply of the liquid, and then supplying a gas into the gap between the plate and the target substrate with the first distance therebetween; and expanding the distance between the plate and the target substrate to a second distance larger than the first distance, while supplying the gas.  
         [0016]     In the liquid processing method according to the fourth aspect, the method may further comprise: rotating the target substrate, while supplying the gas into the gap between the plate and the target substrate with the first distance therebetween; and providing an increase in rotation number of the target substrate, when expanding the distance between the plate and the target substrate to the second distance while supplying the gas. The method may further comprise supplying a rinsing liquid into the gap between the plate and the target substrate. After supplying the rinsing liquid, the method may further comprise expanding the distance between the plate and the target substrate to a third distance larger than the second distance, and stopping supply of the rinsing liquid. The liquid supplied into the gap between the plate and the target substrate with the first distance therebetween may be a chemical liquid, or may be a chemical liquid and a rinsing liquid supplied subsequently to a chemical liquid process.  
         [0017]     According to a fifth aspect of the present invention, there is provided a liquid processing method comprising: placing a plate adjacently to at least one of surfaces of a target substrate, and supplying a process liquid into a gap between the plate and the target substrate, thereby forming a liquid film of the process liquid; subjecting the target substrate to a process using a state with the liquid film thus formed; and expanding the gap having the liquid film of the process liquid formed therein, while supplying a liquid-phase fluid into the gap to follow a change of the gap, thereby breaking the liquid film, after finishing the process.  
         [0018]     In the liquid processing method according to the fifth aspect, the process liquid may be supplied into the gap between the plate and the target substrate from a nozzle disposed at a central portion of the plate. The process liquid for forming the liquid film may be a chemical liquid. The liquid-phase fluid may be a rinsing liquid. The method may further comprise: rotating the target substrate at a first rotation number that defines a relatively lower speed, while breaking the liquid film; and then further expanding the gap while increasing the rotation number of the target substrate to a second rotation number that defines a higher speed than the speed defined by the first rotation number. In this case, the first rotation number may be set to be 10 to 100 rpm, and the second rotation number may be set to be 100 to 1,000 rpm. The method may further comprise: supplying a rinsing liquid onto the target substrate while rotating the target substrate; and rotating the target substrate, thereby performing throwing-off and drying.  
         [0019]     According to a sixth aspect of the present invention, there is provided a liquid processing method comprising: placing a plate adjacently to at least one of surfaces of a target substrate, and supplying a process liquid into a gap between the plate and the target substrate, thereby forming a liquid film of the process liquid; subjecting the target substrate to a process using a state with the liquid film thus formed; expanding the gap having the liquid film of the process liquid formed therein, while supplying a liquid-phase fluid into the gap to follow a change of the gap, thereby breaking the liquid film, after finishing the process; removing the liquid film from the gap; performing rinsing on a surface of the target substrate facing the plate; and performing throwing-off and drying on the target substrate.  
         [0020]     According to a seventh aspect of the present invention, there is provided a liquid processing method comprising: placing a plate adjacently to a back surface of a target substrate, and supplying a process liquid into a gap between the plate and the target substrate, thereby forming a liquid film of the process liquid; subjecting the target substrate to a process using a state with the liquid film thus formed; rotating the target substrate at a first rotation number that defines a relatively lower speed, and expanding the gap having the liquid film of the process liquid formed therein, while supplying a liquid-phase fluid into the gap to follow a change of the gap, thereby breaking the liquid film, after finishing the process; increasing the rotation number of the target substrate to a second rotation number that defines a relatively higher speed, thereby removing the liquid film from the gap; supplying a rinsing liquid onto the back surface of the target substrate while rotating the target substrate, thereby performing rinsing thereon; supplying a process liquid onto a front surface of the target substrate, thereby subjecting the front surface to a process, while the process on the back surface of the target substrate is proceeding; supplying a rinsing liquid onto the front surface of the target substrate, thereby performing rinsing thereon, after finishing the process on the front surface of the target substrate; and switching the rinsing liquid supplied onto the front surface of the target substrate to a two-fluid spray comprising purified water atomized by a gas, at timing when the first rotation number is increased to the second rotation number.  
         [0021]     In the liquid processing method according to the seventh aspect, the first rotation number may be set to be 10 to 100 rpm, and the second rotation number may be set to be 100 to 1,000 rpm. The method may further comprise rotating the target substrate at a high speed, thereby performing throwing-off and drying.  
         [0022]     According to an eighth aspect of the present invention, there is provided a liquid processing method comprising: placing a plate to face at least one of surfaces of a target substrate with a first distance therebetween, and supplying a first liquid into a gap between the plate and the target substrate, thereby performing a liquid process; expanding the gap having the liquid film of the process liquid formed therein to a second distance, while supplying a second liquid into the gap to follow a change of the gap, thereby breaking the liquid film, after finishing the process; and expanding the gap further to a third distance, and removing the liquid film.  
         [0023]     In the liquid processing method according to the eighth aspect, the method may further comprise rotating the target substrate at a first rotation number while breaking the liquid film, and increasing the rotation number of the target substrate to a second rotation number that defines a higher speed than a speed defined by the first rotation number, thereby removing the liquid film. After removing the liquid film, the method may further comprise supplying a rinsing liquid into the gap between the plate and the target substrate. The first liquid may be a chemical liquid and the second liquid may be a rinsing liquid.  
         [0024]     A according to a ninth aspect of the present invention, there is provided a liquid processing apparatus comprising: a substrate holding portion configured to hold a target substrate in a horizontal state; at least one plate configured to be placed at a position adjacent to at least one of surfaces of the target substrate, and to be separated therefrom; a process liquid supply member configured to supply a process liquid into a gap between the plate and the target substrate to form a liquid film of the process liquid; a gas supply mechanism configured to supply a gas to the liquid film to break the liquid film; and a control mechanism configured to carry out control such that, after a process using the liquid film is finished, the gas is supplied to the liquid film to break the liquid film, and then the plate is separated from the target substrate.  
         [0025]     According to a tenth aspect of the present invention, there is provided a liquid processing apparatus comprising: a substrate holding portion configured to hold a target substrate in a horizontal state; at least one plate configured to be placed at a position adjacent to at least one of surfaces of the target substrate, and to be separated therefrom; a process liquid supply member configured to supply a process liquid into a gap between the plate and the target substrate to form a liquid film of the process liquid; a liquid-phase fluid supply mechanism configured to supply a liquid-phase fluid into the gap; and a control mechanism configured to carry out control such that, after a process using the liquid film is finished, the gap having the liquid film of the process liquid formed therein is expanded, while the liquid-phase fluid is supplied into the gap to follow a change of the gap, so as to break the liquid film.  
         [0026]     A according to an eleventh aspect of the present invention, there is provided a computer readable storage medium that stores a control program for execution on a computer, wherein the control program, when executed, causes the computer to control a liquid processing apparatus to conduct a liquid processing method comprising: placing a plate adjacently to at least one of surfaces of a target substrate, and supplying a process liquid into a gap between the plate and the target substrate, thereby forming a liquid film of the process liquid; subjecting the target substrate to a process using a state with the liquid film of the process liquid thus formed; and supplying a gas to the liquid film of the process liquid, thereby breaking the liquid film, after finishing the process.  
         [0027]     According to a twelfth aspect of the present invention, there is provided a computer readable storage medium that stores a control program for execution on a computer, wherein the control program, when executed, causes the computer to control a liquid processing apparatus to conduct a liquid processing method comprising: placing a plate adjacently to at least one of surfaces of a target substrate, and supplying a process liquid into a gap between the plate and the target substrate, thereby forming a liquid film of the process liquid; subjecting the target substrate to a process using a state with the liquid film thus formed; and expanding the gap having the liquid film of the process liquid formed therein, while supplying a liquid-phase fluid into the gap to follow a change of the gap, thereby breaking the liquid film, after finishing the process.  
         [0028]     According to one manner of the present invention, a plate is placed adjacently to at least one of surfaces of a target substrate, and a process liquid is supplied into a gap between the plate and the target substrate, so that a liquid film of the process liquid is formed. Then, the target substrate is subjected to a process using a state with the liquid film thus formed. Then, a gas is supplied to the liquid film of the process liquid to break the liquid film, after the process is finished. Consequently, when the plate is separated from the target substrate, the gap between the plate and the target substrate does not fall into a vacuum state, and the target substrate is thereby prevented from suffering warp and/or crack generation.  
         [0029]     According to another manner of the present invention, a plate is placed adjacently to at least one of surfaces of a target substrate, and a process liquid is supplied into a gap between the plate and the target substrate, so that a liquid film of the process liquid is formed. Then, the target substrate is subjected to a process using a state with the liquid film thus formed. After the process is finished, the gap having the liquid film of the process liquid formed therein is expanded, while a liquid is supplied into the gap, to break the liquid film. Consequently, when the gap between the target substrate and the plate is expanded, the gap does not fall into a vacuum state, and the target substrate is thereby prevented from suffering warp and/or crack generation. Further, once the liquid film is broken, another liquid film is not formed in the gap thereafter, and thus the rotation number of the substrate can be increased for the subsequent step. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING  
       [0030]      FIG. 1  is a plan view schematically showing an example of a cleaning apparatus usable for performing a method according to an embodiment of the present invention;  
         [0031]      FIG. 2  is a sectional view schematically showing the cleaning apparatus shown in  FIG. 1 ;  
         [0032]      FIG. 3  is a view showing a liquid and gas supply system used in the cleaning apparatus shown in  FIG. 1 ,  
         [0033]      FIG. 4  is a flowchart for explaining an example of the sequence of a cleaning process for the back surface of a wafer, performed by the cleaning apparatus shown in  FIG. 1 ;  
         [0034]      FIGS. 5A  to  5 E are schematic views for explaining the state inside the apparatus step by step in performing the sequence shown in  FIG. 4 ;  
         [0035]      FIG. 6  is a flowchart showing an example of the sequence of a cleaning process for the front surface of a wafer, performed by the cleaning apparatus shown in  FIG. 1 , in relation to the cleaning process for the back surface shown in  FIG. 4 ;  
         [0036]      FIG. 7  is a flowchart for explaining another example of the sequence of a cleaning process for the back surface of a wafer, performed by the cleaning apparatus shown in  FIG. 1 ;  
         [0037]      FIGS. 8A  to  8 E are schematic views for explaining the state inside the apparatus step by step in performing the sequence shown in  FIG. 7 ;  
         [0038]      FIG. 9  is a flowchart showing an example of the sequence of a cleaning process for the front surface of a wafer, performed by the cleaning apparatus shown in  FIG. 1 , in relation to the cleaning process for the back surface shown in  FIG. 7 ; and  
         [0039]      FIG. 10  is a sectional view schematically showing the structure of another example of a cleaning apparatus usable for implementing the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0040]     An embodiment of the present invention will now be described with reference to the accompanying drawings. Hereinafter, an explanation will be given of a case where the present invention is applied to a cleaning apparatus that can perform cleaning processes on the front and back surfaces of a wafer simultaneously.  
         [0041]      FIG. 1  is a plan view schematically showing an example of a cleaning apparatus usable for performing a method according to an embodiment of the present invention.  FIG. 2  is a sectional view schematically showing the cleaning apparatus shown in  FIG. 1 . The cleaning apparatus  100  includes a housing  1 , in which an outer chamber  2 , a liquid delivery nozzle arm shed  3 , and a two-fluid spray nozzle arm shed  4  are disposed. The outer chamber  2  is arranged to accommodate a wafer to be subjected to a cleaning process. The liquid delivery nozzle arm shed  3  is arranged to store a liquid delivery nozzle arm  31  for a liquid delivery nozzle. The two-fluid spray nozzle arm shed  4  is arranged to store a two-fluid spray nozzle arm  32  for a two-fluid spray nozzle.  
         [0042]     Further, the cleaning apparatus  100  includes an inner cup  11  ( FIG. 2 ) disposed inside the outer chamber  2 . A spin chuck  12  is disposed inside the inner cup  11  to hold a wafer W. An under plate  13  is disposed to face the back surface of the wafer W held by the spin chuck  12  and to be movable up and down.  
         [0043]     The housing  1  has a window portion  14  formed therein as a wafer transfer port and provided with a first shutter  15  capable of opening/closing the window portion  14 . The window portion  14  is set in an opened state when the wafer W is loaded or unloaded, and is otherwise set in the closed state by the first shutter  15 . The first shutter  15  is arranged to open and close the window portion  14  from inside the housing  1 , so that the inner atmosphere of the housing  11  is effectively prevented from leaking even when the interior of the housing  1  has a positive pressure.  
         [0044]     The outer chamber  2  has a window portion  16  formed in the sidewall as a wafer transfer port at a position corresponding to the window portion  14 . The window portion  16  is provided with a second shutter  17  capable of opening/closing the window portion  16 . The window portion  16  is set in an opened state when the wafer W is loaded or unloaded, and is otherwise set in the closed state by the second shutter  17 . The wafer W is subjected to a cleaning process within the outer chamber  2 . When the wafer W is loaded or unloaded, both the window portions  14  and  16  are set in an opened state. Then, a transfer arm (not shown) is inserted into the outer chamber  2  from outside, and the wafer W is transferred to the spin chuck  12  or from the spin chuck  12 .  
         [0045]     The second shutter  17  is arranged to open and close the window portion  16  from inside the outer chamber  2 , so that the inner atmosphere of the outer chamber  2  is effectively prevented from leaking even when the interior of the outer chamber  2  has a positive pressure.  
         [0046]     A gas supply port  18  is disposed on the top wall of the outer chamber  2  to supply an inactive gas, such as N 2  gas, into the outer chamber  2 . The gas supply port  18  is arranged to form a downflow within the outer chamber  2 , so that the outer chamber  2  is prevented from being filled with vapor of a chemical liquid delivered onto the wafer W held by the spin chuck  12 . Further, where this downflow is formed, there is also provided the effect of preventing water marks from being formed on the front surface of the wafer W. The outer chamber  2  has a drain portion  19  formed at the bottom, so that gas and liquid can be exhausted through the drain portion  19 .  
         [0047]     The inner cup  11  surrounds the spin chuck  12 , so that the chemical liquid and/or purified water delivered onto the wafer W are prevented from scattering around the inner cup  11 . The inner cup  11  has a tapered portion  11   a  formed on the upper side, and a drain portion  20  formed in the bottom wall. The inner cup  11  is movable up and down between a process position (denoted by a solid line in  FIG. 2 ) and a retreat position (denoted by a dotted line in  FIG. 2 ). In the process position, the upper end of the inner cup  11  is positioned higher than the wafer W held by the spin chuck  12  and the tapered portion surrounds the wafer W. In the retreat position, the upper end of the inner cup  11  is positioned lower than the wafer W held by the spin chuck  12 .  
         [0048]     When the wafer W is loaded or unloaded, the inner cup  11  is set in the retreat position so as not to obstruct the incoming/outgoing movement of the transfer arm (not shown). On the other hand, when a cleaning process is performed on the wafer W held by the spin chuck  12 , the inner cup  11  is set in the process position. The chemical liquid used for the cleaning process of the wafer W is guided into the drain portion  20 . The drain portion  20  is connected to a chemical liquid recovery line and an exhaust duct (both not shown). With this arrangement, mist or the like generated within the inner cup  11  is prevented from diffusing into the outer chamber  12 .  
         [0049]     The spin chuck  12  includes a rotary plate  41  and a rotary cylindrical body  42  connected to the rotary plate  41  at the central portion thereof and extending downward from the rotary plate  41 . Support pins  44   a  for supporting the wafer W and holding pins  44   b  for holding the wafer W are attached to the peripheral portion of the rotary plate  41 . When the wafer W is transferred between the transfer arm (not shown) and spin chuck  12 , the support pins  44   a  are utilized for this transfer. In order to reliably support the wafer W, the support pins  44   a  are preferably disposed in at least three positions. The holding pins  44   b  are arranged not to obstruct the operation for transferring the wafer W between the transfer arm (not shown) and spin chuck  12 . For this purpose, a pushing mechanism (not shown) is disposed to push the portions of the holding pins  44   b  below the rotary plate  41  toward the rotary plate  41 , so that the upper ends of the holding pins  44   b  are inclined out of the rotary plate  41 . In order to reliably hold the wafer W, the holding pins  44   b  are preferably disposed in at least three positions.  
         [0050]     A belt  45  is wound around the outer surface of the rotary cylindrical body  42  near the lower end, and is arranged to be driven by a motor  66 . With this arrangement, the rotary cylindrical body  42  and rotary plate  41  are rotatable along with the wafer W held by the holding pins  44   b.    
         [0051]     The under plate  13  is connected to a shaft (support column)  47  extending through the central portion of the rotary plate  41  and the rotary cylindrical body  42 . The lower end of the shaft  47  is fixed to a horizontal plate  48 . The horizontal plate  48  and the shaft  47  are integrally movable up and down by an elevating mechanism  49 , such as an air cylinder. When the wafer W is transferred between the spin chuck  59  and transfer arm (not shown), the under plate  13  is moved down by the elevating mechanism  49  to a position adjacent to the rotary plate  41  so as not to collide with the transfer arm. When a puddle (liquid film) is formed to perform a cleaning process on the back surface of the wafer W, the under plate  13  is moved up by the elevating mechanism  49  to a position adjacent to the back surface of the wafer W. After the cleaning process utilizing a puddle is finished, the under plate  13  is moved down by the elevating mechanism  49  to a suitable position. It may be arranged such that the rotary cylindrical body  42  is moved up and down while the under plate  13  is set stationary at a prescribed height, to adjust the relative positions of the wafer W held by the holding pin  64   b  and the under plate  13 .  
         [0052]     A back surface cleaning nozzle  50  is formed in the under plate  13  and shaft  47  to extend therethrough. The back surface cleaning nozzle  50  is arranged to supply a chemical liquid used as a cleaning liquid, purified water used as a rinsing liquid, and a liquid film breaking gas (for example, nitrogen gas) toward the back surface of the wafer W. The under plate  13  has a heater  33 , built therein and arranged to be supplied with electricity from a power supply (not shown), to control the temperature of the wafer W through the under plate  13 .  
         [0053]     The liquid delivery nozzle arm shed  3  has a window portion  21  formed adjacently to the outer chamber  2  and provided with a third shutter  22  capable of opening/closing the window portion  21 . The third shutter  22  is set in the closed state when the liquid delivery nozzle arm shed  3  is isolated from the atmosphere inside the outer chamber  2 . The two-fluid spray nozzle arm shed  4  has a window portion  23  formed adjacently to the outer chamber  2  and provided with a fourth shutter  24  capable of opening/closing the window portion  23 . The fourth shutter  24  is set in the closed state when the two-fluid spray nozzle arm shed  4  is isolated from the atmosphere inside the outer chamber  2 .  
         [0054]     The liquid delivery nozzle arm  31  is stored in the liquid delivery nozzle arm shed  3 , and is movable by a driving mechanism  52  disposed at the proximal end. Specifically, the arm  31  is rotatable between a position inside the liquid delivery nozzle arm shed  3  and a position above the center of the wafer W inside the outer chamber  2 , and is further movable up and down. The distal end of the arm  31  supports a liquid delivery nozzle  51  for delivering a chemical liquid used as a cleaning liquid and purified water used as a rinsing liquid.  
         [0055]     On the other hand, the two-fluid spray nozzle arm  32  is stored in the two-fluid spray nozzle arm shed  4 , and is movable by a driving mechanism  54  disposed at the proximal end. Specifically, the arm  32  is rotatable between a position inside the two-fluid spray nozzle arm shed  4  and a position above the center of the wafer W inside the outer chamber  2 , and is further movable up and down. The distal end of the arm  32  supports a two-fluid spray nozzle  53  for spraying N 2  gas and purified water atomized by N 2  gas.  
         [0056]      FIG. 3  is a view schematically showing a fluid supply system used in the cleaning apparatus  100 . As shown in  FIG. 3 , the back surface cleaning nozzle  50  is connected to a fluid supply line  61 . The fluid supply line  61  is connected to a chemical liquid supply line  62  and a purified water supply line  63  respectively through valves  64  and  65 , so as to supply a chemical liquid used as a cleaning liquid and purified water used as a rinsing liquid onto the back surface of the wafer W. The fluid supply line  61  is connected, through a valve  67  disposed on the way, to an N 2  gas supply line  66  for supplying a N 2  gas. The N 2  gas supply line  66  is provided with a regulator  68 , a flow meter  69 , and a filter  70  disposed thereon in this order from the upstream side. Further, at a position downstream from the filter  70 , the N 2  gas supply line  66  is connected to a release line  71  for releasing the N 2  gas pressure outside. The release line  71  is provided with a switching valve  71   a  disposed thereon.  
         [0057]     On the other hand, the liquid delivery nozzle  51  disposed above the front surface of the wafer is connected to a liquid supply line  72 . The liquid supply line  72  is connected to a chemical liquid supply line  73  and a purified water supply line  74  respectively through valves  75  and  76 , so as to supply a chemical liquid used as a cleaning liquid and purified water used as a rinsing liquid onto the front surface of the wafer W. The two-fluid spray nozzle  53  is connected to an N 2  gas line  77  and purified water line  78 , so as to atomize purified water by N 2  gas and to spray the atomized purified water along with N 2  gas therefrom.  
         [0058]     Each of the components in the cleaning apparatus  100  is connected to and controlled by the process controller  90  having a CPU. The process controller  90  is connected to a user interface  91 , which includes, e.g., a keyboard and a display, wherein the keyboard is used for a process operator to input commands for operating the components in the cleaning apparatus  100 , and the display is used for showing visualized images of the operational status of the components in the cleaning apparatus  100 . Further, the process controller  90  is connected to the memory portion  92 , which stores recipes with control programs and process condition data recorded therein, for realizing various processes performed in the cleaning apparatus  100  under the control of the process controller  90 .  
         [0059]     A required recipe is retrieved from the storage portion  92  and executed by the process controller  90  in accordance with an instruction or the like input through the user interface  91 . Consequently, each of various predetermined processes is performed in the cleaning apparatus  100  under the control of the process controller  90 . A recipe may be stored in a readable storage medium, such as a CD-ROM, hard disk, flexible disk, or nonvolatile memory. Further, a recipe may be utilized on-line, while it is transmitted from a suitable apparatus through, e.g., a dedicated line, as needed.  
         [0060]     Next, an explanation will be given of a first example of a cleaning process performed in the cleaning apparatus described above. At first, the following state is set up. Specifically, the first shutter  15  of the housing  1  and the second shutter  17  of the outer chamber  2  are opened. The inner cup  11  is set in the retreat position, and the under plate  13  is put in waiting at a position adjacent to the rotary plate  41 . Further, the liquid delivery nozzle arm  31  and two-fluid spray nozzle arm  32  are respectively stored in the liquid delivery nozzle arm shed  3  and two-fluid spray nozzle arm shed  4 .  
         [0061]     In this state, a wafer W is loaded, and then the front and back surfaces of the wafer W are simultaneously cleaned. For the sake of convenience, cleaning performed on the back surface of the wafer W will be first explained.  FIG. 4  is a flowchart for explaining an example of the sequence of a cleaning process for the back surface of the wafer W.  FIGS. 5A  to  5 E are schematic views for explaining the process state in main steps in performing the sequence shown in  FIG. 4 .  
         [0062]     At first, the wafer W is transferred by the transfer arm (not shown) onto the support pins  44   a  disposed on the spin chuck  12  (Step  1 ). After the wafer W is supported on the support pin  44   a  and the transfer arm is moved out of the outer chamber  2 , the first shutter  15  and second shutter  17  are closed, and the inner cup  11  is moved up to the process position. At this time, the under plate  13  is set at a position to make a gap of 4 mm or more, such as 10 mm or more, between the wafer W and the under plate  13 , so as not to obstruct the loading of the wafer W by the under plate  13 .  
         [0063]     Then, as shown in  FIG. 5A , the under plate  13  is moved up to a position adjacent to the back surface of the wafer W held by the spin chuck  12  (Step  2 ). At this time, the gap between the wafer W and the under plate  13  is set to be 0.5 to 3 mm, such as 0.8 mm. In light of chemical liquid saving, the gap used at this time is preferably set to be as small as possible. Further, at this time, the wafer W is heated by the heater  33  to control the temperature. Also in light of this temperature control, the gap is preferably set to be as small as possible.  
         [0064]     Then, a predetermined chemical liquid used as a cleaning liquid is supplied into the gap between the wafer W and the under plate  13  through the chemical liquid supply line  62 , fluid supply line  61 , and back surface cleaning nozzle  50 . Consequently, as shown in  FIG. 5B , a puddle (liquid film) of the chemical liquid is formed on the back surface of the wafer W (Step  3 ). At this time, the wafer W may be set in a stationary state or may be rotated at a low speed of 100 rpm or less to swiftly spread the chemical liquid. Thus, a puddle  101  of the chemical liquid is formed in several seconds, such as 3 seconds. Then, the puddle  101  of the chemical liquid promotes cleaning on the back surface of the wafer W (Step  4 ). At this time, the wafer W may be set in a stationary state or may be rotated at a very low speed to agitate the chemical liquid. The time period of this chemical liquid cleaning process is arbitrarily set in accordance with the cleaning level.  
         [0065]     After the chemical liquid cleaning process is finished, purified water used as a rinsing liquid is supplied into the gap between the back surface of the wafer W and the under plate  13  through the purified water supply line  63 , fluid supply line  61 , and back surface cleaning nozzle  50  (Step  5 ). This step is performed, while the wafer W is rotated at a low speed of 10 to 100 rpm, such as 50 rpm. Consequently, as shown in  FIG. 5C , the chemical liquid of the puddle  101  between the back surface of the wafer W and the under plate  13  is partly or entirely replaced with purified water used as a rinsing liquid, and a liquid film  101   a  is thereby formed. This step is performed to replace the chemical liquid in the back surface cleaning nozzle  50  and the chemical liquid on the under plate  13  with purified water used as a rinsing liquid. Accordingly, this step needs to be performed only for a short time of several seconds, such as 2 seconds. This step is not indispensable, and the chemical liquid puddle  101  may be maintained as it is, if this step is not performed.  
         [0066]     Subsequently, while the wafer W is rotated at a low speed of 10 to 100 rpm, such as 50 rpm, N 2  gas is supplied in the gap between the wafer W and the under plate  13  through the N 2  gas line  66 , fluid supply line  61 , and back surface cleaning nozzle  50 . Consequently, the liquid film formed in the gap (the liquid film  101   a  formed by partly or entirely replacing the chemical liquid with purified water, or the chemical liquid puddle  101  not replaced with purified water) is broken by N 2  gas thus supplied into the liquid film (Step  6 ). At this time, as shown in  FIG. 5D , the liquid filling the gap between the wafer W and the under plate  13  is partly spilled out of this gap, and the liquid is thereby mixed with gas  102 . This step needs to be performed also only for a short time of 1 to 5 seconds, such as 3 seconds.  
         [0067]     At this time, there may be a case where the gas pressure inside the N 2  gas line  66  is too high. In this case, when the valve  67  is opened, N 2  gas is rapidly supplied into the gap between the wafer W and the under plate  13 , and causes a problem such that the wafer W is raised or the like. In order to prevent such a problem, the switching valve  71   a  of the release line  71  is preferably opened in advance to release the pressure inside the N 2  gas supply line  66  in Step  5 .  
         [0068]     Then, while N 2  gas is kept supplied and the wafer W is kept rotated at a low speed, the under plate  13  is moved down to expand the gap between the wafer W and the under plate  13  to 1.5 to 4 mm, such as 1.5 mm, as shown in  FIG. 5E  (Step  7 ). The liquid film formed in the gas between the wafer W and the under plate  13  has been broken by N 2  gas supplied in Step  6  and mixed with N 2  gas. Further, at this time, air enters the liquid film from outside. Consequently, the wafer W is never stuck on the under plate  13 , and the wafer W is thereby prevented from suffering warp and/or crack generation.  
         [0069]     Subsequently, while N 2  gas is kept supplied, the rotation number of the wafer W is increased to 300 rpm or more, such as 1,000 rpm (Step  8 ). Consequently, the liquid droplets remaining between the wafer W and the under plate  13  are thrown off. At this time, the rotation number of the wafer W should be not too high, because, if the rotation number of the wafer W is too high, the wafer W is stuck on the under plate  13 . Each of Steps  6  and  7  needs to be performed also only for a short time of several seconds, such as 2 seconds for Step  6  and 3 seconds for Step  7 .  
         [0070]     Thereafter, while the gap between the wafer W and the under plate  13  and the rotation number of the wafer W are maintained, supply of N 2  gas is stopped, and purified water used as a rinsing liquid is supplied into the gap between the wafer W and the under plate  13  through the purified water supply line  63 , fluid supply line  61 , and back surface cleaning nozzle  50  (Step  9 ). At this time, purified water is supplied to collide with the back surface of the wafer W and thereby spread, so that the purified water is not stagnated between the wafer W and the under plate  13 .  
         [0071]     Thereafter, supply of purified water is stopped, and the under plate  13  is further moved down to expand the gap between the wafer W and the under plate  13  to 4 mm or more, such as 10 mm. Further, the rotation number of the wafer W is set to be 300 rpm or more, such as 1,000 rpm, to perform throwing-off and drying (Step  10 ). At this time, N 2  gas may be supplied to promote drying.  
         [0072]     Thereafter, while the gap between the wafer W and the under plate  13  is maintained at 4 mm or more, such as 10 mm, the transfer arm (not shown) is inserted to a position below the wafer W, and then receives the wafer W (Step  11 ).  
         [0073]     Thus, the back surface cleaning process is finished. Table 1 shows a typical example of the sequence of the back surface cleaning process described above.  
                                                                                                                           TABLE 1                                       Step                        3           6                               1       Formation           Breaking       8           11           Transfer       of   4   5   of liquid       Increase   9       Transfer           by   2   chemical   Chemical   Purified   film on   7   in wafer   Purified   10   by           transfer   Setting   liquid   liquid   water   back   Expanding   rotation   water   Spin-   transfer           arm   of gap   puddle   process   rinsing   surface   of gap   number   rinsing   drying   arm                        Wafer   0 rpm   0 rpm   100 rpm˜0 rm   0 rpm   50 rpm   50 rpm   50 rpm   50         1000 rpm   1000 rpm   1000 rpm   0 rpm       rotation       number       Processing   —   —   About 3   Arbitrary   2 seconds   3 seconds   2 seconds   3 seconds   20 seconds   30 seconds   —       time           seconds   value       Chemical   —   —   Delivery   Chemical   Purified   N 2     N 2     N 2     Purified   —   —       liquid           of   liquid   water               water       nozzle for           chemical   (stop)       back           liquid       surface       Position   Gap   Gap   Gap   Gap   Gap   Gap   Gap   Gap   Gap   Gap   Gap       of under   10 mm   0.8 mm   0.8 mm   0.8 mm   0.8 mm   0.8 mm   1.5 mm   1.5 mm   1.5 mm   10 mm   10 mm       plate                  
 
         [0074]     While the back surface of the wafer W is subjected to the cleaning described above, the front surface of the wafer W is simultaneously subjected to cleaning.  FIG. 6  is a flowchart showing a cleaning process for the front surface of the wafer, in relation to the cleaning process for the back surface shown in  FIG. 4 . As shown in  FIG. 6 , at first, the liquid delivery nozzle arm  31  is moved into the outer chamber  2 , so that the liquid delivery nozzle  51  is positioned above the center of the front surface of the wafer W (Step  21 ).  
         [0075]     Then, when the chemical liquid puddle is formed on the back surface of the wafer W in Step  2 , and the back surface cleaning process is performed by the chemical liquid in Step  3 , a chemical liquid is supplied onto the front surface of the wafer W through the chemical liquid supply line  73 , liquid supply line  72 , and liquid delivery nozzle  51 , to perform a cleaning process (Step  22 ). At this time, a predetermined amount of chemical liquid may be supplied onto the front surface of the wafer W to form a puddle (liquid film) to promote the cleaning process. Alternatively, where the back surface cleaning is performed while the wafer W is rotated at a low speed, the front surface cleaning may be performed while the chemical liquid is in a flowing state.  
         [0076]     After the chemical liquid cleaning process is finished, purified water is supplied onto the front surface of the wafer W through the purified water supply line  73 , liquid supply line  72 , and liquid delivery nozzle  51 , to perform a rinsing process (Step  23 ), at the timing when Steps  4  to  7  of the back surface cleaning are performed.  
         [0077]     While Step  23  is being performed, the two-fluid spray nozzle arm  32  is moved into the outer chamber  2 , so that the two-fluid spray nozzle  52  is put in waiting above the liquid delivery nozzle  51  (Step  24 ).  
         [0078]     Then, at the timing when the wafer starts being rotated at a high speed in Step  8  after the liquid film on the back surface is broken and the gap is expanded, the liquid delivery nozzle  51  is retreated. Further, the two-fluid spray nozzle  52  is moved down to perform two-fluid spray cleaning on the front surface of the wafer W (Step  25 ). In this two-fluid spray cleaning, two fluids, i.e., atomized purified water and N 2  gas, are sprayed from the two-fluid spray nozzle  52  and supplied onto the front surface of the wafer W. Consequently, particles and so forth present on the front surface can be removed very efficiently.  
         [0079]     Thereafter, at the timing when the throwing-off and drying of the back surface cleaning starts in Step  10 , supply of the two-fluid spray is stopped to perform throwing-off and drying also on the front surface (Step  26 ).  
         [0080]     As described above, when the chemical liquid puddle is broken and the gap is expanded while the wafer is rotated at a low speed after the chemical liquid cleaning in the back surface cleaning, purified water is supplied onto the front surface of the wafer W to perform rinsing and to prevent drying. Then, at the timing when the wafer W is rotated at a high speed, the wafer front surface is cleaned by the two-fluid spray. Consequently, the front surface cleaning can be performed under suitable conditions, which are also suitable for the back surface cleaning.  
         [0081]     Next, an explanation will be given of a second example of a cleaning process performed in the cleaning apparatus described above. At first, as in the first example, the following state is set up. Specifically, the first shutter  15  of the housing  1  and the second shutter  17  of the outer chamber  2  are opened. The inner cup  11  is set in the retreat position, and the under plate  13  is put in waiting at a position adjacent to the rotary plate  41 . Further, the liquid delivery nozzle arm  31  and two-fluid spray nozzle arm  32  are respectively stored in the liquid delivery nozzle arm shed  3  and two-fluid spray nozzle arm shed  4 .  
         [0082]     In this state, a wafer W is loaded, and then the front and back surfaces of the wafer W are simultaneously cleaned. For the sake of convenience, cleaning performed on the back surface of the wafer W will be first explained.  FIG. 7  is a flowchart for explaining an example of the sequence of a cleaning process for the back surface of the wafer W.  FIGS. 8A  to  8 E are schematic views for explaining the process state in main steps in performing the sequence shown in  FIG. 7 .  
         [0083]     At first, the wafer W is transferred by the transfer arm (not shown) onto the support pins  44   a  disposed on the spin chuck  12  (Step  31 ). After the wafer W is supported on the support pin  44   a  and the transfer arm is moved out of the outer chamber  2 , the first shutter  15  and second shutter  17  are closed, and the inner cup  11  is moved up to the process position. At this time, the under plate  13  is set at a position to make a gap of 4 mm or more, such as 10 mm or more, between the wafer W and the under plate  13 , so as not to obstruct the loading of the wafer W by the under plate  13 .  
         [0084]     Then, as shown in  FIG. 8A , the under plate  13  is moved up to a position adjacent to the back surface of the wafer W held by the spin chuck  12  (Step  32 ). At this time, the gap between the wafer W and the under plate  13  is set to be 0.5 to 3 mm, such as 0.8 mm. In light of chemical liquid saving, the gap used at this time is preferably set to be as small as possible. Further, at this time, the wafer W is heated by the heater  33  to control the temperature. Also in light of this temperature control, the gap is preferably set to be as small as possible.  
         [0085]     Then, a predetermined chemical liquid used as a cleaning liquid is supplied into the gap between the wafer W and the under plate  13  through the chemical liquid supply line  62 , fluid supply line  61 , and back surface cleaning nozzle  50 . Consequently, as shown in  FIG. 8B , a puddle (liquid film) of the chemical liquid is formed on the back surface of the wafer W (Step  33 ). At this time, the wafer W may be set in a stationary state or may be rotated at a low speed of 100 rpm or less to swiftly spread the chemical liquid. Thus, a puddle  101  of the chemical liquid is formed in several seconds, such as 3 seconds. Then, the puddle  101  of the chemical liquid promotes cleaning on the back surface of the wafer W (Step  34 ). At this time, the wafer W may be set in a stationary state or may be rotated at a very low speed to agitate the chemical liquid. The time period of this chemical liquid cleaning process is arbitrarily set in accordance with the cleaning level.  
         [0086]     After the chemical liquid cleaning process is finished, the under plate  13  is moved down to expand the gap between the wafer W and the under plate  13 . Simultaneously, purified water used as a rinsing liquid is supplied into the gap between the wafer W and the under plate  13  through the purified water supply line  63 , fluid supply line  61 , and back surface cleaning nozzle  50 , so as to break the liquid film (Step  35 ). At this time, the purified water is supplied to follow the change of the gap, so that the amount of purified water reaches a value equal to or more than an increase in the volume of the gap. In this case, when the gap between the wafer W and the under plate  13  is expanded to 3 mm or more, such as 4 mm, the liquid film is broken. This step is performed, while the wafer W is rotated at a low speed of 10 to 100 rpm, such as 50 rpm.  
         [0087]     According to this step, as shown in  FIG. 8C , when the gap between the wafer W and the under plate  13  is expanded, purified water is supplied to follow the change of the gap. In this case, the gap can maintain a state of being filled with a puddle  101   a  formed of a mixture of the chemical liquid and purified water. Consequently, the gap does not fall into a vacuum state, and the wafer W is thereby prevented from being stuck on the under plate  13  and thus prevented from suffering warp and/or crack generation. When the gap is expanded to the distance described above, as shown in  FIG. 8D , air gradually flows into the gap from outside, so gas  102  is mixed into the liquid and the puddle (liquid film) is broken. Once the puddle (liquid film) is broken, another puddle cannot be formed in the gap thereafter, and thus the rotation number can be increased for the subsequent step. Step  35  is preformed for about 5 to 15 seconds, such as 10 seconds.  
         [0088]     Subsequently, while the rotation number of the wafer W is increased to 300 rpm or more, such as 1,000 rpm, the gap between the wafer W and the under plate  13  is further expanded to 4 mm or more, such as 10 mm. Consequently, as shown in  FIG. 8E , the liquid film is removed from the gap between the wafer W and the under plate  13  (Step  36 ). Step  36  needs to be performed only for a short time of several seconds, such as 3 seconds.  
         [0089]     Thereafter, while the gap between the wafer W and the under plate  13  is maintained and the rotation number of the wafer W is maintained at 300 rpm or more, such as 1,000 rpm, purified water used as a rinsing liquid is supplied into the gap between the wafer W and the under plate  13  to perform a rinsing process (Step  37 ). At this time, purified water is supplied to collide with the back surface of the wafer W and thereby spread, so that the purified water is not stagnated between the wafer W and the under plate  13 .  
         [0090]     Thereafter, while supply of purified water is stopped, and the gap between the wafer W and the under plate  13  is maintained, the rotation number of the wafer W is set to be 300 rpm or more, such as 1,000 rpm, to perform throwing-off and drying (Step  38 ). At this time, N 2  gas may be supplied to promote drying.  
         [0091]     Thereafter, while the gap between the wafer W and the under plate  13  is maintained at 4 mm or more, such as 10 mm, the transfer arm (not shown) is inserted to a position below the wafer W, and then receives the wafer W (Step  39 ).  
         [0092]     Thus, the back surface cleaning process is finished. Table 2 shows a typical example of the sequence of the back surface cleaning process described above.  
                                                                                                           TABLE 2                                       Step                                35                                   33       Purified           31       Formation       water   36           Transfer       of   34   rinsing at   Increase           by   32   chemical   Chemical   low speed   in wafer   37       39           transfer   Setting   liquid   liquid   (expanding   rotation   Rinsing   38   Transfer by           arm   of gap   puddle   process   of gap)   number   process   Spin-drying   transfer arm                        Wafer   0 rpm   0 rpm   100 rpm˜0 rm   0 rpm   50 rpm   50         1000 rpm   1000 rpm   1000 rpm   0 rpm       rotation       number       Processing   —   —   About 3   Arbitrary   10 seconds   3 seconds   Arbitrary   30 seconds   —       time           seconds   value           value       Chemical   —   —   Delivery   stop   Purified   Purified   Purified   —   —       liquid           of       water   water   water       nozzle for           chemical       back           liquid       surface       Gap   10 mm   0.88 mm   0.8 mm   0.8mm   0.8 mm         4 mm   4 mm         10 mm   10 mm   10 mm   10 mm                  
 
         [0093]     While the back surface of the wafer W is subjected to the cleaning described above, the front surface of the wafer W is simultaneously subjected to cleaning.  FIG. 9  is a flowchart showing a cleaning process for the front surface of the wafer, in relation to the cleaning process for the back surface shown in  FIG. 7 . As shown in  FIG. 9 , at first, the liquid delivery nozzle arm  31  is moved into the outer chamber  2 , so that the liquid delivery nozzle  51  is positioned above the center of the front surface of the wafer W (Step  41 ).  
         [0094]     Then, when the chemical liquid puddle is formed on the back surface of the wafer W in Step  32 , and the back surface cleaning process is performed by the chemical liquid in Step  33 , a chemical liquid is supplied onto the front surface of the wafer W through the chemical liquid supply line  73 , liquid supply line  72 , and liquid delivery nozzle  51 , to perform a cleaning process (Step  42 ). At this time, a predetermined amount of chemical liquid may be supplied onto the front surface of the wafer W to form a puddle (liquid film) to promote the cleaning process. Alternatively, where the back surface cleaning is performed while the wafer W is rotated at a low speed, the front surface cleaning may be performed while the chemical liquid is in a flowing state.  
         [0095]     After the chemical liquid cleaning process is finished, purified water is supplied onto the front surface of the wafer W through the purified water supply line  73 , liquid supply line  72 , and liquid delivery nozzle  51 , to perform a rinsing process (Step  43 ), at the timing when Steps  34  to  35  of the back surface cleaning are performed.  
         [0096]     While Step  43  is being performed, the two-fluid spray nozzle arm  32  is moved into the outer chamber  2 , so that the two-fluid spray nozzle  52  is put in waiting above the liquid delivery nozzle  51  (Step  44 ).  
         [0097]     Then, at the timing when the wafer starts being rotated at a high speed in Step  36 , the liquid delivery nozzle  51  is retreated. Further, the two-fluid spray nozzle  52  is moved down to perform two-fluid spray cleaning on the front surface of the wafer W (Step  45 ). In this two-fluid spray cleaning, two fluids, i.e., atomized purified water and N 2  gas, are sprayed from the two-fluid spray nozzle  52  and supplied onto the front surface of the wafer W. Consequently, particles and so forth present on the front surface can be removed very efficiently.  
         [0098]     Thereafter, at the timing when the throwing-off and drying of the back surface cleaning starts in Step  38 , supply of the two-fluid spray is stopped to perform throwing-off and drying also on the front surface (Step  46 ).  
         [0099]     As described above, when the gap is expanded while the wafer is rotated at a low speed after the chemical liquid cleaning in the back surface cleaning, purified water is supplied onto the front surface of the wafer W to perform rinsing and to prevent drying. Then, at the timing when the wafer W is rotated at a high speed, the wafer front surface is cleaned by the two-fluid spray. Consequently, the front surface cleaning can be performed under suitable conditions, which are also suitable for the back surface cleaning.  
         [0100]     In the embodiment described above, the under plate  13  is disposed in association with the back surface of the wafer W to form a puddle between the back surface of the wafer W and the under plate  13 . Similarly, as shown in  FIG. 10 , a top plate  103  may be disposed above a wafer W to form a chemical liquid puddle between the front surface of the wafer W and the top plate  103 .  
         [0101]     A detailed explanation will be given of this structure, with reference to  FIG. 10 . The top plate  103  is connected to the lower end of a rotary shaft  104  extending downward inside the outer chamber  2  from above the outer chamber  2 . The rotary shaft  104  is rotatably supported at the upper end by a horizontal plate  105 . The horizontal plate  105  is arranged to be moved up and down by an elevating mechanism  106 , such as an air cylinder, fixed to the top wall of the outer chamber  2 . The top plate  103  is movable up and down by the elevating mechanism  106  through the horizontal plate  105  and rotary shaft  104 . A belt  107  is wound around the rotary shaft  104 , and is arranged to be driven by a motor  108 . When the belt  107  is driven by the motor  108 , the top plate  103  is rotated through the rotary shaft  104 . Although the top plate  103  is not necessarily required to be rotatable, this arrangement is effective in a case where a relative movement between the wafer W and top plate is required in the front surface cleaning while the wafer W needs to be stationary in the back surface cleaning.  
         [0102]     A front surface cleaning nozzle  110  is formed in the horizontal plate  105 , rotary shaft  104 , and top plate  103  to extend therethrough. The front surface cleaning nozzle  110  is connected to a fluid supply line  111 . The fluid supply line  111  is connected to a chemical liquid supply line  112  and a purified water supply line  113  respectively through valves  114  and  115 , so as to supply a chemical liquid used as a cleaning liquid and purified water used as a rinsing liquid onto the front surface of the wafer W. The fluid supply line  111  is connected, through a valve  117  disposed on the way, to an N 2  gas supply line  116  for supplying a N 2  gas. Since the N 2  gas supply line  116  is arranged to be the same as the N 2  gas supply line  66 , the structure thereof will not explained in detail.  
         [0103]     With this arrangement, while the top plate  103  is set to be adjacent to the front surface of the wafer W, a chemical liquid is supplied into the gap between the front surface of the wafer W and the top plate  103 . Consequently, a puddle (liquid film) of the chemical liquid is formed in the gap and promotes the cleaning process. Thus, a series of processes can be performed in the same sequence as that of the cleaning for the back surface of the wafer W. Namely, a chemical liquid puddle is formed, then a chemical liquid cleaning process is performed, then the chemical liquid puddle is broken, then the top plate is separated, then a rinsing process is performed, and then a drying process is performed. However, since the wafer front surface requires high cleanliness, two-fluid spray cleaning is preferably performed as described above after the rinsing process. In this case, after the rinsing process, the top plate is retreated upward. Then, the two-fluid spray nozzle arm  32  is moved in the outer chamber  2 , and atomized purified water and N 2  gas are supplied from the two-fluid spray nozzle  52 .  
         [0104]     As described above, a cleaning process is performed on the front surface of the wafer W while a puddle (liquid film) is formed between the top plate and wafer W. However, also in this case, when the top plate is separated from the wafer W, the wafer W is prevented from being stuck on the top plate. Consequently, the wafer W is prevented from suffering warp and/or breakage generation.  
         [0105]     The present invention is not limited to the embodiments described above, and it may be modified in various manners. For example, in the embodiments described above, a method according to the present invention is used for cleaning the back surface or back and front surfaces of a wafer treated as a target substrate. Alternatively, a method according to the present invention may be used for cleaning only a front surface of a wafer treated as a target substrate.  
         [0106]     In the first example described above of a cleaning process according to the embodiments, N 2  gas is used as a gas for breaking a liquid film, but this is not limiting. A gas selected from other inactive gases, such as Ar gas, and other various gases may be used for this purpose, as long as it does not affect the liquid process.  
         [0107]     In the second example described above of a cleaning process according to the embodiments, purified water used as a rinsing liquid is utilized as a liquid for breaking the liquid film. However, another liquid may be used for this purpose, as long as it does not affect the substrate process.  
         [0108]     Further, in the embodiments described above, a semiconductor wafer is treated as a target substrate. However, the present invention may be applied to another substrate, such as a substrate for a flat panel display (FPD), representative of which is a glass substrate for a liquid crystal display (LCD).  
         [0109]     Furthermore, in the embodiments described above, the present invention is applied to a cleaning process. However, the present invention may be applied to another liquid process.