JP2001142541A - Mass flow controller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a mass flow controller which can precisely control a flow rate with respect to a plurality of types of flow rate zones, for example to the flow rate zones of about 100 ccm and 10 ccm by a single controller. SOLUTION: A fluid passage 2 where a part is separated into a bypass passage 12 and a sensor passage 14, a flow rate control valve 8 installed in the fluid passage, a bridge circuit 16 comprising winding wire resistance wound to the sensor passage, a gain means 24 having a plurality of gain circuits which selectively apply different gains to the output of the bridge circuit and obtain sensor outputs, a gain switch means 32 which selectively switches the plurality of gain circuits on the basis of a switch signal S3 inputted from the outside for specifying the mode of a flow rate change and a valve control means 22 controlling the flow rate control valve on the basis of an outer input signal SG1 in which a plurality of modes of the flow rate changes exist with respect to a voltage change in a prescribed voltage range and on the basis of sensor output S2 are installed. Thus, a flow rate is precisely controlled with respect to the plurality of types of flow rate zones, for example the flow rate zones of about 100 ccm and 10 ccm by one controller.

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 precisely controlling a mass flow rate of a fluid such as a source gas used in a semiconductor manufacturing apparatus or the like.

[0002]

2. Description of the Related Art Generally, in the case of a raw material gas or a raw material liquid used in a semiconductor manufacturing apparatus or the like, the flow rate of the raw material gas or liquid is precisely controlled during the process in order to maintain high electrical characteristics of an integrated circuit to be manufactured. You need to control.
For this reason, a mass flow controller (mass flow meter) is generally used as a device for accurately controlling the flow rate of this type of raw material fluid. Here, a general mass flow controller is disclosed in, for example, JP-A-9-2
This mass flow controller is described in, for example, US Pat.

FIG. 8 is a schematic configuration diagram showing a conventional mass flow controller. In the illustrated example, reference numeral 2 denotes a fluid passage in the mass flow controller, one end of which is connected to the source gas source, and the other end of which is connected to a gas using system, for example, a film forming apparatus. A flow control valve 8 having a diaphragm 4 and an actuator 6 of, for example, a laminated piezoelectric element for pressing the diaphragm 4 with a small stroke is provided downstream of the fluid passage 2.
The opening degree of 0, that is, the valve opening degree is adjusted to control the flow rate of the raw material fluid. The fluid passage 2 on the upstream side of the flow control valve 8 is separated into a bypass passage 12 and a sensor passage 14 formed of a thin tube parallel to the bypass passage 12.
The raw material fluid flows through the two flow paths 12 and 14 at a predetermined split ratio predetermined in design. Two winding resistors 18A and 18B constituting a part of the bridge circuit 16 are wound around the sensor flow path 14, and heat transfer caused by the flow of the raw material fluid from the upstream side to the downstream side is performed. Is regarded as an unbalance of the bridge circuit, the flow rate of the raw material fluid flowing through the sensor flow path 14 can be determined, whereby the flow rate flowing through the entire fluid passage 2 can be determined. That is, the bridge output signal S1 of the bridge circuit 16 is input to the gain means 20, where it is subjected to a predetermined gain, for example, 140 to 280, and is subjected to a differentiation process to enhance the response of the signal. To obtain a sensor output S2 through a linearizer. The sensor output S2 represents a flow rate for a full scale with a voltage value having a certain width, and usually indicates the flow rate in a range of 0 to 5 V (volt).

On the other hand, a flow rate of a raw material fluid required during the process is input as an external input signal SG1 from a main control unit of a film forming apparatus (not shown). The external input signal SG1 also indicates the flow rate with respect to the full scale with a voltage value having a certain width, and also in this case, the flow rate is usually expressed in the range of 0 to 5 V (volt). Then, the valve control means 22 determines that the external input signal SG1 and the sensor output S2
The flow rate of the raw material fluid is controlled by controlling the valve opening of the flow rate control valve 8 so that the values of the flow rate control valve 8 and the flow rate control valve 8 match. For example, when controlling the flow rate at which the full scale is 100 ccm, when the external input signal SG1 is set to 5 V, the entire fluid passage 2 (the sum of the flow rate of the bypass flow path 12 and the flow rate of the sensor flow path 14) becomes 100 ccm,
The sensor output S2 indicates 5V.

In this case, the flow rate of the sensor flow path 14 and the characteristics of the sensor output generally have good linearity when the flow rate flowing through the sensor flow path 14 is small as shown in FIG.
As the flow rate increases, the characteristic becomes a curved shape, and finally becomes saturated. In the illustrated example, the flow rate of the sensor channel is 0 to 6
Very good linearity up to about ccm, 6 ccm
As the flow rate increases, the linearity gradually deteriorates, but increases in a curved shape up to about 25 ccm.
When the flow rate exceeds about 25 ccm, the sensor output is saturated and thereafter starts to decrease. Therefore, when designing a mass flow controller, the fluid passage 2
The total flow passage area of the bypass flow passage 12 is selected such that a flow ratio of, for example, 6 ccm flows into the sensor flow passage 14 when a fluid having a design maximum flow rate (full scale) flows therein. Thus, the flow rate control is performed in the region A where the linearity is very good.

[0006]

In the semiconductor manufacturing process, the same source fluid may be used in a relatively small flow rate region or a relatively large flow rate region. For example, a film forming gas, which is a raw material fluid, may be used at a flow rate of about 100 ccm in the preliminary process and may be used at a flow rate of about 10 ccm in the subsequent process. In this case, the error range of the mass flow controller flow rate is generally ± several% relative to the full scale,
For example, since the flow rate is specified as about ± 5%, a flow rate error of ± 5 ccm is allowed when designed at a full scale of 100 ccm. Therefore, a minute flow rate of about 10 ccm can be reduced using this mass flow controller. When controlling, ± 5c even in the flow rate range of 10ccm
A flow rate error of about cm had to be recognized, and in this case, a very large error was caused.

Therefore, in such a case, conventionally, two mass flow controllers having a full-scale flow rate of 100 ccm and two mass-flow controllers having a full-scale flow rate of 10 ccm are provided. Switching was used. For this reason, there is a problem that the number of expensive mass flow controllers installed increases and the cost increases. The present invention has been devised in view of the above problems and effectively solving them. An object of the present invention is to provide a mass flow controller capable of accurately controlling a flow rate of a plurality of types of flow zones, for example, about 100 ccm and about 10 ccm by one unit.

[0008]

According to a first aspect of the present invention, there is provided a fluid passage partially separated into a bypass passage and a sensor passage, a flow control valve interposed in the fluid passage, A bridge circuit including a winding resistor wound around the sensor flow path;
A gain means having a plurality of gain circuits for selectively applying different gains to the output of the bridge circuit to obtain a sensor output; and the plurality of gain circuits based on a switching signal input from the outside to specify an aspect of a flow rate change. Gain switching means for selectively switching a gain circuit; and controlling the flow rate control valve based on an external input signal and the sensor output such that there are a plurality of flow rate change modes with respect to a voltage change within a predetermined voltage range. Valve control means.

According to this configuration, the gain means uses a gain circuit having the first gain so as to correspond to one mode of the flow rate change when the full scale is large, for example, when the full scale is large, and the full scale is small when the full scale is large. The time is switched to use the gain circuit having the second gain so as to correspond to the other mode of the flow rate change. From the bridge circuit, an output having a magnitude corresponding to the flow rate flowing through the sensor flow path is obtained. The valve control means controls the flow control valve so that the voltage value of the sensor output and the voltage value of the external input signal are the same. As described above, when the flow rate control is performed for different flow rate ranges, the gain is switched so as to switch the flow rate to be the full scale. Therefore, a plurality of different flow rates, for example, two flow rate ranges are controlled by one mass flow controller. Thus, flow rate control with high accuracy can be performed.

The invention defined in claim 2 provides a fluid passage partially separated into a bypass passage and a sensor passage, a flow control valve interposed in the fluid passage, and a coil wound around the sensor passage. A gain circuit having a plurality of gain circuits for selectively applying different gains to the output of the bridge circuit to obtain a sensor output; and a predetermined gain circuit for a voltage change within a predetermined voltage range. A signal of the same voltage according to the voltage value of the external input signal indicating the aspect of the flow rate change, or a signal of a voltage that has been scale-compressed and amplified at a predetermined ratio is output as a new external input signal, and a switching signal is output. External input signal converting means, gain switching means for selectively switching the plurality of gain circuits based on the switching signal, and the flow rate control based on the sensor output and the new external input signal. Controlling the and a valve control unit.
Thus, the external input signal converting means converts the same voltage or the voltage obtained by the scale compression amplification to the new external signal in accordance with the voltage value of the external input signal sent from, for example, the main control unit of the semiconductor manufacturing apparatus. The switching signal is output as an input signal and is used to select a gain circuit to be used. By this switching signal, the gain means uses, for example, a gain circuit having a first gain so as to correspond to one mode of the flow rate change when the full scale is large, and to correspond to the other mode of the flow rate change when the full scale is small. To switch to using a gain circuit having a second gain. From the bridge circuit, an output having a magnitude corresponding to the flow rate flowing through the sensor flow path is obtained. The valve control means controls the flow control valve so that the voltage value of the sensor output and the voltage value of the external input signal are the same. As described above, when the flow rate control is performed for different flow rate ranges, the gain is switched so as to switch the flow rate to be the full scale. Therefore, a plurality of different flow rates, for example, two flow rate ranges are controlled by one mass flow controller. Thus, flow rate control with high accuracy can be performed.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the mass flow controller according to the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a block diagram showing a mass flow controller according to the present invention, FIG. 2 is a block diagram showing a gain means, and FIG.
Is a graph showing the relationship between the external input signal and the flow rate, and FIG. 4 is a graph showing the sensor output. In FIG. 1, the same parts as those shown in FIG. The feature of the present invention is that when a sensor flow path having a characteristic curve as shown in FIG. 9 is used, the linearity of the characteristic is inferior, but the area B in which the sensor output tends to increase with respect to the flow rate of the sensor flow path is In this case, the area B is allocated to a control area of a large flow rate, and the area A having excellent linearity of characteristics is allocated to a control area of a small flow rate. The assignment is switched by switching the value of the gain applied to the output of the bridge circuit as described later.

In FIG. 1, reference numeral 2 denotes a fluid passage in the mass flow controller, one end of which is connected to a source gas source, and the other end of which is connected to a gas using system, for example, a film forming apparatus. Downstream of the fluid passage 2, there is provided a flow rate control valve 8 comprising a diaphragm 4 and an actuator 6 of, for example, a laminated piezoelectric element for pressing the diaphragm 4 with a small stroke. Degree, that is, the valve opening degree is adjusted to control the flow rate of the raw material fluid. The fluid passage 2 on the upstream side of the flow control valve 8 is separated into a bypass passage 12 and a sensor passage 14 composed of a thin tube arranged in parallel with the bypass passage 12. The raw material fluid flows at a predetermined fixed split ratio. Two winding resistors 18A and 18B constituting a part of the bridge circuit 16 are wound around the sensor flow path 14, and heat transfer caused by the flow of the raw material fluid from the upstream side to the downstream side is performed. Is regarded as an unbalance of the bridge circuit, the flow rate of the raw material fluid flowing through the sensor flow path 14 can be determined, whereby the flow rate flowing through the entire fluid passage 2 can be determined.
That is, the bridge output signal S of the bridge circuit 16
1 is input to the gain means 24, where a predetermined gain is applied to the signal to perform differential processing, thereby improving the response of the signal, and further obtaining the sensor output S2 through the linearizer. The sensor output S2 represents a flow rate for a full scale with a voltage value having a certain width, and usually indicates the flow rate in a range of 0 to 5 V (volt).

On the other hand, the switching signal S3 and the flow rate of the raw material fluid required in the process are input as an external input signal SG1 from a main control unit of a film forming apparatus (not shown). The external input signal SG1 also indicates the flow rate with respect to the full scale with a voltage value having a certain width, and also in this case, the flow rate is usually expressed in the range of 0 to 5 V (volt). Here, the important point is that the main control unit operates in a state where there are a plurality of flow rate change modes (modes) for a voltage change within a predetermined voltage range, for example, 0 to 5 V, as described later. Output the input signal. As a result, even when the external input signal has the same voltage value, the flow rate varies depending on the mode. This mode, that is, mode switching is performed by a switching signal S3 as described later. The valve control means 22 controls the flow rate of the raw material fluid by controlling the valve opening of the flow control valve 8 so that the value of the external input signal SG1 and the value of the sensor output S2 match. ing. For example, when controlling the flow rate at which the full scale is 100 ccm, the external input signal SG1 is set to 5V.
At this time, the flow rate control is performed so that the entire fluid passage 2 (the sum of the flow rate of the bypass flow path 12 and the flow rate of the sensor flow path 14) is 100 ccm and the sensor output S2 also shows 5V.

Here, the gain means 24, which is a feature of the present invention, will be described with reference to FIG. In this embodiment,
It has a plurality of, for example, two full scales (design maximum flow rates), which are, for example, 100 ccm and 10 ccm. Therefore, a gain circuit 2 having two kinds of gains
8A and 28B and correspondingly differentiating circuits 30A and 30B having a predetermined time constant to increase the response speed are provided. Each of the gain circuits 28A and 28B and the differentiating circuits 30A and 30B are connected in series, and both circuit systems are switched by a gain switching means 32 provided at the preceding stage and operated by a switching signal S3. A linearizer 34 is provided downstream of the two differentiating circuits 30A and 30B.
Is provided to output the sensor output S2 from the output of the differentiating circuit 30A or 30B. The value of the sensor output S2 is, for example, in the range of 0 to 5V.

Here, in the present invention, two settings of 100 ccm and 10 ccm are set as the full scale of the flow rate as described above, and the flow rate is designed to be controlled with good accuracy near these two flow rate ranges. . This point will be described in detail. As shown in FIG. 5, which shows the same characteristic curve as FIG. 9, the gas flow rate having excellent linearity is up to approximately 6 ccm in the sensor flow path 14 (region A). Ignoring this linearity within the range where does not saturate, approximately 20
It can flow up to ccm (region B). Therefore, the flow rate of the sensor channel 14 can be increased to about 3.3 times (= 20/6). Therefore, in order to satisfy the above requirement, the bypass flow path 12 is set to 30 ccm (= 100 ccm /
3.3). When the 30 ccm bypass flow path 12 is used to flow the sensor flow path 14 at a flow rate of 20 ccm, a mass flow controller of 100 ccm can be obtained. At this time, the gain is a normal value (140 to
280), it is necessary to set the value to 1 / 3.3 times, that is, 42 to 84. Therefore, the gain value of one gain circuit 28A is set to 42 to 84.

Conversely, when the full scale is 10 ccm,
By setting the gain value to three times the normal value, that is, 420 to 840, the gain value can be reduced to 1 using the bypass flow path 12 for 30 cm.
It can be a mass flow controller of 0 ccm. At this time, the flow rate of the sensor flow path 14 is 2 ccm. When the flow rate flowing through the sensor flow path 14 is largely changed, it is desirable to change the time constant of the differentiating circuit in order to correspond to the response. This differentiation circuit 30A, 3
Although 0B is provided to perform phase matching of the sensor output, it is needless to say that this need not be provided separately. As described above, this mass flow controller has a full scale range of 10 ccm (the flow rate of the sensor channel is 0 to approximately 2 ccm) (aspect 1: mode 1) and a full scale of 100 ccm.
ccm (The flow rate of the sensor channel is approximately 0 ccm to approximately 20 cc.
m) (mode 2: mode 2), and the gain value is switched in each range.

Next, the operation of the embodiment constructed as described above will be described with reference to FIGS. FIG. 3 shows the relationship between the external input signal and the flow rate in the case of mode 1 and mode 2, and FIG. 4 shows the sensor output S2 in the case of mode 1 and mode 2. As described above, it is assumed that the external input signal SG1 and the sensor output S2 fluctuate within a range of 0 to 5V. A signal indicating the gas flow rate required for the process is output from the main control unit of the film forming apparatus as an external input signal SG 1, which is input to the external input signal conversion means 26. Here, the external input signal S
G1 value of 0 to 5 V is 0 to 10 in mode 1 (aspect 1).
ccm, and the flow rate is 0 to 10 in mode 2 (aspect 2).
Corresponds to 0 ccm. This mode switching is performed by a switching signal output together with external input signal SG1. In this film forming apparatus, for example, a preliminary process requiring a gas flow rate of about 100 ccm and a main process requiring a gas flow rate of about 10 ccm are continuously performed.

Further, the gain circuit is switched to switch the gain value in accordance with the mode switching.
The switching signal S3 for switching the gain value is a signal for instructing whether to use the mode 1 or the mode 2, and is output from the film forming apparatus according to the type of the process as described above. Sensor output S of mode 1 and mode 2
2 is as shown in FIG. 4, and the sensor output S2 is also switched according to the selected mode, and the output becomes the same as the external input signal SG1. That is, when the preliminary process is performed at a gas flow rate of about 100 ccm in the film forming apparatus, the gain switching means 30 switches the one gain circuit 28 so as to select one mode 2 by the switching signal S3.
A, switching to the differentiating circuit 30A side, the valve control means 22 controls the valve opening of the flow control valve 8 so that the voltage values of the external input signal SG1 and the sensor output S2 coincide.

When the preparatory process is completed and the present process is performed at a gas flow rate of about 10 ccm, the gain switching means 30 switches the other gain circuit 28B so that the other mode 1 is selected by the switching signal S3. Differentiating circuit 30
The valve control means 22 controls the valve opening of the flow control valve 8 so that the voltage value of the external input signal SG1 and the voltage value of the sensor output S2 match. As described above, according to the present embodiment, the gain is switched as necessary, so that the flow rate can be accurately and stably set in a plurality of regions, for example, a region where the total flow is about 100 ccm and a region where the total flow is about 10 ccm. It becomes possible to control it.

In the above embodiment, the switching signal S3 is output from the main control unit of the film forming apparatus, and the external input signal SG1 is given a meaning so as to indicate a different flow rate depending on the mode even with the same voltage value. However, instead of this, only a single flow rate is given to the external input signal, and a new external input signal conversion means is provided so that the switching signal S3 and the new external input signal are formed here. It may be. FIG. 6 is a block diagram showing a modification of the present invention as described above, and FIG. 7 is a graph showing a relationship between an external input signal and a new external input signal in the modification shown in FIG. In this external input signal converting means, the gain switching means 30 changes the flow rate of the external input signal SG1 depending on whether it is large or small with the point P1 as a boundary.
Is generated. Actually, the point P1 in FIG.
The flow rate is set to a point that is considerably larger than 0 ccm, and the flow rate control can be stably performed even if overshoot or the like occurs during control.

In this embodiment, the flow rate of the raw material fluid required for the process is input as an external input signal SG1 'from a main control unit of a film forming apparatus (not shown).
The external input signal SG1 'also indicates the flow rate for full scale with a voltage value having a certain width, and also in this case, the flow rate is usually uniquely expressed in the range of 0 to 5 V (volt). In the present embodiment, the external input signal SG
The external input signal conversion means 26 converts 1 'into a new external input signal SG2 and outputs a switching signal S3 for switching a mode (aspect) for switching a gain circuit to be used.
Is provided. The valve control means 22 controls the valve opening of the flow control valve 8 so that the value of the new external input signal SG2 matches the value of the sensor output S2, thereby controlling the flow rate of the raw material fluid. Has become. For example, when controlling the flow rate at which the full scale is 100 ccm, when the new external input signal SG2 is 5 V, the entire fluid passage 2 (the sum of the flow rate of the bypass flow path 12 and the flow rate of the sensor flow path 14) is 100 ccm. Thus, the flow rate control is performed so that the sensor output S2 also indicates 5V. In this embodiment, as in the previous embodiment, a plurality of, for example, two full scales (design maximum flow rates) are provided.
0 ccm.

The operation of this embodiment will be described. From the main control unit of the film forming apparatus, a signal indicating the gas flow rate required for the process is output as an external input signal SG1 ', which is input to the external input signal conversion means 26. Here, the value 0 to 5 V of the external input signal SG1 is 0
Uniquely corresponds to ~ 100 ccm. In this film forming apparatus, for example, a preliminary process requiring a gas flow rate of about 100 ccm and a main process requiring a gas flow rate of about 10 ccm are continuously performed.

If the total flow rate indicated by the input external input signal SG1 'is larger than the point P1 slightly exceeding 10 ccm (when the voltage is converted to approximately 0.5 V or more, Case), the external input signal SG1 ′
Is output as a new external input signal SG2 as it is. On the other hand, when the total flow rate indicated by the input external input signal SG1 'is smaller than the point P1 slightly exceeding 10 ccm, the voltage value scale-converted at a rate of 5 V at the flow rate of 10 ccm is calculated. New external input signal SG2
Output as The external input signal conversion means 26 outputs the new external input signal SG2 as described above, and switches the voltage to switch the signal to indicate that the mode has changed.
3 is also output at the same time.

Then, in the film forming apparatus, a gas flow rate of about 1
When the preliminary process is performed at 00 ccm, the gain switching means 30 is switched to one of the gain circuit 28A and the differentiating circuit 30A in order to select the mode 2, and the external input signal conversion means 26 A new external input signal SG2 having the same voltage value as SG1 'is output to the valve control means 22, and the valve opening of the flow control valve 8 is controlled so that the two voltage values match. When the preliminary process is completed and the present process is performed at a gas flow rate of about 10 ccm, the gain switching means 30 has switched to the other gain circuit 28B and the differentiating circuit 30B in order to select mode 1. , The external input signal converting means 26 outputs a voltage value obtained by converting the value of the external input signal SG1 'by approximately 10 times as a new external input signal SG2, and the valve control means 22 makes the two voltage values coincide. The valve opening of the flow control valve 8 is controlled as described above.

As described above, even in the case of this modified example, the gain is switched as required, so that the flow rate can be reduced in a plurality of regions, for example, a region where the total flow is about 100 ccm and a region where the total flow is about 10 ccm. It is possible to perform stable and accurate control. Further, in each of the embodiments described above, the case where the gain is switched in two flow regions is described as an example. However, the present invention is not limited to this, and the flow region may be divided into three or more regions. Further, each numerical example shown here is merely an example for easy understanding, and it is a matter of course that the present invention is not limited to this. Further, it goes without saying that the device configuration as described above may be an analog circuit or a digital circuit.

[0026]

As described above, according to the mass flow controller of the present invention, the following excellent functions and effects can be exhibited. According to the present invention, when the flow rate control is performed for different flow rate ranges, the gain is switched so as to switch the flow rate to be a full scale.
For example, highly accurate flow rate control can be performed for two flow rate ranges.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a mass flow controller according to the present invention.

FIG. 2 is a block diagram showing a gain unit.

FIG. 3 is a graph showing a relationship between an external input signal and a flow rate.

FIG. 4 is a graph showing a sensor output.

FIG. 5 is a graph showing characteristics of a flow rate of a sensor channel and a sensor output.

FIG. 6 is a configuration diagram showing a modification of the present invention.

FIG. 7 is a graph showing a relationship between an external input signal and a new external input signal in the modification shown in FIG. 6;

FIG. 8 is a schematic configuration diagram showing a conventional mass flow controller.

FIG. 9 is a graph showing a characteristic of a flow rate of a sensor flow path and a sensor output.

[Explanation of symbols]

 Reference Signs List 2 fluid passage 4 diaphragm 8 flow control valve 12 bypass flow path 14 sensor flow path 16 bridge circuit 18 winding resistance 22 valve control means 24 gain means 26 external input signal conversion means 28A, 28B gain circuits 30A, 30B differentiation circuit 32 gain switching Means 34 Linearizer S1 Bridge output signal S2 Sensor output S3 Switching signal SG1, SG1 'External input signal SG2 New external input signal

 ──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Masamichi Hara 650 Mitsuzawa, Hosaka-cho, Nirasaki-shi, Yamanashi Prefecture F-term (reference) in Tokyo Electron Yamanashi Co., Ltd. 2F030 CA10 CC11 CD13 CE02 CF05 CF08 CF09 2F035 EA04 EA06 EA09 5H307 BB01 DD06 EE02 EE07 EE19 FF06 GG03 GG11 GG15 HH04

Claims (2)

[Claims] A bridge including a fluid passage partially separated into a bypass passage and a sensor passage, a flow control valve provided in the fluid passage, and a winding resistance wound around the sensor passage. Circuit, a gain means having a plurality of gain circuits for selectively applying different gains to the output of the bridge circuit to obtain a sensor output, and a switching signal input from the outside for specifying the mode of the flow rate change. Gain switching means for selectively switching the plurality of gain circuits; and the flow rate control based on an external input signal and the sensor output such that there are a plurality of flow rate change modes with respect to a voltage change within a predetermined voltage range. A mass flow controller comprising: valve control means for controlling a valve. 2. A bridge including a fluid passage partially separated into a bypass passage and a sensor passage, a flow control valve provided in the fluid passage, and a winding resistance wound around the sensor passage. FIG. 2 shows a circuit, a gain means having a plurality of gain circuits for selectively applying different gains to the output of the bridge circuit to obtain a sensor output, and a mode of a predetermined flow rate change with respect to a voltage change within a predetermined voltage range. External input signal converting means for outputting a signal of the same voltage according to the voltage value of the external input signal, or a signal of a voltage which has been scale-compressed and amplified at a predetermined ratio as a new external input signal, and outputting a switching signal; Gain switching means for selectively switching the plurality of gain circuits based on the switching signal, and valve control means for controlling the flow control valve based on the sensor output and the new external input signal. A mass flow controller comprising: