Abstract:
A method of operating an on-off valve comprises closing one of two openings of a valve body with a seal member of a closure element within the valve body, the valve body being within an evacuation pipe connected between a process chamber and an evacuation apparatus; moving the closure element, using a linear driver, so that the seal member is moved away from the one of the two openings; and positioning the closure element into a retreat portion in an surface of the valve body, using the linear driver and a pivotal driver adapted to pivot the closure element between the one of the two openings and the retreat portion, so that the seal member is closed inside a protection seal member of the closure element to surround the seal member, thereby preventing the seal member from being directly exposed to the process gas.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is a divisional application under 35 U.S.C. 121 of U.S. patent application Ser. No. 12/076,129 filed on Mar. 14, 2008, now U.S. Pat. No. 8,123,194 which claims the benefit of the priority based on Japanese Patent Application No. 2007-070362, the entire contents of which are hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an on-off valve provided between an evacuation apparatus and a process chamber in which a semiconductor wafer or the like is processed under reduced pressure, and to a process apparatus employing the on-off valve. 
     2. Description of the Related Art 
     When semiconductor devices are fabricated, various vacuum processes including a thin film deposition process, an etching process, and the like are carried out in process apparatuses having a chamber that can be evacuated to reduced pressure. A semiconductor wafer, which will be subjected to one or more of the above processes, is transferred into the chamber, and undergoes predetermined processes while the chamber is evacuated by an evacuation apparatus such as a vacuum pump connected to the chamber via a vacuum line. 
     During the process in the chamber, the chamber pressure is controlled by adjusting the degree of opening a pressure control valve located in the vacuum line between the chamber and the vacuum pump. 
     In addition to the pressure control valve, an on-off valve is provided upstream or downstream of the vacuum pump in the vacuum line, in order to prevent the interior of the vacuum line from being unduly exposed to the atmosphere when the process apparatus and/or the vacuum apparatus is down for maintenance. 
     An example of such an on-off valve is disclosed in Patent Document 1 (Japanese Patent Application Laid-Open Publication No. H09-89139). As described in the publication, a conventional on-off valve is closed when a closure element comes in tight contact with a valve seat having an opening in order to close the opening, and opened when the closure element comes off the valve seat in order to allow a gas flow path through the opening. In order to ensure a tight closure of the valve, a ring-shaped seal member made of an elastic material is attached on the closure element. The seal member is elastically deformed when the closure element is pressed onto the valve seal in order to fully eliminate a gap between the closure element (the sealing member) and the valve seat. 
     Patent Document 1: Japanese Patent Application Laid-Open Publication No. H09-89139 
     In the above conventional on-off valve, since the closure element is linearly movable, the closure element is positioned away from the valve seat in order to face the opening of the valve seat when the valve is open. Therefore, the seal member attached on the closure element of the on-off valve is exposed to gases including CF gas and O 2  gas, which are used as a process gas or a cleaning gas in the process chamber of the process apparatus employing the on-off valve, when the on-off valve is open. Due to the exposure to the gases or to active species (radicals, ions) activated by plasma in the process chamber, the seal member may become deteriorated, so that sealing performance is impaired and particles may be caused to break off. As a result, the process apparatus has to be frequently down for maintenance in order to replace the seal members of the on-off valve. 
     In order to reduce the frequency of seal member replacements, a seal member made of a fluorinated rubber, which has high resistance to plasma and/or active species, is being used in response to a recent trend of high energy plasma being used in plasma processes. However, even such a seal member is not free from deterioration, which requires replacement of the seal member, for example, every several months. In addition, the seal member made of the fluorinated rubber is very expensive, which may increase maintenance costs. Moreover, since the process apparatus has to be down for maintenance when the seal members are being replaced, total fabrication throughput is impaired. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in view of the above, and is directed to an on-off valve that can lengthen the working life of the seal member, and a process apparatus employing the on-off valve. 
     A first aspect of the present invention provides an on-off valve provided between an evacuation apparatus and a process chamber that can be evacuated to reduced pressure by the evacuation apparatus. The on-off valve includes a valve body having two openings that may place the process chamber and the evacuation apparatus in pressure communication with each other; a closure element located inside the valve body and adapted to close one of the two openings; a seal member provided in the closure element and adapted to seal the one of the two openings when the closure element closes the one of the two openings; a linear motion driver that linearly moves the closure element; a retreat portion located away from the two openings; and a pivotal motion driver adapted to pivot the closure element between a first position corresponding to the one of the two openings and a second position corresponding to the retreat portion, where the closure element is moved to the retreat portion by the linear motion driver and the pivotal motion driver in order to be located in the retreat portion when the closure element is away from the one of the two openings. 
     A second aspect of the present invention provides an on-off valve according to the first aspect, where the retreat portion is located in an inner wall portion of the valve body, the inner wall portion being away from the two openings, and wherein the linear motion driver linearly moves the closure element to the retreat portion. 
     A third aspect of the present invention provides an on-off valve according to the first or the second aspect, where the linear motion driver includes a cam mechanism. 
     A fourth aspect of the present invention provides an on-off valve according to the third aspect, where the cam mechanism is a plate cam having a groove formed therein. 
     A fifth aspect of the present invention provides an on-off valve according to any one of the first through the fourth aspects, where the pivot motion driver pivots the closure element and the cam mechanism. 
     A sixth aspect of the present invention provides an on-off valve according to any one of the first through the fourth aspects, where the closure element has a protection seal member around the seal member, and wherein the protection seal member contacts the retreat portion in order to hermetically enclose the seal member. 
     A seventh aspect of the present invention provides an on-off valve according to the six aspect, which further includes a groove portion around one of the two openings, wherein the protection seal member is fitted in the groove portion when the closure element closes the one of the two openings. 
     An eighth aspect of the present invention provides a process apparatus including a chamber in which an object to be processed is housed, the chamber being evacuated to reduced pressure; a process mechanism adapted to carry out a predetermined process on the object to be processed; an evacuation apparatus adapted to evacuate the chamber; and an on-off valve provided between the chamber and the evacuation apparatus. In this process apparatus, the on-off valve includes a valve body having two openings that may place the process chamber and the evacuation apparatus in pressure communication with each other, a closure element located inside the valve body and adapted to close one of the two openings, a seal member provided in the closure element and adapted to seal the one of the two openings when the closure element closes the one of the two openings, a linear motion driver that linearly moves the closure element, a retreat portion located away from the two openings, and a pivotal motion driver adapted to pivot the closure element between a first position corresponding to the one of the two openings and a second position corresponding to the retreat portion, wherein the closure element is moved to the retreat portion by the linear motion driver and the pivotal motion driver in order to be located in the retreat portion when the closure element is away from the one of the two openings. 
     According to the on-off valve according to an embodiment of the present invention, because the closure element can be moved into the retreated portion, the seal member provided in the closure element is prevented from being directly exposed to gases or active species flowing into the valve body from the chamber, thereby reducing deterioration of the seal member. Therefore, the operational life of the seal member is lengthened, the running cost of the process apparatus employing the on-off valve can be reduced, and production throughput can be increased. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other objects, features and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a schematic diagram of a Radial Slot Line Antenna microwave plasma apparatus according to an embodiment of the present invention; 
         FIG. 2A  is a cross-sectional view of an on-off valve according to an embodiment of the present invention, taken along B-B line in  FIG. 2B ; 
         FIG. 2B  is another cross-sectional view of the on-off valve, taken along A-A line in  FIG. 2A ; 
         FIG. 3  is an enlarged schematic view showing a cam mechanism; and 
         FIGS. 4A through 4E  are cross-sectional views illustrating an operation of the on-off valve shown in  FIGS. 2A and 2B . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the accompanying drawings, an on-off valve according to exemplary embodiments of the present invention is described. In the drawings, the same or corresponding reference marks are given to the same or corresponding members or components. It is to be noted that the drawings are illustrative of the invention, and there is no intention to indicate scale or relative proportions among the members or components. Therefore, the specific size should be determined by a person having ordinary skill in the art in view of the following non-limiting embodiments. 
       FIG. 1  is a cutaway schematic diagram of a Radial Line Slot Antenna (RLSA) microwave plasma process apparatus employing a pressure control valve according to an embodiment of the present invention. As shown in  FIG. 1 , the RLSA microwave plasma process apparatus  10  includes a substantially cylindrical chamber  11  that can be evacuated to vacuum pressure, a susceptor  12  provided on the bottom surface of the chamber  11  to support a semiconductor substrate S, a gas inlet portion  13  that is substantially ring-shaped and introduces process gases into the chamber  11 , a planar antenna  14  located at the upper portion of the chamber  11  in order to oppose the susceptor  12 , the antenna  14  having plural slots  14  for radiating microwaves to the process chamber  11 , a microwave generator  15  for generating microwaves, a microwave transmitting mechanism  16  for guiding the microwaves generated by the microwave generator  15  to the planar antenna  14 , and a process gas supplying system  17  for supplying the process gases to the gas inlet portion  13 . 
     A microwave transmission plate  21  is provided below the planar antenna  14 , and a shield member  22  is provided above the planar antenna  14 . The microwave transmission mechanism  16  includes a waveguide pipe  31  extending horizontally from the microwave generator  15 , a co-axial waveguide pipe  32  having an inner conductor  33  and an outer conductor  34 , both of which extend upward from the planar antenna  14 , and a mode conversion mechanism  35  provided between the waveguide pipe  31  and the co-axial waveguide pipe  32 . 
     An evacuation mechanism  24  including valves, an evacuation apparatus, and other equipment is connected to the chamber  11 . The evacuation mechanism  24  has an evacuation pipe  23  connected to an evacuation opening  11   a  formed in the bottom portion of the chamber  11 . In addition, the evacuation mechanism  24  includes a drag pump  53  located at the upstream portion of the evacuation pipe  23 , and a dry pump  54  located at the downstream portion of the evacuation pipe  23 . The dry pump  54  serves as a roughing pump that evacuates the chamber  11  to low vacuum, and the drag pump  53  can evacuate the chamber  11  to a higher vacuum corresponding to a lower pressure. 
     Upstream of the drag pump  53  in the evacuation pipe  23 , a pressure control valve  60  is provided. The chamber  11  has a pressure sensor  55  that detects the inner pressure of the chamber  11 , and the degree of opening of the pressure control valve  60  is adjusted in accordance with the inner pressure detected by the pressure sensor  55 . Moreover, the evacuation mechanism  24  includes an on-off valve  100  according to this embodiment of the present invention between the drag pump  53  and the dry pump  54 . Furthermore, another on-off valve  101 , which is substantially the same as the on-off valve  100 , is provided between the pressure control valve  60  and the chamber  11 . 
     In the side wall of the chamber  11 , a transfer opening  25  is provided along with a gate valve G that can open/close the transfer opening  25 , so that the substrate S is transferred into/out from the chamber  11  through the opening  25  when the gate valve G is opened. The susceptor  12  has a heater  18  embedded therein. 
     The process gas supplying system  17  has plural gas sources corresponding to process gases such as CF gas and O 2  gas, and these gases are supplied to the chamber  11  from the corresponding gas sources through a commonly used gas supplying line  19  connected to the gas inlet portion  13 . Although not shown, the gas supplying line  19  is provided with on-off valves and flow rate controlling devices such as mass flow controllers. 
     The RLSA microwave plasma process apparatus  10  has a process controller  50  that typically includes a microprocessor (computer). The process controller  50  is electrically connected to the constituent components or devices in the process apparatus  10 , which are in turn controlled by the process controller  50 . For example, the pressure control valve  60  is controlled by the process controller  50  in accordance with a signal provided by the pressure sensor  55 , and the on-off valve  100  is opened or closed under control of the process controller  50 . Furthermore, the process controller  50  includes a keyboard that may be used by an operator of the process apparatus  10  when inputting commands in order to run the RLSA microwave plasma process apparatus  10 , and a user interface  51  having a display or the like showing, for example, on-going operations of the process apparatus  10 . 
     The process controller  50  is connected to a memory device  52  that stores programs by which the controller  50  causes the plasma process apparatus  10  to carry out various processes. The programs include a control program for controlling the various processes carried out in the plasma process apparatus  10  under control of the controller  50 , and a program (i.e., a recipe) for causing the various components or devices of the plasma process apparatus  10  to perform in accordance with process conditions. In addition, these programs may be stored in a computer-readable storage medium  52   a  and downloaded to the memory device  52 . The computer-readable storage medium  52   a  may be a hard disk apparatus (including a portable hard disk device), a semiconductor memory including a flash memory, an optical disk including a CD-ROM, a CD-R/RW, and a DVD-R/RW, a magnetic disk including a Floppy Disk, a USB memory, etc. In addition, the programs may be downloaded to the memory device  53  from another apparatus such as a server through a network. 
     A particular program stored in the memory device  52  is read by the process controller  50  and run in accordance with an instruction input through the user interface  51 , so that a corresponding process is carried out in the plasma process apparatus  10 . 
     Next, an example of a process carried out in the RLSA microwave plasma process apparatus  10  is described. 
     First, the substrate S is transferred into the chamber  11  and placed on the susceptor  12 . While the chamber  11  is being evacuated by the evacuation mechanism  24 , the process gasses such as the CF gas and O 2  gas are supplied into the chamber  11  from the gas supplying system  17  through the gas supplying line  19  and the gas inlet portion  13 , so that an etching process or the like is carried out. 
     In the plasma process apparatus  10 , since microwave plasma, which is characterized by radical-rich plasma, low electron temperature, and high density, is produced, only a significantly reduced amount of damage is incurred on the substrate S due to the plasma. 
     When plural process are carried out in the plasma process apparatus  10 , a purge gas such as argon (Ar) gas prepared in the process gas supplying system  17  is supplied to the chamber  11 , which is still being evacuated by the evacuation apparatus  24 , in order to purge the remaining process gases used in a first process from the chamber  11  after the first process is completed. Then, a predetermined gas to be used in a second process is supplied into the chamber  11 , and microwave plasma is produced so that the second process is carried out. 
       FIG. 2A  is a cross-sectional view of the on-off valve  100  ( 101 ) according to the embodiment of the present invention taken along the B-B line in  FIG. 2B , and  FIG. 2B  is another cross-sectional view taken along the A-A line in  FIG. 2A . 
     The on-off valve  100  has a valve body  110  that has a substantial cubic shape. The valve body  110  has an opening  111  as a gas inlet port in one end and an opening  112  as a gas outlet port in the opposing end. The openings  111 ,  112  are in pressure communication with each other through a passage way  113  formed in the valve body  110 , the passage way having a substantially cylindrical shape. 
     In the passage way  113 , a closure element  120  is provided to be contactable with a circumferential portion  113   a  that defines the opening  111 . A groove  111   a  is formed around the circumferential portion  113   a . The closure element  120  is substantially disk-shaped and has a ring-shaped seal member  120   b  embedded therein that corresponds to the circumferential portion  113   a , in order to hermetically close the opening  111 . In addition, the closure element  120  has a protection seal member  120   a  embedded outside of the seal member  120   b  to surround the seal member  120   b . The seal member  120   b  is preferably made of complete fluorinated rubber. The protection seal member  120   a  may be made of the same material as the seal member  120   b  or other materials in other embodiments. Behind the closure element  120 , there is provided a valve rod  122  which slidably goes through a frame body  130  housed in the passage way  113 . Between the closure element  120  and the frame body  130 , a spring member  124  is provided that can push the closure element  120  toward the opening  111  to force the closure element  120  onto the circumferential portion  113   a . The spring member  124  is a spring coil in this embodiment. 
     In a middle of the valve rod  122 , a pin  123  ( FIG. 2B ) is located to protrude from both sides of the valve rod  122 . Both ends of the pin  123  are inserted into cam grooves  132  of corresponding plate cams  131  as a cam mechanism. The pin  123  has a slight gap in relation to the cam grooves  132  but is pressed onto one of the side walls of the cam grooves  132  by the spring member  124 . The plate cams  131  are located inside the frame body  130  to sandwich the valve rod  122 . In addition, the plate cams  131  are connected to a driving member  135  located outside of the valve body  100  via a rod  136 . The rod  136  goes through the frame body  130  and the valve body  110 . The driving member  135 , which includes a linear motor and an air cylinder, can move the rod  136  along directions shown by a two-headed arrow in  FIG. 2B , and thus move the plate cams  131  connected to the rod  136 . 
       FIG. 3  is an enlarged diagram showing the closure element  120  and the plate cams  131 . The cam grooves  132  of the corresponding plate cams  131  face each other as if one of the cam grooves  132  were a mirror image of the other of the cam grooves  132 . Each of the cam grooves  132  has straight portions  132   a ,  132   c  that extend in the direction along which the rod  136  is driven (a Y axis direction in  FIG. 3 ), and an oblique portion  132   b  that extends in a direction changing in the X axis direction and is in pressure communication with the straight portions  132   a ,  132   c.    
     The plate cams  131  are moved in the Y axis direction by the rod  136 . On the other hand, the valve rod  122  and the pin  123  inserted into the valve rod  122  cannot be moved in the Y axis direction since both ends of the valve rod  122  are supported by the frame body  130  that is attached on both inner walls of the valve body  110  (see  FIGS. 2A and 2B ). Therefore, when the plate cams  131  are moved in the Y axis direction, the pin  123  can only be moved along the cam grooves  132 . 
     When the plate cams  131  are moved in a negative Y axis direction and the pin  123  is moved in the oblique portion  132   b  of the cam groove  132 , the closure element  120  is pulled away from the opening  111  and, thus, the valve  100  is opened. After the pin  123  reaches the straight portion  132   a , the closure element  120  stays a predetermined distance away from the opening  111 . 
     On the contrary, when the plate cam  131  moves upward (along a positive Y axis direction), the pin  123  is moved downward from the top most portion of the straight portion  132   a  of the cam groove  132  in relation to the plate cam  131 , and reaches to the oblique portion  132   b . Then, when the pin  123  continues to move in the oblique portion  132   b , the closure element  120  is moved closer to the opening  111 . By the time the pin  123  enters the straight portion  132   c , the closure element  120  is pressed onto the circumferential portion of the opening  111  and the seal member  120   b  is elastically deformed onto the circumferential portion  113   a , thereby hermetically closing the opening  111 , which thus closes the valve  100 . 
     When the plate cam  131  is moved further upward, the pin  123  enters and moves in the straight portion  132   c . At this time the seal element  120   b  of the closure element  120  is maintained to be pressed onto the circumferential portion  113   a . In other words, since the pin  123  can stay in the straight portion  132   c , the pin  123  does not go back to the oblique portion  132   b . As a result, the seal element  120   b  is continuously pressed onto the circumferential portion  113   a , thereby maintaining the valve  100  closed. Furthermore, the driving member  135 , the rod  136 , the plate cam  131 , the pin  123 , and the valve rod  122  together serve as a linear driving mechanism  140  of the closure element  120 . 
     In addition to the linear driving mechanism  140 , the on-off valve is provided with a pivotal driving mechanism  150  ( FIG. 2B ), which can pivot the driving member  135 , the rod  136 , the frame body  130 , the plate cam  131 , the valve rod  122 , and the closure element  120  in unison around the center axis of the rod  136 . Specifically, the pivotal driving mechanism  150  can turn the closure element  120 , the valve rod  122 , and the frame body about 90 degrees in the passage way  113 , so that the closure element can face the opening  111  and a retreat portion  113   b  that is about 90 degrees away from the opening  111 . The pivotal driving mechanism  150  is operated cooperatively with the driving member  135  by a controller (not shown) under instructions of the process controller  50 . With this configuration, the closure element  120  can be directed toward the retreat portion  113   b  by the pivotal driving mechanism  150  and then moved toward the retreat portion  113   b . As a result, the protection seal member  120   a  is pressed onto the retreat portion  113   b . A motor with a velocity reducer may be used as the pivotal driving mechanism  150 . 
     Next, according to the embodiment of the present invention, operations of the on-off valve  100  are described in detail, referring to  FIGS. 4A through 4E . 
       FIG. 4A  shows that the closure element  120  closes the opening  111  and thus the on-off valve is closed. Then, the rod  136  is moved to the uppermost position, which in turn moves the plate cams  131  to the uppermost position, and thus the pin  123  is located at the lowermost position of the straight portion  132   c , as stated above in reference to  FIG. 3 . Therefore, the seal member  120   b  embedded in the closure element  120  is pressed onto the circumferential portion  113   a  around the opening  111 , whereas the protection seal member  120   a  surrounding the seal member  120   b  is fitted into the concave groove  111   a  so that the protection seal member  120   a  is not pressed onto the bottom surface of the concave groove  11   a . With this, the protection seal member  120   a  cannot be affected by unnecessary repeated deformation, which can lengthen the operational life of the protection seal member  120   a.    
       FIG. 4B  shows that the closure element  120  is moved away from the opening  111 , which allows the openings  111 ,  112  to be in pressure communication with each other, and thus the valve  100  is opened. Then, the rod  136  is moved to the lowermost position, which in turn moves the plate cams  131  to the lowermost position, and thus the pin  123  is located at the uppermost position of the straight portion  132   a , as stated above (see  FIG. 3 ). Specifically, the on-off valve  100  is opened by the plate cams  131  that move from the uppermost position to the lowermost position. 
       FIG. 4C  shows that the closure element  120  and other components that constitute the linear driving portion  140  are turned about 45 degrees by the pivotal driving mechanism  150 . The closure element  120  is away from the opening  111  and does not hit any portions of the inner wall of the valve body  110  when the closure element  120  is turned in the passage way  113  since the passage way  130  is formed into a cylindrical shape. Furthermore, the passage way  130  may assume different shapes such as, for example, a sphere in other embodiments, as long as the closure element  120  does not hit the inner wall of the valve body  110 . 
       FIG. 4D  shows that the closure element  120  is further turned by 90 degrees by the pivotal driving mechanism  150 . At this time, the closure element  120  is about 90 degrees away from the original position shown in  FIG. 4A  in which the closure element is directed toward the opening  111 . In  FIG. 4D , the closure element  120  is directed toward the retreat portion  113   b.    
     Then, the driving member  135  operates to move the valve rod  136  upward, which then moves the plate cams  131  upward. With such a movement of the plate cams  131 , the pin  123  is moved downward relative to the cam grooves  132  to reach the lowermost portion of the straight portion  132   c . As a result, the closure element  120  is pushed toward and reaches the retreat portion  113   b . In this position, only the protection seal member  120   a  may be pressed onto the retreat portion  113   b , and the seal member  120   b  does not contact the retreat portion  113   b.    
     When a plasma process is carried out in the chamber  11 , the on-off valve  100  is open in such a manner shown in  FIG. 4E . In this case, the gases or the active species flow into the passage way  113  from the chamber  11  ( FIG. 11 ) through the opening  111  and out from the passage way  113  through the opening  112 . Even in this situation, because the closure element  120  stays in the retreat portion  113   b , the seal member  120   b  faces the inner wall of the valve body  110 , so that the seal member  120   b  is not directly exposed to the gasses or the like. Therefore, the operational life of the seal member  120   b  is lengthened, thereby reducing the frequency of replacing the seal members  120   b . As a result, the running cost of the plasma process apparatus  10  can be reduced and the production throughput can be increased. 
     In addition, when the closure element  120  is in the retreat portion  113   b , the seal member  120   b  is slightly away from the inner wall of the valve body  110 , and not deformed. Therefore, deterioration of the seal member  120   b  due to undue repeated deformation can be avoided and the operational life of the seal member  120   b  can be lengthened. In addition, the frequency of replacing the seal members  120   b  (or the valve rods  122  and the closure elements  120 ) and thus the apparatus downtime can be reduced. Moreover, the production throughput can be increased. 
     While the present invention has been described in reference to the foregoing embodiments, the present invention is not limited to these embodiments, but may be modified or altered within the scope of the accompanying claims. For example, although the passage way  113  is formed into a cylindrical shape as described in reference to  FIG. 2 , the shape may also be spherical, as briefly mentioned above. In the case of the spherical passage way  113 , the entire protection seal member  120   a  can contact the spherically curved inner wall of the valve body  110  in the retreat portion  113   b , when the valve  100  is opened. Therefore, the seal member  120   b  can be enclosed in a space defined by the closure element  120  (the protection seal member  120   a ) and the spherically curved retreat portion  113   b . As a result, the seal member  120   b  is completely protected from the gases or the active species from the chamber  11 , therefore further lengthening the operational life of the seal member  120   b . Furthermore, the protection seal member  120   a  is fitted into the concave groove  111   a  when the valve  100  is closed, which contributes to a longer operational life of the protection seal member  120   a , as stated above. Therefore, the protection seal member  120   a  can assuredly protect the seal member  120   b  for a longer period of time, especially when the inner wall of the valve body  110  is spherically shaped. 
     In addition, when the passage way  113  in the valve body  110  is formed into a cubic shape, the seal member  120   b  entirely contacts the planer inner wall of the valve body  110 . Even in this case, since the seal member  120   b  is not exposed to the gases or the active species from the chamber  11 , the operational life of the seal member  120   b  can be lengthened. Moreover, in the case of the planar inner wall, a concave portion is preferably made in the inner wall, which can prevent the seal member  120   b  from being pressed onto the inner wall, thereby avoiding deterioration of the seal member  120   b  due to undue repeated deformation. 
     On the other hand, the seal member  120   b  is not necessarily enclosed in a closed environment. For example, even when the closure element  120  is away from the retreat portion  113   b  as shown in  FIG. 4D , the closure element  120  is not directed toward the opening  111 , when the valve  100  is open. (In other words, the position away from the retreat portion  113   b  in the above embodiment can work as another retreat portion in other embodiments.) Therefore, the seal member  120   b  is not directly exposed to the gases or the active species. Namely, the operational life of the seal member  120   b  can be lengthened even in this situation, compared to when the closure element is directed toward the inlet port in a conventional on-off valve when the valve is open. 
     Moreover, although the on-off valve  100  is employed in the RLSA microwave plasma process apparatus  10  in the above embodiment, the on-off valve  100  can be employed in other plasma apparatuses, chemical vapor deposition apparatuses, and etching apparatuses in other embodiments. 
     The present application contains subject matter related to Japanese Patent Application No. 2007-070362 filed with the Japanese Patent Office on Mar. 19, 2007, the entire contents of which are incorporated herein by reference.