Chemistry: electrical and wave energy – Apparatus – Vacuum arc discharge coating
Reexamination Certificate
2001-12-11
2004-05-18
Cantelmo, Gregg (Department: 1745)
Chemistry: electrical and wave energy
Apparatus
Vacuum arc discharge coating
Reexamination Certificate
active
06736949
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to deposition apparatus. Specifically, the invention relates to apparatus and processes for deposition of optical quality coatings such as: tetrahedral amorphous carbon (TAC); metal oxides, nitrides, hydrides, carbon-containing compounds; and other compounds and alloys of metals.
Various methods are known in the prior art for depositing thin-films on substrates. In the field of physical vapor deposition, with which the invention is concerned, these methods include various sputtering techniques such as RF or magnetron sputtering, and the use of filtered cathodic arc sources of positive ions.
U.S. Pat. No. 4,851,095 describes apparatus and process for magnetron sputtering to obtain thin coatings on a range of substrates. Magnetron sputtering can produce a broad beam of coating particles and is thus a suitable technique for the coating of large substrate areas. To date, the films produced by magnetron sputtering are not of sufficient quality in terms of hardness, uniformity and smoothness to be suitable for commercial production of coatings for optical equipment. U.S. Pat. No. 4,851,095 also describes a coating chamber that incorporates a rotatable drum on which is mounted substrates to be coated.
Deposition of coatings using a filtered cathodic arc source is also known in the art, and reviewed by P. J. Martin in Surface Engineering, Volume 9, (1993) No. 1, pages 51-57.
Filtered cathodic arcs known in the art are typically used for short periods of time, or in pulsed and non-continuous mode for coating individual substrates one at a time. The problems associated with commercial use of this technology have not been solved. Further, known filtered cathodic arc sources typically produce a plasma beam no more than 3 cm in diameter. This is not a suitable size for coating large substrate areas.
Neither known physical vapour deposition or chemical vapour deposition techniques have previously been considered suitable for use on a commercial scale.
There has thus been appreciated the need to be able to deposit high quality thin films on substrates in a commercial process using apparatus that can be used continuously for relatively long periods of time.
SUMMARY OF THE INVENTION
It is an object of the invention to provide deposition apparatus for commercial deposition of high quality thin films onto substrates. It is another object of the invention to provide deposition apparatus for deposition of high quality thin films onto large substrate areas. A further object of the invention is to provide deposition apparatus for applying multi-layer coatings onto substrates.
These objects are achieved at least in part by the combination of a coating chamber and a filtered cathodic arc source.
According to the invention there is provided apparatus for applying a coating of positive ions to a substrate comprising:
a vacuum chamber,
a filtered cathodic arc source providing a plasma beam containing the positive ions,
a substrate to be coated, and
a substrate holder,
wherein the substrate holder is adapted to move the substrate across the beam of positive ions thereby to coat the substrate with the positive ions.
In an embodiment of the invention, the apparatus comprises magnetic means for scanning the plasma beam over a coating area greater than the area of the plasma beam.
The invention thus enables a large area of substrate to be coated as the substrate is moved through the beam of positive ions generated by the filtered cathodic arc. This enables efficient commercial scale deposition of positive ions onto substrates. By scanning the plasma bean into a coating area of greater size than the area of the plasma beam emitted from the filtered cathodic arc, coating of substrate over an especially large surface area is enabled. Further, the coating beam is necessarily of lower density than the smaller area plasma beam prior to scanning. Therefore, the deposition rate of the scanned beam is lower than the deposition rate of an unscanned beam and deposition on the substrate occurs more slowly. This enables greater control over the depth of deposition on the substrate.
In an embodiment of the invention, the substrate holder is adapted for rotation of the substrate through the plasma beam. In a preferred embodiment, the substrate holder is a rotatable drum and the substrate is mounted on the inner or outer periphery of the drum.
In use of this embodiment immediately above described, one or a plurality of substrates are mounted on the drum periphery and by rotation of the drum while a plasma beam is generated from the filtered cathodic arc a layer of positive ions is deposited onto each substrate in turn as it passes through the plasma beam, which is preferably scanned into a coating beam. The rate of deposition of positive ions onto the substrates is conveniently monitored using techniques known in the art, for example using a crystal rate monitoring system.
In a particular embodiment of the invention the rate of deposition on the substrate is monitored and this deposition information is fed back into the magnetic beam scanning apparatus so as to control the rate of deposition on any particular area of the substrate.
In a further embodiment of the invention, scanning of the plasma beam occurs downstream of filtering of the plasma beam by the filtered cathodic arc source. In another embodiment of the invention the magnetic scanning means scans the plasma beam in a raster scan. The width of the raster is preferably at least 10 cm wide, more preferably at least 20 cm wide and most preferably at least 30 cm wide.
The apparatus of the invention uses a filtered cathodic arc source for continuous coating of one or a plurality of substrates with positive ions from a target at the cathode of the cathode arc source. This is made possible by the filtered cathodic arc source being suitable for continuous use without overheating. This can be achieved by the provision of a water-cooled anode and a water-cooled cathode in the filtered cathodic arc source, making the source suitable for continuous or long term use. Typically, for a filtered cathodic arc source, continuous use means use for a period of at least 3 minutes, but can also mean use until the target, located at the cathode and from which the positive ions in the coating beam are generated, is substantially consumed. As will be appreciated by a person of skill in the art, complete consumption of the target material is rare as contamination of the plasma beam by ions generated from the cathode material is preferably to be avoided; in practice the target is generally not allowed to be consumed beyond a point at which there is a risk of contaminating the plasma by arcing directly between cathode and anode.
A particularly preferred filtered cathodic arc source for use in the apparatus of the invention is described and claimed in a co-pending International patent application Publication No. WO 96/26531, which corresponds to U.S. Ser. No. 08/894,420, filed Nov. 21, 1997, now U.S. Pat. No. 6,031,239.
In a particularly preferred embodiment of the invention suitable for applying multi-layer coatings of positive ions to a substrate, the apparatus further comprises at least a second filtered cathodic arc source providing a plasma beam containing positive ions, and a substrate holder adapted to move the substrate across the beams from the respective filtered cathodic arc sources.
In use of an embodiment of the invention, a first filtered cathodic arc source is used to place a first coating layer on a substrate; subsequently, this first cathodic arc source is stopped and a second cathodic arc source is used to place a second layer of a different material onto the substrate. This technique is advantageously used to deposit multi-layer coatings onto optical elements. A multi-layer coating made using the invention comprises a first layer of tetrahedral amorphous carbon, a second layer of silicon dioxide, a third layer of tetrahedral amorphous carbon and a fourth layer of silicon dioxide. Another optical coating obtainable us
Flynn David Ian
Fulton Michael
Shi Xu
Tan Hong Siang
Tay Beng Kang
Cantelmo Gregg
Filplas Vacuum Technology Pte Ltd.
Kirschstein et al.
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