JPH09222344A - Mass flow controller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the realiability of alarm function by setting an allowable quantity at a desired flow rate and to be variable and issuing an alarm when a difference between the set flow rate and actual flow rate is out of the predetermined allowable quantity. SOLUTION: When a gas flows in a sensor passage 31, a heat generating on an upstream-side coil 32 is taken out and a downstream-side coil 33 is preheated. A difference of the corresponding electric resistance values is picked up as an unbalanced voltage through a bridge circuit 6, and it is inputted as a mass flow rate signal (b) into a comparison part 11. On the other hand, a mass flow rate setting signal a is inputted into the part 11 from a flow rate setting part 9. Then (a) signal (h) proportional to the difference between the signals (a) and (b) is outputted into a valve drive voltage determination circuit 12 so as to drive a flow rate control valve 5 and control it at such a control flow rate corresponding to the signal (a). When a difference between the set flow rate and actual flow rate is out of the predetermined allowable quantity, an alarm function issues an alarm.

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 for controlling a mass flow rate of various gases used in a semiconductor manufacturing process or the like, and particularly an alarm alarm is issued when an actual flow rate exceeds a permissible amount with respect to a set flow rate. The present invention relates to a mass flow controller having an alarm function.

[0002]

2. Description of the Related Art An example of a mass flow controller is shown in FIG. This MFC has a fluid inflow path 50, a bypass flow path 51 for flowing the fluid in the inflow path 50 at a predetermined ratio, a sensor flow path 52 made of a thin tube, and a mass flow rate sensor 55 provided in the sensor flow path. And the bypass channel 51 and the sensor channel
An outflow path 53 where the fluid of 52 merges, a flow rate control valve 54 provided in the middle of the outflow path 53, an amplification circuit 56 for amplifying the detection signal of the mass flow rate sensor 55, and this amplified detection signal is preset. Compared with the mass flow rate setting signal 57, the flow rate control valve
It comprises a comparison control circuit unit 58 which outputs a drive signal to 54. As the mass flow rate sensor 55, for example, the inner diameter is
A coil 62 and a coil 63 are wound on the upstream side and the downstream side of the outer peripheral surface of a thin tube 52 made of stainless steel having a thickness of about 0.5 mm, and the coil 62, the coil 63 and another resistance element, usually two bridges. There is a thermal mass flowmeter that constitutes circuit 60. (See, for example, Japanese Examined Patent Publication No. 56-23094)

In recent years, with the progress of the semiconductor manufacturing process, the kinds of fluids to be flown to the MFC are increasing and diversifying. In such a situation, for example, if a gas having corrosiveness or a gas that is easily decomposed by heat is passed through the MFC for a long time,
In the narrow tube used for the sensor part, gas may decompose and solidify, and may adhere to the inner wall, or a substance that reacts by reacting with other gas may adhere to the narrow tube and cause clogging.
As a result, the sensitivity of the sensor part changes, and the flow rate flowing through the sensor part decreases even though sufficient fluid is flowing in the bypass channel, increasing the actual flow rate (actual flow rate) relative to the set flow rate. Occurs. For this reason, the mass flow controller has a so-called alarm function that issues an alarm (alarm sound, alarm lamp, etc.) when the difference between the actual flow rate and the set flow rate deviates from a preset allowable amount (hereinafter referred to as alarm width). Is done.

[0004]

However, in the prior art, the setting of the alarm is to set an allowable amount of ± several% (often around 10%) with respect to the full-scale flow rate of each mass flow controller. It was done only in (see FIG. 3 (b)). In this case, the alarm width when the maximum flow rate was applied worked effectively over the entire flow rate range (0 to 100%), and the alarm width was always a fixed amount. Therefore, the alarm detection width does not change even when the set flow rate is changed and used.
The alarm flow occupies a large proportion of the control flow rate. That is, the allowable range is relatively widened, and in the small flow rate range, there is a problem that the alarm cannot be issued even if the difference between the set flow rate and the actual flow rate becomes large.

Therefore, it is an object of the present invention to solve the above-mentioned problems and to provide a Maslow controller with improved reliability of an alarm function.

[0006]

The present invention has an inflow passage, a bypass flow passage, a sensor flow passage, a mass flow sensor, a flow control valve, a control circuit section, and an outflow passage. A mass flow controller having an alarm function that issues an alarm when the difference between the actual flow rate and the set flow rate deviates from a preset allowable flow rate, and the allowable flow rate is variably set at an arbitrary set flow rate. It is a mass flow controller that is made possible.

According to this mass flow controller, as shown by the solid line (b) in FIG. 3, the allowable amount with respect to the full scale flow rate is conventionally used, and the alarm detection width is uniform over the entire flow rate range. On the other hand, in the present invention,
The setting of the allowable amount and the alarm width can be made independent and variable with respect to the set flow rate (hereinafter also referred to as set point flow rate) to be controlled by the flow rate.
For example, as shown by the dotted line (a) in FIG. 3, the alarm width (which is considered to be the allowable amount) is large in the large flow rate range, and conversely, narrowed in the small flow rate range. It is possible to have a wide tolerance, and as a result, the error of the alarm function is small and the reliability is high. Also, for example, if the mass flow controller is only for purging, the size of the alarm width can be ignored. In this case, therefore, it is sufficient to set the alarm width only for the full-scale flow rate as in the conventional case. The alarm detection range can be set according to the purpose of use, and the range of alarm function selections has expanded.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a functional block diagram of a mass flow controller with an alarm function showing an embodiment. The mass flow controller of this embodiment is basically the same as the conventional mass flow controller with an alarm function added. However, it is not limited that these components are provided integrally or close to each other.

First, the mass flow controller portion will be described. In FIG. 1, a fluid to be measured, for example, a process gas passes from an inflow port of a mass flow controller through an inflow channel 1 and is branched into a bypass flow channel 2 and a sensor flow channel 31 which are divided in parallel at a predetermined ratio. Further, the gas that has passed through the bypass flow passage 2 and the sensor flow passage 31 merges again and flows through the outflow passage 4, and the flow rate is controlled by the flow control valve 5 provided in the outflow passage 4, and the gas flows out from the outlet. .

The sensor channel 31 is provided with a sensor 3 for outputting a mass flow rate signal according to the flow rate. Normally, the upstream coil 32 and the downstream coil 33 have the same electric resistance value, and when a constant current flows. Generates the same amount of heat. When the gas flows in the sensor flow path 31, the gas takes away the amount of heat generated in the upstream coil 32, and the downstream coil 33 is heated by the gas whose temperature has risen. As a result, the temperature of the downstream coil 33 becomes higher than that of the upstream coil 32, and accordingly, the electric resistance value also varies. When this difference is taken out as an unbalanced voltage via the bridge circuit 6, the mass flow rate of the gas flowing in the sensor flow path 31 has a relationship with this unbalanced voltage. Therefore, the mass flow rate is detected by detecting the unbalanced voltage. Can be measured. A constant temperature sensor (Japanese Patent Publication No. 4-48993) and a constant temperature difference sensor (Japanese Patent Laid-Open No. 1-150817) can be used as the thermal mass flow rate sensor.

The detected unbalanced voltage e is applied to the amplifier circuit 7 and A
The mass flow rate signal b is amplified through the / D converter 8 and input to the comparison unit 11. On the other hand, the mass flow rate setting signal a (voltage) corresponding to the control flow rate is sent to the comparison section 11 by the flow rate setting section 9
Further, it is inputted through the A / D converter 10. Therefore, the comparison unit 11 compares the mass flow rate signal b detected by the sensor unit with the mass flow rate setting signal a, and outputs a signal h proportional to this difference to the valve drive voltage determination circuit 12. In the valve drive voltage determination circuit 12, PID control is performed by a built-in valve drive voltage determination program based on the signal h and the current drive signal, and the valve drive signal V
Is output. Then, it is input as a drive voltage to the actuator of the flow control valve 5 via the D / A converter 13, and as a result, the flow control valve 5 is driven and the valve opening changes so as to reduce the above difference. Thus, the flow rate control valve 5 is controlled so that the valve opening degree is adjusted and the control flow rate according to the mass flow rate setting signal a is maintained.

Next, the alarm function will be described with reference to the flowchart showing the alarm detection routine of FIG. First, various alarm functions (set flow rate vs. actual flow rate mismatch error,
Check if output is OFF (CPU error, communication error, power supply voltage abnormality, etc.) (Fig. 2-), and then check if output of set flow rate / actual flow rate mismatch alarm, which is also the present invention, is OFF. (Fig. 2-). If the output is turned off in any of the above, the alarm function is turned off (FIG. 2).

Now, in the flow rate setting unit 9, an arbitrary set flow rate,
A so-called set point flow rate can be set instead of the output voltage of 0 to 5 V, and this is output as the signal a of the set flow rate value. The switch 14 switches between the set flow rate value a and the full scale flow rate value f which is an output voltage signal at the full scale flow rate. Here, the alarm setting for the set flow rate or the alarm for the full scale flow rate is set. Made it possible to select whether to use the setting (Fig. 2-).

If the alarm of the set flow rate is selected, the set flow rate value a is input to the multiplication circuit 23.
On the other hand, an arbitrary alarm width, for example, a signal i of 5% or the like is also input from the alarm width memory 22 to determine an allowable amount g by multiplying both. Then, the allowable amount g is output to the comparison circuit 26. On the other hand, the set flow rate value a and the mass value signal b from the sensor enter the subtraction circuit 24, and the set flow rate value-
The flow rate difference value c of the actual flow rate value (C = ab) is output, and the flow rate difference value c subsequently becomes the signal value d that has been absolute valued by the absolute circuit 25. Then, the signal d is output to the comparison circuit 26. The comparison circuit 26 compares the allowable amount g with the flow rate difference value d, and outputs a signal R when g <d (FIG. 2). Output is turned on (Fig. 2) and alarm 27 is output.

On the other hand, when it is desired to set an alarm for the full-scale flow rate in FIG. 2, the switch 14 is switched to the full-scale value side, and the full-scale flow rate value f is input to the multiplication circuit 23 as the signal j. After that, the flow of FIG. 2 is entered, and the same multiplication / subtraction and comparison as described above are performed, so the following description will be omitted.

[0016]

As described above, according to the present invention, an alarm can be set for a full-scale flow rate or an arbitrary set (set point) flow rate, so that the alarm width can be adjusted to the flow rate and the accuracy of the alarm function can be improved. It became a mass flow controller with high reliability and less error.

[Brief description of drawings]

FIG. 1 is a block diagram of a mass flow controller showing an embodiment of the present invention.

FIG. 2 is a flowchart showing an alarm detection routine of the embodiment.

FIG. 3 is a diagram illustrating setting of an alarm width.

FIG. 4 is a block diagram showing a basic configuration of a mass flow controller.

[Explanation of symbols]

1 ... Inflow path 2 ... Bypass flow path 3 (32, 33) ... Mass flow sensor 4 ... Outflow path 5 ... Flow control valve 6 ... Bitch circuit 7 ... Amplifier 8, 10 ... A
/ D converter 9 ... Mass setting unit 11 ... Comparison unit 12 ... Valve drive voltage determination circuit 13 ... D / A
Converter 14… Changeover switch 20… Full scale flow rate value 21… Alarm mode memory 22… Alarm width memory 23… Multiplication circuit 24… Subtraction circuit 25… Absolute value circuit 26… Comparison circuit 27… Alarm output section

Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location H01L 21/3065 H01L 21/302 B

Claims (2)

[Claims] 1. An inflow path, a bypass flow path, a sensor flow path, a mass flow sensor, a flow control valve, a control circuit section,
A mass flow controller having an outflow path and having an alarm function for issuing an alarm when the difference between the actual flow rate and the set flow rate deviates from a preset allowable flow rate, wherein the allowable flow rate is an arbitrary set flow rate. The mass flow controller is characterized in that it can be set variably. 2. The alarm function comprises an alarm width setting means, a means for multiplying a full scale flow rate value signal or a set flow rate value signal and an alarm width to obtain an allowable value, a set flow rate signal and an actual flow rate value signal. 2. The mass flow controller according to claim 1, further comprising: a unit for taking an absolute value of a difference between the two, a unit for comparing the allowable value with the absolute value, and an alarm output unit.