Patent Publication Number: US-2023140781-A1

Title: Valve for semiconductor manufacturing device

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to valves for semiconductor manufacturing devices and, in particular, a high-pressure valve suitable for a fluid affecting a valve seat such as corrosive gas to flow with high pressure. 
     Description of the Related Art 
     In semiconductor manufacturing process, various high-pressure fluids including corrosive gas are often used. The valve for semiconductor manufacturing device that controls these fluids requires a strong fastening load for valve closing to reliably prevent leakage. For this reason, by way of example, in a high-pressure diaphragm valve, the valve seat for sealing is prone to receive damage because of its fastening load together with corrosiveness of a fluid. If the valve is continuously used in this state, the valve seat is plastically deformed to be progressively crushed and broken, and the high-pressure fluid penetrates from its surface or a damaged portion to make the valve seat more prone to be broken. If the seat is broken and peeled off, the flow path may be clogged with this seat to become blocked, or breakage of the seat may cause leakage at valve closing. 
     To prevent damage to the valve seat, in general, a seat material with high load-bearing ability may be used to enhance strength, or a fastening load applied to the valve seat at valve closing, that is, a thrust from the stem for pressurizing the diaphragm (valve disk) may be reduced. Also, an effective area of the valve seat, that is, a pressurized area of the valve seat from a diaphragm side (area in contact with the diaphragm) may be increased to decrease a surface pressure (load applied per unit area) to the valve seat, thereby suppressing this surface pressure to load-bearing ability of the material of the valve seat or lower. 
     On the other hand, the metal diaphragm valve of Japanese Unexamined Patent Application No. 6-94142 is configured to have a cushioning body provided between the valve seat and the drive-side output shaft. In this diaphragm valve, when the output shaft is driven to a valve-closing direction, this output shaft causes the metal diaphragm to press-fit to the valve seat via the cushioning body, thereby mitigating the impact on the seal portion at valve closing by the cushioning body. 
     In the diaphragm valve of Japanese Unexamined Patent Application No. 2020-63777, a film-shaped diaphragm made of a resin material is provided. To the drive-side piston shaft (output shaft), a cushioning body made of an elastic rubber material is assembled so as to be positioned between this piston shaft and a center portion of the diaphragm. When the piston shaft is driven to a valve-closing direction, the force from this piston shaft is reduced by the cushioning body. 
     Meanwhile, the valve for use in semiconductor manufacturing process is often utilized as combined and integrated with a plurality of other valves, a control device, and so forth. Thus, the valve of this type is desired to have a compact outer size so as not to occupy a space at its installation location as much as possible. In this case, with reduction in size of the valve, reduction in size (reduction in diameter) of the valve mechanism, that is, the valve seat, is also required. When the valve is a diaphragm valve, even if the diameter of the valve seat is reduced to decrease the pressurized area (area in contact) with the diaphragm, high seal performance is required to be exerted without leakage of the high-pressure fluid at valve closing. 
     BRIEF SUMMARY OF THE INVENTION 
     In the above-described valves, when a seat material with high load-bearing ability to prevent damage to the valve seat is used, if the valve is a diaphragm valve, a material for general use in semiconductor manufacturing, for example, a fluororesin such as PCTFE or PFA, is normally used in consideration of performance of chemical resistance to the fluid and, therefore, options are very scarce. Moreover, only by providing a valve seat by using a resin material such as a fluororesin as described above, the strong fastening load at valve closing cannot be sufficiently mitigated only by the characteristics of the material, and it is difficult to prevent damage to the valve seat. 
     On the one hand, to reduce the thrust from the stem to decrease the force applied to the valve seat, decreasing the thrust (fastening load) of the stem directly leads to a decrease of a pressure resistance limit of the valve, making it difficult to obtain a fastening force required to reliably prevent leakage of the high-pressure fluid. Thus, this valve is not suitable for high-pressure fluids against which valve closing and sealing are performed. 
     On the other hand, to increase the effective area (pressurized area) of the valve seat to decrease the surface pressure on the valve seat, the diameter of the valve seat is enlarged to an outer diameter direction to enlarge the area in order to maintain a predetermined flow path diameter to ensure a flow rate. In this case, a problem arises in which, with an increase of the outer diameter of the valve seat, a gap between a flow path on this valve seat side and a flow path on the other side is widened to increase the outer size. In addition to this, when the valve is a diaphragm valve, the outer diameter of the diaphragm is also increased, and the thrust of the stem for reliable fastening is also increased with respect to the effective area of this diaphragm. 
     Also, the diaphragm valves of Japanese Unexamined Patent Application No. 6-94142 and Japanese Unexamined Patent Application No. 2020-63777 have a structure in which the cushioning body is interposed in series between the valve seat and the output shaft. At the time of fastening at valve closing, in any cases, the thrust from the output shaft side is absorbed by the cushioning body, and this thrust is decreased and transferred to the valve seat. Thus, when these valves are used as high-pressure valves for semiconductor manufacturing, sufficient seal capability cannot be exerted, and leakage may occur when a high-pressure fluid is let flow. 
     Moreover, in both of the above-described cases, when the valve is provided in a compact manner in accordance with integration or the like, the diameter of the valve seat is also decreased accordingly, thereby decreasing the area of contact with a valve disk side (for example, diaphragm). With this decrease of the seal area, an excessive surface pressure is applied to the valve seat when a strong thrust corresponding to the high-pressure fluid acts from a stem side, and this makes the valve seat prone to damage. When the valve seat receives damage exceeding its load-bearing ability, this valve seat may be crushed or broken, possibly leading to clogging of a flow path, leakage, or the like. 
     From these reasons, to let a fluid such as corrosive gas flow with high pressure at valve opening and reliably inhibit leakage of this high-pressure fluid at valve closing, the thrust from the stem side is strongly ensured so as not to impair seal capability. On the other hand, the occurrence of damage to the valve seat has to be tolerated. 
     The present invention was developed to solve the above-described problems, and has an object of providing a valve for semiconductor manufacturing device excellent in corrosion resistance, in which, while an increase of the diameter of the valve seat is prevented to maintain overall compactness, a thrust required for preventing leakage of a high-pressure fluid is exerted to allow sealability at valve closing to be ensured, and an excessive surface pressure to the valve seat is prevented to improve durability. 
     To achieve the object described above, a first aspect of the present invention is directed to a valve for semiconductor manufacturing device which opens or closes in accordance with contact or non-contact between a diaphragm and a valve seat provided in a valve main body, wherein the valve main body is provided with an opening/closing mechanism which pressurizes the diaphragm to cause valve closing, a load distributing member is provided inside the opening/closing mechanism, the load distributing member is arranged so that a portion provided contiguously to the opening/closing mechanism and the load distributing member have a predetermined gap therebetween when the load distributing member is in parallel with the valve seat and in a valve-open state, the valve main body has a duplexed structure in which, while a thrust produced by the opening/closing mechanism is maintained, a fastening load required at valve closing is received as being distributed to the valve seat and the load distributing member. 
     A second aspect of the present invention is directed to the valve for semiconductor manufacturing device, in which the load distributing member is provided to a portion not in contact with a fluid in a flow path of the valve main body. 
     A third aspect of the present invention is directed to the valve for semiconductor manufacturing device, in which the load distributing member is a resin-made, ring-shaped load distributing seat or a disc spring having spring characteristics. 
     A fourth aspect of the present invention is directed to the valve for semiconductor manufacturing device, in which the opening/closing mechanism is configured of a piston or a spring of an actuator when the valve is an automatic valve, and is a stem provided to a handle when the valve is a manual valve. 
     A fifth aspect of the present invention is directed to the valve for semiconductor manufacturing device, in which the load distributing member is arranged at a position where the thrust from the piston or the spring of the actuator or the stem provided to the handle is applied simultaneously with a time when the diaphragm and the valve seat make contact with each other. 
     According to the first aspect of the present invention, the load distributing member provided inside the opening/closing mechanism is provided in parallel with the valve seat, and is arranged so that the portion provided contiguously to the opening/closing mechanism and the load distributing member have a predetermined gap therebetween in a valve-open state. The valve main body has a duplexed structure in which a fastening load required at valve closing is received as being distributed to the valve seat and the load distributing member. Thus, while an increase of the diameter of the valve seat is prevented, this valve seat is attached to the valve main body to maintain overall compactness. At valve closing, a thrust required for preventing leakage of a high-pressure fluid can be exerted to allow sealability at valve closing to be ensured. Also, by preventing an excessive surface pressure to the valve seat, durability can be improved to prevent damage to the valve seat. In this case, with the valve seat made of a resin material excellent in chemical resistance being provided to improve corrosion resistance, by using the load distributing member provided as being made of an elastic material, it is possible to distribute the fastening load to ensure durability. 
     According to the second aspect of the present invention, the load distributing member to which the thrust from the opening/closing mechanism is applied is provided to the portion not in contact with the fluid in the flow path of the valve main body. Thus, this load distributing member is less prone to influences by corrosive gas, heat, and so forth, and its functionalities can be maintained. With this, even if the valve seat is softened by influences of corrosive gas, heat, and so forth, the thrust from the opening/closing mechanism can be reliably transferred via the load distributing member. By the load distributing seat receiving the load in this manner, sinking of the valve seat because of being crushed, a decrease of the seal height, or destruction of the valve seat is prevented to maintain excellent seal performance. 
     According to the third aspect of the present invention, a resin-made, ring-shaped load distributing seat or a disc spring having spring characteristics can be provided as the load distributing member. By providing a load distributing seat made of a resin material such as a fluororesin, corrosion resistance and chemical resistance can be improved. On the other hand, by providing a disc spring as the load distributing member, while the thrust produced by the opening/closing mechanism is maintained, the load can be mitigated to improve durability. 
     According to the fourth aspect of the present invention, the opening/closing mechanism is provided by using the piston or the spring of the actuator or the stem provided to the valve. Thus, the present invention can support both of an automatic valve and a manual valve, and can provide a valve in which while overall compactness is maintained, the thrust required at valve closing is maintained to ensure sealability. 
     According to the fifth aspect of the present invention, the load distributing member is prevented from first making contact with the piston or the spring of the actuator or the stem provided to the handle to produce leakage. Also, the load is inhibited from being first applied to the valve seat to cause damage. The thrust produced at valve closing is applied as being distributed to each of the load distributing seat and the valve seat. Thus, the burden on the valve seat can be reliably suppressed to a pressure resistance limit of the material configuring this valve seat or lower. Alternatively, a valve seat made of a low-strength material can be provided. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a central longitudinal sectional view of an embodiment of a valve for semiconductor manufacturing device in the present invention; 
         FIG.  2 A  is an enlarged sectional view of main portions of  FIG.  1   ; 
         FIG.  2 B  is an enlarged sectional view of the main portions in a valve-closed state of  FIG.  2 A ; 
         FIG.  3    is a central longitudinal sectional view of another embodiment of the valve for semiconductor manufacturing device in the present invention: and 
         FIG.  4 A  is an enlarged sectional view of main portions of  FIG.  3   ; and 
         FIG.  4 B  is an enlarged sectional view of the main portions in a valve-closed state of  FIG.  4 A . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the following, embodiments of a valve for semiconductor manufacturing device in the present invention are described in detail based on the drawings. 
       FIG.  1    depicts an embodiment of a valve for semiconductor manufacturing device (hereinafter referred to as a valve main body  1 ) of the present invention. In the drawing, the valve main body  1  is formed of an automatic valve, and includes a body  2 . a base body  3 , a stem member  4 , a diaphragm piece  5 , a diaphragm  6 , and a valve seat  7 . The valve main body  1  is a valve for semiconductor manufacturing device formed of a diaphragm valve which opens or closes in accordance with contact or non-contact between the diaphragm  6  and the valve seat  7 . This valve main body  1  is provided with an opening/closing mechanism  8  which pressurizes the diaphragm  6  to cause valve closing. Inside this opening/closing mechanism  8 , a load distributing member  10  is provided. 
     The valve main body  1  includes an actuator  11  provided on an upper portion. By this actuator  11 , the valve main body  1  is provided so as to be controllable to open and close by automatic operation. 
     In  FIG.  1   , a primary flow path  12  and a secondary flow path  13  are provided in a left direction and a right direction, respectively, of the body  2  of the valve main body  1 . Between these primary flow path  12  and secondary flow path  13 , a valve chamber  14  is provided. Inside the valve chamber  14 , an annular attachment groove  15  is formed. On an upper side of the valve chamber  14 . an opening  16  is provided. On an inner circumferential side of an upper portion of the opening  16 , a female thread  17  is formed. Between a portion on a lower side of the female thread  17  and the valve chamber  14 , a circular-hole-shaped fitting-in portion  18  is formed. 
     The valve seat  7  is formed in a ring shape made of a fluororesin such as a resin material, for example, PCTFE (polychlorotrifluoroethylene), PFA (copolymer of tetrafluoroethylene and perfluoroalkoxyethylene), or the like. With a seal surface  7   a  at a tip side protruding to a valve chamber  14  side so as to be sealable by the diaphragm  6 . the valve seat  7  is inserted into the attachment groove  15 . The valve seat  7  is arranged so as to be opposed to the diaphragm  6  to control a flow of the fluid. 
     The diaphragm  6  is configured with a plurality of sheets made of a thin-plate-shaped metal material stacked together, and is provided so as to have a disk shape with a moderate convex curve surface toward one side (upward) with a center portion as an apex in a natural state. This shape has a self-restorable resilient force. The diaphragm  6  is inserted into the fitting-in portion  18  on an upper portion side of the valve seat  7 . 
     In an upper portion of the diaphragm  6 , a bonnet  19  formed in a cylindrical shape fits through the fitting-in portion  18 . At the center of this bonnet  19 , the diaphragm piece  5  formed in a substantially columnar shape is insertably attached so as to be slidable in a vertical direction. The diaphragm piece  5  is provided so as to be movable by the stem member  4  in the vertical direction with respect to the bonnet  19 . Via this diaphragm piece  5 , the diaphragm  6  is pressurized to a valve seat  7  direction. 
     The base body  3  has a through hole  20  at the center, and has a male thread  21  screwable into the female thread  17  formed on an outer circumferential side of a lower portion of the through hole  20 . On an upper portion of the base body  3 , a circular recessed groove  22  is formed. This recessed groove  22  is provided with a closed bottom surface portion  23 . On the other hand, a male thread portion  24  is formed on the outer circumference of the upper portion of the base body  3 . With the diaphragm  6 , the bonnet  19 , and the diaphragm piece  5  attached between the base body  3  and the body  2 , the base body  3  is attached to an upper portion of the bonnet  19  by screwed attachment between the male thread  21  and the female thread  17 . After this screwed attachment, the bonnet  19  is pressurized by the bottom surface side of the base body  3  and, by this bonnet  19 , the diaphragm  6  is positioned and fixed at a predetermined location between the bonnet  19  and the body  2 . 
     The stem member  4  is provided to have a shape including a shaft portion  4   a  formed on a lower portion side, a diameter-enlarged step portion  4   b  with its diameter slightly enlarged from this shaft portion  4   a , and a diameter-enlarged annular portion  4   c  with its diameter further enlarged from this diameter-enlarged step portion  4   b . The shaft portion  4   a  is insertably attached into the through hole  20  as being sealed with an O ring  25 , thereby allowing the stem member  4  to ascend and descend with respect to the base body  3 . A lower end side of the stem member  4  abuts on an upper end face side of the diaphragm piece  5 . With ascending/descending movement of the stem member  4 , the diaphragm  6  pressurizes the valve seat  7  via the diaphragm piece  5 . 
     Between the diameter-enlarged annular portion  4   c  and an annular attachment groove  26  formed on an outer diameter side of the through hole  20 , a coil spring  27  is attached in a spring-back state. By this spring  27 , the stem member  4  is always pressed upward with respect to the base body  3 . 
     The actuator  11  has a substantially cylindrical cover  30 , an annular casing  31 , a piston  32 , and a coil-shaped spring  33 . In a lower portion of the center of the cover  30 , a guide hole  34  is formed. On an upper portion of this guide hole  34 , an air supply and exhaust port  35  is formed so as to communicate therewith. On an outer diameter side of the guide hole  34 , an annular attachment groove  36  is formed. In this attachment groove  36 , the spring  33  is provided so as to be able to be inserted therein. 
     In the guide hole  34 , a diameter-reduced shaft  32   a  formed on the piston  32  is insertably attached. Between the piston  32  and the attachment groove  36 . the spring  33  is insertably attached. On an outer circumferential side of a lower portion of the cover  30 , the inner circumference of the casing  31  is integrated by screwing. Between the piston  32  and the casing  31 , a cylinder chamber  37  to which compressed air is supplied is provided. On an inner circumferential side of a lower portion of the casing  31 , a female thread portion  38  is formed. 
     The actuator  11  is attachably fixed to and integrated with the base body  3  by screwing between the female thread portion  38  and the male thread portion  24 . After assembling of the actuator  11 , the piston  32  is attached, with its lower end face side abutting on an upper surface side of the diameter-enlarged annular portion  4   c , so as to be able to reciprocate in the vertical direction. This piston  32  is provided so as to be able to descend with respect to the casing  31  by being pressed by the spring-back force of the spring  33 . Also, the piston  32  is provided so that compressed air can be supplied from the air supply and exhaust port  35  via a flow path hole  32   b  formed in the piston  32  to the cylinder chamber  37  and, by this compressed air, the piston  32  can ascend against the spring-back pressing force of the spring  33 . 
     With this structure, when the piston  32  descends at the time of stop of supply of compressed air in  FIG.  2 B , the stem member  4  is pressurized downward by this piston  32  to pressurize the diaphragm  6  via the diaphragm piece  5 , and a valve-closed sealed state occurs when this diaphragm  6  is seated on the valve seat  7 . On the other hand, when the piston  32  ascends at the time of supply of compressed air in  FIG.  2 A , pressurization to the diaphragm  6  by the stem member  4  and the diaphragm piece  5  is released, and the diaphragm  6  is returned by the above-described self-restorable force to have the convex curve surface with the center portion as an apex, thereby going away from the valve seat  7  to cause a valve-open state. 
     In the case of an automatic valve using the actuator of the present embodiment, the above-described opening/closing mechanism  8  is configured of the piston  32  or the spring  33  of the actuator  11  and, by these piston  32  and spring  33 , a thrust is produced to cause the diaphragm to perform valve-opening or valve-closing operation. 
     The thrust produced from the opening/closing mechanism  8  is represented by thrust [N]=pressurized area [mm 2 ]×pressure [MPa]. Based on this relational expression, the thrust is transferred from the piston  32  to the stem member  4 . In the above-mentioned relational expression, the pressurized area is a total area where the thrust is applied, and the pressure is a force applied per unit area of the pressurized area. 
     The load distributing member  10  arranged inside the opening/closing mechanism  8  is formed of a load distributing seat formed in a ring shape made of an elastic material such as, for example, fluororesin such as PCTFE or PFA, nylon, or a resin material such as ABS. In the present embodiment, the load distributing seat  10  is formed by using a fluororesin. 
     The load distributing seat  10  is attached between the diameter-enlarged step portion  4   b  of the stem member  4 , which is a portion provided contiguously to the opening/closing mechanism  8  (piston  32 , spring  33 ) and the bottom surface portion  23  of the base body  3 , as being placed on the bottom surface portion  23 . This load distributing seat  10  allows distribution of the load from the piston  32  (stem member  4 ). 
     In this case, with the diaphragm  6  tightly attached between the body  2  and the bonnet  19  to seal against the fluid, the load distributing seat  10  is in a state of being arranged at a portion not in contact with the fluid in the flow paths (the primary flow path  12 , the secondary flow path  13 , and valve chamber  14 ) of the valve main body  1 . 
     The load distributing seat  10  is provided in a parallel state with respect to the valve seat  7 . Also, in a valve-open state, the load distributing seat  10  and the above-described portion provided contiguously to the opening/closing mechanism  8  (the diameter-enlarged step portion  4   b  of the stem member, the bottom surface portion  23  of the base body) are arranged so as to have a predetermined gap X 1  depicted in  FIG.  2 A . In the present embodiment, the load distributing seat  10  and the valve seat  7  are attached so as to be parallel to each other. 
     On the other hand, on a diaphragm  6  attachment side, in a valve-open state, the bottom surface side of the diaphragm  6  and the seal surface  7   a  of the valve seat  7  are provided so as to have a predetermined gap X 2 , which is a stroke of the diaphragm  6 . 
     These gap X 1  and gap X 2  in a valve-open state have a relation of gap X 1 =gap X 2 . In valve-closing operation, the diaphragm  6  abuts on (is seated on) the valve seat  7  and, at the same time, an abutting side of the diameter-enlarged step portion  4   b  makes contact with the load distributing seat  10 , and the thrust from the piston  32  and the spring  33  of the actuator  11  is applied also to the load distributing seat  10 . 
     Thus, the valve main body  1  has a duplexed structure in which, while a thrust produced by the opening/closing mechanism  8  is maintained, a fastening load required at valve closing is received as being distributed to the valve seat  7  and the load distributing seat  10 . 
     When the above-described load distributing seat  10  and the valve seat  7  are provided, it is required to split (distribute) the load transferred from the piston  32  to both of these load distributing seat  10  and the valve seat  7  in a balanced manner. Thus, it is required to set the dimensions of both of the seats  7  and  10  in consideration of the range of elastic deformation, mechanical tolerance range after arrangement, and so forth. 
     For example, at the time of valve closing, when the diameter-enlarged step portion  4   b  makes contact with the load distributing seat  10  before the diaphragm  6  is seated on the valve seat  7 , a valve-closed sealed state does not occur and leakage of the fluid occurs. On the other hand, when the diaphragm  6  is seated on the valve seat  7  before the diameter-enlarged step portion  4   b  makes contact with the load distributing seat  10 , the entire load by the piston  32  concentrates on this valve seat  7  from a diaphragm  6  side. In either of these cases, the load cannot be distributed by the duplexed structure by the valve seat  7  and the load distributing seat  10 . 
     In addition to this, it is difficult to make a dimensional error due to variations in mechanical processing to be zero. Thus, in consideration of process tolerance and so forth, it is required to design a balanced and effective arrangement so that the diameter-enlarged step portion  4   b  makes contact with the load distributing seat  10  in an allowable range of elastic deformation of the valve seat  7 . 
     When these seats  7  and  10  are provided, firstly, area allocation when each of the seats  7  and  10  receives a load is set, and the thickness on a valve seat  7  side (height of the seal surface  7   a ) is set based on the hardness of the load distributing seat  10  and a ratio of elastically deformable dimensions with respect to a thickness direction. Also, as required, the thickness of the load distributing seat  10  may be designed so as to be sufficiently large. The reason for these is that, by setting a large thickness of the valve seat  7 . an expansion range in which the valve seat  7  can be safely elastically deformed can be increased and, furthermore, even if the thickness of the load distributing seat  10  is increased, the range of elastic deformation can be similarly increased. 
     As described above, by increasing the thickness of the load distributing seat  10  and the valve seat  7 , it is possible to prevent leakage from occurring because the load distributing seat  10  first makes contact with the stem member  4  to cause the load to concentrate on this portion to make valve closing incomplete, or to prevent the load from concentrating on this valve seat  7  to cause damage because the diaphragm  6  first makes contact with the valve seat  7 . 
     As a specific example, for example, when these seats  7  and  10  made of PCTFE are provided and when elastic deformation in the load range not exceeding the limit of pressure resistance of this PCTFE is set at 10% at maximum and the stacking error between the valve seat  7  and the load distributing seat  10  in a height direction occurring due to complex influences of process tolerance and assembling error of the diaphragm  6  and the stem member  4  is ±0.1 mm (0.2 mm as a width value), the material thickness of the valve seat  7  is provided to be equal to or larger than the width of this error 0.2 [mm]/10 [%]=2.0 mm. 
     If the thickness of the valve seat  7  cannot be sufficiently allocated due to some reason, in place of this valve seat  7 , the thickness of the load distributing seat  10  is set similarly to the above. However, when the load distributing seat  10  is thickened, its range of elastic deformation is increased. Thus, when the valve seat  7  is softened, it is required to take it into consideration that the function of maintaining the thickness with respect to sinking of this valve seat  7  may become slightly decreased. 
     For example, if the load to be received by the load distributing seat  10  is constant irrespective of the thickness and the load distributing seat  10  is deformed by the load by 10%, 10% deformation when the thickness is 1.0 mm is 0.1 mm. Also, 10% deformation when the thickness is 2.0 mm is 0.2 mm. In comparison between these, a difference in deformation is 0.1 mm, and thus a difference in range of elastic deformation is widened. Thus, there is a possibility that a phenomena occurs in which when the valve seat  7  is softened, this valve seat  7  may sink too much. 
     Moreover, when the material of the load distributing seat  10  is set, it is required to consider material characteristics such as elasticity and hardness. Furthermore, other than this, it is also desirable to consider external environments such as the characteristics of components surrounding the arrangement position of the load distributing seat  10 , such as the stem member  4  and the base body  3 ; affinity with grease to be applied inside; and use temperature of the valve main body  1 , and so forth. 
     Note that the load distributing member  10  can be provided to any form, such as any of various materials except those made of resin, any of various shapes except a ring-shaped seat, and so forth. Although not depicted, a disc spring or a plate spring having spring characteristics can be used as the load distributing member, and any of these disc spring and plate spring can be attached between the diameter-enlarged step portion and the bottom surface portion (not depicted). 
     Also, with the duplexed structure in which the fastening load required at valve closing is received in a distributed manner by the load distributing member  10  and the valve seat  7  while the thrust is maintained, the load distributing member  10  may be configured to be fixed to a bottom surface portion  23  side of the base body  3  or a diameter-enlarged step portion  4   b  side of the stem member  4 . Furthermore, the load distributing seat  10  is not limited to be between the stem member  4  and the base body  3 , and can be provided at any positions inside the valve main body  1 . 
     When the load distributing seat  10  is provided, a difference in size can be provided between the gap X 1  and the gap X 2 . With the duplexed structure in which the fastening load required at valve closing is distributed to the valve seat  7  and the load distributing seat  10 , for example, the elastic force and/or material of the load distributing seat  10  or the shape, material, and/or the like of the diaphragm  6  may be set as appropriate and the gap X 1  and the gap X 2  may be set accordingly as appropriate. 
     While an example has been described in the present embodiment in which a the present embodiment is applied to a diaphragm valve as a valve for semiconductor manufacturing device, application is not limited to the diaphragm valve, and the present embodiment can be applied to any of various valves such as, for example, those of a needle shape or a globe shape not depicted. 
     Next, the operation and action of the above-described embodiment of the valve for semiconductor manufacturing device of the present invention are described. 
     In  FIG.  1   ,  FIG.  2 A , and  FIG.  2 B , in the valve main body  1 , the components such as the opening/closing mechanism  8 , the stem member  4 , the diaphragm piece  5 , and the coil spring  27  operate in conjunction with the operation of the actuator  11  to transfer the produced thrust to the diaphragm  6  and the valve seat  7  to cause seal portions of these to be closely attached to cause a valve-closed or valve-open state, thereby allowing control of the flow of the fluid. 
     In  FIG.  1    and  FIG.  2 A , when compressed air passes from the air supply and exhaust port  35  through the flow path hole  32   b  to the cylinder chamber  37 , the piston  32  ascends by this compressed air against the spring-back pressing force of the spring  33 . With this, pressurization to the diaphragm  6  by the stem member  4  and the diaphragm piece  5  is released, and the diaphragm  6  goes away from the valve seat  7  to cause a valve-open state. 
     In this case, the diameter-enlarged step portion  4   b  of the stem member  4 , which is a portion provided contiguously to the opening/closing mechanism  8  (piston  32 , spring  33 ), and the bottom surface portion  23  of the base body  3 , and the load distributing seat  10  are arranged so as to have the predetermined gap X 1 , and no fastening load is applied from the piston  32 . Thus, the thrust by the opening/closing mechanism  8  does not act on any of the load distributing seat  10  and the valve seat  7 . 
     On a valve seat  7  side, the gap X 2  having a height equal to that of the gap X 1  is provided between this valve seat  7  and the diaphragm  6 . This gap X 2  reliably allocates flow paths, allowing the fluid to smoothly flow from the primary flow path  12  to the secondary flow path  13 . 
     On the other hand, in  FIG.  2 B , when the supply of compressed air stops, a force of causing the piston  32  to ascend is stopped. Also, by the spring-back pressing force of the spring  33 , a force of causing the piston  32  to descend acts. By the action of the forces of this piston  32 , the stem member  4  and the diaphragm piece  5  are pressurized downward, and the diaphragm  6  is pressurized by the diaphragm piece  5 . With this, the diaphragm  6  is seated on the valve seat  7  to cause a valve-closed sealed state. 
     As described above, with the duplex structure in which the fastening load required at valve closing is received in a distributed manner by the valve seat  7  and the load distributing seat  10  arranged separately from this valve seat  7  as a different member inside the opening/closing mechanism  8  in a parallel state while the thrust produced by the opening/closing mechanism  8  is maintained, it is possible, without changing the magnitude of the thrust by the fastening load of the piston  32  required at valve closing and sealing, to distribute pressure by this thrust to the valve seat  7  and the load distributing seat  10 . 
     Here, since the valve seat  7  and the load distributing seat  10  are provided in a parallel state, from the above-described relational expression of thrust=pressurized area×pressure, it is possible to represent as follows: thrust by the piston  32 =(pressurized area of the valve seat  7 ×pressure applied to the valve seat  7 )+(pressurized area of the load distributing seat  10 ×pressure applied to the load distributing seat  10 ). 
     With this, while the surface pressure received by the valve seat  7  (load to be carried per unit area) is reduced to allow reduction of damage to be received by the valve seat  7 , it is not required to decrease the thrust produced by the opening/closing mechanism  8 , thereby exerting sufficient fastening capability also to a high fluid pressure. In this case, without decreasing the fastening force by the piston  32 , it is possible to cause the thrust having a predetermined magnitude required to prevent leakage to act on the valve seat  7  and the load distributing seat  10 , with each pressure (surface pressure) decreased. Compared with a case in which the load distributing seat  10  is not provided, a burden on the valve seat  7  is to reduced. Thus, fluororesin, which is excellent in chemical resistance, is selected for the valve seat  7  and the load distributing seat  10 , and the fastening load is mitigated without adding a superfluous load (thrust) from an actuator  11  side, thereby allowing prevention of damage to the valve seat  7  and the load distributing seat  10  and a failure of the valve main body  1 . 
     Without increasing the size of this valve seat  7  to suppress the pressure onto the valve seat  7  to increase the pressurized area, it is possible to prevent an increase in size of the valve main body  1  and also ensure compactness. It is also not required to limit the magnitude of the pressure of the fluid flowing inside the valve main body  1 . By decreasing only the surface pressure (pressure) applied to the valve seat  7 , the high-pressure fluid can be let flow while functionalities such as seal performance and flowrate characteristics required for the valve main body  1  are ensured. With this, even when the valve main body  1  is provided in a compact manner by integration or the like, the fastening load is distributed with a duplexed structure for the diameter-decreased valve seat  7  to prevent an excessive surface pressure and improve durability. 
     Since the load distributing seat  10  is provided on a recessed groove  22  side which is not in contact with the fluid inside the valve main body  1 , degradation and breakage of the load distributing seat  10  can be prevented. Thus, even if the valve seat  7  is softened by a corrosive fluid, it is possible for the load distributing seat  10  to bear the load borne by the valve seat  7  instead. This can prevent loss of seal capability due to continuous crush of the valve seat  7  and can provide the valve main body  1  with high durability capable of continuously performing normal operation against softening of the valve seat  7 . 
     Even if a pressure is received in a direction of opening the valve by the fluid at the time of valve closing while designing is performed by calculating the spring load pushing the piston  32  and the specifications of air pressure for driving and so forth in advance, natural valve-opening operation by the thrust produced from the piston  32  can be prevented. Note that a similar function can be applied also to a manual valve using a handle, which will be described further below and, in that case, the thrust produced from the handle is used as a fastening load and designing is performed by calculating a thread diameter and thread pitch provided to the handle in advance, thereby inhibiting natural valve-opening operation. 
     When the valve main body  1  is provided, in particular, a valve for high pressure requires a larger fastening load so that operation is not inhibited by a high-pressure fluid, and it is thus required to set a large thrust of the piston  32 . In this case, for example, when PCTFE is used as the material of the valve seat  7 , the tensile strength of this PCTFE is known to be on the order of 41 MPa at maximum. When this value is taken as a limit value, if the valve seat  7  is singly provided without provision of the load distributing seat  10 , there is a possibility that the valve seat  7  is plastically deformed to be crushed or destroyed when a surface pressure exceeding 41 MPa is applied to the valve seat  7 . When the load distributing seat  10  is provided, the surface pressure is applied as being distributed to this load distributing seat  10 , thereby making it possible to prevent application of a surface pressure exceeding 41 MPa to the valve seat  7 . 
     In  FIG.  3   ,  FIG.  4 A , and  FIG.  4 B , another embodiment of the valve for semiconductor manufacturing device of the present invention is depicted. Note in this embodiment that a portion identical to that of the above-described embodiment is indicated by the same reference character and description of the identical portion is omitted. 
     A valve main body  40  of this embodiment is formed of a manual valve formed of a diaphragm valve including a body  41 , a base body  42 , a stem  43 , a diaphragm piece  44 , a diaphragm  45 , a valve seat  46 , a load distributing seat (load distributing member)  47 , and a handle  48 . 
     The valve main body  40  is provided with an opening/closing mechanism  43 . This opening/closing mechanism  43  is configured of a stem provided to the handle  48 . Through this stem  43 , the diaphragm  45  is pressurized to allow valve closing. At a predetermined position inside the body  41 , the valve seat  46  is attached similarly to the above-described embodiment. With the diaphragm  45  being inserted from above this valve seat  46 , the diaphragm piece  44  is attached to the body  41  via the bonnet  49 . 
     The base body  42  is cylindrically formed, and has a through hole  50  formed at the center and a female thread  52  formed in a lower portion, the female thread  52  into which a male thread  51  formed on an upper portion of the body  41  is screwed. The base body  42  is integrated with the body  41  by screwing between these male thread  51  and female thread  52 . Here, a pressurizing surface  53  provided on a bottom surface side of the inner circumference of the base body  42  pressurizes a bonnet upper surface  49   a . and thus the bonnet  49  pressurizes the diaphragm  45  and the diaphragm  45  is positioned and fixed between the bonnet  49  and the body  41 . On an upper portion side of the through hole  50 , a female thread portion  54  is formed. 
     On the outer circumference of the stem  43 , a male thread portion  55  which is screwed into the female thread portion  54  is formed. By screwing these male thread portion  55  and female thread portion  54 , the stem  43  is attached so as to be in a state capable of ascending and descending with respect to the base body  42 . On an upper end side of the stem  43 , the handle  48  is fixed with a set screw  56 . By operating the handle  48  for rotation, the stem  43  rotates integrally with this handle  48  to ascend and descend with respect to the base body  42 . On a bottom surface side of the stem  43 , a diameter-reduced protruding portion  43   a  is formed. On an upper portion side of this protruding portion  43   a . a diameter-enlarged step portion  43   b  with its diameter further enlarged is formed. When the stem  43  is caused to descend, the protruding portion  43   a  pressurizes the diaphragm piece  44  and the diaphragm  45  to allow the flow paths to be closed. When the stem  43  is caused to ascend, the protruding portion  43   a  releases pressurization of the diaphragm piece  44  and the diaphragm  45  to allow the flow paths to be opened. 
     The load distributing seat  47  is attached as being positioned between the outer circumferential side of the stem protruding portion  43   a  and a bonnet upper surface  49   a . With this, as with the above-described embodiment the load distributing seat  47  is arranged in parallel with the valve seat  46 . 
     In  FIG.  4 A , in a valve-open state in which the stem  43  as an opening/closing mechanism ascends, the diameter-enlarged step portion  43   b  as a portion provided contiguously to the opening/closing mechanism  43  and the load distributing seat  47  are arranged so as to have a predetermined gap Y 1 . 
     Here, on a diaphragm  45  attachment side, in a valve-open state, the bottom surface side of the diaphragm  45  and a seal surface  46   a  of the valve seat  46  are open as having a gap Y 2 , which is a stroke of the diaphragm  45 . In a valve-open state, these gap Y 1  and gap Y 2  have a relation of gap Y 1 =gap Y 2 . 
     On the other hand, in  FIG.  4 B , a duplexed structure is provided, in which a thrust is produced when the handle  48  is rotated to cause the stem  43  to descend and, while this thrust is maintained, a fastening load required at valve closing can be received in a distributed manner by the valve seat  46  and the load distributing seat  47 . That is, the load distributing seat  47  is arranged at a position where the thrust from the stem  43  provided to the handle  48  is applied when the diaphragm  45  and the valve seat  46  make contact with each other. 
     As described above, by applying the opening/closing mechanism  43  to a manual valve and distributing the fastening load to the valve seat  46  and the load distributing seat  47 , a function similar to that of the above-described embodiment can be exerted. In particular, it is possible to prevent destruction or the like of the valve seat  46  by fastening the handle  48  too much and, in addition, even if a large thrust is designed, its influence on the valve seat  46  is suppressed as much as possible to allow sufficient seal capability to be maintained. Thus, shortages of each of sliding resistance between the bottom surface side of the protruding portion  43   a  and the diaphragm piece  44  and sliding resistance between the male thread portion  55  and the female thread portion  54 , which are prone to occur when the fastening load is suppressed, are prevented from running short, and an occurrence of an inconvenience in closing and stopping by a return phenomenon of the handle  48  due to this shortage of this sliding resistance is also suppressed. 
     EXAMPLES 
     Next, examples when the valve seat and the load distributing seat of the valve for semiconductor manufacturing device are set are described. 
     In the valve main body  1  of the embodiment having the structure of  FIG.  1   , to compare between a case in which a fastening force (thrust) is received singly by the valve seat  7  without provision of the load distributing seat  10  and a case in which a thrust is provided by both of the load distributing seat  10  and the valve seat  7  in the above-described embodiment, the magnitudes of forces applied to the seats  7  and  10  in each case were calculated. 
     As a condition for a valve for high-pressure gas, for example, the valve main body  1  usable to a pressure of 20.6 MPa was provided. In this case, a design margin was set at 10%, an effective area of the diaphragm  6  was provisionally set at 88.4 mm 2 , and a reactive force P produced by fluid pressure on the diaphragm  6  was set at P=88.4×20.6×1.1≅2003 [N]. To pressurize the diaphragm  6  receiving this reactive force P to reliably cause valve-closing operation, the entire opening/closing mechanism  8  and each of the other components were designed so that a thrust F by the spring  33  exceeds the reactive force P, also in consideration of its spring load. Furthermore, the seal load produced by the thrust F at the time of valve closing was always applied continuously even if the supply of the fluid stopped and no internal pressure was produced. 
     The size of the seal surface  7   a  of the valve seat  7  for use in the above-described valve main body  1  was set at ϕ6.6 mm in outer diameter and ϕ3.6 mm in inner diameter, and its effective area was set at (6.6/2) 2 ×π-(3.6/2) 2 ×π≅24.0 mm 2 . 
     Firstly, when only the valve seat  7  was provided without provision of the load distributing seat  10  inside the valve main body  1 , the surface pressure by the reactive force P was 2003/24.0=83.5 [MPa] at maximum. 
     As described above, when the load distributing seat  10  was not provided, the result was that surface pressure (83.5 MPa) significantly exceeded 41 MPa indicating a load-bearing ability (tensile strength) of PCTFE described above. Thus, it was observed that after repeated use, there was a high possibility that the valve seat  7  was not able to withstand the surface pressure to become plastically deformed, damaged, or ruptured. 
     On the other hand, when the valve seat  7  and the load distributing seat  10  were provided in parallel, in addition to the valve seat  7  having a seal surface size (effective area) of 24.0 mm 2 , the load distribution seat  10  having an effective area (area opposed to each of the diameter-enlarged step portion and the bottom surface portion) of 26.0 mm 2  was used. With this, a total of the effective areas of the valve seat  7  and the load distributing seat  10  (total area) became 50.0 mm 2 . 
     From this, the surface pressure by the reactive force P (2003 [N]) to this total area of 50 mm 2  became 2003/50.0≅40 [MPa]. 
     When the load distributing seat  10  was provided as described above, for 41 MPa, which is a general load-bearing ability of PCTFE, the surface pressure received by the valve seat  7  falls within numerical values in a pressure resistance limit of the material. Thus, the valve seat  7  was able to be inhibited from being damaged. 
     Furthermore, damage to the valve seat  7  was able to be also reduced when corrosive gas or the like penetrated through the valve seat  7  to soften this valve seat  7 . 
     For example, when the load-bearing ability of the valve seat  7  is decreased to 20.5 MPa (50% of 41 MPa, which is a general value) by a chemical agent or the like, if the load distributing seat  10  is not provided, the surface pressure of 83.5 MPa is applied only to the valve seat  7 . Thus, a ratio between these is 83.5 [MPa]/20.5 [MPa]=4.1. Upon reception of this 4.1 -fold surface pressure, it was observed that destruction or the like became prone to proceed. 
     By contrast, when the valve seat  7  and the load distributing seat  10  are both used, the surface pressure applied to the total area of these is 40 MPa. Thus, a ratio between this surface pressure and the load-bearing ability of the valve seat  7  is  40  [MPa]/20.5 [MPa]=1.95. Thus, by suppressing the surface pressure to 1.95 fold, damage was able to be significantly suppressed, compared with the case in which the load distributing seat  10  was not provided. 
     Furthermore, in the above, the load distributing seat  10  was designed in consideration of relations with the thrust applied to the valve seat  7 , the load-bearing ability thereof, and so forth. Specifically, a thrust limit of the valve seat  7  alone (thrust not causing plastic deformation) when the load-bearing ability of the valve seat  7  is decreased to 20.5 MPa is 24.0 [mtn 2 ]×20.5 [MPa]=492 [N], from the area of the seal surface (effective area)×pressure resistance after softening. Since the total thrust produced by the piston is 2003 [N], the thrust to be received by the valve seat  7  alone when the load distributing seat  10  is provided is 2003 [N]-492 [N]=1511 [N]. 
     In contrast to this thrust, the surface pressure received by the load distributing seat  10  is 1511 [N]/26.0 [mm 2 ]=58.1 [MPa]. Thus, the pressure resistance of the load distributing seat  10  was set to be larger than 58.1 MPa and, in the present example. MC Nylon (registered trademark) (load-bearing ability of 96 MPa) was used as a material. In this case, even if the valve seat  7  was softened and crushed, the load distributing seat  10  was able to singly receive a relatively high load, thereby preventing deformation exceeding a range of elastic deformation of the valve seat  7 , such as crush. 
     While the load distributing seat  10  was set as described above to appropriately distribute the thrust, the valve main body  1  was able to be manufactured with compactness being maintained, without design limitations being applied to the performance, product size, and so forth of the valve main body  1 . Also, it was confirmed that the load-bearing ability of the valve seat  7  was not lost and its functionalities were not impaired. 
     While the embodiments of the present invention have been described in detail in the foregoing, the present invention is not limited to the description of the above embodiments and can be variously modified in a scope not deviating from the spirit of the invention described in the claims of the present invention.