Abstract:
In a substrate treatment method for supplying a coating solution to a substrate with projections and depressions on a front surface thereof to form a coating film on the front surface of the substrate, the coating solution is supplied to the rotating substrate to form a coating film on the front surface of the substrate, and the substrate having the coating film formed thereon is heated to adjust an etching condition of the coating film. Next, the etching solution is supplied to the rotating substrate to etch the coating film, and thereafter the coating solution is supplied to the substrate to form a flat coating film on the front surface of the substrate. Thereafter, the substrate is heated to cure the coating film. This flattens the coating film with uniformity and high accuracy without undergoing a high-load process such as chemical mechanical polishing.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. Ser. No. 11/562,909, filed Nov. 22, 2006, the entire contents of which is incorporated herein by reference. U.S. Ser. No. 11/562,909 claims the benefit of priority under 35 U.S.C. §119(e) of U.S. Provisional Application No. 60/830,120, filed Jul. 12, 2006, and claims the benefit of priority under 35 U.S.C. §119 from Japanese Patent Application Nos. 2005-338114, filed on Nov. 24, 2005 and 2006-183981, filed on Jul. 4, 2006. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a substrate treatment method and a substrate treatment apparatus and, more specifically, to a substrate treatment method of applying a coating solution to a substrate, for example, a semiconductor wafer, an LCD substrate and the like to form a coating film on the front surface of the substrate and an apparatus therefor. 
     2. Description of the Related Art 
     Conventionally, a technology of forming multilayer wiring on the substrate is employed with an increase in integration of semiconductor devices, in which a silicon oxide film-based glass that is referred to as SOG (Spin On Glass) is used as a film for insulating wirings in the multilayer wiring, that is, circuit patterns from each other. 
     The method of forming the SOG film is generally a method of applying a glass component molten in an organic solvent onto the substrate by a spin-coat method, and drying and burning it by thermal treatment such as baking or curing to bond the glass component thereto, thus forming a film. 
     However, a circuit pattern with projections and depressions is formed on the front surface of the substrate, and therefore when a typical spin coating method and thermal drying are performed, unevenness in shape of the film surface following the shape of level differences of the projections and depressions occurs, causing problems in subsequent process steps. The problems are, for example, that for lithography, if performed, various poor conditions are caused, such as degradation in line width (CD) due to an increased focal depth, an increase in level difference with stacking of films and so on. 
     Hence, there is a need to flatten the coating film. As the method of flattening the coating film, a chemical mechanical polishing (CMP) technology is known in which after the coating film is cured by thermal treatment, a polishing solution containing mechanical polishing particles and chemical polishing particles is then dropped onto the surface of a polishing cloth being a polishing member, and the surface of the polishing cloth is pressed against the coating film on the substrate to remove a part of the coating film. 
     Besides, as another flattening method without undergoing the high-load process such as CMP, a coating method and apparatus are known in which a coating solution is supplied to the substrate surface having an uneven surface so that a coating film is spread out to be thin over the surface of the substrate by a scanner plate, and an air pressure from a nozzle in a slit form is used to evenly press it (see Claims and FIG. 1, FIG. 2, and FIG. 4 in Japanese Patent Application Laid-open No. Hei 7-47324). As still another means, a coating method and apparatus are known in which a coating solution is supplied to the surface of the substrate, a gas containing a solvent vapor is then supplied to thereby make the coating film thin and even (see paragraph number 0142 and FIG. 8 and FIG. 13 in Japanese Patent Application Laid-open No. Hei 11-329938). 
     SUMMARY OF THE INVENTION 
     However, the technology described in Japanese Patent Application Laid-open No. Hei 7-47324 has a problem. The problem is that since air is blown to the coating solution, the coating solution evaporates to harden, resulting in a decrease in flowability to fail to sufficiently uniformize the coating film. 
     In the technology described in Japanese Patent Application Laid-open No. Hei 11-329938, evaporation of the coating solution can be suppressed more as compared to the former technology since the solvent vapor is sent to the coating solution, but the coating solution evaporates to harden as in the former technology due to influence of the surrounding environment in the treatment section, resulting in a decrease in flowability. Accordingly, this technology also has a problem of the coating film being not sufficiently uniformized. 
     The present invention has been developed in consideration of the above circumstances, and its object is to flatten the coating film with uniformity and high accuracy without undergoing a high-load process such as CMP. 
     In order to attain the above object, the present invention includes: a first coating step of supplying a coating solution to the substrate with projections and depressions on the front surface thereof to form a coating film on the front surface of the substrate; a first drying step of heating the substrate having the coating film formed thereon to adjust an etching condition of the coating film; an etching step of supplying an etching solution for etching the coating film formed on the substrate to etch the coating film; a second coating step of supplying the coating solution to the substrate to form a flat coating film on the front surface of the substrate; and after the second coating step, a second drying step of heating the substrate to cure the coating film. 
     According to the present invention, it is possible that after the coating film is formed on the front surface of the substrate with projections and depressions on the front surface, the substrate is heated to adjust the etching conditions of the coating film, such as the etching amount, the etching time, and so on, the etching solution is used to etch the coating film in the etching step so as to remove the excessive film, thereafter the coating solution is supplied again onto the etched coating film to form a flat coating film, and the substrate is heated to cure (bake) the coating film. 
     After the second drying step, the second coating step and second drying step are repeatedly performed, thereby making it possible to stack the cured coating films one on the other and to further decrease the level difference on the front surface of the coating film. In such a viewpoint, the first coating step, first drying step, etching step, second coating step, and second drying step may be repeatedly performed. 
     After each of the first drying step and second drying step, a cooling step of cooling the substrate may be provided. This can rapidly lower the temperature of the substrate which has been at a high temperature in the first drying step and second drying step to an optimum temperature for the etching step being a subsequent step. 
     In the substrate treatment method, when the first coating step, first drying step, etching step, second coating step, and second drying step are repeatedly performed, a plurality of the substrates for which treatments for the first time have been finished may be temporarily housed in a buffer unit in sequence, and after the first coating step for the last substrate in a lot is finished, treatments for the second time for the substrates sequentially carried out of the buffer unit may be started. 
     In the first and second coating steps, the coating solution may be supplied to the front surface of the substrate with the substrate being horizontally rotated, and in the etching step, the etching solution may be supplied to the front surface of the substrate with the substrate being horizontally rotated. This makes it possible to uniformly form the coating film on the entire front surface of the substrate in the first coating step, to etch the coating film uniformly in the horizontal direction and in the depth direction in the etching step, and to uniformly form the coating film on the front surface of the etched coating film in the second coating step. 
     In the first drying step and second drying step, the substrate may be horizontally rotated, and a drying gas may be supplied to the substrate. This allows a centrifugal force caused by the rotation of the substrate to remove the etching solution served for the treatment and the supply of the drying gas to dry the substrate. 
     In the present invention, the temperature of the etching solution is preferably adjusted, for example, to 20° C. to 50° C. Further, as the etching solution, one of a solvent for the coating solution, a hydrofluoric acid solution, an acid solution and an alkaline solution can be used. 
     According to another aspect, a substrate treatment apparatus of the present invention includes: a holding means for holding the substrate to be horizontally rotatable; a coating solution supply nozzle for supplying the coating solution to the substrate held by the holding means; an etching solution supply nozzle for supplying an etching solution for etching the coating film formed on the substrate held by the holding means; a heating means for heating the substrate; a temperature adjusting means for adjusting the temperature of the heating means; and a control means for conducting rotation control of the holding means, supply control of the coating solution supply nozzle and etching solution supply nozzle, and temperature control of the temperature adjusting means. The control means executes a step of supplying the coating solution to the substrate rotated by the holding means to form a coating film on the front surface of the substrate, thereafter a step of heating the substrate having the coating film formed thereon to adjust an etching condition of the coating film, a step of supplying the etching solution to the substrate to etch the coating film, thereafter a step of supplying the coating solution to the substrate to form a flat coating film on the front surface of the substrate, and then a step of heating the substrate to cure the coating film. In this case, the heating means may be embedded in the holding means. The substrate treatment apparatus may further include a cooling means for cooling the substrate. 
     According to still another aspect, the substrate treatment apparatus of the present invention is a substrate treatment apparatus for supplying a coating solution to a substrate with projections and depressions on a front surface thereof to form a coating film on the front surface of the substrate, including: a coating unit for forming the coating film on the front surface of the substrate; an etching unit for etching the coating film formed on the substrate; a heating unit having a heating means for heating the substrate; a temperature adjusting means for adjusting the temperature of the heating means; a cooling unit having a cooling means for cooling the substrate; a carrier unit for carrying-in/out the substrate between the coating unit, etching unit, heating unit, and cooling unit; and a control means for controlling the units and the temperature adjusting means. The coating unit includes a holding means for holding the substrate to be horizontally rotatable and a coating solution supply nozzle for supplying the coating solution to the substrate held by the holding means, and the etching unit includes a holding means for holding the substrate to be horizontally rotatable and an etching solution supply nozzle for supplying an etching solution for etching the coating film formed on the substrate. The control means executes a step of supplying the coating solution to the substrate rotated by the holding means of the coating unit to form a coating film on the front surface of the substrate, a step of heating the substrate having the coating film formed thereon to adjust an etching condition of the coating film, a step of supplying the etching solution to the substrate to etch the coating film, a step of supplying the coating solution to the substrate to form a flat coating film on the front surface of the substrate, and then a step of heating the substrate to cure the coating film. 
     In this case, the etching unit may further have a cleaning solution supply nozzle for supplying a cleaning solution for suppressing etching to the substrate. Further, the coating unit has an etching solution supply nozzle for supplying an etching solution for etching the coating film formed on the substrate. 
     The substrate treatment apparatus may further include a buffer unit to/from which the carrier unit is capable of delivering and receiving the substrate, and which is capable of housing a plurality of the substrates. Further, in the substrate treatment apparatus, the etching unit may have a drying gas supply nozzle for supplying a drying gas to the substrate. 
     Further, in the substrate treatment apparatus, the etching unit may be composed of a plurality of units capable of supplying different kinds of etching solutions different from each other so that the etching unit selected according to a condition of the film thickness or the like of the coating film is usable. This makes it possible to etch the coating film using a most suitable etching solution for the condition of the film thickness or the like of the coating film. 
     Further, in the substrate treatment apparatus, the etching unit may have a temperature adjusting means for adjusting the temperature of the etching solution to a predetermined temperature, the temperature adjusting means being provided along a supply pipe connecting an etching solution supply source and the etching solution supply nozzle. 
     Further, the etching unit may include a concentration adjusting means for adjusting the concentration of the etching solution to a predetermined concentration. As the etching solution, for example, one of a solvent for the coating solution, a hydrofluoric acid solution, an acid solution and an alkaline solution can be used. 
     As described above, according to the present invention, the coating film can be formed with its initial level difference due to projections and repressions being made small within an allowable range, so that the coating film can be flattened with uniformity and high accuracy. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic side view showing a first embodiment of a substrate treatment apparatus according to the present invention; 
         FIG. 2A  to  FIG. 2C  are enlarged cross-sectional views of a main part each showing a film formation state of a coating film in the first embodiment of a substrate treatment method according to the present invention; 
         FIG. 3A  to  FIG. 3F  are schematic perspective views each showing each step in the present invention; 
         FIG. 4  is a flowchart showing a procedure of film formation of a coating film in the first embodiment of the substrate treatment method according to the present invention; 
         FIG. 5  is a graph showing the relation between the etching amount of a solvent and the heating time in the present invention; 
         FIG. 6  is a flowchart showing a procedure of film formation of the coating film in a second embodiment of the substrate treatment method according to the present invention; 
         FIG. 7A  to  FIG. 7D  are enlarged cross-sectional views of a main part each showing a film formation state of the coating film in the second embodiment of the substrate treatment method according to the present invention; 
         FIG. 8  is a flowchart showing a procedure of film formation of the coating film in a third embodiment of the substrate treatment method according to the present invention; 
         FIG. 9A  to  FIG. 9F  are enlarged cross-sectional views of a main part each showing a film formation state of the coating film in the third embodiment of the substrate treatment method according to the present invention; 
         FIG. 10  is a schematic cross-sectional view showing a second embodiment of the substrate treatment apparatus according to the present invention; 
         FIG. 11A  to  FIG. 11E  are schematic perspective views each showing each step when the substrate treatment apparatus shown in  FIG. 10  is used; 
         FIG. 12A  is a schematic plan view showing an example of a substrate processing system including the substrate treatment apparatus according to the present invention,  FIG. 12B  is a schematic side view showing a first unit group in the substrate processing system, and  FIG. 12C  is a schematic side view showing a second unit group; 
         FIG. 13  is a schematic cross-sectional view showing an example of an etching unit in the present invention; 
         FIG. 14  is a flowchart showing a procedure of film formation of the coating film in a fourth embodiment of the substrate treatment method according to the present invention; and 
         FIG. 15  is a flowchart showing a procedure of film formation of the coating film in a fifth embodiment of the substrate treatment method according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. A case will be described now in which the substrate treatment method according to the present invention is applied to the SOG film forming method for a semiconductor wafer. 
       FIG. 1  is a schematic cross-sectional view showing a first embodiment of a substrate treatment apparatus according to the present invention. The substrate treatment apparatus includes a spin chuck  10  that is a rotating and holding means for holding and horizontally rotating a semiconductor wafer W (hereinafter, referred to as a wafer W) that is a substrate having an uneven surface, a heating means  20  for heating the wafer W to a predetermined temperature, a cooling means  22  for cooling the wafer W heated by the heating means  20 , a coating solution supply nozzle  30  for dropping (supplying) an SOG solution, such as polysilazane that is a coating solution onto the front surface of the wafer W, and a solvent supply nozzle  40  for dropping (supplying) a solvent for the coating solution (SOG) as an etching solution, such as dibutyl ether onto the front surface of the wafer W. 
     The spin chuck  10  is housed in a cup  50  composed of an outer cup  51  capable of rising and lowering and an inner cup  52 , and coupled to a motor  12  via a rotation axis  11  passing through a bottom portion  53  of the inner cup  52  in a manner to be able to rise and lower. The motor  12  rotates at a predetermined number of rotations based on a control signal from a controller  60  constituted by a control means, for example, a central processing unit (CPU). The spin chuck  10  is also configured to be able to rise and lower by means of a not-shown raising and lowering means. The spin chuck  10  is configured to receive the wafer W from a carrier arm (not shown) being a carrier unit moved to a position above the spin chuck  10 , which is movable in a horizontal X-Y direction and a vertical Z-direction and horizontally rotatable, hold the wafer W thereon by suction, and pass the wafer W to the carrier arm raised and moved to the position above the spin chuck  10  after a later-described treatment for a coating film is finished. Note that the carrier arm is controlled by the controller  60 . 
     The heating means  20  is composed of a hot plate incorporating a heater  20   a  disposed in a heating unit  200  located outside a coating unit  100  in which the spin chuck  10  and the cup  50  are disposed, and connected to a temperature adjuster  21  that is a temperature adjusting means. The heating means  20  is configured to be set a predetermined temperature, that is, a temperature to adjust etching conditions, for example, 150° C. and a temperature to cure (bake) the coating film, for example, 160° C. by the temperature adjuster  21  being controlled based on the control signal from the controller  60 . 
     In this case, the etching conditions can be appropriately selected from the relation between the etching amount and heating time (etching time). For example, when the solvent (dibutyl ether) for the coating solution (SOG) was discharged (dropped, supplied) to a central position of the wafer W for 10 seconds at 1 cc/sec, and the relation between the etching amount (nm) and the heating time (sec) under a condition of a heating temperature of 150° C. was evaluated, the result shown in  FIG. 5  was obtained. As can be seen from the evaluation result, if the heating time is long, etching no longer proceeds, whereas if the heating time is short, complete peeling occurs. The heating time is selected based on the evaluation result. For example, when a heating time of 120 (sec) is selected, the etching amount is 120 (nm), whereas when a heating time of 210 (sec) is selected, the etching amount is about 50 (nm). 
     The control of the etching amount can be conducted by the heating conditions such as the heating temperature, the heating time and so on, by the solvent conditions of the discharge amount (the drop amount, the supply amount), the discharge time and so on of the solvent, or by a combination of both the heating conditions and the solvent conditions. 
     The cooling means  22  is composed of a cooling plate incorporating a coolant pipe  22   a  disposed in a cooling unit  300  located under the heating unit  200 , and connected to a cooling temperature adjuster  23  that is a cooling temperature adjusting means. The cooling means  22  is set to lower the temperature of the wafer W heated by the heating means  20  to a predetermined temperature, for example, 23° C. by the cooling temperature adjuster  23  being controlled based on the control signal from the controller  60 . Note that the cooling means  22  may be provided beside the heating means  20 . 
     A carry-in/out port  400  for the wafer W is provided at the side of each of the coating unit  100 , the heating unit  200  and the cooling unit  300 , and can be opened/closed by a shutter  500  which is raised and lowered by a not-shown raising and lowering mechanism. Further, a not-shown carrier arm controlled by the controller  60  can deliver the wafer W between the coating unit  100 , the heating unit  200  and the cooling unit  300 . 
     On the other hand, the coating solution supply nozzle  30  is connected to a coating solution supply source  32  via a coating solution supply pipe  31  provided with an open/close valve V 1 . Besides, the solvent supply nozzle  40  is disposed adjacent to the coating solution supply nozzle  30  and connected to a solvent supply source  42  via a solvent solution supply pipe  41  provided with an open/close valve V 2 . Note that a temperature adjuster  80  that is a temperature adjusting means for adjusting the temperature of the coating solution and the solvent to a predetermined temperature, for example, 20° C. to 50° C. is provided along the coating solution supply pipe  31  and the solvent supply pipe  41 . The coating solution supply nozzle  30  and the solvent supply nozzle  40  are formed to be able to move, by means of a nozzle moving mechanism  70 , to a position above a central position of the spin chuck  10  and to a waiting position outside the cup  50 . In this case, the nozzle moving mechanism  70  moves the coating solution supply nozzle  30  and the solvent supply nozzle  40  to the position above the central position of the spin chuck  10  and to the waiting position outside the cup  50  based on the control signal from the controller  60 . 
     Next, the operational aspect of the substrate treatment apparatus according to the present invention configured as described above will be described with reference to  FIG. 1 ,  FIGS. 2A to 2C ,  FIGS. 3A to 3F , and the flowchart shown in  FIG. 4 . 
     First of all, an unprocessed wafer W is carried into the coating unit  100  and delivered to the spin chuck  10  by the not-shown carrier arm. The carrier arm then retracts, and the outer cup  51  rises. In this state, the open/close valve V 1  provided along the coating solution supply pipe  31  is opened based on the control signal from the controller  60 , and the motor  12  of the spin chuck  10  is driven. This allows the coating solution to be dropped (supplied) from the coating solution supply nozzle  30  onto the front surface of the wafer W rotating with the rotation of the spin chuck  10  as shown in  FIG. 3A  to form a coating film T of the coating solution with a level difference H on the front surface of the wafer W (see  FIG. 2A ) {first coating step: step S 4 - 1 }. After the formation of the coating film, the open/close valve V 1  is closed based on the control signal from the controller  60  and the motor  12  is stopped. 
     Next, the carrier arm receives the wafer W on the spin chuck  10  and delivers the wafer W onto the hot plate  20  being the heating means in the heating unit  200 . Based on the control signal from the controller  60 , the temperature adjuster  21  operates to raise the temperature of the heater  20   a  of the heating means  20  to, for example, 150° C. to heat the wafer W for a heating time selected in advance from  FIG. 5  to adjust the etching condition. This evaporates a part of liquid in the coating film T to slightly decrease the level difference in the coating film T as shown in  FIG. 3B  {first drying step: step S 4 - 2 }. 
     Next, the carrier arm receives the wafer W on the hot plate  20  and delivers the wafer W onto the cooling plate  22  being the cooling means in the cooling unit  300 . Based on the control signal from the controller  60 , the cooling temperature adjuster  23  operates to set the temperature of the coolant of the cooling means  22  to, for example, 23° C. to lower the temperature of the wafer W to 23° C. as shown in  FIG. 3C  {cooling step: step S 4 - 3 }. 
     Next, the carrier arm receives the wafer W on the cooling plate  22  and delivers the wafer W to the spin chuck  10  in the coating unit  100 . Based on the control signal from the controller  60 , the solvent supply nozzle  40  then moves to a position above the central portion of the wafer W, the open/close valve V 2  provided along the solvent supply pipe  41  is opened, and the motor  12  of the spin chuck  10  is driven. This allows the solvent to be dropped (supplied) from the solvent supply nozzle  40  onto the front surface of the wafer W rotating with the rotation of the spin chuck  10  as shown in  FIG. 3D  to isotropically etch the coating film T (see  FIG. 2B ) {etching step: step S 4 - 4 }. After the isotropic etching with the solvent, the solvent (etching solution) is shaken out. 
     After the etching treatment, based on the control signal from the controller  60 , the open/close valve V 2  is closed, while the coating solution supply nozzle  30  moves again to the position above the central portion of the wafer W. In this state, the open/close valve V 1  is opened based on the control signal from the controller  60 , the coating solution is dropped (supplied) from the coating solution supply nozzle  30  onto the front surface of the wafer W rotating with the rotation of the spin chuck  10  as shown in  FIG. 3E  to form a substantially flat coating film T with a small level difference h within an allowable range on the front surface of the wafer W (see  FIG. 2C ) {second coating step: step S 4 - 5 }. 
     After the coating film is formed as described above, based on the control signal from the controller  60 , the open/close valve V 1  is closed, and the motor  12  is stopped. The carrier arm then receives the wafer W on the spin chuck  10  and delivers the wafer W onto the hot plate  20  (heating means) in the heating unit  200 . Based on the control signal from the controller  60 , the temperature adjuster  21  operates to raise the temperature of the heater  20   a  to, for example, 160° C. to heat the wafer W to thereby cure (bake) the coating film as shown in  FIG. 3F  {second drying step: step S 4 - 6 }. 
     After the curing (baking) treatment of the coating film T is performed as described above, the outer cup  51  is lowered and the spin chuck  10  is raised to pass the wafer W to the carrier arm which moves to the position above the spin chuck  10 , so that the wafer W is carried out by the carrier arm from the substrate treatment apparatus. 
     While a case in which a flat coating film is formed on the front surface of the wafer W with projections and depressions through the first coating step, the first drying step, the cooling step, the etching step, the second coating step, and the second drying step has been described in the above embodiment, the second coating step and the second drying step may be repeatedly performed in order to further decrease the level difference in the coating film T. More specifically, as shown in  FIG. 6 , the first coating step (step S 6 - 1 ), the first drying step (step S 6 - 2 ), the first cooling step (step S 6 - 3 ), the etching step (step S 6 - 4 ), the second coating step (step S 6 - 5 ), the second drying step (step S 6 - 6 ), and the second cooling step (step S 6 - 7 ) are performed as in the first embodiment to form a coating film T with a level difference h smaller than the level difference H in the initial coating film T, as shown in  FIG. 7C , and thereafter the second coating step for the second time (step S 6 - 8 ) and the second drying step for the second time (step S 6 - 9 ) may be performed. This ensures that the coating films T are stacked and a coating film T with a level difference h 0  smaller than the level difference h is formed. 
     In place of the second embodiment, the first coating step, the first drying step, the first cooling step, the etching step, the second coating step, the second drying step, and the second cooling step may be repeatedly performed a plurality of times. For example, as shown in  FIG. 8 , the first coating step (step S 8 - 1 , see  FIG. 9A ), the first drying step (step S 8 - 2 ), the first cooling step (step S 8 - 3 ), the etching step (step S 8 - 4 , see  FIG. 9B ), the second coating step (step S 8 - 5 ), the second drying step (step S 8 - 6 ), and the second cooling step (step S 8 - 7 ) are performed as in the first embodiment to form a coating film T with a level difference h 1  smaller than the level difference H in the initial coating film T, as shown in  FIG. 9C , and thereafter the first coating step for the second time (step S 8 - 8 ) may be performed to form a coating film T with a level difference h 2  smaller than the level difference h 1  (see  FIG. 9D ), and then the first drying step for the second time (step S 8 - 9 ), the first cooling step for the second time (step S 8 - 10 ), the etching step for the second time (step S 8 - 11 , see  FIG. 9E ), the second coating step for the second time (step S 8 - 12 ), and the second drying step for the second time (step S 8 - 13 ) may be performed. This ensures that the coating films T are stacked and a coating film T with a level difference h 3  further smaller than the level difference h 2  is formed (see  FIG. 9F ). 
     Note that while a case in which the heating means  20  is disposed in the heating unit  200  outside the coating unit  100  has been described in the above-described embodiments, the heating means may be composed of a heater  20   a  embedded in the spin chuck  10  as shown in  FIG. 10 . Note that in  FIG. 10 , other portions are the same as those shown in  FIG. 1 , and therefore the same numbers are given to those same portions to omit their description. 
     According to the substrate treatment apparatus configured as described above, a coating film can be formed on the wafer W as follows. 
     Namely, as shown in  FIG. 11 , an unprocessed wafer W is carried into the cup  50  and delivered to the spin chuck  10  by a not-shown carrier arm. The carrier arm then retracts, and the outer cup  50  rises. In this state, the open/close valve V 1  provided along the coating solution supply pipe  31  is opened based on the control signal from the controller  60 , and the motor  12  of the spin chuck  10  is driven. This allows the coating solution to be dropped (supplied) from the coating solution supply nozzle  30  onto the front surface of the wafer W rotating with the rotation of the spin chuck  10  as shown in  FIG. 11A  to form a coating film T of the coating solution with a level difference H on the front surface of the wafer W (see  FIG. 2A ) {first coating step}. 
     After the formation of the coating film, the open/close valve V 1  is closed based on the control signal from the controller  60  and the motor  12  is stopped. Next, based on the control signal from the controller  60 , the temperature adjuster  21  operates to raise the temperature of the heater  20   a  being a heating means to, for example, 150° C. to heat the wafer W for a heating time selected in advance from  FIG. 5  to adjust the etching condition. This evaporates a part of liquid in the coating film T to slightly decrease the level difference in the coating film T as shown in  FIG. 11B  {first drying step}. After the first drying step, the wafer W is cooled to, for example, 23° C. {first cooling step}. 
     Based on the control signal from the controller  60 , the solvent supply nozzle  40  then moves to a position above the central portion of the wafer W, the open/close valve V 2  provided along the solvent supply pipe  41  is opened, and the motor  12  of the spin chuck  10  is driven. This allows the solvent to be dropped (supplied) from the solvent supply nozzle  40  onto the front surface of the wafer W rotating with the rotation of the spin chuck  10  as shown in  FIG. 11C  to isotropically etch the coating film T (see  FIG. 2B ) {etching step}. 
     After the etching treatment, based on the control signal from the controller  60 , the open/close valve V 2  is closed, while the coating solution supply nozzle  30  moves again to the position above the central portion of the wafer W. In this state, the open/close valve V 1  is opened based on the control signal from the controller  60 , the coating solution is dropped (supplied) from the coating solution supply nozzle  30  onto the front surface of the wafer W rotating with the rotation of the spin chuck  10  as shown in  FIG. 11D  to form a substantially flat coating film T with a small level difference h within an allowable range on the front surface of the wafer W (see  FIG. 2C ) {second coating step}. 
     After the coating film is formed as described above, based on the control signal from the controller  60 , the open/close valve V 1  is closed, and the motor  12  is stopped. Based on the control signal from the controller  60 , the temperature adjuster  21  then operates to raise the temperature of the heater  20   a  to, for example, 160° C. to heat the wafer W to thereby cure (bake) the coating film as shown in  FIG. 11E  {second drying step}. 
     After the curing (baking) treatment of the coating film T is performed as described above, the outer cup  51  is lowered and the spin chuck  10  is raised to pass the wafer W to the carrier arm which moves to the position above the spin chuck  10 , so that the wafer W is carried out by the carrier arm from the substrate treatment apparatus. 
     While a case in which a flat coating film is formed on the front surface of the wafer W with projections and depressions through the first coating step, the first drying step, the first cooling step, the etching step, the second coating step, and the second drying step has been described in the above embodiment, the second coating step and the second drying step may be repeatedly performed in order to further decrease the level difference in the coating film T as in the above description. Alternatively, the first coating step, the first drying step, the first cooling step, the etching step, the second coating step, the second drying step, and the second cooling step may be repeatedly performed a plurality of times. 
     While a case in which the etching solution for etching the coating film is a solvent for SOG, such as dibutyl ether has been described, etching solutions other than the solvent for SOG, for example, a hydrofluoric acid solution such as HF, BHF or the like, an acid solution such as hydrochloric acid, sulfuric acid or the like, or an alkaline solution such as NaOH, KOH or the like can be used depending on the conditions of the film thickness and so on of SOG in the present invention. 
     Next, an example of a substrate processing system employing a substrate treatment apparatus capable of treatment using different etching solutions will be described. 
     The primary part of the substrate processing system is composed of, as shown in  FIG. 12A , a cassette station  1  which functions as a carry-in portion and a carry-out portion for carrying-in/out a plurality of, for example, 25 wafers W per wafer cassette C as a unit from/to the outside to/from the system and carrying-in/out the wafers W from/to the wafer cassette C; a processing station  2  for performing formation of a coating film T, etching treatment and the like on the wafer W; and an interface station  3  provided between the cassette station  1  and the processing station  2  for transferring the wafer W. 
     The interface station  3  is configured such that, as shown in  FIG. 12A , a plurality of, for example, up to four wafer cassettes C are mounted on a cassette mounting table  1   a  in a line along a horizontal X-direction with the respective wafer ports facing toward the processing station  2 , and a pair of tweezers  4  for wafer carriage, which is movable in a cassette-arrangement direction (an X-direction) and in a wafer-arrangement direction of the wafers W housed in the wafer cassette C (a Z-direction), performs selective carriage for each of the wafer cassettes. The pair of tweezers  4  for wafer carriage is configured to be rotatable in a θ-direction and can deliver the wafer W to a later-described transfer unit (TRS 1 , TRS 2 ) included in a multi-tired unit section in a first unit group G 1  on the processing station  2  side. 
     The processing station  2  comprises, as shown in  FIG. 12A , two coating units  100 A and  100 B each for forming a coating film of SOG on the wafer W, three etching units composed of a hydrofluoric acid solution etching unit  600 A, an acid solution etching unit  600 B, and an alkaline solution etching unit  600 C, the first unit group G 1  disposed on the interface station  3  side in the processing station  2 , a second unit group G 2  disposed almost at central portion in the processing station  2 , a first carrier arm  5 A disposed between the coating units  100 A and  100 B, the first unit group G 1 , the second unit group G 2 , and a later-described buffer unit  700  to deliver the wafer W between the coating units  100 A and  100 B, the first unit group G 1 , the second unit group G 2 , and the buffer unit  700 , and a second carrier unit  5 B disposed between the second unit group G 2 , the hydrofluoric acid solution etching unit  600 A, the acid solution etching unit  600 B, and the alkaline solution etching unit  600 C to deliver the wafer W between the second unit group G 2 , the hydrofluoric acid solution etching unit  600 A, the acid solution etching unit  600 B, and the alkaline solution etching unit  600 C. Note that the buffer unit  700  is formed to be able to house a plurality of wafers W therein. 
     In the first unit group G 1 , as shown in  FIG. 12B , a first to a fourth heating unit (HP 1  to HP 4 ), the first and second transfer units (TRS 1 , TRS 2 ), and a first and a second cooling unit (COL 1 , COL 2 ) are stacked in order from the upper side to the lower side. 
     In the second unit group G 2 , as shown in  FIG. 12C , a fifth to a seventh heating unit (HP 5  to HP 7 ), a third and a fourth transfer unit (TRS 3 , TRS 4 ), and a third and a fourth cooling unit (COL 3 , COL 4 ) are stacked in order from the upper side to the lower side. 
     In the substrate processing system configured as described above, the first and second coating units  100 A and  100 B are configured similarly to the coating unit  100  in the first embodiment, and therefore their description will be omitted here. Further, the first to seventh heating units HP 1  to HP 7  and the first to fourth cooling units COL 1  to COL  4  are also configured similarly to the heating unit  200  and the cooling unit  300  in the first embodiment, respectively. 
     On the other hand, the hydrofluoric acid solution etching unit  600 A, the acid solution etching unit  600 B, and the alkaline solution etching unit  600 C are similarly configured except that those etching solutions are different from each other. Hereinafter, the hydrofluoric acid solution etching unit  600 A will be described as a representative. 
     The hydrofluoric acid solution etching unit  600 A comprises, as shown in  FIG. 13 , a spin chuck  10 A that is a rotating and holding means for holding and horizontally rotating the wafer W, an etching solution supply nozzle  6  for dropping (supplying) a hydrofluoric acid solution that is the etching solution onto the front surface of the wafer W, a cleaning solution supply nozzle  7  for supplying a cleaning solution for suppressing (stopping) the etching, for example, pure water onto the wafer W, and a drying gas supply nozzle  8  for supplying (jetting) a drying gas, for example, a nitrogen (N 2 ) gas or clean air to the wafer W. 
     The spin chuck  10 A is housed in a cup  50 A composed of an outer cup  51 A capable of rising and lowering and an inner cup  52 A, and coupled to a motor  12 A via a rotation axis  11 A passing through a bottom portion  53 A of the inner cup  52 A in a manner to be able to rise and lower. The motor  12 A rotates at a predetermined number of rotations based on a control signal from a controller  60 A that is a control means. The spin chuck  10 A is also configured to be able to rise and lower by means of a not-shown raising and lowering means. The spin chuck  10 A is configured to receive the wafer W from the first carrier arm  5 A being a carrier unit moved to a position above the spin chuck  10 A, which is movable in a horizontal X-Y direction and a vertical Z-direction and horizontally rotatable, hold the wafer W thereon by suction, and pass the wafer W to the first carrier arm  5 A raised and moved to the position above the spin chuck  10 A after a later-described coating film treatment is finished. Note that the first carrier arm  5 A and the second carrier arm  5 B are controlled by the controller  60 A. 
     The etching supply nozzle  6  is connected via an etching solution supply pipe  6   a  to a hydrofluoric acid solution tank  6   b  storing an etching solution (hydrofluoric acid solution) that is the etching solution supply source. The cleaning solution supply nozzle  7  is connected via a pure water supply pipe  7   a  to a pure water tank  7   b  storing pure water that is a cleaning solution supply source used also for a diluted hydrofluoric acid solution. In this case, the etching solution supply pipe  6   a  is provided with a pump P 1 , a flow rate control valve FV 1 , and a switching valve CV from the hydrofluoric acid solution tank  6   b  side. Further, the pure water supply pipe  7   a  is provided with a pump P 2  and a flow rate control valve FV 2  from the pure water tank  7   b  side, and a branch pipe  7   c  branching from the secondary side of the flow rate control valve FV 2  is connected to the switching valve CV. The flow rate control valve FV 1 , the flow rate control valve FV 2  and the switching valve CV constitute a concentration adjusting means  90  for the hydrofluoric acid solution. More specifically, the flow rate control valve FV 1 , the flow rate control valve FV 2  and the switching valve CV are controlled by the controller  60 A so that based on the control signal previously stored in the controller  60 A, the hydrofluoric acid solution adjusted by the flow rate control valve FV 1  and the pure water adjusted by the flow rate control valve FV 2  can be mixed to obtain a hydrofluoric acid solution with a predetermined concentration. 
     The etching solution supply pipe  6   a  is provided with a temperature adjuster  80  that is a temperature control means for adjusting the temperature of the etching solution to a predetermined temperature, for example, 20° C. to 50° C. The temperature adjuster  80  is controlled by the control signal from the controller  60 A to adjust the temperature of the etching solution to a predetermined temperature, for example, 20° C. to 50° C. depending on the conditions of the film thickness and so on of the coating film T. 
     The drying gas supply nozzle  8  is connected via a drying gas supply pipe  8   a  provided with an open/close valve V 3  to a drying gas supply source, for example, a N2 gas supply source  8   b.    
     The etching solution supply nozzle  6  and the cleaning solution supply nozzle  7  are configured to be able to move by means of a nozzle moving mechanism  70 A to a position above a central position of the spin chuck  10 A and to a waiting position outside the cup  50 A. The drying gas supply nozzle  8  is also configured to be able to move by means of a nozzle moving mechanism  70 B to a position above a central position of the spin chuck  10 A and to a waiting position outside the cup  50 A. Note that the drying gas supply nozzle  8  is preferably inclined to supply (jet) the N2 gas from the center of the wafer toward the peripheral side. Further, the drying gas supply nozzle  8  preferably supplies (jets) the N2 gas while scanning from a position above the center of the wafer W to a position above the periphery. In this case, the nozzle moving mechanisms  70 A and  70 B move the etching solution supply nozzle  6  and the cleaning solution supply nozzle  7 , and the drying gas supply nozzle  8  to the position above the central position of the spin chuck  10 A and to the waiting positions outside the cup  50 A based on the control signal from the controller  60 A, respectively. 
     Note that the acid solution etching unit  600 B and the alkaline solution etching unit  600 C are configured similarly to the hydrofluoric acid solution etching unit  600 A except that those etching solutions are different, that is, the etching solution tank connected to the etching solution supply nozzle  6  is an acid solution tank or an alkaline solution tank in replace of the hydrofluoric acid solution tank  6   b.    
     Next, a method of forming the coating film T in the substrate processing system will be described with reference to  FIGS. 2A to 2C ,  FIG. 5 , and  FIGS. 12A to 12C  through  FIG. 15 . 
     &lt;In the Case of Etching with the Solvent for the Coating Film&gt; 
     First of all, in the cassette station  1 , the pair of tweezers  4  for wafer carriage accesses the cassette C housing unprocessed wafers W on the cassette mounting table  1   a  and takes out one wafer W from the cassette C (step S 14 - 1 ). After taking out the wafer W from the cassette C, the pair of tweezers  4  for wafer carriage delivers the wafer W to a mounting table (not shown) in the first transfer unit TRS 1  disposed in the first unit group G 1  on the processing station  2  side (step S 14 - 2 ). The first carrier arm  5 A then receives the wafer W from the first transfer unit TRS 1  and delivers the wafer W onto the cooling plate (not shown) in the first cooling unit COL 1  disposed in the first unit group G 1  to lower the temperature of the wafer W to 23° C. {pre-treatment cooling step: step S 14 - 3 }. 
     The first carrier arm  5 A then receives the wafer W on the cooling plate in the first cooling unit COL 1  and delivers the wafer W onto the spin chuck  10  in the first coating unit  100 A. Thereafter, the coating solution is dropped (supplied) from the coating solution supply nozzle  30  onto the front surface of the wafer W rotating with the rotation of the spin chuck  10  as shown in  FIG. 3A  to form a coating film T with a level difference H on the front surface of the wafer W as in the first embodiment (see  FIG. 2A ) {first coating step: step S 14 - 4 }. 
     The first carrier arm  5 A then receives the wafer W on the spin chuck  10  and delivers the wafer W onto the hot plate (not shown) in the first or second heating unit HP 1  or HP 2  in the first unit group G 1 . The wafer W is then heated for a heating time selected in advance from  FIG. 5  to adjust the etching condition. This evaporates a part of liquid in the coating film T to slightly decrease the level difference in the coating film T as shown in  FIG. 3B  {first drying step: step S 14 - 5 }. 
     The first carrier arm  5 A then receives the wafer W on the hot plate in the first or second heating unit HP 1  or HP 2  and delivers the wafer W onto the cooling plate in the first or second cooling unit COL 1  or COL 2  disposed in the first unit group G 1  to lower the temperature of the wafer W to 23° C. {first cooling step: step S 14 - 6 }. 
     The first carrier arm  5 A then receives the wafer W on the cooling plate in the first or second cooling unit COL 1  or COL 2  and delivers the wafer W onto the spin chuck  10  in the second coating unit  100 B. Thereafter, the solvent is dropped (supplied) from the solvent supply nozzle  40  onto the front surface of the wafer W rotating with the rotation of the spin chuck  10  as shown in  FIG. 3D  to isotropically etch the coating film T as in the first embodiment (see  FIG. 2B ) {etching step: step S 14 - 7 }. After the isotropic etching with the solvent, the solvent (etching solution) is shaken out. 
     After the etching treatment, the coating solution is dropped (supplied) from the coating solution supply nozzle  30  onto the front surface of the wafer W rotating with the rotation of the spin chuck  10  as shown in  FIG. 3E  to form a substantially flat coating film T with a small level difference h within an allowable range on the front surface of the wafer W as in the first embodiment (see  FIG. 2C ) {second coating step: step S 14 - 8 }. 
     After the coating film is formed as described above, the first carrier arm  5 A then receives the wafer W on the spin chuck  10  and delivers the wafer W onto the hot plate (not shown) in the third or fourth heating unit HP 3  or HP 4  disposed in the first unit group G 1 . The coating film is cured (baked) as shown in  FIG. 3F  {second drying step: step S 14 - 9 }. 
     After the curing (baking) treatment of the coating film T is performed as described above, the first carrier arm  5 A receives the wafer W on the hot plate in the third or fourth heating unit HP 3  or HP 4  and delivers the wafer W onto the cooling plate in the second cooling unit COL 2  to lower the temperature of the wafer W to 23° C. {second cooling step: step S 14 - 10 }. 
     The first carrier arm  5 A then receives the wafer W on the cooling plate in the second cooling unit COL 2  and delivers the wafer W onto the mounting table (not shown) in the second transfer unit TRS 2  (step S 14 - 11 ). The pair of tweezers  4  for wafer carriage then receives the wafer W on the mounting table in the second transfer unit TRS 2  and houses (carries) the wafer W into the cassette C on the cassette mounting table  1   a  to end the processing (step S 14 - 12 ). 
     Note that while a case in which a flat coating film is formed on the front surface of the wafer W with projections and depressions through the first coating step, the first drying step, the first cooling step, the etching step, the second coating step, the second drying step, and the second cooling step has been described in the above description, the second coating step and the second drying step may be repeatedly performed in order to further decrease the level difference in the coating film T. Alternatively, the first coating step, the first drying step, the first cooling step, the etching step, the second coating step, the second drying step, and the second cooling step may be repeatedly performed a plurality of times. 
     Further, when the first coating step, the first drying step, the first cooling step, the etching step, the second coating step, the second drying step, and the second cooling step are repeatedly performed a plurality of times, the wafer W for which treatments for the first time have been finished is not returned to the cassette station  1 , but the wafers W on the mounting table in the second transfer unit TRS 2  are temporarily housed in the buffer unit  700  in sequence by the first carrier arm  5 A, so that after the first treatment for the first time for the last wafer W in a lot is finished, treatments for the second time for the wafers W sequentially carried out of the buffer unit  700  by the first carrier arm  5 A are performed. 
     Besides, while a case in which the supply nozzle  40  for the solvent being the etching solution is disposed in each of the coating units  100 A and  100 B so that the film forming treatment and the etching treatment of the coating film T are performed in each of the coating units  100 A and  100 B has been described in the above-described embodiments, a dedicated etching unit comprising a solvent supply nozzle may be separately provided to perform etching treatment separately from the coating units  100 A and  100 B. Accordingly, when such process is performed, the solvent supply nozzle  40  may not be provided in each of the coating units  100 A and  100 B. 
     &lt;In the Case of Etching with Hydrofluoric Acid&gt; 
     First of all, in the cassette station  1 , the pair of tweezers  4  for wafer carriage accesses the cassette C housing unprocessed wafers W on the cassette mounting table  1   a  and takes out one wafer W from the cassette C (step S 15 - 1 ). After taking out the wafer W from the cassette C, the pair of tweezers  4  for wafer carriage delivers the wafer W to the mounting table (not shown) in the first transfer unit TRS 1  disposed in the first unit group G 1  on the processing station  2  side (step S 15 - 2 ). The first carrier arm  5 A then receives the wafer W from the first transfer unit TRS 1  and delivers the wafer W onto the cooling plate (not shown) in the first cooling unit COL 1  disposed in the first unit group G 1  to lower the temperature of the wafer W to 23° C. {pre-treatment cooling step: step S 15 - 3 }. 
     The first carrier arm  5 A then receives the wafer W on the cooling plate in the first cooling unit COL 1  and delivers the wafer W onto the spin chuck  10  in the first coating unit  100 A. Thereafter, the coating solution is dropped (supplied) from the coating solution supply nozzle  30  onto the front surface of the wafer W rotating with the rotation of the spin chuck  10  as shown in  FIG. 3A  to form a coating film T with a level difference H on the front surface of the wafer W as in the first embodiment (see  FIG. 2A ) {first coating step: step S 15 - 4 }. 
     The first carrier arm  5 A then receives the wafer W on the spin chuck  10  and delivers the wafer W onto the hot plate (not shown) in the first, second, or third heating unit HP 1 , HP 2 , or HP 3  in the first unit group G 1 . The wafer W is heated for a heating time selected in advance from  FIG. 5  to adjust the etching condition. This evaporates a part of liquid in the coating film T to slightly decrease the level difference in the coating film T {first drying step: step S 15 - 5 }. 
     The first carrier arm  5 A then receives the wafer W on the hot plate in the first, second, or third heating unit HP 1 , HP 2 , or HP 3  and delivers the wafer W onto the cooling plate (not shown) in the second cooling unit COL 2  disposed in the first unit group G 1  to lower the temperature of the wafer W to 23° C. {first cooling step: step S 15 - 6 }. 
     The first carrier arm  5 A then receives the wafer W on the cooling plate in the second cooling unit COL 2  and delivers the wafer W onto the mounting table (not shown) in the third transfer unit TRS 3  disposed in the second unit group G 2 . The second carrier arm  5 B then receives the wafer W on the mounting table in the third transfer unit TRS 3  and delivers the wafer W on the spin chuck  10 A in the hydrofluoric acid solution etching unit  600 A. Thereafter, the hydrofluoric acid solution is dropped (supplied) being the etching solution from the etching solution supply nozzle  6  onto the front surface of the wafer W rotating with the rotation of the spin chuck  10 A to isotropically etch the coating film T (see  FIG. 2B ) {hydrofluoric acid solution etching step: step S 15 - 7 }. In this event, pure water is supplied from the cleaning solution supply nozzle  7  to suppress (stop) the etching. After the isotropic etching with the hydrofluoric acid solution, the hydrofluoric acid solution (etching solution) is shaken out {shaking-out drying step: step S 15 - 8 }. In this event, the centrifugal force caused by the rotation of the spin chuck  10 A driven by the motor  12  and the wafer W is used to remove the hydrofluoric acid solution served for the etching, and the drying gas, for example, a N 2  gas is supplied (jetted) from the drying gas supply nozzle  8 , which horizontally scans from the position above the center of the wafer toward the peripheral portion, onto the front surface of the wafer W to blow the hydrofluoric acid solution served for etching to the outside to thereby remove it. 
     After the etching treatment, the second carrier arm  5 B receives the wafer W on the spin chuck  10 A in the hydrofluoric acid solution etching unit  600 A and delivers the wafer W onto, for example, the mounting table (not shown) in the fourth transfer unit TRS 4  disposed in the second unit group G 2 . The second carrier arm  5 B then receives the wafer W on the mounting table in the fourth transfer unit TRS 4  and delivers the wafer W on the cooling plate (not shown) in the third or fourth cooling unit COL 3  or COL 4  disposed in the second unit group G 2  to lower the temperature of the wafer W, which will be subjected to coating treatment, to 23° C. {pre-treatment cooling step: step S 15 - 9 }. 
     The first carrier arm  5 A then receives the wafer W on the cooling plate in the third or fourth cooling unit COL 3  or COL 4  and delivers the wafer W onto the spin chuck  10  in the second coating unit  100 B. Thereafter the coating solution is dropped (supplied) from the coating solution supply nozzle  30  onto the front surface of the wafer W rotating with the rotation of the spin chuck  10  to form an almost flat coating film T with a small level difference h within an allowable range on the front surface of the wafer W (see  FIG. 2C ) {second coating step: step S 15 - 10 }. 
     After the coating film is formed as described above, the first carrier arm  5 A receives the wafer W on the spin chuck  10  and delivers the wafer W onto the hot plate (not shown) in the fifth, sixth, or seventh heating unit HP 5 , HP 6 , or HP 7  disposed in the second unit group G 2 . The coating film is then cured (baked) {second drying step: step S 15 - 11 }. 
     After the curing (baking) treatment of the coating film T is performed as described above, the first carrier arm  5 A receives the wafer W on the hot plate in the fifth, sixth, or seventh heating unit HP 5 , HP 6 , or HP 7  and delivers the wafer W onto the cooling plate (not shown) in the second cooling unit COL 2  in the first unit group G 1  to lower the temperature of the wafer W to 23° C. {second cooling step: step S 15 - 12 }. 
     The first carrier arm  5 A then receives the wafer W on the cooling plate in the second cooling unit COL 2  and delivers the wafer W onto the mounting table (not shown) in the second transfer unit TRS 2  (step S 15 - 13 ). The pair of tweezers  4  for wafer carriage then receives the wafer on the mounting table in the second transfer unit TRS 2  and houses the wafer W into the cassette C on the cassette mounting table  1   a  to end the processing (step S 15 - 14 ). 
     While a case in which a flat coating film is formed on the front surface of the wafer W with projections and depressions through the first coating step, the first drying step, the first cooling step, the hydrofluoric acid solution etching step, the second coating step, the second drying step, and the second cooling step has been described in the above description, the second coating step and the second drying step may be repeatedly performed as in the above description in order to further decrease the level difference in the coating film T. Alternatively, the first coating step, the first drying step, the first cooling step, the hydrofluoric acid solution etching step, the second coating step, the second drying step, and the second cooling step may be repeatedly performed a plurality of times. 
     Further, when the first coating step, the first drying step, the first cooling step, the hydrofluoric acid solution etching step, the second coating step, the second drying step, and the second cooling step are repeatedly performed a plurality of times, the wafer W for which treatments for the first time have been finished is not returned to the cassette station  1 , but the wafers W on the mounting table in the second transfer unit TRS 2  are temporarily housed in the buffer unit  700  in sequence by the first carrier arm  5 A, so that after the treatment for the first time in the first treatment unit, for example, the cooling unit, for the last wafer W in a lot is finished, treatments for the second time for the wafers W sequentially carried out of the buffer unit  700  by the first carrier arm  5 A are performed. 
     Note that while a case in which the etching solution is the hydrofluoric acid solution has been described in the above description, if an acid solution or an alkaline solution is used in place of the hydrofluoric acid solution to perform etching treatment, the wafer W having the coating film T formed thereon can be carried to the acid solution etching unit  600 B or the alkaline solution etching unit  600 C in place of the carriage flow to the hydrofluoric acid solution etching unit  600 A. 
     According to the present invention, it is also possible that when the treatments are repeatedly performed a plurality of times, for example, the treatments can be performed with the etching conditions being selectively changed according to the condition of the SOG film thickness, such that the etching for the first time is performed using the hydrofluoric acid solution and the etching for the second time is performed using the acid solution or the alkaline solution, or the etching for the first time is performed using the alkaline solution and the etching for the second time is performed using the acid solution or the like, in addition to the case in which the etching conditions are changed by the etching time. 
     Note that while a case in which the coating solution is the SOG solution has been described in the above embodiments, the film formation technology according to the present invention is also applicable to the coating solution other than the SOG solution, such as a resist, and is also applicable to a substrate other than the wafer W, such as an LCD substrate as a matter of course.