MXPA99006935A - Coatings, methods and apparatus for reducing reflection from optical substrates - Google Patents

Abstract

A method of coating optical substrates with anti-reflection (AR) coatings is described. The thickness and composition of the coating is determined by minimizing the product of the Fresnel reflection coefficients for a coating with the angular- and wavelength-dependent sensitivity of the human visual system to minimize the perceived reflectance for the coated article. A compact chamber is evacuated and flushed with chemically inert gas such as argon or nitrogen. One or more molecular precursors are deposited using plasma enhanced chemical vapor deposition (PECVD) to form AR films. Single-layer AR coatings based on fluoropolymer films of controlled thickness, as well as organic, organosilicon, and/or inorganic multilayers are described. Also provided is a method for monitoring film growth optically, using a polarized, light-emitting diode, a polarizing optical filter, and a photodiode. Feedback from the monitor is used to control the precursor flow to produce single layers and multilayers with prescribed anti-reflection properties.

Description

COATINGS, METHODS AND APPARATUS TO REDUCE THE REFLECTION ARISING FROM OPTICAL SUBSTRATES BACKGROUND OF THE INVENTION The present invention relates in general to the improvement of the transmission of light through optical materials, such as eyeglass lenses and, at the same time, to reduce the reflection of the deflected light which leads to the glare coming from the optical materials. All optically transparent, coated materials reflect a portion of the incident light. The amount of reflection varies with the wavelength, polarization, and angle of incidence of the light, as well as the refractive index that depends on the wavelength, of the transparent material. This Fresnel reflection is described by Maxwell's equations for electromagnetic radiation, as is known to those of experience in the optics art and described for example, by M_. Born and E. Wolf in Principi es de Opti cs, New York, Pergamon Press (1980). It is also known that the layers of transmissive materials with refractive indexes REF .: 30914 different from that of the substrate, can reduce the amount of reflection. The amount of this reduction depends on the refractive index depending on the wavelength of the coating materials and their thickness, as well as the wavelength, polarization and angle of incidence of the light. The design and manufacture of these coatings is completely described in Chapters 3 and 9 of H.A. Macleod, Thi n Fi lm Opti cal Fi l t ers, (New York: McGraw-Hill) (1989). The sensitivity of the human visual system also varies with the wavelength of light and its angle of incidence, as described, for example, in Col o Sci en: Concepts and Me th ods r Quan ti ta ti ve Da ta and Formul ae by Gunter Wyszecki and. S. Stiles (New York: Wiley) (1982) and Vi sual Percepti on by Nicholas Wade and Michael Swanston (London: Routledge) (1991). It could be advantageous to exploit this human visual response function by designing and manufacturing coated optical articles having thicknesses and coating compositions that result in a minimization of the perceived angular variation and the wavelength of the Fresnel reflection from the articles.

Previous methods for the creation of anti-reflection (AR) coatings employ physical vapor deposition in which high-energy electron beams are used to heat samples of inorganic materials such as titanium (Ti), silicon (Si) or fluoride of magnesium (MgF2) in a vacuum chamber until they evaporate and settle on the coldest substrate. The flow of evaporated material is isotropic and decreases with the square of the distance between the substrate to be coated and the source of evaporation. The method requires a vacuum chamber whose dimensions are large compared to the dimensions of the substrate. Typical implementations of such methods are found in the Model 1100 High Vacuum Deposition System (Leybold-Hereaus GmgH, Hanáu, Germany) and the BAK 760 High Vacuum Coating System (Balzers A.G., Liechtenstein). The speed of production of the AR coatings with the previous methods, as well as the high cost to acquire, operate and maintain the apparatus, restricts its use to the central production facilities. It is therefore desirable to provide a method for producing AR coatings on eyeglass lenses, which requires only physical equipment, compact, cheap and can be done anywhere, such as in the ophthalmologist's office or the optician's office. The evaporation method also causes the heating of the substrate because the convection cooling is inefficient in a vacuum and the hot elemental materials emit thermal radiation that can be absorbed by the substrate. Heating may cause damage to the substrate, such as internal stress and twisting, especially with plastic substrates. Therefore, it is desirable to produce the AR coating at or near room temperature to avoid this damage. The known AR coatings use one or more layers of refractory materials, such as oxides, nitrides or inorganic fluorides, to achieve a reduction in reflection. The common thin film materials used for such AR coatings are described in Chapter 9 and in Appendix I of Macleod, and include the oxides of Al, Sb, Be, Bi, Ce, Hf, La, Mg Nd, Pr, Se, Yes, Ta, Ti, Th, Y and Zr. The Macleod tabulation also includes the fluorides of Bi, Ca, Ce, Na, Pb, Li, Mg, Nd, a, and Th, as well as a few sulfides and selenides. A Similar tabulation is found in Table 4.1 on page 179 of Opti cs of Mullet yesterday Sys tems (Sh A. Furman and A.V. Tikhonravov, Editions Frontieres: Gif-sur-Yvette, France, 1992). One problem with these AR coatings is that the mechanical characteristics of the inorganic compounds, such as the coefficient of thermal expansion and the elastic modulus, are very different from those of the plastic substrates. It could therefore be advantageous to produce an organic AR coating layer. It is also desirable to produce an AR coating layer whose properties are intermediate between the known inorganic AR coatings and the plastic substrates, to act as a transition layer between the organic and inorganic layers. The reflectance of a coated optical article depends crucially on the thickness of the AR coating layer or layers. In the prior art, the coating thickness has been periodically verified using a quartz microbalance in si t u, to measure the rate or rate of mass deposition. The mass of the film does not enter directly into the equations that describe the optical properties of the layer. It could be highly advantageous to periodically verify the growth of the film with an optical signal that is more directly linked to the AR properties of the coated article.

BRIEF DESCRIPTION OF THE INVENTION In accordance with the present invention, an anti-reflection coating (AR) is designed using the wavelength and angle dependent refraction properties of one or more thin layers on an optical substrate. A perceived reflectance, which weights the Fresnel reflectance dependent on the angle and wavelength, by the sensitivity to the angle and wavelength of the human visual system, is minimized and subject to the constraints imposed by the available layer materials . Layers (also referred to as 'coatings' or 'films') are formed by deposition of chemical vapor augmented by plasma (PECVD) of the volatile precursors such as c-C_F8, Si (CH3) 4, Ti (OC2H5p, C4H4O, and C6H6.) The composition of the precursors includes organic and organometallic compounds, and the resulting layers they can be optically dispersive (for example, they have a variation of the refractive index with the wavelength). Alternatively, the resulting layer or layers may not be optically dispersive. A compact chamber, slightly larger than the substrate to be coated, is evacuated and flushed with a chemically inert gas. Electrical energy is deposited within the gas, either directly, using electrodes and applying a static electric field, or indirectly, through capacitive or inductive coupling using electric fields that vary with time. The result is a weakly ionized plasma. The substrate is preferably cleaned by, for example, sputtering the surface with positive ions produced in an inert gas plasma (e.g. Helium, Argon, N2) or by etching the surface in a reactive plasma (e.g. 02, HBr). One or more volatile molecular precursors are then admitted to the chamber, either alone or mixed with the flow of inert gas, and electrically excited. Electric energy excites, dissociates, and ionizes the precursor (s), producing reactive fragments that are transported to the surface of the lens and polymerized or coalesced to form a film. In one embodiment of the invention, an AR layer is formed by cations (eg, C2F4 +, Si (CH3) 3+) which are accelerated by the shield or electrostatic layer at the plasma boundary to the super-thermal kinetic energies (greater than 0.025). eV). These layers have refractive properties that depend on the precursor, the deposition conditions and the thickness of the film. Single and multiple layer AR coatings are prepared in this way. In a preferred embodiment, an AR film has at least one layer of a polymeric fluorocarbon, such as is produced by PECVD of c-C4F8, C2F4, or other perfluorinated precursor materials. These fluoropolymer films generally have refractive indexes less than 1.4 and can serve as single-layer AR coatings, useful as well as elements in multi-layer designs. In yet another embodiment, an organometallic layer such as that formed by PECVD of (CH 3) 4 Si or (CH 3) 3 Si is used to improve the bond between an organic substrate or layer and an inorganic substrate or layer. In Yet another embodiment, one or more optically thin metallic layers, such as a chromium layer, can be deposited through an organometallic precursor, such as chromyl chloride, to improve the adhesion of the layer or layers. The present invention also provides a method for periodically verifying optically the cleaning of the substrate and the growth of the film - using a polarized light-emitting diode, an optical polarization filter, and a photodiode. The feedback from the optical monitor is used to control the cleaning and deposition of the AR by, for example, controlling the precursor flow rates, the chamber pressure, or the electrical excitation, either alone or in combination, to produce single-layer and multi-layer coating films with the prescribed anti-reflection properties.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a three-dimensional plot of the polarized reflectance s as a function of the wavelength and incident angle for a AR coating according to one embodiment of the invention; Figure 2 is a three-dimensional plot of the polarized reflectance p as a function of the wavelength and the incident angle-angle for the target coating AR, of Figure 1; Figure 3 is a graph of human visual response as a function of wavelength; Figure 4 is a graph of the human visual response as a function of the incident angle; Figure 5 is a graph of the reflectance as a function of the wavelength for various optical thicknesses of the coating AR of Figure 6; Figure 6 is a graph of the reflectance as a function of the wavelength for various optical thicknesses of an AR coating according to yet another embodiment of the invention; Figure 7 is a graph of polarized reflectance s as a function of optical thickness over various angles of incidence for an AR coating according to yet another embodiment of the invention; Figure 8 is a graph of polarized reflectance p as a function of optical thickness, over various angles of incidence for the coating AR of Figure 5; Figure 9 is a schematic drawing of an apparatus for optical verification or monitoring of the growth of the film __ on the substrate; Figure 10 is a schematic drawing of a preferred apparatus for the production of AR coatings on optical substrates according to the present invention; Figure 11 is a plot of the reflectance as a function of the wavelength for a multilayer AR coating according to yet another embodiment of the invention; Figure 12 is a graph of the polarized reflectance s as a function of the wavelength for the coating AR of Figure 11; Figure 13 is a schematic cross-sectional view of an ophthalmic lens made in accordance with the present invention, with a simple AR layer; Y Figure 14 is a schematic cross-sectional view of an ophthalmic lens made in accordance with the present invention, with two layers AR.

DESCRIPTION OF THE PREFERRED MODALITIES The present invention provides methods and apparatus for reducing reflection on optical substrates, and new single and multi-layer AR coatings, on optical substrates. As used herein, the terms "optical materials", "optical substrates" and "optical articles" refer to normally transparent or translucent materials such as glass and plastic, and articles made of such materials.

Non-limiting examples of such items include lenses, windows, television and computer screens, and windshields. The reflectance R, is the ratio of the intensity of the reflected portion of light, Ir, to the intensity of the incident probe light,! _ .; R (?,?, P) The reflectance varies with the wavelength of light,?, The angle of incidence,?, And the polarization of light P. This is equal to the product of the reflection coefficient Fresnel p, and its complex conjugate p *, which can to be expressed in terms of the optical admittances for the substrate medium? 0 and the incident medium? ±. Optical admittance is y = 2.6544xl0-3 (n-ik) = (C / B) 2) where n is the real part of the refractive index, k is the absorptive (imaginary) part of the refractive index, and the numerical constant is a conversion factor for the units of the international system. The optical admittance of an article optical of when one or more thin layers are added to a substrate whose admittance is? m becomes y = (C / B) where C and B are computed by solving the matrix equation cossr (i sensr) /? _ ?? r sensr cossr? »(3) where? m is the inclined optical admittance of a particular layer. Equation (3) is the argument of the trigonometric functions for each layer r whose physical thickness is dr, is d = 2p (n-ik) dr eos (? r) / ?, (4) At normal incidence, (? = 0) and the admittance is the same for any polarization. At other angles of incidence, the incident wave is divided into two polarizations, p and s, and defines the inclined optical admittances ? p = 2.6544 x 1 0 ~. { n -ik) / cos (?; = 2.6544 x 10"3 (n-i ^) x cos (?; 5) leading to the general reflectance R, the transmission T, and the absorption A - by means of the formulas: 4? 0Re (? M) 4? 0Re (BC * -? M) A = ¡? OB + C) (? 0B + C) where the subscripts 0 and m refer to the incident medium and the substrate, respectively. The derivation of these equations is described in chapter I by H.A. Macleod ", cited reference The examples of the solution of these equations using wavelengths between 300 and 750 nm and angles up to 60 degrees for a polycarbonate substrate coated with 200 nm of Si02 and 135 nm of Cfx polymer are shown for the polarized light syp in Figures 1 and 2. The changes to the substrate, the refractive properties of the layers, or the order in which they are coated on the substrate, they lead to complex but easily calculable changes in the reflectance R (?,?, P). The sensitivity of human vision varies with the optical wavelength and the angle of incidence, as discussed, for example, in Col or Sci en: Concepts and Methods, Quanti ta ti ve Da ta and Formul by Gunter Wyszecki and .S. Stiles (New York: Wiley) (1982) and Vi s ual Percepti on by Nicholas Wade and Micháel Swanston (London: Routledge) (1991). The human visual system however was not sensitive to polarization. ?! The variation of the human visual sensitivity with the wavelength, S (?), Is graphically presented in Figure 3, which shows the sensitivity for each cone pigment (nominally, red, green _ and blue), as well as the sum of the answer. The sum is referred to as the photopic response. Figure 4 illustrates the average values for human visual sensitivity to light, as a function of the angle, S (?), Over a range of angles. Although the human eye detects light that is refracted through the cornea on a horizontal angular diffusion of 208 degrees and a vertical diffusion of 120 degrees, the eye does not detect light at all along this interval of angles with equal sensitivity and fidelity; this variability is described by S (?). As is the case for ophthalmic prescriptions, there are average values and standard deviations from these average values, which are reported in Brian Wandell, Founda ti ons of Vi si on, (Sunderland, MA: Sinauer Associates) (1995). As shown in Figure 3, the highest human visual sensitivity at wavelength occurs at approximately 550 nm. As shown in Figure 4, the highest human visual sensitivity to the angle occurs within approximately twenty degrees of central fixation. The S (?) Function depends on physiologically variable details such as size and site of the nose, corneal structure and optical homogeneity, and other factors familiar to those with experience in the technique of psychophysical perception. According to the present invention, the design of an AR coating is based on the perceived reflection. The perceived reflection, F, of light coming from a surface by a human observer is defined as the integral of the product of the reflectance, R (?,?) and the function of human sensitivity, S (?,?): F = U s. { ? ) R. { ? ) d? d? (7) where R (?,?) is the average of the polarized reflectances p and s and are used because the human visual system is not sensitive to polarization. The value of F depends on the refractive indices dependent on the wavelength of the substrate and on the layer means, and on the thickness of the layers. - According to one aspect of the invention, the statistically determined average values of S (?.?) For a given population of humans, are used to determine the preferred response factor that will be used in the design of an AR coating. . However, the construction of individual profiles for individuals with peculiar S (?) Constraints such as might occur, for example, in individuals who are blind in one eye or who suffer from macular degeneration, are also encompassed by the invention.

The perceived reflectance, F, is numerically evaluated for one or more layers in an optical substrate, as a function of the thickness, the composition and the order in which they are coated on the substrate. R (?,?) Is calculated over a range of thicknesses for each layer of an AR coating. For a multi-layer AR coating, R (?,?) Is calculated over a range of thicknesses for each layer, while the thicknesses of the other layers are kept constant, while, for a single-layer AR coating, R ( ?,?) is merely calculated over a range of thicknesses for the single layer. For example, in the design of an optical multi-layer AR coating, comprising one. first layer of TiO, on the substrate, having a physical thickness of di, and a second layer of Cfx, having a physical thickness d2, R (?,?) is calculated for a given d2 of the Cfx layer, by Example 10 nm, and so on, in succession, such that a range di di is calculated over a range of d2, that is, again, over 5-300 nm at intervals of 5 nm. From equation (7), the perceived reflectance F, is calculated for this coating AR from the product R (?,?) XS (?,?) For_ the calculated values of R (?,?, D) on he thickness range di (= 5 to 300 nm) and d2 (= 5 to 300 nm). One or more minimum values of F are then determined from the calculated values of F over the thickness interval di, d2. The composition and order can be constrained by other material factors such as adhesion, surface energy, chemical resistance, etc. According to the present invention, the preferred thickness, the composition, and the order of the layers in an AR coating minimizes the F value subject to these constraints. According to one embodiment of the invention, an optical substrate having an average perceived reflectance of F0 is coated with an AR coating designed as described above, such that the reflectance perceived by the coated article, FAR is less than F0, and preferably less than or equal to about one half of F0. As used herein, the 'average perceived reflectance' is the perceived reflectance calculated from the statistically determined average values of the human sensitivity response, S (?,?). Once a preferred substrate and system layer or layers is defined (in terms of the compositions, thicknesses and deposition orders), the next step is the preparation of the coated article. In accordance with the present invention, one or more substrates, such as an ophthalmic lens, is placed in a compact chamber, slightly larger than the substrate (s) to be coated. Preferably, the chamber has a volume no greater than about twice the volume of the substrate or substrates to be coated. The chamber is evacuated and purged with a chemically inert gas, such as argon or nitrogen. The inert gas is excited with electrical energy to produce a plasma. The surface • of the substrate is cleaned, either by crackling from the inert gas (e.g., helium, nitrogen, argon) or by chemical etching of the surface using reactive gas (e.g., 02, HBr), as is familiar to those of skill in the art of plasma processing. one or more molecular precursors (described below) are mixed with the flow of inert gas and excited with electrical energy to produce a plasma. The plasma excites, dissociates and ionizes the precursor, producing reactive fragments which are transported to the surface of the substrate and polymerized to form films. These films have reflective properties that depend on the precursors, the deposition conditions, and the film thicknesses; therefore, a wide variety of single-layer and multi-layer coatings that reduce reflection can be synthesized. Non-limiting examples of the molecular precursors, the composition of the resulting film, and the average refractive index of the film are presented in Table I.

Table I: Typical precursors for low-pressure plasma synthesis of antireflective films before Film Precursor Phase index Refraction Si02 - Si (OC2H5) 4 1.52 liquid SiC3 Si (CH3) 4 1.45 liquid SiC3 _ HSi (CH3) 3 1.45 gas -CSC2H2C- X4H4S (thiophene) 1.60 liquid -COC2H4C- C4H4O (furan) 1.55 liquid - C6H4 - C6H6 (benzene) 1.65 liquid Film Precursor Phase index Refraction TiOx Ti (OC2H5) 4 2, .2 Liquid TiNx Ti (N (C2H5) 2) 4 2. .3 Liquid CFX C2F4 1. .35--1. .4 CFX gas others 1. .35--1. .4 variable fluorocarbons It has been found that a particularly useful class of precursors comprises perfluorinated organic compounds, such as perfluoroaliphatic, perfluorocycloaliphatic, and other fluorocarbon compounds. "Non-limiting examples include perfluorocyclobutane, hexafluoroethane, tetrafluoroethylene, and hexafluoropropene." Polymeric fluorocarbon films made by plasma deposition of such precursors have very low refractive indices, typically less than 1.4, making them very suitable for use in coatings. The theoretical basis for the low refractive index of fluoropolymer materials is discussed by W. Groh and A. Zimmerman in Ma cromol ecul es, 24, 6660-3 (1991).

Previously, fluoropolymer films have been widely used for their beneficial lubricating properties, as well as for their ability to repel water and improve substrate cleanliness. Such properties typically do not vary appreciably with the thickness of the fluoropolymer film. A typical illustration of the change in reflectance with the thickness of a single-layer AR coating is shown in Figure 5. The reflectance of the 250 nm layer at an optical wavelength of 500 nm is equal to that of a substrate uncoated, while that of a 387 nm layer (3/4 wave at 516 μm) is reduced to a value equal to that observed for a quarter wave layer, from (125 nm) to 500 nm. in other words, a fluorocarbon composition is not, by itself, adequate to provide A properties. The thickness of the layer must be chosen and controlled in a precise way to achieve the properties of AR that are going to be achieved. In the case of a single layer fluoropolymer film, local minima of the perceived reflectance function F are obtained when the optical thickness is odd multiples of 550/4. (The optical thickness_, ndr is the product of refractive index, n, of a layer, and its physical thickness, is dr). An important feature of the present invention is that the reflection of polarized light at one or more wavelengths and at one or more angles of incidence is used to periodically check and control the growth of the AR coating. After selecting the layer thickness (s) and layer (s), equations (2) to (6) are resolved for discrete values of layer thicknesses up to the inclusion of the preferred thickness. For each intermediate thickness, the results are three-dimensional surfaces, one for the reflectance and another for the polarized reflectance p, as shown in Figures 1 and 2. Figure 6 shows the cross sections of these surfaces at normal incidence (? = 0) for a polymeric fluorocarbon film on polycarbonate, with optical thickness in the range of 90 nm to 180 nm and optical wavelengths between 350 and 750 nm. Figures 7 and 8 show cross-sections through the same surfaces at angles of incidence of 0, 10, 20, 30, 40 and 50 degrees and a fixed wavelength of 500 nm. (It is recalled from equation (5) that the reflectance p and s are identical to normal incidence). Using the reflectance variation, R (?,?, P), one or more "probe wavelengths" and one or more probe angles are selected for the periodic verification in situ of the AR coating process with the film thickness. The selection is based on the variation of reflectance over the range of thicknesses where control is needed, for example, when switching between two film precursors.Preferably, the probe wavelength is further selected such that the wavelengths where the Plasma emission could interfere with the detector, they are avoided In a similar way, the probe angle is constrained by the geometry of the reactor and common sense, angles less than approximately equal approximately 90 ° should be avoided, as should be angles where electrodes or other structural elements could interfere with the transmission or reception of light beam probe. On the substrate it is checked periodically, optically, using an optical radiation emitter, for example, a polarized light emitting diode, and a detector, such as an optical polarization filter in -combination with a photodiode. The measurements from the film growth monitor are used by a feedback system to control the deposition rate of the films, allowing coatings to be produced with the prescribed anti-reflection properties. The feedback system controls the rate of deposition by controlling the flow rate of the precursor, the excitation of the plasma, and / or the pressure of the chamber. An embodiment of the optical monitor 14 is schematically illustrated in Figure 9. A light source 36 emits a probe light 37 with a defined wavelength and polarization. In this embodiment, the light source 36 is a lamp 38 with a polarization filter 40 and an interference filter 42. Alternatively, the light source is a laser or a polarized light emitting diode. The beam of .light probe can be monochromatic, but this is not required. The wavelength of the probe light may comprise a narrow or even moderate bandw, as long as it provides readily detectable changes in reflectance at the desired deposition thickness for the system. feedback discussed in more detail later. The wavelength, or bandw, of the filtered probe light is selected to be different from the wavelengths of the ambient light or of the light emitted by the active plasma during PECVD. Does the probe light have a defined incident angle? on the surface of the substrate. The probe light passes through a window 44 en route to the substrate. The face of the window 44 is placed perpendicular to the incident light beam, and the window is mounted on the end of a narrow tube 46, which must be long enough to exclude the deposition of the film on its internal surface, for example , typically more than four times its diameter. The angle of incidence of the probe light on the substrate is constrained in part by the array and the optical properties of the window 44. The angle can be in the range of 0 to 90 °, with a preferred angle between approximately 5 ° and 50 °. to avoid interference by the reflections coming from the window surfaces and to facilitate the alignment. A portion of the light probe reflects off the surface of the substrate, while a portion not "reflected" is refracted and / or absorbed as it passes through the "deposited film and the underlying substrate. The reflected portion of the probe light passes through a properly placed detector array, which includes a tube 48, the window 50, the interference filter 52, the polarization filter 54, and a detector 56, eg, a photomultiplier compact or photodiode. Again, the length of the tube 48 should be approximately four times its diameter to protect the window surface from the film precursors. The influence of the emission of. Plasma light is controlled by the selection of a probe wavelength, or bandwidth, at which the plasma does not emit. The interference and polarization filters allow the performance of only the wavelength of the probe light, with which an accurate reading of the intensity of the reflected portion of the probe light is ensured. Figure 10 illustrates schematically a chemical vapor deposition apparatus 10, improved by plasma (PECVD) according to a preferred embodiment of the invention, with the physical dimensions designed to accommodate a pair of lenses ophthalmic (eyeglasses), which can be made of glass or plastic (for example, polycarbonate, bis-phenol A resins such as CR-39MR, available from PPG Industries, etc.). The PECVD apparatus includes a microprocessor 12, the optical monitor 14, the reagent source 16, the input plurality 18, the pressure control valve 20, the flow control valve 22, the plasma reactor 24, the supply of energy 26, the holder of the substrate 28, the vacuum pump 30, and the exhaust filter 32. The ophthalmic substrates of plastic or glass 34, 35 are mounted or placed on the holder of the substrate 28 and inserted into the chamber of the plasma reactor, which preferably has a volume of less than about twice that of the one or more substrates to be coated. The PECVD involves placing the substrate in a reactor chamber, passing at least one precursor material capable of forming the desired layer, through the chamber in a laminar flow relative to the surface of the coating and at a suitable pressure, and then generating an electric field to form a plasma with the precursor (s). The accommodation of energy within of gas occurs by means of electric fields that can be static (coupled by direct current), or dynamic (coupled by alternating current). The coupling of A.C. (alternating current) can be either capacitive, inductive or both. The precursor (s) are decomposed and reacted in the plasma and on the coating surface to form the desired layer. Depending on the composition of the precursor (s), the strength of the electric field and other parameters, the film may have extended arrays of regularly repeating molecular constituents, amorphous regions, or mixtures of ordered and unordered polymer regions. Most of the precursor compounds listed in Table I are liquids at room temperature, and at ambient pressure. In a preferred embodiment, the liquid precursor is degassed by cooling it and then subjecting it to a vacuum. Depending on its boiling point, the liquid is then heated to room temperature or a higher temperature in order to provide sufficient positive vapor pressure to flow through a piping system. Alternatively, a carrier gas, such as helium, it can be blown through the liquid to obtain a diluted vapor mixture of the desired composition. The gaseous precursors forming AR coatings of the present invention can be supplied from an external source through a series of inlet tubes and into the reactor chamber. The technical peculiarities of the channeling of various gases within the reactor chamber are well known in the art.The flow of the carrier and reactant gases within the reactor can be controlled by the flow control valves, which are well known in the art and serve to measure the flow of gases and to control such flow.In addition, carrier gas, when used, can be premixed with gaseous reactants or fed into the central feed line by a Separate input As shown in Figure 10, the pressure and flow of the precursor gas within the plasma reactor 24 are electronically controlled by the flow control valves 22. The temperature of the chamber is preferably close to the ambient temperature.

The apparatus 10 includes a feedback system to allow precise control over the deposition of an AR coating on the substrates. The coating AR may consist of a single layer or multiple layers, each layer having a predetermined thickness. It is important that the thickness of each layer corresponds precisely to the thickness of the predetermined design, to maximize the anti-reflection properties of the coating. The feedback system measures the thickness of each cap as it is being deposited, and controls the speed p deposition ratio accordingly, in order to precisely control the thickness of the deposited layer. The feedback system includes the microprocessor 12, the optical monitor 14, and one or more pressure control valves 20, flow control valve 22, and the plasma reactor 24, including a plasma generator and a reactor chamber, and an energy supply 26. Preferably, the microprocessor is connected to all control valves and to the power supply. The primary control elements governed by the microprocessor 12 in response to a feedback signal from the optical monitor 14, are the gas flow velocities through the flow control valve 22 and the excitation of the plasma by the power supply 26"for the plasma reactor 24. In some embodiments, it is advantageous to regulate the pressure of the chamber with the valve 24 of pressure control when connected between the steps of cleaning or chemical etching of the substrate or substrates and depositing in multiple layers of coating materials - The following are some examples of reflectance profiles calculated from equations (1) - (6) for different AR coatings It is intended that these examples be considered as illustrative of the invention, rather than limiting, which is otherwise described and claimed herein Figure 1 and 2 illustrate the reflectance of the components polarized syps from a non-polarized light source from a two-layer AR coating, typical on, an ophthalmic plastic substrate. a 135 nm layer of fluoropolymer (Cfx) on a 200 nm layer of Si02 on a polycarbonate substrate. Figure 7 shows a polarized reflectance s from the thin films of fluoropolymer at a typical wavelength of 500 n, calculated at six different angles of incidence in the range of 0 to 50 degrees. Figure 8 shows the polarized reflectance p from thin films of fluoropolymer at an optical length of 500 nm, calculated at six different angles of incidence of 0 to 50 degrees. The variation of polarized reflected light p with the coating thickness and the angle of incidence is very different from that of the polarized light s, as seen by Comparative Figures 7 and 8. Consider a desired optical film thickness of 125 nm measured with a green probe light (500 nm) at a 50 ° angle as an example of this diagnosis. The polarized reflectance of 9.6% at an optical thickness of 90 nm, drops to 6% according to the "target thickness changes from 80 to 125 nm, as shown in Figure 7. Over the same range of film thicknesses, reflectance polarized p falls from 0.5% to 0.4% (Figure 8), a very small change and more difficult to measure accurately.All other factors being equal, the polarized signal s could be selected for the feedback control of the deposition process at an angle of 50 ° of incidence of the light probe. In other words, in one aspect of the invention, an objective optical thickness is identified for one or more layers, and equations (1) - (6) are then resolved to find the variation of the polarized reflectances with wavelength, angle of incidence, and layer thickness. One or more angles and one or more wavelengths are chosen to probe (check periodically) the layer during deposition. When the reflected light intensity reaches the reflected value for the target thickness at the wave length or wavelengths and the chosen angle or angles, the deposition process is terminated, for example by the microprocessor 12. This procedure is easily generalized to more than a Cape. In some embodiments, it is advantageous to form a multiple layer, rather than a simple, coating layer. Multilayer coatings can provide a wider spectral region with low reflectance, which can be achieved with a single layer coating. Other material considerations include adhesion, scratch resistance, chemical resistance (such as stain resistance), wear resistance, and other desired properties. Figure 11 provides the computed average reflectance data for a non-limiting example of a two-layer coating on a polycarbonate substrate. The first layer is TiO with an optical thickness of 180 nm (physical thickness of 81.8 nm), formed by chemical vapor deposition of Ti (i-PrO) 4. This is followed by a layer of fluorocarbon film (Cfx) (optical thickness of 125 'nm), made using c-C4F8 as a precursor. Note that the region of low reflectance is hooked in comparison to that. found for a simple CFX coating in Figure 6. As with single layer AR coatings or films, polarized reflectance at various angles and wavelengths can be used to control the deposition process in the preparation of an AR film of multiple layers. For example, Figure 12 shows the polarized reflectance at angles of 0-50 ° for a two-layer finished coating. A family of curves similar to those shown in Figures 7 and 8 can be used for the coating of simple fluoropolymer, to compute the polarized reflectance, with values selectable polarized reflectance corresponding to a desired thickness, triggering the switching or change of TiO to the CFX precursor. The unpolarized probe light can also be resolved using a polarization beam splitter between the polarization filter 54 and two : coupled detectors, which replace the simple detector 56 (Figure 9). The proportion of the detector outputs is equal to the proportion of the square of the corresponding Fresnel reflection coefficients, calculable from equations (1) - (6) above. This proportion 'produces a response surface characterized by the ratio of Figures 1 and 2 for a single thickness film and a family of such surfaces for a growing film or multiple layers.- In some embodiments, it is advantageous to select more than one length of incident light wave and / or polarization, particularly if more than one precursor is used, or if a wavelength is optimal for the cleaning step, and a different wavelength for deposition is preferred. The composition of the substrate enters equation (2) through its optical admittance, y0.

As a practical matter, the differences in the thickness of the substrate do not enter into the equations, since the thickness of the ophthalmic substrates is much greater than the optical wavelengths of the incident light. The shape of the substrate does not enter the equations, as long as the ratio of the radius of curvature of the substrate. through the radius of the point of light where the probe makes contact with the lens, it is much larger than one, a condition that is always satisfied for a sufficiently small probe point ~~ on the ophthalmic substrates. According to one embodiment, prior to deposition of the film, the substrate is cleaned by exposing it to a plasma of inert gaseous ions, reactive radicals, or by other means known in the art. The method of generating and applying the electric field to create the plasma is not critical to this process. For example, the field can be generated by direct, inductive, or capacitive coupling systems. Non-limiting examples of such systems are found in Thin-Film Deposi ti on r Principle and Pra cti ce by Don Smith, (New York: McGraw Hill) 1995.

The steps used to clean a substrate vary with the composition of the substrate, the degree and type of contamination, and the range of plasma conditions that result from the electrical and flow constraints of the particular plasma chamber used. It is common, for example, to etch the organic material with an oxygen plasma for a few minutes before the deposition of the thin film. The etching of organic contaminants and surface oxide can also be achieved by discharged halogenated gases such as HBr. In one embodiment, the cleaning step is initiated by activating the vacuum pump 30 and admitting argon gas to the tube at pressures of 1-20 millibars. A plasma is ignited by applying an energy of 50 kHz to the ring electrodes mounted inside (for direct coupling) or outside (for "capacitive or inductive coupling") of the plasma reactor 24. Electrons, Ar + ions, species excited, and light collide on both sides of the substrate, removing adsorbed impurities and activating the surface for adhesion of the AR coating.

This surface preparation can modify the refractive index of the surface layers. The modification of a refractive index can also be used to periodically verify the cleaning step optically. A change in the refractive index of the surface layer causes a change in the Fresnel reflection from that surface, a change that can be measured with the optical monitor 14. The cleaning step can be controlled using the feedback system of the present invention, as described above, by continuing the cleaning step until a desired refractive index corresponding to a sufficiently clean substrate is detected. According to another additional embodiment, the cleaning process is verified by observing the fluorescence from impurities as they are purged from the plasma reactor 24. For example, excited OH is produced from the dissociative excitation of water vapor by the impact with electrons, which produces observable fluorescent emissions. According to the concentration of water vapor in the reactor plasma 24 decreases during plasma cleaning, the intensity of these fluorescent emissions decays. The reactor chamber is evacuated before the entry of gaseous reactants. The chamber pressures, suitable for the process of the present invention, are generally less than one-twentieth of an atmosphere and typically fall within the range of about 50 m Torr to about 10 Torr. As the precursor (s) enters the reaction chamber after the coating surface is cleaned and treated as described above, an electric field is generated under conditions of frequency of preselected energy to ionize the gas mixture, thereby a plasma is formed. When a low pressure discharge occurs in the gaseous precursor or film-forming precursors, the precursor (s) is ionized, forming a plasma. A portion of the material is in the form of ions, electrons, and neutral free radicals generated in the plasma prior to the formation of the film, on or on top of the substrate. Methods for generating an electric field between electrodes are well known in the art and described, for example in Thin Film Deposi ti on: Principal and Practi ce (ibi d). A preferred deposition rate is between about 0.1 and 10 nanometers per second; nevertheless, they are possible speeds up to approximately 65 nm / sec. The rate of deposition is constrained only by the speed at which a homogeneous plasma can be produced in order to form a uniform deposited layer. Preferably, the coating AR - is continuously deposited without interruption between layers. This is achieved by reducing the flow rate in a first precursor, while simultaneously increasing an increase in the flow of the second precursor such that both materials are being deposited simultaneously. In this way, more gradual changes in the profile of the refractive index can be created. Alternatively, there may be cases where a cleaning or intermediate activation step is desirable, for example to relax internal stresses or improve adhesion at the interlayer interface. Preferably, the multilayer AR coating is 'cased' with a layer optically thin (e.g., ndr < 20 nm) of hydrophobic material. For example, a hydrophobic polymeric fluorocarbon film can be made from a precursor. such as a "perfluorinated organic compound, for example, perfluorocyclobutane (c-C4F ~ 8), trifluoromethane (HCF3), tetrafluoroethylene (C2F4) or hexafluoropropene (C3F6) .The presence of such a layer makes it easier to clean the coated substrate and inhibits the formation of water or oily stains According to yet another embodiment of the invention a smooth transition between the cleaning step and the deposition step is provided.At the end of the cleaning cycle, the deposition precursor material is slid into the chamber , and the cleaning reagent, for example oxygen, is gradually restricted in a balanced manner, so that the surface is continually bombarded by energetic particles during the formation of the first film layer., This is important, since a impurity present at a concentration even of 10 ~ 6- Torr will form a monolayer in less than a second.The change or switch smoothly from cleaning to deposition ón: in this way, it also improves the adhesion of the film.

PECVD by reactive ions is suitable for coating substrates with regular as well as irregular surfaces, including the ridges found in bifocal ophthalmic lenses. During deposition, the ion flow direction that the thin polymer coating produces is determined by. the cover or electrostatic sheath and the ratio of the ionic thermal temperature (in eV) to the potential of sheath or cover. The cover or cover is oriented normal to the plane tangent to the surface of the substrate, and it is not modified when the spatial scale of the structure is smaller than approximately 10 Debies in length. A length debie is a plasma parameter that describes the distance over which an electric field can be maintained in the electrically conductive plasma medium. If the number of electrons per cubic centimeter is Ne and the electron temperature in eV is Te, then the length debie, I, in centimeters is 525 TeN6) * á Under a typical group of plasma conditions, with an electronic density of 109 cm-3 and an electron temperature of 2 electron volts (eV), This debie length is 0.02 cm, so that the characteristics with a radius of curvature of less than about 10-? = 2 mm will not affect the direction of the electric field of the case or cover. The angular divergence of the ion flux is given by the inverse tangent of the square root of the ratio of the ionic thermal energy to the shell or shell potential: 7 This angular divergence is 9o for a typical ionic temperature of 600 ° K and a sheath potential of 2 eV. This angular average produces more uniform coverage over the topography than would be the case for a monoenergetic ion beam without transverse energy. The confrmational coverage of steps of practical interest to ophthalmic substrates, for example, edges for bifocal lenses, can be obtained by altering plasma conditions, for example, by raising the Te or decreasing the Ne, to extend the spatial scales for the conformational coating.

It will be appreciated that, in addition to the methods and apparatus described above, the invention also provides unique articles of manufacture, characterized by low reflectance. In general, articles are transparent, for example, ophthalmic lenses, windows, windshields, television screens, computer monitors, etc. The articles and transparent substrates do not have light absorption on the region of the spectrum detected by the human visual system, ie, between about 350 and about 750 nm. In some modalities, however, the article may be translucent. Translucent articles and substrates transmit light at some visible wavelengths, but absorb some or all of the light at one or more visible wavelengths. Non-limiting examples of translucent articles include dyed or shaded solar glass, stained glass windows and pigmented windshields. In one embodiment, a low reflection, transparent or translucent article comprises an optical substrate and one or more layers of AR material. Preferably, at least one of the layers is a thin fluoropolymer film. Figure 13 is a schematic illustration of the cross section of such an article, a lens 100 for spectacles. The lens' consists of an optical preform 102 having first and second opposing surfaces 104, 106 and a layer of material AR 108 coated (more precisely, deposited) on at least a portion of the first surface 104 of the ophthalmic lens. In other embodiments (not shown) the material AR is deposited on the lower surface of the lens, both on the upper part and on the lower surfaces of the lens, and / or on the edge of the lens. Figure 14 is a schematic illustration of the cross section of another low reflection article, an ophthalmic lens 100. The lens consists of an optical preform 102 coated with two different layers 110 and 112 of AR material, both layers being considered as deposited or 'coated' on the optical substrate, although, as shown, only one such layer 110 is adjacent to the substrate, the other layer 112 being adjacent to the first layer of material AR. It will be readily appreciated that low reflection articles having more than two layers of material deposited on an underlying optical substrate are within the scope of the present invention.

The invention has been described in the preferred and exemplary embodiments, but is not limited thereto. A variety of modifications, modes of operations and modalities, all within the skill and experience of those of skill in the art, can be realized without departing from the present invention. For example, AR coatings and methods for designing and applying them can be used on a variety of optical substrates in addition to ophthalmic lenses. Even to large items, like car windshields, they can be given an AR coating if an adequately large reactor is built. All references herein are incorporated by reference as described herein, in their entirety. In the text and in the claims, the use of the word "approximately" in relation to a range of numbers is intended to modify the established high and low values.

It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Claims (10)

CLAIMS Having described the invention as above, the content of the following claims is claimed as property:

1. A transparent or translucent coated article that has a perceived reflectance, FAR, where FAR = // S (?,?) R (?,?) D? D? where ? Is it wavelength,? is incident angle, S (?,?) is the human sensitivity function as a function of the wavelength and the incident angle, and ~~ R (?,?) is an average of the polarized reflectances pys, the article comprising coated: an optical substrate; and one or more layers of anti-reflective material coated on at least a portion of the optical substrate, a thickness of one or more of the layers of anti-reflection material is selected such that the perceived reflectance FAR of the coated article is minimized.

2. A coated article according to claim 1, characterized in that at least one layer of anti-reflection material comprises a fluorocarbon film.

3. An apparatus for depositing an anti-reflection film on an optical substrate, characterized in that it comprises: a reactor chamber for receiving an optical substrate; a plasma generator coupled to the reactor chamber and adapted to introduce a plasma into the reactor chamber; and an optical monitor close to the reactor chamber, adapted to control the film thickness of the anti-reflective film.

4. The apparatus according to claim 3, characterized in that the optical monitor comprises: a polarized light emitter for directing a beam of polarized light of a selected wavelength or bandwidth on the substrate at a selected angle of incidence; a light detector for measuring the intensity of a reflected portion of the polarized light directed from the substrate; and a microprocessor coupled to the light detector and to one or more of the flow control valve, the pressure control valve, and the power supply, the microprocessor is capable of controlling one or more of the flow control valve , the pressure control valve and the power supply, in response to the intensity of the reflected portion of the polarized light detected by the light detector.

5. The apparatus according to claim 3, characterized in that the microprocessor is programmed to: - (A) determine the thickness of the anti-reflective film from an intensity of the reflected portion of the polarized light; (B) controlling the flow control valve to allow or selectively restrict the flow of one or more precursor materials to the plasma generator; and (C) controlling the deposition rate of one or more precursor materials, by means of the control of one or more of the flow control valve, the pressure control valve, and the power source.

6. A method for depositing an anti-reflection coating on an optical substrate, characterized in that it comprises: the start of the deposition of a layer of at least one anti-reflection material on the substrate; the optical verification of the thickness of the layer as it is being deposited; and the termination of the deposition when the layer reaches a desired thickness.

7. The method according to claim 6, characterized in that the thickness of the layer is optically verified by the reflection of a polarized light beam having a selected intensity and a selected wavelength or bandwidth of a surface of the substrate on which layer of material is being deposited, at a selected angle of incidence; detecting an intensity of a reflected portion of the polarized light beam; Y determining the thickness of the layer from the intensity of the reflected portion of the light beam.

8. A method according to claim 6, characterized in that it further comprises: the generation of a plasma adjacent to the substrate; initiating the flow of a first ionized material in the plasma for deposition on the substrate, to form a first layer; periodically checking optically the thickness of the first layer as it is being deposited; terminating the flow of the first material when the first layer reaches a first desired thickness; the start of the flow of a second material in the plasma for deposition on the substrate, to form a second layer; periodically checking optically the thickness of the second layer as it is being deposited; Y the completion of the deposition of the second material when the second layer reaches a second desired thickness.

9. A method according to claim 6, characterized in that the ... desired thickness is calculated by minimizing a perceived reflectance, F: - F = // S (?,?) R (?,?) D? D ?, where S (?,?) is a function of human sensitivity and R (?,?) is an average of the polarized reflectances p and s, over a predetermined interval of wavelengths,?, and angles?.

10. A method according to claim 42, characterized in that S (?.?) Has a statistically determined average value.