JPH0934556A - Mass flow controller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a mass flow controller which can satisfy both requests of high and low accuracy for small and large flow rates respectively in a simple way and at low cost. SOLUTION: A mass flow controller includes a sensor part which detects the mass flow rate in a sensor flow passage 2, a bypass flow passage 3 where a fluid flows, a control circuit part 6 which compares the detection signal sent from the sensor part with a set signal and controls both signals, and a valve part 7 which controls the mass flow rate based on the comparison/control results of the part 6. The passage 2 is made of a metallic material that has the heat conductivity higher than the stainless steel. At the same time, the total flow rate of both passages 2 and 3 is set at a prescribed flow rate ratio and then corrected at the flow rate less than 50% of the full-scale flow rate of the mass flow rate 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 controlling a mass flow rate of a fluid used in a semiconductor manufacturing process or the like.

[0002]

2. Description of the Related Art Conventionally, in a semiconductor manufacturing process, a sensor section for detecting a mass flow rate in a sensor channel, a bypass channel through which a fluid flows, and a control circuit for comparing and controlling a detection signal and a setting signal from the sensor section. A mass flow controller having a section and a valve section that controls a flow rate based on the comparison control is used. By the way, in the semiconductor manufacturing process, the flow rate is relatively small, but the accuracy is high, for example, 30 ± 0.
Etching process requiring 1 sccm (cm ³ / min in standard state) and low accuracy but relatively large flow rate,
For example, the ashing process requiring 100 ± 10 sccm may be repeated. In order to meet these requirements, conventionally, two types of mass flow controllers were arranged in parallel, a mass flow controller with a full-scale flow rate of 30 sccm was calibrated in full scale, and a mass flow controller with a full-scale flow rate of 100 sccm was also calibrated in full scale. However, both the mass flow controllers are switched to cope with the measurement of the small flow rate and the measurement of the large flow rate.

[0003]

However, in the above-mentioned conventional technique, since two types of mass flow controllers are used, the cost is high, and since two types of mass flow controllers are switched and used, it is troublesome. Therefore, it is an object of the present invention to provide an inexpensive mass-flow controller that can satisfy both the requirement of high accuracy with a small flow rate and the requirement of large flow rate with a low accuracy.

[0004]

The present invention uses only one mass flow controller and has a full scale 50
The above object was achieved by calibrating the sensor unit at a flow rate of not more than%. That is, the present invention provides a sensor section for detecting a mass flow rate in a sensor channel, a bypass channel through which a fluid flows, a control circuit section for comparing and controlling a detection signal and a setting signal from the sensor section, and this comparison control. A mass flow controller having a valve section for controlling the flow rate based on the above, wherein the sensor channel is formed of a metal material having a higher thermal conductivity than stainless steel, and the flow rate and the sensor channel flowing through the sensor channel are The total flow rate in the bypass flow path is set to a predetermined flow rate ratio, and is calibrated at a flow rate of 50% or less of the full-scale flow rate of the mass flow controller.

[0005]

First, the sensor section is provided with heat-sensitive coils on the upstream side and the downstream side of the sensor pipe, and the temperature difference between the heat-sensitive coils due to heat transfer (of the sensor pipe) caused by the flow of fluid is proportional to the mass flow rate. Since the sensor channel, that is, the sensor pipe is formed of a metal material having a higher thermal conductivity than that of conventional stainless steel, for example, nickel or its alloy, the sensor pipe on the downstream side having a high temperature is used. Therefore, heat is easily supplied to the upstream side where the temperature is low, and it becomes difficult to detect the temperature difference of the fluid itself. Therefore, although the sensitivity as a flow meter is low, the flow rate measurement range (sensor output and flow rate proportional range)
Becomes wider. Next, since this mass flow controller measures the total flow rate by multiplying the flow rate measured in the sensor channel by the flow rate ratio, if the calibration is performed in the flow rate range of 50% or less of the full scale flow rate, the small flow rate will be obtained. However, a highly accurate mass flow controller can be obtained. On the other hand, even if the flow rate is increased to the full-scale flow rate, the measurable flow rate range of this sensor is wide. Therefore, the calibration accuracy increases only in a substantially proportional manner. Become.

[0006]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. FIG. 1 shows an embodiment of a mass flow controller according to the present invention. The conduit 1 through which a fluid flows has, for example, a thermal conductivity k = 94 W / m /
The sensor channel 2 and the bypass channel 3 formed of K nickel are provided in parallel. Coils are wound around the sensor channel 2 on the upstream side and the downstream side, and the flow rate of the sensor channel 2 is measured by detecting a change in the resistance value of both coils by the bridge circuit 4. . still,
The sensor portion is formed by winding a heat sensitive coil of a temperature sensor / heater for measuring the temperature of the fluid on the upstream side and the downstream side of the outer circumference of the sensor pipe. The sensor type is a constant current sensor that measures by detecting the temperature distribution on the upstream side and the downstream side that changes due to the flow of fluid as an unbalanced voltage of the bridge circuit; and a constant temperature circuit (bridge circuit) including a heat sensitive coil. Is provided independently on each of the upstream side and the downstream side, and a constant temperature sensor including a constant temperature sensor and a constant temperature difference circuit (which measures by detecting the difference in energy required for keeping the temperature of both heat sensitive coils constant) ( A constant temperature difference sensor that measures by detecting the difference in energy required to keep the difference between the temperature of both heat sensitive coils and the ambient temperature always constant by providing a bridge circuit) independently on the upstream side and the downstream side. and so on. In the embodiment, these sensors may be selectively used.

On the other hand, the flow rate ratio between the two flow paths 2 and 3 has been verified in advance, and in this embodiment, the flow rate 5 times the flow rate of the sensor flow path 2 is adjusted to flow through the bypass flow path 3. Therefore, by multiplying the flow rate in the sensor channel 2 by 6, the flow rate in the conduit 1 can be measured, which is incorporated in the bridge circuit 4. The output of the bridge circuit 4 is linearized by the linearization circuit 5, and the output of the linearization circuit 5 is sent to the control circuit unit 6. The control circuit unit 6 controls the opening degree of the control valve 7 attached to the pipeline 1. Have control. still,
The linearization circuit 5 includes a circuit that further counts ΔR + aΔR ² (where a is a constant) with respect to the difference ΔR in electrical resistance between the upstream coil and the downstream coil.

The full scale of this mass flow controller is 100 sccm. Therefore, when a flow rate of 100 sccm of the full scale flows through the entire pipeline 1, the sensor flow channel 2 has 100/6, that is, 16.6.
It flows by 7 sccm. The sensor channel 2 is made of nickel. As shown in FIG. 2, the stainless sensor pipe has a measurement limit of about 6 sccm, but the nickel sensor pipe can measure the flow rate almost accurately up to about 18 sccm. In this embodiment, only 16.67 sccm flows in the sensor channel 2 even in the full-scale state, so that the flow rate in the sensor channel 2 can be measured almost accurately.

FIG. 3 shows the relationship with the set flow rate after calibration of the mass flow controller, which is 30% of full scale,
That is, the mass flow controller is calibrated at 30 sccm. However, the horizontal axis of FIG. 3 is based on the output of the bridge circuit 4, and is a calibration curve at the stage where linearization is not performed. The accuracy of the calibration is calibrated so that the flow rate of the conduit 1 is 30 sccm ± 0.3%, that is, 30 ± 0.09 sccm when the mass flow controller instructs 30 sccm so as to satisfy the standard. However, since this mass flow controller can flow a calibrated flow rate, that is, a flow rate larger than 30 sccm, and the sensor flow rate can be linearly measured up to a large flow rate, it can measure almost accurately up to 100 sccm. However, since it is calibrated at 30 sccm, an error occurs at 100 sccm, but 100 sccm
The tolerance of the error in cm is large. That is, in this embodiment, the actual flow rate was 108.9 sccm when the mass flow controller indicated 100 sccm, but the allowable error is 100 ± 10 sccm, so the calibration is performed within the allowable range.

In this embodiment, nickel is used as the material of the sensor conduit 2, but nickel alloy can also be used. Further, FIG. 3 shows a calibration curve in a stage before the linearization circuit 5, and the accuracy standard is satisfied even in this state.
Therefore, by using the linearization circuit 5 to match the measured flow rate with the actual flow rate, the accuracy of the mass flow controller can be further improved.

[0011]

As described above, according to the present invention, a single mass flow controller can meet the demand for high precision with a small flow rate and the demand for high flow rate with a low precision. The cost required for the mass flow controller is low, and since it is not necessary to switch the flow paths, the flow rate can be easily measured.

[Brief description of drawings]

FIG. 1 is a schematic system diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between a sensor flow rate and a sensor output.

FIG. 3 is a diagram showing characteristics of one embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Pipe line 2 ... Sensor flow path 3 ... Bypass flow path 4 ... Bridge circuit 5 ... Linearization circuit 6 ... Control circuit part 7 ... Control valve

Claims (3)

[Claims] A sensor circuit for detecting a mass flow rate in a sensor flow path; a bypass flow path through which a fluid flows; a control circuit for comparing and controlling a detection signal from the sensor part with a setting signal;
A mass flow controller having a valve section for controlling a flow rate based on this comparison control, wherein the sensor channel is formed of a metal material having a higher thermal conductivity than stainless steel, and the flow rate and the sensor flowing through the sensor channel are A mass flow controller characterized in that a total flow rate of the flow path and the bypass flow path is set to a predetermined flow rate ratio and calibrated at a flow rate of 50% or less of a full-scale flow rate of the mass flow controller. 2. The mass flow controller according to claim 1, wherein the sensor flow path is formed of nickel or an alloy thereof. 3. The mass flow controller according to claim 1, wherein the sensor unit has a linearization circuit so that the measured flow rate matches the actual flow rate.