JP2021026811A - Plasma processing device - Google Patents

Abstract

To provide a technique useful for detecting occurrence of a defect in a plasma processing device.SOLUTION: Disclosed is a plasma processing device for performing plasma processing by generating a plasma between a first electrode part and a second electrode part, which includes: a power supply part which applies an AC voltage between the first electrode part and the second electrode part; a detection part for detecting discharge between the first electrode part and the second electrode part; and an arithmetic processing part for obtaining the number of times of occurrence of the discharge per predetermined period for each polarity of the AC voltage, and detecting the abnormality in the plasma processing.SELECTED DRAWING: Figure 1

Description

The present invention relates to a plasma processing apparatus.

Conventionally, a technique for detecting an abnormal discharge in a plasma processing apparatus is known (see, for example, Patent Document 1). For example, a current sensor that measures the return current flowing from the plasma generated in the chamber toward the ground potential is attached to the side wall of the chamber to which the ground wire of the plasma processing device is attached. An abnormal discharge detection unit is electrically connected to the current sensor, and it is determined whether or not an abnormal discharge has occurred based on the measured return current.

The abnormal discharge detection unit captures the measured return current as a voltage value, and determines the number of times the measured voltage value exceeds a predetermined threshold voltage and the voltage value when the measured voltage value exceeds the threshold voltage. It has a function to determine that an abnormal discharge has occurred based on. The predetermined threshold is set based on the return current measured when no abnormal discharge has occurred.

Japanese Unexamined Patent Publication No. 2012-9243

In a configuration in which an AC voltage is applied to generate plasma, discharge when the polarity of the applied voltage is positive and discharge when the polarity of the applied voltage is negative are usually alternately performed. If any abnormality occurs in the plasma processing equipment, there is a possibility that an abnormality may occur in the relationship between the positive discharge and the negative discharge, and this viewpoint is considered to be useful for detecting the defect of the plasma processing equipment. ..

An object of the present invention is to provide a technique useful for detecting the occurrence of a defect in a plasma processing apparatus that performs plasma processing by applying an AC voltage to generate plasma.

An exemplary plasma processing apparatus of the present invention is a plasma processing apparatus that generates plasma between a first electrode portion and a second electrode portion to perform plasma processing, and the first electrode portion and the second electrode portion. The power supply unit that applies an AC voltage between the units, the detection unit that detects the discharge between the first electrode unit and the second electrode unit, and the AC voltage that determines the number of times the discharge occurs per predetermined period. It is provided with an arithmetic processing unit for detecting an abnormality during the plasma processing, which is obtained for each polarity of.

According to an exemplary invention, it is possible to easily detect the occurrence of a defect in a plasma processing apparatus that performs plasma processing by applying an AC voltage to generate plasma.

FIG. 1 is a diagram showing a schematic configuration of a plasma processing apparatus according to an embodiment of the present invention. FIG. 2 is a diagram illustrating a time change between a voltage V measured by a voltage measuring unit and a current I measured by a current measuring unit in the plasma processing apparatus according to the embodiment of the present invention. FIG. 3 is a diagram showing a configuration of a peak hold unit and a comparison unit included in the plasma processing apparatus according to the embodiment of the present invention. FIG. 3A is a circuit diagram showing a configuration example of the first peak hold circuit. FIG. 3B is a circuit diagram showing a configuration of a modified example of the first peak hold circuit. FIG. 4 is a diagram for explaining the operation of the first comparison unit and the second comparison unit. FIG. 5 is a block diagram showing a function of an arithmetic processing unit included in the plasma processing apparatus according to the embodiment of the present invention. FIG. 6 is a flowchart showing an example of a flow of abnormality detection by the arithmetic processing unit included in the plasma processing apparatus according to the embodiment of the present invention. FIG. 7 is a diagram showing an example of a state in which discharge is normally performed in a predetermined period. FIG. 8 is a diagram showing an example of a state in which an abnormality has occurred in the discharge during a predetermined period. FIG. 9 is a diagram for explaining an example of measures for identifying the cause of an abnormality when an abnormality is detected by the arithmetic processing unit.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings. In the present specification, in the description of the plasma processing apparatus 100, the vertical direction is defined with the side on which the object to be processed 2 is arranged facing up with respect to the stage S. Further, the direction parallel to the plane orthogonal to the vertical direction is defined as the horizontal direction. These directions are names used to explain the shape and positional relationship of each part, and do not mean to limit the actual positional relationship and direction.

<1. Overview of plasma processing equipment>
FIG. 1 is a diagram showing a schematic configuration of a plasma processing apparatus 100 according to an embodiment of the present invention. As shown in FIG. 1, the plasma processing apparatus 100 generates plasma P between the first electrode portion 1 and the second electrode portion 2 to perform plasma processing. The plasma treatment includes, for example, a surface modification treatment, a thin film formation treatment, an ashing treatment, a cleaning treatment, and the like.

In the present embodiment, the second electrode portion 2 is composed of an object to be treated by plasma treatment. That is, the plasma processing device 100 is a so-called direct type plasma processing device. Hereinafter, the object to be processed that constitutes the second electrode portion 2 may be referred to as the object to be processed 2. In the direct type plasma processing apparatus 100, since the distance between the location where the plasma P is generated and the object to be processed 2 can be shortened, the active species generated by the plasma P can be efficiently brought into contact with the object to be processed 2. Can be done. The object 2 to be treated has a conductive portion on the surface or inside. The object 2 to be processed may be, for example, a metal member, a member having a portion covered with a metal foil such as aluminum, a member having a metal vapor deposition surface, or the like. Further, the object 2 to be processed may be, for example, a conductive member having an insulating member having a thickness capable of discharging for plasma generation on its surface. The insulating member may be, for example, an insulating film formed by spray coating with ceramic powder or the like, a thin laminated resin, or the like. Further, the object 2 to be processed can take various shapes.

The present invention may be applied to other than the direct type plasma processing apparatus. The present invention may be applied to, for example, a remote type plasma processing apparatus that blows an active species generated by plasma generated between two electrode portions onto an object to be processed. In the case of such a configuration, the plasma processing apparatus includes a second electrode portion as a component of the apparatus.

Further, in the present embodiment, the plasma treatment is performed under atmospheric pressure. According to this, the work efficiency can be improved as compared with the case where the object to be processed is arranged in the closed container and the plasma treatment is performed under reduced pressure. Further, since a strong closed container that can withstand decompression is not required, plasma treatment can be performed at low cost. However, the present invention may be applied to a plasma processing apparatus that performs plasma processing under reduced pressure. Further, it is not necessary to maintain the environmental temperature and the environmental humidity during the treatment at a particularly high temperature or low temperature, or at a particularly high humidity or low humidity. However, the treatment environment may be maintained at a high temperature or a low temperature, or at a high humidity or a low humidity.

As shown in FIG. 1, the plasma processing device 100 includes a power supply unit 10, a detection unit DU, and an arithmetic processing unit 70. The plasma processing apparatus 100 also includes a stage S, a first electrode unit 1, and a voltage adjusting unit 90.

The stage S is provided for mounting the object 2 to be processed. The stage S is made of a conductive member such as metal and has a plate shape that spreads in the horizontal direction. The upper surface of the stage S faces the first electrode portion 1 in the vertical direction. The object 2 to be processed is placed on the upper surface of the stage S.

The first electrode portion 1 is arranged so as to face the object to be processed (second electrode portion) 2 placed on the stage S. Specifically, the first electrode portion 1 is arranged on the upper side of the object to be processed 2 placed on the stage S via the gap G. The first electrode portion 1 is a columnar shape extending vertically. In the present embodiment, the first electrode portion 1 is generally composed of a conductive member such as metal. The first electrode portion 1 includes a dielectric 1a that covers the lower surface of the conductive member. For this reason, the object 2 to be processed faces the dielectric 1a in the vertical direction via the gap G. The dielectric 1a is made of a ceramic material such as alumina, zirconia, or free-cutting ceramic.

The power supply unit 10 applies an AC voltage between the first electrode unit 1 and the second electrode unit 2. The power supply unit 10 is an AC high-voltage power supply. As a preferred embodiment, the power supply unit 10 applies a high voltage at a high frequency. The frequency of the voltage applied by the power supply unit 10 is, for example, 1 kHz to 100 kHz. The waveform of the voltage applied by the power supply unit 10 is preferably a pulse waveform. However, the waveform of the applied voltage may be another waveform such as a sine wave or a rectangular wave. The magnitude of the voltage applied by the power supply unit 10 is, for example, 5 kVpp to 20 kVpp.

The power supply unit 10 includes a first terminal 11 and a second terminal 12. The first terminal 11 is conducted to the first electrode portion 1 by the first line L1. The second terminal 12 is conducted to the second electrode portion 2 by the second line L2. In the present embodiment, the first terminal 11 is a voltage output terminal, and the second terminal 12 is a ground terminal.

The object 2 to be processed is placed on the stage S, and a high AC voltage is applied by the power supply unit 10. As a result, a dielectric barrier discharge is performed between the first electrode portion 1 and the second electrode portion (object to be processed) 2, and the processing gas supplied to the gap G is turned into plasma. The active species generated by the plasma P comes into contact with the surface of the object to be processed 2, and the surface of the object to be processed 2 is plasma-treated. Dielectric barrier discharge is a type of discharge for plasma generation.

The processing gas may be supplied to the gap G from the outside by a gas supply means (not shown). However, the gas supply means may not be arranged, and the processing gas may be a gas that is naturally supplied to the gap G. Further, the type of the processing gas may be appropriately selected according to the purpose of the processing, and is not particularly limited. For example, when removing a residue such as cutting oil adhering to the surface of a metal object 2 to be treated, the treatment gas may be a mixed gas in which oxygen or the like is added to nitrogen.

Further, when the arc discharge can be suppressed by controlling the voltage and waveform applied by the power supply unit 10, the first electrode unit 1 does not have to have the dielectric 1a. That is, the dielectric 1a of the first electrode portion 1 is not essential. The configuration of the first electrode portion 1 of the present embodiment is a configuration example when it is not desirable to generate an arc discharge.

The detection unit DU detects the discharge between the first electrode unit 1 and the second electrode unit 2. The detection unit DU includes a current measurement unit 20. The detection unit DU further includes a peak hold unit 30, a comparison unit 40, a voltage measurement unit 50, and a discrimination unit 60.

The current measuring unit 20 measures the discharge current generated by the discharge between the first electrode unit 1 and the second electrode unit 2. The current measuring unit 20 is arranged on the second line L2 as a preferable form. That is, the current measuring unit 20 detects the discharge current flowing through the second line L2 via the object 2 to be processed and the stage S by the dielectric barrier discharge. The current measuring unit 20 is configured by using a shunt resistor that converts a current into a voltage. That is, the discharge current is converted into a voltage and measured. The current measuring unit 20 may have another configuration, for example, a configuration that detects an induced voltage using an air core coil, a configuration that detects a magnetic field generated by a current, such as a Hall element, or the like. ..

Further, voltage limiting elements may be provided at both ends of the shunt resistor constituting the current measuring unit 20, and the expected discharge current may be limited to an appropriately large value or more. As a result, even if an excessive discharge current flows, it is possible to prevent the circuit that receives the signal from being damaged.

The peak hold unit 30 holds the peak current of the discharge current. The details of the peak hold unit 30 will be described later. A transmission line such as a coaxial cable is arranged between the current measuring unit 20 composed of the shunt resistor and the peak hold unit 30 or its preprocessing unit. The voltage signal, which is the result of measuring the discharge current with the shunt resistor, is transmitted to the peak hold unit 30 or its preprocessing unit by the transmission line.

The comparison unit 40 compares the hold value of the peak hold unit 30 with a predetermined threshold value. In the present embodiment, the predetermined threshold value is set to a value that makes it possible to determine whether or not a discharge has occurred between the first electrode portion 1 and the second electrode portion 2. The predetermined threshold value may be obtained by calculation from the circuit design, or may be determined experimentally, for example. When the hold value exceeds a predetermined threshold value, it can be determined that a discharge has occurred. That is, the detection unit DU detects the discharge based on the measurement result of the current measurement unit 20. According to this configuration, the discharge current generated when a discharge occurs between the first electrode portion 1 and the second electrode portion 2 is used, and the occurrence of the discharge can be accurately detected. The comparison unit 40 is, for example, a comparator. The predetermined threshold value can be set by the value of the reference voltage of the comparator. The comparison unit 40 outputs a signal to the arithmetic processing unit 70 according to the comparison result. That is, the detection unit DU detects the discharge based on the measurement result of the current measurement unit 20 and notifies the arithmetic processing unit 70. The details of the comparison unit 40 will be described later.

According to the detection unit DU of the present embodiment, since the peak hold unit 30 for holding the peak current of the discharge current is provided, it is possible to capture the current value of the current flowing in a short time such as nanoseconds. Then, it is possible to determine whether or not a discharge has occurred based on the supplemented current value.

The voltage measuring unit 50 measures the AC voltage. In the present embodiment, the voltage measuring unit 50 measures the voltage between the first terminal 11 and the second terminal 12. In other words, the voltage measuring unit 50 measures the applied voltage of the power supply unit 10. The voltage measuring unit 50 may be configured to measure the divided voltage of the applied voltage instead of the applied voltage of the power supply unit 10. That is, the AC voltage measured by the voltage measuring unit 50 may be either the applied voltage of the power supply unit 10 or the divided voltage of the applied voltage. However, since the applied voltage is a high voltage on the order of kVpp, it is preferable to have a configuration in which the divided voltage of the applied voltage is measured because subsequent signal processing can be easily performed.

The determination unit 60 determines whether the polarity of the AC voltage applied by the power supply unit 10 is positive or negative according to the measurement result of the voltage measurement unit 50. The determination unit 60 outputs a polarity signal according to the polarity determination result to the peak hold unit 30.

The plasma processing device 100 may include a voltage holding unit that holds a predetermined value of the AC voltage measured by the voltage measuring unit 50. According to this, when plasma processing is performed, predetermined voltage value information can be acquired in addition to the discharge current obtained by the peak hold unit 30, so that the processing quality and processing accuracy of plasma processing can be controlled. It can be made easier to do. Further, since not only the discharge current value but also the AC voltage value can be acquired by using the hold function, the arithmetic processing unit 70 can give a time allowance when acquiring these values. The voltage hold unit may be, for example, a sample hold unit that holds the AC voltage at the time of discharge. Further, the hold unit for voltage may be, for example, a peak hold unit that detects the peak value of the AC voltage.

The arithmetic processing unit 70 is, for example, a microcomputer, and controls the entire plasma processing apparatus 100 in an integrated manner. The arithmetic processing unit 70 includes a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM (Read Only Memory), and the like. Various functions of the arithmetic processing unit 70 are realized, for example, by the CPU performing arithmetic processing according to a computer program stored in the ROM.

In the present embodiment, the arithmetic processing unit 70 is provided so that the peak current can be acquired from the peak hold unit 30. Specifically, the arithmetic processing unit 70 performs an operation for acquiring a peak current from the peak hold unit 30 in response to a signal from the comparison unit 40. Details of this point will be described later. Further, in the present embodiment, the arithmetic processing unit 70 performs a process for detecting an abnormality of the own device 100. The details of this point will also be described later.

The voltage adjusting unit 90 adjusts the voltage input from an external power source (for example, 100V AC power source) (not shown). Specifically, the voltage adjusting unit 90 is based on a command of the arithmetic processing unit 70 in order to cause the power supply unit 10 to adjust the voltage of the high voltage output applied between the first terminal 11 and the second terminal 12. Adjust the supply voltage to the power supply unit 10.

<2. Details of peak hold section and comparison section>
FIG. 2 is a diagram illustrating a time change between the voltage V measured by the voltage measuring unit 50 and the current I measured by the current measuring unit 20 in the plasma processing apparatus 100 according to the embodiment of the present invention.

As shown in FIG. 2, in the plasma processing device 100, since the AC voltage is applied by the power supply unit 10, the waveform of the voltage measured by the voltage measuring unit 50 includes a voltage having a positive polarity and a voltage having a negative polarity. Becomes a waveform that changes every half cycle. A pulsed discharge current is generated immediately after the polarity of the voltage V is switched. For example, in region A of FIG. 2, a pulsed discharge current is generated. Since the discharge current is pulsed and the pulse width is as short as nanoseconds to several hundred nanoseconds, it is difficult to capture the current value of the discharge current. In consideration of this point, in the present embodiment, the peak hold unit 30 for holding the peak value of the measurement signal input from the current measurement unit 20 is provided.

FIG. 3 is a diagram showing a configuration of a peak hold unit 30 and a comparison unit 40 included in the plasma processing apparatus 100 according to the embodiment of the present invention. As shown in FIG. 3, the peak hold unit 30 includes a first peak hold circuit 31 and a second peak hold circuit 32. In other words, the detection unit DU includes a first peak hold circuit 31 and a second peak hold circuit 32.

The first peak hold circuit 31 holds the peak current on the positive side of the discharge current when the polarity of the AC voltage applied by the power supply unit 10 is positive. Here, the peak current on the positive side refers to the current value at which the absolute value becomes maximum in the positive direction. Whether the polarity of the AC voltage is positive or negative can be determined by the polarity signals PS (+) and PS (−) input from the discriminating unit 60.

Specifically, the first peak hold circuit 31 keeps updating the hold value every time the value measured by the current measuring unit 20 exceeds the previously held value during the first predetermined period. In the present embodiment, the first predetermined period is from the time when the polarity of the applied voltage of the power supply unit 10 is switched to positive to the time when the polarity is switched to negative. That is, the first predetermined period corresponds to a half cycle in which the polarity of the AC voltage applied by the power supply unit 10 is positive. The first predetermined period is not limited to this, and may be, for example, a period shorter than a half cycle.

FIG. 3A is a circuit diagram showing a configuration example of the first peak hold circuit 31. As shown in FIG. 3A, the first peak hold circuit 31 may have a known configuration including an operational amplifier OP, a diode D, a capacitor C, and a voltage follower VoF. The capacitor (hold capacitor) C constituting the first peak hold circuit 31 is calculated from the capacity of the operational amplifier OP or the like for charging the capacitor C, and is 1/2 or less of the pulse width of the discharge current, more preferably discharge. It is preferable that the capacitance can be charged with 1/10 or less of the pulse width of the current. As a result, peak hold charging can be performed without delay for a pulsed discharge current signal having a narrow width, and the detection accuracy of the current value of the discharge current can be improved. FIG. 3B is a circuit diagram showing a configuration of a modified example of the first peak hold circuit 31. As shown in FIG. 3B, the first peak hold circuit 31 may have a configuration in which the diode D and the capacitor C are arranged outside the feedback loop of the operational amplifier OP. Then, in the first peak hold circuit 31, there is a dead band near the zero volt of the input, in other words, in the characteristics between the input and output, the output voltage becomes almost zero when the input signal is equal to or less than the forward voltage drop voltage VF of the diode D. It may be configured to perform signal processing in the subsequent stage as having (having a section for VF of the diode D). As a result, when a high-speed operational amplifier OP is used, the possibility of oscillation of the operational amplifier OP can be suppressed, and peak hold can be stably performed. Further, for example, the accuracy of peak hold can be improved by compensating for the loss of the capacitor charge charge due to the recovery current and the junction capacitance of the diode D constituting the first peak hold circuit 31.

The first peak hold circuit 31 includes a first reset unit 31a that resets the hold value when the polarity of the AC voltage is negative. When the applied voltage of the power supply unit 10 has a negative polarity, the first peak hold circuit 31 does not exhibit the peak hold function due to the action of the first reset unit 31a. In the present embodiment, the first reset unit 31a is a switch device that short-circuits the hold capacitor C when the polarity is negative, in other words, resets the first peak hold circuit 31. As shown in FIG. 3A, one end of the switch device SW constituting the first reset unit 31a is connected to the ground. The other end of the switch device SW is connected to the other end of the hold capacitor C whose one end is connected to the ground. The switch device SW can be turned on by the control signal line (more specifically, the polarity signal PS (+) described above) shown by the arrow in FIG. 3A, and the capacitor C can be short-circuited to make the voltage zero. it can. The coupling capacitance between the switch device SW and the control signal line is preferably smaller than the capacitance of the hold capacitor C, and is preferably 1/10 or less of the capacitance of the hold capacitor C, for example. This makes it possible to reduce charge injection and loss during switch on / off operation. The switch device SW may be a semiconductor device, for example, ICs called transistors or analog switches.

The second peak hold circuit 32 holds the peak current on the negative side of the discharge current when the polarity of the AC voltage applied by the power supply unit 10 is negative. Here, the peak current on the minus side refers to the current value at which the absolute value becomes maximum in the minus direction. In the second peak hold circuit 32 as well, as in the first peak hold circuit 31, whether the polarity of the AC voltage is positive or negative is determined by the polarity signal PS (−) input from the discriminating unit 60. be able to.

Specifically, in the second peak hold circuit 32, the plus and minus signs of the measurement signal of the current measuring unit 20 are inverted. The second peak hold circuit 32 keeps updating the hold value every time the inverted value of the sign of the value measured by the current measuring unit 20 exceeds the previously held value during the second predetermined period. In the present embodiment, the second predetermined period is from the time when the polarity of the applied voltage of the power supply unit 10 is switched to minus to the time when the polarity is switched to plus. That is, the second predetermined period corresponds to a half cycle in which the polarity of the AC voltage applied by the power supply unit 10 is negative. The second predetermined period is not limited to this, and may be, for example, a period shorter than a half cycle.

In the present embodiment, the second peak hold circuit 32 also includes the operational amplifier OP, the diode D, and the capacitor C, similarly to the first peak hold circuit 31. Further, the same signal may be used as the polarity signal PS (+) and the polarity signal PS (−), and the first and second predetermined periods may be determined by the level of the same signal.

The second peak hold circuit 32 includes a second reset unit 32a that resets the hold value when the polarity of the AC voltage is positive. When the voltage applied to the power supply unit 10 is positive, the second peak hold circuit 32 does not exhibit the peak hold function due to the action of the second reset unit 32a. In the present embodiment, the second reset unit 32a is a switch device that short-circuits the hold capacitor C and resets the second peak hold circuit 32 when the polarity is positive. The configuration of the switch device SW is the same as that of the first peak hold circuit 31, and the coupling capacitance between the switch device and the control signal line is smaller than that of the hold capacitor, as in the case of the first peak hold circuit 31. Is preferable.

In the present embodiment, the peak hold portion 30 is configured to include a first peak hold circuit 31 for plus and a second peak hold circuit 32 for minus, and has a polarity that matches the polarity of the applied AC voltage. Peak current can be obtained. Therefore, according to this configuration, even when the discharge current is likely to generate vibration due to the inductance or capacitance component in the discharge path, it is possible to prevent the reverse polarity component generated by the vibration from being mistakenly recognized as the discharge current. ..

Further, in the present embodiment, the first peak hold circuit 31 is provided with the first reset unit 31a, and the second peak hold circuit 32 is provided with the second reset unit 32a. Therefore, it is possible to acquire only the peak current having a polarity that matches the polarity of the applied AC voltage. That is, according to this configuration, it is possible to prevent erroneous capture of a current peak having a reverse polarity that should not occur originally due to vibration in the circuit or the like. Further, according to this configuration, the peak hold value of the opposite polarity (plus in this example) is reset every time the polarity of the applied AC voltage changes (for example, from plus to minus). Therefore, every time the polarity of the applied AC voltage changes to the original polarity (plus in this example), a new peak hold value can be acquired regardless of the previous peak hold value of the same polarity. it can. That is, when the polarity of the applied AC voltage changes, the peak value of the discharge current for each discharge after the change, in other words, the state of plasma processing can be confirmed.

As shown in FIG. 3, the comparison unit 40 includes a first comparison unit 41 and a second comparison unit 42. In other words, the detection unit DU includes a first comparison unit 41 and a second comparison unit 42. In the present embodiment, both the first comparison unit 41 and the second comparison unit 42 are comparators.

The first comparison unit 41 compares the peak hold value of the first peak hold circuit 31 with the first current threshold value. The first current threshold value is an example of the above-mentioned predetermined threshold value, and is determined so as to enable discharge determination. The comparator constituting the first comparison unit 41 is not required to have high speed because the comparison target is the peak hold value. The first comparison unit 41 inputs the first flag signal FS1 to the arithmetic processing unit 70 when the hold value of the first peak hold circuit 31 exceeds the first current threshold value. The first flag signal FS1 is an example of the first signal of the present invention. Specifically, the first comparison unit 41 detects the discharge when the hold value of the first peak hold circuit 31 exceeds the first current threshold value, and inputs the first flag signal FS1 to the arithmetic processing unit 70.

The second comparison unit 42 compares the peak hold value of the second peak hold circuit 32 with the second current threshold value. The second current threshold value is an example of the above-mentioned predetermined threshold value, and is determined so as to enable discharge determination. The comparator constituting the second comparison unit 42 is not required to have high speed because the comparison target is the peak hold value. The second comparison unit 42 inputs the second flag signal FS2 to the arithmetic processing unit 70 when the hold value of the second peak hold circuit 32 exceeds the second current threshold value. The second flag signal FS2 is an example of the second signal of the present invention. Specifically, the second comparison unit 42 detects the discharge when the hold value of the second peak hold circuit 32 exceeds the second current threshold value, and inputs the second flag signal FS2 to the arithmetic processing unit 70. In the present embodiment, the second current threshold value is the same as the first current threshold value. However, the first current threshold value and the second current threshold value may be different values.

FIG. 4 is a diagram for explaining the operation of the first comparison unit 41 and the second comparison unit 42. FIG. 4A shows the waveform of the AC voltage applied by the power supply unit 10 (for convenience of explanation, it is shown as a sinusoidal signal different from that shown in FIG. 2). FIG. 4B shows a waveform of a discharge current generated when the AC voltage shown in FIG. 4A is applied. FIG. 4C shows a positive peak hold waveform obtained by the first peak hold circuit 31 when the discharge current shown in FIG. 4B is generated. FIG. 4D shows a negative peak hold waveform obtained by the second peak hold circuit 32 when the discharge current shown in FIG. 4B is generated. In FIGS. 4A to 4D, the horizontal axis is time. The alternate long and short dash line shown in FIG. 4 (c) is the first current threshold value TH1. The alternate long and short dash line shown in FIG. 4D is the second current threshold value TH2. The first threshold value TH1 and the second threshold value TH2 may be defined by circuit constants or may be variably set by the arithmetic processing unit 70 or the like.

During the period T1 in which the AC voltage having a positive polarity is applied by the power supply unit 10, the first comparison unit 41 performs the peak hold of the first peak hold circuit 31 when the time t1 has passed due to the generation of the discharge current. It is detected that the value exceeds the first current threshold value TH1. As a result, the first comparison unit 41 inputs the first flag signal FS1 to the arithmetic processing unit 70. Since the second peak hold circuit 32 is in the reset state during the period T1, the second comparison unit 42 does not detect a peak hold value that exceeds the second current threshold value TH2.

Further, in the period T2 in which the AC voltage having a negative polarity is applied by the power supply unit 10, the second comparison unit 42 of the second peak hold circuit 32 when the time t2 has passed due to the generation of the discharge current. It is detected that the peak hold value exceeds the second current threshold value TH2. As a result, the second comparison unit 42 inputs the second flag signal FS2 to the arithmetic processing unit 70. Since the first peak hold circuit 31 is in the reset state during the period T2, the first comparison unit 41 does not detect a peak hold value that exceeds the first current threshold value TH1.

In the present embodiment, the first peak hold circuit 31 for the plus side and the second peak hold circuit 32 for the minus side can be divided, and it can be determined whether or not a discharge has occurred in each of them. Therefore, the plasma processing in the plasma processing apparatus 100 can be precisely analyzed.

When the first flag signal FS1 is input from the first comparison unit 41, the arithmetic processing unit 70 acquires the peak current from the first peak hold circuit 31 via the signal line SL1. The arithmetic processing unit 70 generates an interrupt by inputting the first flag signal FS1, performs A / D conversion of the peak hold value of the first peak hold circuit 31 as the interrupt processing, and peaks of the first peak hold circuit 31. Get the current. The peak current may match the peak hold value when the start of discharge is detected, but may not match the peak hold value (for example, when a larger peak current is detected). However, in view of the purpose of capturing the peak (maximum) current value at each discharge, there is no particular problem in such a case. Further, the arithmetic processing unit 70 acquires the peak current from the second peak hold circuit 32 via the signal line SL2 when the second flag signal FS2 is input from the second comparison unit 42. The arithmetic processing unit 70 generates an interrupt by inputting the second flag signal FS2, performs A / D conversion of the peak hold value of the second peak hold circuit 32 as the interrupt processing, and peaks of the second peak hold circuit 32. Get the current. That is, the arithmetic processing unit 70 acquires a peak current having a polarity that matches the polarity of the applied AC voltage.

In the present embodiment, the arithmetic processing unit 70 detects the occurrence of discharge when the flag signals FS1 and FS2 are input, and collects the peak hold value of the peak hold unit 30 in response to the detection. The arithmetic processing unit 70 does not need to monitor the presence or absence of discharge in order to collect data on the discharge current, and can process another task until the flag signals FS1 and FS2 are input. Therefore, according to the present embodiment, the processing capacity of the arithmetic processing unit 70 can be effectively utilized. In addition, it is possible to suppress applying a large load to the arithmetic processing unit 70. The arithmetic processing unit 70 can perform, for example, quantitative analysis of the discharge state based on the collected data on the discharge current.

<3. Details of arithmetic processing unit>
The arithmetic processing unit 70 obtains the number of times of discharge generation per predetermined period for each polarity of the AC voltage and detects an abnormality during plasma processing. According to this, it is possible to make a finer judgment regarding the abnormality as compared with the case where the number of discharges per predetermined period is simply measured and the processing abnormality is detected without dividing by polarity. According to this configuration, since the number of discharges per predetermined period is obtained for each polarity of the AC voltage applied by the power supply unit 10, it is possible to easily identify the cause of the abnormality generated during the plasma processing. The predetermined period may be appropriately determined, but may be, for example, 1 millisecond or the like.

The arithmetic processing unit 70 that exerts the above-described effects will be described in detail. FIG. 5 is a block diagram showing a function of the arithmetic processing unit 70 included in the plasma processing apparatus 100 according to the embodiment of the present invention. The arithmetic processing unit 70 includes a first measurement unit 71, a second measurement unit 72, and a determination unit 73.

The first measurement unit 71, the second measurement unit 72, and the determination unit 73 are functions realized by the CPU executing a computer program stored in a ROM or the like included in the arithmetic processing unit 70. Further, each of the functional units 71 to 73 included in the arithmetic processing unit 70 is a conceptual component. The functions executed by one component may be distributed to a plurality of components, or the functions of the plurality of components may be integrated into one component.

The first measuring unit 71 measures the first number of times of discharge, which is the number of times of discharge when the polarity of the AC voltage applied by the power supply unit 10 is positive. In the present embodiment, the first measurement unit 71 recognizes that when the first flag signal FS1 is input from the first comparison unit 41, there is a discharge when the polarity of the applied voltage is positive. That is, the first measurement unit 71 may count the number of inputs of the first flag signal FS1 in order to measure the first number of occurrences. However, the first measurement unit 71 may be configured to count the number of current values acquired from the first peak hold circuit 31 for measuring the number of first occurrences, for example.

The second measuring unit 72 measures the second number of times of discharge, which is the number of times of discharge when the polarity of the AC voltage applied by the power supply unit 10 is negative. In the present embodiment, the second measurement unit 72 recognizes that when the second flag signal FS2 is input from the second comparison unit 42, there is a discharge when the polarity of the applied voltage is negative. That is, the second measurement unit 72 may count the number of inputs of the second flag signal FS2 in order to measure the number of second occurrences. The second measurement unit 72 may be configured to count the number of current values acquired from the second peak hold circuit 32 for measuring the number of second occurrences, for example.

The determination unit 73 determines the presence or absence of an abnormality during plasma processing based on the first occurrence number and the second occurrence number. According to this configuration, the number of discharges generated per predetermined period is measured separately for each polarity of the AC voltage applied by the power supply unit 10, and the abnormality that occurs during plasma processing is based on the measurement result of the number of times the discharges are generated. Can be detected. Since the number of discharges generated per predetermined period can be counted for each polarity, the presence or absence of an abnormality can be accurately determined and the abnormality can be detected accurately. The details of the determination process of the determination unit 73 will be described later.

FIG. 6 is a flowchart showing an example of a flow of abnormality detection by the arithmetic processing unit 70 included in the plasma processing apparatus according to the embodiment of the present invention.

In step S1, the first measurement unit 71 and the second measurement unit 72 start measuring the number of times of discharge. The measurement of the number of times of discharge occurs is started, for example, when the application of the AC voltage by the power supply unit 10 is started. When the measurement of the number of discharge occurrences is started, the first measurement unit 71 detects the occurrence of discharge when the polarity of the applied voltage of the power supply unit 10 is positive, and the number of first occurrences for each detection. Add 1 to. Further, the second measurement unit 72 detects the occurrence of discharge when the polarity of the applied voltage of the power supply unit 10 is negative, and adds 1 to the number of second occurrences for each detection. The number of first occurrences and the second number of occurrences are set to 0 at the start of measurement of the number of discharge occurrences. In the first measurement unit 71 and the second measurement unit 72, the discharge is detected, for example, by inputting the flag signals FS1 and FS2 to the arithmetic processing unit 70.

When the measurement of the number of times of discharge occurs is started, the process of step S2 is performed at predetermined time intervals. The predetermined time interval is set shorter than the predetermined period in step S2 described below. The predetermined time interval may be, for example, about the same as the time interval at which the discharge occurs.

In step S2, the first measurement unit 71 and the second measurement unit 72 confirm whether or not a predetermined period has elapsed since the measurement of the number of times of discharge was started. The predetermined period is determined, for example, by experiment or simulation, and is set to, for example, 1 millisecond. If the predetermined period has not elapsed (No in step S2), the process proceeds to the next step S3. When the predetermined period has elapsed (Yes in step S2), the measurement of the number of times of discharge occurrence by the first measurement unit 71 and the second measurement unit 72 is completed, and the process proceeds to step S4.

In step S3, the first measurement unit 71 and the second measurement unit 72 continue to measure the number of discharges generated. The first measurement unit 71 and the second measurement unit 72 detect the occurrence of the corresponding discharge and appropriately perform the addition processing of the number of times of the corresponding discharge occurrence. Also in the process of step S3, the process is returned to step S2 according to the predetermined time interval described in step S1.

In step S4, the determination unit 73 confirms whether or not the number of first occurrences per predetermined period measured by the first measurement unit 71 is equal to or greater than the predetermined number of times threshold value. The number-of-times threshold value is a determination value for determining whether or not an abnormality has occurred, and is determined by an experiment or the like. When the number of first occurrences per predetermined period is equal to or greater than the predetermined number of times threshold value (Yes in step S4), the determination unit 73 proceeds to step S5. When the number of first occurrences per predetermined period is smaller than the predetermined number of times threshold value (No in step S4), the determination unit 73 determines that an abnormality has occurred in the discharge on the plus side, and proceeds to step S7.

In step S5, the determination unit 73 confirms whether or not the number of second occurrences per predetermined period measured by the second measurement unit 72 is equal to or greater than the predetermined number of times threshold value. The number-of-times threshold is the same as the number-of-times threshold in step S4. However, the number of times threshold value may be different between step S4 and step S5. When the number of second occurrences per predetermined period is equal to or greater than the predetermined number of times threshold value (Yes in step S5), the determination unit 73 proceeds to step S6. When the number of second occurrences per predetermined period is smaller than the predetermined number of times threshold value (No in step S5), the determination unit 73 determines that an abnormality has occurred in the discharge on the minus side, and proceeds to step S7.

In step S6, the determination unit 73 determines the difference value between the first occurrence number per predetermined period measured by the first measurement unit 71 and the second occurrence number per predetermined period measured by the second measurement unit 72. Check if the absolute value is smaller than the predetermined difference threshold. The difference threshold value is a determination value for determining whether or not an abnormality has occurred, and is determined by an experiment or the like. When the absolute value of the difference value between the first occurrence number and the second occurrence number is smaller than the predetermined difference threshold value (Yes in step S6), the determination unit 73 determines that no abnormality has occurred during the plasma processing, and temporarily processes the difference value. To finish. The abnormality detection process described above may be repeated at a predetermined cycle. When the absolute value of the difference value between the first occurrence number and the second occurrence number is equal to or more than a predetermined difference threshold value (No in step S6), the determination unit 73 determines that an abnormality has occurred during plasma processing and steps S7. Proceed to processing.

In step S7, the determination unit 73 performs error processing. The error processing may include, for example, a processing for safely terminating the running plasma processing. Further, the error processing may include a processing for notifying an operator or the like that an abnormality has occurred during the plasma processing. The processing for the notification may include, for example, a processing for outputting an alarm sound, a processing for displaying that an abnormality has occurred on the monitor, a processing for emitting a warning light, and the like.

The order of the three determination processes of step S4, step S5, and step S6 in FIG. 6 may be changed. For example, the determination process for the second occurrence number may be performed before the determination process for the first occurrence number. Further, the process of step S6 may be omitted. Further, the processing of step S4 and step S5 may be omitted, and only the determination processing of step S6 may be performed.

As described above, in the present embodiment, the determination unit 73 determines whether or not there is an abnormality by comparing the first occurrence number of times with the predetermined number of times threshold value, and compares the second occurrence number of times with the predetermined number of times threshold value. It is possible to determine the presence or absence. According to this configuration, it is possible to distinguish between an abnormality that occurs when the polarity of the AC voltage applied by the power supply unit 10 is positive and an abnormality that occurs when the polarity is negative.

Further, in the present embodiment, the determination unit 73 is provided so that the presence or absence of an abnormality can be determined by comparing the first occurrence number and the second occurrence number. According to this configuration, when an abnormality occurs in which the polarity of the AC voltage applied by the power supply unit 10 is biased to either positive or negative, the discharge occurs. Can be detected.

In the present embodiment, the difference value between the first occurrence number and the second occurrence number is calculated to determine the presence or absence of an abnormality, but a configuration different from this may be used. For example, the ratio of the first occurrence number to the second occurrence number may be calculated, and the calculated ratio may be compared with the comparison value prepared in advance to determine the presence or absence of an abnormality.

FIG. 7 is a diagram showing an example of a state in which discharge is normally performed in a predetermined period. FIG. 7A shows a positive peak hold waveform obtained by the first peak hold circuit 31. FIG. 7B shows a peak hold waveform on the minus side obtained by the second peak hold circuit 32. In FIG. 7, the horizontal axis is time. When the discharge is performed normally, rectangular waves are alternately obtained on the plus side and the minus side. The number of rectangular waves per predetermined period is the same on the plus side and the minus side. In this case, no abnormality is found in any of the three determination processes of step S4, step S5, and step S6 in FIG.

FIG. 8 is a diagram showing an example of a state in which an abnormality has occurred in the discharge during a predetermined period. FIG. 8A shows a peak hold waveform on the plus side obtained by the first peak hold circuit 31. FIG. 8B shows a peak hold waveform on the minus side obtained by the second peak hold circuit 32. In FIG. 8, the horizontal axis is time. In FIG. 8, an abnormality is observed in the peak hold waveform on the minus side. The broken line in FIG. 8 indicates a state in which the rectangular wave that should be originally obtained is not obtained.

Here, consider a case where the presence or absence of an abnormality is determined by the total number of discharge occurrences without dividing the polarity. It is assumed that an abnormality is detected when the total number of discharges is less than 85% of the normal time. In the example shown in FIG. 8, the total number of times of discharge in the normal state is 16 times. Therefore, when the total number of discharges is less than 14, an abnormality is detected. In the example shown in FIG. 8, the total number of times of discharge is 14, and even though an abnormality has occurred, no abnormality is detected.

On the other hand, in the present embodiment, the presence or absence of an abnormality is determined by the number of times of discharge for each polarity. It is assumed that an abnormality is detected when the number of discharges generated in each polarity is less than 85% of the normal state. In the example shown in FIG. 8, the number of times of normal discharge is 8 times at each polarity. Therefore, in each polarity, an abnormality is detected when the number of discharges is less than 7. In the example shown in FIG. 8, the number of times of discharge is 6 times on the minus side, and an abnormality that cannot be detected by the total number of times of discharge is detected. According to the flowchart shown in FIG. 6, an abnormality is detected in step S5.

In the normal case, there is no difference in the number of discharges between the plus side and the minus side. Therefore, in the example shown in FIG. 8, if step S6 is performed prior to steps S4 and S5 in FIG. , It is possible to quickly detect that an abnormality has occurred. When an abnormality is detected, the numerical values of the first occurrence number and the second occurrence number may be analyzed in detail.

FIG. 9 is a diagram for explaining an example of measures for identifying the cause of the abnormality when the arithmetic processing unit 70 detects the abnormality. Instead of the power supply unit 10, a pulse generator 110 capable of freely generating a pulse is connected to the detection unit DU. For example, when there is an abnormality in the detection unit DU such as an abnormality in the peak hold unit 30 or the comparison unit 40, the processing result of the arithmetic processing unit 70 is used by inputting a dummy signal using the pulse generator 110. The abnormality can be detected and the cause of the abnormality can be clarified. On the other hand, if no abnormality is detected by inputting a dummy signal by the pulse generator 110, deterioration of the electrode portion 1 can be suspected, for example. Further, for example, it is possible to suspect that the plasma processing may have a problem.

<4. Notes>
The various technical features disclosed herein can be modified in various ways without departing from the gist of the technical creation. In addition, a plurality of embodiments and modifications shown in the present specification may be combined and implemented to the extent possible.

The present invention can be used in an apparatus for performing plasma processing of a work.

1 ... 1st electrode unit 2 ... 2nd electrode unit 10 ... Power supply unit 20 ... Current measurement unit 31 ... 1st peak hold circuit 32 ... 2nd peak hold circuit 41 ...・ 1st comparison unit 42 ・ ・ ・ 2nd comparison unit 70 ・ ・ ・ Arithmetic processing unit 71 ・ ・ ・ 1st measurement unit 72 ・ ・ ・ 2nd measurement unit 73 ・ ・ ・ Judgment unit 100 ・ ・ ・ Plasma processing device DU ···Detection unit

Claims (6)

A plasma processing apparatus that generates plasma between the first electrode portion and the second electrode portion to perform plasma processing.
A power supply unit that applies an AC voltage between the first electrode unit and the second electrode unit,
A detection unit that detects a discharge between the first electrode unit and the second electrode unit,
An arithmetic processing unit that obtains the number of times the discharge occurs per predetermined period for each polarity of the AC voltage and detects an abnormality during the plasma processing, and an arithmetic processing unit.
A plasma processing device. The arithmetic processing unit
A first measuring unit that measures the first number of occurrences of the discharge when the polarity of the AC voltage is positive, and
A second measuring unit that measures the second number of occurrences of the discharge when the polarity of the AC voltage is negative, and
A determination unit that determines the presence or absence of the abnormality based on the first occurrence number and the second occurrence number.
The plasma processing apparatus according to claim 1. The determination unit determines the presence or absence of the abnormality by comparing the first occurrence number and the predetermined number of times threshold value, and determines the presence or absence of the abnormality by comparing the second occurrence number of times with the predetermined number of times threshold value. The plasma processing apparatus according to claim 2, which is provided as possible. The plasma processing apparatus according to claim 2 or 3, wherein the determination unit is provided so that the presence or absence of the abnormality can be determined by comparing the first occurrence number and the second occurrence number. The detection unit includes a current measurement unit that measures the discharge current generated by the discharge.
The plasma processing apparatus according to any one of claims 1 to 4, wherein the detection unit detects the discharge based on the measurement result of the current measurement unit. The detection unit
A first peak hold circuit that holds the peak current on the positive side of the discharge current when the polarity of the AC voltage is positive, and
A second peak hold circuit that holds the peak current on the negative side of the discharge current when the polarity of the AC voltage is negative, and
A first comparison unit that inputs a first signal to the arithmetic processing unit when the hold value of the first peak hold circuit exceeds the first current threshold value.
A second comparison unit that inputs a second signal to the arithmetic processing unit when the hold value of the second peak hold circuit exceeds the second current threshold value.
The plasma processing apparatus according to claim 5.

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