Patent Publication Number: US-2009226621-A1

Title: Coating treatment method, computer-readable storage medium, and coating treatment apparatus

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a coating treatment method, a computer-readable storage medium, and a coating treatment apparatus each for applying a water-soluble coating solution onto a substrate such as a semiconductor wafer or the like. 
     2. Description of the Related Art 
     In a photolithography process in a manufacturing process of a semiconductor device, for example, a resist coating treatment of applying a resist solution onto a semiconductor wafer (hereinafter, referred to as a “wafer”) to form a resist film, exposure processing of exposing a predetermined pattern to light on the resist film, a developing treatment of developing the exposed resist film and so on are performed in sequence to form a predetermined resist pattern on the wafer. 
     In various coating treatments such as the above-described resist coating treatment, a so-called spin coating method is frequently used in which a coating solution is supplied from a nozzle to a central portion of the rotated wafer and the centrifugal force is utilized to diffuse the coating solution over the wafer to thereby apply the coating solution on the wafer. In this spin coating method, a method in which, for example, a solvent for the coating solution is supplied onto the wafer to prewet the wafer, the rotation of the wafer is then accelerated to a first rotation number, the coating solution is then supplied to the rotated wafer, subsequently the rotation of the wafer is temporarily decelerated to a second rotation number to adjust the film thickness of the coating solution on the wafer, and the rotation of the wafer is then accelerated again to a third rotation number to thereby spin-dry the coating solution on the wafer, has been proposed as a method of uniformly applying a small mount of coating solution (Japanese Patent No. 3330324). 
     SUMMARY OF THE INVENTION 
     When, for example, the water-soluble coating solution is applied to a wafer using the above-described spin coating method, for example, pure water is supplied onto the wafer as the solvent for the coating solution. The pure water, however, has a large contact angle, so that the pure water diffuses over the wafer immediately after it is supplied. Since the pure water has poor “wettability” as described above, some portions could be remained unwet with the pure water even after the prewetting. In this case, even if the coating solution is subsequently supplied onto the wafer, the flowability of the coating solution is not improved. Accordingly, supply of a large amount of coating solution could be required to uniformly apply the coating solution within the wafer. 
     The present invention has been developed in consideration of the above point, and its object is to reduce the supply amount of a coating solution while uniformly applying the coating solution within a substrate, when a water-soluble coating solution is applied over the substrate. 
     To achieve the above object, the present invention is a coating treatment method of applying a water-soluble coating solution onto a substrate, including: a first step of supplying pure water to a central portion of the substrate in a manner that the pure water does not diffuse over an entire surface of the substrate; a second step of subsequently supplying the water-soluble coating solution to a central portion of the pure water on the substrate to form a mixed layer of the coating solution and the pure water, under the coating solution; and a third step of subsequently diffusing the mixed layer over the substrate to diffuse the coating solution over the entire surface of the substrate. 
     In the present invention, the formed mixed layer is smaller in contact angle than the pure water and therefore becomes better in wettability. As a result, the mixed layer then diffuses over the substrate, and the coating solution is led by the mixed layer and thereby becomes easy to diffuse over the substrate. Accordingly, the coating solution can be uniformly applied within the substrate, and the supply amount of the coating solution can also be reduced. 
     According to another aspect, the present invention is a computer-readable storage medium storing a program running on a computer of a control unit which controls a coating treatment apparatus in order to cause the coating treatment apparatus to execute a coating treatment method. 
     According to still another aspect, the present invention is a coating treatment apparatus for applying a water-soluble coating solution onto a substrate, including: a coating solution nozzle for supplying the coating solution to the substrate at a predetermined timing; a pure water nozzle for supplying pure water to the substrate at a predetermined timing; and a control unit. The control unit controls operations of at least the coating solution nozzle and the pure water nozzle to execute a first step of supplying pure water to a central portion of the substrate by the pure water nozzle in a manner that the pure water does not diffuse over an entire surface of the substrate; a second step of subsequently supplying the water-soluble coating solution to a central portion of the pure water on the substrate by the coating solution nozzle to form a mixed layer of the coating solution and the pure water, under the coating solution; and a third step of subsequently diffusing the mixed layer over the substrate to diffuse the coating solution over the entire surface of the substrate. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a longitudinal sectional view showing the outline of a configuration of a coating treatment apparatus according to an embodiment; 
         FIG. 2  is a transverse sectional view showing the outline of the coating treatment apparatus; 
         FIG. 3  is a flowchart showing main steps of a coating treatment process; 
         FIG. 4  is a graph showing the numbers of rotations of a wafer and supply timings of a coating solution and pure water in the steps of the coating treatment process; 
         FIG. 5  is an explanatory view schematically showing a state of a solution film on the wafer in each of the steps of the coating treatment process; and 
         FIG. 6  is a graph showing a measurement result of the film thickness of the coating film formed on the wafer after the coating treatment in an example. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, a preferred embodiment of the present invention will be described.  FIG. 1  is a longitudinal sectional view showing the outline of a configuration of a coating treatment apparatus  1  according to this embodiment, and  FIG. 2  is a transverse sectional view showing the outline of the configuration of the coating treatment apparatus  1 . Note that in this embodiment, an anti-reflection film liquid material to be applied onto a wafer W on which a resist film has been formed is used as a coating solution in order to form an anti-reflection film for preventing reflection of light at exposure processing. The anti-reflection film liquid material as the coating solution contains, for example, a water-soluble resin and a low-molecular organic compound such as carboxylic acid or sulfonic acid. 
     The coating treatment apparatus  1  has a treatment container  10  as shown in  FIG. 1 , and a spin chuck  20  as a rotating and holding member which holds and rotates the wafer W thereon is provided at a central portion in the treatment container  10 . The spin chuck  20  has a horizontal upper surface, and the upper surface is provided with, for example, a suction port (not shown) which sucks the wafer W. Suction through the suction port allows the wafer W to be suction-held on the spin chuck  20 . 
     The spin chuck  20  has a chuck drive mechanism  21  equipped with, for example, a motor or the like and can be rotated at a predetermined speed by the chuck drive mechanism  21 . Further, the chuck drive mechanism  21  is provided with a raising and lowering drive source such as a cylinder so that the spin chuck  20  is vertically movable. 
     Around the spin chuck  20 , a cup  22  is provided which receives and collects liquid splashing or dropping from the wafer W. A drain pipe  23  for draining the collected liquid and an exhaust pipe  24  for exhausting the atmosphere in the cup  22  are connected to the bottom surface of the cup  22 . 
     As shown in  FIG. 2 , on the side of the negative direction in an X-direction (the lower direction in  FIG. 2 ) of the cup  22 , a rail  30  is formed which extends along a Y-direction (the right-to-left direction in  FIG. 2 ). The rail  30  is formed, for example, from the outside on the negative direction side in the Y-direction of the cup  22  (the left direction in  FIG. 2 ) to the outside on the positive direction side in the Y-direction (the right direction in  FIG. 2 ). To the rail  30 , for example, two arms  31  and  32  are attached. 
     On the first arm  31 , a coating solution nozzle  33  which supplies the coating solution is supported as shown in  FIG. 1  and  FIG. 2 . The first arm  31  is movable on the rail  30  by means of a nozzle drive unit  34  shown in  FIG. 2 . This allows the coating solution nozzle  33  to move from a waiting section  35  provided at the outside on the positive direction side in the Y-direction of the cup  22  to a position above a central portion of the wafer W in the cup  22  and further move in a direction of the diameter of the wafer W above the wafer W. The first arm  31  freely rises and lowers by means of the nozzle drive unit  34  to be able to adjust the height of the coating solution nozzle  33 . 
     To the coating solution nozzle  33 , a supply pipe  37  communicating with a coating solution supply source  36  is connected as shown in  FIG. 1 . In the coating solution supply source  36 , the coating solution is stored. The supply pipe  37  is provided with a supply equipment group  38  including a valve for controlling the flow of the coating solution, a flow regulator and so on. 
     On the second arm  32 , a pure water nozzle  40  is supported which supplies a solvent for the coating solution, for example, pure water. The second arm  32  is movable on the rail  30  by means of a nozzle drive unit  41  shown in  FIG. 2  and can move the pure water nozzle  40  from a waiting section  42  provided at the outside on the negative direction side in the Y-direction of the cup  22  to the position above the central portion of the wafer W in the cup  22 . The second arm  32  freely rises and lowers by means of the nozzle drive unit  41  to be able to adjust the height of the pure water nozzle  40 . 
     To the pure water nozzle  40 , a supply pipe  44  communicating with a pure water supply source  43  is connected as shown in  FIG. 1 . In the pure water supply source  43 , pure water is stored. The supply pipe  44  is provided with a supply equipment group  45  including a valve for controlling the flow of the pure water, a flow regulator and so on. Note that though the coating solution nozzle  33  for supplying the coating solution and the pure water nozzle  40  for supplying the pure water are supported on separate arms in the above configuration, they may be supported on the same arm, and movement and supply timings of the coating solution nozzle  33  and the pure water nozzle  40  may be controlled by control of the movement of the arm. 
     The operations of a drive system such as the above-described rotation operation and vertical operation of the spin chuck  20 , the movement operation of the coating solution nozzle  33  by the nozzle drive unit  34 , the supply operation of the coating solution of the coating solution nozzle  33  by the supply equipment group  38 , the movement operation of the pure water nozzle  40  by the nozzle drive unit  41 , the supply operation of the pure water of the pure water nozzle  40  by the supply equipment group  45  and so on are controlled by a control unit  50 . The control unit  50  is composed of, for example, a computer including a CPU and a memory and can realize the resist coating treatment in the coating treatment apparatus  1 , for example, by executing programs stored in the memory. Note that various programs used to realize the resist coating treatment in the coating treatment apparatus  1  are ones which are recorded, for example, on a storage medium H such as a computer-readable hard disk (HD), flexible disk (FD), compact disk (CD), magneto-optical disk (MO), or a memory card, and installed from the storage medium H into the control unit  50 . 
     Next, the process of the coating treatment performed in the coating treatment apparatus  1  configured as described above will be described.  FIG. 3  is a flowchart showing main steps of the coating treatment process in coating treatment apparatus  1 .  FIG. 4  is a graph showing the numbers of rotations (rpm) of the wafer W and the supply timings of the coating solution and the pure water in the steps of the coating treatment process.  FIG. 5  schematically shows the state of a solution film on the wafer in each of the steps of the coating treatment process. Note that the length of time of the process in  FIG. 4  does not necessarily correspond to the actual length of time for easy understanding of technique. Further, the resist film which has been formed on the wafer in advance is not shown in  FIG. 5 . 
     The wafer W transferred in the coating treatment apparatus  1  is first suction-held on the spin chuck  20 . Subsequently, the pure water nozzle  40  at the waiting section  42  is moved by the second arm  32  to the position above the central portion of the wafer W. Then, the chuck drive mechanism  21  is controlled as shown in  FIG. 4  to cause the spin chuck  20  to rotate the wafer W, for example, at 1 rpm to 30 rpm that is a first rotation number, 10 rpm in this embodiment. Concurrently with the rotation of the wafer W, a pure water P is supplied from the pure water nozzle  40  to the central portion of the wafer W as shown in  FIG. 5(   a ) (Step S 1  in  FIG. 3  and  FIG. 4) . In the case where the wafer W is rotated at a low speed at the first rotation number as described above, the pure water P supplied on the wafer W hardly diffuses over the wafer W. Further, the rotation at the low speed exerts the centrifugal force on the pure water P, whereby a peripheral portion P 1  of the pure water P is higher than a central portion P 2  such that the central portion P 2  of the surface of the pure water P becomes concave downward. Note that the Step S 1  is performed, for example, for 4 seconds. 
     After the supply of the pure water P is finished, the pure water nozzle  40  is moved from the position above the central portion of the wafer W, and the coating solution nozzle  33  at the waiting section  35  is moved by the first arm  31  to the position above the central portion of the wafer W. 
     Subsequently, the rotation of the wafer W is accelerated, for example, to 30 rpm to 100 rpm that is a second rotation number, 40 rpm in this embodiment, and thereafter the wafer W is rotated at the second rotation number as shown in  FIG. 4 . Concurrently with the acceleration of the rotation of the wafer W, a coating solution T is supplied from the coating solution nozzle  33  to the central portion P 2  of the pure water P as shown in  FIG. 5(   b ) (Step S 2  in  FIG. 3  and  FIG. 4) . When the wafer W is rotated at a low speed at the second rotation number as described above, the pure water P hardly diffuses over the wafer W. Further, a mixed layer C in which the coating solution T and the pure water P are mixed together is formed under the coating solution T. Note that the Step S 2  is performed, for example, for 0.5 seconds. 
     After the mixed layer C is formed under the coating solution T, the rotation of the wafer W is accelerated, for example, to 2000 rpm to 4000 rpm that is a third rotation number, 3600 rpm in this embodiment, and thereafter the wafer W is rotated at the third rotation number as shown in  FIG. 4 . In this event, the coating solution T is continuously supplied from the coating solution nozzle  33  as shown in  FIG. 5(   c ). When the wafer W is rotated at a high speed at the third rotation number as described above, the mixed layer C diffuses over the wafer W, and the coating solution T is led by the mixed layer C and diffuses over the wafer W (Step S 3  in  FIG. 3  and  FIG. 4) . The mixed layer C is smaller in contact angle and better in wettability than the pure water P, so that the coating solution T can smoothly and uniformly diffuse over the entire surface of the wafer W. Note that the Step S 3  is performed, for example, for 1.1 seconds. 
     After the coating solution diffuses over the entire surface of the wafer W, the rotation of the wafer W is decelerated, for example, to 100 rpm that is a fourth rotation number as shown in  FIG. 4 . During the rotation of the wafer W at the fourth rotation number as described above, a force directing to the center is exerted on the coating solution T on the wafer W, whereby the film thickness of the coating solution T on the wafer W is adjusted as shown in  FIG. 5(   d ) (Step S 4  in  FIG. 3  and  FIG. 4) . This Step S 4  is performed, for example, for 1 second. 
     After the film thickness of the coating solution T on the wafer W is adjusted, the rotation of the wafer W is accelerated, for example, to 1250 rpm that is a fifth rotation number as shown in  FIG. 4 . During the rotation of the wafer W at the fifth rotation number as described above, the coating solution T diffused over the entire surface of the wafer W is dried as shown in  FIG. 5(   e ), whereby a coating film F is formed (Step S 5  in  FIG. 3  and  FIG. 4) . Note that the Step S 5  is performed, for example, for 18 seconds. 
     According to the above embodiment, since the wafer W is rotated at the low speed at the first rotation number and the pure water P is supplied onto the rotated wafer W, the pure water P does not diffuse over the wafer W so that the front surface of the pure water P can be concaved downward. This ensures that when the wafer W is then rotated at the second rotation number and the coating solution T is supplied to the central portion P 2  of the pure water P, the coating solution T never flows out from the top of the pure water P. Further, since the wafer W is rotated at the second rotation number and the coating solution T is supplied to the central portion P 2  of the pure water P, the mixed layer C of the coating solution T and the pure water P can be formed under the coating solution T. This makes the mixed layer C smaller in contact angle and better in wettability than the pure water P, thus ensuring that when the wafer W is then rotated at the high speed at the third rotation number, the coating solution T is led by the mixed layer C and can smoothly and uniformly diffuse over the entire surface of the wafer W. Accordingly, the coating solution T can be uniformly applied within the wafer W and the supply amount of the coating solution T can also be reduced. 
     In the above-described embodiment, since the wafer W is rotated at the low speed at the fourth rotation number after the coating solution T diffuses over the entire surface of the wafer W, the force directing to the center is exerted on the coating solution T on the wafer W, whereby the film thickness of the coating solution T can be adjusted. 
     A preferred embodiment of the present invention has been described above with reference to the accompanying drawings, but the present invention is not limited to the embodiment. It should be understood that various changes and modifications are readily apparent to those skilled in the art within the spirit as set forth in claims, and those should also be covered by the technical scope of the present invention. The present invention is not limited to this example but can take various forms. For example, while the above-described embodiment has been described taking the coating solution to form the anti-reflection film as the water-soluble coating solution as an example, the present invention is also applicable to a resist pattern dimension shrinking agent (RELACS agent) in RELACS (Resolution Enhancement Lithography Assisted by Chemical Shrink) technique. Further, though the coating treatment is performed on the wafer in the above-described embodiment, the present invention is also applicable to the coating treatment for substrates other than the wafer, such as an FPD (Flat Panel Display), a mask reticle for a photomask and the like. 
     Hereinafter, in a more concrete example in which the coating solution is applied onto the wafer, the uniformity of the film thickness of the coating film formed on the wafer after the coating treatment will be described. Note that the coating treatment apparatus  1  shown in  FIG. 1  and  FIG. 2  was used as a coating treatment apparatus for performing the coating treatment on the wafer W. Further, the recipe of the timings to supply the coating solution T and the pure water P, the number of rotations of the wafer W or the like is the same as the recipe previously shown in  FIG. 4 . 
     Under such conditions, the target film thickness of the coating film F to be formed on the wafer W after the coating treatment was set to 3400 Å, and the coating treatment was performed on 18 wafers W with the same recipe in the coating treatment apparatus  1 . The result is shown in  FIG. 6 . The horizontal axis in  FIG. 6  indicates the numbers of the wafers W in order, the number being given to the 18 treated wafers W in treatment order. The “Thickness” (the vertical axis on the right side in  FIG. 6 ) at the vertical axis in  FIG. 6  indicates the average film thickness within the wafer W of the coating film F formed on the wafer W, and the “Range” (the vertical axis on the left side in  FIG. 6 ) indicates the difference between the maximum film thickness and the minimum film thickness of the coating film F within the wafer W. 
     As shown in  FIG. 6 , it was found that when the coating treatment method of the present invention was used, the average value of the average film thickness “Thickness” of the coating film F was 3400.55 Å and the coating film F can be formed in substantially the same film thickness as the target film thickness. Further, it was found that the average of the difference between the maximum film thickness and the minimum film thickness “Average” of the coating film F was as small as 16.28 Å and the coating solution T can be uniformly applied within the wafer W. 
     The supply amount of the coating solution T supplied to the wafer W when performing this example was 1.0 cc. On the other hand, from the check by the inventors, it was found that when the coating solution T was applied by the conventional coating treatment method proposed in Patent Document 1, the supply amount of the coating solution required for uniformly applying the coating solution T within the wafer W was 2.5 cc. Accordingly, it was found that when the coating treatment method of the present invention is used, the supply amount of the coating solution T can be considerably reduced. 
     The present invention is useful for applying a water-soluble coating solution onto a substrate such as a semiconductor wafer or the like.