JP7307697B2 - Method and plasma source for detecting the state of a plasma source - Google Patents

Description

The present invention relates to a method and plasma source for detecting the state of a plasma source.

Inductively Coupled Plasma (hereinafter referred to as "ICP") is used in various applications including the manufacture of semiconductor devices. Used. Patent Documents 1 and 2 disclose techniques for manufacturing semiconductor devices using ICP.

In a plasma source that generates ICP (inductively coupled plasma source), in order to generate ICP, first, a capacitively coupled plasma (hereinafter referred to as "CCP") is generated and then converted into ICP. It is In this case, it is important to detect when the plasma changes from CCP to ICP.

In the prior art, when detecting the change from CCP to ICP, the luminescence from the plasma was measured and confirmed based on the luminescence intensity. Patent Documents 1 and 2 also make determinations based on emission intensity.

Japanese Patent Application Laid-Open No. 2002-343600 JP 2008-198695 A

However, the conventional technique has a problem that it is difficult to accurately detect that the plasma has changed from CCP to ICP.

For example, when making a judgment based on the emission intensity as in Patent Documents 1 and 2, the plasma emits light when it is ignited as a CCP in the first place. difficult to do It is generally known that ICP is brighter and has a higher emission intensity, but it is difficult to set a threshold that allows accurate determination.

In addition, since the emission intensity of CCP and ICP varies depending on the type of gas that constitutes the plasma, it is difficult to set a threshold that can be used in common for various gases, and a single threshold functions effectively. Conditions are restrictive.

SUMMARY OF THE INVENTION The present invention has been made to solve such problems, and an object of the present invention is to provide a method and a plasma source capable of more accurately detecting the change of plasma from CCP to ICP.

An example of the method according to the invention comprises:
A method for detecting the state of an inductively coupled plasma source, comprising:
The plasma source comprises a DC power supply circuit, an inverter circuit, a resonance circuit, and a discharge section,
The method includes:
generating a capacitively coupled plasma in the discharge section;
After the capacitively coupled plasma is generated, a first power corresponding to the output power of the DC power supply circuit and a phase difference between current and voltage in at least a part of at least one of the resonance circuit and the discharge section are obtained. a step;
a step of outputting a first signal when a value obtained by differentiating the phase difference with the first power changes from an increase to a decrease;
Prepare.

In one example, the first signal is a signal representing that the plasma has changed from the capacitively coupled plasma to the inductively coupled plasma.

In one example, the output terminal of the DC power supply circuit and the input terminal of the inverter circuit are connected,
an output end of the inverter circuit and an input end of the resonance circuit are connected;
An output end of the resonance circuit and an input end of the discharge section are connected.

An example of a plasma source according to the present invention is
An inductively coupled plasma source,
The plasma source comprises a DC power supply circuit, an inverter circuit, a resonance circuit, and a discharge section,
The plasma source is
generating a capacitively coupled plasma in the discharge section;
After the capacitively coupled plasma is generated, the first power corresponding to the power at the output end of the DC power supply circuit and the phase difference between the current and the voltage in at least a part of at least one of the resonance circuit and the discharge section Acquired,
A first signal is output when the value obtained by differentiating the phase difference with the first power changes from increasing to decreasing.

According to the plasma source state detection method and plasma source according to the present invention, it is possible to more accurately detect when the plasma changes from CCP to ICP.

1 is a diagram showing an example of the configuration of a plasma source according to Embodiment 1 of the present invention; FIG. 4 is a graph showing the relationship between the power measured in Embodiment 1 and the phase of current. 4 is a flow chart of a method for detecting the state of a plasma source according to Embodiment 1;

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

Embodiment 1.
FIG. 1 shows an example configuration of a plasma source 10 according to the first embodiment. Plasma source 10 is an inductively coupled plasma source. In the first embodiment, detection is performed according to the change in the phase difference between the current and voltage with respect to the power increase in the plasma source 10 .

The plasma source 10 includes a DC power supply circuit 20 , an inverter circuit 30 , a resonance circuit 40 , a discharge section 50 and control means 60 .

DC power supply circuit 20, inverter circuit 30, resonance circuit 40 and discharge section 50 are connected in this order. That is, the output terminal of the DC power supply circuit 20 and the input terminal of the inverter circuit 30 are connected, the output terminal of the inverter circuit 30 and the input terminal of the resonance circuit 40 are connected, and the output terminal of the resonance circuit 40 and the discharge section 50 are connected. input terminal is connected.

A DC power supply circuit 20 supplies a DC voltage. The inverter circuit 30 converts a DC voltage into an AC voltage. The frequency of the alternating voltage is for example an RF frequency, more specifically 2 MHz or about 2 MHz.

The resonance circuit 40 uses an AC voltage to cause a resonance phenomenon, and supplies the resonance voltage to the discharge unit 50 . In this embodiment, the resonance circuit 40 includes an LC circuit section 41 and a capacitor 42 , and the capacitor 42 is connected to the LC circuit section 41 in parallel with the discharge section 50 . Note that the configuration of the resonance circuit 40 is not limited to that illustrated.

The discharge section 50 includes a discharge tube (not particularly shown) and an antenna 51 .
A discharge tube is, for example, a cylindrical discharge vessel made of a dielectric (insulator), in which plasma is generated. The antenna 51 is a conductor formed in a coil shape so as to surround the discharge tube, and is connected to the resonance circuit 40 . Although FIG. 1 shows a resistor 52 connected in series with the antenna 51 in the discharge section 50, this resistor 52 is the resistance value of the coil when there is no load.

Note that the shape of the antenna 51 is not limited to a coil shape. Further, the antenna 51 may have a pipe shape and a coolant such as water may flow inside in order to cool the discharge tube. Further, the antenna 51 does not necessarily have to be formed so as to surround the discharge tube, and may be formed inside the dielectric (insulator) forming the discharge tube.

The discharge unit 50 generates plasma using the supplied voltage. For example, when an AC voltage is applied to the antenna 51 while gas is circulating in the discharge vessel, the gas is ionized by the voltage across the coil of the antenna 51 to generate plasma. This is the plasma coupled by the electric field between the terminals of the coil, ie the CCP.

When the voltage applied to the antenna 51 is further increased while the CCP is occurring, a magnetic field is formed around the coil to generate an induced electric field, thereby generating ICP. ICP is plasma used in the manufacture of semiconductor devices, etc., and is maintained and managed according to the application.

A control means 60 controls the operation of the plasma source 10 . For example, control means 60 is connected to DC power supply circuit 20 via driver amplifier 70 and to inverter circuit 30 via driver amplifier 80 .

The control means 60 acquires measurement signals representing the state of the DC power supply circuit 20 (for example, the voltage signal C1 and the current signal C2) and controls the plasma source 10 accordingly. The plasma source 10 is controlled by, for example, sending a control signal C3 to the DC power supply circuit 20 and sending a control signal C4 to the inverter circuit 30 .

The control means 60 can also obtain the voltages and currents in the circuits of the plasma source 10 . For this purpose, the plasma source 10 is equipped with measuring means. In the first embodiment, the measuring means is the VI sensor 90, which is arranged between the inverter circuit 30 and the resonance circuit 40. FIG. The control means 60 obtains the voltage and current by receiving the measurement signal C5 from the VI sensor 90. FIG. It should be noted that the position of the VI sensor 90 in FIG. 1 is an example, and can be changed to an appropriate position according to the circuit portion to measure the voltage and current.

A power supply (not shown) is connected to the DC power supply circuit 20, the control means 60, the driver amplifier 70, and the driver amplifier 80 to supply power thereto.

FIG. 2 is a graph showing the relationship between the power measured at each part and the phase difference between current and voltage when ICP is generated using the plasma source 10 . The horizontal axis represents the power [W] at the output end of the DC power supply circuit 20 measured by power measuring means (not shown). The left vertical axis represents the phase difference [degrees] between the current and voltage measured by the VI sensor 90 . The vertical axis on the right side is the differential value of the phase difference.

In FIG. 2, the ▪ symbol indicates the phase difference [degrees] between the current and the voltage, and the x symbol indicates the value obtained by differentiating the phase difference [degrees] between the current and the voltage with respect to the electric power.

In Embodiment 1, a mixture of hydrogen and nitrogen was supplied as the gas in the discharge vessel. The flow rates of hydrogen and nitrogen were both 1000 sccm, and the gas pressure was 87 Pa in total.

The low power range (roughly around 1800 W or less) corresponds to no-load conditions with no plasma and CCPs. In this range, current monotonically increases and voltage monotonically decreases with increasing power.

When the power reaches approximately 1800 W (indicated by the dashed line), the plasma changes from CCP to ICP. In the graph of FIG. 2, when the power exceeds about 1800 W (dashed line), the differential value of the phase difference [degrees] between the current and the voltage changes from increasing to decreasing. Thus, the power at the point where the plasma changes from CCP to ICP and the power at the point where the differential value of the phase difference changes from increasing to decreasing (inflection point of the phase difference) are in good agreement.

FIG. 3 is a flow chart of a method for detecting the state of a plasma source according to Embodiment 1; Plasma source 10 detects the state of plasma source 10 by performing this method. The state of plasma source 10 includes, for example, the state of plasma generated by plasma source 10 . The plasma state represents, for example, whether the plasma is CCP or ICP. With gas flowing through the discharge vessel of the plasma source 10, the method of FIG. 3 begins.

First, a voltage is applied to the discharge section 50 of the plasma source 10 to generate CCP in the discharge section 50 (step S1). After the CCP occurs, the control means 60 measures and obtains the power (first power) associated with the plasma source 10 and the phase difference between the current and the voltage (step S2).

In the example of FIG. 1, this measurement is made via VI sensor 90 . That is, the control means 60 measures the power at the connection point of the inverter circuit 30 and the resonance circuit 40 and the phase difference between the current and voltage flowing at the connection point.

Here, since the output power of the DC power supply circuit 20 can be calculated based on the power measured by the VI sensor 90, the power (first power) measured by the VI sensor 90 corresponds to the output power of the DC power supply circuit 20. It can be said that it is the power to

The method of measuring the first power and the phase difference between the current and the voltage acquired in step S2 is not limited to the method using the VI sensor 90 shown in FIG. For example, the power is equivalent as long as it can be converted to the output power of the DC power supply circuit 20. It may be a value obtained by measuring the power at the terminal, a value obtained by measuring the power at the output terminal of the inverter circuit 30, or a value obtained by measuring the power at the input terminal of the resonant circuit 40. However, it may be a value obtained by measuring the power at the output end of the resonance circuit 40 or a value obtained by measuring the power at the input end of the discharge section 50 .

Moreover, the phase difference between the current and the voltage may be the phase difference in at least part of at least one of the resonance circuit 40 and the discharge section 50 . For example, it may be a value obtained by measuring the phase difference between the input terminal and the output terminal of the resonant circuit 40, a value obtained by measuring the phase difference in the capacitor 42, or a measured value of the phase difference in the discharge section 50. It may be a value obtained by The determination method of this embodiment functions appropriately regardless of which part of the phase difference is used.

After step S2, the control means 60 obtains a value (differential value) obtained by differentiating the phase difference between the current and the voltage with the first power obtained in step S2, and the differential value changes from increasing to decreasing. It is determined whether or not (step S3). For example, the control means 60 may monitor the behavior of the phase difference while controlling the DC power supply circuit 20 to increase the power.

Differential values are also called differential coefficients or derivatives. A specific method for obtaining the differential value can be appropriately designed by those skilled in the art based on known techniques. to another value C+ΔC, ΔC/ΔP can be calculated as a differential value of the phase difference. As another example, a known differentiator or differentiation circuit may be used.

If the differential value of the phase difference has not changed from increasing to decreasing (for example, if the differential value is decreasing without increasing, if the differential value continues to increase, etc.), steps S2 and S3 are performed. is repeated. For example, the control means 60 increases the power each time steps S2 and S3 are performed.

On the other hand, when the differential value of the phase difference changes from increasing to decreasing, the control means 60 outputs a signal (first signal) indicating this (step S4). This corresponds to determining that the plasma has changed from CCP to ICP. That is, it can be said that the first signal is a signal representing that the plasma has changed from CCP to ICP.

In the first embodiment, since the emission intensity is not used for this determination, it is possible to perform the determination more accurately than in the prior art. In particular, since this method does not depend on the emission intensity, it can be applied to various kinds of gases with different emission intensities, and can also be applied to different gas pressures. As a modified example, it is also possible to use the emission intensity in combination for the determination.

A person skilled in the art can appropriately design the content, format, output mode and utilization method of the first signal. For example, a display device may be connected to the control means 60, and information indicating that the first signal has been output may be displayed on the display device. A specific example of the information may be a message or image indicating that the plasma state has changed from CCP to ICP.

Also, for example, the control means 60 may start executing a specific process in response to the output of the first signal. As a more specific example, a timer may be started. The value of this timer can be used as a value indicating the elapsed time after the occurrence of ICP.

As described above, according to the plasma source 10 according to the first embodiment and the method shown in FIG. 3, it is possible to more accurately detect that the plasma has changed from CCP to ICP.

DESCRIPTION OF SYMBOLS 10... Plasma source 20... DC power supply circuit 30... Inverter circuit 40... Resonance circuit 41... LC circuit part 42... Capacitor 50... Discharge part 51... Antenna 52... Resistor 60... Control means 70, 80... Driver amplifier 90... VI sensor

Claims (4)

A method for detecting the state of an inductively coupled plasma source, comprising:
The plasma source comprises a DC power supply circuit, an inverter circuit, a resonance circuit, and a discharge section,
The method includes:
generating a capacitively coupled plasma in the discharge section;
After the capacitively coupled plasma is generated, a first power corresponding to the output power of the DC power supply circuit and a phase difference between current and voltage in at least a part of at least one of the resonance circuit and the discharge section are obtained. a step;
a step of outputting a first signal when a value obtained by differentiating the phase difference with the first power changes from an increase to a decrease;
A method. 2. The method of claim 1, wherein said first signal is a signal indicative of a change in plasma from said capacitively coupled plasma to inductively coupled plasma. an output terminal of the DC power supply circuit and an input terminal of the inverter circuit are connected,
an output end of the inverter circuit and an input end of the resonance circuit are connected;
an output terminal of the resonant circuit and an input terminal of the discharge unit are connected;
3. A method according to claim 1 or 2. An inductively coupled plasma source,
The plasma source comprises a DC power supply circuit, an inverter circuit, a resonance circuit, and a discharge section,
The plasma source is
generating a capacitively coupled plasma in the discharge section;
After the capacitively coupled plasma is generated, the first power corresponding to the power at the output end of the DC power supply circuit and the phase difference between the current and the voltage in at least a part of at least one of the resonance circuit and the discharge section Acquired,
outputting a first signal when a value obtained by differentiating the phase difference with the first power changes from an increase to a decrease;
plasma source.

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