Linear microwave source for plasma surface treatment

The invention relates to a linear microwave source for the treatment of surfaces comprising: PA1 a tight enclosure (1), PA1 means (B.sub.1, B.sub.2 ; A.sub.1, A.sub.2) for producing a magnetic field in the enclosure and for generating a plasma layer (P), PA1 coupling means between the microwave emission means and the enclosure (1), PA1 at least one target (2), PA1 pumping means (3), PA1 gas injection means (9) for checking the ion species of the plasma layer (P). Particular application to plasma surface treatment.

TECHNICAL FIELD 
The present invention relates to a linear microwave source for plasma 
surface treatment. 
PRIOR ART 
In electron cyclotron resonance sources, the ions are obtained by ionizing, 
within a sealed enclosure of the superhigh frequency cavity type and 
having an axis of symmetry, a gaseous medium constituted by one or more 
gases or metal vapours. This ionization results from an interaction 
between the gaseous medium and a plasma of electrons highly accelerated by 
electron cyclotron resonance. This resonance is obtained by means of the 
combined action of a high frequency electromagnetic field injected at a 
first end of the enclosure and a magnetic field having an axial symmetry 
prevailing in said same enclosure. 
French patent application 86 10066 of Jul. 10, 1986 describes such a 
cyclotron resonance ion source having: 
a sealed enclosure with a longitudinal axis of symmetry, a first and a 
second ends oriented in accordance with said axis, said enclosure 
containing a gas for forming by cyclotron resonance a plasma confined 
within said enclosure; 
a device for injecting at the first end of the enclosure a high frequency 
electromagnetic field; 
a magnetic structure arranged around the enclosure and having an axis of 
symmetry coinciding with that of the enclosure, producing axial and 
radial, local magnetic fields, defining at least one equimagnetic layer on 
which the electron cyclotron resonance condition is satisfied, said 
magnetic structure comprising: 
a first and a second coils positioned on either side and equidistantly with 
respect to a median plane, perpendicular to the longitudinal axis of the 
enclosure and passing through the centre of the cavity, said two coils 
being traversed by currents having opposing flow directions and 
means for concentrating magnetic force lines surrounding the enclosure in 
the median plane and locally reinforcing the radial magnetic fields in 
said plane; 
a system for extracting from the enclosure the ions formed and located at 
the second end of the enclosure. 
Several other prior art documents relate to plasma sources. 
Patent application WO-A-92/21136 (Material Research Co.) describes an 
apparatus for the treatment of electronic "wafers" having the following 
features: 
the device revolves about an axis, 
the microwave power is applied by a cylindrical cavity excited by an array 
of distributed loops, 
the magnetic field is produced by distributed magnets, said field having a 
symmetry of revolution and being highly inhomogeneous, 
for compensating said inhomogeneity of the field and the plasma the magnets 
rotate. 
Such a source with a revolution geometry cannot be transposed to a linear 
geometry. 
Japanese abstract (Vol. 10, no. 158, 6.6.1986; JP-A-61-013 634) describes a 
device whose magnetic configuration is of revolution. 
The configuration of the cusp is that used in fusion machines. The cusp 
configuration is used for eliminating in the radial direction high energy 
particles, which can cause defects in the deposition. In said 
configuration the cusp is not an active element. 
Patent application EP-A-252,845 (CEA) describes an electron cyclotron 
resonance ion source. This source has an enclosure containing a gas for 
forming a confined plasma, a device for injecting at one end of the 
enclosure a hf electromagnetic field, two coils arranged around the 
enclosure and supplied in opposition, located on either side of a median 
plane perpendicular to the longitudinal axis of the enclosure, a 
ring-shaped, soft iron shield surrounding the enclosure and located in the 
median plane, the coils and the shield defining at least one equimagnetic 
layer on which the electron cyclotron resonance condition is satisfied, as 
well as a system for extracting the ions formed and located at the second 
end of the enclosure. 
Several prior art documents deal with couplers: 
The article entitled "Lower-hybrid plasma heating via a new launchers--The 
multijunction grill" by Gormezano et al (Nuclear Fusion, vol. 25, No. 4, 
1985, Vienna, Austria, pp. 419-423). 
The article entitled: "Coupling of slow waves near the lower hybrid 
frequency in JET" by Litaudon et al (Nuclear Fusion, vol. 30, no. 3, 1990, 
Vienna, Austria, pp. 471-484). 
The article entitled: "A 4 waveguide multijunction antenna for L. H. H. in 
PETULA" by N'Guyen et al (Proceedings of the 13th symposium on fusion 
technology, vol. 1, 24-28 Sep. 1984, Varese Italy, pp. 663-668). 
The article entitled: "The 15 Mw microwave generator and launcher of the 
lower hybrid current drive experiment on JET" by Pain et al (Proceedings 
of the IEEE 13th symposium on fusion engineering, 2-6 Oct. 1989, vol. 2, 
Knoxville, USA, pp. 1083-1088). 
The article entitled: "First operation of multijunction launcher on JT-60" 
by Ikeda et al (Proceedings of the 8th topical conference on 
radiofrequency power in plasmas, 1-3 May 1989, no. 190, Irvin, Canada, pp. 
138-141). 
The article entitled: "Technological developments in lower hybrid coupling 
structures in FT and FTU" by Ferro et al (Proceedings of the 11th 
symposium on fusion engineering, 18-22 Nov. 1985, vol. 2, Austin, Tex., 
pp. 1210-1213). 
U.S. Pat. No. 4,110,595 (Brambilla et al). 
In all these documents the aim is to slow down a wave. This is brought 
about by associating guides by the large side and imposing a regular phase 
shift .DELTA..psi. between each guide. The coupling of the wave is 
obtained by placing said array of guides perpendicular to the magnetic 
field. 
In all these documents there is a superimposing of independent VHF modules 
in order to make available the maximum power in the surface of a fusion 
machine (JET, JT 60, TORE SUPRA). These guides are associated in each 
module by the large side and are perpendicular to the magnetic field. 
However, the field of the present invention is the production of very long 
plasma layers (e.g. exceeding 1 meter) and coupling a microwave power with 
said plasma layer with a view to the treatment of large surfaces. 
To this end, the invention aims at solving a certain number of problems 
existing in the prior art devices, in order to reduce costs, facilitate 
use and obtain better results, in particular: 
producing a planar magnetic configuration, whose plane of symmetry is 
identical to that of the plasma layer, 
production over the entire width of the plasma layer of a constant magnetic 
field making it possible to obtain the resonance condition between the 
frequency of the wave and the electron cyclotron frequency over the entire 
width of said layer, 
possibility of varying the magnetic configuration in order to adapt the 
characteristics of the plasma to the chosen surface treatment type, 
use of the coupler ensuring a uniform distribution of the microwave power 
over the plasma layer and a wave plane perpendicular to the magnetic 
field, 
desired modularity of the source, 
obtaining homogeneous target wear, 
obtaining a good adaptation of the different elements used: coupler, 
plasma, target, to the desired deposit, 
obtaining a good operation despite the large dimensions of the 
installations, 
obtaining a controlled deposit independently of the formation of the plasma 
layer. 
DESCRIPTION OF THE INVENTION 
The invention proposes a linear microwave source functioning without an 
electrode, in a wide pressure range and generating a plasma layer whose 
dimensions are adapted to the treatment of large surfaces. 
This linear microwave source for the plasma treatment of surfaces is 
characterized by the implementation of: 
a tight enclosure, 
an array of coils and/or magnets making it possible to generate planar 
magnetic configurations, whose plane of symmetry corresponds to that of 
the plasma layer, 
coupling means between the microwave power sources and the plasma layer in 
the enclosure, 
at least one target, constituted by at least one element to be deposited, 
which is electrically insulated from the enclosure and raised to a bias 
voltage relative to the plasma layer, 
pumping means for producing the vacuum in the enclosure, 
gas injection means for checking the ion species of the plasma layer, 
a magnetic field having a plane of symmetry coinciding with that of the 
plasma layer and that of the enclosure, 
a constant magnetic field in the direction of the plasma layer width, which 
makes it possible to obtain the resonance condition 2.pi.f.sub.0 =e 
B.sub.RES /m over the entire plasma layer width. 
Apart from the advantage of functioning without an electrode in a wide 
pressure range and generating a plasma layer whose dimensions are 
adaptable to the application adopted, the microwave source according to 
the invention can, as a function of the arrangement of the coils and 
permanent magnets, function with several magnetic configuration types: 
a planar configuration of the "magnetic mirror" type making it possible to 
produce a very dense plasma layer and an ion flux, whose characteristics 
are particularly appropriate to a process for the coating of large parts 
by target sputtering; 
a planar configuration of the "magnetic cusp" type appropriate for the 
production of a metallic plasma layer for depositing thin metallic or 
alloy films on substrates; 
a planar configuration of the "hybrid" type favouring the production of 
multicharged ions for the requirements of ion implantation on large 
surfaces. 
The coupling of the microwave power with the plasma layer is brought about 
by waveguides associated or joined along their large or small sides, 
permitting a uniform distribution of said power over the entire plasma 
layer and the excitation of a wave or vibration plane perpendicular to the 
magnetic field. 
In a preferred embodiment the coupler is constituted by identical VHF 
modules, each module grouping several guides joined along the large side 
and supplied from a main guide by means of a planar multijunction E or 
several secondary guides joined along the small side and supplied from a 
main guide by means of a taper E and H and a mode converter. At a 
frequency of 2.45 GHz, this solution is particularly simple and economic, 
because each VHF module can be supplied by a magnetron-type, medium power, 
microwave emitter or transmitter. 
This method of associating or joining guides makes it possible to adapt the 
surface of the plasma layer generated in the source to the dimensions of 
the parts to be treated and in particular to large parts. 
Advantageously the coupling means are at least partly made from a material 
which is that of the target, which makes it possible to obtain high 
quality metal deposits, contamination by impurities then being reduced. 
The source assembly is grounded or earthed. The enclosure has a 
parallelepipedic shape. The frequency of the electromagnetic field 
produced within the enclosure is in the range 1 to 10 GHz. 
In a first variant, the means for producing a magnetic field comprise 
coils, the length of the coils exceeding the length of the vacuum 
enclosure, so as to eliminate the edge effects linked with the return of 
the current. 
In a second variant, the means for producing a magnetic field comprise 
permanent magnet blocks located on either side of the vacuum enclosure, 
the permanent magnet blocks being extended beyond the vacuum enclosure in 
order to prevent edge effects. 
In a first embodiment, the source according to the invention has a 
mirror-type magnetic configuration comprising two identical coil arrays 
traversed by equal currents flowing in the same direction, or two 
identical magnet blocks hollowed out in their central portion and located 
on either side of the vacuum enclosure, the magnetic field having two 
maxima B.sub.MAX and one minimum B.sub.MIN between said maxima, the 
condition B.sub.MAX &gt;B.sub.RES &gt;B.sub.MIN being satisfied over the entire 
width of the plasma layer, B.sub.RES being the value of the magnetic field 
for which the cyclotron angular frequency of the electron is equal to the 
angular frequency of the electromagnetic wave used for producing the 
plasma. 
Compared with the magnetron method currently used for this coating process, 
this type of source offers numerous advantages. The ionization of the gas, 
the sputtering of the target, the recombination of the target atoms on the 
part to be treated are very strongly decoupled, which gives a very 
considerable flexibility in the performance of the process. The ion 
density n.sub.i in the source is fixed by the gas flow rate .left 
brkt-top.o and the microwave power P.sub.VHF and the velocity of the ions 
V.sub.2, which bombard the target by the voltage of said target V.sub.c. 
The deposition rate on the part, which is proportional to the ion flux on 
the target, can thus be controlled in independent manner by the three 
parameters .left brkt-top.o, P.sub.VHF and V.sub.c. This e.g. makes it 
possible to optimize the coefficient of sputtering of ions on the target 
by the target V.sub.c and optimize the density in the source n.sub.i with 
the parameters .left brkt-top.o and P.sub.VHF. Moreover, in said sources 
the neutral atoms emitted by the target recombine on the part to be 
treated in a region which does not face the plasma. Thus, for a constant 
ion flux supplied by the source, the pressure in the work frame or rack 
can be lowered by using a differential pumping. The wave ionization 
mechanism used enables the ion flux given to the target to operate with 
lower pressures in the source, which limits the density of occluded gases 
in the deposit. The material balance is improved because the entire 
surface of the target is bombarded by the plasma layer. In addition, the 
target can be charged without dismantling the source or passing in front 
of the ion beam for carrying out a continuous process. 
In this embodiment the source can be used for supplying a beam of ions or 
electrons. 
For this embodiment the target is replaced by extraction electrodes. The 
first electrode facing the plasma layer is placed at the potential of the 
vacuum enclosure and the second electrode is positively polarized in order 
to extract the electrons or negatively polarized to extract the ions. 
In a second embodiment the source according to the invention has a magnetic 
cusp configuration in which the currents passing through the coils or 
magnetization vector in the magnet blocks have opposite signs, the coils 
and the magnets being dimensioned so as to satisfy the condition 
B.sub.xMAX, B.sub.yMAX &gt;B.sub.RES over the entire plasma layer width. 
Apart from the possibility of producing deposits on large substrates, by 
its very operating principle this type of source has, compared with the 
generally used sources, a number of important advantages. The wave 
ionization mechanism eliminates pollution of the deposit linked with the 
use of an emissive cathode and permits an operation of the source at low 
pressure, which limits the density of the occluded gases. The magnetic 
cusp configuration offers a new possibility of checking the nature and 
quality of the deposit. The latter point is important with respect to the 
flexibility of use of such sources. 
In a third embodiment, the source according to the invention has a hybrid 
magnetic configuration generated by the superimposing of a mirror-type 
magnetic field produced by two coils surrounding the vacuum enclosure and 
a transverse magnetic field produced by two permanent magnet blocks 
located on either side of the vacuum enclosure. 
The advantage of this configuration is that it generates a planar surface 
in the plasma, where the resonance condition 
.vertline.B.vertline.=B.sub.RES is satisfied at all points of said 
surface. This property is essential for the formation of multicharged ions 
in the plasma. 
The field of application of this type of source covers all the fields of 
application of conventional ion sources, namely ion implantation, 
deposition with ion assistance, etc. The unique advantage of this type of 
source is that it permits the performance of such processes on an 
industrial level as a result of the dimensions and performance 
characteristics of the generated ion beam. 
In each of these embodiments, the absence of an emissive cathode makes it 
possible to enable the sources to operate with reactive gases under 
permanent conditions with a remarkable reliability and service life.

DETAILED DESCRIPTION OF EMBODIMENTS 
According to the invention specific properties of a plasma layer created in 
a cyclotron resonance ion source and the generation of a plasma, such as 
the density, ionization rate and dimensions are based on the simultaneous 
implementation of a linear magnetic configuration, the ionization of the 
gas by a wave of frequency f.sub.o, the use of the resonant properties of 
said wave at the electron cyclotron resonance f.sub.o =f.sub.ce =eB/m (e: 
electron charge; B magnetic field module, m electron mass) and the 
possibilities thereof of propagating at high density in the form of the 
lower hybrid mode and the uniform excitation of said wave throughout the 
plasma layer by means of a coupler constituted by identical, juxtaposed 
associated waveguides. 
The magnetic configuration of such a source is produced by coils or 
permanent magnets. As a function of the direction and intensity of the 
current in the coils or the magnetization in the permanent magnets, it is 
possible to obtain three magnetic configuration classes: 
a mirror-type magnetic configuration, 
a cusp-type magnetic configuration, 
a hybrid magnetic configuration. 
These sources, as a function of the magnetic configuration used, generate a 
plasma, whose characteristics are specifically adapted to the 
requirements: 
of coating by sputtering (first configuration), 
the deposition of thin metal layers (second configuration), 
ion assistance and implantation (third configuration). 
In the following description, the frequency f.sub.o of the wave is not 
defined, because the source according to the invention operates in a wide 
frequency range between a few hundred megahertz (MHz) and a few dozen 
gigahertz (GHz). Within said range 1 to 10 GHz offers numerous advantages. 
Thus, power emitters exist, the performance characteristics of the 
permanent magnets are compatible with the resonance condition of the wave 
f.sub.o =eB/2.pi.m and the characteristics of the plasma are adapted to 
the envisaged applications. In particular at the industrial frequency of 
2.45 GHz, for which there are numerous small and medium power emitters of 
the magnetron type and high power emitters of the klystron type, there is 
a great flexibility in the distribution of said power over the guides of 
the coupler and a good compromise between the price of these sources and 
the performance characteristics of the plasma. 
The basic circuit of a magnetic mirror-type source used for coating a part 
by sputtering a target 2 by ion bombardment is illustrated in FIGS. 1a to 
1c and 2a to 2c. In FIGS. 1b and 1c the magnetic mirror is produced by 
coils B.sub.1 and B.sub.2 and in FIGS. 2b and 2c by permanent magnets 
A.sub.1 and A.sub.2. FIGS. 1a and 2a show the variation of the magnetic 
field Bx in the plane of symmetry of the source (Y=0). FIGS. 1b and 2b 
correspond to a section of the source in the form of a planar 
cross-section (xOy plane) and FIGS. 1c and 2c to a section according to a 
longitudinal cross-section (yOz plane). This source is constituted by a 
vacuum enclosure 1, an array of coils B.sub.1, B.sub.2 or permanent 
magnets A.sub.1, A.sub.2 creating the magnetic configuration and a coupler 
distributing within the enclosure the VHF power generated by the microwave 
emitter or emitters. 
The vacuum enclosure 1 is parallelepipedic. The height of its cross-section 
(xOy plane; FIGS. 1b and 2b) is chosen so as to permit the passage of the 
waveguides of the coupler. The width is determined by the dimensions of 
the coils and the magnets. The length of its longitudinal cross-section 
(yOz plane) is only fixed by the size of the parts to be treated. The 
enclosure 1 is connected to the work frame or rack 4 by means of a clamp 
8. As a function of the type of use, the vacuum in the enclosure is 
produced by an autonomous pumping unit or by the work frame pumping unit 
3. 
In FIGS. 1b and 1c, as well as 2b and 2c the coupler permitting the 
transfer of the microwave power P.sub.VHF to the plasma layer is 
constituted by guides associated or joined along the large side. In this 
case the guides are grouped by identical modules. Each VHF module is 
supplied by a main guide 13 via an adapter, a main guide/overdimensioned 
guide transition 12, a planar division E 11, a tight window 10 and several 
secondary guides 15. The association of these VHF modules makes it 
possible to adapt the size of the generated plasma layer to the size of 
the parts to be treated. 
The coupler emits a plasma layer P in the direction of the target 2 
polarized at voltage V.sub.c. A flow 6 of neutral charges from the target 
is then emitted in the direction of the part 5 to be treated on which is 
produced a deposit 7. 
The enclosure 1 is equipped with at least one gas injection system 9 for 
checking ion species of the plasma. 
In the configuration shown in FIGS. 1b and 1c the magnetic field is 
produced by two coil arrays B.sub.1 and B.sub.2 traversed by currents 
I.sub.1 and I.sub.2 in the same direction. These coils surround the vacuum 
enclosure 1. Their length exceeds that of the enclosure in order to 
eliminate the edge effects linked with the return of the current. Under 
these conditions the vector potential A generated by these coils has a 
single component in the volume of the enclosure A.sub.z (x,y) and the two 
components of the magnetic field Bx and By are fixed by the relations 
##EQU1## 
For two identical coil arrays B.sub.1 and B.sub.2 traversed by identical 
currents I.sub.1 and I.sub.2 in the same direction, the magnetic field B 
in the plane of symmetry (y=0) has the conventional shape of so-called 
magnetic mirror fields used in revolution geometry fusion machines. This 
field has two maxima B.sub.MAX at the centre of the coils and one minimum 
B.sub.MIN between the coils. The shape of the coils, the distance 
separating them and the currents flowing through them are chosen so as to 
satisfy the condition B.sub.MAX &gt;B.sub.RES &gt;B.sub.MIN over the entire 
plasma layer width. B.sub.RES is the magnetic field value for which the 
cyclotron angular frequency of the electron ce=eB.sub.RES /m is equal to 
the angular frequency of the electromagnetic wave used for producing said 
plasma .omega..sub.o =2.pi.f.sub.0 =e B.sub.RES /m. 
The use of coils for generating the magnetic configuration has the 
advantage of a high source operating flexibility. Within the condition 
B.sub.MAX &gt;B.sub.RES &gt;B.sub.MIN the characteristics of the magnetic mirror 
can easily be modified by acting on the currents I.sub.1 and I.sub.2, the 
distance between the coils and the number of windings supplied in each 
coil. 
This in particular makes it possible to adjust the position of the 
cyclotron resonance (B.sub.RES) in the mirror and with respect to the 
coupler in order to optimize the characteristics of the plasma (density, 
electron temperature, working pressure), modify the mirror ratio in order 
to act on the leakage flux of the plasma on the extraction side or check 
the impact surface of the plasma on the target. FIGS. 3a and 3b illustrate 
a variant of the source according to FIGS. 1a to 1c with an asymmetrical 
magnetic mirror. In this case the target is moved closer to the coupler 
and positioned between the coils B.sub.1 and B.sub.2. According to the 
adopted sputtering deposition process, this source operating variant is of 
interest, because it makes it possible to very easily vary, by acting on 
the current I.sub.2, the density of the ion flux bombarding the target. It 
also makes it possible to adjust the magnetic field gradient 2B/2.sub.x to 
the frequency of the wave used. 
A linear configuration with a magnetic mirror like that shown in FIGS. 1b 
and 1c can be obtained on the basis of samarium-cobalt or 
iron-neodymium-boron, parallelepipedic permanent magnets. These magnets 
are assembled to form two identical blocks A.sub.1 and A.sub.2 arranged on 
either side of the vacuum enclosure, as shown in FIG. 2b. In the 
longitudinal direction (Oz), said blocks are extended beyond the vacuum 
enclosure to avoid edge effects, as shown in FIG. 2c. These two magnet 
blocks A.sub.1 and A.sub.2 are hollowed out in the central portion. The 
characteristics of the magnetic mirror (B.sub.MAX, B.sub.MIN, mirror 
length and ratio) are fixed by the widths and heights of the two external 
blocks of the mirror l.sub.1 and h.sub.1 and the central block l.sub.2 and 
h.sub.2, as shown in FIG. 4. 
Within the condition B.sub.MAX &gt;B.sub.RES &gt;B.sub.MIN, the characteristics 
of the mirror can be adjusted by acting on the distance between the magnet 
and the enclosure e, on the gaps between the magnet blocks, or by 
supplying metal parts, which are arranged in known manner for the purpose 
of modifying the magnetic field lines. 
The great advantage of using magnets is to produce a magnetic configuration 
without an electric power source. As the microwave power is transmitted to 
the plasma by waveguides, the source assembly is earthed, which 
facilitates the integration of such a source type into an industrial 
process. 
The power supplied in this way by the microwave emitter or emitters 
P.sub.VHF is introduced into the enclosure 1 by means of waveguides 
located at the end of the magnetic mirror. 
At low power, the electric E(.omega..sub.o) and magnetic H(.omega..sub.o) 
fields excited in the guides are essentially perpendicular to the magnetic 
field direction, which permits the propagation of the wave in the form of 
the Whistler mode. In the mirror the wave encounters the resonance 
condition .omega..sub.o =2.pi.f.sub.o =e B.sub.RES /m. Close to said zone 
the wave-electron interaction becomes resonant and a large part of the 
energy of the wave is transferred to the electrons in the form of kinetic 
energy perpendicular to the force lines of the magnetic field. As a result 
of this energy gain, the accelerated electrons are trapped in the magnetic 
configuration, which increases their free average passage and ensures an 
effective ionization of the gas in a pressure range which is not 
accessible to conventional discharges, where the ionization of the gas 
takes place by the application of a static electric field. 
Another advantage of using the Whistler mode is the avoiding of the 
limitation of the electron density of the plasma ne, due to the space 
charge by the condition: 
EQU .omega..sub.o =2.pi.f.sub.o &lt;.omega.pe=.vertline.e.sup.2 ne/.epsilon..sub.o 
m.vertline..sup.1/2 
For example at a frequency of 2.45 GHz, a power density of 10 to 20 
w/cm.sup.2 makes it possible to obtain with an argon gas at a pressure of 
2 to 5.10.sup.-4 mbar a density close to 10.sup.12 p/cm.sup.3, i.e. 
approximately 10 times the density fixed by the cutoff condition 
.omega..sub.o =.omega..sub.p. 
For a higher power, the increase in the density leads to a marked decrease 
in the phase velocity of the wave in the direction of the magnetic field 
and the wave propagates perpendicular to the magnetic lines in the form of 
the lower hybrid mode. For such operating conditions the density of the 
plasma is fixed by the dispersion relation of the lower hybrid mode 
defined hereinafter: 
##EQU2## 
in which .omega..sub.pe, i are the electron and ion plasma angular 
frequencies, .omega..sub.ce the electron cyclotron angular frequency, m 
the mass of the electron and the ion, k the wave number and k.sub.// its 
component along the magnetic field. For the example considered 
hereinbefore at a frequency of 2.45 GHz, a power density of 100 to 200 
W/cm.sup.2 makes it possible to obtain densities of approximately 
10.sup.13 p/cm.sup.3, which are not accessible in discharges for the same 
working pressures. 
As the electromagnetic energy is located within the waveguides and at the 
working pressures of the source, the movement of the particles being 
linked with the magnetic lines, the dimensions of the plasma generated by 
each guide are essentially determined by the dimensions of said guide. The 
contiguous association of guides makes it possible to generate a wave 
plane perpendicular to the magnetic field over the entire surface of the 
guides, obtain the resonance condition 2.pi.f.sub.o =eB.sub.RES /m over 
the entire width of said surface and produce a plasma layer, whose 
dimensions are fixed by the number of associated guides or the number of 
guides supplied, as will be explained hereinafter. 
These guides can be associated or joined by their large side a in the form 
of rows and columns, as shown in FIG. 5. This principle is used for 
coupling the power in the sources shown in FIGS. 1b/1c and 2b/2c. 
These guides can be associated or joined by their small side b, as shown in 
FIG. 6. The couplers of the sources shown in FIGS. 7a to 7c, 8a to 8c and 
9 use this principle. 
This method of associating guides makes it possible to adapt the surface of 
the plasma layer generated in the source to the dimensions of the parts to 
be treated and in particular to the case of large parts. For example, at a 
frequency of 2.45 GHz, an association by the large side of N=24 standard 
guides (a=8.6 cm, b=4.3 cm) generates a plasma layer of height 8.6 cm and 
length 100 cm, whilst the association of N=12 of said same guides along 
the small side generates a layer of the same length and of height 4.3 cm. 
The procedure used for uniformly distributing the microwave power between 
the guides of the coupler is dependent on the application adopted. This 
power is proportional to the width of the layer and therefore to the 
dimensions of the parts to be treated. This power can e.g. be supplied by: 
an array of identical, low power emitters P.sub.VHF .apprxeq.1 KW of the 
magnetron type, each magnetron supplying via an adapter and tight window 
one guide of the coupler; 
by an array of identical, medium power emitters P.sub.VHF .apprxeq.5 KW of 
the magnetron type, each magnetron supplying several guides of the coupler 
grouped into identical VHF modules, via an adapter, a planar division E 
and a tight window; 
a high power emitter P.sub.VHF .apprxeq.50 KW of klystron type and an equal 
distribution of said power between the guides of the coupler by 
conventional division methods by 3 db coupler or branch guide couplers and 
automatic adaptation. 
A preferred embodiment of the source consists of using a coupler with 
guides associated or joined along their small side according to FIGS. 7a 
to 7c, 8a to 8c and 9, said solution permitting: 
the reduction of the volume to be magnetized and therefore the volume of 
the permanent magnets and coils and the price of the source, 
reducing the microwave power to be used, 
facilitating the implementation of the coupler by reducing the number of 
guides to be associated for treating a given part width, 
facilitating the uniform distribution of the microwave power between the 
guides of the coupler by supplying each of said guides with a 
magnetron-type emitter via an adapter or supplying several guides of the 
coupler grouped into identical VHF modules via a taper E and H followed by 
a mode converter adapted to the number of guides of the module. 
FIGS. 1a to 1c and 2a to 2c show a conventional example of the use of such 
sources for coating parts by target sputtering. The neutral gas (Ag,Xe, 
etc.) introduced into the vacuum enclosure is ionized by the wave and 
forms a plasma layer, whose dimensions are fixed by those of the coupler. 
In this plasma the electron and ion particles follow magnetic lines and 
intercept the target over a width fixed by the expansion or opening out of 
the force lines and over the entire length of the plasma target. The 
target (Ti, Cr, etc) is electrically insulated from the enclosure. The 
application of a negative voltage relative to the plasma leads to a 
bombardment of the target by the ions of the plasma and the emission of a 
flux of atoms, which are deposited on the part to be treated. 
Compared with the magnetron method currently used for this coating process, 
this type of source offers numerous advantages. The ionization of the gas, 
the sputtering of the target, the recombination of the target atoms on the 
part to be treated are very strongly decoupled, which gives a very 
considerable flexibility in the performance of the process. The ion 
density n.sub.i in the source is fixed by the gas flow rate .left 
brkt-top.o and the microwave power P.sub.VHF and the velocity of the ions 
V.sub.i bombarding the target by the voltage of the target V.sub.c. The 
deposition rate on the part which is proportional to the ion flux on the 
target, can thus be controlled independently by means of three parameters 
.left brkt-top.o, P.sub.VHF and V.sub.c. This e.g. makes it possible to 
optimize the sputtering coefficient of the ions on the target by the 
target voltage V.sub.c and optimize the density in the source n.sub.i with 
the parameters .left brkt-top.o and P.sub.VHF. Moreover, in such sources 
the neutral atoms emitted by the target recombine on the part to be 
treated in an area not facing the plasma. Therefore, for a constant ion 
flux supplied by the source, the pressure in the work frame can be lowered 
by using a differential pumping. The mechanism of ionizing by the wave 
used permits, for a given ion flux on the target, to operate with lower 
pressures in the source, which limits the density of the occluded gases in 
the deposit. The material balance is improved because the entire surface 
of the target is bombarded by the plasma layer. Moreover, the target can 
be changed without dismantling the source or passing in front of the ion 
beam for carrying out a continuous process. 
The wave/particle energy transfer fixing the properties of the plasma takes 
place through the electrons. Thus, these sources operate with all gases, 
gas mixtures and reactive gases. 
To obtain high quality metal deposits, the contamination by impurities can 
be reduced by using a coupler made at least partly from the material of 
the target employed. 
Moreover, in such sources, the plasma density varies linearly with the VHF 
power density and can approach 10.sup.14 p/cm.sup.3 for a power density of 
approximately 1 KW/cm.sup.2 at a frequency of 2.45 GHz, which corresponds 
to an ion flux close to 10.sup.20 /cm.sup.2 /s. For such high flux 
operating conditions, the target, the enclosure, and the coupler must be 
cooled. In the proposed solution, each of these elements can be cooled by 
a simple, known procedure of using a double wall with a flow of cooling 
fluid in the interior, which is controlled in an independent manner and 
the VHF windows are protected against the bombardment of the plasma. 
In this source operating mode, the density performances of the plasma layer 
can be used for generating electron or ion beams. FIG. 2d illustrates a 
use of said source for producing electron or ion beams. In this case the 
target is eliminated and replaced by two extraction electrodes, which make 
it possible as a function of the polarization to extract the ions or the 
electrons in the form of a linear beam 17, whose length is fixed by that 
of the coupler. 
Another embodiment is represented by cusp-type linear microwave sources. 
The basic diagram of such a source type used for depositing metal layers 
on substrates is illustrated in FIGS. 13a to 13c and 14a to 14c. FIGS. 13a 
to 13c correspond to the case where the magnetic configuration is produced 
by coils. FIGS. 14a to 14c correspond to the case where it is produced by 
permanent magnets. 
In these drawings, the elements which are identical to those of FIGS. 1a to 
1c and 2a to 2c are given the same references. 
Such a source uses, as the aforementioned magnetic mirror source, the same 
wave-based gas ionization mechanism, the same coupling system by 
associated guides making it possible to obtain a wave plane perpendicular 
to the magnetic field and the resonance condition 2.pi.f.sub.o =B.sub.RES 
/m over the entire plasma layer width. 
The special nature of this source type is based on the fact that the 
currents flowing through the coils B.sub.1 and B.sub.2 (FIG. 13b) or the 
magnetization vector in the magnet blocks A.sub.1 and A.sub.2 (FIG. 14b) 
have opposite signs, which makes it possible to generate a cusp-type 
linear magnetic configuration. This configuration is characterized by a 
zero field line on the axis of symmetry of the configuration, a module of 
the field B.sub.x.sup.2 +B.sub.y.sup.2 =B.sup.2 which increases at all 
points around said axis, four maxima of the field to the right of the 
coils or magnets, two on the axis Ox, B.sub.xMAX, two in the median plane 
of the source B.sub.yMAX. The coils and magnets are dimensioned so as to 
satisfy the condition 
EQU B.sub.xMAX, B.sub.yMAX &gt;B.sub.RES =2.pi.f.sub.o m/e 
over the entire plasma layer width. 
Within this condition, the cusp characteristics can vary by acting on the 
currents in the coils, the distance between the coils or the magnets, by 
adding metal parts, arranged in the known manner, so as to modify the 
magnetic field lines. 
In this configuration, the magnetic field lines from the wave guides of the 
coupler intercept the two targets 2 placed in the enclosure and are 
subject to the bombardment of the plasma (FIGS. 7b and 8b). These targets 
are electrically insulated. The application of a positive potential leads 
to an ion bombardment of said targets and the emission of a neutral atom 
flux. On penetrating the plasma, these neutral atoms are ionized by high 
energy electrons created by the wave and form a plasma of metal ions 
having the composition of the target. By following the field lines, these 
ions recombine on the substrate placed at the end of the cusp in order to 
form a metal deposit, whose width is fixed by the opening out of the 
magnetic lines and the length by that of the coupler. 
Apart from the possibility of producing deposits on large substrates, by 
its very operating principle this type of source has, compared with other 
sources which are generally used several significant advantages, namely 
the ionization mechanism using the wave eliminates pollution of the 
deposit linked with the use of the emissive cathode and permits an 
operation of the source at low voltage, which limits the density of the 
occluded gases and the cusp-type magnetic configuration adds a new 
possibility of checking the nature and quality of the deposit. 
The latter point is an important element with regards to the flexibility of 
use of such sources. The plasma ensuring the bombardment of the targets 2 
and the emission of the atom flux is generated by the ionization by the 
wave of a carrier gas or metal vapour introduced into the enclosure. The 
properties of the deposit on the substrate are fixed by the relative 
concentrations of the different ion species in the plasma and the relative 
densities of the excited or neutral atoms and free radicals. These 
concentrations can be controlled by independent settings: 
of the ion flux bombarding the targets and which is dependent on the 
position, the bias voltage and the temperature of the target, or by the 
density of the magnetic lines intercepted by the target; 
the composition, flow rate of the carrier gas or gases and their injection 
point into the source. 
For example, for carbon deposits, the carbon concentration can be 
controlled by the ion flux on graphite targets, by the choice of the 
carrier gas in hydrocarbon form (methane, propane, etc.) carbon oxides 
(CO, CO.sup.2, etc.) and the localized independent injection of hydrogen 
or oxygen. 
These sources also operate with refractory material targets, such as oxides 
of uranium, aluminium, as well as boron and its compounds. In this case, 
the checking or control of the magnetic configuration makes it possible to 
vary the density of the magnetic lines intercepted by the targets and 
therefore the energy density deposited by the plasma and the flow of 
neutral atoms reemitted by the target. The control of this flow, the flow 
rate and the nature of the carrier gas (nitrogen, oxygen, etc.) makes it 
possible to modify the properties of the deposit, as in the case of metal 
targets. 
The absence of an emissive cathode enables the sources to be operated with 
reactive gases under permanent operating conditions with a remarkable 
reliability and service life. 
Another embodiment is represented by hybrid configuration, linear microwave 
sources. Such a source, like the cusp or magnetic mirror sources described 
hereinbefore, uses the same mechanism of ionizing the gas by the wave and 
the same system of coupling the microwave power with the plasma. 
The special nature of this source type is the magnetic configuration. This 
so-called hybrid configuration shown in FIG. 15 is generated by 
superimposing a magnetic field with mirror B.sub.y (x) created by the two 
coils B.sub.1 and B.sub.2 surrounding the vacuum enclosure and a 
transverse magnetic field B.sub.x (y) produced by the two permanent magnet 
blocks A.sub.1 and A.sub.2 arranged on either side of the vacuum 
enclosure. 
The special property of this configuration is that the location of the 
points in the plane xOy, where the module of the magnetic field 
.vertline.B.vertline..sup.2 =B.sub.x.sup.2 +B.sub.y.sup.2 !.sup.1/2 is 
equal to the resonant magnetic field .vertline.B.vertline.=B.sub.RES 
=2.pi.f.sub.o m/e is a closed curve C contained within the vacuum 
enclosure. As the fields B.sub.x and B.sub.y in the volume of the 
enclosure are independent of the longitudinal direction Oz, the resonance 
condition .vertline.B.vertline.=B.sub.RES is satisfied on the same closed 
curve C in all the planes xOy of the vacuum enclosure and therefore on the 
entire surface obtained by the translation of said curve in the direction 
Oz. 
The existence of this closed resonance surface makes it possible to obtain 
in such a source a plasma with a very high energy electron population 
which, by successive ionizations, removes the neutral atoms from the gas 
or metal vapour introduced into the enclosure. The ions, charged one or 
more times as a function of the value of the pressure of the gas in the 
source and which are generated in this magnetic configuration, are 
extracted from the vacuum enclosure by extraction electrodes located at 
the end of the mirror in the form of a linear beam, whose length is fixed 
by that of the coupler. 
The properties of the closed resonance surfaces have been successfully used 
for the production of circular, multicharged ion beams in magnetic 
configurations with a symmetry of revolution. 
As a result of the use of a linear magnetic configuration and the 
generation of a layer-type plasma by associating guides according to their 
large or small side, the present invention generalizes the concept of 
closed resonance surfaces with symmetry of revolution to linear surfaces 
and makes it possible to obtain linear ion beams of very large dimensions 
with high current densities. 
The field of application of such sources covers all the conventional 
applications of ion sources, such as ion implantation, deposition with ion 
assistance, etc. 
The advantage of this type of source is that it makes it possible to 
perform these processes on an industrial scale as a result of the 
dimensions and performance characteristics of the beam of generated ions.