United States Patent 55
`5,952,084
`[11] Patent Number:
`
`[45] Date of Patent: Sep. 14, 1999
`Andersonet al.
`
`US005952084A
`
`[54]
`
`[75]
`
`TRANSPARENT SUBSTRATE PROVIDED
`WITH A THIN-FILM COATING
`
`[56]
`
`References Cited
`
`Inventors: Charles-Edward Anderson,
`Courbevoie; Jean-Paul Rousseau,
`Boulogne, both of France
`
`Assignee: Saint Gobain Vitrage, Courbevoie,
`France
`
`Appl. No.: 08/804,187
`
`Filed:
`
`Feb. 21, 1997
`
`Foreign Application Priority Data
`
`~ 22,1996
`
`[FR]
`
`France wees seeeeeeee 96 02194
`
`Int. Clo ccc B32B 17/06; B32B 7/02
`US. C1. cece 428/212; 359/359; 359/580;
`359/585; 359/586; 359/588; 428/432; 428/433;
`428/697; 428/699; 428/701; 428/702
`Field of Search o....c.cccccccceeeeee 428/212, 697,
`428/699, 701, 702, 704, 432, 433; 359/359,
`580, 585, 586, 588
`
`U.S. PATENT DOCUMENTS
`
`1/1976 Franz woe eeeeectecesecneeeneeees 428/433
`3,935,351
`5,254,392 10/1993 Burnset al
`w. 428/432
`5,332,618
`7/1994 Austin .....
`ws 428/216
`5,342,676
`8/1994 Zagdoun .....
`ws 428/702
`...
`5,645,923
`7/1997 Matsuoet al.
`we 428/701
`5,776,603
`7/1998 Zagdoun etal. oo...ee 428/336
`
`
`
`
`Primary Examiner—Atrchene Turner
`Attorney, Agent, or Firm—Pennie & Edmonds LLP
`
`[57]
`
`ABSTRACT
`
`The subject of the invention is a transparent substrate (1), in
`particular a glass substrate, including a coating (6) of one or
`more thin films on at least one of its faces, comprising at
`least one A film containing an aluminum fluoride or alumi-
`x yo 2?
`num oxyfluoride AL,O,F., with y20.
`
`14 Claims, 1 Drawing Sheet
`
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`5,952,084
`
`1
`TRANSPARENT SUBSTRATE PROVIDED
`WITH A THIN-FILM COATING
`
`BACKGROUND OF THE INVENTION
`
`The invention relates to transparent substrates, in particu-
`lar glass substrates, which are provided with coatings com-
`posed of one or more thin films which have interference-
`scale thicknesses and are designed to give specific properties
`to the substrates which bear them, for example, thermal,
`optical or electrical properties.
`The invention also relates to the use of these coated
`
`substrates, in particular to produce glazing, as well as to the
`method of obtaining them.
`The coatings mentioned abovetherefore consist of stacks
`of films with varied chemical composition and properties.
`They are most often dielectric films, for example of the
`metal oxide or nitride or silicon oxide type, and/or conduc-
`tive films, for example films of metal such as silver or doped
`metal oxide. For optical reasons,
`in many cases these
`coatings include films whose refractive index is to be
`carefully selected.
`Atype of coating, referred to as an anti-reflection coating,
`is thus known which usually consists of an alternating
`sequence of dielectric films with high and low refractive
`indices. Deposited on a transparent substrate, a coating of
`this type has the function of reducing the light reflection
`factor of this substrate, and therefore of increasing its light
`transmission factor. A substrate coated in this way will thus
`have an increase in its transmitted-light/reflected-lightratio,
`which improvesthe visibility of objects placed behind it. It
`can then be used in many applications, for example to
`protect a picture illuminated by a light placed behind the
`observer, or to constitute or form part of a shop window,in
`order more clearly to discern what
`is contained in the
`window, even whenthe interior lighting is low compared to
`the exterior lighting, or alternatively in interior furniture or
`as an anti-glare screen arranged in front of computerscreens.
`The performance of an anti-reflection coating can be
`measured or evaluated on the basis of various criteria.
`Firstly, of course, are the optical criteria. It may be consid-
`ered that a “good” anti-reflection coating should be able to
`lower the light reflection factor of a standard clear glass
`substrate to a given value, for example 2%, or 1% and less.
`Similarly,
`it may be important for this coating to keep a
`satisfactory colorimetry for the substrate, in particular in
`reflection, for example an extremely neutral one which is
`very close to that of the bare substrate. Other criteria may
`also be taken into account depending on the application
`which is envisaged,
`in particular the chemical and/or
`mechanical durability of the coating, the cost of the mate-
`rials which are used, the manufacturing time or the tech-
`niques to be used for manufacturing it.
`In this type of anti-reflection stack, as in others, it must
`therefore be possible to manufacture films of material with
`low refractive index, for example with an index of less than
`1.65.
`
`Various materials currently meet this criterion. Mention
`may be made of magnesium fluoride MgF., with an index of
`about 1.38, which can be deposited in the form of a thin film
`by a technique of the vacuum evaporation type. This is a
`technique whichis reliable for deposits on small surfaces,
`for example surfaces of spectacles or lenses, but becomes
`expensive and complicated when deposition on larger sur-
`faces is involved, for example on glazing.
`Silicon oxide Si0,, with a refractive index of about 1.45,
`may also be mentioned. This material can be deposited using
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`a cathodic sputtering technique, which techniqueis entirely
`suitable for deposits on large surfaces of the glazing type.
`However, it is not very easy to deposit SiO, by reactive
`sputtering in the presence of oxygen. Further to the fact that
`it
`is necessary to dope the silicon target with another
`element, in particular boron or aluminium, the deposition
`rate of the SiO, film when using this technique is low, and
`the deposition conditions are sometimesdifficult to stabilize
`and control.
`
`SUMMARYOF THE INVENTION
`
`The object of the invention is therefore to overcome these
`drawbacks, by seeking a novel type of material with low
`refractive index, which can be deposited, on an industrial
`scale, in the form of a high-quality thin film, with a manu-
`facturing method whichis satisfactory, in particular in terms
`of cost, ease of use and/or efficiency.
`The subject of the invention is a transparent substrate, in
`particular a glass substrate, which includes a coating of one
`or more thin films on at least one of its faces. This coating
`comprisesat least one film containing an aluminium fluoride
`or an aluminium oxyfluoride Al,O,F. (with y20) which film
`will hereafter be denoted, by convention andfor the sake of
`convenience, by the term “A film”. This material actually
`has several advantages, primarily in terms of its manufac-
`turing process: aluminium fluoride or aluminium oxyfluo-
`ride can in fact be deposited in a thin film using a vacuum
`technique of the cathodic sputtering type, optionally mag-
`netic field-enhanced cathodic sputtering.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a schematic view of a section of a substrate
`covered with an anti-reflection stack employing at least one
`A film according to the invention.
`
`DETAILED DESCRIPTION OF THE
`INVENTION
`
`In contrast to a technique of the thermal evaporation type,
`the cathodic sputtering techniqueis of great benefit; it makes
`it possible to mass-produce complex thin-film stacks by
`successive deposits on the same production line, and can be
`adapted to widely varying substrate sizes, in particular large
`sizes; it is thus entirely appropriate for manufacturing coat-
`ings for windowsintended for the building or automotive
`industries.
`
`Furthermore, using a technique of this type for depositing
`aluminium oxyfluoride does not entail problems: in contrast
`to silicon oxide deposition,
`in which use is made of a
`low-conductivity silicon target which must be doped, a
`standard metal target made of aluminium is usedin this case
`(the term “standard” target is intended to mean a plane
`geometrical configuration for
`the target, as opposed to
`rotationally cylindrical targets, which may clearly also be
`used). The A film is then deposited in a reactive atmosphere
`comprising an oxidizing gas, such as oxygen, and a fluori-
`nated gas, with a standard DC electrical supply. The deposits
`thus produced are to a great extent reproducible and easy to
`control. Furthermore, the deposition rate of a film of this
`type is much higher than that of an S10, film deposited by
`sputtering, and is high enough to makeit fully compatible
`with the short manufacturing time requirements relevant to
`mass production of coatings, more particularly for glazing.
`Furthermore, the A film manufactured in this way, which
`is of high quality, is also advantageousin termsof its optical
`properties: pure aluminium oxide Al,O, has a refractive
`
`3
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`3
`
`

`

`5,952,084
`
`3
`index of about 1.65. By introducing fluorine to obtain an
`oxyfluoride, or even by fully substituting fluorine for oxygen
`to obtain a fluoride, the index of the film can be reduced in
`controlled fashion, since the refractive index of the film
`decreases as its fluorine content increases. By adapting the
`deposition conditions, and in particular by altering the level
`of fluorinated gas relative to the oxidizing gas in the
`cathodic-sputtering deposition atmosphere, an A film with
`variable fluorine level can be obtained, up to complete
`fluorine saturation in the absence of oxidizing gas, the index
`of which film can be set very accurately within a wide range
`of values. The index of the A film is thus chosen to be less
`
`than 1.63, and is preferably chosen between 1.60 and 1.32,
`in particular between 1.35 and 1.45. This flexibility in terms
`of the choice of refractive index makes the A film very
`beneficial because it can be adapted as a function of the
`optical role which it is intended to fulfill within a given
`thin-film stack.
`In the formula Al,O,F.,
`the equation:
`3x=2y+zIs satisfied, it being understood that “y” is allowed
`to be greater than or equal to zero.
`The level of fluorine in the A film can thus be advanta-
`geously chosen so that the F/Al atomic ratio in the film is
`between 0.1 and 3.0, in particular between 0.10 and 2.50,
`preferably between 0.16 and 2.45. Similarly, the O/F atomic
`ratio can be adjusted so that it is between O and 10, in
`particular between 0.1 and 10, preferably between 0.15 and
`9,
`
`Various considerations may also lead to elements other
`than oxygen,fluorine and aluminium being introduced into
`the A film. This may, in particular, involve an oxide or a
`mixture of oxides, preferably belonging to the following
`group: silicon oxide SiO,tin oxide SnO,,, nickel oxide NiO.
`Since all these oxides have an index of at most 1.9, adding
`them to the film maybe an additional meansof adjusting the
`index of the film, as a function of its fluorine content,
`without increasing it in undesirable proportions. They may
`furthermore have a good influence on the mechanical or
`chemical durability of the film, which may prove important
`when the A film is the outermost film in the film stack of
`which it forms part, and therefore, in fact, when it may be
`exposed directly to attack such as mechanical abrasion,
`exposure to corrosive chemical products or unfavourable
`weather conditions.
`
`Alowsilicon oxide content thus provides an improvement
`in the chemical durability of the A film, in particular an
`increase in its resistance to moisture. The A film advanta-
`geously comprises a mixture of aluminium fluoride or
`aluminium oxyfluoride/silicon oxide.
`In this case,
`it
`is
`preferable to choose an Si/Al atomic ratio of between 0.05
`and 1.00, preferably between 0.06 and 0.10; an O/F atomic
`ratio of between 0.2 and 10, and preferably between 0.25
`and 8.70, and an F/Al atomic ratio of between 0.1 and 2.5,
`preferably between 0.18 and 2.40.
`Accordingto a first, non-limiting embodiment, the A film
`formspart of a thin-film stack with reflection properties in
`the infrared and/orin the solar radiation range, in particular
`stacks comprising at least one metal film, of the silver type,
`arranged between twodielectric coatings. In view ofits low
`refractive index,it is particularly well-suited for acting as an
`intermediate film with a lower index than the substrate, and
`arranged between the substrate and the stack, as described in
`patent EP-0,745,569.
`According to another non-limiting embodiment of the
`invention, the A film formspart of an anti-reflection coating
`including an alternating sequence of dielectric films with
`high and lowreflective indices, at least one of the low-index
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`films in the stack consisting of an A film. This maybe thelast
`film in the anti-reflection coating, or alternatively all the
`low-index films therein.
`In the context of the invention, the term “low index” is
`intended to mean refractive indices of between 1.65 and
`1.32, in particular less than 1.60, and the term “high index”
`is intended to mean refractive indices of at least 1.60, in
`particular between 1.9 and 2.45.
`Using films of the A type as low-index films in an
`anti-reflection coating is actually quite advantageous: it may
`be substituted for thesilica films conventionally used in this
`type of coating. It is then possible to make two different
`choices: either the A film has a fluorinelevel selected so that
`
`it has an index close to that of silica, that is to say close to
`1.45 In this case, one material has been “replaced” by
`another material which is easier to deposit by cathodic
`sputtering but is optically equivalent in the anti-reflection
`stack. Alternatively, the A film is chosen so that it has a
`substantially lower index thansilica, in particular less than
`1.40, for example of the order of 1.37 to 1.38. In this case,
`it allows a much wider choice of possible high-index mate-
`rials. Considering in broad outline the method of evaluating
`the performanceof an anti-reflection coating, it can be stated
`that
`the capacity of such a coating to lower the light
`reflection factor value of the substrate bearing it is correlated
`with the difference between the refractive indices of the
`high- and low-index films which form the stack, and more
`particularly with the difference between the indices of the
`last two high- and low-indexfilmstherein.It has to date been
`conventional to combine a high-index film of the titantum
`oxide type, that is to say one having an index ofatleast 2.25,
`with a low-index silica film. As soon as a material with lower
`
`index becomes preferable to silica, it is acceptable for the
`high-indexfilms used to be films of a material withrelatively
`lower index, for example simply at least 1.9 to 2.2, without
`sacrificing the optical performance of the anti-reflection
`coating.
`Thus, the anti-reflection coating which includesat least
`one film of type A as a low-index film, may use high-index
`films, of actually very high index, of at least 2.25 such as
`niobium oxide, Nb,O,, zirconium oxide ZrO,,
`titanium
`oxide TiO, bismuth oxide Bi,0, or cerium oxide CeO,. But
`it is nevertheless possible to employ high-index films with
`slightly lower index, in particular of the order of 1.90 to
`2.20, for example tungsten oxide WO, tin oxide SnO., zinc
`oxide ZnO, aluminium nitride AIN,silicon nitride Si,N, or
`tantalum oxide Ta,O,;. Even with this type of material, a
`refractive index difference of at least 0.5, in particular about
`0.8, may actually be maintained between high- and low-
`index films.
`It may also be industrially beneficial,
`for
`example, to use WO, or SnO, rather than Nb,O, or TiO, as
`a high-index film,
`in particular because the former films
`have a muchgreater cathodic-sputtering deposition rate than
`the latter.
`
`Furthermore, the use in anti-reflection stacks of A films
`having a lower index than silica presents two additional
`advantages in terms of optics, and moreparticularly in terms
`of the calorimetric appearance in reflection:
`the residual
`colour in reflection of the coated substrate is made more
`
`neutral, and the variations in colour as a function of the angle
`of incidence at which the coated substrate is observed are
`found to be muchless.
`
`An anti-reflection coating according to the invention,
`comprising at least one A film, may comprise only two
`successive sequences of high- and low-index films. Four
`films may in fact be sufficient
`to obtain a remarkable
`anti-reflection effect.
`
`4
`
`4
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`

`

`5,952,084
`
`5
`Examples of an anti-reflection coating having this con-
`figuration may thus be stacks of the type:
`Sn0,/Si0,/Nb,0,/A film or
`Sn0,/A film/Nb,0./A film.
`The Nb,O,films may also be advantageously replaced by
`SnO., WO,, Bi,O, or TiO, films.
`the anti-reflection
`According to another configuration,
`stack may comprise not two but three sequences of high- and
`low-index films. The anti-reflection effect may then be even
`greater and combined with a more neutral residual colour in
`reflection, but manufacturing the stack takes a little longer
`and is slightly more expensive.
`According to another configuration, the first sequence of
`high- and low-indexfilms in the anti-reflection coating (the
`term “first sequence” is used to denote the sequence closest
`to the surface of the substrate bearing the coating),
`is
`substituted by a single film having an intermediate refractive
`index of between 1.65 and 1.80. An intermediate-index film
`of this type has an optical effect similar to that of a
`high-index film/low-index film sequence and has the advan-
`tage of reducing the overall numberof films in the stack.
`According to yet another configuration,at least one of the
`so-called high-index films in the anti-reflection stack, and in
`particular the film in the second sequence, may be a high-
`index “overall”film, the term “overall” indicating that it is
`in fact a superposition of high-index films, in particular two
`or three. In terms of optics, this “overall”film broadly fulfils
`the role of a single film with an index intermediate between
`the refractive indices of the various films which form it.
`
`It is thus possible to have stacks of the type:
`glass/SnO./A film/Bi,0,/Sn0./Bi,0,/A film or
`glass/SnO./A film/Nb,O./SnO./A film.
`The anti-reflection stack can thus be given an additional
`anti-static function by incorporating a film of a conductive
`material in the stack, in particular a material of the doped
`metal oxide type, such as tin-doped indium oxide ITO.
`Each of the faces of the substrate is preferably covered
`with an anti-reflection stack of this type, in order to obtain
`the maximum anti-reflection effect.
`With the anti-reflection stacks described above, a reduc-
`tion in the light reflection factor values R, of the substrates
`is achieved to values of at most 2%, in particular at most 1%
`or at most 0.5%. This provides an aesthetic and pleasant
`calorimetric appearance in reflection,
`in particular subtle
`blue or blue-green tints, which is expressed in the (L*, a*,
`b*) colorimetry system by negative a* and b* values of at
`most 3.5 in absolute value for a* and at most 1.5 in absolute
`value for b*.
`
`A further subject of the invention is coatings which,
`further to at least one film of type A, comprise at least one
`film with given thermal properties,
`in particular with a
`sun-protection property or with low emissivity, of the metal
`type, such as silver or aluminium, or of the doped metal
`oxide type, for example fluorine-doped tin oxide SnO,:F or
`tin-doped indium oxide ITO.
`A further subject of the invention is glazing incorporating
`the coated substrates,
`irrespective of whether they are
`monolithic, laminated, or multiple with one or more inter-
`mediate gas layers.
`This glazing can be used either as interior or exterior
`windowsfor buildings or as glass for protecting an object,
`such as a picture, shop-window display, glazed furniture
`such as a counteror refrigerated display window,etc., or as
`motor-vehicle windows such as a laminated windscreen, as
`mirrors, anti-glare screens for computers, or decorative
`glass.
`A further subject of the invention is the method for
`manufacturing transparent substrates,
`in particular glass
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`substrates, with coatings containing A films. One method
`consists in depositing all the films, successively one after the
`other, using the vacuum technique, in particular by magnetic
`field-enhanced cathodic sputtering. It is thus possible to
`deposit the oxide films by reactive sputtering of the metal in
`question in the presence of oxygen, the nitride films in the
`presence of nitrogen, and the A films by reactive sputtering
`from a target containing aluminium,
`in the presence of
`fluorinated gas in order to obtain a fluoride, and in the
`presence of fluorinated gas and oxidizing gas, such as
`oxygen, in order to obtain an oxyfluoride.
`It is not, however, ruled out that some of the films in the
`stack, with the exception of the A films, be deposited by
`another technique employing a vacuum,or by a technique of
`the pyrolysis type, in particularthe first film in the stack (or
`the first two) directly in contact with the substrate bearing
`the coating, when this substrate is made of glass.
`The invention places no limitation in terms of the nature
`of the transparent substrate bearing the coating, which may
`therefore be made of glass or plastic.
`The advantageous characteristics and details of the inven-
`tion will presently emerge from the following non-limiting
`examples, with reference to FIG. 1.
`This figure very schematically represents a section of a
`substrate covered with an anti-reflection stack employing at
`least one A film according to the invention (for the sake of
`clarity,
`the relative proportions of the substrate and film
`thicknesses have not been respected). In fact, each of the
`faces of the substrate is provided with an identical stack, but
`for simplicity only a single stack has been represented.
`Throughout the following examples, a coating was used on
`each of the faces of the substrate.
`the
`in these examples,
`It should be pointed out that,
`successive thin-film deposits were made by magnetic field-
`enhanced reactive cathodic sputtering.
`The substrates on which the anti-reflection coatings are
`deposited are clear silica-soda-lime substrates of the Pla-
`nilux type marketed by Saint-Gobain Vitrage, with a thick-
`ness of 3 to 6 mm, in particular 4 mm.
`FIG. 1 represents the glass substrate 1 which, according to
`a first embodiment,
`is coated on its two faces with a
`four-film stack 6 including an alternating sequence of high-
`index thin films 2, 4 and low-index thin films 3, 5.
`A first series of examples was carried out with niobium
`oxide in film 4 and tin oxide in film 2 for the high-index
`films:
`
`EXAMPLE1
`
`This example uses a four-film coating composed of the
`following sequence (the geometrical
`thicknesses of the
`films, in nanometers, are indicated under each of them):
`
`glass‘)/Sn07)/Si0,0)/Nb,05(9/A film
`19-29
`117.84
`
`Films 2, 3 and 4 are respectively obtained from tin,
`doped-silicon and niobium targets in the presence of
`oxygen.
`The A film, with formula Al,O,F, is obtained from an
`aluminium target, in the presence of oxygen and CF,
`(other fluorinated gases may be used in combination
`with or in place of CF,, for example C,F,). The CF,
`level is adjusted to obtain a film with a refractive index
`of about 1.37. The light reflection factor R,, based on
`the D,; illuminant, measured on the coated substrate is
`0.80%. The values of a*(g) and b* gy in reflection
`
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`5,952,084
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`7
`according to the (L*, a*, b*) colorimetry system are
`respectively about -3 and -1. The deposition rate of the
`A film is much greater than that of the silica film 3.
`
`EXAMPLE 2
`
`8
`coated substrate has an R, value of about 0.35%, and
`a* and b* values of respectively about -3 and -1.
`One example wascarried out with titantum oxide for film
`4 and tin oxide for film 2:
`
`This example uses a four-film coating which this time
`employs two A films,
`in the following sequence (same
`conventions, as in all the examples
`
`EXAMPLE6
`
`A stack is used with the following sequence:
`
`10
`
`glass‘)/Sn0.2)/A Film/Nb,05(9/A Film®)
`241
`23
`11585
`
`glass‘)/Sn0.7)/Si0,©)/TIOM/A film
`26
`34
`108
`95
`
`These films are obtained as in the previous example, and
`the A films have an index of about 1.37. The coated
`substrate has an R, value of 0.96%, and a* and b*
`values of respectively about -3 and -1.
`
`EXAMPLE3
`
`A similar stack to example 2 is used, but the “outer” A
`film, numbered 5 in the figure, is this time deposited under
`conditions whichlead to a refractive index of about 1.42, the
`other A film still having an index of about 1.37.
`The A film of index 1.37 is obtained as before, this film
`therefore corresponding to the formula Al.O,F..
`The A film of index 1.42 is obtained using a target which
`is no longer made of pure aluminium, but of
`aluminium-silicon alloy with a low silicon content This
`film therefore corresponds to the formula Al,O,F-.Si,.
`The sequence is as follows:
`
`glass‘)/Sn0.2)/A Film/Nb,05(9/A Film®)
`20
`27
`117.84
`
`The coated substrate has an R; value of 0.80%, and a* and
`b* values of respectively about -3 and -1.
`A second example series was carried out with tungsten
`oxide in film 4 and tin oxide in film 2:
`the films are
`fabricated as before, the tungsten oxide being deposited by
`reactive sputtering of a metallic tungsten target
`in the
`presence of oxygen.
`
`EXAMPLE4
`
`A stack is used with the following sequence:
`
`glass‘)/Sn022)/A Film/wO3;/A Film®
`18
`33
`126
`92
`
`The first A film® has an index of about 1.37, and the
`second of about 1.42. They are obtained as in Example
`3. The coated substrate has an R, value of about 0.33%,
`with a* and b* valuesin reflection of respectively about
`-3 and -1.
`
`EXAMPLE5
`
`A stack is used with the following sequence:
`
`glass()/Sn02?/Si0,®/WO3/A film
`1736
`125
`92
`
`The A film has an index of about 1.42, and, as in Example
`3, is obtained from an Al/Si metal alloy target. The
`
`15
`
`The A film here has an index of 1.37 andis obtained as in
`
`Example 1. The coated substrate has an R, value of
`about 0.90%, and a* and b* of values ofstill respec-
`tively about -3 and -1.
`the anti-reflection
`According to a second embodiment,
`coating containing at least one A film according to the
`invention is designed so that the high-index oxide film 4 is
`in fact an “overall” film consisting of the superposition of
`two or three high-index oxide films.
`
`EXAMPLE 7
`
`A stack with 5 films in the following sequenceis used:
`
`glass‘)/Sn0,2)/A film®/[Nb305/Sn0.](9/A film®)
`22
`30
`106
`22
`80
`
`The first A filmhas an index of about 1.37, and the
`second A film®has an index of about 1.42. They are
`obtained as in Example 3.
`The coated substrate has an R, value of about 0.50% and
`a* and b* valuesin reflection of respectively about -3
`and -1.
`
`It is also possible to substitute the Nb,O, in this stack by,
`in particular, a TiO, or Bi,O, film.
`
`EXAMPLE8
`
`A stack with 6 films in the following sequenceis used:
`
`glass‘)/Sn0,2)/A film®/[Nb305/SnO/Nb,05]/A film®
`26-26
`65
`28
`«23S
`
`The two A films®and ©have an index of 1.37 and are
`obtained as in Example 4.
`The coated substrate has an R, value of about 0.52%, and
`a* and b* valuesinreflection of respectively about -3.1
`and -1.2.
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`Here again, the [Nb,0,/SnO,/Nb,0.] sequence may be
`substituted by the sequence [Bi,O,/SnO./Bi,0,] or
`[TiO,/Sn0./TiO,].
`Lastly, comparative examples were carried out using
`anti-reflection coatings employing exclusively SiO, films
`for the low-index film.
`
`65
`
`A last example according to the invention wascarried out
`with an anti-reflection coating in whichthe first sequence of
`high- and low-index films (2, 3)
`is replaced by an
`intermediate-index film (7):
`
`6
`
`6
`
`

`

`9
`EXAMPLE 9
`
`5,952,084
`
`Astack with three films in the following sequenceis used:
`
`glass“/mixed Al and Sn oxidewwOx%/A film®
`index 1.8
`index 1.37
`\55 nm
`89 nm
`
`113 nm
`
`10
`CS10F type loaded with 500 grams. The light trans-
`mission factor TL based on the D,, illuminant and the
`blurring level F (diffuse light transmission) were mea-
`sured at the start, then after 150, 350 and 650 turns. The
`result is given in the following table:
`
`10
`
`Numberofturns
`0
`150
`350
`650
`
`TL (%)
`92.2
`92.4
`93.6
`91.6
`
`F (%)
`1.32
`2.18
`2.74
`2.68
`
`The mixedoxide film™ is obtained by reactive sputtering
`in the presence of oxygen from an Al/Sn target. The A
`film®is obtained as in Example 4.
`The coated substrate has an R; value of 0.66%, and a* and
`b* values in reflection of respectively -3.1 and -1.1.
`COMPARATIVE EXAMPLE 10
`
`15
`
`20
`
`It is indeed observed that the variations in T, and blur F
`are small.
`We claim:
`1. An article comprising:
`This is comparable to Example 1, since it uses the same
`a transparent substrate having opposite faces; and
`sequence, replacing the film 5 byasilica film. The stack is
`therefore as follows:
`an anti-reflection coating comprising two or more adja-
`cent dielectric films disposed over at least one of the
`faces, said coating containing an alternating sequence
`of adjacentfilms having high and lowrefractive indices
`with at least one of the films having a low refractive
`index being positioned as an outermost layer of the
`coating and comprising (1) an aluminum fluoride or
`aluminum oxyfluoride material, wherein the aluminum
`material has an O/F atomicratio of less than 10, and (2)
`at least one oxide component selected from the group
`consisting of silicon oxide, tin oxide, nickel oxide and
`mixtures thereof.
`
`glass/Sn037)/Si039/Nb205(9/SiO
`21
`34
`119
`85
`
`The R, value of the coated substrate is 0.55%.
`The following conclusions can be drawn from this set of
`results:
`incorporating films of the A type in the anti-
`reflection stacks is advantageous: the production cycle time
`can be reduced very substantially by employing these flu-
`orinated films rather than silica films.
`
`25
`
`30
`
`This substitution is not accompanied by any drawback in
`terms of the properties of the stack, more particularly the
`optical properties: the A films, with adjustable index, make
`it possible to obtain very low R, values, at least as low as
`with silica films. They also makeit possible to obtain a very
`pale green-blue appearance in reflection, which tint is cur-
`rently highly desirable.
`The thicknesses of each of the films were actually
`selected, more particularly the thicknesses of the A films, in
`order to obtain this colorimetry in conjunction with a low
`light reflection factor value. It is clear that modifying the
`thicknesses of these films, in particular by +20% relative to
`the thicknesses indicated,
`in particular with the aim of
`obtaining a slightly different colorimetry in reflection, would
`not depart from the scope of the invention.
`Furthermore, the use, as in Example 3, of an “exterior” A
`film made of fluorinated alumina additionally containing a
`small amount ofsilica. provides two advantages: this allows
`finer adjustmentof the index of the film, and it increases the
`chemicalresistance of the film comparedto a film consisting
`of only silica or only fluorinated alumina.
`This is beneficial when the substrate may be incorporated
`in glazing with the film stack facing the exterior (damage
`due to the weather) or the interior (damage due to abrasive
`cleaning).
`A test furthermore demonstrated good mechanical dura-
`bility:
`An A film according to the invention, with an index of
`1.42, consisting of a mixture of aluminium oxyfluoride
`and silica, and with a thickness of 100 nm, was depos-
`ited directly on a glass substrate. This substrate was
`subjected to the so-called Taber Abrasion Test, which
`test
`is carried out using wheels made of abrasive
`powder embedded in an elastomer. The machine is
`manufactured by the company Taber Instrument Cor-
`poration in the United States. It
`is the model 174
`“Standard Abrasion Tester”, and the wheels are of the
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`2. The article according to claim 1, wherein each low-
`refractive index film in the anti-reflection coating comprises
`aluminum fluoride.
`
`3. The article according to claim 1, wherein each film
`having the high refractive index has an index ofat least 1.80
`and comprises compoundsselected from the group consist-
`ing of tungsten oxide,
`tin oxide, zinc oxide, aluminum
`nitride, silicon nitride, tantalum oxide, niobium oxide, tita-
`nium oxide, bismuth oxide, zirconium oxide, cerium oxide,
`and mixtures thereof.
`
`4. The article according to claim 1, wherein each film
`having the high refractive index has an index ofat least 2.25
`and comprises compoundsselected from the group consist-
`ing of niobium oxide, titantum oxide, bismuth oxide, zirco-
`nium oxide, cerium oxide, and mixtures thereof.
`5. The article according to claim 1, wherein the difference
`in refractive index between two adja