CA1335887C

CA1335887C - Neutral sputtered films of metal alloy oxides

Info

Publication number: CA1335887C
Application number: CA000594451A
Authority: CA
Inventors: Frank Howard Gillery
Original assignee: PPG Industries Inc
Current assignee: PPG Industries Ohio Inc
Priority date: 1988-04-01
Filing date: 1989-03-22
Publication date: 1995-06-13
Anticipated expiration: 2012-06-13
Also published as: CN1016188B; HK1006834A1; NO891207D0; NO891207L; DK157189A; US4834857A; FI891527A0; CN1037550A; KR890015968A; ES2051316T3; DK157189D0; FI891527A; DK171096B1; NO302901B1; ATE101588T1; AU3232189A; MY103862A; JP2505276B2; DE68913068D1; EP0339274A1

Abstract

A method for producing visually neutral high transmittance low emissivity coated articles comprising infrared reflective metal and antireflective metal oxide layers and an improved multiple layer coated article produced thereby comprising a high refractive index neutral metal oxide layer between the antireflective metal oxide layer and the infrared reflective metal layer are disclosed.

Description

1- .

NEUTRAL SPUTTERED FILMS OF METAL ALLOY OXIDES

1 Background of the Invention The pre6ent invention relates generally to the art of - - 3 cathode sputtering of metal oxide films, and more particularly to the art of magnetic sputtering of multiple layer films of metal and metal 5 oxide.
U.S. Patent No. 4,094,763 to Gillery et al discloses 7 producing transparent, electroconductive articles by cathode sputtering metals such as tin and indium onto refractory substrates 9 such as glass at a temperature above 400F. in a low pressure atmosphere contain;ng a controlled amount of oxygen.
11 U.S. Patent No. 4,113,599 to Gillery teaches a cathode sputtering technique for the reactive deposition of indium oxide in 13 which the flow rate of oxygen is adjusted to maintain a constant discharge current while the flow rate of argon is adjusted to 15 maintain a constant pressure in the sputtering chamber.
U.S. Patent No. 4,166,018 to Chapin describes a sputtering 17 apparatus in which a magnetic field is formed adjacent a planar sputtering surface, the field comprising arching lines of flux over a 19 closed loop erosion region on the sputtering surface.
U.S. Patent No. 4,201,649 to Gillery discloses a method for 21 making low resistance indium oxide thin films by first depositing a very thin primer layer of indium oxide at low temperature before 23 heating the substrate to deposit the major thickness of the ~ ~

l conductive layer of lndium oxide by cathode sputtering at typically high cathode sputtering temperatures.
3 U.S. ~atent No. 4,3Z7,967 to Groth di6clo6es a heat-reflecting panel having a neutral-color outer appearance 5 comprising a glass pane, an interference film having a refractive index greater than 2 on the glas6 surface, a heat reflecting gold 7 film over the interference film and a neutral~zation film of chromium, iron, nickel, titanium or alloys thereof over the gold film.
9 U.S. Patent No. 4,349,425 to Miyake et al discloses d-c reactive sputtering of cadmium-tin alloys in argon ~gen mixture6 to 11 form cadmium-tin oxide films having low electrical resistlvity and high optical tran8parency.
13 U.S. Patent No. 4,462,883 to Hart discloses a low emissivity coating produced by cathode sputtering a layer of silver, a small 15 amount of metal other than silver, and an antireflection layer of metal oxide onto a transparent substrate such as glass. The 17 antireflection layer may be tln oxide, titanium oxide, zinc oxlde, ind~um oxide, bismuth oxide or zirconium oxide.
l9 U~S. reissue No. 27,473 to Mauer discloses a multilayer transparent article comprising a thin layer of golt or copper 21 sandwiched between two layers of transparent material such aB Vsrious metal6, titanium oxide, lead oxide or bismuth oxide.
23 In the intere6t of improving the energy efficiency of double-glazed w~ndow units, it iB desirable to provlde a coating on 25 one of the gl8ss surfaces which increases the insulating capability of the unit by reducing radiative heat transfer. The coating 27 therefore must have a low emi6sivity in the infrared wavelength range of ~he radiation spectrum. ~or practical reasons, the coating mu6t 29 have a high transmittance in the visible wavelength range. ~or aesthetic reasons, the coating should have a low luminous reflectance 31 and preferably be essentially colorless.
High transmittance, low emissivity coatings as described 33 above generally comprise a thin metallic layer, for infrared reflectance and low emissivity, sandwiched between dielectric layers 35 of metal oxides to reduce the visible reflectance. These multiple layer films are typically produced by cathode sputtering, especlally 37 magnetron sputtering. The metallic layer may be gold or copper, but 1 is generally silver. The metal oxide layers described in the prior art include tin oxide, indium oxide, titanium oxide, bismuth oxide, 3 zinc oxide, zirconium oxide and lead oxide. In some cases, these oxides incorporate small amounts of other metals, such as manganese 5 in bismuth oxide, indium in tin oxide and vice versa, to overcome certain disadvantages such as poor durability or marginal 7 emissivity. However, all of these metal oxides have some deficiency.
Although the coating may be maintained on an interior 9 surface of a double-glazed window unit in use, where it is protected from the elements and environmental agents which would cause its 11 deterioration, a durable effective coating able to withstand handling, packaging, washing and other fabrication processes 13 encountered between manufacture and installation is particularly desirable. These properties are sought in the metal oxide. However, 15 in addition to hardness which provides mechanical durability, inertness which provides chemical durability, and good adhesion to 17 both the glass and the metal layer, the metal oxide should have the following properties as well.
19 The metal oxide must have a reasonably high refractive index, preferably greater than 2.0, to reduce the reflection of the 21 metallic layer and thus enhance the transmittance of the coated product. The metal oxide must also have ;ni -1 absorption to 23 ~ ~ze the transmittance of the coated product. For commercial rea~ons, the metal oxide should be reasonably priced, have a 25 relatively fast deposition rate by magnetron sputtering, and be nontoxic.
27 Perhaps the most important, and most difficult to satisfy, requirements of the metal oxide film relate to its interaction with 29 the metallic film. The metal oxide film must have low porosity, to protect the underlying metallic film from external agents, and low 31 diffusivity for the metal to maintain the integrity of the separate layers. Finally, and above all, the metal oxide must provide a good 33 nucleation surface for the deposition of the metallic layer, so that à continuous metallic film can be deposited with minimum resistance 35 and ~ i transmittance. The characteristics of continuous and discontinuous silver films are described in U.S. Patent No. 4,462,884 37 to Gillery et al.

133~887 1 Of the metal oxide films in general use, zinc oxide and bismuth oxide are insufficiently durable, being soluble in both acid 3 and alkaline agents, degraded by fingerprints, and destroyed in salt, sulfur dioxide and humidity tests. Indium oxide, preferably doped 5 with tin, is more durable; however, indium sputters slowly and is relatively expensive. Tin oxide, which may be doped with indium or 7 antimony, is also more durable, but does not provide a suitable surface for nucleation of the silver film, resulting in high 9 resistance and low transmittance. The characteristics of a metal oxide film which result in proper nucleation of a subsequently ll deposited silver film have not been established; however, trial-and-error experimentation has been widely practiced with the 13 metal oxides described above.
U.S. Patent No. 4,610,771 to Gillery provides a novel film 15 composition of an oxide of a metal alloy, as well as a novel multiple-layer film of metal and metal alloy oxide layers for use as 17 a high transmittance, low emissivity coating.
Summ~ry of the Invention 19 The present invention improves the durability of metal alloy oxide films, especially multiple layer films comprising metal alloy 21 oxides and metals such as silver, by providing a preferably titanium oxide layer which improves the adhesion between the metal and metal oxide layers and 23 also produces a coated article which is visually neutral. Because the preferred titanium oxide film of the present invention is thicker 25 than conventional primer layers, it may be advantageous to deposit a slightly thinner underlying antireflective metal oxide layer.
27 Brief Description of the Drawing Figure 1 is a chromaticity diagram illustrating the 29 chromaticity coordinates of a film of the present invention and a film of the prior art as described herein.
31 Det~ailed Description of the Preferred Embodiments In a three-layer induced transmission type coating where a 33 silver, copper or gold layer is antireflected with two transparent oxide coatings, more silver can be incorporated without changing the 35 color or reflectance of the coating by using oxide coatings with a higher refractive index. Unfortunately, most fast sputtering oxides ~ 5 ~ ~ 8 8 7 1 such as those of tin, indium, zinc have refractive indices of about 2Ø The higher refractive index transparent oxides such as titanium 3 oxide or zirconium oxide sputter too slowly to be commercially practical.
However, it has been discovered that relatively small amounts of, for example, titanium oxide, can be useful in creating 7 the desired high refractive index effect if it is incorporated in the optimum location in the film sequence, specifically between the first 9 deposited antireflective metal oxide layer and the infrared reflective metal, such as silver. Deposition of titanium oxide in 11 other positions in the coating sequence is relatively ineffective.
To prevent undesirable color changes in the multilayer coating it is 13 usually necessary to remove optical thickness from the adjacent oxide layer; that is, to make the underlying antireflective metal oxide 15 layer slightly thinner. The invention can be made clearer by reference to Figure 1.
17 The color of a coating on the chromaticity diagram moves from the point x = 0.283, y = 0.303 to the point x = 0.2g5, y = 0.295 19 as the silver layer is increased in thickness from 95 Angstroms to 110 Angstroms. A change in the thickness of the oxide layers moves 21 the color in directions about perpendicular to this direction. Thus, only by using a thin silver layer can the ideal optical properties of 23 color and reflectance of the 95 Angstrom film point be retained.
However, a thin silver layer usually implies inferior properties of 25 the coating such as electrical conductivity, reduced solar heat reflectance or reduced infrared reflectance.
27 By incorporating 50 Angstroms of titanium oxide as taught in the present invention, the chromaticity coordinates of the film 29 incorporating 110 Angstroms of silver are moved from the point x =
0.294, y = 0.295 back to the point x = 0.284, y = 0.301. The first 31 antireflective metal oxide layer in this case is decreased in thickness from 380 Angstroms to 320 Angstroms to compensate for the 33 optical thickness of the titanium oxide.
A preferred antireflective metal oxide film composition 35 comprising an oxide of a metal alloy is preferably deposited by cathode sputtering, particularly magnetron sputtering. Cathode 37 targets are preferably prepared comprising the desired ratio of metal 1 elements. The targets are then sputtered in a reactive atmosphere, preferably containing oxygen in order to deposit a metal alloy oxide 3 film on a surface of a substrate.
A preferred metal alloy oxide in accordance with the present 5 invention is an oxide of an alloy comprising zinc and tin. A
zinc/tin alloy oxide film may be deposited in accordance with the 7 present invention by cathode sputtering, preferably magnetically enhanced. Cathode sputtering is also a preferred method for 9 depositing high transmittance, low emissivity films in accordance with the present invention. Such films typically comprise multiple 11 layers, preferably a layer of a highly reflective metal such as gold or silver sandwiched between antireflective metal oxide layers such 13 as indium oxide or titanium oxide, or preferably an oxide of an alloy of zinc and tin which preferably comprises zinc stannate.
While various metals may be sputtered to form metal alloy oxide films, in order to produce a preferred high transmittance, low 17 emissivity multiple layer film in accordance with the present invention, alloys of tin and zinc are preferred. A particularly 19 preferred alloy comprises zinc and tin, preferably in proportions of 10 to 90 percent zinc and 90 to 10 percent tin. A preferred zinc/tin 21 alloy ranges from 30 to 60 percent zinc, preferably having a zinc/tin ratio from 40:60 to 60:40. A most preferred range is 46:54 to 50:50 23 by weight tin to zinc. A cathode of zinc/tin alloy reactively sputtered in an oxidizing atmosphere results in the deposition of a 25 metal oxide layer comprising zinc, tin and oxygen, preferably comprising zinc stannate, Zn2SnO4.
27 In a conventional magnetron sputtering process, a substrate is placed within a coating chamber in facing relation with a cathode 29 having a target surface of the material to be sputtered. Preferred substrates in accordance with the present invention include glass, 31 ceramics and plastics which are not detrimentally affected by the operating conditions of the coating process.
33 The cathode may be of any conventional design, preferably an elongated rectangular design, connected with a source of electrical 35 potential, and preferably employed in combination with a magnetic field to enhance the sputtering process. At least one cathode target 37 surface preferably comprises a metal alloy such as zinc/tin which is 1 6puttered in a reactive atmosphere to form a metal alloy oxide film.
Alternatively, separate targets of zinc and tin may be sputtered 3 6ubstantially simultaneously. The anode is preferably a 6ymmetrically designed and positioned assembly as taught in U.S.
5 Patent No. 4,478,702 to Gillery et al.

7 In a preferred embodiment of the present invention, a multiple layer film is deposited by cathode sputtering to form a high 9 tran6mittance, low emissivity coating. In addition to the metal alloy target, at least one other cathode target surface compri6es a 11 metal to be sputtered to form a reflective metallic layer. At least one additional cathode target surface compri6e6 titanium for 13 6puttering in an oxidizing atmosphere to depo6it a titanium oxide layer. A durable multiple layer coating having a reflective metallic 15 fil~ in combination with an antireflective metal alloy oxide film is produced as follows, using a titanium oxide layer to improve the 17 adhesion between the metal and metal oxide films while producing a neutral coated article.
19 A clean glass substrate is placed in a coating chamber which i6 evacuated, preferably to less than 10-4 torr, more preferably less 21 than 2 X 10-5 torr. A selected atmosphere of inert and reactive gas¢6, preferably argon and oxygen, i6 establi6hed in the chamber to 23 a pres6ure between 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 25 of the substrate to be coated. The target metal is sputtered, reacting with the atmosphere in the chamber to depo6it a zinc/tin 27 alloy oxide coating layer on the glas6 6urface.
After the initial layer of zinc/tin alloy oxide is 29 deposited, a cathode having a target surface of titanium metal i6 sputtered to deposit a layer of titanium oxide over the zinc/tin 31 allay oxide layer. The titanium oxide layer is preferably about 50 to 100 Angstroms thick, significantly thicker than conventional 33 primer layers. A cathode having a target surface of 6ilver is then sputtered to deposit a reflective layer of metallic silver over the 35 titanium oxide layer which improves the adhesion of the silver film to the underlying metal oxide film while producing a visually neutral 37 multiple layer low emissivity coating. A thicker 6ilver film may be 1 deposited in accordance with the present invention without altering the spectral properties of the multilayer film. An additional primer 3 layer is then deposited by sputtering a metal such as copper or titanium over the reflective silver layer to improve the adhesion 5 between the silver film and the overlying metal oxide film subsequently deposited. Finally, a second layer of zinc/tin alloy 7 oxide is deposited over the second primer layer under essentially the same conditions used to deposit the first zinc/tin alloy oxide layer.
9 In most preferred embodiments of the present invention, a protective overcoat is deposited over the final metal oxide film.
11 The protective overcoat is preferably deposited by sputtering over the metal oxide film a layer of a metal such as disclosed in U.S.
13 Patent No. 4,594,137 to Gillery et al. Suitable metals for the protective overcoat include alloys of iron or nickel, such as 15 stainless steel or Inconel. Titanium is a most preferred overcoat because of its high transmittance. In an alternative embodiment, the 17 protective layer may be a particularly chemical resistant material such as titanium oxide as disclosed in U.S. Patent No. 4,716,086 to 19 Gillery et al.

21 The present invention will be further understood from the description of a specific example which follows. In the example, the 23 zinc/tin alloy oxide film is referred to as zinc stannate although the film composition need not be precisely Zn2SnO4.
EXAMPLE
A multiple layer film is deposited on a soda-lime-silica 27 glass substrate to produce a high transmittance, low emissivity coated product. A stationary cathode measuring 5 by 17 inches (12.7 29 by 43.2 centimeters) comprises a sputtering surface of zinc/tin alloy con8isting of 52.4 weight percent zinc and 47.6 percent tin. A
31 soda-lime-silica glass substrate is placed in the coating chamber which is evaluated to establish a pressure of 4 millitorr in an 33 atmosphere of 50/50 argonjoxygen. The cathode is sputtered in a magnetic field at a power of 1.7 kilowatts while the glass is 35 co.l~yed past the sputtering surface at a rate of 110 inches (2.8 meters) per minute. A film of zinc stannate is deposited on the 37 glass surface. Three passes produce a film thickness of about 320 *Trade mark - - -1 Angstroms, resulting in a decrease in transmittance from 90 percent for the glass substrate to 82 percent for the zinc stannate coated 3 glass substrate. A stationary cathode with a titanium target is then sputtered to produce a titanium oxide layer about 50 Angstroms thick 5 over the zinc stannate, reducing the transmittance to about 78 percent. Next, a layer of silver is deposited over the titanium - 7 oxide layer by sputtering a silver cathode target in an atmosphere of argon gas at a pressure of 4 millitorr to deposit silver to a film 9 thickness of about 110 Angstroms, decreasing the transmittance of the coated substrate to about 66 percent. A thin neutral titanium primer 11 layer is sputtered over the silver layer to improve the adhesion and protect the silver layer before the final antireflective layer of 13 zinc stannate is deposited. The titanium primer layer is about 10 Angstroms thick and in the metallic state reduces the transmittance 15 to about 60 percent. However, the titanium primer layer oxidizes and the transmittance increases as the subsequent metal oxide layer is 17 depasited. Finally, the zinc/tin alloy cathode target is sputtered in an oxidizing atmosphere to produce a zinc stannate film. Four 19 passes at a rate of 110 inches (2.8 meters) per minute produce a film thickness of about 380 Angstroms, increasing the transmittance of the 21 coated product to 85 percent. The final coated product has a surface resistance of 8 ohms per square and a neutral reflectance from both 23 sides, with a luminous reflectance of 5 percent from the coated side and 6 percent from the uncoated side. In comparison, prior art films 25 using copper primer layers exhibit a slightly reddish-blue reflectance from both the coated and uncoated glass surfaces.
27 The above example is offered to illuætrate the present invention. Various modifications of the product and the process are 29 included. For example, other coating compositions are within the scope of the present invention. Depending on the proportions of zinc 31 and tin when a zinc/tin alloy is sputtered, the coating may contain widely varying amounts of zinc oxide and tin oxide in addition to 33 zinc stannate. The adhesion between a wide variety of metal and metal oxide films may be improved by means of titanium oxide layers 35 to produce visually neutral coatings in accordance with the present invention. Since the process does not require very high 37 temperatures, substrates other than glass, such as various plastics, _ ~ -- 10 --1 may be coated. A scanning cathode may be used with a stationary substrate. Process parameters such as pressure and concentration of 3 gases may be varied over a broad range. Primer layers may comprise other metals such as zirconium which produce oxides which provide 5 neutral reflectance in the multiple layer low emissivity coatings of the present invention. The scope of the present invention is defined 7 by the following claims.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY OR PRIVILEGE
IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A visually neutral reflectance, high transmittance, low emissivity article comprising:
a. a transparent nonmetallic substrate;
b. a first transparent antireflective metal oxide film having a refractive index of about 2.0 deposited on a surface of said substrate;
c. a transparent metal oxide layer having a refractive index greater than 2.0 deposited on said first antireflective metal oxide film;
d. a transparent infrared reflective metallic film deposited on said metal oxide layer;
e. a transparent metal layer deposited on said infrared reflective metallic film; and f. a second transparent antireflective metal oxide film deposited on said metal layer.

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

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

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

5. An article according to claim 4, wherein the antireflective metal oxide comprises zinc stannate.

6. An article according to claim 1, wherein the metal oxide film deposited between the antireflective metal oxide film and the infrared reflective metallic film is selected from the group consisting of titanium oxide and zirconium oxide.

7. An article according to claim 6, wherein said metal oxide film comprises titanium oxide.

8. An article according to claim 7, wherein the titanium oxide layer has a thickness of about 50 to 100 Angstroms.

9. An article according to claim 8, wherein the metal layer deposited on the infrared reflective metallic film comprises titanium.

10. An article according to claim 9, further comprising a titanium oxide overcoat on the second antireflective metal oxide film.

11. A method for depositing a visually neutral, high transmittance, low emissivity film, comprising the steps of:
a. sputtering a metal cathode target in a reactive atmosphere comprising oxygen thereby depositing a transparent antireflective metal oxide film having a refractive index of about 2.0 on a surface of a transparent substrate;
b. sputtering in a reactive atmosphere a transparent neutral metal oxide layer having a refractive index greater than 2.0 over said anti-reflective metal oxide film;
c. sputtering a transparent infrared reflective metallic film over said neutral metal oxide layer;
d. sputtering a transparent neutral metal layer over said infrared reflective metallic film; and e. sputtering in a reactive atmosphere a second transparent anti-reflective metal oxide film over said neutral metal layer.

12. A method according to claim 11, wherein said neutral metal oxide layer is selected from the group consisting of titanium oxide and zirconium oxide.

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

14. A method according to claim 13, wherein said antireflective metal oxide films comprise an oxide reaction product comprising zinc and tin.

15. A method according to claim 14, wherein said antireflective metal oxide films comprise zinc stannate.

16. A method for making a visually neutral, 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 zinc and tin in a reactive atmosphere comprising oxygen to deposit a first transparent, antireflective, zinc/tin metal alloy oxide film on a surface of said substrate;
c. sputtering a titanium target in an oxidizing atmosphere to deposit a neutral titanium oxide layer on said antireflective zinc/tin oxide film;
d. sputtering a silver cathode target in an inert atmosphere to deposit a transparent metallic silver film on said titanium oxide layer;
e. sputtering a titanium target in an inert atmosphere to deposit a neutral titanium layer on said silver film; and f. sputtering a cathode target comprising zinc and tin in a reactive atmosphere comprising oxygen to deposit a second transparent, antireflective zinc/tin metal alloy oxide film on said titanium layer.

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

18. The method according to claim 16, wherein said first and second zinc/tin metal alloy oxide films comprise zinc stannate.

19. The method according to claim 16, further comprising the step of sputtering a titanium oxide overcoat on the second zinc/tin oxide film.