Suspected load and method for obtaining calibration information using the suspected load

Abstract

To provide a pseudo load to be used during the work of acquiring information for calibration to calibrate a detected value based on a detection signal of a sensor for the radio frequency band provided between a high frequency power supply unit 10 and a plasma generating unit 8, which constitute a plasma source 1.SOLUTION: A pseudo load 9 includes a metal conductor 92 having an inner core part 921 and a plurality of outer circumferential parts 922a, 922b. The metal conductor 92 is used in a state where it is inserted inside a discharge tube 80 of a plasma generating part 8 and functions as a pseudo load when a high frequency voltage is output from a high frequency power supply unit 10 and a high frequency current flows in a discharge coil 81 of the plasma generating part 8. At least one of the plurality of outer circumferential parts 922a, 922b is also capable of moving along the inner core part 921.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] This embodiment relates to a dummy load used during an acquisition operation of calibration information, and a method for acquiring calibration information using the dummy load.

Background Art

[0002] A plasma processing apparatus generates plasma in a plasma generation unit using high-frequency power supplied from a high-frequency power source, and performs plasma processing such as etching on an object to be processed such as a wafer. There are various types of plasma processing apparatuses. For example, there is a plasma processing apparatus that performs plasma processing such as etching in a plasma processing unit using the plasma generated in a plasma source including a high-frequency power source unit and a plasma generation unit.

[0003] In the plasma processing apparatus including the above plasma source, high-frequency parameters such as high-frequency voltage, high-frequency current, high-frequency power, and reflection coefficient are monitored and used for control. For example, when the high-frequency voltage output to a load (equipment downstream from the output terminal of the high-frequency power source unit) exceeds a reference value or when the current flowing through the load exceeds a reference value, control such as reducing the output high-frequency voltage is performed to protect the equipment. Therefore, a high-frequency voltage sensor and a high-frequency current sensor are provided. Then, control is performed using the detection signal detected by the high-frequency voltage sensor and the detection signal detected by the high-frequency current sensor.

[0004] Generally, since the sensitivity of sensors varies, the detection values (for example, voltage values of high-frequency voltage) calculated based on the detection signals of the sensors (for example, detection signals of high-frequency voltage) vary from sensor to sensor. Therefore, calibration is performed to reduce the influence of variations in sensitivity (so-called machine differences) for each sensor.

[0005] When acquiring information necessary for performing calibration as described above (calibration information) (for example, a detection signal of a high-frequency voltage or a detection signal of a high-frequency current), the device equipped with the sensor is connected to a dummy load (also referred to as a dummy load) that can reproduce a predetermined reference load (for example, a load with a predetermined impedance) (see Patent Document 1).

[0006] However, when the device for performing calibration is a plasma source, it is difficult to connect the plasma source to a dummy load. This is because the output of the plasma source is plasma. Therefore, in the same manner as during actual operation, the plasma source is connected to the plasma processing unit, and the operation of acquiring calibration information is performed in a state where plasma is generated in the plasma generation unit of the plasma source.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0008] The present invention has been made in view of the above, and provides a dummy load applicable to a plasma source.

Means for Solving the Problems

[0009] According to one embodiment, the dummy load used during the operation of acquiring calibration information for calibrating a detection value based on a detection signal of a sensor for a radio frequency band provided between a high-frequency power supply unit and a plasma generation unit constituting a plasma source includes a metal conductor having an inner core and a plurality of outer peripheral portions. The metal conductor is used in a state of being inserted into the discharge tube of the plasma generation unit, and functions as a dummy load when a high-frequency voltage is output from the high-frequency power supply unit and a high-frequency current flows through the coil of the plasma generation unit, and at least one of the plurality of outer peripheral portions is movable along the inner core.

Effects of the Invention

[0010] According to the present invention, it is possible to provide a dummy load for calibrating a plasma source having a high-frequency power supply unit and a plasma generation unit.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Modes for Carrying Out the Invention

[0012] (Embodiment) FIG. 1 is a diagram showing a configuration example of a plasma source according to the present embodiment. The plasma source 1 is used as a part of a plasma processing apparatus that performs plasma processing such as etching in a semiconductor manufacturing process.

[0013] The plasma source 1 is an inductively coupled plasma (hereinafter referred to as "ICP") type plasma generation apparatus. The plasma source 1 includes a high-frequency power supply unit 10 and a plasma generation unit 8. The high-frequency power supply unit 10 includes a rectifying and smoothing circuit 2, a step-up / down chopper 3 (an example of a voltage conversion circuit), an inverter circuit 4, a resonance circuit 5, a plasma generation unit 8, and a control unit 7. Further, it includes a DC voltage sensor 61, a DC current sensor 62, a high-frequency voltage sensor 63, and a high-frequency current sensor 64.

[0014] The rectifying and smoothing circuit 2 is a circuit for converting the AC power of a commercial power supply (reference symbol AC in FIG. 1) into DC power. The rectifying and smoothing circuit 2 includes, for example, a rectifying circuit formed by bridge-connecting a plurality of semiconductor elements and a circuit for smoothing the rectified current (pulsating current).

[0015] The buck-boost chopper 3 is a circuit that boosts or buck-boosts a DC input voltage and outputs a DC voltage Vdc. This buck-boost chopper 3 is provided with, for example, a switching element inside, and the switching of the switching element is controlled based on a command signal from the control unit 7 to boost or buck-boost the output DC voltage Vdc.

[0016] As shown in FIG. 1, a DC voltage sensor 61 and a DC current sensor 62 are provided at the output terminal of the buck-boost chopper 3. In FIG. 1, the DC voltage sensor 61 is installed closer to the buck-boost chopper 3 than the DC current sensor 62, but the DC current sensor 62 may be installed closer to the buck-boost chopper 3 than the DC voltage sensor 61. The DC voltage sensor 61 detects the DC voltage Vdc output from the buck-boost chopper 3 and sends a detection signal of the DC voltage Vdc to the control unit 7. The DC current sensor 62 detects the DC current Idc flowing through the output terminal of the buck-boost chopper 3 and sends a detection signal of the DC current Idc to the control unit 7. In the control unit 7 described later, the impedance Rdc at the output terminal of the buck-boost chopper 3 is calculated based on the detection signal of the DC voltage Vdc and the detection signal of the DC current Idc. Specifically, it may be calculated as in the following formula (1). Note that the detection signal of the DC voltage Vdc and the detection signal of the DC current Idc may be analog signals or digital signals. In the case of analog signals, they are usually AD-converted in the control unit 7. Also, for simplicity of explanation, the symbols in formula (1) are the same as above, but Vdc is the voltage value of the DC voltage Vdc, and Idc is the current value of the DC current Idc. Rdc = Vdc / Idc ···· (1)

[0017] The inverter circuit 4 converts the DC voltage Vdc output from the buck-boost chopper 3 into a high-frequency voltage Vrf having a frequency in the radio frequency band and outputs it. The frequency in the high-frequency band is, for example, 2 MHz. Of course, other frequencies are also applicable. Also, for example, the frequency can be increased or decreased with respect to 2 MHz. Usually, the inverter circuit 4 is provided with a switching element, and its switching is controlled by the control unit 7.

[0018] The resonance circuit 5 includes an inductor 51 and a capacitor 52 connected in series between the inverter circuit 4 and one end portion P1 of the plasma generation unit 8, and an inductor 53 and a capacitor 54 connected in series between the inverter circuit 4 and the other end portion P2 of the plasma generation unit 8. The resonance circuit 5 further includes a capacitor 55 between the one end portion P1 and the other end portion P2. Note that it is preferable that the capacitor 52 and the capacitor 54 have substantially the same capacitance, and the inductor 51 and the inductor 53 have substantially the same inductance. In this way, since the circuit configuration of the resonance circuit 5 between the one end portion P1 of the plasma generation unit 8 and the inverter circuit 4 is the same as the circuit configuration of the resonance circuit 5 between the other end portion P2 of the plasma generation unit 8 and the inverter circuit 4, the maximum voltage value of the one end portion P1 and the maximum voltage value of the other end portion P2 become approximately the same. Since the plasma generated in the discharge tube 80 described later tends to be attracted to the inner wall portion of the discharge tube 80 as the potential difference with respect to the reference potential is larger, by equalizing the maximum voltage values at both ends as described above, the uneven wear of the discharge tube 80 can be reduced, and thus the life of the discharge tube 80 can be extended.

[0019] The plasma generation unit 8 has a discharge coil 81. This discharge coil 81 is on the outer peripheral side of a discharge tube 80 (see FIG. 2) described later, and is wound from the inlet side to the outlet side of the discharge tube 80. Note that the discharge coil 81 functions as a part of the resonance circuit 5. The discharge tube 80 is made of a non-conductive material such as quartz or alumina. The discharge coil 81 is a coil made of a conductive material such as copper. Also, by flowing cooling water through the discharge coil 81, the temperature rise of the discharge tube 80 can be reduced.

[0020] Since the high-frequency voltage Vrf output from the inverter circuit 4 is supplied to the plasma generation unit 8 via the resonance circuit 5, a high-frequency current Irf flows through the discharge coil 81. When generating plasma in the plasma generation unit 8, a material gas is supplied into the discharge tube 80. As a result, the material gas is plasmaized by inductive coupling by the high-frequency current flowing through the discharge coil 81, and plasma is generated. Using this plasma, various processes (such as etching) are performed in a plasma processing unit (not shown).

[0021] The high-frequency voltage sensor 63 detects the high-frequency voltage Vrf (alternating voltage between one end P1 and the other end P2 of the plasma generation unit 8) output from the resonance circuit 5, and sends a detection signal of the high-frequency voltage Vrf to the control unit 7. The high-frequency current sensor 64 detects the high-frequency current Irf (alternating current flowing through the discharge coil 81) flowing through the output terminal of the resonance circuit 5, and sends a detection signal of the high-frequency current Irf to the control unit 7. The high-frequency voltage sensor 63 and the high-frequency current sensor 64 are sensors for the radio frequency band. In FIG. 1, the high-frequency current sensor 64 is provided on the other end P2 side of the plasma generation unit 8, but it may be provided on the one end P1 side of the plasma generation unit 8. Also, the detection signal of the high-frequency voltage Vrf sent from the high-frequency voltage sensor 63 to the control unit 7 and the detection signal of the high-frequency current Irf sent from the high-frequency current sensor 64 to the control unit 7 may be analog signals or digital signals. In the case of analog signals, they are usually AD-converted in the control unit 7.

[0022] The control unit 7 is a device that executes control processing and arithmetic processing for various controls. The control unit 7 includes an MPU (Micro-processing unit), a system LSI (Large-Scale Integration), or an FPGA (Field-Programmable Gate Array) equipped with a storage unit (not shown) such as a RAM (Random Access Memory) or a ROM (Read Only Memory), and reads and executes programs and data stored in the storage unit to perform various control processes and arithmetic processes. For example, the control unit 7 calculates the power value of the power supplied to the plasma generation unit 8 based on the detection signal of the DC voltage Vdc and the detection signal of the DC current Idc, and controls the output of the buck-boost chopper 3 so that the power value becomes the target value.

[0023] <Regarding Calibration> As described above, sensors such as the high-frequency voltage sensor 63 and the high-frequency current sensor 64 have variations in sensitivity, so the detection values calculated based on the detection signals of the sensors also vary. Therefore, calibration is performed to reduce the influence of variations in sensitivity (so-called machine differences) for each sensor. Note that calibration may adjust the magnitude of the detection signal output from the sensor, or may adjust the parameters used when calculating the detection value based on the detection signal.

[0024] <Regarding the dummy load 9> In the calibration in this embodiment, different from the prior art such as Patent Document 1, the dummy load for the plasma source 1 is used in a state where it is inserted inside the plasma generation unit 8. Hereinafter, the dummy load 9 used in this embodiment will be described with reference to FIG. 2. FIG. 2 is a diagram showing an example of the main part of the plasma generation unit 8 and the dummy load 9 according to this embodiment. Note that the plasma generation unit 8 in FIG. 2 is shown as a cross-sectional perspective view of the main part. As described above, the plasma generation unit 8 includes a discharge tube 80 and a discharge coil 81. The dummy load 9 includes a ceramic tube 91 and a metal conductor 92.

[0025] The ceramic tube 91 can prevent metal contamination inside the discharge tube 80 by covering the metal conductor 92. Thus, it is desirable to provide the ceramic tube 91. However, if metal contamination inside the discharge tube 80 is not a problem, the ceramic tube 91 may not be provided. When inserting the metal conductor 92 into the discharge tube 80, in order to prevent the discharge tube 80 from being scratched or cracked due to rubbing or collision between the metal conductor 92 and the discharge tube 80, it is desirable that there is a gap between the discharge tube 80 and the ceramic tube 91.

[0026] The metal conductor 92 is provided inside the discharge tube 80 and the ceramic tube 91. The plasma source 1 supplies a high-frequency voltage Vrf to the plasma generation unit 8 to cause a high-frequency current Irf to flow through the discharge coil 81 wound around the discharge tube 80. As a result, magnetic flux is generated in the discharge coil 81, and an induced current flows through the metal conductor 92 in a direction to cancel the magnetic flux. As a result, without generating plasma inside the discharge tube 80, the metal conductor 92 can be used as a dummy load. That is, the metal conductor 92 undertakes the function of power consumption by plasma. Therefore, when calibration is performed, the connection between the plasma source 1 and the plasma processing unit is unnecessary. Also, the supply line for the material gas and the exhaust line such as the vacuum pump are unnecessary.

[0027] Subsequently, the structure of the metal conductor 92 will be described with reference to FIG. 3. As shown in FIG. 3(a), the metal conductor 92 has an inner core portion 921 and an outer peripheral portion 922. The inner core portion 921 and the outer peripheral portion 922 are made of the same material.

[0028] Also, as shown in FIG. 3(b), the outer peripheral portion 922 of the metal conductor 92 has a first outer peripheral portion 922a and a second outer peripheral portion 922b that are separable from each other. And the first outer peripheral portion 922a is movable along the inner core portion 921. Thereby, the position of the first outer peripheral portion 922a can be adjusted. By changing the position of the first outer peripheral portion 922a, the coupling ratio changes. Thereby, the impedance in the stage subsequent to the high-frequency power supply unit 10 of the plasma source 1 (the stage subsequent to one end portion P1 and the other end portion P2 of the plasma generation unit 8) can be changed. Consequently, the impedance in the stage subsequent to the output end of the buck-boost chopper 3 can be changed. Of course, instead of the first outer peripheral portion 922a, the second outer peripheral portion 922b may be made movable, or both the first outer peripheral portion 922a and the second outer peripheral portion 922b may be made movable. Also, the outer peripheral portion 922 may be composed of three or more members. Further, the shape of the metal conductor 92 does not have to be cylindrical.

[0029] <Regarding the calibration method> Next, the calibration procedure will be described using the flowchart shown in FIG. 4. · Step 1 (S1): With the high-frequency power supply unit 10 not outputting the high-frequency voltage Vrf, a dummy load 9 is inserted inside the discharge tube 80.

[0030] · Step 2 (S2): The position of the first outer peripheral portion 922a is adjusted to the initial position. For example, as shown in FIG. 3(a), the first outer peripheral portion 922a and the second outer peripheral portion 922b are brought into a closely attached state.

[0031] · Step 3 (S3): The high-frequency power supply unit 10 of the plasma source 1 outputs the high-frequency voltage Vrf and supplies it to the plasma generation unit 8. Thereby, a high-frequency current Irf flows through the discharge coil 81, and an induced current flows through the metal conductor 92. Therefore, the metal conductor 92 can be used as a dummy load.

[0032] · Step 4 (S4): Detect the DC voltage Vdc output from the buck-boost chopper 3 with the DC voltage sensor 61, and send the detection signal to the control unit 7. Also, detect the DC current Idc flowing through the output terminal of the buck-boost chopper 3 with the DC current sensor 62, and send the detection signal to the control unit 7. The control unit 7 calculates the impedance Rdc based on the received detection signals of the DC voltage Vdc and the DC current Idc (see Equation (1)), and outputs the calculated impedance Rdc. Note that it is assumed that the DC voltage sensor 61 and the DC current sensor 62 have already been calibrated. Also, since the DC voltage sensor 61 and the DC current sensor 62 are for DC detection, calibration can be easily performed. Therefore, even when the high-frequency current Irf has not been calibrated by the high-frequency voltage sensor 63 and the high-frequency current sensor 64, a predetermined reference load can be reproduced.

[0033] · Step 5 (S5): While the operator checks the output impedance Rdc, the operator adjusts the position of the first outer peripheral portion 922a so that the impedance Rdc becomes the target value. The position where the impedance Rdc becomes the target value or the error from the target value is within the allowable range is set as the outer peripheral portion setting position. Record the information of this outer peripheral portion setting position (for example, the distance between the first outer peripheral portion 922a and the second outer peripheral portion 922b). When manually adjusting the position of the first outer peripheral portion 922a, for safety, adjust the position of the first outer peripheral portion 922a with the high-frequency voltage Vrf not being output from the high-frequency power supply unit 10, and then output the high-frequency voltage Vrf from the high-frequency power supply unit 10 after the adjustment. Also, when there are multiple target values for the impedance Rdc, the above operation may be performed for each target value. Also, when there are multiple target values for the power supplied to the plasma generation unit 8, the above operation may be performed for each target value.

[0034] · Step 6 (S6): Connect an oscilloscope, which is a reference detector, between one end portion P1 and the other end portion P2 shown in FIG. 1. Note that since the oscilloscope is an example of a reference detector, other devices may also be used.

[0035] · Step 7 (S7): Set the position of the first outer peripheral portion 922a of the dummy load 9 to the outer peripheral portion setting position (see Step 5). If the position of the first outer peripheral portion 922a of the dummy load 9 has not been moved from the stage of Step 5, this step is omitted.

[0036] · Step 8 (S8): Output a high-frequency voltage Vrf from the high-frequency power supply unit 10 of the plasma source 1. Then, detect the high-frequency voltage Vrf with the high-frequency voltage sensor 63 and detect the high-frequency current Irf with the high-frequency current sensor 64. At the same time, also detect the high-frequency voltage Vrf and the high-frequency current Irf with an oscilloscope. These detection signals are transmitted to the control unit 7. The control unit 7 records the detection signals. Note that the magnitude of the high-frequency voltage Vrf output from the high-frequency power supply unit 10 of the plasma source 1 is adjusted, for example, so that the power value supplied from the high-frequency power supply unit 10 of the plasma source 1 to the plasma generation unit 8 becomes a predetermined target power value. Or, it is adjusted so that the high-frequency voltage Vrf output from the high-frequency power supply unit 10 of the plasma source 1 becomes a predetermined target voltage value.

[0037] · Step 9 (S9): Perform calibration based on the detection signal of the high-frequency voltage sensor 63, the detection signal of the high-frequency current sensor 64, and the detection value of the oscilloscope obtained in Step 8. As the calibration method, a known method can be applied. Since the detection value of the reference detector has been calibrated, by obtaining the detection signal of the sensor to be calibrated and the detection value of the reference detector under the same conditions, the detection value based on the detection signal of the sensor to be calibrated can be adjusted to approach the correct value.

[0038] By performing calibration according to the procedure described above, the calibration of the sensors mounted on the plasma source 1 can be performed. At this time, since the dummy load 9 for the plasma source 1 is used, it is not necessary to connect the plasma source 1 to the plasma processing unit and perform calibration in a state where plasma is generated in the plasma generation unit 8 as in the prior art. Therefore, the calibration work can be performed with simple equipment. On the other hand, if plasma is actually generated as in the prior art, not only the plasma processing unit but also a supply line for the material gas and an exhaust line such as a vacuum pump are required. Further, since the state of the plasma changes depending on the state such as the gas flow rate, pressure, and temperature, it is difficult to reproduce the same load. Therefore, the effect of using the dummy load 9 described in the present embodiment is great. In addition, since the dummy load 9 has a simple configuration, it is easy to handle and the manufacturing cost is also low.

[0039] Although some embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalent scope thereof.

Explanation of Reference Numerals

[0040] 1 Plasma source, 10 High-frequency power supply unit, 2 Rectifying and smoothing circuit, 3 Buck-boost chopper (an example of a voltage conversion circuit), 4 Inverter circuit, 5 Resonant circuit, 61 DC voltage sensor, 62 DC current sensor, 63 High-frequency voltage sensor, 64 High-frequency current sensor, 7 Control unit, 8 Plasma generation unit, 9 Dummy load, 91 Ceramic tube, 92 Metal conductor, 921 Inner core part, 922a First outer peripheral part, 922b Second outer peripheral part.

Claims

1. A dummy load used in an operation of acquiring calibration information for calibrating a detected value based on a detection signal of a sensor for a radio frequency band provided between a high-frequency power supply unit and a plasma generation unit that constitute a plasma source, wherein the dummy load includes a metal conductor having an inner core and a plurality of outer peripheral portions, the metal conductor is used in a state of being inserted into a discharge tube of the plasma generation unit, and when a high-frequency voltage is output from the high-frequency power supply unit and a high-frequency current flows through a coil of the plasma generation unit, it functions as a dummy load, and at least one of the plurality of outer peripheral portions is movable along the inner core. The dummy load.

2. The dummy load according to claim 1, further comprising a ceramic tube covering the metal conductor.

3. A method for acquiring calibration information using the dummy load according to claim 1 or 2, wherein the high-frequency power supply unit includes a rectifying and smoothing circuit, a voltage conversion circuit, an inverter circuit, a resonance circuit, a control unit, a DC voltage sensor, and a DC current sensor, the DC voltage sensor and the DC current sensor are provided between the voltage conversion circuit and the inverter circuit, when a high-frequency voltage is output from the high-frequency power supply unit and a high-frequency current flows through the coil, the impedance calculated from the DC voltage detection value based on the detection signal detected by the DC voltage sensor and the DC current detection value based on the detection signal detected by the DC current sensor is set to a predetermined value. A step of determining the position of the movable outer peripheral portion; A step of acquiring a detection signal of the sensor for the radio frequency band with the position of the movable outer peripheral portion set to the determined position; A method for acquiring calibration information including the above.

4. The method for acquiring calibration information according to claim 3, wherein the sensor for the radio frequency band is a sensor for detecting a high-frequency voltage and a sensor for detecting a high-frequency current.

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