Abstract:
Disclosed is a substrate processing apparatus, comprising a processing chamber to accommodate one or more substrates, a gas supply section to supply processing gas into the processing chamber, a gas discharge section to discharge the processing gas from the processing chamber, at least a pair of electrodes provided inside the heating section to plasma-excite the processing gas, a protection container made of dielectric to air-tightly accommodate the electrodes, an electricity-receiving section which is electrically connected to the electrodes and which is accommodated in the protection container, and an electricity-feeding section to which high frequency electric power is applied and which is provided near the electricity-receiving section in a state in which at least a wall of the protection container is interposed between the electricity-receiving section and the electricity-feeding section, wherein electric power is supplied from the electricity-feeding section to the electricity-receiving section by electromagnetism coupling.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a substrate processing apparatus, and more particularly, to a substrate processing apparatus for etching a surface of a substrate such as a silicon wafer by utilizing plasma, and for forming a thin film on the surface of the substrate by utilizing plasma. 
     2. Description of the Related Art 
     As a substrate processing apparatus for processing a silicon wafer utilizing plasma, there is an apparatus as shown in  FIGS. 1 and 2 .  FIG. 1  is a schematic explanatory transverse sectional view of a vertical type substrate processing furnace of a conventional substrate processing apparatus.  FIG. 2  is a schematic vertical sectional view taken along the line A-A in  FIG. 1 . 
     A thin and long buffer chamber  237  is provided in a vertical direction near an inner wall surface of a reaction tube  203 . In the buffer chamber  237 , two rod-like discharge electrodes  269  covered with electrode protection tubes  275  made of dielectric, and a gas nozzle  233  for obtaining a uniform gas flow in the buffer chamber  237  are disposed. 
     High frequency electric power generated by an oscillator of a high frequency power supply  273  is applied to ends  301  of the discharge electrodes  269  to generate plasma  224  between the discharge electrodes  269  in the buffer chamber  237 , and thereby to excite reaction gas supplied from a gas nozzle  233  with plasma, and the plasma-excited reaction gas is supplied to wafers  200  which are substrates to be processed in the reaction tube  203  from a gas supply hole  248   a  formed in a sidewall of the buffer chamber  237 . 
     While the wafers  200  are processed, gas in the electrode protection tubes  275  is continuously replaced by inert gas to prevent the discharge electrode from being oxidized. 
     However, the inside of the reaction tube  203  is heated to about 600 to 900° C. to process the wafers  200 , and as a result, the discharge electrodes  269  are discolored or deteriorated due to slight residual oxygen in the inert gas in the electrode protection tubes  275  or a sealing failure at a portion from which the discharge electrode  269  is pulled outside, and the performance of the electrodes can not be maintained. 
     As conventional techniques, other than the above-described technique, there are one in which a flexible electrode (weaved electrode) is used (Japanese Patent Application No. 2004-055446 (International Application No. PCT/JP 2005/002306)), and one in which high frequency electric power is supplied through a power transformer (Japanese Patent Application No. 2003-056772 (International Application No. PCT/JP 2004/002735, International Laid-open No. WO2004/079813)).
     [Patent document 1] Japanese Patent Application No. 2004-055446 (International Application No. PCT/JP 2005/002306)   [Patent document 2] Japanese Patent Application No. 2003-056772 (International Application No. PCT/JP 2004/002735, International Laid-open No. WO2004/079813)   

     SUMMARY OF THE INVENTION 
     Hence, it is a main object of the present invention to provide a substrate processing apparatus for plasma-exciting processing gas to process one or more substrates, which can prevent or restrain discharge electrodes for plasma-exciting the processing gas from being deteriorated, and which can increase the lifetime of the discharge electrodes. 
     According to one aspect of the present invention, there is provided a substrate processing apparatus, comprising: 
     a processing chamber to accommodate one or more substrates; 
     a heating section disposed such as to surround the processing chamber from outside; 
     a gas supply section to supply processing gas into the processing chamber; 
     a gas discharge section to discharge the processing gas from the processing chamber; 
     at least a pair of electrodes provided inside the heating section to plasma-excite the processing gas; 
     a protection container made of dielectric to air-tightly accommodate the electrodes; 
     an electricity-receiving section which is electrically connected to the electrodes and which is accommodated in the protection container; and 
     an electricity-feeding section to which high frequency electric power is applied and which is provided near the electricity-receiving section in a state in which at least a wall of the protection container is interposed between the electricity-receiving section and the electricity-feeding section, wherein 
     electric power is supplied from the electricity-feeding section to the electricity-receiving section by electromagnetism coupling. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic transverse sectional view for explaining a vertical type substrate processing furnace of a conventional substrate processing apparatus. 
         FIG. 2  is a schematic vertical sectional view taken along the line A-A in  FIG. 1 . 
         FIG. 3  is a schematic vertical sectional view for explaining a vertical type substrate processing furnace of a substrate processing apparatus according to a preferred first embodiment of the present invention. 
         FIG. 4  is a schematic transverse sectional view for explaining a vertical type substrate processing furnace of a substrate processing apparatus according to a preferred first embodiment of the invention. 
         FIG. 5  is a schematic vertical sectional view taken along the line B-B in  FIG. 4 . 
         FIG. 6  is a schematic vertical sectional view taken along the line C-C in  FIG. 4 . 
         FIG. 7  is a schematic perspective view for explaining the substrate processing apparatuses according to preferred first to fifth embodiments of the present invention. 
         FIG. 8  is a schematic vertical sectional view for explaining the substrate processing apparatuses according to the preferred first to fifth embodiments of the present invention. 
         FIG. 9  is a schematic transverse sectional view for explaining a vertical type substrate processing furnace of a substrate processing apparatus according to the preferred second embodiment of the present invention. 
         FIG. 10  is a schematic vertical sectional view taken along the line D-D in  FIG. 9 . 
         FIG. 11  is a schematic vertical sectional view taken along the line E-E in  FIG. 9 . 
         FIG. 12  is a schematic transverse sectional view for explaining a vertical type substrate processing furnace of a substrate processing apparatus according to the preferred third embodiment of the present invention. 
         FIG. 13  is a schematic vertical sectional view taken along the line F-F in  FIG. 12 . 
         FIG. 14  is a schematic vertical sectional view taken along the line G-G in  FIG. 12 . 
         FIG. 15  is a schematic transverse sectional view for explaining a vertical type substrate processing furnace of a substrate processing apparatus according to the preferred fourth embodiment of the invention. 
         FIG. 16  is a schematic vertical sectional view taken along the line H-H in  FIG. 15 . 
         FIG. 17  is a schematic vertical sectional view taken along the line I-I in  FIG. 15 . 
         FIG. 18  is a schematic transverse sectional view for explaining a vertical type substrate processing furnace of a substrate processing apparatus according to the preferred fifth embodiment of the present invention. 
         FIG. 19  is a schematic vertical sectional view taken along the line J-J in  FIG. 18 . 
         FIG. 20  is a schematic vertical sectional view taken along the line K-K in  FIG. 18 . 
         FIG. 21  is a schematic vertical sectional view for explaining a structure of a resonance capacitor  343  used in the substrate processing apparatus of the preferred fifth embodiment of the present invention. 
         FIG. 22  is a circuit diagram of a discharge electric power supply circuit used in the substrate processing apparatus of the preferred fifth embodiment of the invention. 
         FIG. 23  is an equivalent circuit diagram in  FIG. 22 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Next, preferred embodiments of the present invention will be explained. 
     In the preferred embodiments of the present invention, an apparatus includes a vertical type reaction tube for processing layered substrates, a gas supply system for supplying a plurality of processing gases to the substrates, a buffer chamber which once stores gas to be supplied to the substrates from the gas supply system and equally supplies the gas to the layered substrates, and a pair of capacitive coupling electrodes for producing plasma in the buffer chamber. The electrodes for producing plasma are sealed in electrode protection tubes made of insulator disposed in the buffer chamber. Discharge electric power is supplied to the electrodes sealed in the electrode protection tubes disposed in the buffer chamber by inductive coupling. 
     Next, the preferred embodiments of the invention will be explained in more detail with reference to the drawings. 
     First, film forming processing using an ALD (Atomic Layer Deposition) method which was carried out in the embodiments will be explained briefly. 
     According to the ALD method, raw material gases of two kinds (or more) of gases used for forming a film are alternately supplied onto a substrate one kind by one kind under given film forming conditions (temperature, time and the like), the gases are adsorbed in one atomic unit, and the film is formed utilizing surface reaction. 
     When a SiN (silicon nitride) film is to be formed for example, in the ALD method, the utilized chemical reaction can form the film of high quality at low a temperature in a range of 300 to 600° C. using DCS (SiH 2 Cl 2 , dichlorsilane) and NH 3  (ammonia). The plurality kinds of reaction gases are alternately supplied one kind by one kind. The film thickness is controlled based on the number of supply cycles of reaction gases (for example, if the film forming speed is 1 Å/cycle, the processing is carried out by 20 cycles when a film of 20 Å is to be formed). 
     First Embodiment 
       FIG. 3  is a schematic diagram for explaining a structure of a vertical type substrate processing furnace of the present embodiment, and shows a processing furnace portion in vertical cross section.  FIG. 4  is a schematic diagram for explaining a structure of the vertical type substrate processing furnace of the present embodiment, and shows the processing furnace portion in transverse cross section.  FIG. 5  is a schematic vertical sectional view taken along the line B-B in  FIG. 4 .  FIG. 6  is a schematic vertical sectional view taken along the line C-C in  FIG. 4 . 
     A quartz reaction tube  203  as a reaction container is provided inside a heater  207  which is heating means. The reaction tube  203  processes wafers  200  as substrates. A lower end opening of the reaction tube  203  is air-tightly closed by a seal cap  219  which is a lid through an O-ring  220  as an airtight member. A thermal insulation member  208  is provided outside the reaction tube  203  and the heater  207 . The thermal insulation member  208  covers an upper end of the heater  207 . At least the heater  207 , the thermal insulation member  208 , the reaction tube  203  and the seal cap  219  form a processing furnace  202 . The reaction tube  203 , the seal cap  219  and a later-described buffer chamber  237  formed in the reaction tube  203  form a processing chamber  201 . A boat  217  which is substrate-holding means stands on the seal cap  219  through a quartz cap  218 . The quartz cap  218  functions as a holding body which holds the boat  217 . The boat  217  is inserted into the processing furnace  202 . A plurality of wafers  200  to be batch processed are stacked on the boat  217  in the vertical direction in many layers in an axial direction of the tube in their horizontal attitudes. The heater  207  heats the wafers  200  inserted into the processing furnace  202  to a predetermined temperature. 
     The processing furnace  202  is provided with two gas supply tubes  232   a  and  232   b  as supply tubes for supplying a plurality kinds (two kinds, in this embodiment) of gases to the processing furnace  202 . A reaction gas is supplied from a gas supply tube  232   a  to the processing chamber  201  through a mass flow controller  241   a  which is a flow rate control means, and a valve  243   a  which is an open/close valve, and the buffer chamber  237  formed in the reaction tube  203 . Further, another reaction gas is supplied to the processing chamber  201  from a gas supply tube  232   b  through a mass flow controller  241   b  which is a flow rate control means, a valve  243   b  which is an open/close valve, a gas reservoir  247 , a valve  243   c  which is an open/close valve, and a later-described gas supply section  249 . 
     Tube heaters (not shown) are mounted on the two gas supply tubes  232   a  and  232   b , which are capable of heating the gas supply tubes to about 120° C., for preventing NH 4 Cl, which is a reaction by-product, from adhering to the tubes. 
     The processing chamber  201  is connected to a vacuum pump  246  which is exhausting means through a valve  243   d  by a gas exhaust tube  231  which is an exhaust tube through which gas is exhausted so that the processing chamber  201  is evacuated. The valve  243   d  is an open/close valve, and the processing chamber  201  can be evacuated and the evacuation can be stopped by opening and closing the valve  243   d . If the opening of the valve is adjusted, the pressure in the processing chamber  201  can be adjusted. 
     The buffer chamber  237  which is a gas dispersing space is provided in an arc space between the reaction tube  203  constituting the processing chamber  201  and the wafers  200 . The buffer chamber  237  is provided along the stacking direction of the wafers  200  and along an inner wall of the reaction tube  203  from a lower portion to a higher portion of the reaction tube  203 . Gas supply holes  248   a  which are supply holes through which gas is supplied are formed in an inner wall of the buffer chamber  237  near an end portion of the inner wall adjacent to the wafers  200 . The gas supply holes  248   a  are opened toward the center of the reaction tube  203 . The gas supply holes  248   a  have the same opening areas over a predetermined length from a lower portion to an upper portion along the stacking direction of the wafers  200 , and pitches between the gas supply holes  248   a  are equal to each other. 
     A nozzle  233  is disposed near another end of the buffer chamber  237  on the opposite side from the end of the buffer chamber  237  where the gas supply holes  248   a  are provided. The nozzle  233  is disposed along the stacking direction of the wafers  200  from the lower portion to the upper portion of the reaction tube  203 . The nozzle  233  is provided with a plurality of gas supply holes  248   b  which are supply holes through which gas is supplied. The plurality of gas supply holes  248   b  are disposed along the stacking direction of the wafers  200  over the same predetermined length as that of the gas supply holes  248   a . The plurality of gas supply holes  248   b  and the plurality of gas supply holes  248   a  are disposed at corresponding locations, respectively. 
     When a pressure difference between the buffer chamber  237  and the processing furnace  202  is small, it is preferable that the opening areas of the gas supply holes  248   b  are equal to each other from an upstream side to a downstream side and opening pitches are the same, but when the pressure difference is large, it is preferable that the opening area is increased or the opening pitches are reduced from the upstream side toward the downstream side. 
     By adjusting the opening areas or opening pitches of the gas supply holes  248   b  from the upstream side to the downstream side, gas is ejected with a substantially uniform flow rate although the velocities of flows of the gas through the respective gas supply holes  248   b  are different from each other. The gas ejected from the gas supply holes  248   b  is ejected into the buffer chamber  237 . The gas is once introduced into the buffer chamber  237 , which makes it possible to equalize the velocities of flows of gases. 
     That is, in the buffer chamber  237 , the particle velocity of the gas ejected from each gas supply hole  248   b  is moderated in the buffer chamber  237  and then, the gas is ejected into the processing chamber  201  from the gas supply hole  248   a . During that time, the gas ejected from each gas supply hole  248   b  becomes gas having an equal flow rate and a equal velocity of flow when the gas is ejected from the gas supply hole  248   a.    
     A pair of thin and long rod-like discharge electrodes  269  are disposed in the buffer chamber  237  from the upper portion to the lower portion of the buffer chamber  237 . Lower ends of the two discharge electrodes  269  are connected to a coupling coil  311  at a lower portion of the reaction tube  203 . The discharge electrodes  269  and the coupling coil  311  are air-tightly sealed and covered with the electrode protection tubes  275  made of dielectric. Inert gas is charged into the electrode protection tubes  275 , and the inert gas is sealed in the electrode protection tubes  275 . 
     An induction coil  312  connected to the high frequency power supply  273  through the matching device  272  is disposed outside the reaction tube  203 , and the induction coil  312  is inductive-coupled to the coupling coil  311 . High frequency electric power from the high frequency power supply  273  is transferred to the discharge electrodes  269  through the induction coil  312  and the coupling coil  311  to generate plasma  224  at an opposed portion of the discharge electrodes  269 . 
     The discharge electrodes  269  are sealed in the electrode protection tubes  275  in which inert gas is sealed. This prevents oxygen from being mixed from outside, and deterioration of the electrodes by oxidation can be prevented or restrained. Electric connection to the discharge electrodes  269  is eliminated. Therefore, it is possible to prevent the discharge electrodes from being damaged at the time of maintenance of the reaction tube. 
     A gas supply section  249  is formed on an inner wall separated from the position of the gas supply holes  248   a  by about 120° along an inner periphery of the reaction tube  203 . The gas supply section  249  is a supply section which shares the gas supply species with the buffer chamber  237  when the plurality kinds of gases are alternately supplied to the wafers  200  one kind by one kind when films are formed by the ALD method. 
     Like the buffer chamber  237 , the gas supply section  249  also has gas supply holes  248   c  which are supply holes through which gas is supplied to positions adjacent to the wafers at the same pitch, and the gas supply section  249  is connected to a gas supply tube  232   b  at a lower portion thereof. 
     When a pressure difference between the buffer chamber  237  and the processing chamber  201  is small, it is preferable that the opening areas of the gas supply holes  248   c  are equal to each other from the upstream side to the downstream side and the opening pitches are the same, but when the pressure difference is large, it is preferable that the opening area is increased or the opening pitches are reduced from the upstream side toward the downstream side. 
     The boat  217  is provided at a central portion in the reaction tube  203 , and the plurality of wafers  200  are placed in many layers at equal distances from one another in the vertical direction. The boat  217  can be brought into and out from the reaction tube  203  by a boat elevator mechanism (not shown). To enhance the uniformity of the processing, a boat rotating mechanism  267  which is a rotating means for rotating the boat  217  is provided. By rotating the boat rotating mechanism  267 , the boat  217  held by the quartz cap  218  is rotated. 
     A controller  321  which is a control means is connected to the mass flow controllers  241   a  and  241   b , the valves  243   a ,  243   b ,  243   c  and  243   d , the heater  207 , the vacuum pump  246 , the boat rotating mechanism  267 , the boat elevator  121 , the high frequency power supply  273  and the matching device  272 . The controller  321  adjusts flow rates of the mass flow controllers  241   a  and  241   b , opens and closes valves  243   a ,  243   b  and  243   c , opens and closes the valve  243   d , performs a pressure adjustment operation of the valve  243   d , opens and closes a regulator  302 , adjusts a pressure of the regulator  302 , adjusts the temperature of the heater  207 , actuates and stops the vacuum pump  246 , adjusts rotation of the boat rotating mechanism  267 , controls a vertical motion of the boat elevator  121 , controls supply of electric power of the high frequency power supply  273 , and controls impedance by the matching device  272 . 
     Next, an example of the film forming operation by the ALD method will be explained based on a case wherein SiN films are formed using DCS gas and NH 3  gas. 
     First, wafers  200  on which films are to be formed are mounted on the boat  217 , and the boat  217  is brought into the processing furnace  202 . Then, the following three steps are carried out in sequence. 
     [Step 1] 
     In step 1, NH 3  gas which is required to be plasma-excited, and DCS gas which is not required to be plasma-excited are fed together. First, the valve  243   a  provided in the gas supply tube  232   a  and the valve  243   d  provided in the gas exhaust tube  231  are both opened, NH 3  gas whose flow rate is adjusted by the mass flow controller  243   a  is sent from the gas supply tube  232   a  and ejected into the buffer chamber  237  from the gas supply holes  248   b  of the nozzle  233 , high frequency electric power is applied between the discharge electrodes  269  from the high frequency power supply  273  through the matching device  272 , the induction coil  312  and the coupling coil  311 , and the gas is supplied to the processing chamber  201  as active species and in this state, gas is exhausted from the gas exhaust tube  231 . When flowing the NH 3  gas by plasma-exciting the NH 3  gas, the valve  243   d  is appropriately adjusted, and a pressure in the processing chamber  201  is adjusted to 10 to 100 Pa. A supply flow rate of NH 3  controlled by the mass flow controller  241   a  is in a range of 1,000 to 10,000 sccm. Time during which the wafers  200  are exposed to active species obtained by plasma-exciting NH 3  is in a range of 2 to 120 seconds. The temperature of the heater  207  at that time is set such that the temperature of the wafer becomes 500 to 600° C. Since the reaction temperature of NH 3  is high, the NH 3  does not react at the temperature of the wafer. Therefore, NH 3  is fed as active species by plasma-exciting the same, which makes it possible to feed the NH 3  while keeping the wafers at the set low temperature range. 
     When NH 3  is plasma-excited and fed as active species, the valve  243   b  located upstream of the gas supply tube  232   b  is opened and the valve  243   c  located downstream is closed so that DCS flows also. With this, DCS is stored in the gas reservoir  247  provided between the valves  243   b  and  243   c . Gas flowing into the processing chamber  201  is the active species obtained by plasma-exciting the NH 3 , and DCS does not exist. Therefore, NH 3  does not generate a vapor-phase reaction, and the NH 3  which becomes the active species by plasma excitation surface-reacts with a foundation film on the wafer  200 . 
     [Step 2] 
     In step 2, the valve  243   a  of the gas supply tube  232   a  is closed to stop the supply of NH 3 , but the supply to the gas reservoir  247  is continued. If a predetermined amount of DCS having a predetermined pressure is stored in the gas reservoir  247 , the upstream valve  243   b  is also closed, and DCS is confined in the gas reservoir  247 . The valve  243   d  of the gas exhaust tube  231  is held opened, the processing chamber  201  is evacuated by the vacuum pump  246  to 20 Pa or lower, and remaining NH 3  is exhausted from the processing chamber  201 . At that time, if inert gas such as N 2  is supplied to the processing chamber  201 , the effect for exhausting the residual NH 3  is further enhanced. The DCS is stored in the gas reservoir  247  such that the pressure therein becomes 20,000 Pa or higher. Further, the apparatus is constituted such that the conductance between the gas reservoir  247  and the processing chamber  201  becomes 1.5×10 −3  m 3 /s or higher. If a ratio between a capacity of the reaction tube  203  and a capacity of the gas reservoir  247  is considered, when the capacity of the reaction tube  203  is 1.00 l (100 liters), it is preferable that the capacity of the gas reservoir  247  is in a range of 100 to 300 cc, and it is preferable that as the capacity ratio, the capacity of the gas reservoir  247  is 1/1,000 to 3/1,000 times of the capacity of the reaction chamber. 
     [Step 3] 
     If the exhausting operation of the processing chamber  201  is completed, the valve  243   c  of the gas exhaust tube  231  is closed to stop the exhausting operation. The valve  243   c  located downstream of the gas supply tube  232   b  is opened. With this, DCS stored in the gas reservoir  247  is supplied to the processing chamber  201  at a dash. At that time, since the valve  243   d  of the gas exhaust tube  231  is closed, the pressure in the processing chamber  201  is increased abruptly to about 931 Pa (7 Torr). Time during which DCS was supplied is set to two to four seconds, and time during which the wafers are exposed to the increased pressure atmosphere is set to two to four seconds, and total time is set to six seconds. The temperature of the wafers at that time is the same as the temperature when NH 3  is supplied, i.e., 500 to 600° C. By supplying the DCS, the NH 3  and the DCS on the foundation film surface-react with each other, and SiN films are formed on the wafers  200 . After the films are formed, the valve  243   c  is closed and the valve  243   d  is opened, and the processing chamber  201  is evacuated, and residual DCS gas which contributed to the formation of films is exhausted. At that time, if inert gas such as N 2  is supplied to the processing chamber  201 , the effect for exhausting the residual DCS gas after it contributed to the formation of films from the processing chamber  201  is enhanced. The valve  243   b  is opened and supply of DCS into the gas reservoir  247  is started. 
     The above steps 1 to 3 are defined as one cycle, and this cycle is repeated a plurality of times, and SiN films each having a predetermined thickness are formed on the wafers. 
     In the ALD apparatus, gas is adsorbed on a foundation film surface. The adsorption amount of gas is proportional to pressure of gas and exposure time of gas. Therefore, in order to adsorb a desired amount of gas for a short time, it is necessary to increase the pressure of gas for a short time. In the embodiment, since DCS stored in the gas reservoir  247  is momentarily supplied in a state where the valve  243   d  is closed, the pressure of DCS in the processing chamber  201  can be increased abruptly, and a desired amount of gas can be adsorbed momentarily. 
     In the embodiment, NH 3  gas is plasma-excited and supplied as active species and the processing chamber  201  is evacuated while DCS is stored in the gas reservoir  247 . Such operations are necessary steps in the ALD method. Therefore, a special step for storing the DCS is not required. Further, the processing chamber  201  is evacuated and NH 3  gas is removed and then, DCS flows. Therefore, these gases do not react when they are sent toward the wafers  200 . The supplied DCS can effectively react only with NH 3  which is adsorbed on the wafers  200 . 
     Next, an outline of the substrate processing apparatus of the embodiment will be explained with reference to  FIGS. 7 and 8 . 
     A cassette stage  105  as a holder delivery member which delivers cassettes  100  as substrate accommodating containers to and from an external transfer device (not shown) is provided on a front side in a case  101 . A cassette elevator  115  as elevator means is provided behind the cassette stage  105 . A cassette transfer device  114  as transfer means is mounted on the cassette elevator  115 . Cassette shelves  109  as mounting means of the cassettes  100  are provided behind the cassette elevator  115 . Auxiliary cassette shelves  110  are also provided above the cassette stage  105 . A clean unit  118  is provided above the auxiliary cassette shelves  110  and clean air flows through the case  101 . 
     The processing furnace  202  is provided on the rear side and at an upper portion in the case  101 . The boat elevator  121  as elevator means is provided below the processing furnace  202 . The boat elevator  121  vertically brings the boat  217  as the substrate holding means into and from the processing furnace  202 . The boat  217  holds the wafers  200  as substrates in many layers in their horizontal attitudes. The seal cap  219  as a lid is mounted on a tip end of the elevator member  122  which is mounted on the boat elevator  121 , and the seal cap  219  vertically supports the boat  217 . A transfer elevator  113  as elevator means is provided between the boat elevator  121  and the cassette shelf  109 , and a wafer transfer device  112  as transfer means is mounted on the transfer elevator  113 . A furnace opening shutter  116  as closing means which air-tightly closes a lower side of the processing furnace  202  is provided beside the boat elevator  121 . The furnace opening shutter  116  has an opening/closing mechanism. 
     The cassette  100  in which wafers  200  are loaded is transferred onto the cassette stage  105  from an external transfer device (not shown) in such an attitude that the wafers  200  are oriented upward, and the cassette  100  is rotated by the cassette stage  105  by 90° such that the wafers  200  are oriented horizontally. The cassette  100  is transferred from the cassette stage  105  onto the cassette shelf  109  or the auxiliary cassette shelf  110  by a combination of vertical and lateral motions of the cassette elevator  115 , and advancing and retreating motions and a rotation motion of the cassette transfer device  114 . 
     Some of the cassette shelves  109  are transfer shelves  123  in which cassettes  100  to be transferred by the wafer transfer device  112  are accommodated. Cassettes  100  to which the wafers  200  are transferred are transferred to the transfer shelf  123  by the cassette elevator  115  and the cassette transfer device  114 . 
     If the cassette  100  is transferred to the transfer shelf  123 , the transfer shelf  123  transfers the wafers  200  to the lowered boat  217  by a combination of advancing and retreating motions and a rotation motion of the wafer transfer device  112 , and a vertical motion of the transfer elevator  113 . 
     If a predetermined number of wafers  200  are transferred to the boat  217 , the boat  217  is inserted into the processing furnace  202  by the boat elevator  121 , and the seal cap  219  air-tightly closes the processing furnace  202 . The wafers  200  are heated in the air-tightly closed processing furnace  202 , processing gas is supplied into the processing furnace  202 , and the wafers  200  are processed. 
     If the processing of the wafers  200  is completed, the wafers  200  are transferred to the cassette  100  of the transfer shelf  123  from the boat  217 , the cassette  100  is transferred to the cassette stage  105  from the transfer shelf  123  by the cassette transfer device  114 , and is transferred out from the case  101  by the external transfer device (not shown) through the reversed procedure. When the boat  217  is in its lowered state, the furnace opening shutter  116  air-tightly closes the lower surface of the processing furnace  202  to prevent outside air from being drawn into the processing furnace  202 . 
     The transfer motions of the cassette transfer device  114  and the like are controlled by transfer control means  124 . 
     Second Embodiment 
     Referring to  FIGS. 9 to 11 , two discharge electrodes  269  are connected to electrostatic coupled plates  331  at a lower portion of the reaction tube  203 . The discharge electrodes  269  and the electrostatic coupled plates  331  are covered with a dielectric tube (electrode protection tube)  275  and an inner wall of the reaction tube  203 , and the dielectric tube  275  is filled with inert gas. Electric power supply plates  332  connected to a transmitter (high frequency power supply)  273  is disposed outside the reaction tube  203 . The electric power supply plates  332  are disposed at a position where the electric power supply plates  332  are electrostatically coupled to the electrostatic coupled plates  331 . The high frequency electric power of the transmitter  273  is transferred to the discharge electrodes  269  through the electric power supply plates  332  and the electrostatic coupled plates  331 , and plasma  224  is generated at the opposed portions of the discharge electrodes. 
     If each of the electric power supply plates and the electrostatic coupled plates has an area of 10,000 mm 2  (10 cm×10 cm) and a quartz glass having a thickness of 5 mm is sandwiched between the plates, the capacity becomes about 70 PF, which allows high frequency current to be transferred sufficiently. Current is slightly varied depending upon the shape of the discharge electrodes, though. At that time, it is necessary for the dielectric protection tubes  276 , in which the electrodes are disposed, to be filled with inert gas having a sufficient pressure. If the pressure is insufficient, there is a possibility that electric discharge is generated in the dielectric protection tube. Although there is no problem if the pressure is 100 Torr or higher, it is preferable that the pressure is equal to the atmospheric pressure (760 Torr) or higher. 
     The inert gas is filled in the following manner. That is, an inert gas charging port  23  is provided when the reaction tube is produced, and after the reaction tube is completed, gas in the dielectric protection tube is purged and then, the inert gas having a predetermined pressure is filled, and the sealing port  23  is sealed. 
     Third Embodiment 
     Referring to  FIGS. 12 to 14 , the two discharge electrodes  269  are connected to the coupling coil  311  at a lower portion of the reaction tube  203 . The discharge electrodes  269  and the coupling coil  311  are covered with the dielectric tube  275  and an inner wall of the reaction tube  203 , and the dielectric tube  275  is filled with inert gas. The induction coil  312  connected to the transmitter  273  is disposed outside the reaction tube  203 , and is inductive coupled to the coupling coil  311 . High frequency electric power of the transmitter  273  is transferred to the discharge electrode  269  through the induction coil  312  and the coupling coil  311 , and plasma  224  is generated at the opposed portions of the discharge electrodes. When circular coils of φ60 were used as the induction coil and the coupling coil, and a quartz glass having a thickness of 5 mm was sandwiched between the coils, discharge could be generated between the discharge electrodes with high frequency electric power of 300 W in nitrogen gas atmosphere of 1 Torr. 
     Fourth Embodiment 
     As a method for enhancing the transfer efficiency of high frequency electric power, there is a method in which solenoid coils are disposed concentrically so as to couple the induction coil  342  and the coupling coil  341  more densely (see  FIGS. 15 to 17 ). 
     Fifth Embodiment 
     Referring to  FIGS. 18 to 20 , the two discharge electrodes  269  are connected to a coupling coil  341  at a lower portion of the reaction tube  203 . The discharge electrodes  269  are covered with the dielectric tube  275  and the inner wall of the reaction tube  203 . The coupling coil  341  is disposed in a form of solenoid along the inner wall of the quartz projected in a columnar shape from the wall of the reaction tube. The resonance capacitor  343  is disposed at a backdeep of the coupling coil  341 , and the electrodes of the resonance capacitor  343  is connected to the coupling coil  341 . 
     The resonance capacitor  343  is disposed in the reaction tube, and is heated to a temperature as high as 600° C. Therefore, quartz plates  345  of about 2 to 5 mm are respectively sandwiched between sheets  344  of a metal having a high melting point such as Ni as shown in  FIG. 21 . An area of the metal sheet, and the number of laminated metal sheets or quartz sheets are adjusted in accordance with a necessary capacity. 
       FIG. 22  is a circuit diagram, and  FIG. 23  shows an equivalent circuit. If inductances of the induction coil  342  and the coupling coil  341  are defined as “L”, and coupling coefficients of the induction coil  342  and the coupling coil  341  are defined as “K”, a leakage inductance is expressed as “(1−K)L”. When there is an insulator such as quartz between the induction coil  342  and the coupling coil  341  in this manner, the coupling coefficient K is small and the leakage inductance  346  becomes large. When the leakage inductance  346  and the resonance capacitor  343  are not in a resonance state, applied voltage from the oscillator  273  is simply divided by the leakage inductance  346  and the resonance capacitor  343 . Therefore, voltage sufficient for a plasma electrode  269  is not applied. 
     When the leakage inductance  346  and the resonance capacitor  343  are in the resonance state, magnetic energy of current flowing through the leakage inductance  346  is converted into electric field energy by resonance phenomenon, and it is converted into voltage between terminals of the resonance capacitor  343 . With this, the supply electric power from the oscillator  273  efficiently becomes energy for producing plasma. 
     When capacitance itself between the discharge electrodes  269  can be regarded as the resonance capacitor (when leakage inductance  346  and capacitance between the discharge electrodes  269  are in a resonance state), the external resonance capacitor  343  is unnecessary. 
     As a means for maintaining the resonance state of the leakage inductance  346  and the resonance capacitor  343 , there is a method in which oscillation frequency of the oscillator  273  is adjusted in accordance with a phase difference between voltage and current applied to the induction coil  342  so that the oscillation frequency is made equal to the resonance frequency, or the leakage inductance is changed by adjusting the position of the induction coil  342  with respect to the coupling coil  341  so that the resonance frequency is made equal to the oscillation frequency. 
     As explained above, according to the preferred embodiments, the discharge electrodes are sealed in the reaction tube, thereby preventing oxygen from being mixed into from outside, and deterioration of the electrodes by oxidation can be prevented. 
     Since there is no electrical contact with the electrodes, it is possible to prevent the discharge electrode ends from being damaged at the time of maintenance of the reaction tube. 
     If the resonance capacitor is added on the secondary side of the coupling coil and the electric power is transferred in the resonance state as in the fifth embodiment, it is possible to efficiently transfer electric power to the coupling coil from the induction coil. 
     Since the electrodes are air-tightly sealed in the protection container, the maintenance operation or the exchanging operation of the electrodes becomes unnecessary. With this, since it becomes unnecessary to detach the electrodes at the time of maintenance, a trouble (problem that repeatability of electrode position does not appear) caused when the electrodes are again inserted is not generated. 
     Since the electrodes are air-tightly sealed in the protection container and thus it becomes unnecessary to detach the electrodes, and therefore simple rod-like electrodes can be used. It is unnecessary to employ the weaved structure for obtaining flexibility like the above-described Japanese Patent Application No. 2004-055446 (International Application No. PCT/JP 2005/002306), and it is only necessary that the surface areas are the same. 
     By the dielectric coupling or electrostatic coupling, abnormal discharge in the reaction chamber can be suppressed like the case where electric power is supplied through a power transformer of the prior application of Japanese Patent Application No. 2003-056772 (International Application No. PCT/JP 2004/002735, International Laid-open No. WO2004/079813). 
     The entire disclosure of Japanese Patent Application 2004-379002 filed on Dec. 28, 2004 including description, claims, drawings and abstract are incorporated herein by reference. 
     While various typical embodiments of the present invention have been shown and described, the present invention is not limited to these embodiments. Thus, the scope of the invention can only be limited by the following claims. 
     As described above, the deterioration of discharge electrodes for plasma-exciting the processing gas can be prevented or restrained, and the lifetime of the discharge electrodes can be increased according to preferred embodiments of the present invention. Hence, the present invention is particularly suitable for a substrate processing apparatus for plasma-exciting processing gas to process a substrate.