BACKGROUND OF THE INVENTION 
     The present invention relates to substrate processing method and apparatus for processing a surface to be processed of a substrate with a processing liquid. More particularly, the present invention relates to a substrate processing method and apparatus suitable for use in a coating process for forming a thin film on a substrate or in an etching process for thinly removing the surface of a substrate in semiconductor manufacturing processes. 
     In semiconductor device manufacturing processes, various processing operations using processing liquids are performed on substrate surfaces to be processed. In such a case, it is necessary to uniformly supply processing liquids to the processing surface of the substrate. For example, to coat a substrate surface with a resist uniformly and to uniformly effect development after exposure, it is necessary that processing liquids used in the resist coating process and the developing process be supplied uniformly to the substrate surface. In the developing process in particular, the development processing area per unit area of the substrate varies from place to place to a considerable extent, depending on the exposure pattern (i.e. in a region where the development area is large, the concentration of the developing solution is likely to be reduced, while in a region where the development area is small, the concentration of the developing solution is likely to be increased, resulting in a large difference in concentration from region to region). Therefore, it is difficult to carry out development processing uniformly. 
     SUMMARY OF THE INVENTION 
     In view of the above-described problem, an object of the present invention is to provide substrate processing method and apparatus capable of uniformly supplying a processing liquid having a uniform concentration to a substrate surface in substrate processing such as development processing without affecting the physical properties of the processing liquid and without damaging the substrate. 
     To attain the above-described object, the present invention provides substrate processing method and apparatus for processing a surface of a substrate with a processing liquid. The substrate is placed horizontally, and a rotating blade is disposed above the substrate so as to face it. The processing liquid is supplied to the surface of the substrate, and the rotating blade is rotated while being kept out of contact with the processing liquid to induce a gas current over the processing liquid. The gas current forms a mass of processing liquid having a surface current and an internal circulating current on the surface of the substrate. 
     As stated above, the rotating blade disposed to face the substrate is rotated while being kept out of contact with the processing liquid, thereby inducing a gas current over the processing liquid. The gas current forms a mass of processing liquid having a surface current on the substrate surface below the rotating blade. The surface current induces an internal circulating current in the mass of processing liquid. As a result, the processing liquid can be supplied uniformly to the substrate surface by the internal circulating current. Furthermore, because the processing liquid is stirred by the internal circulating current, it is possible to dissolve a concentration difference in the processing liquid that occurs as the processing progresses and hence it is possible to uniformize the concentration. In addition, because the substrate is placed in a stationary state and the rotating blade rotates out of contact with the processing liquid, the substrate is not shocked or stressed. Accordingly, there is no likelihood of the substrate being damaged. 
     Preferably, the rotating shaft of the rotating blade and the rotor of a motor for driving the rotating blade are supported with magnetic bearings. 
     When the rotating shaft of the rotating blade and the rotor of the motor for driving the rotating blade are supported in a magnetic levitation manner with magnetic bearings, there is no possibility that the substrate or the processing space will be contaminated with particles or the like that would otherwise be generated by friction. 
     The substrate processing method or apparatus may include a step or device for moving the rotating blade in parallel to the substrate. 
     By moving the rotating blade parallel to the substrate, the gas current induced by the rotating blade also moves along with the movement of the rotating blade, therefore, the mass of processing liquid formed by the gas current on the substrate surface below the rotating blade also moves on the substrate surface as the rotating blade moves. Therefore, even a large-sized substrate can be uniformly processed over the whole surface thereof. 
     Preferably, the rotating blade is a planar disk. 
     The rotating blade in the shape of a planar disk makes it easy to form a mass of processing liquid having an internal circulating current on the substrate surface below the rotating blade. That is, the rotating blade in the shape of planer disk does not form any downward gas current toward the substrate, which makes the formation of the gas current from the substrate toward the rotating blade easy; thus, the formation of the mass of processing liquid is also made easy. 
     The above and other objects, features and advantages of the present invention will become more apparent from the following description of the preferred embodiments thereof, taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagram showing schematically a structural example of the substrate processing apparatus according to the present invention. 
     FIG. 2 is a diagram for illustrating a surface current in a mass of processing liquid formed in the substrate processing apparatus according to the present invention. 
     FIG. 3 is a diagram for illustrating an internal circulating current in a mass of processing liquid formed in the substrate processing apparatus according to the present invention. 
     FIG. 4 is a diagram showing formation of a mass of processing liquid of the same size as the substrate size in the substrate processing apparatus according to the present invention. 
     FIG. 5 is a diagram showing a structural example of a motor used in the substrate processing apparatus according to the present invention. 
     FIG. 6 is a diagram showing schematically another structural example of the substrate processing apparatus according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. 
     FIG. 1 is a diagram showing schematically a structural example of the substrate processing apparatus according to the present invention. Referring to FIG. 1, a substrate  1 , e.g. a semiconductor wafer, is placed horizontally. A rotating blade  2  is disposed to face the substrate  1 . The rotating blade  2  is secured to a rotating shaft  3  of a motor  4 . Thus, the rotating blade  2  is rotated by the motor  4 . 
     In the substrate processing apparatus with the above-described arrangement, when the rotating blade  2  is rotated, a gas current  6  is induced as shown in the figure. That is, the gas current  6  flows toward the center of the substrate  1  from the outer periphery thereof, ascends at the center of the substrate  1  and further flows toward the outer periphery of the rotating blade  2 . That is, when the rotating blade  2  is rotated, a radially outward gas flow  6 - 1  along the lower surface of the rotating blade  2  is caused by the friction between the surface of the rotating blade and the gas and the centrifugal force acting on the gas. To fill the central portion of the rotating blade, an ascending gas flow  6 - 2  is caused at the central portion of the rotating blade  2 , which in turn causes a radially inward gas flow  6 - 3  along the upper surface of the substrate  1 . If a processing liquid is supplied to the upper surface of the substrate  1  in this state, the processing liquid is induced to form an approximately conical mass  5  of processing liquid by the gas current  6 . 
     As shown in FIG. 2, the conical mass  5  of processing liquid has a vortical surface current.  7  induced therein to flow toward the center of the mass  5  of processing liquid by the gas current  6 . As shown in FIG. 3, the surface current  7  induces an internal circulating current  8  in the mass  5  of processing liquid. The circulating current  8  flows toward the center of the mass  5  of processing liquid from the outer periphery thereof, descends at the center and further flows on the upper surface of the substrate  1  toward the outer periphery from the center thereof. The circulating current  8  allows the processing liquid to be supplied uniformly to the upper surface of the substrate  1 . Moreover, the processing liquid is stirred by the stirring action of the circulating current  8 . Thus, it is possible to dissolve a concentration difference in the processing liquid that occurs as the processing progresses. 
     The diameter of the conical mass  5  of processing liquid can be controlled at will by the configuration of the rotating blade  2 , the number of revolutions of the rotating blade  2  and the distance between the rotating blade  2  and the substrate  1 . Accordingly, the mass  5  of processing liquid can be formed with the same diameter as the diameter of the substrate  1  as shown in FIG.  4 . Thus, the processing liquid having a uniform concentration can be supplied uniformly to the whole surface of the substrate  1 , and the whole surface of the substrate  1  can be processed uniformly. 
     The rotating blade  2  may have a general blade structure in which wing-shaped blades are provided in a side-by-side relation to each other on the lower side of a plate. However, as stated above, the, rotating blade  2  in the shape of a planar disk allows the mass  5  of processing liquid to be readily induced as shown in FIGS. 1 to  3 . 
     FIG. 5 is a diagram showing a structural example of a motor for driving the rotating blade  2 . As illustrated in the figure, the rotating shaft  3  of the motor  4  and the rotating shaft of the rotating blade  2  are integrated into one rotating shaft. A rotor  4 - 1  of the motor  4  is secured to the rotating shaft  3 . A stator  4 - 2  of the motor  4  is disposed to face the outer periphery of the rotor  4 - 1  and secured to a casing  11 . Rotors  12 - 1  and  13 - 1  of radial magnetic bearings  12  and  13  are secured to the rotating shaft  3 . Stators  12 - 2  and  13 - 2  of the radial magnetic bearings  12  and  13  are disposed to face the outer peripheries of the rotors  12 - 1  and  13 - 1 , respectively, and secured to the casing  11 . In addition, radial gap sensors  14  and  15  are mounted on the casing  11 . Targets  14 - 1  and  15 - 1  of the radial gap sensors  14  and  15  are secured to the rotating shaft  3 . 
     A disk-shaped rotor  16 - 1  of an axial magnetic bearing  16  is secured to the upper end of the rotating shaft  3 . Stators  16 - 2  of the axial magnetic bearing  16  are secured to the casing  11  so as to face the rotor  16 - 1 . An axial gap sensor  17  is mounted on the casing  11 , and a target  17 - 1  of the axial gap sensor  17  is secured to the center of the rotor  16 - 1 . 
     The rotating shaft  3  is supported in a non-contact, magnetic levitation manner with two radial magnetic bearings  12  and  13  (upper and lower) and one axial magnetic bearing  16 . On the basis of signals output from the radial gap sensors  14  and  15  and the axial gap sensor  17 , a control unit (not shown) controls exciting currents to be supplied to the stators  12 - 2  and  13 - 2  of the radial magnetic bearings  12  and  13  and to the stators  16 - 2  of the axial magnetic bearing  16  so that the rotating shaft  3  assumes a predetermined proper position. 
     As stated above, the rotating shaft  3  is supported in a magnetic levitation manner with the radial magnetic bearings  12  and  13  and the axial magnetic bearing  16 . Therefore, there is no possibility that the substrate  1  or the processing space will be contaminated with particles or the like that would otherwise be generated by friction. It should be noted that the structure of the motor  4  for driving the rotating blade  2  that is shown in FIG. 5 is merely an example and the present invention is not necessarily limited thereto. The essential thing is to support the rotating shaft of the rotating blade and the rotor of the motor in a non-contact manner with magnetic bearings. 
     FIG. 6 is a diagram showing schematically an another structural example of the substrate processing apparatus according to the present invention. The illustrated substrate processing apparatus is applied to a large-sized substrate  1 . The substrate processing apparatus has a device (not shown) for moving the rotating blade  2  and the motor  4  in parallel to the substrate  1 . That is, the rotating blade  2  and the motor  4  can be moved in parallel to the substrate  1  in the direction of the arrow A by the moving device. As the rotating blade  2  is moved in the direction of the arrow A, the gas current  6  formed by the rotating blade  2  also moves along with the rotating blade  2  and, therefore, the conical mass  5  of processing liquid formed by the gas current  6  on the upper surface of the substrate  1  below the rotating blade  2  also moves in the direction of the arrow B. Thus, even if the size of the substrate  1  is large, the processing liquid having a uniform concentration can be supplied uniformly to the whole surface of the substrate  1 . Accordingly, it is possible to process the whole substrate surface uniformly. 
     As has been stated above, the present invention provides the following advantageous effects. 
     According to the present invention, the rotating blade disposed to face the substrate is rotated while being kept out of contact with the processing liquid, thereby inducing a gas current. The gas current forms a mass of processing liquid having a surface current on the substrate surface below the rotating blade. The surface current induces a circulating current in the mass of processing liquid. As a result, the processing liquid can be supplied uniformly to the substrate surface. Furthermore, because the processing liquid is stirred by the circulating current, it is possible to dissolve a concentration difference in the processing liquid that occurs as the processing progresses and hence it is possible to uniformize the concentration. In addition, because the substrate is placed in a stationary state and the rotating blade rotates out of contact with the processing liquid, the substrate is not shocked or stressed. Accordingly, there is no likelihood of the substrate being damaged. 
     According to an another aspect of the present invention, the rotating shaft of the rotating blade and the rotor of a motor for driving the rotating blade may be supported in a magnetic levitation manner with magnetic bearings. Therefore, there is no possibility that the substrate or the processing space will be contaminated with particles or the like that would otherwise be generated by friction. 
     According to a further aspect of the present invention, the substrate processing apparatus may further include a step or device for moving the rotating blade in parallel to the substrate. Therefore, by moving the rotating blade parallel to the substrate, the mass of processing liquid formed on the substrate surface below the rotating blade also moves on the substrate surface as the rotating blade moves. Therefore, even a large-sized substrate can be uniformly processed over the whole surface thereof. 
     According to a further aspect of the present invention, the rotating blade may be a planar disk. Therefore, it is easy to form a mass of processing liquid having a circulating current therein on the substrate surface below the rotating blade. 
     It should be noted that the present invention is not necessarily limited to the foregoing embodiments but can be modified in a variety of ways.
A substrate processing method and apparatus capable of uniformly supplying a processing liquid to a substrate surface in substrate processing such as development processing without exerting an influence on the physical properties of the processing liquid and without damaging the substrate. A rotating blade is disposed above the horizontally placed substrate so as to face the substrate. The processing liquid is supplied to the surface of the substrate, and the rotating blade is rotated while being kept out of contact with the processing liquid to induce a gas current. The gas current forms a mass of processing liquid having an internal circulating current on the substrate surface below the rotating blade.