Electric lamp and discharge devices: systems – Discharge device load with fluent material supply to the... – Electron or ion source
Reexamination Certificate
2000-10-13
2001-07-17
Philogene, Haissa (Department: 2821)
Electric lamp and discharge devices: systems
Discharge device load with fluent material supply to the...
Electron or ion source
C315S111710, C204S298120, C204S298150, C204S192380
Reexamination Certificate
active
06262539
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a cathode arc source, in particular to a cathode arc source adapted for industrial or long term operation.
Cathode arc deposition of tetrahedral amorphous carbon, metallic, dielectric and other such coatings is known in the art and offers the potential for deposition of thin films of high quality. Applications in scratch resistant optical coatings and hard disc media coatings are but two of a wide range of proposed uses.
Hitherto, deposition of films by the cathode arc process has been mainly limited to laboratory use, in general because of difficulties in the art in reliably depositing films that are free of or have acceptably low contamination by macroparticles—large, neutral particles.
Provision of improved means for filtering macroparticles from the arc plasma has recently been described in WO-A-96/26531 and also in as yet unpublished International patent application no. PCT/GB97/01992.
Existing filtered cathode arc sources can not yet, however, be continuously used, or used for long periods of time. This renders them unattractive for use in industrial processes. Existing cathode arc sources have to be shut down frequently so as to change or adjust or tidy up the target—this is time-consuming and wastes energy in reestablishment of the vacuum in the chamber and reestablishment of the arc. Whenever an arc is stopped and then restruck, the first plasma discharge from the arc is typically dirty and should preferably not be used for deposition on the substrate. Thus, when the arc is frequently stopped and restarted much operator interaction is required to obtain the best possible coating quality.
In use of known cathode arc sources, it is observed that target erosion is typically uneven, with the cathode spot moving erratically across the target surface. A relatively smooth target surface is preferred for deposition of plasma using a cathode arc source, but the smooth surface is rapidly lost by action of the arc spot.
Shutting down the arc and opening the chamber, including breaking vacuum in the chamber, in order to adjust or clean the target is undesirable for the reasons explained above.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a cathode arc source that can be used continuously or at least for longer periods of time than prior art sources. A further object of the invention is to provide a cathode arc source that can maintain its cathode target in suitable condition for obtaining plasma therefrom.
Accordingly, a first aspect of the invention provides apparatus for feeding a target into a chamber of a cathode arc source, comprising:
support structure for attachment to or integration with the cathode arc source;
a cathode station for receiving a target in electrical connection with an arc power supply, wherein the cathode station is mounted for movement on the support structure; and
means for movement of the cathode station relative to the chamber so as to feed the target into the chamber.
This apparatus confers the advantage that when coupled with a cathode arc source, operation of the source can be continued for a longer time than hitherto possible—as consumed target can be replaced in situ with target fed into the chamber without breaking vacuum.
The cathode station is conveniently adapted to be mounted in an initial position, distal from the chamber and to receive a target thereon and is further adapted to be advanced in a substantially linear path towards the chamber so as to advance the target into the chamber. It is preferable that movement of the target into the chamber of a cathode arc source can be accurately and finely controlled—the rate of erosion of the target may only be at a very low level—and suitable apparatus can feed the target at very small increments, preferably as little as 0.05 mm or 0.1 mm at a time for a graphite target. Though as will be appreciated, rate of erosion can vary with target material and other increments will be appropriate for targets made of other materials. Apparatus of the invention is suitably adapted for feeding the target into the chamber at a rate of between 0.05 mm per second and 10 mm per second.
In an embodiment of the invention, a pinion is mounted on the cathode station and engages with a rack attached to the chamber or attached to the support structure and wherein action of the pinion on the rack moves the cathode station towards or away from the chamber. The pinion is optionally turned by a handle or lever projecting from the apparatus and accessible to an operator. It is further optional for a ratchet mechanism to be incorporated into the apparatus so that movement of the target into the chamber can be in one direction only until the ratchet is released, for example for replacement of a used target. The arrangement could also be reversed, with the pinion on the chamber or the support structure.
Movement of the cathode station is alternatively achieved via an electric motor, optionally controlled by arc power supply circuitry. Monitoring means associated with the arc power supply may be used to determine the rate of deposition and can be used to trigger advancement of the target into the chamber at an appropriate rate or time.
A sealing member is optionally provided, adapted to provide a seal between the edge of the target and the chamber whilst the target is fed into the chamber, to maintain vacuum in the chamber. A further option is to provide a housing surrounding the cathode station and adapted for sealing engagement with the chamber of the cathode arc source. The housing may be adapted to receive water for cooling of the cathode station or the target or both. The housing may also comprise a feedthrough for an electrical supply to the cathode station, or a feedthrough for a handle that enables manual movement of the cathode station by an external operator.
A particular housing is adapted to be evacuated, such as a vacuum bellows, as described in a specific embodiment of the invention below.
For operation of the cathode arc source there must be electrical connection with the target, either indirectly such as via the cathode station or directly with the target itself. In an embodiment of the invention, power supply to the target is via one or a plurality of electrical brushes with which the target is in electrical engagement whilst being fed into the chamber. As the target moves past the brushes electrical contact is sufficient for an arc to be struck and maintained between the anode and the target. Preferably, a plurality of brushes are provided, located around the target. The target can be circular in cross-section, thus in a particular embodiment of the invention the apparatus comprises a plurality of brushes substantially evenly spaced around the circumference of the target. This arrangement is of advantage in that brushes can maintain electrical contact whilst allowing the target smoothly to be fed into the chamber.
In a second aspect, the invention provides a method of depositing a coating of positive ions on a substrate, by deposition of plasma obtained from an arc between an anode and a cathode target in a vacuum chamber, comprising striking an arc between the anode and the target and feeding the target into the chamber without breaking vacuum in the chamber.
A preferred method according to the invention comprises striking the arc, stopping the arc, feeding the target into the chamber and thereafter restriking the arc. Thus as target material is consumed so an operator can continually introduce fresh target into the chamber and in the correct location for striking of the arc thereon. Advantageously, it thus becomes less frequently necessary to open the chamber to replace a spent or disfigured target.
In another embodiment of the invention the method comprises striking the arc, feeding the target into the chamber and maintaining the arc whilst the target is being fed into the chamber. In this way operation of the cathode arc and deposition of coatings therewith is not periodically stopped and started. As the
Shi Xu
Tan Hong Siang
Tay Beng Kang
Filplas Vacuum Technology PTE Ltd
Philogene Haissa
Sterne Kessler Goldstein & Fox P.L.L.C.
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