Patent Publication Number: US-2011065277-A1

Title: Reflow method, pattern generating method, and fabrication method for tft for lcd

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a resist reflow process in a pattern formation phase for semiconductor devices such as thin-film transistors (TFTs), a pattern formation method using the reflow process, and a method of fabricating a TFT for an LCD using the same. 
     2. Description of the Related Art 
     In recent years, semiconductor devices have been further highly integrated and miniaturized. However, the more integration and miniaturization progress, the more complex the semiconductor fabrication process becomes, resulting in higher fabrication cost. Accordingly, consolidating multiple mask-pattern fabrication processes using photolithography is considered, thereby reducing the total number of such processes in order to considerably lower the fabrication cost. 
     A reflow process allowing omission of some mask-pattern fabrication processes by soaking the resist with an organic solvent to soften the resist and thereby changing the shape of the initial resist pattern is proposed (e.g., see Japanese Patent Application Laid-open No. 2002-334830). 
     However, the method disclosed in Japanese Patent Application Laid-open No. 2002-334830 has a problem that it is difficult to control the coverage area and the orientation for softening and spreading the initial resist. The fourth embodiment of the above-mentioned Japanese Patent Application Laid-open No. 2002-334830, for example, discloses a technique that ref lows a resist mask having differing thicknesses to cover the channel regions of TFTs; wherein as shown in  FIG. 1A , for example, while resists  507   a  and  507   b  having differing thicknesses are used as masks for the previous etching process, they are formed having the area as an ohmic contact layer  505  and source/drain electrode  506 , which are underlying layers, thereupon. 
     Therefore, as shown in  FIG. 1B , the modified ref lowed resist  511  after completion of the reflow process goes beyond the area of the ohmic contact layer  505  and the source/drain electrode  506 , further extending onto an underlying a−Si layer  504 . In other words, since it extends up to peripheral regions Z 1  enclosed by dotted lines in  FIG. 1B  as well as the target region (i.e., channel region  510 ) for the reflow process, the area (dot area) necessary for fabrication of a single TFT, for example, becomes larger, resulting in difficulty in further improving integrity and miniaturization. Note that reference numeral  503  denotes an insulating film made of a silicon nitride, for example, and reference numeral  510  denotes a channel region, however the gate electrode thereof is omitted for convenience in  FIGS. 1A and 1B  (the same holds true for  FIGS. 2A to 2C ). 
     According to the fifth embodiment in the above-mentioned Japanese Patent Application Laid-open No. 2002-334830, a technique of performing an ashing process using O 2  plasma before resists  507  and  507   b  having respective differing thicknesses are subjected to a reflow process as shown in  FIG. 2A  has been proposed as shown in  FIG. 2A . As shown in  FIG. 2B , the thin region of the resist mask is removed through the O 2  plasma ashing process, reducing the coverage areas of the resists  508   a  and  508   b,  which are left adjacent to the channel region  510 . Afterwards, the reflow process is performed. However, when the O 2  plasma ashing process is performed, the resist is generally also removed along the width, resulting in formation of steps D between the ends of the underlying layer (source and drain electrodes  506 ) and the sides of the resists  508   a  and  508   b  facing the channel region  510 . The steps D cause the softened resist to take a longer time to go over the steps D than flat surfaces, and flow of the resist then stops. Consequently, it is difficult to control the flow orientation. 
     Even in the case of the flow of the softened resist stopping at the steps D, the flow progresses in a direction without steps. As a result, an incomplete coverage area by the deformed resist is formed, and at its worst, the deformed resist  511  may not cover the entirety of the channel region  510  as shown in  FIG. 2C , and/or may cover a peripheral resist inflow prohibiting region Z 2 , bringing about failure in device performance. Furthermore, the stoppage of the softened resist flow at the steps D may cause the reflow process to take longer, decreasing the TFT fabrication throughput. 
     As described above, according to the technique disclosed in Japanese Patent Application Laid-open No. 2002-334830, if the resist area before the reflow process and the underlying layer are corresponded, flow of the softened resist toward the peripheral regions cannot stop, making it difficult to miniaturize TFTs. On the other hand, if the resist area is reduced relative to that of the underlying layer, steps may develop in a desired spreading direction of the softened resist, stopping the flow (i.e., area extension) of the softened resist at the steps into the target regions, and the functionality thereof as a mask may thus be lost. 
     SUMMARY OF THE INVENTION 
     An objective of the present invention is to provide a reflow method capable of controlling flow orientation and flow area of a softened resist. 
     Another objective of the present invention is to provide a pattern formation method applying such a reflow method. 
     Yet another objective of the present invention is to provide a fabrication method for a TFT for an LCD applying the reflow method. 
     According to a first aspect of the present invention, a reflow method, including: preparing a to-be-processed object, which includes an underlying layer and a resist film which has a pattern and which includes different regions in thickness of at least a thick region and a thin region relatively thinner than the thick region, where said pattern allows formation of an exposure region of the underlying layer exposed on an upper layer than the underlying layer and a coverage region in which the underlying layer is covered; and covering a part of or all of the exposure region by softening and ref lowing the resist film. 
     In the above-given reflow method, the flow orientation of the softened resist may be controlled by arrangement of the thick region and the thin region, and the coverage area by the resist may also be controlled by the arrangement of the thick region and the thin region. 
     Furthermore, the thick region may be provided on a side where spreading of the softened resist should be promoted, and the thin region may be provided on a side where spreading of the resist should be controlled. Alternatively, the thin region maybe provided on a side where spreading of the softened resist should be promoted, and the thick region may be provided on a side where spreading of the resist should be controlled. 
     Deformation of the resist may be performed in an organic solvent atmosphere. 
     Furthermore, flow orientation of the softened resist may be controlled by a flat shape of the resist film, and a coverage area by the softened resist may be controlled by a flat shape of the resist film. 
     Further, a step may be formed between the resist mask and the exposure region. 
     Yet even further, the thick region and the thin region of the resist film may be formed through half-exposure processing using a half-tone mask and development processing thereafter. 
     According to a second aspect of the present invention, a pattern formation method includes: forming a resist film in an upper layer than a to-be-etched film of a to-be-processed object; patterning the resist film so as to form different regions of the resist film in thickness including at least a thick region and a thin region relatively thinner than the thick region; redeveloping the patterned resist film and reducing coverage area by the patterned resist film; softening the resist film to be in a reflowed state, and covering a target region of the to-be-etched film by the reflowed resist while controlling flow orientation and flow rate of the softened resist based on the locations of the thick region and the thin region; etching an exposed region of the to-be-etched film using the resist deformed by said reflowing as a mask; removing the resist; and etching a target region of the to-be-etched film re-exposed through removal of the resist. 
     In the above-given pattern formation method, the same method as the reflow method according to the first aspect may be employed when the resist film is subjected to reflowing. 
     Further in the aforementioned pattern formation method, a damaged layer on the resist surface may be removed before redeveloping of the patterned resist film. 
     Moreover, the to-be-processed body has a stacked structure in which a gate line and a gate electrode are formed on a substrate, a gate insulating film is formed to cover them, and an a−Si film, a Si film for ohmic contact, and a metallic film for source and drain are then formed on the gate insulating film in order from bottom up, and the to-be-etched film may be the Si film for ohmic contact. 
     In this case, a step may be formed between an end of the resist film on a side facing the target region and an end of the metallic film for source and drain in an underlayer thereto through the redeveloping. 
     According to a third aspect of the present invention, a fabrication method for a TFT for an LCD includes: forming a gate line and a gate electrode on a substrate; forming a gate insulating film that covers the gate line and the gate electrode; depositing an a−Si film, a Si film for ohmic contact, and a metallic film for source and drain on the gate insulating film in order from the bottom; forming a resist film on the metallic film for source and drain; forming a resist mask for a source electrode and a resist mask for a drain electrode through half-exposure processing and development processing, so as to form different regions of the resist film in thickness including at least a thick region and a thin region relatively thinner than the thick region; etching the metallic film for source and drain using the resist mask for a source electrode and the resist mask for a drain electrode as a mask, forming a metallic film for a source electrode and a metallic film for a drain electrode, and exposing a Si film for ohmic contact in an underlying layer to a concave region for a channel region between the metallic film for the source electrode and a metallic film for the drain electrode; redeveloping the patterned resist mask for the source electrode and resist mask for the drain electrode, and reducing respective coverage areas by them with the thick region and the thin region left as they are; making an organic solvent act on the resist mask for the reduced source electrode and resist mask for the drain electrode to soften them to be in a reflowed state and deformed, and covering by the reflowed resist the Si film for ohmic contact within the concave region for the channel region between the metallic film for the source electrode and the metallic film for the drain electrode; etching the Si film for ohmic contact and the a−Si film in underlayers using the deformed resist resulting from reflowing, the metallic film for a source electrode, and the metallic film for a drain electrode as a mask; removing the resist and re-exposing the Si film for ohmic contact within the concave part for a channel region between the metallic film for a source electrode and the metallic film for a drain electrode; and etching the Si film for ohmic contact exposed to the concave part for a channel region between the metallic film for a source electrode and the metallic film for a drain electrode using the films as a mask. 
     In the above-given fabrication method for a TFT for an LCD, the same method as the reflow method according to the first aspect may be employed when the resist film is subjected to ref lowing. 
     Furthermore, the thick region may be formed in the concave part for the channel region between the metallic film for the source electrode and the metallic film for the drain electrode, and the thin region may be formed in the concave part for the channel region. 
     Moreover, distance between the resist mask for the source electrode and the resist mask for the drain electrode in the concave part for the channel region may be formed greater than distance between metallic film for the source electrode and the metallic film for the drain electrode in an underlayer thereto through the redeveloping. 
     According to a fourth aspect of the present invention, a storage medium, which is stored with a program for controlling a processing unit to be executed by a computer, is provided. The program is executed by the computer to control the processing unit, so as to implement a reflow method including: preparing a to-be-processed object, which includes an underlying layer and a resist film patterned so that an exposure region in which the underlying layer is exposed in an upper layer to the underlying layer and a coverage region in which the underlying layer is covered are formed, wherein the resist film has a shape comprising different regions in thickness, which include at least a thick region and a thin region relatively thinner than the thick region, and covering a part of or all of the exposure region by softening and ref lowing the resist film. 
     According to the present invention, use of a resist film having a thick region and a thin region for ref lowing controls flow orientation and flow area (spreading area) of softened resist. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A and 1B  are cross-sections explaining a conventional reflow method; 
         FIGS. 2A through 2C  are cross-sections explaining the conventional reflow method; 
         FIG. 3  is a top view of an outline of a reflow processing system; 
         FIG. 4  is a top view of an outline of a redevelopment/remover unit; 
         FIG. 5  is a cross-section of a general structure of the redevelopment/remover unit; 
         FIG. 6  is a cross-section of a general structure of the reflow processing unit (REFLW); 
         FIGS. 7A through 7C  show a principle of the conventional reflow method; 
         FIGS. 8A through 8C  show a principle of a reflow method according to an embodiment of the present invention; 
         FIGS. 9A through 9C  show a principle of a reflow method according to another embodiment of the present invention; 
         FIG. 10A  is a graph explaining a relationship between the flow speed of a softened resist and thinner concentration; 
         FIG. 10B  is a graph explaining a relationship between the flow speed of the softened resist and temperature; 
         FIG. 10C  is a graph explaining a relationship between the flow speed of the softened resist and applied pressure; 
         FIG. 10D  is a graph explaining a relationship between the flow speed of the softened resist and the thinner flow; 
         FIGS. 11 and 12  are references explaining a principle of a reflow method; 
         FIG. 13A  shows a principle of a reflow method according to another embodiment of the present invention; 
         FIG. 13B  is a cross-section of a resist shown in  FIG. 13A ; 
         FIG. 14  is a vertical cross-section of a substrate in which a gate electrode and a laminated film are formed on an insulating substrate in a TFT fabrication process; 
         FIG. 15  is a vertical cross-section of a substrate having a resist film formed thereupon in the TFT fabrication process ; 
         FIG. 16  is a vertical cross-section of the substrate being subjected to half-exposure processing in the TFT fabrication process; 
         FIG. 17  is a vertical cross-section of the substrate after the half-exposure processing is completed in the TFT fabrication process; 
         FIG. 18  is a vertical cross-section of the substrate after development in the TFT fabrication process; 
         FIG. 19  is a vertical cross-section of the substrate after a metallic film for electrodes in the TFT fabrication process ; 
         FIG. 20  is a vertical cross-section of the substrate after a preprocess and redevelopment in the TFT fabrication process; 
         FIG. 21  is a vertical cross-section of the substrate after a reflow process in the TFT fabrication process; 
         FIG. 22  is a vertical cross-section of the substrate after an n+Si film and an a−Si film are etched in the TFT fabrication process; 
         FIG. 23  is a vertical cross-section of the substrate after a deformed resist is removed in the TFT fabrication process ; 
         FIG. 24  is a vertical cross-section of the substrate having a channel region formed therein in the TFT fabrication process; 
         FIG. 25  is a top view of the substrate shown in  FIG. 20 ; 
         FIG. 26  is a top view of the substrate shown in  FIG. 21 ; and 
         FIG. 27  is a flowchart explaining the TFT fabrication process. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments according to the present invention are described forthwith while referencing the drawings. 
       FIG. 3  is a top view of an entire reflow processing system available according to a reflow method of the present invention. Here, a reflow processing system including a reflow processing unit, which softens and deforms a resist film formed on an LCD glass substrate (hereafter simply called ‘substrate’) after development and then performs ref lowing tore-cover, and a redevelopment/remover unit (REDEV/REMV), which performs redevelopment and preprocessing before reflowing, is described as an example. This reflow processing system  100  includes a cassette station (carry-in/out unit)  1  in which each cassette C accommodating multiple substrates G is placed, a processing station (processing unit)  2 , which includes multiple processing units for performing successive processing such as reflow processing and redevelopment processing for each substrate G, and a control unit  3 , which controls each unit of the reflow processing system  100 . Note that the direction along the length of the reflow processing system  100  is defined as X direction while direction perpendicular to the X direction on a plane is defined as Y direction in  FIG. 1 . 
     The cassette station  1  is deployed next to an end of the processing station  2 . The cassette station  1  including a transfer unit  11 , which carries in and out the substrates G between the cassette C and the processing station  2 , and carries in and out the cassettes C from/to the outside. The transfer unit  11  has a transfer arm  11   a  movable along a transfer path  10  extending in the Y direction in which the cassettes C are aligned. This transfer arm  11   a  is provided capable of moving back and forth in the X direction, moving up and down, and rotating, allowing transfer of the substrates G between the cassette C and the processing station  2 . 
     The processing station  2  includes multiple processing units, which perform successive processes for resist reflowing, preprocessing, and redevelopment processing for the substrates G. Each of these processing units processes the substrates G one by one. The processing station  2  also includes a central transfer path  20  for transferring the substrates G basically extending in the X direction. The processing units are deployed at both ends of this central transfer path  20 , facing the central transfer path  20 . 
     A transfer unit  21 , which carries in and out the substrates G between each processing unit, is provided along the central transfer path  20  and has a transfer arm  21   a  movable in the X direction in which the processing units are deployed. This transfer arm  21   a  is provided capable of moving back and forth in the Y direction, moving up and down, and rotating, allowing transfer of the substrates G between each processing unit. 
     On one side along the central transfer path  20  of the processing station  2 , a redevelopment/remover unit (REDEV/REMV)  30  and a reflow processing unit (REFLW)  60  are aligned in this order from the cassette station  1  side while at the other side along the central transfer path  20  of the processing station  2 , three heating/cooling units (HP/COLs)  80   a,    80   b,  and  80   c  are deployed in a line. Each of the heating/cooling units (HP/COLs)  80   a,    80   b,  and  80   c  is made up of multiple layers stacked vertically (omitted from the drawing). 
     The redevelopment/remover unit (REDEV/REMV)  30  is a processing unit, which performs preprocessing for removal of a damaged layer in a metal etching process or other related processes by another processing system not shown in the drawing and redevelopment processing for redevelopment of a resist pattern previous to ref lowing. This redevelopment/remover unit (REDEV/REMV)  30  includes a fluid spinning/processing unit, which has a redevelopment chemical discharge nozzle for redevelopment and a removal fluid discharge nozzle for preprocessing to discharge a treatment fluid onto a substrate G while holding and rotating the substrate G at a fixed speed to allow application of the processing liquid for redevelopment and preprocessing (i.e., removing the damaged layer on the resist surface). 
     Now, the redevelopment/remover unit (REDEV/REMV)  30  is described while referencing  FIGS. 4 and 5 .  FIG. 4  is a top view of the redevelopment/remover unit (REDEV/REMV)  30  while  FIG. 5  is a cross-section of a cup of the redevelopment/remover unit (REDEV/REMV)  30 . As shown in  FIG. 2 , the entirety of the redevelopment/remover unit (REDEV/REMV)  30  is enclosed by a sink  31 . As shown in  FIG. 3 , the redevelopment/remover unit (REDEV/REMV)  30  has a holding means such as a spin chuck  32 , which holds a substrate G mechanically and is rotated by a rotation driving mechanism  33  such as a motor. A cover  34  enclosing the rotation driving mechanism  33  is deployed under this spin chuck  32 . The spin chuck  32  is capable of moving up and down under the control of a lifting mechanism not shown in the drawing, transferring the substrate G from/to the transfer arm  21   a  at a lifting position. This spin chuck  32  is capable of adsorptive retention of the substrate G using vacuum attracting force or other forces. 
     Two undercups  35  and  36  are deployed on the periphery of a cover  34  at a distance from each other. Above the two undercups  35  and  36 , an innercup  37 , which mainly passes a redevelopment chemical downwards, is provided to freely move up and down. At the outside of the undercup  36 , an outercup  38 , which mainly passes a rinsing fluid downwards, is integrally provided capable of moving up and down in conjunction with the innercup  37 . Note that rising positions of the innercup  37  and the outercup  38  when the redevelopment chemical is being discharged are shown on the left side of  FIG. 5 , and lowering positions thereof when the rinsing fluid is being discharged are shown on the right side. 
     An exhaust outlet  39  is provided on the inner bottom of the undercup  35  to evacuate the unit when spinning and drying. A drain pipe  40   a  is deployed between the two undercups  35  and  36  to mainly drain the redevelopment chemical, and a drain pipe  40   b  is deployed on the outer bottom of the undercup  36  to mainly drain rinsing fluid. 
     As shown in  FIG. 4 , on one side of the outercup  38 , a nozzle holding arm  41  for supplying the redevelopment chemical and removal fluid is deployed, wherein the nozzle holding arm  41  accommodates a redevelopment chemical discharge nozzle  42   a  for applying the redevelopment chemical  25 , to substrate G and a removal fluid discharge nozzle  42   b.    
     A nozzle holding arm  41  is structured movable along the length of a guide rail  43  across the substrate G under the control of a drive mechanism  44  for driving a belt and the like. For application of the redevelopment chemical and discharge of the removal fluid, the nozzle holding arm  41  scans a stationary substrate G while the redevelopment chemical discharge nozzle  42   a  is discharging the redevelopment chemical or the removal fluid discharge nozzle  42   b  is discharging the removal fluid. 
     The redevelopment chemical discharge nozzle  42   a  and the removal fluid discharge nozzle  42   b  can be retracted in a nozzle retraction region  45 , which accommodates a nozzle cleaning mechanism  46  for cleaning the redevelopment chemical discharge nozzle  42   a  and the removal fluid discharge nozzle  42   b.    
     On the other side of the outercup  38 , a nozzle holding arm  47  for discharging a rinsing fluid such as pure water is deployed while a rinsing fluid discharge nozzle  48  is deployed at the edge of the nozzle holding arm  47 . The rinsing fluid discharge nozzle  48  may have a pipe-shaped discharge opening, for example. The nozzle holding arm  47  is structured capable of sliding along the length of a guide rail  43  under the control of a drive mechanism  49  and scanning the substrate G while the rinsing fluid discharge nozzle  48  is discharging the rinsing fluid. 
     Next, an outline of preprocessing and redevelopment processing using the aforementioned redevelopment/remover unit (REDEV/REMV)  30  is described. First, the innercup  37  and the outercup  38  are positioned at a lower position (i.e., the position shown on the right side of  FIG. 5 ), the transfer arm  21   a  holding a substrate G is inserted to the redevelopment/remover unit (REDEV/REMV)  30 , the spin chuck  32  is lifted at the same timing, and the substrate G is then transferred into the spin chuck  32 . Once the transfer arm  21   a  is retracted from the redevelopment/remover unit (REDEV/REMV)  30 , the spin chuck  32  on which the substrate G is mounted is lowered and then kept at a predetermined position. Then, the nozzle holding arm  41  moves to and stays at the predetermined position in the innercup  37 , a lifting mechanism  50   b  is extended to move and hold only the removal fluid discharge nozzle  42   b  at a lower position, and an alkaline removal fluid is discharged onto the substrate G using the removal fluid discharge nozzle  42   b  while the substrate G is scanned. A strong alkaline aqueous solution, for example, may be used as the removal fluid. During a predetermined reaction time, the lifting mechanism  50   b  contracts to return the removal fluid discharge nozzle  42   b  to an upper position and stay there, the nozzle holding arm  41  is retracted from the innercup  37  and the outercup  38 , the nozzle holding arm  47  is then driven instead to move the rinsing fluid discharge nozzle  48  up to a predetermined position on the substrate G. Afterwards, the innercup  37  and the outercup  38  are lifted and then kept at the upper position (on the left side of  FIG. 5 ). 
     The substrate G is then rotated at a low speed, and as the removal fluid on the substrate G is about to be shaken off, the rinsing fluid discharge nozzle  48  starts discharging the rinsing fluid. At almost the same time as this operation starts, an exhaust outlet  39  starts evacuating. The removal fluid and the rinsing fluid scattering towards the outer area of the substrate G after the substrate G starts rotating hit the tapered part of the innercup  37  and/or external wall (vertical side wall) and are then guided down to drain from the drain pipe  40   a.    
     After a predetermined time has elapsed since the substrate G as started rotating, the innercup  37  and the outercup  38  are lowered and then kept at a lower position while discharging the rinsing fluid and also rotating the substrate G. At the lower position, the horizontal position of the substrate G is set to be almost the same as that of the tapered part of the outercup  38 . In order to decrease the amount of residual removal fluid, the rotation speed of the substrate G is set to be greater than the initial rotation speed that allows the removal fluid to be shaken off. The operation of increasing the rotation speed of this substrate G may be performed any time such as at the same time as, after, or before the innercup  37  and the outercup  38  are lowered. In this manner, treatment fluid mainly made of rinsing fluid scattering from the substrate G hits the tapered part of the outercup  38  and/or the external wall and is then drained from the drain pipe  40   b.  Next, discharging the rinsing fluid is stopped, the rinsing fluid discharge nozzle  48  is stored at a predetermined position, and the rotation speed of the substrate G is further increased and then kept for a predetermined duration. In other words, spin drying for drying the substrate G is performed by rotating it at a high speed. 
     Next, the nozzle holding arm  41  is moved to a predetermined position in the innercup  37 , and then kept there. Afterwards, the lifting mechanism  50   a  is extended, then only the redevelopment chemical discharge nozzle  42   a  is lowered and kept at a low position where a predetermined redevelopment chemical is applied onto the substrate G using the redevelopment chemical discharge nozzle  42   a,  thereby forming a redevelopment chemical puddle while the substrate G is being scanned. Once the redevelopment chemical puddle is formed, during a predetermined redevelopment processing time (redevelopment reaction time), the lifting mechanism  50   a  returns the redevelopment chemical discharge nozzle  42   a  to the upper position and holds it there. The nozzle holding arm  41  is retracted from the innercup  37  and the outercup  38  and the nozzle holding arm  47  is then driven instead, keeping the rinsing fluid discharge nozzle  48  at a predetermined position above the substrate G. Afterwards, the innercup  37  and the outercup  38  are lifted and then kept at an upper position (on the left side in  FIG. 5 ). 
     The substrate G is then rotated at a low speed, and as the redevelopment chemical on the substrate G is about to be shaken off, the rinsing fluid discharge nozzle  48  starts discharging the rinsing fluid. At almost the same time as this operation starts, the exhaust outlet  39  starts evacuating. In other words, before the redevelopment reaction time elapses, it is preferable for the exhaust outlet  39  not to function, and thus no adverse influence such as air current development due to the operation of the exhaust outlet  39  develops on the redevelopment chemical puddle formed on the substrate G. 
     The redevelopment chemical and the rinsing fluid scattering towards the outer area of the substrate G after the substrate G starts rotating hit the tapered part of the innercup  37  and/or external wall (vertical side wall) and are then guided down to drain from the drain pipe  40   a.  After a predetermined time has elapsed since rotation of the substrate G has started, the innercup  37  and the outercup  38  are lowered and then kept at a lower position while discharging rinsing fluid and also rotating the substrate G. At the lower position, the horizontal position of the substrate G is set to be almost the same as that of the tapered part of the outercup  38 . In order to decrease the amount of residual removal fluid, the rotation speed of the substrate G is set to be greater than the initial rotation speed that allows removal fluid to be shaken off. The operation of increasing the rotation speed of this substrate G may be performed any time such as at the same time as, after, or before the innercup  37  and the outercup  38  are lowered. In this manner, treatment fluid mainly made of rinsing fluid scattering from the substrate G hits the tapered part of the outercup  38  and/or the external wall and is then drained from the drain pipe  40   b.  Next, discharging the rinsing fluid is stopped, the rinsing fluid discharge nozzle  48  is stored at a predetermined position, and the rotation speed of the substrate G is further increased and then kept for a predetermined duration. In other words, spin drying for drying the substrate G is performed by rotating it at a high speed. 
     In this manner described above, successive processing by the redevelopment/remover unit (REDEV/REMV)  30  is completed. Afterwards, in the reverse order to that described above, the transfer arm  21   a  carries the processed substrate G out from the redevelopment/remover unit (REDEV/REMV)  30 . 
     On the other hand, the reflow processing unit (REFLW)  60  of the processing station  2  performs reflowing by softening a resist formed on the substrate G using an organic solvent such as a thinner atmosphere and thereby re-covering. 
     Now, the structure of the reflow processing unit (REFLW)  60  is described in detail.  FIG. 6  is a cross-section of an outline of the reflow processing unit (REFLW)  60 . The reflow processing unit (REFLW)  60  includes a chamber  61 . The chamber  61  includes a lower chamber  61   a  and an upper chamber  61   b  connected to the upper part of the lower chamber  61   a.  The upper chamber  61   b  and the lower chamber  61   a  are structured to be able to open and close by an open/close mechanism not shown in the drawing; wherein the transfer unit  21  carries in/out the substrate G when it is closed. 
     Within this chamber  61 , a supporting table  62  horizontally supporting the substrate G is provided. The supporting table  62  is made of a material such as aluminum superior in thermal conductivity. 
     The supporting table  62  includes three lifting pins  63  (only two are illustrated in  FIG. 6 ), which are driven by a lifting mechanism to lower and raise the substrate G and pass through the supporting table  62 . These lifting pins  63  lift the substrate G from the supporting table  62  up to a predetermined position when the substrate G is transferred between the lifting pins  63  and the transfer unit  21 , and they are held so that the tips thereof are in height the same as the upper surface of the supporting table  62  while the substrate G is being subjected to ref lowing. 
     Exhaust outlets  64   a  and  64   b  connected to an exhaust system  64  are formed at the bottom of the lower chamber  61   a . The ambient gas in the chamber  61  is evacuated through this exhaust system  64 . 
     A temperature adjustment medium flow path  65  is provided in the supporting table  62 . A temperature adjustment medium such as temperature control coolant is introduced to this temperature adjustment medium flow path  65  via a temperature adjustment medium introduction pipe  65   a  and then drained from the temperature adjustment medium drain pipe  65   b  and circulated. The heat (e.g., for cooling) is transferred via the supporting table  62  to the substrate. G, thereby controlling the temperature of the to-be-processed surface of the substrate G to be a predetermined temperature. 
     A shower head  66  is provided on the ceiling of the chamber  61 , facing the supporting table  62 . Numerous gas discharge holes  66   b  are formed in the undersurface  66   a  of this shower head  66 . 
     A gas lead-in part  67  is provided at the upper center of the shower head  66  and coupled to a space  68  formed inside of the shower head  66 . A gas supplying pipe  69  is connected to the gas lead-in part  67 , and a bubbler tank  70 , which supplies an organic solvent such as thinner vapor, is connected to the other end of the gas supplying pipe  69 . Note that an on-off valve  71  is provided on the gas supplying pipe  69 . 
     A N 2  gas supplying pipe  74  connected to a N 2  gas supplying source not shown in the drawing is provided as a bubble generation means to vaporize thinner at the bottom of the bubbler tank  70 . A mass flow controller  72  and an on-off valve  73  are provided on the N 2  gas supplying pipe  74 . The bubbler tank  70  includes a temperature adjustment mechanism not shown in the drawing, which adjusts the temperature of the thinner stored inside to a predetermined temperature. It is structured to allow introduction of N 2  gas from the N 2  gas supplying source not shown in the drawing to the bottom of the bubbler tank  70  under the control of the mass flow controller  72  that controls the flow thereof, vaporization of the thinner in the bubbler tank  70  in which the temperature is adjusted to a predetermined temperature, and introduction of the resulting gas to the chamber  61  via the gas supplying pipe  69 . 
     Multiple purge gas lead-in parts  75  are provided at the upper rim of the shower head  66 , and a purge gas supplying pipe  76 , which supplies a purge gas such as N 2  gas to the chamber  61 , is connected to each purge gas lead-in part  75 . The purge gas supplying pipe  76  is connected to a purge gas supplying source not shown in the drawing, and an on-off valve  77  is provided therebetween. 
     First, in such a structure of the reflow processing unit (REFLW)  60 , the upper chamber  61   b  is disconnected from the lower chamber  61   a.  In this state, the transfer arm  21   a  of the transfer unit  21  carries in a substrate G having a resist pattern provided through preprocessing and redevelopment, and then mounts it on the supporting table  62 . The upper chamber  61   b  is connected to the lower chamber  61   a,  and the chamber  61  is then closed. Afterwards, the on-off valve  71  of the gas supplying pipe  69  and the on-off valve  73  of the N 2  gas supplying pipe  74  are opened. The N 2  gas flow is adjusted by the mass flow controller  72  and a vaporized amount of thinner is controlled. The bubbler tank  70  sends the resultant thinner vapor to the space  68  of the shower head  66  via the gas supplying pipe  69  and the gas lead-in part  67 , and the vapor is then output from the gas discharge holes  66   b.  Consequently, the chamber  61  confines a predetermined density of thinner atmosphere. 
     Since a resist pattern is formed on the substrate G mounted on the supporting table  62  in the chamber  61 , this resist is exposed to the thinner atmosphere, resulting in penetration of the thinner into the resist. As a result, the resist softens and its fluidity increases, and the resist deforms, covering a predetermined area (target region) of the surface of the substrate G. At this time, the temperature adjustment medium is introduced to the temperature adjustment medium flow path  65  provided in the supporting table  62 , heat thereof transfers to the substrate G via the supporting table  62 , and the temperature of the to-be-processed surface of the substrate G is adjusted to a predetermined temperature such as 20C. degrees. Once the gas including thinner discharged onto the surface of the substrate G from the shower head  66  hits the surface of the substrate G, it flows towards the exhaust outlets  64   a  and  64   b  and is consequently discharged out from the chamber  61 . 
     As described above, after the reflow processing unit (REFLW)  60  has completed reflowing, the on-off valve  77  on the purge gas supplying pipe  76  is opened while continuing to discharge, and N 2  gas as a purge gas is introduced to the chamber  61  via the purge gas lead-in part  75 , replacing the inner-chamber atmosphere. Afterwards, the upper chamber  61   b  is disconnected from the lower chamber  61   a.  In reverse order to that described above, the transfer arm  21   a  carries out the substrate G subjected to reflowing from the reflow processing unit (REFLW)  60 . 
     Each of the three heating/cooling units (HP/COL)  80   a ,  80   b,  and  80   c  includes a hot plate unit (HP) for heating each substrate G and a cooling plate unit (COL) for cooling down each substrate G, which are stacked (not shown in the drawing). These heating/cooling units (HP/COL)  80   a,    80   b,  and  80   c  heat and cool down the substrate G subjected to preprocessing, redevelopment processing, and ref lowing as necessary. 
     As shown in  FIG. 3 , each unit of the reflow processing system  100  is connected to process controller  90 , which includes a CPU in the control unit  3 . The process controller  90  has a user interface  91  connected thereto, which includes a keyboard used by a process manager to enter commands for managing the reflow processing system  100  and a display or the like for displaying a visualized operating status of the reflow processing system  100 . 
     The process controller  90  also has a storage unit  92  connected thereto, which is stored with recipes including control programs to be executed for a variety of processes by the process controller  90  in the reflow processing unit  100  and process condition data, etc. 
     In conformity with a command or the like from the user interface  91 , a recipe is then retrieved from the storage unit  92  as necessary and executed by the process controller  90 ; in other words, a desired process is performed by the reflow processing unit  100  under the control of the process controller  90 . The recipes described above may be stored in computer-readable storage media such as CD-ROM, hard disk, flexible disk, or flash memory, or they may be transmitted from other apparatus via a dedicated communication line, for example. 
     In the reflow processing unit  100  structured as described above, first, the transfer arm  11   a  of the transfer unit  11  in the cassette station  1  accesses a cassette C accommodating unprocessed substrates G and retrieves a single substrate G. The substrate G is transferred from the transfer arm  11   a  of the transfer unit  11  down to the transfer arm  21   a  of the transfer unit  21  running along the central transfer path  20  in the processing station  2 ; this transfer unit  21  carries it into the redevelopment/remover unit (REDEV/REMV)  30 . Afterwards, once the redevelopment/remover unit (REDEV/REMV)  30  has performed preprocessing and redevelopment processing, the substrate G is retrieved from the redevelopment/remover unit (REDEV/REMV)  30  by the transfer unit  21 , and then carried to one of the heating/cooling units (HP/COL)  80   a,    80   b,  and  80   c.  The substrate G subjected to the predetermined heating and cooling in each of the heating/cooling units (HP/COL)  80   a ,  80   b,  and  80   c  is carried to the reflow processing unit (REFLW)  60 , which then performs ref lowing. After the reflowing is completed, predetermined heating and cooling is performed by each of the heating/cooling units (HP/COL)  80   a,    80   b,  and  80   c  as necessary. The substrate G gone through such successive processing is transferred down to the transfer unit  11  of the cassette station  1  by the transfer unit  21 . 
     Next, a principle of the reflow method used in the reflow processing unit (REFLW)  60  is described. 
       FIG. 7A  shows a simplified cross-section of a resist  103  formed around the surface of a substrate G, explaining a conventional reflow method. The shape of the resist  103  surface is flat herein. An underlying layer  101  and an underlying layer  102  are stacked on the substrate G. Further on the resulting surface, the patterned resist  103  is formed. 
     According to the example of  FIG. 7A , target region S 1  exists on the surface of the underlying layer  101 . Softened resist  103  flows to this target region S 1  and covers it. On the other hand, prohibiting region S 2  such as an etching region exists on the surface of the underlying layer  102 , wherein this underlying layer  102  must avoid being covered by the resist  103 . The end of the underlying layer  102  protrudes laterally towards the target region S 1  rather than the side of the resist  103 , and a step D is formed therebetween. Such a step D is formed by redeveloping the resist  103  and thereby shaving the resist  103  laterally. 
     In the state shown in  FIG. 7A , an organic solvent such as thinner is made to touch and penetrate into the resist to soften and deform the resist  103  as shown in  FIG. 7B . Since the softened resist  103  increases in fluidity, it spreads across the surface of the underlying layer  102 . However, since it cannot go over the step D until the thickness of the flowing resist  103  exceeds a fixed height, the moving speed of the resist  103  gets slower at the stage D where the resist  103  stops moving ahead. 
     Due to such stoppage at around this step D, the resist  103  moves in the opposite direction to the step D where it is easy to flow. In other words, most of it tends to move towards a prohibiting region S 2  where coverage with the resist should be avoided. As shown in  FIG. 7C , the resist  103  does not cover the target region S 1  sufficiently, but reaches the prohibiting region S 2  and covers the surface thereof. When coverage of the target region S 1  is not complete such that the resist  103  reaches the prohibiting region S 2  where coverage with the resist is not desired, precision of the etched shape formed using, for example, the reflowed resist  103  decreases, resulting in failures in devices such as TFTs and decrease in yield. The state of the resist  103  described with reference to  FIGS. 7A through 7C  emanates from not being able to control the flow direction of the resist  103  softened by, the organic solvent. 
       FIGS. 8A through 8C  and  9 A through  9 C describe an idea of the reflow method according to the present invention. 
       FIG. 8A  shows a simplified cross-section of the resist  103  formed around the surface of the substrate G. The target region S 1 , the prohibiting region S 2  and the structure where an underlying layer  101  and an underlying layer  102  are stacked and formed, thereupon the patterned resist  103  is then formed, and the step D is formed at the end of the underlying layer  102 , are the same as those shown in  FIG. 7A . 
     The resist  103  according to the present invention has parts differing in thickness, and a step on the surface. In other words, there are different regions in height on the surface of the resist  103 , having a thick region  103   a  and a thin region  103   b  thinner than this thick region  103   a . The thick region  103   a  is formed on the target region S 1  side while the thin region  103   b  is formed on the prohibiting region S 2  side. 
     In the state shown in  FIG. 8A , an organic solvent such as thinner is made to touch the resist to soften and deform the resist  103 . The softened resist  103  increases in fluidity, spreading across the surface of the underlying layer  102 . As described above, since the resist  103  includes the thick region  103   a  and the thin region  103   b,  the flow orientation for the softened resist  103  can be controlled. Since the thick region  103   a,  for example, has a large exposed area to the thinner atmosphere, the thinner penetrates easily, resulting in a faster softening speed and high fluidity. Furthermore, since the thick region  103   a  has a relatively fast softening speed and has a large volume, the stagnant period until it goes over the step D is shortened, making it easier for the resist  103  to reach the target region S 1 , as shown in  FIG. 8 . 
     On the other hand, the thin region  103   b  has a smaller exposed area to the thinner atmosphere than the thick region  103   a,  thus softening speed thereof is not fast and fluidity does not increase as much as the thick region  103   a . Furthermore, the thin region  103   b  has a slower softening speed and a smaller volume than the thick region  103   a,  and thus flow of the resist  103  towards the prohibiting region S 2  is controlled, and as shown in  FIG. 8C , deformation stops without reaching the prohibiting region S 2 . This allows secure etching precision using the reflowed resist  103  as a mask, and favorable device characteristics. 
     In this manner, use of the resist  103  having the thick region  103   a,  the thin region  103   b,  and different regions in height on the surface allows control of the flow direction in which the resist  103  spreads, and secure sufficient etching precision. 
       FIGS. 9A through 9C  show simplified cross-sections of a resist  103  formed near the surface of a substrate G of another example. 
     As shown in  FIG. 9A , the target region S 1 , the prohibiting region S 2 , and the structure where an underlying layer  101  and an underlying layer  102  are stacked and formed, thereupon the patterned resist  103  is then formed, and the step D is formed at the end of the underlying layers  10  and  102 , are the same as those shown in  FIGS. 7A and 8A . The resist  103  according to this example has different regions in height on the surface, the thick region  103   a,  and the thin region  103   b  relatively thinner than the thick region  103   a.  However, in this example, the positional relationship of the thick region  103   a  and the thin region  103   b  relative to the target region S 1  and the prohibiting region S 2  is reverse to that in  FIG. 8A , wherein the thin region  103   b  is formed on the target region S 1  side and the thick region  103   a  is formed on the prohibiting region S 2  side. 
     In the state shown in  FIG. 9A , an organic solvent such as thinner is made to touch the resist  103  to soften and be deformed. The softened resist  103  increases in fluidity, spreading across the surface of the underlying layer  102 . As described above, since the resist  103  includes the thick region  103   a  and the thin region  103   b,  the flow direction of the softened resist  103  can be controlled. The thick region  103   a,  for example, has a large exposed area to the thinner atmosphere; however the lateral width (thickness)) is also formed to be thick. Therefore, it takes a long time for the thinner to penetrate into the center of the thick region  103   a  when the thinner concentration in the atmosphere is weak, and as shown in  FIG. 9B , and the entire thick region  103   a  never softens immediately nor becomes a ref lowed state. Accordingly, in a state where the inside of the thick region  103   a  does not soften, the thick region  103   a  acts as a dam, controlling the flow of the softened resist  103  towards the prohibiting region S 2 . 
     The thin region  103   b  has a smaller exposed area to the thinner atmosphere than the thick region  103   a,  however the entire volume is also small. Therefore, the thinner permeates quickly into the center even when the thinner concentration in the atmosphere is weak, softening relatively quickly. Furthermore, a reaction against the flow of the softened resist  103  towards the prohibiting region S 2  controlled by the thick region  103   a  acting as a dam is that the flow towards the target region S 1  increases and that the stagnant period until it goes over the step D is shortened, making it easier for the resist  103  to reach the target region S 1 . 
     In this manner, as a result of it taking a long time to soften up to the center of the thick region  103   a  due to a slower softening speed than the thin region  103   b,  the flow of the softened resist  103  stops without reaching the prohibiting region S 2 . This allows secure etching precision using the reflowed resist  103  as a mask, and favorable device characteristics. 
     In this manner, use of the resist  103  having the thick region  103   a,  the thin region  103   b,  and different regions in height on the surface allows control of the flow direction in which the resist  103  spreads, and secure sufficient etching precision. 
     The control of the resist flow orientation shown in  FIGS. 8A through 8C  and  9 A through  9 C may seem conflicting at first glance. However, the reflowed state of the resist  103  changes in conformity with conditions such as thinner concentration, flow rate, temperature of the substrate G (supporting table  62 ), inner pressure of the chamber  61  during ref lowing by the reflow processing unit (REFLW)  60 , for example. 
     As shown in  FIGS. 10A through 10D , for example, while thinner concentration, flow rate, and chamber inner pressure increase and flow speed of the resist also increases, flow speed of the resist  103  tends to decrease as the temperature increases. In other words, even if the form and location of the thick region  103   a  and the thin region  103   b  were the same, the degree of softening of the resist would change due to the thinner concentration within the chamber  61 , for example, and behaviors such as flow orientation and flow speed would be different. Accordingly, use of the resist  103  having different regions in height (the thick region and the thin region) on the surface allows control of its flow orientation and coverage area as needed under determined and selected experimental optimum conditions such as combined conditions of organic solvent concentration, flow rate, substrate temperature and pressure during ref lowing. 
       FIGS. 11 and 12  are top views of main parts on a substrate G surface describing yet another example. In this example, by designing a resist  103  having a flat shape instead of having different regions in height (the thick region and the thin region) on the surface as shown in  FIGS. 8A and 9A  as already described, control of the flow orientation thereof as needed is attempted. Note that a state of the resist  103  before subjected to ref lowing is shown on the left side of  FIGS. 11 and 12  while the state of the resist  103  during ref lowing is shown in the center, and the state of the ref lowed resist  103  is shown on the right side. 
       FIG. 11  shows how the deformed resist  103  resulting from subjecting an original square resist  103  when seen from above to reflowing spreads. From  FIG. 11 , it can be seen that the resist  103  spreads in an approximate circle centered on the original resist  103  (square) indicated by a dotted line. On the other hand,  FIG. 12  shows how the resist  103  resulting from subjecting an original rectangle resist  103  to reflowing to dissolve itself spreads. It can be seen also in this case that the resist  103  spreads in an approximate circle centered on the original resist  103  (rectangle) indicated by a dotted line. 
     As shown in these  FIGS. 11 and 12 , regardless of the flat shape of the original resist  103 , the softened resist  103  has a characteristic of spreading in an approximate circle due to surface tension as a characteristic of the reflowing. Use of this characteristic of how this resist  103  spreads allows control of the flow orientation thereof. More specifically, we can see that L 1  is almost equal to L 2 , but L 3  is a larger flow distance than L 4 , through comparison of distances L 1  and L 2  from the reflowed original resist  103  of  FIG. 11  with flow distances L 3  and L 4  from the reflowed original resist  103  of  FIG. 12 . In other words, a difference in the flow distances L 3  and L 4  can be provided by using a flat quadrilateral resist  103  and adjusting the horizontal and vertical dimensions thereof. In this manner, the flow orientation and the flow distance (coverage area) of the softened resist  102  can be controlled by devising the flat shape of the resist  105 . 
     For example, as shown in  FIG. 13A , a rectangle resist  103  (see the cross section of  FIG. 13B ) having thick regions  103   a  and a thin region  103   b  deployed therebetween along the length thereof is prepared. When the resist  103  shown in  FIG. 13A  is subjected to reflowing, a flow distance L 5  of the resist  103  extending vertically in this drawing is greater than a flow distance L 6  of the resist  103  extending along the width of this drawing because the resist has a rectangular shape. Furthermore, since the resist  103  having the thick regions  103   a  along the length is used, the flow distance L 5  further increases, resulting in an oval re-coverage area by the resist  103  when viewed from above. In this manner, combination of such a plane shape and such a cross sectional shape of the resist  103  allows further effective control of the flow orientation and the flow distance (coverage area) of the resist  103 . 
     Next, an embodiment where the reflow method according to the present invention is applied to a fabrication process for a TFT for an LCD is described while referencing  FIGS. 14 through 26 . Note that the main processes are also shown in a flowchart of  FIG. 27 . 
     First, as shown in  FIG. 14 , a gate electrode  202  and a gate line not shown in the drawing are formed on an insulating substrate  201  made of a transparent substrate such as glass, and a gate insulating film  203  such as a silicon nitride film, an amorphous silicon (a−Si) film  204 , an n+Si film  205  to be used as an ohmic layer, and a metallic film  206  for electrodes are stacked and deposited in this order (Step S 1 ). 
     Next, as shown in  FIG. 15 , a resist  207  is formed on the metallic film  206  for electrodes (Step S 2 ). As shown in  FIG. 16 , exposure processing is then performed using a half-tone mask  300  as an exposure mask, which have regions different from each other in transmissivity of light and is capable of varying light exposure for respective regions of the resist  207  (Step S 3 ). This half-tone mask  300  may be structured to provide three different exposures for the resist  207 . Performing half-exposure on the resist  207  in this manner results in formation of exposed resist regions  208  and unexposed resist regions  209 , as shown in  FIG. 17 . The unexposed resist regions  209  are formed into a staircase shape at the borders with the exposed resist regions  208  due to the transmissivity of the mask  300 . 
     Development is performed after exposure, thereby removing the exposed resist regions  208 , leaving the unexposed resist regions  209  on the metallic film  206  for electrodes, as shown in  FIG. 18  (Step S 4 ). The unexposed resist regions  209  are separated into a resist mask  210  for source electrodes and a resist mask  211  for drain electrodes, configuring a pattern. The resist mask  210  for source electrodes includes a first thick region  210   a,  a second thick region  210   b , and a third thick region  210   c  in order of thickness formed in a staircase shape through half-exposure. The resist mask  211  for drain electrodes includes a first thick region  211   a,  a second thick region  211   b,  and a third thick region  211   c  in order of thickness formed in a staircase shape through half-exposure. 
     Afterwards, the metallic film  206  for electrodes is etched using the remaining unexposed resist regions  209  as an etching mask, and as shown in  FIG. 19 , a concave portion  220 , which will become a channel region later, is formed (Step S 5 ). As a result of this etching, a source electrode  206   a  and a drain electrode  206   b  may be formed to expose the surface of the n+Si film  205  within the concave portion  220  between the electrodes. Furthermore, thin surface damaged layers  301  are formed through etching near the surfaces of the resist mask  210  for source electrodes and the resist mask  211  for drain electrodes. 
     Next, wet processing is performed using a removal fluid, the surface damaged layers  301  are removed (preprocessing) after the metallic film  206  for electrodes are etched, and redevelopment processing is then performed for partially removing the unexposed resist regions  209  on the source electrode  206   a  and the drain electrode  206   b  (Step S 6 ). This preprocessing and redevelopment processing may be continuously performed by the redevelopment/remover unit (REDEV/REMV)  30  of the reflow processing system  100 . 
     Through this redevelopment processing, the coverage areas by the resist mask  210  for source electrodes and the resist mask  211  for drain electrodes are considerably reduced, as shown in  FIG. 20 . More specifically, of the resist mask  210  for source electrodes, the third thick region  210   c  is completely removed, and the first thick region  210   a  and the second thick region  210   b  are left on the source electrode  206   a.  Furthermore, even of the resist mask  211  for drain electrodes, the third thick region  211   c  is completely removed, and the first thick region  211   a  and the second thick region  211   b  are left on the drain electrode  206   b.    
     In this manner, the coverage areas by the resist mask  210  for source electrodes and the resist mask  211  for drain electrodes are reduced through redevelopment processing, thereby preventing the deformed ref lowed resist from protruding out from the end of the source electrode  206   a  or the end of the drain electrode  206   b  that are on opposite sides of a target region (concave portion  220 ) and covering underlayers. As a result, miniaturization of TFTs is possible. 
     Note that in  FIG. 20 , contours of the resist mask  210  for source electrodes and the resist mask  211  for drain electrodes before redevelopment processing are indicated by dotted lines for comparison. The top view corresponding to the cross-section shown in  FIG. 20  is shown in  FIG. 25 . 
     Furthermore, thicknesses of the first thick region  210   a  and the second thick region  210   b  (or the first thick region  211   a  and the second thick region  211   b ), and total lateral thicknesses (widths) L 8  become smaller than total lateral thicknesses (widths) L 7  (see  FIG. 19 ) before redevelopment through redevelopment processing. A step D is then formed in the concave part  220  due to misalignment of the edge of the first thick region  210   a  of the resist mask  210  for source electrodes in the concave part  220  from the edge of the source electrode  206   a  directly therebelow. Similarly, a step D is formed in the concave part  220  due to misalignment of the edge of the first thick region  211   a  of the resist mask  211  for drain electrodes in the concave part  220  from the edge of the source electrode  206   b  directly therebelow. 
     In other words, as a result of the resist mask  210  for source electrodes and the resist mask  211  for drain electrodes also shaved laterally through redevelopment, the distance between the end of the resist mask  210  for source electrodes in the concave part  220  and the end of the resist mask  211  for drain electrodes is greater than distance between the source electrode  206   a  and the drain electrode  206   b  in the layer therebelow. 
     When such steps D are formed, not only does control of the flow orientation of the softened resist when covering the target region (in this case, the concave part  220 ) with the softened resist in the subsequent reflow process become difficult, but it also causes increase in ref lowing time and decrease in throughput since the flow stops until it goes over the steps D. 
     Therefore, with this embodiment, the first thick regions  210   a  and  211   a  as thick regions and the second thick regions  210   b  and  211   b  as thin regions are provided to the resist mask  210  for source electrodes and the resist mask  211  for drain electrodes, respectively, and control of the flow orientation of the softened resist and shortening of the processing time are implemented, so as for the softened resist to easily go over the steps D and flow into the concave part  220  of the target region. In the ref lowing (Step S 7 ), the resist softened by an organic solvent such as thinner is then made to flow into the concave part  220 , which is intended to become a channel region later, in a short time, and thus the concave part  220  may be securely covered. This reflowing is performed by the reflow processing unit (REFLW)  60  of  FIG. 6 . 
       FIG. 21  shows the periphery of the concave part  220  being covered by a deformed resist  212 . The top view corresponding to the cross-section shown in  FIG. 21  is shown in  FIG. 26 . 
     With the conventional technology, there is a problem that since the deformed resist  212  spreads up to the other side of the concave part  220  of the source electrode  206   a  and the drain electrode  206   b,  for example, and covers the n+Si film  205 , which is an ohmic contact layer, the covered parts are not etched in the following silicon etching process, and etching precision is lost, thereby bringing about TFT failure and reduction in yield. Furthermore, there is a problem that if the coverage area by the deformed resist  212  is largely estimated beforehand and then designed, necessary area (dot area) for fabricating a single TFT increases, and high integration and miniaturization of TFTs is difficult. 
     On the contrary, with this embodiment, since reflowing is performed after drastically reducing the volume of the resist mask  210  for source electrodes and the resist mask  211  for drain electrodes through redevelopment processing, the covered region by the deformed resist  212  is limited to the periphery of the concave part  220 , which is the target region for reflowing, and the thickness of the deformed resist  212  is formed thin. This allows high integration and miniaturization of TFTs. 
     Next, as shown in  FIG. 22 , the n+Si film  205  and the a−Si film  204  are etched using the source electrode  206   a , the drain electrode  206   b  and the deformed resist  212  as an etching mask (Step S 8 ). Afterwards, as shown in  FIG. 23 , the deformed resist  212  is removed through wet processing or other related processing, for example (Step S 9 ). The n+Si film  205  exposed in the concave part  220  is then etched using the source electrode  206   a  and the drain electrode  206   b  as an etching mask (Step S 10 ). As a result, a channel region  221  is formed, as shown in  FIG. 24 . 
     While subsequent processes have been omitted from the drawings, an organic film is formed so as to cover the channel region  221 , the source electrode  206   a,  and the drain electrode  206   b  (Step S 11 ), a contact hole connected to the source electrode  206   a  (drain electrode  206   b ) is formed through photolithography and etching (Step S 12 ), and a transparent electrode made of indium-tin oxide (ITO) or the like is then formed (Step S 13 ). As a result, a TFT for an LCD is fabricated. 
     As is comprehensible from the description of this embodiment given above, according to the present invention, use of a resist film having thick regions and thin regions for ref lowing allows control of the flow orientation and flow area (spreading area) of softened resist. Therefore, use of the reflow method according to the present invention for fabrication of semiconductor devices such as TFTs having an etching process repeatedly conducted using a resist as a mask allows omission of masks and reduction in number of processes. Accordingly, it is possible to achieve reduction in processing time and improvement in etching precision, and contribute to high integration and miniaturization of semiconductor devices. 
     Note that the present invention is not limited to the above-given embodiment, and various modifications are possible within the scope of the present invention. For example, the example of TFT fabrication using a glass substrate for an LCD is given in the above-given description; however, the present invention may also be applied to ref lowing for a resist formed on a substrate such as another flat panel display (FPD) substrate or a semiconductor substrate. Furthermore, while the resist film is structured including thick films and thin films in the above-given embodiment, change in resist thickness is not limited to two levels and may have three or more levels. Moreover, not only can the resist thickness be varied to be a staircase shape, but it may be formed to have a slanted surface such that the thickness gradually varies. In this case, a slanted surface may be formed on the resist surface after half-exposure by giving a slant to the applied film thickness of the resist in advance.