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 in plasma processing equipment.SOLUTION: The plasma potential measuring device includes: a detection electrode 162b placed facing plasma P generated in a chamber for inducing charge corresponding to the plasma potential; a potential change circuit 203 for changing a reference potential of the detection electrode 162b; and a detection circuit 202 for detecting the amount of charge induced by the detection electrode 162b.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a plasma potential measuring device and a plasma potential measuring method. [Background technology]

[0002] In various processes for manufacturing electronic components and circuit boards, plasma processing equipment is used to generate plasma in a processing chamber and etch the surface of the workpiece. To determine whether plasma discharge is occurring normally in the processing chamber, some systems have a probe electrode attached to the sidewall of the processing chamber for measuring the plasma potential. The probe electrode detects the charge or potential induced in response to changes in the plasma discharge.

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

[0004] The charge or potential of the probe electrode is usually converted into a digital value by an analog-to-digital converter (ADC), and the time-series data of the digital value is mathematically processed to determine whether or not an abnormal discharge has occurred. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 3773189 specification Summary of the Invention [Problem to be solved by the invention]

[0006] Normally, the detection sensitivity of the charge or potential induced in response to changes in plasma discharge is determined by the configuration of the plasma processing device and the arrangement of the probe electrode, and is fixed. If the detection sensitivity is too high or too low, it is necessary to change the circuit (e.g., amplifier circuit) connected to the probe electrode. [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 plasma generated in a chamber and in which a charge corresponding to the potential of the plasma is induced; a potential changing circuit that changes the reference potential of the detection electrode; and a detection circuit that detects the amount of charge or potential induced in the detection electrode.

[0008] Another aspect of the present invention relates to a plasma potential measurement method in a plasma potential measurement device including a detection electrode disposed opposite to plasma generated in a chamber and in which a charge corresponding to the potential of the plasma is induced, the method including the steps of detecting the amount of charge or potential induced in the detection electrode and changing the reference potential of the detection electrode in accordance with the amount of charge or potential induced. [Effects of the Invention]

[0009] According to the present invention, the detection sensitivity of the plasma potential can be adjusted by a simple method, so that the state of the plasma generated in the chamber can be detected with high accuracy. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a conceptual diagram showing, in cross section, the schematic structure of an example of a plasma processing apparatus used in a plasma potential measuring apparatus and a measuring method according to an embodiment of the present invention; [Figure 2] 1 is a conceptual diagram showing a cross section of an example of a main part of a plasma potential measuring device according to an embodiment of the present invention. [Figure 3] FIG. 2 is a circuit diagram showing an example of the configuration of a potential detection unit provided in a plasma potential measuring device. [Figure 4] FIG. 10 is a circuit diagram showing another example of the configuration of the potential detection unit provided in the plasma potential measuring device. DETAILED DESCRIPTION OF THE INVENTION

[0011] A plasma potential measuring device according to one embodiment of the present invention comprises a detection electrode that is positioned opposite the plasma generated in a chamber and in which a charge corresponding to the plasma potential is induced, a potential changing circuit that changes the reference potential of the detection electrode, and a detection circuit that detects the amount of charge or potential induced in the detection electrode.

[0012] The detection electrode is capacitively coupled to the plasma, and a charge corresponding to the state of the plasma is induced in the detection electrode. Therefore, the state of the plasma can be detected by measuring the amount of charge induced in the detection electrode. Alternatively, the amount of charge induced in the detection electrode can be detected by measuring the potential of the detection electrode caused by the induced charge (e.g., the potential change from a reference potential), thereby detecting the amount of charge induced in the detection electrode and detecting the state of the plasma.

[0013] As will be described later, the capacitive coupling between the detection electrode and plasma changes depending on the reference potential of the detection electrode. Therefore, by providing a potential changing circuit that changes the reference potential of the detection electrode, the capacitive coupling value between the detection electrode and plasma can be manipulated, and the detection sensitivity of the plasma potential can be adjusted in a simple manner.

[0014] The potential change circuit is preferably virtually short-circuited to the detection electrode, so that the charge induced in the detection electrode does not flow into the potential change circuit, nor is the charge supplied from the potential change circuit to the detection electrode, allowing the amount of charge induced in the detection electrode to be accurately detected.

[0015] Here, the term "the potential change circuit is virtually short-circuited with the detection electrode" means that the potential of the detection electrode is controlled to be the same as the output voltage of the potential change circuit. However, unlike a normal short circuit, current does not necessarily flow from the detection electrode to the potential change circuit or from the potential change circuit to the detection electrode, and the current flowing to the detection electrode can be controlled independently of the current supplied from the potential change circuit.

[0016] Any circuit configuration can be used as a method of virtual short-circuiting, as long as the reference potential of the detection electrode is controlled as described above in accordance with the output voltage of the potential change circuit. The virtual short-circuiting can be achieved, for example, by interposing an operational amplifier circuit between the detection electrode and the potential change circuit. For example, a typical operational amplifier circuit includes a current mirror circuit configured by combining multiple transistors. A commercially available IC chip may also be used as a typical operational amplifier circuit.

[0017] Preferably, the detection circuit includes an operational amplifier. One input terminal of the operational amplifier (either the non-inverting input terminal or the inverting input terminal) is connected to the detection electrode, and the operational amplifier amplifies the amount of charge induced in the detection electrode or the change in potential of the detection electrode caused by the induced charge within the operating voltage range of the operational amplifier, and outputs a voltage corresponding to the amount of induced charge to its output terminal. The one input terminal of the operational amplifier is virtually short-circuited to the other input terminal of the operational amplifier (the other of the non-inverting input terminal or the inverting input terminal), so that the detection electrode connected to the one input terminal of the operational amplifier is also virtually short-circuited to the other input terminal of the operational amplifier. Therefore, the reference potential of the detection electrode can be changed by changing the voltage input to the other input terminal of the operational amplifier.

[0018] By changing the reference potential of the detection electrode, the voltage input to one input terminal of the operational amplifier can be adjusted so that the voltage output to the output terminal of the operational amplifier shows, for example, a linear change in response to expected changes in plasma potential, thereby improving detection sensitivity.

[0019] For example, by applying a constant voltage equal to the reference potential to the other input terminal of the operational amplifier and configuring the potential modification circuit to be able to modify the voltage applied to the other input terminal of the operational amplifier, the reference potential of the detection electrode can be modified, the capacitive coupling value between the detection electrode and plasma can be easily manipulated, and the detection sensitivity of the plasma potential can be adjusted in a simple manner. In this case, the charge induced in the detection electrode does not flow into the potential modification circuit connected to the other input terminal of the operational amplifier, and the amount of charge induced in the detection electrode can be accurately detected.

[0020] The potential change circuit may be capable of generating at least two or more different reference potentials and of switching the reference potential to be output as needed. The potential change circuit may be capable of continuously changing the reference potential to be output within a predetermined voltage range. An example of the potential change circuit is a switching power supply circuit. The switching power supply circuit can change the reference potential to be output to any potential by changing the on / off ratio (duty ratio) when controlling the switching of the input voltage. The switching method is not particularly limited. The switching power supply circuit may be an AC / DC converter that uses an AC power supply as an input voltage, or a DC / DC converter that uses a DC power supply as an input voltage.

[0021] A plasma potential detection method according to one embodiment of the present invention includes, in a plasma potential measurement device having a detection electrode positioned opposite to plasma generated in a chamber and in which a charge corresponding to the plasma potential is induced, the steps including: (i) detecting the amount of charge or potential induced in the detection electrode; and (ii) changing the reference potential of the detection electrode in accordance with the detected amount of charge or potential.

[0022] The detection electrode may be connected to one input terminal of an operational amplifier, which is virtually short-circuited to the other input terminal of the operational amplifier. In this case, for example, in step (ii), the reference potential can be changed by changing the voltage applied to the other input terminal of the operational amplifier.

[0023] The plasma potential detection device and plasma potential detection method of this embodiment will be described in detail below with reference to the drawings, along with a specific example of a plasma processing apparatus that generates the plasma to be detected.

[0024] (Plasma processing equipment) The plasma processing apparatus includes a processing chamber, an electrode unit provided in the processing chamber and on which an object to be processed is placed, and a high-frequency power supply unit that applies high-frequency power to the electrode unit. Plasma is generated within the processing chamber when a plasma generating gas is supplied to the processing chamber and high-frequency power is applied to the electrode unit. The generated plasma can be used, for example, to etch the surface of the object to be processed placed on the electrode unit. A detection circuit for detecting the plasma potential is connected to the plasma processing apparatus. The output of the detection circuit is connected to a signal analysis unit. The signal analysis unit 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.

[0025] FIG. 1 is a conceptual cross-sectional view of a plasma processing apparatus 100 that generates plasma, the plasma potential of which is to be detected. The processing chamber 103a is formed by sealing a vacuum chamber 103, which is composed of a horizontal base 101 and a lid 102. The lid 102 is arranged so that it can be raised and lowered by a lifting mechanism (not shown). When the lid 102 descends and abuts against the upper surface of the base 101, the vacuum chamber 103 is sealed. A seal member 104 is interposed between the lid 102 and the base 101, ensuring that the processing chamber 103a is sealed. In the processing chamber 103a, a processing target 109 is subjected to plasma processing. An opening 101a is provided in the base 101, and an electrode 105 is fitted in the opening 101a via an insulating member 106. The upper surface of the electrode 105 is covered with an insulating layer 107. On the upper surface of the insulating layer 107, a guide member 108 for positioning the processing object 109 is arranged.

[0026] A through-hole 101b is formed around the periphery of the opening 101a of the base 101. A conduit 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 conduit 111. A gas supply unit 116 and a vacuum pump 117 are 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, gas is discharged from the processing chamber 103a, creating a reduced pressure. The degree of vacuum in the processing chamber 103a is measured by the vacuum gauge 115. Meanwhile, when the gas supply valve 113 is opened, 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 adjustment function, which adjusts the flow rate of the plasma generating gas supplied into the processing chamber 103a. When the vent valve 112 is opened, the atmosphere is supplied into the processing chamber 103a.

[0027] The electrode 105 is electrically connected to a high-frequency power supply 119 via a matching box 118. Meanwhile, the lid 102 is grounded to a grounding unit 110. When plasma generating gas is supplied into the processing chamber 103a and the high-frequency power supply 119 is operated, a high-frequency voltage is applied between the electrode 105 and the lid 102. This generates plasma within the processing chamber 103a. The matching box 118 matches the impedance between the high-frequency power supply 119 and a plasma discharge circuit (not shown) that generates plasma. The vent valve 112, gas supply valve 113, vacuum valve 114, vacuum gauge 115, gas supply unit 116, vacuum pump 117, and high-frequency power supply 119 are controlled by an apparatus control unit 124 within the control unit 120. That is, the apparatus control unit 124 has a normal operational control function for executing plasma processing operations. A display unit 130, an input unit 140, and a potential detection unit 200 are connected to the control unit 120. The display unit 130 displays the results of abnormality determination by a signal analysis unit (to be described later), etc. The input unit 140 receives input of a process recipe, etc.

[0028] A plasma potential detection sensor 160 is disposed so as to cover the opening 102a provided in the lid portion 102. The plasma potential detection sensor 160 includes a dielectric member 161 and a probe electrode unit 162. The plasma potential detection sensor 160 and the potential detection portion 200 constitute a plasma potential measuring device.

[0029] (Plasma potential measuring device and measuring method) FIG. 2 is a conceptual cross-sectional view of an example of a plasma potential detection sensor 160, which is a main component of the plasma potential measuring device. The plasma potential measuring device includes the plasma potential detection sensor 160 and a potential detection unit 200. The plasma potential detection sensor 160 is fixed to the outer side of the lid 102 (the side opposite the processing chamber 103a) by a support member 170 on the sidewall surface of the chamber of the plasma processing device. The dielectric member 161 is flat, with one surface facing the processing chamber 103a where 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. The material of the support member 170 is not particularly limited as long as it is conductive, and may be, for example, a metal.

[0030] The probe electrode unit 162 is composed of a probe electrode (detection electrode) 162b disposed on the dielectric member 161 side, a shield electrode 162c disposed opposite the probe electrode 162b, and a glass plate 162a interposed therebetween. The probe electrode 162b and the dielectric member 161 are fixed by a support member 170 so as to be in close contact with each other. The probe electrode 162b is connected to the potential detection unit 200 via a detection lead 162d. The shield electrode 162c electrically shields the probe electrode unit 162 from the outside. The probe electrode 162b and the shield electrode 162c are formed by coating the surface of the glass plate 162a with a transparent conductive material such as ITO (indium tin oxide). Therefore, the interior of the processing chamber 103a can be viewed from the outside via the plasma potential detection sensor 160.

[0031] A predetermined reference potential is applied to the probe electrode 162b and the shield electrode 162c. The reference potential is usually the ground potential. However, in this embodiment, the reference potential applied to the probe electrode 162b is configured to be changeable from the ground potential.

[0032] 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 a 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 which a capacitor C1 formed by the dielectric member 161, a capacitor C2 having a capacitance equivalent to the sheath S, and a resistance due to the plasma P are connected in series, and a potential and charge corresponding to the state of the plasma P are induced in the probe electrode 162b. That is, the amount of charge injected into the probe electrode 162b represents a change in the plasma potential, which reflects the state of the plasma P. Meanwhile, the charge generated in the shield electrode 162c is released to the grounded lid 102 via the support member 170, thereby reducing noise.

[0033] Therefore, the sensitivity of plasma potential detection sensor 160 depends on the capacitances of capacitors C1 and C2. Of these, the capacitance of capacitor C1 is determined by the configuration of the plasma processing apparatus and is difficult to change. However, the capacitance of capacitor C2 is approximately inversely proportional to the thickness of sheath S and can be adjusted by changing the reference voltage applied to probe electrode 162b from the ground voltage.

[0034] Normally, the plasma potential is a positive potential with respect to the ground potential and is higher than the potential of the probe electrode 162b. In this case, if the reference potential of the probe electrode 162b is increased from the ground potential, the voltage applied to the sheath S (i.e., the potential difference across the capacitor C2) decreases. As a result, the thickness of the sheath S decreases, and the capacitance of the capacitor C2 increases. On the other hand, if the potential of the probe electrode 162b is decreased below the ground potential, the voltage applied to the sheath S (i.e., the potential difference across the capacitor C2) increases. As a result, the thickness of the sheath S increases, and the capacitance of the capacitor C2 decreases.

[0035] The amount of charge injected into the probe electrode 162b is roughly proportional to the product of the combined capacitance of capacitors C1 and C2 and the plasma potential, and if the effect of capacitor C1 is not taken into account, it is roughly proportional to the product of the capacitance of capacitor C2 and the plasma potential. Therefore, the larger the capacitance of capacitor C2, the higher the detection sensitivity, and the smaller the capacitance of capacitor C2, the lower the detection sensitivity. Therefore, by changing the reference potential applied to the probe electrode 162b, the capacitance of capacitor C2 changes, and thereby the detection sensitivity can be adjusted.

[0036] From another perspective, the thickness of the sheath S can be changed by changing the reference potential applied to the probe electrode 162b. The thinner the sheath S, the closer the probe electrode 162b and the plasma are, and therefore the higher the detection sensitivity. On the other hand, the thicker the sheath S, the farther the probe electrode 162b and the plasma are, and therefore the lower the detection sensitivity.

[0037] (potential detection section) 3 is a circuit diagram showing an example of the configuration of the potential detection unit 200. The potential detection unit 200 includes an input terminal 201 connected to the probe electrode 162b via the detection conductor 162d, an operational amplifier 202, and a reference power supply 203 which is a potential changing circuit.

[0038] One input terminal (inverting input terminal in FIG. 3) of the operational amplifier 202 is connected to the input terminal 201 via a resistor R1. The other input terminal (non-inverting input terminal in FIG. 3) of the operational amplifier 202 is connected to a reference power supply 203. A reference potential V1 is applied to the other input terminal of the operational amplifier 202 via the reference power supply 203. A constant voltage (e.g., ground potential) V0 is applied to one end of the reference power supply 203. The reference power supply 203 generates a voltage difference V1-V0 and supplies a potential (i.e., reference potential V1) that is higher than V0 by V1-V0 to the other input terminal of the operational amplifier 202. The reference power supply 203 can change the voltage it generates via a control unit of the plasma processing apparatus. That is, the reference potential V1 supplied to the other input terminal of the operational amplifier 202 is changed by controlling the reference power supply 203.

[0039] The output terminal of the operational amplifier 202 is connected to one of its input terminals via a feedback resistor R2. As a result, the operational amplifier 202, together with the resistors R1 and R2, constitutes an inverting amplifier circuit (detection circuit). The operational amplifier 202 amplifies the potential Vin of the probe electrode 162b within the operating voltage range of the operational amplifier 202, and outputs the amplified voltage Vout to its output terminal. The voltage Vout is input to a signal analysis unit 121. Although not shown in FIG. 1, the signal analysis unit 121 is provided, for example, in a control unit of the plasma processing apparatus.

[0040] One input terminal of the operational amplifier 202 is virtually short-circuited to the other input terminal, so that the potential of the probe electrode 162b is controlled to the reference potential V1, which is the potential of the other input terminal of the operational amplifier 202, due to the effect of the virtual short-circuit.

[0041] According to the potential detection unit 200 of this embodiment, the reference potential V1 applied to the probe electrode 162b can be changed via the reference power supply 203. This allows the thickness of the sheath S to be changed according to the reference potential V1, thereby adjusting the detection sensitivity of the plasma potential detection sensor 160. For example, if the potential Vin of the probe electrode 162b during normal plasma discharge is low and the voltage Vout at the output terminal is expected to fall within a voltage range narrower than the operating voltage range of the operational amplifier 202 even during an expected abnormal discharge, the reference potential V1 can be increased by the reference power supply 203 to increase the detection sensitivity. On the other hand, if the potential Vin of the probe electrode 162b during normal plasma discharge is sufficiently high and the voltage Vout at the output terminal is near the upper or lower limit of the operating voltage range of the operational amplifier 202 during normal discharge, the voltage V1 can be decreased by the reference power supply 203 to decrease the detection sensitivity.

[0042] When the reference potential V1 is increased to increase the detection sensitivity, the potential Vin of the probe electrode 162b increases. When the reference potential V1 is decreased to decrease the detection sensitivity, the potential Vin of the probe electrode 162b decreases. The reference power supply 203 may be controlled to change the reference potential V1 so that the potential Vin of the probe electrode 162b falls within a predetermined voltage range.

[0043] 4 shows another example of the configuration of the potential detection unit 200. As shown in FIG. 4, in the operational amplifier 202, instead of the feedback resistor R2, a capacitor 205 may be connected between the output terminal and the inverting input terminal. In this case, the operational amplifier 202 forms an integrating circuit and amplifies the amount of charge induced in the probe electrode 162b. Then, a voltage corresponding to the amplified amount of charge is output to the output terminal.

[0044] (Control unit) The control unit 120 includes a signal analysis unit. The signal analysis unit determines whether the plasma state is normal or not based on the voltage output from the potential detection unit 200. If it is determined that the plasma state is not normal and is in an abnormal discharge state, a retry process, a cumulative plasma process, a maintenance determination, etc. may be performed. Note that it is not necessary to perform all of the retry process, the cumulative plasma process, and the maintenance determination, and one or more of these processes may be performed.

[0045] Methods for determining whether the plasma is in an abnormal discharge state include, but are not limited to, determining that an abnormal discharge state has occurred when the output voltage from the potential detection unit 200 exceeds a predetermined threshold voltage (or falls below the threshold voltage), or calculating the time average value of the output voltage from the potential detection unit 200 over a predetermined period based on the time series data of the output voltage from the potential detection unit 200, and determining that an abnormal discharge has been detected when the time average value exceeds a predetermined value.

[0046] (Device Control Unit) Although not shown, the device control unit 124 may also include a processing history storage unit, a retry processing unit, a cumulative plasma processing unit, and a maintenance determination function unit. In other words, 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 results obtained 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 cumulative plasma processing unit, and the maintenance determination unit. The processing history storage unit stores, as processing history data for the plasma processing apparatus 100, the temporal change in the output voltage from the potential detection unit 200, which is temporarily recorded in memory, and intermediate data required by the signal analysis unit to determine the detection of abnormal discharge. This allows detailed processing history data to be obtained for the processing object 109 processed by the plasma processing apparatus 100, ensuring traceability for quality control and production management. [Industrial Applicability]

[0047] The plasma potential measuring device and method according to the present invention can be applied to a plasma processing apparatus. [Explanation of symbols]

[0048] 100: Plasma processing device 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: Processing object 110: Grounding part 111: Pipeline 112: Vent valve 113: Gas supply valve 114: Vacuum valve 115: Vacuum gauge 116: Gas supply unit 117: Vacuum pump 118: Matching box 119: High frequency power supply section 120: Control unit 121: Signal analysis section 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: Shield electrode 162d: Detection lead 170: Support member 200: Potential detection unit 201: Input terminal 202: Operational amplifier 203: Reference power supply

Claims

1. a detection electrode disposed opposite to the plasma generated in the chamber, in which a charge corresponding to the potential of the plasma is induced; a potential changing circuit for changing the reference potential of the detection electrode; a detection circuit that detects the amount of charge or potential induced in the detection electrode.

2. 2. The plasma potential measuring device according to claim 1, wherein the potential changing circuit is virtually short-circuited to the detection electrode.

3. the detection circuit includes an operational amplifier; one input terminal of the operational amplifier is connected to the detection electrode; 3. The plasma potential measuring device according to claim 1, wherein the detection electrode is virtually short-circuited to the other input terminal of the operational amplifier.

4. a constant voltage equal to the reference potential is applied to the other input terminal of the operational amplifier; 4. The plasma potential measuring device according to claim 3, wherein the potential changing circuit is capable of changing the voltage applied to the other input terminal of the operational amplifier.

5. 1. A plasma potential measuring device comprising: a detection electrode disposed opposite to plasma generated in a chamber, in which a charge corresponding to the potential of the plasma is induced; detecting the amount of charge or potential induced in the detection electrode; and changing the reference potential of the detection electrode in accordance with the detected charge amount or potential.

6. the detection electrode is connected to one input terminal of an operational amplifier; one input terminal of the operational amplifier is virtually short-circuited to the other input terminal of the operational amplifier, 6. The plasma potential measuring method according to claim 5, wherein the reference potential is changed by changing the voltage applied to the other input terminal of the operational amplifier.

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