Power supply system for electrostatic chuck and power supply method

Abstract

To provide a power supply system for an electrostatic chuck capable of stably detaching a substrate regardless of the state of the substrate after processing or the occurrence of re-adsorption.SOLUTION: A vacuum processing apparatus including a power supply system includes: DC power supply parts 6a and 6b that apply a DC voltage to electrodes 3a and 3b provided in an electrostatic chuck Ec; an AC power supply part 7 that supplies an AC current passing through an electrostatic capacitance of the electrostatic chuck; a detector 9 that detects an AC current at that time; and a control unit Uc. When a DC voltage is applied to each electrode to release the substrate attracted to the electrostatic chuck, the control unit decreases the DC voltage and controls the DC voltage to increase or decrease based on an actual measurement value of the detector, and determines that the substrate is released at a time point when a change amount per unit time of the actual measurement value converges to a predetermined range.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a power supply system and a power supply method for an electrostatic chuck that attracts and releases a substrate with the electrostatic chuck. [Background technology]

[0002] In semiconductor manufacturing processes, various processes are performed in a vacuum atmosphere on substrates such as silicon wafers and glass substrates to obtain desired device structures. These processes include film formation processes using methods such as sputtering and plasma CVD, heat treatment, ion implantation, and etching. Vacuum processing equipment used to perform these processes typically includes an electrostatic chuck for positioning and holding the substrate within a vacuum chamber. The electrostatic chuck includes, for example, a metal base and a ceramic plate (chuck plate) made of, for example, PBN (pyrolytic boron nitride) attached to the base. The chuck plate is provided with a pair of electrodes (a so-called bipolar type). A DC voltage (chucking voltage) is applied between the pair of electrodes, generating an electrostatic force that attracts the substrate to the surface of the chuck plate (chucking process: chucking operation). After the desired process is completed, the application of the DC voltage between the pair of electrodes is stopped, and the substrate is released from the chuck (dechucking process: dechucking operation). Thereafter, the substrate is released from the chuck plate by, for example, lift pins attached to the electrostatic chuck (release operation), and is transported to the next process.

[0003] A conventional power supply system for supplying power to such an electrostatic chuck is generally known, which includes a DC power supply that applies a DC voltage between a pair of electrodes, an AC power supply that passes an AC current through the capacitance of the chuck plate of the electrostatic chuck, and a detector that detects the AC current or capacitance at that time, and which can manage the attraction and release of a substrate by the electrostatic chuck based on the detected value of the detector (see, for example, Patent Documents 1 and 2). During a chucking operation, as a substrate is attracted to the surface of the chuck plate by application of a voltage to the electrodes, the gap between the substrate and the chuck plate narrows, and the capacitance gradually increases accordingly. When the detected value of the detector exceeds a predetermined threshold, it is determined that the substrate has been successfully attracted to the surface of the chuck plate. During a dechucking operation, as the substrate is separated from the chuck plate due to, for example, the cessation of voltage application, the gap between the substrate and the chuck plate widens, and the capacitance gradually decreases accordingly. When the detected value of the detector falls below a predetermined threshold, it is determined that the substrate has been successfully released from the chuck plate.

[0004] The state of a substrate after various processes are performed on the chuck plate of an electrostatic chuck often varies depending on the type of process performed in the vacuum chamber. Furthermore, even after sequentially performing predetermined processes on multiple substrates in the same vacuum processing system, the state of the substrate often varies from substrate to substrate (significant individual variations). Therefore, setting a threshold value to determine whether a substrate has been attracted or released, as in the conventional example described above, requires multiple experiments and evaluations for each process, resulting in a lack of versatility. Furthermore, during a dechucking operation, even if the detection value of the detector falls below a preset threshold due to, for example, the cessation of voltage application, the detection value may rise again depending on the state of the substrate after processing. Through extensive research, the inventors of the present application have found that this is due to the substrate being re-attached to the chuck plate. While the exact reason is unclear, performing a dechucking operation while the substrate is re-attached not only risks damage to the substrate (not only cracking or chipping of the substrate but also displacement relative to the chuck plate) but also places an unnecessary load on the chuck plate, reducing its durability. It is also possible to apply a reverse voltage appropriately during the dechucking operation, but it has been found that this may not be effective in preventing the substrate from being re-attached. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Re-tabled publication 2020 / 003746 [Patent Document 2] Patent Publication No. 2022-155113 Summary of the Invention [Problem to be solved by the invention]

[0006] In view of the above, an object of the present invention is to provide a power supply system and a power supply method for an electrostatic chuck that can stably release a substrate regardless of the state of the substrate after processing or whether re-adsorption occurs. [Means for solving the problem]

[0007] In order to achieve the above object, a power supply system for an electrostatic chuck according to the present invention, which attracts and releases a substrate with an electrostatic chuck, includes a DC power supply unit that applies a DC voltage to an electrode provided on the electrostatic chuck, an AC power supply unit that supplies an AC current that passes through the capacitance of the electrostatic chuck, a detector that detects the AC current or the capacitance at that time, and a control unit that controls the DC power supply unit and the AC power supply unit. The control unit is configured to reduce the DC voltage when the DC voltage is applied to the electrode to release a substrate attracted to the electrostatic chuck, and to increase or decrease the DC voltage based on an actual measurement value of the detector, and to determine that the substrate has been released when a change in the actual measurement value per unit time converges within a predetermined range.

[0008] According to the above, for example, a substrate is placed on an electrostatic chuck (chuck plate) installed in a vacuum chamber of a vacuum processing apparatus, and the substrate is attracted and held by applying a DC voltage between a pair of electrodes from a DC power supply. At this time, an AC power supply passes an AC current through the electrostatic capacitance of the electrostatic chuck, and the attraction of the substrate is controlled based on the value detected by a detector (attraction process). In this state, a predetermined process is performed on the substrate. After the process, the DC voltage (applied voltage) applied by the DC power supply is reduced to release the substrate from the attraction process so that the substrate can be transported to the next process (release process).

[0009] In the release step, the control unit uses time and applied voltage as control parameters, reduces the applied voltage, and increases or decreases the DC voltage based on the actual measurement value of the detector. It determines that the substrate has been released when the change in the actual measurement value per unit time converges within a predetermined range. Specifically, for example, the control unit controls the DC voltage as a control parameter (using a differential value, etc., as appropriate) to determine the change in the actual measurement value (slope of the actual measurement value) in the first unit time. When this change converges within a predetermined range (first range), it determines the next unit time and applied voltage (the range of the applied voltage to be increased or decreased), and determines the change in the actual measurement value in the next unit time (slope of the actual measurement value). When this operation is repeated and the change in the actual measurement value per unit time converges within a predetermined range (e.g., 3 μA / 3 sec or less), it is determined that the value detected by the detector no longer changes and is stable (in other words, it is determined that the substrate is held in a state where it is maximally separated from the electrostatic chuck). At this time, the application of the DC voltage to the electrodes is not stopped, and the applied voltage is maintained until the amount of change in the measured value per unit time converges within a predetermined range.

[0010] When it is determined that the change in the measured value per unit time has converged within a predetermined range (the end of the dechucking operation), a signal from the control unit activates, for example, lift pins attached to the electrostatic chuck, which lift the substrate from the chuck plate and dechucking it (the dechucking operation). In this case, the voltage application may be stopped immediately before or simultaneously with the activation of the lift pins and appropriately grounded. Thus, in the present invention, the end of the dechucking operation is not determined by an absolute threshold value, but rather by minimizing the measured value as much as possible. The end of the dechucking operation is determined by creating a state in which the substrate is maximally dechucked based on the change in the measured value per unit time using time and applied voltage as control parameters, and the substrate is dechucking while maintaining this state. As a result, the substrate can be dechucking reliably without damaging the substrate and without applying any unnecessary load to the electrostatic chuck, regardless of the state of the substrate after processing or the occurrence of re-adhesion.

[0011] In the present invention, the control unit may detect the AC current or the capacitance when the substrate is placed on the electrostatic chuck prior to the attraction of the substrate to the electrostatic chuck, store the detected value as an initial value, and perform proportional control, integral control, or differential control based on the deviation between the initial value and an actual measurement value, or perform PID control, and determine that the substrate has been released when the rate of change per unit time of the actual measurement value converges within a predetermined range. In this manner, by using the state of the substrate when it was placed on the electrostatic chuck as a reference, the applied voltage can be quickly reduced, allowing for more stable desorption of the substrate.

[0012] In order to achieve the above object, a power supply method for an electrostatic chuck of the present invention, which attracts and releases a substrate with an electrostatic chuck, includes an attracting step of placing a substrate on the electrostatic chuck and applying a DC voltage to an electrode provided on the electrostatic chuck to electrostatically attract the substrate, and a releasing step of reducing the DC voltage to release the electrostatic attraction of the substrate to be processed. The releasing step further includes a determining step of increasing or decreasing the DC voltage based on an actual measurement value from a detector and determining that the substrate has been released when a rate of change in the actual measurement value per unit time has converged within a predetermined range, and at this time, the DC voltage applied to the substrate is maintained for a predetermined time. In this case, the attracting step may include a step of detecting the AC current or the electrostatic capacitance when the substrate is placed on the electrostatic chuck prior to attracting the substrate to the electrostatic chuck, and storing the detected value as an initial value. The chuck may perform any one of proportional control, integral control, and differential control based on a deviation between the initial value and an actual measurement value, or may perform PID control, and determine that the substrate has been released when a change in the actual measurement value per unit time converges within a predetermined range. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a schematic diagram illustrating, with some parts omitted, a vacuum processing apparatus including a power supply system according to an embodiment of the present invention; [Figure 2] FIG. 3 is a control flow diagram illustrating the operation of the power supply system. [Figure 3]6 is a graph illustrating changes in DC voltage and AC current in a release process. [Figure 4] Graph showing the experimental results of confirming re-adhesion to an electrostatic chuck. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, with reference to the drawings, an embodiment of a power supply system PS for an electrostatic chuck and a power supply method of the present invention will be described, in which the substrate is a silicon wafer (hereinafter referred to as "wafer Sw") and the electrostatic chuck Ec is a bipolar type, and the electrostatic chuck Ec attracts and releases the wafer Sw. In the following, directions such as up and down will be described based on the attitude of the electrostatic chuck shown in FIG.

[0015] Referring to FIG. 1, Vc denotes a vacuum chamber of the vacuum processing apparatus VM. The vacuum processing apparatus VM performs various processes, such as film formation processes using methods such as sputtering and plasma CVD, heat treatment, ion implantation, and etching. Since these processes are performed using known systems, detailed descriptions are omitted here. The vacuum processing apparatus VM includes a control unit Uc. The control unit Uc is a known system including a microcomputer, a sequencer, and a memory, and controls the various components (vacuum pump, vacuum gauge, gas introduction means, heater, etc.) provided in the vacuum chamber Vc to perform the specified processes. In this embodiment, the control unit Uc also controls the operation of the electrostatic chuck Ec. An electrostatic chuck Ec is provided in the vacuum chamber Vc to position and hold the wafer Sw during processing.

[0016] The electrostatic chuck Ec comprises a metal base 1 and a dielectric chuck plate 2 mounted on the upper surface of the base 1. The base 1 is an aluminum cylinder with a contour corresponding to the wafer Sw. Inside the base 1, a heating unit 11 for heating the wafer Sw and a cooling unit (not shown) for circulating a refrigerant to cool the wafer Sw are mounted. This allows the wafer Sw to be heated or cooled during processing. The chuck plate 2 is made of PBN, ALN, or silicone rubber and is provided with a pair of electrodes 3a, 3b via an insulating layer (not shown). A plurality of through holes 4 are formed in the base 1 and the chuck plate 2, penetrating them vertically. A lift pin 5 is inserted into each through hole 4. The lift pin 5 moves up and down relative to the chuck plate 2 by actuating a driving unit 51, such as an air cylinder, in response to a signal from a control unit Uc. A power supply system PS according to this embodiment is provided to attract and release the wafer Sw on the electrostatic chuck Ec.

[0017] The power supply system PS includes DC power supplies 6a and 6b that apply a DC voltage (chucking voltage) between the pair of electrodes 3a and 3b, and an AC power supply 7 that passes an AC current through the capacitance of the chuck plate 2. The power supply system PS further includes switching means 8a and 8b that switch between the first circuit C1 and the second circuit C2, and a first circuit C1 that applies a DC voltage between the DC power supplies 6a and 6b and the electrodes 3a and 3b to attract the wafer Sw to the chuck plate 2 and a second circuit C2 that connects the electrodes 3a and 3b to ground potential after processing. Specifically, in the first circuit C1, a positive (high-voltage) output 61 of one DC power supply 6a is connected to one electrode 3b via one switching means 8a, and the other electrode 3a is connected to a negative (low-voltage) output 64 of the other DC power supply 6b via the other switching means 8b. As a result, a DC voltage is applied between the electrodes 3a and 3b to attract the wafer Sw to the chuck plate 2. When the switching means 8a and 8b are switched, one electrode 3b is connected to the negative output 62 of one DC power supply unit 6a via one switching means 8a, and the other electrode 3a is connected to the positive output 63 of the other DC power supply unit 6b via the other switching means 8b, and is therefore connected to the ground potential.

[0018] The DC power supplies 6a and 6b are known devices capable of applying a DC voltage of 0.1 to 4 kV between the electrodes 3a and 3b depending on the type of chuck plate 2, but the magnitude of the DC voltage is not limited thereto. In this embodiment, two DC power supplies 6a and 6b are used as an example, but this is not limiting. For example, a single known device may be used. The AC power supply 7, although not specifically shown or described, includes a power supply that generates an AC voltage of a predetermined frequency and a transformer. The secondary side of the transformer is connected between the negative output 62 of one DC power supply 6a of the second circuit C2 and the positive output 63 of the other DC power supply 6b, and is connected to ground potential (0 V) via a resistor R1. An ammeter 9 is connected in parallel with the resistor R1 as a detector for detecting AC current. Known devices such as relays are used as the switching means 8a and 8b. This allows AC current to flow and be measured by the ammeter 9 in either the first circuit C1 or the second circuit C2. The power supply method (control flow) for the electrostatic chuck of this embodiment will be described below with reference to FIGS.

[0019] When a predetermined process is performed on a wafer Sw in the vacuum chamber Vc, as shown in FIG. 2, first, the switching means 8a and 8b are used to switch to the second circuit C2, and the wafer Sw is placed on the upper surface of the electrostatic chuck Ec (S11). In this case, the lift pins 5 are moved to a position where they protrude from the upper surface of the chuck plate 2, and in this state, a transfer robot (not shown) transfers the wafer Sw and hands it over to the lift pins 5. Then, when the lift pins 5 are moved to a position where they are retracted into the chuck plate 2, the wafer Sw is placed on the upper surface of the chuck plate 2. At this time, the AC power supply unit 7 applies an AC current through the electrostatic capacitance of the chuck plate 2 on which the wafer Sw is placed, and the AC current value at this time is detected by the ammeter 9. The detected value at this time is sent to the control unit Uc and stored as an initial value Ia (S12).

[0020] Next, the chucking operation is started (S13), and the control unit Uc switches to the first circuit C1 using the switching means 8a, 8b to apply a DC voltage between the electrodes 3a, 3b via the DC power supply units 6a, 6b (hereinafter also referred to as "applied voltage Av"). Then, the wafer Sw is attracted to the upper surface of the chuck plate 2 by electrostatic force generated by the DC voltage applied between the electrodes 3a, 3b. As the wafer Sw is attracted to the upper surface of the chuck plate 2, the gap between them becomes narrower. At this time, the detection value detected by the ammeter 9 (hereinafter referred to as "measured value Ma") gradually increases. When the capacitance Ma exceeds a threshold value experimentally determined in advance, it is determined that the wafer Sw has been normally attracted to the surface of the chuck plate 2. Then, a predetermined process is performed on the wafer Sw in the vacuum chamber Vc. The measured value Ma can also be calculated as the capacitance based on the AC current value detected by the ammeter 9. That is, as the wafer Sw is attracted to the upper surface of the chuck plate 2, the distance between them narrows, increasing the capacitance, and as the wafer Sw is peeled off from the chuck plate 2 by a dechucking operation (described later), the capacitance decreases.

[0021] When processing of the wafer Sw is completed (S14), the dechucking operation (S15) typically begins. After determining the completion of the dechucking operation, the wafer Sw is lifted from the chuck plate 2 by the lift pins 5 (de-chucking operation) and then transported to the next process by a transfer robot. While the completion of the dechucking operation can be determined using an experimentally determined threshold value, this method requires experimentation and evaluation for each process performed in the vacuum chamber Vc, making it less versatile. Furthermore, as shown in Figure 4, the change in the measured value Ma from the chucking operation to the dechucking operation indicates that, as indicated by the dashed-dotted line in Figure 4, when the wafer Sw is placed on the top surface of the chuck plate 2, the measured value Ma is approximately constant. As the applied voltage Av increases, as indicated by the solid line in Figure 3, the measured value Ma gradually increases and eventually reaches an approximately constant value. Then, when the applied voltage Av is reduced to 0 V and the wafer Sw is separated (peeled off) from the upper surface of the chuck plate 2, the distance between them increases, and the actual measurement value Ma gradually decreases and drops to near the initial value Ia, but the actual measurement value Ma may rise again in a short period of time.

[0022] The inventors conducted extensive research using a displacement meter (not shown) and discovered that, as shown by the dotted line in FIG. 4 , the displacement (mm) of the wafer Sw relative to the chuck plate 2 correlates with changes in the measured value Ma, and therefore that a re-increase in the measured value Ma is due to the wafer Sw being re-attached to the chuck plate 2. In such a case, it is necessary to determine the end of the dechucking operation so as to avoid damaging the wafer Sw or reducing the durability of the chuck plate 2. In this embodiment, the end of the dechucking operation is not determined based on an absolute threshold value, but rather aims to minimize the detected value (measured value Ma) of the ammeter 9 as much as possible, and the end of the dechucking operation is determined based on the change in the measured value Ma per unit time using time and applied voltage as control parameters, when the wafer Sw has been maximally delaminated. This will be described in detail below.

[0023] After starting the dechucking operation (S15), the control unit Uc sets the initial value Ia as a temporary target value and performs PID control based on the deviation between the initial value Ia and the actual measurement value Ma. Then, it determines whether the actual measurement value Ma is equal to or less than a value obtained by multiplying the initial value Ia by a coefficient (e.g., 1.05 times) (S16). When the actual measurement value Ma is equal to or less than this value, it determines whether the amount of change in the actual measurement value Ma per unit time is equal to or less than a predetermined value (e.g., 3 μA / 3 sec) (i.e., whether the amount of change (slope) per unit time of the actual measurement value Ma has converged within a predetermined range) (S17). Even if the actual measurement value Ma is higher than this value, it may be determined whether the amount of change has converged within the predetermined range (S17) after a predetermined time (e.g., 15 seconds) has elapsed (S18).

[0024] When the change in the actual measurement value Ma becomes equal to or less than a preset value, it is determined that the wafer Sw has been released. In other words, when the change in the actual measurement value Ma per unit time becomes a predetermined value, it is determined that the actual measurement value Ma no longer changes and is stable (in other words, it is determined that the wafer Sw is held in a state where it is maximally separated from the chuck plate 2). At this time, the application of the DC voltage between the pair of electrodes 3a, 3b is not stopped, and the applied voltage when the wafer Sw was released is maintained. In this state, the control unit Uc activates the lift pins 5 to lift and separate the wafer Sw from the chuck plate 2 (a separation operation). The control unit Uc may switch to the second circuit C2 by the switching means 8a, 8b immediately before the lift pins 5 are activated, thereby appropriately grounding the circuit.

[0025] According to the above-described embodiment, the end of the dechucking operation is determined by creating a state in which the substrate is maximally dechucked based on the change in the actual measurement value Ma per unit time using time and applied voltage as control parameters, and the wafer Sw is dechucking while maintaining this state. As a result, the substrate can be stably dechucking without damaging the wafer Sw, without applying an unnecessary load to the electrostatic chuck Ec, and regardless of the state of the wafer Sw after processing or the occurrence of re-adsorption. Furthermore, by using the state when the wafer Sw was placed on the chuck plate 2 as a reference and performing PID control based on the deviation between the initial value Ia and the actual measurement value Ma, the applied voltage can be quickly reduced, thereby enabling more stable dechucking of the substrate.

[0026] Although the above describes an embodiment of the present invention, the present invention is not limited thereto and various modifications are possible without departing from the spirit and scope of the present invention. In the above embodiment, the electrostatic chuck Ec is applied to a so-called bipolar electrostatic chuck. However, the present invention is not limited thereto and can also be applied to a monopolar electrostatic chuck. Furthermore, in the above embodiment, an initial value Ia is set as a target value, PID control is performed based on the deviation between the initial value Ia and the actual measurement value Ma, and the end of the dechucking operation is determined based on whether the change (slope) of the actual measurement value Ma per unit time converges within a predetermined range. However, the present invention is not limited thereto and may instead increase or decrease the DC voltage applied to the pair of electrodes 3a, 3b through feedback control based on the actual measurement value Ma of the detector 9, and determine that the substrate has been released when the change in the actual measurement value Ma per unit time converges within a predetermined range.

[0027] The control unit Uc controls the DC voltage as a control parameter (using a differential value, etc., as appropriate) to determine the change in the actual measurement value Ma over the first unit time (the slope of the actual measurement value). When this change converges within a predetermined range (first range), the next unit time and the applied voltage (the range of the applied voltage to be increased or decreased) are determined, and the change in the actual measurement value over the next unit time (the slope of the actual measurement value) is determined. This operation is repeated until the change in the actual measurement value per unit time converges within a predetermined range (e.g., 3 μA / 3 sec or less), at which point the detected value by the detector 9 is deemed stable and no further change occurs, and the dechucking operation is determined to be complete. Furthermore, in the above embodiment, PID control based on the deviation between the initial value Ia and the actual measurement value Ma is described as an example. However, feedback control is not limited to this. For example, proportional control, integral control, or differential control can be used, or a combination of these can be used. [Explanation of symbols]

[0028] PS...power supply system, Ec...electrostatic chuck, Sw...wafer (substrate), Uc...control unit, 2...chuck plate, 3a, 3b...electrodes, 6a, 6b...DC power supply unit, 7...AC power supply unit, Ia...initial value, Ma...measured value.

Claims

1. A power supply system for an electrostatic chuck that attracts and releases a substrate on the electrostatic chuck, An electrostatic chuck including a DC power supply unit that applies a DC voltage to an electrode provided on the electrostatic chuck, an AC power supply unit that causes an AC current to flow through the capacitance of the electrostatic chuck, a detector that detects the AC current or the capacitance at that time, and a control unit that controls the DC power supply unit and the AC power supply unit, the control unit is configured to, when a DC voltage is applied to the electrode to release the substrate attracted to the electrostatic chuck, reduce the DC voltage and increase or decrease the DC voltage based on an actual measurement value of the detector, and determine that the substrate has been released when a rate of change in the actual measurement value per unit time converges within a predetermined range.

2. the control unit detects the AC current or the electrostatic capacitance when the substrate is placed on the electrostatic chuck prior to the attraction of the substrate to the electrostatic chuck, and stores the detected value as an initial value; 2. The power supply system for an electrostatic chuck according to claim 1, wherein any one of proportional control, integral control, and differential control is performed based on a deviation between an initial value and an actual measurement value, and it is determined that the substrate has been released when a change in the actual measurement value per unit time converges within a predetermined range.

3. the control unit detects the AC current or the electrostatic capacitance when the substrate is placed on the electrostatic chuck prior to the attraction of the substrate to the electrostatic chuck, and stores the detected value as an initial value; 2. The power supply system for an electrostatic chuck according to claim 1, wherein PID control is performed based on a deviation between an initial value and an actual measurement value, and when a change in the actual measurement value per unit time converges within a predetermined range, it is determined that the substrate has been released.

4. A power supply method for an electrostatic chuck that attracts and releases a substrate with the electrostatic chuck, comprising: The method includes a chucking step of placing a substrate on an electrostatic chuck and electrostatically attracting the substrate by applying a DC voltage to an electrode provided on the electrostatic chuck, and a release step of releasing the electrostatic attraction of the substrate to be processed by reducing the DC voltage, the releasing step further includes a determining step of increasing or decreasing the DC voltage based on an actual measurement value of the detector, and determining that the substrate has been released when a change in the actual measurement value per unit time converges within a predetermined range.

5. 5. The power supply method for an electrostatic chuck according to claim 4, wherein the attracting step includes a step of detecting the AC current or the electrostatic capacitance when the substrate is placed on the electrostatic chuck prior to attracting the substrate to the electrostatic chuck, and storing the detected value as an initial value, and performing any one of proportional control, integral control, and differential control based on a deviation between the initial value and an actual measurement value, and determining that the substrate has been released when a change in the actual measurement value per unit time converges within a predetermined range.

6. 5. The power supply method for an electrostatic chuck according to claim 4, wherein the attracting step includes a step of detecting the AC current or the electrostatic capacitance when the substrate is placed on the electrostatic chuck prior to attracting the substrate to the electrostatic chuck, and storing the detected value as an initial value, and performing PID control based on a deviation between the initial value and an actual measured value, and determining that the substrate has been released when a change in the actual measured value per unit time converges within a predetermined range.

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