Cathode arc source for metallic and dielectric coatings

Details Cathode arc source for metallic and dielectric coatings Cathode arc source for metallic and dielectric coatings

2000-10-12

2002-07-02

VerSteeg, Steven H. (Department: 1753)

Chemistry: electrical and wave energy

Processes and products

Vacuum arc discharge coating

C204S298410

Reexamination Certificate

active

06413387

ABSTRACT:

The present invention relates to a cathode arc source, in particular a filtered cathode arc source for metallic and dielectric coatings, to an anode liner for a cathode arc source, to a method of operation of a cathode arc source and to a striker for a cathode arc source.
The source of the invention is suitable for use with or without filtering apparatus, though it is conveniently used with a double bend filter duct as previously developed and described in WO-A-96/26531 by the same applicant.
Filtered cathode arc sources are known for producing thin metallic and dielectric films on a variety of substrates. An acknowledged problem in prior art sources is that the intense arc spots of the sources produce large quantities of macroparticles that contaminate the deposited films. The problem of reducing the number of macroparticles in the films is conventionally addressed by provision of means for filtering macroparticles from the beam of positive ions emitted from the cathode target of the source.
Known commercial apparatus, described in U.S. Pat. No. 5,433,836, incorporates a 45° angle bend to filter macroparticles from the beam. Apparatus described by the present inventors in WO-A-96/26531 describes a double bend filter duct for the same purpose. While the quality of tetrahedral amorphous carbon films obtained using the latter apparatus is high, the search for improvements in the quality of metal and dielectric films continues.
It has also been observed that in use of known apparatus, the surface of the target is consumed in an uneven manner, as the arc spot moves erratically about the surface of the target. This movement of the arc on the surface of the target is uncontrollable and deposition rate falls when the spot approaches the edge of the target. Targets have to be replaced well before all the target material is consumed, which is inefficient.
In theory, multi-layer coatings produced using a sequence of metal targets would produce highly desirable properties in the composite film obtained. However, known apparatus does not permit commercial manufacture of these coatings as interchange of targets is awkward. In addition, existing apparatus are not suitable for long term, industrial use, being designed only for laboratory use. Thus, to realise the theoretical properties of multi-layer coatings an improved apparatus is needed.
To ignite an arc in known apparatus requires a striker, conventionally moveable and located at or very close to the cathode target. A disadvantage of this arrangement is that in use of the arc source the striker often interferes with the arc: by interfering with the electric field at or around the target, by physically preventing cooling of an area of the vacuum chamber wall or by introducing contaminants into the plasma. An alternative striker mechanism would be desirable.
The present invention seeks to provide a new design of cathode and anode, a new striker mechanism and new operational methods and other features that, separately or in combination, eliminate or at least ameliorate some of the problems identified in the prior art.
It is thus an object of the invention to provide method and apparatus to generate an arc from a cathode target which in use emits fewer macroparticles compared to the prior art. A further object is to provide method and apparatus for producing multi layer coatings on a substrate. A still further object is to provide method and apparatus for coating of a substrate, simultaneously from more than one target. A still further object is to provide apparatus for use in combination with a known vacuum chamber that adapts that vacuum chamber for use as a cathode arc source of positive ions. Another object is to provide a cathode arc source capable of long term operation. A yet further object is to provide improved arc striking in the source.
According to a first aspect of the invention there is provided a cathode arc source comprising a cathode station to receive a target and means for generating a magnetic field radially parallel to the target which has near zero normal field strength.
The field is suitably the resultant of fields above and below the target such that there is a significant lateral component to the field at or just above the target surface. This lateral (or radial) field is for maintaining the arc spot on the target surface and it has advantageously been found that target utilisation is improved, for example is more even, and that the arc is more stably maintained when operating a source having such a lateral field.
A field generating means may be located at or below the cathode station so that the target when at its station is a short distance above the top of the first generating means, suitably at least 2 mm. The magnetic field at the target surface thus has two components, and preferably both can be adjusted. One component is substantially perpendicular (normal) to the target while the other is substantially in the lateral (radial) direction. The lateral field helps to steer the arc spot, to ensure high target utilization, and keep the normal field strength low. The combination promotes stable arc operation.
The source is for generating a metallic and/or dielectric coating and therefore comprises a target made of a material other than graphite. Suitable target materials include solid metals and semiconductors, but exclude carbon. Examples of suitable target materials include gold, platinum, silver, titanium, lead, copper, tungsten, molybdenum, silicon, aluminum, gallium, germanium. Coatings deposited using the arc source of the invention optionally contain gas such as oxygen or nitrogen in combination with one or more target materials. The cathode arc source of the invention is thus suitable for incorporation into apparatus for deposition of metal, oxide, nitride and ceramic coatings.
In an embodiment of the invention, a cathode arc source for generating positive ions from a cathode target, said ions being emitted in a direction normal to a front surface of the cathode target, comprises a vacuum chamber and means for generating a magnetic field in the vacuum chamber, wherein the magnetic field has direction normal to the front surface of the target and zero field strength at a position above the target. The cathode arc source preferably comprises means for generating a first magnetic field proximal to and below the target and having a first field direction and means for generating a second magnetic field distal to and above the target and having a field direction opposite to that of the first. The resultant magnetic field inside the vacuum chamber includes a point above the target at which the field strength is zero in a direction normal to the front surface of the cathode target, and at the same time a field is provided on the target surface with a strong radial component. This radial field preferably has strength of at least 5 Gauss, typically not more than 40 Gauss and more preferably 15-25 Gauss. In scaled-up apparatus, though, the radial field strength may have to be altered.
In use, the cathode arc source of the invention produces a plasma beam of positive ions and electrons having reduced numbers of macroparticles. The invention thus addresses the problem of how to remove macroparticles from plasma by control of a magnetic field within the vacuum chamber of the source so that fewer macroparticles are generated ab initio. Filtering of the plasma beam further to reduce macroparticles is an option and is a feature of preferred embodiments of the invention.
In a particular embodiment of the invention, a cathode arc source for generating positive ions from a cathode target comprises means for generating a magnetic field wherein:
(1) at a front surface of the target, field direction normal to the front surface is towards the front surface;
(2) magnetic field strength normal to the front surface decreases with increasing distance from the target to a point of zero field strength normal to the front surface; and
(3) from the point of zero normal field strength, with increasing distance from the target, field direc

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