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  Sputtering devices and methodsUSPTO Application #: 20060207871Title: Sputtering devices and methods Abstract: The invention provides devices and methods for depositing uniform coatings using cylindrical magnetron sputtering. The devices and methods of the invention are useful in depositing coatings on non-cylindrical workpiece surfaces. An assembly of electromagnets located within the bore of a hollow cylindrical emitter is used to form a magnetic field exterior to and near the exterior surface of the emitter. The magnet assembly configuration is selected to provide a magnetic field configuration compatible with the workpiece surface contour. The electromagnet assembly may be a plurality of magnet units, each unit having at least one electromagnet. The magnetic field strength from each magnet unit is separately and electrically adjustable. Each electromagnet in the assembly has a coil of electrically conducting material surrounding a specially shaped core of magnetic material. (end of abstract) Agent: Greenlee Winner And Sullivan P C - Boulder, CO, US Inventors: Gennady Yumshtyk, Dmitri Ivanov USPTO Applicaton #: 20060207871 - Class: 204192100 (USPTO) Related Patent Categories: Chemistry: Electrical And Wave Energy, Non-distilling Bottoms Treatment, Coating, Forming Or Etching By Sputtering The Patent Description & Claims data below is from USPTO Patent Application 20060207871. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND OF THE INVENTION [0001] The present invention relates to methods and devices for applying coatings by cylindrical magnetron sputtering, in particular devices and methods where a magnetic field is created by an assembly of electromagnets. [0002] Magnetron sputtering processes are classified as planar or cylindrical. The planar (circular, rectangular and triangular shaped) magnetron sputtering devices generally suffer from non-uniform erosion, with the area of maximum erosion in the shape of a racetrack centered around the magnet position, rendering the target unusable after use, even while relatively large amounts of useful target material still remain. Also, planar magnetrons often employ large magnet assemblies, which are not useful for creating films inside structures with hollow workpieces having annular cavities, such as narrow diameter pipes. [0003] Several different types of cylindrical magnetron sputtering devices have been developed, as disclosed and summarized by Thornton et al., "Cylindrical Magnetron Sputtering", 1978 Academic Press, Inc., pp. 75-113. Cylindrical magnetron sputtering devices are used to coat cylindrical workpieces, such as the inside surfaces of pipes. Basically, the target material in a cylindrical magnetron sputtering device is in the form of an elongated tube. [0004] U.S. Pat. No. 4,031,424, issued to Penfold, describes solenoid coil configurations used to provide a confining magnetic field around a hollow cathode having a cylindrical barrel and end flanges. In one configuration, the workpiece is placed inside the cathode and the solenoid coil(s) are placed outside the cathode. In another configuration, the workpiece is placed outside the cathode in a vacuum chamber. One solenoid coil winding is disposed about the outer wall of the vacuum chamber and another solenoid coil winding is disposed within the cathode. Both arrangements are stated to employ a magnetic field whose lines are generally parallel to the axis of the cathode barrel. Externally positioned solenoid coils are not useful for coating the surfaces of ferrous pipes since externally positioned coils magnetize the workpieces creating magnetic shields, and complicate the deposition process, especially when coating pipes with non-constant wall thickness or tapered inside diameter. [0005] U.S. Pat. No. 4,376,025 issued to Zega orients the magnetic flux lines circularly around the axis of the elongated rod-like target material, as opposed to the axial orientation used by Penfold. Zega describes a cylindrical magnetron device utilizing a tubular current-carrying anode disposed within a tubular target cathode. The disadvantage of this approach is that, while very efficient with small diameter targets, it becomes less efficient as the target diameter increases. Further disadvantages of this high current approach are the considerable additional power input needed for the large diameter/high electrical resistance target and practical limitations of the system to uniformly coat non-cylindrical, or tapered inside surfaces of elongated components. [0006] U.S. Pat. No. 4,407,713 issued to Zega describes a magnetron sputtering device which creates a magnetic field with an assembly of permanent magnets. The magnet assembly consists of a plurality of equiangularly spaced axially extending radially magnetized magnets arranged in such a manner that their flux lines form over the sputtering face a plurality of equiangularly spaced axially extending straight arch portions connected to each other by arcuate arch end-portions, whereby defining at least one closed-loop arch over the sputtering face. The magnetic assembly may be axially rotated relative to the target. The device is cumbersome for use in small diameter pipes and has little application for hollow workpieces having complex shapes. [0007] Alternative cylindrical sputtering devices are disclosed in U.S. Pat. No. 4,221,652 to Kuriyama, and in U.S. Pat. No. 4,179,351 to Hawton et al. In both devices, a cylindrical cathode comprising the material to be deposited is placed within a substantially cylindrical workpiece. Within the cylindrical cathode are one or more cylindrical magnets oriented symmetrically about the axis of the cylinder for generating a toroidal magnetic field. The cathode surface is located in close proximity of the magnet poles such that magnetic field lines penetrate the cathode and form a closed ring gap. Within the cylindrical cathode also exists a pipeline for introducing a coolant. The multiple permanent magnets produce multiple toroidal volumes or particle racetracks, in which the charged particles are concentrated. This results in multiple erosion zones, each zone being centered upon the center of a magnet, rather than in a single erosion zone, as would be obtained from a single magnet. U.S. Pat. No. 4,221,652 describes movement of a single magnet along the axis of the target to obtain uniformity in thickness of a metallic film deposited on a workpiece. [0008] The figures of JP Patent Publication No. 55-27627, corresponding to JP Patent 52095581 A, listing inventors Misumi, Takashi and Hosokawa, Naokichi also illustrate one or more magnets within a sputtering target. Movement of the magnet(s) within the target is indicated. [0009] U.S. Pat. Nos. 4,356,073 and 4,422,916, issued to McKelvey, describe rotatable magnetron sputtering apparatus where magnetic means are mounted within a tubular cathode. The magnets described are U-shaped permanent magnets. [0010] U.S. Pat. No. 4,904,362 issued to Gaertner et al. describes a cathode arrangement having an internal, cooled permanent magnet system. The permanent magnets inside the target are cut so that their end faces are at an angle of 45 degrees to 75 degrees to the longitudinal axis of the cathode arrangement and are magnetized so that their poles lie in the end faces. The magnets are disposed so like poles are adjacent. Rotation of the magnets causes rotation of the plasma zones. The surfaces to be sputtered are subjected to a mutual relative motion in the longitudinal direction of the cathode arrangement or carrier tube. The disadvantage of the apparatus described by Gaertner et al is use of magnets with constant, un-adjustable magnetic field and relatively complicated design of the permanent magnet assembly. [0011] U.S. Pat. No. 6,436,252 issued to Tzatzov et al. describes a cathode assembly for magnetron sputtering of a cylindrical workpiece which assembly includes a magnet package consisting of a plurality of spaced permanent magnets of alternating polarity. The magnets may be joined with ferromagnetic spacers. The magnet package is positioned on the inside of the cathode such that a driving force applied to the magnet package or to the cathode, or to both independently, imparts relative longitudinal movement between the magnet package and the cathode. [0012] In summary, there is a still a need for an device that can be used to provide uniform coatings on the inside surfaces of tubular components such as tapered pipes, and do so with flexibility to apply the desired levels of magnetic field to specific areas on the cathode that correspond to the specific irregular internal surface of the elongated workpiece. SUMMARY OF THE INVENTION [0013] The invention provides an emitter assembly for cylindrical magnetron sputtering which is useful in producing coatings at high deposition rates. The coatings of the invention, when applied to non-cylindrical workpieces, have improved uniformity compared to coatings applied with methods which do not compensate for variations in emitter to workpiece distance. The coatings produced by the methods of the invention can be used for a variety of purposes, including improving wear or corrosion resistance and rebuilding of worn-out parts. [0014] The coating can be sputtered onto either the interior or the exterior of a workpiece or concurrently sputtered onto both the interior and exterior surfaces of the workpiece. In an embodiment, the workpiece is elongate, having a greater length than width. The workpiece is external to the hollow cylindrical emitter and may be oriented vertically or horizontally. The emitter, also referred to herein as the target, is part of an emitter assembly. The emitter is elongate, having a greater length than width. The emitter assembly comprises a magnet assembly capable of providing a magnetic field external to the emitter and in the vicinity of the external surface of the emitter. The magnet assembly comprises a plurality of electromagnets. [0015] The invention provides an emitter assembly suited for sputter deposition of coatings on cylindrical and non-cylindrical workpiece surfaces. Examples of non-cylindrical workpiece surfaces, include, but are not limited to, tapered surfaces or surfaces having cavities. A workpiece surface which is non-cylindrical as a whole can have one or more sections which are cylindrical. For example, a tube may have an inner surface with a cylindrical portion connected to a tapered portion. [0016] In the present invention, the longitudinal axis of the workpiece is parallel to the longitudinal axis of the emitter. In this configuration, the distance between the cylindrical surface of the emitter and a non-cylindrical workpiece surface is not constant along the length of the workpiece. One way to improve the coating uniformity for such a surface is to adjust the strength of the magnetic field along the length of the emitter to compensate for differences in emitter-to-workpiece distance. For example, a stronger magnetic field can compensate for more distant workpiece surfaces. In general, the magnetic flux produced by the assembly is affected by the number of turns in each electromagnet coil, the current supplied to each coil, the polarity of each coil, the distance between the coils, and the core material. Each of these factors can be independently controlled to tailor the coating deposition to the workpiece surface. [0017] In an embodiment, the invention provides an emitter assembly comprising a magnetic assembly comprising a plurality of magnet units, each magnet unit comprising at least one electromagnet. The magnetic field from each magnet unit is separately and electrically adjustable. Electrical adjustment of the field from each magnet unit permits convenient adjustment of the magnetic field along the emitter. In comparison, to adjust the magnetic field along the emitter of a magnet assembly using permanent magnets either magnets must be replaced and/or the magnet configuration modified. The ability to electrically adjust the field of separate magnet units allows faster optimization of coating conditions for a given workpiece shape. The emitter assemblies of the present invention can also allow convenient reconfiguration of the magnet assembly for different workpiece shapes or dimensions. The magnet assemblies of the present invention are also capable of providing a stronger magnetic field than a permanent magnet assembly, especially for an emitter with a relatively small inner diameter. [0018] In this embodiment, the invention provides an emitter assembly for magnetron sputtering a coating onto a workpiece surface, the emitter assembly comprising: [0019] a. an elongate cylindrical emitter having a longitudinal axis, the emitter being in the form of a tube having an inner bore; [0020] b. a magnet assembly capable of providing a magnetic field exterior to the emitter, the magnet assembly having two ends and being located within the inner bore of the emitter, the magnetic assembly comprising at least one magnet unit, the magnet unit comprising at least one electromagnet, where the number of magnet units and the number of electromagnets in each magnet unit is selected so that the magnet assembly comprises a plurality of electromagnets, and at least one nonmagnetic spacing connector between neighboring electromagnets; [0021] c. at least one adjustable source of electrical current, the number of current sources being equal to the number of magnet units, each current source being connected to a different magnet unit; and [0022] d. at least one nonmagnetic end connector at each end of the magnet assembly. [0023] In an embodiment, the emitter assembly of the invention contains an assembly of electromagnets whose longitudinal axes are aligned with that of the emitter. Each of the electromagnets in the assembly comprises an electrically-conductive coil and a specially-shaped magnetic core. The core of the electromagnet is "dumbbell"-shaped, with a central portion and two end portions whose maximum diameter is larger than that of the central portion. The coil is located around the central portion of the dumbbell. The magnetic flux generated by flow of current through the coil is transmitted to the two end portions of the dumbbell outside the coil. The electromagnets are spaced so that the magnetic cores are not in contact with each other. [0024] In an embodiment, the invention provides an emitter assembly for magnetron sputtering comprising: [0025] a. an elongate cylindrical emitter having a longitudinal axis, the emitter being in the form of a tube having an inner bore; [0026] b. a magnet assembly having two ends, the magnet assembly being located within the inner bore of the emitter, the magnet assembly comprising: [0027] a plurality of electromagnets, each electromagnet comprising an electrically conductive coil and a hollow core of magnetic material, the longitudinal axis of the coil and core lying along the longitudinal axis of the emitter and the core having a central portion around which the coil is located and two end portions, the maximum diameter of each end portion being equal to or greater than the outer diameter of the central portion. [0028] at least one nonmagnetic spacing connector between neighboring electromagnets; and [0029] c. at least one nonmagnetic end connector at both ends of the magnetic assembly. [0030] The invention also provides a method for applying a coating onto the interior surface of a hollow elongate workpiece. In this embodiment, the method comprises the steps of [0031] a. providing an emitter assembly of the present invention; [0032] b. positioning the emitter assembly within the workpiece so that the longitudinal axis of the emitter is coaxial with the longitudinal axis of the workpiece; [0033] c. providing a low pressure environment containing a sputtering gas exterior to the emitter and interior to the workpiece; [0034] d. creating a plasma field between the emitter and the workpiece; and [0035] e. creating a magnetic field around the emitter by flowing current through the electromagnets of the magnet assembly. [0036] The invention also provides a method for applying a coating onto the exterior surface of an elongate workpiece comprising the steps of: [0037] a. providing an emitter assembly of the present invention; [0038] b. placing the emitter assembly so that the longitudinal axis of the emitter is parallel to the longitudinal axis of the workpiece; [0039] c. providing a low pressure environment containing a sputtering gas exterior to the emitter and the workpiece; [0040] d. rotating the workpiece about its longitudinal axis; [0041] e. creating a plasma field between the emitter and the workpiece; and [0042] f. creating a magnetic field around the emitter by flowing current through the electromagnets of the magnet assembly. Continue reading... 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