Abstract:
A resist coating/developing apparatus includes: a resist film-forming unit configured to apply a resist onto a substrate to form thereon a resist film; a resist developing unit configured to develop the resist film after exposure to pattern the resist film; a solvent gas generator configured to generate a solvent gas containing a vapor of a solvent having a property of dissolving the resist film; a solvent gas conditioner connected to the solvent gas generator and configured to condition the solvent gas generated in the solvent gas generator; a processing chamber configured to house the substrate having thereon the resist film which has been developed and patterned in the resist developing unit, and connected to the solvent gas conditioner so that the solvent gas, which has been conditioned in the solvent gas conditioning section, is supplied to the substrate housed in the processing chamber; and an exhaust system connected to the processing chamber to evacuate the processing chamber to a reduced pressure.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Technical Field 
         [0002]    The present invention relates to a resist coating and developing (hereinafter abbreviated as “coating/developing”) apparatus and method for coating a substrate with a resist film, and developing the resist film after exposure to form a resist pattern, and more particularly to a resist coating/developing apparatus and method which, by flattening the resist pattern, can reduce the line width roughness of the resist pattern. 
         [0003]    2. Background Art 
         [0004]    In order to manufacture semiconductor integrated circuits with higher levels of integration, there is a demand for the production of finer circuit patterns. For example, the critical dimension of (CD) of an etching mask is reaching 32 nm or even 22 nm, which values are lower than the resolution limits of existing exposure apparatuses. In the formation of the channel of a field-effect transistor (FET), having such a width, a large line width roughness (LWR) of resist pattern will lead to variation in the threshold voltage of the FET, causing problems such as worsening of properties or abnormal operation of the resulting integrated circuit. 
         [0005]    To address such problems, Japanese Patent Laid-Open Publication No. 2005-19969 (JP2005-019969A) describes a method for flattening surface irregularities of a resist film uniform by supplying a solvent gas to a resist film to dissolve the surface of the resist film. 
         [0006]    When supplying a solvent gas to a resist film in a resist coating/developing apparatus, it is possible that the solvent gas may diffuse in the resist coating/developing apparatus and a resist film before development may be exposed to the solvent gas. In the case where the resist film is formed of a chemically-amplified resist, an acidic component in the resist film can be neutralized by an alkaline component contained in the solvent, which may inhibit development of the resist film and can even make patterning of the resist film impossible. 
         [0007]    Some solvents have a strong pungent odor. If a gas of such a solvent leaks from a resist coating/developing apparatus into the surrounding space, the diffused gas will give an unpleasant feeling to an operator of the apparatus. 
       SUMMARY OF THE INVENTION 
       [0008]    The present invention provides a resist coating/developing apparatus and a resist coating/developing method, which can effectively reduce the line width roughness of a resist pattern while preventing a solvent gas from diffusing outside. 
         [0009]    According to a first aspect of the present invention, there is provided a resist coating/developing apparatus comprising: a resist film-forming unit configured to apply a resist onto a substrate to form thereon a resist film; a resist developing unit configured to develop the resist film after exposure to pattern the resist film; a solvent gas generator configured to generate a solvent gas containing a vapor of a solvent having a property of dissolving the resist film; a solvent gas conditioner connected to the solvent gas generator and configured to condition the solvent gas generated in the solvent gas generator; a processing chamber configured to house the substrate having thereon the resist film which has been developed and patterned in the resist developing unit, and connected to the solvent gas conditioner so that the solvent gas, which has been conditioned in the solvent gas conditioner, is supplied to the substrate housed in the processing chamber; and an exhaust system connected to the processing chamber to evacuate the processing chamber to a reduced pressure. 
         [0010]    According to a second aspect of the present invention, there is provided a resist coating/developing method comprising: applying a resist onto a substrate to form a resist film; exposing the resist film using a photomask; developing and patterning the exposed resist film; housing the substrate having the patterned resist film in a processing chamber; evacuating the processing chamber to a reduced internal pressure; generating a solvent gas containing a vapor of a solvent having a property of dissolving the resist film; conditioning the solvent gas; and supplying the conditioned solvent gas to the substrate housed in the processing chamber. 
         [0011]    The embodiments of the resist coating/developing apparatus and method according to the present invention can effectively reduce the line width roughness of a resist pattern while avoiding contamination of the process atmosphere. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a schematic plan view showing the construction of a resist coating/developing apparatus according to an embodiment of the present invention; 
           [0013]      FIG. 2  is a schematic front view of the resist coating/developing apparatus of  FIG. 1 ; 
           [0014]      FIG. 3  is a schematic back view of the resist coating/developing apparatus of  FIG. 1 ; 
           [0015]      FIG. 4  is a schematic plan view of a resist film processing apparatus included in the resist coating/developing apparatus shown in  FIGS. 1 through 3 ; 
           [0016]      FIG. 5  is a schematic cross-sectional view showing the resist film processing apparatus of  FIG. 4 , a solvent gas generator and a solvent gas conditioner. 
           [0017]      FIG. 6A  is a perspective view showing the mist removal nozzle of the solvent gas conditioner shown in  FIG. 5 , 
           [0018]      FIG. 6B  is a side view of the mist removal nozzle of  FIG. 6A  as viewed in the direction of arrow AR 1  shown in  FIG. 6A ;  FIG. 6C  is a side view of the mist removal nozzle of  FIG. 6A  as viewed in the direction of arrow AR 2  shown in  FIG. 6A ; 
           [0019]      FIG. 7  is a diagram illustrating the effect of the resist film processing apparatus shown in  FIG. 4 ; 
           [0020]      FIG. 8  is a diagram showing a variation of the solvent gas generator shown in  FIG. 5 ; and 
           [0021]      FIG. 9  is a diagram showing a variation of the solvent gas conditioner shown in  FIG. 5 . 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0022]    Non-limitative exemplary embodiments of the present invention will now be described with reference to the drawings. In the drawings, the same reference numerals are used for the same or equivalent members or components, and a duplicate description thereof will be omitted. 
         [0023]      FIG. 1  is a schematic plan view showing the construction of a resist coating/developing apparatus  1  according to an embodiment of the present invention;  FIG. 2  is a schematic front view of the resist coating/developing apparatus  1 ; and  FIG. 3  is a schematic back view of the resist coating/developing apparatus  1 . As shown in  FIG. 1 , the resist coating/developing apparatus  1  includes a cassette station  2 , a processing station  3  and an interface section  4 . 
         [0024]    The cassette station  2  includes a stage section  6  on which a cassette C, e.g. housing  25  wafers, is placed, and a wafer transporter  7  for taking a wafer W out of the cassette C placed on the stage section  6 , and transferring the wafer W between the cassette C and the processing station  3 . A plurality of (e.g. four) cassettes C can be placed on the stage section  6  along the X direction (longitudinal direction of the cassette station  2 ) of  FIG. 1 . The wafer transporter  7  is disposed between the stage section  6  of the cassette station  2  and the processing station  3 , and can move in the X direction along a transport route  8 . The wafer transporter  7  has a wafer transport arm  7   a  which is movable in the Y direction, Z direction (vertical direction) and θ direction (direction of rotation around Z axis) shown in  FIG. 1 . The wafer transporter  7  having such construction can selectively reach one of the cassettes C placed on the stage section  6  and sequentially take out wafers W which are housed in multiple stages in the Z direction in the cassette C, and can transport the respective wafers W to the below-described third processing apparatus group G 3  of the processing station  3 . The wafer transporter  7  preferably has an alignment function of performing alignment of each wafer W. 
         [0025]    The processing station  3  includes a main transport apparatus  13  provided generally centrally in the processing station  3 , and four processing apparatus groups G 1 , G 2 , G 3 , G 4  disposed around the main transport apparatus  13 . These processing apparatus groups each have various processing apparatuses disposed in multiple stages, as will be described later. The first processing apparatus group G 1  and the second processing apparatus group G 2  are disposed on one side of the main transport apparatus  13  in the X direction. The third processing apparatus group G 3  and the fourth processing apparatus group G 4  are disposed on both sides of the main transport apparatus  13  in the Y direction. In particular, the third processing apparatus group G 3  is disposed adjacent to the cassette station  2 , and the fourth processing apparatus group G 4  is disposed adjacent to the interface section  4 . 
         [0026]    The main transport apparatus  13  can carry a wafer W into and out of the below-described various processing apparatuses, disposed in the processing apparatus groups G 1 , G 2 , G 3 , G 4 , and the below-described resist film processing apparatus  60 . 
         [0027]    As shown in  FIG. 2 , the first processing apparatus group G 1  and the second processing apparatus group G 2  each include a resist coating apparatus  17  for applying a resist solution onto a wafer W to form a resist film, and a developing apparatus  18 , disposed above the resist coating apparatus  17 , for developing the resist film after exposure. 
         [0028]    As shown in  FIG. 3 , the third processing apparatus group G 3  includes, in ascending order beginning with the lowest apparatus, a cooling apparatus  30  for cooling the wafer W, an adhesion-enhancing apparatus  31  for carrying out adhesion-enhancing processing to enhance fixing of the resist solution to the wafer W, an extension apparatus  32  for transferring the wafer W, pre-baking apparatuses  33 ,  34  for carrying out baking to evaporate a solvent from the resist solution on the wafer W, an auxiliary baking apparatus  35 , and a post-baking apparatus  36  for carrying out post-baking to heat the developed resist film. 
         [0029]    As shown in  FIG. 3 , the fourth processing apparatus group. G 4  includes, in ascending, order beginning with the lowest apparatus, a cooling apparatus  40 , an extension/cooling apparatus  41  for naturally cooling the wafer W, an extension apparatus  42  for transferring the wafer W between the main transport apparatus  13  and the below-described wafer transporter  50 , a cooling apparatus  43 , post-exposure baking apparatuses  44 ,  45  for heating the resist film after exposure, a preliminary baking apparatus  46 , and a post-baking apparatus  47 . 
         [0030]    The number and the arrangement of such processing apparatus groups, and the number, the types and the arrangement of processing apparatuses provided in each processing apparatus group, may be arbitrarily selected depending on the particular processing carried out in the resist coating/developing apparatus  1 , the type of the device to be produced, etc. 
         [0031]    Referring again to  FIG. 1 , a wafer transporter  50  is provided centrally in the interface section  4 . The wafer transporter  50  is configured to be movable in the X and Z directions and rotatable in the θ direction. The wafer transporter  50  can transport a wafer W to the extension/cooling apparatus  41  and the extension apparatus  42 , both belonging to the fourth processing apparatus group G 4 , a peripheral exposure apparatus  51  and an exposure apparatus  5 . 
         [0032]    A resist film processing apparatus  60 , disposed in the processing station  3 , will now be described by referring to  FIGS. 4 through 6 . 
         [0033]    Referring to  FIG. 4 , the resist film processing apparatus  60  includes a processing chamber  62  for carrying out processing of a resist film, and a load lock chamber  64  connected via a gate valve GV 1  to the processing chamber  62 . In the processing chamber  62  is disposed a susceptor  62 S for placing a wafer W on it. The susceptor  62 S has three through-holes and three lifting pins  62 P which move vertically though the through-holes to place the wafer W on the susceptor  62 S and lift it up from the susceptor  62 S. The susceptor also has a built-in heating section  62 H ( FIG. 5 ) e.g. comprised of a heating wire. To the heating section  62 H are connected a power source, a temperature measurement section, a temperature regulator, etc., not shown, so that the susceptor  62 S and the wafer W placed on it can be heated at a predetermined temperature. The susceptor  62 S preferably also has an electrostatic chuck. 
         [0034]    A plurality of (e.g. four as shown in  FIG. 4 ) exhaust ports  62 E are formed in the bottom of the processing chamber  62 , so that the interior of the processing chamber  62  can be kept at a reduced pressure by means of an exhaust system  70  (shown schematically) connected to the exhaust ports  62 E. The exhaust system  70  preferably has a turbo-molecular pump which can achieve a high exhaust velocity. A pressure regulating valve (not shown) is provided in piping connecting the exhaust ports  62  and the exhaust system. The pressure regulating valve, together with a pressure gauge, etc. (not shown) provided in the processing chamber  62 , is controlled by a control section (not shown), whereby the pressure in the processing chamber  62  can be adjusted. 
         [0035]    The load lock chamber  64  is provided with a transport arm  64 A for supporting and transporting a wafer W. The transport arm  64 A is movably supported by a guide rail  66  ( FIG. 5 ) and can be reciprocated by means of a not-shown driving device along the guide rail  66  in the Y direction shown in  FIG. 5 . The transport arm  64 A has two slit portions through which three lifting pins  64 P can move vertically. By the vertical movement of the lifting pins  64 P, the wafer W is placed on the transport arm  64 A and lifted up from the transport arm  64 A. In this embodiment a conduit for passage of a fluid is provided within the transport arm  64 A, and a temperature-controlled fluid can be passed through the conduit by means of a not-shown fluid circulating device. This can cool the wafer W placed on the transport arm  64 A. Because the transport arm  64 A can make contact with the wafer W in a large area except the slit portions that permit the vertical movement of the lifting pins  64 P, the wafer W can be cooled efficiently. 
         [0036]    The load lock chamber  64  has a gate valve GV 2  that faces the main transport apparatus  13 . When the gate valve GV 2  is open, the main transport apparatus  13  can carry the wafer W into and out of the load lock chamber  64 . When the gate valve GV 2  is closed, the load lock chamber  64  can be kept airtight. A plurality of (e.g. four as shown in  FIGS. 4 and 5 ) exhaust ports  64 E are formed in the bottom of the load lock chamber  64 , so that the interior of the load lock chamber  64  can be kept at a reduced pressure by means of an exhaust system connected to the exhaust ports  64 E. 
         [0037]    Referring to  FIGS. 4 and 5 , the load lock chamber  64  is provided with an ultraviolet lamp UV disposed near the ceiling portion and extending along the gate valve GV 1 . The ultraviolet lamp UV may be a xenon excimer lamp that emits ultraviolet light whose dominant wavelength is 172 nm. By using the ultraviolet lamp UV disposed as shown in the Figures, the wafer W can be irradiated with ultraviolet light when carrying the wafer W from the load lock chamber  64  to the processing chamber  62  (or carrying the wafer W from the processing chamber  62  to the load lock chamber  64 ) by the transport arm  64 A. It is also possible to provide the ultraviolet lamp UV near the ceiling portion of the load lock chamber  64  such that it extends along the gate valve GV 2 . This makes it possible to irradiate the wafer W with ultraviolet light when carrying the wafer W into or out of the load lock chamber  64  by the main transport apparatus  13 . Further, it is also possible to dispose a xenon excimer lamp above the wafer W placed on the transport arm  64 A and to irradiate the entire surface of the wafer W with, ultraviolet light by using a mirror, a reflector, or the like. 
         [0038]    Referring to  FIG. 5 , to the resist film processing apparatus  60  are connected a solvent gas generator  67 A for generating a solvent gas to be supplied to a resist film on the wafer W, and a solvent gas conditioner  65 A for conditioning the solvent gas generated by the solvent gas generator  67 A. For convenience of illustration, the solvent gas generator  67 A and the solvent vapor conditioner  65 A are depicted next to the processing chamber  62  of the resist film processing apparatus  60 ; however, their location is not limited to such a position. For example, the solvent gas generator  67 A and the solvent vapor conditioner  65 A may be disposed next to the load lock chamber  64  of the resist film processing apparatus  60 , or disposed above the resist film processing apparatus  60 . In  FIGS. 1 and 4 , an illustration of the solvent gas generator  67 A and the solvent vapor conditioner  65 A is omitted. 
         [0039]    As schematically shown in  FIG. 5 , a bubbler tank is used as the solvent gas generator  67 A in this embodiment. In particular, a solvent (liquid) is held in the solvent gas generator  67 A. To the solvent gas generator  67 A are connected a gas intake pipe  67 B for taking in a carried gas that causes bubbling of the solvent, and a bridge pipe  65 B for feeding a solvent gas containing the carrier gas and a vapor of the solvent produced by bubbling of the solvent to the solvent gas conditioner  65 A. The carrier gas may be an inert gas, such as argon (Ar) gas or helium (He) gas, or nitrogen (N 2 ) gas, and is supplied to the gas intake pipe  67 B from a not-shown carrier gas supply source. In another embodiment, a solvent gas may be composed of a vapor of a solvent without including a carrier gas. 
         [0040]    In this embodiment the solvent gas generator  67 A is housed in a thermostatic container  67 T, so that the solvent gas generator  67 A, the gas intake pipe  67 B and the bridge pipe  65 B can be kept at approximately the same temperature. The temperature may be such a temperature as not cause decomposition or denaturation of the solvent, for example, in the range of 80° C. to 120° C., and in particular about 100° C. The temperature of the solvent gas generator  67 A is preferably higher than the temperature of the solvent gas conditioner  65 A, as will be described later. A tape-shaped heater  65 H is wound around the bridge pipe  65 B in its portion lying outside the thermostatic container  67 T. By heating the bridge pipe  65 B with the heater  65 H, condensation of the solvent gas in the bridge pipe  65 B can be prevented. 
         [0041]    The solvent held in the solvent gas generator  67 A preferably has the property of dissolving a resist film. Even if the solvent cannot dissolve a resist film, it is sufficient that the solvent has the property of being absorbed into the resist film and swelling the solvent-absorbed portion of the resist film. Such property is herein included in the resist film-dissolving property of the solvent. Specific examples of preferable solvents may include acetone, propylene glycol monomethyl ether acetate (PGMEA), N-methyl-2-pyrrolidinone (NMP), etc. 
         [0042]    The gas intake pipe  67 B of the solvent gas generator  67 A, in its portion lying between the carrier gas supply source (not shown) and the solvent gas generator  67 A, is provided with an on-off valve (not shown) for starting/stopping the supply of the carrier gas and a flow controller (not shown) for controlling the flow rate of the carrier gas. The start/stop of the supply of the carried gas and the gas flow rate are controlled by a not-shown control section. 
         [0043]    The solvent gas conditioner  65 A is comprised of a hollow tank e.g. having a similar size to the bubbler tank. To the solvent gas conditioner  65 A is connected the bridge pipe  65 B from the solvent gas generator  67 A, so that the solvent gas generated by the solvent gas generator  67 A can be fed into the solvent gas conditioner  65 A. To the solvent gas conditioner  65 A is also connected a bridge pipe  6213  as a delivery pipe whereby the solvent gas is sent from the solvent gas conditioner  65 A to the processing chamber  62 . The solvent gas conditioner  65 A is housed in a thermostatic container  65 T, so that the solvent gas conditioner  65 A, the bridge pipe  65 B and the bridge pipe  62 B can be kept at approximately the same temperature. The temperature may be, for example, in the range of about 70° C. to about 90° C. and preferably about 80° C. Further, the temperature is preferably lower than the temperature of the solvent gas generator  67 A. 
         [0044]    In the interior of the solvent gas conditioner  65 A is provided a mist removal nozzle  65 C connected to the bridge pipe  65 B from the solvent gas generator  67 A. As shown in  FIG. 6A , the mist removal nozzle  65 C includes a funnel portion  65 C 1  connected to the bridge pipe  65 B, and a flat rectangular conduit portion  65 C 2  connected to the funnel portion  65 C 1 . 
         [0045]    The funnel portion  65 C 1  is comprised of two plate-like members having a generally triangular shape, and is connected to the bridge pipe  65 B at the apex of the triangle and to the rectangular conduit portion  65 C 2  in the base of the triangle. The funnel portion  65 C 1  is sealed in the side walls of the two plate-like members, and has a flat funnel-like shape as a whole. 
         [0046]      FIG. 6B  is a side view of the mist removal nozzle  65 C as viewed in the direction of arrow AR 1  shown in  FIG. 6A . As shown in the Figure, the thickness of the funnel portion  65 C 1  gradually decreases from the bridge pipe  65 B side, having the maximum thickness equal to the outside diameter of the bridge pipe  65 B, to the rectangular conduit portion  65 C 2  side, having the minimum thickness equal to the thickness of the flat rectangular conduit portion  65 C 2 . The flow passage of the solvent gas is thus converted from the flow passage having a circular cross-section in the bridge pipe  65 B into the flow passage having a rectangular cross-section in the rectangular conduit portion  65 C 2 . 
         [0047]    The rectangular conduit portion  65 C 2  is open at the end connecting to the funnel portion  65 C 1  and at the opposite end so that the solvent gas, fed through the bridge pipe  65 B, is ejected into the solvent gas conditioner  65 A. As shown in  FIGS. 6A and 6C  (side view of the mist removal nozzle  65 C as viewed in the direction of arrow AR 2  shown in  FIG. 6A ), in the interior of the rectangular conduit portion  65 C 2  are provided a number of partition walls  65 C 3  extending in the gas flow direction in which the solvent gas flows from the funnel portion  65 C 1  to the rectangular conduit portion  65 C 2 . The partition walls  65 C 3  can increase the surface area of the interior surface of the rectangular conduit portion  65 C 2 . As shown in  FIG. 5 , the rectangular conduit portion  65 C 2  is provided with a thermocouple TC so that the temperature of the rectangular conduit portion  65 C 2  (mist removal nozzle  65 C) can be controlled. 
         [0048]    According to the solvent gas conditioner  65 A thus constructed, if a mist or minute droplets are contained in the solvent gas supplied from the solvent gas generator  67 A to the solvent gas conditioner  65 A, the mist or minute droplets are adsorbed mainly onto the interior surface of the rectangular conduit portion  65 C 2  when the solvent gas collides against the interior surface. The mist or the like can thus be securely removed from the solvent gas. The solvent gas conditioner  65 A having the mist removal nozzle  65 C may be most preferably used when using, as the solvent gas generator  67 A, a sprayer or ultrasonic atomizer which directly sprays the solvent in the form of a mist. 
         [0049]    Because the solvent gas conditioner  65 A is housed in the thermostatic container  65 T and, in addition, the rectangular conduit portion  65 C 2  is provided with the thermocouple TC, the solvent gas conditioner  65 A can be kept at a lower temperature than the solvent gas generator  67 A. Accordingly, the temperature of the solvent gas, passing through the solvent gas conditioner  65 A, can be made lower than that in the solvent gas generator  67 A. Therefore, if the solvent gas is not fully saturated e.g. due to high flow rate of the carrier gas, the degree of saturation of the solvent gas (the concentration of the solvent vapor in the carrier gas) can be increased (to supersaturation) by passing the solvent gas through the solvent gas conditioner  65 A. 
         [0050]    Referring again to  FIG. 5 , the bridge pipe  62 B from the solvent gas conditioner  65 A is connected to the ceiling portion of the processing chamber  62 . The outlet opening of the bridge pipe  6213  connected to the processing chamber  62  is located above approximately the center of the susceptor  62 S, so that the solvent gas can be supplied to the entire surface of the wafer W placed on the susceptor  62 S. 
         [0051]    As shown in  FIG. 5 , a tape-shaped heater  62 H 1  is wound around the processing chamber  62  and a tape-shaped heater  62 H 2  is wound around the bridge pipe  62 B, so that the temperature of the processing chamber  62  and the temperature of the bridge pipe  62 B can be controlled. The temperatures may be, for example, in the range of about 70° C. to about 90° C. and is preferably equal to the temperature of the solvent gas conditioner  65 A. Such temperature control can prevent the solvent gas from condensing onto the interior surfaces of the bridge pipe  6213  and the processing chamber  62 . 
         [0052]    The operation of the resist coating/developing apparatus  1  provided with the resist film processing apparatus  60  (process to be carried out in the resist coating/developing apparatus  1 ) according to the present invention will now be described. 
         [0053]    First, an unprocessed wafer W is taken out of the cassette C by the wafer transporter  7  ( FIG. 1 ), and the wafer W is transported to the extension apparatus  32  ( FIG. 3 ) of the third processing apparatus group G 3 . The wafer W is then carried by the main transport apparatus  13  into the adhesion-enhancing apparatus  31  of the third processing apparatus group G 3 , where hexamethyldisilazane (HMDS), for example, is applied to the wafer W in order to enhance the adhesion of a resist solution to the wafer W. The wafer W is then transported to the cleaning apparatus  30 , where the wafer W is cooled to a predetermined temperature. Thereafter, the wafer W is transported to the resist coating apparatus  17 , where a resist solution is applied onto the rotating wafer W to form a resist film. 
         [0054]    The wafer W having the resist film is transported by the main transport apparatus  13  to the pre-baking apparatus  33 , where pre-baking of the resist film is carried out. The wafer W is then transported by the main transport apparatus  13  to the extension/cooling apparatus  41 , where the wafer W is cooled. Thereafter, the wafer W is transported by the wafer transporter  50  to the peripheral exposure apparatus  51  and then to the exposure apparatus  5 . The substrate W is subjected to predetermined processing in the respective apparatuses. After carrying out exposure of the resist film using a photomask in the exposure apparatus  5 , the wafer W is transported by the wafer transporter  50  to the extension apparatus  42  of the fourth processing apparatus group G 4 . 
         [0055]    Thereafter, the wafer W is transported by the main transport apparatus  13  to the post-exposure baking apparatus  44 , where post-exposure baking of the exposed resist film is carried out. The wafer W is then transported to the cooling apparatus  43 , where the wafer W is cooled. The wafer W is then transported by the main transport apparatus  13  to the developing apparatus  18  of the first processing apparatus group G 1  or the second processing apparatus group G 2 , where development of the exposed resist film is carried out. A patterned resist film (resist mask) is thus formed on the wafer W. 
         [0056]    The wafer W after the development is transported by the main transport apparatus  13  to the resist film processing apparatus  60  ( FIGS. 4 and 5 ). Specifically, after setting the internal pressure of the load lock chamber  64  of the resist film processing apparatus  60  at atmospheric pressure, the gate valve GV 2  ( FIG. 4 ) is opened and the wafer W is carried by the main transport apparatus  13  into the load lock chamber  64  and held above the three lifting pins  64 P. The lifting pins  64 P then move upward and receive the wafer W from the main transport apparatus  13 . After the main transport apparatus  13  exits the load lock chamber  64 , the lifting pins  64 P move downward to place the wafer W on the transport arm  64 A. After closing the gate valve GV 2 , the load lock chamber  64  is evacuated and kept at a predetermined internal pressure. The pressure in the load lock chamber  64  may be, for example, in the range of about 7 Torr (0.933 kPa) to about 10 Torr (1.33 kPa). 
         [0057]    The wafer W is then carried from the load lock chamber  64  to the processing chamber  62 . In particular, the gate valve GV 1  between the load lock chamber  64  and the processing chamber  62  is opened, and the transport arm  64 A moves along the guide rail  66  to carry the wafer W to the processing chamber  62  and hold the wafer W above the susceptor  62 S. Preferably, the ultraviolet lamp UV provided in the load lock chamber  64  is lit to irradiate the wafer W with ultraviolet light during transportation of the wafer W to the processing chamber  62 . The ultraviolet light irradiation is preferred especially when the resist film is an ArF resist having low solubility in a solvent. This is because lactone, contained in the ArF resist, will be decomposed by the ultraviolet light irradiation. 
         [0058]    The lifting pins.  62 P then move upward and receive the wafer W from the transport arm  64 A. After the transport arm  64 A exits the processing chamber  62 , the lifting pins  62 P move downward to place the wafer W on the susceptor  62 S. Thereafter, the gate valve GV 1  is closed, and the processing chamber  62  is evacuated through the exhaust ports  62 E by means of the exhaust system (not shown) to keep the processing chamber  62  at a predetermined internal pressure. Preferably, the pressure is lower than the below-described pressure during processing of the resist film and is such a pressure as not to considerably lower the throughput due to the time taken for the evacuation, for example, about 0.1 Torr (13.3 Pa) to about 7 Torr (0.933 kPa). 
         [0059]    Thereafter, the resist film of the wafer W is subjected to processing to flatten the patterned resist film, carried out in the following manner: First, the valve  67 V is opened to supply the carrier gas from the not-shown carrier gas supply source to the gas intake pipe  67 B of the solvent gas generator  67 A. The carrier gas is ejected from the gas intake pipe  67 B into the solvent held in the solvent gas generator  67 A. The carrier gas, while flowing in the solvent, takes in a vapor of the solvent and is supplied, as a solvent gas, through the bridge pipe  65 B to the solvent gas conditioner  65 A. 
         [0060]    The solvent gas from the bridge pipe  656  is ejected through the mist removal nozzle  65 C into the solvent gas conditioner  65 A. Especially when the solvent gas passes through the mist removal nozzle  65 C, a mist or the like, contained in the solvent gas, is removed through collision of the solvent gas against the interior surface. Because the temperature of the solvent gas conditioner  65 A is lower than the temperature of the solvent gas generator  67 A, the solvent gas having a high temperature, generated by the solvent gas generator  67 A, is cooled by the solvent gas conditioner  65 A (especially by the mist removal nozzle  65 C). Thus, the solvent gas (carrier gas containing a vapor or gas of the solvent), containing no mist or the like and having a high degree of saturation, is supplied through the bridge pipe  62 B to the processing chamber  62  of the resist film processing apparatus  60 . 
         [0061]    When the solvent gas is supplied to the processing chamber  62 , the processing chamber  62  becomes filled with the solvent gas at a predetermined pressure and the resist film on the wafer W becomes exposed to the solvent gas. The pressure in the processing chamber  62  may be lower than atmospheric pressure, and preferably in the range of about 1 Torr (0.133 kPa) to about 10 Torr (1.33 kPa). Such a pressure enables the resist film on the wafer W to be moderately exposed to the solvent gas. 
         [0062]    After exposing the resist film to the solvent gas for a predetermined period of time, the valve  67 V is closed and the supply of the carrier gas is stopped to terminate the resist film processing for the wafer W. After the resist film processing, the susceptor  62 S and the wafer W placed on it are heated with the heating section  62 H embedded in the susceptor  62 . The heating temperature may be, for example, in the range of about 70° C. to about 130° C. 
         [0063]    The mechanism of flattening of the resist film by the above processing will now be described.  FIG. 7(   a ) is a diagram schematically showing a cross section of a “line” of a resist film having a line and space pattern. As shown in the Figure, the resist film R 1  after development has surface irregularities especially in the side surfaces. Such irregularities are considered to be produced e.g. by interference of exposing light in the resist film during exposure. When the resist film is exposed to a solvent gas, the solvent is adsorbed onto the surface (upper surface and side surfaces) of the resist film. The adsorbed solvent dissolves the resist film and/or is absorbed into the resist film, thereby swelling the resist film as shown in  FIG. 7(   b ). The surface portion of the swollen resist film R 2  is liquefied and the surface is flattened by the surface tension. When the solvent is evaporated by the subsequent heating, the swollen portion of the resist film contracts, whereby the resist film is further flattened. A resist film R 3 , having a flattened surface as shown in  FIG. 7(   c ), can thus be obtained. The heating of the resist film R 2  also has the effect of preventing lowering of the etching resistance of the resist film. 
         [0064]    After completion of the flattening processing, the wafer W is carried from the processing chamber  62  to the load lock chamber  64  according to the inverse procedure to the above-described procedure for carrying the wafer W from the load lock chamber  64  to the processing chamber  62 . Upon the transportation, the wafer W is cooled quickly by the transport arm  64 A of the load lock chamber  64 . 
         [0065]    The wafer W is then carried by the main transport apparatus  13  out of the load lock chamber  64  and transported to the post-baking apparatus  47  of the fourth processing apparatus group G 4 , where post-baking of the resist film is carried out. The wafer W is then transported by the main transport apparatus  13  to the cooling apparatus  40  of the fourth processing apparatus group G 4 , where the wafer W is cooled. Thereafter, the wafer W is returned via the extension apparatus  32  to the original cassette C, thereby completing the sequence of process steps including the resist coating, exposure and development. 
         [0066]    As described hereinabove, according to the resist coating/developing apparatus  1  of this embodiment, a resist film which has been patterned by development is exposed to a solvent gas under reduced pressure in the resist film processing apparatus  60  and the solvent, adsorbed onto the resist film, dissolves and swells the surface of the resist film, thereby flattening surface irregularities of the resist film. This can reduce the line width roughness (LWR) of the resist pattern. It therefore becomes possible to reduce variation in the threshold voltage of a field-effect transistor (FET) even when the gate of the FET is formed with a small critical dimension, such as 32 nm or 22 nm. 
         [0067]    Because the solvent gas is supplied into the processing chamber  62  which is kept at a reduced pressure, and is discharged by means of the exhaust system, the solvent gas will not diffuse out of the resist processing apparatus  60 . Further, the solvent gas generator  67 A holding the solvent is hermetically closed, and the gas intake pipe  6713  and the bridge pipe  65 B are hermetically connected to the solvent gas generator  67 A. Therefore, there is no possibility of a vapor of the solvent diffusing in the interior space of the resist coating/developing apparatus  1 . Accordingly, a wafer W will not be exposed to the solvent in the interior space of the resist coating/developing apparatus  1 . This can prevent the lowering of the resist film-developing effect caused by the solvent. 
         [0068]    In this embodiment the solvent and the solvent gas are confined to a limited region. Accordingly, even when a flammable solvent is used, there is no fear of ignition of the solvent gas caused by an ignition source which may be a device in the resist coating/developing apparatus  1  or a device in a clean room. 
         [0069]    The resist film processing apparatus  60  of this embodiment is provided with the solvent gas conditioner  65 A which performs conditioning of the solvent gas, such as removal of a mist or the like from the solvent gas generated in the solvent gas generator  67 A and increase of the solvent saturation of the solvent gas. If a solvent gas containing a mist or the like is supplied to the processing chamber  62  and the mist or the like adheres to a patterned resist film, the resist film can be dissolved excessively in the surface portion, resulting in deformation of the resist pattern. According to this embodiment, a mist or the like is removed from the solvent gas by the solvent gas conditioner  65 A having the mist removal nozzle  65 C. This enables uniform swelling of a resist film and flattening of the film surface. Further, by bringing the solvent gas to supersaturation by means of the solvent gas conditioner  65 A, a vapor or gas of the solvent can be supplied at a high concentration to the processing chamber  62 . This can promote flattening of a resist film. Further, the use of a supersaturated solvent gas can improve the reproducibility of the solvent concentration, leading to improved process reproducibility. 
         [0070]    While the present invention has been described with reference to the embodiments thereof, it will be understood by those skilled in the art that the present invention is not limited to the particular embodiments disclosed, but it is intended to cover modifications within the scope of the present invention as defined by the appended claims. 
         [0071]    For example, in the processing chamber  62  of the resist film processing apparatus  60 , it is possible to divide the front end of the bridge pipe  62 B into a plurality of branches or to attach a shower head to the front end in order to supply the solvent gas uniformly to a wafer W. It is also possible to design the susceptor  62  to be movable in a horizontal direction, and to supply the solvent gas to a wafer W while moving the wafer W placed on the susceptor  62 S. 
         [0072]    Instead of the bubbler tank shown in  FIG. 5  or the above-described sprayer or ultrasonic atomizer as a solvent gas generator, it is possible to use a vapor supply device as shown in  FIG. 8 . In the solvent gas generator  67 A 1  of  FIG. 8 , unlike the bubbler tank, the gas intake pipe  67 B does not reach into the solvent. Thus, the carrier gas, supplied to the solvent gas. generator  67 A 1 , takes in a vapor of the solvent that fills the space over the solvent and is sent through the bridge pipe  65 B. 
         [0073]    Instead of the mist removal nozzle  65 C, it is possible to use a plurality of baffle plates  65 F as shown in  FIG. 9  in a solvent gas conditioner. In the embodiment shown in  FIG. 9 , the solvent gas ejected from the front end of the gas intake pipe  65 B into the solvent gas conditioner  65 A 1  flows upward while passing through the openings  65 Q of the lowest baffle plate  65 F. The openings  65 Q of the second-stage baffle plate  65 F are not in alignment with the openings  65 Q of the lowest baffle plate  65 F in the vertical direction. Accordingly, the solvent gas collides against the lower surface of the second-stage baffle plate  65 F and changes the flow direction, and then passes through the openings  65 Q and flows upward. Upon the collision of the solvent gas against the lower surface of the second-stage baffle plate  65 F, a mist or the like contained in the solvent gas is adsorbed onto the lower surface. The mist or the like can thus be removed from the solvent gas. Instead of the use of the three baffle plates  65 F, two or four or more baffle plates  65 F may of course be used. It is, of course, possible to provide a thermocouple in any of the baffle plates  65 F in order to perform temperature adjustment. 
         [0074]    The baking after exposure of a patterned resist film to the solvent gas may be carried out not by means of the susceptor  62 S in the processing chamber  62 , but by means of e.g. the baking apparatus  46  or the post-baking apparatus  47  of the fourth processing apparatus group G 4 . That is, it is possible to carry out only post-baking without carrying out baking in the processing chamber  62 . Further, instead of the provision of the heating section  62 H in the susceptor  62 S, it is possible to provide a heating lamp in the ceiling portion of the load lock chamber  64  and carry out baking with the heating lamp 
         [0075]    The above-described exemplary temperatures of the solvent gas generator  67 A and the solvent gas conditioner  65 A may of course be changed depending on the type of the solvent used, the concentration of the solvent in the solvent gas, etc. The generator  67 A and the conditioner  65 A may be set at such temperatures as not to cause thermal denaturing or decomposition of the solvent and to avoid condensation of the solvent gas e.g. in the bridge pipes  65 B,  62 B. 
         [0076]    The irradiation of a resist film, especially an ArF resist film, with ultraviolet light may not necessarily be performed with the ultraviolet light UV disposed in the load lock chamber  64  of the resist film processing apparatus  60 . For example, it is possible to provide a processing apparatus for ultraviolet irradiation in the fourth processing apparatus group G 4 , and perform ultraviolet irradiation of a resist film in the processing apparatus. 
         [0077]    Though a semiconductor wafer has been described as a substrate on which a resist film is to be formed, it is also possible to use a substrate for a flat panel display (FPD). Thus, the resist coating/developing apparatus and method of the present invention may be used for the production of an FPD.