JP2007281205A - Plasma processor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology for easily setting measurements of voltage and phase to the predetermined target even under resonance phenomenon to be generated with electrostatic capacitance of ion sheath formed at the front surface of an electrode for capacitance coupling with plasma such as inductance, stray capacitance or wafer in the high frequency power feeding system. <P>SOLUTION: The plasma processor includes a lower electrode for setting a sample provided with a relevant vacuum vessel, a matching unit connected to the relevant lower electrode, and a power supply for feeding electrical power to the lower electrode via the relevant matching unit. In this plasma processor, an electrostatic chuck electrode for holding the sample and a voltage measuring circuit for measuring a voltage of the relevant electrostatic chuck electrode and outputting the voltage as a DC voltage are provided within the lower electrode. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention belongs to semiconductor manufacturing technology. In particular, the present invention relates to a plasma processing apparatus suitable for plasma processing of a semiconductor wafer using plasma.

  As semiconductor devices have been highly integrated in recent years, circuit patterns have been increasingly miniaturized, and the required processing dimension accuracy has become increasingly severe. In addition, the wafer diameter has been increased to 300 mm for the purpose of reducing the manufacturing cost of semiconductor devices, but for the purpose of increasing the yield, the plasma is made uniform in a wide range from the center of the wafer to the vicinity of the outer periphery and high quality is achieved. Therefore, it is required that uniform processing can be performed. In product processing, a high frequency bias is generally applied to form a fine circuit pattern by anisotropic processing. At this time, the values of the high-frequency voltage and self-bias voltage generated on the wafer are important parameters in processing, and it is important to accurately monitor them.

  In order to achieve such an object, conventionally, a high frequency voltage is detected between a wafer and a matching unit of a high frequency power source (for example, Patent Documents 1 and 2).

  Apart from this, the fact that the high-frequency transmission line affects the high-frequency voltage / current and phase difference is different in the high-frequency waveform at the output part of the high-frequency matching unit and the wafer, and therefore to obtain information on the potential of the wafer. In addition, it is known that a wafer potential probe method for directly measuring the wafer potential is effective (see, for example, Patent Document 3).

  Conventionally, in a parallel plate type plasma generating apparatus composed of an upper metal plate electrode and a lower wafer (operating as an electrode), a high frequency bias of the same frequency is applied to each of the upper electrode and the lower electrode (wafer). To do. In order to control the high-frequency voltage phase between the biases, a method of monitoring the voltage and phase of the upper electrode and the lower electrode is known (see, for example, Patent Document 4).

JP 2003-174015 A JP 2002-203835 A JP 2001-338917 A JP-A-8-162292

  In the plasma processing apparatus, a problematic phenomenon is resonance generated by the inductance and stray capacitance of a high-frequency power feeding system or the capacitance of an ion sheath formed on the front surface of an electrode capacitively coupled to plasma such as a wafer. The resonance due to the stray capacitance and the inductance of the power feeding system is independent from the resonance due to the electrostatic capacitance of the ion sheath and the inductance of the power feeding system. That is, two resonance phenomena occur simultaneously. This causes a problem that information such as the voltage obtained from the measurement point shows a value far from the state of voltage or the like actually generated on the wafer or electrode. The problem with the prior art is that essentially these resonance phenomena are not taken into account.

  The technique of Patent Document 1 clearly has a precondition that information obtained from a measurement point such as a voltage is the same as or the same as that of wafer information. If this precondition is broken, the accuracy of the present technology is significantly reduced.

  Patent Document 2 focuses on the fact that the precondition is broken in a general plasma processing apparatus. In this invention, by accurately specifying the equivalent circuit between the measurement point such as the voltage and the wafer, information such as the load voltage viewed from the wafer as well as the voltage, current, and phase of the wafer can be obtained from the measurement point information. Obtainable. However, even with this technology, the influence of the resonance phenomenon in question cannot be avoided. This is because the inductance component and the stray capacitance that cause resonance are incorporated in an equivalent circuit in the present technology, but the capacitance of the ion sheath to be paired is not incorporated in the equivalent circuit. This resonance phenomenon caused by plasma is an unpredictable phenomenon according to the present technology.

  Furthermore, it is very difficult and practically impossible to accurately evaluate the capacitance of the ion sheath by incorporating it in the equivalent circuit. This capacitance is determined by many parameters such as gas pressure / component and high frequency power for plasma generation (electron density, electron temperature, gas density, etc. and their distribution on the wafer) This is because the value cannot be accurately calculated because it is determined by the high frequency bias power applied to the wafer. Of course, there is a theory to calculate the capacitance, but it is not possible to know the exact value to be substituted into the theory. In other words, accuracy cannot be guaranteed.

  Further, the capacitance of the ion sheath is a large factor that determines the value of the load impedance as viewed from the wafer. The high-frequency voltage generated on the wafer is determined by the combination of the circuit from the matching circuit to the wafer and this load impedance. However, the capacitance of the ion sheath has the property that it is determined by the high-frequency voltage generated on the wafer. That is, the capacitance and the wafer voltage are in a non-linear relationship that they are interdependent. Therefore, the determination of the capacitance and the wafer voltage cannot be solved by a normal equivalent circuit simulation, and cannot be determined unless the convergence calculation by the numerical calculation method is performed. It is very difficult to perform this calculation in real time from the viewpoints of preparing the numerical values of the basic data for starting the calculation and the calculation time.

  The conclusion obtained from the above is that the resonance phenomenon which is a problem cannot be solved using the technique of using an equivalent circuit. Even if an equivalent circuit is used, the calculation cannot be performed or the accuracy cannot be guaranteed.

  In contrast to the technique of Patent Document 1 or 2 described above, the technique of Patent Document 3 is a technique for directly measuring the potential of the wafer, and in principle, a problematic resonance phenomenon can be avoided. However, this technology has a problem of reliability and is difficult to put into practical use. The present technology achieves direct measurement of the wafer voltage by piercing the oxide film or nitride film on the back surface of the wafer with a hard needle of WC (tungsten carbide). The problem is that in a semiconductor manufacturing apparatus that processes 500,000 to 1,000,000 wafers one after another, it cannot be guaranteed that the film on the back surface of the wafer is reliably broken to realize stable measurement. Designing such a structure is very difficult.

  Regarding the phase, it is well known that the phase greatly changes before and after the resonance point, and the phase is reversed in an extreme case. In this sense as well, even in the technique of phase control as in Patent Document 4, the resonance in question gives serious trouble to the control performance. The resonance in question is a phenomenon in which the inductance of the high-frequency transmission line and the capacitance of the ion sheath cause resonance, and not only the application of a high-frequency bias to the wafer but also the high frequency of the electrode facing the wafer as in Patent Document 4. This phenomenon occurs even when a bias is applied. Also in Patent Document 4, the resonance in question is not taken into consideration with respect to the phase measurement point, and it can be understood that the resonance phenomenon in question gives serious trouble as in Patent Documents 1-3.

  Hereinafter, the resonance phenomenon found by the inventors will be described in detail. Here, as an example, an electrode on which a wafer is mounted is taken up. However, these two resonance problems occur in exactly the same way for any electrode that is capacitively coupled to the plasma. First, the structure of the electrode is converted into an equivalent circuit, and voltage measurement (here, peak-to-peak voltage: Vpp) is taken as an example to explain that a resonance phenomenon can be seen without plasma. This is the first resonance, the resonance due to stray capacitance and the inductance of the high-frequency transmission system. Next, the resonance phenomenon when there is plasma will be described. This is the second resonance, that is, the resonance caused by the capacitance of the ion sheath and the inductance of the high-frequency transmission system. Exactly the same conclusions can be made regarding phase measurement.

The first resonance, the resonance due to the stray capacitance and the inductance of the high-frequency transmission system is shown. FIG. 1 schematically shows a block diagram of components configured from a wafer bias RF power source to electrodes. From the output of the wafer bias RF power source, a matching circuit, a Vpp detector, a power supply cable, and an electrode are configured in this order. The RF power supply to the power supply cable are in the atmosphere, and the electrode on which the wafer is mounted is in a vacuum. When the block diagram of FIG. 1 is replaced with an equivalent circuit, a circuit as shown in FIG. 2 is obtained. The power supply cable is a common coaxial line, and has an inductance (L1 + L2) of the central conductor and a stray capacitance (C1). The electrode is divided into a high-frequency transmission part (equivalent circuit is the same as the coaxial structure) and a sprayed film (C3 + R1) that electrostatically attracts the wafer. A high voltage probe (8 pF, 10 MΩ) for voltage measurement is connected to the wafer, but since the impedance is very high and can be ignored, it is not written in the equivalent circuit. The equivalent circuit of FIG. 2 is a general one, and the actual electrode has been devised in many ways such as a focus ring, and Cs1,
Because of the stray capacitance indicated by Cs2, it is more complicated than that of FIG.

  FIG. 3 shows the result of measuring frequency characteristics with the configuration of FIG. 1 using actual electrodes. The horizontal axis represents the frequency applied as a bias, and the vertical axis represents the voltage ratio at positions V1 and V2 in FIG. It can be seen that several resonance points appear above 4 MHz. Therefore, the inductance and capacitance of the electrodes were measured, and an equivalent circuit was created and simulated. This result is shown in FIG. 4, and it was found that the measured resonance phenomenon can be reproduced. This is the generally known resonance frequency

によって理解できる。図２の等価回路において、伝送線路のトータルのインダクタンス
Ｌｔは、約１.７μＨ 、伝送線路と電極のトータルの浮遊容量Ｃｔは、約９０８ｐＦであった。これを、前記式１に代入すると４.１ＭＨｚ となり、前記測定結果をよく説明する。しかし、共振現象そのものは、シミュレーションによって再現できるものの、電圧比は再現できていない。これは、実際の構造物の電気特性を、測定精度を保証できるだけの正確な等価回路に置き換えることがほとんど不可能なためである。

Can be understood. In the equivalent circuit of FIG. 2, the total inductance Lt of the transmission line is about 1.7 μH, and the total stray capacitance Ct of the transmission line and the electrode is about 908 pF. Substituting this into Equation 1 yields 4.1 MHz, which explains the measurement results well. However, although the resonance phenomenon itself can be reproduced by simulation, the voltage ratio cannot be reproduced. This is because it is almost impossible to replace the electrical characteristics of an actual structure with an accurate equivalent circuit that can guarantee measurement accuracy.

  As described above, if resonance occurs at 4 MHz, the reliability of voltage measurement when using a frequency lower than the resonance frequency (in this case, 2 MHz or more) depends on the resonance bandwidth (Q value). Sexuality decreases. It is important that the above-described inductance Lt and stray capacitance Ct are 1.7 μH and 908 pF, which are not so large values. When a high-frequency transmission line of several meters is connected to the electrode, the inductance and stray capacitance that are easily generated. According to the inventors' experience, this resonance phenomenon needs to be taken into account when using a bias having a frequency of 1 MHz or higher, although it depends on the design method and the device configuration.

Next, the second resonance, that is, the resonance due to the capacitance of the ion sheath and the inductance of the high frequency transmission system will be described. If there is a plasma, the wafer is capacitively coupled to the plasma. Therefore, it is necessary to consider a new capacitance due to the plasma. Furthermore, when there is plasma, it is conceivable that the resonance frequency may be further lowered than in the case of FIGS. This new capacitance is dominated by the capacitance of the ion sheath formed on the front surface of the wafer. The thickness d _sh of the ion sheath is theoretically given by the following equation.

ここで、λ_db：デバイ長、ｅ：素電荷、ｋ_B：ボルツマン定数、Ｔ_e：電子温度である。
Ｖ_sh：シースの平均電圧は次式で定義できる。

Here, lambda _db: Debye length, e: elementary charge, k _B: Boltzmann constant, T _e: is an electron temperature.
V _sh : The average voltage of the sheath can be defined by the following equation.

ここで、τ：バイアスの角周波数、Ｖ_s（τ）：プラズマ空間電位、Ｖ_B（τ）：バイアス電位である。

Here, τ: angular frequency of bias, V _s (τ): plasma space potential, and V _B (τ): bias potential.

The capacitance of the final ion sheath is calculated using the ion sheath thickness d _sh

である。ここで、ε₀：真空の誘電率、Ｓ_W：ウエハ面積である。

It is. Here, ε _{0 is} the dielectric constant of vacuum, and S _W is the wafer area.

  In Equation 4, since the wafer area is constant, it can be seen that the capacitance of the ion sheath is inversely proportional to the thickness of the ion sheath. That is, the condition for reducing the ion sheath thickness is equal to the condition for decreasing the resonance frequency. The Debye length is the basic length of the electric field shielding ability of the plasma, but it becomes shorter in inverse proportion to the plasma density. Even if the electron temperature is large in the plasma, only a few tens of percent changes. If this is ignored, the condition that the ion sheath thickness is reduced is that when the plasma density is high and the bias voltage is low. I know that there is. The conclusion obtained from this is that the resonance frequency in question is not constant, and even in the same apparatus, if the apparatus is different, it varies depending on the plasma generation conditions and the wafer processing conditions.

Usually, plasma used for processing semiconductor products has an electron temperature of about 3 eV and a plasma density of 10 ¹⁰ to 10 ¹² cm ⁻³ . The bias voltage is 100 to 4000 Vpp. The electrostatic capacity of the ion sheath obtained from this is about 200 to 8000 pF. This was used to simulate resonance. A schematic equivalent circuit is shown in FIG. This is obtained by adding a plasma load to the equivalent circuit of FIG. Here, when C5 = 2000 pF and R3 = 160Ω (value corresponding to a 300 mm wafer) were given as a typical plasma circuit, the result of FIG. 6 was obtained. From this, it was found that the resonance frequency decreased to 3 MHz. As can be seen from FIG. 6, there is C3 in series with C5, that is, the capacitance of the electrode sprayed film. It is the combined capacitance of C3 and C5 that causes resonance with the inductance (L1 to L4) of the transmission line. Here, if C3 = 7500 pF (corresponding to 300 mm wafer), the combined capacity is 1579.
pF. Substituting this value and 1.7 μH, which is the inductance Lt of the transmission line, into Formula 1, a value of 3.1 MHz is obtained, and the simulation results are well described. This indicates that the resonance frequency when there is plasma is determined by the combined capacitance of the capacitance of the ion sheath and the capacitance of the electrode sprayed film, and the inductance of the transmission line. Since the capacitance of the electrode sprayed film takes a value specific to the apparatus, it can be concluded that the resonance phenomenon itself is generated by the inductance of the transmission line and the capacitance of the ion sheath.

  This was actually verified using the device. FIG. 7 shows frequency characteristics when the wafer bias power source is output so that Vpp on the electrode is constant at 20V. As predicted from theory, the resonance frequency is extremely low, and in this case, it is 2 MHz or less. When the transmission line inductance Lt is calculated at 1.7 μH 2, the combined capacitance can be estimated to be about 4300 pF. In this case, since Vpp is extremely low, the capacitance of the sheath reaches about 10,000 pF. As described above, as the theoretical prediction shows, the resonance frequency greatly decreases when the bias voltage is low.

  The conclusions and problems obtained from the above are summarized. First, there are two resonance phenomena in question. The first is caused by the inductance and stray capacitance of the high-frequency transmission line. The second is generated by the inductance of the high-frequency transmission line and the capacitance of the ion sheath. By this principle, the resonance phenomenon itself cannot disappear. The resonance frequency derived from the electrostatic capacitance of the ion sheath has a strong dependence on the bias voltage and the plasma density, and varies greatly depending on the processing conditions of the wafer.

  From Equation 1, the lower the inductance and capacitance, of course, the higher the resonance frequency, which is more convenient. When the frequency of the high frequency used as the bias is in the vicinity of this resonance frequency, the voltage measurement value at the measurement point is far from the voltage actually generated on the wafer. Further, the ratio between the voltage at the measurement point and the voltage at the wafer varies depending on the wafer processing conditions and does not become a constant value. It is practically impossible to quantitatively calculate the voltage generated on the wafer by an equivalent circuit. The conclusion is the same for phase and current measurements.

  From past to present, the dimensions of semiconductor processing equipment such as wafers and liquid crystal substrates have increased. This is to reduce manufacturing costs. This trend depends on the development of technology but can be expected to continue. As described above, an increase in the size of a substrate such as a wafer, that is, an area increases the capacitance of the sheath, as shown in Equation 4, so that the resonance frequency is lowered. Therefore, the technology provided by the present invention will be an indispensable technology for the future application of high frequency in semiconductor manufacturing.

  An object of the present invention is to provide a technique that can easily set the measurement of voltage and phase to an arbitrary target accuracy even in the presence of the resonance phenomenon.

  In order to achieve the above object, the present invention is characterized in that a vacuum vessel, a lower electrode provided in the vacuum vessel for placing a sample, a matching unit connected to the lower electrode, and the matching unit In the plasma processing apparatus having a power supply for supplying power to the lower electrode, an electrostatic chuck electrode for holding the sample is measured inside the lower electrode, and a voltage of the electrostatic chuck electrode is measured and output as a DC voltage. And a voltage measuring circuit for performing the above.

  Further, a vacuum vessel, a lower electrode provided in the vacuum vessel and containing an electrostatic chuck electrode for holding a sample, a matching unit connected to the lower electrode, and the lower unit via the matching unit In a plasma processing apparatus having a power source for supplying power to an electrode, a voltage measuring circuit provided under atmospheric pressure for measuring a voltage of the electrostatic chuck electrode and outputting the voltage as a DC voltage, the electrostatic chuck electrode, and the voltage A coaxial line for connecting the measurement circuit is provided.

  According to the present invention, it is possible to realize a detection circuit that is not affected by the presence of resonance. Thereby, the high frequency voltage and the phase can be accurately detected. In addition, it is possible to stably operate the plasma processing apparatus in an optimum state.

  As described above, since resonance does not disappear and correction by calculation and calibration cannot be performed, the voltage and phase information at the electrode to be measured (electrode such as a wafer that is capacitively coupled to the plasma) can be solved. On the other hand, it can be seen that it is important to configure the apparatus so that the voltage and phase information at the measurement point are equivalent or homogeneous. Specifically, the detection circuit is configured not to be affected even if resonance exists.

Such a configuration can be achieved by incorporating the Vpp detector incorporated in the matching unit in FIGS. 1 and 2 into the electrode. This configuration is shown in FIG. With this configuration, the Vpp detector is not affected by the resonances L1 to L4 that generate resonance, and can directly convert the voltage generated at the electrode into a DC voltage and output it.

  A first embodiment embodying the structure of FIG. 8 is shown below.

FIG. 9 is a longitudinal sectional view of the etching chamber used in the present invention. In this example, VHF
It is an example of the VHF plasma etching apparatus which forms a plasma using (Very High Frequency) and a magnetic field. The vacuum container 101 includes a cylindrical processing container 104, a flat antenna electrode 103 made of a conductor such as aluminum or nickel, and an upper portion composed of a dielectric window 102 made of quartz or sapphire that can transmit electromagnetic waves. The opening is placed in an airtight manner via a vacuum seal material 127 such as an O-ring, and forms a processing chamber 105 therein. A magnetic field generating coil 114 is provided on the outer periphery of the processing vessel 104 so as to surround the processing chamber. The antenna electrode 103 has a porous structure for flowing an etching gas. Freon gas such as CF ₄ , C ₄ F ₆ , C ₄ F ₈ , C ₅ F ₈ , CHF ₃ , CH ₂ F ₂ , inert gas such as Ar and N ₂ , and oxidation containing gas such as O ₂ and CO Control is performed by a flow rate adjusting means (not shown) including an MFC (mass flow controller) provided in the gas supply device 107, and the gas supply device 107 introduces the gas into the processing chamber 105. Further, a vacuum evacuation device 106 is connected to the vacuum vessel 101, and a vacuum evacuation means (not shown) composed of a TMP (turbo molecular pump) installed in the vacuum evacuation device 106 and a pressure regulating means (not shown) composed of APC. Thus, the inside of the processing chamber 105 is held at a predetermined pressure.

A coaxial line 111 is provided above the antenna electrode 103, and a high-frequency power source (first high-frequency power source) 108 (for example, a frequency of 200 MHz) for plasma generation is provided via the coaxial line 111, the coaxial waveguide 125, and the matching unit 109. It is connected. A substrate electrode 115 on which a wafer 116 can be placed is provided in the lower part of the vacuum vessel 101. Similar to the antenna electrode 103, the substrate electrode 115 is provided with a coaxial line 151. A wafer bias power source (second high-frequency power source) is provided via the coaxial line 151, the coaxial waveguide 152, the power supply cable 153, and the matching unit 118. ) 119 (for example, frequency 4 MHz) is connected. The coaxial line 151 and the coaxial waveguide 152 are, for example, high-frequency transmission parts of the electrodes in FIG. 2 and are in a vacuum. The power supply cable 153 is on the atmospheric pressure side. The substrate electrode 115 also has an electrostatic chuck function for electrostatically attracting the wafer 116, and an electrostatic chuck power source 123 is connected via a filter 122 to the embedded electrostatic chuck electrode 124. Here, the filter 122 passes the DC power from the electrostatic chuck power source 123 and effectively cuts the power from the plasma generating high frequency power source 108 and the wafer bias power source 119.

  In this configuration, the wafer voltage measurement circuit 154 is built directly under the electrostatic chuck electrode 124 in vacuum. Thus, by directly attaching a measurement circuit to a place where a voltage to be measured is generated, converting it to a DC voltage on the spot and taking out the signal outside the vacuum, the influence of resonance is eliminated. Here, the combined impedance of C6 and C7 in the voltage measurement circuit 154 shown in FIG. 8 must be sufficiently high. How high it must be will be explained in the second embodiment. However, this method has several problems. These problems are as follows: (1) The electrical components used (resistors, capacitors, coils, diodes, etc.) are assumed to be used in the atmosphere, and performance is not guaranteed when used in a vacuum; (2 ) Heat generation from electrical parts is unavoidable, but since heat hardly escapes in vacuum, it cannot be used continuously. (3) Parts are likely to deteriorate due to corrosive gas. (4) Film deposition If it occurs, there is a high possibility that the circuit operation will be affected. (5) The circuit is likely to be damaged by the wraparound of the high frequency for plasma generation. (6) Similarly, the wraparound of the high frequency for plasma generation There is a high possibility that plasma is generated around the circuit and the circuit is damaged or the circuit operation is affected. All these problems are not unsolvable. For example, the entire voltage measurement circuit 154 is embedded with resin, the entire voltage measurement circuit 154 is housed in an airtight structure to protect it from corrosive gas, and the entire voltage measurement circuit 154 is housed in an airtight container capable of electromagnetic shielding. Can be solved.

  FIG. 10 shows a second embodiment that better solves the problem of the first embodiment.

  In this configuration, as in FIG. 9, the voltage measurement point is the electrostatic chuck electrode 124, but this voltage is taken out of the vacuum using the coaxial cable 157. The voltage taken out of the vacuum is converted into a DC voltage signal by using the voltage measurement circuit 154. The merit of this configuration is that the demerit of FIG. 9 disappears because the voltage measurement circuit 154 can be arranged on the atmospheric pressure side. Regarding voltage measurement, since the voltage of the electrostatic chuck electrode 124 and the voltage of the voltage measurement circuit 154 need only be equal, the above-described resonance phenomenon is irrelevant.

  In order to make the voltage of the electrostatic chuck electrode 124 equal to the voltage of the voltage measurement circuit 154, the coaxial cable 157 and the voltage measurement circuit 154 require special measures.

  An equivalent circuit of FIG. 10 is shown in FIG. The difference from FIG. 8 is that a coaxial cable is inserted between the electrode and the voltage measurement circuit. The special idea mentioned above is that the combined impedance Zs of the coaxial cable and the voltage measuring circuit must be sufficiently higher than the load impedance Zp including plasma. When Zs is small, a voltage drop due to Zs occurs, and there is a large reactive current, which increases the burden on the power transmission system. When the RF power source of FIG. 11 is controlled to output constant power, such a demerit does not become zero, but can be suppressed to a negligible level within an allowable range.

The relationship between Zp and Zs will be described in detail. When viewed from the RF power source of FIG. 11, Zp and Zs are connected in parallel as a load circuit. From this, the load impedance Z when Zs is not connected is Z = Zp, and when Zs is connected, Z ′ = Zp · Zs /
(Zp + Zs). On the other hand, V1 which is a voltage to be measured is determined by V1 = (WZ) ^ 0.5, where W is RF power when an RF power supply is used for power control. As a result, the ratio of the voltage V1 ′ when Zs is not connected to the voltage V1 when it is connected is V1 ′ / V1 = (Zs /
(Zp + Zs)) ^ 0.5. Here, if V1 ′ / V1 = α, then α is the accuracy of the voltage measurement value with the voltage measurement circuit connected. Therefore, α is a number from 0 to 1. From the above, the relationship between α and Zp, Zs is as follows.

この式より、例えば、電圧検出制度を９５％以上とする場合は、ＺｓはＺｐの９.３ 倍以上のインピーダンスを持つ必要があることが判る。また、電圧測定回路のＣ６，Ｃ７は抵抗に置き換えることも可能であるが、十分高い抵抗で無い限り（例えば１０ＭΩ以上）、抵抗で電力損失が生じるので、注意を要する。

From this equation, it can be seen that, for example, when the voltage detection system is 95% or more, Zs needs to have an impedance of 9.3 times or more of Zp. In addition, although it is possible to replace C6 and C7 of the voltage measuring circuit with resistors, power loss is caused by the resistors unless the resistors are sufficiently high (for example, 10 MΩ or more), so care must be taken.

This will be described with specific numerical values. The combined impedance Zp on the plasma side from the position of V1 in FIG. 11 is about | Zp | = 15Ω when calculated including C5 = 2000 pF, R3 = 160Ω and other constants.

  Next, the combined impedance Zs on the voltage measurement circuit side is obtained from the location of V1. From the viewpoint of withstand voltage, assuming a coaxial cable equivalent to 3D2V, the inductance and capacitance per unit length are 0.27 μH / m 2 and 103 pF / m, respectively. These correspond to L5, L6, and C9 in FIG. Here, assuming that the combined capacitance of C6 and C7 is 8 pF and the length of the coaxial cable is 1 m, Zs = −355 iΩ. Here, i is an imaginary number. Thus, | Zs / Zp | = 24, and the measurement accuracy can be sufficiently increased.

FIG. 12 shows an equivalent circuit simulation result when the above circuit constants are used. FIG.
(A) is a voltage ratio of V1 and V2 (described in FIG. 11) when the voltage measurement circuit is not connected, and is the same result as FIG. FIG. 12B shows the ratio of V1 / V2 and V1 / V3 when the voltage measuring circuit having the above circuit constant is connected. From the V1 / V2 ratio, it can be seen that in FIGS. 12 (a) and 12 (b), the influence of the voltage measurement circuit is seen at 40 MHz or more, but the influence of the voltage measurement circuit is hardly seen at 10 MHz or less.

  Looking at the V1 / V3 ratio in FIG. 12 (b), a voltage ratio decrease due to resonance is seen near 40 MHz. The resonance frequency of this voltage measurement circuit is calculated as follows.

  First, in FIG. 11, the combined impedance of L6, C6, and C7 is obtained. Since L6 corresponds to a 50 cm coaxial cable, L6 = 0.135 μH. Since the combined capacitance of C6 and C7 is 8 pF, the combined impedance of L6 and C6 and C7 is −5 ikΩ. Since this is a capacitive impedance, it is 8.005 pF when converted into a capacitance. With this, the combined capacitance of C9 is 103 pF + 8.005 pF = 111.005 pF. Since this combined capacitance and L5 (= 0.135 μH) cause series resonance, the resonance frequency (hereinafter referred to as “Reso_Measure”) is 41.113 MHz from Equation 1.

Because of voltage fluctuations due to resonance of the voltage measurement circuit, there must be a certain relationship between the frequency of the voltage to be measured and the resonance frequency. In order to set the voltage measurement accuracy to ± 5%, when the frequency satisfying V1 / V3> 0.95 is examined in detail in the graph of V1 / V3 ratio in FIG. 12B, it is 8.9 MHz or less. Therefore, if the frequency of the voltage to be measured is fB, Reso_Measure /
fB> 41.113 / 8.9 = 4.6. From this, when the inductance and capacitance that determine the resonance frequency of the voltage measurement circuit are represented by L and C, respectively, the following equation must be established using Equation 1.

係数の９.２ は、必ずしもこの数値である必要は無い。この係数は、電圧測定精度によって定まるので、必要な測定精度に対して、シミュレーションなり実測により、この係数を決定するべきである。例えば、図１２（ｂ）と同じ条件で、測定精度を±１０％とするならば、Ｖ１／Ｖ３＞０.９０ となる周波数は、１２.６ＭＨｚ 以下となり、係数は、
６.５（＝４１.１１３／１２.６＊２）になる。

The coefficient 9.2 need not necessarily be this number. Since this coefficient is determined by the voltage measurement accuracy, this coefficient should be determined by simulation or actual measurement for the required measurement accuracy. For example, if the measurement accuracy is ± 10% under the same conditions as in FIG. 12B, the frequency where V1 / V3> 0.90 is 12.6 MHz or less, and the coefficient is
It becomes 6.5 (= 41.113 / 12.6 * 2).

  Next, phase measurement will be described. In the voltage measurement circuit of FIGS. 8 and 11, the voltage phase can be measured by replacing the rectifier circuit by the diode D1 with a phase detection circuit. Block diagrams corresponding to FIGS. 8 and 11 are shown in FIGS. FIG. 15 shows the result of simulating the phase difference between V1 / V2 and V1 / V3 in FIG. 14 under the same conditions as in FIG. The phase difference between V1 / V2 shows a complicated behavior, but the phase difference between V1 / V3 changes suddenly from 0 ° to 180 ° at the resonance frequency of 41 MHz. This is because the phase detection circuit is configured only by inductance and capacitance without using a resistor. If a resistor is used, the phase difference will show a relatively gentle change, which is not good. From this result, it can be seen that there is no problem with the phase measurement as long as the constraint of Equation 6 is followed.

  The circuit relating to voltage measurement and phase measurement described above is applicable not only to the electrode on which the wafer is mounted as shown in FIG. 10, but also to all electrodes capacitively coupled to plasma. Next, this embodiment will be described.

FIG. 16 is a longitudinal sectional view of the etching chamber used in this example. The difference from FIG. 10 is that a high-frequency power source (first high-frequency power source) 108 (for example, a frequency of 200 MHz) for plasma generation is connected to the antenna electrode 103 through the matching unit 109 and at the same time through the matching unit 112. 3 is connected to an antenna bias power source 113 which is a high frequency power source 3. The antenna bias power source 113 and the wafer bias power source 119 are connected to the phase control unit 120 so that the phase of the high frequency output from the antenna bias power source 113 and the wafer bias power source 119 can be controlled. In this case, the antenna bias power supply 113 and the wafer bias power supply 119 have the same frequency (for example, 4 MHz). This system controls the phase difference (for example, 180 °) between the high frequency for antenna bias appearing on the antenna electrode 103 and the high frequency for wafer bias appearing on the wafer 116, and can effectively apply a bias to the antenna electrode 103 and the wafer 116. It is a system. For this reason, the voltage is extracted to the atmospheric pressure side using the coaxial cable 157 and the phase measurement circuit 155 is provided so as to detect the voltage and phase of the electrostatic chuck electrode 124. In addition, in order to detect the voltage and phase of the upper antenna electrode 103, the voltage of the antenna electrode 103 was taken out to the atmospheric pressure side using the coaxial cable 159 as in the lower electrode, and a phase measurement circuit 156 was provided. The phase control unit 120 compares the phases obtained from these two phase measurement circuits 155 and 156, and the phase control unit 120 determines the level of the high frequency sent to the antenna bias power supply 113 and the wafer bias power supply 119 so that a predetermined phase difference is generated. Determine the phase difference.

  In addition, the matching unit 109 incorporates a filter 110 that cuts the frequency of the antenna bias power supply 113 in order to increase control reliability. Similarly, the matching unit 112 includes a filter 121 that cuts the frequency of the plasma generating high frequency power supply 108. The outputs of the two matching units 109 and 112 are combined using a coaxial cable 158 and connected to a coaxial line 111 which is a high-frequency transmission system for antenna electrodes.

It is a block diagram of the components comprised from a wafer bias RF power supply to an electrode. FIG. 2 is an equivalent circuit diagram of the block diagram of FIG. 1. It is a frequency characteristic chart in the structure of FIG. It is a simulation result in the equivalent circuit of FIG. It is an equivalent circuit diagram from a wafer bias RF power supply to plasma. It is a simulation result in the equivalent circuit of FIG. It is a frequency characteristic chart when Vpp on an electrode is made constant 20V. It is an equivalent circuit diagram which incorporated the Vpp detector in the electrode. It is the schematic which shows the 1st Example of a plasma etching apparatus. It is the schematic which shows the 1st Example of a plasma etching apparatus. FIG. 11 is an equivalent circuit diagram of the configuration diagram of FIG. 10. It is a simulation result in the equivalent circuit of FIG. It is an equivalent circuit diagram in which a phase detector is built in an electrode. It is the equivalent circuit diagram which installed the phase detector in the electrode exterior. It is a simulation result of the phase difference in the equivalent circuit of FIG. It is the schematic which shows the plasma etching apparatus which is a 3rd Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 ... Vacuum container, 102 ... Dielectric window, 103 ... Antenna electrode, 104 ... Processing container,
DESCRIPTION OF SYMBOLS 105 ... Processing chamber, 106 ... Vacuum exhaust apparatus, 107 ... Gas supply apparatus, 108 ... High frequency power supply for plasma generation, 109, 112, 118 ... Matching device, 110, 121, 122 ... Filter, 111, 151 ... Coaxial line, 113 DESCRIPTION OF SYMBOLS ... Antenna bias power supply, 114 ... Coil for magnetic field generation, 115 ... Substrate electrode, 116 ... Wafer, 119 ... Wafer bias power supply, 120 ... Phase control unit, 123 ... Electrostatic chuck power supply, 124 ... Electrostatic chuck electrode, 125, 152 ... coaxial waveguide, 127 ... vacuum seal material, 153 ... power supply cable, 154 ... voltage measurement circuit, 155, 156 ... phase measurement circuit, 157, 158, 159 ... coaxial cable.

Claims (7)

A plasma provided with a vacuum vessel, a lower electrode provided in the vacuum vessel on which a sample is placed, a matching unit connected to the lower electrode, and a power source for supplying power to the lower electrode through the matching unit In the processing device,
A plasma processing apparatus comprising: an electrostatic chuck electrode for holding the sample; and a voltage measuring circuit for measuring a voltage of the electrostatic chuck electrode and outputting the voltage as a DC voltage inside the lower electrode. In the plasma processing apparatus of claim 1,
The plasma processing apparatus, wherein the voltage measurement circuit is installed in a container that blocks at least corrosive gas. In the plasma processing apparatus of claim 1,
The plasma processing apparatus, wherein the voltage measurement circuit is capable of detecting a phase signal. A vacuum vessel, a lower electrode provided in the vacuum vessel and having a built-in electrostatic chuck electrode for holding a sample, a matching unit connected to the lower electrode, and the lower electrode via the matching unit In a plasma processing apparatus equipped with a power supply for supplying power,
A voltage measuring circuit provided under atmospheric pressure for measuring the voltage of the electrostatic chuck electrode and outputting it as a DC voltage;
A plasma processing apparatus comprising a coaxial line connecting the electrostatic chuck electrode and the voltage measurement circuit. In the plasma processing apparatus of claim 4,
The plasma processing apparatus, wherein a combined impedance of the voltage measuring circuit and the coaxial line is larger than a load impedance from the electrostatic chuck electrode to the plasma. In the plasma processing apparatus of claim 4,
The plasma processing apparatus, wherein the voltage measurement circuit is capable of detecting a phase signal. A vacuum vessel, a lower electrode provided in the vacuum vessel and containing an electrostatic chuck electrode for holding a sample, an upper electrode provided at a position facing the lower electrode, and the lower electrode A first matching unit; a first power source for supplying power to the lower electrode via the first matching unit; a second matching unit connected to the upper electrode; and the second matching unit In a plasma processing apparatus comprising a second power source for supplying power to the upper electrode via
A first phase measuring circuit provided under atmospheric pressure for measuring a phase of a voltage applied to the electrostatic chuck electrode;
A first coaxial line connecting the electrostatic chuck electrode and the phase measurement circuit;
A second phase measuring circuit provided under atmospheric pressure for measuring the phase of the voltage applied to the upper electrode;
A second coaxial line connecting the electrostatic chuck electrode and the phase measurement circuit;
A plasma processing apparatus comprising: a control unit that controls the first power source and the second power source based on output signals of the first phase measuring circuit and the second phase measuring circuit.

Images