Durable sputtered films of metal alloy oxides.

<td></td><td>(12) LETTERS (19) NO (id 174286 ¢ 13) B (they) Int Cl⁵ B 32 B 17/06, C 03 C 17/36,</td>

<td>NORWAY</td><td>C 23 C 14/08, 14/35, G 02 B 1/10</td>

The Board of Industrial Law Protection

<td>(21) Application no (22) Starting day (24) Race day (41) Alm. avail. (44) Explanation date</td><td>865236 (86) Int. Day and day 22.12.86 application nuns 22.12.86 (85) Continuation Day 24.06.87 (30) Priority 23.12.85, US, 812680 01/03/94</td>

<td>(71) Patent applicant (72) Inventor</td><td>PPG Industries Inc., One PPG Place, Pittsburgh, PA 15272, US Frank Howard Gillery, Allison Park, PA, US James Joseph Finley, Pittsburgh, PA, US Russell Caldwell Criss, Pittsburgh, PA, US</td>

<td>(74) Agent</td><td>Jan Helgerud, Bryns Patentkontor AS, Oslo</td>

<td>(54) Designation</td><td>Object with high transmittance and low anissivity</td>

(56) Published publications NO 854274, 863995, EP 35906, DE 1088198, US 4327967.

<td>(57) Summary</td><td>Non-metallic surfaces, preferably glass, can be coated with a high-transmittance, low-emulsion multilayer coating and with improved chemical resistance as a result of a protective top coat of preferably titanium oxide.</td>

The present invention relates to an object of high transmittance and low emissivity.

More specifically, the invention comprises an object of high transmittance and low emissivity comprising

a. a transparent, non-metallic substrate;

b - a first transparent antireflective film comprising a metal oxide deposited on a surface of the substrate;

c. a transparent Infrared reflective metallic film deposited after the first anti-reflective metal oxide film;

d. a second, transparent anti-reflective film comprising zinc, tin or zinc / tin oxide deposited after the infrared reflective metallic film, and the article is characterized by

e. a protective titanium oxide top coat deposited after the second antireflective metal oxide film.

US-A-4,094,763 discloses the preparation of transparent, electroconductive articles by cathode sputtering of metals such as tin and indium on refractory substrates such as glass, at a temperature above 200 ° C in a low pressure atmosphere containing a controlled amount of oxygen.

US-A-4,113,599 discloses a cathode sputtering technique for reactive deposition of indium oxide in which the flow rate of oxygen is adjusted to maintain a constant discharge current while the flow rate of argon is adjusted to maintain a constant pressure in the sputtering chamber.

US-A-4,166,018 discloses a sputtering apparatus in which a magnetic field is formed near a planar sputtering surface, the field comprising curved flow lines over a closed loop erosion region of the sputtering surface.

U.S. Patent No. 4,201,649 discloses a process for making low-resistance indium oxide films by first depositing a very thin primer layer of low temperature indium oxide before heating the substrate to deposit the main thickness of the conductive layer of indium oxide at cathode sputtering at characteristic high cathode sputtering temperatures.

US-A-4,327,967 discloses a heat-reflecting plate having a neutral colored outer appearance comprising a glass plate, an interference film having a refractive index of more than 2 on the glass surface, a heat-reflecting gold film over the interference film and a chromium, iron, nickel, neutralization film. alloys thereof over the gold film.

U.S. Pat. No. 4,349,425, describes DC reactive sputtering of cadmium tin alloys in argon oxygen mixtures to form cadmium tin oxide films with low electrical resistivity and high optical transparency.

US-A-4,462,883 discloses a low-mission coating made by cathode sputtering a layer of silver, a small amount of metal other than silver, and an anti-reflection layer of metal oxide on a transparent substrate such as glass. The anti-reflection layer may be tin oxide, titanium oxide, zinc oxide, indium oxide, bismuth oxide or zirconia.

US-Reissue 27,473 discloses a multilayer transparent article utilizing a thin layer of gold or copper arranged between two layers of transparent material such as different metals, titanium oxide, lead oxide or bismuth oxide.

In order to improve the energy efficiency of double glazing units, it is desirable to provide a coating on one of the glass surfaces which increases the insulation capacity of the unit by reducing the radiant heat transfer. Therefore, the coating must have low emissivity in the infrared wavelength range of the radiation spectrum. For practical reasons, the coating must have high transmission in the visible wavelength range. For aesthetic reasons, the coating should have a low light reflectance and preferably be substantially colorless.

Coatings with high transmittance and low emissivity as described above generally comprise a thin metallic layer of Infrared reflectance and low emissivity, arranged between the electrical layers of metal oxides to reduce visible reflectance. These multilayer films are characteristically prepared by cathode sputtering, especially magnetron sputtering. The metallic layers may be gold or copper, but are generally silver. The metal oxide layers described in the prior art include the tin, indium, titanium, bismuth, zinc, zircon and lead oxide. In some cases, these oxides contain small amounts of other metals such as manganese in bismuth oxide, indium in tin oxide and vice versa, to overcome certain deficiencies such as poor stability or marginal emissivity. However, all of these metal oxides have certain shortcomings.

Although the coating can be maintained on an inner surface of a double-glazed unit in use, where it is protected from elements and environmental impacts that would cause deterioration, it is nevertheless a stable, effective coating that can withstand treatment, packaging, washing and other manufacturing and installation processes, especially desirable. These properties are sought for in 1 metal oxide. In addition to hardness that provides mechanical stability, inertness that provides chemical stability and good adhesion to both the glass and metal layers, the metal oxide should also have the following properties.

The metal oxide must have a reasonably high refractive index, preferably greater than 2.0, to reduce reflection in the metallic layer and thus improve transmission 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 reasonable, have a relatively high deposition rate in magnetron sputtering, and be non-toxic.

The most important and also most difficult criterion to satisfy for the metal oxide film is the interaction with the metallic film. The metal oxide film must have low porosity to protect the underlying metal film from external influence, and low diffusivity of the metal to maintain the integrity of the separate layers. Finally, and above all, the metal oxide must provide a good nucleation surface for depositing the metallic layer so that a metallic film can be deposited with minimum resistance and maximum transmittance. The properties of continuous and discontinuous silver films are described in U.S. Patent No. 4,462,884.

Of the metal oxide multilayer films in general use, those comprising zinc oxide and bismuth oxide are insufficiently stable, these oxides being soluble in both acidic and alkaline substances, so that the multilayer film is broken down by fingerprints and destroyed in salt, sulfur dioxide and moisture samples. Indium oxide, preferably doped with tin, is more durable and protective for an underlying metal layer; however, indium sputters slowly and is relatively expensive. Tin oxide which can be doped with indium or antimony is also more stable and protective for an underlying metal layer but does not provide a suitable surface for silver film nucleation resulting in high resistance and low transmittance. The properties of a metal oxide film resulting in poor nucleation for a subsequently deposited silver film have not been demonstrated. However, experiments have been extensively practiced with the metal oxides as described above.

US-SN 665,680 provides a new film composition of an oxide of a metal alloy as well as a new multilayer film of metal and metal alloy oxide layers for use as coatings with high transmittance and low emissivity.

Accordingly, the invention improves the stability of multilayer films, especially multilayer films comprising metal and / or metal alloy oxide layers and metal layers such as silver, by providing an outer protective layer of a particularly chemically resistant material such as tlethane oxide.

A film composition preferably consisting of a metal or metal alloy oxide is preferably deposited by cathode sputtering, preferably magnetron sputtering. A cathode target is prepared comprising the desired metal or metal alloy elements. The target is then sputtered in a reactive atmosphere, preferably containing oxygen, to deposit a metal or metal alloy oxide film on a surface of a substrate.

A usable metal alloy oxide is an oxide of an alloy comprising zinc and tin. A zinc tin alloy oxide film can be deposited by cathode sputtering, preferably magnetically supported. Cathode sputtering is also a preferred method for depositing films with high transmittance and low emissivity. Such films characteristically comprise several layers and preferably a layer of highly reflective metal such as gold or silver, arranged between anti-reflective metal oxide layers such as indium or titanium oxide, or preferably an oxide of an alloy of zinc and tin which preferably comprises nickel stannate.

While various metal alloys may be sputtered to form metal alloy oxide films, to make a preferred multi-layer film with high transmittance and low emissivity, tin and zinc alloys are preferred. For example, a usable alloy comprises zinc and tin, preferably in proportions of 10 to 90 $ zinc and 90 to 10 $ tin. For example, such a zinc / tin alloy contains from 30-60 $ zinc and has a zinc: tin ratio of 40:60 to 60:40. A very useful range is 46:54 to 50:50 sink: tin. A cathode of zinc / tin alloys is reactively sputtered in an oxidizing atmosphere and results in the deposition of a metal oxide layer comprising zinc, tin and oxygen, preferably consisting of zinc stannate, Zn.₂SnO4.

In a conventional magnetron sputtering process, a substrate is arranged in a coating chamber opposite a cathode with a target surface of material to be sputtered. Preferred substrates according to the invention are glass, ceramics and plastics which are not adversely affected by the operating conditions of the coating process.

The cathode may be of any conventional construction, preferably an elongated rectangular structure, connected to an electrical voltage source, and preferably used in combination with a magnetic field to improve 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 constructed and arranged device as described in US-A-4,478,702.

In one embodiment, for example, a multilayer film is deposited by cathode sputtering to thereby form a coating of high transmittance and low emissivity. In addition to the metal alloy target, at least one second cathode surface comprises a metal to be sputtered to form a reflective metallic layer. The at least one additional cathode target surface comprises the metal to be deposited as the primer layer. A stable multilayer coating with a reflective metallic film in combination with an anti-reflective metallic alloy oxide film is prepared as follows using the primer layer to improve adhesion between metal and metal oxide films.

A clean glass substrate is placed in a coating chamber which is evacuated, preferably to less than 10^-4 dry, and preferably less than 2 x 10^-5 dry. A selected atmosphere of inert and reactive gases, preferably argon and oxygen, is created in the chamber to a pressure of between 5 x 10^-4 and 10^-2 dry. A cathode having a target surface of zinc / tin metal alloys is operated over the surface of the substrate to be coated. The target metal is sputtered, reacts with the atmosphere in the chamber and deposits a zinc / tin alloy oxide coating layer on the glass surface.

After the first layer of the zinc / tin alloy oxide is deposited, the coating chamber is evacuated and an inert atmosphere such as pure argon is created at a pressure between approx. 5 x 10 "⁴ and 10^-2 dry. A cathode having a target surface of a metal layer that is copper sputtered to deposit a primer layer over the zinc / tin alloy oxide layer. A cathode with a silver target surface is then sputtered to deposit a reflective layer of metallic silver over the primer layer which improves the adhesion of the silver film to the underlying metal oxide film. A further primer layer is then deposited by sputtering a metal which coats over the reflective silver layer to improve the adhesion between the silver film and the overlying metal oxide film which is then deposited. Finally, a second layer of slink / tin alloy oxide is deposited over the first primer layer under substantially the same conditions used to deposit the first slink / tin alloy oxide layer.

It is beneficial if a protective titanium oxide top coat is deposited over the last metal oxide film. This top protective coating is preferably deposited by sputtering over the metal oxide film layer, a layer of a metal as disclosed in US-SN 530,579.

The chemical resistance of a multilayer film is best enhanced by the deposition of a protective coating comprising titanium oxide over the multilayer film. Preferably, protective titanium oxide coatings are deposited by cathode sputtering at relatively high deposition rates and low expression, preferably ca. 3 millitrr. A titanium oxide protective coating can be formed by sputtering titanium in an oxygen-sufficient atmosphere to deposit titanium oxide directly.

Furthermore, a protective coating comprising titanium oxide can be formed by sputtering titanium in an inert atmosphere, thereby depositing a titanium-containing film which is then oxidized to titanium oxide by exposure to an oxidizing atmosphere such as air.

The invention will be explained in more detail from the description of a particular example below. In the examples, the zinc tin alloy oxide film is referred to as zinc stannate although the film composition is not necessarily Zn₂SN04.

EXAMPLE

A multilayer film is deposited on a soda / calcium silica glass substrate to obtain a coated product with high transmittance and low emissivity. A stationary cathode measuring 12.7 cm x 43.2 cm comprises a zinc alloy sputtering surface consisting of 50.4 wt. And 47.6 wt. Tin. The glass substrate is placed in the coating chamber which is evacuated to create a pressure of 4 millitons in an atmosphere of 50:50 argon: oxygen. The cathode is sputtered in a magnetic field at a power of 1.7 kW while the glass is transported past the sputtering surface at a feed rate of 2.8 m / min. A film of zinc plated is deposited on the glass surface. Three passes in a film thickness of approx. 340 Angstroms, resulting in a reduction of transmittance from 90 # for the glass substrate to 83 # for the zinc stannate coated glass substrate. A stationary cathode with a copper target is then sputtered to produce a copper primer layer over the slurry stannate, reducing the transmittance to approx. 80.6 #. Then, a layer of silver is deposited over the copper primer layer by sputtering a silver cathode target in an argon atmosphere under a pressure of 4 millitons. With the substrate passed below the silver cathode target at the same rate, two bypasses are required to deposit 10 µg of silver / cm², which corresponds to a thickness of approx. 90 Angle current and which reduces the transmittance of the coated substrate to approx. 70.3 #. A second copper primer layer is sputtered over the silver layer to improve adhesion and to protect the silver layer before depositing the final anti-reflective layer of zinc stannate. Because the copper primer layers reduce transmittance, their thickness is preferably minimal. Copper primers are deposited by sputtering a copper target at minimum power in argon under a pressure of 4 millitons. The transmittance of the sample is reduced to $ 68.3 after deposition of the second copper primer layer. Then, the zinc alloy cathode target is sputtered in an oxidizing atmosphere to give a zinc stannate flicker. Four passes at a speed of 2.8 m / min. gives a film thickness of approx. 430 Angstroms and increases the transmittance of the coated product from 68.3 to $ 83.2. The multilayer coating has a surface resistance of 10 ohms / m 2 and a light bluish reflectance from both sides with a lumen reflectance of 5 $ from the coated side and 6 $ from the uncoated side. Finally, a stationary titanium cathode of 12.7 cm long 43.2 cm is sputtered at 10 kW in an atmosphere of equal volumes of argon and oxygen under a pressure of 3 millitons. Two transfers of the substrate at a rate of 2.8 m / min. is sufficient to deposit a liquid coating of titanium oxide having a thickness of approx. 15 to 20 Angstroms. The protective coating of titanium oxide does not significantly affect the resistance and reflectance properties of the multilayer coating and does not change transmittance more than approx. 1 $.

The improved stability of the coated article obtained by the improved adhesion between the metal and metal oxide films as a result of the primer layers of the invention is readily demonstrated by a simple abrasion test consisting of rubbing the coated surface with a damp cloth. A surface coated with zinc stannate / silver / zinc stannate without a primer layer according to the invention has an increase in reflectance from approx. $ 6 to $ 18 after multiple transfers of a damp cloth, indicating removal of both the top zinc stannate layer and the underlying silver film. In contrast, for a damp cloth, no visible prolonged violent rubbing with change for a zinc stannate / copper / silver / copper / zinc stannate 35 coated article comprises the primer layers of the invention.

Preferred titanium oxide protective coatings have thicknesses in the range of approx. 10-50 Angstroms. With a titanium oxide protective coating of approx. 20 Angstroms thick, the duration of a multilayer coating according to this example is increased from 2 hours to 22 hours in a 2.5 $ saline at ambient temperature and from 5 hours to 1 week at the Cleveland moisture test, performed with a Q-plate Cleveland Condensation Tester model QCT -ADO containing deionized water of approx. 66 ° C.

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