Plasma potential measuring device and plasma potential measuring method

Abstract

To provide a plasma potential measuring device capable of precisely detecting the state of plasma generated by plasma processing equipment.SOLUTION: The plasma potential measuring device includes: a detection electrode 162b that is placed facing plasma P generated in a chamber for inducing a charge corresponding to the plasma potential; a first electrode 162c on the opposite side from plasma P facing detection electrode 162b; and a first insulating member 162a interposed between the detection electrode 162b and the first electrode 162c. The first electrode 162c is virtually shorted to the detection electrode 162b.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to a plasma potential measurement device and a plasma potential measurement method.

Background Art

[0002] In various processes for manufacturing electronic components and circuit boards, a plasma processing device that generates plasma in a processing chamber to etch the surface of an object to be processed is used. In order to determine whether plasma discharge is occurring normally in the processing chamber, there is a configuration in which a probe electrode for plasma potential measurement is provided on the side wall of the processing chamber. The probe electrode detects charges or potentials induced in response to changes in plasma discharge.

[0003] For example, in Patent Document 1, there is proposed a window-type probe having a conductive support member provided with an opening at least in part of a surface facing the plasma, and a dielectric member installed in the opening of the conductive support member, and a probe electrode provided on one side surface of the dielectric member.

[0004] The charge or potential of the probe electrode is usually converted into a digital value by an analog-digital converter (ADC), and it is determined whether abnormal discharge has occurred by mathematically processing the time-series data of the digital values.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] In Patent Document 1, the back side of the probe electrode (the side not facing the plasma) is covered with an insulating film, and furthermore, an ITO shielding electrode for electromagnetically shielding the probe electrode covers the insulating film. In this case, a back capacitance may be formed between the probe electrode and the ITO shielding electrode. Due to this back capacitance, the potential of the probe electrode is affected, which may reduce the sensitivity of detecting the potential caused by the plasma. [Means for solving the problem]

[0007] One aspect of the present invention relates to a plasma potential measuring device comprising: a detection electrode positioned opposite to a plasma generated in a chamber, which induces a charge corresponding to the potential of the plasma; a first electrode on the opposite side from the plasma and opposite to the detection electrode; and a first insulating member interposed between the detection electrode and the first electrode, wherein the first electrode is virtually short-circuited with the detection electrode.

[0008] Another aspect of the present invention relates to a plasma potential measuring device comprising: a detection electrode positioned opposite to a plasma generated in a chamber, on which a charge corresponding to the potential of the plasma is induced; a first electrode facing the detection electrode on the opposite side from the plasma; and a first insulating member interposed between the detection electrode and the first electrode, wherein the charge or potential induced in the detection electrode by the plasma is measured while the first electrode is virtually short-circuited with the detection electrode. [Effects of the Invention]

[0009] According to the present invention, the state of the plasma inside the chamber can be detected with high accuracy. [Brief explanation of the drawing]

[0010] [Figure 1] This is a conceptual diagram showing a schematic cross-sectional view of an example of a plasma processing apparatus used in a plasma potential measuring device and measuring method according to an embodiment of the present invention. [Figure 2]This is a conceptual diagram showing a cross-sectional view of an example of the main parts of a plasma potential measuring device according to an embodiment of the present invention. [Figure 3] This is a circuit diagram showing an example of the configuration of a detection circuit installed in a plasma potential measuring device. [Figure 4] This is a conceptual diagram showing another example of the main part of a plasma potential measuring device according to an embodiment of the present invention, in cross-section. [Modes for carrying out the invention]

[0011] A plasma potential measuring device according to one embodiment of the present invention comprises a detection electrode (hereinafter also called a "probe electrode") positioned opposite the plasma generated in the chamber and on which a charge corresponding to the plasma potential is induced, a first electrode on the opposite side from the plasma and facing the detection electrode, and a first insulating member interposed between the detection electrode and the first electrode.

[0012] The detection electrode is capacitively coupled to the plasma, and a potential and charge are induced in the detection electrode according to the state of the plasma. Therefore, the state of the plasma can be detected by measuring the potential or charge of the detection electrode.

[0013] The first electrode may have the function of shielding the detection electrode from electromagnetic waves from outside the chamber and preventing electromagnetic waves inside the chamber from leaking out. However, since the first electrode faces the detection electrode via the first insulating member, a back capacitance is formed between the first electrode and the detection electrode. When a back capacitance exists, as the plasma state changes, charge accumulated on the detection electrode may move to the back capacitance, or charge accumulated in the back capacitance may move to the detection electrode, resulting in a redistribution of charge between the detection electrode and the back capacitance. As a result, the detection accuracy of the plasma state may decrease by the amount of charge that has moved to the back capacitance or the detection electrode.

[0014] The first electrode is virtually short-circuited with the detection electrode. This allows the current and potential flowing through the detection electrode to be measured without being affected by back capacitance, improving the accuracy of plasma state measurement.

[0015] Here, the virtual short circuit between the first electrode and the detection electrode means that the potential of the first electrode is controlled to be the same as that of the detection electrode in response to potential fluctuations in the detection electrode. However, unlike a normal short circuit, current does not necessarily flow from the detection electrode to the first electrode, or from the first electrode to the detection electrode; the current flowing through the detection electrode can be controlled independently of the current flowing through the first electrode. A virtual short circuit can be realized, for example, by interposing an operational amplifier circuit between the detection electrode and the first electrode.

[0016] As a method for virtual short-circuiting, any circuit configuration can be used as long as the potential and current of the detection electrode and the first electrode are controlled as described above. For example, a typical operational amplifier circuit includes a current mirror circuit composed of multiple transistors. A commercially available IC chip that functions as a general operational amplifier circuit may also be used.

[0017] The plasma potential measuring device may further include a second electrode opposite the detection electrode and facing the first electrode. A second insulating member is interposed between the first electrode and the second electrode. The second insulating member may be made of the same material as the first dielectric member. The second electrode serves to shield the detection electrode and the first electrode from electromagnetic waves from outside the chamber, and also to prevent electromagnetic waves inside the chamber from leaking out. A constant voltage may be applied to the second electrode. For example, the voltage applied to the second electrode may be the same as the voltage applied to the side wall of the chamber, or it may be the ground voltage.

[0018] The plasma potential detection method according to an embodiment of the present invention is a plasma potential measurement device including a detection electrode disposed to face the plasma generated in the chamber, where charges corresponding to the potential of the plasma are induced, a first electrode disposed on the side opposite to the plasma and facing the detection electrode, and a first insulating member interposed between the detection electrode and the first electrode. In this device, the charge or potential induced in the detection electrode by the plasma is measured in a state where the first electrode is virtually short-circuited with the detection electrode. Thereby, the current and potential flowing through the detection electrode can be measured without being affected by the back capacitance. In the above plasma potential detection method, the plasma potential measurement device may further include a second electrode disposed on the side opposite to the detection electrode and facing the first electrode, and a second dielectric member interposed between the first electrode and the second electrode.

[0019] Hereinafter, the plasma potential detection device and the plasma potential detection method of the present embodiment will be described in detail with reference to the drawings in conjunction with a specific example of a plasma processing device that generates the plasma to be detected.

[0020] (Plasma processing device) The plasma processing device includes a processing chamber, an electrode portion provided in the processing chamber on which a processing object is placed, and a high-frequency power supply portion that applies high-frequency power to the electrode portion. When a plasma generation gas is supplied to the processing chamber and high-frequency power is applied to the electrode portion, plasma is generated in the processing chamber. The generated plasma can be used, for example, for etching the surface of the processing object placed on the electrode portion. A detection circuit for detecting the plasma potential is connected to the plasma processing device. The output of the detection circuit is connected to a signal analysis portion. The signal analysis portion detects the plasma potential based on the output of the detection circuit, and determines whether the generated plasma is normal based on the detected plasma potential.

[0021] FIG. 1 is a conceptual diagram showing in cross section the schematic structure of a plasma processing apparatus 100 in which a plasma to be detected for plasma potential is generated. A processing chamber 103a is formed by sealing a vacuum chamber 103 composed of a horizontal base portion 101 and a lid portion 102. The lid portion 102 is disposed to be movable up and down by a lifting means (not shown). When the lid portion 102 descends and abuts against the upper surface of the base portion 101, the vacuum chamber 103 is sealed. At this time, a seal member 104 is interposed between the lid portion 102 and the base portion 101, whereby the sealed state of the processing chamber 103a is ensured. In the processing chamber 103a, the object to be processed 109 is plasma-processed. An opening 101a is provided in the base portion 101, and an electrode portion 105 is fitted through an insulating member 106 so as to close the opening 101a. The upper surface of the electrode portion 105 is covered with an insulating layer 107. A guide member 108 for positioning the object to be processed 109 is disposed on the upper surface of the insulating layer 107.

[0022] A through hole 101b is formed at the periphery of the opening 101a of the base portion 101. A pipe line 111 is inserted into the through hole 101b, and a vent valve 112, a gas supply valve 113, a vacuum valve 114 and a vacuum gauge 115 are connected to the pipe line 111. A gas supply unit 116 and a vacuum pump 117 are further connected to the gas supply valve 113 and the vacuum valve 114, respectively. By opening the vacuum valve 114 and operating the vacuum pump 117, the gas in the processing chamber 103a is discharged and the pressure is reduced. The degree of vacuum in the processing chamber 103a is measured by the vacuum gauge 115. On the other hand, when the gas supply valve 113 is opened, the plasma generating gas is supplied from the gas supply unit 116 into the processing chamber 103a. The gas supply unit 116 has a built-in flow rate adjusting function, and the flow rate of the plasma generating gas supplied into the processing chamber 103a is adjusted. When the vent valve 112 is opened, the atmosphere is supplied into the processing chamber 103a.

[0023] The electrode section 105 is electrically connected to the high-frequency power supply section 119 via a matching unit 118. Meanwhile, the lid section 102 is grounded to the grounding section 110. When plasma generation gas is supplied into the processing chamber 103a and the high-frequency power supply section 119 is operated, a high-frequency voltage is applied between the electrode section 105 and the lid section 102. As a result, plasma is generated in the processing chamber 103a. The matching unit 118 matches the impedance between the plasma discharge circuit (not shown) that generates the plasma and the high-frequency power supply section 119. The vent valve 112, gas supply valve 113, vacuum valve 114, vacuum gauge 115, gas supply section 116, vacuum pump 117, and high-frequency power supply section 119 are controlled by the device control section 124 within the control unit 120. That is, the device control section 124 has the normal operation control function to execute the plasma processing operation. The control unit 120 is connected to the display section 130, input section 140, and detection circuit 200. The display unit 130 shows the results of the abnormality detection performed by the signal analysis unit, which will be described later. The input unit 140 receives the process recipe and other information.

[0024] A plasma potential detection sensor 160 is positioned to cover the opening 102a provided in the lid portion 102. The plasma potential detection sensor 160 comprises a dielectric member 161 and an electrode unit 162. The plasma potential detection sensor 160 and the detection circuit 200 constitute a plasma potential measuring device.

[0025] (Plasma potential measurement device and measurement method) Figure 2 is a conceptual diagram showing a cross-sectional view of an example of the main components of a plasma potential measuring device. The plasma potential measuring device comprises a plasma potential detection sensor 160 and a detection circuit 200. The plasma potential detection sensor 160 is fixed to the side wall surface of the chamber of the plasma processing device by a support member 170. The dielectric member 161 is flat, with one surface facing the processing chamber 103a where the plasma is generated, and the other surface facing the probe electrode 162b that constitutes the electrode unit 162. The material of the dielectric member 161 is, for example, optically transparent glass.

[0026] The electrode unit 162 consists of a probe electrode 162b (detection electrode) positioned on the dielectric member 161 side, a first electrode 162c positioned opposite it, and a glass plate 162a (first insulating member) interposed between them. The probe electrode 162b and the dielectric member 161 are fixed together by a support member 170 so as to be in close contact. The probe electrode 162b is connected to the detection circuit 200 via a detection wire 163a. ​​The first electrode 162c electrically shields the probe electrode unit 162 from the outside. The probe electrode 162b and the first electrode 162c are formed, for example, by coating the surface of the glass plate 162a with a transparent conductive material such as ITO (indium tin oxide). Therefore, the inside of the processing chamber 103a can be viewed from the outside via the plasma potential detection sensor 160.

[0027] The material of the support member 170 is not particularly limited; for example, it may be metal. However, if a conductive material is used for the support member 170, it is insulated from and electrically isolated from the first electrode 162c.

[0028] When a plasma discharge occurs inside the processing chamber 103a, the probe electrode 162b is electrically connected to the plasma P via the dielectric member 161 and the sheath (space charge layer) S formed at the interface between the generated plasma P and the dielectric member 161. That is, an electrical circuit is formed in series, consisting of a capacitor C1 formed by the dielectric member 161, a capacitor C2 having capacitance corresponding to the sheath S, and the resistance due to the plasma P. As a result, a potential and charge corresponding to the state of the plasma P are induced in the probe electrode 162b. In other words, the amount of charge injected into the probe electrode 162b represents a change in the plasma potential that reflects the state of the plasma P.

[0029] In the example shown in Figure 2, a back capacitance C3 is formed by a glass plate 162a interposed between the probe electrode 162b and the first electrode 162c. The back capacitance C3 is connected in series with capacitors C1 and C2. In this case, the charge accumulated on the probe electrode 162b according to the state of the plasma P is redistributed with the back capacitance C3 via capacitors C1 and C2, which may make it impossible to accurately detect the state of the plasma based on the potential or charge amount induced on the probe electrode 162b.

[0030] However, by virtually short-circuiting the probe electrode 162b and the first electrode 162c, charge is not accumulated in the back capacitance C3, and fluctuations in the accumulated charge of the probe electrode 162b due to the back capacitance C3 are suppressed. Therefore, by measuring the charge or potential induced in the probe electrode 162b while the probe electrode 162b and the first electrode 162c are virtually short-circuited, the plasma state can be accurately detected based on the measured amount of charge or potential.

[0031] Figure 3 is a circuit diagram showing an example of the configuration of a detection circuit 200 to which the probe electrode 162b and the first electrode 162c are connected, and shows an example of a circuit that virtually short-circuits the probe electrode 162b and the first electrode 162c. The detection circuit 200 comprises a first operational amplifier 202 and a second operational amplifier 204.

[0032] The non-inverting input terminal of the first operational amplifier 202 is connected to the probe electrode 162b via wiring 163a. ​​The output terminal of the first operational amplifier 202 is connected to the first electrode 162c via wiring 163b. The output terminal of the first operational amplifier 202 is also connected to the inverting input terminal of the first operational amplifier 202 without a feedback resistor. As a result, the first operational amplifier 202 constitutes a non-inverting amplifier circuit with a gain of 1, and the probe electrode 162b connected to the non-inverting input terminal of the first operational amplifier 202 and the first electrode 162c connected to the inverting input terminal of the first operational amplifier 202 are virtually short-circuited.

[0033] Due to the virtual short-circuit effect of the operational amplifier, the voltage at the inverting input terminal of the first operational amplifier 202 connected to the first electrode 162c operates to be the same as the voltage at the non-inverting input terminal of the first operational amplifier 202 connected to the probe electrode 162b. As a result, no voltage is applied to the back capacitance C3, allowing the potential or charge induced on the probe electrode 162b to be detected with reduced influence from the back capacitance C3, and enabling accurate detection of the plasma state.

[0034] The inverting input terminal of the second operational amplifier 204 is connected to the probe electrode 162b via resistor R1. The non-inverting input terminal of the second operational amplifier 204 is grounded. The output terminal of the second operational amplifier 204 is connected to the inverting input terminal of the second operational amplifier 204 via feedback resistor R2. As a result, the second operational amplifier 204 constitutes an inverting amplifier circuit, and the amplified voltage of the potential of the probe electrode 162b is output to the output terminal of the second operational amplifier 204. The output voltage is transmitted to the signal analysis unit of the control unit 120.

[0035] In the second operational amplifier 204, a capacitor C2 (not shown) may be connected between the output terminal and the inverting input terminal instead of the feedback resistor R2. In this case, the second operational amplifier 204 constitutes an integrating circuit, amplifying the amount of charge induced on the probe electrode 162b, and a voltage corresponding to the amplified amount of charge is output to the output terminal.

[0036] The first electrode 162c may also serve to electromagnetically shield the probe electrode 162b from external sources. External noise may induce a charge on the first electrode 162c, causing a current to flow through the wiring 163b to the inverting input terminal of the first operational amplifier 202. However, this current is supplied from the power supply voltage of the first operational amplifier 202 and does not flow to the non-inverting input terminal of the first operational amplifier 202 connected to the probe electrode 162b. Therefore, it is possible to accurately detect the charge or potential induced on the probe electrode 162b while reducing the influence of external noise.

[0037] Figure 4 is a conceptual diagram showing a cross-sectional view of another example of the main components of a plasma potential measuring device. In the example of Figure 4, the electrode unit 162 further comprises a second electrode 162d that faces the first electrode 162c on the opposite side of the probe electrode 162b, via a glass plate 162a (second insulating member). In other words, the first electrode 162c is sandwiched between the probe electrode 162b and the second electrode 162d such that the insulating glass plate 162a is interposed between the probe electrode 162b and the first electrode 162c, and between the second electrode 162d and the first electrode 162c. The second electrode 162d is, for example, an ITO transparent electrode similar to the probe electrode 162b and the first electrode 162c. In the example of Figure 4, the first electrode 162c is positioned to be embedded in the glass plate 162a, but it may also be sandwiched between two glass plates (insulating members). In this case, the insulating member interposed between the probe electrode 162b and the first electrode 162c (first insulating member) and the insulating member interposed between the second electrode 162d and the first electrode 162c (second insulating member) may be made of the same material or different materials. The insulating member may be made of a low dielectric constant material from the viewpoint of reducing the back capacitance generated between electrodes 162b and 162d.

[0038] The probe electrode 162b and the first electrode 162c are connected to the detection circuit 200 via wiring 163a and 163b, respectively. The detection circuit can be configured in the same way as the circuit shown in Figure 3 above.

[0039] The second electrode 162d electromagnetically shields the probe electrode 162b and the first electrode 162c from the outside. In this example, the material of the support member 170 is a conductive material such as metal, and the second electrode 162d and the lid 102 may be electrically connected. Charge generated on the second electrode 162d due to external noise is dissipated to the lid 102 via the support member 170, thereby reducing the noise. A constant voltage may be applied to the second electrode 162d. When a constant voltage is applied to the second electrode 162d, it is preferable that the constant voltage is the same as the voltage applied to the lid 102. The constant voltage may be the ground voltage.

[0040] The first electrode 162c and the second electrode 162d are capacitively coupled via an insulating material (glass plate 162a). As a result, when charge generated on the second electrode 162d due to external noise escapes to the cover 102, a corresponding current may flow to the inverting input terminal of the first operational amplifier 202 connected to the first electrode 162c. However, this current is supplied from the power supply voltage of the first operational amplifier 202 and does not flow to the non-inverting input terminal of the first operational amplifier 202 connected to the probe electrode 162b. Therefore, the charge or potential induced on the probe electrode 162b can be accurately detected with reduced influence from external noise.

[0041] (Control Unit) The control unit 120 includes a signal analysis unit (not shown) and determines whether the plasma state is normal or not based on the voltage output from the detection circuit 200. If it is determined that the plasma state is not normal and is in an abnormal discharge state, retry processing, cumulative plasma processing, maintenance determination, etc., may be performed. Note that it is not necessary for all of the retry processing, cumulative plasma processing, and maintenance determination to be performed; one or more of these processes may be executed.

[0042] While there are no limited methods for determining an abnormal discharge state of plasma, some methods include determining an abnormal discharge state when the output voltage from the detection circuit 200 exceeds (or falls below) a predetermined threshold voltage, or calculating the time-averaged value of the output voltage from the detection circuit 200 over a predetermined period based on time-series data of the output voltage from the detection circuit 200, and determining that an abnormal discharge has been detected when the time-averaged value exceeds a predetermined value.

[0043] (Device Control Unit) The device control unit 124, although not shown, may include a processing history storage unit, a retry processing unit, an accumulated plasma processing unit, and a maintenance determination function unit. That is, in addition to the normal operation control functions described above, the device control unit 124 can determine the state of plasma discharge in the processing chamber 103a based on the abnormal discharge detection result by the signal analysis unit and reset the plasma processing. The determination of the plasma discharge state and the resetting of the plasma processing can be performed by the retry processing unit, the accumulated plasma processing unit, and the maintenance determination unit. The processing history storage unit stores the time change of the output voltage from the detection circuit 200, which is temporarily recorded in memory, and the intermediate data required by the signal analysis unit to determine the detection of abnormal discharge, as processing history data from the plasma processing device 100. This makes it possible to obtain detailed processing history data for the object 109 processed by the plasma processing device 100, ensuring traceability for quality control and production control. [Industrial applicability]

[0044] The plasma potential measuring apparatus and measuring method according to the present invention can be applied to a plasma processing apparatus. [Explanation of Symbols]

[0045] 100: Plasma processing equipment 101: Base section 101a: Opening 101b: Through hole 102: Lid part 102a: Opening 103: Vacuum Chamber 103a: Processing Room 104: Sealing material 105: Electrode part 106: Insulating material 107: Insulating layer 108: Guide member 109: Object to be processed 110: Grounding part 111: Pipeline 112: Vent valve 113: Gas supply valve 114: Vacuum valve 115: Vacuum gauge 116: Gas Supply Department 117: Vacuum pump 118: Matching box 119: High frequency power supply section 120: Control Unit 124: Device Control Unit 130: Display section 140: Input section 160: Plasma potential detection sensor 161: Dielectric material 162: Probe electrode unit 162a: Glass plate 162b: Probe electrode 162c: First electrode 162d: Second electrode 163a, 163b: Wiring 170: Support member 200: Detection circuit 202: First operational amplifier 204: Second operational amplifier

Claims

1. A detection electrode is positioned opposite the plasma generated in the chamber, and a charge corresponding to the potential of the plasma is induced in it. On the opposite side of the plasma, a first electrode facing the detection electrode, A first insulating member interposed between the detection electrode and the first electrode, A second electrode is located on the opposite side of the detection electrode and facing the first electrode, The device comprises a second dielectric member interposed between the first electrode and the second electrode, A plasma potential measuring device in which the first electrode is virtually short-circuited with the detection electrode.

2. The plasma potential measuring device according to claim 1, wherein the first electrode is virtually short-circuited with the detection electrode via an operational amplifier.

3. The plasma potential measuring device according to claim 1 or 2, wherein a constant voltage is applied to the second electrode.

4. A plasma potential measuring device comprising: a detection electrode positioned opposite to the plasma generated in a chamber and which induces a charge corresponding to the potential of the plasma; a first electrode facing the detection electrode on the opposite side from the plasma; a first insulating member interposed between the detection electrode and the first electrode; a second electrode facing the first electrode on the opposite side from the detection electrode; and a second dielectric member interposed between the first electrode and the second electrode, A plasma potential measurement method comprising measuring the charge or potential induced in the detection electrode by the plasma while the first electrode is virtually short-circuited with the detection electrode.

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