JP2009252832A - Abnormal discharge detection method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an abnormal discharge detection method for detecting abnormal discharge in a transition period from start of output of high frequency power to a steady state of high frequency power. <P>SOLUTION: When supplying high frequency power to a processing chamber 4 by a high frequency power supply 2, generating plasma in the processing chamber 4, and processing a body to be processed X, abnormal discharge in the transition period from start of output of high frequency power to a steady state of high frequency power is detected in the abnormal discharge detection method. The method includes a current detection step (S101) for detecting discharge current flowing in a circuit to which high frequency power is applied, fall detection steps (S102 to S104) for detecting fall of a waveform curve formed based on detected discharge current, and determining steps (S104 to S105) determining that abnormal discharge exists when the waveform curve falls. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for detecting abnormal discharge in a plasma apparatus.

  For example, when plasma is generated in a processing chamber by high-frequency power and an object to be processed placed in the processing chamber is subjected to an etching treatment or the like, if an abnormal discharge occurs in the processing chamber, the object to be processed is of course In addition, various devices and members in the processing chamber may be damaged.

  Therefore, for example, in the abnormal discharge detection method described in Japanese Patent Laid-Open No. 2002-324783 (Patent Document 1), the voltage or current in the circuit is detected, and the abnormal discharge is recognized from the amplitude modulation. More specifically, a threshold is set for the amplitude modulation of the current, and abnormal discharge is detected using whether or not the amplitude modulation of the current exceeds the threshold as one determination factor.

Conventionally, a method has also been proposed in which abnormal discharge is recognized by detecting a reflected wave using a reflected wave that is generated as a result of an impedance matching state breaking when an abnormal discharge occurs.
Japanese Patent Laid-Open No. 2002-324783

  However, any of the above conventional methods is a method for detecting an abnormal discharge after the high frequency power reaches a set value (after a transient period). For example, when an abnormal discharge is detected by providing a threshold value for current amplitude modulation, the threshold value is set based on the current value (current value after plasma stabilization) of the discharge current in a steady state. The discharge current does not reach the reference until the high frequency power reaches the set power (steady state), and the abnormal discharge during the transient period is not determined.

  Also, at the start of discharge (when high-frequency power is in a transient period), the impedance is not perfectly matched, so in most cases a reflected wave appears. Therefore, even if the reflected wave is detected, it cannot be determined whether it is caused by the alignment delay or abnormal discharge in the transient period. In other words, the conventional method of detecting abnormal discharge using the reflected wave cannot detect abnormal discharge during the transient period.

  The present invention has been made in view of such circumstances, and an abnormal discharge detection method capable of detecting an abnormal discharge in a transition period from when the output of high-frequency power is started until the high-frequency power reaches a steady state. The purpose is to provide.

  The abnormal discharge detection method of the present invention supplies high-frequency power to a processing chamber from a high-frequency power source, generates plasma in the processing chamber, and processes the object to be processed. An abnormal discharge detection method for detecting an abnormal discharge in a transition period until a steady state reaches a steady state, which is formed based on a current detection step for detecting a discharge current flowing in a circuit to which high-frequency power is applied, and the detected discharge current A decrease detection step for detecting a decrease in the waveform curve, and a determination step for determining that an abnormal discharge has occurred when the waveform curve decreases.

  The waveform curve means, for example, an envelope or a curve connecting each positive peak value at a high frequency. The locus of the waveform curve continues to rise (increase) from when the discharge current starts to flow until the discharge current reaches a steady state. The discharge current is in a steady state after the high frequency power is in a steady state (after the transient period). That is, if the waveform curve is normal, the waveform curve is formed to increase (increase) with time during the transition period.

  Here, when there is an abnormal discharge, the waveform curve based on the discharge current temporarily rises and falls. That is, during abnormal discharge, a peak (maximum) appears in the waveform curve. The present invention uses the property that the waveform curve continues to rise (increase) during the transition period if it is normal. That is, if there is no abnormal discharge, the waveform curve will not drop (decrease), so it is determined that there was abnormal discharge at that time by detecting that the waveform curve has a downward trend.

  The decrease in the waveform curve appears, for example, when the current value on the detected waveform curve becomes smaller than the current value on the previous waveform curve. Alternatively, the fall of the waveform curve appears when the differential value of the waveform curve becomes negative.

  In the present invention, when a discharge current is detected (current detection step) and a decrease in the waveform curve is detected (decrease detection step), it is determined that an abnormal discharge has occurred at that time (determination step). Thereby, the abnormal discharge during the transient period of the high frequency power can be detected.

  Here, in the current detection step, the discharge current is preferably detected by a clamp meter. As a result, the measuring instrument does not become a resistor, and adverse effects on the circuit can be prevented. Moreover, since alternating current is converted into direct current and it can detect as an envelope of a discharge current, it is suitable for the detection of the fall of a waveform curve.

  According to the abnormal discharge detection method of the present invention, it is possible to detect abnormal discharge in a transition period from when the output of high-frequency power is started until the high-frequency power reaches a steady state.

Next, the present invention will be described in more detail with reference to embodiments.
First, a plasma processing system 1 used in this embodiment will be described with reference to FIG. FIG. 1 is a schematic diagram showing a plasma processing system 1. In this embodiment, a plasma processing system used to form a substrate is taken as an example. As shown in FIG. 1, the plasma processing system 1 mainly includes an RF power supply device 2 (high frequency power supply), an RF matching unit 3, a processing chamber 4, and an abnormality determination unit 6.

  The RF power supply device 2 is connected to the RF matching device 3 and outputs high-frequency power (hereinafter referred to as an input wave) to the processing chamber 4 via the RF matching device 3. The RF power supply device 2 adjusts the output so that the input wave becomes a set value. That is, if the input wave rises to the set value after the input wave output start (ON), a steady state is obtained.

  The RF matching device 3 is connected between the RF power supply device 2 and the processing chamber 4 and matches impedances on the RF power supply device 2 side and the processing chamber 4 side. Normally, the resistance in the processing chamber 4 changes due to the rise of the input wave, so that the matching is not stable until the input wave reaches a steady state, and a reflected wave is generated.

  The processing chamber 4 has a first electrode 41 and a second electrode 42, the first electrode 41 is connected to the RF matcher 3, and the second electrode 42 is connected to the ground. The substrate X that is the object to be processed is placed on the second electrode 42 side. After an input wave is started to be supplied from the RF power supply device 2 (RF is turned on), discharge is started between the electrodes 41 and 42 after a while.

  In this embodiment, the clamp meter 5 is applied to the wiring connecting the RF matching unit 3 and the processing chamber 4 in order to detect the discharge current flowing between the RF power supply device 2 and the processing chamber 4 during the transition period. Information (such as a current value) obtained by the clamp meter 5 is sent to the abnormality determination unit 6. The abnormality determination unit 6 determines the presence or absence of abnormal discharge based on the information. Further, matching information (control signal Load / Tune or PHASE / MAG or the like) of the RF matcher 3 is sent to the RF power supply device 2. In the RF power supply device 2, an input wave and a reflected wave are also detected. The RF power supply device 2 outputs set power so as to be in a stable steady state from the matching information, the input wave, and the reflected wave.

  Here, transition of various signals monitored by the plasma processing system 1 will be described with reference to FIG. FIG. 2 is a diagram showing the transition of various signals monitored by the plasma processing system 1 during normal operation. As shown in FIG. 2, the input wave continues to rise (increase) from when the RF power supply device 2 starts output (ON) until it reaches a set value (transient period). The incident wave then stabilizes in a steady state after the transient period.

  When the incident wave is output, the reflected wave is generated due to the impedance matching shift. The reflected wave rises and falls in a convex shape, and is not generated when the incident wave is in a steady state and impedance matching is achieved completely.

  The discharge current begins to flow after a while from the start of the incident wave output, and discharge is started between the electrodes 41 and 42 in the processing chamber 4. The envelope of the discharge current (corresponding to the “waveform curve” in the present invention) continues to rise and reaches a steady state at a predetermined value. This envelope is drawn based on the discharge current. When the discharge current is in a steady state, the plasma in the processing chamber 4 is stabilized.

  The two control signals generated by the RF matching unit 3 match the phase of the current (voltage) of the power (incident wave) supplied to the processing chamber 4 and the voltage, and match the impedances of the RF power supply 2 side and the processing chamber 4 side. These rise and fall until the plasma stabilizes. As described above, it is the incident wave and the discharge current that does not drop during the transient period.

  Here, various signals when abnormal discharge occurs during the transient period will be described with reference to FIG. FIG. 3 is a diagram showing transition of various signals monitored by the plasma processing system 1 when there is an abnormal discharge.

  As shown in FIG. 3, the discharge current changes in a spike shape corresponding to the occurrence / convergence of abnormal discharge. As shown in FIG. 2, the discharge current is a signal that simply rises (increases) within a normal transient period. However, if there is an abnormal discharge, it rises and falls correspondingly. That is, if there is an abnormal discharge during the transition period, a downward trend clearly appears in the envelope of the discharge current.

  The input wave during the transition period changes in degree of increase due to abnormal discharge, but does not decrease (decrease). Other signals also change due to abnormal discharge, but are irregular curves, so it is difficult to detect a difference based on the presence or absence of abnormal discharge.

  In the present embodiment, during the transition period, it is detected that an abnormal discharge has occurred by detecting a decrease in the envelope of the discharge current. In the present embodiment, the CPU in the abnormality determination unit 6 determines the presence or absence of abnormal discharge based on information from the clamp meter 5 transmitted to a CPU (not shown) in the abnormality determination unit 6.

  Here, an abnormal discharge detection method in the present embodiment will be described with reference to FIG. FIG. 4 is a diagram illustrating a flow of the abnormal discharge detection method. As shown in FIG. 4, when the incident wave starts to be output from the RF power supply device 2, a discharge current is detected by the clamp meter 5 (S101). The detection value (current value) converted from alternating current to direct current by the clamp meter 5 is transmitted to the CPU in the abnormality determination unit 6, and the CPU samples the current value at predetermined intervals (S102). That is, the discharge current detected by the clamp meter 5 is sampled.

Then, comparing the value _{I n} sampled values _{I n-1,} which was previously sampled (S103). Then, it result, when the current sampling value I _n is smaller than the previous sampled value I _n-1 (I _{n-1> I n),} the slope at a point with envelope line (differential value) is negative This means that a downward trend appears in the envelope (S104: Yes). Thus, if the fall of an envelope is detected, it will determine with having abnormal discharge, and will perform the process at the time of abnormality (S105). The abnormal process is, for example, lighting of a warning lamp that notifies that abnormal discharge has occurred, storage of abnormal discharge information (number of times, timing, etc.), and the like. In the present embodiment, even when an abnormal discharge is detected, the plasma processing system 1 is not stopped and the film forming process for the substrate X is continued. Then, the abnormal discharge detection is continued during the transition period (S106).

On the other hand, in S104, when the current sampling value _{I n} is greater than the previous sampling value _{I n-1 (I n-} 1 ≦ I n), no decrease in the current value at that time, the downward trend in the envelope It does not appear (S104: No). In this case, it is determined that there is no abnormal discharge, and if it is during the transition period, this abnormal discharge detection is continued (S106).

  In summary, the abnormal discharge detection method according to the present embodiment is a method for detecting abnormal discharge during a transient period, and the discharge current flowing through the circuit connecting the RF power supply device 2 and the processing chamber 4 is detected by the clamp meter 5. (Current detection step), detecting a decrease in the envelope (waveform curve) formed based on the detected value (decrease detection step), and determining that there was abnormal discharge when the envelope decreased (Judgment step).

  According to this method, it is possible to detect an abnormal discharge generated during the transient period without missing it. The abnormal process (S105) allows the operator to know that an abnormal discharge has occurred, and to use the information for confirming the processed object, planning the maintenance time of the processing chamber 4, and the like. it can. When the abnormal discharge occurs, for example, the first electrode 41 in the processing chamber 4 melts, and the splashes adhere to the substrate X, the second electrode 42, and the like. By detecting the abnormal discharge during the transient period that has been overlooked in the past, it is possible to more accurately grasp how much the processing chamber 4 is damaged, and it is possible to perform maintenance effectively.

Further, according to the method of the present embodiment, abnormal discharge during a transient period can be detected by the same method even for another plasma processing system having a different size or processing target. In this method, since it is not necessary to set a threshold value or the like, it is not necessary to calculate a unique threshold value corresponding to each plasma processing system. However, a threshold value may be set to identify the degree of abnormal discharge. In this case, on the condition that the fall of the waveform curve is detected, the degree of abnormal discharge can be estimated based on whether or not the current value at the time of the fall is larger than the threshold value. For example, I _n-1 when the descent is detected is compared with a threshold value, and if I _n-1 is large, a warning lamp different from S105 is turned on. Thereby, in addition to the presence or absence of abnormal discharge, the extent can also be grasped.

  In the present embodiment, the detection of the discharge current is not limited to the above, and a measuring instrument other than the clamp meter may be used. However, by using an induction ammeter such as the clamp meter 5, it is possible to suppress adverse effects on the circuit due to the resistance and capacitance of the measuring instrument itself. Further, the waveform curve of the discharge current can be directly detected.

  Further, the descent of the waveform curve may be detected by calculating the differential value at each moment of the waveform curve by a program and by positive / negative of the differential value. In the present invention, it is not necessary to detect (draw) the waveform curve itself, as long as it detects the fall of the waveform curve.

1 is a schematic diagram showing a plasma processing system 1. FIG. It is a figure which shows the transition of the various signals monitored with the plasma processing system 1 at the time of normal. It is a figure which shows transition of the various signals monitored with the plasma processing system 1 when there exists abnormal discharge. It is a figure which shows the flow of the abnormal discharge detection method.

Explanation of symbols

1: plasma processing system, 2: RF power supply (high frequency power supply), 3: RF matching unit,
4: processing chamber, 5: clamp meter, 6: abnormality determination unit, X: substrate (object to be processed)

Claims (2)

When high-frequency power is supplied to the processing chamber by a high-frequency power source and plasma is generated in the processing chamber to process the object to be processed, the output of the high-frequency power is started until the high-frequency power reaches a steady state. An abnormal discharge detection method for detecting abnormal discharge in a transient period of
A current detection step of detecting a discharge current flowing in a circuit to which the high-frequency power is applied;
A descent detection step for detecting a descent of a waveform curve formed based on the detected discharge current;
A determination step for determining that there was abnormal discharge when the waveform curve was lowered;
An abnormal discharge detection method comprising:   The abnormal discharge detection method according to claim 1, wherein in the current detection step, the discharge current is detected by a clamp meter.

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