Abstract:
An apparatus for cleaning a substrate comprises a spin chuck for holding a substrate substantially horizontally a rotation driving mechanism for rotating the spin chuck, a lower nozzle having a plurality of liquid outlet ports facing both a peripheral portion and a center portion of a lower surface oaf the substrate held by the spin chuck, a process liquid supply mechanism for supplying a first process liquid to the lower nozzle, and a controller for controlling operations of the process liquid supply mechanism and the rotation driving mechanism, individually, in which the controller controls the rotation driving mechanism to rotate the spin chuck and controls the process liquid supply mechanism to supply a first process liquid to the lower nozzle, thereby outputting the first process liquid toward the peripheral portion and the center portion of the lower surface of the substrate.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a substrate cleaning apparatus and method of cleaning both surfaces of a substrate such a semiconductor wafer or an LCD substrate. 
     In a process for manufacturing semiconductor devices, it is very important to maintain both surfaces of a semiconductor wafer at clean conditions. Therefore, it is necessary to remove contaminants, such as particles, organic substances, and metallic ions, attached to both surfaces of the semiconductor wafer. The contaminants are removed from front and rear surfaces of the semiconductor wafer by using a single-processing apparatus for cleaning both surfaces as disclosed, for example, in U.S. patent application Ser. No. 09/135,478 (filed on Aug. 17, 1998). 
     In a conventionally used cleaning apparatus  100  shown in FIG. 1, a wafer W is horizontally held by a peripheral holding member  103 . While the wafer W is rotated by means of a spin chuck  101 , a process liquid is supplied to the center portion of an upper surface (front surface) of the wafer W from an upper nozzle (not shown); at the same time, a process liquid is supplied to the center portion of a lower surface (rear surface) of the wafer W from a lower nozzle  102 . However, the process liquid  104  supplied to the lower surface of the wafer W falls down from the wafer W before it reaches to the peripheral portion of the wafer W. As a result, the process liquid  104  may not be supplied to the peripheral portion of the wafer W in a sufficient amount. In addition, the surfaces of the wafer W are hydrophobic, so that the process liquid  104  is likely to be repelled from the lower surface of the wafer W and fall off. It follows that the lower peripheral portion of the wafer W is washed insufficiently. In particular, when a large-sized wafer (e.g., 8 or 12 inch diameter) is used, the process liquid  104  rarely reaches the lower peripheral portion of the wafer W, with the result that the lower peripheral portion is cleaned but incompletely. 
     In a step of manufacturing a semiconductor device, a silicon oxide film (insulating film) is often formed on the wafer W. The silicon oxide film (insulating film) is, however, an unnecessary film for a non-pattern formation region (rear surface) of the wafer W. The insulating film must be removed from the rear surface of the wafer. However, when the insulating film is tried to remove from the rear surface of the wafer, the pattern formed on the front surface is sometimes damaged. 
     BRIEF SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a substrate cleaning apparatus and method capable of supplying a process liquid in a sufficient amount even to a peripheral portion of a rear surface of the substrate, and uniformly cleaning the entire rear surface of the substrate, without damaging an upper surface of the substrate. 
     According to the present invention, there is provided an apparatus for cleaning the substrate, comprising: 
     a spin chuck for holding a substrate substantially horizontally; 
     a rotation driving mechanism for rotating the spin chuck; 
     a lower nozzle having a plurality of liquid outlet ports facing both a peripheral portion and a center portion of a lower surface of the substrate held by the spin chuck; 
     a process liquid supply mechanism for supplying a first process liquid to the lower nozzle; and 
     a controller for controlling operations of the process liquid supply mechanism and the rotation driving mechanism, individually, 
     in which the controller controls the rotation driving mechanism to rotate the spin chuck and controls the process liquid supply mechanism to supply the first process liquid to the lower nozzle, thereby outputting the first process liquid toward the peripheral portion and the center portion of the lower surface of the substrate. 
     According to the present invention, there is provided a method of cleaning a substrate comprising the steps of: 
     (a) holding a substrate rotatably and substantially horizontally; 
     (b) rotating the substrate; and 
     (c) supplying a first process liquid from a lower nozzle to both a peripheral portion and a center portion of a lower surface of the substrate held by a spin chick, substantially simultaneously, and supplying a second process liquid from an upper nozzle to an upper surface of the substrate held. 
     In this case, the second process liquid is pure wafer for protecting the upper surface of the substrate. The first process liquid is an etching solution for dissolving and removing a thin film coated over the lower surface of the substrate. More specifically, the first process liquid is one selected from the group consisting of an ammonia/hydrogen peroxide solution mixture, an hydrochloric acid/hydrogen peroxide solution mixture, and an aqueous hydrofluoric acid solution. 
     According to the present invention, the first process liquid is supplied from the lower nozzle uniformly to the region extending from the center portion to any peripheral portion of the lower surface of the substrate. It is therefore possible to uniformly dissolve and remove the oxide film from the lower surface of the substrate. 
     Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
     The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate presently preferred embodiments of the invention, and together with the general description given above and the detailed description of the preferred embodiments given below, serve to explain the principles of the invention. 
     FIG. 1 is a cross-sectional view of a gist portion of a conventionally-used cleaning apparatus; 
     FIG. 2 is a perspective view of a wafer cleaning system, partly cut away, for showing an inner structure; 
     FIG. 3 is a cross sectional view of a cleaning apparatus according to a first embodiment of the present invention, accompanying a block diagram of peripheral elements; 
     FIG. 4 is a plan view of a lower nozzle as viewed from an upper side; 
     FIG. 5 is a schematic plan view of the cleaning apparatus; 
     FIG. 6 is a block diagram showing a liquid supply route for supplying a process liquid to a cleaning nozzle according to the first embodiment; 
     FIG. 7 is a block diagram showing a gas supply route for supplying a gas to a drying nozzle according to the first embodiment; 
     FIG. 8 is a block diagram showing a liquid supply route for supplying a process liquid to a cleaning nozzle according to another embodiment; 
     FIG. 9 is a flow chart showing the steps for cleaning both surfaces of a substrate; 
     FIG. 10 is a cross sectional view of a cleaning apparatus according to another embodiment of the present invention, accompanying a block diagram of peripheral elements; 
     FIG. 11 is a perspective view of a lower nozzle according to a first embodiment; 
     FIG. 12 is a longitudinal sectional view of the lower nozzle according to the first embodiment; 
     FIG. 13 is a perspective view of a lower nozzle according to a second embodiment; 
     FIG. 14 is a side view of the lower nozzle according to the second embodiment; 
     FIG. 15 is a perspective view of the lower nozzle according to a third embodiment; 
     FIG. 16 is a plan view of a lower nozzle according to a fourth embodiment; 
     FIG. 17 is a side view of the lower nozzle according to the forth embodiment; 
     FIG. 18 is a perspective view of the lower nozzle according to a fifth embodiment; and 
     FIGS. 19A and 19B are perspective sectional views respectively showing a wafer and a cleaning apparatus during washing both surfaces. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Now, various preferred embodiments of the present invention will be explained with reference to the accompanying drawings. 
     A cleaning system  1  has a load/unload section  2  for loading/unloading a cassette C storing one lot of semiconductor wafers W (25 sheets). A transportation passage (not shown) for a cassette transport robot is provided in front of the load/unload section  2 . In the load/unload section  2 , a mounting table  2   a  extending in an X-direction is arranged. On the mounting table  2   a,  for example, three cassettes C are mounted. A transport section  3  is provided along the mounting table  2   a.  A transport arm mechanism  5  is placed within the transport section  3 . The transport arm mechanism  5  has an arm portion A consisting of three arms  5   a,    5   b,    5   c.  The transport arm mechanism  5  has a back-and-forth moving mechanism for moving each of arms  5   a,    5   b,    5   c,  back and forth, an X-axis moving mechanism for moving the arm portion  5 A in the X-axis direction, a Z-axis moving mechanism for moving the arm portion  5 A in a Z-axis direction, and a θ-rotation mechanism for rotating the arm portion  5 A around the Z-axis. 
     The processing section  4  is arranged at the rear side of the transporting section  3  and has six processing units  6 - 11 . Loading/unloading ports  6   a - 11   a  are provided in front surfaces of the processing units  6 - 11 , respectively. The loading/unloading ports  6   a - 11   a  are opened/closed by a shutter (not shown). The wafer W is loaded into/unloaded from each of the processing units  6 - 11  by the transport arm mechanism  5  through the loading/unloading ports  6   a - 11   a,  respectively. The processing units  6  and  9 , which are adjacent units vertically arranged, are responsible for washing the wafer W with the same type of chemical solution. The processing units  7  and  10 , which are adjacent units vertically arranged, are responsible for washing the wafer W with the same type of chemical solution. The processing units  8  and  11 , which are adjacent units vertically arranged, are responsible for washing the wafer W with the same type of chemical solution. At a back surface side of the processing section  4 , a chemical solution supply unit (not shown) and a waste fluid collecting unit (not shown) are arranged. 
     Now, referring to FIGS. 3-7, the cleaning unit for removing an oxide film formed on the rear surface of a wafer without affecting the semiconductor device formed on the upper surface of the wafer. Since the cleaning units  19  of the processing units  6 - 11  are substantially equal to each other, the cleaning unit  19  placed in the first processing unit  6  will be representatively explained. 
     As shown in FIG. 3, the cleaning unit  19  has a cup  20 , a spin chuck  21 , various types of nozzles  45 ,  73 ,  77 ,  81 , first and second process liquid supply units  83 ,  86 , a gas supply unit  99 , and a controller  120 . The cup  20  surrounds a spin chuck  21  and receives liquid and mist scattered from the wafer. A plurality of drainage passages  46  are formed in the bottom surface of the cup  20 . The drainage passages  46  communicate with a waste fluid tank (not shown) and an exhaust unit to discharge the received waster fluid and mist. 
     A rotatory hollow shaft  22  passes through the center of the bottom surface of the cup  20 . The upper end of the shaft  22  is connected to the spin chuck  21 . The rotatory hollow shaft  22  is rotated directly by a motor  23 . A plurality of mechanical chucks  24  are arranged so as to stand in the upper peripheral portion. The wafer W is held by the mechanical chucks  24 . The rotatory hollow shaft  22  is connected to a liftable mechanism (not shown) driven by a cylinder (not shown) to move the spin chuck  21  up and down. 
     As shown in FIG.  3  and FIG. 5, two upper nozzles  45 ,  77  are supported by the corresponding moving mechanisms (not shown) so as to move between a home position and an operation position. In the home positions, nozzle stand-by regions (not shown) are formed to allow the upper nozzles  45 ,  77  to stand-by. The operation positions for the upper nozzles  45 ,  77  are right above the wafer held by the spin chuck  21 . 
     As shown in FIG. 6, the nozzle  45  communicates with a first process liquid supply unit  83  through passages  82 ,  84  and communicates with a second process liquid supply unit  86  through passages  82 ,  87 . A valve  93  is provided in the passage  84 . A valve  96  is provided in the passage  88 . Furthermore, the passage  43  communicates with the passage  84  through a first bypass passage  85 . The passage  82  communicates with the passage  88  through a second bypass passage  87 . The first bypass passage  85  is equipped with a valve  94 . The second bypass passage  87  is equipped with a valve  95 . The open/shut operations of the valves  93 ,  94 ,  95 ,  96  are individually controlled by a controller  120 . The first process liquid supply unit  83  houses a process liquid supply source and a flow rate control mechanism. Pure wafer is contained as a process liquid for supplying on the front surface of the substrate, in the process liquid supply source of the unit  83 . 
     As shown in FIG. 7, the upper nozzle  77  communicates with a gas supply unit  99  through passages  89 ,  91 . The gas supply unit  99  houses a gas supply source and a flow rate control mechanism which are controlled by the controller  120 . The gas supply source of the unit  99  contains a non acidic gas such as nitrogen gas. Note that a valve  97  is interposed between the passage  89  and  91  from the gas supply unit  99  to the nozzle  77 . A dehumidifier may be fit to the passages  89 ,  91  to dry the gas. Furthermore, a heater may be fitted to the passages  89 ,  91  to heat the gas. 
     As shown in FIG. 3, two lower nozzles  73 ,  81  are arranged immediately under the wafer W held by the spin chuck  21 . Each of the outlet ports  41 ,  81   a  is faced to the lower surface (non pattern formation region) of the wafer. These two lower nozzles  73 ,  81  are attached to a supporting disk  75  supported by the hollow supporting shaft  76 . 
     As shown in FIG. 6, the lower nozzle  73  communicates with the second process liquid supply unit  86  through the passages  43 ,  88  and communicates with the first process liquid supply unit  83  through the passages  43 ,  85 . The second process liquid supply unit  86  houses a chemical solution supply source and a flow rate control mechanism which are controlled by the controller  120 . The chemical solution supply unit of the unit  86  contains, for example, an ammonia/hydrogen peroxide solution mixture (APM solution), a hydrochloric acid/hydrogen peroxide solution mixture (HPM solution) or an aqueous hydrofluoric acid solution (DHF solution). The process liquid supply passages  82 ,  84 ,  85 ,  87 ,  88  are equipped with filters (not shown) for removing impurities and foreign substances. 
     As shown in FIG. 7, the lower nozzle  81  communicates with the gas supply unit  99  through passages  90 ,  92 . The lower nozzle  81  has a gas outlet port  81   a  for spraying a gas toward the lower surface of the wafer W. The gas flow passages  90 ,  92  are equipped with a valve  98  controlled by the controller  120 , which controls the amount of gas to be supplied to the lower nozzle  81 . 
     As shown in FIG. 4, the lower nozzle  73  is a tube  70  (consisting of four branched tubes), having a cruciform plan view. A liquid inlet port communicating with the passage  43  is formed at a point of the intersection (the cruciform) of the lower nozzle  73 . Numerous holes  41  are formed in the upper surface of the four branched (cruciform) tubes  70  and face the lower surface of the wafer W. The holes  41  are arranged at regular intervals along a longitudinal portion of the tube  70 . Note that the distance L 1  from the lower nozzle  73  to the lower surface of the wafer W desirably falls within the range of 2-20 mm. The distance L 2  (the height of a lower space  25 ) from the upper surface of the spin chuck  21  to the lower surface of the wafer W desirably falls within the range of 20-50 mm. 
     When the process liquid is introduced into the lower nozzle  73 , the process liquid is equally distributed to the four branched tubes  70 . The process liquid is sprayed simultaneously toward the peripheral portion and the center portion of the lower surface of the wafer. The passage  43  communicating with these holes  41  is inserted into the hollow supporting shaft  76 , which is further inserted into a rotatory hollow shaft  22 . In other words, the nozzles  73 ,  81  pass through the hollow supporting shaft  76  and opened at the space  25 . Note that the controller  120  controls open/shut operations of the valves  93 ,  94 ,  95 ,  96  to switch supply of the process liquid to the lower nozzle  73  between the first ( 83 ) and second process liquid supply unit  86 . To describe more specifically, the valve  96  is closed and the valve  94  is opened to thereby switch the route to the lower nozzle  73  from the passages  88 ,  43  to the passages  85 ,  43  and switch supply of the process liquid to the lower nozzle  73  from a chemical cleaning liquid (DHF solution, APM solution or HPM solution) to a rinse solution (pure wafer). If the valves  95 ,  96  are closed and the valves  93 ,  94  are opened, the rinse solution (pure water) can be supplied simultaneously to the upper and lower nozzles  45 ,  73 . 
     Note that the liquid inlet port is not always communicated with the point of intersection of the lower nozzle  73 . The inlet port may be communicated with tip portions of the four branched tubes  70 , or two of them. 
     Alternatively, a plurality of lower nozzles  81  may be arranged so as to face the lower surface of the wafer W. In this case, it is desirable to define the direction of the gas spray ports of the nozzles  81  in such a way that gas flows sprayed from the nozzles  81  are not interfered with each other. This is because if the gas flows are hit to each other, a turbulent flow is generated, decreasing a drying efficiency. 
     The process liquid is supplied from the cruciform nozzle  73  of the aforementioned embodiment uniformly to the entire lower surface of the wafer W, although the space occupied by the nozzle is small. 
     Now, referring to FIG. 9, we will explain how to wash and clean the both surfaces of the wafer W by using the aforementioned substrate cleaning apparatus. 
     First, the cassette C is loaded into the load/unload section  2  by the transport robot (not shown). In the cassette C, 25 sheets of silicon wafers W (8 inch or 12 inch diameter) are stored. A pattern is formed on the front surface of each of the wafers W. An identification code having data of processing conditions for a specific lot, recorded thereon, is displayed at an appropriate portion of the cassette C. The identification code is read by an optical sensor (not shown) and the read data is input into the controller  120 . The controller sends instruction signals to the transport arm mechanism  5  and each of the processing units  6 - 11  on the basis of the input data. The transport arm mechanism  5  and the processing units  6 - 11  are operated in accordance with the instruction signals. 
     The wafer W is taken out from the cassette C by the transport arm mechanism  5 , and transported to the processing unit  7  of the processing section  4 . Then, the shutter of the unit  7  is moved down to load the wafer W into the process unit  7  through the loading/unloading port  7   a  (Step S 1 ). 
     After transferring of the wafer W onto the spin chuck  21 , the arm  5   b  is withdrawn and the loading/unloading port  7   a  is closed. Subsequently, rotation of the wafer W is initiated by the spin chuck  21  (Step S 2 ). Then, the valves  93 ,  94  are opened and the valves  95 ,  96  are closed to supply APM solution to the upper surface of the wafer W from the upper nozzle  45  (Step S 3 ) and to supply an APM solution serving as a removing liquid from the lower surface of the wafer W from the lower nozzle  73  (Step  4 ). The rotation speed of the spin chuck  21  ranges from 10 to 30 rpm. The lower side supply amount of the APM solution is 0.5 to 4.0 L/min. The upper side supply amount of the APM solution is 0.5 to 4.0 L/min. When the APM solution is simultaneously output from the output holes  41  toward the peripheral portion and the center portion of the wafer W, the silicon oxide film coated over the rear surface of the wafer W is uniformly etched and removed therefrom. 
     The valves  93 - 96  are closed and the supply of the APM solution to the rear surface of the wafer W is terminated (Step S 5 ). Simultaneously, the supply of the APM solution to the front surface is terminated (Step S 6 ). After completion of the rear surface cleaning, the valves  93 ,  94  are closed and the valves  95 ,  96  are opened to supply pure wafer to the upper surface of the wafer W from the upper nozzle  45 ; at the same time, pure wafer is supplied to the lower surface of the wafer W from the lower nozzle  73 . In this manner, both surfaces of the wafer W are cleaned. 
     Subsequently, the valves  97 ,  98  are opened and nitrogen gas is sprayed toward the upper and lower surfaces of the wafer W in rotatory motion, from the upper and lower nozzles  77 ,  81 . In this manner, both surfaces of the wafer W are dried (Step S 7 ). In the drying step S 7 , the rotation speed of the spin chuck  21  is further increased to actively remove the attached liquid from the wafer W. Note that the inner space of the cup  20  is forcibly evacuated by an exhaust apparatus (not shown). In this manner, both surfaces of the wafer W are dried up. 
     When the wafer W is completely dried up, the rotation of the spin chuck  21  is terminated (Step S 8 ). Then, the shutter is opened, the transport arm  5   c  is inserted into the processing unit  7  through the loading/unloading port  7   a,  and the wafer W is unloaded from the processing unit  7  by the transfer arm  5   c.  Subsequently, the wafer W is transported to a next processing unit  8 , in which both surfaces of the wafer W are washed with, for example, the aqueous hydrofluoric acid solution (DHF cleaning). After the DHF cleaning, the wafer W is rinsed with pure water and rotated by the spin chuck  21  at a high speed to remove the attached liquid from the wafer W. Simultaneously, nitrogen gas is sprayed onto the wafer W to dry both surfaces. 
     Thereafter, the shutter is opened to unload the wafer W from the processing unit  8  by the transport arm  5   a.  The substrate transport arm mechanism  5  is turned again to the loader/unloader  2  from the processing section  4 . The substrate transport arm mechanism  5  then moves the transport arm  5   a  forward to store the wafer W into the cassette C. In this way, the first wafer W 1  to the 25th wafer W 25  washed successively, are stored into the cassette C, and then, the transport robot (not shown) unloads the cassette C out of the system  1  through the loader/unloader section  2  and transports the cassette C to a next process (Step  9 ). 
     Now, referring to FIGS. 8,  10 - 12 , a second embodiment of the present invention will be explained. Note that explanation for the same structural elements of the second embodiment as in the first embodiment will be omitted. 
     As shown in FIG. 10, the cleaning apparatus  19 A has a lower nozzle  30  which includes a cup  20 , a spin chuck  21 , and a liquid reservoir chamber  42 , an hindrance board  44 , an upper nozzle  45 , first and third process liquid supply units  83 ,  111 , and a controller  120 . 
     The third process liquid supply unit  111  houses a chemical solution supply source and a flow rate control mechanism which are controlled by the controller  120 . The chemical solution supply source of the apparatus  111  contains an ammonia/hydrogen peroxide solution mixture (APM solution), a hydrochloric acid/hydrogen peroxide solution mixture (HPM solution) or an aqueous hydrofluoric acid solution (DHF solution). Note that pure wafer serving as a protect liquid is contained in a liquid supply source of the first process liquid supply unit  83 . 
     A rotatory hollow shaft  22  passes through the center bottom of the cup  20 . The upper end of the rotatory hollow shaft  22  is connected to the spin chuck  21 . The rotatory hollow shaft  22  is directly rotated by a motor  23 . A plurality of mechanical chucks  24  are arranged so as to stand at the upper peripheral surface of the spin chuck  21 . The wafer W is held by these mechanical chucks  24 . Furthermore, the rotatory hollow shaft  22  is connected to a liftable cylinder mechanism (not shown) to move the spin chuck  21  up and down. 
     In the rotatory hollow shaft  22 , a hollow support shaft  40   c  is inserted. In the hollow support shaft  40   c,  a process liquid supply pipe  43  is further inserted. The supply port  43   a  of the process liquid supply pipe  43  is formed so as to spray the liquid upward. The upper end of the hollow support shaft  40   c  is connected to the bottom of the lower nozzle main body  40   b.  The lower end (not shown) of the hollow support shaft  40   c  is connected to the liftable cylinder mechanism (not shown). 
     As shown in FIG. 11, the upper portion  40   a  of the lower nozzle  30  is flat. The size and shape of the upper portion  40   a  correspond to those of the wafer W. Numerous liquid outlet holes  41 A are formed in the nozzle upper portion  40   a.  The liquid outlet holes  41  are not localized in a specific region of the nozzle upper portion  40   a  but present uniformly over the entire nozzle upper portion  40   a.  By virtue of this, the process liquid can be supplied uniformly to the entire lower surface of the wafer W. The holes  41  are arranged at regular intervals along a longitudinal portion of each tube  70 . The distance L 1  from the lower nozzle  73  to the lower surface of the wafer W desirably falls within the range of 2 to 20 mm. The distance L 2  (height of a lower space  25 ) from the upper surface of the spin chuck  21  to the lower surface of the wafer W desirably falls within the range of 20 to 50 mm. The diameters of the liquid outlet ports  41 A desirably fall within the range of 0.5 to 3.0 mm, and the interval (pitch) between adjacent holes  41  desirably falls within the range of 4 to 30 mm. 
     As shown in FIG. 12, within the nozzle main body  40   b,  the liquid reservoir chamber  42  is formed which communicates with the liquid outlet holes  41 . The liquid reservoir chamber  42  communicates with the hollow portion of the hollow support shaft  40   c  through a communication opening  42   a.  In the liquid reservoir chamber  42 , the hindrance board  44  is placed. The hindrance board  44  is supported by a plurality of support rods  44  and arranged so as to face a liquid outlet hole formation region  41 A. The process liquid is introduced from a supply port  43   a,  passed through the communication opening  42   a,  and hits to the hindrance board  44 . Then, the process liquid is dispersed from the center region of the liquid reservoir chamber  42  toward the peripheral region thereof, reaches around the upper portion of the hindrance board  44 , and output upward trough numerous holes  41 A. By virtue of the presence of the hindrance board  44 , supply pressure of the process liquid is equalized, so that the process liquid is output from the center holes  41  and the peripheral holes  41  at the same flow rate. 
     As shown in FIG. 10, the upper nozzle  45  communicates with the first process liquid supply unit  83  through passages  82 ,  84  and communicated with the third process liquid supply unit  111  through passages  82 ,  85  and  112 . A valve  93  is interposed between the passage  82  and the passage  84 . A bypass passage  85  is equipped with a valve  94 . A passage  112  is equipped with a valve  113 . The open/shut operation of each of the valves  93 ,  94 ,  113  is controlled by the controller  120 . Filters (not shown) are attached to the process liquid supply routes  82 ,  84 ,  85 ,  87 ,  112  to remove impurities and foreign substances from the process liquid. 
     Now, referring to FIGS. 19A and 19B, we will explain how to clean the semiconductor wafer W by using the cleaning apparatus  19 A. 
     The wafer W is loaded into the process unit  9  having a cleaning apparatus  19 A by the transport arm  5   b.  The wafer W is then transferred from the transport arm  5   b  to the spin chuck  21  and held by the mechanical chuck  24 . The spin chuck  21  is rotated by the controller  120  at, for example, 20 rpm. Subsequently, the protect liquid (pure water) is supplied to the upper surface of the wafer W from the upper nozzle  45 . The removal solution (hydrofluoric acid solution) is supplied to the lower surface of the wafer W from the lower nozzle  30 . As a result, the silicon oxide film is removed from the lower surface (rear surface) of the wafer W. 
     Thereafter, a valve  113  is opened. Simultaneously, pure wafer is supplied to the upper nozzle  45  and the lower nozzle  30  from the third process liquid supply unit  111  through the bypass route  85  to rinse both surfaces of the wafer W. 
     After rinse, the rotation speed of the wafer W is increased to shake off the attached liquid from the wafer W to dry up the wafer W. Note that the process liquid for use in washing the lower surface of the wafer W may be either a chemical washing solution (DHF solution) or a rinse solution (pure wafer) in this embodiment. 
     The rotation of the spin chuck  21  is terminated and the shutter is opened. Then, wafer W is unloaded from the processing unit by the transfer arm  5   a.  The substrate transport arm mechanism  5  transports the wafer W to the loader/unloader section  2  to store the wafer W into the cassette C. When the first wafer W 1  to the 25th wafer W 25  successively washed are thus stored in the cassette C, the transfer robot (not shown) unloads the cassette C out of the system  1  through the loader/unloader section  2  and transfer the cassette C to a next processing unit. 
     Referring to FIGS. 13-18, a lower nozzle of another embodiment will be explained. 
     As shown in FIGS. 13 and 14, the upper portion  51  of the lower nozzle  50  may be formed in a convex form so that the center portion of the nozzle is higher than the peripheral portion thereof. The holes  41  may be formed over the entire surface of the nozzle upper portion  51  so as to supply and spray the process liquid uniformly to the entire surface of the lower surface of the wafer W. Due to the convex-form lower nozzle  50 , the process liquid sprayed does not stay the nozzle upper portion  51 , with the result that the nozzle upper portion  51  is maintained clean. 
     As shown in FIG. 15, the lower nozzle may be formed in virtually a cruciform. The upper portion  56  of the nozzle is flat. The holes  41  are formed over the entire surface of the nozzle upper portion  56 . 
     The lower nozzle  60  may have an eight-letter form like a curved tube  62  shown in a plan view of FIG.  16 . As shown in FIG. 17, the lower nozzle  60 , which is fixed on the support table  63 , may have a convex form as viewed from the side. Liquid outlet holes  41  are formed at regular intervals in the nozzle upper portion  61 . The lower nozzle  60  of an 8-letter form is advantageous in that the total opening area of the liquid outlet holes  41  is suppressed as small as possible, and the process liquid can be supplied simultaneously to the peripheral portion and the center portion of the lower surface of the wafer W. Furthermore, liquid is not accumulated in the nozzle upper portion  61 . 
     The lower nozzle  60 A may be formed in an 8-letter form like a curved pipe  62 A in the plan view shown in FIG.  18 . The nozzle upper portion  61 A is flat. One of ends of the supply port  64   a  communicates with a first supply pipe  65   a.  The other end thereof communicates with a second supply pipe  65 B. In the lower nozzle  60 A, since the process liquid is introduced into the tube  62 A through two supply ports  64   a,    64   b,  the process liquid is sprayed more uniformly. 
     Now, referring to FIGS. 19A and 19B, we will explain how to remove the silicon oxide film coated over the rear surface of the wafer W by using the apparatus according to this embodiment. 
     As shown in FIG. 19A, the valves  93 ,  113  are opened to supply the DHF solution to the rear surface (lower surface) of the wafer W from the lower nozzle  30  and to supply pure water to the front surface (upper surface) of the wafer W from the upper nozzle  45 . The surface of the wafer W is thus covered with pure wafer, so that the DHF solution supplied to the rear surface of the wafer is prevented from reaching the upper surface of the wafer W. The silicon oxide film  114  is therefore completely removed from the rear surface of the wafer W. 
     As shown in FIG. 19B, the valve  113  is closed and the open/shut valve  94  is opened to supply pure water to the rear surface of the wafer W from the lower nozzle  30 . After the DHF solution is washed away from the wafer W in this way, the open/shut valves  93 ,  94  are closed and the rotation table  21  is rotated at a high speed to dry up the wafer. As described, the surface of the wafer can be easily protected from the DHF solution only by supplying pure water to the upper surface of the wafer W. Therefore, it is possible to omit a resist coating step and a resist removing step etc., which are performed to prevent the surface of the wafer in the conventional method. Hence, even if the semiconductor device etc., are formed on the surface of the wafer W, it is possible to remove the silicon oxide film  114  coated over the rear surface of the wafer W for a short time. Furthermore, the manufacturing cost can be reduced. 
     The substrate to be used in the present invention is not limited to a semiconductor wafer. Other types of substrates such as an LCD substrate, a glass substrate, a CD substrate, a photomask, a printing substrate and a ceramic substrate may be applicable in the present invention. 
     Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.