Patent Application
20050224343
A portion of the disclosure of this patent document contains material that is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent disclosure as it appears in the Patent and Trademark Office patent files or records but otherwise reserves all copyright rights whatsoever.
The present invention relates to systems and methods for coating substances. In particular, but not by way of limitation, the present invention relates to systems and methods for sputtering material onto a substrate using a rotating magnetron system.
Glass is irreplaceable in a broad range of applications, such as window panes, automotive glazing, displays, and TV or computer monitor tubes. Glass possesses a unique combination of properties: it is transparent, dimensionally and chemically stable, highly scratch resistant, non-polluting, and environmentally beneficial. Nonetheless glass can be improved, particularly its optical and thermal properties
Vacuum coating is the technology of choice for adapting glass surfaces and other surfaces to suit specialized requirements or demanding applications. Vacuum coating is capable of depositing ultra-thin, uniform films on large-area substrates. Vacuum-coating technology is also the least polluting of current coating technologies. Notably, vacuum coating can be used to coat materials other than glass, including plastics and metal.
Common vacuum-coating systems sputter conductive and dielectric material from rotating magnetrons onto a substrate such as glass, plastic, or metal. Rotating magnetrons driven by direct current (DC) have been known for several years. And recently magnetrons driven by high-voltage alternating current (AC) have been introduced. These AC systems are advantageous but have been plagued by reliability and expense problems caused by the unique properties of a high-power AC system.
For example, high-power AC systems generate heat through a process known as inductive heating. This heat causes conventional bearings and seals in the vacuum-coating system to fail.
Inductive heating arises when an alternating current flows through a conductive material such as metal. The current generates an electromagnetic field that affects nearby and adjacent materials in two ways. First, magnetic materials develop a magnetic resistance to the fluctuating electromagnetic field. This resistance causes the materials to heat up. Second, the field causes electron flows (current) within conductive materials. The internal resistance to these current flows generates heat. Non-conductive materials do not heat because they have no free electrons to create the current flow.
Engineers have developed several designs to minimize the impact of inductive heating in high-power, AC-coating systems. These designs, however, have proven to be difficult to service and expensive to implement. Accordingly, a system and method are needed to address this and other shortfalls of present technology and to provide other new and innovative features.
Exemplary embodiments of the present invention that are shown in the drawings are summarized below. These and other embodiments are more fully described in the Detailed Description section. It is to be understood, however, that there is no intention to limit the invention to the forms described in this Summary of the Invention or in the Detailed Description. One skilled in the art can recognize that there are numerous modifications, equivalents, and alternative constructions that fall within the spirit and scope of the invention as expressed in the claims.
The present invention can provide a system and method for coating a substrate. One embodiment includes a high-power sputtering system with a power coupler configured to deliver power to a rotatable target. The power coupler is positioned to minimize the generation of inductive heating in bearings, seals, and/or rotary water unions. Other embodiments include liquid-metal electrical connectors, dry bearings designed to withstand the inductive heating associated with high-power electrical systems, and/or rotary unions.
As previously stated, the above-described embodiments and implementations are for illustration purposes only. Numerous other embodiments, implementations, and details of the invention are easily recognized by those of skill in the art from the following descriptions and claims.
Various objects and advantages and a more complete understanding of the present invention are apparent and more readily appreciated by reference to the following Detailed Description and to the appended claims when taken in conjunction with the accompanying Drawings wherein:
Referring now to the drawings, where like or similar elements are designated with identical reference numerals throughout the several views, and referring in particular to
In certain embodiments, the tubes are actually constructed of the target material rather than coated with it. For example, the tube can be constructed of titanium, which is also the target material. Accordingly, the term “tube” can refer to a tube covered with target material or a tube constructed partially or entirely of the target material.
The plasma is formed by exciting a gas that is introduced into the vacuum chamber 115 at an inlet 125 and removed through an outlet 130. The sputtering effect is focused using a stationary magnet system 135 mounted inside the rotating tubes. An exemplary system is described in Japanese Laid-Open Patent Application 6-17247 (“Haranou”) entitled High-efficiency alternating-current magnetron sputtering device, assigned to Asahi Glass.
Referring now to
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Seals 187 are used to maintain the pressure differential between the outside world and the inside of the vacuum chamber 115. Traditionally, these seals have been ferro-fluidic seals, which are costly and difficult to maintain. In particular, the ferro-fluid in the seals is subject to inductive heating in high-power AC systems. To prevent the seals from failing, they often require water cooling and high-temperature ferro-fluid—both of which add significant complexity and expense to the seal.
The bearings 230 in the bearing and seal assembly 205 are subjected to the inductive heating effects in a high-power AC system. To prevent overheating and failure, the bearings 205 can be made of a non-metallic material such as ceramic. Ceramic bearings, however, are typically expensive and require a significant lead time to acquire. To limit the costs, bearings with metallic races and ceramic balls can be used. These hybrid bearings generally require cooling of the races. In the present invention, the cooling is provided by the water supply system 220.
In an alternate embodiment, high-temperature metallic bearings that run dry can be used instead of ceramic bearings. These metallic bearings heat like ordinary bearings but do not lose lubricant at high temperatures. One such bearing is constructed of a cobalt alloy known as Mp35N and is sold by Impact Bearings of Capo Beach, Calif. This bearing is presently rated to operate at 520 C and is considerably cheaper than a ceramic bearing. Another metallic bearing that can be used in the present invention is a standard steel bearing possibly coated with Molydisulfide or TiN. These bearings are presently rated to operate at 300 C.
Referring again to
Referring now to
The seals in this embodiment would be subject to inductive heating. Accordingly, conductive components would need to be minimized or eliminated.
Referring now to
The water inlet 290 is coupled to the inner shaft through connector 305. This connector 305 can be profiled to prevent it from rotating with the outer shaft 200. It can also include a groove for an O-ring 310 and a slot 315 for a key or set screw.
The outer shaft 200 is connected to the flange assembly 330 by a quick coupler, bolts or other connector. When the quick coupler, for example, is disengaged, the rotary union 285 can be disengaged from the outer shaft 200 and the inner shaft (not shown) so that the tube 195 can be quickly replaced.
Because the outer shaft 200 rotates, the flange assembly 330 is configured to rotate on bearings 335. And to prevent water from escaping from the flange assembly 330, a face seal 340 is used to form a water-tight connection. The face seal 340 can be formed of silicon carbide. An exemplary face seal is manufactured by Garlock Sealing Technologies of Palmyra, N.Y.
In certain embodiments, a lip seal can be used instead of a face seal. Lip seals, however, are highly susceptible to particles and debris. If a particle gets caught between the lip (rubber) and the shaft it will both wear into the shaft and will destroy the rubber lip—leading to leaks and a premature shaft replacement. To prevent this type of damage, lip seals are often combined with water filtration systems down to 50 micron. This filtration requires significant expense, including monthly maintenance to clean or change the filters.
The bearings 335, seals 340, inlet 290, and return 320 are housed inside a stainless steel housing 345. This housing 345, which can be formed of other materials, is encased in an electrically and/or thermally insulating casing 350 made of, for example, Delrin, Teflon, and/or plastic. This casing prevents condensation, thereby dramatically reducing the risk of direct electrical shock and electrical shorts. Condensation and leaks are a problem with traditional rotary-union designs. Some manufacturers drain off any excess water and others provide leak detection hardware to address the problem.
This connector 210 includes a plurality of brushes 355 located inside an outer housing 360 that is coated or covered with a non-conductive material 365. The brushes 355 can be formed of a low-resistance material such as silver graphite. Exemplary brushes are manufactured by Advance Carbon Products of Hayward, Calif. The brushes 350 engage the rotating shaft 200 and transfer power from the outer housing 360 to the shaft 200. Power is delivered to the outer housing 360 through the water inlet 370 and/or the water return 375, which are generally formed of copper.
The water inlet 370 and water return 375 circulate water through the outer housing 360. The water cools the outer housing 360 and the brushes 355. By keeping the brushes 355 cool, the life of the connector 210 is extended.
In one embodiment, the outer housing 360 is supported by an insulated support structure 380. The support structure 380 is coated with a non-conducting material to prevent arcing. Alternatively, the support structure 380 can be formed of a non-conductive material. The support member 380 and the outer housing 360 are connected through a seal assembly 385.
In conclusion, the present invention provides, among other things, a system and method for constructing and operating magnetron systems. Those skilled in the art can readily recognize that numerous variations and substitutions may be made in the invention, its use and its configuration to achieve substantially the same results as achieved by the embodiments described herein. Accordingly, there is no intention to limit the invention to the disclosed exemplary forms. Many variations, modifications and alternative constructions fall within the scope and spirit of the disclosed invention as expressed in the claims.
