Flow control device and zero point adjustment method for piezoelectric valve

Abstract

To provide a flow control device and a zero point adjustment method of a piezoelectric valve, capable of canceling effects caused by hysteresis characteristics and a creep phenomenon, to obtain a repeatable strain zero position (zero point position).SOLUTION: A flow control device 1 comprises: a piezoelectric valve 4 comprising a metal diaphragm valve body 3 that is opened and closed by a piezoelectric actuator 2; a strain sensor 5 that detects a displacement amount of the piezoelectric actuator 2; and a control circuit 6 that receives a detection signal D2 from the strain sensor 5, and controls a drive voltage of the piezoelectric actuator 2. The control circuit 6 is configured to apply a positive drive voltage once or multiple times to the piezoelectric actuator 2 when desired, and then apply a negative drive voltage multiple times, thereby bringing a strain amount detected by the strain sensor 5 closer to zero when no drive voltage is applied to the piezoelectric actuator 2.SELECTED DRAWING: Figure 8

Description

[Technical field]

[0001] The present invention relates to a flow control device and a zero point adjustment method for a piezoelectric valve, and more particularly to a flow control device and a zero point adjustment method for a piezoelectric valve used in semiconductor manufacturing equipment, chemical plants, etc. [Background technology]

[0002] In semiconductor manufacturing equipment and chemical plants, various types of flow meters and flow control devices are used to control the flow rates of material gases and etching gases. Flow control devices generally include a control valve that controls the flow rate. As a control valve, a piezoelectric element-driven valve (piezo valve) configured to open and close a metal diaphragm valve body by a piezoelectric actuator is known. Details of the piezo valve are disclosed, for example, in Patent Document 1.

[0003] Piezo actuators are capable of relatively high-speed operation, but because they have hysteresis characteristics and creep phenomena, the expansion of the piezo actuator is not strictly proportional to the magnitude of the drive voltage.Therefore, a piezo valve is known that provides a strain sensor that measures the displacement of the piezo actuator and feedback controls the drive voltage based on the strain signal (displacement output) of the strain sensor to control the valve opening at high speed and with high precision (Patent Documents 2 and 3, etc.).

[0004] Fig. 1 is a graph showing the drive voltage and the displacement output of the strain sensor in a normally closed type piezoelectric valve when the valve opening is controlled by applying a drive voltage to the piezoelectric actuator without feedback control of the drive voltage based on the displacement output of the strain sensor, and Fig. 2 and Fig. 3 are graphs showing the part surrounded by the dashed dotted line in Fig. 1 enlarged and scaled. Fig. 2 shows that even if the drive voltage of the piezoelectric actuator is stable, the displacement output of the strain sensor fluctuates due to the creep phenomenon of the piezoelectric element. Fig. 3 shows that the displacement output of the strain sensor when the drive voltage of the piezoelectric actuator is commanded to be 0V is not 0 due to the influence of hysteresis.

[0005] Fig. 4 is a graph showing the drive voltage and the displacement output of the strain sensor when the drive voltage of the piezo actuator is controlled based on the displacement output of the strain sensor in a normally closed type piezo valve, and Figs. 5 and 6 are graphs showing the part surrounded by the dashed line in Fig. 4 enlarged and scaled. Fig. 5 shows that the fluctuation of the displacement output due to the creep phenomenon is suppressed by overshooting the drive voltage. Fig. 6 shows the state in which a negative voltage is applied to the piezo actuator to suppress the deviation of the displacement output due to hysteresis as shown in Fig. 3, and the drive voltage is controlled so that the displacement output becomes the set value (0V).

[0006] A piezoelectric valve having a strain sensor can accurately grasp the open / closed state and has high responsiveness, and therefore can be suitably used to supply gas in a pulsed manner at a desired flow rate in applications where high-speed (very short cycle) pulse control signals are given, such as ALD (Atomic Layer Deposition) processes and ALE (Atomic Layer Etching) processes. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2007-192269 A [Patent Document 2] International Publication No. 2018 / 123852 [Patent Document 3] International Publication No. 2019 / 107215 Summary of the Invention [Problem to be solved by the invention]

[0008] However, as mentioned above, if control (also called strain control) is continued by applying a negative voltage to the piezoelectric actuator as shown in Figure 6 in order to suppress deviations in displacement output due to hysteresis, the valve opening continues to change slightly, making it impossible to perform accurate flow control.

[0009] Furthermore, referring to the hysteresis characteristic model of the piezoelectric actuator in Fig. 7, the (0,0) point in Fig. 7 where the applied voltage is 0V and the displacement is 0μm is an indefinite point that is not determined depending on the assembly state of the piezoelectric actuator, the ambient temperature, etc. If the position of the initial zero strain is indefinite, zero point adjustment to correct the strain deviation cannot be performed, and it cannot be used as accurate displacement information to control the valve opening.

[0010] Therefore, the main object of the present invention is to provide a flow control device and a zero point adjustment method for a piezoelectric valve that can cancel the effects of hysteresis characteristics and creep phenomena and obtain a reproducible zero strain position (zero point position). [Means for solving the problem]

[0011] In order to achieve the above object, a flow control device according to one embodiment of the present invention comprises a piezo valve having a metal diaphragm valve body that is opened and closed by a piezo actuator, a strain sensor that detects the displacement of the piezo actuator, and a control circuit that receives a detection signal from the strain sensor and controls a drive voltage for the piezo actuator, the control circuit being configured to apply a positive drive voltage one or more times to the piezo actuator when desired, and then apply a negative drive voltage multiple times, so that the amount of strain detected by the strain sensor approaches zero when no drive voltage is applied to the piezo actuator. The negative drive voltage may be applied multiple times while gradually increasing the voltage.

[0012] Another embodiment of the present invention is a zero point adjustment method for a piezo valve equipped with a metal diaphragm valve body that opens and closes by a piezo actuator, comprising a first step of detecting the displacement amount of the piezo actuator by a strain sensor, a second step of applying a positive drive voltage to the piezo actuator one or more times, and a step of applying a negative drive voltage multiple times after the second step to bring the amount of strain detected by the strain sensor closer to zero when no drive voltage is applied to the piezo actuator. After the second step, the negative drive voltage may be applied multiple times while gradually increasing the voltage. Effect of the Invention

[0013] According to the embodiment of the present invention, the influence of the hysteresis characteristic and the creep phenomenon can be cancelled, and a reproducible zero strain position (zero point position) can be obtained. [Brief description of the drawings]

[0014] [Figure 1] 1 is a graph showing the drive voltage of a piezo valve and the displacement output of a strain sensor. [Diagram 2] 2 is a graph showing a portion of the bluff of FIG. 1 at an enlarged scale. [Diagram 3] 2 is a graph showing another part of the graph in FIG. 1 with an enlarged scale. [Figure 4] 1 is a graph showing the drive voltage of a piezo valve and the displacement output of a strain sensor. [Diagram 5] 5 is a graph showing a portion of the bluff of FIG. 4 at an enlarged scale. [Figure 6] 5 is a graph showing another part of the graph in FIG. 4 with an enlarged scale. [Figure 7] 1 is a graph showing the hysteresis characteristics of a piezoelectric element. [Figure 8] 1 is a schematic diagram showing an embodiment of a flow rate control device according to the present invention; [Figure 9] 5 is a graph showing the drive voltage and strain output over time due to zero point adjustment of a piezo valve according to an embodiment of the present invention. [Figure 10] 10 is a graph showing the graph of FIG. 9 with an enlarged scale. [Figure 11] 13 is a graph showing the drive voltage and strain output over time due to zero point adjustment of a piezo valve according to another embodiment of the present invention. [Figure 12] 12 is a graph showing the graph of FIG. 11 with an enlarged scale. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] An embodiment of a flow rate control device according to the present invention will be described below with reference to FIGS.

[0016] 8, the flow rate control device 1 includes a piezoelectric valve 4 having a metal diaphragm valve element 3 that is opened and closed by a piezoelectric actuator 2, a strain sensor 5 that detects the amount of displacement of the piezoelectric actuator 2, and a control circuit 6 that receives a detection signal from the strain sensor 5 and controls the drive voltage of the piezoelectric actuator 2. The piezoelectric actuator 2 is displaced by the expansion and contraction of a piezoelectric element 2a in response to the drive voltage.

[0017] The metal diaphragm valve element 3 is interposed in the flow path 7, and opens and closes the flow path 7 in accordance with the displacement operation of the piezoelectric actuator 2. The valve opening degree of the metal diaphragm valve element 3 is controlled by controlling the displacement amount of the piezoelectric actuator 2. A fluid G, which is, for example, a pressure-adjusted process gas, is supplied from the upstream side of the flow path 7, and the downstream side of the flow path 7 is connected to a process chamber (not shown) of a semiconductor manufacturing device. A vacuum pump is connected to the process chamber, and typically, the pressure-adjusted fluid G is supplied to the process chamber while the inside of the process chamber is evacuated.

[0018] The piezoelectric actuator 2 may be, for example, one sold by NTK Ceratec Co., Ltd. The piezoelectric actuator 2 may be composed of a plurality of piezoelectric elements housed in a cylindrical casing and stacked. The metal diaphragm valve body 3 may be a self-elastic return type metal diaphragm valve body formed of a thin plate such as nickel-chromium alloy steel. The specific structure of the piezoelectric valve 4 is publicly known from JP 2007-192269 A and the like, so a detailed description thereof will be omitted.

[0019] The strain sensor 5 can be directly attached to the piezoelectric element 2a by adhesive or the like. For example, KFR-02N, KFGS-1, KFGS-3, or the like manufactured by Kyowa Electric Industry Co., Ltd. can be used as the strain sensor 5. Note that the strain sensor 5 can also be provided on the outside of a casing that houses the piezoelectric element 2a, as disclosed in, for example, International Publication No. 2018 / 123852.

[0020] The control circuit 6 may be built into the flow control device 1, or may be provided externally to the flow control device 1. The control circuit 6 is typically configured with a CPU, a memory (storage device) M such as a ROM or RAM, an A / D converter, etc., and may include a computer program configured to execute a flow control operation described below. The control circuit 6 may be realized by a combination of hardware and software.

[0021] The control circuit 6 amplifies the minute resistance change of the strain gauge constituting the strain sensor 5 using a Wheatstone bridge circuit, extracts it as a voltage change, and converts the amount of strain into a voltage based on a certain relationship between the extracted voltage change and strain. The converted amount of strain corresponds to the amount of displacement of the piezo actuator 2, and the amount of displacement of the piezo actuator 2 corresponds to the valve opening degree of the metal diaphragm valve element 3.

[0022] When controlling the flow rate of the fluid G (flow rate control mode), the control circuit 6 feedback controls the drive voltage V of the piezoelectric actuator 2 so that the difference between the set displacement D1 sent from an external device (e.g., semiconductor manufacturing equipment) 8 and the displacement amount (strain amount) of the piezoelectric actuator 2 obtained from the detection signal D2 of the strain sensor 5 becomes zero. This makes it possible to maintain the valve opening degree of the metal diaphragm valve element 3 at a predetermined opening degree, and to maintain the flow rate of the fluid G passing through the flow path 7 at a predetermined value.

[0023] The control circuit 6 can execute sequence control to perform zero point adjustment of the strain sensor 5 when desired (for example, when the number of opening and closing times of the piezo valve reaches a predetermined number (for example, 10 million times), or during maintenance, etc.) (hereinafter, also referred to as zero point adjustment mode). A sequence program for executing the sequence control of the zero point adjustment mode can be stored in advance in the memory device M built into the control circuit 6 or in an external memory device. Switching from the control mode for controlling the flow rate to the zero point adjustment mode can be done manually or automatically by a program.

[0024] FIG. 9 is a graph showing the change in the amount of strain (strain output) in an embodiment in which sequence control is performed in the zero point adjustment mode in a normally closed type piezo valve. In this example, for example, the strain output (amount of strain) of the strain sensor when a positive drive voltage of 130V is applied is set to 100%. The graph in FIG. 10 is a graph showing an enlarged scale of FIG. 9. In the example of the zero point adjustment mode shown in FIG. 9 and FIG. 10, a positive drive voltage is applied to the piezo actuator 2 three times, and then a negative drive voltage is applied multiple times while gradually increasing the voltage. Specifically, after 130V (30 seconds) → 0V (30 seconds) is repeated three times, a negative drive voltage is applied multiple times in the following sequence. -20V (2 seconds) → 0V (4 seconds) → -19V (2 seconds) → 0V (4 seconds) → -18V (2 seconds) → 0V (4 seconds) → -17V (2 seconds) → 0V (4 seconds) → -16V (2 seconds) → 0V (4 seconds) → -15V (2 seconds) → 0V (4 seconds) → -14V (2 seconds) → 0V (4 seconds) → -13V (2 seconds) → 0V (4 seconds) → -12V (2 seconds) → 0V (4 seconds) → -11V (2 seconds) → 0V (4 seconds) → -10V (2 seconds) → 0V (4 seconds) → -9V (2 seconds) → 0V (4 seconds) → -8V (2 seconds) → 0V (4 seconds) → -7V (2 seconds) → 0V (4 seconds) → -6V (2 seconds) → 0V (4 seconds) → -5V (2 seconds) → 0V (4 seconds) → -4V (2 seconds) → 0V (4 seconds) → -3V (2 seconds) → 0V (4 seconds) → -2V (2 seconds) → 0V (4 seconds) → -1V (2 seconds) → 0V (end).

[0025] Before executing the sequence control of the zero point adjustment mode, i.e., during the time period from 0 to 30 seconds in Fig. 9, a positive drive voltage of about 0.3V is applied to control the distortion so that the distortion amount becomes 0(%). When the drive voltage is zero, a positive distortion control voltage is applied if the output (amount of distortion) of the distortion sensor is negative, and a negative distortion control voltage is applied if the output of the distortion sensor is positive, thereby controlling distortion.

[0026] 9 and 10 show that even if the applied voltage is set to 0V after the application of a positive drive voltage (130V), the amount of distortion of the piezoelectric element 2a remains at about 5 to 6% due to the influence of the hysteresis characteristic and the creep phenomenon. Also, FIG. 9 and FIG. 10 show that by applying a positive drive voltage (130V) multiple times and then applying a negative drive voltage multiple times while gradually increasing the voltage, the amount of distortion gradually converges and approaches zero, and finally, when the drive voltage is 0V, the amount of distortion is approximately 0(%). Therefore, by executing the sequence of the zero point adjustment mode, the residual distortion due to the hysteresis characteristic and the creep phenomenon can be canceled and the amount of distortion at a drive voltage of 0V can be made approximately zero.

[0027] The graph in FIG. 11 shows the result of executing a zero-point adjustment sequence in which a positive drive voltage of 130V was applied to a normally closed piezo valve, the application time was 0.5 seconds, and the number of applications was one, and a negative drive voltage was applied while gradually increasing by 1V from -20V to -10V. FIG. 12 is a graph with the scale of FIG. 11 enlarged. In this example of the zero-point adjustment mode, the sequence of -20V→0V→-19V→0V→-18V→0V→-17V→0V→-16V→0V→-15V→0V→-14V→0V→-13V→0V→-12V→0V→-11V→0V→-10V→0V was executed in 5 seconds. The graphs in FIG. 11 and FIG. 12 show that it is possible to cancel the effects of the hysteresis characteristic and creep phenomenon and reduce the distortion amount at the drive voltage of 0V to almost 0 in an adjustment time of about 5.5 seconds. In the sequence of the zero point adjustment mode shown in the graph of FIG. 9, the sequence execution time, i.e., the zero point adjustment time, was approximately 300 seconds.

[0028] In the sequence for executing the zero point adjustment mode, the applied voltage, number of applications, and application time of the positive drive voltage, and the applied voltage, number of applications, and application time of the negative drive voltage can be appropriately set by changing the parameters of the control program, and by changing these parameters, it is possible to shorten the execution time of the sequence of the zero point adjustment mode, i.e., the zero point adjustment time. In addition, although an example in which the negative drive voltage is applied multiple times while gradually increasing it has been shown in the embodiment, the application pattern of the negative drive voltage can adopt other patterns, such as applying the same voltage multiple times.

[0029] The present invention is not limited to normally closed type piezo valves, but can also be applied to normally open type piezo valves. The present invention should not be construed as being limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention. [Explanation of symbols]

[0030] 1 Flow control device 2 Piezo Actuator 2a Piezo element 3 Metal diaphragm valve body 4 Piezo valve 5 Strain Sensor 6 Control Circuit G fluid

Claims

1. a piezo valve having a metal diaphragm valve body that is opened and closed by a piezo actuator; A strain sensor that detects a displacement amount of the piezoelectric actuator; a control circuit that receives a detection signal from the strain sensor and controls a drive voltage of the piezoelectric actuator; The control circuit is configured to, when desired, apply a positive drive voltage one or more times to the piezoelectric actuator, and then apply a negative drive voltage multiple times to the piezoelectric actuator, so that the amount of strain detected by the strain sensor approaches zero when no drive voltage is being applied to the piezoelectric actuator. Flow control device.

2. 2. The flow rate control device according to claim 1, wherein the negative drive voltage is applied while gradually increasing the voltage.

3. A method for adjusting the zero point of a piezo valve having a metal diaphragm valve body that is opened and closed by a piezo actuator, comprising the steps of: A first step of detecting a displacement amount of the piezoelectric actuator by a strain sensor; a second step of applying a positive drive voltage to the piezoelectric actuator one or more times; and applying a negative drive voltage multiple times after the second step, thereby bringing the amount of strain detected by the strain sensor closer to zero when no drive voltage is applied to the piezoelectric actuator. A method for adjusting the zero point of the piezoelectric valve.

4. 4. The method for adjusting the zero point of the piezo valve according to claim 3, wherein the negative drive voltage is applied while gradually increasing the voltage.

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