JPH11194833A - Mass flow controller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a mass flow controller which is increased in full-open flow rate and then shortened in response time by improving the precision and response of flow rate control and sealing performance. SOLUTION: The mass flow controller has a flow rate sensor part 2 which detects the flow rate of fluid flowing in a sensor flow passage, a flow rate control valve 6 which controls the flow rate of the fluid, and a control circuit part 3 and the flow rate control valve 6 consists of a flow rate control valve main body having an inflow-side flow passage 12 and an outflow-side flow passage 13, a valve seat 4 provided at an end of the inflow-side flow passage, a metallic diaphragm 5 having a flat part contacting and leaving the valve seat, and an actuator 60 which is positioned above the metallic diaphragm 5 and generates a pressing force on the valve seat side; and a diaphragm spacer 61 which presses the metallic diaphragm 5 is provided below the actuator 60 and a recessed part 61a is formed on the depression surface of the diaphragm spacer 61 except the contact surface between the valve seat 4 and metallic diaphragm 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mass flow controller capable of precisely controlling a mass flow rate of a fluid such as a gas.

[0002]

2. Description of the Related Art In order to manufacture a semiconductor product by performing a film forming process, an etching process and the like with high precision, it is necessary to flow a small amount of process gas while controlling it with high precision. At this time, a mass flow controller is generally used as a flow control device.

A conventional mass flow controller M is shown in FIG.
As shown in FIG. 2, a sensor unit 2 for detecting a mass flow rate of a trace fluid (hereinafter, described as an example of a gas), a flow control valve 8 provided with an actuator unit 80, and a control circuit unit 3 for controlling these (details will be described below). (Not shown). In the mass flow controller M, first, gas flowing from an inflow port (inflow side joint) 71 is supplied to an inflow channel 72.
In the middle of a, the sensor pipe 20 and the same pipe as this pipe are packed into a predetermined number and branched into a bypass pipe 75 set at a predetermined flow ratio, and they flow again. It flows to the inflow channel 72c.

Here, the sensor pipe 20 is, for example, a stainless pipe having an inner diameter of about 0.5 mm formed in a substantially U-shape, and both ends are open to the inflow channel 72. The upstream and downstream sides of the sensor pipe 20 are heat-sensitive coils 2 respectively.
1 and 22 are wound, and a bridge circuit is formed by combining with other resistors. The sensor circuit 2 is formed by these. The heat sensitive coils 21 and 22 of this sensor
Is heated to a constant temperature higher than the gas temperature,
The upstream heat-sensitive coil 21 is deprived of heat by the flow of gas, and its temperature is lowered. The temperature of the other downstream coil 22 is raised because the gas warmed on the upstream side flows. Occurs. Such heat transfer is detected as an unbalanced voltage in the bridge circuit, and this potential difference is proportional to the mass flow rate, and thus functions as a mass flow sensor. The types of such mass flow sensors include a constant current sensor (Japanese Patent Publication No. 56-23094), a constant temperature sensor (Japanese Patent Publication No. 4-49893), and a constant temperature difference sensor (Japanese Patent Laid-Open No. 1-150817).
No.), etc., and these sensors can be appropriately used.

Next, the flow signal from the mass flow sensor 2 is amplified by an amplifier circuit and then input to a comparison control circuit. Here, a drive signal (valve drive voltage) that is compared with a preset set flow rate signal and eliminates the difference is input to the actuator unit, and as a result,
The gas flow rate can be controlled by adjusting the opening of the flow control valve 8. These controls are performed by the control circuit unit 3 (not shown). Further, in order to precisely control the valve opening, it is necessary to control the stroke within a stroke range of about several tens of μm. Therefore, as the actuator section 80, a laminate that can generate a large thrust with a small stroke. A piezoelectric element is generally used.

[0006] The actuator portion of the flow control valve 8 in FIG. 4 also uses a laminated piezoelectric element body 80 (hereinafter, referred to as a piezoelectric actuator), and directly moves a metal diaphragm (hereinafter, referred to as a metal diaphragm) up and down to flow the gas. It is a flow control valve to be controlled. This flow control valve is provided with an inflow passage 72c.
And a metal valve seat 81 provided at an end of the metal plate, and a peripheral edge thereof is sandwiched by a diaphragm holder 83 so as to face the valve seat 81, and has a flat portion at the center and a semi-circular elastic deformation portion formed outside the flat portion. Metal diaphragm 82, a valve rod 84 that accommodates the laminated piezoelectric element body 80 therein and presses the metal diaphragm 82, and the valve rod 84 is always in the valve seat 8
1 and a spring member 88 for bringing the valve into a closed state. Here, the upper end of the laminated piezoelectric element body 80 is locked by an adjusting member 89, and one lower end is connected to the valve rod 8.
4 and is supported by a bridge member 85 placed on the block-shaped main body 7. In order to press the space between the metal diaphragm 5 and the metal valve seat 81, a pressing portion 86 is provided together with the valve stem in this example so as to apply pressure to the diaphragm from above. In addition, the diaphragm spacer member may be provided separately.

[0007] Therefore, when the laminated piezoelectric element body 80 is expanded by applying a voltage, the direction of the thrust is reversed by the bridge member 85 and acts in the direction of pushing up the valve stem 84 against the spring member 88. As a result, the metal diaphragm 82 is separated from the valve seat 81 by its own restoring force and the flow rate is adjusted. Although this example shows a normally closed type flow control valve, a normally open type flow control valve in which the structure of a bridge member or a spring member is changed has been conventionally used.

[0008]

As described above, in a flow control valve in which a metal diaphragm is directly brought into contact with or separated from a metal valve seat (contact and separation), the contact surface (because of the low rigidity of the metal diaphragm). (Hereinafter referred to as a sealing surface.) In some cases, the sealing property at the time of closing and closing is relatively poor. Therefore, after the metal diaphragm is brought into contact with the valve seat, a further pressing force is applied to increase the seal surface pressure. The pressing force at this time is called a preload.
When a piezoelectric actuator that generates a displacement of 0 μm is used, about 32 μm (80%) of the total displacement is used for a flow control stroke until it comes into contact with a valve seat, and the remaining about 8 μm (20%) Is used for displacement (actually, at this time, the diaphragm is already in contact with the valve seat and is simply pressed against the valve seat without displacement) after the contact of the valve seat.

However, (1) Conventionally, since the lower end portion of the valve stem and the pressing surface of the diaphragm spacer are flat, the pressing force is scattered over almost the entire surface of the metal diaphragm, causing a reduction in the sealing performance with the valve seat. Had become. It was also considered to be the cause of undulation and partial deformation of the diaphragm. (2) Further, since the pressing surface of the diaphragm spacer is cut by a milling machine in processing, a convex portion that cannot be cut remains at the center of the surface. Therefore, when the diaphragm spacer pushes down and elastically deforms the metal diaphragm, the metal diaphragm causes an unexpected displacement due to the convex portion, thereby deteriorating the sealing performance. As described above, when the sealing performance is deteriorated, there is a problem that the response time is delayed and the fully open flow rate is reduced.

In view of the above, the present invention has been made to solve the above-mentioned problem, and has an object to provide a mass flow controller in which the response time is increased by increasing the fully open flow rate by improving the sealing performance of the flow rate control.

[0011]

SUMMARY OF THE INVENTION The present invention relates to a mass flow controller having a flow sensor for detecting a flow rate of a fluid flowing in a sensor flow path, a flow control valve for controlling a flow rate of the fluid, and a control circuit. The flow control valve, a flow control valve body having an inflow side flow path and an outflow side flow path,
A valve seat provided at the end of the inflow-side flow path, a metal diaphragm having a flat portion which comes into contact with and separates from the valve seat, and an actuator which is located above the metal diaphragm and generates a pressing force on the valve seat side; And a diaphragm spacer for pressing the metal diaphragm below the actuator, and a concave portion provided on a pressing surface of the diaphragm spacer excluding a contact surface between the valve seat and the metal diaphragm. Here, in order to enhance the sealing property between the valve seat and the metal diaphragm, it is desirable that the portion of the diaphragm spacer that is in contact with the diaphragm is set to be on the same plane so that pressure is evenly applied.

According to the present invention, the provision of the concave portion reduces the pressing area with the diaphragm spacer that presses the metal diaphragm, so that pressure can be concentrated on the seal between the valve seat and the metal diaphragm.
The sealing performance against gas can be improved. Also,
Since the concave portion is provided at the center of the diaphragm spacer, the convex portion which has conventionally occurred is removed at the same time, and the displacement and deformation of the metal diaphragm are not adversely affected. As described above, the displacement of the piezoelectric actuator, which has been conventionally used to increase the seal surface pressure, can be used by transferring it to the stroke side for adjusting the flow rate. Therefore, the controllable flow rate range is expanded and the valve drive voltage can be reduced. The shape of the contact portion of the diaphragm spacer is usually annular, but is selected based on the relationship between the shape and dimensions of the diaphragm and the valve seat, the type of gas, and the like. Good. Also, the contact surface does not have to be perpendicular to the vertical movement direction of the diaphragm spacer.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a longitudinal sectional view showing one embodiment of the mass flow controller of the present invention. FIG. 2 is an enlarged view around the valve seat. Here, the same components as those in FIG. 4 are denoted by the same reference numerals. First, the overall configuration of the mass flow controller 1A in FIG. 1 will be described. The mass flow controller main body 1 is composed of a main body 1a made of stainless steel (SUS316L) or the like and having an outflow-side joint and a main body 1b having an inflow-side joint. The main body 1a is an integrated block including a flow control valve main body part and a joint part, and its flow path is an inflow flow path 12a connected to the inflow port 11,
A metal valve seat 4 made of stainless steel (SUS316L) or the like is attached to an end of the flow path 12c by a caulking means. A metal diaphragm 5 (hereinafter, referred to as a metal diaphragm) is disposed so as to face the valve seat 4, and the metal diaphragm 5 separates the inflow-side flow path 12 and the outflow-side flow path 13 from each other. Reference numeral 5 directly contacts and separates from the sealing surface of the valve seat 4. Further, the outflow channel 13a extends directly around the valve seat 4 partitioned by the metal diaphragm 5, and the inner wall 13w of the outflow channel 13a is a mounting portion of the valve seat. The outflow channel 13a is bent at 90 degrees and is connected to the outflow channel 13b and the outflow port 14. Therefore, the inflow side flow path 12
From c to the outflow channel 13b is a flow control valve portion,
Hereinafter, this part is particularly referred to as a flow control valve main body in the mass flow controller main body.

Further, the main body 1a may have a separate outlet-side joint portion as in the prior art. However, the main body 1a is preferably integrated with the inlet-side channels 12b and 12c, the outlet-side channel 13b, and the upper-opening channel 13a. In concentric processing. In order to attach the valve seat 4 to the main body 1a, a screwing means may be used. Alternatively, the valve seat 4 may be formed integrally with the main body 1a by being cut out from the main body 1a. However, it is preferable that the size of the mounting portion is substantially the same as the conventional one, and the diameter of the valve seat inlet 41 is as large as possible in view of the wall thickness. A tapered inner surface 42 that extends outward from the middle of the inflow port 41 forms a valve seat opening 43 that extends as far as possible to the outer peripheral side. At the same time, at least the height position of the upper surface 16 of the flow control valve main body and the contact surface 44 (hereinafter referred to as a sealing surface 44) of the valve seat outlet is formed on the same surface. The upper surface 16 of the main body can be simultaneously lap-finished. In this lapping, the entire upper surface 16 of the mass flow controller main body 1a is finally finished to a mirror surface of about 0.2S, so that the sealing surface of the metal O-ring of the sensor portion is also good, and the processing and assembly are extremely efficient. It is a target.

Then, the mirror-finished main body upper surface 1
6, a metal O-ring 69b and a spacer 69a,
The metal diaphragm 5 is placed via a valve seat spacer (approximately 80 μm) 69c, the peripheral portion of the metal diaphragm 5 is clamped by the diaphragm retainer 62, and the housing 63 and the lid 64 are mounted on the main body using bolts. 1a. On the other hand, a disk-shaped diaphragm spacer 61 is mounted on the upper surface of the metal diaphragm 5, and the concave portion 61 a is provided at the center except for the sealing surface 44 with the metal diaphragm 5 as described above. Usually, since the metal diaphragm 5 is circular so as to match the shape of the sealing surface 44 of the valve seat, the concave portion 61a of the diaphragm spacer 61 is also provided in a circular shape with respect to the contact surface so that the pressing surface pressure is evenly applied to the metal diaphragm. Is good. Diaphragm spacer 61
Is designed to transmit the pressing force of the piezoelectric actuator 60 via the hard ball 65 having the centering action, the piezo spacer 66, and the bearing 66a.

The piezoelectric actuator 60 is formed by sealing a laminated piezoelectric element in a case made of a metal such as stainless steel, preferably a metal material having a thermal expansion coefficient close to that of the laminated piezoelectric element. 68
a and the nut 68b are screwed and assembled to the housing 63 in a state where the axes are aligned. In this mass flow controller, the piezoelectric actuator 60 is normally pushed up by the spring 67, and thus the metal diaphragm 5 is in a valve-open state in which the metal diaphragm 5 is separated by its own elastic force. Then, this is a normally open type mass flow controller for controlling the flow rate by adjusting the amount of movement of the metal diaphragm 5 by pushing down the diaphragm spacer 61 against the spring force by energization. This can be configured as a normally closed mass flow controller similar to the above-described conventional one.

Each of the above members is basically made of stainless steel (SUS316L or the like). However, for the metal diaphragm 5, a Co-based alloy or a Ni—Co alloy, for example, Ni 13-18%,
Cr 18-23%, Mo 5-9%, Co 38-44%,
It is made of a highly elastic metal material composed of a balance of Fe and impurities, has high corrosion resistance and durability, and has a self-restoring force. A circular thin plate having a thickness of about 0.15 mm has a flat portion 51 in the center, an elastically deformable portion 52 having a semicircular cross-section outside the center, and a sandwiching peripheral portion 53 outside the flat portion 51. . In order to further increase the rigidity, it is also possible to use a flat thin plate made of a circular thin plate of the same material integrally attached by spot welding or an adhesive.

Next, the mass flow controller 1A will be further described with reference to FIG. First, as described above, the sealing surface 44 of the valve seat 4 and at least the upper surface 1 of the flow control valve body
6 is assembled so that it is on the same surface, and then lapping is performed. As a result, the flatness of the sealing surface 44 of the valve seat, the surface on which the metal diaphragm 5 and the diaphragm retainer 62 are stacked coincide, and the axis of the actuator coincides with the axis of the valve seat, the metal diaphragm, and the diaphragm spacer. . Therefore, the entire stroke of the piezoelectric actuator can be effectively used without waste. In addition, since the sealing surface of the valve seat and the flat portion of the metal diaphragm always move while keeping the plane, more precise flow control can be performed.

Next, the inner surface 42 of the valve seat 4 is tapered, and the valve seat outlet 43 at the end is located in the outermost peripheral region of the flat portion 51 of the metal diaphragm, and a sealing surface 44 is formed. ing. In this embodiment, the outer diameter of the diaphragm spacer 61 is made slightly larger than that of the sealing surface 44, and a concave portion 61a is provided on the inner side to increase the surface pressure and to make it possible to ignore the undulation and deformation at the center of the metal diaphragm. Improves sealing performance. At this time, the width, depth, and the like of the concave portion 61a provided in the diaphragm spacer 61 must be set so as not to impair the rigidity of the diaphragm spacer 61.

[0020]

As described above, the mass flow controller of the present invention has the following advantages. (1) The contact area between the diaphragm and the valve seat is reduced by providing a concave portion in the diaphragm spacer to reduce the contact area with the metal diaphragm. The gap between the valve seats was sufficient, and the sealing performance with the valve seat was improved. (2) The center of the metal diaphragm can be deformed symmetrically by eliminating the convex portion of the contact surface of the diaphragm spacer with the metal diaphragm which remains after the cutting, and the sealing performance with respect to the gas and the valve seat is improved.

The displacement (preload) used to increase the sealing surface pressure by improving the sealing performance.
And the amount can be used on the stroke side for adjusting the flow rate. Therefore, as shown in FIG. 3, (1) the fully open flow rate increased (Q ₁ <Q ₂ ). (2) The starting voltage is reduced (V ₂ <V ₁ ), thereby reducing the dead time in terms of control and leading to a reduction in response time. As described above, by improving the sealing performance, it was possible to provide a mass flow controller having an increased full open flow rate and a quick response time.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a mass flow controller showing one embodiment of the present invention.

FIG. 2 is an enlarged sectional view of a valve seat portion of FIG.

FIG. 3 is a schematic diagram showing a relationship between a flow rate and a valve voltage.

FIG. 4 is a longitudinal sectional view showing an example of a conventional mass flow controller.

[Explanation of symbols]

1A, M: Mass flow controller 2: Sensor part 3: Control circuit part 4: Valve seat 5: Metal diaphragm 6: Flow control valve 11: Inlet 12
(A, b, c): Inflow channel 13 (a, b): Outflow channel 14:
Outlet 15: Bypass flow path 20:
Sensor pipe 21: Upstream coil 22:
Downstream coil 41: Inlet of valve seat 42:
Tapered inner surface 43: Valve seat opening 44:
Seal surface of valve seat 51: Flat portion of metal diaphragm 52:
Elastic deformation part 53: Peripheral part of metal diaphragm 60: Piezoelectric actuator 61:
Diaphragm spacer 61a: Diaphragm spacer recess 62:
Diaphragm holder 63: Housing 64:
Lid 65: Hard ball 66:
Piezo spacer 66a: Bearing 67:
Spring 68a: Housing cap 68
b: Nut 69a: Outer diameter spacer 69
b: Metal O-ring 69c: Valve seat spacer

Claims (1)

[Claims] 1. A mass flow controller comprising: a flow sensor for detecting a flow rate of a fluid flowing in a sensor flow path; a flow control valve for controlling a flow rate of a fluid; and a control circuit, wherein the flow control valve includes an inflow A flow control valve main body having a side flow path and an outflow side flow path, a valve seat provided at an end of the inflow side flow path, a metal diaphragm having a flat portion which comes into contact with and separates from the valve seat, and the metal diaphragm An actuator that generates a pressing force on the valve seat side, and a diaphragm spacer that presses the metal diaphragm is provided below the actuator, and a contact surface between the valve seat and the metal diaphragm is formed. A mass flow controller characterized in that a concave portion is provided on a pressing surface of a diaphragm spacer to be removed.