Control Method of Plasma Measurement System and Plasma Measurement System

Abstract

Provided are a control method for a plasma measurement system that measures the state of a plasma and a plasma measurement system. 【Solution means】A control method for a plasma measurement system that measures the state of a plasma using a probe device provided in a plasma processing apparatus and a measurement circuit including a signal transmitter that outputs an alternating voltage, the method comprising: (A) a step of outputting a fundamental voltage from the signal transmitter to the plasma to be measured; (B) a step of detecting an output terminal alternating voltage at an output terminal of the signal transmitter; and (C) a step of superimposing a voltage of a harmonic voltage component that reduces the amplitude of the harmonic voltage component included in the output terminal alternating voltage on the fundamental voltage and outputting the voltage from the signal transmitter.

Description

Technical Field

[0001] The present disclosure relates to a method for controlling a plasma measurement system and a plasma measurement system.

Background Art

[0002] In Patent Document 1, an antenna unit attached to an opening formed in a wall of a processing container or a mounting table via a seal member that seals between a vacuum space and an atmospheric space, an electrode connected to the antenna unit, and a dielectric support portion formed of a dielectric and supporting the antenna unit from the periphery are provided. The opposing surface between the antenna unit and the wall or the mounting table is isolated by a predetermined width, and the surface of the antenna unit exposed from the opening is recessed more than the surface on the plasma generation space side of the wall or the mounting table in which the opening is formed. A plasma probe device is disclosed.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] On one aspect, the present disclosure provides a method for controlling a plasma measurement system and a plasma measurement system that measures the state of a plasma.

Means for Solving the Problems

[0005] To solve the above problems, according to one aspect, there is provided a control method for a plasma measurement system that measures the state of plasma using a probe device provided in a plasma processing apparatus and a measurement circuit including a signal generator that outputs an alternating voltage, the method comprising: (A) a step of outputting a fundamental voltage from the signal generator to the plasma to be measured; (B) a step of detecting an output terminal alternating voltage at an output terminal of the signal generator; and (C) a step of superimposing a voltage of a harmonic voltage component that reduces an amplitude of the harmonic voltage component included in the output terminal alternating voltage on the fundamental voltage and outputting the voltage from the signal generator.

Effect of the Invention

[0006] According to one aspect, it is possible to provide a control method for a plasma measurement system that measures the state of plasma and a plasma measurement system.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Mode for Carrying Out the Invention

[0008] Hereinafter, embodiments for carrying out the present disclosure will be described with reference to the drawings. In each drawing, the same reference numerals are assigned to the same components, and duplicate descriptions may be omitted.

[0009] [Plasma Processing Apparatus] FIG. 1 shows an example of a cross-sectional view of a plasma processing apparatus 100 according to an embodiment of the present invention. The plasma processing apparatus 100 has a processing container 1 that houses a substrate W, such as a semiconductor wafer, as an example. The plasma processing apparatus 100 is an example of a plasma processing apparatus that performs plasma processing on the substrate W using surface waves formed on the lower surface of the top wall 10 of the processing container 1 by microwaves. Examples of plasma processing include film formation processing, etching processing, or ashing processing using plasma.

[0010] The plasma processing apparatus 100 has a processing container 1, a microwave plasma source 2, and a control device 3. The processing container 1 is a substantially cylindrical container made of a metal material such as aluminum or stainless steel that is configured to be airtight and is grounded.

[0011] The processing container 1 has a top wall 10 and forms a space (plasma generation space U) for plasma processing the substrate W inside. The top wall 10 is disk-shaped and is a lid that closes the upper opening of the processing container 1. A support ring 129 is provided on the contact surface between the processing container 1 and the top wall 10, whereby the inside of the processing container 1 is airtightly sealed. The top wall 10 is formed of a metal material such as aluminum or stainless steel.

[0012] The microwave plasma source 2 includes a microwave output unit 30, a microwave transmission unit 40, and a microwave radiation mechanism 50. The microwave output unit 30 outputs microwaves by distributing them to a plurality of paths. The microwaves are introduced into the interior of the processing vessel 1 through the microwave transmission unit 40 and the microwave radiation mechanism 50. The gas supplied into the processing vessel 1 is excited by the electric field of the introduced microwaves, thereby forming a surface wave plasma.

[0013] A mounting table 11 for mounting the substrate W is provided inside the processing vessel 1. The mounting table 11 is supported by a cylindrical support member 12 erected at the center of the bottom of the processing vessel 1 via an insulating member 12a. Examples of the materials constituting the mounting table 11 and the support member 12 include metals such as aluminum whose surfaces are subjected to alumite treatment (anodic oxidation treatment), and insulating members (such as ceramics) having electrodes for high frequencies inside. The mounting table 11 may be provided with an electrostatic chuck for electrostatically attracting the substrate W, a temperature control mechanism, a gas flow path for supplying a gas for heat transfer to the back surface of the substrate W, and the like.

[0014] A high-frequency bias power supply 14 is connected to the mounting table 11 via a matcher 13. When high-frequency power is supplied from the high-frequency bias power supply 14 to the mounting table 11, ions in the plasma are drawn to the substrate W side. Note that the high-frequency bias power supply 14 may not be provided depending on the characteristics of the plasma treatment.

[0015] An exhaust pipe 15 is connected to the bottom of the processing vessel 1, and an exhaust device 16 including a vacuum pump is connected to the exhaust pipe 15. When the exhaust device 16 is operated, the interior of the processing vessel 1 is evacuated, whereby the interior of the processing vessel 1 is rapidly decompressed to a predetermined degree of vacuum. An carry-in / out port 17 for carrying in and out the substrate W and a gate valve 18 for opening and closing the carry-in / out port 17 are provided on the side wall of the processing vessel 1.

[0016] The microwave transmission unit 40 transmits the microwave output from the microwave output unit 30. FIG. 2 shows the A-A cross-section of FIG. 1 and shows an example of the lower surface of the top wall of the plasma processing apparatus 100. Referring to FIG. 2, the central microwave introduction unit 43b in the microwave transmission unit 40 is disposed at the center of the top wall 10, and the six peripheral microwave introduction units 43a are disposed at equal intervals in the circumferential direction around the top wall 10. The central microwave introduction unit 43b and the six peripheral microwave introduction units 43a respectively have the function of introducing the microwave output from the amplifier unit 42 shown in FIG. 1 into the microwave radiation mechanism 50 and the function of matching the impedance. Hereinafter, the peripheral microwave introduction unit 43a and the central microwave introduction unit 43b are also collectively referred to as the microwave introduction unit 43.

[0017] As shown in FIGS. 1 and 2, the six dielectric windows 123 on the outer peripheral side are disposed inside the top wall 10 below the six peripheral microwave introduction units 43a. Also, the one central dielectric window 133 is disposed inside the top wall 10 below the central microwave introduction unit 43b. Note that the number of the peripheral microwave introduction units 43a and the dielectric windows 123 is not limited to six and may be two or more. However, the number of the peripheral microwave introduction units 43a is preferably three or more, and may be, for example, three to six.

[0018] The microwave radiation mechanism 50 shown in FIG. 1 includes the retarder plates 121, 131, the slots 122, 132, and the dielectric windows 123, 133. The retarder plates 121, 131 are formed of a disk-shaped dielectric that transmits microwaves and are disposed on the upper surface of the top wall 10. The retarder plates 121, 131 are formed of, for example, ceramics such as quartz and alumina (Al2O3), a fluororesin such as polytetrafluoroethylene, or a polyimide resin, whose relative dielectric constant is larger than that of a vacuum. Thereby, the retarder plates 121, 131 have the function of shortening the wavelength of the microwave passing through the inside of the retarder plates 121, 131 to be shorter than the wavelength of the microwave propagating in a vacuum and reducing the size of the antenna including the slots 122, 132.

[0019] Below the retardation plates 121 and 131, the dielectric windows 123 and 133 are abutted against the back surface of the opening of the ceiling wall 10 through the slots 122 and 132 formed in the ceiling wall 10. The dielectric windows 123 and 133 are formed of, for example, ceramics such as quartz and alumina (Al₂O₃), fluororesins such as polytetrafluoroethylene, and polyimide resins. The dielectric windows 123 and 133 are provided at positions recessed from the ceiling surface by the thickness of the opening formed in the ceiling wall 10, and supply microwaves to the plasma generation space U.

[0020] The peripheral microwave introduction part 43a and the central microwave introduction part 43b coaxially arrange a cylindrical outer conductor 52 and a rod-shaped inner conductor 53 provided at the center thereof. Between the outer conductor 52 and the inner conductor 53, microwave power is fed, and it serves as a microwave transmission path 44 through which microwaves propagate toward the microwave radiation mechanism 50.

[0021] The peripheral microwave introduction part 43a and the central microwave introduction part 43b are provided with a slug 54 and an impedance adjustment member 140 positioned at the tip thereof. By moving the slug 54, it has a function of matching the impedance of the load (plasma) in the processing container 1 to the characteristic impedance of the microwave power source in the microwave output part 30. The impedance adjustment member 140 is formed of a dielectric and adjusts the impedance of the microwave transmission path 44 according to its relative permittivity.

[0022] The ceiling wall 10 is provided with a gas introduction part 21 having a shower structure. The gas supplied from the gas supply source 22 passes through the gas introduction part 21 from the gas diffusion chamber 62 through the gas supply pipe 111 and is supplied in a shower shape into the processing container 1. The gas introduction part 21 is an example of a gas shower head that supplies gas from a plurality of gas supply holes 60 formed in the ceiling wall 10. Examples of the gas include, for example, a plasma generation gas such as Ar gas, a gas that is desired to be decomposed with high energy such as O₂ gas and N₂ gas, and a processing gas such as silane gas.

[0023] Each part of the plasma processing apparatus 100 is controlled by the control device 3. The control device 3 includes a microprocessor 4, a ROM (Read Only Memory) 5, and a RAM (Random Access Memory) 6. The ROM 5 and RAM 6 store the process sequence and process recipe, which are the control parameters of the plasma processing apparatus 100. The microprocessor 4 controls each part of the plasma processing apparatus 100 based on the process sequence and process recipe. The control device 3 also has a communication interface (I / F) 7, enabling communication with other devices. Furthermore, the control device 3 has a display 8, which can display the results of predetermined control operations performed according to the process sequence and process recipe.

[0024] When performing plasma processing in the plasma processing apparatus 100 with the above configuration, first, the substrate W is carried into the processing container 1 through the opening gate valve 18 and the loading port 17 while being held on a transport arm (not shown). When the substrate W is transported to above the mounting table 11, it is transferred from the transport arm to a pusher pin, and the pusher pin descends to place it on the mounting table 11. The gate valve 18 is closed after the substrate W has been loaded. The pressure inside the processing container 1 is maintained at a predetermined vacuum level by the exhaust device 16. Processing gas is introduced into the processing container 1 in a shower-like manner from the gas introduction section 21. Microwaves emitted from the microwave radiation mechanism 50 via the microwave introduction section 43 propagate near the bottom surface, which is the inner surface of the top wall 10. The electric field of the surface wave microwaves excites the gas, and the substrate W is subjected to plasma processing by the surface wave plasma generated in the plasma generation space U below the top wall 10 inside the processing container 1.

[0025] [Probe device] The description of the probe device 70 will continue with reference to Figures 1 and 3. Figure 3 is a diagram showing an example of the functional configuration of a measurement system and control device according to one embodiment. As shown in Figure 1, one or more openings 1b are formed in the circumferential direction on the side wall of the processing container 1, and one or more probe devices 70 are attached via sealing members (not shown) that seal the space between the vacuum space and the atmospheric space.

[0026] A gap of a predetermined width is formed between the tip surface of the probe device 70 and the back surface near the opening 1b in the wall of the processing container 1. This gap is designed to be wide enough so that the probe device 70 is not DC-connected to the wall of the processing container 1, but narrow enough so that plasma or gas does not enter. However, the probe device 70 may also be attached to the mounting base 11 via a sealing member through an opening formed therein.

[0027] As shown in Figure 3, the measurement system for measuring the plasma state consists of a probe device 70 and a measurement circuit 85. The measurement circuit 85 includes a monitor device 80, a blocking capacitor 72, and a coaxial cable 81. The monitor device 80 is communicated to the control device 3.

[0028] The probe device 70 is connected to the monitor device 80 via a coaxial cable 81 outside the plasma processing device 100. The monitor device 80 has a signal transmitter 82, which outputs an AC voltage signal of a predetermined frequency to the coaxial cable 81. The AC voltage signal is transmitted through the coaxial cable 81, and the AC voltage is applied to the probe device 70. A blocking capacitor 72 is connected to the coaxial cable 81 and transmits the AC voltage signal to the probe device 70, blocking the DC voltage signal. As a result, the monitor device 80 receives only the AC voltage signal from the plasma side.

[0029] The probe device 70 senses the plasma generated in the plasma generation space U. The probe device 70 detects the current signal flowing to the plasma side with respect to the signal transmitted to the plasma side, and transmits it to the monitor device 80. The current signal flowing to the plasma side is transmitted from the monitor device 80 to the control device 3 and received by the communication unit 32 of the control device 3. The current value of the received signal is stored in the storage unit 31. The analysis unit 34 of the control unit 33 performs FFT (Fast Fourier Transform) analysis on the current value of the received signal. The calculation unit 35 of the control unit 33 calculates the plasma electron temperature Te and the plasma ion density ni based on the analysis result. Thereby, the plasma state can be accurately estimated. Thus, the plasma measurement system for measuring the plasma state includes the probe device 70, the measurement circuit 85, and the control device 3 (control unit 33).

[0030] Note that the storage unit 31 is realized by the RAM 6 shown in FIG. 1. The communication unit 32 is realized by the communication interface 7. The analysis unit 34 and the calculation unit 35 of the control unit 33 are realized by the microprocessor 4.

[0031] FIG. 4 is a flowchart showing an example of the control method of the plasma processing apparatus 100.

[0032] In step S101, substrate processing is performed. Here, the control device 3 controls the gas supply source 22 to supply a processing gas (film-forming gas, etching gas, etc.) from the gas supply hole 60 to the plasma generation space U, and controls the microwave output unit 30 and the high-frequency bias power supply 14 to generate plasma of the processing gas in the plasma generation space U, and performs a desired process (film-forming process, etching process, etc.) on the substrate W. At this time, an AC voltage is applied to the probe device 70 from the signal transmitter 82, and the probe device 70 senses the plasma generated in the plasma generation space U. Then, the control unit 33 calculates the plasma electron temperature Te and the plasma ion density ni, and estimates the plasma state.

[0033] Here, when the substrate processing is a process of forming an insulating film on the substrate W, an insulator (for example, SiN, SiO₂, etc.) is also deposited on the surface exposed to the plasma generation space U of the probe device 70 (such as the tip surface of the probe device 70) to form an insulating film. Note that the substrate processing is not limited to the film formation process of the insulating film, and an insulator is formed as a reaction by-product, and a process (for example, etching process, etc.) in which the reaction by-product (insulator) is deposited on the surface exposed to the plasma generation space U of the probe device 70 to form an insulating film may also be used.

[0034] In step S101, the substrate processing is repeated until the cleaning start conditions such as a predetermined number of processed sheets and processing time are satisfied. When the predetermined cleaning start conditions are satisfied, the processing of the control device 3 proceeds to step S102.

[0035] In step S102, a cleaning process (dry cleaning process: a cleaning process using a cleaning gas without opening the processing container to the atmosphere) is performed. Here, the control device 3 controls the gas supply source 22 to supply a cleaning gas containing fluorine (F) (for example, NF₃, etc.) from the gas supply hole 60 to the plasma generation space U, and controls the microwave output unit 30 and / or the high-frequency bias power supply 14 to generate a plasma of the cleaning gas in the plasma generation space U, and removes the insulating film deposited in the processing container 1. Also, the insulating film deposited on the surface exposed to the plasma generation space U of the probe device 70 is removed.

[0036] Here, in the cleaning process, a fluoride having conductivity adheres and deposits on the surface exposed to the plasma generation space U of the probe device 70 to form a conductive deposition film. The fluoride having conductivity is, for example, a metal fluoride (for example, AlF) containing a metal (for example, Al) derived from the inner wall of the processing container 1, dielectric windows 123, 133 formed of alumina (Al₂O₃), etc. and fluorine (F) derived from the cleaning gas. The deposited metal fluoride has conductivity due to having lattice defects.

[0037] In step S103, it is determined whether to end the repetition. If the repetition is not ended (S103·NO), the process of the control device 3 returns to step S101, and the substrate process and the cleaning process are repeated. If the repetition is ended (S103·YES), the process of the control device 3 is ended. Also, a cleaning process (wet cleaning: a cleaning process in which the processing container is opened to the atmosphere) or the like is performed.

[0038] Here, an example of measuring the plasma state will be described. FIG. 5 is a graph showing an example of a reception signal received from the plasma side.

[0039] FIG. 5(a) is a graph showing an example of raw data of a reception signal detected by the probe device 70 and received by the monitor device 80. The horizontal axis represents time, and the vertical axis represents the intensity (current value) of the reception signal. As shown in FIG. 5(a), the monitor device 80 receives the reception signal 200 from the probe device 70.

[0040] FIG. 5(b) is a graph showing an example of the analysis result of the analysis unit 34 of the control unit 33. The analysis unit 34 performs FFT (Fast Fourier Transform) analysis on the current value of the reception signal 200. Thereby, the reception signal 200 is decomposed into frequency components such as a fundamental wave component (first harmonic component) 201, a second harmonic component 202, a third harmonic component 203, a fourth harmonic component 204, and the like. Then, the calculation unit 35 of the control unit 33 calculates the plasma electron temperature Te and the plasma ion density ni based on the FFT analysis result. Thereby, the plasma state is measured. Note that the calculation of the plasma electron temperature Te and the plasma ion density ni is calculated based on the fundamental wave component 201 and the second harmonic component 202 as will be described later.

[0041] [Method for Measuring Plasma State] Next, a method for measuring the plasma electron temperature Te and the plasma ion density ni will be described using FIG. 6. FIG. 6 is an example of a circuit model of the measurement system.

[0042] As shown in FIG. 6, the probe device 70 has a capacitance component C due to the deposition of an insulating film. Let the voltage of the insulating film (capacitance component C) be Vc and the voltage of the plasma be Vp. Further, the monitor device 80 has a voltage measurement unit (not shown) that measures the voltage (output terminal AC voltage) supplied to the plasma at the output terminal of the signal transmitter 82 and a current measurement unit (not shown) that measures the current. Here, R0 is a resistor for measuring the current, the resistance value is known, and it is sufficiently small compared to the resistance value of the plasma. By measuring the voltage across both ends of R0, the current supplied to the plasma is measured.

[0043] Here, by regarding the plasma as a pure resistor (phase difference 0°) and the insulating film as having a capacitance component C with a phase difference of 90°, it is possible to separately estimate the thickness of the insulating film (capacitance component C) and the state of the plasma (plasma electron temperature Te, plasma ion density ni).

[0044] The current I flowing through the circuit model can be expressed by the following equation using the plasma voltage Vp. Here, Iis is the ion saturation current, Ies is the electron saturation current, Vf is the floating voltage, φp is the plasma voltage, Te is the plasma electron temperature (in eV units), ne is the plasma electron density, ni is the plasma ion density, S is the probe area. Also, Mi is the ion mass (in kg units), and me is the electron mass (in kg units).

[0045]

Equation

[0046] Next, let \(V_p = V_0=A\cos\omega t\). Here, \(A\) is the amplitude of the alternating voltage output by the signal generator 82. The expression for the current \(I\) flowing through the circuit model described above is transformed using the first-kind modified Bessel function \(I_k(x)\). Thereby, the expression for the current \(I\) is decomposed into frequency components.

[0047]

Number

[0048] Here, the information on the plasma electron density \(n_e\) is only included in the coefficients (\(I_{es}\)) of each frequency component. Therefore, by dividing the fundamental wave current \(i_{1\omega}\) by the second harmonic current \(i_{2\omega}\), the plasma electron density \(n_e\) is removed from the equation.

[0049]

Number

[0050] The plasma electron temperature \(T_e\) is calculated from the above equation.

[0051] Also, the plasma ion density \(n_i\) can be expressed by the following equation. The plasma ion density \(n_i\) can be calculated using the following equation, the calculated plasma electron temperature \(T_e\), and the fundamental wave current \(i_{1\omega}\).

[0052]

Number

[0053] [Measurement method of plasma state considering parasitic capacitance] FIG. 7 is an example of a circuit model of a measurement system including parasitic capacitance (stray capacitance). FIG. 8 is an example of a vector diagram showing current vectors and voltage vectors.

[0054] The voltage Vtotal is the voltage measured by a voltage measurement unit (not shown) of the monitor device 80. The current Itotal is the current measured by a current measurement unit (not shown) of the monitor device 80. The voltage Vplasma is the voltage of the plasma. The current Iplasma is the current of the plasma. The voltage Vplasma and the current Iplasma are used when measuring the state of the plasma (plasma electron temperature Te, plasma ion density ni).

[0055] Here, the circuit includes a series capacitance Cadd in series with the signal transmitter 82 and a parasitic capacitance Cstray in parallel with the signal transmitter 82. Therefore, there is a deviation between the plasma voltage Vplasma and current Iplasma used when measuring the state of the plasma (plasma electron temperature Te, plasma ion density ni) and the voltage Vtotal and current Itotal measured by the monitor device 80.

[0056] The parasitic capacitance Cstray in parallel with the signal transmitter 82 is dominated by the component that leaks from the capacitance existing on a circuit such as the coaxial cable 81 to the ground voltage (GND). Therefore, it occurs regardless of the presence or absence of the plasma. Thus, in the extinguished state of the plasma, the current Istray is measured from the current Itotal measured by a current measurement unit (not shown) of the monitor device 80.

[0057] And in the plasma ignition state, as shown in Fig. 8(a), the current Itotal is represented by the vector sum of the current Iplasma and the current Istray. Therefore, the current vector of the plasma current Iplasma can be calculated by calculating the current vector difference obtained by subtracting the current vector of the pre-measured current Istray from the current vector of the current Itotal measured by the current measurement unit (not shown) of the monitor device 80.

[0058] The series capacitor Cadd in series with the signal transmitter 82 represents series capacitance components such as the capacitor placed in the probe device 70 for insulation and the insulating film (such as SiN) formed by deposits. When the current Iplasma flows, a voltage Vadd that is 90 degrees delayed from the current Iplasma is generated. It is assumed that the influence of the parallel parasitic capacitance Cstray on the plasma is sufficiently small. Also, it is assumed that the plasma voltage Vplasma and the current Iplasma are in the same phase.

[0059] As shown in Fig. 8(b), the voltage Vtotal is represented by the vector sum of the voltage Vplasma and the voltage Vadd. Therefore, using the phase difference θ between the voltage Vplasma and the voltage Vtotal, the voltage Vplasma=Vtotal×cosθ can be calculated.

[0060] In this way, the calculation unit 35 can accurately calculate the plasma voltage Vplasma and current Iplasma by correcting (calibrating) the deviation caused by the series capacitance Cadd and the parasitic capacitance Cstray from the measured voltage Vtotal and current Itotal. As a result, the state of the plasma (plasma electron temperature Te, plasma ion density ni) can be accurately measured.

[0061] [Second harmonic current] Due to the non-linear current generated in the plasma, a higher-order voltage is generated across the capacitor inserted in the circuit model of the measurement system. Due to this effect, a higher-order current is superimposed on the plasma (see Fig. 5). Similar to the case of the fundamental wave (first harmonic) described using Figs. 7 and 8, since the vector of the total higher-order current and the vector of the generated higher-order current are orthogonal, it can be corrected (calibrated) by measuring the phase between the fundamental wave and the second harmonic currents.

[0062] Hereinafter, the second harmonic current will be described. Fig. 9 is an example of the circuit model of the measurement system in the second harmonic. Fig. 10 is an example of a vector diagram showing current vectors and voltage vectors.

[0063] The voltage Vplasma is the voltage obtained by dividing the voltage Vtotal (see Fig. 7) into the voltage Vadd and the voltage Vplasma, provided that the voltage Vplasma is only the fundamental wave voltage. That is, the signal generator 82 outputs the fundamental wave voltage. Therefore, in the circuit model of the measurement system in the second harmonic shown in Fig. 9, the signal generator 82 is not present.

[0064] The voltage V2,plasma is the second harmonic voltage applied to the plasma required to flow the current I2,cancel described later through the plasma.

[0065] The current I2,plasma is a second harmonic current derived by applying the voltage Vplasma to the plasma. This is generated because the current response in the plasma is non-linear.

[0066] The voltage V2,plasma,add is a second harmonic voltage generated by the second harmonic current I2,plasma flowing through the series capacitor Cadd. The voltage V2,plasma,add can be expressed by the following equation. Vx,plasma,add=I2,plasma×(1 / iωCadd)

[0067] The voltage V2,cancel is a voltage generated by the newly flowing second harmonic current I2,cancel to cancel the required voltage V2,plasma,add according to Kirchhoff's law. The voltage V2,cancel can be expressed by the following equation. V2,cancel=-V2,plasma,add

[0068] The current I2,cancel is a second harmonic current flowing to generate the voltage V2,cancel. The current I2,cancel can be expressed by the following equation. Let the pure resistance of the plasma be Rp. Note that the current I2,cancel also flows through the series capacitor Cadd, so a voltage is also generated there. I2,cancel=V2,cancel / (1 / iωCadd+Rp) =-I2,plasma×(1 / iωCadd) / (1 / iωCadd+Rp)

[0069] The current I2,total is the amount of the second harmonic current flowing through the entire circuit, and is the sum of the current I2,plasma and the current I2,cancel. That is, the current I2,total can be expressed by the following equation. I2,total=I2,plasma+I2,cancel =I2,plasma×(Rp) / (1 / iωCadd+Rp)

[0070] Here, since the current I2,total corresponds to the real part when the current I2,plasma is expressed in the complex space, it can be expressed by the following equation. I2,plasma=I2,total / cosθ

[0071] Here, the current I2,plasma is the second harmonic current generated by the fundamental wave voltage Vplasma calculated by the above-mentioned equation. Therefore, the second harmonic current I2,plasma is in the same phase as the fundamental wave current Iplasma. Therefore, the phase θ represents the phase difference between the fundamental wave current and the second harmonic current.

[0072] Also, I2,total=I2,plasma+I2,cancel I2,total(1 / iωCadd+Rp)=(I2,plasma+I2,cancel)(1 / iωCadd+Rp) I2,total(1 / iωCadd+Rp)=I2,plasma×Rp This results in the following. Thus, it shows that the current I2,total is the current where the current I2,cancel and the current I2,plasma cancel each other out. Rp / (1 / iωCadd+Rp) represents the cosine of the phase angle θ of the current I2,total with respect to the current I2,plasma. The current I2,plasma is in the same phase as the plasma voltage Vplasma and in the same phase as the fundamental wave current I.

[0073] As described above, by accurately obtaining the fundamental wave current and the second harmonic current, the state of the plasma (plasma electron temperature Te, plasma ion density ni) can be accurately obtained.

[0074] [Control of Second Harmonic Current] In the circuit model of the measurement system in the second harmonic shown in FIG. 9, it was described assuming that it does not have the signal generator 82. In other words, the harmonic voltage components (second harmonic voltage component, third harmonic voltage component, fourth harmonic voltage component,...) measured by the voltage measurement unit of the monitor device 80 were described as being zero.

[0075] Here, the signal transmitter 82 has a signal generation unit that generates a signal with a small amplitude, and an amplification unit that amplifies and outputs the signal with a small amplitude generated by the signal generation unit. For the amplification unit, for example, an operational amplifier or the like is used. Thereby, the signal transmitter 82 controls the amplitude of the fundamental wave (first harmonic) by the amplification unit.

[0076] Also, by applying a fundamental wave voltage from the signal transmitter 82 to the plasma, a second harmonic current flows through the circuit due to the non-linear current generated in the plasma. Therefore, a second harmonic voltage is generated by the resistance component (internal impedance) of the amplification unit of the signal transmitter 82 and the second harmonic current flowing through the circuit. Therefore, in the voltage measurement unit of the actual monitor device 80, the second harmonic voltage is measured.

[0077] Here, by regarding the plasma as a pure resistor (phase difference 0°) and the insulating film having a capacitance component C with a phase difference of 90°, the thickness of the insulating film (capacitance component C) and the state of the plasma (plasma electron temperature Te, plasma ion density ni) can be separated and estimated. On the other hand, the amplification unit of the signal transmitter 82 is arranged in series with the plasma, and it is difficult to separate the second harmonic voltage in the amplification unit and the second harmonic voltage of the plasma.

[0078] Therefore, the signal transmitter 82 of the present embodiment superimposes the fundamental wave voltage and a second harmonic voltage (generated second harmonic) that cancels the second harmonic voltage in the amplification unit of the signal transmitter 82, and applies it to the plasma. Thereby, since the apparent voltage of the second harmonic voltage in the amplification unit of the signal transmitter 82 can be set to zero [V], it is possible to prevent the unnecessary second harmonic voltage caused by the non-linear current (second harmonic current) generated in the plasma and the resistance component of the amplification unit from being applied to the plasma. Thereby, using the processes shown in FIGS. 6 to 10, the state of the plasma can be accurately measured.

[0079] FIG. 11 is a diagram showing an example of a voltage vector. As shown in FIG. 11(a), when the double-frequency current generated by the plasma flows through the amplifier section, a double-frequency voltage vector 500 is generated. As shown in FIG. 11(b), the monitor device 80 controls the signal transmitter 82 to generate a double-frequency voltage vector (generated double frequency) 510 that cancels the double-frequency voltage vector 500. Thereby, the apparent voltage of the double-frequency voltage can be set to zero [V].

[0080] Here, when the amount of double-frequency current flowing through the amplifier section of the signal transmitter 82 changes, the voltage in the amplifier section of the signal transmitter 82 also changes. Therefore, the generated double frequency controls the phase and amplitude by feedback control.

[0081] FIG. 12 is a diagram showing an example of feedback control. In FIGS. 12(a) to 12(c), a line 601 having a phase difference of ±π / 2 [rad] from the detected double frequency 600 is illustrated by a thin broken line. Also, a line 602 having a phase difference of π [rad] from the detected double frequency 600 is illustrated by a thick broken line.

[0082] First, the control unit 33 performs FFT (Fast Fourier Transform) analysis on the raw data of the received signal detected by the voltage measurement unit of the monitor device 80 (see FIG. 5(a)) by the analysis unit 34. Thereby, information on the phase (the direction of the vector of the detected double frequency 600) and amplitude (the length of the vector of the detected double frequency 600) of the double-frequency voltage (detected double frequency 600) is obtained. Note that the detected double frequency 600 corresponds to a composite vector of a voltage vector caused by the double-frequency current flowing from the plasma to the circuit flowing through the resistance component (internal impedance) of the amplifier section and a voltage vector of the double-frequency voltage (generated double frequency 610) generated by the signal transmitter 82.

[0083] Further, the control unit 33 acquires information on the phase (the direction of the vector of the generated second harmonic 610) of the second harmonic voltage (generated second harmonic 610) generated by the signal transmitter 82 from the signal transmitter 82. Note that the phase of the second harmonic voltage (generated second harmonic 610) is calculated from the fundamental wave phase. Further, the control unit 33 may acquire information on the amplitude (the length of the vector of the generated second harmonic 610) of the second harmonic voltage (generated second harmonic 610) generated by the signal transmitter 82 from the signal transmitter 82. Note that in the control described later, the apparent voltage of the second harmonic voltage is set to zero [V] by increasing or decreasing the amplitude of the generated second harmonic 610, and the information on the amplitude (the length of the vector of the generated second harmonic 610) of the second harmonic voltage (generated second harmonic 610) may not be acquired.

[0084] As shown in FIG. 12(a), when the phase difference between the detected second harmonic 600 and the generated second harmonic 610 is separated by π / 2 [rad] or more, the voltage (amplitude) of the generated second harmonic 610 is increased (arrow S11), and the phase of the generated second harmonic 610 is brought closer to the phase +π [rad] direction of the detected second harmonic 600 (arrow S12). In other words, while increasing the voltage (amplitude) of the generated second harmonic 610, the phase of the generated second harmonic 610 is changed in the direction away from the detected second harmonic 600 (the direction in which the phase difference increases). Thereby, the amplitude (the length of the vector of the detected second harmonic 600) of the detected second harmonic 600 can be reduced.

[0085] As shown in FIG. 12(b), when the phase difference between the detected second harmonic 600 and the generated second harmonic 610 is closer than π / 2 [rad], the voltage (amplitude) of the generated second harmonic 610 is decreased (arrow S21), and the phase of the generated second harmonic 610 is brought closer to the phase [rad] direction of the detected second harmonic 600 (arrow S22). In other words, while decreasing the voltage (amplitude) of the generated second harmonic 610, the phase of the generated second harmonic 610 is changed in the direction approaching the detected second harmonic 600 (the direction in which the phase difference decreases). Thereby, the amplitude (the length of the vector of the detected second harmonic 600) of the detected second harmonic 600 can be reduced.

[0086] As shown in Fig. 12(c), when the voltage of the generated second harmonic wave 610 is zero, the phase [rad] of the generated second harmonic wave 610 is set to the phase of the detected second harmonic wave 600 + π [rad], and the voltage (amplitude) of the generated second harmonic wave 610 is increased (arrow S31).

[0087] In addition, in the state shown in Fig. 12(b), even if the voltage (amplitude) of the generated second harmonic wave 610 is decreased, if the amplitude of the detected second harmonic wave 600 (the length of the vector of the detected second harmonic wave 600) does not become sufficiently small, eventually the voltage of the generated second harmonic wave 610 will become zero (see Fig. 12(c)), and a generated second harmonic wave 610 in the opposite direction to the detected second harmonic wave 600 will be generated. As a result, the state shown in Fig. 12(a) is reached. Then, by repeating the feedback control, the apparent voltage of the second harmonic wave in the amplifier section of the signal transmitter 82 can be made zero [V].

[0088] In the example of Fig. 12, the case of simultaneously performing feedback control on the phase and amplitude of the generated second harmonic wave 610 has been described as an example, but it is not limited to this.

[0089] Fig. 13 is a flowchart showing another example of feedback control.

[0090] In step S201, the detected second harmonic wave 600 and the generated second harmonic wave 610 are acquired. Here, the control unit 33 acquires at least the phase and amplitude of the detected second harmonic wave 600 and the phase of the generated second harmonic wave 610.

[0091] In step S202, the phases of the detected second harmonic wave 600 and the generated second harmonic wave 610 are made the same. Here, the control unit 33 controls the signal transmitter 82 to adjust the phase of the generated second harmonic wave 610 while maintaining the amplitude of the generated second harmonic wave 610, thereby making the phases of the detected second harmonic wave 600 and the generated second harmonic wave 610 the same (reducing the phase difference).

[0092] In step S203, the amplitude of the detected second harmonic wave 600 is acquired.

[0093] In step S204, it is determined whether the amplitude of the detected second harmonic wave 600 detected in step S203 has changed in the decreasing direction as compared to the amplitude of the detected second harmonic wave 600 detected in step S201.

[0094] If the amplitude of the detected second harmonic wave 600 has changed in the decreasing direction (S204·YES), the process of the control unit proceeds to step S205. In step S205, the amplitude of the generated second harmonic wave 610 is adjusted.

[0095] If the amplitude of the detected second harmonic wave 600 has not changed in the decreasing direction (S204·NO), the process of the control unit proceeds to step S206. In step S206, the phase of the generated second harmonic wave 610 is adjusted.

[0096] By repeating the control shown in FIG. 13, the apparent voltage of the second harmonic voltage in the amplifier section of the signal transmitter 82 can be set to zero [V].

[0097] As described above, the plasma processing apparatus 100 has been described. However, the present disclosure is not limited to the above-described embodiments and the like, and various modifications and improvements can be made within the scope of the gist of the present disclosure described in the claims.

Description of Reference Numerals

[0098] 33 Control unit 70 Probe device 72 Blocking capacitor 80 Monitor device 81 Coaxial cable 82 Signal transmitter 85 Measurement circuit 100 Plasma processing apparatus W Substrate U Plasma generation space

Claims

1. A control method for a plasma measurement system that measures the state of plasma using a probe device provided in a plasma processing apparatus and a measurement circuit including a signal generator that outputs an alternating voltage, comprising: (A) a step of outputting a fundamental wave voltage from the signal generator to the plasma to be measured; (B) a step of detecting an output terminal alternating voltage at an output terminal of the signal generator; (C) superimposing a voltage of a harmonic voltage component that reduces the amplitude of the harmonic voltage component included in the output terminal alternating voltage on the fundamental wave voltage and outputting from the signal generator. A control method for a plasma measurement system.

2. The harmonic voltage component is a second harmonic component. The control method for a plasma measurement system according to Claim 1.

3. The harmonic voltage component included in the output terminal alternating voltage is a detected second harmonic, and the voltage of the harmonic voltage component superimposed on the fundamental wave voltage is a generated second harmonic. The control method for a plasma measurement system according to Claim 2.

4. When the phase difference between the detected second harmonic and the generated second harmonic is π / 2 [rad] or more, increasing the amplitude of the generated second harmonic and moving the phase of the generated second harmonic away from the phase of the detected second harmonic. The control method for a plasma measurement system according to Claim 3.

5. When the phase difference between the detected second harmonic and the generated second harmonic is less than π / 2 [rad], decreasing the amplitude of the generated second harmonic and moving the phase of the generated second harmonic closer to the phase of the detected second harmonic. The control method for a plasma measurement system according to Claim 3.

6. When the amplitude of the generated second harmonic is zero, setting the phase of the generated second harmonic to the phase of the detected second harmonic + π [rad] and increasing the amplitude of the generated second harmonic. The control method for a plasma measurement system according to Claim 3.

7. Repeating the step (B) and the step (C). The control method for a plasma measurement system according to Claim 1.

8. A plasma measurement system including a probe device provided in a plasma processing apparatus and a measurement circuit including a signal generator that outputs an alternating voltage, and a control unit, for measuring the state of plasma, wherein the control unit (A) a step of outputting a fundamental wave voltage from the signal generator to the plasma to be measured; (B) a step of detecting an output terminal alternating voltage at an output terminal of the signal generator; Step of superimposing a voltage of a harmonic voltage component that reduces the amplitude of the harmonic voltage component included in the output terminal AC voltage on the fundamental voltage and outputting the same from the signal transmitter; configured to be executable; Plasma measurement system.

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