JPH079607B2 - Mass flow controller - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention is for controlling the flow rate of various gases used in the manufacturing process of semiconductors, ICs, etc. (hereinafter, “flow rate” means mass flow rate). The present invention relates to an improvement of a preferable mass flow controller.

[Prior Art] Conventionally, there is known a mass flow rate control device 1 as shown in Fig. 4 which includes a valve using a thermal mass flow rate sensor and utilizing thermal expansion of metal. In the figure, 2 indicates a gas inlet, and 3 indicates a gas outlet. When the gas enters the inlet section 2, it is branched into a bypass section 4 and a sensor tube 5. A pair of resistance heating elements 6A and 6B are wound around the sensor tube 5 on the upstream side and the downstream side of the gas flow. The resistance heating elements 6A and 6B are connected to the bridge circuit 7. When the gas passes through the sensor tube 5, the resistance heating elements 6A and 6B take heat. At this time, the temperature of the resistance heating element 6A is lower than that of the resistance heating element 6B, and the temperature difference caused by this is taken out as a resistance value change in the bridge circuit 7. The mass flow rate of the gas flowing through the sensor tube 5 can be detected based on the change in the resistance value. On the other hand, since the diversion ratio between the sensor pipe 5 and the bypass section 4 is predetermined, the mass flow rate of the gas flowing through the sensor pipe 5 becomes a value that reflects the mass flow rate of the entire flowing gas. Reference numeral 8 denotes a metal mesh interposed in the bypass section 4, and the mesh 8 maintains a predetermined diversion ratio of the gas flowing through the bypass section 4 and the sensor pipe 5. Further, 9 is a casing of the sensor portion, and the casing 9 prevents the resistance heating elements 6A and 6B from being affected from the outside, and enables accurate mass flow rate detection. The output signal of the bridge circuit 7 is amplified by the amplifier circuit 10 and is output from the sensor output terminal 11 to an external display (not shown) or the like, and is also output to the comparison circuit 12. A setting signal corresponding to a predetermined value of a desired mass flow rate is externally applied to the comparison circuit 12 via a setting signal input terminal 13. The comparison circuit 12 compares the output signal of the amplification circuit 10 with the setting signal and outputs a signal according to the difference. This signal is given to the valve drive circuit 14, and the valve drive circuit 14 gives a drive voltage to the valve heater 15 based on the above signal. 16 indicates a valve. The valve 16 is a normally open type (the valve is in the (open) state when no voltage is applied, and the valve is in the (closed) state when voltage is applied). The valve heater 15 is placed in the metal pin 17, and due to the expansion of the metal pin 17 due to the heat generation of the valve heater 15, the spherical valve body 18 fixed to the tip of the metal pin moves up and down to form an orifice for the gas passage. adjust.

According to the mass flow rate control device 1 configured as described above, since the signal corresponding to the mass flow rate detected in the sensor tube 5 portion reflects the mass flow rate of the entire gas, this signal and the setting signal By controlling the valve 16 so that there is no difference between the two, it is possible to control the mass flow rate appropriately.

By the way, since the mass flow controller is used for mass control of gases used in the manufacturing process of semiconductors and ICs,
High reliability is required to improve the processing accuracy of semiconductors and ICs. Therefore, in order to notify the abnormality of the mass flow rate control device, it is proposed to provide a means for detecting that a difference more than a predetermined value has occurred between the signal output from the amplifier circuit 10 and the setting signal. ing.

[Problems to be Solved by the Invention and Object of the Invention] However, according to the above means, an abnormality may not be detected until the function of the mass flow controller 1 is completely impaired. For example, if minute dust or the like adheres to the inside of the sensor tube 5, the output of the sensor decreases, and the signal output from the amplifier circuit 12 becomes a signal corresponding to a flow rate smaller than the actual flow rate of gas. Therefore, the output of the comparison circuit 12 is the valve
Acts to open 16. As a result, when the valve 16 is in the operating range, the flow rate of the gas flowing through the bypass section 4 increases, and the values of the output signal of the amplifier circuit 10 and the setting signal are balanced. In this way, the apparent balance is maintained,
Although an abnormality actually occurred, the abnormality could not be detected.

In addition to this, dust and the like adhere to the bypass section 4, the space between the spherical valve body 18 and the valve seat, etc., but the above-mentioned means did not detect any abnormality as described above. Therefore, when using the above mass flow rate controller in the manufacturing process of semiconductors, ICs, etc.,
When an abnormality is found, a large amount of semiconductors and ICs already in production
It was often after the damage, etc., which was a big problem. In addition, the number of man-hours and time required for inspection and maintenance by stopping the operation of the manufacturing line after detecting an abnormality is great. Furthermore, when using dangerous gases such as HC1, BF3, and NH3, there is a problem that safety cannot be ensured.

Also, if the valve 16 is a normally closed type,
As the voltage above the rated value is applied more often, the valve 16
There was a great possibility of shortening the life of the.

Therefore, in the mass flow rate control device as shown in FIG. 4, it is determined whether the flow rate data obtained by the flow rate sensor is compared with the set flow rate data input from the outside based on the valve drive signal generated based on the valve drive signal. There is a determination section that does.

According to the mass flow controller having such a configuration, it is abnormal that the valve drive signal deviates from its normal value. That is, since an absolute signal called a valve drive signal is used, such abnormality detection is performed before the function of the mass flow rate control device is completely impaired.

FIG. 1 shows a block diagram of an apparatus according to the above idea. In the figure, the same components as those in FIG. 4 are designated by the same reference numerals. Reference numeral 21 denotes the resistance of the valve heater 15, which has a resistance value of usually 60Ω to 70Ω, one end of which is connected to the ground and the other end of which is connected to the determination circuit 23 in the determination unit 22. The end of the resistor 21 that is not connected to the ground is connected to the collector of the transistor 24. A voltage of -15V is applied to the emitter of the transistor 24. The base of the transistor 24 is connected to the output side of the comparison circuit 10 via the resistor 27. The discrimination circuit 23 includes
Normal value indicating means for holding the maximum value | MAXV _R | and the minimum value | MINV _R | of the valve drive voltage V _R when the valve 16 operates normally is included. The determination circuit 23 obtains the valve drive voltage V _R from the valve heater 15 and determines whether | MAXV _R | ≧ | V _R | ≧ | MINV _R | ... (1) holds. The signal of this determination result is given to the timer circuit 25. When the timer circuit 25 continuously detects a signal indicating that the expression (1) is not satisfied for a predetermined time, it outputs an abnormal signal to the output terminal 26. In this way, the timer circuit 25
Indicates that the valve drive voltage V _R temporarily fluctuates greatly-for example, it fluctuates greatly when the setting signal is changed abruptly-
This prevents a signal indicating an abnormality from being erroneously output.

By adding such a configuration to the mass flow controller 1 of FIG. 4, the following operation is performed.

For example, the dust on the sensor tube 5 is attached, the valve drive voltage V _R is applied so that the valve 16 is opened as described above. The valve drive voltage V _R is not satisfied equation (1), the predetermined time in this state is continued, the timer circuit
A signal indicating an abnormality is output from 25. This signal can be given from an output terminal 26 to a display device (not shown) (for example, an LED or the like) to notify the abnormality by a lighting display.

In the above configuration example _{| MAXV R | = | -13.3 |} (V) | MINV R |
= | -1.7 | (V), if a setting signal is input to obtain the maximum flow rate (100%), an abnormality can be detected when a 10% flow rate error occurs. Further, by setting the predetermined time monitored by the timer circuit 25 to 30 seconds, even if there is a rapid change in the setting signal, the malfunction can be absorbed and the abnormality can be accurately detected.

According to the present configuration example, since the valve drive voltage V _R can be prevented from being applied beyond the standard, it is possible to increase the life of the valve 16, also a semiconductor or IC
It is extremely convenient because measures can be taken before the decisive damage appears in the manufacturing process.

However, even in the above configuration example, it may not be possible to accurately detect an abnormality in the mass flow rate control device due to fluctuations in the pressure and temperature of the fluid whose mass flow rate is to be detected.

The present invention has been made as an improvement of the above point, and an object thereof is to provide a mass flow rate control device capable of accurately detecting an abnormality in response to fluctuations in pressure and temperature of a fluid whose mass flow rate is to be detected. Is to provide.

[Means for Solving the Problem] In the present invention, therefore, the mass flow rate sensor is compared with the mass flow rate data obtained from the mass flow rate sensor and the set mass flow rate data set and input, and the valve drive is performed based on the comparison result. A mass flow rate control device comprising a means for generating a signal and a valve whose opening is adjusted by a valve drive signal generated by the means, wherein the mass flow rate sensor detects the pressure of a target fluid for detecting a mass flow rate. A pressure sensor, a temperature sensor for detecting the temperature of a fluid whose mass flow rate sensor detects a mass flow rate, a mass flow rate signal obtained by the mass flow rate sensor, a pressure signal obtained by the pressure sensor, and the Based on the temperature signal obtained by the temperature sensor, the data corresponding to the valve drive signal when the mass flow controller is operating normally is calculated and instructed. A value instructing unit and a determination unit for determining normality / abnormality of the mass flow controller based on the data instructed by the normal value instructing unit and the data of the signal obtained by monitoring the valve drive signal are provided. And

[Operation of the Invention] According to the mass flow rate control device having such a configuration, data corresponding to the valve drive signal of the mass flow rate control device at the normal time is calculated from the mass flow rate signal, the pressure signal, and the temperature signal,
Based on the data obtained by the calculation and the data of the signal monitoring the valve drive signal, it is judged whether the mass flow control device is normal or abnormal, and the abnormality is detected with high accuracy before the device completely impairs its function. .

[Embodiment of the Invention] Hereinafter, a mass flow controller according to an embodiment of the present invention will be described with reference to the accompanying drawings. FIG. 2 is a block diagram of the essential parts of an embodiment of the present invention.

In this embodiment, the pressure sensor 31 and the temperature sensor 32 are installed in the passage between the bypass section 4 and the inlet section 2 of the mass flow controller 1 shown in FIG. The signal obtained by the pressure sensor 31 is amplified by the amplifier circuit 33 and sent to the discrimination unit 34.
Further, the signal obtained by the temperature sensor 32 is amplified by the amplifier circuit 35 and sent to the discriminating unit 34. The determination unit 34 has a 10-bit A / D
The converter 36, a valve drive signal V _R, the flow rate signal F, the pressure signal P, the temperature signal T is given, which are transmitted is digitized to the arithmetic circuit 37. The arithmetic circuit 37 has a so-called microcomputer configuration and includes an 8-bit microprocessor, a program ROM, a working register RAM, and necessary buses and ports. This microprocessor operates according to the program of the flow chart shown in FIG. 3 in the program ROM.
It has a function of a normal value instruction means for calculating a value of a signal necessary for adjusting the opening degree of the valve 16 when the valve 16 is operating normally and instructing the value.

Next, the operation of the arithmetic circuit 37 will be described with reference to FIG.
First, the arithmetic circuit 37 in step 101 two or flow data F which is digitized from the A / D converter 36, the pressure data P, the temperature data T, taking a valve driving data V _R.
Next, the arithmetic circuit 37 obtains the reference voltage data V ₁ of the valve 16 determined by the flow rate data F and the pressure data P in step 102 from V ₁ = g (F, P) (2). Here, g (F, P) is a function that is constantly determined depending on the type of gas, and is held in the program ROM.

Next, in step 103, the arithmetic circuit 37 sets the normal drive voltage data V ₂ of the valve 16 determined by the reference voltage V ₁ and the temperature data T obtained by the equation (2) to V ₂ = V ₁ · h (T )… (3) Here, h (T) is a function for correcting the temperature of the reference voltage data V ₁ , which is fixed depending on the type of gas and is held in the program ROM.

Next, in step 104, the arithmetic operation circuit 37 determines whether or not the allowable valve drive voltage error K is | V ₂ −V _R | <K. That is, the valve drive voltage V _R currently applied to the valve 16 is the error K of the normal drive voltage data V ₂ .
If it is within the range, it is normal and the register n is cleared in step 105 and the process returns to step 101. When the error K is exceeded, it is abnormal and therefore register n is registered in step 106.
1 is added to indicate the abnormal period (time). Further arithmetic circuit
The process proceeds to step 107 to determine whether the data n in the register n is smaller than the predetermined value M, and checks whether the abnormal period has continued for M seconds. If n <M, step 10
Returning to 1 and if n = M, in step 108 the arithmetic circuit 37
Outputs an abnormal signal.

Thus, in this embodiment by utilizing the fact that actual flow rate of gas, pressure, uniquely normal valve driving voltage from the temperature is determined, which the actual error between the valve drive voltage V _R is equal to or greater than a predetermined When it becomes, the abnormality is detected and the abnormality of the mass flow rate control device can be detected more accurately. In the case of the present embodiment, if the error voltage is set within several tens to several hundreds of mV, an abnormality can be detected when the flow rate error is 2 to 5%.

In this embodiment, depending on the type of gas, the above (2),
When the function of the equation (3) is different and the calculation condition needs to be changed, it is convenient because it can be dealt with only by converting the program ROM.

Further, in the embodiment, the calculation is performed using the equations (2) and (3), but V ₁ and V ₂ are obtained in advance by changing the flow rate F, the pressure P and the temperature T variously depending on the type of gas. It is also possible to store this in the program ROM and obtain V ₁ and V ₂ by a table search based on the fetched flow rate F, pressure P, and temperature T. Further, the program ROM used in the construction of FIG. 1 in _{| MAXV R |, | MINV R} | allowed to store the determination circuit 23 to the microprocessor to perform the function of the timer circuit 25 in addition to this example You may do it.

Further, in the above embodiments, the valve drive voltage is used as the determination target, but the current may be used as the determination target. As a driving method of the valve, there is a method of giving a driving signal as a pulse, and a signal (pulse) given also for this can be a target of determination. Further, the present invention can be realized by making a determination target a signal that controls a valve whose opening is adjusted by a motor solenoid in addition to utilizing thermal expansion.

Further, the determination unit can be provided inside or outside the mass flow controller 1.

[Effects of the Invention] As described above, according to the present invention, data corresponding to the valve drive signal of the mass flow rate control device at the normal time is calculated from the mass flow rate signal, the pressure signal, and the temperature signal, and this data is calculated. Since the abnormality of the mass flow control device is determined based on the valve drive signal, the abnormality can be detected with high accuracy before the device completely impairs its function. Therefore, when the device of the present invention is used in a semiconductor or IC manufacturing process, an abnormality can be known before the manufacturing process is significantly harmed.
The measures can be taken earlier, and maintenance time can be greatly reduced. Therefore, in a semiconductor manufacturing process using a silane-based gas, minute dust adheres to the sensor tube, the valve, and the bypass portion. In such a case, the present invention is particularly effective. Of course, the present invention can detect an abnormality even when the signal line or the like for supplying the drive signal to the valve is broken or short-circuited.

[Brief description of drawings]

FIG. 1 is a block diagram of a main part of a configuration example of a mass flow controller having an abnormality detecting function, FIG. 2 is a block diagram of a main part of an embodiment of the present invention, and FIG. 3 shows an operation of the device of FIG. 4 is a block diagram of a conventional mass flow rate control device. 1 ... Mass flow controller, 2 ... Bypass section, 5 ... Sensor tube, 6A, 6B ... Resistance heating element, 12 ... Comparison circuit, 13 ... Setting signal input terminal, 14 ... Valve drive circuit, 15 …… Valve heater, 16 …… Valve, 22,34 …… Judgment part, 23 …… Judgment circuit, 25 …… Timer, 31 …… Pressure sensor, 32 …… Temperature sensor, 36 …… A / D converter, 37 …… Arithmetic circuit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-59-52306 (JP, A) JP-A-57-101910 (JP, A) Actually opened 59-88712 (JP, U)

Claims (1)

[Claims] 1. A mass flow rate sensor, means for comparing mass flow rate data obtained from the mass flow rate sensor with preset mass flow rate data set and inputted, and means for generating a valve drive signal based on the comparison result, and this means. In a mass flow rate control device comprising a valve whose opening is adjusted by a valve drive signal generated by a mass flow rate sensor, the mass flow rate sensor detects a pressure of a fluid to be detected by the mass flow rate sensor, and the mass flow rate sensor. Is a temperature sensor for detecting the temperature of the target fluid for detecting the mass flow rate, a mass flow rate signal obtained by the mass flow rate sensor, a pressure signal obtained by the pressure sensor, and a temperature signal obtained by the temperature sensor. From this, the normal value indicating means for calculating and instructing the data corresponding to the valve drive signal at the time of normal operation of the mass flow controller, and the normal value instruction A mass flow rate control device comprising: a determination unit that determines whether the mass flow rate control device is normal or abnormal based on the data instructed by the indicating means and the data of the signal obtained by monitoring the valve drive signal.