Method of treating a surface of at least one part by means of individual sources of an electron cyclotron resonance plasma

CA 02700575 2015-11-05 PROCESS FOR SURFACE TREATMENT OF AT LEAST ONE PART BY MEANS OF ELEMENTARY SOURCES OF PLASMA BY ELECTRONIC CYCLOTRON RESONANCE The invention relates to the technical sector of plasma production by electron cyclotron resonance (ECR) at starting from a gaseous medium and relates more particularly to a surface treatment.

In a manner perfectly known to a person skilled in the art, the plasma generated by electronic cyclotron resonance can be used in the surface treatment of metallic or non-metallic parts, such as the cleaning of the parts by ion pickling, ionic assistance in a PVD deposition process. , the activation of gaseous species to make PACVD coatings ...

These plasma surface treatment methods can be used, among others, in the field of mechanics, optics, corrosion protection or surface treatment for energy production.

The invention finds a particularly advantageous application in the treatment of one or more parts having multiple faces to be treated, or else of so-called complex shapes.

In a known manner, to carry out a plasma treatment on parts of complex shapes, a polarization of said parts is carried out which can be carried out continuously, in pulsed or radiofrequency, in order to create a plasma directly on the surface of the parts to be treat.

This solution has the drawback that the production of plasma and the bombardment of the surface by the ions of the plasma are not independent since the working voltage determines both the density of the plasma and the energy of the ions which arrive. on the surface.

It is also observed that this polarization is effective, only at pressures of about 1 to 10 Pa.

However, such a pressure, which is relatively high for a plasma treatment, corresponds to a low average free path, which makes the transport of material from or to the parts to be treated, particularly difficult and promotes the formation of hollow cathodes between the parts. parts, so that the treatment CA 02700575 2015-11-05 2 obtained is not homogeneous.

To avoid the formation of hollow cathodes, it is necessary to be particularly attentive to the distances between the parts to be treated.

Even when the working pressure is lowered by using an external source for the creation of the plasma, for example radiofrequency waves or microwaves, the problem of the homogeneous treatment of the parts remains.

Many technical solutions have been proposed to create a homogeneous plasma on the surface of the part or parts to be treated.

According to the teaching of patent FR 2,658,025, the homogeneous plasma is obtained by applying a magnetic field that is homogeneous in volume.

The homogeneous treatment of the part therefore results from the homogeneity of the plasma.

In addition, this type of configuration is extremely limiting given that parts of the ferromagnetic type necessarily modify the homogeneity of the magnetic field and consequently the homogeneity of the treatment.

Patent FR 2,838,020 proposes a distribution of sources on the periphery of a reactor to produce confinement of the plasma so that it is homogeneous in volume to obtain a homogeneous treatment.

According to this solution, the magnetic nature or not of the parts is not important but the homogeneity of the plasma is necessarily affected by the presence of the parts.

In fact, obtaining a plasma that is homogeneous in volume results from the sum of the contributions of the elementary sources distributed on the wall of the treatment system.

The fact of placing an object in the plasma necessarily induces a shading of the sources which adversely affects the homogeneity of the plasma and of the treatment.

A solution for the treatment of objects of plane geometry or having a geometry of slightly curved surface type emerges from the teaching of patent FR 2,797,372.

According to the teaching of this patent, the plasma sources are positioned at a constant distance from the surface of the parts to be treated, so that the plasma is homogeneous on this surface.

However, as indicated, this solution is specific to the determined geometry of parts.

For each new geometry, it is necessary to modify the reactor and more particularly the position of the plasma sources.

CA 02700575 2015-11-05 3 Another solution, for the treatment of objects of plane geometry, emerges from the teaching of patent W02007 / 023350.

This patent uses an unusual resonance condition at magnetic induction B - = Tr mf / e where f is the frequency of the electromagnetic wave and in and e are the mass and charge of the electron.

According to the teaching of this patent, a homogeneous treatment zone is obtained by bringing the elementary sources sufficiently close in order to obtain an isosurface of the common induction B which fulfills the above resonance condition. At the frequency usually used of 2.45 GHz, this condition is fulfilled for a field of approximately 437 Gauss.

This solution then requires that relatively small distances between the elementary sources of less than 5 cm be observed regardless of the pressure.

11 It is therefore necessary to have many individual sources, which increases the cost of treatment.

Likewise, the magnetic field in front of the sources is reinforced, which can be detrimental if it is desired to treat magnetic parts.

Another solution emerges from the teaching of patent FR 2,826,506 which relates to a device for amplifying the current of an abnormal electric discharge.

The device amplifies an existing plasma and therefore requires, in order to function, a combination with another electrode such as a magnetron cathode.

The plasma is amplified by the application of a positive voltage.

However, a very positive plasma has, as a potential drawback, the spraying of the walls of the reactor and consequently the contamination of the parts to be treated.

The object of the invention is to remedy these drawbacks in a simple, safe, efficient and rational manner.

The problem which the invention proposes to solve is to be able to carry out a surface treatment making it possible to treat parts of complex shapes in a homogeneous manner, in other words to allow a homogeneous treatment in volume although the plasma itself is not homogeneous. in volume, which limits the number of individual sources and lowers the cost of treatment.

CA 02700575 2015-11-05 4 To solve such a problem, a method and a device for the surface treatment of at least one part have been designed and developed by means of elementary sources of plasma by electron cyclotron resonance.

The method consists in subjecting the part or parts to at least one movement relative to at least one fixed linear row of elementary sources.

The invention consists of a method of treating a surface of at least one part having multiple faces with a non-uniform plasma generated by means of elementary sources of plasma by electron cyclotron resonance, the method comprising the following steps:

subjecting the at least one part to at least one movement of revolution with respect to at least one fixed linear row of elementary plasma sources, each source comprising a coaxial waveguide and a tip containing a magnet for electronic cyclotron resonance;

establish a spacing between the adjacent sources of the at least one fixed linear row between a minimum distance of about twice a diameter of the magnet, and a maximum distance Dmax determined by the formula:

Dmax ¨ 2 Rmaxo Po / P formula in which: Rmaxo is 5 cm, Po is 2.10-3 mbar, and P is the working pressure in mbar, said linear row or rows of elementary sources being arranged parallel to an axis of revolution at least one room; and providing a uniform surface treatment in volume of the at least one part even if the plasma itself is not uniform in volume, so that the uniform surface treatment on the multiple faces of the at least one part is carried out without modifying an equipment geometry as a function of a geometry of the at least one part.

CA 02700575 2015-11-05 The device comprises at least one fixed linear row of elementary sources arranged opposite the part or parts subject to means to be subjected to at least one movement of revolution.

So that the plasmas of the elementary sources are superimposed and give rise to a homogeneous treatment along the row of elementary sources, the linear row or rows of elementary sources is (are) arranged in a manner parallel to the axis of revolution of the part (s).

In the case of using several linear rows, these rows are arranged so that they do not magnetically interfere with each other.

According to these characteristics, the elementary sources of plasma constitute a localized treatment zone, so that the scale extension becomes extremely simple.

Advantageously, the movement of revolution is in the form of a single rotation or in the form of a planetary movement, single or double.

To achieve the condition of electronic cyclotron resonance, the elementary sources can consist of a coaxial waveguide and a tip containing a magnet determined to allow electronic cyclotron resonance and adapted to the frequency of the supply generator (s). of said sources, as described in patent FR 2,797,372.

To preserve the symmetry of revolution of the guide and to guarantee that the trajectories of the electrons close in on themselves, the supply axis of the magnet is collinear with the axis of the waveguide.

According to another characteristic, the elementary sources can be supplied by a single generator, the power of which is divided into equal parts between the sources as is apparent from patent FR 2,798,552.

The elementary sources can be supplied by generators CA 02700575 2015-11-05 6 whose power is adjusted to have a homogeneous treatment along the row of said sources.

The minimum distance separating two sources is imposed by their magnetic interaction.

It is of the order of twice the diameter of the magnet of an elementary source.

Below, the interaction between magnets, shifts the RCE area.

In the case of opposite polarities between the two magnets, the zone gets too close to the surface of the source; in the other case, it moves too far away from it.

From the surface of the source, the plasma spreads over a distance Rmaxo of about 5 cm at a pressure Po of 2.10-3 mbar.

The maximum spacing Dmax between two sources is therefore limited to twice this distance (approximately 10cm). At lower pressure, the maximum spacing may be greater and, at higher pressure, it will be smaller.

This distance is therefore inversely proportional to the pressure.

Dmax = 2 Rmaxo Po / P The invention is explained below in more detail with the aid of the figures of the appended drawings in which:

- Figure 1 is a front view of a purely schematic character of a simplified embodiment of the treatment device according to the invention;

FIG. 2 is a top view corresponding to FIG. 1 in the case where the movement is of the revolution type, in the form of a simple rotation;

FIG. 3 is a view similar to FIG. 2 in the case where the movement is of the revolution type, in the form of a simple planetary movement;

FIG. 4 is a view similar to FIG. 3 in the case of a movement of the revolution type in the form of a double planetary movement;

CA 02700575 2015-11-05 7 - Figures 5 and 6 show two arrangements of elementary sources having a power supply of different polarities (Figure 5) or, preferably, of the same polarities (Figure 6);

FIG. 7 is a perspective view of an exemplary embodiment of an elementary source;

- Figures 8a and 8b show the measurement of static carbon deposition by PACVD, with magnets of the same polarity (Fig. 8a) or of alternating polarity (Fig. 8b);

- Figures 9a and 9b show the measurement of carbon deposition by PACVD, with magnets of the same polarity (Fig. 9a) or of alternating polarity (Fig. 9b); and FIG. 10 illustrates the decrease in the deposition rate when the distance from the row of sources increases.

FIG. 1 shows the general structure of the device for treating the surface of at least one part (1) by means of elementary sources of plasma (2) by electron cyclotron resonance.

According to the invention, the device comprises at least one fixed linear row of elementary sources (2) arranged opposite the part or parts (1).

Importantly, the part (s) (1) is or are subject (s) to any type of known and appropriate means to be subjected (s) to at least one movement, in particular a movement of revolution.

This combination of a movement of revolution of the parts with the linear arrangements of the elementary sources of plasma by electronic cyclotron resonance, makes it possible to produce a homogeneous treatment of the three-dimensional surfaces of the complex parts.

CA 02700575 2015-11-05 8 The movement is adapted to the size and geometry of the parts to be treated and to the loading of the vacuum chamber.

For a large part (figure 2), this movement can be constituted by a simple rotation.

For smaller parts the movement can be of the single planetary type (figure 3) or of the double planetary type (figure 4).

In one embodiment, each elementary source (2) consists of a coaxial waveguide (2a) and a tip (2b) containing a sufficiently powerful magnet (3) to achieve electronic cyclotron resonance. The magnetization axis of the magnet is collinear with the axis of the coaxial guide (2a).

These arrangements make it possible to preserve the symmetry of revolution of the guide and to guarantee that the trajectories of the electrons close in on themselves.

The magnetization of the different sources (2) can be freely determined, so that adjacent sources can have the same polarity (figure 6) or different polarities (figure 5).

In the case where the polarities of two neighboring magnets are opposite, field lines pass from the pole of one magnet to the opposite pole of the other magnet.

Hot electrons will then be trapped on its lines and go back and forth between the two magnets.

This localization of electrons is in the space in front of and between two sources and gives rise to a stronger plasma there.

This results in a higher deposition rate between two magnets.

In the case where the polarization of the sources is the same, the field lines of two neighboring magnets repel each other and no line connects the two magnets.

The localization of hot electrons in the space in front of and between the sources then does not take place and the deposit is more homogeneous.

To find an equivalent homogeneity with the alternating polarizations, the distance between sources and substrate can be increased by a few centimeters, but in this case the deposition rate is lost.

For these reasons, the preferred arrangement of the magnets is that where the polarity is the same everywhere.

CA 02700575 2015-11-05 9 Example 1 non-compliant: Static deposition of carbon by PACVD Two configurations of the polarities of the magnets were used: 6 end caps with the same polarity (Figure 8a) and 6 end caps with alternating polarity (Figure 8b.

The substrates are placed in front of the sources and remain fixed during the treatment.

The thickness measurements reported in Figures 8a and 8b show that the static deposition is not homogeneous.

The alternating polarities configuration (Figure 8b) gives a slightly better result but still exhibits thickness variations of 30 to 40%.

Compliant Example 2: Carbon deposition by PACVD This deposition is made from a hydrocarbon as precursor gas.

Two configurations of the polarities of the magnets were used: 6 tips of the same polarity (Figure 9a) and 6 tips of alternating polarity (Figure 9b).

The thickness measurements of the deposit reported in Figures 9a and 9b show two things:

the average deposition rate is higher in the configuration using magnets of alternating polarity; and the uniformity of deposition is better in the configuration using magnets of the same polarity.

These examples show that the association of a row of sources with a movement around an axis parallel to the row of sources gives a homogeneous treatment even if a static treatment gives a very inhomogeneous treatment.

The elementary sources (2) are supplied by a single generator, the power of which is divided equally between the sources.

Or the elementary sources (2) are supplied by generators whose power is adjusted to increase the degree of homogeneity of the CA 02700575 2015-11-05 treatment.

The generator (s) are, for example, of the microwave type, typically of 2.45 gigahertz.

According to the invention, as shown in Figure 1, several sources (2) are arranged along a line parallel to the axis of rotation of the parts.

The result is that the plasma zones of the 5 elementary sources (2) are superimposed, making it possible to obtain a homogeneous treatment along the row of elementary sources.

The minimum distance Dmin separating two sources is imposed by their magnetic interaction.

It is of the order of twice the diameter of the magnet of an elementary source.

Below, the interaction between magnets, shifts the RCE area.

In the case of opposite polarities between the two magnets, the zone gets too close to the surface of the source; in the other case, it moves too far away from it.

From the surface of the source, the plasma spreads over a distance Rmaxo of about 5 cm at a pressure Po of 2.10-3 mbar. The maximum spacing Dmax between two sources is therefore limited to twice this distance (approximately 10cm). At lower pressure, the maximum spacing may be greater and, at higher pressure, it will be smaller.

This distance is therefore inversely proportional to the pressure:

Dmax = 2 Rmaxo Po / P To produce a homogeneous treatment according to the height of the reactor, the relative position of the different sources must therefore be between Dmin and Dmax.

In an exemplary embodiment, the parts to be treated can be placed on a substrate with a capacity for rotation according to one or more movements and of the type of those used in the field of PVD deposition such as magnetron sputtering.

The minimum distance of the parts from the sources is defined as being the distance considered as close as possible during the movement.

Referring to the results presented in FIG. 10, it has been observed that a minimum distance of between 40 and 160 mm approximately gives a quality of treatment which is adequate at the level of the desired homogeneity.

CA 02700575 2015-11-05 11 In this example, we look at the thickness homogeneity of a deposit produced from microwave RCE sources using a hydrocarbon as gaseous precursor.

The test pieces are arranged at different minimum distances from the sources opposite them.

We compare a static treatment, that is to say with the substrates remaining immobile, and a treatment with planetary motion.

Figure 10 illustrates the decrease in deposition rate as the distance to the row of sources increases.

In the case of planetary motion, the source-substrate distance corresponds to the minimum distance from the substrate to the sources during the movement.

It is clearly seen that the movement makes it possible to attenuate the drop in the deposition rate.

The invention finds an advantageous application for the surface treatment at different levels, such as, in an indicative and in no way limiting manner, the cleaning of parts by ion pickling, ionic assistance to a PVD deposition process or even activation. of gaseous species to make PACVD coatings.

As indicated in the preamble, these plasma treatment techniques are used in many fields, such as mechanics, optics, corrosion protection or surface treatment for energy production.

The advantages emerge clearly from the description, in particular it is emphasized and recalled that the method and the device for treatment by means of elementary sources of plasma by electron cyclotron resonance make it possible:

the treatment of metal parts or not, of variable geometry and any, using a unique configuration of equipment;

obtaining homogeneous treatment on complex and varied surfaces, without it being necessary to modify the geometry of the equipment according to the geometry of the parts.