(51) Int.Cl.⁶:

C 03 C 17/36

(19) Federal Republic of Germany C 03 C 17/09

[emblem] C 23 C 14/14

German Patent Office C 23 C 14/35

(12) Patent

(10) DE 195 33 053 C1

(21) Application number: 195 33 053.6-45

(22) Filing date: July 7, 1995

(43) Disclosure date: -

(45) Publication date

of patent grant: April 17, 1997

Opposition may be lodged within three months following publication of grant.

(73) Patent holder:

VEGLA Vereinigte Glaswerke GmbH, 52066 Aachen, DE

(72) Inventors:

Huhn Norbert, 5213 Herzogenrath, DE;

Heinz, Bernhard, Dr., 52074 Aachen, DE

(56) Documents taken into consideration to evaluate patentability:

DE 28 36 943 B2

DE 28 30 7223 A1

EP 02 81 894 B1

(54) Method for Coating a Glass Pane with a Stack of Layers Exhibiting at Least one Silver Layer

(57) Described is a method for manufacturing flexible and/or prestressable stacks of layers with a silver coating as the functional layer by cathode sputtering. The multilayer exhibits above and, if desired, also below the silver layer a thin metallic protective layer, which has a high oxygen affinity and which is deposited by oxidation during heat treatment for bending and/or prestressing. The silver coating is formed by sputtering in an oxygen-containing working mixture, which contains preferably 20 to 70 % by vol. of oxygen. IN a subsequent heat treatment, the oxygen migrates out of the silver layer into the adjacent protective layers. Since the lattice sites in the silver coating become free, their structure and stress states are influenced in such a manner that the thermal stability of the silver coating is increased.

DE 195 33 053 C1

FEDERAL PRINTING OFFICE 02.97 702 116/268 20

Specification

The invention relates to a method for manufacturing a thermally stressable substrate, which is made of glass or plastic and which is provided with a stack of layers by the cathode sputtering method. This stack of layers exhibits one or more layers of silver; and said layer(s) of silver exhibit(s) exhibit immediately adjacent protective layers, which are made of a metal or a metal alloy or a hypostoichiometrically oxidized metal or a hypostoichiometrically oxidized metal compound.

Layer systems exhibiting one or more metallic layer(s) of silver as their functional layer have, compared to other layers or layer systems, the advantage that at a high transmission in the visible part of the spectrum and a high reflection in the infrared spectral range said layers look neutral in the see-through mode or reflective mode. In addition, the layers of silver exhibit a relatively high electric conductivity, so that glass panes, which are provided with such layer systems, can also be used as heatable glass panes. In this case the multiple layers can be arranged either on the surface of a glass pane or on a transparent carrier foil, which is sandwiched, for example, between two glass panes and is connected to them by means of adhesive layers in order to form a composite glass pane. The transmission and reflection properties of the silver layer in the visible part of the spectrum can be further improved by means of the other layers of the layer system. Owing to their especially good properties, layer systems with one silver layer or with a plurality of silver layers as the actual functional layer are used on a large scale in both the construction sector and for glazing vehicles.

Usually the layer(s) of silver are applied, according to the invention conforming to it genre, by sputtering in a pure argon atmosphere without any oxygen content, whereas the other layers, in particular the metal oxide layers, are applied by reactive sputtering in an oxygen-containing argon or argon nitrogen atmosphere. A method of this type is known, for example, from the EP 0 281 894 B1.

The DE 28 30 723 A1 discloses a method for manufacturing multilayer systems, which contain a silver layer. In this method the silver layer and the adjacent dielectric layers are applied in essence by cathode sputtering in the same oxygen-containing atmosphere with an oxygen content of a maximum of 10%. In this case the maximum amount of oxygen is supposed to be determined in such a manner that the silver layer that is applied does not differ from a layer applied by sputtering in the purest protective gas atmosphere. In the field examples, the oxygen content is at most 2.5%. This prior art method exploits the knowledge that silver can be applied with a limited amount of oxygen in the working gas without impairing the optical properties of the layer.

In a method for reactive vapor deposition of a layer system comprising TiO_x - AG - TiO_x, where 1 < x < 2 it is known from the DE 28 36 943 B2 to carry out the vapor deposition process in an oxygen-containing atmosphere. However, at the same time the oxygen partial pressure is adjusted in such a way that the titanium oxide base layer is extremely underoxidized, so that it still exhibits the required properties for the silver layer to form nuclei.

[column 2]

In this prior art method a subsequent heating in air to approximately 250 deg. C is recommended for post-oxidation deposition of the TiO_x layers.

Even though for the application in the construction sector and for use in vehicles, the glass panes must often be subjected to a heat treatment at relatively high temperatures when, for example, they are bent and/or thermally prestressed. In order to bend and/or thermally prestress, the glass planes must be heated to a temperature of approximately 650 deg. C. If the glass panes are coated and if the coating was applied on the glass pane prior to this heat treatment, the layers also reach these high temperatures. This feature puts high demands on the stack of layers. Even if the layers are disposed on a polymer film, a heat treatment at raised temperatures may follow, for example during the further processing of the layered films to form a composite glass.

When a coated glass pane is heat treated at high temperatures, the silver layer is especially apt to change so that the transmission is reduced, and the coated glass pane looks matte and spotty. In addition, the electrical surface resistance of the silver layer may be modified. These effects are known. It is also known that the observed changes in the silver layer are induced by the oxygen, which penetrates into the silver layer at the high temperatures.

In order to decrease or eliminate the unfavorable effect of the oxygen during heat treatment, a thin metal layer is disposed on the silver layer, or the silver layer is embedded between the two thin metal layers. These metal layers, which are also referred to as the "sacrificial metal layers" or as the "blocker layers", have the task of binding the oxygen, penetrating in the direction of the silver layer, while forming metal oxides. However, the application of such metal layers is limited because as the thickness of the metal layers increases, the transmission decreases. Since, on the other hand, the transmission increases to the degree that the metal layers are deposited by oxidation, the metal layers may only be so thick that during the heat treatment they are transformed as much as possible into oxide layers. However, on the other hand, the metal layers are supposed to absorb all of the oxygen. Therefore, for these reasons the layer thickness of the sacrificial metals must be adapted exactly to the subsequent heat treatment process. In the field it is extremely difficult so that the desired effect cannot be achieved with certainty in this way.

The object of the invention is to improve the method described in the introductory part to the effect that the method for producing thermally stressable layers under the conditions of the field becomes more reliable, so that the risk of impairing the silver layer(s) during the heat treatment is further reduced; and simultaneously the deposition by oxidation of the adjacent protective layers for increasing the transmission is promoted.

The invention achieves this objective in that the silver layer(s) is/are deposited by sputtering with a working gas mixture that contains 10 to 90 % by vol. of oxygen; and after the stack of layers has been applied, a heat treatment is carried out.

[column 3]

It is desirable that the working gas mixture contains between 20 and 70 % by vol. of oxygen.

The additional gases of the working gas mixture may be the customary working gases, in particular argon and nitrogen, but it is clear that other working gases may also be used.

For the metal layers, between which the silver layer is embedded, a further development of the invention uses in a practical way metals with a high affinity for oxygen - that is, in particular the metals Al, Ti, Ta, W, Zr, Ce, V, Mo, Ni, Cr and Nb or alloys or mixtures of these metals. Instead of pure metals or metal alloys, these layers may also be made of underoxidized metal oxides or other metal compounds - for example, nitrides or oxinitrides - provided they are not deposited by oxidation in stoichiometric amounts but rather are still capable of absorbing additional oxygen.

It has been demonstrated surprisingly that the stability of the silver layer against the influence of oxygen at high temperatures is improved in that following the additional of oxygen to the working gas an oxygen-containing silver layer is deposited by sputtering. Contrary to all expectations, the oxygen, which is incorporated in this way into the silver layer from the beginning, has a positive effect on the silver layers during the subsequent heat treatment.

The reason for the unexpected stabilizing effect of the oxygen in the silver layer has not been known to date. However, it may be assumed that the silver oxide, which is produced during deposition by sputtering, disassociates at the temperatures of the heat treatment, and that the oxygen atoms, which are split off and/or which are present in the silver layer, migrate to one of the adjacent metal layers and contribute to the deposition by oxidation of the metal layers and, thus, contribute to the transformation into absorption-free layers of metal compounds.

If one agrees with the attempts in the EP 0281894 B1 to give a reason for the deterioration of the silver layer and the good influences of the adjacent metal layers that are deposited by oxidation, then the deterioration of the silver layer is due to the silver forming agglomerates. Said deterioration is favored by the compressive stresses that promote the formation of agglomerates as a consequence of the varying thermal expansion of the glass substrate. The deposition by oxidation of the adjacent metal layers is associated with an increase in the volume, which in turn induces tensile stresses in the silver layer and the tensile stresses counteract the aforementioned compressive stresses. If one accepts this type of mechanism, then the observed good effect of the invention can be explained by the fact that the emigration of the oxygen atoms inside the silver layer forms voids, which lead to a further reduction in the compressive stresses in the silver layer and, thus, to a further decrease in the formation of agglomerates.

The method of the invention and the improvements to be achieved with said method is explained below with the aid of one embodiment and a comparison example.

[column 4]

Embodiment

In a conventional magnetron coating system the following layer system was produced with the layer thicknesses that are listed as follows.

Float Glass

SnO₂ 40 nm

Nb₂O₅ 12 nm

NB 2 nm

Ag 10 nm

Nb 4 nm

SnO₂ 40 nm

The oxide layers were deposited by sputtering in a working gas mixture comprising 40 % by vol. of argon and 60 % by vol. of oxygen at a total pressure of 3.5 · 10^-3. The metal Nb layers were deposited by sputtering in pure argon atmosphere at a pressure of 3 · 10^-3, whereas the silver layer was deposited by sputtering in working gas atmosphere comprising 37.5 % by vol. of argon and 62.5 % by vol. of oxygen at a total pressure of 3.5 · 10^-3.

The glass pane with the layer that was produced in this manner exhibits a transmission TL of 54% and a surface resistance R of 5 ohm per square area.

The coated glass pane was heated to a temperature of 660 deg. C, heat at this temperature for a period of 5 min. and then cooled to room temperature in resting air. Then the transmission and the surface resistance were measured again. As a consequence of the deposition by oxidation of the Nb layers, the transmission had risen to 84%. The surface resistance was unchanged at 5 ohm/square area. The layer did not exhibit any optical defects.

Comparison Example

In the same conventional magnetron coating system, the same layer system as in the embodiment was produced on the same float glass and with the same layer thickness. The only difference in the production was that the silver layer was deposited by sputtering in the customary way in a pure argon atmosphere at the same working gas pressure.

The glass pane that was coated in this manner exhibits a transmission TL of 45% and a surface resistance of 5 ohm/square area.

Then the coated glass pane was subjected to the same heat treatment under the exact same conditions as described in the embodiment. After cooling to room temperature, the coated glass pane exhibited a transmission TL of 56%. The surface resistance of the layer was so high that it could no longer be measured. Under normal daylight illumination the layer showed optical defects and was cloudy and had spots of red corrosion.

Patent Claims

1. Method for manufacturing a thermally stressable substrate, which is made of glass or plastic, wherein the substrate is provided, according to the method of cathode sputtering, with a stack of layers, which exhibits one or more silver layers; and the silver layer(s) exhibit(s) adjacent protective layers, which made of a metal or a metal alloy or a hypostoichiometrically oxidized metal or a hypostoichiometrically oxidized metal compound, characterized in that the silver layer(s) is/are deposited by sputtering with a working gas mixture that contains 10 to 90 % by vol. of oxygen; and after the stack of layers has been applied, a heat treatment is carried out.

[column 5]

2. Method, as claimed in claim 1, characterized in that the working gas mixture contains 20 to 70 % by vol. of oxygen.

3. Method, as claimed in claim 1 or 2, characterized by the use of metals or metal compounds having a high oxygen affinity for the protective layers that are adjacent to the silver layer.

4. Method, as claimed in claim 3, characterized in that Ti, Al, W, Ta, Zr, Hf, Ce, V, Ni, Cr, Zn or Nb or alloys or mixtures of these metals or hypostoichiometrically oxidized oxides or other oxygen-absorbing compounds of these metals are used for the protective layers.

5. Method, as claimed in any one of the claims 1 to 4, characterized in that the protective layers, which are adjacent to the silver layer, are deposited by sputtering in a thickness ranging from 1 to 20 nm..