Abstract:
A method for removing water molecules from a vacuum chamber for carrying out a process on a target object in vacuum includes the steps of introducing into the vacuum chamber a water molecule removal gas including at least a reduction gas which reduces the water molecules to produce hydrogen molecules and a halogen-based gas which reacts with the produced hydrogen molecules to produce acid, exhausting gases in the vacuum chamber measuring an amount of water molecules present inside the vacuum chamber, and determining whether or not the measured amount of water molecules is greater than or equal to a threshold value, wherein if the measured amount of water molecules is greater than or equal to the threshold value, the water molecule removal gas is introduced into the vacuum chamber in the introducing step.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This document claims priority to Japanese Patent Application Number 2005-79165, filed Mar. 18, 2005 and U.S. Provisional Application No. 60/666,717, filed Mar. 31, 2005, the entire content of which are hereby incorporated by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates to a method for removing water molecules from a vacuum chamber, a program for executing the method, and a storage medium storing the program.  
       BACKGROUND OF THE INVENTION  
       [0003]     Conventionally, a plasma processing is carried out on a wafer serving as a substrate in a vacuum chamber, an inner wall thereof being coated with sprayed ceramic such as yttrium oxide (Y 2 O 3 ) (yttria) and aluminum oxide (Al 2 O 3 ). In General, since ceramic has a high reactivity with water molecules or moisture in the air, when the chamber is opened to the atmosphere by opening its lid during a regular examination or wet cleaning thereof, the water molecules may get attached to, for example, the inner wall of the chamber or an upper electrode therein.  
         [0004]      FIG. 5  is a graph showing measurement results of an atmosphere in a plasma etching chamber (etcher) for performing a plasma etching process on the wafer, obtained by a quadropole mass spectrometer (QMS), wherein a vertical axis represents the QMS count and a horizontal axis represents the mass number.  
         [0005]     The measurement is made right after closing the lid of the plasma etching chamber which has been opened to the atmosphere. Further, the plasma etching chamber is made of aluminum, and its inner wall is coated with alumite.  
         [0006]      FIG. 5  shows that a peak due to molecules having a mass number of 18, which is the mass number of water molecules, is the highest, and it can be deduced therefrom that there are a large amount of water molecules present in the plasma etching chamber right after the lid has been closed. The large amount of water molecules may cause the following problems:  
         [0007]     1) To create a vacuum inside the chamber, the inside thereof must be exhausted, and the presence of the water molecules therein increases the time required to reach the required vacuum and reduces an efficiency of a processing apparatus;  
         [0008]     2) During a metal film forming on a wafer in a chamber of a CVD apparatus, the presence of water molecules inside the chamber may cause a number of abnormalities such as forming of an oxide film, peeling of film layers from the wafer surface and increasing of wafer surface resistance;  
         [0009]     3) In etching of the oxide film, an etching rate of a wafer lot right after the chamber&#39;s lid is closed is different from that of the wafer lot in the chamber whose inside has become stable after a specified time period;  
         [0010]     4) When the wafer is etched by using plasma generated by a plasma generation gas containing fluorine, water molecules in the chamber react with the plasma generation gas to form fluoric acid, the fluoric acid, in turn, corroding the inner wall surface, generating peeled particles.  
         [0011]     5) An abnormal discharge occurring due to the presence of water molecules inside the chamber may damage the wafer and facilitate a generation of the peeled particles.  
         [0012]     To solve the above-mentioned problems, there is known a technology wherein HCl, BCl 3 , DCP (dichloropropane) and DMP (dimethylpropane) are introduced into the chamber (etcher) whose inner wall is coated with alumite to accelerate the removal of water molecules in the chamber (see, e.g., Journal of Vacuum Science and Technology, A14, 1266 (1996)).  
         [0013]     In the technology, however, HCl, BCl 3 , DCP and DMP do not readily react with water molecules. Thus, all of the water molecules emitted in form of an out gas from pores in the alumite cannot be processed, and as a result, although HCl, BCl 3 , DCP and DMP are introduced in the chamber, it is difficult to accelerate the removal of water molecules in the chamber (etcher).  
       SUMMARY OF THE INVENTION  
       [0014]     It is, therefore, an object of the present invention to provide a method for removing water molecules from a vacuum chamber, a program for executing the method, and a storage medium storing the program capable of accelerating the removal of water molecules in the chamber.  
         [0015]     To achieve the object, in accordance with a first aspect of the present invention, there is provided a method for removing water molecules from a vacuum chamber for carrying out a process on a target object in vacuum, the method including the steps of introducing into the vacuum chamber a water molecule removal gas including at least a reduction gas which reduces the water molecules to produce hydrogen molecules and a halogen-based gas which reacts with the produced hydrogen molecules to produce acid; and exhausting gases in the vacuum chamber.  
         [0016]     Further, in accordance with a second aspect of the present invention, there is provided a program executable on a computer for performing a method for removing water molecules from a vacuum chamber for carrying out a process on a target object in vacuum, including an introduction module for introducing into the vacuum chamber a water molecule removal gas including at least a reduction gas which reduces the water molecules to produce hydrogen molecules and a halogen-based gas which reacts with the produced hydrogen molecules to produce acid; and an exhaust module for exhausting gases in the vacuum chamber.  
         [0017]     Further, in accordance with a third aspect of the present invention, there is provided a computer readable storage medium for storing therein a program executable on a computer for performing a method for removing water molecules from a vacuum chamber for carrying out a specified process on a target object in vacuum, wherein the program includes an introduction module for introducing into the vacuum chamber a water molecule removal gas including at least a reduction gas which reduces the water molecules to produce hydrogen molecules and a halogen-based gas which reacts with the produced hydrogen molecules to produce acid; and an exhaust module for exhausting gases in the vacuum chamber.  
         [0018]     Accordingly, The reduction of water molecules is accelerated in the vacuum chamber and, further, the reduced water molecules can be exhausted as acid, accelerating the removal of water molecules in the vacuum chamber.  
         [0019]     In the method for removing the water molecules from the vacuum chamber, the reduction gas may be carbon monoxide and the halogen-based gas may be carbon fluoride. Accordingly, the reduction of water molecules is further accelerated in the vacuum chamber, thereby allowing an efficient removal of water molecules from the vacuum chamber. Therefore, the removal of water molecules in the chamber can be accelerated.  
         [0020]     In the method for removing the water molecules from the vacuum chamber, the reduction gas may be carbon monoxide and the halogen-based gas may be chlorine. Accordingly, the reduction of water molecules is further accelerated in the vacuum chamber, thereby efficiently removing water molecules from the vacuum chamber. Therefore, the removal of water molecules in the chamber can be accelerated.  
         [0021]     The method for removing the water molecules from the vacuum chamber further includes the steps of measuring an amount of water molecules present inside the vacuum chamber; and determining whether or not the measured amount of water molecules is greater than or equal to a threshold value, wherein if the measured amount of water molecules is greater than or equal to the threshold value, the water molecule removal gas is introduced into the vacuum chamber in the introducing step. Accordingly, the water molecule removal processing in the vacuum chamber can be automatized. Thus, it is possible to reduce a downtime of an object processing apparatus including the vacuum chamber.  
         [0022]     In the method for removing the water molecules from the vacuum chamber, the process may be an etching process carried out on the target object. Accordingly, it is possible to resolve an etching rate difference between object lots.  
         [0023]     In the method for removing the water molecules from the vacuum chamber, the process may be a transfer process for transferring the target object. Accordingly, it is possible to prevent water molecules from being attached to the target object when it is transferred. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0024]     The above and other objects and features of the present invention will become apparent from the following description of preferred embodiments, given in conjunction with the accompanying drawings, in which:  
         [0025]      FIG. 1  is a cross sectional view showing a schematic configuration of a substrate processing apparatus including a plasma processing apparatus formed of a vacuum chamber in accordance with a preferred embodiment of the present invention;  
         [0026]      FIG. 2  is a vertical sectional view showing a schematic configuration of the plasma processing apparatus shown in  FIG. 1 ;  
         [0027]      FIG. 3  is a graph showing measurement results of an atmosphere in the chamber shown in  FIG. 2 , which changes as a function of elapsed time and obtained by a quadropole mass spectrometer (QMS);  
         [0028]      FIG. 4  is a flowchart showing a sequence of water molecule removal processing performed by a system controller in the substrate processing apparatus shown in  FIG. 1 ; and  
         [0029]      FIG. 5  is a graph showing measurement results of an atmosphere in an etcher for performing a plasma etching process on a wafer, obtained by the quadropole mass spectrometer. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0030]     A preferred embodiment of the present invention will now be described with reference to the accompanying drawings.  
         [0031]      FIG. 1  is a cross sectional view showing a schematic configuration of a substrate processing apparatus including a plasma processing apparatus formed of a vacuum chamber in accordance with the preferred embodiment of the present invention.  
         [0032]     The substrate processing apparatus  1  shown in  FIG. 1  includes two process ships  11  for carrying out a reactive ion etching (RIE) process on a wafer for semiconductor devices (hereinafter, simply referred to as a “wafer”) W; and a loader module  13  that is a rectangular in shape and functions as a common transfer chamber to which the two process ships  11  are connected.  
         [0033]     In addition to the process ships  11 , connected to the loader module  13  are three FOUP mounting tables  15 , each one mounting thereon a FOUP (Front Opening Unified Pod)  14  serving as a container for accommodating twenty-five wafers W; and an orienter  16  for performing a pre-alignment of the wafer W unloaded from the FOUP  14 .  
         [0034]     The two process ships  11  are connected to one of long sidewalls of the loader module  13 . The three mounting tables  15  are connected to one of the other long sidewalls of the loader module  13  to face the process ships  11 . The orienter  16  is coupled to one short sidewall of the loader module  13 .  
         [0035]     The loader module  13  includes a transfer arm unit  19  for transferring the wafer W disposed therein; and three wafer loading ports  20  formed at portions of the sidewall corresponding to the FOUP mounting tables  15 . The wafer W is unloaded by the transfer arm unit  19  from the FOUP  14  mounted on the FOUP mounting table  15  through the loading port  20  to be loaded into the process ship  11  or the orienter  16 .  
         [0036]     The process ship  11  includes a plasma processing apparatus  100  formed of a vacuum chamber for performing an RIE process on the wafer W; and a load-lock module  27  having a transfer arm  26  for transferring the wafer W to the plasma processing apparatus  100 .  
         [0037]     The loader module  13  is maintained at an atmospheric pressure therein, whereas the plasma processing apparatus  100  of the process ship  11  is kept at a vacuum level therein. Accordingly, the load-lock module  27  is configured as a vacuum preliminary transfer chamber whose inner pressure can be controlled by a vacuum gate valve  29  and an atmospheric gate valve  30  disposed to communicate with the plasma processing apparatus  100  and the loader module  13 , respectively.  
         [0038]     A transfer arm  26  is installed in an approximately central portion of the load-lock module  27 . A first buffer  31  is installed between the transfer arm  26  and the plasma processing apparatus  100  and a second buffer  32  is installed between the transfer arm  26  and the loader module  13 . The first and the second buffers  31  and  32  are installed on a moving path of a wafer supporting portion  33  disposed at a leading end of the transfer arm  26 . The RIE processed wafer W is temporarily moved upward from the path of the supporting portion  33  to thereby facilitate a smooth exchange of a processed wafer W with an unprocessed wafer W and vice versa in the plasma processing apparatus  100 .  
         [0039]     Further, for controlling the operations of the process ships  11 , the loader module  13  and the orienter  16  (hereinafter, referred to as “each component”), the substrate processing apparatus  1  includes a system controller (not shown); and an operation controller  88  disposed at one end portion of the loader module  13 .  
         [0040]     The system controller controls an operation of each component based on a recipe, i.e., a program, corresponding to an RIE process or a wafer transfer process. The operation controller  88  includes a display unit formed of, e.g., LCD (Liquid Crystal Display), wherein the display unit presents an operation status of each component.  
         [0041]      FIG. 2  is a vertical sectional view showing a schematic configuration of the plasma processing apparatus shown in  FIG. 1 .  
         [0042]     Referring to  FIG. 2 , a plasma processing apparatus  100  includes a cylindrical chamber  111  made of aluminum, having therein a cylindrical susceptor  112  employed as a mounting table for mounting thereon the wafer W of, e.g., 300 mm in diameter.  
         [0043]     In the plasma processing apparatus  100 , a gas exhaust passageway  113  serving as a flow path for discharging gas molecules from a space above the susceptor  112  to the outside is formed by an inner wall of the chamber  111  and a side surface of the susceptor  112 . An annular baffle plate  114  for preventing plasma leakage is disposed in the middle of the gas exhaust passageway  113 . Further, a space at the downstream side of the gas exhaust passageway  113  below the baffle plate  114  is crooked in such a way as to pass below the susceptor  112  to communicate with an automatic pressure control valve (APC)  115  that is a variable butterfly valve. The APC  115  is coupled to a turbo molecular pump (TMP)  116  employed as a gas exhaust pump for vacuum exhaust, and, further, coupled to a dry pump (DP)  117  employed as a gas exhaust pump through the TMP  116 . Hereinafter, a gas exhaust channel formed of APC  115 , TMP  116  and DP  117  is referred to as a “main exhaust line”, which performs a pressure control in the chamber  111  by using the APC  115 , and depressurizes the inside of the chamber  111  to a near-vacuum state by using the TMP  116  and the DP  117 .  
         [0044]     Further, the aforementioned space at the downstream side of the gas exhaust passageway  113  below the baffle plate  114  is also coupled to an additional gas exhaust channel (hereinafter, referred to as a “rough exhaust line”), separated from the main exhaust line. The rough exhaust line includes a gas exhaust line  118  having a diameter of, e.g., 25 mm, which communicates with the aforementioned space and the DP  117 ; and a valve  119  disposed in the middle of the gas exhaust line  118 . By using the valve  119 , the aforementioned space can be isolated from the DP  117 . The rough exhaust line discharges gases from the chamber  111  by the DP  117 .  
         [0045]     A lower electrode high frequency power supply  120  is connected to the susceptor  112  through a power feed rod  121  and a matching unit  122  and supplies a predetermined high frequency power to the susceptor  112 . Accordingly, the susceptor  112  serves as a lower electrode. Further, the matching unit  122  functions to maximize a supply efficiency of a high frequency power supplied to the susceptor  112  by reducing the high frequency power reflected from the susceptor  112 .  
         [0046]     At an inner upper portion of the susceptor  112 , there is disposed a circular electrode plate  123  made of a conductive film. A DC power supply  124  is electrically connected to the electrode plate  123 . The wafer W is adsorbed and supported on a top surface of the susceptor  112  by Columbic force or Johnsen-Rahbek force generated by a DC voltage applied from the DC power supply  124  to the electrode plate  123 . Further, a circular focus ring  125  is disposed on top of the susceptor  112  to surround a periphery of the wafer W, which is adsorbed and supported on the top surface of the susceptor  112 . The focus ring  125  is exposed to a space S, which will be explained later, and functions to focus ions or radicals produced in the space S onto the surface of the wafer W, thereby improving an RIE processing efficiency.  
         [0047]     Further, an annular coolant chamber  126  extending, e.g., in the circumferential direction, is provided in the susceptor  112 . A coolant, e.g., cooling water, maintained at a specified temperature is supplied to be circulated in the coolant chamber  126  from a chiller unit (not shown) through a coolant piping  127 . Therefore, a processing temperature of the wafer W, which is adsorbed and supported on the top surface of the susceptor  112 , is controlled by the temperature of the coolant.  
         [0048]     At a part on the top surface of the susceptor  112  where the wafer W is adsorbed and supported (hereinafter, referred to as an “adsorption surface”), there are formed a plurality of heat transfer gas supply holes  128  and heat transfer gas supply grooves (not shown). The heat transfer gas supply holes  128  and the heat transfer gas supply grooves are coupled to a heat transfer gas supply unit  130  through a heat transfer gas supply line  129  disposed in the susceptor  112 . The heat transfer gas supply unit  130  supplies a heat transfer gas, e.g., He gas, to a gap between the adsorption surface and a backside surface of the wafer W. Further, the heat transfer gas supply line  129  is connected to the gas exhaust line  118  and configured to vacuum-exhaust the gap between the adsorption surface and the backside surface of the wafer W by using the DP  117 .  
         [0049]     At the adsorption surface of the susceptor  112 , there is disposed a plurality of pusher pins  131  serving as lift pins, which can be deliberately made to protrude above the top surface of the susceptor  112 . These pusher pins  131 , coupled to a motor (not shown) through a ball screw (not shown), move in up and down directions of  FIG. 2  by a rotational movement of the motor, which is converted into a rectilinear movement by the ball screw. While the wafer W is adsorbed on the adsorption surface and the RIE process is carried out on the wafer W, the pusher pins  131  are lowered down into the susceptor  112 . On the other hand, when the RIE processed wafer W is unloaded from the chamber  11 , the pusher pins  131  are protrude from the top surface of the susceptor  112  to separate the wafer W from the susceptor  112  and lift it upward.  
         [0050]     At a ceiling portion of the chamber  111 , there is disposed a gas introduction shower head  132  to face the susceptor  112 . The gas introduction shower head  132  is connected to an upper electrode high frequency power supply  134  through a matching unit  133 . The upper electrode high frequency power supply  134  supplies a predetermined high frequency power to the gas introduction shower head  132 , allowing the gas introduction shower head  132  to serve as an upper electrode. Further, the matching unit  133  serves similar functions as the aforementioned matching unit  122 .  
         [0051]     The gas introduction shower head  132  includes a bottom electrode plate  136  having a plurality of gas holes  135 ; and an electrode supporting member  137  for detachably supporting the electrode plate  136 . Further, in the electrode supporting member  137 , there is provided a buffer chamber  138  to which a processing gas supply unit (not shown) is connected via a processing gas inlet pipe  139 . A pipe insulator  140  is disposed in the middle of the processing gas inlet pipe  139 . The pipe insulator  140  is made of an insulator and serves to prevent a high frequency power supplied to the gas introduction shower head  132  from leaking out to the processing gas supply unit through the processing gas inlet pipe  139 . Through the gas holes  135 , the gas introduction shower head  132  supplies into the chamber  111  a processing gas fed from the processing gas inlet pipe  139  to the buffer chamber  138  and a water removal gas to be described later.  
         [0052]     Further, a loading/unloading port  141  of the wafer W is provided in a sidewall of the chamber  111  at a position corresponding to the height of the wafer W when lifted upward from the susceptor  112  by the pusher pins  131 ; and a gate valve  142  for opening or closing the loading/unloading port  141  is attached thereto.  
         [0053]     Furthermore, in order to monitor an amount of water molecules or moisture in the chamber  111 , the chamber  111  is connected to a spectrometer (not shown) capable of measuring the amount, for example, a quadropole mass spectrometer, an infrared absorption/emission spectrometer and an ICP mass spectrometer.  
         [0054]     In the chamber  111  of the plasma processing apparatus  100 , as mentioned above, high frequency powers are applied to the space S between susceptor  112  and the gas introduction shower head  132  by supplying high frequency powers thereto. Hence, the processing gas, which has been supplied through the gas introduction shower head  132 , is converted into a high-density plasma in the space S, and the RIE process is carried out on the wafer W using therewith.  
         [0055]     Specifically, to carry out the RIE process on the wafer W in the plasma processing apparatus  100 , first, the gate valve  142  is opened to load the wafer W serving as an object to be processed into the chamber  111 , and a DC voltage is applied to the electrode plate  123  to adsorb and support the loaded wafer W on the adsorption surface of the susceptor  112 . Further, the processing gases (e.g., gaseous mixture including CF 4  gas, O 2  gas and Ar gas, having a specified flow rate ratio) are supplied through the gas introduction shower head  132  into the chamber  111  at specified flow rates and flow rate ratio; and, at the same time, the inner pressure of the chamber  111  is set to be kept at a predetermined value by the APC  115  or the like. Still further, high frequency powers are applied to the space S in the chamber  111  by the susceptor  112  and the gas introduction shower head  132 . Accordingly, the processing gases introduced through the gas introduction shower head  32  are converted into a plasma, generating ions or radicals in the space S, and the generated radicals or ions are focused on the surface of the wafer W by the focus ring  125  to etch the surface of the wafer W physically or chemically.  
         [0056]     Further, a regular examination or wet cleaning is performed in the chamber  111  with its lid (not shown) opened and, then, a gaseous mixture including CF 4  and CO (hereinafter, referred to as a “water molecule removal gas”) is introduced through the gas introduction shower head  132  into the chamber  111  with its lid closed. At this time, CF 4  and CO introduced into the chamber  111  react with H 2 O molecules existing therein introduced from the outside when the lid was opened or emitted from pores of the alumite coating on the inner wall of the chamber  111  as represented by the following equation (1):
 
CF 4 +CO+H 2 O→CO 2 +HF+(CF x +F 2 )  (1)
 
 wherein the valence is not considered. 
 
         [0057]     As shown in equation (1), CO 2 , HF, CF x  and F 2  are produced due to a reaction between the water molecule removal gas introduced through the gas introduction shower head  132  and H 2 O molecules in the chamber  111 . In particular, H 2 O molecules are reduced by CO in the water molecule removal gas to produce hydrogen molecules, and the produced hydrogen molecules react with CF 4  in the water molecule removal gas to produce HF. The reduction of H 2 O molecules is accelerated due to the presence of CO with a strong reducibility. Further, CF 4  is easy to be reduced and, thus, rapidly reacts with the produced hydrogen molecules, meaning that the reaction represented by equation (1) proceeds extremely rapidly. The produced CO 2 , HF, CF x  and F 2  are discharged to the outside from the chamber  111  by an evacuation of the TMP  116  and the DP  117 .  
         [0058]     Hereinafter, there will be described an atmosphere change in the chamber  111  caused by the reaction represented by equation (1).  
         [0059]      FIG. 3  is a graph showing measurement results of an atmosphere in the chamber shown in  FIG. 2 , which changes as a function of elapsed time and obtained by a quadropole mass spectrometer (QMS), wherein a vertical axis represents the QMS count and a horizontal axis, the elapsed time.  
         [0060]     The measurements were made from the time at which the chamber  111  that had become isolated from the atmosphere when its lid was closed after having been exposed thereto when the lid thereof was opened began to be exhausted by the TMP  116  and the DP  117  until after the water molecule removal gas is introduced into the chamber  111 . Further, a dashed double-dotted line represents HF; a dashed dotted line, CF 4 ; a dashed line, CO; and a solid line, H 2 O.  
         [0061]     From the results of  FIG. 3 , it can be known that the amount of H 2  O molecules gradually decreases as a function of the elapsed time due to the chamber being exhausted by the TMP  116  and the DP  117 , and the amount of H 2 O molecules rapidly decreases at a time of about 170000 ms which coincides with the introduction of the water molecule removal gas, a gaseous mixture including CF 4  and CO. That is because the reaction represented by equation (1) extremely rapidly proceeds in the chamber  111  with the introduction of the water molecule removal gas.  
         [0062]     As described above, by introducing the water molecule removal gas into the chamber  111  through the gas introduction shower head  132 , the reduction of H 2 O molecules is accelerated in the chamber  111  and, further, the reduced H 2 O molecules are exhausted as HF, resulting in an efficient removal of H 2 O molecules from the inside of the chamber  111 . Moreover, since CF 4  gas is used as a processing gas, the gas introduction shower head  132  can be also employed as a unit for introducing the water molecule removal gas. Thus, there is no need to provide new piping and the like, making it possible to suppress a cost increase of the substrate processing apparatus  1  as well as the plasma processing apparatus  100 .  
         [0063]      FIG. 4  is a flowchart showing a sequence of water molecule removal processing performed by the system controller in the substrate processing apparatus shown in  FIG. 1 .  
         [0064]     The processes shown in  FIG. 4  is performed on the substrate processing apparatus that had undergone a regular examination of the plasma processing apparatus  100  or a wet cleaning of the chamber  111  during which the inside of the chamber  111  gets exposed to the atmosphere as a result of the lid being opened.  
         [0065]     Referring to  FIG. 4 , the system controller controls the plasma processing apparatus  100  such that the lid of the chamber is closed (step S 401 ); the chamber  111  is exhausted by the TMP  116  and the DP  117  (step S 402 ); and the amount of water molecules present inside the chamber  111  is monitored by the spectrometer connected to the chamber  111  (step S 403 ).  
         [0066]     Subsequently, in step S 404 , it is determined whether or not the amount of water molecules present inside the chamber  111  is greater than or equal to a predetermined value at which the above-mentioned problems 1) to 5) occur. If the amount of water molecules present inside the chamber  111  is smaller than the predetermined value, the process is completed, whereas if the amount of water molecules present inside the chamber  111  is greater than or equal to the predetermined value, the water molecule removal gas is introduced through the gas introduction shower head  132  by controlling the processing gas supply unit (step S 405 ).  
         [0067]     In the next step S 406 , the amount of water molecules present inside the chamber  111  is monitored repeatedly to determine whether or not the amount of water molecules in the chamber  111  is greater than or equal to the predetermined value (step S 407 ). If the amount of water molecules in the chamber  111  is monitored to be greater than or equal to the predetermined value, the process returns to the step S 405 . If the amount of water molecules in the chamber  111  is found to be smaller than the predetermined value, the process is stopped immediately.  
         [0068]     Further, while the processes shown in  FIG. 4  are performed, the surface of the inner wall of the chamber  111  is maintained at a high temperature. The reason thereof will be described below.  
         [0069]     The vapor pressure of HF produced by the reaction between the water molecule removal gas and H 2 O molecules is 20 KPa at a temperature of −20° C.; 30.9 KPa at −10° C.; 47.3 KPa at 0° C.; 70.7 KPa at 10° C.; 102 KPa at 20° C.; and 139 KPa at 30° C. Accordingly, in a depressurized state where the pressure inside the chamber  111  is lower than a standard atmospheric pressure (about 101 KPa), HF is assumed to get vaporized at a temperature of about 20° C. or more. In other words, it is supposed that if the temperature of the inner wall surface of the chamber  111  is greater than or equal to the room temperature, the produced HF is vaporized and then discharged to the outside from the chamber  111  by the TMP  116  and the DP  117  without getting attached to the inner wall surface of the chamber  111 . Therefore, by maintaining the surface of the inner wall of the chamber  111  at a high temperature, it is possible to surely prevent the produced HF from being attached to the inner wall surface of the chamber  111  and prevent the vaporized HF from being re-attached to the inner wall surface of the chamber  111 , thereby preventing the inner wall surface of the chamber  111  from being corroded due to HF attached thereto.  
         [0070]     Further, by maintaining the inner wall surface of the chamber  111  coated with a ceramic material having a plurality of pores, such as alumite, at a high temperature, H 2 O molecules included in the pores to become an out gas by being vaporized, accelerating the removal of water molecules.  
         [0071]     According to the processes shown in  FIG. 4 , the system controller of the plasma processing apparatus  100  conducts an evacuation of the chamber  111  by using the TMP  116  and the DP  117  (step S 402 ). When the amount of water molecules in the chamber  111  becomes greater than or equal to the predetermined value (YES at step S 404 ), the water molecule removal gas gets introduced through the gas introduction shower head  132  (step S 405 ), resulting in an efficient removal of H 2 O molecules present in the chamber  111 , accelerating the removal of water molecules in the chamber  111 . Further, after closing the lid of the chamber  111  which had been exposed to the atmosphere, the amount of water molecules in the chamber  111  can be automatically made to be less than the predetermined value, thus providing an environment for automatically starting the wafer processing, which is known as an auto-standby function, making it possible to reduce a downtime of the plasma processing apparatus  100  including the chamber  111 .  
         [0072]     Although, the water molecule removal gas including CF 4  and CO is introduced through the gas introduction shower head  132  in this embodiment, any gaseous mixture including a halogen-based processing gas (e.g., chlorine gas) and a reduction gas may be used as the water molecule removal gas without being limited thereto.  
         [0073]     Although the water molecule removal gas is only introduced through the gas introduction shower head  132  in this embodiment, a non-reactive gas such as argon and nitrogen may be introduced together with the gaseous mixture, which, as well as providing an environmental consideration by reducing the amount of CF 4  or CO used, makes it possible to curtail the time from an end of the water molecule removal processing to a start of the wafer processing by generating a viscous flow, attracting HF and the like, as a consequence of the pressure in the chamber  111  being increased.  
         [0074]     Although the inner wall surface of the chamber  111  is coated with alumite in this embodiment, the inner wall surface may be coated with Y 2   0   3  by spraying, resulting in relatively large pores being present on the surface of the inner wall of the chamber  111 . In the relatively large pores, the water molecule removal gas introduced may easily enter the pores and H 2 O molecules included therein may easily be vaporized to become an out gas, thereby accelerating the removal of water molecules in the chamber.  
         [0075]     Further, instead of the sprayed Y 2 O 3 , hydration-treated Y(OH) 3  may be used. The hydration treatment is to form Y(OH) 3 , a hydroxide, by reacting Y 2 O 3  with H 2 O. Since Y(OH) 3  is extremely stabilized and has a hydrophobic property, allowing it to prevent a separation of chemically adsorbed H 2 O and to suppress further an adsorption of H 2 O molecules, the inner wall surface of the chamber  111  thus sprayed becomes hydrophobic, whereby, as well as making the inner wall surface of the chamber  111  denser, H 2 O molecule attachment can be minimized, making it possible to reduce the generation of an out gas therefrom, further accelerating the removal of water molecules in the chamber  111 .  
         [0076]     Further, the inner wall surface of the chamber  111  may be coated with metal such as aluminum and stainless steel, quartz or the like, instead of ceramic materials such as Al 2 O 3  and Y 2 O 3 . Since metals such as aluminum and stainless steel, quartz or the like have therein less concentration of pores, the correspondingly less amount of H 2 O molecules present in the chamber  111  are prevented from being attached to the inner wall surface of the chamber  111 , which will further accelerate the removal of water molecules in the chamber  111 .  
         [0077]     Further, when the exhaust of the chamber  111  is performed by using the TMP  116  and the DP  117 , pumping and purging, that is, gas introduction and exhaust, may be repeated. During the pumping and purging, the exhaust is performed in a state where the viscous flow is generated due to an increased pressure in the chamber  111  by the gas introduction, allowing an efficient removal of water molecules from the chamber  111 .  
         [0078]     Moreover, the chamber  111  may include a cryo pump which has a very low temperature surface, allowing the exhaust to be carried out by condensing or adsorbing gas molecules on the very low temperature surface, resulting in accelerating the removal of water molecules from the chamber  111 .  
         [0079]     Although the processes shown in  FIG. 3  are carried out to remove water molecules from the chamber  111  in this embodiment, the processes may performed for the removal of water molecules in the load-lock module  27  without being limited thereto. Accordingly, it is possible to reduce a downtime of the load-lock module  27  and also prevent H 2 O molecules from being attached to the wafer W when the wafer W is transferred.  
         [0080]     Although the processes shown in  FIG. 3  are performed after the chamber  111  has been exposed to the atmosphere in this embodiment, the processes may be performed for each wafer lot without being limited thereto. Accordingly, the amount of water molecules in the chamber  111  can be always maintained below a fixed level, thereby resolving an etching rate difference between wafer lots.  
         [0081]     Further, a storage medium storing therein program codes of software for realizing the functions of the aforementioned preferred embodiments is provided to the system controller. CPU or MPU included in the system controller reads the program codes stored in the storage medium and executes them, so that the object of the present invention can be achieved ultimately.  
         [0082]     In this case, the program codes read from the storage medium execute themselves the functions of the preferred embodiments described above, meaning that the program codes and the storage medium storing therein the program codes are also part of the present invention.  
         [0083]     Further, floppy (registered trademark) disk, hard disk, optical disk, magneto-optical disk, CD-ROM, CD-R, CD-RW, DVD-ROM, DVD-RAM, DVD-RW, DVD+RW, magnetic tape, nonvolatile memory card, ROM, etc. can be employed as the storage medium for providing the program codes. In addition, the program codes may be downloaded through the network.  
         [0084]     Although the functions of the aforementioned preferred embodiments are realized by executing the program codes read by the CPU in the above-described case, based on instructions of the program codes, OS (operating system) operating on the CPU may execute the functions partially or entirely, and such an approach is also included in the present invention.  
         [0085]     Further, after the program codes read from the storage medium are stored in a memory included in a function extension board inserted in the system controller or a function extension unit connected to the system controller, based on instructions of the program codes, CPU and the like included in the function extension board or the function extension unit may partially or entirely execute the functions of the above-described preferred embodiments. This approach is also part of the present invention.  
         [0086]     While the invention has been shown and described with respect to the preferred embodiments, it will be understood by those skilled in the art that various changes and modifications may be without departing from the spirit and scope of the invention as defined in the following claims.