JP7675608B2 - Inductively Coupled Plasma Source - Google Patents

Description

The present invention relates to an inductively coupled plasma source.

Inductively coupled plasma (ICP) is used for various applications including the manufacture of semiconductor devices. For example, in the manufacture of semiconductor devices, it is used in the etching process for silicon wafers and in the production of films by CVD. Patent documents 1 and 2 disclose semiconductor device manufacturing technologies using ICP.

In a plasma source that generates ICP (inductively coupled plasma source), it is known that a capacitively coupled plasma (CCP) is first generated and then changed to ICP in order to generate ICP. In this case, it is important to detect when the plasma has changed from CCP to ICP.

In conventional technology, when detecting a change from CCP to ICP, the light emitted from the plasma is measured and confirmed based on the light emission intensity. Patent documents 1 and 2 also make a judgment based on the light emission intensity.

JP 2002-343600 A JP 2008-198695 A

However, with conventional technology, it was difficult to accurately detect when the plasma had changed from CCP to ICP.

For example, when making a judgment based on the emission intensity as in Patent Documents 1 and 2, it is difficult to distinguish between the generation of a CCP and the change from a CCP to an ICP, because plasma emits light when it is ignited as a CCP. It is known that an ICP is generally brighter and has a greater emission intensity, but it is difficult to set a threshold value that allows for an accurate judgment.

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 value that can be used commonly for various gases, and the conditions under which a single threshold value functions effectively are limited.

The present invention has been made to solve these problems, and aims to provide an inductively coupled plasma source that can more accurately detect when the plasma has changed 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 for converting a DC voltage output from the DC power supply circuit into an AC voltage;
a resonant circuit disposed between the inverter circuit and the discharge unit;
a sensor for detecting a voltage value of a voltage and a current value of a current corresponding to a voltage applied to the antenna and a current flowing through the antenna;
A control unit that controls an output voltage value of the DC power supply circuit or the inverter circuit so as to change the voltage value;
A determination unit for determining a state of plasma inside the discharge tube;
Equipped with
The determination unit determines that the plasma has changed into an inductively coupled plasma when a stability of a ratio of the voltage value to the current value is within a predetermined range after the plasma is generated.

In one example, the control unit is configured to control an output voltage value of the DC power supply circuit or the inverter circuit so that a power value of the power supplied to the antenna increases after the plasma is generated, and then control the output voltage value of the DC power supply circuit or the inverter circuit so that the power value becomes a constant value;
While the control unit is controlling so that the power value increases, the determination unit calculates the stability of the ratio of the voltage value to the current value based on the voltage value of the voltage and the current value of the current detected by the sensor.

In one example, the determination unit determines that the plasma has changed to inductively coupled plasma when the ratio of the voltage value to the current value calculated based on the voltage value of the voltage and the current value of the current detected by the sensor becomes equal to or less than a predetermined threshold value.

In one example, the sensor is disposed between the DC power supply circuit and the inverter circuit,
The sensor includes:
an output voltage value of the DC power supply circuit;
a current value of a current flowing between the DC power supply circuit and the inverter circuit; and
Detect.

In one example, the antenna is a conductor formed into a coil shape that surrounds the discharge tube.

The inductively coupled plasma source of the present invention allows for more accurate detection of the change of plasma from CCP to ICP.

FIG. 2 is a diagram showing an example of the configuration of a plasma source according to the first embodiment of the present invention. 6 is a graph showing an example of a transition of a power value according to the first embodiment. 5 is a graph showing an example of the relationship between power value and impedance measured in the first embodiment. 11 is another graph showing an example of the relationship between the power value and the impedance measured in the first embodiment. 4 is a flowchart of a method for detecting a state of a plasma source according to the first embodiment. 6 is a flowchart showing a modified example of the method for detecting the state of the plasma source according to the first embodiment shown in FIG. 5 .

Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.
Embodiment 1.
1 shows an example of the configuration of a plasma source 10 according to embodiment 1. The 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 resonant circuit 40, a discharge unit 50, a control means 60, and a VI sensor 90.

The DC power supply circuit 20, inverter circuit 30, resonant circuit 40 and discharge unit 50 are connected in this order. For example, the output terminal of the DC power supply circuit 20 is connected to the input terminal of the inverter circuit 30 (via the VI sensor 90 in the example of FIG. 1), the output terminal of the inverter circuit 30 is connected to the input terminal of the resonant circuit 40, and the output terminal of the resonant circuit 40 is connected to the input terminal of the discharge unit 50.

The DC power supply circuit 20 outputs a DC voltage, and the plasma source 10 operates on 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 AC voltage is, for example, an RF frequency (RF: Radio Frequency), and more specifically, 2 MHz or approximately 2 MHz. Of course, other frequencies are also applicable.

The resonant circuit 40 is disposed between the inverter circuit 30 and the discharge unit 50. The resonant circuit 40 uses an AC current to cause a resonance phenomenon and supplies the resonated power to the discharge unit 50. The resonant circuit 40 includes, for example, an LC circuit unit 41 and a capacitor 42, and the capacitor 42 is connected in parallel with the discharge unit 50 and the LC circuit unit 41. Note that the configuration of the resonant circuit 40 is not limited to that shown in the figure.

The discharge unit 50 has a discharge tube (not shown) for generating plasma inside, and an antenna 51. The antenna 51 is, for example, a conductor formed in a coil shape to surround the discharge tube. The discharge unit 50 has a dielectric (not shown in particular) that insulates the antenna 51 from the plasma. This dielectric can be, for example, a cylindrical discharge vessel. Note that in FIG. 1, a resistor 52 is arranged in series with the antenna 51 in the discharge unit 50, which represents the power consumption due to 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, generating plasma. This is plasma bound by the electric field between the terminals of the coil, i.e., CCP.

When CCP is occurring, if the current in antenna 51 is further increased, a magnetic field is formed around the coil, generating an induced electric field, which in turn generates ICP. ICP is a type of plasma used in the manufacture of semiconductor devices, and is maintained and managed according to the application.

The gas conditions (composition, pressure, flow rate, etc.) in the discharge vessel can be designed as appropriate by those skilled in the art. For example, a mixture of oxygen and nitrogen can be used as the composition. As an example of the flow rates, 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.

The control means 60 controls the operation of the plasma source 10. For example, the control means 60 functions as a control unit 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. The control means 60 also functions as a determination unit that determines the state of the plasma inside the discharge tube.

In this embodiment, the VI sensor 90 is disposed 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 and a current value signal C2 corresponding to the detected current value. Note that if the VI sensor 90 is provided at the output end of the DC power supply circuit 20, the voltage value and 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. That is, in the configuration of FIG. 1, it indicates the power value of the DC power output from the DC power supply circuit 20, but as the DC power output from the DC power supply circuit 20 increases or decreases, the power value supplied to the antenna 51 also 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 power value supplied to the antenna 51.

In addition, as the DC power output from the DC power supply circuit 20 increases or decreases, the current value supplied to the antenna 51 also 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 is 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 a switching element in the DC power supply circuit 20 based on the control signal C3. This type of control makes it possible to adjust the power value of the power supplied to the antenna 51.

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, not the DC power supply circuit 20, and increasing or decreasing the output voltage of the inverter circuit 30. In this case, the VI sensor 90 is provided after the inverter circuit 30. The control means 60 also transmits a control signal C4 to the inverter circuit 30 so that the detected power value is 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. The method for adjusting the power value of the power supplied to the antenna 51 can 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 switching elements in the DC power supply circuit 20 and the drive amplifier that provides drive signals to 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.

2 is a graph showing an example of the transition of the power value according to the first embodiment. The horizontal axis represents time, and the vertical axis represents the power value related to the plasma. The power value related to the plasma is, for example, the power value of the power supplied to the antenna 51, but in this embodiment, it is substituted with the power value represented by the product of the voltage value and the current value detected by the VI sensor 90 (the product of the voltage value signal C1 and the current value signal C2). Alternatively, as a modified example, 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 include a current detector and a voltage detector. The power detector may be connected to the output terminal of the DC power supply circuit 20 or to the output terminal 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. 2. The operation of the plasma source 10 includes a power increase phase and a constant power phase.

In the power increase stage, the control means 60 increases the output voltage value of the DC power supply circuit 20 or the inverter circuit 30, thereby increasing the voltage value of the voltage applied to the antenna 51, and thereby increasing the power value of the power supplied to the antenna 51. The duration of the power increase stage can be designed as desired, 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 Figure 2, the power value is 0 W at the start of the power increase phase and 5000 W at the end. In this power increase phase, plasma is generated and changes from CCP to ICP. Note that in the example of Figure 2, the power value increases continuously with time, but in practice it may be increased in steps.

In addition, during this power increase stage, the impedance stability (e.g., 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, and a judgment is made using the impedance stability as described below.

The constant power stage is the stage after the power value reaches a predetermined value (5000 W in the example of Figure 2), and that power value is maintained. This predetermined value can be designed, for example, as a value at which the ICP is maintained stably. In the constant power stage, the plasma can be used for various applications (such as etching processes and CVD processes).

3 is a graph showing an example of the relationship between the power value and impedance measured in the first embodiment. The horizontal axis represents the power value [W] of the power supplied to the antenna 51 (calculated, for example, based on the voltage value and current value measured by the VI sensor 90). The range of the power value is the range of the power increase steps described above. In FIG. 2, it is 0 to 2500 [W].
The vertical axis represents the impedance [Ω] (i.e., 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. As described above, the voltage and current values measured by the VI sensor 90 are not limited to those related to the position of the VI sensor 90 shown in FIG. 1.

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

When the power value was further increased to 1200W, the plasma state became unstable, fluctuating between CCP and ICP. As a result, the impedance also became unstable, and at 1300W, 1400W, and 1600W, different impedances were measured at different times for the same power value. Impedance generally decreased as the power value increased, but at 1200W to 1600W it was always within the range of 20Ω to 40Ω.

When the power value was further increased to 1700W, impedances below 15Ω were measured at certain times, and a stable ICP was maintained. At 1700W, the impedance was not stable, exceeding 15Ω at certain times, but the plasma state was stable at ICP.

When the power value was further increased to 1800W or more, the impedance stabilized. Furthermore, the ICP remained stable even at 1800W or more.

As described above, when the impedance falls below a predetermined CCP threshold (second threshold, which can be set to, for example, 50 Ω in the example of FIG. 3) with an increase in the power value, it can be said that CCP occurs. Also, when the impedance falls below a predetermined ICP threshold (first threshold, which can be set to, for example, 15 Ω in the example of FIG. 3) with a further increase in the power value, it can be said that CCP changes to ICP, i.e., ICP occurs. Also, when the impedance stabilizes after CCP occurs, it can be said that CCP has changed to ICP, i.e., ICP has occurred.

In consideration of the applications of the plasma source 10, it is important to maintain a stable ICP. For this reason, as described above, although there are times when ICP actually occurs temporarily even in the region of 1600 W or less, it is more preferable to determine that ICP has occurred in the region of 1800 W or more where ICP is maintained stably, rather than determining that ICP has occurred in such a region.

Figure 4 is another graph showing an example of the relationship between the power value and impedance measured in embodiment 1. The right end of the graph in Figure 4, i.e., the position of 5000 W, corresponds to the constant power stage in Figure 2.

Figure 4 shows three different graphs depending on the gas conditions, corresponding to low pressure and small flow rate gas (black triangles), medium pressure and medium flow rate gas (black circles), and high pressure and large flow rate gas (black squares). 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 whether plasma has changed from CCP to ICP based on changes in impedance. With low pressure and small flow rate gas, ICP was stably maintained at 5000 W, and impedance Zicp was stable at approximately 13-14 Ω. With medium pressure and medium flow rate gas, the plasma state was unstable at 5000 W (i.e., it was either CCP or ICP depending on the timing), and impedance Zccp/icp was unstable at approximately 14-21 Ω. With high pressure and large flow rate gas, plasma remained CCP at 5000 W (i.e., it did not change to ICP), and impedance Zccp was stable at around 40 Ω.

From the graph in Figure 4, it can be said that after a CCP occurs, when the impedance (the ratio of the voltage value to the current value) becomes a small value (below a predetermined ICP threshold), the CCP changes to an ICP, i.e., an ICP has occurred.

That is, since the relationship shown in equation (1) exists, it is possible to determine the state of plasma by monitoring the impedance value and setting an appropriate threshold value (ICP threshold value).
Zicp < Zccp/icp < Zccp... (1)

The above-mentioned plasma stability can be expressed, for example, by the standard deviation of the impedance. Of course, the stability can also be expressed by other indices (variance, etc.), but in this embodiment, the standard deviation will be used for explanation.
When the stability of plasma is expressed by the standard deviation of impedance, the standard deviation σccp/icp is the largest when the plasma state is unstable, as in the case of using a medium pressure/medium flow rate gas in FIG. 4, the standard deviation σicp in the case of ICP is the second largest, and the standard deviation σccp in the case of ccp is the third largest (smallest). That is, there is a relationship shown in formula (1). In the above, it has been 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.

σccp < σicp < σccp/icp... (2)

As described above, since the impedance Zicp and the impedance Zccp/icp are relatively close values, it is possible to add the stability of the plasma (e.g., the standard deviation of the impedance) to the judgment conditions in order to more reliably determine that an ICP has occurred. To do so, an appropriate standard deviation threshold value may be set.

In this case, the standard deviation threshold for determining whether or not an ICP has occurred may be set in consideration of the relationship in formula (2). That is, it is preferable that the standard deviation threshold be a range specification.
Therefore, it is preferable to determine that ICP has occurred when the standard deviation of the impedance is within a specified range (a predetermined range).

The impedance at the time when ICP occurs varies depending on the type of gas, flow rate, pressure, etc., so the ICP threshold and standard deviation threshold used for the judgment can be determined by conducting experiments such as those shown in Figures 3 and 4.

Figure 5 is a flowchart showing an example of a method for detecting the state of the plasma source according to the first embodiment, based on the principle described in Figures 3 and 4. The plasma source 10 detects the state of the plasma source 10 by executing this method. The state of the plasma source 10 includes, for example, the state of the plasma generated by the plasma source 10. The state of the plasma is classified, for example, into a state in which no plasma is generated, a state in which a CCP is generated, a state in which an ICP is generated (i.e., a state in which a CCP has changed to an ICP), and the like.

Step S1: The control means 60 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 (or to change the voltage value of the voltage corresponding to the voltage applied to the antenna 51). This controls the power value of the power supplied to the antenna 51. Such power control is performed from the power increase stage to the constant power stage shown in FIG. 2.

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

Step S3: The control means 60 determines whether or not the impedance calculated based on the voltage value (voltage value signal C1) of the voltage and the current value (current value signal C2) of the current detected by the VI sensor 90 is equal to or less than a predetermined CCP threshold value. If it is determined in step S3 that the impedance is equal to or less than the CCP threshold value (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, as described above, power control is performed from the power increase stage to the constant power stage. Therefore, as the control progresses, the target power value increases in the power increase stage, and the target power value is constant in the constant power stage. Furthermore, the calculation of the impedance and the determination in step S3 are performed from the power increase stage to the constant power stage.
In addition, since the CCP is generated by repeating steps S1 to S3, steps S1 to S3 can be said to be steps for generating the CCP in the discharge unit 50 of the plasma source 10.

As an optional process, if it is determined in step S3 that the impedance exceeds the CCP threshold (No), the process may proceed via step S7, as indicated by the dotted arrow. In this case, since the impedance standard deviation is not within the predetermined range (determined as No) in step S7, the process returns to step S1. By performing such optional process, the impedance standard deviation at this point can be confirmed.

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

Step S5: The control means 60 determines that an ICP has not occurred but that plasma has been generated as a CCP, and outputs a CCP determination signal (second signal) indicating that plasma has been generated as a CCP. For example, in the example of FIG. 3, an impedance of 50Ω or less is measured at 200W, so it is determined that an ICP has not occurred at the time point of 200W but that a CCP has occurred, and step S5 is executed. After executing step S5, proceed to step S7.

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

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

The specific value of the threshold can be, for example, 1 Ω, 5 Ω, etc., and can be appropriately designed by a person skilled in the art after confirming it through experiments or the like.
According to the present embodiment, the determination in step S7 is made based on the stability of multiple measured values, not a single measured value, so that a more accurate determination can be made. Also, the determination can be made by a method that is easy to calculate, namely, standard deviation.

In addition, in this embodiment, the standard deviation of the impedance is calculated using the voltage value (voltage value signal C1) and current value (current value signal C2) detected by the VI sensor 90 during the power increase phase. Therefore, detection data is acquired multiple times to calculate the standard deviation of the impedance. Therefore, at the first data acquisition stage, etc., the standard deviation of the impedance cannot yet be calculated. In such a case, the processing of steps S7 and S8 can be skipped.

It is also possible to calculate the standard deviation of impedance in the above-mentioned processes proceeding in the order of step S3 → step S7, or in the process proceeding in the order of step S4 → step S5 → step S7.
Therefore, a process may be performed in the middle of the power increase phase to determine whether the standard deviation of the impedance is within a predetermined range, or after the constant power phase is reached, a process may be performed to calculate the standard deviation of the impedance based on the acquired detection data and determine whether the standard deviation of the impedance is within a predetermined range.

As described above, when the standard deviation of impedance 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 can be skipped during the increased power stage.

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, it can be determined more reliably that the plasma has changed from CCP to ICP.

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

As described above, the plasma source 10 according to embodiment 1 determines the occurrence of ICP based on the impedance value and impedance stability, so that it is possible to more accurately detect the change of plasma from CCP to ICP.

In this embodiment, since the emission intensity is not used for detection, it is possible to perform a more accurate judgment than the conventional technology. In addition, since this method does not depend on the emission intensity, it can be applied to various types of gases with different emission intensities. It can also be applied when the gas pressure is different. As a modified example, it is also possible to use the emission intensity in the judgment.

In addition to simply detecting whether the plasma has changed to an inductively coupled plasma, the stability of the inductively coupled plasma can also be determined.

In addition, the generation of plasma as a CCP is also determined based on the impedance falling below a threshold, allowing for more accurate detection of plasma generation.

In addition, in this embodiment, the VI sensor 90 is disposed between the DC power supply circuit 20 and the inverter circuit 30, so that the current value and voltage value can be easily detected.

<How to determine the threshold>
The specific values of the CCP threshold, ICP threshold and standard deviation threshold of the impedance that are the criteria for the judgment can be easily determined by a person skilled in the art based on experiments, etc. An example will be described below.

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

The power does not need to be increased in a short time as in Figure 2, but can be increased slowly to allow sufficient time for observation. Also, the increase in power value may be stopped during observation and the power value may be kept constant.

Embodiment 2.
Fig. 6 is a flowchart 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 processes that are the same as or similar to those in the flowchart of Fig. 5. Note that the configuration of the plasma source 10 is similar to that of the plasma source 10 according to the first embodiment (Fig. 1), and therefore a description thereof will be omitted. Below, a method for detecting the state of the plasma source 10 according to the second embodiment will be described, focusing on the differences from the flowchart of Fig. 5. Steps S1 to S2 and step S9 are similar to those in Fig. 5, and therefore a description thereof will be omitted.

Step S3: The control means 60 determines whether the impedance calculated based on the voltage value (voltage value signal C1) of the voltage and the current value (current value signal C2) of the current detected by the VI sensor 90 is equal to or less than a predetermined CCP threshold. 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. The calculation of the impedance and the determination in step S3 are performed from the power increase stage to the constant power stage.

Step S5: The control means 60 determines that an ICP has not occurred but that plasma has been generated as a CCP, and outputs a CCP determination signal indicating that plasma has been generated as a CCP. For example, in the example of FIG. 3, an impedance of 50Ω or less is measured at 200W, so it is determined that an ICP has not occurred at the time point of 200W but that a CCP has occurred, and step S5 is executed. After executing step S5, proceed to step S7.

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

As explained in step S7 of FIG. 5, if the standard deviation of impedance 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, step S7 can be skipped during the increased power stage.

Step S4: The control means 60 judges whether the impedance is equal to or less than a predetermined ICP threshold. If the impedance exceeds the ICP threshold in step S4 (No), the process proceeds to step S1. If the impedance is judged to be equal to or less than the ICP threshold (Yes), the process proceeds to step S6. The calculation of the impedance and the judgment in step S4 are performed from the power increase stage to the constant power stage.

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

Compared to the flowchart of FIG. 5, the flowchart of FIG. 6 does not have a process equivalent to step S8 in FIG. 5. However, since it is determined in step S7 whether the standard deviation of the impedance is within a predetermined range, the ICP determination signal output in step S6 is substantially the same as the stable determination signal output in step S8 in FIG. 5, and therefore the same effect can be obtained as when the flowchart of FIG. 5 is executed.

<Modification 1 of FIG. 6>
6, the order of steps S7 and S4 may be reversed, with the same effect being obtained.

<Modification 2 of FIG. 6>
As explained in Fig. 4, depending on the gas pressure and flow rate, it can be determined that an ICP has occurred when the plasma state stabilizes after the CCP has occurred. For example, as shown in Fig. 4, when the gas pressure is low and the gas flow rate is small, the impedance fluctuates little, and it can be determined that an ICP has occurred.
6, if it is determined in step S7 that the standard deviation of the impedance is within a predetermined range (Yes), the process may proceed to step S6 as shown by the dotted arrow. That is, the process of determining whether the impedance is equal to or less than a predetermined ICP threshold in step S4 is omitted. Even in this way, it is possible to determine that the plasma has changed from CCP to ICP.

As explained in step S7 of FIG. 5, if the standard deviation of impedance is calculated based on the acquired detection data after the constant power stage is reached, step S7 can be skipped during the power increase stage. In other words, during the power increase stage, no determination is made as to whether the plasma has changed from CCP to ICP.

<Other Modifications>
The contents, format, output manner, and usage method of the CCP determination signal and the ICP determination signal can be appropriately designed by those skilled in the art. 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 the information include a message or image indicating that a CCP has occurred, and a message or image indicating that the plasma state has changed from a CCP to an ICP.

For example, the control means 60 may start executing a specific process in response 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 since the occurrence of ICP.

In the processing of steps S1 and S2 in FIG. 5 and FIG. 6, if the power value exceeds a predetermined threshold, an error process may be performed. For example, if an error signal is output when the power value is 5000 W or more, it is possible to appropriately respond to cases where plasma is not generated due to a fault or the like.

Steps S3 and S5 in Figures 5 and 6 may be omitted. In other words, the determination that a CCP has occurred may be omitted. Even in such a case, plasma is generated and changes to an ICP as the power value increases, so the occurrence of an ICP can be properly determined.

REFERENCE SIGNS LIST 10: Plasma source 20: DC power supply circuit 30: Inverter circuit 40: Resonant circuit 41: LC circuit section 42: Capacitor 50: Discharge section 51: Antenna 52: Resistor 60: Control means (control section, determination section)
90...VI sensor (sensor)

Claims (5)

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 for converting a DC voltage output from the DC power supply circuit into an AC voltage;
a resonant circuit disposed between the inverter circuit and the discharge unit;
a sensor for detecting a voltage value of a voltage and a current value of a current corresponding to a voltage applied to the antenna and a current flowing through the antenna;
A control unit that controls an output voltage value of the DC power supply circuit or the inverter circuit so as to change the voltage value;
A determination unit for determining a state of plasma inside the discharge tube;
Equipped with
The inductively coupled plasma source, wherein the determination unit determines that the plasma has changed to inductively coupled plasma when, after the plasma is generated, the stability of the ratio of the voltage value to the current value is within a range between a predetermined upper threshold and a lower threshold . the control unit is configured to control an output voltage value of the DC power supply circuit or the inverter circuit so that a power value of the power supplied to the antenna increases after the plasma is generated, and then control the output voltage value of the DC power supply circuit or the inverter circuit so that the power value becomes a constant value;
2. The inductively coupled plasma source according to claim 1, wherein the determination unit calculates a stability of a ratio of the voltage value to the current value based on a voltage value of the voltage and a current value of the current detected by the sensor while the control unit is controlling so that the power value increases. The inductively coupled plasma source according to claim 1 or 2, wherein the determination unit determines that the plasma has changed to inductively coupled plasma when the ratio of the voltage value to the current value calculated based on the voltage value of the voltage and the current value of the current detected by the sensor becomes equal to or less than a predetermined threshold value. the sensor is disposed between the DC power supply circuit and the inverter circuit,
The sensor includes:
an output voltage value of the DC power supply circuit;
a current value of a current flowing between the DC power supply circuit and the inverter circuit; and
The inductively coupled plasma source according to any one of claims 1 to 3, wherein The inductively coupled plasma source according to any one of claims 1 to 4, wherein the antenna is a conductor formed in a coil shape so as to surround the discharge tube.

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