Plasma generator

Abstract

The invention relates to devices intended for treatment of materials in gas discharge plasma of low temperature, namely the induction plasma generator, placed inside the process volume (working chamber). The technical problem to be solved by the proposed invention is to increase the efficiency of the device; to improve the reliability of the device, increase purity of plasma environment and increase density of plasma generated; increase the life of device; reduce the level of noise; reduce the size of the device.

Claims

1. Plasma generator comprising a spiral coil, placed inside a conducting screen, an inner surface of which has a cylindrical shape, wherein space between windings of the spiral coil and between the spiral coil and the screen is filled with a dielectric having an outer surface, the spiral coil is flat, the distance from the plane of the spiral coil to an outer surface of the dielectric is less than double thickness of the spiral coil, and a distance from the plane of the coil to the base of the inner surface of the screen is greater than double distance from the plane of the spiral coil to the outer surface of the dielectric.

2. Plasma generator as set forth in claim 1 wherein coaxial input provided for supplying high frequency current to the spiral coil, an inner conductor of which is connected to one end of the spiral coil, and an outer conductor is connected to the other end of the spiral coil.

3. The plasma generator as set forth in claim 2 wherein the coaxial input is arranged to supply therethrough a cooling fluid or gas to the spiral coil.

4. Plasma generator as set forth in claim 1 wherein the outer surface of the dielectric is closed by at least one dielectric screen made of a material resistant to plasma, with the distance from the plane of the spiral coil to the outer surface of the dielectric screen less than double thickness of the spiral coil.

5. Plasma generator as set forth in claim 4, characterized by the presence of a gap between the dielectric screen and the outer surface of the dielectric.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) The essence of claimed invention is explained by drawings, where on FIG. 1 there is a sectional view of proposed device structure; on FIG. 2 there is a sectional view of construction with coaxial input, the inner conductor is connected to one end of the coil, and outer conductor is connected to the other end of the coil; on FIGS. 3 and 5 there are sectional views that show how the outer surface of insulator is closed by dielectric screen made of material resistant to plasma; on FIG. 4 there is a sectional view of construction with dielectric separating the coil from the working surface of the device made of a material resistant to plasma; on FIG. 6 there is a sectional view that shows how the outer surface of the insulator is closed by dielectric screen made of material resistant to plasma, with the distance from the plane of the coil to outer surface of dielectric screen less than double thickness of the coil; on FIG. 7 there is a sectional view that shows insulating filling that consists of a dielectric cylinder, separating the coil from the base of inner surface of the screen, dielectric inserts, filling the space between the coil windings, and dielectric plate separating the coil from working surface of the device.

(2) The figures contain the following items:

(3) 1flat spiral coil;

(4) 2conductive screen;

(5) 3dielectric filler;

(6) 3adielectric cylinder (FIG. 7);

(7) 3bdielectric inserts (FIG. 7);

(8) 4outer conductor of coaxial input;

(9) 5inner conductor of coaxial input;

(10) 6dielectric plate, resistant to plasma;

(11) 7dielectric screen;

(12) Adistance from plane of the coil to dielectric surface;

(13) Bcoil thickness;

(14) Cdistance from plane of the coil to the base of inner surface of the screen.

(15) Following terms have the following meanings:

(16) High frequencyfrequency in the range of 0.5 . . . 100 MHz.

(17) High-density plasmaplasma with an electron density of at least 10.sup.11 cm.sup.3.

(18) Coilconductor in the form of single or multi-start helix. Multiple-spiral is at least two spiral conductors of the same shape arranged with the rotation relative to each other about a common axis. In present description a ring is considered to be a single-pass single-turn coil.

(19) Coaxial inputdevice comprises a hollow conductor in the inner cavity of which at least one inner conductor is placed.

(20) Flat coilcoil which can be inscribed in a cylinder which height is no more than twice greater than two values: winding pitch and the largest linear dimension of cross section of the coil. The plane of the coila plane equidistant from the base of the cylinder.

(21) Thickness of flat coil means height of the cylinder.

(22) The plasma generator (1) comprises a helical coil 1 that is placed inside conducting screen 2, the inner surface of which is of a nearly cylindrical shape. The space between the coil windings and between coil 1 and screen 2 is filled with dielectric 3. In particular, there are dielectric inserts between the coil windings.

(23) The coil 1 is flat. Flat coil design ensures simultaneously maximum inductive coupling between coil and plasma and minimal inductive coupling between coil and screen within given size of device.

(24) Distance from plane of the coil to outer surface of dielectric is chosen smaller than double thickness of the coil that provides increased inductive coupling between coil and plasma and increased capacitance between the outer surface of dielectric and windings that facilitates breakdown of gaseous working medium volume. This increases the reliability of discharge ignition and stability of device over a wide range of process environment parameters.

(25) Distance C from plane of the coil to the base of inner surface of the screen is selected greater than double distance A from plane of the coil to outer surface of insulator that provides a reduction in inductive coupling between the coil and conductive screen. Proposed design increases the inductance of the system, allowing you to get sufficient voltage for discharge ignition on coil windings when current in coil windings is close to desired plasma generator operating mode values and small values of eddy currents in the screen, causing wasteful high-frequency generator power losses for screen heating.

(26) For supplying high frequency current to the coil 1 plasma generator may be provided with a coaxial input (FIG. 2), the outer conductor 4 of which is connected to one end of the coil and the inner conductor 5 is connected to other end of the coil;

(27) Coaxial input can be arranged to supply therethrough a cooling fluid or gas to the coil. Coil conductors may be hollow to supply therethrough a cooling fluid or gas.

(28) The use of coaxial input allows reducing the inductance of plasma generator power circuits, its supply voltage and noise level.

(29) An insulator separating the coil from working surface of device may be made of material resistant to plasma such as quartz or ceramic plate 6 (FIG. 3).

(30) The outer surface of insulator may be closed by at least one dielectric screen 7 made of material resistant to plasma, with the distance from plane of the coil to outer surface of dielectric screen less than double thickness of the coil 7 (FIG. 5).

(31) The outer surface of insulator is closed by at least two dielectric screens 7, one of which is made of a material resistant to plasma, with a gap between the screens (FIG. 6).

(32) Insulating filling may consist of dielectric cylinder 3a, separating the coil 1 from the base of inner surface of the screen, dielectric inserts 3b, filling the space between the coil windings, and dielectric plate 6 separating the coil from the working surface of the device (FIG. 7).

(33) Plasma generator of second embodiment has flat coil 1.

(34) Flat coil design ensures simultaneously maximum inductive coupling between coil and plasma and minimal inductive coupling between coil and screen within given size of device.screen 2 is designed as a ring which axis is perpendicular to plane of the coil, the edge of the ring facing the volume, where it is required to generate plasma, is enclosed with dielectric. The ring is made of conductive material (e.g., aluminum or aluminum alloy).screen ring design can limit (localize) the scope of high-frequency electromagnetic fields, which increases the efficiency of power input to plasma in working volume, prevents the occurrence of spurious discharge around the device that leads to useless energy losses and reduces the stability and reliability of operation. Also, the use of screen of well conductive material (e.g. aluminum) allows to avoid interference in the surrounding parts of the working chamber and tooling that often are made of poorly conducting materials (e.g., stainless steel), so that crosstalk leads to considerable losses of high-frequency power.

(35) Plasma generator of the third embodiment has the screen electrically connected to one end of the coil. The permittivity of dielectric between the coil windings and between the coil and the screen is in the range of 2.5 to 50.

(36) Use of dielectric of 2.5 to 50 dielectric capacitivity increases the capacitance of the coil to the screen, connected to one end of the coil that can partially compensate coil self-inductance, to reduce high frequency current required to power the device and to reduce energy losses in power supply circuits. The use of dielectric with dielectric constant of less than 2.5 will not lead to significant increase in capacitance and of higher than 50 will lead to substantial increase of interturn capacitance.

(37) In addition, plasma generators of all three embodiments have dielectric that separates coil from the working surface of the device made of material resistant to plasma. The outer surface of insulator is closed by at least one dielectric screen made of material resistant to plasma, with the distance from plane of the coil to outer surface of dielectric screen less than double thickness of the coil. There is a gap between the screen and outer surface of dielectric. The outer surface of insulator can be also closed by at least two dielectric screens, one of which is made of material resistant to plasma, with a gap between the screens.

(38) Insulating filling consists of dielectric cylinder, separating the coil from the base of inner surface of the screen, dielectric inserts, filling the space between the coil windings, and dielectric plate separating the coil from working surface of device. Dielectric plate is made of material resistant to plasma. Between dielectric plate and coil, as well as between dielectric plate and dielectric inserts, there is a gap. The outer surface of insulator is closed by at least one dielectric screen made of material resistant to plasma, with the distance from plane of the coil to outer surface of dielectric screen less than double thickness of the coil. There is a gap between the screen and outer surface of dielectric.

(39) The plasma generator operates as follows. The device is placed in the working chamber; the outer surface of dielectric should be in that part of the chamber, where it is required to generate plasma of maximum density. The camera is pressurized to 0.01 . . . 500 Pa. Flow of current in the coil is provided by supplying high-frequency voltage to the coil. If amperage value is sufficient for the emergence and maintenance of high-frequency inductive discharge plasma, plasma is generated in working chamber. High-frequency electromagnetic field is displaced from plasma and is compressed against the coil. Good electromagnetic coupling between the coil and plasma is able because the distance from coil to outer surface of dielectric is not more than double thickness of the coil.

(40) Proposed constructive design of generator provides higher plasma density and increased purity of plasma environment than in prior one, under the same conditions in the discharge chamber and at the same RF power supply. Proposed device has high efficiency, is reliable in operation, has an extended lifetime and compact size.

(41) While the invention has been described with reference to an exemplary embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.