Method and device for generating a plasma excited by a microwave energy in the electron cyclotron resonance (ECR) domain, in order to carry out a surface treatment or produce a coating around a filiform element

Abstract

According to the process, the filiform component is continuously linearly moved through magnetic dipoles arranged opposite each other and around a tube constituting a treatment chamber, and the microwave energy is introduced between at least two magnetic dipoles.

Claims

1. A process to generate a plasma excited by microwave energy in a field of electron cyclotron resonance (ECR), to execute a surface treatment or coating around a filiform component, comprising: arranging at least two annular magnets constituting magnetic dipoles at atmospheric pressure opposite each other and mounted concentrically around a tube constituting a treatment chamber, to produce axisymmetric magnetic field lines parallel to the filiform component, continuously linearly moving the filiform component through the at least two annular magnets and the tube constituting a treatment chamber, introducing the microwave energy to the tube, between the at least two annular magnets via a microwave applicator mounted between the at least two annular magnets, and thereby generating a linear axisymmetrical plasma confined around the filiform component in the treatment chamber.

2. The process according to claim 1, wherein the surface treatment comprises a cleaning, a pickling, a functionalisation, or a grafting.

3. The process according to claim 1, wherein the coating is obtained by PECVD (plasma-enhanced chemical vapour deposition).

4. A device to generate a microwave excited plasma by electron cyclotron resonance (ECR), around a continuously linearly driven filiform component, comprising: at least one module composed of two annular magnets constituting magnetic dipoles arranged at atmospheric pressure opposite each other and mounted concentrically around a tube constituting a treatment chamber, and producing axisymmetric magnetic field lines parallel to the filiform component wherein the filiform component to be treated is linearly moved through the two annular magnets and through the tube constituting the treatment chamber, and wherein the device further includes a microwave applicator connected to the tube, between the two annular magnets to introduce microwave energy between the two annular magnets, thus generating a linear axisymmetrical plasma confined around the filiform component in the treatment chamber.

5. The device according to claim 4, wherein the annular magnets comprise permanent magnets.

6. The device according to claim 4, wherein the annular magnets comprise electromagnet coils.

7. The device according to claim 4, wherein the microwave applicator is arranged perpendicularly to a central axis of the tube.

8. The device according to claim 4, wherein the tube constitutes a Tee having a median branch and two other branches on either side of said median branch, the median branch receives the microwave applicator and the other two branches receive the annular magnets.

9. The device according to claim 4, wherein the device comprises several modules mounted in series and in linear alignment and connected together by a sealing ring.

10. The device according to claim 9, wherein each sealing ring acts as a pumping zone being connected to a gas pumping collector.

11. The device according to claim 9, wherein the sealing ring acts alternatively as a gas pumping zone and as a gas injection zone.

12. The device according to claim 4, wherein the filiform component is electrically polarised to allow an ion bombardment of the plasma.

Description

BRIEF DESCRIPTION OF THE DRAWING FIGURES

(1) The invention is set out below in more detail with the help of the appended figure drawings in which:

(2) FIG. 1 shows a principle diagram of a reactor according to the prior art to generate a deposition on a wire to be coated;

(3) FIG. 2 is a view corresponding to FIG. 1 showing the principle of the device according to the invention;

(4) FIG. 3 is a perspective view of a basic module of the device according to the invention;

(5) FIG. 4 is a perspective view showing the assembly of several modules of the device to increase the treatment speed,

(6) FIG. 5 is a curve of the FITR analyses very classically showing that the deposition approaches all the more to the SiO.sub.2 when the O.sub.2/HMDSO ratio is high.

DETAILED DESCRIPTION

(7) As indicated, the invention finds a particularly advantageous application to generate a plasma with a view to the surface treatment of any type of filiform component, including a conductor, of the wire type, fibres, tubes, sleeves, etc and more particularly any component (F) of a significant length with respect to its diameter. The aim sought according to the invention is to continuously treat the component (F) on passing, in other words, by linear driving of the wire.

(8) According to the invention, the device or reactor comprises, at least one module comprised of two magnetic dipoles (1) and (2) arranged opposite and preferably mounted around a tube (3), constituting a treatment chamber. Each magnetic dipole (1) and (2) is for example made up of an annular magnet arranged concentrically to the tube (3). This assembly facilitates in particular the cooling of the magnets. In fact, as opposed to the ECR applicators described in the state of the art, the magnets are not under vacuum. Component (F) is engaged coaxially with the tube (3) and continuously linearly driven by any known and suitable means. A microwave applicator (4), of any known and appropriate type, is mounted between the two magnets (1) and (2). The microwave applicator (4) is arranged perpendicularly to the centre line of the tube (3). Preferably the opposite polarities are opposite so that the field lines are parallel to component F. Reference is made to FIG. 2 which shows that the plasma at the ECR area is on the wire. An axisymmetry of the magnetic field lines (C) is also ascertained allowing for a homogeneous deposition to be made on component (F).

(9) In one form of embodiment, the tube (3) constitutes a Tee, the median branch of which (3a) receives the microwave applicator (4), in particular its coaxial guide (4a). The other two branches (3b) and (3c) of the Tee receive the magnets (1) and (2) on either side of the median branch (3a).

(10) From this basic design of the device, it is possible to serial mount and in linear alignment several modules as shown in FIG. 4). In this configuration, the connection between the modules is provided by a sealing ring (5) which also acts as a pumping zone being connected to a connector (6) to pump gas. In this configuration the plasma and any reactive gases are preferably injected opposite the microwave applicators (injection not shown in the figure). An alternative configuration to the one shown consists in that the sealing rings alternatively act as a gas pumping zone and as a gas injection area.

(11) The pumping is distributed between the centre of the reactor and the right and left ends of the latter. The filiform component (F) is linearly inserted into the treatment chamber resulting from the tube made up of a linear alignment and the series mounting of the different branches (3b), (3c) tubes and rings (5). To increase the running speed of the filiform component (F), it suffices to multiply the number of modules.

(12) It is to be noted that it is not possible to inject, into each module, a suitable precursor and to laminate the pumping circuits to adjust the working pressures of each module.

(13) Tests were performed with samarium cobalt (Sm.sub.2Co.sub.17) magnets without excluding any other material to generate a magnetic field of 875 G such as neodymium iron boron.

(14) These tests were performed according to two configurations.

(15) First Configuration:

(16) The magnets have the following dimensions: inside diameter 20 mm, outside diameter 28 mm, thickness 20 mm, polarisation according to thickness, distance between magnets: 31.5 mm opposite polarities between magnets.

(17) Second Configuration:

(18) The magnets have the following dimensions: inside diameter 33.8 mm, outside diameter 50 mm, thickness 25 mm, polarisation according to thickness, distance between magnets: 46 mm characteristics of tube acting as treatment chamber: ND 25 i.e. 33.7 mm of outside diameter opposite polarities between magnets.

(19) In these two configurations: The microwaves are injected in the middle of the space between the two magnets. The penetration depth of the microwave injector should be optimised to facilitate priming and operation of the plasma. The magnets are at atmospheric pressure. The magnets are cooled on contact with an external casing in which a fluid circulates, for example water. The gas pumping zones and gas injection zones have been alternated. The magnets are maintained in the system by three pressure screws to prevent being attracted.

(20) The advantages are made well apparent from the description, the following is highlighted and recalled in particular: the generation of a linear plasma confined around the component to be treated in order to minimise the volume of the chamber and as a consequence, to minimise the investments and consumption of precursor gas and energy, the generation of an axisymmetrical plasma in order to guarantee the homogeneity of the deposition on the component to be treated, the possibility of treating all types of filiform components including conductors of the wire type, fibres and more generally all products the length of which is greater than the diameter.

(21) As an example, SiO.sub.x deposition tests by PECVD ECR in a reactor according to the second configuration are described below.

(22) First PECVD Process Flow rate of TMS (Tetramethylsilane): 5 sccm Flow rate of O.sub.2 (oxygen): 18 sccm Pressure: 1.3.10.sup.?2 mbar Microwave injection power: 100 W

(23) With this O.sub.2/TMS ratio of 3.6 the deposition speed found between the two magnets in the middle of the chamber is 250 nm/min.

(24) The deposition speed is measured on a silicon plate placed in the centre of the reactor.

(25) Second PECVD Process Pressure: 1.10.sup.?2 mbar Microwave injection power: 50 W

(26) Use of a O.sub.2/HMDSO Mix

(27) TABLE-US-00001 O.sub.2/HMDSO ratio Deposition speed nm/min 9 530 3 875 1.7 1100