Hard Material Layer

Abstract

A hard material layer is deposited on a workpiece as a functional layer by an arc-PVD method. The layer is essentially an electrically insulating oxide of at least one of the metals (Me) of the transition metals of the sub-groups IV, V, VI of the periodic table and Al, Si, Fe, Co, Ni, Co, or Y and the functional layer (32) contains no noble gas or halogen.

Description

FIELD AND BACKGROUND OF THE INVENTION[0001]The invention relates to a hard material layer deposited as oxidic arc PVD functional layer (32) on a workpiece (30) according to the preamble of claim 1 as well as to a method for coating a workpiece with a hard material layer according to the preamble of claim 21.[0002]The operation of arc evaporator sources, also known as spark cathodes, by feeding with electrical pulses has been known in prior art for a relatively long time. With arc evaporator sources high evaporation 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...

AI Technical Summary

Benefits of technology

This approach allows for the deposition of high-quality, oxidic hard material layers with improved homogeneity and reduced surface roughness, achieving stable process conditions and enabling the production of alpha aluminum oxide layers at lower temperatures, enhancing the tribological properties and economic viability.

Problems solved by technology

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.

With high requirements made of the layer quality, layers generated thusly, can often not be commercially applied.

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 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 evaporator 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.

In the reactive coating by means of arc evaporator source there is a lack of reactivity and process stability, especially in the production of insulating layers.

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.

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 evaporation 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.

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 U.S. Pat. No. 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 method most frequently mentioned is dual magnetron sputtering, which in this application entails great disadvantages with respect to process reliability and costs.

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 evaporation.

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 evaporator 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 splatters: conglomerates (splatters) are not fully through-reacted, wherein metallic components occur in the layer, increased roughness of the layer surface is generated and the constancy of the layer composition and the 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 evaporation.

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 evaporator source, for example in oxygen atmosphere, additionally a thin oxide layer forms, which tends to increased splatter formation.

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