Process for depositing a layer

Abstract

A process for depositing on a surface of a substrate a layer based on a metal oxide doped with magnesium or a mixed metal oxide containing magnesium. The process includes providing a substrate having a surface, forming a gaseous mixture comprising a non-halogenated source of a metal and a source of magnesium, delivering the gaseous mixture to the surface of the substrate, and depositing the layer based on a metal oxide doped with magnesium or a mixed metal oxide containing magnesium on the surface of the substrate.

Claims

1. A process for depositing on a surface of a transparent glass substrate a layer based on a metal oxide doped with magnesium or a mixed metal oxide containing magnesium, said process comprising: providing a transparent glass substrate having a surface, forming a gaseous mixture comprising a non-halogenated source of a metal and a source of magnesium, the source of magnesium being selected from one or more of bis(cyclopentiadienyl) magnesium (magnesocene) and bis(methylcyclopentadienyl) magnesium, delivering the gaseous mixture to the surface of the substrate, and depositing the layer based on a metal oxide doped with magnesium or a mixed metal oxide containing magnesium on the surface of the substrate, wherein the process is carried out using chemical vapour deposition carried out in conjunction with the manufacture of the substrate formed utilizing a float glass manufacturing process; wherein said layer based on a metal oxide doped with magnesium or a mixed metal oxide containing magnesium has a thickness of at least 1 nm and at most 20 nm and is deposited over and contacts a buffer layer based on an undoped tin oxide; and wherein said buffer layer contacts a subjacent layer based on a transparent conductive oxide and said layer based on a transparent conductive oxide contacts a subjacent layer based on silica.

2. The process according to claim 1, wherein the non-halogenated source of a metal is selected from one or more of a metal alkoxide, metal acetylacetonate, metal acetate, and metal alkyl.

3. The process according to claim 2, wherein the metal alkoxide is titanium tetraisopropoxide (TTIP).

4. The process according to claim 2, wherein the metal acetylacetonate is titanium acetylacetonate.

5. The process according to claim 2, wherein the metal acetate is selected from one or more of a titanium acetate.

6. The process according to claim 2, wherein the metal alkyl is a titanium alkyl.

7. The process according to claim 1, wherein the layer based on a metal oxide doped with magnesium comprises at least 1 atomic % magnesium and at most 20 atomic % magnesium.

8. The process according to claim 1, wherein the formation of the gaseous mixture comprises heating the source of magnesium using a thin film evaporator system to a temperature of at least 110° C. and at most 210° C.

9. The process according to claim 1, wherein the gaseous mixture further comprises one or more carrier gas or diluents.

10. The process according to claim 1, wherein the layer based on a metal oxide doped with magnesium or a mixed metal oxide containing magnesium is deposited over the surface of the substrate with one or more previously deposited, intervening layers.

11. The process according to claim 2, wherein the metal alkoxide is a titanium alkoxide.

12. The process according to claim 2, wherein the metal acetate is titanium tetraacetate.

13. The process according to claim 1, wherein the metal oxide doped with magnesium is titanium oxide:Mg or wherein the mixed metal oxide containing magnesium is magnesium titanium oxide.

14. The process according to claim 1, wherein the layer based on a metal oxide doped with magnesium comprises at least 2.5 atomic % magnesium and at most 10 atomic % magnesium.

15. The process according to claim 1, wherein the formation of the gaseous mixture comprises heating the source of magnesium using a thin film evaporator system to a temperature of at least 140° C. and at most 180° C.

16. The process according to claim 1, wherein the formation of the gaseous mixture comprises heating the source of magnesium using a thin film evaporator system to a temperature of at least 150° C. and at most 170° C.

17. The process according to claim 1, wherein the formation of the gaseous mixture comprises heating the source of magnesium using a thin film evaporator system to a temperature of at least 155° C. and at most 165° C.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will now be further described by way of the following specific embodiments, which are given by way of illustration and not of limitation, with reference to the accompanying drawings in which:

(2) FIG. 1 is a schematic view, in cross-section, of a coated glazing in accordance with certain embodiments of the present invention;

(3) FIG. 2 is a schematic view, in vertical section, of an installation for practicing the float glass process which incorporates several CVD apparatuses for manufacturing a coated glazing in accordance with certain embodiments of the present invention;

(4) FIG. 3 is a SEM image of Comparative Example 1 following washing.

DETAILED DESCRIPTION OF THE INVENTION

(5) FIG. 1 shows a cross-section of a coated glazing 1 according to certain embodiments of the present invention. Coated glazing 1 comprises a transparent float glass substrate 2 that has been sequentially coated using CVD with a layer based on SiO.sub.2 3, a layer based on fluorine doped tin oxide (SnO.sub.2:F) 4 and a layer based on magnesium doped titanium oxide (TiO.sub.2:Mg) 5.

(6) As discussed above, the process of the present invention may be carried out using CVD in conjunction with the manufacture of the glass substrate in the float glass process. The float glass process is typically carried out utilizing a float glass installation such as the installation 10 depicted in FIG. 2. However, it should be understood that the float glass installation 10 described herein is only illustrative of such installations.

(7) As illustrated in FIG. 2, the float glass installation 10 may comprise a canal section 20 along which molten glass 19 is delivered from a melting furnace, to a float bath section 11 wherein the glass substrate is formed. In this embodiment, the glass substrate will be referred to as a glass ribbon 8. However, it should be appreciated that the glass substrate is not limited to being a glass ribbon. The glass ribbon 8 advances from the bath section 11 through an adjacent annealing lehr 12 and a cooling section 13. The float bath section 11 includes: a bottom section 14 within which a bath of molten tin 15 is contained, a roof 16, opposite side walls (not depicted) and end walls 17. The roof 16, side walls and end walls 17 together define an enclosure 18 in which a non-oxidizing atmosphere is maintained to prevent oxidation of the molten tin 15.

(8) In operation, the molten glass 19 flows along the canal 20 beneath a regulating tweel 21 and downwardly onto the surface of the tin bath 15 in controlled amounts. On the molten tin surface, the molten glass 19 spreads laterally under the influence of gravity and surface tension, as well as certain mechanical influences, and it is advanced across the tin bath 15 to form the glass ribbon 8. The glass ribbon 8 is removed from the bath section 11 over lift out rolls 22 and is thereafter conveyed through the annealing lehr 12 and the cooling section 13 on aligned rolls. The deposition of coatings preferably takes place in the float bath section 11, although it may be possible for deposition to take place further along the glass production line, for example, in the gap 28 between the float bath 11 and the annealing lehr 12, or in the annealing lehr 12.

(9) As illustrated in FIG. 2, four CVD apparatuses 9, 9A, 9B, 9C are shown within the float bath section 11. Thus, depending on the frequency and thickness of the coating layers required it may be desirable to use some or all of the CVD apparatuses 9, 9A, 9B, 9C. One or more additional coating apparatuses (not depicted) may be provided. One or more CVD apparatus may alternatively or additionally be located in the lehr gap 28. Any by-products are removed through coater extraction slots and then through a pollution control plant. For example, in an embodiment, a silica layer is formed utilizing using CVD apparatus 9A, a fluorine doped tin oxide layer is formed utilizing CVD apparatus 9, and adjacent apparatuses 9B and 9C are utilized to form a magnesium doped titanium oxide layer.

(10) A suitable non-oxidizing atmosphere, generally nitrogen or a mixture of nitrogen and hydrogen in which nitrogen predominates, may be maintained in the float bath section 11 to prevent oxidation of the molten tin 15 comprising the float bath. The atmosphere gas is admitted through conduits 23 operably coupled to a distribution manifold 24. The non-oxidizing gas is introduced at a rate sufficient to compensate for normal losses and maintain a slight positive pressure, on the order of between about 0.001 and about 0.01 atmosphere above ambient atmospheric pressure, so as to prevent infiltration of outside atmosphere. For the purposes of describing the invention, the above-noted pressure range is considered to constitute normal atmospheric pressure.

(11) CVD is generally performed at essentially atmospheric pressure. Thus, the pressure of the float bath section 11, annealing lehr 12, and/or in the gap 28 between the float bath 11 and the annealing lehr 12 may be essentially atmospheric pressure. Heat for maintaining the desired temperature regime in the float bath section 11 and the enclosure 18 is provided by radiant heaters 25 within the enclosure 18. The atmosphere within the lehr 12 is typically atmospheric air, as the cooling section 13 is not enclosed and the glass ribbon 8 is therefore open to the ambient atmosphere. The glass ribbon 8 is subsequently allowed to cool to ambient temperature. To cool the glass ribbon 8, ambient air may be directed against the glass ribbon 8 by fans 26 in the cooling section 13. Heaters (not shown) may also be provided within the annealing lehr 12 for causing the temperature of the glass ribbon 8 to be gradually reduced in accordance with a predetermined regime as it is conveyed therethrough.

EXAMPLES

(12) All Comparative Examples and Examples of the invention were prepared on an on-line coatings mini dynamic coater. The glass dimensions were 10 cm×45 cm for the samples coated with magnesium doped titania and 30 cm×120 cm for the samples coated with a mixed oxide of magnesium and zinc. Samples were prepared using CVD. A furnace set at 600° C. and a total flow rate of 12 standard litres per minute (slm) were used for the deposition of magnesium doped titania coatings. A furnace set at 630° C. and a total flow rate of 36 standard litres per minute (slm) were used for the deposition of a mixed oxide of magnesium and zinc. The mini dynamic coater produces dynamic samples by moving a heated substrate beneath a coater head allowing the chemical vapour to evenly coat the substrate. The speed of the substrate can vary between 1-4 m/min.

(13) Oxygen-free nitrogen was used as the carrier gas, supplied by a boil off liquid nitrogen feed or oxygen free nitrogen gas cylinders. Titanium tetrachloride (TiCl.sub.4) and titanium isopropoxide (TTIP) were used as titanium precursors, heated to temperatures varying between 50-180° C. (dependant on precursor) and then delivered via a bubbler. Diethylzinc (DEZ, Zn(CH.sub.2CH.sub.3).sub.2) was used as a zinc precursor, heated to a temperature of 100° C. and then delivered via a bubbler. Ethyl Acetate (EtOAc, 99.7% Sigma-Aldrich), tertiary butyl acetate (TBAc, <99.9% Sigma-Aldrich) or nitrous oxide (N.sub.2O, 99% Sigma-Aldrich) were used as oxidants in some of the reactions. Oxidants were delivered via 20 cm.sup.3 syringe, inserted into a watlow tube heater, set to 200° C. or, in the case of the deposition of a mixed oxide of magnesium and zinc, the Ethyl Acetate and tertiary butyl acetate were heated to a temperature of 65° C. and 85° C. respectively and delivered via a bubbler. All gas flows were controlled by Bronkhorst™ Mass-View, Mass Flow controllers. All magnesium doped titania coatings were deposited on NSG TEC™ SB or NSG TEC™ 15. All coatings of mixed oxide of magnesium and zinc were deposited on NSG TEC™ SB.

(14) Computer modelling was used to estimate Ti.sub.xO.sub.yMg.sub.z layer thickness. Ultrascan measurements were made for each sample then, using their b*, Y (glass reflection) properties and modelling software, a thickness of coating was estimated.

Comparative Examples: Mg(MeCp).SUB.2.+TiCl.SUB.4.+TBAc→Ti.SUB.x.O.SUB.y.Mg.SUB.z

(15) Comparative Examples were prepared using methyl magnesocene, titanium tetrachloride and tertiary butyl acetate with the conditions set out in Table 1 below with a line speed of 1/m/min to deposit a magnesium doped titania layer. The temperatures indicated in Table 1 refer to the temperature to which the methyl magnesocene or titanium tetrachloride was heated prior to delivery via a bubbler to form a gaseous mixture. Table 1 also shows the thickness of the layers obtained.

(16) TABLE-US-00001 TABLE 1 Summary of conditions and obtained layer thicknesses for CVD using Mg(MeCp).sub.2 + TiCl.sub.4 + TBAc TBAc Mg(MeCP).sub.2 Mg(MeCP).sub.2 TiCl.sub.4 TiCl.sub.4 Syringe Layer Comparative Temp Flow Temp Flow Flow Thickness Example Substrate (° C.) (slm) (° C.) (slm) (cc/hr) (nm) 1 NSG TEC.sup.( ™.sup.) SB 180 1.2 90 1 66.5 85 2 NSG TEC.sup.( ™.sup.) 15 180 1.2 89 1 66.5 28 3 NSG TEC.sup.( ™.sup.) 15 180 1 91 1 66.5 24

(17) Comparative Examples 1-3 were analysed both before washing and after washing (using deionised water in an ultrasonic bath) by X-ray photoelectron spectroscopy (XPS) using a Thermo K-alpha instrument which found no evidence for Mg doping in the titania layers. Mg was only detected as a surface contaminant. However, the detection limit of XPS is of the order of 0.5 atomic %, and it is therefore possible that Mg is present as a dopant at a lower concentration, undetectable by XPS.

(18) Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) analysis of Comparative Example 1 using an ION-TOF 5 Time of Flight Secondary Ion Mass Spectrometer suggested that Mg was present within the titania layer, both in depth profiling (i.e. analysis of the variation of composition with depth below the initial surface of the layer) and using Mg:Ca ratios. However ToF-SIMS does not provide any information regarding the level of Mg doping in the titania layer.

(19) Scanning electron microscope (SEM) analysis of Comparative Example 1 (using an FEI Nova NanoSEM 450 and EDAX Octane plus EDS detector with TEAM software) showed that once washed, large regions of the titania layer had de-bonded from the substrate (see FIG. 3 which is a SEM image of Comparative Example 1 following washing). FIG. 3 shows a dark region on the left of the image where the titania layer has de-bonded and consequently been removed by the washing process. The lighter region to the right of the image is a region where the titania coating remains following washing.

(20) Comparative Example 2 was analysed by X-ray diffraction (XRD) using an X′pert MRD—PANalytical instrument which identified the titania layer as merely anatase titania, with no Mg dopant detected.

(21) In addition, whilst performing CVD to prepare Comparative Examples 1-3, regular blockages in the coating equipment occurred near and around the Mg(MeCp).sub.2 bubbler, and mix pipe, connecting the manifold to the coater head. Accordingly, an alternative process was sought.

Examples: TTIP+Mg(MeCp).SUB.2.→Ti.SUB.x.O.SUB.y.Mg.SUB.z

(22) Samples were prepared using methyl magnesocene and titanium tetraisopropoxide with the conditions set out in Table 2 below to deposit a magnesium doped titania layer. The temperatures indicated in Table 2 refer to the temperature to which the methyl magnesocene or titanium tetraisopropoxide was heated prior to delivery via a bubbler to form a gaseous mixture. The substrate used for Examples 1-4 and 6-9 was NSG TEC™ SB, while the substrate used for Example 5 was NSG TEC™ 15. The line speed was 1 m/m in and the flow rate for TTIP was 1 slm for Examples 1-9. Table 2 also shows the atomic percentages, stoichiometry and thickness of the layers obtained.

(23) TABLE-US-00002 TABLE 2 Summary of conditions and obtained layers for CVD using Mg(MeCp).sub.2 + TTIP Mg(MeCP).sub.2 Mg(MeCP).sub.2 TTIP Stoichiometry Layer Temp Flow Temp Concentration of elements in of deposited thickness Example (° C.) (slm) (° C.) deposited layer (atomic %) layer (nm) 1 115 1 154 Ti (37.5), O (62.5) TiO.sub.1.7 32.4 2 132 1 154 Ti (37.7), O (62.3) TiO.sub.1.7 30.4 3 146 1 155 Ti (37.3), O (61.5), Mg (1.2) TiO.sub.1.6 36.7 4 148 1 155 Ti (37.7), O (62.2), Mg (0.1) TiO.sub.1.7 20-30 5 149 0.25 150 Ti (30.9), O (60.0), Mg (7.7), TiO.sub.1.9Mg.sub.0.2 14 C (0.7), Na (0.7) 6 150 1 155 Ti (34.3), O (61.1), Mg (4.6) TiO.sub.1.8Mg.sub.0.1 20-30 7 152 1 155 Ti (10.8), O (45.6), Mg (25.5), TiO.sub.4.2Mg.sub.2.4C.sub.1.7 20-30 C(18.1) 8 160 1 155 Ti (20.4), O (58.1), Mg (21.5) TiO.sub.2.8Mg 14.4 9 176 1 155 Ti (8.3), O (55.3), Mg (35.8), MgO.sub.1.5Ti.sub.0.2 8 C (0.6)

(24) Examples 1-9 were analysed via XPS as detailed above to determine the concentration of elements in the deposited layers. Table 2 shows that layers of titania doped with magnesium can be reliably deposited using the non-halogenated precursor TTIP. The level of Mg dopant present in the deposited layer generally varies with the temperature to which methyl magnesocene is heated. As noted previously, ranges of around 1-15 atomic % can provide advantages in terms of optimising solar cell efficiency.

(25) It is worth noting that the preparation of Examples 1-9 did not suffer from the regular blockages that were experienced with the use of a halogenated source of titanium. Furthermore, Examples 1-9 exhibited no de-bonding upon washing.

Examples: DEZ+[Mg(MeCp).SUB.2 .or MgCp.SUB.2.]+[TBAc, EtOAc or N.SUB.2.O]→Zn.SUB.x.O.SUB.y.Mg.SUB.z

(26) Samples were prepared using methyl magnesocene or magnesocene and DEZ with the conditions set out in Table 3 below to deposit a layer of a mixed oxide of magnesium and zinc. The MgCp.sub.2 and Mg(MeCp).sub.2 were heated to a temperature of 200° C. and 180° C. respectively prior to delivery via a bubbler to form a gaseous mixture. Example 14 was carried out in the presence of 15% ethylene by volume of the total gas flow. A line speed of 5 m/min was used in the preparation of Examples 10-12, whilst for Examples 13 and 14 a line speed of 3.8 m/min was used. Table 3 also shows the relative atomic percentages of Zn and Mg and thickness of the layers obtained.

(27) TABLE-US-00003 TABLE 3 Summary of conditions and obtained layers for CVD using DEZ + [Mg(MeCp).sub.2 or MgCp.sub.2] + [TBAc, EtOAc or N.sub.2O] Percentage volume of total gas flow Zn Mg Layer Relative atomic percentage precursor precursor Oxidant thickness Zn/ Mg/ Example DEZ MgCp.sub.2 TBAc (nm) (Zn + Mg) (Zn + Mg) 10 1.0% 1.0%  5.0% 62.0 40.5% 59.5% 11 1.5% 1.5% 10.0% 67.5 25.0% 75.0% 12 1.5% 0.5% 10.0% 33.0 66.7% 33.3% DEZ MgCp.sub.2 EtOAc 13 2.0% 0.5% 5.0% 34.8 66.7% 33.3% DEZ Mg(MeCp).sub.2 N.sub.2O 14 0.8% 0.1% 10.0% 18.0 82.1% 17.9%

(28) Examples 10-14 were analysed via XPS as detailed above to determine the concentration of elements in the deposited layers. Table 3 shows that layers of mixed oxide of magnesium and zinc can be reliably deposited using the non-halogenated precursor DEZ. The level of Mg present in the deposited layer generally varies with the proportion of the Mg precursor in the total gas flow.

(29) It is worth noting that the preparation of Examples 10-14 did not suffer from blockages and the samples obtained exhibited no de-bonding upon washing.

(30) The invention is not restricted to the details of the foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.