JP2023045797A - Induction coupling type plasma source - Google Patents

Abstract

To provide an induction coupling type plasma source that can more accurately detect that plasma changes from CCP to ICP.SOLUTION: An induction coupling type plasma source comprises: a discharge unit that has a discharge tube and an antenna; a DC power supply circuit that outputs DC voltage; an inverter circuit that converts the DC voltage output from the DC power supply circuit into AC voltage; a resonance circuit that is arranged between the inverter circuit and the discharge unit; a sensor that detects a voltage value of a voltage corresponding to a voltage applied to the antenna and a current value of a current corresponding to a current flowing in the antenna; a control unit that controls an output voltage value of the DC power supply circuit or the inverter circuit to change the voltage value; and a determination unit that determines the state of plasma inside the discharge tube. After the generation of the plasma, when the ratio of the voltage value to the current value becomes equal to or less than a first threshold, the determination unit determines whether the plasma changes to inductive coupling plasma.SELECTED DRAWING: Figure 5

Description

The present invention relates to an inductively coupled 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, since the plasma emits light when it is ignited as a CCP, the generation of CCP and the change from CCP to ICP are distinguished and judged. 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 It is an object of the present invention to provide an inductively coupled plasma source capable of more accurately detecting the change of plasma from CCP to ICP.

An example of an inductively coupled plasma source according to the present invention is
a discharge unit having a discharge tube and an antenna for generating plasma therein;
a DC power supply circuit that outputs a DC voltage;
an inverter circuit that converts a DC voltage output from the DC power supply circuit into an AC voltage;
a resonance circuit arranged between the inverter circuit and the discharge section;
a sensor for detecting the voltage value of the voltage and the current value of the current corresponding to the voltage applied to the antenna and the current flowing through the antenna;
a control unit that controls the output voltage value of the DC power supply circuit or the inverter circuit so as to change the voltage value;
a determination unit that determines the state of the plasma inside the discharge tube;
with
The determination unit outputs a first signal indicating that the plasma has changed to inductively coupled plasma when a ratio of the voltage value to the current value becomes equal to or less than a first threshold value after the plasma is generated. .

In one example, the control unit controls the output voltage value of the DC power supply circuit or the inverter circuit so that the power value of the power supplied to the antenna increases after the plasma is generated, and then the power value is configured to control the output voltage value of the DC power supply circuit or the inverter circuit so that is a constant value,
The determination unit determines the current value of the voltage value based on the voltage value of the voltage and the current value of the current detected by the sensor while the control unit is controlling to increase the power value. After the plasma is generated, if the stability of the ratio of the voltage value to the current value is within a predetermined range, it is determined that the plasma has changed to an inductively coupled plasma judge.

In one example, the determination unit determines that the plasma is generated when a ratio of the voltage value to the current value becomes equal to or less than a second threshold after the supply of voltage to the antenna is started. Output a signal.

In one example, the sensor is arranged between the DC power supply circuit and the inverter circuit,
The sensor is
an output voltage value of the DC power supply circuit;
a current value of current flowing between the DC power supply circuit and the inverter circuit;
to detect

In one example, the antenna is a conductor coiled to surround the discharge tube.

According to the inductively coupled plasma source of the present invention, it is possible to more accurately detect the change of plasma 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 an example of transition of power values according to the first embodiment; 4 is a graph showing an example of the relationship between power values and impedances measured in the first embodiment; 4 is another graph showing an example of the relationship between the power value and impedance measured in Embodiment 1. FIG. 4 is a flow chart of a method for detecting the state of a plasma source according to Embodiment 1; 6 is a flow chart showing a modification of the method for detecting the state of the plasma source according to Embodiment 1 shown in FIG. 5;

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. The plasma source 10 includes a DC power supply circuit 20 , an inverter circuit 30 , a resonance circuit 40 , a discharge section 50 , a control means 60 and a VI sensor 90 .

DC power supply circuit 20, inverter circuit 30, resonance circuit 40 and discharge section 50 are connected in this order. For example, the output end of the DC power supply circuit 20 and the input end of the inverter circuit 30 are connected (through the VI sensor 90 in the example of FIG. 1), and the output end of the inverter circuit 30 and the input end of the resonance circuit 40 are connected. , and the output end of the resonance circuit 40 and the input end of the discharge section 50 are connected.

The DC power supply circuit 20 outputs a DC voltage, and the plasma source 10 operates with this DC voltage. The inverter circuit 30 converts the DC voltage output from the DC power supply circuit 20 into an AC voltage. The frequency of the alternating voltage is, for example, an RF frequency (RF: Radio Frequency), and a more specific example is 2 MHz or about 2 MHz. Of course, other frequencies are also applicable.

Resonant circuit 40 is arranged between inverter circuit 30 and discharge section 50 . The resonance circuit 40 uses alternating current to cause a resonance phenomenon, and supplies the resonance power to the discharge unit 50 . Resonance circuit 40 includes, for example, LC circuit section 41 and capacitor 42 , and capacitor 42 is connected to LC circuit section 41 in parallel with discharge section 50 . Note that the configuration of the resonance circuit 40 is not limited to that illustrated.

The discharge unit 50 has a discharge tube (not shown) for generating plasma inside and an antenna 51 . Antenna 51 is, for example, a conductor formed in a coil shape so as to surround the discharge tube. The discharge section 50 has a dielectric (not shown) that insulates the antenna 51 from the plasma. This dielectric can be, for example, a cylindrical discharge vessel. In FIG. 1, a resistor 52 is arranged in series with the antenna 51 in the discharge section 50, and this represents power consumption by the generated plasma.

The discharge unit 50 generates plasma using the supplied power. For example, when an alternating current flows through the antenna 51 while gas is circulating in the discharge vessel, the gas is ionized by the voltage between the terminals of 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 current of 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.

The gas conditions (composition, pressure, flow rate, etc.) in the discharge vessel can be appropriately designed by those skilled in the art. As for the composition, for example, a mixture of oxygen and nitrogen can be used. As an example of the flow rate, the oxygen flow rate may be 1000 sccm (Standard Cubic Centimeter per Minute) and the nitrogen flow rate may be 100 sccm. Alternatively, the oxygen flow rate may be 1500 sccm and the nitrogen flow rate may be 100 sccm.

A control means 60 controls the operation of the plasma source 10 . For example, the control means 60 functions as a control section that controls the output voltage value of the DC power supply circuit 20 or the inverter circuit 30 so as to change the voltage value of the voltage applied to the antenna 51 . Further, the control means 60 functions as a determination section that determines the state of the plasma inside the discharge tube.

In this embodiment, the VI sensor 90 is arranged between the DC power supply circuit 20 and the inverter circuit 30 . The VI sensor 90 detects the output voltage value of the DC power supply circuit 20 and the current value of the current flowing between the DC power supply circuit 20 and the inverter circuit 30, and outputs a voltage value signal C1 corresponding to the detected output voltage value. A current value signal C2 corresponding to the detected current value is output. If the VI sensor 90 is provided at the output terminal of the DC power supply circuit 20, the voltage value and the current value can be easily detected.

The detected power value represented by the product of the voltage value signal C1 and the current value signal C2 indicates the power value at the position of the VI sensor 90. FIG. That is, in the configuration of FIG. 1, the power value of the DC power output from the DC power supply circuit 20 is shown. There is Therefore, the power value represented by the product of the voltage value signal C1 and the current value signal C2 can be said to be information directly or indirectly indicating the power value supplied to the antenna 51 .

Further, there is a relation that the current value supplied to the antenna 51 also increases or decreases as the DC power output from the DC power supply circuit 20 increases or decreases. Therefore, the power value represented by the product of the voltage value signal C1 and the current value signal C2 can be said to be information that directly or indirectly indicates the current value supplied to the antenna 51 .

The control means 60 transmits a control signal C3 to the DC power supply circuit 20 so that the detected power value becomes equal to the target power value. The DC power supply circuit 20 increases or decreases the output voltage value based on the control signal C3. For example, the DC power supply circuit 20 increases or decreases the output voltage value by increasing or decreasing the duty ratio of the switching element in the DC power supply circuit 20 based on the control signal C3. The power value of the power supplied to the antenna 51 can be adjusted by such control.

Of course, the power value of the power supplied to the antenna 51 can be adjusted by adjusting the duty ratio of the switching element in the inverter circuit 30 instead of the DC power supply circuit 20 to increase or decrease the output voltage of the inverter circuit 30. . In this case, the VI sensor 90 is provided after the inverter circuit 30 . Also, the control means 60 sends a control signal C4 to the inverter circuit 30 so that the detected power value becomes equal to the target power value, for example.

Because of the above relationship, the voltage value and current value detected by the VI sensor 90 correspond to the voltage value applied to the antenna 51 and the current value flowing through the antenna, respectively.

As described above, there are multiple methods for adjusting the power supplied to the antenna 51 . Which method is used to adjust the power value of the power supplied to the antenna 51 may be appropriately designed according to the configurations of the DC power supply circuit 20 and the inverter circuit 30 .

In FIG. 1, the illustration and description of the drive amplifier and the like that apply drive signals to the switching elements in the DC power supply circuit 20 and the switching elements in the inverter circuit 30 are omitted. A power supply (not shown) is connected to the DC power supply circuit 20, the inverter circuit 30, and the control means 60 to supply power thereto.

FIG. 2 is a graph showing an example of transition of power values according to the first embodiment. The horizontal axis represents time, and the vertical axis represents power values related to plasma. The power value related to the plasma is, for example, the power value of the power supplied to the antenna 51. In this embodiment, the product of the voltage value and the current value detected by the VI sensor 90 (the voltage value signal C1 and the current value A power value represented by the product of the signal C2) is used instead. Alternatively, as a modification, instead of or in addition to the VI sensor 90, a power detector that detects the power supplied to the antenna 51 may be additionally provided. The power detector may comprise a current detector and a voltage detector. The power detector may be connected to the output end of the DC power supply circuit 20 or may be connected to the output end of the inverter circuit 30 .

The control means 60 controls the power value related to the plasma by controlling the power output from the DC power supply circuit 20 or the inverter circuit 30 as shown in FIG. Operation of plasma source 10 includes a power ramp-up phase and a power constant phase.

In the power increasing stage, the control means 60 increases the voltage value of the voltage applied to the antenna 51 by increasing the output voltage value of the DC power supply circuit 20 or the inverter circuit 30, thereby increasing the power supplied to the antenna 51. increase the power value of The duration of the power-up phase can be designed arbitrarily, but is for example several milliseconds to several tens of milliseconds (50 milliseconds in the example of FIG. 2). The range can be, for example, 10 milliseconds or less, or 100 milliseconds or less.

In the example of FIG. 2, the power value is 0W at the beginning of the power-up phase and 5000W at the end. During this power-up phase, a plasma is generated and changes from CCP to ICP. Although the power value increases continuously with time in the example of FIG. 2, it may actually increase stepwise.

Note that the impedance stability (for example, standard deviation) is calculated using the voltage value (voltage value signal C1) and current value (current value signal C2) detected by the VI sensor 90 in this power increasing stage, and as will be described later. is determined using impedance stability.

The constant power stage is a stage after the power value reaches a predetermined value (5000 W in the example of FIG. 2), and the power value is maintained. This predetermined value can be designed, for example, as a value at which ICP is stably maintained. During the constant power phase, the plasma can be used for a variety of purposes, such as etching processes and performing CVD processes.

FIG. 3 is a graph showing an example of the relationship between power values and impedances measured in the first embodiment. The horizontal axis represents the power value [W] of the power supplied to antenna 51 (calculated, for example, based on the voltage value and current value measured by VI sensor 90). The range of power values is the range of the power increase stage. In FIG. 2, it is 0 to 2500 [W].
The vertical axis represents the impedance [Ω] (that is, the ratio of the voltage value to the current value, which may be a resistance value) measured by the VI sensor 90 . A mixture of oxygen and nitrogen was used as the gas in the discharge vessel. Also, as described above, the voltage value and current value measured by the VI sensor 90 are not limited to those related to the position of the VI sensor 90 shown in FIG.

The inventors have found that the state of plasma can be determined based on the change in impedance that accompanies an increase in power value. In the example of FIG. 3, when the power value was 100 W, no plasma was generated and the impedance exceeded 50Ω. When the power value was increased to 200 W, the impedance dropped below 50Ω and CCP occurred. After that, CCP did not change to ICP until the power value reached 1000W.

When the power value was further increased to 1200 W, the plasma state became unstable, resulting in CCP and ICP. In addition, the impedance also became unstable along with this, and at 1300 W, 1400 W and 1600 W, different impedances were measured at different timings with respect to the same power value. Impedance generally decreased with increasing power, but was always in the range of 20Ω to 40Ω between 1200W and 1600W.

When the power value was further increased to 1700 W, an impedance of less than 15Ω was measured depending on the timing, and the ICP was stably maintained. At 1700 W, the impedance was not stable and exceeded 15Ω depending on the timing, but the plasma state was stable at ICP.

When the power value was further increased to 1800 W or more, the impedance stabilized. The ICP was stably maintained even at 1800 W or higher.

As described above, it can be said that CCP occurs when the impedance becomes equal to or less than a predetermined CCP threshold (second threshold; for example, 50Ω in the example of FIG. 3) as the power value increases. Further, as the power value further increases, when the impedance becomes equal to or less than a predetermined ICP threshold (first threshold; for example, 15Ω in the example of FIG. 3), CCP changes to ICP, that is, ICP occurs. It can be said that Also, after the CCP is generated, when the impedance is stabilized, it can be said that the CCP is changed to the ICP, that is, the ICP is generated.

Considering the use of the plasma source 10, it is important to stably maintain the ICP. For this reason, as described above, there is actually a timing at which ICP occurs temporarily even in the area of 1600 W or less, but rather than determining that ICP has occurred in such an area, ICP is stably maintained at 1800 W It is preferable to determine that ICP has occurred in the above regions.

FIG. 4 is another graph showing an example of the relationship between the power value and impedance measured in the first embodiment. 4 corresponds to the constant power stage in FIG.

FIG. 4 shows three different graphs depending on the gas conditions: low-pressure, low-flow gas (black triangles), medium-pressure, medium-flow gas (black circles), and high-pressure, high-flow gas, respectively. Corresponds to gas (black square). A mixture of oxygen and nitrogen was used as the gas in the discharge vessel.

The inventors have found that it is possible to determine that the plasma has changed from CCP to ICP based on the change in impedance. At low pressure and low flow rate, the ICP was stably maintained at 5000 W, and the impedance Zicp was stable at about 13-14Ω. At medium pressure and medium flow rate gas, the plasma state was unstable at 5000 W (ie, CCP or ICP depending on the timing), and the impedance Zccp/icp was not stable at about 14 to 21Ω. At high pressure and high flow rate, the plasma remained CCP at 5000 W (that is, did not change to ICP), and the impedance Zccp was stable around 40Ω.

From the graph in FIG. 4 as well, after the CCP occurs, when the impedance (ratio of the voltage value to the current value) becomes a small value (below the predetermined ICP threshold value), the CCP changes to the ICP, that is, the ICP occurs. can be done.

That is, since there is a relationship shown in Equation (1), the plasma state can be determined by monitoring the impedance value and setting an appropriate threshold value (ICP threshold value).
Zicp<Zccp/icp<Zccp (1)

In addition, the stability of plasma as described above can be represented by, for example, the standard deviation of impedance. Of course, it is also possible to express the stability by another index (variance, etc.), but in this embodiment, the standard deviation will be used for explanation.
When the stability of the plasma is expressed by the standard deviation of the impedance, the standard deviation σccp/icp is the largest when the plasma state is unstable as in the case of using the medium pressure and medium flow rate gas in FIG. The standard deviation σicp for ICP is the second largest, and the standard deviation σccp for ccp is the third largest (smallest). That is, there is a relationship shown in Equation (1). In the above description, it was explained that both the standard deviation σccp of impedance when CCP occurs and the standard deviation σicp of impedance when ICP occurs are stable, but strictly speaking, the standard deviation σccp of impedance when CCP occurs is more stable. there is

σccp < σicp < σccp/icp (2)

As described above, the impedance Zicp and the impedance Zccp/icp are relatively close values. Therefore, in order to more reliably determine that ICP has occurred, the stability of the plasma (for example, the standard deviation of the impedance) is used as the determination condition. can be added to This can be done by setting an appropriate standard deviation threshold.

In this case, the standard deviation threshold for determining the occurrence of ICP may be set in consideration of the relationship of Equation (2). That is, the standard deviation threshold is preferably specified within a range.
Therefore, it is preferable to determine that ICP has occurred when the standard deviation of impedance is within a predetermined range (within a predetermined range).

Since the impedance when ICP occurs varies depending on the type of gas, flow rate, pressure, etc., the ICP threshold value and standard deviation threshold value used for determination can be determined by conducting experiments such as those shown in FIGS. You just have to decide.

FIG. 5 is a flow chart showing an example of a method for detecting the state of the plasma source according to Embodiment 1, based on the principle explained in FIGS. 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 state of plasma is classified into, for example, a state in which plasma is not generated, a state in which CCP is generated, a state in which ICP is generated (that is, a state in which CCP is changed to ICP), and the like.

Step S1: The control means 60 changes the voltage value of the voltage applied to the antenna 51 (or changes the voltage value of the voltage corresponding to the voltage applied to the antenna 51). 20 or the output voltage value of the inverter circuit 30 is controlled. Thereby, the power value of the power supplied to the antenna 51 is controlled. Such power control is performed from the power increasing stage to the power constant stage shown in FIG.

Step S2: The VI sensor 90 detects a voltage value (voltage value signal C1) and a current value (current value signal C2) corresponding to the voltage applied to the antenna 51 and the current flowing through the antenna 51. . The control means 60 acquires the voltage value of the detected voltage and the current value of the current.

Step S3: The control means 60 determines that the impedance calculated based on the voltage value (voltage value signal C1) and the current value (current value signal C2) of the voltage detected by the VI sensor 90 is equal to or less than a predetermined CCP threshold. It is determined whether or not. If it is determined in step S3 that the impedance is equal to or less than the CCP threshold (Yes), the process proceeds to step S4.
If it is determined in step S3 that the impedance exceeds the CCP threshold (No), the process returns to step S1. In step S1, power control is performed from the power increase stage to the power constant stage as described above. Therefore, as the control progresses, the target power value increases in the power increasing stage and becomes constant in the power constant stage. Also, the calculation of the impedance and the determination in step S3 are performed from the power increase stage to the power constant stage.
Since CCP is generated by repeating steps S1 to S3, steps S1 to S3 can be said to be steps for generating CCP in the discharge section 50 of the plasma source 10. FIG.

As an optional process, when it is determined that the impedance exceeds the CCP threshold in step S3 (No), step S7 may be routed as indicated by the dotted arrow. In this case, in step S7, the standard deviation of the impedance is not within the predetermined range (determined as No), so the process returns to step S1. By performing such optional processing, it is possible to confirm the standard deviation of the impedance at this point.

Step S4: The control means 60 determines whether the impedance is equal to or less than a predetermined ICP threshold. When the impedance exceeds the ICP threshold in step S4 (No), the process proceeds to step S5, and when it is determined that the impedance is equal to or less than the ICP threshold (Yes), the process proceeds to step S6. Also, the calculation of the impedance and the determination in step S4 are performed from the power increase stage to the power constant stage.

Step S5: The control means 60 determines that plasma is generated as CCP although ICP is not generated, and outputs a CCP determination signal (second signal) indicating that plasma is generated as CCP. For example, in the example of FIG. 3, since an impedance of 50Ω or less is measured at 200 W, it is determined that ICP is not occurring at 200 W, but CCP is occurring, and step S5 is executed. After execution of step S5, the process proceeds to step S7.

Step S6: The control means 60 determines that the plasma is generated as ICP, outputs an ICP determination signal (first signal) indicating that the plasma is generated as ICP, and proceeds to step S7. This indicates that the plasma has changed from CCP to ICP.

Step S7: The control means 60 determines whether the standard deviation of impedance is within a predetermined range. If it is determined that the impedance standard deviation is not within the predetermined range (No), the process returns to step S1, and if it is determined that the impedance standard deviation is within the predetermined range (Yes), the process proceeds to step S8. When returning from step S7 to step S1, steps S1 to S6 are repeated.
This step S7 is a step for determining the stability of the plasma state. In this embodiment, the standard deviation of impedance is used as the stability, but it is also possible to express the stability by another index (dispersion, etc.).

Note that the specific value of the threshold can be set to 1Ω, 5Ω, or the like, for example, and can be appropriately designed by a person skilled in the art after confirming it through experiments or the like.
In addition, according to the present embodiment, the determination in step S7 is performed based on the stability of multiple measured values instead of one measured value, so that more accurate determination is possible. In addition, it can be determined by a technique called standard deviation, which is easy to calculate.

In this embodiment, the standard deviation of impedance is calculated using the voltage value (voltage value signal C1) and current value (current value signal C2) detected by the VI sensor 90 in the power increasing stage. Therefore, the standard deviation of the impedance is calculated by acquiring the detection data a plurality of times. Therefore, the standard deviation of the impedance cannot be calculated at the stage of data acquisition such as the first time. In such a case, the processing of steps S7 and S8 should be skipped.

Further, as described above, it is possible to calculate the standard deviation of the impedance even in the case of the process proceeding in the order of step S3→step S7 and the process proceeding in the order of step S4→step S5→step S7.
Therefore, during the power increase stage, it may be determined whether or not the standard deviation of the impedance is within a predetermined range. A process of calculating the deviation and determining whether or not the standard deviation of the impedance is within a predetermined range may be performed.

As described above, when the impedance standard deviation is calculated based on the voltage value (voltage value signal C1) and current value (current value signal C2) detected by the VI sensor 90 after the constant power stage is reached, Steps S7 and S8 may be skipped in the power up phase.

Step S8: The control means 60 outputs a stability determination signal (third signal) indicating that the impedance is stable, and proceeds to step S9.
As described above, it has already been determined that the plasma has changed from CCP to ICP by the processing of steps S4 and S6, but by performing the processing of steps S7 and S8, the plasma can more reliably change from CCP to ICP. I know it has changed.

Step S9: The control means 60 determines whether or not to stop the power supply. If it is determined not to stop the power supply (No), the process returns to step S1, and if it is determined to stop the power supply (Yes), the control ends. For example, when a series of processes from the power increase stage to the power constant stage are completed, the power supply is stopped. When returning from step S9 to step S1, steps S1 to S8 are repeated.

As described above, according to the plasma source 10 according to the first embodiment, the occurrence of ICP is determined based on the value of impedance and the stability of impedance. can be detected.

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

In addition, it is possible to determine the stability of the inductively coupled plasma as well as simply detect that the plasma has changed to the inductively coupled plasma.

It should be noted that the generation of plasma as a CCP is also determined based on the fact that the impedance becomes equal to or less than the threshold value, so the generation of plasma can be detected more accurately.

Further, in this embodiment, since the VI sensor 90 is arranged between the DC power supply circuit 20 and the inverter circuit 30, it is possible to easily detect the current value and the voltage value.

<Method for determining threshold>
Specific values of the CCP threshold, ICP threshold, and standard deviation threshold of impedance, which serve as criteria for determination, can be easily determined by those skilled in the art based on experiments and the like. An example is described below.

First, the operating conditions (power, gas composition, pressure, flow rate, etc.) for generating the desired ICP are determined, and the plasma source 10 is specifically constructed accordingly. Then, using the plasma source 10, the impedance is measured while the power is increased, and whether or not CCP and ICP are generated is observed and recorded.

Here, it is not necessary to increase the power in a short time as in FIG. 2, but it can be done slowly so that sufficient time for observation can be obtained. Also, during observation, the increase in the power value may be stopped and the power value may be kept constant.

Embodiment 2.
FIG. 6 is a flow chart showing an example of a method for detecting the state of the plasma source 10 according to the second embodiment. In the flowchart of FIG. 6, the same step numbers are used for the same or similar processes as in the flowchart of FIG. The configuration of the plasma source 10 is the same as the configuration of the plasma source 10 according to Embodiment 1 (FIG. 1), so the description thereof is omitted. A method for detecting the state of the plasma source 10 according to the second embodiment will be described below, focusing on differences from the flowchart of FIG. Steps S1 to S2 and step S9 are the same as those in FIG. 5, so description thereof will be omitted.

Step S3: The control means 60 determines that the impedance calculated based on the voltage value (voltage value signal C1) and the current value (current value signal C2) of the voltage detected by the VI sensor 90 is equal to or less than a predetermined CCP threshold. It is determined whether or not. If it is determined in step S3 that the impedance is equal to or less than the CCP threshold (Yes), the process proceeds to step S5. If it is determined in step S3 that the impedance exceeds the CCP threshold (No), the process returns to step S1. Also, the calculation of the impedance and the determination in step S3 are performed from the power increase stage to the power constant stage.

Step S5: The control means 60 determines that plasma is generated as CCP although ICP is not generated, and outputs a CCP determination signal indicating that plasma is generated as CCP. For example, in the example of FIG. 3, since an impedance of 50Ω or less is measured at 200 W, it is determined that ICP is not occurring at 200 W, but CCP is occurring, and step S5 is executed. After execution of step S5, the process proceeds to step S7.

Step S7: The control means 60 determines whether the standard deviation of impedance is within a predetermined range. If it is determined that the impedance standard deviation is not within the predetermined range (No), the process returns to step S1, and if it is determined that the impedance standard deviation is within the predetermined range (Yes), the process proceeds to step S4. When returning from step S7 to step S1, steps S1, S2, S3 and S5 are repeated.

Similar to the description of step S7 in FIG. 5, after entering the constant power stage, impedance standardization is performed based on the voltage value (voltage value signal C1) and current value (current value signal C2) detected by the VI sensor 90. When calculating the deviation, step S7 may be skipped in the power increase stage.

Step S4: The control means 60 determines whether the impedance is equal to or less than a predetermined ICP threshold. When the impedance exceeds the ICP threshold in step S4 (No), the process proceeds to step S1, and when it is determined that the impedance is equal to or less than the ICP threshold (Yes), the process proceeds to step S6. Also, the calculation of the impedance and the determination in step S4 are performed from the power increase stage to the power constant stage.

Step S6: The control means 60 determines that the plasma is generated as ICP, outputs an ICP determination signal indicating that the plasma is generated as ICP, and proceeds to step S9. This indicates that the plasma has changed from CCP to ICP.

Compared with the flowchart of FIG. 5, the flowchart of FIG. 6 does not have the process corresponding to step S8 of FIG. However, since it is determined in step S7 whether or not the standard deviation of the impedance is within the predetermined range, the ICP determination signal output in step S6 is substantially the same as the stability determination signal output in step S8 of FIG. Since it is practically the same, it is possible to obtain the same effect as when executing the flowchart of FIG.

<Modification 1 of FIG. 6>
As a modification of FIG. 6, the order of steps S7 and S4 may be reversed. Similar effects can be obtained in this way as well.

<Modification 2 of FIG. 6>
As described with reference to FIG. 4, depending on the gas pressure and flow rate, it can be determined that ICP has occurred when the plasma state stabilizes after CCP has occurred. For example, as shown in FIG. 4, when the gas pressure is low and the gas flow rate is small, it can be determined that there is little impedance variation and ICP is occurring.
Therefore, as a second modification of FIG. 6, when it is determined that the standard deviation of the impedance is within the predetermined range (Yes) in step S7, the process proceeds to step S6 as indicated by the dotted arrow. That is, the process of determining whether the impedance in step S4 is equal to or less than the predetermined ICP threshold is omitted. Even in this way, it can be determined that the plasma has changed from CCP to ICP.

As in the description of step S7 in FIG. 5, when the standard deviation of impedance is calculated based on the acquired detection data after the constant power stage, step S7 may be skipped in the power increase stage. . That is, the power-up phase does not determine whether the plasma has changed from CCP to ICP.

<Other Modifications>
A person skilled in the art can appropriately design the content, format, output mode and usage of the CCP decision signal and the ICP decision signal. For example, a display device may be connected to the control means 60, and information indicating that these signals have been output may be displayed on the display device. Specific examples of information may be a message or image indicating that CCP has occurred and a message or image indicating that the state of the plasma has changed from CCP to ICP.

Also, for example, the control means 60 may start execution of specific processing according to the output of these signals. As a more specific example, a timer may be started together with the output of the ICP determination signal. The value of this timer can be used as a value indicating the elapsed time after the occurrence of ICP.

In the processing of steps S1 to S2 in FIGS. 5 and 6, error processing may be performed when the power value exceeds a predetermined threshold. For example, by outputting an error signal when the power value is 5000 W or more, it is possible to appropriately cope with the case where plasma is not generated due to an obstacle or the like.

Steps S3 and S5 in FIGS. 5 and 6 may be omitted. That is, the determination of occurrence of CCP may be omitted. Even in such a case, as the power value increases, plasma is generated and changes to ICP, so the occurrence of ICP can be determined appropriately.

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... Resistance 60... Control means (control part, determination part)
90... VI sensor (sensor)

Claims (5)

a discharge section having a discharge tube and an antenna for generating plasma therein;
a DC power supply circuit that outputs a DC voltage;
an inverter circuit that converts a DC voltage output from the DC power supply circuit into an AC voltage;
a resonance circuit arranged between the inverter circuit and the discharge section;
a sensor for detecting the voltage value of the voltage and the current value of the current corresponding to the voltage applied to the antenna and the current flowing through the antenna;
a control unit that controls the output voltage value of the DC power supply circuit or the inverter circuit so as to change the voltage value;
a determination unit that determines the state of the plasma inside the discharge tube;
with
The determination unit outputs a first signal indicating that the plasma has changed to inductively coupled plasma when a ratio of the voltage value to the current value becomes equal to or less than a first threshold value after the plasma is generated. , an inductively coupled plasma source. The controller controls the output voltage value of the DC power supply circuit or the inverter circuit so that the power value of the power supplied to the antenna increases after the plasma is generated, and then the power value remains constant. configured to control the output voltage value of the DC power supply circuit or the inverter circuit so that
The determination unit determines the current value of the voltage value based on the voltage value of the voltage and the current value of the current detected by the sensor while the control unit is controlling to increase the power value. After the plasma is generated, if the stability of the ratio of the voltage value to the current value is within a predetermined range, it is determined that the plasma has changed to an inductively coupled plasma 2. The inductively coupled plasma source of claim 1, wherein determining. The determination unit outputs a second signal indicating that the plasma is generated when a ratio of the voltage value to the current value becomes equal to or less than a second threshold after voltage supply to the antenna is started. 3. The inductively coupled plasma source according to claim 1 or 2, wherein The sensor is arranged between the DC power supply circuit and the inverter circuit,
The sensor is
an output voltage value of the DC power supply circuit;
a current value of current flowing between the DC power supply circuit and the inverter circuit;
The inductively coupled plasma source according to any one of claims 1 to 3, which detects 5. The inductively coupled plasma source according to claim 1, wherein said antenna is a conductor formed in a coil shape so as to surround the discharge tube.

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