CA1288383C - Durable sputtered films of metal alloy oxides - Google Patents

Abstract

Abstract A high transmittance, low emissivity article particularly an architectural glass product having a transparent non-metallic substrate, a first metal oxide film on the substrate, a metal containing primer layer on the metal oxide film, a reflective metallic film on the primer, a second metal containing primer on the metallic film and a final film of metal oxide on the second primer. All the layers are transparent. A method of making the product by sputtering is also described. Good adhesion between the metal and metal oxide layers is obtained by use of the primer.

Description

~8t~3 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.

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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; !

~8~3 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.

- 5a -~2~3~33S13 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.

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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 ; - 8 -"

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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.

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.

Claims (20)

1. A high transmittance, low emissivity article comprising:
a. a transparent nonmetallic substrate;
b. a first transparent film comprising a metal oxide deposited on a surface of said substrate;
c. a first metal-containing transparent primer layer deposited on said first metal oxide film;
d. a transparent reflective metallic film deposited on said primer layer;
e. a second metal-containing transparent primer layer deposited on said reflective metallic film; and f. a second transparent film comprising a metal oxide deposited on said second primer layer.

2. An article according to claim 1, wherein the substrate is glass.

3. An article according to claim 2, wherein the reflective metallic film is silver.

4. An article according to claim 3, wherein the metal oxide comprises an oxide reaction product of an alloy comprising zinc and tin.

5. An article according to claim 4, wherein the transparent film comprising an oxide reaction product of a metal alloy comprises zinc stannate.

6. An article according to claim 1, wherein the primer films deposited between the reflective metallic film and the transparent metal oxide film are selected from the group consisting of copper, indium and the oxides thereof.

7. An article according to claim 6, wherein the primer films comprise copper.

8. An article according to claim 6, wherein each primer layer is of a thickness which decreases the transmittance of the article between 0.5 and 10 percent.

9. An article according to claim 8, wherein the transmittance of the article is decreased between 1 and 5 percent by each primer layer.

10. An article according to claim 9, wherein the primer layer comprises copper oxide.

11. 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 of a non-metallic substrate;
b. sputtering a metal-containing primer layer over said metal oxide film;
c. sputtering a reflective metallic film over said primer layer;

d. sputtering a second metal-containing primer layer over said reflective metallic film; and e. sputtering a second metal alloy oxide film over said second primer layer.

12. A method according to claim 11, wherein said primer layer is selected from the group consisting of copper, indium and the oxides thereof.

13. A method according to claim 12, wherein said substrate is glass.

14. A method according to claim 13, wherein said metal oxide film comprises an oxide reaction product of an alloy comprising zinc and tin.

15. A method according to claim 14, wherein said film comprises zinc stannate.

16. A method for making a multiple layer high transmittance, low emissivity coated product comprising the steps of:
a. placing a transparent, nonmetallic substrate in a sputtering chamber;
b. sputtering a cathode target comprising an alloy of zinc and tin in a reactive atmosphere comprising oxygen to deposit a transparent metal alloy oxide film on a surface of said substrate;

c. sputtering a copper target to deposit a primer layer on said oxide film;
d. sputtering a silver cathode target, in an inert atmosphere to deposit a transparent silver film on said primer layer;
e. sputtering a copper target to deposit a second primer layer on said silver film; and f. sputtering A cathode target comprising an alloy of zinc and tin in a reactive atmosphere comprising oxygen to deposit a metal alloy oxide film on said second primer layer.

17. The method according to claim 16, wherein the substrate is glass.

18. The method according to claim 17, wherein said metal alloy consists essentially of zinc and tin.

19. The method according to claim 18, wherein said metal alloy oxide film comprises zinc stannate.

20. The method according to claim 16, wherein said primer layers comprise copper oxide.