1.  Field of the Invention
The present invention relates to a technique of feeding coating liquid to various substrates such as a semiconductor wafer, a glass substrate for liquid crystal display or a reticle substrate for photomask, to form a liquid film of the coating liquid on the surface of such a substrate. 
2.  Description of the Background Art
Conventionally, the coating process of resist liquid performed to obtain a desired circuit pattern in manufacturing of a semiconductor device or the like has been carried out by a so-called spin coating method.  This method is to form a liquid film (resist film) on the entire surface of a wafer by feeding coating liquid from a nozzle provided above a middle portion of the wafer, which is a substrate to be processed, horizontally held by a rotatable spin chuck or the like, while rotating the wafer for diffusion of the resist liquid by the centrifugal force of the wafer. 
To accommodate the recently-increasing demand of miniaturization of circuit patterns, it is required to reduce the thickness of the resist film.  In the spin coating method, the number of rotations of the wafer has been increased to meet such a requirement.  If the wafer is rotated at a high speed, however, turbulent flow is likely to occur on the wafer surface especially when the wafer has a large size.  The turbulent flow would cause unevenness of the film thickness on the entire wafer, which would make difficult to reduce the size of a pattern.  Accordingly, the inventors have studied application of a coating film forming apparatus not using the spin coating method. 
FIG.  23 shows an example of a nozzle unit in which a nozzle and a driving mechanism for moving the nozzle in the X-direction (from side to side) are integrated.  A case body 11 shown in FIG.  23 is constituted by a front portion 12 and a rear portion 13.  The upper and lower surfaces of front portion 12 are each provided with a slit 14 (not shown for the lower surface side), which defines the direction of movement of a coating liquid feed tube 15 provided through slit 14.  A nozzle portion 16 for discharging the coating liquid downward is arranged at a tip of coating liquid feed tube 15.  Coating liquid feed tube 15 and nozzle portion 16 are configured to move back and forth within an area defined by slit 14, by actuation of a belt driving portion 17 provided in rear portion 13. 
At the coating process, nozzle portion 16 is moved back and forth (a scan is performed) in the X-direction as described above, while a wafer W placed below nozzle portion 16 is intermittently fed in the Y-direction.  Further, the width of movement in the X-direction is changed in accordance with the width of a region to be fed with coating liquid, every time the intermittent feeding in the Y-direction is performed, to allow the coating liquid to be fed onto the surface of wafer W in the manner of a so-called single stroke of the blush. 
However, as the method above is to form a liquid film on the entire wafer surface by lining up linear coated regions side by side, scanning time per one row of nozzle portion 16 must be shortened in order to reduce the total time required.  For the time reduction, it is effective to move nozzle portion 16 at a high speed.  Such operation, however, causes large vibration at e.g. belt driving portion 17, which is propagated to pulsate the coating liquid in coating liquid feed tube 15, causing variation in the pressure within coating liquid feed tube 15.  The change in the pressure in coating liquid feed tube 15 is directly reflected in the discharge pressure of the coating liquid at nozzle portion 16, resulting in non-uniform feeding of the coating liquid from discharge opening 16a of nozzle portion 16, as shown in FIG.  26.