Note: Descriptions are shown in the official language in which they were submitted.
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Hard Material Layer
The invention relates to a hard material layer deposited as oxidic arc PVD
functional
layer (32) on a workpiece (30) as well as to a method for coating a workpiece
with a
hard material layer.
The operation of arc vaporizer sources, also known as spark cathodes, by
feeding
with electrical pulses has been known in prior art for a relatively long time.
With arc
vaporizer sources high vaporization rates, and therewith high deposition
rates, can be
achieved economically in coating. In addition, the structure of such a source
can
technically be realized relatively simply. These sources operate at currents
typically
in the range of approximately 100 A and more and at voltages of a few volts to
a few
tens of volts, which can be realized with relatively cost-effective DC power
supplies.
A significant disadvantage with these sources comprises that in the proximity
of the
cathode spot very rapidly proceeding melting occurs on the target surface,
whereby
drops are formed, so-called droplets, which are hurled away as splatters and
subsequently condense on the workpiece and consequently have an undesirable
effect on the layer properties. For example, thereby the layer structure
becomes
inhomogeneous and the surface roughness becomes inferior. With high
requirements made of the layer quality, layers generated thusly, can often not
be
commercially applied. Attempts have therefore already been made to reduce
these
problems by operating the arc vaporizer source in pure pulse operation of the
power
supply. However, until now only marginal improvements in the splatter
formation
could be achieved therewith.
The use of reactive gases for the deposition of compounds from a metallic
target in a
reactive plasma was until now limited to the production only of electrically
conductive
layers. In the production of electrically nonconducting, thus dielectric
layers, such
as for
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CA 02601722 2007-09-17
example of oxides using oxygen as the reactive gas, the problem of splatter
formation is
intensified. The re-coating of the target surfaces of the arc vaporizer and of
the
counterelectrodes, such as the anodes and also other parts of the vacuum
process
installation, with a non-conducting layer leads to entirely unstable
conditions and even
to the quenching of the arc. In this case the latter would have to be
repeatedly newly
ignited or it would thereby become entirely impossible to conduct the process.
EP 0 666 335 B1 proposes for the deposition of purely metallic materials with
an arc
vaporizer to superimpose onto the DC current a pulsing current in order to be
able to
lower hereby the DC base current for the reduction of the splatter formation.
Pulse
currents up to 5000 A are herein necessary, which are to be generated with
capacitor
discharges at relatively low pulse frequencies in the range of 100 Hz to 50
kHz. This
approach is proposed to prevent the droplet formation in the non-reactive
vaporization
of purely metallic targets with an arc vaporizer source. A solution for the
deposition of
non-conducting dielectric layers is not stated in this document.
In the reactive coating by means of arc vaporizer source there is a lack of
reactivity and
process stability, especially in the production of insulating layers. In
contrast to other
PVD processes (for example sputtering), insulating layers can currently only
be
produced by means of arc vaporization with electrically conducting targets.
Working
with high frequency, such as is the case during sputtering, has so far failed
due to the
lacking technique of being able to operate high-power supplies with high
frequencies.
Working with pulsed power supplies appears to be an option. However, in this
case the
spark, as stated, must be ignited repeatedly or the pulse frequency must be
selected so
large that the spark is not extinguished. This appears to function to some
degree in
applications for special materials, such as graphite, as described in DE
3901401. It
should, however, be noted that graphite is not an insulator, but rather is
electrically
conductive, even if it is a poorer conductor than normal metals.
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In oxidized target surfaces a renewed igniting with mechanical contact and by
means of
DC supplies is not possible. The actual problem in reactive arc vaporization
are the
coatings with insulating layers on the target and the anode, or on the coating
chamber
connected as the anode. In the course of their formation, these insulating
coatings
increase the burn voltage of the spark discharge, lead to increased splatters
and
sparkovers, an unstable process, which ends in an interruption of the spark
discharge.
Entailed therein is a coating of the target with island growth, which
decreases the
conducting surface. A highly diluted reactive gas (for example argon/oxygen
mixture)
can delay the accretion on the target, however it cannot solve the fundamental
problem
of process instability. While the proposal according to US 5,103,766 of
alternately
operating the cathode and the anode with renewed ignition each time results in
process
stability, it does however lead to increased splatters.
The resolution via a pulsed power supply as is possible for example in
reactive
sputtering, cannot be applied in classic spark vaporization. The reason lies
therein that
a glow discharge has a "longer life" than a spark when the power supply is
interrupted.
In order to circumvent the problem of the coating of the target with an
insulating layer, in
reactive processes for the production of insulating layers either the reactive
gas inlet is
locally separated from the target (in that case the reactivity of the process
is only
ensured if the temperature on the substrate also permits an oxidation
reaction) or a
separation between splatters and ionized fraction is carried out (so-called
filtered arc)
and after the filtering the reactive gas is added to the ionized vapor.
There is further the wish for additional reduction or scaling capability of
the thermal
loading of the substrates and the ability to conduct low-temperature processes
in
cathodic spark coating.
In WO 03018862 the pulse operation of plasma sources is described as a
feasible path
for reducing the thermal loading on the substrate. However, the reasons
offered there
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apply to the field of sputter processes. No reference is established to spark
vaporization.
In the application field of hard material coatings there has in particular
been for a long
time the need to be able to produce oxidic hard materials with appropriate
hardness,
adhesive strength and under control according to the desired tribological
properties.
Herein aluminum oxides, in particular aluminum chromoxides, could play an
important role. Prior art in the field of PVD (Physical Vapor Deposition)
deals herein
most often only with the production of gamma and alpha aluminum oxide. The
method most frequently mentioned is dual magnetron sputtering, which in this
application entails great disadvantages with respect to process reliability
and costs.
Japanese patents concentrate more on layer systems in connection with the
tools
and cite, for example, the arc ion plating process as the production method.
There is
the general wish to be able to deposit alpha aluminum oxide. However, in
current
PVD methods, substrate temperatures of approximately 700 C or more are
required
in order to obtain this structure. Some users elegantly attempt to avoid these
high
temperatures through nucleation layers (oxidation of TiAIN, Al-Cr-0 system).
However, this does not necessarily make the process less expensive and faster.
Until now it also did not appear possible to be able to produce satisfactorily
alpha
aluminum oxide layers by means of arc vaporization.
With respect to prior art the following disadvantages are summarized, in
particular
regarding the production of oxidic layers with reactive process:
1. Stable conduction of the process is not possible for the deposition of
insulating
layers, if there is no spatial separation between arc vaporizer cathode or
anode of the
arc discharge and the substrate region with reactive gas inlet.
2. There is no fundamental solution of the problematic of droplets:
conglomerates
(droplets, splatters) are not fully through-reacted, wherein metallic
components occur
in the layer, increased roughness of the layer surface is generated and the
uniformity
of
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CA 02601722 2007-09-17
,
the layer structure and stoichiometry is disturbed.
3. Insufficient possibilities for realizing low-temperature processes,
since
insufficiently the thermal loading of the substrate is too high for the
production of oxides
with high-temperature phases.
4. The production of flat graduated intermediate layers for insulating
layers has so
far not been possible by means of arc vaporization.
In contrast to sputtering, coating by means of cathodic spark is substantially
a
vaporization process. It is supposed that in the transition between hot
cathode spot and
its margin parts are entrained which are not of atomic size. These
conglomerates
impinge as such onto the substrate and result in rough layers, and it has not
been
possible fully to react-through the splatters. Avoidance or fragmentation of
these
splatters was so far not successful, especially not for reactive coating
processes. In
these, on the cathode of the arc vaporizer source, for example in oxygen
atmosphere,
additionally a thin oxide layer forms, which tends to increased splatter
formation.
The present invention addresses the problem of eliminating the listed
disadvantages of
prior art. The problem addressed is in particular to deposit economically
layers with
better properties with at least one arc vaporizer source, such that the
reactivity in the
process is increased through better ionization of the vaporized material, and
of the
reactive gas involved in the process is increased. In this reactive process
the size and
frequency of the splatters is to be significantly reduced, in particular in
reactive
processes for the production of insulating layers. Further, better process
control is to be
made possible, such as the control of the vaporization rates, increase of the
layer
quality, settability of the layer properties, improvement of homogeneity of
the reaction,
as well as the reduction of surface roughness of the deposited layer. These
improvements are in particular also of importance in the production of
graduated layers
and/or alloys. The process stability in reactive processes for the production
of insulating
layers is to be generally increased.
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In particular, an arc vaporization process is to be made possible which
permits the
economic deposition of oxidic hard material layers, aluminum oxide and/or
aluminum
chromoxide layers which preferably have substantially alpha and/or gamma
structure.
Moreover, a low-temperature process should be realized, preferably below 700
C,
also at high economy of process. Furthermore the expenditure for the device
and in
particular for the power supply for pulsed operation should be kept low. Said
tasks
may occur singly as well as also combined with one another, depending on the
particular required application area.
The problem is solved according to the invention through a hard material layer
applied with an arc vaporization PVD method.
The problem is solved according to the invention thereby that a hard material
layer is
deposited as arc PVD functional layer onto a workpiece, this layer
substantially being
formed as an electrically insulating oxide, comprised of at least one of the
metals
(Me) Al, Cr, Fe, Ni, Co, Zr, Mo, Y and the functional layer comprises a
content of inert
gases and/or halogens of less than 2%. The content of inert gases is
preferably less
than 0.1%, in particular less than 0.05% or even better is zero and/or the
content of
halogens is less than 0.5%, in particular less than 0.1%, or even better is
zero.
These gases should be incorporated into the layer to as small an extent as
possible
and the arc vaporization process should therefore exclusively take place with
pure
reactive gas or a pure reactive gas mixture without inert gas component, such
as He,
Ne, Ar, or halogen gases, such as F2, C12, Br2, .12, or halogen-containing
compounds
such as CFsor the like.
The known CVD processes use halogen with which at undesirably high
temperatures
of approximately 1100 C a layer is deposited. Even under reactive process
conditions, the known sputter processes are operated with a high proportion of
inert
gas, such as with argon. The content of such gases in the layer should be
below said
values or preferably be zero. The pulse arc vaporization process according to
the
invention also permits sufficing without such process gases.
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The preceding patent application with the application number CH00518/05 shows
essentially already an approach to a solution. A first solution is specified
which is
especially well suited for completely reacted target surfaces and has a marked
reduction of splatter formation compared to DC-operated arc vaporizer targets.
This
application proposes superimposing a high-current pulse onto the DC feed of an
arc
vaporizer source with a pulsed power supply, as is shown schematically in
Figure 2.
A further reduction of the splatters and their size at higher economy is
attained
through the approach according to the succeeding patent application CH
01289/05
which claims priority of CH 00518/05 and represents a further development. In
this
application a vacuum process installation for the surface working of
workpieces with
at least one arc vaporizer source is provided comprising a first electrode
connected to
a DC power supply, a second electrode disposed separated from the arc
vaporizer
source being provided and that the two electrodes are connected to a single
pulsed
power supply. Between the two electrodes, consequently an additional discharge
gap is operated with only a single pulsed power supply which makes possible an
especially high ionization of the involved materials at very good
controllability of the
process.
The second electrode can herein be a further arc vaporizer source, a workpiece
holder or the workpiece itself, whereby in this case the second electrode can
also be
implemented as a vaporization crucible forming the anode of a low-voltage arc
vaporizer.
According to another aspect of the present invention, there is a provided hard
material layer as arc PVD layer with incompletely reacted conglomerates which
form
the metal parts in the layer deposited on a workpiece made of metal material,
which
is a cutting, forming, injection moulding or punching tool or a machine
component,
wherein this layer is formed as an electrically isolating oxide of at least
one of the
metals (Me)
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from the transition metals Zr, Cr, Mo and Al, Si, Fe, Co, Ni, or Y, wherein
the layer
has a noble gas and a halogen content of less than 2%.
According to still another aspect of the present invention, there is a
provided
workpiece with a hard material layer as defined herein, which is characterised
a tool,
or a machine component.
According to yet another aspect of the present invention, there is provided
method for
coating a workpiece in a vacuum processing plant with a hard material layer
deposited as a function layer which is formed as an electrically isolating
oxide of at
least one of the metals (Me) of the transition metals of the co-sets IV, V, VI
of the
periodic system and Al, Si, Fe, Co, Ni, Co, or Y, and that the layer is
deposited with
an arc vaporisation source which includes a target, the arc vaporisation
source is
operated with a DC power supply over which is laid a pulsed current supply,
wherein
the target of the arc vaporisation source contains one of the metals and the
target is
operated in a oxygen atmosphere in reactive mode so that an electrically non-
conductive oxide is generated and deposited as a layer.
An especially preferred embodiment comprises that both electrodes are the
cathodes of
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one arc vaporizer source each and that each of these arc vaporizer sources by
itself is
connected directly to a DC power supply for the purpose of maintaining a
holding
current and wherein the two cathodes are connected to a single pulsed power
supply
such that the arcs, or the arc discharges, of the two sources are not
extinguished in
operation. In this configuration, consequently, only one pulsed power supply
is required
since this supply is interconnected directly between the two cathodes of the
arc
vaporizers. Apart from the high degree of ionization and the good
controllability of the
process, high efficiency of the configuration also results. Between these two
electrodes
and the pulse discharge gap additionally generated thereby, compared to this
discharge
gap, a bipolar pulse forms electrically from negative and positive components,
whereby
the entire period duration of this fed AC voltage can be utilized for the
process. In fact,
no unused pulse pauses are generated and the negative as well as also the
positive
pulses without interruption contribute overall to the process. The deposition
rate can
thereby be additionally increased without having to employ additional
expensive pulsed
power supplies. This configuration with two arc vaporizer sources is
especially suited
for the deposition of layers from a metallic target utilizing reactive gas.
With this
configuration it becomes even possible to omit entirely supporting inert
gases, such as
argon, and it is possible to work with pure reactive gas, even unexpectedly
with pure
oxygen. Through the high degree of ionization attainable therewith of the
vaporized
material as well as also of the reactive gas, such as for example oxygen,
nonconducting
layers with high quality are generated which nearly reach the quality of the
bulk
material. The process runs very stably and herein the splatter formation is,
unexpectedly, also reduced or entirely avoided. However, said advantages can
also be
attained by using other sources as the second electrode, such as, for example,
a bias
electrode or a low-voltage arc vaporizer crucible, although said advantageous
effects
are not attained to the same degree as in the implementation of the
configuration with
two arc vaporizers.
The present application claims priority of the two cited preceding
applications CH
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00518/05 and 01289/05 which substantially disclose a first approach to a
solution for
the present problem formation of the deposition of electrically nonconducting
oxidic
layers. The invention introduced in the present patent application represents
a further
development regarding the conduction of the process and the application. These
two
applications are consequently an integrating component of the present
application.
In the following the invention will be described in further detail by example
and
schematically with Figures. Therein depict:
Fig. 1 schematically an illustration of an arc vaporizer coating installation,
such as
corresponds to prior art,
Fig. 2 a first configuration according to the invention with a DC-fed arc
vaporizer source
in operation with superimposed high-current pulse,
Fig. 3 a second configuration with two DC-fed arc vaporizer sources and high-
power
pulsed supply connected between them according to the invention, a dual pulse
arc vaporizer configuration,
Fig. 4 a cross section through a deposited layer as a multilayer according to
the
invention,
Fig. 5 an enlarged cross section of the layer according to Figure 4.
Figure 1 shows a vacuum process installation which depicts a configuration
known from
prior art for operating an arc vaporizer source 5 with a DC power supply 13.
The
installation 1 is equipped with a pump system 2 for setting up the required
vacuum in
the chamber of the vacuum process installation 1. The pump system 2 permits
the
operation of the coating installation at pressures < 10-1 mbar and also
ensures the
operation with the typical reactive gases, such as 02, N2, Sil-14,
hydrocarbons, etc. The
reactive gases are introduced via a gas inlet 11 into the chamber 1 and here
distributed
accordingly. It is additionally possible to introduce additional reactive
gases through
further gas inlets or also inert gases, such as argon, as is necessary, for
example, for
etching processes or for the deposition of nonreactive layers in order to use
the gases
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singly and/or in mixtures. The workpiece holder 3 located in the installation
serves for
receiving and for electrical contacting of the workpiece, not shown here,
which are
conventionally fabricated of metallic materials, and for the deposition of
hard material
layers using such processes. A bias power supply 4 is electrically connected
with the
workpiece holder 3 for applying a substrate voltage or a bias voltage to the
workpieces.
The bias power supply 4 can be a DC, an AC or a bipolar or a unipolar pulse
substrate
power supply. Via a process gas inlet 11 an inert or a reactive gas can be
introduced in
order to set and to control process pressure and gas composition in the
treatment
chamber.
Component parts of the arc vaporizer source 5 are a target 5' with cooling
plate placed
behind it, and an ignition finger 7, which is disposed in the peripheral
region of the target
surface, as well as an anode encompassing the target. A switch 14 permits
selecting
between a floating operation of the anode 6 of the positive pole of the power
supply 13
and operation with defined zero or ground potential. When igniting the arc of
the arc
vaporizer source 5 a brief contact is established of the ignition finger 7
with the cathode
and the former is subsequently withdrawn whereby a spark is ignited. The
ignition
finger 7 is for this purpose connected via a current limiter resistor to anode
potential.
The vacuum process installation 1 can additionally optionally, should the
conduction of
the process require such, be equipped with an additional plasma source 9. In
this case
the plasma source 9 is implemented as a source for generating a low-voltage
arc with a
hot cathode. The hot cathode is, for example, formed as a filament disposed in
a small
ionization chamber, in which with a gas inlet 8 a working gas, such as for
example
argon, is introduced for the generation of a low-voltage arc discharge which
extends into
the main chamber of the vacuum process installation 1. An anode 15 for
developing the
low-voltage arc discharge is located at an appropriate position in the chamber
of the
vacuum process installation 1 and is operated, in known manner, with a DC
power
supply between cathode and plasma source 9 and anode 15. If required,
additional
coils 10, 10' can be provided, such as for example Helmholtz-like
configurations which
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are placed about the vacuum process installation 1 for the magnetic focusing
or guiding
of the low-voltage arc plasma.
Proceeding according to the invention, as depicted in Figure 2, the arc
vaporizer source
is operated being fed additionally with a pulsed high-power supply 16'. This
pulsed
power supply 16' is advantageously directly superimposed onto the DC power
supply. It
is understood that for their protection the two supplies must be operated
electrically
decoupled with respect to each other. This can be carried out in conventional
manner
with filters, such as with inductors, such as is familiar to a person of skill
in the art. With
this configuration it is already possible according to the invention to
deposit layers
exclusively with pure reactive gas or reactive gas mixtures, such as oxides,
nitrides,
etc., without undesirable support gas components, such as for example argon in
PVD
sputter processes or halogens of the precursors in CVD processes. It is, in
particular,
possible to generate therewith the pure, electrically nonconducting oxides,
which are
very difficult to obtain economically, in the desired crystalline form and to
deposit them
as layers. This reactive pulsed arc vaporization method is herewith denoted as
RPAE
method.
In a further improved and preferred embodiment of a vacuum process
configuration,
apart from a first arc vaporizer source 5, a second arc vaporizer source 20 is
provided
with the second target electrode 20', as is shown in Figure 3. Both arc
vaporizer
sources 5, 20 are operated with one DC power supply 13 and 13' each, such that
the
DC power supplies ensure with a base current the maintenance of the arc
discharge.
The DC power supplies 13, 13' correspond to prior art and can be realized cost-
effectively. The two electrodes 5', 20', which form the cathode of the two arc
vaporizer
sources 5, 20, are connected according to the present invention to a single
pulsed
power supply 16, which is capable of outputting to the two electrodes 5', 20'
high pulse
currents with defined form and edge slope of the pulses. In the depicted
configuration
according to Figure 3 the anodes 6 of the two arc vaporizer sources 5, 20 are
referred
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to the electrical potential of the ground of the process installation 1. This
is herewith
also denoted as dual pulsed arc vaporization (DPAE).
It is possible to operate the spark discharges with reference to ground or
also floatingly.
In the preferred case of floating operation, the first DC power supply 13 is
connected
with its negative pole to the cathode 5' of the first arc vaporizer source 5
and its positive
pole with the opposing anode of the second arc vaporizer source 20. The second
arc
vaporizer source 20 is operated analogously and the second power supply 13' is
connected to the positive pole of the anode of the first arc vaporizer source
5. This
opposing operation of the anodes of the arc vaporizer sources leads to better
ionization
of the materials in the process. However, the ground-free operation, or the
floating
operation, of the arc vaporizer source 5, 20 can also take place without using
the
opposing anode feed. In addition, it is possible to provide a switch 14, as
shown in
Figure 1, in order to be able to change over optionally between floating and
ground-tied
operation.
The supply for this "Dual Pulsed Mode" must be able to cover different
impedance
ranges and yet not be "hard" in the voltage. This means that the supply must
supply
high current, yet, in spite of it, be largely operable voltage-stably. An
application of an
example of such a supply was filed under the No. CH 518/05 parallel with the
same
date as said patent application No. CH 1289/05.
The first and preferred application field of this invention is that of
cathodic spark
vaporization with two pulsed arc vaporizer sources (5, 20) as is depicted in
Figure 3.
For these applications the impedances are at intervals of approximately 0.01
S2 to 1 Q.
It should be noted here that usually the impedances of the sources, between
which
"dual pulsing" is carried out are different. The reason may be that these are
comprised
of different materials or alloys, that the magnetic field of the sources is
different or that
the material erosion of the sources is at a different state. The "Dual Pulsed
Mode" now
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=
permits a balance via the setting of the pulse width such that both sources
draw the
same current. This leads consequently to different voltages at the sources.
The supply
can, of course, also be loaded asymmetrically with respect to the current if
such
appears desirable for the process conduction, which is the case, for example,
for
graduated layers of different materials. The voltage stability of a supply is
increasingly
more difficult to realize the lower the impedance of the particular plasma.
The capability
of change-over switching or the controlled active tracking of a supply to
different output
impedances is of therefore of special advantage if the full range of its power
is to be
utilized, thus for example in the range of 500 V/100 A to 50 V/1000 A or as it
is realized
in the parallel application No. CH 518/05.
The advantages of such dual pulsed cathode configuration and in particular one
comprised of two arc vaporizer sources are summarized as follows:
I. Increased electron emission at steep pulses results in higher
current (also
substrate current) and increased ionization of the vaporized material and of
the reactive
gas.
2. The increased electron density contributes also to a fast discharge of
the
substrate surface in the production of insulating layers, i.e. relatively
short charge-
reversal times on the substrate (or also only pulse pauses of the bias
voltage) are
sufficient in order to discharge the insulating layer which is forming.
3. The bipolar operation between the two cathodic arc vaporizer sources
permits a
quasi-100% pulse pause ratio (duty cycle), while the pulsing of a source along
always
necessarily requires a pause and therefore the efficiency is not so high.
4. The dual pulsed operation of two cathode spark sources, which are
opposite to
one another, immerses the substrate region into a dense plasma and increases
the
reactivity in this region even of the reactive gas. This is also reflected in
the increase of
the substrate current.
5. In reactive processes under oxygen atmosphere in pulsed operation still
higher
electron emission values can be attained, and it appears that a melting of the
spark
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1
,
region, as is the case in classic vaporization of metallic targets, can be
largely avoided.
Working in purely oxidic reactive mode without further foreign or support
gases is now
readily possible.
To be able to attain said advantageous process properties in said different
possible
embodiments of the invention, the pulsed power supply 16, 16' must satisfy
different
conditions. In bipolar pulse presentation it should be possible to carry out
the process
at a frequency which is in the range of 10 Hz to 500 kHz. Due to the
ionization
conditions, herein the maintainable edge slopes of the pulses is important.
The
magnitudes of the leading edges U2/(t2 - t1), U1/(t6 - t5), as well as also of
the trailing
edges U2/(t4 - t3) and U1/(t8 - t7) should have a slope in the range of 0.02
V/ns to 2
V/ns and this at least in open-circuit operation, thus without load, however
preferably
also under load. It is understood that the edge slope has an effect in
operation,
depending on the corresponding magnitude of the load or the connected
impedance of
the corresponding settings. The pulse widths in bipolar presentation for t4 to
t1 and t8
to t5 are advantageously 1 is, the pauses t5 to t4 and t9 to t8 can
advantageously be
essentially 0, however, under certain conditions, they can also be 0 ws. If
the pulse
pauses are > 0, this operation is referred to as time-gapped and through, for
example,
variable time shift of the pulse gap widths the specific and purposeful
introduction of
energy into a plasma and its stabilization can be set. It is especially
advantageous if the
pulsed power supply is laid out such that a pulse option up to 500 A at 1000 V
voltage is
possible, wherein herein the pulse/pause ratio (duty cycle) must be
appropriately taken
into consideration or must be adapted for the laid out possible power of the
supply.
Apart from the edge slope of the pulse voltage it is necessary to observe that
the pulsed
power supply (16) is capable of handling a current rise to 500 A in at least 1
s.
With the operation introduced here of arc vaporizer sources with DC feed and
superimposed high-current pulsed feed (RPAE, DPAE) it is possible to deposit
with high
quality starting from one or several metal targets with reactive gas
atmosphere
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corresponding metal compounds onto a workpiece 30. This is in particular
suited for
the generation of purely oxidic layers, since the method does not require
additional
support gases, such as inert gases, customarily argon. The plasma discharge of
the
arc vaporizer 5, 20 can thus, for example and preferably, take place in pure
oxygen
atmosphere at desired working pressure without the discharge being unstable,
is
prevented or yields unusable results, as too high a splatter formation or poor
layer
properties. It is also not necessary to use, as is the case in CVD methods,
halogen
compounds. This permits, first, to produce economically wear-resistant oxidic
hard
material layers of high quality at low process temperatures, preferably below
500 C,
which, as a result, are nevertheless high temperature-resistant, preferably >
800 C
and which are chemically highly stable, such as, for example, have high
resistance to
oxidation. Furthermore, to attain a stable layer system the diffusion of
oxygen with
the oxidation entailed therein in the deeper layer system and/or on the
workpiece
should as much as possible be avoided.
It is now readily possible to produce oxidic layers in pure oxygen as reactive
gas from
the transition metals of the subgroups IV, V, VI of the periodic system of
elements
and Al, Si, Fe, Co, Ni, Y, with Al, Cr, Mo, Zr as well as Fe, Co, Ni, Y being
preferred.
The functional layer 32 is to contain as the oxide one or several of these
metals, no
inert gas and/or halogen, such as Cl, however at least less than 0.1% or
better less
than 0.05% inert gas and less than 0.5% or better less than 0.1% halogen in
order to
attain the desired layer quality.
Such functional layers 32 or multiple layer system 33 (multilayer) should, in
particular,
as hard material layer have a thickness in the range of 0.5 to 12 pm,
preferably from
1.0 to 5.0 pm. The functional layer can be deposited directly onto the
workpiece 30
which is a tool, a machine part, preferably a cutting tool, such as an
indexable insert.
Between this layer and the workpiece 30 at least one further layer or a layer
system
can also be deposited, in particular for the formation of an intermediate
layer 31,
which forms in particular an adhesion layer and comprises preferably one of
the
metals of the
CA 02601722 2007-09-17
subgroups IVa, Va and Via of the periodic system of elements and/or Al or Si
or a
mixture of these. Good adhesive properties are achieved with compounds of
these
metals with N, C, 0, B or mixtures thereof, the compound comprising N being
preferred.
The layer thickness of the intermediate layer 31 should be in the range of
0.05 to 5 Jim,
preferably 0.1 to 0.5 gm. At least one of the functional layers 32 and/or of
the
intermediate layer 31 can advantageously be implemented as a progression layer
34,
whereby a better transition of the properties of the particular layers is
brought about.
The progression can be from metallic over nitridic to nitrooxidic and up to
the pure
oxide. Thus a progression region 34 is formed where the materials of the
abutting
layers, or, if no intermediate layer is present, the workpiece material, are
mixed into one
another.
On the functional layer 32 a further layer or a layer system 35 can be
deposited as
cover layer, should this be required. A cover layer 35 can be deposited as
additional
friction-reducing layer for further improvement of the tribological behavior
of the coated
workpiece 30.
Depending on the requirements, one or more layers of said layers or layer
systems can
be developed as progression layers 34 in the region where they border on one
another
or within individual layers concentration gradients of any type can be
generated. In the
present invention this is simply possible through the controlled introduction
of the
reactive gases into the vacuum process installation 1 for setting the
particular types of
gas necessary for this purpose and of the gas quantities for the reactive arc
plasma
process.
As functional layer 32 with the desired hard material properties, now aluminum
oxide
layers (A1203), layers can now readily be produced which even have
substantially
stoichiometric composition. Especially advantageous hard material layers as
functional
layer 32 are substantially comprised of an
(AlxMel,)yOz, where Me is preferably one
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,
of the metals Cr, Fe, Ni, Co, Zr, Mo, Y singly or also in mixtures, settable
depending on
the desired proportions x, y and z of the involved substances. Further is
especially
preferred chromium as the metal Me in the metal mixed oxide of the
(AlxMe1_x)y0, which
consequently forms (AlxCr1_.)y0 z or (AlCr)yOz. Herein the proportion 1-x of
the metal
chromium in the layer should be 5 to 80 atom %, preferably 10 to 60 atom %.
Well suited as hard material functional layer 32 is also a metal nitride, in
particular the
aluminum chromium nitride (AlCr)yN , or at most also (AlTi)yN,.
Through the intentional capability of process conduction it is now also
possible in the
case of aluminum and aluminum chromoxides to be able to attain the especially
desired
alpha and/or gamma structure.
Due to said simple settability of the layer conditions with their composition
via the
control of the supply of the reactive gases and due to the stable process
condition, it is
for the first time possible to produce multilayer systems (multilayer) 33 with
any number
of layers and any composition and even with progressions. Several layers can
herein
be generated of different materials or, and this appears often to be of
advantage, with
the alternating identical materials as a type of sandwich. For functional hard
material
layers 32, a layer system with repeated layer sequence pairs 33, in which the
material
composition changes periodically, is advantageous. Especially a structure from
Mei to
an Me2 -oxide and/or from an Mei -nitride to an Mel -oxide and/or from an Mei -
nitride
to an Me2 -oxide yields excellent results with respect to endurance and less
fissuring of
the functional layer or of this layer system. An example of a functional layer
32 as a
multilayer 33 is shown in Figure 4 and in enlarged cross section in Figure 5.
Shown is a
preferred material pairing of alternating aluminum chromium nitride (AlCr),Ny,
with
aluminum chromoxide (A1Cr),(0y produced with the method according to the
invention,
preferably in stoichiometric material composition. The layer packet in this
example
comprises 42 layer pairs with alternating materials, as stated above. The
entire layer
thickness of this functional layer 32 as multilayer system 33 is approximately
4.1 m,
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,
the thickness of a layer pair, thus two deposits, being 98 nm. Further
preferred material
pairings are alternating aluminum zirconium nitride (AlZr),N y with aluminum
zirconium
oxide (AlZr)x0 y produced with the method according to the invention,
preferably in
stoichiometric material composition. For hard material layers as functional
layer 32 it is
of advantage if the multilayer system 33 includes at least 20 deposits,
preferably up to
500 deposits. The thickness per deposit should be in the range from 0.01 to
0.511,m,
preferably in the range from 0.2 to 0.1 pm. In the region of the individual
bordering
deposits of the layers progressions 34 are also evident, which ensure for good
behavior
of the transitions.
In the example according to Figure 4 as an example a cover layer 35 is also
deposit as
a friction-reducing layer over the functional layer 32, 33. The cover layer is
comprised
of titanium nitride and is approximately 0.83 p.m thick.
Under the functional layer as an example additionally an intermediate layer 31
is
disposed as adhesion layer which is approximately 1.31 gm thick and has been
deposited as an Al-Cr-N intermediate layer with RPAE onto the workpiece 30.
The coatings introduced here, whether single layer or multilayer system should
preferably have an Rz value of not less than 2 pm and/or an Ra value of not
less than
0.2 gm. These values are in each instance measured directly on the surface
before a
potential after-treatment of the surface, such as brushing, blasting,
polishing, etc. Thus,
the values represent a purely process-dependent surface roughness. By Ra value
is
understood the mean rough value according to DIN 4768. This is the arithmetic
mean
of all deviations of the roughness profile R from the center line within the
total
measuring path le,. By Rz is understood the mean roughness depth according to
DIN
4768. This is the mean value of the individual roughness depths of five
successive
individual measuring paths le in the roughness profile. IR, depends only on
the distance
of the highest peaks to the deepest valleys. By forming the mean value the
effect of an
individual peak (valley) is reduced and the mean width of the band, in which
the R
profile is included, is calculated.
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The introduced coating according to the invention is especially suited for
workpieces
such as cutting, forming, injection molding or punching and stamping tools,
however,
very specifically for indexable inserts.
In the following a typical sequence of a substrate treatment in a reactive
pulse arc
vaporization coating process is described using the present invention. Apart
from the
coating process proper, in which the invention is realized, the other process
steps will
also be described, which involve the pretreatment and posttreatment of the
workpieces.
All of these steps allow wide variations, some can also be omitted under
certain
conditions, shortened or extended or be combined differently.
In a first step the workpieces are customarily subjected to wet-chemical
cleaning, which,
depending on the material and prior history, is carried out in different
manner.
Example 1:
Description of a typical process sequence for the production of an Al-Cr-0
layer 32 (as
well as of an Al-Cr-N/Al-Cr-0 multilayer 33) and Al-Cr-N intermediate layer 31
by means
of RPAE (reactive pulse arc vaporization) for coating workpieces 30, such as
cutting
tools, preferably indexable inserts.
1. Pretreatment (cleaning, etc.) of the workpieces (30) (substrates) as
known to the
person of skill in the art.
2. Placing the substrates into the holders intended for this purpose and
transfer into
the coating system.
3. Pumping the coating chamber 1 to a pressure of approximately 10-4 mbar
by
means of a pump system as known to the person of skill in the art
(forepumps/diffusion
pump, forepumps/turbomolecular pump, final pressure approximately 104 mbar
attainable).
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µ
4. Starting the substrate pretreatment in vacuo with a heating step in an
argon-
hydrogen plasma or another known plasma treatment. Without restrictions, this
pretreatment can be carried out with the following parameters:
Plasma of a low-voltage arc discharge with approximately 100 A discharge
current, up
to 200 A, to 400 A, the substrates are preferably connected as anode for this
low-
voltage arc discharge:
Argon flow 50 sccm
Hydrogen flow 300 sccm
Substrate temperature 500 C (partially through plasma heating, partially
through
radiative heating)
Process time 45 min
It is preferred that during this step a supply is connected between substrate
30 and
ground or another reference potential, which can act on the substrates with DC
(preferably positive) or DC pulsed (unipolar, bipolar) or as IF (intermediate
frequency) or
RF (high frequency).
5. As the next process step etching is started. For this purpose the low-
voltage arc
is operated between the filament and the auxiliary anode. A DC, pulsed DC, IF
or RF
supply is connected between substrates and ground and the substrates are
preferably
acted upon with negative voltage. In the pulsed and IF, RF supplies positive
voltage is
also impressed on the substrates. The supplies 4 can be operated unipolarly or
bipolarly. The typical, however not exclusive, process parameters during this
step are:
Argon flow 60 sccm
Discharge current low-voltage arc 150 A
Substrate temperature 500 C (partially through plasma heating, partially
through
radiative heating)
Process time 30 min
To ensure the stability of the low-voltage arc discharge during the production
of
insulating layers, the work is either carried out with a hot, conductive
auxiliary anode 15,
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or a pulsed high-power supply is connected between auxiliary anode and ground.
6. Start of coating with the intermediate layer 31 (approximately 15 min)
CrN intermediate layer 300 nm by means of spark vaporization (source current
140 A,
Ar 80 sccm, N2 1200 sccm, with bias of -80 V or of -100 V down to - 60 V or 40
V,
respectively.
The coating can take place with and without low-voltage arc.
7. Transition to the functional layer 32 (approximately 5 min)
In the transition to the functional layer proper, onto the spark sources are
additionally
superposed unipolar DC pulses of a second power supply connected in parallel,
which
can be operated with 50 kHz (Fig. 2). An Al target is additionally operated in
the same
manner in order to produce AlCr as a layer. In the example work took place
with 10 ps
pulse/10 lis pause and in the pulsed currents up to 150 A generated. Oxygen at
200
sccm was subsequently let in.
8. Driving back of the AlCrN coating
After the oxygen gas flow has been stabilized, the AlCrN coating is brought
down. For
this purpose the N2 gas flow is reduced. This ramp takes place over
approximately 10
min. The Ar flow is subsequently reduced to zero (unless work is carried out
with low-
voltage arc).
9. Coating with functional layer 32
The coating of the substrates with the functional layer proper takes place in
pure
reactive gas (in this case oxygen). The most important process parameters are:
Oxygen flow 400 sccm
Substrate temperature 500 C
DC source current 60 A
Onto the DC source current a pulsed DC current (unipolar) of 150 A is
superimposed
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,
with a pulse frequency of 50 kHz and a pulse characteristic of 10 ms pulse/10
ps pause.
Process pressure in the coating chamber 9x10-3 mbar. The bias at the
substrates is
reduced to -40 V. Since aluminum oxide layers are insulating layers, a bias
supply is
utilized, which is operated either DC pulsed or as IF (50 kHz - 350 kHz).
The coating can also be carried out simultaneously with the low-voltage arc.
In this
case a higher reactivity is attained. The simultaneous use of the low-voltage
arc during
the coating has furthermore the advantage that the DC component in the sources
can
be reduced. At higher arc current, it can be further reduced.
The coating process conducted in this way is stable even over several hours.
The
target 5, 5' is covered with a thin smooth oxide layer. However, no insulating
islands
are formed, although the target surface changes through the oxygen, which is
also
reflected in the increase of the burn voltage. The target surface remains
significantly
smoother. The spark runs quieter and divides into several smaller sparks. The
number
of splatters is significantly reduced.
The described process is a fundamental preferred version since it keeps the
requirements made of the pulsed power supply low. The DC supply supplies the
minimum or holding current for the spark and the pulsed high-power supply 16,
16'
serves for avoiding the splatters and ensures the process.
One feasibility of generating multilayer systems 33, thus multiple layers 33,
for the
above layer example comprises that the oxygen flow during the layer deposition
is
decreased or even switched off entirely, while the nitrogen flow is added.
This can take
place periodically as well as aperiodically, with layers of exclusive or mixed
oxygen-
nitrogen concentration. In this way multilayers 33 are produced such as are
shown in
Figure 4, and enlarged in Figure 5, by example in cross section. In many cases
this
functional layer 32 forms the termination of the coating to the outside,
without a further
layer following thereon.
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Depending on the application and requirement, wear properties can be "topped"
with
one or several cover layers 35. The example of the AlCrN/A1Cr0 multilayer
already
described above with a TiN top layer is also shown in Figure 4. The at least
one cover
layer 35 can in this case be, for example, a friction-reducing layer, wherein
in this case
the hard material layer 32, or the functional layer or the multiple layer
serves as support
layer for the friction-reducing layer 35.
If there is the wish to produce multilayer functional layers 33 or multilayer
intermediate
layers with especially thin oxide-containing layer thickness, in a preferred
process
variant this can also take place thereby that the operation of the oxide-
forming target
under oxygen flow takes place just until the target exhibits first poisoning
signs (voltage
rise, most often after a few minutes) and then switching again to, for
example, nitrogen
flow. The process variant is especially simple and can be realized with the
existing prior
art (Fig. 1) thus without target pulse operation. However, this does not
permit a free
adaptation of the layer thickness to the particular requirements.
The implementation of said example in dual pulsed operation with two or more
arc
vaporizer sources yields, in addition, advantages with respect to the
conduction of the
process and economy.
Example 2:
Coating of workpieces 30, such as cutting tools, preferably indexable inserts,
with an Al-
Cr-0 hard material layer system 32 and Cr-N intermediate layer 31 by means of
DPAE
(Dual Pulsed Arc Vaporizer)
Steps 1 to and including 5 analogous to Example 1.
6. Starting the coating with the intermediate layer (approximately 15 min)
AlCrN intermediate layer 300 nm by means of spark vaporization (target
material AlCr
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,
(50%, 50%), source current 180 A, N2 800 sccm, with bipolar bias of -180 V (36
gs
negative, 4 gs positive).
The coating can take place with and without low-voltage arc.
Up to this point the method follows prior art such as is shown for example in
Fig. 1.
7. Transition to functional layer 32 (approximately 5 min)
In the transition to the functional layer 32 proper, the nitrogen is ramped
down from 800
sccm to approximately 600 sccm and subsequently an oxygen flow of 400 sccm is
switched on. The nitrogen flow is now switched off.
8. Coating with the functional layer 32
The bipolar pulsed high-power supply 16, as shown in Fig. 3, between both arc
vaporizer cathodes 5, 20 is now taken into operation. In the described process
work
took place with a positive or negative time mean value of the current of
approximately
50 A. The pulse durations were each 10 gs for the positive as well as negative
voltage
range with 10 :s pauses each in between at a voltage of 160 V. The peak value
of the
current through the bipolar pulsed power supply 16 depends on the particular
pulse
form. The difference of DC current through the particular arc vaporizer
cathode 5, 20
and peak value of the bipolarly pulsed current must not fall below the so-
called holding
current of the arc vaporizer cathode 5, 20, since otherwise the arc (spark) is
extinguished.
During the first 10 minutes of the coating the bias is ramped from -180 V to -
60 V. The
typical coating rates for double rotating workpieces 30 are between 3 p.m/hr
and 6
gm/hr.
The coating of the workpieces 30 with the functional layer 32 proper thus
takes place in
pure reactive gas (in this example oxygen). The most important process
parameters
are once again summarized:
Oxygen flow 400 sccm
Workpiece temperature 500 C
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DC source current 180 A, for the Al as well as also for the Cr source.
The bipolarly pulsed DC current between the two cathodes has a frequency of 25
kHz.
Process pressure approximately 9x10-3 mbar.
As already stated, the coating can also take place simultaneously with the
operation of
the low-voltage arc. In this case a further increase of the reactivity
especially in the
proximity of the workpiece is attained. In addition, the simultaneous
utilization of the
low-voltage arc during the coating has also the advantage that the DC
component at the
sources can be reduced. With higher arc current, this can be further reduced.
The coating process conducted in this way is stable even over several hours.
Targets
5', 20' of the arc vaporizers 5, 20 are covered with thin, smooth oxide layer.
This is
desirable and is also the precondition for a largely splatter-free and stable
process. The
covering is manifested in an increase of the voltage at the target.
Workpieces were coated with different coatings and under the same conditions
subjected to a practical comparison test.
Test conditions for the rotation tests:
As the measure for these tests known TiAIN layers and known alpha aluminum
oxide
layers deposited by means of CVD are used. In all test layers a layer
thickness of 4 gm
was tested. As test material were used stainless steel (1.1192). As rotation
cycles
were selected 1, 2 and 4 min each. The cutting rate was 350 m/min, advance 0.3
mm/rev, engagement depth 2 mm. The conditions were selected such that short
test
times are attainable at high temperatures on the cutting edge of the
workpiece.
The wear on the end flank and the chipping edge as well as the surface
roughness of
the worked steel were tested, and the length of time was determined before a
certain
increased roughness occurred. As the quantitative measure for wear, this
service time
was determined.
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Results:
a) CVD layer alpha aluminum oxide (prior art)
layer thickness d = 4 gm
The tool survived the 4-minute test. However, after the test in the SEM there
was no longer any layer material on the chipping edge.
b) TiAIN layer (prior art), d = 4 gm
This layer showed already after less than 2 min initial signs of destructions
and
supplied a rough surface on the workpiece.
Invention:
c) AlCrN intermediate layer, d = 0.4 gm
AlCrN/A1Cr0 multilayer, d = 3.6 gm
TiN top layer, d = 0.8 :m
Endurance 4 min
d) AlCrN intermediate layer, d = 0.4 gm
AlCrN/A1Cr0 multilayer, d = 3.6 gm
3 min 40 s
e) AlCrN intermediate layer, d = 0.3 gm
AlCr0 single layer, d = 2.9 gm
TIN top layer, d = 0.9 gm
4 min
AlCrN intermediate layer, d = 0.35 gm
AlCr0 single layer, d = 3.5 gm
3 min 20 s
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=
g) ZrN intermediate layer, d = 0.3 pm
ZrN/A1Cr0 multilayer, d = 3.8 p.m
ZrN top layer, d = 0.5 p.m
3 min 10 s
h) ZrN intermediate layer, d = 0.2 pm
ZrO/A1Cr0 multilayer, d = 6.4 p.m
ZrN top layer, d = 0.8 gm
4 min
i) AlCrN intermediate layer, d = 0.5 m
AlCrO/alpha alumina multilayer, d = 8.2 p.m
4 min
k) (Ti, AlCrN) intermediate layer, d = 0.4 pm
AlCrOfTiAlCrN multilayer, d = 4.5
3 min 50 s
Layers of or multilayers comprising oxidic layers of the stated materials show
markedly
less wear at high cutting rates. Conducting layers (TiAIN) according to prior
art at high
cutting rates are markedly inferior to the oxide systems according to the
invention.
Systems according to the present invention of (AlCr)yOz and (AlZr)yOz show
similarly
low wear as known CVD layers of V-aluminum oxide, however without its
disadvantage
of high temperature loading or loading through aggressive chemicals of the
workpiece
during the coating process. The conduction of the process, furthermore, can be
carried
out substantially simpler, for example through changing-over of gases or
controlled
change of the gas components (for example 02 to N2) and/or changing-over from
one
target, or changing of the components of the target feed under control, to the
other,
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,
while in CVD processes intermediate flushing as well as adaptation of the
temperature
level for individual layers of a multilayer layer system are necessary.
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