SLOTTED CYLINDRICAL HOLLOW CATHODE/MAGNETRON SPUTTERING DEVICE
BACKGROUND OF THE INVENTION 5
1. Field of the Invention
This invention relates generally to electrode type glow discharge devices used in the field of thin film deposition and, more particularly, to an improved magnetron sputtering device that may be used for sputtering planar substrates in a continuous pass-by mode.
2. Description of Related Art
Sputtering is a well known technique for applying a thin film of material to a substrate. The process involves J5 placing a "target" comprised of or coated with the material to be sputtered into a chamber containing a low pressure gas. The material to be sputtered is ejected from the target by connecting the target as a cathode and creating a low pressure gas discharge between the 2Q target and a nearby anode. A negative voltage is applied to the cathode at a high current level so that gas ions bombard its surface with high energy and thereby eject (sputter) atoms that will deposit on the substrate. The process is self-sustaining because many of the incident 25 gas ions, rather than ejecting an atom of the material to be sputtered, create a shower of electrons that collide with neutral gas atoms and create even more gas ions.
The general concept of cathodic sputtering is set forth in great detail in U.S. Pat. No. 2,146,025, issued to 30 Penning on Feb. 7, 1939. After Penning, the advances in sputtering were few until the early sixties when, contrary to earlier thought, it was theoretically shown that sputtering was primarily due to momentum transfer between the incident ions and the target. This new 35 theory soon led to a variety of sputtering devices having different geometries and using magnetic fields of various shapes to direct and guide the gas discharge. Such devices are generally known as magnetron sputtering devices. 40
For example, U.S. Pat. No. 3,884,793, issued to Penfold et al. on May 20, 1975, discloses a magnetron sputtering device having either a solid or hollow cylindrical target and using a magnetic field that is parallel to the long axis of the cylindrical surface to maintain the gas 45 discharge near the surface of the target. Although the Penfold et al. device was an advancement in the field, its efficient use was limited to the sputtering of long cylindrical substrates such as wires or optical fibers.
Two other patents of interest, U.S. Pat. No. 50 3,616,450, issued to Clarke on Oct. 26, 1971, and U.S. Pat. No. 3,711,398 also issued to Clarke on Jan. 16,1973, relate to magnetron sputtering devices having target and magnetic field geometries that make them best suited for the sputtering of silicon wafers and the like. 55 The devices disclosed by Clarke use a cylindrical cathode with a plurality of permanent magnets disposed circumferentially around the cathode. The magnetic field of the Clarke devices pierce the cylindrical cathode in such a way that a toroidal gas discharge occurs 60 along a portion of the cathode's interior. The Clarke devices are undesirable because the size and shape of the work pieces that may be sputtered are limited by the fact that sputtered atoms can only escape from the end • of the cylinder. This spot-source mode of operation 65 limits the device to stationary or batch-type usages rather than continuous pass-by usage. Moreover, the cathode must be replaced before it is completely used
up because the gas discharge occurs along a limited portion of its surface.
At least two inventors approached the cathode geometry problem with planar substrates in mind. In particular, U.S. Pat. No. 3,878,085, issued to Corbani on Apr. 15, 1975, and U.S. Pat. No. 4,166,018, issued to Chapin on Aug. 28, 1979, both disclose sputtering devices that use a substantially planar cathode along with magnetic flux lines that bisect the planar cathode. In the preferred embodiments of both inventors, the magnetic flux lines are created so as to define a "race track" like tunnel on the surface of the cathode. The Corbani/Chapin devices are very suited to coating planar substrates. However, like the Clarke devices, the cathodemagnetic field geometry is such that the cathode wears unevenly beneath the magnetic "race track."
It was the problem of uneven cathode erosion that led to U.S. Pat. Nos. 4,356,073 and 4,422,916, both issued to McKelvey on Oct. 26, 1982 and Dec. 27, 1983, respectively. McKelvey, like Corbani and Chapin, uses a magnetic field that bisects the cathode in order to maintain the glow discharge on the surface of the cathode. However, McKelvey used a cylindrical cathode rather than a planar cathode. McKelvey's solution to uneven erosion is to mechanically rotate the cylindrical cathode around a plurality of permanent magnets arranged longitudinally within the cathode. Although the McKelvey device solves the problem of uneven cathode erosion, it leads to further problems. Specifically, it requires additional drive components that are both costly and, like all mechanical things, prone to breaking down. Minimizing mechanical down time is particularly important where the sputtering device forms part of an assembly line, such as a mill-type environment architectural glass or magnetic media.
SUMMARY OF THE INVENTION
The present invention is directed towards a new and different magnetron sputtering device that is suitable for depositing a thin film of sputtered material onto a substantially planar substrate. Unlike the prior art devices, the present invention provides such a magnetron sputtering device with a cathode that wears evenly during operation and without requiring any moving parts.
According to the invention, the magnetron sputtering device is comprised of a hollow longitudinal cathode means that is either made from or has its interior wall coated with the material to be sputtered. A longitudinal wall of said cathode means defines an elongated hollow central portion in which sputtering may occur and further defines a longitudinal aperture from which sputtered material may exit. An anode is placed in proximity of the cathode and a power supply is used to apply a negative potential to the cathode in order to initiate and maintain a glow discharge between the cathode and the anode. A magnetic means is used to provide magnetic flux lines that are substantially parallel to the longitudinal axis of the cathode and contiguous with the interior wall. The magnetic flux lines ensure that the glow discharge occurs near and along all portions of the cathode's interior wall such that high current densities may be achieved and so that even wear of the cathode surface occurs. A first portion of the sputtered material will escape from the longitudinal slot and be available for coating a substantially planar work piece that is moved by the slot. A second portion of the sputtered
material will recollect on the interior of the cathode and again be available for sputtering.
These and other benefits of the invention will be made more apparent from the following detailed description of the preferred embodiment taken together 5 with the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an axial cross-section of a preferred magnetron sputtering device according to the present inven- 10 tion;
FIG. 2 is a radial cross-section of the device of FIG.
l;
FIG. 3 is a diagrammatic elevational end view of the device of FIGS. 1 and 2 positioned within a vacuum 15 chamber 100 and below a moving planar substrate 90 to be coated;
FIGS. 4a, 4b, and 4c are a top view, a sectional side view, and an end view, respectively, of a cylindrical cathode member 20 and cathode wings 25 according to 20 the present invention;
FIGS. 5a and Sb are a top view and a sectional side view, respectively, of a flange member 70 according to the present invention;
FIGS. 6a, 6b, and 6c are a top view, a side view, and 25 a sectional end view, respectively, of an insulator 60 according to the present invention; and
FIGS, la, lb, and 7c are a top view, a side view, and an end view, respectively, of a water jacket 30 according to the present invention. 30
DESCRIPTION OF THE PREFERRED
EMBODIMENT
The following description is provided to enable any person skilled in the art to make and use the invention 35 and sets forth the best modes contemplated by the inventor of carrying out his invention. Various modifications, however, will remain readily apparent to those skilled in the art, since the generic principles of the present invention have been defined herein specifically 40 to provide a slotted cathode magnetron sputtering device.
FIG. 3 is a schematic cross-sectional end view of a vacuum chamber 100 having a magnetron sputtering device 10 according to the present invention mounted 45 to a support flange 102 carried by the chamber 100. A planar substrate 90 is placed adjacent to the magnetron sputtering device 10 in order to coat the substrate 90 with sputtered atoms 12 that are emitted from a slot in the side of the magnetron sputtering device. The sub- 50 strate 90 may be stationary or, as represented by an arrow in FIG. 3, the substrate 90 may be moved'relative to the magnetron sputtering device in order to coat a larger area. The actual construction of the preferred embodiment is best understood with reference to FIGS. 55 1 and 2, and in particular, with reference to component FIGS. 4 through 7.
A preferred magnetron sputtering device 10 is comprised of a cylindrical cathode member 20 having a wall configuration that defines a sputtering cavity 22 and a 60 cathode slot 26. As is well known in the prior art, the cathode member 20 is either constructed of or coated with at least one material to be sputtered. Where a metal is to be sputtered, the device is generally operated with DC current as known in the art. Alternatively, RF 65 energy may be used when a nonmetal is to be sputtered.
In the preferred embodiment, the cylindrical cathode member 20 is removably attached to a pair of annular
cathode wings 25, one cathode wing 25 being threaded into each end of the cylindrical cathode member 20. The annular cathode wings 25 combine with the cylindrical cathode member 20 to define a hollow flanged cathode similar to that disclosed in U.S. Pat. No. 3,884,793 issued to Alan Penfold and John Thornton on May 20, 1975, the disclosure of which is incorporated by reference as if fully set forth herein. This novel, multi-component construction of a hollow flanged cathode provides a cathode target (cathode member 20) that may be cost effectively manufactured and easily replaced.
A pair of anodes 40 are positioned near the cathode wings 25 and on either side of the cathode member 20. In order to provide a continuous circuit for maintenance of a glow discharge, the anodes 40 include end portions 46 that are exposed to the sputtering cavity 22 through the annular cathode wings 25. The anodes 40 are releasably fastened to the cylindrical cathode member 20 with clamps 41 that engage an anode shoulder 43 and an annular slot 23 defined on each end of the cathode member 20. A pair of annular insulators 44 are disposed between the cathode member 20 and each anode 40 to prevent direct electrical contact therebetween and a pair of O-rings 42 are used to seal anodes 40 against the cathode member 20. It is understood that the exact interrelationship between the anodes 40 and the hollow flanged cathode defined by the cathode member 20 and the cathode wings 25 may be other than as defined herein and, since U.S. Pat. No. 3,884,793 sets forth such relationship in great detail, the herein description has been simplified.
As suggested by FIG. 3, a slotted flange member 70 is provided for mounting the sputtering device 10 to a support flange 102 (mounting means not shown). The flange member 70 is preferably constructed of aluminum or stainless steel. Referring to FIGS. 1 and 2, the flange member 70 includes an upper plate 71 and a lip 77 that extends downwardly therefrom. The lip 77 defines a flange slot 76 that is substantially inline with the cathode slot 26 when the sputtering device 10 is assembled. An O-ring 74 is provided to make a good seal around the periphery of the flange slot 76 and between the exterior of the support flange 102 and the upper surface of the upper plate 71.
A slotted insulator 60 is connected to the slotted flange member 70 at the underside of the flange plate 71 with fasteners 75. The cathode member 20 itself is then connected to the insulator 60 with fasteners 65. As shown in FIG. 2, the insulator 60 includes a slot 68 through which the lip 77 of the flange member 70 may extend. In order to isolate the cathode slot 26 from a water jacket 30 (described further herein) carried by the insulator 60, the insulator 60 includes a channel 63 along a surface of the insulator 60 that surrounds cathode slot 26. A cathode slot O-ring 62 is placed in the channel 63 and then compressed against the cathode member around the perimeter of cathode slot 26 with the fasteners 65.
The cathode member 20 is encased within a water jacket 30 in order to provide the necessary cooling. The water jacket 30 should be comprised of a material that is a good electrical insulator such as ceramic, nylon, teflon, Delrin, or polyvinylchlpride (PVC).
The water jacket 30 is comprised of a mounting block 35 and a cylindrical member 37 and, like the insulator 60, is supported from the flange member 70 by the fasteners 75. In particular, the mounting block 35 has an
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