WO2001071054A1

WO2001071054A1 - Process for coating glass surfaces

Info

Publication number: WO2001071054A1
Application number: PCT/GB2001/001091
Authority: WO
Inventors: Jose Manuel Gallego; John Robert Siddle
Original assignee: Pilkington Plc
Priority date: 2000-03-22
Filing date: 2001-03-13
Publication date: 2001-09-27
Also published as: GB0006801D0; AU4080901A

Abstract

A process for the production of a coated substrate by depositing an electrically conductive metal oxide layer on to a surface of a substrate by a low pressure deposition process performed in a coating atmosphere containing a gaseous hydrocarbon. Coated substrates produced by this process have less batch to batch variation in conductivity. The preferred metal oxide is indium tin oxide, the preferred hydrocarbon is methane and the preferred substrate is glass. Preferably, the substrate is at a temperature of below 250 °C.

Description

PROCESS FOR COATING GLASS SURFACES

The present invention relates to a process for the production of a coated substrate by depositing an electrically conductive metal oxide layer on to the surface of a substrate by a low pressure deposition process.

It is known to deposit metal oxide layers on to the surface of substrates by. low pressure deposition processes (usually performed at pressures of 10^"1 mbar and below), including evaporation and sputtering. EP O 983 973 A2 discloses deposition of non- conductive tin oxide and zinc oxide layers in a coating atmosphere containing methane. Particularly useful are electrically conductive metal oxide layers deposited on to glass substrates for use in infra-red reflecting insulating glazings, as substrates for electronics applications or as components in electrochromic, variable transmission windows.

A known electrically conductive metal oxide suitable for forming transparent coating layers on glass or other substrates is indium tin oxide (ITO) which consists of indium oxide doped with, usually, 5-10 atomic % tin. ITO coating layers are often deposited by DC magnetron sputtering from a substoichiometric indium tin oxide target. Substoichiometric ITO targets have sufficient electrical conductivity to support efficient DC magnetron sputtering but to obtain the electrical and optical properties required in the deposited layer, it is necessary to add oxygen to the sputtering atmosphere and so adjust the oxygen content of the ITO layer.

ITO layers are usually deposited at temperatures of 250°C or greater, because at these deposition temperatures the electrical conductivity of the ITO layer is relatively high (i.e. the resistivity is relatively low). For example, EP 0 801 145 Al discloses deposition of ITO by sputtering at 250°C or 400°C from a sputtering atmosphere containing carbon dioxide.

Under certain deposition conditions oxygen vacancies in electrically conductive metal oxide layers, especially ITO, have a large effect on the conductivity so that under deposition conditions that are nominally the same, small variations in e.g. oxygen or water vapour content from air leaks can have a large effect on conductivity, leading to poorly reproducible conductivity. The present invention aims to address this problem, and provide a process for depositing electrically conductive metal oxide layers with more reproducible batch to batch conductivity.

The present invention accordingly provides a process for the production of a coated substrate comprising depositing an electrically conductive metal oxide layer on to the surface of a substrate by a low pressure deposition process performed in a coating atmosphere containing a gaseous hydrocarbon.

This is advantageous because the reproducibility of the conductivity of the deposited layer is improved by the presence of the gaseous hydrocarbon (i.e. there is less batch to batch variation in conductivity).

Electrically conductive metal oxides that may be suitable for use in the invention include, doped tin oxide (for example fluorine doped or antimony doped tin oxide), doped zinc oxide (especially aluminium doped zinc oxide and indium doped zinc oxide), cadmium stannate and indium oxide. Preferably the electrically conductive metal oxide layer comprises indium oxide, more preferably doped indium oxide and most preferably indium tin oxide (ITO, i.e. indium oxide doped with tin).

In principle, the gaseous hydrocarbon may be any hydrocarbon which is relatively volatile under the conditions of low pressure deposition. Preferably the gaseous hydrocarbon comprises a to C hydrocarbon, especially an alkane. The most preferred gaseous hydrocarbon comprises methane, because it is inexpensive, volatile and provides excellent reproducibility of the conductivity of the deposited layer. In addition, relatively small amounts of methane are required in order to produce the surprising effects of the invention, which is advantageous because small amounts of methane do not unacceptably increase the pressure of the coating atmosphere during the low pressure deposition process.

It is preferred if the process according to the invention is performed wherein the layer is deposited onto the substrate when the substrate is at a temperature of below 250°C, preferably 200°C or below and more preferably 100°C or below. Most preferably the substrate is at a temperature of about room temperature.

Temperatures below 250°C are advantageous because other layers that may be deposited before the electrically conductive metal oxide layer may be damaged by higher temperatures. This is especially important for such applications as electrochromic glazings which may require the deposition of multilayer coatings. Low temperatures also cause less stress in the substrate, reducing the possibility of breakage. Furthermore, lower temperatures reduce the need for cooling or temperature cycling which has the advantage of speeding up the production process. Previously, depositing ITO layers at temperatures below 250°C has resulted in layers with poor mechanical properties, the layers frequently peeling off the substrate. The presence of a gaseous hydrocarbon improves the mechanical properties of the coating, enabling ITO layers to be successfully deposited at relatively low temperatures of below 250°C.

The electrically conductive metal oxide layer deposited according to the invention may be the only coating layer or be one layer in a multilayer coating.

Low pressure deposition processes are processes conducted at pressures of usually below about 10^"1 mbar and include evaporation, low pressure CND, and sputtering. The preferred low pressure deposition process is sputtering, especially DC magnetron sputtering. If the layer is deposited using sputtering from a metallic or substoichiometric oxide target (especially metallic In/Sn targets or substoichiometric ITO targets) the coating atmosphere will contain an inert gas (preferably argon) and will preferably also contain a source of oxygen.

Thus, preferably, the low pressure deposition process is sputtering and the coating atmosphere additionally contains a source of oxygen. The source of oxygen is preferably oxygen gas.

Surprisingly, addition of a gaseous hydrocarbon to a coating atmosphere of e.g. argon and oxygen can increase substantially the conductivity of the deposited layer. However, too much gaseous hydrocarbon may cause the conductivity of the layer to reduce. It is therefore advantageous for the coating atmosphere to contain gaseous hydrocarbon equivalent to about 20-100 vol % of the amount of oxygen in order to provide the surprising increase in conductivity.

The relative proportions of the inert gas, source of oxygen and gaseous hydrocarbon in the coating atmosphere may be adjusted by trial and error to provide suitable conductivities and optical properties of the deposited layer.

The substrate on which the process of the invention is performed may be any suitable material but is preferably glass, especially soda lime silicate float glass. Thus, the present invention further provides a coated glass obtainable by a process comprising depositing an electrically conductive metal oxide layer on to the surface of a glass substrate by a low pressure deposition process performed in a coating atmosphere containing a gaseous hydrocarbon.

Coated glasses according to the invention have many uses, especially as transparent electrically conductive substrates in electronic applications, in liquid crystal or other displays and in electrochromic variable transmission glazings. A further use of coated glasses according to the invention is as infra-red reflecting glazings.

The invention is illustrated but not limited by the following Examples in which all coatings were deposited by DC magnetron sputtering using a vertical in-line sputter system. The coating atmosphere consisted of a mixture of flowing, gases with a total pressure of about 2 x 10^"3 mbar. The sputtering power was 1000 W (dc) on a racetrack 25cm long using a 37.5 cm x 10 cm target. All coatings were deposited on substrates at about room temperature (20°C). The gases used to form the coating atmosphere were argon (zero grade, supplied by BOC Ltd), oxygen (zero grade, supplied by BOC Ltd) and methane (zero grade, supplied by BOC Ltd). The flow rates of gases in the Examples are given in seem (i.e. cm min of gas measured at standard temperature and pressure).

The coatings described in Examples 1 to 12 and Comparative Examples A to I were deposited using substoichiometric targets of indium tin oxide (10 atomic % tin, 99.99 grade) obtained from Testbourne Ltd (United Kingdom).

The coatings described in Examples 13 to 23 were deposited using substoichiometric targets of indium tin oxide containing either 5 atomic % or 10 atomic % tin.

The resistivity of the coatings was measured by the four point probe technique. The thicknesses of the layers of ITO were measured by a Dektak surface profilometer. The substrate used in all cases was soda-lime silicate float glass (40 cm x 40 cm, by 3 mm thick). Coatings were deposited on the air side of the glass after it had been thoroughly cleaned and dried. Examples 1 to 4

In this series of Examples layers of indium tin oxide were sputter-deposited on to glass substrates using a coating atmosphere consisting of 40 seem Ar, 5 seem O and 3 seem CH₄. The layer thickness and resistivity for each of the Examples 1-4 is described in Table 1. There was little variation in the resistivity of the coated glass between each Example. Table 1

Comparative Examples A to H

Comparative Examples A - H were conducted to show the poor consistency and reproducibility of the resistivity of layers of ITO deposited under nominally the same conditions at around room temperature in the absence of methane. Layers of indium tin oxide were deposited on to glass substrates using a coating atmosphere consisting of 40 seem Ar and 3 seem O₂ (this flow rate of oxygen was selected by trial and error to provide resistivities of similar magnitude to those obtained in Examples 1-4). The layer thickness and resistivity of each of the coated glasses for Comparative Examples A - H are described in Table 2. Examples 5 to 9 and Comparative Example I

Examples 5 to 9 and Comparative Example I were conducted to investigate the effect of varied methane flow rate on the resistivity of deposited layers at constant argon and oxygen flow rates. The coating atmosphere consisted of 40 seem Ar, 5 seem O₂ (the same flow rates of these gases as in Examples 1-4) and methane. The flow rate of methane was varied from 0 (Comparative Example I) to 5 seem (Example 9). The methane flow rates, layer thickness and resistivity of the deposited ITO layers are described in Table 3 for each Example 5 to 9 and Comparative Example I.

The resistivity of the deposited ITO coating was high (40 x 10^"4 Ω.cm) at 0 seem methane, addition of even a small amount of methane (1 seem) in Example 5 significantly reduced the resistivity to 8.1 x 10^"4 Ω.cm. Addition of higher flow rates of methane reduced the resistivity of the ITO layer further until a minimum was reached at 2-3 seem methane (6.4 x 10^"4 and 6.77 x 10^"4 Ω.cm, Examples 6 and 7). Addition of higher flow rates of methane than 3 seem resulted in a higher resistivity of 26 x 10^"4 Ω.cm in Example 9 (5 seem methane). Table 2

Table 3

Examples 10 to 12

Examples 10 to 12 were conducted to investigate the effect of varying the oxygen flow rate in the coating atmosphere at constant methane and argon flow rates. The coating atmosphere consisted of 40 seem Ar and 1 seem CH₄ with the oxygen flow rate varying from 3.5 seem (Example 10) to 6 seem (Example 12). The oxygen flow rate, layer thickness and resistivity of the deposited ITO layers are described in Table 4 for each of the Examples 10 to 12. Table 4

Comparative Examples J, K and L

Comparative Examples J, K and L were conducted to investigate deposition of ITO layers in the absence of methane and with varying oxygen flow rates. Each Comparative Example was conducted in a coating atmosphere consisting of 40 seem Ar and oxygen flow rate of 0 (Comparative Example J) to 6 seem (Comparative Example L).

The oxygen flow rate, layer thickness and resistivity of deposited ITO layers for each of the Comparative Examples J-L is described in Table 5.

Table 5

Examples 13 to 18

In this series of Examples, layers of indium tin oxide deposited using targets containing either 5 atomic % or 10 atomic % tin were sputter deposited on to the glass substrates using a coating atmosphere of 40 seem Ar, 2 seem CH₄ and oxygen. The flow rate of oxygen was varied from 3 seem (Example 13) to 8 seem (Example 18). The oxygen flow rate and resistivity of the ITO layers deposited using targets containing 5 atomic % and 10 atomic % tin are described in Table 6 for each Example 13 to 18. Table 6

Examples 19 to 23

In this series of Examples, layers of indium tin oxide deposited from a target containing 5 atomic % tin were sputter deposited on to glass substrates using a coating atmosphere of 40 seem Ar, 5 seem oxygen and methane. The methane flow rate was varied between 1 seem (Example 19) and 5 seem (Example 23). The methane flow rate and resistivity of the ITO layers are described in Table 7 for each of the Examples 19 to 23.

Table 7

Claims

1. A process for the production of a coated substrate comprising depositing an electrically conductive metal oxide layer on to the surface of a substrate by a low pressure deposition process performed in a coating atmosphere containing a gaseous hydrocarbon.

2. A process as claimed in claim 1 wherein the electrically conductive metal oxide layer comprises indium oxide.

3. A process as claimed in claim 2 wherein the electrically conductive metal oxide layer comprises indium tin oxide.

4. A process as claimed in any one of the preceding claims wherein the gaseous hydrocarbon comprises a Ci to C hydrocarbon.

5. A process as claimed in claim 4 wherein the gaseous hydrocarbon comprises methane.

6. A process as claimed in any one of the preceding claims wherein the substrate is at a temperature of below 250°C.

7. A process as claimed in claim 6 wherein the substrate is at a temperature of 200°C or below.

8. A process as claimed in claim 7 wherein the substrate is at a temperature of 100°C or below.

9. A coated glass obtainable by a process comprising depositing an electrically conductive metal oxide layer on to the surface of a glass substrate by a low pressure deposition process performed in a coating atmosphere containing a gaseous hydrocarbon.

0. A process for the production of a coated substrate comprising, a) providing a substrate having at least one surface, b) providing a coating atmosphere comprising a gaseous hydrocarbon, c) depositing an electrically conductive metal oxide layer on to the surface of the substrate by a low pressure deposition process performed in the coating atmosphere.