Hollow cathode arc plasma device

Abstract

This invention provides an apparatus for generating plasma from a process gas, comprising: a) a power source; b) a hollow cathode arc tube including: i) an inert gas inlet, ii) a cathode tube connected to the power source and configured to be negatively biased when the power source is turned on, iii) an anode tube connected to the power source and configured to be positively biased when the power source is turned on, iv) an electron beam outlet; c) an ionization chamber including: i) an electron beam inlet, ii) a process gas inlet, iii) an interior space in which the process gas can be ionized to form plasma, iv) a plasma outlet; d) a first magnetic field source for confining the plasma within the ionization chamber; and e) a second magnetic field source for guiding and scanning the plasma away from the plasma outlet. The invention further provides a method for generating a plasma beam.

Description

Technical Field

[0001] The present invention relates to an apparatus for generating plasma from process gas, and a method for generating a plasma beam. Background Technology

[0002] Plasma sources can be used for large-area coating applications, including plasma etching, sputtering, and reactive coating processes.

[0003] Known plasma sources for such applications include capacitively coupled plasma (CCP), inductively coupled plasma (ICP), and electron cyclotron resonance (ECR), all of which utilize high-energy electrons generated by the plasma source to ionize the process gas. Other known plasma sources include end-Hall ion sources and linear ion beam sources.

[0004] There are many problems associated with these known plasma sources. CCP plasma sources cannot generate sufficiently high plasma densities, resulting in deposition qualities lower than required for many applications. ICP plasma sources are often highly contaminated by other gases, thus damaging the plasma. Microwave plasma sources, such as ECR, are difficult to extend to large-area coating applications.

[0005] Filament arc sources, such as end Hall ion sources and linear ion beam sources, typically have a short lifespan because the high temperatures they require can damage the filament itself and the substrate.

[0006] Furthermore, many known plasma sources cannot coat large-area substrates. Several solutions have been proposed to address this issue, such as using 2D spools to move the substrate through the coating beam, and using spot beam arrays, allowing the entire surface to be coated, although each beam only reaches a small area. The disadvantage of using 2D spools is their high cost, thus significantly increasing the cost of the coating method. The disadvantage of using spot beam arrays is that the coating typically cannot uniformly cover the entire surface of the substrate.

[0007] Therefore, there is a need for cost-effective plasma sources that can efficiently generate high-density plasmas and can scan large areas to effectively cover substrates. Summary of the Invention

[0008] This invention provides an apparatus for generating plasma from process gas, the apparatus comprising: a) Power supply, b) A hollow cathode arc tube, comprising: i) Inert gas inlet, ii) A cathode tube, which is connected to a power supply and is configured to be negatively biased when the power is on. iii) An anode tube, which is connected to a power supply and is configured to be positively biased when the power is on. iv) Electron beam exit, c) An ionization chamber, which includes: i) Electron beam inlet, ii) Process gas inlet, iii) An indoor space in which process gases can be ionized to form plasma. iv) Plasma outlet, d) A first magnetic field source, used to confine the plasma within the ionization chamber. e) A second magnetic field source, which is used to guide and scan the plasma away from the plasma outlet.

[0009] It has been found that the device of the present invention can effectively generate high-density plasma with low pollution. The generated plasma can be effectively used to coat large-area substrates.

[0010] The plasma generated by the device of the present invention is also referred to as process gas plasma.

[0011] The apparatus of the present invention includes a hollow cathode arc tube that generates an electron beam usable downstream of the apparatus. The hollow cathode arc tube includes: (i) an inert gas inlet, (ii) a cathode tube connected to a power source and configured to be negatively biased when the power source is turned on, (iii) an anode tube connected to a power source and configured to be positively biased when the power source is turned on, and (iv) an electron beam outlet.

[0012] The inert gas inlet is an aperture in the cathode tube and / or anode tube through which inert gas can enter the hollow cathode arc tube. The inert gas inlet may further include a tube that allows the inert gas to be easily injected (e.g., from the outside of any housing surrounding the device). The inert gas inlet may include a tube separated by an insulating connector (e.g., a ceramic connector). For example, the tube may include two parts connected by an insulating connector to prevent the upstream end of the inert gas inlet tube from being charged (through the hollow cathode arc tube). The inner diameter of the inert gas inlet tube may be 2 mm to 6 mm, preferably 3 mm to 5 mm.

[0013] The cathode tube is arranged such that it is negatively biased when the power is on, thus acting as the cathode when the power is on. Therefore, the cathode tube can be connected to the negative terminal of the power supply.

[0014] The cathode tube can be of any shape with upstream and downstream openings. For example, the cathode tube can be approximately cylindrical, i.e., having continuous sidewalls (with a circular cross-section) and two circular end walls, each with an opening. Alternatively, the cathode tube can be tubular, i.e., having continuous sidewalls (with a circular cross-section), wherein the open end of the tube serves as an opening. In a further embodiment, the cathode tube can be partially cylindrical and partially tubular, i.e., having continuous sidewalls (with a circular cross-section), wherein one end (preferably the upstream end) is open and serves as an opening, and the other end (preferably the downstream end) has a circular end wall with an opening. Typically, the inner diameter of the cathode tube is generally greater than 1.5 mm, for example greater than 2 mm, and can also be 5 mm or smaller, for example 4 mm or smaller. The outer diameter of the cathode tube can be from 5 mm to 8 mm.

[0015] Cathode tubes are typically made of conductive materials such as metals. In one embodiment, the cathode tube may be formed of a thermionic emission material (discussed in further detail below). For example, the cathode tube may be formed of tantalum. Thus, the cathode tube may contain 90% or more (by weight), such as 95% or more, or 98% or more of a thermionic emission material (e.g., tantalum).

[0016] The anode tube is arranged such that it is positively biased when the power is on, and thus acts as the anode when the power is on. Therefore, the anode tube can be connected to the positive terminal of the power supply. The anode tube preferably at least partially surrounds (e.g., completely surrounds) the cathode tube; for example, the tubes can be approximately concentric.

[0017] Therefore, the anode tube can be any shape having upstream and downstream holes that allow it to at least partially surround the cathode tube. For example, as described with reference to the cathode tube above, the anode tube can be cylindrical, tubular, or partially cylindrical and partially tubular. Typically, the inner diameter of the anode tube is 25 mm or greater, such as 30 mm or greater, and can be 50 mm or smaller, such as 40 mm or smaller.

[0018] Anode tubes are typically made of conductive materials such as metals. As an alternative to metals, the anode can be formed from graphite, which is also conductive.

[0019] The electron beam exit is an aperture through which the electron beam exits the hollow cathode arc tube. Typically, the electron beam exit can be a channel passing through a first aperture in the cathode tube and a second aperture in the anode tube. The diameter of the electron beam exit channel can be 10 mm or larger, such as 15 mm or larger, and can be 30 mm or smaller, such as 25 mm or smaller.

[0020] In operation, when the power is turned on, a voltage is applied between the cathode and anode tubes, causing the cathode tube to be negatively biased and act as the cathode, and the anode tube to be positively biased and act as the anode. Inert gas is then injected into the hollow cathode arc tube through the inert gas inlet. The inert gas passing through the cathode tube initiates a glow discharge, which eventually evolves into an arc discharge and forms an inert gas plasma. Electrons in the inert gas plasma are accelerated towards the anode, forming an electron beam, which exits the hollow cathode arc tube through the electron beam outlet.

[0021] The hollow cathode arc tube may additionally include one or more of the following: (i) a thermionic emitter (e.g., the cathode tube may include a thermionic emitter), (ii) a coil heater, and / or (iii) an insulator. One or more portions of the hollow cathode arc tube may also be coupled to a cooling system.

[0022] A thermionic emitter is a material that emits electrons when heated. The presence of a thermionic emitter increases the density of electrons generated in a hollow cathode tube. The thermionic emitter can be positioned inside the cathode tube and can be connected to the cathode tube such that the thermionic emitter is also negatively biased when the power is turned on. In alternative and preferred embodiments, the cathode tube itself may include or be formed of a thermionic emitter, for example, the material of the cathode tube may be a thermionic emitter (e.g., tantalum, tungsten, or graphite).

[0023] Examples of thermionic emission materials include tungsten, graphite, thorium-tungsten, tantalum, barium oxide, strontium oxide, calcium oxide, rare earth metal oxides (e.g., lanthanum oxide, neodymium oxide, gadolinium oxide, cerium oxide, dysprosium oxide, indium oxide, samarium oxide), and rare earth metal hexaborides (e.g., lanthanum hexaboride, cerium hexaboride). In a preferred embodiment, the thermionic emitter is selected from tantalum, tungsten, and graphite.

[0024] The hollow cathode arc tube may further include a heater. The heater may be positioned such that it heats the cathode (e.g., the cathode tube) and / or thermionic material (if present), for example, the heater may be adjacent to the cathode and / or thermionic material (if present). The heater may be a coiled heater, and in a preferred embodiment, it may be wound around the cathode tube. When present, the heater may have its own independent power supply, or be connected to the same power supply as the cathode and anode tubes. The heater preferably heats the cathode tube and / or thermionic emitter to a temperature that triggers electron emission from the thermionic emitter material.

[0025] In certain implementations, a heater is not required, and the hollow cathode arc tube made of thermionic emission material can be directly heated by glow discharge, which is initiated by a specific gas flow and an electric field between the cathode and anode. The glow discharge is used to raise the temperature of the cathode tube to the thermionic emission point, and then initiates the arc discharge.

[0026] The hollow cathode arc tube may further include an insulator located between the cathode tube (cathode) and the anode tube (anode), typically in an annular space between concentric cathode and anode tubes, or upstream of the cathode tube at its attachment point to the anode tube. The insulator may be an electrical insulator and / or a thermal insulator. The insulator may be made of any suitable electrical and / or thermal insulating material. For example, the insulator may be a ceramic material, such as alumina.

[0027] One or more components of the hollow cathode arc tube can be further connected to a cooling system. In a preferred embodiment, the anode tube, i.e., the anode, is connected to the cooling system. The cooling system can be any system capable of reducing the temperature of one or more components of the hollow cathode arc tube; for example, the cooling system can be a water cooling system. If present, the water cooling system may include a series of pipes having a cold water inlet, a warm water outlet, and a pump for pumping cold water to the cold water inlet. In a particularly preferred embodiment, a water cooling system is present, and the pipes of the water cooling system can run near the anode.

[0028] In a preferred embodiment of the invention, the hollow cathode arc tube includes one or more, or two or more, of a thermionic electron emitter, a coil heater, and an insulator. In some embodiments, the hollow cathode arc tube includes a thermionic electron emitter, a coil heater, and an insulator.

[0029] The power source supplies power to at least the cathode and anode tubes. The power supply to each of the cathode and anode tubes can be controlled independently or together. In some embodiments of the invention, the same power source can control other elements of the device, such as electrostatic lenses, and, if present, the magnetic field around the hollow cathode arc tube and one or more magnetic fields around the ionization chamber. However, in alternative embodiments, the powered elements can have independent power sources. The arrangement of power supplies relative to each element of the device is considered conventional.

[0030] The ionization chamber of the device includes: (i) an electron beam inlet; (ii) a process gas inlet; (iii) an interior space in which the process gas can be ionized to form plasma; and (iv) a plasma outlet. The ionization chamber may be defined by an outer shell primarily made of stainless steel.

[0031] The electron beam inlet is an aperture through which the electron beam (formed upstream of the device) enters the ionization chamber. Therefore, the electron beam inlet is typically located on the upstream side of the ionization chamber, such as on the upstream surface of the ionization chamber. Here, the term "upstream" refers to the direction closest to the hollow cathode arc tube. The electron beam inlet typically has a diameter greater than 25 mm, for example, greater than 30 mm. The diameter is typically less than 50 mm, and in examples can be between 25 mm and 35 mm.

[0032] The electron beam inlet can be surrounded by a ring-shaped anode to accelerate the electron beam through the inlet. If present, the ring-shaped anode is formed of a conductive material and connected to a power source, providing a positive bias when the power is switched on. The anode can be shaped as a ring or disk with an approximately central hole. The anode can be formed of the same material as the anode tube; for example, the anode can be made of metal or graphite.

[0033] The process gas inlet is an orifice through which process gas can be injected into the ionization chamber. The process gas inlet is typically located on a surface of the ionization chamber other than the surface with the electron beam inlet; for example, the process gas inlet can be located on a surface of the ionization chamber adjacent to the surface with the electron beam inlet. Preferably, the process gas inlet is orthogonal to the electron beam inlet. The inlet may be fitted with a gas spray ring comprising multiple holes (wherein the diameter of the holes is 0.5 mm to 1.5 mm). The process gas can then enter the ionization chamber through these multiple holes.

[0034] The ionization chamber also includes an interior space where the process gas can be ionized to form a plasma. The shape of the ionization chamber is not critical, but it is typically cylindrical to facilitate the positioning of other components around it. When the ionization chamber is cylindrical, its diameter can be 150 mm to 250 mm, for example, 180 mm to 200 mm, and its length can be 80 mm to 120 mm, for example, 90 mm to 100 mm. Therefore, the ionization chamber typically has a diameter of 1400 cm². 3 Up to 6000cm 3 The preferred volume is 2200 cm³. 3 Up to 3200cm 3 The volume.

[0035] The plasma outlet is an aperture through which the process gas plasma formed in the ionization chamber can exit the ionization chamber. Therefore, the plasma outlet is typically located on the downstream side of the ionization chamber, such as on the downstream surface of the ionization chamber. The plasma outlet can thus be positioned on one side of the ionization chamber opposite the electron beam inlet and orthogonal to the process gas inlet. The diameter of the plasma outlet is typically 150 mm to 250 mm, for example, 180 mm to 200 mm.

[0036] The plasma outlet can be connected to optional additional features of the device. For example, the plasma outlet can be connected to the coating chamber.

[0037] A first magnetic field source (also called a confinement magnetic field source) for confining plasma within the ionization chamber may be concentrically positioned around the ionization chamber. The confinement magnetic field source may be used to confine plasma within the ionization chamber and is preferably concentrated toward the center of the ionization chamber to avoid plasma contact with the walls of the ionization chamber.

[0038] The confined magnetic field source itself can be formed by two or more, or four or more, preferably six or more (e.g., eight or twelve) magnets, which are preferably permanent magnets. Electromagnets can also be used if the desired magnetic field can be achieved similarly. Preferably, the confined magnetic field source is formed by an even number of magnets. Particularly preferred is that, when present, the confined magnetic field source is formed by an even number of alternating polarity magnets. Preferably, the alternating polarity magnets are uniformly spaced in a circular pattern. In a particularly preferred embodiment, the confined magnetic field source can be a multi-point magnetic field source. A multi-point magnetic field source is a magnetic field source that generates a magnetic field having multiple points (i.e., multiple points where the magnetic field changes direction) equidistantly distributed around a circumference. In a particularly preferred embodiment, the circle on which the points are positioned can be concentric with the ionization chamber.

[0039] Each magnet can provide a magnetic field strength greater than 4000 Gauss (0.4T), for example greater than 5000 Gauss (0.5T). Due to the alternating polarities of the magnets arranged in a circular, equidistant pattern, the magnetic field strength at the center of the ionization chamber is typically about zero (e.g., less than 0.05T, for example less than 0.02T).

[0040] The magnet can be an electromagnet formed from a coil of conductive metal wire (preferably copper wire), optionally having a soft magnetic core. In embodiments where the magnet is an electromagnet, the electromagnet has a soft magnetic core, wherein the material of the soft magnetic core is preferably selected from iron, iron-silicon alloys, nickel-iron alloys, and ceramic materials (e.g., soft ferrite).

[0041] The limiting magnetic field source can be connected to a power source to power the electromagnets, and preferably can be controlled independently of other power supply components within the device. However, in embodiments where the limiting magnetic field source is formed by two or more electromagnets, it is preferable that the multiple electromagnets of the limiting magnetic field source are controlled together.

[0042] In practice, a confining magnetic field source around the ionization chamber applies a magnetic field within the chamber, preferably a multi-point magnetic field. Without being bound by theoretical constraints, it is believed that the magnetic field increases the electron lifetime within the ionization chamber by preventing electron loss through contact with the chamber walls, thus increasing the probability of process gas ionization. The generated magnetic field is also thought to confine the plasma, leading to an increase in the density of the process gas plasma and the generation of a more uniform and dense process gas plasma.

[0043] A second magnetic field source (also known as a guiding magnetic field source) for guiding and scanning the plasma out of the plasma outlet can be positioned at a point on the circumference of the ionization chamber (i.e., the guiding magnetic field source may not be concentric with the ionization chamber). The guiding magnetic field source can be used to control and guide the plasma in a desired direction. The second magnetic field source may have the same characteristics and / or features as the magnetic device for scanning the plasma beam described in earlier patent application No. PCT / GB96 / 00390 (publication number WO 96 / 26532).

[0044] The scanning characteristics of the second magnetic field source allow for variation in the relative position of the plasma beam exiting the ionization chamber within the plasma outlet. The relative position is variable in at least one dimension, but preferably in two dimensions. Therefore, the second magnetic field source preferably comprises two electromagnets arranged to provide adjustable orthogonal magnetic fields. This scanning allows the plasma beam to be directed over large 2D regions. For example, scanning the plasma beam allows for coating or etching of relatively large substrate surfaces without requiring substrate movement.

[0045] The second magnetic field source can be any suitable magnetic field source with adjustable magnetic field strength. In a preferred embodiment, the guiding magnetic field source is an electromagnet, such as a C-shaped scanning electromagnet, which includes a C-shaped soft magnetic core with two open magnetic poles and a wire wound around the center of the C-shaped soft magnetic core, serving as a solenoid. The wire is connected to a power source, so that when the power is turned on, a magnetic field can be generated between the two poles of the C-shaped scanning electromagnet.

[0046] Preferably, when the guiding magnetic field source is formed by a soft magnetic core surrounded by a wire, the soft magnetic core can be formed of any soft magnetic material, such as iron, iron-silicon alloy, nickel-iron alloy, or ceramic material (e.g., soft ferrite). The wire is preferably copper wire.

[0047] In use, a guiding magnetic field source surrounding the ionization chamber applies an adjustable magnetic field within the chamber. The magnetic field can be adjusted by changing the current supplied to the conductors, thus enabling manipulation of the process gas plasma. The adjustable magnetic field allows the process gas plasma to move horizontally and / or vertically within a plane orthogonal to the original plasma trajectory. Deposition rates in different regions of the substrate can be monitored, and the relevant data is fed back to the scanning control components. The desired deposition rate can be controlled in each deposition region. Therefore, the second magnetic field source enables efficient and uniform coating of large-area two-dimensional substrates.

[0048] In some embodiments, the guiding magnetic field source may include two electromagnets, such as two C-shaped scanning electromagnets. In embodiments where the guiding magnetic field source includes two electromagnets, the electromagnets may be positioned such that they are complementary to each other; for example, both electromagnets may be positioned on a circumference around the ionization chamber, preferably with the circumference on which the electromagnets are positioned concentric with the ionization chamber. In a preferred embodiment, the angle between the two electromagnets on the circumference may be from 10 degrees to 180 degrees, preferably from 30 degrees to 150 degrees, most preferably from 60 degrees to 120 degrees, for example, about 90 degrees.

[0049] In embodiments where the guiding magnetic field source includes two electromagnets, these two electromagnets can work together to manipulate process gas plasma in both horizontal and vertical directions. Therefore, the electromagnets together can contribute to the generation of high-density plasma and a uniform, dense coating on the substrate.

[0050] In a preferred embodiment, the circles on which each of the limiting magnetic field source and the guiding magnetic field source is positioned are concentric with each other, and preferably also concentric with the ionization chamber.

[0051] In a preferred embodiment of the invention, the device includes a magnetic field source for increasing the electron beam density within the hollow cathode arc tube and / or an electrostatic lens for focusing the electron beam. In a particularly preferred embodiment, the device includes a magnetic field source for increasing the electron beam density within the hollow cathode arc tube and an electrostatic lens for focusing the electron beam.

[0052] The apparatus according to the invention may include a magnetic field source (also referred to as a density-increasing magnetic field source) for increasing the electron beam density within the cathode tube. In a preferred embodiment, the density-increasing magnetic field source may be concentrically positioned around the cathode tube. In a particularly preferred embodiment, the density-increasing magnetic field source may be a solenoid formed of a conductor (preferably copper wire) concentrically wound around the cathode tube. The magnetic field source typically provides a magnetic field strength greater than 100 Gauss (0.01 T), for example greater than 200 Gauss (0.02 T), at the center of the cathode tube. Here, the center of the cathode tube refers to the longitudinal axis of the cathode tube.

[0053] In operation, a density-increasing magnetic field source applies a magnetic field within the hollow cathode arc tube. In a preferred embodiment, for example when the magnetic field source is a solenoid, the applied magnetic field is an axial magnetic field relative to the axes of the anode and cathode tubes. Typically, the current direction through the solenoid is such that the upstream end of the solenoid is the north pole and the downstream end is the south pole. Without being bound by theoretical constraints, it is assumed that the magnetic field causes electrons to move in a helical trajectory, increasing the lifetime of each electron and thus increasing the probability of inert gas ionization. This, in turn, leads to lower inert gas flow rate requirements and increased plasma density, and consequently, increased electron beam density.

[0054] The apparatus according to the invention may additionally include an electrostatic lens for focusing the electron beam. The electrostatic lens is typically located downstream of the hollow cathode arc tube and upstream of the ionization chamber. An electrostatic lens is a lens that focuses electrons and guides them from one region to another. Thus, the electrostatic lens focuses the electron beam generated by the hollow cathode arc tube before it enters the ionization chamber. The electrostatic lens of the invention (if present) can be any known electrostatic lens, such as a cylindrical lens, an Einzel lens, a quadrupole lens, or a magnetic lens. Preferably, when present, the electrostatic lens can focus the electron beam without altering the energy of the electron beam. In a preferred embodiment, the electrostatic lens is present in the apparatus of the invention. In a particularly preferred embodiment, the apparatus includes an Einzel lens comprising alternating disks of conductive material and disks of electrically insulating material.

[0055] In this particularly preferred embodiment, the alternating discs have a central hole, approximately annular in shape, the inner diameter of which can be 40 mm to 70 mm, preferably 50 mm to 60 mm. The thickness of each alternating disc is typically 2 mm to 10 mm, preferably 3 mm to 7 mm, and more preferably 4 mm to 6 mm.

[0056] In a preferred embodiment where the electrostatic lens is formed of alternating disks of conductive and electrically insulating materials, the outer disk (i.e., the disk at either end of the electrostatic lens) is typically an electrically insulating disk, while the conductive disk is usually located inside the electrostatic lens. In such a preferred embodiment, there are typically 2 to 10 electrically insulating disks and 1 to 9 conductive disks, preferably 3 to 8 electrically insulating disks and 2 to 7 conductive disks, and most preferably 4 to 6 electrically insulating disks and 3 to 5 conductive disks.

[0057] The conductive material of the electrostatic lens can be a conductive metal, preferably a metal that is stable at high temperatures (e.g., stable at temperatures above 500°C). For example, the conductive material can be steel (e.g., stainless steel) or a nickel-chromium-based alloy. The electrical insulating material of the electrostatic lens can be a ceramic material, such as alumina.

[0058] The conductive pads of the electrostatic lens can be connected to a power source, so that the conductive pads have a positive bias when the power is turned on. Each conductive pad can be equipped with an independent power source, or they can all be powered by the same power source. In a preferred embodiment, all conductive pads are biased to the same voltage, such as 10kV to 100kV, 15kV to 70kV, or 20kV to 50kV.

[0059] In operation, the electrostatic lens collimates and focuses the electron beam from the hollow cathode arc tube into the ionization chamber. The electrostatic lens increases the electron beam density, thus resulting in a higher density of process gas plasma in the ionization chamber.

[0060] In a preferred embodiment, the present invention can therefore provide an apparatus for generating plasma from a process gas, the apparatus comprising: a) Power supply, b) A hollow cathode arc tube, comprising: i) Inert gas inlet, ii) A cathode tube, which is connected to a power supply and is configured to be negatively biased when the power is on. iii) An anode tube, which is connected to a power supply and is configured to be positively biased when the power is on. iv) Electron beam exit, c) A magnetic field source, used to increase the electron beam density inside the hollow cathode arc tube. d) An ionization chamber, comprising: i) Electron beam inlet, ii) Process gas inlet, iii) An indoor space in which process gases can be ionized to form plasma. iv) Plasma outlet, e) A first magnetic field source, used to confine the plasma within the ionization chamber. f) A second magnetic field source, which is used to guide and scan the plasma as it leaves the plasma outlet.

[0061] In a further preferred embodiment, the device includes an electrostatic lens for focusing the electron beam.

[0062] In a preferred embodiment, the present invention can therefore provide an apparatus for generating plasma from a process gas, the apparatus comprising: a) Power supply, b) A hollow cathode arc tube, comprising: i) Inert gas inlet, ii) A cathode tube, which is connected to a power supply and is configured to be negatively biased when the power is on. iii) An anode tube, which is connected to a power supply and is configured to be positively biased when the power is on. iv) Electron beam exit, c) Electrostatic lenses, used to focus electron beams. d) An ionization chamber, comprising: i) Electron beam inlet, ii) Process gas inlet, iii) An indoor space in which process gases can be ionized to form plasma. iv) Plasma outlet, e) A first magnetic field source, used to confine the plasma within the ionization chamber. f) A second magnetic field source, which is used to guide and scan the plasma as it leaves the plasma outlet.

[0063] In a particularly preferred embodiment, the present invention can provide an apparatus for generating plasma from a process gas, the apparatus comprising: a) Power supply, b) A hollow cathode arc tube, comprising: i) Inert gas inlet, ii) A cathode tube, which is connected to a power supply and is configured to be negatively biased when the power is on. iii) An anode tube, which is connected to a power supply and is configured to be positively biased when the power is on. iv) Electron beam exit, c) A magnetic field source, used to increase the electron beam density inside the hollow cathode arc tube. d) An electrostatic lens, used to focus an electron beam. e) An ionization chamber, comprising: i) Electron beam inlet (optionally including an annular anode for accelerating the electron beam). ii) Process gas inlet, iii) An indoor space in which process gases can be ionized to form plasma. iv) Plasma outlet, f) A first magnetic field source, which is used to confine the plasma within the ionization chamber. g) A second magnetic field source, which is used to guide and scan the plasma away from the plasma outlet.

[0064] The present invention further provides a method for generating a plasma beam, comprising: i) Generate inert gas plasma containing electrons and inert gas ions through arc discharge; ii) Accelerate and focus the electron beam into the ionization chamber; iii) Injecting process gas into the ionization chamber, causing it to be ionized by an electron beam to form process gas plasma in the ionization chamber; iv) Focusing process gas plasma using a magnetic field, and optionally scanning the process gas plasma using one or more electromagnets to form a plasma beam.

[0065] To initiate the generation of the inert gas plasma in step (i), an inert gas needs to be introduced. The inert gas can be selected from argon, helium, and neon. Preferably, the inert gas is argon.

[0066] The process of initiating the generation of inert gas plasma can itself be a two-step process. Initially, inert gas is introduced at a first continuous flow rate, while a first power source supplies a first current to the cathode. Once glow discharge has begun, the flow rate of the inert gas is reduced to a second continuous flow rate, and the current supplied to the cathode is increased to a higher second current, thereby generating an arc discharge.

[0067] The initial inert gas flow rate is typically 150 sccm to 350 sccm, preferably 200 sccm to 300 sccm. The flow rate is then typically reduced to a second flow rate of 10 sccm to 60 sccm, preferably 20 sccm to 50 sccm (e.g., about 30 sccm).

[0068] The first current provided is typically 0.1A to 4A, preferably 0.5A to 3A, and more preferably 0.5A to 2A. The current is then typically increased to a second current of 1A to 5A, preferably 1.5A to 4A, for example, about 3A. Preferably, the second current is higher than the first current. It should be noted that, in order to maintain a nearly constant current, when the cathode tube begins to emit thermionic electrons, it may be necessary to adjust (e.g., reduce) the voltage of the power supply as the cathode tube heats up during use (because the resistivity of the cathode increases with the temperature of the hollow cathode tube). Typically, as the cathode heats up, it is necessary to reduce the voltage from an initial approximately 300V to 4000V to approximately 50V to 100V.

[0069] In step (iii), the process gas can be selected according to the desired application of the resulting plasma beam. The process gas can be selected from any of argon, oxygen, nitrogen, and hydrocarbon gases (e.g., methane, ethane, propane, butane, ethylene, propylene, butene, acetylene). When the process gas is a hydrocarbon gas, acetylene is preferred. In an embodiment where the resulting plasma beam is used for plasma etching, the process gas is preferably argon. In an embodiment where the resulting plasma beam is used for sputtering, the process gas is preferably selected from argon, oxygen, or nitrogen. In an embodiment where the resulting plasma beam is used for a reactive coating process, the process gas is preferably selected from oxygen, nitrogen, or a hydrocarbon gas. In an embodiment where the resulting plasma beam is used for coating a substrate with diamond-like carbon (DLC), the process gas is preferably a hydrocarbon gas, such as acetylene.

[0070] The input flow rate of the process gas is typically from 5 sccm to 700 sccm, preferably from 10 sccm to 500 sccm.

[0071] The method according to the invention is generally carried out using the apparatus of the invention as described above. Therefore, the step of generating inert gas plasma is typically performed in the hollow cathode arc tube of the invention. The step of accelerating and focusing the electron beam is generally a result of the electric field generated by an electrostatic lens (optionally combined with a ring anode contained within the electron beam inlet of the ionization chamber).

[0072] The method according to the invention may further include the step of using a magnetic field to enhance the density of the inert gas plasma. As described above, the magnetic field can be generated by a magnetic field source around the hollow cathode arc tube. The magnetic field can also be generated by a solenoid.

[0073] The method of the present invention may independently include one or more additional steps of confining and / or guiding the plasma beam.

[0074] Confining the plasma beam refers to the steps of ensuring that the plasma beam remains within the ionization chamber without contacting the walls of the ionization chamber. As mentioned above, the plasma beam can be confined by a confining magnetic field source (e.g., a multi-point magnetic field source). As mentioned above, the confining magnetic field source can also enhance the plasma beam density.

[0075] Guiding a plasma beam refers to the step of manipulating a plasma beam to travel in a desired direction. The desired direction of travel for the plasma beam can include guiding the plasma beam through a plasma outlet, guiding the plasma beam toward a substrate, and / or guiding the plasma beam toward a target. The step of guiding the plasma beam may preferably include scanning the plasma beam across the substrate surface to uniformly coat and / or etch the substrate. As described above, the plasma beam can be guided by a guiding magnetic field source (e.g., one or more C-shaped scanning electromagnets). The plasma beam can be guided by changing the magnetic field strength of the guiding magnetic field source, for example, by changing the current supplied to the one or more electromagnets.

[0076] Step (ii) of the method may additionally involve collimating the electron beam. Collimation is the process of aligning the paths of all electrons in the electron beam so that they all travel along substantially parallel paths. Collimation of the electron beam can be achieved using an electrostatic lens, such as an Einzel lens, as described above. Attached Figure Description

[0077] The invention will now be described in more detail with reference to the accompanying drawings, in which: Figure 1 A schematic diagram of an apparatus for generating plasma according to the present invention is shown.

[0078] Figure 2 A schematic diagram of a hollow cathode arc tube used in the apparatus of the present invention is shown.

[0079] Figure 3 A schematic diagram of an alternative cathode arc tube used in the apparatus of the present invention is shown. Detailed Implementation

[0080] Figure 1A schematic diagram of the device according to the invention is shown. The device has an inert gas inlet 1 with a diameter of 4 mm, which is connected to a hollow cathode tube 2 via an insulating ceramic gas flow connector 3. The hollow cathode tube 2 is a conventional hollow cathode tube for generating plasma and has a refractory metal tube (i.e., cathode) made of tantalum, which is surrounded by a coil heater (not shown) and embedded in a retainer anode (i.e., electron gun anode) 5. The refractory metal cathode tube has an outer diameter of 6 mm and an inner diameter of 2 mm or 4 mm, and is made of tantalum. The retainer anode tube 5 has an inner diameter of 32.5 mm and is made of graphite. The refractory metal cathode tube and the retainer anode are electrically insulated from each other using alumina (not shown). Both the refractory metal tube and the retainer anode have small outlets located downstream of the inert gas inlet (not shown). The hollow cathode tube has two independent power sources (not shown), both connected to the retainer anode 5 and the cathode, which provide a positive bias to the anode and a negative bias to the cathode, and also power the coil heater. The first power supply is the starter power supply (10kW SPT DC power supply), and the second power supply is the retainer power supply (100V / 200A DC power supply). The hollow cathode tube 2 is further surrounded by a solenoid 4 with an independent power supply (not shown). The solenoid power supply is a 160V / 25A DC power supply.

[0081] Downstream of the hollow cathode tube 2 is an electrostatic lens 6 formed by alternating rings of insulating alumina 7 and stainless steel conductive rings 8. The electrostatic lens also has its own independent power supply (not shown). The rings are 5 mm thick with an outer diameter of 155 mm, and the electrostatic lens has an inner diameter of 55 mm.

[0082] Further downstream is a positively charged graphite annular anode 9 with a central aperture of 32.5 mm. Anode 9 is thermally coupled to the water cooling system 14.

[0083] Anode 9 is located upstream of ionization chamber 10, which is surrounded by multi-pointed magnet 12 and C-shaped scanning electromagnets 13. Ionization chamber 10 itself is defined by a stainless steel casing having an inlet 11 for process gases. The ionization chamber is cylindrical in shape with a diameter of 190 mm and a length of 94.5 mm. Multi-pointed magnet 12 is formed by a ring of eight radially arranged magnets with alternating polarities. The two scanning electromagnets 13 are formed by C-shaped soft magnetic cores with two open poles, surrounded by wire, and thus function as solenoids.

[0084] In operation, inert gas is injected through inert gas inlet 1 at a rate of 10 sccm to 50 sccm and passes through hollow cathode tube 2 via ceramic gas flow connector 3. Ceramic connector 3 acts as a voltage divider between the negatively biased hollow cathode 2 and the grounded inert gas inlet 1. The starter power supply (not shown) is turned on, and a glow discharge occurs in the negatively charged hollow cathode 2. Over time, the glow discharge evolves into an arc discharge, the starter power supply is turned off, the retainer power supply (not shown) is turned on, and inert gas plasma is formed.

[0085] A solenoid 4, coaxially surrounding the hollow cathode tube 2, is charged to ~20A by its power supply, generating an axial magnetic field within the hollow cathode tube. This axial magnetic field causes electrons (formed through arc discharge) to move in a helical trajectory, increasing the lifetime of each electron and the probability of inert gas ionization, thereby increasing the inert gas plasma density while allowing for the use of a lower inert gas flow.

[0086] Electrons from the inert gas plasma are accelerated through the first anode 5 and enter the electrostatic lens 6. The electrostatic lens 6 collimates the electron beam and focuses it into the ionization chamber 10 through the second anode 9.

[0087] Process gas is injected into ionization chamber 10 via process gas inlet 11 at a flow rate of 10 sccm to 500 sccm (depending on the intended use of the process gas plasma). An electron beam ionizes the process gas, forming a process gas plasma. The ionization chamber is surrounded by a multi-pointed magnet 12 and a C-shaped scanning electromagnet 13. The multi-pointed magnet 12 creates a multi-pointed magnetic field within the ionization chamber 10, which reflects electrons back into the plasma, increasing the lifetime of ionized electrons and resulting in an increase in the density of the process gas plasma, while also confining and stabilizing the process gas plasma.

[0088] Figure 1 The illustrated apparatus shows two C-shaped electromagnets. The magnetic field generated by the C-shaped scanning electromagnet 13 can be controlled by controlling the current flow through the wires. Thus, the C-shaped electromagnets can be used together as needed to control and guide plasma. For example, the C-shaped scanning electromagnet can be used to guide process gas plasma through a plasma outlet (not shown) and onto a substrate for plasma etching.

[0089] Figure 2 A schematic diagram of a hollow cathode arc tube used in the apparatus of the present invention is shown. The hollow cathode arc tube has a cathode tube 16, which is partially tubular and partially cylindrical, with continuous sidewalls having a circular cross-section, an upstream end 17 serving as a hole, and a downstream end 18 having a circular end wall with the hole therein. The hollow cathode tube also has an anode tube 20, which is partially tubular and partially cylindrical in the same manner as the cathode tube 16.

[0090] Between the cathode tube 16 and the anode tube 20, i.e., in the annular space between the cathode tube and the anode tube, there is a coil heater 21 formed by a stainless steel wire coil wound around the cathode tube. An alumina insulator 22 may also be present between the cathode tube 16 and the anode tube 20.

[0091] The hollow cathode arc tube also has an electron beam exit 24, which is formed by a hole in the downstream end wall of the anode tube and the cathode tube. The electron beam exit 24 can be considered as a channel between the hole in the downstream end wall of the anode tube and the downstream end wall of the cathode tube.

[0092] In operation, inert gas is injected into the hollow cathode arc tube from the upstream end in the direction indicated by arrow 15. Inside the hollow cathode arc tube, the coil heater 21 heats the tantalum thermionic electron emitter 23 and emits electrons, initially causing a glow discharge. Over time, the arc discharge replaces the initial glow discharge, forming an inert gas plasma inside the cathode tube 16. The insulator 22 significantly reduces the heating effect of the coil heater on the anode tube 20, preventing the anode tube from overheating during operation. Electrons in the inert gas plasma are accelerated toward the positively charged anode tube 20 and exit the hollow cathode arc tube via the electron beam exit 24.

[0093] Figure 3 A schematic diagram of an alternative hollow cathode arc tube for use in the apparatus of the present invention is shown. The hollow cathode arc tube has a cathode tube 116, which is tubular with a circular cross-section, open at its downstream end and also having an opening 117 at its upstream end, the opening 117 serving as an inert gas inlet. The hollow cathode also has a tubular anode tube 120 outside the cathode tube 116. The cathode tube is formed of tantalum and serves as the thermionic emission material.

[0094] In this arrangement, there is no heater, and the glow discharge of the inert gas causes a sufficient increase in temperature, thereby inducing thermionic emission from the tantalum cathode tube.

[0095] The hollow cathode arc tube also has an electron beam outlet 124, which is formed by holes / openings in the downstream ends of the anode and cathode tubes.

[0096] Figure 2 or Figure 3 All the hollow cathode arc tubes shown can be used in the device of this invention.

[0097] Example Example 1 - Operating the device of the present invention according to Figure 1 (As described above) Manufacturing apparatus, the apparatus having the above reference Figure 3 The hollow cathode arc tube is described above. The operation of this device is as follows.

[0098] start up: 1. Power on the holders of the anode and cathode of the hollow cathode arc tube, and set them to provide a voltage of 0V and a current of 0A.

[0099] 2. Start the gas flow of the hollow cathode with argon at approximately 250 sccm.

[0100] 3. Power on the starter power supply of the anode and cathode of the hollow cathode arc tube, and set it to provide a voltage of 0V and a current of 0A.

[0101] 4. Increase the starter power supply current from 0A to 2.0A, and then allow time until the voltage suddenly drops from 300V to 80V and stabilizes.

[0102] 5. Reduce the gas flow rate of the hollow cathode to 30 sccm.

[0103] 6. Switch the hollow cathode from using starter power to using retainer power.

[0104] 7. Increase the current supply to the retainer from 0A to 3A and turn off the starter power.

[0105] It is important that the starter power supply is started from 0V, 0A to minimize arcing issues in the tantalum tube during the initial glow discharge. The retainer power supply will always be set to a specific output current, such as 20A in constant current mode. Before the cathode and anode are switched from the starter power supply to the retainer power supply, the retainer will show zero voltage or zero current due to being unconnected. Once the retainer power supply is connected, it will typically provide a current of 5A to 30A (e.g., 20A) at a voltage between 20V and 80V.

[0106] run: 1. Inject acetylene process gas into the ionization chamber and apply a bias voltage to the metal substrate held in the rotating support.

[0107] 2. Turn on the solenoid power supply and increase the current to 20A.

[0108] 3. Start supplying power to the electrostatic lens and the anode between the electrostatic lens and the ionization chamber at approximately 5A and 4000V and 30A and 50V respectively.

[0109] 4. Turn on the power supply of the C-shaped scanning electromagnet and set the current to vary within the range of -7A to 7A.

[0110] 5. Increase the current of the retainer power supply to approximately 20A.

[0111] 6. The current supplied to the C-shaped scanning electromagnet is varied as needed to guide the plasma beam and coat the substrate.

[0112] Switch to idle mode: 1. Close the process gas inlet.

[0113] 2. Reduce the current in the solenoid coil to 0A.

[0114] 3. Reduce the current supply to the retainer to 2A.

[0115] This deposits a uniform and dense diamond-like carbon coating on the metal substrate.

[0116] Example 2 – Testing a Solenoid The solenoid was tested using the apparatus of Example 1. The observation window in the apparatus housing allows a view of the downstream side of the ionization chamber inlet (i.e., the ionization chamber inlet can be seen from inside the ionization chamber).

[0117] First, all the "start-up" steps of the method in Example 1 are performed. The multi-point magnet comprises a permanent magnet. Initially, the solenoid power is turned off. The inlet emits light, indicating that a self-sustaining arc discharge has occurred. However, no clear electron beam enters the chamber.

[0118] The solenoid power supply was then switched on and increased to 20A. No other parameters or power supply were adjusted. After allowing some equilibration time, the entrance to the ionization chamber was observed again. A distinct beam of luminescent electrons could be seen entering the ionization chamber.

[0119] Therefore, it is clear that the solenoid leads to increased plasma density and collimation.

[0120] Example 3—Testing a Multi-Point Magnet The multi-point magnet was tested using the apparatus of Example 1 and the same viewing window used in Example 2 to observe the downstream side of the ionization chamber inlet.

[0121] First, all the “start-up” steps of the method in Example 1 are performed. The solenoid power supply is then turned on and increased to 20A. Initially, there is no multi-point magnet. A beam of luminous electrons can be seen, but it diffuses outward as it enters the ionization chamber further (i.e., the diameter of the electron beam increases as it enters the ionization chamber further).

[0122] Then, add a multi-pointed magnet. After allowing some equilibration time, observe the entrance to the ionization chamber again. The luminous electron beam can be seen again, but as it enters the ionization chamber, there is no longer significant diffusion. Instead, as the electron beam enters the ionization chamber, its diameter becomes roughly uniform.

Claims

1. An apparatus for generating plasma from a process gas, the apparatus comprising: a) Power supply, b) A hollow cathode arc tube, comprising: i) Inert gas inlet, ii) A cathode tube, which is connected to a power supply and is configured to be negatively biased when the power is on. iii) An anode tube, which is connected to a power supply and is configured to be positively biased when the power is on. iv) Electron beam exit, c) An ionization chamber, which includes: i) Electron beam inlet, ii) Process gas inlet, iii) Indoor spaces where process gases can be ionized to form plasma. iv) Plasma outlet, d) A first magnetic field source, used to confine the plasma within the ionization chamber. e) A second magnetic field source, which is used to guide and scan the plasma away from the plasma outlet.

2. The apparatus for generating plasma from process gas according to claim 1, further comprising a magnetic field source surrounding the hollow cathode arc tube.

3. The apparatus for generating plasma from process gas according to claim 2, wherein the magnetic field source surrounding the hollow cathode arc tube is a solenoid coil.

4. The apparatus for generating plasma from process gas according to claim 1, further comprising an electrostatic lens for focusing an electron beam.

5. The apparatus for generating plasma from process gas according to claim 4, wherein the electrostatic lens comprises alternating disks of electrically insulating material and disks of conductive material.

6. The apparatus for generating plasma from process gas according to claim 1, wherein the first magnetic field source for confining the plasma within the ionization chamber comprises four or more magnetic field sources of alternating polarities.

7. The apparatus for generating plasma from process gas according to claim 1, wherein, The second magnetic field source used to guide and scan the plasma away from the plasma outlet has an adjustable magnetic field.

8. The apparatus for generating plasma from process gas according to claim 1, wherein the second magnetic field source for guiding and scanning the plasma away from the plasma outlet comprises two electromagnets.

9. The apparatus for generating plasma from process gas according to claim 1, wherein the electron beam inlet includes an annular anode for accelerating the electron beam through the electron beam inlet.

10. A method for generating a plasma beam, characterized in that, include: i) Generate inert gas plasma containing electrons and inert gas ions through arc discharge; ii) Accelerate and focus the electron beam into the ionization chamber; iii) Injecting process gas into the ionization chamber, causing it to be ionized by an electron beam to form process gas plasma in the ionization chamber; iv) Focus the process gas plasma using a magnetic field and scan the process gas plasma using one or more electromagnets to form a plasma beam.

11. The method of generating a plasma beam according to claim 10, wherein the method further comprises using a magnetic field to enhance the density of the inert gas plasma.

12. The method for generating a plasma beam according to claim 11, wherein a magnetic field generated by a solenoid is used to enhance the density of the inert gas plasma.

13. The method of generating a plasma beam according to claim 10, wherein the method further comprises using a multi-point magnetic field to enhance the process gas plasma density.

14. The method for generating a plasma beam according to claim 10, wherein in step ii), the electron beam is additionally collimated by an electrostatic lens.

15. The method for generating a plasma beam according to claim 10, wherein the inert gas is argon.

16. The method for generating a plasma beam according to claim 10, wherein the process gas is selected from nitrogen, oxygen and hydrocarbon gases.

17. The method for generating a plasma beam according to any one of claims 10-16, wherein the apparatus for generating plasma from a process gas according to any one of claims 1-9 is used.

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