Unignited plasma state discrimination device and unignited plasma state discrimination method

Abstract

In detecting the unignited state of plasma based on a reflected wave, false detection during a normal plasma ignition time is prevented so as to detect the unignited state during plasma abnormality. When a pulse output is supplied to a plasma load by pulse driving from an RF power source, the unignited state of plasma abnormality is detected on the basis of the continuous state of the reflected wave, whereby a total reflected wave generated in the unignited state during plasma abnormality is detected in distinction from the reflected wave generated in the normal ignited state. With this configuration, in detecting the unignited state by comparing a peak value of the reflected wave with a threshold, it is possible to prevent that a reflected wave generated in the normal ignited state is erroneously detected as the total reflected wave that is generated in the abnormal unignited state.

Claims

1. An unignited plasma state discrimination method in supplying a pulse output from a radio frequency power source to a plasma load by pulse driving, comprising, detecting reflected wave voltage traveling from the plasma load to the radio frequency power source, obtaining an equivalent amount corresponding to an amount of heat applied to an RF power amplifier element of the radio frequency power source, on the basis of a peak value and a fluctuation state of the reflected wave voltage, comparing the equivalent amount being obtained with a threshold to discriminate an unignited state of plasma, of plasma, an allowable heat quantity of the RF power amplifier element is set as the threshold, and discriminating an unignited state of plasma on the basis of a result of the comparison.

2. The unignited plasma state discrimination method according to claim 1, comprising, a first conversion step of obtaining a first converted value corresponding to the amount of heat applied to the RF power amplifier element of the radio frequency power source, on the basis of the reflected wave voltage and a duration of time thereof, a second conversion step of obtaining a second converted value corresponding to an amount of heat dissipated from the RF power amplifier element of the radio frequency power source, on the basis of an elapsed time from when a peak value of the reflected wave voltage V.sub.r becomes zero, or an elapsed time from when application of the pulse output is started, in every cycle of the pulse driving, a third conversion step of obtaining a third converted value corresponding to an amount of heat storage in the RF power amplifier element of the radio frequency power source, from a difference between the first converted value and the second converted value, and a comparison step of comparing the third converted value with the threshold corresponding to the allowable heat quantity of the RF power amplifier element, wherein, in the comparison step, the unignited state of plasma is discriminated when the third converted value reaches or exceeds the threshold.

3. The unignited plasma state discrimination method according to claim 2, wherein, a discharging time constant (.sub.disc) is selected in such a manner as being longer than a charging time constant (.sub.c), not allowing charging and discharging voltage to reach a voltage level of a device protection sensing level, under the condition that a pulse frequency of the pulse driving in a normal time is a maximum settable value and a duty ratio of RF.sub.on interval in one cycle of the pulse driving is a maximum settable value, in the first conversion step, charging voltage obtained by charging the peak value of the reflected wave voltage at the charging time constant (.sub.c) is considered as the first converted value, in the second and third conversion steps, voltage obtained by discharging from the charging voltage at the discharging time constant (.sub.disc) in a time width when the peak value of the reflected wave is zero, is considered as the third converted value, and in the comparison step, the charging voltage corresponding to the allowable heat quantity of the RF power amplifier element is considered as the threshold.

4. The unignited plasma state discrimination method according to claim 2, wherein, when a time width of interval for outputting pulses is RF.sub.on, and a time width of interval not outputting pulses is RF.sub.off, the first converted value is calculated according to (V.sub.rk.sub.1.sub.0.sup.RFontdt) indicating time integration of a product (V.sub.rk.sub.1) of the peak value V.sub.r of the reflected wave voltage, and a coefficient k.sub.1 corresponding to a heat generation coefficient of the RF power amplifier element, the second converted value is calculated according to (k.sub.2.sub.0.sup.RFofftdt) indicating the time integration of the coefficient k.sub.2 to the heat dissipation coefficient of the RF power amplifier element, the third converted value is calculated by an operation for subtracting the second converted value from the first converted value {(V.sub.rk.sub.1.sub.0.sup.RFontdt)(k.sub.2.sub.0.sup.RFofftdt)} where zero is the lowermost value, and the first converted value, the second converted value, and the third converted value are calculated in every cycle of plasma driving, and the third converted value obtained in a previous period is used as an initial value of the first converted value in a subsequent period.

5. An unignited plasma state discrimination device for discrimination an unignited state of plasma of a plasma load, in supplying a pulse output from a radio frequency power source to the plasma load by pulse driving, comprising, a detection means configured to detect reflected wave voltage traveling from the plasma load to the radio frequency power source, a conversion means configured to obtain an equivalent amount corresponding to an amount of heat applied to an RF power amplifier element of the radio frequency power source, on the basis of a peak value and a fluctuation state of the reflected wave voltage, and a comparison means configured to compare the equivalent amount obtained in the conversion means with a threshold to discriminate an unignited state of plasma, of plasma, an allowable heat quantity of the RF power amplifier element is set as the threshold, wherein, the unignited state of plasma is discriminated on the basis of a result of the comparison means.

6. The unignited plasma state discrimination device according to claim 5, wherein, the conversion means comprises, a first conversion means configured to obtain a first converted value corresponding to the amount of heat applied to the RF power amplifier element of the radio frequency power source, on the basis of the reflected wave voltage and a duration of time thereof, a second conversion means configured to obtain a second converted value corresponding to an amount of heat dissipated from the RF power amplifier element of the radio frequency power source, on the basis of an elapsed time from when a peak value of the reflected wave voltage V.sub.r becomes zero, or an elapsed time from when application of the pulse output is started, in every cycle of the pulse driving, and a third conversion means configured to obtain a third converted value corresponding to an amount of heat stored in the RF power amplifier element of the radio frequency power source, from a difference between the first converted value and the second converted value, wherein, the comparison means compares the third converted value obtained in the third conversion means, with the threshold corresponding to the allowable heat quantity of the RF power amplifier element, and discriminates the unignited state of plasma when the third converted value reaches or exceeds the threshold.

7. The unignited plasma state discrimination device according to claim 6, further comprising, a charging and discharging circuit configured to charge the reflected wave voltage and to discharge voltage being charged, and a comparator configured to input an output from the charging and discharging circuit, wherein, a discharging time constant (.sub.disc) is selected in such a manner as being longer than a charging time constant (.sub.c), not allowing the charging and discharging voltage to reach a voltage level of the device protection sensing level in charging and discharging, under the condition that a pulse frequency of the pulse driving in a normal time is a maximum settable value and a duty ratio of RF.sub.on interval in one cycle of the pulse driving is a maximum settable value, the first conversion means is configured by a charging part of the charging and discharging circuit, and the charging part outputs as the first converted value, charging voltage obtained by charging the reflected wave voltage detected by the detection means at the charging time constant (.sub.c), the second means and third conversion means are configured by a discharging part of the charging and discharging circuit, and the discharging part outputs as the third converted value, voltage obtained by discharging from the charging voltage at the discharging time constant (.sub.disc) in a time width when the peak value of the reflected wave is zero, and the comparison means is configured by the comparator that uses the charging voltage corresponding to the allowable heat quantity of the RF power amplifier element as the threshold, and compares the third converted value outputted from the charging and discharging circuit with the threshold.

8. The unignited plasma state discrimination device according to claim 6, further comprising, an A/D conversion circuit configured to convert the reflected wave voltage V.sub.r detected by the detection means into a digital value, an operation circuit configured to perform a digital operation using the digital value as an input value, wherein, in the operation circuit, when a time width of interval for outputting pulses is RF.sub.on, and a time width of interval not outputting pulses is RF.sub.off, the first conversion means comprises a first operation part configured to calculate the first converted value according to an operation of (V.sub.rk.sub.1.sub.0.sup.RFontdt) indicating time integration of a product (V.sub.rk.sub.1) of the peak value V.sub.r of the reflected wave voltage and a coefficient k.sub.1 corresponding to a heat generation coefficient of the RF power amplifier element, the second conversion means comprises a second operation part configured to calculate the second converted value according to the operation of (k.sub.2.sub.0.sup.RFofftdt) indicating the time integration of the coefficient k.sub.2 corresponding to the heat dissipation coefficient of the RF power amplifier element, and the third conversion means comprises a third operation part configured to calculate the third converted value by the operation for subtracting the second converted value from the first converted value a {(V.sub.rk.sub.1.sub.0.sup.RFontdt)(k.sub.2.sub.0.sup.RFofftdt)} where the lowermost value is zero, wherein, the first converted value, the second converted value, and the third converted value are calculated in every cycle of the plasma driving, and the third converted value obtained in a previous period is used as an initial value of the first converted value in a subsequent period.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 illustrates a schematic configuration for performing power control on the basis of detection of unignited plasma state of a plasma load;

(2) FIG. 2 illustrates a schematic configuration for detecting the unignited state according to the present invention;

(3) FIG. 3 illustrates signal diagrams showing the ignited state according to the present invention;

(4) FIG. 4 illustrates signal diagrams showing the unignited state according to the present invention;

(5) FIG. 5 is a flowchart illustrating steps of detecting the unignited state according to the present invention;

(6) FIG. 6 illustrates a schematic configuration for detecting the unignited state by using a voltage value of a reflected wave according to the present invention;

(7) FIG. 7 illustrates an analogue circuit configuration for detecting the unignited state on the basis of charging and discharging voltage of the reflected wave voltage according to the present invention;

(8) FIG. 8 illustrates a signal example of a normal operating state in a low-frequency pulse mode;

(9) FIG. 9 illustrates a signal example of the normal operating state in a high-frequency pulse mode;

(10) FIG. 10 illustrates a signal example of an abnormal operating state in the low-frequency pulse mode;

(11) FIG. 11 illustrates an allowable on-time t.sub.2;

(12) FIG. 12 illustrates a signal example of the abnormal operation state in the high-frequency pulse mode;

(13) FIG. 13 illustrates a circuit configuration of a charging and discharging circuit 20a of an unignited state detection circuit 20.sub.circuit;

(14) FIG. 14 illustrates an example of input voltage V.sub.in;

(15) FIG. 15 illustrates the circuit state when there is an input signal (in the state where RF signal is on);

(16) FIG. 16 illustrates the circuit state when there is no input signal (in the state where RF signal is off);

(17) FIG. 17 illustrates an example of waveform according to numerical values;

(18) FIG. 18 illustrates an example where the unignited state detection device of the present invention is configured by a digital circuit;

(19) FIG. 19 illustrates an example where the unignited state detection device of the present invention is configured by a counting circuit; and

(20) FIG. 20 is a schematic view illustrating a plasma load driving by a radio-frequency power source (RF power source).

BEST MODE FOR CARRYING OUT THE INVENTION

(21) Preferred embodiments of the present invention will now be described in detail, with reference to the accompanying drawings. An unignited plasma state detection device and a detection method thereof according to the present invention will be described as the following; with reference to FIG. 1, a connecting condition between the unignited plasma state detection device and a power sensor will be described, with reference to FIGS. 2 to 4, a schematic configuration of the unignited plasma state detection will be described, with reference to a flowchart of FIG. 5, steps of the unignited plasma state detection will be described, with reference to FIGS. 6 to 17, a mode for detecting the unignited plasma state by accumulating the reflected wave voltage according to an analogue circuit configuration will be described, and with reference to FIGS. 18 and 19, a mode for detecting the unignited plasma state by accumulating the reflected wave voltage according to a digital circuit configuration will be described. FIGS. 6 to 17 illustrate a configuration example where accumulation of the reflected wave voltage is performed by charging and discharging the reflected wave voltage.

(22) Radio frequency outputs (RF outputs) are supplied from the radio frequency power source (RF power source) by pulse driving, to a plasma load of a plasma processor such as semiconductor producing equipment and electronic device manufacturing equipment, or to a plasma load of a plasma generator such as a CO.sub.2 laser beam machine. This pulse driving performs on/off control on the pulse output at a predetermined frequency according to a control signal with a predetermined duty ratio at predetermined intervals, thereby supplying power to the load so as to generate and maintain plasma. The pulse output is supplied to the load while the control signal is on, and supplying of the pulse output is stopped while the control signal is off. Then, according to the duty ratio between on-time and off-time of the control signal (time ratio), the power supplied to the load is controlled. The power controller controls the pulse driving. A frequency of the pulse output of the pulse driving can be provided in accordance with the frequency of the radio frequency output (RF output) that is supplied to the plasma load.

(23) FIG. 1 illustrates a schematic configuration for performing power control, on the basis of detection whether or not the plasma load is in the unignited plasma state, in the pulse driving of the plasma load by a radio frequency power source (RF power source). FIG. 1 illustrates only a partial configuration for controlling power directed to the plasma load, on the basis of detection of the unignited plasma state.

(24) In FIG. 1, the power sensor 2 is connected between the radio frequency power source (RF power source) and the plasma load, and detects voltage of forward wave power (forward wave voltage V.sub.f) directed to the plasma load from the radio frequency power source (RF power source), and voltage of reflected wave power (reflected wave voltage V.sub.r) returning from the plasma load to the radio frequency power source (RF power source). The unignited state detection device 1 detects the unignited state of plasma, on the basis of the reflected wave voltage V.sub.r detected by the power sensor 2, and outputs an unignited state detection signal V.sub.fail when it is detected that the plasma is unignited.

(25) The power controller 3 controls the pulse driving of the radio frequency power source (RF power source), according to the forward wave voltage V.sub.f and the reflected wave voltage V.sub.r, both being inputted from the power sensor 2. By way of example, when the plasma is in the normal ignited state, the power controller controls a duty ratio of a control signal, so that the forward wave voltage V.sub.f becomes a predetermined value on the basis of the forward wave voltage V.sub.f detected by the power sensor 2. On the other hand, when the plasma is in an abnormal state and it is not ignited yet, the power controller 3 performs drooping or suspension control of the radio frequency output.

(26) The unignited state detection device 1 detects the unignited state of plasma, as an abnormal state of plasma. The power controller 3 performs drooping or suspension control of the radio frequency output, on the basis of the unignited state detection signal V.sub.fail that is outputted when the unignited state detection device 1 detects the unignited state of plasma.

(27) [Schematic Configuration for Detecting Unignited State According to the Present Invention]

(28) As for the detection of the unignited state of the present invention, a schematic configuration thereof will be described with reference to FIGS. 2 to 4, and a schematic process flow will be described with reference to a flowchart of FIG. 5.

(29) For detecting the unignited plasma state according to the present invention, the unignited state of the plasma is detected on the basis of the state where a reflected wave is generated from the reflected wave voltage V.sub.r that travels from the plasma load to the RF power source.

(30) FIG. 2 illustrates a schematic configuration of the detection of the unignited state according to the present invention. The unignited state detection device 10 is provided with a conversion means 11 configured to obtain an equivalent amount corresponding to the heat applied to the RF power amplifier element of the RF power source, on the basis of a peak value and a fluctuation state of the reflected wave voltage V.sub.r, and a comparison means 12 configured to compare the equivalent amount obtained by the conversion means 11 with a threshold corresponding to an allowable heat quantity of the RF power amplifier element.

(31) The conversion means 11 is provided with a first conversion means 11A, a second conversion means 11B, and a third conversion means 11C.

(32) The first conversion means 11A inputs the reflected wave voltage V.sub.r (S1 in FIG. 5) detected by the power sensor, and on the basis of the reflected wave voltage V.sub.r and a duration time of the reflected wave voltage V.sub.r, the first converted value (equivalent value of applied heat) is obtained, which corresponds to an amount of heat applied to the RF power amplifier element of the RF power source (S2 in FIG. 5).

(33) The second conversion means 11B obtains, in every cycle of pulse driving, a second converted value corresponding to the amount of heat dissipation from the RF power amplifier element of the RF power source, on the basis of an elapsed time from when the peak value of the reflected wave voltage V.sub.r becomes zero, or an elapsed time from a start of applying the pulse output.

(34) In the mode where the second converted value is obtained on the basis of the elapsed time from when the peak value of the reflected wave voltage V.sub.r becomes zero, the conversion is performed under the assumption that the amount of heat dissipation from the RF power amplifier element mostly corresponds to the amount of heat dissipation while application of the reflected wave to the RF power amplifier element is stopped and thus the amount of heat dissipation during the period when the reflected wave is applied to the RF power amplifier element is just a small amount.

(35) On the other hand, in the mode where the second converted value is obtained on the basis of the elapsed time from starting application of the pulse output, the conversion is performed considering the amount of heat dissipation during the period when the reflected wave is applied to the RF power amplifier element (S3 in FIG. 5).

(36) The third conversion means 11C obtains a third converted value (an equivalent amount of heat storage), corresponding to the amount of heat storage in the RF power amplifier element of the RF power source, on the basis of a difference between the first converted value and the second converted value (54 in FIG. 5).

(37) The comparison means 12 compares the third converted value obtained by the third conversion means 11C with a threshold in association with an allowable heat quantity of the RF power amplifier element. The threshold represents a device protection sensing level for protecting the RF power amplifier element, and when the third converted value reaches or exceeds the threshold, it is determined that the amount of heat accumulated in the RF power amplifier element reaches or exceeds the device protection sensing level of the RF power amplifier element (S5 in FIG. 5), and the unignited plasma state is detected (S6 in FIG. 5).

(38) In the case where the unignited plasma state is detected, the power controller performs drooping or suspension control of the radio frequency output (RF output), thereby executing a protecting operation (S7 in FIG. 5).

(39) Power supplying from the RF power source by pulse driving may be described according to two pulse modes; low-frequency pulse mode and high-frequency pulse mode, on the basis of whether or not an amount of the heat storage still remains at the end of the period, as a result of dissipating the amount of heat being applied in one cycle of the pulse driving.

(40) In the low-frequency pulse mode, a period of pulse driving includes a sufficiently long time width of time for dissipating an amount of heat having been applied, and at the end of the period of pulse driving, there is no remaining amount of heat storage. In this mode, an equivalent amount of heat storage is equal to zero. The equivalent amount of heat storage converted in the low-frequency pulse mode starts summation from an initial value being zero in every cycle of pulse driving.

(41) On the other hand, in the high-frequency pulse mode, a period of the pulse drive does not include a time length long enough to dissipate the total amount of heat being applied, and at the end of the period of pulse driving, there still remains an amount of heat storage. In this mode, an equivalent amount of heat storage still remains. The equivalent amount of heat storage converted in the high-frequency pulse mode starts summation from an initial value which is the heat storage converted value at the end of the previous period, in every cycle of pulse driving.

(42) Under the condition of pulse driving where the duty ratio of the pulse output is equal and also the peak value of a reflected wave voltage is equal, if one cycle T of pulse driving is long and the amount of accumulated heat at the end of one cycle is zero, the pulse is in the low-frequency mode, whereas if one cycle T of pulse driving is short and an amount of heat storage still remains at the end of one cycle, the pulse is in the high-frequency mode.

(43) The low-frequency mode and the high-frequency mode in the ignited state will be described, with reference to the signal diagram as shown in FIG. 3, and the low-frequency mode and the high-frequency mode in the unignited state will be described with reference to the signal diagram as shown in FIG. 4.

(44) In the plasma ignited state, FIG. 3A to FIG. 3D illustrate respectively, forward wave voltage V.sub.f, reflected wave voltage V.sub.r, an equivalent amount of heat storage H.sub.ac, and an unignited state detection signal in the low-frequency pulse mode, FIG. 3E to FIG. 3H illustrate the forward wave voltage V.sub.f, the reflected wave voltage V.sub.r, the equivalent amount of heat storage H.sub.ac, and the unignited state detection signal in the high-frequency pulse mode.

(45) The forward wave voltage V.sub.f delivers the pulse output at a predetermined frequency, in the RF.sub.on interval having a duration of time t.sub.1 in one cycle (FIG. 3A and FIG. 3E). If the plasma is ignited normally, a mismatch at a rise and a fall of the pulse output may cause pulse-like reflected wave voltage V.sub.r (FIG. 3B and FIG. 3F).

(46) In FIG. 3C and FIG. 3G, the equivalent amount of heat storage H.sub.ac indicates a converted value of an amount of heat that is accumulated while the reflected wave voltage V.sub.r is applied to the RF power amplifier element, and the dashed-dotted line indicates an allowable amount against thermal failure in the RF power amplifier elements, representing a device protection sensing level for protecting the RF power amplifier element against a damage due to the reflected wave.

(47) In the case where the plasma is in the ignited state, in any of the low frequency mode and the high frequency mode, the equivalent amount of heat storage H.sub.ac returns to zero without reaching the device protection sensing level in every period of the driving mode, and therefore, no unignited state detection signal is outputted.

(48) On the other hand, when the plasma is in the unignited state, FIG. 4A to FIG. 4D illustrate respectively, the forward wave voltage V.sub.f, the reflected wave voltage V.sub.r, the equivalent amount of heat storage H.sub.ac, and the unignited state detection signal V.sub.fail in the low-frequency pulse mode, and FIG. 4E to FIG. 4H illustrate respectively, the forward wave voltage V.sub.f, the reflected wave voltage V.sub.r, the equivalent amount of heat storage H.sub.ac, and the unignited state detection signal V.sub.fail in the high-frequency pulse mode.

(49) The forward wave voltage V.sub.f delivers the pulse output at a predetermined frequency, in the RF.sub.on interval having a duration of time t.sub.1 in one cycle (FIG. 4A and FIG. 4E). If the plasma has not been ignited yet, a rectangular-like reflected wave voltage V.sub.r is generated in the RF.sub.on interval when the pulse output is delivered (FIG. 4B and FIG. 4F).

(50) In FIG. 4C and FIG. 4G, the equivalent amount of heat storage H.sub.ac indicates a converted value of heat that is accumulated while the reflected wave voltage V.sub.r is applied to the RF power amplifier element, and the dashed-dotted line indicates the allowable amount against thermal failure of the RF power amplifier element, representing a device protection sensing level for protecting the RF power amplifier element against a damage due to the reflected wave.

(51) When the plasma is in the unignited state, in the low frequency mode, the equivalent amount of heat storage H.sub.ac reaches the device protection sensing level within the period of the driving mode (FIG. 4C), and therefore, an unignited state detection signal V.sub.fail is outputted (FIG. 4D). FIG. 4C shows the case where the equivalent amount of heat storage H.sub.ac reaches the device protection sensing level at the end of the RF.sub.on interval. However, if the peak value of the reflected wave voltage V.sub.r is large, the equivalent amount of heat storage H.sub.ac reaches the device protection detection level at a point before the end of the RF.sub.on interval, and the ignition determination signal V.sub.fail is outputted.

(52) In the high frequency mode, storing of heat is repeated over plural periods, and the equivalent amount of heat storage H.sub.ac reaches the device protection sensing level accordingly (FIG. 4G), and then, the ignition determination signal V.sub.fail is outputted (FIG. 4H). FIG. 4G shows that the equivalent amount of heat storage H.sub.ac reaches the device protection sensing level in the fifth period. However, in what period number the equivalent amount of heat storage H.sub.ac reaches the device protection sensing level may vary depending on the peak value and the duty ratio of the reflected wave voltage V.sub.r.

(53) [Mode for Detecting the Unignited State by the Use of Charging and Discharging Voltage of a Reflected Wave Voltage Value]

(54) A schematic configuration for detecting the unignited state by the use of charging and discharging of a reflected wave voltage value, will now be described with reference to FIG. 6.

(55) The unignited state detection device 20 has a configuration to obtain a voltage value in association with a duration of time of the reflected wave and detect the unignited plasma state, by the use of charging and discharging of the voltage value of the reflected wave, and the device is provided with a conversion means 21 and a voltage comparison means 22.

(56) It is further provided with a charging voltage calculation means 21A configured to calculate charging voltage by charging the reflected wave voltage V.sub.r, a discharging voltage calculation means 21B configured to calculate discharging voltage, and a charging and discharging voltage calculation means 21C configured to calculate a difference between the charging voltage and the discharging voltage, so as to obtain the charging and discharging voltage V.sub.a.

(57) A calculated value by the charging voltage calculation means 21A corresponds to the first converted value (equivalent amount of heat application), a calculated value by the discharging voltage calculation means 21B corresponds to the second converted value (equivalent amount of heat dissipation), and the charging and discharging voltage V.sub.a calculated by the charging and discharging voltage calculation means 21C corresponds to the third converted value (equivalent amount of heat storage).

(58) The voltage comparison means 22 compares the charging and discharging voltage V.sub.a obtained by voltage conversion by the conversion means 21, with a threshold.

(59) As the threshold, set voltage V.sub.ref is used. The set voltage V.sub.ref is allowable voltage being associated with allowable power that tolerates a loss of the RF power amplifier element, caused by the reflected wave.

(60) The voltage comparison means 22 detects the unignited plasma state by comparing the charging and discharging voltage V.sub.a with the set voltage V.sub.ref, and outputs an unignited state detection signal V.sub.fail when the unignited state is detected.

(61) The conversion means 21 and the voltage comparison means 22 detect the unignited state, in the low-frequency pulse mode and in the high-frequency pulse mode.

(62) In pulse driving of the low-frequency pulse mode, the conversion means 21 acquires the charging and discharging voltage V.sub.a in association with the duration of time of the reflected wave voltage V.sub.r in one cycle, and the voltage comparison means 22 compares the charging and discharging voltage V.sub.a with the set voltage V.sub.ref, thereby detecting the unignited plasma state and outputting the unignited state detection signal V.sub.fail.

(63) On the other hand, in pulse driving of the high-frequency pulse mode, the conversion means 21 acquires the charging and discharging voltage V.sub.a obtained by accumulating voltage in association with the duration of time of the reflected wave voltage V.sub.r in every period, over the continuous periods when the reflected wave is generated, and the voltage comparison means 22 compares the charging and discharging voltage V.sub.a with the set voltage V.sub.ref, thereby detecting the unignited plasma state and outputting the unignited state detection signal V.sub.fail.

(64) (Mode for Detecting the Unignited State on the Basis of Charging and Discharging Voltage of Reflected Wave Voltage)

(65) In detecting the unignited state on the basis of reflected wave voltage, a configuration example for obtaining the reflected wave voltage according to the charging and discharging voltage will now be described with reference to FIGS. 7 to 17.

(66) With reference to FIG. 7, an example will be described, which configures a circuit for detecting the unignited state on the basis of charging and discharging voltage of the reflected wave voltage, employing the charging and discharging circuit which is an RC circuit.

(67) The unignited state detection circuit 20.sub.circuit inputs the reflected wave voltage V.sub.r detected by the power sensor 2 via the buffer 4, and outputs an unignited state detection signal V.sub.fail. The unignited state detection circuit 20.sub.circuit is provided with a charging and discharging circuit 20a and a comparator 20b, and the charging and discharging circuit 20a inputs the output from the buffer 4, via the block diode D.

(68) The charging and discharging circuit 20a is configured by connecting a charging and discharging resistance R.sub.1 in series with the input side of the parallel circuit of the capacitor C and the discharging resistance R.sub.2. The comparator 20b compares the charging and discharging voltage V.sub.a being the output voltage from the capacitor C in the charging and discharging circuit 20a, with the set voltage V.sub.ref, and outputs the unignited state detection signal V.sub.fail when the charging and discharging voltage V.sub.a reaches or exceeds the set voltage V.sub.ref. In the charging and discharging circuit 20a, the charging time constant .sub.c is set to be shorter than the discharging time constant .sub.disc. In addition, the charging time constant .sub.c is set in such a manner that the charging voltage becomes equal to or less than the set voltage V.sub.ref, when charging is performed in the time length of the period T of the low-frequency pulse mode. The charging time constant .sub.c and the discharging time constant .sub.disc can be set by selecting values of the charging and discharging resistance R.sub.1, the discharging resistance R.sub.2, and the capacitor C.

(69) (Operation Example in a Normal Time)

(70) With reference to FIGS. 8 and 9, an operation example of the unignited state detection device 20 in a normal time will described. FIG. 8 illustrates a signal example of the normal operation state of the low-frequency pulse mode where; FIG. 8(a) illustrates the forward wave voltage V.sub.f, FIG. 8 (b) illustrates the reflected wave voltage V.sub.r, and FIG. 8(c) illustrates the charging and discharging voltage V.sub.a in the charging and discharging circuit. The example here shows the case where the duty ratio of pulse driving is 50%.

(71) FIG. 9 illustrates a signal example of the normal operation state of the high-frequency pulse mode where; FIG. 9(a) illustrates the forward wave voltage V.sub.f, FIG. 9(b) illustrates the reflected wave voltage V.sub.r, and FIG. 9(c) illustrates the charging and discharging voltage V.sub.a in the charging and discharging circuit. The example here shows the case where the duty ratio of pulse driving is 50%.

(72) Even in the normal state, reflected wave voltage V.sub.r is generated at a rise and a fall of the RF.sub.on interval, when the forward wave voltage V.sub.f is switched from the off-state to the on-state and when the forward wave voltage V.sub.f is switched from the on-state to the off-state (at the time of plasma ignition).

(73) The circuit constants (charging and discharging resistance R.sub.1, discharging resistance R.sub.2, and capacitor C) of the charging and discharging circuit are selected, in such a manner that the charging time constant .sub.c allows the charging and discharging voltage V.sub.a of the charging and discharging circuit to have a margin with respect to the set voltage V.sub.ref, under the condition that pulse driving is performed with setting the pulse frequency to be a maximum and the duty ratio of the RF.sub.on interval and the RF.sub.off interval in one cycle to be a maximum.

(74) In the charging and discharging circuit configuration of the RC circuit as shown in FIG. 7,

(75) the charging time constant .sub.c is expressed by:
.sub.c=C.Math.R.sub.p
R.sub.p=R.sub.1.Math.R.sub.2/(R.sub.1+R.sub.2)
and the discharging time constant .sub.disc is expressed by:
.sub.disc=C.Math.R.sub.2

(76) Since the reflected wave voltage V.sub.r is generated within a short time in the normal state, a peak value of the charging and discharging voltage V.sub.a obtained by the charging and discharging circuit, is sufficiently lower than the set voltage V.sub.ref being the unignited state detection level, and the unignited state detection signal is not outputted.

(77) (Operation Example in an Abnormal Time)

(78) With reference to FIGS. 10 to 12, an operation example at the abnormality of the unignited state detection device 20 will be described. FIG. 10 shows a signal example of an abnormal operation state of low-frequency pulse mode; where FIG. 10(a) illustrates the forward wave voltage V.sub.f, FIG. 10(b) illustrates the reflected wave voltage V.sub.r, FIG. 10(c) illustrates the charging and discharging voltage V.sub.a in the charging and discharging circuit, and FIG. 10(d) illustrates the unignited state detection signal V.sub.fail. The example here shows the case where the duty ratio of pulse driving is 50%.

(79) The set voltage V.sub.ref is provided, considering a margin component with respect to the allowable loss (damage level) of the RF power amplifier element. It should be noted that the set voltage V.sub.ref is a value that depends on a voltage value of the reflected wave and the charging time constant .sub.c. When the charging and discharging voltage V.sub.a obtained by charging a reflected wave voltage reaches the set voltage V.sub.ref being the device protection sensing level, after a lapse of the duration of time t.sub.1, the unignited state detection signal is outputted. The power controller performs control for drooping or suspension of the radio frequency output (RF output) on the basis of the unignited state detection signal.

(80) FIG. 11 is a signal diagram for describing allowable on-time t.sub.2 of the unignited state detection device 20. FIG. 11(a) illustrates the forward wave voltage V.sub.f, FIG. 11(b) illustrates the reflected wave voltage V.sub.r, FIG. 11(c) illustrates the charging and discharging voltage V.sub.a in the charging and discharging circuit, and FIG. 11(d) illustrates the unignited state detection signal V.sub.fail.

(81) The allowable on-time t.sub.2 indicates a time width that accepts allowable voltage of the total reflection on the RF power amplifier element. If the time width (duration t.sub.1) of the reflected wave applied to the RF power amplifier element is equal to or less than the allowable on-time t.sub.2, and if the charging and discharging voltage V.sub.a is zero at the end of a period of pulse driving, i.e., in the low-frequency pulse mode, even though a reflected wave (in the unmatching state where a reflection coefficient is approximately 1 (1)) is generated, the RF power amplifier element may not come to the element destruction due to total reflection. Therefore, it is possible to continue applying the forward wave voltage without drooping or suspension of the radio frequency output (RF output).

(82) Therefore, in the case where the duration of time t.sub.1 of the reflected wave is shorter than the allowable on-time t.sub.2, and the charging and discharging voltage V.sub.a is zero at the end of the pulse driving period, that is, in the low-frequency pulse mode, the charging and discharging voltage V.sub.a does not reach the set voltage V.sub.ref being the device protection sensing level, and thus the unignited state detection signal is not outputted.

(83) In the case where a device with a plasma load, such as a laser beam machine, is kept non-operated for a long period of time, moisture or the like, may be generated in plasma atmosphere in a laser oscillator, or the like, and this may lead to the atmosphere that makes plasma ignition more difficult. In such plasma atmosphere where igniting is difficult, the time width of the reflected wave applied to the RF power amplifier element is set to be equal to or shorter than the allowable on-time t.sub.2, so as not to cause drooping nor suspension of the radio frequency output (RF output), thereby enabling repetitive application of the radio frequency output (RF output) when the plasma is not ignited yet. As described above, by repeatedly applying the radio frequency output (RF output), the atmosphere inside the laser oscillator is stabilized with prompting the ignition.

(84) FIG. 12 shows a signal example of the abnormal operation state in the high-frequency pulse mode; where FIG. 12(a) illustrates the forward wave voltage V.sub.f, FIG. 12(b) illustrates the reflected wave voltage V.sub.r, FIG. 12(c) illustrates the charging and discharging voltage V.sub.a of the charging and discharging circuit, and FIG. 12(d) illustrates the unignited state detection signal V.sub.fail. The example here shows the case where the duty ratio of pulse driving is 50%.

(85) In the high-frequency pulse mode, the time width when the forward wave voltage V.sub.r is applied is short, and during anomalies, the time width t.sub.3 of the reflected wave is also short. The charging and discharging voltage V.sub.a charged in the time width t.sub.3 according to the charging time constant .sub.c is lower than the voltage charged during one period T in the low-frequency pulse mode, and it does not reach the set voltage V.sub.ref.

(86) Since the charging time constant .sub.r of the charging and discharging circuit is set to be smaller than the discharging time constant .sub.disc (charging time constant .sub.c<discharging time constant .sub.disc), voltage after discharging in one period does not return to zero, and repeating application of pulse output over plural periods may accumulate the charging and discharging voltage V.sub.a and raise the voltage. When the charging and discharging voltage V.sub.a reaches the set voltage V.sub.ref, the unignited state detection signal V.sub.fail is outputted.

(87) Charging and discharging voltage and accumulated charging and discharging voltage in the charging and discharging circuit will now be described. FIG. 13 illustrates a circuit configuration of the charging and discharging circuit 20a in the unignited state detection circuit 20.sub.circuit as shown in FIG. 7. The charging and discharging circuit 20a is configured by connecting the charging and discharging resistance R.sub.1 in series with the input side of a parallel circuit consisted of the capacitor C and the discharging resistance R.sub.2, and input voltage V.sub.in is inputted in the charging and discharging resistance R.sub.1, via the block diode D, and the voltage across the capacitor C is outputted as the charging and discharging voltage V.sub.a. FIG. 14 shows one example of the input voltage V.sub.in, and assuming the on-time width as to and the off-time width as (t.sub.bt.sub.a), pulses at a predetermined frequency are outputted during the on-time width t.sub.a.

(88) Since the circuit configuration of the charging and discharging circuit 20a is a nonlinear circuit provided with a diode, an analysis is carried out separately in the following states; in the state where there is an input signal (RF signal is on) and in the state where there is no input signal (RF signal is off).

(89) FIG. 15 illustrates a circuit state where there is an input signal (when the RF signal is on). In the circuit state as shown in FIG. 15, a circuit equation is expressed as the following formulas 1 to 4, where charging and discharging voltage is V.sub.a, the current passing through the charging and discharging resistance R.sub.1 is i.sub.1, the current passing through the discharging resistance R.sub.2 is i.sub.2, and the current passing into the capacitor C is i.sub.c:

(90) $\begin{array}{cc}{v}_a\left(t1\right)=\frac{1}{c}{}_0^{t1}{i}_c\left(t\right)t+v_a\left(0\right)& \left(1\right)\\ i_1\left(t\right)=i_2\left(t\right)+i_c\left(t\right)& \left(2\right)\\ i_1\left(t\right)=\frac{v_{\mathrm{in}}\left(t\right)-v_a\left(t\right)}{R_1}& \left(3\right)\\ i_2\left(t\right)=\frac{v_a\left(t\right)}{R_2}& \left(4\right)\end{array}$

(91) Assuming the input voltage V.sub.in as the step voltage E.sub.m, charging and discharging voltage V.sub.a(t.sub.1) is obtained in the RF.sub.on interval (0 to t.sub.1) when the RF signal is on, and it is expressed by the following formula 5.

(92) $\begin{array}{cc}{v}_a\left(t1\right)=\frac{R_1{R}_2}{R_1+R_2}\left(1-{}^{-\frac{1}{{\mathrm{CR}}_p}t1}\right)& \left(5\right)\end{array}$

(93) In the formula 5, assuming that R.sub.p=R.sub.1.Math.R.sub.2/(R.sub.1+R.sub.2), the charging time constant is represented by C.Math.R.sub.p.

(94) On the other hand, FIG. 16 illustrates a circuit state when there is no input signal (when the RF signal is off). In the circuit state as shown in FIG. 16, a circuit equation is expressed as the following formulas 6 and 7, where charging and discharging voltage is V.sub.a, current passing through the discharging resistance R.sub.2 is i.sub.2, and current passing into the capacitor C is i.sub.c:

(95) $\begin{array}{cc}{v}_a\left(t2\right)=\frac{1}{C}{}_{t1}^{t2}{i}_c\left(t\right)t+v_a\left(t1\right)& \left(6\right)\\ i_c\left(t\right)=-i_2\left(t\right)=-\frac{v_a\left(t\right)}{R_2}& \left(7\right)\end{array}$

(96) By using the formulas 6 and 7, the charging and discharging voltage V.sub.a when the RF signal is off is expressed by the following formula 8:

(97) $\begin{array}{cc}{v}_a\left(t2\right)=v_a\left(t1\right){}^{-\frac{1}{\mathrm{CR}2}t2}& \left(8\right)\end{array}$

(98) There are provided following numerical values for the charging and discharging voltage V.sub.a as expressed by the formula 5 when the RF signal is on, and the charging and discharging voltage V.sub.a as expressed by the formula 8 when the RF signal is off:

(99) Pulse frequency of input voltage V.sub.in: 50 kHz

(100) ON duty ratio of input voltage V.sub.in: 30%

(101) Charging and discharging resistance R.sub.1: 1.8

(102) Discharging resistance: 3.6

(103) Capacitance of capacitor C: 0.01 F

(104) Those numerical values are used for dissolution by the Euler's method at a fixed time step of 0.01 s, and the waveform as shown in FIG. 17 is obtained.

(105) A configuration of the unignited state detection device is not limited to an analogue circuit as described so far, but it may be configured by digital operation processing such as DSP and FPGA. If software is employed, the device may be configured by a CPU, a memory, and the like, which stores programs to instruct the CPU to perform processing for detecting the unignited state.

(106) (Configuration Example According to Digital Operation Processing)

(107) With reference to FIGS. 18 and 19, an example for configuring the unignited state detection device by digital operation processing will now be described.

First Configuration Example

(108) FIG. 18 is an example configuring the unignited state detection device by a digital circuit. In the example here, it is shown that the digital circuit configures the aforementioned charging and discharging circuit.

(109) In FIG. 18A, a conversion means 31 of the unignited state detection device 30 is provided with, a first integrating circuit 31A, a second integrating circuit 31B, a hold circuit 31C, switching circuits 31D and 31E, and a comparator 32 is also provided.

(110) The switching circuit 31D inputs a voltage value X obtained by sampling the reflected wave voltage and by performing A/D conversion, into the first integrating circuit 31A, only during the RF.sub.on interval. The first integrating circuit 31A digitally integrates the voltage value X inputted via the switching circuit 31D, and calculates a first converted value corresponding to an amount of heat that is applied to the RF power amplifier element of the RF power source.

(111) The second integrating circuit 31B digitally integrates a voltage component lowered by discharging only within the RF.sub.off interval, and calculates a second converted value corresponding to an amount of heat dissipated from the RF power amplifier element of the RF power source.

(112) The hold circuit 31C inputs the first converted value of the first integrating circuit 31A and the second converted value of the second integrating circuit 31B, obtains a difference between the first converted value and the second converted value, and then outputs a third converted value to the comparator 32. The comparator 32 compares the third converted value inputted from the hold circuit 31C, with the set voltage V.sub.ref corresponding to the device protection sensing level, and outputs an unignited state detection signal, when the third converted value reaches or exceeds the set voltage V.sub.ref.

(113) FIG. 18B shows a general schematic configuration of the digital circuit constituting the integrating circuit. The integrating circuit is made up of coefficient units, an adder, and a delay device. The coefficient units are provided with coefficients of a and 1a, respectively.

(114) The coefficient a provided in the coefficient unit of the first integrating circuit 31A is expressed as:
a=.sub.1/(.sub.1+T),
and the coefficient a provided in the coefficient unit of the second integrating circuit 31B is expressed as:
a=.sub.2/(.sub.2+T)

(115) Here, the time constants .sub.1 and .sub.2 are respectively expressed as;
.sub.1=C.Math.R.sub.p
.sub.2=C.Math.R.sub.2
and T indicates a period of pulse driving.

Second Configuration Example

(116) FIG. 19 shows a configuration example where a counting circuit constitutes the unignited state detection device.

(117) The conversion means 41 of the unignited state detection device 40 is provided with an addition circuit 41A, a subtraction circuit 41B, an adder 41C, and a switching circuit 41D, and a comparator 42 is also provided. The addition circuit 41A calculates a first converted value corresponding to an amount of heat that is applied to the RF power amplifier element of the RF power source, by adding a voltage value X that is obtained by sampling reflected wave voltage and performing A/D conversion. The subtraction circuit 41B counts a numerical value corresponding to the discharging time constant .sub.disc during the RF.sub.off interval, calculates a second converted value corresponding to an amount of heat dissipated from the RF power amplifier element of the RF power source, further calculates a third converted value corresponding to a difference between the first converted value and the second converted value, and then outputs the result to the comparator 42.

(118) The comparator 42 compares the third converted value inputted from the subtraction circuit 41B with the set voltage V.sub.ref corresponding to the device protection sensing level, and when the third converted value reaches or exceeds the set voltage V.sub.ref, an unignited state detection signal is outputted.

(119) At the time when the operations in one cycle are completed, an added and subtracted value obtained from the subtraction circuit 41B is returned to the adder 41C as an initial value, and a third converted value over plural periods is calculated in association with the high-frequency pulse mode.

(120) The preferred embodiments and modifications described above are examples of the unignited plasma state detection method and the detection device relating to the present invention. The present invention is not limited to those exemplary embodiments and various modifications are possible on the basis of the spirit of the present invention, and all such modifications are intended to be included within the scope of the invention.

INDUSTRIAL APPLICABILITY

(121) The unignited plasma state detection device and the detection method thereof according to the present invention can be applied to power supply to a plasma load. And it is applicable to a film forming apparatus to produce a thin film, such as a semiconductor, liquid crystal, and solar panel, and to plasma generation by high frequency wave (RF) in a CO.sub.2 laser beam machine, or the like.

DESCRIPTION OF SYMBOLS

(122) 1 unignited state detection device 2 power sensor 3 power Controller 4 buffer 10 unignited state detection device 11 conversion means 11A conversion means 11B conversion means 11C conversion means 12 comparison means 20 unignited state detection device 20a Charging and discharging circuit 20b comparator 20.sub.circuit ignited state detection circuit 21 conversion means 21A Charging voltage calculation means 21B discharging voltage calculation means 21C charging and discharging voltage calculation means 22 voltage comparison means 30 unignited state detection device 31 conversion means 31A integrating circuit 31B integrating circuit 31C hold circuit 31D, 31E switching circuit 32 comparator 40 unignited state detection device 41 conversion means 41A addition circuit 41B subtraction circuit 41C adder 41D switching circuit 42 comparator 101 matching box 102 plasma load a coefficient C capacitor D block diode E.sub.m step voltage H.sub.ac equivalent amount of heat storage i.sub.1 current i.sub.2 current i.sub.c current k.sub.1 coefficient k.sub.2 coefficient R.sub.1 charging and discharging resistance R.sub.2 discharging resistance T period t.sub.1 duration t.sub.2 allowable on-time t.sub.3 time width t.sub.a on-time width V.sub.a charging and discharging voltage V.sub.f forward wave voltage V.sub.fail unignited state detection signal V.sub.in input voltage V.sub.r reflected wave voltage V.sub.ref set voltage X voltage value reflection coefficient .sub.1 time constant .sub.c charging time constant .sub.disc discharging time constant