JP2018535532A - Plasma device driven by polyphase alternating current or pulsed current and method for generating plasma - Google Patents

Abstract

A plasma source and a method for generating a plasma are provided. The plasma source includes at least three holocathodes including a first holocathode, a second holocathode, and a third holocathode, each holocathode having a plasma exit region. The plasma source also includes a power source capable of forming a plurality of output waves, including a first output wave, a second output wave, and a third output wave. And the second output wave are out of phase, the second output wave and the third output wave are out of phase, and the first output wave and the third output wave are out of phase. Each of the holocathodes is electrically connected to the first output wave, the second holocathode is electrically connected to the second output wave, and the third holocathode is electrically connected to the third output wave. So that it is electrically connected to the power source.

Description

  Traditionally, holocathode plasma sources are commonly used in coating and surface treatment applications. These plasma sources include one or more holocathodes that are electrically connected to a power source. These plasma sources can use several types of holocathodes, including point sources and linear holocathodes.

  A typical power supply used in a holocathode plasma source supplies either a direct current, an alternating current, or a pulsed current (ie, a current having a square or rectangular waveform with a duty cycle of less than 100%) to the holocathode. It is configured. Currently, bipolar power supplies (ie, two-phase power supply) are also used to supply alternating or pulsed current to the holocathode plasma source.

  If direct current is used when the linear holocathode plasma source is in operation, the plasma is generated primarily in a single region rather than the entire length of the linear holocathode. Some types of plasma sources that use direct current can effectively generate a plasma using a magnet effectively, but a linear holo cathode cannot do this. However, many applications, such as glass coating using plasma chemical vapor deposition, require a high degree of uniformity (which cannot be achieved using direct current in a linear holocathode plasma source).

  The inventors have previously discovered that a uniform linear plasma can be achieved by using a two-phase (bipolar) AC or pulsed power supply with a holocathode plasma source. However, there are several problems with using a two-phase power source with a holocathode plasma source. For example, since there is an alternating power source, there is a time period during which plasma is not actively generated in the plasma source during operation time (ie, there is no active electron emission). In typical applications, the time during which this plasma is not actively generated is about 25% of the power supply period. Another problem is that the plasma source wears significantly due to the use of a two-phase power source and the operating life of the plasma source is reduced.

  Thus, there is a need in the prior art for a plasma source that overcomes these deficiencies and the like in known plasma sources.

  U.S. Patent Application No. 12 / 535,447 (currently U.S. Patent No. 8,652,586), U.S. Patent Application Nos. 14 / 148,612 and 14 assigned to the same assignee as the present application. No./148,606, No. 14 / 486,726, No. 14 / 486,779, PCT / US14 / 068919, PCT / US14 / 68858, each of which is incorporated herein in its entirety. Describes various holocathode plasma sources, such as those that can be used in embodiments of the present invention.

  Advantages of embodiments of the present invention include, but are not limited to, improved plasma source operating lifetime, improved deposition rate, and improved plasma generation time. Further, in the embodiment of the present invention, the dissociation energy of the raw material gas used is increased, resulting in a coating with higher density when using plasma chemical vapor deposition.

  According to a first aspect of the present invention, a plasma source is provided. The plasma source includes at least three holocathodes including a first holocathode, a second holocathode, and a third holocathode. Each holocathode has a plasma exit region. The plasma source also includes a power source capable of forming a plurality of output waves, including a first output wave, a second output wave, and a third output wave. The first output wave and the second output wave are out of phase, the second output wave and the third output wave are out of phase, and the first output wave and the third output wave are out of phase. It's off. Each of the holocathodes is electrically connected to the first output wave, the second holocathode is electrically connected to the second output wave, and the third holocathode is electrically connected to the third output wave. So that it is electrically connected to the power source. Current flows between at least three holocathodes that are out of electrical phase. The plasma source can generate a plasma between the holocathodes.

  According to a second aspect of the present invention, a method for generating plasma is provided. The method includes providing at least three holocathodes including a first holocathode, a second holocathode, and a third holocathode. Each holocathode has a plasma exit region. The method also includes providing a power source capable of forming a plurality of output waves, including a first output wave, a second output wave, and a third output wave. The first output wave and the second output wave are out of phase, the second output wave and the third output wave are out of phase, and the first output wave and the third output wave are out of phase. It's off. Each of the holocathodes is electrically connected to the first output wave, the second holocathode is electrically connected to the second output wave, and the third holocathode is electrically connected to the third output wave. So that it is electrically connected to the power source. Current flows between at least three holocathodes that are out of electrical phase. Plasma is generated between the holocathodes. In some embodiments, the method further includes providing the substrate and forming a coating on the substrate using plasma enhanced chemical vapor deposition.

  In some embodiments (according to any aspect of the invention), the plasma generated by the plasma source includes active electron emission for at least substantially 80% of the period of the plurality of output waves. In other embodiments, the plasma source includes active electron emission for at least substantially 90% or at least substantially 100% of the plurality of output wave periods.

  In some embodiments, the at least three holocathodes are 180 ° out of phase with each other in electrical phase. In some embodiments, the at least three holocathodes are 120 ° out of phase in electrical phase. In some embodiments, two adjacent ones of at least three holocathodes are each out of phase by the same phase angle as the other two adjacent ones of at least three holocathodes. In some embodiments, the at least three holocathodes are linear holocathodes. In some embodiments, each of the at least three holocathodes includes an elongated cavity. In some embodiments, the plasma exit region of each of the at least three holocathodes includes a plurality of plasma exit orifices. In some embodiments, the plasma exit region of each of the at least three holocathodes includes a plasma exit groove.

  In some embodiments, each of the at least three holocathodes is electrically isolated such that only the inner surface of the holocathode and the plasma exit region emits and receives electrons. In some embodiments, substantially all of the generated plasma flows through the plasma exit region of each of the at least three holocathodes. In some embodiments, the current consists of electrons from secondary electron emission. In some embodiments, the current consists of electrons derived from thermionic emission electrons.

  In some embodiments, the at least three holocathodes are arranged linearly. In some embodiments, the at least three holocathodes are configured such that each of the plasma exit regions is directed to a common line. In some embodiments, the distance between any two of the at least three holocathodes is the same. In some embodiments, current flowing between at least three holocathodes that are out of phase causes a potential difference (maximum value, minimum potential difference, etc.) between the at least three holocathodes. In some embodiments, the potential difference is at least 50V between any two of the at least three holocathodes. In some embodiments, the potential difference is at least 200V between any two of the at least three holocathodes. In some embodiments, the plurality of output waves include a square wave, so that the potential difference (maximum value, minimum potential difference, etc.) is smaller than the sine wave when the power input is the same as a whole. In some embodiments, the power source is in the form of AC electrical energy. In some embodiments, the power source is in the form of pulsed electrical energy.

  In some embodiments, the generated plasma is substantially uniform throughout its length in the absence of substantially magnetic field driven closed circuit electron drift. In some embodiments, the plasma is generated substantially uniformly throughout a length of about 0.1 m to about 1 m. In some embodiments, the plasma is generated substantially uniformly throughout a length of about 1 m to about 4 m. In some embodiments, the frequency of each of the plurality of output waves is equal and ranges from about 1 kHz to about 500 MHz. In some embodiments, the frequency of each of the plurality of output waves is equal and ranges from about 1 kHz to about 1 MHz. In some embodiments, the frequency of each of the plurality of output waves is equal and ranges from about 10 kHz to about 200 kHz. In some embodiments, the frequency of each of the plurality of output waves is equal and ranges from about 20 kHz to about 100 kHz. In some embodiments, electrons from the emission surface are confined by the holocathode effect. In some embodiments, electrons from the emission surface of each of the at least three holocathodes are not confined by the magnetic field. In some embodiments, at least one of the plurality of output waves generated by the power source is configured to power a plurality of at least three holocathodes.

The accompanying drawings, which are incorporated in and form a part of this specification, illustrate various embodiments of the present disclosure and, together with the description of the specification, explain the principles of the disclosure and include It helps to enable those skilled in the art to make and use the disclosed embodiments. In the drawings, like reference numbers indicate identical or functionally similar elements.
FIG. 1 illustrates a three-phase sinusoidal waveform according to an exemplary embodiment of the present invention. FIG. 2 shows a voltage plot and a current plot between two holocathodes in a bipolar holocathode plasma source. FIG. 3 shows a cross-sectional view of a conventional bipolar holocathode plasma source at different times. FIG. 4 shows a time zone without plasma in a conventional bipolar holocathode plasma source. FIG. 5 shows voltage and current plots between two holocathodes in a multiphase holocathode plasma source, according to an illustrative embodiment of the invention. FIG. 6 shows cross-sectional views at different times of a multiphase holocathode plasma source, according to an illustrative embodiment of the invention. FIG. 7 illustrates a method according to an exemplary embodiment of the present invention. FIG. 8 shows a coating formed by a method according to an exemplary embodiment of the present invention. FIG. 9 illustrates a multiphase holocathode plasma source including a holocathode having a plasma exit region, according to an illustrative embodiment of the invention. FIG. 10 illustrates a multiphase holocathode plasma source including a holocathode having a grooved confined plasma exit region, according to an illustrative embodiment of the invention. FIG. 11 illustrates a multi-phase holocathode plasma source including six holocathodes and six phases, according to an illustrative embodiment of the invention. FIG. 12 shows a multi-phase holocathode plasma source including six holocathodes and three phases, according to an illustrative embodiment of the invention. FIG. 13 illustrates a multiphase holocathode plasma source including three equally spaced holocathodes according to an exemplary embodiment of the present invention. FIG. 14A shows the electron density of plasma formation in and around the holocathode in a bipolar holocathode plasma source. FIG. 14B shows the electron density of plasma formation in and around the holocathode in a multiphase holocathode plasma source, according to an illustrative embodiment of the invention. FIG. 15A shows the ion density of the plasma formation in and around the holocathode in a bipolar holocathode plasma source. FIG. 15B shows the ion density of plasma formation in and around a hollow cathode in a multiphase holocathode plasma source, according to an illustrative embodiment of the invention. FIG. 16A shows the absorption of ions along the walls of the holocathode cavity in both a bipolar holocathode plasma source and a multiphase holocathode plasma source according to an exemplary embodiment of the present invention. FIG. 16B shows an indicator along the wall of the holocathode cavity shown in the graph of FIG. 16A.

First, the sine wave Asin2πft + · (where A is the amplitude, f is the frequency, and · is the phase angle) is considered. The phase angle · indicates a place where vibration is present at time t = 0. For two sine waves A ₁ sin2πft + · ₁ and A ₂ sin2πft + · ₂ , the phase difference between the two waves is defined as the difference of the phase angle • ₂ − · ₁ . It should be noted that because of this definition, the phase difference depends on which wave is considered as the first wave and which wave is considered as the second wave. That is, when the order changes, the sign of the phase difference also changes. The wave with the larger phase angle is called the preceding wave, and the wave with the smaller phase angle is called the delayed wave. If the preceding wave is the first wave, the phase difference is. If the delayed wave is the first wave, the phase difference is-. Normally, the sign of the phase difference is not treated as important in this specification, and the order of waves is not emphasized. In the above formula,. Is expressed in radians, but in the present application, the phase angle or phase difference is usually discussed in terms of the degree of the angle (for convenience). Since the sine wave has exactly a cycle or period of 360 ° (ie 2π radians), the phase angle can be expressed as a number between −180 ° (ie −π radians) and + 180 ° (ie + π radians). it can. The phase difference is independent of the amplitude A and is only properly defined between two waves with the same frequency f.

  If the phase angles of the two waves match, there is no phase difference and the waves are said to be in phase with each other. If the phase angles of the two waves do not match, the waves are said to be out of phase. If the phase difference is 180 °, the two waves are said to be in antiphase. The phase difference is a characteristic between two waves. Two waves that are out of phase with each other may be referred to as being offset or offset from the other phase. Those skilled in the art will also understand that phase differences can be defined for waveforms such as square waves and pulse waves.

  If two holocathodes are powered by two waves out of phase, the present application will refer to these holocathodes by a specific phase angle defined as the phase difference between the two waves feeding the holocathodes ( They are said to be out of phase. Thus, it can be said that both the wave and the holocathode are (with synonyms) phase offset from each other. Alternatively, if the two waves are in phase, the two holocathodes can be said to be in phase (synonymously).

  “Thermionic” is taken to mean the emission of electrons from the surface, which is greatly accelerated as the surface temperature increases. The thermionic temperature is generally about 600 ° C. or higher.

  “Secondary electrons” or “secondary electron current” are taken to mean the emission of electrons from the surface and the resulting current, respectively, when a particle collides with a solid surface. The electron emission surface according to the embodiment of the present invention can generate plasma, and electrons or ions further collide with the surface. When electrons or ions collide with the electron emission surface, secondary electrons are emitted from the electron emission surface. Secondary electron emission is important because the flow of secondary electrons helps to generate high density plasma.

  FIG. 1 shows a three-phase sinusoidal waveform according to an embodiment of the present invention. The three different sine waves (A, B, C) in the waveform plot 100 are out of phase with each other by ± 120 °. Specifically, the combination of the waves A and B and the combination of the waves B and C are shifted by + 120 °, and the combination of the waves A and C is shifted by −120 °.

FIG. 2 shows a voltage and current plot between a pair of holocathodes in a bipolar holocathode plasma source. Time points t ₁ , t ₂ , t ₃ , t ₄ , t ₅ , and t ₆ are displayed on the voltage plot 202 and the current plot 204, indicating various points of interest.

FIG. 3 shows a cross-sectional view of a conventional bipolar holocathode plasma source at different times. The bipolar holocathode arrangement 300 includes holocathodes 302 and 304 and a bipolar power supply 310. When power is supplied by the power source 310, plasma 320 is generated between the holo cathodes 302 and 304. Voltage plot 202 and current plot 204 show the voltage and current between holocathodes 302 and 304, respectively. The power source 310 supplies an alternating current, and the holo cathodes 302 and 304 alternately function as a cathode and an anode. In this arrangement, the holocathodes 302, 304 are out of phase (ie, 180 degrees out of phase). Time points t ₁ , t ₂ , t ₃ , t ₄ , t ₅ , t ₆ are displayed on the voltage plot 202 and current plot 204, and various points of interest corresponding to different views of the holocathode arrangement 300 shown in FIG. Show.

The diagram corresponding to t ₁ shows when both the AC voltage input and the resulting current reach a zero value. At this point, plasma is not actively generated. diagram corresponding to t _2, the potential difference between the hollow cathode 302, 304 reaches the maximum, it indicates the time when the plasma 320 is ignited. The diagram corresponding to t ₃ shows the point in time when the current is maximized when the plasma 320 is fully established between the two holocathodes 302, 304. The diagram corresponding to t ₄ shows a bipolar holocathode arrangement 300 in which there is a plasma 320 with a current that is equal to the current at time t ₂ and has a reduced intensity (as compared to the diagram corresponding to t ₃ , etc.). . drawing corresponding to t ₅ indicates the next zero crossing, the plasma generation is once stopped at this point. diagram corresponding to t _6, the plasma 320 is generated again, indicating that the cycle is continued in reverse to the case role of hollow cathode 302 and hollow cathode 304 (cathode or anode) is t _2.

  The role switching between the cathode and the anode will be briefly described. First, the first electron emission surface is driven to a negative voltage by a bipolar power source to enable plasma formation, and the second electron emission surface is driven to a positive voltage so as to function as an anode of a voltage application circuit. Thereafter, the first electron emission surface is driven to a positive voltage, and the roles of the cathode and the anode are reversed. When one of the electron emission surfaces is driven negative, a discharge occurs in the corresponding cavity. The other cathode becomes the anode, and an electron current flows from the holocathode on the cathode side to the holocathode on the anode side.

  FIG. 4 shows a time zone without plasma in a conventional bipolar holocathode plasma source. Specifically, in FIG. 4, a time zone in which there is not enough potential difference to actively generate plasma between the holocathodes is identified along the voltage plot 202 and the current plot 204. In the non-plasma production zones 402, 404, 406, the bipolar holocathode arrangement 300 stops producing plasma for approximately 25% of the respective wave period. In contrast, one advantage of embodiments of the present invention is to reduce or eliminate the time during which plasma is not formed in embodiments of the present invention by maintaining a sufficient potential difference between the plasma generating holocathodes. There is a point that can be.

FIG. 5 shows a voltage plot and a current plot between two holocathodes in a multiphase holocathode plasma source according to an embodiment of the present invention. The time points t ₁₀ , t ₁₁ , t ₁₂ , t ₁₃ , t ₁₄ , and t ₁₅ are displayed in the voltage plots 502, 506, 510 and the current plots 504, 508, 512, and various points of interest are shown.

FIG. 6 shows cross-sectional views at different times of a multiphase holocathode plasma source according to an embodiment of the present invention. The multiphase holocathode arrangement 600 includes holocathodes 602, 604, 606 and a multiphase power source 610. When power is supplied by the power source 610, plasma 620 is generated between the holocathodes 602, 604, and 606. Specifically, plasma 620 is generated between each of the two holocathodes 602 and 604, 604 and 606, and 602 and 606. Voltage plots 502, 506, 510 and current plots 504, 508, 512 (shown in FIG. 5) are respectively two holocathodes 602 and 604 (labeled “AB” in FIG. 5), 604 and 606 ( FIG. 5 shows the voltage and current between 602 and 606 (shown as “A-C” in FIG. 5). In case of combination). The power source 610 supplies an alternating current, and the holo cathodes 602, 604, and 606 alternately function as a cathode and an anode. In this arrangement, the combination of holocathodes 602 and 604, 604 and 606 has a phase shift of + 120 °, and the combination of holocathodes 602 and 606 has a phase shift of −120 °. Time points t ₁₀ , t ₁₁ , t ₁₂ , t ₁₃ , t ₁₄ , t ₁₅ are displayed on the voltage plots 502, 506, 510 and the current plots 504, 508, 512, and different views of the holocathode arrangement 600 shown in FIG. Various points of interest corresponding to are shown.

  The plasma generated between any two holocathodes is somewhat affected by the distance between the two holocathodes. In some embodiments, the distance between two adjacent holocathodes (eg, a combination of holocathodes 602 and 604, 604 and 606) is the same or substantially the same, but not adjacent to each other (eg, The distance between 602 and 606) is longer than the distance between two adjacent ones. If the distance between the pair of holocathodes is too long, plasma may not be formed between them. As will be appreciated by those skilled in the art, the distance between the holocathodes is process dependent. As the distance increases, the voltage required for plasma formation also increases. In some embodiments, the distance between the holocathodes is less than 500 mm, or less than 400 mm, or less than 200 mm. In some embodiments, the distance between the holocathodes is about 100 mm. In some cases, plasmas can be formed at longer distances, but for typical processes and power sources, the maximum distance would be 500 mm. In addition, the magnetic field may affect the effective space.

  The generated plasma is somewhat affected by the voltage and current between the pair of holocathodes. For example, plasma may be generated between a plurality of pairs of holocathodes, but the plasma density may not be uniform due to the voltage and current differences between the holocathodes in different combinations to some extent. For example, this non-uniform state is unlikely to be used for coating a substrate using plasma enhanced chemical vapor deposition. This is because the non-uniform state occurs only for a short time, and the region where the plasma density is high and the region where the plasma density is low are switched many times before the substrate clearly moves. Furthermore, in the in-line coating process, the substrate is processed evenly as it moves under the plasma source and passes under each holocathode.

  Multiphase power supply 610 may include a single power supply or a plurality of power supplies. Specifically, the multiphase power supply 610 can form a plurality of output waves (eg, waves A, B, C in the waveform plot 100), in which case the plurality of output waves (as well as those waves) The holocathodes that supply power are each out of timing. In some embodiments, adjacent holocathodes, eg, two holocathodes 602 and 604, 604 and 606, are in phase with each other (eg, 120 ° for a three-phase power source and 90 ° for a four-phase power source). The five-phase power supply is shifted by 72 °, the six-phase power supply is 60 °, and the n-phase power supply is shifted by 360 ° for n). In a linear embodiment with three holocathodes in three phases (ie, the holocathodes are arranged linearly), if the two adjacent holocathodes 602 and 604, 604 and 606 are 120 ° out of phase, they are adjacent The two holocathodes 602 and 606 that are not are out of phase by -120 °. In a linear embodiment with four phases and four holocathodes, if the two adjacent phases are 60 ° out of phase, the first and third two holocathodes that are not adjacent in a straight line are out of phase by 120 °, The first and fourth holocathodes that are not adjacent on a straight line are 180 ° out of phase.

diagram corresponding to t _10, while the current between the hollow cathode 602 and 604 is maximized, indicating the time at which current between the hollow cathode 604 and 606 is about half the maximum value. In the diagram corresponding to t ₁₁ , the current between the holocathodes 602 and 604 becomes zero and current begins to flow between the holocathodes 602 and 606. At this same time (t ₁₁ ), the current between the holocathodes 604 and 606 reaches its maximum value. Cycle, current between the hollow cathode 602 and 606 reaches the maximum value, t ₁₂ current begins to flow again during the certain but hollow cathode 602 and 604 in a direction opposite to the direction shown in diagram corresponding to t ₁₀ Continue in the figure corresponding to. corresponding to t13 FIG, while current flowing between the hollow cathode 602 and 604 becomes maximum, the cycle from drawing corresponding to t ₁₀ the current between the hollow cathode 604 and 606 is about half the maximum value The opposite end is shown. Figure of current corresponding to t ₁₃ flows in a direction opposite to the current in the view corresponding to t _10, the hollow cathode which has been functioning as a cathode to which functions as an anode here. diagram corresponding to t _14, the current shows a situation where the flow in the opposite direction as that described in diagram corresponding to t _11, drawing corresponding to t ₁₅ are those described in FIG current corresponds to t ₁₂ Indicates a situation in which it flows in the opposite direction.

  One feature of the multi-phase holocathode arrangement 600 shown in FIG. 6 (as well as other embodiments of the present invention) is that between any holocathodes in other combinations at any point where the current approaches zero between any two holocathodes. The voltage difference and current are not zero. With this arrangement, it is possible to manufacture a plasma device in which the above-described plasma-free time zone does not occur in a conventional plasma source driven by a bipolar power source. That is, embodiments of the present invention effectively avoid non-plasma production zones 402, 404, and 406 inherent in the prior art bipolar holocathode arrangement 300, as described above. According to an embodiment of the present invention, an apparatus for continuously generating a plasma by maintaining at least three currents and the resulting plasma generation by including at least three holocathodes and a multi-phase power supply. Including improved plasma properties are obtained. By using at least three phase offset waves and at least three holocathodes, the time without plasma in which waves are generated by the AC power supply will be substantially eliminated. For pulsed power, the time without plasma can be substantially from 0% to about 20%, depending on design parameters. For example, using at least three phase offset waves and at least three holocathodes, the plasma-free time is substantially 20% (or plasma is actively generated during 80% of the wave period), The time without plasma is substantially 10% (or plasma is actively generated during 90% of the wave period), and the time without plasma is substantially 0% (or 100 of the wave period). %, Plasma is actively generated). There is a decay time associated with the plasma (ie, even after the voltage drops to zero between a pair of holocathodes, even though the plasma is not actively generated, a short time after the voltage drop. In this application, the time during which electrons are actively emitted is referred to as plasma being actively generated.

  In some embodiments, holocathodes 602, 604, 606 (or other holocathode arrangements described herein or enabled by this specification) may include elongated cavities. The holocathode may include a plasma exit region, the plasma exit region may include a single plasma exit orifice, or may include multiple plasma exit orifices or plasma exit grooves, some of these plasma exit regions. May be included. In some embodiments, the holocathodes are each electrically isolated such that only the inner surface of the holocathode and the plasma exit region emit and receive electrons. In some embodiments, substantially continuously generated plasma flows through the plasma exit region of each holocathode. In some embodiments, the current consists of secondary electron emission or thermionic emission electrons or some combination of these currents. In some embodiments, current flows between the holocathodes due to the potential difference. In some embodiments, this potential difference is at least 50V or at least 200V between any two holocathodes. In some embodiments, a multi-phase power source that forms a plurality of output waves generates a plurality of output waves consisting of square waves, thereby reducing the potential difference even closer to a sine wave. A multi-phase power source is in the form of AC electrical energy, in the form of pulsed electrical energy, or some combination of these forms of electrical energy. In some embodiments, the generated plasma is substantially uniform throughout its length in the absence of substantially magnetic field driven closed circuit electron drift. In some embodiments, the plasma is generated substantially uniformly over a length of about 0.1 m to about 1 m or about 1 m to about 4 m. In some embodiments, the frequency of each of the plurality of output waves is equal and is in the range of about 1 kHz to about 1 MHz or about 10 kHz to about 200 kHz or about 20 kHz to about 100 kHz. In some embodiments, electrons emitted from the emission surface are confined by the holocathode effect. In some embodiments, electrons emitted from the emission surface are not confined by the magnetic field.

  One factor that affects the electron current is the temperature of the holocathode cavity wall. In a holocathode configuration with a cavity wall temperature below 1000 ° C., electron emission is dominated by secondary electron emission. When ions collide with the cavity wall, electron emission from the wall surface is induced by the kinetic energy and negative potential of the colliding ions. In general, these “cold” holocathodes are operated at a cavity wall temperature of 50 ° C. to 500 ° C. Usually, cooling methods are applied to maintain the holocathode structure at such temperatures. Often, a water-cooled channel is incorporated into the holocathode structure. The operating voltage for cold holocathode discharge is typically 300 to 1000 volts.

  Alternatively, the holocathode may be operated in the thermoelectron mode. In order to generate thermionic emission, the temperature of the holocathode cavity wall is usually in the range of 1000 to 2000 ° C. In the thermionic holocathode, a heater may be incorporated around the cavity wall to assist in heating, or for further simplification, the cavity wall may be heated using plasma energy transfer. Typically, hot cavities are insulated to reduce heat loss due to heat conduction or heat dissipation. The operating voltage for thermionic holocathode discharge is typically 10 to 300 volts, more typically 10 to 100 volts.

  A PECVD process with a sufficiently high deposition rate and commercially useful relies on some form of densified plasma. The holocathode effect is one of the specific methods for confining electrons with high density by using an electric field in a closed space or a partially closed space. By enclosing the negative electric field, free electrons in the gas phase are trapped and oscillate between the surrounding wall or the oppositely negatively biased wall. When electrons vibrate, the movement path of the electrons becomes longer, and as a result, the possibility of gas phase collision increases. When such a collision occurs, gas molecules are ionized, and electrons and cations are generated. The positive ions are accelerated and strike the negatively biased holocathode wall. When a cation collides with the wall, more electrons are generated by secondary electron emission. According to the literature, the holocathode plasma is usually a higher density plasma than that obtained by confinement by a magnetic field, such as used in an electron confinement process with closed drift (such as magnetron sputtering).

  Another advantage of the embodiment in FIG. 6 is that, like other embodiments of the invention, increasing the holocathode produces a wider plasma and improves the deposition rate in PECVD.

  FIG. 7 illustrates a method according to an embodiment of the invention. A multi-phase holocathode arrangement 600 (and other holocathode arrangements described in this disclosure and enabled by this disclosure) can be utilized to continuously generate a plasma. The method 700 for generating plasma includes providing at least three holocathodes (step 702). Each holocathode has a plasma exit region. The method also includes providing a power source capable of forming a plurality of output waves (step 704). Each holocathode is electrically connected to this power source. Multiple output waves generated by the power source are out of phase so that any holocathode is out of phase with the other holocathode. Current flows between at least three holocathodes that are out of electrical phase. Plasma is continuously generated between the holocathodes. In some embodiments, the method further includes providing a substrate (step 706) and applying a coating to the substrate using plasma CVD (step 708). In FIG. 7, the steps 706 and 708 are surrounded by a dotted line, indicating that these steps are optional. Coating the substrate using plasma CVD (PECVD) may include providing a source gas, a process gas, a reactant gas, or a combination thereof in the holocathode cavity or through a manifold adjacent to the holocathode. Good. One skilled in the art will also appreciate that other processes applicable to PECVD may be included.

  FIG. 8 shows a coating formed by a method according to an embodiment of the invention. The coating 802 is formed on the substrate 804 resulting in a coating-substrate combination 800. In some embodiments, the substrate 804 is glass. In other embodiments, the substrate 804 may include plastic, metal, semiconductor material, or other suitable material for a PECVD process. In some embodiments, the coating 802 may be a single layer or film or may include multiple layers or films. In some embodiments, the coating 802 may be a low radiation coating and the substrate 804 may be a glass window so that the coating and substrate combination 800 is suitable for architectural use. In some embodiments, the coating 802 may be another coating for a particular application, such as an anti-fog coating used on refrigerator doors or a transparent conductive oxide coating used on photovoltaic cells. .

  FIG. 9 illustrates a multiphase holocathode plasma source including a holocathode with a plasma exit region according to an embodiment of the present invention. The linear multiphase holocathode arrangement 600 (shown in FIG. 9) includes holocathodes 602, 604, 606 and a multiphase power source 610. The holocathodes 602, 604, and 606 are each supplied with electric power from the multiphase power supply 610 by an AC power supply or a pulse power supply so that the phases of the holocathodes are shifted. Each of the holocathodes 602, 604, and 606 includes a holocathode cavity 904 and a plasma output path 902. In the embodiment shown in FIG. 9, the holocathodes 602, 604, 606 have two side regions that are spaced apart from each other, an upper region that defines a cavity 904, and an open bottom that defines a plasma output path 902. Area. Reactant gas (or process gas or source gas or a combination of these gases) may be present in the holocathode cavity 904 of each holocathode 602, 604, 606. A reactant gas (or process gas or source gas or a combination of these gases) may be present in the reaction zone 910. In some embodiments, the reaction region 910 may include a substrate, such as the substrate 804, and in some embodiments, a coating may be formed on the substrate in the reaction region 910. When electric power is supplied from the multiphase power source 610, electrons alternately flow between the holocathodes 602, 604, and 606 to generate plasma that flows out from the plasma output path 902 to the reaction region 910.

  FIG. 10 illustrates a multi-phase holocathode plasma source including a holocathode having a grooved limited plasma exit region, according to an embodiment of the present invention. The embodiment of FIG. 10 is a modification of the embodiment of FIG. 9, and the plasma output path 902 is replaced with a groove-shaped plasma output path 1002. Each of the holocathodes 602, 604, and 606 includes a holocathode cavity 904 and a plasma output path 1002. In the embodiment shown in FIG. 10, the holocathode 602, 604, 606 includes two side regions spaced apart from each other and a top region remote from the bottom region, and the plasma output path 1002 is defined by a groove in the bottom region. It is like that. Because of the plasma output path 1002, the gas pressure in the holocathode 602, 604, 606 can be increased when the process gas is in the holocathode cavity 904.

As described above, a multi-phase plasma source according to an embodiment of the present invention can include an embodiment where there are three holocathodes out of phase, ie three phases and three holocathodes. It will be appreciated by those skilled in the art that other embodiments, such as four-phase, five-phase, or six-phase embodiments are possible, and in general, a multi-phase holocathode arrangement can be provided in n-phase embodiments (where n is greater than 2). You can understand that. Using an additional holocathode and out-of-phase waves makes it possible to generate a plasma with the desired properties for a given process or application. As shown in the embodiments of FIGS. 9 and 10 (and described below), an n-phase holocathode arrangement according to embodiments of the present invention can include m holocathodes, where n is less than or equal to m. is there).

  FIG. 12 illustrates a multiphase holocathode plasma source including six holocathodes and three phases according to an embodiment of the present invention. That is, in this embodiment, m = 3 and n = 6. The holocathode arrangement 1200 includes holocathodes 1102, 1104, 1106, 1108, 1110, 1112 connected to a multiphase power supply 1210. The multiphase power supply 1210 forms three phase offset waves 1220, 1222, 1224. In this embodiment, wave 1220 powers horocathodes 1102 and 1108, wave 1222 powers horocathodes 1104 and 1110, and wave 1224 powers horocathodes 1106 and 1112. In some embodiments, the waves 1220, 1222, and 1224 are each offset by the same phase angle (eg, 120 °). In the embodiment shown in FIG. 12, non-adjacent combinations 1102 and 1108, 1104 and 1110, 1106 and 1112 are in phase with each other. This is because power is supplied from the same waves 1220, 1222, and 1224 to each set of holocathodes. The phase difference between the two holocathodes shown in FIG. 12 where the two adjacent phases are shifted by 120 ° is shown in the table below.

  FIG. 13 shows a multiphase holocathode plasma source that includes three holocathodes that are equally spaced. Arrangement 1300 includes three holocathodes 602, 604, 606, each having a plasma output path 1002 directed to a common line (since FIG. 13 is a cross-sectional view, each output path is directed to a common point. looks like). Of course, the embodiment shown in FIG. 13 includes a variety of other holocathodes, with the plasma output path of each holocathode (or some subset of holocathodes) being directed to the same line (or set of lines). It can also be included in various geometric configurations. In some embodiments, the distance between holocathodes (between adjacent holocathodes and non-adjacent holocathodes) is equal. For example, FIG. 13 shows that the distance between the two holocathodes 602 and 604 is substantially the same as the distance between the two holocathodes 602 and 606 and the holocathodes 604 and 606. In some embodiments, the distance between two holocathodes may be measured from the center of the holocathode, measured from the plasma output path of the holocathode, or from other points in, on or near the holocathode. Good. Using the embodiment shown in FIG. 13 or a similar embodiment, a coating can be applied to a two-dimensional substrate, such as a wire or optical fiber coating. For example, by passing such an elongated substrate in the same direction, a two-dimensional substrate can be uniformly coated.

  14A and 14B show the electron density of plasma formation in and around the holocathode in both bipolar and multiphase holocathode plasma sources according to embodiments of the present invention. As shown, the level of electron density outside the holocathode cavity, ie in the reaction region, is equivalent for bipolar (FIG. 14A) and multiphase plasma source (FIG. 14B), whereas the electron density in the holocathode cavity is A bipolar plasma source is significantly higher than a multiphase plasma source (FIG. 14B).

  15A and 15B show the ion density of plasma formation in and around the holocathode for both bipolar and multiphase holocathode plasma sources according to embodiments of the present invention. As shown, the level of ion density outside the holocathode cavity, ie in the reaction region, is equivalent for bipolar (FIG. 15A) and multiphase plasma source (FIG. 15B), whereas the ion density in the holocathode cavity is A bipolar plasma source is significantly higher than a multiphase plasma source (FIG. 15B).

  FIG. 16A shows the absorption of ions along the walls of the holocathode cavity in both bipolar and multiphase holocathode plasma sources according to embodiments of the present invention. As shown, the amount of ions absorbed along the walls of the holocathode cavity is significantly greater in the bipolar plasma source than in the multiphase plasma source. This figure also shows that the amount of absorbed ions is the lowest at the corners (index values 8, 63, 89, 144) of the holocathode cavity. According to the figure, the absorptivity is about 88% lower in the multiphase arrangement compared to the bipolar arrangement (this value varies depending on, for example, the power level used when the plasma source is in operation).

  FIG. 16B shows an indicator along the wall of the holocathode cavity shown in the graph of FIG. 16A. Specifically, the values shown along the wall of the holocathode cavity 600 in FIG. 16B correspond to values on the x-axis in FIG. 16A (“Indicator along the cavity wall”).

  14 to 16B are obtained as a result of simulating both a bipolar holocathode arrangement (similar to arrangement 300) and a multiphase holocathode arrangement (similar to arrangement 600). For example, referring to FIGS. 14A and 15A, this bipolar arrangement includes two linear holocathodes 1402a, 1404a (antiphase) located within a vacuum chamber 1430. FIG. Source gas flows through source manifold 1410. Plasma is formed in the reaction region 1420. Referring now to FIGS. 14B and 15B, this multiphase arrangement includes three linear holocathodes 1402b, 1404b, 1406b (120 ° out of phase with each other) located within the vacuum chamber 1430. Source gas flows through source manifold 1410. Plasma is formed in the reaction region 1420. Simulation settings are further described below. Argon gas was used as the process gas in the holocathode cavity. Other process gases may be used according to embodiments of the present invention, including but not limited to oxygen, nitrogen, argon, helium, krypton, neon, xenon, hydrogen, fluorine, chlorine and mixtures thereof. Examples of the reactive gas include H2, H2O, H2O2, N2, NO2, N2O, NH3, CH4, CO, CO2, SH2, other sulfur gases, halogen, bromine, phosphorus gases, and mixtures thereof.

  Specifically, referring to FIG. 14 to FIG. 16B, the plasma density in the plasma generation region outside the holocathode is the same level in both the two-phase arrangement and the three-phase arrangement (the plasma density and the ion density). The level of wear in the holocathode cavity (indicated by density, ion absorption) is significantly less in the three-phase arrangement according to embodiments of the present invention. In embodiments of the present invention, this can provide a longer operating life for the holocathode than for the bipolar plasma source. The operating lifetime depends on what process the plasma source is used for, among other factors. In a typical PECVD application related to glass coating, a three-phase, three holocathode arrangement improves the expected operating life by approximately 60% compared to a conventional bipolar arrangement. Yes. In some embodiments, this is equivalent to an increase in lifetime of about 200 hours, and may be equivalent to an operating lifetime of 500 hours for a baseline of 300 hours, for example. This advantage is not simply the result of adding a holocathode, but a multiphase power arrangement.

  The present inventors have found that the amount of sputtering at the holocathode cavity surface is related to the amount of reactive ions absorbed at the holocathode cavity surface determined by numerical simulation.

  The simulation software used for the simulation of gas flow and gas discharge is a program called PIC-MC developed by Fraunhofer-Institute for Surface Engineering and Thin Films IST in Braunschweig, Germany. This software combines gas flow, magnetic field and plasma simulations. There, the direct simulation Monte Carlo (DSMC) method is used for gas flow simulation, the boundary element method (BEM) is used for magnetic field simulation, and the in-cell particle Monte Carlo method (PIC-MC) is used for plasma simulation.

  The simulation was performed using a pseudo 2D model, which is a section obtained by cutting a holocathode plasma source in the transverse direction with a thickness of 1.016 mm. Pseudo 2D means that the thickness of the slice is small, and the condition is applied at a constant period in the transverse direction with respect to each surface.

Many different gases that form the plasma can be used for the simulation, argon was used in the previous example. In order to limit the calculation time, Si ₂ H ₆ was selected as the coating raw material, and the following two were selected from the reactions that could occur.
Si ₂ H ₆ + e ⁻ → Si ₂ H ₄ ⁺ + 2H + 2e ⁻ (1)
Si ₂ H ₆ + e ⁻ → SiH ₃ + SiH ₂ + H + e ⁻ (2)

  Hydrogen species were not included in the simulation.

For each set of input parameters, the simulation provides data on the number and velocity of these gas phase species in the entire space occupied by different gas phase species (atoms, ions, molecules, electrons). From this data, some values such as density and flux can be calculated. Here, the flux is the flow rate of gas phase species per unit area (unit: mol · m ⁻² · s ⁻¹ ).

  Another useful calculation is the flux absorbed at the surface. Given some anchoring factor for the cathode cavity material, the amount of ions absorbed at the surface can be calculated from the ion flux directed at that surface. By correlating the results obtained by the operation of the bipolar holocathode with the simulation data, the inventors have found that according to the simulation model, the formation of debris observed in the actual plasma source, and thus the sputtering at the surface of the cavity, We found that it is related to the absorption level of ionized plasma species at the surface of the holocathode cavity.

  The amount of argon absorbed is one of the characteristics that can be easily derived from the plasma simulation used. Furthermore, the absorption amount of argon is an effective index indicating the particle flux and ion energy incident on the electrode surface. One skilled in the art will understand that ion energy and particle flux are the main factors that trigger physical processes such as sputtering and electrode erosion. Debris occurs when the balance between the deposition amount of the material sputtered from the nearby surface and the sputtering rate is biased toward the net deposition amount. This effect can be observed in FIGS. 16A and 16B. The figure shows that there is less net deposition and spatter at the corners of the rectangular electrode where the absorption of ions was found to be minimal (by simulation).

  Thus, although the simulation does not measure the actual sputtering value, we use the argon absorption value as an indicator of sputtering or electrode erosion in the multiphase embodiments described herein. did.

  A low level of ionized plasma species absorbed at the cavity surface of the holocathode means a low level of sputtering in the cavity and less debris formation. As shown in FIGS. 16A and 16B, sputtering and wear increased in the bipolar plasma source on most electrode surfaces where the plasma energy of both bipolar and multiphase plasma sources in the process chamber were equal. . When material is further sputtered from a bipolar plasma source, it can be applied to surfaces that are not subject to strong sputtering, such as the corners of electrode cavities and surfaces outside the plasma source (floating or grounded and not subject to sputtering). When deposited, it can further increase debris. The nature and amount of such debris is highly dependent on the combination of electrode surface material and plasma gas.

  Another important quantity is the generated electron density. The electron density has a great influence on the surface treatment or coating efficiency, and the higher the electron density, the higher the surface treatment or coating efficiency. In this simulation, the electron density was determined in a vacuum chamber on a line set at a distance of 2.54 mm from the chamber structure supporting the plasma source and averaged.

  The inventors surprisingly found that when using three holocathodes with a phase shift of 120 °, the cathode cavity compared to one configuration with two holocathodes with a phase shift of 180 °. We have found that the level of ionized plasma species absorbed at the surface of the metal is low.

  According to this embodiment of the present invention, the inventors surprisingly found that the reaction outside the holocathode was observed when three holocathodes were arranged in three phases and two holocathodes were arranged in two phases. We found that the electron density in the region is similar. This is surprising. This is because, for example, if three holocathodes are arranged in three phases, the area where plasma is concentrated becomes larger than that in which two holocathodes are arranged in two phases, and wear in the holocathodes is reduced.

  As those skilled in the art will appreciate from the present disclosure, a particular arrangement can be designed to suit a particular application, and the holocathode and multiphase power input can be combined in many other ways.

  While various embodiments have been described above, it should be understood that all are not limiting and are merely exemplary. Accordingly, the scope and spirit of the present disclosure should not be limited by any of the above-described exemplary embodiments. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the disclosure unless otherwise indicated herein or otherwise clearly contradicted by context.

Furthermore, although the process described and illustrated above is shown as a series of steps, this is for convenience of explanation. Therefore, some steps may be added, some steps may be omitted, the order of steps may be changed, and some steps may be performed simultaneously.

Claims (69)

At least three holocathodes comprising a first holocathode, a second holocathode, and a third holocathode, each having a plasma exit region;
A plasma source comprising a power source capable of forming a plurality of output waves, including a first output wave, a second output wave, and a third output wave,
The first output wave and the second output wave are out of phase, the second output wave and the third output wave are out of phase, and the first output wave and the third output wave are out of phase. The output wave of is out of phase,
Each of the holocathodes is electrically connected to the first output wave, the second holocathode is electrically connected to the second output wave, and the third holocathode is electrically connected to the first output wave. Electrically connected to the power source so as to be electrically connected to a third output wave;
A current flows between the at least three holocathodes that are out of electrical phase;
The plasma source can generate plasma between the holocathodes.   The plasma source of claim 1, wherein the plasma generated by the plasma source includes active electron emission for at least substantially 80% of the period of the plurality of output waves.   The plasma source of claim 1, wherein the plasma generated by the plasma source includes active electron emission for at least substantially 90% of the period of the plurality of output waves.   The plasma source of claim 1, wherein the plasma generated by the plasma source includes active electron emission for at least substantially 100% of the period of the plurality of output waves.   The plasma source according to claim 1, wherein the at least three holocathodes are 180 degrees out of phase in electrical phase with each other.   The plasma source of claim 1, wherein the at least three holocathodes are 120 ° out of phase in electrical phase.   The plasma source of claim 1, wherein two adjacent ones of the at least three holocathodes are each out of electrical phase by the same phase angle as the other two adjacent ones of the at least three holocathodes.   The plasma source of claim 1, wherein the at least three holocathodes are linear holocathodes.   The plasma source of claim 1, wherein each of the at least three holocathodes includes an elongated cavity.   The plasma source of claim 1, wherein the plasma exit region of each of the at least three holocathodes includes a plurality of plasma exit orifices.   The plasma source of claim 1, wherein the plasma exit region of each of the at least three holocathodes includes a plasma exit groove.   The plasma source of claim 1, wherein each of the at least three holocathodes is electrically isolated such that only the inner surface of the holocathode and the plasma exit region emits and receives electrons.   The plasma source of claim 1, wherein the generated plasma flows substantially through the plasma exit region of each of the at least three holocathodes.   The plasma source according to claim 1, wherein the current is composed of electrons derived from secondary electron emission.   The plasma source according to claim 1, wherein the current is composed of electrons derived from thermoelectron emission electrons.   The plasma source of claim 1, wherein the at least three holocathodes are arranged linearly.   The plasma source of claim 1, wherein the at least three holocathodes are configured such that each of the plasma exit regions faces a common line.   The plasma source of claim 1, wherein the distance between any two of the at least three holocathodes is the same.   The plasma source of claim 1, wherein the current flowing between the at least three holocathodes that are out of electrical phase is caused by a potential difference between the at least three holocathodes.   The plasma source of claim 19, wherein the potential difference is at least 50 V between any two of the at least three holocathodes.   The plasma source of claim 19, wherein the potential difference is at least 200 V between any two of the at least three holocathodes.   2. The plasma source according to claim 1, wherein the plurality of output waves include square waves, so that the potential difference is smaller than that of a sine wave when the power input is the same as a whole.   The plasma source of claim 1, wherein the power source is in the form of AC electrical energy.   The plasma source of claim 1, wherein the power source is in the form of pulsed electrical energy.   The plasma source of claim 1, wherein the generated plasma is substantially uniform throughout its length in the absence of substantially magnetic field driven closed circuit electron drift.   The plasma source of claim 1, wherein the plasma is generated substantially uniformly over a length of about 0.1 m to about 1 m.   The plasma source of claim 1, wherein the plasma is generated substantially uniformly over a length of about 1 m to about 4 m.   The plasma source of claim 1, wherein each of the plurality of output waves has an equal frequency and ranges from about 1 kHz to about 500 MHz.   The plasma source of claim 1, wherein each of the plurality of output waves has an equal frequency and ranges from about 1 kHz to about 1 MHz.   The plasma source of claim 1, wherein each of the plurality of output waves has an equal frequency and ranges from about 10 kHz to about 200 kHz.   The plasma source of claim 1, wherein each of the plurality of output waves has an equal frequency and ranges from about 20 kHz to about 100 kHz.   The plasma source of claim 1, wherein the electrons from the emission surface are confined by the holocathode effect.   The plasma source of claim 1, wherein the electrons from the emission surface of each of the at least three holocathodes are not confined by a magnetic field.   The plasma source of claim 1, wherein at least one of the plurality of output waves generated by the power source is configured to supply power to a plurality of the at least three holocathodes. Providing at least three holocathodes, each including a first holocathode, a second holocathode, and a third holocathode, each having a plasma exit region;
A method for generating plasma, comprising preparing a power source capable of forming a plurality of output waves, including a first output wave, a second output wave, and a third output wave. And
The first output wave and the second output wave are out of phase, the second output wave and the third output wave are out of phase, and the first output wave and the third output wave are out of phase. The output wave of is out of phase,
Each of the holocathodes is electrically connected to the first output wave, the second holocathode is electrically connected to the second output wave, and the third holocathode is electrically connected to the first output wave. Electrically connected to the power source so as to be electrically connected to a third output wave;
A current flows between the at least three holocathodes that are out of electrical phase;
A method wherein plasma is generated between the holocathodes.   36. The method of claim 35, wherein the plasma includes active electron emission for at least substantially 80% of the period of the plurality of output waves.   36. The method of claim 35, wherein the plasma includes active electron emission for at least substantially 90% of the period of the plurality of output waves.   36. The method of claim 35, wherein the plasma includes active electron emission for at least substantially 100% of the period of the plurality of output waves.   36. The method of claim 35, wherein the at least three holocathodes are 180 degrees out of phase in electrical phase with each other.   36. The method of claim 35, wherein the at least three holocathodes are 120 degrees out of phase in electrical phase.   36. The method of claim 35, wherein two adjacent two of the at least three holocathodes are each out of electrical phase by the same phase angle as the other two adjacent ones of the at least three holocathodes.   36. The method of claim 35, wherein the at least three holocathodes are linear holocathodes.   36. The method of claim 35, wherein the at least three holocathodes each include an elongated cavity.   36. The method of claim 35, wherein the plasma exit region of each of the at least three holocathodes includes a plurality of plasma exit orifices.   36. The method of claim 35, wherein the plasma exit region of each of the at least three holocathodes includes a plasma exit groove.   36. The method of claim 35, wherein each of the at least three holocathodes is electrically isolated such that only the inner surface of the holocathode and the plasma exit region emits and receives electrons.   36. The method of claim 35, wherein the generated plasma flows substantially all through the plasma exit region of each of the at least three holocathodes.   36. The method of claim 35, wherein the current consists of electrons derived from secondary electron emission.   36. The method of claim 35, wherein the current consists of electrons derived from thermionic emission electrons.   36. The method of claim 35, wherein the at least three holocathodes are arranged linearly.   36. The method of claim 35, wherein the at least three holocathodes are configured such that each of the plasma exit regions is directed to a common line.   36. The method of claim 35, wherein the distance between any two of the at least three holocathodes is the same.   36. The method of claim 35, wherein the current flowing between the at least three holocathodes that are out of electrical phase is caused by a potential difference between the at least three holocathodes.   54. The method of claim 53, wherein the potential difference is at least 50V between any two of the at least three holocathodes.   54. The method of claim 53, wherein the potential difference is at least 200V between any two of the at least three holocathodes.   36. The method of claim 35, wherein the plurality of output waves include square waves so that the potential difference is less than a sine wave when the power inputs are the same overall.   36. The method of claim 35, wherein the power source is in the form of AC electrical energy.   36. The method of claim 35, wherein the power source is in the form of pulsed electrical energy.   36. The method of claim 35, wherein the continuously generated plasma is substantially uniform throughout its length in the substantial absence of magnetic field driven closed circuit electron drift.   36. The method of claim 35, wherein the plasma is generated substantially uniformly over a length of about 0.1 m to about 1 m.   36. The method of claim 35, wherein the plasma is generated substantially uniformly over a length of about 1 m to about 4 m.   36. The method of claim 35, wherein the frequency of each of the plurality of output waves is equal and ranges from about 1 kHz to about 500 MHz.   36. The method of claim 35, wherein the frequency of each of the plurality of output waves is equal and ranges from about 1 kHz to about 1 MHz.   36. The method of claim 35, wherein the frequency of each of the plurality of output waves is equal and ranges from about 10 kHz to about 200 kHz.   36. The method of claim 35, wherein the frequency of each of the plurality of output waves is equal and ranges from about 20 kHz to about 100 kHz.   36. The method of claim 35, wherein the electrons from the emission surface are confined by the holocathode effect.   36. The method of claim 35, wherein the electrons from the emission surface of each of the at least three holocathodes are not confined by a magnetic field.   36. The method of claim 35, wherein at least one of the plurality of output waves generated by the power source is configured to provide power to a plurality of the at least three holocathodes. Prepare the board
36. The method of claim 35, further comprising forming a coating on the substrate using plasma enhanced chemical vapor deposition.

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