Stock material or miscellaneous articles – Circular sheet or circular blank – Recording medium or carrier
Reexamination Certificate
2001-01-30
2003-07-22
Kiliman, Leszek (Department: 1773)
Stock material or miscellaneous articles
Circular sheet or circular blank
Recording medium or carrier
C428S064700, C428S412000, C428S900000, C428S690000, C427S128000, C427S129000, C427S130000, C359S580000, C359S582000, C359S586000, C359S588000, C204S192150, C204S192260
Reexamination Certificate
active
06596368
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims priority from International Application No. PCT/EP 99/01817 filed on Mar. 18, 1999, which was published in English as WO 99/49097 on Sep. 30, 1999, and which in turn claims priority from FP 98400721.1 filed on Mar. 26, 1998.
BACKGROUND OF THE INVENTION
The present invention relates to an organic substrate having optical layers deposited by magnetron sputtering, and to a method for preparing it.
In the ophthalmic field, substrates in transparent organic materials obtained, for example, by polymerizing acrylic, allylic, methacrylic or vinylic monomers are in everyday use. Deposition of thin films on lenses, such as ophthalmic lenses, in such organic materials, or in inorganic materials is also in common use. This for example makes it possible to provide anti-reflective treatment, by successive deposition of different thin films. It is necessary, in such applications, to accurately control the nature and thickness of the various layers deposited.
Conventionally, deposition of thin anti-reflective layers on ophthalmic lenses is done by vacuum evaporation. An organic substrate to be coated with or without an anti-abrasive layer, is placed in a vacuum chamber and the material to be deposited is thermally evaporated by heating or by electron bombardment. In order to improve adhesion of the thin films obtained, the substrates to be coated are heated. In the case of an organic material, the substrate must not be heated beyond 100° C.
Such a technique suffers from disadvantages. It is difficult to automate and does not allow continuous flow coating of substrates. Furthermore, stability and reproducibility of the method are not strictly guaranteed.
The layers of the anti-reflective stack can also be deposited by radiofrequency oxide sputtering, but the low rate of deposition renders this technique barely suitable for industrial use. Moreover, this type of method is poorly adapted to the use of targets of large dimensions, thereby limiting the size of the coated substrates.
As against this, cathodic sputtering, which is readily automated, makes it possible to coat substrates of varying dimensions, using continuous or semi-continues flow, while simultaneously ensuring the process is stable. It has thus been proposed to deposit thin films using magnetron sputtering at direct current (DC). This technique consists in vaporizing a solid target which has been brought to a negative potential by the action of a plasma, typically of an inert gas such as argon. Particles detached from the target are deposited on the surface to be coated at a rate, and density, which are far superior to those obtainable with low temperature vacuum deposition. The presence of a magnetic field close to the target, having lines of force parallel to the surface of the target, improves deposition rate by increasing the number of atoms that are vaporized; magnets are used for creating such a field close to the target. The operation is performed in an enclosure under high vacuum, and is called magnetron sputtering.
The technique of magnetron sputtering is well suited to the deposition of metals. In optical applications, it is necessary to deposit layers such as ZrO
2
, SiO
2
, TiO
2
, Nb
2
O
5
, Al
2
O
3
, Ta
2
O
5
, HfO
2
, Pr
2
O
3
, Sb
2
O
5
, Y
2
O
3
, WO
3
, In
2
O
3
, SnO
2
, Cr
2
O
3
and mixtures thereof. However, these materials, which are non conducting, are poorly adapted to direct current magnetron sputtering. It has thus been suggested to use a metal target and a plasma consisting not only of argon, but also of oxygen, so that the metal atoms detached from the target become oxidized. This reactive sputtering technique is difficult to implement, notably in view of the difficulty of accurately maintaining constant the amount of oxygen in the plasma. Correct operating equilibrium is unstable and contamination of the target causes deposition rate to diminish.
In order to improve stability of the system, it is also been proposed to apply an alternating voltage to the cathode, rather than a DC voltage, of a sinewave or square wave type. On the positive half-cycle, the cathode is discharged. This technique is known as pulsed magnetron sputtering (PMS) and is disclosed in patent DE-A-37 00 633.
In order to still further improve operation of such a system, patent DD-A-252 205 or DE-A-38 02 852 discloses the use of two cathodes. An AC voltage is applied to each cathode, one cathode discharging while the other is being charged up under the effect of the voltage applied for vaporizing the target. This technique, called Double Magnetron Sputtering (DMS) or Twin Mag, makes it possible to avoid electric arcs.
In order to avoid excessive contamination of the target by oxygen, during sputtering, and to ensure sufficient oxidation of the layer at substrate level, it has also been proposed in patent DD-A-239 810 to regulate the oxygen throughput in the enclosure, as a function of the intensity of a spectral line of the plasma. The intensity of the spectral line emitted by the excited atoms, removed from the target, is proportional to the state of oxidation of the target. This technique is known as Plasma Emitting Monitoring (PEM).
Another method for controlling oxygen flow consists in adjusting the voltage applied to the cathode with respect to a set value. This technique is described in patent DE-A-4106513 or EP-A-501016.
It has been proposed, for example in U.S. Pat. No. 4,572,842, to introduce the reactive gas only close to the surface to be coated, thereby avoiding contamination of the target to be vaporized. U.S. Pat. No. 4,572,842 discloses the use of a septum separating the process cavity into two zones; this patent discloses an example of anti-reflective deposition on a glass substrate; the high inert gas pressure, used in conjunction with a septum, makes it possible to obtain the best reduction of contamination of the metal target by oxygen. Thus, this patent makes it possible to increase deposition rate while still ensuring operation. Patent DD-A-21 48 65 discloses a method for on-line treatment using high inert gas pressure to avoid contaminating the metal target.
It has also been proposed to proceed sequentially with the deposition of a thin metal layer using sputtering followed by oxidation thereof, this technique of sputtering followed by oxidation makes it possible to deposit a metal film under an inert gas such as argon, while preserving rate of deposition. The practical difficulty in implementing this technique is that of preventing contamination of the metal target by the oxygen used for oxidising the metal layer. An apparatus for implementing such a sequential method is disclosed in U.S. Pat. No. 4,420,385: separation of the deposition and oxidation zones which are adjacent, is achieved by means of baffles. Another apparatus is disclosed in EP-A-0,428,358. This apparatus is marketed by Optical Coating Laboratory Inc. (OCLI) under the trade name Metamode™. The deposition and oxygen zones are elongate zones parallel to the axis of the drum carrying the surfaces to be coated. A further apparatus is disclosed in WO-A-92 13114 in the name of Applied Vision Ltd. This apparatus is marketed by the company under the trade name Plasmacoat ARx10™. Oxidation is achieved using a plasma source.
The invention concerns the new problem of adhesion of thin films deposited on a transparent organic material substrate, optionally having received an anti-abrasive treatment, with use of a magnetron sputtering technique. It applies to techniques in which oxidation is sequential as well as to those using sputtering in a reactive atmosphere.
EP-A-0,428,358 mentions, in example 2, “Glass Eyeglass Lenses” that the sequential deposition and oxidation method makes it possible to obtain anti-reflective films having good abrasion resistance, for surfaces to be treated in inorganic glass. It does not mention results of tests for example 4, corresponding to anti-reflective deposition on an ophthalmic lens in organic material. WO-A-92 13114 does not mention the problem of adhesion
Bosmans Richard
Comble Pascal
Goedicke Klaus
Keller Gerhard
Kirchhoff Volker
Baker & Botts L.L.P.
Essilor International
Kiliman Leszek
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