JP7568459B2 - DC pulse power supply device and plasma processing device - Google Patents

Description

The present invention relates to a DC pulse power supply device and a plasma processing device.

Plasma processing apparatuses used in processes such as etching, deposition, oxidation, and sputtering in the manufacture of semiconductor devices and flat panel displays are equipped with a high-frequency power supply device for generating plasma (see, for example, Patent Document 1). In addition to the high-frequency power supply device, plasma processing apparatuses equipped with a DC pulse power supply device that generates DC pulses have also been proposed.

A DC pulse power supply is a circuit that generates a pulse voltage whose amplitude changes in only one direction by performing ON/OFF control of a DC voltage at a specified timing. Such a DC pulse power supply is provided to correct the unevenness of the so-called self-bias voltage that occurs between the electrodes of a plasma processing device due to the application of high-frequency power. For example, a phenomenon may occur in which the self-bias voltage that occurs between the electrodes of a plasma processing device is high near the center of the electrodes and low near the periphery. This phenomenon is particularly likely to occur when the device has deteriorated over time.

By applying a DC pulse from a DC pulse power supply, the non-uniformity of the self-bias voltage can be corrected and a uniform self-bias voltage can be generated between the electrodes. This allows high ion acceleration energy to be generated uniformly between the electrodes in the plasma processing device, making it possible to irradiate the object to be processed uniformly with ions at high speed.

A DC pulse power supply device is provided with a voltage detection circuit for detecting the voltage value of the generated DC pulse. This voltage detection circuit is provided with a voltage divider circuit that divides the input voltage. The voltage divider circuit is composed of multiple resistance elements and/or capacitors connected in series, and outputs a voltage according to the voltage division ratio. The voltage value of the generated DC pulse is calculated based on the value of the output voltage. When detecting a high voltage, a resistance element or capacitor with high impedance is used in the voltage divider circuit to reduce the impact on the main circuit.

The voltage detection circuit in a DC pulse power supply is required to have stable frequency characteristics up to several times the pulse frequency (fundamental frequency). In general, the higher the resistance of a resistive element, the lower the impedance tends to be even in the low frequency range. Also, the lower the capacitance of a capacitor, the higher the impedance becomes and the better the frequency characteristics become, but it is affected by parasitic capacitance that occurs between wiring, boards, or housings. For these reasons, it is difficult to obtain stable frequency characteristics when detecting the voltage of a DC pulse in the voltage detection circuit in a DC pulse power supply, and therefore it is difficult to measure the value of the DC pulse voltage with high accuracy.

JP 2015-90770 A

The present invention aims to provide a DC pulse power supply device and a plasma processing device that can measure the voltage value of a DC pulse with high accuracy.

In order to solve the above problems, the DC pulse power supply device according to the present invention includes a pulse conversion unit that includes a first switching element and a second switching element and converts a DC voltage into a DC pulse by switching the conductive state of the first switching element and the second switching element, a voltage detection unit that includes a voltage divider circuit and detects the voltage value of the DC pulse voltage, a calibration data generation unit that generates, as calibration data, an inverse function of the transfer function of the voltage detection unit obtained based on the output signal of the voltage detection unit relative to the input signal to the voltage detection unit, and a voltage calibration unit that calibrates the output of the voltage detection unit based on the calibration data.

The plasma processing apparatus according to the present invention includes a first electrode disposed in a processing vessel, a second electrode disposed in the processing vessel so as to face the first electrode and on whose surface a workpiece can be placed, a high frequency power supply device that outputs high frequency power to the first electrode, and a DC pulse power supply device that outputs a DC pulse to the first electrode. The DC pulse power supply device includes a pulse conversion unit that includes a first switching element and a second switching element and converts a DC voltage into a DC pulse by switching the conductive state between the first switching element and the second switching element, a voltage detection unit that includes a voltage divider circuit and detects the voltage value of the DC pulse voltage, a calibration data generation unit that generates, as calibration data, an inverse function of the transfer function of the voltage detection unit acquired based on the output signal of the voltage detection unit relative to the input signal to the voltage detection unit, and a voltage calibration unit that outputs the voltage detection unit based on the calibration data.

The present invention provides a DC pulse power supply device and a plasma processing device that can measure the voltage value of a DC pulse with high accuracy.

1 is a block diagram illustrating a configuration of a plasma processing apparatus 100 using a DC pulse power supply apparatus 200 according to an embodiment. FIG. 2 is a circuit diagram for explaining the configuration of the DC pulse power supply device 200 in further detail. 2 is a circuit diagram illustrating a configuration of a voltage detection unit 209. FIG. 2 is an operational diagram for explaining the operations of a calibration signal generating section 213, a calibration data generating section 214, and a voltage calibrating section 215. FIG. An example of the circuit constants of the voltage detection unit 209, an example of the transfer function G(s), and an example of the inverse function G ⁻¹ (s) are shown below. 11 is a graph showing an example of an input signal to a voltage detection unit 209, an output signal, and a calibrated output signal. An example of setting the circuit constants of the voltage detection unit 209, an example of the transfer function G(s), and another example of the inverse function G ⁻¹ (s) are shown below. 11 is a graph showing an example of an input signal to a voltage detection unit 209, an output signal, and a calibrated output signal.

Hereinafter, the present embodiment will be described with reference to the attached drawings. In the attached drawings, functionally identical elements may be indicated by the same numbers. Note that the attached drawings show embodiments and implementation examples according to the principles of the present disclosure, but these are for understanding the present disclosure and are in no way used to interpret the present disclosure in a restrictive manner. The descriptions in this specification are merely typical examples and do not limit the scope or application examples of the present disclosure in any sense.

In this embodiment, the disclosure is described in sufficient detail for a person skilled in the art to implement the disclosure, but it should be understood that other implementations and forms are possible, and that changes to the configuration and structure and substitutions of various elements are possible without departing from the scope and spirit of the technical ideas of the disclosure. Therefore, the following description should not be interpreted as being limited to this.

Figure 1 is a block diagram illustrating the configuration of a plasma processing apparatus 100 using a DC pulse power supply apparatus 200 according to an embodiment. The plasma processing apparatus 100 is provided with a cathode electrode 101 (first electrode) that is disposed in a processing vessel and to which a high-frequency power and a DC pulse, which will be described later, are applied, and a counter electrode 102 (second electrode) that is disposed opposite the cathode electrode 101 and on whose surface a workpiece (e.g., a semiconductor wafer) can be placed. The workpiece can be fixed to the counter electrode 102 by an electrostatic chuck (not shown) installed on the counter electrode 102.

The counter electrode 102 is electrically grounded together with the processing vessel. In the processing vessel, for example, an object to be processed is placed on the surface of the counter electrode 102. The processing vessel is connected to a processing gas supply device (not shown) and also to an exhaust device (not shown).

High frequency power is applied from the high frequency power supply device 400 to the cathode electrode 101, and a DC pulse whose amplitude changes only in the negative direction (negative polarity) is applied from the DC pulse power supply device 200 to the cathode electrode 101. The high frequency power supply device 400 may be a high frequency power supply device that outputs a single frequency, or may be a high frequency power supply device that outputs multiple, for example, two types of frequencies superimposed. As an example, it may be a high frequency power supply device that generates a high frequency (e.g., about 13.56 MHz to 60 MHz) and a low frequency (e.g., about 400 kHz to 2 MHz) superimposed.

As is well known, the DC pulse applied from the DC pulse power supply device 200 is applied to correct the non-uniformity of the self-bias voltage and to uniformly generate the self-bias voltage between the electrodes when the high frequency power supply device 400 excites a discharge plasma in the processing vessel. The voltage value of the DC pulse supplied from the DC pulse power supply device 200 is set to, for example, about -1500V when the self-bias voltage is about -1000V. That is, the voltage value of the DC pulse is set to a voltage whose absolute value is greater than that of the self-bias voltage. A low-pass filter 300 is connected between the DC pulse power supply device 200 and the plasma processing device 100 to block the high frequency from the high frequency power supply device 400. A matching device 500 is connected between the high frequency power supply device 400 and the plasma processing device 100 to match the load impedance of the plasma processing device 100 to the impedance of the high frequency power supply device 400. A higher-level control device 600 is provided as a control unit for controlling the high frequency power supply device 400 and the DC pulse power supply device 200.

The configuration of the DC pulse power supply device 200 will be described in more detail with reference to FIG. 2. This DC pulse power supply device 200 includes a DC power supply 201, a DC/DC conversion unit 202, a DC/DC control unit 203, a voltage detection unit 204, a pulse conversion unit 205, a damping resistor 206, a voltage detection unit 209, a current detection unit 210, a pulse control unit 211, a loss calculation unit 212, a calibration signal generation unit 213, a calibration data generation unit 214, a voltage calibration unit 215, and an abnormality detection unit 216.

The DC power supply 201 is a power supply circuit that generates a DC voltage for generating a DC pulse. The DC/DC conversion unit 202 is a circuit that further converts the DC voltage into a DC voltage of a different voltage value. The DC/DC conversion unit 202 operates according to control from the DC/DC control unit 203. The DC/DC control unit 203 controls the DC/DC conversion unit 202 according to a voltage set value Vset that is set externally. The voltage detection unit 204 detects the voltage value of the DC voltage output by the DC/DC conversion unit 202 and outputs the detection result to the DC/DC control unit 203. The DC/DC control unit 203 controls the output voltage of the DC/DC conversion unit 202 according to this detection result.

The pulse conversion unit 205 includes a transistor Q1 as a first switching element (high-side switching element) and a transistor Q2 as a second switching element (low-side switching element). The transistors Q1 and Q2 are connected in series between the input terminal and the reference terminal (ground terminal) of the pulse conversion unit 205 via a damping resistor 206. The gate terminals of the transistors Q1 and Q2 are supplied with gate signals SW1 and SW2 from the pulse control unit 211, and the transistors Q1 and Q2 are alternately switched to a conductive state. This causes a DC pulse to be supplied via the damping resistor 206. The pulse control unit 211 is operable in synchronization with the high-frequency power supply device 400 according to a synchronization signal Ssy received from the high-frequency power supply device 400. As an example, the pulse conversion unit 205 is a high-side grounded type pulse conversion unit in which the drain of the transistor Q1 is electrically grounded. Alternatively, it is possible to use a low-side installation type pulse conversion unit in which the drain of the transistor Q2 is electrically grounded.

The damping resistor 206 is configured by connecting a first resistive element 207 and a second resistive element 208 in series. The voltage detection unit 209 is configured to detect the voltage of the connection node between the first resistive element 207 and the second resistive element 208. The configuration of the voltage detection unit 209 will be described in detail later. The current detection unit 210 is provided after the voltage detection unit 209 and detects the current flowing through the damping resistor 206 (the first resistive element 207 or the second resistive element 208). The voltage detection unit 209 and the current detection unit 210 may be installed in the opposite positions.

The calibration signal generating unit 213 generates a calibration signal for calibrating the voltage detection unit 209 according to a signal from the voltage detection unit 209. The calibration signal is, for example, the transfer function G(s) of the voltage detection unit 209. For example, the calibration signal generating unit 213 generates an input signal x(t) and inputs it to the voltage detection unit 209, and obtains the output signal y(t), thereby obtaining the transfer function G(s)=y(t)/x(t) of the voltage detection unit 209. The input signal x(t) is, for example, an AC signal of about 100 Hz to 1 MHz. The calibration data generating unit 214 generates calibration data for calibrating the voltage detection unit 209 according to the calibration signal. When the calibration signal is the transfer function G(s) of the voltage detection unit 209, the calibration data can be the inverse function 1/G(s) of the transfer function. The voltage calibration unit 215 calibrates the detection voltage of the voltage detection unit 209 according to the calibration data obtained by the calibration data generation unit 214. The output signal of the voltage calibration unit 215 (calibrated detection signal) is output to the loss calculation unit 212 and the abnormality detection unit 216.

The loss calculation unit 212 calculates the loss of the DC pulse power supply device 200 according to the gate signals SW1 and SW2, the output signal of the voltage calibration unit 215, and the output signal of the current detection unit 210, and if the loss exceeds the threshold value THloss, outputs an abnormality signal Sab1 to the DC/DC control unit 203 and the upper control device 600. When the DC/DC control unit 203 receives the abnormality signal Sab1, it controls the DC/DC conversion unit 202 to stop the supply of DC voltage. In addition, when the upper control device 600 receives the abnormality signal Sab1, it controls the high frequency power supply device 400 to stop the output of the high frequency signal.

When the output of the voltage calibration unit 215 exceeds the voltage upper limit value THv, the abnormality detection unit 216 outputs an abnormality signal Sab2 to the DC/DC control unit 203 and the upper control device 600. When the DC/DC control unit 203 receives the abnormality signal Sab2, it controls the DC/DC conversion unit 202 to stop the supply of DC voltage. When the upper control device 600 receives the abnormality signal Sab2, it controls the high frequency power supply device 400 to stop the output of the high frequency signal.

The configuration of the voltage detection unit 209 will be described in more detail with reference to FIG. 3. In the voltage detection unit 209, a first resistive element 2091 (resistance value R3) and a second resistive element 2092 (resistance value R4) are connected in series between nodes O1 and O4 via node O2. Node O1 is the input terminal of the voltage detection unit 209. Similarly, a first capacitor 2093 (capacitance value C3) and a second capacitor 2094 (capacitance value C4) are connected in series between nodes O1 and O4 via node O3. Nodes O2 and O3 are used as output terminals of the voltage detection unit 209.

Next, the operation of the calibration signal generating unit 213, the calibration data generating unit 214, and the voltage calibration unit 215 will be described with reference to FIG. 4. When performing the calibration operation, the output terminal of the current detection unit 210 and the output terminal of the calibration signal generating unit 213 are connected by a coaxial cable. Then, the calibration signal generating unit 213 inputs the input signal x(t) to the voltage detection unit 209 via the current detection unit 210 and receives the output signal y(t). Based on the input signals x(t) and y(t), the calibration signal generating unit 213 obtains the transfer function G(s)=y(t)/x(t) of the voltage detection unit 209.

The calibration data generator 214 obtains an inverse function G ^{−1 (s)=1/G(s) of the transfer function G(s) from the obtained transfer function G(s). The voltage calibration unit 215 multiplies the output signal of the voltage detector 209 by this inverse function G −1 (} s), thereby calibrating the output signal of the voltage detector 209.

In addition, in the case of the voltage detection unit 209 (voltage divider circuit) in FIG. 3, when R3×C3=R4×C4 holds, theoretically the transfer function G(s) of the voltage detection unit 209 is a constant (=R4/(R3+R4)), and has no frequency dependency. However, it is difficult to avoid the effects of parasitic capacitance that occurs in the surrounding wiring, elements, boards, housings, etc. Also, even if there is no frequency dependency at the time of design or shipment, it is possible that frequency dependency will gradually occur due to deterioration of the elements over time. Therefore, it is difficult to eliminate frequency dependency from the voltage detection unit 209.

On the other hand, according to the method of this embodiment, it is possible to obtain the output of the voltage detection unit 209 from which frequency dependency has been removed by software calculation. Since it is not affected by deterioration over time, it is possible to detect the voltage value of a DC pulse with high accuracy and reliability. In addition, since the transfer function of the voltage detection unit 209 is obtained, it is possible to guarantee the transfer function in a form that includes parasitic capacitance components resulting from the structure of the wiring and the like around the voltage detection unit 209.

5 shows an example ((b)) of a transfer function G(s) and an example ((c)) of its inverse function G −1 (s) in the case ((a)) where R3=10 MΩ, R4=10 kΩ, C3=0.5 pF, and C4=1000 pF are set in the first resistor element 2091, the second resistor element 2092, the first capacitor 2093, and the second capacitor 2094 of the voltage detection unit ^209. FIG. 6 shows an example ((a)) of the waveform of an input signal to the voltage detection unit 209 in FIG. 5(a), the waveform ((b)) of an output signal from the voltage detection unit 209, and the waveform ((c)) of an output signal after calibration. When the circuit constants are set as in FIG. 5(a), the voltage division ratio of the voltage division circuit of the first resistor element 2091 and the second resistor element 2092 is 10 kΩ/10 MΩ=1/1000, and the attenuation rate is −60 dB. On the other hand, the voltage division ratio of the voltage divider circuit of the first capacitor 2093 and the second capacitor 2094 is 0.5 pF/1000 pF=1/2000, the attenuation rate is -66 dB, and there is a difference of -6 dB. Also, the inflection point (cutoff frequency) is 1/(2πR1·C1)=16 kHz, 1/(2πR2·C2)=32 kHz.

When the voltage detection unit 209 has a transfer function G(s) as shown in FIG. 5(b), even if a square wave as shown in FIG. 6(a) is input to the voltage detection unit 209, the output signal will be a blunted signal as shown in FIG. 6(b). However, by calculating the inverse function G-1(s) of the transfer function G(s) and multiplying this by the output signal of the voltage detection unit 209 to calibrate it, the calibrated signal can become a square wave with the blunting removed as shown in FIG. 6(c). In other words, it becomes possible to detect voltages that are not frequency dependent.

7 shows an example ((b)) of a transfer function G(s) and an example ((c)) of its inverse function G −1 (s) in the case ((a)) of the first resistor 2091, the second resistor 2092, the first capacitor 2093, and the second capacitor 2094 of the voltage detection unit 209, where R3=10 ^MΩ , R4=10 kΩ, C3=2 pF, and C4=1000 pF. FIG. 8 shows an example ((a)) of the waveform of an input signal to the voltage detection unit 209 in FIG. 7(a), the waveform ((b)) of an output signal from the voltage detection unit 209, and the waveform ((c)) of an output signal after calibration. When the circuit constants are set as in FIG. 7(a), the voltage division ratio of the voltage division circuit of the first resistor 2091 and the second resistor 2092 is 10 kΩ/10 MΩ=1/1000, and the attenuation rate is −60 dB. On the other hand, the voltage division ratio of the voltage divider circuit of the first capacitor 2093 and the second capacitor 2094 is 2 pF/1000 pF = 1/500, and the attenuation rate is -54 dB, which is a difference of 6 dB. Also, the inflection point (cutoff frequency) is 1/(2πR1·C1) = 16 kHz, 1/(2πR2·C2) = 8 kHz.

When the voltage detection unit 209 has a transfer function G(s) as shown in FIG. 7(b), even if a square wave as shown in FIG. 8(a) is input to the voltage detection unit 209, the output signal will be a blunted signal as shown in FIG. 8(b). However, by calculating the inverse function G-1(s) of the transfer function G(s) and multiplying this by the output signal of the voltage detection unit 209 to calibrate it, the calibrated signal can become a square wave with the blunting removed as shown in FIG. 8(c). In other words, it becomes possible to detect voltages that are not frequency dependent.

The present invention is not limited to the above-described embodiments, but includes various modified examples. For example, the above-described embodiments have been described in detail to clearly explain the present invention, and are not necessarily limited to those having all of the configurations described. It is also possible to replace part of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of one embodiment. It is also possible to add, delete, or replace part of the configuration of each embodiment with other configurations.

REFERENCE SIGNS LIST 100...plasma processing apparatus, 101...cathode electrode, 102...counter electrode, 200...DC pulse power supply device, 201...DC power supply, 202...DC/DC conversion unit, 203...DC/DC control unit, 204...voltage detection unit, 205...pulse conversion unit, 206...damping resistor, 207...first resistive element, 208...second resistive element, 209...voltage detection unit, 210...current detection unit, 211...pulse control unit, 212...loss calculation unit, 213...calibration signal generation unit, 214...calibration data generation unit, 215...voltage calibration unit, 216...abnormality detection unit, 300...low-pass filter, 400...high-frequency power supply device, 500...matching unit, 600...high-order control unit, 2091...first resistive element, 2092: second resistor element; 2093: first capacitor; 2094: second capacitor; Q1: transistor; Q2: transistor.

Claims (5)

A DC pulse power supply device,
a pulse converter including a first switching element and a second switching element, and configured to convert a DC voltage into a DC pulse by switching a conductive state between the first switching element and the second switching element;
A voltage detection unit that detects a voltage value of the DC pulse;
a calibration signal generating unit that generates a calibration signal for calibrating the voltage detection unit;
a calibration data generating unit that generates calibration data for calibrating the voltage detection unit based on the calibration signal;
a voltage calibration unit that calibrates a detection voltage of the voltage detection unit based on the calibration data generated by the calibration data generation unit,
the calibration signal is generated by acquiring, at a plurality of frequencies within a predetermined frequency range, a transfer function (G(s)=y(t)/x(t)) of the voltage detection unit, which is calculated based on an input signal (x(t)) and an output signal (y(t)) output from an output terminal of the voltage detection unit, when an AC input signal x(t) is input to an input terminal of the voltage detection unit or an output terminal of the DC pulse power supply device,
the calibration data is an inverse function of the transfer function (1/G(s));
the voltage calibration unit calibrates the output signal of the voltage detection unit by multiplying the output signal of the voltage detection unit by the inverse function (1/G(s));
DC pulse power supply. The voltage detection unit
a plurality of resistive elements connected in series between the input terminal and a reference terminal;
a plurality of capacitance elements connected in series between the input terminal and the reference terminal;
a connection node between the plurality of resistive elements and the plurality of capacitive elements is used as the output terminal;
2. The DC pulse power supply device according to claim 1. A voltage divider circuit;
a damping resistor including a first resistor element and a second resistor element connected in series between the first switching element and the second switching element,
3. The DC pulse power supply device according to claim 1, wherein the voltage divider circuit is configured to measure a voltage at a connection node between the first resistance element and the second resistance element. The DC pulse power supply device according to claim 3, further comprising a current detection unit provided between the voltage detection unit and an output terminal of the DC pulse power supply device, for detecting a current flowing through the damping resistor. A first electrode disposed in the processing chamber;
a second electrode disposed in the processing vessel so as to face the first electrode and on a surface of which a workpiece can be placed;
a high frequency power supply device that outputs high frequency power to the first electrode;
a DC pulse power supply device that outputs a DC pulse to the first electrode,
The DC pulse power supply device comprises:
a pulse converter including a first switching element and a second switching element, and configured to convert a DC voltage into a DC pulse by switching a conductive state between the first switching element and the second switching element;
A voltage detection unit that detects a voltage value of the DC pulse;
a calibration signal generating unit that generates a calibration signal for calibrating the voltage detection unit;
a calibration data generating unit that generates calibration data for calibrating the voltage detection unit based on the calibration signal;
a voltage calibration unit that calibrates a detection voltage of the voltage detection unit based on the calibration data generated by the calibration data generation unit,
the calibration signal is generated by acquiring, at a plurality of frequencies within a predetermined frequency range, a transfer function (G(s)=y(t)/x(t)) of the voltage detection unit, which is calculated based on an input signal (x(t)) and an output signal (y(t)) output from an output terminal of the voltage detection unit, when an AC input signal x(t) is input to an input terminal of the voltage detection unit or an output terminal of the DC pulse power supply device,
the calibration data is an inverse function of the transfer function (1/G(s));
the voltage calibration unit calibrates the output signal of the voltage detection unit by multiplying the output signal of the voltage detection unit by the inverse function (1/G(s));
Plasma processing equipment.