Note: Descriptions are shown in the official language in which they were submitted.
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Background of;the Invention
This invention relates generallv eo the art of magnetic
sputtering, and more parelcularly to the a~t of anode designs fcr
magnetlc sputtering.
U.S. Patent No. 4,166,018 to Chapin describes a sputtering
apparatus in which a magnetic field i9 formed adjacent a planar
sputtering surface, the field comprising arcbing llnes of flux over a
closed loop eroslon region on the sputtering surface. Chapln teaches
that the conf~guration of the anode is relatlvely unimportant, but it ls
preferred that the anode be of relatlvely small size compared to the :
cathode surface. In the illustrated embodimen~, the anode comprises a
bar of relatlvely small cross-section which extends around the cathode
spaced from its perimeter.
In prior art literature on magnetic sputtering, the design of
the anode system is typically either~ignored or dismissed as relatlvely
unimportan~t, However, it is disclosed iD U.S. Patent No. ~f~ 7~, 7Z~ to
Gillery et al that appropriate anode design is essentlal to attaining
very uniform sputeered films, particularly in reactlve sp~lttPring
processes, and most especially when depositing insulating layers, s~lch as
titanium oxide.
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_ummary of the Invention
The present invention involves an anode system designed
to provide a thickness gradient in a sputtered fil~ across and
along a substrate surface. The new anode system is particularly
well designed for use with an elongated rectangular cathode of the
type typically used in a scanning magentron sputtering coating
apparatus. The anode system may comprise a single anode, but
generally comprises two separate anode plates disposed on opposite
sides of the cathode or on opposite sides of the substrate. The
configuration of the anodes ls very inportant. The length of the
anode is determined by the pattern of coating desired. The width
of the anode is less important, but is preferably substantially
less than the length, since the effectiveness of the anode
diminshes with distance from the cathode. The thickness of the
anode is preferably =inimal. An elongated strip of metal of the
desired configuration provides a particularly suitable anode plate.
In a preferred embodiment of the present invention, anode
systems are shaped to provide coatings with uniform gradients of
thickness deposlted with either stationary or scanning cathodes.
This feature is of particular importance in the sputtering of
electrocnoductive materials, which, as a result, can be deposlted
as fllms with gradient conductivity.
Brief Description of the Drawin~
Figure 1 illustrates an elongated rectangular cathode 1
with a single elongated shaped anode 2 pnsitioned above the
substrate 3. The pattern of gradient coating obtained is shown on
the surface of substrate 3 with broken lines.
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Figure 2 illustrates an elongated rectangular cathode 1 with apair of elongated shaped anodes 2 positioned on opposite sides of the
cathode 1 above substrate 3. The pattern of gradient caating i5 shown on
the surface of substrate 3 with broken lines.
Detailed Description of the Preferred Embodiments
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In a typical commercially available magnetic sputtering coating
apparatus, the anode supplied consists of an elongated loop of copper
tubing disposed on one side of an elongated rectangular ca~hode. In
operation, this system deposits a coating of extremely poor uniformity.
For example, when sputtering a titanium oxide film from a titanium metal
cathode 40 inches (l meter) long and 6 inches (15 centimeters) wide
scanning over a distance of 24 inches (61 centimeters) at a distance o 3
inches (7.6 centimeters) from the substrate in an atmosphere of 13
percent oxygen in argon at an average current density of 0.0625 amps per
square inch (0.0097 amps per square centimeter), the thickness of the
coating varies by 30 percent. Typically, a thick band of coating is
formed along one edge of the substrate and bands of varying thickness are
formed in the center.
In the development of the present invention~ it was deduced
from a series of experiments that as electrons lPave the face of the
cathode and travel in the magnetic tunnel created by the magnetic field
developed by the sputtering apparatus, they begin to lose Qnergy and are
attracted to the anode. As a result, it was discovered, the shape of the
anode and its proximity to the maguetic tunnel tend to affect the curren~
flow along the cathode, thereby determine the rate o~ deposition of the
coating, and ultlmntely control the film thickness.
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The ne~ anode designs provide for the deposition of a
desired gradient film, and may comprise either a single anode or a
pair of anodes disposed on opposite sides of a cathode, or
positioned adjacent the substrate. The effective surfaces of the
anodes may be parallel with the sputtering surface of the cathode,
or tangentially spaced from the major dimension of the glo~
discharge area.
In one preferred embodiment of the present invention, a
pair of shaped anodes 2 is disposed on opposite sides of a
substrate as in Figure 2. The effective surfaces of the anodes
are the top surfaces which are parallel, in fact essentailly
coplanar, with the sputtering surface of the scanning cathode.
The anode plates are typically strips of copper metal, preferably
water-cooled. The length of the anodes is substantially equal to
the parallel dimension of the substrate surface on which the
thickest area of coating is to be deposited. The ~idth is less
important, since the effectiveness of the anode surface decreases
wlth distance from the catbode. The thickness of the anodes is
even less important, and may be minimal. Elongated strips of
metal, preferably copper, provide particlarly suit~ble anodes.
When the anode design described above is used in the
deposition of titanium oxide from a titanium metal cathode, the
effective surface6 of the andes tend to lose efficiency as they
become coated with an insulation layer of titanium oxide ~hich is
scattered back from the substrate surface olltQ the anode
surfaces. For this reason, a more preferred embodiment of the
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present invention is an anodes design wherein a pair of elongated
shaped anodes is disposed on opposite sides of an elongated
rectangular cathode. The anodes may be spaced laterally from the
cathode, but are preferably also vertically displaced, typically
by about l.S inches (about 3.8 centimeters). In this embodiment,
the upper surfaces of the anode are the effective sur~aces.
Although sputtered material will eventually be deposited on the
top surface of the anodes as well as the bottom surfaces, the
effective upper surfaces uill be coated with titanium oxide in a
more reduced, and-thus more conductive, state, and will therefore
not decrease in efficiency as quickly.
As here discribed, an asymmetrical anode design is
required in order to from a coating of gradient thickness.
Asymmetry with respect to both the major and minor axes of the
sputtering surface is preferred. Although the present invention
has been discussed in detail above with respect to a titanium
cathode, copper anodes and a scanning apparatus, various other
target materials, such as indium, may be used, as well as other
anode metals and configurations. Either scanning or stationary
cathodes may be used to produce gradient coatings. The present
invention will be ur~her understood from the description of the
specific examples which follow.
Example I
A stationary titanium cathodes with a sputtering surface
measuring 6 by 40 inches (15 by 102 centime~ s) ls spaced about 3
inches (about 7.6 centimeters) from a glass substrate having
approximately th same dimensions.
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A single copper anode shaped and positioned as
illustrated in Figure 1 is used in this example. The cathode is
sputtered at an average current density of 0.0625 a~ps per square
inch (0.0097 amps per square centimeter) ~or about S minutes in an
atmosphere of 13 percent oxygen in argon at a pressure of 6 x
Torr. The
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resultant titanium oxide coating has a thickness pattern as sho~m by the
dotted lines in Figure 1. The thlckest ~rea of coating in the smaller
ellipse has a thickness of about Z700 Angstroms. The thickness of the
coating gradiently decreases outwardly such that at the area depicted by
the larger ellipse, the coating has a thickness of about 2000 Angstroms.
The curved broken llnes represent coating arens having thicknesses of
about 1400 and 700 Angstroms respectively.
Example II
A stationary cathode is sputtered to coat a glass substrate
with titanium oxide as in Example I except that a pair of copper anodes
shaped and posi~ioned as in Figure 2 is employed. A titanium oxide
coating with a uniform thickness gradient is produced. The thickest
portion of the coating, as illustrated by the central ellipse in Figure
2, has a thickness of about 2700 Angstroms. The coating thickness
decreases gradually toward the perimeter of the substrate. In the area
shown by the curved lines in Figure 2, the coating has a thickness of
about 1400 Angstroms.
The above examples are offered only to illustrate the pxesent
invention. Other anode shapes, sizes and positions may be employed to
form coatings of other gradient thicknesses. While the examples above
employ a stationary cathode, a scanning cathode or moving substrate may
be employed to form coatings with bands of gradient thickness. Of
course, the cathode, anode and substrate may be comprised of a variety of
materials lnown in the art. The scope of the inventlon is defined by the
following claims.
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