RU2277763C2 - Method and device for getting stationary combined discharge of low-pressure low-temperature plasma - Google Patents

Abstract

FIELD: plasma equipment.

SUBSTANCE: method of getting stationary combined discharge of low-pressure low-temperature plasma at end part of treated electro-conducting object provided with protruding parts or sharp edges is based upon application of positive potential. Positive potential forms electro-static field around the object. Microwave electromagnetic field is applied onto electrostatic field at the level of microwave power being lower than required one for exciting and keeping electrode-free microwave frequency discharge but being sufficient for exciting and keeping stationary combined discharge of low-pressure low-temperature plasma. Device for realization of the method has cylindrical resonator, microwave frequency power generator, excitation system, and unit for applying potential to treated electro-conducting object, vacuum system and gas leak-in system. Cylindrical resonator is excited by waveguide-slot aerial which is folded to form a ring. Positive potential is applied to object to be treated by means of holder. Holder is disposed in part of cylindrical resonator to be treated under vacuum.

EFFECT: improved wear resistance; improved adhesion of coatings applied before.

4 cl, 4 dwg

Description

The invention relates to the field of methods and apparatus for creating a low-temperature low-pressure plasma formed around the end part of an electrically conductive object and can be used for structural changes in the surface of the treated object, increase its wear resistance, increase the adhesion of coatings, as well as the deposition of thin films from the gas phase.

Known combined discharges excited by the method of applying a microwave electromagnetic field to an arc or corona discharges at atmospheric pressure (Batenin V.M., Klimovsky II, Lysov G.V., Troitsky V.N. Microwave plasma generators: Physics, technology , application. M: Energoatomizdat, 1988, RF patent No. 2166240, filed 04/27/99, IPC N 05 N 1/18 "Method and device for producing non-equilibrium microwave plasma in high pressure gases", Lysov G .V. Et al.), However, under reduced pressure, combined discharges of this type cannot be realized and due to the physical nature of the arc or corona discharges.

In addition, the conditions of gas breakdown and excitation of a stationary electrodeless microwave discharge of low-temperature low-pressure plasma are known (Mac-Donald A. Microwave breakdown in gases, translated from English by M. Savchenko M. M .: Mir, 1969), where The main processes are: ionization obtained due to collisions with electrons of gas molecules having a high speed of vibrational motion; loss of electrons as a result of diffusion onto walls from the discharge gap, recombination, and adherence to neutral molecules. Breakdown in a gas occurs in a certain region of space, provided that the rate of formation of electrons even slightly exceeds the rate of loss, which leads to a sharp increase in their density. The minimum breakdown fields in gases at a continuous generation mode at a frequency of 2.8 GHz correspond to a pressure of 300 Pa (Mac-Donald A. Microwave breakdown in gases, translated from English by M. Savchenko M. M .: Mir, 1969), when pulsed at a frequency of 2.5 GHz, to a pressure of 3 Pa (Raytsyn D.G., Electric strength. M: Soviet radio, 1977

Traditional microwave plasma technologies under reduced pressure involve the creation of a certain plasma volume, which is then transformed and delivered to the processed object. In such systems, the plasma formation zone and the treated object can be significantly spaced in space, such as, for example, in ion doping plants. In this case, most of the energy consumed is spent on creating plasma and maintaining the conditions for its generation, separation and delivery of active particles with a given energy to the processing object, followed by scanning the beam on the surface. When processing complex surfaces, this method of forming and delivering active plasma particles to the surface of the object is not effective, because protruding elements form shadows when scanning an ion beam.

The present invention allows for the efficient processing of the terminal part of an electrically conductive object of complex shape (hereinafter referred to as the object to be processed) in order to increase their wear resistance, increase the adhesion of previously applied coatings, and also to deposit thin films from the gas phase at low energy costs.

The essence of the invention lies in the fact that the processed object having protruding parts or pointed edges is supplied with a positive potential that forms an electrostatic field around the terminal part of the object, on which a microwave electromagnetic field is applied at a microwave power level lower than that necessary to excite and maintain a stationary electrodeless Microwave discharge of a low-temperature plasma of reduced pressure, but sufficient to excite and maintain a stationary combination low-temperature plasma discharge vannogo reduced pressure.

The chaotic thermal motion of electrons oscillating with an ultrahigh frequency of an electromagnetic field in an electrostatic field acquires directional motion toward a positive electrode (the object being processed). The movement of electrons in an electrostatic field leads to an increase in both energy and electron density. Under these conditions, the electron balance is restored near the end of the object being processed, their energy and density increase and become sufficient for inelastic interaction with heavy gas particles, thereby creating conditions for gas breakdown and a luminous region of a stationary combined discharge plasma appears at the end of the object being processed, shown figure 1, 2.

The non-luminous part of the space, in which the microwave electromagnetic field and the electrostatic field are jointly present, is the volume cathode and constantly feeds the plasma with electrons and negative ions.

In the region of the outer boundary of plasma 1 (Fig. 3), the electromagnetic wave attenuates strongly in the skin layer as a result of the effective transfer of field energy to electrons, which in turn transfer the stored energy through inelastic collisions to heavy plasma particles. Further electron drift from the skin layer in the inner volume 2 is carried out only under the influence of an increasing positive electrostatic field. In this field, electrons along with elementary processes are able to create new free electrons as a result of volume ionization. In region 3, a sharp increase in the electrostatic field occurs, as a result of which the process of volume ionization of the gas develops into an avalanche-like one. Here, positive ions are locked and create a spatial charge, which additionally accelerates the electrons. The density of charged particles in this region increases, and the average distance between them decreases so that the Coulomb interaction begins to appear, leading to the emergence of ambipolar diffusion, as a result of which the electrons are slowed down by the ions, and the ions are accelerated by the electrons, which leads to the formation of local flows of electrons and ions directed to the surface of the processed object. Such a plasma flow has the greatest effect on the protruding parts of the treated surface, sharp edges, surface irregularities, where the concentration of the lines of force of the electrostatic field is maximum. This plasma region is visible in figure 2 as a bright strip.

Particle energy in the plasma stream is controlled by changing the microwave power, the location of the processed object and the value of the positive potential supplied to the processed object.

The specified method is implemented in a device containing a cylindrical resonator, the internal evacuated volume of which is limited by a radiolucent cylinder, an excitation system, a microwave energy generator, a microwave energy generator power supply, a potential supply unit to a processing object, a vacuum system, a gas inlet system, and a cylindrical resonator excited by a waveguide-slot antenna, rolled into a ring, and a positive potential is supplied to the processed object by means of a holder located in a vacuum Asti cylindrical resonator

The processed object 1, as shown in Fig. 4, is fixed in a replaceable collet 2 of the holder 3 located in the processing chamber 4. A part of the surface of the processed object and the collet 2 are insulated with a transparent material 5, the surface to be processed remains open. The object to be processed and the holder are located in a certain way in the processing chamber 4, which is pumped out using the vacuum system 6 to the maximum pressure and the working pressure of the process gas, for example nitrogen, is established in the processing chamber through the gas inlet system 7. From the potential supply unit 8 through a sealed connector 9, a cable with multilayer protection elements 10 and a holder 3, a positive potential of a certain value is supplied to the object to be processed. From the microwave energy generator 11 through the waveguide-slot antenna, rolled into a ring 12 in a cylindrical resonator 13, microwave frequencies are excited. When applying electrostatic and microwave electromagnetic fields at the end of the workpiece, a combined discharge of reduced pressure 14 occurs.

Depending on the energy of plasma particles, various processes can be carried out: smoothing the surface, polymerization with the formation of a close-packed polymer film on the surface, diffusion processes and doping, which together leads to structural changes on the surface and in the surface layer of the treated object. The result is changes in the microhardness HV, ohmic resistance, roughness in Ra, and structure in a volume of up to 300 μm, which leads to an increase in the wear resistance of the surface of the treated object.

A set of interchangeable collets allows you to fix the workpiece in the holder, for example, drills, taps, finger mills with a diameter of 0.6-15 mm.

Example:

A cylindrical resonator with a diameter of 150 mm and a length of 320 mm is excited by a slot-waveguide antenna, which is a 45 × 90 mm section rolled up into a ring waveguide with eight radiating slits cut in parallel to the axis of the wide waveguide wall, 62 × 6 mm in size. At the input of the waveguide slot antenna, a divider is installed. In such a device, when a potential of 30 V is supplied to a drill with a diameter of 0.6 mm, at a working pressure of 300 Pa, a stationary combined discharge of low-temperature plasma occurs at a supplied microwave power of ~ 20 W (anode magnetron current 10-12 mA) at a frequency of 2450 MHz.

Claims (3)

1. The method of obtaining a stationary combined discharge of low-temperature plasma of low pressure at the end of the processed electrically conductive object having protruding parts or pointed edges, which consists in the fact that a positive potential is applied to the object, forming an electrostatic field around the object, on which a microwave electromagnetic field is applied at a level The microwave power is lower than that required to excite and maintain an electrodeless microwave discharge of a low-temperature plasma low pressure, but sufficient to excite and maintain a stationary combined discharge of low temperature low pressure plasma. 2. The method according to claim 1, wherein the electron source is a bulk cathode arising in an area in which a microwave electromagnetic field and an electrostatic field are present together. 3. A device for producing a stationary combined discharge of a low-temperature low-pressure plasma containing a cylindrical resonator, an excitation system, a microwave energy generator, a potential supply unit for a conductive object being processed, a vacuum system and a gas inlet system, the cylindrical resonator being excited by a slotted waveguide-antenna into the ring, and the positive potential is fed to the workpiece by means of a holder located in the evacuated part of the cylindrical resonator.

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