JP4417905B2 - Calculation method of actual resistance of impedance matching unit - Google Patents

Description

  The present invention relates to a method for calculating an actual resistance of an impedance matching unit used when high-frequency power is supplied from a high-frequency power source to a plasma processing chamber and various plasma processing is performed.

In recent years, plasma treatment has been widely used for surface treatment of substances such as fine processing by dry etching and thin film formation. In particular, it is indispensable for the manufacture of semiconductors.
In a plasma processing apparatus, an impedance matching unit is used to efficiently transmit high-frequency energy supplied from a high-frequency power source to a load resistance in a processing chamber where plasma processing is performed, and process the equivalent output impedance (50Ω) of the high-frequency power source. It is matched to the room impedance.

In order to improve the impedance matching and provide a stable power supply, it is necessary to match the impedance in accordance with the load variation of the processing chamber. For this reason, generally, a capacitor, a coil and the like in the impedance matching device are variably controlled.
In order to variably control these capacitors and coils, for example, as disclosed in Japanese Patent Application Laid-Open No. 2001-16779, impedance measuring means is provided between the impedance matching device and the plasma load, and the impedance of the measured plasma load is measured. Based on the value and the current capacity value of the variable capacitor, the capacity of the variable capacitor to be changed by the control means is accurately calculated, and the capacity of the variable capacitor is controlled based on the calculation result.

In addition to what is shown in the above publication, as disclosed in JP-A-11-112440, a monitor is provided between the impedance matching device and the plasma load, and the electrical physical quantity detected by this monitor and a preset value are set. Some of them compare and evaluate the plasma generation status.
Also, as disclosed in Japanese Patent Application Laid-Open No. 2003-282542, a high-frequency current detector is provided between the impedance matching device and the plasma load, the leakage current before plasma generation is measured, and this is compared with a reference value. The one controlled by is also known.
JP 2001-16779 A JP-A-11-112440 JP 2003-282542 A

However, the control device for the conventional plasma processing apparatus requires an impedance measuring device, a monitor, and a high-frequency current measuring device between the impedance matching device and the plasma processing chamber. These measuring instruments and monitors require a converter that converts a high-frequency analog signal into a digital signal as an actual device, and are expensive.
In addition, if the measuring device or monitor is provided between the impedance matching unit and the plasma processing chamber, the matching state between the impedance matching unit and the plasma processing chamber changes and various conditions change. It becomes difficult to rub.

  The present invention provides a plasma processing apparatus, an evaluation method thereof, and a control method thereof that do not require an impedance measuring instrument, a monitor, or a high-frequency current measuring instrument, and that can satisfactorily set the conditions of the plasma processing chamber. For the purpose.

  The method of calculating the actual resistance of the impedance matching device according to the present invention converts the power transfer efficiency η of the impedance matching device using a large number of S parameters measured by changing the value of the variable capacitor of the impedance matching device, and the impedance matching device. When the actual resistance of the load connected to RL is RL, the actual resistance Rm of the impedance matching device is obtained from Rm = (RL / η) −RL. Further, the S parameter is measured by a high frequency network analyzer.

The forward transmission parameter S21 is used as the S parameter.
Furthermore, when the matching state between the impedance matching unit and the load shifts, the impedance matching unit automatically detects the shift and adjusts the value of the built-in variable capacitor to bring the impedance matching unit and the load into a matching state. It is an impedance matching device.

  According to the plasma processing apparatus of the present invention, there is no need to provide an expensive impedance measuring device, monitor, or high-frequency current measuring device between the impedance matching device and the plasma processing chamber as in the prior art. In addition, there are no various harmful effects caused by providing a measuring instrument or a monitor between the impedance matching unit and the plasma processing chamber, and the conditions of the plasma processing chamber can be set satisfactorily. In order to measure the S parameter of the impedance matching device, a high-frequency network analyzer is required, but this requires only one manufacturer at the time of measuring the impedance matching device, and does not increase the cost of the entire plasma processing apparatus.

  Further, according to the evaluation method of the plasma processing apparatus of the present invention, it is possible to know numerically how much power is supplied to the plasma processing chamber, which could only be known by estimation, and impedance matching. The actual resistance Rm of the vessel can also be known numerically. And the process in a plasma processing chamber can be favorably performed with the measured power transmission efficiency calculated | required from S parameter.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram of a plasma processing apparatus in one embodiment of the present invention.
As shown in FIG. 1, the high frequency output (13.56 MHz) of the high frequency power source 1 is supplied to the plasma processing chamber 3 via the impedance matching unit 2. The high frequency power source 1 and the impedance matching unit 2 are connected by a coaxial cable. The impedance matching unit 2 and the plasma processing chamber 3 are directly connected (a coaxial cable is used at 500 W or less, and a bar such as a copper plate is used at 500 W or more).

The impedance matching unit 2 is an automatic impedance matching unit based on a general LC circuit. The plasma processing chamber 3 is also generally known. Discharge electrodes are arranged at regular intervals, and an object to be processed such as a wafer is placed between them, so that a high vacuum state can be maintained at the time of plasma generation. The surface of the object to be processed can be plasma-processed.
Reference numeral 4 denotes a plasma processing control unit which performs vacuum degree control, gas concentration control, processing chamber temperature control, high-frequency power source control, matching device control, and the like, and the basic part of this apparatus is also commercially available. . Reference numeral 5 denotes a calculation / storage unit, which includes an input / output control unit 6, a calculation unit 7, a VCI, VC2 storage unit 8, an S parameter storage unit 9, an efficiency η storage unit 10, a matching impedance ZP storage unit 11, and a matching impedance Zin storage unit. 12. The plasma processing unit 4 is different from a commercially available one in that signals are exchanged with the input / output control unit 6 of the calculation / storage unit 5.

Furthermore, a monitor / operation unit 13 is provided and connected to the input / output control unit 6 to exchange signals. A personal computer is used for the monitor / operation unit.
FIG. 2 is a system for measuring the data of the impedance matching unit 2 at the manufacturing site of the entire system. The port I of the RF network analyzer 14 is the same length as the coaxial cable (the coaxial cable connecting 1 and 2 in FIG. 1). The coaxial cable) 15 is connected to the input terminal of the impedance matching device 2, and the port II is connected to the output terminal of the impedance matching device 2 through the measurement coaxial cable 16. The tip of the measurement coaxial cable 16 on the impedance matching unit 2 side is a substantial port II. After the measurement coaxial cable 16 is connected to the port II of the RF network analyzer, error correction (calibration: generally known as a function possessed by the RF network analyzer) of the port II is performed, and the above substance is thus obtained. Port II can be created virtually. The data output terminal of the RF network analyzer 14 is connected to the input / output control unit 6 of the calculation / storage unit 5 via the measurement signal cable 17 to exchange signals.

  The RF network analyzer 14 may be a commercially available one that can measure the reflection characteristic and transmission characteristic of the circuit network of the electronic component from the amplitude and phase relationship between the input signal and the output signal of the electronic component. And the transfer characteristics of the attenuator. As the RF network analyzer 14, one having a matching circuit function on the port 2 side is used.

  FIG. 3 is an equivalent circuit diagram at the time of conjugate matching between the impedance matching device 2 and the plasma processing chamber 3 shown in FIG. The impedance matching unit 2 includes variable capacitors VC1 and VC2, a coil L1, and an actual resistance (a sum of all resistances of the impedance matching unit 2) Rm, and the high frequency power source 1 is connected to the input terminals T1 and T2. Zin is a matching impedance on the input side (input terminals T1, T2). ZR is the matching impedance on the output side (output terminals T3, T4).

  ZP (R ± jX) is the matching impedance of the plasma processing chamber 3, and the actual resistance is represented by RL. If the impedance viewed from the input terminals T1 and T2 on the high frequency power supply 1 side is, for example, 50Ω, and the impedance viewed from the impedance matching unit 2 side is also 50Ω, the input terminals T1 and T2 are matched. On the other hand, the impedance ZR when the impedance matching device 2 side is viewed from the output terminals T3 and T4 is 1Ω. This is obtained as matching impedance ZR = RZ−Rm = 1.3Ω−0.3Ω = 1Ω by converting the above 50Ω into 1.3Ω by the capacitors VC1 and VC2. Rm can be calculated as 0.3 ohm. Details will be described later.

If the impedance (resistance component RL) viewed from the plasma processing chamber 3 side is 1Ω, for example, the impedance matching unit 2 and the plasma processing chamber are matched. It should be noted that the imaginary parts of ZR and Zp do not need to be considered in a state where matching is achieved, and this state is said to be in a conjugate matching state.
When the matching state (50Ω-50Ω-1Ω-1Ω) is deviated, the phase / amplitude detector 2A shown in FIG. 3 detects a change in phase / amplitude, and the control unit 2B controls the rotation of the motors 2C, 2D. . When the phase shifts, the motor 2D rotates and the capacitor VC2 is adjusted. When the amplitude deviates, the motor 2C rotates and the capacitor VC1 is adjusted to be in a matching state. This is called an automatic impedance matching device and is commercially available.

FIG. 4 is a connection diagram when the S parameter of the impedance matching device 2 is measured by the RF network analyzer 14.
Next, the measurement of the S parameter of the impedance matching device 2 will be described. The data of the impedance matching unit 2 manufactured at the manufacturing site is measured by the RF network analyzer 14, the data is stored in the storage units 8 and 9 of the calculation / storage unit 5, and the data of the storage units 8 and 9 is used. Calculation is performed by the calculator 7, and the power transfer efficiency η and the matching impedance ZP, Zin are stored in the storage units 10, 11, 12.

The impedance matching unit 2 and the calculation / storage unit 5 storing the data of the impedance matching unit 2 may be replaced with other ones as necessary (high-frequency power source 1, plasma processing chamber 3, plasma processing control unit 4, monitor / operation unit, etc. ) And sold.
In FIG. 5, an S parameter S11 is a forward reflection coefficient, which is a reflection coefficient when signals are input from the input terminals T1 and T2 of the impedance matching device 2. S21 is a forward transmission coefficient, which is a transmission coefficient when a signal is input from the input terminals T1 and T2 of the impedance matching device 2. S21 is a reverse reflection coefficient, which is a reflection coefficient when a signal is input from the output terminals T3 and T4 of the impedance matching device 2. S12 is a reverse transmission coefficient, which is a transmission coefficient when a signal is input from the output terminals T3 and T4 of the impedance matching device 2.

As shown in FIGS. 2 and 3, a signal having the same frequency (13.56 MHz) as the output of the high frequency power supply 1 is applied from the port I of the RF network analyzer 14 to the input terminals T <b> 1 and T <b> 2 of the impedance matching device 2.
For example, as shown in FIG. 6, the S parameter is measured by setting the positions of the variable capacitors VC1 and VC2 of the impedance matching unit 2 to 1,000, and totaling 1 million positions. In FIG. 6, the capacitors VC1 and VC2 are set at every ten positions. One million pieces may be measured, or 10 jumps may be measured, and the numbers in between may be supplemented later by calculation.

All parameters (S11, S21, S12, S22) of measurement linked to the positions of VC1 and VC2 are stored, circuit optimization is performed by circuit optimization (matching) of the matching circuit function of the RF network analyzer 14, and the matching is performed. The electrical physical quantity of impedance ZP and electric power transmission efficiency (eta) is memorize | stored.
First, the S parameter S11 is S11≈0 (for example, 1/10000) at any position of the capacitors VC1 and VC2, and this value is confirmed. Although not actually matched with the RF network analyzer 14 on the output side of the impedance matching device 2, it is measured by converting to a characteristic in which a matching circuit is equivalently connected to the port II side of the RF network analyzer 14 (with a matching circuit function) Therefore, the output side impedance of the impedance matching device 2 can be recognized as 1Ω-1Ω, and the input side can be recognized as 50Ω-50Ω.
It should be a non-reflecting wave. First, in order to confirm this, S11 is measured for all the positions of the capacitors VC1 and VC2, and this is stored in the S parameter storage unit 9.

At this time, since the matching circuit impedance is equal to the matching impedance ZP, the matching impedance is stored in the matching impedance ZP storage unit 11.
Next, the S parameter S21 is measured for each of the above positions, and the S parameter storage unit 9
To remember. Since the actual resistance Rm of the impedance matching device 2 changes for each position, the transmission coefficient S21 takes different values. These values are given in decibels. For example, assuming that 1000 W of power is supplied from the high frequency power supply 1 to the impedance matching unit 2, if S21 is 3 dB, the transmission rate is 50% and 500 W of power is supplied to the plasma processing chamber 3. . If S21 is 6 dB, the transmission rate is 25%, and only 250 W is supplied to the plasma processing chamber 3.

  Next, a signal is output from the port II of the RF network analyzer 14, and the S parameter S22 is measured for each position. It is confirmed that the S parameter S22 is S22 = 0, that is, there is no reflection at any position of the capacitors VC1 and VC2. This is the same idea as in the case of S11. S22 is measured for all the positions of the capacitors VC1 and VC2, and stored in the S parameter storage unit 9.

Finally, the S parameter S12 is measured for each position and stored in the S parameter storage unit 9. Since the actual resistance Rm and the load RL of the impedance matching device 2 change for each position, the reverse transmission coefficient S12 takes different values.
Next, the calculation unit 7 converts S21 into a power transfer efficiency η using a predetermined conversion formula (an expression for converting decibels into a power ratio), and stores this in the efficiency η storage unit 10. The predetermined conversion formula is built in the calculation unit 7 and is generally known for converting the S parameter S21 into efficiency.

Since η is expressed by η = RL / (Rm + RL), Rm can be obtained from this equation as Rm = (RL / η) −RL. In this way, it is possible to know the actual resistance Rm of the impedance matching device 2 that could not be known so far.
Next, a case where a wafer is processed in the plasma processing chamber 3 will be described.
A user forms a system as shown in FIG. When the new plasma processing chamber 3 is used, a large number of samples are processed to check whether the processing is good and the same state can be performed, and the conditions of the plasma processing chamber 3 are set.

  First, the degree of vacuum, gas amount, temperature, and the like of the plasma processing chamber 3 are set to predetermined values, and a wafer is put in and prepared. When the high-frequency power source 1 is turned on, the system is not in an aligned state, so that the plasma processing chamber 3 is not sufficiently powered, but the plasma processing chamber 3 is weakly ignited with a small amount of power. The automatic impedance matching unit 2 operates, and the impedance matching unit 2 enters the matching state in 1 to 2 seconds. The plasma processing chamber 3 is supplied with sufficient power and enters a stable state.

Speaking only of the conditions of the power supplied from the high frequency power source 1 and the processing time, for example, the A processing is 3 minutes at the power 1000 W of the high frequency power source 1 (the power entering the plasma processing chamber 3 is estimated to be about 700 W), B The processing is one minute at a power of 1000 W of the high-frequency power source 1 (the power entering the plasma processing chamber 3 is estimated to be about 700 W). The electric power of about 700 W is an estimated value, and it is not known how much electric power is supplied to the plasma processing chamber 3 unless actually measured. When setting the conditions, for example, 1000 W of electric power is output from the high frequency power source 1, the positions of the variable capacitors VC 1 and VC 2 of the impedance matching unit 2 are set, and the desired power is supplied to the plasma processing 3. η = 700/1000 = 0.70, Rm = (RL / η) −From RL, Rm =
(1.0 / 0.7) −1.0 = 0.428857Ω.

  In the state where the wafer is being processed in the plasma processing chamber 3, for example, the state of the plasma processing chamber 3 is changed by cutting the wafer. Then, the matching impedance of the plasma processing chamber 3 originally changed from RL = 1Ω to RL = 1.1Ω, for example. Then, since the matching state is lost, the automatic impedance matching unit 2 operates, and the impedance viewed from the impedance matching unit 2 side from the output terminals T3 and T4 of the impedance matching unit 2 is set to 1.1Ω to achieve matching.

At this time, since Rm is 0.42857Ω and RL is 1.1Ω, the efficiency η is η ′ = 1.1 / (0.42857 + 1.1) = 0.71963 (the input power of the plasma processing chamber 3 = 719.63 W). )
In this series of operations, as a result of changing the values of the capacitors VC1 and VC2, η = RL / (Rm + RL), that is, the power transfer efficiency η of the impedance matching device 2 is changed. Therefore, the electric power supplied to the plasma processing chamber 3 has changed, and it is questionable whether the wafer can be processed normally in this state.

  Therefore, the values of the capacitors VC1 and VC2 of the impedance matching unit 2 are added to the input / output control unit 6 of the calculation / storage unit 5 via the plasma control unit 4, and the VC1 and VC2 storage unit 7 are referred to. If the position X is 6, the value in the S parameter storage unit 9 at that time is referred to, and the power transmission efficiency ηx at the position X of VC1 and VC2 is extracted from the efficiency η storage unit 10. This power transmission efficiency ηx is applied to the plasma processing control unit 4 to appropriately control the conditions of the plasma processing chamber 3.

Regarding how to use the power transfer efficiency ηx, for example, in the plasma processing control unit 4, when the power transfer rate ηx = 0.71963, the output power of the high frequency power supply 1 is 0.70 / 0.71963 × It is conceivable to set 1000 = 972.72 (W) so that the supplied power is substantially supplied to the plasma processing chamber 3.
Since the user of the plasma processing chamber 3 knows empirically what conditions should be adjusted with the power transfer efficiency ηx, the plasma processing chamber 3 can be operated at a high frequency. The output power of the power source 1, the degree of vacuum in the plasma processing chamber 3, the gas concentration, the processing chamber temperature, and the like may be appropriately selected and controlled.

  In FIG. 2, an S parameter storage unit 9, an efficiency η storage unit 10, a matching impedance ZP storage unit 11, and a matching impedance Zin storage unit 12 are provided in the calculation / storage unit 5, but only the S parameter storage unit 9 is provided. The subsequent data may be calculated by the calculation unit 7 and output. Further, the calculation unit 7 may calculate the efficiency η from the S parameter and store it in the efficiency η storage unit 10. At least one of the S parameter and the power transmission efficiency η may be stored.

  The present invention is particularly useful for evaluating and controlling plasma processing used during semiconductor manufacturing.

It is a block diagram which shows the use condition of the apparatus for demonstrating the evaluation method of the plasma processing apparatus in one Example of this invention, and its control method. It is a block diagram which shows the same measurement state. It is the equivalent circuit diagram of a part at the time of the use. It is the equivalent circuit schematic of a part at the time of the measurement. It is a figure for S parameter explanation of the impedance matching device of the device. It is a figure for explanation of an impedance matching device of the same device.

Explanation of symbols

1: high frequency power supply 2: impedance matching unit 3: plasma processing chamber 4: plasma processing control unit 5: calculation / storage unit 6: input / output control unit 7: calculation unit 8: VC1, VC2 storage unit 9: S parameter storage unit 10 : Efficiency η storage unit 11: Matching impedance ZP storage unit 12: Matching impedance Zin storage unit 13: Monitor / operation unit 14: RF network analyzer

Claims (4)

When the power transfer efficiency η of the impedance matching device is converted using many S parameters measured by changing the value of the variable capacitor of the impedance matching device, and the actual resistance of the load connected to the impedance matching device is RL A method for calculating an actual resistance of an impedance matching device in a plasma processing apparatus , wherein an actual resistance Rm of the impedance matching device is obtained from Rm = (RL / η) −RL. 2. The method of calculating an actual resistance of an impedance matching unit in a plasma processing apparatus according to claim 1, wherein the S parameter is measured with a high frequency network analyzer. 2. The method of calculating an actual resistance of an impedance matching unit in a plasma processing apparatus according to claim 1, wherein a forward transmission parameter S21 is used as the S parameter. When the matching state between the impedance matching unit and the load is deviated, the impedance matching unit detects the deviation and adjusts the value of a built-in variable capacitor to automatically match the impedance matching unit and the load. 2. The method of calculating an actual resistance of an impedance matching unit in a plasma processing apparatus according to claim 1, wherein the matching unit is a matching unit.

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