plasma source

Abstract

To expand application ranges of a voltage limit value and a current limit value to be applied during a period until it is determined that plasma generated in a discharge tube is transient from capacitive coupling plasma to inductive coupling plasma.SOLUTION: A plasma source comprises a discharge unit which generates plasma and a high frequency power source which supplies power to the discharge unit. The high frequency power source includes a DC power supply circuit, an inverter circuit, a resonance circuit and a control section. The control section changes an output voltage value of the DC power supply circuit or the inverter circuit in such a manner that a voltage value and a current value of power supplied to the discharge unit do not exceed predetermined limit values during a period from applying a voltage to an antenna of the discharge unit to determining that plasma is transient from capacitive coupling plasma to inductive coupling plasma. The limit values are values which are respectively set within such ranges of voltage values and current values that an element in the high frequency power source is not damaged.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a plasma source. [Background technology]

[0002] In semiconductor manufacturing processes, plasma is used to perform film formation processes, etching processes, etc. on semiconductor wafers. Patent Document 1 discloses a plasma generator as an inductively coupled plasma (ICP) type plasma source. The plasma generator includes an antenna coil wound around a cylindrical vacuum vessel (discharge tube), and a high-frequency power supply that supplies high-frequency power to the antenna coil.

[0003] A known plasma source for generating ICP is one that supplies high-frequency power to an antenna coil to generate capacitively coupled plasma (CCP), and then increases the high-frequency power to change the capacitively coupled plasma to inductively coupled plasma.

[0004] In such a plasma source, in order to protect, for example, the circuit elements of the high-frequency power supply and the resonant circuit, limit values ​​for the voltage and current values ​​of the high-frequency power supplied to the antenna coil are set in accordance with the derating of each element. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2020-057464 Summary of the Invention [Problem to be solved by the invention]

[0006] However, if the derating is set large in consideration of the temperature rise caused by heat generation of the element, the applicable range of voltage and current values ​​is unnecessarily restricted. Unnecessarily restricting the applicable range of voltage and current values ​​makes it difficult to generate capacitively coupled plasma and to transition from capacitively coupled plasma to inductively coupled plasma. Furthermore, unnecessarily restricting the applicable range of voltage and current values ​​leads to a narrowing of the applicable range of plasma generation conditions other than voltage and current values, such as gas pressure and gas flow rate.

[0007] In view of the above, the present invention aims to expand the range of application of voltage limit values ​​and current limit values ​​that are applied during the period until it is determined that the plasma generated in the discharge tube has transitioned from capacitively coupled plasma to inductively coupled plasma. [Means for solving the problem]

[0008] A plasma source according to an embodiment includes a discharge unit having a discharge tube used to generate plasma by ionizing a gas and a conductive antenna formed in a coil shape surrounding the discharge tube, and a high-frequency power supply that supplies power to the discharge unit. The high-frequency power supply includes a DC power supply circuit, an inverter circuit, a resonant circuit, and a control unit. The DC power supply circuit outputs a DC voltage. The inverter circuit converts the DC voltage output from the DC power supply circuit into a voltage having a frequency in a radio frequency band. The resonant circuit is disposed between the inverter circuit and the discharge unit. During a first period from when the voltage is applied to the antenna to when it is determined that the plasma generated in the discharge tube has transitioned from capacitively coupled plasma to inductively coupled plasma, the control unit changes the output voltage of the DC power supply circuit or the inverter circuit so that the voltage value applied to the antenna does not exceed a predetermined first voltage limit value, and changes the output voltage of the DC power supply circuit or the inverter circuit so that the current value flowing through the antenna does not exceed a predetermined first current limit value. The first voltage limit value is a value that is set individually within a range of voltage values ​​that will not damage elements in the inverter circuit and elements in the resonant circuit, and the first current limit value is a value that is set individually within a range of current values ​​that will not damage elements in the inverter circuit and elements in the resonant circuit.

[0009] In the plasma source according to the embodiment, the first voltage limit value and the first current limit value are each set so that the plasma in the discharge tube can transition from capacitively coupled plasma to inductively coupled plasma under gas conditions flowing into the discharge tube set within a desired range.

[0010] In the plasma source according to the embodiment, during a second period after the first period, the control unit changes the output voltage value of the DC power supply circuit or the inverter circuit so that the voltage value of the voltage applied to the antenna does not exceed a second voltage limit value that is smaller than the predetermined first voltage limit value, and also changes the output voltage value of the DC power supply circuit or the inverter circuit so that the current value of the current flowing through the antenna does not exceed a second current limit value that is smaller than the predetermined first current limit value.

[0011] In the plasma source according to the embodiment, a limit value transition period is provided between the first period and the second period. The voltage limit value during the limit value transition period is transitioned from the first voltage limit value to the second voltage limit value. The current limit value during the limit value transition period is transitioned from the first current limit value to the second current limit value. The control unit changes the output voltage value of the DC power supply circuit so that the voltage value of the voltage applied to the antenna does not exceed the voltage limit value during the limit value transition period, and also changes the output voltage value of the DC power supply circuit so that the current value of the current flowing through the antenna does not exceed the current limit value during the limit value transition period.

[0012] The plasma source according to the embodiment further includes a determination unit that determines whether the plasma in the discharge tube has transitioned from capacitively coupled plasma to inductively coupled plasma based on the voltage value of the voltage applied to the antenna and the current value of the current flowing through the antenna. [Effects of the Invention]

[0013] According to the present invention, it is possible to expand the range of application of the voltage limit value and the current limit value that are applied during the period until it is determined that the plasma generated in the discharge tube has transitioned from capacitively coupled plasma to inductively coupled plasma. [Brief explanation of the drawings]

[0014] [Figure 1]FIG. 1 is a diagram showing an example of the configuration of a plasma source according to an embodiment. [Figure 2] FIG. 2 is a diagram showing an example of a waveform of high-frequency power output from the DC power supply circuit or the inverter circuit of FIG. [Figure 3] FIG. 3 is a diagram for explaining the concept of setting the applicable range of high frequency power according to the embodiment. [Figure 4] FIG. 4 is a diagram for explaining an example of setting the application range of high frequency power according to the embodiment. [Figure 5] FIG. 5 is a diagram for explaining the range of gas conditions according to the embodiment. [Figure 6] FIG. 6 is a flowchart showing an example of the flow of a plasma generation process performed in the plasma source according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, a plasma source according to an embodiment will be described in detail with reference to the drawings, although the present invention is not limited to the present embodiment.

[0016] In the description of this embodiment, components having the same or substantially the same functions as those described above with respect to the previous drawings may be given the same reference numerals, and their description may be omitted as appropriate. Furthermore, even when the same or substantially the same parts are shown, the dimensions and proportions may be different depending on the drawing. Furthermore, for example, in order to ensure the visibility of the drawings, reference numerals may be given to only the main components in the description of each drawing, and reference numerals may not be given to components having the same or substantially the same functions as those described above with respect to the previous drawings.

[0017] 1 is a diagram showing an example of the configuration of a plasma source 10 according to an embodiment. The plasma source 10 is configured to be able to generate inductively coupled plasma (ICP). As shown in FIG. 1, 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 circuit 60, a DC voltage sensor 91, a DC current sensor 92, a high-frequency voltage sensor 93, and a high-frequency current sensor 94. The DC power supply circuit 20, the inverter circuit 30, the resonant circuit 40, and the control circuit 60 are an example of a high-frequency power supply that supplies power to the discharge unit 50.

[0018] The DC power supply circuit 20 is connected to an AC power supply. The AC power supply is provided, for example, outside the plasma source 10, but may be provided as a component of the plasma source 10 or the DC power supply circuit 20. The DC power supply circuit 20 is configured to output a DC voltage using an AC voltage from the AC power supply. As an example, the DC power supply circuit 20 includes a rectifier / smoothing circuit (not shown) and a step-up / step-down chopper (not shown). The rectifier / smoothing circuit is configured to convert the AC voltage supplied from the AC power supply into a DC voltage. The step-up / step-down chopper is configured to step-up or step-down the DC voltage from the rectifier / smoothing circuit to a voltage value corresponding to a control signal S3 from the control circuit 60. The plasma source 10 is configured to operate using this DC voltage.

[0019] The inverter circuit 30 is provided at a subsequent stage of the DC power supply circuit 20. In the example of FIG. 1, the input terminal of the inverter circuit 30 is connected to the output stage of the DC power supply circuit 20 via a DC voltage sensor 91 and a DC current sensor 92. The inverter circuit 30 is configured to convert the DC voltage output from the DC power supply circuit 20 into an AC voltage. The AC voltage has, for example, a frequency in the radio frequency band (RF: Radio Frequency). For example, the frequency is about 2 MHz.

[0020] The resonant circuit 40 is provided between the inverter circuit 30 and the discharge unit 50. Specifically, the input terminal of the resonant circuit 40 is connected to the output terminal of the inverter circuit 30. The resonant circuit 40 is configured to generate high-frequency power through a resonance phenomenon using the AC current from the inverter circuit 30. In the example of FIG. 1, the resonant circuit 40 has an LC circuit unit 41 and a capacitor 42. The input terminal of the LC circuit unit 41 is connected to the output terminal of the inverter circuit 30. The capacitor 42 is connected in parallel with the discharge unit 50 in the subsequent stage to the output terminal of the LC circuit unit 41. Note that the resonant circuit 40 is not limited to the configuration shown in FIG. 1.

[0021] The discharge unit 50 is provided downstream of the resonant circuit 40. Specifically, the power input terminal of the discharge unit 50 is connected to the output terminal of the resonant circuit 40. In the example of FIG. 1, the power input terminal of the discharge unit 50 is connected to the output terminal of the LC circuit 41 via a high-frequency voltage sensor 93 and a high-frequency current sensor 94. The discharge unit 50 includes a discharge tube (not shown) and an antenna 51. The discharge tube is used to generate plasma by ionizing a gas and has an inlet and an outlet for the source gas at both ends. The discharge tube is formed, for example, in a tubular (cylindrical) shape. The discharge tube is formed using a non-conductive material or a dielectric, such as quartz or alumina, to insulate the antenna 51 from the plasma. In the example of FIG. 1, the antenna 51 is connected in parallel with the upstream capacitor 42 to the output terminal of the LC circuit 41. The antenna 51 is, for example, a conductor formed in a coil shape to surround the discharge tube. 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 is configured to generate plasma using high-frequency power supplied to the discharge tube and antenna. For example, when an alternating current Irf flows through the antenna 51 while a source gas is flowing through the discharge tube, the source gas is ionized by the voltage Vrf between the terminals of the coil of the antenna 51, generating plasma. This is plasma coupled by an electric field between the terminals of the coil, i.e., capacitively coupled plasma (CCP). When the high-frequency current Irf of the antenna 51 is further increased while CCP is being generated, a magnetic field is formed around the coil, generating an induced electric field, thereby generating ICP. ICP is a type of plasma used in the manufacture of semiconductor devices and is maintained and managed according to the application.

[0023] The gas conditions (composition, pressure, flow rate, etc.) for the material gas in the discharge tube can be designed appropriately by those skilled in the art. For example, a mixture of oxygen and nitrogen can be used as the composition. For example, 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.

[0024] The control circuit 60 is configured to control the operation of the plasma source 10. For example, the control circuit 60 is configured to operate 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. Furthermore, for example, the control circuit 60 is configured to operate as a determination unit that determines the state of plasma inside the discharge tube. The control circuit 60 may have a processor and memory as hardware resources and be configured to realize the functions of the control unit and / or determination unit by executing a control program loaded into the memory. Alternatively, the control circuit 60 may have, as hardware resources, a dedicated circuit configured to realize the functions of the control unit and / or determination unit.

[0025] The DC voltage sensor 91 and the DC current sensor 92 are disposed between the DC power supply circuit 20 and the inverter circuit 30. The DC voltage sensor 91 is configured to detect the voltage value of the output voltage Vdc of the DC power supply circuit 20 and output a voltage value signal S1 corresponding to the detected output voltage value. The DC current sensor 92 is configured to detect the current value of the DC current Idc flowing between the DC power supply circuit 20 and the inverter circuit 30 and output a current value signal S2 corresponding to the detected current value.

[0026] The high-frequency voltage sensor 93 and the high-frequency current sensor 94 are disposed between the resonant circuit 40 and the discharge unit 50. The high-frequency voltage sensor 93 is configured to detect the voltage value of the AC voltage Vrf applied to the antenna 51 and output a voltage value signal S5 corresponding to the detected output voltage value. The high-frequency current sensor 94 is configured to detect the current value of the AC current flowing between the resonant circuit 40 and the discharge unit 50, i.e., the AC current Irf flowing through the antenna 51, and output a current value signal S6 corresponding to the detected current value.

[0027] 1 does not show or describe switching elements in the DC power supply circuit 20 or a drive amplifier that provides a drive signal to the switching elements in the inverter circuit 30. The DC power supply circuit 20, the inverter circuit 30, and the control circuit 60 are each connected to a power supply (not shown), and are supplied with power from the power supply.

[0028] Next, an example of the operation of the plasma source 10 having the above configuration will be described with reference to the drawings.

[0029] As an example, the control circuit 60 calculates a detected power value based on a voltage detection signal S1 detected by a DC voltage sensor 91 and a current detection signal S2 detected by a DC current sensor 92. Here, the voltage detection signal S1 includes information on a voltage value. The current detection signal S2 includes information on a current value. The detected power value is expressed as the product of the voltage detection signal S1 and the current detection signal S2, and indicates the power value at the output terminal of the buck-boost chopper of the DC power supply circuit 20.

[0030] Here, as the DC power value output from the buck-boost chopper of the DC power supply circuit 20 increases or decreases, the power value supplied to the antenna 51 also increases or decreases. Also, there is a correlation between the DC power value output from the buck-boost chopper of the DC power supply circuit 20 and the power value supplied to the antenna 51. Therefore, the power value supplied to the antenna 51 can be estimated from the DC power value output from the buck-boost chopper of the DC power supply circuit 20.

[0031] Therefore, the control circuit 60 can control the power value supplied to the antenna 51 by setting a DC power value corresponding to the power value to be supplied to the antenna 51 as a target power value. Specifically, the control circuit 60 transmits a control signal S3 to the buck-boost chopper of the DC power supply circuit 20 so that the detected power value becomes equal to the target power value. The buck-boost chopper of the DC power supply circuit 20 increases or decreases the output voltage value based on the control signal S3. For example, the buck-boost chopper of the DC power supply circuit 20 increases or decreases the output voltage value by increasing or decreasing the duty ratio of an internal switching element based on the control signal S3.

[0032] In this way, the control circuit 60 controls the output voltage of the step-up / step-down chopper of the DC power supply circuit 20 to increase or decrease so that the detected power value becomes the target power value, thereby adjusting the power value supplied to the antenna 51. Control that indirectly calculates the detected power value supplied to the antenna 51 has the advantage of being able to calculate the power value more easily than control that uses the values ​​detected by the high-frequency voltage sensor 93 and the high-frequency current sensor 94. That is, a configuration in which the DC voltage sensor 91 and the DC current sensor 92 are provided at the output end of the DC power supply circuit 20 allows for easy detection of the voltage and current values. This is because, while detecting high-frequency power requires consideration of factors such as the phase difference between voltage and current, detecting DC power requires only calculating the product of the voltage and current. Note that when performing this control, the plasma source 10 does not need to have the high-frequency voltage sensor 93 and the high-frequency current sensor 94.

[0033] As another example, the control circuit 60 can adjust the power value of the power supplied to the antenna 51 by adjusting the duty ratio of the switching element in the inverter circuit 30 to increase or decrease the output voltage of the inverter circuit 30, instead of using the step-up / step-down chopper of the DC power supply circuit 20.

[0034] Specifically, the control circuit 60 calculates the detected power value to be supplied to the antenna 51 based on the detection signal S5 of the high-frequency voltage sensor 93 and the detection signal S6 of the high-frequency current sensor 94. The control circuit 60 also transmits a control signal S4 to the inverter circuit 30 so that the detected power value is equal to the target power value. The inverter circuit 30 increases or decreases the output voltage value based on the control signal S4. For example, the inverter circuit 30 increases or decreases the output voltage value by increasing or decreasing the duty ratio of an internal switching element based on the control signal S4.

[0035] Even with this control, it is possible to adjust the power value of the power supplied to the antenna 51. When performing this control, the plasma source 10 does not need to have the DC voltage sensor 91 and the DC current sensor 62.

[0036] In addition, when the voltage value or current value exceeds each limit value, the control circuit 60 controls the step-up / step-down chopper of the DC power supply circuit 20 or the output voltage value of the inverter circuit 30 using control signals S3 and S4 to protect the elements in the inverter circuit 30 and the resonant circuit 40.

[0037] As described above, the power supplied to the antenna 51 can be adjusted by a plurality of methods. The method for adjusting the power value of the power supplied to the antenna 51 may be appropriately designed depending on the configurations of the DC power supply circuit 20 and the inverter circuit 30.

[0038] Fig. 2 is a diagram showing an example of a waveform of high frequency power output from the step-up / step-down chopper or inverter circuit 30 of the DC power supply circuit 20 in Fig. 1. In Fig. 2, the horizontal axis and vertical axis represent time and power values ​​related to plasma, respectively.

[0039] The control circuit 60 controls the power value related to the plasma by controlling the power output from the step-up / step-down chopper or inverter circuit 30 of the DC power supply circuit 20 as shown in Fig. 2. The operation of the plasma source 10 includes a power increase stage and a constant power stage.

[0040] In the power increase stage, the control circuit 60 increases the output voltage of the buck-boost chopper or inverter circuit 30 of the DC power supply circuit 20, 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 arbitrarily. The duration is, for example, from several milliseconds to several tens of milliseconds (50 milliseconds in the example of FIG. 2), but is not limited to this. The duration may be, for example, about 100 milliseconds.

[0041] In the example of Fig. 2, the power value of the power increase stage is 0 W at the start and 5000 W at the end. During this power increase stage, plasma (CCP) is generated, and the plasma state transitions from CCP to ICP. Note that in the example of Fig. 2, the power value increases continuously over time, but this is not limiting. The power value may also increase in steps over time.

[0042] After the power increase phase, the system transitions to a constant power phase. The constant power phase is the phase after the power value reaches a predetermined value (5000 W in the example of Figure 2), and the power value is maintained. Since the plasma state usually transitions from CCP to ICP during the power increase phase, the predetermined value can be designed, for example, to be a value at which ICP is stably maintained.

[0043] 3 is a diagram for explaining the concept of setting the applicable range of high frequency power according to the embodiment, in which the horizontal axis and vertical axis represent time and the limit value for the detected power value of high frequency power, respectively.

[0044] As shown in FIG. 3, the limit value for the detected power value of the high frequency power includes a first limit value C1 for ICP ignition and a second limit value C2 while the ICP is being maintained.

[0045] The first limit value C1 is a limit value applied to a first period from when a high-frequency voltage is applied to the antenna 51 until it is determined that the state of plasma generated in the discharge tube has transitioned from CCP to ICP. The first limit value C1 is a value that is individually set within a range of voltage or current values ​​that will not damage each element in the inverter circuit 30 and the resonant circuit 40. Here, the first limit value C1 for the voltage value is an example of a first voltage limit value. Also, the first limit value C1 for the current value is an example of a first current limit value. Note that in this embodiment, for the sake of simplicity, the first limit value C1 for the voltage value and the first limit value C1 for the current value are given the same symbol, but in reality, the first limit value C1 for the voltage value and the first limit value C1 for the current value are different.

[0046] The second limit value C2 is a limit value applied after the first period, i.e., during a second period during which the ICP is maintained. The second limit value C2 is smaller than the first limit value C1. Here, the second limit value C2 for the voltage value is an example of a second voltage limit value. Furthermore, the second limit value C2 for the current value is an example of a second current limit value. In this embodiment, for the sake of simplicity, the second limit value C2 for the voltage value and the second limit value C2 for the current value are given the same symbol, but in reality, the second limit value for the voltage value and the second limit value for the current value are different.

[0047] Furthermore, a limit value transition period is provided between the first period and the second period. During the limit value transition period, the transition limit value C3 for the detected power value of the high frequency power is transitioned from a first limit value C1 to a second limit value C2. This limit value transition period will be described later.

[0048] During the first period, the control circuit 60 changes the output voltage value of the DC power supply circuit 20 or the inverter circuit 30 so that the voltage value of the voltage Vrf applied to the antenna 51 does not exceed a first limit value C1 for a predetermined voltage value, and also changes the output voltage value of the DC power supply circuit 20 or the inverter circuit 30 so that the current value of the current Irf flowing through the antenna 51 does not exceed the first limit value C1 for a predetermined current value.

[0049] In the second period, the control circuit 60 changes the output voltage value of the DC power supply circuit 20 or the inverter circuit 30 so that the voltage value of the voltage Vrf applied to the antenna 51 does not exceed the second limit value C2 for a predetermined voltage value, and also changes the output voltage value of the DC power supply circuit 20 or the inverter circuit 30 so that the current value of the current Irf flowing through the antenna 51 does not exceed the second limit value C2 for a predetermined current value.

[0050] According to this configuration, the first limit value C1 can be set for each high-frequency power supply within a range up to the maximum value that does not damage the elements of that high-frequency power supply. That is, the range of application of high-frequency power during the first period for each high-frequency power supply can be maximized, and the voltage and current values ​​supplied to the antenna 51 can be increased while protecting the elements of the high-frequency power supply. If the voltage and current values ​​supplied to the antenna 51 can be increased, the source gas can be more easily ionized, making it easier to generate CCP and to transition from CCP to ICP. That is, according to the above configuration, it is possible to make it easier to generate ICP.

[0051] Furthermore, since it becomes easier to ionize the gas if the voltage and current values ​​supplied to the antenna 51 can be increased, maximizing the adjustment range of the first limit value C1 can expand the range of application of other plasma generation conditions (e.g., gas pressure and gas flow rate) for that power value.

[0052] 4 is a diagram illustrating an example of setting the application range of high frequency power according to the embodiment, in which the horizontal and vertical axes represent time and the limit value for the detected power value of high frequency power, respectively.

[0053] In this embodiment, the first limit value C1 is set for each discharge tube, i.e., for each plasma source 10, so that the plasma in the discharge tube transitions from CCP to ICP under gas conditions that are set within a desired range and that flow into the discharge tube. As an example, Fig. 4 illustrates a case in which the first limit value C1 is divided into a first limit value C11 for discharge tube A and a first limit value C12 for discharge tube B. The first limit value C11 for discharge tube A is set based on a threshold value TA for the power value that realizes ICP ignition in discharge tube A. The first limit value C12 for discharge tube B is set based on a threshold value TB for the power value that realizes ICP ignition in discharge tube B.

[0054] The first limit value C11 is set to be larger than the threshold value TA by a predetermined value. The predetermined value is determined appropriately depending on the situation. The first limit value C12 is set to be larger than the threshold value TB by a predetermined value. The predetermined value is determined appropriately depending on the situation.

[0055] When manufacturing multiple plasma sources 10, variations in the manufacturing accuracy of the antenna 51 and the manufacturing accuracy of the discharge unit 50, such as the degree of adhesion between the discharge tube and the antenna 51, can cause differences in the plasma generation conditions that can generate ICP for each plasma source 10. Here, the plasma generation conditions include the voltage value, current value, and gas conditions that realize ICP ignition in each plasma source 10. The gas conditions are, for example, at least one of the gas pressure and the gas flow rate.

[0056] FIG. 5 is a diagram illustrating the range of gas conditions according to an embodiment. As an example, FIG. 5 illustrates the range of gas conditions for discharge tube A and the range of gas conditions for discharge tube B. FIG. 5 also illustrates the pressure [Pa] of oxygen as a material gas as a gas condition. Here, discharge tube A and discharge tube B are assumed to be discharge tubes of the discharge units 50 of different plasma sources 10. (1) of FIG. 5 illustrates the gas conditions when the common first limit value C1 used in the example of FIG. 3 is applied to discharge tube A and discharge tube B. (2) of FIG. 5 illustrates the gas conditions when the first limit values ​​C11 and C12 are applied to discharge tube A and discharge tube B, respectively.

[0057] For example, depending on the gas conditions, such as the gas condition of 320 Pa to 360 Pa illustrated in (1) of Fig. 5, the first limit value C12 suitable for discharge tube B may be smaller than the common first limit value C1, while the first limit value C11 suitable for discharge tube A may be larger than the common first limit value C1, as illustrated in Fig. 4. Such variations in the range of gas conditions may cause variations in the quality of products processed using plasma source 10.

[0058] In this situation, with the above configuration, the first limit values ​​C11 and C12 are set for each discharge tube, i.e., for each plasma source 10. This reduces the variation in the range of gas conditions that can generate ICP, i.e., the differences between individual units, as illustrated in FIG. 5(2). FIG. 5(2) illustrates gas conditions when the first limit values ​​C11 and C12 are applied to discharge tubes A and B, respectively. Reducing the variation in the range of gas conditions contributes to reducing the variation in the quality of products processed using the plasma source 10. Furthermore, since the adjustment range of the first limit values ​​C11 and C12 during the first period is maximized, the range of gas conditions can be expanded while reducing the variation in the range of gas conditions compared to when a common first limit value C1 is used for multiple plasma sources 10.

[0059] The second limit value C2 shown in Fig. 4 is a limit value applied after the first period, i.e., during the second period during which the ICP is maintained, as in Fig. 3. The second limit value C2 is smaller than the first limit values ​​C11 and C12.

[0060] According to this configuration, the maximum values ​​of the voltage and current required to maintain the ICP in the second period are smaller than those in the first period, and therefore it is not necessary to determine the second limit value C2 for each plasma source 10. In other words, according to the above configuration, even when multiple high frequency power supplies are manufactured, a common second limit value C2 can be applied to the multiple high frequency power supplies as long as the elements of the high frequency power supplies are not damaged.

[0061] Furthermore, a limit value transition period is provided between the first period and the second period shown in Fig. 4, similar to Fig. 3. The limit values ​​(transition limit values ​​C3, C31, C32) for the detected power value of the high frequency power during the limit value transition period are transitioned from the first limit values ​​C1, C11, C12 to the second limit value C2, respectively, during the limit value transition period.

[0062] In the example of Fig. 4, in contrast to the common transition limit value C3 used in the example of Fig. 3, the transition limit value C31 is used in the discharge tube A, and the transition limit value C32 is used in the discharge tube B. Also, the transition limit values ​​C3, C31, and C32 are set for the voltage value and the current value, respectively, like the first limit value C1 and the second limit value C2 described above, but for the sake of simplicity, the same symbols are used.

[0063] During the limit value transition period, the control circuit 60 changes the output voltage value of the DC power supply circuit 20 or the inverter circuit 30 so that the voltage value of the voltage Vrf applied to the antenna 51 does not exceed the transition limit value C3 for the voltage value at that time, and also changes the output voltage value of the DC power supply circuit 20 or the inverter circuit 30 so that the current value of the current Irf flowing through the antenna 51 does not exceed the transition limit value C3 for the current value at that time.

[0064] The transition from CCP to ICP is completed in a relatively short time (e.g., about 4 msec), but not instantaneously. In other words, during the transition from CCP to ICP, the proportion of CCP decreases, while the proportion of ICP increases. Therefore, even if a transition from CCP to ICP is determined to have occurred, if the limit value is suddenly reduced from the first limit value C1 to the second limit value C2, depending on the proportion of CCP present at that time, the voltage or current may exceed the limit value, even if the transition is normal. In this case, the output voltage from the DC power supply circuit 20 or the inverter circuit 30 is significantly reduced to protect the elements, and the voltage Vrf applied to the antenna 51 may also be reduced before the proportion of ICP increases sufficiently. As a result, the transition from CCP to ICP may fail.

[0065] Furthermore, if the transition from CCP to ICP has been completely completed, suddenly reducing the limit value will not affect the transition from CCP to ICP. However, if an error occurs in the timing of the transition determination, the transition from CCP to ICP may fail.

[0066] In this situation, according to the above configuration, a limit value transition period is provided, so that the limit value can be appropriately transitioned and the transition from CCP to ICP can be appropriately performed.

[0067] Furthermore, the control circuit 60 determines whether the state of plasma in the discharge tube has transitioned from CCP to ICP based on the voltage value of the voltage Vrf applied to the antenna 51 and the current value of the current Irf flowing through the antenna 51. As described above, since there is a correlation between the power value at the output end of the buck-boost chopper of the DC power supply circuit 20 and the power value supplied to the antenna 51, in the following examples, the voltage Vdc and current Idc may be interpreted as the voltage Vrf and current Irf, as appropriate. Similarly, the DC power value output from the buck-boost chopper of the DC power supply circuit 20 may be interpreted as the power value supplied to the antenna 51.

[0068] As an example, the control circuit 60 determines whether or not a transition to ICP has occurred based on a current increase rate that represents the ratio of the increase in the current Idc to the increase in the voltage Vdc. Specifically, the control circuit 60 acquires a first current increase rate, which is the current increase rate of the current Idc at an arbitrary time point in a CCP-occurring state, i.e., after the high-frequency voltage is applied to the antenna 51, and a second current increase rate, which is the current increase rate at an arbitrary time point after the first current increase rate. Furthermore, the control circuit 60 determines that a transition to ICP has occurred when the ratio of the second current increase rate to the first current increase rate exceeds a predetermined threshold.

[0069] As an example, the control circuit 60 determines whether or not a transition to ICP has occurred based on the value obtained by differentiating the voltage Vdc or the current Idc with respect to the power value at the output terminal of the buck-boost chopper of the DC power supply circuit 20. Specifically, after a CCP occurs, the control circuit 60 acquires the power value and the voltage Vdc or the current Idc. Furthermore, the control circuit 60 determines that a transition to ICP has occurred when the value obtained by differentiating the voltage Vdc with respect to the power changes from a decrease to an increase. Alternatively, the control circuit 60 determines that a transition to ICP has occurred when the value obtained by differentiating the current Idc with respect to the power changes from an increase to a decrease.

[0070] As an example, the control circuit 60 determines whether or not the transition to ICP has occurred based on a change in the current Idc relative to the voltage Vdc. Specifically, the control circuit 60 acquires the voltage Vdc and the current Idc. Furthermore, the control circuit 60 determines that the transition to ICP has occurred when the current Idc decreases relative to an increase in the voltage Vdc.

[0071] As an example, the control circuit 60 determines whether or not a transition to ICP has occurred based on a value obtained by differentiating the phase difference between the current Irf and the voltage Vrf in at least a portion of at least one of the resonant circuit 40 and the discharge unit 50 with respect to the power at the output end of the buck-boost chopper of the DC power supply circuit 20. Specifically, the control circuit 60 acquires the power value and the phase difference. Furthermore, the control circuit 60 determines that a transition to ICP has occurred when the value obtained by differentiating the phase difference with respect to the power value changes from an increase to a decrease.

[0072] As an example, the control circuit 60 determines whether or not the transition to ICP has occurred based on the value of Vdc / Idc (impedance value), which indicates the relative value of the voltage Vdc relative to the current Idc. For example, the control circuit 60 determines that the transition to ICP has occurred when the impedance value is equal to or less than a predetermined threshold. Note that the control circuit 60 may also determine that the transition to ICP has occurred when the stability of the impedance value is within a predetermined range. Here, the stability of the impedance value can be, for example, a statistical value of the impedance value, such as standard deviation or variance, as appropriate.

[0073] The control circuit 60 may be configured to determine that a CCP has occurred when the impedance value falls below a predetermined threshold value that is greater than the threshold value for transition to an ICP. Alternatively, the control circuit 60 may determine whether or not a transition to an ICP has occurred based on the rate of decrease in the impedance value.

[0074] As described above, whether the plasma state has transitioned from CCP to ICP can be determined by a number of methods. The method to be used can be determined as appropriate based on the design. Two or more methods may also be used in combination.

[0075] In this way, by making a determination based on the voltage value of the voltage Vdc and the current value of the current Idc, or the voltage value of the voltage Vrf and the current value of the current Irf, a sensor for detecting the emission intensity can be eliminated.

[0076] Of course, the plasma source 10 according to the embodiment may further include a sensor configured to detect the emission intensity of the plasma. In this case, the control circuit 60 determines whether the transition from CCP to ICP has occurred based on a change in the emission intensity. Specifically, the control circuit 60 acquires the detection result of the emission intensity from the sensor, and determines that the transition to ICP has occurred when light emission with an intensity greater than that of light emitted when ignited as a CCP is detected.

[0077] FIG. 6 is a flowchart showing an example of the flow of a plasma generation process executed in the plasma source 10 according to the embodiment. As described with reference to FIG. 2, the control circuit 60 applies a voltage to the antenna 51 by controlling the output voltage of the buck-boost chopper or inverter circuit 30 of the DC power supply circuit 20, thereby generating a CCP (S11). As described with reference to FIGS. 3 and 4, the control circuit 60 also controls the output voltage of the buck-boost chopper or inverter circuit 30 of the DC power supply circuit 20 using the first limit value C1, thereby transitioning the plasma state from a CCP to an ICP (S12). The control circuit 60 then determines whether the plasma state has transitioned from a CCP to an ICP (S13). If it is not determined that the plasma state has transitioned from a CCP to an ICP (S13: No), the flow of FIG. 6 returns to the process of S12. On the other hand, when it is determined that the CCP has been shifted to the ICP (S13: Yes), the control circuit 60 maintains the ICP by controlling the output voltage value of the buck-boost chopper or inverter circuit 30 of the DC power supply circuit 20 using the second limit value C2 that is smaller than the first limit value C1, as described with reference to Figures 3 and 4 (S14). Thereafter, when the use of the ICP ends, the flow in Figure 6 ends.

[0078] According to at least one of the embodiments described above, it is possible to expand the range of application of the voltage limit value and the current limit value that are applied during the period until it is determined that the plasma generated in the discharge tube has transitioned from capacitively coupled plasma to inductively coupled plasma.

[0079] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, as well as within the scope of the invention described in the claims and their equivalents. [Explanation of symbols]

[0080] 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 circuit (control section, determination section), 91... DC voltage sensor, 92... DC current sensor, 93... high frequency voltage sensor, 94... high frequency current sensor

Claims

1. A plasma source comprising: a discharge unit having a discharge tube used to generate plasma by ionizing a gas and a conductive antenna formed in a coil shape so as to surround the discharge tube; and a high frequency power supply that supplies power to the discharge unit, The high frequency power source is 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 a voltage having a frequency in a radio frequency band; a resonant circuit disposed between the inverter circuit and the discharge unit; a control unit that, during a first period from when the voltage is applied to the antenna until it is determined that the plasma generated in the discharge tube has transitioned from capacitively coupled plasma to inductively coupled plasma, changes an output voltage value of the DC power supply circuit or the inverter circuit so that the voltage value of the voltage applied to the antenna does not exceed a predetermined first voltage limit value, and changes an output voltage value of the DC power supply circuit or the inverter circuit so that the current value of the current flowing through the antenna does not exceed a predetermined first current limit value; Equipped with the first voltage limit value is a value that is set individually within a range of voltage values ​​that do not damage elements in the inverter circuit and elements in the resonant circuit, the first current limit value is a value that is set individually within a range of current values ​​that do not damage elements in the inverter circuit and elements in the resonant circuit; Plasma source.

2. 2. The plasma source of claim 1, wherein the first voltage limit value and the first current limit value are each set so that plasma in the discharge tube can transition from capacitively coupled plasma to inductively coupled plasma under gas conditions set within a desired range to be flowed into the discharge tube.

3. 3. The plasma source according to claim 1, wherein, during a second period after the first period, the control unit changes the output voltage value of the DC power supply circuit or the inverter circuit so that the voltage value of the voltage applied to the antenna does not exceed a second voltage limit value that is smaller than the predetermined first voltage limit value, and changes the output voltage value of the DC power supply circuit or the inverter circuit so that the current value of the current flowing through the antenna does not exceed a second current limit value that is smaller than the predetermined first current limit value.

4. a limit value transition period is provided between the first period and the second period, the voltage limit value during the limit value transition period is transitioned from the first voltage limit value to the second voltage limit value during the limit value transition period; the current limit value during the limit value transition period is transitioned from the first current limit value to the second current limit value during the limit value transition period; the control unit changes the output voltage value of the DC power supply circuit so that the voltage value of the voltage applied to the antenna does not exceed the voltage limit value during the limit value transition period, and changes the output voltage value of the DC power supply circuit so that the current value of the current flowing through the antenna does not exceed the current limit value during the limit value transition period. The plasma source of claim 3 .

5. 5. The plasma source according to claim 1, further comprising a determination unit that determines whether or not the plasma in the discharge tube has transitioned from capacitively coupled plasma to inductively coupled plasma based on a voltage value of a voltage applied to the antenna and a current value of a current flowing through the antenna.

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