FR2859486A1 - Deposition of an amorphous layer mainly containing fluorine and carbon on an optical substrate, notably for the production of low refractive index ophthalmic lenses - Google Patents

Abstract

The deposition under vacuum of an amorphous layer containing mainly fluorine and carbon is carried out using an ion canon able to eject ions in the form of a beam of accelerated ions created from at least one compound containing the fluorine and carbon in the form of a gas or a saturated vapor feeding the ion canon. An independent claim is also included for a device for putting this method into service.

Description

1 2859486

  The subject of the present invention is a process for the vacuum deposition of a fluorinated, in particular fluorocarbonated, amorphous layer on a substrate.

  Some fluorocarbon materials, when used in thin layers, are transparent in the visible and have a low refractive index, for example polytetrafluoroethylene (n = 1.35 at 630 nm).

  Their use as a low index layer in an anti-reflection treatment is therefore particularly appropriate because they allow a low level of reflection and a perfect transparency throughout the spectral range of the visible. Particularly in the field of antireflection on ophthalmic lenses, it is advantageous to have a material with a refractive index lower than that of silica (n -1.47 at 630 nm), a material that is currently in common use, since this makes it possible to optimize the effectiveness of antireflections while maintaining a limited number of layers.

  However, fluorocarbon materials often have poor adhesion to most materials. This is for example the case when one deposits by evaporation under vacuum a fluorocarbon compound, such as amorphous Teflon. This poor adhesion is a brake on their development, especially in the case of common items whose use is intensive such as ophthalmic lenses, which should be cleaned frequently.

  Another method used in the industry is Plasma Enhanced Chemical Vapor Deposition (PECVD) which is described, for example, in International Patent Application WO 98/33077. The method is based on the use of plasmas to dissociate precursor gases and thus create free resulting radicals, able to re-associate to form a homogeneous material adhering to the surface of the objects introduced into the reaction chamber. This technique is satisfactory but requires the use of expensive equipment.

  In addition, the transparency of the fluorocarbon layers obtained by PECVD is disappointing because said layers are generally yellowish in color.

  This is why a new deposition strategy is proposed here, which consists of using an ion gun for ejecting fluorinated ions under the form of an accelerated ion beam, which will bombard the substrate while providing the electrons necessary for the constitution of electrically neutral fluorinated compounds.

  This method makes it possible to ensure in a simple and effective manner the adhesion of a low refractive index amorphous fluorocarbon layer to an optical substrate or an underlying layer, so as to constitute an anti-reflective layer or stack. suitable for use in the production of ophthalmic lenses having very good impact and scratch resistance, perfect transparency and a very low refractive index.

  In addition, this process can be easily implemented in a conventional evaporation machine, which allows the evaporation of the first layers, followed directly by the deposition of the amorphous fluorocarbon layer.

  The invention, as a whole, thus relates to a method of vacuum deposition of an amorphous fluorinated layer on a substrate, characterized in that it comprises the step of depositing this layer by means of a gun to ions capable of ejecting fluorinated ions in the form of an accelerated ion beam created from at least one gaseous fluorinated compound or saturated vapor supplying the ion gun.

  According to preferred arrangements: the ion gun is fed with at least one fluorinated compound, mixed with oxygen, or at least one rare gas; and / or the ion gun is fed with at least one aliphatic or cyclic fluorocarbon compound, at least one aliphatic or cyclic fluorinated hydrocarbon, or a mixture thereof.

  The fluorocarbon layer obtainable according to the invention consists of an aggregate of compounds consisting essentially of fluorine and carbon atoms. It is intended to cover the surface of the substrate or an underlying layer in a continuous manner with a thickness that typically varies between 1 and 500 nm. It has in particular a low refractive index and a low dielectric constant.

  Such a fluorocarbon layer is amorphous insofar as the fluorocarbon molecules which compose it do not generally form a polymer or a large crystalline structure.

  In order to improve the efficiency of the process, perfluorocyclobutane (c-C4F6) or a mixture of this compound with at least one other fluorocarbon compound, especially tetrafluoromethane (CF4) or hexafluoromethane (C2 F6), will be used more preferentially. ), or at least one rare gas.

  The rare gas is preferably argon or xenon.

  Positive ions created from a fluorocarbon gas are predominantly CF3 +, CF2 +, CF +, C + and F + in proportions that depend primarily on the fluorocarbon gas used, but also the presence of an additive gas.

  It is also possible according to the method of the invention to obtain a higher deposition rate by increasing the anode voltage, which has the effect of facilitating the dissociation of the fluorinated gas and increasing the ion energy.

  The ion gun that is generally used is an ion gun of the kind having an annular anode, a filament which serves as a cathode and extends diametrically above the annular anode and a magnet disposed below the annular anode. , which may or may not be permanent. The gas distributor, which supplies the gun with gas, is preferably arranged between the anode and the magnet.

  Thus, electrons are emitted by the cathode, which travel on a path defined by the magnetic field lines. The latter are accelerated towards a so-called discharge zone near the anode where they undergo collisions with the molecules of the fluorinated compounds. These collisions produce the ionization and dissociation of the fluorinated compounds. Ions and electrons form a conductive gas, or plasma.

  In such a context, the ions formed are accelerated in all directions of space. They will cross the axis of the barrel several times before escaping from the discharge zone in a divergent ion beam.

  Finally, the positive charge of the ions is neutralized by a part of the electrons coming from the cathode, so that when they reach the substrate, the electric current of the beam is almost zero.

  The deposition mode provided by the invention allows the use of different substrates, which may be of mineral material or, more advantageously, plastic.

  It may be in particular a resin such as CR-39, marketed by PPG Industries, which may in some cases be coated with an abrasion-resistant varnish and then marketed under the name ORMA SUPRA.

  The method may be used for the deposition of a single amorphous fluorinated layer, however the invention provides for stacks of variable refractive index layers, comprising a fluorinated layer deposited according to the method of the invention, in order to manufacture, among others, ophthalmic lenses treated anti-reflective.

  In use of the method of the present invention in the context of an antireflection stack, the fluorinated layer is generally used to form the low index outer layer.

  The invention can thus consist in manufacturing an antireflection stack by successive steps of physical vapor deposition under vacuum (PVD) of three layers having, respectively, from inside the stack to the outside, a high index a refractive index / a low refractive index I a high refractive index, the stack of these layers preferably corresponding to a ZrO 2 / SiO 2 ZrO 2 type stack, where ZrO 2 and SiO 2 denote the materials of which these layers are made; then depositing the amorphous fluorinated outer layer by means of a clean ion gun to eject fluorinated ions.

  Traditionally, anti-glare stacks on ophthalmic lenses have a final anti-fouling layer. The deposition of such a layer is not necessary in the context of the invention, since the amorphous fluorinated layer according to the invention already has this anti-soiling property.

  Preferably, each vacuum gas phase physical deposition step discussed above includes evaporation of the electron gun deposition material.

  In practice, each gas phase physical deposition step is carried out at a pressure of less than or equal to 10 -2 Pa.

  The invention also relates to the use of the method as defined above for improving the adhesion of a refractive index-based outer layer to the underlying layer of an antireflection stack.

  The invention finally relates to a device for implementing the method according to the invention, characterized in that it comprises: - an ion gun; 2859486 - means for supplying the ion gun of fluorinated compound in gas or vapor form; and a substrate holder above the ion gun.

  The ion gun is preferably of the kind defined above.

  It is further provided that the ion gun and the substrate holder are housed in a chamber and that a pumping system for evacuating said chamber is part of the device.

  In addition to the device, can be added, a cold trap to increase the pumping speed of water and an electron gun for evaporation by electron bombardment of the materials to be deposited.

  The features and advantages of the invention will become apparent from the following description, which refers to the appended diagrammatic drawings, in which: FIG. 1 is a diagrammatic representation of a device for implementing the method according to FIG. FIG. 2 is a diagrammatic representation in section of an ion gun that can be used for the method according to the invention; and FIG. 3 represents an antireflection stack obtained according to a preferred embodiment of the invention.

  In the embodiment shown, the device 10 for carrying out the deposition method on a substrate 9 is in the form of a chamber 8, which can be evacuated, and inside which are arranged an ion gun 1 of the MarK II type (marketed by Commonwealth Scientific), comprising a fixed magnet 6, and in the axis of the barrel a substrate holder 3, situated in the direction of exit of the fluorinated 14 ions.

  The substrate 9 is carried by a substrate holder 3 which, in practice, is part of a conventional carousel.

  The gas supplying the ion gun of fluorinated compounds is released from below the annular anode 4 by means of a gas distributor 2 consisting of a plate pierced with orifices. The quantity of gas is regulated upstream by a supply means 7 connected to one or more mass flowmeters of the MKS type.

  Electrons are emitted by a cathode 5 and follow approximately lines of the magnetic field 13 visible in Figure 2. They are accelerated to the discharge zone near the anode 4, and undergo collisions with the 6 2859486 atoms or molecules . Part of these collisions produce ions. The mixture of electrons and ions in the discharge region forms a conductive gas, or plasma. The formed ions are accelerated as shown in Figure 2, and can traverse the axis of the ion gun several times before leaving the source. At the exit they form a divergent beam.

  Then, the positive space charge of these ions is neutralized by a part of the electrons of the cathode 5.

  A pumping system 11 is provided to evacuate inside the deposition chamber 8, and a cold trap (Meissner trap), which is not shown here for the sake of simplification, is disposed of inside the enclosure to increase the speed of pumping water. It is thus possible to obtain in a few minutes, the pressure of the order of 10-2 Pa necessary for the deposition.

  An electron gun 12 of the Leybold ESV6 type with a four-cavity rotating crucible is also provided for evaporation by electron bombardment of the materials to be deposited.

  It should also be noted that the cathode 5 is in the form of a filament extending diametrically above the annular anode 4.

  An example of a stack obtainable by the method according to the invention is illustrated in FIG.

  According to the embodiment illustrated in this figure, an organic substrate 19 coated with an abrasion-resistant varnish 20 available commercially under the name ORMA-SUPRA is coated with an antireflection stack comprising an alternation of thin layers at high and low refractive index 21 (ad).

  According to the preferred embodiment illustrated in FIG. 2, the first layer 21a is made of a material with a high refractive index, that is to say greater than 1.6. This material is here composed of zirconium oxide (ZrO2), which is deposited on a physical thickness typically between 35 and 75 nm.

  The second layer 21b deposited on the first layer 21a is here composed of silica (SiO2), that is to say a material with a low refractive index, and with a thickness typically between 20 and 40 nm.

  The third layer 21c deposited here is identical to the first layer 21a (ZrO 2 layer), except for the thickness, which is between 120 and 190 nm.

  These three layers were successively deposited by means of a vacuum depressed gas phase physical deposition (PVD) technique, previously defined, using the electron gun 12.

  Note that other suitable materials and well known to those skilled in the art could be used in the first part of this stack without fundamentally changing the performance.

  According to the preferred embodiment, an amorphous fluorocarbon layer 21d forms an outer layer with a low refractive index of the stack. It is deposited using an ion gun according to the device of Figure 1. Its thickness is between 70 and 110 nm.

  The deposition is performed directly on the third layer 21c with a high refractive index, by placing the sample directly above the ion gun, preferably so that the angle formed between the axis of the stack and that of the ion gun does not exceed 30. Of course, carousel rotation is also possible.

  The deposition is carried out using a quantity of c-C4F8 in gaseous form of 2 sccm (cm3 / min under normal conditions), for projecting flurocarbon ions.

  As the anode voltage is set at approximately 100 V, an anode current of between 0.8 and 1 A is obtained, which allows a deposition rate of the order of 3 Angstrom / s for a gun-substrate distance. about 30 cm.

  Note that it is possible to optimize the efficiency of the deposit, by introducing a mixed rare gas such as xenon, or simply by increasing the anode voltage. These manipulations have the effect of further splitting the ions that are emitted by the barrel 1.

  The amorphous layer deposited was first inspected with the naked eye: it is transparent.

  A very low refractive index, on the order of 1.3 to 600 nm, has also been found for this type of layer.

  In addition, a contact angle for water greater than 90 has been obtained.

  No trace of abrasion was found during friction tests with a flexible fabric, in usual conditions of cleaning ophthalmic lenses.

  The adhesion to the underlying layer is quite satisfactory and in any case better than the adhesion of a layer obtained by vacuum evaporation.

  It has therefore been found that the process of the invention makes it possible to obtain antireflection stacks having very dense thin layers and having very satisfactory characteristics from the point of view of adhesion and scratch resistance.

  The stacks obtained are therefore perfectly suitable for use on ophthalmic lenses.

  Of course, the present invention is not limited to the embodiment described and shown, but encompasses any alternative embodiment.

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Claims (16)

  1. Process for the vacuum deposition of an amorphous fluorinated layer on a substrate, characterized in that it comprises the step of depositing this layer by means of an ion gun capable of ejecting fluorinated ions in the form of an accelerated ion beam created from at least one gaseous fluorinated compound or saturated vapor supplying the ion gun.   2. Method according to claim 1, characterized in that the fluorinated layer is the low outer layer indicative of an antireflection stack deposited on the substrate.   3. Method according to any one of claims 1 and 2, characterized in that the ion gun is fed with at least one fluorinated compound in a mixture with oxygen, or at least one rare gas.   4. Method according to any one of claims 1 to 3, characterized in that the ion gun is fed with at least one aliphatic or cyclic fluorocarbon compound, at least one aliphatic or cyclic fluorohydrocarbon, or a mixture thereof .   5. Method according to claim 4, characterized in that the ion gun is fed with perfluorocyclobutane (c-C4F8) or a mixture of this compound with at least one other fluorocarbon compound, especially tetrafluoromethane (CF4) or the hexafluoromethane (C2F6), or at least one rare gas.   6. Method according to any one of claims 1 to 5, characterized in that the substrate is a plastic substrate.   7. Method according to claim 2 and any one of claims 3 to 6, characterized in that it consists in producing an antireflection stack by the successive steps - physical vapor phase (PVD) vacuum of three layers having respectively, from the inside to the outside, a high refractive index / a low refractive index / a high refractive index, preferably of the ZrO 2 / SiO 2 / ZrO 2 type; depositing the amorphous fluorinated outer layer with the aid of an ion gun capable of ejecting fluorinated ions.   2859486 8. Process according to claim 7, characterized in that each physical vapor deposition step in vacuum comprises the evaporation of the material to be deposited by electron bombardment.   9. The method of claim 7 or 8, characterized in that each deposition step is performed at a pressure less than or equal to 10-2 Pa.   10. Use of the method according to any one of claims 1 to 9 for improving the adhesion of a low refractive index outer layer on the underlying layer of an antireflection stack.   11. A device suitable for carrying out the method according to any one of claims 1 to 9 and comprising: an ion gun (1); - Supply means (7) of the fluorinated compound ion gun; and a substrate holder (3) above the ion gun.   12. Device according to claim 11, characterized in that the ion gun comprises an annular anode (4), a filament serving as a cathode (5) and extending diametrically above the annular anode and a magnet ( 6) disposed below the annular anode.   13. Device according to claim 12, characterized in that the ion gun (1) comprises a gas distributor (2) between the annular anode and the magnet.   14. Device according to claim 12 or 13, characterized in that it comprises a chamber (8) in favor of which are housed the ion gun (1) and the substrate holder (3), and a pumping system. (11) to empty the room.   15. Device according to claim 14, characterized in that it comprises a cold trap capable of increasing the pumping speed of the water.   16. Device according to any one of claims 11 to 15, characterized in that it comprises an electron gun (12) for evaporation by electron bombardment of the materials to be deposited.