JP6582292B2 - Discharge analysis method and discharge analysis apparatus - Google Patents

Description

  The present invention relates to a discharge analysis method and a discharge analysis apparatus, and more particularly to a method and apparatus for distinguishing various discharge phenomena that occur in a plasma atmosphere. The present invention also relates to a plasma processing apparatus, and in particular, damage to an object to be processed due to abnormal discharge generated in a plasma chamber, damage to a chamber internal structure, damage to a power circuit for plasma excitation, and a circuit for controlling the plasma processing apparatus. The present invention relates to a plasma processing apparatus that can prevent electromagnetic interference of peripheral devices and electromagnetic interference of peripheral devices.

  In a semiconductor device manufacturing process, many plasma processing apparatuses such as a plasma CVD apparatus and a plasma etching apparatus are used. In these plasma processing apparatuses, electrodes are arranged in a plasma chamber, and plasma can be excited by applying an AC voltage and / or a DC voltage to the electrodes. In the plasma excited state, the constituent atoms or constituent molecules of the process gas in the plasma chamber are activated by ionization collision with the electrons accelerated by the applied voltage to become radicals. It becomes possible to cause a reaction at a low temperature.

  However, in the plasma CVD apparatus and the plasma etching apparatus, abnormal discharge may occur in the plasma chamber, which may cause a failure such as damage to a part of the semiconductor wafer. Such abnormal discharge may occur not only in the plasma CVD apparatus and the plasma etching apparatus but also in other plasma processing apparatuses such as an ion milling apparatus, an ion implantation apparatus, and a sputtering apparatus. In order to solve such a problem, the present inventor has proposed a technique for detecting abnormal discharge using electromagnetic waves generated along with abnormal discharge (see Patent Documents 1 and 2).

  According to this method, since abnormal discharge can be detected more reliably, it is expected to improve the yield of various devices such as semiconductor devices produced using a plasma processing apparatus.

Japanese Patent No. 3631212 Japanese Patent No. 5159055

  There are various types of abnormal discharges that occur in the plasma chamber, and among these, the one that damages the workpiece is mainly arc discharge. However, since the arc discharge that damages the workpiece and the corona discharge that hardly damages the workpiece have almost the same frequency of the radiated electromagnetic wave, it is difficult to distinguish the two.

  Accordingly, an object of the present invention is to provide a discharge analysis method, a discharge analysis apparatus, and a plasma processing apparatus that can correctly determine the occurrence of arc discharge.

  Further, the present inventor has studied a method of detecting a discharge phenomenon that is a sign of arc discharge and stopping application of an AC voltage or a DC voltage to the plasma chamber when a discharge phenomenon that is a sign is generated. In this case, since the discharge phenomenon as a precursor emits an electromagnetic wave of about 1 to 3 GHz, it is considered preferable to perform observation using a loop antenna that can accurately observe the electromagnetic wave in this frequency band.

  However, the arc discharge discharges an electromagnetic wave of about 0.1 to 300 MHz while the discharge phenomenon that becomes a sign emits an electromagnetic wave of about 1 to 3 GHz. Therefore, when the loop antenna is used, the discharge phenomenon becomes a sign. As a trigger, there is no difference in the subsequent observation results between when the application of AC voltage or DC voltage is stopped and when it is not stopped. That is, it is not possible to verify whether arc discharge has occurred. For this reason, it was difficult to verify whether it was necessary to stop the AC voltage, and it was difficult to feed back observation results.

  Accordingly, another object of the present invention is to provide a discharge analysis method, a discharge analysis apparatus, and a plasma processing apparatus capable of correctly observing both a discharge phenomenon as a precursor and an arc discharge.

  As a result of research over many years, the present inventor has found that there is a certain rule in the order of occurrence of abnormal discharge in the plasma atmosphere. Specifically, it was found that the discharge occurs in the order of corona discharge, Townsend spark, and arc discharge. Further, it has also been found that the townsend discharge is accompanied by a discharge having a frequency component equivalent to that of the townsend discharge, which is called “Pre-Spark”, and lasting for about 5 μs to 1 ms. The present invention has been made based on such findings.

  The discharge analysis method according to the present invention detects a townsend discharge generated in plasma and a first discharge having a frequency of radiated electromagnetic wave lower than that of the townsend discharge, and the first discharge is generated following the townsend discharge. In this case, it is determined that the first discharge is an arc discharge.

  According to the present invention, since townsend discharge is detected as a sign of arc discharge, it is possible to accurately predict the occurrence of arc discharge that damages the workpiece. In addition, although arc discharge may be accompanied by glow discharge immediately before that, distinction of both is not important in the present invention. Therefore, even if a glow discharge is interposed between the townsend discharge and the arc discharge, it may be considered that arc discharge has occurred following the townsend discharge.

  A discharge analyzer according to the present invention includes a magnetic field probe for detecting a discharge generated in a plasma chamber, and the output signal of the magnetic field probe indicates the occurrence of a townsend discharge, and then the frequency of a radiated electromagnetic wave is lower than that of the townsend discharge. And a detection device that determines that the first discharge is an arc discharge when the occurrence of the first discharge is indicated.

  According to the present invention, since the Townsend discharge is detected using the magnetic field probe having a wide frequency band characteristic, it is possible to correctly observe both the Townsend discharge and the arc discharge having a frequency lower than that.

  The plasma processing apparatus according to the present invention includes a plasma chamber, a power supply device that supplies an AC voltage or a DC voltage for exciting the plasma to the plasma chamber, a magnetic field probe that detects a discharge generated in the plasma chamber, and the magnetic field probe. And a control device for controlling the power supply device, the frequency of the output signal is 1 to 3 GHz, and the detection device detects that this has continued for 5 μs or more. In response, the control device stops the power supply device or reduces the AC voltage or DC voltage.

  According to the present invention, since the application of AC voltage or DC voltage for plasma excitation is stopped or reduced in response to detection of a discharge phenomenon that is a sign of arc discharge, damage to the workpiece due to arc discharge is prevented. This can be prevented beforehand.

  As described above, according to the present invention, it is possible to correctly determine the occurrence of arc discharge, and to correctly observe both a discharge phenomenon and arc discharge as a sign.

FIG. 1 is a schematic view schematically showing a configuration of a plasma processing apparatus according to an embodiment of the present invention. FIG. 2 is a table showing the order of occurrence of abnormal discharge. FIG. 3 is a diagram showing a waveform of the output signal S1 that appears due to the occurrence of press park and townsend discharge. 4A and 4B are diagrams showing the evaluation results by the evaluation device 26. FIG. 4A shows a case where the operation is continued as it is even when the control signal S2 is activated, and FIG. 4B is a response to the activation of the control signal S2. The case where the RF power supply device 21 is stopped is shown. FIG. 5 is a first flowchart for explaining operations of the detection device 25 and the control device 27. FIG. 6 is a second flowchart for explaining operations of the detection device 25 and the control device 27. FIG. 7 is a third flowchart for explaining the operations of the detection device 25 and the control device 27.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a schematic view schematically showing a configuration of a plasma processing apparatus according to an embodiment of the present invention.

  As shown in FIG. 1, the plasma processing apparatus according to the present embodiment is a plasma etching apparatus, and includes a plasma chamber 10 and an RF power supply device 21 that applies an AC voltage to an electrode 11 disposed in the plasma chamber 10. Yes.

  The electrode 11 provided in the plasma chamber 10 also serves as a stage on which a semiconductor wafer 12 as a processing target is placed. In addition to the electrode 11, the plasma chamber 10 is provided with an electrode 14 that also serves as a blow-out port 14 a for the process gas 13. A ground potential is applied to the electrode 14. The process gas 13 is introduced into the plasma chamber 10 through the pipe 15, passes through the vicinity of the semiconductor wafer 12, and is discharged by the vacuum pump 16. When an AC voltage is applied to the electrode 11 using the RF power supply device 21, the process gas 13 between the electrode 11 and the electrode 14 is turned into plasma, and the plasma etches the film formed on the surface of the semiconductor wafer 12. . Although not particularly limited, the output of the RF power supply device 21 is set to about 200 W to 5 kW.

  The RF power supply device 21 is a circuit that generates an AC voltage of 13.56 MHz, for example, and the generated AC voltage is applied to the electrode 11 in the plasma chamber 10 via the RF matching unit 22. As the AC frequency, a lower frequency or higher frequency AC such as 100 KHz or 2.45 GHz may be used. In addition, a DC voltage may be used instead of an AC voltage.

  In the present embodiment, the magnetic field probe 23 is provided close to the wiring L1 that connects the RF power supply device 21 and the RF matching unit 22. The magnetic field probe 23 detects a magnetic field radiated by the current flowing through the wiring L1 as an electric field, and the Maxwell's equation is applied as it is for the characteristic. Further, the coupling capacitance of the magnetic field probe 23 can be regarded as substantially zero. The type of the magnetic field probe 23 to be used is not particularly limited, and may be a type using a multilayer wiring board or a type that clamps the periphery of the wiring L1.

  In the example shown in FIG. 1, the magnetic field probe 23 is provided close to the wiring L <b> 1 that connects the RF power supply device 21 and the RF matching unit 22, but the position where the magnetic field probe 23 is provided is limited to this. As long as the high frequency component superimposed on an alternating voltage is observable, you may provide in any position. For example, the magnetic field probe 23 may be provided close to the wiring L2 connecting the electrode 11 and the RF matching unit 22.

  The output signal S1 of the magnetic field probe 23 is distributed by the distributor 24 and supplied to the detection device 25 and the evaluation device 26, respectively. The detection device 25 is a device that detects an abnormal discharge generated inside the plasma chamber 10 by observing the output signal S1, and a control signal S2 that is the detection result is given to the control device 27. As the control signal S2, a 1-bit binary signal (for example, a TTL signal) can be used. The control device 27 controls the operation of the RF power supply device 21 based on the control signal S2. The evaluation device 26 includes, for example, an oscilloscope that observes the output signal S1.

  In addition, a glass window 17 is provided on the outer wall of the plasma chamber 10, from which the inside can be observed. In the present embodiment, a photo sensor 28 is provided outside the glass window 17, thereby detecting plasma light. The output signal S3 of the photo sensor 28 is supplied to the control device 27.

  The above is the configuration of the plasma processing apparatus according to the present embodiment.

  The plasma processing apparatus according to the present embodiment includes the magnetic field probe 23 as described above, and thereby detects an abnormal discharge generated inside the plasma chamber 10. The magnetic field probe 23 is more resistant to ambient noise than a loop antenna or the like, and has a wide observable frequency band. Specifically, components from the MHz band to the GHz band can be observed with high accuracy.

  As a result of research over many years, the present inventor has found that there is a certain rule in the order of occurrence of abnormal discharge in the plasma atmosphere. FIG. 2 is a table showing the order of occurrence of abnormal discharge.

  Abnormal discharge begins with the occurrence of corona discharge. The corona discharge is caused by a local high electric field, the frequency is 0.1 to 300 MHz, and the duration is 10 ms or more. Since the frequency band of corona discharge is almost the same as that of arc discharge, it is difficult to distinguish corona discharge from arc discharge by directly observing this.

  When corona discharge lasts for a certain period of time, a predictive phenomenon called press park occurs thereafter. The press park is generated by an increase in corona density, and the frequency thereof is 1 to 3 GHz and has a duration of about 5 μs to 1 ms. However, even if corona discharge occurs, a press park does not always occur.

  When the press park lasts for a certain period of time, a Townsend discharge with a high current density that induces arc discharge occurs. Townsend discharge is generated by an increase in press park density, its vibration frequency is 1 to 3 GHz, and has a transient response of several ns.

  When townsend discharge occurs, it is induced to generate glow discharge and arc discharge. However, the frequencies of glow discharge and arc discharge are both 0.1 to 300 MHz, and it is difficult to distinguish them from each other. However, in the present invention, it is not necessary to distinguish between the two, and it is determined that an abnormal discharge of about 0.1 to 300 MHz occurring before the Townsend discharge is a corona discharge, and a 0.1 to 300 MHz generated after the Townsend discharge. What is necessary is just to determine that the abnormal discharge of a grade is an arc discharge. Such determination can be performed by the detection device 25 or the evaluation device 26.

  The glow discharge has a duration of about several ms. The arc discharge is a complete avalanche breakdown phenomenon in which thermionic electrons are emitted for 100 ms or longer and damages the semiconductor wafer 12 that is the object to be processed. Alternatively, particle scattering, burnout, film thickness abnormality, characteristic fluctuation, and the like are caused. Even if townsend discharge occurs, glow discharge and arc discharge do not always occur.

  FIG. 3 is a diagram showing a waveform of the output signal S1 that appears due to the occurrence of press park and townsend discharge.

  As shown in FIG. 3, the press park occurs in a short cycle of about 1 μs, and its duration is about 5 μs to 1 μs. Thereafter, Townsend discharge with transient response occurs. It may be regarded as “town sent discharge” including the press park. When the duration of the press park is short, for example, when it is less than 5 μs, the abnormal discharge often ends as it is without shifting to the townsend discharge.

  For this reason, if the detection device 25 that observes the output signal S1 determines that there is a high possibility of arc discharge when the press park continues for a certain time (for example, 5 μs) or longer, and activates the control signal S2. Good. Specifically, when the control signal S2 is a binary signal, the logic level of the control signal S2 is changed from “0” to “1” in response to the press park lasting for a certain time (for example, 5 μs) or longer. You can do it. Further, whether or not the waveform of the output signal S1 indicates a press park can be determined based on the frequency component and the generation period.

  When the control signal S2 is activated, the control device 27 preferably stops the RF power supply device 21. Thereby, damage to the semiconductor wafer 12 due to arc discharge can be prevented in advance. However, the generation of arc discharge may be prevented by reducing the alternating voltage instead of stopping the RF power supply device 21. Furthermore, at the time of evaluation, even if the control signal S2 is activated, the application of the AC voltage by the RF power supply device 21 may be continued as it is. Thereby, the behavior of abnormal discharge can be continuously observed using the evaluation apparatus 26, and productivity can be improved by feeding back the result. That is, the occurrence of arc discharge can be prevented with higher probability by feedback, and the number of cases where the RF power supply device 21 is stopped unnecessarily can be reduced.

  Although it is possible to activate the control signal S2 by using a townsend discharge as a trigger instead of a press park, the townsend discharge is a transient response and the generation time is extremely short. Even if this is done, the occurrence of arc discharge may not be prevented correctly. Therefore, it is preferable to use a press park as a trigger for stopping the RF power supply device 21.

  4A and 4B are diagrams showing the evaluation results by the evaluation device 26. FIG. 4A shows a case where the operation is continued as it is even when the control signal S2 is activated, and FIG. 4B is a response to the activation of the control signal S2. The case where the RF power supply device 21 is stopped is shown. In FIG. 4, “RF” represents the output of the RF power supply device 21, and “S 1” represents the output signal S 1 of the magnetic field probe 23. FIG. 4 also shows the output signal of the loop antenna and the output signal S3 of the photosensor 28.

  In the example shown in FIG. 4A, corona discharge and arc discharge are observed, and higher-frequency townsend discharge (including press park) is observed between them. Townsend discharge is also observed by the loop antenna, but corona discharge and arc discharge cannot be observed by the loop antenna.

  In the example shown in FIG. 4B, the RF power supply device 21 is stopped in response to the press park lasting for a certain period of time. Then, after 80 ms has elapsed, the application of the AC voltage by the RF power supply device 21 is resumed. The resumption of application of the AC voltage is preferably performed by so-called ramp-up in which the output is gradually increased.

  As shown in FIG. 4B, it can be seen that the occurrence of arc discharge is prevented by performing such an operation. Even in this case, corona discharge occurs, but this does not damage the semiconductor wafer 12. Further, when the RF power supply device 21 is stopped in response to the occurrence of corona discharge, the number of cases where the RF power supply device 21 is stopped is increased even though the arc discharge does not actually occur, and productivity may be reduced. There is. However, in the present embodiment, since the RF power supply device 21 is stopped in response to the press park lasting for a certain time, the occurrence of arc discharge can be prevented and the RF power supply device 21 is stopped unnecessarily. The number of cases can be reduced.

  FIG. 5 is a first flowchart for explaining operations of the detection device 25 and the control device 27.

  In the example shown in FIG. 5, first, the RF power supply device 21 is turned on (S <b> 11), and an AC voltage is applied to the plasma chamber 10. During this time, the detection device 25 monitors the output signal S1 of the magnetic field probe 23 and waits for the occurrence of a press park that lasts for a certain time (S12). And if generation | occurrence | production of the press park which continues for a fixed time is detected, control signal S2 will be activated and RF power supply device 21 will be stopped via the control apparatus 27 (S13). Thereafter, the control device 27 monitors the output signal S3 of the photosensor 28, and in response to confirming the disappearance of the plasma light (S14), turns on the RF power supply device 21 again (S11). Thereby, the sign of arc discharge can be prevented in advance, and the application of AC voltage can be resumed after the plasma discharge is completely terminated. Note that the RF power supply 21 may be turned on again with the trigger that the plasma light has been reduced to a predetermined illuminance, instead of using the trigger that the plasma light has completely disappeared.

  FIG. 6 is a second flowchart for explaining operations of the detection device 25 and the control device 27.

  The example shown in FIG. 6 is different from the first flowchart shown in FIG. 5 in that step S15 for detecting corona discharge is added between step S11 and step S12. Other points are the same as those in the first flowchart. In this example, since step S15 for detecting corona discharge is added, it is possible to reduce the number of unnecessary stop times of the RF power supply device 21 due to erroneous detection of a press park.

  FIG. 7 is a third flowchart for explaining the operations of the detection device 25 and the control device 27.

  The example shown in FIG. 7 is different from the first flowchart shown in FIG. 5 in that step S16 for measuring a predetermined time is used instead of step S14. Other points are the same as those in the first flowchart. In this example, the disappearance of the plasma light is not used as a trigger, but the application of the AC voltage by the RF power supply device 21 is restarted with a predetermined time elapsed after the RF power supply device 21 is stopped. This eliminates the need for the photosensor 28 and simplifies the control.

  As described above, according to the present embodiment, the occurrence of arc discharge can be prevented in advance. In addition, since the magnetic field probe 23 is used, a series of abnormal discharges, that is, corona discharge, townsend discharge, and arc discharge, which are generated when the application of the AC voltage is continued, can be observed, and the feedback of the observation results Becomes easy.

  It is also possible to correctly distinguish between corona discharge and arc discharge, which has been difficult to identify in the past.

  The preferred embodiments of the present invention have been described above, but the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention. Needless to say, it is included in the range.

  For example, in the above-described embodiment, the low-pressure plasma processing apparatus that performs the plasma processing on the semiconductor wafer 12 has been described as an example. However, the application target of the present invention is not limited thereto, and a normal-pressure plasma processing apparatus, etc. It is also possible to apply to other plasma processing apparatuses.

  Moreover, in the said embodiment, although AC voltage is used in order to excite plasma within the plasma chamber 10, you may use DC voltage instead of AC voltage. In this case, a DC power supply device may be used instead of the RF power supply device 21.

  Furthermore, the principle of the present invention can be applied not only to a plasma processing apparatus but also to all apparatuses or situations in which a plasma phenomenon can occur. For example, reticle (exposure mask) fabrication process, magnetic head fabrication process, flat display fabrication process, liquid crystal color filter fabrication process, CCD device fabrication process, sheet printing process, light emitting diode or laser diode fabrication process, powder Prevention of powder explosion in body transportation, laser exposure process, immersion exposure process, electron microscope, EB direct drawing, rectifier module for in-vehicle Li battery, in-vehicle electronic device, auto-cruise device, portable terminal high-frequency module, general-purpose switch, MEMS Can be applied to transformers.

DESCRIPTION OF SYMBOLS 10 Plasma chamber 11 Electrode 12 Semiconductor wafer 13 Process gas 14 Electrode 14a Outlet 15 Piping 16 Vacuum pump 17 Glass window 21 RF power supply device 22 RF matching unit 23 Magnetic field probe 24 Distributor 25 Detection device 26 Evaluation device 27 Control device 28 Photo sensor L1 wiring L2 wiring S1 output signal S2 control signal S3 output signal

Claims (7)

A method of analyzing a discharge generated in the plasma chamber based on a magnetic field generated in a wiring for supplying an AC voltage or a DC voltage for exciting plasma to the plasma chamber , the Townsend discharge and the Townsend based on the magnetic field. When the first and second discharges having a frequency of radiated electromagnetic waves lower than that of the discharge are detected and the first discharge is generated following the townsend discharge, it is determined that the first discharge is an arc discharge. and, when said second discharge occurs in front of the Townsend discharge, the discharge analytical method for determining the second discharge to be corona discharge. The discharge analysis method according to claim 1 , wherein the Townsend discharge emits an electromagnetic wave of 1 GHz to 3 GHz . The discharge analysis method according to claim 2 , wherein each of the arc discharge and the corona radiates an electromagnetic wave of 0.1 MHz to 300 MHz . A sign discharge generated between the corona discharge and the Townsend discharge, emit electromagnetic waves of 1 GHz ~3GHz, and further detected based a sign discharge lasting more than 5μs to the magnetic field, to claim 3 The discharge analysis method described. Detected using the same magnetic field probe the first and second discharge and the Townsend discharge, discharge analysis method according to any one of claims 1 to 4. A magnetic field probe for detecting a discharge generated in the plasma chamber based on a magnetic field generated in a wiring for supplying an AC voltage or a DC voltage for exciting plasma to the plasma chamber;
The first discharge is an arc discharge when the output signal of the magnetic field probe indicates the occurrence of a Townsend discharge and then the occurrence of a first discharge having a lower frequency of the radiated electromagnetic wave than the Townsend discharge. And when the output signal of the magnetic field probe indicates the occurrence of a Townsend discharge, and before that indicates the occurrence of a second discharge having a frequency of radiated electromagnetic waves lower than that of the Townsend discharge, a detection device for determining the second discharge to be corona discharge, discharge analyzer equipped with. The detection device further detects a predictive discharge generated between the corona discharge and the townsend discharge, wherein the frequency of the output signal is 1 GHz to 3 GHz and lasts for 5 μs or more. Item 7. The discharge analyzer according to Item 6 .