Abstract:
A gas removal system that removes a halogen gas remaining inside a processing chamber after executing a specific type of processing inside the processing chamber maintained in an airtight state with plasma obtained through discharge dissociation of the halogen gas supplied from a gas supply device comprises a pressure control device that controls the pressure inside the processing chamber, an air supply device that supplies the atmospheric air into the processing chamber after the pressure inside the processing chamber is lowered by the pressure control device, a control device that controls the air supply device and an evacuation device that evacuates a gas produced through a reaction of the halogen gas and the atmospheric air having occurred inside the processing chamber.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application is a national phase application based on PCT/JP01/10714, filed Dec. 7, 2001, the content of which is incorporated herein by reference, and claims the priority of Japanese Patent Application no. 2000-374438, filed Dec. 8, 2000, the content of which is incorporated herein by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a gas removal method, a gas removal system and a plasma processing apparatus that are ideal in applications in which plasma processing is executed with a gas containing halogen (a halogen gas). 
   2. Description of the Related Art 
   Plasma processing apparatuses that execute plasma processing by using a halogen gas such as a chlorine-based gas are utilized in the field of semiconductor production in the related art. During an etching process executed by using a chlorine-based gas, a chlorine-based reaction product becomes deposited at the inner wall surfaces of the processing chamber and internal members constituting the processing apparatus and the etching process is adversely affected by the chlorine-based reaction product deposit. For this reason, it is necessary to regularly clean the inside of the processing chamber with an organic solvent such as alcohol. However, the chlorine-based gas, as well as the chlorine-based reaction product, is present inside the processing chamber immediately after the process and it is dangerous to open the processing chamber in such a state. 
   Accordingly, the chlorine-based gas is removed while maintaining the processing chamber in an airtight state in the related art. When the atmospheric air and N2 are supplied into the processing chamber in a sealed state, the chlorine-based gas is transformed to acid by the moisture contained in the atmospheric air. By evacuating this acid through an acid evacuation line, the chlorine-based gas is removed from the processing chamber. Only after the chlorine-based gas is removed as described above and safety is thus assured, the processing chamber is opened to the atmosphere for cleaning. 
   However, since the atmospheric air and N2 are supplied into the sealed processing chamber, there is a limit to the quantities of atmospheric air and N2 that can be taken in and it takes a considerable length of time to supply the atmospheric air and N2 and to transform the chlorine-based gas to acid in the related art described above. It takes as long as approximately 300 minutes to lower the chlorine-based gas concentration to the level at which the processing chamber can be safely opened, i.e., under 2 ppm, in a standard plasma processing apparatus, to lead to an increase in the down time of the apparatus and a poor operating rate. 
   SUMMARY OF THE INVENTION 
   An object of the present invention, which has been completed by addressing the problems of the related art discussed above, is to provide a new ad improved gas removal method and a new and improved gas removal system that make it possible to reduce the length of time required to remove the halogen gas in the processing chamber and a plasma processing apparatus adopting the gas removal method and the gas removal system. 
   In order to achieve the object described above, in a first aspect of the present invention, a gas removal method for removing a halogen gas remaining in a processing chamber after executing a specific type of processing inside the processing chamber in an airtight state with plasma obtained through discharge dissociation of the halogen gas, comprises a step in which the pressure inside the processing chamber is reduced to a level lower than the atmospheric pressure, a step in which atmospheric air is supplied into the processing chamber and a step in which a gas produced through a reaction of the halogen gas and the atmospheric air having occurred inside the processing chamber is evacuated. 
   By adopting this gas removal method in which the pressure inside the processing chamber is reduced to a level that is at least lower than the atmospheric pressure (reduced to a negative pressure), the gas is not allowed to become diffused to the outside of the processing chamber when the atmospheric air is supplied into the processing chamber. In addition, since the pressure inside the processing chamber is sustained at a low level, the atmospheric air can be supplied with ease. As a result, the reaction product resulting from the reaction of the supplied atmospheric air and the gas present in the processing gas can be evacuated to achieve fast and reliable gas removal. Furthermore, since the pressure inside the processing chamber is sustained at a negative level, there is no irritating odor of the gas and the gas leakage detector does not go off during the subsequent maintenance work, thereby assuring safety of the maintenance personnel. 
   It is desirable that the atmospheric air be supplied into the processing chamber by using a supply path through which the process gas used for the plasma processing is supplied into the processing chamber. Since the process gas supply device used to supply the process gas for the plasma processing and the system utilized to supply the atmospheric air into the processing chamber can be partially integrated in this manner, the gas can be evacuated through a simpler structure. In addition, since a large drive system is not required, the gas removal can be automated with ease. 
   Moreover, during the step in which the atmospheric air is supplied into the processing chamber, the processing chamber may be opened to the atmosphere. Since the atmospheric air can be taken in a large quantity by opening the processing chamber to the atmosphere, the length of time required for the gas removal can be greatly reduced. 
   The halogen gas may be a chlorine-based gas such as chlorine or it may be a bromine-based gas such as hydrogen bromide. 
   In order to achieve the object described above, a gas removal system that removes a halogen gas remaining inside a processing chamber after executing a specific type of processing inside the processing chamber in an airtight state with plasma obtained through discharge dissociation of a process gas containing the halogen gas supplied from a process gas supply device comprising a pressure control device that controls the pressure inside the processing chamber, an air supply device that supplies atmospheric air into the processing chamber after lowering the pressure inside the processing chamber with the pressure control device, a control device that controls the air supply device and an evacuation device that evacuates a gas produced through a reaction of the halogen gas and the atmospheric air having occurred in the processing chamber is provided in a second aspect of the present invention. 
   By adopting this gas removal system in which the pressure inside the processing chamber is reduced to a level that is at least lower than the atmospheric pressure (reduced to a negative pressure), the gas is not allowed to become diffused to the outside of the processing chamber when the atmospheric air is supplied into the processing chamber. In addition, since the pressure inside the processing chamber is sustained at a lower level, the atmospheric air can be supplied with ease. As a result, the reaction product resulting from the reaction of the supplied atmospheric air and the gas present in the processing gas can be evacuated and the gas can be removed promptly with a high degree of reliability. In addition, since the pressure inside the processing chamber is sustained at a negative level, there is no irritating odor of the gas and the gas leakage detector does not go off during the subsequent maintenance work, thereby assuring safety of the maintenance personnel. 
   It is desirable that the air supply device supply the atmospheric air into the processing chamber via a supply port through which the process gas is supplied by the process gas supply device into the processing chamber or that a supply path through which the process gas is supplied into the processing chamber by the process gas supply device be partially shared by the gas supply device. Since this achieves a partial integration of the process gas supply device which supplies the process gas for the plasma processing and the air supply device which supplies the atmospheric air into the processing chamber, the gas can be evacuated through a simple structure. In addition, since a large drive system is not required, the gas removal system can be automated with ease. 
   Alternatively, the air supply device may supply the atmospheric air into the processing chamber via a supply port other than the supply port through which the process gas is supplied into the processing chamber by the air supply device. By adopting such a structure, too, the gas can be promptly removed with a high degree of reliability, and since a large drive system is not required, the gas removal system can be automated with ease. 
   Furthermore, the air supply device may comprise an atmosphere opening device that opens the processing chamber to the atmosphere. Since the atmospheric air can be taken in large quantity into the processing chamber by providing such an atmosphere opening device, the length of time required for the gas removal can be greatly reduced. 
   The atmosphere opening device may comprise a rotating mechanism for the process gas supply device. By opening the processing chamber to the atmosphere by utilizing the rotating mechanism of the process gas supply device, the gas removal system can be achieved without having to greatly modify the structure of the processing apparatus. 
   It is desirable that a sensor which detects the extent to which the processing chamber is open to the atmosphere by the means for atmosphere opening be provided to facilitate the gas removal control. 
   As an example, the gas removal control achieved by utilizing the sensor may adopt the following structure. Namely, the processing chamber may be opened to the atmosphere by the means for atmosphere opening to a first degree at which the processing chamber is not opened to the atmosphere at all, a second degree at which the processing chamber is opened to the atmosphere to a predetermined extent to remove the gas or a third degree at which the processing chamber is completely opened to the atmosphere, and the sensor may comprise a first sensor having a detection range from the first degree to the second degree and a second sensor having a detection range from the second degree to the third degree. 
   This structure facilitates verification of the state of the processing chamber by using the first sensor and the second sensor, i.e., if the processing chamber is in a fully closed state, if the process of gas removal is in progress at the processing chamber or if the processing chamber is in a fully open state. For instance, a light emitting diode may emit light in response to a signal provided by the first or second sensor to alert the operator to the state of the processing chamber and the means for atmosphere opening. 
   The degree to which the processing chamber is open to the atmosphere for gas removal (the second degree) should be set to, for instance, approximately 2% of the degree at which the processing chamber is completely open (the third degree). It is to be noted that the second degree does not need to be fixed at 2% of the third degree, and it can be adjusted in correspondence to the pressure inside the processing chamber. Namely, the extent to which the processing chamber is open to the atmosphere during gas removal can be increased as the pressure inside the processing chamber becomes lower. 
   In addition, it is desirable that the means for atmosphere opening issue a warning if the first sensor detects that the extent to which the processing chamber is open to the atmosphere is the first degree before a predetermined length of time elapses. The predetermined length of time in this case refers to the length of time that must elapse before a gas concentration level at which the processing chamber can be opened safely is achieved following a gas removal executed through the gas removal system according to the present invention. By issuing a warning if the processing chamber enters the fully closed state (i.e., if the first sensor detects that the processing chamber is open to the atmosphere to the first degree) before the gas concentration level at which the processing chamber can be safely opened is achieved, an efficient gas removal is assured. 
   Moreover, it is desirable that the means for atmosphere opening issue a warning if the second sensor detects that the extent to which the processing chamber is open to the atmosphere is the third degree before a predetermined length of time elapses. The predetermined length of time in this case refers to the length of time that must elapse before a gas concentration level at which the processing chamber can be opened safely is achieved following a gas removal executed through the gas removal system according to the present invention. By issuing a warning if the processing chamber enters the fully open state (i.e., if the second sensor detects that the processing chamber is open to the atmosphere to the third degree) before the gas concentration level at which the processing chamber can be safely opened is achieved, any leakage of the gas is prevented and the safety of the chlorine-based gas removal process is increased. 
   The halogen gas may be a chlorine-based gas such as chlorine or it may be a bromine-based gas such as hydrogen bromide. 
   In addition, the present invention provides a plasma processing apparatus employed to execute plasma processing on a workpiece inside a processing chamber, which removes the gas inside the processing chamber by utilizing the gas removal system achieving outstanding advantages as described above. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  schematically illustrates a plasma processing apparatus; 
       FIG. 2  schematically illustrates the processing apparatus achieved in a first embodiment; 
       FIG. 3  illustrates the structure adopted in an upper electrode rotating mechanism; 
       FIG. 4  illustrates sensor detection ranges; 
       FIG. 5  illustrates the sequence of the gas removal processing; 
       FIG. 6  shows the relationship between the length of the gas removal time and the gas concentration; 
       FIG. 7  schematically illustrates the plasma processing apparatus achieved in a second embodiment; and 
       FIG. 8  schematically illustrates the plasma processing apparatus achieved in a third embodiment. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The following is a detailed explanation of the preferred embodiments of the gas removal method, the gas removal system and the plasma processing apparatus according to the present invention, given in reference to the attached drawings. It is to be noted that in the specification and the drawings, the same reference numerals are assigned to components achieving substantially identical functions and structural features to preclude the necessity for a repeated explanation thereof. It is to be also noted that the term “halogen gas” used in the description of the present invention specifically refers to a chlorine-based gas such as Cl 2  or a bromine-based gas such as HBr (hydrogen bromide) that is likely to generate a hazardous substance when it reacts mainly with the atmospheric air. The following explanation is given on the assumption that a chlorine-based gas such as Cl 2  is used. 
   (Basic Structure of Plasma Processing Apparatus) 
   First, in reference to  FIG. 1 , the basic structure of a plasma processing apparatus  100  according to the present invention is explained. 
   A processing chamber  102  of the plasma processing apparatus  100  is formed inside an airtight and electrically conductive processing container  104 . An electrically conductive lower electrode  106  is provided inside the processing chamber  102 . The lower electrode  106  also functions as a stage on which a workpiece such as a semiconductor wafer (hereafter referred to as a “wafer” W is placed. 
   In addition, an electrostatic chuck  112  is provided at the surface of the lower electrode  106  on which the workpiece is placed. When a high DC voltage is applied to the electrostatic chuck  112 , it firmly holds the wafer W placed on the chuck surface. In addition, an insulating ring body  116  is provided at the lower electrode  106  so as to enclose the wafer W placed on the electrostatic chuck  112 . A baffle plate  120  is provided via an insulating member  118  around the lower electrode  106 . 
   An elevator shaft  122  is connected to the lower electrode  106  via an electrically conductive member  124  and the insulating member  118 . Thus, the lower electrode  106  is made to move upward/downward as a drive mechanism (not shown) connected to the elevator shaft  122  engages in operation. In addition, a bellows  126  constituted of an electrically conductive and airtight member capable of expanding and contracting and an electrically conductive bellows cover  128  are provided around the elevator shaft  122 . The bellows  126  and the  128  are each connected to the electrically conductive member  124  and the bottom of the processing container  104  at the two ends. 
   An upper electrode  134  is also provided inside the processing chamber  102  so as to face opposite the mounting surface of the lower electrode  106  on which the workpiece is placed. The upper electrode  134  also constitutes part of a process gas supply device  200  that supplies a process gas used to execute a specific type of processing with plasma. At the outlet-side end of the process gas supply device  200 , i.e., at the portion of the upper electrode  134  facing the internal space of the processing chamber, numerous gas outlet holes  134   a  are formed to function as process gas supply ports. In addition, a chlorine-based gas supply system  208  or the like that supplies, for instance, a chlorine-based gas such as Cl 2  is connected to the gas outlet holes  134   a.    
   The chlorine-based gas supply system  208  is connected with a chlorine-based gas supply source  206  from which the chlorine-based gas is supplied via a switching valve  202  and a flow-regulating valve  204 . 
   A magnet  136  is provided outside the side wall of the processing chamber  102 . The magnet  136  is capable of forming a rotating magnetic field between the upper electrode  134  and the lower electrode  106 . 
   It is to be noted that components that do not bear direct relevance to the present invention are not mentioned in the explanation given in reference to  FIG. 1 . In addition, the present invention is not limited to the plasma processing apparatus  100  described above and it may be adopted in all types of processing apparatuses. For instance, it may be adopted in a plasma etching apparatus with no magnet or a plasma etching apparatus in which high-frequency power is applied to the lower electrode alone (or the upper electrode alone). 
   Next, three embodiments of the halogen gas removal system and, more specifically, the air supply device, that characterizes the present invention are explained. 
   (First Embodiment) 
   Now, the first embodiment of the present invention is explained. This embodiment is characterized in that an atmosphere opening device for opening the processing chamber  102  to the atmosphere is included to constitute the air supply device of the chlorine based gas removal system utilized to remove the chlorine based gas from the processing chamber  102 . Namely, as shown in  FIG. 3 , which presents an enlargement of the essential portion of the plasma processing apparatus in  FIG. 2 , a rotating mechanism  135  that rotates the upper electrode  134  is provided as the atmosphere opening device used to open the processing chamber  102  to the atmosphere. The rotating mechanism  135  is capable of freely rotating the upper electrode  134  around a support shaft  135   a.    
     FIG. 4  shows the relationship between the rotating angle of the upper electrode  134  to which the upper electrode  134  is caused to rotate by the rotating mechanism  135  shown in  FIG. 3  and the sensors utilized to detect the rotating angle. In order to improve the control, two sensors (a first sensor and a second sensor) are used in combination in the embodiment.
     1) The detection range of the first sensor is θ0 (the processing chamber is fully closed: 0°)˜θ2 (the gas removal position: approximately 2°). The first sensor judges that the processing chamber is closed when the angle to which the upper electrode  134  is rotated by the rotating mechanism  135  is equal to or smaller than a threshold value θ1 (approximately 1°) and judges that the processing chamber is in an open state when the rotating angle is equal to or greater than θ1. When the rotating angle achieved by the rotating mechanism  135  is within the range of θ1 (approximately 1°)˜θ2 (the gas removal position: approximately 2°) and thus, the processing chamber is determined to be in an open state, the first sensor outputs a processing chamber open signal S 1  to a control unit  160 . It is to be noted that the first sensor constitutes a component that characterizes the embodiment and is a new sensor which is not used in processing apparatuses in the related art.   2) The second sensor is the type of sensor provided in standard processing apparatuses. The detection range of the second sensor is θ2 (the gas removal position: approximately 2°)˜θ4 (the processing chamber is fully open: over 90°). The second sensor judges that the processing chamber is closed when the angle to which the upper electrode  134  is rotated by the rotating mechanism  135  is equal to or smaller than a threshold value θ3 (approximately 45°) and judges that the processing chamber is in an open state when the rotating angle is equal to or greater than θ3. Thus, the gas removal position (θ2= approximately 2°) is set to approximately 2% of the position corresponding to the fully open state of the processing chamber (θ4= over 90°). When the rotating angle achieved by the rotating mechanism  135  is within the range of θ3 (approximately 45°)˜θ4 (the processing chamber is fully open: 90°) and thus, the processing chamber is determined to be in an open state, the second sensor outputs a processing chamber open signal S 2  to the control unit  160 .   
   In order to remove the chlorine-based gas, N2 is supplied in addition to the atmospheric air. N2 is supplied into the processing chamber  102  through an N2 supply line  140 . The pressure of the N2 is controlled through a pressure switch  142  provided at the N2 supply line. An N2 supply piping  144  is coated with Teflon for rust prevention. 
   The chlorine-based gas in the processing chamber  102  is removed by supplying N2 and atmospheric air into the processing chamber  102  and causing a reaction between the moisture in the atmospheric air and the chlorine-based gas. Acid produced through the reaction of the moisture in the atmospheric air and the chlorine-based gas is then evacuated through an acid evacuation line  150 . The evacuation pressure is achieved by the negative pressure of the suction force applied for plant acid removal. An acid evacuation-side SUS piping  152  is coated with Teflon for rust prevention. 
   Two air operation valves (a front-stage air operation valve  154  and a rear-stage air operation valve  156 ) that are heated with a heater are mounted side-by-side onto the acid evacuation line  150 . The specifications of these air operation valves  154  and  156  are as follows.
         150° C. self temperature control (control range: 130˜170° C.)   power consumption: 72 W, 100V×2   capable of outputting an alarm when the temperature deviates from the control range or a disconnection occurs, power is cut off at a thermal fuse when the temperature rises to an abnormal level       

   It is to be noted that they are set in an ON state at all times since it takes 0.5˜1 hour before the temperature becomes stable. 
   The front-stage air operation valve  154  and the rear-stage air operation valve  156  are controlled through different methods. Refer to the explanation of the control sequence provided later.
         special quadruple-mount type solenoid valves are provided as a new feature       

   The control unit  160 , which is connected to a power supply  180 , controls the power supply to the air operation valves  154  and  156  (S 11  and S 16 ) and also implements specific control by using various signals including heater temperature control error detection signal (S 13  and S 14 ) input from the air operation valves  154  and  156  and ON/OFF signals (S 12  and S 15 ). In addition, the processing chamber open signal S 1  from the first sensor, the processing chamber open signal S 2  from the second sensor, an atmospheric air signal S 3  from a convectron and a roughing evacuation start signal S 4  are input to the control unit  160 . In response to the signals S 1 ˜S 4 , the control unit  160  turns on/off or blinks the light emitting diodes to alert the operator to a specific state. 
   A green light emitting diode (green LED  191 ) is turned on when the processing chamber can be opened. A yellow light emitting diode (yellow LED  192 ) flashes when the apparatus has entered a standby state for an acid evacuation count start and is turned on while the acid evacuation count is in progress. A red light emitting diode (red LED  193 ) is turned on when the processing chamber cannot be opened. A white light emitting diode (white LED  194 ) flashes when the heater temperature is out of the control temperature range and is turned on when the heater temperature is at a normal level. 
   The gas removal method achieved in the plasma processing apparatus  100  adopting the gas removal system described above is now explained.  FIG. 4  shows the sequence of the gas processing. In addition,  FIG. 5  presents a graph of the relationship between the length of the gas removal time and the gas concentration. 
   1) Atmospheric Air Detection 
   When the atmospheric air signal S 3  provided by the convectron is detected, both the front-stage air operation valve  154  and the rear-stage air operation valve  156  are opened. Since the processing chamber  102  is still closed at this point, a slight negative pressure is generated inside the processing chamber  102  due to the plant acid removal suction force. The yellow LED  192  starts to blink when the atmospheric air is detected to notify the operator that the apparatus has entered a standby state for a gas removal count start. 
   2) Count Start 
   As the upper electrode is moved to a specific position (the gas removal position θ2) while the yellow LED  192  is blinking, the processing chamber open signal S 1  from the first sensor is detected and the count of the gas removal time starts. At this point, the yellow LED  192  which has been blinking enters a steady ON state to notify the operator that the gas removal count is in progress. It is to be noted that the length of time to elapse between “1) Atmospheric air detection” and “2) Count start” may be set freely by the operator. 
   3) During Gas Removal Count 
   During the gas removal process, the length of which has been preset, the gas inside the processing chamber  102  is evacuated. During this process, the red LED is on (indicating that the processing chamber  102  cannot be opened to the atmosphere) and the yellow LED is on (indicating that the gas removal count is in progress). In the graph shown in  FIG. 5 , the gas concentration goes under 5 ppm when 180 minutes elapses and it falls substantially to 0 ppm when 240 minutes elapses. Accordingly, it is recommended that the gas removal be executed for 240 minutes or more. However, it has been confirmed that through continuous evacuation, the gas concentration can be lowered to an acceptable level of less than 2 ppm within 180 minutes. 
   4) The Processing Chamber Opened to the Atmosphere During the Count 
   If the processing chamber is opened to the atmosphere while the gas removal count is in progress (if the processing chamber open signal S 2  from the second sensor is detected), the rotating mechanism  135  for the upper electrode  134  issues a warning to alert the operator. Since fully opening the processing chamber during the gas removal count is strictly due to an operating error, it is assumed that the operator promptly closes the processing chamber in response to the warning. Thus, the gas removal timer continues to count the time elapsing during this erroneous operation. 
   5) The Processing Chamber Closed During the Count 
   If the processing chamber becomes closed during the gas removal count (if the processing chamber open signal from the first sensor is not detected), the rotating mechanism  135  of the upper electrode  134  issues a warning to alert the operator. However, unlike in the state described in 4), the processing chamber may become completely closed during the gas removal count out of necessity (there is a possibility that the processing chamber may remain in a closed state over an extended period of time) and, accordingly, the gas removal timer count becomes temporarily halted while the processing chamber is in a closed state. The count is resumed when the upper electrode is moved back to the gas removal position (θ1) (when the processing chamber open signal S 1  from the first sensor is detected). It is to be noted that since the two valves remain open while the count is temporarily halted, the pressure inside the processing chamber is sustained at a negative level and, for this reason, the chlorine-based gas is not allowed to flow out of the processing chamber when the processing chamber is opened to the atmosphere again. 
   6) End of the Preset Length of Time 
   7) Maintenance Start 
   When the gas removal count reaches the preset length of time, the green LED  191  is turned on (the yellow LED  192  and the red LED  193  become turned off) to indicate that the processing chamber can be opened to the atmosphere and thus the maintenance work can be initiated. It is to be noted that the length of time to elapse between “6) End of the preset length of time” and “7) Maintenance start” may be freely set by the operator. 
   8) During the Maintenance 
   Since the two valves remain in an open state during the maintenance work, a down flow is created inside the processing chamber to prevent the residual chlorine-based gas from flowing out toward the operator. 
   9) Closing the Processing Chamber Completely During Maintenance 
   If the processing chamber becomes fully closed (due to a temporary halt to the maintenance work or the like) during the maintenance process, the front-stage air operation valve  154  alone is closed in preparation for a roughing start (so as to prevent a backward flow of the gas from the plant acid removal line at the start of the roughing process. If the processing chamber is opened again without starting a roughing process, the front-stage air operation valve  154  is opened again and the operation returns to the maintenance mode described in 8) above. 
   10) Maintenance End 
   As the maintenance work is completed and the processing chamber is set in a fully closed state (θ0) in preparation for a roughing start, the front-stage air operation valve  154  alone is closed prior to the start of the roughing process. This state is identical to the state described in 9) above. 
   11) Roughing Start 
   Upon detecting the roughing start signal S 4 , the rear-stage air operation valve  156 , too, becomes closed. Since the front-stage air operation valve  154  has been in a closed state prior to this time point, the gas is not allowed to flow back into the processing chamber through the plant acid removal line. In response, the green LED  191  is turned off and the red LED  193  is turned on (to indicate that the processing chamber  102  cannot be opened to the atmosphere). It is to be noted that the length of time to elapse between “10) Maintenance end” and “11) Roughing start” may be set freely by the operator. 
   In addition, if the upper electrode is at the gas removal position (θ2) (if the processing chamber open signal S 1  from the first sensor is detected) when the maintenance work is completed and the roughing start signal S 4  is detected, the second sensor may erroneously assume that the upper electrode at the gas removal position θ2 is at the “closed” position and, as a result, the roughing process may start while the processing chamber is still open to the atmosphere. For this reason, if the upper electrode is at the gas removal position (θ2) when the roughing start signal S 4  is detected, a pseudo open signal is provided to the second sensor. Then, after the processing chamber becomes fully closed (θ0), the roughing process is started. 
   If an error occurs in the temperature control system for the air operation valves  154  and  156  (if the heater temperature deviates from the control temperature range) in any of the steps taken during the sequence, the white LED  194  blinks (it remains on in a normal state). However, the gas removal sequence itself is not affected at all due to a forcible interruption or the like. 
   As explained above, in the embodiment in which the pressure inside the processing chamber  102  is reduced to a level which is at least lower than the atmospheric pressure (a negative pressure), the chlorine-based gas is not allowed to become diffused into the atmosphere even when the processing chamber  102  is open to the atmosphere. Thus, by opening the processing chamber  102  to the atmosphere, the atmospheric air can be taken in a large quantity. Since a large quantity of atmospheric air can be taken in by opening the processing chamber  102  to the atmosphere, the length of time required to produce acid through a reaction of the atmospheric air and the chlorine-based gas to remove the chlorine-based gas can be greatly reduced. In other words, while it takes approximately 300 minutes to achieve a chlorine-based gas concentration of less than 2 ppm at which the processing chamber can be opened safely in the related art, it becomes possible to remove the chlorine-based gas in 180 minutes or less through continuous evacuation. 
   In addition, since the processing chamber  102  can be opened to the atmosphere by using the rotating mechanism  135  of the upper electrode  134 , the structure of the apparatus does not need to be modified greatly. 
   Furthermore, since a locking mechanism that locks the atmosphere opening device when the pressure inside the processing chamber is equal to or higher than a predetermined level is provided, any leakage of the chlorine-based gas is prevented and thus, the safety of the maintenance work can be increased. 
   Moreover, better control is achieved with two sensors, the first sensor and the second sensor. 
   While the rotating mechanism  135  issues a warning for the operator if the processing chamber becomes open to the atmosphere or becomes closed while a gas removal count is in progress in the embodiment described above, the present invention is not limited to this example. For instance, the upper electrode  134  may be locked at a fixed position so as to disallow rotation thereof during a gas removal count to ensure that the processing chamber does not become opened to the atmosphere or completely closed off. 
   In addition, the processing chamber may be determined to have been opened to the atmosphere during a gas removal count when the upper electrode  134  is set to the full open position (θ4) or when it is decided that the processing chamber is in an open state (θ3)˜(θ4). Likewise, the processing chamber may be determined to have been completely closed when the upper electrode  134  is set to the full closed position (θ0) or when it is decided that the processing chamber is in a closed state (θ0)˜(θ1). 
   (Second Embodiment) 
   Next, the second embodiment of the present invention is explained. This embodiment is characterized in that the air supply device is constituted of a device that supplies a gas to be used for chlorine-based gas removal into the processing chamber  102  through the supply ports through which the process gas used in the plasma processing executed in the processing chamber  102  is supplied, i.e., through the gas outlet holes  134   a  in this example, instead of the atmosphere opening device in the first embodiment. Namely, the supply paths for the process gas and the atmospheric air are partially integrated. 
     FIG. 7  shows the features of the embodiment. It is to be noted that the components in  FIG. 7  that are identical to those in the first embodiment are not explained. 
   A process gas supply device  200  is constituted of a chlorine-based gas supply system  208 , gas outlet holes  134   a  and the like. In the embodiment, an atmospheric air supply system  300  and a switching valve  301  to be utilized to supply the atmospheric air present around the processing chamber into the processing chamber through the gas outlet holes  134   a  are connected to the chlorine-based gas supply system  208  at a specific position. It is to be noted that a mesh  302  may be provided at the atmosphere-side end of the atmospheric air supply system  300  to function as a filter that prevents entry of dust in the atmosphere into the atmospheric air supply system  300 . 
   During the actual chlorine-based gas removal process executed by adopting the structure described above, the air operation valves  154  and  156  are first opened to reduce the pressure inside the processing chamber  102 . As a sensor detects that the pressure inside the processing chamber  102  has been lowered to a predetermined level (approximately 2Torr), the switching valve  301  is opened to let the atmospheric air into the atmospheric air supply system  300 . Since the pressure inside the processing chamber has been lowered, the chlorine-based gas inside the processing chamber is not released to the outside through the atmospheric air supply system and, instead, the atmospheric air present around the processing chamber travels through the atmospheric air supply system  300  and is supplied into the processing chamber through the gas outlet holes  134   a.    
   The moisture in the atmospheric air supplied into the processing chamber reacts with the chlorine-based gas inside the processing chamber and produces acid which is then evacuated through the acid evacuation line  150 . 
   By allowing the process gas supply device  200  to bypass the atmospheric air supply system  300 , supplying the atmospheric air from the environment into the processing chamber through the atmospheric air supply system  300  after lowering the pressure inside the processing chamber and evacuating the acid produced through the reaction of the moisture in the atmospheric air and the chlorine-based gas in the processing chamber as in the embodiment, the chlorine-based gas can be evacuated in a manner similar to that achieved in the first embodiment and furthermore, the chlorine-based gas evacuation is achieved through a simpler structure compared to the first embodiment. Moreover, since a large drive system is not required, the chlorine-based gas removal system can be automated with ease. 
   (Third Embodiment) 
   The third embodiment of the present invention is now explained. While the air supply device in the second embodiment is achieved by allowing the process gas supply device  200  to bypass the atmospheric air supply system  300 , in the third embodiment, the atmospheric air supply system is made to directly connect the processing chamber to enable removal of the chlorine-based gas inside the processing chamber . 
     FIG. 8  shows the features of the embodiment. It is to be noted that the components in  FIG. 8  that are identical to those in the first embodiment are not explained. 
   As  FIG. 8  clearly illustrates, an atmospheric air supply system  400  is directly connected at the external surface of the processing chamber  102  in order to directly supply the atmospheric air present in the vicinity of the processing chamber into the processing chamber and a hole  403  is formed at the top of the processing chamber to allow the atmospheric air to flow from the atmospheric air supply system  400  into the processing chamber  102 . The atmospheric air supply system  400  includes a switching valve  401 . In addition, as in the second embodiment, a mesh  402  may be provided at the atmosphere-side end of the atmospheric air supply system  400  to function as a filter which prevents entry of dust in the atmosphere into the atmospheric air supply system  400 . 
   During the actual chlorine-based gas removal process executed by adopting the structure described above, the air operation valves  154  and  156  are first opened to reduce the pressure inside the processing chamber  102 , as in the second embodiment. As a sensor detects that the pressure inside the processing chamber  102  has been lowered to a predetermined level (approximately 2Torr), the switching valve  401  is opened to let the atmospheric air into the atmospheric air supply system  400 . Since the pressure inside the processing chamber  102  has been lowered, the chlorine-based gas inside the processing chamber  102  is not released to the outside through the atmospheric air supply system  400  and, instead, the atmospheric air present in the environment travels through the atmospheric air supply system  400  and through the hole  403  formed at the processing chamber and is supplied into the processing chamber  102  through an atmospheric air outlet hole  404 . 
   The moisture in the atmospheric air supplied into the processing chamber reacts with the chlorine-based gas inside the processing chamber and produces acid which is then evacuated through the acid evacuation line  150 . 
   By allowing the atmospheric air supply system  400  to directly connect to the processing chamber  102 , providing the hole  403  and the atmospheric air outlet hole  404  at the processing chamber  102  supplying the atmospheric air around the processing chamber  102  into the processing chamber and evacuating the acid produced through the reaction of the moisture in the atmospheric air and the chlorine-based gas inside the processing chamber as in the embodiment, the chlorine-based gas can be evacuated as effectively as in the first embodiment. Furthermore, the chlorine-based gas evacuation can be achieved through a simpler structure compared to the first embodiment. Moreover, since a large drive system is not required, the chlorine-based gas removal system can be automated with ease. 
   While the invention has been particularly shown and described with respect to preferred embodiments of the halogen gas removal method and the halogen gas removal system according to the present invention by referring to the attached drawings, the present invention is not limited to these examples and it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit, scope and teaching of the invention. 
   As explained above, according to the present invention, in which the pressure inside the processing chamber is reduced to a level which is at least lower than the atmospheric pressure (reduced to a negative pressure), the halogen gas is not allowed to become diffused to the outside of the processing chamber when the atmospheric air is supplied into the processing chamber. As a result, the reaction product, i.e., acid, resulting from the reaction of the supplied atmospheric air and the gas present in the processing gas can be evacuated to achieve quick and reliable removal of the gas. In addition, since the pressure inside the processing chamber is sustained at a negative level, there is no irritating odor of the gas and the gas leakage detector does not go off during the subsequent maintenance work, thereby assuring safety of the maintenance personnel. 
   The present invention may be adopted in plasma processing executed by using a halogen gas during the process of manufacturing, for instance, semiconductor devices.