Device for synthesis of diamond in a plasma glow discharge dc

 

(57) Abstract:

The invention relates to the technique of plasma-chemical plants, in particular to devices for diamond using gas glow DC discharge at a pressure below atmospheric. The technical result is increased productivity and efficiency of the process of growing diamond. The essence of the technical solution is that polictial installed with the possibility of axial movement and has a heater substrate, the magnetic coil is installed outside of the discharge chamber, and a secondary power source negative pole is connected with podarkticules and the positive terminal to the anode. 1 Il.

The invention relates to the technique of plasma-chemical installations, namely, devices for obtaining diamond using gas glow DC discharge at a pressure below atmospheric.

The number of known devices designed for growing diamond by using a plasma chemical technologies based on various methods of excitation of plasma: arc discharge, microwave discharge, a glow discharge.

Installation using arc discharge, for example (EP 0388861 A2, 1990), allow to grow the cm2and with high energy consumption and high flow rate of the working gas mixture.

Installation on the basis of microwave discharge, for example (EP 0343017 A2, 1989), allow to grow diamond films with a diameter of 3-8 cm, but with a low rate of 0.5-2 μm/hour. Such performance does not meet modern requirements, and for its improvement requires the use of microwave high-power sources, which complicates the design and operation of the plant.

More promising from the point of view of productivity and cost reduction process for the synthesis of diamond using plasma glow discharge DC.

The device Diamond and Related Materials, 1993, v. 2, p.357 for growing diamond in the plasma glow discharge DC contains a discharge chamber, a cooled cathode and the anode facing the cathode front surface, a magnetic coil, coaxial with the cathode and the anode and is not covered by the anode, the feeder of the working gas mixture of hydrogen and methane and a pumping chamber. On the surface of the anode facing the cathode, there is a flat ceramic insulator, the surface of which is a substrate for the synthesis of diamond, or metal ring. The rotation of the plasma column on the surface of the Academy of Sciences of the ASS="ptx2">

In such a device will not be a significant increase in the area of synthesis of diamond, as in the case of increasing the diameter of the anode and connected with him substrate electrical discharge tends to approach the center of the anode and the substrate as the distance of the cathode center of the anode is less than the distance cathode - edge of the anode. In addition, the ceramic insulator relatively quickly (40-60 minutes) napylyaetsya carbon is offset from the glow discharge to the center of the substrate and often stall it in the arc discharge.

These drawbacks are largely overcome in the device described in Diamond and Related Materials, 1997, v. 6, p. 426-429). It is the prototype of the present invention.

The device contains the same basic elements: a sealed chamber, which is equipped with a cooled cathode and the anode, the substrate holder with the flat substrate in the form of a disk for the synthesis of diamond, the magnetic coil located inside the chamber below the anode, means for pumping and inlet working gas, the power sources.

In this device, the anode is made in the form of a ring in the hole which is polictial separated from the anode by a gap and electrically isolated from it. So polictial and paramania plasma column along the surface of the anode is electrodynamic force, resulting in crossed electric and magnetic fields. The working gas used is a mixture of hydrogen and methane (2-5%) at a pressure of about 150 Torr. The area of the substrate 60-80 cm2the growth rate of diamond 3-10 μm/hour.

The main drawback of the prototype is the inability to increase the diameter of the substrate for growing the diamond that you want to improve the performance of the process determined by the product of the square of the synthesis on the growth rate of the diamond, and reduce the cost of electricity and gas per unit of production to improve the efficiency of the process.

This disadvantage is a consequence of such factors:

- heating of the substrate is plasma, since the plasma is inhomogeneous temperature with increase of the diameter of the substrate are growing temperature gradients across its surface, increasing the heterogeneity of the growth and quality of the diamond.

to achieve the required temperature synthesis for large size substrate is required to install above the plane of the anode, which leads to the transfer of a glow discharge in the arc that goes on a substrate with podarkticules, and not on the anode;

- increasing the diameters of the mean is adelene magnetic field. When placing a magnet inside the chamber increases its size leads to deterioration of the quality of the gas environment in the chamber due to increased outgassing from the magnetic coil.

In addition to these, the device also has the following disadvantages: lack of opportunities for optimization of the electric potential of the substrate and its location relative to the plane of the anode and the need for airtight current to power the magnetic coil, complicating the design.

The aim of the invention is to eliminate these drawbacks of the prototype to improve the performance and efficiency of the process of growing diamond by plasma glow discharge DC by a significant increase in the area of the substrate on which is grown diamond with acceptable growth rate and high quality.

To this end introduced into the facility the following engineering changes (distinguishing features):

- polictial installed with the possibility of axial movement;

- in the design of podarkticules introduced electric heater substrate;

- magnetic coil is installed outside the discharge chamber;

- introduced dopolnitelnye.

The design of the device is schematically represented in the drawing.

The unit contains the following main elements (drawing): cylindrical hermetic discharge chamber 1, in the upper plate of which is fixed a cooled cathode 2 has a cylindrical shape, is electrically isolated from the camera 1 through the insulator 3. The flat end surface of the cathode 2 is turned in the direction of the cooled anode 4 having a Central hole, in which is placed polictial to false, set in the Central portion of the chamber 1 and electrically connected with it. The anode 4 is ring shaped with a flat surface facing the cathode 2. The outer diameter of the end face of the cathode 2 is substantially smaller than the inner diameter of the anode 4. Polictial 5 cylindrical upper part enters the hole of the anode 4, and the lower part of the second lock insulator 6, for example PTFE, installed in the bottom plate of the camera 1 and plays the role of a hermetic seal. Polictial has the possibility of axial movement with the actuator located outside the chamber (not shown). On the top of podarkticules 5, a part of the inside of the anode 4 and separated from it by a gap, fixed come podarkticules 5 is an electric heater substrate 8, the food chain which is derived through the axial hole in the body of podarkticules 5. On the outer surface of the camera 1 is fixed magnetic coil 9, coaxially with the cathode 2 and the anode 4. Camera 1 is equipped with nozzles for pumping 10 and inlet working gas mixture 11.

The unit includes power sources: the main source 12, a positive pole connected to the camera, and the negative to the cathode 2, an additional source 13, a positive pole connected to the anode and negative with podarkticules 5, and the source 14 power magnetic coil 9 and the source 15 heater supply substrate 8.

The device operates as follows.

Before working chamber 1 is pumped out to a pressure of the order of 10-2Torr. Include a water cooling system of the cathode 2, the anode 4 and the camera 1. Polictial 5 is lowered below the plane of the anode 4. Include power sources 13, 14, 15. Then through pipe 11 putting into the chamber 1 working gas mixture of hydrogen and methane to a pressure of about 1 Topp, include the primary power source 12 and set the power supply voltage of about 1 kV. Excited glow discharge between the cathode 2 and the anode 4, rotating in a magnetic field coil 9 picturetel 5 to level optimal from the point of view of the process of synthesis of diamond. The negative potential on polictial 5 from source 13 prevents the bombardment of the substrate 7 by the electrons of the plasma glow discharge. The desired temperature of the substrate is adjusted by adjusting the power mode of the heater substrate 8.

Optimization of synthesis process of diamond growth rate and purity of its structure is made by varying the main parameters: the concentration of a component of the working gas and the operating pressure, the power introduced into the plasma rotation frequency of the plasma, the substrate temperature.

In the experimental verification of the proposed device the received characteristics substantially above the level of known devices, including the prototype. Implemented the growth rate of diamond within 10-30 μm/h when the area of synthesis of 150-300 cm2. The average performance of the synthesis of diamond 2 carat/hour. The layout of the installation of continuous stable operation for at least 8 hours a day.

Technical advantages of the proposed device prior known devices of the same purposes, including the prototype, are to increase the productivity and efficiency of PR is high quality.

These advantages of the proposed device are implemented through the introduction of new characters to significantly increase the area of the substrate, which is a synthesis of diamond with the required uniformity.

The increase in the area of the synthesized diamond, in addition to increasing productivity, it is important from the point of view of the possibility of obtaining large diamond films and plates required for various technical applications, in particular for creating a vacuum-tight radiation transparent window output power heavy duty microwave vacuum devices.

Device for synthesis of diamond in a plasma glow discharge DC, including the discharge chamber and placed in it a cooled cathode and the anode facing the cathode front surface and having a Central hole, in which is placed polictial with the substrate, the magnetic coil and the power source connected to the cathode, characterized in that polictial installed with the possibility of axial movement and has a heater substrate, the magnetic coil is installed outside of the discharge chamber, the device contains an additional power source, which tricate

 

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FIELD: carbon materials.

SUBSTANCE: invention concerns manufacture of diamond films that can find use in biology, medicine, and electronics. Initial powder containing superdispersed diamonds with level of incombustible residue 3.4 wt %, e.g. diamond blend, is placed into quartz reactor and subjected to heat treatment at 600-900оС in inert of reductive gas medium for 30 min. When carbon-containing reductive gas medium is used, heat treatment is conducted until mass of powder rises not higher than by 30%. After heat treatment, acid treatment and elevated temperatures is applied. Heat treatment and acid treatment can be repeated several times in alternate mode. Treated powder is washed and dried. Level of incombustible impurities is thus reduced to 0.55-0.81 wt %.

EFFECT: reduced level of incombustible impurities.

4 cl, 3 ex

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