Note: Descriptions are shown in the official language in which they were submitted.
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Back round of the Invention
g
Thls lnventlon relates generally to the art of magnetic
~putterlng, ant more partlcularly to the art of anode deslgns for
magnetlc sputterlng.
U.S. Patent No. 4,166,018 to Chapln descrlbes a sputtering
apparatu6 ln whlch a magnetlc fleld is formet ad~acent a planar
sputterlng surface, the flelt comprlslng archlng lines of flux over a
closet loop ero~ion reglon on the sputtering surface. Chapin teaches
that the configuratlon of the anode 18 relatlvely unlmportant, but lt ls
preferred that the snote be of relatlvely small slze comparet to the
cathote surface. In the lllustratet embotlment, the anode comprlses a
bar of relatlvely small cross-sectlon whlch extends around the cathode
spacet from lts perlmeter.
In prlor art llterature on magnetlc sputterlng, the deslgn of
the anode ~ystem 18 typically elther lgnored or tlsmlsset as relatlvely
unlmportant. However, lt 18 tlscloset ln U.S. Patent No. ~,~ to
Glllery et al that approprlate anote deslgn is essential to attaining
i very unlform sputtered fllms, particularly in reactive sputtering
processes, ant most especially when depositing insulating layers, such as
tltanlum oxlte.
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Here described ls an improved anode system utillzing a metal mesh
rather than a metal plate as the anode. Because the mesh design allows free
flow of the reactive atmosphere in the sputtering chamber, the mesh anode may
be oriented vertically instead of horizontally. The new anode system is
particularly well designed for use with an elongated rectangular cathode of
the type typically used in a scanning magnetron sputtering coating apparatus.
The anode system may comprise a single anode, but generally comprises two
separate anode mesh structures disposed on opposite sides of the cathode or on
opposite sides of the substrate. The configuration, dimensions and placement
of the anodes are very important. For a uniform thickness coating, each anode
sbould be at least substantially the same length as the dimenslon which it
parallels of the substrate to be coated, typically about the same length as
the cathode. For a gradient thickness coating, the length and width of the
anote i8 determined by the pattern of coating desired. The thickness of the
anode i9 preferably minimal. As expanded metal mesh of the desired
configuration provides a particularly suitable anode structure.
In a preferred embodiment of the present invention, an expanded metal
mesh anode system is positioned along the cathode oriented with the effective
surace of the anote perpendicular to the sputtering surface of the cathode
and the surfsce of the substrate to be coated. In addition to permitting
vertical orientat~on of the anode, the new metal mesh anode design reduces or
eliminates the need for cooling of the anode.
In accordance with the invention, there is provided in an apparatus
for coating a substrate compr,ising a
cathode havlng a substantially planar surface consisting of a material to
be sputtered, magnet means for produclng a magnetlc ficlt havlng llnes of
flux wlllch extend ln a curve from sald sputterlng surface and return
thereto to form a magnetlc tunnel over a closet loop erosion region on
sald 6putterlng surface, an anode positlonet to produce an acceleratlng
electric fleld ad~acent sald sputterlng surface for produclng a glow
dlscharge conflned by sald magnetlc fleld to the reglon adjacent sald
6putterlng surface and wlthln said magnetlc tunnel, and means for
connectlng sald cathode and sald anode to a source of electrlcal
potentlal, the lmprovement wheroin said anode comprises a metal
me~h otructure spaced feom the ma~or dlmenslon of &ald magnetlc tunnel
out~lde the zone of glow dlscharge conflnement
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Brlef Description of the Drawing
Figure 1 lllustrates an elongated rectangular cathode 1 with a
pair of elongated mesh anodes 2 positioned on opposite sides of the
cathode 1, and oriented with the effective surfaces of the anodes
perpendicular to the sputtering surface of the cathode 1.
Detailed Description of the Preferred Embodiments
In a typical co~merclally available magnetic sputtering coating
apparatus, the anode supplled consists of an elongated loop of copper
tubing di~posed on one slde of an elongated rectangulas cathode. In
operatlon, this system deposits a coating of extremely poor uniformity.
For example, when sputterlng a titanium oxide film from a titanium metal
cathote 40 inches (1 meter) long and 6 inches (15 centlmeters) wlde
scanning over a distance of 24 inches (61 centimeters) at a dlstance of 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 2mps pe~ square centimeter), the thickness of the
coatlng varies by 30 percent. Typically, a thick band of coating is
formed along one edge of the substrate and bands of varying thickness are
formet in the center.
In the development leading to the present invention, it was deduced
from a series of experiments that as electrons leave the face of the
cathode and travel in the magnetic tunnel created by the magnetlc field
developed by the sputtering apparatus, they begin to lose energy and are
attracted to the anode. As a result, it was discovered, the shape of the
anode and its proxlmity to the magnetic tunnel tend to affect the current
flow along the cathode, thereby determine the rate of deposition of the
coating, and ultimately control the film thickness.
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Metal mesh anode designs en~bodying the presënt invention oriented
vertically in relation to a horizontal cathode provide uniform current
flow along the cathode, which promotes a unlform deposi~ion rate, which
results in a uniorm fllm. Symmetrlcal metal mesh anode designs for
depo~iting uni~orm films embodying the invention
comprise a pair of anodes dlsposed on opposite sides of a cathode,
whereln the ma~or dimension (length) of the anodes is substantially equal
to the ma~or dimension (length) of the cathode, and the spaclng between
the cathode and each anode i8 uniform along its length, The effective
1 surfaces of the anodes are perpendicular to the sputtering surface of
the cathode.
In one preferred embodlment of the present invention, a pair of
elongated rectangular anodes 2 is disposed on opposite sides of an
elongated rectangular cathode 1 as in Figure 1. The anodes typically
comprlse an expanded mesh of mild steel, which withstands the heat
bulld-up incltental to cathdde sputterlng without requiring cooling.
The new metal mesh anode deslgns may also be shaped to
provlde for the deposition of a desired gradlent film.
Although the present invention has been discussed in detail
above with respect to a titanium cathode, steel mesh anodes and a
scanning apparatus, various other target materials, such as indium, may
be used, as well as other expanded metals and configurations for the
anote. Either scanning or stationary cathodes may be used to produce
either uniform or gradient coatings. The present lnvention will be
further unterstood from the descrlption of the specific example which
follows.
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Example I
A stationary titanium cathode with a sputtering surface
measuring 6 by 40 inches (15 by 102 centimeters) is spaced about 3 inches
(about 7.6 centimeters) from a glass substrate having approximately the
same dimensions. A pair of mild steel expanded mesh anodes shaped and
positioned as lllustrated in Figure 1 is used in this example. The
cathode is sputtcred at an average current density of 0.0625 amps per
square inch (0.0097 amps per square centimeter) for about 5 minutes in an
atmosphere of 13 percent oxygen in argon at a pressure of 6 x 10 4 Torr
to produce a uniform titanium oxide film on the glass surface.
The above example is offered only to illustrate the present
invention. Other anode shapes, sizes and positions may be employed to
form coatlngs. Whlle the example above employs a stationary cathode, a
scanning cathode or moving substrate may be employed. The cathode, anode
and substrate may be comprised of a variety of materials known in the
art. The scope of the inventlon ls defined by the following claims.
