Chemistry: electrical and wave energy – Apparatus – Coating – forming or etching by sputtering
Reexamination Certificate
2001-02-12
2002-04-23
Nguyen, Nam (Department: 1753)
Chemistry: electrical and wave energy
Apparatus
Coating, forming or etching by sputtering
C204S298220
Reexamination Certificate
active
06375814
ABSTRACT:
The present invention relates to an improved rotating cathode magnetron suitable for sputtering or reactive sputtering of materials from a tubular cathode target onto a stationary or moving substrate as well as a method of operating the magnetron. The magnet assembly of the inventive magnetron is arranged in such a way that local variations in the plasma race-track are generated which may provide novel advantages to the sputtering process. In addition, the novel magnet assembly is particularly suitable for curvilinear arrangements.
TECHNICAL BACKGROUND
In standard non-reactive metallic sputter mode, sputtering with planar magnetrons is known. The most important inconvenience is the formation of a groove of erosion in the target material, whereby this groove, and the plasma generating it, are often referred to as a “race track”. The non-uniform erosion profile is inherently associated with the magnet configuration below the target. As a consequence, the target has to be replaced just before the erosion groove depth at any point equals the target thickness. Typically only 30% of the target material is consumed before the target has to be changed which makes it a very costly process because of labour costs, down time as well as the expense of target materials.
During reactive sputtering (i.e. the plasma contains one or more gases that will react with the target material) using planar magnetrons, additional problems of arcing and plasma instability are encountered. Both of these problems have been overcome by the introduction of cylindrical rotating target magnetrons. Firstly, with rotating target magnetrons no race track erosion profile (corresponding to the magnet configuration) is formed and the material consumption on the target can be up to 80%. Secondly, due to the nature of the rotating cathode, less problems and more stable processes are encountered during reactive sputter deposition. Nevertheless, large amounts of material are deposited on shields which are physically located between the target and the substrate to inhibit the deposition of target material on those locations where it is not desired. Therefore, regular cleaning and extensive precautions (e.g. water cooling) have to be foreseen on these shields to reduce the risk of flaking. Flakes of material from shields can contaminate the sputtered surface.
Coating of large substrates in a uniform way during a single passage (i.e. typical condition in glass and web coating), is one of the most critical processes. Control may be obtained by placing additional wedge shaped shields (introducing another source of contaminating particle generation) or by changing the strength of the magnetic field lines (using magnets with different magnetisation or at different distances from the target). The latter solution may introduce non-uniform wear and/or consumption of the target material.
Cylindrical magnetrons have some other disadvantages which are typical for their geometry. The magnets are mounted on a static bar which is located within the rotating cylindrical target tube. The width of the magnet configuration is kept small which means that the turns at the end are quite sharp. Known magnet assemblies do not allow optimal configuration of the magnets in an end turn which results in reduced plasma confinement and increased electron loss at both ends of the target. It is desirable to have the magnets as close as possible to the target tube in order to produce the highest magnetic field strength at the surface of the cathode. In addition, at both ends of the target tube, where the magnets (and the race track) form a U-bend, sore target material is removed. The top of the “U”—bend presents a length of the plasma race-track which remains at the same longitudinal position as the target rotates. This leaves a circular groove round the target tubes at both ends. Eventually, target life is limited by the depth of this groove as it is highly undesirable to deposit the underlying material of the tube onto the substrate.
Rotating cathode sputtering magnetrons with a stationary internal magnet assembly are known, e.g. from U.S. Pat. Nos. 4,422,916, 5,364,518 or WO 96/21750. In particular U.S. Pat. No. 5,364,518 and WO 96/21750 propose magnet assemblies which produce an elongate plasma “race-track” above the target which has a shape comprising a spaced apart pair of parallel straight lengths terminated at each end by end portions or “U” turns. U.S. Pat. No. 5,364,518 proposes controlling target erosion in the end portions by means of widening the track of the race-track in the end positions. As explained in WO 96/21750, the method according to U.S. Pat. No. 5,364,518 has the disadvantage that the wider track of the race-track in the end portions may result in instability of the plasma due to the reduced field strength and resulting electron loss caused by the wider spacing of the magnets. Instead, WO 97/21750 proposes to make the end portions of the race-track “pointed”, i.e. to elongate the end portions into an acute angle, e.g. triangular or to make them semi-elliptical or parabolic in form. The disadvantage of making the end portions pointed, in particular triangular in shape is that the radius at the point is very small. This results in a high loss of electrons as they attempt to navigate this tight bend. To achieve reduce electron loss it may be considered to increase the magnetic field in this position in order to bind the electrons more closely to the track. However, increasing the magnetic field increases the plasma density and hence, the target erosion. Further, although WO 97/21750 proposes sophisticated geometrical shapes for the end portions of the race-track, e.g. parabolic or semi-elliptic, the only disclosed method of producing such refined track geometries is the use of discrete sections of magnets, the so-called “lumped” magnet method. It is not possible to accurately tailor the race-track to a sophisticated geometric form such as a parabola by means of lumped magnets—the steps between the magnets generate a castellated appearance which bears little relationship to a smooth curve (see
FIG. 3
in the following).
U.S. Pat. No. 5,645,699 describes the use of anodes to influence the deposition rate onto the substrate during reactive sputtering. This known method starts from the assumption that there is inevitable loss of electrons in the turns at the end of the race-track.
The present invention has the object of providing a sputtering magnetron and a method of operating the same which provides improved control over sputtering performance.
A further object of the present invention is to provide a sputtering magnetron and a method of operating the same which provides improved uniformity of erosion at the ends of the target.
Still a further object of the present invention is to provide a sputtering magnetron and a method of operating the same which provides improved uniformity of deposition onto the substrate.
Another object of the present invention is to provide a sputtering magnetron and a method of operating the same which provides a plasma race-track with reduced loss of electrons in the end portions thereof.
Yet a further object of the present invention is to provide a sputtering magnetron and a method of operating the same which provides improved target utilisation while allowing novel and useful ways of altering the coating sputtered onto the substrate.
SUMMARY OF THE INVENTION
The present invention may provide a sputtering magnetron with a rotating cylindrical target and a stationary magnet assembly, said magnet assembly being adapted to produce an elongate plasma race-track on the surface of said target, said elongate race-track having substantially parallel tracks over a substantial portion of its length and being closed at each end by end portions, wherein the spacing between the tracks of said race-track is increased locally to materially effect sputtering onto a substrate.
The present invention also includes a method of operating a sputtering magnetron with a rotating cylindrical target and a stationary magnet assem
De Bosscher Wilmert
Lievens Hugo
Cantelmo Gregg
Musgrove Jack V.
Nguyen Nam
Sinvaco N.V.
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