Electromagnet control device and electromagnet system

Abstract

The invention provides an electromagnet control device and an electromagnet system. The objective of the present invention is to accurately match a target value of a magnetic flux density with an actually obtained magnetic flux density. The electromagnet control device is provided with a driver and a current value determination unit for determining the value of the current flowing to the coil on the basis of the magnetic flux density command value, the current value determination unit executing: a second process for determining the current value on the basis of a second function when the magnetic flux density is reduced from the first magnetization state; and a fourth process for converting the second function into a fourth function by expanding or reducing the second function at the first expansion / reduction rate when the magnetic flux density is reduced from the third magnetization state, and determining the current value on the basis of the converted fourth function. The current value determination unit is further configured to determine the first scaling ratio so that the second function conforms to actual measurement data obtained by reducing the magnetic flux density from the third magnetization state in advance. The driver applies a step-waveform or ramp-waveform current to the coil in accordance with the determined current value.

Description

[0001] This application is a divisional application of the following patent application:

[0002] Application number: 202010861348.5

[0003] Application date: August 25, 2020

[0004] Invention title: Electromagnet control device and electromagnet system Technical Field

[0005] The present invention relates to a technology for controlling a current flowing to a coil of an electromagnet having a yoke and a coil. Background Art

[0006] In the past, in plasma processing devices (e.g., plasma etching devices, etc.), etching methods using magnetron discharge have been put into practical use. This method is as follows: in a chamber into which etching gas is introduced, electric fields and magnetic fields in mutually orthogonal directions are applied, and the drift motion of electrons generated at this time is used to efficiently etch the surface of the wafer.

[0007] In this etching device, in order to control the distribution of plasma density in the chamber, the magnetic field generated by the magnet disposed outside the chamber is controlled. As methods for controlling the magnetic field, for example, there are known methods of mechanically moving the permanent magnet and controlling the current applied to the electromagnet. In the method of mechanically moving the permanent magnet, since the magnetic field intensity generated by the permanent magnet is fixed, it is difficult to fine-tune the plasma density distribution. Therefore, in the past, a method of controlling the current applied to the electromagnet was used.

[0008] On the other hand, it is known that there is a magnetic hysteresis (hereinafter, also simply referred to as magnetic hysteresis) between the control current applied to the electromagnet and the magnetic flux density generated. That is, since the magnetic flux density obtained with respect to the current applied to the electromagnet is affected by the residual magnetic field, the same magnetic flux density value is not necessarily reproduced every time with respect to the same applied current.

[0009] One method of reducing the influence of such residual magnetism is to correct the current value in consideration of the hysteresis characteristics (for example, see Patent Document 1 listed below).

[0010] Patent Document 1: Japanese Patent Application Publication No. 2017-084563

[0011] It is desirable to make the target value of the magnetic flux density and the actually obtained magnetic flux density match with good accuracy. Summary of the invention

[0012] The present invention has been made to solve at least a part of the above-mentioned problems, and can be implemented as the following aspects.

[0013] According to a first aspect of the present invention, an electromagnet control device is provided for controlling a current flowing to the coil of an electromagnet having a yoke and a coil, the electromagnet control device comprising: a command value acquisition unit, the command value acquisition unit being configured to acquire a magnetic flux density command value equivalent to a target value of a magnetic flux density obtained by causing a current to flow to the coil, or information capable of determining the magnetic flux density command value; a current value determination unit, the current value determination unit determining a value of a current flowing to the coil based on the magnetic flux density command value; a storage unit, the storage unit storing a first function, a second function, and a third function based on actual measurement data of the hysteresis of the electromagnet; and a driver, the driver applying a current of a step waveform or a ramp waveform to the coil according to the determined value of the current, the current value determination unit being configured to perform the following processing: a first processing, in which the value of the current flowing to the coil is determined based on the first function when the magnetic flux density is increased from the demagnetized state of the yoke; and a second processing, in which the value of the current flowing to the coil is determined based on the second function when the magnetic flux density is reduced from the first magnetized state of the yoke. ; a third process, in which, when the magnetic flux density is increased from the second magnetization state of the yoke, the value of the current flowing to the coil is determined based on the third function; a fourth process, in which, when the magnetic flux density is reduced from the third magnetization state of the yoke, the second function is converted into a fourth function by expanding or reducing the second function at a first expansion / contraction ratio, and the value of the current flowing to the coil is determined based on the converted fourth function; and a fifth process, in which, when the magnetic flux density is increased from the fourth magnetization state of the yoke, the third function is converted into a fifth function by expanding or reducing the third function at a second expansion / contraction ratio, and the value of the current flowing to the coil is determined based on the converted fifth function, the current value determination unit being configured such that, in the fourth process, the first expansion / contraction ratio is determined so that the second function conforms to the actual measurement data obtained by reducing the magnetic flux density from the third magnetization state in advance, and in the fifth process, the second expansion / contraction ratio is determined so that the third function conforms to the actual measurement data obtained by increasing the magnetic flux density from the fourth magnetization state in advance.

[0014] According to the electromagnet control device, by using three functions separately according to the history of current application, the current flowing to the coil is controlled, so that no matter how the history of current application is, the influence of residual magnetism caused by hysteresis can be reduced, so that the magnetic flux density command value and the magnetic flux density value actually obtained by making the current flow to the coil are more accurately consistent than before. As a result, in a plasma processing device equipped with the electromagnet control device, it is possible to achieve the improvement of the reproducibility of the process use conditions in the same plasma processing device or reduce the individual differences between plasma processing devices of the same specifications. And, no matter how the size of the hysteresis of the yoke is, the magnetic flux density command value and the magnetic flux density value actually obtained are accurately consistent. Therefore, it is also possible to make the yoke not use materials with less hysteresis. As a result, cheap materials that can be easily obtained can be used for the yoke. That is, the cost of the electromagnet control device and the time required from the ordering of the electromagnet control device to the delivery can be reduced.

[0015] In addition, according to the electromagnet control device, the second function and the third function are enlarged or reduced by using the expansion and contraction rate based on the actual measurement data to obtain the fourth function and the fifth function, so that the actual magnetic flux density based on the control current value determined according to the fourth function and the fifth function can be accurately consistent with the magnetic flux density command value.

[0016] According to a second aspect of the present invention, in the first aspect, the step width of the step waveform current is set so that the step width converted into magnetic flux density is equal to or close to the interval of magnetic flux density when actual measurement data of hysteresis of the electromagnet is obtained.

[0017] According to this aspect, the magnetic flux density command value and the actual magnetic flux density generated by the electromagnet can be made to match with higher accuracy.

[0018] According to the third mode of the present invention, in the first mode, the first function, the second function and the third function are functions representing the relationship between the magnetic flux density and the current. According to this mode, there is no need to convert to other parameters, and the current flowing to the coil can be directly determined according to the desired magnetic flux density. Therefore, the calculation load of the electromagnet control device can be reduced.

[0019] According to a fourth aspect of the present invention, there is provided an electromagnet system comprising: the electromagnet control device according to the first aspect; and the electromagnet. According to this electromagnet system, the same effects as those of the first aspect are achieved.

[0020] The present invention is not limited to the above-described embodiment, and can be implemented in various forms such as an electromagnet control method, an electromagnet control program, and a storage medium recording the program in a computer-readable form. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a block diagram showing a schematic configuration of a plasma etching system as one embodiment of the present invention.

[0022] Figure 2 It is a partial cross-sectional view showing a schematic structure of an electromagnet.

[0023] Figure 3 This is an explanatory diagram showing the concept of determining the current value based on a function.

[0024] Figure 4 : is a flowchart showing the flow of the current value determination process.

[0025] Figure 5 This is a schematic diagram showing the concept of determining the current value when the magnetic flux density is increased from the demagnetized state.

[0026] Figure 6 It means from Figure 5 Schematic diagram of the concept of determining the current value when the magnetic flux density is further increased in the state.

[0027] Figure 7 This is a schematic diagram showing the concept of determining the current value when reducing the magnetic flux density from the magnetized state.

[0028] Figure 8 This is a schematic diagram showing the concept of determining the current value when the magnetic flux density is increased from the magnetized state.

[0029] Fig. 9 This is a schematic diagram conceptually showing a method of determining the expansion / contraction ratio when the second function line F2 is expanded or reduced.

[0030] Fig.10 This is a schematic diagram conceptually showing a method of determining an expansion / contraction ratio when the third function line F3 is expanded or reduced.

[0031] Fig.11 This is a schematic diagram conceptually showing a method of determining the expansion / contraction ratio when switching the increase / decrease of the magnetic flux density command value in a magnetization state in which actual measurement data does not exist.

[0032] Fig.12 This is a diagram illustrating an example of a step waveform current output by a driver.

[0033] Fig.13A This is an example of data obtained by actually measuring the hysteresis of an electromagnet.

[0034] Fig. 13B This is an example of data obtained by actually measuring the hysteresis of an electromagnet.

[0035] Fig. 13C This is an example of data obtained by actually measuring the hysteresis of an electromagnet.

[0036] Fig.14 This is an example of the evaluation result of the deviation of the offset amount ΔB of the magnetic flux density generated by the electromagnet when the output current of the driver is set to a step waveform.

[0037] Fig.15 A diagram illustrating the current of a ramp waveform output by a driver.

[0038] Fig.16 This is an example of the evaluation result of the deviation of the offset amount ΔB of the magnetic flux density generated by the electromagnet when the output current of the driver is set to a ramp waveform.

[0039] Explanation of symbols

[0040] 20 Plasma treatment system

[0041] 21 Plasma Etching Device

[0042] 22 Command Department

[0043] 30 Electromagnet system

[0044] 40 electromagnet

[0045] 41 coils

[0046] 42 yoke iron

[0047] 50 Solenoid control device

[0048] 60 command value acquisition unit

[0049] 70 current value determination unit

[0050] 80 Drive

[0051] 85 Degaussing Department

[0052] 90 Storage

[0053] 91 First Function

[0054] 92 Second Function

[0055] 93The third function. DETAILED DESCRIPTION

[0056] A. First embodiment:

[0057] Figure 11 is a block diagram showing a schematic structure of a plasma processing system 20 as one embodiment of the present invention. In this embodiment, the plasma processing system 20 is a system for performing plasma etching, for example, for etching a substrate (for example, a wafer) in a semiconductor manufacturing process. Figure 1 As shown, the plasma processing system 20 includes a plasma etching device 21, a command unit 22 and an electromagnet system 30. The plasma etching device 21 includes a chamber (not shown). Plasma is generated in the chamber, and the object to be processed is etched by the ions and free radicals generated thereby. The command unit 22 is a personal computer in this embodiment, and is connected to be able to communicate with the electromagnet system 30 (more specifically, the electromagnet control device 50 described later). The command unit 22 can be any device that gives instructions to the electromagnet system 30, for example, it can also be a sequencer, etc.

[0058] The electromagnet system 30 includes an electromagnet 40 and an electromagnet control device 50. In order to control the plasma density distribution in the plasma etching device 21 by the magnetic field generated by the electromagnet 40, the electromagnet 40 is arranged outside the above-mentioned chamber adjacent to the chamber. The electromagnet control device 50 receives a command from the command unit 22 and controls the current flowing to the electromagnet 40 to obtain a desired magnetic flux density. The electromagnet control device 50 is configured to control the plasma density distribution according to the processing conditions in the plasma etching device 21, and controls the current (in other words, the magnetic flux density) to increase (or decrease) before reaching a predetermined maximum (or minimum) current value (in other words, the magnetic flux density value).

[0059] Figure 2 4 is a cross-sectional view showing a schematic structure of the electromagnet 40. The electromagnet 40 includes a coil 41 and a yoke 42. In order to simplify the description, the electromagnet 40 includes one coil 41 in this embodiment. However, the electromagnet 40 may include any number of coils 41. The coil 41 is arranged in a circular shape when viewed from above, but Figure 2 In the electromagnet 40 , only one side is shown with respect to the center of the circle. In the electromagnet 40 , the current flowing to the coil 41 is controlled so that a desired magnetic flux density is obtained at a measurement point M1 (a point in the chamber) separated from the coil 41 by a predetermined distance.

[0060] However, the yoke 42 formed of a magnetic material has magnetic hysteresis. Therefore, if the current flowing to the coil 41 is simply calculated based on the desired magnetic flux density (in this embodiment, the magnetic flux density command value input from the command unit 22), a difference occurs between the desired magnetic flux density and the magnetic flux density measured at the measuring point M1, corresponding to the history of the current applied to the coil 41. The electromagnet control device 50 has a function to reduce the influence of such hysteresis (that is, the inconsistency between the desired magnetic flux density and the magnetic flux density measured at the measuring point M1).

[0061] like Figure 1 As shown, the electromagnet control device 50 includes a command value acquisition unit 60, a current value determination unit 70, a driver 80, a demagnetization unit 85, and a storage unit 90. The command value acquisition unit 60 receives the magnetic flux density command value from the command unit 22. In addition, the command value acquisition unit 60 converts the received magnetic flux density command value into a current value of the current flowing to the coil 41 assuming that there is no hysteresis (that is, assuming that the current flowing to the coil 41 is proportional to the magnetic flux density measured at the measurement point M1). The current value converted in this way is also called a current command value I. The command value acquisition unit 60 outputs the calculated current command value I to the current value determination unit 70.

[0062] The current value determination unit 70 corrects the current command value I in consideration of the hysteresis of the electromagnet 40, and determines the current value (also referred to as the control current value I') actually flowing to the coil 41. This processing is performed based on the first function 91, the second function 92, and the third function 93. These functions are pre-stored in the storage unit 90. Among them, these functions can also be obtained from the outside (for example, the instruction unit 22) through communication. In addition, sometimes, as described later, the second function 92 and the third function 93 are transformed corresponding to the situation, but the current value determination unit 70 can also obtain the transformed function from the outside through communication. The details of these functions will be described later.

[0063] Furthermore, the current value determination unit 70 outputs the determined control current value I' to the driver 80. The driver 80 controls the current supply to the coil 41. That is, the driver 80 causes the current of the input control current value I' to flow to the coil 41 of the electromagnet 40. The demagnetization unit 85 demagnetizes the yoke 42. Specifically, in the present embodiment, if the demagnetization unit 85 receives a demagnetization instruction from the instruction unit 22, it obtains the demagnetization parameters (for example, the amplitude and frequency of the AC demagnetization, etc.) from the storage unit 90. Furthermore, the demagnetization unit 85 outputs an instruction corresponding to the obtained parameters to the driver 80. The driver 80 converts the current into a desired waveform based on the input instruction and outputs it.

[0064] Figure 3This is an explanatory diagram of the concept of determining the control current value I' based on the first function 91, the second function 92, and the third function 93. The ideal straight line F0 represents the ideal relationship between the current flowing into the coil 41 and the magnetic flux density obtained thereby (that is, the relationship when there is no hysteresis). In the ideal straight line F0, the current and the magnetic flux density are in a proportional relationship passing through the origin. In contrast, the first function line F1, the second function line F2, and the third function line F3 conceptually represent the relationship between the current and the magnetic flux density after correction considering the influence of hysteresis. It is hoped that you will notice that in Figure 3 The first function line F1, the second function line F2, and the third function line F3 shown in the figure do not map the first function 91, the second function 92, and the third function 93 as they are, but conceptually represent how the current command value I is corrected relative to the ideal straight line F0 through these functions. The first function line F1 is located above the ideal straight line F0. The second function line F2 is located below the ideal straight line F0, and the third function line F3 is located above the second function line F2. Figure 3 In the example shown, the entire third function line F3 is located below the ideal straight line F0 . However, depending on the material of the yoke 42 , a portion of the third function line F3 may be located above the ideal straight line F0 .

[0065] Function lines F1 to F3 are determined approximately based on the results of actually measuring the hysteresis characteristics of the electromagnet 40 in advance. The first function 91, the second function 92, and the third function 93 are determined approximately in such a way that the current value on the determined function lines F1 to F3 is obtained as the control current value I'. In this embodiment, the first function 91, the second function 92, and the third function 93 are each defined as an interval linear function. That is, the first function 91, the second function 92, and the third function 93 each have a shape in which a plurality of lines are connected at an inflection point when they are graphed. Among them, the first function 91, the second function 92, and the third function 93 can also be defined as a simple linear function without a defined interval, or can also be defined as an arbitrary function.

[0066] The first function 91 is used when the magnetic flux density is increased from the demagnetized state of the yoke 42. Figure 3 The first function line F1 is defined between the origin and the maximum value Bmax of the magnetic flux density. That is, the illustrated first function line F1 approximately represents the relationship between the current value flowing to the coil 41 and the magnetic flux density obtained at the measuring point M1 when the current is increased from zero to a current value (current value Imax) corresponding to the maximum value Bmax at a constant amplitude.

[0067] The second function 92 is used when reducing the magnetic flux density from the magnetized state of the yoke 42. Figure 3The second function line F2 is defined between the maximum value Bmax and the point on the x-axis (current value zero). That is, the second function line F2 shown in the figure approximately represents the relationship between the current value flowing to the coil 41 and the magnetic flux density obtained at the measuring point M1 when the current is reduced from the current value corresponding to the maximum value Bmax to the current value zero at a constant amplitude.

[0068] The third function 93 is used when the magnetic flux density is increased from the magnetized state of the yoke 42. Figure 3 The third function line F3 is defined between the point (current value zero) on the x-axis and the maximum value Bmax. That is, the third function line F3 shown in the figure approximately represents the relationship between the current value flowing to the coil 41 and the magnetic flux density obtained at the measurement point M1 when the current is reduced from the current value corresponding to the maximum value Bmax to the current value zero and then increased again at a constant amplitude to the current value corresponding to the maximum value Bmax.

[0069] Hope to notice Figure 3 In the figure, only the first quadrant is shown, but it can also be obtained in each quadrant from the second to the fourth quadrant. Figure 3 The graph of the line and origin object is shown, and in addition, a first function 91, a second function 92 and a third function 93 are defined in a corresponding manner.

[0070] Figure 4 1 is a flowchart showing an example of the flow of the current value determination process performed by the electromagnet control device 50. The current value determination process is a process for determining the current value of the current flowing to the coil 41 based on the command value input from the command unit 22. The current value determination process is repeatedly executed when the command value is input from the command unit 22 to the electromagnet control device 50. Figure 4 In order to simplify the description, the current value and the magnetic flux density value are shown to be controlled within a range above zero (ie, Figure 3 When the current value determination process is started, first, the command value acquisition unit 60 receives the magnetic flux density command value input from the command unit 22, and calculates the current command value I n (Step S110) The suffix "n" of the current command value I indicates that it corresponds to the magnetic flux density command value input for the nth time. n is based on Figure 3 Calculated based on the ideal straight line F0 shown.

[0071] When calculating the current command value I n When the command value acquisition unit 60 calculates the current command value I n The current command value I is stored in the storage unit 90 (step S120), and the current command value I is output to the current value determination unit 70. nIn this embodiment, the current command value I stored in the storage unit 90 is n It is cleared when the current value determination process to be executed next time is completed.

[0072] The current value determination unit 70 determines the input current command value I n Whether it indicates an instruction to increase the magnetic flux density from the demagnetized state (step S130). Here, the "instruction to increase the magnetic flux density from the demagnetized state" includes an instruction to increase the initial magnetic flux density from the initial state (i.e., no residual magnetism), and an instruction to increase the magnetic flux density in the middle stage when the magnetic flux density is increased in stages without decreasing the magnetic flux density once from the initial state. In the present embodiment, the judgment is based on whether the current command value I is stored in step S120 of the current value determination process executed last time. n-1 When the current value determination process is initially executed, the current command value I is not stored. n-1 In addition, in the present embodiment, when demagnetization is performed by the demagnetization unit 85 after the n-th current value determination process, the current command value I stored in the storage unit 90 is n Therefore, the current value determination unit 70 can determine the current value based on the current command value I n-1 The input current command value I is determined whether it is stored in the storage unit 90. n Does it indicate the initial increase in magnetic flux density from the initial state? The input current command value I n Whether or not the increase in magnetic flux density in the middle stage is indicated can be determined by a function flag described later. This determination will be described later.

[0073] When the judgment result is that the current command value I n In the case of an instruction indicating an increase in the magnetic flux density from the demagnetized state (step S130: yes), the current value determination unit 70 selects the first function 91 and sets the function flag to the value 1 (step S140). The function flag is written to a flag area secured in the storage unit 90. The method of using the function flag will be described later. Next, the current value determination unit 70 determines the current correction amount Ic using the first function 91 (step S150). In the present embodiment, the first function 91 is a function indicating the correspondence between the magnetic flux density command value B (or the current command value I) and the current correction amount Ic. This is also the same for the second function 92 and the third function 93. The method of determining the current correction amount Ic here will be described later. Next, the current value determination unit 70 compares the current correction amount Ic with the current command value I calculated in the above-mentioned step S110. n Add and calculate the control current value I n '(Step S210). Then, the current value determination unit 70 controls the current value I n'Stored in the storage unit 90 (step S220), and output to the driver 80 the control current value I n '(Step S230), the current value determination process ends.

[0074] On the other hand, when the current command value I n When there is no instruction to increase the magnetic flux density from the demagnetized state (step S130: No), that is, when the yoke 42 is in the magnetized state, the current value determination unit 70 determines the current command value I n Is it better than the current command value I n-1 The current command value I n-1 In the above-mentioned step S120 of the current value determination process executed last time, the current command value I n Specific current command value I n-1 When the current value is small (step S160: Yes), that is, when the instruction to reduce the magnetic flux density is input, the current value determination unit 70 selects the second function 92 and sets the function flag to the value 2 (step S170). Next, the current value determination unit 70 determines the current correction amount Ic based on the second function 92 (step S180). The method for determining the current correction amount Ic here will be described later. Then, the current value determination unit 70 advances the processing to the above-mentioned step S210.

[0075] The result of the judgment is that the current command value I n Specific current command value I n-1 When the current value determination unit 70 is large (step S160: No), that is, when a command to increase the magnetic flux density is input, the current value determination unit 70 selects the third function 93 and sets the function flag to the value 3 (step S190). Next, the current value determination unit 70 determines the current correction amount Ic based on the third function 93 (step S200). The method for determining the current correction amount Ic here will be described later. Then, the current value determination unit 70 advances the processing to the above-mentioned step S210.

[0076] Figures 5 to 8 A specific example of the method of determining the current correction amount Ic in the above-mentioned steps S150 , S180 , and S200 is conceptually shown. Figure 5 This represents the concept of determining the current value when the magnetic flux density is increased from the demagnetized state, and corresponds to the above-mentioned step S150. Figure 5 As shown in FIG. 1 , if a magnetic flux density command value B1 smaller than the maximum value Bmax is input, the electromagnet control device 50 calculates the current command value I1 using the ideal straight line F0 (step S110 ). Figure 5In the example, point P1 is a point on the ideal straight line F0 corresponding to the maximum value Bmax. Point P2 is a point on the ideal straight line F0 determined based on the magnetic flux density command value B1 and corresponds to the current command value I1. Furthermore, the electromagnet control device 50 uses the first function 91 to determine the current correction amount I C1 (Step S150), the current correction amount I C1 The control current value I'1 is calculated by adding the current command value I1. Point P3 is a point on the first function line F1, and corresponds to the magnetic flux density command value B1 and the control current value I'1. That is, when the magnetic flux density is increased from the demagnetized state to the magnetic flux density command value B1, the current value increases from zero to the control current value I'1 corresponding to the point P3 on the first function line F1. In the first function 91, the correspondence between the current command value I and the current correction amount Ic is defined in such a way as to obtain such a result.

[0077] Figure 6 Indicates that from Figure 5 The concept of determining the current value when the magnetic flux density is further increased in the state. If the magnetic flux density command value B2 (B2>B1) is input, the electromagnet control device 50 uses the ideal straight line F0 to calculate the current command value I2 (corresponding to point P4) (step S110). In addition, the electromagnet control device 50 uses the first function 91 to determine the current correction amount I C2 (Step S150), the current correction amount I C2 The current command value I2 is added to calculate the control current value I'2 (corresponding to point P5). That is, as long as the input magnetic flux density command value continues to increase from the demagnetized state, the first function 91 is continuously used to determine the control current value I' to be a value corresponding to the point on the first function line F1. It is possible to refer to the function flag to determine whether the input magnetic flux density command value continues to increase from the demagnetized state. Specifically, when a magnetic flux density command value larger than the last time is input in a state where the function flag is set to a value of 1, it can be determined that the input magnetic flux density command value continues to increase from the demagnetized state.

[0078] Figure 7 This concept indicates the determination of the current value when the magnetic flux density is reduced from the magnetized state. Figure 6 When the magnetic flux density command value B3 (B3 < B2) is input in the state shown, that is, when the magnetic flux density command value switches from increasing to decreasing, the electromagnet control device 50 uses the ideal straight line F0 to calculate the current command value I3 (corresponding to point P6) (step S110). Furthermore, the electromagnet control device 50 determines the current correction amount I based on the second function 92. C3 (Step S150), the current correction amount I C3The current command value I3 is added to calculate the control current value I'3 (corresponding to point P7). Point P7 is a point on the second function conversion line F2'. Since the second function conversion line F2' is below the ideal straight line F0, the current correction value I C3 is calculated as a negative value.

[0079] The second function transformation line F2' is a line that is a transformation of the second function line F2. Specifically, the second function transformation line F2' is a line that is transformed in a manner that is located between the second function line F2 and the ideal straight line F0. For example, the second function transformation line F2' can be obtained as follows. First, the second function line F2 is parallel moved in a manner that point P1 (the end point of the second function line F2 on the opposite side of the origin) is located at point P5 (the point on the first function line F1 corresponding to the magnetic flux density B2 when the magnetic flux density (in other words, the current) changes from increasing to decreasing). And, as Figure 7 As shown, the second function line F2 that has been parallel-translated is enlarged or reduced. The method for determining the enlargement or reduction ratio at this time will be described later. The second function line F2 that has been size-converted in this way is a second function conversion line F2'.

[0080] Current correction value I C3 The control current value I'3 is determined so as to be located on such a second function conversion line F2'. In other words, the second function 92 is used after being converted so as to obtain such a result.

[0081] exist Figure 7 After the state shown, as long as the input magnetic flux density command value continues to decrease, the same function (the second function 92 transformed as described above) is used to determine the control current value I' to a value corresponding to a point on the second function transformation line F2'. It is possible to refer to the function flag to determine whether the input magnetic flux density command value continues to decrease from the magnetized state. Specifically, when a magnetic flux density command value smaller than the last time is input in a state where the function flag is set to a value of 2, it can be determined that the input magnetic flux density command value continues to decrease from the magnetized state. In addition, when the magnetic flux density command value switches from increasing to decreasing after the magnetic flux density command value reaches point P1, the control current value I' is determined in such a way that the control current value I' will not be located on the second function transformation line F2' but on the second function line F2.

[0082] Figure 8 This concept indicates the determination of the current value when the magnetic flux density is increased from the magnetized state. Figure 7When the magnetic flux density command value B4 (B4>B3) is input in the state shown, that is, when the magnetic flux density command value is switched from decreasing to increasing again in the magnetized state, the electromagnet control device 50 uses the ideal straight line F0 to calculate the current command value I4 (corresponding to point P8) (step S110). It is possible to refer to the function flag to determine whether the magnetic flux density command value is switched from decreasing to increasing again in the magnetized state. Specifically, when a magnetic flux density command value larger than the previous time is input in the state where the function flag is set to value 2, it can be determined that the magnetic flux density command value is switched from decreasing to increasing again in the magnetized state.

[0083] Then, the electromagnet control device 50 determines the current correction amount I based on the third function 93. C4 (Step S150), the current correction amount I C4 The current command value I4 is added to calculate the control current value I'4 (corresponding to point P9). Point P9 is a point on the third function conversion line F3'. Since the third function conversion line F3' is below the ideal straight line F0, the current correction value I C4 is calculated as a negative value.

[0084] The third function transformation line F3' is a line transformed from the third function line F3. For example, the third function transformation line F3' can be obtained as follows. First, the third function line F3 is parallel shifted so that the endpoint on the origin side of the third function line F3 is located at point P7 (a point on the second function transformation line F2' when the magnetic flux density (in other words, the current) changes from decreasing to increasing). And, as Figure 8 As shown in FIG. 1 , the third function line F3 that has been parallel-translated is enlarged or reduced. The method for determining the enlargement or reduction ratio at this time will be described later. The third function line F3 that has been resized in this way is a third function conversion line F3'.

[0085] Current correction value I C4 The control current value I'4 is determined to be located on the third function conversion line F3'. In other words, the third function 93 is used after being converted so as to obtain such a result.

[0086] exist Figure 8After the state shown, as long as the input magnetic flux density command value continues to increase in the magnetized state, the same function (the third function 93 after the transformation mentioned above) is used to determine the control current value I' to a value corresponding to the point on the third function transformation line F3'. It is possible to refer to the function flag to determine whether the magnetic flux density command value continues to increase in the magnetized state. Specifically, when a magnetic flux density command value larger than the previous one is input in a state where the function flag is set to value 3, it can be determined that the magnetic flux density command value continues to increase in the magnetized state. In addition, when the magnetic flux density turns to decrease again (which can be determined based on the function flag), Figure 7 Similarly to the case shown in FIG. 1 , the control current value I' is determined so that the control current value I' is located on the line after the second function line F2 is transformed. In addition, when the magnetic flux density command value switches from decreasing to increasing after the magnetic flux density command value reaches the minimum value (point on the x-axis) of the second function line F2, the control current value I' is determined so that the control current value I' is not located on the third function transformation line F3' but on the third function line F3. Although the description is omitted, in each of the second to fourth quadrants, the control current value I' is determined in the same manner as in the first quadrant.

[0087] Fig. 9 A specific example of a method for determining the expansion / contraction ratio when the second function line F2 is parallel-translated and then expanded or reduced in order to obtain the second function conversion line F2' (hereinafter referred to as the fourth function line F4) is conceptually shown. Fig. 9 In the middle, the horizontal axis is Figures 5 to 8 The magnetic flux density command value is shown in the same way, but the vertical axis is Figures 5 to 8 The difference indicates the current correction amount Ic.

[0088] Fig. 9 The first function line F1, the second function line F2 and the third function line F3 are consistent with the above ( Figure 3 Similarly, the function lines F1 to F3 of the first function 91, the second function 92, and the third function 93 are respectively based on the first function 91, the second function 92, and the third function 93 pre-stored in the storage unit 90. For example, the first function 91, the second function 92, and the third function 93 are defined as N-order polynomials (for example, N=5) or any other functions. Fig. 9 In the figure, the first function line F1 is defined within the range of zero magnetic flux density and a maximum value Bmax, and the second function line F2 and the third function line F3 are defined within the range of maximum magnetic flux density Bmax and a minimum magnetic flux density Bmin (=-Bmax).

[0089] When the magnetic flux density command value switches from increasing to decreasing after reaching the maximum value Bmax (first magnetization state) as described above, the control current value I' is determined according to the second function line F2. However, when the magnetic flux density command value gradually increases and switches from increasing to decreasing at a predetermined magnetic flux density (third magnetization state) smaller than the maximum value Bmax before reaching the maximum value Bmax, the control current value I' is determined according to the fourth function line F4 which is a transformation of the second function line F2.

[0090] In order to transform the second function line F2 into the fourth function line F4, actual measurement data indicating the correspondence between the magnetic flux density command value (or the current command value I) and the current correction amount Ic when the magnetic flux density command value is switched from increasing to decreasing at a point (e.g., point Q2, Q3, Q4) on the third function line F3 corresponding to the third magnetization state is obtained in advance. Fig. 9 In FIG. 5 , some of such actual measurement data are plotted.

[0091] First, the second function line F2 is parallel-shifted in such a manner that point Q1 (the end point on the second function line F2 corresponding to the first magnetization state) is located at point Q2 (or Q3, Q4) corresponding to the actual measurement data acquired in advance as described above. Furthermore, the expansion / contraction ratio (first expansion / contraction ratio) for the second function line F2 is determined in such a manner that the second function line F2 after the parallel shift conforms to the actual measurement data related to point Q2 (or Q3, Q4). The second function line F2 after the parallel shift is expanded or reduced according to the expansion / contraction ratio, thereby obtaining the fourth function line F4. Regarding the third magnetization state ( Fig. 9 Points Q2, Q3, Q4 on the third function line F3 can be transformed from the second function line F2 to the fourth function line F4 in the same way.

[0092] In this way, the fourth function line F4 is obtained by expanding or contracting the second function line F2 using the expansion / contraction ratio based on the actual measurement data, so that the actual magnetic flux density based on the control current value I' determined according to the fourth function line F4 can be made to be consistent with the magnetic flux density command value with good accuracy. In addition, the expansion / contraction ratio can be independently determined in Fig. 9 The scaling factor for enlarging or reducing the second function line F2 in the horizontal direction, and Fig. 9 The scaling factor used to expand or reduce the second function line F2 in the longitudinal direction. Fig. 9 The second function line F2 is independently enlarged or reduced in the horizontal and vertical directions, so that the second function line F2 is flexibly consistent with the actual measurement data.

[0093] Fig.10 A specific example of a method for determining the expansion / contraction ratio when the third function line F3 is parallel-translated and then expanded or reduced in order to obtain the third function conversion line F3' (hereinafter referred to as the fifth function line F5) is conceptually shown. Fig.10 In, with Fig. 9 Likewise, the horizontal axis and the vertical axis represent the magnetic flux density command value and the current correction amount Ic, respectively.

[0094] Fig.10 The first function line F1, the second function line F2 and the third function line F3 in Fig. 9 The same is true for the case of , which is based on the first function 91, the second function 92 and the third function 93 pre-stored in the storage unit 90. Fig.10 In the figure, the first function line F1 is defined within the range of zero magnetic flux density and a maximum value Bmax, and the second function line F2 and the third function line F3 are defined within the range of maximum magnetic flux density Bmax and a minimum magnetic flux density Bmin (=-Bmax).

[0095] When the magnetic flux density command value is switched from decreasing to increasing after the magnetic flux density command value reaches the minimum value Bmin (second magnetization state) as described above, the control current value I' is determined according to the third function line F3. However, when the magnetic flux density command value is gradually reduced and before reaching the minimum value Bmin, the magnetic flux density command value is switched from decreasing to increasing at a predetermined magnetic flux density (fourth magnetization state) greater than the minimum value Bmin, the control current value I' is determined according to the fifth function line F5 obtained by transforming the third function line F3.

[0096] In order to transform the third function line F3 into the fifth function line F5, actual measurement data indicating the correspondence between the magnetic flux density command value (or the current command value I) and the current correction amount Ic when the magnetic flux density command value is switched from decreasing to increasing at a point (e.g., point Q6, Q7, Q8) on the second function line F2 corresponding to the fourth magnetization state is obtained in advance. Fig.10 In FIG. 5 , some of such actual measurement data are plotted.

[0097] First, the third function line F3 is parallel-shifted in such a manner that point Q5 (the end point on the third function line F3 corresponding to the second magnetization state) is located at point Q6 (or Q7, Q8) corresponding to the actual measurement data acquired in advance as described above. Furthermore, the expansion / contraction ratio (second expansion / contraction ratio) for the third function line F3 is determined in such a manner that the third function line F3 after the parallel shift conforms to the actual measurement data related to point Q6 (or Q7, Q8). The third function line F3 after the parallel shift is expanded or reduced according to the expansion / contraction ratio, thereby obtaining the fifth function line F5. Fig.10 Points Q6, Q7, Q8 on the second function line F2 can be transformed from the third function line F3 to the fifth function line F5 in the same way.

[0098] In this way, the third function line F3 is expanded or reduced using the expansion / contraction ratio based on the actual measurement data to obtain the fifth function line F5, so that the actual magnetic flux density based on the control current value I' determined according to the fifth function line F5 can be made to be consistent with the magnetic flux density command value with good accuracy. In addition, the expansion / contraction ratio can be independently determined in Fig.10 The scaling factor for enlarging or reducing the third function line F3 in the horizontal direction of Fig.10 The scaling factor used to expand or reduce the third function line F3 in the longitudinal direction. Fig.10 The third function line F3 is independently enlarged or reduced in the horizontal and vertical directions, so that the third function line F3 is flexibly consistent with the actual measurement data.

[0099] Fig.11 A specific example of a method for determining the expansion / contraction ratio when switching the increase / decrease of the magnetic flux density command value in a magnetization state where actual measurement data does not exist is conceptually shown. Fig.11 In FIG. 1 , the horizontal axis represents the magnetic flux density command value, and the vertical axis represents the expansion / contraction ratio for converting the size of the function line.

[0100] exist Fig.11 In, according to Fig. 9 and Fig.10 The first scaling ratio and the second scaling ratio determined by the method shown in FIG. Fig.11 The points R2x, R3x and R4x represent the Fig. 9 The points Q2, Q3, Q4 are used to determine Fig. 9 A first scaling factor for enlarging or reducing the second function line F2 in the horizontal direction of the second function line F2, Fig.11 The points R2y, R3y and R4y represent the points about Fig. 9 The points Q2, Q3, Q4 are used to determine Fig. 9 A first scaling factor for scaling the second function line F2 in the longitudinal direction of the second function line F2. Fig.11 Points R6x, R7x and R8x represent the points about Fig.10 The points Q6, Q7, Q8 are used to determine Fig.10 A second scaling factor for enlarging or reducing the third function line F3 in the horizontal direction of the third function line F3, Fig.11 Points R6y, R7y and R8y represent the points about Fig.10 The points Q6, Q7, Q8 are used to determine Fig.10 A second scaling factor for scaling the third function line F3 in the longitudinal direction of the third function line F3. Fig.11 Points R1 and R5 are respectively Fig. 9 Point Q1 and Fig.10 , which corresponds to point Q5, indicating that the expansion / contraction rate is 1 (that is, the second function line F2 and the third function line F3 are used as they are).

[0101] exist Fig. 9 In the example, point Q9 on the third function line F3 represents the fifth magnetization state where there is no actual measurement data such as at points Q2, Q3, and Q4. Therefore, when the magnetic flux density command value is switched from increasing to decreasing at such point Q9, it is impossible to Fig. 9 The expansion / contraction ratio of the second function line F2 is determined by the method shown in FIG. Fig.11 The approximate curve G1 closest to point R1, point R2x, point R3x, point R4x, and the approximate curve G2 closest to point R1, point R2y, point R3y, point R4y are used. Fig. 9 The corresponding expansion ratio of point Q9 is adopted as the Fig. 9 The expansion / contraction ratio (third expansion / contraction ratio) of the second function line F2 in the horizontal direction of the approximate curve G2 is the same as the point R9y (magnetic flux density command value and Fig. 9 The corresponding expansion ratio of point Q9 is adopted as the Fig. 9 The second function line F2 is transformed into a sixth function line by expanding or reducing the second function line F2 (after parallel movement) at the third expansion / contraction rate thus determined, and the control current value I' is determined based on the transformed sixth function line.

[0102] Likewise, in Fig.10In the example, point Q10 on the second function line F2 indicates the sixth magnetization state for which there is no actual measurement data such as points Q6, Q7, and Q8. Therefore, when the magnetic flux density command value is switched from decreasing to increasing at such point Q10, the above-mentioned Fig.10 The expansion / contraction ratio of the third function line F3 is determined by the method shown in FIG. Fig.11 The approximate curve G3 closest to point R5, point R6x, point R7x, point R8x, and the approximate curve G4 closest to point R5, point R6y, point R7y, point R8y are used. Fig.10 The corresponding expansion ratio of the point Q10 is adopted as the Fig.10 The expansion / contraction ratio (fourth expansion / contraction ratio) of the third function line F3 in the horizontal direction of the approximate curve G4 is the same as the point R10y (magnetic flux density command value and Fig.10 The corresponding expansion ratio of the point Q10 is adopted as the Fig.10 The third function line F3 is transformed into a seventh function line by expanding or reducing the third function line F3 (after parallel movement) at the fourth expansion / contraction rate determined in this way, and the control current value I' is determined according to the transformed seventh function line.

[0103] In this way, the multiple expansion and contraction rates determined for the magnetization state in which the actual measurement data is obtained in advance are interpolated using the approximate curve to obtain the expansion and contraction rate relative to the magnetization state for which the actual measurement data does not exist. Therefore, it is not necessary to perform the operation of switching the increase and decrease of the magnetic flux density command value in all magnetization states to obtain the actual measurement data. When the magnetic flux density command value is switched in any magnetization state, the function line can be appropriately expanded or reduced. As a result, in the entire range of magnetic flux density, the magnetic flux density command value can be made to be consistent with the actual magnetic flux density obtained with good accuracy.

[0104] As described above, the control current value I′ taking into account the hysteresis of the electromagnet 40 is determined by the current value determination unit 70 and output to the driver 80 ( Figure 4 The driver 80 applies a current of a predetermined waveform to the coil 41 of the electromagnet 40 according to the control current value I'. For example, the output current waveform from the driver 80 can be a step waveform or a ramp waveform.

[0105] Fig.12 is a diagram illustrating a step waveform current output by the driver 80. Fig.12In the example, the horizontal axis represents time and the vertical axis represents current. n ' (ie, the control current value determined for the nth magnetic flux density command value), the driver 80 changes the output current from the current value I n-1 ' (that is, the control current value determined according to the last current value determination process for the n-1th magnetic flux density command value) every time interval t step According to the step width I step The current value I of the output target is changed in stages. n 'The current. Fig.12 I n '>I n-1 ', that is, the step waveform of the current increase, but at I n '<I n-1 ', of course, it becomes a step waveform with current reduction. Fig.12 In the example, the current flows from I n-1 'Changes to I in 15 stages n ', but the number of stages is based on the initial value of the current I n-1 'With the final value I n ' and the step width I step In addition, the time interval t step It is preferable to set the length so that the next step section starts after the current changed in each step section becomes stable.

[0106] Next, the step width I step The appropriate value of is described below.

[0107] Fig.13A This is an example of data actually measured for the hysteresis of the electromagnet 40, which is shown as the correspondence between the magnetic flux density command value B and the current correction amount Ic. Fig.13A In addition to the plot of the actual measured data, the first function line F1, the second function line F2 and the third function line F3 are also shown after polynomial approximation. The magnetic flux density command value ranges from the minimum value Bmin = -30G (Gauss) to the maximum value Bmax = +30G. Fig.13A In the example, the interval of the magnetic flux density command value is set to 3G, and the data is measured.

[0108] In order to determine the current step width I step The following evaluation experiments were conducted to find the appropriate value of Fig.13AThe first function 91, the second function 92 and the third function 93 of the actual measurement data are stored in the storage unit 90. Furthermore, a plurality of random magnetic flux density command values ​​ranging from Bmin to Bmax are sequentially input from the command unit 22 to the electromagnet control device 50. For each input magnetic flux density command value, the above-mentioned Figure 4 The current value determination process of the flowchart is performed to determine the control current value I'. According to each determined control current value I', a step waveform current is output from the driver 80. Thus, the deviation ΔB between the actual magnetic flux density generated by the electromagnet 40 and the magnetic flux density command value is measured. The step width I of the step waveform current output from the driver 80 is step The step width converted into magnetic flux density is set to 1G, 3G, 6G, and 9G, and the deviation of the offset ΔB is compared in the case of each step width.

[0109] exist Fig.14 The comparison effect is shown in FIG. 8 . As can be seen from this, the step width I of the step waveform current output from the driver 80 is step When the step width is equivalent to 3G converted into magnetic flux density, the index of the deviation of the offset ΔB of the magnetic flux density generated by the electromagnet 40, that is, 3σ (where σ is the standard deviation), is the smallest. Therefore, the driver 80 applies such a step width I to the coil 41 of the electromagnet 40. step The step waveform current can make the magnetic flux density command value and the actual magnetic flux density generated by the electromagnet 40 match more accurately.

[0110] Fig. 13B , 13C is with Fig.13A An example of actual measurement data of the hysteresis of the same electromagnet 40 is that the intervals of the magnetic flux density command values ​​during data measurement are set to 6G and 10G respectively. Fig. 13B and 13C The actual measurement data are also compared with the above Fig.13A The same evaluation experiment is conducted for the same situation, and the deviation of ΔB is compared. Fig.14 The comparison effect is shown in FIG. 1 . As can be seen, when the interval of the magnetic flux density command value is 6G when the actual measurement data of the hysteresis is acquired, the step width I of the output current from the driver 80 is step When the step width is set to 6G, the deviation 3σ of the offset ΔB of the magnetic flux density generated by the electromagnet 40 is minimized. In addition, when the interval of the magnetic flux density command value when the actual measurement data of the hysteresis is obtained is 10G, the step width I of the output current of the driver 80, which is equivalent to 9G in terms of the magnetic flux density conversion, is set to 9G. step , the deviation 3σ of the offset ΔB of the magnetic flux density is the smallest.

[0111] Summarizing the results of the above evaluation experiments, the step width I of the step waveform current output from the driver 80 to the electromagnet 40 is step It is preferably set to step The step width converted into magnetic flux density is equal to or close to the interval of magnetic flux density command values ​​when obtaining actual measurement data of hysteresis of electromagnet 40. Thus, the magnetic flux density command value and the actual magnetic flux density generated by electromagnet 40 can be matched with good accuracy.

[0112] Fig.15 is a diagram illustrating a current having a ramp waveform output by the driver 80. Fig.15 In the example, the horizontal axis represents time and the vertical axis represents current. n ' (ie, the control current value determined for the nth magnetic flux density command value), the driver 80 changes the output current from the current value I n-1 ' (i.e., the control current value determined according to the last current value determination process for the n-1th magnetic flux density command value) changes continuously at a predetermined constant change rate, and finally outputs the target current value I n Here, the migration time t is calculated based on the current of 1A. trans To define the rate of change of current. Fig.15 In the figure, I n '>I n-1 ', that is, the ramp waveform of the current increase, but at I n '<I n-1 ', of course, it becomes a ramp waveform in which the current decreases.

[0113] To determine the transition time t per unit current in the ramp waveform trans The same evaluation experiment as the above-mentioned step waveform was conducted to find the appropriate value of t trans =30, 40, 50, 60, 70, 80, 90, 100 ms / A and obtain the actual measurement data of the hysteresis of the electromagnet 40, and the transition time t trans , the deviation between the magnetic flux density command value and the magnetic flux density deviation amount ΔB actually generated by the electromagnet 40 is compared in the same manner as in the case of the step waveform.

[0114] exist Fig.16 The comparison effect is shown in . It can be seen that the migration time per unit current t transThe longer the output current of the driver 80 is, that is, the more gradual the temporal change is, the smaller the deviation 3σ of the offset ΔB of the magnetic flux density is. Therefore, the driver 80 applies a transition time t per unit current to the coil 41 of the electromagnet 40 trans The current having a ramp waveform can make the magnetic flux density command value and the actual magnetic flux density generated by the electromagnet 40 match more accurately.

[0115] According to the plasma processing system 20 described above, the three functions 91, 92, and 93 are distinguished according to the application history of the current to the coil 41, and the current flowing to the coil 41 is controlled, thereby reducing the influence of the residual magnetism caused by hysteresis regardless of the history of the current application. That is, the magnetic flux density command value can be made to be more accurately consistent with the magnetic flux density value actually obtained by causing the current to flow to the coil 41 than before. As a result, it is possible to achieve the improvement of the reproducibility of the process use conditions in the same plasma processing system 20, or reduce the individual differences between plasma processing systems 20 of the same specifications. In addition, regardless of the size of the hysteresis of the yoke 42, the magnetic flux density command value can be made to be accurately consistent with the magnetic flux density value actually obtained. Therefore, it is also possible to make the yoke 42 not use a material with a small hysteresis. As a result, a cheap material that can be easily obtained can be used for the yoke 42. That is, the cost of the plasma processing system 20 and the time required from the ordering of the plasma processing system 20 to the delivery can be reduced.

[0116] B: Modification:

[0117] In the above-mentioned plasma processing system 20, the command value input from the outside (in this embodiment, the command unit 22) is not limited to the magnetic flux density command value. For example, the magnetic flux density command value may be converted into a current command value I in the command unit 22, and the current command value I may be input to the command value acquisition unit 60. The information acquired by the command value acquisition unit 60 may also be any information that can determine the magnetic flux density command value.

[0118] In addition, functions 91, 92, and 93 are not limited to functions that represent the correspondence between the magnetic flux density command value B (or the current command value I) and the current correction amount Ic. Functions 91, 92, and 93 may also be functions that represent the correspondence between any parameters that will ultimately derive the control current value I' corresponding to the magnetic flux density command value. For example, functions 91, 92, and 93 may also represent the correspondence between magnetic flux density and voltage. Alternatively, functions 91, 92, and 93 may also be functions that represent the relationship between magnetic flux density and current. Alternatively, functions 91, 92, and 93 may also be functions that represent the relationship between magnetic flux density command value and control current value I'. In this way, as long as a function that corresponds magnetic flux density to voltage is used, there is no need to convert to other parameters, and the control current value I' can be directly determined according to the desired magnetic flux density. Therefore, the computational load of the electromagnet control device 50 can be reduced.

[0119] Above, several embodiments of the present invention have been described, but the embodiments of the invention described above are intended to facilitate the understanding of the present invention and do not limit the present invention. The present invention can certainly be changed and improved without departing from its main purpose, and the present invention includes its equivalents. In addition, within the scope of at least a part of the above-mentioned problem that can be solved or within the scope of at least a part of the effect that can be achieved, any combination of the various structural elements described in the scope of the claims and the specification can be achieved, or can be omitted.

Claims

1. An electromagnet control device for controlling a current flowing to a coil of an electromagnet having a yoke and a coil, the electromagnet control device comprising: a command value acquisition unit configured to acquire a magnetic flux density command value corresponding to a target value of magnetic flux density obtained by flowing an electric current through the coil, or information capable of specifying the magnetic flux density command value; and a current value determination unit that determines a value of a current flowing through the coil based on the magnetic flux density command value, The current value determination unit is configured to perform the following processing: a first process of determining a value of a current flowing through the coil based on a first function when the magnetic flux density is increased from a demagnetized state of the yoke; a second process of determining a value of a current flowing through the coil based on a second function when the magnetic flux density is reduced from the first magnetization state of the yoke; a third process of determining a value of a current flowing through the coil based on a third function when the magnetic flux density is increased from the second magnetization state of the yoke; a fourth process of converting the second function into a fourth function by expanding or contracting the second function at a first expansion / contraction ratio when the magnetic flux density is reduced from the third magnetization state of the yoke, and determining a value of the current flowing to the coil based on the converted fourth function; as well as a fifth process, in which, when the magnetic flux density is increased from the fourth magnetization state of the yoke, the third function is converted into a fifth function by expanding or contracting the third function at a second expansion / contraction rate, and a value of the current flowing to the coil is determined based on the converted fifth function, The current value determination unit is configured as follows: In the fourth process, the first expansion / contraction ratio is determined so that the second function conforms to actual measurement data obtained by reducing the magnetic flux density in advance from the third magnetization state. In the fifth process, the second expansion / contraction ratio is determined so that the third function conforms to actual measurement data obtained by increasing the magnetic flux density in advance from the fourth magnetization state.

2. The electromagnet control device according to claim 1, characterized in that: The first function, the second function, and the third function are functions representing the relationship between magnetic flux density and current.

3. The electromagnet control device according to claim 1, characterized in that: The current value determination unit is configured to execute the sixth process and the seventh process, In the sixth processing, when the magnetic flux density is reduced from the fifth magnetization state of the yoke, a plurality of expansion / contraction ratios corresponding to the plurality of magnetization states are determined in such a manner that the second function conforms to each actual measurement data obtained by reducing the magnetic flux density from the plurality of magnetization states of the yoke in advance, a third expansion / contraction ratio is determined by using an approximation of the plurality of expansion / contraction ratios, the second function is converted into a sixth function by expanding or reducing the second function by the third expansion / contraction ratio, and a value of the current flowing to the coil is determined based on the converted sixth function. In the seventh processing, when the magnetic flux density is increased from the sixth magnetization state of the yoke, a plurality of expansion and contraction ratios corresponding to the plurality of magnetization states are determined in such a manner that the third function conforms to the actual measurement data respectively obtained by increasing the magnetic flux density from the plurality of magnetization states of the yoke in advance, a fourth expansion and contraction ratio is determined by using an approximation of the plurality of expansion and contraction ratios, the third function is transformed into a seventh function by expanding or reducing the third function by the fourth expansion and contraction ratio, and the value of the current flowing to the coil is determined based on the transformed seventh function.

4. An electromagnet system, characterized in that: The solenoid system has: The electromagnet control device according to any one of claims 1 to 3; and The electromagnet.

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