Stock material or miscellaneous articles – Composite – Of quartz or glass
Reexamination Certificate
2002-03-11
2004-02-17
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
Composite
Of quartz or glass
C428S551000, C428S655000, C428S660000, C428S663000, C428S665000, C428S666000, C428S662000, C428S668000, C428S673000, C428S674000, C428S680000
Reexamination Certificate
active
06692833
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to metal layers deposited on rigid substrates, the process of their deposition, the substrate formed therefrom, and the utility of such substrates. In particular, the present invention is directed to processes for depositing one or more metal layers, at least one of which based on tungsten-containing or molybdenum-containing precursors, onto rigid substrates by a variety of methods.
BACKGROUND OF THE INVENTION
The present invention relates to rigid substrates, especially transparent or semi-transparent ceramic-type substrates, such as glass or glass-ceramic substrates or substrates that are barely transparent or non-transparent, and therefore relates to substrates that are generally insulating from an electrical standpoint and that are capable of withstanding heat treatments without deterioration.
Although the present invention is not limited to such an application, as other applications will be detailed within, the present invention are first described with reference to the production of electronic devices, especially to the production of emissive screens, more particularly to those called “flat” screens of the plasma-screen type.
A plasma screen essentially consists of two glass substrates constituting the front and rear faces of the screen, on which substrates functional layers have been deposited. Those layers, deposited on the opposing faces of the substrates, comprise, especially, electrodes, at least a coating of a dielectric material and phosphors, these elements being indispensable for the operation of the screen.
The present invention thus concerns the manufacture of substrates provided with electrically conducting layers capable of forming electrodes after suitable etching treatments, most particularly those using layers made of highly conducting metals, such as silver and copper.
It is known that copper and silver layers may be deposited by electrolysis, which is an attractive technique since it is possible to obtain relatively thick metal layers (for example a thickness of between 1 and 5 &mgr;m) that can be necessary to achieve the required level of conductivity in plasma screens. However, electrolysis can only be implemented in a reasonable production time if the substrate to be covered is itself sufficiently conducting at the start. In general, at least for the front faces of plasma screens, provision is made to interpose a transparent electrically conducting layer made of a doped metal oxide between the glass substrate and the metal electrode layer. When one or more of these layers is etched, the doped metal oxide layer may optionally be etched in a pattern different from that of the metal electrode. This transparent layer may be made of, for example, fluorine-doped tin oxide, F:SnO
2
, or of tin-doped indium oxide, Sn:In
2
O
3
. The thicknesses in which the doped metal oxide layer is used are chosen for maintaining its transparency, but proved not to be conductive enough to allow electrolysis under satisfactory conditions.
The impetus for the present invention was therefore to remedy this drawback, especially by developing a novel conducting layer which is especially able to serve for “preparing” the surface of an insulating substrate of the glass, ceramic, or glass-ceramic type, in order to allow another metal conducting layer to be deposited by electrolysis.
SUMMARY OF THE INVENTION
The present invention is directed to a process for depositing at least one metal layer based on tungsten or molybdenum by chemical vapor deposition on a non-conductive substrate, which comprises providing at least one tungsten- or molybdenum-containing precursor in the form of a metal halide or an organometallic compound and at least one reducing agent, such as silane or hydrogen, to form the at least one metal layer.
The metal halide is preferably a metal chloride, such as WCl
6
or MoCl
5
, or a metal fluoride, such as MoF
5
.
The organometallic compound may especially be a metal carbonyl, such as W(CO)
6
, or alkyl-tungsten or allyl-tungsten compounds, such as butadiene-tungsten or bio-benzene tungsten.
Tungsten and molybdenum have a number of advantages when used in the present invention. They are both good electrical conductors, although less conducting than copper or silver. Therefore, these metals may form an integral part of an electrode, consisting essentially of the layer according to the present invention, and/or an integral part of an optional second conducting layer of the copper or silver type, thus contributing to a possible increase in the electrical conductivity that a copper or silver layer alone may have.
Furthermore, these W-based or Mo-based layers lend themselves well to pyrolytic deposition in the vapor phase (also called chemical vapor deposition or CVD) at atmospheric pressure, especially as metal halides, the decomposition temperature of which is typically compatible with the substrates envisaged in the present invention, especially of the glass type. Deposition by CVD may advantageously result in layers which generally adhere well to the substrate and are typically very durable.
Indeed, these W-based or Mo-based layers have proven to be particularly compatible with the materials with which they may come into contact: they coat out well, especially on a surface made of glass and of a metal oxide of the F:SnO
2
or Sn:In
2
O
3
type. Furthermore, molybdenum and tungsten are metals quite similar to copper or silver, particularly in crystal lattice structure. The W and Mo layers also offer nucleation sites for subsequently deposited copper or silver layers, which are deposited very satisfactorily on their surface, to which they tend to adhere very strongly.
Additionally, tungsten and molybdenum are metals which are resistant to solutions usually employed for depositing copper electrolytically, these solutions generally being very highly acidic (pH around 1). Unexpectedly, the W-based or Mo-based layers may however be etched, if necessary, using known chemical etching techniques, especially using oxidizing solutions containing aqua regia and hydrofluoric acid.
Advantageously, when the envisaged substrate is made of glass, a W-based or Mo-based layer may be deposited directly on the ribbon of glass on a float line, especially in the floating chamber. The WCl
6
-type precursors thus decompose at around 600 to 630° C., and at lower temperatures in the case of WF
6
, temperatures at which the ribbon of glass has generally acquired, on the float line, its dimensional stability. The atmosphere of the float bath is favorable for deposition in that it is slightly reducing.
Another advantage of molybdenum and tungsten is that they are not very oxidizable, especially at relatively high temperatures. Thus, if the layers are deposited on the ribbon of glass in the floating chamber, they generally do not exhibit little or no oxidizing while the ribbon of glass passes through the lehr.
According to a first embodiment, the W-based or Mo-based layer according to the present invention may be deposited directly on its carrier substrate, especially directly on the glass.
According to a second variant, the W-based or Mo-based layer may be deposited on a layer deposited beforehand on the substrate. There may be one or more pre-deposited layers on the substrate before the deposition of the W-based or Mo-based layer. As mentioned above, this may be a transparent conducting layer of doped metal oxide type, for example, such as fluorine-doped or antimony-doped tin oxide, aluminum-doped zinc oxide, or tin-doped indium oxide. These layers may also be deposited, in a known manner, by chemical vapor deposition or by pyrolysis in the pulverulent phase (reference may be made, for example, to patents EP 158,399, EP 357,263 and WO 88/00588 for the deposition of F:SnO
2
layers by CVD and to patents EP 573,325 and WO 94/25410 for the deposition of F:SnO
2
layers by pyrolysis of powder). Two successive layers may thus be deposited pyrolytically on the float line when the substrate is a glass substrate. Of course, it is possible
Jones Deborah
Pennie & Edmonds LLP
Piziali Andrew T
Saint-Gobain Vitrage
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