JP2005057122A - Trouble detecting method by plasma emission intensity - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To speedily and easily find a trouble state upon a plasma emission processing with a simplified mechanism. <P>SOLUTION: The existence of the trouble state is judged by subjecting electromagnetic wave emission radiated by plasma discharge upon a plasma emission processing in a reaction chamber to photoelectric conversion to obtain a voltage value 31, and comparing this voltage value 31 with a predetermined non-changing fixed value Th1 along a time axis. This simplifies and facilitates the judgement when compared with prior art where such a judgement is made by making use of a pair of characteristic curves changing along a time axis, so that the need of a complicated system is eliminated to ease a development and design a software program. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an abnormality detection method based on plasma emission intensity.

  For example, in a plasma etching apparatus, a voltage converted value of light emission intensity in plasma light emission processing is stored in advance, and by detecting and monitoring the light emission intensity during plasma light emission processing, process parameter fluctuations are discovered quickly, and semiconductor elements Has been disclosed (see Patent Document 1).

  In Patent Document 1, a pair of upper and lower virtual curves having a predetermined width is set to a normal etching characteristic curve so that the characteristic curve obtained by etching falls within a range between the pair of virtual curves. Monitoring.

JP 2001-15492 A

  In Patent Document 1, it is necessary to create a pair of virtual curves. In particular, since each virtual curve is set as a curve that changes with time, a complicated system is required.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an abnormality detection method using plasma emission intensity that can easily find an abnormal state during plasma emission processing with a simple and simple mechanism.

  In order to solve the above-mentioned problem, the invention according to claim 1 includes a first step of obtaining a voltage value by photoelectrically converting electromagnetic wave emission generated by plasma discharge during plasma emission processing in a reaction chamber; And a second step of comparing the voltage value converted in the step with a predetermined fixed value that does not change along the time axis and determining the presence or absence of an abnormal state.

  According to the first aspect of the present invention, a voltage value is obtained by photoelectrically converting electromagnetic wave emission generated by plasma discharge during plasma emission processing in the reaction chamber, and this voltage value is not changed along the time axis. Compared with the conventional technique that uses a pair of characteristic curves that change along the time axis, the determination is simple and easy, and the presence or absence of an abnormal state is determined by comparing with a fixed value of Since the system is not necessary, the development and design of the software program is easy.

  FIG. 1 is a block diagram showing an etching apparatus and peripheral devices shown as an example to which an abnormality detection method using plasma emission intensity according to an embodiment of the present invention is applied.

  In FIG. 1, the emission intensity in the plasma generated in the etching apparatus 1 is converted into a voltage value by the plasma monitor 2, and the voltage value is acquired by the monitoring apparatus 3 as a characteristic curve that changes over time. A curve is displayed on the display unit 4, and a process abnormality and an apparatus abnormality are detected based on the characteristic curve.

  The etching apparatus 1 shown in FIG. 1 is an RIE (Reactive Ion Etching) apparatus, and includes an introduction pipe 12 that feeds an etching gas from a gas source 11 into a room, and a discharge pipe 14 that discharges exhaust gas from the room by a vacuum pump 13. A pair of electrodes 18 and 19 are electrically connected to a pair of RF power sources 16 and 17, respectively. Among these, one electrode 18 is disposed at the uppermost part in the reaction chamber 15, and the other electrode 19 is disposed at the lowermost part in the reaction chamber 15, whereby both electrodes 18, 19 are opposed in the vertical direction. . The lower electrode 19 functions as a stage, and a semiconductor wafer 21 as an object to be etched is placed on the upper surface thereof.

  The reaction chamber 15 is provided with a window 22 transparent to the emission of electromagnetic waves generated during the etching process, and the plasma monitor 2 is installed adjacent to the window 22.

  The plasma monitor 2 includes an optical filter 23 disposed adjacent to the outside of the window 22 of the reaction chamber 15 and a photoelectric converter 24 installed at a slight distance from the optical filter 23.

  The optical filter 23 allows electromagnetic wave emission of a specific wavelength generated during the etching process to pass to the photoelectric converter 24 side.

  For example, a photodiode, a phototransistor, or the like is used for the photoelectric converter 24, and converts the electromagnetic wave emission that has passed through the optical filter 23 into a voltage value (hereinafter referred to as “photoelectric conversion value”).

The monitoring device 3 uses a general computer 3a having a CPU (microphone processor), and operates in accordance with a predetermined software program in the CPU (microphone processor) to which a ROM, a RAM, and the like are connected in the computer 3a. Is. Then, the monitoring device 3 performs a determination process with a combination arbitrarily selected by the operator among the following seven condition settings (1) to (7), and the process abnormality and the apparatus abnormality are detected by this determination process. To detect.
(1) As shown in FIG. 2, when the photoelectric conversion value 31 given from the photoelectric converter 24 exceeds a predetermined upper limit value Th1 (first abnormality determination condition), it is determined as abnormal.
(2) As shown in FIG. 3, when the photoelectric conversion value 32 given from the photoelectric converter 24 falls below a predetermined lower limit value Th2 (second abnormality determination condition), it is determined as abnormal.
(3) As shown in FIG. 4, even if the photoelectric conversion value 33 given from the photoelectric converter 24 exceeds a predetermined upper limit value Th3 and then a certain time t1 elapses, the photoelectric conversion value 33 exceeds the upper limit value Th3. If the state continues (third abnormality determination condition), it is determined as abnormal.
(4) As shown in FIG. 5, even if the photoelectric conversion value 34 given from the photoelectric converter 24 falls below a predetermined lower limit value Th4 and then a certain time t2 elapses, the photoelectric conversion value 34 falls below the lower limit value Th4. If the state persists (fourth abnormality determination condition), it is determined as abnormal.
(5) As shown in FIG. 6 and FIG. 7, the amount of change per unit time (hereinafter referred to as “voltage change amount”) 36 at each time of the photoelectric conversion value 35 given from the photoelectric converter 24 corresponds to each. A normal voltage change amount (hereinafter referred to as “reference change amount”) 38 of the photoelectric conversion value 37 at the time is compared, and a difference between the voltage change amount 36 and the reference change amount 38 at the corresponding time is a constant threshold value. Is exceeded (fifth abnormality determination condition), it is determined as abnormal.
(6) As shown in FIGS. 8 and 9, when the photoelectric conversion value 39 given from the photoelectric converter 24 exceeds a predetermined upper limit value Th5 as a fixed value, the unit time of the photoelectric conversion value 39 at each time Is compared with the reference change amount 43 of the normal photoelectric conversion value 42 at the corresponding time, and the difference between the voltage change amount 41 and the reference change amount 43 at the corresponding time is constant. When the threshold value D1 is exceeded (sixth abnormality determination condition), it is determined as abnormal.
(7) When the photoelectric conversion value given from the photoelectric converter 24 falls below a predetermined reference value Th6 as a fixed value, it corresponds to the voltage change amount per unit time of the photoelectric conversion value at each time, respectively. When the reference change amount of the photoelectric conversion value at normal time at the time is compared, and the difference at the corresponding time between the voltage change amount and the reference change amount exceeds a certain threshold D2 (seventh abnormality determination condition) Is determined to be abnormal (not shown).

  And said 1st-7th abnormality determination conditions can be set now by arbitrary combinations using predetermined input devices, such as a keyboard or a mouse | mouth. The fixed values Th1 to Th6, D1 and D2 can be freely set in units of 0.01 volts using an input device. Further, the fixed times t1 and t2 can be freely set in units of 0.01 seconds using the input device.

  The display unit 4 is connected to the monitoring device 3 using a general CRT display, a liquid crystal display panel, or the like. Then, as shown in FIGS. 2 to 9, the display unit 4 displays the photoelectric conversion values 31 to 35 and 39 given from the photoelectric converter 24 in real time based on the signal given from the monitoring device 3. In addition, the fixed values Th1 to Th6, t1, t2, D1, and D2 in the first to seventh abnormality determination conditions for which the combination is selected by the input device are displayed together with the photoelectric conversion values 31 to 35 and 39. It has become.

  Next, an abnormality detection method based on plasma emission intensity using the above-described etching apparatus 1, plasma monitor 2, and monitoring apparatus 3 will be described.

  First, the operator selects and sets the first to seventh abnormality determination conditions in an arbitrary combination using a predetermined input device such as a keyboard or a mouse connected to the monitoring device 3. At this time, fixed values Th1 to Th6, t1, t2, D1, and D2 required for the selected first to seventh abnormality determination conditions are set and input using an input device. In this case, the fixed values Th1 to Th6, D1, and D2 are set and inputted in units of 0.01 volts, and the fixed times t1 and t2 are set and inputted in units of 0.01 seconds.

  In addition, the fixed values Th1 to Th6 applied to the selected abnormality determination condition are displayed as graphs on the display unit 4 connected to the monitoring device 3 (see FIGS. 2 to 9).

  Next, the operator places the semiconductor wafer 21 on the stage (lower electrode 19) in the reaction chamber 15 of the etching apparatus 1 shown in FIG. , 17 supplies power to the electrodes 18, 19, and sends an etching gas from the gas source 11 through the introduction pipe 12. Then, the etching process in the reaction chamber 15 is performed.

  At this time, light is emitted by electromagnetic waves generated from both electrodes 18 and 19, and this light is irradiated to the plasma monitor 2 through the window 22. Of this light, only the electromagnetic wave emission of a specific wavelength is transmitted by the optical filter 23, and the electromagnetic wave emission of the specific wavelength is incident on the photoelectric converter 24 side and converted into a photoelectric conversion value as a voltage value. Such photoelectric conversion values are input to the monitoring device 3.

  In the monitoring device 3, the photoelectric conversion values 31, 32, 33, 34, 35, 39 given from the photoelectric converter 24 are temporarily stored in the memory, and then the voltage values are reflected so as to reflect the voltage values shown in FIGS. As shown in FIG. At this time, since the fixed values Th1 to Th6 corresponding to the already selected abnormality determination conditions are displayed on the display unit 4, the operator changes the display time in real time. The displayed photoelectric conversion values 31, 32, 33, 34, 35, and 39 can always be visually compared with the fixed values Th1 to Th6.

  Here, when the first abnormality determination condition is first selected, the monitoring device 3, as shown in FIG. 2, receives the photoelectric conversion value 31 given from the photoelectric converter 24 and the upper limit value Th 1 that is held in advance. And compare. For example, when the voltage value at the time when the plasma emission intensity is stable is 8.20 volts, the upper limit value Th1 is set and inputted in advance, for example, to 8.75 volts, and the monitoring device 3 is supplied from the photoelectric converter 24. It is always determined whether or not the obtained photoelectric conversion value 31 exceeds the upper limit value Th1 of 8.75 volts. When it is determined that the photoelectric conversion value 31 has exceeded the upper limit value Th1, the monitoring device 3 immediately determines that the process is abnormal or abnormal, and transmits a signal indicating that to the etching device 1.

  The etching apparatus 1 stops the etching process, for example, by stopping the operation of the RF power supplies 16 and 17 based on the signal given from the monitoring apparatus 3.

  At the same time, the monitoring device 3 notifies the operator of an abnormal state by displaying a warning on the display unit 4 or blowing a buzzer sound.

  When the second abnormality determination condition is selected, the monitoring device 3 compares the photoelectric conversion value 32 given from the photoelectric converter 24 with the lower limit value Th2 held in advance as shown in FIG. To do. When the photoelectric conversion value 32 falls below a predetermined lower limit Th2, it is immediately determined that this is an abnormal state and the etching apparatus 1 is stopped and at the same time a warning is displayed on the display unit 4, or An abnormal condition is notified to the operator by blowing a buzzer sound.

  Further, when the third abnormality determination condition is selected, the monitoring device 3 uses the photoelectric conversion value 33 given from the photoelectric converter 24 and the predetermined upper limit value Th3 held in advance as shown in FIG. Compare When the photoelectric conversion value 33 exceeds the upper limit value Th3, for example, the time is measured by the CPU, and even when the predetermined time t1 has elapsed thereafter, the photoelectric conversion value 33 exceeds the upper limit value Th3. Determine if it will last. As this fixed time t1, for example, a time previously input as an arbitrary value such as 2.00 seconds is applied. If these determination results are obtained positively, it is determined that there is an abnormality, and the etching apparatus 1 is stopped by a signal from the monitoring apparatus 3, and at the same time, a warning is displayed on the display unit 4 or a buzzer sound is generated. The operator is informed of the abnormal state by sounding.

  Furthermore, when the fourth abnormality determination condition is selected, the monitoring device 3, as shown in FIG. 5, the photoelectric conversion value 34 given from the photoelectric converter 24 and a predetermined lower limit value Th 4 that is held in advance. And compare. When the photoelectric conversion value 34 is below the lower limit value Th4, it is determined whether or not the state in which the photoelectric conversion value 34 falls below the lower limit value Th4 continues even after the predetermined time t2 has elapsed. If such a determination result is obtained positively, it is determined that there is an abnormality, and the etching apparatus 1 is stopped by a signal from the monitoring apparatus 3, and at the same time a warning is displayed on the display unit 4 or a buzzer is sounded. For example, the abnormal state is notified to the operator.

  When the fifth abnormality determination condition is selected, the monitoring device 3 per unit time of the photoelectric conversion value 35 given from the photoelectric converter 24 at each time as shown in FIG. 6 and FIG. A change amount (hereinafter referred to as “voltage change amount”) 36 is compared with a voltage change amount (hereinafter referred to as “reference change amount”) 38 of the photoelectric conversion value 37 at a normal time at each corresponding time. Then, when the difference between the voltage change amount 36 and the reference change amount 38 at the corresponding time exceeds a certain threshold (fifth abnormality determination condition), it is determined as an abnormal state. For example, when the reference change amount (voltage change amount per unit time at normal time) at a certain time is 1.00 volts and the threshold value at the corresponding time is 0.50 volts, the allowable range is 0.50. ~ 1.50 volts. For this reason, for example, when the voltage change amount 36 per unit time of the photoelectric conversion value 37 given from the photoelectric converter 24 exceeds 1.50 volts, it is determined as an abnormal state. If it is determined that the state is abnormal as described above, the etching apparatus 1 is stopped by a signal from the monitoring apparatus 3, and at the same time, a warning is displayed on the display unit 4 or a buzzer is sounded. An abnormal state is notified.

  Furthermore, when the sixth abnormality determination condition is selected, the monitoring device 3, as shown in FIGS. 8 and 9, receives the photoelectric conversion value 39 given from the photoelectric converter 24 and a predetermined upper limit held in advance. The value Th5 is compared. For example, the upper limit value Th5 is set to 5.0 volts, and it is compared whether or not it exceeds 5.0 volts. When the photoelectric conversion value 39 exceeds the upper limit value Th5, the monitoring device 3 detects the voltage change amount 41 per unit time of the photoelectric conversion value 39 at each time and the normal time photoelectric at the corresponding time. The reference change amount 43 of the converted value 42 is compared. When the difference between the voltage change amount 41 and the reference change amount 43 at the corresponding time exceeds a certain threshold value D1, it is determined that the state is abnormal. When the reference change amount 43 (voltage change amount per unit time at normal time) is 1.00 volts and the threshold value is 0.50 volts, for example, the unit of the photoelectric conversion value 39 given from the photoelectric converter 24 When the voltage change amount 41 per hour exceeds 1.50 volts, it is determined as an abnormal state. When the abnormal state is determined in this way, the etching apparatus 1 is stopped based on the signal from the monitoring apparatus 3, and at the same time, a warning is displayed on the display unit 4 or a buzzer is sounded. An abnormal state is notified to a person. However, in the sixth abnormality determination condition, the magnitude determination of the difference between the voltage change amount 41 and the reference change amount 43 is performed only when the photoelectric conversion value 39 exceeds the upper limit value Th5. In addition, when the photoelectric conversion value 39 is equal to or less than the upper limit value Th5, even if the difference between the voltage change amount 41 and the reference change amount 43 exceeds a certain threshold value D1, it is not determined as an abnormal state. Absent.

  Furthermore, when the seventh abnormality determination condition is selected, the monitoring device 3 compares the photoelectric conversion value given from the photoelectric converter 24 with a predetermined reference value Th6 as a fixed value. When the photoelectric conversion value falls below the reference value Th6, the monitoring device 3 further detects the voltage change amount per unit time of the photoelectric conversion value at each time and the normal photoelectric conversion value at each corresponding time. Is compared with the reference change amount. When the difference between the voltage change amount and the reference change amount at a corresponding time exceeds a certain threshold value D2, the monitoring device 3 determines that an abnormality has occurred and simultaneously stops the etching device 1 and simultaneously displays the display unit. 4 is displayed as a warning or a buzzer is sounded to notify the operator of the abnormal state. However, in the seventh abnormality determination condition, only when the photoelectric conversion value falls below the lower limit value Th6, the difference between the voltage change amount and the reference change amount is determined, so that the photoelectric conversion value is greater than or equal to the upper limit value Th6. In this case, even if the difference between the voltage change amount and the reference change amount exceeds a certain threshold value D2, it is not determined as an abnormal state.

  In the fifth to seventh abnormality determination conditions, the amount of change in voltage per unit time is used as a factor for abnormality determination. If this unit time is set short, a value close to the differential value of the photoelectric conversion value is obtained. Abnormality judgment can be made.

  A plurality of these abnormality determination conditions can be initially selected in combination by the operator, and in this case, an abnormal state is determined when any one or more of the selected abnormality determination conditions are satisfied.

  Here, for example, as shown in FIG. 11, it is determined that the voltage conversion value 51 of the plasma emission intensity has exceeded a predetermined set time Ta, or an abnormal state is detected, or the process end times Tb to Td as shown in FIG. Compared with the case where the abnormal state is determined according to the end time of the plasma emission, such as determining the abnormal state with variation, according to this embodiment, the abnormal state is detected and determined immediately in the middle of the process when the abnormality occurs. be able to. Therefore, it is possible to suppress the loss of the semiconductor element to the minimum.

  In this embodiment, the values Th1 to Th6, t1, t2, D1, and D2 as determination criteria required for each abnormality determination condition are all set as non-changeable fixed values along the time axis. Compared to the above-mentioned Patent Document 1 in which determination is made using a pair of characteristic curves that change along the time axis, the determination is simple and easy, and a complicated system is not required. Has the advantage of In addition, since abnormality determination can be performed by combining various abnormality determination conditions, accurate abnormality determination can be performed.

  Further, in particular, in the third and fourth abnormality determination conditions, as a result of the magnitude comparison with a certain voltage value, it is not immediately determined as an abnormal state, but a state in which the voltage value is exceeded or decreased is a predetermined time. Since an abnormal state is determined only when t1 and t2 or more have elapsed, erroneous determination due to noise can be prevented.

  Accordingly, the first and / or second abnormality determination condition can be determined in a situation where noise is low, while the third and / or fourth abnormality determination condition can be determined in a situation where noise is large. . Thus, this embodiment is convenient because a plurality of abnormality determination conditions can be arbitrarily combined depending on the situation.

  Further, in the fifth abnormality determination condition, since the voltage change amount per predetermined unit time is used as a factor of abnormality determination, the abnormality that cannot be detected in the first to fourth abnormality determination conditions for determining abnormality based on the absolute reference of the voltage value. The state can also be detected. In particular, when performing detailed monitoring such as whether the etching conditions such as the etching pressure are not varied from normal, or whether the remaining film etched to switch the etching film type is thinner than normal. In this case, the fifth abnormality determination condition may be selected.

  Therefore, accurate abnormality determination can be performed by making a parallel determination by appropriately combining the first to fourth abnormality determination conditions and the fifth abnormality determination condition.

  Furthermore, in the sixth and seventh abnormality determination conditions, the possibility of an abnormal state is determined based on the absolute reference of the voltage value, and the abnormality determination is further performed based on the determination result based on the voltage change amount per predetermined unit time. Therefore, it is possible to detect a complicated abnormal state that cannot be detected under the first to fifth abnormality determination conditions.

  Therefore, it is possible to make an accurate abnormality determination by appropriately combining the first to fifth abnormality determination conditions and the sixth and seventh abnormality determination conditions.

  In the above embodiment, it has been described that the etching process is stopped by stopping the operation of the RF power sources 16 and 17 when an abnormal state is determined and detected. However, for example, the etching apparatus 1 is operated by operating an interlock. Appropriate control may be performed by providing feedback.

  In the above embodiment, the etching apparatus and its peripheral devices are shown as an example to which the abnormality detection method based on the plasma emission intensity is applied. However, the present invention is not limited to this etching process. For example, an ashing process or a CVD apparatus is used. The present invention can be widely applied to the entire processing of monitoring plasma emission processing with a plasma monitor, such as plasma cleaning processing.

It is a block diagram which shows the etching apparatus used for the abnormality detection method by the plasma luminescence intensity concerning one embodiment of this invention, and its peripheral device. It is a figure which shows the 1st abnormality determination condition of the abnormality detection method by the plasma emission intensity which concerns on one embodiment of this invention. It is a figure which shows the 2nd abnormality judgment condition of the abnormality detection method by the plasma emission intensity which concerns on one embodiment of this invention. It is a figure which shows the 3rd abnormality determination condition of the abnormality detection method by the plasma emission intensity which concerns on one embodiment of this invention. It is a figure which shows the 4th abnormality determination condition of the abnormality detection method by the plasma emission intensity which concerns on one embodiment of this invention. It is a figure which shows the 5th abnormality determination condition of the abnormality detection method by the plasma emitted light intensity which concerns on one embodiment of this invention. It is a figure which shows the 5th abnormality determination condition of the abnormality detection method by the plasma emitted light intensity which concerns on one embodiment of this invention. It is a figure which shows the 6th abnormality determination condition of the abnormality detection method by the plasma emission intensity which concerns on one embodiment of this invention. It is a figure which shows the 7th abnormality determination condition of the abnormality detection method by the plasma emission intensity which concerns on one embodiment of this invention. It is a figure for demonstrating the 7th abnormality determination condition of the abnormality detection method by the plasma emission intensity which concerns on one embodiment of this invention. It is a figure which shows one reference example of the abnormality detection method by plasma luminescence intensity. It is a figure which shows the other reference example of the abnormality detection method by plasma luminescence intensity.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Etching apparatus, 2 Plasma monitor, 3 Monitoring apparatus, 4 Display part, 11 Gas source, 12 Introduction pipe, 13 Vacuum pump, 14 Exhaust pipe, 15 Reaction chamber, 16 RF power supply, 18, 19 Electrode, 21 Semiconductor wafer, 22 Window, 23 Optical filter, 24 Photoelectric converter.

Claims (7)

A first step of photoelectrically converting electromagnetic wave emission generated by plasma discharge during plasma emission treatment in the reaction chamber to obtain a voltage value;
A method for detecting abnormality by plasma emission intensity, comprising: a second step of comparing the voltage value converted in the first step with a predetermined fixed value that does not change along the time axis and determining the presence or absence of an abnormal state. . A first step of photoelectrically converting electromagnetic wave emission generated by plasma discharge during plasma emission treatment in the reaction chamber to obtain a voltage value;
The voltage value converted in the first step is compared with a predetermined fixed value that does not change along the time axis, and as a result of the comparison, a predetermined state of the voltage value with respect to the fixed value is maintained for a certain time. And a second step of determining an abnormal state when it is determined that an abnormality has occurred. An abnormality detection method using plasma emission intensity according to claim 1,
In the second step, the voltage value converted in the first step is compared with a predetermined other fixed value that does not change along the time axis, and as a result of the comparison, the other of the voltage value An abnormality detection method based on plasma emission intensity, which is determined to be an abnormal state even when it is determined that a predetermined state with respect to a fixed value is maintained for a certain time. A first step of photoelectrically converting electromagnetic wave emission generated by plasma discharge during plasma emission treatment in the reaction chamber to obtain a voltage value;
The voltage change amount per unit time at each time of the voltage value converted in the first step is compared with a predetermined reference change amount at each corresponding time, and the voltage change amount and the reference change amount And a second step of determining an abnormal state when the difference in the corresponding time exceeds a predetermined threshold range. An abnormality detection method using plasma emission intensity according to any one of claims 1 to 3,
In the second step, a voltage change amount per unit time at each time of the voltage value converted in the first step is compared with a predetermined reference change amount at a corresponding time, and the voltage change An abnormality detection method based on plasma emission intensity, in which an abnormal state is determined even when a difference between a quantity and a reference change amount at a corresponding time exceeds a predetermined threshold range. A first step of photoelectrically converting electromagnetic wave emission generated by plasma discharge during plasma emission treatment in the reaction chamber to obtain a voltage value;
When the voltage value converted in the first step is compared with a predetermined fixed value that does not change along the time axis, and as a result of the comparison, the voltage value is in a predetermined state with respect to the fixed value In addition, the voltage change amount per unit time at each time of the voltage value converted in the first step is compared with a predetermined reference change amount at each corresponding time, and the voltage change amount and the reference change are compared. An abnormality detection method using plasma emission intensity, comprising: a second step of determining an abnormal state when a difference in time corresponding to each amount exceeds a predetermined threshold range. An abnormality detection method using plasma emission intensity according to any one of claims 1 to 5,
In the second step, the voltage value converted in the first step is compared with a predetermined other fixed value that does not change along the time axis, and as a result of the comparison, the voltage value is further Further, in a predetermined state with respect to another fixed value, the voltage change amount per predetermined unit time at each time of the voltage value converted in the first step is set to a predetermined reference at each corresponding time. An abnormality detection method based on plasma emission intensity, which is determined to be an abnormal state even when a difference at a corresponding time between the voltage change amount and the reference change amount exceeds a predetermined threshold range as compared with a change amount.

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