Patent Publication Number: US-2012043062-A1

Title: Method for cooling object to be processed, and apparatus for processing object to be processed

Description:
FIELD OF THE INVENTION 
     The present invention relates to a cooling method of a target object and an object processing apparatus capable of performing the cooling method. 
     BACKGROUND OF THE INVENTION 
     In a manufacturing process of, e.g., semiconductor devices, a high temperature process such as film formation and thermal treatment is performed on a semiconductor wafer (hereinafter, referred to as a “wafer”) as a target object. In order to unload the wafer that has been processed at a high temperature from a processing apparatus, it is necessary to cool the wafer to a secure temperature. 
     Conventionally, cooling of the wafer is performed in a load-lock chamber that performs pressure conversion between a depressurized state and an atmospheric pressure state, and the wafer is naturally cooled when the depressurized state is converted into the atmospheric pressure state (see, e.g., Japanese Patent Publication Application No. 2001-319885). 
     However, in a case where the wafer is naturally cooled while the depressurized state is converted into the atmospheric pressure state, a decrease in temperature of the wafer is started from an edge of the wafer. Accordingly, a temperature difference is generated between the edge and the center of the wafer. 
     Recently, the wafer has a larger diameter and a temperature difference between the edge and the center tends to increase. Moreover, with the trend of miniaturization of devices, it is strictly required to prevent deformation of the wafer such as warpage of the wafer caused by the temperature difference between the edge and the center. 
     Accordingly, currently, the pressure conversion from the depressurized state to the atmospheric pressure state is performed slowly to suppress an increase in the temperature difference between the edge and the center of the wafer. 
     By this technique, it is possible to suppress an increase in the temperature difference between the edge and the center and prevent the wafer from being warped or cracked. 
     However, since the pressure conversion from the depressurized state to the atmospheric pressure state is performed slowly, a throughput may be reduced. 
     SUMMARY OF THE INVENTION 
     The present invention provides a cooling method of a target object capable of improving a throughput while preventing the warpage or crack of the wafer from being generated to exceed the allowable range, and an object processing apparatus capable of performing the cooling method. 
     In accordance with a first aspect of the present invention, there is provided a cooling method of a target object including placing the object in a heated state on a stage; and cooling the object placed on the stage by injecting a cooling gas to a near-center region of the object including a center thereof. 
     In accordance with a second aspect of the present invention, there is provided an object processing apparatus including a load-lock module for performing pressure conversion between a depressurized state and an atmospheric pressure state; a stage which is provided in the load-lock module and on which a target object is placed; and a cooling gas injection unit which is provided in the load-lock module to face the stage and injects a cooling gas to the object placed on the stage. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a plan view schematically showing an example of an object processing apparatus capable of performing a cooling method of a target object in accordance with an embodiment of the present invention; 
         FIG. 2  is a cross-sectional view schematically showing a first example of a load-lock module; 
         FIG. 3  illustrates a temperature distribution of a wafer; 
         FIGS. 4A to 4C  illustrate relationships between a position in the wafer and a temperature difference; 
         FIG. 5  illustrates a relationship between a position in the wafer and a temperature difference; 
         FIG. 6  is an enlarged cross-sectional view showing the vicinity of a shower head shown in  FIG. 2 ; 
         FIGS. 7A to 7C  illustrate relationships between an in-surface temperature difference of the wafer and a diameter of a shower head; 
         FIG. 8  is a cross-sectional view schematically showing a second example of the load-lock module; 
         FIG. 9  is a cross-sectional view schematically showing a third example of the load-lock module; 
         FIG. 10  is a plan view schematically showing the shower head shown in  FIG. 6 ; 
         FIG. 11  is a cross-sectional view schematically showing a fourth example of the load-lock module; 
         FIGS. 12A and 12B  are cross-sectional views schematically showing a fifth example of the load-lock module; 
         FIGS. 13A and 13B  are cross-sectional views schematically showing a sixth example of the load-lock module; 
         FIG. 14  is a cross-sectional view schematically showing a seventh example of the load-lock module; and 
         FIG. 15  is a plan view schematically showing a modification example of the object processing apparatus. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings which form a part thereof. Further, the same components are denoted by the same reference numerals throughout the drawings. 
       FIG. 1  is a plan view schematically showing an example of an object processing apparatus capable of performing a cooling method of a target object in accordance with the embodiment of the present invention. As an example of the object processing apparatus of this embodiment, there will be described an object processing apparatus for performing a process on a wafer to manufacture semiconductor devices. However, the present invention may be applied to other apparatuses without being limited to the object processing apparatus for performing a process on a wafer. 
     As illustrated in  FIG. 1 , an object processing apparatus  1  in accordance with the embodiment of the present invention includes a processing unit  2  for performing a process on a wafer W, a loading/unloading unit  3  for loading/unloading the wafer W into/from the processing unit  2 , and a control unit  4  for controlling the apparatus  1 . 
     The object processing apparatus  1  of this embodiment is a cluster tool type (multi chamber type) semiconductor manufacturing apparatus. 
     In this embodiment, the processing unit  2  includes two processing modules (PM) (processing modules  21   a  and  21   b ) for performing a process on the wafer W. Each of the processing modules  21   a  and  21   b  can be depressurized to a predetermined vacuum level. For example, in the processing modules  21   a  and  21   b , a PVD process, e.g., a sputtering process is performed at a high vacuum level (low pressure), and a specific metal or metal compound film is formed on a target substrate such as a semiconductor wafer W. The processing modules  21   a  and  21   b  are connected to one transfer module (TM)  22  via gate valves G 1  and G 2 , respectively. 
     The loading/unloading unit  3  includes a loading/unloading module (LM)  31 . The loading/unloading module  31  is configured such that an inner pressure thereof is adjustable to an atmospheric pressure, or near-atmospheric pressure, e.g., a slightly positive pressure compared to the outside air pressure. In this embodiment, the loading/unloading module  31  has a rectangular shape having long sides and short sides perpendicular to the long sides in its plan view. One of the long sides of the loading/unloading module  31  is adjacent to the processing unit  2 . In this embodiment, it is supposed that the long sides are extended in a Y direction, the short sides are extended in an X direction, and a height direction is a Z direction. 
     The loading/unloading module  31  includes load ports LP on which carriers C for accommodating wafers W therein are attached. In this embodiment, three load ports  32   a ,  32   b  and  32   c  for target substrates are arranged in the Y direction on the long side of the loading/unloading module  31  opposite to the processing unit  2 . Although the number of the load ports is three in this embodiment, the number of the load ports may be varied without being limited thereto. Shutters (not shown) are respectively provided at the load ports  32   a ,  32   b  and  32   c . When the carriers C storing the wafers W or empty carriers C are attached on the load ports  32   a ,  32   b  and  32   c , shutters (not shown) are opened such that the carriers C can communicate with the loading/unloading module  31  while preventing infiltration of outside air. 
     Load-lock modules LLM, e.g., two load-lock modules  51   a  and  51   b  in this embodiment, are provided between the processing unit  2  and the loading/unloading unit  3 . Each of the load-lock modules  51   a  and  51   b  is configured such that an inner pressure thereof is switchable between a specific vacuum level and an atmospheric pressure or near-atmospheric pressure. The load-lock modules  51   a  and  51   b  are connected to one side of the loading/unloading module  31  opposite to the load ports  32   a ,  32   b  and  32   c  via respective gate valves G 3  and G 4 . The load-lock modules  51   a  and  51   b  are also connected to two of the other sides of the transfer module  22  than two sides connected to the processing modules  21   a  and  21   b  via respective gate valves G 5  and G 6 . 
     The load-lock modules  51   a  and  51   b  communicate with the loading/unloading module  31  by opening the respective gate valves G 3  and G 4 , and are separated from the loading/unloading module  31  by closing the respective gate valves G 3  and G 4 . Further, the load-lock modules  51   a  and  51   b  communicate with the transfer module  22  by opening the respective gate valves G 5  and G 6 , and are separated from the transfer module  22  by closing the respective gate valves G 5  and G 6 . 
     A loading/unloading mechanism  35  is provided in the loading/unloading module  31 . The loading/unloading mechanism  35  performs loading/unloading of the wafer W into/from the carriers C for target substrates. Moreover, the loading/unloading mechanism  35  performs loading/unloading of the wafer W into/from the load-lock modules  51   a  and  51   b . The loading/unloading mechanism  35  has, e.g., two multi-joint arms  36   a  and  36   b  and is movable on a rail  37  extending in the Y direction. Hands  38   a  and  38   b  are respectively attached to leading ends of the multi-joint arms  36   a  and  36   b . The wafer W is loaded on the hand  38   a  or  38   b  when the above-described loading/unloading of the wafer W is performed. 
     Provided in the transfer module  22  is a transfer mechanism  24  for performing transfer of the wafer W between the processing modules  21   a  and  21   b  and the load-lock modules  51   a  and  51   b . The transfer mechanism  24  is located at an approximately central portion in the transfer module  22 . The transfer mechanism  24  has, e.g., a plurality of rotatable and extensible/contractible transfer arms. In this embodiment, the transfer mechanism  24  has, e.g., two transfer arms  24   a  and  24   b . Holders  25   a  and  25   b  are respectively attached to leading ends of the transfer arms  24   a  and  24   b . The wafer W is supported by the holder  25   a  or  25   b  when the transfer of the wafer W is performed between the processing modules  21   a  and  21   b  and the load-lock modules  51   a  and  51   b  as described above. 
     The control unit  4  includes a process controller  41 , a user interface  42  and a storage unit  43 . 
     The process controller  41  has a microprocessor (computer). 
     The user interface  42  includes a keyboard through which commands are inputted, a display for displaying an operation status of the object processing apparatus  1  and the like in order to allow an operator to manage the object processing apparatus  1 . 
     The storage unit  43  stores control programs for performing a process in the object processing apparatus  1  under control of the process controller  41 , various types of data, and recipes for performing a process in the object processing apparatus  1  under processing conditions. The recipes are stored in a storage medium of the storage unit  43 . 
     The storage medium may be a computer-readable medium, e.g., a hard disk, or a portable medium such as a CD-ROM, a DVD and a flash memory. Further, the recipes may be appropriately transmitted from another apparatus via, e.g., a dedicated line. Upon receipt of a command from the user interface  42 , the process controller  41  retrieves a desired recipe from the storage unit  43 , and the process controller  41  executes a process corresponding to the retrieved recipe, so that a desired process is performed on the wafer W in object processing apparatus  1  under the control of the process controller  41 . 
       FIG. 2  is a cross-sectional view schematically showing a first example of the load-lock module  51   a  or  51   b.    
     As illustrated in  FIG. 2 , provided in the load-lock module  51   a  or  51   b  is a stage on which the wafer W is mounted, e.g., a cooling stage in this embodiment, e.g., a cooling stage  52  having a water cooling mechanism  52   a.    
     At a ceiling wall  53  of the load-lock module  51   a  or  51   b , there is provided a cooling gas injection unit, e.g., a shower head  54  in this embodiment. The shower head  54  is provided to face the cooling stage  52 . The wafer W is mounted on the cooling stage  52  such that the center of the wafer W is aligned with the center of the shower head  54 . 
     A cooling gas is supplied into the shower head  54  from a cooling gas supply mechanism  60  through a flow control valve  61 . For example, a rare gas or an inert gas such as N 2  gas, He gas and Ar gas may be used as the cooling gas. A plurality of cooling gas injection holes  54   a  are formed on a surface of the shower head  54  facing the cooling stage  52 . 
     Further, in this embodiment, a diameter ΦS of the shower head  54  is set to be smaller than a diameter ΦW of the wafer W. By setting the diameter ΦS to be smaller than the diameter ΦW, the cooling gas  70  can be locally injected to a near-center region of the wafer W including the center thereof instead of being injected uniformly to the entire surface of the wafer W. 
     A gas exhaust port  56  is formed at a bottom wall  55  of the load-lock module  51   a  or  51   b . The gas exhaust port  56  is connected to a gas exhaust unit  62  for evacuating the load-lock module  51   a  or  51   b  to a predetermined vacuum level. 
     Further, a gas inlet port  57  is formed at the bottom wall  55  of the load-lock module  51   a  or  51   b . The gas inlet port  57  is connected to the cooling gas supply mechanism  60  through a flow control valve  63  in this embodiment. The inner pressure of the load-lock module  51   a  or  51   b  may be increased to a pressure approximately equal to the inner pressure of the loading/unloading module  31 , e.g., an atmospheric pressure or a pressure slightly lower than the inner pressure of the loading/unloading module  31  by introducing the cooling gas from the gas inlet port  57  and the shower head  54 .  FIG. 3  illustrates an in-surface temperature distribution of the wafer W. 
     As illustrated in  FIG. 3 , when the wafer W is naturally cooled, the temperature of the edge of the wafer W decreases at the fastest rate, whereas the temperature of the center of the wafer W decreases at the slowest rate. Accordingly, while the temperature of the wafer W decreases, there occurs an in-surface temperature difference in such a way that the temperature is high at the center and low at the edge (see the curve I of  FIG. 3 ). If there is a large difference in the in-surface temperature, the wafer W may be warped or cracked during the cooling. An allowable warpage range of the wafer W is, e.g., equal to or smaller than 0.6 mm in the wafer having a diameter ΦW of 300 mm. 
     The in-surface temperature difference generated in the wafer W will be described in detail with reference to  FIGS. 4A to 4C . 
       FIG. 4A  illustrates an in-surface temperature difference when the ambient pressure of the wafer W is 1 Pa and the wafer W is heated to a temperature of about 500° C. The diameter ΦW of the wafer W is 300 mm, and the temperature is measured at the center (0 mm), the middle (±75 mm from the center) and the near-edge (±140 mm from the center). 
     In  FIG. 4A , the temperature of the near-edge is about 500° C. From the measurement results, it is seen that the temperature of the middle is about 20° C. higher than the temperature of the near-edge (i.e., about 520° C.) and the temperature of the center is about 25° C. higher than the temperature of the near-edge (i.e., about 525° C.). 
     The wafer W is exposed to the air at a time, so that the state of the wafer W is changed from the depressurized state of  FIG. 4A  to a state in which the ambient pressure of the wafer W is an atmospheric pressure (about 100000 Pa) and the temperature of the wafer W is decreased to about 70° C.  FIG. 4C  illustrates a state in which the wafer W is cooled to a temperature of about 70° C. 
     As illustrated in  FIG. 4C , when the wafer W is cooled to a temperature of about 70° C., the in-surface temperature difference in the center, the middle and the near-edge is equal to or smaller than about 6° C. (the temperature of the center is about 70° C. and the temperature of the near-edge is about 64° C.). That is, the in-surface temperature difference is reduced compared to a maximum difference of about 25° C. before the start of cooling. 
     However, since the decrease in the temperature of the wafer W is started from the edge during the cooling, the temperature of the center decreases at the slowest rate. In particular, this tendency appears remarkably in the cooling after the wafer W is exposed to the air at a time, i.e., the wafer W is subjected to the natural cooling. Accordingly, as shown in  FIG. 4B , the in-surface temperature difference increases during the cooling. The increase in the in-surface temperature difference may cause a warpage or crack of the wafer W, which exceeds, e.g., 0.6 mm. 
     In order to prevent the warpage or crack from being generated, pressure conversion is slowly performed from the depressurized state to the atmospheric pressure state, and rapid decrease in the temperature of the edge is suppressed during the cooling to reduce the in-surface temperature difference (see the curve II of  FIG. 3 , and  FIG. 5 ). However, since the pressure conversion from the depressurized state to the atmospheric pressure state is performed slowly, the throughput may be reduced. 
     Accordingly, in this embodiment, the cooling gas  70  is locally injected to the near-center region of the wafer W including the center thereof by using the shower head  54 . By this configuration, it is possible to control the temperature decrease in the near-center region of the wafer W to be equivalent to the temperature decrease in the near-edge region of the wafer W. 
     The spray of the cooling gas  70 , i.e., the cooling of the wafer W is performed when the pressure conversion is performed from the depressurized state to the atmospheric pressure state in the load-lock module  51   a  or  51   b . In this case, the cooling gas may be also supplied from the gas inlet port  57  into the load-lock module  51   a  or  51   b  to perform the pressure conversion from the depressurized state to the atmospheric pressure state. 
     Further, since the cooling stage  52  has the cooling mechanism  52   a  for cooling the wafer W in this embodiment, the cooling of the wafer W is performed by using the cooling gas  70  and the cooling mechanism  52   a.    
     As described above, in this embodiment, the cooling gas  70  is locally sprayed to the near-center region of the wafer W including the center thereof to accelerate the decrease in the temperature of the near-center region of the wafer W. Accordingly, it is possible to cool the wafer W at the faster rate compared to a case where the pressure conversion is slowly performed from the depressurized state to the atmospheric pressure state while the rapid decrease in the temperature of the edge of the wafer W is suppressed during the cooling. 
     Further, the temperature decrease in the near-center region of the wafer W is controlled to be equivalent to the temperature decrease in the near-edge region of the wafer W. Accordingly, it is possible to prevent the wafer W from being warped or cracked to exceed the allowable range. 
     FIRST EXAMPLE 
       FIG. 6  is an enlarged cross-sectional view showing the vicinity of the shower head  54  shown in  FIG. 2 . 
     As shown in  FIG. 6 , the cooling gas  70  injected from the shower head  54  has a flow velocity distribution in which the flow velocity is high in the center and becomes lower as it approaches the edge of the wafer W (see the curve III of  FIG. 6 ). This flow velocity distribution is formed by setting the diameter ΦS of the shower head  54  to be smaller than the diameter ΦW of the wafer W, for example. 
     Further, when the wafer W is mounted on the stage  52  such that the center of the wafer W is aligned with the center of the shower head  54 , the flow velocity of the cooling gas  70  can be maximized at the center of the wafer W. Further, the flow velocity distribution of the cooling gas  70  may be formed in such a way that the flow velocity is high in the near-center region of the wafer W including the center thereof and becomes lower as it goes from the near-center region toward the edge of the wafer W. 
     By such flow velocity distribution, it is possible to efficiently cool the center of the wafer W in which the temperature decreases at the slowest rate, and reduce a cooling effect as it goes toward the edge of the wafer W in which the temperature decreases at the faster rate. Accordingly, it is possible to easily allow the temperature of the center of the wafer W to approximate the temperature of the edge of the wafer W. 
     Next, an example of setting the diameter ΦS of the shower head  54  will be described. 
     For example, the diameter ΦS of the shower head  54  may be set according to the in-surface temperature difference of the wafer W before the start of cooling. 
     For example, in case of reducing the temperature of a region of the wafer W having an in-surface temperature difference of 20° C. or more, the diameter ΦS of the shower head  54  may have a size corresponding to the region having an in-surface temperature difference of 20° C. or more. 
       FIG. 7A  illustrates an in-surface temperature distribution when the wafer W having a diameter ΦW of 300 mm was heated to about 500° C. The in-surface temperature distribution of  FIG. 7A  is equivalent to the in-surface temperature distribution of  FIG. 4A . As shown in  FIG. 7A , the region having an in-surface temperature difference of 20° C. or more corresponds to a region in which a distance from the center falls within a range from −75 mm to +75 mm. In this case, the diameter ΦS of the shower head  54  is set to be 150 mm. Further, the wafer W may be mounted on the stage  52  such that the center of the wafer W is aligned with the center of the shower head  54 . In this case, the near-center region of the wafer W including the center thereof corresponds to a region within an area having a radius of 75 mm from the center of the wafer W. 
     It goes without saying that the region of the wafer W, the temperature of which is intended to be reduced, may be varied without being limited to the region having an in-surface temperature difference of 20° C. or more. As for the wafer W that has the diameter ΦW of 300 mm and is heated to a temperature of about 500° C., for example, in a case where the region of the wafer W, the temperature of which is intended to be reduced, is a region having an in-surface temperature difference of 15° C. or more, it is preferable that the diameter ΦS of the shower head  54  is set to be 200 mm as shown in  FIG. 7B . 
     In the same way, the wafer W may be mounted on the stage  52  such that the center of the wafer W is aligned with the center of the shower head  54 . In this case, the near-center region of the wafer W including the center thereof corresponds to a region within an area having a radius of 100 mm from the center of the wafer W. 
     Further, in the wafer W that has the diameter ΦW of 300 mm and is heated to a temperature of about 500° C., for example, in a case where the region of the wafer W, the temperature of which is intended to be reduced, is a region having an in-surface temperature difference of 22° C. or more, it is preferable that the diameter ΦS of the shower head  54  is set to be 100 mm as shown in  FIG. 7C . In this case, the near-center region of the wafer W including the center thereof corresponds to a region within an area having a radius of 50 mm from the center of the wafer W. 
     That is, the diameter ΦS of the shower head  54  may be set based on the diameter ΦW of the wafer W and the size of the region, the temperature of which is intended to be reduced. Further, the size of the region, the temperature of which is intended to be reduced, may be determined based on the in-surface temperature difference generated in the wafer W while the wafer W is heated. 
     It is not limited to the wafer W having the diameter ΦW of 300 mm, and the wafer W may have the diameter ΦW of 450 mm. 
     SECOND EXAMPLE 
     Further, the flow velocity distribution represented by the curve III of  FIG. 6  may be obtained by providing a nozzle  54   b  as shown in  FIG. 8  instead of the shower head  54 . 
     THIRD EXAMPLE 
     Further, in case of using the shower head  54 , the inside of the shower head  54  may be divided into a plurality of spaces, e.g., two or more concentric spaces such as spaces  54   c  and  54   d  as shown in  FIG. 9 .  FIG. 10  is a plan view of the spaces  54   c  and  54   d  shown in  FIG. 9 . 
     In case of providing the concentric spaces  54   c  and  54   d , the flow velocity of the cooling gas  70  injected from the space  54   c  including the center of the shower head  54  may be set to be higher than the flow velocity of the cooling gas  70  injected from the space  54   d  provided outside the space  54   c  by varying a flow rate of the cooling gas supplied to the space  54   c , for example. That is, the cooling gas  70  is sprayed at the higher flow velocity to a portion particularly close to the center in the near-center region including the center of the wafer W, thereby further improving cooling efficiency of the near-center region of the wafer W including the center thereof. 
     In order to control the flow velocity of the cooling gas  70 , a flow velocity controller, e.g., a speed controller, may be provided in a supply path of the cooling gas, so that the flow velocity of the injected cooling gas  70  can be controlled by using the speed controller. 
     Further, if the flow velocity of the injected cooling gas  70  is defined as follows: 
     Flow velocity of cooling gas=Flow rate of cooling gas/total area of cooling gas injection holes  54   a , the flow velocity of the injected cooling gas  70  can be controlled by adjusting the flow rate of the cooling gas  70 . In this case, a flow rate controller, e.g., a mass flow controller, may be provided in the supply path of the cooling gas, so that the flow rate of the cooling gas can be adjusted by using the mass flow controller. 
     Further, in a case where the inside of the shower head  54  is divided into a plurality of spaces, e.g., the spaces  54   c  and  54   d , a first cooling gas having a high cooling effect may be introduced into the space  54   c  including the center of the shower head  54 , and a second cooling gas having a cooling effect lower than that of the first cooling gas may be introduced into the space  54   d  provided outside the space  54   c . For example, He gas and N 2  gas may be used as the first gas and the second gas, respectively. 
     Further, when the first gas is He gas and the second gas is N 2  gas, the flow velocity of the He gas may be set to be higher than the flow velocity of the N 2  gas, thereby further improving cooling efficiency of the near-center region of the wafer W including the center thereof. 
     In accordance with the shower head  54  shown in  FIGS. 9 and 10 , it is possible to further enhance cooling efficiency in the center of the wafer W, and also reduce a cooling effect as it goes toward the edge of the wafer W. 
     FOURTH EXAMPLE 
     Further, in accordance with the shower head  54  shown in  FIGS. 9 and 10 , the diameter of the shower head  54  may be increased to be equal to the diameter of the wafer W as shown in  FIG. 11 . 
     In a case where the diameter of the shower head  54  is increased to be equal to the diameter of the wafer W, three or more spaces such as concentric spaces  54   d ,  54   e ,  54   f  and  54   g  may be formed outside the space  54   c  including the center of the shower head  54 . The flow velocities of the cooling gases injected from the spaces  54   d ,  54   e ,  54   f  and  54   g  may be sequentially reduced in an outward direction to obtain the flow velocity distribution represented by the curve III of  FIG. 11 . 
     In order to control the flow velocity of the injected cooling gas  70 , as described in the third example, a flow velocity controller such as a speed controller, or a flow rate controller, e.g., a mass flow controller, may be provided in the supply path of the cooling gas, so that the flow velocity or the flow rate of the injected cooling gas  70  can be controlled by using the flow velocity controller or the flow rate controller. 
     Further, a first cooling gas (e.g., He gas) having a high cooling effect may be introduced into the space  54   c  including the center of the shower head  54  or the space  54   c  including the center and the space  54   d  adjacent to the space  54   c , and a second cooling gas (e.g., N 2  gas) having a cooling effect lower than that of the first cooling gas may be introduced into the spaces  54   d  to  54   g  provided outside the space  54   c , or the spaces  54   e  to  54   g  provided outside the space  54   d.    
     FIFTH EXAMPLE 
     Further, the temperature decrease of the wafer W is closely dependent on a distance D between the shower head  54  and the wafer W. For example, if the distance D between the shower head  54  and the wafer W is short, the cooling effect is high, and if the distance D is long, the cooling effect is low. The temperature decrease of the wafer W may be controlled by using this tendency. 
     Accordingly, as shown in  FIGS. 12A and 12B , the distance D between the shower head  54  and the wafer W may be varied by using a structure capable of adjusting a vertical level of the stage  52 . 
     SIXTH EXAMPLE 
     In case of varying the distance between the shower head  54  and the wafer W, the structure capable of adjusting the vertical level of the stage  52  is used in the fifth example. However, as shown in  FIGS. 13A and 13B , it is possible to employ a structure capable of adjusting a vertical level of the shower head  54 . 
     Also in the sixth example, it is possible to obtain an advantage of the fifth example by varying the distance D between the wafer W and the shower head  54 . 
     SEVENTH EXAMPLE 
     In the first to sixth examples, one shower head  54  or one nozzle  54   b  is installed in the load-lock module  51   a  or  51   b.    
     However, as shown in  FIG. 14 , a plurality of shower heads  54  or nozzles  54   b  may be installed in the load-lock module  51   a  or  51   b  to simultaneously cool a plurality of wafers W.  FIG. 14  illustrates an example in which two shower heads  54  of the first example shown in  FIG. 6  are attached to the ceiling wall  53 . 
     The modification of the seventh example may be applied to any one of the second to sixth examples without being limited to the first example. 
     Modification Example of Object Processing Apparatus 
     In the first to seventh examples, the wafer W is cooled in the load-lock module  51   a  or  51   b  of the object processing apparatus  1 . 
     However, as shown in  FIG. 15 , a cooling module (CM)  81  for cooling the wafer W may be provided in the processing unit  2  such that the wafer W can be cooled in the cooling module  81  instead of the load-lock module  51   a  or  51   b  during or after a process. In this case, the cooling module  81  employs the structure of the first to seventh examples. Accordingly, also in the cooling module  81  provided in the processing unit  2 , it is possible to obtain the same advantage as those of the first to seventh examples. 
     Heating Temperature of Target Object Preferably Used in the Embodiment 
     The target object may have a deformation point as a temperature at which rapid deformation occurs. For example, in a case where the target object is the wafer W and is made of silicon, a temperature of about 450° C. is the deformation point. The silicon wafer undergoes rapid deformation when it is heated to exceed the temperature of 450° C. from the temperature of 450° C. or less. On the other hand, the silicon wafer undergoes rapid deformation when it is cooled below the temperature of 450° C. from the temperature of 450° C. or more. 
     Accordingly, the above-described embodiment may be preferably applied to a cooling process performed after a silicon wafer serving as a target object is heated to a temperature of 450° C. or more. 
     Further, a physical upper limit of the heating temperature is a melting point of silicon that ranges from about 1410 to 1420° C. or less. Furthermore, a practical upper limit of the heating temperature in an actual process may be 900° C. 
     As described above, in accordance with the embodiment of the present invention, it is possible to provide a cooling method of a target object capable of improving a throughput while preventing the wafer from being warped or cracked to exceed the allowable range, and an object processing apparatus using the cooling method. 
     Although the present invention has been described using the embodiment, the present invention is not limited thereto, and modifications may be appropriately made without departing from the spirit of the present invention. Further, the above-described embodiment of the present invention is not the only embodiment. 
     For example, although the cooling stage  52  having the cooling mechanism  52   a  for cooling the wafer W is used in the above-described embodiment, the stage may not necessarily include the cooling mechanism  52   a.    
     Further, in the aforementioned embodiment, the gas inlet port  57  is provided in the load-lock module  51   a  or  51   b  and, in the pressure conversion from the depressurized state to the atmospheric pressure state, the cooling gas is also introduced from the gas inlet port  57  to create an atmospheric pressure state. 
     However, the gas inlet port  57  may not be provided, and the introduction of the cooling gas from the gas inlet port  57  may not be performed in the pressure conversion from the depressurized state to the atmospheric pressure state. In this case, the pressure conversion from the depressurized state to the atmospheric pressure state is performed only by the introduction of the cooling gas from the cooling gas injection unit, i.e., the shower head  54  or the nozzle  54   b  in this embodiment. 
     Further, the target object, e.g., the wafer W, after being heated is placed in a high depressurized state having a pressure of 1 Pa and then cooled until the depressurized state is converted into the atmospheric pressure state in the above-described embodiment. However, the cooling process may be performed even when the ambient pressure of the wafer W is not 1 Pa, for example, when the pressure state ranging from 1 to 70000 Pa is converted into the atmospheric pressure state (about 100000 Pa). 
     In the same way, the cooling process may be performed even when it is not converted into the atmospheric pressure state, for example, when it is converted into a pressure ranging from, e.g., 20000 Pa to an atmospheric pressure. 
     Further, the semiconductor wafer is used as an example of the target object and the silicon wafer is used as an example of the semiconductor wafer in the above-described embodiment. However, the present invention may be also applied to other semiconductor wafers such as SiC, GaAs, InP wafers without being limited to the silicon wafer. 
     Further, the target object may be a glass substrate used for the manufacture of a flat panel display (FPD) or solar cell without being limited to the semiconductor wafer. The present invention may be applied to any object capable of being heated. 
     In accordance with the embodiment of the present invention, it is possible to provide a cooling method of a target object capable of improving a throughput while preventing the wafer from being warped or cracked to exceed the allowable range, and an object processing apparatus using the cooling method.