RU2225684C2 - Microwave plasma-chemical reactor - Google Patents

Abstract

FIELD: electronic engineering and other industries; microwave reactors with larger amount of plasma. SUBSTANCE: unit for admitting microwave energy into discharge chamber is connected to top end plate of the latter and is made in the form of two coaxial metal tubes, external one being connected to side wall of discharge chamber through adapter unit that has metal body and metal casing; diameter of discharge chamber is much larger than that of external tube; metal body is disposed around internal tube of microwave energy admission unit and is made in the form of truncated cone whose large base is part of top end plate of discharge chamber; metal casing is arranged coaxially to metal body and case-to-body clearance receives insulating ring mounted on top end plate face of discharge chamber; installed into internal bore of body is second insulating ring that receives internal tube of microwave energy admission unit designed for axial displacement; two or four ports are made in external tube wall of microwave energy admission unit to attach rectangular waveguides whose wide walls are parallel to tube axis; coaxial-to- waveguide adapter is joined to top end plate of microwave energy admission unit so that its central conductor is connected through taper to internal tube butt end of microwave energy admission unit; central conductor is insulated from coaxial-to-waveguide adapter shell and external conductor that functions as casing is connected to top end plate of microwave energy admission unit; insulating cylinder is mounted about bore in top end plate between the latter and internal tube of microwave energy admission unit; internal tube accommodates adjusting microwave component made, for instance, in the form of shorted movable piston; workpiece- carrying platform is installed on bottom end plate for displacement relative to the latter; working gas inlet nozzles are disposed in side wall of discharge chamber, at its bottom end plate, tangentially to side wall; additional vortex gas flow generator made in the form of vortex generator nozzles disposed in clearance between internal tube wall and adjusting microwave component is arranged at edge of internal tube of microwave energy admission unit, on its inner wall, conical metal body being joined to adjusting microwave component so that its vertex is outward-directed along tube axis and emerges from internal tube through distance equal to one or two radii of internal tube; working gas inlet nozzles disposed in side wall of discharge chamber may be placed in cavity formed by bottom end plate of discharge chamber and metal or insulating cylinder coaxial to discharge chamber that forms clearance between its outer surface and discharge chamber wall, its size being equal to one through five diameters of nozzle outlet hole; hollow of this cavity is disposed close to lower working position plane of workpiece- carrying platform. EFFECT: enhanced microwave power injected in discharge, working pressure in discharge chamber; enlarged workpiece diameter; enhanced reliability and output capacity of reactor. 2 cl, 5 dwg

Description

 The invention relates to microwave (microwave) plasma reactors with increased plasma volume.

 The proposed device is intended for deposition on substrates of various materials layers of various coatings, including a diamond layer, and can be used in the manufacture of electronic devices, tools for processing materials and in other areas.

 Microwave plasma is widely used for surface treatment and film deposition. The discharge is maintained in a reduced pressure working gas (less than 100 mmHg), since only in this case it is possible to carry out a diffuse (relatively uniform in volume) discharge due to the relatively small specific energy input required in this case to maintain it. Due to the small amount of working substance, the process of technological processing and deposition is very long, which inhibits its wide industrial use. The need to increase the productivity of equipment requires an increase in the working gas pressure and the microwave power invested in the discharge.

 In this case, two problems arise: the destruction of the dielectric window separating the reactor itself, where the discharge is supported, and the system for supplying microwave energy to the reactor; disintegration of the discharge into separate zones (usually in the form of thin plasma channels).

 The first problem is related to the thermal and ultraviolet effects on the surface of the dielectric window from the side of the plasma, which significantly increase with increasing gas pressure in the reactor and the supplied microwave power, and lead to the destruction of the window. This problem is solved by removing the window from the zone of direct exposure to radiation from the plasma [1], or by significantly reducing the microwave energy flux density in the window region [2].

 However, the above devices provide a diffuse discharge only at reduced gas pressure and in a limited volume, the characteristic scale of which is determined by the length of the used electromagnetic wave.

 With an increase in gas pressure and a corresponding increase in the specific energy input, various types of instabilities appear in the discharge, which violate its diffuse shape. The main type of instability is ionization-overheating, which is caused by an increase in the frequency of ionization collisions in a gas in places of local overheating. This leads to an increase in the electrical conductivity of the gas and the energy input and further local overheating. As a result, the discharge decays into separate channels along the electric field lines.

 It is possible to overcome this discharge behavior by maintaining a microwave discharge when the electric field strength is much lower than its breakdown value and subject to gas recirculation in the discharge zone [3, 4]. In this case, the ionized gas stream, leaving the zone of the main microwave energy input, returns to it again, preserving the degree of ionization, which determines the conductivity sufficient for the required microwave energy input. As a result, the discharge is maintained not in the mode of electric breakdown, as in the case of devices [1, 2], but in the mode of non-self-sustained (actually with preliminary ionization) discharge and exists when the electric field strength is much lower than the breakdown value.

 In this case, using a microwave electromagnetic wave that has an electric field strength normal to it at the discharge boundary, it is possible to avoid the manifestation of ionization-overheating instability and maintain the diffuse nature of the discharge, since with a local increase in electrical conductivity, the electric field strength in this region will decrease. As a result, it is possible to obtain a diffuse microwave discharge at a gas pressure close to and above atmospheric.

The prototype of our device that implements the above method for producing a plasma volume of a microwave discharge at high gas pressure is a device [5], which is a metal cylindrical chamber with a height equal to λ / 2 (λ is the length of the electromagnetic wave used to obtain and maintain the discharge ), with end bottoms, at least two rectangular waveguides are connected to the side surface of the chamber, the wide walls of which are parallel to the axis of the chamber, and the gas immersion swirl Located in one of the bottoms. In one of the bottoms at a radius of r = (0.6-0.8) R _k , where R _k is the radius of the chamber, openings for gas exit are made.

 The disadvantage of this device is the location of the input windows of microwave energy directly in the side wall of the discharge chamber, which creates the possibility of destruction of dielectric windows under the influence of plasma radiation and the electrical breakdown initiated by this radiation on the surface of the windows, which limits the level of microwave power introduced into the discharge.

 The aim of the invention is to eliminate the described drawback, namely increasing the reliability of the device, increasing the input microwave power, and thereby increasing productivity.

 This goal is achieved by the fact that in the proposed device, a fundamentally new design of the node for inputting microwave energy into the discharge chamber is used. The site of input of microwave energy into the discharge chamber. The node for introducing microwave energy into the discharge chamber is connected to the upper bottom of the discharge chamber and is made in the form of two coaxial metal pipes, the outer one of which is connected to the side wall of the discharge chamber, having a diameter significantly larger than the diameter of the outer pipe of the microwave energy input node using a transition unit, consisting of a metal body and a metal casing, while the metal body is located around the inner tube of the microwave energy input unit and has the shape of a truncated cone, the large base of which is the upper bottom of the discharge chamber, and the metal casing is located around the metal body coaxially with it, and in the gap between the casing and the body, a dielectric ring is installed in the plane of the upper bottom of the discharge chamber, and a second dielectric ring is installed in the inner hole of the body, into which it can axially move the inner tube of the microwave energy input unit, two or four windows are made in the wall of the external pipe of the microwave energy input unit, to which rectangular waveguides are connected, wide walls of which They are parallel to the pipe axis, and a coaxial waveguide transition is connected to the upper bottom of the microwave energy input unit so that its central conductor is connected smoothly to the end of the inner pipe of the microwave energy input unit, while the central conductor is isolated from the housing of the coaxial waveguide transition and the external conductor - the casing - is connected to the upper bottom of the microwave energy input unit, a dielectric cylinder is installed around the hole in the upper bottom between it and the internal pipe of the microwave energy input unit, inside a microwave adjustment element is located in it, made, for example, in the form of a moving shorting piston, a platform is installed on the lower bottom of the discharge chamber to accommodate the workpiece with the ability to move relative to the bottom, tangentially to the side wall of the nozzle are located in the side wall of the discharge chamber at its lower bottom for introducing the working gas, and at the edge of the inner tube of the microwave energy input unit from the side of the discharge chamber, an additional vortex shaper is located on the inner wall of the inner tube gas flow in the discharge chamber, made in the form of swirl nozzles located in the gap between the wall of the inner pipe and the microwave tuning element, to which a metal cone-shaped body is connected, the apex of which is directed outward along the pipe axis and leaves the inner pipe by a distance equal to 1-2 values of the radius of the inner pipe: and the working gas inlet nozzles located in the side wall of the discharge chamber can be enclosed inside the cavity formed by the lower bottom of the discharge chamber, and metal or die an electric cylinder coaxial with the discharge chamber and forming a gap between its outer surface and the wall of the discharge chamber, the size of which is 1-5 the diameter of the nozzle outlet, and the hole of this cavity is located near the plane of the lower working position of the platform on which the workpiece is placed.

 On figa, 1b shows the proposed design of the device.

Figure 2 shows the electric field pattern for waves of type H ₂₁ and H ₁₁ in the cross section of the discharge chamber.

Figure 3 shows a picture of the electric field for waves of type E ₀₁ .

 In FIG. 4 shows a connection diagram of microwave energy sources to a microwave plasma-chemical reactor.

The proposed device, shown in figa, 1b, consists of a cylindrical discharge chamber 1, on the bottom 2 of which there is a platform 3 for installing the plasma-processed part, and a microwave energy input unit 4 connected to the discharge chamber 1 through its upper end. The microwave energy input unit 4 has an external cylindrical metal pipe 5, in the wall of which there are two (with a 180 ^o offset around the axis) or four (with a 90 ^o offset around the axis) sealed windows 6 to which rectangular waveguides 7 are connected, so that their wide walls are parallel to the axis of the pipe 5. Microwave energy generators are connected to these waveguides.

 Inside the outer pipe 5, the inner metal pipe 8 is coaxially axially displaceable. Inside the pipe 8 there is a movable shorting piston 9.

 In the side wall of the discharge chamber 1 at its bottom there are nozzles 10 tangential to the side wall for supplying the gas mixture to the discharge chamber, and openings 11 for the exit of the gas mixture are made in the lower bottom of the discharge chamber 1.

 The upper bottom 12 of the input node of the microwave energy 4 is made with the possibility of axial movement. Between the upper bottom 12 and the inner tube 8 is installed a dielectric cylinder 13.

 In the lateral wall of the discharge chamber, a movable pin electrode 14 is mounted on an airtight bellows to initiate a discharge.

 Between the microwave energy input unit 4 and the discharge chamber 1, a transition unit 15 is inserted located around the pipe 8 of the microwave energy input unit.

 The transition assembly 15 includes a metal conical body 16 and a conical metal casing 17 connecting the outer pipe 5 of the microwave energy input unit 4 to the wall of the discharge chamber 1. The gap between the casing 17 and the conical body 16 is approximately equal to the difference between the radii of the outer 5 and inner 8 pipes microwave energy input unit. In this gap, a dielectric ring 16 is installed in the plane of the upper bottom of the discharge chamber 16. A second dielectric ring 19 is installed in the inner hole of the conical body 16, into which the inner tube 8 of the microwave energy input unit is axially movable.

 The coaxial waveguide transition 20 is connected to the upper bottom of the microwave energy input unit 12, its central conductor 21 is connected by a smooth transition 22 to the end of the inner pipe 8, and the outer conductor - the casing 23 - to the upper bottom around the hole in which the dielectric cylinder 13 is mounted. The central conductor 21 is isolated from the housing of the coaxial waveguide transition using a gap between it and the housing, in the housing of the coaxial waveguide transition there is a throttle element 24 that prevents microwave radiation outside and along the central ovodnika.

 Shaper 25 additional vortex gas flow in the discharge chamber is located inside the inner pipe. It can be made in the form of nozzles in the wall of the inner pipe, similarly to nozzles in the side wall of the discharge chamber or in the form of a swirl of gas supplied through the inner pipe located in the gap between the wall of the pipe 8 and the moving shorting piston 9, in this case the swirl is two coaxial cylinder, in the gap between which inclined vanes are placed.

 A conical shaped metal body 26 is connected to the movable shorting piston 9, the apex of which is directed outward along the axis of the pipe and leaves the inner pipe 8 to a distance of 1-2 radiuses of the inner pipe, which reduces the concentration of electric field lines at the pipe edges.

 The working gas inlet nozzles located in the side wall of the discharge chamber are enclosed in a cavity 27 formed by the bottom of the discharge chamber and a metal or dielectric cylinder 28 coaxial with the discharge chamber and forming a gap between its outer surface and the wall of the discharge chamber, the size of which is 1-5 the diameter of the nozzle outlet, the hole of this cavity being located near the plane of the lower working position of the platform 3, on which the workpiece is located.

The proposed device operates as follows. Microwave energy is introduced into the microwave plasma-chemical reactor through two opposing waveguides 7. When the phase shift of the electromagnetic waves at the input to the input device of microwave energy 4 by 180 ^o in the discharge chamber 1, an electromagnetic wave H ₂₁ or higher order is excited, if allows the ratio of wavelength and pipe sizes 5 and 8.

The picture of the electric field for the wave H ₂₁ in the cross section of the discharge chamber 1 is shown in figure 2. The electric field of this wave is located on the periphery of the discharge chamber; therefore, the microwave energy transferred by this wave will be released on the periphery of the plasma formation formed in the discharge chamber. In this case, the plasma formation rotating around the axis will be alternately affected by the azimuthal or radial component of the electric field, which contributes to the formation of a diffuse type of discharge (without the formation of separate filamentary channels).

When in-phase supply of microwave energy to the waveguides 7 in the discharge chamber, an H ₁₁ wave will be excited, the electric field of which also fills the axial region of the discharge chamber.

When microwave energy is introduced into the microwave plasma-chemical reactor alternately by pulses in-phase and antiphase at the inlet of the reactor, it is possible to control the energy input over the entire cross section of the plasma formation. When microwave energy is introduced into the reactor through a coaxial waveguide transition 20, an azimuthally symmetric electric wave of type E _{01 is} excited in the discharge chamber 1, the field pattern of which is shown in FIG. 3.

 The lines of force of the electric field of this wave are concentrated in the axial zone of the discharge chamber 1 and are perpendicular to the lines of force of the electric field of waves of type H, therefore, the use of this input of microwave energy also contributes to the formation of a diffuse type of microwave discharge and to improve the uniformity of the energy input over the cross section of the plasma formation.

 Using the described modes of energy input into the microwave plasma-chemical reactor, it is possible to increase the average value of the microwave power deposited in the discharge without increasing the pulse values that can cause a violation of the stable mode of discharge burning.

 The location in the inner tube of the protruding metal conical body 26 leads to a decrease in the electric field at the edges of the inner tube and thereby prevents breakdowns between the edges of the tube and the plasma.

 The working gas mixture is blown into the discharge chamber through tangential nozzles 10. The location of these nozzles inside the cavity facilitates better mixing of individual jets and improves the azimuthal uniformity of the vortex flow inside the discharge chamber. This gas stream flows around the wall of the discharge chamber, its upper bottom and forms a recycle stream in the axial zone, in which the plasma formation is formed.

 An additional vortex stream is blown through the former 25 located inside the inner pipe 8, which compensates for the loss of the rotational moment of the main stream.

 The working gas flows from the discharge chamber through the outlet openings 11.

 The discharge is ignited by introducing into the center of the recirculation zone a special metal pin electrode 14 initiating an electrical breakdown.

 After ignition of the discharge, the plasma fills the recirculation zone, isolating itself from the side wall of the discharge chamber 1 and the upper bottom of the discharge chamber formed by dielectric rings 18, 19 and a metal conical body 16, a vortex gas flow.

 Here is an example of the implementation of the design of the proposed device and its operating modes when using three sources of microwave energy pulsed mode.

 As sources of microwave energy can be used industry-produced energy sources with a pulse power of 10 kW at a frequency of 2450 MHz with an average power of up to 5 kW.

 A connection diagram of microwave energy sources to a microwave plasma-chemical reactor is shown in FIG. 4. Sources 29 and 30 are connected to the untied shoulders of the double waveguide bridge 31, the output arms of which are symmetrically connected to the opposing rectangular waveguides of the microwave energy input unit.

 A source 32 is connected to the coaxial waveguide junction 20 of the microwave energy input unit.

Microwave energy from a source 30 connected to the shoulder of the waveguide bridge 32 in the H plane approaches the microwave energy input node in phase at each input 7 and is introduced into the discharge chamber 1 on the H ₁₁ wave.

Microwave energy from a source 29 connected to the shoulder of the waveguide bridge 31 in the E plane approaches the microwave energy input node out of phase at the inputs 7 and is introduced into the discharge chamber 1 on the H ₂₁ wave.

Microwave energy from source 32 is introduced into the discharge chamber 1 on an azimuthally electric wave of type E ₀₁ .

Microwave pulses from each of the sources of microwave energy are introduced into the microwave plasma-chemical reactor simultaneously or with a shift relative to each other in time. The characteristic duration of microwave pulses is τ = (10-100) 10 ^-6 s with a pause duration of T = (1-5) τ.
The gas pressure in the reactor can vary from 0.5 atm to 5 atm while maintaining a stable diffuse plasma formation above platform 3 with the workpiece.

The proposed device has the following main advantages in comparison with the prototype:
1. An increase in the microwave power invested in the discharge.

 2. The increase in working pressure in the discharge chamber.

 3. A further increase in the diameter of the discharge chamber and, accordingly, the diameter of the workpiece.

 Thus, the proposed device allows for a further increase in the productivity of the technological process of deposition of coatings on substrates.

LITERATURE
1. US patent 5501740 (application 219208, 03/29/1994).

 2. German patent 19507077 from 04.25.1996.

 3. Bazhenin V. M., Klimovsky II, Lysov G.V., Troitsky Z.N. Microwave plasma generators. Physics, technology, application. - M .: Energoatomizdat, 1988, p. 162-164.

 4. Low temperature plasma. Volume 6, RF and microwave plasmatrons. - Novosibirsk: Nauka, 1992, p. 185-189.

 5. RF patent 1602376.

Claims (2)

1. A microwave plasma-chemical reactor consisting of a metal discharge chamber in the form of a cylindrical tube with end bottoms, in the lower bottom of which holes are made for gas outlet, and a vortex gas flow former is located at one of the bottoms, and a microwave energy input unit including rectangular waveguides connected to the lateral surfaces of the cylindrical tube so that their wide walls are oriented parallel to the axis of the discharge chamber, and the windows for connecting the waveguides are closed by dielectric inserts, and A cathode placed in the side wall of the discharge chamber, characterized in that the node for introducing microwave energy into the discharge chamber, made in the form of two coaxial metal pipes, is connected to the upper bottom of the discharge chamber by means of a transitional unit consisting of a metal body located around the inner pipe a microwave energy input unit, and a metal casing located around the metal body coaxially with it and connecting the external pipe of the microwave energy input unit to the side wall of the discharge chamber, the diameter of which is the diameter of the outer tube of the microwave energy input unit is increased, while in the wall of the external pipe of the microwave energy input node two or four windows are made to which rectangular waveguides are connected, and the metal body has the shape of a truncated cone, the large base of which is part of the upper bottom of the discharge chamber and a dielectric ring is installed in the gap between the casing and the metal body, the lower surface of which forms part of the upper bottom of the discharge chamber, while the inner tube has the ability to move inside tally body, and inside the inner tube there is a movable microwave tuning element, on the lower bottom of the discharge chamber there is a platform for placing the workpiece with the ability to move relative to the bottom, and in the side wall of the discharge chamber at its lower bottom are tangential to the side wall of the nozzle for inputting the working gas, and a coaxial-wave transition is connected to the upper bottom of the microwave energy input unit so that its central conductor is connected by a smooth transition to the end of the inner pipe evil input microwave energy, wherein the central conductor isolated from the body coaxially-wave transition, and the outer conductor-enclosure is connected to the upper bottom node input of microwave energy, wherein the hole in the bottom between the jacket and the central conductor inserted into a dielectric ring. 2. The microwave plasma-chemical reactor according to claim 1, characterized in that a dielectric ring is inserted between the inner tube of the microwave energy input unit and the metal body of the transition unit with the ability to move the inner pipe inside this ring, and to the microwave tuning element located inside the inner pipe, a conical shaped metal body is connected, the apex of which is directed outward along the pipe axis and leaves the inner pipe to a distance equal to 1-2 radii of the inner pipe, and at the edge of the inner pipe of the microwave energy input unit on the side of the discharge chamber, in the gap between the wall of the inner pipe and the microwave tuning element, there is an additional eddy gas flow former, and the working gas inlet nozzles located in the side wall of the discharge chamber are enclosed inside the cavity formed by the lower bottom of the discharge chamber and a metal or dielectric cylinder, coaxial with the discharge chamber and forming a gap between its outer surface and the wall of the discharge chamber, the size of which is equal to 1-5 diameters of the nozzle outlet, the versts of this cavity are located near the plane of the lower position of the platform on which the workpiece is placed.

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