Patent Publication Number: US-6706322-B2

Title: Film forming apparatus and film forming method

Description:
This application is a divisional of U.S. application Ser. No. 09/366,959 filed Aug. 4, 1999, now U.S. Pat. No. 6,361,600. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a film forming supplying process solution to a substrate that is rotated so as to spread out the process solution on the substrate and form a film of the process solution on the substrate. 
     2. Description of the Related Art 
     In the art of semiconductor fabrication, when a semiconductor layer, an insulation layer, and an electrode layer on an LCD (Liquid Crystal Display) substrate are selectively patterned and etched, as with the case of a semiconductor wafer, a resist film is formed on the front surface of the LCD substrate. To form such a resist film, a spin coater has been used. 
     The spin coater has a spin chuck, a rotation cup, and a driving motor. The spin chuck rotates an LCD substrate thereon. The rotation cup surrounds all the periphery of the spin chuck. The driving motor rotates the spin chuck and the rotation cup. When a resist film is formed on an LCD substrate by the spin coater, resist solution is dropped at the center portion of the LCD substrate that is rotated. Thus, the resist solution is concentrically spread out by centrifugal force. 
     Although the resist solution dropped on the LCD substrate starts concentrically spreading out, the resist solution may not equally reach the periphery of the LCD substrate. In this case, the resist solution may break on the LCD substrate. Thus, the resist film may not be equally formed on the LCD substrate. To solve this problem, the resist solution is excessively dropped to the LCD substrate. Thus, the resist solution is fully formed on the entire front surface of the LCD substrate. In this method, however, it is impossible to reduce the quantity of the resist solution. In addition, when the rotating acceleration of the LCD substrate is low, the resist solution that concentrically spreads out breaks on the LCD substrate. Thus, the resist solution cannot be fully formed on the front surface of the LCD substrate. 
     To solve such a problem, conventionally, a high torque motor was sometimes used. In other words, by rotating the LCD substrate with a high torque motor, centrifugal force applied to the resist solution is strengthened. Thus, the resist solution equally and concentrically spreads out from the center of the LCD substrate to the periphery thereof. Consequently, the quantity of the resist solution can be reduced. In addition, the resist film with an equal thickness can be formed on the front surface of the LCD substrate. 
     However, since the sizes of LCD substrates are becoming large, they are becoming heavy. Thus, it is difficult to rotate an LCD substrate at a large rotating acceleration. In addition, a high torque motor that can rotates an LCD substrate at a large rotating acceleration is currently not available. Even if such a motor becomes available, the apparatus becomes large and expensive. In addition, the footprint becomes large. Moreover, until the LCD substrate rotates at a predetermined rotating speed, it takes a long time. Thus, the resist solution may not equally spread out from the center of the LCD substrate to the periphery thereof. Consequently, unless the resist solution is excessively dropped, the resist film with the equal thickness cannot be formed. 
     SUMMARY OF THE INVENTION 
     The present invention is made from the above-described point of view. An object of the present invention is to provide a film forming apparatus and a film forming method that allow the quantity of process solution supplied to a substrate to be decreased and a film of the process solution to be formed on a process surface of the substrate at low cost. 
     An aspect of the present invention is a film forming apparatus for supplying process solution to a substrate, spreading out the process solution on the substrate, and forming a film of the process solution on the substrate, comprising a driving means for rotating the substrate, wherein said driving means has a main driving mechanism, an auxiliary driving mechanism for assisting the driving of said main driving mechanism, and a controlling means for causing the operation time of said assisting driving mechanism to overlap with the operation time of said main driving mechanism. 
     According to the present invention, the operation time of the main driving mechanism and the operation time of the auxiliary driving mechanism that assists the driving of the main driving mechanism can be temporarily overlapped. Thus, even if the size of a substrate becomes large, it can be rotated at a large rotating acceleration. Consequently, the process solution supplied to the substrate can be equally and concentrically spread out to the periphery of the substrate. As a result, the film of the process solution can be formed on the substrate with an equal thickness. 
     These and other objects, features and advantages of the present invention will become more apparent in light of the following detailed description of a best mode embodiment thereof, as illustrated in the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a perspective view showing the exterior of a coating/developing apparatus having a coating/periphery removing unit according to an embodiment of the present invention; 
     FIG. 2 is a plan view showing the coating/developing apparatus shown in FIG. 1; 
     FIG. 3 is a plan view showing the coating/periphery removing unit according to the embodiment of the present invention; 
     FIG. 4A is a sectional view showing the structure of a supplying system of the coating/periphery removing unit shown in FIG. 3; 
     FIG. 4B is a block diagram for explaining the structure of a controlling portion of an auxiliary driving mechanism; 
     FIG. 5 is a schematic diagram for explaining the state that an LCD substrate is loaded to the supplying system shown in FIG. 4A; 
     FIG. 6 is a schematic diagram for explaining the state that a rotation cup that accommodates an LCD substrate is closed with a lit; 
     FIG. 7 is a graph showing the relation between rotating accelerations of three LCD substrates in different sizes and the quantity of resist solution consumed therewith; 
     FIG. 8 is a graph showing the relation between rotating accelerations of three LCD substrates in different sizes shown in FIG.  7  and the consumption rates of resist solution therewith; 
     FIG. 9 is a graph showing a chronological change of revolutions of an LCD substrate; 
     FIG. 10 is a sectional view showing a first modification of the supplying system shown in FIG. 4A; 
     FIG. 11 is a sectional view showing a second modification of the supplying system shown in FIG. 4A; and 
     FIG. 12 is a sectional view showing a third modification of the supplying system shown in FIG.  4 A. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENT 
     FIG. 1 is a perspective view showing the structure of a coating/developing apparatus. FIG. 2 is a plan view of FIG.  1 . 
     As shown in FIGS. 1 and 2, the coating/developing apparatus  1  is composed of a loader portion  2 , a first process portion  3 , a second process portion  5 , and an interface portion  7 . The loader portion  2  loads and unloads for example a rectangular LCD substrate G. The first process portion  3  processes an LCD substrate G. The second process portion  5  is connected to the first process portion  3  through an interface portion  4 . The interface portion  7  transfers an LCD substrate G between the second process portion  5  and for example an exposing unit (not shown). 
     The loader portion  2  has a cassette table  10 . The cassette table  10  holds a plurality of cassettes  11  and a plurality of cassettes  12 . Each of the cassettes  11  accommodates a plurality of raw LCD substrates. Each of the cassettes  12  accommodates a plurality of processed LCD substrates. The cassettes  11  and  12  are placed on the cassette table  10  in such a manner that access openings of the cassettes  11  and  12  face the first process portion  3 . In addition, the loader portion  2  has a sub-conveying unit  13  that conveys an LCD substrate G. 
     The sub-conveying unit  13  can travel in the direction along a conveying rail  13   a  (Y direction) and the accommodating direction of LCD substrates G (Z direction) in the cassettes  11  and  12 . In addition, the sub-conveying unit  13  can rotate in the θ direction. The sub-conveying unit  13  can access a transferring table  14  and place an LCD substrate G thereon. 
     Various process units that perform predetermined processes for LCD substrates G are disposed on both sides of a conveying rail  16 . On one side of the conveying rail  16 , a scrubber cleaning unit  17  and a developing unit  18  are adjacently disposed. The scrubber cleaning unit  17  cleans an LCD substrate G unloaded from each of the cassettes  11 . The developing unit  18  performs a developing process for an LCD substrate G. On the other side of the conveying rail  16 , an ultraviolet ray ozone cleaning unit  19 , two cooling units  20  and  21 , and two heating units  22  are disposed. Part of the ultraviolet ray ozone cleaning unit  19  is disposed above the cooling unit  21 . The heating unit  22  is disposed above the cooling unit  20 . The main conveying unit  15  has a conveying arm  15   a . The conveying arm  15   a  loads and unloads an LCD substrate G to/from these process units. The interface portion  4  disposed between the first process portion  3  and the second process portion  5  has a transferring table  23  on which an LCD substrate G can be placed. 
     The second process portion  5  has a main conveying unit  25  and a conveying rail  26 . On one side of the conveying rail  26 , a coating/periphery removing unit  27  according to the embodiment of the present invention is disposed. On the other side of the conveying rail  26 , a hydrophobic process unit  28 , a cooling unit  29 , and two heating units  30  are adjacently disposed. The hydrophobic process unit  38  performs a hydrophobic process for an LCD substrate G. The cooling unit  29  cools an LCD substrate G. Each of the heating units  30  heats an LCD substrate G. In FIG. 1, two heating units  30  are disposed above two heating units  30 . The main conveying unit  25  also has an conveying arm  25   a . The conveying arm  25   a  loads and unloads an LCD substrate G to/from each process unit of the second process portion  5 . 
     The interface portion  7  has a transferring table  32  and a sub-conveying unit  33 . The transferring table  32  temporarily holds a cassette  31  that accommodates an LCD substrate G as to adjust a tact between the coating/developing apparatus  1  and the exposing unit (not shown). The sub-conveying unit  33  conveys an LCD substrate G to each of the cassettes  31 , the conveying table  32 , and the exposing unit (not shown). 
     The coating/developing apparatus  1  is structured as described above. Next, the coating/periphery removing unit  27  disposed in the coating/developing apparatus  1  will be described. 
     As shown in FIG. 3, the coating/periphery removing unit  27  has a supplying system  34  and a periphery removing system  35  that are adjacently disposed. The supplying system  34  supplies resist solution to the front surface of an LCD substrate G. The periphery removing system  35  removes an unnecessary resist film on the periphery of an LCD substrate G. The coating/periphery removing unit  27  has a conveying mechanism (not shown). The conveying mechanism conveys an LCD substrate G between the supplying system  34  and the periphery removing system  35 . 
     As shown in FIG. 4A, the supplying system  34  has a spin chuck  40  that vacuum sucks an LCD substrate G. A rotating shaft  43  is connected to a lower portion of the spin chuck  40 . The rotating shaft  43  is connected to a lifting cylinder  42  through a vacuum seal portion  41 . Spline bearings  44  and  45  are disposed at an upper position and a lower position of the rotating shaft  43 , respectively. A groove (not shown) is formed on the outer peripheral surface of the rotating shaft  43  and the inner peripheral surfaces of the spline bearings  44  and  45  along the elongation direction of the rotating shaft  43 . Thus, the spin chuck  40  is lifted up and down corresponding to the movement of the lifting cylinder  42 . 
     A rotation cup  55  is disposed at the outer peripheral portion of the spin chuck  40 . The rotation cup  55  surrounds the spin chuck  40 . A sealing member such as an O ring is disposed on the bottom surface of the rotation cup  55 . In the rotation cup  55 , a process chamber  58  is formed with the bottom surface of the rotation cup  55 , a side wall of the rotation cup  55 , and a lid  84  (that will be described later). 
     The bottom surface of the rotation cup  55  is connected to the upper end of a connecting pipe  60 . The lower end of the connecting pipe  60  is connected to the upper end of a ring-shaped rotating outer pipe  61 . The rotating outer pipe  61  is connected to a ring-shaped fixed shaft  63  through a bearing  62 . A ring-shaped rotating inner pipe  65  is disposed in the fixed shaft  63  through a bearing  64 . The above-mentioned rotating shaft  43  is disposed in the rotating inner pipe  65  through spline bearings  44  and  45 . Thus, the rotating shaft  43  is lifted up and down against the rotating inner pipe  65 . In addition, the rotating shaft  43  is rotated along with the rotating inner pipe  65 . 
     A follower pulley  67  as a main driving mechanism is disposed in the rotating outer pipe  61 . In addition, a follower pulley  66  is disposed in the rotating inner pipe  65 . A belt  70  is passed from the follower pulley  66  to a driving pulley  69  driven by a driving motor  68 . A belt  71  is passed from the follower pulley  67  to the driving pulley  69  driven by the driving motor  68 . Thus, the spin chuck  40  and the rotation cup  55  are synchronously rotated by the same driving motor  68 . The lower portion of the spin chuck  40  and the inner lower surface of the rotation cup  55  have respective fitting portions. When the spin chuck  40  is lifted down, it fits the rotation cup  55 . Thus, the spin chuck  40  and the rotation cup  55  are synchronously rotated. 
     The side wall  57  of the rotation cup  55  is upwardly tapered. A flange is formed at the upper end portion of the side wall  57 . Air intake openings (not shown) are peripherally formed at predetermined intervals in the flange. An air exhaust opening (not shown) is formed between the lower surface of the rotation cup  55  and the side wall  57 . Thus, when the rotation cup  55  is rotated, atmospheric gas flows from the air intake openings (not shown) to the process chamber  58 . The atmospheric gas in the process chamber  58  is exhausted from the exhaust opening (not shown) to a ring-shaped drain cup  76 . 
     The drain cup  76  is disposed on the outer periphery of the rotation cup  55 . The drain cup  76  has an inner ring-shaped path  77 . The ring-shaped path  77  is partitioned by walls  78  and  79 . The wall  78  rises from the bottom portion of the drain cup  76 . The wall  79  hangs from the ceiling portion of the drain cup  76 . Drain holes  80  are peripherally formed at predetermined intervals in the bottom portion formed between the walls  78  and  79 . The walls  78  and  79  are disposed so as to cause gaseous mist entered into the drain cup  76  to collide with the walls  78  and  79  and liquify the mist due to inertia collisions. 
     The above-mentioned lid  84  can be freely placed and removed to/from the upper opening portion of the rotation cup  55 . A pipe  85  is disposed at the center portion of the lid  84  through a bearing  86 . Resist solution is coated to an LCD substrate G through the pipe  85 . Solvent of resist solution is sprayed to the inner periphery of the rotation cup  55 . The lid  84  is connected to a lifting mechanism (not shown). The lid  84  is lifted up and down by the lifting mechanism (not shown). 
     In the supplying system  34 , for example a follower pulley  90  as a first auxiliary driving mechanism is disposed to the rotating outer pipe  61 . A belt  94  is passed from the follower pulley  90  to a driving pulley  93  disposed to a driving shaft  92  of an air motor  91 . The air motor  91  functions as an auxiliary driving means that assists the driving of the driving motor  68 . Since the air motor  91  assists the driving of the driving motor  68 , the rotation cup  55  that accommodates an LCD substrate G can be rotated at a predetermined rotating acceleration. As a second auxiliary driving mechanism, a follower pulley  97  is disposed to the rotating outer pipe  61 . A belt  98  is passed from the follower pulley  97  to a driving pulley  101  disposed to a driving shaft  100  of an air motor  99 . 
     The air motor  99  functions as a second auxiliary driving means that assists the driving of the driving motor  68 . Since the air motor  99  assists the driving of the driving motor  68 , the rotation cup  55  that accommodates an LCD substrate G can be rotated at a predetermined rotating acceleration. The gear ratio of the first auxiliary driving mechanism is different from the gear ratio of the second auxiliary driving mechanism. The gear ratio between the driving pulley  93  and the follower pulley  90  of the first auxiliary driving mechanism is larger than the gear ratio between the driving pulley  101  and the follower pulley  97  of the second auxiliary driving mechanism. The gear ratio of the second auxiliary driving mechanism is larger than the gear ratio between the driving pulley  69  and the follower pulley  67  of the main driving mechanism. The gear ratio of each auxiliary driving mechanism is larger than the gear ratio of the main driving mechanism. Thus, the rotating acceleration of the second auxiliary driving mechanism is larger than the rotating acceleration of the main driving mechanism. The rotating acceleration of the first auxiliary driving mechanism is larger than the rotating acceleration of the second auxiliary driving mechanism. 
     The air motors  91  and  99  are driven by compressed air supplied from an air supply source  95 . The pressure of the compressed air is controlled by adjusting units  96  and  102 . An air operating valve  103  is disposed between the air motor  91  and the adjusting unit  96 . An air operating valve  104  is disposed between the air motor  99  and the adjusting unit  102 . As shown in FIG. 4B, a control section  105  that causes the air operating valves  103  and  104  to be opened and closed is disposed. The control section  105  also causes the air motors  91  and  99  to be started and stopped. When the air motors  91  and  99  are not driven, their rotation resistance is very low. Thus, even if the air motors  91  and  99  are not driven, they do not disturb the rotating acceleration of the driving motor  68 . The control section  105  causes the driving motor  68  to be started and stopped. Since the main driving mechanism and the auxiliary driving mechanisms are connected to the rotation cup  55 , the revolution speed of the main driving mechanism is almost the same as the revolution speed of each of the auxiliary driving mechanisms. The control section  105  designates the revolution speed of the rotation cup  55  corresponding to the revolution speed of the main driving mechanism and/or the revolution speed of each of the auxiliary driving mechanisms. 
     The coating/periphery removing unit  27  is structured as described above. Next, the operation and effect of the coating/periphery removing unit  27  will be described. 
     When a cassette  11  that accommodates raw LCD substrates G is placed on the cassette table  10 , the sub-conveying unit  13  accesses the cassette  11  and unloads one LCD substrate G therefrom. The sub-conveying unit  13  conveys the LCD substrate G to the transferring table  14  disposed in the loader portion  2  and places the LCD substrate G on the transferring table  14 . 
     The main conveying unit  15  holds the LCD substrate G with the conveying arm  15   a  and conveys the LCD substrate G to the ultraviolet ray ozone cleaning unit  19 . The ultraviolet ray ozone cleaning unit  19  cleans the LCD substrate G of organic contaminations. The main conveying unit  15  conveys the resultant LCD substrate G to the scrubber cleaning unit  17 . The scrubber cleaning unit  17  performs a scrubber cleaning process for the LCD substrate G. The main conveying unit  15  holds the LCD substrate G with the conveying arm  15   a  and conveys the LCD substrate G to the transferring table  23 . 
     The main conveying unit  25  holds the LCD substrate G on the transferring table  23  with the conveying arm  25   a  and conveys the LCD substrate G to the hydrophobic process unit  28 . After the hydrophobic process unit  28  has performed the hydrophobic process for the LCD substrate G, the main conveying unit  25  holds the LCD substrate G with the conveying arm  25   a  and conveys the LCD substrate G to the coating/periphery removing unit  27 . 
     The main conveying unit  25  conveys the LCD substrate G to the supplying system  34  of the coating/periphery removing unit  27 . At this point, the spin chuck  40  is placed in a ready position denoted by dotted line shown in FIG.  5 . The main conveying unit  25  holds the LCD substrate G with the conveying arm  25   a  and conveys the LCD substrate G to the spin chuck  40  placed in the ready position. The spin chuck  40  vacuum sucks the LCD substrate G. The lifting cylinder  42  lifts down the spin chuck  40  from the ready position denoted by the dotted line shown in FIG. 5 to a process position denoted by solid line shown in FIG.  5 . After the spin chuck  40  has lifted down to the process position, the spin chuck  40  fits the rotation cup  55  through their fitting portions. 
     After the conveying arm  25  has transferred the LCD substrate G to the spin chuck  40  and retreated from the supplying system  34 , the lifting mechanism (not shown) lifts down the lid  84  from an open position denoted by a solid line shown in FIG. 6 to a close position denoted by a dotted line shown in FIG.  6 . Thus, the lid  84  closes the upper opening portion of the rotation cup  55 . The control section  105  causes the driving motor  68  to rotate the spin chuck  40  and the rotation cup  55 . Thus, the LCD substrate G placed in the rotation cup  55  rotates. Thereafter, the control section  105  causes the air operating valve  103  to open and the air motor  91  to assist the driving of the driving motor  68 . At this point, the air operating valve  104  is closed. Thus, air does not flow to the air motor  99 . The gear ratio of the air motor  91  is larger than the gear ratio of the driving motor  68 . Thus, the rotating acceleration of the LCD substrate G becomes larger than the case that only the driving motor  68  is driven. 
     Next, solvent and resist solution are successively dropped from the pipe  85  to the center of the LCD substrate G. Thereafter, the control section  105  causes the air operating valve  104  to open and the air motor  99  to drive. At this point, the operation time of the air motor  91  overlaps with the operation time of the air motor  99 . After a predetermined time period has elapsed, the rotating acceleration of the air motor  99  becomes stable. The control section  105  causes the air operating valve  103  to close and thereby stop supplying air to the air motor  91 . The control section  105  causes the air motor  99  to assist the driving of the driving motor  68  so as to accelerate the rotation of the driving motor  68 . When the driving motor  68  starts rotating, since a large shaft rotating force is required due to moment of inertia, the air motor  91  is driven. After the rotation of the driving motor  68  is accelerated, the air motor  99  assists the driving of the driving motor  68 . Thus, while the driving motor  68  is being driven, the auxiliary driving mechanisms are driven in the order of larger gear ratios. Consequently, a larger rotating acceleration can be obtained than the case that only the driving motor  68  is driven. In addition, after the predetermined time period elapses before a predetermined revolution speed (for example, 1500 rpm) is obtained, the air operating valve  104  is closed and thereby air supply to the air motor  99  is sopped. Thereafter, the LCD substrate G is rotated at a predetermined rotating acceleration until the maximum revolution speed (for example, 1500 rpm) is obtained. Thus, the resist solution concentrically spreads out to the periphery of the LCD substrate G. 
     When the LCD substrate G is rotated at the maximum revolution for a several seconds, a resist film with an equal thickness can be formed on the LCD substrate G. 
     After the resist film is formed on the LCD substrate G, the spin chuck  40  and the rotation cup  55  are decelerated and stopped. In the deceleration range, the air motors  91  and  99  do not assists the driving of the driving motor  68 . The lifting mechanism (not shown) lifts up the lid  84  and opens the upper opening portion of the rotation cup  55 . The lifting cylinder  42  lifts up the spin chuck  40 . The conveying arm  25   a  unloads the LCD substrate G from the rotation cup  55 . Next, the conveying mechanism (not shown) conveys the LCD substrate G from the supplying system  34  to the periphery removing system  35 . 
     The main conveying unit  25  unloads the LCD substrate G from the coating/periphery removing unit  27  with the conveying arm  25   a . The main conveying unit  25  holds the LCD substrate G with the conveying arm  25   a  and conveys the LCD substrate G to the heating unit  30 . The heating unit  30  performs a predetermined heating process for the LCD substrate G. 
     In the coating/periphery removing unit  27 , the air motors  91  and  99  assist the driving of the driving motor  68 . In at least part of the acceleration region, the LCD substrate G is accelerated by a plurality of driving mechanisms. Thus, even if an LCD substrate G becomes large, it can be rotated at a predetermined rotating acceleration along with the rotation cup  55 . Consequently, the resist solution equally and concentrically spreads out to the periphery of the LCD substrate G. As a result, a resist film with an equal thickness is formed on the LCD substrate G with a smaller quantity of resist solution than the conventional apparatus. 
     FIG. 7 shows the relation between rotating accelerations of three LCD substrates G in different sizes and the quantity of resist solution consumed therewith. In FIG. 7, the quantity of resist solution consumed with three LCD substrates G in three sizes of 370×470 mm, 400×500 mm, and 550×650 mm is plotted in the case that they are rotated at three rotating accelerations of 500 rpm/sec, 800 rpm/sec, and 1000 rpm/sec. In FIG. 7, the vertical axis and the horizontal axis represent the quantity of resist solution consumed with the LCD substrates G and the rotating accelerations thereof, respectively. 
     In FIG. 7, three lines that decline are obtained. Thus, it is clear that as an LCD substrate G is rotated at a larger rotating acceleration, the quantity of resist solution consumed therewith decreases. 
     Corresponding to the graph data shown in FIG. 7, the ratio of the quantity of resist solution consumed with each LCD substrate G rotated at a rotating acceleration of 500 (rpm/sec), the quantity of resist solution consumed with each LCD substrate G rotated at a rotating acceleration of 800 (rpm/sec), and the quantity of resist solution consumed with each LCD substrate G rotated at a rotating accelerating of 1000 (rpm/sec) is calculated and plotted as consumption rate of resist solution on the vertical axis. The rotating accelerations of the LCD substrates are plotted on the horizontal axis. The plotted data is shown in FIG.  8 . FIG. 8 shows that as an LCD substrate G is rotated at a larger rotating acceleration, the consumption rate of the resist solution largely decreases. The effect becomes remarkable as the size of the LCD substrate G becomes large. 
     To form a resist film with an equal film thickness, as denoted by a dotted line shown in FIG. 9, until the revolution speed of an LCD substrate G becomes the maximum revolution speed (1500 rpm), it is not necessary to cause the air motors  91  and  99  to assist the driving of the driving motor  69 . Instead, before the revolution speed of the LCD substrate G becomes the predetermined revolution speed, the air motors  91  and  99  can be stopped. For example, as denoted by a solid line shown in FIG. 9, until the revolution speed of the LCD substrate G becomes A that is in the middle of the maximum revolution speed, the air motors  91  and  99  successively assist the driving of the driving motor  68 . Thereafter, the LCD substrate G is driven by only the driving motor  68 . 
     According to the embodiment, the rotating shaft  43  is rotated by the driving motor  68  and the air motors  91  and  99  through the spline shaft  45 . However, according to the present invention, the portions that transfer the driving force of the driving motor  68  and the air motors  91  and  99  are not limited to those of the embodiment. 
     For example, as shown in FIG. 10, the follower pulley  67  is disposed to the rotating outer pipe  61  of the rotation cup  55 . The follower pulleys  90  and  97  are disposed to the rotating inner pipe  65 . When resist solution dropped to the LCD substrate G is spread out on the LCD substrate G, the driving motor  68  that rotates the rotating shaft  43  may be assisted by the air motors  91  and  99 . 
     In other words, since the spin chuck  40  and the rotation cup  55  are connected and synchronously rotated, the LCD substrate G and the rotation cup  55  can be rotated at a predetermined rotating acceleration. Thus, as with the embodiment, since resist solution dropped on the LCD substrate G is equally spread out to the periphery thereof, a resist film with a predetermined film thickness can be formed. 
     Since the LCD substrate G and the rotation cup  55  are rotated together, the rotation of the LCD substrate G does not disturb the atmosphere in the process chamber  58 . Thus, since the film thickness of the resist film does not vary, the equality of the film thickness of the resist film improves. 
     According to the present invention, a supplying system  100  shown in FIG. 11 can be used instead of the supplying system  34  of the embodiment. The supplying system  100  has intermediate rings  101  and  102 . The intermediate ring  101  is disposed between a spline bearing  44  and a rotating outer pipe  61 . The intermediate ring  102  is disposed between a spline bearing  45  and the rotating outer pipe  61 . A spin chuck  40  freely lifts up and down against a rotation cup  55 . The spin chuck  40  and the rotation cup  55  rotate together. Follower pulleys  66 ,  90 , and  97  are disposed to the rotating outer pipe  61 . The follower pulley  66  is rotated by the rotating drive force of a driving motor  68 . The follower pulley  90  is rotated by rotating drive force of an air motor  91 . The follower pulley  97  is rotated by rotating drive force of the air motor  99 . 
     In the supplying system  100 , the spin chuck  40  and the rotation cup  55  are synchronously rotated. Thus, the spin chuck  40  and the rotation cup  55  can be rotated at a large rotating acceleration by the driving motor  68  and the air motors  91  and  99 . 
     In the embodiment, two auxiliary driving mechanisms are disposed. However, it should be noted that the number of auxiliary driving mechanisms is not limited to two. In other words, at least one auxiliary driving mechanism can be used. When one auxiliary driving mechanism is disposed, the number of structural parts of the apparatus can be reduced. Thus, the apparatus becomes small. In addition, since the control mechanism of the apparatus is simplified, the reliability of the apparatus improves. In contrast, when three or more auxiliary driving mechanisms are disposed, since three or more gear ratios are used, the rotation of an LCD substrate G can be smoothly accelerated. Thus, a film of process solution with an equal thickness can be formed on the substrate. In addition, since the gear ratios are finely designated, the auxiliary driving mechanisms can accelerate the rotation of the substrate to some extent. Consequently, the size of the main driving mechanism can be further reduced. 
     In the embodiment, before the air motor  91  is operated, the driving motor  68  is operated. Alternatively, the air motor  91  and the driving motor  68  can be operated at the same time. In this case, the rotation of the LCD substrate G can be accelerated in a shorter time period. Thus, the throughput of the apparatus improves. 
     In the embodiment, the operation time of the air motor  91  at least partly overlaps with and the operation time of the air motor  99 . However, it should be noted that the operation time of the air motor  91  may not overlap with the operation time of the air motor  99 . In this case, the quantity of air consumed by the air motors  91  and  99  can be reduced. After the air motor  91  is stopped, until the rotating acceleration of the air motor  99  becomes stable, the rotating acceleration of the LCD substrate G is low. However, since the driving motor  68  is operated, the rotation of the LCD substrate G is not decelerated. Thus, the revolution speed of the driving motor  68  can be maintained at the point. Thus, after the rotating acceleration of the air motor  99  becomes stable, the rotation of the LCD substrate G can be further accelerated. 
     It should be noted that the control section  105  causes the adjusting units  96  and  102  to adjust the pressure of compressed air supplied to the air motors  9 l and  99 . In this case, the control section  105  can adjust the rotating acceleration of the LCD substrate G. 
     The effects of the air motors  91  and  99  can be accomplished by conventional electric motors. 
     The timings of the operations of the air motors  91  and  99  may be varied from those of the embodiment. 
     Instead of the pipe  85  disposed at the center of the lid  84 , an arm with the pipe  85  may be disposed outside the rotation cup  55 . Resist solution and solvent are supplied from the pipe  85  disposed on the arm. In this case, when the resist solution and solvent are supplied from the pipe  85 , the lid  84  is lifted up. 
     As shown in FIG. 12, the follower pulleys  66  and  90  may be disposed to the rotating shaft  43  through the spline bearing  45 . In the embodiment, LCD substrates are used. However, according to the present invention, instead of LCD substrates, for example, CD substrates and semiconductor wafers may be used. 
     Although the present invention has been shown and described with respect to a best mode embodiment thereof, it should be understood by those skilled in the art that the foregoing and various other changes, omissions, and additions in the form and detail thereof may be made therein without departing from the spirit and scope of the present invention.