DE102008021912C5 - coating process - Google Patents

Abstract

A process for pretreating and coating bodies using magnetron sputtering with at least two HIPIMS power supplies in a coating chamber, characterized in that - a first HIPIMS power supply (1) is connected to a magnetron sputtering source (3), - a second HIPIMS power supply (2) is connected as a supply to the bodies to be pretreated and coated, and - the HIPIMS power supplies are synchronized, - wherein a transition layer is first formed by implanting metal ions from the magnetron sputtering source (3) into the body - and then an adhesive layer is applied, which also contains metal ions from the magnetron (3). - And then a carbon-based layer is generated, which contains hydrogen and / or nitrogen.

Description

The invention relates to a method for coating and treating bodies by means of the so-called magnetron sputtering.

It is known to provide bodies or parts of bodies with a surface coating for improving the mechanical properties. In particular, plasma-assisted PVD processes, such as arc evaporation and magnetron sputtering, have proved successful here, with the coating material being removed from so-called targets by means of plasma action and subsequently being deposited on the substrates.

The magnetron contains, in addition to the target, cooling devices, possibly electrical shields, in particular means for generating magnetic fields, which increase the plasma density in front of the target. The target acts as a cathode and is connected against the chamber and / or the shield of the magnetron or against a separate electrode which acts as an anode.

Compared to arc evaporation, magnetron sputtering has advantages because the liquid phase is avoided. Thus, an almost unlimited range of layered alloys is possible and the layers are free of growth defects, so-called. Droplets.

However, the degree of ionization of the coating particles in conventional magnetron sputtering is a maximum of a few percent. The ionization is highest in front of the target and hardly expands into the coating space. This can be somewhat improved by asymmetric magnetic fields behind the magnetron, so-called unbalanced magnetron, but is not sufficient even with large coating volumes, as are customary in commercial installations. Furthermore, the ionization consists predominantly of ions of the working gas and only a very small part of ionized material of the target.

Metal ions have u. a. the advantage that they can be chosen so that they are part of the coating material and do not contaminate the layer. Furthermore, they have lower ionization energy than the usual process gases.

A variant of this method, which avoids this disadvantage, is the so-called "high-power pulsed magnetron sputtering" or HIPIMS (English "High Power Impulse Magnetron Sputtering"). Also commonly used is the term HPPMS (High Power Pulse Magnetron Sputtering). Here is achieved by short but very high-energy pulses of electric plasma generators, a high ionization density of the coating particles in front of the magnetron, which come close to 100%. With a sufficiently high-energy pulse, the current increases so rapidly that the plasma states of the glow discharge and the high-current arc discharge (arc) are traversed so fast that a stable plasma with very high carrier density can form before the magnetron. The maximum power supplied during a pulse can extend into the megawatt range and the power supplied to the target per cm ² target area in the kilowatt range, so that the pulse time must be selected to be short in order to avoid damage to the magnetron.

HIPIMS offers many advantages. By electrical and magnetic fields, both the energy and the direction or trajectory of the ionized coating particles can be determined. As a result of the negative potential (bias) usually applied to the substrate during magnetron sputtering, cavities or surfaces of the substrate that are not in line of sight are now also well achieved. The bias also determines the energy of the ions, on which numerous layer properties depend. On the side of the magnetron a much better utilization of the coating material or the target is achieved by the high ion bombardment. In addition, the so-called target poisoning is prevented by reaction with reactive gases. In conventional magnetron sputtering of metal targets, insulating reactive layers form on the magnetron, which can prevent effective sputtering of the metal and lead to insulating layers and charges and arcs. If this is prevented by lowering the reactive gas pressure, the layers, on the other hand, have too high a metal content and reduced hardness. However, hard coatings are usually composed of compounds with a fixed stoichiometric ratio of metals and nonmetals. You have to choose a compromise between layer rate and reactive gas flow, which must be strictly adhered to during the process. However, with HIPIMS, which has a high ionic content of the target, especially metal ions, some metal ions are re-accelerated to the target and target poisoning is inhibited. The exact operating point is thus less critical and it can be coated in reactive processes with a conventional sputtering layer rate.

However, for purely metallic layers that do not involve poisoned targets, the layer rate for HIPIMS may lag behind that of conventional magnetron sputtering.

The high ionization affects not only the existing sputtering and reactive gases but also the released from the HIPIMS target Ions of the target, preferably the metal target. The HIPIMS process can also be operated at very low pressures, so that the HIPIMS electrode can almost exclusively serve as a source of metal ions. The metal ions can be used for coating but also for the pretreatment of the substrates. The pretreatment is carried out in particular by way sputtering of impurities or by the implantation of metal ions into the substrate. For this purpose, a higher bias voltage is applied to the substrate.

The basics of HIPIMS can be found in Kouznetsov, especially in the PCT application WO 98/040532 A1 , The execution of special power supplies can be found in the US 6,296,742 B1 , The font EP 1 609 882 A1 represents various ways to direct the ions after the pulse on the substrates. DJ Christie explains in "Target material pathways model for high power pulsed magnetron sputtering" in J. Vac. Sci. Tech. A, 23 (2) (2005) 330, the effects leading to rate loss in HIPIMS.

The ion density and energy in particular of the favorable metal ions is still too low on the substrate side. If one tries to increase the ion energy by high bias voltages, this leads only to a moderate increase of the ion density. The cleaning effects during pretreatment are too low; as well as the bombardment by ions during the coating. As a result, the layers do not receive the necessary density and hardness. On the other hand, the substrate temperature is thereby increased. Higher substrate temperatures can change the substrates, for example, reduce the hardness of steel, and usually increase the layer stresses. Compared to conventional metal ion etching by means of magnetron sputtering ( 1 ) have been achieved by pretreating the substrates advantages by operating a HIPIMS magnetron ( 2 ). This can generate a high metal ion content and the bias voltages can be reduced in many cases. Nevertheless, the fundamental problem still persists. The bias voltages are still too high and the high ion density is only available during the short pulse times of the HIPIMS, for example. There is also a strong interference between the bias supply and the HIPIMS power supply.

In the article by W.-D. Coin "HIPIMS: The New PVD Technology" in Vacuum in Research and Practice 19 (2007) No. 1, 12-17 is reported to use extremely high pulse powers of 4-6 MW in pulse-sputtering techniques. Typical pulse parameters are peak voltages of 1.5-2.5 kV, peak currents of 0.5-4 kA and more. The pulse current, based on the total area of the target, is 1 A or higher. Pulse duration and repetition rates are between 15 and 200 μs and between 50 and 200 Hz. In a coating system four cathodes are included, two of which are intended for HIPIMS operation, a third cathode for UBM and a fourth cathode, optionally as HIPIMS or UBM can be operated.

In the DE 10 2006 017 382 A1 describes a method for coating and / or treating surfaces by means of high power impulse magnetron sputtering (HIPIMS). At least two cathodes connected to a common power supply via a switching device are pulsed simultaneously or sequentially.

In the WO 2008/043606 A1 the coating of workpieces by means of a layer system with a mixed crystal layer of a Mehrfachoxids is described, which is suitable for high temperature applications. The multiple oxides can be produced by arc evaporation, in particular arc methods with a perpendicular magnetic field and pulse-superimposed arc methods are mentioned, and by arc or sputtering, in which high current pulses applied to the material sources or superimposed on the DC basic operation , As a way to increase the plasma impedance, the pulsing of a source magnetic field is called. The workpieces may be supplied with a negative bias voltage, a pulsed DC or an AC-powered MF or RF supply between the workpieces and ground.

It is therefore an object of the invention to describe a method in which the aforementioned disadvantages of the prior art are avoided.

This object is achieved by a method according to claim 1. Dependent claims relate to advantageous embodiments of the invention.

The basic idea of the invention is to further improve the advantages of the HIPIMS method, in that pulses are also used on the substrate side and these are additionally synchronized in a specific manner with the pulses on the HIPIMS magnetron. This is in 3 illustrated. 4 shows an example of a corresponding device. A HIPIMS magnetron ( 3 ) serves to deliver metal atoms and metal ions for pretreatment and coating of the bodies. It is powered by a HIPIMS power supply ( 1 ). The bodies to be coated are located on a substrate table ( 4 ). This is also connected to a HIPIMS power supply ( 2 ) connected. The power supply ( 2 ) is also referred to herein for convenience as a HIPIMS power supply, although it is not connected to a magnetron. But she has one in principle similar construction, and is preferably also constructed of a charging device, a capacitor and a controlled switching element, as is known in the art in HIPIMS magnetron sputtering. This does not exclude that other realizations are possible. The current values, voltage values, pulse times do not have to match those of the HIPIMS power supply ( 1 ) of the magnetron and depend on the conditions on the substrate side. But they are comparable. However, it is preferred that a same frequency is selected for both HIPIMS power supplies in order to facilitate the synchronization. The synchronization is performed by a control device ( 5 ) which can trigger and control pulses for both HIPIMS power supplies. Preferably, the pulses are first used for HIPIMS power supply ( 1 ) and the pulses for HIPIMS power supply ( 2 ) synchronized accordingly. In principle, however, the reverse way is possible. In a preferred embodiment of the method, at each pulse of the HIPIMS power supply ( 1 ) at the same time a pulse of the HIPIMS power supply ( 2 ). In this case, a high voltage is applied to the substrate table at the time when a high number of metal ions are available. However, even in cases where the overall ion bombardment is too high, the control device may ( 5 ) a signal for a pulse for the HIPIMS power supply ( 2 ) be suppressed or postponed. In the latter case, the temporal overlap of the pulses would be lower and thus also the ion bombardment. For example, during the coating, a lower ion bombardment is necessary than during the etching. This gives an additional parameter to control the properties of the layers. In this case, these include in particular the layer adhesion, layer stress, the hardness and density of the layer. The substrate temperature can also be influenced. A short delay for the HIPIMS power supply pulse ( 2 ) of, for example, 10 μs can also lead to a higher ion bombardment, since the pulse is applied to the substrate table only when the ion density is fully developed. Furthermore, shortly after the end of the pulse, the HIPIMS power supply ( 1 ) ions are still present, which can then be further accelerated to the substrate.

The terms substrate and body are used synonymously in this document. It is spoken by bodies in the plural; this does not exclude that even a single body can be pretreated and coated according to the invention. The bodies are preferably charged on a rotatable substrate table, which can also have several axes of rotation, so that the bodies can be guided past the magnetron or the magnetrons in a planetary rotation. By pretreatment are meant process steps that facilitate the application of the actual layer and contribute to the necessary adhesion of the layer. These include cleaning, etching and activating the substrates by ion bombardment and implanting ions in the surface zone of the substrate. For this the highest ion energies are necessary.

Due to the continuous lowering of the ion energy, an adhesion-promoting intermediate layer can be produced from the implantation via the etching to the coating.

During coating, the ion bombardment can usually be lower than during the pretreatment steps. The ion energy and density can also during coating by the pulse duration, pulse frequency, pulse voltage, pulse current, especially at the HIPIMS power supply ( 2 ) to be controlled; but also by the synchronization of the two HIPIMS power supplies, be it by changing the overlap of the pulses or by the exposure of pulses.

During the etching, the peak voltage of the pulse in the HIPIMS power supply ( 2 ), for example at least 300 V, preferably at least 400 V, particularly preferably at least 500 V; and at most 1000 V, preferably at most 800 V, particularly preferably at most 700 V. The peak voltage of the HIPIMS power supply ( 1 600-1000 V. Typical pulse durations are at least 40 .mu.s, preferably at least 50 .mu.s, more preferably at least 80 .mu.s, and at most 200 .mu.s, preferably at most 150 .mu.s, particularly preferably highest 120 .mu.s. The pressure range is preferably between 10 ^-3 and 10 ^-2 mbar. For a metallic chamber, the positive poles of the HIPIMS power supplies can be connected to the chamber wall. The shielding of the magnetrons is also at chamber potential. For large coating volumes, it may also be useful to operate the magnetrons against a separate anode to produce a more uniform gas ionization in the entire Beschichtungsrum. Likewise, the Substratbias can be switched against this anode and the anode relative to the chamber can be raised to a more positive potential.

With the method according to the invention, in principle, any body can be pretreated and arbitrary layers are applied, in particular is intended to resistant and / or hard protective coatings on components and tools, in particular tools for machining. But also on hard material layers and protective layers for wearing parts and data carriers.

There may be more magnetrons in the system. These may be further HIPIMS magnetrons which are synchronized or not, are synchronized according to the invention or in another way, or which are conventional magnetrons.

In the following an example. In a ca. 0.7 m ³ large, metallic coating chamber based on 4 is located near the chamber wall a HIPIMS magnetron ( 3 ) with a Cr target and a HIPIMS power supply ( 1 ) in front of a rotating substrate table ( 4 ) with substrates made of stainless steel. The maximum values of the pulse peaks of this power supply are fixed at 1000 V and 800 A. Argon is admitted to a pressure of 4 × 10 ^-3 mbar and ignited a plasma. About the HIPIMS power supply ( 2 ), the substrates are biased. This power supply ( 2 ) is set to a pulse peak maximum of 600V. The pulses of the HIPIMS power supplies are 100% synchronized and overlap completely. After 30 minutes, the etching is stopped, nitrogen introduced as a reactive gas and deposited with a conventional magnetron with a carbon target, a CN _x layer of about 1 micron thickness. The layer contains about 24% nitrogen.

In 7 is a Rockwell C test impression in a layer produced in this way. After the adhesion test according to DIN 50103 results in an excellent adhesion of HF = 1.

5 shows a corresponding test impression in a layer that with the conventional metal ion etching after 1 was produced with a low adhesive strength of HF = 5.

6 shows a corresponding test impression on a layer following with HIPIMS metal ion etch 2 was prepared with an average adhesive strength of HF = 2-4.

Claims (18)

A method of pretreating and coating bodies using magnetron sputtering with at least two HIPIMS power supplies in a coating chamber, characterized in that - a first HIPIMS power supply ( 1 ) to a magnetron sputtering source ( 3 ), - a second HIPIMS power supply ( 2 ) is connected as a supply to the body to be pretreated and coated, and - the HIPIMS power supplies are synchronized, - wherein a transition layer is first generated by metal ions from the Magnetronsputterquelle ( 3 ) are implanted in the body - and then an adhesive layer is applied, which also contains metal ions from the magnetron ( 3 ) contains. - And then a carbon-based layer is generated, which contains hydrogen and / or nitrogen. A method according to the preceding claim, characterized in that the second HIPIMS power supply ( 2 ) acts as a bias supply for the body. A method according to at least one of the preceding claims, characterized in that first a gas is admitted, a plasma in front of the magnetron ( 3 ) is ignited, this plasma by the first HIPIMS power supply ( 1 ) and the substrate bias through the second HIPIMS power supply (FIG. 2 ), wherein the pulses of the power supplies are synchronized with each other. A method according to at least one of the preceding claims, characterized in that by the first HIPIMS power supply ( 1 ) Gas and metal ions are generated while through the second HIPIMS power supply ( 2 ) Energy is supplied to accelerate the gas and metal ions on the body. A method according to at least one of the preceding claims, characterized in that the bodies are cleaned and etched for pretreatment. A method according to at least one of the preceding claims, characterized in that the transition layer is generated by the peak voltage of the second HIPIMS power supply ( 2 ) is continuously reduced. A method according to at least one of the preceding claims 1-5, characterized in that the transition layer is generated by the power of the second HIPIMS power supply ( 2 ) is continuously reduced. A method according to at least one of the preceding claims, characterized in that a metallic coating chamber is used. A method according to any one of the preceding claims, characterized in that a DLC layer or a DLC-containing layer is produced. A method according to any of the preceding claims 1-8, characterized in that a carbonitride layer or a carbonitride-containing layer is produced. A method according to the preceding claim, characterized in that a hydrogen-containing layer is produced. Method according to one of the preceding claims, characterized in that the body is a tool. Method according to one of the preceding claims 1 to 11, characterized in that the body is a wearing part. Method according to one of the preceding claims 1 to 11, characterized in that the body is a storage medium. Method according to one of the preceding claims, characterized in that a hard material layer is produced. Method according to one of the preceding claims, characterized in that metals are used for implanting, cleaning and etching of the body, and for applying the transition or adhesive layer, from the group comprising the metals of 4-6. Subgroup of the periodic table, Si and Al. A method according to at least one of the preceding claims, characterized in that the pulses are synchronized such that at least 20% of the power pulses of the first HIPIMS power supply ( 1 ) a temporal overlap with the power pulse of the second HIPIMS power supply ( 2 ) takes place. A method according to at least one of the preceding claims, characterized in that the pulses are synchronized so that the pulse voltage at the second HIPIMS power supply ( 2 ) during at least 20% of the total pulse time provided by the first HIPIMS power supply ( 1 ) pulses applied.

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