Note: Descriptions are shown in the official language in which they were submitted.
CA 02317235 2000-08-30
FIELD OF THE INVENTION
This invention relates to improved razors and razor blades and to processes
for producing
razor blades or similar cutting tools with sharp and durable cutting edges,
and in particular to
amorphous diamond coating of blades using a filtered cathodic arc plasma
source. The invention
has particular utility for forming a very hard and rigid coating of high
aspect ratio on very thin
cutting edges of razor blades.
This application is a division of copending commonly owned Canadian Patent
Application
Serial No.2,188,022 of April 21, 1995.
BACKGROUND OF THE INVENTION
I 0 A razor blade typically is formed of suitable substrate material such as
metal or ceramic,
and an edge is formed with wedge-shape configuration with an ultimate edge or
tip that has a
radius of less than about 1,000 angstroms, the wedge shaped surfaces having an
included angle
of less than 30°. As shaving action is severe and blade edge damage
frequently results and to
enhance shavability, the use of one or more layers of supplemental coating
material has been
proposed for shave facilitation, and/or to increase the hardness and/or
corrosion resistance of the
shaving edge.
A number of such coating materials have been proposed, such as polymeric
materials and
metals, as well as other materials including diamond-like carbon (DLC)
material. Each such layer
or layers of supplemental material must have adhesion compatibility so that
each layer remains
firmly adhered to the substrate throughout the useful life of the razor blade,
and desirably provide
characteristics such as improved shavability, improved hardness and/or
corrosion resistance while
not adversely affecting the geometry and cutting effectiveness of the shaving
edge.
United States Patent No. 5,032,243 of Bache et al. describes blade substrate
materials
sharpened by ion bombardment from ion sources having the axes of their beams
directed at the
edges of the razor blades. United States Patent No. 5,232,568 of Parent et al.
and United States
Patent No. 5,295,305 of Hahn et al. show blades which have an interlayer
interposed between the
substrate and the diamond-like coating, wherein the interlayer is deposited on
the substrate and
then the diamond-like coating is deposited on the interlayer.
The prior solutions are not entirely successful, and it would be desirable
simply to use
mechanical honing processes to form the sharpened substrate (rather than the
ion beam formation
shown in Bache et al.) followed by a direct deposition of amorphous diamond
coating on the
CA 02317235 2000-08-30
substrate (without the intervening step of depositing an interlayer). It would
be desirable,
therefore, to be able to start with a thin blade substrate produced by
mechanical honing and to
impart both rigidity and hardness to the substrate by depositing an amorphous
diamond coating
directly on the substrate.
SUMMARY OF THE INVENTION
According to this invention, the cutting edges of razor blades are provided
with improved
mechanical properties by applying to the sharpened edge of the substrate a
coating of an
amorphous diamond material. Such materials may be characterized as having at
least 40 percent
spa carbon bonding, a hardness of at least 45 gigapascals and a modulus of at
least 400
gigapascals. In addition, such materials are not corroded by hot aqueous
solutions and compounds
commonly used in shaving. Materials having these characteristics will be
denoted as amorphous
diamond in the further course of this disclosure. In contrast to the amorphous
diamond material
of this invention, traditional diamond-like carbon coatings (DLC) produced by
such traditional
methods as sputtering do not exhibit such high hardnesses. Unlike the
amorphous diamond of this
disclosure, DLC coatings typically have hardnesses not exceeding 30
gigapascals.
The extreme hardness and rigidity of the applied amorphous diamond coating can
provide
strength to a very thin razor blade edge. United States Patent No. 4,720,918
of Curry et al.
describes edges of this type, and they are included here as examples and need
not be considered
limiting. A very thin blade edge can provide increased shaving comfort, but is
practical only if the
edge is strong enough to withstand shaving. A thin edge, including but not
limited to those
described in United States Patent No. 4,720,918, strengthened by 400 to 2000
angstroms of
amorphous diamond will comprise a finished edge which is significantly thinner
than edges
presently used for shaving, coupled with sufficient strength to withstand
shaving, this due to the
extraordinary strength of the amorphous diamond coating.
Further contributing to a thin edge is the large aspect ratio attainable by
the particular
cathodic arc deposition process used in this invention for manufacture of
amorphous diamond
coatings. The "aspect ratio" is explained in greater detail with reference to
FIG. 3 in the discussion
which follows, but may be understood for purposes of this summary as being the
ratio of (a) to
(b) where (a) is a first distance from the tip of the coating to the tip of
the substrate, and (b) is a
second distance from a surface of the coating to the tip of the substrate.
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CA 02317235 2001-06-05
The aspect ratio provides a useful measure of the effect of a coating on the
underlying
blade edge geometry of the substrate--the larger or higher the aspect ratio of
the coating, the
"sharper" is the coated blade compared to a blade coated at a lower aspect
ratio. As a further
consequence of the extraordinary strength of the amorphous diamond coatings of
this invention,
application of such a coating to a razor blade of normal cross-section will be
expected to provide
longer shaving life.
In accordance with one aspect of the invention, there is provided a wedge-
shaped edge and
a layer of amorphous diamond on the tip and flanks of the wedge-shaped edge,
preferably with
a thickness of at least 400 angstroms, which defines a tip radius of less than
about 500 angstroms
and an aspect ratio of 2:1 to 4: I . The blade exhibits excellent shaving
properties and long life.
In preferred embodiments, the razor blade substrate is steel, the amorphous
diamond
coating is at least four times as hard as the steel substrate; the wedge-
shaped edge is formed by
a sequence of mechanical abrading steps; and the layer of amorphous diamond is
formed of carbon
ions provided from a graphite target used as a filtered cathodic arc source.
I 5 In accordance with another aspect of the invention, there is provided a
process for forming
a razor blade that includes the steps of providing a substrate; forming on an
edge of the substrate
a wedge-shaped sharpened edge that has an included angle of less than
30° and a tip radius (i.e.
the estimated radius of the largest circle that may be positioned within the
ultimate tip of the edge
when such ultimate tip is viewed under a scanning electron microscope at
magnifications of at least
25,000) preferably of less than 1,200 angstroms; and depositing, by filtered
cathodic arc
evaporation, a layer of amorphous diamond on the sharpened edge to provide a
radius at the
ultimate tip of the amorphous diamond layer of less than about 1000 angstroms.
The amorphous
diamond layer may be deposited by several techniques, all having in common the
energetic
deposition of carbon as a highly ionized species. While methods of cathodic
arc, anodic arc,
plasma decomposition of hydrocarbon gases, sputtering with post-ionization by
inductively
coupled rf, laser ablation, laser absorptive wave deposition (LAWD) and direct
ion beam
deposition might be used for this purpose, the preferred embodiment of this
invention uses a
filtered cathodic arc.
In a particular process, the substrate is mechanically abraded in a sequence
of honing steps
to form the sharpened edge; a layer of amorphous diamond is deposited by
filtered cathodic arc,
the amorphous diamond coating on the cutting edge having a thickness of at
least 400 angstroms,
3
CA 02317235 2000-08-30
the layer of amorphous diamond having at least 40 percent spa carbon bonding,
a hardness of at
least 45 gigapascals; and an adherent polymer coating may be applied on the
amorphous diamond
coated cutting edge.
In accordance with another aspect of the invention, there is provided a
shaving unit that
comprises blade support structure that has external surfaces for engaging user
skin ahead and
rearwardly of the blade edge or edges and at least one blade member secured to
the support
structure. The razor blade structure secured to the support structure includes
a substrate with a
wedge-shaped cutting edge defined by facets that have an included angle of
less than seventeen
degrees at a distance of forty micrometers from the sharpened tip, and a layer
of a strengthening
material which has a thickness of at least 400 angstroms from the sharpened
tip of said substrate
to a distance of forty micrometers from the sharpened tip, a radius at the
ultimate tip of the
strengthening material of less than 500 angstroms and an aspect ratio in the
range of 2:1 to 4:1.
In a particular shaving unit, the razor blade structure includes two steel
substrates, the
wedge-shaped edges are disposed parallel to one another between the skin-
engaging surfaces, the
1 S edge strengthening layer is of amorphous diamond with a thickness of about
1000 angstroms
(typically a range of 400-2000 angstroms depending on substrate and processing
parameters) and
is characterized by at least 40 percent spa carbon bonding and a hardness of
at least 45
gigapascals; and an adherent polymer coating is on each layer of amorphous
diamond material.
The shaving unit may be of the disposable cartridge type adapted for coupling
to and
uncoupling from a razor handle or may be integral with a handle so that the
complete razor is
discarded as a unit when the blade or blades become dull. The front and rear
skin engaging
surfaces cooperate with the blade edge (or edges) to define the shaving
geometry. Particularly
preferred shaving units are of the types shown in United States Patent No.
3,876,563 and in
United States Patent No. 4,586,255.
The invention of the parent application may be summarized therefore as
providing a razor
blade comprising a substrate with a wedge-shaped edge defined by facets that
have a width of at
least about 0.1 millimetre and an included angle of less than 20 degrees and a
layer of amorphous
diamond material having been deposited by a high energy source.
On the other hand, the invention of this application may be summarized,
broadly, as
providing a process for forming a razor blade comprising the steps of : (a)
providing a substrate;
(b) forming a wedge-shaped sharpened edge on the substrate that has an
included angle of less
4
CA 02317235 2000-08-30
than thirty degrees and a tip radius of less than 1,200 angstroms; and (c)
depositing a layer of
amorphous diamond as a coating on the sharpened edge, applying an initial high
bias to the
substrate during deposition, and then applying a second lower bias to the
substrate during
deposition.
Other features and advantages of the invention, including process conditions
for applying
the desired amorphous diamond coating will be seen as the following
description of particular
embodiments progresses, in conjunction with the drawings.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of a shaving unit in accordance with the
invention;
FIG. 2 is a perspective view of another shaving unit in accordance with the
invention;
FIG. 3 is a diagrammatic view illustrating one example of razor blade edge
geometry in
accordance with the invention;
FIG. 4 is a diagrammatic view of apparatus for the practice of the invention.
FIGS. 1 A-6A are illustrations of co-pending United States Patent Application
No.
08/233,006, hereinafter described in Attachment A.
DETAILED DESCRIPTION OF THE INVENTION
In the description which follows, the characteristics and properties of
various preferred
embodiments of the blade, substrate and amorphous diamond coating will be
disclosed, followed
by a disclosure of process conditions for depositing the desired coating.
With reference to FIG. 1, shaving unit 10 includes structure for attachment to
a razor
handle, and a platform member 12 molded of high-impact polystyrene that
includes structure
defining forward, transversely-extending skin engaging surface 14. Mounted on
platform member
12 are leading blade 16 having sharpened edge 18 and following blade 20 having
sharpened edge
22. Cap member 24 of molded high-impact polystyrene has structure defining
skin-engaging
surface 26 that is disposed rearwardly of blade edge 22, and affixed to cap
member 24 is shaving
aid composite 28.
The shaving unit 30 shown in FIG. 2 is of the type shown in United States
Patent No.
4,586,255 of Jacobson and includes molded body 32 with front portion 34 and
rear portion 36.
S
CA 02317235 2000-08-30
Resiliently secured in body 32 are guard member 38, leading blade unit 40 and
trailing blade unit
42. Each blade unit 40, 42 includes a blade member 44 that has a sharpened
edge 46. A shaving
aid composite 48 is frictionally secured in a recess in rear portion 36.
A diagrammatic view of the edge region of the blades 16, 20 and 44 is shown in
FIG. 3,
from which the aspect ratio may be better understood. The blade includes
stainless steel body
portion 50 with a wedge-shaped sharpened edge formed in a sequence of edge
forming honing
operations that forms a tip portion 52 that has a radius typically less than
500 angstroms with
facets 54 and 56 that diverge at an angle of about 13 °. Deposited on
tip 52 and facets 54, 56 is
amorphous diamond 60 that has a thickness of about 2,000 angstroms, with an
aspect ratio (the
ratio at distance (a) from amorphous diamond tip 70 to stainless steel tip 52,
and the width (b) of
the amorphous diamond coating 60 to tip 52) of about 3:1.
Deposited on layer 60 is an adherent telomer layer 72 that has a substantial
as deposited
thickness but is reduced to monolayer thickness during initial shaving.
An apparatus for processing blades ofthe type shown in FIG. 3 is schematically
illustrated
in FIG. 4. That apparatus includes a filtered cathodic arc deposition system,
such as one
manufactured by vapor Technologies of Boulder, Colo. that has stainless steel
chamber 80 which
is coupled to a vacuum pumping system (not shown) through valve 82. Mounted in
chamber 80
is an electrically isolated, water cooled substrate platform 84 on which is
disposed a rotatable
fixture 86 which holds a stack of razor blades 88.
The sharpened edges are aligned perpendicularly to the plane of the drawing
and face
downward from the support 86. Motor 90 fixed outside the chamber 80 provides
180 degrees of
rotation of the blade stack at predetermined intervals for the purpose of
alternately exposing each
blade edge to the beam of carbon ions from a single cathodic arc source 92,
insuring uniform
deposition on both blade bevels.
Also disposed in chamber 80 are two filtered cathodic arc sources 92, 94, each
consisting
of a graphite target 96 (cathode, 99.99% purity), an arc striking mechanism
98, and a filter or duct
100. The filter 100 serves to direct the flow of carbon ions (the arc plasma)
from the cathode 96
to the blade stack 88, through the use of solenoidal magnetic fields produced
by electrical
windings 102 along the length of the duct and an electromagnet 104 positioned
under the duct.
The cathodic arc source may also be of the type described in, and the magnetic
fields may be
controlled so as to optimize the performance of the arc relative to the
sources as described in
6
CA 02317235 2001-06-05
United States Application No. 08/233,006 of Welty, now US Patent No.
5,480,527, the
description of which is included in this application identified as Attachment
A. Water cooling lines
106, 108 and 110 are provided for the target 96, duct 92 and blade support 86,
respectively.
The duct is so directed to provide an angle of 40 degrees between the plane
112 presented
by the blade tips and the center axis 114 of the duct exit 114. This angle is
chosen to insure that
a fully dense coating is deposited. The graphite target 96 is approximately 30
centimeters long by
2.5 centimeters wide and is electrically insulated from the chamber 80, while
the duct 100 is at
ground potential. The graphite target 96 is connected to a DC power supply 118
through switch
120. Electrical wiring is provided to connect blade stack 88 through switch
122 to DC power
supply 124 or through switch 126 to RF power supply 128. The details of a
preferred filtered
cathodic arc design and operation are discussed further in the previously
mentioned United States
Application. No. 08/233,006 of Welty.
Rotatable mount 86 supports the blade stack 88 with edges spaced 15
centimeters from
the mouth of the filter duct. The blade stack 88 is rotated between a position
where one bevel
faces the duct 92, and a similar position where the opposite bevel faces the
duct 92. This rotation
of 180 degrees is carried out every 10 seconds, insuring the bevels are coated
equally.
In one example of a particular processing sequence, a stack of blades 88 (2.5
centimeters
long) is secured on the rotatable mount 86, the support cooling water is
turned on, and the
chamber 80 is evacuated. The pressure to chamber 80 is adjusted to 50
millitorr with flowing
argon. Switch 122 is closed to provide -400 volts DC to the blade stack,
igniting a DC plasma
discharge in which the blades are cleaned for ten minutes. After the cleaning
step, (i) the pressure
in the chamber is adjusted to 0.1 millitorr of argon, (ii) the field coils 102
to a single duct 92 are
energized, (iii) switch 120 to graphite target 96 is closed, (iv) the power
supply 124 to the blades
is adjusted to -1000 volts DC, and (v) an arc is struck/initiated on graphite
target 96 with
mechanical striker 98. The arc current is set to 100 A. An intense plasma of
carbon ions is emitted
from duct 92 and is deposited on the blades 88, which rotate 180 degrees every
10 seconds.
After the arc has run for 2 minutes, the bias supply 124 is set to -50 volts
and deposition
continues for a total time of 16 minutes. The resultant amorphous diamond
blade coating is
approximately 1000 angstroms in thickness on each facet. The blade tip radius
is approximately
350 angstroms, and the aspect ratio is approximately 2.5:1.
In another example of the processing sequence, the two cathodic arc sources
are
7
CA 02317235 2001-06-05
simultaneously operated, with the second source 94 positioned opposite the
first source 92, so that
both blade facets are simultaneously coated at approximately the same angle of
incidence. In this
case, the blade stack 88 is not rotated, but is rather translated through the
region where the
plasmas emitted from both sources intersect. All other aspects of the
processing sequence are
identical to those indicated above.
A coating 72 of polyterrafluorethylene (PTFE) telomer is then applied to the
amorphous
diamond coated edges of the blades. The process involves heating the blades in
a neutral
atmosphere of argon and providing on the cutting edges of the blades an
adherent and
friction-reducing polymer coating of solid PTFE. Coatings 72 and 60 were
firmly adherent to the
blade body 50, provided low wet wool felt cutter force (the lowest of the
first five cuts with wet
wool felt (LS) being about 0.45 kilogram), and withstood repeated applications
of wool felt cutter
forces indicating that the amorphous diamond coating 60 is substantially
unaffected by exposure
to the severe conditions of this felt cutter test and remains firmly adhered
to the blade body 50,
even after immersion in 80° C distilled water for sixteen hours.
Resulting blade elements 44 were assembled in cartridge units 30 ofthe type
shown in FIG.
2 and shaved with excellent shaving results.
PROCESS CONDITIONS
The foregoing disclosure ofthe characteristics and properties ofthe blades,
substrates and
amorphous diamond coatings may be further understood and enhanced by the
following specific
description of suitable process conditions generally described above. First,
the preferred cathodic
arc sources will be summarized. Then various preferred process conditions will
be described.
Cathodic Arc Source. A deposition coating of amorphous diamond may be applied
using
conventional filtered cathodic arc plasma source material as described in
United States Patent No.
5,279,723 of Falabella et al. However, in a preferred embodiment, the
deposition coating is
applied according to the previously referenced application which is appended
as Attachment A
hereto. Although the rectangular source of Attachment A is particularly suited
to the practice of
this invention, the invention is not so limited. Likewise, an unfiltered or
other conventional source
may be used, and this invention should not be understood as being limited to
filtered cathodic arc
sources.
Process Conditions and Adjustments. Process conditions include a mufti-step
bias to the
8
CA 02317235 2000-08-30
substrate; an equal average deposition on both sides of the blade; and
attention to the angle of
presentation.
An initial high bias in the range of 200-2000 volts is applied to the
substrate during
deposition for up to two minutes to establish adhesion. A second stage lower
bias in the range of
10-200 volts is then applied to optimize the structure of the amorphous
diamond hard carbon
coating and to establish the desired crystal structure. Although at least the
foregoing two stages
are desirable according to this invention, it may also be desirable to provide
a further "step down"
incremental bias voltage reduction as, for example by adding an intermediate
bias stage at 500
volts.
The amorphous diamond deposition is laid down at an equal average rate (or
simultaneously) on both sides of the blade. By setting at least dual sources
for simultaneous
deposition and/or cycling the angle of presentation of the blade set relative
to the deposition
source, the coating layer will be applied equally or at an equal average rate
of deposit, on both
sides. In light of the fact that the blades each have a cutting edge bounded
by a first inclined
surface and a second inclined surface, coming to a tip at the juncture of the
inclined surfaces and
that a set of blades:
~ may be disposed as a stack of blades presenting a plane surface formed by
the tips, or
~ may be disposed in a carousel, or otherwise; the layered concept involves
either (i) using
at least two sources so that the deposition rate is instantaneously equal on
both sides of the cutting
edge, or (ii) employing a movement of the blade set (stack or carousel)
relative to a single source
(a cyclic alternation of the presentation of the blades with respect to the
source, as by a flipping
of the stack, a rotation of the carousel, or other sequential presentation) in
order that a coating will
be laid down on both sides of the cutting edge of each razor at an
approximately equal rate over
time.
That is, in order to apply a coating of 1000 angstroms in thickness, a
preferred method of
this invention would not lay down all 1000 angstroms on the first side and
then lay down all 1000
angstroms on the second side of a blade stack--instead, it would be either (i)
a simultaneous
deposition on both sides or (ii) a cyclic alternation in a range of 3 to 500
angstroms on the first
side then 3 to 500 angstroms on the second side, and so on until the 1000
angstrom or other
desired thickness is built on both sides of the cutting edge of each blade.
While the foregoing is
a preferred method, the invention is not to be understood as so limited, and
may be practiced with
9
CA 02317235 2001-06-05
an uneven or unbalanced layering.
It should be understood that the angle of presentation is of some concern. The
low
pressure (high vacuum) conditions produce a highly directional plasma stream
of ionized carbon.
The blades are presented at an angle measured from a line normal to the plane
formed by the tips
of the stacked blades (or measured from the line bisecting the angle enclosed
by the tip and the
first and second inclined surfaces of the cutting edge of an unstacked blade)
that is greater that 20°
but less than 90°. The angle of presentation is intended to direct the
plasma stream more
directionally against one or the other sides of the cutting edges of the
blades.
As is conventionally known, the deposition process ofthis invention may be
operated with
or without a process gas such as argon; cleaning of the chamber may be
accomplished with RF
or DC glow discharge; and biasing of the substrate may be done with DC or RF
sources (and such
biasing may be used to shape the tip of the blade).
It should now be seen that this invention permits the strengthening of a thin
blade while
maintaining sharpness (that is, imparting stiffness and rigidity to the thin
blade without ruining the
acuteness or sharpness of the tip). Where a more conventional razor blade
might be coated to a
thickness in the order of a magnitude of about 100 to 3 50 angstroms, the
method of this invention
will deposit an amorphous diamond coat perhaps as high as 3,000 angstroms in
thickness (as
measured on the blade surface disposed away from the tip) and as high as 5,000
angstroms
measured at the tip. As previously mentioned, all of this is achieved while
maintairring a high
aspect ratio.
It might be noted that the razor blades intended to be coated by this method
are expeet~eci
to be thinner than the usual razor blade, and sharper, and that the 2:1 and
higher aspect ratios
permitted by the process of this invention, coupled with the enormous strength
of the amorphous
diamond hard carbon coating, puts the blade in a class by itself.
10
CA 02317235 2000-08-30
ATTACHMENT A
RECTANGULAR VACUUM-ARC PLASMA SOURCE
FIELD OF THE INVENTION
This invention relates to vacuum arc evaporation, and more particularly to
filtered cathodic
arc evaporation of a rectangular planar cathode mounted in a rectangular
plasma duct. The
rectangular source may be extended indefinitely in length, thus the invention
has particular utility
for coating or ion implantation on a long or large substrate.
This invention realizes the benefits of a filtered cathodic arc (fully ionized
vapor stream,
elimination of splattered droplets) in combination with the benefits of a
rectangular source
(uniform evaporation from the source and uniform deposition on the substrate
using linear motion)
in order to attain uniform coating or implantation on a large substrate with
minimal contamination
of the substrate by droplets of the molten source material.
BACKGROUND OF THE INVENTION
In the last decade or so, vacuum arc evaporation has come into wide commercial
use for
deposition of metal, alloy, and metal compound coatings on a substrate to be
coated. Vacuum arc
discharges have also been used as ion sources for such applications as ion
implantation, beam
accelerators, and rocket propulsion.
The process of vacuum arc evaporation for coating or implanting a substrate
includes a
cathode target composed of the material to be deposited, and a substrate which
is to be coated.
The target is vaporized by a high current, low voltage arc plasma discharge in
a vacuum chamber
which has been evacuated to a pressure of typically less than 0.001 mbar. The
substrates to be
coated or implanted are usually placed in the vacuum chamber facing the
evaporable surface of the
target, at a distance of typically 10-100 cm. Typical arc currents range
between 25 and 1000
amperes, with voltages between 15 and 50 volts.
The arc plasma discharge conducts electric current between a cathode and an
anode
through the plasma created by vaporization and ionization of the target
material by the arc. The
cathode (negative electrode) is an electrically isolated source structure
which is at least partially
consumed during the process. The consumable portion of the cathode is called
the "target" and
is of men fabricated as a replaceable element clamped to a cooled, non-
consumable element cal led
the cathode body. The anode (positive electrode) may be an electrically
isolated structure within
the vacuum chamber or may be the vacuum chamber itself, and is not consumed in
the process.
CA 02317235 2000-08-30
ATTACHMENT A
An arc is ignited on the evaporable surface of the cathode target, commonly by
means of
mechanical contact, high voltage spark, or laser irradiation. The ensuing arc
plasma discharge is
highly localized in one or more mobile arc spots on the cathode target
surface, but is distributed
over a large area at the anode. The extremely high current density in the arc
spot at the cathode,
estimated to be 1 O6-10g amperes/cmz, results in local heating, evaporation,
and ionization of the
cathode source material.
Each arc spot emits a jet of plasma in a direction approximately perpendicular
to the
cathode target surface, forming a luminous plume extending into the region
between the cathode
and anode. The substrate to be coated or implanted is placed between or
adjacent to the cathode
and anode. The vapor of cathode material is typically further accelerated
toward the substrate
surface by an applied voltage, and condenses onto or becomes imbedded into the
surface of the
substrate. Reactive gasses may be introduced into the vacuum chamber during
the evaporation
process, resulting in the formation of material compounds involving the target
material, reactive
gas, and/or the substrate material.
I 5 Below about 70-100 amperes of arc current, depending on the target
material, only a single
arc spot exists on the surface of the cathode source material. At higher arc
currents, multiple arc
spots can exist simultaneously on the target surface, each carrying an equal
fraction of the total
arc current. An arc spot, in the absence of applied magnetic fields, tends to
move randomly around
the target surface, leaving a trail of microscopic crater-like features on the
target surface.
An externally applied magnetic field exerts a force on the arc jet in a
direction
perpendicular to both the field lines and the jet, and can have a dominant
influence on the
large-scale average movement of the arc spot although the small-scale motion
of the arc remains
semi-random. The direction of the motion of the arc spot in a magnetic field
is opposite or
"retrograde" to the vector JxB direction expected based on ampere's law,
considering the electron
current emitted from the cathode. This phenomenon is due to complex dynamic
effects within the
arc jet, and has been widely reported and discussed. _
An undesirable side effect of the vaporization of the target material at the
arc spot is the
generation of droplets of molten target material, which are ejected from the
target by reaction
forces due to expansion of the vapor jet. These droplets are commonly called
macroparticles, and
12
CA 02317235 2000-08-30
ATTACHMENT A
range in diameter from sub-micron to tens of microns. The macroparticles can
become imbedded
in the coating when they land on the substrate to be coated, forming
objectionable irregularities,
or the macroparticles can stick to the substrate and later fall off, causing
pits in the coating.
Various strategies have been devised to reduce the number of macroparticles
incorporated
into the coating on the substrate. These strategies fall generally into two
categories: ( 1 ) a first
category using some form of magnetic field to control and accelerate the arc,
thus reducing
macroparticle generation, and (2) a second category using a filtering
apparatus between the
cathode source and the substrate so as to transmit the ionized fraction of the
cathode output to
the substrate, but to block the molten droplets.
The magnetic methods of the first category are generally simpler than the
filtering methods,
but do not completely eliminate macroparticle generation. The filtering
methods of the second
category are generally more effective at removing macroparticles than the
magnetic methods, but
require complex apparatus and reduce the source output significantly.
Filtering methods work by placing the substrate out of the line of sight of
the cathode
1 S target surface, so that macroparticles emitted from the cathode do not
impinge directly on the
substrate. An angled filtering duct is interposed between the cathode and the
substrate to transport
the plasma to the substrate.
In order to reach the substrate, the charged plasma emitted from the cathode
source is
deflected electromagnetically within the filtering duct through an angle of 45-
180° so as to pass
through the bend in the filtering duct and to impinge on the substrate. The
uncharged
macroparticles are not deflected by the electromagnetic field and continue in
a course which hits
the walls of the filtering duct so that ideally the macroparticles do not
reach the substrate. In
practice, however, bouncing of macroparticles off the filter walls and/or
entrainment of small
particles in the plasma can result in transmission of some macroparticles
through the filter to reach
the substrate.
Prior filtered cathodic arcs have been based upon circular or cylindrical
cathode and filter
geometry, generally limiting potential applications to small substrates or
special shapes.
Examples of the early work done in the field of arc evaporation are described
in several
United States patents, including United States Patent No. 484,582 of Edison
which describes the
use of vacuum arc evaporation for depositing a coating onto a substrate;
United States Patent No.
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ATTACHMENT A
2,972,695 of Wroe which describes a magnetically stabilized vacuum arc
evaporation apparatus;
United States Patent Nos. 3,625,848 and 3,836,451 of Snaper which describe arc
evaporation
apparatus with particular electrode configurations, and the use of a magnetic
field to increase the
evaporation rate and to direct ions to the substrate; and United States Patent
Nos. 3,783,231 and
3,793,179 of Sablev, et al. which describe particular configurations of
electrodes and shields, and
describe use of a magnetic field activated whenever the arc spot moves off the
desired evaporation
surface of the cathode source material.
Examples of cathodic arcs confined within a circular or racetrack path upon
the cathode
are illustrated by United States Patent Nos. 4,724,058 of Morrison; 4,673,477
of Ramalingam, et
al.; and 4,849,088 of Veltrop, et al. Each of the foregoing references
describe an arc evaporation
apparatus using an arched magnetic field in the shape of a closed loop tunnel,
which confines the
arc spot to a closed loop racetrack trajectory at a fixed or movable location
on the cathode
surface. Confinement and acceleration of the arc by the magnetic field is said
to reduce generation
of macroparticles by the arc discharge. The means required to generate such a
magnetic field are
widely known in the art of planar magnetron sputtering. It is also known, for
example, to move
the electro-magnetic field generating means of the arc, either mechanically as
taught by
Ramalingam, et al. and by Veltrop, et al., or by use of multiple
electromagnets as taught by
Morrison.
Examples of elongated, cylindrical cathodes are included in United States
Patent Nos.
4,609,564 and 4,859,489 of Pinkhasov; 5,037,522 of Vergason; and 5,269,898 of
Welty, all of
which describe the use of an elongated cathode in the form of a cylinder or
rod, and make use of
the self magnetic field of the arc current to force its motion along the
length of the cathode. Welty
teaches that macroparticle generation can be reduced by application of an
additional axial magnetic
field component to accelerate and control the arc motion.
United States Patent No. 4,492,845 of Kljuchko, al. describes an arc
evaporation apparatus
using an annular cathode, and in which the evaporable cathode surface is its
outer wall, facing a
cylindrical anode of larger diameter and greater length than the cathode. The
substrates to be
coated are disposed inside the annular cathode, not facing the evaporable
surface, and are coated
by ionized material reflected back by the electromagnetic field at the anode.
A coaxial magnetic
field is described for enhancing the reflection from the anode. Macroparticles
ejected from the
14
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ATTACHMENT A
cathode
surface are not reflected electrically by the anode (although they may bounce
off it mechanically).
As a result, macroparticle incorporation in the coating is reduced.
Examples of efforts to reduce the number of macroparticles incorporated into
the coating
on the substrate by using some form of a filtering apparatus between the
cathode source and the
substrate to transmit the charged ionized fraction of the cathode output and
to block the
uncharged macroparticles are shown in work done by Aksenov/Axenov, Falabella
and Sanders.
A publication by Aksenov, et al. ("Transport of plasma streams in a
curvilinear
plasma-optics system", Soviet Journal of Plasma Physics, 4(4), 1978) describes
the use of a
cylindrical plasma duct containing a 90 degree bend, with electromagnet coils
to create a
solenoidal magnetic field through the duct, and with a circular arc
evaporation cathode at one end
of the duct and a substrate at the other end. The plasma emitted by the
cathode is reflected from
the duct walls by the magnetic and electric fields present, and transported
along the magnetic field
through the duct to the substrate, while the uncharged macroparticles are not
deflected by the
magnetic or electrostatic fields and are intercepted by the duct walls.
United States Patent No. 5,279,723 of Falabella et al. describes an apparatus
essentially
similar to the original Aksenov filter, using a cylindrical duct with a 45
degree bend, a circular or
conical cathode and anode, and including improvements to various components
including the
shape of the cathode and the internal baffles which reduce macroparticle
transmission.
United States Patent No. 4,452,686 of Axenov et al. describes a straight
cylindrical
filtering duct with no bend, a circular cathode located at one end of the
duct, electromagnet coils
to generate a solenoidal magnetic field through the duct, and with an
additional electrode located
in the center of the duct which blocks direct line of sight deposition from
the cathode to the
substrate. Plasma emitted by the cathode is deflected by the magnetic and
electric fields at the duct
wall and central electrode, and transported along the magnetic field through
the duct and around
the central electrode. The uncharged macroparticles are not deflected by the
magnetic or electric
fields and are intercepted by the central electrode.
United States Patent No. 5,282,944 of Sanders, et al. describes a device
somewhat similar
to that of United States Patent No. 4,452,686 of Axenov, using a straight
cyclindrical filtering duct
and a central shield which prevents macroparticles emitted at low angles from
the cathode from
CA 02317235 2000-08-30
ATTACHMENT A
reaching the substrate directly. Electromagnet coils generate a magnetic field
within the duct which
is substantially solenoidal near the duct wall. The evaporable surface of the
cathode in this case
is the outer surface of a short cylinder oriented coaxially with the filter
duct, such that the plasma
emitted from the cathode is directed radially at the outer wall of the filter
duct and is deflected
through approximately 90 degrees by the magnetic field and the electric field
at the duct walls, and
transported along the magnetic field to the end of the duct at which the
substrate is located.
Internal electrodes are disclosed to enhance deflection of the plasma at the
end of the circular
filtering duct opposite to the end at which the substrate is located.
None of the references of the prior art disclose a cathode having an
evaporable surface of
rectangular shape and using magnetic field polarity reversal to control the
movement of the arc
on the cathode surface, nor is a filtering duct having rectangular cross
section disclosed.
Accordingly, despite the work illustrated above, there is still a need for an
improved filtered
cathodic arc. Preferably, the filtered cathodic arc would include a
rectangular deposition source.
Rectangular deposition sources are desirable for the coating of large
substrates, coating
of sheet material in roll form, and for coating of continuous streams of
smaller substrates on a
linear conveyor or circular carousel. Development of rectangular planar
magnetron sputtering
cathodes in the 1970's has led to widespread commercialization of sputtering
for the coating of
substrates in such configurations (see, for example the magnetron sputtering
cathode of Welty,
United States Patent Nos. 4,865,708 and 4,892,633).
Filtered cathodic arc sources have the advantage that the stream of vapor of
cathode
material emitted from the source is fully ionized, unlike non-arc-based
deposition methods such
as evaporation and sputtering. The fully ionized vapor stream from a
rectangular source would
allow greater control over the energy of the atoms arriving at the substrate
for coating or
implantation, and would increase the reactivity of the vapor in forming
compounds with reactive
gases in the system, or with the substrate directly.
The present invention realizes the benefits of a filtered cathodic arc (fully
ionized vapor
stream, elimination of splattered droplets) and the benefits of a rectangular
source (uniform
evaporation from the source and uniform deposition on the substrate using
linear motion) in order
to coat or implant a long or large substrate. It is a goal of the present
invention, therefore, to
provide a filtered cathodic arc on a rectangular vacuum-arc cathode to
accomplish the tasks that
16
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ATTACHMENT A
cannot be accomplished by the prior art.
SUMMARY OF THE INVENTION
The present invention provides means to generate and direct a plasma beam over
a
rectangular area, for the purpose of forming a coating or performing ion
implantation on a
substrate. A rectangular cathode is mounted in an angled duct of rectangular
cross section, which
confines the plasma and deflects it toward the substrate region while
intercepting the molten
droplets of cathode material also generated by the arc. The region of the
plasma duct in which the
cathode is mounted is referred to herein as the entrance arm of the duct,
while the substrate is
mounted adjacent to the exit arm of the duct.
A magnetic field is created within the duct which directs the plasma through
the duct while
simultaneously causing the arc to move in one direction down the length of the
rectangular
cathode. When the arc reaches the end of the cathode, a sensor provides a
signal upon which the
polarity of at least a portion of the magnetic field is reversed, causing the
arc to reverse direction
and move toward the opposite end of the cathode. The polarity of the magnetic
field is switched
whenever the arc reaches either end of the cathode, thus scanning the arc back
and forth along the
length of the rectangular cathode.
Although the polarity (direction) of the magnetic field is reversed
repetitively, the shape
of the magnetic field and its orientation with respect to the duct
preferentially remain substantially
the same, and plasma is transmitted through the duct in either polarity. In a
preferred embodiment
of the invention, a region of converging magnetic field lines adjacent to the
cathode forms a
magnetic mirror which reflects plasma toward the exit of the duct.
The movement of the arc along the length of the cathode target is due to the
component
of the magnetic field adjacent to the target surface which is parallel to the
plane of the target
surface and perpendicular to the long axis of the rectangular target. For
magnetic flux components
in this orientation, two polarities (directions) are possible. When the field
has one polarity the arc
moves along the length of the cathode in the direction given by the retrograde
JxB vector as
described above. When the field has the opposite polarity, the arc moves along
the length of the
cathode in the opposite direction.
By reversing the polarity of the magnetic field based on signals from the
sensors located
at the ends of the cathode, while maintaining the orientation of the flux
lines with respect to the
17
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ATTACHMENT A
target surface, the direction of the movement of the arc along the length of
the cathode can be
reversed periodically, causing the arc to scan back and forth along the length
of the rectangular
cathode along a relatively straight line.
The reversible magnetic field adj acent to the evaporable surface of the
target, which causes
the arc to move along the length of the target, may be generated using
electromagnet coils located
outside the duct or within the cathode body. It is known in the prior art to
generate a reversible
field using the self magnetic field of the arc current flowing through the
rectangular cathode. For
example, connecting the arc current simultaneously to both ends of the
rectangular cathode and
varying the fraction of the total current which flows to each end of the
cathode, based on the
signals from the sensors located at the ends of the cathodes, will generate a
magnetic field
component in the orientation required to cause the arc to move along the
length of the cathode,
as described in United States Patent No. 5,269,898 of Welty.
As the direction in which the majority of the arc current flows within the
rectangular
cathode is reversed based on signals from the sensors, the polarity
(direction) of the magnetic field
component parallel to the target surface also reverses, thus reversing the
direction of arc travel
along the length of the target. Likewise, as also described in United States
Patent No. 5,269,898,
the magnetic field component which causes the arc scanning may also be
generated by passing a
control current along the length of the cathode and reversing its direction
based on the sensor
signals, or by switching the arc current input from one end of the cathode to
the other as described
in United States Patent No. 5,037,522 of Vergason. No suggestion has been made
in the prior art
to generate the reversible magnetic field using magnetic means independent of
currents flowing
through the cathode itself.
Transport of the plasma through the duct is due primarily to the component of
the
magnetic field adjacent to the duct walls which is parallel to the plane of
the walls and parallel to
the axis of the duct. Diffusion of the electrons of the plasma through the
magnetic field toward the
duct walls creates an electric field component perpendicular to the duct wall
which reflects the
positively charged ions, thus allowing them to continue travel along the duct
and around the bend
in the duct. The uncharged macroparticles are not reflected and are therefore
intercepted by the
duct walls, or by baffles which may be mounted perpendicular to the duct wall
and extending a
short distance into the duct to reduce bouncing of the macroparticles off the
duct walls. The
18
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ATTACHMENT A
polarity of the magnetic field components within the duct and adjacent to the
duct walls is
preferentially switched simultaneously with the polarity of the field
component adjacent to the
target surface which causes the arc scanning, such that the shape of the
magnetic field throughout
the duct remains the same despite the reversals in polarity. It is also within
the scope of the present
invention, however, to reverse the polarity of the field only in the region of
the target surface while
maintaining a static (non-reversing) magnetic field in the rest of the duct
using electromagnets or
permanent magnets. Variations in the net shape of the magnetic field in this
latter case may cause
periodic variations in transmission of plasma through the duct as a function
of the reversal of the
field near the target surface.
Since the plasma jet is emitted from the cathode primarily in the direction
perpendicular
to the evaporable surface, it tends to impinge on the duct wall most strongly
in the region of the
outer radius of the bend in the duct. In order to increase the transmission of
plasma through the
duct it is desirable to intensify the strength of the magnetic field in this
region. An additional factor
is that cathode target materials of differing atomic weight and melting point
are emitted from the
target with different velocities and kinetic energies. It is therefore
desirable to vary the strength
of the magnetic field, particularly in the region of the bend in the duct, to
optimize the transmission
for various materials. Accordingly, in a preferred embodiment of the present
invention a separate
electromagnet coil is provided in the vicinity of the outer radius of the bend
in the duct, opposite
the evaporable surface of the target, in which the current may preferably be
varied independent of
the current in the other coils generating portions of the magnetic field in
the duct.
It should be noted that in the prior art of cylindrical plasma ducts (or in
the straightforward
way that the prior arm might have been extended to a rectangular duct), in
which one or more
electromagnet coils are disposed encircling the duct in order to create a
solenoidal magnetic field
through the duct, the wires comprising the coils) must necessarily be spaced
more closely
together at the inside radius of the bend in the duct than at the outside
radius. This results in the
magnetic field inside the duct having greater strength towards the inner
radius of the duct where
the wires are spaced more closely, and lower strength towards the outer radius
of the duct where
the arc plasma jet impinges. The prior art therefore teaches away from this
aspect of the present
invention, in which the magnetic field strength inside the duct at the outer
radius of the bend can
be strengthened to equal or exceed the field strength at the inner radius, in
order to increase the
19
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ATTACHMENT A
transmission of plasma through the duct.
The electric field perpendicular to the duct wall, which reflects the
positively charged ions
from the duct wall in the prior art and in the aspects of the present
invention described above, is
created by diffusion of the plasma electrons transversely through a magnetic
field substantially
S parallel to the filter duct walls. It is also possible to reflect ions away
from duct wall by a second
method, namely by creating near the wall a region in which the magnetic flux
lines converge as
they approach the wall in an approximately perpendicular direction, creating a
region known as
a magnetic mirror. Plasma electrons approaching the wall are reflected or
retarded as they enter
the region of converging flux lines, creating an electron density gradient
resulting in an electric
field which reflects the plasma ions as well. Magnetic mirrors are commonly
used for plasma
confinement in laboratory apparatus and other plasma devices.
The utility of a magnetic mirror field is disclosed in the present invention
for the first time
in the art of filtered vacuum-arc plasma sources. The need for the function
provided by the mirror
field is illustrated, for example, in the prior art illustrated by United
States Patent No. 5,282,944
of Sanders, et al. in which a number of insulating rings, labelled 21 in FIGS.
2 and 3 thereof, are
pointed out as necessary to prevent plasma loss to the duct walls in the areas
where the magnetic
field passes through the duct wall. The inclusion of a magnetic mirror field
region in the entrance
arm of a preferred embodiment of the present invention creates a preferred
direction for plasma
flow toward the exit arm of the duct, while simultaneously providing the
magnetic field component
(parallel to the surface of the target and perpendicular to its long axis)
which causes the arc to
move down the length of the target. Reversal of the polarity of the magnetic
mirror field, and thus
the field component parallel to the target surface, causes the direction of
travel of the arc on the
target surface to reverse without changing the shape or function of the mirror
field.
The combination and superposition of independently variable magnetic field
sources
providing a solenoidal magnetic field region in the exit arm of the plasma
duct, a "bumper" field
region near the outer radius of the bend in the duct, and a magnetic mirror
field region in the
entrance arm of the duct adjacent to the cathode provide sufficient
adjustability to allow
optimization of plasma transport through the duct for a wide variety of target
materials. It is to
be understood, however, that not all of these elements need be present in an
embodiment of the
present invention, and that the elements present need not be independently
variable, particularly
CA 02317235 2000-08-30
ATTACHMENT A
in the case of a source which is optimized for a single target material. For
example, depending on
the method used for reversing the polarity of the magnetic field region near
the target surface, a
single solenoidal electromagnet surrounding the entire duct may be sufficient.
The present invention differs from the prior art in the rectangular shape of
the cathode and
plasma duct, in the method of control of arc movement on the cathode, and in
the shape and
control of the magnetic field in the plasma duct.
In particular, the disclosed magnetic field shape and control methods make it
possible to
construct a compact, efficient plasma source with a rectangular output
aperture which can be made
as long as desired, thus providing the benefits of a filtered cathodic arc in
combination with the
benefits of a rectangular deposition source. The field reversal technique for
arc control on the
cathode surface allows the width of the cathode to be made much smaller than
is possible using
the race-track-style magnetic field of the prior art.
The plasma duct can therefore be made much narrower and shorter, resulting in
a compact
design which is easier to integrate into a vacuum system than the bulky
filters of the prior art,
particularly in systems containing multiple plasma sources. The narrow cathode
and scanned arc
also permit more uniform erosion of the target along its length and higher
target material
utilization than is possible with planar racetrack-style cathodes.
The advantages of the present invention permit the source to be extended
indefinitely in
length, thus providing the benefits of filtered arc deposition or implantation
to applications
requiring rectangular or extended vapour sources.
DESCRIPTION OF THE DRAWINGS
FIG. 1 A is a schematic illustration of a prior art filtered vacuum arc using
a circular
cathode and a cylindrical plasma duct.
FIG. 2A is a schematic view of the filtered arc plasma source of the present
invention.
FIG. 3A is a perspective view of the duct assembly and magnets of the present
invention.
FIG. 4A is an end elevational cross section of the duct assembly of the
present invention.
FIG. SA is a side elevational cross section of the duct assembly of the
present invention.
FIG. 6A is an end cut-away view showing the magnetic field lines and magnetic
field
mirror of the present invention in relation to the duct assembly and magnet
sets thereof.
21
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ATTACHMENT A
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention provides a way to generate and direct a plasma beam over
a
rectangular area for the purpose of forming a coating or performing ion
implantation on a
substrate.
FIG. 1 A shows a prior art cathode 20 coupled to a filter 22 capable of
separation of
macroparticles from an ion flux produced by cathodic arc discharge. The
cathode 20 is
frustrum-shaped, having a circular face and tapered sides. The filter 22
includes two solenoids, end
to end, but placed at a 45 ° angle to one another for preventing line
of sight from an arc spot on
the cathode to a substrate 24 to be coated while providing a path for the ions
and electrons to
flow, and it includes a series of baffles for trapping the macroparticles.
With reference to the schematic view of FIG. 2A, one preferred embodiment of
this
invention can be understood to include a cathode target 30 on cathode body 31.
Target 30 has an
evaporable surface 33 of substantially rectangular shape. In a preferred
embodiment, the cathode
30 is carbon, but it may be composed of any suitable evaporable material. The
cathode body 31
is mounted on a holder 32 and situated in entrance arm 36 of plasma duct 34.
Cathode 30 is
connected to the negative output of an arc power supply 28, and plasma duct 34
(which also
serves as an anode) is connected to the positive output of the arc power
supply. An arc striker 35
is provided for igniting an arc discharge between cathode 30 and anode 34.
Cathode 30 and
evaporable surface 33 may also be surrounded by insulators 86 (reference FIG.
4A). With
continued reference to FIG. 4A, it may be seen that an internal electrode 82
is mounted within the
plasma duct 34, as is sensor 84.
Plasma duct 34 has a rectangular cross-sectional shape of similar dimensions
to cathode
30. The plasma duct includes a bend in the axis along the centerline of the
plasma duct. In the
embodiment shown here, an equivalent inner radius bend point 37 is shown on
one of the walls
of the duct and is approximately 90 °, but an inner radius angle in the
range of approximately 15 °
to 120° is suitable for the practice of this invention. An equivalent
outer radius bend-is indicated
generally at reference numeral 39. The plasma duct 34 has an entrance arm 36
and an exit arm 38
on either side of inner radius bend point 37. The cathode 30 is mounted on an
isolated holder 32
at or near the end of the entrance arm so that the evaporable surface 33 of
the cathode faces into
the plasma duct. One or more substrates 44 to be coated may be located in an
area at or near the
22
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ATTACHMENT A
end of exit arm 38.
A set of electromagnets is disposed about plasma duct 34. Magnet 46 is
connected to coil
power supply 52 and is located near the entrance arm 36 of the plasma duct.
Magnet 48 is
connected to coil power supply 52 and is located near the outer radius 39 of
the bend in plasma
duct 34. Magnet 50 is a solenoid connected to coil power supply 52 and it
wraps around a portion
of the exit arm 38 of the plasma duct. The perspective view of FIG. 3A shows
magnets 46, 48 and
50 in relation to the plasma duct 34, with magnet 46 near the entrance arm 38,
magnet 48 near the
outer radius 39 of the bend, and magnet 50 coiled around the exit arm 38.
With reference to FIG. 4A, it may be understood that magnet 46 includes a coil
70
wrapped around a central pole 72 of magnetically permeable material, with end
plates 74 attached
to each end of the central pole. Likewise, magnet 48 includes a coil 76
wrapped around a central
pole 78 of magnetically permeable material, with end plates 80 attached to
each end of the central
pole. In the embodiment shown, end plates 80 of magnet 48 are made of
magnetically permeable
material, while the end plates 74 of magnet 46 are made of nonpermeable
material, in order to
1 S shape the magnetic field in the desired manner.
Again with reference to FIG. 2A, it may be seen that conduit 54 feeds water to
the cathode
30. Plasma duct 34 and internal electrode 82 may also preferably be water
cooled, but provisions
for such cooling are not shown. A bias voltage may be applied to the substrate
44, and the
substrate may be conventionally rotated and/or translated during deposition.
In a preferred
embodiment, the plasma duct 34 and substrate 44 are enclosed within a chamber
(not shown) and
a vacuum is drawn. In another preferred embodiment of the invention, the
plasma duct 34 and
cathode holder 32 of the duct are in vacuum, while the outside of the duct is
at atmospheric
pressure.
Proceeding to the cross sectional views of FIGS. 4 and 5, which are numbered
with the
same reference numerals previously used, certain additional details ofthe
system ofthis invention
may now be understood. It may be seen that the bend in the plasma duct 34
serves to prevent a
line-of sight between the cathode 30 and the substrate 44 (not shown in FIGS.
4 or S, but
understood to be located at or near the end of the exit arm 38 of the duct).
The inside walls of the
exit arm 38, the entrance arm 36 and the bend of the plasma duct 34 are
preferentially lined with
a number of spaced apart baffles 52 which are substantially perpendicular to
the inside walls and
23
CA 02317235 2000-08-30
ATTACHMENT A
substantially parallel to one another.
With reference to FIG. 4A, an electrically isolated internal electrode 82 may
be seen
mounted inside the plasma duct 34. It may be electrically floating with
respect to the anode, or it
may be biased positively with respect to the anode. With reference to FIG. SA,
a pair.of sensors
54 are located adjacent to each end of the evaporable surface of cathode 30,
with 54A adjacent
the left end and 54B adjacent the right end.
The magnets 46, 48 and 50 generate a magnetic field represented by magnetic
flux lines
that may be better understood with reference to FIG. 6A. Magnetic flux lines
60 are oriented in
a direction substantially parallel to the axis of plasma duct 34 within exit
arm 38. Magnetic flux
lines 62 are oriented in a direction substantially parallel to the evaporable
surface 33 (not shown
in FIG. 6A, but understood with reference to FIGS. 2, 4 and S) of cathode 30
within the region
of the entrance arm 36 near the cathode. Magnetic flux lines converge at a
region 64 within the
entrance arm 36, forming a magnetic mirror adjacent to the evaporable surface
33 (not shown in
FIG. 6A, but understood with reference to FIGS. 2, 4 and 5) of cathode 30.
The representation of magnetic flux lines 60 shown in FIG. 6A was generated by
a
commercially available finite element magnetic analysis program. In the
particular case shown,
magnets 50 and 46 have 600 amp-turns, while magnet 48 has 200 amp-turns. In
this case, the field
strength in the center of the exit arm 38 of the duct is approximately 50
gauss. It can be seen in
this case that the flux density (field strength) at the outer radius 39 of the
bend in the duct is
approximately equal to the flux density at the inner radius 3 7 of the bend.
By adj usting the number
of turns in coil 76 of magnet 48, or the current flowing through it (i.e.,
adjusting the amp-turns),
the flux density at the outer radius 39 of the bend may be adjusted
independently of the flux
density elsewhere in the duct.
The sensors 54A and 54B (reference FIG. SA) are able to sense an arc spot and
to produce
a signal whenever the arc spot approaches either the left or right end,
respectively, of the cathode
30. Sensors 54 may, for example, consist of electrically isolated wires
extending into the plasma
duct 34, with the wires connected to the anode through a resistor (not shown)
of, say, 1000 ohms,
thus providing an electrical voltage whenever the arc approaches the wire.
Alternatively, sensors
54 may comprise a light-sensitive diode which detects the optical emission
from the arc jet, or a
magnetic field detector which senses the magnetic field of the arc. The coil
power supply 52
24
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ATTACHMENT A
(reference FIG. 2A) has a switch 53 capable of reversing the direction of
current flow through the
magnets, and it is connected by conventional control means (not shown) to the
sensors 54 so as
to actuate a magnetic field reversal. The magnetic field reversal can occur
simultaneously in all of
the magnets and will reverse the direction ofthe magnetic flux lines without
substantially changing
the shape of the flux lines or their orientation with respect to the plasma
duct. Alternatively, only
one or both of magnets 46 and magnet 48 may be reversed.
In a desirable configuration of the system of this invention (not separately
shown), the
magnets are powered independently by more than one coil power supply 52. The
use of more than
one coil power supply permits the current of the magnets to be varied
independently of one
another for adjusting the magnetic field strength independently in different
parts of plasma duct
34. At the same time, the separate coil power supplies are each provided with
control systems so
that they all reverse the direction of current simultaneously upon actuation
by a signal from sensors
54.
From the foregoing description, it may be readily understood that the system
of this
I S invention operates as follows.
Arc starter 35 ignites an arc discharge between cathode 30 and the plasma duct
34 which
serves as the anode. The arc discharge originates in an arc spot on the
evaporable surface of the
cathode and generates a plasma containing an ionized vapour of the cathode
material.
Plasma duct 34 directs the plasma generated by the arc discharge from the
cathode to a
substrate 44 to be coated and/or implanted and which is located at or near the
exit arm 38 of the
duct. The plasma duct 34 has a rectangular cross-sectional shape of similar
dimensions to the
cathode 30, and has a bend of approximately 15-180 degrees in the axis along
its centerline (in the
embodiment illustrated, the inner radius 37 of the bend is 90 degrees), with
the entrance arm 36
and exit arm 38 separated from line-of sight of one another by the bend. The
cathode 30 is located
at or near the end of entrance arm 36 with its evaporable surface facing into
the plasma duct, and
the substrate 44 is located in an area at or near the end of exit arm 38.
The magnets 46, 48 and 50 generate within the plasma duct 34 and over the
evaporable
surface of cathode 30 a magnetic field, which is represented by magnetic flux
lines. Magnetic flux
lines are oriented in a direction substantially parallel to the axis of duct
34 within exit arm 38.
Magnetic flux lines are oriented substantially parallel to the evaporable
surface of cathode 30
CA 02317235 2000-08-30
ATTACHMENT A
within the region of entrance arm 36 at or near the cathode. Magnetic flux
lines also converge in
a region within entrance arm 36 ofplasma duct 34, forming a magnetic mirror
adjacent and parallel
to the rectangular cathode 30. The magnetic flux lines direct the ionized
vapor through the bend
in the plasma duct and urge the arc spot into a generally linear motion along
the length of the
evaporable surface 33 of the cathode 30. The magnetic minor is oriented in a
direction which
reflects plasma towards the exit arm 38 of plasma duct 34.
The sensors 54 sense the arc spot, and produce a signal whenever the arc spot
approaches
either end of said evaporable surface. The signal from the sensors actuates a
control system which
reverses the current in the coil power supply 52, thereby reversing the
direction of the magnetic
flux lines without substantially changing the shape of the flux lines or their
orientation with respect
to plasma duct 34. Thus, the arc spot is urged, not only to scan in a linear
direction over the
surface of the rectangular cathode 30, but to scan back and forth in a
generally end to end path.
The inside walls of the plasma duct 34 are lined with baffles 52.
Macroparticles are filtered
by the bend in the duct, and the baffles serve to trap the macroparticles.
I 5 The system of this invention includes a long and narrow rectangular source
and a relatively
compact duct having a rectangular cross section of dimensions similar to the
source. A compact
duct is thereby created. For example, good results have been obtained using a
cathode target
approximately 30 centimeters long by 2.5 centimeters wide, or a ratio between
the length and the
width of about twelve to one. Because the rectangular cathode of this
invention may be extended
indefinitely, it is expected that even higher ratios are attainable.
Accordingly, it can be understood that this invention provides a way to
generate and direct
a plasma beam over a rectangular area, for the purpose of forming a coating or
performing ion
implantation on a substrate.
As has been explained, the benefits of the present invention are realized by:
(a) the
rectangular shape of the cathode source material, (b) the rectangular cross
sectional shape of the
plasma duct, (c) the control of the arc movement on the cathode by reversing
polarity of the
magnetic field to cause the arc to scan generally in a linear direction back
and forth across the
length of the rectangular source, and (d) the shape and control of the
magnetic field in the plasma
duct.
In particular, the magnetic field shape and control of the arc upon the
rectangular source
26
CA 02317235 2000-08-30
ATTACHMENT A
of the present invention make it possible to construct a compact, efficient
plasma source with a
rectangular output aperture which can be made as long as desired, thus
providing the benefits of
a filtered cathodic arc in combination with the benefits of a rectangular
deposition source. The
field reversal technique for arc control allows the width of the cathode
source to be made much
smaller than is possible using the racetrack-style magnetic field of the prior
art.
The plasma filtering duct can therefore be made much narrower and shorter,
resulting in
a compact design which is easier to integrate into a vacuum system than the
bulky filters of the
prior art. The narrow cathode and narrow linearly scanning arc also permit
more uniform erosion
of the target along its length and results in higher source material
utilization than is possible with
planar racetrack-style cathodes.
The advantages of the present invention permit the source to be extended
indefinitely in
length, thus providing the benefits of filtered arc deposition or implantation
to applications
requiring rectangular or extended vapor sources.
27
