A calibration system for a mass flow controller and its calibration method

Abstract

The present invention provides a calibration method for a mass flow controller, comprising: obtaining a plurality of set flow values of the mass flow controller, and detecting a plurality of first standard flow values corresponding to the plurality of flow set values of the mass flow controller through a standard flow detection device; calculating a plurality of first theoretical flow values corresponding to the plurality of set flow values according to the flow control curve currently stored in the mass flow controller; calculating deviation values between the plurality of first standard flow values and the corresponding set flow values, and compensating the plurality of deviation values to the plurality of first theoretical flow values to obtain a new flow control curve; using the new flow control curve as the flow control curve currently stored in the mass flow sensor for calibration. The calibration method provided by the present invention can adjust the previously determined flow control curve based on the standard flow detection device, improving the accuracy of the mass flow controller in controlling the flow. The present invention also provides a calibration system for a mass flow controller.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor processes, and in particular, to a calibration method for a mass flow controller and a calibration system for a mass flow controller. Background Art

[0002] A mass flow controller (MFC) is a commonly used device for precisely measuring and controlling mass flow, and is widely used in various fields such as semiconductor process equipment, integrated circuit processes, special materials disciplines, chemical industries, petroleum industries, pharmaceuticals, and environmental protection. In the field of semiconductor process equipment, typical application scenarios of mass flow controllers include: microelectronic processes (such as diffusion, oxidation, epitaxy, CVD, plasma etching, sputtering, ion implantation) and coating equipment, optical fiber melting, micro reaction devices, gas mixing and gas distribution systems, gas sampling, capillary measurement, gas chromatographs, and other analytical instruments.

[0003] Before leaving the factory, a mass flow controller needs to be calibrated for accuracy using a high-precision flow detection standard device, that is, the corresponding relationship between the opening of the mass flow controller and its actual flow is accurately marked. However, affected by factors such as ambient temperature, the sensor of the MFC may have a temperature drift phenomenon, resulting in a change in accuracy. After a period of accumulation, the accuracy of the MFC will be lower than the minimum accuracy requirement of the product, thereby affecting the quality of the products produced by semiconductor process equipment. The existing calibration schemes for mass flow controllers have limited calibration accuracy and are difficult to meet the increasing high-precision requirements.

[0004] Therefore, how to provide a calibration method that can improve the calibration accuracy of a mass flow controller has become an urgent technical problem in this field. Summary of the Invention

[0005] The present invention aims to provide a calibration method for a mass flow controller and a calibration system for a mass flow controller, and this calibration method can calibrate the mass flow controller more precisely.

[0006] To achieve the above object, as one aspect of the present invention, there is provided a calibration method for a mass flow controller. By using a standard flow detection device to calibrate the mass flow controller, the method includes:

[0007] Obtain a plurality of set flow values of the mass flow controller, and detect a plurality of first standard flow values corresponding to the plurality of flow set values of the mass flow controller through the standard flow detection device;

[0008] Calculate a plurality of first theoretical flow values corresponding to the plurality of set flow values according to the flow control curve currently stored in the mass flow controller;

[0009] Calculate the deviation values between the plurality of first standard flow values and the corresponding set flow values;

[0010] Compensate the plurality of deviation values to the plurality of first theoretical flow values to obtain a new flow control curve;

[0011] Use the new flow control curve as the flow control curve currently stored in the mass flow sensor for calibration.

[0012] Optionally, using the new flow control curve as the flow control curve currently stored in the mass flow sensor for calibration includes:

[0013] Obtain a plurality of second standard flow values corresponding to the plurality of flow set values detected by the standard flow detection device;

[0014] Compare whether the deviation values between the plurality of second standard flow values and the corresponding set flow values are all less than a preset threshold. If there is at least one deviation value not less than the preset threshold, obtain a new flow control curve again by compensating the deviation values between the plurality of first standard flow values and the corresponding set flow values to the plurality of first theoretical flow values until the plurality of deviation values are all less than the preset threshold.

[0015] Optionally, obtaining the plurality of set flow values of the mass flow controller includes:

[0016] Select a plurality of set flow values based on different proportions of the full-scale flow of the mass flow controller.

[0017] Optionally, the number of the set flow values is greater than or equal to 5.

[0018] Optionally, the number of the set flow values is 6, which are 7%, 15%, 25%, 50%, 75% and 100% of the full-scale flow of the mass flow controller respectively.

[0019] Optionally, the preset threshold does not exceed 1% of the full-scale flow of the mass flow controller.

[0020] Optionally, compensating the plurality of deviation values to the plurality of first theoretical flow values to obtain a new flow control curve includes;

[0021] According to the plurality of compensated first theoretical values and the corresponding plurality of set flow values, perform fitting calculation by the least square method to obtain the new flow control curve.

[0022] Optionally, the formula adopted by the least squares method is f(X) = a×X n +b×X n-1 +c×X n-2 +d×X n-3 +…+n, and n is greater than or equal to 4, where X is the set flow value, f(X) is the theoretical flow value, and a, b, c, d, … n are constants.

[0023] As a second aspect of the present invention, a calibration system for a mass flow controller is provided, including a standard flow detection device, a mass flow controller, and a host computer module. The host computer module is used to set the set flow value of the standard flow detection device and the set flow value of the mass flow controller, and the host computer module is used to implement the calibration method described above, where the built-in memory of the mass flow controller is used to store the currently stored flow control curve.

[0024] Optionally, the mass flow controller further includes a solenoid valve, and the mass flow controller is used to control the drive voltage of the solenoid valve according to the set flow value to change the flow rate of the mass flow controller.

[0025] In the calibration method and calibration system of the mass flow controller provided by the present invention, the host computer module can compensate the deviation value between multiple first standard flow values and the corresponding set flow values to multiple first theoretical flow values, and obtain a new flow control curve based on the compensated theoretical flow values, so as to adjust the previously determined flow control curve based on the standard flow detection device, making the new flow control curve closer to the actual flow characteristic curve of the mass flow controller, thereby improving the accuracy of the mass flow controller in controlling the flow rate. Description of the Drawings

[0026] The drawings are used to provide a further understanding of the present invention, and constitute a part of the specification. They are used together with the following specific embodiments to explain the present invention, but do not constitute a limitation to the present invention. In the drawings:

[0027] Figure 1 is a schematic structural diagram of a calibration system for a mass flow controller provided by an embodiment of the present invention;

[0028] Figure 2 is a schematic flow chart of a calibration method for a mass flow controller provided by an embodiment of the present invention;

[0029] Figure 3 is a schematic flow chart of a calibration method for a mass flow controller provided by another embodiment of the present invention. Detailed Description of the Invention

[0030] The following will describe in detail the specific embodiments of the present invention with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only for explaining and understanding the present invention, and are not used to limit the present invention.

[0031] The existing calibration method for a mass flow controller usually involves collecting the measured flow values of the mass flow controller at multiple set flow values, and fitting a curve formula between the flow and the set flow value based on the multiple set flow values and the measured flow values, that is, obtaining a flow control curve. The abscissa of this curve is the set flow value (or the control signal value corresponding to the magnitude of the set flow value, for example, the driving voltage of the solenoid valve), and the ordinate is the calibrated theoretical flow. However, due to the limited number of sampling points, there will still be a deviation between the flow control curve measured by this method and the true flow characteristic curve of the mass flow controller, making it difficult to meet the increasing high-precision requirements.

[0032] To solve the above technical problems, as one aspect of the present invention, a calibration method for a mass flow controller is provided. By using a standard flow detection device to calibrate the mass flow controller, as Figure 2 shown, the method includes:

[0033] Step S1: Obtain multiple set flow values X of the mass flow controller, and detect multiple first standard flow values Y3 corresponding to the multiple flow set values of the mass flow controller through a standard flow detection device;

[0034] Step S2: Calculate multiple first theoretical flow values Y2 corresponding to the multiple set flow values X according to the current flow control curve stored in the mass flow controller (if the mass flow controller has not been calibrated, the initial flow control curve is the flow Y1 = f(X) = X);

[0035] Step S3: Calculate the deviation value (i.e., the precision error) between the multiple first standard flow values Y3 and the corresponding set flow values X;

[0036] Step S4: Compensate the multiple deviation values to the multiple first theoretical flow values Y2 to obtain a new flow control curve;

[0037] Step S5: Use the new flow control curve as the current flow control curve stored in the mass flow sensor for calibration.

[0038] It should be noted that in the present invention, compensating the deviation value to the first theoretical flow value Y2 means adding the deviation value (i.e., the precision error) to the corresponding first theoretical flow value Y2, and fitting a new flow control curve based on the multiple calculated flow values (Y4) obtained by addition and the corresponding multiple set flow values X.

[0039] The calibration method provided by the present invention compensates the deviation values between multiple first standard flow values Y3 and the corresponding set flow values X to multiple first theoretical flow values Y2, and obtains a new flow control curve based on the compensated theoretical flow values, so as to adjust the previously determined flow control curve (i.e., the flow control curve currently stored in the mass flow controller) based on the standard flow detection device, making the new flow control curve closer to the actual flow characteristic curve of the mass flow controller, thereby improving the accuracy of the mass flow controller in controlling the flow rate.

[0040] To further improve the accuracy of the mass flow controller in controlling the flow rate, as a preferred embodiment of the present invention, the step of compensating the deviation value to the theoretical flow value can be repeatedly executed multiple times until the new flow control curve is close enough to the actual flow characteristic curve. Specifically, as Figure 3 shown, the step S5 of calibrating with the new flow control curve as the flow control curve currently stored in the mass flow sensor may include:

[0041] Step S51: Obtain multiple second standard flow values Y6 corresponding to multiple flow set values detected by the standard flow detection device;

[0042] Step S52: Compare whether the deviation values between the multiple second standard flow values Y6 and the corresponding set flow values X are all less than a preset threshold. If there is at least one deviation value not less than the preset threshold, then obtain a new flow control curve again by compensating the deviation values between the multiple first standard flow values Y3 and the corresponding set flow values X to the multiple first theoretical flow values Y2 (that is, repeat steps S1 to S4) until all the deviation values are less than the preset threshold (and then use the new flow control curve as the flow control curve currently stored in the mass flow sensor for calibration).

[0043] In the embodiment of the present invention, each execution of steps S1 to S4 is based on the standard flow values detected by the standard flow detection device to adjust the previously determined flow control curve. Therefore, the more times of calibration, the higher the accuracy of the obtained new flow control curve, making the new flow control curve gradually approach the true flow characteristic curve until the deviation value between the standard flow value corresponding to each set flow value X and the set flow value X is small enough (less than the preset threshold), further improving the accuracy of the mass flow controller in controlling the flow rate.

[0044] It should be noted that when it is determined in step S52 that there is a deviation value not less than the preset threshold (that is, it is determined that steps S1 to S4 need to be repeatedly executed), the first standard flow value Y3 when steps S1 to S4 are executed in the next round is the second standard flow value Y6 obtained in step S51. Therefore, when steps S1 to S4 are repeatedly executed in the next round, the previously obtained second standard flow value Y6 can be directly used as the first standard flow value Y3, and the deviation value between the previously obtained second standard flow value Y6 and the set flow value X can be directly used as the deviation value between the first standard flow value Y3 and the set flow value X in steps S1 to S4 in the next round.

[0045] Optionally, multiple set flow values X and their corresponding standard flow values and theoretical flow values can be represented by an array. Specifically, multiple first theoretical flow values Y2 corresponding to multiple set flow values X can be represented as an array [(X1, Y21), (X2, Y22), (X3, Y23), … (Xn, Y2n)]; multiple first standard flow values Y3 corresponding to multiple set flow values X can be represented as an array [(X1, Y31), (X2, Y32), (X3, Y33), … (Xn, Y3n)]; multiple flow calculation values Y4 corresponding to multiple set flow values X can be represented as an array [(X1, Y41), (X2, Y42), (X3, Y43), … (Xn, Y4n)].

[0046] As an optional implementation manner of the present invention, obtaining multiple set flow values X of the mass flow controller includes: selecting multiple set flow values X based on different proportions of the full-scale flow of the mass flow controller.

[0047] To ensure the reliability of the flow control curve, preferably, the number of set flow values X is greater than or equal to 5. For example, as an optional implementation manner of the present invention, the number of set flow values X can be 6, which are 7%, 15%, 25%, 50%, 75%, and 100% of the full-scale flow of the mass flow controller respectively.

[0048] The embodiment of the present invention does not specifically limit the size of the preset deviation value. The preset deviation value can be determined by those skilled in the art according to the specifications of the current mass flow controller. For example, as an optional implementation manner of the present invention, the preset threshold does not exceed 1% of the full-scale flow F.S. (Full Scale) of the mass flow controller.

[0049] The embodiment of the present invention does not specifically limit the calculation method for fitting the flow control curve. For example, as an optional implementation manner of the present invention, compensating multiple deviation values to multiple first theoretical flow values Y2 to obtain a new flow control curve includes;

[0050] Based on multiple compensated first theoretical values and their corresponding multiple set flow values X, a new flow control curve is obtained through least squares fitting calculation.

[0051] In the embodiments of the present invention, no specific limitation is imposed on the maximum exponent of the set flow value X in the formula adopted by the least squares method. For example, optionally, the formula adopted by the least squares method can be a quartic function, and its formula can be expressed as f(X) = a×X n +b×X n-1 +c×X n-2 +d×X n-3 +…+n, and n is greater than or equal to 4, where X is the set flow value X, f(X) is the theoretical flow value, and a, b, c, d, … n are constants.

[0052] As Figure 1 shown, the mass flow controller may include a built-in memory EEPROM for storing the formula of the flow control curve. After each calibration and obtaining a new flow control curve, the formula corresponding to the new flow control curve is stored in the built-in memory and replaces the currently stored flow control curve in the built-in memory. Specifically, after each calibration, the constants a0, b0, c0, d0, e0 in the flow control curve formula f(X)0 = a0×X 4 +b0×X 3 +c0×X 2 +d0×X + e0 stored in the built-in memory EEPROM are replaced by the constants a1, b1, c1, d1, e1 in the calibrated new flow control curve f(X)1 = a1×X 4 +b1×X 3 +c1×X 2 +d1×X + e1, thereby updating the flow control curve stored in the mass flow controller.

[0053] For the convenience of those skilled in the art to understand, the following provides a specific embodiment of calibrating a mass flow controller by the calibration method provided by the present invention. In this embodiment, the formula adopted by the least squares method for fitting the flow control curve is a quartic function, and the number n of selected set flow values X is 6. The mass flow controller has been calibrated once. Before calibration by the calibration method provided by the embodiments of the present invention, the stored flow control curve is Y2 = f(X)0 = 0.641953X 4 -1.5647X 3 +1.12649X 2 +0.800394X + 0.0010721.

[0054] As shown in Table 1-1 below, the data determined in steps S1 to S3 in this embodiment are presented (the values in the table are all full-scale percentage values). It can be seen from Table 1-1 that before calibrating the mass flow controller using the calibration method provided by the embodiment of the present invention, the mass flow controller controls the flow using the control curve Y2 = f(X)0 previously stored in the mass flow controller. There are multiple cases where the deviation values (i.e., precision errors) between the actual control effects (i.e., multiple first standard flow values Y3) corresponding to multiple set flow values X and each set flow value X are greater than the preset threshold (1% F.S.).

[0055] Table 1-1

[0056]

[0057] Based on the multiple first standard flow values Y3 and multiple first theoretical flow values Y2 in Table 1, steps S1 to S4 in the calibration method provided by the embodiment of the present invention are executed. The deviation values (i.e., precision errors) between the multiple first standard flow values Y3 and the corresponding set flow values X are compensated to the multiple first theoretical flow values Y2, and thus the numerical values of each item in the array [(X1, Y41), (X2, Y42), (X3, Y43),... (Xn, Y4n)] corresponding to multiple set flow values X and multiple flow calculation values Y4 can be obtained. And a new flow control curve function Y5 = f(X)1 = 0.132957X 4 -0.246339X 3 +0.0583752X 2 +1.05955X + 0.000596375 is obtained by fitting according to this array.

[0058] Table 1-2

[0059]

[0060] Then steps S51 to S52 are executed to determine whether the new flow control curve meets the requirements. It can be seen from Table 1-2 that the differences between each second standard flow value Y6 and the corresponding set flow value X are all less than the preset threshold 1% F.S. Therefore, it is not necessary to execute another round of steps S1 to S4, and the new flow control curve Y5 = f(X)1 can be directly stored in the mass flow sensor.

[0061] As the second aspect of the present invention, a calibration system for a mass flow controller is provided, including a standard flow detection device, a mass flow controller, and an upper computer module. The upper computer module is used to set the set flow value X of the standard flow detection device and the set flow value X of the mass flow controller. The upper computer module is used to implement the calibration method provided by the embodiment of the present invention, and the built-in memory EEPROM of the mass flow controller is used to store the currently stored flow control curve.

[0062] In the calibration system of the mass flow controller provided by the present invention, the host computer module can compensate the deviation between multiple first standard flow values Y3 and the corresponding set flow values X to multiple first theoretical flow values Y2, and obtain a new flow control curve based on the compensated theoretical flow values, so as to adjust the previously determined flow control curve based on the standard flow detection device, making the new flow control curve closer to the actual flow characteristic curve of the mass flow controller, thereby improving the accuracy of the mass flow controller in controlling the flow rate.

[0063] As an alternative embodiment of the present invention, the mass flow controller further includes a solenoid valve, and the mass flow controller is used to control the driving voltage of the solenoid valve according to the set flow value X to change the flow rate of the mass flow controller.

[0064] The embodiment of the present invention does not specifically limit the structure of the host computer module. For example, optionally, as Figure 1 shown, the host computer module may include a central control unit (CPU) for performing various functions such as signal acquisition, calculation, setting flow signals, controlling the driving voltage of the solenoid valve, receiving signals from the thermal flow sensor, collecting temperature sensor signals, and PID calculation.

[0065] In the present invention, the central control unit collects the set flow signal (i.e., receives the target flow value) and the flow detection signal of the thermal flow sensor, and after calculation by the PID algorithm, controls the opening degree of the solenoid valve through the solenoid valve drive circuit, so that the fluid flow rate in the mass flow controller approaches the target flow value, achieving the purpose of adjusting the fluid flow rate.

[0066] Optionally, as Figure 1 shown, the mass flow controller further includes a temperature sensor for detecting the fluid temperature in the gas passage, and the central control unit collects the temperature signal through the A / D conversion circuit to achieve temperature compensation. It can be understood that the above embodiments are only exemplary embodiments adopted to illustrate the principle of the present invention, and the present invention is not limited thereto. For those of ordinary skill in the art, various modifications and improvements can be made without departing from the spirit and essence of the present invention, and these modifications and improvements are also regarded as the protection scope of the present invention.

Claims

1. A calibration method for a mass flow controller, which calibrates the mass flow controller by using a standard flow detection device, is characterized in that The method includes: Obtaining a plurality of set flow values of the mass flow controller, and detecting a plurality of first standard flow values corresponding to the plurality of set flow values of the mass flow controller by means of the standard flow detection device; Calculating a plurality of first theoretical flow values corresponding to the plurality of set flow values according to the flow control curve currently stored in the mass flow controller, where the currently stored flow control curve is not the initial flow control curve, and the initial flow control curve is f(X)=X, where X is the set flow value; Calculating the deviation values between the plurality of first standard flow values and the corresponding set flow values; Compensating the plurality of deviation values to the plurality of first theoretical flow values to obtain a new flow control curve; Using the new flow control curve as the flow control curve currently stored in the mass flow controller for calibration.

2. The calibration method according to claim 1, wherein The using the new flow control curve as the flow control curve currently stored in the mass flow controller for calibration includes: Obtaining a plurality of second standard flow values corresponding to the plurality of set flow values detected by the standard flow detection device; Comparing whether the deviation values between the plurality of second standard flow values and the corresponding set flow values are all less than a preset threshold. If there is at least one deviation value not less than the preset threshold, then again obtaining a new flow control curve by compensating the deviation values between the plurality of first standard flow values and the corresponding set flow values to the plurality of first theoretical flow values until the plurality of deviation values are all less than the preset threshold.

3. The calibration method according to claim 2, wherein The obtaining a plurality of set flow values of the mass flow controller includes: Selecting a plurality of set flow values based on different proportions of the full-scale flow of the mass flow controller.

4. The calibration method according to claim 3, wherein The number of the set flow values is greater than or equal to 5.

5. The calibration method according to claim 4, characterized in that, The number of the set flow values is 6, which are 7%, 15%, 25%, 50%, 75% and 100% of the full-scale flow of the mass flow controller respectively.

6. The calibration method according to claim 2, characterized in that The preset threshold does not exceed 1% of the full-scale flow of the mass flow controller.

7. The calibration method according to claim 1, wherein The compensating the plurality of deviation values to the plurality of first theoretical flow values to obtain a new flow control curve includes; Performing fitting calculation by the least square method according to the plurality of compensated first theoretical flow values and the corresponding plurality of set flow values to obtain the new flow control curve.

8. The calibration method according to claim 7, wherein The formula adopted by the least squares method is f(X) = a×X n + b×X n-1 + c×X n-2 + d×X n-3 + … + n, and n is greater than or equal to 4, where X is the set flow value, f(X) is the theoretical flow value, and a, b, c, d, … n are constants.

9. A calibration system for a mass flow controller, characterized in that, It includes a standard flow detection device, a mass flow controller and a host computer module. The host computer module is used to set the set flow value of the standard flow detection device and the set flow value of the mass flow controller. The host computer module is used to implement the calibration method according to any one of claims 1 to 8, where the built-in memory of the mass flow controller is used to store the currently stored flow control curve.

10. The calibration system according to claim 9, wherein The mass flow controller further includes a solenoid valve. The mass flow controller is used to control the driving voltage of the solenoid valve according to the set flow value to change the flow rate of the mass flow controller.

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