Inductively coupled plasma source

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

Technical Field

[0001] The present invention relates to an inductively coupled plasma source.

Background Art

[0002] Inductively Coupled Plasma (hereinafter referred to as "ICP") is used in various applications including the manufacture of semiconductor devices. For example, in the manufacture of semiconductor devices, it is used for etching processes on silicon wafers and for forming films by CVD methods. Patent Documents 1 and 2 disclose manufacturing techniques for semiconductor devices using ICP.

[0003] In a plasma source (inductively coupled plasma source) for generating ICP, in order to generate ICP, it is known to first generate capacitively coupled plasma (hereinafter referred to as "CCP") and then change it to ICP. In this case, it is important to detect that the plasma has changed from CCP to ICP.

[0004] In the prior art, when detecting the change from CCP to ICP, the light emission from the plasma was measured and confirmed based on the light emission intensity. In Patent Documents 1 and 2 as well, determination based on the light emission intensity is performed.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, in the prior art, there has been a problem that it is difficult to accurately detect that the plasma has changed from CCP to ICP.

[0007] For example, when judging based on the emission intensity as in Patent Documents 1 and 2, since the plasma emits light when it ignites as CCP in the first place, it is difficult to distinguish and judge between the generation of CCP and the change from CCP to ICP. Generally, it is known that ICP is brighter and has a greater emission intensity, but it is difficult to set an accurate judgment threshold.

[0008] In addition, since the emission intensities of CCP and ICP change depending on the type of gas constituting the plasma, it is difficult to set a threshold value that can be commonly used for various gases, and the conditions under which a single threshold value functions effectively are limited.

[0009] The present invention has been made to solve such problems, and an object thereof is to provide an inductively coupled plasma source that can more accurately detect that the plasma has changed from CCP to ICP.

Means for Solving the Problems

[0010] An example of the inductively coupled plasma source according to the present invention is a discharge part having a discharge tube and an antenna for generating plasma inside, a DC power supply circuit that outputs a DC voltage, an inverter circuit that converts the DC voltage output from the DC power supply circuit into an AC voltage, a resonance circuit disposed between the inverter circuit and the discharge part, a sensor that detects 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 part 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 part that determines the state of the plasma inside the discharge tube, and includes After the plasma is generated, when the ratio of the voltage value to the current value is equal to or less than a first threshold value, the determination unit outputs a first signal indicating that the plasma has changed to inductively coupled plasma.

[0011] In one example, after the plasma is generated, 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, and then controls 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 detected by the sensor and the current value of the current, and after the plasma is generated, when 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 inductively coupled plasma.

[0012] In one example, after the supply of voltage to the antenna is started, when the ratio of the voltage value to the current value is equal to or less than a second threshold value, the determination unit outputs a second signal indicating that the plasma has been generated.

[0013] In one example, the sensor is disposed between the DC power supply circuit and the inverter circuit. The sensor detects the output voltage value of the DC power supply circuit and the current value of the current flowing between the DC power supply circuit and the inverter circuit. and

[0014] In one example, the antenna is a conductor formed in a coil shape so as to surround a discharge tube.

Advantages of the Invention

[0015] According to the inductively coupled plasma source of the present invention, it is possible to more accurately detect that the plasma has changed from CCP to ICP.

Brief Description of the Drawings

[0016]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Mode for Carrying Out the Invention

[0017] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Embodiment 1. FIG. 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 resonance circuit 40, a discharge unit 50, a control means 60, and a VI sensor 90.

[0018] The DC power supply circuit 20, the inverter circuit 30, the resonance circuit 40, and the discharge unit 50 are connected in this order. For example, the output terminal of the DC power supply circuit 20 and the input terminal of the inverter circuit 30 are connected (via the VI sensor 90 in the example of FIG. 1), 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 input terminal of the discharge unit 50 are connected.

[0019] The DC power supply circuit 20 outputs a DC voltage, and the plasma source 10 operates by 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 as a more specific example, it is 2 MHz or about 2 MHz. Of course, other frequencies are also applicable.

[0020] The resonance circuit 40 is arranged between the inverter circuit 30 and the discharge unit 50. The resonance circuit 40 causes a resonance phenomenon using an alternating current and supplies the resonated power to the discharge unit 50. The resonance circuit 40 includes, for example, an LC circuit section 41 and a capacitor 42, and the capacitor 42 is connected in parallel with the discharge unit 50 with respect to the LC circuit section 41. Note that the configuration of the resonance circuit 40 is not limited to that shown in the figure.

[0021] 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 so as to surround the discharge tube. The discharge unit 50 includes a dielectric (not particularly shown) that insulates the antenna 51 from the plasma. This dielectric can be, for example, a cylindrical discharge container. 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.

[0022] The discharge unit 50 generates plasma using the supplied power. For example, when an alternating current flows through the antenna 51 with gas flowing inside the discharge container, the gas is ionized by the voltage between the terminals of the coil of the antenna 51, and plasma is generated. This is plasma coupled by the electric field between the terminals of the coil, that is, CCP.

[0023] When the current of the antenna 51 is further increased in a state where CCP is generated, a magnetic field is formed around the coil and an induced electric field is generated, thereby generating ICP. ICP is the plasma used in the manufacture of semiconductor devices, etc., and is maintained and managed according to the application.

[0024] The conditions (composition, pressure, flow rate, etc.) of the gas in the discharge capacitor can be appropriately designed by those skilled in the art. As the composition, for example, oxygen and nitrogen can be mixed and used. As an example of the flow rate, the flow rate of oxygen may be 1000 sccm (Standard Cubic Centimeter per Minute) and the flow rate of nitrogen may be 100 sccm. Or, the flow rate of oxygen may be 1500 sccm and the flow rate of nitrogen may be 100 sccm.

[0025] 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. Further, the control means 60 functions as a determination unit that determines the state of the plasma inside the discharge tube.

[0026] 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 the current value can be easily detected.

[0027] 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. However, 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, it can be said that the power value represented by the product of the voltage value signal C1 and the current value signal C2 directly or indirectly indicates the information on the power value supplied to the antenna 51.

[0028] 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 indicating directly or indirectly the current value supplied to the antenna 51.

[0029] 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. By such control, the power value of the power supplied to the antenna 51 can be adjusted.

[0030] Of course, instead of the DC power supply circuit 20, the duty ratio of the switching element in the inverter circuit 30 can be adjusted, and the output voltage of the inverter circuit 30 can be increased or decreased to adjust the power value of the power supplied to the antenna 51. In this case, the VI sensor 90 is provided at the subsequent stage of the inverter circuit 30. Further, the control means 60 transmits a control signal C4 to the inverter circuit 30 so that, for example, the detected power value becomes equal to the target power value.

[0031] Due to the above relationship, the voltage value and the 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.

[0032] 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.

[0033] Note that in FIG. 1, illustration and description of a drive amplifier or the like that supplies a drive signal to a switching element in the DC power supply circuit 20 or a switching element in the inverter circuit 30 are omitted. Further, power supplies (not shown) are connected to the DC power supply circuit 20, the inverter circuit 30, and the control means 60 to supply power to these components.

[0034] FIG. 2 is a graph showing an example of the transition of the power value according to Embodiment 1. 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. In this embodiment, however, it is substituted by 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 modification, instead of or in addition to the VI sensor 90, a power detector for detecting 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 the output terminal of the inverter circuit 30.

[0035] 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 increasing stage and a power constant stage.

[0036] In the power increasing 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 increasing stage can be arbitrarily designed, for example, from several milliseconds to several tens of milliseconds (50 milliseconds in the example of FIG. 2). As a range, for example, it can be 10 milliseconds or less, or 100 milliseconds or less.

[0037] In the example of FIG. 2, at the start of the power increase stage, the power value is 0 W, and at the end, the power value is 5000 W. During this power increase stage, plasma is generated and changes from CCP to ICP. In the example of FIG. 2, the power value increases continuously with time, but in reality, it may increase in steps.

[0038] Note that in this power increase stage, the stability of the impedance (for example, the standard deviation) is calculated using the voltage value (voltage value signal C1) and the current value (current value signal C2) detected by the VI sensor 90, and a determination using the stability of the impedance is made as described later.

[0039] The constant power stage is the 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 the ICP is stably maintained. In the constant power stage, the plasma can be used for various applications (such as an etching process or the implementation of the CVD method).

[0040] FIG. 3 is a graph showing an example of the relationship between the power value and the impedance measured in Embodiment 1. The horizontal axis represents the power value [W] of the power supplied to the antenna 51 (calculated based on the voltage value and the current value measured by the VI sensor 90, for example). The range of the power value is the range of the above-mentioned power increase stage. In FIG. 2, it is 0 to 2500 [W]. The vertical axis represents the impedance [Ω] measured by the VI sensor 90 (that is, the ratio of the voltage value to the current value. It may be a resistance value). As the gas in the discharge container, a mixture of oxygen and nitrogen was used. Also, as described above, the voltage value and the 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. 1.

[0041] The inventors have found that the state of the plasma can be determined based on the change in impedance accompanying the increase in the power value. 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 decreased below 50 Ω and a CCP was generated. Thereafter, until the power value reached 1000 W, the CCP did not change to an ICP.

[0042] When the power value was further increased to 1200 W, the state of the plasma became unstable, sometimes becoming a CCP and sometimes an ICP. Along with this, the impedance also became unstable, and at 1300 W, 1400 W, and 1600 W, different impedances were measured at different timings for the same power value. Generally, the impedance decreases as the power value increases, but it was always within the range of 20 Ω to 40 Ω at 1200 W to 1600 W.

[0043] When the power value was further increased to 1700 W, an impedance of less than 15 Ω was sometimes measured depending on the timing, and the ICP was stably maintained. Note that at 1700 W, the impedance was not stable and sometimes exceeded 15 Ω depending on the timing, but the state of the plasma was stable in the ICP.

[0044] When the power value was further increased to 1800 W or more, the impedance became stable. Note that the ICP was also stably maintained at 1800 W or more.

[0045] As described above, as the power value increases, when the impedance becomes equal to or lower than a predetermined CCP threshold value (the second threshold value; for example, it can be 50 Ω in the example of FIG. 3), it can be said that CCP occurs. Further, as the power value further increases, when the impedance becomes equal to or lower than a predetermined ICP threshold value (the first threshold value; for example, it can be 15 Ω in the example of FIG. 3), CCP changes to ICP, that is, it can be said that ICP occurs. Also, after CCP occurs, when the impedance stabilizes, it can be said that CCP changes to ICP, that is, ICP occurs.

[0046] In addition, considering the use of the plasma source 10, it is important to stably maintain ICP. For this reason, as described above, although there is a timing when ICP temporarily occurs even in the region of 1600 W or less in actuality, it is more suitable to determine that ICP has occurred in the region of 1800 W or more where ICP is stably maintained than to determine that ICP has occurred in such a region.

[0047] FIG. 4 is another graph showing an example of the relationship between the power value and the impedance measured in Embodiment 1. The right end of the graph in FIG. 4, that is, the position of 5000 W, corresponds to the constant power stage in FIG. 2.

[0048] FIG. 4 shows three different graphs according to the gas conditions, corresponding to low-pressure and small-flow gas (black triangles), medium-pressure and medium-flow gas (black circles), and high-pressure and large-flow gas (black squares), respectively. Note that a mixture of oxygen and nitrogen was used as the gas in the discharge container.

[0049] 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. For low-pressure and low-flow gases, ICP was stably maintained at 5000 W, and the impedance Zicp was stable at about 13 - 14 Ω. For medium-pressure and medium-flow gases, the plasma state was unstable at 5000 W (i.e., it was CCP or ICP depending on the timing), and the impedance Zccp / icp was not stable at about 14 - 21 Ω. For high-pressure and high-flow gases, the plasma remained CCP at 5000 W (i.e., it did not change to ICP), and the impedance Zccp was stable at about 40 Ω.

[0050] From the graph of FIG. 4, it can also be seen that after CCP occurs, when the impedance (the ratio of the voltage value to the current value) becomes a small value (below a predetermined ICP threshold), CCP has changed to ICP, that is, ICP has occurred.

[0051] That is, because of the relationship shown in Equation (1), it is possible to determine the state of the plasma by monitoring the impedance value and setting an appropriate threshold (ICP threshold). Zicp < Zccp / icp < Zccp ··· (1)

[0052] In addition, the stability of the plasma as described above can be represented, for example, by the standard deviation of the impedance. Of course, it is also possible to represent the stability by other indicators (such as variance), but in this embodiment, the standard deviation is used for explanation. When the stability of the plasma is represented 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 medium-pressure and medium-flow 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 (the smallest). That is, there is the relationship shown in Equation (1). In the above, it was explained that both the standard deviation σccp of the impedance at the time of CCP generation and the standard deviation σicp of the impedance at the time of ICP generation are stable, but strictly speaking, the standard deviation σccp of the impedance at the time of CCP generation is more stable.

[0053] σccp < σicp < σccp / icp ··· (2)

[0054] As described above, since the impedance Zicp and the impedance Zccp / icp are relatively close values, in order to more surely determine that ICP has occurred, it is possible to add the stability of the plasma (for example, the standard deviation of the impedance) as a determination condition. For this purpose, an appropriate standard deviation threshold value may be set.

[0055] In this case, a standard deviation threshold value for determining that ICP has occurred may be set in consideration of the relationship in Equation (2). That is, it is preferable to set the standard deviation threshold value as a range specification. Therefore, it is preferable to determine that ICP has occurred when the standard deviation of the impedance is within a predetermined range (a range determined in advance).

[0056] Note that since the impedance at the time of ICP generation varies depending on the type, flow rate, pressure, etc. of the gas, the ICP threshold value and the standard deviation threshold value used for determination may be determined by conducting experiments such as those shown in Fig. 3 and Fig. 4.

[0057] FIG. 5 is a flowchart showing an example of a method for detecting the state of the plasma source according to Embodiment 1 based on the principles described with reference to FIGS. 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 where no plasma is generated, a state where CCP is generated, a state where ICP is generated (i.e., a state where CCP has changed to ICP), and the like.

[0058] 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 so as to change the voltage value of the voltage corresponding to the voltage applied to the antenna 51). Thereby, the power value of the power supplied to the antenna 51 is controlled. Such power control is performed from the power increase stage to the constant power stage shown in FIG. 2.

[0059] Step S2: The VI sensor 90 detects the voltage value (voltage value signal C1) of the voltage corresponding to the voltage applied to the antenna 51 and the current value (current value signal C2) of the current flowing through the antenna 51. The control means 60 acquires the detected voltage value and current value.

[0060] 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 detected by the VI sensor 90 and the current value (current value signal C2) of the current 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. In step S3, if it is determined 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, the target power value increases in the power increase stage and becomes constant in the constant power stage as the control progresses. Also, the calculation of the impedance and the determination in step S3 are performed from the power increase stage to the constant power 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 unit 50 of the plasma source 10.

[0061] Also, as an optional process, when it is determined in step S3 that the impedance exceeds the CCP threshold (No), as indicated by the dotted arrow, step S7 may be passed through. In this case, in step S7, since the standard deviation of the impedance is not within the predetermined range (determined as No), the process returns to step S1. By performing such an optional process, the standard deviation of the impedance at this point can be confirmed.

[0062] 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, and if 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 constant power stage.

[0063] Step S5: The control means 60 determines that no ICP is generated but plasma is generated as CCP, and outputs a CCP determination signal (second signal) indicating that the plasma has been generated as CCP. For example, in the example of FIG. 3, since an impedance of 50 Ω or less is measured at 200 W, it is determined that no ICP is generated but CCP is generated at the time of 200 W, and step S5 is executed. After the execution of step S5, the process proceeds to step S7.

[0064] 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 has been generated as ICP, and proceeds to step S7. Thereby, it can be understood that the plasma has changed from CCP to ICP.

[0065] Step S7: The control means 60 determines whether or not the standard deviation of the impedance is within a predetermined range. If it is determined that the standard deviation of the impedance is not within the predetermined range (No), the process returns to step S1. If it is determined that the standard deviation of the impedance 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 the present embodiment, the standard deviation of the impedance is used as the stability, but it is also possible to represent the stability by other indexes (such as variance).

[0066] Note that the specific value of the threshold can be, for example, 1 Ω, 5 Ω, etc., and can be appropriately designed by those skilled in the art through experiments and the like. Further, according to the present embodiment, the determination in step S7 is made based on the stability of a plurality of measurement values instead of a single measurement value, so that a more accurate determination can be made. In addition, the determination can be made by a method that is easy to calculate the standard deviation.

[0067] Also, in the present 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 increase stage. Therefore, the standard deviation of impedance is calculated by acquiring detection data multiple times. Therefore, at the stage of the first acquisition of data, etc., the standard deviation of impedance cannot yet be calculated. In such a case, the processes of steps S7 and S8 may be skipped.

[0068] Also, as described above, in the case of the process that proceeds in the order of step S3 → step S7 and the process that proceeds in the order of step S4 → step S5 → step S7, it is also possible to calculate the standard deviation of impedance. Therefore, it is also possible to perform a process of determining whether the standard deviation of impedance is within a predetermined range during the power increase stage, or to calculate the standard deviation of impedance based on the acquired detection data after the power constant stage is reached, and perform a process of determining whether the standard deviation of impedance is within a predetermined range.

[0069] As described above, when calculating the standard deviation of impedance based on the voltage value (voltage value signal C1) and current value (current value signal C2) detected by the VI sensor 90 after the power constant stage is reached, steps S7 and S8 may be skipped in the power increase stage.

[0070] 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 processes of steps S4 and S6. However, by performing the processes of steps S7 and S8, it can be more surely known that the plasma has changed from CCP to ICP.

[0071] Step S9: The control means 60 determines whether to stop the power supply. If it is determined not to stop the power supply (No), the process returns to step S1. 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 constant power stage are completed, the power supply is stopped. When returning from step S9 to step S1, steps S1 to S8 are repeated.

[0072] As described above, according to the plasma source 10 according to Embodiment 1, since the generation of ICP is determined based on the impedance value and the impedance stability, it is possible to more accurately detect that the plasma has changed from CCP to ICP.

[0073] In this embodiment, since the emission intensity is not used for detection, determination can be performed more accurately than in the prior art. Further, 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 pressures are different. As a modification, it is also possible to use the emission intensity in combination for determination.

[0074] Also, not only can it simply detect that the plasma has changed to inductively coupled plasma, but also the stability of the inductively coupled plasma can be determined.

[0075] Regarding the generation of plasma as CCP, since it is determined based on the impedance being below the threshold value, the generation of plasma can be detected more accurately.

[0076] Also, in this embodiment, since the VI sensor 90 is arranged between the DC power supply circuit 20 and the inverter circuit 30, the current value and the voltage value can be easily detected.

[0077] <Method for Determining Threshold Value> Specific values of the CCP threshold, ICP threshold, and standard deviation threshold of the impedance serving as the determination criteria can be easily determined by those skilled in the art based on experiments and the like. An example will be described below.

[0078] First, determine the operating conditions (power, gas composition, pressure, flow rate, etc.) for generating the target ICP, and specifically construct the plasma source 10 accordingly. Then, while increasing the power using the plasma source 10, measure the impedance, and observe and record whether a CCP has occurred and whether an ICP has occurred.

[0079] Here, the increase in power does not need to be performed in a short time as shown in FIG. 2, and it can be performed slowly so that sufficient time for observation can be obtained. Also, when observing, the increase in the power value may be stopped and set to a constant power value.

[0080] Embodiment 2. FIG. 6 is a flowchart showing an example of a method for detecting the state of the plasma source 10 according to Embodiment 2. In the flowchart of FIG. 6, the same or similar processes as those in the flowchart of FIG. 5 use the same step numbers. Note that since the configuration of the plasma source 10 is the same as that of the plasma source 10 according to Embodiment 1 (FIG. 1), the description thereof is omitted. Hereinafter, a method for detecting the state of the plasma source 10 according to Embodiment 2 will be described centering on the differences from the flowchart of FIG. 5. Steps S1 to S2 and step S9 are the same as those in FIG. 5, so the description thereof is omitted.

[0081] Step S3: The control means 60 determines whether the impedance calculated based on the voltage value (voltage value signal C1) of the voltage detected by the VI sensor 90 and the current value (current value signal C2) of the current 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 S5. If it is determined in step S3 that the impedance exceeds the CCP threshold value (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.

[0082] Step S5: The control means 60 determines that ICP is not generated but plasma is generated as CCP, and outputs a CCP determination signal indicating that the plasma is generated as CCP. For example, in the example of FIG. 3, since an impedance of 50 Ω or less is measured at 200 W, it is determined that ICP is not generated but CCP is generated at the time of 200 W, and step S5 is executed. After the execution of step S5, the process proceeds to step S7.

[0083] Step S7: The control means 60 determines whether or not the standard deviation of the impedance is within a predetermined range. If it is determined that the standard deviation of the impedance is not within the predetermined range (No), the process returns to step S1. If it is determined that the standard deviation of the impedance 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.

[0084] Similar to the description in step S7 of FIG. 5, when calculating the standard deviation of the impedance based on the voltage value (voltage value signal C1) and the current value (current value signal C2) detected by the VI sensor 90 after the constant power stage, step S7 may be skipped in the power increasing stage.

[0085] Step S4: The control means 60 determines whether or not the impedance is equal to or less than a predetermined ICP threshold value. If the impedance exceeds the ICP threshold value in step S4 (No), the process proceeds to step S1. If it is determined that the impedance is equal to or less than the ICP threshold value (Yes), the process proceeds to step S6. Further, the calculation of the impedance and the determination in step S4 are performed from the power increasing stage to the constant power stage.

[0086] 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. Thereby, it can be seen that the plasma has changed from CCP to ICP.

[0087] When comparing with the flowchart of FIG. 5, the flowchart of FIG. 6 does not have a process corresponding to step S8 of 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 stability determination signal output in step S8 of FIG. 5. Therefore, the same effect as when executing the flowchart of FIG. 5 can be obtained.

[0088] <Modification Example 1 of FIG. 6> As a modification example of FIG. 6, the order of step S7 and step S4 may be reversed. Even in this case, the same effect can be obtained.

[0089] <Modification Example 2 of FIG. 6> As described with reference to FIG. 4, depending on the pressure and flow rate of the gas, after CCP occurs and when the state of the plasma stabilizes, it can be determined that ICP has occurred. For example, as shown in FIG. 4, when the gas pressure is low and the gas flow rate is small, the impedance fluctuation is small, and it can be determined that ICP has occurred. Therefore, as a second modification example of FIG. 6, when it is determined in step S7 that the standard deviation of the impedance is within a predetermined range (Yes), as indicated by the dotted arrow, it may proceed to step S6. That is, the process of determining whether the impedance in step S4 is equal to or less than a predetermined ICP threshold value is omitted. Even in this case, it is possible to determine that the plasma has changed from CCP to ICP.

[0090] Note that, similar to the description of step S7 in FIG. 5, when calculating the standard deviation of the impedance based on the acquired detection data after the constant power stage, step S7 may be skipped in the power increasing stage. That is, in the power increasing stage, it is not determined whether the plasma has changed from CCP to ICP.

[0091] <Other Modification Examples> The content, format, output mode, 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 may include 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.

[0092] Also, 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 ICP occurred.

[0093] In the processes of steps S1 to S2 in FIGS. 5 and 6, when the power value becomes equal to or greater than a predetermined threshold value, error processing 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 even when plasma is not generated due to a failure or the like.

[0094] Steps S3 and S5 in FIGS. 5 and 6 may be omitted. That is, the determination of the occurrence of CCP may be omitted. Even in such a case, since plasma is generated and changes to ICP as the power value increases, the occurrence of ICP can be appropriately determined.

Explanation of Signs

[0095] 10…Plasma source 20…DC power supply circuit 30…Inverter circuit 40…Resonance circuit 41…LC circuit section 42…Capacitor 50…Discharge section 51…Antenna 52…Resistor 60…Control means (control unit, determination unit) 90…VI sensor (sensor)

Claims

1. A discharge unit having a discharge tube and an antenna for generating plasma therein, A DC power supply circuit for outputting a DC voltage, An inverter circuit for converting the DC voltage output from the DC power supply circuit into an AC voltage, A resonance 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 the voltage applied to the antenna and the current flowing through the antenna, A control unit for controlling 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 the state of the plasma inside the discharge tube, Comprising, After the plasma is generated, when the ratio of the voltage value to the current value becomes equal to or less than a first threshold value, the determination unit outputs a first signal indicating that the plasma has changed to inductively coupled plasma, The sensor is disposed between the DC power supply circuit and the inverter circuit, or between the inverter circuit and the resonance circuit, When the sensor is disposed between the DC power supply circuit and the inverter circuit, the control unit controls the output voltage value of the DC power supply circuit so as to change the voltage value. When the sensor is disposed between the inverter circuit and the resonance circuit, the control unit controls the output voltage value of the inverter circuit so as to change the voltage value. An inductively coupled plasma source.

2. After the plasma is generated, 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, and then controls 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 of the voltage detected by the sensor to the current value of the current based on the voltage value and the current value, and after the plasma is generated, when 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 inductively coupled plasma. The inductively coupled plasma source according to claim 1.

3. After the supply of voltage to the antenna is started, when the ratio of the voltage value to the current value becomes equal to or less than a second threshold value, the determination unit outputs a second signal indicating that the plasma has been generated. The inductively coupled plasma source according to claim 1 or 2.

4. The sensor is disposed between the DC power supply circuit and the inverter circuit. The sensor detects the output voltage value of the DC power supply circuit and the current value of the 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.

5. The antenna is a conductor formed in a coil shape so as to surround the discharge tube. The inductively coupled plasma source according to any one of claims 1 to 4.

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