Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Device and Process for the Vaporization of Material
This invention relates to a device for vaporizing
material using a vacuum arc discharge in a vacuum chamber
with a self-consuming cathode (2) having a coolable cathode
supply (1) to which the cathode is attached and a self-con-
suming hot anode, wherein, via connecting member (7a), a
crucible (7) is attached to the anode base plate (6), and a
diaphragm (13) shielding the cathode (2) is arranged above
same, the crucible (7) consists of an electrically conductive
and heat-conductive material, and the connecting member (7a),
due to its material properties or geometrical properties,
permits electrically conductive and heat-insulating attach-
ment of crucible (7) to the anode base plate (6). Further-
more, the invention relates to a process fox vaporizing mate-
rial.
In recent years, plasma- and ion-supported coating
processes have increasingly come to the fare in producing
thin coatings on articles by vapor-depositing materials in
vacuum. This is due to the improved quality of the coatings
produced which, in particular, are outstanding because of
their better adhesion of layers arid a more compact layer
structure as compared to the classical processes.
Hitherto industrially employed familiar plasma- sup-
ported coating processes include cathode sputtering, ion
plating and vaporization by arcs. The arcs are operated with
glow cathodes (U. S. 4,197,157) or hollow cathodes (U. S.
3,562,141). For maintaining the arc discharge, both types of
cathodes require a process gas.
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Another group of arcs are the so-called vacuum arcs
operating without process gas. Here, vaporized electrode
material takes over the function of the process gas. Material
vapor generated by the self-consuming electrodes, in addition
to maintaining the arc discharge, serves to produce coatings
on articles. Thus, from D.M. Sanders, "Review of Ton-Based
Coating Processes Derived from the Cathodic Arc", J.Vac.Sci.
Technol. A7, No. 3, 2339 (1989), there is known a vacuum arc
with a self-consuming cold cathode and furthermore, from DE
3,413,891, a vacuum arc wherein the electrons produced by a
self-consuming cold cathode are used to vaporize material at
the anode.
Therein, the anode designed as a vaporization cruci-
ble is arranged with respect to a cold cathode such that the
plasma jets emerging from the cathode spots on the working
surface of the cold cathode heat up the exterior wall of the
anodic vaporization crucible to such extent that the vapori-
zation material located within the vaporization crucible is
vaporized, and the resulting material vapor above the cruci-
ble interacts with the plasma jets emerging from the cathode
spots so that the material vapor is ionized.
A common drawback of the mentioned plasma-supported
coating techniques is to be seen in the low coating rates
being below 1 ~m/min in industrially practicable devices.
This, with the practicability of plasma-supported processes
on an industrial scale, results in low production rates
which, in terms of costs, are not capable of competing with
the classical thermal vapor coating processes operating with-
out conversion of the vaporization material into the plasma
state.
The technical problem of the invention is to provide
a device and a process fox vaporizing material allowing for
coating rates of more than 1 ~m/min to permit low-cost, high
quality vacuum vapor coating of bulk goods.
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The technical problem is solved by arranging the
crucible (7) laterally above the working surface of the cath-
ode (2a) that close to said working surface that the solid
angle formed by the metal vapor plasma (9) flowing off from
the anode crucible (7) is just not decreased by the diaphragm
(13) in such fashion that tromogenous vapor coating of sub-
strates above the crucible (7) is no longer possible, and
arranging cathode (2) and anode opposite to each other.
Furthermore, the techniacl problem is solved by a
process for vaporizing material using a vacuum arc disckiarge
in a vacuum chamber with a self-consuming cathode (2) having
a coolable cathode supply (1) and a self-consuming hot anode
consisting of anode base plate (6), a connecting member (7a)
and a crucible (7), wherein heat transmission from anode
crucible (7) to anode base plate (6) is held low, the plasma
jets (5a,5b) emerging from the cathode spots are unimpeded in
their action on the outer wall (7b) of the crucible (7) and
on the material vapor (9) above crucible so that a high de-
gree of vaporization is obtained, and the crucible (7) con-
sists of an electrically conductive and heat conductive mate-
rial.
In a particularly preferred embodiment the crucible
consists of titanium diboride, tungsten or a mixed ceramic
of boron nitride, titanium diboride and aluminum nitride.
Using process and device of the invention, high qual-
ity coatings with coating rates on articles of more than
1 ~Cm/s are possible, so that bulk production under economic
aspects becomes feasible.
With the process of the invention, coating rates in
a distance 15 cm from the arc as illustrated in table 1 could
be obtained. The power associated with the arc was 3 kW each.
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TABLE 1
Vaporization Crucible Distance Coating Rate
Material Material Anode-Cathode
Aluminum TiB2 5 cm 4.8 ~m/min
Copper W 5 cm 6.0 ~m/min
Silver W 5 cm 9.0 ~m/min
The values for the coating rate listed herein may be
increased by using higher arc power.
The indicated coating rates exceed by far those val-
ues obtainable with other plasma-supported or ion-supported
processes. Thus, when using cathode sputtering which is most
frequently employed for coatings, coating rates of more than
1 um/min are barely obtained, even when applying extreme
power of <_ 50 kW.
On the basis of power fed into the arc, the coating
rates of the process according to the invention exceed by far
those obtained when using arcs with glow cathode, hollow
cathode or self-consuming cold cathode without anode vapori-
zation.
Thus, the present process according to the invention
is outstanding for the effective utilization of power fed
into the arc for the vaporization process. Due to this effec-
tiveness, high vaporization rates can be obtained with rela-
tively low electric power.
Furthermore, the effective utilization of power fed
into the arc results in lower heat generation and thus, to
lower thermal load on the articles to be coated and to lower
consumption of electric energy and cooling water.
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Due to rapid heating of the vaporization material and
subsequent high vaporization rate, the process according to
the invention is also suited for a quasi-continous type of
production, wherein the articles to be coated enter or exit
the vaporization chamber via gates and the vapor deposition
process is active only during the residence time of the arti-
cle in the vacuum chamber.
Figure 1 shows a device suitable fox operating the
process according to the invention.
Figure 2 shows the same device, however, with cathode
and anode arranged in undesirable fashion with respect to
each other.
Figure 3 shows a preferred arrangement of the device
according to figure 1, wherein cathode and anode are arranged
inclinedly towards to each other.
Figure 1 shows a cooled cathode supply (1) with the
cathode material (2) and a support device (3) for the cathode
material. Device (3) also serves to fixate the cathode spots
(5) on the working surface (2a) of the cathode material (2).
The arc discharge is ignited according to prior art using an
ignition unit (4) which is shown as a symbol only.
The anode consists of an anode holder (anode base
plate) (6), an anode crucible (7) and an electrically conduc-
tive connection (7a) between holder (6) and crucible (7). Due
to its material or geometrical properties, the connecting
member (7a) permits an electrically conductive and heat-in-
sulating attachment of crucible (7) to the anode base plate
(6). In a preferred embodiment, the connecting member (7a)
has an electrical resistance dimensioned such that i~t is
heated up by the current flowing to the crucible.
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It is advantageous to design the connection (7a) in
such fashion that low heat transmission from crucible (7) to
the holder (6) takes place.
Within the anode crucible (7), the vaporization mate-
rial (8) is located. Consumed vaporization material (8) may
be re-supplied by material in the form of a wire (10). For
this purpose, the re--supplyable material (10) is stored on a
wire roll and is fed to the vaporization crucible (7) via
driving pulleys (1Z) and a guiding tube (12) in the usual
manner.
The anode crucible (7) has a geometrical arrangement
with respect to the working surface of cathode (2a) such that
plasma jets (5a,5b) emerging from the cathode spots act both
on the outer wall (7b) of the crucible and the material vapor
(9) above the crucible. In a preferred embodiment, each.plas--
ma jet (5a,5b) may originate from different cathodes. The
plasma jet (5a) impinging on the outer wall (7b) of crucible
( 7 ) , due to the high energies of the particles ( 5 ) carried
along with the plasma jet, causes rapid and strong heating of
the crucible and thus, strong heating of the vaporization
material. Therefore, it is particularly advantageous if the
crucible consists of a material having good heat conductance.
This strong heating results in vigorous vaporization of the
vaporization material (8). The plasma jet (5b) interacts with
the material vapor (9) above the crucible. As a consequence
of inelastic collision processes between particles of the
plasma jet (5b) and the material vapor, this interaction
results in formation of a dense plasma above the crucible.
This plasma impinges on the vaporization material (8) in the
crucible (7), resulting in a further energy supply to the
vaporization material and thus, to an increase in vaporiza-
tion rate. The ionized metal vapor flowing out of the ionized
cloud of vapor above the crucible into the surrounding
vacuum may then be used for coating purposes.
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For a high quality coating it is necessary to keep
metal droplets emerging from the cathode spots (5) and being
entrained by the plasma jet (5a,5b) away from the object to
be coated. For this purpose, the diaphragm (13) illustrated
in figure 1 is arranged above the cathode, restricting the
cathodic plasma jet (5a,5b) to a space zone outside the
object to be coated. The diaphragm (13) requires a minimum
distance between working surface (2a) of the cathode and the
anode crucible (7) since too small a distance results in an
undesirable spatial restriction (14) of metal vapor plasma
(9) flowing off from the anode crucible {7). Therefore, the
crucible (7) is arranged laterally above the working surface
(2a) of cathode (2) that close to said working surface that
the solid angle formed by the metal vapor plasma (9j flowing
off from the anode crucible {7) is just not decreased by the
diaphragm {13) so that homogenous vapor coating of substrates
above the crucible (7) takes place yet.
Figure 2 shows an undesirable arrangement of anode
and cathode. Here, the distance between working surface (2a)
of the cathode and the anode crucible (7) is so small that
metal vapor plamsa (9) flowing off is hindered by the
diaphragm (13). If the electrodes are too close together, a
solid angle will no longer be utilized due to the shielding
{14), and objects arranged in this direction will not be
Coated.
In order to achieve high vaporization rates, it is
advantageous if the connecting member (7a) providing elec-
trical contact of vaporization material (g) and/or Crucible
(7) hinders heat transmission between crucible (7) and holder
(6). In a preferred embodiment, the hindrance of heat trans-
mission may be achieved in that the connecting member (7a) is
relatively long (about 5 cm) and designed with low cross-
section. However, this geometrically caused decrease of heat
transmission is limited by the required mechanical stability
of connecting member (7a). Furthermore, in a particularly
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preferred embodiment, it may be advantageous if the connect-
ing member (7a) has an electrical resistance dimensioned such
that due to the f lux of current in the arc, the connecting
member (7a) is heated up by this flux of current and hereby,
heat flow-off from the crucible (7) to the holder (6) is
prevented, or the electrical heating of connecting member
(7a) by the flux of current even causes additional supply of
energy to the crucible (7). Furthermore, it is advantageous
if a portion of the crucible outer wall (7b) as large as
possible is impinged by the plasma jet (5a). In a particular-
ly favorable fashion, this is achieved in that the anode is
arranged opposite to the cathode, and the crucible (7) is
arranged laterally above the working surface of the cathode
(2a). Furthermore, the crucible (7) should consist of a mate-
rial having good heat conductance so that heat from the outer
wall (7b) of the crucible will be effectively transmitted to
the vaporization material.
Figure 3 shows an arrangement, wherein a cathode and
an anode are arranged somewhat inclined to each other. This
arrangement offers the advantage that, on the one hand, the
molten vaporization material (8) flows to the anode tip [end
of the vaporization crucible (7) pointing to the cathode] due
to gravity. The anode tip, because of the proximity to the
cathode, is heated particularly strongly by the plasma jet
(5a). The inclination of the crucible (7) causes continuous
perfusion of the anode tip with molten vaporization material
and thus, effective vaporization.
On the other hand, the inclination causes further
restriction of the space zone interspersed by the plasma jet
(5a,5b) above crucible (7) so that a larger space zone is
available for coating purposes.
