Patent Application
20060065524
The present invention relates to systems and methods for sputtering. In particular, but not by way of limitation, the present invention relates to non-bonded rotatable targets usable for sputtering.
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.
One problem with rotating magnetrons involves the target assembly, which includes the material being sputtered. Depending upon the application, target assemblies can be formed of several different materials. And these materials vary significantly in their behavior. Certain materials, for example, are subject to thermal expansion and cracking. Unfortunately, when a target assembly cracks, it often must be replaced, even though it still may have significant amounts of sputtering material left on it. And with certain target assemblies, nodules could form on them and again force premature replacement.
Premature replacement of target assemblies and any reduced performance in sputtering caused by damaged target assemblies results in significant extra costs to manufacturers and consumers. And although present targets and target assemblies are functional, they can be improved.
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.
In one exemplary embodiment, the present invention can include a rotatable sputtering target. This target includes a target backing tube having an exterior surface; a backing layer in contact with the exterior surface of the target backing tube, the backing layer being electrically conductive and thermally non-conductive; and a plurality of target cylinders located around the target backing tube and in contact with the backing layer.
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
The plasma is formed inside the vacuum chamber 115 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 target assemblies 105. 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.
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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.
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The target backing tube 205, in this embodiment, includes a thermally conductive tube and two stops (220, 225), one located on each end of the tube. Generally, one stop is fixed and the other is removable. Although in some embodiments, both stops are removable, and in other embodiments both stops are fixed. And in yet another embodiment, one of the stops is loaded with the tension of a spring to cause the cylindrical target portions 215 to be in close contact. With this set up, the cylindrical target portions 215 may expand due to the heat load caused by the sputtering process, but no gaps occur between the single cylindrical target portions 215. By this means, damage to the backing material 210 caused by the magnetron plasma is prevented. Furthermore, a potential sputtering of the backing material 210 out of a gap between the cylindrical target portions 215 will not occur and contamination will be prevented.
In another embodiment, the target backing tube 205 is constructed of a non-thermally-conductive material. A backing material 210 can be placed over the outside circumference of the target backing tube 205. The backing material 210 is generally electrically conductive and thermally non-conductive. The backing material 210 is often thermally non-conductive to reduce or eliminate the amount of contact cooling of the cylindrical target portions 215 caused by water flowing through the inside of the target backing tube 205. For many target materials, a reduction in contact cooling is important to prevent the target material from cracking and to resist the tendency for nodule formation.
The backing material 210 can include a fiber mesh (or paper composed of a material such as graphite), such as a graphite mesh, applied to the length of the target backing tube 205. The mesh could be secured to the backing tube 205 by a mechanical or chemical fastener. Alternatively, the mesh could be secured only by friction.
In another embodiment, the backing material 210 could be attached directly to the inside surface of the cylindrical target portions 215. For example, a graphite mesh could be attached to the inside surface of the cylindrical target portions 215. The rings could be joined by the mesh or the rings could remain separated by individual mesh portions.
Typical target material includes any ceramic, conductive, oxide targets, including, but not limited to, indium tin oxide (ITO), aluminum zinc oxide, etc. Other target materials are known to those of skill in the art. Similarly, the thermal and structural properties of these materials are known to those of skill in the art.
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One further advantage of note is that presently-known target assemblies bond the target material to the backing tube with indium solder or other alloy. This is costly, time consuming and has several drawbacks. For example, the solder material can flow out between the gaps of the target and therefore contaminate the sputtered film. Further, the solder in these old systems is not evenly distributed such that there are voids that create a large thermal gradient over a small area of the target and typically results in cracking. But the design of this implementation of the present invention reduces or eliminates these drawbacks.
This implementation of the cylindrical target portions 215 comes in at least two configurations: single cylinder and multiple-adjacent cylinders. The single cylinder embodiment includes a single cylinder that is roughly the length of the target backing tube. In other embodiments, however, the cylindrical target portions 215 are formed of several individual cylinders placed around the outside surface of the target backing tube 205. The use of cylindrical target portions 215 is advantageous because it prevents stress build up and prevents the target material from cracking.
These cylindrical target portions 215 are generally formed of the same material and have flat side edges so that they can be compressed together laterally and present a uniform outside surface for sputtering. Additionally, the flat side edges prevent gaps from opening between the cylindrical target portions 215 and help to assure that the current is evenly distributed across the entire target surface. Note that the side edges can be angled to improve the fit between the cylindrical target portions 215.
In another embodiment, the side edges of the cylindrical target portion 215 are provided with a contour in the shape of a tongue and groove, at which the tongue of one cylindrical target portion 215 mates with the groove of the adjacent cylindrical target portion 215. In this way, there will remain little to no direct gap that may allow the plasma to attack the target backing tube 205. Other similar configurations could also be used.
The cylindrical target portions 215 can be slipped onto the target backing tube 205 by removing one stop. Because some target materials are subject to thermal expansion, a gap can be left between the cylindrical target portions 215 and at least one of the stops (220, 225). This gap(s) helps prevent cracking of the cylindrical target portions 215 due to expansion. This gap could also be filled with a compressible material that engages the stop (220, 225) and one of the cylindrical target portions 215.
In one embodiment of the present invention, the backing material 210 is eliminated and the target material 215 is allowed to directly contact the target backing tube 205. The water flow through the target backing tube 205 can be reduced to minimize any contact cooling between the target backing tube 205 and the cylindrical target portions 215. For example, the water flow could be reduced to the point where the magnets operate at a temperature just below their Curie temperature. In other embodiments, a special coolant with a higher boiling point than water, such as oil, can be used.
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In conclusion, the present invention provides, among other things, non-bonded rotatable targets. 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.
