Note: Descriptions are shown in the official language in which they were submitted.
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RECTANGULAR CATHODIC ARC SOURCE AND
METHOD OF STEERING AN ARC SPOT
Field of Invention
This invention relates to apparatus for the production of coatings in a
vacuum. In particular, this invention relates to a vacuum arc coating
apparatus having
a rectangular cathodic arc source providing improved arc spot scanning and a
plasma
focusing system.
Background of the Invention
Many types of vacuum arc coating apparatus utilize a cathodic arc
source in which an electric arc is formed between an anode and a cathode plate
in a
vacuum chamber. The arc generates a cathode spot on a target surface of the
cathode,
which evaporates the cathode material into the chamber. The cathodic evaporate
disperses as a plasma within the chamber, and upon contact with one or more
substrates coats the substrates with the cathode material, which may be metal,
ceramic
etc. An example of such an arc coating apparatus is described in U.S. Patent
No.
3,793,179 issued February 19, 1974 to Sablev.
An arc coating apparatus of this type is advantageous for use in the
coating of large substrates and multiple substrates, due to the large surface
area of the
cathode which can be evaporated into a large volume coating chamber. However,
in a
large surface area cathode arc coating apparatus of this type a significant
portion of the
target evaporation surface of the cathode plate goes largely unused, due to
the
scanning pattern of arc spots which follows certain physical principles:
1. The arc discharge tends to move in a direction which reduces
the voltage drop in the arc circuit, and the are spot thus tends to migrate to
regions on
the target surface which are closest to the anodic current conductor. Where
multiple
current conductors traverse the cathode the arc spot will occasionally migrate
into the
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region between conductors where it may remain for a considerable time because
no
steering mechanism is present to move the arc spot back to the desired
evaporation
zone.
2. In the case of metal cathodes the arc spot follows a retrograde
motion according to the "anti-ampere force" principle, and is thus attracted
to the
coaxial magnetic force lines generated by the anodic current conductor.
3. In the case of a cathode formed from a material which does not
have a melting phase, for example a sintered or graphite cathode, the arc spot
moves
according to the "ampere force" principle and is repelled from the coaxial
magnetic
force lines generated by the anodic current conductor.
4. The arc spot is attracted to the region where the tangential
component of a transverse magnetic field is strongest.
5. The arc spot tends to migrate away from the apex of an acute
angle at the point of intersection between a magnetic field line and the
cathode target
surface (the "acute angle" rule).
These effects result in a limited erosion zone relative to the available
area of the target surface of the cathode plate, reducing the life of the
cathode and
dispersing cathodic evaporate into the coating chamber in non-uniform
concentrations.
In a large area cathode arc coating apparatus using a metal cathode
plate the anti-ampere motion of the arc spot and the tendency of the arc to
seek the
lowest voltage drop combine to largely confine the arc spot to the vicinity of
the
anodic conductor, substantially limiting the erosion zone to the region of the
target
surface surrounding the anodic conductor. This results in a very small area
inside the
coating chamber in which the cathodic evaporate is concentrated enough to
apply a
uniform coating to the substrates. However, it is not possible to construct
the cathode
plate so that the desired coating material is located only in the erosion
zone, since the
arc spot will occasionally stray out of the erosion zone and if the target
surface is not
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entirely composed of the selected coating material the cathodic evaporate from
outside
the desired erosion zone will contaminate the coating on the substrates.
In the case of a cathode plate formed from a material which does not
have a melting phase, the tendency of the arc spot to move in an ampere
direction,
away from the region of the anodic conductor, is opposed by the tendency of
the arc
discharge to settle toward the region of lowest voltage drop. In these cases
the arc
spot tends to move chaotically over the target surface of the cathode and the
cathodic
evaporate accordingly disperses in random locations and non-uniform
concentrations
within the coating chamber, rendering uniform coating of the substrates
improbable.
This random motion also causes the are spot to move off of the target surface
of the
cathode and causes undesirable erosion of non-target portions of the cathode
plate, for
example the side edges.
U.S. Patent No. 4,448,659 issued May 15, 1984 to Morrison, which is
incorporated herein by reference, describes an arc coating apparatus providing
a
cathode in the form of a plate with a large target surface for creating
cathodic
evaporate. A confinement ring composed of a magnetically permeable material
surrounds the cathode to confine the arc spot to the target surface. Such
plasma
sources can be used for the production of coatings on large and long articles,
but
present the following disadvantages:
1. Despite the initial low probability of the presence of cathodic
spots on the protective ring, over time the cathodic evaporate coats the ring
and
cathodic spots are produced on the ring with increasing frequency. This
results in
contamination of the coating by the ring material, and ultimately in ring
failure.
2. In self-steering cathodic arc sources it is not possible to use
external magnetic fields in the vicinity of the target surface of the cathode.
It is
therefore not possible in such an apparatus to use a plasma-focusing magnetic
field, as
the influence of the focusing magnetic field makes the distribution of
cathodic spots
on the working surface of the cathode irregular and non-uniform. Any external
magnetic field, for example for focusing or deflecting the arc plasma flow,
interferes
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with the self-sustained magnetic field generated by the cathode and anode
current
conductors and disrupts the self-steering character of the cathode spot.
However, the
absence of magnetic focusing reduces the efficiency of the coating process and
impairs the quality of substrate coatings, because the content of the neutral
component
(macroparticles, clusters and neutral atoms) in the region of the substrates,
and thus in
the substrate coating, increases.
3. A cathode in this type of plasma source rapidly becomes
concave due to evaporative decomposition, and its useful life is therefore
relatively
short. Moreover, since the evaporation surface of the cathode becomes concave
in a
relatively short time it is practically impossible to use a high voltage pulse
spark
igniter in such a design, so that a mechanical igniter must be used which
lowers
working reliability and stability.
4. While the confinement ring prevents the arc spot from straying
off of the target surface, it does not affect the tendency of the arc spot to
migrate
toward the anodic conductor in the case of metal cathodes, or to move
chaotically over
the target surface in the case of non-metal cathodes.
Accordingly, self-steering arc plasma sources tend to use the target
surface inefficiently and the cathode thus has a relatively short useful life.
The erosion efficiency of the target surface can be improved by
providing an are spot steering system to steer the arc spot along a selected
path about
the target surface. This increases the size of the region within the coating
chamber in
which coating can occur.
For example, the scanning pattern of a cathode spot can be controlled
by providing a closed-loop magnetic field source disposed beneath the target
surface
of the cathode, in a manner similar to that described in U.S. Patent No.
4,724,058
issued February 9, 1988 to Morrison. The magnetic field source establishes a
magnetic field in a selected direction over the target surface, which directs
the cathode
spot in a direction substantially perpendicular to the direction of the
magnetic field
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and thus provides more efficient evaporation of the target surface. This
approach is
based on the principle of arc spot motion whereby an arc spot is attracted to
the region
where the tangential component of a transverse magnetic field is strongest.
However, this still significantly limits the area of the target surface of
the cathode which is available for erosion, because this type of arc coating
apparatus
creates a stagnation zone in the region where the tangential component of the
magnetic field is strongest. The cathode spot eventually settles in the
stagnation zone,
tracing a retrograde path about the erosion zone and creating a narrow erosion
corridor
on the target surface. This limits the uniformity of the coating on the
substrates and
reduces the working life of the cathode.
U.S. Patent No. 4,673,477 to Ramalingam proposes that the magnetic
field source can be moved to shift the magnetic field lines and increase the
utilization
efficiency of the target surface. However, the mechanical adaptations required
for
such a system make the apparatus too complicated and expensive to be
practical.
Where an external magnetic field is present the arc spot follows the
"acute angle" rule, according to which the arc spot tends to migrate away from
the
apex of an acute angle at the point of intersection between a magnetic field
line and
the cathode target surface. The basic principle is that a cathodic spot formed
by a
vacuum arc in a fairly strong magnetic field (in the order of 100 Gauss), the
force lines
of which cross the surface of the cathode at an acute angle, will move in a
reverse
(retrograde) direction perpendicular to the tangential component of the field
and,
concurrently, displace away from the apex of the angle (for example, see
Cathodic
Processes of Electric Arc by Kesaev I.G., Nauka, 1968). This results in the
arc spot
settling beneath the apex of the arch-shaped portion of the magnetic field
which
projects over the target surface.
U.S. Patent No. 5,587,207 issued December 24, 1996 to Gorokhovsky,
teaches that cathode spot confinement under a closed loop-type linear anode
can be
enhanced by a conductor which encases the anode to form a closed loop magnetic
coil, with the magnetic field lines oriented in the direction shown in Figures
29 and 30
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therein. Simultaneous use of both the closed-loop magnetic steering coil
behind the
cathode and a closed-loop linear anode in front of the target evaporation
surface (with
or without an enclosed magnetic coil) results in a synergistic improvement of
arc
discharge stability and thus cathode spot motion. The anode can be configured
in any
desired pattern, the configuration thereof being limited only by the periphery
of the
target surface. The arc spot will scan the target surface under the influence
of the
transverse magnetic field (in an ampere direction in the case of cathodes of
carbon and
related sintered materials or in an anti-ampere direction in the case of metal
cathodes),
virtually unaffected by the current flowing through the anodic conductor.
A disadvantage of this approach is that the arc spot will occasionally
migrate from the selected erosion zone to another part of the cathode target
surface
where the intensity of the transverse magnetic field is small and, there being
no means
available to return the arc spot to the desired erosion zone, will stagnate in
the low
magnetic field region. In the case of a carbon-based cathode plate, when the
velocity
of arc spot movement is low enough the are spot can settle in any stagnation
zone
where the transverse magnetic field is close to zero, and will not return to
the erosion
zone.
Summary of the Invention
The present invention overcomes these disadvantages by providing a
steering magnetic field source comprising a plurality of electrically
independent
closed-loop steering conductors disposed in the vicinity of the target
surface. In the
preferred embodiment each steering conductor can be controlled independently
of the
other steering conductors. Increasing the current through one steering
conductor
increases the strength of the magnetic field generated by that conductor
relative to the
strength of the magnetic field of the steering conductor along the opposite
side of the
cathode plate, shifting the magnetic field on the opposite side of the cathode
plate
transversely. Selective unbalancing of the steering conductor currents thus
increases
the effective breadth of the erosion zone and thus provides more uniform
erosion of
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the target surface and a larger area within the coating chamber in which the
cathodic
evaporate is dispersed at concentrations sufficient to uniformly coat the
substrates.
The steering conductors may be disposed in front of or behind the
target surface of the cathode plate. When disposed in front of the target
surface the
steering magnetic field lines intersect with the target surface at an obtuse
angle, which
obviates the motion-limiting effect of the acute angle principle and allows
the arc spot
to move over a larger region of the target surface, thereby further increasing
the size of
the erosion zone.
In a further embodiment, groups of steering conductors are disposed
along opposite sides of the cathode plate. By selectively applying a current
through
one conductor in each group, the path of the arc spot shifts to an erosion
corridor
defined by the active steering conductor.
The present invention further provides means for restricting the
cathode spot from migrating into selected regions of the target evaporation
surface
outside of the desired erosion zone. The invention accomplishes this by
providing a
shield at floating potential positioned over one or more the selected regions
of the
target evaporation surface, which prevents the are spot from forming in or
moving
into the shielded region. In one preferred embodiment the shield is positioned
immediately above the region of the target surface in the vicinity of the
anode, spaced
from the target surface. The evaporation zone is thus restricted to the area
of the
target surface surrounding the shield, protecting the anode from deposition of
cathodic
evaporate and providing better distribution of cathodic evaporate over the
substrates to
be coated, which results in more uniform coatings over a greater coating area.
The shield can be used to keep arc spots away from any region where
the negative conductor traverses the cathode, which represents the lowest
voltage drop
relative to the anode. Where a large anode or multiple anodes are provided the
shield
restrains the arc spot from migrating into the region of the cathode located
beneath an
anode, where most of evaporated material would be trapped by the anode rather
than
flowing to the substrate.
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Further, the presence of the shield allows the target evaporation surface
of the cathode plate to be constructed of a combination of the coating
material and
another material, for example an expensive coating material such as titanium
or
platinum in the desired erosion zone and an inexpensive material such as steel
outside
of the erosion zone. The steel portion of the target surface may be shielded
by a
floating shield of the invention to prevent cathode spot formation and motion
thereon,
and thus prevent contamination of the coating while optimizing utilization of
the
expensive coating material.
In an arc coating apparatus utilizing a magnetic steering system,
regions where the transverse magnetic field is low can be shielded in the same
manner
to exclude movement of the arc spot into these regions and create the desired
pattern
of erosion. In this embodiment of the invention the target may be placed on
the poles
of magnetron-type magnetic system of the type described in U.S. Patent No.
4,724,058
issued February 9, 1988 to Morrison. The region of the evaporation surface
located
about the central part of target cathode, where the tangential component of
the
magnetic field is too weak to confine are spots, may be shielded by a floating
shield
which prevents the arc spot from migrating into the stagnation area created
between
the magnetic fields generated by the magnetron.
The invention further provides a magnetic focusing system which
confines the flow of plasma between magnetic fields generated on opposite
sides of
the coating chamber. This prevents the plasma from contacting the surface of
the
housing, to avoid premature deposition, and increases the concentration of
plasma in
the vicinity of the substrate holder.
In a further embodiment the plasma focusing system can be used to
deflect the plasma flow off of the working axis of the cathode, to remove the
neutral
component of the plasma which otherwise constitutes a contaminant. In this
embodiment the plasma focusing coils are disposed in progressively asymmetric
relation to the working axis of the cathode, to deflect the flow of plasma
along a
curvate path toward a substrate holder.
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The present invention thus provides a vacuum arc coating apparatus
comprising a rectangular cathode plate having opposed long sides connected to
a
negative pole of an arc current source, the cathode plate having an
evaporation
surface, a coating chamber defined by the evaporation surface and a housing, a
substrate holder within the coating chamber, at least one anode within the
coating
chamber spaced from the evaporation surface, connected to a positive pole of a
current
source, an arc igniter for igniting an arc between the cathode and the anode
and
generating an arc spot on the evaporation surface, and a magnetic steering
system
comprising at least first and second steering conductors arranged along
opposite sides
of the cathode plate, the first and second steering conductors being disposed
in the
vicinity of the evaporation surface so that a magnetic field generated thereby
exerts a
magnetic influence on the arc spot, the first steering conductor being
electrically
independent of the second steering conductor, wherein by varying a level of
current
applied through the first steering conductor relative to the second steering
conductor
the magnetic field generated by the first steering conductor shifts toward a
long side of
the cathode plate.
The present invention further provides a vacuum arc coating apparatus
comprising a rectangular cathode plate having opposed long sides connected to
a
negative pole of an arc current source, the cathode plate having an
evaporation
surface, a coating chamber defined by the evaporation surface and a housing, a
substrate holder within the coating chamber, at least one anode within the
coating
chamber spaced from the evaporation surface, connected to a positive pole of a
current
source, an arc igniter for igniting an arc between the cathode and the anode
and
generating an arc spot on the evaporation surface, and a magnetic steering
system
comprising groups of steering conductors arranged along each of the long sides
of the
cathode plate, the steering conductors each being disposed in the vicinity of
the
evaporation surface so that a magnetic field generated thereby exerts a
magnetic
influence on the arc spot, each steering conductor being electrically
independent of the
other steering conductors, wherein an erosion zone on the evaporation surface
defined
within the magnetic field is shifted by selectively reducing a current from
one steering
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conductor and applying a current through another steering conductor in the
same
group.
The present invention further provides a method of steering an are spot
on an evaporation surface of a rectangular cathode plate in an arc coating
apparatus,
the cathode plate being connected to a negative pole of an arc current source
and
disposed within a coating chamber defined by the evaporation surface and a
housing,
the apparatus having a magnetic steering system comprising steering conductors
arranged along opposite long sides of the cathode plate and being disposed in
the
vicinity of the evaporation surface so that a magnetic field generated thereby
exerts a
1o magnetic influence on an arc spot generated on the evaporation surface,
comprising
the steps of modulating each steering conductor independently of the other
steering
conductors, and varying a level of current applied through a first steering
conductor
relative to a second steering conductor to shift a magnetic field generated by
the first
steering toward a long side of the cathode plate.
The present invention further provides a vacuum arc coating apparatus
comprising a cathode connected to a negative pole of an arc current source,
having an
evaporation surface, a coating chamber defined by the evaporation surface and
a
housing, a substrate holder within the coating chamber, at least one anode
within the
coating chamber spaced from the target surface, connected to the positive pole
of a
current source, an arc igniter for igniting an arc between the cathode and the
anode
and generating an arc spot on the target evaporation surface, a magnetic
focusing
system comprising a plurality of magnetic focusing conductors disposed about
the
housing, the focusing conductors being spaced apart and generating magnetic
fields
within the housing which confine a flow of plasma to a plasma flow path, and a
substrate holder within the plasma flow path.
The present invention further provides a vacuum arc coating apparatus
comprising a cathode plate connected to a negative pole of an arc current
source,
having an evaporation surface, a coating chamber defined by the evaporation
surface
and a housing, at least one anode within the coating chamber spaced from the
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evaporation surface, connected to the positive pole of an arc current source,
and an arc
igniter for igniting an arc between the cathode and the anode and generating
an arc
spot on the evaporation surface, wherein the anode comprises a substantially
planar
anode body disposed in a direction substantially tangential to a direction of
a magnetic
field surrounding the anode.
The present invention further provides a vacuum arc coating apparatus
comprising a cathode plate connected to a negative pole of an arc current
source,
having a target evaporation surface, a coating chamber defined by the target
evaporation surface and a housing, a first anode within the coating chamber
spaced
from the target surface, connected to the positive pole of the arc current
source, a
substrate holder disposed within the coating chamber separated from the target
surface
by a plasma duct defined within the housing, an arc igniter for igniting an
arc between
the cathode and the anode and generating an arc spot on the target evaporation
surface.
and a second anode disposed within the plasma duct comprising an anode body
disposed in a direction substantially tangential to a direction of a magnetic
field
surrounding the second anode.
The present invention further provides a vacuum arc coating apparatus
comprising a cathode plate connected to a negative pole of an arc current
source,
having an evaporation surface, a coating chamber defined by the evaporation
surface
and a housing, a substrate holder within the coating chamber, at least one
anode
within the coating chamber spaced from the target surface, connected to the
positive
pole of the arc current source, an arc igniter for igniting an arc between the
cathode
and the anode and generating an arc spot on the target evaporation surface,
and at least
one electrically conductive shield maintained at floating potential spaced
from at least
one shielded region of the evaporation surface, wherein the shield prevents
movement
of the are spot into the shielded region.
The present invention further provides a vacuum arc coating apparatus
comprising a pair of opposed rectangular cathode plates each having opposed
long
sides connected to a negative pole of an arc current source and an evaporation
surface,
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a coating chamber defined by the evaporation surfaces and a housing, a
substrate
holder within the coating chamber, anodes within the coating chamber spaced
from
each evaporation surface, connected to a positive pole of a current source, an
arc
igniter for igniting an arc between each cathode and anode and generating an
are spot
on the evaporation surfaces, and a magnetic focusing system comprising a
plurality of
magnetic focusing conductors disposed about the housing, the focusing
conductors
being spaced apart and generating magnetic fields within the housing which
confine a
flow of plasma to a plasma flow path, wherein the focusing conductors direct
the
plasma toward the substrate holder.
Brief Description of the Drawings
In drawings which illustrate by way of example only a preferred
embodiment of the invention,
Figure 1 is a schematic cross-section of a prior art large area cathode
vacuum arc plasma source having a magnetic steering system disposed behind the
cathode plate;
Figure 2 is a partial perspective view illustrating the distribution of
magnetic field lines produced by a magnetic steering system according to one
embodiment of the invention;
Figure 2a is a schematic elevation illustrating balanced magnetic field
lines produced by the magnetic steering system of Figure 2;
Figure 2b is a schematic elevation illustrating an erosion corridor
produced by the magnetic steering system of Figure 2 unbalanced in a first
direction;
Figure 2c is a schematic elevation illustrating an erosion corridor
produced by the magnetic steering system of Figure 2 unbalanced in a second
direction;
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Figure 3 is a schematic elevation illustrating a variation of the
embodiment of Figure 2 in which multiple steering conductors are disposed
along the
long sides of the cathode plate;
Figure 4 is a plan view of a further preferred embodiment of a large
area cathode arc source of the invention;
Figure 5 is a cross-section of the apparatus of Figure 4 taken along the
line 5-5;
Figure 6 is a cross-section of the apparatus of Figure 4 taken along the
line 6-6;
Figure 7a is a plan view of an arc coating apparatus embodying a
plasma focusing system according to the invention;
Figure 7b is a side elevation of the arc coating apparatus of Figure 7a;
Figure 8 is a plan view of a variation of the arc coating apparatus of
Figure 7a providing neutralizing conductors for modulating the steering and
focusing
conductors;
Figure 9 is a plan view of an arc coating apparatus embodying a
deflecting electromagnetic system according to the invention for guiding
cathodic
evaporate to a substrate holder disposed remote from the working axis of the
cathode
plate; and
Figure 10 is a plan view of a dual arc coating apparatus embodying the
magnetic steering, focusing and deflecting aspects of the invention.
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Detailed Description of the Invention
Figure 1 illustrates a prior art large area rectangular cathode vacuum
arc plasma source of the type described and illustrated in U.S. Patent No.
4,724,058 to
Morrison. The apparatus 10 comprises a cathode plate 12 having a target
evaporation
surface 14 which may be circumscribed by a confinement member 16 composed of a
magnetically permeable material. As described in U.S. Patent No. 5,587,207
issued
December 24, 1996 to Gorokhovsky, an anode 15 disposed opposite the target
surface
14, which may be composed of a metallic or a non-metallic coating material.
A current applied between the cathode 12 and the anode 15 creates an
arc which generates an arc spot on the target surface 14. In the prior art
apparatus
shown the scanning pattern of the cathode spot is controlled by a closed-loop
magnetic field source 18 disposed behind the cathode 12. The magnetic field
source
18 establishes magnetic fields 19a, 19b in a opposite directions over the
target surface
14 which moves the arc spot in a retrograde motion according to the formula
Vcs - -C[Ias(Bt)]
in which Vcs is the velocity of the arc spot, las is the arc spot current, Bt
is the
strength of the transverse magnetic field, and c is a coefficient based on the
material of
the target surface 14. The arc spot thus traces a retrograde path about the
cathode
plate following the length of the magnetic field source.
When trapped within the static magnetic field produced by the
magnetic field source 18, the cathode spot is directed toward the apex of the
magnetic
field lines, the region where the tangential component of a magnetic field is
strongest,
which causes the target surface 14 to evaporate along a narrow evaporation
corridor
14a. Further, the oppositely oriented magnetic field lines 19a, 19b create a
stagnation
zone at 22 in which the cathode spot can settle and remain for prolonged
periods,
eroding the target surface 14 unduly in the stagnation zone 22. Both of these
effects
result in poor utilization efficiency of the target surface 14. Accordingly,
in the
apparatus described in U.S. Patent No. 4,724,058 the magnetic field is
activated only
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intermittently during the coating process, the are spot being free to scan
randomly
most of the time. Since the cathode spot is largely self-steering, magnetic
fields
cannot be used for plasma focusing.
Figure 2 illustrates a preferred embodiment of a cathode spot steering
system 60 according to the invention. In the embodiment illustrated in Figure
2 the
steering system 60 is disposed behind the cathode plate 32 (i.e. on the side
of the
cathode plate 32 opposite to the target evaporation surface 34), which has
long sides
32a, 32b and short sides 32c, 32d. The steering system 60 comprises linear
conductors 62 and 64 respectively disposed in parallel with the long sides
32a, 32b of
the cathode plate 32 having a current ILs applied thereto in the direction
shown, and
linear conductors 66 and 68 respectively disposed in parallel with the short
sides 32c,
32d of the cathode plate 32 having a current Iss applied thereto in the
direction shown.
The conductors 62, 64 are disposed behind the cathode plate in the vicinity of
the
target surface 34 so that the magnetic fields generated thereby intersect the
target
surface 34, and thus influence arc spot formation and motion. The steering
conductors
62, 64, 66, 68 may alternatively be disposed in front of the cathode plate, as
in the
embodiment illustrated in Figures 4 to 6, described below. In either case the
steering
magnetic field source 60 generates a magnetic field defining an erosion zone
70 along
the target surface 34.
The configuration and polarities of the magnetic fields generated by the
steering conductors 62, 64, 66 and 68 are illustrated by the magnetic field
lines in
Figure 2. The magnetic field lines projecting above the target surface 34 are
arch-
shaped, and on opposite sides of the cathode 32 are oriented in opposite
directions.
Arc spots moving within the erosion zone 70 are attracted toward the apex of
the arch-
shaped magnetic field lines, where the tangential component of the magnetic
field
which projects beyond the target surface 34 is strongest. When the current
through
opposite conductors, for example steering conductors 62 and 64, is equal or
balanced
(i.e. I1 =1z), the arc spot travels along a narrow erosion corridor largely
confining the
erosion zone 70 beneath the apex of the magnetic field lines symmetrically
about the
longitudinal centre of the cathode plate 32, as shown in Figure 2a.
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According to one aspect of the invention, by increasing the current in
one steering conductor relative to the current in the steering conductor on
the opposite
side of the cathode plate 32, the magnetic field becomes unbalanced and the
magnetic
field lines on the side of the cathode 32 with the weaker magnetic field shift
toward
the side of the cathode 32 with the stronger magnetic field. In the preferred
embodiment each linear conductor 62, 64, 66, 68 is thus electrically
independent and
can be controlled in isolation.
For example, in Figure 2b the current in steering conductor 62 has been
increased relative to the current in steering conductor 64, so that I1 < 12.
The resulting
unbalancing of the strength of the magnetic fields generated thereby distorts
the
magnetic field generated by the conductor 64 and shifts its magnetic field
lines toward
the conductor 62. The point of the magnetic field generated by conductor 64
where
the tangential component of the transverse magnetic field is strongest has
thus shifted
away from the side 32a and toward the centre of the cathode 32, and are spots
accordingly trace a path closer to the centre of the cathode 32. By
unbalancing the
current in conductors 62, 64 so that conductor 64 generates the stronger
magnetic field
and I1 > 12, the path of the arc spot shifts away from the side 32b and toward
the centre
of the cathode, as shown in Figure 2c.
The degree of unbalancing, i.e. the current differential between
conductors 62 and 64, determines the extent of the magnetic field shift. By
unbalancing the conductors 62, 64 at selected current levels and in properly
timed
intervals coinciding with the motion of the arc spot, a plurality of are spot
paths are
created. This substantially increases utilization efficiency of the target
surface.
A similar effect is achieved along the short sides 32c, 32d of the
cathode 32 by unbalancing the current through the conductors 66, 68. The path
of the
arc spot will shift toward the centre of the cathode 32 along the side with
the weaker
magnetic field. However, it will be appreciated that if the cathode plate 32
is narrow
enough that the magnetic fields generated along the long sides 32a, 32b by
conductors
62, 64 are relatively close together, the conductors 66, 68 along the short
sides 32c,
CA 02268659 2006-06-23
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32d may become unnecessary; the arc spot will naturally migrate back and forth
between the long magnetic fields, or as the arc spot reaches the end of its
path along
one long side 32a or 32b the magnetic field can be selectively decreased or
momentarily deactivated along that side and the arc spot will move to the
other side
32b or 32a where the magnetic field is stronger.
The closing conductors 62a, 64a, 66a, 68a, which are parallel to the
target surface 34 and respectively complete the circuit for each steering
conductor 62,
64, 66, 68, are maintained well away from the cathode plate 32 and the housing
38.
This ensures that the magnetic fields generated by the closing conductors 62b,
64b,
66b, 68b or 72a, 72b do not influence are spot formation or plasma flow
patterns.
In operation, when an arc is created by applying a current between the
anode and the cathode plate, an arc spot generated on the target surface 34
settles in an
erosion corridor 70 defined within the steering magnetic fields generated by
the
steering conductors 62, 64, 66, 68. The arc spot follows a retrograde motion
along the
erosion zone 70. The magnetic field is periodically unbalanced by a control
switch
(not shown), which intermittently increases the current through conductor 62
to
increase the strength of the magnetic field generated thereby and shift the
are spot path
away from the side 32a, and alternately increases the current through
conductor 64 to
increase the strength of the magnetic field generated thereby and shift the
arc spot path
away from the side 34a. This effectively widens the erosion zone 70 to
increase the
utilization efficiency of the target surface, improving the quality of the
coating and the
durability of the cathode 32.
In a variation of this embodiment, illustrated in Figure 3, a plurality of
steering conductors 62b, 62c, 62d and 64b, 64c, 64d are provided respectively
along
the long sides of the cathode plate 32. In this variation the steering
conductors 62b,
62c, 62d and 64b, 64c, 64d are activated or modulated alternatively so that
the erosion
corridor, being located generally above the currently active steering
conductor 62b,
62c or 62d on one side and 64b, 64c or 64d on the other side, can be shifted
in a
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widthwise direction over the cathode plate 32 to increase the breadth of the
erosion
zone 70.
In the embodiment of Figure 3 as many steering conductors may be
provided as the size of the cathode plate 32 will practically allow. One
steering 5 conductor 62b, 62c or 62d and 64b, 64c or 64d should be active on
each side of the
cathode plate 32 at any particular time, in order to avoid creating a
stagnation zone in
which the cathode spot may become trapped. However, where the conductors on
each
side of the cathode 32 are close together, simultaneously exciting more than
one
conductor on each side of the cathode 32 can allow for a more elaborate
erosion
pattern which, properly controlled, can increase the utilization efficiency of
the target
surface 34 even further.
In the operation of this embodiment, when an arc is created by applying
a current between the anode and the cathode plate, an arc spot generated on
the target
surface 34 settles in an erosion corridor 70 defined within the steering
magnetic fields
generated by the active steering conductors, for example 62b and 64b. The
magnetic
field is periodically shifted by a control switch (not shown), which switches
the
current between the conductors 62b, 62c and 62d on the long side 32a and
between
the conductors 64b, 64c and 64d on the long side 32b, to thereby and shift the
arc spot
path to the vicinity of the active steering conductor. This widens the erosion
zone 70
to increase the utilization efficiency of the target surface, improving the
quality of the
coating and the durability of the cathode 32.
It will be appreciated that in each of these embodiments the active
steering conductor does not need to be deactivated completely when another
steering
conductor is activated, or fully energized when activated, in order to achieve
the
desired erosion pattern in the erosion zone 70. The current can be modulated
differentially as between the various steering conductors to generate the same
result.
Figures 4 to 6 illustrate a further embodiment of the invention
providing arc spot shielding. An arc coating apparatus is provided with a
rectangular
cathode plate 32 comprising a target evaporation surface 34 and a supporting
plate 36
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mounted to a cathode holder 42, within a coating chamber defined by the target
surface 34 and a housing 38. In the preferred embodiment the target surface
34, which
may be composed of any suitable metallic or a non-metallic coating material,
has long
sides 32a, 32b and short sides 32c, 32d and is electrically insulated from the
housing
38 by dielectric spacers 39 isolating the cathode holder 42 from the
supporting plate
36 and spaced from the housing 38 by a gap 40. The target surface 34 may be
formed
from different materials, for example titanium and aluminum or titanium and
chromium, integrated in a mosaic fashion along the erosion zone 70 to produce
a
composite metallic plasma for applying coatings such as TiA1N, TiCrN or the
like.
The cathode plate 32 is spaced from the cathode holder 42 to create a
coolant chamber 44 for circulating a coolant such as water, and is connected
to the
negative pole of an arc current source (not shown). A conventional high
voltage pulse
igniter 48 is mounted through a dielectric sleeve traversing the wall of the
housing 38.
Suspended from the housing 38 by a mounting assembly 51 is a linear
anode 50, spaced from the cathode plate 32 and mounted to an anode holder 52
which
may be provided with a coolant channel 53 for circulation of a coolant such as
water.
The anode 50 is connected to the positive pole of the arc current source 46.
In the
preferred embodiment the anode 50 comprises a series of baffles or "fins" 50a
which
may be disposed generally orthogonally in relation to an anode body 50b, to
increase
the effective anodic surface area. The fins 50a and anode body 50b are each
preferably oriented in a direction parallel to the direction of the plasma
flow, i.e.
parallel to the direction of any focusing magnetic fields in the vicinity of
the anode 50
as described below, to reduce the opportunity for vapour deposition on the
anodic
surfaces and thus reduce diffusion losses.
Arc spot formation is confined by steering magnetic fields produced by
a steering magnetic field source 60 comprising linear conductors 62 and 64
respectively disposed along the long sides 32a, 32b of the cathode plate 32
and linear
conductors 66 and 68 respectively disposed along the short sides 32c, 32d of
the
cathode plate 32. In this embodiment the conductors 66, 68 are disposed behind
the
CA 02268659 2006-06-23
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cathode plate 32 as in the previous embodiments, but the conductors 62, 64 are
disposed in front of the cathode plate 32. The conductors 62, 64 are still
disposed in
the vicinity of the target surface 34 so that the magnetic fields generated
thereby
influence arc spot formation and motion, and the operation of the steering
system 60
in this embodiment is substantially as described in respect of the embodiment
of
Figure 2.
However, in the embodiment of Figures 4 to 6 the steering magnetic
fields do not confine arc spots, as in the embodiment of Figure 2, because the
magnetic field lines are not arch-shaped and intersect the target surface 34
on only one
side, as seen by the magnetic field lines shown in Figure 5. Thus, because of
the acute
angle principle arc spots are guided toward the central region of the cathode
plate 32,
away from the acute angle formed where the magnetic field lines intersect the
target
surface 34. Arc spots therefore have a broader range of motion available in
this
embodiment. Moreover, in the embodiments in which the steering conductors are
located behind the cathode plate 32, in which the portion of the steering
magnetic
fields projecting above the target surface 34 is closed (i.e. intersects the
target surface
34 along both sides), the magnetic fields confine not only the are spot but
also the
plasma generated as the target surface 34 evaporates. As shown in Figure 5, by
disposing the conductors 62, 64 in front of the target surface 34 the cathodic
evaporate
has an open path to the substrate holder 6.
Are spots are thus guided toward the central region of the cathode plate
32, from both long sides 32a, 32b. To avoid creating a stagnation zone in the
central
region of the cathode plate 32, a conductive shield 54 maintained at floating
potential
is mounted to the anode holder 52, insulated therefrom and spaced from the
target
evaporation surface 34, which precludes any cathode spot activity in the
central region
of the cathode plate 12. Preferably the shield 54 is spaced from the target
surface 34
between 2 mm and 6 mm; less than about 2 mm is likely to cause the arc to
short
circuit through the shield 54 and more than about 6 mm allows the arc spot to
creep
under the edges of the shield 54. The shield 54 thus prevents evaporation of
the
cathode 32 in the shadow of the anode 50, confining arc spot formation to an
erosion
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zone 70 surrounding the shadow of the anode 50. This protects the anode 50
from
deposition of cathodic evaporate and provides a better distribution of coating
material
over the substrates (not shown) mounted on the substrate holder 6.
One or more floating shields 54 may be positioned over any selected
portion(s) of the target evaporation surface 34, to prevent arc spots from
moving into
the shielded region. In the embodiment illustrated the shield 54, positioned
immediately above the target surface 34 in the vicinity of the anode 50,
prevents arc
spots from forming in or moving into the area of the target surface 34
surrounding the
shield 54. This is advantageous in embodiments in which the steering
conductors are
disposed in front of the cathode plate 32. However, a floating shield 54 can
be used to
keep arc spots away from any desired region of the cathode plate 32. For
examplc, the
floating shield 54 allows the target evaporation surface of the cathode plate
to be
constructed of more than one material; in this case an expensive coating
material such
as tungsten or platinum can be omitted from the region beneath the shield 54,
and
since arc spots will not form or move in that region there is no possibility
that the
coating will be contaminated.
In operation, a current is applied between the anode 50 and the cathode
plate 32 and a high pulse voltage applied to igniter 48 initiates a vacuum arc
on t:le
target surface 34 of the cathode plate 32. The are spot settles in an erosion
corridor 70
defined between the steering magnetic fields generated by the conductors 62,
64 and
the shielded region of the target surface 34 behind the conductive shield 54.
The arc
spot follows a retrograde motion along one long side 32a or 32b of the target
surface
34, and moves to the other long side 32b or 32a traveling beneath the apex of
the
magnetic field generated by the steering conductor 66 or 68 disposed behind
the
cathode plate 32. As the target surface 34 evaporates the plasma is guided
between
the magnetic fields generated by the conductors 62, 64 and flows toward the
substrate
holder 6, as shown by the arrows in Figure 5.
Because the preferred embodiments of the invention employ a
magnetic steering system, it is possible to use a plasma focusing system to
guide the
CA 02268659 2006-06-23
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cathodic evaporate toward the substrate holder 6. A magnetic field forms a
barrier
which is largely opaque to plasma. Thus, focusing magnetic fields can be
generated
about the housing 38 to confine the plasma to a plasma flow region between
magnetic
fields, and positioning the substrate holder 6 in the plasma flow region to
increases the
concentration of plasma about the substrates and improves the quality of the
coating.
In the embodiment illustrated in Figures 4 to 6 the conductors 62, 64,
being disposed in front of the target surface 34 of the cathode plate 32, can
also serve
as focusing conductors in a plasma focusing system. A plasma flow path is
defined
between the magnetic fields generated by the conductors 62, 64, as shown by
the
magnetic field lines in Figure 5, such that plasma is guided along a central
region of
the housing 38 to the substrate holder 6.
To focus the plasma flow, additional plasma focusing conductors may
be provided in series to elongate the plasma flow path. For example, Figures
7a and
7b illustrate an embodiment of the invention in which groups of plasma
focusing
conductors 82, 84 and 92, 94 are disposed on opposite sides of the housing 38
and,
within each group, progressively further from the cathode 32. This creates a
plasma
confining zone between the magnetic fields generated on opposite sides of the
housing
38, thus defining a plasma flow path between the target surface 34 and the
substrate
holder 6.
The focusing conductors 82, 84 and 92, 94 are disposed too far from
the cathode plate 32 to influence arc spot formation or motion, and preferably
the
focusing conductors in each group 82, 84 or 92, 94 are disposed in closely
spaced
relation so that their respective magnetic fields overlap to create a
continuous
magnetic wall confining the plasma to the plasma flow path and magnetically
isolating
the wall of the housing 38 from the plasma flow. As in the case of the
steering
conductors, the closing conductors 82a, 84a of the focusing conductors 82, 84
and the
closing conductors 92a, 94a of the focusing conductors 92, 94 are maintained
well
away from the housing 38 and the cathode plate 32 to eliminate any canceling
effect
of the magnetic fields generated thereby in the region of the housing 38
(plasma duct).
CA 02268659 2006-06-23
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In the operation of this embodiment, as the target surface 34 evaporates
the plasma is concentrated between the focusing magnetic fields generated by
focusing conductors 82, 84 and 92, 94. The plasma thereby flows toward the
substrate
holder 6 without contacting the housing 38.
The focusing conductors 82, 84 and 92, 94 are preferably
independently powered, so that the intensity of the magnetic field generated
by each
conductor 82, 84, 92, 94 can be varied independently of the others. Closed
loop
focusing conductors can be disposed on only one side of the housing 38,
however in
the preferred embodiment illustrated in Figures 7a, 7b pairs of independent
focusing
conductors 82 and 92, and 84 and 94, respectively, are disposed on opposite
sides of
the housing 38 parallel to the long sides 32a, 32b of the cathode 32. The
closing
conductors 82a, 84a, 92a and 94a are maintained well away from the housing 38
and
the cathode plate 32.
In a further embodiment illustrated in Figure 8 the opposed focusing
conductors 82, 92 and 84, 94 are formed from the same closed loop conductor
with
the focusing conductors 82, 92, 84 and 94 disposed parallel to the long sides
32a, 32b
of the cathode 32 with closing conductors 82a, 92a, 84a and 94a disposed
parallel to
the short sides 32c, 32d of the cathode 32.
By connecting focusing conductors 82, 84 and 92, 94 independently to
the power supply it is also possible to "raster" the plasma flow by varying
the current
through opposed focusing conductors 82, 92 and/or 84, 94. This helps to
distribute
the plasma more uniformly about the plasma duct and to create a more
homogeneous
plasma mixture. Within the coating chamber the focusing conductors 82, 84 and
92,
94 can be independently activated to deflect plasma toward the substrate
holder 6.
Figure 8 illustrates an alternative mode of modulating the focusing
conductors 82, 92 and/or 84, 94 using neutralizing conductors 140 disposed
alongside
focusing conductors 82, 92 and 84, 94, but in an opposite orientation. When
activated
the neutralizing conductors 140 interfere with the magnetic fields generated
by one or
CA 02268659 2006-06-23
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more of the focusing conductors 82, 92 or 84, 94 to reduce the effect of the
magnetic
field generated thereby and deflect the plasma flow.
In all embodiments the closing conductors 82a, 84a, 92a and 94a are
maintained well away from the housing 38 and the cathode plate 32 to eliminate
any
canceling effect of the magnetic fields generated thereby in the region of the
housing
38 (especially the plasma duct region of the housing 38).
The plasma focusing system of the invention can also be used as a
plasma deflecting system 100, allowing the substrate holder 6 to be disposed
remote
from the working axis of the cathode plate 32, designated 33 in Figure 9, to
eliminate
from the plasma the neutral component (macroparticles, clusters and neutral
atoms)
which are unaffected by the focusing magnetic field and further improve the
quality of
the coating. As shown in Figure 9, by arranging deflecting conductors 86, 87,
88 and
96, 97, 98 along a curvate housing 38 in a progressively asymmetrical pattern
relative
to the working axis 33 of the cathode plate 32, the plasma is deflected toward
the
substrate holder 6 while the inertia of the plasma causes the neutral
component to
separate from the plasma in the deflection region.
The conductors 86, 87, 88 and 96, 97, 98 thereby create a chain of
deflecting conductors to form a deflecting electromagnetic system. As in the
previous
embodiments, closing conductors 86a, 87a, 88a and 96a, 97a, 98a are maintained
well
away from the housing 38 (especially the plasma duct region) and the cathode
plate
32. The closing conductors 86a, 87a, 88a and 96a, 97a, 98a may be disposed on
the
same side of the housing 38 as the deflecting conductors 86, 87, 88 and 96,
97, 98 of
the deflecting system, for example by disposing the closing conductors 86a,
87a, 88a
and 96a, 97a, 98a well above or below the level of the housing 38.
Alternatively the
closing conductors 86a, 87a, 88a and 96a, 97a, 98a may be disposed on the
opposite
side of the housing 38 but remote therefrom, in which case it is preferable
that the
distance S between the closing conductors and focusing conductors on one side
of the
housing (for example focusing conductors 86, 87, 88 and closing conductors
96a, 97a,
98a) be governed by the formula
CA 02268659 2006-06-23
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S=1.5-2H
where H is the width (transverse) of the housing 38.
In the operation of this embodiment, as the target surface 34 evaporates
the plasma is concentrated between the magnetic fields generated by the
conductors
62, 64 and flows into the deflection region defined between the magnetic
fields
generated by deflecting conductors 86, 87, 88 and 96, 97, 98. The plasma is
thereby
deflected along a flow path coinciding with the asymmetrical pattern of the
deflecting
conductors 86, 87, 88 and 96, 97, 98 and flows toward the substrate holder 6
without
contacting the housing 38. The plasma remains confined between magnetic fields
and is thereby deflected away from the working axis 33 of the cathode plate
32. The
neutral component continues in a generally straight direction and settles on
an interior
wall of the housing 38 in the vicinity of the working axis 33 of the cathode
plate 32,
while the plasma continues along the plasma duct into the coating chamber to
the
substrate holder 6.
Figure 10 illustrates a preferred embodiment of an arc coating
apparatus according to the invention, providing a pair of cathode plates 32
disposed at
opposite ends of the housing 38. Internal linear anodes 50 configured as
described
above are suspended above each target surface 34, separated therefrom by a
shield 54.
Anodes 50 are defined herein as "internal" because they are disposed within
the
plasma duct, which is defined between the cathode plates 32 and the substrate
holder
6. A further internal anode 120 comprising a linear plate 122 having baffles
124 is
disposed along the plasma duct at the approximate center between the two
cathode
plates 32. The baffles increase the anodic surface area, effectively
functioning as a
chain of internal anodes, which provides better stabilization and steering of
are spots.
As in the previous embodiment, the baffles 124 are oriented as much as
possible
parallel to the direction of the magnetic field to reduce diffusion losses.
This
"dividing" anode 120 also serves to repel ions and thus deflect the plasma
streams
toward the substrate holder 6.
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In this embodiment focusing conductors 82, 84, 92 and 94 are disposed
parallel to the long sides 32a, 32b of the cathode plates both about the
regions in front
of the cathode plates 32 and about the exit of the plasma duct in the coating
chamber.
In between the sets of focusing conductors 82, 92 and 84, 94, deflecting
conductors
86, 96 are disposed about the portion of the housing 38 where the plasma duct
turns
toward the axis of the substrate holder 6, to deflect plasma toward the
substrate holder
6.
The embodiment of Figure 10 also provides one or more external
anodes 130 surrounding the substrate holder 6. Anodes 130 are defined herein
as
"external" because they are disposed outside of the plasma duct. Thus, the
external
anodes 130 do not deflect the plasma, but instead repel ions to prevent
diffusion losses
on the walls of the housing 38 and prolong ionization of the coating material
to
improve coating efficiency. Such external anodes 130 can also be provided
about any
desired portion of the housing 38.
Further, since the housing 38 is insulated from the cathode plates 32 by
dielectric spacers 39, a current can be applied as shown in Figure 5, or the
housing 38
may be left at floating potential, to effectively turn the housing 38 (or any
portion
thereof) into an external anode, which produces the effects described above
and
prevents the arc from approaching the housing walls.
The internal anodes 32, 120 and external anode 130 are preferably
electrically isolated and thus each is provided with an independent power
supply,
which allows for better control over their independent functions.
It is also possible to differentially activate the focusing conductors 82,
84 and 92, 94 to trap the metal vapour component of the plasma within the
plasma
duct while allowing the electron current to flow freely through the coating
chamber to
CA 02268659 2006-06-23
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the auxiliary anodes 130 surrounding the substrate holder 6. This mode of
operation
is a "plasma immersed" mode, which provides a high degree of ionization and
activation of the gaseous plasma environment in the coating chamber without
deposition of metal cathodic arc plasma coatings. The plasma immersed mode
supports several different types of plasma processes, such as fast ion
cleaning, ion
nitriding, ion implantation, and arc plasma-assisted low pressure CVD coating
processes. For example, the first stage of a particular coating process may
require ion
cleaning. The cathodic arc sources 34 may be used as a powerful electron
emitters, to
extract electron current from the cathode to the external anode 130
surrounding the
substrate holder 6, providing a plasma immersed environment for fast ion
cleaning.
Argon may be injected as a plasma-created gas in conjunction with an RF
generator
providing a self bias potential at the substrate holder for effective ion
bombardment,
as illustrated by the following examples.
Example 1
Deposition of a diamond-like coating (DLC) on set of knives such as
scalpels, razors, knives for cutting papers using two rectangular arc sources
mounted
in the dual rectangular plasma guide chamber of Fig. 10 with deposition zone
500 mm
height x 300 mm width. The array of knives was installed on a rotating
substrate
platform facing the filtered arc source over the entire area of the deposition
zone, with
uniform rotation speed between about 10 to 20 rpm. A graphite rectangular
plate
evaporation target was attached to the cathode plate assembly. The current in
the
vertical steering conductors was set to 2000 amps, and the current in the
horizontal
steering conductors was set to 1300 amps. The arc current between the cathode
and
the primary (internal) anode plate was set to 300 amps. After igniting the arc
with an
impulse high voltage igniter, the arc spot began moving along an erosion
corridor with
an average speed ranging from 20 to 30 cm/s. About three to five cathodic are
spots
subsisted simultaneously on the target surface. The current in the deflecting
coils was
set to 1500 amps each.
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The first stage of the process involved ion cleaning. At this stage the
cathodic arc sources were used as a powerful electron emitters. The deflecting
conductors were turned off and electron current was extracted from the cathode
to the
auxiliary (external) anode surrounding the substrate platform, providing a
plasma
immersed environment for fast ion cleaning. Argon was injected as a plasma-
created
gas with pressure of about 4 x 10-2 Pa and an RF generator provided a 400 volt
self
bias potential at the substrate platform for effective ion bombardment.
During the deposition stage the pressure in the vacuum chamber was
set to 10-3 Pa. The RF generator having a 13.56 MHz frequency provided a self
bias
potential ranging from 40 V to 60 V during deposition. The deflecting coils
were
turned off during deposition periodically with a duty cycle of 20s on/5s off
to prevent
overheating of the coating. The time of deposition was 20 minutes. The
thickness of
the coating, as measured by micro cross section, ranged from 0.3 to 0.35 mkm
which
corresponds to a deposition rate of about 1 mkm/hr with a uniformity of +/-
10%.
Example 2
Deposition of graphite coating on molybdenum glass for using as a
substrate for flat panel display using rectangular molybdenum glass plates
with
dimensions 400mm height x 200 mm width x 3 mm thick installed vertically on
the
rotating substrate platform. Each glass plate was attached to a metal plate-
holder and a
self bias of about 150 V was applied to the substrate platform using an RF
generator
with a 13.56 MHz frequency. The dual filtered cathodic are source of Figure 10
was
provided with one aluminum target evaporation surface and one graphite target
evaporation surface. The pressure during coating deposition was maintained at
about
10-3 Pa. The temperature during deposition of the graphite coating was about
400 C,
provided by an array of radiative electrical heaters.
In the first stage the arc was ignited on the aluminum target, providing
an aluminum sublayer with thickness about 50 nm. In the second stage a
graphite
CA 02268659 2006-06-23
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coating with thickness about 150 nm was deposited over the aluminum sublayer
during a coating interval of 30 minutes.
Example 3
Deposition of TiA1N coatings on an array of hobs and end mills. The
array of hobs and end mills was installed on substrate platform facing the
filtered arc
source exit over the entire area of the deposition zone, the substrate
platform having a
double (satellite) rotation with platform rotation speed 12 rpm. The dual
rectangular
filtered arc source of Figure 10 was provided with an aluminum target
evaporation
surface mounted to one cathode and a titanium target evaporation surface
mounted to
the second cathode, for deposition of the TiA1N coating. The current for the
titanium
target was set at about 150 amps while current for the aluminum target was set
at
about 60 amps.
In the first stage the current of the auxiliary (external) anode was set at
about 70 amps, providing a high density gaseous plasma immersed environment
during both fast ion cleaning and coating deposition. The self bias potential
of
substrate platform provided by a RF 13.56 MHz generator was maintained at
about
400 volts during ion cleaning in argon, and at about 40 volts during
deposition of
TiA1N coating in nitrogen. The time for ion cleaning was 5 minutes, and for
deposition was about 2 hours. The argon pressure during ion cleaning was set
at 6 x
10-2 Pa of argon, and for the deposition stage it was set at 2 x 10-2 Pa of
nitrogen. The
deposition rate for TiA1N coating for double rotated hobs and end mills was
found to
be about 1-1.5 m/hr.
Example 4
Deposition of multi-layer coatings on dies and molds. An array of
forging dies and extrusion molds was installed on the substrate platform with
uniform
rotation speed 20 rpm facing the filtered arc source exit in the dual
rectangular filtered
3o arc source of Figure 10, for the deposition of Ti/TiN multi-layer coating
with
thickness ratio 0.05 m of Ti and 0.3 m of TiN. Before deposition of the
coatings
CA 02268659 2006-06-23
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fast ion cleaning and arc plasma immersed ion nitriding was performed to
provide
gradually increased hardness of near surface layer in a transition zone
between bulk
material of coating parts and the coating layer. The thickness of nitriding
layer was
about 40 gm, provided by an auxiliary arc discharge with the current of
auxiliary
(external) anode set at about 90 amps and a pressure of nitrogen set at about
6 x 10-2
Pa. The number of coating layers was 11 with total thickness about 3.5 m. The
current of the auxiliary anode during the deposition stage was set at about
120 amps,
providing maximum total current at both titanium targets of about 500 amps.
The DC
bias during the ion cleaning/ion nitriding stage was set at about 200 volts,
and during
the deposition stage the current was reduced to 40 volts. The temperature of
substrates
was maintained at about 400 C during all stages of the vacuum plasma
treatment
cycle.
Preferred embodiments of the invention having been thus described by
way of example, modifications and adaptations will be apparent to those
skilled in the
art. The invention includes all such modifications and adaptations as fall
within the
scope of the appended claims.
