Note: Descriptions are shown in the official language in which they were submitted.
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DURA~LE SPUTTERED FIL21S OF METAL ALLOY OXIDES
Background of the Invention
The preseDt invention relates generally to the art of cathode
sputtering of metal oxide films, and more particularly to the art of
magnetic sputtering of multiple layer films of me~al and ~etal oxide.
U.S. Patent No. ll,O94,763 to Gillery et al dlscloses producing
transparent, electro~onductive articles by cathode sputterlng metals such
as tin and indium onto refractory substrates such as glass at a
temperature above 400F. in a low pressure atmosphere containing a
controlled amount of oxygen.
U.S. Patent No. 4,113,599 to Gillery teaches a cathode
sputtering technique for the reactive deposition of indium oxide in which
the flow rate of oxygen i9 adJusted to maintain a constant discharge
current while the flow rate of argon is adjusted to maintain a constant
pressure in the sputtering chamber.
U.S. Patent No. 4,1669018 to Chapin describes a sputtering
apparatus in which a magnetic field is formed adjacent a planar
sputtering surface, the field comprising arching lines of flux over a
closed loop ero~ion ragion on the sputtering surface.
U.S. Patent No. 4,201,649 to Gillery discloses a method for
making low resistance indium oxide thin films by first depositlng a very
thin primer layer of indium oxide at low temperature before heating the
substrate to deposit the major thickness of the conductive layer of
indium oxide by cathode sputtering at typically high cathode sputtering
temperatures.
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U.S. Patent No. 4,327,967 to Groth discloses a heat-reflecting
panel having a neutral-color outer appearance comprlsing a gla8s pane, an
interference fllm having a refractive index greater than 2 on the glass
surface, a heat reflecting gold film over the interference film and a
neutralization film of chromium, iron, nickel, tltanlum or alloys thereof
over the gold fllm.
U.S. Paten~ No. 4,349,425 to Miyake et al discloses d-c
re&ctive sputtering of cadmium-tin alloys ln argon-oxygen mixtures to
form cadmium-tln oxide films having low electrical resis~lvity and high
optlcal transparency.
U.S. Patent No. 4,462,883 to llart dlscloses a low emissivity
coating produced by cathode sputtering a l~yer of silver, a small amount
o metal other than silver, and an anti-reflection layer of metal oxide
onto a transparent substrate such as glass. The anti-reflection layer
may be tin oxide, titanium oxide, zinc oxide, indium oxide, bismuth oxide
or zirconium oxide.
t Reissue No 27,473 to Mauer discloses a multilayer transparent
article comprising a ~hin layer of gold or copper sandwiched between two
layers of transparent material such as various metals, titanium oxide,
lead oxide or bismuth oxide.
In the interest of improving the energy efficlency of
double-glazed window units, it is desirable to provide a coating on one
of the glass surfaces which increases the insulating capability of the
unit by reducing radiative heat transfer. The coating therefore must
have a low emissivity in the infrared wavelength range of the radiation
spectrum. For practical reasons, the coating must have a high
transmittance in the visible wavelength range. For aesthetic reasons,
31 ~88~3
the coating should have a low luminous reflectance and preferably be
essentially colorless.
High transmlttance, low emiLssivity coatings as described above
generally comprise a thin metallic layer, for infrared reflectance and
low emissivity, sandwiched between dielectric layers o~ metal oxides to
reduce the vislble reflectance. Thefle multiple layer films are typically
produced by cathode sputtering, especially magnetron sputtering. The
metallic layer may be gold or copper, buc i8 generally silver. The metal
oxide layers described in the prlor art include tin oxide, indium oxide,
tltanium oxide, bismuth oxide, zinc oxide, zirconium oxide and lead
oxide. In some cases, these oxldes incorporate small amounts of other
metals, such as manganese in bismuth oxide, indium in tin oxide and vice
versa, to overcome certain disadvantages such as poor durability or
marginal e~issivity. However, all of these metal oxides have some
deficiency.
Although the coating may be maintained on an inter~or surface
of a double-glazed window unit in use, where it is pro~ected from the
elements and environmental agents which would cause its deterioration, a
durable effective coating able to withstand handllng, packaglng, washing
and other fabrication processes encountered between manufacture and
installation is particularly desirable. These properties are sought in
the metal oxide. Rowever, in addition to hardness which provides
mechanical durability, inertness which provides chemical durability, and
good adhesion to both the glass and the metal layer, the metal oxide
should have the following properties as well.
The metal oxide mus~ have a reasonably high refractive index,
preferably greater than 2.0, to reduce the reflectlon of ehe metallic
~2883~
layer and thus enhance the transmittance of the coated product. The
metal oxide must also have minimal absorption to maximize the
transmittance of the coated product. For commercial reasons, the metal
oxide should be reasonably priced, have a relatively fast deposition rate
by magnetron sputtering, and be nontoxic.
Perhaps the most important, and mos-t difficult to satisfy,
requirements of the metal oxide film relate to its interaction wi~h the
metallic film. The metal oxide film must have low porosity, to protect
the unde.rlying metallic film from external agents, and low diffusivity
for the metal to maintain the integrity of the separate layers. Finally,
and above all, the metal oxide must provide a good nucleation surface for
the deposition of the metallic layer, so that a continuous metallic film
can be deposited with minimum resistance and maximum transmittance. The
characteristics of continuous and discontinuous silver films are
described in U.S. Patent No. ~,462,88~ to Gillery et al.
Of the metal oxide films in general use, zinc oxide and bismuth
oxide are insufficiently durable, being soluble in both acid and alkaline
agents, degraded by fingerprints, and destroyed in salt, sulfur dioxide
and humidity tests. Indium oxide, preferably doped with tin, is more
` 20 durable; however, indium sputters slowly and is relatively expensive.
Tin oxide, which may be doped with indium or antimony, is also more
durable, but does not provide a suitable surface for nucleation of the
silver film, resulting in high resistance and low transmittance. The
characteristics of a metal film which result in proper nucleatlon of a
subsequently deposited silver film have not been established; however,
trial-and-error experimentation has been widely practiced with the metal
oxides described above.
3~
U.S. Patent No. 4,610,771 to F.H. Gillery, provides a novel film
cornpositlon of an oxide of a metal alloy, as well as a novel multiple-layer
film of metal and metal alloy oxi.de layers for use as a high transmittance,
low emissivity coating.
Summarv of the Inventlon
The present invention improves the durabillty of metal alloy oxide
films, especially multiple layer films comprising metal alloy oxides and
metals such a5 silver, by providing a primer layer which improves the
adhesion between ~he metal and metal oxide layers.
In its broadest aspect, the invention comprises a method for
depositing a durable film comprising the steps of:
a. sputtering a metal cathode target in a reactive atmosphere
comprising oxygen thereby depositing a metal oxide film on a
surface oi a non-metallic substrate;
b. sputtering a metal-containing primer layer over the metal oxide
fil~,
c. sputtering a reE].ective metallic film over the primer layer;
d. sputtering a second metal-containing primer layer over the
reflective metallic film; and
e. sputtering a second metal alloy oxide film over the second
primer layer.
The invention is especially useful in the manufacture of
transparent products (such as glass products) having high transmittance and
low emissivlty. Thus, according to ~ further aspect of the invention, there
is provided a method for making a multiple layer high transmittance, low
emissivity coated product comprising the steps of:
a. placing a transparent, non-metallic substrate in a sputtering
chamber;
b. sputtering a cathode target comprising an alloy of ~inc and tin
in a reactive atmosphere comprising oxygen to deposit a
transparent metal alloy oxide film on a surface of the
substrate; !
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c. sputtering a copper target to deposit a primer layer on the
oxlde film;
d. sputtering a silver cathods target, in an inert atmosphere to
deposit a transparent silve:r film on the primer layer;
e. sputtering a copper target to deposit A second primer layer on
the silver film; and
f. sputtering a cathode target comprislng an alloy of zinc and tin
in a reactive atmosphere comprising oxygen to deposit a metal
alloy oxide iilm on the second primer layer.
The invention further contempla~es articles made by the foregoing
process and especially high transmittance, low emissivity artlcles
comprising:
a. a transparent non-metallic substrate;
b. a first transparent film comprising a metal oxide deposited on
a surface of the substrate;
c. a first metal-containing transparent primer layer deposited on
; the first metal oxide i`ilm;
d. a transparent reflective metallic film deposited on the primer
layer;
e. a second metal-containing transparent primer layer deposited on
the reflective metallic film; and
f. a second transparent film comprising a metal oxide deposited on
the second primer layer.
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Detailed Description of the Preferred Embodiments
A fllm composltlon preferably comprising an oxide of a metal
alloy is preferably deposited by cathode 6puttering, preferably magne~ron
sputterlng. ~ cathode target is prepared comprising the deslred ratio of
metal alloy elements. The target i8 then sputtered in a reactive
atmosphere, preferably contalning oxygen in order to deposlt a metal
alloy oxide film on a surface of a substrate.
A prcferred metal alloy oxide in accordance with the present
lnventlon is an oxide of an alloy compri~ing zinc and tin. A zinc/~in
alloy oxide fllm may be deposited in accordance with the present
invention by cathode sputtering, preferably magnetically enhanced.
Cathode sputtering is also a preferred method for depositing high
transmi~tance, low emissivity films in accordance with the present
invention Such films typically comprise multiple layers, preferably a
layer of a highly reflec~ive metal such as gold or silver sandwlched
between anti-reflective mPtal oxide layers such as indium oxide or
titanium oxide, or preferably an oxide of an ~lloy of zinc and tln which
preferably comprises zinc stannate.
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:~.
~1~288~83
While various metal alloys may be sputtered to form metal alloy
oxide films, in order to produce a preferred high transmittance, low
emissivity multiple layer film in accordance with the present invention,
alloys of tin and zinc are preferred. A particularly preferred alloy
comprises zinc and tin, preferably in proportions of 10 to 90 percent
zinc and 90 to 10 percent tin. A preferred zinc/tln alloy ranges from 30
to 60 percent æinc, preferably having a zinc/tin ratio from 40:60 to
60:40. A most preferred range ls 46:54 to 50:50 by weight tin to zinc.
A cathode of zinc/tin alloy relative:Ly sputtered in an oxidizing
atmosphere results in the deposition of a metal oxide layer comprising
zinc, tin and oxygen, preferably comprising zinc stannate, Zn2SnO4.
In a conventional magnetron sputtering process, a substrate i6
placed within a coating chamber in facing relation with a cathode having
a target surface of the material to be sputtered. Preferred substrates
` in accordance with the present invention include glass, ceramics and
~ plastics which are not detrimentally affected by the operating conditions
d~ of the coating process.
The cathode may be of any conventional design, preferably an
elongated rectangular design, connected with a source of electrical
potential, and preferably employed in combination with a magnetic field
to enhance the sputtering process. At least one cathode target surface
comprises a metal alloy such as zinc/tin which is sputtered in a reactive
atmosphere to form a metal alloy oxide film. The anode is preferably a
symmetrically designed and positioned assembly as taught in U.S. Patent
4,478,702 to Gillery et al.
In a preferr~d embodiment of the present lnventlon, a multiple
layer film is cleposlted by cathode sp~tterin~ ~o form a high
transmlttance, low emissivity coating. In additlon to the metal alloy
target, at least one other cathode target surface comprises a metal to be
sputtered to form a reflectlve metallic layer. At least one additional
cathode target surface comprises the metal to be deposited as the prlmer
layer. A durable multiple layer coating havlng a reflectlve metall~c
film in combination with an anti-reflective metal alloy oxide fllm is
produced as follows, using primer layers to improve the adheslon between
the metal and metal oxide fi]ms.
A clean glass substrate is placed in a coating chamber which is
evacuated, preferably to less than 10 4 torr, more preferably less than
2 X 10 5 torr. A selected atmosphere of inert and reac~ive gases 9
preferably argon and oxygen, is established in the chamber to a pressure
bet~een about 5 X 10 4 and 10 2 torr. A cathode having a target
surface of zinc/tin metal alloy is operated over the surface of the
substrate to be coated. The target metal i8 sputtered, reactlng with the
atmosphere in the chamber to deposlt a zinc/tin alloy oxlde coating layer
on the glass surface.
After the initial layer of zinc/tin alloy ox de is deposited,
the coating chamber is evacuated, and an inert atmosphere such as pure
argon is established at a pressure between about 5 X 10 4 and 10 2
torr. A cathode having a target surface of a metal such as copper is
spu~tered to deposit a primer layer over the zinc/tin alloy oxide layer.
A cathode having a target surface of silver is than sputtered to deposit
a reflective layer of metallic silver over the primer layer which
lmproves the adhesion of the silver film to the underlying metal oxide
~28~33
film. An additional primer layer is then deposited by sputtering a metal
such as copper over the reflective silver layer to improve the adhesion
between the silver film and the overlying metal oxide film subsequently
i deposited. Finally, a second layer of zinc/tin alloy oxide is deposited
over the second primer layer under essentially the same conditlons used
to deposit the first zinc/tin alloy oxide layer.
In most preferred embodiments oE the present inventlon, a
protective overcoat is deposlted over the flnal metal oxide fllm. The
protectlve overcoat is preferably deposited by sputtering over the metal
oxide film a layer of a metal such as disclosed ln U.S. Patent No.
; 4,594,137 to Gillery et al. Preferred metals for the protectlve
overcoat include alloys of iron or nickel, such as stainless steel
or Inconel*. Titanium is a most preferred overcoat because of its
high transmittance.
The present invention will be further understood from the
descriptlon of a specific example which follows. In ~he example, the
zinc/tin alloy oxide film is referred to as zinc stannate although the
- film composition need not be precisely Zn2SnO4.
;~ ~ E~AMPLE
A multiple layer film is deposited on a soda-llme sillca glass
substrate to produce a high transmittance, low emissivity coated
product. A stationary cathode measuring 5 by 17 inches (12.7 by 43.2
~ centimeters~ comprises a sputtering surface of zinc/tin alloy consisting
; of 52.4 welght percent zinc and 47.6 percent tin. A soda-lime-silica
glass substrate is placed in the coating chamber which is evacuated to
establish a pressure of 4 millitorr in an atmosphere of 50/50
*Trade Mark
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"
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axgon/oxygen. The cathode is sputtered in a magnetic field at a power of
1.7 kllowatts while the glass is conveyed past the sputtering surface at
a rate of llO inches (2.8 m~ters) per minute. A film of z-lnc s~annate is
deposited on the glass surface. Three pas~es produce a film thickness of
about 340 Angstroms, resulting in a decrease in transmittance from 90
percent for the glass substrate to 83 percent for the zinc stannate
coated glass substrate. A stationary cathode with a copper target is
then sputtered to produce a copper pri~ler layer over the zinc stannate,
reduclng the transmittance to about 80.6 percent. Next, a layer of
sllver is deposited over the copper primer layer by sputtering a silver
cathode target in an atmosphere of argon gas at a pressure of 4
mlllitorr. With the substrate pafising under the silver cathode target at
the same rate, two passes are necessary to deposit eleven micrograms of
silver per square centimeter, corresponding to a f$1m thickness of about
90 Angstroms, decreasing the transmittance of the coated substrate to
about 70.3 percent. A second copper primer layer is sputtered over the
silver layer to improve the adhesion and protect the silver layer before
the final anti-reflective layer of zinc stannate is deposited. Since the
c.opper primer layers decrease the transmi~tance, their thlcknesses are
preferably minimal. The copper primer layers are deposited by sputtering
a copper target at minimum power in argon at a pressure of 4 millitorr.
The transmittance of the sample decreases to 68.3 percent after
deposition of the second copper primer layer. Finally, the zinc/tin
alloy cathode target is sput~ered in an oxidizing atmosphere to produce a
rinc stannate film. Four passes at a rate of 110 inches (2.8 meters) per
minute produce a film thiclcness of about 430 Angstroms, increasing the
transmittance of the coated product from 68.3 to 83~2 percent. The final
83~33
coated product has a surace resistance of lO o'hms per square and a
slightly bluish reflectance from both sldes, with a luminous reflectance
of 5 percent from the coated side and 6 percen~ from the u~coated side.
The improved durability of the coated article resulting from
the improved adhesion between the metal and metal oY.ide films as a result
of the primer layers of the present invention i8 readlly demonstrated by
a slmple abrasion test consisting of wiping the coated surface with a
damp cloth. A surface coated with zinc stannate/silver/zinc stannate
having no pr-lmer layers ln accordance with the present inventlon
increases in reflectance from about 6 percent to about 1~ percent after
several pasaes of a damp cloth, indicating removal of both the top zinc
stannate and the underlying silver ~ilms~ In contrast, prolonged
vigorous rubbing with a damp cloth produces no visible change in a zinc
stannate/copper/silver/copper/zinc stannate coated article comprising the
primer layers of the present invention.
~ The above example is o~'fered to illustrate the present
-~ invention. Various modifications of the produc~ and the process are
included. For example, other coating compositions are within the scope
of the present invention. Depending on ~he proportions o~ zinc and tin
when a zinc/ti~ alloy is sputtered, the coating may contain widely
varying amounts of zinc oxide and tin oxide in addition to zinc
stannate. The adhesion between a wide variety of metal and metal oxide
films may be improved by means of primer layers in accordance with the
present invention. Since the process does not require very high
temperatures, substrates other than ~lass, such as various plastics, may
be coated. A scanning cathode may be used with a stationary substrate.
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3a383
Process parameters æuch ~s pressur and concentration of gases may be
varied over a broad range. Primer layers may comprise other metals such
as indlum, or oxides such as copper oxide or indium oxide. The scope of
the preæent invention is defined by the following claims.
