Chemistry: electrical and wave energy – Apparatus – Coating – forming or etching by sputtering
Reexamination Certificate
2000-03-01
2001-11-13
McDonald, Rodney G. (Department: 1753)
Chemistry: electrical and wave energy
Apparatus
Coating, forming or etching by sputtering
C204S298070, C204S298110, C204S298260, C204S298270, C204S298280
Reexamination Certificate
active
06315877
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application is a U.S. National Stage Application of International Application No. PCT/DE98/02376, filed on Aug. 12, 1998, and claims priority under 35 U.S.C. §119 of German Application No. 197 38 234.7, filed on Sep. 2, 1997.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention concerns a device for the sputter application of hard material coatings at high temperatures. A preferred area of application is the coating with hard material of forming tools and Cutting tools by high-rate sputtering using magnetrons. More particularly, the invention concerns devices for coating temperatures of 400° C. to 800° C.
2. Description of Background and Relevant Information
It is generally known to coat workpieces, especially tools for the cutting of metals, and forming tools with hard, wear-resistant, protective coatings by means of physical vapor deposition (PVD). The most frequently employed PVD processes for these applications are vacuum arc evaporation and magnetron sputtering. Coatings of titanium nitride continue to enjoy the most widespread use (Sue, J. A.; Troue, H. H.; Friction and wear properties of titanium nitride coating in sliding contact with AISI 01 steel; Surf. Coat. Technol. no. 43/44 (1990) p. 709-720).
In addition, a large number of other coatings, such as nitrides, carbides, carbonitrides, and oxynitrides of the metals chromium, niobium, zirconium, titanium, etc., arc known as hard material coatings (DE 295 10 545; U.S. Pat. No. 4,169,913).
Moreover, extensive efforts are underway to use diamond-like carbon layers to achieve hard and wear-resistant coatings on workpieces (EP 0 503 822).
All these coatings applied by means of PVD are deposited at comparatively low temperatures, i.e., in the range between room temperature and approximately 400° C.
Known PVD devices, as they are used for coating by means of sputtering sources, have one or more magnetron sources for the coating material. The workpieces to be coated are held in fixtures, and rotate about one or more axes during the coating process. Adequate uniformity of the coating is ensured in this manner. The largest number of workpieces per coating process and the greatest uniformity of coating thickness are achieved when the workpieces are arranged on a rotating device in fixtures that are part of planetary drives and thus rotate about the primary axis of the planetary drive and also about their own axes. For economic reasons, the diameter of these fixtures is chosen to be as large as possible. Consequently, their diameter is approximately 30 to 40 percent of the diameter of the rotating device.
Arranged on the circumference of such PVD devices, outside the region of the rotating fixtures, are laminar heating devices. They customarily consist of heating elements that are embedded in stainless steel tubes and are electrically insulated therefrom. In order to ensure workpiece temperatures of 400° C. during coating, surface temperatures of the heating devices of at least 600 to 700° C. are necessary, and a noticeable portion, as a rule, 20 to 30 percent, of the circumference of the rotating device must be enclosed by the heating device. In this situation, it is unavoidable that a large portion of the heat output reaches the walls of the vacuum chamber. For this reason, the walls are equipped with water cooling. After the coating process is completed, the vacuum chamber is ventilated. The coated workpieces are removed from their fixtures and other workpieces to be coated are inserted. During this process, the rotating device can be disconnected from the drive elements and removed from the vacuum chamber as a unit. The heating devices always remain in the vacuum chamber. The shortest changeover times are achieved when a second rotating device filled with workpieces stands ready and is loaded into the vacuum chamber.
The disadvantages of such devices arc that the power density of the heating elements cannot be increased sufficiently for a workpiece temperature of 800° C. to be reached. In other words, they cannot be used at temperatures above approximately 500° C. Furthermore, even in the temperature ranges up to 500° C., the temperature differences among the workpieces as well as within each individual workpiece increase with increasing temperature. At the same time, the temperature of the individual workpiece is subject to large variations over time. Thus, supercritical internal stresses arise in the deposited coatings, which lead to flaking of the coatings.
The fact that the fixtures, the rotating device, the heating devices, and all internal surfaces of the vacuum chamber are coated as well the workpieces, leads to the further major disadvantage that coating particles are released from these surfaces. These coating particles, known as flakes, some of which are electrically charged, lead to substantial problems since they adversely affect the quality of hard material coatings deposited by sputtering to such a degree that the service life of workpieces coated in this manner is very short.
Lastly, the heat output available to heat the workpieces is reduced by the layers precipitating on the heating devices, and the heat losses toward the walls of the vacuum chamber take on unacceptably high values. Cleaning of the device, especially of the heating devices, involves difficulties.
SUMMARY OF THE INVENTION
The invention therefore provides a device for the sputter application of hard material coatings at high temperatures of up to 800° C. Using the device, it should be possible to coat parts, especially workpieces, such that large temperature gradients do not arise either between parts or within the individual parts, in order to be able to deposit high-quality coatings by sputtering. The intent is to prevent internal stresses within the coating and to minimize the number of defects. Furthermore, the device is intended to limit the generation of interfering particles, especially flakes. The device is also intended to facilitate the pretreatment required for the overall process of sputter application. The times for loading and unloading of parts should be short in order to increase productivity. The cost of cleaning the device should also be reduced.
The invention provides for a device for the sputter application of hard material coatings, consisting of an exhaustible vacuum chamber, at least one sputtering source with at least one target of sputtering material or the components thereof, a mechanism with several parts to be coated mounted in fixtures on planet gears that are movable by means of a planetary drive, a heating device, a reactive gas inlet, and movable screens to cover the sputtering sources, characterized in that the fixtures are surrounded by coaxially arranged screens, in that the heating device is arranged in the center of the planetary drive, in that the heating device, the screens and the planetary drive constitute an assembly that can be replaced to load and unload the parts, in that the screens have openings in the region of the outlet areas of the particles deposited by the sputtering sources, in that the screens are radially movable independently of one another such that they cover individual or all sputtering sources, in that shield plates that close off the sputtering region are arranged to be stationary above and below the parts to be coated, in that the diameter of the pitch circle of the planet wheels is at least ¾ of the diameter of the base plate, and in that the fixtures are arranged to be electrically insulated.
The device may be characterized in that the heating device consists of a carbon tube through which current passes. The device may be characterized in that the tube is structured by parting lines, preferably in a meander pattern. The device may be characterized in that the inner screen and the inner shield plates are made of a material with high roughness on their inner sides. The device may be characterized in that at least the outer screen and the outer shield plate have a highly reflective surface. The device may be
Fietzke Fred
Goedicke Klaus
Fraunhofer-Gesellschaft zur Foerdering der Angewandten Forschung
Greenblum & Bernstein P.L.C.
McDonald Rodney G.
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