METHOD FOR MANUFACTURING POORLY CONDUCTIVE LAYERS

Abstract

Method for producing poorly conductive and in particular nonconductive layers on at least one work piece by means of a vacuum-coating process in which an electric arc discharge is activated between at least one anode and the cathode of an arc source in a reactive-gas atmosphere, whereby on the surface of a target that is electrically connected to the cathode either none or only a small outer magnetic field is generated that extends essentially perpendicular to the target surface for assisting the evaporation process, the degree of recoating of the target surface by other coating sources is less than 10%, and the magnetic field is generated with a magnet system that encompasses at least one axially polarized coil with a geometry similar to the circumference of the target.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The following describes this invention in more detail with the aid of drawings which merely illustrate various implementation examples and in which:

FIG. 1 shows surfaces of reactively arced targets;

FIG. 2 depicts an arc source with magnet system;

FIG. 3 shows field intensity Z by a conventional method;

FIG. 4 shows field intensity V by a conventional method;

FIG. 5 depicts an arc source with coil;

FIG. 6 shows the field intensity by the method according to the invention.

FIG. 1 reveals the surface condition of different spark targets employed in a pure oxygen atmosphere. For this test, targets having a diameter of 160 mm and a thickness of 6 mm were mounted on a Balzers standard arc source in an RCS coating system and run for 50 minutes using different magnet systems with a source current of 180 A in a pure oxygen atmosphere. The operating parameters were as follows:

Source currentarc:   180 A
O2 flow:             Incrementally increased from 400 sccm to 1600
                     sccm, working in a pure oxygen atmosphere.
Increment size/span: 300 sccm/10 min.
Process pressure:    0.44 to 4.9 Pa
Substrate voltage:   Bipolar asymmetric pulse: −100 V/36 μs,
                     +100 V/4 μs
Tsubstrate:          550° C.

In FIG. 1, “MAG Z” and “MAG V” designate two targets that were operated with a relatively strong magnetic field having a well-defined radial component B_r. In both cases the surface reveals a very irregular erosion pattern as well as distinct, essentially circular spark tracks. The spark has left relatively deep grooves and, already visually recognizable, maximal erosion in the center of the target. In both cases, the surface is so rough and damaged that without resurfacing both targets are no longer reusable. The spark path itself grows progressively narrower during the operation, the result being an unstable process. Until now, a pattern such as this could be largely avoided only by means of a pulsed target current as described in CH 00518/05 and CH 1289/2005. That, however, requires an additional investment and special power supplies.

The surface of “MAG S” in FIG. 1, on the other hand, exhibits an altogether different picture. Except for the magnetic field, it was operated under application of the same parameters as for the surfaces of targets MAG Z and MAG V in FIG. 1. The surface appears to have been ablated evenly across the entire region, which was then verified by profilometric measurements. This result requires a small magnetic field with at least one small radial component. The vertical component can be selected somewhat more freely. The following will briefly discuss the major differences between the magnet systems employed.

FIG. 2 is a schematic cross-sectional view of an arc source with a magnet system of the type used for the targets MAG Z and MAG V in FIG. 1. Surrounding the surface 2 of a target 1 mounted on a cooling plate 4 is a continuous confinement ring 3 serving to confine the spark to the target surface. The usual counter-electrode, typically a cathode that is itself annular, is not shown here. Positioned in the central rear section of the target is the power input 5 which may include cooling-water infeed and outlet tubing, again not illustrated. Also located in the central rear section is an annular inner permanent magnet 6 while an annular outer magnet 7 is positioned near the perimeter of the target. The two annular magnets are axially magnetized with mutually opposite polarity, whereby part of the lines of flux exiting from the upper side of the outer annular magnet 7 reenter in the upper side of the inner annular magnet 6, while the electric flux pattern on the back side in relation to the circular plane is essentially mirror-inverted. The field intensity can be modified for instance by means of magnets of different magnetic strength and, additionally, a coil such as the one in FIG. 5, or by other means.

FIG. 3 shows the local field intensity of a magnet system on the surface of an arc target in a

corresponding configuration employing a Balzers production-type “MAG Z” magnet system. The diagram shows the field-intensity curve of the vertical component B_z and of the radial component B_r on one half of the target. B_z reaches a maximum in the center (0-coordinate) and again at the edge (75 mm) while traversing the zero line at about 45 mm. The 45° point defined by the intersection of the absolute components, meaning the point or section where the lines of flux impinge on the target surface at an angle of 45°, is located near 27 and, respectively, 59 mm. In the intermediate region the radial component B_r is greater than B_z and passes through a maximum. Unlike B_z, B_r does not change direction in the target half concerned but intersects the zero line at the zero point and at the edge of the target. As was to be expected, the intermediate region in which the spark(s) traveling across the target is/are subjected to relatively high radial acceleration forces, is a preferred destination, which is clearly visible in the corresponding “MAG Z” erosion pattern shown in FIG. 1. On the other hand, as a result of the very small radial component in the central region of the target and the correspondingly slow movement of individual sparks that are leaving the preferred destination, overheating and associated explosive evaporation cause increased erosion, surface damage and an increase in droplet formation. This effect is of less significance at the target perimeter because, compared to the central region, fewer sparks per area unit cross over from the preferred destination while at the same time an eddy-current field self-induced in the confinement ring, consisting of a metal such as copper, pushes the spark back.

FIG. 4 shows the corresponding characteristic field-intensity curve for the evaporation of the target illustrated in FIG. 1, using the “MAG V” magnet system. With a basically similar characteristic curve, the magnetic field differs from that in FIG. 3 by a field intensity which on average is about 50% higher for both components. Accordingly, the “MAG V” target surface in FIG. 1 exhibits stronger erosion even in the outer region. In this case as well, the surface is seriously damaged.

Finally, FIG. 5 is a schematic cross-sectional illustration of an arc source employing a “MAG S” magnet system 8, used for evaporating the surface of the “MAG S” target in FIG. 1 through application of the method according to the invention. In lieu of the annular permanent magnets 6 and 7 in FIG. 2, the configuration in this case employs an electromagnetic coil 8 mounted behind the target 1 within the projection area of the target circumference.

Along this concept, advantageous magnet system designs are composed of one or several electromagnetic coils without, or with only minor, support provided by strong permanent magnets. These systems permit coil-current changes to match changes in the condition of the target surface. For example, in the creation of a continuous transition from a conductive nitridic hard layer to a nonconductive oxidic layer, the magnetic field can be downward-adjusted parallel to the nitrogen ramp while the oxygen flow is continuously increased. It is thus possible even without a pulsed arc-source operation to produce any desired continuous transitions with materials that require magnetic-field support for evaporating the conductive surface.

FIG. 6 illustrates the field intensity obtained when operating this type of magnet system at low currents. In this particular case, a Balzers production “MAG S” magnet system (432 coil turns) was operated with a 1 A current. It is thus possible, as illustrated, to obtain magnetic fields with a highly uniform progression of the B_z component as well as a B_r component with a very low average value. It will be advantageous to select a B_z component of less than 50 Gauss, in particular less than or equal to 30 Gauss. While, surprisingly, the arc sources can be operated in an oxygen atmosphere basically without magnetic-field support, at an acceptable rate and with an erosion pattern similar to that of “MAG S” in FIG. 1, the use of a magnet system as just described will nevertheless result in a somewhat better distribution pattern. Such an effect has been noticed even in the case of fields with a B_z of less than 10 Gauss, for instance 3 and 5 Gauss. A concomitant benefit is a highly uniform B_z curve which over much of the target surface does not fluctuate by more than 10 to a maximum of 20%. A slightly larger deviation is acceptable only in the peripheral region of the target, about 10 to 20 mm from the target rim. Moreover, a magnet system of that type facilitates coating processes in which the target is sequentially used for generating conductive and marginally conductive or nonconductive layers, since it allows an adjustment of the fields to the respective processing step. Of course, to optimize these processes, other magnet systems known to those skilled in the art may be employed as well. For example, in some processes the use of an additional system that is vertically adjustable relative to the target plane would prove beneficial in obtaining, with larger magnetic fields on the target surface, a favorable magnetic-field distribution perhaps

comparable to FIGS. 3 and 4, for instance in the production of certain metal nitrides.

The following example describes the complete progression of a coating process according to the invention, using a weak, essentially vertical magnetic field in the area of the target surface.

After the work pieces were mounted on appropriate bi- or triaxially rotatable holders and the holders were moved into the vacuum processing system, the processing chamber was pumped down to a pressure of about 10⁻⁴ mbar.

For setting the process temperature, a low voltage arc (LVA) plasma, assisted by radiant heater elements, was ignited in an argon-hydrogen atmosphere between a baffle-separated cathode chamber with a hot cathode and the anodic work pieces.

The parameters for the heating process were selected as follows:

Discharge current LVA 250 A
Argon flow            50 sccm
Hydrogen flow         300 sccm
Process pressure      1.4 × 10−2 mbar
Substrate temperature approx. 550° C.
Process duration      45 min.

Those skilled in the art are aware of possible alternatives. As a matter of preference, the substrates were connected to function as anodes for the low voltage arc and were additionally pulsed in unipolar or bipolar fashion.

The next procedural step was the initiation of the etching process by activating the low voltage arc between the filament and the auxiliary anode. Here as well, a DC, pulsed DC or alternating-current MF or RF supply may be interpolated between the work pieces and frame ground. Preferably, however, the work pieces are fed a negative bias voltage.

The etching parameters were selected as follows:

Argon flow             60 sccm
Process pressure       2.4 × 10−3 mbar
Discharge current, LVA 150 A
Substrate temperature  approx. 500° C.
Process duration       45 min.
Bias                   200–250 V

To ensure a stable low voltage arc (LVA) discharge during the generation of nonconductive layers, all LVA-assisted process steps included either the use of a hot, conductive auxiliary anode or the interconnection of a pulsed high-current power supply between the auxiliary anode and frame ground.

The next procedural step was the coating of the substrate with an AlCrO layer and a TiAlN intermediate layer. If a higher ionization level is needed, all coating processes can be further assisted by the plasma of the low voltage arc.

The parameters for depositing the intermediate TiAlN layer were selected as follows:

Argon flow              0 sccm (no argon added)
Nitrogen flow           Pressure-controlled at 3 Pa
Process pressure        3 × 10−2
DC source current, TiAl 200 A
Source magnetic field   1 A
current (MAG S)
DC substrate bias       U = −40 V
Substrate temperature   approx. 550° C.
Process duration        25 min.

For the transition of about 15 minutes to the actual functional layer the AlCr arc sources were powered with a DC source current of 200 A, with the positive pole of the DC source connected to the annular anode of the source and to frame ground. During that phase the substrate was fed a DC substrate bias of −40 V. 5 minutes after activation of the AlCr target the oxygen infeed was started and then adjusted within 10 minutes from 50 to 1000 sccm. At the same time, the N₂ flow was reduced to about 100 sccm. Just prior to the oxygen intake the substrate bias was switched from DC to bipolar pulsed operation and increased to U=−60 V. At the end of the oxygen ramp the two TiAl targets were turned off. The intermediate layer and the graduated transition to the functional layer were now complete.

Coating the substrate with the actual functional layer is performed in pure oxygen. Since aluminum oxide is an insulating layer, either a pulsed or an AC bias supply must be used.

The main parameters for the functional layer were selected as follows:

Oxygen flow           1000 sccm
Process pressure      2 × 10−2 mbar
DC source current, Al 200 A
Source magnetic field 0.5 A
current (MAG S)
Substrate bias        U = 60 V (bipolar, 36 μs negative,
                      4 μs positive)
Substrate temperature approx. 550° C.
Process duration      60 to 120 min.

The process described above yielded well-bonding, hard layers. Comparison tests performed on drilling and milling tools revealed a product life distinctly longer than that obtainable with conventional TiAlN layers, although surface roughness significantly exceeded the roughness level of optimized, pure TiAlN layers.

Claims

1) Method for producing poorly conductive and in particular nonconductive layers on at least one work piece by means of a vacuum-coating process in which an electric arc discharge is activated between at least one anode and a cathode of an arc source in a reactive-gas atmosphere, characterized in that on the surface of a target that is electrically connected to the cathode a small outer magnetic field is generated, extending essentially perpendicular to the target surface and encompassing a vertical component Bz for assisting the evaporation process, in that a magnet system consisting of at least one axially polarized coil with a geometry similar to the target circumference is fed an excitation current.

2) Method as in claim 1, characterized in that the vertical component Bz on the target surface is selected within a range of between 3 and 50 Gauss but preferably within a range of between 5 and 25 Gauss.

3) Method as in claim 1, characterized in that the magnet system is positioned essentially on one level with the target surface or preferably behind the target surface.

4) Method as in claim 1, characterized in that the spark discharge or at least the minimum of one arc source is simultaneously fed a direct current as well as a pulsed or alternating current.

5) Method as in claim 4, characterized in that by means of an insulating layer on the target surface an increase of the DC component of the source voltage by at least 10% and preferably by at least 20% compared to the operation with a surface without an insulating layer is achieved.

6) Method as in claim 4, characterized in that a pulsed current supply is interpolated between the cathode of an arc source as the first electrode and a second electrode that is positionally separated from the arc source.

7) Method as in claim 6, characterized in that the said second electrode functions as the cathode of another arc source which on its part is connected to a DC power supply.

8) Method as in claim 6, characterized in that the said second interconnected electrode is a sputter cathode.

9) Method as in claim 1, characterized in that at least two targets are functionally arranged in a mutually angled or opposite position and that at least one work piece is placed between the targets.

10) Method as in claim 1, characterized in that the excitation current is a direct current and/or the pulsed or alternating current fed from a power source to the cathode via the said coil.

11) Method as in claim 10, characterized in that the coil is so configured that, when the excitation current is flowing, the outer magnetic field essentially adjusts itself to the value of the intrinsic magnetic field of the arc current.

12) Method as in claim 11, characterized in that a coil with between 1 and 20, preferably between 1 and 10 and in particular between 1 and 5 turns is employed.

13) Method as in claim 1, characterized in that a target of an aluminiferous alloy is used and that an aluminiferous alloy or an aluminous-alloy compound is evaporated off the target surface.

14) Method as in claim 13, characterized in that said alloy contains pure aluminum or an alloy of the aluminum with one or several of the subgroup IV to VI transition metals as well as Fe, Si, B and C, but preferably an AlTi, AlTa, AlV, AlCr or AlZr alloy.

15) Method as in claim 1, characterized in that the reactive-gas atmosphere contains oxygen or consists of oxygen and that an oxidic layer, preferably an oxide, is deposited.

16) Method as in claim 15, characterized in that in addition to a minimum of one oxidic layer at least one other bonding and/or hard layer is deposited on the work piece, with the final coating step preferably consisting in the deposition of an oxidic layer, preferably an oxide.

17) Method as in claim 16, characterized in that at least once between two directly successive bonding, hard and/or oxide layers a transition layer, containing elements of the two directly successive layers, is deposited.

18) Method as in claim 1, characterized in that the reactive-gas atmosphere contains a boronic compound or consists of a boronic compound and that a boronic layer, preferably a boride and most preferably TiB2, is deposited.

19) Method for producing poorly conductive and in particular nonconductive layers on at least one work piece by means of a vacuum-coating process in which an electric arc discharge is activated between at least one anode and the cathode of an arc source in a reactive-gas atmosphere, characterized in that on the surface of a target that is electrically connected to the cathode either none or only a small outer magnetic field is generated, extending essentially perpendicular to the target surface and encompassing a vertical component Bz as well as an essentially smaller radial or surface-parallel component Br, for assisting the evaporation process, and that the arc source is operated in a vacuum coating system either by itself or other coating sources are functionally integrated into the system in a manner whereby the degree of recoating of the target surface is less than 10%, preferably less than 5% and most preferably less than 1% of the amount of metal evaporated by the cathode.

20) Method as in claim 19, characterized in that the vertical component Bz on the target surface is set at less than 50 but preferably less than 25 Gauss.

21) Method for producing poorly conductive and in particular nonconductive layers on at least one work piece by means of a vacuum-coating process in which an electric arc discharge is activated between a cathode and an anode of an arc source in a reactive-gas atmosphere, characterized in that the arc discharge is operated with a direct-current and/or a pulsed or alternating-current generator, that on the surface of a target that is electrically connected to the cathode only a small outer magnetic field is generated, extending essentially perpendicular to the target surface for assisting the evaporation process, and that between the cathode and the anode, electrically insulated from both, a confinement ring is positioned which consists either of an electrically insulating material such as BN or of a highly conductive metal such as Al, Cu or Ag.