GB2116590A

GB2116590A - Sputter coated glass panes

Info

Publication number: GB2116590A
Application number: GB08301382A
Authority: GB
Inventors: Wolf-Dieter Munz
Original assignee: Leybold Heraeus GmbH
Current assignee: Balzers und Leybold Deutschland Holding AG
Priority date: 1982-01-21
Filing date: 1983-01-19
Publication date: 1983-09-28
Also published as: FR2520008B1; CA1189823A; FR2520008A1; AT380030B; GB8301382D0; ATA455182A; SE8300247D0; SE8300247L; GB2116590B; DE3201783A1

Abstract

The invention relates to the production of layer-coated glass panes which are substantially achromatic to reflected and transmitted light, and which reflect a high percentage of the infrared radiation, by cathode sputtering of targets containing indium and tin. With a view to minimising the use of costly materials such as gold and indium and to producing layers possessing improved stability, a glass substrate has applied thereto the following layers: (a) At least one layer of indium/tin oxide containing from 50 to 98% indium and having a layer thickness ranging from 50 to 500 nm, and preferably from 100 to 400 nm, and (b) At least a surface layer of at least one of the oxides of tin, bismuth titanium and tantalum and having a layer thickness ranging from 400 to 1500 nm, and preferably from 600 to 900nm. The indium in layer (a) may be substituted by cadmium.

Description

SPECIFICATION Glass panes and a method of making them The invention relates to a method for the production of glass panes which are substantially achromatic to reflected and transmitted light, and which reflect a high percentage of the infrared radiation, by cathode sputtering of targets containing indium and tin or cadmium and tin.

Glass panes produced by methods of this type serve to keep infrared or heat radiation out of rooms closed by such panes and/or to retain them therein. Preferred fields of application are the glazing of buildings and automobiles.

It is known to produce infrared-reflecting panes by coating achromatic glass with combinations of dielectric layers and layers of metals from the group consisting of gold, silver and copper. These layers must be well protected against mechanical and chemical influences. Silver and copper undergo slight chemical changes where they are in contact with the atmosphere. The use of gold is limited for reasons of cost. Moreover, such layer systems cannot be heated to the temperatures employed in the bending of automobile glass if the glass was coated while flat. The protection afforded by laminated safety glass having an air space is not available in automobile glasswork anyhow.

Attempts have been made to use semiconductor based monolithic layers having comparable properties. It has been found empirically that the degree of infrared reflection by thin layers increases approximately with the electrical conductivity. In some cases, the electrical conductivity is used, in addition, to heat the panes, as, for example, in the case of automobile glass. Prior art monolithic layers of this type are formed of tin oxide, indium/tin oxide or cadmium/tin oxide, optionally with additional doping agents. The cadmium/tin oxide used is preferably present in the form of cadmium stannate.

To produce sufficiently low surface resistivity or high infrared reflection, the tin oxide layers must be applied in such thickness that they result in undesired chromaticity when viewed in both incident and transmitted light. Suficiently thick layers which have a high indium component and which per se are achromatic are impracticable because of the high cost of indium, which is in short supply throughout the world. (It should be borne in mind that the indium content of such layers typically is about 90%.) Layers containing cadmium are increasingly being rejected because of the toxicity of this material, unless they are provided with a protective layer.

All percentages given herein are by weight unless expressly stated otherwise.

The object of the invention thus is to provide a method of the type outlined above which permits substantial savings in expensive materials such as gold and indium and results in layers having improved resistance to mechanical action upon the surface as well as improved chemical stability, particularly to the action of oxygen.

In accordance with one aspect of the invention, this object is accomplished by depositing by sputtering, in an oxygen-containing inert gas atmosphere and in any desired sequence, (a) at least one layer of indium/tin oxide containing from 50 to 98% indium until a layer thickness ranging from 50 to 500 nm, and preferably from 100 to 400 nm, has been obtained, and (b) at least one layer of at least one of the oxides of tin, bismuth, titanium and tantalum until a layer thickness ranging from 400 to 1 500 nm, and preferably from 600 to 900 nm, has been obtained.

It has surprisingly been found that the layer with the costly indium component can be substantially reduced with respect to the thickness normally required for monolithic layers and replaced by a layer of at least one of the oxides of tin, bismuth, titanium and tantalum without the optical properties in reflected and transmitted light being adversely affected thereby. Such layers can readily be used in place of layers which originally could be produced only with the inclusion of metals such as gold. The layers in accordance with the invention possess improved resistance to mechanical action upon the surface and improved chemical resistance to atmospheric contamination, detergents, etc., and particularly to the action of oxygen.

Either or both of the layers (a) and (b) may be divided into individual layers, and layers of the types (a) and (b) may be arranged to alternate so that a multiple-layer system is formed. When the layers of the types (a) and (b) are divided into a plurality of individual layers, "layer thickness" means the total thickness of the layers, in other words, the sum of all individual layers of the same type, (a) or (b).

The target material for the type (a) layer may be a metallic, sheetlike target formed of an indium/tin combination containing from 50 to 98% indium, the rest being tin. "Indium/tin combination" means both alloys and powder blends as well as matrix arrangements wherein one of the metals in rod or platelet form is embedded in the surface of the other metal. Such a target material is sputtered in an oxygen-containing argon atmosphere, and the layer so deposited is subjected to a heat treatment at a temperature between 2500C and the softening temperature of the glass substrate. This softening temperature, which depends on the kind of glass used, will be found in the pertinent handbooks.

The use of a metallic target material has the special advantage that the residue left after the target has become exhausted can be reprocessed, which cannot be done, or cannot readily be done, with an oxidic target material.

However, it is readily possible to use also a hotpressed, electrically conductive target material consisting of an indium/tin oxide mixture wherein the indium/tin ratio ranges from 98:2 to 50:50.

Whereas in the sputtering of a metallic target material the sputtering gas must have a high oxygen content, in the sputtering of an oxidic target material the oxygen content can be substantially reduced, it being even possible in the limiting case to carry out the sputtering operation in a neutral atmosphere.

All targets may be sputtered with a directcurrent voltage as the sputtering voltage. This is true also of oxidic targets since in the hot pressing by which they were produced sufficient electrical conductivity was imparted to them so that the use of the high frequency normally required in the sputtering of oxidic targets can be dispensed with.

In some applications in which the pane must be bent after it has been coated, the described layer system can be expected to offer advantages over systems provided with a conductive metal layer.

The effects of diffusion processes on the conductive layer can then be substantially reduced through the great thickness of the semiconductive layer.

The object of the invention is also accomplished according to another aspect of the invention, in a method of the type described above, by the cathode sputtering of targets containing cadmium and tin for depositing, in an oxygen-containing inert gas atmosphere, (a) at least one layer of cadmium/tin oxide containing from 50 to 98% cadmium until a layer thickness ranging from 50 to 500 nm, and preferably from 100 to 400 nm, has been obtained, and (b) at least one layer of at least one of the oxides of tin, bismuth, titanium and tantalum until a layer thickness ranging from 400 to 1 500 nm, and preferably from 600 to 900 nm, has been obtained, one of said layers forming the top layer.

A layer system produced in this manner offers the same advantages, the toxicological effects of cadmium being neutralized by applying the cadmium-containing layer as the first layer t6 the substrate rather than locating it on the surface, while the top layer formed of an oxide which does not contain cadmium completes the layer system.

The requisite layer properties will be attained if the indium/tin oxide layer or the cadmium/tin oxide layer is deposited in such a layer thickness that the surface resistivity will range from 3 to 1 5 ohms, and preferably from 10 to 13 ohms.

An example of the simplest of the possible layer systems is illustrated in the accompanying drawing, which shows a section through a glass substrate 1 with an indium/tin oxide layer 2 applied directly thereto and a top layer 3 of tin oxide applied as a surface layer.

EXAMPLES In a type Z600 cathode-sputtering apparatus made by Leybold-Heraeus GmbH, panes of window glass 3 mm thick and measuring 40 x 40 cm were coated as substrate at a distance of 58 mm from the target surfaces of a system of two type PK500L high-power cathodes (with magnetic-field amplification). The cathodes were connected to a source of direct current which at a maximum sputtering voltage of 750 volts delivered a maximum power of 7.5 kilowatts. The target dimensions (surfaces) were in all cases 500 x 88 mm. The substrates were displaced in a direction transverse to the major target axis and to the cathodes at a rate of 20 cm/min. The operation was performed at a total pressure of 5 > c x 10-3 millibars after the apparatus had been evacuated to 2 x 10-5 millibars.

EXAMPLE 1 The first target consisted of a hot-pressed oxide mixture with an indium/tin ratio of 90:10. With a specific power of 1.6 watts per square centimetre of target surface, seven passes of the pane were required to obtain a layer thickness of 370 nm.

The surface resistivity of this layer was 13 ohms.

During sputtering, sputtering gas consisting of argon and oxygen in a volume of 24:1 was introduced.

The second target was pure metallic tin. With a specific power of 5.5 watts per square centimetre of target surface, eight passes of the pane were required to obtain a layer thickness of 620 nm.

The volume ratio of argon to oxygen in the sputtering gas introduced was 1:1.

EXAMPLE 2 The first target consisted of an indium/tin alloy with an indium/tin ratio of 95 :5.

With a specific power of 5 watts per square centimetre of target surface, five passes of the pane were required to obtain a layer thickness of 260 nm. The surface resistivity of this layer was 1 3 ohms. During sputtering, sputtering gas consisting of argon and oxygen in a volume ratio of 1:1 was introduced.

The second target was pure metallic tin. With a specific power of 5.5 watts per square centimetre of target surface, eleven passes of the pane were required to obtain a layer thickness of 850 nm.

The volume ratio of argon to oxygen in the sputtering gas introduced was 1:1. The above surface resistivity was achieved after a 2-hour annealing operation at 400cm.

EXAMPLE 3 The first target consisted of hot-pressed cadmium stannate with a cadmium/tin ratio of 93:7.

With a specific power of 2.0 kolowatts per square centimetre of target surface, six passes of the pane were required to obtain a layer thickness of 400 nm. The surface resistivity of this layer was 11 ohms.

During sputtering, sputtering gas consisting of argon and oxygen in a volume ratio of 20:1 was introduced.

The second target was pure metallic tin. With a specific power of 5.5 watts per square centimetre of target surface, ten passes of the pane were required to obtain a layer thickness of 750 nm.

The volume ratio of argon to oxygen in the sputtering gas was 1:1.

EVALUATION The products obtained in accordance with Examples 1 to 3 were subjected to the following tests: 1. The transmission pattern was measured in the light wavelength range from 300 to 850 nm.

Above 450 nm, transmission values of better than 70% were observed.

2. Infrared reflection of the layer systems in the measure range from 4000 to 1 5000 nm was better than 75%.

3. The achromaticity was determined with a Macbeth type 1 500 colorimeter by means of reflection measurement and the measurements were analyzed by means of a microprocessor. The colour interpretation was in CIELAB units "a" and "b" on the basis of measurements made on the layer through the pane and directly on the layer.

Typical values for "a" were 2.5 units, and for "b", -3.0 units, which indicate substantial achromaticity.

4. As a chemical test, the condensation water/climatic changes test with an SO2containing atmosphere in conformity with DIN 50018 was performed. Moreover, a saltwater spray test was run with a 4% salt (sodium chloride) solution at 400 C. In keeping with the requirements of the glass industry, these tests can be regarded as having been passed.

5. As a mechanical test, the grid-cut test in conformity with DIN 53151 was performed. It proved possible to satisfy testing stage Gt2. In keeping with the requirements of the glass industry, the mechanical properties of the layers can be regarded as quite good.

In the production of hot pressing of targets from oxides or oxide mixtures which are not limited to specific target configurations, the use of elevated temperatures and pressures is a factor.

An important factor is the "degree of compaction", which is the ratio between the density obtained during the pressing of the target and the theoretical density of the solid, or nonporous, material. While the degree of compaction usually is only in the 50 to 70% range for reasons of economy, here it is at least 75%, and preferably at least 80%, of the density of the solid material. With the degrees of compaction used up to now, and with the experimental use of direct current, sputtering gradually comes to a standstill; but using the high degree of compaction specified has surprisingly made it possible to maintain the sputtering process for practically any desired length of time even when direct current is used. Research has shown that with the low degrees of compaction used in the prior art and the considerable porosity of the target there is evidently a migration of oxygen into the target material which results in reciprocal insulation of the oxide particles at the grain boundaries. In contrast thereto, it has been found that when the 75% lower iimit for the degree of compaction is exceeded this growing insulating effect within the target is apparently suppressed.

Claims

1. A method for the production of glass panes which are substantially achromatic to reflected and transmitted light, and which reflect a high percentage of the infrared radiation, by cathode sputtering of targets containing indium and tin, characterised in that there are deposited by sputtering, in an oxygen-containing inert gas atmosphere, and in any desired sequence, (a) at least one layer of indium/tin oxide containing from 50 to 98% indium until a layer thickness ranging from 50 to 500 nm has been obtained, and (b) at least one layer of at least one of the oxides of tin, bismuth, titanium and tantalum until a layer thickness ranging from 400 to 1 500 nm has been obtained.

2. A method according to Claim 1, wherein the indium/tin oxide layer has a thickness of between 100 and 400 nm.

3. A method according to Claim 1, wherein the indium/tin oxide layer is deposited in such layer thickness that the surface resistivity ranges from 3 to 1 5 ohms.

4. A method according to Claim 3, wherein the indium/tin oxide layer has a surface resistivity of between 10 and 13 ohms.

5. A method according to any one of Claims 1 to 4, wherein a metallic target consisting of an indium/tin combination (an alloy, powder blend, or matrix arrangement) containing from 50 to 98% indium, the rest being tin, is used as target material and that the layer so produced in an oxygen-containing argon atmosphere is subjected to a heat treatment at a temperature between 2500C and the softening temperature of the glass substrate.

6. A method according to Claim 1, characterised in that the target material is a hotpressed electrically conductive target of indium/tin oxide wherein the ratio of indium to tin ranges from 98:2 to 50:50.

7. A method according to any one of the preceding Claims, wherein the oxide layer (b) has a thickness of between 600 and 900 nm.

8. A method for the production of glass panes which are substantially achromatic to reflected and transmitted light, and which reflect a high percentage of the infrared radiation, by cathode sputtering of targets containing cadmium and tin, characterised in that there are deposited, in an oxygen-containing inert gas atmosphere, (a) at least one layer of cadmium/tin oxide containing from 50 to 98% cadmium until a layer thickness ranging from 50 to 500 nm has been obtained, and (b) at least one layer of at least one of the oxides of tin, bismuth, titanium and tantalum until a layer thickness ranging from 400 to 1 500 nm has been obtained, one of said layers forming the top layer.

9. A method according to Claim 8, wherein the cadmium/tin oxide layer has a thickness of between 100 and 400 nm.

10. A method according to Claim 8 or Claim 9 wherein the oxide layer (b) has a thickness of between 600 and 900 nm.

11. A method according to any one of the preceding Claims, wherein a said oxide layer (b) is applied as the first layer and a further said oxide layer (b) is applied as a top layer.

12. A glass pane having the properties of being substantially achromatic to reflected and transmitted light and reflecting a high percentage of the infrared radiation, said properties being produced by thin layers containing indium and tin, and comprising (a) at least one layer of indium/tin oxide containing from 50 to 98% indium and having a layer thickness ranging from 50 to 500 nm and (b) at least one layer of at least one of the oxides of tin, bismuth, titanium and tantalum and having a layer thickness ranging from 400 to 1500 nm.

13. A glass pane having the properties of being substantially achromatic to reflected and transmitted light and reflecting a high percentage of the infrared radiation, said properties being produced by thin layers containing cadmium and tin, characterised by (a) at least one layer of cadmium/tin oxide containing from 50 to 98% cadmium and having a layer thickness ranging from 50 to 500 nm and (b) at least one layer of at least one of the oxides of tin, bismuth, titanium and tantalum and having a layer thickness ranging from 400 to 1 500 nm, one of the last-mentioned layers forming the top layer.

14. A glass pane according to Claim 12 or Claim 13, wherein the oxide layer (a) has a thickness of between 100 and 400 nm.

1 5. A glass pane according to Claim 12 or Claim 13, wherein the oxide layer (b) has a thickness of between 600 or 700 nm and 900 nm.

16. A glass pane according to Claim 7 or Claim 8, characterised in that a said oxide layer (b) is applied as a first layer directly to the substrate and a further said oxide layer (b) is provided as a top layer.

1 7. A method for the production of glass panes which are substantially achromatic to reflected and transmitted light, substantially as hereinbefore described with reference to the Examples.

18. A 8. glass pane when produced by the method of any of Claims 1 to 11 and 17.