FLUID SUPPLY APPARATUS

Abstract: A fluid feeding apparatus for use in a gas supply system as in semiconductor manufacturing facilities which permits high-precision control of the flow of fluid without causing transient overshooting phenomena of fluid at the start of fluid feeding or fluid changeover. The fluid feeding apparatus of the present invention comprises a pressure flow controller to regulate the flow of fluid, a fluid changeover valve to open and close the fluid passage on the secondary side of the pressure flow controller and a fluid feeding control unit to control the actuation of the pressure flow controller and the fluid changeover valve, said pressure flow controller including: an orifice 5, a control valve 1 provided on the upstream side of the orifice 5, a pressure detector 3 provided between the control valve 1 and the orifice 5 and a calculation control unit 6 which inputs in a drive 2 for said control valve 1 a difference between a flow rate signal Qc and a flow rate specifying signal Qs as control signal Qy, said flow rate signal Qc calculated with flow rate Qc = KP 1 (K = constant) on the basis of a pressure P 1 detected by the pressure detector 3, wherein the flow rate on the downstream side of the orifice 5 is controlled by regulating the pressure P 1 on the upstream side of the orifice 5 through the opening and closing of said control valve 1.

Description: Field of the Invention The present invention relates to an improvement of an apparatus for feeding various kinds of fluids such as gas for use in the manufacture of semiconductors, chemicals, precision machine parts and the like, and more particularly to a fluid feeding apparatus which permits control with high precision of the flow rate of fluid at the time of starting to feed a fluid and switching fluids from one kind to another. Description of the Prior Art Fluid feeding apparatuses requiring control with high precision of the flow rate are used in semiconductor manufacturing facilities and chemical production plants. Most of those apparatuses are equipped with a so-called mass flow controller. Such a mass flow controller is shown in US-A-5 445 032. Fig. 8 shows an apparatus for feeding fluid (gas) used for in a high-purity moisture generator in semiconductor manufacturing facilities. It is so designed that H 2 and O 2 are fed to a reactor 51 from a gas feeding apparatus 50 at specific flow rates and are radicalized with a platinum catalyst and allowed to react with each other in non-combustion state to generate moisture gas (water vapor). The moisture gas thus generated in the reactor 51 is then supplied to an oxidizing furnace 52. In Fig.8, the reference numeral 54 designates a circuit for measuring the moisture generation responsiveness of the reactor 51, and includes a suction-rate regulating valve 55, a quadrupole mass spectrometer (Q-mass spectrometer) 56, a turbo molecular pump 57 and a vacuum pump 58. The Q-mass 56 is for measuring of ion concentrations of H 2 O, H 2 , O 2 and N 2 . A quadrupole mass analyzer MSQ-150A (ULVAC Corporation, Japan) is used for the purpose. The aforesaid gas feeding apparatus 50 is formed out of three mass flow controllers MFC 1 , MFC 2 and MFC 3 , changeover valves V 1 , V 2 and V 3 , gas storage containers (not shown), pressure regulators (not shown) and others. The changeover valves V 1 , V 2 and V 3 in this example are of the electric metal diaphragm type. To the primary sides of the three mass flow controllers MFC 1 , MFC 2 and MFC 3 are supplied H 2 at a gauge pressure of 2 kgf/cm 2 , O 2 at a gauge pressure of 2 kgf/cm 2 and N 2 at a gauge pressure of 6 kgf/cm 2 from the respective gas storage containers (not shown). To generate moisture in the reactor 51, in the meantime, the flow rates and other conditions of the three mass flow controllers MFC 1 , MFC 2 and MFC 3 in the gas feeding apparatus 50 are set, and then the system is purged with N 2 with V 1 and V 2 closed and V 3 opened. Then, V 3 is closed and V 2 is opened to supply O 2 , and at the same time that O 2 is supplied or about 3 seconds after the O 2 supply, V 1 is opened to supply H 2 . Thus, moisture gas (water vapor) starts to be generated in the reactor 51. Part of the moisture gas or the like from the reactor 51 is sucked into the measurement circuit 54 for a specific time by operating the suction-regulating valve 55, where the concentrations of H 2 , O 2 , H 2 O and N 2 in the generated moisture are measured by the Q-mass 56. Figs. 9 to 11 illustrate the concentrations of H 2 , O 2 , N 2 and H 2 O measured by the Q-mass 56 in the moistures produced in a moisture-generating testing arrangement. The testing arrangement was provided with the gas feeding apparatus 50 equipped with the mass flow controllers as shown in Fig. 8. And the measurements were taken under the following conditions (1), (2) and (3). The gauge pressures of H 2 , O 2 and N 2 on the primary sides of the mass flow controllers in the gas feeding apparatus 50 were 2 kgf/cm 2 , 2 kgf/cm 2 and 6 kgf/cm 2 respectively. (1) Pressure on the secondary side of the mass flow controllers: 1 kg/cm 2 abs H 2 : 50 sccm + O 2 : 1,000 sccm N 2 : 1,000 sccm H 2 starts to be fed 3 seconds after O 2 supply. (2) Pressure on the secondary side of the mass flow controllers: 0.5-kg/cm 2 abs H 2 : 50 sccm + O 2 : 1,000 sccm N 2 : 1,000 sccm H 2 starts to be fed 3 seconds after O 2 supply. (3) Pressure on the secondary side of the mass flow controllers: 0.2-g/cm 2 abs H 2 : 50 sccm + O 2 : 1,000 sccm N 2 : 1,000 sccm H 2 starts to be fed 3 seconds after O 2 supply. It is to be understood that "sccm" is a unit indicating the flow rate/minute in volume (cm 3 ) of H 2 , O 2 , N 2 etc in the standard state. As is evident from Figs. 9 to 11, the concentration of H 2 rises and peaks at a peak P H2 at the start of the gas feeding as the pressure decreases on the secondary side of the mass flow controllers MFC's (pressure reduction) in the moisture generation testing arrangement provided with the gas feeding apparatus 50 equipped with mass flow controllers. Along with that, there appears a peak P H2O in the concentration of H 2 O. H 2 and H 2 O peak at PH 2 and P H2O in the initial stage of the gas feeding. That means, it is impossible to precisely effect H 2 concentration control (flow rate control); the mass flow controller can not meet the demand for high-precision control of the flow rate of H 2 . It also should be noted that if the peak P H2 of the concentration of H 2 rises by several percent, there will arise a possibility of hydrogen exploding in the downstream oxidizing furnace 52, raising a safety problem. On the other hand, Figs. 12 to 13 also show the concentrations of H 2 , O 2 , N 2 and H 2 O measured by the Q-mass 56 in the moistures produced in the moisture-generating testing arrangement. The testing arrangement was provided with the gas feeding apparatus 50 equipped with the mass flow controllers as shown in Fig. 8. And the measurements were taken under the following conditions (1) and (2). The supply pressures (gauge pressures) of H 2 , O 2 and N 2 on the primary sides of the mass flow controllers were 2 kgf/cm 2 , 2 kgf/cm 2 and 6 kgf/cm 2 respectively. (1) Pressure on the secondary side of the mass flow controllers: 0.5 kg/cm 2 abs H 2 : 100 sccm + O 2 : 50 sccm (H 2 : O 2 = 2 : 1) N 2 : 1,000 sccm H 2 and O 2 started to be fed simultaneously and were cut off at the same time. (2) Pressure on the secondary side of the mass flow controllers: 0.5 kg/cm 2 abs H 2 : 100 sccm + O 2 : 50 sccm (H 2 : O 2 = 2 : 1) N 2 : 1,000 sccm H 2 started to be fed 3 seconds after O 2 supply and the feeding of H 2 was cut off three minutes earlier than O 2 cut-off. As is clear from Fig. 12, the concentration peak P H2 of H 2 in the initial stage of gas feeding rises to some 10 percent if H 2 and O 2 are fed simultaneously in the gas feeding apparatus 50 equipped with the prior art mass flow controller and there arises a safety question. Furthermore, the concentration P O2 of O 2 suddenly falls in the region where a peak P H2 of H 2 is observed because O 2 is consumed in its reaction with H 2 . As a result, it will be impossible to generate an intended quantity of moisture. Also, as is shown in Fig. 13, the concentration peak P H2 of H 2 increases to more than some 50 percent at the beginning of gas feeding in the gas feeding apparatus 50 using the prior art mass flow controller, further increasing the danger. In addition, a large quantity of O 2 is consumed at the aforesaid peak P H2 of H 2 , resulting in a substantial fall in the concentration O 2 . That makes it difficult to produce a required amount of moisture. As set forth above, the gas feeding apparatus 50 equipped with the prior art mass flow controllers has a problem that the flow rate of H 2 and O 2 is impossible to control with high precision because H 2 and O 2 flow in excessively in what is called an overshooting in the initial stage of the gas feeding or suspension. In generation of moisture in the gas feeding apparatus 50 with the mass flow controllers, it is natural that the amount of moisture generated deviates from the set level greatly because of the overshooting of H 2 and O 2 and it is difficult to control the generation of moisture with high precision. In the manufacture of semiconductors or the like, in the meantime, it is often necessary to feed many different kinds of gases at specific flow rates to specific places or switch the feeding from one kind to another Also, it is necessary to supply to specific places high-purity water produced through a reaction between H 2 O and O 2 . It is always required that the supply or switchover of gases and H 2 should be effected quickly with high precision. That is because high-precision control of the flow of gases and moisture is indispensable in improving or securing the production yield as well as the quality of finished products or semiconductors. SUMMARY OF THE INVENTION The present invention is to address the foregoing problems encountered with the apparatus for feeding gases or the like which is equipped with the prior art mass flow controller. That is, the prior art fluid feeding apparatus provided with mass flow controller fails to control the flow of fluid with high precision on account of what is called the overshooting of fluid occurring in the initial stage of the fluid supply. It would be desirable to provide a fluid feeding apparatus that permits control of the flow rate of gases with very high precision over the whole process from the start of fluid feeding to its suspension without causing transient phenomena such as the overshooting of feeding gases. Steps towards achieving this may be taken by adopting a pressure flow controller in place of the mass flow controller in the fluid feeding apparatus and optionally employing a solenoid driven high-speed actuating-type changeover valve as the fluid switchover control valve. A pressure flow controller is disclosed in EP-A-0 749 058. When used in semiconductor manufacturing facilities, for example, this feeding apparatus makes it possible to realize ideal initial film formation of semiconductors of high integration by controlling the generation of moisture with high precision. To find the cause of the overshooting phenomenon of fluids just after the start and suspension of supply of fluids, various experiments were carried out using the moisture generation testing arrangement shown in Fig. 8. As a result, it was discovered that most of the overshooting fluid (gas) in the fluid feeding apparatus 50 with the prior art mass flow controller is the fluid (gas) dwelling in pipe sections L 1 to L 3 connecting the respective changeover valves V 1 to V 3 and mass flow controllers MFC 1 to MFC 3 . The experiments also indicated that the construction of the mass flow controllers MFC 1 to MFC 3 was responsible for increasing the dwelling of fluid (gas), that is, the cause of the aforesaid overshooting. Fig. 14 is a block diagram showing the basic configuration of the prior art mass flow controller. In Fig. 14, the gas flowing in from the primary side is divided into portions flowing through in a laminar flow bypass 59 and a sensor bypass 60. In the sensor bypass 60, the mass flow of the fluid is determined by a sensor 61 in the form of temperature change in proportion thereto. The determined temperature change is converted into electric signals in a bridge circuit 62 and output through an amplifier circuit 63 and others to a display 64 and also to a comparison control circuit 65 as linear voltage signals. Meanwhile, the set signals from outside are input from a setter 66 into the comparison control circuit 65, where the difference between the aforesaid detected signals and the set signals is calculated. The signal difference is then sent into a valve drive 67, which actuates a flow control valve 68 to bring the signal difference to zero. Now, if the changeover valve V 1 mounted on the secondary side is suddenly closed while the mass flow controller is in operation, the gas flowing through the sensor 61 comes to a standstill. Then, the control system of the mass flow controller works transiently to increase the flow of gas and the flow control valve 68 is opened. As a result, the gas pressure in the secondary line L 1 rises, causing the gas to dwell therein. And next time the changeover valve V 1 is opened, the dwelling gas rushes into the gas consuming side through the changeover valve V 1 , causing a gas overshooting phenomenon. Finding such structural characteristics in the mass flow controller, the inventors conceived an idea of constructing in the following manner a fluid feeding apparatus free from causing the aforesaid transient phenomena such as the overshooting of fluid. That is, this apparatus has adopted "a flow rate control mechanism which involves actuating the flow rate control valve by pressure detection signals" instead of "by mass flow rate detection signals." The present invention was designed on the basis of the aforesaid idea. According to one aspect of the present invention there is provided a fluid feeding apparatus which comprises: a pressure flow controller comprising a plurality of pressure flow controller units to regulate the flow of fluid; a plurality of fluid changeover values; a plurality of fluid passages ; a fluid feeding control unit to control the actuation of the pressure flow controller units and the fluid changeover valves; and a fluid consumer; wherein the primary side of each pressure flow controller unit is connectable to a different, respective, gas storage container and the secondary side of each pressure flow controller unit is connected to a respective fluid passage, each fluid changeover valve is arranged on the secondary side of a respective pressure flow controller unit and is operable to open and close the respective fluid passage, the outlet of each fluid changeover valve is in communication with the fluid consumer when the respective changeover valve is open, and each pressure flow controller unit comprises: an orifice, a control valve provided on the upstream side of the orifice, a pressure detector provided between the control valve and the orifice and a calculation control unit which inputs a difference between a flow rate signal Qc and a flow rate specifying signal Qs as control signal Qy into a drive for said control valve, said flow rate signal Qc calculated with flow rate Qc = Kp 1 (K = constant) on the basis of a pressure P 1 detected by the pressure detector, the flow rate on the downstream side of the orifice being controlled by regulating the pressure P 1 on the upstream side of the orifice through the opening and closing of said control valve. The present invention may also provide a fluid feeding apparatus which permits the opening and closing of the control valve with the pressure P 1 on the upstream side of the aforesaid orifice held some twice or more as high as the pressure P 2 on the downstream side. The fluid feeding apparatus may use an electric high-speed actuating fluid changeover valve as the fluid changeover valve. The electric high-speed actuating type fluid changeover valve may be a solenoid-driven type-high speed actuating fluid changeover valve. According to another aspect of the present invention there is provided a method as described by claim 8. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a block diagram of a gas feeding apparatus A showing an embodiment of the present invention. Fig. 2 is a block diagram showing an embodiment of a pressure flow controller C used in the present invention. Fig. 3 is a vertical, sectional view of a fluid changeover valve D used in the preferred embodiment of the present invention. Fig. 4 is a diagram showing changes with time in concentrations of H 2 , O 2 , N 2 and H 2 O with the pressure on the secondary side of the pressure flow controllers according to the preferred embodiment of the present invention set at. 1 kg/cm 2 abs using a testing arrangement shown in Fig. 8. Fig. 5 is a diagram showing changes with time in concentrations of H 2 , O 2 , N 2 and H 2 O with the pressure on the secondary side of the pressure flow controllers set at 0.5 kg/cm 2 abs. Fig. 6 is a diagram showing changes with time in concentrations of H 2 , O 2 , N 2 and H 2 O with the pressure on the secondary side of the pressure flow controllers set at 0.2 kg/cm 2 abs. Fig. 7 is a diagram showing changes with time in concentrations of H 2 , O 2 , N 2 and H 2 O with the pressure on the secondary side of the pressure flow controllers set at 1 kg/cm abs and with the feeding of H 2 and O 2 at the ratio of 2 to 1 started and suspended simultaneously in the testing arrangement shown in Fig. 8. Fig. 8 is an overall system diagram of an moisture generation testing arrangement equipped with a gas feeding apparatus in which the prior art mass flow controllers are mounted. Fig. 9 is a diagram showing changes with time in concentrations of H 2 , O 2 , N 2 and H 2 O with the pressure on the secondary side of the mass flow controllers set at 1 kg/cm 2 abs in the testing arrangement shown in Fig. 8. Fig. 10 is a diagram showing changes with time in the respective concentrations of H 2 , O 2 , N 2 and H 2 O with the pressure on the secondary side of the mass flow controllers set at 0.5 kg/cm 2 abs. Fig. 11 is a diagram showing changes with time in concentrations of H 2 , O 2 , N 2 and H 2 O with the pressure on the secondary side of the mass flow controllers set at 0.2 kg/cm 2 abs. Fig. 12 is a diagram showing changes with time in concentrations of H 2 , O 2 , N 2 and H 2 O with the pressure on the secondary side of the mass flow controllers set at 1 kg/cm abs and with the feeding of H 2 and O 2 at the ratio of 2 to 1 started and suspended simultaneously in an testing arrangement shown in Fig. 8. Fig. 13 is a diagram showing changes with time in concentrations of H 2 , O 2 , N 2 and H 2 O with the feeding of H 2 started three minutes after O 2 supply and suspended three seconds earlier than O 2 suspension in the same test as in Fig. 12. Fig. 14 is a block diagram showing the basic configuration of the prior art mass flow controller. The following reference letters and numerals used herein refer to the following parts in the accompanying drawings. A Fluid feeding apparatus B Fluid feeding control unit C Pressure flow controller D Fluid changeover valve E Fluid consumer 1 Control valve 2 Control valve drive 3 Pressure detector 4 Temperature detector 5 Orifice 6 Calculation control unit 7 Amplifier 8 A/D converter 9 Inversion amplifier 10 Valve block 11 Electric actuator (solenoid) 12 Shield case 13 Flow channel 14 Seat 15 Block 16 Metal diaphragm 17 Bonnet 18 Bonnet nut 19 Stem 20 Diaphragm press 21 Spring 22 Nut 23 Main case 24 Plunger 25 Exciting coil 26 Lead 27 Peripheral wall 28 Upper wall 29 Through hole 30 Ferrite bead DESCRIPTION OF PREFERRED EMBODIMENT Now, there will be described a fluid feeding apparatus A embodying the present invention with reference to the drawings. Fig. 1 is a block diagram showing the fluid feeding apparatus A. The fluid feeding apparatus A comprises a fluid feeding control unit B, pressure flow controllers C and fluid changeover valves D. The present embodiment comprises three pressure flow controllers C and three fluid changeover valves D so that the supply of gas to the fluid consumer can be freely switched among H 2 , O 2 and N 2 . It goes without saying that the number of pressure flow controllers may be one or four or more. To the primary sides of the pressure flow controllers C, H 2 , O 2 and N 2 are led at about a specific pressure from gas storage containers (not shown) through pressure regulators (not shown). And to each pressure flow controller C is input each specific flow rate specifying signal Qs from the fluid feeding control unit B. Then, the gas from the secondary side of each pressure controller C is controlled by opening the valve D to a specific set flow rate Qs and supplied to the fluid consumer E. Fig. 2 shows a pressure flow controller C used in an embodiment of the present invention. The pressure flow controller C includes a control valve 1, a control valve drive 2, a pressure detector 3, a temperature detector 4, orifice 5, a calculation control unit 6, amplifiers 7a, 7b, A/D converters 8a, 8b and others. The control valve 1 is a so-called direct touch-type metal diaphragm valve, and its drive is a piezoelectric element-type drive. The pressure detector 3 is a semiconductor strain type pressure sensor. The temperature detector 4 is a thermocouple type temperature sensor. Needless to say, the aforesaid drive, pressure sensor, temperature sensor etc. may be of any type. The orifice 5 is an orifice made by electric discharge machining on a plate-shaped metal gasket. Also, an ultrathin pipe or an orifice formed in a metal film by etching may be used as orifice 5. The calculation control unit 6 is formed of what is called the control circuit board and is equipped with a temperature correction circuit 6a, a flow rate calculation circuit 6b, a comparison circuit 6c, an amplifier circuit 6d etc. It is noted that in case the calculation control unit 6 is used in an atmosphere at a constant temperature as in a clean room, the temperature correction circuit 6a may be omitted without affecting the performance of the calculation control unit 6. Fig. 3 is a vertical, sectional view showing a fluid changeover valve D used in an embodiment of the present invention. The main part of the changeover valve D includes a valve body 10, an electric actuator 11 and a shield case 12. In this example, the electric actuator 11 is a solenoid. The valve block 10 controls the flow of fluid by opening and closing the valve. The valve used in this example is of the normally closed type. That is, the valve block 10 is formed out of a body 15 provided with a flow channel 13 and a seat 14 therein, a diaphragm 16 made of metal (nickel-based alloy) so provided to be able to sit on the seat 14, a bonnet 17, a bonnet nut 18, a stem 19 extending through the bonnet and movable up and down, a diaphragm presser 20 to press the diaphragm 16 and a spring 21 to always thrust the stem 19 downward (to close the valve). The electric actuator 11 is a solenoid. The electric actuator 11 comprises a case 23 fastened to the bonnet 17 by a nut 22, a plunger 24 provided in continuity with the stem 19 of the valve block 10, an exciting coil 25 and an iron rod 25a for moving the plunger 24, and a lead 26. The case 23 is made of aluminum, but may be made of a high magnetic permeability material such as permalloy. The case 12 is provided outside of the main case 23 with a small space provided therebetween and prevents the leakage of the magnetic field. In the present example, the shield case 12, cylindrical and opening at the lower end, comprises a peripheral wall 27 covering the outside of the electric actuator 11, an upper wall 28 covering the upper side of the electric actuator 11 and a through hole 29 with the lead 26 extending therethrough, and is fit over the main case 23. The shield case 12 is made of a one-mm-thick sheet of permalloy or malleable iron. The shield case 12 to contain the magnetic field has the ferrite bead 30 at a portion where the lead 26 passes through the upper wall 28. The ferrite bead is ring-formed and fitted around the lead 26 inside (under) the upper wall 28 so as to fill up the gap between the lead 26 and the through hole 29. Next, the operation of the fluid feeding apparatus A will be explained. Referring to Figs. 1 and 2, the gas pressure P 1 on the outlet of the control valve 1, that is, on the upstream side of the orifice 5 is detected by the pressure detector 3 and sent to the amplifier 7a and the A/D converter 8a to be digitized. The signals thus digitized are then input in the flow calculation circuit 6b. Likewise, the gas temperature T1 on the upstream side of the orifice 5 is detected by the temperature detector 4 and referred to the amplifier 7b and A/D converter 8b to be digitized. The digitized signals are then input in the temperature correction circuit 6a. In case the temperature correction circuit 6a is omitted, flow rate calculation can be done with analog signals so as to simplify the control circuit. The calculation control unit 6 calculates the flow rate Q' = KP1 on the basis of the upstream fluid pressure P 1 and effects the temperature correction of the flow rate Q' according to correction signals from the temperature correction circuit 6a. The calculated flow rate signal Qc is then input in the comparison circuit 6c. In the meantime, the flow rate specifying signal Qs has been input in the comparison circuit 6c, where the calculated flow rate signal Qc and the flow rate specifying signal Q are compared and the differential signal Qy = Q c-Qs is output as control signal to the drive 2 of the control valve 1. If the calculated flow rate signal Qc is larger than the flow rate specifying signal Qs, the drive 2 moves to close the control valve 1. If the signal Qc is smaller than the signal Qs, the drive 2 moves to open the valve 1. That way, the control valve 1 is opened or closed automatically to bring the signal Qc equal to the signal Qs. Needless to say, it is desirable in the preferred embodiment of the present invention that the ratio of the fluid pressure P 2 on the downstream side of the orifice 5 to the upstream fluid pressure P 1 on the upstream side, that is, P 2 /P 1 , is always not larger than some 0.5. That means that the fluid pressure P 1 on the upstream side of the orifice 5 is about twice or more as high as the fluid pressure P 2 on the downstream side. In this regard, it may be so configured that the fluid pressure P 1 on the upstream side of the orifice 5 and the fluid pressure P 2 on the downstream side are input in the inversion amplifier 9 wherein if the pressure P 1 and the pressure P 2 are reversed in the amount - a situation in which the back flow may arise - or P 2 / P 1 > 0.5 occurs - a situation in which while there is no back flow, the flow cannot be controlled with high precision, the control valve 1 will be automatically shut up. In case the solenoid 11 is not excited, the plunger 24, the stem 19 and the diaphragm presser 20 are brought down by the elastic force of the spring 21 so that the diaphragm 16 is forced to nest on the seat 14 through the diaphragm presser 20 as shown in Fig. 3. That way, the fluid changeover valve D is closed. If the solenoid is energized, then the plunger 24, the stem 19 and the diaphragm presser 20 go up against the elastic force of the spring 21 and the diaphragm 16 will return to its original form by its own elastic force and leave the seal 14. As a result, the fluid changeover valve D will open. The electric high-speed actuating type fluid changeover valve in the embodiment of the present invention will open or close in less than 10 msec as against an average 100 msec for the prior art pneumatic fluid changeover valve. That is, the electric high-speed changeover valve works some 10 time as fast. It is also noted that when the solenoid 11 is energized (in the initial energizing and holding energizing), the magnetic field leaks out from the exciting coil 25. But since the shield case 12 is provided outside of the solenoid 11, the leaked magnetic field is contained and shut off by the shield case 12. In the pressure flow controller C in the present embodiment, if the fluid changeover valve D is actuated in the direction in which the valve D is closed, the fluid pressure P 1 on the primary side of the orifice 5 will rise and the fluid flow rate Q' = KP 1 will increase as shown in Fig. 2. Then, the difference Qy from the set flow rate Qs (Qs = 0) will grow. To bring that down, that is, to decrease the fluid pressure P 2 on the secondary side, the control valve 1 will be closed. The actuating mechanism of the pressure flow controller C according to the preferred embodiment of the present invention is summarized in comparison with that of the prior art, that is, the mass flow controller as in the following table. Because of its mechanism, the pressure flow controller C according to the present invention does not allow the fluid to dwell on the secondary side L of the controller C. Closing of high-speed switch-over valve → Mass flow controller Control valve opens → Secondary side pressure increases → Fluid dwells Pressure flow controller Control valve closes → Secondary side pressure decreases → No fluid dwells Fig. 4 shows changes with time in concentrations of H 2 , O 2 , N 2 and H 2 O measured when moisture was generated under the same conditions as in Fig. 9 in the same moisture generating testing arrangement as shown in Fig. 8 except that the pressure flow controllers C 1 to C 3 were installed in place of the prior art mass flow controllers MFC 1 to MFC 3 . Likewise, Fig. 5 shows changes with time in concentrations of H 2 , O 2 , N 2 and H 2 O measured in the moisture generating tests under the same conditions as in Fig. 10 using the fluid feeding apparatus A embodying the present invention. Fig. 6 shows changes with time in concentrations of H 2 , O 2 , N 2 and H 2 O measured in the moisture generating tests under the same conditions as in Fig. 11 using the fluid feeding apparatus A embodying the present invention. Fig. 7 shows changes with time in concentrations of H 2 , O 2 , N 2 and H 2 O measured in the moisture generating tests under the same conditions as in Fig. 12 - 100 sccm H 2 + 50 sccm O 2 , that is, H 2 : O 2 = 2 : 1 □ using the fluid feeding apparatus A embodying the present invention. As comparisons between Figs. 4 and 9, Figs. 5 and 10, Figs. 6 and 11, Figs. 7 and 13 indicate, it has been found that even if the set pressure on the secondary side is lowered in the fluid feeding apparatus A embodying the present invention, peak values of H 2 and H 2 O will not appear at all. The fluid feeding apparatus embodying the present invention shown in Fig. 1 has three units of the pressure flow controller C installed therein. It is understood that the number of units is changed depending on the number of kinds of fluids (gases) to be supplied. It is also noted that in the fluid feeding apparatus embodying the present invention, a solenoid-driven high-speed actuating valve is used as electric fluid changeover valve D. The type of the fluid changeover valve D is not limited to the solenoid-type high-speed actuating changeover valve but may be of the piezoelectric element drive type such as piezoelectric ceramic. (Effects of the invention) In the present invention, the flow rate regulator, which is the core of the fluid feeding apparatus, is a pressure flow controller. This pressure flow controller is actuated to decrease the pressure on the secondary side when the flow changeover valve is closed. Thus, the structural characteristics of the pressure flow controller is utilized effectively in this fluid feeding apparatus. That makes it possible to control the flow of fluid or the moisture generation with high precision without giving rise to transient phenomena such as overshooting of fluid even at the start of fluid feeding or in a transient state such as switchover of feeding fluids. Furthermore, if the fluid changeover valve adopted is a solenoid-driven high-speed actuating valve, this speeds up such operations as changeover from one kind of fluid to another. That and no fluid overshooting help to form ideal initial film in the manufacture of semiconductors and contributes greatly to improvement of high-integration semiconductors. Thus, the above embodiments of the present invention would bring about highly practical effects.

Claims: A fluid feeding apparatus which comprises: a pressure flow controller (C) comprising a plurality of pressure flow controller units (C 1 to C n ) to regulate the flow of fluid; a plurality of fluid changeover valves (D 1 to D n ); a plurality of fluid passages (L 1 to L n ); a fluid feeding control unit (B) to control the actuation of the pressure flow controller units (C 1 to C n ) and the fluid changeover valves (D 1 to D n ); and a fluid consumer (E) wherein the primary side of each pressure flow controller unit (C n ) is connectable to a different, respective, gas storage container and the secondary side of each pressure flow controller unit (C n ) is connected to a respective fluid passage (L n ), each fluid changeover valve (D n ) is arranged on the secondary side of a respective pressure flow controller unit (C n ) and is operable to open and close the respective fluid passage (L n ), the outlet of each fluid changeover valve (D n ) is in communication with the fluid consumer (E) when the respective changeover valve (D n ) is open, and each pressure flow controller unit (C n ) comprises: an orifice (5), a control valve (1) provided on the upstream side of the orifice (5), a pressure detector (3) provided between the control valve (1) and the orifice (5) and a calculation control unit (6) which inputs a difference between a flow rate signal Qc and a flow rate specifying signal Qs as control signal Qy into a drive (2) for said control valve (1), said flow rate signal Qc calculated with flow rate Qc = KP 1 (K = constant) on the basis of a pressure P 1 detected by the pressure detector (3), the flow rate on the downstream side of the orifice (5) being controlled by regulating the pressure P 1 on the upstream side of the orifice (5) through the opening and closing of said control valve (1). A fluid feeding apparatus according to claim 1, wherein each control valve (1) is controlled to open and close with the pressure P 1 on the upstream side of the respective orifice (5) held some twice or more as high as the downstream pressure P 2 . A fluid feeding apparatus according to claim 1 or claim 2, wherein at least one of the control valves (1) is controlled to automatically shut up when the pressure P 1 on the upstream side and the pressure P 2 on the downstream side of the respective orifice (5) satisfy the inequality P 2 / P 1 > 0.5. A fluid feeding apparatus according to claim 1, claim 2 or claim 3, wherein each fluid changeover valve (D n ) is an electric high-speed actuating type fluid changeover valve. A fluid feeding apparatus according to claim 4, wherein the electric high-speed actuating type fluid changeover valve is a solenoid-driven high-speed actuating type fluid changeover valve. A fluid feeding apparatus according to any of claims 1 to 5, wherein there are three pressure flow controller units (C 1 to C 3 ) and each of these is connected to a different, respective, gas cylinder. A fluid feeding apparatus according to claim 6, wherein the three pressure flow controller units (C 1 to C 3 ) are connected to a H 2 storage container, an O 2 storage container and an N 2 storage container respectively. A method of operating a fluid feeding apparatus according to any of the preceding claims to generate moisture, comprising the steps of: purging the fluid consumer (E) with N 2 ; supplying O 2 to the fluid container (E); and supplying H 2 either at the same time that O 2 is supplied or 3 seconds after the O 2 supply is opened.

Inventors: DOHI RYOUSUKE, IKEDA NOBUKAZU, KAGAZUME TETU, KAWATA KOUJI, MINAMI YUKIO, NISHINO KOUJI, OHMI TADAHIRO, SUGIYAMA KAZUHIKO, YAMAJI MICHIO, DOHI, RYOUSUKE, IKEDA, NOBUKAZU, KAGAZUME, TETU, KAWATA, KOUJI, MINAMI, YUKIO, NISHINO, KOUJI, OHMI, TADAHIRO, SUGIYAMA, KAZUHIKO, YAMAJI, MICHIO, DOHI, Ryousuke, Kabushiki-Kaisha Fujikin, IKEDA, Nobukazu, Kabushiki-Kaisha Fujikin, KAGAZUME, Tetu, Tokyo Electron Yamanashi Ltd., KAWATA, Kouji, Kabushiki-Kaisha Fujikin, MINAMI, Yukio, Kabushiki-Kaisha Fujikin, NISHINO, Kouji, Kabushiki-Kaisha Fujikin, SUGIYAMA, Kazuhiko, Tokyo Electron Yamanashi Ltd., YAMAJI, Michio, Kabushiki-Kaisha Fujikin
Applicants: FUJIKIN KK, OHMI TADAHIRO, TOKYO ELECTRON LTD, FUJIKIN INC., OHMI, TADAHIRO, TOKYO ELECTRON LIMITED
Application year: 1999
Main classification: G05D7
IPC codes: F16K31, G05D7, C01B5, G05D21, G05D11